Speed up union construction with sorted-run merging and cheaper membership check by jakebailey · Pull Request #65033 · microsoft/TypeScript

Jake Bailey (jakebailey) · 2026-10-29T20:53:42Z

Thanks Steven (@teamchong) for finding these!

addTypesToUnion collected the constituents of every source type into one list and then sorted the whole list with a stable sort. Most of that work is redundant: the constituents of each source union are already sorted by CompareTypes, and unions are very often built from just a few such lists (for example, a union plus `undefined`, or two unions). The full sort re-compares elements whose relative order is already known, and CompareTypes is not cheap for many kinds of types. Instead, note where each source type's sorted run begins out of order with the previous run, and merge those runs pairwise. When the input is already in order no sorting is done at all. Because CompareTypes is a total order that only reports equality for identical types, the merged result is exactly the list the stable sort produced. Co-authored-by: Steven Chong <[email protected]>

containsType is called frequently on union constituent lists (during relation checks, narrowing, and union reduction) and always did a binary search, paying for several CompareTypes calls even when the answer is obvious. Since type lists are sorted primarily by their sort order flags, a type whose flags fall outside the range spanned by the first and last elements cannot be in the list, which can be decided with two cheap flag reads. For short lists, a linear identity scan is also cheaper than the comparisons a binary search requires. Co-authored-by: Steven Chong <[email protected]>

When reducing a union, removeRedundantLiteralTypes drops a fresh literal type if its regular counterpart is also present, and did so by binary searching the whole type set for every fresh literal. Unions of many fresh literals (common for inferred literal-heavy expressions) therefore paid a full search per member. A fresh literal type and its regular type have the same flags, symbol and value, so CompareTypes only distinguishes them by type ID, and no other type can sort between them. The regular type, if present, must therefore be immediately before or after the fresh type in the sorted set, which can be checked directly. Co-authored-by: Steven Chong <[email protected]>

When a union contains both string literals and pattern template literal types, every string literal is tested against every template to see whether it is subsumed. Each test goes through template literal inference, which allocates and does a fair amount of work before discovering that most literals do not even begin and end with the template's fixed leading and trailing text. Check those fixed texts directly first. This is the same condition inference rejects on, so only literals that could actually match pay for the full check. Co-authored-by: Steven Chong <[email protected]>

Jake Bailey (jakebailey) · 2026-10-29T21:10:21Z

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

typescript-automation · 2026-10-29T21:10:26Z

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

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

Copilot

🟡 Changes recommended

Reslicing the run-index buffer to zero retains arbitrarily large allocations for the checker’s lifetime, even when deduplication leaves only two union constituents.

1 open issue

Discard oversized run-index buffers after type-set reslicing · New

What changed in this PR

This PR optimizes union construction and membership checks in the native TypeScript checker.

Changes:

Merge already-sorted constituent runs instead of sorting the entire union.
Use adjacent checks for fresh literal counterparts and cheaper membership checks for short lists.
Reject impossible string-literal/template matches before running full matching logic.

File	Description
`tsc/internal/checker/checker.go`	Adds sorted-run merging, reusable run-index storage, and faster union membership and literal-reduction checks.

_{Review effort: Balanced}

The run-start buffer is kept on the checker for reuse across union constructions. Inputs with many short sorted runs, such as alternating primitives, can grow it far beyond the size of the resulting union, and that capacity would then be retained for the checker's lifetime. Discard buffers above the same 4096-element cutoff used for temporary type sets, while still reusing smaller ones.

Copilot

🟢 Approval recommended

There are no active review issues for the union-type construction optimizations.

