Restrict representation inference to avoid truncation of phi inputs.

test/mjsunit/compiler/regress-446778.js

+// Copyright 2015 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+function Module() {
+  "use asm";
+  function f() {
+   var i = (140737463189505);
+   do {
+    i = i + i | 0;
+    x = undefined + i | 0;
+   } while (!i);
+  }
+  return { f: f };
+}
+
+Module().f();