Avoid temporary composite mapper allocations by jakebailey · Pull Request #4798 · microsoft/typescript-go

jakebailey · 2026-07-30T20:30:07Z

I thew copilot at #4579's case and while it didn't fix anything, it did find a perf optimization:

Check time: 4.923s → 4.791s (2.7%)
Peak RSS: 738MB → 697MB (5.5%)
Allocations: 434MB → 342MB (21%)

jakebailey · 2026-07-30T20:30:22Z

typescript-automation · 2026-07-30T20:30:27Z

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

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

typescript-automation · 2026-07-30T20:56:12Z

@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=6}
_Symbols	_119,733	_119,733	_~	_~	_~	_{p=1.000 n=6}
_Types	_99,032	_99,032	_~	_~	_~	_{p=1.000 n=6}
_{Memory Used}	_{152,987k (± 0.68%)}	_{151,535k (± 0.72%)}	_~	_150,296k	_152,997k	_{p=0.065 n=6}
_{Memory Allocs}	_{2,275,772 (± 0.00%)}	_{2,275,803 (± 0.01%)}	_~	_2,275,436	_2,275,993	_{p=0.240 n=6}
_{Config Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=6}
_{Parse Time}	_{0.050s (±10.77%)}	_{0.051s (± 3.28%)}	_~	_0.048s	_0.053s	_{p=0.972 n=6}
_{Bind Time}	_{0.018s (± 7.31%)}	_{0.018s (±19.18%)}	_~	_0.012s	_0.022s	_{p=0.634 n=6}
_{Check Time}	_{0.757s (± 0.87%)}	_{0.762s (± 0.81%)}	_~	_0.754s	_0.772s	_{p=0.147 n=6}
_{Emit Time}	_{0.300s (± 3.02%)}	_{0.311s (± 3.08%)}	_~	_0.304s	_0.330s	_{p=0.165 n=6}
_{Total Time}	_{1.133s (± 1.17%)}	_{1.149s (± 1.14%)}	_~	_1.130s	_1.169s	_{p=0.071 n=6}
_{angular-1 - native}
_Errors	₃	₃	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_{873,032 (± 0.19%)}	_{871,536 (± 0.12%)}	_~	_870,289	_872,901	_{p=0.093 n=6}
_Types	_{263,962 (± 0.00%)}	_{263,961 (± 0.00%)}	_~	_263,960	_263,962	_{p=0.177 n=6}
_{Memory Used}	_{808,871k (± 0.11%)}	_{808,109k (± 0.13%)}	_~	_806,746k	_809,568k	_{p=0.240 n=6}
_{Memory Allocs}	_{13,150,552 (± 0.16%)}	_{13,129,026 (± 0.01%)}	_{-21,526 (- 0.16%)}	_13,127,187	_13,130,269	_{p=0.002 n=6}
_{Config Time}	_{0.017s (± 4.71%)}	_{0.017s (± 2.98%)}	_~	_0.017s	_0.018s	_{p=1.000 n=6}
_{Parse Time}	_{0.240s (± 4.71%)}	_{0.239s (± 4.26%)}	_~	_0.224s	_0.253s	_{p=0.968 n=6}
_{Bind Time}	_{0.047s (±37.98%)}	_{0.044s (±10.73%)}	_~	_0.040s	_0.053s	_{p=0.199 n=6}
_{Check Time}	_0s	_0s	_~	_~	_~	_{p=1.000 n=6}
_{Emit Time}	_{1.892s (± 2.46%)}	_{1.885s (± 0.59%)}	_~	_1.874s	_1.901s	_{p=0.589 n=6}
_{Total Time}	_{2.211s (± 1.84%)}	_{2.196s (± 0.84%)}	_~	_2.171s	_2.221s	_{p=0.699 n=6}
_{mui-docs - native}
_Errors	_{11,281 (± 0.01%)}	_{11,280 (± 0.03%)}	_~	_11,274	_11,282	_{p=0.697 n=6}
_Symbols	_4,386,587	_4,386,587	_~	_~	_~	_{p=1.000 n=6}
_Types	_1,537,077	_1,537,077	_~	_~	_~	_{p=1.000 n=6}
_{Memory Used}	_{4,961,353k (± 0.03%)}	_{4,963,576k (± 0.04%)}	_{+2,223k (+ 0.04%)}	_4,962,032k	_4,967,716k	_{p=0.009 n=6}
_{Memory Allocs}	_{46,006,787 (± 0.11%)}	_{45,349,229 (± 0.14%)}	_{-657,558 (- 1.43%)}	_45,284,521	_45,453,167	_{p=0.002 n=6}
_{Config Time}	_{0.018s (± 9.38%)}	_0.016s	_~	_~	_~	_{p=0.061 n=6}
_{Parse Time}	_{0.498s (± 3.88%)}	_{0.493s (± 2.46%)}	_~	_0.476s	_0.507s	_{p=1.000 n=6}
