Faster insert for the index == len case
#282
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By skipping the call to `copy` with a zero length. This makes it closer to `push`. This speeds up rustc (which uses `SmallVec` extensively) by 2% on one benchmark. Also clarify the panic condition.
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This is the relevant use point within Rust, if you are curious. |
mbrubeck
approved these changes
Jun 24, 2022
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Thanks! Released as v1.8.1: https://crates.io/crates/smallvec/1.8.1 |
nnethercote
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Jun 26, 2022
This pulls in servo/rust-smallvec#282, which gives some small wins for rustc.
bors
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Jun 29, 2022
Update `smallvec` to 1.8.1. This pulls in servo/rust-smallvec#282, which gives some small wins for rustc. r? `@lqd`
nnethercote
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Jul 1, 2022
By skipping the call to `copy` with a zero length. This makes it closer to `push`. I did this recently for `SmallVec` (servo/rust-smallvec#282) and it was a big perf win in one case. Although I don't have a specific use case in mind, it seems worth doing it for `Vec` as well. Things to note: - In the `index < len` case, the number of conditions checked is unchanged. - In the `index == len` case, the number of conditions checked increases by one, but the more expensive zero-length copy is avoided. - In the `index > len` case the code now reserves space for the extra element before panicking. This seems like an unimportant change.
bors
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Jul 3, 2022
Optimize `Vec::insert` for the case where `index == len`. By skipping the call to `copy` with a zero length. This makes it closer to `push`. I did this recently for `SmallVec` (servo/rust-smallvec#282) and it was a big perf win in one case. Although I don't have a specific use case in mind, it seems worth doing it for `Vec` as well. Things to note: - In the `index < len` case, the number of conditions checked is unchanged. - In the `index == len` case, the number of conditions checked increases by one, but the more expensive zero-length copy is avoided. - In the `index > len` case the code now reserves space for the extra element before panicking. This seems like an unimportant change. r? `@cuviper`
bjorn3
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Jul 3, 2022
This pulls in servo/rust-smallvec#282, which gives some small wins for rustc.
workingjubilee
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Sep 15, 2022
By skipping the call to `copy` with a zero length. This makes it closer to `push`. I did this recently for `SmallVec` (servo/rust-smallvec#282) and it was a big perf win in one case. Although I don't have a specific use case in mind, it seems worth doing it for `Vec` as well. Things to note: - In the `index < len` case, the number of conditions checked is unchanged. - In the `index == len` case, the number of conditions checked increases by one, but the more expensive zero-length copy is avoided. - In the `index > len` case the code now reserves space for the extra element before panicking. This seems like an unimportant change.
workingjubilee
pushed a commit
to tcdi/postgrestd
that referenced
this pull request
Sep 15, 2022
Optimize `Vec::insert` for the case where `index == len`. By skipping the call to `copy` with a zero length. This makes it closer to `push`. I did this recently for `SmallVec` (servo/rust-smallvec#282) and it was a big perf win in one case. Although I don't have a specific use case in mind, it seems worth doing it for `Vec` as well. Things to note: - In the `index < len` case, the number of conditions checked is unchanged. - In the `index == len` case, the number of conditions checked increases by one, but the more expensive zero-length copy is avoided. - In the `index > len` case the code now reserves space for the extra element before panicking. This seems like an unimportant change. r? `@cuviper`
eddyb
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Nov 14, 2022
This pulls in servo/rust-smallvec#282, which gives some small wins for rustc. [git filter-repo] original commit: rust-lang/rust@7c40661
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This case popped up within rustc, where
insertwas repeatedly used for apush-like operation. (But in a context wherepushwasn't always appropriate.) It speeds up rustc on one benchmark by 2% -- not huge, but also not bad for such a small change.Here is some before and after results for the new benchmark along with the existing
pushbenchmarks.Old:
New
The first two are testing identical code, and show that the time variation is non-trivial. The latter two show the effect of this PR's code changes, which are well beyond the timing variation.