heap: Add flag v8_enable_inner_pointer_resolution_osb

This CL introduces a compile flag v8_enable_inner_pointer_resolution_osb
behind which lies the experimental implementation of the object start
bitmap. It disassociates the object start bitmap from the compile flag
v8_enable_conservative_stack_scanning. At the moment the former flag is
a prerequisite for the latter, as conservative stack scanning requires
some mechanism for inner pointer resolution and the object start bitmap
provides one such mechanism.

Bug: v8:12851
Change-Id: I24c6b389453fbaefc79ae50c34c5ec7a1bf23347
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3717322
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Nikolaos Papaspyrou <nikolaos@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81295}

BUILD.gn

@@ -576,6 +576,10 @@ assert(!cppgc_enable_young_generation || cppgc_enable_caged_heap,
 assert(!cppgc_enable_pointer_compression || cppgc_enable_caged_heap,
        "Pointer compression in CppGC requires caged heap")
 
+assert(!v8_enable_conservative_stack_scanning ||
+           v8_enable_inner_pointer_resolution_osb,
+       "Conservative stack scanning requires inner pointer resolution (OSB)")
+
 if (v8_enable_single_generation == true) {
   assert(
       v8_enable_unconditional_write_barriers || v8_disable_write_barriers,
@@ -931,6 +935,9 @@ config("features") {
   if (v8_enable_conservative_stack_scanning) {
     defines += [ "V8_ENABLE_CONSERVATIVE_STACK_SCANNING" ]
   }
+  if (v8_enable_inner_pointer_resolution_osb) {
+    defines += [ "V8_ENABLE_INNER_POINTER_RESOLUTION_OSB" ]
+  }
   if (v8_disable_write_barriers) {
     defines += [ "V8_DISABLE_WRITE_BARRIERS" ]
   }
@@ -3674,8 +3681,11 @@ v8_header_set("v8_internal_headers") {
   }
 
   if (v8_enable_conservative_stack_scanning) {
+    sources += [ "src/heap/conservative-stack-visitor.h" ]
+  }
+
+  if (v8_enable_inner_pointer_resolution_osb) {
     sources += [
-      "src/heap/conservative-stack-visitor.h",
       "src/heap/object-start-bitmap-inl.h",
       "src/heap/object-start-bitmap.h",
     ]

gni/v8.gni

@@ -81,6 +81,9 @@ declare_args() {
   # Scan the call stack conservatively during garbage collection.
   v8_enable_conservative_stack_scanning = false
 
+  # Use the object start bitmap for inner pointer resolution.
+  v8_enable_inner_pointer_resolution_osb = false
+
   v8_enable_google_benchmark = false
 
   cppgc_is_standalone = false

src/flags/flag-definitions.h

@@ -477,6 +477,15 @@ DEFINE_BOOL_READONLY(conservative_stack_scanning,
                      V8_ENABLE_CONSERVATIVE_STACK_SCANNING_BOOL,
                      "use conservative stack scanning")
 
+#ifdef V8_ENABLE_INNER_POINTER_RESOLUTION_OSB
+#define V8_ENABLE_INNER_POINTER_RESOLUTION_OSB_BOOL true
+#else
+#define V8_ENABLE_INNER_POINTER_RESOLUTION_OSB_BOOL false
+#endif
+DEFINE_BOOL_READONLY(inner_pointer_resolution_osb,
+                     V8_ENABLE_INNER_POINTER_RESOLUTION_OSB_BOOL,
+                     "use object start bitmap for IPR")
+
 #ifdef V8_ENABLE_FUTURE
 #define FUTURE_BOOL true
 #else

src/heap/heap-allocator-inl.h

@@ -15,9 +15,9 @@
 #include "src/heap/read-only-spaces.h"
 #include "src/heap/third-party/heap-api.h"
 
-#ifdef V8_ENABLE_CONSERVATIVE_STACK_SCANNING
+#ifdef V8_ENABLE_INNER_POINTER_RESOLUTION_OSB
 #include "src/heap/object-start-bitmap-inl.h"
-#endif
+#endif  // V8_ENABLE_INNER_POINTER_RESOLUTION_OSB
 
 namespace v8 {
 namespace internal {
@@ -148,13 +148,13 @@ V8_WARN_UNUSED_RESULT V8_INLINE AllocationResult HeapAllocator::AllocateRaw(
       }
     }
 
