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Is there some way to write unit tests for cases where you know vectorisation should have been applied? I guess micro benchmarks should cover the performance part. We have ArchUnit to cover code structures, it would be nice if something similar exists for generated assembly.

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I've been begging for years for a a [[must_vectorize]] annotation that I can place before a loop I care about, and turn it into a compile error if the compiler can't figure it out.

this would be amazing

Just don't do it like Rust inlining annotations:

<No annotation> – Gently suggests inlining

#[inline] - Really suggests inlining

#[inline(always)] – Really Really suggests inlining (still not guaranteed!)

https://nnethercote.github.io/perf-book/inlining.html

The gcc torture test suite has for most vect/ tests ast checks to see such regressions. LLVM missed it.

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