mouse@mcgill-vision.UUCP (der Mouse) (03/07/89)
In article <1028@frog.UUCP>, john@frog.UUCP (John Woods) writes: > In article <3121@ficc.uu.net>, peter@ficc.uu.net (Peter da Silva) writes: >> Can anyone think of any pure system calls? ioctl(fd, TCGETA, tbuf)? This really belongs in an OS-specific group. Let's see....I just ran through the table of syscalls on this system and getpagesize() and getdtablesize() are the only really pure syscalls I see there. > I think that if > (getpid() != getpid()) > ever evaluated to 1, I would be severely astonished. Signal handlers aside, that's not the point. If I write int pid1; int pid2; pid1 = getpid(); runinchild(); pid2 = getpid(); then I don't want the compiler to decide that it can rewrite the second one to "pid2 = pid1;" because getpid() is pure - presumably runinchild() will fork. Here's a quick test: a function is pure if it can be replaced with a memo-function wrapper without changing the semantics. This is not true of getpid() or sync(), to pick two examples that are tempting. der Mouse old: mcgill-vision!mouse new: mouse@larry.mcrcim.mcgill.edu
davidsen@steinmetz.ge.com (William E. Davidsen Jr) (03/09/89)
Our old Heneywell system had a FORTRAN optimizer which would pass over
the source code and emit restructured source code with global
optimizations performed. The main thing it did was pull things out of
loops, I believe, but I haven't used it in ten years or so.
Question: has anyone done a similar thing for C? It seems like a
reasonable thing to do, given all of the non-optimizing and peephole
optimizing compilers in the world.
Yes, I know you can do a better job with a builtin optimizer in the
compiler, that's NOT the question.
--
bill davidsen (wedu@ge-crd.arpa)
{uunet | philabs}!steinmetz!crdos1!davidsen
"Stupidity, like virtue, is its own reward" -me