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

Review URL: http://codereview.chromium.org/6647019

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@7108 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/hydrogen.cc

@@ -640,7 +640,7 @@ void HGraph::OrderBlocks() {
   HBasicBlock* start = blocks_[0];
   Postorder(start, &visited, &reverse_result, NULL);
 
-  blocks_.Clear();
+  blocks_.Rewind(0);
   int index = 0;
   for (int i = reverse_result.length() - 1; i >= 0; --i) {
     HBasicBlock* b = reverse_result[i];

src/hydrogen.h

@@ -379,7 +379,7 @@ class HEnvironment: public ZoneObject {
   void ClearHistory() {
     pop_count_ = 0;
     push_count_ = 0;
-    assigned_variables_.Clear();
+    assigned_variables_.Rewind(0);
   }
 
   void SetValueAt(int index, HValue* value) {

src/lithium-allocator.cc

@@ -1436,7 +1436,7 @@ void LAllocator::AllocateDoubleRegisters() {
 
 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) {
@@ -1448,6 +1448,7 @@ void LAllocator::AllocateRegisters() {
   SortUnhandled();
   ASSERT(UnhandledIsSorted());
 
+  ASSERT(reusable_slots_.is_empty());
   ASSERT(active_live_ranges_.is_empty());
   ASSERT(inactive_live_ranges_.is_empty());
 
@@ -1532,8 +1533,9 @@ void LAllocator::AllocateRegisters() {
     }
   }
 
-  active_live_ranges_.Clear();
-  inactive_live_ranges_.Clear();
+  reusable_slots_.Rewind(0);
+  active_live_ranges_.Rewind(0);
+  inactive_live_ranges_.Rewind(0);
 }