[heap] make FreeListCategory::is_linked() more precise

Change-Id: I2e0632756ac92b18d2d9a30b03b698b533b34862
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1722564Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Darius Mercadier <dmercadier@google.com>
Cr-Commit-Position: refs/heads/master@{#63061}

src/heap/spaces-inl.h

@@ -318,7 +318,8 @@ MemoryChunk* OldGenerationMemoryChunkIterator::next() {
 FreeList* FreeListCategory::owner() { return free_list_; }
 
 bool FreeListCategory::is_linked() {
-  return prev_ != nullptr || next_ != nullptr;
+  return prev_ != nullptr || next_ != nullptr ||
+         free_list_->categories_[type_] == this;
 }
 
 AllocationResult LocalAllocationBuffer::AllocateRawAligned(

src/heap/spaces.cc

@@ -2972,7 +2972,7 @@ void FreeListCategory::Free(Address start, size_t size_in_bytes,
   set_top(free_space);
   available_ += size_in_bytes;
   length_++;
-  if ((mode == kLinkCategory) && (prev() == nullptr) && (next() == nullptr)) {
+  if ((mode == kLinkCategory) && !is_linked()) {
     owner()->AddCategory(this);
   }
 }
@@ -3313,7 +3313,7 @@ bool FreeList::AddCategory(FreeListCategory* category) {
   FreeListCategory* top = categories_[type];
 
   if (category->is_empty()) return false;
-  if (top == category) return false;
+  DCHECK_NE(top, category);
 
   // Common double-linked list insertion.
   if (top != nullptr) {