[Bug fortran/54767] New: Incorrect code generated with "-O2 -fcheck=bounds"

[Bug fortran/54767] New: Incorrect code generated with "-O2 -fcheck=bounds"

[arnaud02 at users dot sourceforge.net]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54767

             Bug #: 54767
           Summary: Incorrect code generated with "-O2 -fcheck=bounds"
    Classification: Unclassified
           Product: gcc
           Version: 4.7.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: arnaud02@users.sourceforge.net


Using the code attached:

>gfortran --version | head -2
GNU Fortran (GCC) 4.7.1
Copyright (C) 2012 Free Software Foundation, Inc.
>gfortran -O0 -fcheck=bounds xxx_1.f xxx_2.f
>/a.out
           2           1
           3           2
 T
>gfortran -O2 -fcheck=bounds xxx_1.f xxx_2.f
>./a.out
           2           1
           3           1
 F

The results are different and incorrect when compiling with "-O2
-fcheck=bounds". They are still correct when compiling with "-O1
-fcheck=bounds".

[Bug fortran/54767] Incorrect code generated with "-O2 -fcheck=bounds"

[arnaud02 at users dot sourceforge.net]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54767

--- Comment #1 from Arnaud Desitter <arnaud02 at users dot sourceforge.net> 2012-10-01 15:08:57 UTC ---
Created attachment 28313
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=28313
test case

[Bug fortran/54767] [4.7/4.8 Regression] Incorrect code generated with "-O2 -fcheck=bounds"

[dominiq at lps dot ens.fr]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54767

Dominique d'Humieres <dominiq at lps dot ens.fr> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2012-10-01
      Known to work|                            |4.4.6, 4.5.3, 4.6.3
            Summary|Incorrect code generated    |[4.7/4.8 Regression]
                   |with "-O2 -fcheck=bounds"   |Incorrect code generated
                   |                            |with "-O2 -fcheck=bounds"
     Ever Confirmed|0                           |1
      Known to fail|                            |4.7.1, 4.7.2, 4.8.0

--- Comment #2 from Dominique d'Humieres <dominiq at lps dot ens.fr> 2012-10-01 17:45:19 UTC ---
This seems to be a 4.7/4.8 regression. Compiling the test with ' -Wall -Wextra
-Wuninitialized -O3 -fbounds-check' gives the expected results for 4.4.6,
4.5.3, and 4.6.3, but not for 4.7.2 or trunk.
Revision 176696 (2011-07-23) is OK, but not revision 177649 (2011-08-11).

If I initialize iaii as iaii=huge(0), I get the expected result.

Note to be pedantic, the use of INTENT in the subroutine requires an interface
(but it does not change anything either to add the interface or to remove the
intent).

[Bug fortran/54767] [4.7/4.8 Regression] Incorrect code generated with "-O2 -fcheck=bounds"

[burnus at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54767

--- Comment #3 from Tobias Burnus <burnus at gcc dot gnu.org> 2012-10-01 18:01:26 UTC ---
Confirmed.

For the failure, it is sufficient to use:
  gfortran -fcheck=bounds -O1 -fstrict-overflow -ftree-pre -ftree-vrp xxx_2.f

(xxx_1.f can be compiled with any option.)

[Bug fortran/54767] [4.7/4.8 Regression] Incorrect code generated with "-O2 -fcheck=bounds"

[burnus at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54767

Tobias Burnus <burnus at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |burnus at gcc dot gnu.org
   Target Milestone|---                         |4.7.3

[Bug fortran/54767] [4.7/4.8 Regression] Incorrect code generated with "-O2 -fcheck=bounds"

[janus at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54767

janus at gcc dot gnu.org changed:

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

--- Comment #4 from janus at gcc dot gnu.org 2012-10-01 18:22:40 UTC ---
Here is a reduced test case, which shows the same behavior:


  SUBROUTINE XXX (IL, IU)
    implicit none
    integer, INTENT(IN) :: IL, IU

    integer :: NXX (3) = (/ 0, 1, 2 /)
    integer :: ivvv, ia, iyyye, ja, iaii
    logical :: qop, qvv

    IYYYE=-1
    QOP=.FALSE.

