bug in parallel assignment

R=r
DELTA=40  (40 added, 0 deleted, 0 changed)
OCL=29850
CL=29855

test/bugs/bug159.go

+// $G $D/$F.go && $L $F.$A && ./$A.out || echo BUG: bug159
+
+// Copyright 2009 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
+
+import "os"
+
+func main() {
+	ok := true;
+	var a, b, c, x, y, z int;
+	f := func() int { b--; return -b };
+
+	// this fails on 6g: apparently it rewrites
+	// the list into
+	//	z = f();
+	//	y = f();
+	//	x = f();
+	// so that the values come out backward.
+	x, y, z = f(), f(), f();
+	if x != 1 || y != 2 || z != 3 {
+		println("xyz: expected 1 2 3 got", x, y, z);
+		ok = false;
+	}
+
+	// this fails on 6g too.  one of the function calls
+	// happens after assigning to b.
+	a, b, c = f(), f(), f();
+	if a != 4 || b != 5 || c != 6 {
+		println("abc: expected 4 5 6 got", a, b, c);
+		ok = false;
+	}
+
+	if !ok {
+		os.Exit(1);
+	}
+}

test/golden.out

@@ -101,6 +101,11 @@ BUG should compile
 5 7
 BUG: should crash
 
+=========== bugs/bug159.go
+xyz: expected 1 2 3 got 3 2 1
+abc: expected 4 5 6 got -4 4 4
+BUG: bug159
+
 =========== fixedbugs/bug016.go
 fixedbugs/bug016.go:7: constant -3 overflows uint