Prepare for 0.15.0 release

Signed-off-by: deadprogram <ron@hybridgroup.com>
atsamd2x: fix BAUD value
2026-07-26 14:48:40 +00:00 · 2020-09-17 11:48:55 +02:00 · 2020-09-17 09:46:15 +02:00 · 2020-09-17 09:46:15 +02:00 · 2020-09-17 07:46:29 +02:00 · 2020-09-17 07:46:29 +02:00
521 changed files with 29001 additions and 7939 deletions
@@ -14,18 +14,16 @@ commands:
      - run:
          name: "Install apt dependencies"
          command: |
-            echo 'deb http://apt.llvm.org/stretch/ llvm-toolchain-stretch<<parameters.llvm>> main' | sudo tee /etc/apt/sources.list.d/llvm.list
+            echo 'deb https://apt.llvm.org/buster/ llvm-toolchain-buster-<<parameters.llvm>> main' | sudo tee /etc/apt/sources.list.d/llvm.list
            wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key|sudo apt-key add -
            sudo apt-get update
            sudo apt-get install \
-                llvm<<parameters.llvm>>-dev \
-                clang<<parameters.llvm>> \
-                libclang<<parameters.llvm>>-dev \
-                lld<<parameters.llvm>> \
+                llvm-<<parameters.llvm>>-dev \
+                clang-<<parameters.llvm>> \
+                libclang-<<parameters.llvm>>-dev \
+                lld-<<parameters.llvm>> \
                gcc-arm-linux-gnueabihf \
-                libc6-dev-armel-cross \
                gcc-aarch64-linux-gnu \
-                libc6-dev-arm64-cross \
                qemu-system-arm \
                qemu-user \
                gcc-avr \
@@ -39,39 +37,83 @@ commands:
            sudo tar -C /usr/local -xf node-v10.15.1-linux-x64.tar.xz
            sudo ln -s /usr/local/node-v10.15.1-linux-x64/bin/node /usr/bin/node
            rm node-v10.15.1-linux-x64.tar.xz
+  install-chrome:
+    steps:
+      - run:
+          name: "Install Chrome"
+          command: |
+            wget https://dl.google.com/linux/direct/google-chrome-stable_current_amd64.deb
+            sudo apt install ./google-chrome-stable_current_amd64.deb
+  install-xtensa-toolchain:
+    parameters:
+      variant:
+        type: string
+    steps:
+      - run:
+          name: "Install Xtensa toolchain"
+          command: |
+            curl -L https://github.com/espressif/crosstool-NG/releases/download/esp-2020r2/xtensa-esp32-elf-gcc8_2_0-esp-2020r2-<<parameters.variant>>.tar.gz -o xtensa-esp32-elf-gcc8_2_0-esp-2020r2-<<parameters.variant>>.tar.gz
+            sudo tar -C /usr/local -xf xtensa-esp32-elf-gcc8_2_0-esp-2020r2-<<parameters.variant>>.tar.gz
+            sudo ln -s /usr/local/xtensa-esp32-elf/bin/xtensa-esp32-elf-ld /usr/local/bin/xtensa-esp32-elf-ld
+            rm xtensa-esp32-elf-gcc8_2_0-esp-2020r2-<<parameters.variant>>.tar.gz
  llvm-source-linux:
    steps:
      - restore_cache:
          keys:
-            - llvm-source-9-v0
+            - llvm-source-10-v1
      - run:
          name: "Fetch LLVM source"
          command: make llvm-source
      - save_cache:
-          key: llvm-source-9-v0
+          key: llvm-source-10-v1
          paths:
            - llvm-project
+  build-wasi-libc:
+    steps:
+      - restore_cache:
+          keys:
+            - wasi-libc-sysroot-v3
+      - run:
+          name: "Build wasi-libc"
+          command: make wasi-libc
+      - save_cache:
+          key: wasi-libc-sysroot-v3
+          paths:
+            - lib/wasi-libc/sysroot
  test-linux:
+    parameters:
+      llvm:
+        type: string
    steps:
      - checkout
      - submodules
      - apt-dependencies:
-          llvm: "-9"
+          llvm: "<<parameters.llvm>>"
      - install-node
+      - install-chrome
      - restore_cache:
          keys:
            - go-cache-v2-{{ checksum "go.mod" }}-{{ .Environment.CIRCLE_PREVIOUS_BUILD_NUM }}
            - go-cache-v2-{{ checksum "go.mod" }}
      - llvm-source-linux
-      - run: go install .
-      - run: go test -v ./cgo ./compileopts ./interp ./transform .
+      - run: go install -tags=llvm<<parameters.llvm>> .
+      - restore_cache:
+          keys:
+            - wasi-libc-sysroot-systemclang-v2
+      - run: make wasi-libc
+      - save_cache:
+          key: wasi-libc-sysroot-systemclang-v2
+          paths:
+            - lib/wasi-libc/sysroot
+      - run: go test -v -tags=llvm<<parameters.llvm>> ./cgo ./compileopts ./interp ./transform .
      - run: make gen-device -j4
-      - run: make smoketest
+      - run: make smoketest XTENSA=0
+      - run: make tinygo-test
+      - run: make wasmtest
      - save_cache:
          key: go-cache-v2-{{ checksum "go.mod" }}-{{ .Environment.CIRCLE_BUILD_NUM }}
          paths:
            - ~/.cache/go-build
-            - ~/.cache/tinygo
            - /go/pkg/mod
      - run: make fmt-check
  assert-test-linux:
@@ -92,6 +134,8 @@ commands:
                gcc-avr \
                avr-libc
      - install-node
+      - install-xtensa-toolchain:
+          variant: "linux-amd64"
      - restore_cache:
          keys:
            - go-cache-v2-{{ checksum "go.mod" }}-{{ .Environment.CIRCLE_PREVIOUS_BUILD_NUM }}
@@ -99,7 +143,7 @@ commands:
      - llvm-source-linux
      - restore_cache:
          keys:
-            - llvm-build-9-linux-v0-assert
+            - llvm-build-10-linux-v1-assert
      - run:
          name: "Build LLVM"
          command: |
@@ -117,10 +161,11 @@ commands:
              make ASSERT=1 llvm-build
            fi
      - save_cache:
-          key: llvm-build-9-linux-v0-assert
+          key: llvm-build-10-linux-v1-assert
          paths:
            llvm-build
      - run: make ASSERT=1
+      - build-wasi-libc
      - run:
          name: "Test TinyGo"
          command: make ASSERT=1 test
@@ -128,7 +173,6 @@ commands:
          key: go-cache-v2-{{ checksum "go.mod" }}-{{ .Environment.CIRCLE_BUILD_NUM }}
          paths:
            - ~/.cache/go-build
-            - ~/.cache/tinygo
            - /go/pkg/mod
      - run: make gen-device -j4
      - run: make smoketest TINYGO=build/tinygo
@@ -150,6 +194,8 @@ commands:
                gcc-avr \
                avr-libc
      - install-node
+      - install-xtensa-toolchain:
+          variant: "linux-amd64"
      - restore_cache:
          keys:
            - go-cache-v2-{{ checksum "go.mod" }}-{{ .Environment.CIRCLE_PREVIOUS_BUILD_NUM }}
@@ -157,7 +203,7 @@ commands:
      - llvm-source-linux
      - restore_cache:
          keys:
-            - llvm-build-9-linux-v0
+            - llvm-build-10-linux-v1
      - run:
          name: "Build LLVM"
          command: |
@@ -175,24 +221,32 @@ commands:
              make llvm-build
            fi
      - save_cache:
-          key: llvm-build-9-linux-v0
+          key: llvm-build-10-linux-v1
          paths:
            llvm-build
+      - build-wasi-libc
      - run:
          name: "Test TinyGo"
          command: make test
+      - run:
+          name: "Install fpm"
+          command: |
+            sudo apt-get install ruby ruby-dev
+            sudo gem install --no-document fpm
      - run:
          name: "Build TinyGo release"
          command: |
-            make release -j3
+            make release deb -j3
            cp -p build/release.tar.gz /tmp/tinygo.linux-amd64.tar.gz
+            cp -p build/release.deb    /tmp/tinygo_amd64.deb
      - store_artifacts:
          path: /tmp/tinygo.linux-amd64.tar.gz
+      - store_artifacts:
+          path: /tmp/tinygo_amd64.deb
      - save_cache:
          key: go-cache-v2-{{ checksum "go.mod" }}-{{ .Environment.CIRCLE_BUILD_NUM }}
          paths:
            - ~/.cache/go-build
-            - ~/.cache/tinygo
            - /go/pkg/mod
      - run:
          name: "Extract release tarball"
@@ -209,27 +263,29 @@ commands:
      - run:
          name: "Install dependencies"
          command: |
-            curl https://dl.google.com/go/go1.13.darwin-amd64.tar.gz -o go1.13.darwin-amd64.tar.gz
-            sudo tar -C /usr/local -xzf go1.13.darwin-amd64.tar.gz
+            curl https://dl.google.com/go/go1.14.darwin-amd64.tar.gz -o go1.14.darwin-amd64.tar.gz
+            sudo tar -C /usr/local -xzf go1.14.darwin-amd64.tar.gz
            ln -s /usr/local/go/bin/go /usr/local/bin/go
            HOMEBREW_NO_AUTO_UPDATE=1 brew install qemu
+      - install-xtensa-toolchain:
+          variant: "macos"
      - restore_cache:
          keys:
            - go-cache-macos-v2-{{ checksum "go.mod" }}-{{ .Environment.CIRCLE_PREVIOUS_BUILD_NUM }}
            - go-cache-macos-v2-{{ checksum "go.mod" }}
      - restore_cache:
          keys:
-            - llvm-source-9-macos-v0
+            - llvm-source-10-macos-v1
      - run:
          name: "Fetch LLVM source"
          command: make llvm-source
      - save_cache:
-          key: llvm-source-9-macos-v0
+          key: llvm-source-10-macos-v1
          paths:
            - llvm-project
      - restore_cache:
          keys:
-            - llvm-build-9-macos-v0
+            - llvm-build-10-macos-v1
      - run:
          name: "Build LLVM"
          command: |
@@ -241,9 +297,19 @@ commands:
              make llvm-build
            fi
      - save_cache:
-          key: llvm-build-9-macos-v0
+          key: llvm-build-10-macos-v1
          paths:
            llvm-build
+      - restore_cache:
+          keys:
+            - wasi-libc-sysroot-macos-v2
+      - run:
+          name: "Build wasi-libc"
+          command: make wasi-libc
+      - save_cache:
+          key: wasi-libc-sysroot-macos-v2
+          paths:
+            - lib/wasi-libc/sysroot
      - run:
          name: "Test TinyGo"
          command: make test
@@ -261,44 +327,106 @@ commands:
            tar -C /usr/local/opt -xf /tmp/tinygo.darwin-amd64.tar.gz
            ln -s /usr/local/opt/tinygo/bin/tinygo /usr/local/bin/tinygo
            tinygo version
-      - run:
-          name: "Download SiFive GNU toolchain"
-          command: |
-            curl -O https://static.dev.sifive.com/dev-tools/riscv64-unknown-elf-gcc-8.2.0-2019.05.3-x86_64-apple-darwin.tar.gz
-            sudo tar -C /usr/local --strip-components=1 -xf riscv64-unknown-elf-gcc-8.2.0-2019.05.3-x86_64-apple-darwin.tar.gz
      - run: make smoketest AVR=0
      - save_cache:
          key: go-cache-macos-v2-{{ checksum "go.mod" }}-{{ .Environment.CIRCLE_BUILD_NUM }}
          paths:
            - ~/.cache/go-build
-            - ~/.cache/tinygo
            - /go/pkg/mod
-
+  arch-release:
+    steps:
+      - run:
+          name: Install dependencies
+          command: pacman -Sy --noconfirm openssh git pacman-contrib binutils
+      - run:
+          name: Create TinyGo user
+          command: useradd -m tinygo
+      - run:
+          name: Start SSH Agent
+          user: tinygo
+          command: eval $(ssh-agent -s)
+      - run:
+          name: Add ARCH_RELEASE_SSH_PRIVATE_KEY identity
+          user: tinygo
+          command: echo "${ARCH_RELEASE_SSH_PRIVATE_KEY}" | tr -d '\r' | ssh-add -
+      - run:
+          name: Create SSH directory
+          user: tinygo
+          command: mkdir -p ~/.ssh && chmod 700 ~/.ssh
+      - run:
+          name: Add aur.archlinux.org to known hosts
+          user: tinygo
+          command: ssh-keyscan aur.archlinux.org >> ~/.ssh/known_hosts
+      - run:
+          name: Clone tinygo-bin repo
+          user: tinygo
+          command: git clone ssh://aur@aur.archlinux.org/tinygo-bin.git ~/tinygo-bin
+      - run:
+          name: Update package version
+          user: tinygo
+          command: sed -i -E "s/(pkgver=)(.*)$/\1${CIRCLE_TAG}/" ~/tinygo-bin/PKGBUILD
+      - run:
+          name: Update file checksums
+          user: tinygo
+          command: cd ~/tinygo-bin && updpkgsums
+      - run:
+          name: Update .SRCINFO
+          user: tinygo
+          command: cd ~/tinygo-bin && makepkg --printsrcinfo > .SRCINFO
+      # Commit the update
+      - run:
+          name: Set git commit config
+          user: tinygo
+          command: |
+            git config --global user.email "tinygo-bot@tinygo.org" &&
+            git config --global user.name "TinyGo Release Bot"
+      - run:
+          name: Commit and push changes
+          user: tinygo
+          command: |
+            cd ~/tinygo-bin &&
+            git commit -a -m "Update tinygo-bin to v${CIRCLE_TAG}" &&
+            git push origin master

 jobs:
  test-llvm9-go111:
    docker:
-      - image: circleci/golang:1.11-stretch
+      - image: circleci/golang:1.11-buster
    steps:
-      - test-linux
-  test-llvm9-go112:
+      - test-linux:
+          llvm: "9"
+  test-llvm10-go112:
    docker:
-      - image: circleci/golang:1.12-stretch
+      - image: circleci/golang:1.12-buster
    steps:
-      - test-linux
-  test-llvm9-go113:
+      - test-linux:
+          llvm: "10"
+  test-llvm10-go113:
    docker:
-      - image: circleci/golang:1.13-stretch
+      - image: circleci/golang:1.13-buster
    steps:
-      - test-linux
+      - test-linux:
+          llvm: "10"
+  test-llvm10-go114:
+    docker:
+      - image: circleci/golang:1.14-buster
+    steps:
+      - test-linux:
+          llvm: "10"
+  test-llvm10-go115:
+    docker:
+      - image: circleci/golang:1.15-buster
+    steps:
+      - test-linux:
+          llvm: "10"        
  assert-test-linux:
    docker:
-      - image: circleci/golang:1.13-stretch
+      - image: circleci/golang:1.14-stretch
    steps:
      - assert-test-linux
  build-linux:
    docker:
-      - image: circleci/golang:1.13-stretch
+      - image: circleci/golang:1.14-stretch
    steps:
      - build-linux
  build-macos:
@@ -306,6 +434,11 @@ jobs:
      xcode: "10.1.0"
    steps:
      - build-macos
+  arch-release:
+    docker:
+      - image: archlinux:latest
+    steps:
+      - arch-release



@@ -314,8 +447,19 @@ workflows:
  test-all:
    jobs:
      - test-llvm9-go111
-      - test-llvm9-go112
-      - test-llvm9-go113
+      - test-llvm10-go112
+      - test-llvm10-go113
+      - test-llvm10-go114
+      - test-llvm10-go115
      - build-linux
      - build-macos
      - assert-test-linux
+  release:
+    jobs:
+      - arch-release:
+          filters:
+            branches:
+              ignore: /.*/
+            tags:
+              # Runs on every semver release
+              only: /v[0-9]+(\.[0-9]+)*(-.*)*/
@@ -3,14 +3,19 @@ docs/_build
 src/device/avr/*.go
 src/device/avr/*.ld
 src/device/avr/*.s
+src/device/esp/*.go
 src/device/nrf/*.go
 src/device/nrf/*.s
+src/device/nxp/*.go
+src/device/nxp/*.s
 src/device/sam/*.go
 src/device/sam/*.s
 src/device/sifive/*.go
 src/device/sifive/*.s
 src/device/stm32/*.go
 src/device/stm32/*.s
+src/device/kendryte/*.go
+src/device/kendryte/*.s
 vendor
 llvm-build
 llvm-project
@@ -14,3 +14,9 @@
 	path = lib/compiler-rt
 	url = https://github.com/llvm-mirror/compiler-rt.git
 	branch = release_80
+[submodule "lib/wasi-libc"]
+	path = lib/wasi-libc
+	url = https://github.com/CraneStation/wasi-libc
+[submodule "lib/picolibc"]
+	path = lib/picolibc
+	url = https://github.com/keith-packard/picolibc.git
@@ -10,6 +10,14 @@ This guide describes how to statically link TinyGo against LLVM, libclang and
 lld so that the binary can be easily moved between systems. It also shows how to
 build a release tarball that includes this binary and all necessary extra files.

+**Note**: this documentation describes how to build a statically linked release
+tarball. If you want to develop TinyGo, you will probably want to follow a
+different guide:
+
+  * [Linux](https://tinygo.org/getting-started/linux/#source-install)
+  * [macOS](https://tinygo.org/getting-started/macos/#source-install)
+  * [Windows](https://tinygo.org/getting-started/windows/#source-install)
+
 ## Dependencies

 LLVM, Clang and LLD are quite light on dependencies, requiring only standard
@@ -84,6 +92,10 @@ Now that we have a working static build, it's time to make a release tarball:

    make release

+If you did not clone the repository with the `--recursive` option, you will get errors until you initialize the project submodules:
+
+    git submodule update --init
+
 The release tarball is stored in build/release.tar.gz, and can be extracted with
 the following command (for example in ~/lib):

@@ -1,3 +1,330 @@
+0.15.0
+---
+
+* **command-line**
+  - add cached GOROOT to info subcommand
+  - embed git-hash in tinygo-dev executable
+  - implement tinygo targets to list usable targets
+  - use simpler file copy instead of file renaming to avoid issues on nrf52840 UF2 bootloaders
+  - use ToSlash() to specify program path
+  - support flashing esp32/esp8266 directly from tinygo
+  - when flashing call PortReset only on other than openocd
+* **compiler**
+  - `compileopts`: add support for custom binary formats
+  - `compiler`: improve display of goroutine wrappers
+  - `interp`: don't panic in the Store method
+  - `interp`: replace some panics with error messages
+  - `interp`: show error line in first line of the traceback
+  - `loader`: be more robust when creating the cached GOROOT
+  - `loader`: rewrite/refactor much of the code to use go list directly
+  - `loader`: use ioutil.TempDir to create a temporary directory
+  - `stacksize`: deal with DW_CFA_advance_loc1
+* **standard library**
+  - `runtime`: use waitForEvents when appropriate
+* **wasm**
+  - `wasm`: Remove --no-threads from wasm-ld calls.
+  - `wasm`: update wasi-libc dependency
+* **targets**
+  - `arduino-mega2560`: fix flashing on Windows
+  - `arm`: automatically determine stack sizes
+  - `arm64`: make dynamic loader structs and constants private
+  - `avr`: configure emulator in board files
+  - `cortexm`: fix stack size calculation with interrupts
+  - `flash`: add openocd settings to atsamd21 / atsamd51
+  - `flash`: add openocd settings to nrf5
+  - `microbit`: reelboard: flash using OpenOCD when needed
+  - `nintendoswitch`: Add dynamic loader for runtime loading PIE sections
+  - `nintendoswitch`: fix import cycle on dynamic_arm64.go
+  - `nintendoswitch`: Fix invalid memory read / write in print calls
+  - `nintendoswitch`: simplified assembly code
+  - `nintendoswitch`: support outputting .nro files directly
+* **boards**
+  - `arduino-zero`: Adding support for the Arduino Zero (#1365)
+  - `atsamd2x`: fix BAUD value
+  - `atsamd5x`: fix BAUD value
+  - `bluepill`: Enable stm32's USART2 for the board and map it to UART1 tinygo's device
+  - `device/atsamd51x`: add all remaining bitfield values for PCHCTRLm Mapping
+  - `esp32`: add libgcc ROM functions to linker script
+  - `esp32`: add SPI support
+  - `esp32`: add support for basic GPIO
+  - `esp32`: add support for the Espressif ESP32 chip
+  - `esp32`: configure the I/O matrix for GPIO pins
+  - `esp32`: export machine.PortMask* for bitbanging implementations
+  - `esp8266`: add support for this chip
+  - `machine/atsamd51x,runtime/atsamd51x`: fixes needed for full support for all PWM pins. Also adds some useful constants to clarify peripheral clock usage
+  - `machine/itsybitsy-nrf52840`: add support for Adafruit Itsybitsy nrf52840 (#1243)
+  - `machine/stm32f4`: refactor common code and add new build tag stm32f4 (#1332)
+  - `nrf`: add SoftDevice support for the Circuit Playground Bluefruit
+  - `nrf`: call sd_app_evt_wait when the SoftDevice is enabled
+  - `nrf52840`: add build tags for SoftDevice support
+  - `nrf52840`: use higher priority for USB-CDC code
+  - `runtime/atsamd51x`: use PCHCTRL_GCLK_SERCOMX_SLOW for setting clocks on all SERCOM ports
+  - `stm32f405`: add basic UART handler
+  - `stm32f405`: add STM32F405 machine/runtime, and new board/target feather-stm32f405
+* **build**
+  - `all`: run test binaries in the correct directory
+  - `build`: Fix arch release job
+  - `ci`: run `tinygo test` for known-working packages
+  - `ci`: set git-fetch-depth to 1
+  - `docker`: fix the problem with the wasm build (#1357)
+  - `Makefile`: check whether submodules have been downloaded in some common cases
+* **docs**
+  - add ESP32, ESP8266, and Adafruit Feather STM32F405 to list of supported boards
+
+0.14.1
+---
+* **command-line**
+  - support for Go 1.15
+* **compiler**
+  - loader:  work around Windows symlink limitation
+
+0.14.0
+---
+* **command-line**
+  - fix `getDefaultPort()` on non-English Windows locales
+  - compileopts: improve error reporting of unsupported flags
+  - fix test subcommand
+  - use auto-retry to locate MSD for UF2 and HEX flashing
+  - fix touchSerialPortAt1200bps on Windows
+  - support package names with backslashes on Windows
+* **compiler**
+  - fix a few crashes due to named types
+  - add support for atomic operations
+  - move the channel blocked list onto the stack
+  - fix -gc=none
+  - fix named string to `[]byte` slice conversion
+  - implement func value and builtin defers
+  - add proper parameter names to runtime.initAll, to fix a panic
+  - builder: fix picolibc include path
+  - builder: use newer version of gohex
+  - builder: try to determine stack size information at compile time
+  - builder: remove -opt=0
+  - interp: fix sync/atomic.Value load/store methods
+  - loader: add Go module support
+  - transform: fix debug information in func lowering pass
+  - transform: do not special-case zero or one implementations of a method call
+  - transform: introduce check for method calls on nil interfaces
+  - transform: gc: track 0-index GEPs to fix miscompilation
+* **cgo**
+  - Add LDFlags support
+* **standard library**
+  - extend stdlib to allow import of more packages
+  - replace master/slave terminology with appropriate alternatives (MOSI->SDO
+    etc)
+  - `internal/bytealg`: reimplement bytealg in pure Go
+  - `internal/task`: fix nil panic in (*internal/task.Stack).Pop
+  - `os`: add Args and stub it with mock data
+  - `os`: implement virtual filesystem support
+  - `reflect`: add Cap and Len support for map and chan
+  - `runtime`: fix return address in scheduler on RISC-V
+  - `runtime`: avoid recursion in printuint64 function
+  - `runtime`: replace ReadRegister with AsmFull inline assembly
+  - `runtime`: fix compilation errors when using gc.extalloc
+  - `runtime`: add cap and len support for chans
+  - `runtime`: refactor time handling (improving accuracy)
+  - `runtime`: make channels work in interrupts
+  - `runtime/interrupt`: add cross-chip disable/restore interrupt support
+  - `sync`: implement `sync.Cond`
+  - `sync`: add WaitGroup
+* **targets**
+  - `arm`: allow nesting in DisableInterrupts and EnableInterrupts
+  - `arm`: make FPU configuraton consistent
+  - `arm`: do not mask fault handlers in critical sections
+  - `atmega2560`: fix pin mapping for pins D2, D5 and the L port
+  - `atsamd`: return an error when an incorrect PWM pin is used
+  - `atsamd`: add support for pin change interrupts
+  - `atsamd`: add DAC support
+  - `atsamd21`: add more ADC pins
+  - `atsamd51`: fix ROM / RAM size on atsamd51j20
+  - `atsamd51`: add more pins
+  - `atsamd51`: add more ADC pins
+  - `atsamd51`: add pin change interrupt settings
+  - `atsamd51`: extend pinPadMapping
+  - `arduino-nano33`: use (U)SB flag to ensure that device can be found when
+     not on default port
+  - `arduino-nano33`: remove (d)ebug flag to reduce console noise when flashing
+  - `avr`: use standard pin numbering
+  - `avr`: unify GPIO pin/port code
+  - `avr`: add support for PinInputPullup
+  - `avr`: work around codegen bug in LLVM 10
+  - `avr`: fix target triple
+  - `fe310`: remove extra println left in by mistake
+  - `feather-nrf52840`: add support for the Feather nRF52840
+  - `maixbit`: add board definition and dummy runtime
+  - `nintendoswitch`: Add experimental Nintendo Switch support without CRT
+  - `nrf`: expose the RAM base address
+  - `nrf`: add support for pin change interrupts
+  - `nrf`: add microbit-s110v8 target
+  - `nrf`: fix bug in SPI.Tx
+  - `nrf`: support debugging the PCA10056
+  - `pygamer`: add Adafruit PyGamer suport
+  - `riscv`: fix interrupt configuration bug
+  - `riscv`: disable linker relaxations during gp init
+  - `stm32f4disco`: add new target with ST-Link v2.1 debugger
+  - `teensy36`: add Teensy 3.6 support
+  - `wasm`: fix event handling
+  - `wasm`: add --no-demangle linker option
+  - `wioterminal`: add support for the Seeed Wio Terminal
+  - `xiao`: add support for the Seeed XIAO
+
+0.13.1
+---
+* **standard library**
+  - `runtime`: do not put scheduler and GC code in the same section
+  - `runtime`: copy stack scan assembly for GBA
+* **boards**
+  - `gameboy-advance`: always use ARM mode instead of Thumb mode
+
+
+0.13.0
+---
+* **command line**
+  - use `gdb-multiarch` for debugging Cortex-M chips
+  - support `tinygo run` with simavr
+  - support LLVM 10
+  - support Go 1.14
+  - retry 3 times when attempting to do a 1200-baud reset
+* **compiler**
+  - mark the `abort` function as noreturn
+  - fix deferred calls to exported functions
+  - add debug info for local variables
+  - check for channel size limit
+  - refactor coroutine lowering
+  - add `dereferenceable_or_null` attribute to pointer parameters
+  - do not perform nil checking when indexing slices and on `unsafe.Pointer`
+  - remove `runtime.isnil` hack
+  - use LLVM builtins for runtime `memcpy`/`memmove`/`memzero` functions
+  - implement spec-compliant shifts on negative/overflow
+  - support anonymous type asserts
+  - track pointer result of string concatenation for GC
+  - track PHI nodes for GC
+  - add debug info to goroutine start wrappers
+  - optimize comparing interface values against nil
+  - fix miscompilation when deferring an interface call
+  - builder: include picolibc for most baremetal targets
+  - builder: run tools (clang, lld) as separate processes
+  - builder: use `-fshort-enums` consistently
+  - interp: add support for constant type asserts
+  - interp: better support for interface operations
+  - interp: include backtrace with error
+  - transform: do not track const globals for GC
+  - transform: replace panics with source locations
+  - transform: fix error in interface lowering pass
+  - transform: make coroutine lowering deterministic
+  - transform: fix miscompilation in func lowering
+* **cgo**
+  - make `-I` and `-L` paths absolute
+* **standard library**
+  - `machine`: set the USB VID and PID to the manufacturer values
+  - `machine`: correct USB CDC composite descriptors
+  - `machine`: move `errors.New` calls to globals
+  - `runtime`: support operations on nil maps
+  - `runtime`: fix copy builtin return value on AVR
+  - `runtime`: refactor goroutines
+  - `runtime`: support `-scheduler=none` on most platforms
+  - `runtime`: run package initialization in the main goroutine
+  - `runtime`: export `malloc` / `free` for use from C
+  - `runtime`: add garbage collector that uses an external allocator
+  - `runtime`: scan callee-saved registers while marking the stack
+  - `runtime`: remove recursion from conservative GC
+  - `runtime`: fix blocking select on nil channel
+  - `runtime/volatile`: include `ReplaceBits` method
+  - `sync`: implement trivial `sync.Map`
+* **targets**
+  - `arm`: use `-fomit-frame-pointer`
+  - `atmega1284`: support this chip for testing purposes
+  - `atsamd51`: make QSPI available on all boards
+  - `atsamd51`: add support for ADC1
+  - `atsamd51`: use new interrupt registration in UART code
+  - `attiny`: clean up pin definitions
+  - `avr`: use the correct RAM start address
+  - `avr`: pass the correct `-mmcu` flag to the linker
+  - `avr`: add support for tasks scheduler (disabled by default)
+  - `avr`: fix linker problem with overlapping program/data areas
+  - `nrf`: fix typo in pin configuration options
+  - `nrf`: add lib/nrfx/mdk to include dirs
+  - `nrf52840`: implement USB-CDC
+  - `riscv`: implement VirtIO target and add RISC-V integration test
+  - `riscv`: add I2C support for the HiFive1 rev B board
+  - `stm32`: refactor GPIO pin handling
+  - `stm32`: refactor UART code
+  - `stm32f4`: add SPI
+  - `wasm`: support Go 1.14 (breaking previous versions)
+  - `wasm`: support `syscall/js.CopyBytesToJS`
+  - `wasm`: sync polyfills from Go 1.14.
+* **boards**
+  - `arduino-mega2560`: add the Arduino Mega 2560
+  - `clue-alpha`: add the Adafruit CLUE Alpha
+  - `gameboy-advance`: enable debugging with GDB
+  - `particle-argon`: add the Particle Argon board
+  - `particle-boron`: add the Particle Boron board
+  - `particle-xenon`: add the Particle Xenon board
+  - `reelboard`: add `reelboard-s140v7` SoftDevice target
+
+0.12.0
+---
+* **command line**
+  - add initial FreeBSD support
+  - remove getting a serial port in gdb subcommand
+  - add support for debugging through JLinkGDBServer
+  - fix CGo when cross compiling
+  - remove default port check for Digispark as micronucleus communicates directly using HID
+  - differentiate between various serial/USB error messages
+* **builder**
+  - improve detection of Clang headers
+* **compiler**
+  - fix assertion on empty interface
+  - don't crash when encountering `types.Invalid`
+  - revise defer to use heap allocations when running a variable number of times
+  - improve error messages for failed imports
+  - improve "function redeclared" error
+  - add globaldce pass to start of optimization pipeline
+  - add support for debugging globals
+  - implement RISC-V CSR operations as intrinsics
+  - add support for CGO_ENABLED environment variable
+  - do not emit debug info for extern globals (bugfix)
+  - add support for interrupts
+  - implement maps for arbitrary keys
+  - interp: error location for "unknown GEP" error
+  - wasm-abi: create temporary allocas in the entry block
+* **cgo**
+  - add support for symbols in `#define`
+  - fix a bug in number tokenization
+* **standard library**
+  - `machine`: avoid bytes package in USB logic
+  - `runtime`: fix external address declarations
+  - `runtime`: provide implementation for `internal/bytealg.IndexByte`
+* **targets**
+  - `atsamd51`: fix volatile usage
+  - `atsamd51`: fix ADC, updating to 12-bits precision
+  - `atsamd51`: refactor SPI pin configuration to only look at pin numbers
+  - `atsamd51`: switch UART to use new pin configuration
+  - `atsamd51`: fix obvious bug in I2C code
+  - `atsamd51`: use only the necessary UART interrupts
+  - `atsamd51`: refactor I2C pin handling to auto-detect pin mode
+  - `avr`: use a garbage collector
+  - `fe310`: use CLINT peripheral for timekeeping
+  - `fe310`: add support for PLIC interrupts
+  - `fe310`: implement UART receive interrupts
+  - `riscv`: support sleeping in QEMU
+  - `riscv`: add bare-bones interrupt support
+  - `riscv`: print exception PC and code
+  - `wasm`: implement memcpy and memset
+  - `wasm`: include wasi-libc
+  - `wasm`: use wasi ABI for basic startup/stdout
+* **boards**
+  - `arduino`: make avrdude command line compatible with Windows
+  - `arduino-nano`: add this board
+  - `arduino-nano33`: fix UART1 and UART2
+  - `circuitplay-bluefruit`: add this board
+  - `digispark`: add clock speed and pin mappings
+  - `gameboy-advance`: include compiler-rt in build
+  - `gameboy-advance`: implement interrupt handler
+  - `hifive1b`: add support for gdb subcommand
+  - `pyportal`: add this board
+  - `pyportal`: remove manual SPI pin mapping as now handled by default
+
+
 0.11.0
 ---
 * **command line**
@@ -32,7 +32,7 @@ Microcontrollers have lots of peripherals (I2C, SPI, ADC, etc.) and many don't h

 ## How to use our Github repository

-The `master` branch of this repo will always have the latest released version of TinyGo. All of the active development work for the next release will take place in the `dev` branch. TinyGo will use semantic versioning and will create a tag/release for each release.
+The `release` branch of this repo will always have the latest released version of TinyGo. All of the active development work for the next release will take place in the `dev` branch. TinyGo will use semantic versioning and will create a tag/release for each release.

 Here is how to contribute back some code or documentation:

@@ -15,3 +15,4 @@ Ayke van Laethem <aykevanlaethem@gmail.com>
 Daniel Esteban <conejo@conejo.me>
 Loon, LLC.
 Ron Evans <ron@hybridgroup.com>
+Nia Weiss <niaow1234@gmail.com>
@@ -1,10 +1,10 @@
-# TinyGo base stage installs Go 1.13, LLVM 9 and the TinyGo compiler itself.
-FROM golang:1.13 AS tinygo-base
+# TinyGo base stage installs Go 1.14, LLVM 10 and the TinyGo compiler itself.
+FROM golang:1.14 AS tinygo-base

 RUN wget -O- https://apt.llvm.org/llvm-snapshot.gpg.key| apt-key add - && \
-    echo "deb http://apt.llvm.org/buster/ llvm-toolchain-buster-9 main" >> /etc/apt/sources.list && \
+    echo "deb http://apt.llvm.org/buster/ llvm-toolchain-buster-10 main" >> /etc/apt/sources.list && \
    apt-get update && \
-    apt-get install -y llvm-9-dev libclang-9-dev git
+    apt-get install -y llvm-10-dev libclang-10-dev lld-10 git

 COPY . /tinygo

@@ -12,8 +12,11 @@ COPY . /tinygo
 # after copying the tinygo directory in the previous step.
 RUN cd /tinygo/ && \
    rm -rf ./lib/* && \
+    git submodule sync && \
    git submodule update --init --recursive --force

+COPY ./lib/picolibc-include/* /tinygo/lib/picolibc-include/
+
 RUN cd /tinygo/ && \
    go install /tinygo/

@@ -24,10 +27,10 @@ COPY --from=tinygo-base /go/bin/tinygo /go/bin/tinygo
 COPY --from=tinygo-base /tinygo/src /tinygo/src
 COPY --from=tinygo-base /tinygo/targets /tinygo/targets

-RUN wget -O- https://apt.llvm.org/llvm-snapshot.gpg.key| apt-key add - && \
-    echo "deb http://apt.llvm.org/buster/ llvm-toolchain-buster-9 main" >> /etc/apt/sources.list && \
+RUN cd /tinygo/ && \
    apt-get update && \
-    apt-get install -y libllvm9 lld-9
+    apt-get install -y make clang-10 libllvm10 lld-10 && \
+    make wasi-libc

 # tinygo-avr stage installs the needed dependencies to compile TinyGo programs for AVR microcontrollers.
 FROM tinygo-base AS tinygo-avr
@@ -58,7 +61,7 @@ COPY --from=tinygo-base /tinygo/lib /tinygo/lib

 RUN cd /tinygo/ && \
    apt-get update && \
-    apt-get install -y apt-utils make clang-9 && \
+    apt-get install -y apt-utils make clang-10 && \
    make gen-device-nrf && make gen-device-stm32

 # tinygo-all stage installs the needed dependencies to compile TinyGo programs for all platforms.
@@ -70,7 +73,7 @@ COPY --from=tinygo-base /tinygo/lib /tinygo/lib

 RUN cd /tinygo/ && \
    apt-get update && \
-    apt-get install -y apt-utils make clang-9 binutils-avr gcc-avr avr-libc && \
+    apt-get install -y apt-utils make clang-10 binutils-avr gcc-avr avr-libc && \
    make gen-device

 CMD ["tinygo"]
@@ -1,7 +1,7 @@
-Copyright (c) 2018-2019 TinyGo Authors. All rights reserved.
+Copyright (c) 2018-2020 TinyGo Authors. All rights reserved.

 TinyGo includes portions of the Go standard library.
-Copyright (c) 2009-2019 The Go Authors. All rights reserved.
+Copyright (c) 2009-2020 The Go Authors. All rights reserved.

 TinyGo includes portions of LLVM, which is under the Apache License v2.0 with
 LLVM Exceptions. See https://llvm.org/LICENSE.txt for license information.
@@ -4,8 +4,30 @@ all: tinygo

 # Default build and source directories, as created by `make llvm-build`.
 LLVM_BUILDDIR ?= llvm-build
-CLANG_SRC ?= llvm-project/clang
-LLD_SRC ?= llvm-project/lld
+LLVM_PROJECTDIR ?= llvm-project
+CLANG_SRC ?= $(LLVM_PROJECTDIR)/clang
+LLD_SRC ?= $(LLVM_PROJECTDIR)/lld
+
+# Try to autodetect LLVM build tools.
+ifneq (, $(shell command -v llvm-build/bin/clang 2> /dev/null))
+    CLANG ?= $(abspath llvm-build/bin/clang)
+else
+    CLANG ?= clang-10
+endif
+ifneq (, $(shell command -v llvm-build/bin/llvm-ar 2> /dev/null))
+    LLVM_AR ?= $(abspath llvm-build/bin/llvm-ar)
+else ifneq (, $(shell command -v llvm-ar-10 2> /dev/null))
+    LLVM_AR ?= llvm-ar-10
+else
+    LLVM_AR ?= llvm-ar
+endif
+ifneq (, $(shell command -v llvm-build/bin/llvm-nm 2> /dev/null))
+    LLVM_NM ?= $(abspath llvm-build/bin/llvm-nm)
+else ifneq (, $(shell command -v llvm-nm-10 2> /dev/null))
+    LLVM_NM ?= llvm-nm-10
+else
+    LLVM_NM ?= llvm-nm
+endif

 # Go binary and GOROOT to select
 GO ?= go
@@ -18,7 +40,7 @@ MD5SUM = md5sum
 TINYGO ?= tinygo

 # Use CCACHE for LLVM if possible
-ifneq (, $(shell which ccache))
+ifneq (, $(shell command -v ccache 2> /dev/null))
    LLVM_OPTION += '-DLLVM_CCACHE_BUILD=ON'
 endif

@@ -29,9 +51,9 @@ else
    LLVM_OPTION += '-DLLVM_ENABLE_ASSERTIONS=OFF'
 endif

-.PHONY: all tinygo test $(LLVM_BUILDDIR) llvm-source clean fmt gen-device gen-device-nrf gen-device-avr
+.PHONY: all tinygo test $(LLVM_BUILDDIR) llvm-source clean fmt gen-device gen-device-nrf gen-device-nxp gen-device-avr

-LLVM_COMPONENTS = all-targets analysis asmparser asmprinter bitreader bitwriter codegen core coroutines coverage debuginfodwarf executionengine instrumentation interpreter ipo irreader linker lto mc mcjit objcarcopts option profiledata scalaropts support target
+LLVM_COMPONENTS = all-targets analysis asmparser asmprinter bitreader bitwriter codegen core coroutines coverage debuginfodwarf executionengine frontendopenmp instrumentation interpreter ipo irreader linker lto mc mcjit objcarcopts option profiledata scalaropts support target

 ifeq ($(OS),Windows_NT)
    EXE = .exe
@@ -81,8 +103,8 @@ LLD_LIBS = $(START_GROUP) -llldCOFF -llldCommon -llldCore -llldDriver -llldELF -
 # For static linking.
 ifneq ("$(wildcard $(LLVM_BUILDDIR)/bin/llvm-config*)","")
    CGO_CPPFLAGS=$(shell $(LLVM_BUILDDIR)/bin/llvm-config --cppflags) -I$(abspath $(LLVM_BUILDDIR))/tools/clang/include -I$(abspath $(CLANG_SRC))/include -I$(abspath $(LLD_SRC))/include
-    CGO_CXXFLAGS=-std=c++11
-    CGO_LDFLAGS+=$(LIBCLANG_PATH) -std=c++11 -L$(abspath $(LLVM_BUILDDIR)/lib) $(CLANG_LIBS) $(LLD_LIBS) $(shell $(LLVM_BUILDDIR)/bin/llvm-config --ldflags --libs --system-libs $(LLVM_COMPONENTS)) -lstdc++ $(CGO_LDFLAGS_EXTRA)
+    CGO_CXXFLAGS=-std=c++14
+    CGO_LDFLAGS+=$(LIBCLANG_PATH) -std=c++14 -L$(abspath $(LLVM_BUILDDIR)/lib) $(CLANG_LIBS) $(LLD_LIBS) $(shell $(LLVM_BUILDDIR)/bin/llvm-config --ldflags --libs --system-libs $(LLVM_COMPONENTS)) -lstdc++ $(CGO_LDFLAGS_EXTRA)
 endif


@@ -96,9 +118,10 @@ fmt-check:
 	@unformatted=$$(gofmt -l $(FMT_PATHS)); [ -z "$$unformatted" ] && exit 0; echo "Unformatted:"; for fn in $$unformatted; do echo "  $$fn"; done; exit 1


-gen-device: gen-device-avr gen-device-nrf gen-device-sam gen-device-sifive gen-device-stm32
+gen-device: gen-device-avr gen-device-esp gen-device-nrf gen-device-sam gen-device-sifive gen-device-stm32 gen-device-kendryte gen-device-nxp

 gen-device-avr:
+	@if [ ! -e lib/avr/README.md ]; then echo "Submodules have not been downloaded. Please download them using:\n  git submodule update --init"; exit 1; fi
 	$(GO) build -o ./build/gen-device-avr ./tools/gen-device-avr/
 	./build/gen-device-avr lib/avr/packs/atmega src/device/avr/
 	./build/gen-device-avr lib/avr/packs/tiny src/device/avr/
@@ -107,53 +130,79 @@ gen-device-avr:
 build/gen-device-svd: ./tools/gen-device-svd/*.go
 	$(GO) build -o $@ ./tools/gen-device-svd/

+gen-device-esp: build/gen-device-svd
+	./build/gen-device-svd -source=https://github.com/posborne/cmsis-svd/tree/master/data/Espressif-Community -interrupts=software lib/cmsis-svd/data/Espressif-Community/ src/device/esp/
+	GO111MODULE=off $(GO) fmt ./src/device/esp
+
 gen-device-nrf: build/gen-device-svd
 	./build/gen-device-svd -source=https://github.com/NordicSemiconductor/nrfx/tree/master/mdk lib/nrfx/mdk/ src/device/nrf/
 	GO111MODULE=off $(GO) fmt ./src/device/nrf

+gen-device-nxp: build/gen-device-svd
+	./build/gen-device-svd -source=https://github.com/posborne/cmsis-svd/tree/master/data/NXP lib/cmsis-svd/data/NXP/ src/device/nxp/
+	GO111MODULE=off $(GO) fmt ./src/device/nxp
+
 gen-device-sam: build/gen-device-svd
 	./build/gen-device-svd -source=https://github.com/posborne/cmsis-svd/tree/master/data/Atmel lib/cmsis-svd/data/Atmel/ src/device/sam/
 	GO111MODULE=off $(GO) fmt ./src/device/sam

 gen-device-sifive: build/gen-device-svd
-	./build/gen-device-svd -source=https://github.com/posborne/cmsis-svd/tree/master/data/SiFive-Community lib/cmsis-svd/data/SiFive-Community/ src/device/sifive/
+	./build/gen-device-svd -source=https://github.com/posborne/cmsis-svd/tree/master/data/SiFive-Community -interrupts=software lib/cmsis-svd/data/SiFive-Community/ src/device/sifive/
 	GO111MODULE=off $(GO) fmt ./src/device/sifive

+gen-device-kendryte: build/gen-device-svd
+	./build/gen-device-svd -source=https://github.com/posborne/cmsis-svd/tree/master/data/Kendryte-Community -interrupts=software lib/cmsis-svd/data/Kendryte-Community/ src/device/kendryte/
+	GO111MODULE=off $(GO) fmt ./src/device/kendryte
+
 gen-device-stm32: build/gen-device-svd
 	./build/gen-device-svd -source=https://github.com/posborne/cmsis-svd/tree/master/data/STMicro lib/cmsis-svd/data/STMicro/ src/device/stm32/
 	GO111MODULE=off $(GO) fmt ./src/device/stm32


 # Get LLVM sources.
-llvm-project/README.md:
-	git clone -b release/9.x https://github.com/llvm/llvm-project
-llvm-source: llvm-project/README.md
+$(LLVM_PROJECTDIR)/README.md:
+	git clone -b xtensa_release_10.0.1 --depth=1 https://github.com/tinygo-org/llvm-project $(LLVM_PROJECTDIR)
+llvm-source: $(LLVM_PROJECTDIR)/README.md

 # Configure LLVM.
 TINYGO_SOURCE_DIR=$(shell pwd)
 $(LLVM_BUILDDIR)/build.ninja: llvm-source
-	mkdir -p $(LLVM_BUILDDIR); cd $(LLVM_BUILDDIR); cmake -G Ninja $(TINYGO_SOURCE_DIR)/llvm-project/llvm "-DLLVM_TARGETS_TO_BUILD=X86;ARM;AArch64;RISCV;WebAssembly" "-DLLVM_EXPERIMENTAL_TARGETS_TO_BUILD=AVR" -DCMAKE_BUILD_TYPE=Release -DLIBCLANG_BUILD_STATIC=ON -DLLVM_ENABLE_TERMINFO=OFF -DLLVM_ENABLE_ZLIB=OFF -DLLVM_ENABLE_PROJECTS="clang;lld" -DLLVM_TOOL_CLANG_TOOLS_EXTRA_BUILD=OFF $(LLVM_OPTION)
+	mkdir -p $(LLVM_BUILDDIR); cd $(LLVM_BUILDDIR); cmake -G Ninja $(TINYGO_SOURCE_DIR)/$(LLVM_PROJECTDIR)/llvm "-DLLVM_TARGETS_TO_BUILD=X86;ARM;AArch64;RISCV;WebAssembly" "-DLLVM_EXPERIMENTAL_TARGETS_TO_BUILD=AVR;Xtensa" -DCMAKE_BUILD_TYPE=Release -DLIBCLANG_BUILD_STATIC=ON -DLLVM_ENABLE_TERMINFO=OFF -DLLVM_ENABLE_ZLIB=OFF -DLLVM_ENABLE_LIBEDIT=OFF -DLLVM_ENABLE_Z3_SOLVER=OFF -DLLVM_ENABLE_OCAMLDOC=OFF -DLLVM_ENABLE_PROJECTS="clang;lld" -DLLVM_TOOL_CLANG_TOOLS_EXTRA_BUILD=OFF $(LLVM_OPTION)

 # Build LLVM.
 $(LLVM_BUILDDIR): $(LLVM_BUILDDIR)/build.ninja
 	cd $(LLVM_BUILDDIR); ninja


+# Build wasi-libc sysroot
+.PHONY: wasi-libc
+wasi-libc: lib/wasi-libc/sysroot/lib/wasm32-wasi/libc.a
+lib/wasi-libc/sysroot/lib/wasm32-wasi/libc.a:
+	@if [ ! -e lib/wasi-libc/Makefile ]; then echo "Submodules have not been downloaded. Please download them using:\n  git submodule update --init"; exit 1; fi
+	cd lib/wasi-libc && make -j4 WASM_CC=$(CLANG) WASM_AR=$(LLVM_AR) WASM_NM=$(LLVM_NM)
+
+
 # Build the Go compiler.
 tinygo:
 	@if [ ! -f "$(LLVM_BUILDDIR)/bin/llvm-config" ]; then echo "Fetch and build LLVM first by running:"; echo "  make llvm-source"; echo "  make $(LLVM_BUILDDIR)"; exit 1; fi
-	CGO_CPPFLAGS="$(CGO_CPPFLAGS)" CGO_CXXFLAGS="$(CGO_CXXFLAGS)" CGO_LDFLAGS="$(CGO_LDFLAGS)" $(GO) build -o build/tinygo$(EXE) -tags byollvm .
+	CGO_CPPFLAGS="$(CGO_CPPFLAGS)" CGO_CXXFLAGS="$(CGO_CXXFLAGS)" CGO_LDFLAGS="$(CGO_LDFLAGS)" $(GO) build -buildmode exe -o build/tinygo$(EXE) -tags byollvm -ldflags="-X main.gitSha1=`git rev-parse --short HEAD`" .

-test:
-	CGO_CPPFLAGS="$(CGO_CPPFLAGS)" CGO_CXXFLAGS="$(CGO_CXXFLAGS)" CGO_LDFLAGS="$(CGO_LDFLAGS)" $(GO) test -v -tags byollvm ./cgo ./compileopts ./interp ./transform .
+test: wasi-libc
+	CGO_CPPFLAGS="$(CGO_CPPFLAGS)" CGO_CXXFLAGS="$(CGO_CXXFLAGS)" CGO_LDFLAGS="$(CGO_LDFLAGS)" $(GO) test -v -buildmode exe -tags byollvm ./cgo ./compileopts ./interp ./transform .

+# Test known-working standard library packages.
+# TODO: do this in one command, parallelize, and only show failing tests (no
+# implied -v flag).
+.PHONY: tinygo-test
 tinygo-test:
-	cd tests/tinygotest && tinygo test
+	$(TINYGO) test container/list
+	$(TINYGO) test container/ring
+	$(TINYGO) test text/scanner

 .PHONY: smoketest
 smoketest:
 	$(TINYGO) version
-	# test all examples
+	# test all examples (except pwm)
 	$(TINYGO) build -size short -o test.hex -target=pca10040            examples/blinky1
 	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=pca10040            examples/adc
@@ -174,7 +223,7 @@ smoketest:
 	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=microbit            examples/microbit-blink
 	@$(MD5SUM) test.hex
-	$(TINYGO) build -size short -o test.hex -target=pca10040            examples/pwm
+	$(TINYGO) build -size short -o test.hex -target=pca10040            examples/pininterrupt
 	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=pca10040            examples/serial
 	@$(MD5SUM) test.hex
@@ -185,6 +234,8 @@ smoketest:
 	# test simulated boards on play.tinygo.org
 	$(TINYGO) build             -o test.wasm -tags=arduino              examples/blinky1
 	@$(MD5SUM) test.wasm
+	$(TINYGO) build             -o test.wasm -tags=hifive1-qemu         examples/serial
+	@$(MD5SUM) test.wasm
 	$(TINYGO) build             -o test.wasm -tags=hifive1b             examples/blinky1
 	@$(MD5SUM) test.wasm
 	$(TINYGO) build             -o test.wasm -tags=reelboard            examples/blinky1
@@ -200,6 +251,8 @@ smoketest:
 	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=microbit            examples/echo
 	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=microbit-s110v8     examples/echo
+	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=nrf52840-mdk        examples/blinky1
 	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=pca10031            examples/blinky1
@@ -226,8 +279,16 @@ smoketest:
 	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=stm32f4disco        examples/blinky2
 	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=stm32f4disco-1      examples/blinky1
+	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=feather-stm32f405   examples/blinky1
+	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=circuitplay-bluefruit examples/blinky1
+	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=circuitplay-express examples/i2s
 	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=clue_alpha          examples/blinky1
+	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.gba -target=gameboy-advance     examples/gba-display
 	@$(MD5SUM) test.gba
 	$(TINYGO) build -size short -o test.hex -target=itsybitsy-m4        examples/blinky1
@@ -238,6 +299,14 @@ smoketest:
 	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=metro-m4-airlift    examples/blinky1
 	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=pyportal            examples/blinky1
+	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=particle-argon      examples/blinky1
+	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=particle-boron      examples/blinky1
+	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=particle-xenon      examples/blinky1
+	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=nucleo-f103rb       examples/blinky1
 	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=pinetime-devkit0    examples/blinky1
@@ -246,23 +315,78 @@ smoketest:
 	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=pca10056-s140v7     examples/blinky1
 	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=reelboard-s140v7    examples/blinky1
+	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=wioterminal         examples/blinky1
+	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=pygamer             examples/blinky1
+	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=xiao                examples/blinky1
+	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=circuitplay-express examples/dac
+	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=pyportal            examples/dac
+	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=feather-nrf52840  	examples/blinky1
+	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=itsybitsy-nrf52840  examples/blinky1
+	@$(MD5SUM) test.hex
+	# test pwm
+	$(TINYGO) build -size short -o test.hex -target=itsybitsy-m0        examples/pwm
+	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=itsybitsy-m4        examples/pwm
+	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=feather-m4          examples/pwm
+	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=pyportal            examples/pwm
+	@$(MD5SUM) test.hex
 ifneq ($(AVR), 0)
+	$(TINYGO) build -size short -o test.hex -target=atmega1284p         examples/serial
+	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=arduino             examples/blinky1
 	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=arduino             examples/pwm
+	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=arduino -scheduler=tasks  examples/blinky1
+	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=arduino-nano        examples/blinky1
+	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=digispark           examples/blinky1
 	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=digispark -gc=leaking examples/blinky1
+	@$(MD5SUM) test.hex
+endif
+ifneq ($(XTENSA), 0)
+	$(TINYGO) build -size short -o test.bin -target=esp32-wroom-32      examples/blinky1
+	@$(MD5SUM) test.bin
+	$(TINYGO) build -size short -o test.bin -target=nodemcu             examples/blinky1
+	@$(MD5SUM) test.bin
 endif
 	$(TINYGO) build -size short -o test.hex -target=hifive1b            examples/blinky1
 	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=maixbit             examples/blinky1
+	@$(MD5SUM) test.hex
 	$(TINYGO) build             -o wasm.wasm -target=wasm               examples/wasm/export
 	$(TINYGO) build             -o wasm.wasm -target=wasm               examples/wasm/main
+	# test various compiler flags
+	$(TINYGO) build -size short -o test.hex -target=pca10040 -gc=none -scheduler=none examples/blinky1
+	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=pca10040 -opt=1     examples/blinky1
+	@$(MD5SUM) test.hex
+	$(TINYGO) build             -o test.nro -target=nintendoswitch      examples/serial
+	@$(MD5SUM) test.nro

-release: tinygo gen-device
+wasmtest:
+	$(GO) test ./tests/wasm
+
+build/release: tinygo gen-device wasi-libc
 	@mkdir -p build/release/tinygo/bin
 	@mkdir -p build/release/tinygo/lib/clang/include
 	@mkdir -p build/release/tinygo/lib/CMSIS/CMSIS
 	@mkdir -p build/release/tinygo/lib/compiler-rt/lib
 	@mkdir -p build/release/tinygo/lib/nrfx
+	@mkdir -p build/release/tinygo/lib/picolibc/newlib/libc
+	@mkdir -p build/release/tinygo/lib/wasi-libc
 	@mkdir -p build/release/tinygo/pkg/armv6m-none-eabi
 	@mkdir -p build/release/tinygo/pkg/armv7m-none-eabi
 	@mkdir -p build/release/tinygo/pkg/armv7em-none-eabi
@@ -275,9 +399,28 @@ release: tinygo gen-device
 	@cp -rp lib/compiler-rt/LICENSE.TXT  build/release/tinygo/lib/compiler-rt
 	@cp -rp lib/compiler-rt/README.txt   build/release/tinygo/lib/compiler-rt
 	@cp -rp lib/nrfx/*                   build/release/tinygo/lib/nrfx
+	@cp -rp lib/picolibc/newlib/libc/ctype       build/release/tinygo/lib/picolibc/newlib/libc
+	@cp -rp lib/picolibc/newlib/libc/include     build/release/tinygo/lib/picolibc/newlib/libc
+	@cp -rp lib/picolibc/newlib/libc/locale      build/release/tinygo/lib/picolibc/newlib/libc
+	@cp -rp lib/picolibc/newlib/libc/string      build/release/tinygo/lib/picolibc/newlib/libc
+	@cp -rp lib/picolibc/newlib/libc/tinystdio   build/release/tinygo/lib/picolibc/newlib/libc
+	@cp -rp lib/picolibc-include         build/release/tinygo/lib
+	@cp -rp lib/wasi-libc/sysroot        build/release/tinygo/lib/wasi-libc/sysroot
 	@cp -rp src                          build/release/tinygo/src
 	@cp -rp targets                      build/release/tinygo/targets
-	./build/tinygo build-builtins -target=armv6m-none-eabi  -o build/release/tinygo/pkg/armv6m-none-eabi/compiler-rt.a
-	./build/tinygo build-builtins -target=armv7m-none-eabi  -o build/release/tinygo/pkg/armv7m-none-eabi/compiler-rt.a
-	./build/tinygo build-builtins -target=armv7em-none-eabi -o build/release/tinygo/pkg/armv7em-none-eabi/compiler-rt.a
+	./build/tinygo build-library -target=armv6m-none-eabi  -o build/release/tinygo/pkg/armv6m-none-eabi/compiler-rt.a compiler-rt
+	./build/tinygo build-library -target=armv7m-none-eabi  -o build/release/tinygo/pkg/armv7m-none-eabi/compiler-rt.a compiler-rt
+	./build/tinygo build-library -target=armv7em-none-eabi -o build/release/tinygo/pkg/armv7em-none-eabi/compiler-rt.a compiler-rt
+	./build/tinygo build-library -target=armv6m-none-eabi  -o build/release/tinygo/pkg/armv6m-none-eabi/picolibc.a picolibc
+	./build/tinygo build-library -target=armv7m-none-eabi  -o build/release/tinygo/pkg/armv7m-none-eabi/picolibc.a picolibc
+	./build/tinygo build-library -target=armv7em-none-eabi -o build/release/tinygo/pkg/armv7em-none-eabi/picolibc.a picolibc
+
+release: build/release
 	tar -czf build/release.tar.gz -C build/release tinygo
+
+deb: build/release
+	@mkdir -p build/release-deb/usr/local/bin
+	@mkdir -p build/release-deb/usr/local/lib
+	cp -ar build/release/tinygo build/release-deb/usr/local/lib/tinygo
+	ln -sf ../lib/tinygo/bin/tinygo build/release-deb/usr/local/bin/tinygo
+	fpm -f -s dir -t deb -n tinygo -v $(shell grep "const Version = " goenv/version.go | awk '{print $$NF}') -m '@tinygo-org' --description='TinyGo is a Go compiler for small places.' --license='BSD 3-Clause' --url=https://tinygo.org/ --deb-changelog CHANGELOG.md -p build/release.deb -C ./build/release-deb
@@ -43,27 +43,47 @@ See the [getting started instructions](https://tinygo.org/getting-started/) for

 You can compile TinyGo programs for microcontrollers, WebAssembly and Linux.

