From: Cherry Zhang <cherryyz@google.com>
Date: Mon, 3 Oct 2016 19:21:16 +0000 (-0400)
Subject: cmd/compile: remove unnecessary write barriers for APPEND
X-Git-Tag: go1.8beta1~1070
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=d0e92f61e5c5c59395d9b1a3b4f5c7b90dec5bc8;p=gostls13.git

cmd/compile: remove unnecessary write barriers for APPEND

Updates #17330.

Change-Id: I83fe80139a2213f3169db884b84a4c3bd15b58b6
Reviewed-on: https://go-review.googlesource.com/30140
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
---

diff --git a/src/cmd/compile/internal/gc/ssa.go b/src/cmd/compile/internal/gc/ssa.go
index f5e1c5f0c7..419240eab7 100644
--- a/src/cmd/compile/internal/gc/ssa.go
+++ b/src/cmd/compile/internal/gc/ssa.go
@@ -667,7 +667,7 @@ func (s *state) stmt(n *Node) {
 				r = s.expr(rhs)
 			}
 		}
-		if rhs != nil && rhs.Op == OAPPEND {
+		if rhs != nil && rhs.Op == OAPPEND && needwritebarrier(n.Left, rhs) {
 			// The frontend gets rid of the write barrier to enable the special OAPPEND
 			// handling above, but since this is not a special case, we need it.
 			// TODO: just add a ptr graying to the end of growslice?