8g: out of register bug

Fixes #806.

R=ken2
CC=golang-dev
https://golang.org/cl/1281042

src/cmd/8g/cgen.c

@@ -10,6 +10,8 @@
 void
 mgen(Node *n, Node *n1, Node *rg)
 {
+	Node n2;
+
 	n1->op = OEMPTY;
 
 	if(n->addable) {
@@ -18,11 +20,13 @@ mgen(Node *n, Node *n1, Node *rg)
 			reg[n->val.u.reg]++;
 		return;
 	}
-	if(n->type->width > widthptr && !isfloat[n->type->etype])
-		tempname(n1, n->type);
-	else
-		regalloc(n1, n->type, rg);
+	tempname(n1, n->type);
 	cgen(n, n1);
+	if(n->type->width <= widthptr || isfloat[n->type->etype]) {
+		n2 = *n1;
+		regalloc(n1, n->type, rg);
+		gmove(&n2, n1);
+	}
 }
 
 void

test/fixedbugs/bug283.go

+// $G $D/$F.go || echo BUG: should compile
+
+// 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=806
+// triggered out of registers on 8g
+
+package main
+
+type Point struct {
+	x int
+	y int
+}
+
+func dist(p0, p1 Point) float64 {
+	return float64((p0.x-p1.x)*(p0.x-p1.x) + (p0.y-p1.y)*(p0.y-p1.y))
+}