[PATCH] D12125: [DAGCombiner] Fold CONCAT_VECTORS of EXTRACT_SUBVECTOR (or undef) to VECTOR_SHUFFLE.

[Simon Pilgrim via llvm-commits]

RKSimon created this revision.
RKSimon added reviewers: chandlerc, qcolombet, andreadb, spatel.
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Check to see if this is a CONCAT_VECTORS of a bunch of EXTRACT_SUBVECTOR operations. If so, and if the EXTRACT_SUBVECTOR vector inputs come from at most two distinct vectors the same size as the result, attempt to turn this into a legal shuffle.

Repository:
  rL LLVM

http://reviews.llvm.org/D12125

Files:
  lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  test/CodeGen/X86/pr15267.ll
  test/CodeGen/X86/vector-shuffle-256-v16.ll
  test/CodeGen/X86/vector-shuffle-256-v4.ll
  test/CodeGen/X86/vector-shuffle-256-v8.ll

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