No open issues 🎉

1 resolved since last review

Discard oversized run-index buffers after type-set reslicing

_{Review effort: Balanced}

typescript-automation · 2026-10-29T22:09:39Z

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=20}
_Symbols	_88,466	_88,466	_~	_~	_~	_{p=1.000 n=20}
_Types	_79,607	_79,607	_~	_~	_~	_{p=1.000 n=20}
_{Memory Used}	_{104,127k (± 0.02%)}	_{104,141k (± 0.02%)}	_~	_104,060k	_104,216k	_{p=0.499 n=20}
_{Memory Allocs}	_{1,263,774 (± 0.01%)}	_{1,263,828 (± 0.01%)}	_~	_1,263,405	_1,264,053	_{p=0.268 n=20}
_{Config Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Parse Time}	_{0.023s (± 3.66%)}	_{0.022s (± 3.20%)}	_~	_0.020s	_0.025s	_{p=0.153 n=20}
_{Bind Time}	_{0.009s (± 5.60%)}	_{0.009s (±11.40%)}	_~	_0.007s	_0.016s	_{p=0.817 n=20}
_{Check Time}	_{0.215s (± 0.52%)}	_{0.212s (± 0.62%)}	_{-0.003s (- 1.37%)}	_0.208s	_0.218s	_{p=0.001 n=20}
_{Emit Time}	_{0.139s (± 0.87%)}	_{0.139s (± 1.01%)}	_~	_0.132s	_0.144s	_{p=0.741 n=20}
_{Total Time}	_{0.389s (± 0.35%)}	_{0.385s (± 0.69%)}	_{-0.004s (- 0.98%)}	_0.376s	_0.400s	_{p=0.008 n=20}
_{angular-1 - native}
_Errors	₃	₃	_~	_~	_~	_{p=1.000 n=20}
_Symbols	_{586,519 (± 0.01%)}	_{586,512 (± 0.02%)}	_~	_586,172	_586,819	_{p=0.683 n=20}
_Types	_{241,688 (± 0.00%)}	_{241,688 (± 0.00%)}	_~	_241,685	_241,698	_{p=0.718 n=20}
_{Memory Used}	_{517,904k (± 0.02%)}	_{518,011k (± 0.02%)}	_~	_517,715k	_518,396k	_{p=0.071 n=20}
_{Memory Allocs}	_{7,798,961 (± 0.14%)}	_{7,809,581 (± 0.23%)}	_~	_7,785,500	_7,940,222	_{p=0.355 n=20}
_{Config Time}	_{0.008s (± 3.21%)}	_{0.008s (± 3.34%)}	_~	_0.008s	_0.010s	_{p=0.459 n=20}
_{Parse Time}	_{0.127s (± 2.31%)}	_{0.128s (± 2.69%)}	_~	_0.115s	_0.146s	_{p=0.722 n=20}
_{Bind Time}	_{0.047s (±12.31%)}	_{0.044s (± 8.64%)}	_~	_0.037s	_0.064s	_{p=0.875 n=20}
_{Check Time}	_0s	_0s	_~	_~	_~	_{p=1.000 n=20}
_{Emit Time}	_{0.879s (± 2.01%)}	_{0.874s (± 1.60%)}	_~	_0.837s	_0.974s	_{p=0.899 n=20}
_{Total Time}	_{1.071s (± 2.01%)}	_{1.067s (± 1.51%)}	_~	_1.022s	_1.171s	_{p=0.941 n=20}
_{arktype - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=20}
_Symbols	_685,920	_685,920	_~	_~	_~	_{p=1.000 n=20}
_Types	_939,467	_939,467	_~	_~	_~	_{p=1.000 n=20}
_{Memory Used}	_{497,279k (± 0.01%)}	_{497,359k (± 0.01%)}	_{+80k (+ 0.02%)}	_497,168k	_497,571k	_{p=0.027 n=20}
_{Memory Allocs}	_{12,108,478 (± 0.01%)}	_{12,110,886 (± 0.02%)}	_{+2,409 (+ 0.02%)}	_12,104,975	_12,119,448	_{p=0.049 n=20}
_{Config Time}	_0.001s	_0.001s	_~	_~	_~	_{p=1.000 n=20}
_{Parse Time}	_{0.042s (± 2.91%)}	_{0.042s (± 3.77%)}	_~	_0.038s	_0.049s	_{p=0.898 n=20}
