https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96760
Bug ID: 96760
Summary: Faulty optimization in nested loops with -O2
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: zhige.yu18 at imperial dot ac.uk
Target Milestone: ---
The following code snippet:
#include <stdio.h>
char a = 0, f = 0, c = 5;
unsigned long d = 0;
int g = 0;
int *e = &g;
int main() {
char b = 0;
for (;;) {
for (a = 20; a; a++) {
if (c) {
printf("%lu\n", d);
return 0;
}
}
f = (d++, *e);
}
}
> $ /usr/gcc-trunk/bin/gcc -O2 bug.c; ./a.out
> 140728921720328
> $ gcc-9 -O2 bug.c; ./a.out
> 0
When compiled with -O2, it prints out a random value instead of 0. This bug can
be found on GCC-11.0.0 20200823. GCC-10.2 and earlier GCCs do not have this
bug.
