dan/oxc
1
0
Fork 0
mirror of https://github.com/danbulant/oxc synced 2026-05-24 12:21:58 +00:00
Code Issues Projects Releases Packages Wiki Activity Actions

perf(parser): byte_search macro always unroll main loop (#2439)

Browse source 
Refactor `byte_search!` macro to move logic out of the main loop. This ensures the compiler unrolls the loop.

This speeds up lexing single-line comments by 20%-25% on the benchmarks which contain enough comments for the change to register. Presumably the loop wasn't unrolled previously.

The code required to do this is a little odd. It adds an extra `loop {}` which always exits on the first turn (so not really a useful loop), but is required to be able to use `break` to exit that "loop", making 2 different paths for (1) matching byte found and (2) `for` loop completed without finding any match.

This is only way I could find to produce this behavior without using a macro. Is there a more "normal" way to get the same logic?
This commit is contained in:
overlookmotel 2024-02-20 02:39:52 +00:00 committed by GitHub
parent 27b2c212c4
commit 996a9d27eb
No known key found for this signature in database
GPG key ID: B5690EEEBB952194
1 changed files with 41 additions and 30 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

71
crates/oxc_parser/src/lexer/search.rs
View file

@ -495,45 +495,56 @@ macro_rules! byte_search {
let mut $pos = $start;
#[allow(unused_unsafe)] // Silence warnings if macro called in unsafe code
loop {
'outer: loop {
#[allow(clippy::redundant_else)]
if $pos.addr() <= $lexer.source.end_for_batch_search_addr() {
// Search a batch of `SEARCH_BATCH_SIZE` bytes.
// The compiler unrolls this loop.
//
// `'inner: loop {}` is not a real loop - it always exits on first turn.
// Only using `loop {}` so that can use `break 'inner` to get out of it.
// This allows complex logic of `$should_continue` and `$match_handler` to be
// outside the `for` loop, keeping it as minimal as possible, to encourage
// compiler to unroll it.
//
// SAFETY:
// `$pos.addr() > lexer.source.end_for_batch_search_addr()` check above ensures there are
// at least `SEARCH_BATCH_SIZE` bytes remaining in `lexer.source`.
// `$pos.addr() <= lexer.source.end_for_batch_search_addr()` check above ensures
// there are at least `SEARCH_BATCH_SIZE` bytes remaining in `lexer.source`.
// So calls to `$pos.read()` and `$pos.add(1)` in this loop cannot go out of bounds.
for _i in 0..crate::lexer::search::SEARCH_BATCH_SIZE {
// SAFETY: `$pos` cannot go out of bounds in this loop (see above).
let $match_byte = unsafe { $pos.read() };
if $table.matches($match_byte) {
// Found match.
// Check if should continue.
{
let $continue_byte = $match_byte;
if $should_continue {
// Not a match after all - continue searching.
// SAFETY: `pos` is not at end of source, so safe to advance 1 byte.
// See above about UTF-8 character boundaries invariant.
$pos = unsafe { $pos.add(1) };
continue;
}
let $match_byte = 'inner: loop {
for _i in 0..crate::lexer::search::SEARCH_BATCH_SIZE {
// SAFETY: `$pos` cannot go out of bounds in this loop (see above)
let byte = unsafe { $pos.read() };
if $table.matches(byte) {
break 'inner byte;
}
// Advance `lexer.source`'s position up to `$pos`, consuming unmatched bytes.
// SAFETY: See above about UTF-8 character boundaries invariant.
$lexer.source.set_position($pos);
let $match_start = $start;
return $match_handler;
// No match - continue searching batch.
// SAFETY: `$pos` cannot go out of bounds in this loop (see above).
// Also see above about UTF-8 character boundaries invariant.
$pos = unsafe { $pos.add(1) };
}
// No match in batch - search next batch
continue 'outer;
};
// No match - continue searching
// SAFETY: `$pos` cannot go out of bounds in this loop (see above).
// Also see above about UTF-8 character boundaries invariant.
$pos = unsafe { $pos.add(1) };
// Found match. Check if should continue.
{
let $continue_byte = $match_byte;
if $should_continue {
// Not a match after all - continue searching.
// SAFETY: `pos` is not at end of source, so safe to advance 1 byte.
// See above about UTF-8 character boundaries invariant.
$pos = unsafe { $pos.add(1) };
continue;
}
}
// No match in batch - loop round and searching next batch
// Advance `lexer.source`'s position up to `$pos`, consuming unmatched bytes.
// SAFETY: See above about UTF-8 character boundaries invariant.
$lexer.source.set_position($pos);
let $match_start = $start;
return $match_handler;
} else {
// Not enough bytes remaining to process as a batch.
// This branch marked `#[cold]` as should be very uncommon in normal-length JS files.