-The following 22 microcontroller boards are currently supported:
+The following 44 microcontroller boards are currently supported:

+* [Adafruit Circuit Playground Bluefruit](https://www.adafruit.com/product/4333)
 * [Adafruit Circuit Playground Express](https://www.adafruit.com/product/3333)
+* [Adafruit CLUE Alpha](https://www.adafruit.com/product/4500)
 * [Adafruit Feather M0](https://www.adafruit.com/product/2772)
 * [Adafruit Feather M4](https://www.adafruit.com/product/3857)
+* [Adafruit Feather nRF52840 Express](https://www.adafruit.com/product/4062)
+* [Adafruit Feather STM32F405 Express](https://www.adafruit.com/product/4382)
 * [Adafruit ItsyBitsy M0](https://www.adafruit.com/product/3727)
 * [Adafruit ItsyBitsy M4](https://www.adafruit.com/product/3800)
+* [Adafruit ItsyBitsy nRF52840](https://www.adafruit.com/product/4481)
 * [Adafruit Metro M4 Express Airlift](https://www.adafruit.com/product/4000)
 * [Adafruit PyBadge](https://www.adafruit.com/product/4200)
+* [Adafruit PyGamer](https://www.adafruit.com/product/4242)
+* [Adafruit PyPortal](https://www.adafruit.com/product/4116)
 * [Adafruit Trinket M0](https://www.adafruit.com/product/3500)
+* [Arduino Mega 2560](https://store.arduino.cc/arduino-mega-2560-rev3)
+* [Arduino Nano](https://store.arduino.cc/arduino-nano)
 * [Arduino Nano33 IoT](https://store.arduino.cc/nano-33-iot)
 * [Arduino Uno](https://store.arduino.cc/arduino-uno-rev3)
+* [Arduino Zero](https://store.arduino.cc/usa/arduino-zero)
 * [BBC micro:bit](https://microbit.org/)
 * [Digispark](http://digistump.com/products/1)
+* [ESP32](https://www.espressif.com/en/products/socs/esp32)
+* [ESP8266](https://www.espressif.com/en/products/socs/esp8266)
 * [Game Boy Advance](https://en.wikipedia.org/wiki/Game_Boy_Advance)
 * [Makerdiary nRF52840-MDK](https://wiki.makerdiary.com/nrf52840-mdk/)
+* [Nintendo Switch](https://www.nintendo.com/switch/)
 * [Nordic Semiconductor PCA10031](https://www.nordicsemi.com/eng/Products/nRF51-Dongle)
 * [Nordic Semiconductor PCA10040](https://www.nordicsemi.com/eng/Products/Bluetooth-low-energy/nRF52-DK)
 * [Nordic Semiconductor PCA10056](https://www.nordicsemi.com/Software-and-Tools/Development-Kits/nRF52840-DK)
+* [Particle Argon](https://docs.particle.io/datasheets/wi-fi/argon-datasheet/)
+* [Particle Boron](https://docs.particle.io/datasheets/cellular/boron-datasheet/)
+* [Particle Xenon](https://docs.particle.io/datasheets/discontinued/xenon-datasheet/)
 * [Phytec reel board](https://www.phytec.eu/product-eu/internet-of-things/reelboard/)
 * [PineTime DevKit](https://www.pine64.org/pinetime/)
+* [PJRC Teensy 3.6](https://www.pjrc.com/store/teensy36.html)
+* [Seeed Wio Terminal](https://www.seeedstudio.com/Wio-Terminal-p-4509.html)
+* [Seeed Seeeduino XIAO](https://www.seeedstudio.com/Seeeduino-XIAO-Arduino-Microcontroller-SAMD21-Cortex-M0+-p-4426.html)
+* [Seeed Sipeed MAix BiT](https://www.seeedstudio.com/Sipeed-MAix-BiT-for-RISC-V-AI-IoT-p-2872.html)
 * [SiFIve HiFive1](https://www.sifive.com/boards/hifive1)
 * [ST Micro "Nucleo F103RB"](https://www.st.com/en/evaluation-tools/nucleo-f103rb.html)
 * [ST Micro STM32F103XX "Bluepill"](http://wiki.stm32duino.com/index.php?title=Blue_Pill)
@@ -128,4 +148,6 @@ The original reasoning was: if [Python](https://micropython.org/) can run on mic

 This project is licensed under the BSD 3-clause license, just like the [Go project](https://golang.org/LICENSE) itself.

-Some code has been copied from the LLVM project and is therefore licensed under [a variant of the Apache 2.0 license](http://releases.llvm.org/9.0.0/LICENSE.TXT). This has been clearly indicated in the header of these files.
+Some code has been copied from the LLVM project and is therefore licensed under [a variant of the Apache 2.0 license](http://releases.llvm.org/10.0.0/LICENSE.TXT). This has been clearly indicated in the header of these files.
+
+Some code has been copied and/or ported from Paul Stoffregen's Teensy libraries and is therefore licensed under PJRC's license. This has been clearly indicated in the header of these files.
@@ -1,7 +1,7 @@
 # Avoid lengthy LLVM rebuilds on each newly pushed branch. Pull requests will
 # be built anyway.
 trigger:
- master
+- release
 - dev

 jobs:
@@ -10,21 +10,29 @@ jobs:
  pool:
    vmImage: 'VS2017-Win2016'
  steps:
+    - task: GoTool@0
+      inputs:
+        version: '1.15'
    - checkout: self
-    - task: CacheBeta@0
+      fetchDepth: 1
+    - task: Cache@2
      displayName: Cache LLVM source
      inputs:
-        key: llvm-source-9-windows-v0
+        key: llvm-source-10-windows-v1
        path: llvm-project
    - task: Bash@3
      displayName: Download LLVM source
      inputs:
        targetType: inline
-        script: make llvm-source
+        script: |
+          make llvm-source
+          # Workaround for bad symlinks:
+          # https://github.com/microsoft/azure-pipelines-tasks/issues/13418
+          rm -f llvm-project/libcxx/test/std/input.output/filesystems/Inputs/static_test_env/bad_symlink
    - task: CacheBeta@0
      displayName: Cache LLVM build
      inputs:
-        key: llvm-build-9-windows-v0
+        key: llvm-build-10-windows-v1
        path: llvm-build
    - task: Bash@3
      displayName: Build LLVM
@@ -34,23 +42,29 @@ jobs:
          if [ ! -f llvm-build/lib/liblldELF.a ]
          then
            choco install ninja
-            # LLVM 9 cannot be built with MinGW 8.
-            # For details: https://reviews.llvm.org/D70266
-            choco uninstall mingw
-            choco install mingw --version=7.3.0
            make llvm-build
          fi
    - task: Bash@3
      displayName: Install QEMU
      inputs:
        targetType: inline
-        script: choco install qemu
+        script: choco install qemu --version=2020.06.12
+    - task: CacheBeta@0
+      displayName: Cache wasi-libc sysroot
+      inputs:
+        key: wasi-libc-sysroot-v3
+        path: lib/wasi-libc/sysroot
+    - task: Bash@3
+      displayName: Build wasi-libc
+      inputs:
+        targetType: inline
+        script: PATH=/usr/bin:$PATH make wasi-libc
    - task: Bash@3
      displayName: Test TinyGo
      inputs:
        targetType: inline
        script: |
-          export PATH="/c/Go1.13/bin:$PATH:./llvm-build/bin:/c/Program Files/qemu"
+          export PATH="$PATH:./llvm-build/bin:/c/Program Files/qemu"
          unset GOROOT
          make test
    - task: Bash@3
@@ -58,17 +72,17 @@ jobs:
      inputs:
        targetType: inline
        script: |
-          export PATH="/c/Go1.13/bin:$PATH:./llvm-build/bin:/c/Program Files/qemu"
+          export PATH="$PATH:./llvm-build/bin:/c/Program Files/qemu"
          unset GOROOT
-          make release -j4
-    - publish: $(System.DefaultWorkingDirectory)/build/release.tar.gz
-      displayName: Publish tarball as artifact
-      artifact: tinygo.windows-amd64.tar.gz
+          make build/release -j4
+    - publish: $(System.DefaultWorkingDirectory)/build/release/tinygo
+      displayName: Publish zip as artifact
+      artifact: tinygo
    - task: Bash@3
      displayName: Smoke tests
      inputs:
        targetType: inline
        script: |
-          export PATH="/c/Go1.13/bin:$PATH:./llvm-build/bin:/c/Program Files/qemu"
+          export PATH="$PATH:./llvm-build/bin:/c/Program Files/qemu"
          unset GOROOT
-          make smoketest TINYGO=build/tinygo AVR=0
+          make smoketest TINYGO=build/tinygo AVR=0 XTENSA=0
@@ -4,11 +4,14 @@
 package builder

 import (
+	"debug/elf"
+	"encoding/binary"
 	"errors"
 	"fmt"
 	"io/ioutil"
 	"os"
 	"path/filepath"
+	"sort"
 	"strconv"
 	"strings"

@@ -16,43 +19,59 @@ import (
 	"github.com/tinygo-org/tinygo/compiler"
 	"github.com/tinygo-org/tinygo/goenv"
 	"github.com/tinygo-org/tinygo/interp"
+	"github.com/tinygo-org/tinygo/stacksize"
+	"github.com/tinygo-org/tinygo/transform"
+	"tinygo.org/x/go-llvm"
 )

+// BuildResult is the output of a build. This includes the binary itself and
+// some other metadata that is obtained while building the binary.
+type BuildResult struct {
+	// A path to the output binary. It will be removed after Build returns, so
+	// if it should be kept it must be copied or moved away.
+	Binary string
+
+	// The directory of the main package. This is useful for testing as the test
+	// binary must be run in the directory of the tested package.
+	MainDir string
+}
+
 // Build performs a single package to executable Go build. It takes in a package
 // name, an output path, and set of compile options and from that it manages the
 // whole compilation process.
 //
 // The error value may be of type *MultiError. Callers will likely want to check
 // for this case and print such errors individually.
-func Build(pkgName, outpath string, config *compileopts.Config, action func(string) error) error {
-	c, err := compiler.NewCompiler(pkgName, config)
+func Build(pkgName, outpath string, config *compileopts.Config, action func(BuildResult) error) error {
+	// Compile Go code to IR.
+	machine, err := compiler.NewTargetMachine(config)
 	if err != nil {
 		return err
 	}
-
-	// Compile Go code to IR.
-	errs := c.Compile(pkgName)
-	if len(errs) != 0 {
+	buildOutput, errs := compiler.Compile(pkgName, machine, config)
+	if errs != nil {
 		return newMultiError(errs)
 	}
+	mod := buildOutput.Mod
+
 	if config.Options.PrintIR {
 		fmt.Println("; Generated LLVM IR:")
-		fmt.Println(c.IR())
+		fmt.Println(mod.String())
 	}
-	if err := c.Verify(); err != nil {
+	if err := llvm.VerifyModule(mod, llvm.PrintMessageAction); err != nil {
 		return errors.New("verification error after IR construction")
 	}

-	err = interp.Run(c.Module(), config.DumpSSA())
+	err = interp.Run(mod, config.DumpSSA())
 	if err != nil {
 		return err
 	}
-	if err := c.Verify(); err != nil {
+	if err := llvm.VerifyModule(mod, llvm.PrintMessageAction); err != nil {
 		return errors.New("verification error after interpreting runtime.initAll")
 	}

 	if config.GOOS() != "darwin" {
-		c.ApplyFunctionSections() // -ffunction-sections
+		transform.ApplyFunctionSections(mod) // -ffunction-sections
 	}

 	// Browsers cannot handle external functions that have type i64 because it
@@ -61,7 +80,7 @@ func Build(pkgName, outpath string, config *compileopts.Config, action func(stri
 	// stack-allocated values.
 	// Use -wasm-abi=generic to disable this behaviour.
 	if config.Options.WasmAbi == "js" && strings.HasPrefix(config.Triple(), "wasm") {
-		err := c.ExternalInt64AsPtr()
+		err := transform.ExternalInt64AsPtr(mod)
 		if err != nil {
 			return err
 		}
@@ -71,23 +90,30 @@ func Build(pkgName, outpath string, config *compileopts.Config, action func(stri
 	// exactly.
 	errs = nil
 	switch config.Options.Opt {
-	case "none:", "0":
-		errs = c.Optimize(0, 0, 0) // -O0
+	/*
+		Currently, turning optimizations off causes compile failures.
+		We rely on the optimizer removing some dead symbols.
+		Avoid providing an option that does not work right now.
+		In the future once everything has been fixed we can re-enable this.
+
+		case "none", "0":
+			errs = transform.Optimize(mod, config, 0, 0, 0) // -O0
+	*/
 	case "1":
-		errs = c.Optimize(1, 0, 0) // -O1
+		errs = transform.Optimize(mod, config, 1, 0, 0) // -O1
 	case "2":
-		errs = c.Optimize(2, 0, 225) // -O2
+		errs = transform.Optimize(mod, config, 2, 0, 225) // -O2
 	case "s":
-		errs = c.Optimize(2, 1, 225) // -Os
+		errs = transform.Optimize(mod, config, 2, 1, 225) // -Os
 	case "z":
-		errs = c.Optimize(2, 2, 5) // -Oz, default
+		errs = transform.Optimize(mod, config, 2, 2, 5) // -Oz, default
 	default:
 		errs = []error{errors.New("unknown optimization level: -opt=" + config.Options.Opt)}
 	}
 	if len(errs) > 0 {
 		return newMultiError(errs)
 	}
-	if err := c.Verify(); err != nil {
+	if err := llvm.VerifyModule(mod, llvm.PrintMessageAction); err != nil {
 		return errors.New("verification failure after LLVM optimization passes")
 	}

@@ -97,21 +123,34 @@ func Build(pkgName, outpath string, config *compileopts.Config, action func(stri
 	// pointers are flash and which are in RAM so that pointers can have a
 	// correct address space parameter (address space 1 is for flash).
 	if strings.HasPrefix(config.Triple(), "avr") {
-		c.NonConstGlobals()
-		if err := c.Verify(); err != nil {
+		transform.NonConstGlobals(mod)
+		if err := llvm.VerifyModule(mod, llvm.PrintMessageAction); err != nil {
 			return errors.New("verification error after making all globals non-constant on AVR")
 		}
 	}

+	// Make sure stack sizes are loaded from a separate section so they can be
+	// modified after linking.
+	var stackSizeLoads []string
+	if config.AutomaticStackSize() {
+		stackSizeLoads = transform.CreateStackSizeLoads(mod, config)
+	}
+
 	// Generate output.
 	outext := filepath.Ext(outpath)
 	switch outext {
 	case ".o":
-		return c.EmitObject(outpath)
+		llvmBuf, err := machine.EmitToMemoryBuffer(mod, llvm.ObjectFile)
+		if err != nil {
+			return err
+		}
+		return ioutil.WriteFile(outpath, llvmBuf.Bytes(), 0666)
 	case ".bc":
-		return c.EmitBitcode(outpath)
+		data := llvm.WriteBitcodeToMemoryBuffer(mod).Bytes()
+		return ioutil.WriteFile(outpath, data, 0666)
 	case ".ll":
-		return c.EmitText(outpath)
+		data := []byte(mod.String())
+		return ioutil.WriteFile(outpath, data, 0666)
 	default:
 		// Act as a compiler driver.

@@ -124,29 +163,39 @@ func Build(pkgName, outpath string, config *compileopts.Config, action func(stri

 		// Write the object file.
 		objfile := filepath.Join(dir, "main.o")
-		err = c.EmitObject(objfile)
+		llvmBuf, err := machine.EmitToMemoryBuffer(mod, llvm.ObjectFile)
 		if err != nil {
 			return err
 		}
-
-		// Load builtins library from the cache, possibly compiling it on the
-		// fly.
-		var librt string
-		if config.Target.RTLib == "compiler-rt" {
-			librt, err = loadBuiltins(config.Triple())
-			if err != nil {
-				return err
-			}
+		err = ioutil.WriteFile(objfile, llvmBuf.Bytes(), 0666)
+		if err != nil {
+			return err
 		}

 		// Prepare link command.
 		executable := filepath.Join(dir, "main")
 		tmppath := executable // final file
 		ldflags := append(config.LDFlags(), "-o", executable, objfile)
+
+		// Load builtins library from the cache, possibly compiling it on the
+		// fly.
 		if config.Target.RTLib == "compiler-rt" {
+			librt, err := CompilerRT.Load(config.Triple())
+			if err != nil {
+				return err
+			}
 			ldflags = append(ldflags, librt)
 		}

+		// Add libc.
+		if config.Target.Libc == "picolibc" {
+			libc, err := Picolibc.Load(config.Triple())
+			if err != nil {
+				return err
+			}
+			ldflags = append(ldflags, libc)
+		}
+
 		// Compile extra files.
 		root := goenv.Get("TINYGOROOT")
 		for i, path := range config.ExtraFiles() {
@@ -160,16 +209,17 @@ func Build(pkgName, outpath string, config *compileopts.Config, action func(stri
 		}

 		// Compile C files in packages.
-		for i, pkg := range c.Packages() {
-			for _, file := range pkg.CFiles {
-				path := filepath.Join(pkg.Package.Dir, file)
-				outpath := filepath.Join(dir, "pkg"+strconv.Itoa(i)+"-"+file+".o")
-				err := runCCompiler(config.Target.Compiler, append(config.CFlags(), "-c", "-o", outpath, path)...)
-				if err != nil {
-					return &commandError{"failed to build", path, err}
-				}
-				ldflags = append(ldflags, outpath)
+		for i, file := range buildOutput.ExtraFiles {
+			outpath := filepath.Join(dir, "pkg"+strconv.Itoa(i)+"-"+filepath.Base(file)+".o")
+			err := runCCompiler(config.Target.Compiler, append(config.CFlags(), "-c", "-o", outpath, file)...)
+			if err != nil {
+				return &commandError{"failed to build", file, err}
 			}
+			ldflags = append(ldflags, outpath)
+		}
+
+		if len(buildOutput.ExtraLDFlags) > 0 {
+			ldflags = append(ldflags, buildOutput.ExtraLDFlags...)
 		}

 		// Link the object files together.
@@ -178,6 +228,26 @@ func Build(pkgName, outpath string, config *compileopts.Config, action func(stri
 			return &commandError{"failed to link", executable, err}
 		}

+		var calculatedStacks []string
+		var stackSizes map[string]functionStackSize
+		if config.Options.PrintStacks || config.AutomaticStackSize() {
+			// Try to determine stack sizes at compile time.
+			// Don't do this by default as it usually doesn't work on
+			// unsupported architectures.
+			calculatedStacks, stackSizes, err = determineStackSizes(mod, executable)
+			if err != nil {
+				return err
+			}
+		}
+		if config.AutomaticStackSize() {
+			// Modify the .tinygo_stacksizes section that contains a stack size
+			// for each goroutine.
+			err = modifyStackSizes(executable, stackSizeLoads, stackSizes)
+			if err != nil {
+				return fmt.Errorf("could not modify stack sizes: %w", err)
+			}
+		}
+
 		if config.Options.PrintSizes == "short" || config.Options.PrintSizes == "full" {
 			sizes, err := loadProgramSize(executable)
 			if err != nil {
@@ -197,21 +267,278 @@ func Build(pkgName, outpath string, config *compileopts.Config, action func(stri
 			}
 		}

+		// Print goroutine stack sizes, as far as possible.
+		if config.Options.PrintStacks {
+			printStacks(calculatedStacks, stackSizes)
+		}
+
 		// Get an Intel .hex file or .bin file from the .elf file.
-		if outext == ".hex" || outext == ".bin" || outext == ".gba" {
+		outputBinaryFormat := config.BinaryFormat(outext)
+		switch outputBinaryFormat {
+		case "elf":
+			// do nothing, file is already in ELF format
+		case "hex", "bin":
+			// Extract raw binary, either encoding it as a hex file or as a raw
+			// firmware file.
 			tmppath = filepath.Join(dir, "main"+outext)
-			err := objcopy(executable, tmppath)
+			err := objcopy(executable, tmppath, outputBinaryFormat)
 			if err != nil {
 				return err
 			}
-		} else if outext == ".uf2" {
+		case "uf2":
 			// Get UF2 from the .elf file.
 			tmppath = filepath.Join(dir, "main"+outext)
-			err := convertELFFileToUF2File(executable, tmppath)
+			err := convertELFFileToUF2File(executable, tmppath, config.Target.UF2FamilyID)
 			if err != nil {
 				return err
 			}
+		case "esp32", "esp8266":
+			// Special format for the ESP family of chips (parsed by the ROM
+			// bootloader).
+			tmppath = filepath.Join(dir, "main"+outext)
+			err := makeESPFirmareImage(executable, tmppath, outputBinaryFormat)
+			if err != nil {
+				return err
+			}
+		default:
+			return fmt.Errorf("unknown output binary format: %s", outputBinaryFormat)
+		}
+		return action(BuildResult{
+			Binary:  tmppath,
+			MainDir: buildOutput.MainDir,
+		})
+	}
+}
+
+// functionStackSizes keeps stack size information about a single function
+// (usually a goroutine).
+type functionStackSize struct {
+	humanName        string
+	stackSize        uint64
+	stackSizeType    stacksize.SizeType
+	missingStackSize *stacksize.CallNode
+}
+
+// determineStackSizes tries to determine the stack sizes of all started
+// goroutines and of the reset vector. The LLVM module is necessary to find
+// functions that call a function pointer.
+func determineStackSizes(mod llvm.Module, executable string) ([]string, map[string]functionStackSize, error) {
+	var callsIndirectFunction []string
+	gowrappers := []string{}
+	gowrapperNames := make(map[string]string)
+	for fn := mod.FirstFunction(); !fn.IsNil(); fn = llvm.NextFunction(fn) {
+		// Determine which functions call a function pointer.
+		for bb := fn.FirstBasicBlock(); !bb.IsNil(); bb = llvm.NextBasicBlock(bb) {
+			for inst := bb.FirstInstruction(); !inst.IsNil(); inst = llvm.NextInstruction(inst) {
+				if inst.IsACallInst().IsNil() {
+					continue
+				}
+				if callee := inst.CalledValue(); callee.IsAFunction().IsNil() && callee.IsAInlineAsm().IsNil() {
+					callsIndirectFunction = append(callsIndirectFunction, fn.Name())
+				}
+			}
+		}
+
+		// Get a list of "go wrappers", small wrapper functions that decode
+		// parameters when starting a new goroutine.
+		attr := fn.GetStringAttributeAtIndex(-1, "tinygo-gowrapper")
+		if !attr.IsNil() {
+			gowrappers = append(gowrappers, fn.Name())
+			gowrapperNames[fn.Name()] = attr.GetStringValue()
+		}
+	}
+	sort.Strings(gowrappers)
+
+	// Load the ELF binary.
+	f, err := elf.Open(executable)
+	if err != nil {
+		return nil, nil, fmt.Errorf("could not load executable for stack size analysis: %w", err)
+	}
+	defer f.Close()
+
+	// Determine the frame size of each function (if available) and the callgraph.
+	functions, err := stacksize.CallGraph(f, callsIndirectFunction)
+	if err != nil {
+		return nil, nil, fmt.Errorf("could not parse executable for stack size analysis: %w", err)
+	}
+
+	// Goroutines need to be started and finished and take up some stack space
+	// that way. This can be measured by measuing the stack size of
+	// tinygo_startTask.
+	if numFuncs := len(functions["tinygo_startTask"]); numFuncs != 1 {
+		return nil, nil, fmt.Errorf("expected exactly one definition of tinygo_startTask, got %d", numFuncs)
+	}
+	baseStackSize, baseStackSizeType, baseStackSizeFailedAt := functions["tinygo_startTask"][0].StackSize()
+
+	sizes := make(map[string]functionStackSize)
+
+	// Add the reset handler function, for convenience. The reset handler runs
+	// startup code and the scheduler. The listed stack size is not the full
+	// stack size: interrupts are not counted.
+	var resetFunction string
+	switch f.Machine {
+	case elf.EM_ARM:
+		// Note: all interrupts happen on this stack so the real size is bigger.
+		resetFunction = "Reset_Handler"
+	}
+	if resetFunction != "" {
+		funcs := functions[resetFunction]
+		if len(funcs) != 1 {
+			return nil, nil, fmt.Errorf("expected exactly one definition of %s in the callgraph, found %d", resetFunction, len(funcs))
+		}
+		stackSize, stackSizeType, missingStackSize := funcs[0].StackSize()
+		sizes[resetFunction] = functionStackSize{
+			stackSize:        stackSize,
+			stackSizeType:    stackSizeType,
+			missingStackSize: missingStackSize,
+			humanName:        resetFunction,
+		}
+	}
+
+	// Add all goroutine wrapper functions.
+	for _, name := range gowrappers {
+		funcs := functions[name]
+		if len(funcs) != 1 {
+			return nil, nil, fmt.Errorf("expected exactly one definition of %s in the callgraph, found %d", name, len(funcs))
+		}
+		humanName := gowrapperNames[name]
+		if humanName == "" {
+			humanName = name // fallback
+		}
+		stackSize, stackSizeType, missingStackSize := funcs[0].StackSize()
+		if baseStackSizeType != stacksize.Bounded {
+			// It was not possible to determine the stack size at compile time
+			// because tinygo_startTask does not have a fixed stack size. This
+			// can happen when using -opt=1.
+			stackSizeType = baseStackSizeType
+			missingStackSize = baseStackSizeFailedAt
+		} else if stackSize < baseStackSize {
+			// This goroutine has a very small stack, but still needs to fit all
+			// registers to start and suspend the goroutine. Otherwise a stack
+			// overflow will occur even before the goroutine is started.
+			stackSize = baseStackSize
+		}
+		sizes[name] = functionStackSize{
+			stackSize:        stackSize,
+			stackSizeType:    stackSizeType,
+			missingStackSize: missingStackSize,
+			humanName:        humanName,
+		}
+	}
+
+	if resetFunction != "" {
+		return append([]string{resetFunction}, gowrappers...), sizes, nil
+	}
+	return gowrappers, sizes, nil
+}
+
+// modifyStackSizes modifies the .tinygo_stacksizes section with the updated
+// stack size information. Before this modification, all stack sizes in the
+// section assume the default stack size (which is relatively big).
+func modifyStackSizes(executable string, stackSizeLoads []string, stackSizes map[string]functionStackSize) error {
+	fp, err := os.OpenFile(executable, os.O_RDWR, 0)
+	if err != nil {
+		return err
+	}
+	defer fp.Close()
+
+	elfFile, err := elf.NewFile(fp)
+	if err != nil {
+		return err
+	}
+
+	section := elfFile.Section(".tinygo_stacksizes")
+	if section == nil {
+		return errors.New("could not find .tinygo_stacksizes section")
+	}
+
+	if section.Size != section.FileSize {
+		// Sanity check.
+		return fmt.Errorf("expected .tinygo_stacksizes to have identical size and file size, got %d and %d", section.Size, section.FileSize)
+	}
+
+	// Read all goroutine stack sizes.
+	data := make([]byte, section.Size)
+	_, err = fp.ReadAt(data, int64(section.Offset))
+	if err != nil {
+		return err
+	}
+
+	if len(stackSizeLoads)*4 != len(data) {
+		// Note: while AVR should use 2 byte stack sizes, even 64-bit platforms
+		// should probably stick to 4 byte stack sizes as a larger than 4GB
+		// stack doesn't make much sense.
+		return errors.New("expected 4 byte stack sizes")
+	}
+
+	// Modify goroutine stack sizes with a compile-time known worst case stack
+	// size.
+	for i, name := range stackSizeLoads {
+		fn, ok := stackSizes[name]
+		if !ok {
+			return fmt.Errorf("could not find symbol %s in ELF file", name)
+		}
+		if fn.stackSizeType == stacksize.Bounded {
+			stackSize := uint32(fn.stackSize)
+
+			// Adding 4 for the stack canary. Even though the size may be
+			// automatically determined, stack overflow checking is still
+			// important as the stack size cannot be determined for all
+			// goroutines.
+			stackSize += 4
+
+			// Add stack size used by interrupts.
+			switch elfFile.Machine {
+			case elf.EM_ARM:
+				// On Cortex-M (assumed here), this stack size is 8 words or 32
+				// bytes. This is only to store the registers that the interrupt
+				// may modify, the interrupt will switch to the interrupt stack
+				// (MSP).
+				// Some background:
+				// https://interrupt.memfault.com/blog/cortex-m-rtos-context-switching
+				stackSize += 32
+			}
+
+			// Finally write the stack size to the binary.
+			binary.LittleEndian.PutUint32(data[i*4:], stackSize)
+		}
+	}
+
+	// Write back the modified stack sizes.
+	_, err = fp.WriteAt(data, int64(section.Offset))
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// printStacks prints the maximum stack depth for functions that are started as
+// goroutines. Stack sizes cannot always be determined statically, in particular
+// recursive functions and functions that call interface methods or function
+// pointers may have an unknown stack depth (depending on what the optimizer
+// manages to optimize away).
+//
+// It might print something like the following:
+//
+//     function                         stack usage (in bytes)
+//     Reset_Handler                    316
+//     examples/blinky2.led1            92
+//     runtime.run$1                    300
+func printStacks(calculatedStacks []string, stackSizes map[string]functionStackSize) {
+	// Print the sizes of all stacks.
+	fmt.Printf("%-32s %s\n", "function", "stack usage (in bytes)")
+	for _, name := range calculatedStacks {
+		fn := stackSizes[name]
+		switch fn.stackSizeType {
+		case stacksize.Bounded:
+			fmt.Printf("%-32s %d\n", fn.humanName, fn.stackSize)
+		case stacksize.Unknown:
+			fmt.Printf("%-32s unknown, %s does not have stack frame information\n", fn.humanName, fn.missingStackSize)
+		case stacksize.Recursive:
+			fmt.Printf("%-32s recursive, %s may call itself\n", fn.humanName, fn.missingStackSize)
+		case stacksize.IndirectCall:
+			fmt.Printf("%-32s unknown, %s calls a function pointer\n", fn.humanName, fn.missingStackSize)
 		}
-		return action(tmppath)
 	}
 }
@@ -1,12 +1,7 @@
 package builder

 import (
-	"io/ioutil"
-	"os"
-	"path/filepath"
 	"strings"
-
-	"github.com/tinygo-org/tinygo/goenv"
 )

 // These are the GENERIC_SOURCES according to CMakeList.txt.
@@ -156,105 +151,20 @@ var aeabiBuiltins = []string{
 	"arm/aeabi_uldivmod.S",
 }

-func builtinFiles(target string) []string {
-	builtins := append([]string{}, genericBuiltins...) // copy genericBuiltins
-	if strings.HasPrefix(target, "arm") {
-		builtins = append(builtins, aeabiBuiltins...)
-	}
-	return builtins
-}
-
-// builtinsDir returns the directory where the sources for compiler-rt are kept.
-func builtinsDir() string {
-	return filepath.Join(goenv.Get("TINYGOROOT"), "lib", "compiler-rt", "lib", "builtins")
-}
-
-// Get the builtins archive, possibly generating it as needed.
-func loadBuiltins(target string) (path string, err error) {
-	// Try to load a precompiled compiler-rt library.
-	precompiledPath := filepath.Join(goenv.Get("TINYGOROOT"), "pkg", target, "compiler-rt.a")
-	if _, err := os.Stat(precompiledPath); err == nil {
-		// Found a precompiled compiler-rt for this OS/architecture. Return the
-		// path directly.
-		return precompiledPath, nil
-	}
-
-	outfile := "librt-" + target + ".a"
-	builtinsDir := builtinsDir()
-
-	builtins := builtinFiles(target)
-	srcs := make([]string, len(builtins))
-	for i, name := range builtins {
-		srcs[i] = filepath.Join(builtinsDir, name)
-	}
-
-	if path, err := cacheLoad(outfile, commands["clang"][0], srcs); path != "" || err != nil {
-		return path, err
-	}
-
-	var cachepath string
-	err = CompileBuiltins(target, func(path string) error {
-		path, err := cacheStore(path, outfile, commands["clang"][0], srcs)
-		cachepath = path
-		return err
-	})
-	return cachepath, err
-}
-
-// CompileBuiltins compiles builtins from compiler-rt into a static library.
-// When it succeeds, it will call the callback with the resulting path. The path
-// will be removed after callback returns. If callback returns an error, this is
-// passed through to the return value of this function.
-func CompileBuiltins(target string, callback func(path string) error) error {
-	builtinsDir := builtinsDir()
-
-	builtins := builtinFiles(target)
-	srcs := make([]string, len(builtins))
-	for i, name := range builtins {
-		srcs[i] = filepath.Join(builtinsDir, name)
-	}
-
-	dirPrefix := "tinygo-builtins"
-	remapDir := filepath.Join(os.TempDir(), dirPrefix)
-	dir, err := ioutil.TempDir(os.TempDir(), dirPrefix)
-	if err != nil {
-		return err
-	}
-	defer os.RemoveAll(dir)
-
-	// Compile all builtins.
-	// TODO: use builtins optimized for a given target if available.
-	objs := make([]string, 0, len(builtins))
-	for _, name := range builtins {
-		objname := name
-		if strings.LastIndexByte(objname, '/') >= 0 {
-			objname = objname[strings.LastIndexByte(objname, '/'):]
+// CompilerRT is a library with symbols required by programs compiled with LLVM.
+// These symbols are for operations that cannot be emitted with a single
+// instruction or a short sequence of instructions for that target.
+//
+// For more information, see: https://compiler-rt.llvm.org/
+var CompilerRT = Library{
+	name:      "compiler-rt",
+	cflags:    func() []string { return []string{"-Werror", "-Wall", "-std=c11", "-nostdlibinc"} },
+	sourceDir: "lib/compiler-rt/lib/builtins",
+	sources: func(target string) []string {
+		builtins := append([]string{}, genericBuiltins...) // copy genericBuiltins
+		if strings.HasPrefix(target, "arm") || strings.HasPrefix(target, "thumb") {
+			builtins = append(builtins, aeabiBuiltins...)
 		}
-		objpath := filepath.Join(dir, objname+".o")
-		objs = append(objs, objpath)
-		srcpath := filepath.Join(builtinsDir, name)
-		// Note: -fdebug-prefix-map is necessary to make the output archive
-		// reproducible. Otherwise the temporary directory is stored in the
-		// archive itself, which varies each run.
-		args := []string{"-c", "-Oz", "-g", "-Werror", "-Wall", "-std=c11", "-fshort-enums", "-nostdlibinc", "-ffunction-sections", "-fdata-sections", "-Wno-macro-redefined", "--target=" + target, "-fdebug-prefix-map=" + dir + "=" + remapDir}
-		if strings.HasPrefix(target, "riscv32-") {
-			args = append(args, "-march=rv32imac", "-mabi=ilp32", "-fforce-enable-int128")
-		}
-		err := runCCompiler("clang", append(args, "-o", objpath, srcpath)...)
-		if err != nil {
-			return &commandError{"failed to build", srcpath, err}
-		}
-	}
-
-	// Put all the object files in a single archive. This archive file will be
-	// used to statically link compiler-rt.
-	arpath := filepath.Join(dir, "librt.a")
-	err = makeArchive(arpath, objs)
-	if err != nil {
-		return err
-	}
-
-	// Give the caller the resulting file. The callback must copy the file,
-	// because after it returns the temporary directory will be removed.
-	return callback(arpath)
+		return builtins
+	},
 }
@@ -48,6 +48,7 @@
 #include "llvm/Support/Host.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/Path.h"
+#include "llvm/Support/Process.h"
 #include "llvm/Support/Signals.h"
 #include "llvm/Support/SourceMgr.h"
 #include "llvm/Support/TargetRegistry.h"
@@ -70,12 +71,12 @@ bool AssemblerInvocation::CreateFromArgs(AssemblerInvocation &Opts,
  bool Success = true;

  // Parse the arguments.
-  std::unique_ptr<OptTable> OptTbl(createDriverOptTable());
+  const OptTable &OptTbl = getDriverOptTable();

  const unsigned IncludedFlagsBitmask = options::CC1AsOption;
  unsigned MissingArgIndex, MissingArgCount;
-  InputArgList Args = OptTbl->ParseArgs(Argv, MissingArgIndex, MissingArgCount,
-                                        IncludedFlagsBitmask);
+  InputArgList Args = OptTbl.ParseArgs(Argv, MissingArgIndex, MissingArgCount,
+                                       IncludedFlagsBitmask);

  // Check for missing argument error.
  if (MissingArgCount) {
@@ -88,7 +89,7 @@ bool AssemblerInvocation::CreateFromArgs(AssemblerInvocation &Opts,
  for (const Arg *A : Args.filtered(OPT_UNKNOWN)) {
    auto ArgString = A->getAsString(Args);
    std::string Nearest;
-    if (OptTbl->findNearest(ArgString, Nearest, IncludedFlagsBitmask) > 1)
+    if (OptTbl.findNearest(ArgString, Nearest, IncludedFlagsBitmask) > 1)
      Diags.Report(diag::err_drv_unknown_argument) << ArgString;
    else
      Diags.Report(diag::err_drv_unknown_argument_with_suggestion)
@@ -181,6 +182,7 @@ bool AssemblerInvocation::CreateFromArgs(AssemblerInvocation &Opts,
  Opts.RelaxAll = Args.hasArg(OPT_mrelax_all);
  Opts.NoExecStack = Args.hasArg(OPT_mno_exec_stack);
  Opts.FatalWarnings = Args.hasArg(OPT_massembler_fatal_warnings);
+  Opts.NoWarn = Args.hasArg(OPT_massembler_no_warn);
  Opts.RelocationModel = Args.getLastArgValue(OPT_mrelocation_model, "pic");
  Opts.TargetABI = Args.getLastArgValue(OPT_target_abi);
  Opts.IncrementalLinkerCompatible =
@@ -208,8 +210,8 @@ getOutputStream(StringRef Path, DiagnosticsEngine &Diags, bool Binary) {
    sys::RemoveFileOnSignal(Path);

  std::error_code EC;
-  auto Out = llvm::make_unique<raw_fd_ostream>(
-      Path, EC, (Binary ? sys::fs::F_None : sys::fs::F_Text));
+  auto Out = std::make_unique<raw_fd_ostream>(
+      Path, EC, (Binary ? sys::fs::OF_None : sys::fs::OF_Text));
  if (EC) {
    Diags.Report(diag::err_fe_unable_to_open_output) << Path << EC.message();
    return nullptr;
@@ -245,7 +247,9 @@ bool ExecuteAssembler(AssemblerInvocation &Opts, DiagnosticsEngine &Diags) {
  std::unique_ptr<MCRegisterInfo> MRI(TheTarget->createMCRegInfo(Opts.Triple));
  assert(MRI && "Unable to create target register info!");

-  std::unique_ptr<MCAsmInfo> MAI(TheTarget->createMCAsmInfo(*MRI, Opts.Triple));
+  MCTargetOptions MCOptions;
+  std::unique_ptr<MCAsmInfo> MAI(
+      TheTarget->createMCAsmInfo(*MRI, Opts.Triple, MCOptions));
  assert(MAI && "Unable to create target asm info!");

  // Ensure MCAsmInfo initialization occurs before any use, otherwise sections
@@ -269,7 +273,7 @@ bool ExecuteAssembler(AssemblerInvocation &Opts, DiagnosticsEngine &Diags) {
  // MCObjectFileInfo needs a MCContext reference in order to initialize itself.
  std::unique_ptr<MCObjectFileInfo> MOFI(new MCObjectFileInfo());

-  MCContext Ctx(MAI.get(), MRI.get(), MOFI.get(), &SrcMgr);
+  MCContext Ctx(MAI.get(), MRI.get(), MOFI.get(), &SrcMgr, &MCOptions);

  bool PIC = false;
  if (Opts.RelocationModel == "static") {
@@ -326,7 +330,8 @@ bool ExecuteAssembler(AssemblerInvocation &Opts, DiagnosticsEngine &Diags) {
  raw_pwrite_stream *Out = FDOS.get();
  std::unique_ptr<buffer_ostream> BOS;

-  MCTargetOptions MCOptions;
+  MCOptions.MCNoWarn = Opts.NoWarn;
+  MCOptions.MCFatalWarnings = Opts.FatalWarnings;
  MCOptions.ABIName = Opts.TargetABI;

  // FIXME: There is a bit of code duplication with addPassesToEmitFile.
@@ -340,7 +345,7 @@ bool ExecuteAssembler(AssemblerInvocation &Opts, DiagnosticsEngine &Diags) {
    std::unique_ptr<MCAsmBackend> MAB(
        TheTarget->createMCAsmBackend(*STI, *MRI, MCOptions));

-    auto FOut = llvm::make_unique<formatted_raw_ostream>(*Out);
+    auto FOut = std::make_unique<formatted_raw_ostream>(*Out);
    Str.reset(TheTarget->createAsmStreamer(
        Ctx, std::move(FOut), /*asmverbose*/ true,
        /*useDwarfDirectory*/ true, IP, std::move(CE), std::move(MAB),
@@ -351,7 +356,7 @@ bool ExecuteAssembler(AssemblerInvocation &Opts, DiagnosticsEngine &Diags) {
    assert(Opts.OutputType == AssemblerInvocation::FT_Obj &&
           "Invalid file type!");
    if (!FDOS->supportsSeeking()) {
-      BOS = make_unique<buffer_ostream>(*FDOS);
+      BOS = std::make_unique<buffer_ostream>(*FDOS);
      Out = BOS.get();
    }

@@ -436,7 +441,7 @@ static void LLVMErrorHandler(void *UserData, const std::string &Message,
  Diags.Report(diag::err_fe_error_backend) << Message;

  // We cannot recover from llvm errors.
-  exit(1);
+  sys::Process::Exit(1);
 }

 int cc1as_main(ArrayRef<const char *> Argv, const char *Argv0, void *MainAddr) {
@@ -464,11 +469,11 @@ int cc1as_main(ArrayRef<const char *> Argv, const char *Argv0, void *MainAddr) {
    return 1;

  if (Asm.ShowHelp) {
-    std::unique_ptr<OptTable> Opts(driver::createDriverOptTable());
-    Opts->PrintHelp(llvm::outs(), "clang -cc1as [options] file...",
-                    "Clang Integrated Assembler",
-                    /*Include=*/driver::options::CC1AsOption, /*Exclude=*/0,
-                    /*ShowAllAliases=*/false);
+    getDriverOptTable().PrintHelp(
+        llvm::outs(), "clang -cc1as [options] file...",
+        "Clang Integrated Assembler",
+        /*Include=*/driver::options::CC1AsOption, /*Exclude=*/0,
+        /*ShowAllAliases=*/false);
    return 0;
  }

@@ -485,7 +490,7 @@ int cc1as_main(ArrayRef<const char *> Argv, const char *Argv0, void *MainAddr) {
  // FIXME: Remove this, one day.
  if (!Asm.LLVMArgs.empty()) {
    unsigned NumArgs = Asm.LLVMArgs.size();
-    auto Args = llvm::make_unique<const char*[]>(NumArgs + 2);
+    auto Args = std::make_unique<const char*[]>(NumArgs + 2);
    Args[0] = "clang (LLVM option parsing)";
    for (unsigned i = 0; i != NumArgs; ++i)
      Args[i + 1] = Asm.LLVMArgs[i].c_str();
@@ -499,6 +504,7 @@ int cc1as_main(ArrayRef<const char *> Argv, const char *Argv0, void *MainAddr) {
  // If any timers were active but haven't been destroyed yet, print their
  // results now.
  TimerGroup::printAll(errs());
+  TimerGroup::clearAll();

  return !!Failed;
 }
@@ -11,8 +11,6 @@
 //
 //===----------------------------------------------------------------------===//

-#include "llvm/ADT/ArrayRef.h"
-
 /// Helper class for representing a single invocation of the assembler.
 struct AssemblerInvocation {
  /// @name Target Options
@@ -82,6 +80,7 @@ struct AssemblerInvocation {
  unsigned RelaxAll : 1;
  unsigned NoExecStack : 1;
  unsigned FatalWarnings : 1;
+  unsigned NoWarn : 1;
  unsigned IncrementalLinkerCompatible : 1;
  unsigned EmbedBitcode : 1;

@@ -107,6 +106,7 @@ public:
    RelaxAll = 0;
    NoExecStack = 0;
    FatalWarnings = 0;
+    NoWarn = 0;
    IncrementalLinkerCompatible = 0;
    DwarfVersion = 0;
    EmbedBitcode = 0;
@@ -52,8 +52,7 @@ bool tinygo_clang_driver(int argc, char **argv) {
 			std::unique_ptr<clang::CompilerInstance> Clang(new clang::CompilerInstance());
 			bool success = clang::CompilerInvocation::CreateFromArgs(
 					Clang->getInvocation(),
-					const_cast<const char **>(CCArgs.data()),
-					const_cast<const char **>(CCArgs.data()) + CCArgs.size(),
+					CCArgs,
 					Diags);
 			if (!success) {
 				return false;
@@ -74,7 +73,8 @@ bool tinygo_clang_driver(int argc, char **argv) {
 		} else if (strcmp(*CCArgs.data(), "-cc1as") == 0) {
 			// This is the assembler frontend. Parse the arguments.
 			AssemblerInvocation Asm;
-			if (!AssemblerInvocation::CreateFromArgs(Asm, llvm::ArrayRef<const char*>(CCArgs).slice(1), Diags))
+			ArrayRef<const char *> Argv = llvm::ArrayRef<const char*>(CCArgs);
+			if (!AssemblerInvocation::CreateFromArgs(Asm, Argv.slice(1), Diags))
 				return false;

 			// Execute the invocation, unless there were parsing errors.
@@ -6,25 +6,28 @@ import (
 	"os/exec"
 	"runtime"
 	"strings"
+
+	"tinygo.org/x/go-llvm"
 )

 // Commands lists command alternatives for various operating systems. These
 // commands may have a slightly different name across operating systems and
 // distributions or may not even exist in $PATH, in which case absolute paths
 // may be used.
-var commands = map[string][]string{
-	"clang":   {"clang-9"},
-	"ld.lld":  {"ld.lld-9", "ld.lld"},
-	"wasm-ld": {"wasm-ld-9", "wasm-ld"},
-}
+var commands = map[string][]string{}

 func init() {
-	// Add the path to a Homebrew-installed LLVM 9 for ease of use (no need to
+	llvmMajor := strings.Split(llvm.Version, ".")[0]
+	commands["clang"] = []string{"clang-" + llvmMajor}
+	commands["ld.lld"] = []string{"ld.lld-" + llvmMajor, "ld.lld"}
+	commands["wasm-ld"] = []string{"wasm-ld-" + llvmMajor, "wasm-ld"}
+	// Add the path to a Homebrew-installed LLVM for ease of use (no need to
 	// manually set $PATH).
 	if runtime.GOOS == "darwin" {
-		commands["clang"] = append(commands["clang"], "/usr/local/opt/llvm@9/bin/clang-9")
-		commands["ld.lld"] = append(commands["ld.lld"], "/usr/local/opt/llvm@9/bin/ld.lld")
-		commands["wasm-ld"] = append(commands["wasm-ld"], "/usr/local/opt/llvm@9/bin/wasm-ld")
+		prefix := "/usr/local/opt/llvm@" + llvmMajor + "/bin/"
+		commands["clang"] = append(commands["clang"], prefix+"clang-"+llvmMajor)
+		commands["ld.lld"] = append(commands["ld.lld"], prefix+"ld.lld")
+		commands["wasm-ld"] = append(commands["wasm-ld"], prefix+"wasm-ld")
 	}
 	// Add the path for when LLVM was installed with the installer from
 	// llvm.org, which by default doesn't add LLVM to the $PATH environment
@@ -34,11 +37,12 @@ func init() {
 		commands["ld.lld"] = append(commands["ld.lld"], "lld", "C:\\Program Files\\LLVM\\bin\\lld.exe")
 		commands["wasm-ld"] = append(commands["wasm-ld"], "C:\\Program Files\\LLVM\\bin\\wasm-ld.exe")
 	}
-	// Add the path to the llvm90 installed from ports
+	// Add the path to LLVM installed from ports.
 	if runtime.GOOS == "freebsd" {
-		commands["clang"] = append(commands["clang"], "/usr/local/llvm90/bin/clang-9")
-		commands["ld.lld"] = append(commands["ld.lld"], "/usr/local/llvm90/bin/ld.lld")
-		commands["wasm-ld"] = append(commands["wasm-ld"], "/usr/local/llvm90/bin/wasm-ld")
+		prefix := "/usr/local/llvm" + llvmMajor + "/bin/"
+		commands["clang"] = append(commands["clang"], prefix+"clang-"+llvmMajor)
+		commands["ld.lld"] = append(commands["ld.lld"], prefix+"ld.lld")
+		commands["wasm-ld"] = append(commands["wasm-ld"], prefix+"wasm-ld")
 	}
 }

@@ -1,60 +0,0 @@
-// +build byollvm
-
-package builder
-
-import (
-	"errors"
-	"os"
-	"os/exec"
-	"unsafe"
-
-	"github.com/tinygo-org/tinygo/goenv"
-)
-
-/*
-#cgo CXXFLAGS: -fno-rtti
-#include <stdbool.h>
-#include <stdlib.h>
-bool tinygo_clang_driver(int argc, char **argv);
-*/
-import "C"
-
-// runCCompiler invokes a C compiler with the given arguments.
-//
-// This version invokes the built-in Clang when trying to run the Clang compiler.
-func runCCompiler(command string, flags ...string) error {
-	switch command {
-	case "clang":
-		// Compile this with the internal Clang compiler.
-		headerPath := getClangHeaderPath(goenv.Get("TINYGOROOT"))
-		if headerPath == "" {
-			return errors.New("could not locate Clang headers")
-		}
-		flags = append(flags, "-I"+headerPath)
-		flags = append([]string{"tinygo:" + command}, flags...)
-		var cflag *C.char
-		buf := C.calloc(C.size_t(len(flags)), C.size_t(unsafe.Sizeof(cflag)))
-		cflags := (*[1 << 10]*C.char)(unsafe.Pointer(buf))[:len(flags):len(flags)]
-		for i, flag := range flags {
-			cflag := C.CString(flag)
-			cflags[i] = cflag
-			defer C.free(unsafe.Pointer(cflag))
-		}
-		ok := C.tinygo_clang_driver(C.int(len(flags)), (**C.char)(buf))
-		if !ok {
-			return errors.New("failed to compile using built-in clang")
-		}
-		return nil
-	default:
-		// Running some other compiler. Maybe it has been defined in the
-		// commands map (unlikely).
-		if cmdNames, ok := commands[command]; ok {
-			return execCommand(cmdNames, flags...)
-		}
-		// Alternatively, run the compiler directly.
-		cmd := exec.Command(command, flags...)
-		cmd.Stdout = os.Stdout
-		cmd.Stderr = os.Stderr
-		return cmd.Run()
-	}
-}
@@ -1,24 +0,0 @@
-// +build !byollvm
-
-package builder
-
-// This file provides a way to a C compiler as an external command. See also:
-// clang-external.go
-
-import (
-	"os"
-	"os/exec"
-)
-
-// runCCompiler invokes a C compiler with the given arguments.
-//
-// This version always runs the compiler as an external command.
-func runCCompiler(command string, flags ...string) error {
-	if cmdNames, ok := commands[command]; ok {
-		return execCommand(cmdNames, flags...)
-	}
-	cmd := exec.Command(command, flags...)
-	cmd.Stdout = os.Stdout
-	cmd.Stderr = os.Stderr
-	return cmd.Run()
-}
@@ -21,12 +21,12 @@ func NewConfig(options *compileopts.Options) (*compileopts.Config, error) {
 	if goroot == "" {
 		return nil, errors.New("cannot locate $GOROOT, please set it manually")
 	}
-	major, minor, err := getGorootVersion(goroot)
+	major, minor, err := goenv.GetGorootVersion(goroot)
 	if err != nil {
 		return nil, fmt.Errorf("could not read version from GOROOT (%v): %v", goroot, err)
 	}
-	if major != 1 || (minor != 11 && minor != 12 && minor != 13) {
-		return nil, fmt.Errorf("requires go version 1.11, 1.12, or 1.13, got go%d.%d", major, minor)
+	if major != 1 || minor < 11 || minor > 15 {
+		return nil, fmt.Errorf("requires go version 1.11 through 1.15, got go%d.%d", major, minor)
 	}
 	clangHeaderPath := getClangHeaderPath(goenv.Get("TINYGOROOT"))
 	return &compileopts.Config{
@@ -1,71 +1,13 @@
 package builder

 import (
-	"errors"
-	"fmt"
-	"io"
 	"io/ioutil"
 	"os"
 	"os/exec"
 	"path/filepath"
-	"regexp"
 	"sort"
-	"strings"
 )

