[PATCH] D123628: [InstCombine] Fold memrchr calls with an excessive size to null.

[Dávid Bolvanský via Phabricator via llvm-commits]

xbolva00 added inline comments.


================
Comment at: llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp:903
+      // Fold out-of-bounds accesses to null.
+      return Constant::getNullValue(CI->getType());
+  }
----------------
xbolva00 wrote:
> msebor wrote:
> > nikic wrote:
> > > While this is correct, I do wonder whether we should be going out of our way to fold this to null, rather than simply bailing out of the transform. In particular, I wonder whether this will end up suppressing an asan/msan warning. It's okay to do that, as these are "best effort", but it's probably better to avoid if it doesn't cost us any additional effort?
> > I don't yet know what the LLVM policy is for dealing with provably undefined code.  I chose this because it seems like the lesser of the two evils (e.g., when passing in a negative/very large size).  But I'm aware that some other handlers punt invalid calls to the library and I'm fine with that if it helps sanitizers detect the problem.
> Or insert UnreachableInst?
But generally not worth to catch all UBs and fold them, so I agree with @nikic


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  https://reviews.llvm.org/D123628/new/

https://reviews.llvm.org/D123628