Avoid sharing AccessorPairs during Genesis.

src/heap.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 5044 matching lines @@
 
   old_pointer_space_->Verify(&visitor);
   map_space_->Verify(&visitor);
 
   VerifyPointersVisitor no_dirty_regions_visitor;
   old_data_space_->Verify(&no_dirty_regions_visitor);
   code_space_->Verify(&no_dirty_regions_visitor);
   cell_space_->Verify(&no_dirty_regions_visitor);
 
   lo_space_->Verify();
+
+  // TODO(svenpanne) We should enable this when our fast->slow->fast-mode dance
+  // for setting accessor properties is fixed.
+  // VerifyNoAccessorPairSharing();
 }
 
+
+void Heap::VerifyNoAccessorPairSharing() {
+  // Verification is done in 2 phases: First we mark all AccessorPairs, checking
+  // that we mark only unmarked pairs, then we clear all marks, restoring the
+  // initial state. We use the LSB of the AccessorPair's getter as the marking

[Michael Starzinger, 2012/02/17 13:33:28]

Actually we want to use the "Smi tag" which happens to be the "LSB".

[Sven Panne, 2012/02/20 08:26:03]

Done.

+  // bit, because we can never see a Smi as the getter.
+  for (int phase = 0; phase < 2; phase++) {
+    HeapObjectIterator iter(map_space());
+    for (HeapObject* obj = iter.Next(); obj != NULL; obj = iter.Next()) {
+      if (obj->IsMap()) {
+        DescriptorArray* descs = Map::cast(obj)->instance_descriptors();
+        for (int i = 0; i < descs->number_of_descriptors(); i++) {
+          if (descs->GetType(i) == CALLBACKS &&
+              descs->GetValue(i)->IsAccessorPair()) {
+            AccessorPair* accessors = AccessorPair::cast(descs->GetValue(i));
+            uintptr_t before = reinterpret_cast<intptr_t>(accessors->getter());
+            uintptr_t after = (phase == 0) ? (before & ~1) : (before | 1);

[Michael Starzinger, 2012/02/17 13:33:28]

Please use the kHeapObjectTag[Mask] and kSmiTag[Mask] constants here to do the
masking. Also HasHeapObjectTag() and HasSmiTag() might come in handy.

[Sven Panne, 2012/02/20 08:26:03]

Done.

+            CHECK(before != after);
+            accessors->set_getter(reinterpret_cast<Object*>(after));
+          }
+        }
+      }
+    }
+  }
+}
 #endif  // DEBUG
 
 
 MaybeObject* Heap::LookupSymbol(Vector<const char> string) {
   Object* symbol = NULL;
   Object* new_table;
   { MaybeObject* maybe_new_table =
         symbol_table()->LookupSymbol(string, &symbol);
     if (!maybe_new_table->ToObject(&new_table)) return maybe_new_table;
   }
@@ skipping 1804 matching lines @@
   isolate_->heap()->store_buffer()->Compact();
   isolate_->heap()->store_buffer()->Filter(MemoryChunk::ABOUT_TO_BE_FREED);
   for (chunk = chunks_queued_for_free_; chunk != NULL; chunk = next) {
     next = chunk->next_chunk();
     isolate_->memory_allocator()->Free(chunk);
   }
   chunks_queued_for_free_ = NULL;
 }
 
 } }  // namespace v8::internal