[cleanup] Make MentionedObjectCache GC-safe

This changes DebugObjectCache to be a vector of Handles rather than
tagged pointers, meaning it's not GC-safe.

This will allow PrintStack to allocate memory if required (if for
instance source positions must be regenerated).

Bug: v8:8834, v8:8510
Change-Id: Ieec9a827af9abbcb9b5b237d79984eedf0cdcc57
Reviewed-on: https://chromium-review.googlesource.com/c/1494755Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59952}

src/isolate.cc

@@ -1241,8 +1241,6 @@ static void PrintFrames(Isolate* isolate,
 }
 
 void Isolate::PrintStack(StringStream* accumulator, PrintStackMode mode) {
-  // The MentionedObjectCache is not GC-proof at the moment.
-  DisallowHeapAllocation no_gc;
   HandleScope scope(this);
   DCHECK(accumulator->IsMentionedObjectCacheClear(this));
 

src/isolate.h

@@ -357,7 +357,7 @@ V8_EXPORT_PRIVATE void FreeCurrentEmbeddedBlob();
   V(int, suffix_table, (kBMMaxShift + 1))                                      \
   ISOLATE_INIT_DEBUG_ARRAY_LIST(V)
 
-typedef std::vector<HeapObject> DebugObjectCache;
+using DebugObjectCache = std::vector<Handle<HeapObject>>;
 
 #define ISOLATE_INIT_LIST(V)                                                   \
   /* Assembler state. */                                                       \

src/string-stream.cc

@@ -190,17 +190,18 @@ void StringStream::PrintObject(Object o) {
   if (o->IsHeapObject() && object_print_mode_ == kPrintObjectVerbose) {
     // TODO(delphick): Consider whether we can get the isolate without using
     // TLS.
+    Isolate* isolate = Isolate::Current();
     DebugObjectCache* debug_object_cache =
-        Isolate::Current()->string_stream_debug_object_cache();
+        isolate->string_stream_debug_object_cache();
     for (size_t i = 0; i < debug_object_cache->size(); i++) {
-      if ((*debug_object_cache)[i] == o) {
+      if (*(*debug_object_cache)[i] == o) {
         Add("#%d#", static_cast<int>(i));
         return;
       }
     }
     if (debug_object_cache->size() < kMentionedObjectCacheMaxSize) {
       Add("#%d#", static_cast<int>(debug_object_cache->size()));
-      debug_object_cache->push_back(HeapObject::cast(o));
+      debug_object_cache->push_back(handle(HeapObject::cast(o), isolate));
     } else {
       Add("@%p", o);
     }
@@ -364,7 +365,7 @@ void StringStream::PrintMentionedObjectCache(Isolate* isolate) {
       isolate->string_stream_debug_object_cache();
   Add("==== Key         ============================================\n\n");
   for (size_t i = 0; i < debug_object_cache->size(); i++) {
-    HeapObject printee = (*debug_object_cache)[i];
+    HeapObject printee = *(*debug_object_cache)[i];
     Add(" #%d# %p: ", static_cast<int>(i),
         reinterpret_cast<void*>(printee->ptr()));
     printee->ShortPrint(this);