[heap] Make slow path in concurrent allocator more explicit

Restructure code to make slow path of allocation more obvious.

Bug: v8:10315
Change-Id: Ic3e3b866b144b6f2877acac4accf87377f757172
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2276273
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68651}

src/heap/concurrent-allocator-inl.h

@@ -33,49 +33,18 @@ Address ConcurrentAllocator::AllocateOrFail(int object_size,
                                             AllocationAlignment alignment,
                                             AllocationOrigin origin) {
   AllocationResult result = Allocate(object_size, alignment, origin);
-  if (!result.IsRetry()) return result.ToObjectChecked().address();
+  if (!result.IsRetry()) return result.ToObject().address();
   return PerformCollectionAndAllocateAgain(object_size, alignment, origin);
 }
 
 AllocationResult ConcurrentAllocator::AllocateInLab(
     int object_size, AllocationAlignment alignment, AllocationOrigin origin) {
-  AllocationResult allocation;
-  if (!lab_.IsValid() && !EnsureLab(origin)) {
-    return AllocationResult::Retry(space_->identity());
-  }
-  allocation = lab_.AllocateRawAligned(object_size, alignment);
+  AllocationResult allocation = lab_.AllocateRawAligned(object_size, alignment);
   if (allocation.IsRetry()) {
-    if (!EnsureLab(origin)) {
-      return AllocationResult::Retry(space_->identity());
+    return AllocateInLabSlow(object_size, alignment, origin);
   } else {
-      allocation = lab_.AllocateRawAligned(object_size, alignment);
-      CHECK(!allocation.IsRetry());
-    }
-  }
     return allocation;
-}
-
-bool ConcurrentAllocator::EnsureLab(AllocationOrigin origin) {
-  auto result = space_->SlowGetLinearAllocationAreaBackground(
-      local_heap_, kLabSize, kMaxLabSize, kWordAligned, origin);
-
-  if (!result) return false;
-
-  if (local_heap_->heap()->incremental_marking()->black_allocation()) {
-    Address top = result->first;
-    Address limit = top + result->second;
-    Page::FromAllocationAreaAddress(top)->CreateBlackAreaBackground(top, limit);
-  }
-
-  HeapObject object = HeapObject::FromAddress(result->first);
-  LocalAllocationBuffer saved_lab = std::move(lab_);
-  lab_ = LocalAllocationBuffer::FromResult(
-      local_heap_->heap(), AllocationResult(object), result->second);
-  DCHECK(lab_.IsValid());
-  if (!lab_.TryMerge(&saved_lab)) {
-    saved_lab.CloseAndMakeIterable();
   }
-  return true;
 }
 
 }  // namespace internal

src/heap/concurrent-allocator.cc

@@ -98,12 +98,47 @@ void ConcurrentAllocator::UnmarkLinearAllocationArea() {
   }
 }
 
+AllocationResult ConcurrentAllocator::AllocateInLabSlow(
+    int object_size, AllocationAlignment alignment, AllocationOrigin origin) {
+  if (!EnsureLab(origin)) {
+    return AllocationResult::Retry(OLD_SPACE);
+  }
+
+  AllocationResult allocation = lab_.AllocateRawAligned(object_size, alignment);
+  DCHECK(!allocation.IsRetry());
+
+  return allocation;
+}
+
+bool ConcurrentAllocator::EnsureLab(AllocationOrigin origin) {
+  auto result = space_->SlowGetLinearAllocationAreaBackground(
+      local_heap_, kLabSize, kMaxLabSize, kWordAligned, origin);
+
+  if (!result) return false;
+
+  if (local_heap_->heap()->incremental_marking()->black_allocation()) {
+    Address top = result->first;
+    Address limit = top + result->second;
+    Page::FromAllocationAreaAddress(top)->CreateBlackAreaBackground(top, limit);
+  }
+
+  HeapObject object = HeapObject::FromAddress(result->first);
+  LocalAllocationBuffer saved_lab = std::move(lab_);
+  lab_ = LocalAllocationBuffer::FromResult(
+      local_heap_->heap(), AllocationResult(object), result->second);
+  DCHECK(lab_.IsValid());
+  if (!lab_.TryMerge(&saved_lab)) {
+    saved_lab.CloseAndMakeIterable();
+  }
+  return true;
+}
+
 AllocationResult ConcurrentAllocator::AllocateOutsideLab(
     int object_size, AllocationAlignment alignment, AllocationOrigin origin) {
   auto result = space_->SlowGetLinearAllocationAreaBackground(
       local_heap_, object_size, object_size, alignment, origin);
+  if (!result) return AllocationResult::Retry(OLD_SPACE);
 
-  if (result) {
   HeapObject object = HeapObject::FromAddress(result->first);
 
   if (local_heap_->heap()->incremental_marking()->black_allocation()) {
@@ -112,9 +147,6 @@ AllocationResult ConcurrentAllocator::AllocateOutsideLab(
   }
 
   return AllocationResult(object);
-  } else {
-    return AllocationResult::Retry(OLD_SPACE);
-  }
 }
 
 }  // namespace internal

src/heap/concurrent-allocator.h

@@ -55,7 +55,10 @@ class ConcurrentAllocator {
   void UnmarkLinearAllocationArea();
 
  private:
-  inline bool EnsureLab(AllocationOrigin origin);
+  V8_EXPORT_PRIVATE AllocationResult AllocateInLabSlow(
+      int object_size, AllocationAlignment alignment, AllocationOrigin origin);
+  bool EnsureLab(AllocationOrigin origin);
+
   inline AllocationResult AllocateInLab(int object_size,
                                         AllocationAlignment alignment,
                                         AllocationOrigin origin);

src/heap/heap-inl.h

@@ -61,6 +61,11 @@ HeapObject AllocationResult::ToObjectChecked() {
   return HeapObject::cast(object_);
 }
 
+HeapObject AllocationResult::ToObject() {
+  DCHECK(!IsRetry());
+  return HeapObject::cast(object_);
+}
+
 Isolate* Heap::isolate() {
   return reinterpret_cast<Isolate*>(
       reinterpret_cast<intptr_t>(this) -

src/heap/heap.h

@@ -194,6 +194,7 @@ class AllocationResult {
 
   inline bool IsRetry() { return object_.IsSmi(); }
   inline HeapObject ToObjectChecked();
+  inline HeapObject ToObject();
   inline AllocationSpace RetrySpace();
 
   template <typename T>