I've had to spend 21 hours compiling something (a compiler) before. However, it's a one time thing, and once compiled, all my compilation times would decrease d

I've had to spend 21 hours compiling something (a compiler) before. However, it's a one time thing, and once compiled, all my compilation times would decrease dramatically. Why is it unreasonable that for this one time thing, the OS gets out of the way, and allows me to make a single exception?