[PATCH] D65884: [ARM] MVE Tail Predication

[Sam Parker via Phabricator via llvm-commits]

samparker marked an inline comment as done.
samparker added inline comments.


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Comment at: lib/Target/ARM/MVETailPredication.cpp:364
+  // Search for Elems in the following SCEV:
+  // (1 + ((-VF + (VF * (((VF - 1) + %Elems) /u VF))<nuw>) /u VF))<nuw><nsw>
+  const SCEV *Elems = nullptr;
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SjoerdMeijer wrote:
> What we are doing here, is looking at generated code to get `%Elems`. But the vectorizer has generated this code, so somewhere this knowledge is present. The only question is, I guess, how easily accessible. Can we query SCEV or something else to avoid this pattern matching?
I've had a play with some other parts of SCEV, the helpers for delinearization, to see if it could answer the size of the array accessed by the loop. I can't seem to get this to work with the GEPs in the tests as they're not be represented by clean AddRecExprs. I presume it's not unreasonable for SCEV to not be that useful //after// vectorization..? It does looks like it could be used though, but I don't think I have the knowledge to do it safely! I'll add a TODO / FIXME.


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