Avoid unnecessary work and allocations when instantiating type by jakebailey · Pull Request #65035 · microsoft/TypeScript

Jake Bailey (jakebailey) · 2026-10-29T20:55:21Z

Thanks Steven (@teamchong) for finding these!

Many types passed to instantiation cannot contain type variables, and whether they can is already cached in their object flags. Check that cached bit inline at the top of instantiateTypeWithAlias so the common "nothing to do" case doesn't go through an indirect call. getPermissiveInstantiation and getRestrictiveInstantiation previously did a map lookup and one or two map inserts for every non-primitive type, even though instantiating a variable-free type always yields the type itself. Return such types directly instead. The restrictive self-entry is only consulted for conditional types, which are never variable-free, so skipping it is unobservable. instantiateSymbol unconditionally fetched the symbol's value links, allocating them for symbols whose types were never resolved just to find them empty. Only look the links up, and check the cheap this-only mapper case first. Co-authored-by: Steven Chong <[email protected]>

instantiateTypeAlias allocated a new TypeAlias on every call, even though instantiateTypes already returns the original argument slice when no argument changes. This happens frequently, e.g. for aliases without type arguments or whose arguments are unaffected by the mapper, and the result is passed along on most object, union and indexed access instantiations. Return the existing alias in that case, extending the copy-on-change behavior of list instantiation to the alias itself. Aliases are never mutated after being attached to a type, and are compared by content rather than identity, so sharing them is safe. Co-authored-by: Steven Chong <[email protected]>

When instantiating an anonymous, mapped or deferred object type, and when instantiating a type reference, we computed the new type arguments into a freshly allocated slice, then used them to look up an existing instantiation. Most of these lookups hit, at which point the slice was simply discarded. Compute the type arguments into a stack buffer instead, look up the cache with it, and only copy the arguments to the heap when a new instantiation is actually created. For type references that need no tuple normalization, the cache key computed for the lookup is reused when creating the reference. Co-authored-by: Steven Chong <[email protected]>

Jake Bailey (jakebailey) · 2026-10-29T21:10:41Z

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

typescript-automation · 2026-10-29T21:10:47Z

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

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

Copilot

🟡 Changes recommended

Unconditional cloning of already-owned type-argument slices introduces redundant allocations and copies on cache misses in both type-reference and anonymous-type instantiation paths.

2 open issues

What changed in this PR

This PR reduces unnecessary work and allocations during type instantiation in the native TypeScript checker.

Changes:

Avoids allocating symbol links unnecessarily and reuses unchanged type aliases.
Uses temporary argument buffers and checks caches before retaining new instantiations.
Adds a shared type-variable-free check to skip unnecessary instantiation work.

File	Description
`tsc/internal/checker/checker.go`	Optimizes symbol, type-reference, and object instantiation through early returns, temporary buffers, and cache reuse.

_{Review effort: Balanced}

When more type arguments are instantiated than fit in the stack buffer, the list is already freshly allocated and owned by the caller. Cloning it again before creating a new instantiation added a second allocation and copy on every cache miss, making these cases more expensive than before the buffer was introduced. Only clone arguments that were written into the buffer, and pass heap-allocated lists through as-is.

Copilot

🔵 Needs a closer look

Temporary argument buffers still escape to the heap in both instantiation paths, causing avoidable allocations for unchanged arguments and cache hits, plus extra allocations on small-argument cache misses.

No open issues 🎉

1 previously missed issue

In code that hasn't changed since last review

Prevent temporary buffer escape and excess allocations

tsc/internal/checker/checker.go:22991

The conditional clone leaves an escape path from buf to newTypeReferenceInstantiation, so the temporary buffer is heap-allocated even when the arguments are unchanged or the cache hits. The same issue occurs in getObjectTypeInstantiation at line 23073, where small-argument cache misses also allocate the cloned slice in addition to the buffer. Separate temporary storage from retained argument storage so neither buffer can escape, then verify allocation counts for unchanged arguments, cache hits, and cache misses.

