Performance regression with `--incremental` between `native-preview-0.20251211.1` and `0.20251209.1`

[gggdomi]

Hi,

Apologies for the absence of repro. Hopefully with the small time range it will still be helpful to pinpoint a potential regression.

We noticed today that tsgo was noticeably slower on our codebase.
We found that the difference was :

• between versions typescriptteam.native-preview-0.20251209.1 (fast) and typescriptteam.native-preview-0.20251211.1 (slow)
• only when using --incremental, and only on first run (ie. no pre-existing .tsbuildinfo)

We reproduced multiple times, on multiple machines, but on a single codebase.

Metric	0.20251209.1	0.20251211.1	Notes
Check time (incremental, first run)	6.642s	19.916s	Large slowdown
CPU (incremental, first run)	419% CPU	186% CPU	Multi-threading issue?
Check time (incremental, next runs)	<0.01s	<0.01s	No difference
Check time (incremental = false)	~6.5s	~6.5s	No difference

Detailed logs

time and extendedDiagnostics logs of first --incremental run, with each version.
(there was no meaningful differences/logs for other configurations)

# ✅ version 0.20251209.1 is fast
➜ rm -f .tsconfig.tsbuildinfo
➜ time /Users/gui/.vscode/extensions/typescriptteam.native-preview-0.20251209.1-darwin-arm64/lib/tsgo --noEmit --project tsconfig.json --incremental  --extendedDiagnostics
Files:                    9918
Lines:                 1489421
Identifiers:           1767364
Symbols:               8496581
Types:                 2938919
Instantiations:       10101417
Memory used:          5176707K
Memory allocs:        70927013
Config time:            0.094s
BuildInfo read time:    0.000s
Parse time:             0.718s
Bind time:              0.000s
Check time:             6.642s
Emit time:              0.386s
Changes compute time:   0.168s
Total time:             8.011s

time:  41.01s user 2.36s system 419% cpu 10.350 total

# ❌ version 0.20251211.1 is slow
➜ rm -f .tsconfig.tsbuildinfo
➜ time /Users/gui/.vscode/extensions/typescriptteam.native-preview-0.20251211.1-darwin-arm64/lib/tsgo --noEmit --project tsconfig.json --incremental  --extendedDiagnostics
Files:                    9918
Lines:                 1489421
Identifiers:           1767364
Symbols:               8496581
Types:                 2938919
Instantiations:       10101417
Memory used:          5173748K
Memory allocs:        71095193
Config time:            0.102s
BuildInfo read time:    0.000s
Parse time:             0.715s
Bind time:              0.001s
Check time:            19.916s
Emit time:              0.447s
Changes compute time:   0.269s
Total time:            21.456s

time:  43.04s user 2.15s system 186% cpu 24.246 total

[jakebailey]

There were many changes in between these two versions. Could you build from source and git bisect?

[gggdomi]

Sure, could you point me to which commits correspond to the two releases?
I can't find tags/release or publish commits.

[jakebailey]

The npm package has that in the package.json, but I guess not the VS Code extension.

It'd be 8372401 to ddf0b72

8372401...ddf0b72

[jakebailey]

If it's #2314 I'm going to be very sad