[Thumb2] BXJ should be undefined for v7M, v8A

The Thumb2 BXJ instruction (Branch and Exchange Jazelle) is not
defined for v7M or v8A. It is defined for all other Thumb2-supporting
architectures (v6T2, v7A and v7R).



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218445 91177308-0d34-0410-b5e6-96231b3b80d8
[x86] Teach the new vector shuffle lowering a fancier way to lower
256-bit vectors with lane-crossing.

Rather than immediately decomposing to 128-bit vectors, try flipping the
256-bit vector lanes, shuffling them and blending them together. This
reduces our worst case shuffle by a pretty significant margin across the
board.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218446 91177308-0d34-0410-b5e6-96231b3b80d8