Revert of [wasm] WebAssembly.Memory object can be referenced by multiple...

Revert of [wasm] WebAssembly.Memory object can be referenced by multiple Instance objects. (patchset #10 id:180001 of https://codereview.chromium.org/2471883003/ )

Reason for revert:
Breaks gc stress:
https://build.chromium.org/p/client.v8/builders/V8%20Linux%20-%20gc%20stress/builds/7114

Original issue's description:
> [wasm] WebAssembly.Memory object can be referenced by multiple Instance objects.
>
> Add support for WebAssembly.Memory objects to be simultaneously referenced by multiple Instance objects. GrowingMemory should maintain a consistent view of memory across instances.
>  - Store a link to instances that share WebAssembly.Memory in the WasmMemoryObject, updated on instantiate.
>  - Implement WasmInstanceWrapper as a wrapper around the instance object to keep track of previous/next instances, instance object is stored as a WeakCell that can be garbage collected.
>  - MemoryInstanceFinalizer maintains a valid list of instances when an instance is garbage collected.
>  - Refactor GrowInstanceMemory to GrowMemoryBuffer that allocates a new buffer, and UncheckedUpdateInstanceMemory that updates memory references for an instance.
>
>  R=titzer@chromium.org, mtrofin@chromium.org, bradnelson@chromium.org
>
> Committed: https://crrev.com/30ef8e33f3a199a27ca8512bcee314c9522d03f6
> Cr-Commit-Position: refs/heads/master@{#41121}

TBR=bradnelson@chromium.org,mtrofin@chromium.org,titzer@chromium.org,gdeepti@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Review-Url: https://codereview.chromium.org/2512323004
Cr-Commit-Position: refs/heads/master@{#41122}

src/runtime/runtime-wasm.cc

@@ -58,7 +58,7 @@ RUNTIME_FUNCTION(Runtime_WasmGrowMemory) {
     instance = handle(owning_instance, isolate);
   }
   return *isolate->factory()->NewNumberFromInt(
-      wasm::GrowMemory(isolate, instance, delta_pages));
+      wasm::GrowInstanceMemory(isolate, instance, delta_pages));
 }
 
 RUNTIME_FUNCTION(Runtime_WasmThrowTypeError) {

src/wasm/wasm-js.cc

@@ -28,6 +28,12 @@ using v8::internal::wasm::ErrorThrower;
 
 namespace v8 {
 
+enum WasmMemoryObjectData {
+  kWasmMemoryBuffer,
+  kWasmMemoryMaximum,
+  kWasmMemoryInstanceObject
+};
+
 namespace {
 i::Handle<i::String> v8_str(i::Isolate* isolate, const char* str) {
   return isolate->factory()->NewStringFromAsciiChecked(str);
@@ -224,7 +230,6 @@ void WebAssemblyInstance(const v8::FunctionCallbackInfo<v8::Value>& args) {
           i_isolate);
     } else {
       thrower.TypeError("Argument 2 must be a WebAssembly.Memory");
-      return;
     }
   }
   i::MaybeHandle<i::JSObject> instance =
@@ -525,15 +530,31 @@ void WebAssemblyMemoryGrow(const v8::FunctionCallbackInfo<v8::Value>& args) {
 
