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…ions, r=compiler-errors Use `ThinVec` for PredicateObligation storage ~~I noticed while profiling clippy on a project that a large amount of time is being spent allocating `Vec`s for `PredicateObligation`, and the `Vec`s are often quite small. This is an attempt to optimise this by using SmallVec to avoid heap allocations for these common small Vecs.~~ This PR turns all the `Vec<PredicateObligation>` into a single type alias while avoiding referring to `Vec` around it, then swaps the type over to `ThinVec<PredicateObligation>` and fixes the fallout. This also contains an implementation of `ThinVec::extract_if`, copied from `Vec::extract_if` and currently being upstreamed to mozilla/thin-vec#66. This leads to a small (0.2-0.7%) performance gain in the latest perf run.
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…ions, r=compiler-errors Use `ThinVec` for PredicateObligation storage ~~I noticed while profiling clippy on a project that a large amount of time is being spent allocating `Vec`s for `PredicateObligation`, and the `Vec`s are often quite small. This is an attempt to optimise this by using SmallVec to avoid heap allocations for these common small Vecs.~~ This PR turns all the `Vec<PredicateObligation>` into a single type alias while avoiding referring to `Vec` around it, then swaps the type over to `ThinVec<PredicateObligation>` and fixes the fallout. This also contains an implementation of `ThinVec::extract_if`, copied from `Vec::extract_if` and currently being upstreamed to mozilla/thin-vec#66. This leads to a small (0.2-0.7%) performance gain in the latest perf run.
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…ompiler-errors Use `ThinVec` for PredicateObligation storage ~~I noticed while profiling clippy on a project that a large amount of time is being spent allocating `Vec`s for `PredicateObligation`, and the `Vec`s are often quite small. This is an attempt to optimise this by using SmallVec to avoid heap allocations for these common small Vecs.~~ This PR turns all the `Vec<PredicateObligation>` into a single type alias while avoiding referring to `Vec` around it, then swaps the type over to `ThinVec<PredicateObligation>` and fixes the fallout. This also contains an implementation of `ThinVec::extract_if`, copied from `Vec::extract_if` and currently being upstreamed to mozilla/thin-vec#66. This leads to a small (0.2-0.7%) performance gain in the latest perf run.
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This is now stable for Vec, so could we make it stable here too?
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@nicoburns I've updated this to match the current implementation in std, fixed the CI failures, and removed the unstable gating. I've also disabled stacked borrows in CI as std doesn't pass it, and left a comment in the Miri CI to document this for the future. |
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Closes #64
This is a cleaned-up copy paste of the std implementation.