[libc++] Add [[nodiscard]] extensions in <math.h>

[philnik]

Summary

There are quite a few functions marked [[gnu::const]] inside the compiler. This patch adds [[nodiscard]] to libc++-provided overloads of these functions to match the diagnostics produced.

[Mordante]

libcxx/test/libcxx/diagnostics/math_nodiscard_extensions.verify.cpp

19

Can you update the documentation for the nodiscard extension?

[philnik]

Address comments

libcxx/include/math.h

 
 #    ifdef isunordered
 #      undef isunordered
 #    endif
 
 // signbit
 
 template <class _A1, std::__enable_if_t<std::is_floating_point<_A1>::value, int> = 0>
-inline _LIBCPP_HIDE_FROM_ABI bool signbit(_A1 __x) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI bool signbit(_A1 __x) _NOEXCEPT {
   return __builtin_signbit(__x);
 }
 
 template <class _A1, std::__enable_if_t<std::is_integral<_A1>::value && std::is_signed<_A1>::value, int> = 0>
-inline _LIBCPP_HIDE_FROM_ABI bool signbit(_A1 __x) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI bool signbit(_A1 __x) _NOEXCEPT {
   return __x < 0;
 }
 
 template <class _A1, std::__enable_if_t<std::is_integral<_A1>::value && !std::is_signed<_A1>::value, int> = 0>
-inline _LIBCPP_HIDE_FROM_ABI bool signbit(_A1) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI bool signbit(_A1) _NOEXCEPT {
   return false;
 }
 
 // fpclassify
 
 template <class _A1, std::__enable_if_t<std::is_floating_point<_A1>::value, int> = 0>
-inline _LIBCPP_HIDE_FROM_ABI int fpclassify(_A1 __x) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI int fpclassify(_A1 __x) _NOEXCEPT {
   return __builtin_fpclassify(FP_NAN, FP_INFINITE, FP_NORMAL, FP_SUBNORMAL, FP_ZERO, __x);
 }
 
 template <class _A1, std::__enable_if_t<std::is_integral<_A1>::value, int> = 0>
-inline _LIBCPP_HIDE_FROM_ABI int fpclassify(_A1 __x) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI int fpclassify(_A1 __x) _NOEXCEPT {
   return __x == 0 ? FP_ZERO : FP_NORMAL;
 }
 
 // The MSVC runtime already provides these functions as templates
 #ifndef _LIBCPP_MSVCRT
 
 // isfinite
 
 template <class _A1,
           std::__enable_if_t<std::is_arithmetic<_A1>::value && std::numeric_limits<_A1>::has_infinity, int> = 0>
-_LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isfinite(_A1 __x) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT _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>
-_LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isfinite(_A1) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isfinite(_A1) _NOEXCEPT {
   return true;
 }
 
 // isinf
 
 template <class _A1,
           std::__enable_if_t<std::is_arithmetic<_A1>::value && std::numeric_limits<_A1>::has_infinity, int> = 0>
-_LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isinf(_A1 __x) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT _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>
-_LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI
+_LIBCPP_NODISCARD_EXT _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_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isinf(float __x) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isinf(float __x) _NOEXCEPT {
   return __builtin_isinf(__x);
 }
 
-inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI _LIBCPP_PREFERRED_OVERLOAD bool isinf(double __x) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _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 bool isinf(long double __x) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT 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>
-_LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isnan(_A1 __x) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT _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>
-_LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isnan(_A1) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isnan(_A1) _NOEXCEPT {
   return false;
 }
 
 #      ifdef _LIBCPP_PREFERRED_OVERLOAD
-inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isnan(float __x) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isnan(float __x) _NOEXCEPT {
   return __builtin_isnan(__x);
 }
 
-inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI _LIBCPP_PREFERRED_OVERLOAD bool isnan(double __x) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _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 bool isnan(long double __x) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT 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>
-_LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isnormal(_A1 __x) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT _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>
-_LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isnormal(_A1 __x) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isnormal(_A1 __x) _NOEXCEPT {
   return __x != 0;
 }
 
