Reuse backing store of two zone lists by using Rewind(0) instead of Clear().

src/lithium-allocator.cc

 // Copyright 2010 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1418 matching lines @@
 void LAllocator::AllocateDoubleRegisters() {
   HPhase phase("Allocate double registers", this);
   num_registers_ = DoubleRegister::kNumAllocatableRegisters;
   mode_ = DOUBLE_REGISTERS;
   AllocateRegisters();
 }
 
 
 void LAllocator::AllocateRegisters() {
   ASSERT(mode_ != NONE);
-  reusable_slots_.Clear();
+  ASSERT(unhandled_live_ranges_.is_empty());
 
   for (int i = 0; i < live_ranges_.length(); ++i) {
     if (live_ranges_[i] != NULL) {
       if (RequiredRegisterKind(live_ranges_[i]->id()) == mode_) {
         AddToUnhandledUnsorted(live_ranges_[i]);
       }
     }
   }
   SortUnhandled();
   ASSERT(UnhandledIsSorted());
 
+  ASSERT(reusable_slots_.is_empty());
   ASSERT(active_live_ranges_.is_empty());
   ASSERT(inactive_live_ranges_.is_empty());
 
   if (mode_ == DOUBLE_REGISTERS) {
     for (int i = 0; i < fixed_double_live_ranges_.length(); ++i) {
       LiveRange* current = fixed_double_live_ranges_.at(i);
       if (current != NULL) {
         AddToInactive(current);
       }
     }
@@ skipping 64 matching lines @@
     bool result = TryAllocateFreeReg(current);
     if (!result) {
       AllocateBlockedReg(current);
     }
 
     if (current->HasRegisterAssigned()) {
       AddToActive(current);
     }
   }
 
-  active_live_ranges_.Clear();
-  inactive_live_ranges_.Clear();
+  reusable_slots_.Rewind(0);
+  active_live_ranges_.Rewind(0);
+  inactive_live_ranges_.Rewind(0);
 }
 
 
 void LAllocator::Setup() {
   LConstantOperand::SetupCache();
   LStackSlot::SetupCache();
   LDoubleStackSlot::SetupCache();
   LRegister::SetupCache();
   LDoubleRegister::SetupCache();
 }
@@ skipping 537 matching lines @@
     LiveRange* current = live_ranges()->at(i);
     if (current != NULL) current->Verify();
   }
 }
 
 
 #endif
 
 
 } }  // namespace v8::internal