codegen: Optimize multiline comments handling with SIMD processing #13593
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Co-authored-by: Dunqing <[email protected]>
CodSpeed Instrumentation Performance ReportMerging #13593 will not alter performanceComparing Summary
Footnotes |
| // Compiler vectorizes this loop to a few SIMD ops | ||
| let mut contains_line_terminator = false; | ||
| for &byte in chunk { | ||
| if matches!(byte, b'\r' | b'\n' | LS_OR_PS_FIRST_BYTE) { | ||
| contains_line_terminator = true; | ||
| break; | ||
| } | ||
| _ => {} | ||
| } |
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Compiler does not vectorize this. The match is too complicated, and it uses byte-by-byte search.
https://godbolt.org/z/o3hP4cEMv
(for context, if it was using SIMD, it'd be about ~8 instructions, and you'd see instructions using xmm registers)
It's really hard to get the compiler to auto-vectorize cases like this.
The premise of this PR is that it's using SIMD for better perf. But as it's not actually using SIMD, unfortunately I doubt this PR has much value. It may even regress perf as it's searching bytes twice instead of once.
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This works better: https://godbolt.org/z/r795Gsq3T (but still not quite ideal - it should be possible to use only 1 pmovmskb instruction, rather than 3).
| let line = self.text.get_unchecked(..index); | ||
| self.text = self.text.get_unchecked(index + 1..); | ||
| return Some(line); | ||
| // Line terminators will be very rare in most text. So we try to make the search as quick as possible by: |
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I'm not sure if this assumption is correct. Line breaks are fairly common in block comments.
This PR implements a significant performance optimization for multiline comment processing in the codegen by replacing sequential byte iteration with SIMD-friendly chunked processing.
Changes
The
LineTerminatorSplitterincrates/oxc_codegen/src/comment.rshas been optimized to use the same high-performance pattern asprint_str_escaping_script_close_tag:chunks_exact(16)\r,\n,0xE2)Performance Benefits
Implementation Details
The optimization follows the established pattern from
print_str_escaping_script_close_tagwhich already implements this technique for<character detection. Line terminators are rare in most text, making this an ideal candidate for SIMD acceleration.The implementation maintains exact behavioral compatibility - all existing tests pass without modification, ensuring identical output to the original sequential approach.
Testing
Fixes #13188.
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