 // isgreater
 
 template <class _A1,
           class _A2,
           std::__enable_if_t<std::is_arithmetic<_A1>::value && std::is_arithmetic<_A2>::value, int> = 0>
-inline _LIBCPP_HIDE_FROM_ABI bool isgreater(_A1 __x, _A2 __y) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI bool isgreater(_A1 __x, _A2 __y) _NOEXCEPT {
   typedef typename std::__promote<_A1, _A2>::type type;
   return __builtin_isgreater((type)__x, (type)__y);
 }
 
 // isgreaterequal
 
 template <class _A1,
           class _A2,
           std::__enable_if_t<std::is_arithmetic<_A1>::value && std::is_arithmetic<_A2>::value, int> = 0>
-inline _LIBCPP_HIDE_FROM_ABI bool isgreaterequal(_A1 __x, _A2 __y) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI bool isgreaterequal(_A1 __x, _A2 __y) _NOEXCEPT {
   typedef typename std::__promote<_A1, _A2>::type type;
   return __builtin_isgreaterequal((type)__x, (type)__y);
 }
 
 // isless
 
 template <class _A1,
           class _A2,
           std::__enable_if_t<std::is_arithmetic<_A1>::value && std::is_arithmetic<_A2>::value, int> = 0>
-inline _LIBCPP_HIDE_FROM_ABI bool isless(_A1 __x, _A2 __y) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI bool isless(_A1 __x, _A2 __y) _NOEXCEPT {
   typedef typename std::__promote<_A1, _A2>::type type;
   return __builtin_isless((type)__x, (type)__y);
 }
 
 // islessequal
 
 template <class _A1,
           class _A2,
           std::__enable_if_t<std::is_arithmetic<_A1>::value && std::is_arithmetic<_A2>::value, int> = 0>
-inline _LIBCPP_HIDE_FROM_ABI bool islessequal(_A1 __x, _A2 __y) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI bool islessequal(_A1 __x, _A2 __y) _NOEXCEPT {
   typedef typename std::__promote<_A1, _A2>::type type;
   return __builtin_islessequal((type)__x, (type)__y);
 }
 
 // islessgreater
 
 template <class _A1,
           class _A2,
           std::__enable_if_t<std::is_arithmetic<_A1>::value && std::is_arithmetic<_A2>::value, int> = 0>
-inline _LIBCPP_HIDE_FROM_ABI bool islessgreater(_A1 __x, _A2 __y) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI bool islessgreater(_A1 __x, _A2 __y) _NOEXCEPT {
   typedef typename std::__promote<_A1, _A2>::type type;
   return __builtin_islessgreater((type)__x, (type)__y);
 }
 
 // isunordered
 
 template <class _A1,
           class _A2,
           std::__enable_if_t<std::is_arithmetic<_A1>::value && std::is_arithmetic<_A2>::value, int> = 0>
-inline _LIBCPP_HIDE_FROM_ABI bool isunordered(_A1 __x, _A2 __y) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI bool isunordered(_A1 __x, _A2 __y) _NOEXCEPT {
   typedef typename std::__promote<_A1, _A2>::type type;
   return __builtin_isunordered((type)__x, (type)__y);
 }
 
 #endif // _LIBCPP_MSVCRT
 
 // abs
 //
atan2(_A1 __y, _A2 __x) _NOEXCEPT
     static_assert((!(std::_IsSame<_A1, __result_type>::value &&
                      std::_IsSame<_A2, __result_type>::value)), "");
     return ::atan2((__result_type)__y, (__result_type)__x);
 }
 
 // ceil
 
 #    if !defined(__sun__)
-inline _LIBCPP_HIDE_FROM_ABI float       ceil(float __x) _NOEXCEPT       {return __builtin_ceilf(__x);}
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI float       ceil(float __x) _NOEXCEPT       {return __builtin_ceilf(__x);}
 
 template <class = int>
-_LIBCPP_HIDE_FROM_ABI double ceil(double __x) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI double ceil(double __x) _NOEXCEPT {
   return __builtin_ceil(__x);
 }
 
