Revert r216805 "[MachineCombiner][AArch64] Use the correct register class for MADD, SUB, and OR."

I think this broke the build bot. Reverting it for now until I have time to take a closer look.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@216813 91177308-0d34-0410-b5e6-96231b3b80d8
InstCombine: Try harder to combine icmp instructions

consider: (and (icmp X, Y), (and Z, (icmp A, B)))
It may be possible to combine (icmp X, Y) with (icmp A, B).
If we successfully combine, create an 'and' instruction with Z.

This fixes PR20814.

N.B. There is room for improvement after this change but I'm not
convinced it's worth chasing yet.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@216814 91177308-0d34-0410-b5e6-96231b3b80d8