[PATCH] D101294: [LoopVectorize] Fix scalarisation crash in widenPHIInstruction for scalable vectors

[David Sherwood via Phabricator via llvm-commits]

david-arm marked 2 inline comments as done.
david-arm added inline comments.


================
Comment at: llvm/lib/Transforms/Vectorize/LoopVectorize.cpp:4783
+      Value *UnitStepVec = nullptr, *PtrIndSplat = nullptr;
+      if (!IsUniform && VF.isScalable()) {
+        Type *VecIVTy = VectorType::get(PtrInd->getType(), VF);
----------------
sdesmalen wrote:
> Can we unify this approach for both scalable and fixed-width vectors? Or phrased differently, is there still value in the per-lane calculation for fixed-width vectors? I would expect InstCombine to simplify any extract-elements from the splat + stepvector, if those are needed individually.
Hi @sdesmalen, so I looked into this and there is a problem for fixed-width vectors because the vector GEP could be created in a different block to the actual extractelement operation. I have added an appropriate fold in instcombine anyway - see D101900 - as you're right that this is useful. However, for non-uniform scalarisation with scalable vectors I have changed the code below to avoid caching the per-lane values with the `continue;` line.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D101294/new/

https://reviews.llvm.org/D101294