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From: Michael Ubell <ubell@mindspring.com> To: nobody@gcc.gnu.org Cc: gcc-prs@gcc.gnu.org, Subject: Re: c/10339: strncmp generates imPure code Date: Mon, 07 Apr 2003 20:56:00 -0000 [thread overview] Message-ID: <20030407205601.19789.qmail@sources.redhat.com> (raw) The following reply was made to PR optimization/10339; it has been noted by GNATS. From: Michael Ubell <ubell@mindspring.com> To: Andreas Schwab <schwab@suse.de> Cc: Falk Hueffner <falk.hueffner@student.uni-tuebingen.de>, Wolfgang Bangerth <bangerth@ices.utexas.edu>, gcc-bugs@gcc.gnu.org, gcc-gnats@gcc.gnu.org Subject: Re: c/10339: strncmp generates imPure code Date: Mon, 07 Apr 2003 13:53:09 -0700 I think I see what is happening. I guess computers are smarter ;-) Andreas Schwab wrote: > Michael Ubell <ubell@mindspring.com> writes: > > |> Do you mean you want me to set up a case where it runs off the > |> end of memory? > > Yes. Can't happen. > > |> I think it is sufficient that it is reading memory > |> that is not allocated, no? > > No, it is not. Well it would be but memcmp does not read the memory. > > It is. Memory returned by malloc is required to be correctly aligned for > any type. > I'm still not clear what alignment has to do with it. The optimization takes advantage of the fact that a properly formatted string which is shorter than the constant string cannot compare passed its end because there must be a null byte there. Purify must have a different model of what memcmp does. I'll send it to them. Thanks Mike
next reply other threads:[~2003-04-07 20:56 UTC|newest] Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top 2003-04-07 20:56 Michael Ubell [this message] -- strict thread matches above, loose matches on Subject: below -- 2003-04-08 1:56 Hans-Peter Nilsson 2003-04-07 21:46 Andreas Schwab 2003-04-07 21:46 Michael Ubell 2003-04-07 21:36 Michael Ubell 2003-04-07 21:26 Andreas Schwab 2003-04-07 20:06 Michael Ubell 2003-04-07 20:06 Andreas Schwab 2003-04-07 19:56 Michael Ubell 2003-04-07 19:36 Andreas Schwab 2003-04-07 19:36 Falk Hueffner 2003-04-07 19:06 Falk Hueffner 2003-04-07 19:06 Michael Ubell 2003-04-07 18:16 Wolfgang Bangerth 2003-04-07 17:06 Michael Ubell 2003-04-07 16:48 bangerth 2003-04-07 16:16 ubell
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