[PATCH] D112734: [SCEVExpander] Drop poison generating flags when reusing instructions

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev added inline comments.


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Comment at: llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp:1947
+          !programUndefinedIfPoison(I))
+        I->dropPoisonGeneratingFlags();
+
----------------
reames wrote:
> mkazantsev wrote:
> > Will we drop flags if both copies had them?
> What do you mean by "both copies"?
The comment before this code mentions that we are CSEing two copies of same instruction with potentially different flags, and drop them if we failed to prove legality. But what if both of these copies had the same flags, do we still need to try to prove something and drop the flags? Why?


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D112734/new/

https://reviews.llvm.org/D112734