I've been looking at trying to optimize the performance of code for programs that use functions like qsort where a function is passed the name of a function and some constant parameter(s).
The function qsort itself is an excellent example of what I'm trying to show what I want to do, except for being in a library, so please ignore that while I proceed assuming that that qsort is not in a library. In qsort the user passes in a size of the array elements and comparison function name in addition to the location of the array to be sorted. I noticed that for a given call site that the first two are always the same so why not create a specialized version of qsort that eliminates them and internally uses a constant value for the size parameter and does a direct call instead of an indirect call. The later lets the comparison function code be inlined. This seems to me to be a very useful optimization where heavy use is made of this programming idiom. I saw a 30%+ overall improvement when I specialized a function like this by hand in an application. My question is does anything inside gcc do something similar? I don't want to reinvent the wheel and I want to do something that plays nicely with the rest of gcc so it makes it into real world. Note, I should mention that I'm an experienced compiler developed and I'm planning on adding this optimization unless it's obvious from the ensuing discussion that either it's a bad idea or that it's a matter of simply tweaking gcc a bit to get this optimization to occur. Thanks, Gary Oblock
