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LibJS: Align codegen AwaitExpressions to YieldExpressions

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We use generators in bytecode to approximate async functions, but the
code generated by AwaitExpressions did not have the value processing
paths that Yield requires, eg the `generator.throw()` path, which is
used by AsyncFunctionDriverWrapper to signal Promise rejections.
This commit is contained in:
Hendiadyoin1 2022-12-25 17:15:29 +01:00 • committed by Linus Groh
parent 1f6a0ef6e0
commit de514f29ad
4 changed files with 47 additions and 3 deletions
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39
Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp
View file

@ -2369,12 +2369,49 @@ Bytecode::CodeGenerationErrorOr<void> AwaitExpression::generate_bytecode(Bytecod
{
VERIFY(generator.is_in_async_function());
// Transform `await expr` to `yield expr`
// Transform `await expr` to `yield expr`, see AsyncFunctionDriverWrapper
// For that we just need to copy most of the code from YieldExpression
auto received_completion_register = generator.allocate_register();
auto received_completion_type_register = generator.allocate_register();
auto received_completion_value_register = generator.allocate_register();
auto type_identifier = generator.intern_identifier("type");
auto value_identifier = generator.intern_identifier("value");
TRY(m_argument->generate_bytecode(generator));
auto& continuation_block = generator.make_block();
generator.emit<Bytecode::Op::Yield>(Bytecode::Label { continuation_block });
generator.switch_to_basic_block(continuation_block);
// The accumulator is set to an object, for example: { "type": 1 (normal), value: 1337 }
generator.emit<Bytecode::Op::Store>(received_completion_register);
generator.emit<Bytecode::Op::GetById>(type_identifier);
generator.emit<Bytecode::Op::Store>(received_completion_type_register);
generator.emit<Bytecode::Op::Load>(received_completion_register);
generator.emit<Bytecode::Op::GetById>(value_identifier);
generator.emit<Bytecode::Op::Store>(received_completion_value_register);
auto& normal_completion_continuation_block = generator.make_block();
auto& throw_value_block = generator.make_block();
generator.emit<Bytecode::Op::LoadImmediate>(Value(to_underlying(Completion::Type::Normal)));
generator.emit<Bytecode::Op::StrictlyEquals>(received_completion_type_register);
generator.emit<Bytecode::Op::JumpConditional>(
Bytecode::Label { normal_completion_continuation_block },
Bytecode::Label { throw_value_block });
// Simplification: The only abrupt completion we receive from AsyncFunctionDriverWrapper is Type::Throw
// So we do not need to account for the Type::Return path
generator.switch_to_basic_block(throw_value_block);
generator.emit<Bytecode::Op::Load>(received_completion_value_register);
generator.perform_needed_unwinds<Bytecode::Op::Throw>();
generator.emit<Bytecode::Op::Throw>();
generator.switch_to_basic_block(normal_completion_continuation_block);
generator.emit<Bytecode::Op::Load>(received_completion_value_register);
return {};
}