_{Bind Time}	_{0.014s (±10.86%)}	_{0.014s (±10.15%)}	_~	_0.011s	_0.019s	_{p=0.701 n=20}
_{Check Time}	_{0.958s (± 0.44%)}	_{0.962s (± 0.55%)}	_~	_0.943s	_0.978s	_{p=0.433 n=20}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Total Time}	_{1.044s (± 0.33%)}	_{1.048s (± 0.39%)}	_~	_1.034s	_1.063s	_{p=0.193 n=20}
_{class-transformer - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=20}
_Symbols	_45,376	_45,376	_~	_~	_~	_{p=1.000 n=20}
_Types	_7,573	_7,573	_~	_~	_~	_{p=1.000 n=20}
_{Memory Used}	_{27,838k (± 0.02%)}	_{27,836k (± 0.02%)}	_~	_27,818k	_27,849k	_{p=0.644 n=20}
_{Memory Allocs}	_{248,631 (± 0.06%)}	_{248,677 (± 0.06%)}	_~	_248,205	_249,303	_{p=0.512 n=20}
_{Config Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Parse Time}	_{0.011s (± 4.18%)}	_{0.010s (± 3.68%)}	_~	_0.009s	_0.012s	_{p=0.417 n=20}
_{Bind Time}	_{0.004s (±12.97%)}	_{0.003s (±11.33%)}	_~	_0.003s	_0.006s	_{p=0.067 n=20}
_{Check Time}	_{0.008s (± 4.96%)}	_{0.008s (± 4.26%)}	_{🔻+0.001s (+ 6.54%)}	_0.007s	_0.010s	_{p=0.037 n=20}
_{Emit Time}	_{0.009s (± 5.73%)}	_{0.008s (± 8.53%)}	_~	_0.007s	_0.013s	_{p=0.077 n=20}
_{Total Time}	_{0.032s (± 2.14%)}	_{0.031s (± 2.66%)}	_~	_0.029s	_0.036s	_{p=0.151 n=20}
_{effect - native}
_Errors	₁₂	₁₂	_~	_~	_~	_{p=1.000 n=20}
_Symbols	_1,235,115	_1,235,115	_~	_~	_~	_{p=1.000 n=20}
_Types	_894,113	_894,113	_~	_~	_~	_{p=1.000 n=20}
_{Memory Used}	_{940,516k (± 0.02%)}	_{940,608k (± 0.02%)}	_~	_939,818k	_941,368k	_{p=0.414 n=20}
_{Memory Allocs}	_{12,670,243 (± 0.02%)}	_{12,672,552 (± 0.04%)}	_~	_12,661,907	_12,703,493	_{p=0.883 n=20}
_{Config Time}	_0.002s	_0.002s	_~	_~	_~	_{p=1.000 n=20}
_{Parse Time}	_{0.152s (± 1.62%)}	_{0.150s (± 1.67%)}	_~	_0.138s	_0.161s	_{p=0.206 n=20}
_{Bind Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Check Time}	_{0.986s (± 0.83%)}	_{0.979s (± 0.72%)}	_~	_0.960s	_1.011s	_{p=0.250 n=20}
_{Emit Time}	_{0.525s (± 2.18%)}	_{0.537s (± 1.85%)}	_~	_0.502s	_0.575s	_{p=0.109 n=20}
_{Total Time}	_{1.765s (± 0.70%)}	_{1.773s (± 0.53%)}	_~	_1.738s	_1.806s	_{p=0.245 n=20}
_{mui-docs - native}
_Errors	_11,405	_11,405	_~	_~	_~	_{p=1.000 n=20}
_Symbols	_3,784,019	_3,784,019	_~	_~	_~	_{p=1.000 n=20}
_Types	_1,355,974	_1,355,974	_~	_~	_~	_{p=1.000 n=20}
_{Memory Used}	_{1,837,203k (± 0.08%)}	_{1,836,475k (± 0.08%)}	_~	_1,831,427k	_1,841,601k	_{p=0.512 n=20}
_{Memory Allocs}	_{26,027,094 (± 0.14%)}	_{26,017,983 (± 0.13%)}	_~	_25,934,420	_26,158,034	_{p=0.461 n=20}
_{Config Time}	_{0.009s (± 2.37%)}	_{0.009s (± 3.06%)}	_~	_0.008s	_0.010s	_{p=0.731 n=20}
