Debug garbage collector does not correctly remove cross-gen garbage

runtime/vm/heap.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/heap.h"
 
 #include "platform/assert.h"
 #include "platform/utils.h"
 #include "vm/flags.h"
 #include "vm/isolate.h"
@@ skipping 20 matching lines @@
            intptr_t max_new_gen_semi_words,
            intptr_t max_old_gen_words,
            intptr_t max_external_words)
     : isolate_(isolate),
       new_space_(this, max_new_gen_semi_words, kNewObjectAlignmentOffset),
       old_space_(this, max_old_gen_words, max_external_words),
       barrier_(new Monitor()),
       barrier_done_(new Monitor()),
       read_only_(false),
       gc_new_space_in_progress_(false),
-      gc_old_space_in_progress_(false) {
+      gc_old_space_in_progress_(false),
+      debug_gc_in_progress_(false) {
   UpdateGlobalMaxUsed();
   for (int sel = 0; sel < kNumWeakSelectors; sel++) {
     new_weak_tables_[sel] = new WeakTable();
     old_weak_tables_[sel] = new WeakTable();
   }
   stats_.num_ = 0;
 }
 
 
 Heap::~Heap() {
@@ skipping 316 matching lines @@
 void Heap::CollectNewSpaceGarbage(Thread* thread,
                                   ApiCallbacks api_callbacks,
                                   GCReason reason) {
   ASSERT((reason == kNewSpace) || (reason == kFull));
   if (BeginNewSpaceGC(thread)) {
     bool invoke_api_callbacks = (api_callbacks == kInvokeApiCallbacks);
     RecordBeforeGC(kNew, reason);
     VMTagScope tagScope(thread, VMTag::kGCNewSpaceTagId);
     TIMELINE_FUNCTION_GC_DURATION(thread, "CollectNewGeneration");
     NOT_IN_PRODUCT(UpdateClassHeapStatsBeforeGC(kNew));
-    new_space_.Scavenge(invoke_api_callbacks);
+    if (debug_gc_in_progress_) {
+      new_space_.Evacuate();
+    } else {
+      new_space_.Scavenge(invoke_api_callbacks);
+    }
     NOT_IN_PRODUCT(isolate()->class_table()->UpdatePromoted());
     RecordAfterGC(kNew);
     PrintStats();
     NOT_IN_PRODUCT(PrintStatsToTimeline(&tds));
     EndNewSpaceGC();
     if ((reason == kNewSpace) && old_space_.NeedsGarbageCollection()) {
       // Old collections should call the API callbacks.
       CollectOldSpaceGarbage(thread, kInvokeApiCallbacks, kPromotion);
     }
   }
@@ skipping 48 matching lines @@
     CollectOldSpaceGarbage(thread, kInvokeApiCallbacks, kOldSpace);
   } else {
     ASSERT(space == kNew);
     CollectNewSpaceGarbage(thread, kInvokeApiCallbacks, kNewSpace);
   }
 }
 
 
 void Heap::CollectAllGarbage() {
   Thread* thread = Thread::Current();
+  debug_gc_in_progress_ = true;

[rmacnak, 2017/06/19 19:29:00]

Can this be

new_space_.Evacuate();
CollectOldSpaceGarbage(thread, kInvokeApiCallbacks, kFull);

? Without introducing a new state on the heap?

   CollectNewSpaceGarbage(thread, kInvokeApiCallbacks, kFull);
   CollectOldSpaceGarbage(thread, kInvokeApiCallbacks, kFull);
+  debug_gc_in_progress_ = false;
 }
 
 
 void Heap::WaitForSweeperTasks(Thread* thread) {
   MonitorLocker ml(old_space_.tasks_lock());
   while (old_space_.tasks() > 0) {
     ml.WaitWithSafepointCheck(thread);
   }
 }
 
@@ skipping 395 matching lines @@
   Dart::vm_isolate()->heap()->WriteProtect(false);
 }
 
 
 WritableVMIsolateScope::~WritableVMIsolateScope() {
   ASSERT(Dart::vm_isolate()->heap()->UsedInWords(Heap::kNew) == 0);
   Dart::vm_isolate()->heap()->WriteProtect(true);
 }
 
 }  // namespace dart