[Bug c++/107458] std::fma generates slow scalar-call

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107458

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |INVALID

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Your definition of fma_manually is broken really.

The following is closer to being correct though there is still an extra
rounding step so it is still not 100%.

inline constexpr float fma_manually(const float a, const float b, const float
c)  noexcept
{
    double
        res = a;

    res *= b;
    res += c;
    return res;
}
inline constexpr double fma_manually(const double a, const double b, const
double 
 c)  noexcept
{
    long double
        res = a;

    res *= b;
    res += c;
    return res;
}

But GCC does the correct thing for fma and fmaf with x86-64-v3 and use the fma
instruction.

So closing as invalid.