-#ifdef V8_ENABLE_CONSERVATIVE_STACK_SCANNING
+#ifdef V8_ENABLE_INNER_POINTER_RESOLUTION_OSB
     if (AllocationType::kReadOnly != type) {
       DCHECK_TAG_ALIGNED(object.address());
       Page::FromHeapObject(object)->object_start_bitmap()->SetBit(
           object.address());
     }
-#endif  // V8_ENABLE_CONSERVATIVE_STACK_SCANNING
+#endif  // V8_ENABLE_INNER_POINTER_RESOLUTION_OSB
 
     for (auto& tracker : heap_->allocation_trackers_) {
       tracker->AllocationEvent(object.address(), size_in_bytes);

src/heap/heap.cc

@@ -1444,9 +1444,9 @@ void Heap::GarbageCollectionEpilogueInSafepoint(GarbageCollector collector) {
     TRACE_GC(tracer(), GCTracer::Scope::HEAP_EPILOGUE_REDUCE_NEW_SPACE);
     ReduceNewSpaceSize();
 
-#ifdef V8_ENABLE_CONSERVATIVE_STACK_SCANNING
+#ifdef V8_ENABLE_INNER_POINTER_RESOLUTION_OSB
     new_space()->ClearUnusedObjectStartBitmaps();
-#endif  // V8_ENABLE_CONSERVATIVE_STACK_SCANNING
+#endif  // V8_ENABLE_INNER_POINTER_RESOLUTION_OSB
   }
 
   // Ensure that unmapper task isn't running during full GC. We need access to

src/heap/memory-chunk-layout.h

@@ -11,9 +11,9 @@
 #include "src/heap/progress-bar.h"
 #include "src/heap/slot-set.h"
 
-#ifdef V8_ENABLE_CONSERVATIVE_STACK_SCANNING
+#ifdef V8_ENABLE_INNER_POINTER_RESOLUTION_OSB
 #include "src/heap/object-start-bitmap.h"
-#endif
+#endif  // V8_ENABLE_INNER_POINTER_RESOLUTION_OSB
 
 namespace v8 {
 namespace internal {
@@ -71,9 +71,9 @@ class V8_EXPORT_PRIVATE MemoryChunkLayout {
     FIELD(CodeObjectRegistry*, CodeObjectRegistry),
     FIELD(PossiblyEmptyBuckets, PossiblyEmptyBuckets),
     FIELD(ActiveSystemPages, ActiveSystemPages),
-#ifdef V8_ENABLE_CONSERVATIVE_STACK_SCANNING
+#ifdef V8_ENABLE_INNER_POINTER_RESOLUTION_OSB
     FIELD(ObjectStartBitmap, ObjectStartBitmap),
-#endif
+#endif  // V8_ENABLE_INNER_POINTER_RESOLUTION_OSB
     kMarkingBitmapOffset,
     kMemoryChunkHeaderSize = kMarkingBitmapOffset,
     kMemoryChunkHeaderStart = kSlotSetOffset,

src/heap/memory-chunk.cc

@@ -130,10 +130,10 @@ MemoryChunk::MemoryChunk(Heap* heap, BaseSpace* space, size_t chunk_size,
                          PageSize page_size)
     : BasicMemoryChunk(heap, space, chunk_size, area_start, area_end,
                        std::move(reservation))
-#ifdef V8_ENABLE_CONSERVATIVE_STACK_SCANNING
+#ifdef V8_ENABLE_INNER_POINTER_RESOLUTION_OSB
       ,
       object_start_bitmap_(PtrComprCageBase{heap->isolate()}, area_start)
-#endif
+#endif  // V8_ENABLE_INNER_POINTER_RESOLUTION_OSB
 {
   base::AsAtomicPointer::Release_Store(&slot_set_[OLD_TO_NEW], nullptr);
   base::AsAtomicPointer::Release_Store(&slot_set_[OLD_TO_OLD], nullptr);

src/heap/memory-chunk.h

@@ -215,9 +215,13 @@ class MemoryChunk : public BasicMemoryChunk {
   // read-only space chunks.
   void ReleaseAllocatedMemoryNeededForWritableChunk();
 
