[PATCH] D102367: [Intrinsics] is_constant intrinsic on undef evaluates to false

[Joerg Sonnenberger via Phabricator via llvm-commits]

joerg added a comment.

One of the mots important use cases of __builtin_constant_p is ensuring that inline assembler variants that require immediate arguments are DCE'ed. There are some other use cases where it is used for compile-time assertions of invariants, so we do want to be as correct as possible. All that said, I fully agree that `is.constant(undef)` should fold to false as it is consistent with the `immarg` parameter attribute and other places. Even stronger, I would argue that it applies even to `is.constant(freeze undef)`.


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https://reviews.llvm.org/D102367