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* [Bug c/58275] New: __builtin_constant_p( expr ) returns true if expr is eliminated by CSE
@ 2013-08-29 19:40 tijl at coosemans dot org
2013-08-29 19:46 ` [Bug c/58275] " glisse at gcc dot gnu.org
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: tijl at coosemans dot org @ 2013-08-29 19:40 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58275
Bug ID: 58275
Summary: __builtin_constant_p( expr ) returns true if expr is
eliminated by CSE
Product: gcc
Version: 4.9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: tijl at coosemans dot org
It appears that whenever the expression in __builtin_constant_p( expression )
can be eliminated __builtin_constant_p returns true even if expression is not a
compile-time constant.
Here is an example program. When compiled with -O it returns 1 instead of 2:
int main( int argc, char **argv ) {
return( argc == 23 ? 0 : __builtin_constant_p( argc != 23 ) ? 1 : 2 );
}
% gcc49 -o test test.c -O
% ./test ; echo $?
1
If you change the first 23 into 24 the program returns 2.
(gcc49 (FreeBSD Ports Collection) 4.9.0 20130818 (experimental))
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c/58275] __builtin_constant_p( expr ) returns true if expr is eliminated by CSE
2013-08-29 19:40 [Bug c/58275] New: __builtin_constant_p( expr ) returns true if expr is eliminated by CSE tijl at coosemans dot org
@ 2013-08-29 19:46 ` glisse at gcc dot gnu.org
2013-08-29 20:16 ` jakub at gcc dot gnu.org
2013-08-29 20:33 ` tijl at coosemans dot org
2 siblings, 0 replies; 4+ messages in thread
From: glisse at gcc dot gnu.org @ 2013-08-29 19:46 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58275
--- Comment #1 from Marc Glisse <glisse at gcc dot gnu.org> ---
Where do you see a bug? The test argc!=23 is always true in this branch, so it
*is* a compile-time constant. It is very much on purpose that
__builtin_constant_p returns true.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c/58275] __builtin_constant_p( expr ) returns true if expr is eliminated by CSE
2013-08-29 19:40 [Bug c/58275] New: __builtin_constant_p( expr ) returns true if expr is eliminated by CSE tijl at coosemans dot org
2013-08-29 19:46 ` [Bug c/58275] " glisse at gcc dot gnu.org
@ 2013-08-29 20:16 ` jakub at gcc dot gnu.org
2013-08-29 20:33 ` tijl at coosemans dot org
2 siblings, 0 replies; 4+ messages in thread
From: jakub at gcc dot gnu.org @ 2013-08-29 20:16 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58275
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
CC| |jakub at gcc dot gnu.org
Resolution|--- |INVALID
--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Yeah.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c/58275] __builtin_constant_p( expr ) returns true if expr is eliminated by CSE
2013-08-29 19:40 [Bug c/58275] New: __builtin_constant_p( expr ) returns true if expr is eliminated by CSE tijl at coosemans dot org
2013-08-29 19:46 ` [Bug c/58275] " glisse at gcc dot gnu.org
2013-08-29 20:16 ` jakub at gcc dot gnu.org
@ 2013-08-29 20:33 ` tijl at coosemans dot org
2 siblings, 0 replies; 4+ messages in thread
From: tijl at coosemans dot org @ 2013-08-29 20:33 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58275
--- Comment #3 from Tijl Coosemans <tijl at coosemans dot org> ---
Eh, of course.
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2013-08-29 20:33 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2013-08-29 19:40 [Bug c/58275] New: __builtin_constant_p( expr ) returns true if expr is eliminated by CSE tijl at coosemans dot org
2013-08-29 19:46 ` [Bug c/58275] " glisse at gcc dot gnu.org
2013-08-29 20:16 ` jakub at gcc dot gnu.org
2013-08-29 20:33 ` tijl at coosemans dot org
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