[turbofan] Reduce ~~x to x.

TEST=unittests
R=dcarney@chromium.org

Review URL: https://codereview.chromium.org/666723005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24770 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/compiler/machine-operator-reducer.cc

@@ -173,6 +173,12 @@ Reduction MachineOperatorReducer::Reduce(Node* node) {
         return ReplaceInt32(m.left().Value() ^ m.right().Value());
       }
       if (m.LeftEqualsRight()) return ReplaceInt32(0);  // x ^ x => 0
+      if (m.left().IsWord32Xor() && m.right().Is(-1)) {
+        Int32BinopMatcher mleft(m.left().node());
+        if (mleft.right().Is(-1)) {  // (x ^ -1) ^ -1 => x
+          return Replace(mleft.left().node());
+        }
+      }
       break;
     }
     case IrOpcode::kWord32Shl: {

test/unittests/compiler/machine-operator-reducer-unittest.cc

@@ -481,6 +481,45 @@ TEST_F(MachineOperatorReducerTest, TruncateInt64ToInt32WithConstant) {
 }
 
 
+// -----------------------------------------------------------------------------
+// Word32Xor
+
+
+TEST_F(MachineOperatorReducerTest, Word32XorWithWord32XorAndMinusOne) {
+  Node* const p0 = Parameter(0);
+
+  // (x ^ -1) ^ -1 => x
+  Reduction r1 = Reduce(graph()->NewNode(
+      machine()->Word32Xor(),
+      graph()->NewNode(machine()->Word32Xor(), p0, Int32Constant(-1)),
+      Int32Constant(-1)));
+  ASSERT_TRUE(r1.Changed());
+  EXPECT_EQ(r1.replacement(), p0);
+
+  // -1 ^ (x ^ -1) => x
+  Reduction r2 = Reduce(graph()->NewNode(
+      machine()->Word32Xor(), Int32Constant(-1),
+      graph()->NewNode(machine()->Word32Xor(), p0, Int32Constant(-1))));
+  ASSERT_TRUE(r2.Changed());
+  EXPECT_EQ(r2.replacement(), p0);
+
+  // (-1 ^ x) ^ -1 => x
+  Reduction r3 = Reduce(graph()->NewNode(
+      machine()->Word32Xor(),
+      graph()->NewNode(machine()->Word32Xor(), Int32Constant(-1), p0),
+      Int32Constant(-1)));
+  ASSERT_TRUE(r3.Changed());
+  EXPECT_EQ(r3.replacement(), p0);
+
+  // -1 ^ (-1 ^ x) => x
+  Reduction r4 = Reduce(graph()->NewNode(
+      machine()->Word32Xor(), Int32Constant(-1),
+      graph()->NewNode(machine()->Word32Xor(), Int32Constant(-1), p0)));
+  ASSERT_TRUE(r4.Changed());
+  EXPECT_EQ(r4.replacement(), p0);
+}
+
+
 // -----------------------------------------------------------------------------
 // Word32Ror