> A block of memory cannot be read as an array of simd types sometimes and scalar types otherwise.

As far as I can tell, it is currently the case that, using raw pointers, this is not actually undefined behavior (but I never entirely trust my conclusions on these matters).

"&mut T and &T follow LLVM’s scoped noalias model" [1][referring to 2 and 3] but I am fairly sure this does not currently apply to raw pointers, and "provenance is implicitly shared with all pointers transitively derived from the original pointer through operations like offset, borrowing, and pointer casts." [4]

[1] https://doc.rust-lang.org/reference/behavior-considered-unde...

[2] https://llvm.org/docs/LangRef.html#pointeraliasing

[3] "noalias" under https://llvm.org/docs/LangRef.html#parameter-attributes

[4] https://doc.rust-lang.org/core/ptr/index.html

Also excellent are

https://faultlore.com/blah/fix-rust-pointers

https://www.ralfj.de/blog/2018/07/24/pointers-and-bytes.html

https://www.ralfj.de/blog/2020/12/14/provenance.html

https://www.ralfj.de/blog/2022/04/11/provenance-exposed.html

It seems likely you'd already be familiar with these; I'm just putting them out there for anyone interested.