[InstCombine] Teach foldSelectICmpAndOr to handle vector splats

This was pretty close to working already. While I was here I went ahead and passed the ICmpInst pointer from the caller instead of doing a dyn_cast that can never fail.

Differential Revision: https://reviews.llvm.org/D37237

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@311960 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed