Skip assignments when narrowing identifiers by jakebailey · Pull Request #64878 · microsoft/TypeScript

Jake Bailey (jakebailey) · 2026-10-19T20:44:03Z

See the two commits for more info.

Narrowing an identifier walks back through every assignment on its flow path. In long straight-line functions each reference walks past every earlier declaration, so the walk length grows with the function and most of the time goes to cache misses loading each declaration and its name, only to find a different name. The binder now records a hash of the identifier each assignment flow node can target, in what was padding in FlowNode. Walks for an identifier skip assignments whose recorded name differs without touching their syntax. Assignments that could matter for any reference, like for-in variables, are recorded as unknown and still checked in full. --checkers 4, n=8: │ before │ after │ │ sec/op │ sec/op vs base │ Tsc/bluesky 2.794 ± 3% 2.757 ± 2% ~ (p=0.195 n=8) Tsc/sentry 11.02 ± 2% 11.17 ± 3% ~ (p=0.505 n=8) Tsc/t3code-server 13.10 ± 2% 12.04 ± 2% -8.14% (p=0.000 n=8) geomean 7.388 7.184 -2.77% │ before │ after │ │ rss-B │ rss-B vs base │ Tsc/bluesky 1.193Gi ± 2% 1.191Gi ± 1% ~ (p=0.574 n=8) Tsc/sentry 3.357Gi ± 4% 3.626Gi ± 8% ~ (p=0.105 n=8) Tsc/t3code-server 2.888Gi ± 3% 2.855Gi ± 3% -1.16% (p=0.038 n=8) geomean 2.262Gi 2.310Gi +2.14% │ before │ after │ │ heap-B │ heap-B vs base │ Tsc/bluesky 934.7Mi ± 0% 934.8Mi ± 0% ~ (p=0.645 n=8) Tsc/sentry 2.609Gi ± 0% 2.608Gi ± 0% ~ (p=0.130 n=8) Tsc/t3code-server 2.302Gi ± 0% 2.303Gi ± 0% ~ (p=0.878 n=8) geomean 1.763Gi 1.763Gi -0.02%

Narrowing a property access like x.y walks the same long assignment chains as narrowing an identifier, and was still visiting the syntax of every assignment on the way. Such a reference can only be affected by assignments to x itself or to access chains rooted at x. Record the root identifier of access chain assignment targets as well, marked so that identifier references still ignore them, and let walks for access chains rooted at an identifier skip assignments rooted at any other name. --checkers 4, n=6: │ before │ after │ │ sec/op │ sec/op vs base │ Tsc/bluesky 2.750 ± 6% 2.814 ± 4% ~ (p=0.084 n=6) Tsc/sentry 11.28 ± 2% 11.34 ± 2% ~ (p=0.818 n=6) Tsc/t3code-server 12.19 ± 9% 11.01 ± 4% -9.71% (p=0.002 n=6) Tsc/vscode 12.93 ± 5% 12.90 ± 1% ~ (p=0.589 n=6) geomean 8.363 8.203 -1.91% │ before │ after │ │ rss-B │ rss-B vs base │ Tsc/bluesky 1.197Gi ± 2% 1.200Gi ± 2% ~ (p=0.818 n=6) Tsc/sentry 3.527Gi ± 5% 3.512Gi ± 5% ~ (p=0.937 n=6) Tsc/t3code-server 2.859Gi ± 3% 2.840Gi ± 2% ~ (p=0.818 n=6) Tsc/vscode 4.826Gi ± 3% 4.969Gi ± 3% +2.96% (p=0.026 n=6) geomean 2.763Gi 2.777Gi +0.51% │ before │ after │ │ heap-B │ heap-B vs base │ Tsc/bluesky 934.7Mi ± 0% 934.7Mi ± 0% ~ (p=0.937 n=6) Tsc/sentry 2.607Gi ± 0% 2.608Gi ± 0% ~ (p=0.937 n=6) Tsc/t3code-server 2.303Gi ± 0% 2.303Gi ± 0% ~ (p=0.589 n=6) Tsc/vscode 4.104Gi ± 0% 4.104Gi ± 0% ~ (p=0.589 n=6) geomean 2.178Gi 2.178Gi +0.01%

Jake Bailey (jakebailey) · 2026-10-19T20:44:15Z

TypeScript Bot (@typescript-bot) perf test this faster

typescript-automation · 2026-10-19T20:44:21Z

Starting jobs; this comment will be updated as builds start and complete.

