[libcxx-commits] [libcxx] Replace uses of `__libcpp_ctz` by `__countr_zero` (PR #132639)

[Mark de Wever via libcxx-commits]

mordante wrote:

> > > Hi @mordante, thank you for the update on the current status of removing Clang 18 support, which is currently blocked by some CI runners. I understand that the changes in this patch will need to be put on hold until Clang 18 support is officially dropped (@PaulXiCao).
> > 
> > 
> > Looking at the status of the CI this works in Clang-18; the ARM runners are still on Clang-18.
> 
> The primary goal of #131179 (based on my discussion with @ldionne in [#122641 (comment)](https://github.com/llvm/llvm-project/pull/122641#discussion_r1972052176) ) was to eliminate all usages of `__libcpp_ctz` in favor of the built-in implementation available since Clang 19. Ultimately, this allows us to remove functions like `__libcpp_ctz`, but only when we officially drop support for Clang 18.

I didn't look into the patch or which Clang version supports the built-in. If you say that's Clang-19 this patch indeed needs to be post-poned until we can drop Clang-18 support. I mainly wanted to update you on the status of Clang-18 support.


https://github.com/llvm/llvm-project/pull/132639