Pre-size member, export, and locals symbol tables by jakebailey · Pull Request #65025 · microsoft/TypeScript

Jake Bailey (jakebailey) · 2026-10-29T20:18:05Z

Symbol tables created on demand by GetMembers, GetExports, and GetLocals always started empty, so binding a class, interface, enum, object literal, namespace, or source file grew the entry slice repeatedly and, once past the linear-search limit, built the hash index and rebuilt it again as it filled up.

The declaration that owns the table already tells us roughly how many entries it will receive: the number of class/interface/type literal members, object literal properties, enum members, top-level statements, or parameters and type parameters. Use that count as a capacity hint when the table is first created so it is usually allocated once at the right size. The hint only affects allocation; insertion order, and therefore iteration order, is unchanged.

Thanks Steven (@teamchong) for finding this!

Symbol tables created on demand by GetMembers, GetExports, and GetLocals always started empty, so binding a class, interface, enum, object literal, namespace, or source file grew the entry slice repeatedly and, once past the linear-search limit, built the hash index and rebuilt it again as it filled up. The declaration that owns the table already tells us roughly how many entries it will receive: the number of class/interface/type literal members, object literal properties, enum members, top-level statements, or parameters and type parameters. Use that count as a capacity hint when the table is first created so it is usually allocated once at the right size. The hint only affects allocation; insertion order, and therefore iteration order, is unchanged. Co-authored-by: Steven Chong <25894545+teamchong@users.noreply.github.com>

Jake Bailey (jakebailey) · 2026-10-29T20:18:37Z

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

typescript-automation · 2026-10-29T20:18:43Z

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

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

Copilot

🟡 Changes recommended

The capacity hints count all statements rather than export-producing declarations, causing excessive memory allocation and unnecessary hashed lookups in modules with few exports.

1 open issue

Avoid oversized export table hints from private declarations · New

What changed in this PR

This PR pre-sizes lazily created symbol tables in the native TypeScript compiler using declaration syntax, aiming to reduce allocations during binding without changing insertion order.

Changes:

Initialize members, exports, and locals tables with capacity hints.
Estimate capacity from member, property, statement, parameter, and type-parameter counts.

File	Description
`tsc/internal/ast/utilities.go`	Adds capacity estimators and uses them when initializing symbol tables.

_{Review effort: Balanced}

The capacity hints for source file and namespace symbol tables used the number of top-level statements. That badly overshoots whenever most statements declare nothing that lands in the table: a module with many private declarations and a single export reserved an entry slot, and past the linear-search limit a hash index, for every statement in its exports table, and expression-heavy scripts did the same for locals. Besides the wasted memory, a hint above the linear-search limit forces hashed lookups on a table that ends up tiny. Instead, count what the binder will actually declare, in a single pass over the statements without allocating. Exports count declarations with an export modifier (or every declaration in an ambient export context), export specifiers, `export * as ns`, export assignments, and one shared entry for any number of plain `export *` declarations. Locals count declarations (one per variable declarator), import bindings, and non-exported import aliases, leaving out unnamed default exports and exported import aliases, which only produce exports.

Copilot

🔵 Needs a closer look

The class instance-member hint incorrectly counts static elements, causing oversized slice and hash-index allocations for classes with few instance members.

No open issues 🎉

1 previously missed issue

In code that hasn't changed since last review

Exclude static elements from class instance-member hint

tsc/internal/ast/utilities.go:137

The class member hint counts static elements, but declareClassMember puts static members in exports, not members. A class with many static members and one constructor therefore reserves a large entry slice and hash index for an instance table containing only the constructor. Exclude static elements, including static blocks, from the class instance-member hint using IsStatic.

