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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug middle-end/105346] [11/12 Regression] -Wno-free-nonheap-object
 false positive (on Bison-generated grammar code)
Date: Tue, 26 Apr 2022 09:56:06 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D105346

--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Started with r11-5732-gdce6c58db87ebf7f4477bd3126228e73e4eeee97
The IL at -O0 -Wall looks during waccess pass like:
void foo ()
{
  char * bufp;
  char buf[20];

  <bb 2> :
  bufp_2 =3D &buf;
  if (&buf !=3D bufp_2)
    goto <bb 3>; [INV]
  else
    goto <bb 4>; [INV]

  <bb 3> :
  __builtin_free (bufp_2);

  <bb 4> :
  buf =3D{v} {CLOBBER(eol)};
  return;

}

So, I think the waccess pass must be walking SSA_NAME_DEF_STMT to figure ou=
t it
is a free of non-heap.  Either it shouldn't do that at -O0, or it should on=
ly
walk them when they are in the same bb as the free call, or it needs to be =
able
to detect also conditionals like the above.=