Avoid sharing AccessorPairs during Genesis.

src/heap.cc

Index: src/heap.cc
diff --git a/src/heap.cc b/src/heap.cc
index cd8a03e3a6ddf90af03129d78a17e060f6385927..81fda47d37947ec83bfb76862dc7abc7e4a2589a 100644
--- a/src/heap.cc
+++ b/src/heap.cc
@@ -5062,8 +5062,37 @@ void Heap::Verify() {
   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