[Bug tree-optimization/101401] strlen of a constant char vector not folded

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101401

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Here is some more:
```
void f1 ()
{
  char c8[8];
  for(int i = 0;i < 8;i ++)
  {
    c8[i] = i < 4 ? ('a'+i) : 0;
  }
  if (__builtin_strlen (&c8[0]) != 4)
    __builtin_abort ();
}

void g1 (void)
{
  __attribute__ ((vector_size (8))) char c8 = { 1, 2, 3 };
  char *t = (char*)&c8;
  if (__builtin_strlen (t) != 3)
    __builtin_abort ();
}
```

So it looks like strlen pass understands VECTOR_CST just fine (f1 is handled
just fine). just not `vector char` types as an array I think.