I've had a smaller but similar dive recently while working on embedded machine (32 bit) with Rust. Clippy was pushing me to use move/copy instead of reference for passing a [u8; 8].

I thought this strange on a 32bit machine so I dived in and it turned out the "rule" is supposed to be "up to 2 register sized" variables are supposed to be copied, anything bigger is supposed to be referenced.

The trick here is that due to compatibility and no knowlege of target platform and setup clippy assumes 32bit register size. So on 64 bit platforms you'll only get this warning up to 8 bytes as well for example.

I never went in to actually see if it makes any sense on that particular 32bit platform, so good to see someone taking a dive on the actual compiled code side.