2 resolved since last review

_{Review effort: Balanced}

typescript-automation · 2026-10-29T22:06:46Z

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}	_{104,147k (± 0.03%)}	_{104,120k (± 0.02%)}	_~	_104,019k	_104,215k	_{p=0.465 n=20}
_{Memory Allocs}	_{1,263,790 (± 0.01%)}	_{1,254,200 (± 0.01%)}	_{-9,590 (- 0.76%)}	_1,253,799	_1,254,494	_{p=0.000 n=20}
_{Config Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Parse Time}	_{0.022s (± 2.36%)}	_{0.023s (± 2.03%)}	_~	_0.021s	_0.025s	_{p=0.183 n=20}
_{Bind Time}	_{0.008s (± 3.69%)}	_{0.008s (± 6.60%)}	_~	_0.007s	_0.012s	_{p=0.689 n=20}
_{Check Time}	_{0.214s (± 1.17%)}	_{0.214s (± 1.18%)}	_~	_0.207s	_0.229s	_{p=0.920 n=20}
_{Emit Time}	_{0.138s (± 1.23%)}	_{0.137s (± 0.97%)}	_~	_0.131s	_0.146s	_{p=0.651 n=20}
_{Total Time}	_{0.385s (± 0.83%)}	_{0.386s (± 0.77%)}	_~	_0.377s	_0.398s	_{p=0.560 n=20}
_{angular-1 - native}
_Errors	₃	₃	_~	_~	_~	_{p=1.000 n=20}
_Symbols	_{586,480 (± 0.01%)}	_{586,548 (± 0.02%)}	_~	_586,154	_586,787	_{p=0.199 n=20}
_Types	_{241,688 (± 0.00%)}	_{241,687 (± 0.00%)}	_~	_241,683	_241,690	_{p=0.962 n=20}
_{Memory Used}	_{517,909k (± 0.02%)}	_{517,836k (± 0.02%)}	_~	_517,424k	_518,210k	_{p=0.344 n=20}
_{Memory Allocs}	_{7,805,394 (± 0.12%)}	_{7,790,668 (± 0.30%)}	_{-14,725 (- 0.19%)}	_7,762,169	_7,939,910	_{p=0.000 n=20}
_{Config Time}	_{0.009s (± 2.78%)}	_{0.009s (± 2.52%)}	_~	_0.008s	_0.009s	_{p=0.514 n=20}
_{Parse Time}	_{0.129s (± 3.65%)}	_{0.129s (± 2.07%)}	_~	_0.120s	_0.139s	_{p=0.233 n=20}
_{Bind Time}	_{0.050s (±11.10%)}	_{0.045s (± 8.18%)}	_~	_0.040s	_0.070s	_{p=0.164 n=20}
_{Check Time}	_0s	_0s	_~	_~	_~	_{p=1.000 n=20}
_{Emit Time}	_{0.886s (± 1.54%)}	_{0.881s (± 1.23%)}	_~	_0.863s	_0.949s	_{p=0.644 n=20}
_{Total Time}	_{1.085s (± 1.76%)}	_{1.076s (± 1.31%)}	_~	_1.049s	_1.161s	_{p=0.663 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}	_{497,299k (± 0.01%)}	_{495,464k (± 0.01%)}	_{-1,836k (- 0.37%)}	_495,291k	_495,691k	_{p=0.000 n=20}
_{Memory Allocs}	_{12,108,850 (± 0.02%)}	_{11,289,251 (± 0.02%)}	_{🟩-819,599 (- 6.77%)}	_11,283,876	_11,301,116	_{p=0.000 n=20}
_{Config Time}	_0.001s	_0.001s	_~	_~	_~	_{p=1.000 n=20}
_{Parse Time}	_{0.042s (± 3.37%)}	_{0.042s (± 3.16%)}	_~	_0.036s	_0.046s	_{p=0.602 n=20}
_{Bind Time}	_{0.013s (±10.40%)}	_{0.013s (± 9.26%)}	_~	_0.011s	_0.018s	_{p=0.793 n=20}
_{Check Time}	_{0.965s (± 0.52%)}	_{0.962s (± 0.46%)}	_~	_0.947s	_0.985s	_{p=0.180 n=20}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Total Time}	_{1.050s (± 0.48%)}	_{1.046s (± 0.42%)}	_~	_1.033s	_1.069s	_{p=0.189 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}	_{27,836k (± 0.02%)}	_{27,829k (± 0.02%)}	_{-7k (- 0.03%)}	_27,803k	_27,865k	_{p=0.034 n=20}
_{Memory Allocs}	_{248,630 (± 0.05%)}	_{248,025 (± 0.06%)}	_{-605 (- 0.24%)}	_247,474	_248,587	_{p=0.000 n=20}
