Patch to add support for target shuffle combining of X86ISD::VPERMV3 nodes, including support for detecting unary shuffles.
This uncovered several issues with the X86ISD::VPERMV shuffle mask decoding of non-64 bit shuffle mask elements - the bit masking wasn't being correctly computed. A similar issue exists with X86ISD::VPERMV nodes that will need to be fixed when this is setup as well, but I will create repro test cases before pushing another patch for review.