   uint32_t delta = args[0]->Uint32Value(context).FromJust();
   i::Isolate* i_isolate = reinterpret_cast<i::Isolate*>(isolate);
-  i::Handle<i::Object> receiver =
-      i::Handle<i::Object>::cast(Utils::OpenHandle(*args.This()));
-  int32_t ret = i::wasm::GrowWebAssemblyMemory(i_isolate, receiver, delta);
+  i::Handle<i::JSObject> receiver =
+      i::Handle<i::JSObject>::cast(Utils::OpenHandle(*args.This()));
+  i::Handle<i::Object> instance_object(
+      receiver->GetInternalField(kWasmMemoryInstanceObject), i_isolate);
+  i::Handle<i::WasmInstanceObject> instance(
+      i::Handle<i::WasmInstanceObject>::cast(instance_object));
+
+  // TODO(gdeepti) Implement growing memory when shared by different
+  // instances.
+  int32_t ret = internal::wasm::GrowInstanceMemory(i_isolate, instance, delta);
   if (ret == -1) {
     v8::Local<v8::Value> e = v8::Exception::Error(
         v8_str(isolate, "Unable to grow instance memory."));
     isolate->ThrowException(e);
     return;
   }
+  i::MaybeHandle<i::JSArrayBuffer> buffer =
+      internal::wasm::GetInstanceMemory(i_isolate, instance);
+  if (buffer.is_null()) {
+    v8::Local<v8::Value> e = v8::Exception::Error(
+        v8_str(isolate, "WebAssembly.Memory buffer object not set."));
+    isolate->ThrowException(e);
+    return;
+  }
+  receiver->SetInternalField(kWasmMemoryBuffer, *buffer.ToHandleChecked());
   v8::ReturnValue<v8::Value> return_value = args.GetReturnValue();
   return_value.Set(ret);
 }
@@ -549,9 +570,10 @@ void WebAssemblyMemoryGetBuffer(
     return;
   }
   i::Isolate* i_isolate = reinterpret_cast<i::Isolate*>(isolate);
-  i::Handle<i::WasmMemoryObject> receiver =
-      i::Handle<i::WasmMemoryObject>::cast(Utils::OpenHandle(*args.This()));
-  i::Handle<i::Object> buffer(receiver->get_buffer(), i_isolate);
+  i::Handle<i::JSObject> receiver =
+      i::Handle<i::JSObject>::cast(Utils::OpenHandle(*args.This()));
+  i::Handle<i::Object> buffer(receiver->GetInternalField(kWasmMemoryBuffer),
+                              i_isolate);
   DCHECK(buffer->IsJSArrayBuffer());
   v8::ReturnValue<v8::Value> return_value = args.GetReturnValue();
   return_value.Set(Utils::ToLocal(buffer));

src/wasm/wasm-module.h

@@ -422,8 +422,8 @@ bool GetPositionInfo(Handle<WasmCompiledModule> compiled_module,
 // Returns nullptr on failing to get owning instance.
 WasmInstanceObject* GetOwningWasmInstance(Code* code);
 
-MaybeHandle<JSArrayBuffer> GetInstanceMemory(Isolate* isolate,
-                                             Handle<JSObject> instance);
+MaybeHandle<JSArrayBuffer> GetInstanceMemory(
+    Isolate* isolate, Handle<WasmInstanceObject> instance);
 
 int32_t GetInstanceMemorySize(Isolate* isolate,
                               Handle<WasmInstanceObject> instance);
@@ -434,14 +434,6 @@ int32_t GrowInstanceMemory(Isolate* isolate,
 Handle<JSArrayBuffer> NewArrayBuffer(Isolate* isolate, size_t size,
                                      bool enable_guard_regions);
 
-int32_t GetInstanceMemorySize(Isolate* isolate, Handle<JSObject> instance);
-
-int32_t GrowWebAssemblyMemory(Isolate* isolate, Handle<Object> receiver,
-                              uint32_t pages);
-
-int32_t GrowMemory(Isolate* isolate, Handle<WasmInstanceObject> instance,
-                   uint32_t pages);
-
 void UpdateDispatchTables(Isolate* isolate, Handle<FixedArray> dispatch_tables,
                           int index, Handle<JSFunction> js_function);
 

src/wasm/wasm-objects.cc

@@ -184,8 +184,6 @@ Handle<WasmMemoryObject> WasmMemoryObject::New(Isolate* isolate,
 }
 
 DEFINE_ACCESSORS(WasmMemoryObject, buffer, kArrayBuffer, JSArrayBuffer)
-DEFINE_OPTIONAL_ACCESSORS(WasmMemoryObject, instances_link, kInstancesLink,
-                          WasmInstanceWrapper)
 
 uint32_t WasmMemoryObject::current_pages() {
   return SafeUint32(get_buffer()->byte_length()) / wasm::WasmModule::kPageSize;
@@ -201,26 +199,10 @@ WasmMemoryObject* WasmMemoryObject::cast(Object* object) {
   return reinterpret_cast<WasmMemoryObject*>(object);
 }
 