1 resolved since last review

Avoid oversized export table hints from private declarations

_{Review effort: Balanced}

The class members hint counted every class element, but the binder declares static elements in the class's exports rather than its members, and static blocks and stray semicolons declare nothing. A class made up mostly of static members therefore reserved a large entry slice, and past the linear-search limit a hash index, for an instance member table that might hold only a constructor, while its exports table still started empty and grew one entry at a time. Count the class elements once and attribute each to the table it lands in: instance elements, a single constructor entry shared by all of its overloads, and constructor parameter properties go to members; static elements plus the implicit `prototype` property go to exports. Overloaded methods and accessor pairs may still be counted more than once, which keeps the hint within a small constant factor of the actual size.

typescript-automation · 2026-10-29T21:27:54Z

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}	_{104,134k (± 0.03%)}	_{104,106k (± 0.02%)}	_~	_104,033k	_104,222k	_{p=0.087 n=20}
_{Memory Allocs}	_{1,263,820 (± 0.01%)}	_{1,261,747 (± 0.01%)}	_{-2,073 (- 0.16%)}	_1,261,380	_1,262,090	_{p=0.000 n=20}
_{Config Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Parse Time}	_{0.023s (± 2.68%)}	_{0.023s (± 2.71%)}	_~	_0.020s	_0.025s	_{p=0.967 n=20}
_{Bind Time}	_{0.008s (± 5.51%)}	_{0.008s (± 5.47%)}	_~	_0.007s	_0.010s	_{p=0.235 n=20}
_{Check Time}	_{0.212s (± 0.72%)}	_{0.214s (± 0.79%)}	_~	_0.206s	_0.221s	_{p=0.052 n=20}
_{Emit Time}	_{0.137s (± 0.72%)}	_{0.136s (± 0.94%)}	_~	_0.131s	_0.141s	_{p=0.404 n=20}
_{Total Time}	_{0.383s (± 0.36%)}	_{0.384s (± 0.49%)}	_~	_0.373s	_0.393s	_{p=0.211 n=20}
_{angular-1 - native}
_Errors	₃	₃	_~	_~	_~	_{p=1.000 n=20}
_Symbols	_{586,509 (± 0.02%)}	_{586,515 (± 0.01%)}	_~	_586,177	_586,887	_{p=0.779 n=20}
_Types	_{241,688 (± 0.00%)}	_{241,688 (± 0.00%)}	_~	_241,685	_241,697	_{p=0.780 n=20}
_{Memory Used}	_{517,954k (± 0.02%)}	_{517,853k (± 0.01%)}	_~	_517,576k	_518,207k	_{p=0.114 n=20}
_{Memory Allocs}	_{7,799,312 (± 0.14%)}	_{7,764,555 (± 0.08%)}	_{-34,757 (- 0.45%)}	_7,754,770	_7,801,240	_{p=0.000 n=20}
_{Config Time}	_0.009s	_0.009s	_~	_~	_~	_{p=1.000 n=20}
_{Parse Time}	_{0.126s (± 2.61%)}	_{0.127s (± 3.76%)}	_~	_0.115s	_0.156s	_{p=0.952 n=20}
_{Bind Time}	_{0.043s (±10.45%)}	_{0.042s (± 8.75%)}	_~	_0.038s	_0.065s	_{p=0.141 n=20}
_{Check Time}	_0s	_0s	_~	_~	_~	_{p=1.000 n=20}
_{Emit Time}	_{0.850s (± 1.07%)}	_{0.849s (± 1.07%)}	_~	_0.827s	_0.908s	_{p=0.825 n=20}