_{Parse Time}	_{0.322s (± 3.00%)}	_{0.316s (± 2.46%)}	_~	_0.292s	_0.358s	_{p=0.298 n=20}
_{Bind Time}	_0.001s	_0.001s	_~	_~	_~	_{p=1.000 n=20}
_{Check Time}	_{3.332s (± 0.97%)}	_{3.297s (± 1.10%)}	_~	_3.148s	_3.514s	_{p=0.057 n=20}
_{Emit Time}	_{0.262s (± 3.43%)}	_{0.260s (± 1.55%)}	_~	_0.249s	_0.277s	_{p=0.963 n=20}
_{Total Time}	_{4.465s (± 1.04%)}	_{4.402s (± 1.02%)}	_{-0.063s (- 1.41%)}	_4.232s	_4.646s	_{p=0.019 n=20}
_{sentry - native}
_Errors	₂	₂	_~	_~	_~	_{p=1.000 n=20}
_Symbols	_4,793,245	_4,793,245	_~	_~	_~	_{p=1.000 n=20}
_Types	_2,607,045	_2,607,045	_~	_~	_~	_{p=1.000 n=20}
_{Memory Used}	_{2,880,000k (± 0.03%)}	_{2,881,342k (± 0.03%)}	_{+1,342k (+ 0.05%)}	_2,878,819k	_2,885,459k	_{p=0.013 n=20}
_{Memory Allocs}	_{75,361,153 (± 0.27%)}	_{75,404,272 (± 0.22%)}	_~	_74,876,719	_76,016,145	_{p=0.512 n=20}
_{Config Time}	_{0.026s (± 1.00%)}	_{0.026s (± 1.53%)}	_~	_0.025s	_0.029s	_{p=0.713 n=20}
_{Parse Time}	_{0.508s (± 4.36%)}	_{0.504s (± 5.20%)}	_~	_0.447s	_0.704s	_{p=0.560 n=20}
_{Bind Time}	_{0.191s (± 9.56%)}	_{0.195s (±10.02%)}	_~	_0.146s	_0.255s	_{p=0.952 n=20}
_{Check Time}	_{7.178s (± 1.50%)}	_{7.103s (± 1.45%)}	_~	_6.852s	_7.722s	_{p=0.239 n=20}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Total Time}	_{7.960s (± 1.30%)}	_{7.886s (± 1.31%)}	_~	_7.643s	_8.483s	_{p=0.231 n=20}
_{social-app - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=20}
_Symbols	_1,883,074	_1,883,074	_~	_~	_~	_{p=1.000 n=20}
_Types	_1,158,168	_1,158,168	_~	_~	_~	_{p=1.000 n=20}
_{Memory Used}	_{972,347k (± 0.01%)}	_{972,366k (± 0.02%)}	_~	_971,288k	_972,885k	_{p=0.862 n=20}
_{Memory Allocs}	_{13,575,166 (± 0.29%)}	_{13,573,547 (± 0.09%)}	_~	_13,525,250	_13,625,879	_{p=0.060 n=20}
_{Config Time}	_0.008s	_0.008s	_~	_~	_~	_{p=1.000 n=20}
_{Parse Time}	_{0.156s (± 2.57%)}	_{0.159s (± 2.75%)}	_~	_0.147s	_0.186s	_{p=0.233 n=20}
_{Bind Time}	_{0.050s (±10.54%)}	_{0.046s (± 9.84%)}	_~	_0.038s	_0.069s	_{p=0.263 n=20}
_{Check Time}	_{1.480s (± 0.58%)}	_{1.473s (± 0.55%)}	_~	_1.436s	_1.512s	_{p=0.285 n=20}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Total Time}	_{1.713s (± 0.56%)}	_{1.703s (± 0.61%)}	_~	_1.668s	_1.756s	_{p=0.159 n=20}
_{strada-build-src - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=20}
_Symbols	_1,184,972	_1,184,972	_~	_~	_~	_{p=1.000 n=20}
_Types	_438,963	_438,963	_~	_~	_~	_{p=1.000 n=20}
_{Memory Used}	_{1,167,337k (± 0.39%)}	_{1,165,555k (± 0.35%)}	_~	_1,151,305k	_1,186,290k	_{p=0.659 n=20}
_{Memory Allocs}	_{47,706,257 (± 0.13%)}	_{47,672,121 (± 0.12%)}	_~	_47,466,009	_47,886,345	_{p=0.369 n=20}
