When it comes to procedural programming, functional decomposition is ideal for maintaining complicated code. However, functions are expensive- adding to the call stack, passing parameters, storing return addresses. all of this takes extra time! When speed is crucial, how can I get the best of both worlds? I want a highly decomposed program without any necessary overhead introduced by function calls. I'm familiar with the keyword: "inline" but that seems to be only be a suggestion to the compiler, and if used incorrectly by the programmer it will yield an even slower program. I'm using g++, so will the -03 flag optimize away my functions that call functions that call functions.. I just wanted to know, if my concerns are valid and if there are any methods to combat this issue.
First, as always when dealing with performance issues, you should try and measure what are your bottlenecks with a profiler. The first thing coming out is usually not function calls and by a large margin. If you did this, then please read on.
Then, you can anticipate a bit what functions you want inlined by using the inline keyword. The compiler is usually smart enough to know what to inline and what not to inline (it can inline functions you forgot and may not inline some you mentionned if he thinks it won't help).
If (really) you still want to improve performance on function calls and want to force inlining, some compilers allow you to do so (see this question). Please consider that massive inlining may actually decrease performance: your code will use a lot of memory and you may get more cache misses on the code than before (which is not good).