cmd/gc: allocate stack buffer for ORUNESTR

If result of string(i) does not escape,
allocate a [4]byte temp on stack for it.

Change-Id: If31ce9447982929d5b3b963fd0830efae4247c37
Reviewed-on: https://go-review.googlesource.com/3411
Reviewed-by: Russ Cox <rsc@golang.org>

1 files changed, 9 insertions, 2 deletions

diff --git a/src/runtime/string.go b/src/runtime/string.go
index 9ec6f320eb..58198d0e1b 100644
--- a/src/runtime/string.go
+++ b/src/runtime/string.go
@@ -185,8 +185,15 @@ type stringStruct struct {
 	len int
 }
 
-func intstring(v int64) string {
-	s, b := rawstring(4)
+func intstring(buf *[4]byte, v int64) string {
+	var s string
+	var b []byte
+	if buf != nil {
+		b = buf[:]
+		s = slicebytetostringtmp(b)
+	} else {
+		s, b = rawstring(4)
+	}
 	n := runetochar(b, rune(v))
 	return s[:n]
 }