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deps: fix async await desugaring in V8 #12004

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Mar 27, 2017
+187 −47
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deps: fix async await desugaring in V8 #12004

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2 changes: 1 addition & 1 deletion deps/v8/include/v8-version.h
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Original file line number Diff line number Diff line change
Expand Up @@ -11,7 +11,7 @@
#define V8_MAJOR_VERSION 5
#define V8_MINOR_VERSION 5
#define V8_BUILD_NUMBER 372
#define V8_PATCH_LEVEL 42
#define V8_PATCH_LEVEL 43

// Use 1 for candidates and 0 otherwise.
// (Boolean macro values are not supported by all preprocessors.)
Expand Down
15 changes: 14 additions & 1 deletion deps/v8/src/parsing/parser-base.h
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Expand Up @@ -411,14 +411,23 @@ class ParserBase {
}

void set_promise_variable(typename Types::Variable* variable) {
DCHECK(variable != NULL);
DCHECK_NOT_NULL(variable);
DCHECK(IsAsyncFunction(kind()));
promise_variable_ = variable;
}
typename Types::Variable* promise_variable() const {
return promise_variable_;
}

void set_async_return_variable(typename Types::Variable* variable) {
DCHECK_NOT_NULL(variable);
DCHECK(IsAsyncFunction(kind()));
async_return_variable_ = variable;
}
typename Types::Variable* async_return_variable() const {
return async_return_variable_;
}

const ZoneList<DestructuringAssignment>&
destructuring_assignments_to_rewrite() const {
return destructuring_assignments_to_rewrite_;
Expand Down Expand Up @@ -488,6 +497,8 @@ class ParserBase {
// For async functions, this variable holds a temporary for the Promise
// being created as output of the async function.
Variable* promise_variable_;
Variable* async_return_variable_;
Variable* is_rejection_variable_;

FunctionState** function_state_stack_;
FunctionState* outer_function_state_;
Expand Down Expand Up @@ -1468,6 +1479,8 @@ ParserBase<Impl>::FunctionState::FunctionState(
expected_property_count_(0),
generator_object_variable_(nullptr),
promise_variable_(nullptr),
async_return_variable_(nullptr),
is_rejection_variable_(nullptr),
function_state_stack_(function_state_stack),
outer_function_state_(*function_state_stack),
destructuring_assignments_to_rewrite_(16, scope->zone()),
Expand Down
194 changes: 153 additions & 41 deletions deps/v8/src/parsing/parser.cc
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Expand Up @@ -1701,10 +1701,17 @@ Expression* Parser::RewriteReturn(Expression* return_value, int pos) {
return_value = factory()->NewConditional(is_undefined, ThisExpression(pos),
is_object_conditional, pos);
}

if (is_generator()) {
return_value = BuildIteratorResult(return_value, true);
} else if (is_async_function()) {
return_value = BuildResolvePromise(return_value, return_value->position());
// In an async function,
// return expr;
// is rewritten as
// return .async_return_value = expr;
return_value = factory()->NewAssignment(
Token::ASSIGN, factory()->NewVariableProxy(AsyncReturnVariable()),
return_value, kNoSourcePosition);
}
return return_value;
}
Expand Down Expand Up @@ -2991,72 +2998,168 @@ Block* Parser::BuildParameterInitializationBlock(
return init_block;
}

Block* Parser::BuildRejectPromiseOnExceptionForParameters(Block* inner_block) {
// .promise = %AsyncFunctionPromiseCreate();
// try {
// <inner_block>
// } catch (.catch) {
// return %RejectPromise(.promise, .catch), .promise;
// }
Block* result = factory()->NewBlock(nullptr, 2, true, kNoSourcePosition);
{
// .promise = %AsyncFunctionPromiseCreate();
Expression* create_promise = factory()->NewCallRuntime(
Context::ASYNC_FUNCTION_PROMISE_CREATE_INDEX,
new (zone()) ZoneList<Expression*>(0, zone()), kNoSourcePosition);
Assignment* assign_promise = factory()->NewAssignment(
Token::INIT, factory()->NewVariableProxy(PromiseVariable()),
create_promise, kNoSourcePosition);
Statement* set_promise =
factory()->NewExpressionStatement(assign_promise, kNoSourcePosition);
result->statements()->Add(set_promise, zone());
}
// catch (.catch) {
// return %RejectPromise(.promise, .catch), .promise;
// }
Scope* catch_scope = NewScope(CATCH_SCOPE);
catch_scope->set_is_hidden();
Variable* catch_variable =
catch_scope->DeclareLocal(ast_value_factory()->dot_catch_string(), VAR,
kCreatedInitialized, NORMAL_VARIABLE);
Block* catch_block = factory()->NewBlock(nullptr, 1, true, kNoSourcePosition);
{
// return %RejectPromise(.promise, .catch), .promise;
Expression* reject_return_promise = factory()->NewBinaryOperation(
Token::COMMA, BuildRejectPromise(catch_variable),
factory()->NewVariableProxy(PromiseVariable(), kNoSourcePosition),
kNoSourcePosition);
catch_block->statements()->Add(
factory()->NewReturnStatement(reject_return_promise, kNoSourcePosition),
zone());
}
TryStatement* try_catch_statement =
factory()->NewTryCatchStatementForAsyncAwait(inner_block, catch_scope,
catch_variable, catch_block,
kNoSourcePosition);
result->statements()->Add(try_catch_statement, zone());
return result;
}

Block* Parser::BuildRejectPromiseOnException(Block* inner_block, bool* ok) {
// .is_rejection = false;
// .promise = %AsyncFunctionPromiseCreate();
// try {
// <inner_block>
// } catch (.catch) {
// %RejectPromise(.promise, .catch);
// return .promise;
// .is_rejection = true;
// .async_return_value = .catch;
// } finally {
// .is_rejection
// ? %RejectPromise(.promise, .async_return_value)
// : %ResolvePromise(.promise, .async_return_value);
// %AsyncFunctionPromiseRelease(.promise);
// return .promise;
// }
Block* result = factory()->NewBlock(nullptr, 2, true, kNoSourcePosition);
Block* result = factory()->NewBlock(nullptr, 3, true, kNoSourcePosition);

// .promise = %AsyncFunctionPromiseCreate();
Statement* set_promise;
Variable* is_rejection_var =
scope()->NewTemporary(ast_value_factory()->empty_string());
{
// .is_rejection = false;
Assignment* set_is_rejection = factory()->NewAssignment(
Token::INIT, factory()->NewVariableProxy(is_rejection_var),
factory()->NewBooleanLiteral(false, kNoSourcePosition),
kNoSourcePosition);
result->statements()->Add(
factory()->NewExpressionStatement(set_is_rejection, kNoSourcePosition),
zone());
// .promise = %AsyncFunctionPromiseCreate();
Expression* create_promise = factory()->NewCallRuntime(
Context::ASYNC_FUNCTION_PROMISE_CREATE_INDEX,
new (zone()) ZoneList<Expression*>(0, zone()), kNoSourcePosition);
Assignment* assign_promise = factory()->NewAssignment(
Token::INIT, factory()->NewVariableProxy(PromiseVariable()),
create_promise, kNoSourcePosition);
set_promise =
Statement* set_promise =
factory()->NewExpressionStatement(assign_promise, kNoSourcePosition);
result->statements()->Add(set_promise, zone());
}
result->statements()->Add(set_promise, zone());

// catch (.catch) { return %RejectPromise(.promise, .catch), .promise }
// catch (.catch) {
// .is_rejection = true;
// .async_return_value = .catch;
// }
Scope* catch_scope = NewScope(CATCH_SCOPE);
catch_scope->set_is_hidden();
Variable* catch_variable =
catch_scope->DeclareLocal(ast_value_factory()->dot_catch_string(), VAR,
kCreatedInitialized, NORMAL_VARIABLE);
Block* catch_block = factory()->NewBlock(nullptr, 1, true, kNoSourcePosition);

Expression* promise_reject = BuildRejectPromise(
factory()->NewVariableProxy(catch_variable), kNoSourcePosition);
ReturnStatement* return_promise_reject =
factory()->NewReturnStatement(promise_reject, kNoSourcePosition);
catch_block->statements()->Add(return_promise_reject, zone());
{
// .is_rejection = true;
DCHECK_NOT_NULL(is_rejection_var);
Assignment* set_is_rejection = factory()->NewAssignment(
Token::ASSIGN, factory()->NewVariableProxy(is_rejection_var),
factory()->NewBooleanLiteral(true, kNoSourcePosition),
kNoSourcePosition);
catch_block->statements()->Add(
factory()->NewExpressionStatement(set_is_rejection, kNoSourcePosition),
zone());
// .async_return_value = .catch;
Assignment* set_async_return_var = factory()->NewAssignment(
Token::ASSIGN, factory()->NewVariableProxy(AsyncReturnVariable()),
factory()->NewVariableProxy(catch_variable), kNoSourcePosition);
catch_block->statements()->Add(factory()->NewExpressionStatement(
set_async_return_var, kNoSourcePosition),
zone());
}

TryStatement* try_catch_statement =
factory()->NewTryCatchStatementForAsyncAwait(inner_block, catch_scope,
catch_variable, catch_block,
kNoSourcePosition);

