Added descriptor lookup cache to eliminate some search overhead....

src/heap.cc

Index: src/heap.cc
===================================================================
--- src/heap.cc	(revision 2237)
+++ src/heap.cc	(working copy)
@@ -502,6 +502,7 @@
   // maps.
   KeyedLookupCache::Clear();
   ContextSlotCache::Clear();
+  DescriptorLookupCache::Clear();
 
   CompilationCache::MarkCompactPrologue();
 
@@ -630,6 +631,9 @@
   // Implements Cheney's copying algorithm
   LOG(ResourceEvent("scavenge", "begin"));
 
+  // Clear descriptor cache.
+  DescriptorLookupCache::Clear();
+
   // Used for updating survived_since_last_expansion_ at function end.
   int survived_watermark = PromotedSpaceSize();
 
@@ -1392,6 +1396,9 @@
   // Initialize context slot cache.
   ContextSlotCache::Clear();
 
+  // Initialize descriptor cache.
+  DescriptorLookupCache::Clear();
+
   // Initialize compilation cache.
   CompilationCache::Clear();
 
@@ -3559,6 +3566,17 @@
 int KeyedLookupCache::field_offsets_[KeyedLookupCache::kLength];
 
 
+void DescriptorLookupCache::Clear() {
+  for (int index = 0; index < kLength; index++) keys_[index].array = NULL;
+}
+
+
+DescriptorLookupCache::Key
+DescriptorLookupCache::keys_[DescriptorLookupCache::kLength];
+
+int DescriptorLookupCache::results_[DescriptorLookupCache::kLength];
+
+
 #ifdef DEBUG
 bool Heap::GarbageCollectionGreedyCheck() {
   ASSERT(FLAG_gc_greedy);