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builder: add real ThinLTO mode

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We use ThinLTO for linking, but we use it in a way that doesn't give
most of its benefits: we merge all the bitcode files into a single LLVM
module and run some optimizations on it before linking. Therefore, this
works more like a traditional "full" LTO link rather than a true thin
link.

This commit adds a new experimental -lto=thin option to do a true
ThinLTO link. The main benefit is that linking will be a lot faster,
especially for large programs consisting of many packages.

At the moment, it only works for programs that don't do interface type
asserts and don't call interface methods. It also probably won't work on
WebAssembly and baremetal systems. But it's part of a larger goal
towards a truly incremental build system:
https://github.com/tinygo-org/tinygo/issues/2870
Once interface type asserts and method calls are converted to a
vtable-like implementation, most programs should just work on
linux/darwin/windows.
This commit is contained in:
Ayke van Laethem
2023-02-26 22:18:45 +01:00
parent 9b91cbb841
commit 2de0635140
9 changed files with 108 additions and 27 deletions
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builder/build.go
+47 -10
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@@ -176,6 +176,7 @@ func Build(pkgName, outpath, tmpdir string, config *compileopts.Config) (BuildRe
DefaultStackSize: config.StackSize(),
NeedsStackObjects: config.NeedsStackObjects(),
Debug: true,
LTO: config.LTO() != "legacy",
}
// Load the target machine, which is the LLVM object that contains all
@@ -452,18 +453,24 @@ func Build(pkgName, outpath, tmpdir string, config *compileopts.Config) (BuildRe
if err != nil {
return err
}
if runtime.GOOS == "windows" {
// Work around a problem on Windows.
// For some reason, WriteBitcodeToFile causes TinyGo to
// exit with the following message:
// LLVM ERROR: IO failure on output stream: Bad file descriptor
buf := llvm.WriteBitcodeToMemoryBuffer(mod)
if compilerConfig.LTO {
buf := llvm.WriteThinLTOBitcodeToMemoryBuffer(mod)
defer buf.Dispose()
_, err = f.Write(buf.Bytes())
} else {
// Otherwise, write bitcode directly to the file (probably
// faster).
err = llvm.WriteBitcodeToFile(mod, f)
if runtime.GOOS == "windows" {
// Work around a problem on Windows.
// For some reason, WriteBitcodeToFile causes TinyGo to
// exit with the following message:
// LLVM ERROR: IO failure on output stream: Bad file descriptor
buf := llvm.WriteBitcodeToMemoryBuffer(mod)
defer buf.Dispose()
_, err = f.Write(buf.Bytes())
} else {
// Otherwise, write bitcode directly to the file (probably
// faster).
err = llvm.WriteBitcodeToFile(mod, f)
}
}
if err != nil {
// WriteBitcodeToFile doesn't produce a useful error on its
@@ -609,8 +616,38 @@ func Build(pkgName, outpath, tmpdir string, config *compileopts.Config) (BuildRe
},
}
// Add job to create the runtime.initAll function in a new module.
initAllJob := &compileJob{
description: "create runtime.initAll",
result: filepath.Join(tmpdir, "runtime-initAll.bc"),
run: func(job *compileJob) (err error) {
// Create module with runtime.initAll.
ctx := llvm.NewContext()
defer ctx.Dispose()
initAllMod := createInitAll(ctx, config, compilerConfig, lprogram.Sorted())
defer initAllMod.Dispose()
// Write module to bitcode file.
llvmBuf := llvm.WriteThinLTOBitcodeToMemoryBuffer(initAllMod)
defer llvmBuf.Dispose()
return os.WriteFile(job.result, llvmBuf.Bytes(), 0666)
},
}
// Prepare link command.
linkerDependencies := []*compileJob{outputObjectFileJob}
var linkerDependencies []*compileJob
switch config.LTO() {
case "legacy":
// Link all Go bitcode files together into a single large module and
// then do a ThinLTO link with the resulting large module + extra C
// files (from CGo etc).
linkerDependencies = append(linkerDependencies, outputObjectFileJob)
case "thin":
// Do a real thin link, with each Go package in a separate translation
// unit. This is faster than merging them into one big LTO module.
linkerDependencies = append(linkerDependencies, packageJobs...)
linkerDependencies = append(linkerDependencies, initAllJob)
}
result.Executable = filepath.Join(tmpdir, "main")
if config.GOOS() == "windows" {
result.Executable += ".exe"