// There is no TryCatchFinally node, so wrap it in an outer try/finally
Block* outer_try_block =
factory()->NewBlock(nullptr, 1, true, kNoSourcePosition);
outer_try_block->statements()->Add(try_catch_statement, zone());

// finally { %AsyncFunctionPromiseRelease(.promise) }
// finally {
// .is_rejection
// ? %RejectPromise(.promise, .async_return_value)
// : %ResolvePromise(.promise, .async_return_value);
// %AsyncFunctionPromiseRelease(.promise);
// return .promise;
// }
Block* finally_block =
factory()->NewBlock(nullptr, 1, true, kNoSourcePosition);
{
// .is_rejection
// ? %RejectPromise(.promise, .async_return_value)
// : %ResolvePromise(.promise, .async_return_value);
Expression* resolve_or_reject_promise =
factory()->NewConditional(factory()->NewVariableProxy(is_rejection_var),
BuildRejectPromise(AsyncReturnVariable()),
BuildResolvePromise(), kNoSourcePosition);
finally_block->statements()->Add(
factory()->NewExpressionStatement(resolve_or_reject_promise,
kNoSourcePosition),
zone());
// %AsyncFunctionPromiseRelease(.promise);
ZoneList<Expression*>* args = new (zone()) ZoneList<Expression*>(1, zone());
args->Add(factory()->NewVariableProxy(PromiseVariable()), zone());
Expression* call_promise_release = factory()->NewCallRuntime(
Context::ASYNC_FUNCTION_PROMISE_RELEASE_INDEX, args, kNoSourcePosition);
Statement* promise_release = factory()->NewExpressionStatement(
call_promise_release, kNoSourcePosition);
finally_block->statements()->Add(promise_release, zone());

// return .promise;
Statement* return_promise = factory()->NewReturnStatement(
factory()->NewVariableProxy(PromiseVariable()), kNoSourcePosition);
finally_block->statements()->Add(return_promise, zone());
}

Statement* try_finally_statement = factory()->NewTryFinallyStatement(
outer_try_block, finally_block, kNoSourcePosition);

result->statements()->Add(try_finally_statement, zone());
return result;
}
Expand All @@ -3072,31 +3175,25 @@ Expression* Parser::BuildCreateJSGeneratorObject(int pos, FunctionKind kind) {
pos);
}

Expression* Parser::BuildResolvePromise(Expression* value, int pos) {
// %ResolvePromise(.promise, value), .promise
Expression* Parser::BuildResolvePromise() {
// %ResolvePromise(.promise, .async_return_variable), .promise
ZoneList<Expression*>* args = new (zone()) ZoneList<Expression*>(2, zone());
args->Add(factory()->NewVariableProxy(PromiseVariable()), zone());
args->Add(value, zone());
Expression* call_runtime =
factory()->NewCallRuntime(Context::PROMISE_RESOLVE_INDEX, args, pos);
return factory()->NewBinaryOperation(
Token::COMMA, call_runtime,
factory()->NewVariableProxy(PromiseVariable()), pos);
args->Add(factory()->NewVariableProxy(AsyncReturnVariable()), zone());
return factory()->NewCallRuntime(Context::PROMISE_RESOLVE_INDEX, args,
kNoSourcePosition);
}

Expression* Parser::BuildRejectPromise(Expression* value, int pos) {
// %RejectPromiseNoDebugEvent(.promise, value, true), .promise
Expression* Parser::BuildRejectPromise(Variable* value) {
// %RejectPromiseNoDebugEvent(.promise, .value, true)
// The NoDebugEvent variant disables the additional debug event for the
// rejection since a debug event already happened for the exception that got
// us here.
ZoneList<Expression*>* args = new (zone()) ZoneList<Expression*>(2, zone());
args->Add(factory()->NewVariableProxy(PromiseVariable()), zone());
args->Add(value, zone());
Expression* call_runtime = factory()->NewCallRuntime(
Context::REJECT_PROMISE_NO_DEBUG_EVENT_INDEX, args, pos);
return factory()->NewBinaryOperation(
Token::COMMA, call_runtime,
factory()->NewVariableProxy(PromiseVariable()), pos);
args->Add(factory()->NewVariableProxy(value), zone());
return factory()->NewCallRuntime(
Context::REJECT_PROMISE_NO_DEBUG_EVENT_INDEX, args, kNoSourcePosition);
}

Variable* Parser::PromiseVariable() {
Expand All @@ -3111,6 +3208,19 @@ Variable* Parser::PromiseVariable() {
return promise;
}

Variable* Parser::AsyncReturnVariable() {
// Based on the various compilation paths, there are many different
// code paths which may be the first to access the return value
// temporary. Whichever comes first should create it and stash it in
// the FunctionState.
Variable* async_return = function_state_->async_return_variable();
if (async_return == nullptr) {
async_return = scope()->NewTemporary(ast_value_factory()->empty_string());
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I realize the original CL does that too but do you happen to know why it uses empty_string() instead of undefined_value() or the_hole_value()?

