Clear next map word when folding allocations into js arrays.

src/hydrogen-instructions.cc

 // Copyright 2012 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 3189 matching lines @@
       !dominator_allocate_instr->IsNewSpaceAllocation() ||
       !dominator_size->IsInteger32Constant()) {
     if (FLAG_trace_allocation_folding) {
       PrintF("#%d (%s) cannot fold into #%d (%s)\n",
           id(), Mnemonic(), dominator->id(), dominator->Mnemonic());
     }
     return;
   }
 
   // First update the size of the dominator allocate instruction.
-  int32_t dominator_size_constant =
+  int32_t original_object_size =
       HConstant::cast(dominator_size)->GetInteger32Constant();
+  int32_t dominator_size_constant = original_object_size;
   int32_t current_size_constant =
       HConstant::cast(current_size)->GetInteger32Constant();
   int32_t new_dominator_size = dominator_size_constant + current_size_constant;
 
   if (MustAllocateDoubleAligned()) {
     if (!dominator_allocate_instr->MustAllocateDoubleAligned()) {
       dominator_allocate_instr->MakeDoubleAligned();
     }
     if ((dominator_size_constant & kDoubleAlignmentMask) != 0) {
       dominator_size_constant += kDoubleSize / 2;
@@ skipping 13 matching lines @@
   Zone* zone = block->zone();
   HInstruction* new_dominator_size_constant =
       HConstant::New(zone, context(), new_dominator_size);
   new_dominator_size_constant->InsertBefore(dominator_allocate_instr);
   dominator_allocate_instr->UpdateSize(new_dominator_size_constant);
 
 #ifdef VERIFY_HEAP
   if (FLAG_verify_heap) {
     dominator_allocate_instr->MakePrefillWithFiller();
   }
+#else

[Michael Starzinger, 2013/08/27 08:41:24]

The #ifdef is not entirely correct. If we compile with the heap verifier but
don't enable it, nobody will smash garbage.

[Hannes Payer (out of office), 2013/08/27 12:50:54]

Done.

+  // TODO(hpayer): This is a short-term hack to make allocation mementos
+  // work again in new space.
+  if (dominator_allocate_instr->clear_next_map_word_) {
+    HObjectAccess access =
+        HObjectAccess::ForJSObjectOffset(original_object_size);
+    HStoreNamedField* clear_next_map =
+        HStoreNamedField::New(zone, context(), dominator_allocate_instr, access,
+            block->graph()->GetConstantNull());
+    clear_next_map->ClearAllSideEffects();
+    clear_next_map->InsertAfter(dominator_allocate_instr);
+  }
+  dominator_allocate_instr->clear_next_map_word_ = clear_next_map_word_;
 #endif
 
   // After that replace the dominated allocate instruction.
   HInstruction* dominated_allocate_instr =
       HInnerAllocatedObject::New(zone,
                                  context(),
                                  dominator_allocate_instr,
                                  dominator_size_constant,
                                  type());
   dominated_allocate_instr->InsertBefore(this);
@@ skipping 739 matching lines @@
       break;
     case kExternalMemory:
       stream->Add("[external-memory]");
       break;
   }
 
   stream->Add("@%d", offset());
 }
 
 } }  // namespace v8::internal