[DEBUGINFO] Prevent Instcombine from dropping debuginfo when removing zexts

Zexts can be treated like no-op casts when it comes to assessing whether their
removal affects debug info.

Reviewer: aprantl

Differential Revision: https://reviews.llvm.org/D60641


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@358431 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed