Revert "[heap, runtime] Fix conversion of large strings to thin strings."

This reverts commit b35a0789bc.

Reason for revert: Roll blocker for https://chromium-review.googlesource.com/c/607193

Original change's description:
> [heap, runtime] Fix conversion of large strings to thin strings.
> 
> This patch removes creation of fillers in the middle of a large page and
> fixes assert in Heap::NotifyObjectLayoutChange.
> 
> The fillers in large pages are useless since we do not sweep large
> object space.
> 
> Bug: chromium:752426
> Change-Id: I01c230223f28d6d54b7362ee70e9d83de50678fd
> Reviewed-on: https://chromium-review.googlesource.com/601994
> Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
> Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#47221}

TBR=ulan@chromium.org,jkummerow@chromium.org,mlippautz@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: chromium:752426
Change-Id: I58a632af37fa018d82693099a7a395ca5db5af0f
Reviewed-on: https://chromium-review.googlesource.com/609404
Reviewed-by: Michael Hablich <hablich@chromium.org>
Commit-Queue: Michael Hablich <hablich@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47262}

src/heap/heap.cc

@@ -3307,11 +3307,6 @@ AllocationResult Heap::AllocateBytecodeArray(int length,
 
 HeapObject* Heap::CreateFillerObjectAt(Address addr, int size,
                                        ClearRecordedSlots mode) {
-  // In large object space fillers can be created only at the beginning
-  // of the large page.
-  DCHECK_IMPLIES(
-      lo_space_->ContainsSlow(addr),
-      HeapObject::cast(lo_space_->FindObject(addr))->address() == addr);
   if (size == 0) return nullptr;
   HeapObject* filler = HeapObject::FromAddress(addr);
   if (size == kPointerSize) {
@@ -3518,15 +3513,6 @@ void Heap::RightTrimFixedArray(FixedArrayBase* object, int elements_to_trim) {
   }
 }
 
-void Heap::RightTrimString(String* string, int old_size, int new_size) {
-  if (old_size == new_size) return;
-  DCHECK_LE(new_size, old_size);
-  if (!lo_space_->Contains(string)) {
-    Address filler = string->address() + new_size;
-    CreateFillerObjectAt(filler, old_size - new_size, ClearRecordedSlots::kNo);
-  }
-  AdjustLiveBytes(string, -(old_size - new_size));
-}
 
 AllocationResult Heap::AllocateFixedTypedArrayWithExternalPointer(
     int length, ExternalArrayType array_type, void* external_pointer,
@@ -4625,8 +4611,7 @@ void Heap::RegisterDeserializedObjectsForBlackAllocation(
 
 void Heap::NotifyObjectLayoutChange(HeapObject* object, int size,
                                     const DisallowHeapAllocation&) {
-  DCHECK(InOldSpace(object) || InNewSpace(object) ||
-         (lo_space()->Contains(object) && object->IsString()));
+  DCHECK(InOldSpace(object) || InNewSpace(object));
   if (FLAG_incremental_marking && incremental_marking()->IsMarking()) {
     incremental_marking()->MarkBlackAndPush(object);
     if (InOldSpace(object) && incremental_marking()->IsCompacting()) {

src/heap/heap.h

@@ -721,8 +721,6 @@ class Heap {
   // Trim the given array from the right.
   void RightTrimFixedArray(FixedArrayBase* obj, int elements_to_trim);
 
-  void RightTrimString(String* string, int old_size, int new_size);
-
   // Converts the given boolean condition to JavaScript boolean value.
   inline Oddball* ToBoolean(bool condition);
 

src/objects.cc

@@ -2625,7 +2625,8 @@ bool String::MakeExternal(v8::String::ExternalStringResource* resource) {
 
   // Byte size of the external String object.
   int new_size = this->SizeFromMap(new_map);
-  heap->RightTrimString(this, size, new_size);
+  heap->CreateFillerObjectAt(this->address() + new_size, size - new_size,
+                             ClearRecordedSlots::kNo);
   if (has_pointers) {
     heap->ClearRecordedSlotRange(this->address(), this->address() + new_size);
   }
@@ -2637,6 +2638,8 @@ bool String::MakeExternal(v8::String::ExternalStringResource* resource) {
   ExternalTwoByteString* self = ExternalTwoByteString::cast(this);
   self->set_resource(resource);
   if (is_internalized) self->Hash();  // Force regeneration of the hash value.
+
+  heap->AdjustLiveBytes(this, new_size - size);
   return true;
 }
 
@@ -2693,7 +2696,8 @@ bool String::MakeExternal(v8::String::ExternalOneByteStringResource* resource) {
 
   // Byte size of the external String object.
   int new_size = this->SizeFromMap(new_map);
-  heap->RightTrimString(this, size, new_size);
+  heap->CreateFillerObjectAt(this->address() + new_size, size - new_size,
+                             ClearRecordedSlots::kNo);
   if (has_pointers) {
     heap->ClearRecordedSlotRange(this->address(), this->address() + new_size);
   }
@@ -2705,6 +2709,8 @@ bool String::MakeExternal(v8::String::ExternalOneByteStringResource* resource) {
   ExternalOneByteString* self = ExternalOneByteString::cast(this);
   self->set_resource(resource);
   if (is_internalized) self->Hash();  // Force regeneration of the hash value.
+
+  heap->AdjustLiveBytes(this, new_size - size);
   return true;
 }
 
@@ -17080,7 +17086,13 @@ void MakeStringThin(String* string, String* internalized, Isolate* isolate) {
     string->synchronized_set_map(*map);
     ThinString* thin = ThinString::cast(string);
     thin->set_actual(internalized);
-    isolate->heap()->RightTrimString(thin, old_size, ThinString::kSize);
+    Address thin_end = thin->address() + ThinString::kSize;
+    int size_delta = old_size - ThinString::kSize;
+    if (size_delta != 0) {
+      Heap* heap = isolate->heap();
+      heap->CreateFillerObjectAt(thin_end, size_delta, ClearRecordedSlots::kNo);
+      heap->AdjustLiveBytes(thin, -size_delta);
+    }
   }
 }
 

test/cctest/test-strings.cc

@@ -1220,33 +1220,6 @@ TEST(InternalizeExternal) {
   CcTest::CollectGarbage(i::OLD_SPACE);
 }
 
-TEST(LargeThinString) {
-  CcTest::InitializeVM();
-  i::Isolate* isolate = CcTest::i_isolate();
-  Heap* heap = isolate->heap();
-  v8::HandleScope handle_scope(CcTest::isolate());
-  const char* string_generator =
-      "var result = 'a';"
-      "for (var i = 0; i < 20; i++) { result += result;}"
-      "result;";
-  v8::Local<v8::String> v8_string1 =
-      CompileRun(string_generator)
-          ->ToString(CcTest::isolate()->GetCurrentContext())
-          .ToLocalChecked();
-  Handle<String> string1 = v8::Utils::OpenHandle(*v8_string1);
-  isolate->factory()->InternalizeName(string1);
-  v8::Local<v8::String> v8_string2 =
-      CompileRun(string_generator)
-          ->ToString(CcTest::isolate()->GetCurrentContext())
-          .ToLocalChecked();
-  Handle<String> string2 = v8::Utils::OpenHandle(*v8_string2);
-  string2 = String::Flatten(string2);
-  isolate->factory()->InternalizeName(string2);
-  CHECK(heap->lo_space()->Contains(*string2));
-  CHECK(string2->IsThinString());
-  CcTest::CollectGarbage(i::OLD_SPACE);
-}
-
 TEST(SliceFromExternal) {
   FLAG_string_slices = true;
   CcTest::InitializeVM();