[PATCH] D31979: [LV] Fix the vector code generation for first order recurrence

[Anna Thomas via Phabricator via llvm-commits]

anna created this revision.
Herald added a subscriber: mzolotukhin.

In first order recurrences where phi's are used outside the loop,
we should generate an additional vector.extract of the second last element from
the vectorized phi update.
This is because we require the phi itself (which is the value at the second last
iteration of the vector loop) and not the phi's update within the loop.

Fixes PR32396.


https://reviews.llvm.org/D31979

Files:
  lib/Transforms/Utils/LoopUtils.cpp
  lib/Transforms/Vectorize/LoopVectorize.cpp
  test/Transforms/LoopVectorize/AArch64/loop-vectorization-factors.ll
  test/Transforms/LoopVectorize/first-order-recurrence.ll

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