[libcxx-commits] [PATCH] D131362: [libc++] Implement `operator<=> for `thread::id`

[Adrian Vogelsgesang via Phabricator via libcxx-commits]

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According to the standard, the `operator<=>` should be a free-standing
function instead of a hidden friend. However, the existing comparison
operators are also implemented as hidden friends (in contradiction to
the standard). Hence, this commit follows the prior art and also
implements `operator<=>` as hidden friend.

The new `operator<=>` is mapped onto the existing functions
`__libcpp_thread_id_equal` and `__libcpp_thread_id_less`. Introducing a
new `__libcpp_thread_id_compare_three_way` might lead to more efficient
code. Given that we can still introduce `__libcpp_thread_id_compare_three_way`
later, for this commit I opted to not break ABI. If requested, I will
add `__libcpp_thread_id_compare_three_way` in a follow-up commit.

Implements part of P1614R2 "The Mothership has Landed"


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D131362

Files:
  libcxx/docs/Status/SpaceshipProjects.csv
  libcxx/include/__threading_support
  libcxx/include/thread
  libcxx/test/std/thread/thread.threads/thread.thread.class/thread.thread.id/cmp.pass.cpp
  libcxx/test/std/thread/thread.threads/thread.thread.class/thread.thread.id/eq.pass.cpp
  libcxx/test/std/thread/thread.threads/thread.thread.class/thread.thread.id/lt.pass.cpp

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