-void WasmMemoryObject::AddInstance(Isolate* isolate,
-                                   Handle<WasmInstanceObject> instance) {
-  Handle<WasmInstanceWrapper> instance_wrapper;
-  if (has_instances_link()) {
-    Handle<WasmInstanceWrapper> current_wrapper(get_instances_link());
-    DCHECK(WasmInstanceWrapper::IsWasmInstanceWrapper(*current_wrapper));
-    DCHECK(!current_wrapper->has_previous());
-    instance_wrapper = WasmInstanceWrapper::New(isolate, instance);
-    instance_wrapper->set_next_wrapper(*current_wrapper);
-    current_wrapper->set_previous_wrapper(*instance_wrapper);
-  } else {
-    instance_wrapper = WasmInstanceWrapper::New(isolate, instance);
-  }
-  set_instances_link(*instance_wrapper);
-  instance->set_instance_wrapper(*instance_wrapper);
-}
-
-void WasmMemoryObject::ResetInstancesLink(Isolate* isolate) {
-  Handle<Object> undefined = isolate->factory()->undefined_value();
-  SetInternalField(kInstancesLink, *undefined);
+void WasmMemoryObject::AddInstance(WasmInstanceObject* instance) {
+  // TODO(gdeepti): This should be a weak list of instance objects
+  // for instances that share memory.
+  SetInternalField(kInstance, instance);
 }
 
 DEFINE_ACCESSORS(WasmInstanceObject, compiled_module, kCompiledModule,
@@ -233,8 +215,6 @@ DEFINE_OPTIONAL_ACCESSORS(WasmInstanceObject, memory_object, kMemoryObject,
                           WasmMemoryObject)
 DEFINE_OPTIONAL_ACCESSORS(WasmInstanceObject, debug_info, kDebugInfo,
                           WasmDebugInfo)
-DEFINE_OPTIONAL_ACCESSORS(WasmInstanceObject, instance_wrapper,
-                          kWasmMemInstanceWrapper, WasmInstanceWrapper)
 
 WasmModuleObject* WasmInstanceObject::module_object() {
   return WasmModuleObject::cast(*get_compiled_module()->wasm_module());
@@ -405,34 +385,3 @@ int WasmCompiledModule::GetFunctionOffset(uint32_t func_index) const {
             functions[func_index].code_start_offset);
   return static_cast<int>(functions[func_index].code_start_offset);
 }
-
-Handle<WasmInstanceWrapper> WasmInstanceWrapper::New(
-    Isolate* isolate, Handle<WasmInstanceObject> instance) {
-  Handle<FixedArray> array =
-      isolate->factory()->NewFixedArray(kWrapperPropertyCount, TENURED);
-  Handle<WasmInstanceWrapper> instance_wrapper(
-      reinterpret_cast<WasmInstanceWrapper*>(*array), isolate);
-  instance_wrapper->set_instance_object(instance, isolate);
-  return instance_wrapper;
-}
-
-bool WasmInstanceWrapper::IsWasmInstanceWrapper(Object* obj) {
-  if (!obj->IsFixedArray()) return false;
-  FixedArray* array = FixedArray::cast(obj);
-  if (array->length() != kWrapperPropertyCount) return false;
-  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;
-}
-
-void WasmInstanceWrapper::set_instance_object(Handle<JSObject> instance,
-                                              Isolate* isolate) {
-  Handle<WeakCell> cell = isolate->factory()->NewWeakCell(instance);
-  set(kWrapperInstanceObject, *cell);
-}

src/wasm/wasm-objects.h

@@ -17,7 +17,6 @@ struct WasmModule;
 class WasmCompiledModule;
 class WasmDebugInfo;
 class WasmInstanceObject;
-class WasmInstanceWrapper;
 
