Performance regression in TS 5.4 about typescript

[Andarist]

Would you be able to apply the patch from this PR and test the perf?

[MichaelMitchell-at]

Would you be able to apply the patch from this PR and test the perf?

Sure, will try it now

[MichaelMitchell-at]

Would you be able to apply the patch from this PR and test the perf?

I applied the patch and this brought typechecking time down to ~331 s.

[Andarist]

Is there any difference there between when you typecheck + emit dts and when you just typecheck?

[MichaelMitchell-at]

Is there any difference there between when you typecheck + emit dts and when you just typecheck?

Since this is a composite project, subprojects must emit dts for parent projects to use.

[RyanCavanaugh]

We need a way to repro this in order to investigate. None of our perf tests showed a significant drop in performance over the prior release, so it's something specific to the code here that we'd need to be able to look at to make further progress.

[MichaelMitchell-at]

I can send over any traces or profiles you want so long as I can redact any actual code/code paths. Since I lack the knowledge or tools to identify what the performance hotspots in the code actually are (a frustration that arises frequently when trying to optimize our typechecking perf in general), there's just no way for me to construct a shareable repo that can illustrate the regression.

[jakebailey]

If you use https://www.npmjs.com/package/pprof-it on tsc.js and set PPROF_SANITIZE=true, the output profiles should be free of any references to code or even to the paths on your machine. Getting profiles before/after the bad commit would be most helpful.

[MichaelMitchell-at]

If you use https://www.npmjs.com/package/pprof-it on tsc.js and set PPROF_SANITIZE=true, the output profiles should be free of any references to code or even to the paths on your machine. Getting profiles before/after the bad commit would be most helpful.

Thanks I'll do this over the weekend

[MichaelMitchell-at]

Here are some profiles from pprof-it

Before regression
pprof-heap-17148.pb.gz
pprof-time-17148.pb.gz

After regression
pprof-heap-22618.pb.gz
pprof-time-22618.pb.gz