[Bug tree-optimization/101031] New: wrong code at -O2 on x86_64-linux-gnu

[qrzhang at gatech dot edu via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101031

            Bug ID: 101031
           Summary: wrong code at -O2 on x86_64-linux-gnu
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: qrzhang at gatech dot edu
  Target Milestone: ---

It appears to be a recent regression.


$ gcc-trunk -v
Supported LTO compression algorithms: zlib
gcc version 12.0.0 20210611 (experimental) [master revision
336c41dbcb2:00da4bcb67d:36943c6bdd3d3b535b24872bbd802d91ef0c6299] (GCC)


$ gcc-trunk abc.c ; ./a.out
0

$ gcc-trunk -O2 abc.c ; ./a.out
1


$ cat abc.c
int a;
char b, e;
static char *c = &b;
static long d;
void f(void);
void h() {
  int g = 0;
  for (; g < 2; ++g) {
    d = *c;
    *c = 1;
    b = 0;
  }
  f();
}
void f() {
  if (d++)
    c = &e;
  for (; a;)
    ;
}
int main() {
  h();
  printf("%d\n", b);
}