[libcxx-commits] [clang] [libcxx] [clang & libcxx] constexpr pointer tagging (DO NOT MERGE) (PR #111861)

[William Tran-Viet via libcxx-commits]

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smallp-o-p wrote:

This has gotten suddenly relevant for libc++ in #203782, where we're using a tagged pointer as the basis for an iterator. I wonder if it might be feasible to bring forward the `clang` side of the changes and leverage the added builtins wherever possible, so that things like `optional::iterator` are allowed to be `constexpr`, at least for `clang`.

WDYT @ldionne 

This would also require some kind of discussion with the Clang folks I assume.

https://github.com/llvm/llvm-project/pull/111861