    DO IA=IL,IU

      JA=NXX(IA)
      QVV=JA.GT.0
      IF (.NOT. QOP .and. QVV) THEN
    IAII=IA
    ivvv=1
    QOP=.TRUE.
      ENDIF

      IF (QOP) THEN
    IF (QVV) THEN
      ivvv=IA-IAII+1       ! mis-compiled
      write(*,*) ia,ivvv
    ELSE IF (IA+IYYYE<1) THEN
      QOP=.FALSE.
      IYYYE=0
    ENDIF
      ENDIF

    ENDDO

    write(*,*) ivvv==2

  END subroutine


program p
  implicit none
  CALL XXX (1, 3)
end

[Bug fortran/54767] [4.7/4.8 Regression] Incorrect code generated with "-O2 -fcheck=bounds"

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54767

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P4
                 CC|                            |jakub at gcc dot gnu.org

[Bug fortran/54767] [4.7/4.8 Regression] Incorrect code generated with "-O2 -fcheck=bounds"

[mikael at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54767

Mikael Morin <mikael at gcc dot gnu.org> changed:

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

--- Comment #5 from Mikael Morin <mikael at gcc dot gnu.org> 2013-01-14 21:01:34 UTC ---
Workaround: -fno-tree-vrp

[Bug fortran/54767] [4.7/4.8 Regression] Incorrect code generated with "-O2 -fcheck=bounds"

[hjl.tools at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54767

H.J. Lu <hjl.tools at gmail dot com> changed:

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

--- Comment #6 from H.J. Lu <hjl.tools at gmail dot com> 2013-01-14 21:46:17 UTC ---
It is caused by revision 176918:

http://gcc.gnu.org/ml/gcc-cvs/2011-07/msg01186.html

[Bug fortran/54767] [4.7/4.8 Regression] Incorrect code generated with "-O2 -fcheck=bounds"

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54767

--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-01-15 10:47:36 UTC ---
Yeah, indeed.  The bug seems to be in the second vrp pass on xxx function.
iaii_23: [_79, _79]  EQUIVALENCES: { } (0 elements)
looks wrong (iaii_23 is only conditionally equal to _79 (in the first iteration
that sets iaii, i.e. ia = 2, second iteration), it can be the value from
previous cycle too (in the ia = 3, third iteration).
This then leads to
  _35 = prephitmp_50 - iaii_23;
being
_35: [0, 0]
(again, wrong) and that is why we end up with 1 instead of 2 in the second row.

There is:
Visiting PHI node: iaii_23 = PHI <iaii_1(11), prephitmp_50(10)>

    Argument #0 (11 -> 12 not executable)

    Argument #1 (10 -> 12 executable)
        prephitmp_50
        Value: [_79, _79]  EQUIVALENCES: { _79 } (1 elements)
Found new range for iaii_23: [_79, _79]

which is wrong, but not sure if this is the first spot in the dump.  iaii_1
here is only conditionally UNDEFINED, it might be iaii value from previous
iteration too.

[Bug tree-optimization/54767] [4.7/4.8 Regression] Incorrect code generated with "-O2 -fcheck=bounds"

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54767

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
          Component|fortran                     |tree-optimization
         AssignedTo|unassigned at gcc dot       |rguenth at gcc dot gnu.org
                   |gnu.org                     |

--- Comment #8 from Richard Biener <rguenth at gcc dot gnu.org> 2013-01-15 10:49:49 UTC ---
I don't see anything wrong by what VRP does:

Visiting statement:
prephitmp_2 = _79;

Found new range for prephitmp_2: [_79, _79]

Simulating statement (from ssa_edges): iaii_23 = PHI <iaii_1(11),
prephitmp_2(10)>

Visiting PHI node: iaii_23 = PHI <iaii_1(11), prephitmp_2(10)>

    Argument #0 (11 -> 12 executable)
        iaii_1
        Value: [_79, _79]

    Argument #1 (10 -> 12 executable)
        prephitmp_2
        Value: [_79, _79]  EQUIVALENCES: { _79 } (1 elements)
Meeting
  [_79, _79]
and
  [_79, _79]  EQUIVALENCES: { _79 } (1 elements)
to
  [_79, _79]
Found new range for iaii_23: [_79, _79]

Simulating statement (from ssa_edges): _35 = prephitmp_2 - iaii_23;

Visiting statement:
_35 = prephitmp_2 - iaii_23;

Found new range for _35: [0, 0]

Visiting statement:
ivvv.5_36 = _35 + 1;

Found new range for ivvv.5_36: [1, 1]


Now changed behavior is from:

Visiting PHI node: iaii_1 = PHI <iaii_18(D)(4), iaii_48(17)>

    Argument #0 (4 -> 5 executable)
        iaii_18(D)
        Value: UNDEFINED

    Argument #1 (17 -> 5 executable)
        iaii_48
        Value: [_79, _79]
Meeting
  UNDEFINED
and
  [_79, _79]
to
  [_79, _79]
Found new range for iaii_1: [_79, _79]

and this is all in a cycle.