-// getGorootVersion returns the major and minor version for a given GOROOT path.
-// If the goroot cannot be determined, (0, 0) is returned.
-func getGorootVersion(goroot string) (major, minor int, err error) {
-	s, err := GorootVersionString(goroot)
-	if err != nil {
-		return 0, 0, err
-	}
-
-	if s == "" || s[:2] != "go" {
-		return 0, 0, errors.New("could not parse Go version: version does not start with 'go' prefix")
-	}
-
-	parts := strings.Split(s[2:], ".")
-	if len(parts) < 2 {
-		return 0, 0, errors.New("could not parse Go version: version has less than two parts")
-	}
-
-	// Ignore the errors, we don't really handle errors here anyway.
-	var trailing string
-	n, err := fmt.Sscanf(s, "go%d.%d%s", &major, &minor, &trailing)
-	if n == 2 && err == io.EOF {
-		// Means there were no trailing characters (i.e., not an alpha/beta)
-		err = nil
-	}
-	if err != nil {
-		return 0, 0, fmt.Errorf("failed to parse version: %s", err)
-	}
-	return
-}
-
-// GorootVersionString returns the version string as reported by the Go
-// toolchain for the given GOROOT path. It is usually of the form `go1.x.y` but
-// can have some variations (for beta releases, for example).
-func GorootVersionString(goroot string) (string, error) {
-	if data, err := ioutil.ReadFile(filepath.Join(
-		goroot, "src", "runtime", "internal", "sys", "zversion.go")); err == nil {
-
-		r := regexp.MustCompile("const TheVersion = `(.*)`")
-		matches := r.FindSubmatch(data)
-		if len(matches) != 2 {
-			return "", errors.New("Invalid go version output:\n" + string(data))
-		}
-
-		return string(matches[1]), nil
-
-	} else if data, err := ioutil.ReadFile(filepath.Join(goroot, "VERSION")); err == nil {
-		return string(data), nil
-
-	} else {
-		return "", err
-	}
-}
-
 // getClangHeaderPath returns the path to the built-in Clang headers. It tries
 // multiple locations, which should make it find the directory when installed in
 // various ways.
@@ -0,0 +1,153 @@
+package builder
+
+// This file implements support for writing ESP image files. These image files
+// are read by the ROM bootloader so have to be in a particular format.
+//
+// In the future, it may be necessary to implement support for other image
+// formats, such as the ESP8266 image formats (again, used by the ROM bootloader
+// to load the firmware).
+
+import (
+	"bytes"
+	"crypto/sha256"
+	"debug/elf"
+	"encoding/binary"
+	"fmt"
+	"io/ioutil"
+	"sort"
+)
+
+type espImageSegment struct {
+	addr uint32
+	data []byte
+}
+
+// makeESPFirmare converts an input ELF file to an image file for an ESP32 or
+// ESP8266 chip. This is a special purpose image format just for the ESP chip
+// family, and is parsed by the on-chip mask ROM bootloader.
+//
+// The following documentation has been used:
+// https://github.com/espressif/esptool/wiki/Firmware-Image-Format
+// https://github.com/espressif/esp-idf/blob/8fbb63c2a701c22ccf4ce249f43aded73e134a34/components/bootloader_support/include/esp_image_format.h#L58
+// https://github.com/espressif/esptool/blob/master/esptool.py
+func makeESPFirmareImage(infile, outfile, format string) error {
+	inf, err := elf.Open(infile)
+	if err != nil {
+		return err
+	}
+	defer inf.Close()
+
+	// Load all segments to be written to the image. These are actually ELF
+	// sections, not true ELF segments (similar to how esptool does it).
+	var segments []*espImageSegment
+	for _, section := range inf.Sections {
+		if section.Type != elf.SHT_PROGBITS || section.Size == 0 || section.Flags&elf.SHF_ALLOC == 0 {
+			continue
+		}
+		data, err := section.Data()
+		if err != nil {
+			return fmt.Errorf("failed to read section data: %w", err)
+		}
+		for len(data)%4 != 0 {
+			// Align segment to 4 bytes.
+			data = append(data, 0)
+		}
+		if uint64(uint32(section.Addr)) != section.Addr {
+			return fmt.Errorf("section address too big: 0x%x", section.Addr)
+		}
+		segments = append(segments, &espImageSegment{
+			addr: uint32(section.Addr),
+			data: data,
+		})
+	}
+
+	// Sort the segments by address. This is what esptool does too.
+	sort.SliceStable(segments, func(i, j int) bool { return segments[i].addr < segments[j].addr })
+
+	// Calculate checksum over the segment data. This is used in the image
+	// footer.
+	checksum := uint8(0xef)
+	for _, segment := range segments {
+		for _, b := range segment.data {
+			checksum ^= b
+		}
+	}
+
+	// Write first to an in-memory buffer, primarily so that we can easily
+	// calculate a hash over the entire image.
+	// An added benefit is that we don't need to check for errors all the time.
+	outf := &bytes.Buffer{}
+
+	// Image header.
+	switch format {
+	case "esp32":
+		// Header format:
+		// https://github.com/espressif/esp-idf/blob/8fbb63c2/components/bootloader_support/include/esp_image_format.h#L58
+		binary.Write(outf, binary.LittleEndian, struct {
+			magic          uint8
+			segment_count  uint8
+			spi_mode       uint8
+			spi_speed_size uint8
+			entry_addr     uint32
+			wp_pin         uint8
+			spi_pin_drv    [3]uint8
+			reserved       [11]uint8
+			hash_appended  bool
+		}{
+			magic:          0xE9,
+			segment_count:  byte(len(segments)),
+			spi_mode:       0, // irrelevant, replaced by esptool when flashing
+			spi_speed_size: 0, // spi_speed, spi_size: replaced by esptool when flashing
+			entry_addr:     uint32(inf.Entry),
+			wp_pin:         0xEE, // disable WP pin
+			hash_appended:  true, // add a SHA256 hash
+		})
+	case "esp8266":
+		// Header format:
+		// https://github.com/espressif/esptool/wiki/Firmware-Image-Format
+		// Basically a truncated version of the ESP32 header.
+		binary.Write(outf, binary.LittleEndian, struct {
+			magic          uint8
+			segment_count  uint8
+			spi_mode       uint8
+			spi_speed_size uint8
+			entry_addr     uint32
+		}{
+			magic:          0xE9,
+			segment_count:  byte(len(segments)),
+			spi_mode:       0,    // irrelevant, replaced by esptool when flashing
+			spi_speed_size: 0x20, // spi_speed, spi_size: replaced by esptool when flashing
+			entry_addr:     uint32(inf.Entry),
+		})
+	default:
+		return fmt.Errorf("builder: unknown binary format %#v, expected esp32 or esp8266", format)
+	}
+
+	// Write all segments to the image.
+	// https://github.com/espressif/esptool/wiki/Firmware-Image-Format#segment
+	for _, segment := range segments {
+		binary.Write(outf, binary.LittleEndian, struct {
+			addr   uint32
+			length uint32
+		}{
+			addr:   segment.addr,
+			length: uint32(len(segment.data)),
+		})
+		outf.Write(segment.data)
+	}
+
+	// Footer, including checksum.
+	// The entire image size must be a multiple of 16, so pad the image to one
+	// byte less than that before writing the checksum.
+	outf.Write(make([]byte, 15-outf.Len()%16))
+	outf.WriteByte(checksum)
+
+	if format == "esp32" {
+		// SHA256 hash (to protect against image corruption, not for security).
+		hash := sha256.Sum256(outf.Bytes())
+		outf.Write(hash[:])
+	}
+
+	// Write the image to the output file.
+	return ioutil.WriteFile(outfile, outf.Bytes(), 0666)
+}
@@ -0,0 +1,105 @@
+package builder
+
+import (
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"github.com/tinygo-org/tinygo/goenv"
+)
+
+// Library is a container for information about a single C library, such as a
+// compiler runtime or libc.
+type Library struct {
+	// The library name, such as compiler-rt or picolibc.
+	name string
+
+	cflags func() []string
+
+	// The source directory, relative to TINYGOROOT.
+	sourceDir string
+
+	// The source files, relative to sourceDir.
+	sources func(target string) []string
+}
+
+// fullPath returns the full path to the source directory.
+func (l *Library) fullPath() string {
+	return filepath.Join(goenv.Get("TINYGOROOT"), l.sourceDir)
+}
+
+// sourcePaths returns a slice with the full paths to the source files.
+func (l *Library) sourcePaths(target string) []string {
+	sources := l.sources(target)
+	paths := make([]string, len(sources))
+	for i, name := range sources {
+		paths[i] = filepath.Join(l.fullPath(), name)
+	}
+	return paths
+}
+
+// Load the library archive, possibly generating and caching it if needed.
+func (l *Library) Load(target string) (path string, err error) {
+	// Try to load a precompiled library.
+	precompiledPath := filepath.Join(goenv.Get("TINYGOROOT"), "pkg", target, l.name+".a")
+	if _, err := os.Stat(precompiledPath); err == nil {
+		// Found a precompiled library for this OS/architecture. Return the path
+		// directly.
+		return precompiledPath, nil
+	}
+
+	outfile := l.name + "-" + target + ".a"
+
+	// Try to fetch this library from the cache.
+	if path, err := cacheLoad(outfile, commands["clang"][0], l.sourcePaths(target)); path != "" || err != nil {
+		// Cache hit.
+		return path, err
+	}
+	// Cache miss, build it now.
+
+	dirPrefix := "tinygo-" + l.name
+	remapDir := filepath.Join(os.TempDir(), dirPrefix)
+	dir, err := ioutil.TempDir(os.TempDir(), dirPrefix)
+	if err != nil {
+		return "", err
+	}
+	defer os.RemoveAll(dir)
+
+	// Precalculate the flags to the compiler invocation.
+	args := append(l.cflags(), "-c", "-Oz", "-g", "-ffunction-sections", "-fdata-sections", "-Wno-macro-redefined", "--target="+target, "-fdebug-prefix-map="+dir+"="+remapDir)
+	if strings.HasPrefix(target, "arm") || strings.HasPrefix(target, "thumb") {
+		args = append(args, "-fshort-enums", "-fomit-frame-pointer", "-mfloat-abi=soft")
+	}
+	if strings.HasPrefix(target, "riscv32-") {
+		args = append(args, "-march=rv32imac", "-mabi=ilp32", "-fforce-enable-int128")
+	}
+	if strings.HasPrefix(target, "riscv64-") {
+		args = append(args, "-march=rv64gc", "-mabi=lp64")
+	}
+
+	// Compile all sources.
+	var objs []string
+	for _, srcpath := range l.sourcePaths(target) {
+		objpath := filepath.Join(dir, filepath.Base(srcpath)+".o")
+		objs = append(objs, objpath)
+		// Note: -fdebug-prefix-map is necessary to make the output archive
+		// reproducible. Otherwise the temporary directory is stored in the
+		// archive itself, which varies each run.
+		err := runCCompiler("clang", append(args, "-o", objpath, srcpath)...)
+		if err != nil {
+			return "", &commandError{"failed to build", srcpath, err}
+		}
+	}
+
+	// Put all the object files in a single archive. This archive file will be
+	// used to statically link this library.
+	arpath := filepath.Join(dir, l.name+".a")
+	err = makeArchive(arpath, objs)
+	if err != nil {
+		return "", err
+	}
+
+	// Store this archive in the cache.
+	return cacheStore(arpath, outfile, commands["clang"][0], l.sourcePaths(target))
+}
@@ -1,71 +0,0 @@
-// +build byollvm
-
-package builder
-
-// This file provides a Link() function that uses the bundled lld if possible.
-
-import (
-	"errors"
-	"os"
-	"os/exec"
-	"unsafe"
-
-	"github.com/tinygo-org/tinygo/goenv"
-)
-
-/*
-#include <stdbool.h>
-#include <stdlib.h>
-bool tinygo_link_elf(int argc, char **argv);
-bool tinygo_link_wasm(int argc, char **argv);
-*/
-import "C"
-
-// link invokes a linker with the given name and flags.
-//
-// This version uses the built-in linker when trying to use lld.
-func link(linker string, flags ...string) error {
-	switch linker {
-	case "ld.lld":
-		flags = append([]string{"tinygo:" + linker}, flags...)
-		var cflag *C.char
-		buf := C.calloc(C.size_t(len(flags)), C.size_t(unsafe.Sizeof(cflag)))
-		cflags := (*[1 << 10]*C.char)(unsafe.Pointer(buf))[:len(flags):len(flags)]
-		for i, flag := range flags {
-			cflag := C.CString(flag)
-			cflags[i] = cflag
-			defer C.free(unsafe.Pointer(cflag))
-		}
-		ok := C.tinygo_link_elf(C.int(len(flags)), (**C.char)(buf))
-		if !ok {
-			return errors.New("failed to link using built-in ld.lld")
-		}
-		return nil
-	case "wasm-ld":
-		flags = append([]string{"tinygo:" + linker}, flags...)
-		var cflag *C.char
-		buf := C.calloc(C.size_t(len(flags)), C.size_t(unsafe.Sizeof(cflag)))
-		defer C.free(buf)
-		cflags := (*[1 << 10]*C.char)(unsafe.Pointer(buf))[:len(flags):len(flags)]
-		for i, flag := range flags {
-			cflag := C.CString(flag)
-			cflags[i] = cflag
-			defer C.free(unsafe.Pointer(cflag))
-		}
-		ok := C.tinygo_link_wasm(C.int(len(flags)), (**C.char)(buf))
-		if !ok {
-			return errors.New("failed to link using built-in wasm-ld")
-		}
-		return nil
-	default:
-		// Fall back to external command.
-		if cmdNames, ok := commands[linker]; ok {
-			return execCommand(cmdNames, flags...)
-		}
-		cmd := exec.Command(linker, flags...)
-		cmd.Stdout = os.Stdout
-		cmd.Stderr = os.Stderr
-		cmd.Dir = goenv.Get("TINYGOROOT")
-		return cmd.Run()
-	}
-}
@@ -1,27 +0,0 @@
-// +build !byollvm
-
-package builder
-
-// This file provides a Link() function that always runs an external command. It
-// is provided for when tinygo is built without linking to liblld.
-
-import (
-	"os"
-	"os/exec"
-
-	"github.com/tinygo-org/tinygo/goenv"
-)
-
-// link invokes a linker with the given name and arguments.
-//
-// This version always runs the linker as an external command.
-func link(linker string, flags ...string) error {
-	if cmdNames, ok := commands[linker]; ok {
-		return execCommand(cmdNames, flags...)
-	}
-	cmd := exec.Command(linker, flags...)
-	cmd.Stdout = os.Stdout
-	cmd.Stderr = os.Stderr
-	cmd.Dir = goenv.Get("TINYGOROOT")
-	return cmd.Run()
-}
@@ -8,12 +8,12 @@ extern "C" {

 bool tinygo_link_elf(int argc, char **argv) {
 	std::vector<const char*> args(argv, argv + argc);
-	return lld::elf::link(args, false);
+	return lld::elf::link(args, false, llvm::outs(), llvm::errs());
 }

 bool tinygo_link_wasm(int argc, char **argv) {
 	std::vector<const char*> args(argv, argv + argc);
-	return lld::wasm::link(args, false);
+	return lld::wasm::link(args, false, llvm::outs(), llvm::errs());
 }

 } // external "C"
@@ -4,12 +4,15 @@ import (
 	"debug/elf"
 	"io/ioutil"
 	"os"
-	"path/filepath"
 	"sort"

 	"github.com/marcinbor85/gohex"
 )

+// maxPadBytes is the maximum allowed bytes to be padded in a rom extraction
+// this value is currently defined by Nintendo Switch Page Alignment (4096 bytes)
+const maxPadBytes = 4095
+
 // objcopyError is an error returned by functions that act like objcopy.
 type objcopyError struct {
 	Op  string
@@ -71,7 +74,12 @@ func extractROM(path string) (uint64, []byte, error) {
 	var rom []byte
 	for _, prog := range progs {
 		if prog.Paddr != progs[0].Paddr+uint64(len(rom)) {
-			return 0, nil, objcopyError{"ROM segments are non-contiguous: " + path, nil}
+			diff := prog.Paddr - (progs[0].Paddr + uint64(len(rom)))
+			if diff > maxPadBytes {
+				return 0, nil, objcopyError{"ROM segments are non-contiguous: " + path, nil}
+			}
+			// Pad the difference
+			rom = append(rom, make([]byte, diff)...)
 		}
 		data, err := ioutil.ReadAll(prog.Open())
 		if err != nil {
@@ -93,7 +101,7 @@ func extractROM(path string) (uint64, []byte, error) {

 // objcopy converts an ELF file to a different (simpler) output file format:
 // .bin or .hex. It extracts only the .text section.
-func objcopy(infile, outfile string) error {
+func objcopy(infile, outfile, binaryFormat string) error {
 	f, err := os.OpenFile(outfile, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0666)
 	if err != nil {
 		return err
@@ -107,24 +115,20 @@ func objcopy(infile, outfile string) error {
 	}

 	// Write to the file, in the correct format.
-	switch filepath.Ext(outfile) {
-	case ".gba":
-		// The address is not stored in a .gba file.
-		_, err := f.Write(data)
-		return err
-	case ".bin":
-		// The address is not stored in a .bin file (therefore you
-		// should use .hex files in most cases).
-		_, err := f.Write(data)
-		return err
-	case ".hex":
+	switch binaryFormat {
+	case "hex":
+		// Intel hex file, includes the firmware start address.
 		mem := gohex.NewMemory()
 		err := mem.AddBinary(uint32(addr), data)
 		if err != nil {
 			return objcopyError{"failed to create .hex file", err}
 		}
-		mem.DumpIntelHex(f, 16) // TODO: handle error
-		return nil
+		return mem.DumpIntelHex(f, 16)
+	case "bin":
+		// The start address is not stored in raw firmware files (therefore you
+		// should use .hex files in most cases).
+		_, err := f.Write(data)
+		return err
 	default:
 		panic("unreachable")
 	}
@@ -0,0 +1,127 @@
+package builder
+
+import (
+	"path/filepath"
+
+	"github.com/tinygo-org/tinygo/goenv"
+)
+
+// Picolibc is a C library for bare metal embedded devices. It was originally
+// based on newlib.
+var Picolibc = Library{
+	name: "picolibc",
+	cflags: func() []string {
+		picolibcDir := filepath.Join(goenv.Get("TINYGOROOT"), "lib/picolibc/newlib/libc")
+		return []string{"-Werror", "-Wall", "-std=gnu11", "-D_COMPILING_NEWLIB", "-nostdlibinc", "-Xclang", "-internal-isystem", "-Xclang", picolibcDir + "/include", "-I" + picolibcDir + "/tinystdio", "-I" + goenv.Get("TINYGOROOT") + "/lib/picolibc-include"}
+	},
+	sourceDir: "lib/picolibc/newlib/libc",
+	sources: func(target string) []string {
+		return picolibcSources
+	},
+}
+
+var picolibcSources = []string{
+	"string/bcmp.c",
+	"string/bcopy.c",
+	"string/bzero.c",
+	"string/explicit_bzero.c",
+	"string/ffsl.c",
+	"string/ffsll.c",
+	"string/fls.c",
+	"string/flsl.c",
+	"string/flsll.c",
+	"string/gnu_basename.c",
+	"string/index.c",
+	"string/memccpy.c",
+	"string/memchr.c",
+	"string/memcmp.c",
+	"string/memcpy.c",
+	"string/memmem.c",
+	"string/memmove.c",
+	"string/mempcpy.c",
+	"string/memrchr.c",
+	"string/memset.c",
+	"string/rawmemchr.c",
+	"string/rindex.c",
+	"string/stpcpy.c",
+	"string/stpncpy.c",
+	"string/strcasecmp.c",
+	"string/strcasecmp_l.c",
+	"string/strcasestr.c",
+	"string/strcat.c",
+	"string/strchr.c",
+	"string/strchrnul.c",
+	"string/strcmp.c",
+	"string/strcoll.c",
+	"string/strcoll_l.c",
+	"string/strcpy.c",
+	"string/strcspn.c",
+	"string/strdup.c",
+	"string/strerror.c",
+	"string/strerror_r.c",
+	"string/strlcat.c",
+	"string/strlcpy.c",
+	"string/strlen.c",
+	"string/strlwr.c",
+	"string/strncasecmp.c",
+	"string/strncasecmp_l.c",
+	"string/strncat.c",
+	"string/strncmp.c",
+	"string/strncpy.c",
+	"string/strndup.c",
+	"string/strnlen.c",
+	"string/strnstr.c",
+	"string/strpbrk.c",
+	"string/strrchr.c",
+	"string/strsep.c",
+	"string/strsignal.c",
+	"string/strspn.c",
+	"string/strstr.c",
+	"string/strtok.c",
+	"string/strtok_r.c",
+	"string/strupr.c",
+	"string/strverscmp.c",
+	"string/strxfrm.c",
+	"string/strxfrm_l.c",
+	"string/swab.c",
+	"string/timingsafe_bcmp.c",
+	"string/timingsafe_memcmp.c",
+	"string/u_strerr.c",
+	"string/wcpcpy.c",
+	"string/wcpncpy.c",
+	"string/wcscasecmp.c",
+	"string/wcscasecmp_l.c",
+	"string/wcscat.c",
+	"string/wcschr.c",
+	"string/wcscmp.c",
+	"string/wcscoll.c",
+	"string/wcscoll_l.c",
+	"string/wcscpy.c",
+	"string/wcscspn.c",
+	"string/wcsdup.c",
+	"string/wcslcat.c",
+	"string/wcslcpy.c",
+	"string/wcslen.c",
+	"string/wcsncasecmp.c",
+	"string/wcsncasecmp_l.c",
+	"string/wcsncat.c",
+	"string/wcsncmp.c",
+	"string/wcsncpy.c",
+	"string/wcsnlen.c",
+	"string/wcspbrk.c",
+	"string/wcsrchr.c",
+	"string/wcsspn.c",
+	"string/wcsstr.c",
+	"string/wcstok.c",
+	"string/wcswidth.c",
+	"string/wcsxfrm.c",
+	"string/wcsxfrm_l.c",
+	"string/wcwidth.c",
+	"string/wmemchr.c",
+	"string/wmemcmp.c",
+	"string/wmemcpy.c",
+	"string/wmemmove.c",
+	"string/wmempcpy.c",
+	"string/wmemset.c",
+	"string/xpg_strerror_r.c",
+}
@@ -84,7 +84,18 @@ func loadProgramSize(path string) (*programSize, error) {
 		if section.Type != elf.SHT_PROGBITS && section.Type != elf.SHT_NOBITS {
 			continue
 		}
-		if section.Type == elf.SHT_NOBITS {
+		if section.Name == ".stack" {
+			// HACK: this works around a bug in ld.lld from LLVM 10. The linker
+			// marks sections with no input symbols (such as is the case for the
+			// .stack section) as SHT_PROGBITS instead of SHT_NOBITS. While it
+			// doesn't affect the generated binaries (.hex and .bin), it does
+			// affect the reported size.
+			// https://bugs.llvm.org/show_bug.cgi?id=45336
+			// https://reviews.llvm.org/D76981
+			// It has been merged in master, but it has not (yet) been
+			// backported to the LLVM 10 release branch.
+			sumBSS += section.Size
+		} else if section.Type == elf.SHT_NOBITS {
 			sumBSS += section.Size
 		} else if section.Flags&elf.SHF_EXECINSTR != 0 {
 			sumCode += section.Size
@@ -0,0 +1,54 @@
+// +build byollvm
+
+package builder
+
+import (
+	"errors"
+	"unsafe"
+)
+
+/*
+#cgo CXXFLAGS: -fno-rtti
+#include <stdbool.h>
+#include <stdlib.h>
+bool tinygo_clang_driver(int argc, char **argv);
+bool tinygo_link_elf(int argc, char **argv);
+bool tinygo_link_wasm(int argc, char **argv);
+*/
+import "C"
+
+const hasBuiltinTools = true
+
+// RunTool runs the given tool (such as clang).
+//
+// This version actually runs the tools because TinyGo was compiled while
+// linking statically with LLVM (with the byollvm build tag).
+func RunTool(tool string, args ...string) error {
+	args = append([]string{"tinygo:" + tool}, args...)
+
+	var cflag *C.char
+	buf := C.calloc(C.size_t(len(args)), C.size_t(unsafe.Sizeof(cflag)))
+	defer C.free(buf)
+	cflags := (*[1 << 10]*C.char)(unsafe.Pointer(buf))[:len(args):len(args)]
+	for i, flag := range args {
+		cflag := C.CString(flag)
+		cflags[i] = cflag
+		defer C.free(unsafe.Pointer(cflag))
+	}
+
+	var ok C.bool
+	switch tool {
+	case "clang":
+		ok = C.tinygo_clang_driver(C.int(len(args)), (**C.char)(buf))
+	case "ld.lld":
+		ok = C.tinygo_link_elf(C.int(len(args)), (**C.char)(buf))
+	case "wasm-ld":
+		ok = C.tinygo_link_wasm(C.int(len(args)), (**C.char)(buf))
+	default:
+		return errors.New("unknown tool: " + tool)
+	}
+	if !ok {
+		return errors.New("failed to run tool: " + tool)
+	}
+	return nil
+}
@@ -0,0 +1,15 @@
+// +build !byollvm
+
+package builder
+
+import "errors"
+
+const hasBuiltinTools = false
+
+// RunTool runs the given tool (such as clang).
+//
+// This version doesn't actually run the tool: TinyGo has not been compiled by
+// statically linking to LLVM.
+func RunTool(tool string, args ...string) error {
+	return errors.New("cannot run tool: " + tool)
+}
@@ -0,0 +1,59 @@
+package builder
+
+import (
+	"errors"
+	"os"
+	"os/exec"
+
+	"github.com/tinygo-org/tinygo/goenv"
+)
+
+// runCCompiler invokes a C compiler with the given arguments.
+func runCCompiler(command string, flags ...string) error {
+	if hasBuiltinTools && command == "clang" {
+		// Compile this with the internal Clang compiler.
+		headerPath := getClangHeaderPath(goenv.Get("TINYGOROOT"))
+		if headerPath == "" {
+			return errors.New("could not locate Clang headers")
+		}
+		flags = append(flags, "-I"+headerPath)
+		cmd := exec.Command(os.Args[0], append([]string{"clang"}, flags...)...)
+		cmd.Stdout = os.Stdout
+		cmd.Stderr = os.Stderr
+		return cmd.Run()
+	}
+
+	// Running some other compiler. Maybe it has been defined in the
+	// commands map (unlikely).
+	if cmdNames, ok := commands[command]; ok {
+		return execCommand(cmdNames, flags...)
+	}
+
+	// Alternatively, run the compiler directly.
+	cmd := exec.Command(command, flags...)
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+	return cmd.Run()
+}
+
+// link invokes a linker with the given name and flags.
+func link(linker string, flags ...string) error {
+	if hasBuiltinTools && (linker == "ld.lld" || linker == "wasm-ld") {
+		// Run command with internal linker.
+		cmd := exec.Command(os.Args[0], append([]string{linker}, flags...)...)
+		cmd.Stdout = os.Stdout
+		cmd.Stderr = os.Stderr
+		return cmd.Run()
+	}
+
+	// Fall back to external command.
+	if cmdNames, ok := commands[linker]; ok {
+		return execCommand(cmdNames, flags...)
+	}
+
+	cmd := exec.Command(linker, flags...)
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+	cmd.Dir = goenv.Get("TINYGOROOT")
+	return cmd.Run()
+}
@@ -11,26 +11,33 @@ import (
 	"bytes"
 	"encoding/binary"
 	"io/ioutil"
+	"strconv"
 )

 // convertELFFileToUF2File converts an ELF file to a UF2 file.
-func convertELFFileToUF2File(infile, outfile string) error {
+func convertELFFileToUF2File(infile, outfile string, uf2FamilyID string) error {
 	// Read the .text segment.
 	targetAddress, data, err := extractROM(infile)
 	if err != nil {
 		return err
 	}

-	output, _ := convertBinToUF2(data, uint32(targetAddress))
+	output, _, err := convertBinToUF2(data, uint32(targetAddress), uf2FamilyID)
+	if err != nil {
+		return err
+	}
 	return ioutil.WriteFile(outfile, output, 0644)
 }

 // convertBinToUF2 converts the binary bytes in input to UF2 formatted data.
-func convertBinToUF2(input []byte, targetAddr uint32) ([]byte, int) {
+func convertBinToUF2(input []byte, targetAddr uint32, uf2FamilyID string) ([]byte, int, error) {
 	blocks := split(input, 256)
 	output := make([]byte, 0)

-	bl := newUF2Block(targetAddr)
+	bl, err := newUF2Block(targetAddr, uf2FamilyID)
+	if err != nil {
+		return nil, 0, err
+	}
 	bl.SetNumBlocks(len(blocks))

 	for i := 0; i < len(blocks); i++ {
@@ -41,7 +48,7 @@ func convertBinToUF2(input []byte, targetAddr uint32) ([]byte, int) {
 		bl.IncrementAddress(bl.payloadSize)
 	}

-	return output, len(blocks)
+	return output, len(blocks), nil
 }

 const (
@@ -65,18 +72,32 @@ type uf2Block struct {
 }

 // newUF2Block returns a new uf2Block struct that has been correctly populated
-func newUF2Block(targetAddr uint32) *uf2Block {
+func newUF2Block(targetAddr uint32, uf2FamilyID string) (*uf2Block, error) {
+	var flags uint32
+	var familyID uint32
+	if uf2FamilyID != "" {
+		flags |= flagFamilyIDPresent
+		v, err := strconv.ParseUint(uf2FamilyID, 0, 32)
+		if err != nil {
+			return nil, err
+		}
+		familyID = uint32(v)
+	}
 	return &uf2Block{magicStart0: uf2MagicStart0,
 		magicStart1: uf2MagicStart1,
 		magicEnd:    uf2MagicEnd,
 		targetAddr:  targetAddr,
-		flags:       0x0,
-		familyID:    0x0,
+		flags:       flags,
+		familyID:    familyID,
 		payloadSize: 256,
 		data:        make([]byte, 476),
-	}
+	}, nil
 }

+const (
+	flagFamilyIDPresent = 0x00002000
+)
+
 // Bytes converts the uf2Block to a slice of bytes that can be written to file.
 func (b *uf2Block) Bytes() []byte {
 	buf := bytes.NewBuffer(make([]byte, 0, 512))
@@ -14,7 +14,9 @@ package cgo
 import (
 	"fmt"
 	"go/ast"
+	"go/scanner"
 	"go/token"
+	"path/filepath"
 	"sort"
 	"strconv"
 	"strings"
@@ -39,6 +41,7 @@ type cgoPackage struct {
 	elaboratedTypes map[string]*elaboratedTypeInfo
 	enums           map[string]enumInfo
 	anonStructNum   int
+	ldflags         []string
 }

 // constantInfo stores some information about a CGo constant found by libclang
@@ -154,7 +157,7 @@ typedef unsigned long long  _Cgo_ulonglong;
 // newly created *ast.File that should be added to the list of to-be-parsed
 // files. If there is one or more error, it returns these in the []error slice
 // but still modifies the AST.
-func Process(files []*ast.File, dir string, fset *token.FileSet, cflags []string) (*ast.File, []error) {
+func Process(files []*ast.File, dir string, fset *token.FileSet, cflags []string) (*ast.File, []string, []error) {
 	p := &cgoPackage{
 		dir:             dir,
 		fset:            fset,
@@ -168,11 +171,28 @@ func Process(files []*ast.File, dir string, fset *token.FileSet, cflags []string
 		enums:           map[string]enumInfo{},
 	}

+	// Disable _FORTIFY_SOURCE as it causes problems on macOS.
+	// Note that it is only disabled for memcpy (etc) calls made from Go, which
+	// have better alternatives anyway.
+	cflags = append(cflags, "-D_FORTIFY_SOURCE=0")
+
 	// Add a new location for the following file.
 	generatedTokenPos := p.fset.AddFile(dir+"/!cgo.go", -1, 0)
 	generatedTokenPos.SetLines([]int{0})
 	p.generatedPos = generatedTokenPos.Pos(0)

+	// Find the absolute path for this package.
+	packagePath, err := filepath.Abs(fset.File(files[0].Pos()).Name())
+	if err != nil {
+		return nil, nil, []error{
+			scanner.Error{
+				Pos: fset.Position(files[0].Pos()),
+				Msg: "cgo: cannot find absolute path: " + err.Error(), // TODO: wrap this error
+			},
+		}
+	}
+	packagePath = filepath.Dir(packagePath)
+
 	// Construct a new in-memory AST for CGo declarations of this package.
 	unsafeImport := &ast.ImportSpec{
 		Path: &ast.BasicLit{
@@ -338,7 +358,21 @@ func Process(files []*ast.File, dir string, fset *token.FileSet, cflags []string
 						p.addErrorAfter(comment.Slash, comment.Text[:lineStart+colon+1], err.Error())
 						continue
 					}
+					makePathsAbsolute(flags, packagePath)
 					cflags = append(cflags, flags...)
+				case "LDFLAGS":
+					flags, err := shlex.Split(value)
+					if err != nil {
+						// TODO: find the exact location where the error happened.
+						p.addErrorAfter(comment.Slash, comment.Text[:lineStart+colon+1], "failed to parse flags in #cgo line: "+err.Error())
+						continue
+					}
+					if err := checkLinkerFlags(name, flags); err != nil {
+						p.addErrorAfter(comment.Slash, comment.Text[:lineStart+colon+1], err.Error())
+						continue
+					}
+					makePathsAbsolute(flags, packagePath)
+					p.ldflags = append(p.ldflags, flags...)
 				default:
 					startPos := strings.LastIndex(line[4:colon], name) + 4
 					p.addErrorAfter(comment.Slash, comment.Text[:lineStart+startPos], "invalid #cgo line: "+name)
@@ -392,7 +426,31 @@ func Process(files []*ast.File, dir string, fset *token.FileSet, cflags []string
 	// Print the newly generated in-memory AST, for debugging.
 	//ast.Print(fset, p.generated)

-	return p.generated, p.errors
+	return p.generated, p.ldflags, p.errors
+}
+
+// makePathsAbsolute converts some common path compiler flags (-I, -L) from
+// relative flags into absolute flags, if they are relative. This is necessary
+// because the C compiler is usually not invoked from the package path.
+func makePathsAbsolute(args []string, packagePath string) {
+	nextIsPath := false
+	for i, arg := range args {
+		if nextIsPath {
+			if !filepath.IsAbs(arg) {
+				args[i] = filepath.Join(packagePath, arg)
+			}
+		}
+		if arg == "-I" || arg == "-L" {
+			nextIsPath = true
+			continue
+		}
+		if strings.HasPrefix(arg, "-I") || strings.HasPrefix(arg, "-L") {
+			path := arg[2:]
+			if !filepath.IsAbs(path) {
+				args[i] = arg[:2] + filepath.Join(packagePath, path)
+			}
+		}
+	}
 }

 // addFuncDecls adds the C function declarations found by libclang in the
@@ -11,6 +11,7 @@ import (
 	"go/types"
 	"io/ioutil"
 	"path/filepath"
+	"regexp"
 	"runtime"
 	"strings"
 	"testing"
@@ -19,6 +20,21 @@ import (
 // Pass -update to go test to update the output of the test files.
 var flagUpdate = flag.Bool("update", false, "Update images based on test output.")

+// normalizeResult normalizes Go source code that comes out of tests across
+// platforms and Go versions.
+func normalizeResult(result string) string {
+	actual := strings.Replace(result, "\r\n", "\n", -1)
+
+	// Make sure all functions are wrapped, even those that would otherwise be
+	// single-line functions. This is necessary because Go 1.14 changed the way
+	// such functions are wrapped and it's important to have consistent test
+	// results.
+	re := regexp.MustCompile(`func \((.+)\)( .*?) +{ (.+) }`)
+	actual = re.ReplaceAllString(actual, "func ($1)$2 {\n\t$3\n}")
+
+	return actual
+}
+
 func TestCGo(t *testing.T) {
 	var cflags = []string{"--target=armv6m-none-eabi"}

@@ -34,7 +50,7 @@ func TestCGo(t *testing.T) {
 			}

 			// Process the AST with CGo.
-			cgoAST, cgoErrors := Process([]*ast.File{f}, "testdata", fset, cflags)
+			cgoAST, _, cgoErrors := Process([]*ast.File{f}, "testdata", fset, cflags)

 			// Check the AST for type errors.
 			var typecheckErrors []error
@@ -74,7 +90,7 @@ func TestCGo(t *testing.T) {
 			if err != nil {
 				t.Errorf("could not write out CGo AST: %v", err)
 			}
-			actual := strings.Replace(string(buf.Bytes()), "\r\n", "\n", -1)
+			actual := normalizeResult(string(buf.Bytes()))

 			// Read the file with the expected output, to compare against.
 			outfile := filepath.Join("testdata", name+".out.go")
@@ -15,7 +15,7 @@ import (
 )

 /*
-#include <clang-c/Index.h> // if this fails, install libclang-9-dev
+#include <clang-c/Index.h> // if this fails, install libclang-10-dev
 #include <stdlib.h>
 #include <stdint.h>

@@ -246,9 +246,9 @@ func tinygo_clang_globals_visitor(c, parent C.GoCXCursor, client_data C.CXClient
 		}
 		value := source[len(name):]
 		// Try to convert this #define into a Go constant expression.
-		expr, err := parseConst(pos+token.Pos(len(name)), p.fset, value)
-		if err != nil {
-			p.errors = append(p.errors, err)
+		expr, scannerError := parseConst(pos+token.Pos(len(name)), p.fset, value)
+		if scannerError != nil {
+			p.errors = append(p.errors, *scannerError)
 		}
 		if expr != nil {
 			// Parsing was successful.
@@ -1,13 +1,14 @@
 // +build !byollvm
+// +build !llvm9

 package cgo

 /*
-#cgo linux  CFLAGS: -I/usr/lib/llvm-9/include
-#cgo darwin CFLAGS: -I/usr/local/opt/llvm@9/include
-#cgo freebsd CFLAGS: -I/usr/local/llvm90/include
-#cgo linux  LDFLAGS: -L/usr/lib/llvm-9/lib -lclang
-#cgo darwin LDFLAGS: -L/usr/local/opt/llvm@9/lib -lclang -lffi
-#cgo freebsd LDFLAGS: -L/usr/local/llvm90/lib -lclang
+#cgo linux  CFLAGS: -I/usr/lib/llvm-10/include
+#cgo darwin CFLAGS: -I/usr/local/opt/llvm@10/include
+#cgo freebsd CFLAGS: -I/usr/local/llvm10/include
+#cgo linux  LDFLAGS: -L/usr/lib/llvm-10/lib -lclang
+#cgo darwin LDFLAGS: -L/usr/local/opt/llvm@10/lib -lclang -lffi
+#cgo freebsd LDFLAGS: -L/usr/local/llvm10/lib -lclang
 */
 import "C"
@@ -0,0 +1,14 @@
+// +build !byollvm
+// +build llvm9
+
+package cgo
+
+/*
+#cgo linux  CFLAGS: -I/usr/lib/llvm-9/include
+#cgo darwin CFLAGS: -I/usr/local/opt/llvm@9/include
+#cgo freebsd CFLAGS: -I/usr/local/llvm9/include
+#cgo linux  LDFLAGS: -L/usr/lib/llvm-9/lib -lclang
+#cgo darwin LDFLAGS: -L/usr/local/opt/llvm@9/lib -lclang -lffi
+#cgo freebsd LDFLAGS: -L/usr/local/llvm9/lib -lclang
+*/
+import "C"
@@ -3,7 +3,7 @@
 // are slightly different from the ones defined in libclang.go, but they
 // should be ABI compatible.

-#include <clang-c/Index.h> // if this fails, install libclang-9-dev
+#include <clang-c/Index.h> // if this fails, install libclang-10-dev

 CXCursor tinygo_clang_getTranslationUnitCursor(CXTranslationUnit tu) {
 	return clang_getTranslationUnitCursor(tu);
@@ -9,6 +9,9 @@ package main

 #cgo CFLAGS: -DFOO

+#cgo CFLAGS: -Iinclude
+#include "foo.h"
+
 #if defined(FOO)
 #define BAR 3
 #else
@@ -18,9 +21,17 @@ package main
 #if defined(NOTDEFINED)
 #warning flag must not be defined
 #endif
+
+// Check Compiler flags
+#cgo LDFLAGS: -lc
+
+// This flag is not valid ldflags
+#cgo LDFLAGS: -does-not-exists
+
 */
 import "C"

 var (
 	_ = C.BAR
+	_ = C.FOO_H
 )
@@ -1,6 +1,7 @@
 // CGo errors:
 //     testdata/flags.go:5:7: invalid #cgo line: NOFLAGS
 //     testdata/flags.go:8:13: invalid flag: -fdoes-not-exist
+//     testdata/flags.go:29:14: invalid flag: -does-not-exists

 package main

@@ -9,6 +10,7 @@ import "unsafe"
 var _ unsafe.Pointer

 const C.BAR = 3
+const C.FOO_H = 1

 type C.int16_t = int16
 type C.int32_t = int32
@@ -0,0 +1 @@
+#define FOO_H 1
@@ -62,12 +62,18 @@ type C.union3_t = C.union_1
 type C.union_nested_t = C.union_3
 type C.unionarray_t = struct{ arr [10]C.uchar }

-func (s *C.struct_4) bitfield_a() C.uchar          { return s.__bitfield_1 & 0x1f }
-func (s *C.struct_4) set_bitfield_a(value C.uchar) { s.__bitfield_1 = s.__bitfield_1&^0x1f | value&0x1f<<0 }
+func (s *C.struct_4) bitfield_a() C.uchar {
+	return s.__bitfield_1 & 0x1f
+}
+func (s *C.struct_4) set_bitfield_a(value C.uchar) {
+	s.__bitfield_1 = s.__bitfield_1&^0x1f | value&0x1f<<0
+}
 func (s *C.struct_4) bitfield_b() C.uchar {
 	return s.__bitfield_1 >> 5 & 0x1
 }
-func (s *C.struct_4) set_bitfield_b(value C.uchar) { s.__bitfield_1 = s.__bitfield_1&^0x20 | value&0x1<<5 }
+func (s *C.struct_4) set_bitfield_b(value C.uchar) {
+	s.__bitfield_1 = s.__bitfield_1&^0x20 | value&0x1<<5
+}
 func (s *C.struct_4) bitfield_c() C.uchar {
 	return s.__bitfield_1 >> 6
 }
@@ -94,25 +100,45 @@ type C.struct_type1 struct {
 }
 type C.struct_type2 struct{ _type C.int }

-func (union *C.union_1) unionfield_i() *C.int   { return (*C.int)(unsafe.Pointer(&union.$union)) }
-func (union *C.union_1) unionfield_d() *float64 { return (*float64)(unsafe.Pointer(&union.$union)) }
-func (union *C.union_1) unionfield_s() *C.short { return (*C.short)(unsafe.Pointer(&union.$union)) }
+func (union *C.union_1) unionfield_i() *C.int {
+	return (*C.int)(unsafe.Pointer(&union.$union))
+}
+func (union *C.union_1) unionfield_d() *float64 {
+	return (*float64)(unsafe.Pointer(&union.$union))
+}
+func (union *C.union_1) unionfield_s() *C.short {
+	return (*C.short)(unsafe.Pointer(&union.$union))
+}

 type C.union_1 struct{ $union uint64 }

-func (union *C.union_2) unionfield_area() *C.point2d_t  { return (*C.point2d_t)(unsafe.Pointer(&union.$union)) }
-func (union *C.union_2) unionfield_solid() *C.point3d_t { return (*C.point3d_t)(unsafe.Pointer(&union.$union)) }
+func (union *C.union_2) unionfield_area() *C.point2d_t {
+	return (*C.point2d_t)(unsafe.Pointer(&union.$union))
+}
+func (union *C.union_2) unionfield_solid() *C.point3d_t {
+	return (*C.point3d_t)(unsafe.Pointer(&union.$union))
+}

 type C.union_2 struct{ $union [3]uint32 }

-func (union *C.union_3) unionfield_point() *C.point3d_t    { return (*C.point3d_t)(unsafe.Pointer(&union.$union)) }
-func (union *C.union_3) unionfield_array() *C.unionarray_t { return (*C.unionarray_t)(unsafe.Pointer(&union.$union)) }
-func (union *C.union_3) unionfield_thing() *C.union3_t     { return (*C.union3_t)(unsafe.Pointer(&union.$union)) }
+func (union *C.union_3) unionfield_point() *C.point3d_t {
+	return (*C.point3d_t)(unsafe.Pointer(&union.$union))
+}
+func (union *C.union_3) unionfield_array() *C.unionarray_t {
+	return (*C.unionarray_t)(unsafe.Pointer(&union.$union))
+}
+func (union *C.union_3) unionfield_thing() *C.union3_t {
+	return (*C.union3_t)(unsafe.Pointer(&union.$union))
+}

 type C.union_3 struct{ $union [2]uint64 }

-func (union *C.union_union2d) unionfield_i() *C.int      { return (*C.int)(unsafe.Pointer(&union.$union)) }
-func (union *C.union_union2d) unionfield_d() *[2]float64 { return (*[2]float64)(unsafe.Pointer(&union.$union)) }
+func (union *C.union_union2d) unionfield_i() *C.int {
+	return (*C.int)(unsafe.Pointer(&union.$union))
+}
+func (union *C.union_union2d) unionfield_d() *[2]float64 {
+	return (*[2]float64)(unsafe.Pointer(&union.$union))
+}

 type C.union_union2d struct{ $union [2]uint64 }
 type C.enum_option C.int
@@ -5,6 +5,7 @@ package compileopts
 import (
 	"errors"
 	"fmt"
+	"path/filepath"
 	"regexp"
 	"strconv"
 	"strings"
@@ -21,6 +22,29 @@ type Config struct {
 	TestConfig     TestConfig
 }

+// FuncValueImplementation is an enum for the particular implementations of Go
+// func values.
+type FuncValueImplementation int
+
+// These constants describe the various possible implementations of Go func
+// values.
+const (
+	FuncValueNone FuncValueImplementation = iota
+
+	// A func value is implemented as a pair of pointers:
+	//     {context, function pointer}
+	// where the context may be a pointer to a heap-allocated struct containing
+	// the free variables, or it may be undef if the function being pointed to
+	// doesn't need a context. The function pointer is a regular function
+	// pointer.
+	FuncValueDoubleword
+
+	// As funcValueDoubleword, but with the function pointer replaced by a
+	// unique ID per function signature. Function values are called by using a
+	// switch statement and choosing which function to call.
+	FuncValueSwitch
+)
+
 // Triple returns the LLVM target triple, like armv6m-none-eabi.
 func (c *Config) Triple() string {
 	return c.Target.Triple
@@ -65,8 +89,14 @@ func (c *Config) BuildTags() []string {
 	return tags
 }

+// CgoEnabled returns true if (and only if) CGo is enabled. It is true by
+// default and false if CGO_ENABLED is set to "0".
+func (c *Config) CgoEnabled() bool {
+	return goenv.Get("CGO_ENABLED") == "1"
+}
+
 // GC returns the garbage collection strategy in use on this platform. Valid
-// values are "none", "leaking", and "conservative".
+// values are "none", "leaking", "extalloc", and "conservative".
 func (c *Config) GC() string {
 	if c.Options.GC != "" {
 		return c.Options.GC
@@ -74,26 +104,33 @@ func (c *Config) GC() string {
 	if c.Target.GC != "" {
 		return c.Target.GC
 	}
-	return "conservative"
+	for _, tag := range c.Target.BuildTags {
+		if tag == "baremetal" || tag == "wasm" {
+			return "conservative"
+		}
+	}
+	return "extalloc"
 }

 // NeedsStackObjects returns true if the compiler should insert stack objects
 // that can be traced by the garbage collector.
 func (c *Config) NeedsStackObjects() bool {
-	if c.GC() != "conservative" {
+	switch c.GC() {
+	case "conservative", "extalloc":
+		for _, tag := range c.BuildTags() {
+			if tag == "baremetal" {
+				return false
+			}
+		}
+
+		return true
+	default:
 		return false
 	}
-	for _, tag := range c.BuildTags() {
-		if tag == "baremetal" {
-			return false
-		}
-	}
-
-	return true
 }

-// Scheduler returns the scheduler implementation. Valid values are "coroutines"
-// and "tasks".
+// Scheduler returns the scheduler implementation. Valid values are "none",
+//"coroutines" and "tasks".
 func (c *Config) Scheduler() string {
 	if c.Options.Scheduler != "" {
 		return c.Options.Scheduler
@@ -105,6 +142,21 @@ func (c *Config) Scheduler() string {
 	return "coroutines"
 }

+// FuncImplementation picks an appropriate func value implementation for the
+// target.
+func (c *Config) FuncImplementation() FuncValueImplementation {
+	// Always pick the switch implementation, as it allows the use of blocking
+	// inside a function that is used as a func value.
+	switch c.Scheduler() {
+	case "none", "coroutines":
+		return FuncValueSwitch
+	case "tasks":
+		return FuncValueDoubleword
+	default:
+		panic("unknown scheduler type")
+	}
+}
+
 // PanicStrategy returns the panic strategy selected for this target. Valid
 // values are "print" (print the panic value, then exit) or "trap" (issue a trap
 // instruction).
@@ -112,6 +164,16 @@ func (c *Config) PanicStrategy() string {
 	return c.Options.PanicStrategy
 }

+// AutomaticStackSize returns whether goroutine stack sizes should be determined
+// automatically at compile time, if possible. If it is false, no attempt is
+// made.
+func (c *Config) AutomaticStackSize() bool {
+	if c.Target.AutoStackSize != nil && c.Scheduler() == "tasks" {
+		return *c.Target.AutoStackSize
+	}
+	return false
+}
+
 // CFlags returns the flags to pass to the C compiler. This is necessary for CGo
 // preprocessing.
 func (c *Config) CFlags() []string {
@@ -119,6 +181,14 @@ func (c *Config) CFlags() []string {
 	for _, flag := range c.Target.CFlags {
 		cflags = append(cflags, strings.Replace(flag, "{root}", goenv.Get("TINYGOROOT"), -1))
 	}
+	if c.Target.Libc == "picolibc" {
+		root := goenv.Get("TINYGOROOT")
+		cflags = append(cflags, "-nostdlibinc", "-Xclang", "-internal-isystem", "-Xclang", filepath.Join(root, "lib", "picolibc", "newlib", "libc", "include"))
+		cflags = append(cflags, "-I"+filepath.Join(root, "lib/picolibc-include"))
+	}
+	if c.Debug() {
+		cflags = append(cflags, "-g")
+	}
 	return cflags
 }

@@ -169,6 +239,31 @@ func (c *Config) Debug() bool {
 	return c.Options.Debug
 }

+// BinaryFormat returns an appropriate binary format, based on the file
+// extension and the configured binary format in the target JSON file.
+func (c *Config) BinaryFormat(ext string) string {
+	switch ext {
+	case ".bin", ".gba", ".nro":
+		// The simplest format possible: dump everything in a raw binary file.
+		if c.Target.BinaryFormat != "" {
+			return c.Target.BinaryFormat
+		}
+		return "bin"
+	case ".hex":
+		// Similar to bin, but includes the start address and is thus usually a
+		// better format.
+		return "hex"
+	case ".uf2":
+		// Special purpose firmware format, mainly used on Adafruit boards.
+		// More information:
+		// https://github.com/Microsoft/uf2
+		return "uf2"
+	default:
+		// Use the ELF format for unrecognized file formats.
+		return "elf"
+	}
+}
+
 // Programmer returns the flash method and OpenOCD interface name given a
 // particular configuration. It may either be all configured in the target JSON
 // file or be modified using the -programmmer command-line option.
@@ -215,6 +310,25 @@ func (c *Config) OpenOCDConfiguration() (args []string, err error) {
 	return args, nil
 }

+// CodeModel returns the code model used on this platform.
+func (c *Config) CodeModel() string {
+	if c.Target.CodeModel != "" {
+		return c.Target.CodeModel
+	}
+
+	return "default"
+}
+
+// RelocationModel returns the relocation model in use on this platform. Valid
+// values are "static", "pic", "dynamicnopic".
+func (c *Config) RelocationModel() string {
+	if c.Target.RelocationModel != "" {
+		return c.Target.RelocationModel
+	}
+
+	return "static"
+}
+
 type TestConfig struct {
 	CompileTestBinary bool
 	// TODO: Filter the test functions to run, include verbose flag, etc
@@ -1,5 +1,17 @@
 package compileopts

+import (
+	"fmt"
+	"strings"
+)
+
+var (
+	validGCOptions            = []string{"none", "leaking", "extalloc", "conservative"}
+	validSchedulerOptions     = []string{"none", "tasks", "coroutines"}
+	validPrintSizeOptions     = []string{"none", "short", "full"}
+	validPanicStrategyOptions = []string{"print", "trap"}
+)
+
 // Options contains extra options to give to the compiler. These options are
 // usually passed from the command line.
 type Options struct {
@@ -13,6 +25,7 @@ type Options struct {
 	VerifyIR      bool
 	Debug         bool
 	PrintSizes    string
+	PrintStacks   bool
 	CFlags        []string
 	LDFlags       []string
 	Tags          string
@@ -21,3 +34,53 @@ type Options struct {
 	TestConfig    TestConfig
 	Programmer    string
 }
+
+// Verify performs a validation on the given options, raising an error if options are not valid.
+func (o *Options) Verify() error {
+	if o.GC != "" {
+		valid := isInArray(validGCOptions, o.GC)
+		if !valid {
+			return fmt.Errorf(`invalid gc option '%s': valid values are %s`,
+				o.GC,
+				strings.Join(validGCOptions, ", "))
+		}
+	}
+
+	if o.Scheduler != "" {
+		valid := isInArray(validSchedulerOptions, o.Scheduler)
+		if !valid {
+			return fmt.Errorf(`invalid scheduler option '%s': valid values are %s`,
+				o.Scheduler,
+				strings.Join(validSchedulerOptions, ", "))
+		}
+	}
+
+	if o.PrintSizes != "" {
+		valid := isInArray(validPrintSizeOptions, o.PrintSizes)
+		if !valid {
+			return fmt.Errorf(`invalid size option '%s': valid values are %s`,
+				o.PrintSizes,
+				strings.Join(validPrintSizeOptions, ", "))
+		}
+	}
+
+	if o.PanicStrategy != "" {
+		valid := isInArray(validPanicStrategyOptions, o.PanicStrategy)
+		if !valid {
+			return fmt.Errorf(`invalid panic option '%s': valid values are %s`,
+				o.PanicStrategy,
+				strings.Join(validPanicStrategyOptions, ", "))
+		}
+	}
+
+	return nil
+}
+
+func isInArray(arr []string, item string) bool {
+	for _, i := range arr {
+		if i == item {
+			return true
+		}
+	}
+	return false
+}
@@ -0,0 +1,138 @@
+package compileopts_test
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/tinygo-org/tinygo/compileopts"
+)
+
+func TestVerifyOptions(t *testing.T) {
+
+	expectedGCError := errors.New(`invalid gc option 'incorrect': valid values are none, leaking, extalloc, conservative`)
+	expectedSchedulerError := errors.New(`invalid scheduler option 'incorrect': valid values are none, tasks, coroutines`)
+	expectedPrintSizeError := errors.New(`invalid size option 'incorrect': valid values are none, short, full`)
+	expectedPanicStrategyError := errors.New(`invalid panic option 'incorrect': valid values are print, trap`)
+
+	testCases := []struct {
+		name          string
+		opts          compileopts.Options
+		expectedError error
+	}{
+		{
+			name: "OptionsEmpty",
+			opts: compileopts.Options{},
+		},
+		{
+			name: "InvalidGCOption",
+			opts: compileopts.Options{
+				GC: "incorrect",
+			},
+			expectedError: expectedGCError,
+		},
+		{
+			name: "GCOptionNone",
+			opts: compileopts.Options{
+				GC: "none",
+			},
+		},
+		{
+			name: "GCOptionLeaking",
+			opts: compileopts.Options{
+				GC: "leaking",
+			},
+		},
+		{
+			name: "GCOptionExtalloc",
+			opts: compileopts.Options{
+				GC: "extalloc",
+			},
+		},
+		{
+			name: "GCOptionConservative",
+			opts: compileopts.Options{
+				GC: "conservative",
+			},
+		},
+		{
+			name: "InvalidSchedulerOption",
+			opts: compileopts.Options{
+				Scheduler: "incorrect",
+			},
+			expectedError: expectedSchedulerError,
+		},
+		{
+			name: "SchedulerOptionNone",
+			opts: compileopts.Options{
+				Scheduler: "none",
+			},
+		},
+		{
+			name: "SchedulerOptionTasks",
+			opts: compileopts.Options{
+				Scheduler: "tasks",
+			},
+		},
+		{
+			name: "SchedulerOptionCoroutines",
+			opts: compileopts.Options{
+				Scheduler: "coroutines",
+			},
+		},
+		{
+			name: "InvalidPrintSizeOption",
+			opts: compileopts.Options{
+				PrintSizes: "incorrect",
+			},
+			expectedError: expectedPrintSizeError,
+		},
+		{
+			name: "PrintSizeOptionNone",
+			opts: compileopts.Options{
+				PrintSizes: "none",
+			},
+		},
+		{
+			name: "PrintSizeOptionShort",
+			opts: compileopts.Options{
+				PrintSizes: "short",
+			},
+		},
+		{
+			name: "PrintSizeOptionFull",
+			opts: compileopts.Options{
+				PrintSizes: "full",
+			},
+		},
+		{
+			name: "InvalidPanicOption",
+			opts: compileopts.Options{
+				PanicStrategy: "incorrect",
+			},
+			expectedError: expectedPanicStrategyError,
+		},
+		{
+			name: "PanicOptionPrint",
+			opts: compileopts.Options{
+				PanicStrategy: "print",
+			},
+		},
+		{
+			name: "PanicOptionTrap",
+			opts: compileopts.Options{
+				PanicStrategy: "trap",
+			},
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			err := tc.opts.Verify()
+			if tc.expectedError != err {
+				if tc.expectedError.Error() != err.Error() {
+					t.Errorf("expected %v, got %v", tc.expectedError, err)
+				}
+			}
+		})
+	}
+}
@@ -32,6 +32,9 @@ type TargetSpec struct {
 	Compiler         string   `json:"compiler"`
 	Linker           string   `json:"linker"`
 	RTLib            string   `json:"rtlib"` // compiler runtime library (libgcc, compiler-rt)
+	Libc             string   `json:"libc"`
+	AutoStackSize    *bool    `json:"automatic-stack-size"` // Determine stack size automatically at compile time.
+	DefaultStackSize uint64   `json:"default-stack-size"`   // Default stack size if the size couldn't be determined at compile time.
 	CFlags           []string `json:"cflags"`
 	LDFlags          []string `json:"ldflags"`
 	LinkerScript     string   `json:"linkerscript"`
@@ -43,9 +46,14 @@ type TargetSpec struct {
 	FlashMethod      string   `json:"flash-method"`
 	FlashVolume      string   `json:"msd-volume-name"`
 	FlashFilename    string   `json:"msd-firmware-name"`
+	UF2FamilyID      string   `json:"uf2-family-id"`
+	BinaryFormat     string   `json:"binary-format"`
 	OpenOCDInterface string   `json:"openocd-interface"`
 	OpenOCDTarget    string   `json:"openocd-target"`
 	OpenOCDTransport string   `json:"openocd-transport"`
+	JLinkDevice      string   `json:"jlink-device"`
+	CodeModel        string   `json:"code-model"`
+	RelocationModel  string   `json:"relocation-model"`
 }

 // copyProperties copies all properties that are set in spec2 into itself.
@@ -82,6 +90,15 @@ func (spec *TargetSpec) copyProperties(spec2 *TargetSpec) {
 	if spec2.RTLib != "" {
 		spec.RTLib = spec2.RTLib
 	}
+	if spec2.Libc != "" {
+		spec.Libc = spec2.Libc
+	}
+	if spec2.AutoStackSize != nil {
+		spec.AutoStackSize = spec2.AutoStackSize
+	}
+	if spec2.DefaultStackSize != 0 {
+		spec.DefaultStackSize = spec2.DefaultStackSize
+	}
 	spec.CFlags = append(spec.CFlags, spec2.CFlags...)
 	spec.LDFlags = append(spec.LDFlags, spec2.LDFlags...)
 	if spec2.LinkerScript != "" {
@@ -109,6 +126,12 @@ func (spec *TargetSpec) copyProperties(spec2 *TargetSpec) {
 	if spec2.FlashFilename != "" {
 		spec.FlashFilename = spec2.FlashFilename
 	}
+	if spec2.UF2FamilyID != "" {
+		spec.UF2FamilyID = spec2.UF2FamilyID
+	}
+	if spec2.BinaryFormat != "" {
+		spec.BinaryFormat = spec2.BinaryFormat
+	}
 	if spec2.OpenOCDInterface != "" {
 		spec.OpenOCDInterface = spec2.OpenOCDInterface
 	}
@@ -118,6 +141,16 @@ func (spec *TargetSpec) copyProperties(spec2 *TargetSpec) {
 	if spec2.OpenOCDTransport != "" {
 		spec.OpenOCDTransport = spec2.OpenOCDTransport
 	}
+	if spec2.JLinkDevice != "" {
+		spec.JLinkDevice = spec2.JLinkDevice
+	}
+	if spec2.CodeModel != "" {
+		spec.CodeModel = spec2.CodeModel
+	}
+
+	if spec2.RelocationModel != "" {
+		spec.RelocationModel = spec2.RelocationModel
+	}
 }

