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From: "kreckel at ginac dot de" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/29186] optimzation breaks floating point exception flag reading
Date: Sat, 23 Sep 2006 22:58:00 -0000	[thread overview]
Message-ID: <20060923225827.32389.qmail@sourceware.org> (raw)
In-Reply-To: <bug-29186-1882@http.gcc.gnu.org/bugzilla/>



------- Comment #9 from kreckel at ginac dot de  2006-09-23 22:58 -------
(In reply to comment #8)
I am still not entirely sure whether we are really talking about the same
problem. The original problem was that the compiler optimized assuming that the
floating point division cannot have side effects, such that the offending
division happens after the call to fetestexcept(3):

#include <fenv.h>
#include <stdio.h>
int main()
{
   double x = (double)printf("") + 1.0; // one
   double y = (double)printf(""); // zero
   feclearexcept(FE_ALL_EXCEPT);
   double z = x / y;  // should set FE_DIVBYZERO
   if (fetestexcept(FE_ALL_EXCEPT)) {
       printf("flag set after call.\n");
   }
   printf("%f/%f==%f\n",x,y,z);
}

Neither -ftrapping-math, nor -frounding-math change anything, as long as -O1 is
turned on: The printf inside the if statement is *not* executed.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29186


  parent reply	other threads:[~2006-09-23 22:58 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2006-09-22 19:13 [Bug c/29186] New: " kreckel at ginac dot de
2006-09-22 19:24 ` [Bug c/29186] " pinskia at gcc dot gnu dot org
2006-09-22 19:25 ` pinskia at gcc dot gnu dot org
2006-09-22 19:28 ` pinskia at gcc dot gnu dot org
2006-09-22 22:34 ` kreckel at ginac dot de
2006-09-23 21:41 ` kreckel at ginac dot de
2006-09-23 21:52 ` joseph at codesourcery dot com
2006-09-23 22:11 ` kreckel at ginac dot de
2006-09-23 22:19 ` joseph at codesourcery dot com
2006-09-23 22:58 ` kreckel at ginac dot de [this message]
2006-09-23 23:02 ` joseph at codesourcery dot com
2006-09-24  0:35 ` pinskia at gmail dot com
2006-09-24 16:51 ` kreckel at ginac dot de
2006-09-25  7:40 ` kreckel at ginac dot de
2006-10-25  7:54 ` kreckel at ginac dot de
2006-10-25  7:57 ` pinskia at gcc dot gnu dot org
2006-10-25 13:22 ` kreckel at ginac dot de
2006-10-31 11:49 ` kreckel at ginac dot de
2006-11-06 22:23 ` kreckel at ginac dot de
2006-11-19 11:22 ` kreckel at ginac dot de
2006-11-19 12:14 ` rguenth at gcc dot gnu dot org
2009-05-04  6:47 ` kreckel at ginac dot de
2009-12-29 21:48 ` fxcoudert at gcc dot gnu dot org
     [not found] <bug-29186-4@http.gcc.gnu.org/bugzilla/>
2020-11-09 11:55 ` kreckel at ginac dot de
2020-11-09 12:41 ` rguenth at gcc dot gnu.org
2021-06-14 19:06 ` pinskia at gcc dot gnu.org

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