_{Total Time}	_{1.038s (± 1.10%)}	_{1.036s (± 1.15%)}	_~	_1.009s	_1.107s	_{p=0.713 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}	_{497,298k (± 0.01%)}	_{497,256k (± 0.01%)}	_~	_496,985k	_497,447k	_{p=0.274 n=20}
_{Memory Allocs}	_{12,108,970 (± 0.02%)}	_{12,095,724 (± 0.01%)}	_{-13,247 (- 0.11%)}	_12,091,592	_12,101,756	_{p=0.000 n=20}
_{Config Time}	_0.001s	_0.001s	_~	_~	_~	_{p=1.000 n=20}
_{Parse Time}	_{0.041s (± 2.72%)}	_{0.041s (± 2.78%)}	_~	_0.038s	_0.046s	_{p=0.701 n=20}
_{Bind Time}	_{0.013s (±10.64%)}	_{0.012s (± 7.50%)}	_~	_0.011s	_0.019s	_{p=0.079 n=20}
_{Check Time}	_{0.986s (± 0.86%)}	_{1.000s (± 1.10%)}	_{+0.014s (+ 1.39%)}	_0.962s	_1.057s	_{p=0.029 n=20}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Total Time}	_{1.071s (± 0.70%)}	_{1.083s (± 0.98%)}	_{+0.012s (+ 1.12%)}	_1.050s	_1.140s	_{p=0.048 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 (± 0.01%)}	_{27,825k (± 0.01%)}	_{-13k (- 0.05%)}	_27,809k	_27,850k	_{p=0.000 n=20}
_{Memory Allocs}	_{248,534 (± 0.05%)}	_{244,454 (± 0.05%)}	_{-4,080 (- 1.64%)}	_244,001	_244,917	_{p=0.000 n=20}
_{Config Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Parse Time}	_{0.012s (± 2.77%)}	_{0.011s (± 5.13%)}	_~	_0.008s	_0.012s	_{p=0.546 n=20}
_{Bind Time}	_{0.003s (±11.29%)}	_{0.004s (±11.02%)}	_~	_0.002s	_0.005s	_{p=0.201 n=20}
_{Check Time}	_{0.008s (± 4.78%)}	_{0.008s (± 5.20%)}	_~	_0.007s	_0.010s	_{p=0.431 n=20}
_{Emit Time}	_{0.009s (± 6.78%)}	_{0.009s (± 5.10%)}	_~	_0.007s	_0.010s	_{p=0.922 n=20}
_{Total Time}	_{0.032s (± 1.93%)}	_{0.032s (± 2.72%)}	_~	_0.028s	_0.036s	_{p=0.430 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}	_{940,498k (± 0.02%)}	_{940,882k (± 0.02%)}	_{+384k (+ 0.04%)}	_940,108k	_941,841k	_{p=0.005 n=20}
_{Memory Allocs}	_{12,670,876 (± 0.02%)}	_{12,620,149 (± 0.03%)}	_{-50,728 (- 0.40%)}	_12,609,096	_12,644,576	_{p=0.000 n=20}
_{Config Time}	_{0.002s (± 5.09%)}	_0.002s	_~	_~	_~	_{p=1.000 n=20}
_{Parse Time}	_{0.152s (± 2.41%)}	_{0.153s (± 1.78%)}	_~	_0.142s	_0.166s	_{p=0.533 n=20}
_{Bind Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Check Time}	_{0.967s (± 1.04%)}	_{0.980s (± 1.50%)}	_~	_0.922s	_1.074s	_{p=0.213 n=20}
_{Emit Time}	_{0.516s (± 2.01%)}	_{0.522s (± 2.91%)}	_~	_0.470s	_0.592s	_{p=0.625 n=20}
_{Total Time}	_{1.738s (± 0.84%)}	_{1.750s (± 1.02%)}	_~	_1.675s	_1.823s	_{p=0.324 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}	_{1,837,729k (± 0.07%)}	_{1,838,043k (± 0.07%)}	_~	_1,832,881k	_1,844,493k	_{p=0.989 n=20}
_{Memory Allocs}	_{26,024,298 (± 0.16%)}	_{25,970,866 (± 0.15%)}	_{-53,432 (- 0.21%)}	_25,857,272	_26,190,162	_{p=0.033 n=20}
_{Config Time}	_{0.008s (± 1.77%)}	_0.008s	_~	_~	_~	_{p=0.487 n=20}
_{Parse Time}	_{0.301s (± 2.26%)}	_{0.302s (± 2.49%)}	_~	_0.271s	_0.330s	_{p=0.941 n=20}
_{Bind Time}	_0.001s	_0.001s	_~	_~	_~	_{p=1.000 n=20}
_{Check Time}	_{3.060s (± 0.44%)}	_{3.071s (± 0.50%)}	_~	_3.012s	_3.115s	_{p=0.317 n=20}
_{Emit Time}	_{0.238s (± 0.93%)}	_{0.239s (± 1.20%)}	_~	_0.229s	_0.249s	_{p=0.498 n=20}
_{Total Time}	_{4.095s (± 0.36%)}	_{4.109s (± 0.41%)}	_~	_4.051s	_4.174s	_{p=0.163 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}	_{2,881,285k (± 0.04%)}	_{2,881,130k (± 0.03%)}	_~	_2,878,957k	_2,885,245k	_{p=0.904 n=20}
_{Memory Allocs}	_{75,736,179 (± 0.82%)}	_{75,174,812 (± 0.23%)}	_~	_74,633,077	_76,289,170	_{p=0.102 n=20}
_{Config Time}	_{0.026s (± 0.88%)}	_{0.026s (± 1.10%)}	_~	_0.025s	_0.027s	_{p=0.085 n=20}
_{Parse Time}	_{0.499s (± 4.58%)}	_{0.497s (± 5.83%)}	_~	_0.439s	_0.697s	_{p=0.763 n=20}
_{Bind Time}	_{0.175s (±11.70%)}	_{0.171s (±10.39%)}	_~	_0.136s	_0.236s	_{p=0.490 n=20}
_{Check Time}	_{6.794s (± 0.70%)}	_{6.821s (± 0.77%)}	_~	_6.673s	_7.036s	_{p=0.512 n=20}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Total Time}	_{7.546s (± 0.58%)}	_{7.569s (± 0.80%)}	_~	_7.420s	_7.883s	_{p=0.878 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}	_{972,531k (± 0.01%)}	_{972,809k (± 0.02%)}	_{+278k (+ 0.03%)}	_971,910k	_973,511k	_{p=0.018 n=20}
_{Memory Allocs}	_{13,579,132 (± 0.16%)}	_{13,548,298 (± 0.27%)}	_{-30,834 (- 0.23%)}	_13,482,267	_13,811,492	_{p=0.006 n=20}
_{Config Time}	_{0.008s (± 1.30%)}	_{0.008s (± 1.30%)}	_~	_0.008s	_0.009s	_{p=1.000 n=20}
_{Parse Time}	_{0.166s (± 2.04%)}	_{0.168s (± 2.60%)}	_~	_0.147s	_0.187s	_{p=0.432 n=20}
_{Bind Time}	_{0.047s (± 8.78%)}	_{0.045s (± 9.22%)}	_~	_0.039s	_0.066s	_{p=0.143 n=20}
_{Check Time}	_{1.525s (± 0.70%)}	_{1.518s (± 0.59%)}	_~	_1.479s	_1.542s	_{p=0.324 n=20}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Total Time}	_{1.766s (± 0.58%)}	_{1.758s (± 0.56%)}	_~	_1.720s	_1.817s	_{p=0.103 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}	_{1,168,555k (± 0.20%)}	_{1,174,730k (± 0.65%)}	_~	_1,159,528k	_1,220,768k	_{p=0.841 n=20}
_{Memory Allocs}	_{47,753,816 (± 0.08%)}	_{47,571,178 (± 0.12%)}	_{-182,638 (- 0.38%)}	_47,374,273	_47,785,520	_{p=0.000 n=20}
_{Config Time}	_{0.002s (±18.03%)}	_{0.002s (±18.87%)}	_~	_0.000s	_0.002s	_{p=0.242 n=20}
_{Parse Time}	_{0.146s (± 2.50%)}	_{0.146s (± 2.17%)}	_~	_0.134s	_0.166s	_{p=0.888 n=20}
_{Bind Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Check Time}	_{0.845s (± 1.40%)}	_{0.845s (± 1.48%)}	_~	_0.814s	_0.894s	_{p=0.867 n=20}
_{Emit Time}	_{0.148s (± 2.30%)}	_{0.151s (± 3.48%)}	_~	_0.139s	_0.178s	_{p=0.605 n=20}
_{Total Time}	_{9.867s (± 1.76%)}	_{9.903s (± 1.52%)}	_~	_9.474s	_10.526s	_{p=0.583 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}	_{224,643k (± 0.02%)}	_{224,552k (± 0.03%)}	_{-91k (- 0.04%)}	_224,247k	_224,751k	_{p=0.044 n=20}
