I'm guessing that f32::clone showing up in the profile isn't actually a call to f32::clone, because you have optimizations on (if it actually is a call to a "movd xmm0,dword ptr [rdi]; ret" instruction pair, that's a bug in the compiler). Rather it's the result of the compiler choosing to attribute seemingly-random lines to f32::clone, because when lines from multiple functions are fused into one instruction the compiler will just pick one, and it happened to pick f32::clone to write into the debug info. You really want to look at instruction-level profiling when you're profiling at that level instead of the individual functions, since debug info is going to be very unreliable.