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

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

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

Tobias Schlüter <tobi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |tobi at gcc dot gnu.org

--- Comment #1 from Tobias Schlüter <tobi at gcc dot gnu.org> ---
There's a typo in the example, /= instead of !=.  Fixed example below:

I sprinkled const's all over foo's prototype and 'i' still gets reloaded so it
stands to reason that the compiler doesn't see the optimization opportunity. 

======================

void foo (int *);

void bar (int n)
{
  int i;
  for (i=0; i<n; i++)
    foo(&i);
}

void baz(int n)
{
  int i, j;
  for (i=0; i<n; i++)
    {
      j = i;
      foo (&i);
      if (j != i)
        __builtin_unreachable();
    }
}

======================