Preserve marking bits across scavenges if incremental marker is running.

src/incremental-marking.cc

Index: src/incremental-marking.cc
diff --git a/src/incremental-marking.cc b/src/incremental-marking.cc
index a5c4ce111ffab26204527f4427cf13d24a6f83d5..ef29a3b7984f3bc5a67990d69d19f3ac2950a553 100644
--- a/src/incremental-marking.cc
+++ b/src/incremental-marking.cc
@@ -163,6 +163,18 @@ static void PatchIncrementalMarkingRecordWriteStubs(bool enable) {
   }
 }
 
+static VirtualMemory* marking_stack_memory = NULL;
+
+static void EnsureMarkingStackIsCommitted() {
+  if (marking_stack_memory == NULL) {
+    marking_stack_memory = new VirtualMemory(4*MB);
+    marking_stack_memory->Commit(
+        reinterpret_cast<Address>(marking_stack_memory->address()),
+        marking_stack_memory->size(),
+        false);  // Not executable.
+  }
+}
+
 
 void IncrementalMarking::Start() {
   if (FLAG_trace_incremental_marking) {
@@ -174,18 +186,19 @@ void IncrementalMarking::Start() {
 
   PatchIncrementalMarkingRecordWriteStubs(true);
 
-  Heap::EnsureFromSpaceIsCommitted();
+  // Heap::EnsureFromSpaceIsCommitted();
+  EnsureMarkingStackIsCommitted();
 
   // Initialize marking stack.
-  marking_stack_.Initialize(Heap::new_space()->FromSpaceLow(),
-                            Heap::new_space()->FromSpaceHigh());
+  Address addr = static_cast<Address>(marking_stack_memory->address());
+  marking_stack_.Initialize(addr,
+                            addr + marking_stack_memory->size());
 
   // Clear markbits.
-  Address new_space_bottom = Heap::new_space()->bottom();
-  uintptr_t new_space_size =
-      RoundUp(Heap::new_space()->top() - new_space_bottom, 32 * kPointerSize);
-
-  Marking::ClearRange(new_space_bottom, new_space_size);
+  Address new_space_low = Heap::new_space()->ToSpaceLow();
+  Address new_space_high = Heap::new_space()->ToSpaceHigh();
+  Marking::ClearRange(new_space_low,
+                      static_cast<int>(new_space_high - new_space_low));
 
   ClearMarkbits();
 
@@ -204,6 +217,42 @@ void IncrementalMarking::Start() {
 }
 
 
+void IncrementalMarking::PrepareForScavenge() {
+  if (IsStopped()) return;
+
+  Address new_space_low = Heap::new_space()->FromSpaceLow();
+  Address new_space_high = Heap::new_space()->FromSpaceHigh();
+  Marking::ClearRange(new_space_low,
+                      static_cast<int>(new_space_high - new_space_low));
+}
+
+
+void IncrementalMarking::UpdateMarkingStackAfterScavenge() {
+  if (IsStopped()) return;
+
+  HeapObject** current = marking_stack_.low();
+  HeapObject** top = marking_stack_.top();
+  HeapObject** new_top = current;
+
+  while (current < top) {
+    HeapObject* obj = *current++;
+    if (Heap::InNewSpace(obj)) {
+      MapWord map_word = obj->map_word();
+      if (map_word.IsForwardingAddress()) {
+        HeapObject* dest = map_word.ToForwardingAddress();
+        MarkWhiteObjectGrey(dest, Marking::MarkBitFrom(dest));
+        *new_top++ = dest;
+        ASSERT(Color(obj) == Color(dest));
+      }
+    } else {
+      *new_top++ = obj;
+    }
+  }
+
+  marking_stack_.set_top(new_top);
+}
+
+
 void IncrementalMarking::Hurry() {
   if (state() == MARKING) {
     double start = 0.0;
@@ -254,17 +303,12 @@ void IncrementalMarking::MarkingComplete() {
 
 
 void IncrementalMarking::Step(intptr_t allocated_bytes) {
-  if (state_ == MARKING) {
+  if (state_ == MARKING && Heap::gc_state() == Heap::NOT_IN_GC) {
     allocated += allocated_bytes;
 
     if (allocated >= kAllocatedThreshold) {
       intptr_t bytes_to_process = allocated * kAllocationMarkingFactor;
       int count = 0;
-      double start = 0;
-      if (FLAG_trace_incremental_marking) {
-        PrintF("[IncrementalMarking] Marking %d bytes\n", bytes_to_process);
-        start = OS::TimeCurrentMillis();
-      }
 
       Map* filler_map = Heap::one_pointer_filler_map();
       while (!marking_stack_.is_empty() && bytes_to_process > 0) {
@@ -285,12 +329,6 @@ void IncrementalMarking::Step(intptr_t allocated_bytes) {
         }
         count++;
       }
-      if (FLAG_trace_incremental_marking) {
-        double end = OS::TimeCurrentMillis();
-        PrintF("[IncrementalMarking]     %d objects marked, spent %d ms\n",
-               count,
-               static_cast<int>(end - start));
-      }
       allocated = 0;
       if (marking_stack_.is_empty()) MarkingComplete();
     }