[Bug tree-optimization/126465] [16/17 Regression] Wrong code with IFN_COND_FMA folding on SVE

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126465

--- Comment #4 from ktkachov at gcc dot gnu.org ---
(In reply to Drea Pinski from comment #1)
> r16-6508-g772b847d99d5e3 .
> 
> 
>   (simplify
>    (negate (fmas@3 @4 @0 @1 @2 @5))
>    (if (!HONOR_SIGN_DEPENDENT_ROUNDING (type) && single_use (@3))
>     (IFN_COND_FNMS @4 @0 @1 @2 @5))))
> 
> 
> The negate also applies to the other non-fma part while afterwards it does
> not.
> 
>  (simplify
>   (negate (IFN_FMS@3 @4 @0 @1 @2 @5))
>    (if (!HONOR_SIGN_DEPENDENT_ROUNDING (type) && single_use (@3))
>     (IFN_COND_FNMA @4 @0 @1 @2 @5)))
> 

More worryingly, why is IFN_FMS taking 4 here when it is a ternary IFN and how
come genmatch didn't catch it?