[Bug tree-optimization/121422] New: [16 Regression] wrong code for proping zero incorrectly

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121422

            Bug ID: 121422
           Summary: [16 Regression] wrong code for proping zero
                    incorrectly
           Product: gcc
           Version: 14.2.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: pinskia at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---

testcase:
```
struct s1
{
  char a[4];
};
struct s1 b;
char t[4];

__attribute__((noipa,noinline))
void f(void)
{
  b = (struct s1){};
  b.a[3] = 1;
  __builtin_memcpy(&t[0], &b.a[1], 3*sizeof(t[0]));
}


int main()
{
  f();
  for(int i = 0; i < 4; i++)
  {
        if (t[i] != (i == 2 ? 1 : 0))
          __builtin_abort();
  }
}
```