Index conditional CSS import deduplication

perfloop/esbuild · INEFFICIENT ALGORITHM

https://perfloop.ai/t/oss/case_c30r8wd9tr

Verdict

VERIFIED · settled 2026-08-17

What happened: The paired measurements met the required improvement.

Hypothesis

The target stores duplicate positions in slices and repeatedly scans them at lines 3573-3580, 3583-3593, and 3695-3739; each candidate invokes isConditionalImportRedundant, which compares condition tokens. Its returned order is consumed as importsInChunkInOrder by computeChunks, which calls this once for each eligible CSS chunk (a CSS entry point or a JS entry point with imported CSS) on each chunk-computation run. I ran a temporary, no-error CLI fixture with one shared stylesheet imported under distinct layer(lNNNNN) conditions: normal bundle elapsed time was 61.5 ms at 1,000 imports, 178.7 ms at 2,000, and 658.1 ms at 4,000. The CLI's built-in repeated-run --cpuprofile on the 2,000-import fixture attributed 74.87% cumulative samples to findImportedFilesInCSSOrder and 68.07% to isConditionalImportRedundant, with token comparison beneath it. That measures this synthetic repeated-import trigger, not its prevalence or hotness in production; the proposed index is hypothesized to remove the incompatible pairwise token comparisons while retaining the predicate for compatible candidates. A case session should benchmark 1,000/2,000/4,000 repeated imports plus representative CSS graphs, require the target/helper CPU share and superlinear curve to fall, and run a baseline output differential covering equal and distinct nested layer, supports, and media condition prefixes.

Change to test: Maintain a collision-checked condition-prefix index within each source/path and layer duplicate group, so the existing redundancy predicate only validates compatible later imports instead of scanning every prior duplicate; preserve the current last-wins order and emitted import-order semantics.

Where it lives

perfloop/esbuild · pkg/api/api_impl.go

Evidence

Bundle=true API Context.Rebuild of a CSS entry point with 1,000 shared imports under distinct layers · 10 sample pairs

metric baseline candidate paired median change confidence range required result
ns/op 36235588 4253168 −88.3% (−31994525) −32236942 to −31725041 < −1811779 PASSED

Bundle=true API Context.Rebuild of a CSS entry point with 2,000 shared imports under distinct layers · 10 sample pairs

metric baseline candidate paired median change confidence range required result
ns/op 134188721 7685976 −94.3% (−126592904) −128093827 to −125246953 < −6709436 PASSED

Bundle=true API Context.Rebuild of a CSS entry point with 4,000 shared imports under distinct layers · 10 sample pairs

metric baseline candidate paired median change confidence range required result
ns/op 520064296 15319394 −97% (−504558693) −510275320 to −502394639 < −26003215 PASSED
B/op 12082566 12426833 +2.8% (+343274) +175281 to +347941 ≤ 500000 PASSED
allocs/op 81173 81253 +0.1% (+78) +1 to +90 ≤ 250 PASSED

Bundle=true API Context.Rebuild of a CSS entry point with 1,000 same-layer imports under distinct media conditions · 10 sample pairs

metric baseline candidate paired median change confidence range required result
ns/op 61139729 4988310 −91.6% (−55991883) −58171277 to −55301612 < −3056986 PASSED

Bundle=true API Context.Rebuild of a CSS entry point with 2,000 same-layer imports under distinct media conditions · 10 sample pairs

metric baseline candidate paired median change confidence range required result
ns/op 225829325 9390871 −95.9% (−216480522) −218817366 to −214963576 < −11291466 PASSED

Bundle=true API Context.Rebuild of a CSS entry point with 4,000 same-layer imports under distinct media conditions · 10 sample pairs

metric baseline candidate paired median change confidence range required result
ns/op 917395333 18475524 −98% (−899076786) −915868913 to −881003472 < −45869767 PASSED
B/op 14984108 15298821 +2.1% (+314888) +284349 to +342599 ≤ 500000 PASSED
allocs/op 125219 125241 +20.5 −49 to +68 ≤ 250 PASSED

Bundle=true API Context.Rebuild of a CSS entry point with 1,000 imports of the same external URL under distinct media conditions · 10 sample pairs

metric baseline candidate paired median change confidence range required result
ns/op 59053046 3561867 −94.1% (−55544675) −56533013 to −54755709 < −2952652 PASSED

Bundle=true API Context.Rebuild of a CSS entry point with 2,000 imports of the same external URL under distinct media conditions · 10 sample pairs

metric baseline candidate paired median change confidence range required result
ns/op 224375073 6495890 −97.1% (−217816135) −221304808 to −216038346 < −11218754 PASSED

Bundle=true API Context.Rebuild of a CSS entry point with 4,000 imports of the same external URL under distinct media conditions · 10 sample pairs

metric baseline candidate paired median change confidence range required result
ns/op 932219769 13118932 −98.6% (−918822727) −936491367 to −894291358 < −46610988 PASSED

Bundle=false default-mode API Context.Rebuild of a CSS entry point with 1,000 shared imports under distinct layers · 10 sample pairs

metric baseline candidate paired median change confidence range required result
ns/op 35280233 3165442 −91% (−32112932) −32637674 to −32009745 < −1764012 PASSED

Bundle=false default-mode API Context.Rebuild of a CSS entry point with 2,000 shared imports under distinct layers · 10 sample pairs

metric baseline candidate paired median change confidence range required result
ns/op 133025081 5445401 −95.9% (−127551738) −130141818 to −126159614 < −6651254 PASSED

Bundle=false default-mode API Context.Rebuild of a CSS entry point with 4,000 shared imports under distinct layers · 10 sample pairs

metric baseline candidate paired median change confidence range required result
ns/op 513002204 10308327 −98% (−502680800) −508724011 to −499978287 < −25650110 PASSED

Bundle=true API Context.Rebuild of a JavaScript entry point importing 2,000 distinct CSS layers · 10 sample pairs

metric baseline candidate paired median change confidence range required result
ns/op 134728784 8082637 −93.9% (−126521021) −127739073 to −125858859 < −6736439 PASSED

Bundle=true API Context.Rebuild of a CSS entry point with 1,000 repeated full import conditions · 10 sample pairs

metric baseline candidate paired median change confidence range required result
ns/op 3037033 3121204 +1.9% (+58916) +29428 to +100514 ≤ 151852 PASSED

Bundle=true API Context.Rebuild of a CSS entry point with a representative import graph of 512 files · 10 sample pairs

metric baseline candidate paired median change confidence range required result
ns/op 23555108 23535794 +0.1% (+17154) −308525 to +356679 ≤ 500000 PASSED

Bundle=true API Context.Rebuild of a CSS entry point with a shared nested layer prefix across 256 imports · 10 sample pairs

metric baseline candidate paired median change confidence range required result
ns/op 15034616 13000647 −13.8% (−2073269) −2207764 to −1893679 ≤ 400000 PASSED

Checks: 4 of 4 passed. Verification: no defect found.

Timeline