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LibJS: Remove dedicated iterator result instructions in favor of GetById

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When iterating over an iterable, we get back a JS object with the fields
"value" and "done".

Before this change, we've had two dedicated instructions for retrieving
the two fields: IteratorResultValue and IteratorResultDone. These had no
fast path whatsoever and just did a generic [[Get]] access to fetch the
corresponding property values.

By replacing the instructions with GetById("value") and GetById("done"),
they instantly get caching and JIT fast paths for free, making iterating
over iterables much faster. :^)

26% speed-up on this microbenchmark:

    function go(a) {
        for (const p of a) {
        }
    }
    const a = [];
    a.length = 1_000_000;
    go(a);
This commit is contained in:
Andreas Kling 2023-12-07 16:12:12 +01:00
parent 8d68f94282
commit 350e6c54d7
8 changed files with 26 additions and 96 deletions
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26
Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp
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@ -1344,7 +1344,7 @@ static Bytecode::CodeGenerationErrorOr<void> generate_array_binding_pattern_byte
generator.emit<Bytecode::Op::IteratorNext>();
generator.emit<Bytecode::Op::Store>(temp_iterator_result_reg);
generator.emit<Bytecode::Op::IteratorResultDone>();
generator.emit_iterator_complete();
generator.emit<Bytecode::Op::Store>(is_iterator_exhausted_register);
// We still have to check for exhaustion here. If the iterator is exhausted,
@ -1358,7 +1358,7 @@ static Bytecode::CodeGenerationErrorOr<void> generate_array_binding_pattern_byte
// Get the next value in the iterator
generator.emit<Bytecode::Op::Load>(temp_iterator_result_reg);
generator.emit<Bytecode::Op::IteratorResultValue>();
generator.emit_iterator_value();
auto& create_binding_block = generator.make_block();
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { create_binding_block });
@ -1798,7 +1798,7 @@ Bytecode::CodeGenerationErrorOr<void> YieldExpression::generate_bytecode(Bytecod
generator.emit<Bytecode::Op::Store>(inner_result_register);
// iv. Let done be ? IteratorComplete(innerResult).
generator.emit<Bytecode::Op::IteratorResultDone>();
generator.emit_iterator_complete();
// v. If done is true, then
auto& type_is_normal_done_block = generator.make_block();
@ -1811,7 +1811,7 @@ Bytecode::CodeGenerationErrorOr<void> YieldExpression::generate_bytecode(Bytecod
// 1. Return ? IteratorValue(innerResult).
generator.emit<Bytecode::Op::Load>(inner_result_register);
generator.emit<Bytecode::Op::IteratorResultValue>();
generator.emit_iterator_value();
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { loop_end_block });
generator.switch_to_basic_block(type_is_normal_not_done_block);
@ -1822,7 +1822,7 @@ Bytecode::CodeGenerationErrorOr<void> YieldExpression::generate_bytecode(Bytecod
// FIXME: Yield currently only accepts a Value, not an object conforming to the IteratorResult interface, so we have to do an observable lookup of `value` here.
// This only matters for non-async generators.
generator.emit<Bytecode::Op::IteratorResultValue>();
generator.emit_iterator_value();
generate_yield(generator, Bytecode::Label { continuation_block }, received_completion_register, received_completion_type_register, received_completion_value_register, type_identifier, value_identifier, AwaitBeforeYield::No);
@ -1871,7 +1871,7 @@ Bytecode::CodeGenerationErrorOr<void> YieldExpression::generate_bytecode(Bytecod
generator.emit<Bytecode::Op::Store>(inner_result_register);
// 5. Let done be ? IteratorComplete(innerResult).
generator.emit<Bytecode::Op::IteratorResultDone>();
generator.emit_iterator_complete();
// 6. If done is true, then
auto& type_is_throw_done_block = generator.make_block();
@ -1884,7 +1884,7 @@ Bytecode::CodeGenerationErrorOr<void> YieldExpression::generate_bytecode(Bytecod
// a. Return ? IteratorValue(innerResult).
generator.emit<Bytecode::Op::Load>(inner_result_register);
generator.emit<Bytecode::Op::IteratorResultValue>();
generator.emit_iterator_value();
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { loop_end_block });
generator.switch_to_basic_block(type_is_throw_not_done_block);
@ -1895,7 +1895,7 @@ Bytecode::CodeGenerationErrorOr<void> YieldExpression::generate_bytecode(Bytecod
// FIXME: Yield currently only accepts a Value, not an object conforming to the IteratorResult interface, so we have to do an observable lookup of `value` here.
// This only matters for non-async generators.
generator.emit<Bytecode::Op::IteratorResultValue>();
generator.emit_iterator_value();
generate_yield(generator, Bytecode::Label { continuation_block }, received_completion_register, received_completion_type_register, received_completion_value_register, type_identifier, value_identifier, AwaitBeforeYield::No);
@ -1970,7 +1970,7 @@ Bytecode::CodeGenerationErrorOr<void> YieldExpression::generate_bytecode(Bytecod
generator.emit<Bytecode::Op::Store>(inner_return_result_register);
// vii. Let done be ? IteratorComplete(innerReturnResult).
generator.emit<Bytecode::Op::IteratorResultDone>();
generator.emit_iterator_complete();
// viii. If done is true, then
auto& type_is_return_done_block = generator.make_block();
@ -1983,7 +1983,7 @@ Bytecode::CodeGenerationErrorOr<void> YieldExpression::generate_bytecode(Bytecod
// 1. Let value be ? IteratorValue(innerReturnResult).
generator.emit<Bytecode::Op::Load>(inner_result_register);
generator.emit<Bytecode::Op::IteratorResultValue>();
generator.emit_iterator_value();
// 2. Return Completion Record { [[Type]]: return, [[Value]]: value, [[Target]]: empty }.
generator.perform_needed_unwinds<Bytecode::Op::Yield>();
@ -1997,7 +1997,7 @@ Bytecode::CodeGenerationErrorOr<void> YieldExpression::generate_bytecode(Bytecod
// FIXME: Yield currently only accepts a Value, not an object conforming to the IteratorResult interface, so we have to do an observable lookup of `value` here.
// This only matters for non-async generators.
generator.emit<Bytecode::Op::IteratorResultValue>();
generator.emit_iterator_value();
generate_yield(generator, Bytecode::Label { continuation_block }, received_completion_register, received_completion_type_register, received_completion_value_register, type_identifier, value_identifier, AwaitBeforeYield::No);
@ -2825,8 +2825,8 @@ static Bytecode::CodeGenerationErrorOr<void> for_in_of_body_evaluation(Bytecode:
// d. Let done be ? IteratorComplete(nextResult).
auto iterator_result_register = generator.allocate_register();
generator.emit<Bytecode::Op::Store>(iterator_result_register);
generator.emit_iterator_complete();
generator.emit<Bytecode::Op::IteratorResultDone>();
// e. If done is true, return V.
auto& loop_continue = generator.make_block();
generator.emit<Bytecode::Op::JumpConditional>(
@ -2836,7 +2836,7 @@ static Bytecode::CodeGenerationErrorOr<void> for_in_of_body_evaluation(Bytecode:
// f. Let nextValue be ? IteratorValue(nextResult).
generator.emit<Bytecode::Op::Load>(iterator_result_register);
generator.emit<Bytecode::Op::IteratorResultValue>();
generator.emit_iterator_value();
// g. If lhsKind is either assignment or varBinding, then
if (head_result.lhs_kind != LHSKind::LexicalBinding) {