A good optimizing compiler will transform tail-recursive functions to run as fast as imperative code. - SO

see also

• C++ Super Optimization: 1000X Faster - general overview of constexpr usage and optimisation
  • demo with recursive Fibonacci and prime number

#include <cstdint>

constexpr int64_t ipow(int64_t base, int exp, int64_t result = 1) {
  return exp < 1 ? result : ipow(base*base, exp/2, (exp % 2) ? result*base : result);
}