[libcxx-commits] [libcxx] [libcxx] Allow string to use SSO in constant evaluation. (PR #66576)

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cor3ntin wrote:

This looks like a good motivation for both [Exposing the diagnostic engine to C++](https://discourse.llvm.org/t/exposing-the-diagnostic-engine-to-c/73092) (LLVM) and [P2758 Emitting messages at compile time](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/p2758r0.html). 

And of course, folks are still working on allocation propagation which would make the need for a warning here moot.

I'm not sure how easy it would be for us to track the uses of basic strings in context that are potentially evaluated and not constant evaluated. For example what about constexpr functions that themselves are only used at compile time?

https://github.com/llvm/llvm-project/pull/66576