That is just dumb and overly reductive. There is just lot of properties about programs that can not be expressed to compiler with portable ISO C but could be ex

That is just dumb and overly reductive. There is just lot of properties about programs that can not be expressed to compiler with portable ISO C but could be exploited for optimization. Of course reducing portability progressively improves situation, like using GCC extensions or machine-specific intrinsics. But even then its ridiculous to claim that C compilers could in general case generate true optimal code.