I'm sure I'm not alone here, but I get frustrated sometimes that the debug compiler is so slow when compiling the standard library during a debug build. I looked into this a bit and found that the debug build of the swift compiler can easily be at least 20% faster with some judicious use of the always inline attribute. This isn't really surprising. So-called "zero-cost" abstractions are really expensive when optimizations are disabled. In any case, I filed a bug against clang to allow developers to run the normal inliner at -O0 to get this kind of performance improvement without massively annotating functions as being "always inline". There isn't really any downside to forcing inlining at -O0 unless you think having multiple breakpoint locations per breakpoint is bad.
If people wants to CC themselves, here is the bug: