[x86] Re-work a bunch of the v32i8 test cases to actually involve byte
shuffles rather than word shuffles.

As you might guess, these were built starting from the word shuffle test
cases and I failed to properly port a bunch of them and left them as
widened word shuffle test cases. We still have a couple of tests that
check our ability to widen shuffles, but now we will test the actual
byte shuffle quite a bit better.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218438 91177308-0d34-0410-b5e6-96231b3b80d8
[x86] More tweaks to the v32i8 test cases.

I made a mistake in the previous commit and produced the wrong pattern.
Fix that. Also make one more shuffle pattern byte-based rather than
word-based, and add two more blend patterns.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218439 91177308-0d34-0410-b5e6-96231b3b80d8
[x86] Implement AVX2 support for v32i8 in the new vector shuffle
lowering.

This completes the basic AVX2 feature support, but there are still some
improvements I'd like to do to really get the last mile of performance
here.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218440 91177308-0d34-0410-b5e6-96231b3b80d8