Disable expression type caching in CFA for loops by ahejlsberg · Pull Request #64018 · microsoft/TypeScript

Anders Hejlsberg (ahejlsberg) · 2026-08-25T21:09:02Z

This PR disables expression type caching during control flow analysis of loops. Previously, when resolving an expression type that we were going to cache, we'd first save off the flop loop caches in order to start expression type resolution from a known point. However, this could cause infinite recursion.

This PR supersedes #64013, which had the same effect but kept old redundant logic.

Fixes #64012.

Anders Hejlsberg (ahejlsberg) · 2026-08-25T21:09:52Z

TypeScript Bot (@typescript-bot) test it

typescript-automation · 2026-08-25T21:09:57Z

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

Command	Status	Results
`test top400`	✅ Started	✅ Results
`user test this`	✅ Started	✅ Results
`run dt`	✅ Started	✅ Results
`perf test this faster`	✅ Started	👀 Results

typescript-automation · 2026-08-25T21:33:32Z

Anders Hejlsberg (@ahejlsberg) Here are the results of running the user tests with tsc comparing main and refs/pull/64018/merge:

There were infrastructure failures potentially unrelated to your change:

2 instances of "Package install failed"
1 instance of "Git clone failed"

Otherwise...

Everything looks good!

typescript-automation · 2026-08-25T21:38:26Z

Anders Hejlsberg (@ahejlsberg)
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	_115,480	_115,480	_~	_~	_~	_{p=1.000 n=12}
_Types	_96,945	_96,945	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{148,392k (± 0.45%)}	_{148,338k (± 0.47%)}	_~	_146,295k	_150,406k	_{p=0.977 n=12}
_{Memory Allocs}	_{2,271,203 (± 0.01%)}	_{2,268,233 (± 0.00%)}	_{-2,969 (- 0.13%)}	_2,267,845	_2,268,507	_{p=0.000 n=12}
_{Config Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Parse Time}	_{0.041s (± 3.40%)}	_{0.042s (± 3.97%)}	_~	_0.038s	_0.048s	_{p=0.090 n=12}
_{Bind Time}	_{0.012s (±12.49%)}	_{0.013s (±13.03%)}	_~	_0.010s	_0.019s	_{p=0.295 n=12}
_{Check Time}	_{0.496s (± 1.26%)}	_{0.487s (± 0.70%)}	_{-0.009s (- 1.76%)}	_0.482s	_0.499s	_{p=0.019 n=12}
_{Emit Time}	_{0.271s (± 2.00%)}	_{0.262s (± 1.18%)}	_{🟩-0.008s (- 3.11%)}	_0.255s	_0.273s	_{p=0.005 n=12}
_{Total Time}	_{0.826s (± 1.06%)}	_{0.811s (± 0.62%)}	_{-0.014s (- 1.76%)}	_0.801s	_0.831s	_{p=0.002 n=12}
_{angular-1 - native}
_Errors	₃	₃	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_{847,447 (± 0.08%)}	_{841,724 (± 0.09%)}	_{-5,723 (- 0.68%)}	_839,456	_843,518	_{p=0.000 n=12}
_Types	_{249,858 (± 0.00%)}	_{248,657 (± 0.00%)}	_{-1,201 (- 0.48%)}	_248,654	_248,667	_{p=0.000 n=12}
_{Memory Used}	_{793,658k (± 0.06%)}	_{790,960k (± 0.06%)}	_{-2,699k (- 0.34%)}	_789,429k	_791,976k	_{p=0.000 n=12}
_{Memory Allocs}	_{12,956,092 (± 0.04%)}	_{12,913,586 (± 0.06%)}	_{-42,505 (- 0.33%)}	_12,906,822	_12,954,131	_{p=0.000 n=12}
_{Config Time}	_{0.016s (± 1.51%)}	_0.016s	_~	_~	_~	_{p=0.478 n=12}
_{Parse Time}	_{0.272s (± 2.83%)}	_{0.275s (± 2.62%)}	_~	_0.259s	_0.288s	_{p=0.416 n=12}
_{Bind Time}	_{0.067s (±17.46%)}	_{0.066s (±12.19%)}	_~	_0.058s	_0.094s	_{p=0.372 n=12}
_{Check Time}	_0s	_0s	_~	_~	_~	_{p=1.000 n=12}
_{Emit Time}	_{1.636s (± 1.30%)}	_{1.616s (± 1.13%)}	_{-0.021s (- 1.25%)}	_1.594s	_1.693s	_{p=0.034 n=12}
_{Total Time}	_{2.010s (± 1.42%)}	_{1.990s (± 1.38%)}	_~	_1.944s	_2.085s	_{p=0.103 n=12}
