MIPS: Remove unsafe EmitLoadRegister usage in AddI/SubI for constant right operand.

test/mjsunit/regress/regress-500176.js

Index: test/mjsunit/regress/regress-500176.js
diff --git a/test/mjsunit/regress/regress-500176.js b/test/mjsunit/regress/regress-500176.js
new file mode 100644
index 0000000000000000000000000000000000000000..6700ef0f3340c29fdf0883d39f7164a2af89e817
--- /dev/null
+++ b/test/mjsunit/regress/regress-500176.js
@@ -0,0 +1,13 @@
+// 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 __f_0(p) {
+  var __v_0 = -2147483642;
+  for (var __v_1 = 0; __v_1 < 10; __v_1++) {
+    if (__v_1 > 5) { __v_0 = __v_0 + p; break;}
+  }
+}
+for (var __v_2 = 0; __v_2 < 100000; __v_2++) __f_0(42);
+__v_2 = { f: function () { return x + y; },
+          2: function () { return x - y} };