_{Config Time}	_{0.002s (± 7.57%)}	_{0.002s (± 9.24%)}	_~	_0.001s	_0.002s	_{p=0.369 n=20}
_{Parse Time}	_{0.139s (± 1.47%)}	_{0.138s (± 1.19%)}	_~	_0.133s	_0.146s	_{p=0.296 n=20}
_{Bind Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Check Time}	_{0.807s (± 0.50%)}	_{0.805s (± 0.37%)}	_~	_0.794s	_0.819s	_{p=0.524 n=20}
_{Emit Time}	_{0.139s (± 0.98%)}	_{0.139s (± 1.73%)}	_~	_0.133s	_0.157s	_{p=0.984 n=20}
_{Total Time}	_{9.373s (± 0.36%)}	_{9.353s (± 0.37%)}	_~	_9.218s	_9.469s	_{p=0.616 n=20}
_{strada-compiler - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=20}
_Symbols	_263,511	_263,511	_~	_~	_~	_{p=1.000 n=20}
_Types	_196,116	_196,116	_~	_~	_~	_{p=1.000 n=20}
_{Memory Used}	_{224,567k (± 0.01%)}	_{224,655k (± 0.03%)}	_{+88k (+ 0.04%)}	_224,298k	_224,986k	_{p=0.001 n=20}
_{Memory Allocs}	_{2,401,203 (± 0.01%)}	_{2,401,471 (± 0.01%)}	_~	_2,400,220	_2,402,225	_{p=0.056 n=20}
_{Config Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Parse Time}	_{0.050s (± 4.32%)}	_{0.051s (± 3.04%)}	_~	_0.044s	_0.056s	_{p=0.192 n=20}
_{Bind Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Check Time}	_{0.379s (± 0.81%)}	_{0.379s (± 1.32%)}	_~	_0.369s	_0.412s	_{p=0.394 n=20}
_{Emit Time}	_{0.048s (± 6.04%)}	_{0.047s (± 4.97%)}	_~	_0.042s	_0.057s	_{p=0.691 n=20}
_{Total Time}	_{0.503s (± 0.89%)}	_{0.505s (± 0.96%)}	_~	_0.488s	_0.528s	_{p=0.723 n=20}
_{t3code-server - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=20}
_Symbols	_4,350,661	_4,350,661	_~	_~	_~	_{p=1.000 n=20}
_Types	_3,040,644	_3,040,644	_~	_~	_~	_{p=1.000 n=20}
_{Memory Used}	_{2,433,947k (± 0.03%)}	_{2,434,100k (± 0.03%)}	_~	_2,432,019k	_2,436,627k	_{p=0.738 n=20}
_{Memory Allocs}	_{37,415,189 (± 0.11%)}	_{37,379,564 (± 0.07%)}	_~	_37,300,497	_37,547,593	_{p=0.192 n=20}
_{Config Time}	_0.003s	_0.003s	_~	_~	_~	_{p=1.000 n=20}
_{Parse Time}	_{0.255s (± 2.05%)}	_{0.254s (± 2.65%)}	_~	_0.229s	_0.282s	_{p=0.995 n=20}
_{Bind Time}	_{0.085s (± 8.77%)}	_{0.085s (± 8.17%)}	_~	_0.075s	_0.124s	_{p=0.931 n=20}
_{Check Time}	_{7.207s (± 0.70%)}	_{7.201s (± 0.55%)}	_~	_7.089s	_7.391s	_{p=0.952 n=20}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Total Time}	_{7.561s (± 0.67%)}	_{7.553s (± 0.50%)}	_~	_7.439s	_7.757s	_{p=0.878 n=20}
_{tanstack-router - native}
_Errors	₁	₁	_~	_~	_~	_{p=1.000 n=20}
_Symbols	_571,756	_571,756	_~	_~	_~	_{p=1.000 n=20}
_Types	_397,689	_397,689	_~	_~	_~	_{p=1.000 n=20}
_{Memory Used}	_{331,412k (± 0.01%)}	_{331,419k (± 0.01%)}	_~	_331,132k	_331,520k	_{p=0.331 n=20}
_{Memory Allocs}	_{4,388,454 (± 0.11%)}	_{4,389,491 (± 0.16%)}	_~	_4,378,286	_4,431,961	_{p=0.512 n=20}
