[Bug tree-optimization/84712] New: Missed evaluating to constant at tree level

["prathamesh3492 at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84712

            Bug ID: 84712
           Summary: Missed evaluating to constant at tree level
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: prathamesh3492 at gcc dot gnu.org
  Target Milestone: ---

Hi,
It seems GCC does not evaluate the following function to a constant at the tree
level:

int sum(void)
{
  int a[] = {1, 2, 3, -1};
  int x = 0;

  for (int i = 0; i < 4; i++)
    if (a[i] < 0)
      break;
    else
      x += a[i];

  return x;
}

optimized dump shows:
sum ()
{
  int x;
  int a[4];
  int _25;
  int _33;
  int _41;

  <bb 2> [local count: 261993005]:
  MEM[(int *)&a] = { 1, 2, 3, -1 };
  _25 = a[1];
  if (_25 < 0)
    goto <bb 5>; [7.91%]
  else
    goto <bb 3>; [92.09%]

  <bb 3> [local count: 246744733]:
  x_30 = _25 + 1;
  _33 = a[2];
  if (_33 < 0)
    goto <bb 5>; [7.91%]
  else
    goto <bb 4>; [92.09%]

  <bb 4> [local count: 232383926]:
  x_38 = x_30 + _33;
  _41 = a[3];
  if (_41 < 0)
    goto <bb 5>; [7.91%]
  else
    goto <bb 6>; [92.09%]

  <bb 5> [local count: 47244641]:
  # x_17 = PHI <x_30(3), 1(2), x_38(4)>
  goto <bb 7>; [100.00%]

  <bb 6> [local count: 218858940]:
  x_10 = x_38 + _41;

  <bb 7> [local count: 261993005]:
  # x_2 = PHI <x_17(5), x_10(6)>
  a ={v} {CLOBBER};
  return x_2;

}

However at RTL, cprop seems to do the constant folding and set return value
register to 6.

Thanks,
Prathamesh