These test files are copied directly from AArch64. Some of the cases
may benefit from ANDN with the Zbb extension. Somes cases already
improve use ANDN.
selectcc-to-shiftand.ll also contains tests that test select->and
conversion even when a ANDN isn't needed. I think this improves our
coverage of these optimizations.
I think we normally use a 2 space indent for this, not four?