builder: remove non-ThinLTO build mode

All targets now support ThinLTO so let's remove the old unused code.

Author: aykevl

builder/build.go

@@ -594,12 +594,7 @@ func Build(pkgName, outpath, tmpdir string, config *compileopts.Config) (BuildRe
 			defer llvmBuf.Dispose()
 			return result, os.WriteFile(outpath, llvmBuf.Bytes(), 0666)
 		case ".bc":
-			var buf llvm.MemoryBuffer
-			if config.UseThinLTO() {
-				buf = llvm.WriteThinLTOBitcodeToMemoryBuffer(mod)
-			} else {
-				buf = llvm.WriteBitcodeToMemoryBuffer(mod)
-			}
+			buf := llvm.WriteThinLTOBitcodeToMemoryBuffer(mod)
 			defer buf.Dispose()
 			return result, os.WriteFile(outpath, buf.Bytes(), 0666)
 		case ".ll":
@@ -621,16 +616,7 @@ func Build(pkgName, outpath, tmpdir string, config *compileopts.Config) (BuildRe
 		dependencies: []*compileJob{programJob},
 		result:       objfile,
 		run: func(*compileJob) error {
-			var llvmBuf llvm.MemoryBuffer
-			if config.UseThinLTO() {
-				llvmBuf = llvm.WriteThinLTOBitcodeToMemoryBuffer(mod)
-			} else {
-				var err error
-				llvmBuf, err = machine.EmitToMemoryBuffer(mod, llvm.ObjectFile)
-				if err != nil {
-					return err
-				}
-			}
+			llvmBuf := llvm.WriteThinLTOBitcodeToMemoryBuffer(mod)
 			defer llvmBuf.Dispose()
 			return os.WriteFile(objfile, llvmBuf.Bytes(), 0666)
 		},
@@ -664,7 +650,7 @@ func Build(pkgName, outpath, tmpdir string, config *compileopts.Config) (BuildRe
 		job := &compileJob{
 			description: "compile extra file " + path,
 			run: func(job *compileJob) error {
-				result, err := compileAndCacheCFile(abspath, tmpdir, config.CFlags(), config.UseThinLTO(), config.Options.PrintCommands)
+				result, err := compileAndCacheCFile(abspath, tmpdir, config.CFlags(), config.Options.PrintCommands)
 				job.result = result
 				return err
 			},
@@ -682,7 +668,7 @@ func Build(pkgName, outpath, tmpdir string, config *compileopts.Config) (BuildRe
 			job := &compileJob{
 				description: "compile CGo file " + abspath,
 				run: func(job *compileJob) error {
-					result, err := compileAndCacheCFile(abspath, tmpdir, pkg.CFlags, config.UseThinLTO(), config.Options.PrintCommands)
+					result, err := compileAndCacheCFile(abspath, tmpdir, pkg.CFlags, config.Options.PrintCommands)
 					job.result = result
 					return err
 				},
@@ -741,36 +727,34 @@ func Build(pkgName, outpath, tmpdir string, config *compileopts.Config) (BuildRe
 				}
 				ldflags = append(ldflags, dependency.result)
 			}
-			if config.UseThinLTO() {
-				ldflags = append(ldflags, "-mllvm", "-mcpu="+config.CPU())
-				if config.GOOS() == "windows" {
-					// Options for the MinGW wrapper for the lld COFF linker.
-					ldflags = append(ldflags,
-						"-Xlink=/opt:lldlto="+strconv.Itoa(optLevel),
-						"--thinlto-cache-dir="+filepath.Join(cacheDir, "thinlto"))
-				} else if config.GOOS() == "darwin" {
-					// Options for the ld64-compatible lld linker.
-					ldflags = append(ldflags,
-						"--lto-O"+strconv.Itoa(optLevel),
-						"-cache_path_lto", filepath.Join(cacheDir, "thinlto"))
-				} else {
-					// Options for the ELF linker.
-					ldflags = append(ldflags,
-						"--lto-O"+strconv.Itoa(optLevel),
-						"--thinlto-cache-dir="+filepath.Join(cacheDir, "thinlto"),
-					)
-				}
-				if config.CodeModel() != "default" {
-					ldflags = append(ldflags,
-						"-mllvm", "-code-model="+config.CodeModel())
-				}
-				if sizeLevel >= 2 {
-					// Workaround with roughly the same effect as
-					// https://reviews.llvm.org/D119342.
-					// Can hopefully be removed in LLVM 15.
-					ldflags = append(ldflags,
-						"-mllvm", "--rotation-max-header-size=0")
-				}
+			ldflags = append(ldflags, "-mllvm", "-mcpu="+config.CPU())
+			if config.GOOS() == "windows" {
+				// Options for the MinGW wrapper for the lld COFF linker.
+				ldflags = append(ldflags,
+					"-Xlink=/opt:lldlto="+strconv.Itoa(optLevel),
+					"--thinlto-cache-dir="+filepath.Join(cacheDir, "thinlto"))
+			} else if config.GOOS() == "darwin" {
+				// Options for the ld64-compatible lld linker.
+				ldflags = append(ldflags,
+					"--lto-O"+strconv.Itoa(optLevel),
+					"-cache_path_lto", filepath.Join(cacheDir, "thinlto"))
+			} else {
+				// Options for the ELF linker.
+				ldflags = append(ldflags,
+					"--lto-O"+strconv.Itoa(optLevel),
+					"--thinlto-cache-dir="+filepath.Join(cacheDir, "thinlto"),
+				)
+			}
+			if config.CodeModel() != "default" {
+				ldflags = append(ldflags,
+					"-mllvm", "-code-model="+config.CodeModel())
+			}
+			if sizeLevel >= 2 {
+				// Workaround with roughly the same effect as
+				// https://reviews.llvm.org/D119342.
+				// Can hopefully be removed in LLVM 15.
+				ldflags = append(ldflags,
+					"-mllvm", "--rotation-max-header-size=0")
 			}
 			if config.Options.PrintCommands != nil {
 				config.Options.PrintCommands(config.Target.Linker, ldflags...)
@@ -1069,10 +1053,6 @@ func optimizeProgram(mod llvm.Module, config *compileopts.Config) error {
 		}
 	}
 
