cmd/compile/internal/gc: avoid stringsCompare for string literals

Passes go build -a -toolexec 'toolstash -cmp' std cmp.

Change-Id: I7567355d405c976c5d91a0cd4e9486ebeb348dbb
Reviewed-on: https://go-review.googlesource.com/14682Reviewed-by: Dave Cheney <dave@cheney.net>
Run-TryBot: Dave Cheney <dave@cheney.net>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

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

@@ -986,37 +986,37 @@ func evconst(n *Node) {
 		goto setfalse
 
 	case OEQ<<16 | CTSTR:
-		if cmpslit(nl, nr) == 0 {
+		if strlit(nl) == strlit(nr) {
 			goto settrue
 		}
 		goto setfalse
 
 	case ONE<<16 | CTSTR:
-		if cmpslit(nl, nr) != 0 {
+		if strlit(nl) != strlit(nr) {
 			goto settrue
 		}
 		goto setfalse
 
 	case OLT<<16 | CTSTR:
-		if cmpslit(nl, nr) < 0 {
+		if strlit(nl) < strlit(nr) {
 			goto settrue
 		}
 		goto setfalse
 
 	case OLE<<16 | CTSTR:
-		if cmpslit(nl, nr) <= 0 {
+		if strlit(nl) <= strlit(nr) {
 			goto settrue
 		}
 		goto setfalse
 
 	case OGE<<16 | CTSTR:
-		if cmpslit(nl, nr) >= 0 {
+		if strlit(nl) >= strlit(nr) {
 			goto settrue
 		}
 		goto setfalse
 
 	case OGT<<16 | CTSTR:
-		if cmpslit(nl, nr) > 0 {
+		if strlit(nl) > strlit(nr) {
 			goto settrue
 		}
 		goto setfalse
@@ -1341,8 +1341,9 @@ func defaultlit2(lp **Node, rp **Node, force int) {
 	Convlit(rp, Types[TINT])
 }
 
-func cmpslit(l, r *Node) int {
-	return stringsCompare(l.Val().U.(string), r.Val().U.(string))
+// strlit returns the value of a literal string Node as a string.
+func strlit(n *Node) string {
+	return n.Val().U.(string)
 }
 
 func Smallintconst(n *Node) bool {

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

@@ -1356,7 +1356,7 @@ func walkexpr(np **Node, init **NodeList) {
 		}
 
 		// s + "badgerbadgerbadger" == "badgerbadgerbadger"
-		if (n.Etype == OEQ || n.Etype == ONE) && Isconst(n.Right, CTSTR) && n.Left.Op == OADDSTR && count(n.Left.List) == 2 && Isconst(n.Left.List.Next.N, CTSTR) && cmpslit(n.Right, n.Left.List.Next.N) == 0 {
+		if (n.Etype == OEQ || n.Etype == ONE) && Isconst(n.Right, CTSTR) && n.Left.Op == OADDSTR && count(n.Left.List) == 2 && Isconst(n.Left.List.Next.N, CTSTR) && strlit(n.Right) == strlit(n.Left.List.Next.N) {
 			r := Nod(int(n.Etype), Nod(OLEN, n.Left.List.N, nil), Nodintconst(0))
 			typecheck(&r, Erv)
 			walkexpr(&r, init)