[PATCH] D153504: [DAG][AArch64] Fold shuffle_vector<4,5,6,7> to extract_subvector

[Dave Green via Phabricator via llvm-commits]

dmgreen created this revision.
dmgreen added reviewers: RKSimon, SjoerdMeijer, craig.topper, spatel.
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During legalization, we can end up with shuffles that are identity masks, so act like extract_subvector, but do not simplify to extract_subvector. This adjusts the profitability heuristic in foldExtractSubvectorFromShuffleVector to allow identity vectors that do not start at element 0. Undef masks elements are excluded as it can be more useful to keep the undef elements.


https://reviews.llvm.org/D153504

Files:
  llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  llvm/test/CodeGen/AArch64/add-extract.ll
  llvm/test/CodeGen/AArch64/shuffles.ll
  llvm/test/CodeGen/AArch64/sve-fixed-length-shuffles.ll

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