[PATCH] D72958: [InstSimplify] fold select of vector constants that include undef elements

[Nikita Popov via Phabricator via llvm-commits]

nikic added inline comments.


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Comment at: llvm/lib/Analysis/InstructionSimplify.cpp:4044
+        NewC.push_back(TEltC);
+      }
+    }
----------------
I'm having a bit of a hard time convincing myself that this is always correct. In particular, the relationship between isElementWiseEqual(), which is based on `ConstantExpr::getICmp()` and this code, which is based on simple identity comparison, is not entirely clear. If the vector includes complex constant expressions, and `ConstantExpr::getICmp()` manages to fold that code while the identity comparison fails, this would trigger an assertion failure here. Or is there an invariant that this cannot happen?


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D72958/new/

https://reviews.llvm.org/D72958