[llvm] [VPlan] Use DL index type consistently for GEPs (PR #169396)

[Florian Hahn via llvm-commits]

https://github.com/fhahn approved this pull request.

LGTM, thanks.

This should be fine as the offset must effectively fit into the index type; in most cases, the existing GEPs will be folded by InstCombine to be i8 based, which also uses the index type.

https://github.com/llvm/llvm-project/pull/169396