Command	Status	Results
`perf test this faster`	✅ Started	👀 Results

Copilot

🔵 Needs a closer look

The optimization bypasses core narrowing checks, and compiler-suite validation was unavailable to establish behavioral equivalence.

No open issues 🎉

What changed in this PR

Optimizes control-flow narrowing by skipping assignments that cannot affect the reference being checked.

Changes:

Adds hashed assignment-target metadata to flow nodes.
Populates that metadata during binding.
Uses reference-root hashes to skip unrelated assignments during narrowing.

File	Description
`tsc/internal/checker/flow.go`	Skips assignments using reference-root hashes.
`tsc/internal/binder/binder.go`	Records assignment-target metadata during binding.
`tsc/internal/ast/flow.go`	Defines target metadata and hashing helpers.

_{Review effort: Balanced}

typescript-automation · 2026-10-19T21:14:25Z

Jake Bailey (@jakebailey)
The results of the perf run you requested are in!

Here they are:

tsc

Comparison Report - baseline..pr

_Metric	_baseline	_pr	_Delta	_Best	_Worst	_p-value
_{Compiler-Unions - native}
_Errors	₄₁	₄₁	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_115,276	_115,276	_~	_~	_~	_{p=1.000 n=12}
_Types	_79,613	_79,613	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{113,497k (± 0.08%)}	_{113,598k (± 0.07%)}	_~	_113,418k	_113,801k	_{p=0.076 n=12}
_{Memory Allocs}	_{2,212,523 (± 0.00%)}	_{2,212,615 (± 0.01%)}	_~	_2,212,348	_2,212,959	_{p=0.514 n=12}
_{Config Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Parse Time}	_{0.040s (± 6.11%)}	_{0.039s (± 2.95%)}	_~	_0.036s	_0.042s	_{p=0.742 n=12}
_{Bind Time}	_{0.014s (± 8.84%)}	_{0.013s (± 7.80%)}	_~	_0.011s	_0.016s	_{p=0.127 n=12}
_{Check Time}	_{0.471s (± 1.08%)}	_{0.466s (± 0.84%)}	_~	_0.457s	_0.479s	_{p=0.138 n=12}
_{Emit Time}	_{0.264s (± 1.75%)}	_{0.266s (± 2.64%)}	_~	_0.253s	_0.291s	_{p=0.831 n=12}
_{Total Time}	_{0.796s (± 0.74%)}	_{0.791s (± 1.09%)}	_~	_0.777s	_0.822s	_{p=0.213 n=12}
_{angular-1 - native}
_Errors	₃	₃	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_{846,592 (± 0.10%)}	_{847,798 (± 0.06%)}	_{+1,206 (+ 0.14%)}	_846,418	_849,017	_{p=0.028 n=12}
_Types	_{247,031 (± 0.00%)}	_{247,029 (± 0.00%)}	_{-3 (- 0.00%)}	_247,027	_247,031	_{p=0.000 n=12}
_{Memory Used}	_{596,378k (± 0.03%)}	_{596,451k (± 0.02%)}	_~	_596,192k	_596,815k	_{p=0.600 n=12}
_{Memory Allocs}	_{13,147,168 (± 0.08%)}	_{13,142,798 (± 0.05%)}	_~	_13,136,642	_13,168,608	_{p=0.514 n=12}
_{Config Time}	_{0.017s (± 1.86%)}	_{0.017s (± 1.95%)}	_~	_0.016s	_0.017s	_{p=1.000 n=12}
_{Parse Time}	_{0.230s (± 3.10%)}	_{0.224s (± 2.83%)}	_~	_0.211s	_0.242s	_{p=0.284 n=12}
_{Bind Time}	_{0.077s (±16.88%)}	_{0.081s (±15.93%)}	_~	_0.058s	_0.105s	_{p=0.660 n=12}
_{Check Time}	_0s	_0s	_~	_~	_~	_{p=1.000 n=12}
_{Emit Time}	_{1.556s (± 1.22%)}	_{1.552s (± 1.38%)}	_~	_1.498s	_1.604s	_{p=0.788 n=12}
_{Total Time}	_{1.897s (± 1.09%)}	_{1.891s (± 1.21%)}	_~	_1.813s	_1.944s	_{p=0.681 n=12}
_{arktype - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_1,757,463	_1,757,463	_~	_~	_~	_{p=1.000 n=12}
_Types	_943,966	_943,966	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{703,778k (± 0.01%)}	_{703,616k (± 0.01%)}	_{-162k (- 0.02%)}	_703,449k	_703,793k	_{p=0.004 n=12}
