[turbofan] Some strength reduction for ConvertTaggedHoleToUndefined.

We can fold ConvertTaggedHoleToUndefined into CheckNumber and
CheckTaggedSigned, as they deoptimize no matter if the input
is undefined or hole.

R=jarin@chromium.org

Review-Url: https://codereview.chromium.org/2233393002
Cr-Commit-Position: refs/heads/master@{#38576}

src/compiler/simplified-operator-reducer.cc

@@ -134,6 +134,14 @@ Reduction SimplifiedOperatorReducer::Reduce(Node* node) {
       }
       break;
     }
+    case IrOpcode::kCheckNumber: {
+      NodeMatcher m(node->InputAt(0));
+      if (m.IsConvertTaggedHoleToUndefined()) {
+        node->ReplaceInput(0, m.InputAt(0));
+        return Changed(node);
+      }
+      break;
+    }
     case IrOpcode::kCheckTaggedPointer: {
       Node* const input = node->InputAt(0);
       if (DecideObjectIsSmi(input) == Decision::kFalse) {
@@ -148,6 +156,11 @@ Reduction SimplifiedOperatorReducer::Reduce(Node* node) {
         ReplaceWithValue(node, input);
         return Replace(input);
       }
+      NodeMatcher m(input);
+      if (m.IsConvertTaggedHoleToUndefined()) {
+        node->ReplaceInput(0, m.InputAt(0));
+        return Changed(node);
+      }
       break;
     }
     case IrOpcode::kObjectIsSmi: {