[AVX-512] Add support for lowering shuffles to VALIGND/VALIGNQ
Summary: VALIGND and VALIGNQ are similar to PALIGNR but instead of working on a 128-bit lane they work on the entire vector register. This change leverages the shuffle rotate detection code used for PALIGNR to detect these cases.
Reviewers: delena, RKSimon
Subscribers: Farhana, llvm-commits
Differential Revision: https://reviews.llvm.org/D26297
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@286709
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