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I agree, there doesn't seem to be a good reason for that. Do you want me to change it for undefined_value()?

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@gsathya ^

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I think the logic is that the initial value won't matter because it's overwritten in all code paths? I'd have used the_hole_value() because its presence traps in many cases and it's something you can unambiguously debug-check since it's never produced by JS code.

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empty_string isn't the value, it's the name of the variable. we never actually lookup the variable by name, so it doesn't need a name.

function_state_->set_async_return_variable(async_return);
}
return async_return;
}

Expression* Parser::BuildInitialYield(int pos, FunctionKind kind) {
Expression* allocation = BuildCreateJSGeneratorObject(pos, kind);
VariableProxy* init_proxy =
Expand Down Expand Up @@ -3235,7 +3345,7 @@ ZoneList<Statement*>* Parser::ParseEagerFunctionBody(

// TODO(littledan): Merge the two rejection blocks into one
if (IsAsyncFunction(kind)) {
init_block = BuildRejectPromiseOnException(init_block, CHECK_OK);
init_block = BuildRejectPromiseOnExceptionForParameters(init_block);
}

DCHECK_NOT_NULL(init_block);
Expand Down Expand Up @@ -4176,14 +4286,16 @@ void Parser::RewriteAsyncFunctionBody(ZoneList<Statement*>* body, Block* block,
// .generator_object = %CreateGeneratorObject();
// BuildRejectPromiseOnException({
// ... block ...
// return %ResolvePromise(.promise, expr), .promise;
// .async_return_var = expr;
// })
// }

return_value = BuildResolvePromise(return_value, return_value->position());
block->statements()->Add(
factory()->NewReturnStatement(return_value, return_value->position()),
zone());
Assignment* set_async_return_var = factory()->NewAssignment(
Token::ASSIGN, factory()->NewVariableProxy(AsyncReturnVariable()),
return_value, kNoSourcePosition);
block->statements()->Add(factory()->NewExpressionStatement(
set_async_return_var, kNoSourcePosition),
zone());
block = BuildRejectPromiseOnException(block, CHECK_OK_VOID);
body->Add(block, zone());
}
Expand Down
9 changes: 5 additions & 4 deletions deps/v8/src/parsing/parser.h
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Expand Up @@ -491,6 +491,7 @@ class Parser : public ParserBase<Parser> {
Block* BuildParameterInitializationBlock(
const ParserFormalParameters& parameters, bool* ok);
Block* BuildRejectPromiseOnException(Block* block, bool* ok);
Block* BuildRejectPromiseOnExceptionForParameters(Block* block);

// Consumes the ending }.
ZoneList<Statement*>* ParseEagerFunctionBody(
Expand Down Expand Up @@ -576,9 +577,10 @@ class Parser : public ParserBase<Parser> {

Expression* BuildInitialYield(int pos, FunctionKind kind);
Expression* BuildCreateJSGeneratorObject(int pos, FunctionKind kind);
Expression* BuildResolvePromise(Expression* value, int pos);
Expression* BuildRejectPromise(Expression* value, int pos);
Expression* BuildResolvePromise();
Expression* BuildRejectPromise(Variable* value);
Variable* PromiseVariable();
Variable* AsyncReturnVariable();

// Generic AST generator for throwing errors from compiled code.
Expression* NewThrowError(Runtime::FunctionId function_id,
Expand Down Expand Up @@ -983,8 +985,7 @@ class Parser : public ParserBase<Parser> {
auto* init_block = BuildParameterInitializationBlock(parameters, ok);
if (!*ok) return;
if (is_async) {
init_block = BuildRejectPromiseOnException(init_block, ok);
if (!*ok) return;
init_block = BuildRejectPromiseOnExceptionForParameters(init_block);
}
if (init_block != nullptr) body->Add(init_block, zone());
}
Expand Down
14 changes: 14 additions & 0 deletions deps/v8/test/mjsunit/regress/regress-5896.js
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@@ -0,0 +1,14 @@
// 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.
// Flags: --allow-natives-syntax
async function foo() {
try {
return 1;
} finally {
return Promise.resolve().then(() => { return 2; });
}
}
foo()
.then(value => { found = value; assertEquals(2, value) })
.catch((e) => { %AbortJS(''+e); });