runtime (gc): add garbage collector that uses an external allocator

Author: niaow

compileopts/config.go

@@ -96,30 +96,37 @@ func (c *Config) CgoEnabled() bool {
 }
 
 // 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
 	}
 	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" {
-		return false
-	}
-	for _, tag := range c.BuildTags() {
-		if tag == "baremetal" {
-			return false
+	switch c.GC() {
+	case "conservative", "extalloc":
+		for _, tag := range c.BuildTags() {
+			if tag == "baremetal" {
+				return false
+			}
 		}
-	}
 
-	return true
+		return true
+	default:
+		return false
+	}
 }
 
 // Scheduler returns the scheduler implementation. Valid values are "coroutines"

main.go

@@ -701,7 +701,7 @@ 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", "", "garbage collector to use (none, leaking, conservative)")
+	gc := flag.String("gc", "", "garbage collector to use (none, leaking, extalloc, conservative)")
 	panicStrategy := flag.String("panic", "print", "panic strategy (print, trap)")
 	scheduler := flag.String("scheduler", "", "which scheduler to use (coroutines, tasks)")
 	printIR := flag.Bool("printir", false, "print LLVM IR")