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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/19430] taking address of a var causes missing
 uninitialized warning (virtual PHI with MEM)
Date: Mon, 29 Aug 2022 13:08:26 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D19430

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|2005-05-03 18:04:44         |2022-8-29

--- Comment #37 from Richard Biener <rguenth at gcc dot gnu.org> ---
Re-confirmed for the original testcase.  The issue is that while we now try=
 to
perform uninitialized diagnostics for memory we do not perform the maybe-un=
init
analysis via PHIs we do for non-memory.  We see

  <bb 2> [local count: 1073741824]:
  # .MEM_5 =3D VDEF <.MEM_3(D)>
  _1 =3D bar (i_4(D));
  if (_1 !=3D 0)
    goto <bb 3>; [33.00%]
  else
    goto <bb 5>; [67.00%]

  <bb 5> [local count: 719407024]:
  goto <bb 4>; [100.00%]

  <bb 3> [local count: 354334800]:
  # .MEM_6 =3D VDEF <.MEM_5>
  baz (&j);

  <bb 4> [local count: 1073741824]:
  # .MEM_2 =3D PHI <.MEM_5(5), .MEM_6(3)>
  # VUSE <.MEM_2>
  _7 =3D j;

so when we are walking and looking for defs of 'j' by means of
walk_aliased_vdefs but that will simply process MEM_6 "unordered"
and record that as possible definition.  We are not properly forking
the walk to discover a path where 'j' is not initialized nor are
we trying to compute predicates which guard the use.=