-inline _LIBCPP_HIDE_FROM_ABI long double ceil(long double __x) _NOEXCEPT {return __builtin_ceill(__x);}
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI long double ceil(long double __x) _NOEXCEPT {return __builtin_ceill(__x);}
 #    endif
 
 template <class _A1>
-inline _LIBCPP_HIDE_FROM_ABI
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI
 typename std::enable_if<std::is_integral<_A1>::value, double>::type
 ceil(_A1 __x) _NOEXCEPT {return __builtin_ceil((double)__x);}
 
 // cos
 
 #    if !defined(__sun__)
 inline _LIBCPP_HIDE_FROM_ABI float       cos(float __x) _NOEXCEPT       {return __builtin_cosf(__x);}
 

 template <class _A1>
 inline _LIBCPP_HIDE_FROM_ABI
 typename std::enable_if<std::is_integral<_A1>::value, double>::type
 exp(_A1 __x) _NOEXCEPT {return __builtin_exp((double)__x);}
 
 // fabs
 
 #    if !defined(__sun__)
-inline _LIBCPP_HIDE_FROM_ABI float       fabs(float __x) _NOEXCEPT       {return __builtin_fabsf(__x);}
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI float       fabs(float __x) _NOEXCEPT       {return __builtin_fabsf(__x);}
 
 template <class = int>
-_LIBCPP_HIDE_FROM_ABI double fabs(double __x) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI double fabs(double __x) _NOEXCEPT {
   return __builtin_fabs(__x);
 }
 
-inline _LIBCPP_HIDE_FROM_ABI long double fabs(long double __x) _NOEXCEPT {return __builtin_fabsl(__x);}
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI long double fabs(long double __x) _NOEXCEPT {return __builtin_fabsl(__x);}
 #    endif
 
 template <class _A1>
-inline _LIBCPP_HIDE_FROM_ABI
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI
 typename std::enable_if<std::is_integral<_A1>::value, double>::type
 fabs(_A1 __x) _NOEXCEPT {return __builtin_fabs((double)__x);}
 
 // floor
 
 #    if !defined(__sun__)
-inline _LIBCPP_HIDE_FROM_ABI float       floor(float __x) _NOEXCEPT       {return __builtin_floorf(__x);}
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI float       floor(float __x) _NOEXCEPT       {return __builtin_floorf(__x);}
 
 template <class = int>
-_LIBCPP_HIDE_FROM_ABI double floor(double __x) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI double floor(double __x) _NOEXCEPT {
   return __builtin_floor(__x);
 }
 
-inline _LIBCPP_HIDE_FROM_ABI long double floor(long double __x) _NOEXCEPT {return __builtin_floorl(__x);}
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI long double floor(long double __x) _NOEXCEPT {return __builtin_floorl(__x);}
 #    endif
 
 template <class _A1>
-inline _LIBCPP_HIDE_FROM_ABI
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI
 typename std::enable_if<std::is_integral<_A1>::value, double>::type
 floor(_A1 __x) _NOEXCEPT {return __builtin_floor((double)__x);}
 
 // fmod
 
 #    if !defined(__sun__)
 inline _LIBCPP_HIDE_FROM_ABI float       fmod(float __x, float __y) _NOEXCEPT             {return __builtin_fmodf(__x, __y);}
 

 
 template <class _A1>
 inline _LIBCPP_HIDE_FROM_ABI
 typename std::enable_if<std::is_integral<_A1>::value, double>::type
 atanh(_A1 __x) _NOEXCEPT {return __builtin_atanh((double)__x);}
 
 // cbrt
 
-inline _LIBCPP_HIDE_FROM_ABI float       cbrt(float __x) _NOEXCEPT       {return __builtin_cbrtf(__x);}
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI float       cbrt(float __x) _NOEXCEPT       {return __builtin_cbrtf(__x);}
 
 template <class = int>
-_LIBCPP_HIDE_FROM_ABI double cbrt(double __x) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI double cbrt(double __x) _NOEXCEPT {
   return __builtin_cbrt(__x);
 }
 
-inline _LIBCPP_HIDE_FROM_ABI long double cbrt(long double __x) _NOEXCEPT {return __builtin_cbrtl(__x);}
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI long double cbrt(long double __x) _NOEXCEPT {return __builtin_cbrtl(__x);}
 
 template <class _A1>
-inline _LIBCPP_HIDE_FROM_ABI
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI
 typename std::enable_if<std::is_integral<_A1>::value, double>::type
 cbrt(_A1 __x) _NOEXCEPT {return __builtin_cbrt((double)__x);}
 
 // copysign
 
 _LIBCPP_CONSTEXPR
 inline _LIBCPP_HIDE_FROM_ABI float __libcpp_copysign(float __x, float __y) _NOEXCEPT {
   return __builtin_copysignf(__x, __y);

 >::type
 __libcpp_copysign(_A1 __x, _A2 __y) _NOEXCEPT {
     typedef typename std::__promote<_A1, _A2>::type __result_type;
     static_assert((!(std::_IsSame<_A1, __result_type>::value &&
                      std::_IsSame<_A2, __result_type>::value)), "");
     return __builtin_copysign((__result_type)__x, (__result_type)__y);
 }
 
-inline _LIBCPP_HIDE_FROM_ABI float copysign(float __x, float __y) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI float copysign(float __x, float __y) _NOEXCEPT {
   return ::__libcpp_copysign(__x, __y);
 }
 
-inline _LIBCPP_HIDE_FROM_ABI long double copysign(long double __x, long double __y) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI long double copysign(long double __x, long double __y) _NOEXCEPT {
   return ::__libcpp_copysign(__x, __y);
 }
 
 template <class _A1, class _A2>
-inline _LIBCPP_HIDE_FROM_ABI
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI
 typename std::__enable_if_t
 <
     std::is_arithmetic<_A1>::value &&
     std::is_arithmetic<_A2>::value,
     std::__promote<_A1, _A2>
 >::type
     copysign(_A1 __x, _A2 __y) _NOEXCEPT {
   return ::__libcpp_copysign(__x, __y);
fma(_A1 __x, _A2 __y, _A3 __z) _NOEXCEPT
     static_assert((!(std::_IsSame<_A1, __result_type>::value &&
                      std::_IsSame<_A2, __result_type>::value &&
                      std::_IsSame<_A3, __result_type>::value)), "");
     return __builtin_fma((__result_type)__x, (__result_type)__y, (__result_type)__z);
 }
 
 // fmax
 
-inline _LIBCPP_HIDE_FROM_ABI float       fmax(float __x, float __y) _NOEXCEPT             {return __builtin_fmaxf(__x, __y);}
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI float       fmax(float __x, float __y) _NOEXCEPT             {return __builtin_fmaxf(__x, __y);}
 
 template <class = int>
-_LIBCPP_HIDE_FROM_ABI double fmax(double __x, double __y) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI double fmax(double __x, double __y) _NOEXCEPT {
   return __builtin_fmax(__x, __y);
 }
 
-inline _LIBCPP_HIDE_FROM_ABI long double fmax(long double __x, long double __y) _NOEXCEPT {return __builtin_fmaxl(__x, __y);}
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI long double fmax(long double __x, long double __y) _NOEXCEPT {return __builtin_fmaxl(__x, __y);}
 
 template <class _A1, class _A2>
-inline _LIBCPP_HIDE_FROM_ABI
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI
 typename std::__enable_if_t
 <
     std::is_arithmetic<_A1>::value &&
     std::is_arithmetic<_A2>::value,
     std::__promote<_A1, _A2>
 >::type
 fmax(_A1 __x, _A2 __y) _NOEXCEPT
 {
     typedef typename std::__promote<_A1, _A2>::type __result_type;
     static_assert((!(std::_IsSame<_A1, __result_type>::value &&
                      std::_IsSame<_A2, __result_type>::value)), "");
     return ::fmax((__result_type)__x, (__result_type)__y);
 }
 
 // fmin
 
-inline _LIBCPP_HIDE_FROM_ABI float       fmin(float __x, float __y) _NOEXCEPT             {return __builtin_fminf(__x, __y);}
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI float       fmin(float __x, float __y) _NOEXCEPT             {return __builtin_fminf(__x, __y);}
 
 template <class = int>
-_LIBCPP_HIDE_FROM_ABI double fmin(double __x, double __y) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI double fmin(double __x, double __y) _NOEXCEPT {
   return __builtin_fmin(__x, __y);
 }
 
-inline _LIBCPP_HIDE_FROM_ABI long double fmin(long double __x, long double __y) _NOEXCEPT {return __builtin_fminl(__x, __y);}
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI long double fmin(long double __x, long double __y) _NOEXCEPT {return __builtin_fminl(__x, __y);}
 
 template <class _A1, class _A2>
-inline _LIBCPP_HIDE_FROM_ABI
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI
 typename std::__enable_if_t
 <
     std::is_arithmetic<_A1>::value &&
     std::is_arithmetic<_A2>::value,
     std::__promote<_A1, _A2>
 >::type
 fmin(_A1 __x, _A2 __y) _NOEXCEPT
 {

 {
     return __builtin_lround((double)__x);
 }
 
 // nan
 
 // nearbyint
 
-inline _LIBCPP_HIDE_FROM_ABI float       nearbyint(float __x) _NOEXCEPT       {return __builtin_nearbyintf(__x);}
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI float       nearbyint(float __x) _NOEXCEPT       {return __builtin_nearbyintf(__x);}
 
 template <class = int>
-_LIBCPP_HIDE_FROM_ABI double nearbyint(double __x) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI double nearbyint(double __x) _NOEXCEPT {
   return __builtin_nearbyint(__x);
 }
 
-inline _LIBCPP_HIDE_FROM_ABI long double nearbyint(long double __x) _NOEXCEPT {return __builtin_nearbyintl(__x);}
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI long double nearbyint(long double __x) _NOEXCEPT {return __builtin_nearbyintl(__x);}
 
 template <class _A1>
-inline _LIBCPP_HIDE_FROM_ABI
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI
 typename std::enable_if<std::is_integral<_A1>::value, double>::type
 nearbyint(_A1 __x) _NOEXCEPT {return __builtin_nearbyint((double)__x);}
 
 // nextafter
 
 inline _LIBCPP_HIDE_FROM_ABI float       nextafter(float __x, float __y) _NOEXCEPT             {return __builtin_nextafterf(__x, __y);}
 
 template <class = int>
remquo(_A1 __x, _A2 __y, int* __z) _NOEXCEPT
     typedef typename std::__promote<_A1, _A2>::type __result_type;
     static_assert((!(std::_IsSame<_A1, __result_type>::value &&
                      std::_IsSame<_A2, __result_type>::value)), "");
     return ::remquo((__result_type)__x, (__result_type)__y, __z);
 }
 
 // rint
 
-inline _LIBCPP_HIDE_FROM_ABI float       rint(float __x) _NOEXCEPT
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI float       rint(float __x) _NOEXCEPT
 {
     return __builtin_rintf(__x);
 }
 
 template <class = int>
-_LIBCPP_HIDE_FROM_ABI double rint(double __x) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI double rint(double __x) _NOEXCEPT {
   return __builtin_rint(__x);
 }
 
-inline _LIBCPP_HIDE_FROM_ABI long double rint(long double __x) _NOEXCEPT
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI long double rint(long double __x) _NOEXCEPT
 {
     return __builtin_rintl(__x);
 }
 
 template <class _A1>
-inline _LIBCPP_HIDE_FROM_ABI
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI
 typename std::enable_if<std::is_integral<_A1>::value, double>::type
 rint(_A1 __x) _NOEXCEPT
 {
     return __builtin_rint((double)__x);
 }
 
 // round
 
-inline _LIBCPP_HIDE_FROM_ABI float       round(float __x) _NOEXCEPT
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI float       round(float __x) _NOEXCEPT
 {
     return __builtin_round(__x);
 }
 
 template <class = int>
-_LIBCPP_HIDE_FROM_ABI double round(double __x) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI double round(double __x) _NOEXCEPT {
   return __builtin_round(__x);
 }
 
