[turbofan] Eliminate unnecessary hole to undefined conversion.

Add simplified operator reduction rule that reduces

  CheckedTaggedSignedToInt32(ConvertTaggedHoleToUndefined(x))

to

  CheckedTaggedSignedToInt32(x)

which avoids the unnecessary hole to undefined conversion, as the check
operation will fail equally on either hole or undefined.

BUG=v8:5267
R=jarin@chromium.org

Review-Url: https://codereview.chromium.org/2384453002
Cr-Commit-Position: refs/heads/master@{#39863}

src/compiler/simplified-operator-reducer.cc

@@ -126,6 +126,14 @@ Reduction SimplifiedOperatorReducer::Reduce(Node* node) {
       }
       break;
     }
+    case IrOpcode::kCheckedTaggedSignedToInt32: {
+      NodeMatcher m(node->InputAt(0));
+      if (m.IsConvertTaggedHoleToUndefined()) {
+        node->ReplaceInput(0, m.InputAt(0));
+        return Changed(node);
+      }
+      break;
+    }
     case IrOpcode::kCheckIf: {
       HeapObjectMatcher m(node->InputAt(0));
       if (m.Is(factory()->true_value())) {