Use Vec::extend in SmallVec::extend when applicable #52859

ljedrz · 2018-07-30T13:17:22Z

As calculated in #52738, Vec::extend is much faster than pushing to it in a loop. We can take advantage of this method in SmallVec too - at least in cases when its underlying object is an AccumulateVec::Heap.

This approach also accidentally improves the push loop of the AccumulateVec::Array variant, because it doesn't utilize SmallVec::push which performs self.reserve(1) with every iteration; this is unnecessary, because we're already reserving the whole space we will be needing by performing self.reserve(iter.size_hint().0) at the beginning.

rust-highfive · 2018-07-30T13:17:25Z

r? @varkor

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Mark-Simulacrum · 2018-07-30T13:43:23Z

Seems good. If you're interested, it'd be great to write some benchmarks for smallvec to have more confidence in such changes.

@bors r+

bors · 2018-07-30T13:43:24Z

📌 Commit c5dfc2d4d2ce94d6316b64d22933110bc9be1a01 has been approved by Mark-Simulacrum

Mark-Simulacrum · 2018-07-30T13:44:00Z

Oh, Travis failed.

@bors r-

ljedrz · 2018-07-30T13:48:25Z

And with an ICE? It seems one can never be too careful; I'll dig some more.

Mark-Simulacrum · 2018-07-30T14:06:04Z

I suspect this is because the lower bound of the size hint may be too small so it's possible we're not switching to the vector early enough -- that is, the array is too short.

ljedrz · 2018-07-30T14:10:42Z

Yes, I was just about to write the same thing; I forgot the lower bound is not to be trusted.

I think adding arr.reserve(1) to the loop will fix this. This will sadly remove the accidental optimization, but the first one is still worthwhile. I'll test it shortly.

ljedrz · 2018-07-30T18:25:21Z

@Mark-Simulacrum ok, I fixed it and successfully ran stage 1 tests; should be all good now.

Mark-Simulacrum · 2018-07-30T20:23:57Z

src/librustc_data_structures/small_vec.rs

+            let iter = iter.into_iter();
+            self.reserve(iter.size_hint().0);
+
+            for el in iter {


Arguably we should match on self here and either extend or push based on that, but maybe it's not worth it. Benchmarks would be good, but that's quite a bit of work.

You mean instead of is_array? I wanted to do that, but I ran into issues with the borrow checker. I'm going to think about some possible benchmarks.

Mark-Simulacrum · 2018-07-30T20:24:09Z

@bors r+

bors · 2018-07-30T20:24:10Z

📌 Commit 9169934 has been approved by Mark-Simulacrum

ljedrz · 2018-07-31T07:24:45Z

I created some simple benchmarks and checked the results of this change; it appears to be beneficial (up to a 4x speedup) when the required capacity is known and is greater than the size of the underlying array; without it with_capacity surprisingly (or rather counter-intuitively) doesn't seem to make any difference.

before:

test small_vec::tests::fill_small_vec_1_10_with_cap  ... bench:         147 ns/iter (+/- 6)
test small_vec::tests::fill_small_vec_1_10_wo_cap    ... bench:         143 ns/iter (+/- 18)
test small_vec::tests::fill_small_vec_1_50_with_cap  ... bench:         403 ns/iter (+/- 19)
test small_vec::tests::fill_small_vec_1_50_wo_cap    ... bench:         388 ns/iter (+/- 77)
test small_vec::tests::fill_small_vec_32_10_with_cap ... bench:          84 ns/iter (+/- 15)
test small_vec::tests::fill_small_vec_32_10_wo_cap   ... bench:          70 ns/iter (+/- 0)
test small_vec::tests::fill_small_vec_32_50_with_cap ... bench:         531 ns/iter (+/- 78)
test small_vec::tests::fill_small_vec_32_50_wo_cap   ... bench:         537 ns/iter (+/- 89)
test small_vec::tests::fill_small_vec_8_10_with_cap  ... bench:         139 ns/iter (+/- 18)
test small_vec::tests::fill_small_vec_8_10_wo_cap    ... bench:         137 ns/iter (+/- 6)
test small_vec::tests::fill_small_vec_8_50_with_cap  ... bench:         372 ns/iter (+/- 18)
test small_vec::tests::fill_small_vec_8_50_wo_cap    ... bench:         367 ns/iter (+/- 18)

after:

