[PATCH] D55452: [CostModel][X86] Teach getArithmeticReductionCost to properly cost the shuffles needed for a PairWise reduction before we reach a legal type. And remove one shuffle from the end of the reduction.

[Craig Topper via Phabricator via llvm-commits]

craig.topper created this revision.
craig.topper added reviewers: RKSimon, spatel.

The loop for handling illegal types queried for extract_subvector shuffle which I think will always return 0 for an illegal type on X86. But that's not the correct shuffle. We really need 2 two source permutes to extract even and odd elements. For non-pairwise we don't need any shuffle so I've removed it entirely.

We were also counting 2 shuffles on the very last reduction step when we need to add element 1 to element 0. But element 0 is already in place. So we only need to move element 1.


https://reviews.llvm.org/D55452

Files:
  include/llvm/CodeGen/BasicTTIImpl.h
  test/Analysis/CostModel/X86/reduction.ll

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