_{Config Time}	_0.001s	_0.001s	_~	_~	_~	_{p=1.000 n=20}
_{Parse Time}	_{0.040s (± 3.71%)}	_{0.041s (± 3.22%)}	_~	_0.037s	_0.047s	_{p=0.454 n=20}
_{Bind Time}	_{0.012s (± 6.95%)}	_{0.013s (±10.54%)}	_~	_0.010s	_0.021s	_{p=0.426 n=20}
_{Check Time}	_{0.560s (± 0.74%)}	_{0.567s (± 0.87%)}	_~	_0.549s	_0.588s	_{p=0.053 n=20}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Total Time}	_{0.632s (± 0.67%)}	_{0.639s (± 0.84%)}	_{+0.007s (+ 1.17%)}	_0.618s	_0.663s	_{p=0.042 n=20}
_{ts-pre-modules - native}
_Errors	₈₇	₈₇	_~	_~	_~	_{p=1.000 n=20}
_Symbols	_231,616	_231,616	_~	_~	_~	_{p=1.000 n=20}
_Types	_181,195	_181,195	_~	_~	_~	_{p=1.000 n=20}
_{Memory Used}	_{193,529k (± 0.02%)}	_{193,562k (± 0.01%)}	_~	_193,511k	_193,661k	_{p=0.060 n=20}
_{Memory Allocs}	_{1,318,038 (± 0.01%)}	_{1,318,144 (± 0.01%)}	_~	_1,317,733	_1,318,722	_{p=0.144 n=20}
_{Config Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Parse Time}	_{0.044s (± 3.80%)}	_{0.044s (± 3.34%)}	_~	_0.037s	_0.049s	_{p=0.920 n=20}
_{Bind Time}	_{0.020s (± 6.72%)}	_{0.021s (± 5.85%)}	_~	_0.018s	_0.026s	_{p=0.186 n=20}
_{Check Time}	_{0.303s (± 0.79%)}	_{0.299s (± 1.14%)}	_~	_0.288s	_0.312s	_{p=0.097 n=20}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Total Time}	_{0.373s (± 0.93%)}	_{0.370s (± 1.02%)}	_~	_0.353s	_0.386s	_{p=0.255 n=20}
_{vscode - native}
_Errors	₁₁	₁₁	_~	_~	_~	_{p=1.000 n=20}
_Symbols	_7,495,436	_7,495,436	_~	_~	_~	_{p=1.000 n=20}
_Types	_4,398,006	_4,398,006	_~	_~	_~	_{p=1.000 n=20}
_{Memory Used}	_{5,193,992k (± 0.02%)}	_{5,195,103k (± 0.02%)}	_~	_5,191,722k	_5,199,297k	_{p=0.108 n=20}
_{Memory Allocs}	_{56,807,601 (± 0.01%)}	_{56,812,035 (± 0.02%)}	_~	_56,787,597	_56,893,461	_{p=0.758 n=20}
_{Config Time}	_{0.034s (± 0.94%)}	_{0.034s (± 0.94%)}	_~	_0.033s	_0.036s	_{p=1.000 n=20}
_{Parse Time}	_{0.914s (± 1.06%)}	_{0.926s (± 1.75%)}	_~	_0.849s	_1.024s	_{p=0.387 n=20}
_{Bind Time}	_{0.312s (± 1.33%)}	_{0.320s (± 3.41%)}	_~	_0.296s	_0.408s	_{p=0.094 n=20}
_{Check Time}	_{7.877s (± 0.65%)}	_{7.956s (± 0.90%)}	_~	_7.705s	_8.230s	_{p=0.069 n=20}
_{Emit Time}	_{2.768s (± 3.96%)}	_{2.743s (± 3.28%)}	_~	_2.611s	_3.527s	_{p=0.365 n=20}
_{Total Time}	_{11.961s (± 1.02%)}	_{12.038s (± 0.91%)}	_~	_11.643s	_12.608s	_{p=0.176 n=20}
_{webpack - native}
_Errors	₆₁₆	₆₁₆	_~	_~	_~	_{p=1.000 n=20}
_Symbols	_917,188	_917,188	_~	_~	_~	_{p=1.000 n=20}
_Types	_636,859	_636,859	_~	_~	_~	_{p=1.000 n=20}
_{Memory Used}	_{693,601k (± 0.01%)}	_{693,594k (± 0.01%)}	_~	_693,261k	_694,080k	_{p=0.952 n=20}
_{Memory Allocs}	_{6,499,681 (± 0.05%)}	_{6,501,158 (± 0.05%)}	_~	_6,495,240	_6,515,816	_{p=0.640 n=20}
