[PATCH] D84792: [InstSimplify/NewGVN] Add option to control the use of undef.

Wed Aug 5 12:31:16 PDT 2020

nikic accepted this revision.
nikic added a comment.
This revision is now accepted and ready to land.

In D84792#2197183 <https://reviews.llvm.org/D84792#2197183>, @fhahn wrote:

> Ping. Should we go with this approach to start with, to unblock some patches and iterate on the details as follow-ups? It's not ideal for CanUseUndef to not cover all cases initially, but I am not sure what the alternative would be.

Yes, that SGTM.

================
Comment at: llvm/include/llvm/Analysis/InstructionSimplify.h:103
+  /// simplifications based on the fact that a value is undef are allowed.
+  bool CanUseUndef;
+
----------------
Possibly be a bit more specific here and say that simplifications that constrain the range of possible values for an undef are not allowed.

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