[turbofan] Reduce shl with sar/shr and same shift amount to bit-and.

test/mjsunit/asm/int32array-unaligned.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.
+
+function Module(stdlib, foreign, heap) {
+  "use asm";
+  var MEM32 = new stdlib.Int32Array(heap);
+  function load(i) {
+    i = i|0;
+    i = MEM32[i >> 2] | 0;
+    return i;
+  }
+  function store(i, v) {
+    i = i|0;
+    v = v|0;
+    MEM32[i >> 2] = v;
+  }
+  return { load: load, store: store };
+}
+
+var m = Module(this, {}, new ArrayBuffer(1024));
+
+m.store(0, 0x12345678);
+m.store(4, -1);
+m.store(8, -1);
+for (var i = 0; i < 4; ++i) {
+  assertEquals(0x12345678, m.load(i));
+}
+for (var i = 4; i < 12; ++i) {
+  assertEquals(-1, m.load(i));
+}
+for (var j = 4; j < 8; ++j) {
+  m.store(j, 0x11223344);
+  for (var i = 0; i < 4; ++i) {
+    assertEquals(0x12345678, m.load(i));
+  }
+  for (var i = 4; i < 8; ++i) {
+    assertEquals(0x11223344, m.load(i));
+  }
+  for (var i = 8; i < 12; ++i) {
+    assertEquals(-1, m.load(i));
+  }
+}