Reverse the logic for valid tail predication instructions and create
a whitelist instead. Added other instruction groups that aren't
obviously safe:
- instructions that 'narrow' their result.
- lane moves.
- byte swapping instructions.
- interleaving loads and stores.
- cross-beat carries.
- top/bottom instructions.
- complex operations.
Hopefully we should be able to add more of these instructions to the
whitelist, once we have a more concrete idea of the transform.
Differential Revision: https://reviews.llvm.org/D67904
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@374887 91177308-0d34-0410-b5e6-96231b3b80d8
