main: add -debug flag that controls debuginfo stripping

Debug information is useful in many case, but in the case of WebAssembly
it increases the binary size by a large amount. It also inhibits
compression of relocations. Therefore I've made debug information
optional and disabled by default.

(Debug information is still generated, but stripped from the binary at
the link step).

compileopts/config.go

@@ -209,7 +209,7 @@ func (c *Config) CFlags() []string {
 		cflags = append(cflags, "-nostdlibinc", "-Xclang", "-internal-isystem", "-Xclang", filepath.Join(root, "lib", "picolibc", "newlib", "libc", "include"))
 		cflags = append(cflags, "-I"+filepath.Join(root, "lib/picolibc-include"))
 	}
-	if c.Debug() {
+	if c.EmitDWARF() {
 		cflags = append(cflags, "-g")
 	}
 	return cflags
@@ -250,10 +250,33 @@ func (c *Config) VerifyIR() bool {
 	return c.Options.VerifyIR
 }
 
-// Debug returns whether to add debug symbols to the IR, for debugging with GDB
-// and similar.
+// EmitDWARF returns whether to add debug symbols to the IR, for debugging with
+// GDB and similar.
+func (c *Config) EmitDWARF() bool {
+	return c.Options.EmitDWARF
+}
+
+// Debug returns whether debug (DWARF) information should be retained by the
+// linker. The default varies by target but can be controlled with the -debug
+// command line flag.
 func (c *Config) Debug() bool {
-	return c.Options.Debug
+	switch c.Options.Debug {
+	case "true":
+		return true
+	case "false":
+		return false
+	case "auto":
+		// Emit debug information everywhere by default except on WebAssembly.
+		for _, tag := range c.BuildTags() {
+			if tag == "tinygo.wasm" {
+				return false
+			}
+		}
+		return true
+	default:
+		// This is already checked so shouldn't happen.
+		panic("unknown -debug flag")
+	}
 }
 
 // BinaryFormat returns an appropriate binary format, based on the file

compileopts/options.go

@@ -9,6 +9,7 @@ import (
 var (
 	validGCOptions            = []string{"none", "leaking", "extalloc", "conservative"}
 	validSchedulerOptions     = []string{"none", "tasks", "coroutines"}
+	validDebugOptions         = []string{"auto", "true", "false"}
 	validSerialOptions        = []string{"none", "uart", "usb"}
 	validPrintSizeOptions     = []string{"none", "short", "full"}
 	validPanicStrategyOptions = []string{"print", "trap"}
@@ -28,7 +29,8 @@ type Options struct {
 	DumpSSA         bool
 	VerifyIR        bool
 	PrintCommands   func(cmd string, args ...string)
-	Debug           bool
+	EmitDWARF       bool
+	Debug           string
 	PrintSizes      string
 	PrintAllocs     *regexp.Regexp // regexp string
 	PrintStacks     bool
@@ -70,6 +72,12 @@ func (o *Options) Verify() error {
 		}
 	}
 
+	if !isInArray(validDebugOptions, o.Debug) {
+		return fmt.Errorf(`invalid debug option '%s': valid values are %s`,
+			o.Debug,
+			strings.Join(validDebugOptions, ", "))
+	}
+
 	if o.PrintSizes != "" {
 		valid := isInArray(validPrintSizeOptions, o.PrintSizes)
 		if !valid {