[PATCH] D136805: [NFC] Make format() more amenable to format attributes

[Eli Friedman via Phabricator via llvm-commits]

efriedma added a comment.

In D136805#3897947 <https://reviews.llvm.org/D136805#3897947>, @fcloutier wrote:

> In D136805#3887165 <https://reviews.llvm.org/D136805#3887165>, @efriedma wrote:
>
>>> since the undefined behavior was evaluated at build time, UBSan wouldn't catch it.
>>
>> Can you file a bug for this?  Opportunistic constant evaluation like that shouldn't bypass ubsan.
>
> I'm not able to reproduce the problem and my setup was janky, so I must have jumped to conclusions too fast after a tangential Godbolt test <https://godbolt.org/z/Y97b61nbx> shows that Clang will evaluate some UB at compile-time (with sanitizers disabled) where GCC won't. This example is probably happening in the back-end instead of the front-end. Sorry for the bad signal.

I managed to come up with a case similar to what you described: https://github.com/llvm/llvm-project/issues/58735 .  I think whether the issue triggers depends on how the result of the call is used.


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