https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111472
Bug ID: 111472
Summary: Wrong code at -Os on x86_64-linux-gnu since
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: shaohua.li at inf dot ethz.ch
CC: amacleod at redhat dot com
Target Milestone: ---
gcc at -Os produced the wrong code.
Bisected to r11-4563-gd0d8b5d836
Compiler explorer: https://godbolt.org/z/EPznGbaje
With -fwrapv the issue goes away.
$ cat a.c
int printf(const char *, ...);
int a, b, e, f;
short c = -1, i;
char g;
int h[4][1] = {8, 5, 8, 5};
int main() {
int *j = &e, *k = &f;
unsigned short d = c;
i = d >> b;
*j = i;
g = 0;
for (; g <= 3; g++)
*k = h[(unsigned char)(1 + e) + g][0];
printf("%d\n", f);
}
$
$ gcc -O0 a.c && ./a.out
5
$ gcc -Os a.c && ./a.out
Segmentation fault
$
$ gcc -fsanitize=undefined a.c && ./a.out
5
$
