[turbofan] put spill slot reuse behind a flag

src/compiler/register-allocator.h

Index: src/compiler/register-allocator.h
diff --git a/src/compiler/register-allocator.h b/src/compiler/register-allocator.h
index 5fbb821ccfbcb90a252caff1a5770342a538511f..98216c3a5152dee9956f7fbd23f5200a2846b7b7 100644
--- a/src/compiler/register-allocator.h
+++ b/src/compiler/register-allocator.h
@@ -360,6 +360,8 @@ class RegisterAllocator FINAL : public ZoneObject {
   // 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();
 
@@ -457,6 +459,8 @@ class RegisterAllocator FINAL : public ZoneObject {
   bool TryAllocateFreeReg(LiveRange* range);
   void AllocateBlockedReg(LiveRange* range);
   SpillRange* AssignSpillRangeToLiveRange(LiveRange* range);
+  void FreeSpillSlot(LiveRange* range);
+  InstructionOperand* TryReuseSpillSlot(LiveRange* range);
 
   // Live range splitting helpers.
 
@@ -563,6 +567,7 @@ class RegisterAllocator FINAL : public ZoneObject {
 
   // Indicates success or failure during register allocation.
   bool allocation_ok_;
+  bool use_spill_ranges_;
 
 #ifdef DEBUG
   LifetimePosition allocation_finger_;