Add %GetUndetectable() test intrinsic and add tests for undetectables.

test/mjsunit/undetectable.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.
+
+// Flags: --allow-natives-syntax
+
+var obj = %GetUndetectable();
+
+function shouldNotBeTaken() {
+  fail("Undetectable branch should not be taken", "branch was taken");
+}
+
+function shouldBeTaken() {
+  fail("Inverted Undetectable branch should be taken", "branch was not taken");
+}
+
+function testCompares() {
+  assertTrue(!obj);
+  assertFalse(!!obj);
+  assertFalse(obj == true);
+  assertFalse(obj == false);
+  assertFalse(obj === true);
+  assertFalse(obj === false);
+  assertEquals(2, obj ? 1 : 2);
+  assertEquals(obj, true && obj);
+  assertEquals(obj, false || obj);
+}
+
+function testIfs() {
+  if (obj) {
+    shouldNotBeTaken();
+  }
+
+  if (obj) {
+    shouldNotBeTaken();
+  } else {
+    // do nothing
+  }
+
+  if (!obj) {
+    // do nothing
+  } else {
+    shouldBeTaken();
+  }
+}
+
+function testWhiles() {
+  while (obj) {
+    shouldNotBeTaken();
+  }
+
+  var i = 0;
+  while (!obj) {
+    i++;
+    break;
+  }
+
+  assertEquals(1, i);
+}
+
+function testFors() {
+  for (var i = 0; obj; i++) {
+    shouldNotBeTaken();
+  }
+
+  var j = 0;
+  for (var i = 0; !obj; i++) {
+    j++;
+    break;
+  }
+
+  assertEquals(1, j);
+}
+
+for (var j = 0; j < 5; j++) {
+  testCompares();
+  testIfs();
+  testWhiles();
+  testFors();
+
+  if (j == 3) {
+    %OptimizeFunctionOnNextCall(testCompares);
+    %OptimizeFunctionOnNextCall(testIfs);
+    %OptimizeFunctionOnNextCall(testWhiles);
+    %OptimizeFunctionOnNextCall(testFors);
+  }
+}