_{mui-docs - native}
_Errors	_{11,278 (± 0.04%)}	_{11,279 (± 0.02%)}	_~	_11,271	_11,282	_{p=0.720 n=12}
_Symbols	_4,456,324	_4,456,314	_{-10 (- 0.00%)}	_~	_~	_{p=0.000 n=12}
_Types	_1,669,869	_1,669,858	_{-11 (- 0.00%)}	_~	_~	_{p=0.000 n=12}
_{Memory Used}	_{5,404,069k (± 0.03%)}	_{5,405,016k (± 0.03%)}	_~	_5,401,090k	_5,409,078k	_{p=0.443 n=12}
_{Memory Allocs}	_{50,697,779 (± 0.03%)}	_{50,695,962 (± 0.04%)}	_~	_50,652,341	_50,740,540	_{p=0.977 n=12}
_{Config Time}	_{0.016s (± 1.14%)}	_{0.016s (± 1.14%)}	_~	_0.015s	_0.016s	_{p=1.000 n=12}
_{Parse Time}	_{0.560s (± 1.27%)}	_{0.546s (± 2.74%)}	_~	_0.496s	_0.581s	_{p=0.103 n=12}
_{Bind Time}	_0.002s	_0.002s	_~	_~	_~	_{p=1.000 n=12}
_{Check Time}	_{16.581s (± 0.24%)}	_{16.545s (± 0.31%)}	_~	_16.412s	_16.661s	_{p=0.242 n=12}
_{Emit Time}	_{0.434s (± 1.47%)}	_{0.437s (± 1.62%)}	_{+0.003s (+ 0.71%)}	_0.431s	_0.462s	_{p=0.015 n=12}
_{Total Time}	_{18.326s (± 0.11%)}	_{18.308s (± 0.23%)}	_~	_18.198s	_18.394s	_{p=0.744 n=12}
_{strada-build-src - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_1,394,339	_1,394,286	_{-53 (- 0.00%)}	_~	_~	_{p=0.000 n=12}
_Types	_443,465	_443,436	_{-29 (- 0.01%)}	_~	_~	_{p=0.000 n=12}
_{Memory Used}	_{1,648,922k (± 0.26%)}	_{1,647,785k (± 0.34%)}	_~	_1,637,805k	_1,664,035k	_{p=0.514 n=12}
_{Memory Allocs}	_{97,072,744 (± 0.04%)}	_{96,959,569 (± 0.04%)}	_{-113,176 (- 0.12%)}	_96,873,569	_97,049,235	_{p=0.001 n=12}
_{Config Time}	_{0.004s (±14.29%)}	_{0.004s (±12.82%)}	_~	_0.003s	_0.006s	_{p=0.976 n=12}
_{Parse Time}	_{0.195s (± 1.88%)}	_{0.200s (± 2.03%)}	_~	_0.190s	_0.211s	_{p=0.080 n=12}
_{Bind Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Check Time}	_{1.793s (± 0.32%)}	_{1.784s (± 0.35%)}	_{-0.008s (- 0.46%)}	_1.773s	_1.808s	_{p=0.040 n=12}
_{Emit Time}	_{0.281s (± 3.34%)}	_{0.282s (± 5.89%)}	_~	_0.243s	_0.330s	_{p=0.966 n=12}
_{Total Time}	_{24.580s (± 0.49%)}	_{24.673s (± 0.94%)}	_~	_24.043s	_25.312s	_{p=0.410 n=12}
_{strada-compiler - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_337,586	_337,560	_{-26 (- 0.01%)}	_~	_~	_{p=0.000 n=12}
_Types	_198,869	_198,858	_{-11 (- 0.01%)}	_~	_~	_{p=0.000 n=12}
_{Memory Used}	_{319,500k (± 0.03%)}	_{319,730k (± 0.08%)}	_{+230k (+ 0.07%)}	_319,342k	_320,937k	_{p=0.028 n=12}
_{Memory Allocs}	_{4,673,065 (± 0.01%)}	_{4,667,245 (± 0.01%)}	_{-5,820 (- 0.12%)}	_4,665,813	_4,668,552	_{p=0.000 n=12}
_{Config Time}	_0.001s	_0.001s	_~	_~	_~	_{p=1.000 n=12}
_{Parse Time}	_{0.112s (± 5.06%)}	_{0.117s (± 5.89%)}	_~	_0.102s	_0.130s	_{p=0.192 n=12}
_{Bind Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Check Time}	_{1.038s (± 0.42%)}	_{1.035s (± 0.49%)}	_~	_1.025s	_1.051s	_{p=0.415 n=12}
_{Emit Time}	_{0.146s (± 8.83%)}	_{0.128s (±13.87%)}	_~	_0.097s	_0.164s	_{p=0.138 n=12}
_{Total Time}	_{1.346s (± 1.07%)}	_{1.337s (± 1.39%)}	_~	_1.303s	_1.383s	_{p=0.272 n=12}
_{ts-pre-modules - native}
_Errors	₈₇	₈₇	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_305,317	_305,293	_{-24 (- 0.01%)}	_~	_~	_{p=0.000 n=12}
_Types	_181,984	_181,978	_{-6 (- 0.00%)}	_~	_~	_{p=0.000 n=12}
_{Memory Used}	_{277,285k (± 0.02%)}	_{277,209k (± 0.02%)}	_{-76k (- 0.03%)}	_277,098k	_277,336k	_{p=0.045 n=12}
_{Memory Allocs}	_{1,642,489 (± 0.01%)}	_{1,639,436 (± 0.01%)}	_{-3,053 (- 0.19%)}	_1,639,076	_1,639,693	_{p=0.000 n=12}