_{Memory Allocs}	_{2,401,453 (± 0.01%)}	_{2,392,419 (± 0.01%)}	_{-9,033 (- 0.38%)}	_2,391,161	_2,393,797	_{p=0.000 n=20}
_{Config Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Parse Time}	_{0.049s (± 3.23%)}	_{0.052s (± 3.39%)}	_{🔻+0.003s (+ 7.05%)}	_0.044s	_0.060s	_{p=0.006 n=20}
_{Bind Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Check Time}	_{0.374s (± 0.67%)}	_{0.376s (± 0.65%)}	_~	_0.369s	_0.388s	_{p=0.120 n=20}
_{Emit Time}	_{0.048s (± 4.97%)}	_{0.048s (± 4.09%)}	_~	_0.042s	_0.054s	_{p=0.995 n=20}
_{Total Time}	_{0.499s (± 0.76%)}	_{0.504s (± 0.64%)}	_{+0.005s (+ 0.97%)}	_0.492s	_0.514s	_{p=0.048 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}	_{2,433,177k (± 0.02%)}	_{2,433,369k (± 0.02%)}	_~	_2,431,332k	_2,435,734k	_{p=0.410 n=20}
_{Memory Allocs}	_{37,412,645 (± 0.13%)}	_{37,273,073 (± 0.10%)}	_{-139,572 (- 0.37%)}	_37,172,488	_37,497,586	_{p=0.000 n=20}
_{Config Time}	_0.003s	_0.003s	_~	_~	_~	_{p=1.000 n=20}
_{Parse Time}	_{0.255s (± 2.61%)}	_{0.251s (± 3.20%)}	_~	_0.227s	_0.289s	_{p=0.351 n=20}
_{Bind Time}	_{0.085s (± 8.82%)}	_{0.096s (±12.25%)}	_~	_0.071s	_0.143s	_{p=0.605 n=20}
_{Check Time}	_{7.182s (± 0.58%)}	_{7.173s (± 0.83%)}	_~	_7.065s	_7.614s	_{p=0.324 n=20}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Total Time}	_{7.536s (± 0.53%)}	_{7.534s (± 0.86%)}	_~	_7.402s	_8.002s	_{p=0.551 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}	_{331,455k (± 0.01%)}	_{331,330k (± 0.02%)}	_{-125k (- 0.04%)}	_331,066k	_331,612k	_{p=0.000 n=20}
_{Memory Allocs}	_{4,392,691 (± 0.16%)}	_{4,373,150 (± 0.13%)}	_{-19,542 (- 0.44%)}	_4,361,842	_4,399,697	_{p=0.000 n=20}
_{Config Time}	_0.001s	_0.001s	_~	_~	_~	_{p=1.000 n=20}
_{Parse Time}	_{0.038s (± 3.35%)}	_{0.039s (± 4.74%)}	_~	_0.032s	_0.045s	_{p=0.170 n=20}
_{Bind Time}	_{0.012s (± 8.01%)}	_{0.012s (± 8.98%)}	_{🟩-0.001s (- 6.83%)}	_0.010s	_0.018s	_{p=0.044 n=20}
_{Check Time}	_{0.558s (± 0.79%)}	_{0.560s (± 1.07%)}	_~	_0.543s	_0.589s	_{p=0.733 n=20}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Total Time}	_{0.627s (± 0.62%)}	_{0.631s (± 1.01%)}	_~	_0.611s	_0.653s	_{p=0.515 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}	_{193,517k (± 0.01%)}	_{193,468k (± 0.01%)}	_{-49k (- 0.03%)}	_193,373k	_193,560k	_{p=0.003 n=20}
_{Memory Allocs}	_{1,318,305 (± 0.02%)}	_{1,311,031 (± 0.03%)}	_{-7,274 (- 0.55%)}	_1,310,263	_1,313,612	_{p=0.000 n=20}
_{Config Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Parse Time}	_{0.043s (± 3.80%)}	_{0.042s (± 2.48%)}	_~	_0.038s	_0.046s	_{p=0.461 n=20}
_{Bind Time}	_{0.020s (± 4.98%)}	_{0.022s (± 4.81%)}	_{🔻+0.002s (+ 8.79%)}	_0.018s	_0.026s	_{p=0.017 n=20}