I think this may be mixing _79 from different iterations.  Reduced testcase,
maybe easier to look at:

SUBROUTINE XXX (IL, IU)
  implicit none
  integer, INTENT(IN) :: IL, IU

  integer :: NXX (3) = (/ 0, 1, 2 /)
  integer :: ivvv, ia, ja, iaii
  logical :: qop

  QOP=.FALSE.

  DO IA=IL,IU
    JA=NXX(IA)
    IF (.NOT. QOP .and. JA.GT.0) THEN
      IAII=IA
      QOP=.TRUE.
    ENDIF

    IF (QOP) THEN
      ivvv=IA-IAII+1       ! mis-compiled
    ENDIF
  ENDDO

  IF (ivvv.NE.2) THEN
    call abort
  ENDIF
END subroutine

program p
  implicit none
  CALL XXX (1, 3)
end

[Bug tree-optimization/54767] [4.7/4.8 Regression] Incorrect code generated with "-O2 -fcheck=bounds"

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54767

--- Comment #9 from Richard Biener <rguenth at gcc dot gnu.org> 2013-01-15 11:28:48 UTC ---
Exactly the same issue as PR53465, just instead of an equivalence we have
a symbolic range [_79, _79] which is of course also an "equivalence".

Trunk fails for the reduced testcase if you enlarge the array:

  integer :: NXX (14) = (/ 0, 1, 2, 3, 4, 5, 6, 7, 9, 10, 11, 12, 13, 14 /)

otherwise the loop is unrolled.

[Bug tree-optimization/54767] [4.7/4.8 Regression] Incorrect code generated with "-O2 -fcheck=bounds"

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54767

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P4                          |P2

--- Comment #10 from Richard Biener <rguenth at gcc dot gnu.org> 2013-01-15 11:36:17 UTC ---
Struggling to build a C testcase with the bounds checking made explicit.

[Bug tree-optimization/54767] [4.7/4.8 Regression] Incorrect code generated with "-O2 -fcheck=bounds"

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54767

--- Comment #11 from Richard Biener <rguenth at gcc dot gnu.org> 2013-01-16 13:57:53 UTC ---
Author: rguenth
Date: Wed Jan 16 13:57:48 2013
New Revision: 195238

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=195238
Log:
2013-01-16  Richard Biener  <rguenther@suse.de>

    PR tree-optimization/54767
    PR tree-optimization/53465
    * tree-vrp.c (vrp_meet_1): Revert original fix for PR53465.
    (vrp_visit_phi_node): For PHI arguments coming via backedges
    drop all symbolical range information.
    (execute_vrp): Compute backedges.

    * gfortran.fortran-torture/execute/pr54767.f90: New testcase.

Added:
    trunk/gcc/testsuite/gfortran.fortran-torture/execute/pr54767.f90
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree-vrp.c

[Bug tree-optimization/54767] [4.7 Regression] Incorrect code generated with "-O2 -fcheck=bounds"

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54767

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|                            |4.8.0
            Summary|[4.7/4.8 Regression]        |[4.7 Regression] Incorrect
                   |Incorrect code generated    |code generated with "-O2
                   |with "-O2 -fcheck=bounds"   |-fcheck=bounds"
      Known to fail|4.8.0                       |

--- Comment #12 from Richard Biener <rguenth at gcc dot gnu.org> 2013-01-16 15:23:06 UTC ---
Fixed on trunk sofar.

[Bug tree-optimization/54767] [4.7 Regression] Incorrect code generated with "-O2 -fcheck=bounds"

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54767

--- Comment #13 from Richard Biener <rguenth at gcc dot gnu.org> 2013-02-05 12:54:17 UTC ---
Author: rguenth
Date: Tue Feb  5 12:54:12 2013
New Revision: 195754

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=195754
Log:
2013-02-05  Richard Biener  <rguenther@suse.de>

    PR tree-optimization/54767
    * tree-vrp.c (vrp_visit_phi_node): For PHI arguments coming via
    backedges drop all symbolical range information.
    (execute_vrp): Compute backedges.

    * gfortran.fortran-torture/execute/pr54767.f90: New testcase.

Added:
   
branches/gcc-4_7-branch/gcc/testsuite/gfortran.fortran-torture/execute/pr54767.f90
Modified:
    branches/gcc-4_7-branch/gcc/ChangeLog
    branches/gcc-4_7-branch/gcc/testsuite/ChangeLog
    branches/gcc-4_7-branch/gcc/tree-vrp.c

[Bug tree-optimization/54767] [4.7 Regression] Incorrect code generated with "-O2 -fcheck=bounds"

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54767

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

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

--- Comment #14 from Richard Biener <rguenth at gcc dot gnu.org> 2013-02-05 12:54:41 UTC ---
Fixed.