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

[A. Jiang via libcxx-commits]

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frederick-vs-ja wrote:

Ditto double underscore. IIUC, `_alignment_needed` etc. are not even resolved here per the C++ core language specifications, and users are even permitted to observe such a spelling.

```suggestion
  static constexpr unsigned __alignment_needed = (1u << Bits);
  static constexpr uintptr_t __tag_mask        = (__alignment_needed - 1u);
  static constexpr uintptr_t __pointer_mask    = ~__tag_mask;
```

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