[promises] Refactor CreatePromise

src/builtins/builtins-promise.cc

Index: src/builtins/builtins-promise.cc
diff --git a/src/builtins/builtins-promise.cc b/src/builtins/builtins-promise.cc
index aa38002218e744fd87a221fe753230a78487f337..e84e50c9771fe3978587737e6a2d3a1a6b257dba 100644
--- a/src/builtins/builtins-promise.cc
+++ b/src/builtins/builtins-promise.cc
@@ -57,6 +57,23 @@ BUILTIN(CreateResolvingFunctions) {
                                                      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));
@@ -104,10 +121,7 @@ void Builtins::Generate_PromiseConstructor(
 
   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);
   }
@@ -196,13 +210,7 @@ void Builtins::Generate_PromiseInternalConstructor(
   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);
@@ -216,14 +224,8 @@ void Builtins::Generate_PromiseCreateAndSet(
   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);
 }