It is very common to clutter libraries with `#[inline]` annotations on small/trivial functions to ensure that they optimize well. It shouldn't really be necessary to do this by hand so often. Instead, the compiler could use its inlining heuristic (which already exists for the MIR inliner) to decide when it is likely to be beneficial to make a function inlineable. This was previously attempted in https://github.com/rust-lang/rust/pull/70550