[wasm] Cleanup unneeded casts to WasmInstanceObject

Plus another minor refactoring.

R=titzer@chromium.org

Review-Url: https://codereview.chromium.org/2590563002
Cr-Commit-Position: refs/heads/master@{#41853}

src/frames.cc

@@ -1559,10 +1559,10 @@ Address WasmFrame::GetCallerStackPointer() const {
 }
 
 WasmInstanceObject* WasmFrame::wasm_instance() const {
-  Object* ret = wasm::GetOwningWasmInstance(LookupCode());
-  // This is a live stack frame, there must be a live wasm instance available.
-  DCHECK_NOT_NULL(ret);
-  return WasmInstanceObject::cast(ret);
+  WasmInstanceObject* obj = wasm::GetOwningWasmInstance(LookupCode());
+  // This is a live stack frame; it must have a live instance.
+  DCHECK_NOT_NULL(obj);
+  return obj;
 }
 
 uint32_t WasmFrame::function_index() const {

src/runtime/runtime-wasm.cc

@@ -20,23 +20,25 @@
 namespace v8 {
 namespace internal {
 
-RUNTIME_FUNCTION(Runtime_WasmMemorySize) {
-  HandleScope scope(isolate);
-  DCHECK_EQ(0, args.length());
-
-  Handle<WasmInstanceObject> instance;
-  {
-    // Get the module JSObject
+namespace {
+Handle<WasmInstanceObject> GetWasmInstanceOnStackTop(Isolate* isolate) {
   DisallowHeapAllocation no_allocation;
   const Address entry = Isolate::c_entry_fp(isolate->thread_local_top());
   Address pc =
       Memory::Address_at(entry + StandardFrameConstants::kCallerPCOffset);
-    Code* code =
-        isolate->inner_pointer_to_code_cache()->GetCacheEntry(pc)->code;
+  Code* code = isolate->inner_pointer_to_code_cache()->GetCacheEntry(pc)->code;
+  DCHECK_EQ(Code::WASM_FUNCTION, code->kind());
   WasmInstanceObject* owning_instance = wasm::GetOwningWasmInstance(code);
   CHECK_NOT_NULL(owning_instance);
-    instance = handle(owning_instance, isolate);
-  }
+  return handle(owning_instance, isolate);
+}
+}  // namespace
+
+RUNTIME_FUNCTION(Runtime_WasmMemorySize) {
+  HandleScope scope(isolate);
+  DCHECK_EQ(0, args.length());
+
+  Handle<WasmInstanceObject> instance = GetWasmInstanceOnStackTop(isolate);
   return *isolate->factory()->NewNumberFromInt(
       wasm::GetInstanceMemorySize(isolate, instance));
 }
@@ -45,19 +47,7 @@ RUNTIME_FUNCTION(Runtime_WasmGrowMemory) {
   HandleScope scope(isolate);
   DCHECK_EQ(1, args.length());
   CONVERT_UINT32_ARG_CHECKED(delta_pages, 0);
-  Handle<WasmInstanceObject> instance;
-  {
-    // Get the module JSObject
-    DisallowHeapAllocation no_allocation;
-    const Address entry = Isolate::c_entry_fp(isolate->thread_local_top());
-    Address pc =
-        Memory::Address_at(entry + StandardFrameConstants::kCallerPCOffset);
-    Code* code =
-        isolate->inner_pointer_to_code_cache()->GetCacheEntry(pc)->code;
-    WasmInstanceObject* owning_instance = wasm::GetOwningWasmInstance(code);
-    CHECK_NOT_NULL(owning_instance);
-    instance = handle(owning_instance, isolate);
-  }
+  Handle<WasmInstanceObject> instance = GetWasmInstanceOnStackTop(isolate);
   return *isolate->factory()->NewNumberFromInt(
       wasm::GrowMemory(isolate, instance, delta_pages));
 }

src/wasm/wasm-module.cc

@@ -786,7 +786,7 @@ WasmInstanceObject* wasm::GetOwningWasmInstance(Code* code) {
   DisallowHeapAllocation no_gc;
   FixedArray* deopt_data = code->deoptimization_data();
   DCHECK_NOT_NULL(deopt_data);
-  DCHECK(deopt_data->length() == 2);
+  DCHECK_EQ(2, deopt_data->length());
   Object* weak_link = deopt_data->get(0);
   DCHECK(weak_link->IsWeakCell());
   WeakCell* cell = WeakCell::cast(weak_link);