[turbofan] Allow OptionalOperator to return a placeholder.

src/compiler/machine-operator.h

 // Copyright 2013 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.
 
 #ifndef V8_COMPILER_MACHINE_OPERATOR_H_
 #define V8_COMPILER_MACHINE_OPERATOR_H_
 
 #include "src/base/flags.h"
 #include "src/machine-type.h"
 
 namespace v8 {
 namespace internal {
 namespace compiler {
 
 // Forward declarations.
 struct MachineOperatorGlobalCache;
 class Operator;
 
 
 // For operators that are not supported on all platforms.
 class OptionalOperator final {
  public:
-  explicit OptionalOperator(const Operator* op) : op_(op) {}
+  OptionalOperator(bool supported, const Operator* op)
+      : supported_(supported), op_(op) {}
 
-  bool IsSupported() const { return op_ != nullptr; }
+  bool IsSupported() const { return supported_; }
+  // Gets the operator only if it is supported.
   const Operator* op() const {
-    DCHECK_NOT_NULL(op_);
+    DCHECK(supported_);
     return op_;
   }
+  // Always gets the operator, even for unsupported operators. This is useful to
+  // use the operator as a placeholder in a graph, for instance.
+  const Operator* placeholder() const { return op_; }
 
  private:
+  bool supported_;
   const Operator* const op_;
 };
 
 
 // A Load needs a MachineType.
 typedef MachineType LoadRepresentation;
 
 LoadRepresentation LoadRepresentationOf(Operator const*);
 
 // A Store needs a MachineType and a WriteBarrierKind in order to emit the
@@ skipping 160 matching lines @@
   const Operator* Word32Xor();
   const Operator* Word32Shl();
   const Operator* Word32Shr();
   const Operator* Word32Sar();
   const Operator* Word32Ror();
   const Operator* Word32Equal();
   const Operator* Word32Clz();
   const OptionalOperator Word32Ctz();
   const OptionalOperator Word32Popcnt();
   const OptionalOperator Word64Popcnt();
-  const Operator* Word64PopcntPlaceholder();
   const OptionalOperator Word32ReverseBits();
   const OptionalOperator Word64ReverseBits();
   bool Word32ShiftIsSafe() const { return flags_ & kWord32ShiftIsSafe; }
 
   const Operator* Word64And();
   const Operator* Word64Or();
   const Operator* Word64Xor();
   const Operator* Word64Shl();
   const Operator* Word64Shr();
   const Operator* Word64Sar();
   const Operator* Word64Ror();
   const Operator* Word64Clz();
   const OptionalOperator Word64Ctz();
-  const Operator* Word64CtzPlaceholder();
   const Operator* Word64Equal();
 
   const Operator* Int32PairAdd();
   const Operator* Int32PairSub();
   const Operator* Int32PairMul();
   const Operator* Word32PairShl();
   const Operator* Word32PairShr();
   const Operator* Word32PairSar();
 
   const Operator* Int32Add();
@@ skipping 433 matching lines @@
 };
 
 
 DEFINE_OPERATORS_FOR_FLAGS(MachineOperatorBuilder::Flags)
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_MACHINE_OPERATOR_H_