[llvm] WIP: AMDGPU: Handle multiple AGPR MFMA rewrites (PR #147975)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> > What if src2 is 0?
> > ```
> > DefMI %631:av_512_align2 = COPY %632:vreg_512_align2
> > 
> > CopySrcMI %632:vreg_512_align2 = contract V_MFMA_F32_32X32X2F32_vgprcd_e64 %628.sub0:av_128_align2, %234.sub0:vreg_128_align2, **0**, 0, 0, 0, implicit $mode, implicit $exec
> > ```
> > 
> > 
> >     
> >       
> >     
> > 
> >       
> >     
> > 
> >     
> >   
> > This will crash.
> 
> It's broken, but it was already broken before this patch

https://github.com/llvm/llvm-project/pull/150552

https://github.com/llvm/llvm-project/pull/147975