[Bug tree-optimization/90994] Bogus Wmaybe-uninitialized with fnon-call-exceptions

[Bug tree-optimization/90994] Bogus Wmaybe-uninitialized with fnon-call-exceptions

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90994

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2021-04-07
      Known to fail|                            |10.2.0, 11.0, 9.2.0
                 CC|                            |msebor at gcc dot gnu.org

--- Comment #1 from Martin Sebor <msebor at gcc dot gnu.org> ---
Confirmed.  The warning sees the IL below.  The reason for the false positive
is the assignment in bb 5 marked not handled.  The warning walks up the control
flow graph from the point of the possibly uninitialized use to the definition
of the a_33 variable (a PHI), looking for predicates that guard it to try to
determine if they are mutually exclusive with those guarding the uninitialized
operand to the PHI.  It recongnizes conditional expressions and switch
statements but nothing else (such the assignment here).  As a result, the logic
fails to detect that the conditionals prevent the uninitialized variable from
being used.

int incorrectWarning ()
{
  int D.2387;
  int D.2383;
  unsigned char b;
  unsigned char a;
  int _3;
  int _5;
  int _6;
  bool prephitmp_10;
  unsigned char _17;
  int _18;
  void * _19;
  unsigned char _20;
  void * _22;

  <bb 2> [local count: 1073741824]:
  # VUSE <.MEM_8(D)>
  _17 ={v} MEM[(volatile unsigned char *)1234B];

  <bb 9> [local count: 1073741824]:

  <bb 3> [local count: 1073741824]:
  # _18 = PHI <0(9), -1(4)>                        <<< _18 != 0 in bb 4
  # .MEM_23 = PHI <.MEM_8(D)(9), .MEM_26(4)>
  # a_33 = PHI <_17(9), a_35(D)(4)>                <<< a_33 uninitialized if
_18 != 0
  # prephitmp_10 = PHI <0(9), 1(4)>
  __asm__ __volatile__("




" :  : "X" prephitmp_10);
  if (_18 != 0)
    goto <bb 10>; [51.12%]
  else
    goto <bb 5>; [48.88%]                          <<< _18 == 0 implies a_33 =
_17(9)

  <bb 10> [local count: 548896824]:
  goto <bb 8>; [100.00%]

  <bb 4> [count: 0]:
<L8>:
  # VUSE <.MEM_8(D)>
  _19 = __builtin_eh_pointer (3);
  # .MEM_25 = VDEF <.MEM_8(D)>
  __cxa_begin_catch (_19);
  # .MEM_26 = VDEF <.MEM_25>
  __cxa_end_catch ();
  goto <bb 3>; [0.00%]

  <bb 5> [local count: 524845000]:
  # VUSE <.MEM_23>
  _20 ={v} MEM[(volatile unsigned char *)1234B];   <<< not handled

  <bb 6> [local count: 524845000]:
  _3 = (int) a_33;                                 <<< -Wmaybe-uninitialized
  # .MEM_13 = VDEF <.MEM_23>
  printval (_3);
  _5 = (int) _20;
  # .MEM_14 = VDEF <.MEM_13>
  printval (_5);
  goto <bb 8>; [100.00%]

  <bb 7> [count: 0]:
<L10>:
  # VUSE <.MEM_23>
  _22 = __builtin_eh_pointer (4);
  # .MEM_29 = VDEF <.MEM_23>
  __cxa_begin_catch (_22);
  # .MEM_30 = VDEF <.MEM_29>
  __cxa_end_catch ();

  <bb 8> [local count: 1073741824]:
  # _6 = PHI <0(6), 1(7), 1(10)>
  # .MEM_7 = PHI <.MEM_14(6), .MEM_30(7), .MEM_23(10)>
  # VUSE <.MEM_7>
  return _6;

}

[Bug tree-optimization/90994] Bogus Wmaybe-uninitialized with fnon-call-exceptions

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90994

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rguenth at gcc dot gnu.org

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Interestingly the factoring into gimple-predicate-analysis.cc,
r12-3640-g94c12ffac234b2 contains

-         else
-           {
-             has_valid_pred = false;
-             break;
-           }
+         else
+           {
+             /* Disabled.  See PR 90994.
+                has_valid_pred = false;  */
+             break;
+           }

in all the noise, without explanation or testcase.

[Bug tree-optimization/90994] Bogus Wmaybe-uninitialized with fnon-call-exceptions

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90994

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |rguenth at gcc dot gnu.org

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
I'm testing a real fix.

[Bug tree-optimization/90994] Bogus Wmaybe-uninitialized with fnon-call-exceptions

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90994

--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Richard Biener <rguenth@gcc.gnu.org>:

https://gcc.gnu.org/g:88f29a8aa82f2788baf2f9865940d4c83012c580

commit r13-2310-g88f29a8aa82f2788baf2f9865940d4c83012c580
Author: Richard Biener <rguenther@suse.de>
Date:   Wed Aug 31 14:04:46 2022 +0200

    tree-optimization/90994 - fix uninit diagnostics with EH

    r12-3640-g94c12ffac234b2 sneaked in a hack to avoid the diagnostic
    for the testcase in PR90994 which sees non-call EH control flow
    confusing predicate analysis.  The following patch instead adjusts
    the existing code handling EH to handle non-calls and do what I
    think was intented.

            PR tree-optimization/90994
            * gimple-predicate-analysis.cc (predicate::init_from_control_deps):
            Ignore exceptional control flow and skip the edge for the purpose
of
            predicate generation also for non-calls.

            * g++.dg/torture/pr90994.C: New testcase.

[Bug tree-optimization/90994] Bogus Wmaybe-uninitialized with fnon-call-exceptions

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90994

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
      Known to work|                            |13.0
         Resolution|---                         |FIXED

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
Fixed properly for GCC 13, hacked around for GCC 12.