-inline _LIBCPP_HIDE_FROM_ABI long double round(long double __x) _NOEXCEPT
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI long double round(long double __x) _NOEXCEPT
 {
     return __builtin_roundl(__x);
 }
 
 template <class _A1>
-inline _LIBCPP_HIDE_FROM_ABI
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI
 typename std::enable_if<std::is_integral<_A1>::value, double>::type
 round(_A1 __x) _NOEXCEPT
 {
     return __builtin_round((double)__x);
 }
 
 // scalbln
 

 
 template <class _A1>
 inline _LIBCPP_HIDE_FROM_ABI
 typename std::enable_if<std::is_integral<_A1>::value, double>::type
 tgamma(_A1 __x) _NOEXCEPT {return __builtin_tgamma((double)__x);}
 
 // trunc
 
-inline _LIBCPP_HIDE_FROM_ABI float       trunc(float __x) _NOEXCEPT
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI float       trunc(float __x) _NOEXCEPT
 {
     return __builtin_trunc(__x);
 }
 
 template <class = int>
-_LIBCPP_HIDE_FROM_ABI double trunc(double __x) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI double trunc(double __x) _NOEXCEPT {
   return __builtin_trunc(__x);
 }
 
-inline _LIBCPP_HIDE_FROM_ABI long double trunc(long double __x) _NOEXCEPT
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI long double trunc(long double __x) _NOEXCEPT
 {
     return __builtin_truncl(__x);
 }
 
 template <class _A1>
-inline _LIBCPP_HIDE_FROM_ABI
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI
 typename std::enable_if<std::is_integral<_A1>::value, double>::type
 trunc(_A1 __x) _NOEXCEPT
 {
     return __builtin_trunc((double)__x);
 }
 
 } // extern "C++"
 

libcxx/include/stdlib.h

 # undef labs
 #endif
 #ifdef llabs
 # undef llabs
 #endif
 
 // MSVCRT already has the correct prototype in <stdlib.h> if __cplusplus is defined
 #if !defined(_LIBCPP_MSVCRT) && !defined(__sun__)
-inline _LIBCPP_INLINE_VISIBILITY long abs(long __x) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_INLINE_VISIBILITY long abs(long __x) _NOEXCEPT {
   return __builtin_labs(__x);
 }
-inline _LIBCPP_INLINE_VISIBILITY long long abs(long long __x) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_INLINE_VISIBILITY long long abs(long long __x) _NOEXCEPT {
   return __builtin_llabs(__x);
 }
 #endif // !defined(_LIBCPP_MSVCRT) && !defined(__sun__)
 
 #if !defined(__sun__)
-inline _LIBCPP_INLINE_VISIBILITY float abs(float __lcpp_x) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_INLINE_VISIBILITY float abs(float __lcpp_x) _NOEXCEPT {
   return __builtin_fabsf(__lcpp_x); // Use builtins to prevent needing math.h
 }
 
-inline _LIBCPP_INLINE_VISIBILITY double abs(double __lcpp_x) _NOEXCEPT {
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_INLINE_VISIBILITY double abs(double __lcpp_x) _NOEXCEPT {
   return __builtin_fabs(__lcpp_x);
 }
 
-inline _LIBCPP_INLINE_VISIBILITY long double
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_INLINE_VISIBILITY long double
 abs(long double __lcpp_x) _NOEXCEPT {
   return __builtin_fabsl(__lcpp_x);
 }
 #endif // !defined(__sun__)
 