_{Memory Allocs}	_{13,290,981 (± 0.01%)}	_{13,294,422 (± 0.02%)}	_{+3,441 (+ 0.03%)}	_13,289,888	_13,302,985	_{p=0.024 n=12}
_{Config Time}	_0.002s	_0.002s	_~	_~	_~	_{p=1.000 n=12}
_{Parse Time}	_{0.068s (± 3.29%)}	_{0.072s (± 4.45%)}	_~	_0.065s	_0.080s	_{p=0.137 n=12}
_{Bind Time}	_{0.022s (± 9.82%)}	_{0.023s (±15.46%)}	_~	_0.018s	_0.033s	_{p=0.920 n=12}
_{Check Time}	_{2.063s (± 0.31%)}	_{2.064s (± 0.50%)}	_~	_2.036s	_2.095s	_{p=0.898 n=12}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Total Time}	_{2.197s (± 0.25%)}	_{2.205s (± 0.46%)}	_~	_2.177s	_2.239s	_{p=0.183 n=12}
_{mui-docs - native}
_Errors	_11,405	_11,405	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_4,331,983	_4,331,983	_~	_~	_~	_{p=1.000 n=12}
_Types	_1,370,520	_1,370,520	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{2,625,451k (± 0.07%)}	_{2,625,969k (± 0.05%)}	_~	_2,622,061k	_2,628,661k	_{p=0.630 n=12}
_{Memory Allocs}	_{27,708,378 (± 0.08%)}	_{27,704,382 (± 0.07%)}	_~	_27,663,046	_27,753,144	_{p=0.755 n=12}
_{Config Time}	_{0.017s (± 1.45%)}	_{0.017s (± 1.07%)}	_~	_0.016s	_0.017s	_{p=1.000 n=12}
_{Parse Time}	_{0.478s (± 1.67%)}	_{0.477s (± 2.44%)}	_~	_0.448s	_0.513s	_{p=0.670 n=12}
_{Bind Time}	_0.002s	_0.002s	_~	_~	_~	_{p=1.000 n=12}
_{Check Time}	_{7.284s (± 0.48%)}	_{7.186s (± 0.76%)}	_{-0.098s (- 1.34%)}	_7.110s	_7.366s	_{p=0.007 n=12}
_{Emit Time}	_{0.499s (±11.85%)}	_{0.520s (±13.33%)}	_~	_0.413s	_0.659s	_{p=0.966 n=12}
_{Total Time}	_{9.020s (± 0.51%)}	_{8.946s (± 0.75%)}	_{-0.074s (- 0.83%)}	_8.733s	_9.054s	_{p=0.037 n=12}
_{sentry - native}
_Errors	₂	₂	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_7,459,653	_7,459,653	_~	_~	_~	_{p=1.000 n=12}
_Types	_2,647,172	_2,647,109	_{-63 (- 0.00%)}	_~	_~	_{p=0.000 n=12}
_{Memory Used}	_{3,804,102k (± 0.04%)}	_{3,804,595k (± 0.04%)}	_~	_3,801,454k	_3,809,411k	_{p=0.671 n=12}
_{Memory Allocs}	_{77,188,195 (± 0.08%)}	_{77,172,538 (± 0.06%)}	_~	_77,020,583	_77,299,229	_{p=0.630 n=12}
_{Config Time}	_{0.060s (± 0.54%)}	_{0.060s (± 0.54%)}	_~	_0.060s	_0.061s	_{p=1.000 n=12}
_{Parse Time}	_{1.048s (± 3.13%)}	_{1.008s (± 3.08%)}	_~	_0.954s	_1.102s	_{p=0.068 n=12}
_{Bind Time}	_{0.296s (±12.09%)}	_{0.361s (±14.21%)}	_{🔻+0.066s (+22.20%)}	_0.264s	_0.456s	_{p=0.034 n=12}
_{Check Time}	_{14.888s (± 0.62%)}	_{14.688s (± 0.45%)}	_{-0.200s (- 1.34%)}	_14.574s	_14.936s	_{p=0.000 n=12}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Total Time}	_{16.363s (± 0.60%)}	_{16.194s (± 0.38%)}	_{-0.169s (- 1.03%)}	_16.062s	_16.429s	_{p=0.001 n=12}
_{social-app - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_2,568,629	_2,568,629	_~	_~	_~	_{p=1.000 n=12}
_Types	_1,163,035	_1,163,035	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{1,213,025k (± 0.01%)}	_{1,212,901k (± 0.02%)}	_~	_1,212,189k	_1,213,549k	_{p=0.369 n=12}
_{Memory Allocs}	_{14,008,484 (± 0.18%)}	_{13,986,422 (± 0.18%)}	_~	_13,935,840	_14,041,915	_{p=0.242 n=12}
_{Config Time}	_0.017s	_{0.017s (± 1.86%)}	_{+0.000s (+ 2.45%)}	_0.017s	_0.018s	_{p=0.037 n=12}
_{Parse Time}	_{0.358s (± 1.09%)}	_{0.355s (± 1.59%)}	_~	_0.338s	_0.366s	_{p=0.600 n=12}
_{Bind Time}	_{0.076s (± 4.35%)}	_{0.084s (±15.21%)}	_~	_0.069s	_0.133s	_{p=0.701 n=12}
