Async/await Promise dependency graph

src/parsing/parser.cc

 // Copyright 2012 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/parsing/parser.h"
 
 #include <memory>
 
 #include "src/api.h"
 #include "src/ast/ast-expression-rewriter.h"
@@ skipping 4852 matching lines @@
   // yield %AsyncFunctionAwait(.generator_object, <operand>)
   Variable* generator_object_variable =
       function_state_->generator_object_variable();
 
   // If generator_object_variable is null,
   if (!generator_object_variable) return value;
 
   const int nopos = kNoSourcePosition;
 
   Variable* temp_var = NewTemporary(ast_value_factory()->empty_string());
   VariableProxy* temp_proxy = factory()->NewVariableProxy(temp_var);

[adamk, 2016/09/08 22:07:31]

Not new to your code, but It seems very wrong that this proxy is referenced in
three places.

[Dan Ehrenberg, 2016/09/08 22:34:46]

I believe we can eliminate the second and third usage sites; will do in a
follow-on patch.

   Block* do_block = factory()->NewBlock(nullptr, 2, false, nopos);
 
   // Wrap value evaluation to provide a break location.
   Expression* value_assignment =
       factory()->NewAssignment(Token::ASSIGN, temp_proxy, value, nopos);
   do_block->statements()->Add(
       factory()->NewExpressionStatement(value_assignment, value->position()),
       zone());
 
   ZoneList<Expression*>* async_function_await_args =
-      new (zone()) ZoneList<Expression*>(2, zone());
+      new (zone()) ZoneList<Expression*>(3, zone());
   Expression* generator_object =
       factory()->NewVariableProxy(generator_object_variable);
   async_function_await_args->Add(generator_object, zone());
   async_function_await_args->Add(temp_proxy, zone());
+  async_function_await_args->Add(BuildDotPromise(), zone());
   Expression* async_function_await =
       factory()->NewCallRuntime(Context::ASYNC_FUNCTION_AWAIT_CAUGHT_INDEX,
                                 async_function_await_args, nopos);
   // Wrap await to provide a break location between value evaluation and yield.
   Expression* await_assignment = factory()->NewAssignment(
       Token::ASSIGN, temp_proxy, async_function_await, nopos);

[adamk, 2016/09/08 22:07:31]

As noted in the JS file, you're just assigning undefined here.

[Dan Ehrenberg, 2016/09/08 22:34:46]

I believe it's assigning .promise, but there's not much point to that; I can
just say that the value of the do-expression is .promise. Will clean up in the
same follow-on patch.

   do_block->statements()->Add(
       factory()->NewExpressionStatement(await_assignment, await_pos), zone());
   Expression* do_expr = factory()->NewDoExpression(do_block, temp_var, nopos);
 
   generator_object = factory()->NewVariableProxy(generator_object_variable);
   return factory()->NewYield(generator_object, do_expr, nopos,
                              Yield::kOnExceptionRethrow);
 }
 
 class NonPatternRewriter : public AstExpressionRewriter {
@@ skipping 1180 matching lines @@
   node->Print(Isolate::Current());
 }
 #endif  // DEBUG
 
 #undef CHECK_OK
 #undef CHECK_OK_VOID
 #undef CHECK_FAILED
 
 }  // namespace internal
 }  // namespace v8