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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: Mon, 06 Nov 2006 22:23:00 -0000 [thread overview]
Message-ID: <20061106222308.11604.qmail@sourceware.org> (raw)
In-Reply-To: <bug-29186-1882@http.gcc.gnu.org/bugzilla/>
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------- Comment #17 from kreckel at ginac dot de 2006-11-06 22:23 -------
(In reply to comment #15)
> Maybe scheduling would have the same issue. The fact that the result of the
> division is not used is a red herring, though. Of course, the assumption is
> that it's actually used.
For the record: Andrew was right and above statement is wrong. The standard
explicitly mandates that unused code must not be removed unless the compiler
can determine that it cannot raise an exception flag [F.8.1]:
: Concern about side effects may inhibit code motion and removal of seemingly
: useless code. For example, in
: #include <fenv.h>
: #pragma STDC FENV_ACCESS ON
: void f(double x)
: {
: /* ... */
: for (i = 0; i < n; i++) x + 1;
: /* ... */
: }
: x + 1 might raise floating-point exceptions, so cannot be removed. And since
: the loop body might not execute (maybe 0 ³ n), x + 1 cannot be moved out of
: the loop. (Of course these optimizations are valid if the implementation can
: rule out the nettlesome cases.)
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29186
next prev parent reply other threads:[~2006-11-06 22:23 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
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 [this message]
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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