 // load reads a target specification from the JSON in the given io.Reader. It
@@ -221,6 +254,14 @@ func LoadTarget(target string) (*TargetSpec, error) {
 		if len(tripleSplit) < 3 {
 			return nil, errors.New("expected a full LLVM target or a custom target in -target flag")
 		}
+		if tripleSplit[0] == "arm" {
+			// LLVM and Clang have a different idea of what "arm" means, so
+			// upgrade to a slightly more modern ARM. In fact, when you pass
+			// --target=arm--linux-gnueabihf to Clang, it will convert that
+			// internally to armv7-unknown-linux-gnueabihf. Changing the
+			// architecture to armv7 will keep things consistent.
+			tripleSplit[0] = "armv7"
+		}
 		goos := tripleSplit[2]
 		if strings.HasPrefix(goos, "darwin") {
 			goos = "darwin"
@@ -229,11 +270,12 @@ func LoadTarget(target string) (*TargetSpec, error) {
 			"i386":    "386",
 			"x86_64":  "amd64",
 			"aarch64": "arm64",
+			"armv7":   "arm",
 		}[tripleSplit[0]]
 		if goarch == "" {
 			goarch = tripleSplit[0]
 		}
-		return defaultTarget(goos, goarch, target)
+		return defaultTarget(goos, goarch, strings.Join(tripleSplit, "-"))
 	}
 }

@@ -247,6 +289,7 @@ func defaultTarget(goos, goarch, triple string) (*TargetSpec, error) {
 		BuildTags:   []string{goos, goarch},
 		Compiler:    "clang",
 		Linker:      "cc",
+		CFlags:      []string{"--target=" + triple},
 		GDB:         "gdb",
 		PortReset:   "false",
 		FlashMethod: "native",
@@ -259,11 +302,13 @@ func defaultTarget(goos, goarch, triple string) (*TargetSpec, error) {
 	if goarch != runtime.GOARCH {
 		// Some educated guesses as to how to invoke helper programs.
 		if goarch == "arm" && goos == "linux" {
+			spec.CFlags = append(spec.CFlags, "--sysroot=/usr/arm-linux-gnueabihf")
 			spec.Linker = "arm-linux-gnueabihf-gcc"
 			spec.GDB = "arm-linux-gnueabihf-gdb"
 			spec.Emulator = []string{"qemu-arm", "-L", "/usr/arm-linux-gnueabihf"}
 		}
 		if goarch == "arm64" && goos == "linux" {
+			spec.CFlags = append(spec.CFlags, "--sysroot=/usr/aarch64-linux-gnu")
 			spec.Linker = "aarch64-linux-gnu-gcc"
 			spec.GDB = "aarch64-linux-gnu-gdb"
 			spec.Emulator = []string{"qemu-aarch64", "-L", "/usr/aarch64-linux-gnu"}
@@ -4,16 +4,19 @@ package compiler
 // required by the Go programming language.

 import (
+	"fmt"
+	"go/token"
 	"go/types"

+	"golang.org/x/tools/go/ssa"
 	"tinygo.org/x/go-llvm"
 )

-// emitLookupBoundsCheck emits a bounds check before doing a lookup into a
+// createLookupBoundsCheck emits a bounds check before doing a lookup into a
 // slice. This is required by the Go language spec: an index out of bounds must
 // cause a panic.
-func (c *Compiler) emitLookupBoundsCheck(frame *Frame, arrayLen, index llvm.Value, indexType types.Type) {
-	if frame.fn.IsNoBounds() {
+func (b *builder) createLookupBoundsCheck(arrayLen, index llvm.Value, indexType types.Type) {
+	if b.fn.IsNoBounds() {
 		// The //go:nobounds pragma was added to the function to avoid bounds
 		// checking.
 		return
@@ -23,41 +26,29 @@ func (c *Compiler) emitLookupBoundsCheck(frame *Frame, arrayLen, index llvm.Valu
 		// Sometimes, the index can be e.g. an uint8 or int8, and we have to
 		// correctly extend that type.
 		if indexType.Underlying().(*types.Basic).Info()&types.IsUnsigned == 0 {
-			index = c.builder.CreateZExt(index, arrayLen.Type(), "")
+			index = b.CreateZExt(index, arrayLen.Type(), "")
 		} else {
-			index = c.builder.CreateSExt(index, arrayLen.Type(), "")
+			index = b.CreateSExt(index, arrayLen.Type(), "")
 		}
 	} else if index.Type().IntTypeWidth() > arrayLen.Type().IntTypeWidth() {
 		// The index is bigger than the array length type, so extend it.
-		arrayLen = c.builder.CreateZExt(arrayLen, index.Type(), "")
+		arrayLen = b.CreateZExt(arrayLen, index.Type(), "")
 	}

-	faultBlock := c.ctx.AddBasicBlock(frame.fn.LLVMFn, "lookup.outofbounds")
-	nextBlock := c.ctx.AddBasicBlock(frame.fn.LLVMFn, "lookup.next")
-	frame.blockExits[frame.currentBlock] = nextBlock // adjust outgoing block for phi nodes
-
 	// Now do the bounds check: index >= arrayLen
-	outOfBounds := c.builder.CreateICmp(llvm.IntUGE, index, arrayLen, "")
-	c.builder.CreateCondBr(outOfBounds, faultBlock, nextBlock)
-
-	// Fail: this is a nil pointer, exit with a panic.
-	c.builder.SetInsertPointAtEnd(faultBlock)
-	c.createRuntimeCall("lookupPanic", nil, "")
-	c.builder.CreateUnreachable()
-
-	// Ok: this is a valid pointer.
-	c.builder.SetInsertPointAtEnd(nextBlock)
+	outOfBounds := b.CreateICmp(llvm.IntUGE, index, arrayLen, "")
+	b.createRuntimeAssert(outOfBounds, "lookup", "lookupPanic")
 }

-// emitSliceBoundsCheck emits a bounds check before a slicing operation to make
+// createSliceBoundsCheck emits a bounds check before a slicing operation to make
 // sure it is within bounds.
 //
 // This function is both used for slicing a slice (low and high have their
 // normal meaning) and for creating a new slice, where 'capacity' means the
 // biggest possible slice capacity, 'low' means len and 'high' means cap. The
 // logic is the same in both cases.
-func (c *Compiler) emitSliceBoundsCheck(frame *Frame, capacity, low, high, max llvm.Value, lowType, highType, maxType *types.Basic) {
-	if frame.fn.IsNoBounds() {
+func (b *builder) createSliceBoundsCheck(capacity, low, high, max llvm.Value, lowType, highType, maxType *types.Basic) {
+	if b.fn.IsNoBounds() {
 		// The //go:nobounds pragma was added to the function to avoid bounds
 		// checking.
 		return
@@ -75,92 +66,164 @@ func (c *Compiler) emitSliceBoundsCheck(frame *Frame, capacity, low, high, max l
 		capacityType = max.Type()
 	}
 	if capacityType != capacity.Type() {
-		capacity = c.builder.CreateZExt(capacity, capacityType, "")
+		capacity = b.CreateZExt(capacity, capacityType, "")
 	}

 	// Extend low and high to be the same size as capacity.
 	if low.Type().IntTypeWidth() < capacityType.IntTypeWidth() {
 		if lowType.Info()&types.IsUnsigned != 0 {
-			low = c.builder.CreateZExt(low, capacityType, "")
+			low = b.CreateZExt(low, capacityType, "")
 		} else {
-			low = c.builder.CreateSExt(low, capacityType, "")
+			low = b.CreateSExt(low, capacityType, "")
 		}
 	}
 	if high.Type().IntTypeWidth() < capacityType.IntTypeWidth() {
 		if highType.Info()&types.IsUnsigned != 0 {
-			high = c.builder.CreateZExt(high, capacityType, "")
+			high = b.CreateZExt(high, capacityType, "")
 		} else {
-			high = c.builder.CreateSExt(high, capacityType, "")
+			high = b.CreateSExt(high, capacityType, "")
 		}
 	}
 	if max.Type().IntTypeWidth() < capacityType.IntTypeWidth() {
 		if maxType.Info()&types.IsUnsigned != 0 {
-			max = c.builder.CreateZExt(max, capacityType, "")
+			max = b.CreateZExt(max, capacityType, "")
 		} else {
-			max = c.builder.CreateSExt(max, capacityType, "")
+			max = b.CreateSExt(max, capacityType, "")
 		}
 	}

-	faultBlock := c.ctx.AddBasicBlock(frame.fn.LLVMFn, "slice.outofbounds")
-	nextBlock := c.ctx.AddBasicBlock(frame.fn.LLVMFn, "slice.next")
-	frame.blockExits[frame.currentBlock] = nextBlock // adjust outgoing block for phi nodes
-
 	// Now do the bounds check: low > high || high > capacity
-	outOfBounds1 := c.builder.CreateICmp(llvm.IntUGT, low, high, "slice.lowhigh")
-	outOfBounds2 := c.builder.CreateICmp(llvm.IntUGT, high, max, "slice.highmax")
-	outOfBounds3 := c.builder.CreateICmp(llvm.IntUGT, max, capacity, "slice.maxcap")
-	outOfBounds := c.builder.CreateOr(outOfBounds1, outOfBounds2, "slice.lowmax")
-	outOfBounds = c.builder.CreateOr(outOfBounds, outOfBounds3, "slice.lowcap")
-	c.builder.CreateCondBr(outOfBounds, faultBlock, nextBlock)
-
-	// Fail: this is a nil pointer, exit with a panic.
-	c.builder.SetInsertPointAtEnd(faultBlock)
-	c.createRuntimeCall("slicePanic", nil, "")
-	c.builder.CreateUnreachable()
-
-	// Ok: this is a valid pointer.
-	c.builder.SetInsertPointAtEnd(nextBlock)
+	outOfBounds1 := b.CreateICmp(llvm.IntUGT, low, high, "slice.lowhigh")
+	outOfBounds2 := b.CreateICmp(llvm.IntUGT, high, max, "slice.highmax")
+	outOfBounds3 := b.CreateICmp(llvm.IntUGT, max, capacity, "slice.maxcap")
+	outOfBounds := b.CreateOr(outOfBounds1, outOfBounds2, "slice.lowmax")
+	outOfBounds = b.CreateOr(outOfBounds, outOfBounds3, "slice.lowcap")
+	b.createRuntimeAssert(outOfBounds, "slice", "slicePanic")
 }

-// emitNilCheck checks whether the given pointer is nil, and panics if it is. It
-// has no effect in well-behaved programs, but makes sure no uncaught nil
+// createChanBoundsCheck creates a bounds check before creating a new channel to
+// check that the value is not too big for runtime.chanMake.
+func (b *builder) createChanBoundsCheck(elementSize uint64, bufSize llvm.Value, bufSizeType *types.Basic, pos token.Pos) {
+	if b.fn.IsNoBounds() {
+		// The //go:nobounds pragma was added to the function to avoid bounds
+		// checking.
+		return
+	}
+
+	// Check whether the bufSize parameter must be cast to a wider integer for
+	// comparison.
+	if bufSize.Type().IntTypeWidth() < b.uintptrType.IntTypeWidth() {
+		if bufSizeType.Info()&types.IsUnsigned != 0 {
+			// Unsigned, so zero-extend to uint type.
+			bufSizeType = types.Typ[types.Uint]
+			bufSize = b.CreateZExt(bufSize, b.intType, "")
+		} else {
+			// Signed, so sign-extend to int type.
+			bufSizeType = types.Typ[types.Int]
+			bufSize = b.CreateSExt(bufSize, b.intType, "")
+		}
+	}
+
+	// Calculate (^uintptr(0)) >> 1, which is the max value that fits in an
+	// uintptr if uintptrs were signed.
+	maxBufSize := llvm.ConstLShr(llvm.ConstNot(llvm.ConstInt(b.uintptrType, 0, false)), llvm.ConstInt(b.uintptrType, 1, false))
+	if elementSize > maxBufSize.ZExtValue() {
+		b.addError(pos, fmt.Sprintf("channel element type is too big (%v bytes)", elementSize))
+		return
+	}
+	// Avoid divide-by-zero.
+	if elementSize == 0 {
+		elementSize = 1
+	}
+	// Make the maxBufSize actually the maximum allowed value (in number of
+	// elements in the channel buffer).
+	maxBufSize = llvm.ConstUDiv(maxBufSize, llvm.ConstInt(b.uintptrType, elementSize, false))
+
+	// Make sure maxBufSize has the same type as bufSize.
+	if maxBufSize.Type() != bufSize.Type() {
+		maxBufSize = llvm.ConstZExt(maxBufSize, bufSize.Type())
+	}
+
+	// Do the check for a too large (or negative) buffer size.
+	bufSizeTooBig := b.CreateICmp(llvm.IntUGE, bufSize, maxBufSize, "")
+	b.createRuntimeAssert(bufSizeTooBig, "chan", "chanMakePanic")
+}
+
+// createNilCheck checks whether the given pointer is nil, and panics if it is.
+// It has no effect in well-behaved programs, but makes sure no uncaught nil
 // pointer dereferences exist in valid Go code.
-func (c *Compiler) emitNilCheck(frame *Frame, ptr llvm.Value, blockPrefix string) {
+func (b *builder) createNilCheck(inst ssa.Value, ptr llvm.Value, blockPrefix string) {
 	// Check whether we need to emit this check at all.
 	if !ptr.IsAGlobalValue().IsNil() {
 		return
 	}

-	// Check whether this is a nil pointer.
-	faultBlock := c.ctx.AddBasicBlock(frame.fn.LLVMFn, blockPrefix+".nil")
-	nextBlock := c.ctx.AddBasicBlock(frame.fn.LLVMFn, blockPrefix+".next")
-	frame.blockExits[frame.currentBlock] = nextBlock // adjust outgoing block for phi nodes
+	switch inst := inst.(type) {
+	case *ssa.IndexAddr:
+		// This pointer is the result of an index operation into a slice or
+		// array. Such slices/arrays are already bounds checked so the pointer
+		// must be a valid (non-nil) pointer. No nil checking is necessary.
+		return
+	case *ssa.Convert:
+		// This is a pointer that comes from a conversion from unsafe.Pointer.
+		// Don't do nil checking because this is unsafe code and the code should
+		// know what it is doing.
+		// Note: all *ssa.Convert instructions that result in a pointer must
+		// come from unsafe.Pointer. Testing here for unsafe.Pointer to be sure.
+		if inst.X.Type() == types.Typ[types.UnsafePointer] {
+			return
+		}
+	}

 	// Compare against nil.
-	var isnil llvm.Value
-	if ptr.Type().PointerAddressSpace() == 0 {
-		// Do the nil check using the isnil builtin, which marks the parameter
-		// as nocapture.
-		// The reason it has to go through a builtin, is that a regular icmp
-		// instruction may capture the pointer in LLVM semantics, see
-		// https://reviews.llvm.org/D60047 for details. Pointer capturing
-		// unfortunately breaks escape analysis, so we use this trick to let the
-		// functionattr pass know that this pointer doesn't really escape.
-		ptr = c.builder.CreateBitCast(ptr, c.i8ptrType, "")
-		isnil = c.createRuntimeCall("isnil", []llvm.Value{ptr}, "")
-	} else {
-		// Do the nil check using a regular icmp. This can happen with function
-		// pointers on AVR, which don't benefit from escape analysis anyway.
-		nilptr := llvm.ConstPointerNull(ptr.Type())
-		isnil = c.builder.CreateICmp(llvm.IntEQ, ptr, nilptr, "")
-	}
-	c.builder.CreateCondBr(isnil, faultBlock, nextBlock)
+	// We previously used a hack to make sure this wouldn't break escape
+	// analysis, but this is not necessary anymore since
+	// https://reviews.llvm.org/D60047 has been merged.
+	nilptr := llvm.ConstPointerNull(ptr.Type())
+	isnil := b.CreateICmp(llvm.IntEQ, ptr, nilptr, "")

-	// Fail: this is a nil pointer, exit with a panic.
-	c.builder.SetInsertPointAtEnd(faultBlock)
-	c.createRuntimeCall("nilPanic", nil, "")
-	c.builder.CreateUnreachable()
-
-	// Ok: this is a valid pointer.
-	c.builder.SetInsertPointAtEnd(nextBlock)
+	// Emit the nil check in IR.
+	b.createRuntimeAssert(isnil, blockPrefix, "nilPanic")
+}
+
+// createNegativeShiftCheck creates an assertion that panics if the given shift value is negative.
+// This function assumes that the shift value is signed.
+func (b *builder) createNegativeShiftCheck(shift llvm.Value) {
+	if b.fn.IsNoBounds() {
+		// Function disabled bounds checking - skip shift check.
+		return
+	}
+
+	// isNegative = shift < 0
+	isNegative := b.CreateICmp(llvm.IntSLT, shift, llvm.ConstInt(shift.Type(), 0, false), "")
+	b.createRuntimeAssert(isNegative, "shift", "negativeShiftPanic")
+}
+
+// createRuntimeAssert is a common function to create a new branch on an assert
+// bool, calling an assert func if the assert value is true (1).
+func (b *builder) createRuntimeAssert(assert llvm.Value, blockPrefix, assertFunc string) {
+	// Check whether we can resolve this check at compile time.
+	if !assert.IsAConstantInt().IsNil() {
+		val := assert.ZExtValue()
+		if val == 0 {
+			// Everything is constant so the check does not have to be emitted
+			// in IR. This avoids emitting some redundant IR.
+			return
+		}
+	}
+
+	faultBlock := b.ctx.AddBasicBlock(b.fn.LLVMFn, blockPrefix+".throw")
+	nextBlock := b.ctx.AddBasicBlock(b.fn.LLVMFn, blockPrefix+".next")
+	b.blockExits[b.currentBlock] = nextBlock // adjust outgoing block for phi nodes
+
+	// Now branch to the out-of-bounds or the regular block.
+	b.CreateCondBr(assert, faultBlock, nextBlock)
+
+	// Fail: the assert triggered so panic.
+	b.SetInsertPointAtEnd(faultBlock)
+	b.createRuntimeCall(assertFunc, nil, "")
+	b.CreateUnreachable()
+
+	// Ok: assert didn't trigger so continue normally.
+	b.SetInsertPointAtEnd(nextBlock)
 }
@@ -0,0 +1,57 @@
+package compiler
+
+import (
+	"golang.org/x/tools/go/ssa"
+	"tinygo.org/x/go-llvm"
+)
+
+// createAtomicOp lowers an atomic library call by lowering it as an LLVM atomic
+// operation. It returns the result of the operation and true if the call could
+// be lowered inline, and false otherwise.
+func (b *builder) createAtomicOp(call *ssa.CallCommon) (llvm.Value, bool) {
+	name := call.Value.(*ssa.Function).Name()
+	switch name {
+	case "AddInt32", "AddInt64", "AddUint32", "AddUint64", "AddUintptr":
+		ptr := b.getValue(call.Args[0])
+		val := b.getValue(call.Args[1])
+		oldVal := b.CreateAtomicRMW(llvm.AtomicRMWBinOpAdd, ptr, val, llvm.AtomicOrderingSequentiallyConsistent, true)
+		// Return the new value, not the original value returned by atomicrmw.
+		return b.CreateAdd(oldVal, val, ""), true
+	case "SwapInt32", "SwapInt64", "SwapUint32", "SwapUint64", "SwapUintptr", "SwapPointer":
+		ptr := b.getValue(call.Args[0])
+		val := b.getValue(call.Args[1])
+		isPointer := val.Type().TypeKind() == llvm.PointerTypeKind
+		if isPointer {
+			// atomicrmw only supports integers, so cast to an integer.
+			val = b.CreatePtrToInt(val, b.uintptrType, "")
+			ptr = b.CreateBitCast(ptr, llvm.PointerType(val.Type(), 0), "")
+		}
+		oldVal := b.CreateAtomicRMW(llvm.AtomicRMWBinOpXchg, ptr, val, llvm.AtomicOrderingSequentiallyConsistent, true)
+		if isPointer {
+			oldVal = b.CreateIntToPtr(oldVal, b.i8ptrType, "")
+		}
+		return oldVal, true
+	case "CompareAndSwapInt32", "CompareAndSwapInt64", "CompareAndSwapUint32", "CompareAndSwapUint64", "CompareAndSwapUintptr", "CompareAndSwapPointer":
+		ptr := b.getValue(call.Args[0])
+		old := b.getValue(call.Args[1])
+		newVal := b.getValue(call.Args[2])
+		tuple := b.CreateAtomicCmpXchg(ptr, old, newVal, llvm.AtomicOrderingSequentiallyConsistent, llvm.AtomicOrderingSequentiallyConsistent, true)
+		swapped := b.CreateExtractValue(tuple, 1, "")
+		return swapped, true
+	case "LoadInt32", "LoadInt64", "LoadUint32", "LoadUint64", "LoadUintptr", "LoadPointer":
+		ptr := b.getValue(call.Args[0])
+		val := b.CreateLoad(ptr, "")
+		val.SetOrdering(llvm.AtomicOrderingSequentiallyConsistent)
+		val.SetAlignment(b.targetData.PrefTypeAlignment(val.Type())) // required
+		return val, true
+	case "StoreInt32", "StoreInt64", "StoreUint32", "StoreUint64", "StoreUintptr", "StorePointer":
+		ptr := b.getValue(call.Args[0])
+		val := b.getValue(call.Args[1])
+		store := b.CreateStore(val, ptr)
+		store.SetOrdering(llvm.AtomicOrderingSequentiallyConsistent)
+		store.SetAlignment(b.targetData.PrefTypeAlignment(val.Type())) // required
+		return store, true
+	default:
+		return llvm.Value{}, false
+	}
+}
@@ -1,8 +1,9 @@
 package compiler

 import (
-	"fmt"
-	"golang.org/x/tools/go/ssa"
+	"go/types"
+	"strconv"
+
 	"tinygo.org/x/go-llvm"
 )

@@ -11,62 +12,80 @@ import (

 // The maximum number of arguments that can be expanded from a single struct. If
 // a struct contains more fields, it is passed as a struct without expanding.
-const MaxFieldsPerParam = 3
+const maxFieldsPerParam = 3

-// Shortcut: create a call to runtime.<fnName> with the given arguments.
-func (c *Compiler) createRuntimeCall(fnName string, args []llvm.Value, name string) llvm.Value {
-	runtimePkg := c.ir.Program.ImportedPackage("runtime")
-	member := runtimePkg.Members[fnName]
-	if member == nil {
-		panic("trying to call runtime." + fnName)
-	}
-	fn := c.ir.GetFunction(member.(*ssa.Function))
-	if fn.LLVMFn.IsNil() {
-		panic(fmt.Errorf("function %s does not appear in LLVM IR", fnName))
-	}
-	if !fn.IsExported() {
-		args = append(args, llvm.Undef(c.i8ptrType))            // unused context parameter
-		args = append(args, llvm.ConstPointerNull(c.i8ptrType)) // coroutine handle
-	}
-	return c.createCall(fn.LLVMFn, args, name)
+// paramInfo contains some information collected about a function parameter,
+// useful while declaring or defining a function.
+type paramInfo struct {
+	llvmType llvm.Type
+	name     string // name, possibly with suffixes for e.g. struct fields
+	flags    paramFlags
 }

-// Create a call to the given function with the arguments possibly expanded.
-func (c *Compiler) createCall(fn llvm.Value, args []llvm.Value, name string) llvm.Value {
+// paramFlags identifies parameter attributes for flags. Most importantly, it
+// determines which parameters are dereferenceable_or_null and which aren't.
+type paramFlags uint8
+
+const (
+	// Parameter may have the deferenceable_or_null attribute. This attribute
+	// cannot be applied to unsafe.Pointer and to the data pointer of slices.
+	paramIsDeferenceableOrNull = 1 << iota
+)
+
+// createCall creates a new call to runtime.<fnName> with the given arguments.
+func (b *builder) createRuntimeCall(fnName string, args []llvm.Value, name string) llvm.Value {
+	fullName := "runtime." + fnName
+	fn := b.mod.NamedFunction(fullName)
+	if fn.IsNil() {
+		panic("trying to call non-existent function: " + fullName)
+	}
+	args = append(args, llvm.Undef(b.i8ptrType))            // unused context parameter
+	args = append(args, llvm.ConstPointerNull(b.i8ptrType)) // coroutine handle
+	return b.createCall(fn, args, name)
+}
+
+// createCall creates a call to the given function with the arguments possibly
+// expanded.
+func (b *builder) createCall(fn llvm.Value, args []llvm.Value, name string) llvm.Value {
 	expanded := make([]llvm.Value, 0, len(args))
 	for _, arg := range args {
-		fragments := c.expandFormalParam(arg)
+		fragments := b.expandFormalParam(arg)
 		expanded = append(expanded, fragments...)
 	}
-	return c.builder.CreateCall(fn, expanded, name)
+	return b.CreateCall(fn, expanded, name)
 }

 // Expand an argument type to a list that can be used in a function call
 // parameter list.
-func (c *Compiler) expandFormalParamType(t llvm.Type) []llvm.Type {
+func expandFormalParamType(t llvm.Type, name string, goType types.Type) []paramInfo {
 	switch t.TypeKind() {
 	case llvm.StructTypeKind:
-		fields := c.flattenAggregateType(t)
-		if len(fields) <= MaxFieldsPerParam {
-			return fields
+		fieldInfos := flattenAggregateType(t, name, goType)
+		if len(fieldInfos) <= maxFieldsPerParam {
+			return fieldInfos
 		} else {
 			// failed to lower
-			return []llvm.Type{t}
 		}
-	default:
-		// TODO: split small arrays
-		return []llvm.Type{t}
+	}
+	// TODO: split small arrays
+	return []paramInfo{
+		{
+			llvmType: t,
+			name:     name,
+			flags:    getTypeFlags(goType),
+		},
 	}
 }

-// Expand an argument type to a list of offsets from the start of the object.
-// Used together with expandFormalParam to get the offset of each value from the
-// start of the non-expanded value.
-func (c *Compiler) expandFormalParamOffsets(t llvm.Type) []uint64 {
+// expandFormalParamOffsets returns a list of offsets from the start of an
+// object of type t after it would have been split up by expandFormalParam. This
+// is useful for debug information, where it is necessary to know the offset
+// from the start of the combined object.
+func (b *builder) expandFormalParamOffsets(t llvm.Type) []uint64 {
 	switch t.TypeKind() {
 	case llvm.StructTypeKind:
-		fields := c.flattenAggregateTypeOffsets(t)
-		if len(fields) <= MaxFieldsPerParam {
+		fields := b.flattenAggregateTypeOffsets(t)
+		if len(fields) <= maxFieldsPerParam {
 			return fields
 		} else {
 			// failed to lower
@@ -78,14 +97,17 @@ func (c *Compiler) expandFormalParamOffsets(t llvm.Type) []uint64 {
 	}
 }

-// Equivalent of expandFormalParamType for parameter values.
-func (c *Compiler) expandFormalParam(v llvm.Value) []llvm.Value {
+// expandFormalParam splits a formal param value into pieces, so it can be
+// passed directly as part of a function call. For example, it splits up small
+// structs into individual fields. It is the equivalent of expandFormalParamType
+// for parameter values.
+func (b *builder) expandFormalParam(v llvm.Value) []llvm.Value {
 	switch v.Type().TypeKind() {
 	case llvm.StructTypeKind:
-		fieldTypes := c.flattenAggregateType(v.Type())
-		if len(fieldTypes) <= MaxFieldsPerParam {
-			fields := c.flattenAggregate(v)
-			if len(fields) != len(fieldTypes) {
+		fieldInfos := flattenAggregateType(v.Type(), "", nil)
+		if len(fieldInfos) <= maxFieldsPerParam {
+			fields := b.flattenAggregate(v)
+			if len(fields) != len(fieldInfos) {
 				panic("type and value param lowering don't match")
 			}
 			return fields
@@ -101,24 +123,98 @@ func (c *Compiler) expandFormalParam(v llvm.Value) []llvm.Value {

 // Try to flatten a struct type to a list of types. Returns a 1-element slice
 // with the passed in type if this is not possible.
-func (c *Compiler) flattenAggregateType(t llvm.Type) []llvm.Type {
+func flattenAggregateType(t llvm.Type, name string, goType types.Type) []paramInfo {
+	typeFlags := getTypeFlags(goType)
 	switch t.TypeKind() {
 	case llvm.StructTypeKind:
-		fields := make([]llvm.Type, 0, t.StructElementTypesCount())
-		for _, subfield := range t.StructElementTypes() {
-			subfields := c.flattenAggregateType(subfield)
-			fields = append(fields, subfields...)
+		paramInfos := make([]paramInfo, 0, t.StructElementTypesCount())
+		for i, subfield := range t.StructElementTypes() {
+			suffix := strconv.Itoa(i)
+			if goType != nil {
+				// Try to come up with a good suffix for this struct field,
+				// depending on which Go type it's based on.
+				switch goType := goType.Underlying().(type) {
+				case *types.Interface:
+					suffix = []string{"typecode", "value"}[i]
+				case *types.Slice:
+					suffix = []string{"data", "len", "cap"}[i]
+				case *types.Struct:
+					suffix = goType.Field(i).Name()
+				case *types.Basic:
+					switch goType.Kind() {
+					case types.Complex64, types.Complex128:
+						suffix = []string{"r", "i"}[i]
+					case types.String:
+						suffix = []string{"data", "len"}[i]
+					}
+				case *types.Signature:
+					suffix = []string{"context", "funcptr"}[i]
+				}
+			}
+			subInfos := flattenAggregateType(subfield, name+"."+suffix, extractSubfield(goType, i))
+			for i := range subInfos {
+				subInfos[i].flags |= typeFlags
+			}
+			paramInfos = append(paramInfos, subInfos...)
 		}
-		return fields
+		return paramInfos
 	default:
-		return []llvm.Type{t}
+		return []paramInfo{
+			{
+				llvmType: t,
+				name:     name,
+				flags:    typeFlags,
+			},
+		}
 	}
 }

-// Return the offsets from the start of the object if this object type were
-// flattened like in flattenAggregate. Used together with flattenAggregate to
-// know the start indices of each value in the non-flattened object.
-func (c *Compiler) flattenAggregateTypeOffsets(t llvm.Type) []uint64 {
+// getTypeFlags returns the type flags for a given type. It will not recurse
+// into sub-types (such as in structs).
+func getTypeFlags(t types.Type) paramFlags {
+	if t == nil {
+		return 0
+	}
+	switch t.Underlying().(type) {
+	case *types.Pointer:
+		// Pointers in Go must either point to an object or be nil.
+		return paramIsDeferenceableOrNull
+	case *types.Chan, *types.Map:
+		// Channels and maps are implemented as pointers pointing to some
+		// object, and follow the same rules as *types.Pointer.
+		return paramIsDeferenceableOrNull
+	default:
+		return 0
+	}
+}
+
+// extractSubfield extracts a field from a struct, or returns null if this is
+// not a struct and thus no subfield can be obtained.
+func extractSubfield(t types.Type, field int) types.Type {
+	if t == nil {
+		return nil
+	}
+	switch t := t.Underlying().(type) {
+	case *types.Struct:
+		return t.Field(field).Type()
+	case *types.Interface, *types.Slice, *types.Basic, *types.Signature:
+		// These Go types are (sometimes) implemented as LLVM structs but can't
+		// really be split further up in Go (with the possible exception of
+		// complex numbers).
+		return nil
+	default:
+		// This should be unreachable.
+		panic("cannot split subfield: " + t.String())
+	}
+}
+
+// flattenAggregateTypeOffset returns the offsets from the start of an object of
+// type t if this object were flattened like in flattenAggregate. Used together
+// with flattenAggregate to know the start indices of each value in the
+// non-flattened object.
+//
+// Note: this is an implementation detail, use expandFormalParamOffsets instead.
+func (c *compilerContext) flattenAggregateTypeOffsets(t llvm.Type) []uint64 {
 	switch t.TypeKind() {
 	case llvm.StructTypeKind:
 		fields := make([]uint64, 0, t.StructElementTypesCount())
@@ -136,15 +232,15 @@ func (c *Compiler) flattenAggregateTypeOffsets(t llvm.Type) []uint64 {
 	}
 }

-// Break down a struct into its elementary types for argument passing. The value
-// equivalent of flattenAggregateType
-func (c *Compiler) flattenAggregate(v llvm.Value) []llvm.Value {
+// flattenAggregate breaks down a struct into its elementary values for argument
+// passing. It is the value equivalent of flattenAggregateType
+func (b *builder) flattenAggregate(v llvm.Value) []llvm.Value {
 	switch v.Type().TypeKind() {
 	case llvm.StructTypeKind:
 		fields := make([]llvm.Value, 0, v.Type().StructElementTypesCount())
 		for i := range v.Type().StructElementTypes() {
-			subfield := c.builder.CreateExtractValue(v, i, "")
-			subfields := c.flattenAggregate(subfield)
+			subfield := b.CreateExtractValue(v, i, "")
+			subfields := b.flattenAggregate(subfield)
 			fields = append(fields, subfields...)
 		}
 		return fields
@@ -153,25 +249,29 @@ func (c *Compiler) flattenAggregate(v llvm.Value) []llvm.Value {
 	}
 }

-// Collapse a list of fields into its original value.
-func (c *Compiler) collapseFormalParam(t llvm.Type, fields []llvm.Value) llvm.Value {
-	param, remaining := c.collapseFormalParamInternal(t, fields)
+// collapseFormalParam combines an aggregate object back into the original
+// value. This is used to join multiple LLVM parameters into a single Go value
+// in the function entry block.
+func (b *builder) collapseFormalParam(t llvm.Type, fields []llvm.Value) llvm.Value {
+	param, remaining := b.collapseFormalParamInternal(t, fields)
 	if len(remaining) != 0 {
 		panic("failed to expand back all fields")
 	}
 	return param
 }

-// Returns (value, remainingFields). Used by collapseFormalParam.
-func (c *Compiler) collapseFormalParamInternal(t llvm.Type, fields []llvm.Value) (llvm.Value, []llvm.Value) {
+// collapseFormalParamInternal is an implementation detail of
+// collapseFormalParam: it works by recursing until there are no fields left.
+func (b *builder) collapseFormalParamInternal(t llvm.Type, fields []llvm.Value) (llvm.Value, []llvm.Value) {
 	switch t.TypeKind() {
 	case llvm.StructTypeKind:
-		if len(c.flattenAggregateType(t)) <= MaxFieldsPerParam {
+		flattened := flattenAggregateType(t, "", nil)
+		if len(flattened) <= maxFieldsPerParam {
 			value := llvm.ConstNull(t)
 			for i, subtyp := range t.StructElementTypes() {
-				structField, remaining := c.collapseFormalParamInternal(subtyp, fields)
+				structField, remaining := b.collapseFormalParamInternal(subtyp, fields)
 				fields = remaining
-				value = c.builder.CreateInsertValue(value, structField, i, "")
+				value = b.CreateInsertValue(value, structField, i, "")
 			}
 			return value, fields
 		} else {
@@ -11,73 +11,89 @@ import (
 	"tinygo.org/x/go-llvm"
 )

-func (c *Compiler) emitMakeChan(frame *Frame, expr *ssa.MakeChan) llvm.Value {
-	elementSize := c.targetData.TypeAllocSize(c.getLLVMType(expr.Type().(*types.Chan).Elem()))
-	elementSizeValue := llvm.ConstInt(c.uintptrType, elementSize, false)
-	bufSize := c.getValue(frame, expr.Size)
-	return c.createRuntimeCall("chanMake", []llvm.Value{elementSizeValue, bufSize}, "")
+func (b *builder) createMakeChan(expr *ssa.MakeChan) llvm.Value {
+	elementSize := b.targetData.TypeAllocSize(b.getLLVMType(expr.Type().Underlying().(*types.Chan).Elem()))
+	elementSizeValue := llvm.ConstInt(b.uintptrType, elementSize, false)
+	bufSize := b.getValue(expr.Size)
+	b.createChanBoundsCheck(elementSize, bufSize, expr.Size.Type().Underlying().(*types.Basic), expr.Pos())
+	if bufSize.Type().IntTypeWidth() < b.uintptrType.IntTypeWidth() {
+		bufSize = b.CreateZExt(bufSize, b.uintptrType, "")
+	} else if bufSize.Type().IntTypeWidth() > b.uintptrType.IntTypeWidth() {
+		bufSize = b.CreateTrunc(bufSize, b.uintptrType, "")
+	}
+	return b.createRuntimeCall("chanMake", []llvm.Value{elementSizeValue, bufSize}, "")
 }

-// emitChanSend emits a pseudo chan send operation. It is lowered to the actual
-// channel send operation during goroutine lowering.
-func (c *Compiler) emitChanSend(frame *Frame, instr *ssa.Send) {
-	ch := c.getValue(frame, instr.Chan)
-	chanValue := c.getValue(frame, instr.X)
+// createChanSend emits a pseudo chan send operation. It is lowered to the
+// actual channel send operation during goroutine lowering.
+func (b *builder) createChanSend(instr *ssa.Send) {
+	ch := b.getValue(instr.Chan)
+	chanValue := b.getValue(instr.X)

 	// store value-to-send
-	valueType := c.getLLVMType(instr.X.Type())
-	valueAlloca, valueAllocaCast, valueAllocaSize := c.createTemporaryAlloca(valueType, "chan.value")
-	c.builder.CreateStore(chanValue, valueAlloca)
+	valueType := b.getLLVMType(instr.X.Type())
+	valueAlloca, valueAllocaCast, valueAllocaSize := b.createTemporaryAlloca(valueType, "chan.value")
+	b.CreateStore(chanValue, valueAlloca)
+
+	// Allocate blockedlist buffer.
+	channelBlockedList := b.mod.GetTypeByName("runtime.channelBlockedList")
+	channelBlockedListAlloca, channelBlockedListAllocaCast, channelBlockedListAllocaSize := b.createTemporaryAlloca(channelBlockedList, "chan.blockedList")

 	// Do the send.
-	c.createRuntimeCall("chanSend", []llvm.Value{ch, valueAllocaCast}, "")
+	b.createRuntimeCall("chanSend", []llvm.Value{ch, valueAllocaCast, channelBlockedListAlloca}, "")

-	// End the lifetime of the alloca.
+	// End the lifetime of the allocas.
 	// This also works around a bug in CoroSplit, at least in LLVM 8:
 	// https://bugs.llvm.org/show_bug.cgi?id=41742
-	c.emitLifetimeEnd(valueAllocaCast, valueAllocaSize)
+	b.emitLifetimeEnd(channelBlockedListAllocaCast, channelBlockedListAllocaSize)
+	b.emitLifetimeEnd(valueAllocaCast, valueAllocaSize)
 }

-// emitChanRecv emits a pseudo chan receive operation. It is lowered to the
+// createChanRecv emits a pseudo chan receive operation. It is lowered to the
 // actual channel receive operation during goroutine lowering.
-func (c *Compiler) emitChanRecv(frame *Frame, unop *ssa.UnOp) llvm.Value {
-	valueType := c.getLLVMType(unop.X.Type().(*types.Chan).Elem())
-	ch := c.getValue(frame, unop.X)
+func (b *builder) createChanRecv(unop *ssa.UnOp) llvm.Value {
+	valueType := b.getLLVMType(unop.X.Type().Underlying().(*types.Chan).Elem())
+	ch := b.getValue(unop.X)

 	// Allocate memory to receive into.
-	valueAlloca, valueAllocaCast, valueAllocaSize := c.createTemporaryAlloca(valueType, "chan.value")
+	valueAlloca, valueAllocaCast, valueAllocaSize := b.createTemporaryAlloca(valueType, "chan.value")
+
+	// Allocate blockedlist buffer.
+	channelBlockedList := b.mod.GetTypeByName("runtime.channelBlockedList")
+	channelBlockedListAlloca, channelBlockedListAllocaCast, channelBlockedListAllocaSize := b.createTemporaryAlloca(channelBlockedList, "chan.blockedList")

 	// Do the receive.
-	commaOk := c.createRuntimeCall("chanRecv", []llvm.Value{ch, valueAllocaCast}, "")
-	received := c.builder.CreateLoad(valueAlloca, "chan.received")
-	c.emitLifetimeEnd(valueAllocaCast, valueAllocaSize)
+	commaOk := b.createRuntimeCall("chanRecv", []llvm.Value{ch, valueAllocaCast, channelBlockedListAlloca}, "")
+	received := b.CreateLoad(valueAlloca, "chan.received")
+	b.emitLifetimeEnd(channelBlockedListAllocaCast, channelBlockedListAllocaSize)
+	b.emitLifetimeEnd(valueAllocaCast, valueAllocaSize)

 	if unop.CommaOk {
-		tuple := llvm.Undef(c.ctx.StructType([]llvm.Type{valueType, c.ctx.Int1Type()}, false))
-		tuple = c.builder.CreateInsertValue(tuple, received, 0, "")
-		tuple = c.builder.CreateInsertValue(tuple, commaOk, 1, "")
+		tuple := llvm.Undef(b.ctx.StructType([]llvm.Type{valueType, b.ctx.Int1Type()}, false))
+		tuple = b.CreateInsertValue(tuple, received, 0, "")
+		tuple = b.CreateInsertValue(tuple, commaOk, 1, "")
 		return tuple
 	} else {
 		return received
 	}
 }

-// emitChanClose closes the given channel.
-func (c *Compiler) emitChanClose(frame *Frame, param ssa.Value) {
-	ch := c.getValue(frame, param)
-	c.createRuntimeCall("chanClose", []llvm.Value{ch}, "")
+// createChanClose closes the given channel.
+func (b *builder) createChanClose(param ssa.Value) {
+	ch := b.getValue(param)
+	b.createRuntimeCall("chanClose", []llvm.Value{ch}, "")
 }

-// emitSelect emits all IR necessary for a select statements. That's a
+// createSelect emits all IR necessary for a select statements. That's a
 // non-trivial amount of code because select is very complex to implement.
-func (c *Compiler) emitSelect(frame *Frame, expr *ssa.Select) llvm.Value {
+func (b *builder) createSelect(expr *ssa.Select) llvm.Value {
 	if len(expr.States) == 0 {
 		// Shortcuts for some simple selects.
-		llvmType := c.getLLVMType(expr.Type())
+		llvmType := b.getLLVMType(expr.Type())
 		if expr.Blocking {
 			// Blocks forever:
 			//     select {}
-			c.createRuntimeCall("deadlock", nil, "")
+			b.createRuntimeCall("deadlock", nil, "")
 			return llvm.Undef(llvmType)
 		} else {
 			// No-op:
@@ -85,7 +101,7 @@ func (c *Compiler) emitSelect(frame *Frame, expr *ssa.Select) llvm.Value {
 			//     default:
 			//     }
 			retval := llvm.Undef(llvmType)
-			retval = c.builder.CreateInsertValue(retval, llvm.ConstInt(c.intType, 0xffffffffffffffff, true), 0, "")
+			retval = b.CreateInsertValue(retval, llvm.ConstInt(b.intType, 0xffffffffffffffff, true), 0, "")
 			return retval // {-1, false}
 		}
 	}
@@ -103,30 +119,30 @@ func (c *Compiler) emitSelect(frame *Frame, expr *ssa.Select) llvm.Value {
 	recvbufAlign := 0
 	hasReceives := false
 	var selectStates []llvm.Value
-	chanSelectStateType := c.getLLVMRuntimeType("chanSelectState")
+	chanSelectStateType := b.getLLVMRuntimeType("chanSelectState")
 	for _, state := range expr.States {
-		ch := c.getValue(frame, state.Chan)
+		ch := b.getValue(state.Chan)
 		selectState := llvm.ConstNull(chanSelectStateType)
-		selectState = c.builder.CreateInsertValue(selectState, ch, 0, "")
+		selectState = b.CreateInsertValue(selectState, ch, 0, "")
 		switch state.Dir {
 		case types.RecvOnly:
 			// Make sure the receive buffer is big enough and has the correct alignment.
-			llvmType := c.getLLVMType(state.Chan.Type().(*types.Chan).Elem())
-			if size := c.targetData.TypeAllocSize(llvmType); size > recvbufSize {
+			llvmType := b.getLLVMType(state.Chan.Type().Underlying().(*types.Chan).Elem())
+			if size := b.targetData.TypeAllocSize(llvmType); size > recvbufSize {
 				recvbufSize = size
 			}
-			if align := c.targetData.ABITypeAlignment(llvmType); align > recvbufAlign {
+			if align := b.targetData.ABITypeAlignment(llvmType); align > recvbufAlign {
 				recvbufAlign = align
 			}
 			hasReceives = true
 		case types.SendOnly:
 			// Store this value in an alloca and put a pointer to this alloca
 			// in the send state.
-			sendValue := c.getValue(frame, state.Send)
-			alloca := llvmutil.CreateEntryBlockAlloca(c.builder, sendValue.Type(), "select.send.value")
-			c.builder.CreateStore(sendValue, alloca)
-			ptr := c.builder.CreateBitCast(alloca, c.i8ptrType, "")
-			selectState = c.builder.CreateInsertValue(selectState, ptr, 1, "")
+			sendValue := b.getValue(state.Send)
+			alloca := llvmutil.CreateEntryBlockAlloca(b.Builder, sendValue.Type(), "select.send.value")
+			b.CreateStore(sendValue, alloca)
+			ptr := b.CreateBitCast(alloca, b.i8ptrType, "")
+			selectState = b.CreateInsertValue(selectState, ptr, 1, "")
 		default:
 			panic("unreachable")
 		}
@@ -134,74 +150,74 @@ func (c *Compiler) emitSelect(frame *Frame, expr *ssa.Select) llvm.Value {
 	}

 	// Create a receive buffer, where the received value will be stored.
-	recvbuf := llvm.Undef(c.i8ptrType)
+	recvbuf := llvm.Undef(b.i8ptrType)
 	if hasReceives {
-		allocaType := llvm.ArrayType(c.ctx.Int8Type(), int(recvbufSize))
-		recvbufAlloca, _, _ := c.createTemporaryAlloca(allocaType, "select.recvbuf.alloca")
+		allocaType := llvm.ArrayType(b.ctx.Int8Type(), int(recvbufSize))
+		recvbufAlloca, _, _ := b.createTemporaryAlloca(allocaType, "select.recvbuf.alloca")
 		recvbufAlloca.SetAlignment(recvbufAlign)
-		recvbuf = c.builder.CreateGEP(recvbufAlloca, []llvm.Value{
-			llvm.ConstInt(c.ctx.Int32Type(), 0, false),
-			llvm.ConstInt(c.ctx.Int32Type(), 0, false),
+		recvbuf = b.CreateGEP(recvbufAlloca, []llvm.Value{
+			llvm.ConstInt(b.ctx.Int32Type(), 0, false),
+			llvm.ConstInt(b.ctx.Int32Type(), 0, false),
 		}, "select.recvbuf")
 	}

 	// Create the states slice (allocated on the stack).
 	statesAllocaType := llvm.ArrayType(chanSelectStateType, len(selectStates))
-	statesAlloca, statesI8, statesSize := c.createTemporaryAlloca(statesAllocaType, "select.states.alloca")
+	statesAlloca, statesI8, statesSize := b.createTemporaryAlloca(statesAllocaType, "select.states.alloca")
 	for i, state := range selectStates {
 		// Set each slice element to the appropriate channel.
-		gep := c.builder.CreateGEP(statesAlloca, []llvm.Value{
-			llvm.ConstInt(c.ctx.Int32Type(), 0, false),
-			llvm.ConstInt(c.ctx.Int32Type(), uint64(i), false),
+		gep := b.CreateGEP(statesAlloca, []llvm.Value{
+			llvm.ConstInt(b.ctx.Int32Type(), 0, false),
+			llvm.ConstInt(b.ctx.Int32Type(), uint64(i), false),
 		}, "")
-		c.builder.CreateStore(state, gep)
+		b.CreateStore(state, gep)
 	}
-	statesPtr := c.builder.CreateGEP(statesAlloca, []llvm.Value{
-		llvm.ConstInt(c.ctx.Int32Type(), 0, false),
-		llvm.ConstInt(c.ctx.Int32Type(), 0, false),
+	statesPtr := b.CreateGEP(statesAlloca, []llvm.Value{
+		llvm.ConstInt(b.ctx.Int32Type(), 0, false),
+		llvm.ConstInt(b.ctx.Int32Type(), 0, false),
 	}, "select.states")
-	statesLen := llvm.ConstInt(c.uintptrType, uint64(len(selectStates)), false)
+	statesLen := llvm.ConstInt(b.uintptrType, uint64(len(selectStates)), false)

 	// Do the select in the runtime.
 	var results llvm.Value
 	if expr.Blocking {
 		// Stack-allocate operation structures.
 		// If these were simply created as a slice, they would heap-allocate.
-		chBlockAllocaType := llvm.ArrayType(c.getLLVMRuntimeType("channelBlockedList"), len(selectStates))
-		chBlockAlloca, chBlockAllocaPtr, chBlockSize := c.createTemporaryAlloca(chBlockAllocaType, "select.block.alloca")
-		chBlockLen := llvm.ConstInt(c.uintptrType, uint64(len(selectStates)), false)
-		chBlockPtr := c.builder.CreateGEP(chBlockAlloca, []llvm.Value{
-			llvm.ConstInt(c.ctx.Int32Type(), 0, false),
-			llvm.ConstInt(c.ctx.Int32Type(), 0, false),
+		chBlockAllocaType := llvm.ArrayType(b.getLLVMRuntimeType("channelBlockedList"), len(selectStates))
+		chBlockAlloca, chBlockAllocaPtr, chBlockSize := b.createTemporaryAlloca(chBlockAllocaType, "select.block.alloca")
+		chBlockLen := llvm.ConstInt(b.uintptrType, uint64(len(selectStates)), false)
+		chBlockPtr := b.CreateGEP(chBlockAlloca, []llvm.Value{
+			llvm.ConstInt(b.ctx.Int32Type(), 0, false),
+			llvm.ConstInt(b.ctx.Int32Type(), 0, false),
 		}, "select.block")

-		results = c.createRuntimeCall("chanSelect", []llvm.Value{
+		results = b.createRuntimeCall("chanSelect", []llvm.Value{
 			recvbuf,
 			statesPtr, statesLen, statesLen, // []chanSelectState
 			chBlockPtr, chBlockLen, chBlockLen, // []channelBlockList
 		}, "select.result")

 		// Terminate the lifetime of the operation structures.
-		c.emitLifetimeEnd(chBlockAllocaPtr, chBlockSize)
+		b.emitLifetimeEnd(chBlockAllocaPtr, chBlockSize)
 	} else {
-		results = c.createRuntimeCall("tryChanSelect", []llvm.Value{
+		results = b.createRuntimeCall("tryChanSelect", []llvm.Value{
 			recvbuf,
 			statesPtr, statesLen, statesLen, // []chanSelectState
 		}, "select.result")
 	}

 	// Terminate the lifetime of the states alloca.
-	c.emitLifetimeEnd(statesI8, statesSize)
+	b.emitLifetimeEnd(statesI8, statesSize)

 	// The result value does not include all the possible received values,
 	// because we can't load them in advance. Instead, the *ssa.Extract
 	// instruction will treat a *ssa.Select specially and load it there inline.
 	// Store the receive alloca in a sidetable until we hit this extract
 	// instruction.
-	if frame.selectRecvBuf == nil {
-		frame.selectRecvBuf = make(map[*ssa.Select]llvm.Value)
+	if b.selectRecvBuf == nil {
+		b.selectRecvBuf = make(map[*ssa.Select]llvm.Value)
 	}
-	frame.selectRecvBuf[expr] = recvbuf
+	b.selectRecvBuf[expr] = recvbuf

 	return results
 }
@@ -210,28 +226,28 @@ func (c *Compiler) emitSelect(frame *Frame, expr *ssa.Select) llvm.Value {
 // when extracting a value from a select statement (*ssa.Select). Because
 // *ssa.Select cannot load all values in advance, it does this later in the
 // *ssa.Extract expression.
-func (c *Compiler) getChanSelectResult(frame *Frame, expr *ssa.Extract) llvm.Value {
+func (b *builder) getChanSelectResult(expr *ssa.Extract) llvm.Value {
 	if expr.Index == 0 {
 		// index
-		value := c.getValue(frame, expr.Tuple)
-		index := c.builder.CreateExtractValue(value, expr.Index, "")
-		if index.Type().IntTypeWidth() < c.intType.IntTypeWidth() {
-			index = c.builder.CreateSExt(index, c.intType, "")
+		value := b.getValue(expr.Tuple)
+		index := b.CreateExtractValue(value, expr.Index, "")
+		if index.Type().IntTypeWidth() < b.intType.IntTypeWidth() {
+			index = b.CreateSExt(index, b.intType, "")
 		}
 		return index
 	} else if expr.Index == 1 {
 		// comma-ok
-		value := c.getValue(frame, expr.Tuple)
-		return c.builder.CreateExtractValue(value, expr.Index, "")
+		value := b.getValue(expr.Tuple)
+		return b.CreateExtractValue(value, expr.Index, "")
 	} else {
 		// Select statements are (index, ok, ...) where ... is a number of
 		// received values, depending on how many receive statements there
 		// are. They are all combined into one alloca (because only one
 		// receive can proceed at a time) so we'll get that alloca, bitcast
 		// it to the correct type, and dereference it.
-		recvbuf := frame.selectRecvBuf[expr.Tuple.(*ssa.Select)]
-		typ := llvm.PointerType(c.getLLVMType(expr.Type()), 0)
-		ptr := c.builder.CreateBitCast(recvbuf, typ, "")
-		return c.builder.CreateLoad(ptr, "")
+		recvbuf := b.selectRecvBuf[expr.Tuple.(*ssa.Select)]
+		typ := llvm.PointerType(b.getLLVMType(expr.Type()), 0)
+		ptr := b.CreateBitCast(recvbuf, typ, "")
+		return b.CreateLoad(ptr, "")
 	}
 }
@@ -16,6 +16,7 @@ package compiler
 import (
 	"github.com/tinygo-org/tinygo/compiler/llvmutil"
 	"github.com/tinygo-org/tinygo/ir"
+	"go/types"
 	"golang.org/x/tools/go/ssa"
 	"tinygo.org/x/go-llvm"
 )
@@ -23,16 +24,18 @@ import (
 // deferInitFunc sets up this function for future deferred calls. It must be
 // called from within the entry block when this function contains deferred
 // calls.
-func (c *Compiler) deferInitFunc(frame *Frame) {
+func (b *builder) deferInitFunc() {
 	// Some setup.
-	frame.deferFuncs = make(map[*ir.Function]int)
-	frame.deferInvokeFuncs = make(map[string]int)
-	frame.deferClosureFuncs = make(map[*ir.Function]int)
+	b.deferFuncs = make(map[*ir.Function]int)
+	b.deferInvokeFuncs = make(map[string]int)
+	b.deferClosureFuncs = make(map[*ir.Function]int)
+	b.deferExprFuncs = make(map[ssa.Value]int)
+	b.deferBuiltinFuncs = make(map[ssa.Value]deferBuiltin)

 	// Create defer list pointer.
-	deferType := llvm.PointerType(c.getLLVMRuntimeType("_defer"), 0)
-	frame.deferPtr = c.builder.CreateAlloca(deferType, "deferPtr")
-	c.builder.CreateStore(llvm.ConstPointerNull(deferType), frame.deferPtr)
+	deferType := llvm.PointerType(b.getLLVMRuntimeType("_defer"), 0)
+	b.deferPtr = b.CreateAlloca(deferType, "deferPtr")
+	b.CreateStore(llvm.ConstPointerNull(deferType), b.deferPtr)
 }

 // isInLoop checks if there is a path from a basic block to itself.
@@ -69,53 +72,54 @@ func isInLoop(start *ssa.BasicBlock) bool {
 	return false
 }

-// emitDefer emits a single defer instruction, to be run when this function
+// createDefer emits a single defer instruction, to be run when this function
 // returns.
-func (c *Compiler) emitDefer(frame *Frame, instr *ssa.Defer) {
+func (b *builder) createDefer(instr *ssa.Defer) {
 	// The pointer to the previous defer struct, which we will replace to
 	// make a linked list.
-	next := c.builder.CreateLoad(frame.deferPtr, "defer.next")
+	next := b.CreateLoad(b.deferPtr, "defer.next")

 	var values []llvm.Value
-	valueTypes := []llvm.Type{c.uintptrType, next.Type()}
+	valueTypes := []llvm.Type{b.uintptrType, next.Type()}
 	if instr.Call.IsInvoke() {
 		// Method call on an interface.

