From 7936ab58f7feb25f8c9b367585886d9872a17ad3 Mon Sep 17 00:00:00 2001
From: Daniel Morsing <daniel.morsing@gmail.com>
Date: Wed, 26 Sep 2012 21:10:29 +0200
Subject: [PATCH] cmd/gc: Don't calculate second value in range if it is blank.

Low hanging fruit optimization. Will remove an expensive copy if the range variable is an array.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/6564052
---
 src/cmd/gc/range.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/cmd/gc/range.c b/src/cmd/gc/range.c
index 459105ee88..741a9ac9a7 100644
--- a/src/cmd/gc/range.c
+++ b/src/cmd/gc/range.c
@@ -71,6 +71,11 @@ typecheckrange(Node *n)
 	v2 = N;
 	if(n->list->next)
 		v2 = n->list->next->n;
+	
+	if(isblank(v2)) {
+		n->list = list1(v1);
+		v2 = N;
+	}
 
 	if(v1->defn == n)
 		v1->type = t1;
-- 
2.48.1