[PATCH] D124158: [Clang][Attr] Skip adding noundef attribute to arguments when function has convergent attribute

[Eli Friedman via Phabricator via llvm-commits]

efriedma added a comment.

The issue you're describing sounds like it's specific to @__shfl_sync.  In general, in C++, you aren't allowed to read from an uninitialized variable; see [basic.indet] in the standard.  But if your testcase doesn't have undefined behavior, CUDA language rules must somehow allow this particular builtin function to take undef variables as input.  (Is this documented somewhere?)

That isn't related to the "convergent" attribute; the transform you're describing doesn't break convergence rules.


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  https://reviews.llvm.org/D124158/new/

https://reviews.llvm.org/D124158