https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111694
Bug ID: 111694
Summary: Wrong behavior for signbit of negative zero when
optimizing
Product: gcc
Version: 13.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: web
Assignee: unassigned at gcc dot gnu.org
Reporter: alonzakai at gmail dot com
Target Milestone: ---
This behaves incorrectly in 13.2.0 with -O1 and above, but is correct in 12,
11, and 10. It is also correct in 13.2.0 without optimizations.
Testcase:
#include <math.h>
#include <stdio.h>
void test(double l, double r) {
if (l == r && l == 0 && (signbit(l) || signbit(r))) {
puts("one is negative");
}
}
int main() {
test(0.0, -0.0);
test(-0.0, 0.0);
}
This should print "one is negative" twice, but only does so once in 13.2.0 with
-O1:
$ gcc-13 a.c -O1 ; ./a.out
one is negative
$ gcc-13 a.c -O0 ; ./a.out
one is negative
one is negative
$
