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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) -- links below jump to the message on this page -- 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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