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STL: Mark simple casting free functions with _MSVC_INTRINSIC #3548

@frederick-vs-ja

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@frederick-vs-ja

#3182 added [[msvc::intrinsic]] attribute to the following reference-casting function templates:

  • forward
  • forward_like
  • move
  • move_if_noexcept

, which made MSVC treat a call to such a function equivalent to a simple static_cast.

Per local verifications and response from @cdacamar on Discord, it works for free functions which is equivalent to a cast. Here is an incomplete list of such functions, including internal helpers, in MSVC STL:

  • Reference casting functions (I've verified locally some of them and believe [[msvc::intrinsic]] works)
    • as_const (in <utility>)
    • _Possibly_const_range (in <xutility>)
    • _As_lvalue (in <ranges>)
  • Pointer casting functions (seemly works, but not very sure)
    • _As_const_pointer (in <xutility>)
  • Integer/enumeration casting functions (seemly works, but not very sure)
    • to_integer (in <cstddef>)
    • to_underlying (in <utility>)

It would be great to find all of these functions and mark them with _MSVC_INTRINSIC.

Note that the [[msvc::intrinsic]] attribute currently doesn't work for member functions (both non-static and static ones), so even though identity::operator() looks like a good candidate, it's better not to mark it with _MSVC_INTRINSIC at this moment.

@JMazurkiewicz suggested that this might be a nice candidate for "good first issue".

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