-	if config.GOOS() != "darwin" && !config.UseThinLTO() {
-		transform.ApplyFunctionSections(mod) // -ffunction-sections
-	}
-
 	// Insert values from -ldflags="-X ..." into the IR.
 	err = setGlobalValues(mod, config.Options.GlobalValues)
 	if err != nil {

builder/cc.go

@@ -56,7 +56,7 @@ import (
 //     depfile but without invalidating its name. For this reason, the depfile is
 //     written on each new compilation (even when it seems unnecessary). However, it
 //     could in rare cases lead to a stale file fetched from the cache.
-func compileAndCacheCFile(abspath, tmpdir string, cflags []string, thinlto bool, printCommands func(string, ...string)) (string, error) {
+func compileAndCacheCFile(abspath, tmpdir string, cflags []string, printCommands func(string, ...string)) (string, error) {
 	// Hash input file.
 	fileHash, err := hashFile(abspath)
 	if err != nil {
@@ -67,11 +67,6 @@ func compileAndCacheCFile(abspath, tmpdir string, cflags []string, thinlto bool,
 	unlock := lock(filepath.Join(goenv.Get("GOCACHE"), fileHash+".c.lock"))
 	defer unlock()
 
-	ext := ".o"
-	if thinlto {
-		ext = ".bc"
-	}
-
 	// Create cache key for the dependencies file.
 	buf, err := json.Marshal(struct {
 		Path        string
@@ -104,7 +99,7 @@ func compileAndCacheCFile(abspath, tmpdir string, cflags []string, thinlto bool,
 		}
 