test small_vec::tests::fill_small_vec_1_10_with_cap  ... bench:          83 ns/iter (+/- 4)
test small_vec::tests::fill_small_vec_1_10_wo_cap    ... bench:         147 ns/iter (+/- 4)
test small_vec::tests::fill_small_vec_1_50_with_cap  ... bench:          95 ns/iter (+/- 3)
test small_vec::tests::fill_small_vec_1_50_wo_cap    ... bench:         425 ns/iter (+/- 56)
test small_vec::tests::fill_small_vec_32_10_with_cap ... bench:          88 ns/iter (+/- 3)
test small_vec::tests::fill_small_vec_32_10_wo_cap   ... bench:          74 ns/iter (+/- 2)
test small_vec::tests::fill_small_vec_32_50_with_cap ... bench:         155 ns/iter (+/- 6)
test small_vec::tests::fill_small_vec_32_50_wo_cap   ... bench:         511 ns/iter (+/- 24)
test small_vec::tests::fill_small_vec_8_10_with_cap  ... bench:          88 ns/iter (+/- 15)
test small_vec::tests::fill_small_vec_8_10_wo_cap    ... bench:         134 ns/iter (+/- 5)
test small_vec::tests::fill_small_vec_8_50_with_cap  ... bench:         100 ns/iter (+/- 4)
test small_vec::tests::fill_small_vec_8_50_wo_cap    ... bench:         364 ns/iter (+/- 56)

Mark-Simulacrum · 2018-07-31T11:48:29Z

Can you push those benchmarks as another commit? That way they will be easier for others to reuse.

ljedrz · 2018-07-31T11:55:50Z

Sure; are they fine as an extension of the existing small_vec.rs file (a test module like in the gist)?

Mark-Simulacrum · 2018-07-31T11:58:29Z

Yes, that should work.

Mark-Simulacrum · 2018-07-31T13:28:47Z

@bors r+

bors · 2018-07-31T13:28:48Z

📌 Commit ca52648 has been approved by Mark-Simulacrum

…-Simulacrum Use Vec::extend in SmallVec::extend when applicable As calculated in rust-lang#52738, `Vec::extend` is much faster than `push`ing to it in a loop. We can take advantage of this method in `SmallVec` too - at least in cases when its underlying object is an `AccumulateVec::Heap`. ~~This approach also accidentally improves the `push` loop of the `AccumulateVec::Array` variant, because it doesn't utilize `SmallVec::push` which performs `self.reserve(1)` with every iteration; this is unnecessary, because we're already reserving the whole space we will be needing by performing `self.reserve(iter.size_hint().0)` at the beginning.~~

@ghost

Rollup of 31 pull requests Successful merges: - #52332 (dead-code lint: say "constructed" for structs) - #52340 (Document From trait implementations for OsStr, OsString, CString, and CStr) - #52628 (Cleanup some rustdoc code) - #52732 (Remove unstable and deprecated APIs) - #52745 (Update clippy to latest master) - #52756 (rustc: Disallow machine applicability in foreign macros) - #52771 (Clarify thread::park semantics) - #52810 ([NLL] Don't make "fake" match variables mutable) - #52821 (pretty print for std::collections::vecdeque) - #52822 (Fix From<LocalWaker>) - #52824 (Fix -Wpessimizing-move warnings in rustllvm/PassWrapper) - #52831 (remove references to AUTHORS.txt file) - #52835 (Fix Alias intra doc ICE) - #52842 (update comment) - #52846 (Add timeout to use of `curl` in bootstrap.py.) - #52851 (Make the tool_lints actually usable) - #52853 (Improve bootstrap help on stages) - #52859 (Use Vec::extend in SmallVec::extend when applicable) - #52861 (Add targets for HermitCore (https://hermitcore.org) to the Rust compiler and port libstd to it.) - #52867 (releases.md: fix 2 typos) - #52870 (Implement Unpin for FutureObj and LocalFutureObj) - #52876 (run-pass/const-endianness: negate before to_le()) - #52878 (Fix wrong issue number in the test name) - #52883 (Include lifetime in mutability suggestion in NLL messages) - #52904 (NLL: sort diagnostics by span) - #52905 (Fix a typo in unsize.rs) - #52907 (NLL: On "cannot move out of type" error, print original before rewrite) - #52908 (Use SetLenOnDrop in Vec::truncate()) - #52914 (Only run the sparc-abi test on sparc) - #52918 (Backport 1.27.2 release notes) - #52929 (Update compatibility note for 1.28.0 to be correct) Failed merges: - #52758 (Cleanup for librustc::session) - #52799 (Use BitVector for global sets of AttrId) r? @ghost

