[all-commits] [llvm/llvm-project] d0cee6: [libc++] Optimize std::{, ranges}::{fill, fill_n} fo...
Peng Liu via All-commits
all-commits at lists.llvm.org
Thu Oct 16 16:41:45 PDT 2025
Branch: refs/heads/main
Home: https://github.com/llvm/llvm-project
Commit: d0cee6939a1a889b14dcfc0bb049f38063c81f9b
https://github.com/llvm/llvm-project/commit/d0cee6939a1a889b14dcfc0bb049f38063c81f9b
Author: Peng Liu <winner245 at hotmail.com>
Date: 2025-10-17 (Fri, 17 Oct 2025)
Changed paths:
M libcxx/docs/ReleaseNotes/22.rst
M libcxx/include/__algorithm/fill.h
M libcxx/include/__algorithm/fill_n.h
M libcxx/include/__algorithm/ranges_fill.h
M libcxx/test/std/algorithms/alg.modifying.operations/alg.fill/fill.pass.cpp
M libcxx/test/std/algorithms/alg.modifying.operations/alg.fill/fill_n.pass.cpp
M libcxx/test/std/algorithms/alg.modifying.operations/alg.fill/ranges.fill.pass.cpp
M libcxx/test/std/algorithms/alg.modifying.operations/alg.fill/ranges.fill_n.pass.cpp
Log Message:
-----------
[libc++] Optimize std::{,ranges}::{fill,fill_n} for segmented iterators (#132665)
This patch optimizes `std::fill`, `std::fill_n`, `std::ranges::fill`,
and `std::ranges::fill_n` for segmented iterators, achieving substantial
performance improvements. Specifically, for `deque<int>` iterators, the
performance improvements are above 10x for all these algorithms. The
optimization also enables filling segmented memory of `deque<int>` to
approach the performance of filling contiguous memory of `vector<int>`.
Benchmark results comparing the before and after implementations are
provided below. For additional context, we’ve included `vector<int>`
results, which remain unchanged, as this patch specifically targets
segmented iterators and leaves non-segmented iterator behavior
untouched.
Fixes two subtasks outlined in #102817.
#### `fill_n`
```
-----------------------------------------------------------------------------
Benchmark Before After Speedup
-----------------------------------------------------------------------------
std::fill_n(deque<int>)/32 11.4 ns 2.28 ns 5.0x
std::fill_n(deque<int>)/50 19.7 ns 3.40 ns 5.8x
std::fill_n(deque<int>)/1024 391 ns 37.3 ns 10.5x
std::fill_n(deque<int>)/8192 3174 ns 301 ns 10.5x
std::fill_n(deque<int>)/65536 26504 ns 2951 ns 9.0x
std::fill_n(deque<int>)/1048576 407960 ns 80658 ns 5.1x
rng::fill_n(deque<int>)/32 14.3 ns 2.15 ns 6.6x
rng::fill_n(deque<int>)/50 20.2 ns 3.22 ns 6.3x
rng::fill_n(deque<int>)/1024 381 ns 37.8 ns 10.1x
rng::fill_n(deque<int>)/8192 3101 ns 294 ns 10.5x
rng::fill_n(deque<int>)/65536 25098 ns 2926 ns 8.6x
rng::fill_n(deque<int>)/1048576 394342 ns 78874 ns 5.0x
std::fill_n(vector<int>)/32 1.76 ns 1.72 ns 1.0x
std::fill_n(vector<int>)/50 3.00 ns 2.73 ns 1.1x
std::fill_n(vector<int>)/1024 38.4 ns 37.9 ns 1.0x
std::fill_n(vector<int>)/8192 258 ns 252 ns 1.0x
std::fill_n(vector<int>)/65536 2993 ns 2889 ns 1.0x
std::fill_n(vector<int>)/1048576 80328 ns 80468 ns 1.0x
rng::fill_n(vector<int>)/32 1.99 ns 1.35 ns 1.5x
rng::fill_n(vector<int>)/50 2.66 ns 2.12 ns 1.3x
rng::fill_n(vector<int>)/1024 37.7 ns 35.8 ns 1.1x
rng::fill_n(vector<int>)/8192 253 ns 250 ns 1.0x
rng::fill_n(vector<int>)/65536 2922 ns 2930 ns 1.0x
rng::fill_n(vector<int>)/1048576 79739 ns 79742 ns 1.0x
```
#### `fill`
```
--------------------------------------------------------------------------
Benchmark Before After Speedup
--------------------------------------------------------------------------
std::fill(deque<int>)/32 13.7 ns 2.45 ns 5.6x
std::fill(deque<int>)/50 21.7 ns 4.57 ns 4.7x
std::fill(deque<int>)/1024 367 ns 38.5 ns 9.5x
std::fill(deque<int>)/8192 2896 ns 247 ns 11.7x
std::fill(deque<int>)/65536 23723 ns 2907 ns 8.2x
std::fill(deque<int>)/1048576 379043 ns 79885 ns 4.7x
rng::fill(deque<int>)/32 13.6 ns 2.70 ns 5.0x
rng::fill(deque<int>)/50 23.4 ns 3.94 ns 5.9x
rng::fill(deque<int>)/1024 377 ns 37.9 ns 9.9x
rng::fill(deque<int>)/8192 2914 ns 286 ns 10.2x
rng::fill(deque<int>)/65536 23612 ns 2939 ns 8.0x
rng::fill(deque<int>)/1048576 379841 ns 80079 ns 4.7x
std::fill(vector<int>)/32 1.99 ns 1.79 ns 1.1x
std::fill(vector<int>)/50 3.05 ns 3.06 ns 1.0x
std::fill(vector<int>)/1024 37.6 ns 38.0 ns 1.0x
std::fill(vector<int>)/8192 255 ns 257 ns 1.0x
std::fill(vector<int>)/65536 2966 ns 2981 ns 1.0x
std::fill(vector<int>)/1048576 78300 ns 80348 ns 1.0x
rng::fill(vector<int>)/32 1.77 ns 1.75 ns 1.0x
rng::fill(vector<int>)/50 4.85 ns 2.31 ns 2.1x
rng::fill(vector<int>)/1024 39.6 ns 36.1 ns 1.1x
rng::fill(vector<int>)/8192 238 ns 251 ns 0.9x
rng::fill(vector<int>)/65536 2941 ns 2918 ns 1.0x
rng::fill(vector<int>)/1048576 80497 ns 80442 ns 1.0x
```
---------
Co-authored-by: Louis Dionne <ldionne.2 at gmail.com>
Co-authored-by: A. Jiang <de34 at live.cn>
To unsubscribe from these emails, change your notification settings at https://github.com/llvm/llvm-project/settings/notifications
More information about the All-commits
mailing list