[X86][SLP] Show example of failure to uniformly commute splats for 'alt' shuffles.

If either the main/alt opcodes isn't commutable we may end up with the splats not correctly commuted to the same side.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@356837 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed