Add a flag to over approximate the weak closure during GC

src/heap/incremental-marking.cc

Index: src/heap/incremental-marking.cc
diff --git a/src/heap/incremental-marking.cc b/src/heap/incremental-marking.cc
index a85d4a8489326ec84afcd2ca4191d45ebdda18fe..abca37ee408aa8d105c22c32e2f464ecc13b15ec 100644
--- a/src/heap/incremental-marking.cc
+++ b/src/heap/incremental-marking.cc
@@ -28,7 +28,8 @@ IncrementalMarking::IncrementalMarking(Heap* heap)
       idle_marking_delay_counter_(0),
       no_marking_scope_depth_(0),
       unscanned_bytes_of_large_object_(0),
-      was_activated_(false) {}
+      was_activated_(false),
+      weak_closure_was_overapproximated_(false) {}
 
 
 void IncrementalMarking::RecordWriteSlow(HeapObject* obj, Object** slot,
@@ -495,6 +496,7 @@ void IncrementalMarking::Start(CompactionFlag flag) {
   ResetStepCounters();
 
   was_activated_ = true;
+  weak_closure_was_overapproximated_ = false;

[Hannes Payer (out of office), 2015/02/03 17:40:11]

Can we do that in the gc epilogue?

[jochen (gone - plz use gerrit), 2015/02/09 16:03:43]

Done

 
   if (!heap_->mark_compact_collector()->sweeping_in_progress()) {
     StartMarking(flag);
@@ -772,13 +774,22 @@ void IncrementalMarking::Finalize() {
 
 
 void IncrementalMarking::MarkingComplete(CompletionAction action) {
-  state_ = COMPLETE;
   // We will set the stack guard to request a GC now.  This will mean the rest
   // of the GC gets performed as soon as possible (we can't do a GC here in a
   // record-write context).  If a few things get allocated between now and then
   // that shouldn't make us do a scavenge and keep being incremental, so we set
   // the should-hurry flag to indicate that there can't be much work left to do.
   set_should_hurry(true);
+  if (FLAG_overapproximate_weak_closure &&
+      !weak_closure_was_overapproximated_ && action == GC_VIA_STACK_GUARD) {
+    if (FLAG_trace_incremental_marking) {

[Hannes Payer (out of office), 2015/02/03 17:40:11]

Can we add a separate method for that and dispatch between over approximate and
dispatch at the call site?

[jochen (gone - plz use gerrit), 2015/02/09 16:03:43]

done

[jochen (gone - plz use gerrit), 2015/02/09 16:03:43]

done

+      PrintF(
+          "[IncrementalMarking] requesting weak closure overapproximation.\n");
+    }
+    heap_->isolate()->stack_guard()->RequestGC();
+    return;
+  }
+  state_ = COMPLETE;
   if (FLAG_trace_incremental_marking) {
     PrintF("[IncrementalMarking] Complete (normal).\n");
   }