[PATCH] D151988: LoopVectorize: extend SelectCmp pattern for non-invariants

[Shiva Chen via Phabricator via llvm-commits]

shiva0217 added inline comments.


================
Comment at: llvm/lib/Analysis/IVDescriptors.cpp:678
+  // If the loop is not invariant, we need to know the direction of the loop.
+  auto Bounds = SE ? Loop->getBounds(*SE) : std::nullopt;
+  if (!Loop->isLoopInvariant(NonPhi) &&
----------------
For the following case, the final value might not be able to pick by the min/max reduction.

   int test(int a[32000]) {
      int k = -1;
      for (int i = 0; i < 32000; i++)
        if (a[i] < 0)
           k = a[i];
    
        return k;
    }

Extra checking of NonPhi might be needed. So the reduction can generate min/max.

  auto *AR = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(NonPhi));
  if (AR) {
    const SCEV *Step = AR->getStepRecurrence(*SE);
    const SCEVConstant *ConstStep = dyn_cast<SCEVConstant>(Step);
    if (!ConstStep && !SE->isLoopInvariant(Step, Loop))
      return InstDesc(false, I);
  } else
    return InstDesc(false, I);

Would it need to check AR->hasNoUnsignedWrap?


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D151988/new/

https://reviews.llvm.org/D151988