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From: "msebor at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/89976] [9/10/11 Regression] missing
 -Wuninitialized for struct member due to sra and TREE_NO_WARNING
Date: Fri, 16 Apr 2021 21:30:55 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D89976

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|c++                         |tree-optimization
            Summary|missing uninitialized       |[9/10/11 Regression]
                   |warning for uninitialized   |missing -Wuninitialized for
                   |struct member (VOPs)        |struct member due to sra
                   |                            |and TREE_NO_WARNING
   Last reconfirmed|2019-11-02 00:00:00         |2021-4-16
                 CC|                            |msebor at gcc dot gnu.org
      Known to fail|                            |10.2.0, 11.0, 4.5.3, 4.6.4,
                   |                            |4.9.4, 5.5.0, 6.4.0, 7.2.0,
                   |                            |8.3.0, 9.1.0

--- Comment #4 from Martin Sebor <msebor at gcc dot gnu.org> ---
In all cases and with -O1 and above, the uninitialized read is clearly visi=
ble
in the IL but it's suppressed because the variable (such as x$x in case 1) =
has
the TREE_NO_WARNING bit set.  This appears to be regression introduced in G=
CC
4.5 in r147980.

gcc -O1 -S -Wall -std=3Dc++14 -fdump-tree-uninit=3D/dev/stdout pr89976.C=20

;; Function foo (_Z3foov, funcdef_no=3D3, decl_uid=3D2098, cgraph_uid=3D4,
symbol_order=3D3)

struct X foo ()
{
  int x$x;                             <<< TREE_NO_WARNING =3D=3D 1
  struct X D.2133;

  <bb 2> [local count: 1073741824]:
  D.2133.x =3D x$x_2(D);                 <<< uninitialized read
  D.2133.y =3D 0;
  return D.2133;

}



;; Function main (main, funcdef_no=3D4, decl_uid=3D2129, cgraph_uid=3D5,
symbol_order=3D4) (executed once)

int main ()
{
  int x$x;                             <<< TREE_NO_WARNING =3D=3D 1
  struct X D.2156;
  struct X x;

  <bb 2> [local count: 1073741824]:
  x =3D{v} {CLOBBER};
  return x$x_5(D);                     <<< uninitialized read

}=