When looking at the rv32imc emitted by the Rust compiler, it's clear that there would be a lot less code if the compiler could choose different registers than those defined in the ABI for the arguments of leaf functions.
Not to mention issues like the op mentions making it impossible to properly take advantage of RVO with stuff like Result<T> and the default ABI.
I would argue that is largely true because we got the ABIs and the hardware to support them to be highly optimized. Thing slow down very quickly if one gets off that hard-won autobahn of ABI efficiency.
When looking at the rv32imc emitted by the Rust compiler, it's clear that there would be a lot less code if the compiler could choose different registers than those defined in the ABI for the arguments of leaf functions.
Not to mention issues like the op mentions making it impossible to properly take advantage of RVO with stuff like Result<T> and the default ABI.
I would argue that is largely true because we got the ABIs and the hardware to support them to be highly optimized. Thing slow down very quickly if one gets off that hard-won autobahn of ABI efficiency.