static inline int my_function() __attribute__((always_inline));
static inline int my_function()
{
//...
}
So I have declared my function as above although in the binary the function is branched to and not inlined, therefore a simple NOP could render the whole function useless.

How can I force Xcode 4.6 to inline the function?
Your function as you give it here has no prototype: you don’t provide the type of the arguments. In C just having
()in the declaration means that the function receives an unknown number of arguments. Probably the compiler then supposes not to know enough about the function to inline it. Use(void)to declare a function without arguments.