[promises] Refactor CreatePromise

src/builtins/builtins-promise.cc

 // 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.
 
 #include "src/builtins/builtins-utils.h"
 #include "src/builtins/builtins.h"
 #include "src/code-factory.h"
 #include "src/code-stub-assembler.h"
 #include "src/promise-utils.h"
 
@@ skipping 39 matching lines @@
                                          &resolve, &reject);
 
   Handle<FixedArray> result = isolate->factory()->NewFixedArray(2);
   result->set(0, *resolve);
   result->set(1, *reject);
 
   return *isolate->factory()->NewJSArrayWithElements(result, FAST_ELEMENTS, 2,
                                                      NOT_TENURED);
 }
 
+namespace {
+
+compiler::Node* CreatePromise(CodeStubAssembler* a, compiler::Node* context) {

[caitp, 2016/12/12 23:41:58]

There are _a lot_ of builtins that need to be able to allocate and initialize
JSPromises. Can we move these helpers to CodeStubAssembler please?

For less-widely needed helpers, I suggest subclassing CodeStubAssembler with
PromiseBuiltinAssembler or something, and installing the helpers directly on it.
Then, you can use the TF_BUILTIN() thing to generate builtins with the
subclassed assembler, and avoid passing a pointer to the assembler everywhere.
IMO it's much easier to read.

Other than those nits, refactoring looks fine to me

+  typedef compiler::Node Node;
+
+  Node* const native_context = a->LoadNativeContext(context);
+  Node* const promise_fun =
+      a->LoadContextElement(native_context, Context::PROMISE_FUNCTION_INDEX);
+  Node* const initial_map =
+      a->LoadObjectField(promise_fun, JSFunction::kPrototypeOrInitialMapOffset);
+  Node* const instance = a->AllocateJSObjectFromMap(initial_map);
+
+  return instance;
+}
+
+}  // namespace
+
 void PromiseInit(CodeStubAssembler* a, compiler::Node* promise,
                  compiler::Node* status, compiler::Node* result) {
   CSA_ASSERT(a, a->TaggedIsSmi(status));
   a->StoreObjectField(promise, JSPromise::kStatusOffset, status);
   a->StoreObjectField(promise, JSPromise::kResultOffset, result);
   a->StoreObjectField(promise, JSPromise::kFlagsOffset, a->SmiConstant(0));
 }
 
 void Builtins::Generate_PromiseConstructor(
     compiler::CodeAssemblerState* state) {
@@ skipping 27 matching lines @@
 
   a.Branch(a.WordEqual(promise_fun, new_target), &if_targetisnotmodified,
            &if_targetismodified);
 
   Variable var_result(&a, MachineRepresentation::kTagged),
       var_reject_call(&a, MachineRepresentation::kTagged),
       var_reason(&a, MachineRepresentation::kTagged);
 
   a.Bind(&if_targetisnotmodified);
   {
-    Node* const initial_map = a.LoadObjectField(
-        promise_fun, JSFunction::kPrototypeOrInitialMapOffset);
-
-    Node* const instance = a.AllocateJSObjectFromMap(initial_map);
+    Node* const instance = CreatePromise(&a, context);
     var_result.Bind(instance);
     a.Goto(&init);
   }
 
   a.Bind(&if_targetismodified);
   {
     Callable fast_new_object_stub = CodeFactory::FastNewObject(isolate);
     Node* const instance =
         a.CallStub(fast_new_object_stub, context, promise_fun, new_target);
 
@@ skipping 68 matching lines @@
     a.Return(a.UndefinedConstant());  // Never reached.
   }
 }
 
 void Builtins::Generate_PromiseInternalConstructor(
     compiler::CodeAssemblerState* state) {
   typedef compiler::Node Node;
   CodeStubAssembler a(state);
 
   Node* const context = a.Parameter(3);
-  Node* const native_context = a.LoadNativeContext(context);
-  Node* const promise_fun =
-      a.LoadContextElement(native_context, Context::PROMISE_FUNCTION_INDEX);
-  Node* const initial_map =
-      a.LoadObjectField(promise_fun, JSFunction::kPrototypeOrInitialMapOffset);
-  Node* const instance = a.AllocateJSObjectFromMap(initial_map);
-
+  Node* const instance = CreatePromise(&a, context);
   PromiseInit(&a, instance, a.SmiConstant(kPromisePending),
               a.UndefinedConstant());
   a.Return(instance);
 }
 
 void Builtins::Generate_PromiseCreateAndSet(
     compiler::CodeAssemblerState* state) {
   typedef compiler::Node Node;
   CodeStubAssembler a(state);
 
   Node* const status = a.Parameter(1);
   Node* const result = a.Parameter(2);
   Node* const context = a.Parameter(5);
-  Node* const native_context = a.LoadNativeContext(context);
 
-  Node* const promise_fun =
-      a.LoadContextElement(native_context, Context::PROMISE_FUNCTION_INDEX);
-  Node* const initial_map =
-      a.LoadObjectField(promise_fun, JSFunction::kPrototypeOrInitialMapOffset);
-  Node* const instance = a.AllocateJSObjectFromMap(initial_map);
-
+  Node* const instance = CreatePromise(&a, context);
   PromiseInit(&a, instance, status, result);
   a.Return(instance);
 }
 
 namespace {
 
 compiler::Node* ThrowIfNotJSReceiver(CodeStubAssembler* a, Isolate* isolate,
                                      compiler::Node* context,
                                      compiler::Node* value,
                                      MessageTemplate::Template msg_template) {
@@ skipping 650 matching lines @@
 
   Label out(&a);
   InternalResolvePromise(&a, context, promise, result, &out);
 
   a.Bind(&out);
   a.Return(a.UndefinedConstant());
 }
 
 }  // namespace internal
 }  // namespace v8