[cremno]

But GCC likely isn't able to do that for libc functions like qsort(). Maybe if LTO is enabled and libc is linked statically, it might.

[bluecalm]

I have no idea when it can and when it can't do that to be honest. I tested qsort vs std::sort on my machine on my data and performance was the same (Windows, MinGW, GCC 4.8, -flto enabled) but other people reported different results.