 		// Obtain hashes of all the files listed as a dependency.
-		outpath, err := makeCFileCachePath(dependencies, depfileNameHash, ext)
+		outpath, err := makeCFileCachePath(dependencies, depfileNameHash)
 		if err == nil {
 			if _, err := os.Stat(outpath); err == nil {
 				return outpath, nil
@@ -117,7 +112,7 @@ func compileAndCacheCFile(abspath, tmpdir string, cflags []string, thinlto bool,
 		return "", err
 	}
 
-	objTmpFile, err := os.CreateTemp(goenv.Get("GOCACHE"), "tmp-*"+ext)
+	objTmpFile, err := os.CreateTemp(goenv.Get("GOCACHE"), "tmp-*.bc")
 	if err != nil {
 		return "", err
 	}
@@ -127,11 +122,8 @@ func compileAndCacheCFile(abspath, tmpdir string, cflags []string, thinlto bool,
 		return "", err
 	}
 	depTmpFile.Close()
-	flags := append([]string{}, cflags...)                                   // copy cflags
-	flags = append(flags, "-MD", "-MV", "-MTdeps", "-MF", depTmpFile.Name()) // autogenerate dependencies
-	if thinlto {
-		flags = append(flags, "-flto=thin")
-	}
+	flags := append([]string{}, cflags...)                                                 // copy cflags
+	flags = append(flags, "-MD", "-MV", "-MTdeps", "-MF", depTmpFile.Name(), "-flto=thin") // autogenerate dependencies
 	flags = append(flags, "-c", "-o", objTmpFile.Name(), abspath)
 	if strings.ToLower(filepath.Ext(abspath)) == ".s" {
 		// If this is an assembly file (.s or .S, lowercase or uppercase), then
@@ -189,7 +181,7 @@ func compileAndCacheCFile(abspath, tmpdir string, cflags []string, thinlto bool,
 	}
 
 	// Move temporary object file to final location.
-	outpath, err := makeCFileCachePath(dependencySlice, depfileNameHash, ext)
+	outpath, err := makeCFileCachePath(dependencySlice, depfileNameHash)
 	if err != nil {
 		return "", err
 	}
@@ -204,7 +196,7 @@ func compileAndCacheCFile(abspath, tmpdir string, cflags []string, thinlto bool,
 // Create a cache path (a path in GOCACHE) to store the output of a compiler
 // job. This path is based on the dep file name (which is a hash of metadata
 // including compiler flags) and the hash of all input files in the paths slice.
-func makeCFileCachePath(paths []string, depfileNameHash, ext string) (string, error) {
+func makeCFileCachePath(paths []string, depfileNameHash string) (string, error) {
 	// Hash all input files.
 	fileHashes := make(map[string]string, len(paths))
 	for _, path := range paths {
@@ -229,7 +221,7 @@ func makeCFileCachePath(paths []string, depfileNameHash, ext string) (string, er
 	outFileNameBuf := sha512.Sum512_224(buf)
 	cacheKey := hex.EncodeToString(outFileNameBuf[:])
 
-	outpath := filepath.Join(goenv.Get("GOCACHE"), "obj-"+cacheKey+ext)
+	outpath := filepath.Join(goenv.Get("GOCACHE"), "obj-"+cacheKey+".bc")
 	return outpath, nil
 }
 

compileopts/config.go

@@ -191,14 +191,6 @@ func (c *Config) StackSize() uint64 {
 	return c.Target.DefaultStackSize
 }
 
-// UseThinLTO returns whether ThinLTO should be used for the given target.
-func (c *Config) UseThinLTO() bool {
-	// All architectures support ThinLTO now. However, this code is kept for the
-	// time being in case there are regressions. The non-ThinLTO code support
-	// should be removed when it is proven to work reliably.
-	return true
-}
-
 // RP2040BootPatch returns whether the RP2040 boot patch should be applied that
 // calculates and patches in the checksum for the 2nd stage bootloader.
 func (c *Config) RP2040BootPatch() bool {