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Lots of "cannot find in scope" errors can make name resolution extraordinarily slow #63478

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scottmcm opened this issue Aug 12, 2019 · 2 comments
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Lots of "cannot find in scope" errors can make name resolution extraordinarily slow #63478

scottmcm opened this issue Aug 12, 2019 · 2 comments
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A-diagnostics Area: Messages for errors, warnings, and lints A-resolve Area: Name resolution I-compiletime Issue: Problems and improvements with respect to compile times. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.

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@scottmcm
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I missed a use and found a check that takes over 4 minutes to fail.

Repro: https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=aaac7e403ced051c0e4165df25a455a5

time-passes blames this on "name resolution"
@petrochenkov
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Suggestion search does a lot of heavy stuff like loading all the known crates and searching names in them (#54391) and maybe something else.

This was never profiled or optimized, AFAIK, due to the general stance that "the error case can be slow".
So it's quite possible there are low-hanging fruits there, someone needs to run a profiler on that.

@jonas-schievink jonas-schievink added A-diagnostics Area: Messages for errors, warnings, and lints A-resolve Area: Name resolution I-compiletime Issue: Problems and improvements with respect to compile times. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Aug 12, 2019
@nathanwhit nathanwhit mentioned this issue Sep 5, 2019
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@Mark-Simulacrum
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The reproduction in this issue fails to compile in a total of 1.3 seconds with 1.24 seconds spent in name resolution -- and duplicating the set a couple times only gets me up to around ~7 seconds so I feel like this can probably be closed now? It seems sort of "expected" that tons of errors will be slow...

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A-diagnostics Area: Messages for errors, warnings, and lints A-resolve Area: Name resolution I-compiletime Issue: Problems and improvements with respect to compile times. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.
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@jonas-schievink @Mark-Simulacrum @petrochenkov @scottmcm