[Bug tree-optimization/89317] Ineffective code from std::copy

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89317

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |TREE

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note on the trunk, these two functions now produce the same code. BUT we are
still missing a gimple level optimization.

The RTL level can figure out:
  _1 = this_6(D) + 16;
  _2 = &this_6(D)->data1;
  _19 = _1 - _2;
  __n_20 = _19 /[ex] 2;
  if (_19 > 0)
    goto <bb 3>; [89.00%]
  else
    goto <bb 18>; [11.00%]

That _19 is 16 and the condition is always true.

Reduced testcase for that issue:
struct { int data[16]; } *x;
int foo (int n1)
{
  int *a = x->data;
  int *b = ((int*)x) + 4;
  return b - a;
}