From: Daniel Morsing <daniel.morsing@gmail.com>
Date: Tue, 18 Sep 2012 15:40:53 +0000 (+0200)
Subject: cmd/gc: fix double evaluation in interface comparison
X-Git-Tag: go1.1rc2~2425
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=804a43ca76a00c207a39d2846e3fe754d761ca2e;p=gostls13.git

cmd/gc: fix double evaluation in interface comparison

During interface compare, the operands will be evaluated twice. The operands might include function calls for conversion, so make them cheap before comparing them.

R=rsc
CC=golang-dev
https://golang.org/cl/6498133
---

diff --git a/src/cmd/gc/walk.c b/src/cmd/gc/walk.c
index 935fa6d65d..c6b7e4278f 100644
--- a/src/cmd/gc/walk.c
+++ b/src/cmd/gc/walk.c
@@ -1194,6 +1194,9 @@ walkexpr(Node **np, NodeList **init)
 			fn = syslook("efaceeq", 1);
 		else
 			fn = syslook("ifaceeq", 1);
+
+		n->right = cheapexpr(n->right, init);
+		n->left = cheapexpr(n->left, init);
 		argtype(fn, n->right->type);
 		argtype(fn, n->left->type);
 		r = mkcall1(fn, n->type, init, n->left, n->right);