[wasm] Make {NativeModule::compiled_module} a phantom reference.

This reduces time it takes for the compiled module to be reclaimed. It
switches the reference in question from a weak reference with finalizer
to a phantom reference, because the finalizer was only clearing the
reference by now anyways.

R=ahaas@chromium.org
BUG=chromium:824443

Change-Id: I51f0dbd487281184f82fd6c79fcf27514721b819
Reviewed-on: https://chromium-review.googlesource.com/978243
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52247}

src/wasm/wasm-code-manager.cc

@@ -520,13 +520,18 @@ void NativeModule::SetLazyBuiltin(Handle<Code> code) {
 }
 
 WasmCompiledModule* NativeModule::compiled_module() const {
+  DCHECK_NOT_NULL(compiled_module_);
   return *compiled_module_;
 }
 
 void NativeModule::SetCompiledModule(
     Handle<WasmCompiledModule> compiled_module) {
-  DCHECK(compiled_module_.is_null());
-  compiled_module_ = compiled_module;
+  DCHECK_NULL(compiled_module_);
+  compiled_module_ = compiled_module->GetIsolate()
+                         ->global_handles()
+                         ->Create(*compiled_module)
+                         .location();
+  GlobalHandles::MakeWeak(reinterpret_cast<Object***>(&compiled_module_));
 }
 
 WasmCode* NativeModule::AddAnonymousCode(Handle<Code> code,
@@ -862,6 +867,12 @@ WasmCode* NativeModule::CloneCode(const WasmCode* original_code,
 NativeModule::~NativeModule() {
   TRACE_HEAP("Deleting native module: %p\n", reinterpret_cast<void*>(this));
   wasm_code_manager_->FreeNativeModuleMemories(this);
+  if (compiled_module_ != nullptr) {
+    Isolate* isolate = compiled_module()->GetIsolate();
+    isolate->global_handles()->Destroy(
+        reinterpret_cast<Object**>(compiled_module_));
+    compiled_module_ = nullptr;
+  }
 }
 
 WasmCodeManager::WasmCodeManager(v8::Isolate* isolate, size_t max_committed)

src/wasm/wasm-code-manager.h

@@ -278,8 +278,8 @@ class V8_EXPORT_PRIVATE NativeModule final {
 
   CompilationState* compilation_state() { return compilation_state_.get(); }
 
-  // TODO(mstarzinger): needed until we sort out source positions, which are
-  // still on the  GC-heap.
+  // TODO(mstarzinger): The link to the {compiled_module} is deprecated and all
+  // uses should vanish to make {NativeModule} independent of the Isolate.
   WasmCompiledModule* compiled_module() const;
   void SetCompiledModule(Handle<WasmCompiledModule>);
 
@@ -340,12 +340,16 @@ class V8_EXPORT_PRIVATE NativeModule final {
 
   std::unique_ptr<CompilationState, CompilationStateDeleter> compilation_state_;
 
+  // A phantom reference to the {WasmCompiledModule}. It is intentionally not
+  // typed {Handle<WasmCompiledModule>} because this location will be cleared
+  // when the phantom reference is cleared.
+  WasmCompiledModule** compiled_module_ = nullptr;
+
   DisjointAllocationPool free_memory_;
   DisjointAllocationPool allocated_memory_;
   std::list<VirtualMemory> owned_memory_;
   WasmCodeManager* wasm_code_manager_;
   base::Mutex allocation_mutex_;
-  Handle<WasmCompiledModule> compiled_module_;
   size_t committed_memory_ = 0;
   bool can_request_more_memory_;
   bool is_executable_ = false;

src/wasm/wasm-objects.cc

@@ -155,14 +155,6 @@ bool IsBreakablePosition(WasmSharedModuleData* shared, int func_index,
 }
 #endif  // DEBUG
 
-void CompiledModuleFinalizer(const v8::WeakCallbackInfo<void>& data) {
-  DisallowHeapAllocation no_gc;
-  JSObject** p = reinterpret_cast<JSObject**>(data.GetParameter());
-  WasmCompiledModule* compiled_module = WasmCompiledModule::cast(*p);
-  compiled_module->reset_native_module();
-  GlobalHandles::Destroy(reinterpret_cast<Object**>(p));
-}
-
 enum DispatchTableElements : int {
   kDispatchTableInstanceOffset,
   kDispatchTableIndexOffset,
@@ -1252,13 +1244,7 @@ Handle<WasmCompiledModule> WasmCompiledModule::New(
     Handle<Foreign> native_module_wrapper =
         Managed<wasm::NativeModule>::From(isolate, native_module);
     compiled_module->set_native_module(*native_module_wrapper);
-    Handle<WasmCompiledModule> weak_link =
-        isolate->global_handles()->Create(*compiled_module);
-    GlobalHandles::MakeWeak(Handle<Object>::cast(weak_link).location(),
-                            Handle<Object>::cast(weak_link).location(),
-                            &CompiledModuleFinalizer,
-                            v8::WeakCallbackType::kFinalizer);
-    compiled_module->GetNativeModule()->SetCompiledModule(weak_link);
+    compiled_module->GetNativeModule()->SetCompiledModule(compiled_module);
   }
 
   // TODO(mtrofin): copy the rest of the specialization parameters over.
@@ -1292,13 +1278,7 @@ Handle<WasmCompiledModule> WasmCompiledModule::Clone(
   Handle<Foreign> native_module_wrapper =
       Managed<wasm::NativeModule>::From(isolate, native_module.release());
   ret->set_native_module(*native_module_wrapper);
-  Handle<WasmCompiledModule> weak_link =
-      isolate->global_handles()->Create(*ret);
-  GlobalHandles::MakeWeak(Handle<Object>::cast(weak_link).location(),
-                          Handle<Object>::cast(weak_link).location(),
-                          &CompiledModuleFinalizer,
-                          v8::WeakCallbackType::kFinalizer);
-  ret->GetNativeModule()->SetCompiledModule(weak_link);
+  ret->GetNativeModule()->SetCompiledModule(ret);
 
   if (module->has_lazy_compile_data()) {
     Handle<FixedArray> lazy_comp_data = isolate->factory()->NewFixedArray(