collections: Optimize Vec when cloning from a slice
llvm is currently not able to conver `Vec::extend` into a memcpy for `Copy` types, which results in methods like `Vec::push_all` to run twice as slow as it should be running. This patch takes the unsafe `Vec::clone` optimization to speed up all the operations that are cloning a slice into a `Vec`. before: test vec::tests::bench_clone_from_0000_0000 ... bench: 12 ns/iter (+/- 2) test vec::tests::bench_clone_from_0000_0010 ... bench: 125 ns/iter (+/- 4) = 80 MB/s test vec::tests::bench_clone_from_0000_0100 ... bench: 360 ns/iter (+/- 33) = 277 MB/s test vec::tests::bench_clone_from_0000_1000 ... bench: 2601 ns/iter (+/- 175) = 384 MB/s test vec::tests::bench_clone_from_0010_0000 ... bench: 12 ns/iter (+/- 2) test vec::tests::bench_clone_from_0010_0010 ... bench: 125 ns/iter (+/- 10) = 80 MB/s test vec::tests::bench_clone_from_0010_0100 ... bench: 361 ns/iter (+/- 28) = 277 MB/s test vec::tests::bench_clone_from_0100_0010 ... bench: 131 ns/iter (+/- 13) = 76 MB/s test vec::tests::bench_clone_from_0100_0100 ... bench: 360 ns/iter (+/- 9) = 277 MB/s test vec::tests::bench_clone_from_0100_1000 ... bench: 2575 ns/iter (+/- 168) = 388 MB/s test vec::tests::bench_clone_from_1000_0100 ... bench: 356 ns/iter (+/- 20) = 280 MB/s test vec::tests::bench_clone_from_1000_1000 ... bench: 2605 ns/iter (+/- 167) = 383 MB/s test vec::tests::bench_from_slice_0000 ... bench: 11 ns/iter (+/- 0) test vec::tests::bench_from_slice_0010 ... bench: 115 ns/iter (+/- 5) = 86 MB/s test vec::tests::bench_from_slice_0100 ... bench: 309 ns/iter (+/- 170) = 323 MB/s test vec::tests::bench_from_slice_1000 ... bench: 2065 ns/iter (+/- 198) = 484 MB/s test vec::tests::bench_push_all_0000_0000 ... bench: 7 ns/iter (+/- 0) test vec::tests::bench_push_all_0000_0010 ... bench: 79 ns/iter (+/- 7) = 126 MB/s test vec::tests::bench_push_all_0000_0100 ... bench: 342 ns/iter (+/- 18) = 292 MB/s test vec::tests::bench_push_all_0000_1000 ... bench: 2873 ns/iter (+/- 75) = 348 MB/s test vec::tests::bench_push_all_0010_0010 ... bench: 154 ns/iter (+/- 8) = 64 MB/s test vec::tests::bench_push_all_0100_0100 ... bench: 518 ns/iter (+/- 18) = 193 MB/s test vec::tests::bench_push_all_1000_1000 ... bench: 4490 ns/iter (+/- 223) = 222 MB/s after: test vec::tests::bench_clone_from_0000_0000 ... bench: 12 ns/iter (+/- 1) test vec::tests::bench_clone_from_0000_0010 ... bench: 123 ns/iter (+/- 5) = 81 MB/s test vec::tests::bench_clone_from_0000_0100 ... bench: 367 ns/iter (+/- 23) = 272 MB/s test vec::tests::bench_clone_from_0000_1000 ... bench: 2618 ns/iter (+/- 252) = 381 MB/s test vec::tests::bench_clone_from_0010_0000 ... bench: 12 ns/iter (+/- 1) test vec::tests::bench_clone_from_0010_0010 ... bench: 124 ns/iter (+/- 7) = 80 MB/s test vec::tests::bench_clone_from_0010_0100 ... bench: 369 ns/iter (+/- 34) = 271 MB/s test vec::tests::bench_clone_from_0100_0010 ... bench: 123 ns/iter (+/- 6) = 81 MB/s test vec::tests::bench_clone_from_0100_0100 ... bench: 371 ns/iter (+/- 25) = 269 MB/s test vec::tests::bench_clone_from_0100_1000 ... bench: 2713 ns/iter (+/- 532) = 368 MB/s test vec::tests::bench_clone_from_1000_0100 ... bench: 369 ns/iter (+/- 14) = 271 MB/s test vec::tests::bench_clone_from_1000_1000 ... bench: 2611 ns/iter (+/- 194) = 382 MB/s test vec::tests::bench_from_slice_0000 ... bench: 7 ns/iter (+/- 0) test vec::tests::bench_from_slice_0010 ... bench: 108 ns/iter (+/- 4) = 92 MB/s test vec::tests::bench_from_slice_0100 ... bench: 235 ns/iter (+/- 24) = 425 MB/s test vec::tests::bench_from_slice_1000 ... bench: 1318 ns/iter (+/- 96) = 758 MB/s test vec::tests::bench_push_all_0000_0000 ... bench: 7 ns/iter (+/- 0) test vec::tests::bench_push_all_0000_0010 ... bench: 70 ns/iter (+/- 4) = 142 MB/s test vec::tests::bench_push_all_0000_0100 ... bench: 176 ns/iter (+/- 16) = 568 MB/s test vec::tests::bench_push_all_0000_1000 ... bench: 1125 ns/iter (+/- 94) = 888 MB/s test vec::tests::bench_push_all_0010_0010 ... bench: 159 ns/iter (+/- 15) = 62 MB/s test vec::tests::bench_push_all_0100_0100 ... bench: 363 ns/iter (+/- 12) = 275 MB/s test vec::tests::bench_push_all_1000_1000 ... bench: 2860 ns/iter (+/- 415) = 349 MB/s
This commit is contained in:
Erick Tryzelaar
parent
065b98d577
commit
f1ea540e90
1 changed files with 44 additions and 31 deletions
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@ -197,7 +197,9 @@ impl<T: Clone> Vec<T> {
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/// ```
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#[inline]
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pub fn from_slice(values: &[T]) -> Vec<T> {
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values.iter().map(|x| x.clone()).collect()
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let mut vector = Vec::with_capacity(values.len());
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vector.push_all(values);
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vector
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}
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/// Constructs a `Vec` with copies of a value.
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@ -238,7 +240,10 @@ impl<T: Clone> Vec<T> {
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/// ```
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#[inline]
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pub fn push_all(&mut self, other: &[T]) {
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self.extend(other.iter().map(|e| e.clone()));
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unsafe {
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self.reserve_additional(other.len());
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unsafe_push_all_clone(self, other)
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}
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}
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/// Grows the `Vec` in-place.
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@ -318,27 +323,15 @@ impl<T: Clone> Vec<T> {
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#[unstable]
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impl<T:Clone> Clone for Vec<T> {
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fn clone(&self) -> Vec<T> {
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let len = self.len;
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let mut vector = Vec::with_capacity(len);
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// Unsafe code so this can be optimised to a memcpy (or something
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// similarly fast) when T is Copy. LLVM is easily confused, so any
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// extra operations during the loop can prevent this optimisation
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{
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let this_slice = self.as_slice();
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while vector.len < len {
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unsafe {
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let len = vector.len;
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ptr::write(
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vector.as_mut_slice().unsafe_mut_ref(len),
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this_slice.unsafe_ref(len).clone());
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}
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vector.len += 1;
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}
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}
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let mut vector = Vec::with_capacity(self.len);
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unsafe_push_all_clone(&mut vector, self.as_slice());
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vector
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}
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}
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fn clone_from(&mut self, other: &Vec<T>) {
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unsafe {
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// drop anything in self that will not be overwritten
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if self.len() > other.len() {
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self.truncate(other.len())
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@ -351,8 +344,10 @@ impl<T:Clone> Clone for Vec<T> {
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// self.len <= other.len due to the truncate above, so the
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// slice here is always in-bounds.
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let len = self.len();
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self.extend(other.slice_from(len).iter().map(|x| x.clone()));
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let slice = other.slice_from(self.len());
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self.reserve_additional(slice.len());
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unsafe_push_all_clone(self, slice)
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}
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}
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}
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@ -1555,6 +1550,24 @@ pub mod raw {
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}
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}
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// Unsafe code so this can be optimised to a memcpy (or something similarly
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// fast) when T is Copy. LLVM is easily confused, so any extra operations
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// during the loop can prevent this optimisation.
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//
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// WARNING: You must preallocate space on the vector before you call this
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// method.
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#[inline(always)]
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unsafe fn unsafe_push_all_clone<T: Clone>(dst: &mut Vec<T>, src: &[T]) {
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let mut dst_len = dst.len();
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for i in range(0, src.len()) {
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ptr::write(
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dst.as_mut_slice().unsafe_mut_ref(dst_len),
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src.unsafe_ref(i).clone());
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dst_len += 1;
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dst.set_len(dst_len);
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}
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}
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#[cfg(test)]
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mod tests {
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