heap: Remove build flag for MinorMC

The build flag is on by default and the actual functionality is guarded
by a runtime flag.

Bug: v8:12612
Change-Id: I6adbd5b766f502400af32eeeb035edca3a3606ef
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3448383Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79036}

BUILD.bazel

@@ -53,7 +53,6 @@ load(":bazel/v8-non-pointer-compression.bzl", "v8_binary_non_pointer_compression
 # v8_can_use_fpu_instructions
 # v8_use_mips_abi_hardfloat
 # v8_enable_gdbjit
-# v8_enable_minor_mc
 # v8_check_header_includes
 # v8_enable_shared_ro_heap
 # v8_enable_lazy_source_positions
@@ -122,11 +121,6 @@ v8_flag(
     default = True,
 )
 
-v8_flag(
-    name = "v8_enable_minor_mc",
-    default = True,
-)
-
 v8_flag(name = "v8_enable_object_print")
 
 v8_flag(name = "v8_enable_slow_dchecks")
@@ -259,7 +253,6 @@ v8_config(
         "v8_enable_hugepage": "ENABLE_HUGEPAGE",
         "v8_enable_future": "V8_ENABLE_FUTURE",
         "v8_enable_lazy_source_positions": "V8_ENABLE_LAZY_SOURCE_POSITIONS",
-        "v8_enable_minor_mc": "ENABLE_MINOR_MC",
         "v8_enable_object_print": "OBJECT_PRINT",
         "v8_enable_slow_dchecks": "ENABLE_SLOW_DCHECKS",
         "v8_enable_snapshot_native_code_counters": "V8_SNAPSHOT_NATIVE_CODE_COUNTERS",

BUILD.gn

@@ -225,9 +225,6 @@ declare_args() {
                       (is_linux || is_chromeos || is_mac)) ||
                      (v8_current_cpu == "ppc64" && (is_linux || is_chromeos))
 
-  # Enable minor mark compact.
-  v8_enable_minor_mc = true
-
   # Check that each header can be included in isolation (requires also
   # setting the "check_v8_header_includes" gclient variable to run a
   # specific hook).
@@ -861,9 +858,6 @@ config("features") {
   if (v8_enable_hugepage) {
     defines += [ "ENABLE_HUGEPAGE" ]
   }
-  if (v8_enable_minor_mc) {
-    defines += [ "ENABLE_MINOR_MC" ]
-  }
   if (v8_enable_object_print) {
     defines += [ "OBJECT_PRINT" ]
   }

src/flags/flag-definitions.h

@@ -1855,14 +1855,9 @@ DEFINE_NEG_NEG_IMPLICATION(text_is_readable, partial_constant_pool)
 //
 // Minor mark compact collector flags.
 //
-#ifdef ENABLE_MINOR_MC
 DEFINE_BOOL(trace_minor_mc_parallel_marking, false,
             "trace parallel marking for the young generation")
 DEFINE_BOOL(minor_mc, false, "perform young generation mark compact GCs")
-#else
-DEFINE_BOOL_READONLY(minor_mc, false,
-                     "perform young generation mark compact GCs")
-#endif  // ENABLE_MINOR_MC
 
 //
 // Dev shell flags

src/heap/heap.cc

@@ -2577,7 +2577,6 @@ void Heap::MarkCompact() {
 }
 
 void Heap::MinorMarkCompact() {
-#ifdef ENABLE_MINOR_MC
   DCHECK(FLAG_minor_mc);
   DCHECK(new_space());
 
@@ -2603,9 +2602,6 @@ void Heap::MinorMarkCompact() {
   minor_mark_compact_collector()->CollectGarbage();
 
   SetGCState(NOT_IN_GC);
-#else
-  UNREACHABLE();
-#endif  // ENABLE_MINOR_MC
 }
 
 void Heap::MarkCompactEpilogue() {
@@ -4669,9 +4665,7 @@ class OldToNewSlotVerifyingVisitor : public SlotVerifyingVisitor {
   void VisitEphemeron(HeapObject host, int index, ObjectSlot key,
                       ObjectSlot target) override {
     VisitPointer(host, target);
-#ifdef ENABLE_MINOR_MC
     if (FLAG_minor_mc) return VisitPointer(host, target);
-#endif
     // Keys are handled separately and should never appear in this set.
     CHECK(!InUntypedSet(key));
     Object k = *key;
@@ -5829,11 +5823,7 @@ void Heap::SetUpSpaces(LinearAllocationArea* new_allocation_info,
   }
 