 		// Get callback type number.
 		methodName := instr.Call.Method.FullName()
-		if _, ok := frame.deferInvokeFuncs[methodName]; !ok {
-			frame.deferInvokeFuncs[methodName] = len(frame.allDeferFuncs)
-			frame.allDeferFuncs = append(frame.allDeferFuncs, &instr.Call)
+		if _, ok := b.deferInvokeFuncs[methodName]; !ok {
+			b.deferInvokeFuncs[methodName] = len(b.allDeferFuncs)
+			b.allDeferFuncs = append(b.allDeferFuncs, &instr.Call)
 		}
-		callback := llvm.ConstInt(c.uintptrType, uint64(frame.deferInvokeFuncs[methodName]), false)
+		callback := llvm.ConstInt(b.uintptrType, uint64(b.deferInvokeFuncs[methodName]), false)

 		// Collect all values to be put in the struct (starting with
 		// runtime._defer fields, followed by the call parameters).
-		itf := c.getValue(frame, instr.Call.Value) // interface
-		receiverValue := c.builder.CreateExtractValue(itf, 1, "invoke.func.receiver")
-		values = []llvm.Value{callback, next, receiverValue}
-		valueTypes = append(valueTypes, c.i8ptrType)
+		itf := b.getValue(instr.Call.Value) // interface
+		typecode := b.CreateExtractValue(itf, 0, "invoke.func.typecode")
+		receiverValue := b.CreateExtractValue(itf, 1, "invoke.func.receiver")
+		values = []llvm.Value{callback, next, typecode, receiverValue}
+		valueTypes = append(valueTypes, b.uintptrType, b.i8ptrType)
 		for _, arg := range instr.Call.Args {
-			val := c.getValue(frame, arg)
+			val := b.getValue(arg)
 			values = append(values, val)
 			valueTypes = append(valueTypes, val.Type())
 		}

 	} else if callee, ok := instr.Call.Value.(*ssa.Function); ok {
 		// Regular function call.
-		fn := c.ir.GetFunction(callee)
+		fn := b.ir.GetFunction(callee)

-		if _, ok := frame.deferFuncs[fn]; !ok {
-			frame.deferFuncs[fn] = len(frame.allDeferFuncs)
-			frame.allDeferFuncs = append(frame.allDeferFuncs, fn)
+		if _, ok := b.deferFuncs[fn]; !ok {
+			b.deferFuncs[fn] = len(b.allDeferFuncs)
+			b.allDeferFuncs = append(b.allDeferFuncs, fn)
 		}
-		callback := llvm.ConstInt(c.uintptrType, uint64(frame.deferFuncs[fn]), false)
+		callback := llvm.ConstInt(b.uintptrType, uint64(b.deferFuncs[fn]), false)

 		// Collect all values to be put in the struct (starting with
 		// runtime._defer fields).
 		values = []llvm.Value{callback, next}
 		for _, param := range instr.Call.Args {
-			llvmParam := c.getValue(frame, param)
+			llvmParam := b.getValue(param)
 			values = append(values, llvmParam)
 			valueTypes = append(valueTypes, llvmParam.Type())
 		}
@@ -127,65 +131,110 @@ func (c *Compiler) emitDefer(frame *Frame, instr *ssa.Defer) {
 		// pointer.
 		// TODO: ignore this closure entirely and put pointers to the free
 		// variables directly in the defer struct, avoiding a memory allocation.
-		closure := c.getValue(frame, instr.Call.Value)
-		context := c.builder.CreateExtractValue(closure, 0, "")
+		closure := b.getValue(instr.Call.Value)
+		context := b.CreateExtractValue(closure, 0, "")

 		// Get the callback number.
-		fn := c.ir.GetFunction(makeClosure.Fn.(*ssa.Function))
-		if _, ok := frame.deferClosureFuncs[fn]; !ok {
-			frame.deferClosureFuncs[fn] = len(frame.allDeferFuncs)
-			frame.allDeferFuncs = append(frame.allDeferFuncs, makeClosure)
+		fn := b.ir.GetFunction(makeClosure.Fn.(*ssa.Function))
+		if _, ok := b.deferClosureFuncs[fn]; !ok {
+			b.deferClosureFuncs[fn] = len(b.allDeferFuncs)
+			b.allDeferFuncs = append(b.allDeferFuncs, makeClosure)
 		}
-		callback := llvm.ConstInt(c.uintptrType, uint64(frame.deferClosureFuncs[fn]), false)
+		callback := llvm.ConstInt(b.uintptrType, uint64(b.deferClosureFuncs[fn]), false)

 		// Collect all values to be put in the struct (starting with
 		// runtime._defer fields, followed by all parameters including the
 		// context pointer).
 		values = []llvm.Value{callback, next}
 		for _, param := range instr.Call.Args {
-			llvmParam := c.getValue(frame, param)
+			llvmParam := b.getValue(param)
 			values = append(values, llvmParam)
 			valueTypes = append(valueTypes, llvmParam.Type())
 		}
 		values = append(values, context)
 		valueTypes = append(valueTypes, context.Type())

+	} else if builtin, ok := instr.Call.Value.(*ssa.Builtin); ok {
+		var funcName string
+		switch builtin.Name() {
+		case "close":
+			funcName = "chanClose"
+		default:
+			b.addError(instr.Pos(), "todo: Implement defer for "+builtin.Name())
+			return
+		}
+
+		if _, ok := b.deferBuiltinFuncs[instr.Call.Value]; !ok {
+			b.deferBuiltinFuncs[instr.Call.Value] = deferBuiltin{
+				funcName,
+				len(b.allDeferFuncs),
+			}
+			b.allDeferFuncs = append(b.allDeferFuncs, instr.Call.Value)
+		}
+		callback := llvm.ConstInt(b.uintptrType, uint64(b.deferBuiltinFuncs[instr.Call.Value].callback), false)
+
+		// Collect all values to be put in the struct (starting with
+		// runtime._defer fields).
+		values = []llvm.Value{callback, next}
+		for _, param := range instr.Call.Args {
+			llvmParam := b.getValue(param)
+			values = append(values, llvmParam)
+			valueTypes = append(valueTypes, llvmParam.Type())
+		}
+
 	} else {
-		c.addError(instr.Pos(), "todo: defer on uncommon function call type")
-		return
+		funcValue := b.getValue(instr.Call.Value)
+
+		if _, ok := b.deferExprFuncs[instr.Call.Value]; !ok {
+			b.deferExprFuncs[instr.Call.Value] = len(b.allDeferFuncs)
+			b.allDeferFuncs = append(b.allDeferFuncs, &instr.Call)
+		}
+
+		callback := llvm.ConstInt(b.uintptrType, uint64(b.deferExprFuncs[instr.Call.Value]), false)
+
+		// Collect all values to be put in the struct (starting with
+		// runtime._defer fields, followed by all parameters including the
+		// context pointer).
+		values = []llvm.Value{callback, next, funcValue}
+		valueTypes = append(valueTypes, funcValue.Type())
+		for _, param := range instr.Call.Args {
+			llvmParam := b.getValue(param)
+			values = append(values, llvmParam)
+			valueTypes = append(valueTypes, llvmParam.Type())
+		}
 	}

 	// Make a struct out of the collected values to put in the defer frame.
-	deferFrameType := c.ctx.StructType(valueTypes, false)
+	deferFrameType := b.ctx.StructType(valueTypes, false)
 	deferFrame := llvm.ConstNull(deferFrameType)
 	for i, value := range values {
-		deferFrame = c.builder.CreateInsertValue(deferFrame, value, i, "")
+		deferFrame = b.CreateInsertValue(deferFrame, value, i, "")
 	}

 	// Put this struct in an allocation.
 	var alloca llvm.Value
 	if !isInLoop(instr.Block()) {
 		// This can safely use a stack allocation.
-		alloca = llvmutil.CreateEntryBlockAlloca(c.builder, deferFrameType, "defer.alloca")
+		alloca = llvmutil.CreateEntryBlockAlloca(b.Builder, deferFrameType, "defer.alloca")
 	} else {
 		// This may be hit a variable number of times, so use a heap allocation.
-		size := c.targetData.TypeAllocSize(deferFrameType)
-		sizeValue := llvm.ConstInt(c.uintptrType, size, false)
-		allocCall := c.createRuntimeCall("alloc", []llvm.Value{sizeValue}, "defer.alloc.call")
-		alloca = c.builder.CreateBitCast(allocCall, llvm.PointerType(deferFrameType, 0), "defer.alloc")
+		size := b.targetData.TypeAllocSize(deferFrameType)
+		sizeValue := llvm.ConstInt(b.uintptrType, size, false)
+		allocCall := b.createRuntimeCall("alloc", []llvm.Value{sizeValue}, "defer.alloc.call")
+		alloca = b.CreateBitCast(allocCall, llvm.PointerType(deferFrameType, 0), "defer.alloc")
 	}
-	if c.NeedsStackObjects() {
-		c.trackPointer(alloca)
+	if b.NeedsStackObjects() {
+		b.trackPointer(alloca)
 	}
-	c.builder.CreateStore(deferFrame, alloca)
+	b.CreateStore(deferFrame, alloca)

 	// Push it on top of the linked list by replacing deferPtr.
-	allocaCast := c.builder.CreateBitCast(alloca, next.Type(), "defer.alloca.cast")
-	c.builder.CreateStore(allocaCast, frame.deferPtr)
+	allocaCast := b.CreateBitCast(alloca, next.Type(), "defer.alloca.cast")
+	b.CreateStore(allocaCast, b.deferPtr)
 }

-// emitRunDefers emits code to run all deferred functions.
-func (c *Compiler) emitRunDefers(frame *Frame) {
+// createRunDefers emits code to run all deferred functions.
+func (b *builder) createRunDefers() {
 	// Add a loop like the following:
 	//     for stack != nil {
 	//         _stack := stack
@@ -202,151 +251,205 @@ func (c *Compiler) emitRunDefers(frame *Frame) {
 	//     }

 	// Create loop.
-	loophead := c.ctx.AddBasicBlock(frame.fn.LLVMFn, "rundefers.loophead")
-	loop := c.ctx.AddBasicBlock(frame.fn.LLVMFn, "rundefers.loop")
-	unreachable := c.ctx.AddBasicBlock(frame.fn.LLVMFn, "rundefers.default")
-	end := c.ctx.AddBasicBlock(frame.fn.LLVMFn, "rundefers.end")
-	c.builder.CreateBr(loophead)
+	loophead := b.ctx.AddBasicBlock(b.fn.LLVMFn, "rundefers.loophead")
+	loop := b.ctx.AddBasicBlock(b.fn.LLVMFn, "rundefers.loop")
+	unreachable := b.ctx.AddBasicBlock(b.fn.LLVMFn, "rundefers.default")
+	end := b.ctx.AddBasicBlock(b.fn.LLVMFn, "rundefers.end")
+	b.CreateBr(loophead)

 	// Create loop head:
 	//     for stack != nil {
-	c.builder.SetInsertPointAtEnd(loophead)
-	deferData := c.builder.CreateLoad(frame.deferPtr, "")
-	stackIsNil := c.builder.CreateICmp(llvm.IntEQ, deferData, llvm.ConstPointerNull(deferData.Type()), "stackIsNil")
-	c.builder.CreateCondBr(stackIsNil, end, loop)
+	b.SetInsertPointAtEnd(loophead)
+	deferData := b.CreateLoad(b.deferPtr, "")
+	stackIsNil := b.CreateICmp(llvm.IntEQ, deferData, llvm.ConstPointerNull(deferData.Type()), "stackIsNil")
+	b.CreateCondBr(stackIsNil, end, loop)

 	// Create loop body:
 	//     _stack := stack
 	//     stack = stack.next
 	//     switch stack.callback {
-	c.builder.SetInsertPointAtEnd(loop)
-	nextStackGEP := c.builder.CreateInBoundsGEP(deferData, []llvm.Value{
-		llvm.ConstInt(c.ctx.Int32Type(), 0, false),
-		llvm.ConstInt(c.ctx.Int32Type(), 1, false), // .next field
+	b.SetInsertPointAtEnd(loop)
+	nextStackGEP := b.CreateInBoundsGEP(deferData, []llvm.Value{
+		llvm.ConstInt(b.ctx.Int32Type(), 0, false),
+		llvm.ConstInt(b.ctx.Int32Type(), 1, false), // .next field
 	}, "stack.next.gep")
-	nextStack := c.builder.CreateLoad(nextStackGEP, "stack.next")
-	c.builder.CreateStore(nextStack, frame.deferPtr)
-	gep := c.builder.CreateInBoundsGEP(deferData, []llvm.Value{
-		llvm.ConstInt(c.ctx.Int32Type(), 0, false),
-		llvm.ConstInt(c.ctx.Int32Type(), 0, false), // .callback field
+	nextStack := b.CreateLoad(nextStackGEP, "stack.next")
+	b.CreateStore(nextStack, b.deferPtr)
+	gep := b.CreateInBoundsGEP(deferData, []llvm.Value{
+		llvm.ConstInt(b.ctx.Int32Type(), 0, false),
+		llvm.ConstInt(b.ctx.Int32Type(), 0, false), // .callback field
 	}, "callback.gep")
-	callback := c.builder.CreateLoad(gep, "callback")
-	sw := c.builder.CreateSwitch(callback, unreachable, len(frame.allDeferFuncs))
+	callback := b.CreateLoad(gep, "callback")
+	sw := b.CreateSwitch(callback, unreachable, len(b.allDeferFuncs))

-	for i, callback := range frame.allDeferFuncs {
+	for i, callback := range b.allDeferFuncs {
 		// Create switch case, for example:
 		//     case 0:
 		//         // run first deferred call
-		block := c.ctx.AddBasicBlock(frame.fn.LLVMFn, "rundefers.callback")
-		sw.AddCase(llvm.ConstInt(c.uintptrType, uint64(i), false), block)
-		c.builder.SetInsertPointAtEnd(block)
+		block := b.ctx.AddBasicBlock(b.fn.LLVMFn, "rundefers.callback")
+		sw.AddCase(llvm.ConstInt(b.uintptrType, uint64(i), false), block)
+		b.SetInsertPointAtEnd(block)
 		switch callback := callback.(type) {
 		case *ssa.CallCommon:
-			// Call on an interface value.
-			if !callback.IsInvoke() {
-				panic("expected an invoke call, not a direct call")
-			}
+			// Call on an value or interface value.

 			// Get the real defer struct type and cast to it.
-			valueTypes := []llvm.Type{c.uintptrType, llvm.PointerType(c.getLLVMRuntimeType("_defer"), 0), c.i8ptrType}
-			for _, arg := range callback.Args {
-				valueTypes = append(valueTypes, c.getLLVMType(arg.Type()))
+			valueTypes := []llvm.Type{b.uintptrType, llvm.PointerType(b.getLLVMRuntimeType("_defer"), 0)}
+
+			if !callback.IsInvoke() {
+				//Expect funcValue to be passed through the defer frame.
+				valueTypes = append(valueTypes, b.getFuncType(callback.Signature()))
+			} else {
+				//Expect typecode
+				valueTypes = append(valueTypes, b.uintptrType, b.i8ptrType)
 			}
-			deferFrameType := c.ctx.StructType(valueTypes, false)
-			deferFramePtr := c.builder.CreateBitCast(deferData, llvm.PointerType(deferFrameType, 0), "deferFrame")
+
+			for _, arg := range callback.Args {
+				valueTypes = append(valueTypes, b.getLLVMType(arg.Type()))
+			}
+
+			deferFrameType := b.ctx.StructType(valueTypes, false)
+			deferFramePtr := b.CreateBitCast(deferData, llvm.PointerType(deferFrameType, 0), "deferFrame")

 			// Extract the params from the struct (including receiver).
 			forwardParams := []llvm.Value{}
-			zero := llvm.ConstInt(c.ctx.Int32Type(), 0, false)
+			zero := llvm.ConstInt(b.ctx.Int32Type(), 0, false)
 			for i := 2; i < len(valueTypes); i++ {
-				gep := c.builder.CreateInBoundsGEP(deferFramePtr, []llvm.Value{zero, llvm.ConstInt(c.ctx.Int32Type(), uint64(i), false)}, "gep")
-				forwardParam := c.builder.CreateLoad(gep, "param")
+				gep := b.CreateInBoundsGEP(deferFramePtr, []llvm.Value{zero, llvm.ConstInt(b.ctx.Int32Type(), uint64(i), false)}, "gep")
+				forwardParam := b.CreateLoad(gep, "param")
 				forwardParams = append(forwardParams, forwardParam)
 			}

-			// Add the context parameter. An interface call cannot also be a
-			// closure but we have to supply the parameter anyway for platforms
-			// with a strict calling convention.
-			forwardParams = append(forwardParams, llvm.Undef(c.i8ptrType))
+			var fnPtr llvm.Value
+
+			if !callback.IsInvoke() {
+				// Isolate the func value.
+				funcValue := forwardParams[0]
+				forwardParams = forwardParams[1:]
+
+				//Get function pointer and context
+				fp, context := b.decodeFuncValue(funcValue, callback.Signature())
+				fnPtr = fp
+
+				//Pass context
+				forwardParams = append(forwardParams, context)
+			} else {
+				// Isolate the typecode.
+				typecode := forwardParams[0]
+				forwardParams = forwardParams[1:]
+				fnPtr = b.getInvokePtr(callback, typecode)
+
+				// Add the context parameter. An interface call cannot also be a
+				// closure but we have to supply the parameter anyway for platforms
+				// with a strict calling convention.
+				forwardParams = append(forwardParams, llvm.Undef(b.i8ptrType))
+			}

 			// Parent coroutine handle.
-			forwardParams = append(forwardParams, llvm.Undef(c.i8ptrType))
+			forwardParams = append(forwardParams, llvm.Undef(b.i8ptrType))

-			fnPtr, _ := c.getInvokeCall(frame, callback)
-			c.createCall(fnPtr, forwardParams, "")
+			b.createCall(fnPtr, forwardParams, "")

 		case *ir.Function:
 			// Direct call.

 			// Get the real defer struct type and cast to it.
-			valueTypes := []llvm.Type{c.uintptrType, llvm.PointerType(c.getLLVMRuntimeType("_defer"), 0)}
+			valueTypes := []llvm.Type{b.uintptrType, llvm.PointerType(b.getLLVMRuntimeType("_defer"), 0)}
 			for _, param := range callback.Params {
-				valueTypes = append(valueTypes, c.getLLVMType(param.Type()))
+				valueTypes = append(valueTypes, b.getLLVMType(param.Type()))
 			}
-			deferFrameType := c.ctx.StructType(valueTypes, false)
-			deferFramePtr := c.builder.CreateBitCast(deferData, llvm.PointerType(deferFrameType, 0), "deferFrame")
+			deferFrameType := b.ctx.StructType(valueTypes, false)
+			deferFramePtr := b.CreateBitCast(deferData, llvm.PointerType(deferFrameType, 0), "deferFrame")

 			// Extract the params from the struct.
 			forwardParams := []llvm.Value{}
-			zero := llvm.ConstInt(c.ctx.Int32Type(), 0, false)
+			zero := llvm.ConstInt(b.ctx.Int32Type(), 0, false)
 			for i := range callback.Params {
-				gep := c.builder.CreateInBoundsGEP(deferFramePtr, []llvm.Value{zero, llvm.ConstInt(c.ctx.Int32Type(), uint64(i+2), false)}, "gep")
-				forwardParam := c.builder.CreateLoad(gep, "param")
+				gep := b.CreateInBoundsGEP(deferFramePtr, []llvm.Value{zero, llvm.ConstInt(b.ctx.Int32Type(), uint64(i+2), false)}, "gep")
+				forwardParam := b.CreateLoad(gep, "param")
 				forwardParams = append(forwardParams, forwardParam)
 			}

-			// Add the context parameter. We know it is ignored by the receiving
-			// function, but we have to pass one anyway.
-			forwardParams = append(forwardParams, llvm.Undef(c.i8ptrType))
+			// Plain TinyGo functions add some extra parameters to implement async functionality and function recievers.
+			// These parameters should not be supplied when calling into an external C/ASM function.
+			if !callback.IsExported() {
+				// Add the context parameter. We know it is ignored by the receiving
+				// function, but we have to pass one anyway.
+				forwardParams = append(forwardParams, llvm.Undef(b.i8ptrType))

-			// Parent coroutine handle.
-			forwardParams = append(forwardParams, llvm.Undef(c.i8ptrType))
+				// Parent coroutine handle.
+				forwardParams = append(forwardParams, llvm.Undef(b.i8ptrType))
+			}

 			// Call real function.
-			c.createCall(callback.LLVMFn, forwardParams, "")
+			b.createCall(callback.LLVMFn, forwardParams, "")

 		case *ssa.MakeClosure:
 			// Get the real defer struct type and cast to it.
-			fn := c.ir.GetFunction(callback.Fn.(*ssa.Function))
-			valueTypes := []llvm.Type{c.uintptrType, llvm.PointerType(c.getLLVMRuntimeType("_defer"), 0)}
+			fn := b.ir.GetFunction(callback.Fn.(*ssa.Function))
+			valueTypes := []llvm.Type{b.uintptrType, llvm.PointerType(b.getLLVMRuntimeType("_defer"), 0)}
 			params := fn.Signature.Params()
 			for i := 0; i < params.Len(); i++ {
-				valueTypes = append(valueTypes, c.getLLVMType(params.At(i).Type()))
+				valueTypes = append(valueTypes, b.getLLVMType(params.At(i).Type()))
 			}
-			valueTypes = append(valueTypes, c.i8ptrType) // closure
-			deferFrameType := c.ctx.StructType(valueTypes, false)
-			deferFramePtr := c.builder.CreateBitCast(deferData, llvm.PointerType(deferFrameType, 0), "deferFrame")
+			valueTypes = append(valueTypes, b.i8ptrType) // closure
+			deferFrameType := b.ctx.StructType(valueTypes, false)
+			deferFramePtr := b.CreateBitCast(deferData, llvm.PointerType(deferFrameType, 0), "deferFrame")

 			// Extract the params from the struct.
 			forwardParams := []llvm.Value{}
-			zero := llvm.ConstInt(c.ctx.Int32Type(), 0, false)
+			zero := llvm.ConstInt(b.ctx.Int32Type(), 0, false)
 			for i := 2; i < len(valueTypes); i++ {
-				gep := c.builder.CreateInBoundsGEP(deferFramePtr, []llvm.Value{zero, llvm.ConstInt(c.ctx.Int32Type(), uint64(i), false)}, "")
-				forwardParam := c.builder.CreateLoad(gep, "param")
+				gep := b.CreateInBoundsGEP(deferFramePtr, []llvm.Value{zero, llvm.ConstInt(b.ctx.Int32Type(), uint64(i), false)}, "")
+				forwardParam := b.CreateLoad(gep, "param")
 				forwardParams = append(forwardParams, forwardParam)
 			}

 			// Parent coroutine handle.
-			forwardParams = append(forwardParams, llvm.Undef(c.i8ptrType))
+			forwardParams = append(forwardParams, llvm.Undef(b.i8ptrType))

 			// Call deferred function.
-			c.createCall(fn.LLVMFn, forwardParams, "")
+			b.createCall(fn.LLVMFn, forwardParams, "")
+		case *ssa.Builtin:
+			db := b.deferBuiltinFuncs[callback]

+			//Get parameter types
+			valueTypes := []llvm.Type{b.uintptrType, llvm.PointerType(b.getLLVMRuntimeType("_defer"), 0)}
+
+			//Get signature from call results
+			params := callback.Type().Underlying().(*types.Signature).Params()
+			for i := 0; i < params.Len(); i++ {
+				valueTypes = append(valueTypes, b.getLLVMType(params.At(i).Type()))
+			}
+
+			deferFrameType := b.ctx.StructType(valueTypes, false)
+			deferFramePtr := b.CreateBitCast(deferData, llvm.PointerType(deferFrameType, 0), "deferFrame")
+
+			// Extract the params from the struct.
+			var forwardParams []llvm.Value
+			zero := llvm.ConstInt(b.ctx.Int32Type(), 0, false)
+			for i := 0; i < params.Len(); i++ {
+				gep := b.CreateInBoundsGEP(deferFramePtr, []llvm.Value{zero, llvm.ConstInt(b.ctx.Int32Type(), uint64(i+2), false)}, "gep")
+				forwardParam := b.CreateLoad(gep, "param")
+				forwardParams = append(forwardParams, forwardParam)
+			}
+
+			b.createRuntimeCall(db.funcName, forwardParams, "")
 		default:
 			panic("unknown deferred function type")
 		}

 		// Branch back to the start of the loop.
-		c.builder.CreateBr(loophead)
+		b.CreateBr(loophead)
 	}

 	// Create default unreachable block:
 	//     default:
 	//         unreachable
 	//     }
-	c.builder.SetInsertPointAtEnd(unreachable)
-	c.builder.CreateUnreachable()
+	b.SetInsertPointAtEnd(unreachable)
+	b.CreateUnreachable()

 	// End of loop.
-	c.builder.SetInsertPointAtEnd(end)
+	b.SetInsertPointAtEnd(end)
 }
@@ -1,5 +1,7 @@
 package compiler

+// This file contains some utility functions related to error handling.
+
 import (
 	"go/scanner"
 	"go/token"
@@ -9,7 +11,8 @@ import (
 	"tinygo.org/x/go-llvm"
 )

-func (c *Compiler) makeError(pos token.Pos, msg string) types.Error {
+// makeError makes it easy to create an error from a token.Pos with a message.
+func (c *compilerContext) makeError(pos token.Pos, msg string) types.Error {
 	return types.Error{
 		Fset: c.ir.Program.Fset,
 		Pos:  pos,
@@ -17,7 +20,7 @@ func (c *Compiler) makeError(pos token.Pos, msg string) types.Error {
 	}
 }

-func (c *Compiler) addError(pos token.Pos, msg string) {
+func (c *compilerContext) addError(pos token.Pos, msg string) {
 	c.diagnostics = append(c.diagnostics, c.makeError(pos, msg))
 }

@@ -6,53 +6,26 @@ package compiler
 import (
 	"go/types"

+	"github.com/tinygo-org/tinygo/compileopts"
 	"golang.org/x/tools/go/ssa"
 	"tinygo.org/x/go-llvm"
 )

-type funcValueImplementation int
-
-const (
-	funcValueNone funcValueImplementation = iota
-
-	// A func value is implemented as a pair of pointers:
-	//     {context, function pointer}
-	// where the context may be a pointer to a heap-allocated struct containing
-	// the free variables, or it may be undef if the function being pointed to
-	// doesn't need a context. The function pointer is a regular function
-	// pointer.
-	funcValueDoubleword
-
-	// As funcValueDoubleword, but with the function pointer replaced by a
-	// unique ID per function signature. Function values are called by using a
-	// switch statement and choosing which function to call.
-	funcValueSwitch
-)
-
-// funcImplementation picks an appropriate func value implementation for the
-// target.
-func (c *Compiler) funcImplementation() funcValueImplementation {
-	// Always pick the switch implementation, as it allows the use of blocking
-	// inside a function that is used as a func value.
-	switch c.Scheduler() {
-	case "coroutines":
-		return funcValueSwitch
-	case "tasks":
-		return funcValueDoubleword
-	default:
-		panic("unknown scheduler type")
-	}
+// createFuncValue creates a function value from a raw function pointer with no
+// context.
+func (b *builder) createFuncValue(funcPtr, context llvm.Value, sig *types.Signature) llvm.Value {
+	return b.compilerContext.createFuncValue(b.Builder, funcPtr, context, sig)
 }

 // createFuncValue creates a function value from a raw function pointer with no
 // context.
-func (c *Compiler) createFuncValue(funcPtr, context llvm.Value, sig *types.Signature) llvm.Value {
+func (c *compilerContext) createFuncValue(builder llvm.Builder, funcPtr, context llvm.Value, sig *types.Signature) llvm.Value {
 	var funcValueScalar llvm.Value
-	switch c.funcImplementation() {
-	case funcValueDoubleword:
+	switch c.FuncImplementation() {
+	case compileopts.FuncValueDoubleword:
 		// Closure is: {context, function pointer}
 		funcValueScalar = funcPtr
-	case funcValueSwitch:
+	case compileopts.FuncValueSwitch:
 		sigGlobal := c.getTypeCode(sig)
 		funcValueWithSignatureGlobalName := funcPtr.Name() + "$withSignature"
 		funcValueWithSignatureGlobal := c.mod.NamedGlobal(funcValueWithSignatureGlobalName)
@@ -73,35 +46,35 @@ func (c *Compiler) createFuncValue(funcPtr, context llvm.Value, sig *types.Signa
 	}
 	funcValueType := c.getFuncType(sig)
 	funcValue := llvm.Undef(funcValueType)
-	funcValue = c.builder.CreateInsertValue(funcValue, context, 0, "")
-	funcValue = c.builder.CreateInsertValue(funcValue, funcValueScalar, 1, "")
+	funcValue = builder.CreateInsertValue(funcValue, context, 0, "")
+	funcValue = builder.CreateInsertValue(funcValue, funcValueScalar, 1, "")
 	return funcValue
 }

 // extractFuncScalar returns some scalar that can be used in comparisons. It is
 // a cheap operation.
-func (c *Compiler) extractFuncScalar(funcValue llvm.Value) llvm.Value {
-	return c.builder.CreateExtractValue(funcValue, 1, "")
+func (b *builder) extractFuncScalar(funcValue llvm.Value) llvm.Value {
+	return b.CreateExtractValue(funcValue, 1, "")
 }

 // extractFuncContext extracts the context pointer from this function value. It
 // is a cheap operation.
-func (c *Compiler) extractFuncContext(funcValue llvm.Value) llvm.Value {
-	return c.builder.CreateExtractValue(funcValue, 0, "")
+func (b *builder) extractFuncContext(funcValue llvm.Value) llvm.Value {
+	return b.CreateExtractValue(funcValue, 0, "")
 }

 // decodeFuncValue extracts the context and the function pointer from this func
 // value. This may be an expensive operation.
-func (c *Compiler) decodeFuncValue(funcValue llvm.Value, sig *types.Signature) (funcPtr, context llvm.Value) {
-	context = c.builder.CreateExtractValue(funcValue, 0, "")
-	switch c.funcImplementation() {
-	case funcValueDoubleword:
-		funcPtr = c.builder.CreateExtractValue(funcValue, 1, "")
-	case funcValueSwitch:
-		llvmSig := c.getRawFuncType(sig)
-		sigGlobal := c.getTypeCode(sig)
-		funcPtr = c.createRuntimeCall("getFuncPtr", []llvm.Value{funcValue, sigGlobal}, "")
-		funcPtr = c.builder.CreateIntToPtr(funcPtr, llvmSig, "")
+func (b *builder) decodeFuncValue(funcValue llvm.Value, sig *types.Signature) (funcPtr, context llvm.Value) {
+	context = b.CreateExtractValue(funcValue, 0, "")
+	switch b.FuncImplementation() {
+	case compileopts.FuncValueDoubleword:
+		funcPtr = b.CreateExtractValue(funcValue, 1, "")
+	case compileopts.FuncValueSwitch:
+		llvmSig := b.getRawFuncType(sig)
+		sigGlobal := b.getTypeCode(sig)
+		funcPtr = b.createRuntimeCall("getFuncPtr", []llvm.Value{funcValue, sigGlobal}, "")
+		funcPtr = b.CreateIntToPtr(funcPtr, llvmSig, "")
 	default:
 		panic("unimplemented func value variant")
 	}
@@ -109,12 +82,12 @@ func (c *Compiler) decodeFuncValue(funcValue llvm.Value, sig *types.Signature) (
 }

 // getFuncType returns the type of a func value given a signature.
-func (c *Compiler) getFuncType(typ *types.Signature) llvm.Type {
-	switch c.funcImplementation() {
-	case funcValueDoubleword:
+func (c *compilerContext) getFuncType(typ *types.Signature) llvm.Type {
+	switch c.FuncImplementation() {
+	case compileopts.FuncValueDoubleword:
 		rawPtr := c.getRawFuncType(typ)
 		return c.ctx.StructType([]llvm.Type{c.i8ptrType, rawPtr}, false)
-	case funcValueSwitch:
+	case compileopts.FuncValueSwitch:
 		return c.getLLVMRuntimeType("funcValue")
 	default:
 		panic("unimplemented func value variant")
@@ -122,7 +95,7 @@ func (c *Compiler) getFuncType(typ *types.Signature) llvm.Type {
 }

 // getRawFuncType returns a LLVM function pointer type for a given signature.
-func (c *Compiler) getRawFuncType(typ *types.Signature) llvm.Type {
+func (c *compilerContext) getRawFuncType(typ *types.Signature) llvm.Type {
 	// Get the return type.
 	var returnType llvm.Type
 	switch typ.Results().Len() {
@@ -152,11 +125,15 @@ func (c *Compiler) getRawFuncType(typ *types.Signature) llvm.Type {
 			// The receiver is not an interface, but a i8* type.
 			recv = c.i8ptrType
 		}
-		paramTypes = append(paramTypes, c.expandFormalParamType(recv)...)
+		for _, info := range expandFormalParamType(recv, "", nil) {
+			paramTypes = append(paramTypes, info.llvmType)
+		}
 	}
 	for i := 0; i < typ.Params().Len(); i++ {
 		subType := c.getLLVMType(typ.Params().At(i).Type())
-		paramTypes = append(paramTypes, c.expandFormalParamType(subType)...)
+		for _, info := range expandFormalParamType(subType, "", nil) {
+			paramTypes = append(paramTypes, info.llvmType)
+		}
 	}
 	// All functions take these parameters at the end.
 	paramTypes = append(paramTypes, c.i8ptrType) // context
@@ -168,24 +145,24 @@ func (c *Compiler) getRawFuncType(typ *types.Signature) llvm.Type {

 // parseMakeClosure makes a function value (with context) from the given
 // closure expression.
-func (c *Compiler) parseMakeClosure(frame *Frame, expr *ssa.MakeClosure) (llvm.Value, error) {
+func (b *builder) parseMakeClosure(expr *ssa.MakeClosure) (llvm.Value, error) {
 	if len(expr.Bindings) == 0 {
 		panic("unexpected: MakeClosure without bound variables")
 	}
-	f := c.ir.GetFunction(expr.Fn.(*ssa.Function))
+	f := b.ir.GetFunction(expr.Fn.(*ssa.Function))

 	// Collect all bound variables.
 	boundVars := make([]llvm.Value, len(expr.Bindings))
 	for i, binding := range expr.Bindings {
 		// The context stores the bound variables.
-		llvmBoundVar := c.getValue(frame, binding)
+		llvmBoundVar := b.getValue(binding)
 		boundVars[i] = llvmBoundVar
 	}

 	// Store the bound variables in a single object, allocating it on the heap
 	// if necessary.
-	context := c.emitPointerPack(boundVars)
+	context := b.emitPointerPack(boundVars)

 	// Create the closure.
-	return c.createFuncValue(f.LLVMFn, context, f.Signature), nil
+	return b.createFuncValue(f.LLVMFn, context, f.Signature), nil
 }
@@ -12,53 +12,59 @@ import (

 // trackExpr inserts pointer tracking intrinsics for the GC if the expression is
 // one of the expressions that need this.
-func (c *Compiler) trackExpr(frame *Frame, expr ssa.Value, value llvm.Value) {
+func (b *builder) trackExpr(expr ssa.Value, value llvm.Value) {
 	// There are uses of this expression, Make sure the pointers
 	// are tracked during GC.
 	switch expr := expr.(type) {
 	case *ssa.Alloc, *ssa.MakeChan, *ssa.MakeMap:
 		// These values are always of pointer type in IR.
-		c.trackPointer(value)
+		b.trackPointer(value)
 	case *ssa.Call, *ssa.Convert, *ssa.MakeClosure, *ssa.MakeInterface, *ssa.MakeSlice, *ssa.Next:
 		if !value.IsNil() {
-			c.trackValue(value)
+			b.trackValue(value)
 		}
 	case *ssa.Select:
-		if alloca, ok := frame.selectRecvBuf[expr]; ok {
+		if alloca, ok := b.selectRecvBuf[expr]; ok {
 			if alloca.IsAUndefValue().IsNil() {
-				c.trackPointer(alloca)
+				b.trackPointer(alloca)
 			}
 		}
 	case *ssa.UnOp:
 		switch expr.Op {
 		case token.MUL:
 			// Pointer dereference.
-			c.trackValue(value)
+			b.trackValue(value)
 		case token.ARROW:
 			// Channel receive operator.
 			// It's not necessary to look at commaOk here, because in that
 			// case it's just an aggregate and trackValue will extract the
 			// pointer in there (if there is one).
-			c.trackValue(value)
+			b.trackValue(value)
+		}
+	case *ssa.BinOp:
+		switch expr.Op {
+		case token.ADD:
+			// String concatenation.
+			b.trackValue(value)
 		}
 	}
 }

 // trackValue locates pointers in a value (possibly an aggregate) and tracks the
 // individual pointers
-func (c *Compiler) trackValue(value llvm.Value) {
+func (b *builder) trackValue(value llvm.Value) {
 	typ := value.Type()
 	switch typ.TypeKind() {
 	case llvm.PointerTypeKind:
-		c.trackPointer(value)
+		b.trackPointer(value)
 	case llvm.StructTypeKind:
 		if !typeHasPointers(typ) {
 			return
 		}
 		numElements := typ.StructElementTypesCount()
 		for i := 0; i < numElements; i++ {
-			subValue := c.builder.CreateExtractValue(value, i, "")
-			c.trackValue(subValue)
+			subValue := b.CreateExtractValue(value, i, "")
+			b.trackValue(subValue)
 		}
 	case llvm.ArrayTypeKind:
 		if !typeHasPointers(typ) {
@@ -66,19 +72,19 @@ func (c *Compiler) trackValue(value llvm.Value) {
 		}
 		numElements := typ.ArrayLength()
 		for i := 0; i < numElements; i++ {
-			subValue := c.builder.CreateExtractValue(value, i, "")
-			c.trackValue(subValue)
+			subValue := b.CreateExtractValue(value, i, "")
+			b.trackValue(subValue)
 		}
 	}
 }

 // trackPointer creates a call to runtime.trackPointer, bitcasting the poitner
 // first if needed. The input value must be of LLVM pointer type.
-func (c *Compiler) trackPointer(value llvm.Value) {
-	if value.Type() != c.i8ptrType {
-		value = c.builder.CreateBitCast(value, c.i8ptrType, "")
+func (b *builder) trackPointer(value llvm.Value) {
+	if value.Type() != b.i8ptrType {
+		value = b.CreateBitCast(value, b.i8ptrType, "")
 	}
-	c.createRuntimeCall("trackPointer", []llvm.Value{value}, "")
+	b.createRuntimeCall("trackPointer", []llvm.Value{value}, "")
 }

 // typeHasPointers returns whether this type is a pointer or contains pointers.
@@ -3,34 +3,46 @@ package compiler
 // This file implements the 'go' keyword to start a new goroutine. See
 // goroutine-lowering.go for more details.

-import "tinygo.org/x/go-llvm"
+import (
+	"go/token"

-// emitStartGoroutine starts a new goroutine with the provided function pointer
+	"github.com/tinygo-org/tinygo/compiler/llvmutil"
+	"tinygo.org/x/go-llvm"
+)
+
+// createGoInstruction starts a new goroutine with the provided function pointer
 // and parameters.
 // In general, you should pass all regular parameters plus the context parameter.
 // There is one exception: the task-based scheduler needs to have the function
 // pointer passed in as a parameter too in addition to the context.
 //
 // Because a go statement doesn't return anything, return undef.
-func (c *Compiler) emitStartGoroutine(funcPtr llvm.Value, params []llvm.Value) llvm.Value {
-	switch c.Scheduler() {
-	case "tasks":
-		paramBundle := c.emitPointerPack(params)
-		paramBundle = c.builder.CreatePtrToInt(paramBundle, c.uintptrType, "")
-
-		calleeValue := c.createGoroutineStartWrapper(funcPtr)
-		c.createRuntimeCall("startGoroutine", []llvm.Value{calleeValue, paramBundle}, "")
+func (b *builder) createGoInstruction(funcPtr llvm.Value, params []llvm.Value, prefix string, pos token.Pos) llvm.Value {
+	paramBundle := b.emitPointerPack(params)
+	var callee, stackSize llvm.Value
+	switch b.Scheduler() {
+	case "none", "tasks":
+		callee = b.createGoroutineStartWrapper(funcPtr, prefix, pos)
+		if b.AutomaticStackSize() {
+			// The stack size is not known until after linking. Call a dummy
+			// function that will be replaced with a load from a special ELF
+			// section that contains the stack size (and is modified after
+			// linking).
+			stackSize = b.createCall(b.mod.NamedFunction("internal/task.getGoroutineStackSize"), []llvm.Value{callee, llvm.Undef(b.i8ptrType), llvm.Undef(b.i8ptrType)}, "stacksize")
+		} else {
+			// The stack size is fixed at compile time. By emitting it here as a
+			// constant, it can be optimized.
+			stackSize = llvm.ConstInt(b.uintptrType, b.Target.DefaultStackSize, false)
+		}
 	case "coroutines":
-		// We roundtrip through runtime.makeGoroutine as a signal (to find these
-		// calls) and to break any optimizations LLVM will try to do: they are
-		// invalid if we called this as a regular function to be updated later.
-		calleeValue := c.builder.CreatePtrToInt(funcPtr, c.uintptrType, "")
-		calleeValue = c.createRuntimeCall("makeGoroutine", []llvm.Value{calleeValue}, "")
-		calleeValue = c.builder.CreateIntToPtr(calleeValue, funcPtr.Type(), "")
-		c.createCall(calleeValue, append(params, llvm.ConstPointerNull(c.i8ptrType)), "")
+		callee = b.CreatePtrToInt(funcPtr, b.uintptrType, "")
+		// There is no goroutine stack size: coroutines are used instead of
+		// stacks.
+		stackSize = llvm.Undef(b.uintptrType)
 	default:
 		panic("unreachable")
 	}
+	b.createCall(b.mod.NamedFunction("internal/task.start"), []llvm.Value{callee, paramBundle, stackSize, llvm.Undef(b.i8ptrType), llvm.ConstPointerNull(b.i8ptrType)}, "")
 	return llvm.Undef(funcPtr.Type().ElementType().ReturnType())
 }

@@ -52,36 +64,58 @@ func (c *Compiler) emitStartGoroutine(funcPtr llvm.Value, params []llvm.Value) l
 // allows a single (pointer) argument to the newly started goroutine. Also, it
 // ignores the return value because newly started goroutines do not have a
 // return value.
-func (c *Compiler) createGoroutineStartWrapper(fn llvm.Value) llvm.Value {
+func (c *compilerContext) createGoroutineStartWrapper(fn llvm.Value, prefix string, pos token.Pos) llvm.Value {
 	var wrapper llvm.Value

+	builder := c.ctx.NewBuilder()
+	defer builder.Dispose()
+
 	if !fn.IsAFunction().IsNil() {
 		// See whether this wrapper has already been created. If so, return it.
 		name := fn.Name()
 		wrapper = c.mod.NamedFunction(name + "$gowrapper")
 		if !wrapper.IsNil() {
-			return c.builder.CreatePtrToInt(wrapper, c.uintptrType, "")
+			return llvm.ConstPtrToInt(wrapper, c.uintptrType)
 		}

-		// Save the current position in the IR builder.
-		currentBlock := c.builder.GetInsertBlock()
-		defer c.builder.SetInsertPointAtEnd(currentBlock)
-
 		// Create the wrapper.
 		wrapperType := llvm.FunctionType(c.ctx.VoidType(), []llvm.Type{c.i8ptrType}, false)
 		wrapper = llvm.AddFunction(c.mod, name+"$gowrapper", wrapperType)
-		wrapper.SetLinkage(llvm.PrivateLinkage)
+		wrapper.SetLinkage(llvm.InternalLinkage)
 		wrapper.SetUnnamedAddr(true)
+		wrapper.AddAttributeAtIndex(-1, c.ctx.CreateStringAttribute("tinygo-gowrapper", name))
 		entry := c.ctx.AddBasicBlock(wrapper, "entry")
-		c.builder.SetInsertPointAtEnd(entry)
+		builder.SetInsertPointAtEnd(entry)
+
+		if c.Debug() {
+			pos := c.ir.Program.Fset.Position(pos)
+			diFuncType := c.dibuilder.CreateSubroutineType(llvm.DISubroutineType{
+				File:       c.getDIFile(pos.Filename),
+				Parameters: nil, // do not show parameters in debugger
+				Flags:      0,   // ?
+			})
+			difunc := c.dibuilder.CreateFunction(c.getDIFile(pos.Filename), llvm.DIFunction{
+				Name:         "<goroutine wrapper>",
+				File:         c.getDIFile(pos.Filename),
+				Line:         pos.Line,
+				Type:         diFuncType,
+				LocalToUnit:  true,
+				IsDefinition: true,
+				ScopeLine:    0,
+				Flags:        llvm.FlagPrototyped,
+				Optimized:    true,
+			})
+			wrapper.SetSubprogram(difunc)
+			builder.SetCurrentDebugLocation(uint(pos.Line), uint(pos.Column), difunc, llvm.Metadata{})
+		}

 		// Create the list of params for the call.
 		paramTypes := fn.Type().ElementType().ParamTypes()
-		params := c.emitPointerUnpack(wrapper.Param(0), paramTypes[:len(paramTypes)-1])
+		params := llvmutil.EmitPointerUnpack(builder, c.mod, wrapper.Param(0), paramTypes[:len(paramTypes)-1])
 		params = append(params, llvm.Undef(c.i8ptrType))

 		// Create the call.
-		c.builder.CreateCall(fn, params, "")
+		builder.CreateCall(fn, params, "")

 	} else {
 		// For a function pointer like this:
@@ -101,22 +135,41 @@ func (c *Compiler) createGoroutineStartWrapper(fn llvm.Value) llvm.Value {
 		// With a bit of luck, identical wrapper functions like these can be
 		// merged into one.

-		// Save the current position in the IR builder.
-		currentBlock := c.builder.GetInsertBlock()
-		defer c.builder.SetInsertPointAtEnd(currentBlock)
-
 		// Create the wrapper.
 		wrapperType := llvm.FunctionType(c.ctx.VoidType(), []llvm.Type{c.i8ptrType}, false)
-		wrapper = llvm.AddFunction(c.mod, ".gowrapper", wrapperType)
+		wrapper = llvm.AddFunction(c.mod, prefix+".gowrapper", wrapperType)
 		wrapper.SetLinkage(llvm.InternalLinkage)
 		wrapper.SetUnnamedAddr(true)
+		wrapper.AddAttributeAtIndex(-1, c.ctx.CreateStringAttribute("tinygo-gowrapper", ""))
 		entry := c.ctx.AddBasicBlock(wrapper, "entry")
-		c.builder.SetInsertPointAtEnd(entry)
+		builder.SetInsertPointAtEnd(entry)
+
+		if c.Debug() {
+			pos := c.ir.Program.Fset.Position(pos)
+			diFuncType := c.dibuilder.CreateSubroutineType(llvm.DISubroutineType{
+				File:       c.getDIFile(pos.Filename),
+				Parameters: nil, // do not show parameters in debugger
+				Flags:      0,   // ?
+			})
+			difunc := c.dibuilder.CreateFunction(c.getDIFile(pos.Filename), llvm.DIFunction{
+				Name:         "<goroutine wrapper>",
+				File:         c.getDIFile(pos.Filename),
+				Line:         pos.Line,
+				Type:         diFuncType,
+				LocalToUnit:  true,
+				IsDefinition: true,
+				ScopeLine:    0,
+				Flags:        llvm.FlagPrototyped,
+				Optimized:    true,
+			})
+			wrapper.SetSubprogram(difunc)
+			builder.SetCurrentDebugLocation(uint(pos.Line), uint(pos.Column), difunc, llvm.Metadata{})
+		}

 		// Get the list of parameters, with the extra parameters at the end.
 		paramTypes := fn.Type().ElementType().ParamTypes()
 		paramTypes[len(paramTypes)-1] = fn.Type() // the last element is the function pointer
-		params := c.emitPointerUnpack(wrapper.Param(0), paramTypes)
+		params := llvmutil.EmitPointerUnpack(builder, c.mod, wrapper.Param(0), paramTypes)

 		// Get the function pointer.
 		fnPtr := params[len(params)-1]
@@ -126,13 +179,13 @@ func (c *Compiler) createGoroutineStartWrapper(fn llvm.Value) llvm.Value {
 		params[len(params)-1] = llvm.Undef(c.i8ptrType)

 		// Create the call.
-		c.builder.CreateCall(fnPtr, params, "")
+		builder.CreateCall(fnPtr, params, "")
 	}

 	// Finish the function. Every basic block must end in a terminator, and
 	// because goroutines never return a value we can simply return void.
-	c.builder.CreateRetVoid()
+	builder.CreateRetVoid()

 	// Return a ptrtoint of the wrapper, not the function itself.
-	return c.builder.CreatePtrToInt(wrapper, c.uintptrType, "")
+	return builder.CreatePtrToInt(wrapper, c.uintptrType, "")
 }
@@ -13,27 +13,6 @@ import (
 	"tinygo.org/x/go-llvm"
 )

-// This is a compiler builtin, which reads the given register by name:
-//
-//     func ReadRegister(name string) uintptr
-//
-// The register name must be a constant, for example "sp".
-func (c *Compiler) emitReadRegister(name string, args []ssa.Value) (llvm.Value, error) {
-	fnType := llvm.FunctionType(c.uintptrType, []llvm.Type{}, false)
-	regname := constant.StringVal(args[0].(*ssa.Const).Value)
-	var asm string
-	switch name {
-	case "device/arm.ReadRegister":
-		asm = "mov $0, " + regname
-	case "device/riscv.ReadRegister":
-		asm = "mv $0, " + regname
-	default:
-		panic("unknown architecture")
-	}
-	target := llvm.InlineAsm(fnType, asm, "=r", false, false, 0)
-	return c.builder.CreateCall(target, nil, ""), nil
-}
-
 // This is a compiler builtin, which emits a piece of inline assembly with no
 // operands or return values. It is useful for trivial instructions, like wfi in
 // ARM or sleep in AVR.
@@ -41,18 +20,18 @@ func (c *Compiler) emitReadRegister(name string, args []ssa.Value) (llvm.Value,
 //     func Asm(asm string)
 //
 // The provided assembly must be a constant.
-func (c *Compiler) emitAsm(args []ssa.Value) (llvm.Value, error) {
+func (b *builder) createInlineAsm(args []ssa.Value) (llvm.Value, error) {
 	// Magic function: insert inline assembly instead of calling it.
-	fnType := llvm.FunctionType(c.ctx.VoidType(), []llvm.Type{}, false)
+	fnType := llvm.FunctionType(b.ctx.VoidType(), []llvm.Type{}, false)
 	asm := constant.StringVal(args[0].(*ssa.Const).Value)
 	target := llvm.InlineAsm(fnType, asm, "", true, false, 0)
-	return c.builder.CreateCall(target, nil, ""), nil
+	return b.CreateCall(target, nil, ""), nil
 }

 // This is a compiler builtin, which allows assembly to be called in a flexible
 // way.
 //
-//     func AsmFull(asm string, regs map[string]interface{})
+//     func AsmFull(asm string, regs map[string]interface{}) uintptr
 //
 // The asm parameter must be a constant string. The regs parameter must be
 // provided immediately. For example:
@@ -63,27 +42,27 @@ func (c *Compiler) emitAsm(args []ssa.Value) (llvm.Value, error) {
 //             "value":  1
 //             "result": &dest,
 //         })
-func (c *Compiler) emitAsmFull(frame *Frame, instr *ssa.CallCommon) (llvm.Value, error) {
+func (b *builder) createInlineAsmFull(instr *ssa.CallCommon) (llvm.Value, error) {
 	asmString := constant.StringVal(instr.Args[0].(*ssa.Const).Value)
 	registers := map[string]llvm.Value{}
-	registerMap := instr.Args[1].(*ssa.MakeMap)
-	for _, r := range *registerMap.Referrers() {
-		switch r := r.(type) {
-		case *ssa.DebugRef:
-			// ignore
-		case *ssa.MapUpdate:
-			if r.Block() != registerMap.Block() {
-				return llvm.Value{}, c.makeError(instr.Pos(), "register value map must be created in the same basic block")
+	if registerMap, ok := instr.Args[1].(*ssa.MakeMap); ok {
+		for _, r := range *registerMap.Referrers() {
+			switch r := r.(type) {
+			case *ssa.DebugRef:
+				// ignore
+			case *ssa.MapUpdate:
+				if r.Block() != registerMap.Block() {
+					return llvm.Value{}, b.makeError(instr.Pos(), "register value map must be created in the same basic block")
+				}
+				key := constant.StringVal(r.Key.(*ssa.Const).Value)
+				registers[key] = b.getValue(r.Value.(*ssa.MakeInterface).X)
+			case *ssa.Call:
+				if r.Common() == instr {
+					break
+				}
+			default:
+				return llvm.Value{}, b.makeError(instr.Pos(), "don't know how to handle argument to inline assembly: "+r.String())
 			}
-			key := constant.StringVal(r.Key.(*ssa.Const).Value)
-			//println("value:", r.Value.(*ssa.MakeInterface).X.String())
-			registers[key] = c.getValue(frame, r.Value.(*ssa.MakeInterface).X)
-		case *ssa.Call:
-			if r.Common() == instr {
-				break
-			}
-		default:
-			return llvm.Value{}, c.makeError(instr.Pos(), "don't know how to handle argument to inline assembly: "+r.String())
 		}
 	}
 	// TODO: handle dollar signs in asm string
@@ -92,13 +71,22 @@ func (c *Compiler) emitAsmFull(frame *Frame, instr *ssa.CallCommon) (llvm.Value,
 	argTypes := []llvm.Type{}
 	args := []llvm.Value{}
 	constraints := []string{}
+	hasOutput := false
+	asmString = regexp.MustCompile("\\{\\}").ReplaceAllStringFunc(asmString, func(s string) string {
+		hasOutput = true
+		return "$0"
+	})
+	if hasOutput {
+		constraints = append(constraints, "=&r")
+		registerNumbers[""] = 0
+	}
 	asmString = regexp.MustCompile("\\{[a-zA-Z]+\\}").ReplaceAllStringFunc(asmString, func(s string) string {
 		// TODO: skip strings like {r4} etc. that look like ARM push/pop
 		// instructions.
 		name := s[1 : len(s)-1]
 		if _, ok := registers[name]; !ok {
 			if err == nil {
-				err = c.makeError(instr.Pos(), "unknown register name: "+name)
+				err = b.makeError(instr.Pos(), "unknown register name: "+name)
 			}
 			return s
 		}
@@ -112,7 +100,7 @@ func (c *Compiler) emitAsmFull(frame *Frame, instr *ssa.CallCommon) (llvm.Value,
 			case llvm.PointerTypeKind:
 				constraints = append(constraints, "*m")
 			default:
-				err = c.makeError(instr.Pos(), "unknown type in inline assembly for value: "+name)
+				err = b.makeError(instr.Pos(), "unknown type in inline assembly for value: "+name)
 				return s
 			}
 		}
@@ -121,9 +109,21 @@ func (c *Compiler) emitAsmFull(frame *Frame, instr *ssa.CallCommon) (llvm.Value,
 	if err != nil {
 		return llvm.Value{}, err
 	}
-	fnType := llvm.FunctionType(c.ctx.VoidType(), argTypes, false)
+	var outputType llvm.Type
+	if hasOutput {
+		outputType = b.uintptrType
+	} else {
+		outputType = b.ctx.VoidType()
+	}
+	fnType := llvm.FunctionType(outputType, argTypes, false)
 	target := llvm.InlineAsm(fnType, asmString, strings.Join(constraints, ","), true, false, 0)
-	return c.builder.CreateCall(target, args, ""), nil
+	result := b.CreateCall(target, args, "")
+	if hasOutput {
+		return result, nil
+	} else {
+		// Make sure we return something valid.
+		return llvm.ConstInt(b.uintptrType, 0, false), nil
+	}
 }

 // This is a compiler builtin which emits an inline SVCall instruction. It can
@@ -137,7 +137,7 @@ func (c *Compiler) emitAsmFull(frame *Frame, instr *ssa.CallCommon) (llvm.Value,
 //
 // The num parameter must be a constant. All other parameters may be any scalar
 // value supported by LLVM inline assembly.
-func (c *Compiler) emitSVCall(frame *Frame, args []ssa.Value) (llvm.Value, error) {
+func (b *builder) emitSVCall(args []ssa.Value) (llvm.Value, error) {
 	num, _ := constant.Uint64Val(args[0].(*ssa.Const).Value)
 	llvmArgs := []llvm.Value{}
 	argTypes := []llvm.Type{}
@@ -150,7 +150,7 @@ func (c *Compiler) emitSVCall(frame *Frame, args []ssa.Value) (llvm.Value, error
 		} else {
 			constraints += ",{r" + strconv.Itoa(i) + "}"
 		}
-		llvmValue := c.getValue(frame, arg)
+		llvmValue := b.getValue(arg)
 		llvmArgs = append(llvmArgs, llvmValue)
 		argTypes = append(argTypes, llvmValue.Type())
 	}
@@ -158,7 +158,52 @@ func (c *Compiler) emitSVCall(frame *Frame, args []ssa.Value) (llvm.Value, error
 	// clobbered. r0 is used as an output register so doesn't have to be
 	// marked as clobbered.
 	constraints += ",~{r1},~{r2},~{r3}"
-	fnType := llvm.FunctionType(c.uintptrType, argTypes, false)
+	fnType := llvm.FunctionType(b.uintptrType, argTypes, false)
 	target := llvm.InlineAsm(fnType, asm, constraints, true, false, 0)
-	return c.builder.CreateCall(target, llvmArgs, ""), nil
+	return b.CreateCall(target, llvmArgs, ""), nil
+}
+
+// This is a compiler builtin which emits CSR instructions. It can be one of:
+//
+//     func (csr CSR) Get() uintptr
+//     func (csr CSR) Set(uintptr)
+//     func (csr CSR) SetBits(uintptr) uintptr
+//     func (csr CSR) ClearBits(uintptr) uintptr
+//
+// The csr parameter (method receiver) must be a constant. Other parameter can
+// be any value.
+func (b *builder) emitCSROperation(call *ssa.CallCommon) (llvm.Value, error) {
+	csrConst, ok := call.Args[0].(*ssa.Const)
+	if !ok {
+		return llvm.Value{}, b.makeError(call.Pos(), "CSR must be constant")
+	}
+	csr := csrConst.Uint64()
+	switch name := call.StaticCallee().Name(); name {
+	case "Get":
+		// Note that this instruction may have side effects, and thus must be
+		// marked as such.
+		fnType := llvm.FunctionType(b.uintptrType, nil, false)
+		asm := fmt.Sprintf("csrr $0, %d", csr)
+		target := llvm.InlineAsm(fnType, asm, "=r", true, false, 0)
+		return b.CreateCall(target, nil, ""), nil
+	case "Set":
+		fnType := llvm.FunctionType(b.ctx.VoidType(), []llvm.Type{b.uintptrType}, false)
+		asm := fmt.Sprintf("csrw %d, $0", csr)
+		target := llvm.InlineAsm(fnType, asm, "r", true, false, 0)
+		return b.CreateCall(target, []llvm.Value{b.getValue(call.Args[1])}, ""), nil
+	case "SetBits":
+		// Note: it may be possible to optimize this to csrrsi in many cases.
+		fnType := llvm.FunctionType(b.uintptrType, []llvm.Type{b.uintptrType}, false)
+		asm := fmt.Sprintf("csrrs $0, %d, $1", csr)
+		target := llvm.InlineAsm(fnType, asm, "=r,r", true, false, 0)
+		return b.CreateCall(target, []llvm.Value{b.getValue(call.Args[1])}, ""), nil
+	case "ClearBits":
+		// Note: it may be possible to optimize this to csrrci in many cases.
+		fnType := llvm.FunctionType(b.uintptrType, []llvm.Type{b.uintptrType}, false)
+		asm := fmt.Sprintf("csrrc $0, %d, $1", csr)
+		target := llvm.InlineAsm(fnType, asm, "=r,r", true, false, 0)
+		return b.CreateCall(target, []llvm.Value{b.getValue(call.Args[1])}, ""), nil
+	default:
+		return llvm.Value{}, b.makeError(call.Pos(), "unknown CSR operation: "+name)
+	}
 }
@@ -16,35 +16,35 @@ import (
 	"tinygo.org/x/go-llvm"
 )

