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* [Bug c/32099] New: a constant value is said to be not constant
@ 2007-05-26 18:15 andrei dot kouznetsov at gmail dot com
2007-05-26 18:27 ` [Bug c/32099] " pinskia at gcc dot gnu dot org
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: andrei dot kouznetsov at gmail dot com @ 2007-05-26 18:15 UTC (permalink / raw)
To: gcc-bugs
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when I'm trying to compile the program
============================
#include <math.h>
static double s = sin(0.0);
int main(){
return 0;
}
============================
with gcc t.c, the compiler produces the warnings
t.c:3: warning: initializer element is not constant
t.c:3: warning: (near initialization for s)
t.c:3: warning: s defined but not used
I'm worried about the first warning, since sin(0) is constant
gcc -v generates:
=======================================
Using built-in specs.
Target: i486-linux-gnu
Configured with: ../src/configure -v
--enable-languages=c,c++,fortran,objc,obj-c++,treelang --prefix=/usr
--enable-shared --with-system-zlib --libexecdir=/usr/lib
--without-included-gettext --enable-threads=posix --enable-nls
--program-suffix=-4.1 --enable-__cxa_atexit --enable-clocale=gnu
--enable-libstdcxx-debug --enable-mpfr --enable-checking=release i486-linux-gnu
Thread model: posix
gcc version 4.1.2 (Ubuntu 4.1.2-0ubuntu4)
--
Summary: a constant value is said to be not constant
Product: gcc
Version: 4.1.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: andrei dot kouznetsov at gmail dot com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32099
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c/32099] a constant value is said to be not constant
2007-05-26 18:15 [Bug c/32099] New: a constant value is said to be not constant andrei dot kouznetsov at gmail dot com
@ 2007-05-26 18:27 ` pinskia at gcc dot gnu dot org
2007-05-26 18:47 ` andrei dot kouznetsov at gmail dot com
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2007-05-26 18:27 UTC (permalink / raw)
To: gcc-bugs
------- Comment #1 from pinskia at gcc dot gnu dot org 2007-05-26 18:26 -------
No, sin(0) is not constant in C. C has specific rules about constant
expression. You can use __builtin_sin(0) to always get the constant folding.
--
pinskia at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution| |INVALID
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32099
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c/32099] a constant value is said to be not constant
2007-05-26 18:15 [Bug c/32099] New: a constant value is said to be not constant andrei dot kouznetsov at gmail dot com
2007-05-26 18:27 ` [Bug c/32099] " pinskia at gcc dot gnu dot org
@ 2007-05-26 18:47 ` andrei dot kouznetsov at gmail dot com
2007-05-28 12:54 ` manu at gcc dot gnu dot org
2007-06-10 3:23 ` [Bug middle-end/32099] not constant folding sin pinskia at gcc dot gnu dot org
3 siblings, 0 replies; 5+ messages in thread
From: andrei dot kouznetsov at gmail dot com @ 2007-05-26 18:47 UTC (permalink / raw)
To: gcc-bugs
------- Comment #2 from andrei dot kouznetsov at gmail dot com 2007-05-26 18:47 -------
Ok, but __builtin_sin(M_PI) is not constant again
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32099
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c/32099] a constant value is said to be not constant
2007-05-26 18:15 [Bug c/32099] New: a constant value is said to be not constant andrei dot kouznetsov at gmail dot com
2007-05-26 18:27 ` [Bug c/32099] " pinskia at gcc dot gnu dot org
2007-05-26 18:47 ` andrei dot kouznetsov at gmail dot com
@ 2007-05-28 12:54 ` manu at gcc dot gnu dot org
2007-06-10 3:23 ` [Bug middle-end/32099] not constant folding sin pinskia at gcc dot gnu dot org
3 siblings, 0 replies; 5+ messages in thread
From: manu at gcc dot gnu dot org @ 2007-05-28 12:54 UTC (permalink / raw)
To: gcc-bugs
------- Comment #3 from manu at gcc dot gnu dot org 2007-05-28 12:54 -------
Worse, with __builtin_sin(M_PI), I get an error:
test.c:2: error: initializer element is not constant
Maybe this is fixed now in GCC 4.3 by using MPFR.
--
manu at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |manu at gcc dot gnu dot org
Status|RESOLVED |UNCONFIRMED
Resolution|INVALID |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32099
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug middle-end/32099] not constant folding sin
2007-05-26 18:15 [Bug c/32099] New: a constant value is said to be not constant andrei dot kouznetsov at gmail dot com
` (2 preceding siblings ...)
2007-05-28 12:54 ` manu at gcc dot gnu dot org
@ 2007-06-10 3:23 ` pinskia at gcc dot gnu dot org
3 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2007-06-10 3:23 UTC (permalink / raw)
To: gcc-bugs
------- Comment #4 from pinskia at gcc dot gnu dot org 2007-06-10 03:23 -------
This is an extension that GCC allows some constant folding with some functions.
So this is just a missed optimization of not constant folding sin.
And yes this is fixed in 4.3.0 by the use of MPFR.
--
pinskia at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Component|c |middle-end
Keywords| |missed-optimization
Resolution| |FIXED
Summary|a constant value is said to |not constant folding sin
|be not constant |
Target Milestone|--- |4.3.0
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32099
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2007-06-10 3:23 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
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2007-05-26 18:15 [Bug c/32099] New: a constant value is said to be not constant andrei dot kouznetsov at gmail dot com
2007-05-26 18:27 ` [Bug c/32099] " pinskia at gcc dot gnu dot org
2007-05-26 18:47 ` andrei dot kouznetsov at gmail dot com
2007-05-28 12:54 ` manu at gcc dot gnu dot org
2007-06-10 3:23 ` [Bug middle-end/32099] not constant folding sin pinskia at gcc dot gnu dot org
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