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From: "matz at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/96373] SVE miscompilation on vectorized division loop, leading to FP exception
Date: Wed, 05 Aug 2020 12:24:03 +0000	[thread overview]
Message-ID: <bug-96373-4-FyaPXTfqRP@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-96373-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96373

--- Comment #10 from Michael Matz <matz at gcc dot gnu.org> ---
(In reply to Andreas Schwab from comment #5)
> > Just note that _all_ floating point operations, not just divisions, can trap
> > (without fast-math).  You never know if the user enabled stops for any of
> > the FP exceptions (overflow, underflow, inexact, invalid op, div-by-zero). 
> 
> You need #pragma STDC FENV_ACCESS ON for that, otherwise it's undefined
> behaviour.

Sure, that's for operations that occur due to normal abstract machine
evaluations.  The point here is that we introduce operations that aren't in the
original
program (for the testcase on "array elements" after [10]), and if we do so
those
must be unobservable.  These pragmas don't give license to introduce additional
faults that can't possibly have happened in the abstract machine.  (To see
this, replace all arrays elements by 1.0, then the FP operations are all exact,
we still get SIGFPE).

  parent reply	other threads:[~2020-08-05 12:24 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-29 15:27 [Bug target/96373] New: " matz at gcc dot gnu.org
2020-08-04 13:41 ` [Bug target/96373] " rsandifo at gcc dot gnu.org
2020-08-04 13:49 ` rguenth at gcc dot gnu.org
2020-08-04 14:38 ` matz at gcc dot gnu.org
2020-08-04 14:59 ` rsandifo at gcc dot gnu.org
2020-08-04 15:46 ` schwab@linux-m68k.org
2020-08-05 10:08 ` rsandifo at gcc dot gnu.org
2020-08-05 10:15 ` rguenther at suse dot de
2020-08-05 10:28 ` rsandifo at gcc dot gnu.org
2020-08-05 11:09 ` rguenther at suse dot de
2020-08-05 12:24 ` matz at gcc dot gnu.org [this message]
2020-08-05 13:02 ` matz at gcc dot gnu.org
2023-01-11 23:50 ` pinskia at gcc dot gnu.org
2023-01-11 23:54 ` pinskia at gcc dot gnu.org
2023-01-27 17:04 ` cvs-commit at gcc dot gnu.org
2023-02-14  2:05 ` cvs-commit at gcc dot gnu.org
2023-02-14  9:18 ` cvs-commit at gcc dot gnu.org
2023-02-27  2:50 ` cvs-commit at gcc dot gnu.org
2023-02-27  2:57 ` cvs-commit at gcc dot gnu.org
2023-04-03  8:58 ` cvs-commit at gcc dot gnu.org
2023-04-14  8:19 ` [Bug target/96373] [10/11 Regression] " rguenth at gcc dot gnu.org
2023-05-29 10:03 ` jakub at gcc dot gnu.org
2024-02-29  5:33 ` [Bug target/96373] [11 " pinskia at gcc dot gnu.org

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