pow() is an overloaded function that already has a pow(double,int) variant, so there is no need to roll your own. If the integer exponent is very small, for example 2 or 3, I would recommend explicit multiplication for best performance. For very large integer exponents the accuracy of the pow(double,int) variant will tend to be lower than the accuracy of the pow(double,double) variant.
The high cost of the pow(double,double) variant in terms of register usage and execution time is a consequence of the excellent accuracy guaranteed across the entire input domain in addition to the handling of numerous special cases according to C99 specifications.
The use of specialized exponentiation functions such as exp(), exp2(), exp10(), sqrt(), rsqrt(), cbrt(), and rcbrt() instead of pow() is advised [where applicable] for performance reasons; in some cases this may also result in slightly better accuracy.
A quick look at the implementation of pow(double,int) shows that it includes a reciprocal computation which is called when the exponent is negative. This would increase the overall register usage for the general case. However, when pow(double,int) is called with a positive integer exponent that is a compile-time constant, the call to the reciprocal routine should be optimized out, and the resulting code should require fewer than 24 registers. I will take a look at the generated code when I get a chance.