_{Config Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Parse Time}	_{0.012s (± 3.09%)}	_{0.012s (± 2.54%)}	_~	_0.010s	_0.013s	_{p=0.283 n=20}
_{Bind Time}	_{0.004s (±11.18%)}	_{0.004s (±15.06%)}	_~	_0.002s	_0.007s	_{p=0.504 n=20}
_{Check Time}	_{0.008s (± 5.20%)}	_{0.008s (± 4.98%)}	_~	_0.007s	_0.010s	_{p=0.933 n=20}
_{Emit Time}	_{0.009s (± 5.77%)}	_{0.009s (± 7.68%)}	_~	_0.007s	_0.012s	_{p=0.876 n=20}
_{Total Time}	_{0.032s (± 1.87%)}	_{0.033s (± 3.16%)}	_~	_0.028s	_0.040s	_{p=0.851 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}	_{940,517k (± 0.01%)}	_{939,961k (± 0.02%)}	_{-556k (- 0.06%)}	_939,349k	_940,706k	_{p=0.000 n=20}
_{Memory Allocs}	_{12,671,890 (± 0.02%)}	_{12,405,573 (± 0.04%)}	_{-266,317 (- 2.10%)}	_12,396,235	_12,441,799	_{p=0.000 n=20}
_{Config Time}	_0.002s	_{0.002s (± 6.84%)}	_~	_0.002s	_0.003s	_{p=0.487 n=20}
_{Parse Time}	_{0.150s (± 1.82%)}	_{0.149s (± 1.78%)}	_~	_0.139s	_0.161s	_{p=0.743 n=20}
_{Bind Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Check Time}	_{0.940s (± 0.87%)}	_{0.934s (± 0.80%)}	_~	_0.906s	_0.959s	_{p=0.365 n=20}
_{Emit Time}	_{0.500s (± 2.35%)}	_{0.501s (± 2.03%)}	_~	_0.466s	_0.530s	_{p=0.909 n=20}
_{Total Time}	_{1.685s (± 0.51%)}	_{1.680s (± 0.49%)}	_~	_1.648s	_1.705s	_{p=0.465 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}	_{1,836,371k (± 0.06%)}	_{1,835,665k (± 0.07%)}	_~	_1,829,905k	_1,840,949k	_{p=0.327 n=20}
_{Memory Allocs}	_{26,017,585 (± 0.13%)}	_{25,069,522 (± 0.13%)}	_{🟩-948,063 (- 3.64%)}	_24,989,366	_25,226,487	_{p=0.000 n=20}
_{Config Time}	_{0.009s (± 1.61%)}	_{0.009s (± 7.60%)}	_~	_0.008s	_0.015s	_{p=0.560 n=20}
_{Parse Time}	_{0.298s (± 2.20%)}	_{0.306s (± 3.17%)}	_~	_0.281s	_0.364s	_{p=0.267 n=20}
_{Bind Time}	_{0.001s (±18.96%)}	_{0.001s (± 9.93%)}	_~	_0.001s	_0.002s	_{p=1.000 n=20}
_{Check Time}	_{3.287s (± 0.73%)}	_{3.285s (± 0.85%)}	_~	_3.177s	_3.377s	_{p=0.952 n=20}
_{Emit Time}	_{0.255s (± 1.53%)}	_{0.264s (± 4.18%)}	_~	_0.246s	_0.329s	_{p=0.297 n=20}
_{Total Time}	_{4.362s (± 0.75%)}	_{4.383s (± 0.62%)}	_~	_4.300s	_4.486s	_{p=0.159 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}	_{2,880,551k (± 0.03%)}	_{2,878,820k (± 0.03%)}	_{-1,730k (- 0.06%)}	_2,875,779k	_2,882,003k	_{p=0.008 n=20}
_{Memory Allocs}	_{75,290,662 (± 0.25%)}	_{74,384,367 (± 0.51%)}	_{-906,295 (- 1.20%)}	_73,757,108	_76,345,422	_{p=0.000 n=20}
_{Config Time}	_{0.025s (± 1.48%)}	_{0.025s (± 1.33%)}	_~	_0.024s	_0.026s	_{p=0.652 n=20}
_{Parse Time}	_{0.482s (± 4.98%)}	_{0.483s (± 4.77%)}	_~	_0.428s	_0.605s	_{p=0.888 n=20}
_{Bind Time}	_{0.153s (± 9.13%)}	_{0.177s (±10.47%)}	_~	_0.137s	_0.242s	_{p=0.142 n=20}
