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* [Bug middle-end/98420] New: Invalid simplification of x - x with -frounding-math
@ 2020-12-22 14:56 ubizjak at gmail dot com
2021-01-05 9:39 ` [Bug middle-end/98420] " rguenth at gcc dot gnu.org
` (4 more replies)
0 siblings, 5 replies; 6+ messages in thread
From: ubizjak at gmail dot com @ 2020-12-22 14:56 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98420
Bug ID: 98420
Summary: Invalid simplification of x - x with -frounding-math
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: ubizjak at gmail dot com
Target Milestone: ---
Split out from PR96793, where Marc says in c13:
-q-
x-x does depend on the rounding mode (the transformation in match.pd gets it
wrong, by the way).
-/q-
The testcase:
--cut here--
#include <fenv.h>
double
__attribute__((noinline))
foo (double a)
{
return a - a;
}
int
main ()
{
double res;
fesetround (FE_DOWNWARD);
res = foo (1.11);
if (__builtin_signbit (res) == 0)
__builtin_abort ();
return 0;
}
--cut here--
aborts with -O2 -ffinite-math-only -frounding-math
Please note that x - x with FE_DOWNWARD should result in -0.0.
The problem is in match.pd, where:
(simplify
(minus @0 @0)
(if (!FLOAT_TYPE_P (type) || !HONOR_NANS (type))
{ build_zero_cst (type); }))
should involve flag_rounding_math in some way.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug middle-end/98420] Invalid simplification of x - x with -frounding-math
2020-12-22 14:56 [Bug middle-end/98420] New: Invalid simplification of x - x with -frounding-math ubizjak at gmail dot com
@ 2021-01-05 9:39 ` rguenth at gcc dot gnu.org
2021-12-13 5:42 ` pinskia at gcc dot gnu.org
` (3 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: rguenth at gcc dot gnu.org @ 2021-01-05 9:39 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98420
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |wrong-code
Ever confirmed|0 |1
Component|tree-optimization |middle-end
Status|UNCONFIRMED |NEW
Last reconfirmed| |2021-01-05
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
probably conditional on HONOR_SIGNED_ZEROS.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug middle-end/98420] Invalid simplification of x - x with -frounding-math
2020-12-22 14:56 [Bug middle-end/98420] New: Invalid simplification of x - x with -frounding-math ubizjak at gmail dot com
2021-01-05 9:39 ` [Bug middle-end/98420] " rguenth at gcc dot gnu.org
@ 2021-12-13 5:42 ` pinskia at gcc dot gnu.org
2022-03-10 23:56 ` roger at nextmovesoftware dot com
` (2 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-12-13 5:42 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98420
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #1)
> probably conditional on HONOR_SIGNED_ZEROS.
That is checked now:
+ || (!tree_expr_maybe_nan_p (@0)
+ && !tree_expr_maybe_infinite_p (@0)))
The part that is missed is the flag_rounding_math .
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug middle-end/98420] Invalid simplification of x - x with -frounding-math
2020-12-22 14:56 [Bug middle-end/98420] New: Invalid simplification of x - x with -frounding-math ubizjak at gmail dot com
2021-01-05 9:39 ` [Bug middle-end/98420] " rguenth at gcc dot gnu.org
2021-12-13 5:42 ` pinskia at gcc dot gnu.org
@ 2022-03-10 23:56 ` roger at nextmovesoftware dot com
2022-03-12 9:23 ` cvs-commit at gcc dot gnu.org
2022-03-14 18:39 ` roger at nextmovesoftware dot com
4 siblings, 0 replies; 6+ messages in thread
From: roger at nextmovesoftware dot com @ 2022-03-10 23:56 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98420
Roger Sayle <roger at nextmovesoftware dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Assignee|unassigned at gcc dot gnu.org |roger at nextmovesoftware dot com
CC| |roger at nextmovesoftware dot com
Status|NEW |ASSIGNED
--- Comment #3 from Roger Sayle <roger at nextmovesoftware dot com> ---
Patch proposed.
https://gcc.gnu.org/pipermail/gcc-patches/2022-March/591583.html
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug middle-end/98420] Invalid simplification of x - x with -frounding-math
2020-12-22 14:56 [Bug middle-end/98420] New: Invalid simplification of x - x with -frounding-math ubizjak at gmail dot com
` (2 preceding siblings ...)
2022-03-10 23:56 ` roger at nextmovesoftware dot com
@ 2022-03-12 9:23 ` cvs-commit at gcc dot gnu.org
2022-03-14 18:39 ` roger at nextmovesoftware dot com
4 siblings, 0 replies; 6+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2022-03-12 9:23 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98420
--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Roger Sayle <sayle@gcc.gnu.org>:
https://gcc.gnu.org/g:72c243017dee611bf3c32ea7bfad6ac538021aaf
commit r12-7621-g72c243017dee611bf3c32ea7bfad6ac538021aaf
Author: Roger Sayle <roger@nextmovesoftware.com>
Date: Sat Mar 12 09:20:52 2022 +0000
PR middle-end/98420: Don't fold x - x to 0.0 with -frounding-math
This patch addresses PR middle-end/98420, which is inappropriate constant
folding of x - x to 0.0 (in match.pd) when -frounding-math is specified.
Specifically, x - x may be -0.0 with FE_DOWNWARD as the rounding mode.
To summarize, the desired IEEE behaviour, x - x for floating point x,
(1) can't be folded to 0.0 by default, due to the possibility of NaN or Inf
(2) can be folded to 0.0 with -ffinite-math-only
(3) can't be folded to 0.0 with -ffinite-math-only -frounding-math
(4) can be folded with -ffinite-math-only -frounding-math -fno-signed-zeros
2022-03-12 Roger Sayle <roger@nextmovesoftware.com>
gcc/ChangeLog
PR middle-end/98420
* match.pd (minus @0 @0): Additional checks for -fno-rounding-math
(the defaut) or -fno-signed-zeros.
gcc/testsuite/ChangeLog
PR middle-end/98420
* gcc.dg/pr98420.c: New test case.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug middle-end/98420] Invalid simplification of x - x with -frounding-math
2020-12-22 14:56 [Bug middle-end/98420] New: Invalid simplification of x - x with -frounding-math ubizjak at gmail dot com
` (3 preceding siblings ...)
2022-03-12 9:23 ` cvs-commit at gcc dot gnu.org
@ 2022-03-14 18:39 ` roger at nextmovesoftware dot com
4 siblings, 0 replies; 6+ messages in thread
From: roger at nextmovesoftware dot com @ 2022-03-14 18:39 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98420
Roger Sayle <roger at nextmovesoftware dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|ASSIGNED |RESOLVED
Resolution|--- |FIXED
Target Milestone|--- |12.0
--- Comment #5 from Roger Sayle <roger at nextmovesoftware dot com> ---
This should now be fixed on mainline.
^ permalink raw reply [flat|nested] 6+ messages in thread
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2020-12-22 14:56 [Bug middle-end/98420] New: Invalid simplification of x - x with -frounding-math ubizjak at gmail dot com
2021-01-05 9:39 ` [Bug middle-end/98420] " rguenth at gcc dot gnu.org
2021-12-13 5:42 ` pinskia at gcc dot gnu.org
2022-03-10 23:56 ` roger at nextmovesoftware dot com
2022-03-12 9:23 ` cvs-commit at gcc dot gnu.org
2022-03-14 18:39 ` roger at nextmovesoftware dot com
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