_{Check Time}	_{3.655s (± 0.24%)}	_{3.597s (± 0.34%)}	_{-0.058s (- 1.58%)}	_3.557s	_3.628s	_{p=0.000 n=12}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Total Time}	_{4.128s (± 0.21%)}	_{4.075s (± 0.36%)}	_{-0.052s (- 1.27%)}	_4.022s	_4.107s	_{p=0.000 n=12}
_{strada-build-src - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_1,388,680	_1,388,680	_~	_~	_~	_{p=1.000 n=12}
_Types	_441,862	_441,858	_{-4 (- 0.00%)}	_~	_~	_{p=0.000 n=12}
_{Memory Used}	_{1,316,830k (± 0.62%)}	_{1,314,476k (± 0.74%)}	_~	_1,296,961k	_1,347,353k	_{p=0.410 n=12}
_{Memory Allocs}	_{78,248,297 (± 0.07%)}	_{78,212,454 (± 0.13%)}	_~	_77,815,183	_78,369,466	_{p=0.932 n=12}
_{Config Time}	_{0.005s (± 9.18%)}	_{0.005s (±10.49%)}	_~	_0.003s	_0.006s	_{p=0.677 n=12}
_{Parse Time}	_{0.313s (± 2.52%)}	_{0.305s (± 1.20%)}	_{-0.008s (- 2.51%)}	_0.296s	_0.316s	_{p=0.032 n=12}
_{Bind Time}	_{0.000s (±217.90%)}	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Check Time}	_{2.001s (± 0.35%)}	_{1.971s (± 0.68%)}	_{-0.030s (- 1.50%)}	_1.941s	_2.011s	_{p=0.000 n=12}
_{Emit Time}	_{0.361s (± 2.60%)}	_{0.367s (± 5.85%)}	_~	_0.321s	_0.418s	_{p=0.966 n=12}
_{Total Time}	_{23.883s (± 0.40%)}	_{23.601s (± 0.52%)}	_{-0.282s (- 1.18%)}	_23.177s	_23.947s	_{p=0.001 n=12}
_{strada-compiler - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_334,953	_334,953	_~	_~	_~	_{p=1.000 n=12}
_Types	_197,616	_197,616	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{247,502k (± 0.02%)}	_{247,546k (± 0.02%)}	_~	_247,425k	_247,715k	_{p=0.143 n=12}
_{Memory Allocs}	_{4,329,613 (± 0.01%)}	_{4,329,958 (± 0.02%)}	_~	_4,328,496	_4,334,301	_{p=0.755 n=12}
_{Config Time}	_0.001s	_0.001s	_~	_~	_~	_{p=1.000 n=12}
_{Parse Time}	_{0.108s (± 4.70%)}	_{0.112s (± 4.78%)}	_~	_0.101s	_0.129s	_{p=0.417 n=12}
_{Bind Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Check Time}	_{0.961s (± 0.69%)}	_{0.944s (± 0.60%)}	_{-0.017s (- 1.73%)}	_0.927s	_0.957s	_{p=0.000 n=12}
_{Emit Time}	_{0.147s (± 4.31%)}	_{0.147s (± 4.66%)}	_~	_0.124s	_0.162s	_{p=0.988 n=12}
_{Total Time}	_{1.271s (± 0.87%)}	_{1.253s (± 0.79%)}	_{-0.018s (- 1.42%)}	_1.231s	_1.282s	_{p=0.023 n=12}
_{t3code-server - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_11,588,087	_11,588,087	_~	_~	_~	_{p=1.000 n=12}
_Types	_3,062,556	_3,062,556	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{3,946,195k (± 0.01%)}	_{3,947,544k (± 0.01%)}	_{+1,349k (+ 0.03%)}	_3,945,776k	_3,948,795k	_{p=0.002 n=12}
_{Memory Allocs}	_{41,536,723 (± 0.05%)}	_{41,551,587 (± 0.05%)}	_~	_41,504,511	_41,616,359	_{p=0.378 n=12}
_{Config Time}	_0.006s	_0.006s	_~	_~	_~	_{p=1.000 n=12}
_{Parse Time}	_{0.563s (± 3.40%)}	_{0.571s (± 1.88%)}	_~	_0.545s	_0.598s	_{p=0.599 n=12}
_{Bind Time}	_{0.203s (±13.87%)}	_{0.169s (± 5.28%)}	_~	_0.153s	_0.190s	_{p=0.203 n=12}
_{Check Time}	_{18.571s (± 0.26%)}	_{14.996s (± 0.50%)}	_{🟩-3.574s (-19.25%)}	_14.803s	_15.148s	_{p=0.000 n=12}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Total Time}	_{19.363s (± 0.24%)}	_{15.760s (± 0.41%)}	_{🟩-3.603s (-18.61%)}	_15.586s	_15.899s	_{p=0.000 n=12}
_{ts-pre-modules - native}
_Errors	₈₇	₈₇	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_303,834	_303,834	_~	_~	_~	_{p=1.000 n=12}
_Types	_181,663	_181,663	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{215,247k (± 0.02%)}	_{215,271k (± 0.02%)}	_~	_215,147k	_215,447k	_{p=0.504 n=12}
