[in-place weak references] Remove Heap::weak_stack_trace_list

It is unused.

BUG=v8:7308

Change-Id: Ib1b51da316c929adcb117901d989180b5b81c42f
Reviewed-on: https://chromium-review.googlesource.com/1146734
Commit-Queue: Marja Hölttä <marja@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54655}

src/heap/heap.cc

@@ -1038,29 +1038,6 @@ void Heap::GarbageCollectionEpilogue() {
   }
 }
 
-
-void Heap::PreprocessStackTraces() {
-  FixedArrayOfWeakCells::Iterator iterator(weak_stack_trace_list());
-  FixedArray* elements;
-  while ((elements = iterator.Next<FixedArray>()) != nullptr) {
-    for (int j = 1; j < elements->length(); j += 4) {
-      Object* maybe_code = elements->get(j + 2);
-      // If GC happens while adding a stack trace to the weak fixed array,
-      // which has been copied into a larger backing store, we may run into
-      // a stack trace that has already been preprocessed. Guard against this.
-      if (!maybe_code->IsAbstractCode()) break;
-      AbstractCode* abstract_code = AbstractCode::cast(maybe_code);
-      int offset = Smi::ToInt(elements->get(j + 3));
-      int pos = abstract_code->SourcePosition(offset);
-      elements->set(j + 2, Smi::FromInt(pos));
-    }
-  }
-  // We must not compact the weak fixed list here, as we may be in the middle
-  // of writing to it, when the GC triggered. Instead, we reset the root value.
-  set_weak_stack_trace_list(Smi::kZero);
-}
-
-
 class GCCallbacksScope {
  public:
   explicit GCCallbacksScope(Heap* heap) : heap_(heap) {
@@ -1925,7 +1902,6 @@ void Heap::MarkCompactEpilogue() {
 
   incremental_marking()->Epilogue();
 
-  PreprocessStackTraces();
   DCHECK(incremental_marking()->IsStopped());
 }
 
@@ -2661,7 +2637,6 @@ bool Heap::RootCanBeWrittenAfterInitialization(Heap::RootListIndex root_index) {
     case kRetainingPathTargetsRootIndex:
     case kFeedbackVectorsForProfilingToolsRootIndex:
     case kNoScriptSharedFunctionInfosRootIndex:
-    case kWeakStackTraceListRootIndex:
     case kSerializedObjectsRootIndex:
     case kSerializedGlobalProxySizesRootIndex:
     case kPublicSymbolTableRootIndex:
@@ -5060,7 +5035,6 @@ void Heap::CompactFixedArraysOfWeakCells() {
 
   // Find known FixedArrayOfWeakCells and compact them.
   CompactFixedArrayOfWeakCells(isolate(), noscript_shared_function_infos());
-  CompactFixedArrayOfWeakCells(isolate(), weak_stack_trace_list());
 
   // Find known WeakArrayLists and compact them.
   Handle<WeakArrayList> scripts(script_list(), isolate());

src/heap/heap.h

@@ -1615,8 +1615,6 @@ class Heap {
 
   int NumberOfScavengeTasks();
 
-  void PreprocessStackTraces();
-
   // Checks whether a global GC is necessary
   GarbageCollector SelectGarbageCollector(AllocationSpace space,
                                           const char** reason);

src/heap/setup-heap-internal.cc

@@ -866,8 +866,6 @@ void Heap::CreateInitialObjects() {
   set_serialized_objects(roots.empty_fixed_array());
   set_serialized_global_proxy_sizes(roots.empty_fixed_array());
 
-  set_weak_stack_trace_list(Smi::kZero);
-
   set_noscript_shared_function_infos(Smi::kZero);
 
   STATIC_ASSERT(interpreter::BytecodeOperands::kOperandScaleCount == 3);

src/roots.h

@@ -244,7 +244,6 @@ namespace internal {
   /* Feedback vectors that we need for code coverage or type profile */      \
   V(Object, feedback_vectors_for_profiling_tools,                            \
     FeedbackVectorsForProfilingTools)                                        \
-  V(Object, weak_stack_trace_list, WeakStackTraceList)                       \
   V(Object, noscript_shared_function_infos, NoScriptSharedFunctionInfos)     \
   V(FixedArray, serialized_objects, SerializedObjects)                       \
   V(FixedArray, serialized_global_proxy_sizes, SerializedGlobalProxySizes)   \