[libc++] Fix acceptance of convertible-to-{float,double,long double} in std::isfinite()

libcxx/include/__math/traits.h

@@ -55,6 +55,18 @@ _LIBCPP_NODISCARD _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isfin
   return true;
 }
 
+_LIBCPP_NODISCARD inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isfinite(float __x) _NOEXCEPT {
+  return __builtin_isfinite(__x);
+}
+
+_LIBCPP_NODISCARD inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isfinite(double __x) _NOEXCEPT {
+  return __builtin_isfinite(__x);
+}
+
+_LIBCPP_NODISCARD inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isfinite(long double __x) _NOEXCEPT {
+  return __builtin_isfinite(__x);
+}
+
 // isinf
 
 template <class _A1, __enable_if_t<is_arithmetic<_A1>::value && numeric_limits<_A1>::has_infinity, int> = 0>

libcxx/test/std/numerics/c.math/isfinite.pass.cpp

@@ -62,9 +62,30 @@ struct TestInt {
   }
 };
 
+struct ConvertibleFloat {
+  int value;
+  ConvertibleFloat(int v) : value(v) {}
+  operator float() const { return static_cast<float>(value); }
+};
+
+struct ConvertibleDouble {
+  int value;
+  ConvertibleDouble(int v) : value(v) {}
+  operator double() const { return static_cast<double>(value); }
+};
+
+struct ConvertibleLongDouble {
+  int value;
+  ConvertibleLongDouble(int v) : value(v) {}
+  operator long double() const { return static_cast<long double>(value); }
+};
+
 int main(int, char**) {
   types::for_each(types::floating_point_types(), TestFloat());
   types::for_each(types::integral_types(), TestInt());
+  assert(std::isfinite(ConvertibleFloat(0)));
+  assert(std::isfinite(ConvertibleDouble(0)));
+  assert(std::isfinite(ConvertibleLongDouble(0)));
 
   return 0;
 }