[turbofan] Allow OptionalOperator to return a placeholder.

test/unittests/compiler/int64-lowering-unittest.cc

 // Copyright 2016 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.
 
 #include "src/compiler/int64-lowering.h"
 #include "src/compiler/common-operator.h"
 #include "src/compiler/linkage.h"
 #include "src/compiler/machine-operator.h"
 #include "src/compiler/node.h"
 
@@ skipping 610 matching lines @@
                            IsInt32Constant(32)),
                 IsWord32Clz(IsInt32Constant(high_word_value(0))),
                 IsMerge(
                     IsIfTrue(AllOf(CaptureEq(&branch_capture), branch_matcher)),
                     IsIfFalse(
                         AllOf(CaptureEq(&branch_capture), branch_matcher)))),
           IsInt32Constant(0), start(), start()));
 }
 
 TEST_F(Int64LoweringTest, I64Ctz) {
-  LowerGraph(graph()->NewNode(machine()->Word64CtzPlaceholder(),
+  LowerGraph(graph()->NewNode(machine()->Word64Ctz().placeholder(),
                               Int64Constant(value(0))),
              MachineRepresentation::kWord64);
   Capture<Node*> branch_capture;
   Matcher<Node*> branch_matcher = IsBranch(
       IsWord32Equal(IsInt32Constant(low_word_value(0)), IsInt32Constant(0)),
       start());
   EXPECT_THAT(
       graph()->end()->InputAt(1),
       IsReturn2(
           IsPhi(MachineRepresentation::kWord32,
@@ skipping 19 matching lines @@
       IsReturn2(IsWord32And(IsInt32Constant(low_word_value(0)),
                             IsWord32And(IsInt32Constant(low_word_value(0)),
                                         IsInt32Constant(low_word_value(1)))),
                 IsWord32And(IsInt32Constant(high_word_value(0)),
                             IsWord32And(IsInt32Constant(high_word_value(0)),
                                         IsInt32Constant(high_word_value(1)))),
                 start(), start()));
 }
 
 TEST_F(Int64LoweringTest, I64Popcnt) {
-  LowerGraph(graph()->NewNode(machine()->Word64PopcntPlaceholder(),
+  LowerGraph(graph()->NewNode(machine()->Word64Popcnt().placeholder(),
                               Int64Constant(value(0))),
              MachineRepresentation::kWord64);
 
   EXPECT_THAT(
       graph()->end()->InputAt(1),
       IsReturn2(IsInt32Add(IsWord32Popcnt(IsInt32Constant(low_word_value(0))),
                            IsWord32Popcnt(IsInt32Constant(high_word_value(0)))),
                 IsInt32Constant(0), start(), start()));
 }
 
@@ skipping 133 matching lines @@
           Float32Constant(2.5));
 }
 
 TEST_F(Int64LoweringTest, I64PhiWord32) {
   TestPhi(this, MachineRepresentation::kWord32, Float32Constant(1),
           Float32Constant(2));
 }
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8