[Bug tree-optimization/98552] Make more use of __builtin_undefined for assuring that variables do not change

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98552

--- Comment #4 from Thomas Koenig <tkoenig at gcc dot gnu.org> ---
Yes, I think that translating a DO loop into something like

int i;

for (i=0; i<n; i++)
{
  const int j = i;
  /* Use j from here on where i is referenced.  */
}

might solve a few of the issues in DO loop optimization.