_{Config Time}	_0.004s	_0.004s	_~	_~	_~	_{p=1.000 n=20}
_{Parse Time}	_{0.143s (± 3.44%)}	_{0.140s (± 3.39%)}	_~	_0.123s	_0.165s	_{p=0.515 n=20}
_{Bind Time}	_{0.048s (± 9.83%)}	_{0.047s (± 8.52%)}	_~	_0.039s	_0.072s	_{p=0.909 n=20}
_{Check Time}	_{1.176s (± 1.95%)}	_{1.158s (± 1.30%)}	_~	_1.112s	_1.246s	_{p=0.409 n=20}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Total Time}	_{1.394s (± 1.96%)}	_{1.374s (± 1.14%)}	_~	_1.343s	_1.473s	_{p=0.794 n=20}
_{xstate-main - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=20}
_Symbols	_640,490	_640,490	_~	_~	_~	_{p=1.000 n=20}
_Types	_387,984	_387,984	_~	_~	_~	_{p=1.000 n=20}
_{Memory Used}	_{351,015k (± 0.03%)}	_{350,960k (± 0.02%)}	_~	_350,750k	_351,360k	_{p=0.490 n=20}
_{Memory Allocs}	_{3,992,380 (± 0.08%)}	_{3,992,414 (± 0.09%)}	_~	_3,982,488	_4,018,128	_{p=0.461 n=20}
_{Config Time}	_0.001s	_0.001s	_~	_~	_~	_{p=1.000 n=20}
_{Parse Time}	_{0.061s (± 3.12%)}	_{0.060s (± 2.50%)}	_~	_0.054s	_0.066s	_{p=0.455 n=20}
_{Bind Time}	_{0.020s (± 8.93%)}	_{0.021s (±11.33%)}	_~	_0.017s	_0.030s	_{p=0.950 n=20}
_{Check Time}	_{0.413s (± 0.84%)}	_{0.413s (± 0.63%)}	_~	_0.405s	_0.428s	_{p=0.835 n=20}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Total Time}	_{0.499s (± 0.88%)}	_{0.500s (± 0.82%)}	_~	_0.489s	_0.522s	_{p=0.804 n=20}

System info unknown

Hosts

native

Scenarios

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

_Benchmark	_Name	_Iterations
_Current	_pr	₂₀
_Baseline	_baseline	₂₀

Developer Information:

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Jake Bailey (jakebailey) and others added 4 commits October 29, 2026 12:36

typescript-automation Bot assigned Jake Bailey (jakebailey) Oct 29, 2026

typescript-automation Bot added Author: Team For Uncommitted Bug PR for untriaged, rejected, closed or missing bug labels Oct 29, 2026

Jake Bailey (jakebailey) added the Domain: Performance Reports of unusually slow behavior label Oct 29, 2026

Jake Bailey (jakebailey) marked this pull request as ready for review October 29, 2026 21:34

Copilot AI balanced review requested due to automatic review settings October 29, 2026 21:34

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Speed up union construction with sorted-run merging and cheaper membership check - #65033

Speed up union construction with sorted-run merging and cheaper membership check#65033
Jake Bailey (jakebailey) wants to merge 5 commits into
microsoft:mainfrom
jakebailey:perf/union-construction

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