gc: bug270

Fixes #746.

R=ken2
CC=golang-dev
https://golang.org/cl/1040042

src/cmd/gc/walk.c

@@ -803,11 +803,8 @@ walkexpr(Node **np, NodeList **init)
 		switch(et) {
 		case I2Isame:
 		case E2Esame:
-			n->rlist = list(list1(r->left), nodbool(1));
-			typechecklist(n->rlist, Erv);
-			goto as2;
 		case I2E:
-			n->list = list(list1(n->right), nodbool(1));
+			n->rlist = list(list1(r->left), nodbool(1));
 			typechecklist(n->rlist, Erv);
 			goto as2;
 		case I2T:

test/fixedbugs/bug270.go

@@ -0,0 +1,21 @@
+// $G $D/$F.go
+
+// Copyright 2010 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// http://code.google.com/p/go/issues/detail?id=746
+
+package main
+
+type I interface { F() }
+
+type T struct{}
+
+func (T) F() {}
+
+func main() {
+	switch I(T{}).(type) {
+	case interface{}:
+	}
+}