gc: bug268

Fixes #745.

R=ken2
CC=golang-dev
https://golang.org/cl/1008045

src/cmd/gc/typecheck.c

@@ -612,6 +612,12 @@ reswitch:
 		defaultlit(&n->left, T);
 		defaultlit(&n->right->left, types[TUINT]);
 		defaultlit(&n->right->right, types[TUINT]);
+		if(isfixedarray(n->left->type)) {
+			// Insert explicit & before fixed array
+			// so that back end knows to move to heap.
+			n->left = nod(OADDR, n->left, N);
+			typecheck(&n->left, top);
+		}
 		implicitstar(&n->left);
 		if(n->right->left == N) {
 			yyerror("missing slice bounds?");

test/fixedbugs/bug268.go

+// $G $D/$F.go && $L $F.$A && ./$A.out
+
+// 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=745
+
+package main
+
+type T1 struct {
+	T2 *T2
+}
+
+type T2 struct {
+	T3 *T3
+}
+
+type T3 struct {
+	T4 []*T4
+}
+
+type T4 struct {
+	X int
+}
+
+func f() *T1 {
+	x := &T1{
+		&T2{
+			&T3{
+				[1]*T4{
+					&T4{5},
+				}[0:],
+			},
+		},
+	}
+	return x
+}
+
+func g(x int) {
+	if x == 0 {
+		return
+	}
+	g(x-1)
+}
+
+func main() {
+	x := f()
+	g(100) // smash temporaries left over on stack
+	if x.T2.T3.T4[0].X != 5 {
+		println("BUG", x.T2.T3.T4[0].X)
+	}
+}