Comment by jonstewart

Probably? A complex function that’s not a good fit for inlining will probably access memory a few times and those accesses are likely to be the bottlenecks for the function. Passing on the stack squeezes that bottleneck tighter — more cache pressure, load/stores, etc. If Rust can pass arguments optimally in a decent ratio of function calls, not only is it avoiding the several clocks of L1 access, it’s hopefully letting the CPU get to those essential memory bottlenecks faster. There are probably several percentage points of win here…? But I am drinking wine and not doing the math, so…