-// parseMakeInterface emits the LLVM IR for the *ssa.MakeInterface instruction.
+// createMakeInterface emits the LLVM IR for the *ssa.MakeInterface instruction.
 // It tries to put the type in the interface value, but if that's not possible,
 // it will do an allocation of the right size and put that in the interface
 // value field.
 //
-// An interface value is a {typecode, value} tuple, or {i16, i8*} to be exact.
-func (c *Compiler) parseMakeInterface(val llvm.Value, typ types.Type, pos token.Pos) llvm.Value {
-	itfValue := c.emitPointerPack([]llvm.Value{val})
-	itfTypeCodeGlobal := c.getTypeCode(typ)
-	itfMethodSetGlobal := c.getTypeMethodSet(typ)
-	itfConcreteTypeGlobal := c.mod.NamedGlobal("typeInInterface:" + itfTypeCodeGlobal.Name())
+// An interface value is a {typecode, value} tuple named runtime._interface.
+func (b *builder) createMakeInterface(val llvm.Value, typ types.Type, pos token.Pos) llvm.Value {
+	itfValue := b.emitPointerPack([]llvm.Value{val})
+	itfTypeCodeGlobal := b.getTypeCode(typ)
+	itfMethodSetGlobal := b.getTypeMethodSet(typ)
+	itfConcreteTypeGlobal := b.mod.NamedGlobal("typeInInterface:" + itfTypeCodeGlobal.Name())
 	if itfConcreteTypeGlobal.IsNil() {
-		typeInInterface := c.getLLVMRuntimeType("typeInInterface")
-		itfConcreteTypeGlobal = llvm.AddGlobal(c.mod, typeInInterface, "typeInInterface:"+itfTypeCodeGlobal.Name())
+		typeInInterface := b.getLLVMRuntimeType("typeInInterface")
+		itfConcreteTypeGlobal = llvm.AddGlobal(b.mod, typeInInterface, "typeInInterface:"+itfTypeCodeGlobal.Name())
 		itfConcreteTypeGlobal.SetInitializer(llvm.ConstNamedStruct(typeInInterface, []llvm.Value{itfTypeCodeGlobal, itfMethodSetGlobal}))
 		itfConcreteTypeGlobal.SetGlobalConstant(true)
 		itfConcreteTypeGlobal.SetLinkage(llvm.PrivateLinkage)
 	}
-	itfTypeCode := c.builder.CreatePtrToInt(itfConcreteTypeGlobal, c.uintptrType, "")
-	itf := llvm.Undef(c.getLLVMRuntimeType("_interface"))
-	itf = c.builder.CreateInsertValue(itf, itfTypeCode, 0, "")
-	itf = c.builder.CreateInsertValue(itf, itfValue, 1, "")
+	itfTypeCode := b.CreatePtrToInt(itfConcreteTypeGlobal, b.uintptrType, "")
+	itf := llvm.Undef(b.getLLVMRuntimeType("_interface"))
+	itf = b.CreateInsertValue(itf, itfTypeCode, 0, "")
+	itf = b.CreateInsertValue(itf, itfValue, 1, "")
 	return itf
 }

 // getTypeCode returns a reference to a type code.
 // It returns a pointer to an external global which should be replaced with the
 // real type in the interface lowering pass.
-func (c *Compiler) getTypeCode(typ types.Type) llvm.Value {
+func (c *compilerContext) getTypeCode(typ types.Type) llvm.Value {
 	globalName := "reflect/types.type:" + getTypeCodeName(typ)
 	global := c.mod.NamedGlobal(globalName)
 	if global.IsNil() {
@@ -91,7 +91,7 @@ func (c *Compiler) getTypeCode(typ types.Type) llvm.Value {
 // makeStructTypeFields creates a new global that stores all type information
 // related to this struct type, and returns the resulting global. This global is
 // actually an array of all the fields in the structs.
-func (c *Compiler) makeStructTypeFields(typ *types.Struct) llvm.Value {
+func (c *compilerContext) makeStructTypeFields(typ *types.Struct) llvm.Value {
 	// The global is an array of runtime.structField structs.
 	runtimeStructField := c.getLLVMRuntimeType("structField")
 	structGlobalType := llvm.ArrayType(runtimeStructField, typ.NumFields())
@@ -228,7 +228,7 @@ func getTypeCodeName(t types.Type) string {

 // getTypeMethodSet returns a reference (GEP) to a global method set. This
 // method set should be unreferenced after the interface lowering pass.
-func (c *Compiler) getTypeMethodSet(typ types.Type) llvm.Value {
+func (c *compilerContext) getTypeMethodSet(typ types.Type) llvm.Value {
 	global := c.mod.NamedGlobal(typ.String() + "$methodset")
 	zero := llvm.ConstInt(c.ctx.Int32Type(), 0, false)
 	if !global.IsNil() {
@@ -271,8 +271,13 @@ func (c *Compiler) getTypeMethodSet(typ types.Type) llvm.Value {
 // getInterfaceMethodSet returns a global variable with the method set of the
 // given named interface type. This method set is used by the interface lowering
 // pass.
-func (c *Compiler) getInterfaceMethodSet(typ *types.Named) llvm.Value {
-	global := c.mod.NamedGlobal(typ.String() + "$interface")
+func (c *compilerContext) getInterfaceMethodSet(typ types.Type) llvm.Value {
+	name := typ.String()
+	if _, ok := typ.(*types.Named); !ok {
+		// Anonymous interface.
+		name = "reflect/types.interface:" + name
+	}
+	global := c.mod.NamedGlobal(name + "$interface")
 	zero := llvm.ConstInt(c.ctx.Int32Type(), 0, false)
 	if !global.IsNil() {
 		// method set already exist, return it
@@ -287,7 +292,7 @@ func (c *Compiler) getInterfaceMethodSet(typ *types.Named) llvm.Value {
 	}

 	value := llvm.ConstArray(c.i8ptrType, methods)
-	global = llvm.AddGlobal(c.mod, value.Type(), typ.String()+"$interface")
+	global = llvm.AddGlobal(c.mod, value.Type(), name+"$interface")
 	global.SetInitializer(value)
 	global.SetGlobalConstant(true)
 	global.SetLinkage(llvm.PrivateLinkage)
@@ -297,7 +302,7 @@ func (c *Compiler) getInterfaceMethodSet(typ *types.Named) llvm.Value {
 // getMethodSignature returns a global variable which is a reference to an
 // external *i8 indicating the indicating the signature of this method. It is
 // used during the interface lowering pass.
-func (c *Compiler) getMethodSignature(method *types.Func) llvm.Value {
+func (c *compilerContext) getMethodSignature(method *types.Func) llvm.Value {
 	signature := ir.MethodSignature(method)
 	signatureGlobal := c.mod.NamedGlobal("func " + signature)
 	if signatureGlobal.IsNil() {
@@ -307,18 +312,18 @@ func (c *Compiler) getMethodSignature(method *types.Func) llvm.Value {
 	return signatureGlobal
 }

-// parseTypeAssert will emit the code for a typeassert, used in if statements
+// createTypeAssert will emit the code for a typeassert, used in if statements
 // and in type switches (Go SSA does not have type switches, only if/else
 // chains). Note that even though the Go SSA does not contain type switches,
 // LLVM will recognize the pattern and make it a real switch in many cases.
 //
 // Type asserts on concrete types are trivial: just compare type numbers. Type
 // asserts on interfaces are more difficult, see the comments in the function.
-func (c *Compiler) parseTypeAssert(frame *Frame, expr *ssa.TypeAssert) llvm.Value {
-	itf := c.getValue(frame, expr.X)
-	assertedType := c.getLLVMType(expr.AssertedType)
+func (b *builder) createTypeAssert(expr *ssa.TypeAssert) llvm.Value {
+	itf := b.getValue(expr.X)
+	assertedType := b.getLLVMType(expr.AssertedType)

-	actualTypeNum := c.builder.CreateExtractValue(itf, 0, "interface.type")
+	actualTypeNum := b.CreateExtractValue(itf, 0, "interface.type")
 	commaOk := llvm.Value{}
 	if _, ok := expr.AssertedType.Underlying().(*types.Interface); ok {
 		// Type assert on interface type.
@@ -329,15 +334,15 @@ func (c *Compiler) parseTypeAssert(frame *Frame, expr *ssa.TypeAssert) llvm.Valu
 		// the main Go compiler, where the runtime checks whether the type
 		// implements each method of the interface. See:
 		// https://research.swtch.com/interfaces
-		methodSet := c.getInterfaceMethodSet(expr.AssertedType.(*types.Named))
-		commaOk = c.createRuntimeCall("interfaceImplements", []llvm.Value{actualTypeNum, methodSet}, "")
+		methodSet := b.getInterfaceMethodSet(expr.AssertedType)
+		commaOk = b.createRuntimeCall("interfaceImplements", []llvm.Value{actualTypeNum, methodSet}, "")

 	} else {
 		// Type assert on concrete type.
 		// Call runtime.typeAssert, which will be lowered to a simple icmp or
 		// const false in the interface lowering pass.
-		assertedTypeCodeGlobal := c.getTypeCode(expr.AssertedType)
-		commaOk = c.createRuntimeCall("typeAssert", []llvm.Value{actualTypeNum, assertedTypeCodeGlobal}, "typecode")
+		assertedTypeCodeGlobal := b.getTypeCode(expr.AssertedType)
+		commaOk = b.createRuntimeCall("typeAssert", []llvm.Value{actualTypeNum, assertedTypeCodeGlobal}, "typecode")
 	}

 	// Add 2 new basic blocks (that should get optimized away): one for the
@@ -351,15 +356,15 @@ func (c *Compiler) parseTypeAssert(frame *Frame, expr *ssa.TypeAssert) llvm.Valu
 	// typeassert should return a zero value, not an incorrectly casted
 	// value.

-	prevBlock := c.builder.GetInsertBlock()
-	okBlock := c.ctx.AddBasicBlock(frame.fn.LLVMFn, "typeassert.ok")
-	nextBlock := c.ctx.AddBasicBlock(frame.fn.LLVMFn, "typeassert.next")
-	frame.blockExits[frame.currentBlock] = nextBlock // adjust outgoing block for phi nodes
-	c.builder.CreateCondBr(commaOk, okBlock, nextBlock)
+	prevBlock := b.GetInsertBlock()
+	okBlock := b.ctx.AddBasicBlock(b.fn.LLVMFn, "typeassert.ok")
+	nextBlock := b.ctx.AddBasicBlock(b.fn.LLVMFn, "typeassert.next")
+	b.blockExits[b.currentBlock] = nextBlock // adjust outgoing block for phi nodes
+	b.CreateCondBr(commaOk, okBlock, nextBlock)

 	// Retrieve the value from the interface if the type assert was
 	// successful.
-	c.builder.SetInsertPointAtEnd(okBlock)
+	b.SetInsertPointAtEnd(okBlock)
 	var valueOk llvm.Value
 	if _, ok := expr.AssertedType.Underlying().(*types.Interface); ok {
 		// Type assert on interface type. Easy: just return the same
@@ -368,74 +373,70 @@ func (c *Compiler) parseTypeAssert(frame *Frame, expr *ssa.TypeAssert) llvm.Valu
 	} else {
 		// Type assert on concrete type. Extract the underlying type from
 		// the interface (but only after checking it matches).
-		valuePtr := c.builder.CreateExtractValue(itf, 1, "typeassert.value.ptr")
-		valueOk = c.emitPointerUnpack(valuePtr, []llvm.Type{assertedType})[0]
+		valuePtr := b.CreateExtractValue(itf, 1, "typeassert.value.ptr")
+		valueOk = b.emitPointerUnpack(valuePtr, []llvm.Type{assertedType})[0]
 	}
-	c.builder.CreateBr(nextBlock)
+	b.CreateBr(nextBlock)

 	// Continue after the if statement.
-	c.builder.SetInsertPointAtEnd(nextBlock)
-	phi := c.builder.CreatePHI(assertedType, "typeassert.value")
+	b.SetInsertPointAtEnd(nextBlock)
+	phi := b.CreatePHI(assertedType, "typeassert.value")
 	phi.AddIncoming([]llvm.Value{llvm.ConstNull(assertedType), valueOk}, []llvm.BasicBlock{prevBlock, okBlock})

 	if expr.CommaOk {
-		tuple := c.ctx.ConstStruct([]llvm.Value{llvm.Undef(assertedType), llvm.Undef(c.ctx.Int1Type())}, false) // create empty tuple
-		tuple = c.builder.CreateInsertValue(tuple, phi, 0, "")                                                  // insert value
-		tuple = c.builder.CreateInsertValue(tuple, commaOk, 1, "")                                              // insert 'comma ok' boolean
+		tuple := b.ctx.ConstStruct([]llvm.Value{llvm.Undef(assertedType), llvm.Undef(b.ctx.Int1Type())}, false) // create empty tuple
+		tuple = b.CreateInsertValue(tuple, phi, 0, "")                                                          // insert value
+		tuple = b.CreateInsertValue(tuple, commaOk, 1, "")                                                      // insert 'comma ok' boolean
 		return tuple
 	} else {
 		// This is kind of dirty as the branch above becomes mostly useless,
 		// but hopefully this gets optimized away.
-		c.createRuntimeCall("interfaceTypeAssert", []llvm.Value{commaOk}, "")
+		b.createRuntimeCall("interfaceTypeAssert", []llvm.Value{commaOk}, "")
 		return phi
 	}
 }

-// getInvokeCall creates and returns the function pointer and parameters of an
-// interface call. It can be used in a call or defer instruction.
-func (c *Compiler) getInvokeCall(frame *Frame, instr *ssa.CallCommon) (llvm.Value, []llvm.Value) {
-	// Call an interface method with dynamic dispatch.
-	itf := c.getValue(frame, instr.Value) // interface
-
-	llvmFnType := c.getRawFuncType(instr.Method.Type().(*types.Signature))
-
-	typecode := c.builder.CreateExtractValue(itf, 0, "invoke.typecode")
+// getInvokePtr creates an interface function pointer lookup for the specified invoke instruction, using a specified typecode.
+func (b *builder) getInvokePtr(instr *ssa.CallCommon, typecode llvm.Value) llvm.Value {
+	llvmFnType := b.getRawFuncType(instr.Method.Type().(*types.Signature))
 	values := []llvm.Value{
 		typecode,
-		c.getInterfaceMethodSet(instr.Value.Type().(*types.Named)),
-		c.getMethodSignature(instr.Method),
+		b.getInterfaceMethodSet(instr.Value.Type()),
+		b.getMethodSignature(instr.Method),
 	}
-	fn := c.createRuntimeCall("interfaceMethod", values, "invoke.func")
-	fnCast := c.builder.CreateIntToPtr(fn, llvmFnType, "invoke.func.cast")
-	receiverValue := c.builder.CreateExtractValue(itf, 1, "invoke.func.receiver")
+	fn := b.createRuntimeCall("interfaceMethod", values, "invoke.func")
+	return b.CreateIntToPtr(fn, llvmFnType, "invoke.func.cast")
+}
+
+// getInvokeCall creates and returns the function pointer and parameters of an
+// interface call.
+func (b *builder) getInvokeCall(instr *ssa.CallCommon) (llvm.Value, []llvm.Value) {
+	// Call an interface method with dynamic dispatch.
+	itf := b.getValue(instr.Value) // interface
+
+	typecode := b.CreateExtractValue(itf, 0, "invoke.typecode")
+	fnCast := b.getInvokePtr(instr, typecode)
+	receiverValue := b.CreateExtractValue(itf, 1, "invoke.func.receiver")

 	args := []llvm.Value{receiverValue}
 	for _, arg := range instr.Args {
-		args = append(args, c.getValue(frame, arg))
+		args = append(args, b.getValue(arg))
 	}
 	// Add the context parameter. An interface call never takes a context but we
 	// have to supply the parameter anyway.
-	args = append(args, llvm.Undef(c.i8ptrType))
+	args = append(args, llvm.Undef(b.i8ptrType))
 	// Add the parent goroutine handle.
-	args = append(args, llvm.Undef(c.i8ptrType))
+	args = append(args, llvm.Undef(b.i8ptrType))

 	return fnCast, args
 }

-// interfaceInvokeWrapper keeps some state between getInterfaceInvokeWrapper and
-// createInterfaceInvokeWrapper. The former is called during IR construction
-// itself and the latter is called when finishing up the IR.
-type interfaceInvokeWrapper struct {
-	fn           *ir.Function
-	wrapper      llvm.Value
-	receiverType llvm.Type
-}
-
-// Wrap an interface method function pointer. The wrapper takes in a pointer to
-// the underlying value, dereferences it, and calls the real method. This
-// wrapper is only needed when the interface value actually doesn't fit in a
-// pointer and a pointer to the value must be created.
-func (c *Compiler) getInterfaceInvokeWrapper(f *ir.Function) llvm.Value {
+// getInterfaceInvokeWrapper returns a wrapper for the given method so it can be
+// invoked from an interface. The wrapper takes in a pointer to the underlying
+// value, dereferences or unpacks it if necessary, and calls the real method.
+// If the method to wrap has a pointer receiver, no wrapping is necessary and
+// the function is returned directly.
+func (c *compilerContext) getInterfaceInvokeWrapper(f *ir.Function) llvm.Value {
 	wrapperName := f.LinkName() + "$invoke"
 	wrapper := c.mod.NamedFunction(wrapperName)
 	if !wrapper.IsNil() {
@@ -445,7 +446,10 @@ func (c *Compiler) getInterfaceInvokeWrapper(f *ir.Function) llvm.Value {

 	// Get the expanded receiver type.
 	receiverType := c.getLLVMType(f.Params[0].Type())
-	expandedReceiverType := c.expandFormalParamType(receiverType)
+	var expandedReceiverType []llvm.Type
+	for _, info := range expandFormalParamType(receiverType, "", nil) {
+		expandedReceiverType = append(expandedReceiverType, info.llvmType)
+	}

 	// Does this method even need any wrapping?
 	if len(expandedReceiverType) == 1 && receiverType.TypeKind() == llvm.PointerTypeKind {
@@ -464,41 +468,37 @@ func (c *Compiler) getInterfaceInvokeWrapper(f *ir.Function) llvm.Value {
 	if f.LLVMFn.LastParam().Name() == "parentHandle" {
 		wrapper.LastParam().SetName("parentHandle")
 	}
-	c.interfaceInvokeWrappers = append(c.interfaceInvokeWrappers, interfaceInvokeWrapper{
-		fn:           f,
-		wrapper:      wrapper,
-		receiverType: receiverType,
-	})
-	return wrapper
-}

-// createInterfaceInvokeWrapper finishes the work of getInterfaceInvokeWrapper,
-// see that function for details.
-func (c *Compiler) createInterfaceInvokeWrapper(state interfaceInvokeWrapper) {
-	wrapper := state.wrapper
-	fn := state.fn
-	receiverType := state.receiverType
 	wrapper.SetLinkage(llvm.InternalLinkage)
 	wrapper.SetUnnamedAddr(true)

+	// Create a new builder just to create this wrapper.
+	b := builder{
+		compilerContext: c,
+		Builder:         c.ctx.NewBuilder(),
+	}
+	defer b.Builder.Dispose()
+
 	// add debug info if needed
 	if c.Debug() {
-		pos := c.ir.Program.Fset.Position(fn.Pos())
-		difunc := c.attachDebugInfoRaw(fn, wrapper, "$invoke", pos.Filename, pos.Line)
-		c.builder.SetCurrentDebugLocation(uint(pos.Line), uint(pos.Column), difunc, llvm.Metadata{})
+		pos := c.ir.Program.Fset.Position(f.Pos())
+		difunc := c.attachDebugInfoRaw(f, wrapper, "$invoke", pos.Filename, pos.Line)
+		b.SetCurrentDebugLocation(uint(pos.Line), uint(pos.Column), difunc, llvm.Metadata{})
 	}

 	// set up IR builder
-	block := c.ctx.AddBasicBlock(wrapper, "entry")
-	c.builder.SetInsertPointAtEnd(block)
+	block := b.ctx.AddBasicBlock(wrapper, "entry")
+	b.SetInsertPointAtEnd(block)

-	receiverValue := c.emitPointerUnpack(wrapper.Param(0), []llvm.Type{receiverType})[0]
-	params := append(c.expandFormalParam(receiverValue), wrapper.Params()[1:]...)
-	if fn.LLVMFn.Type().ElementType().ReturnType().TypeKind() == llvm.VoidTypeKind {
-		c.builder.CreateCall(fn.LLVMFn, params, "")
-		c.builder.CreateRetVoid()
+	receiverValue := b.emitPointerUnpack(wrapper.Param(0), []llvm.Type{receiverType})[0]
+	params := append(b.expandFormalParam(receiverValue), wrapper.Params()[1:]...)
+	if f.LLVMFn.Type().ElementType().ReturnType().TypeKind() == llvm.VoidTypeKind {
+		b.CreateCall(f.LLVMFn, params, "")
+		b.CreateRetVoid()
 	} else {
-		ret := c.builder.CreateCall(fn.LLVMFn, params, "ret")
-		c.builder.CreateRet(ret)
+		ret := b.CreateCall(f.LLVMFn, params, "ret")
+		b.CreateRet(ret)
 	}
+
+	return wrapper
 }
@@ -0,0 +1,92 @@
+package compiler
+
+import (
+	"strconv"
+	"strings"
+
+	"golang.org/x/tools/go/ssa"
+	"tinygo.org/x/go-llvm"
+)
+
+// createInterruptGlobal creates a new runtime/interrupt.Interrupt struct that
+// will be lowered to a real interrupt during interrupt lowering.
+//
+// This two-stage approach allows unused interrupts to be optimized away if
+// necessary.
+func (b *builder) createInterruptGlobal(instr *ssa.CallCommon) (llvm.Value, error) {
+	// Get the interrupt number, which must be a compile-time constant.
+	id, ok := instr.Args[0].(*ssa.Const)
+	if !ok {
+		return llvm.Value{}, b.makeError(instr.Pos(), "interrupt ID is not a constant")
+	}
+
+	// Get the func value, which also must be a compile time constant.
+	// Note that bound functions are allowed if the function has a pointer
+	// receiver and is a global. This is rather strict but still allows for
+	// idiomatic Go code.
+	funcValue := b.getValue(instr.Args[1])
+	if funcValue.IsAConstant().IsNil() {
+		// Try to determine the cause of the non-constantness for a nice error
+		// message.
+		switch instr.Args[1].(type) {
+		case *ssa.MakeClosure:
+			// This may also be a bound method.
+			return llvm.Value{}, b.makeError(instr.Pos(), "closures are not supported in interrupt.New")
+		}
+		// Fall back to a generic error.
+		return llvm.Value{}, b.makeError(instr.Pos(), "interrupt function must be constant")
+	}
+
+	// Create a new global of type runtime/interrupt.handle. Globals of this
+	// type are lowered in the interrupt lowering pass.
+	globalType := b.ir.Program.ImportedPackage("runtime/interrupt").Type("handle").Type()
+	globalLLVMType := b.getLLVMType(globalType)
+	globalName := "runtime/interrupt.$interrupt" + strconv.FormatInt(id.Int64(), 10)
+	if global := b.mod.NamedGlobal(globalName); !global.IsNil() {
+		return llvm.Value{}, b.makeError(instr.Pos(), "interrupt redeclared in this program")
+	}
+	global := llvm.AddGlobal(b.mod, globalLLVMType, globalName)
+	global.SetLinkage(llvm.PrivateLinkage)
+	global.SetGlobalConstant(true)
+	global.SetUnnamedAddr(true)
+	initializer := llvm.ConstNull(globalLLVMType)
+	initializer = llvm.ConstInsertValue(initializer, funcValue, []uint32{0})
+	initializer = llvm.ConstInsertValue(initializer, llvm.ConstInt(b.intType, uint64(id.Int64()), true), []uint32{1, 0})
+	global.SetInitializer(initializer)
+
+	// Add debug info to the interrupt global.
+	if b.Debug() {
+		pos := b.ir.Program.Fset.Position(instr.Pos())
+		diglobal := b.dibuilder.CreateGlobalVariableExpression(b.getDIFile(pos.Filename), llvm.DIGlobalVariableExpression{
+			Name:        "interrupt" + strconv.FormatInt(id.Int64(), 10),
+			LinkageName: globalName,
+			File:        b.getDIFile(pos.Filename),
+			Line:        pos.Line,
+			Type:        b.getDIType(globalType),
+			Expr:        b.dibuilder.CreateExpression(nil),
+			LocalToUnit: false,
+		})
+		global.AddMetadata(0, diglobal)
+	}
+
+	// Create the runtime/interrupt.Interrupt type. It is a struct with a single
+	// member of type int.
+	num := llvm.ConstPtrToInt(global, b.intType)
+	interrupt := llvm.ConstNamedStruct(b.mod.GetTypeByName("runtime/interrupt.Interrupt"), []llvm.Value{num})
+
+	// Add dummy "use" call for AVR, because interrupts may be used even though
+	// they are never referenced again. This is unlike Cortex-M or the RISC-V
+	// PLIC where each interrupt must be enabled using the interrupt number, and
+	// thus keeps the Interrupt object alive.
+	// This call is removed during interrupt lowering.
+	if strings.HasPrefix(b.Triple(), "avr") {
+		useFn := b.mod.NamedFunction("runtime/interrupt.use")
+		if useFn.IsNil() {
+			useFnType := llvm.FunctionType(b.ctx.VoidType(), []llvm.Type{interrupt.Type()}, false)
+			useFn = llvm.AddFunction(b.mod, "runtime/interrupt.use", useFnType)
+		}
+		b.CreateCall(useFn, []llvm.Value{interrupt}, "")
+	}
+
+	return interrupt, nil
+}
@@ -0,0 +1,50 @@
+package compiler
+
+// This file contains helper functions to create calls to LLVM intrinsics.
+
+import (
+	"strconv"
+
+	"golang.org/x/tools/go/ssa"
+	"tinygo.org/x/go-llvm"
+)
+
+// createMemoryCopyCall creates a call to a builtin LLVM memcpy or memmove
+// function, declaring this function if needed. These calls are treated
+// specially by optimization passes possibly resulting in better generated code,
+// and will otherwise be lowered to regular libc memcpy/memmove calls.
+func (b *builder) createMemoryCopyCall(fn *ssa.Function, args []ssa.Value) (llvm.Value, error) {
+	fnName := "llvm." + fn.Name() + ".p0i8.p0i8.i" + strconv.Itoa(b.uintptrType.IntTypeWidth())
+	llvmFn := b.mod.NamedFunction(fnName)
+	if llvmFn.IsNil() {
+		fnType := llvm.FunctionType(b.ctx.VoidType(), []llvm.Type{b.i8ptrType, b.i8ptrType, b.uintptrType, b.ctx.Int1Type()}, false)
+		llvmFn = llvm.AddFunction(b.mod, fnName, fnType)
+	}
+	var params []llvm.Value
+	for _, param := range args {
+		params = append(params, b.getValue(param))
+	}
+	params = append(params, llvm.ConstInt(b.ctx.Int1Type(), 0, false))
+	b.CreateCall(llvmFn, params, "")
+	return llvm.Value{}, nil
+}
+
+// createMemoryZeroCall creates calls to llvm.memset.* to zero a block of
+// memory, declaring the function if needed. These calls will be lowered to
+// regular libc memset calls if they aren't optimized out in a different way.
+func (b *builder) createMemoryZeroCall(args []ssa.Value) (llvm.Value, error) {
+	fnName := "llvm.memset.p0i8.i" + strconv.Itoa(b.uintptrType.IntTypeWidth())
+	llvmFn := b.mod.NamedFunction(fnName)
+	if llvmFn.IsNil() {
+		fnType := llvm.FunctionType(b.ctx.VoidType(), []llvm.Type{b.i8ptrType, b.ctx.Int8Type(), b.uintptrType, b.ctx.Int1Type()}, false)
+		llvmFn = llvm.AddFunction(b.mod, fnName, fnType)
+	}
+	params := []llvm.Value{
+		b.getValue(args[0]),
+		llvm.ConstInt(b.ctx.Int8Type(), 0, false),
+		b.getValue(args[1]),
+		llvm.ConstInt(b.ctx.Int1Type(), 0, false),
+	}
+	b.CreateCall(llvmFn, params, "")
+	return llvm.Value{}, nil
+}
@@ -1,7 +1,8 @@
-package compiler
-
-// This file implements a set of sanity checks for the IR that is generated.
-// It can catch some mistakes that LLVM's verifier cannot.
+// Package ircheck implements a checker for LLVM IR, that goes a bit further
+// than the regular LLVM IR verifier. Note that it checks different things, so
+// this is not a replacement for the LLVM verifier but does catch things that
+// the LLVM verifier doesn't catch.
+package ircheck

 import (
 	"errors"
@@ -10,7 +11,11 @@ import (
 	"tinygo.org/x/go-llvm"
 )

-func (c *Compiler) checkType(t llvm.Type, checked map[llvm.Type]struct{}, specials map[llvm.TypeKind]llvm.Type) error {
+type checker struct {
+	ctx llvm.Context
+}
+
+func (c *checker) checkType(t llvm.Type, checked map[llvm.Type]struct{}, specials map[llvm.TypeKind]llvm.Type) error {
 	// prevent infinite recursion for self-referential types
 	if _, ok := checked[t]; ok {
 		return nil
@@ -81,7 +86,7 @@ func (c *Compiler) checkType(t llvm.Type, checked map[llvm.Type]struct{}, specia
 	return nil
 }

-func (c *Compiler) checkValue(v llvm.Value, types map[llvm.Type]struct{}, specials map[llvm.TypeKind]llvm.Type) error {
+func (c *checker) checkValue(v llvm.Value, types map[llvm.Type]struct{}, specials map[llvm.TypeKind]llvm.Type) error {
 	// check type
 	if err := c.checkType(v.Type(), types, specials); err != nil {
 		return fmt.Errorf("failed to verify type of value: %s", err.Error())
@@ -95,12 +100,30 @@ func (c *Compiler) checkValue(v llvm.Value, types map[llvm.Type]struct{}, specia
 	return nil
 }

-func (c *Compiler) checkInstruction(inst llvm.Value, types map[llvm.Type]struct{}, specials map[llvm.TypeKind]llvm.Type) error {
+func (c *checker) checkInstruction(inst llvm.Value, types map[llvm.Type]struct{}, specials map[llvm.TypeKind]llvm.Type) error {
 	// check value properties
 	if err := c.checkValue(inst, types, specials); err != nil {
 		return errorAt(inst, err.Error())
 	}

+	// The alloca instruction can be present in every basic block. However,
+	// allocas in basic blocks other than the entry basic block have a number of
+	// problems:
+	//   * They are hard to optimize, leading to potential missed optimizations.
+	//   * They may cause stack overflows in loops that would otherwise be
+	//     innocent.
+	//   * They cause extra code to be generated, because it requires the use of
+	//     a frame pointer.
+	//   * Perhaps most importantly, the coroutine lowering pass of LLVM (as of
+	//     LLVM 9) cannot deal with these allocas:
+	//     https://llvm.org/docs/Coroutines.html
+	// Therefore, alloca instructions should be limited to the entry block.
+	if !inst.IsAAllocaInst().IsNil() {
+		if inst.InstructionParent() != inst.InstructionParent().Parent().EntryBasicBlock() {
+			return errorAt(inst, "internal error: non-static alloca")
+		}
+	}
+
 	// check operands
 	for i := 0; i < inst.OperandsCount(); i++ {
 		if err := c.checkValue(inst.Operand(i), types, specials); err != nil {
@@ -111,7 +134,7 @@ func (c *Compiler) checkInstruction(inst llvm.Value, types map[llvm.Type]struct{
 	return nil
 }

-func (c *Compiler) checkBasicBlock(bb llvm.BasicBlock, types map[llvm.Type]struct{}, specials map[llvm.TypeKind]llvm.Type) []error {
+func (c *checker) checkBasicBlock(bb llvm.BasicBlock, types map[llvm.Type]struct{}, specials map[llvm.TypeKind]llvm.Type) []error {
 	// check basic block value and type
 	var errs []error
 	if err := c.checkValue(bb.AsValue(), types, specials); err != nil {
@@ -128,7 +151,7 @@ func (c *Compiler) checkBasicBlock(bb llvm.BasicBlock, types map[llvm.Type]struc
 	return errs
 }

-func (c *Compiler) checkFunction(fn llvm.Value, types map[llvm.Type]struct{}, specials map[llvm.TypeKind]llvm.Type) []error {
+func (c *checker) checkFunction(fn llvm.Value, types map[llvm.Type]struct{}, specials map[llvm.TypeKind]llvm.Type) []error {
 	// check function value and type
 	var errs []error
 	if err := c.checkValue(fn, types, specials); err != nil {
@@ -143,26 +166,25 @@ func (c *Compiler) checkFunction(fn llvm.Value, types map[llvm.Type]struct{}, sp
 	return errs
 }

-func (c *Compiler) checkModule() []error {
+// Module checks the given module and returns a slice of error, if there are
+// any.
+func Module(mod llvm.Module) []error {
 	// check for any context mismatches
 	var errs []error
-	switch {
-	case c.mod.Context() == c.ctx:
-		// this is correct
-	case c.mod.Context() == llvm.GlobalContext():
+	c := checker{
+		ctx: mod.Context(),
+	}
+	if c.ctx == llvm.GlobalContext() {
 		// somewhere we accidentally used the global context instead of a real context
 		errs = append(errs, errors.New("module uses global context"))
-	default:
-		// we used some other context by accident
-		errs = append(errs, fmt.Errorf("module uses context %v instead of the main context %v", c.mod.Context(), c.ctx))
 	}

 	types := map[llvm.Type]struct{}{}
 	specials := map[llvm.TypeKind]llvm.Type{}
-	for fn := c.mod.FirstFunction(); !fn.IsNil(); fn = llvm.NextFunction(fn) {
+	for fn := mod.FirstFunction(); !fn.IsNil(); fn = llvm.NextFunction(fn) {
 		errs = append(errs, c.checkFunction(fn, types, specials)...)
 	}
-	for g := c.mod.FirstGlobal(); !g.IsNil(); g = llvm.NextGlobal(g) {
+	for g := mod.FirstGlobal(); !g.IsNil(); g = llvm.NextGlobal(g) {
 		if err := c.checkValue(g, types, specials); err != nil {
 			errs = append(errs, fmt.Errorf("failed to verify global %s of module: %s", g.Name(), err.Error()))
 		}
@@ -0,0 +1,48 @@
+package ircheck
+
+import (
+	"go/scanner"
+	"go/token"
+	"path/filepath"
+
+	"tinygo.org/x/go-llvm"
+)
+
+// errorAt returns an error value at the location of the instruction.
+// The location information may not be complete as it depends on debug
+// information in the IR.
+func errorAt(inst llvm.Value, msg string) scanner.Error {
+	return scanner.Error{
+		Pos: getPosition(inst),
+		Msg: msg,
+	}
+}
+
+// getPosition returns the position information for the given value, as far as
+// it is available.
+func getPosition(val llvm.Value) token.Position {
+	if !val.IsAInstruction().IsNil() {
+		loc := val.InstructionDebugLoc()
+		if loc.IsNil() {
+			return token.Position{}
+		}
+		file := loc.LocationScope().ScopeFile()
+		return token.Position{
+			Filename: filepath.Join(file.FileDirectory(), file.FileFilename()),
+			Line:     int(loc.LocationLine()),
+			Column:   int(loc.LocationColumn()),
+		}
+	} else if !val.IsAFunction().IsNil() {
+		loc := val.Subprogram()
+		if loc.IsNil() {
+			return token.Position{}
+		}
+		file := loc.ScopeFile()
+		return token.Position{
+			Filename: filepath.Join(file.FileDirectory(), file.FileFilename()),
+			Line:     int(loc.SubprogramLine()),
+		}
+	} else {
+		return token.Position{}
+	}
+}
@@ -24,39 +24,39 @@ func getUses(value llvm.Value) []llvm.Value {
 }

 // createTemporaryAlloca creates a new alloca in the entry block and adds
-// lifetime start infromation in the IR signalling that the alloca won't be used
+// lifetime start information in the IR signalling that the alloca won't be used
 // before this point.
 //
 // This is useful for creating temporary allocas for intrinsics. Don't forget to
 // end the lifetime using emitLifetimeEnd after you're done with it.
-func (c *Compiler) createTemporaryAlloca(t llvm.Type, name string) (alloca, bitcast, size llvm.Value) {
-	return llvmutil.CreateTemporaryAlloca(c.builder, c.mod, t, name)
+func (b *builder) createTemporaryAlloca(t llvm.Type, name string) (alloca, bitcast, size llvm.Value) {
+	return llvmutil.CreateTemporaryAlloca(b.Builder, b.mod, t, name)
 }

 // emitLifetimeEnd signals the end of an (alloca) lifetime by calling the
 // llvm.lifetime.end intrinsic. It is commonly used together with
 // createTemporaryAlloca.
-func (c *Compiler) emitLifetimeEnd(ptr, size llvm.Value) {
-	llvmutil.EmitLifetimeEnd(c.builder, c.mod, ptr, size)
+func (b *builder) emitLifetimeEnd(ptr, size llvm.Value) {
+	llvmutil.EmitLifetimeEnd(b.Builder, b.mod, ptr, size)
 }

 // emitPointerPack packs the list of values into a single pointer value using
 // bitcasts, or else allocates a value on the heap if it cannot be packed in the
 // pointer value directly. It returns the pointer with the packed data.
-func (c *Compiler) emitPointerPack(values []llvm.Value) llvm.Value {
-	return llvmutil.EmitPointerPack(c.builder, c.mod, c.Config, values)
+func (b *builder) emitPointerPack(values []llvm.Value) llvm.Value {
+	return llvmutil.EmitPointerPack(b.Builder, b.mod, b.Config, values)
 }

 // emitPointerUnpack extracts a list of values packed using emitPointerPack.
-func (c *Compiler) emitPointerUnpack(ptr llvm.Value, valueTypes []llvm.Type) []llvm.Value {
-	return llvmutil.EmitPointerUnpack(c.builder, c.mod, ptr, valueTypes)
+func (b *builder) emitPointerUnpack(ptr llvm.Value, valueTypes []llvm.Type) []llvm.Value {
+	return llvmutil.EmitPointerUnpack(b.Builder, b.mod, ptr, valueTypes)
 }

 // makeGlobalArray creates a new LLVM global with the given name and integers as
 // contents, and returns the global.
 // Note that it is left with the default linkage etc., you should set
 // linkage/constant/etc properties yourself.
-func (c *Compiler) makeGlobalArray(buf []byte, name string, elementType llvm.Type) llvm.Value {
+func (c *compilerContext) makeGlobalArray(buf []byte, name string, elementType llvm.Type) llvm.Value {
 	globalType := llvm.ArrayType(elementType, len(buf))
 	global := llvm.AddGlobal(c.mod, globalType, name)
 	value := llvm.Undef(globalType)
@@ -12,6 +12,7 @@ import (
 // EmitPointerPack packs the list of values into a single pointer value using
 // bitcasts, or else allocates a value on the heap if it cannot be packed in the
 // pointer value directly. It returns the pointer with the packed data.
+// If the values are all constants, they are be stored in a constant global and deduplicated.
 func EmitPointerPack(builder llvm.Builder, mod llvm.Module, config *compileopts.Config, values []llvm.Value) llvm.Value {
 	ctx := mod.Context()
 	targetData := llvm.NewTargetData(mod.DataLayout())
@@ -42,6 +43,27 @@ func EmitPointerPack(builder llvm.Builder, mod llvm.Module, config *compileopts.
 		// it in an alloca first for bitcasting (store+bitcast+load).
 		packedAlloc, _, _ = CreateTemporaryAlloca(builder, mod, packedType, "")
 	} else {
+		// Check if the values are all constants.
+		constant := true
+		for _, v := range values {
+			if !v.IsConstant() {
+				constant = false
+				break
+			}
+		}
+
+		if constant {
+			// The data is known at compile time, so store it in a constant global.
+			// The global address is marked as unnamed, which allows LLVM to merge duplicates.
+			funcName := builder.GetInsertBlock().Parent().Name()
+			global := llvm.AddGlobal(mod, packedType, funcName+"$pack")
+			global.SetInitializer(ctx.ConstStruct(values, false))
+			global.SetGlobalConstant(true)
+			global.SetUnnamedAddr(true)
+			global.SetLinkage(llvm.PrivateLinkage)
+			return llvm.ConstBitCast(global, i8ptrType)
+		}
+
 		// Packed data is bigger than a pointer, so allocate it on the heap.
 		sizeValue := llvm.ConstInt(uintptrType, size, false)
 		alloc := mod.NamedFunction("runtime.alloc")
@@ -6,115 +6,167 @@ import (
 	"go/token"
 	"go/types"

+	"golang.org/x/tools/go/ssa"
 	"tinygo.org/x/go-llvm"
 )

-func (c *Compiler) emitMapLookup(keyType, valueType types.Type, m, key llvm.Value, commaOk bool, pos token.Pos) (llvm.Value, error) {
-	llvmValueType := c.getLLVMType(valueType)
+// createMakeMap creates a new map object (runtime.hashmap) by allocating and
+// initializing an appropriately sized object.
+func (b *builder) createMakeMap(expr *ssa.MakeMap) (llvm.Value, error) {
+	mapType := expr.Type().Underlying().(*types.Map)
+	keyType := mapType.Key().Underlying()
+	llvmValueType := b.getLLVMType(mapType.Elem().Underlying())
+	var llvmKeyType llvm.Type
+	if t, ok := keyType.(*types.Basic); ok && t.Info()&types.IsString != 0 {
+		// String keys.
+		llvmKeyType = b.getLLVMType(keyType)
+	} else if hashmapIsBinaryKey(keyType) {
+		// Trivially comparable keys.
+		llvmKeyType = b.getLLVMType(keyType)
+	} else {
+		// All other keys. Implemented as map[interface{}]valueType for ease of
+		// implementation.
+		llvmKeyType = b.getLLVMRuntimeType("_interface")
+	}
+	keySize := b.targetData.TypeAllocSize(llvmKeyType)
+	valueSize := b.targetData.TypeAllocSize(llvmValueType)
+	llvmKeySize := llvm.ConstInt(b.ctx.Int8Type(), keySize, false)
+	llvmValueSize := llvm.ConstInt(b.ctx.Int8Type(), valueSize, false)
+	sizeHint := llvm.ConstInt(b.uintptrType, 8, false)
+	if expr.Reserve != nil {
+		sizeHint = b.getValue(expr.Reserve)
+		var err error
+		sizeHint, err = b.createConvert(expr.Reserve.Type(), types.Typ[types.Uintptr], sizeHint, expr.Pos())
+		if err != nil {
+			return llvm.Value{}, err
+		}
+	}
+	hashmap := b.createRuntimeCall("hashmapMake", []llvm.Value{llvmKeySize, llvmValueSize, sizeHint}, "")
+	return hashmap, nil
+}
+
+// createMapLookup returns the value in a map. It calls a runtime function
+// depending on the map key type to load the map value and its comma-ok value.
+func (b *builder) createMapLookup(keyType, valueType types.Type, m, key llvm.Value, commaOk bool, pos token.Pos) (llvm.Value, error) {
+	llvmValueType := b.getLLVMType(valueType)

 	// Allocate the memory for the resulting type. Do not zero this memory: it
 	// will be zeroed by the hashmap get implementation if the key is not
 	// present in the map.
-	mapValueAlloca, mapValuePtr, mapValueSize := c.createTemporaryAlloca(llvmValueType, "hashmap.value")
+	mapValueAlloca, mapValuePtr, mapValueAllocaSize := b.createTemporaryAlloca(llvmValueType, "hashmap.value")
+
+	// We need the map size (with type uintptr) to pass to the hashmap*Get
+	// functions. This is necessary because those *Get functions are valid on
+	// nil maps, and they'll need to zero the value pointer by that number of
+	// bytes.
+	mapValueSize := mapValueAllocaSize
+	if mapValueSize.Type().IntTypeWidth() > b.uintptrType.IntTypeWidth() {
+		mapValueSize = llvm.ConstTrunc(mapValueSize, b.uintptrType)
+	}

 	// Do the lookup. How it is done depends on the key type.
 	var commaOkValue llvm.Value
+	keyType = keyType.Underlying()
 	if t, ok := keyType.(*types.Basic); ok && t.Info()&types.IsString != 0 {
 		// key is a string
-		params := []llvm.Value{m, key, mapValuePtr}
-		commaOkValue = c.createRuntimeCall("hashmapStringGet", params, "")
+		params := []llvm.Value{m, key, mapValuePtr, mapValueSize}
+		commaOkValue = b.createRuntimeCall("hashmapStringGet", params, "")
 	} else if hashmapIsBinaryKey(keyType) {
 		// key can be compared with runtime.memequal
 		// Store the key in an alloca, in the entry block to avoid dynamic stack
 		// growth.
-		mapKeyAlloca, mapKeyPtr, mapKeySize := c.createTemporaryAlloca(key.Type(), "hashmap.key")
-		c.builder.CreateStore(key, mapKeyAlloca)
+		mapKeyAlloca, mapKeyPtr, mapKeySize := b.createTemporaryAlloca(key.Type(), "hashmap.key")
+		b.CreateStore(key, mapKeyAlloca)
 		// Fetch the value from the hashmap.
-		params := []llvm.Value{m, mapKeyPtr, mapValuePtr}
-		commaOkValue = c.createRuntimeCall("hashmapBinaryGet", params, "")
-		c.emitLifetimeEnd(mapKeyPtr, mapKeySize)
+		params := []llvm.Value{m, mapKeyPtr, mapValuePtr, mapValueSize}
+		commaOkValue = b.createRuntimeCall("hashmapBinaryGet", params, "")
+		b.emitLifetimeEnd(mapKeyPtr, mapKeySize)
 	} else {
-		// Not trivially comparable using memcmp.
-		return llvm.Value{}, c.makeError(pos, "only strings, bools, ints, pointers or structs of bools/ints are supported as map keys, but got: "+keyType.String())
+		// Not trivially comparable using memcmp. Make it an interface instead.
+		itfKey := key
+		if _, ok := keyType.(*types.Interface); !ok {
+			// Not already an interface, so convert it to an interface now.
+			itfKey = b.createMakeInterface(key, keyType, pos)
+		}
+		params := []llvm.Value{m, itfKey, mapValuePtr, mapValueSize}
+		commaOkValue = b.createRuntimeCall("hashmapInterfaceGet", params, "")
 	}

 	// Load the resulting value from the hashmap. The value is set to the zero
 	// value if the key doesn't exist in the hashmap.
-	mapValue := c.builder.CreateLoad(mapValueAlloca, "")
-	c.emitLifetimeEnd(mapValuePtr, mapValueSize)
+	mapValue := b.CreateLoad(mapValueAlloca, "")
+	b.emitLifetimeEnd(mapValuePtr, mapValueAllocaSize)

 	if commaOk {
-		tuple := llvm.Undef(c.ctx.StructType([]llvm.Type{llvmValueType, c.ctx.Int1Type()}, false))
-		tuple = c.builder.CreateInsertValue(tuple, mapValue, 0, "")
-		tuple = c.builder.CreateInsertValue(tuple, commaOkValue, 1, "")
+		tuple := llvm.Undef(b.ctx.StructType([]llvm.Type{llvmValueType, b.ctx.Int1Type()}, false))
+		tuple = b.CreateInsertValue(tuple, mapValue, 0, "")
+		tuple = b.CreateInsertValue(tuple, commaOkValue, 1, "")
 		return tuple, nil
 	} else {
 		return mapValue, nil
 	}
 }

-func (c *Compiler) emitMapUpdate(keyType types.Type, m, key, value llvm.Value, pos token.Pos) {
-	valueAlloca, valuePtr, valueSize := c.createTemporaryAlloca(value.Type(), "hashmap.value")
-	c.builder.CreateStore(value, valueAlloca)
+// createMapUpdate updates a map key to a given value, by creating an
+// appropriate runtime call.
+func (b *builder) createMapUpdate(keyType types.Type, m, key, value llvm.Value, pos token.Pos) {
+	valueAlloca, valuePtr, valueSize := b.createTemporaryAlloca(value.Type(), "hashmap.value")
+	b.CreateStore(value, valueAlloca)
 	keyType = keyType.Underlying()
 	if t, ok := keyType.(*types.Basic); ok && t.Info()&types.IsString != 0 {
 		// key is a string
 		params := []llvm.Value{m, key, valuePtr}
-		c.createRuntimeCall("hashmapStringSet", params, "")
+		b.createRuntimeCall("hashmapStringSet", params, "")
 	} else if hashmapIsBinaryKey(keyType) {
 		// key can be compared with runtime.memequal
-		keyAlloca, keyPtr, keySize := c.createTemporaryAlloca(key.Type(), "hashmap.key")
-		c.builder.CreateStore(key, keyAlloca)
+		keyAlloca, keyPtr, keySize := b.createTemporaryAlloca(key.Type(), "hashmap.key")
+		b.CreateStore(key, keyAlloca)
 		params := []llvm.Value{m, keyPtr, valuePtr}
-		c.createRuntimeCall("hashmapBinarySet", params, "")
-		c.emitLifetimeEnd(keyPtr, keySize)
+		b.createRuntimeCall("hashmapBinarySet", params, "")
+		b.emitLifetimeEnd(keyPtr, keySize)
 	} else {
-		c.addError(pos, "only strings, bools, ints, pointers or structs of bools/ints are supported as map keys, but got: "+keyType.String())
+		// Key is not trivially comparable, so compare it as an interface instead.
+		itfKey := key
+		if _, ok := keyType.(*types.Interface); !ok {
+			// Not already an interface, so convert it to an interface first.
+			itfKey = b.createMakeInterface(key, keyType, pos)
+		}
+		params := []llvm.Value{m, itfKey, valuePtr}
+		b.createRuntimeCall("hashmapInterfaceSet", params, "")
 	}
-	c.emitLifetimeEnd(valuePtr, valueSize)
+	b.emitLifetimeEnd(valuePtr, valueSize)
 }

-func (c *Compiler) emitMapDelete(keyType types.Type, m, key llvm.Value, pos token.Pos) error {
+// createMapDelete deletes a key from a map by calling the appropriate runtime
+// function. It is the implementation of the Go delete() builtin.
+func (b *builder) createMapDelete(keyType types.Type, m, key llvm.Value, pos token.Pos) error {
 	keyType = keyType.Underlying()
 	if t, ok := keyType.(*types.Basic); ok && t.Info()&types.IsString != 0 {
 		// key is a string
 		params := []llvm.Value{m, key}
-		c.createRuntimeCall("hashmapStringDelete", params, "")
+		b.createRuntimeCall("hashmapStringDelete", params, "")
 		return nil
 	} else if hashmapIsBinaryKey(keyType) {
-		keyAlloca, keyPtr, keySize := c.createTemporaryAlloca(key.Type(), "hashmap.key")
-		c.builder.CreateStore(key, keyAlloca)
+		keyAlloca, keyPtr, keySize := b.createTemporaryAlloca(key.Type(), "hashmap.key")
+		b.CreateStore(key, keyAlloca)
 		params := []llvm.Value{m, keyPtr}
-		c.createRuntimeCall("hashmapBinaryDelete", params, "")
-		c.emitLifetimeEnd(keyPtr, keySize)
+		b.createRuntimeCall("hashmapBinaryDelete", params, "")
+		b.emitLifetimeEnd(keyPtr, keySize)
 		return nil
 	} else {
-		return c.makeError(pos, "only strings, bools, ints, pointers or structs of bools/ints are supported as map keys, but got: "+keyType.String())
+		// Key is not trivially comparable, so compare it as an interface
+		// instead.
+		itfKey := key
+		if _, ok := keyType.(*types.Interface); !ok {
+			// Not already an interface, so convert it to an interface first.
+			itfKey = b.createMakeInterface(key, keyType, pos)
+		}
+		params := []llvm.Value{m, itfKey}
+		b.createRuntimeCall("hashmapInterfaceDelete", params, "")
+		return nil
 	}
 }

-// Get FNV-1a hash of this string.
-//
-// https://en.wikipedia.org/wiki/Fowler%E2%80%93Noll%E2%80%93Vo_hash_function#FNV-1a_hash
-func hashmapHash(data []byte) uint32 {
-	var result uint32 = 2166136261 // FNV offset basis
-	for _, c := range data {
-		result ^= uint32(c)
-		result *= 16777619 // FNV prime
-	}
-	return result
-}
-
-// Get the topmost 8 bits of the hash, without using a special value (like 0).
-func hashmapTopHash(hash uint32) uint8 {
-	tophash := uint8(hash >> 24)
-	if tophash < 1 {
-		// 0 means empty slot, so make it bigger.
-		tophash += 1
-	}
-	return tophash
-}
-
 // Returns true if this key type does not contain strings, interfaces etc., so
 // can be compared with runtime.memequal.
 func hashmapIsBinaryKey(keyType types.Type) bool {
@@ -1,153 +0,0 @@
-package compiler
-
-import (
-	"errors"
-
-	"github.com/tinygo-org/tinygo/transform"
-	"tinygo.org/x/go-llvm"
-)
-
-// Run the LLVM optimizer over the module.
-// The inliner can be disabled (if necessary) by passing 0 to the inlinerThreshold.
-func (c *Compiler) Optimize(optLevel, sizeLevel int, inlinerThreshold uint) []error {
-	builder := llvm.NewPassManagerBuilder()
-	defer builder.Dispose()
-	builder.SetOptLevel(optLevel)
-	builder.SetSizeLevel(sizeLevel)
-	if inlinerThreshold != 0 {
-		builder.UseInlinerWithThreshold(inlinerThreshold)
-	}
-	builder.AddCoroutinePassesToExtensionPoints()
-
-	if c.PanicStrategy() == "trap" {
-		transform.ReplacePanicsWithTrap(c.mod) // -panic=trap
-	}
-
-	// run a check of all of our code
-	if c.VerifyIR() {
-		errs := c.checkModule()
-		if errs != nil {
-			return errs
-		}
-	}
-
-	// Run function passes for each function.
-	funcPasses := llvm.NewFunctionPassManagerForModule(c.mod)
-	defer funcPasses.Dispose()
-	builder.PopulateFunc(funcPasses)
-	funcPasses.InitializeFunc()
-	for fn := c.mod.FirstFunction(); !fn.IsNil(); fn = llvm.NextFunction(fn) {
-		funcPasses.RunFunc(fn)
-	}
-	funcPasses.FinalizeFunc()
-
-	if optLevel > 0 {
-		// Run some preparatory passes for the Go optimizer.
-		goPasses := llvm.NewPassManager()
-		defer goPasses.Dispose()
-		goPasses.AddGlobalOptimizerPass()
-		goPasses.AddConstantPropagationPass()
-		goPasses.AddAggressiveDCEPass()
-		goPasses.AddFunctionAttrsPass()
-		goPasses.Run(c.mod)
-
-		// Run Go-specific optimization passes.
-		transform.OptimizeMaps(c.mod)
-		transform.OptimizeStringToBytes(c.mod)
-		transform.OptimizeAllocs(c.mod)
-		transform.LowerInterfaces(c.mod)
-		if c.funcImplementation() == funcValueSwitch {
-			transform.LowerFuncValues(c.mod)
-		}
-
-		// After interfaces are lowered, there are many more opportunities for
-		// interprocedural optimizations. To get them to work, function
-		// attributes have to be updated first.
-		goPasses.Run(c.mod)
-
-		// Run TinyGo-specific interprocedural optimizations.
-		transform.OptimizeAllocs(c.mod)
-		transform.OptimizeStringToBytes(c.mod)
-
-		// Lower runtime.isnil calls to regular nil comparisons.
-		isnil := c.mod.NamedFunction("runtime.isnil")
-		if !isnil.IsNil() {
-			for _, use := range getUses(isnil) {
-				c.builder.SetInsertPointBefore(use)
-				ptr := use.Operand(0)
-				if !ptr.IsABitCastInst().IsNil() {
-					ptr = ptr.Operand(0)
-				}
-				nilptr := llvm.ConstPointerNull(ptr.Type())
-				icmp := c.builder.CreateICmp(llvm.IntEQ, ptr, nilptr, "")
-				use.ReplaceAllUsesWith(icmp)
-				use.EraseFromParentAsInstruction()
-			}
-		}
-
-		err := c.LowerGoroutines()
-		if err != nil {
-			return []error{err}
-		}
-	} else {
-		// Must be run at any optimization level.
-		transform.LowerInterfaces(c.mod)
-		if c.funcImplementation() == funcValueSwitch {
-			transform.LowerFuncValues(c.mod)
-		}
-		err := c.LowerGoroutines()
-		if err != nil {
-			return []error{err}
-		}
-	}
-	if c.VerifyIR() {
-		if errs := c.checkModule(); errs != nil {
-			return errs
-		}
-	}
-	if err := c.Verify(); err != nil {
-		return []error{errors.New("optimizations caused a verification failure")}
-	}
-
-	if sizeLevel >= 2 {
-		// Set the "optsize" attribute to make slightly smaller binaries at the
-		// cost of some performance.
-		kind := llvm.AttributeKindID("optsize")
-		attr := c.ctx.CreateEnumAttribute(kind, 0)
-		for fn := c.mod.FirstFunction(); !fn.IsNil(); fn = llvm.NextFunction(fn) {
-			fn.AddFunctionAttr(attr)
-		}
-	}
-
-	// After TinyGo-specific transforms have finished, undo exporting these functions.
-	for _, name := range c.getFunctionsUsedInTransforms() {
-		fn := c.mod.NamedFunction(name)
-		if fn.IsNil() {
-			continue
-		}
-		fn.SetLinkage(llvm.InternalLinkage)
-	}
-
-	// Run function passes again, because without it, llvm.coro.size.i32()
-	// doesn't get lowered.
-	for fn := c.mod.FirstFunction(); !fn.IsNil(); fn = llvm.NextFunction(fn) {
-		funcPasses.RunFunc(fn)
-	}
-	funcPasses.FinalizeFunc()
-
-	// Run module passes.
-	modPasses := llvm.NewPassManager()
-	defer modPasses.Dispose()
-	builder.Populate(modPasses)
-	modPasses.Run(c.mod)
-
-	hasGCPass := transform.AddGlobalsBitmap(c.mod)
-	hasGCPass = transform.MakeGCStackSlots(c.mod) || hasGCPass
-	if hasGCPass {
-		if err := c.Verify(); err != nil {
-			return []error{errors.New("GC pass caused a verification failure")}
-		}
-	}
-
-	return nil
-}
@@ -10,13 +10,13 @@ import (
 // The original license can be found here:
 //     https://golang.org/LICENSE

