From 804a43ca76a00c207a39d2846e3fe754d761ca2e Mon Sep 17 00:00:00 2001
From: Daniel Morsing <daniel.morsing@gmail.com>
Date: Tue, 18 Sep 2012 17:40:53 +0200
Subject: [PATCH] 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
---
 src/cmd/gc/walk.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/cmd/gc/walk.c b/src/cmd/gc/walk.c
index 935fa6d65d7..c6b7e4278f7 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);