_{Bind Time}	_0.002s	_0.002s	_~	_~	_~	_{p=1.000 n=6}
_{Check Time}	_{15.986s (± 0.20%)}	_{16.007s (± 0.59%)}	_~	_15.905s	_16.137s	_{p=1.000 n=6}
_{Emit Time}	_{0.454s (± 3.50%)}	_{0.470s (± 4.40%)}	_{+0.016s (+ 3.60%)}	_0.448s	_0.490s	_{p=0.032 n=6}
_{Total Time}	_{17.694s (± 0.32%)}	_{17.694s (± 0.62%)}	_~	_17.569s	_17.817s	_{p=1.000 n=6}
_{self-build-src - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_1,394,491	_1,394,491	_~	_~	_~	_{p=1.000 n=6}
_Types	_442,212	_442,212	_~	_~	_~	_{p=1.000 n=6}
_{Memory Used}	_{1,598,657k (± 0.48%)}	_{1,594,316k (± 0.28%)}	_~	_1,588,042k	_1,600,395k	_{p=0.093 n=6}
_{Memory Allocs}	_{97,131,731 (± 0.07%)}	_{97,043,850 (± 0.04%)}	_~	_97,006,504	_97,111,266	_{p=0.065 n=6}
_{Config Time}	_{0.020s (±29.79%)}	_{0.018s (±35.34%)}	_~	_0.010s	_0.027s	_{p=0.485 n=6}
_{Parse Time}	_{0.251s (± 2.67%)}	_{0.257s (± 5.40%)}	_~	_0.239s	_0.276s	_{p=0.411 n=6}
_{Bind Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=6}
_{Check Time}	_{2.182s (± 0.94%)}	_{2.182s (± 1.08%)}	_~	_2.154s	_2.217s	_{p=0.937 n=6}
_{Emit Time}	_{0.299s (± 3.66%)}	_{0.308s (± 6.35%)}	_~	_0.293s	_0.337s	_{p=0.667 n=6}
_{Total Time}	_{28.788s (± 0.94%)}	_{29.027s (± 0.85%)}	_~	_28.665s	_29.390s	_{p=0.132 n=6}
_{self-compiler - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_337,834	_337,834	_~	_~	_~	_{p=1.000 n=6}
_Types	_199,561	_199,561	_~	_~	_~	_{p=1.000 n=6}
_{Memory Used}	_{318,840k (± 0.02%)}	_{318,767k (± 0.04%)}	_~	_318,673k	_319,010k	_{p=0.180 n=6}
_{Memory Allocs}	_{4,677,718 (± 0.01%)}	_{4,675,434 (± 0.01%)}	_{-2,284 (- 0.05%)}	_4,674,940	_4,676,460	_{p=0.002 n=6}
_{Config Time}	_0.001s	_0.001s	_~	_~	_~	_{p=1.000 n=6}
_{Parse Time}	_{0.115s (± 5.19%)}	_{0.114s (± 3.18%)}	_~	_0.108s	_0.117s	_{p=0.725 n=6}
_{Bind Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=6}
_{Check Time}	_{1.275s (± 1.43%)}	_{1.294s (± 0.94%)}	_~	_1.277s	_1.309s	_{p=0.082 n=6}
_{Emit Time}	_{0.114s (±10.97%)}	_{0.120s (± 6.45%)}	_~	_0.109s	_0.128s	_{p=0.407 n=6}
_{Total Time}	_{1.560s (± 1.38%)}	_{1.579s (± 0.99%)}	_~	_1.558s	_1.599s	_{p=0.223 n=6}
_{ts-pre-modules - native}
_Errors	₈₇	₈₇	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_302,246	_302,246	_~	_~	_~	_{p=1.000 n=6}
_Types	_181,595	_181,595	_~	_~	_~	_{p=1.000 n=6}
_{Memory Used}	_{274,829k (± 0.04%)}	_{274,840k (± 0.03%)}	_~	_274,713k	_274,938k	_{p=0.589 n=6}
_{Memory Allocs}	_{1,675,617 (± 0.02%)}	_{1,673,907 (± 0.03%)}	_{-1,710 (- 0.10%)}	_1,673,288	_1,674,346	_{p=0.002 n=6}
_{Config Time}	_0.001s	_0.001s	_~	_~	_~	_{p=1.000 n=6}
_{Parse Time}	_{0.102s (± 6.85%)}	_{0.100s (± 4.24%)}	_~	_0.096s	_0.105s	_{p=0.853 n=6}
_{Bind Time}	_{0.039s (±14.49%)}	_{0.043s (±12.85%)}	_~	_0.034s	_0.050s	_{p=0.294 n=6}
_{Check Time}	_{1.073s (± 0.99%)}	_{1.070s (± 1.04%)}	_~	_1.061s	_1.086s	_{p=0.457 n=6}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=6}
_{Total Time}	_{1.228s (± 1.03%)}	_{1.227s (± 0.94%)}	_~	_1.211s	_1.245s	_{p=1.000 n=6}
_{vscode - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_7,520,316	_7,520,316	_~	_~	_~	_{p=1.000 n=6}
_Types	_2,621,761	_2,621,761	_~	_~	_~	_{p=1.000 n=6}
_{Memory Used}	_{5,025,197k (± 0.03%)}	_{5,025,243k (± 0.02%)}	_~	_5,023,953k	_5,026,389k	_{p=0.937 n=6}
_{Memory Allocs}	_{38,384,658 (± 0.03%)}	_{38,367,679 (± 0.09%)}	_~	_38,328,642	_38,401,073	_{p=0.699 n=6}
_{Config Time}	_{0.073s (±11.28%)}	_{0.078s (± 9.85%)}	_~	_0.067s	_0.089s	_{p=0.190 n=6}
_{Parse Time}	_{0.940s (± 2.94%)}	_{0.902s (± 2.56%)}	_{🟩-0.037s (- 3.99%)}	_0.874s	_0.934s	_{p=0.041 n=6}
_{Bind Time}	_{0.165s (± 1.85%)}	_{0.161s (± 4.12%)}	_~	_0.149s	_0.169s	_{p=0.284 n=6}
_{Check Time}	_{8.653s (± 0.29%)}	_{8.678s (± 1.10%)}	_~	_8.598s	_8.860s	_{p=1.000 n=6}
_{Emit Time}	_{2.683s (± 2.70%)}	_{2.551s (± 8.12%)}	_{🟩-0.132s (- 4.92%)}	_2.172s	_2.698s	_{p=0.041 n=6}
_{Total Time}	_{12.531s (± 0.86%)}	_{12.389s (± 1.23%)}	_{-0.142s (- 1.14%)}	_12.184s	_12.531s	_{p=0.041 n=6}
_{webpack - native}
_Errors	₂	₂	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_195,834	_195,834	_~	_~	_~	_{p=1.000 n=6}
_Types	₃₄₀	₃₄₀	_~	_~	_~	_{p=1.000 n=6}
_{Memory Used}	_{229,898k (± 0.22%)}	_{229,965k (± 0.20%)}	_~	_229,258k	_230,622k	_{p=0.970 n=6}
_{Memory Allocs}	_{978,850 (± 0.50%)}	_{976,030 (± 0.24%)}	_~	_972,892	_978,922	_{p=0.240 n=6}
_{Config Time}	_{0.012s (±16.65%)}	_{0.011s (±16.40%)}	_~	_0.008s	_0.012s	_{p=0.325 n=6}
_{Parse Time}	_{0.148s (± 1.78%)}	_{0.147s (± 4.75%)}	_~	_0.137s	_0.157s	_{p=0.974 n=6}
_{Bind Time}	_0s	_0s	_~	_~	_~	_{p=1.000 n=6}
_{Check Time}	_0s	_0s	_~	_~	_~	_{p=1.000 n=6}
_{Emit Time}	_{0.048s (±14.14%)}	_{0.054s (± 7.41%)}	_~	_0.047s	_0.058s	_{p=0.169 n=6}
_{Total Time}	_{0.209s (± 3.70%)}	_{0.212s (± 2.27%)}	_~	_0.204s	_0.217s	_{p=0.558 n=6}
_{xstate-main - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_1,066,055	_1,066,055	_~	_~	_~	_{p=1.000 n=6}
_Types	_392,847	_392,847	_~	_~	_~	_{p=1.000 n=6}
_{Memory Used}	_{634,811k (± 0.03%)}	_{634,709k (± 0.02%)}	_~	_634,565k	_634,855k	_{p=0.310 n=6}
_{Memory Allocs}	_{5,006,845 (± 0.21%)}	_{4,934,689 (± 0.10%)}	_{-72,156 (- 1.44%)}	_4,927,952	_4,942,549	_{p=0.002 n=6}
_{Config Time}	_{0.005s (± 8.44%)}	_{0.005s (± 8.44%)}	_~	_0.004s	_0.005s	_{p=1.000 n=6}
_{Parse Time}	_{0.126s (± 4.47%)}	_{0.130s (± 2.98%)}	_~	_0.126s	_0.136s	_{p=0.190 n=6}
_{Bind Time}	_{0.036s (±24.07%)}	_{0.033s (±23.84%)}	_~	_0.026s	_0.047s	_{p=0.420 n=6}
_{Check Time}	_{1.242s (± 0.93%)}	_{1.245s (± 0.72%)}	_~	_1.232s	_1.259s	_{p=0.686 n=6}
_{Emit Time}	_0.001s	_0.001s	_~	_~	_~	_{p=1.000 n=6}
_{Total Time}	_{1.414s (± 0.34%)}	_{1.417s (± 0.47%)}	_~	_1.411s	_1.427s	_{p=0.589 n=6}

System info unknown

Hosts

native

Scenarios

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

_Benchmark	_Name	_Iterations
_Current	_pr	₆
_Baseline	_baseline	₆

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Avoid temporary composite mapper allocations - #4798

Avoid temporary composite mapper allocations#4798
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