Revert r1900, r1897 and r1895 which are all gc changes. The changes...

src/heap.cc

Index: src/heap.cc
===================================================================
--- src/heap.cc	(revision 1910)
+++ src/heap.cc	(working copy)
@@ -538,7 +538,7 @@
 
 
 // Shared state read by the scavenge collector and set by ScavengeObject.
-static Address promoted_rear = NULL;
+static Address promoted_top = NULL;
 
 
 #ifdef DEBUG
@@ -554,36 +554,26 @@
     }
   }
 };
+#endif
 
-
-static void VerifyNonPointerSpacePointers() {
-  // Verify that there are no pointers to new space in spaces where we
-  // do not expect them.
-  VerifyNonPointerSpacePointersVisitor v;
-  HeapObjectIterator code_it(Heap::code_space());
-  while (code_it.has_next()) {
-    HeapObject* object = code_it.next();
-    if (object->IsCode()) {
-      Code::cast(object)->ConvertICTargetsFromAddressToObject();
+void Heap::Scavenge() {
+#ifdef DEBUG
+  if (FLAG_enable_slow_asserts) {
+    VerifyNonPointerSpacePointersVisitor v;
+    HeapObjectIterator it(code_space_);
+    while (it.has_next()) {
+      HeapObject* object = it.next();
+      if (object->IsCode()) {
+        Code::cast(object)->ConvertICTargetsFromAddressToObject();
+      }
       object->Iterate(&v);
-      Code::cast(object)->ConvertICTargetsFromObjectToAddress();
-    } else {
-      // If we find non-code objects in code space (e.g., free list
-      // nodes) we want to verify them as well.
-      object->Iterate(&v);
+      if (object->IsCode()) {
+        Code::cast(object)->ConvertICTargetsFromObjectToAddress();
+      }
     }
   }
-
-  HeapObjectIterator data_it(Heap::old_data_space());
-  while (data_it.has_next()) data_it.next()->Iterate(&v);
-}
 #endif
 
-void Heap::Scavenge() {
-#ifdef DEBUG
-  if (FLAG_enable_slow_asserts) VerifyNonPointerSpacePointers();
-#endif
-
   gc_state_ = SCAVENGE;
 
   // Implements Cheney's copying algorithm
@@ -606,70 +596,72 @@
   new_space_.Flip();
   new_space_.ResetAllocationInfo();
 
-  // We need to sweep newly copied objects which can be either in the
-  // to space or promoted to the old generation.  For to-space
-  // objects, we treat the bottom of the to space as a queue.  Newly
-  // copied and unswept objects lie between a 'front' mark and the
-  // allocation pointer.
+  // We need to sweep newly copied objects which can be in either the to space
+  // or the old space.  For to space objects, we use a mark.  Newly copied
+  // objects lie between the mark and the allocation top.  For objects
+  // promoted to old space, we write their addresses downward from the top of
+  // the new space.  Sweeping newly promoted objects requires an allocation
+  // pointer and a mark.  Note that the allocation pointer 'top' actually
+  // moves downward from the high address in the to space.
   //
-  // Promoted objects can go into various old-generation spaces, and
-  // can be allocated internally in the spaces (from the free list).
-  // We treat the top of the to space as a queue of addresses of
-  // promoted objects.  The addresses of newly promoted and unswept
-  // objects lie between a 'front' mark and a 'rear' mark that is
-  // updated as a side effect of promoting an object.
-  //
-  // There is guaranteed to be enough room at the top of the to space
-  // for the addresses of promoted objects: every object promoted
-  // frees up its size in bytes from the top of the new space, and
-  // objects are at least one pointer in size.
-  Address new_space_front = new_space_.ToSpaceLow();
-  Address promoted_front = new_space_.ToSpaceHigh();
-  promoted_rear = new_space_.ToSpaceHigh();
+  // There is guaranteed to be enough room at the top of the to space for the
+  // addresses of promoted objects: every object promoted frees up its size in
+  // bytes from the top of the new space, and objects are at least one pointer
+  // in size.  Using the new space to record promoted addresses makes the
+  // scavenge collector agnostic to the allocation strategy (eg, linear or
+  // free-list) used in old space.
+  Address new_mark = new_space_.ToSpaceLow();
+  Address promoted_mark = new_space_.ToSpaceHigh();
+  promoted_top = new_space_.ToSpaceHigh();
 
