[x64] Fix optimization for certain checked load/stores.

test/mjsunit/asm/float64array-negative-offset.js

Index: test/mjsunit/asm/float64array-negative-offset.js
diff --git a/test/mjsunit/asm/float64array-negative-offset.js b/test/mjsunit/asm/float64array-negative-offset.js
new file mode 100644
index 0000000000000000000000000000000000000000..154bd82cd379a0ea932fb5e6dd989cd0d5b1bbc4
--- /dev/null
+++ b/test/mjsunit/asm/float64array-negative-offset.js
@@ -0,0 +1,42 @@
+// 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.
+
+var stdlib = this;
+var buffer = new ArrayBuffer(64 * 1024);
+var foreign = {}
+
+
+var m = (function Module(stdlib, foreign, heap) {
+  "use asm";
+  var MEM64 = new stdlib.Float64Array(heap);
+  function load(i) {
+    i = i|0;
+    i = +MEM64[i >> 3];
+    return i;
+  }
+  function store(i, v) {
+    i = i|0;
+    v = +v;
+    MEM64[i >> 3] = v;
+  }
+  function load8(i) {
+    i = i|0;
+    i = +MEM64[i + 8 >> 3];
+    return i;
+  }
+  function store8(i, v) {
+    i = i|0;
+    v = +v;
+    MEM64[i + 8 >> 3] = v;
+  }
+  return { load: load, store: store, load8: load8, store8: store8 };
+})(stdlib, foreign, buffer);
+
+assertEquals(NaN, m.load(-8));
+assertEquals(NaN, m.load8(-16));
+m.store(0, 42.0);
+assertEquals(42.0, m.load8(-8));
+m.store8(-8, 99.0);
+assertEquals(99.0, m.load(0));
+assertEquals(99.0, m.load8(-8));