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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/94414] only `--` gives constexpr
Date: Tue, 14 Dec 2021 08:54:20 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D94414

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2021-12-14
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
           Severity|normal                      |enhancement
          Component|c++                         |tree-optimization

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
To me there looks like an unrolling not happening:
  <bb 3> [local count: 1014686026]:
  # __first_35 =3D PHI <__first_15(4), &MEM <const int[4]> [(void *)&arr +
8B](2)>
  _14 =3D MEM[(const int &)__first_35];
  if (_14 <=3D 5)
    goto <bb 4>; [94.50%]
  else
    goto <bb 5>; [5.50%]

  <bb 4> [local count: 958878296]:
  __first_15 =3D __first_35 + 4;
  if (&MEM <const struct array> [(void *)&arr + 16B] !=3D __first_15)
    goto <bb 3>; [94.50%]
  else
    goto <bb 5>; [5.50%]

But from what I can tell it is we unroll the one loop and then we can't unr=
oll
this one until much later on. It is really interesting testcase.=