_{Check Time}	_{6.817s (± 1.16%)}	_{6.765s (± 1.21%)}	_~	_6.585s	_7.129s	_{p=0.351 n=20}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Total Time}	_{7.523s (± 1.19%)}	_{7.505s (± 1.09%)}	_~	_7.301s	_7.814s	_{p=0.693 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}	_{972,538k (± 0.01%)}	_{971,299k (± 0.02%)}	_{-1,239k (- 0.13%)}	_970,642k	_971,962k	_{p=0.000 n=20}
_{Memory Allocs}	_{13,592,734 (± 0.27%)}	_{12,768,191 (± 0.14%)}	_{🟩-824,543 (- 6.07%)}	_12,712,722	_12,862,193	_{p=0.000 n=20}
_{Config Time}	_0.008s	_0.008s	_~	_~	_~	_{p=1.000 n=20}
_{Parse Time}	_{0.158s (± 2.02%)}	_{0.158s (± 1.44%)}	_~	_0.150s	_0.166s	_{p=0.846 n=20}
_{Bind Time}	_{0.048s (±11.56%)}	_{0.044s (± 8.72%)}	_~	_0.039s	_0.066s	_{p=0.412 n=20}
_{Check Time}	_{1.474s (± 0.59%)}	_{1.474s (± 0.48%)}	_~	_1.446s	_1.511s	_{p=0.973 n=20}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Total Time}	_{1.704s (± 0.57%)}	_{1.700s (± 0.37%)}	_~	_1.682s	_1.735s	_{p=0.763 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}	_{1,166,783k (± 0.31%)}	_{1,164,505k (± 0.34%)}	_~	_1,148,248k	_1,185,865k	_{p=0.341 n=20}
_{Memory Allocs}	_{47,638,867 (± 0.09%)}	_{47,187,221 (± 0.11%)}	_{-451,646 (- 0.95%)}	_47,007,245	_47,403,284	_{p=0.000 n=20}
_{Config Time}	_{0.002s (±14.66%)}	_{0.002s (±15.95%)}	_~	_0.001s	_0.003s	_{p=0.962 n=20}
_{Parse Time}	_{0.141s (± 1.86%)}	_{0.142s (± 1.62%)}	_~	_0.133s	_0.153s	_{p=0.489 n=20}
_{Bind Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Check Time}	_{0.825s (± 0.90%)}	_{0.827s (± 0.78%)}	_~	_0.803s	_0.851s	_{p=0.753 n=20}
_{Emit Time}	_{0.140s (± 1.51%)}	_{0.142s (± 2.05%)}	_~	_0.132s	_0.161s	_{p=0.150 n=20}
_{Total Time}	_{9.565s (± 0.65%)}	_{9.595s (± 0.81%)}	_~	_9.344s	_9.870s	_{p=0.602 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}	_{224,595k (± 0.02%)}	_{224,615k (± 0.01%)}	_~	_224,492k	_224,702k	_{p=0.457 n=20}
_{Memory Allocs}	_{2,401,359 (± 0.01%)}	_{2,375,919 (± 0.01%)}	_{-25,441 (- 1.06%)}	_2,375,118	_2,376,822	_{p=0.000 n=20}
_{Config Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Parse Time}	_{0.052s (± 3.71%)}	_{0.053s (± 3.36%)}	_~	_0.046s	_0.060s	_{p=0.930 n=20}
_{Bind Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Check Time}	_{0.410s (± 1.33%)}	_{0.407s (± 1.16%)}	_~	_0.392s	_0.423s	_{p=0.409 n=20}
_{Emit Time}	_{0.051s (± 6.89%)}	_{0.049s (± 4.77%)}	_~	_0.042s	_0.057s	_{p=0.329 n=20}
_{Total Time}	_{0.544s (± 1.20%)}	_{0.537s (± 0.67%)}	_{-0.007s (- 1.33%)}	_0.519s	_0.552s	_{p=0.028 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}	_{2,434,117k (± 0.03%)}	_{2,430,858k (± 0.03%)}	_{-3,259k (- 0.13%)}	_2,428,930k	_2,434,989k	_{p=0.000 n=20}
_{Memory Allocs}	_{37,388,766 (± 0.08%)}	_{34,730,279 (± 0.05%)}	_{🟩-2,658,488 (- 7.11%)}	_34,669,029	_34,808,764	_{p=0.000 n=20}
_{Config Time}	_0.003s	_0.003s	_~	_~	_~	_{p=1.000 n=20}
