[InstCombine] add a wrapper for a common pair of transforms; NFCI

Some of the callers are artificially limiting this transform to integer types;
this should make it easier to incrementally remove that restriction.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@291620 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed