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perf(javascript): keep collapse_vars' state in one object per nesting depth - #22492
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Included review availability: This review used your included allowance. Your plan provides up to 10 included reviews per hour; 3 remain after this review. 📝 WalkthroughWalkthroughThe collapse pass now uses per-nesting-depth ChangesCollapse pass
Suggested labels: Suggested reviewers: Priority: ➖ Normal Change: Refactor Merge Risk: ⚪ Minimal · up to The previously identified stale-scope risk is fixed at the reviewed head. No actionable merge-blocking issue remains in the supplied change. 🚥 Pre-merge checks | ✅ 4✅ Passed checks (4 passed)
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- 🪄 Fix CodeRabbit comments on this PR
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Inline comments:
Review comments at @lib/javascript/syntax-printer.js:
- Around line 21724-21742: Update releaseCollapseState to clear the stack and
reset directives for the reused scanner, multiReplacer, remover, and
leftValueWalker transformers. Ensure no traversal state or AST references
survive between collapse runs.
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Codecov Report❌ Patch coverage is
Additional details and impacted files@@ Coverage Diff @@
## main #22492 +/- ##
========================================
Coverage 96.07% 96.07%
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Files 773 773
Lines 124097 124232 +135
Branches 40579 40610 +31
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+ Hits 119222 119356 +134
- Misses 4875 4876 +1
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Generated code sizeComparing base (
Read No asset changed size. No runtime gained or lost a runtime module. Built |
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Merging this PR will improve performance by 87.45%
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| Mode | Benchmark | BASE |
HEAD |
Efficiency | |
|---|---|---|---|---|---|
| ⚡ | Memory | unit benchmark "js-parser-unit", source 'lodash-es' |
304.8 KB | 107.3 KB | ×2.8 |
| ⚡ | Memory | benchmark "asset-modules-source", scenario '{"name":"mode-production","mode":"production"}' |
8.4 MB | 6.8 MB | +23.63% |
Tip
Curious why performance improved? Comment @codspeedbot explain why performance improved on this PR, or directly use the CodSpeed MCP with your agent.
Comparing perf/minify-collapse-vars-state (1f6f644) with main (4d46ce4)
Footnotes
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6 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩
… depth terser's `collapse` keeps its scan in function-scoped `var`s that its closures share across candidates, and `collapseFrom` built those 25 closures, two transformers, a walker per candidate and a transformer per fold on every call: 37,201 calls and 86 MB per minify of typescript.js. The state now lives in a `CollapseState` held per nesting depth, the helpers are module-level functions handed it, and the scanners, the left-value walker, the remover and the left-value map are built once per state.
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Summary
terser's
collapsekeeps the state of its scan in function-scopedvars that its inner functions share across candidates. Ported as is,collapseFrombuilt those 25 closures, its two transformers, a walker for each candidate's left values and a transformer for each fold on every call: 37,201 calls per minify of typescript.js, the largest allocation site of the compressor at 86 MB.The state now lives in a
CollapseState, one per nesting depth (optimizing a value the fold moves can tighten a body of its own), and every helper is a module-level function handed it. The two scanners, the left-value walker, the remover and the left-value map are built once per state and reused; a run allocates only the candidate paths it finds.This is the first of the per-call allocation sites named in the plan (
collapseFrom,inlineIntoCall,tightenBody); each goes in its own PR.Before / after against
main:passes:2(callgrind, CodSpeed flags, warm)passes:2(callgrind, CodSpeed flags, cold)Output is byte-identical to
main: lodash, acorn and typescript.js under three option sets (default,passes:2+toplevel+unsafe,unused: "keep_assign"), and the terser, swc and oxc corpora (467,874 comparisons, 0 mismatches).What kind of change does this PR introduce?
perf
Did you add tests for your changes?
Output does not change, and the corpora cover every helper moved. Seven compress cases are added to the unit tests, held to terser's output, for the paths the unit and integration suites did not reach before: a variable copying another replaced at every read, a scan into a switch, an immediately invoked function's rest parameter and
thisargument, a scan stopping in a conditional branch, and an assignment read once in each place the scan may stop.Does this PR introduce a breaking change?
No.
If relevant, what needs to be documented once your changes are merged or what have you already documented?
n/a
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thismore consistently.