_{Parse Time}	_{0.257s (± 1.71%)}	_{0.262s (± 2.54%)}	_~	_0.230s	_0.289s	_{p=0.223 n=20}
_{Bind Time}	_{0.097s (±11.36%)}	_{0.094s (±11.29%)}	_~	_0.077s	_0.142s	_{p=0.430 n=20}
_{Check Time}	_{7.335s (± 0.39%)}	_{7.352s (± 0.61%)}	_~	_7.256s	_7.677s	_{p=0.703 n=20}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Total Time}	_{7.703s (± 0.39%)}	_{7.722s (± 0.58%)}	_~	_7.634s	_8.051s	_{p=0.713 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}	_{331,403k (± 0.01%)}	_{331,226k (± 0.01%)}	_{-178k (- 0.05%)}	_331,072k	_331,405k	_{p=0.000 n=20}
_{Memory Allocs}	_{4,391,670 (± 0.14%)}	_{4,092,817 (± 0.19%)}	_{🟩-298,853 (- 6.80%)}	_4,074,592	_4,126,394	_{p=0.000 n=20}
_{Config Time}	_0.001s	_0.001s	_~	_~	_~	_{p=1.000 n=20}
_{Parse Time}	_{0.041s (± 3.63%)}	_{0.040s (± 4.73%)}	_~	_0.035s	_0.049s	_{p=0.084 n=20}
_{Bind Time}	_{0.013s (± 3.91%)}	_{0.015s (±12.33%)}	_~	_0.012s	_0.022s	_{p=0.138 n=20}
_{Check Time}	_{0.587s (± 0.56%)}	_{0.589s (± 0.63%)}	_~	_0.573s	_0.600s	_{p=0.323 n=20}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Total Time}	_{0.663s (± 0.54%)}	_{0.663s (± 0.77%)}	_~	_0.641s	_0.684s	_{p=0.773 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}	_{193,527k (± 0.01%)}	_{193,515k (± 0.02%)}	_~	_193,383k	_193,647k	_{p=0.560 n=20}
_{Memory Allocs}	_{1,318,215 (± 0.02%)}	_{1,291,890 (± 0.01%)}	_{-26,325 (- 2.00%)}	_1,291,298	_1,292,926	_{p=0.000 n=20}
_{Config Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Parse Time}	_{0.043s (± 3.13%)}	_{0.042s (± 2.67%)}	_~	_0.037s	_0.046s	_{p=0.239 n=20}
_{Bind Time}	_{0.022s (± 5.20%)}	_{0.022s (± 5.52%)}	_~	_0.016s	_0.026s	_{p=0.720 n=20}
_{Check Time}	_{0.295s (± 1.20%)}	_{0.297s (± 1.13%)}	_~	_0.287s	_0.308s	_{p=0.198 n=20}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Total Time}	_{0.366s (± 0.90%)}	_{0.367s (± 0.89%)}	_~	_0.355s	_0.379s	_{p=0.507 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}	_{5,194,576k (± 0.02%)}	_{5,188,625k (± 0.01%)}	_{-5,951k (- 0.11%)}	_5,186,032k	_5,191,708k	_{p=0.000 n=20}
_{Memory Allocs}	_{56,816,888 (± 0.03%)}	_{56,427,455 (± 0.02%)}	_{-389,432 (- 0.69%)}	_56,410,273	_56,479,229	_{p=0.000 n=20}
_{Config Time}	_{0.034s (± 1.28%)}	_{0.034s (± 1.24%)}	_~	_0.033s	_0.036s	_{p=0.432 n=20}
_{Parse Time}	_{0.914s (± 1.87%)}	_{0.917s (± 1.18%)}	_~	_0.852s	_0.956s	_{p=0.380 n=20}
_{Bind Time}	_{0.342s (± 8.77%)}	_{0.334s (± 6.96%)}	_~	_0.304s	_0.531s	_{p=0.433 n=20}
_{Check Time}	_{8.029s (± 0.95%)}	_{8.069s (± 0.97%)}	_~	_7.783s	_8.365s	_{p=0.512 n=20}
_{Emit Time}	_{2.892s (± 5.06%)}	_{2.793s (± 4.03%)}	_~	_2.641s	_3.763s	_{p=0.410 n=20}
_{Total Time}	_{12.269s (± 1.16%)}	_{12.206s (± 1.17%)}	_~	_11.758s	_13.098s	_{p=0.525 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}	_{693,532k (± 0.02%)}	_{693,036k (± 0.01%)}	_{-496k (- 0.07%)}	_692,757k	_693,348k	_{p=0.000 n=20}
