Damian Gryski 9c864f0d79 interp: fix switch-instruction handling for LLVM 22's new case-value API
Written entirely by Claude (Anthropic's Claude Code), at the request of
and under the direction of dgryski, on the dgryski/llvm23 branch (LLVM
22 support, in preparation for the eventual LLVM 23 release; the
corresponding go-llvm branch of the same name adds the matching
binding support this depends on).

Found while running real-world Go test suites through a tinygo built
against LLVM 22 (as a smoke test of the earlier captures(none)/
nocapture and lifetime-intrinsic fixes on this branch): `tinygo test`
on github.com/dgryski/go-rc5 panicked at compile time with "unknown
value" inside interp.(*runner).getValue, while compiling
(*sync.Once).Do. Bisecting against LLVM 21 (unaffected) narrowed it to
a change introduced in LLVM 22 specifically, unrelated to the earlier
captures/lifetime work.

Root cause: LLVM 22 stopped exposing switch-instruction case values as
regular instruction operands -- only the condition and
destination-block operands remain. interp/compiler.go's `case
llvm.Switch:` handling walked raw operands assuming the old
alternating (value, label) layout, so under LLVM 22 it read a
destination *block* where it expected an integer case value,
eventually panicking deep inside a getValue call it couldn't resolve.
This only manifested on functions actually compiled by the interp
package (TinyGo's compile-time evaluator for global initializers) that
happen to reach a switch-based dispatch, such as sync.Once's
defer-based Do method -- hence it needed a real, moderately complex
package (crypto/cipher via go-rc5) to surface, and never showed up in
smaller smoke tests.

Fix: use the new version-independent Value.SuccessorsCount()/
Value.Successor(i) and Value.GetSwitchCaseValue(i) helpers just added
to go-llvm, instead of raw Operand() indexing.

Also applies the same captures(none)/nocapture golden-IR normalization
already used in transform/transform_test.go and compiler/compiler_test.go
to interp/interp_test.go's separate copy of the same comparator helper,
which was missed in the earlier pass and started failing two of its
subtests once actually run against LLVM 22.

Verified: `tinygo test` on go-rc5 now passes reliably (repeated runs)
against both LLVM 20 (default) and LLVM 22; full transform/compiler/
interp/cgo/goenv test suites pass on both versions. The `builder`
package has pre-existing, environment-related test failures (stale
GOROOT cache, local clang/target-feature drift) confirmed identical
against an unmodified LLVM 20 build, so unrelated to this change.
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TinyGo - Go compiler for small places

Linux macOS Windows Docker Nix

TinyGo is a Go compiler intended for use in small places such as microcontrollers, WebAssembly (wasm/wasi), and command-line tools.

It reuses libraries used by the Go language tools alongside LLVM to provide an alternative way to compile programs written in the Go programming language.

Important

You can help TinyGo with a financial contribution using OpenCollective. Please see https://opencollective.com/tinygo for more information. Thank you!

Embedded

Here is an example program that blinks the built-in LED when run directly on any supported board with onboard LED:

package main

import (
    "machine"
    "time"
)

func main() {
    led := machine.LED
    led.Configure(machine.PinConfig{Mode: machine.PinOutput})
    for {
        led.Low()
        time.Sleep(time.Millisecond * 1000)

        led.High()
        time.Sleep(time.Millisecond * 1000)
    }
}

The above program can be compiled and run without modification on an Arduino Uno, an Adafruit Circuit Playground Express, a Seeed Studio XIAO-ESP32S3 or any of the many supported boards that have a built-in LED, just by setting the correct TinyGo compiler target. For example, this compiles and flashes an Arduino Uno:

tinygo flash -target arduino-uno examples/blinky1

WebAssembly

TinyGo is very useful for compiling programs both for use in browsers (WASM) as well as for use on servers and other edge devices (WASI).

TinyGo programs can run in Fastly Compute, Fermyon Spin, wazero and many other WebAssembly runtimes.

Here is a small TinyGo program for use by a WASI host application:

package main

//go:wasmexport add
func add(x, y uint32) uint32 {
	return x + y
}

This compiles the above TinyGo program for use on any WASI Preview 1 runtime:

tinygo build -buildmode=c-shared -o add.wasm -target=wasip1 add.go

You can also use the same syntax as Go 1.24+:

GOOS=wasip1 GOARCH=wasm tinygo build -buildmode=c-shared -o add.wasm add.go

Installation

See the getting started instructions for information on how to install TinyGo, as well as how to run the TinyGo compiler using our Docker container.

Supported targets

Embedded

You can compile TinyGo programs for over 150 different microcontroller boards.

For more information, please see https://tinygo.org/docs/reference/microcontrollers/

WebAssembly

TinyGo programs can be compiled for both WASM and WASI targets.

For more information, see https://tinygo.org/docs/guides/webassembly/

Operating Systems

You can also compile programs for Linux, macOS, and Windows targets.

For more information:

Currently supported features:

For a description of currently supported Go language features, please see https://tinygo.org/lang-support/.

Documentation

Documentation is located on our web site at https://tinygo.org/.

You can find the web site code at https://github.com/tinygo-org/tinygo-site.

Getting help

If you're looking for a more interactive way to discuss TinyGo usage or development, we have a #TinyGo channel on the Gophers Slack.

If you need an invitation for the Gophers Slack, you can generate one here which should arrive fairly quickly (under 1 min): https://invite.slack.golangbridge.org

Contributing

Your contributions are welcome!

Please take a look at our Contributing page on our web site for details.

Project Scope

Goals:

  • Have very small binary sizes. Don't pay for what you don't use.
  • Support for most common microcontroller boards.
  • Be usable on the web using WebAssembly.
  • Good CGo support, with no more overhead than a regular function call.
  • Support most standard library packages and compile most Go code without modification.

Non-goals:

  • Be efficient while using zillions of goroutines. However, good goroutine support is certainly a goal.
  • Be as fast as gc. However, LLVM will probably be better at optimizing certain things so TinyGo might actually turn out to be faster for number crunching.
  • Be able to compile every Go program out there.

Why this project exists

We never expected Go to be an embedded language, and so its got serious problems...

-- Rob Pike, GopherCon 2014 Opening Keynote

TinyGo is a project to bring Go to microcontrollers and small systems with a single processor core. It is similar to emgo but a major difference is that we want to keep the Go memory model (which implies garbage collection of some sort). Another difference is that TinyGo uses LLVM internally instead of emitting C, which hopefully leads to smaller and more efficient code and certainly leads to more flexibility.

The original reasoning was: if Python can run on microcontrollers, then certainly Go should be able to run on even lower level micros.

License

This project is licensed under the BSD 3-clause license, just like the Go project itself.

Some code has been copied from the LLVM project and is therefore licensed under a variant of the Apache 2.0 license. 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.

S
Description
Go compiler for small places. Microcontrollers, WebAssembly (WASM/WASI), and command-line tools. Based on LLVM.
Readme BSD-3-Clause 34 MiB
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2025-08-19 12:03:57 +00:00
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