[Bug target/79202] On Power8, consider using vupkhsw/xxpermdi to sign extend an int in a vector register instead of mfvsrwz/mtvsrwa

[bergner at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79202

--- Comment #2 from Peter Bergner <bergner at gcc dot gnu.org> ---
(In reply to Michael Meissner from comment #0)
> It may be more optimal to generate something like:
> 
>         xscvdpsxws 32,1
>         vupkhsw 1,0
>         xxpermdi 2,33,33,3
>         fcfid 3,2

Can we instead do:

        xscvdpsxws 32,1
        vupkhsw 1,0
        xvcvsxwdp 3,33