[wasm] Do not unregister an ArrayBuffer if it is already external

src/wasm/wasm-objects.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/wasm/wasm-objects.h"
 #include "src/utils.h"
 
 #include "src/assembler-inl.h"
 #include "src/base/iterator.h"
 #include "src/compiler/wasm-compiler.h"
@@ skipping 458 matching lines @@
   uint32_t old_size = 0;
   Address old_mem_start = nullptr;
   if (memory_object->has_buffer()) {
     old_buffer = handle(memory_object->buffer());
     old_size = old_buffer->byte_length()->Number();
     old_mem_start = static_cast<Address>(old_buffer->backing_store());
   }
   Handle<JSArrayBuffer> new_buffer;
   // Return current size if grow by 0.
   if (pages == 0) {
-    // Even for pages == 0, we need to attach a new JSArrayBuffer and neuter the
-    // old one to be spec compliant.
-    if (!old_buffer.is_null() && old_buffer->backing_store() != nullptr) {
+    // Even for pages == 0, we need to attach a new JSArrayBuffer with the same
+    // backing store and neuter the old one to be spec compliant.
+    if (!old_buffer.is_null() && old_size != 0) {
       new_buffer = SetupArrayBuffer(isolate, old_buffer->backing_store(),
                                     old_size, old_buffer->is_external(),
                                     old_buffer->has_guard_region());
       memory_object->set_buffer(*new_buffer);
-      old_buffer->set_is_neuterable(true);
-      if (!old_buffer->has_guard_region()) {
-        old_buffer->set_is_external(true);
-        isolate->heap()->UnregisterArrayBuffer(*old_buffer);
-      }
-      // Neuter but don't free the memory because it is now being used by
-      // new_buffer.
-      old_buffer->Neuter();
     }
     DCHECK_EQ(0, old_size % WasmModule::kPageSize);
     return old_size / WasmModule::kPageSize;
   }
   if (!memory_object->has_instances_link()) {
     // Memory object does not have an instance associated with it, just grow
     uint32_t max_pages;
     if (memory_object->has_maximum_pages()) {
       max_pages = static_cast<uint32_t>(memory_object->maximum_pages());
       if (FLAG_wasm_max_mem_pages < max_pages) return -1;
@@ skipping 1081 matching lines @@
   if (!array->get(kWrapperInstanceObject)->IsWeakCell()) return false;
   Isolate* isolate = array->GetIsolate();
   if (!array->get(kNextInstanceWrapper)->IsUndefined(isolate) &&
       !array->get(kNextInstanceWrapper)->IsFixedArray())
     return false;
   if (!array->get(kPreviousInstanceWrapper)->IsUndefined(isolate) &&
       !array->get(kPreviousInstanceWrapper)->IsFixedArray())
     return false;
   return true;
 }