 #define DECLARE_CASTS(name)             \
   static bool Is##name(Object* object); \
@@ -80,14 +79,12 @@ class WasmTableObject : public JSObject {
 class WasmMemoryObject : public JSObject {
  public:
   // TODO(titzer): add the brand as an internal field instead of a property.
-  enum Fields : uint8_t { kArrayBuffer, kMaximum, kInstancesLink, kFieldCount };
+  enum Fields : uint8_t { kArrayBuffer, kMaximum, kInstance, kFieldCount };
 
   DECLARE_CASTS(WasmMemoryObject);
   DECLARE_ACCESSORS(buffer, JSArrayBuffer);
-  DECLARE_OPTIONAL_ACCESSORS(instances_link, WasmInstanceWrapper);
 
-  void AddInstance(Isolate* isolate, Handle<WasmInstanceObject> object);
-  void ResetInstancesLink(Isolate* isolate);
+  void AddInstance(WasmInstanceObject* object);
   uint32_t current_pages();
   int32_t maximum_pages();  // returns < 0 if there is no maximum
 
@@ -108,7 +105,6 @@ class WasmInstanceObject : public JSObject {
     kMemoryArrayBuffer,
     kGlobalsArrayBuffer,
     kDebugInfo,
-    kWasmMemInstanceWrapper,
     kFieldCount
   };
 
@@ -119,7 +115,6 @@ class WasmInstanceObject : public JSObject {
   DECLARE_OPTIONAL_ACCESSORS(memory_buffer, JSArrayBuffer);
   DECLARE_OPTIONAL_ACCESSORS(memory_object, WasmMemoryObject);
   DECLARE_OPTIONAL_ACCESSORS(debug_info, WasmDebugInfo);
-  DECLARE_OPTIONAL_ACCESSORS(instance_wrapper, WasmInstanceWrapper);
 
   WasmModuleObject* module_object();
   wasm::WasmModule* module();
@@ -321,61 +316,6 @@ class WasmDebugInfo : public FixedArray {
                                     int func_index, int byte_offset);
 };
 
-class WasmInstanceWrapper : public FixedArray {
- public:
-  static Handle<WasmInstanceWrapper> New(Isolate* isolate,
-                                         Handle<WasmInstanceObject> instance);
-  static WasmInstanceWrapper* cast(Object* fixed_array) {
-    SLOW_DCHECK(IsWasmInstanceWrapper(fixed_array));
-    return reinterpret_cast<WasmInstanceWrapper*>(fixed_array);
-  }
-  static bool IsWasmInstanceWrapper(Object* obj);
-  bool has_instance() { return get(kWrapperInstanceObject)->IsWeakCell(); }
-  Handle<WasmInstanceObject> instance_object() {
-    Object* obj = get(kWrapperInstanceObject);
-    DCHECK(obj->IsWeakCell());
-    WeakCell* cell = WeakCell::cast(obj);
-    DCHECK(cell->value()->IsJSObject());
-    return handle(WasmInstanceObject::cast(cell->value()));
-  }
-  bool has_next() { return IsWasmInstanceWrapper(get(kNextInstanceWrapper)); }
-  bool has_previous() {
-    return IsWasmInstanceWrapper(get(kPreviousInstanceWrapper));
-  }
-  void set_instance_object(Handle<JSObject> instance, Isolate* isolate);
-  void set_next_wrapper(Object* obj) {
-    DCHECK(IsWasmInstanceWrapper(obj));
-    set(kNextInstanceWrapper, obj);
-  }
-  void set_previous_wrapper(Object* obj) {
-    DCHECK(IsWasmInstanceWrapper(obj));
-    set(kPreviousInstanceWrapper, obj);
-  }
-  Handle<WasmInstanceWrapper> next_wrapper() {
-    Object* obj = get(kNextInstanceWrapper);
-    DCHECK(IsWasmInstanceWrapper(obj));
-    return handle(WasmInstanceWrapper::cast(obj));
-  }
-  Handle<WasmInstanceWrapper> previous_wrapper() {
-    Object* obj = get(kPreviousInstanceWrapper);
-    DCHECK(IsWasmInstanceWrapper(obj));
-    return handle(WasmInstanceWrapper::cast(obj));
-  }
-  void reset_next_wrapper() { set_undefined(kNextInstanceWrapper); }
-  void reset_previous_wrapper() { set_undefined(kPreviousInstanceWrapper); }
-  void reset() {
-    for (int kID = 0; kID < kWrapperPropertyCount; kID++) set_undefined(kID);
-  }
-
- private:
-  enum {
-    kWrapperInstanceObject,
-    kNextInstanceWrapper,
-    kPreviousInstanceWrapper,
-    kWrapperPropertyCount
-  };
-};
-
 #undef DECLARE_ACCESSORS
 #undef DECLARE_OPTIONAL_ACCESSORS
 

