Funny thing is that one of the bigger problems with optimizing compilers is register allocation. Not only is it difficult to write a good algorithm for it, but

Funny thing is that one of the bigger problems with optimizing compilers is register allocation. Not only is it difficult to write a good algorithm for it, but compilers don't always know what variable is most important to keep in a register. Gcc even implemented a weaker allocator [0] as the older one was too complex to decipher problems with it. Instruction scheduling is not a problem on modern cpu's. Not that it's hard either way, just reorder things around memory access and heavy instructions like division. Agner Fog made a nice table of instruction latencies and throughputs [1]. Instruction encoding length... do you use 16bit integers or do you just int everything ? The compiler has to do what you tell it to do. Sure there are plenty of tricks around that but those are not the ones that give the compiler a remarkable advantage over humans. Tricks like using bitwise operations instead of multiplication and such and shortening equations is the advantage that the compiler has. But even that is not that big of a deal. (again, do you use the restrict keyword ? or static/define for constants ? do you know that C treats every "compile unit"(.c file) as a separate program ?) [0] https://gcc.gnu.org/wiki/cauldron2012?action=AttachFile&do=get&target=Local_Register_Allocator_Project_Detail.pdf https://gcc.gnu.org/wiki/cauldron2012?action=AttachFile&do=g... [1] http://www.agner.org/optimize/ http://www.agner.org/optimize/