There are no true zero cost abstractions under all situations. In the general case they make things faster, but I've personally made C++ code faster by un temp

There are no true zero cost abstractions under all situations. In the general case they make things faster, but I've personally made C++ code faster by un templating code to relieve I$ pressure, and also allow the compiler to make smarter optimizations when it has less code to deal with. The optimizer passes practically have a finite window they can look at because of the complexity class of a lot of optimizer algorithms.