The AI Engine
compiler supports the always_inline function attribute to eliminate
function call overhead. An inline function is a function that is
expanded in the line in which it is called. For larger functions, the overhead of the
function call is insignificant compared to the amount of time the function takes to run.
However, for smaller functions, the time needed to make the function call is greater
than the time needed to execute the function’s code. This overhead occurs for small
functions because the execution time of a small function is less than the switching
time.
One advantage of using inline functions is that there is no
function call overhead. Another potential advantage is that the compiler is able to
perform context-specific optimizations which are not possible when the function stands
in its own. The drawbacks are a larger register consumption, an increase of the size of
the program, and the function cannot be profiled as there are no clear start and stop
program counters to check.
The following keywords indicate the usage of the inlining functions to the compiler:
-
inline: This keyword is an indicator that the AI Engine compiler is free to use a inline substitution or function call for any function marked inline. -
inline __attribute__((always_inline))or__attribute__((always_inline)): This forces the compiler to inline the function. -
inline __attribute__((noinline))or__attribute__((noinline)): This forces the compiler to always generate a function call.