cmd/compile: more ssa config flags

To turn ssa compilation on or off altogether, use
-ssa=1 or -ssa=0.  Default is on.

To turn on or off consistency checks, do
-d=ssa/check/on or -d=ssa/check/off.  Default is on for now.

Change-Id: I277e0311f538981c8b9c62e7b7382a0c8755ce4c
Reviewed-on: https://go-review.googlesource.com/20217Reviewed-by: David Chase <drchase@google.com>

src/cmd/compile/internal/gc/lex.go

@@ -231,6 +231,7 @@ func Main() {
 	obj.Flagstr("cpuprofile", "write cpu profile to `file`", &cpuprofile)
 	obj.Flagstr("memprofile", "write memory profile to `file`", &memprofile)
 	obj.Flagint64("memprofilerate", "set runtime.MemProfileRate to `rate`", &memprofilerate)
+	flag.BoolVar(&ssaEnabled, "ssa", true, "use SSA backend to generate code")
 	obj.Flagparse(usage)
 
 	if flag_dynlink {

src/cmd/compile/internal/gc/ssa.go

@@ -17,6 +17,8 @@ import (
 	"cmd/internal/obj/x86"
 )
 
+var ssaEnabled = true
+
 // Smallest possible faulting page at address zero.
 const minZeroPage = 4096
 
@@ -36,6 +38,9 @@ func shouldssa(fn *Node) bool {
 	if Thearch.Thestring != "amd64" {
 		return false
 	}
+	if !ssaEnabled {
+		return false
+	}
 
 	// Environment variable control of SSA CG
 	// 1. IF GOSSAFUNC == current function name THEN

src/cmd/compile/internal/ssa/compile.go

@@ -40,7 +40,9 @@ func Compile(f *Func) {
 	// Run all the passes
 	printFunc(f)
 	f.Config.HTML.WriteFunc("start", f)
-	checkFunc(f)
+	if checkEnabled {
+		checkFunc(f)
+	}
 	const logMemStats = false
 	for _, p := range passes {
 		if !f.Config.optimize && !p.required {
@@ -93,7 +95,9 @@ func Compile(f *Func) {
 				f.logStat("TIME(ns):BYTES:ALLOCS", time, nBytes, nAllocs)
 			}
 		}
-		checkFunc(f)
+		if checkEnabled {
+			checkFunc(f)
+		}
 	}
 
 	// Squash error printing defer
@@ -112,6 +116,9 @@ type pass struct {
 	test     int  // pass-specific ad-hoc option, perhaps useful in development
 }
 
+// Run consistency checker between each phase
+var checkEnabled = true
+
 // PhaseOption sets the specified flag in the specified ssa phase,
 // returning empty string if this was successful or a string explaining
 // the error if it was not. A version of the phase name with "_"
@@ -120,6 +127,14 @@ type pass struct {
 // GO_GCFLAGS=-d=ssa/generic_cse/time,ssa/generic_cse/stats,ssa/generic_cse/debug=3 ./make.bash ...
 //
 func PhaseOption(phase, flag string, val int) string {
+	if phase == "check" && flag == "on" {
+		checkEnabled = val != 0
+		return ""
+	}
+	if phase == "check" && flag == "off" {
+		checkEnabled = val == 0
+		return ""
+	}
 	underphase := strings.Replace(phase, "_", " ", -1)
 	for i, p := range passes {
 		if p.name == phase || p.name == underphase {