[libcxx-commits] [PATCH] D131395: [libc++] Implement `lexicographical_compare_three_way`

[Adrian Vogelsgesang via Phabricator via libcxx-commits]

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The implementation is rather straightforward and unoptimized. A more
performant implementation is possible for most cases, but I think we
should rather fix clang to optimize the code correctly (see
https://godbolt.org/z/7xbMEen5e). This commit makes sure to not call
`operator==` unnecessarily on the iterators, though, as was noted in
LWG 3410.

Implements part of P1614R2 "The Mothership has Landed"

Fixes LWG 3410


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D131395

Files:
  libcxx/docs/Status/Cxx2bIssues.csv
  libcxx/docs/Status/SpaceshipProjects.csv
  libcxx/include/CMakeLists.txt
  libcxx/include/__algorithm/lexicographical_compare_three_way.h
  libcxx/include/algorithm
  libcxx/include/module.modulemap.in
  libcxx/test/std/algorithms/alg.sorting/alg.three.way/lexicographical_compare_three_way.pass.cpp
  libcxx/test/std/algorithms/alg.sorting/alg.three.way/lexicographical_compare_three_way_comp.pass.cpp
  libcxx/test/std/algorithms/alg.sorting/alg.three.way/lexicographical_compare_three_way_comp.verify.cpp

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