all: make garbage collector configurable

compiler/compiler.go

@@ -32,6 +32,7 @@ func init() {
 // Configure the compiler.
 type Config struct {
 	Triple     string   // LLVM target triple, e.g. x86_64-unknown-linux-gnu (empty string means default)
+	GC         string   // garbage collection strategy
 	DumpSSA    bool     // dump Go SSA, for compiler debugging
 	Debug      bool     // add debug symbols for gdb
 	RootDir    string   // GOROOT for TinyGo
@@ -170,6 +171,15 @@ func (c *Compiler) TargetData() llvm.TargetData {
 	return c.targetData
 }
 
+// selectGC picks an appropriate GC strategy if none was provided.
+func (c *Compiler) selectGC() string {
+	gc := c.GC
+	if gc == "" {
+		gc = "dumb"
+	}
+	return gc
+}
+
 // Compile the given package path or .go file path. Return an error when this
 // fails (in any stage).
 func (c *Compiler) Compile(mainPath string) error {
@@ -200,7 +210,7 @@ func (c *Compiler) Compile(mainPath string) error {
 			CgoEnabled:  true,
 			UseAllFiles: false,
 			Compiler:    "gc", // must be one of the recognized compilers
-			BuildTags:   append([]string{"tinygo"}, c.BuildTags...),
+			BuildTags:   append([]string{"tinygo", "gc." + c.selectGC()}, c.BuildTags...),
 		},
 		ParserMode: parser.ParseComments,
 	}

main.go

@@ -25,6 +25,7 @@ var commands = map[string]string{
 
 type BuildConfig struct {
 	opt        string
+	gc         string
 	printIR    bool
 	dumpSSA    bool
 	debug      bool
@@ -36,6 +37,7 @@ type BuildConfig struct {
 func Compile(pkgName, outpath string, spec *TargetSpec, config *BuildConfig, action func(string) error) error {
 	compilerConfig := compiler.Config{
 		Triple:     spec.Triple,
+		GC:         config.gc,
 		Debug:      config.debug,
 		DumpSSA:    config.dumpSSA,
 		RootDir:    sourceDir(),
@@ -433,6 +435,7 @@ func handleCompilerError(err error) {
 func main() {
 	outpath := flag.String("o", "", "output filename")
 	opt := flag.String("opt", "z", "optimization level: 0, 1, 2, s, z")
+	gc := flag.String("gc", "dumb", "garbage collector to use (dumb)")
 	printIR := flag.Bool("printir", false, "print LLVM IR")
 	dumpSSA := flag.Bool("dumpssa", false, "dump internal Go SSA")
 	target := flag.String("target", "", "LLVM target")
@@ -452,6 +455,7 @@ func main() {
 	flag.CommandLine.Parse(os.Args[2:])
 	config := &BuildConfig{
 		opt:        *opt,
+		gc:         *gc,
 		printIR:    *printIR,
 		dumpSSA:    *dumpSSA,
 		debug:      !*nodebug,

src/runtime/gc_dumb.go

@@ -1,5 +1,11 @@
+// +build gc.dumb
+
 package runtime
 
+// This GC implementation is the simplest useful memory allocator possible: it
+// only allocates memory and never frees it. For some constrained systems, it
+// may be the only memory allocator possible.
+
 import (
 	"unsafe"
 )
@@ -22,11 +28,11 @@ func alloc(size uintptr) unsafe.Pointer {
 }
 
 func free(ptr unsafe.Pointer) {
-	// TODO: use a GC
+	// Memory is never freed.
 }
 
 func GC() {
-	// Unimplemented.
+	// No-op.
 }
 
 func KeepAlive(x interface{}) {