[Asooka]

I do believe the C standards committee got it completely backwards with regards to undefined behaviour optimisations. By default the language should act in a way that a human can reason about, in particular it should not be more complicated than assembly. Then, they can add some mechanism for decorating select hot program blocks as amenable to certain optimisations[1]. In the majority of the program the optimisation of not writing a single machine word to memory before calling memcmp is not measurable. The saddest part is that other languages like Rust and Zig have picked all this up like cargo cult language design. Writing code is already complicated enough without having to watch out for pitfalls added so the compiler can achieve one nanosecond faster time on SPECint.

[1] As an aside, the last time I tried to talk to a committee representative about undefined behaviour optimisation pitfalls, I was told that the standard does not prescribe optimisations. Which was quite puzzling, because it obviously prescribes compiler behaviour with the express goal of allowing certain optimisations. If I took that statement at face value, it would follow that undefined behaviour is not there for optimisation's sake, but rather as a fun feature to make programming more interesting...

[steveklabnik]

Rust has no UB in safe Rust, so it’s closer to your ideal than not.

It also doesn’t have UB for cargo cult reasons.