[llvm] [BasicAA] Add Vscale GEP decomposition on variable index (PR #69152)

[Philip Reames via llvm-commits]

preames wrote:

If I'm reading this right, the main goal of this is to be able to represent a gep whose index type is a scalable type?  If so, I'm tempted to suggest an alternative approach.

We seem to generally be moving in the direction of the ptradd (i.e. i8 index types), could we canonicalize a gep <vscale x ...> to a gep i8, <some IR expression>?  Doing so would remove the need for a value to represent vscale when we can't just use the intrinsic.  This would remove the need for the sentinel value, and would simplify this patch significantly (I think).  


https://github.com/llvm/llvm-project/pull/69152