History

Mathias Picker efb651cd33 perf: optimize parser hot paths for ~18% faster compilation (#17811 ) ## Summary Optimizes the Svelte compiler's parser phase — the hot path that runs on every file compilation during development (HMR). The changes are surgical micro-optimizations to 7 files in `packages/svelte/src/compiler/phases/1-parse/`, with no architectural changes. ### Changes - `Parser.match()` — `slice` → `startsWith`: Avoids creating a new substring on every multi-char match call (called thousands of times per compilation) - `Parser.match_regex()` — `slice` → sticky flag: Uses `lastIndex` + `y` flag instead of slicing the entire template string on every regex match. All 14 regex patterns passed to `match_regex`/`read` across 4 files updated with `y` flag. - `Parser.allow_whitespace()` / `require_whitespace()` — regex → charCode: Replaces `regex_whitespace.test()` with numeric charCode comparisons in a tight loop (called hundreds of times per compilation). Covers the full `\s` character set with a fast path for common ASCII whitespace. - Text parser — string concatenation → `slice`: Replaced `data += template[index++]` loop (O(n²)) with tracking start position + single `slice()` call (O(n)) - `read_sequence` — string concatenation → `slice`: Same pattern — derive `raw` from `template.slice()` in `flush()` instead of char-by-char concatenation - `is_valid_element_name()` — inline regexes → module-level constants: Extracted 2 regex literals to module scope - Dynamic `new RegExp()` → `indexOf`: Replaced `parser.read_until(new RegExp(...))` with `template.indexOf()` for script/style closing tags - `match_bracket` — `Array.includes` → `Set.has`: Pre-computes close bracket values as a `Set` for O(1) lookups ## Benchmark A benchmark script was written that: 1. Compiles 5 real test components of varying complexity (a11y validators, form bindings, component migration output, rich selects) 2. Compiles 2 synthetic stress-test templates (500 elements and 2000 elements with expressions and entities) 3. Runs 50 warmup iterations for parse, 20 for compile (JIT warmup) 4. Forces GC between benchmarks via `--expose-gc` 5. Measures both parse-only and full compilation (parse + analyze + transform + codegen) ### Parse-only results \| Component \| Before \| After \| Speedup \| \|---\|---\|---\|---\| \| a11y-role-supports-aria-props (371 lines) \| 2.410ms \| 2.129ms \| -11.7% \| \| form-default-value-spread (199 lines) \| 1.726ms \| 1.360ms \| -21.2% \| \| svelte-component (251 lines) \| 1.925ms \| 1.648ms \| -14.4% \| \| select-with-rich-content (157 lines) \| 0.795ms \| 0.636ms \| -20.0% \| \| rich-select (173 lines) \| 0.807ms \| 0.637ms \| -21.1% \| \| synthetic-large (500 elements) \| 2.560ms \| 1.547ms \| -39.6% \| \| synthetic-huge (2000 elements) \| 136.849ms \| 114.115ms \| -16.6% \| \| Total \| 147.071ms \| 122.072ms \| -17.0% \| ### Full compile results \| Component \| Before \| After \| Speedup \| \|---\|---\|---\|---\| \| a11y-role-supports-aria-props \| 25.407ms \| 21.990ms \| -13.4% \| \| form-default-value-spread \| 10.711ms \| 9.422ms \| -12.0% \| \| svelte-component \| 10.304ms \| 8.481ms \| -17.7% \| \| select-with-rich-content \| 5.986ms \| 4.694ms \| -21.6% \| \| rich-select \| 6.010ms \| 5.059ms \| -15.8% \| \| synthetic-large (500 elements) \| 30.511ms \| 25.196ms \| -17.4% \| \| synthetic-huge (2000 elements) \| 932.801ms \| 764.794ms \| -18.0% \| \| Total \| 1021.729ms \| 839.637ms \| -17.8% \| Benchmarked on macOS, Node.js, Apple Silicon. The parse improvements carry through to end-to-end compile time since the parser is a significant portion of the compilation pipeline. Text-heavy templates benefit the most (up to 40% faster parse). Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>		2 months ago
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README.md	chore: setup changesets (#8668 )	3 years ago
config.json	chore: enter changeset prerelease mode	2 years ago
fast-parser-hotpaths.md	perf: optimize parser hot paths for ~18% faster compilation (#17811 )	2 months ago
rotten-taxes-float.md	chore: more efficient effect scheduling (#17808 )	2 months ago
vast-ties-wash.md	chore: null out current_batch before committing branches (#17809 )	2 months ago

README.md

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