This is split from D63174 to see what it takes to get both pass managers to do the same thing
I've disable -O0 optnone and ran instsimplify on both outputs. This seems to get us converged with some test updates. The only thing I don't like is the tests of true and false comparison predicates with masking. The only IR we ended up with is just loads and stores. The cmp and AND instruction are folded out by instsimplify.
I'll do more tests from D63174 if we think this is a decent direction