[libc++] Optimize rotate

[philnik777]

----------------------------------------------------------
Benchmark                                 old          new
----------------------------------------------------------
BM_std_rotate<int>/1                 0.707 ns      2.83 ns
BM_std_rotate<int>/2                 0.706 ns      2.83 ns
BM_std_rotate<int>/3                  4.93 ns      5.04 ns
BM_std_rotate<int>/4                  5.12 ns      5.14 ns
BM_std_rotate<int>/32                 41.3 ns      16.5 ns
BM_std_rotate<int>/64                 94.1 ns      42.8 ns
BM_std_rotate<int>/512                 764 ns       194 ns
BM_std_rotate<int>/4096               5899 ns      2687 ns
BM_std_rotate<int>/65536             94248 ns     43003 ns
BM_std_rotate<__int128>/1            0.713 ns      2.16 ns
BM_std_rotate<__int128>/2            0.711 ns      2.16 ns
BM_std_rotate<__int128>/3             5.63 ns      5.70 ns
BM_std_rotate<__int128>/4             5.64 ns      5.62 ns
BM_std_rotate<__int128>/32            46.1 ns      29.8 ns
BM_std_rotate<__int128>/64            98.6 ns      75.6 ns
BM_std_rotate<__int128>/512            752 ns       486 ns
BM_std_rotate<__int128>/4096          5849 ns      4913 ns
BM_std_rotate<__int128>/65536        97091 ns     78037 ns
BM_std_rotate<std::string>/1         0.722 ns     0.717 ns
BM_std_rotate<std::string>/2         0.722 ns     0.718 ns
BM_std_rotate<std::string>/3          4.35 ns      4.42 ns
BM_std_rotate<std::string>/4          6.12 ns      6.08 ns
BM_std_rotate<std::string>/32         46.7 ns      46.4 ns
BM_std_rotate<std::string>/64         95.7 ns      94.9 ns
BM_std_rotate<std::string>/512         795 ns       792 ns
BM_std_rotate<std::string>/4096       6500 ns      6442 ns
BM_std_rotate<std::string>/65536    106532 ns    103567 ns

Fixes #54949
Fixes #39644

[github-actions]

⚠️ C/C++ code formatter, clang-format found issues in your code. ⚠️

You can test this locally with the following command:

git-clang-format --diff fd784726db70a5155594c32ee839b8807fafd87d 6399aec8e1b59b0aa436cf5e08ac78cdb18bd3d3 --extensions cpp,h -- libcxx/test/benchmarks/algorithms/rotate.bench.cpp libcxx/include/__algorithm/rotate.h

View the diff from clang-format here.

diff --git a/libcxx/include/__algorithm/rotate.h b/libcxx/include/__algorithm/rotate.h
index 1755a75888..91a073c1be 100644
--- a/libcxx/include/__algorithm/rotate.h
+++ b/libcxx/include/__algorithm/rotate.h
@@ -84,9 +84,9 @@ __rotate_forward(_ForwardIterator __first, _ForwardIterator __middle, _ForwardIt
 
 template <class _AlgPolicy, class _Iter, class _Sent>
 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 _Iter __rotate_random(_Iter __first, _Iter __middle, _Sent __last) {
-  auto __left = _IterOps<_AlgPolicy>::distance(__first, __middle);
+  auto __left  = _IterOps<_AlgPolicy>::distance(__first, __middle);
   auto __right = _IterOps<_AlgPolicy>::distance(__middle, __last);
-  auto __end = __first + __right;
+  auto __end   = __first + __right;
 
   if (__left == 0 || __first == __last)
     return __first;

[ldionne]

@philnik777 Why was this closed?

[philnik777]

@philnik777 Why was this closed?

Because I've accidentally used the main branch of my fork. The new PR is #120890. Sorry for not mentioning it before.