[heap] MinorMC: Only iterate new space global handles for ptr updates

The reason we need this mode is that IterateRoots for the Scavenger only
captures dependent weak nodes. This is also what we do for marking for the
minor MC.

Since the regular marking might also mark objects that are weakly
(non-dependently) pointed to by nodes we need to capture all of them during
pointers updating. The reason this works for the Scavenger is because we do one
pass at the end of the scavenger (combined with resetting) that captures all
those nodes.

BUG=chromium:651354

Review-Url: https://codereview.chromium.org/2869413002
Cr-Commit-Position: refs/heads/master@{#45248}

src/global-handles.cc

@@ -945,6 +945,15 @@ void GlobalHandles::IterateAllRoots(RootVisitor* v) {
   }
 }
 
+DISABLE_CFI_PERF
+void GlobalHandles::IterateAllNewSpaceRoots(RootVisitor* v) {
+  for (int i = 0; i < new_space_nodes_.length(); ++i) {
+    Node* node = new_space_nodes_[i];
+    if (node->IsRetainer()) {
+      v->VisitRootPointer(Root::kGlobalHandles, node->location());
+    }
+  }
+}
 
 DISABLE_CFI_PERF
 void GlobalHandles::ApplyPersistentHandleVisitor(

src/global-handles.h

@@ -130,6 +130,8 @@ class GlobalHandles {
   // Iterates over all handles.
   void IterateAllRoots(RootVisitor* v);
 
+  void IterateAllNewSpaceRoots(RootVisitor* v);
+
   // Iterates over all handles that have embedder-assigned class ID.
   void IterateAllRootsWithClassIds(v8::PersistentHandleVisitor* v);
 

src/globals.h

@@ -590,6 +590,7 @@ enum Executability { NOT_EXECUTABLE, EXECUTABLE };
 
 enum VisitMode {
   VISIT_ALL,
+  VISIT_ALL_IN_MINOR_MC_UPDATE,
   VISIT_ALL_IN_SCAVENGE,
   VISIT_ALL_IN_SWEEP_NEWSPACE,
   VISIT_ONLY_STRONG,

src/heap/heap.cc

@@ -5108,7 +5108,7 @@ void Heap::IterateStrongRoots(RootVisitor* v, VisitMode mode) {
   // Iterate over the builtin code objects and code stubs in the
   // heap. Note that it is not necessary to iterate over code objects
   // on scavenge collections.
-  if (mode != VISIT_ALL_IN_SCAVENGE) {
+  if (mode != VISIT_ALL_IN_SCAVENGE && mode != VISIT_ALL_IN_MINOR_MC_UPDATE) {
     isolate_->builtins()->IterateBuiltins(v);
     v->Synchronize(VisitorSynchronization::kBuiltins);
     isolate_->interpreter()->IterateDispatchTable(v);
@@ -5128,6 +5128,9 @@ void Heap::IterateStrongRoots(RootVisitor* v, VisitMode mode) {
     case VISIT_ALL_IN_SCAVENGE:
       isolate_->global_handles()->IterateNewSpaceStrongAndDependentRoots(v);
       break;
+    case VISIT_ALL_IN_MINOR_MC_UPDATE:
+      isolate_->global_handles()->IterateAllNewSpaceRoots(v);
+      break;
     case VISIT_ALL_IN_SWEEP_NEWSPACE:
     case VISIT_ALL:
       isolate_->global_handles()->IterateAllRoots(v);
@@ -5136,7 +5139,7 @@ void Heap::IterateStrongRoots(RootVisitor* v, VisitMode mode) {
   v->Synchronize(VisitorSynchronization::kGlobalHandles);
 
   // Iterate over eternal handles.
-  if (mode == VISIT_ALL_IN_SCAVENGE) {
+  if (mode == VISIT_ALL_IN_SCAVENGE || mode == VISIT_ALL_IN_MINOR_MC_UPDATE) {
     isolate_->eternal_handles()->IterateNewSpaceRoots(v);
   } else {
     isolate_->eternal_handles()->IterateAllRoots(v);

src/heap/mark-compact.cc

@@ -4377,10 +4377,7 @@ void MinorMarkCompactCollector::UpdatePointersAfterEvacuation() {
              GCTracer::Scope::MC_EVACUATE_UPDATE_POINTERS_TO_NEW);
     UpdateToSpacePointersInParallel(heap_, &page_parallel_job_semaphore_,
                                     *this);
-    // TODO(mlippautz): Iteration mode is not optimal as we process all
-    // global handles. Find a way to only process the ones related to new
-    // space.
-    heap_->IterateRoots(&updating_visitor, VISIT_ALL_IN_SWEEP_NEWSPACE);
+    heap_->IterateRoots(&updating_visitor, VISIT_ALL_IN_MINOR_MC_UPDATE);
     UpdatePointersInParallel<OLD_TO_NEW>(heap_, &page_parallel_job_semaphore_,
                                          this);
   }