_{Memory Allocs}	_{1,401,476 (± 0.02%)}	_{1,401,615 (± 0.02%)}	_~	_1,400,829	_1,402,523	_{p=0.418 n=12}
_{Config Time}	_{0.000s (±217.90%)}	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Parse Time}	_{0.094s (± 3.01%)}	_{0.098s (± 4.22%)}	_~	_0.085s	_0.108s	_{p=0.102 n=12}
_{Bind Time}	_{0.040s (± 9.14%)}	_{0.040s (± 6.79%)}	_~	_0.031s	_0.045s	_{p=0.921 n=12}
_{Check Time}	_{0.744s (± 0.98%)}	_{0.735s (± 0.81%)}	_~	_0.720s	_0.748s	_{p=0.182 n=12}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Total Time}	_{0.893s (± 0.74%)}	_{0.889s (± 0.72%)}	_~	_0.875s	_0.906s	_{p=0.417 n=12}
_{vscode - native}
_Errors	₃₉₆	₃₉₆	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_12,424,509	_12,424,509	_~	_~	_~	_{p=1.000 n=12}
_Types	_4,049,620	_4,049,608	_{-12 (- 0.00%)}	_~	_~	_{p=0.000 n=12}
_{Memory Used}	_{5,828,907k (± 0.02%)}	_{5,828,105k (± 0.01%)}	_~	_5,825,917k	_5,829,732k	_{p=0.291 n=12}
_{Memory Allocs}	_{59,231,297 (± 0.02%)}	_{59,246,603 (± 0.06%)}	_~	_59,215,702	_59,372,256	_{p=0.887 n=12}
_{Config Time}	_{0.062s (± 0.46%)}	_0.062s	_~	_~	_~	_{p=0.217 n=12}
_{Parse Time}	_{1.468s (± 2.57%)}	_{1.485s (± 2.34%)}	_~	_1.392s	_1.577s	_{p=0.443 n=12}
_{Bind Time}	_{0.549s (±15.60%)}	_{0.513s (±14.80%)}	_~	_0.412s	_0.753s	_{p=0.682 n=12}
_{Check Time}	_{12.183s (± 0.75%)}	_{12.077s (± 0.78%)}	_~	_11.811s	_12.210s	_{p=0.143 n=12}
_{Emit Time}	_{4.745s (± 6.04%)}	_{4.482s (± 8.64%)}	_~	_3.811s	_5.378s	_{p=0.266 n=12}
_{Total Time}	_{19.082s (± 1.30%)}	_{18.692s (± 1.85%)}	_{-0.390s (- 2.04%)}	_18.089s	_19.553s	_{p=0.045 n=12}
_{webpack - native}
_Errors	₅₉₈	₅₉₈	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_1,343,495	_1,343,495	_~	_~	_~	_{p=1.000 n=12}
_Types	_651,492	_651,492	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{855,378k (± 0.02%)}	_{855,377k (± 0.01%)}	_~	_855,093k	_855,569k	_{p=0.932 n=12}
_{Memory Allocs}	_{6,770,284 (± 0.02%)}	_{6,768,513 (± 0.01%)}	_~	_6,766,778	_6,770,158	_{p=0.101 n=12}
_{Config Time}	_0.009s	_0.009s	_~	_~	_~	_{p=1.000 n=12}
_{Parse Time}	_{0.310s (± 3.04%)}	_{0.302s (± 3.34%)}	_~	_0.267s	_0.322s	_{p=0.468 n=12}
_{Bind Time}	_{0.079s (±13.47%)}	_{0.079s (± 6.74%)}	_~	_0.068s	_0.097s	_{p=0.323 n=12}
_{Check Time}	_{2.791s (± 0.60%)}	_{2.659s (± 0.31%)}	_{🟩-0.132s (- 4.72%)}	_2.638s	_2.676s	_{p=0.000 n=12}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Total Time}	_{3.228s (± 0.47%)}	_{3.088s (± 0.34%)}	_{🟩-0.140s (- 4.33%)}	_3.048s	_3.112s	_{p=0.000 n=12}
_{xstate-main - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_1,060,810	_1,060,810	_~	_~	_~	_{p=1.000 n=12}
_Types	_389,671	_389,671	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{471,991k (± 0.03%)}	_{471,843k (± 0.02%)}	_~	_471,685k	_472,157k	_{p=0.143 n=12}
_{Memory Allocs}	_{4,223,038 (± 0.06%)}	_{4,217,293 (± 0.08%)}	_{-5,745 (- 0.14%)}	_4,206,475	_4,225,874	_{p=0.008 n=12}
_{Config Time}	_0.003s	_0.003s	_~	_~	_~	_{p=1.000 n=12}
_{Parse Time}	_{0.137s (± 2.49%)}	_{0.133s (± 2.85%)}	_~	_0.127s	_0.145s	_{p=0.146 n=12}
_{Bind Time}	_{0.042s (±16.23%)}	_{0.050s (±12.38%)}	_~	_0.034s	_0.065s	_{p=0.085 n=12}
_{Check Time}	_{1.098s (± 1.24%)}	_{1.081s (± 0.87%)}	_~	_1.066s	_1.121s	_{p=0.103 n=12}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Total Time}	_{1.286s (± 1.07%)}	_{1.275s (± 0.97%)}	_~	_1.243s	_1.298s	_{p=0.131 n=12}

