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> As an aside, the clang bug would also affect Rust if they used that type of optimization (assuming strict aliasing rules). No, this bug cannot affect rust, b
by ordu 6y ago
> As an aside, the clang bug would also affect Rust if they used that type of optimization (assuming strict aliasing rules).
No, this bug cannot affect rust, because rust wouldn't allow to pass into a function three mutable references pointing to the same object. It wouldn't even allow two, nor one mutable and one immutable. Either it pass one mutable reference, or any number of immutable.
- steveklabnik 6y agoThis one (probably) wouldn’t, but there have been codegen bugs in Rust, some that have blocked people from upgrading before they can be fixed. It doesn’t happen often, but it does happen.
- tsimionescu 6y agoNot sure if that bug explicitly, but the fact that clang in noalias mode assumes that two pointers to different variants of the same union are not aliased (if it can't see from the immediate context that they are pointers to the same union variable) can very much affect Rust - if you call one function with a &mut to one field, than another function with a &mut to another field, and the optimizer inlines both functions in a broader context and loses the union information, you may well see reordering issues even in pure safe Rust. Anyway, Rust has found plenty of noalias bugs in clang, which is why it still doesn't compile with noalias optimizations turned on.