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Code Issues Projects Releases Packages Wiki Activity Actions 9

LibJS: Optimize array destructuring assignment for builtin iterators

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...by avoiding `{ value, done }` iterator result value allocation. This
change applies the same otimization 81b6a11 added for `for..in` and
`for..of`.

Makes following micro benchmark go 22% faster on my computer:
```js
function f() {
    const arr = [];
    for (let i = 0; i < 10_000_000; i++) {
        arr.push([i]);
    }
    let sum = 0;
    for (let [i] of arr) {
        sum += i;
    }
}

f();
```
This commit is contained in:
Aliaksandr Kalenik 2025-05-01 16:05:24 +03:00 • committed by Alexander Kalenik
commit 60bd5012fe
Notes: github-actions[bot] 2025-05-01 13:58:54 +00:00
4 changed files with 11 additions and 15 deletions
Download patch file Download diff file Expand all files Collapse all files

10
Libraries/LibJS/Bytecode/ASTCodegen.cpp
View file

@ -1504,8 +1504,8 @@ static Bytecode::CodeGenerationErrorOr<void> generate_array_binding_pattern_byte
generator.switch_to_basic_block(iterator_is_not_exhausted_block);
}
generator.emit<Bytecode::Op::IteratorNext>(temp_iterator_result, iterator);
generator.emit_iterator_complete(is_iterator_exhausted, temp_iterator_result);
auto value = generator.allocate_register();
generator.emit<Bytecode::Op::IteratorNextUnpack>(value, is_iterator_exhausted, iterator);
// We still have to check for exhaustion here. If the iterator is exhausted,
// we need to bail before trying to get the value
@ -1517,10 +1517,6 @@ static Bytecode::CodeGenerationErrorOr<void> generate_array_binding_pattern_byte
generator.switch_to_basic_block(no_bail_block);
// Get the next value in the iterator
auto value = generator.allocate_register();
generator.emit_iterator_value(value, temp_iterator_result);
auto& create_binding_block = generator.make_block();
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { create_binding_block });
@ -3187,7 +3183,7 @@ static Bytecode::CodeGenerationErrorOr<Optional<ScopedOperand>> for_in_of_body_e
auto done = generator.allocate_register();
if (iterator_kind == IteratorHint::Sync) {
generator.emit<Bytecode::Op::ForOfNext>(next_value, done, *head_result.iterator);
generator.emit<Bytecode::Op::IteratorNextUnpack>(next_value, done, *head_result.iterator);
auto& loop_continue = generator.make_block();
generator.emit_jump_if(

2
Libraries/LibJS/Bytecode/Instruction.h
View file

@ -51,7 +51,6 @@
O(EnterObjectEnvironment) \
O(EnterUnwindContext) \
O(Exp) \
O(ForOfNext) \
O(GetById) \
O(GetByIdWithThis) \
O(GetByValue) \
@ -81,6 +80,7 @@
O(InstanceOf) \
O(IteratorClose) \
O(IteratorNext) \
O(IteratorNextUnpack) \
O(IteratorToArray) \
O(Jump) \
O(JumpFalse) \

8
Libraries/LibJS/Bytecode/Interpreter.cpp
View file

@ -612,7 +612,6 @@ FLATTEN_ON_CLANG void Interpreter::run_bytecode(size_t entry_point)
HANDLE_INSTRUCTION_WITHOUT_EXCEPTION_CHECK(Dump);
HANDLE_INSTRUCTION(EnterObjectEnvironment);
HANDLE_INSTRUCTION(Exp);
HANDLE_INSTRUCTION(ForOfNext);
HANDLE_INSTRUCTION(GetById);
HANDLE_INSTRUCTION(GetByIdWithThis);
HANDLE_INSTRUCTION(GetByValue);
@ -642,6 +641,7 @@ FLATTEN_ON_CLANG void Interpreter::run_bytecode(size_t entry_point)
HANDLE_INSTRUCTION(InstanceOf);
HANDLE_INSTRUCTION(IteratorClose);
HANDLE_INSTRUCTION(IteratorNext);
HANDLE_INSTRUCTION(IteratorNextUnpack);
HANDLE_INSTRUCTION(IteratorToArray);
HANDLE_INSTRUCTION_WITHOUT_EXCEPTION_CHECK(LeaveFinally);
HANDLE_INSTRUCTION_WITHOUT_EXCEPTION_CHECK(LeaveLexicalEnvironment);
@ -2982,7 +2982,7 @@ ThrowCompletionOr<void> IteratorNext::execute_impl(Bytecode::Interpreter& interp
return {};
}
ThrowCompletionOr<void> ForOfNext::execute_impl(Bytecode::Interpreter& interpreter) const
ThrowCompletionOr<void> IteratorNextUnpack::execute_impl(Bytecode::Interpreter& interpreter) const
{
auto& vm = interpreter.vm();
auto& iterator_record = static_cast<IteratorRecord&>(interpreter.get(m_iterator_record).as_cell());
@ -3777,9 +3777,9 @@ ByteString IteratorNext::to_byte_string_impl(Executable const& executable) const
format_operand("iterator_record"sv, m_iterator_record, executable));
}
ByteString ForOfNext::to_byte_string_impl(Executable const& executable) const
ByteString IteratorNextUnpack::to_byte_string_impl(Executable const& executable) const
{
return ByteString::formatted("ForOfNext {}, {}, {}",
return ByteString::formatted("IteratorNextUnpack {}, {}, {}",
format_operand("dst_value"sv, m_dst_value, executable),
format_operand("dst_done"sv, m_dst_done, executable),
format_operand("iterator_record"sv, m_iterator_record, executable));

6
Libraries/LibJS/Bytecode/Op.h
View file

@ -2721,10 +2721,10 @@ private:
Operand m_iterator_record;
};
class ForOfNext final : public Instruction {
class IteratorNextUnpack final : public Instruction {
public:
ForOfNext(Operand dst_value, Operand dst_done, Operand iterator_record)
: Instruction(Type::ForOfNext)
IteratorNextUnpack(Operand dst_value, Operand dst_done, Operand iterator_record)
: Instruction(Type::IteratorNextUnpack)
, m_dst_value(dst_value)
, m_dst_done(dst_done)
, m_iterator_record(iterator_record)