src/builtins/builtins-async-function-gen.cc

// Copyright 2017 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-async-gen.h"
#include "src/builtins/builtins-utils-gen.h"
#include "src/builtins/builtins.h"
#include "src/code-stub-assembler.h"
#include "src/objects-inl.h"

namespace v8 {
namespace internal {

class AsyncFunctionBuiltinsAssembler : public AsyncBuiltinsAssembler {
 public:
  explicit AsyncFunctionBuiltinsAssembler(compiler::CodeAssemblerState* state)
      : AsyncBuiltinsAssembler(state) {}

 protected:
  void AsyncFunctionAwait(Node* const context, Node* const generator,
                          Node* const awaited, Node* const outer_promise,
                          const bool is_predicted_as_caught);

  void AsyncFunctionAwaitResumeClosure(
      Node* const context, Node* const sent_value,
      JSGeneratorObject::ResumeMode resume_mode);
};

namespace {

// Describe fields of Context associated with AsyncFunctionAwait resume
// closures.
// TODO(jgruber): Refactor to reuse code for upcoming async-generators.
class AwaitContext {
 public:
  enum Fields { kGeneratorSlot = Context::MIN_CONTEXT_SLOTS, kLength };
};

}  // anonymous namespace

void AsyncFunctionBuiltinsAssembler::AsyncFunctionAwaitResumeClosure(
    Node* context, Node* sent_value,
    JSGeneratorObject::ResumeMode resume_mode) {
  DCHECK(resume_mode == JSGeneratorObject::kNext ||
         resume_mode == JSGeneratorObject::kThrow);

  Node* const generator =
      LoadContextElement(context, AwaitContext::kGeneratorSlot);
  CSA_SLOW_ASSERT(this, HasInstanceType(generator, JS_GENERATOR_OBJECT_TYPE));

  // Inline version of GeneratorPrototypeNext / GeneratorPrototypeReturn with
  // unnecessary runtime checks removed.
  // TODO(jgruber): Refactor to reuse code from builtins-generator.cc.

  // Ensure that the generator is neither closed nor running.
  CSA_SLOW_ASSERT(
      this,
      SmiGreaterThan(
          LoadObjectField(generator, JSGeneratorObject::kContinuationOffset),
          SmiConstant(JSGeneratorObject::kGeneratorClosed)));

  // Resume the {receiver} using our trampoline.
  Callable callable = CodeFactory::ResumeGenerator(isolate());
  CallStub(callable, context, sent_value, generator, SmiConstant(resume_mode),
           SmiConstant(static_cast<int>(SuspendFlags::kGeneratorAwait)));

  // The resulting Promise is a throwaway, so it doesn't matter what it
  // resolves to. What is important is that we don't end up keeping the
  // whole chain of intermediate Promises alive by returning the return value
  // of ResumeGenerator, as that would create a memory leak.
}

TF_BUILTIN(AsyncFunctionAwaitRejectClosure, AsyncFunctionBuiltinsAssembler) {
  CSA_ASSERT_JS_ARGC_EQ(this, 1);
  Node* const sentError = Parameter(Descriptor::kSentError);
  Node* const context = Parameter(Descriptor::kContext);

  AsyncFunctionAwaitResumeClosure(context, sentError,
                                  JSGeneratorObject::kThrow);
  Return(UndefinedConstant());
}

TF_BUILTIN(AsyncFunctionAwaitResolveClosure, AsyncFunctionBuiltinsAssembler) {
  CSA_ASSERT_JS_ARGC_EQ(this, 1);
  Node* const sentValue = Parameter(Descriptor::kSentValue);
  Node* const context = Parameter(Descriptor::kContext);

  AsyncFunctionAwaitResumeClosure(context, sentValue, JSGeneratorObject::kNext);
  Return(UndefinedConstant());
}

// ES#abstract-ops-async-function-await
// AsyncFunctionAwait ( value )
// Shared logic for the core of await. The parser desugars
//   await awaited
// into
//   yield AsyncFunctionAwait{Caught,Uncaught}(.generator, awaited, .promise)
// The 'awaited' parameter is the value; the generator stands in
// for the asyncContext, and .promise is the larger promise under
// construction by the enclosing async function.
void AsyncFunctionBuiltinsAssembler::AsyncFunctionAwait(
    Node* const context, Node* const generator, Node* const awaited,
    Node* const outer_promise, const bool is_predicted_as_caught) {
  CSA_SLOW_ASSERT(this, HasInstanceType(generator, JS_GENERATOR_OBJECT_TYPE));
  CSA_SLOW_ASSERT(this, HasInstanceType(outer_promise, JS_PROMISE_TYPE));

