Better bitwise and binary arithmetic when the left operand is known to be a number.

tests/compiler/dart2js/generate_at_use_site_test.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #import("compiler_helper.dart");
 
 final String FIB = @"""
 fib(n) {
   if (n <= 1) return 1;
-  return fib(n - 1) + fib(n - 2);
+  return add(fib(n - 1), fib(n - 2));
 }
+
+// We need this artificial add method because
+// our optimizer will actually add type checks
+// for the result of recursively calling fib
+// which introduces new variables because we
+// now have multiple users.
+add(x, y) => x + y;
 """;
 
 main() {
   // Make sure we don't introduce a new variable.
   RegExp regexp = new RegExp("var $anyIdentifier =");
   compileAndDoNotMatch(FIB, 'fib', regexp);
 }