[InstCombine] add helper function for icmp (and (sh X, Y), C2), C1 ; NFC

Like other recent changes near here, the goal is to allow vector types for
all of these folds. Splitting things up makes it easier to incrementally 
enhance the code and easier to read.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@279851 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed