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From: Carlos O'Donell <carlos@baldric.uwo.ca> To: nobody@gcc.gnu.org Cc: gcc-prs@gcc.gnu.org, Subject: Re: optimization/7726: Fails to produce the correct implementation-dependant output for loop optimization under x86 -> optimizes away a loop that should complete Date: Fri, 06 Dec 2002 13:26:00 -0000 [thread overview] Message-ID: <20021206212602.7776.qmail@sources.redhat.com> (raw) The following reply was made to PR optimization/7726; it has been noted by GNATS. From: Carlos O'Donell <carlos@baldric.uwo.ca> To: bangerth@dealii.org, gcc-bugs@gcc.gnu.org, gcc-prs@gcc.gnu.org, nobody@gcc.gnu.org, gcc-gnats@gcc.gnu.org Cc: Subject: Re: optimization/7726: Fails to produce the correct implementation-dependant output for loop optimization under x86 -> optimizes away a loop that should complete Date: Fri, 6 Dec 2002 16:23:05 -0500 > State-Changed-From-To: open->feedback > State-Changed-By: bangerth > State-Changed-When: Fri Dec 6 13:01:29 2002 > State-Changed-Why: > Hm, the code goes into an endless loop on my system also > without optimization and with all the compilers I have > (i.e. gcc2.95, 3.0, 3.2, 3.2.2pre, 3.3pre, and icc7). > Are you sure that the overflow you are exploiting is > really defined in ISO C? Unsigned overflow is defined. It is GCC's inconsistent implementation-dependant conversion that is causing the problem. "The comparison is between to signed values that gcc must convert. This conversion is implementation-dependant. As such, the implementation-dependant behaviour cannot be optimized away and must remain consistent across optimization levels." - Carlos c.
next reply other threads:[~2002-12-06 21:26 UTC|newest] Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top 2002-12-06 13:26 Carlos O'Donell [this message] -- strict thread matches above, loose matches on Subject: below -- 2003-02-19 10:00 ebotcazou 2002-12-06 13:28 bangerth 2002-12-06 13:26 Falk Hueffner 2002-12-06 13:01 bangerth 2002-08-26 9:46 carlos
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