test/mjsunit/wasm/import-memory.js

@@ -40,6 +40,7 @@ load("test/mjsunit/wasm/wasm-module-builder.js");
   assertSame(memory, instance.exports.daggle);
 })();
 
+
 (function TestImportExport() {
   print("TestImportExport");
   var i1;
@@ -228,141 +229,3 @@ load("test/mjsunit/wasm/wasm-module-builder.js");
   }
   assertEquals(-1, instance.exports.grow(1));
 })();
-
-(function TestMemoryGrowWebAssemblyInstances() {
-  print("TestMemoryGrowWebAssemblyInstances");
-  let memory = new WebAssembly.Memory({initial: 1, maximum: 15});
-  var builder = new WasmModuleBuilder();
-  builder.addImportedMemory("imported_mem");
-  builder.addFunction("mem_size", kSig_i_v)
-    .addBody([kExprMemorySize, kMemoryZero])
-    .exportAs("mem_size");
-  builder.addFunction("grow", kSig_i_i)
-    .addBody([kExprGetLocal, 0, kExprGrowMemory, kMemoryZero])
-    .exportFunc();
-  var module = new WebAssembly.Module(builder.toBuffer());
-  var instances = [];
-  for (var i = 0; i < 6; i++) {
-    instances.push(new WebAssembly.Instance(module, {imported_mem: memory}));
-  }
-  function verify_mem_size(expected_pages) {
-    assertEquals(expected_pages*kPageSize,
-        memory.buffer.byteLength);
-    for (var i = 0; i < 6; i++) {
-      assertEquals(expected_pages, instances[i].exports.mem_size());
-    }
-  }
-
-  // Verify initial memory size
-  verify_mem_size(1);
-
-  // Verify memory size with interleaving calls to Memory.grow,
-  // GrowMemory opcode.
-  var current_mem_size = 1;
-  for (var i = 0; i < 5; i++) {
-    function grow(pages) { return instances[i].exports.grow(pages); }
-    assertEquals(current_mem_size, memory.grow(1));
-    verify_mem_size(++current_mem_size);
-    assertEquals(current_mem_size, instances[i].exports.grow(1));
-    verify_mem_size(++current_mem_size);
-  }
-
-  assertThrows(() => memory.grow(5));
-})();
-
-(function TestImportedMemoryGrowMultipleInstances() {
-  print("TestImportMemoryMultipleInstances");
-  let memory = new WebAssembly.Memory({initial: 5, maximum: 100});
-  var builder = new WasmModuleBuilder();
-  builder.addImportedMemory("imported_mem");
-  builder.addFunction("mem_size", kSig_i_v)
-    .addBody([kExprMemorySize, kMemoryZero])
-    .exportFunc();
-  builder.addFunction("grow", kSig_i_i)
-    .addBody([kExprGetLocal, 0, kExprGrowMemory, kMemoryZero])
-    .exportFunc();
-  var instances = [];
-  for (var i = 0; i < 5; i++) {
-    instances.push(builder.instantiate({imported_mem: memory}));
-  }
-  function grow_instance_0(pages) { return instances[0].exports.grow(pages); }
-  function grow_instance_1(pages) { return instances[1].exports.grow(pages); }
-  function grow_instance_2(pages) { return instances[2].exports.grow(pages); }