   tracer_.reset(new GCTracer(this));
-#ifdef ENABLE_MINOR_MC
   minor_mark_compact_collector_ = new MinorMarkCompactCollector(this);
-#else
-  minor_mark_compact_collector_ = nullptr;
-#endif  // ENABLE_MINOR_MC
   array_buffer_sweeper_.reset(new ArrayBufferSweeper(this));
   gc_idle_time_handler_.reset(new GCIdleTimeHandler());
   memory_measurement_.reset(new MemoryMeasurement(isolate()));
@@ -5854,11 +5844,9 @@ void Heap::SetUpSpaces(LinearAllocationArea* new_allocation_info,
   LOG(isolate_, IntPtrTEvent("heap-available", Available()));
 
   mark_compact_collector()->SetUp();
-#ifdef ENABLE_MINOR_MC
   if (minor_mark_compact_collector() != nullptr) {
     minor_mark_compact_collector()->SetUp();
   }
-#endif  // ENABLE_MINOR_MC
 
   if (new_space()) {
     scavenge_job_.reset(new ScavengeJob());
@@ -6137,13 +6125,11 @@ void Heap::TearDown() {
     mark_compact_collector_.reset();
   }
 
-#ifdef ENABLE_MINOR_MC
   if (minor_mark_compact_collector_ != nullptr) {
     minor_mark_compact_collector_->TearDown();
     delete minor_mark_compact_collector_;
     minor_mark_compact_collector_ = nullptr;
   }
-#endif  // ENABLE_MINOR_MC
 
   scavenger_collector_.reset();
   array_buffer_sweeper_.reset();

src/heap/heap.h

@@ -483,12 +483,8 @@ class Heap {
   }
 
   static inline GarbageCollector YoungGenerationCollector() {
-#if ENABLE_MINOR_MC
     return (FLAG_minor_mc) ? GarbageCollector::MINOR_MARK_COMPACTOR
                            : GarbageCollector::SCAVENGER;
-#else
-    return GarbageCollector::SCAVENGER;
-#endif  // ENABLE_MINOR_MC
   }
 
   static inline const char* CollectorName(GarbageCollector collector) {

src/heap/incremental-marking.cc

@@ -441,10 +441,8 @@ void IncrementalMarking::UpdateMarkingWorklistAfterScavenge() {
 
   Map filler_map = ReadOnlyRoots(heap_).one_pointer_filler_map();
 
-#ifdef ENABLE_MINOR_MC
   MinorMarkCompactCollector::MarkingState* minor_marking_state =
       heap()->minor_mark_compact_collector()->marking_state();
-#endif  // ENABLE_MINOR_MC
 
   collector_->local_marking_worklists()->Publish();
   MarkingBarrier::PublishAll(heap());
@@ -455,10 +453,8 @@ void IncrementalMarking::UpdateMarkingWorklistAfterScavenge() {
           // this is referred inside DCHECK.
           this,
 #endif
-#ifdef ENABLE_MINOR_MC
-          minor_marking_state,
-#endif
-          cage_base, filler_map](HeapObject obj, HeapObject* out) -> bool {
+          minor_marking_state, cage_base,
+          filler_map](HeapObject obj, HeapObject* out) -> bool {
         DCHECK(obj.IsHeapObject());
         // Only pointers to from space have to be updated.
         if (Heap::InFromPage(obj)) {
@@ -481,24 +477,20 @@ void IncrementalMarking::UpdateMarkingWorklistAfterScavenge() {
           // new space.
           DCHECK(Heap::IsLargeObject(obj) ||
                  Page::FromHeapObject(obj)->IsFlagSet(Page::SWEEP_TO_ITERATE));
-#ifdef ENABLE_MINOR_MC
           if (minor_marking_state->IsWhite(obj)) {
             return false;
           }
-#endif  // ENABLE_MINOR_MC
-        // Either a large object or an object marked by the minor
-        // mark-compactor.
+          // Either a large object or an object marked by the minor
+          // mark-compactor.
           *out = obj;
           return true;
         } else {
           // The object may be on a page that was moved from new to old space.
           // Only applicable during minor MC garbage collections.
           if (Page::FromHeapObject(obj)->IsFlagSet(Page::SWEEP_TO_ITERATE)) {
-#ifdef ENABLE_MINOR_MC
             if (minor_marking_state->IsWhite(obj)) {
               return false;
             }
-#endif  // ENABLE_MINOR_MC
             *out = obj;
             return true;
           }

