[libc++] Implement constexpr {isfinite, isinf, isnan, isnormal}

This starts implementing P0533

Reviewed By: Mordante, #libc

Spies: libcxx-commits

Differential Revision: https://reviews.llvm.org/D140277

NOKEYCHECK=True
GitOrigin-RevId: 52bff450dd46c28e1b2966c13bf0d603046214a5
diff --git a/include/math.h b/include/math.h
index dd68830..14fa9e2 100644
--- a/include/math.h
+++ b/include/math.h
@@ -400,13 +400,13 @@
 
 template <class _A1,
           std::__enable_if_t<std::is_arithmetic<_A1>::value && std::numeric_limits<_A1>::has_infinity, int> = 0>
-inline _LIBCPP_HIDE_FROM_ABI bool isfinite(_A1 __x) _NOEXCEPT {
+_LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isfinite(_A1 __x) _NOEXCEPT {
   return __builtin_isfinite((typename std::__promote<_A1>::type)__x);
 }
 
 template <class _A1,
           std::__enable_if_t<std::is_arithmetic<_A1>::value && !std::numeric_limits<_A1>::has_infinity, int> = 0>
-inline _LIBCPP_HIDE_FROM_ABI bool isfinite(_A1) _NOEXCEPT {
+_LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isfinite(_A1) _NOEXCEPT {
   return true;
 }
 
@@ -414,54 +414,66 @@
 
 template <class _A1,
           std::__enable_if_t<std::is_arithmetic<_A1>::value && std::numeric_limits<_A1>::has_infinity, int> = 0>
-inline _LIBCPP_HIDE_FROM_ABI bool isinf(_A1 __x) _NOEXCEPT {
+_LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isinf(_A1 __x) _NOEXCEPT {
   return __builtin_isinf((typename std::__promote<_A1>::type)__x);
 }
 
 template <class _A1>
-inline _LIBCPP_HIDE_FROM_ABI
+_LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI
     typename std::enable_if< std::is_arithmetic<_A1>::value && !std::numeric_limits<_A1>::has_infinity, bool>::type
     isinf(_A1) _NOEXCEPT {
   return false;
 }
 
 #      ifdef _LIBCPP_PREFERRED_OVERLOAD
-inline _LIBCPP_HIDE_FROM_ABI bool isinf(float __x) _NOEXCEPT { return __builtin_isinf(__x); }
+inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isinf(float __x) _NOEXCEPT {
+  return __builtin_isinf(__x);
+}
 
-inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_PREFERRED_OVERLOAD bool isinf(double __x) _NOEXCEPT { return __builtin_isinf(__x); }
+inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI _LIBCPP_PREFERRED_OVERLOAD bool isinf(double __x) _NOEXCEPT {
+  return __builtin_isinf(__x);
+}
 
-inline _LIBCPP_HIDE_FROM_ABI bool isinf(long double __x) _NOEXCEPT { return __builtin_isinf(__x); }
+inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isinf(long double __x) _NOEXCEPT {
+  return __builtin_isinf(__x);
+}
 #      endif
 
 // isnan
 
 template <class _A1, std::__enable_if_t<std::is_floating_point<_A1>::value, int> = 0>
-inline _LIBCPP_HIDE_FROM_ABI bool isnan(_A1 __x) _NOEXCEPT {
+_LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isnan(_A1 __x) _NOEXCEPT {
   return __builtin_isnan(__x);
 }
 
 template <class _A1, std::__enable_if_t<std::is_integral<_A1>::value, int> = 0>
-inline _LIBCPP_HIDE_FROM_ABI bool isnan(_A1) _NOEXCEPT {
+_LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isnan(_A1) _NOEXCEPT {
   return false;
 }
 
 #      ifdef _LIBCPP_PREFERRED_OVERLOAD
-inline _LIBCPP_HIDE_FROM_ABI bool isnan(float __x) _NOEXCEPT { return __builtin_isnan(__x); }
+inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isnan(float __x) _NOEXCEPT {
+  return __builtin_isnan(__x);
+}
 
-inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_PREFERRED_OVERLOAD bool isnan(double __x) _NOEXCEPT { return __builtin_isnan(__x); }
+inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI _LIBCPP_PREFERRED_OVERLOAD bool isnan(double __x) _NOEXCEPT {
+  return __builtin_isnan(__x);
+}
 
-inline _LIBCPP_HIDE_FROM_ABI bool isnan(long double __x) _NOEXCEPT { return __builtin_isnan(__x); }
+inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isnan(long double __x) _NOEXCEPT {
+  return __builtin_isnan(__x);
+}
 #      endif
 
 // isnormal
 
 template <class _A1, std::__enable_if_t<std::is_floating_point<_A1>::value, int> = 0>
-inline _LIBCPP_HIDE_FROM_ABI bool isnormal(_A1 __x) _NOEXCEPT {
+_LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isnormal(_A1 __x) _NOEXCEPT {
   return __builtin_isnormal(__x);
 }
 
 template <class _A1, std::__enable_if_t<std::is_integral<_A1>::value, int> = 0>
-inline _LIBCPP_HIDE_FROM_ABI bool isnormal(_A1 __x) _NOEXCEPT {
+_LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isnormal(_A1 __x) _NOEXCEPT {
   return __x != 0;
 }