_{Config Time}	_{0.000s (±217.90%)}	_{0.000s (±146.91%)}	_~	_0.000s	_0.001s	_{p=1.000 n=12}
_{Parse Time}	_{0.105s (± 4.29%)}	_{0.100s (± 4.22%)}	_~	_0.090s	_0.112s	_{p=0.074 n=12}
_{Bind Time}	_{0.038s (± 7.66%)}	_{0.040s (±11.26%)}	_~	_0.032s	_0.052s	_{p=0.637 n=12}
_{Check Time}	_{0.830s (± 0.80%)}	_{0.829s (± 0.66%)}	_~	_0.806s	_0.839s	_{p=0.854 n=12}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Total Time}	_{0.986s (± 0.80%)}	_{0.983s (± 0.75%)}	_~	_0.961s	_1.007s	_{p=0.810 n=12}
_{vscode - native}
_Errors	₃₄₇	₃₄₇	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_7,931,112	_7,926,127	_{-4,985 (- 0.06%)}	_~	_~	_{p=0.000 n=12}
_Types	_2,714,263	_2,709,275	_{-4,988 (- 0.18%)}	_~	_~	_{p=0.000 n=12}
_{Memory Used}	_{5,357,067k (± 0.01%)}	_{5,353,533k (± 0.01%)}	_{-3,534k (- 0.07%)}	_5,351,937k	_5,355,216k	_{p=0.000 n=12}
_{Memory Allocs}	_{41,190,465 (± 0.05%)}	_{41,094,031 (± 0.03%)}	_{-96,434 (- 0.23%)}	_41,080,819	_41,155,902	_{p=0.000 n=12}
_{Config Time}	_{0.063s (± 0.39%)}	_{0.064s (± 0.51%)}	_~	_0.063s	_0.064s	_{p=0.089 n=12}
_{Parse Time}	_{1.630s (± 1.87%)}	_{1.621s (± 1.96%)}	_~	_1.522s	_1.680s	_{p=0.724 n=12}
_{Bind Time}	_{0.337s (± 1.43%)}	_{0.356s (± 7.18%)}	_~	_0.334s	_0.469s	_{p=0.064 n=12}
_{Check Time}	_{9.804s (± 0.26%)}	_{9.636s (± 1.12%)}	_{-0.168s (- 1.71%)}	_9.297s	_9.778s	_{p=0.000 n=12}
_{Emit Time}	_{3.025s (± 0.65%)}	_{3.194s (± 7.92%)}	_~	_2.939s	_4.044s	_{p=0.131 n=12}
_{Total Time}	_{14.946s (± 0.29%)}	_{14.963s (± 1.05%)}	_~	_14.745s	_15.509s	_{p=0.193 n=12}
_{webpack - native}
_Errors	₅₃₁	₅₃₁	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_850,254	_850,121	_{-133 (- 0.02%)}	_~	_~	_{p=0.000 n=12}
_Types	_385,198	_385,177	_{-21 (- 0.01%)}	_~	_~	_{p=0.000 n=12}
_{Memory Used}	_{652,001k (± 0.03%)}	_{651,993k (± 0.03%)}	_~	_651,629k	_652,658k	_{p=1.000 n=12}
_{Memory Allocs}	_{4,318,255 (± 0.03%)}	_{4,313,931 (± 0.04%)}	_{-4,324 (- 0.10%)}	_4,311,987	_4,322,581	_{p=0.000 n=12}
_{Config Time}	_0.008s	_0.008s	_~	_~	_~	_{p=1.000 n=12}
_{Parse Time}	_{0.211s (± 2.42%)}	_{0.220s (± 2.54%)}	_{🔻+0.010s (+ 4.71%)}	_0.206s	_0.234s	_{p=0.013 n=12}
_{Bind Time}	_{0.048s (±16.21%)}	_{0.045s (±11.34%)}	_~	_0.040s	_0.070s	_{p=0.965 n=12}
_{Check Time}	_{1.128s (± 1.29%)}	_{1.159s (± 1.31%)}	_{+0.031s (+ 2.78%)}	_1.113s	_1.203s	_{p=0.001 n=12}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Total Time}	_{1.419s (± 0.89%)}	_{1.456s (± 1.00%)}	_{+0.037s (+ 2.63%)}	_1.413s	_1.497s	_{p=0.001 n=12}
_{xstate-main - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_1,022,508	_1,022,506	_{-2 (- 0.00%)}	_~	_~	_{p=0.000 n=12}
_Types	_376,977	_376,974	_{-3 (- 0.00%)}	_~	_~	_{p=0.000 n=12}
_{Memory Used}	_{603,518k (± 0.01%)}	_{603,473k (± 0.01%)}	_~	_603,179k	_603,652k	_{p=0.340 n=12}
_{Memory Allocs}	_{4,755,912 (± 0.05%)}	_{4,754,316 (± 0.04%)}	_~	_4,750,050	_4,760,831	_{p=0.347 n=12}
_{Config Time}	_0.003s	_0.003s	_~	_~	_~	_{p=1.000 n=12}
_{Parse Time}	_{0.146s (± 1.37%)}	_{0.146s (± 3.52%)}	_~	_0.137s	_0.160s	_{p=0.467 n=12}
_{Bind Time}	_{0.042s (±14.44%)}	_{0.045s (±18.52%)}	_~	_0.033s	_0.072s	_{p=0.721 n=12}
_{Check Time}	_{1.041s (± 1.01%)}	_{1.029s (± 0.66%)}	_~	_1.006s	_1.047s	_{p=0.116 n=12}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Total Time}	_{1.244s (± 1.16%)}	_{1.234s (± 0.97%)}	_~	_1.200s	_1.264s	_{p=0.284 n=12}

