[PATCH] D151796: [SCEV] Skip min/max expressions when normalizing/denormalizing SCEV expressions

[Nikita Popov via Phabricator via llvm-commits]

nikic added a comment.

First time I hear about SCEV normalization/denormalization. The entire approach looks highly dubious.

I'm concerned that this is not a complete fix and there are other cases where normalization/denormalization do not round-trip. What is the criterion that distinguishes min/max from other SCEV expressions? Could something similar affect udiv expressions for example?

I also noticed that there is a check in IVUsers for normalization/denormalization roundtrip at https://github.com/llvm/llvm-project/blob/0a3dc73e700b4a37bc435bf7c02213161b27f54a/llvm/lib/Analysis/IVUsers.cpp#L221-L231.



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Comment at: llvm/lib/Analysis/ScalarEvolutionNormalization.cpp:91
+  return Expr;
+}
+
----------------
Presumably umin_seq also needs to be handled.


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Comment at: llvm/test/Transforms/LoopStrengthReduce/pr62563.ll:6
 
-; XFAIL: *
-
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Please precommit this change. This test should be showing a difference in generated IR.


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  https://reviews.llvm.org/D151796/new/

https://reviews.llvm.org/D151796