-type StdSizes struct {
+type stdSizes struct {
 	IntSize  int64
 	PtrSize  int64
 	MaxAlign int64
 }

-func (s *StdSizes) Alignof(T types.Type) int64 {
+func (s *stdSizes) Alignof(T types.Type) int64 {
 	// For arrays and structs, alignment is defined in terms
 	// of alignment of the elements and fields, respectively.
 	switch t := T.Underlying().(type) {
@@ -61,7 +61,7 @@ func (s *StdSizes) Alignof(T types.Type) int64 {
 	return a
 }

-func (s *StdSizes) Offsetsof(fields []*types.Var) []int64 {
+func (s *stdSizes) Offsetsof(fields []*types.Var) []int64 {
 	offsets := make([]int64, len(fields))
 	var o int64
 	for i, f := range fields {
@@ -89,7 +89,7 @@ var basicSizes = [...]byte{
 	types.Complex128: 16,
 }

-func (s *StdSizes) Sizeof(T types.Type) int64 {
+func (s *stdSizes) Sizeof(T types.Type) int64 {
 	switch t := T.Underlying().(type) {
 	case *types.Basic:
 		k := t.Kind()
@@ -26,7 +26,7 @@ type globalInfo struct {

 // loadASTComments loads comments on globals from the AST, for use later in the
 // program. In particular, they are required for //go:extern pragmas on globals.
-func (c *Compiler) loadASTComments(lprogram *loader.Program) {
+func (c *compilerContext) loadASTComments(lprogram *loader.Program) {
 	c.astComments = map[string]*ast.CommentGroup{}
 	for _, pkgInfo := range lprogram.Sorted() {
 		for _, file := range pkgInfo.Files {
@@ -56,25 +56,55 @@ func (c *Compiler) loadASTComments(lprogram *loader.Program) {

 // getGlobal returns a LLVM IR global value for a Go SSA global. It is added to
 // the LLVM IR if it has not been added already.
-func (c *Compiler) getGlobal(g *ssa.Global) llvm.Value {
+func (c *compilerContext) getGlobal(g *ssa.Global) llvm.Value {
 	info := c.getGlobalInfo(g)
 	llvmGlobal := c.mod.NamedGlobal(info.linkName)
 	if llvmGlobal.IsNil() {
-		llvmType := c.getLLVMType(g.Type().(*types.Pointer).Elem())
+		typ := g.Type().(*types.Pointer).Elem()
+		llvmType := c.getLLVMType(typ)
 		llvmGlobal = llvm.AddGlobal(c.mod, llvmType, info.linkName)
 		if !info.extern {
 			llvmGlobal.SetInitializer(llvm.ConstNull(llvmType))
 			llvmGlobal.SetLinkage(llvm.InternalLinkage)
 		}
-		if info.align > c.targetData.ABITypeAlignment(llvmType) {
-			llvmGlobal.SetAlignment(info.align)
+
+		// Set alignment from the //go:align comment.
+		var alignInBits uint32
+		if info.align < 0 || info.align&(info.align-1) != 0 {
+			// Check for power-of-two (or 0).
+			// See: https://stackoverflow.com/a/108360
+			c.addError(g.Pos(), "global variable alignment must be a positive power of two")
+		} else {
+			// Set the alignment only when it is a power of two.
+			alignInBits = uint32(info.align) ^ uint32(info.align-1)
+			if info.align > c.targetData.ABITypeAlignment(llvmType) {
+				llvmGlobal.SetAlignment(info.align)
+			}
+		}
+
+		if c.Debug() && !info.extern {
+			// Add debug info.
+			// TODO: this should be done for every global in the program, not just
+			// the ones that are referenced from some code.
+			pos := c.ir.Program.Fset.Position(g.Pos())
+			diglobal := c.dibuilder.CreateGlobalVariableExpression(c.difiles[pos.Filename], llvm.DIGlobalVariableExpression{
+				Name:        g.RelString(nil),
+				LinkageName: info.linkName,
+				File:        c.getDIFile(pos.Filename),
+				Line:        pos.Line,
+				Type:        c.getDIType(typ),
+				LocalToUnit: false,
+				Expr:        c.dibuilder.CreateExpression(nil),
+				AlignInBits: alignInBits,
+			})
+			llvmGlobal.AddMetadata(0, diglobal)
 		}
 	}
 	return llvmGlobal
 }

 // getGlobalInfo returns some information about a specific global.
-func (c *Compiler) getGlobalInfo(g *ssa.Global) globalInfo {
+func (c *compilerContext) getGlobalInfo(g *ssa.Global) globalInfo {
 	info := globalInfo{}
 	if strings.HasPrefix(g.Name(), "C.") {
 		// Created by CGo: such a name cannot be created by regular C code.
@@ -10,14 +10,14 @@ import (
 	"tinygo.org/x/go-llvm"
 )

-// emitSyscall emits an inline system call instruction, depending on the target
-// OS/arch.
-func (c *Compiler) emitSyscall(frame *Frame, call *ssa.CallCommon) (llvm.Value, error) {
-	num := c.getValue(frame, call.Args[0])
+// createSyscall emits an inline system call instruction, depending on the
+// target OS/arch.
+func (b *builder) createSyscall(call *ssa.CallCommon) (llvm.Value, error) {
+	num := b.getValue(call.Args[0])
 	var syscallResult llvm.Value
 	switch {
-	case c.GOARCH() == "amd64":
-		if c.GOOS() == "darwin" {
+	case b.GOARCH() == "amd64":
+		if b.GOOS() == "darwin" {
 			// Darwin adds this magic number to system call numbers:
 			//
 			// > Syscall classes for 64-bit system call entry.
@@ -28,13 +28,13 @@ func (c *Compiler) emitSyscall(frame *Frame, call *ssa.CallCommon) (llvm.Value,
 			// > All system classes enter the kernel via the syscall instruction.
 			//
 			// Source: https://opensource.apple.com/source/xnu/xnu-792.13.8/osfmk/mach/i386/syscall_sw.h
-			num = c.builder.CreateOr(num, llvm.ConstInt(c.uintptrType, 0x2000000, false), "")
+			num = b.CreateOr(num, llvm.ConstInt(b.uintptrType, 0x2000000, false), "")
 		}
 		// Sources:
 		//   https://stackoverflow.com/a/2538212
 		//   https://en.wikibooks.org/wiki/X86_Assembly/Interfacing_with_Linux#syscall
 		args := []llvm.Value{num}
-		argTypes := []llvm.Type{c.uintptrType}
+		argTypes := []llvm.Type{b.uintptrType}
 		// Constraints will look something like:
 		//   "={rax},0,{rdi},{rsi},{rdx},{r10},{r8},{r9},~{rcx},~{r11}"
 		constraints := "={rax},0"
@@ -50,21 +50,21 @@ func (c *Compiler) emitSyscall(frame *Frame, call *ssa.CallCommon) (llvm.Value,
 				"{r12}",
 				"{r13}",
 			}[i]
-			llvmValue := c.getValue(frame, arg)
+			llvmValue := b.getValue(arg)
 			args = append(args, llvmValue)
 			argTypes = append(argTypes, llvmValue.Type())
 		}
 		constraints += ",~{rcx},~{r11}"
-		fnType := llvm.FunctionType(c.uintptrType, argTypes, false)
+		fnType := llvm.FunctionType(b.uintptrType, argTypes, false)
 		target := llvm.InlineAsm(fnType, "syscall", constraints, true, false, llvm.InlineAsmDialectIntel)
-		syscallResult = c.builder.CreateCall(target, args, "")
-	case c.GOARCH() == "386" && c.GOOS() == "linux":
+		syscallResult = b.CreateCall(target, args, "")
+	case b.GOARCH() == "386" && b.GOOS() == "linux":
 		// Sources:
 		//   syscall(2) man page
 		//   https://stackoverflow.com/a/2538212
 		//   https://en.wikibooks.org/wiki/X86_Assembly/Interfacing_with_Linux#int_0x80
 		args := []llvm.Value{num}
-		argTypes := []llvm.Type{c.uintptrType}
+		argTypes := []llvm.Type{b.uintptrType}
 		// Constraints will look something like:
 		//   "={eax},0,{ebx},{ecx},{edx},{esi},{edi},{ebp}"
 		constraints := "={eax},0"
@@ -77,14 +77,14 @@ func (c *Compiler) emitSyscall(frame *Frame, call *ssa.CallCommon) (llvm.Value,
 				"{edi}",
 				"{ebp}",
 			}[i]
-			llvmValue := c.getValue(frame, arg)
+			llvmValue := b.getValue(arg)
 			args = append(args, llvmValue)
 			argTypes = append(argTypes, llvmValue.Type())
 		}
-		fnType := llvm.FunctionType(c.uintptrType, argTypes, false)
+		fnType := llvm.FunctionType(b.uintptrType, argTypes, false)
 		target := llvm.InlineAsm(fnType, "int 0x80", constraints, true, false, llvm.InlineAsmDialectIntel)
-		syscallResult = c.builder.CreateCall(target, args, "")
-	case c.GOARCH() == "arm" && c.GOOS() == "linux":
+		syscallResult = b.CreateCall(target, args, "")
+	case b.GOARCH() == "arm" && b.GOOS() == "linux":
 		// Implement the EABI system call convention for Linux.
 		// Source: syscall(2) man page.
 		args := []llvm.Value{}
@@ -102,21 +102,21 @@ func (c *Compiler) emitSyscall(frame *Frame, call *ssa.CallCommon) (llvm.Value,
 				"{r5}",
 				"{r6}",
 			}[i]
-			llvmValue := c.getValue(frame, arg)
+			llvmValue := b.getValue(arg)
 			args = append(args, llvmValue)
 			argTypes = append(argTypes, llvmValue.Type())
 		}
 		args = append(args, num)
-		argTypes = append(argTypes, c.uintptrType)
+		argTypes = append(argTypes, b.uintptrType)
 		constraints += ",{r7}" // syscall number
 		for i := len(call.Args) - 1; i < 4; i++ {
 			// r0-r3 get clobbered after the syscall returns
 			constraints += ",~{r" + strconv.Itoa(i) + "}"
 		}
-		fnType := llvm.FunctionType(c.uintptrType, argTypes, false)
+		fnType := llvm.FunctionType(b.uintptrType, argTypes, false)
 		target := llvm.InlineAsm(fnType, "svc #0", constraints, true, false, 0)
-		syscallResult = c.builder.CreateCall(target, args, "")
-	case c.GOARCH() == "arm64" && c.GOOS() == "linux":
+		syscallResult = b.CreateCall(target, args, "")
+	case b.GOARCH() == "arm64" && b.GOOS() == "linux":
 		// Source: syscall(2) man page.
 		args := []llvm.Value{}
 		argTypes := []llvm.Type{}
@@ -132,12 +132,12 @@ func (c *Compiler) emitSyscall(frame *Frame, call *ssa.CallCommon) (llvm.Value,
 				"{x4}",
 				"{x5}",
 			}[i]
-			llvmValue := c.getValue(frame, arg)
+			llvmValue := b.getValue(arg)
 			args = append(args, llvmValue)
 			argTypes = append(argTypes, llvmValue.Type())
 		}
 		args = append(args, num)
-		argTypes = append(argTypes, c.uintptrType)
+		argTypes = append(argTypes, b.uintptrType)
 		constraints += ",{x8}" // syscall number
 		for i := len(call.Args) - 1; i < 8; i++ {
 			// x0-x7 may get clobbered during the syscall following the aarch64
@@ -145,13 +145,13 @@ func (c *Compiler) emitSyscall(frame *Frame, call *ssa.CallCommon) (llvm.Value,
 			constraints += ",~{x" + strconv.Itoa(i) + "}"
 		}
 		constraints += ",~{x16},~{x17}" // scratch registers
-		fnType := llvm.FunctionType(c.uintptrType, argTypes, false)
+		fnType := llvm.FunctionType(b.uintptrType, argTypes, false)
 		target := llvm.InlineAsm(fnType, "svc #0", constraints, true, false, 0)
-		syscallResult = c.builder.CreateCall(target, args, "")
+		syscallResult = b.CreateCall(target, args, "")
 	default:
-		return llvm.Value{}, c.makeError(call.Pos(), "unknown GOOS/GOARCH for syscall: "+c.GOOS()+"/"+c.GOARCH())
+		return llvm.Value{}, b.makeError(call.Pos(), "unknown GOOS/GOARCH for syscall: "+b.GOOS()+"/"+b.GOARCH())
 	}
-	switch c.GOOS() {
+	switch b.GOOS() {
 	case "linux", "freebsd":
 		// Return values: r0, r1 uintptr, err Errno
 		// Pseudocode:
@@ -160,15 +160,15 @@ func (c *Compiler) emitSyscall(frame *Frame, call *ssa.CallCommon) (llvm.Value,
 		//         err = -syscallResult
 		//     }
 		//     return syscallResult, 0, err
-		zero := llvm.ConstInt(c.uintptrType, 0, false)
-		inrange1 := c.builder.CreateICmp(llvm.IntSLT, syscallResult, llvm.ConstInt(c.uintptrType, 0, false), "")
-		inrange2 := c.builder.CreateICmp(llvm.IntSGT, syscallResult, llvm.ConstInt(c.uintptrType, 0xfffffffffffff000, true), "") // -4096
-		hasError := c.builder.CreateAnd(inrange1, inrange2, "")
-		errResult := c.builder.CreateSelect(hasError, c.builder.CreateSub(zero, syscallResult, ""), zero, "syscallError")
-		retval := llvm.Undef(c.ctx.StructType([]llvm.Type{c.uintptrType, c.uintptrType, c.uintptrType}, false))
-		retval = c.builder.CreateInsertValue(retval, syscallResult, 0, "")
-		retval = c.builder.CreateInsertValue(retval, zero, 1, "")
-		retval = c.builder.CreateInsertValue(retval, errResult, 2, "")
+		zero := llvm.ConstInt(b.uintptrType, 0, false)
+		inrange1 := b.CreateICmp(llvm.IntSLT, syscallResult, llvm.ConstInt(b.uintptrType, 0, false), "")
+		inrange2 := b.CreateICmp(llvm.IntSGT, syscallResult, llvm.ConstInt(b.uintptrType, 0xfffffffffffff000, true), "") // -4096
+		hasError := b.CreateAnd(inrange1, inrange2, "")
+		errResult := b.CreateSelect(hasError, b.CreateSub(zero, syscallResult, ""), zero, "syscallError")
+		retval := llvm.Undef(b.ctx.StructType([]llvm.Type{b.uintptrType, b.uintptrType, b.uintptrType}, false))
+		retval = b.CreateInsertValue(retval, syscallResult, 0, "")
+		retval = b.CreateInsertValue(retval, zero, 1, "")
+		retval = b.CreateInsertValue(retval, errResult, 2, "")
 		return retval, nil
 	case "darwin":
 		// Return values: r0, r1 uintptr, err Errno
@@ -178,15 +178,15 @@ func (c *Compiler) emitSyscall(frame *Frame, call *ssa.CallCommon) (llvm.Value,
 		//         err = syscallResult
 		//     }
 		//     return syscallResult, 0, err
-		zero := llvm.ConstInt(c.uintptrType, 0, false)
-		hasError := c.builder.CreateICmp(llvm.IntNE, syscallResult, llvm.ConstInt(c.uintptrType, 0, false), "")
-		errResult := c.builder.CreateSelect(hasError, syscallResult, zero, "syscallError")
-		retval := llvm.Undef(c.ctx.StructType([]llvm.Type{c.uintptrType, c.uintptrType, c.uintptrType}, false))
-		retval = c.builder.CreateInsertValue(retval, syscallResult, 0, "")
-		retval = c.builder.CreateInsertValue(retval, zero, 1, "")
-		retval = c.builder.CreateInsertValue(retval, errResult, 2, "")
+		zero := llvm.ConstInt(b.uintptrType, 0, false)
+		hasError := b.CreateICmp(llvm.IntNE, syscallResult, llvm.ConstInt(b.uintptrType, 0, false), "")
+		errResult := b.CreateSelect(hasError, syscallResult, zero, "syscallError")
+		retval := llvm.Undef(b.ctx.StructType([]llvm.Type{b.uintptrType, b.uintptrType, b.uintptrType}, false))
+		retval = b.CreateInsertValue(retval, syscallResult, 0, "")
+		retval = b.CreateInsertValue(retval, zero, 1, "")
+		retval = b.CreateInsertValue(retval, errResult, 2, "")
 		return retval, nil
 	default:
-		return llvm.Value{}, c.makeError(call.Pos(), "unknown GOOS/GOARCH for syscall: "+c.GOOS()+"/"+c.GOARCH())
+		return llvm.Value{}, b.makeError(call.Pos(), "unknown GOOS/GOARCH for syscall: "+b.GOOS()+"/"+b.GOARCH())
 	}
 }
@@ -8,19 +8,23 @@ import (
 	"tinygo.org/x/go-llvm"
 )

-func (c *Compiler) emitVolatileLoad(frame *Frame, instr *ssa.CallCommon) (llvm.Value, error) {
-	addr := c.getValue(frame, instr.Args[0])
-	c.emitNilCheck(frame, addr, "deref")
-	val := c.builder.CreateLoad(addr, "")
+// createVolatileLoad is the implementation of the intrinsic function
+// runtime/volatile.LoadT().
+func (b *builder) createVolatileLoad(instr *ssa.CallCommon) (llvm.Value, error) {
+	addr := b.getValue(instr.Args[0])
+	b.createNilCheck(instr.Args[0], addr, "deref")
+	val := b.CreateLoad(addr, "")
 	val.SetVolatile(true)
 	return val, nil
 }

-func (c *Compiler) emitVolatileStore(frame *Frame, instr *ssa.CallCommon) (llvm.Value, error) {
-	addr := c.getValue(frame, instr.Args[0])
-	val := c.getValue(frame, instr.Args[1])
-	c.emitNilCheck(frame, addr, "deref")
-	store := c.builder.CreateStore(val, addr)
+// createVolatileStore is the implementation of the intrinsic function
+// runtime/volatile.StoreT().
+func (b *builder) createVolatileStore(instr *ssa.CallCommon) (llvm.Value, error) {
+	addr := b.getValue(instr.Args[0])
+	val := b.getValue(instr.Args[1])
+	b.createNilCheck(instr.Args[0], addr, "deref")
+	store := b.CreateStore(val, addr)
 	store.SetVolatile(true)
 	return llvm.Value{}, nil
 }
@@ -4,11 +4,11 @@ go 1.11

 require (
 	github.com/blakesmith/ar v0.0.0-20150311145944-8bd4349a67f2
-	github.com/creack/goselect v0.1.0 // indirect
+	github.com/chromedp/cdproto v0.0.0-20200116234248-4da64dd111ac
+	github.com/chromedp/chromedp v0.5.3
 	github.com/google/shlex v0.0.0-20181106134648-c34317bd91bf
-	github.com/marcinbor85/gohex v0.0.0-20180128172054-7a43cd876e46
-	go.bug.st/serial.v1 v0.0.0-20180827123349-5f7892a7bb45
-	golang.org/x/sys v0.0.0-20191010194322-b09406accb47 // indirect
-	golang.org/x/tools v0.0.0-20190227180812-8dcc6e70cdef
-	tinygo.org/x/go-llvm v0.0.0-20191215173731-ad71f3d24aae
+	github.com/marcinbor85/gohex v0.0.0-20200531091804-343a4b548892
+	go.bug.st/serial v1.0.0
+	golang.org/x/tools v0.0.0-20200216192241-b320d3a0f5a2
+	tinygo.org/x/go-llvm v0.0.0-20200503225853-345b2947b59d
 )
@@ -1,34 +1,50 @@
 github.com/blakesmith/ar v0.0.0-20150311145944-8bd4349a67f2 h1:oMCHnXa6CCCafdPDbMh/lWRhRByN0VFLvv+g+ayx1SI=
 github.com/blakesmith/ar v0.0.0-20150311145944-8bd4349a67f2/go.mod h1:PkYb9DJNAwrSvRx5DYA+gUcOIgTGVMNkfSCbZM8cWpI=
-github.com/creack/goselect v0.1.0 h1:4QiXIhcpSQF50XGaBsFzesjwX/1qOY5bOveQPmN9CXY=
-github.com/creack/goselect v0.1.0/go.mod h1:gHrIcH/9UZDn2qgeTUeW5K9eZsVYCH6/60J/FHysWyE=
-github.com/golang/protobuf v1.2.0/go.mod h1:6lQm79b+lXiMfvg/cZm0SGofjICqVBUtrP5yJMmIC1U=
+github.com/chromedp/cdproto v0.0.0-20200116234248-4da64dd111ac h1:T7V5BXqnYd55Hj/g5uhDYumg9Fp3rMTS6bykYtTIFX4=
+github.com/chromedp/cdproto v0.0.0-20200116234248-4da64dd111ac/go.mod h1:PfAWWKJqjlGFYJEidUM6aVIWPr0EpobeyVWEEmplX7g=
+github.com/chromedp/chromedp v0.5.3 h1:F9LafxmYpsQhWQBdCs+6Sret1zzeeFyHS5LkRF//Ffg=
+github.com/chromedp/chromedp v0.5.3/go.mod h1:YLdPtndaHQ4rCpSpBG+IPpy9JvX0VD+7aaLxYgYj28w=
+github.com/creack/goselect v0.1.1 h1:tiSSgKE1eJtxs1h/VgGQWuXUP0YS4CDIFMp6vaI1ls0=
+github.com/creack/goselect v0.1.1/go.mod h1:a/NhLweNvqIYMuxcMOuWY516Cimucms3DglDzQP3hKY=
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/gobwas/httphead v0.0.0-20180130184737-2c6c146eadee h1:s+21KNqlpePfkah2I+gwHF8xmJWRjooY+5248k6m4A0=
+github.com/gobwas/httphead v0.0.0-20180130184737-2c6c146eadee/go.mod h1:L0fX3K22YWvt/FAX9NnzrNzcI4wNYi9Yku4O0LKYflo=
+github.com/gobwas/pool v0.2.0 h1:QEmUOlnSjWtnpRGHF3SauEiOsy82Cup83Vf2LcMlnc8=
+github.com/gobwas/pool v0.2.0/go.mod h1:q8bcK0KcYlCgd9e7WYLm9LpyS+YeLd8JVDW6WezmKEw=
+github.com/gobwas/ws v1.0.2 h1:CoAavW/wd/kulfZmSIBt6p24n4j7tHgNVCjsfHVNUbo=
+github.com/gobwas/ws v1.0.2/go.mod h1:szmBTxLgaFppYjEmNtny/v3w89xOydFnnZMcgRRu/EM=
 github.com/google/shlex v0.0.0-20181106134648-c34317bd91bf h1:7+FW5aGwISbqUtkfmIpZJGRgNFg2ioYPvFaUxdqpDsg=
 github.com/google/shlex v0.0.0-20181106134648-c34317bd91bf/go.mod h1:RpwtwJQFrIEPstU94h88MWPXP2ektJZ8cZ0YntAmXiE=
-github.com/marcinbor85/gohex v0.0.0-20180128172054-7a43cd876e46 h1:wXG2bA8fO7Vv7lLk2PihFMTqmbT173Tje39oKzQ50Mo=
-github.com/marcinbor85/gohex v0.0.0-20180128172054-7a43cd876e46/go.mod h1:Pb6XcsXyropB9LNHhnqaknG/vEwYztLkQzVCHv8sQ3M=
-go.bug.st/serial.v1 v0.0.0-20180827123349-5f7892a7bb45 h1:mACY1anK6HNCZtm/DK2Rf2ZPHggVqeB0+7rY9Gl6wyI=
-go.bug.st/serial.v1 v0.0.0-20180827123349-5f7892a7bb45/go.mod h1:dRSl/CVCTf56CkXgJMDOdSwNfo2g1orOGE/gBGdvjZw=
-golang.org/x/net v0.0.0-20180724234803-3673e40ba225/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
-golang.org/x/net v0.0.0-20190213061140-3a22650c66bd/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
-golang.org/x/sync v0.0.0-20181108010431-42b317875d0f/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
-golang.org/x/sys v0.0.0-20191010194322-b09406accb47 h1:/XfQ9z7ib8eEJX2hdgFTZJ/ntt0swNk5oYBziWeTCvY=
-golang.org/x/sys v0.0.0-20191010194322-b09406accb47/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+github.com/knq/sysutil v0.0.0-20191005231841-15668db23d08 h1:V0an7KRw92wmJysvFvtqtKMAPmvS5O0jtB0nYo6t+gs=
+github.com/knq/sysutil v0.0.0-20191005231841-15668db23d08/go.mod h1:dFWs1zEqDjFtnBXsd1vPOZaLsESovai349994nHx3e0=
+github.com/mailru/easyjson v0.7.0 h1:aizVhC/NAAcKWb+5QsU1iNOZb4Yws5UO2I+aIprQITM=
+github.com/mailru/easyjson v0.7.0/go.mod h1:KAzv3t3aY1NaHWoQz1+4F1ccyAH66Jk7yos7ldAVICs=
+github.com/marcinbor85/gohex v0.0.0-20200531091804-343a4b548892 h1:6J+qramlHVLmiBOgRiBOnQkno8uprqG6YFFQTt6uYIw=
+github.com/marcinbor85/gohex v0.0.0-20200531091804-343a4b548892/go.mod h1:Pb6XcsXyropB9LNHhnqaknG/vEwYztLkQzVCHv8sQ3M=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/testify v1.4.0/go.mod h1:j7eGeouHqKxXV5pUuKE4zz7dFj8WfuZ+81PSLYec5m4=
+go.bug.st/serial v1.0.0 h1:ogEPzrllCsnG00EqKRjeYvPRsO7NJW6DqykzkdD6E/k=
+go.bug.st/serial v1.0.0/go.mod h1:rpXPISGjuNjPTRTcMlxi9lN6LoIPxd1ixVjBd8aSk/Q=
+golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
+golang.org/x/crypto v0.0.0-20191011191535-87dc89f01550/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
+golang.org/x/mod v0.1.1-0.20191105210325-c90efee705ee h1:WG0RUwxtNT4qqaXX3DPA8zHFNm/D9xaBpxzHt1WcA/E=
+golang.org/x/mod v0.1.1-0.20191105210325-c90efee705ee/go.mod h1:QqPTAvyqsEbceGzBzNggFXnrqF1CaUcvgkdR5Ot7KZg=
+golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
+golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
+golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20191128015809-6d18c012aee9 h1:ZBzSG/7F4eNKz2L3GE9o300RX0Az1Bw5HF7PDraD+qU=
+golang.org/x/sys v0.0.0-20191128015809-6d18c012aee9/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20200116001909-b77594299b42 h1:vEOn+mP2zCOVzKckCZy6YsCtDblrpj/w7B9nxGNELpg=
+golang.org/x/sys v0.0.0-20200116001909-b77594299b42/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
-golang.org/x/tools v0.0.0-20190227180812-8dcc6e70cdef h1:ymc9FeDom3RIEA3coKokSllBB1hRcMT0tZ1W3Jf9Ids=
-golang.org/x/tools v0.0.0-20190227180812-8dcc6e70cdef/go.mod h1:9Yl7xja0Znq3iFh3HoIrodX9oNMXvdceNzlUR8zjMvY=
-google.golang.org/appengine v1.4.0/go.mod h1:xpcJRLb0r/rnEns0DIKYYv+WjYCduHsrkT7/EB5XEv4=
-tinygo.org/x/go-llvm v0.0.0-20190224120431-7707ae5d1261 h1:rJS2Hga39YAnm7DE4qrPm6Dr/67EOojL0XPzvbEeBiw=
-tinygo.org/x/go-llvm v0.0.0-20190224120431-7707ae5d1261/go.mod h1:fv1F0BSNpxMfCL0zF3M4OPFbgYHnhtB6ST0HvUtu/LE=
-tinygo.org/x/go-llvm v0.0.0-20190818154551-95bc4ffe1add h1:dFjMH1sLhYADg8UQm7DB56B7e+TfvAmWmEZLhyv3r/w=
-tinygo.org/x/go-llvm v0.0.0-20190818154551-95bc4ffe1add/go.mod h1:fv1F0BSNpxMfCL0zF3M4OPFbgYHnhtB6ST0HvUtu/LE=
-tinygo.org/x/go-llvm v0.0.0-20191103182207-90b6e4bdc0b9 h1:d6rAX39a3C0pKrY5HcojEGyN8w9ocU0v7X28lC/TRKU=
-tinygo.org/x/go-llvm v0.0.0-20191103182207-90b6e4bdc0b9/go.mod h1:fv1F0BSNpxMfCL0zF3M4OPFbgYHnhtB6ST0HvUtu/LE=
-tinygo.org/x/go-llvm v0.0.0-20191103200204-37e93e3f04e2 h1:Q5Hv3e5cLMGkiYwYgZL1Zrv6nb/EY+DJpRWrdO6ws6o=
-tinygo.org/x/go-llvm v0.0.0-20191103200204-37e93e3f04e2/go.mod h1:fv1F0BSNpxMfCL0zF3M4OPFbgYHnhtB6ST0HvUtu/LE=
-tinygo.org/x/go-llvm v0.0.0-20191113125529-bad6d01809e8 h1:9Bfvso+tTVQg16UzOA614NaYA4x8vsRBNtd3eBrXwp0=
-tinygo.org/x/go-llvm v0.0.0-20191113125529-bad6d01809e8/go.mod h1:fv1F0BSNpxMfCL0zF3M4OPFbgYHnhtB6ST0HvUtu/LE=
-tinygo.org/x/go-llvm v0.0.0-20191124211856-b2db3df3f257 h1:o8VDylrMN7gWemBMu8rEyuogKPhcLTdx5KrUAp9macc=
-tinygo.org/x/go-llvm v0.0.0-20191124211856-b2db3df3f257/go.mod h1:fv1F0BSNpxMfCL0zF3M4OPFbgYHnhtB6ST0HvUtu/LE=
-tinygo.org/x/go-llvm v0.0.0-20191215173731-ad71f3d24aae h1:s8J5EyxCkHxXB08UI3gk9W9IS/ekizRvSX+PfZxnAB0=
-tinygo.org/x/go-llvm v0.0.0-20191215173731-ad71f3d24aae/go.mod h1:fv1F0BSNpxMfCL0zF3M4OPFbgYHnhtB6ST0HvUtu/LE=
+golang.org/x/tools v0.0.0-20200216192241-b320d3a0f5a2 h1:0sfSpGSa544Fwnbot3Oxq/U6SXqjty6Jy/3wRhVS7ig=
+golang.org/x/tools v0.0.0-20200216192241-b320d3a0f5a2/go.mod h1:TB2adYChydJhpapKDTa4BR/hXlZSLoq2Wpct/0txZ28=
+golang.org/x/xerrors v0.0.0-20191011141410-1b5146add898 h1:/atklqdjdhuosWIl6AIbOeHJjicWYPqR9bpxqxYG2pA=
+golang.org/x/xerrors v0.0.0-20191011141410-1b5146add898/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
+tinygo.org/x/go-llvm v0.0.0-20200503225853-345b2947b59d h1:hcX7vpB067GWM/EH4sGGOti0PMgIx+0bbZwUXctOIvE=
+tinygo.org/x/go-llvm v0.0.0-20200503225853-345b2947b59d/go.mod h1:fv1F0BSNpxMfCL0zF3M4OPFbgYHnhtB6ST0HvUtu/LE=
@@ -18,6 +18,7 @@ var Keys = []string{
 	"GOROOT",
 	"GOPATH",
 	"GOCACHE",
+	"CGO_ENABLED",
 	"TINYGOROOT",
 }

@@ -57,6 +58,13 @@ func Get(name string) string {
 			panic("could not find cache dir: " + err.Error())
 		}
 		return filepath.Join(dir, "tinygo")
+	case "CGO_ENABLED":
+		val := os.Getenv("CGO_ENABLED")
+		if val == "1" || val == "0" {
+			return val
+		}
+		// Default to enabling CGo.
+		return "1"
 	case "TINYGOROOT":
 		return sourceDir()
 	default:
@@ -0,0 +1,68 @@
+package goenv
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"path/filepath"
+	"regexp"
+	"strings"
+)
+
+// Version of TinyGo.
+// Update this value before release of new version of software.
+const Version = "0.15.0"
+
+// GetGorootVersion returns the major and minor version for a given GOROOT path.
+// If the goroot cannot be determined, (0, 0) is returned.
+func GetGorootVersion(goroot string) (major, minor int, err error) {
+	s, err := GorootVersionString(goroot)
+	if err != nil {
+		return 0, 0, err
+	}
+
+	if s == "" || s[:2] != "go" {
+		return 0, 0, errors.New("could not parse Go version: version does not start with 'go' prefix")
+	}
+
+	parts := strings.Split(s[2:], ".")
+	if len(parts) < 2 {
+		return 0, 0, errors.New("could not parse Go version: version has less than two parts")
+	}
+
+	// Ignore the errors, we don't really handle errors here anyway.
+	var trailing string
+	n, err := fmt.Sscanf(s, "go%d.%d%s", &major, &minor, &trailing)
+	if n == 2 && err == io.EOF {
+		// Means there were no trailing characters (i.e., not an alpha/beta)
+		err = nil
+	}
+	if err != nil {
+		return 0, 0, fmt.Errorf("failed to parse version: %s", err)
+	}
+	return
+}
+
+// GorootVersionString returns the version string as reported by the Go
+// toolchain for the given GOROOT path. It is usually of the form `go1.x.y` but
+// can have some variations (for beta releases, for example).
+func GorootVersionString(goroot string) (string, error) {
+	if data, err := ioutil.ReadFile(filepath.Join(
+		goroot, "src", "runtime", "internal", "sys", "zversion.go")); err == nil {
+
+		r := regexp.MustCompile("const TheVersion = `(.*)`")
+		matches := r.FindSubmatch(data)
+		if len(matches) != 2 {
+			return "", errors.New("Invalid go version output:\n" + string(data))
+		}
+
+		return string(matches[1]), nil
+
+	} else if data, err := ioutil.ReadFile(filepath.Join(goroot, "VERSION")); err == nil {
+		return string(data), nil
+
+	} else {
+		return "", err
+	}
+}
@@ -0,0 +1,5 @@
+# Hooks for Docker Hub
+
+Files in this directory are custom commands to be run during the different Docker Hub build phases.
+
+See https://docs.docker.com/docker-hub/builds/advanced/#custom-build-phase-hooks
@@ -0,0 +1,4 @@
+#!/bin/bash
+# Docker hub does a recursive clone, then checks the branch out,
+# so when a PR adds a submodule (or updates it), it fails.
+git submodule update --init
@@ -13,55 +13,46 @@ import (

 // errUnreachable is returned when an unreachable instruction is executed. This
 // error should not be visible outside of the interp package.
-var errUnreachable = errors.New("interp: unreachable executed")
-
-// Unsupported is the specific error that is returned when an unsupported
-// instruction is hit while trying to interpret all initializers.
-type Unsupported struct {
-	ImportPath string
-	Inst       llvm.Value
-	Pos        token.Position
-}
-
-func (e Unsupported) Error() string {
-	// TODO: how to return the actual instruction string?
-	// It looks like LLVM provides no function for that...
-	return scanner.Error{
-		Pos: e.Pos,
-		Msg: "interp: unsupported instruction",
-	}.Error()
-}
+var errUnreachable = &Error{Err: errors.New("interp: unreachable executed")}

 // unsupportedInstructionError returns a new "unsupported instruction" error for
 // the given instruction. It includes source location information, when
 // available.
-func (e *evalPackage) unsupportedInstructionError(inst llvm.Value) *Unsupported {
-	return &Unsupported{
-		ImportPath: e.packagePath,
-		Inst:       inst,
-		Pos:        getPosition(inst),
-	}
+func (e *evalPackage) unsupportedInstructionError(inst llvm.Value) *Error {
+	return e.errorAt(inst, errors.New("interp: unsupported instruction"))
+}
+
+// ErrorLine is one line in a traceback. The position may be missing.
+type ErrorLine struct {
+	Pos  token.Position
+	Inst llvm.Value
 }

 // Error encapsulates compile-time interpretation errors with an associated
 // import path. The errors may not have a precise location attached.
 type Error struct {
 	ImportPath string
-	Errs       []scanner.Error
+	Inst       llvm.Value
+	Pos        token.Position
+	Err        error
+	Traceback  []ErrorLine
 }

 // Error returns the string of the first error in the list of errors.
-func (e Error) Error() string {
-	return e.Errs[0].Error()
+func (e *Error) Error() string {
+	return e.Pos.String() + ": " + e.Err.Error()
 }

 // errorAt returns an error value for the currently interpreted package at the
 // location of the instruction. The location information may not be complete as
 // it depends on debug information in the IR.
-func (e *evalPackage) errorAt(inst llvm.Value, msg string) Error {
-	return Error{
+func (e *evalPackage) errorAt(inst llvm.Value, err error) *Error {
+	pos := getPosition(inst)
+	return &Error{
 		ImportPath: e.packagePath,
-		Errs:       []scanner.Error{errorAt(inst, msg)},
+		Pos:        pos,
+		Err:        err,
+		Traceback:  []ErrorLine{{pos, inst}},
 	}
 }

@@ -4,6 +4,7 @@ package interp
 // functions.

 import (
+	"errors"
 	"strings"

 	"tinygo.org/x/go-llvm"
@@ -21,7 +22,7 @@ type frame struct {
 // Most of it works at compile time. Some calls get translated into calls to be
 // executed at runtime: calls to functions with side effects, external calls,
 // and operations on the result of such instructions.
-func (fr *frame) evalBasicBlock(bb, incoming llvm.BasicBlock, indent string) (retval Value, outgoing []llvm.Value, err error) {
+func (fr *frame) evalBasicBlock(bb, incoming llvm.BasicBlock, indent string) (retval Value, outgoing []llvm.Value, err *Error) {
 	for inst := bb.FirstInstruction(); !inst.IsNil(); inst = llvm.NextInstruction(inst) {
 		if fr.Debug {
 			print(indent)
@@ -94,10 +95,14 @@ func (fr *frame) evalBasicBlock(bb, incoming llvm.BasicBlock, indent string) (re
 			if !operand.IsConstant() || inst.IsVolatile() || (!operand.Underlying.IsAConstantExpr().IsNil() && operand.Underlying.Opcode() == llvm.BitCast) {
 				value = fr.builder.CreateLoad(operand.Value(), inst.Name())
 			} else {
-				value = operand.Load()
+				var err error
+				value, err = operand.Load()
+				if err != nil {
+					return nil, nil, fr.errorAt(inst, err)
+				}
 			}
 			if value.Type() != inst.Type() {
-				return nil, nil, fr.errorAt(inst, "interp: load: type does not match")
+				return nil, nil, fr.errorAt(inst, errors.New("interp: load: type does not match"))
 			}
 			fr.locals[inst] = fr.getValue(value)
 		case !inst.IsAStoreInst().IsNil():
@@ -106,7 +111,10 @@ func (fr *frame) evalBasicBlock(bb, incoming llvm.BasicBlock, indent string) (re
 			if inst.IsVolatile() {
 				fr.builder.CreateStore(value.Value(), ptr.Value())
 			} else {
-				ptr.Store(value.Value())
+				err := ptr.Store(value.Value())
+				if err != nil {
+					return nil, nil, fr.errorAt(inst, err)
+				}
 			}
 		case !inst.IsAGetElementPtrInst().IsNil():
 			value := fr.getLocal(inst.Operand(0))
@@ -121,13 +129,16 @@ func (fr *frame) evalBasicBlock(bb, incoming llvm.BasicBlock, indent string) (re
 					// Not a constant operation.
 					// This should be detected by the scanner, but isn't at the
 					// moment.
-					return nil, nil, fr.errorAt(inst, "todo: non-const gep")
+					return nil, nil, fr.errorAt(inst, errors.New("todo: non-const gep"))
 				}
 				indices[i] = uint32(operand.Value().ZExtValue())
 			}
-			result := value.GetElementPtr(indices)
+			result, err := value.GetElementPtr(indices)
+			if err != nil {
+				return nil, nil, fr.errorAt(inst, err)
+			}
 			if result.Type() != inst.Type() {
-				return nil, nil, fr.errorAt(inst, "interp: gep: type does not match")
+				return nil, nil, fr.errorAt(inst, errors.New("interp: gep: type does not match"))
 			}
 			fr.locals[inst] = result

@@ -182,7 +193,7 @@ func (fr *frame) evalBasicBlock(bb, incoming llvm.BasicBlock, indent string) (re
 					}
 				}
 				// It is not possible in Go to bitcast a map value to a pointer.
-				return nil, nil, fr.errorAt(inst, "unimplemented: bitcast of map")
+				return nil, nil, fr.errorAt(inst, errors.New("unimplemented: bitcast of map"))
 			}
 			value := fr.getLocal(operand).(*LocalValue)
 			fr.locals[inst] = &LocalValue{fr.Eval, fr.builder.CreateBitCast(value.Value(), inst.Type(), "")}
@@ -264,7 +275,11 @@ func (fr *frame) evalBasicBlock(bb, incoming llvm.BasicBlock, indent string) (re
 				if elementCount == 1 {
 					fr.locals[resultInst] = result
 				} else {
-					fr.locals[resultInst] = result.GetElementPtr([]uint32{0, 0})
+					result, err := result.GetElementPtr([]uint32{0, 0})
+					if err != nil {
+						return nil, nil, fr.errorAt(inst, err)
+					}
+					fr.locals[resultInst] = result
 				}
 			case callee.Name() == "runtime.hashmapMake":
 				// create a map
@@ -300,7 +315,10 @@ func (fr *frame) evalBasicBlock(bb, incoming llvm.BasicBlock, indent string) (re
 				}
 				// "key" is a Go string value, which in the TinyGo calling convention is split up
 				// into separate pointer and length parameters.
-				m.PutString(keyBuf, keyLen, valPtr)
+				err := m.PutString(keyBuf, keyLen, valPtr)
+				if err != nil {
+					return nil, nil, fr.errorAt(inst, err)
+				}
 			case callee.Name() == "runtime.hashmapBinarySet":
 				// set a binary (int etc.) key in the map
 				keyBuf := fr.getLocal(inst.Operand(1)).(*LocalValue)
@@ -321,15 +339,24 @@ func (fr *frame) evalBasicBlock(bb, incoming llvm.BasicBlock, indent string) (re
 					fr.builder.CreateCall(callee, llvmParams, "")
 					continue
 				}
-				m.PutBinary(keyBuf, valPtr)
+				err := m.PutBinary(keyBuf, valPtr)
+				if err != nil {
+					return nil, nil, fr.errorAt(inst, err)
+				}
 			case callee.Name() == "runtime.stringConcat":
 				// adding two strings together
 				buf1Ptr := fr.getLocal(inst.Operand(0))
 				buf1Len := fr.getLocal(inst.Operand(1))
 				buf2Ptr := fr.getLocal(inst.Operand(2))
 				buf2Len := fr.getLocal(inst.Operand(3))
-				buf1 := getStringBytes(buf1Ptr, buf1Len.Value())
-				buf2 := getStringBytes(buf2Ptr, buf2Len.Value())
+				buf1, err := getStringBytes(buf1Ptr, buf1Len.Value())
+				if err != nil {
+					return nil, nil, fr.errorAt(inst, err)
+				}
+				buf2, err := getStringBytes(buf2Ptr, buf2Len.Value())
+				if err != nil {
+					return nil, nil, fr.errorAt(inst, err)
+				}
 				result := []byte(string(buf1) + string(buf2))
 				vals := make([]llvm.Value, len(result))
 				for i := range vals {
@@ -365,38 +392,64 @@ func (fr *frame) evalBasicBlock(bb, incoming llvm.BasicBlock, indent string) (re
 					// a bitcast of the original array instead of the GEP,
 					// which breaks our assumptions.
 					// Re-add this GEP, in the hope that it it is then of the correct type...
-					dstArray = dstArray.GetElementPtr([]uint32{0, 0}).(*LocalValue)
-					srcArray = srcArray.GetElementPtr([]uint32{0, 0}).(*LocalValue)
+					dstArrayValue, err := dstArray.GetElementPtr([]uint32{0, 0})
+					if err != nil {
+						return nil, nil, fr.errorAt(inst, err)
+					}
+					dstArray = dstArrayValue.(*LocalValue)
+					srcArrayValue, err := srcArray.GetElementPtr([]uint32{0, 0})
+					if err != nil {
+						return nil, nil, fr.errorAt(inst, err)
+					}
+					srcArray = srcArrayValue.(*LocalValue)
 				}
 				if fr.Eval.TargetData.TypeAllocSize(dstArray.Type().ElementType()) != elementSize {
-					return nil, nil, fr.errorAt(inst, "interp: slice dst element size does not match pointer type")
+					return nil, nil, fr.errorAt(inst, errors.New("interp: slice dst element size does not match pointer type"))
 				}
 				if fr.Eval.TargetData.TypeAllocSize(srcArray.Type().ElementType()) != elementSize {
-					return nil, nil, fr.errorAt(inst, "interp: slice src element size does not match pointer type")
+					return nil, nil, fr.errorAt(inst, errors.New("interp: slice src element size does not match pointer type"))
 				}
 				if dstArray.Type() != srcArray.Type() {
-					return nil, nil, fr.errorAt(inst, "interp: slice element types don't match")
+					return nil, nil, fr.errorAt(inst, errors.New("interp: slice element types don't match"))
 				}
 				length := dstLen.Value().SExtValue()
 				if srcLength := srcLen.Value().SExtValue(); srcLength < length {
 					length = srcLength
 				}
 				if length < 0 {
-					return nil, nil, fr.errorAt(inst, "interp: trying to copy a slice with negative length?")
+					return nil, nil, fr.errorAt(inst, errors.New("interp: trying to copy a slice with negative length?"))
 				}
 				for i := int64(0); i < length; i++ {
 					// *dst = *src
-					dstArray.Store(srcArray.Load())
+					val, err := srcArray.Load()
+					if err != nil {
+						return nil, nil, fr.errorAt(inst, err)
+					}
+					err = dstArray.Store(val)
+					if err != nil {
+						return nil, nil, fr.errorAt(inst, err)
+					}
 					// dst++
-					dstArray = dstArray.GetElementPtr([]uint32{1}).(*LocalValue)
+					dstArrayValue, err := dstArray.GetElementPtr([]uint32{1})
+					if err != nil {
+						return nil, nil, fr.errorAt(inst, err)
+					}
+					dstArray = dstArrayValue.(*LocalValue)
 					// src++
-					srcArray = srcArray.GetElementPtr([]uint32{1}).(*LocalValue)
+					srcArrayValue, err := srcArray.GetElementPtr([]uint32{1})
+					if err != nil {
+						return nil, nil, fr.errorAt(inst, err)
+					}
+					srcArray = srcArrayValue.(*LocalValue)
 				}
 			case callee.Name() == "runtime.stringToBytes":
 				// convert a string to a []byte
 				bufPtr := fr.getLocal(inst.Operand(0))
 				bufLen := fr.getLocal(inst.Operand(1))
-				result := getStringBytes(bufPtr, bufLen.Value())
+				result, err := getStringBytes(bufPtr, bufLen.Value())
+				if err != nil {
+					return nil, nil, fr.errorAt(inst, err)
+				}
 				vals := make([]llvm.Value, len(result))
 				for i := range vals {
 					vals[i] = llvm.ConstInt(fr.Mod.Context().Int8Type(), uint64(result[i]), false)
@@ -416,20 +469,35 @@ func (fr *frame) evalBasicBlock(bb, incoming llvm.BasicBlock, indent string) (re
 				ret = llvm.ConstInsertValue(ret, retLen, []uint32{1}) // len
 				ret = llvm.ConstInsertValue(ret, retLen, []uint32{2}) // cap
 				fr.locals[inst] = &LocalValue{fr.Eval, ret}
+			case callee.Name() == "runtime.typeAssert":
+				actualTypeInt := fr.getLocal(inst.Operand(0)).(*LocalValue).Underlying
+				assertedType := fr.getLocal(inst.Operand(1)).(*LocalValue).Underlying
+				if actualTypeInt.IsAConstantExpr().IsNil() || actualTypeInt.Opcode() != llvm.PtrToInt {
+					return nil, nil, fr.errorAt(inst, errors.New("interp: expected typecode in runtime.typeAssert to be a ptrtoint"))
+				}
+				actualType := actualTypeInt.Operand(0)
+				if actualType.IsAConstant().IsNil() || assertedType.IsAConstant().IsNil() {
+					return nil, nil, fr.errorAt(inst, errors.New("interp: unimplemented: type assert with non-constant interface value"))
+				}
+				assertOk := uint64(0)
+				if llvm.ConstExtractValue(actualType.Initializer(), []uint32{0}) == assertedType {
+					assertOk = 1
+				}
+				fr.locals[inst] = &LocalValue{fr.Eval, llvm.ConstInt(fr.Mod.Context().Int1Type(), assertOk, false)}
 			case callee.Name() == "runtime.interfaceImplements":
 				typecode := fr.getLocal(inst.Operand(0)).(*LocalValue).Underlying
 				interfaceMethodSet := fr.getLocal(inst.Operand(1)).(*LocalValue).Underlying
 				if typecode.IsAConstantExpr().IsNil() || typecode.Opcode() != llvm.PtrToInt {
-					return nil, nil, fr.errorAt(inst, "interp: expected typecode to be a ptrtoint")
+					return nil, nil, fr.errorAt(inst, errors.New("interp: expected typecode to be a ptrtoint"))
 				}
 				typecode = typecode.Operand(0)
 				if interfaceMethodSet.IsAConstantExpr().IsNil() || interfaceMethodSet.Opcode() != llvm.GetElementPtr {
-					return nil, nil, fr.errorAt(inst, "interp: expected method set in runtime.interfaceImplements to be a constant gep")
+					return nil, nil, fr.errorAt(inst, errors.New("interp: expected method set in runtime.interfaceImplements to be a constant gep"))
 				}
 				interfaceMethodSet = interfaceMethodSet.Operand(0).Initializer()
 				methodSet := llvm.ConstExtractValue(typecode.Initializer(), []uint32{1})
 				if methodSet.IsAConstantExpr().IsNil() || methodSet.Opcode() != llvm.GetElementPtr {
-					return nil, nil, fr.errorAt(inst, "interp: expected method set to be a constant gep")
+					return nil, nil, fr.errorAt(inst, errors.New("interp: expected method set to be a constant gep"))
 				}
 				methodSet = methodSet.Operand(0).Initializer()

@@ -529,6 +597,11 @@ func (fr *frame) evalBasicBlock(bb, incoming llvm.BasicBlock, indent string) (re
 					//     interpret anyway and hope for the best.
 					ret, err = fr.function(callee, params, indent+"    ")
 					if err != nil {
+						// Record this function call in the backtrace.
+						err.Traceback = append(err.Traceback, ErrorLine{
+							Pos:  getPosition(inst),
+							Inst: inst,
+						})
 						return nil, nil, err
 					}
 				}
@@ -547,7 +620,7 @@ func (fr *frame) evalBasicBlock(bb, incoming llvm.BasicBlock, indent string) (re
 				fr.locals[inst] = fr.getValue(newValue)
 			} else {
 				if len(indices) != 1 {
-					return nil, nil, fr.errorAt(inst, "interp: cannot handle extractvalue with not exactly 1 index")
+					return nil, nil, fr.errorAt(inst, errors.New("interp: cannot handle extractvalue with not exactly 1 index"))
 				}
 				fr.locals[inst] = &LocalValue{fr.Eval, fr.builder.CreateExtractValue(agg.Underlying, int(indices[0]), inst.Name())}
 			}
@@ -560,10 +633,22 @@ func (fr *frame) evalBasicBlock(bb, incoming llvm.BasicBlock, indent string) (re
 				fr.locals[inst] = &LocalValue{fr.Eval, newValue}
 			} else {
 				if len(indices) != 1 {
-					return nil, nil, fr.errorAt(inst, "interp: cannot handle insertvalue with not exactly 1 index")
+					return nil, nil, fr.errorAt(inst, errors.New("interp: cannot handle insertvalue with not exactly 1 index"))
 				}
 				fr.locals[inst] = &LocalValue{fr.Eval, fr.builder.CreateInsertValue(agg.Underlying, val.Value(), int(indices[0]), inst.Name())}
 			}
+		case !inst.IsASelectInst().IsNil():
+			// var result T
+			// if cond {
+			//   result = x
+			// } else {
+			//   result = y
+			// }
+			// return result
+			cond := fr.getLocal(inst.Operand(0)).(*LocalValue).Underlying
+			x := fr.getLocal(inst.Operand(1)).(*LocalValue).Underlying
+			y := fr.getLocal(inst.Operand(2)).(*LocalValue).Underlying
+			fr.locals[inst] = &LocalValue{fr.Eval, fr.builder.CreateSelect(cond, x, y, "")}

 		case !inst.IsAReturnInst().IsNil() && inst.OperandsCount() == 0:
 			return nil, nil, nil // ret void
@@ -573,17 +658,17 @@ func (fr *frame) evalBasicBlock(bb, incoming llvm.BasicBlock, indent string) (re
 			// conditional branch (if/then/else)
 			cond := fr.getLocal(inst.Operand(0)).Value()
 			if cond.Type() != fr.Mod.Context().Int1Type() {
-				return nil, nil, fr.errorAt(inst, "expected an i1 in a branch instruction")
+				return nil, nil, fr.errorAt(inst, errors.New("expected an i1 in a branch instruction"))
 			}
 			thenBB := inst.Operand(1)
 			elseBB := inst.Operand(2)
 			if !cond.IsAInstruction().IsNil() {
-				return nil, nil, fr.errorAt(inst, "interp: branch on a non-constant")
+				return nil, nil, fr.errorAt(inst, errors.New("interp: branch on a non-constant"))
 			}
 			if !cond.IsAConstantExpr().IsNil() {
 				// This may happen when the instruction builder could not
 				// const-fold some instructions.
-				return nil, nil, fr.errorAt(inst, "interp: branch on a non-const-propagated constant expression")
+				return nil, nil, fr.errorAt(inst, errors.New("interp: branch on a non-const-propagated constant expression"))
 			}
 			switch cond {
 			case llvm.ConstInt(fr.Mod.Context().Int1Type(), 0, false): // false
@@ -591,7 +676,7 @@ func (fr *frame) evalBasicBlock(bb, incoming llvm.BasicBlock, indent string) (re
 			case llvm.ConstInt(fr.Mod.Context().Int1Type(), 1, false): // true
 				return nil, []llvm.Value{elseBB}, nil // else
 			default:
-				return nil, nil, fr.errorAt(inst, "branch was not true or false")
+				return nil, nil, fr.errorAt(inst, errors.New("branch was not true or false"))
 			}
 		case !inst.IsABranchInst().IsNil() && inst.OperandsCount() == 1:
 			// unconditional branch (goto)
@@ -97,7 +97,7 @@ func Run(mod llvm.Module, debug bool) error {
 // function interprets the given function. The params are the function params
 // and the indent is the string indentation to use when dumping all interpreted
 // instructions.
-func (e *evalPackage) function(fn llvm.Value, params []Value, indent string) (Value, error) {
+func (e *evalPackage) function(fn llvm.Value, params []Value, indent string) (Value, *Error) {
 	fr := frame{
 		evalPackage: e,
 		fn:          fn,
@@ -15,6 +15,7 @@ func TestInterp(t *testing.T) {
 		"slice-copy",
 		"consteval",
 		"map",
+		"interface",
 	} {
 		name := name // make tc local to this closure
 		t.Run(name, func(t *testing.T) {
@@ -1,6 +1,7 @@
 package interp

 import (
+	"errors"
 	"strings"