   ScavengeVisitor scavenge_visitor;
   // Copy roots.
   IterateRoots(&scavenge_visitor);
 
-  // Copy objects reachable from weak pointers.
-  GlobalHandles::IterateWeakRoots(&scavenge_visitor);
-
-  // Copy objects reachable from the old generation.  By definition,
-  // there are no intergenerational pointers in code or data spaces.
+  // Copy objects reachable from the old generation.  By definition, there
+  // are no intergenerational pointers in code or data spaces.
   IterateRSet(old_pointer_space_, &ScavengePointer);
   IterateRSet(map_space_, &ScavengePointer);
   lo_space_->IterateRSet(&ScavengePointer);
 
-  do {
-    ASSERT(new_space_front <= new_space_.top());
-    ASSERT(promoted_front >= promoted_rear);
+  bool has_processed_weak_pointers = false;
 
-    // The addresses new_space_front and new_space_.top() define a
-    // queue of unprocessed copied objects.  Process them until the
-    // queue is empty.
-    while (new_space_front < new_space_.top()) {
-      HeapObject* object = HeapObject::FromAddress(new_space_front);
-      object->Iterate(&scavenge_visitor);
-      new_space_front += object->Size();
-    }
+  while (true) {
+    ASSERT(new_mark <= new_space_.top());
+    ASSERT(promoted_mark >= promoted_top);
 
-    // The addresses promoted_front and promoted_rear define a queue
-    // of unprocessed addresses of promoted objects.  Process them
-    // until the queue is empty.
-    while (promoted_front > promoted_rear) {
-      promoted_front -= kPointerSize;
-      HeapObject* object =
-          HeapObject::cast(Memory::Object_at(promoted_front));
-      object->Iterate(&scavenge_visitor);
-      UpdateRSet(object);
+    // Copy objects reachable from newly copied objects.
+    while (new_mark < new_space_.top() || promoted_mark > promoted_top) {
+      // Sweep newly copied objects in the to space.  The allocation pointer
+      // can change during sweeping.
+      Address previous_top = new_space_.top();
+      SemiSpaceIterator new_it(new_space(), new_mark);
+      while (new_it.has_next()) {
+        new_it.next()->Iterate(&scavenge_visitor);
+      }
+      new_mark = previous_top;
+
+      // Sweep newly copied objects in the old space.  The promotion 'top'
+      // pointer could change during sweeping.
+      previous_top = promoted_top;
+      for (Address current = promoted_mark - kPointerSize;
+           current >= previous_top;
+           current -= kPointerSize) {
+        HeapObject* object = HeapObject::cast(Memory::Object_at(current));
+        object->Iterate(&scavenge_visitor);
+        UpdateRSet(object);
+      }
+      promoted_mark = previous_top;
     }
 
-    // Take another spin if there are now unswept objects in new space
-    // (there are currently no more unswept promoted objects).
-  } while (new_space_front < new_space_.top());
+    if (has_processed_weak_pointers) break;  // We are done.
+    // Copy objects reachable from weak pointers.
+    GlobalHandles::IterateWeakRoots(&scavenge_visitor);
+    has_processed_weak_pointers = true;
+  }
 
   // Set age mark.
-  new_space_.set_age_mark(new_space_.top());
+  new_space_.set_age_mark(new_mark);
 
   LOG(ResourceEvent("scavenge", "end"));
 
@@ -890,8 +882,8 @@
       if (target_space == Heap::old_pointer_space_) {
         // Record the object's address at the top of the to space, to allow
         // it to be swept by the scavenger.
-        promoted_rear -= kPointerSize;
-        Memory::Object_at(promoted_rear) = *p;
+        promoted_top -= kPointerSize;
+        Memory::Object_at(promoted_top) = *p;
       } else {
 #ifdef DEBUG
         // Objects promoted to the data space should not have pointers to