System info unknown

Hosts

native

Scenarios

Compiler-Unions - native
angular-1 - native
mui-docs - native
strada-build-src - native
strada-compiler - native
ts-pre-modules - native
vscode - native
webpack - native
xstate-main - native

_Benchmark	_Name	_Iterations
_Current	_pr	₁₂
_Baseline	_baseline	₁₂

Developer Information:

Download Benchmarks

typescript-automation · 2026-08-25T21:43:47Z

Hey Anders Hejlsberg (@ahejlsberg), the results of running the DT tests are ready.

Everything looks the same!

You can check the log here.

typescript-automation · 2026-08-25T22:08:10Z

Anders Hejlsberg (@ahejlsberg) Here are the results of running the top 400 repos with tsc comparing main and refs/pull/64018/merge:

Everything looks good!

Anders Hejlsberg (ahejlsberg) · 2026-08-25T22:47:35Z

TypeScript Bot (@typescript-bot) test top 1000

Anders Hejlsberg (ahejlsberg) · 2026-08-25T22:48:10Z

TypeScript Bot (@typescript-bot) test top1000

typescript-automation · 2026-08-25T22:48:14Z

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

Command	Status	Results
`test top1000`	✅ Started	✅ Results

typescript-automation · 2026-08-26T00:05:37Z

Anders Hejlsberg (@ahejlsberg) Here are the results of running the top 1000 repos with tsc comparing main and refs/pull/64018/merge:

Everything looks good!

Anders Hejlsberg (ahejlsberg) added 2 commits August 25, 2026 14:08

Disable expression type caching in CFA for loops

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Disable expression type caching in CFA for loops - #64018

Disable expression type caching in CFA for loops#64018
Anders Hejlsberg (ahejlsberg) wants to merge 2 commits into
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