[PATCH] D132308: [LV] Replace fixed-order cost model with a SK_Splice shuffle

[Dave Green via Phabricator via llvm-commits]

dmgreen created this revision.
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The existing cost model for fixed-order recurrences models the phi as an extract shuffle of a v1 vector. The shuffle produced should be a splice, taking two vectors are extracting a subset of the lanes. On certain architectures the existing cost model can drastically under-estimate the correct cost for the shuffle, so this changes it to a SK_Splice, and passes a correct Mask through to the getShuffleCost call.

I believe this might be the first use of a SK_Splice shuffle cost model outside of scalable vectors, and some targets may require additions to the cost-model to correctly account for them.
https://godbolt.org/z/r8j69Kz9z


https://reviews.llvm.org/D132308

Files:
  llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
  llvm/test/Transforms/LoopVectorize/ARM/mve-recurrence.ll

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