…-Simulacrum Use Vec::extend in SmallVec::extend when applicable As calculated in rust-lang#52738, `Vec::extend` is much faster than `push`ing to it in a loop. We can take advantage of this method in `SmallVec` too - at least in cases when its underlying object is an `AccumulateVec::Heap`. ~~This approach also accidentally improves the `push` loop of the `AccumulateVec::Array` variant, because it doesn't utilize `SmallVec::push` which performs `self.reserve(1)` with every iteration; this is unnecessary, because we're already reserving the whole space we will be needing by performing `self.reserve(iter.size_hint().0)` at the beginning.~~

@ghost

Rollup of 30 pull requests Successful merges: - #52340 (Document From trait implementations for OsStr, OsString, CString, and CStr) - #52628 (Cleanup some rustdoc code) - #52732 (Remove unstable and deprecated APIs) - #52745 (Update clippy to latest master) - #52771 (Clarify thread::park semantics) - #52778 (Improve readability of serialize.rs) - #52810 ([NLL] Don't make "fake" match variables mutable) - #52821 (pretty print for std::collections::vecdeque) - #52822 (Fix From<LocalWaker>) - #52824 (Fix -Wpessimizing-move warnings in rustllvm/PassWrapper) - #52825 (Make sure #47772 does not regress) - #52831 (remove references to AUTHORS.txt file) - #52842 (update comment) - #52846 (Add timeout to use of `curl` in bootstrap.py.) - #52851 (Make the tool_lints actually usable) - #52853 (Improve bootstrap help on stages) - #52859 (Use Vec::extend in SmallVec::extend when applicable) - #52861 (Add targets for HermitCore (https://hermitcore.org) to the Rust compiler and port libstd to it.) - #52867 (releases.md: fix 2 typos) - #52870 (Implement Unpin for FutureObj and LocalFutureObj) - #52876 (run-pass/const-endianness: negate before to_le()) - #52878 (Fix wrong issue number in the test name) - #52883 (Include lifetime in mutability suggestion in NLL messages) - #52888 (Use suggestions for shell format arguments) - #52904 (NLL: sort diagnostics by span) - #52905 (Fix a typo in unsize.rs) - #52907 (NLL: On "cannot move out of type" error, print original before rewrite) - #52914 (Only run the sparc-abi test on sparc) - #52918 (Backport 1.27.2 release notes) - #52929 (Update compatibility note for 1.28.0 to be correct) Failed merges: r? @ghost

This improves SmallVec.extend even more over rust-lang#52859 Before (as of rust-lang#52859): ``` test small_vec::tests::fill_small_vec_1_10_with_cap ... bench: 31 ns/iter (+/- 5) test small_vec::tests::fill_small_vec_1_10_wo_cap ... bench: 70 ns/iter (+/- 4) test small_vec::tests::fill_small_vec_1_50_with_cap ... bench: 36 ns/iter (+/- 3) test small_vec::tests::fill_small_vec_1_50_wo_cap ... bench: 256 ns/iter (+/- 17) test small_vec::tests::fill_small_vec_32_10_with_cap ... bench: 31 ns/iter (+/- 5) test small_vec::tests::fill_small_vec_32_10_wo_cap ... bench: 26 ns/iter (+/- 1) test small_vec::tests::fill_small_vec_32_50_with_cap ... bench: 49 ns/iter (+/- 4) test small_vec::tests::fill_small_vec_32_50_wo_cap ... bench: 219 ns/iter (+/- 11) test small_vec::tests::fill_small_vec_8_10_with_cap ... bench: 32 ns/iter (+/- 2) test small_vec::tests::fill_small_vec_8_10_wo_cap ... bench: 61 ns/iter (+/- 12) test small_vec::tests::fill_small_vec_8_50_with_cap ... bench: 37 ns/iter (+/- 3) test small_vec::tests::fill_small_vec_8_50_wo_cap ... bench: 210 ns/iter (+/- 10) ``` After: ``` test small_vec::tests::fill_small_vec_1_10_wo_cap ... bench: 31 ns/iter (+/- 3) test small_vec::tests::fill_small_vec_1_50_with_cap ... bench: 39 ns/iter (+/- 4) test small_vec::tests::fill_small_vec_1_50_wo_cap ... bench: 35 ns/iter (+/- 4) test small_vec::tests::fill_small_vec_32_10_with_cap ... bench: 37 ns/iter (+/- 3) test small_vec::tests::fill_small_vec_32_10_wo_cap ... bench: 32 ns/iter (+/- 2) test small_vec::tests::fill_small_vec_32_50_with_cap ... bench: 52 ns/iter (+/- 4) test small_vec::tests::fill_small_vec_32_50_wo_cap ... bench: 46 ns/iter (+/- 0) test small_vec::tests::fill_small_vec_8_10_with_cap ... bench: 35 ns/iter (+/- 4) test small_vec::tests::fill_small_vec_8_10_wo_cap ... bench: 31 ns/iter (+/- 0) test small_vec::tests::fill_small_vec_8_50_with_cap ... bench: 40 ns/iter (+/- 15) test small_vec::tests::fill_small_vec_8_50_wo_cap ... bench: 36 ns/iter (+/- 2) ```

Another SmallVec.extend optimization This improves SmallVec.extend even more over rust-lang#52859 while making the code easier to read. Before ``` test small_vec::tests::fill_small_vec_1_10_with_cap ... bench: 31 ns/iter (+/- 5) test small_vec::tests::fill_small_vec_1_10_wo_cap ... bench: 70 ns/iter (+/- 4) test small_vec::tests::fill_small_vec_1_50_with_cap ... bench: 36 ns/iter (+/- 3) test small_vec::tests::fill_small_vec_1_50_wo_cap ... bench: 256 ns/iter (+/- 17) test small_vec::tests::fill_small_vec_32_10_with_cap ... bench: 31 ns/iter (+/- 5) test small_vec::tests::fill_small_vec_32_10_wo_cap ... bench: 26 ns/iter (+/- 1) test small_vec::tests::fill_small_vec_32_50_with_cap ... bench: 49 ns/iter (+/- 4) test small_vec::tests::fill_small_vec_32_50_wo_cap ... bench: 219 ns/iter (+/- 11) test small_vec::tests::fill_small_vec_8_10_with_cap ... bench: 32 ns/iter (+/- 2) test small_vec::tests::fill_small_vec_8_10_wo_cap ... bench: 61 ns/iter (+/- 12) test small_vec::tests::fill_small_vec_8_50_with_cap ... bench: 37 ns/iter (+/- 3) test small_vec::tests::fill_small_vec_8_50_wo_cap ... bench: 210 ns/iter (+/- 10) ``` After: ``` test small_vec::tests::fill_small_vec_1_10_wo_cap ... bench: 31 ns/iter (+/- 3) test small_vec::tests::fill_small_vec_1_50_with_cap ... bench: 39 ns/iter (+/- 4) test small_vec::tests::fill_small_vec_1_50_wo_cap ... bench: 35 ns/iter (+/- 4) test small_vec::tests::fill_small_vec_32_10_with_cap ... bench: 37 ns/iter (+/- 3) test small_vec::tests::fill_small_vec_32_10_wo_cap ... bench: 32 ns/iter (+/- 2) test small_vec::tests::fill_small_vec_32_50_with_cap ... bench: 52 ns/iter (+/- 4) test small_vec::tests::fill_small_vec_32_50_wo_cap ... bench: 46 ns/iter (+/- 0) test small_vec::tests::fill_small_vec_8_10_with_cap ... bench: 35 ns/iter (+/- 4) test small_vec::tests::fill_small_vec_8_10_wo_cap ... bench: 31 ns/iter (+/- 0) test small_vec::tests::fill_small_vec_8_50_with_cap ... bench: 40 ns/iter (+/- 15) test small_vec::tests::fill_small_vec_8_50_wo_cap ... bench: 36 ns/iter (+/- 2) ```

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Use Vec::extend in SmallVec::extend when applicable

9169934

ljedrz force-pushed the smallvec_true_extend branch from c5dfc2d to 9169934 Compare July 30, 2018 18:24

Mark-Simulacrum approved these changes Jul 30, 2018

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Benchmarks for SmallVec

ca52648

Mark-Simulacrum mentioned this pull request Aug 1, 2018

Rollup of 31 pull requests #52931

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Rollup of 30 pull requests #52937

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ljedrz deleted the smallvec_true_extend branch August 1, 2018 10:45

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Another SmallVec.extend optimization #52942

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Use Vec::extend in SmallVec::extend when applicable #52859

Use Vec::extend in SmallVec::extend when applicable #52859

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Use Vec::extend in SmallVec::extend when applicable #52859

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