From 974c201f74f730737964e5239da473fc548b408e Mon Sep 17 00:00:00 2001
From: Josh Bleecher Snyder <josharian@gmail.com>
Date: Sun, 10 Apr 2016 10:43:04 -0700
Subject: [PATCH] runtime: avoid unnecessary map iteration write barrier

Update #14921

Change-Id: I5c5816d0193757bf7465b1e09c27ca06897df4bf
Reviewed-on: https://go-review.googlesource.com/21814
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
---
 src/runtime/hashmap.go | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/runtime/hashmap.go b/src/runtime/hashmap.go
index 9e18192cd8..d549ce4194 100644
--- a/src/runtime/hashmap.go
+++ b/src/runtime/hashmap.go
@@ -790,7 +790,9 @@ next:
 				}
 			}
 			it.bucket = bucket
-			it.bptr = b
+			if it.bptr != b { // avoid unnecessary write barrier; see issue 14921
+				it.bptr = b
+			}
 			it.i = i + 1
 			it.checkBucket = checkBucket
 			return
-- 
2.48.1