_{Check Time}	_{0.302s (± 1.09%)}	_{0.301s (± 1.17%)}	_~	_0.287s	_0.313s	_{p=0.541 n=20}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Total Time}	_{0.372s (± 0.82%)}	_{0.371s (± 0.88%)}	_~	_0.354s	_0.381s	_{p=0.846 n=20}
_{vscode - native}
_Errors	₁₁	₁₁	_~	_~	_~	_{p=1.000 n=20}
_Symbols	_7,501,886	_7,501,886	_~	_~	_~	_{p=1.000 n=20}
_Types	_4,415,089	_4,415,089	_~	_~	_~	_{p=1.000 n=20}
_{Memory Used}	_{5,203,879k (± 0.01%)}	_{5,204,395k (± 0.01%)}	_~	_5,202,170k	_5,206,725k	_{p=0.265 n=20}
_{Memory Allocs}	_{56,949,900 (± 0.02%)}	_{56,658,299 (± 0.02%)}	_{-291,601 (- 0.51%)}	_56,629,107	_56,712,854	_{p=0.000 n=20}
_{Config Time}	_{0.035s (± 0.67%)}	_{0.035s (± 0.90%)}	_~	_0.035s	_0.037s	_{p=0.514 n=20}
_{Parse Time}	_{0.909s (± 1.25%)}	_{0.890s (± 2.09%)}	_~	_0.814s	_0.939s	_{p=0.365 n=20}
_{Bind Time}	_{0.305s (± 4.06%)}	_{0.340s (±11.84%)}	_~	_0.282s	_0.529s	_{p=0.473 n=20}
_{Check Time}	_{7.759s (± 0.38%)}	_{7.733s (± 0.76%)}	_~	_7.502s	_7.922s	_{p=0.973 n=20}
_{Emit Time}	_{2.709s (± 4.08%)}	_{2.925s (± 6.36%)}	_{🔻+0.216s (+ 7.97%)}	_2.610s	_3.596s	_{p=0.008 n=20}
_{Total Time}	_{11.775s (± 0.91%)}	_{11.982s (± 1.32%)}	_{+0.207s (+ 1.76%)}	_11.665s	_12.611s	_{p=0.008 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}	_{693,477k (± 0.02%)}	_{693,458k (± 0.02%)}	_~	_693,016k	_694,164k	_{p=0.826 n=20}
_{Memory Allocs}	_{6,498,345 (± 0.03%)}	_{6,468,767 (± 0.09%)}	_{-29,578 (- 0.46%)}	_6,456,337	_6,512,338	_{p=0.000 n=20}
_{Config Time}	_0.004s	_{0.004s (±16.78%)}	_~	_0.004s	_0.011s	_{p=1.000 n=20}
_{Parse Time}	_{0.140s (± 3.00%)}	_{0.141s (± 3.65%)}	_~	_0.121s	_0.171s	_{p=0.973 n=20}
_{Bind Time}	_{0.044s (± 7.40%)}	_{0.049s (±11.99%)}	_~	_0.038s	_0.077s	_{p=0.711 n=20}
_{Check Time}	_{1.159s (± 0.91%)}	_{1.176s (± 1.40%)}	_~	_1.117s	_1.252s	_{p=0.082 n=20}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Total Time}	_{1.370s (± 0.85%)}	_{1.397s (± 0.97%)}	_{+0.027s (+ 1.96%)}	_1.349s	_1.467s	_{p=0.005 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}	_{350,927k (± 0.02%)}	_{350,762k (± 0.02%)}	_{-165k (- 0.05%)}	_350,623k	_351,142k	_{p=0.000 n=20}
_{Memory Allocs}	_{3,991,786 (± 0.07%)}	_{3,967,947 (± 0.08%)}	_{-23,839 (- 0.60%)}	_3,957,316	_3,982,121	_{p=0.000 n=20}
_{Config Time}	_0.001s	_0.001s	_~	_~	_~	_{p=1.000 n=20}
_{Parse Time}	_{0.062s (± 3.76%)}	_{0.060s (± 2.31%)}	_~	_0.054s	_0.065s	_{p=0.196 n=20}
_{Bind Time}	_{0.021s (±10.85%)}	_{0.021s (±12.04%)}	_~	_0.017s	_0.033s	_{p=0.177 n=20}
_{Check Time}	_{0.417s (± 1.15%)}	_{0.414s (± 0.69%)}	_~	_0.404s	_0.425s	_{p=0.261 n=20}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=20}
_{Total Time}	_{0.506s (± 1.08%)}	_{0.500s (± 0.82%)}	_~	_0.484s	_0.515s	_{p=0.095 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