-  function grow_instance_3(pages) { return instances[3].exports.grow(pages); }
-  function grow_instance_4(pages) { return instances[4].exports.grow(pages); }
-
-  function verify_mem_size(expected_pages) {
-    assertEquals(expected_pages*kPageSize, memory.buffer.byteLength);
-    for (var i = 0; i < 5; i++) {
-      assertEquals(expected_pages, instances[i].exports.mem_size());
-    }
-  }
-
-  // Verify initial memory size
-  verify_mem_size(5);
-
-  // Grow instance memory and buffer memory out of order and verify memory is
-  // updated correctly.
-  assertEquals(5, grow_instance_0(7));
-  verify_mem_size(12);
-
-  assertEquals(12, memory.grow(4));
-  verify_mem_size(16);
-
-  assertEquals(16, grow_instance_4(1));
-  verify_mem_size(17);
-
-  assertEquals(17, grow_instance_1(6));
-  verify_mem_size(23);
-
-  assertEquals(23, grow_instance_3(2));
-  verify_mem_size(25);
-
-  assertEquals(25, memory.grow(10));
-  verify_mem_size(35);
-
-  assertEquals(35, grow_instance_2(15));
-  verify_mem_size(50);
-  assertThrows(() => memory.grow(51));
-})();
-
-(function TestExportImportedMemoryGrowMultipleInstances() {
-  // TODO(gdeepti):Exported memory objects currently do not take max_size
-  // into account so this can grow past the maximum specified in the exported
-  // memory object. Assert that growing past maximum for exported objects fails.
-  print("TestExportImportedMemoryGrowMultipleInstances");
-  var instance;
-  {
-    let builder = new WasmModuleBuilder();
-    builder.addMemory(1, 11, true);
-    builder.exportMemoryAs("exported_mem");
-    builder.addFunction("mem_size", kSig_i_v)
-      .addBody([kExprMemorySize, kMemoryZero])
-      .exportFunc();
-    instance = builder.instantiate();
-  }
-  var builder = new WasmModuleBuilder();
-  builder.addImportedMemory("imported_mem");
-  builder.addFunction("mem_size", kSig_i_v)
-    .addBody([kExprMemorySize, kMemoryZero])
-    .exportFunc();
-  builder.addFunction("grow", kSig_i_i)
-    .addBody([kExprGetLocal, 0, kExprGrowMemory, kMemoryZero])
-    .exportFunc();
-  var instances = [];
-  for (var i = 0; i < 10; i++) {
-    instances.push(builder.instantiate({
-      imported_mem: instance.exports.exported_mem}));
-  }
-  function verify_mem_size(expected_pages) {
-    for (var i = 0; i < 10; i++) {
-      assertEquals(expected_pages, instances[i].exports.mem_size());
-    }
-  }
-  var current_mem_size = 1;
-  for (var i = 0; i < 10; i++) {
-    function grow(pages) { return instances[i].exports.grow(pages); }
-    assertEquals(current_mem_size, instances[i].exports.grow(1));
-    verify_mem_size(++current_mem_size);
-  }
-})();

