6g: fix uint64(uintptr(unsafe.Pointer(&x)))

Fixes #1417.

R=ken2
CC=golang-dev
https://golang.org/cl/4079042

src/cmd/6g/cgen.c

@@ -431,9 +431,6 @@ agen(Node *n, Node *res)
 	if(n == N || n->type == T)
 		return;
 
-	if(!isptr[res->type->etype] && res->type->etype != TUINTPTR)
-		fatal("agen: not tptr: %T", res->type);
-
 	while(n->op == OCONVNOP)
 		n = n->left;
 

test/fixedbugs/bug319.go

+// $G $D/$F.go
+
+// 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
+
+import "unsafe"
+
+func main() {
+	var x int
+	
+	a := uint64(uintptr(unsafe.Pointer(&x)))
+	b := uint32(uintptr(unsafe.Pointer(&x)))
+	c := uint16(uintptr(unsafe.Pointer(&x)))
+	d := int64(uintptr(unsafe.Pointer(&x)))
+	e := int32(uintptr(unsafe.Pointer(&x)))
+	f := int16(uintptr(unsafe.Pointer(&x)))
+
+	_, _, _, _, _, _ = a, b, c, d, e, f
+}