src/heap/large-spaces.cc

@@ -489,7 +489,6 @@ AllocationResult NewLargeObjectSpace::AllocateRaw(int object_size) {
   page->SetYoungGenerationPageFlags(heap()->incremental_marking()->IsMarking());
   page->SetFlag(MemoryChunk::TO_PAGE);
   UpdatePendingObject(result);
-#ifdef ENABLE_MINOR_MC
   if (FLAG_minor_mc) {
     page->AllocateYoungGenerationBitmap();
     heap()
@@ -497,7 +496,6 @@ AllocationResult NewLargeObjectSpace::AllocateRaw(int object_size) {
         ->non_atomic_marking_state()
         ->ClearLiveness(page);
   }
-#endif  // ENABLE_MINOR_MC
   page->InitializationMemoryFence();
   DCHECK(page->IsLargePage());
   DCHECK_EQ(page->owner_identity(), NEW_LO_SPACE);

src/heap/mark-compact-inl.h

@@ -40,8 +40,6 @@ void MarkCompactCollector::MarkRootObject(Root root, HeapObject obj) {
   }
 }
 
-#ifdef ENABLE_MINOR_MC
-
 void MinorMarkCompactCollector::MarkRootObject(HeapObject obj) {
   if (Heap::InYoungGeneration(obj) &&
       non_atomic_marking_state_.WhiteToGrey(obj)) {
@@ -49,8 +47,6 @@ void MinorMarkCompactCollector::MarkRootObject(HeapObject obj) {
   }
 }
 
-#endif
-
 void MarkCompactCollector::MarkExternallyReferencedObject(HeapObject obj) {
   if (marking_state()->WhiteToGrey(obj)) {
     local_marking_worklists()->Push(obj);

src/heap/mark-compact.cc

@@ -613,9 +613,7 @@ void MarkCompactCollector::CollectGarbage() {
   // update the state as they proceed.
   DCHECK(state_ == PREPARE_GC);
 
-#ifdef ENABLE_MINOR_MC
   heap()->minor_mark_compact_collector()->CleanupSweepToIteratePages();
-#endif  // ENABLE_MINOR_MC
 
   MarkLiveObjects();
   ClearNonLiveReferences();
@@ -4806,8 +4804,6 @@ void MarkCompactCollector::StartSweepSpaces() {
   }
 }
 
-#ifdef ENABLE_MINOR_MC
-
 namespace {
 
 #ifdef VERIFY_HEAP
@@ -5989,7 +5985,5 @@ void MinorMarkCompactCollector::EvacuatePagesInParallel() {
   }
 }
 
-#endif  // ENABLE_MINOR_MC
-
 }  // namespace internal
 }  // namespace v8

src/heap/mark-compact.h

@@ -844,8 +844,6 @@ class V8_NODISCARD EvacuationScope {
   MarkCompactCollector* collector_;
 };
 
-#ifdef ENABLE_MINOR_MC
-
 // Collector for young-generation only.
 class MinorMarkCompactCollector final : public MarkCompactCollectorBase {
  public:
@@ -925,8 +923,6 @@ class MinorMarkCompactCollector final : public MarkCompactCollectorBase {
   friend class YoungGenerationMarkingVisitor;
 };
 
-#endif  // ENABLE_MINOR_MC
-
 }  // namespace internal
 }  // namespace v8
 

src/heap/new-spaces.cc

@@ -24,7 +24,6 @@ Page* SemiSpace::InitializePage(MemoryChunk* chunk) {
   Page* page = static_cast<Page*>(chunk);
   page->SetYoungGenerationPageFlags(heap()->incremental_marking()->IsMarking());
   page->list_node().Initialize();
-#ifdef ENABLE_MINOR_MC
   if (FLAG_minor_mc) {
     page->AllocateYoungGenerationBitmap();
     heap()
@@ -32,7 +31,6 @@ Page* SemiSpace::InitializePage(MemoryChunk* chunk) {
         ->non_atomic_marking_state()
         ->ClearLiveness(page);
   }
-#endif  // ENABLE_MINOR_MC
   page->InitializationMemoryFence();
   return page;
 }

test/cctest/test-strings.cc

@@ -1368,11 +1368,9 @@ class OneByteVectorResource : public v8::String::ExternalOneByteStringResource {
 };
 
 TEST(InternalizeExternal) {
-#ifdef ENABLE_MINOR_MC
   // TODO(mlippautz): Remove once we add support for forwarding ThinStrings in
   // minor MC
   if (FLAG_minor_mc) return;
-#endif  // ENABLE_MINOR_MC
   FLAG_stress_incremental_marking = false;
   CcTest::InitializeVM();
   i::Isolate* isolate = CcTest::i_isolate();