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Optimize seen Predicate filtering. #50932

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merged 1 commit into from May 22, 2018

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nnethercote commented May 21, 2018

This speeds up a few rustc-perf benchmark runs, most notably ones
involving 'coercions', the best by 2%.

Optimize seen Predicate filtering.
This speeds up a few rustc-perf benchmark runs, most notably ones
involving 'coercions', the best by 2%.
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rust-highfive commented May 21, 2018

r? @eddyb

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//
// This code is hot enough that it's worth avoiding the allocation
// required for the FxHashSet when possible. Special-casing lengths 0,
// 1 and 2 covers roughly 75--80% of the cases.

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eddyb May 21, 2018

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What about using sort + dedup? That would avoid the allocation, and also quickly exit on small numbers of elements.

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@ishitatsuyuki

ishitatsuyuki May 21, 2018

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That changes the order, which may break the behavior.

Also, deriving Ord is a pain.

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nnethercote May 21, 2018

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And Predicate is a large type, so moving the values around might be moderately expensive.

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eddyb May 22, 2018

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Oh, I see, the set is used with retain. But you need to clone & move the values into a set anyway. If you want to avoid the cost of data movement, the set could be created using references into the original Vec instead. Except that doesn't work because of the retain...

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eddyb commented May 22, 2018

@bors r+

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bors commented May 22, 2018

📌 Commit 2ff6324 has been approved by eddyb

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eddyb commented May 22, 2018

kennytm added a commit to kennytm/rust that referenced this pull request May 22, 2018

Rollup merge of rust-lang#50932 - nnethercote:seen-Predicates, r=eddyb
Optimize seen Predicate filtering.

This speeds up a few rustc-perf benchmark runs, most notably ones
involving 'coercions', the best by 2%.

bors added a commit that referenced this pull request May 22, 2018

Auto merge of #50968 - kennytm:rollup, r=kennytm
Rollup of 15 pull requests

Successful merges:

 - #50846 (Add E0665)
 - #50849 (CheckLoopVisitor: also visit closure arguments)
 - #50863 (Make `[T]::len` and `str::len` const fn)
 - #50875 (rustdoc: use "short form" doc(cfg) printing even when combined with other conditionals)
 - #50913 (Fix typo in cell.rs)
 - #50914 (Issue #50636: Improve error diagnostic with missing commas after struct fields.)
 - #50931 (Inline `try_get`.)
 - #50932 (Optimize seen Predicate filtering.)
 - #50945 (Stabilize feature from_ref)
 - #50946 (rustc: Fix procedural macros generating lifetime tokens)
 - #50947 (rustdoc: set tab width in rust source blocks)
 - #50952 (Add the 2018 edition of the book to doc.rust-lang.org)
 - #50958 (Micro-optimization on PR#50697)
 - #50961 (Fix FileCheck finding with MSVC)
 - #50963 (Right-size the `VecDeque` in `coerce_unsized`.)

Failed merges:

@bors bors merged commit 2ff6324 into rust-lang:master May 22, 2018

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@nnethercote nnethercote deleted the nnethercote:seen-Predicates branch May 23, 2018

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