349523e26b
Fold:
%gep1 = ptradd %p, C1
%gep2 = ptradd %gep1, %x
%res = ptradd %gep2, C2
To:
%gep = ptradd %gep, %x
%res = ptradd %gep, C1+C2
An alternative to this would be to generally canonicalize constant
offset GEPs to the right. I found the results of doing that somewhat
mixed, so I'm going for this more obviously beneficial change for now.
Proof for flag preservation on reassociation:
https://alive2.llvm.org/ce/z/gmpAMg