[PATCH] D26277: [SLP] Fixed cost model for horizontal reduction.

[Alexey Bataev via llvm-commits]

ABataev created this revision.
ABataev added reviewers: hfinkel, mkuper, mzolotukhin.
ABataev added subscribers: llvm-commits, spatel, RKSimon.

Currently when cost of scalar operations is evaluated the vector type is used for scalar operations. Patch fixes this issue and fixes evaluation of the vector operations cost.
Several test showed that vector cost model is too optimistic. It allowed vectorization of 8 or less `add/fadd` operations, though scalar code is faster. Actually, only for 16 or more operations vector code provides better performance.


https://reviews.llvm.org/D26277

Files:
  include/llvm/CodeGen/BasicTTIImpl.h
  lib/Transforms/Vectorize/SLPVectorizer.cpp
  test/Analysis/CostModel/X86/reduction.ll
  test/Transforms/SLPVectorizer/AArch64/gather-root.ll

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