test/mjsunit/wasm/instantiate-module-basic.js

@@ -215,7 +215,6 @@ assertFalse(WebAssembly.validate(bytes(88, 88, 88, 88, 88, 88, 88, 88)));
 })();
 
 (function MustBeMemory() {
-  print("MustBeMemory...");
   var memory = new ArrayBuffer(65536);
   var module = new WebAssembly.Module(buffer);
   assertThrows(() => new WebAssembly.Instance(module, null, memory), TypeError);

test/mjsunit/wasm/memory-instance-validation.js

-// Copyright 2016 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.
-
-// Flags: --expose-wasm --expose-gc
-
-load("test/mjsunit/wasm/wasm-constants.js");
-load("test/mjsunit/wasm/wasm-module-builder.js");
-
-// This test verifies that when instances are exported, Gc'ed, the other
-// instances in the chain still maintain a consistent view of the memory.
-(function ValidateSharedInstanceMemory() {
-  print("ValidateSharedInstanceMemory");
-  let memory = new WebAssembly.Memory({initial: 5, maximum: 100});
-  var builder = new WasmModuleBuilder();
-  builder.addImportedMemory("imported_mem");
-  builder.addFunction("mem_size", kSig_i_v)
-    .addBody([kExprMemorySize, kMemoryZero])
-    .exportFunc();
-  builder.addFunction("grow", kSig_i_i)
-    .addBody([kExprGetLocal, 0, kExprGrowMemory, kMemoryZero])
-    .exportFunc();
-  var instances = [];
-  for (var i = 0; i < 5; i++) {
-    instances.push(builder.instantiate({imported_mem: memory}));
-  }
-  function grow_instance_0(pages) { return instances[0].exports.grow(pages); }
-  function grow_instance_1(pages) { return instances[1].exports.grow(pages); }
-  function grow_instance_2(pages) { return instances[2].exports.grow(pages); }
-  function grow_instance_3(pages) { return instances[3].exports.grow(pages); }
-  function grow_instance_4(pages) { return instances[4].exports.grow(pages); }
-
-  var start_index = 0;
-  var end_index = 5;
-  function verify_mem_size(expected_pages) {
-    assertEquals(expected_pages*kPageSize, memory.buffer.byteLength);
-    for (var i = start_index; i < end_index; i++) {
-      assertEquals(expected_pages, instances[i].exports.mem_size());
-    }
-  }
-
-  // Verify initial memory size of all instances, grow and verify that all
-  // instances are updated correctly.
-  verify_mem_size(5);
-  assertEquals(5, memory.grow(6));
-  verify_mem_size(11);
-
-  instances[1] = null;
-  gc();
-
-  // i[0] - i[2] - i[3] - i[4]
-  start_index = 2;
-  verify_mem_size(11);
-  assertEquals(11, instances[0].exports.mem_size());
-  assertEquals(11, grow_instance_2(10));
-  assertEquals(21*kPageSize, memory.buffer.byteLength);
-  verify_mem_size(21);
-  assertEquals(21, instances[0].exports.mem_size());
-
-  instances[4] = null;
-  gc();
-
-  // i[0] - i[2] - i[3]
-  assertEquals(21, instances[0].exports.mem_size());
-  assertEquals(21, instances[2].exports.mem_size());
-  assertEquals(21, instances[3].exports.mem_size());
-  assertEquals(21, memory.grow(2));
-  assertEquals(23*kPageSize, memory.buffer.byteLength);
-  assertEquals(23, instances[0].exports.mem_size());
-  assertEquals(23, instances[2].exports.mem_size());
-  assertEquals(23, instances[3].exports.mem_size());
-
-  instances[0] = null;
-  gc();
-
-  // i[2] - i[3]
-  assertEquals(23, instances[2].exports.mem_size());
-  assertEquals(23, instances[3].exports.mem_size());
-  assertEquals(23, grow_instance_3(5));
-  assertEquals(28*kPageSize, memory.buffer.byteLength);
-  assertEquals(28, instances[2].exports.mem_size());
-  assertEquals(28, instances[3].exports.mem_size());
-
-  // Instantiate a new instance and verify that it can be grown correctly.
-  instances.push(builder.instantiate({imported_mem: memory}));
-  function grow_instance_5(pages) { return instances[5].exports.grow(pages); }
-
-  // i[2] - i[3] - i[5]
-  assertEquals(28, instances[2].exports.mem_size());
-  assertEquals(28, instances[3].exports.mem_size());
-  assertEquals(28, instances[5].exports.mem_size());
-  assertEquals(28, grow_instance_5(2));
-  assertEquals(30*kPageSize, memory.buffer.byteLength);
-  assertEquals(30, instances[2].exports.mem_size());
-  assertEquals(30, instances[3].exports.mem_size());
-  assertEquals(30, instances[5].exports.mem_size());
-  assertEquals(30, memory.grow(5));
-  assertEquals(35*kPageSize, memory.buffer.byteLength);
-  assertEquals(35, instances[2].exports.mem_size());
-  assertEquals(35, instances[3].exports.mem_size());
-  assertEquals(35, instances[5].exports.mem_size());
-
-})();