If you're using a language with proper static typing and generics support (so C++, Rust, Swift, Go, etc), disabling the optimizer is typically a 10x hit. Most

If you're using a language with proper static typing and generics support (so C++, Rust, Swift, Go, etc), disabling the optimizer is typically a 10x hit. Most of what the optimizer does relies on statically analyzing call graphs, which it can't do if you're slinging function pointers around all over the place. Godbolt.org has a great example for Swift. Switch the editor to swift mode, load the "Sum over Array" example, and compile it with defaults. It produces reams and reams of assembly code. Now, pass -O in as a compiler flag to enable optimization, and it produces extremely tight code. (Swift 5.0 even noticed the two functions are semantically identical, and deduped them. 5.9 doesn't, but it also produces more compact code.) It's a similar story for rust, since the example is written in a functional style with an iterator. The C and C++ versions only have an imperative for loop variant, so the optimizer doesn't matter as much for them. (Though you could easily produce a C++ version of the code that takes a sum() function, and has similar bloat until optimization is enabled.)