System info unknown

Hosts

native

Scenarios

Compiler-Unions - native
angular-1 - native
arktype - native
mui-docs - native
sentry - native
social-app - native
strada-build-src - native
strada-compiler - native
t3code-server - native
ts-pre-modules - native
vscode - native
webpack - native
xstate-main - native

_Benchmark	_Name	_Iterations
_Current	_pr	₁₂
_Baseline	_baseline	₁₂

Developer Information:

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Ryan Cavanaugh (RyanCavanaugh)

I was on the fence about this until I saw the t3code results... anyway the code is good but the comments aren't fully getting this through my brain without examples

Ryan Cavanaugh (RyanCavanaugh) · 2026-10-30T13:36:39Z

+	return h
+}
+
+// FlowAssignmentTargetHash summarizes which references an assignment flow node


This comment really needs code examples to illustrate what it's talking about

Ryan Cavanaugh (RyanCavanaugh) · 2026-10-30T13:37:00Z

 	return resultType
 }

+// getFlowReferenceRootHash returns the FlowIdentifierHash of the identifier a reference


Less so than the prior one, but same

Jake Bailey (jakebailey) added 2 commits October 19, 2026 09:04

Copilot AI balanced review requested due to automatic review settings October 19, 2026 20:44

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Skip assignments when narrowing identifiers - #64878

Skip assignments when narrowing identifiers#64878
Jake Bailey (jakebailey) wants to merge 2 commits into
microsoft:mainfrom
jakebailey:perf/flow-skip-assignments

Jake Bailey (jakebailey) commented Oct 19, 2026

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tsc

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Jake Bailey (jakebailey) commented Oct 19, 2026

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🔵 Needs a closer look

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tsc

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