DAGCombiner already supports peeking thorough shuffles to improve vector element extraction, but legalization often leaves us in situations where we need to extract vector elements after shuffles have already been lowered.
This patch adds support for VECTOR_EXTRACT_ELEMENT/PEXTRW/PEXTRB instructions to attempt to handle target shuffles as well. I've covered some basic scenarios including handling shuffle mask scaling and the implicit zero-extension of PEXTRW/PEXTRB, there is more that could be done here (that I've mentioned in TODOs) but I haven't found many cases where its worth it.
Differential Revision: https://reviews.llvm.org/D30176
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@296381 91177308-0d34-0410-b5e6-96231b3b80d8
Though such shifts are usually optimized away by combiner, we still can
encounter them after a vector shift is legalized.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@231443 91177308-0d34-0410-b5e6-96231b3b80d8
Ayman Musa