[Bug middle-end/98266] New: bogus array subscript is partly outside array bounds on virtual inheritance

[Bug middle-end/98266] New: bogus array subscript is partly outside array bounds on virtual inheritance

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98266

            Bug ID: 98266
           Summary: bogus array subscript is partly outside array bounds
                    on virtual inheritance
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

As reported in https://bugzilla.redhat.com/show_bug.cgi?id=1907216, GCC 11
issues a spurious -Warray-bounds on the following code (reduced from the
original test case):

$ cat rhbz1738791.C && g++ -O2 -S -Wall rhbz1738791.C
struct A
{
  virtual ~A() noexcept;
  const char* s;
};

struct B: virtual A { };

struct C: virtual B { };

struct D: virtual A { };

struct E: virtual B, virtual D
{
  E (const char*);
};

void f (E);

void g_function ()
{
  f (E (""));
}
rhbz1738791.C: In function ‘void g_function()’:
rhbz1738791.C:11:8: warning: array subscript ‘D[1]’ is partly outside array
bounds of ‘E [1]’ [-Warray-bounds]
   11 | struct D: virtual A { };
      |        ^
rhbz1738791.C:22:11: note: while referencing ‘<anonymous>’
   22 |   f (E (""));
      |           ^
rhbz1738791.C:11:8: warning: array subscript ‘D[1]’ is partly outside array
bounds of ‘E [1]’ [-Warray-bounds]
   11 | struct D: virtual A { };
      |        ^
rhbz1738791.C:22:11: note: while referencing ‘<anonymous>’
   22 |   f (E (""));
      |           ^

[Bug middle-end/98266] [11 Regression] bogus array subscript is partly outside array bounds on virtual inheritance

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98266

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2020-12-13
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=97595
            Summary|bogus array subscript is    |[11 Regression] bogus array
                   |partly outside array bounds |subscript is partly outside
                   |on virtual inheritance      |array bounds on virtual
                   |                            |inheritance
             Status|UNCONFIRMED                 |NEW
             Blocks|                            |56456
     Ever confirmed|0                           |1
   Target Milestone|---                         |11.0
           Keywords|                            |diagnostic

--- Comment #1 from Martin Sebor <msebor at gcc dot gnu.org> ---
The problem is most likely the same as in pr97595 (except in
gimple-array-bounds.cc).


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56456
[Bug 56456] [meta-bug] bogus/missing -Warray-bounds

[Bug middle-end/98266] [11 Regression] bogus array subscript is partly outside array bounds on virtual inheritance

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98266

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

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

[Bug middle-end/98266] [11 Regression] bogus array subscript is partly outside array bounds on virtual inheritance

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98266

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P1

[Bug middle-end/98266] [11 Regression] bogus array subscript is partly outside array bounds on virtual inheritance

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98266

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |patch

--- Comment #2 from Martin Sebor <msebor at gcc dot gnu.org> ---
Patch: https://gcc.gnu.org/pipermail/gcc-patches/2021-January/563894.html

[Bug middle-end/98266] [11 Regression] bogus array subscript is partly outside array bounds on virtual inheritance

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98266

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=22488

--- Comment #3 from Martin Sebor <msebor at gcc dot gnu.org> ---
See pr22488 for the underlying problem with the difference between DECL_SIZE
and TYPE_SIZE of classes with virtual bases.

[Bug middle-end/98266] [11 Regression] bogus array subscript is partly outside array bounds on virtual inheritance

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98266

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

https://gcc.gnu.org/g:f3daa6c0fd8d79ae45eac2dd0f274da1aa71c958

commit r11-7563-gf3daa6c0fd8d79ae45eac2dd0f274da1aa71c958
Author: Martin Sebor <msebor@redhat.com>
Date:   Mon Mar 8 13:37:21 2021 -0700

    PR middle-end/98266 - bogus array subscript is partly outside array bounds
on virtual inheritance

    gcc/ChangeLog:

            PR middle-end/98266
            * gimple-array-bounds.cc (inbounds_vbase_memaccess_p): New
function.
            (array_bounds_checker::check_array_bounds): Call it.

    gcc/testsuite/ChangeLog:

            PR middle-end/98266
            * g++.dg/warn/Warray-bounds-15.C: New test.
            * g++.dg/warn/Warray-bounds-18.C: New test.
            * g++.dg/warn/Warray-bounds-19.C: New test.
            * g++.dg/warn/Warray-bounds-20.C: New test.
            * g++.dg/warn/Warray-bounds-21.C: New test.

[Bug middle-end/98266] [11 Regression] bogus array subscript is partly outside array bounds on virtual inheritance

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98266

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|ASSIGNED                    |RESOLVED

--- Comment #5 from Martin Sebor <msebor at gcc dot gnu.org> ---
Fixed in r11-7563.