Introduce intrinsics for double values in Javascript.

test/mjsunit/double-intrinsics.js

+// Copyright 2014 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
+
+function assertDoubleBits(hi, lo, x) {
+  assertEquals(x, %_ConstructDouble(hi, lo));
+  assertEquals(hi | 0, %_DoubleHi(x));
+  assertEquals(lo | 0, %_DoubleLo(x));
+}
+
+function test() {
+  assertDoubleBits(0x7ff80000, 0x00000000, NaN);
+  assertDoubleBits(0x7ff00000, 0x00000000, Infinity);
+  assertDoubleBits(0xfff00000, 0x00000000, -Infinity);
+  assertDoubleBits(0x80000000, 0x00000000, -0);
+  assertDoubleBits(0x400921fb, 0x54442d18, Math.PI);
+  assertDoubleBits(0xc005bf0a, 0x8b145769, -Math.E);
+  assertDoubleBits(0xbfe80000, 0x00000000, -0.75);
+}
+
+test();
+test();
+%OptimizeFunctionOnNextCall(test);
+test();