Improve type traits usage #1413
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Both sides compile even when `if constexpr` is unavailable.
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CaseyCarter
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| template <class _InIt, class _Ty> | ||
| _NODISCARD constexpr bool _Within_limits(_InIt, const _Ty& _Val) { // check whether _Val is within the limits of _Elem | ||
| using _Elem = remove_pointer_t<_InIt>; | ||
| return _Within_limits(_Val, is_signed<_Elem>{}, is_signed<_Ty>{}, bool_constant<-1 == static_cast<_Ty>(-1)>{}); |
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I don't like this change as much as the others, I think it impacts clarity more. I'm OK with it if the throughput improvement is actually decent though.
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It was enough to show up on @xiangfan-ms's radar. Clarity will be dramatically improved when we can if constexprize this, hopefully soon.
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Fixes MS-internal VSO-1240399 / AB#1240399 reported by @xiangfan-ms.
<random>_Uty(MEOW), which is a functional-syntax C-semantics cast, tostatic_cast<_Uty>(MEOW).is_signedtag dispatch withif _CONSTEXPR_IFis_signed_v. This improves throughput twice (first becauseis_signed_vis silently optimized by MSVC, second becauseif constexpris much cheaper than tag dispatch). Note that even whenif constexpris unavailable, both sides of the branch will compile just fine.<xmemory>is_emptytobool_constantviatypename MEOW::type, wrapis_empty_vinbool_constantbecause MSVC silently optimizesis_empty_v.<xtree>bool_constant<is_same_v<MEOW>>.<xutility>is_signedconverted totrue_typeorfalse_typeduring overload resolution. Again, it's faster to saybool_constant<is_signed_v<MEOW>>. (This logic should be refactored intoif constexprlater, and/or it should use the C++20in_rangetechnique; I am deliberately not pursuing those larger changes now.)