 	"tinygo.org/x/go-llvm"
@@ -40,7 +41,7 @@ type sideEffectResult struct {
 // hasSideEffects scans this function and all descendants, recursively. It
 // returns whether this function has side effects and if it does, which globals
 // it mentions anywhere in this function or any called functions.
-func (e *evalPackage) hasSideEffects(fn llvm.Value) (*sideEffectResult, error) {
+func (e *evalPackage) hasSideEffects(fn llvm.Value) (*sideEffectResult, *Error) {
 	name := fn.Name()
 	switch {
 	case name == "runtime.alloc":
@@ -51,6 +52,8 @@ func (e *evalPackage) hasSideEffects(fn llvm.Value) (*sideEffectResult, error) {
 		return &sideEffectResult{severity: sideEffectNone}, nil
 	case name == "runtime._panic":
 		return &sideEffectResult{severity: sideEffectLimited}, nil
+	case name == "runtime.typeAssert":
+		return &sideEffectResult{severity: sideEffectNone}, nil
 	case name == "runtime.interfaceImplements":
 		return &sideEffectResult{severity: sideEffectNone}, nil
 	case name == "runtime.sliceCopy":
@@ -59,6 +62,10 @@ func (e *evalPackage) hasSideEffects(fn llvm.Value) (*sideEffectResult, error) {
 		return &sideEffectResult{severity: sideEffectNone}, nil
 	case name == "llvm.dbg.value":
 		return &sideEffectResult{severity: sideEffectNone}, nil
+	case name == "(*sync/atomic.Value).Load" || name == "(*sync/atomic.Value).Store":
+		// These functions do some unsafe pointer loading/storing but are
+		// otherwise safe.
+		return &sideEffectResult{severity: sideEffectLimited}, nil
 	case strings.HasPrefix(name, "llvm.lifetime."):
 		return &sideEffectResult{severity: sideEffectNone}, nil
 	}
@@ -97,7 +104,7 @@ func (e *evalPackage) hasSideEffects(fn llvm.Value) (*sideEffectResult, error) {
 			switch inst.InstructionOpcode() {
 			case llvm.IndirectBr, llvm.Invoke:
 				// Not emitted by the compiler.
-				return nil, e.errorAt(inst, "unknown instructions")
+				return nil, e.errorAt(inst, errors.New("unknown instructions"))
 			case llvm.Call:
 				child := inst.CalledValue()
 				if !child.IsAInlineAsm().IsNil() {
@@ -118,6 +125,14 @@ func (e *evalPackage) hasSideEffects(fn llvm.Value) (*sideEffectResult, error) {
 				if child.IsDeclaration() {
 					// External function call. Assume only limited side effects
 					// (no affected globals, etc.).
+					switch child.Name() {
+					case "runtime.alloc":
+						continue
+					case "runtime.typeAssert":
+						continue // implemented in interp
+					case "runtime.interfaceImplements":
+						continue // implemented in interp
+					}
 					if e.hasLocalSideEffects(dirtyLocals, inst) {
 						result.updateSeverity(sideEffectLimited)
 					}
@@ -23,6 +23,8 @@ var scanTestTable = []struct {
 	{"callFunctionPointer", sideEffectAll, []string{"functionPointer"}},
 	{"getDirtyPointer", sideEffectLimited, nil},
 	{"storeToPointer", sideEffectLimited, nil},
+	{"callTypeAssert", sideEffectNone, nil},
+	{"callInterfaceImplements", sideEffectNone, nil},
 }

 func TestScan(t *testing.T) {
@@ -0,0 +1,28 @@
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64--linux"
+
+%runtime.typecodeID = type { %runtime.typecodeID*, i64 }
+%runtime.interfaceMethodInfo = type { i8*, i64 }
+%runtime.typeInInterface = type { %runtime.typecodeID*, %runtime.interfaceMethodInfo* }
+
+@main.v1 = global i1 0
+@"reflect/types.type:named:main.foo" = private constant %runtime.typecodeID { %runtime.typecodeID* @"reflect/types.type:basic:int", i64 0 }
+@"reflect/types.type:basic:int" = external constant %runtime.typecodeID
+@"typeInInterface:reflect/types.type:named:main.foo" = private constant %runtime.typeInInterface { %runtime.typecodeID* @"reflect/types.type:named:main.foo", %runtime.interfaceMethodInfo* null }
+
+
+declare i1 @runtime.typeAssert(i64, %runtime.typecodeID*, i8*, i8*)
+
+define void @runtime.initAll() unnamed_addr {
+entry:
+  call void @main.init()
+  ret void
+}
+
+define internal void @main.init() unnamed_addr {
+entry:
+  ; Test type asserts.
+  %typecode = call i1 @runtime.typeAssert(i64 ptrtoint (%runtime.typeInInterface* @"typeInInterface:reflect/types.type:named:main.foo" to i64), %runtime.typecodeID* @"reflect/types.type:named:main.foo", i8* undef, i8* null)
+  store i1 %typecode, i1* @main.v1
+  ret void
+}
@@ -0,0 +1,9 @@
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64--linux"
+
+@main.v1 = local_unnamed_addr global i1 true
+
+define void @runtime.initAll() unnamed_addr {
+entry:
+  ret void
+}
@@ -1,6 +1,11 @@
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64--linux"

+%runtime.typecodeID = type { %runtime.typecodeID*, i64 }
+
+declare i1 @runtime.typeAssert(i64, %runtime.typecodeID*, i8*, i8*)
+declare i1 @runtime.interfaceImplements(i64, i8**)
+
 define i64 @returnsConst() {
  ret i64 0
 }
@@ -59,3 +64,15 @@ define i64 @callFunctionPointer() {
  %result = call i64 %fp()
  ret i64 %result
 }
+
+define i1 @callTypeAssert() {
+  ; Note: parameters are not realistic.
+  %ok = call i1 @runtime.typeAssert(i64 0, %runtime.typecodeID* null, i8* undef, i8* null)
+  ret i1 %ok
+}
+
+define i1 @callInterfaceImplements() {
+  ; Note: parameters are not realistic.
+  %ok = call i1 @runtime.interfaceImplements(i64 0, i8** null)
+  ret i1 %ok
+}
@@ -1,6 +1,8 @@
 package interp

 import (
+	"errors"
+
 	"tinygo.org/x/go-llvm"
 )

@@ -18,16 +20,23 @@ func getUses(value llvm.Value) []llvm.Value {

 // getStringBytes loads the byte slice of a Go string represented as a
 // {ptr, len} pair.
-func getStringBytes(strPtr Value, strLen llvm.Value) []byte {
+func getStringBytes(strPtr Value, strLen llvm.Value) ([]byte, error) {
 	if !strLen.IsConstant() {
-		panic("getStringBytes with a non-constant length")
+		return nil, errors.New("getStringBytes with a non-constant length")
 	}
 	buf := make([]byte, strLen.ZExtValue())
 	for i := range buf {
-		c := strPtr.GetElementPtr([]uint32{uint32(i)}).Load()
+		gep, err := strPtr.GetElementPtr([]uint32{uint32(i)})
+		if err != nil {
+			return nil, err
+		}
+		c, err := gep.Load()
+		if err != nil {
+			return nil, err
+		}
 		buf[i] = byte(c.ZExtValue())
 	}
-	return buf
+	return buf, nil
 }

 // getLLVMIndices converts an []uint32 into an []llvm.Value, for use in
@@ -3,6 +3,7 @@ package interp
 // This file provides a litte bit of abstraction around LLVM values.

 import (
+	"errors"
 	"strconv"

 	"tinygo.org/x/go-llvm"
@@ -11,13 +12,13 @@ import (
 // A Value is a LLVM value with some extra methods attached for easier
 // interpretation.
 type Value interface {
-	Value() llvm.Value            // returns a LLVM value
-	Type() llvm.Type              // equal to Value().Type()
-	IsConstant() bool             // returns true if this value is a constant value
-	Load() llvm.Value             // dereference a pointer
-	Store(llvm.Value)             // store to a pointer
-	GetElementPtr([]uint32) Value // returns an interior pointer
-	String() string               // string representation, for debugging
+	Value() llvm.Value                     // returns a LLVM value
+	Type() llvm.Type                       // equal to Value().Type()
+	IsConstant() bool                      // returns true if this value is a constant value
+	Load() (llvm.Value, error)             // dereference a pointer
+	Store(llvm.Value) error                // store to a pointer
+	GetElementPtr([]uint32) (Value, error) // returns an interior pointer
+	String() string                        // string representation, for debugging
 }

 // A type that simply wraps a LLVM constant value.
@@ -43,29 +44,32 @@ func (v *LocalValue) IsConstant() bool {
 }

 // Load loads a constant value if this is a constant pointer.
-func (v *LocalValue) Load() llvm.Value {
+func (v *LocalValue) Load() (llvm.Value, error) {
 	if !v.Underlying.IsAGlobalVariable().IsNil() {
-		return v.Underlying.Initializer()
+		return v.Underlying.Initializer(), nil
 	}
 	switch v.Underlying.Opcode() {
 	case llvm.GetElementPtr:
 		indices := v.getConstGEPIndices()
 		if indices[0] != 0 {
-			panic("invalid GEP")
+			return llvm.Value{}, errors.New("invalid GEP")
 		}
 		global := v.Eval.getValue(v.Underlying.Operand(0))
-		agg := global.Load()
-		return llvm.ConstExtractValue(agg, indices[1:])
+		agg, err := global.Load()
+		if err != nil {
+			return llvm.Value{}, err
+		}
+		return llvm.ConstExtractValue(agg, indices[1:]), nil
 	case llvm.BitCast:
-		panic("interp: load from a bitcast")
+		return llvm.Value{}, errors.New("interp: load from a bitcast")
 	default:
-		panic("interp: load from a constant")
+		return llvm.Value{}, errors.New("interp: load from a constant")
 	}
 }

 // Store stores to the underlying value if the value type is a pointer type,
-// otherwise it panics.
-func (v *LocalValue) Store(value llvm.Value) {
+// otherwise it returns an error.
+func (v *LocalValue) Store(value llvm.Value) error {
 	if !v.Underlying.IsAGlobalVariable().IsNil() {
 		if !value.IsConstant() {
 			v.MarkDirty()
@@ -73,45 +77,47 @@ func (v *LocalValue) Store(value llvm.Value) {
 		} else {
 			v.Underlying.SetInitializer(value)
 		}
-		return
+		return nil
 	}
 	if !value.IsConstant() {
 		v.MarkDirty()
 		v.Eval.builder.CreateStore(value, v.Underlying)
-		return
+		return nil
 	}
 	switch v.Underlying.Opcode() {
 	case llvm.GetElementPtr:
 		indices := v.getConstGEPIndices()
 		if indices[0] != 0 {
-			panic("invalid GEP")
+			return errors.New("invalid GEP")
 		}
 		global := &LocalValue{v.Eval, v.Underlying.Operand(0)}
-		agg := global.Load()
+		agg, err := global.Load()
+		if err != nil {
+			return err
+		}
 		agg = llvm.ConstInsertValue(agg, value, indices[1:])
-		global.Store(agg)
-		return
+		return global.Store(agg)
 	default:
-		panic("interp: store on a constant")
+		return errors.New("interp: store on a constant")
 	}
 }

 // GetElementPtr returns a GEP when the underlying value is of pointer type.
-func (v *LocalValue) GetElementPtr(indices []uint32) Value {
+func (v *LocalValue) GetElementPtr(indices []uint32) (Value, error) {
 	if !v.Underlying.IsAGlobalVariable().IsNil() {
 		int32Type := v.Underlying.Type().Context().Int32Type()
 		gep := llvm.ConstGEP(v.Underlying, getLLVMIndices(int32Type, indices))
-		return &LocalValue{v.Eval, gep}
+		return &LocalValue{v.Eval, gep}, nil
 	}
 	if !v.Underlying.IsAConstantExpr().IsNil() {
 		switch v.Underlying.Opcode() {
 		case llvm.GetElementPtr, llvm.IntToPtr, llvm.BitCast:
 			int32Type := v.Underlying.Type().Context().Int32Type()
 			llvmIndices := getLLVMIndices(int32Type, indices)
-			return &LocalValue{v.Eval, llvm.ConstGEP(v.Underlying, llvmIndices)}
+			return &LocalValue{v.Eval, llvm.ConstGEP(v.Underlying, llvmIndices)}, nil
 		}
 	}
-	panic("interp: unknown GEP")
+	return nil, errors.New("interp: unknown GEP")
 }

 // stripPointerCasts removes all const bitcasts from pointer values, if there
@@ -224,7 +230,11 @@ func (v *MapValue) Value() llvm.Value {
 			keyPtr := llvm.ConstExtractValue(llvmKey, []uint32{0})
 			keyLen := llvm.ConstExtractValue(llvmKey, []uint32{1})
 			keyPtrVal := v.Eval.getValue(keyPtr)
-			keyBuf = getStringBytes(keyPtrVal, keyLen)
+			var err error
+			keyBuf, err = getStringBytes(keyPtrVal, keyLen)
+			if err != nil {
+				panic(err) // TODO
+			}
 		} else if key.Type().TypeKind() == llvm.IntegerTypeKind {
 			keyBuf = make([]byte, v.Eval.TargetData.TypeAllocSize(key.Type()))
 			n := key.Value().ZExtValue()
@@ -298,40 +308,45 @@ func (v *MapValue) IsConstant() bool {
 }

 // Load panics: maps are of reference type so cannot be dereferenced.
-func (v *MapValue) Load() llvm.Value {
+func (v *MapValue) Load() (llvm.Value, error) {
 	panic("interp: load from a map")
 }

-// Store panics: maps are of reference type so cannot be stored to.
-func (v *MapValue) Store(value llvm.Value) {
-	panic("interp: store on a map")
+// Store returns an error: maps are of reference type so cannot be stored to.
+func (v *MapValue) Store(value llvm.Value) error {
+	// This must be a bug, but it might be helpful to indicate the location
+	// anyway.
+	return errors.New("interp: store on a map")
 }

 // GetElementPtr panics: maps are of reference type so their (interior)
 // addresses cannot be calculated.
-func (v *MapValue) GetElementPtr(indices []uint32) Value {
-	panic("interp: GEP on a map")
+func (v *MapValue) GetElementPtr(indices []uint32) (Value, error) {
+	return nil, errors.New("interp: GEP on a map")
 }

 // PutString does a map assign operation, assuming that the map is of type
 // map[string]T.
-func (v *MapValue) PutString(keyBuf, keyLen, valPtr *LocalValue) {
+func (v *MapValue) PutString(keyBuf, keyLen, valPtr *LocalValue) error {
 	if !v.Underlying.IsNil() {
-		panic("map already created")
+		return errors.New("map already created")
 	}

 	if valPtr.Underlying.Opcode() == llvm.BitCast {
 		valPtr = &LocalValue{v.Eval, valPtr.Underlying.Operand(0)}
 	}
-	value := valPtr.Load()
+	value, err := valPtr.Load()
+	if err != nil {
+		return err
+	}
 	if v.ValueType.IsNil() {
 		v.ValueType = value.Type()
 		if int(v.Eval.TargetData.TypeAllocSize(v.ValueType)) != v.ValueSize {
-			panic("interp: map store value type has the wrong size")
+			return errors.New("interp: map store value type has the wrong size")
 		}
 	} else {
 		if value.Type() != v.ValueType {
-			panic("interp: map store value type is inconsistent")
+			return errors.New("interp: map store value type is inconsistent")
 		}
 	}

@@ -344,26 +359,31 @@ func (v *MapValue) PutString(keyBuf, keyLen, valPtr *LocalValue) {
 	// TODO: avoid duplicate keys
 	v.Keys = append(v.Keys, &LocalValue{v.Eval, key})
 	v.Values = append(v.Values, &LocalValue{v.Eval, value})
+
+	return nil
 }

 // PutBinary does a map assign operation.
-func (v *MapValue) PutBinary(keyPtr, valPtr *LocalValue) {
+func (v *MapValue) PutBinary(keyPtr, valPtr *LocalValue) error {
 	if !v.Underlying.IsNil() {
-		panic("map already created")
+		return errors.New("map already created")
 	}

 	if valPtr.Underlying.Opcode() == llvm.BitCast {
 		valPtr = &LocalValue{v.Eval, valPtr.Underlying.Operand(0)}
 	}
-	value := valPtr.Load()
+	value, err := valPtr.Load()
+	if err != nil {
+		return err
+	}
 	if v.ValueType.IsNil() {
 		v.ValueType = value.Type()
 		if int(v.Eval.TargetData.TypeAllocSize(v.ValueType)) != v.ValueSize {
-			panic("interp: map store value type has the wrong size")
+			return errors.New("interp: map store value type has the wrong size")
 		}
 	} else {
 		if value.Type() != v.ValueType {
-			panic("interp: map store value type is inconsistent")
+			return errors.New("interp: map store value type is inconsistent")
 		}
 	}

@@ -374,21 +394,26 @@ func (v *MapValue) PutBinary(keyPtr, valPtr *LocalValue) {
 			keyPtr = &LocalValue{v.Eval, keyPtr.Underlying.Operand(0)}
 		}
 	}
-	key := keyPtr.Load()
+	key, err := keyPtr.Load()
+	if err != nil {
+		return err
+	}
 	if v.KeyType.IsNil() {
 		v.KeyType = key.Type()
 		if int(v.Eval.TargetData.TypeAllocSize(v.KeyType)) != v.KeySize {
-			panic("interp: map store key type has the wrong size")
+			return errors.New("interp: map store key type has the wrong size")
 		}
 	} else {
 		if key.Type() != v.KeyType {
-			panic("interp: map store key type is inconsistent")
+			return errors.New("interp: map store key type is inconsistent")
 		}
 	}

 	// TODO: avoid duplicate keys
 	v.Keys = append(v.Keys, &LocalValue{v.Eval, key})
 	v.Values = append(v.Values, &LocalValue{v.Eval, value})
+
+	return nil
 }

 // Get FNV-1a hash of this string.
@@ -27,14 +27,13 @@ type Program struct {
 // Function or method.
 type Function struct {
 	*ssa.Function
-	LLVMFn    llvm.Value
-	module    string     // go:wasm-module
-	linkName  string     // go:linkname, go:export, go:interrupt
-	exported  bool       // go:export
-	nobounds  bool       // go:nobounds
-	flag      bool       // used by dead code elimination
-	interrupt bool       // go:interrupt
-	inline    InlineType // go:inline
+	LLVMFn   llvm.Value
+	module   string     // go:wasm-module
+	linkName string     // go:linkname, go:export
+	exported bool       // go:export
+	nobounds bool       // go:nobounds
+	flag     bool       // used by dead code elimination
+	inline   InlineType // go:inline
 }

 // Interface type that is at some point used in a type assert (to check whether
@@ -64,73 +63,14 @@ const (
 )

 // Create and initialize a new *Program from a *ssa.Program.
-func NewProgram(lprogram *loader.Program, mainPath string) *Program {
+func NewProgram(lprogram *loader.Program) *Program {
 	program := lprogram.LoadSSA()
 	program.Build()

-	// Find the main package, which is a bit difficult when running a .go file
-	// directly.
-	mainPkg := program.ImportedPackage(mainPath)
-	if mainPkg == nil {
-		for _, pkgInfo := range program.AllPackages() {
-			if pkgInfo.Pkg.Name() == "main" {
-				if mainPkg != nil {
-					panic("more than one main package found")
-				}
-				mainPkg = pkgInfo
-			}
-		}
-	}
+	mainPkg := program.ImportedPackage(lprogram.MainPkg().ImportPath)
 	if mainPkg == nil {
 		panic("could not find main package")
 	}
-
-	// Make a list of packages in import order.
-	packageList := []*ssa.Package{}
-	packageSet := map[string]struct{}{}
-	worklist := []string{"runtime", mainPath}
-	for len(worklist) != 0 {
-		pkgPath := worklist[0]
-		var pkg *ssa.Package
-		if pkgPath == mainPath {
-			pkg = mainPkg // necessary for compiling individual .go files
-		} else {
-			pkg = program.ImportedPackage(pkgPath)
-		}
-		if pkg == nil {
-			// Non-SSA package (e.g. cgo).
-			packageSet[pkgPath] = struct{}{}
-			worklist = worklist[1:]
-			continue
-		}
-		if _, ok := packageSet[pkgPath]; ok {
-			// Package already in the final package list.
-			worklist = worklist[1:]
-			continue
-		}
-
-		unsatisfiedImports := make([]string, 0)
-		imports := pkg.Pkg.Imports()
-		for _, pkg := range imports {
-			if _, ok := packageSet[pkg.Path()]; ok {
-				continue
-			}
-			unsatisfiedImports = append(unsatisfiedImports, pkg.Path())
-		}
-		if len(unsatisfiedImports) == 0 {
-			// All dependencies of this package are satisfied, so add this
-			// package to the list.
-			packageList = append(packageList, pkg)
-			packageSet[pkgPath] = struct{}{}
-			worklist = worklist[1:]
-		} else {
-			// Prepend all dependencies to the worklist and reconsider this
-			// package (by not removing it from the worklist). At that point, it
-			// must be possible to add it to packageList.
-			worklist = append(unsatisfiedImports, worklist...)
-		}
-	}
-
 	p := &Program{
 		Program:       program,
 		LoaderProgram: lprogram,
@@ -138,8 +78,8 @@ func NewProgram(lprogram *loader.Program, mainPath string) *Program {
 		functionMap:   make(map[*ssa.Function]*Function),
 	}

-	for _, pkg := range packageList {
-		p.AddPackage(pkg)
+	for _, pkg := range lprogram.Sorted() {
+		p.AddPackage(program.ImportedPackage(pkg.ImportPath))
 	}

 	return p
@@ -243,18 +183,6 @@ func (f *Function) parsePragmas() {
 				f.inline = InlineHint
 			case "//go:noinline":
 				f.inline = InlineNone
-			case "//go:interrupt":
-				if len(parts) != 2 {
-					continue
-				}
-				name := parts[1]
-				if strings.HasSuffix(name, "_vect") {
-					// AVR vector naming
-					name = "__vector_" + name[:len(name)-5]
-				}
-				f.linkName = name
-				f.exported = true
-				f.interrupt = true
 			case "//go:linkname":
 				if len(parts) != 3 || parts[1] != f.Name() {
 					continue
@@ -288,14 +216,6 @@ func (f *Function) IsExported() bool {
 	return f.exported || f.CName() != ""
 }

-// Return true for functions annotated with //go:interrupt. The function name is
-// already customized in LinkName() to hook up in the interrupt vector.
-//
-// On some platforms (like AVR), interrupts need a special compiler flag.
-func (f *Function) IsInterrupt() bool {
-	return f.interrupt
-}
-
 // Return the inline directive of this function.
 func (f *Function) Inline() InlineType {
 	return f.inline
@@ -1,6 +1,7 @@
 package ir

 import (
+	"errors"
 	"go/types"

 	"golang.org/x/tools/go/ssa"
@@ -58,7 +59,7 @@ func signature(sig *types.Signature) string {

 // Simple pass that removes dead code. This pass makes later analysis passes
 // more useful.
-func (p *Program) SimpleDCE() {
+func (p *Program) SimpleDCE() error {
 	// Unmark all functions.
 	for _, f := range p.Functions {
 		f.flag = false
@@ -66,13 +67,21 @@ func (p *Program) SimpleDCE() {

 	// Initial set of live functions. Include main.main, *.init and runtime.*
 	// functions.
-	main := p.mainPkg.Members["main"].(*ssa.Function)
+	main, ok := p.mainPkg.Members["main"].(*ssa.Function)
+	if !ok {
+		if p.mainPkg.Members["main"] == nil {
+			return errors.New("function main is undeclared in the main package")
+		} else {
+			return errors.New("cannot declare main - must be func")
+		}
+	}
 	runtimePkg := p.Program.ImportedPackage("runtime")
 	mathPkg := p.Program.ImportedPackage("math")
+	taskPkg := p.Program.ImportedPackage("internal/task")
 	p.GetFunction(main).flag = true
 	worklist := []*ssa.Function{main}
 	for _, f := range p.Functions {
-		if f.exported || f.Synthetic == "package initializer" || f.Pkg == runtimePkg || (f.Pkg == mathPkg && f.Pkg != nil) {
+		if f.exported || f.Synthetic == "package initializer" || f.Pkg == runtimePkg || f.Pkg == taskPkg || (f.Pkg == mathPkg && f.Pkg != nil) {
 			if f.flag {
 				continue
 			}
@@ -135,4 +144,6 @@ func (p *Program) SimpleDCE() {
 		}
 	}
 	p.Functions = livefunctions
+
+	return nil
 }
@@ -1,9 +1,6 @@
 package loader

-import (
-	"go/token"
-	"strings"
-)
+import "go/scanner"

 // Errors contains a list of parser errors or a list of typechecker errors for
 // the given package.
@@ -16,24 +13,13 @@ func (e Errors) Error() string {
 	return "could not compile: " + e.Errs[0].Error()
 }

-// ImportCycleErrors is returned when encountering an import cycle. The list of
-// packages is a list from the root package to the leaf package that imports one
-// of the packages in the list.
-type ImportCycleError struct {
-	Packages        []string
-	ImportPositions []token.Position
+// Error is a regular error but with an added import stack. This is especially
+// useful for debugging import cycle errors.
+type Error struct {
+	ImportStack []string
+	Err         scanner.Error
 }

-func (e *ImportCycleError) Error() string {
-	var msg strings.Builder
-	msg.WriteString("import cycle:\n\t")
-	msg.WriteString(strings.Join(e.Packages, "\n\t"))
-	msg.WriteString("\n at ")
-	for i, pos := range e.ImportPositions {
-		if i > 0 {
-			msg.WriteString(", ")
-		}
-		msg.WriteString(pos.String())
-	}
-	return msg.String()
+func (e Error) Error() string {
+	return e.Err.Error()
 }
@@ -0,0 +1,281 @@
+package loader
+
+// This file constructs a new temporary GOROOT directory by merging both the
+// standard Go GOROOT and the GOROOT from TinyGo using symlinks.
+
+import (
+	"crypto/sha512"
+	"encoding/hex"
+	"errors"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"os"
+	"os/exec"
+	"path"
+	"path/filepath"
+	"runtime"
+	"sync"
+
+	"github.com/tinygo-org/tinygo/compileopts"
+	"github.com/tinygo-org/tinygo/goenv"
+)
+
+var gorootCreateMutex sync.Mutex
+
+// GetCachedGoroot creates a new GOROOT by merging both the standard GOROOT and
+// the GOROOT from TinyGo using lots of symbolic links.
+func GetCachedGoroot(config *compileopts.Config) (string, error) {
+	goroot := goenv.Get("GOROOT")
+	if goroot == "" {
+		return "", errors.New("could not determine GOROOT")
+	}
+	tinygoroot := goenv.Get("TINYGOROOT")
+	if tinygoroot == "" {
+		return "", errors.New("could not determine TINYGOROOT")
+	}
+
+	// Determine the location of the cached GOROOT.
+	version, err := goenv.GorootVersionString(goroot)
+	if err != nil {
+		return "", err
+	}
+	// This hash is really a cache key, that contains (hopefully) enough
+	// information to make collisions unlikely during development.
+	// By including the Go version and TinyGo version, cache collisions should
+	// not happen outside of development.
+	hash := sha512.New512_256()
+	fmt.Fprintln(hash, goroot)
+	fmt.Fprintln(hash, version)
+	fmt.Fprintln(hash, goenv.Version)
+	fmt.Fprintln(hash, tinygoroot)
+	gorootsHash := hash.Sum(nil)
+	gorootsHashHex := hex.EncodeToString(gorootsHash[:])
+	cachedgorootName := "goroot-" + version + "-" + gorootsHashHex
+	cachedgoroot := filepath.Join(goenv.Get("GOCACHE"), cachedgorootName)
+	if needsSyscallPackage(config.BuildTags()) {
+		cachedgoroot += "-syscall"
+	}
+
+	// Do not try to create the cached GOROOT in parallel, that's only a waste
+	// of I/O bandwidth and thus speed. Instead, use a mutex to make sure only
+	// one goroutine does it at a time.
+	// This is not a way to ensure atomicity (a different TinyGo invocation
+	// could be creating the same directory), but instead a way to avoid
+	// creating it many times in parallel when running tests in parallel.
+	gorootCreateMutex.Lock()
+	defer gorootCreateMutex.Unlock()
+
+	if _, err := os.Stat(cachedgoroot); err == nil {
+		return cachedgoroot, nil
+	}
+	err = os.MkdirAll(goenv.Get("GOCACHE"), 0777)
+	if err != nil {
+		return "", err
+	}
+	tmpgoroot, err := ioutil.TempDir(goenv.Get("GOCACHE"), cachedgorootName+".tmp")
+	if err != nil {
+		return "", err
+	}
+
+	// Remove the temporary directory if it wasn't moved to the right place
+	// (for example, when there was an error).
+	defer os.RemoveAll(tmpgoroot)
+
+	for _, name := range []string{"bin", "lib", "pkg"} {
+		err = symlink(filepath.Join(goroot, name), filepath.Join(tmpgoroot, name))
+		if err != nil {
+			return "", err
+		}
+	}
+	err = mergeDirectory(goroot, tinygoroot, tmpgoroot, "", pathsToOverride(needsSyscallPackage(config.BuildTags())))
+	if err != nil {
+		return "", err
+	}
+	err = os.Rename(tmpgoroot, cachedgoroot)
+	if err != nil {
+		if os.IsExist(err) {
+			// Another invocation of TinyGo also seems to have created a GOROOT.
+			// Use that one instead. Our new GOROOT will be automatically
+			// deleted by the defer above.
+			return cachedgoroot, nil
+		}
+		if runtime.GOOS == "windows" && os.IsPermission(err) {
+			// On Windows, a rename with a destination directory that already
+			// exists does not result in an IsExist error, but rather in an
+			// access denied error. To be sure, check for this case by checking
+			// whether the target directory exists.
+			if _, err := os.Stat(cachedgoroot); err == nil {
+				return cachedgoroot, nil
+			}
+		}
+		return "", err
+	}
+	return cachedgoroot, nil
+}
+
+// mergeDirectory merges two roots recursively. The tmpgoroot is the directory
+// that will be created by this call by either symlinking the directory from
+// goroot or tinygoroot, or by creating the directory and merging the contents.
+func mergeDirectory(goroot, tinygoroot, tmpgoroot, importPath string, overrides map[string]bool) error {
+	if mergeSubdirs, ok := overrides[importPath+"/"]; ok {
+		if !mergeSubdirs {
+			// This directory and all subdirectories should come from the TinyGo
+			// root, so simply make a symlink.
+			newname := filepath.Join(tmpgoroot, "src", importPath)
+			oldname := filepath.Join(tinygoroot, "src", importPath)
+			return symlink(oldname, newname)
+		}
+
+		// Merge subdirectories. Start by making the directory to merge.
+		err := os.Mkdir(filepath.Join(tmpgoroot, "src", importPath), 0777)
+		if err != nil {
+			return err
+		}
+
+		// Symlink all files from TinyGo, and symlink directories from TinyGo
+		// that need to be overridden.
+		tinygoEntries, err := ioutil.ReadDir(filepath.Join(tinygoroot, "src", importPath))
+		if err != nil {
+			return err
+		}
+		for _, e := range tinygoEntries {
+			if e.IsDir() {
+				// A directory, so merge this thing.
+				err := mergeDirectory(goroot, tinygoroot, tmpgoroot, path.Join(importPath, e.Name()), overrides)
+				if err != nil {
+					return err
+				}
+			} else {
+				// A file, so symlink this.
+				newname := filepath.Join(tmpgoroot, "src", importPath, e.Name())
+				oldname := filepath.Join(tinygoroot, "src", importPath, e.Name())
+				err := symlink(oldname, newname)
+				if err != nil {
+					return err
+				}
+			}
+		}
+
+		// Symlink all directories from $GOROOT that are not part of the TinyGo
+		// overrides.
+		gorootEntries, err := ioutil.ReadDir(filepath.Join(goroot, "src", importPath))
+		if err != nil {
+			return err
+		}
+		for _, e := range gorootEntries {
+			if !e.IsDir() {
+				// Don't merge in files from Go. Otherwise we'd end up with a
+				// weird syscall package with files from both roots.
+				continue
+			}
+			if _, ok := overrides[path.Join(importPath, e.Name())+"/"]; ok {
+				// Already included above, so don't bother trying to create this
+				// symlink.
+				continue
+			}
+			newname := filepath.Join(tmpgoroot, "src", importPath, e.Name())
+			oldname := filepath.Join(goroot, "src", importPath, e.Name())
+			err := symlink(oldname, newname)
+			if err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
+// needsSyscallPackage returns whether the syscall package should be overriden
+// with the TinyGo version. This is the case on some targets.
+func needsSyscallPackage(buildTags []string) bool {
+	for _, tag := range buildTags {
+		if tag == "baremetal" || tag == "darwin" || tag == "nintendoswitch" {
+			return true
+		}
+	}
+	return false
+}
+
+// The boolean indicates whether to merge the subdirs. True means merge, false
+// means use the TinyGo version.
+func pathsToOverride(needsSyscallPackage bool) map[string]bool {
+	paths := map[string]bool{
+		"/":                     true,
+		"device/":               false,
+		"examples/":             false,
+		"internal/":             true,
+		"internal/bytealg/":     false,
+		"internal/reflectlite/": false,
+		"internal/task/":        false,
+		"machine/":              false,
+		"os/":                   true,
+		"reflect/":              false,
+		"runtime/":              false,
+		"sync/":                 true,
+		"testing/":              true,
+	}
+	if needsSyscallPackage {
+		paths["syscall/"] = true // include syscall/js
+	}
+	return paths
+}
+
+// symlink creates a symlink or something similar. On Unix-like systems, it
+// always creates a symlink. On Windows, it tries to create a symlink and if
+// that fails, creates a hardlink or directory junction instead.
+//
+// Note that while Windows 10 does support symlinks and allows them to be
+// created using os.Symlink, it requires developer mode to be enabled.
+// Therefore provide a fallback for when symlinking is not possible.
+// Unfortunately this fallback only works when TinyGo is installed on the same
+// filesystem as the TinyGo cache and the Go installation (which is usually the
+// C drive).
+func symlink(oldname, newname string) error {
+	symlinkErr := os.Symlink(oldname, newname)
+	if runtime.GOOS == "windows" && symlinkErr != nil {
+		// Fallback for when developer mode is disabled.
+		// Note that we return the symlink error even if something else fails
+		// later on. This is because symlinks are the easiest to support
+		// (they're also used on Linux and MacOS) and enabling them is easy:
+		// just enable developer mode.
+		st, err := os.Stat(oldname)
+		if err != nil {
+			return symlinkErr
+		}
+		if st.IsDir() {
+			// Make a directory junction. There may be a way to do this
+			// programmatically, but it involves a lot of magic. Use the mklink
+			// command built into cmd instead (mklink is a builtin, not an
+			// external command).
+			err := exec.Command("cmd", "/k", "mklink", "/J", newname, oldname).Run()
+			if err != nil {
+				return symlinkErr
+			}
+		} else {
+			// Try making a hard link.
+			err := os.Link(oldname, newname)
+			if err != nil {
+				// Making a hardlink failed. Try copying the file as a last
+				// fallback.
+				inf, err := os.Open(oldname)
+				if err != nil {
+					return err
+				}
+				defer inf.Close()
+				outf, err := os.Create(newname)
+				if err != nil {
+					return err
+				}
+				defer outf.Close()
+				_, err = io.Copy(outf, inf)
+				if err != nil {
+					os.Remove(newname)
+					return err
+				}
+				// File was copied.
+			}
+		}
+		return nil // success
+	}
+	return symlinkErr
+}
@@ -0,0 +1,30 @@
+package loader
+
+import (
+	"os"
+	"os/exec"
+	"strings"
+
+	"github.com/tinygo-org/tinygo/compileopts"
+)
+
+// List returns a ready-to-run *exec.Cmd for running the `go list` command with
+// the configuration used for TinyGo.
+func List(config *compileopts.Config, extraArgs, pkgs []string) (*exec.Cmd, error) {
+	goroot, err := GetCachedGoroot(config)
+	if err != nil {
+		return nil, err
+	}
+	args := append([]string{"list"}, extraArgs...)
+	if len(config.BuildTags()) != 0 {
+		args = append(args, "-tags", strings.Join(config.BuildTags(), " "))
+	}
+	args = append(args, pkgs...)
+	cgoEnabled := "0"
+	if config.CgoEnabled() {
+		cgoEnabled = "1"
+	}
+	cmd := exec.Command("go", args...)
+	cmd.Env = append(os.Environ(), "GOROOT="+goroot, "GOOS="+config.GOOS(), "GOARCH="+config.GOARCH(), "CGO_ENABLED="+cgoEnabled)
+	return cmd, nil
+}
@@ -2,226 +2,239 @@ package loader

 import (
 	"bytes"
+	"encoding/json"
 	"errors"
+	"fmt"
 	"go/ast"
-	"go/build"
 	"go/parser"
 	"go/scanner"
 	"go/token"
 	"go/types"
+	"io"
 	"os"
+	"os/exec"
 	"path/filepath"
-	"sort"
+	"strconv"
 	"strings"
-	"text/template"
+	"syscall"

 	"github.com/tinygo-org/tinygo/cgo"
+	"github.com/tinygo-org/tinygo/compileopts"
+	"github.com/tinygo-org/tinygo/goenv"
 )

 // Program holds all packages and some metadata about the program as a whole.
 type Program struct {
-	mainPkg      string
-	Build        *build.Context
-	OverlayBuild *build.Context
-	OverlayPath  func(path string) string
-	Packages     map[string]*Package
-	sorted       []*Package
-	fset         *token.FileSet
-	TypeChecker  types.Config
-	Dir          string // current working directory (for error reporting)
-	TINYGOROOT   string // root of the TinyGo installation or root of the source code
-	CFlags       []string
-	ClangHeaders string
+	config       *compileopts.Config
+	clangHeaders string
+	typeChecker  types.Config
+	goroot       string // synthetic GOROOT
+	workingDir   string
+
+	Packages map[string]*Package
+	sorted   []*Package
+	fset     *token.FileSet
+
+	// Information obtained during parsing.
+	LDFlags []string
+}
+
+// PackageJSON is a subset of the JSON struct returned from `go list`.
+type PackageJSON struct {
+	Dir        string
+	ImportPath string
+	ForTest    string
+
+	// Source files
+	GoFiles  []string
+	CgoFiles []string
+	CFiles   []string
+
+	// Dependency information
+	Imports   []string
+	ImportMap map[string]string
+
+	// Error information
+	Error *struct {
+		ImportStack []string
+		Pos         string
+		Err         string
+	}
 }

 // Package holds a loaded package, its imports, and its parsed files.
 type Package struct {
-	*Program
-	*build.Package
-	Imports   map[string]*Package
-	Importing bool
-	Files     []*ast.File
-	Pkg       *types.Package
-	types.Info
+	PackageJSON
+
+	program *Program
+	Files   []*ast.File
+	Pkg     *types.Package
+	info    types.Info
 }

-// Import loads the given package relative to srcDir (for the vendor directory).
-// It only loads the current package without recursion.
-func (p *Program) Import(path, srcDir string, pos token.Position) (*Package, error) {
-	if p.Packages == nil {
-		p.Packages = make(map[string]*Package)
-	}
-
-	// Load this package.
-	ctx := p.Build
-	if newPath := p.OverlayPath(path); newPath != "" {
-		ctx = p.OverlayBuild
-		path = newPath
-	}
-	buildPkg, err := ctx.Import(path, srcDir, build.ImportComment)
-	if err != nil {
-		return nil, scanner.Error{
-			Pos: pos,
-			Msg: err.Error(), // TODO: define a new error type that will wrap the inner error
-		}
-	}
-	if existingPkg, ok := p.Packages[buildPkg.ImportPath]; ok {
-		// Already imported, or at least started the import.
-		return existingPkg, nil
-	}
-	p.sorted = nil // invalidate the sorted order of packages
-	pkg := p.newPackage(buildPkg)
-	p.Packages[buildPkg.ImportPath] = pkg
-
-	if p.mainPkg == "" {
-		p.mainPkg = buildPkg.ImportPath
-	}
-
-	return pkg, nil
-}
-
-// ImportFile loads and parses the import statements in the given path and
-// creates a pseudo-package out of it.
-func (p *Program) ImportFile(path string) (*Package, error) {
-	if p.Packages == nil {
-		p.Packages = make(map[string]*Package)
-	}
-	if _, ok := p.Packages[path]; ok {
-		// unlikely
-		return nil, errors.New("loader: cannot import file that is already imported as package: " + path)
-	}
-
-	file, err := p.parseFile(path, parser.ImportsOnly)
+// Load loads the given package with all dependencies (including the runtime
+// package). Call .Parse() afterwards to parse all Go files (including CGo
+// processing, if necessary).
+func Load(config *compileopts.Config, inputPkgs []string, clangHeaders string, typeChecker types.Config) (*Program, error) {
+	goroot, err := GetCachedGoroot(config)
 	if err != nil {
 		return nil, err
 	}
-	buildPkg := &build.Package{
-		Dir:        filepath.Dir(path),
-		ImportPath: path,
-		GoFiles:    []string{filepath.Base(path)},
+	wd, err := os.Getwd()
+	if err != nil {
+		return nil, err
 	}
-	for _, importSpec := range file.Imports {
-		buildPkg.Imports = append(buildPkg.Imports, importSpec.Path.Value[1:len(importSpec.Path.Value)-1])
-	}
-	p.sorted = nil // invalidate the sorted order of packages
-	pkg := p.newPackage(buildPkg)
-	p.Packages[buildPkg.ImportPath] = pkg
-
-	if p.mainPkg == "" {
-		p.mainPkg = buildPkg.ImportPath
+	p := &Program{
+		config:       config,
+		clangHeaders: clangHeaders,
+		typeChecker:  typeChecker,
+		goroot:       goroot,
+		workingDir:   wd,
+		Packages:     make(map[string]*Package),
+		fset:         token.NewFileSet(),
 	}

-	return pkg, nil
+	// List the dependencies of this package, in raw JSON format.
+	extraArgs := []string{"-json", "-deps"}
+	if config.TestConfig.CompileTestBinary {
+		extraArgs = append(extraArgs, "-test")
+	}
+	cmd, err := List(config, extraArgs, inputPkgs)
+	if err != nil {
+		return nil, err
+	}
+	buf := &bytes.Buffer{}
+	cmd.Stdout = buf
+	cmd.Stderr = os.Stderr
+	err = cmd.Run()
+	if err != nil {
+		if exitErr, ok := err.(*exec.ExitError); ok {
+			if status, ok := exitErr.Sys().(syscall.WaitStatus); ok {
+				os.Exit(status.ExitStatus())
+			}
+			os.Exit(1)
+		}
+		return nil, fmt.Errorf("failed to run `go list`: %s", err)
+	}
+
+	// Parse the returned json from `go list`.
+	decoder := json.NewDecoder(buf)
+	for {
+		pkg := &Package{
+			program: p,
+			info: types.Info{
+				Types:      make(map[ast.Expr]types.TypeAndValue),
+				Defs:       make(map[*ast.Ident]types.Object),
+				Uses:       make(map[*ast.Ident]types.Object),
+				Implicits:  make(map[ast.Node]types.Object),
+				Scopes:     make(map[ast.Node]*types.Scope),
+				Selections: make(map[*ast.SelectorExpr]*types.Selection),
+			},
+		}
+		err := decoder.Decode(&pkg.PackageJSON)
+		if err != nil {
+			if err == io.EOF {
+				break
+			}
+			return nil, err
+		}
+		if pkg.Error != nil {
+			// There was an error while importing (for example, a circular
+			// dependency).
+			pos := token.Position{}
+			fields := strings.Split(pkg.Error.Pos, ":")
+			if len(fields) >= 2 {
+				// There is some file/line/column information.
+				if n, err := strconv.Atoi(fields[len(fields)-2]); err == nil {
+					// Format: filename.go:line:colum
+					pos.Filename = strings.Join(fields[:len(fields)-2], ":")
+					pos.Line = n
+					pos.Column, _ = strconv.Atoi(fields[len(fields)-1])
+				} else {
+					// Format: filename.go:line
+					pos.Filename = strings.Join(fields[:len(fields)-1], ":")
+					pos.Line, _ = strconv.Atoi(fields[len(fields)-1])
+				}
+				pos.Filename = p.getOriginalPath(pos.Filename)
+			}
+			err := scanner.Error{
+				Pos: pos,
+				Msg: pkg.Error.Err,
+			}
+			if len(pkg.Error.ImportStack) != 0 {
+				return nil, Error{
+					ImportStack: pkg.Error.ImportStack,
+					Err:         err,
+				}
+			}
+			return nil, err
+		}
+		p.sorted = append(p.sorted, pkg)
+		p.Packages[pkg.ImportPath] = pkg
+	}
+
+	return p, nil
 }

-// newPackage instantiates a new *Package object with initialized members.
-func (p *Program) newPackage(pkg *build.Package) *Package {
-	return &Package{
-		Program: p,
-		Package: pkg,
-		Imports: make(map[string]*Package, len(pkg.Imports)),
-		Info: types.Info{
-			Types:      make(map[ast.Expr]types.TypeAndValue),
-			Defs:       make(map[*ast.Ident]types.Object),
-			Uses:       make(map[*ast.Ident]types.Object),
-			Implicits:  make(map[ast.Node]types.Object),
-			Scopes:     make(map[ast.Node]*types.Scope),
-			Selections: make(map[*ast.SelectorExpr]*types.Selection),
-		},
+// getOriginalPath looks whether this path is in the generated GOROOT and if so,
+// replaces the path with the original path (in GOROOT or TINYGOROOT). Otherwise
+// the input path is returned.
+func (p *Program) getOriginalPath(path string) string {
+	originalPath := path
+	if strings.HasPrefix(path, p.goroot+string(filepath.Separator)) {
+		// If this file is part of the synthetic GOROOT, try to infer the
+		// original path.
+		relpath := path[len(filepath.Join(p.goroot, "src"))+1:]
+		realgorootPath := filepath.Join(goenv.Get("GOROOT"), "src", relpath)
+		if _, err := os.Stat(realgorootPath); err == nil {
+			originalPath = realgorootPath
+		}
+		maybeInTinyGoRoot := false
+		for prefix := range pathsToOverride(needsSyscallPackage(p.config.BuildTags())) {
+			if !strings.HasPrefix(relpath, prefix) {
+				continue
+			}
+			maybeInTinyGoRoot = true
+		}
+		if maybeInTinyGoRoot {
+			tinygoPath := filepath.Join(goenv.Get("TINYGOROOT"), "src", relpath)
+			if _, err := os.Stat(tinygoPath); err == nil {
+				originalPath = tinygoPath
+			}
+		}
 	}
+	return originalPath
 }

 // Sorted returns a list of all packages, sorted in a way that no packages come
 // before the packages they depend upon.
 func (p *Program) Sorted() []*Package {
-	if p.sorted == nil {
-		p.sort()
-	}
 	return p.sorted
 }

-func (p *Program) sort() {
-	p.sorted = nil
-	packageList := make([]*Package, 0, len(p.Packages))
-	packageSet := make(map[string]struct{}, len(p.Packages))
-	worklist := make([]string, 0, len(p.Packages))
-	for path := range p.Packages {
-		worklist = append(worklist, path)
-	}
-	sort.Strings(worklist)
-	for len(worklist) != 0 {
-		pkgPath := worklist[0]
-		pkg := p.Packages[pkgPath]
-
-		if _, ok := packageSet[pkgPath]; ok {
-			// Package already in the final package list.
-			worklist = worklist[1:]
-			continue
-		}
-
-		unsatisfiedImports := make([]string, 0)
-		for _, pkg := range pkg.Imports {
-			if _, ok := packageSet[pkg.ImportPath]; ok {
-				continue
-			}
-			unsatisfiedImports = append(unsatisfiedImports, pkg.ImportPath)
-		}
-		sort.Strings(unsatisfiedImports)
-		if len(unsatisfiedImports) == 0 {
-			// All dependencies of this package are satisfied, so add this
-			// package to the list.
-			packageList = append(packageList, pkg)
-			packageSet[pkgPath] = struct{}{}
-			worklist = worklist[1:]
-		} else {
-			// Prepend all dependencies to the worklist and reconsider this
-			// package (by not removing it from the worklist). At that point, it
-			// must be possible to add it to packageList.
-			worklist = append(unsatisfiedImports, worklist...)
-		}
-	}
-
-	p.sorted = packageList
+// MainPkg returns the last package in the Sorted() slice. This is the main
+// package of the program.
+func (p *Program) MainPkg() *Package {
+	return p.sorted[len(p.sorted)-1]
 }

-// Parse recursively imports all packages, parses them, and typechecks them.
+// Parse parses all packages and typechecks them.
 //
 // The returned error may be an Errors error, which contains a list of errors.
 //
 // Idempotent.
-func (p *Program) Parse(compileTestBinary bool) error {
-	includeTests := compileTestBinary
-
-	// Load all imports
-	for _, pkg := range p.Sorted() {
-		err := pkg.importRecursively(includeTests)
-		if err != nil {
-			if err, ok := err.(*ImportCycleError); ok {
-				if pkg.ImportPath != err.Packages[0] {
-					err.Packages = append([]string{pkg.ImportPath}, err.Packages...)
-				}
-			}
-			return err
-		}
-	}
-
+func (p *Program) Parse() error {
 	// Parse all packages.
-	for _, pkg := range p.Sorted() {
-		err := pkg.Parse(includeTests)
-		if err != nil {
-			return err
-		}
-	}
-
-	if compileTestBinary {
-		err := p.SwapTestMain()
+	// TODO: do this in parallel.
+	for _, pkg := range p.sorted {
+		err := pkg.Parse()
 		if err != nil {
 			return err
 		}
 	}

 	// Typecheck all packages.
-	for _, pkg := range p.Sorted() {
+	for _, pkg := range p.sorted {
 		err := pkg.Check()
 		if err != nil {
 			return err
@@ -231,83 +244,6 @@ func (p *Program) Parse(compileTestBinary bool) error {
 	return nil
 }

-func (p *Program) SwapTestMain() error {
-	var tests []string
-
-	isTestFunc := func(f *ast.FuncDecl) bool {
-		// TODO: improve signature check
-		if strings.HasPrefix(f.Name.Name, "Test") && f.Name.Name != "TestMain" {
-			return true
-		}
-		return false
-	}
-	mainPkg := p.Packages[p.mainPkg]
-	for _, f := range mainPkg.Files {
-		for i, d := range f.Decls {
-			switch v := d.(type) {
-			case *ast.FuncDecl:
-				if isTestFunc(v) {
-					tests = append(tests, v.Name.Name)
-				}
-				if v.Name.Name == "main" {
-					// Remove main
-					if len(f.Decls) == 1 {
-						f.Decls = make([]ast.Decl, 0)
-					} else {
-						f.Decls[i] = f.Decls[len(f.Decls)-1]
-						f.Decls = f.Decls[:len(f.Decls)-1]
-					}
-				}
-			}
-		}
-	}
-
-	// TODO: Check if they defined a TestMain and call it instead of testing.TestMain
-	const mainBody = `package main
-
-import (
-	"testing"
-)
-
-func main () {
-	m := &testing.M{
-		Tests: []testing.TestToCall{
-{{range .TestFunctions}}
-			{Name: "{{.}}", Func: {{.}}},
-{{end}}
-		},
-	}
-
-	testing.TestMain(m)
-}
-`
-	tmpl := template.Must(template.New("testmain").Parse(mainBody))
-	b := bytes.Buffer{}
-	tmplData := struct {
-		TestFunctions []string
-	}{
-		TestFunctions: tests,
-	}
-
-	err := tmpl.Execute(&b, tmplData)
-	if err != nil {
-		return err
-	}
-	path := filepath.Join(p.mainPkg, "$testmain.go")
-
-	if p.fset == nil {
-		p.fset = token.NewFileSet()
-	}
-
-	newMain, err := parser.ParseFile(p.fset, path, b.Bytes(), parser.AllErrors)
-	if err != nil {
-		return err
-	}
-	mainPkg.Files = append(mainPkg.Files, newMain)
-
-	return nil
-}
-
 // parseFile is a wrapper around parser.ParseFile.
 func (p *Program) parseFile(path string, mode parser.Mode) (*ast.File, error) {
 	if p.fset == nil {
@@ -319,34 +255,26 @@ func (p *Program) parseFile(path string, mode parser.Mode) (*ast.File, error) {
 		return nil, err
 	}
 	defer rd.Close()
-	relpath := path
-	if filepath.IsAbs(path) {
-		rp, err := filepath.Rel(p.Dir, path)
-		if err == nil {
-			relpath = rp
-		}
-	}
-	return parser.ParseFile(p.fset, relpath, rd, mode)
+	return parser.ParseFile(p.fset, p.getOriginalPath(path), rd, mode)
 }

 // Parse parses and typechecks this package.
 //
 // Idempotent.
-func (p *Package) Parse(includeTests bool) error {
+func (p *Package) Parse() error {
 	if len(p.Files) != 0 {
-		return nil
+		return nil // nothing to do (?)
 	}

 	// Load the AST.
-	// TODO: do this in parallel.
 	if p.ImportPath == "unsafe" {
-		// Special case for the unsafe package. Don't even bother loading
-		// the files.
+		// Special case for the unsafe package, which is defined internally by
+		// the types package.
 		p.Pkg = types.Unsafe
 		return nil
 	}

-	files, err := p.parseFiles(includeTests)
+	files, err := p.parseFiles()
 	if err != nil {
 		return err
 	}
@@ -361,11 +289,11 @@ func (p *Package) Parse(includeTests bool) error {
 // Idempotent.
 func (p *Package) Check() error {
 	if p.Pkg != nil {
-		return nil
+		return nil // already typechecked
 	}

 	var typeErrors []error
-	checker := p.TypeChecker
+	checker := p.program.typeChecker // make a copy, because it will be modified
 	checker.Error = func(err error) {
 		typeErrors = append(typeErrors, err)
 	}
@@ -373,7 +301,7 @@ func (p *Package) Check() error {
 	// Do typechecking of the package.
 	checker.Importer = p

-	typesPkg, err := checker.Check(p.ImportPath, p.fset, p.Files, &p.Info)
+	typesPkg, err := checker.Check(p.ImportPath, p.program.fset, p.Files, &p.info)
 	if err != nil {
 		if err, ok := err.(Errors); ok {
 			return err
@@ -385,52 +313,47 @@ func (p *Package) Check() error {
 }

 // parseFiles parses the loaded list of files and returns this list.
-func (p *Package) parseFiles(includeTests bool) ([]*ast.File, error) {
-	// TODO: do this concurrently.
+func (p *Package) parseFiles() ([]*ast.File, error) {
 	var files []*ast.File
 	var fileErrs []error

-	var gofiles []string
-	if includeTests {
-		gofiles = make([]string, 0, len(p.GoFiles)+len(p.TestGoFiles))
-		gofiles = append(gofiles, p.GoFiles...)
-		gofiles = append(gofiles, p.TestGoFiles...)
-	} else {
-		gofiles = p.GoFiles
-	}
-
-	for _, file := range gofiles {
-		f, err := p.parseFile(filepath.Join(p.Package.Dir, file), parser.ParseComments)
-		if err != nil {
-			fileErrs = append(fileErrs, err)
-			continue
+	// Parse all files (incuding CgoFiles).
+	parseFile := func(file string) {
+		if !filepath.IsAbs(file) {
+			file = filepath.Join(p.Dir, file)
 		}
+		f, err := p.program.parseFile(file, parser.ParseComments)
 		if err != nil {
 			fileErrs = append(fileErrs, err)
-			continue
+			return
 		}
 		files = append(files, f)
 	}
+	for _, file := range p.GoFiles {
+		parseFile(file)
+	}
 	for _, file := range p.CgoFiles {
-		path := filepath.Join(p.Package.Dir, file)
-		f, err := p.parseFile(path, parser.ParseComments)
-		if err != nil {
-			fileErrs = append(fileErrs, err)
-			continue
-		}
-		files = append(files, f)
+		parseFile(file)
 	}
+
+	// Do CGo processing.
 	if len(p.CgoFiles) != 0 {
-		cflags := append(p.CFlags, "-I"+p.Package.Dir)
-		if p.ClangHeaders != "" {
-			cflags = append(cflags, "-I"+p.ClangHeaders)
+		var cflags []string
+		cflags = append(cflags, p.program.config.CFlags()...)
+		cflags = append(cflags, "-I"+p.Dir)
+		if p.program.clangHeaders != "" {
+			cflags = append(cflags, "-Xclang", "-internal-isystem", "-Xclang", p.program.clangHeaders)
 		}
-		generated, errs := cgo.Process(files, p.Program.Dir, p.fset, cflags)
+		generated, ldflags, errs := cgo.Process(files, p.program.workingDir, p.program.fset, cflags)
 		if errs != nil {
 			fileErrs = append(fileErrs, errs...)
 		}
 		files = append(files, generated)
+		p.program.LDFlags = append(p.program.LDFlags, ldflags...)
 	}
+
+	// Only return an error after CGo processing, so that errors in parsing and
+	// CGo can be reported together.
 	if len(fileErrs) != 0 {
 		return nil, Errors{p, fileErrs}
 	}
@@ -444,59 +367,14 @@ func (p *Package) Import(to string) (*types.Package, error) {
 	if to == "unsafe" {
 		return types.Unsafe, nil
 	}
-	if _, ok := p.Imports[to]; ok {
-		return p.Imports[to].Pkg, nil
+	if replace, ok := p.ImportMap[to]; ok {
+		// This import path should be replaced by another import path, according
+		// to `go list`.
+		to = replace
+	}
+	if imported, ok := p.program.Packages[to]; ok {
+		return imported.Pkg, nil
 	} else {
 		return nil, errors.New("package not imported: " + to)
 	}
 }
-
-// importRecursively calls Program.Import() on all imported packages, and calls
-// importRecursively() on the imported packages as well.
-//
-// Idempotent.
-func (p *Package) importRecursively(includeTests bool) error {
-	p.Importing = true
-
-	imports := p.Package.Imports
-	if includeTests {
-		imports = append(imports, p.Package.TestImports...)
-	}
-
-	for _, to := range imports {
-		if to == "C" {
-			// Do CGo processing in a later stage.
-			continue
-		}
-		if _, ok := p.Imports[to]; ok {
-			continue
-		}
-		// Find error location.
-		var pos token.Position
-		if len(p.Package.ImportPos[to]) > 0 {
-			pos = p.Package.ImportPos[to][0]
-		} else {
-			pos = token.Position{Filename: p.Package.ImportPath}
-		}
-		importedPkg, err := p.Program.Import(to, p.Package.Dir, pos)
-		if err != nil {
-			if err, ok := err.(*ImportCycleError); ok {
-				err.Packages = append([]string{p.ImportPath}, err.Packages...)
-			}
-			return err
-		}
-		if importedPkg.Importing {
-			return &ImportCycleError{[]string{p.ImportPath, importedPkg.ImportPath}, p.ImportPos[to]}
-		}
-		err = importedPkg.importRecursively(false)
-		if err != nil {
-			if err, ok := err.(*ImportCycleError); ok {
-				err.Packages = append([]string{p.ImportPath}, err.Packages...)
-			}
-			return err
-		}
-		p.Imports[to] = importedPkg
-	}
-	p.Importing = false
-	return nil
-}
--- a/Show More
+++ b/Show More