Fix quadratic performance with lots of use statements #43584
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We already had a cache for file contents, but we read the source-file before testing the cache, causing obvious slowness, so this just avoids loading the source-file when the cache already has the contents.
Instead of finding the next free disambiguator by incrementing it until you find a place, store the next available disambiguator in an hash-map. This avoids O(n^2) performance when lots of items have the same un-disambiguated `DefPathData` - e.g. all `use` items have `DefPathData::Misc`.
eddyb
reviewed
Aug 1, 2017
| if *self.external_src.borrow() == ExternalSource::AbsentOk { | ||
| let src = get_src(); |
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Oh wow, my bad, I didn't notice that it was loading the file each time in the original PR.
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@bors r+ |
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📌 Commit 70478ca has been approved by |
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Thanks for the quick fix @arielb1! |
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Could this be uplifted to beta @arielb1 ? Firefox would love having this in the 1.20 release! |
alexcrichton
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beta-nominated
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I agree with backporting to beta. cc @nikomatsakis |
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☀️ Test successful - status-appveyor, status-travis |
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Tagging as accepted for beta |
alexcrichton
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This fixes 2 problems that caused quadratic performance when lots of use-statements were present. After this patch, performance is linear (and very fast) even with 1M uses.
Fixes #43572.
Fixes #43573.
r? @eddyb