[PATCH] D98495: [CodeGen] Fix issues with scalable-vector INSERT/EXTRACT_SUBVECTORs

[Fraser Cormack via Phabricator via llvm-commits]

frasercrmck marked 2 inline comments as done.
frasercrmck added inline comments.


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Comment at: llvm/lib/CodeGen/SelectionDAG/LegalizeVectorTypes.cpp:1292
+  // of a scalable vector.
+  if (VecVT.isScalableVector() == SubVecVT.isScalableVector() &&
+      IdxVal >= LoElems && IdxVal + SubElems <= VecElems) {
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david-arm wrote:
> Hi @frasercrmck, I'm not sure if this even works for scalable vectors? The LoVT is scalable and you need to know the full number of elements in LoVT rather than the minimum number here. Suppose vscale = 2 and LoElems = 8, then what happens when IdxVal = 9? I think it's still accessing the Lo half in this case since the number of elements in Lo is actually 16.
> 
> I suspect you may need to restrict this further to:
> 
>   if (VecVT.isFixedLengthVector() && SubVecVT.isFixedLengthVector() && ...
Hi. For insert_/extract_subvector, when the subvector is a scalable type, then the index is implicitly multiplied by vscale. So it should be correct to use the minimum number in this case: IdxVal in your example is actually 18.


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