[PATCH] D123587: [SLP] Generate shuffles if we can reorder an existing node

[Dave Green via Phabricator via llvm-commits]

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Whilst vectorizing a tree element, if we detect a list of nodes which is a reordering of an existing tree element, we can create a shuffle instead of falling back to a "build-vector" (i.e inserts that we extract from a vector instruction). This can help reduce the number of insert/extracts sequences that need to be cleaned up by instcombine.


https://reviews.llvm.org/D123587

Files:
  llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
  llvm/test/Transforms/SLPVectorizer/AArch64/loadorder.ll
  llvm/test/Transforms/SLPVectorizer/AArch64/transpose-inseltpoison.ll
  llvm/test/Transforms/SLPVectorizer/AArch64/transpose.ll
  llvm/test/Transforms/SLPVectorizer/X86/extractelement.ll
  llvm/test/Transforms/SLPVectorizer/X86/jumbled-load.ll
  llvm/test/Transforms/SLPVectorizer/X86/lookahead.ll
  llvm/test/Transforms/SLPVectorizer/X86/phi.ll
  llvm/test/Transforms/SLPVectorizer/X86/reorder_diamond_match.ll
  llvm/test/Transforms/SLPVectorizer/X86/reordered-top-scalars.ll

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