  ContextInitializer init_closure_context = [&](Node* context) {
    StoreContextElementNoWriteBarrier(context, AwaitContext::kGeneratorSlot,
                                      generator);
  };

  // TODO(jgruber): AsyncBuiltinsAssembler::Await currently does not reuse
  // the awaited promise if it is already a promise. Reuse is non-spec compliant
  // but part of our old behavior gives us a couple of percent
  // performance boost.
  // TODO(jgruber): Use a faster specialized version of
  // InternalPerformPromiseThen.

  Node* const result = Await(
      context, generator, awaited, outer_promise, AwaitContext::kLength,
      init_closure_context, Context::ASYNC_FUNCTION_AWAIT_RESOLVE_SHARED_FUN,
      Context::ASYNC_FUNCTION_AWAIT_REJECT_SHARED_FUN, is_predicted_as_caught);

  Return(result);
}

// Called by the parser from the desugaring of 'await' when catch
// prediction indicates that there is a locally surrounding catch block.
TF_BUILTIN(AsyncFunctionAwaitCaught, AsyncFunctionBuiltinsAssembler) {
  CSA_ASSERT_JS_ARGC_EQ(this, 3);
  Node* const generator = Parameter(Descriptor::kGenerator);
  Node* const awaited = Parameter(Descriptor::kAwaited);
  Node* const outer_promise = Parameter(Descriptor::kOuterPromise);
  Node* const context = Parameter(Descriptor::kContext);

  static const bool kIsPredictedAsCaught = true;

  AsyncFunctionAwait(context, generator, awaited, outer_promise,
                     kIsPredictedAsCaught);
}

// Called by the parser from the desugaring of 'await' when catch
// prediction indicates no locally surrounding catch block.
TF_BUILTIN(AsyncFunctionAwaitUncaught, AsyncFunctionBuiltinsAssembler) {
  CSA_ASSERT_JS_ARGC_EQ(this, 3);
  Node* const generator = Parameter(Descriptor::kGenerator);
  Node* const awaited = Parameter(Descriptor::kAwaited);
  Node* const outer_promise = Parameter(Descriptor::kOuterPromise);
  Node* const context = Parameter(Descriptor::kContext);

  static const bool kIsPredictedAsCaught = false;

  AsyncFunctionAwait(context, generator, awaited, outer_promise,
                     kIsPredictedAsCaught);
}

TF_BUILTIN(AsyncFunctionPromiseCreate, AsyncFunctionBuiltinsAssembler) {
  CSA_ASSERT_JS_ARGC_EQ(this, 0);
  Node* const context = Parameter(Descriptor::kContext);

  Node* const promise = AllocateAndInitJSPromise(context);

  Label if_is_debug_active(this, Label::kDeferred);
  GotoIf(IsDebugActive(), &if_is_debug_active);

  // Early exit if debug is not active.
  Return(promise);

  BIND(&if_is_debug_active);
  {
    // Push the Promise under construction in an async function on
    // the catch prediction stack to handle exceptions thrown before
    // the first await.
    // Assign ID and create a recurring task to save stack for future
    // resumptions from await.
    CallRuntime(Runtime::kDebugAsyncFunctionPromiseCreated, context, promise);
    Return(promise);
  }
}

TF_BUILTIN(AsyncFunctionPromiseRelease, AsyncFunctionBuiltinsAssembler) {
  CSA_ASSERT_JS_ARGC_EQ(this, 1);
  Node* const promise = Parameter(Descriptor::kPromise);
  Node* const context = Parameter(Descriptor::kContext);

  Label if_is_debug_active(this, Label::kDeferred);
  GotoIf(IsDebugActive(), &if_is_debug_active);

  // Early exit if debug is not active.
  Return(UndefinedConstant());

  BIND(&if_is_debug_active);
  {
    // Pop the Promise under construction in an async function on
    // from catch prediction stack.
    CallRuntime(Runtime::kDebugPopPromise, context);
    Return(promise);
  }
}

}  // namespace internal
}  // namespace v8