compiler: make panic configurable

Currently defined: abort and trap. -panic=unwind should be implemented
in the future.

compiler/compiler.go

@@ -34,6 +34,7 @@ type Config struct {
 	GOOS          string   //
 	GOARCH        string   //
 	GC            string   // garbage collection strategy
+	PanicStrategy string   // panic strategy ("abort" or "trap")
 	CFlags        []string // cflags to pass to cgo
 	LDFlags       []string // ldflags to pass to cgo
 	DumpSSA       bool     // dump Go SSA, for compiler debugging

compiler/optimizer.go

@@ -18,6 +18,10 @@ func (c *Compiler) Optimize(optLevel, sizeLevel int, inlinerThreshold uint) erro
 	}
 	builder.AddCoroutinePassesToExtensionPoints()
 
+	if c.PanicStrategy == "trap" {
+		c.replacePanicsWithTrap() // -panic=trap
+	}
+
 	// Run function passes for each function.
 	funcPasses := llvm.NewFunctionPassManagerForModule(c.mod)
 	defer funcPasses.Dispose()
@@ -113,6 +117,25 @@ func (c *Compiler) Optimize(optLevel, sizeLevel int, inlinerThreshold uint) erro
 	return nil
 }
 
+// Replace panic calls with calls to llvm.trap, to reduce code size. This is the
+// -panic=trap intrinsic.
+func (c *Compiler) replacePanicsWithTrap() {
+	trap := c.mod.NamedFunction("llvm.trap")
+	for _, name := range []string{"runtime._panic", "runtime.runtimePanic"} {
+		fn := c.mod.NamedFunction(name)
+		if fn.IsNil() {
+			continue
+		}
+		for _, use := range getUses(fn) {
+			if use.IsACallInst().IsNil() || use.CalledValue() != fn {
+				panic("expected use of a panic function to be a call")
+			}
+			c.builder.SetInsertPointBefore(use)
+			c.builder.CreateCall(trap, nil, "")
+		}
+	}
+}
+
 // Eliminate created but not used maps.
 //
 // In the future, this should statically allocate created but never modified

main.go

@@ -36,6 +36,7 @@ func (e *commandError) Error() string {
 type BuildConfig struct {
 	opt           string
 	gc            string
+	panicStrategy string
 	printIR       bool
 	dumpSSA       bool
 	debug         bool
@@ -61,6 +62,7 @@ func Compile(pkgName, outpath string, spec *TargetSpec, config *BuildConfig, act
 		GOOS:          spec.GOOS,
 		GOARCH:        spec.GOARCH,
 		GC:            config.gc,
+		PanicStrategy: config.panicStrategy,
 		CFlags:        spec.CFlags,
 		LDFlags:       spec.LDFlags,
 		Debug:         config.debug,
@@ -507,6 +509,7 @@ 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, dumb, marksweep)")
+	panicStrategy := flag.String("panic", "print", "panic strategy (abort, trap)")
 	printIR := flag.Bool("printir", false, "print LLVM IR")
 	dumpSSA := flag.Bool("dumpssa", false, "dump internal Go SSA")
 	target := flag.String("target", "", "LLVM target")
@@ -529,6 +532,7 @@ func main() {
 	config := &BuildConfig{
 		opt:           *opt,
 		gc:            *gc,
+		panicStrategy: *panicStrategy,
 		printIR:       *printIR,
 		dumpSSA:       *dumpSSA,
 		debug:         !*nodebug,
@@ -544,6 +548,12 @@ func main() {
 		config.ldFlags = strings.Split(*ldFlags, " ")
 	}
 
+	if *panicStrategy != "print" && *panicStrategy != "trap" {
+		fmt.Fprintln(os.Stderr, "Panic strategy must be either print or trap.")
+		usage()
+		os.Exit(1)
+	}
+
 	os.Setenv("CC", "clang -target="+*target)
 
 	switch command {