[Development] Implicit VFMADD support (Was: Updating x86 SIMD support in Qt)

[Konstantin Shegunov]

On Mon, Jan 24, 2022 at 8:50 PM Thiago Macieira <thiago.macieira at intel.com>
wrote:

> If you're talking about code in Qt, simply use std::fma and it'll do the
> right
> thing. It becomes my problem to optimise it so we get the shortest code
> emission, not yours.
>

So as it is now in that case. If it's not my problem but yours, then this
works for me wondrously. :)

The compilers also convert *some* instances of plain multiplication
> followed
> by addition into FMA. That depends on compiler flags, often enough,
> because of
> differences in rounding.
>

I will check if I'm not talking nonsense (as I had a few iterations over
that one), but I can't rely on that to happen magically - so I simply
enforce it at this point with std::fma.
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