 // div
 
 #ifdef div

libcxx/test/libcxx/diagnostics/math_nodiscard_extensions.verify.cpp

+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03
+
+// We don't control the implementation of the math.h functions on windows
+// UNSUPPORTED: windows
+
+// check that const cmath functions are declared [[nodiscard]]
+
+#include <cmath>
+
+void test() {
+  std::signbit(0.f);             // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::signbit(0.);              // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::signbit(0.l);             // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::signbit(0);               // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::signbit(0U);              // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+
+  std::fpclassify(0.f);          // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::fpclassify(0.);           // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::fpclassify(0.l);          // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::fpclassify(0);            // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::fpclassify(0U);           // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+
+  std::isfinite(0.f);            // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::isfinite(0.);             // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::isfinite(0.l);            // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::isfinite(0);              // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::isfinite(0U);             // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+
+  std::isinf(0.f);               // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::isinf(0.);                // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::isinf(0.l);               // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::isinf(0);                 // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::isinf(0U);                // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+
+  std::isnan(0.f);               // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::isnan(0.);                // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::isnan(0.l);               // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::isnan(0);                 // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::isnan(0U);                // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+
+  std::isnormal(0.f);            // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::isnormal(0.);             // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::isnormal(0.l);            // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::isnormal(0);              // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::isnormal(0U);             // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+
+  std::isgreater(0.f, 0.f);      // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::isgreater(0., 0.);        // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::isgreater(0.l, 0.l);      // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::isgreater(0, 0);          // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::isgreater(0U, 0U);        // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+
+  std::isgreaterequal(0.f, 0.f); // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::isgreaterequal(0., 0.);   // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::isgreaterequal(0.l, 0.l); // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::isgreaterequal(0, 0);     // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::isgreaterequal(0U, 0U);   // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+
+  std::isless(0.f, 0.f);         // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::isless(0., 0.);           // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::isless(0.l, 0.l);         // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::isless(0, 0);             // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::isless(0U, 0U);           // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+
+  std::islessequal(0.f, 0.f);    // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::islessequal(0., 0.);      // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::islessequal(0.l, 0.l);    // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::islessequal(0, 0);        // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::islessequal(0U, 0U);      // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+
+  std::islessgreater(0.f, 0.f);  // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::islessgreater(0., 0.);    // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::islessgreater(0.l, 0.l);  // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::islessgreater(0, 0);      // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::islessgreater(0U, 0U);    // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+
+  std::isunordered(0.f, 0.f);    // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::isunordered(0., 0.);      // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::isunordered(0.l, 0.l);    // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::isunordered(0, 0);        // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::isunordered(0U, 0U);      // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+
+  std::ceil(0.f);                // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::ceil(0.);                 // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::ceil(0.l);                // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::ceil(0);                  // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::ceil(0U);                 // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+
+  std::fabs(0.f);                // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::fabs(0.);                 // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::fabs(0.l);                // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::fabs(0);                  // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::fabs(0U);                 // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+
+  std::floor(0.f);               // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::floor(0.);                // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::floor(0.l);               // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::floor(0);                 // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::floor(0U);                // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+
+  std::cbrt(0.f);                // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::cbrt(0.);                 // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::cbrt(0.l);                // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::cbrt(0);                  // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::cbrt(0U);                 // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+
+  std::copysign(0.f, 0.f);       // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::copysign(0., 0.);         // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::copysign(0.l, 0.l);       // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::copysign(0, 0);           // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::copysign(0U, 0U);         // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+
+  std::fmax(0.f, 0.f);           // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::fmax(0., 0.);             // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::fmax(0.l, 0.l);           // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::fmax(0, 0);               // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::fmax(0U, 0U);             // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+
+  std::fmin(0.f, 0.f);           // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::fmin(0., 0.);             // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::fmin(0.l, 0.l);           // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::fmin(0, 0);               // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::fmin(0U, 0U);             // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+
+  std::nearbyint(0.f);           // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::nearbyint(0.);            // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::nearbyint(0.l);           // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::nearbyint(0);             // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::nearbyint(0U);            // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+
+  std::rint(0.f);                // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::rint(0.);                 // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::rint(0.l);                // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::rint(0);                  // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::rint(0U);                 // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+
+  std::round(0.f);               // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::round(0.);                // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::round(0.l);               // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::round(0);                 // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::round(0U);                // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+
+  std::trunc(0.f);               // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::trunc(0.);                // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::trunc(0.l);               // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::trunc(0);                 // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+  std::trunc(0U);                // expected-warning-re {{ignoring return value of function declared with {{.*}} attribute}}
+}