gc: fix complex move again

R=ken2
CC=golang-dev
https://golang.org/cl/4443047

src/cmd/gc/cplx.c

@@ -12,6 +12,19 @@ static	void	minus(Node *nl, Node *res);
 
 #define	CASE(a,b)	(((a)<<16)|((b)<<0))
 
+static int
+overlap(Node *f, Node *t)
+{
+	// check whether f and t could be overlapping stack references.
+	// not exact, because it's hard to check for the stack register
+	// in portable code.  close enough: worst case we will allocate
+	// an extra temporary and the registerizer will clean it up.
+	return f->op == OINDREG &&
+		t->op == OINDREG &&
+		f->xoffset+f->type->width >= t->xoffset &&
+		t->xoffset+t->type->width >= f->xoffset;
+}
+
 /*
  * generate:
  *	res = n;
@@ -43,9 +56,10 @@ complexmove(Node *f, Node *t)
 	case CASE(TCOMPLEX64,TCOMPLEX128):
 	case CASE(TCOMPLEX128,TCOMPLEX64):
 	case CASE(TCOMPLEX128,TCOMPLEX128):
-		// complex to complex move/convert
-		// make from addable
-		if(!f->addable) {
+		// complex to complex move/convert.
+		// make f addable.
+		// also use temporary if possible stack overlap.
+		if(!f->addable || overlap(f, t)) {
 			tempname(&n1, f->type);
 			complexmove(f, &n1);
 			f = &n1;

test/fixedbugs/bug329.go

+// $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
+
+type Value struct {
+	X interface{}
+	Y int
+}
+
+type Struct struct {
+	X complex128
+}
+
+const magic = 1 + 2i
+
+func (Value) Complex(x complex128) {
+	if x != magic {
+		println(x)
+		panic("bad complex magic")
+	}
+}
+
+func f(x *byte, y, z int) complex128 {
+	return magic
+}
+
+func (Value) Struct(x Struct) {
+	if x.X != magic {
+		println(x.X)
+		panic("bad struct magic")
+	}
+}
+
+func f1(x *byte, y, z int) Struct {
+	return Struct{magic}
+}
+
+func main() {
+	var v Value
+	v.Struct(f1(nil, 0, 0)) // ok
+	v.Complex(f(nil, 0, 0)) // used to fail
+}