Recommit with changes. Comment out palignr for the

Recommit with changes.  Comment out palignr for the
moment, as there's a testcase that uses it and expects it
to be subject to optimizations; we won't be doing that.
Some adjustments based on feedback from Bill.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@112754 91177308-0d34-0410-b5e6-96231b3b80d8