[dev.ssa] cmd/compile: move rewrite logging behind codegen flag

Generating logging code every time causes large
diffs for small changes.

Since the intent is to use this for debugging only,
generate logging code only when requested.
Committed generated code will be logging free.

Change-Id: I9ef9e29c88b76c2557bad4c6b424b9db1255ec8b
Reviewed-on: https://go-review.googlesource.com/13623Reviewed-by: Keith Randall <khr@golang.org>

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

@@ -9,6 +9,7 @@ package main
 
 import (
 	"bytes"
+	"flag"
 	"fmt"
 	"go/format"
 	"io/ioutil"
@@ -59,6 +60,7 @@ func (a arch) regMaskComment(r regMask) string {
 var archs []arch
 
 func main() {
+	flag.Parse()
 	genOp()
 	genLower()
 }

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

@@ -13,6 +13,7 @@ import (
 	"bufio"
 	"bytes"
 	"crypto/md5"
+	"flag"
 	"fmt"
 	"go/format"
 	"io"
@@ -45,6 +46,10 @@ import (
 
 // If multiple rules match, the first one in file order is selected.
 
+var (
+	genLog = flag.Bool("log", false, "generate code that logs; for debugging only")
+)
+
 type Rule struct {
 	rule   string
 	lineno int
@@ -134,7 +139,9 @@ func genRules(arch arch) {
 	fmt.Fprintf(w, "// autogenerated from gen/%s.rules: do not edit!\n", arch.name)
 	fmt.Fprintln(w, "// generated with: cd gen; go run *.go")
 	fmt.Fprintln(w, "package ssa")
-	fmt.Fprintln(w, "import \"fmt\"")
+	if *genLog {
+		fmt.Fprintln(w, "import \"fmt\"")
+	}
 	fmt.Fprintf(w, "func rewriteValue%s(v *Value, config *Config) bool {\n", arch.name)
 	fmt.Fprintln(w, "b := v.Block")
 
@@ -169,9 +176,9 @@ func genRules(arch arch) {
 			}
 
 			genResult(w, arch, result)
-			fmt.Fprintf(w, "if logRewriteRules {\n")
-			fmt.Fprintf(w, "  fmt.Println(\"rewrite %s.rules:%d\")", arch.name, rule.lineno)
-			fmt.Fprintf(w, "}\n")
+			if *genLog {
+				fmt.Fprintf(w, "fmt.Println(\"rewrite %s.rules:%d\")\n", arch.name, rule.lineno)
+			}
 			fmt.Fprintf(w, "return true\n")
 
 			fmt.Fprintf(w, "}\n")
@@ -275,9 +282,9 @@ func genRules(arch arch) {
 				fmt.Fprintln(w, "b.Likely = BranchUnknown")
 			}
 
-			fmt.Fprintf(w, "if logRewriteRules {\n")
-			fmt.Fprintf(w, "  fmt.Println(\"rewrite %s.rules:%d\")", arch.name, rule.lineno)
-			fmt.Fprintf(w, "}\n")
+			if *genLog {
+				fmt.Fprintf(w, "fmt.Println(\"rewrite %s.rules:%d\")\n", arch.name, rule.lineno)
+			}
 			fmt.Fprintf(w, "return true\n")
 
 			fmt.Fprintf(w, "}\n")
@@ -291,13 +298,14 @@ func genRules(arch arch) {
 
 	// gofmt result
 	b := w.Bytes()
-	b, err = format.Source(b)
+	src, err := format.Source(b)
 	if err != nil {
+		fmt.Printf("%s\n", b)
 		panic(err)
 	}
 
 	// Write to file
-	err = ioutil.WriteFile("../rewrite"+arch.name+".go", b, 0666)
+	err = ioutil.WriteFile("../rewrite"+arch.name+".go", src, 0666)
 	if err != nil {
 		log.Fatalf("can't write output: %v\n", err)
 	}

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

@@ -6,11 +6,6 @@ package ssa
 
 import "fmt"
 
-// Set to true to log all rewrite rules as they occur.
-// This is useful for figuring out whether a rule is triggering
-// and which rules are most heavily used.
-const logRewriteRules = false
-
 func applyRewrite(f *Func, rb func(*Block) bool, rv func(*Value, *Config) bool) {
 	// repeat rewrites until we find no more rewrites
 	var curb *Block