[PATCH] D69563: [LV] Strip wrap flags from vectorized reductions

[Denis Antrushin via Phabricator via llvm-commits]

dantrushin created this revision.
dantrushin added reviewers: fhahn, hsaito, hfinkel.
Herald added subscribers: jfb, rkruppe, hiraditya.
Herald added a project: LLVM.

Wrap flags set on scalar reductions may become invalid after vectorization
After vectorization with interleaving, vectorized reduction might look
like this:

  %vec.phi  = phi <4 x i32> [ <i32 -104, i32 0, i32 0, i32 0>, %vector.ph ], [ %2, %vector.body ]
  %vec.phi2 = phi <4 x i32> [ zeroinitializer, %vector.ph ], [ %3, %vector.body ]
  %2 = sub nuw nsw <4 x i32> %vec.phi, %broadcast.splat
  %3 = sub nuw nsw <4 x i32> %vec.phi2, %broadcast.splat

Note that nowrap flags are invalid (0 - x wraps) and must be reset even
though they were correct in scalar case. Otherwise, InstSimplify will
throw (0-X)<nsw> out as a no-op

Fixes PR43828


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D69563

Files:
  llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
  llvm/test/Transforms/LoopVectorize/X86/tail_loop_folding.ll
  llvm/test/Transforms/LoopVectorize/interleaved-accesses.ll
  llvm/test/Transforms/LoopVectorize/no_int_induction.ll
  llvm/test/Transforms/LoopVectorize/nuw.ll
  llvm/test/Transforms/LoopVectorize/reduction-small-size.ll
  llvm/test/Transforms/LoopVectorize/reduction.ll

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