[Bug c/96549] New: Wrong evaluation of a comparison between long & short

[Bug c/96549] New: Wrong evaluation of a comparison between long & short

[zhige.yu18 at imperial dot ac.uk]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96549

            Bug ID: 96549
           Summary: Wrong evaluation of a comparison between long & short
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zhige.yu18 at imperial dot ac.uk
  Target Milestone: ---

The following code snippet:


#include <stdio.h>
long c = -1L;
long b = 0L;
int main(void) {
  if (3L > (short) ((c ^= (b = 1L)) * 3L))
    printf("hello ");
  printf("world!\n");
}


> $ /usr/gcc-trunk/bin/gcc -O0 bug.c -o a.out; ./a.out 
> world!
> $ clang-10 -O0 bug.c -o a.out; ./a.out
> hello world!


When compiled with -O0/1/2/3, GCC omits the then-branch of the if-statement,
and prints "world!" only. This bug can be found in GCC-10.2.0 and GCC-11.0.0
20200804 (experimental). GCC-9.3.0 and earlier versions of GCC do not have this
bug.

[Bug c/96549] [10/11 Regression] Wrong evaluation of a comparison between long & short

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96549

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
                 CC|                            |jakub at gcc dot gnu.org,
                   |                            |marxin at gcc dot gnu.org
   Last reconfirmed|                            |2020-08-10
            Summary|Wrong evaluation of a       |[10/11 Regression] Wrong
                   |comparison between long &   |evaluation of a comparison
                   |short                       |between long & short

--- Comment #1 from Martin Liška <marxin at gcc dot gnu.org> ---
Thank you for the report!

Slighly modified test-case:

long c = -1L;
long b = 0L;
int main(void) {
  if (3L > (short) ((c ^= (b = 1L)) * 3L))
    return 0;
  __builtin_abort ();
}

Started with r10-7921-gbca558de2a24b2a7.

[Bug middle-end/96549] Wrong evaluation of a comparison between long & short

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96549

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[10/11 Regression] Wrong    |Wrong evaluation of a
                   |evaluation of a comparison  |comparison between long &
                   |between long & short        |short
           Keywords|                            |wrong-code
             Status|NEW                         |UNCONFIRMED
     Ever confirmed|1                           |0
          Component|c                           |middle-end
   Last reconfirmed|2020-08-10 00:00:00         |

[Bug middle-end/96549] [10/11 Regression] Wrong evaluation of a comparison between long & short

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96549

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2020-08-10
     Ever confirmed|0                           |1
            Summary|Wrong evaluation of a       |[10/11 Regression] Wrong
                   |comparison between long &   |evaluation of a comparison
                   |short                       |between long & short
   Target Milestone|---                         |10.3
             Status|UNCONFIRMED                 |NEW

[Bug middle-end/96549] [10/11 Regression] Wrong evaluation of a comparison between long & short

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96549

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

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

[Bug middle-end/96549] [10/11 Regression] Wrong evaluation of a comparison between long & short

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96549

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 49033
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=49033&action=edit
gcc11-pr96549.patch

Untested fix.

[Bug middle-end/96549] [10/11 Regression] Wrong evaluation of a comparison between long & short

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96549

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:6b815e113c9aec397a86d7194f66455eb189cc7a

commit r11-2646-g6b815e113c9aec397a86d7194f66455eb189cc7a
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Aug 11 13:46:14 2020 +0200

    tree: Fix up get_narrower [PR96549]

    My changes to get_narrower to support COMPOUND_EXPRs apparently
    used a wrong type for the COMPOUND_EXPRs, while e.g. the rhs
    type was unsigned short, the COMPOUND_EXPR got int type as that was the
    original type of op.  The type of COMPOUND_EXPR should be always the type
    of the rhs.

    2020-08-11  Jakub Jelinek  <jakub@redhat.com>

            PR c/96549
            * tree.c (get_narrower): Use TREE_TYPE (ret) instead of
            TREE_TYPE (win) for COMPOUND_EXPRs.

            * gcc.c-torture/execute/pr96549.c: New test.

[Bug middle-end/96549] [10 Regression] Wrong evaluation of a comparison between long & short

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96549

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[10/11 Regression] Wrong    |[10 Regression] Wrong
                   |evaluation of a comparison  |evaluation of a comparison
                   |between long & short        |between long & short

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Fixed on the trunk so far.

[Bug middle-end/96549] [10 Regression] Wrong evaluation of a comparison between long & short

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96549

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2

[Bug middle-end/96549] [10 Regression] Wrong evaluation of a comparison between long & short

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96549

--- Comment #5 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-10 branch has been updated by Jakub Jelinek
<jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:db00336a49707327552e678b59da8e85384bdae6

commit r10-8665-gdb00336a49707327552e678b59da8e85384bdae6
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Aug 11 13:46:14 2020 +0200

    tree: Fix up get_narrower [PR96549]

    My changes to get_narrower to support COMPOUND_EXPRs apparently
    used a wrong type for the COMPOUND_EXPRs, while e.g. the rhs
    type was unsigned short, the COMPOUND_EXPR got int type as that was the
    original type of op.  The type of COMPOUND_EXPR should be always the type
    of the rhs.

    2020-08-11  Jakub Jelinek  <jakub@redhat.com>

            PR c/96549
            * tree.c (get_narrower): Use TREE_TYPE (ret) instead of
            TREE_TYPE (win) for COMPOUND_EXPRs.

            * gcc.c-torture/execute/pr96549.c: New test.

    (cherry picked from commit 6b815e113c9aec397a86d7194f66455eb189cc7a)

[Bug middle-end/96549] [10 Regression] Wrong evaluation of a comparison between long & short

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96549

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

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

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Fixed for 10.3+ too.