More efficient use of space in AllocationSite.

src/hydrogen.cc

 // Copyright 2013 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 2622 matching lines @@
   ASSERT(allocation_site != NULL);
   HInnerAllocatedObject* allocation_memento = Add<HInnerAllocatedObject>(
       previous_object, previous_object_size);
   AddStoreMapConstant(
       allocation_memento, isolate()->factory()->allocation_memento_map());
   Add<HStoreNamedField>(
       allocation_memento,
       HObjectAccess::ForAllocationMementoSite(),
       allocation_site);
   if (FLAG_allocation_site_pretenuring) {
-    HValue* memento_create_count = Add<HLoadNamedField>(
+    // We want to add 1 to the memento create count. The field is actually a smi
+    // bitfield, but the memento create count is in the lower 14 bits. Therefore
+    // we don't need to mask and shift.
+    STATIC_ASSERT(AllocationSite::MementoCreateCountBits::kShift == 0);
+    HValue* pretenure_data = Add<HLoadNamedField>(
         allocation_site, HObjectAccess::ForAllocationSiteOffset(
-            AllocationSite::kMementoCreateCountOffset));
-    memento_create_count = AddUncasted<HAdd>(
-        memento_create_count, graph()->GetConstant1());
+            AllocationSite::kPretenureDataOffset));
+    pretenure_data = AddUncasted<HAdd>(
+        pretenure_data, graph()->GetConstant1());
     // This smi value is reset to zero after every gc, overflow isn't a problem
     // since the counter is bounded by the new space size.
-    memento_create_count->ClearFlag(HValue::kCanOverflow);
+    pretenure_data->ClearFlag(HValue::kCanOverflow);
     HStoreNamedField* store = Add<HStoreNamedField>(
         allocation_site, HObjectAccess::ForAllocationSiteOffset(
-            AllocationSite::kMementoCreateCountOffset), memento_create_count);
+            AllocationSite::kPretenureDataOffset), pretenure_data);
     // No write barrier needed to store a smi.
     store->SkipWriteBarrier();
   }
 }
 
 
 HInstruction* HGraphBuilder::BuildGetNativeContext(HValue* closure) {
   // Get the global context, then the native context
   HInstruction* context =
       Add<HLoadNamedField>(closure, HObjectAccess::ForFunctionContextPointer());
@@ skipping 8297 matching lines @@
   if (ShouldProduceTraceOutput()) {
     isolate()->GetHTracer()->TraceHydrogen(name(), graph_);
   }
 
 #ifdef DEBUG
   graph_->Verify(false);  // No full verify.
 #endif
 }
 
 } }  // namespace v8::internal