Afaik loop {} has never been UB, however because llvm started as a c++ compiled where it is, this has been causing miscompilations in rust and C for… nearly two decades (llvm issue 965).
replySure, I think it was still under the same unsound tag regardless.
replyUnsoundness and UB are very different things, UB tells users of the language "don't do that it's wrong", unsoundness tells users of the language "be careful we need to fix that", it's a bug.
replySince the Rust language is defined by the Rust compiler and has no other specification, if it's UB in the compiler then it's UB in the language.
replyAnd this, kids, is how you get called Billy Madison.
replyMay god have mercy on your soul, cowlevel1.
Rust has no formal spec? Really?
replyIt's a work in progress. The Reference (https://doc.rust-lang.org/reference) is slowly getting more complete over time. Other ongoing efforts include a-mir-formality (https://github.com/rust-lang/a-mir-formality), minirust (https://github.com/minirust/minirust), the FLS (https://github.com/rust-lang/fls), and Rust via Desugarings (https://nadrieril.github.io/rust-via-desugarings/). But writing a 100% complete and correct formal spec is hard! Not even C gets this right, the C standard has holes which lead to miscompilations and UB in practice: https://www.ralfj.de/blog/2020/12/14/provenance.html
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