[turbofan] Add backend support for signed loads.

src/compiler/instruction.h

 // Copyright 2014 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_INSTRUCTION_H_
 #define V8_COMPILER_INSTRUCTION_H_
 
 #include <deque>
 #include <map>
 #include <set>
@@ skipping 387 matching lines @@
   ZoneList<InstructionOperand*> untagged_operands_;
   int instruction_position_;
 };
 
 OStream& operator<<(OStream& os, const PointerMap& pm);
 
 // TODO(titzer): s/PointerMap/ReferenceMap/
 class Instruction : public ZoneObject {
  public:
   size_t OutputCount() const { return OutputCountField::decode(bit_field_); }
-  InstructionOperand* Output() const { return OutputAt(0); }
   InstructionOperand* OutputAt(size_t i) const {
     DCHECK(i < OutputCount());
     return operands_[i];
   }
 
+  bool HasOutput() const { return OutputCount() == 1; }
+  InstructionOperand* Output() const { return OutputAt(0); }
+
   size_t InputCount() const { return InputCountField::decode(bit_field_); }
   InstructionOperand* InputAt(size_t i) const {
     DCHECK(i < InputCount());
     return operands_[OutputCount() + i];
   }
 
   size_t TempCount() const { return TempCountField::decode(bit_field_); }
   InstructionOperand* TempAt(size_t i) const {
     DCHECK(i < TempCount());
     return operands_[OutputCount() + InputCount() + i];
@@ skipping 441 matching lines @@
   DeoptimizationVector deoptimization_entries_;
 };
 
 OStream& operator<<(OStream& os, const InstructionSequence& code);
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_INSTRUCTION_H_