[wasm] Call a runtime function for a MemorySize instruction.

src/wasm/wasm-module.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 <memory>
 
 #include "src/base/atomic-utils.h"
 #include "src/code-stubs.h"
 
 #include "src/macro-assembler.h"
@@ skipping 1791 matching lines @@
 
 void SetInstanceMemory(Handle<JSObject> instance, JSArrayBuffer* buffer) {
   DisallowHeapAllocation no_gc;
   DCHECK(IsWasmObject(*instance));
   instance->SetInternalField(kWasmMemArrayBuffer, buffer);
   WasmCompiledModule* module =
       WasmCompiledModule::cast(instance->GetInternalField(kWasmCompiledModule));
   module->set_ptr_to_heap(buffer);
 }
 
+int32_t GetInstanceMemorySize(Isolate* isolate, Handle<JSObject> instance) {
+  MaybeHandle<JSArrayBuffer> maybe_mem_buffer =
+      GetInstanceMemory(isolate, instance);
+  Handle<JSArrayBuffer> old_buffer;

[gdeepti, 2016/10/05 06:52:39]

s/old_buffer/buffer as this is still the buffer associated with the instance. 

+  if (!maybe_mem_buffer.ToHandle(&old_buffer)) {
+    return 0;
+  } else {
+    return old_buffer->byte_length()->Number() / WasmModule::kPageSize;
+  }
+}
+
 int32_t GrowInstanceMemory(Isolate* isolate, Handle<JSObject> instance,
                            uint32_t pages) {
   Address old_mem_start = nullptr;
   uint32_t old_size = 0, new_size = 0;
 
   MaybeHandle<JSArrayBuffer> maybe_mem_buffer =
       GetInstanceMemory(isolate, instance);
   Handle<JSArrayBuffer> old_buffer;
   if (!maybe_mem_buffer.ToHandle(&old_buffer)) {
     // If module object does not have linear memory associated with it,
@@ skipping 80 matching lines @@
   WasmCompiledModule* compiled_module =
       WasmCompiledModule::cast(instance->GetInternalField(kWasmCompiledModule));
   CHECK(compiled_module->has_weak_module_object());
   CHECK(compiled_module->ptr_to_weak_module_object()->cleared());
 }
 
 }  // namespace testing
 }  // namespace wasm
 }  // namespace internal
 }  // namespace v8