gc: select receive bug fix

Affects receive using := when new variable escapes to heap.

Fixes #1468.

R=ken2
CC=golang-dev
https://golang.org/cl/4119052

src/cmd/gc/select.c

@@ -157,7 +157,7 @@ walkselect(Node *sel)
 			if(n->left == N || isblank(n->left))
 				n->left = nodnil();
 			else if(n->left->op == ONAME &&
-					(!n->colas || (n->class&PHEAP) == 0) &&
+					(!n->colas || (n->left->class&PHEAP) == 0) &&
 					convertop(ch->type->type, n->left->type, nil) == OCONVNOP) {
 				n->left = nod(OADDR, n->left, N);
 				n->left->etype = 1;  // pointer does not escape
@@ -170,9 +170,9 @@ walkselect(Node *sel)
 				typecheck(&a, Erv);
 				r = nod(OAS, n->left, tmp);
 				typecheck(&r, Etop);
+				cas->nbody = concat(list1(r), cas->nbody);
 				cas->nbody = concat(n->ninit, cas->nbody);
 				n->ninit = nil;
-				cas->nbody = concat(list1(r), cas->nbody);
 				n->left = a;
 			}
 		}

test/fixedbugs/bug320.go

@@ -0,0 +1,45 @@
+// $G $D/$F.go && $L $F.$A && ./$A.out
+
+// Copyright 2011 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.
+
+package main
+
+func main() {
+	c := make(chan int, 1)
+	dummy := make(chan int)
+	v := 0x12345678
+	for i := 0; i < 10; i++ {
+		// 6g had a bug that caused select to pass &t to
+		// selectrecv before allocating the memory for t,
+		// which caused non-deterministic crashes.
+		// This test looks for the bug by checking that the
+		// value received actually ends up in t.
+		// If the allocation happens after storing through
+		// whatever garbage &t holds, the later reference
+		// to t in the case body will use the new pointer and
+		// not see the received value.
+		v += 0x1020304
+		c <- v
+		select {
+		case t := <-c:
+			go func() {
+				f(t)
+			}()
+			escape(&t)
+			if t != v {
+				println(i, v, t)
+				panic("wrong values")
+			}
+		case dummy <- 1:
+		}
+	}
+}
+
+func escape(*int) {
+}
+
+func f(int) {
+}
+