[turbofan] Support for %_DoubleHi, %_DoubleLo and %_ConstructDouble.

test/mjsunit/asm/construct-double.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 stdlib = this;
+var foreign = {};
+var heap = new ArrayBuffer(64 * 1024);
+
+
+var m = (function(stdlib, foreign, heap) {
+  "use asm";
+  function cd1(i, j) {
+    i = i|0;
+    j = j|0;
+    return +%_ConstructDouble(i, j);
+  }
+  function cd2(i) {
+    i = i|0;
+    return +%_ConstructDouble(0, i);
+  }
+  return { cd1: cd1, cd2: cd2 };
+})(stdlib, foreign, heap);
+
+assertEquals(0.0, m.cd1(0, 0));
+assertEquals(%ConstructDouble(0, 1), m.cd2(1));
+for (var i = -2147483648; i < 2147483648; i += 3999773) {
+  assertEquals(%ConstructDouble(0, i), m.cd2(i));
+  for (var j = -2147483648; j < 2147483648; j += 3999773) {
+    assertEquals(%ConstructDouble(i, j), m.cd1(i, j));
+  }
+}