_{Memory Allocs}	_{6,500,898 (± 0.04%)}	_{6,409,719 (± 0.05%)}	_{-91,178 (- 1.40%)}	_6,399,001	_6,423,214	_{p=0.000 n=20}
_{Config Time}	_0.004s	_0.004s	_~	_~	_~	_{p=1.000 n=20}
_{Parse Time}	_{0.140s (± 3.27%)}	_{0.147s (± 3.89%)}	_{🔻+0.008s (+ 5.36%)}	_0.126s	_0.182s	_{p=0.048 n=20}
_{Bind Time}	_{0.048s (±18.76%)}	_{0.049s (±11.20%)}	_~	_0.039s	_0.075s	_{p=0.420 n=20}
_{Check Time}	_{1.165s (± 1.04%)}	_{1.185s (± 3.08%)}	_~	_1.139s	_1.508s	_{p=0.387 n=20}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Total Time}	_{1.380s (± 1.01%)}	_{1.410s (± 2.60%)}	_~	_1.350s	_1.719s	_{p=0.101 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}	_{350,902k (± 0.02%)}	_{350,777k (± 0.02%)}	_{-125k (- 0.04%)}	_350,491k	_351,190k	_{p=0.009 n=20}
_{Memory Allocs}	_{3,991,533 (± 0.08%)}	_{3,782,135 (± 0.07%)}	_{🟩-209,398 (- 5.25%)}	_3,772,720	_3,794,335	_{p=0.000 n=20}
_{Config Time}	_0.001s	_0.001s	_~	_~	_~	_{p=1.000 n=20}
_{Parse Time}	_{0.061s (± 2.07%)}	_{0.060s (± 2.94%)}	_~	_0.055s	_0.067s	_{p=0.633 n=20}
_{Bind Time}	_{0.022s (± 8.15%)}	_{0.024s (± 9.36%)}	_~	_0.019s	_0.033s	_{p=0.223 n=20}
_{Check Time}	_{0.455s (± 0.75%)}	_{0.453s (± 0.70%)}	_~	_0.443s	_0.468s	_{p=0.702 n=20}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Total Time}	_{0.545s (± 0.71%)}	_{0.544s (± 0.82%)}	_~	_0.527s	_0.559s	_{p=0.909 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:

Download Benchmarks

Jake Bailey (jakebailey) · 2026-10-29T22:08:30Z

This helps a little, but, not really that much? Certainly alloc count though.

Escape analysis does not consider control flow. Because the variable that could point into the stack buffer was also handed to code that retains it, the buffer was moved to the heap on every call, including the unchanged and cache-hit paths that were meant to be allocation free. Keep retained arguments in a separate variable that is only assigned from a fresh allocation or a copy, so the buffer never flows into retained storage and can stay on the stack.

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🟢 Approval recommended

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Jake Bailey (jakebailey) and others added 3 commits October 29, 2026 12:35

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

Copilot started reviewing on behalf of Jake Bailey (jakebailey) October 29, 2026 21:36

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Avoid unnecessary work and allocations when instantiating type - #65035

Avoid unnecessary work and allocations when instantiating type#65035
Jake Bailey (jakebailey) wants to merge 5 commits into
microsoft:mainfrom
jakebailey:perf/variable-free-instantiation

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