-#ifdef V8_ENABLE_CONSERVATIVE_STACK_SCANNING
+#ifdef V8_ENABLE_INNER_POINTER_RESOLUTION_OSB
   ObjectStartBitmap* object_start_bitmap() { return &object_start_bitmap_; }
-#endif
+
+  const ObjectStartBitmap* object_start_bitmap() const {
+    return &object_start_bitmap_;
+  }
+#endif  // V8_ENABLE_INNER_POINTER_RESOLUTION_OSB
 
  protected:
   // Release all memory allocated by the chunk. Should be called when memory
@@ -289,9 +293,9 @@ class MemoryChunk : public BasicMemoryChunk {
 
   ActiveSystemPages active_system_pages_;
 
-#ifdef V8_ENABLE_CONSERVATIVE_STACK_SCANNING
+#ifdef V8_ENABLE_INNER_POINTER_RESOLUTION_OSB
   ObjectStartBitmap object_start_bitmap_;
-#endif
+#endif  // V8_ENABLE_INNER_POINTER_RESOLUTION_OSB
 
  private:
   friend class ConcurrentMarkingState;

src/heap/new-spaces.cc

@@ -405,7 +405,7 @@ void SemiSpace::Verify() const {
     CHECK_EQ(external_backing_store_bytes[t], ExternalBackingStoreBytes(t));
   }
 }
-#endif
+#endif  // VERIFY_HEAP
 
 #ifdef DEBUG
 void SemiSpace::AssertValidRange(Address start, Address end) {
@@ -566,11 +566,11 @@ void NewSpace::VerifyImpl(Isolate* isolate, const Page* current_page,
              ExternalBackingStoreBytes(ExternalBackingStoreType::kArrayBuffer));
   }
 
-#ifdef V8_ENABLED_CONSERVATIVE_STACK_SCANNING
+#ifdef V8_ENABLE_INNER_POINTER_RESOLUTION_OSB
   page->object_start_bitmap()->Verify();
-#endif
+#endif  // V8_ENABLE_INNER_POINTER_RESOLUTION_OSB
 }
-#endif
+#endif  // VERIFY_HEAP
 
 void NewSpace::PromotePageToOldSpace(Page* page) {
   DCHECK(page->InYoungGeneration());
@@ -783,16 +783,16 @@ void SemiSpaceNewSpace::Verify(Isolate* isolate) const {
   from_space_.Verify();
   to_space_.Verify();
 }
-#endif
+#endif  // VERIFY_HEAP
 
-#ifdef V8_ENABLE_CONSERVATIVE_STACK_SCANNING
+#ifdef V8_ENABLE_INNER_POINTER_RESOLUTION_OSB
 void SemiSpaceNewSpace::ClearUnusedObjectStartBitmaps() {
   if (!IsFromSpaceCommitted()) return;
   for (Page* page : PageRange(from_space().first_page(), nullptr)) {
     page->object_start_bitmap()->Clear();
   }
 }
-#endif  // V8_ENABLE_CONSERVATIVE_STACK_SCANNING
+#endif  // V8_ENABLE_INNER_POINTER_RESOLUTION_OSB
 
 bool SemiSpaceNewSpace::ShouldBePromoted(Address address) const {
   Page* page = Page::FromAddress(address);

src/heap/new-spaces.h

@@ -301,9 +301,9 @@ class NewSpace : NON_EXPORTED_BASE(public SpaceWithLinearArea) {
                   Address current_address) const;
 #endif
 
-#ifdef V8_ENABLE_CONSERVATIVE_STACK_SCANNING
+#ifdef V8_ENABLE_INNER_POINTER_RESOLUTION_OSB
   virtual void ClearUnusedObjectStartBitmaps() = 0;
-#endif  // V8_ENABLE_CONSERVATIVE_STACK_SCANNING
+#endif  // V8_ENABLE_INNER_POINTER_RESOLUTION_OSB
 
   virtual iterator begin() = 0;
   virtual iterator end() = 0;
@@ -477,9 +477,9 @@ class V8_EXPORT_PRIVATE SemiSpaceNewSpace final : public NewSpace {
   void Print() override { to_space_.Print(); }
 #endif
 
-#ifdef V8_ENABLE_CONSERVATIVE_STACK_SCANNING
+#ifdef V8_ENABLE_INNER_POINTER_RESOLUTION_OSB
   void ClearUnusedObjectStartBitmaps() override;
-#endif  // V8_ENABLE_CONSERVATIVE_STACK_SCANNING
+#endif  // V8_ENABLE_INNER_POINTER_RESOLUTION_OSB
 
