[turbofan] put spill slot reuse behind a flag

src/compiler/register-allocator.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_REGISTER_ALLOCATOR_H_
 #define V8_REGISTER_ALLOCATOR_H_
 
 #include "src/compiler/instruction.h"
 #include "src/zone-containers.h"
 
@@ skipping 342 matching lines @@
   const ZoneVector<LiveRange*>& fixed_live_ranges() const {
     return fixed_live_ranges_;
   }
   const ZoneVector<LiveRange*>& fixed_double_live_ranges() const {
     return fixed_double_live_ranges_;
   }
   InstructionSequence* code() const { return code_; }
   // This zone is for datastructures only needed during register allocation.
   Zone* local_zone() const { return local_zone_; }
 
+  bool use_spill_ranges() const { return use_spill_ranges_; }
+
   // Phase 1 : insert moves to account for fixed register operands.
   void MeetRegisterConstraints();
 
   // Phase 2: compute liveness of all virtual register.
   void BuildLiveRanges();
   bool ExistsUseWithoutDefinition();
 
   // Phase 3: compute register assignments.
   void AllocateGeneralRegisters();
   void AllocateDoubleRegisters();
@@ skipping 77 matching lines @@
   bool UnhandledIsSorted();
   void ActiveToHandled(LiveRange* range);
   void ActiveToInactive(LiveRange* range);
   void InactiveToHandled(LiveRange* range);
   void InactiveToActive(LiveRange* range);
 
   // Helper methods for allocating registers.
   bool TryAllocateFreeReg(LiveRange* range);
   void AllocateBlockedReg(LiveRange* range);
   SpillRange* AssignSpillRangeToLiveRange(LiveRange* range);
+  void FreeSpillSlot(LiveRange* range);
+  InstructionOperand* TryReuseSpillSlot(LiveRange* range);
 
   // Live range splitting helpers.
 
   // Split the given range at the given position.
   // If range starts at or after the given position then the
   // original range is returned.
   // Otherwise returns the live range that starts at pos and contains
   // all uses from the original range that follow pos. Uses at pos will
   // still be owned by the original range after splitting.
   LiveRange* SplitRangeAt(LiveRange* range, LifetimePosition pos);
@@ skipping 86 matching lines @@
   ZoneList<SpillRange*> spill_ranges_;
 
   RegisterKind mode_;
   int num_registers_;
 
   BitVector* assigned_registers_;
   BitVector* assigned_double_registers_;
 
   // Indicates success or failure during register allocation.
   bool allocation_ok_;
+  bool use_spill_ranges_;
 
 #ifdef DEBUG
   LifetimePosition allocation_finger_;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(RegisterAllocator);
 };
 
 }
 }
 }  // namespace v8::internal::compiler
 
 #endif  // V8_REGISTER_ALLOCATOR_H_