For inlining in general, I think the wikipedia article is good https://en.wikipedia.org/wiki/Inline_expansion https://en.wikipedia.org/wiki/Inline_expansion. T

For inlining in general, I think the wikipedia article is good https://en.wikipedia.org/wiki/Inline_expansion https://en.wikipedia.org/wiki/Inline_expansion. The reason it's so important is that inlining synergises with other optimizations, its often run before or after other passes like constant propagation. Consider something like: fn add(x : usize, y : usize) -> usize { x + y } fn main() { add(5, 1) } Without inlining we can't easily optimize the code of `main`. However, if we inline `add` into main, constant propagation will then directly see `5 + 1` and optimize that into `6`.