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

test/mjsunit/asm/double-lo.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 lo1(i) {
+    i = +i;
+    return %_DoubleLo(i)|0;
+  }
+  function lo2(i, j) {
+    i = +i;
+    j = +j;
+    return %_DoubleLo(i)+%_DoubleLo(j)|0;
+  }
+  return { lo1: lo1, lo2: lo2 };
+})(stdlib, foreign, heap);
+
+assertEquals(0, m.lo1(0.0));
+assertEquals(0, m.lo1(-0.0));
+assertEquals(0, m.lo1(Infinity));
+assertEquals(0, m.lo1(-Infinity));
+assertEquals(0, m.lo2(0.0, 0.0));
+assertEquals(0, m.lo2(0.0, -0.0));
+assertEquals(0, m.lo2(-0.0, 0.0));
+assertEquals(0, m.lo2(-0.0, -0.0));
+for (var i = -2147483648; i < 2147483648; i += 3999773) {
+  assertEquals(%_DoubleLo(i), m.lo1(i));
+  assertEquals(i, m.lo1(%ConstructDouble(0, i)));
+  assertEquals(i, m.lo1(%ConstructDouble(i, i)));
+  assertEquals(i+i|0, m.lo2(%ConstructDouble(0, i), %ConstructDouble(0, i)));
+  assertEquals(i+i|0, m.lo2(%ConstructDouble(i, i), %ConstructDouble(i, i)));
+}