[turbofan] Strength reduce CheckTaggedSigned/Pointer with checked inputs.

Add strength reduction rules to optimize

 CheckTaggedSigned(CheckTaggedSigned(x)) -> CheckTaggedSigned(x)

and

 CheckTaggedPointer(CheckTaggedPointer(x)) -> CheckTaggedPointer(x)

where we do some cleanup optimizations after loop peeling and redundancy
elimination, which can generate these constructs.

BUG=v8:5267

Review-Url: https://codereview.chromium.org/2336093002
Cr-Commit-Position: refs/heads/master@{#39366}

src/compiler/simplified-operator-reducer.cc

@@ -148,6 +148,11 @@ Reduction SimplifiedOperatorReducer::Reduce(Node* node) {
         ReplaceWithValue(node, input);
         return Replace(input);
       }
+      NodeMatcher m(input);
+      if (m.IsCheckTaggedPointer()) {
+        ReplaceWithValue(node, input);
+        return Replace(input);
+      }
       break;
     }
     case IrOpcode::kCheckTaggedSigned: {
@@ -157,7 +162,10 @@ Reduction SimplifiedOperatorReducer::Reduce(Node* node) {
         return Replace(input);
       }
       NodeMatcher m(input);
-      if (m.IsConvertTaggedHoleToUndefined()) {
+      if (m.IsCheckTaggedSigned()) {
+        ReplaceWithValue(node, input);
+        return Replace(input);
+      } else if (m.IsConvertTaggedHoleToUndefined()) {
         node->ReplaceInput(0, m.InputAt(0));
         return Changed(node);
       }

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

@@ -378,6 +378,19 @@ TEST_F(SimplifiedOperatorReducerTest, CheckTaggedPointerWithHeapConstant) {
   }
 }
 
+TEST_F(SimplifiedOperatorReducerTest,
+       CheckTaggedPointerWithCheckTaggedPointer) {
+  Node* param0 = Parameter(0);
+  Node* effect = graph()->start();
+  Node* control = graph()->start();
+  Node* value = effect = graph()->NewNode(simplified()->CheckTaggedPointer(),
+                                          param0, effect, control);
+  Reduction reduction = Reduce(graph()->NewNode(
+      simplified()->CheckTaggedPointer(), value, effect, control));
+  ASSERT_TRUE(reduction.Changed());
+  EXPECT_EQ(value, reduction.replacement());
+}
+
 // -----------------------------------------------------------------------------
 // CheckTaggedSigned
 
@@ -404,6 +417,18 @@ TEST_F(SimplifiedOperatorReducerTest, CheckTaggedSignedWithNumberConstant) {
   EXPECT_EQ(value, reduction.replacement());
 }
 
+TEST_F(SimplifiedOperatorReducerTest, CheckTaggedSignedWithCheckTaggedSigned) {
+  Node* param0 = Parameter(0);
+  Node* effect = graph()->start();
+  Node* control = graph()->start();
+  Node* value = effect = graph()->NewNode(simplified()->CheckTaggedSigned(),
+                                          param0, effect, control);
+  Reduction reduction = Reduce(graph()->NewNode(
+      simplified()->CheckTaggedSigned(), value, effect, control));
+  ASSERT_TRUE(reduction.Changed());
+  EXPECT_EQ(value, reduction.replacement());
+}
+
 // -----------------------------------------------------------------------------
 // NumberAbs