[InstCombine] Simplify gep (gep p, a), (b-a)

Patch by Andrea Canciani.

Differential Revision:  https://reviews.llvm.org/D27413

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@292506 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed