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From: Marco Bernardo <bernardo@sti.uniurb.it> To: nobody@gcc.gnu.org Cc: gcc-prs@gcc.gnu.org, Subject: Re: c/8395: gcc 2.95.4 and 3.2 generate wrong code for double on intel Date: Mon, 04 Nov 2002 09:06:00 -0000 [thread overview] Message-ID: <20021104170607.23608.qmail@sources.redhat.com> (raw) The following reply was made to PR c/8395; it has been noted by GNATS. From: Marco Bernardo <bernardo@sti.uniurb.it> To: Bruce Allen <ballen@gravity.phys.uwm.edu> Cc: Bruce Allen <ballen@aei.mpg.de>, <gcc-gnats@gcc.gnu.org>, <gcc-prs@gcc.gnu.org>, <gcc-bugs@gcc.gnu.org>, <nobody@gcc.gnu.org> Subject: Re: c/8395: gcc 2.95.4 and 3.2 generate wrong code for double on intel Date: Mon, 4 Nov 2002 17:56:51 +0100 (CET) Dear Bruce, Tim and Toone, Thanks for your messages and for the useful information you provided me with. >> 2. I hope we all agree on the fact that the output produced by >> a (sequential) C program is the same for a given input, >> regardless of the compilation options that are used. > >Absolutely false! > >C does not specify the order in which mathematical expressions are >evaluated, unless the programmer makes these completely explicity. > >And indeed compiling with optimizations turned on can eliminate many >subexpressions, cause compile-time evaluatiosn, register sorage etc, which >can also change results. I understand that: - C does not specify the order in which mathematical expressions are evaluated (up to operators precedence and associativity, I guess) - this order is important at run time (as you pointed out to me) - the compiler can change the order in which mathematical expressions are evaluated, especially for optimization purposes However, for a person doing research on the formal semantics of programming languages, it is difficult to accept that two differently compiled versions of the same sequential program return two different values for the same input. The compiler should not be free to alter the semantics of a sequential program, i.e. the program output for a given input! Some consistency should be kept. Anyway, thanks again for your messages. Best regards, Marco @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ Prof. Marco Bernardo Universita` di Urbino Centro per l'Applicazione delle Scienze e Tecnologie dell'Informazione Piazza della Repubblica 13, 61029 Urbino, Italy Phone: +39-0722-4475 - E-mail: bernardo@sti.uniurb.it Fax: +39-0722-4475 - WWW: http://www.sti.uniurb.it/bernardo/ @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
next reply other threads:[~2002-11-04 17:06 UTC|newest] Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top 2002-11-04 9:06 Marco Bernardo [this message] -- strict thread matches above, loose matches on Subject: below -- 2002-11-04 9:06 Joseph S. Myers 2002-11-04 3:06 Bruce Allen 2002-11-02 22:26 Bruce Allen 2002-11-02 22:26 Bruce Allen 2002-11-02 8:26 Tim Prince 2002-11-02 7:56 Toon Moene 2002-11-02 7:46 Marco Bernardo 2002-10-31 0:56 Bruce Allen 2002-10-31 0:46 Marco Bernardo 2002-10-30 12:57 bangerth 2002-10-30 9:36 Bruce Allen 2002-10-30 0:26 bernardo
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