Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cwjcc!tut.cis.ohio-state.edu!bloom-beacon!mcgill-vision!mouse
From: mouse@mcgill-vision.UUCP (der Mouse)
Newsgroups: comp.lang.c
Subject: Re: C optimizer
Message-ID: <1470@mcgill-vision.UUCP>
Date: 15 Mar 89 10:16:51 GMT
References: <36662@think.UUCP> <453@lakart.UUCP>
Organization: McGill University, Montreal
Lines: 21

In article <453@lakart.UUCP>, dg@lakart.UUCP (David Goodenough) writes:
> From article <36662@think.UUCP>, by barmar@think.COM (Barry Margolin):
>> In article <1028@frog.UUCP> john@frog.UUCP (John Woods) writes:
>>> (getpid() != getpid())  [should always be 1]
>> Well, how about
>> (pid = getpid(), (void) fork(), pid != getpid())
> True - but I don't see any references to fork() in Mr.Woods' posting.
> What he is stating is that _IN THE ABSENCE_ of fork() calls, getpid()
> had better return an unchanging value.

Sure - and in the absence of assignments, variables are constant and
can be optimized away.  The whole point of this was to find a pure
syscall, and a routine isn't pure if calling another routine can cause
it to change its return value for a given set of argument values.
Thus, fork()'s changing the return value of getpid() means that
getpid() can't be considered pure.

					der Mouse

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