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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/107618] Incorrect diagnostics when using -Og,
 builtin_expect(), and function attribute "warning" or "error"
Date: Fri, 11 Nov 2022 07:47:37 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 13.0
X-Bugzilla-Keywords: diagnostic
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107618

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
            Version|unknown                     |13.0
           Assignee|unassigned at gcc dot gnu.org      |rguenth at gcc dot =
gnu.org
   Last reconfirmed|                            |2022-11-11
           Keywords|                            |diagnostic
          Component|middle-end                  |tree-optimization
     Ever confirmed|0                           |1

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
We diagnose because we see

int main ()
{
  long int _2;

  <bb 2> [local count: 1073741824]:
  _2 =3D 0;
  if (_2 !=3D 0)
    goto <bb 3>; [10.00%]
  else
    goto <bb 4>; [90.00%]

  <bb 3> [local count: 107374184]:
  a ();

  <bb 4> [local count: 1073741824]:
  return 0;

}

and the reason is that for some reason

      /* Copy propagation also copy-propagates constants, this is necessary
         to forward object-size and builtin folding results properly.  */
      NEXT_PASS (pass_copy_prop);

doesn't work:

--- a-t2.c.224t.strlen2 2022-11-11 08:44:14.044322291 +0100
+++ a-t2.c.225t.copyprop5       2022-11-11 08:44:14.044322291 +0100
...
   <bb 2> [local count: 1073741824]:
   b_5 =3D __builtin_object_size (0B, 0);
-  _1 =3D 0;
-  _2 =3D (long int) _1;
+  _2 =3D 0;
   if (_2 !=3D 0)
     goto <bb 3>; [10.00%]
   else

I will have a look.=