cmd/gc: fix bad checknil with ints on 32 bit compilers

Fixes #7413.

LGTM=rsc
R=remyoudompheng
CC=golang-codereviews, r, rsc
https://golang.org/cl/69180044

src/cmd/gc/pgen.c

@@ -471,8 +471,8 @@ cgen_checknil(Node *n)
 
 	if(disable_checknil)
 		return;
-	// Ideally we wouldn't see any TUINTPTR here, but we do.
-	if(n->type == T || (!isptr[n->type->etype] && n->type->etype != TUINTPTR && n->type->etype != TUNSAFEPTR)) {
+	// Ideally we wouldn't see any integer types here, but we do.
+	if(n->type == T || (!isptr[n->type->etype] && !isint[n->type->etype] && n->type->etype != TUNSAFEPTR)) {
 		dump("checknil", n);
 		fatal("bad checknil");
 	}

test/nilptr4.go

+// build
+
+// Copyright 2014 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.
+
+// Test that the compiler does not crash during compilation.
+
+package main
+
+import "unsafe"
+
+// Issue 7413
+func f1() {
+	type t struct {
+		i int
+	}
+
+	var v *t
+	_ = int(uintptr(unsafe.Pointer(&v.i)))
+	_ = int32(uintptr(unsafe.Pointer(&v.i)))
+}
+
+func main() {}