   Page* first_page() final { return to_space_.first_page(); }
   Page* last_page() final { return to_space_.last_page(); }

src/heap/paged-spaces.cc

@@ -822,9 +822,9 @@ void PagedSpaceBase::Verify(Isolate* isolate, ObjectVisitor* visitor) const {
     CHECK(!page->IsFlagSet(Page::PAGE_NEW_OLD_PROMOTION));
     CHECK(!page->IsFlagSet(Page::PAGE_NEW_NEW_PROMOTION));
 
-#ifdef V8_ENABLED_CONSERVATIVE_STACK_SCANNING
+#ifdef V8_ENABLE_INNER_POINTER_RESOLUTION_OSB
     page->object_start_bitmap()->Verify();
-#endif
+#endif  // V8_ENABLE_INNER_POINTER_RESOLUTION_OSB
   }
   for (int i = 0; i < kNumTypes; i++) {
     if (i == ExternalBackingStoreType::kArrayBuffer) continue;

src/heap/scavenger-inl.h

@@ -14,9 +14,9 @@
 #include "src/objects/objects-inl.h"
 #include "src/objects/slots-inl.h"
 
-#ifdef V8_ENABLE_CONSERVATIVE_STACK_SCANNING
+#ifdef V8_ENABLE_INNER_POINTER_RESOLUTION_OSB
 #include "src/heap/object-start-bitmap-inl.h"
-#endif
+#endif  // V8_ENABLE_INNER_POINTER_RESOLUTION_OSB
 
 namespace v8 {
 namespace internal {

src/heap/sweeper.cc

@@ -335,9 +335,9 @@ int Sweeper::RawSweep(Page* p, FreeSpaceTreatmentMode free_space_treatment_mode,
   // The free ranges map is used for filtering typed slots.
   TypedSlotSet::FreeRangesMap free_ranges_map;
 
-#ifdef V8_ENABLE_CONSERVATIVE_STACK_SCANNING
+#ifdef V8_ENABLE_INNER_POINTER_RESOLUTION_OSB
   p->object_start_bitmap()->Clear();
-#endif
+#endif  // V8_ENABLE_INNER_POINTER_RESOLUTION_OSB
 
   // Iterate over the page using the live objects and free the memory before
   // the given live object.
@@ -371,9 +371,9 @@ int Sweeper::RawSweep(Page* p, FreeSpaceTreatmentMode free_space_treatment_mode,
           MemoryAllocator::GetCommitPageSizeBits());
     }
 
-#ifdef V8_ENABLE_CONSERVATIVE_STACK_SCANNING
+#ifdef V8_ENABLE_INNER_POINTER_RESOLUTION_OSB
     p->object_start_bitmap()->SetBit(object.address());
-#endif
+#endif  // V8_ENABLE_INNER_POINTER_RESOLUTION_OSB
   }
 
   // If there is free memory after the last live object also free that.

test/cctest/heap/test-mark-compact.cc

@@ -227,7 +227,7 @@ HEAP_TEST(DoNotEvacuatePinnedPages) {
 }
 
 HEAP_TEST(ObjectStartBitmap) {
-#ifdef V8_ENABLE_CONSERVATIVE_STACK_SCANNING
+#ifdef V8_ENABLE_INNER_POINTER_RESOLUTION_OSB
   CcTest::InitializeVM();
   Isolate* isolate = CcTest::i_isolate();
   v8::HandleScope sc(CcTest::isolate());
@@ -303,7 +303,7 @@ HEAP_TEST(ObjectStartBitmap) {
     }
     CHECK(page2->object_start_bitmap()->CheckBit(obj2.address()));
   }
-#endif
+#endif  // V8_ENABLE_INNER_POINTER_RESOLUTION_OSB
 }
 
 // TODO(1600): compaction of map space is temporary removed from GC.

test/unittests/BUILD.gn

@@ -517,7 +517,7 @@ v8_source_set("unittests_sources") {
     sources += [ "wasm/wasm-gdbserver-unittest.cc" ]
   }
 
-  if (v8_enable_conservative_stack_scanning) {
+  if (v8_enable_inner_pointer_resolution_osb) {
     sources += [ "heap/object-start-bitmap-unittest.cc" ]
   }