Copilot

🟡 Changes recommended

Declaration-backed symbol-table initialization lacks focused regression tests verifying that predicted-capacity fills avoid further backing-store allocation and retain insertion order, including above the 16-entry hash-index threshold.

1 open issue

Add allocation regression tests for declaration-backed table sizing · New

_{Review effort: Balanced}

-	return GetSymbolTable(&symbol.ensureExtra(arena).members)
+	extra := symbol.ensureExtra(arena)
+	if extra.members == nil {
+		extra.members = NewSymbolTableWithCapacity(membersCapacityHint(symbol))


Copilot · 2026-10-29T21:31:25Z

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Ryan Cavanaugh (RyanCavanaugh)

Reviewed at 8a39fac. The revised hints distinguish private exports and static versus instance class members, and affect capacity without changing symbol insertion order or growth correctness. AST tests and targeted ambient-module, default-export, namespace-merging, and export-star compiler baselines passed. No concrete correctness regression found.

Jake Bailey (jakebailey) · 2026-10-30T18:58:39Z

This does not feel super worth it based on the benchmarks and the amount of code

Copilot AI balanced review requested due to automatic review settings October 29, 2026 20:18

github-project-automation Bot added this to PR Backlog Oct 29, 2026

github-project-automation Bot moved this to Not started in PR Backlog Oct 29, 2026

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

Copilot started reviewing on behalf of Jake Bailey (jakebailey) October 29, 2026 20:18

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Comment thread tsc/internal/ast/utilities.go Resolved

Jake Bailey (jakebailey) requested a balanced review from Copilot October 29, 2026 20:52

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

Jake Bailey (jakebailey) requested a balanced review from Copilot October 29, 2026 21:24

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Comment thread tsc/internal/ast/utilities.go

return GetSymbolTable(&symbol.ensureExtra(arena).members)

extra := symbol.ensureExtra(arena)

if extra.members == nil {

extra.members = NewSymbolTableWithCapacity(membersCapacityHint(symbol))

Ryan Cavanaugh (RyanCavanaugh) approved these changes Oct 30, 2026

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github-project-automation Bot moved this from Not started to Needs merge in PR Backlog Oct 30, 2026

Jake Bailey (jakebailey) marked this pull request as draft October 30, 2026 18:58

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Pre-size member, export, and locals symbol tables - #65025

Pre-size member, export, and locals symbol tables#65025
Jake Bailey (jakebailey) wants to merge 3 commits into
microsoft:mainfrom
jakebailey:perf/presized-symbol-tables

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Jake Bailey (jakebailey) commented Oct 29, 2026 •

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