From 486caa26d7cd40e7aa9b1ca5d1360d093562eef4 Mon Sep 17 00:00:00 2001
From: Josh Bleecher Snyder <josharian@gmail.com>
Date: Sun, 12 Nov 2017 21:36:20 -0800
Subject: [PATCH] runtime: short-circuit typedmemmove when dst==src

Change-Id: I855268a4c0d07ad602ec90f5da66422d3d87c5f2
Reviewed-on: https://go-review.googlesource.com/94595
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Keith Randall <khr@golang.org>
---
 src/runtime/mbarrier.go | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/runtime/mbarrier.go b/src/runtime/mbarrier.go
index c446db93d2..b6c5ee0658 100644
--- a/src/runtime/mbarrier.go
+++ b/src/runtime/mbarrier.go
@@ -154,6 +154,9 @@ import (
 //
 //go:nosplit
 func typedmemmove(typ *_type, dst, src unsafe.Pointer) {
+	if dst == src {
+		return
+	}
 	if typ.kind&kindNoPointers == 0 {
 		bulkBarrierPreWrite(uintptr(dst), uintptr(src), typ.size)
 	}
-- 
2.48.1