[Bug c++/106448] New: [OpenMP] atomic compare – g++ wrongly accepts parenthesized condition

[Bug c++/106448] New: [OpenMP] atomic compare – g++ wrongly accepts parenthesized condition

[burnus at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106448

            Bug ID: 106448
           Summary: [OpenMP] atomic compare – g++ wrongly accepts
                    parenthesized condition
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Keywords: accepts-invalid, diagnostic, openmp
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: burnus at gcc dot gnu.org
                CC: jakub at gcc dot gnu.org
  Target Milestone: ---

The following code is rejected by gcc - but accepted by g++.
(Found via OpenMP examples Issue #291.)

OpenMP permits:
   x = expr ordop x ? expr : x;
   x = x ordop expr ? expr : x;21
   x = x == e ? d : x;

If one now parenthesis the condition, gcc rightly complains:

  error: invalid form of ‘#pragma omp atomic’ before ‘;’ token
    7 |   x = (expr > x) ? expr : x;
      |                            ^

However, g++ accepts that version without an error.


Note that g++ rejects the reverse version already:
 error: invalid form of ‘#pragma omp atomic’ before ‘(’ token
   10 |   x = (x < expr) ? expr : x;  // Rejected by g++ and gcc
      |       ^

--------------
int x, expr;

void
foo (void)
{
  #pragma omp atomic compare
  x = (expr > x) ? expr : x;  // Accepted by g++ [BUG!], rejected by gcc

  #pragma omp atomic compare
  x = (x < expr) ? expr : x;  // Rejected by g++ and gcc

  #pragma omp atomic compare
  x = (x == expr) ? expr : x;  // Rejected by g++ and gcc
}

[Bug c++/106448] [OpenMP] atomic compare – g++ wrongly accepts parenthesized condition

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106448

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
int x;

void
bar (void)
{
  #pragma omp atomic
  x = (x + 6);
  #pragma omp atomic
  x = (x * 6);
}

is incorrectly accepted in C and rejected in C++.

[Bug c++/106448] [OpenMP] atomic compare – g++ wrongly accepts parenthesized condition

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106448

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #1)
> is incorrectly accepted in C and rejected in C++.

I mean is correctly rejected in C++.

[Bug c++/106448] [OpenMP] atomic compare – g++ wrongly accepts parenthesized condition

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106448

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2022-07-28
           Assignee|unassigned at gcc dot gnu.org      |jakub at gcc dot gnu.org

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 53372
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53372&action=edit
gcc13-pr106448.patch

Untested fix (so far just for the C++ FE problem).

[Bug c++/106448] [OpenMP] atomic compare – g++ wrongly accepts parenthesized condition

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106448

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
The C FE issue moved to PR106464.

[Bug c++/106448] [OpenMP] atomic compare – g++ wrongly accepts parenthesized condition

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106448

--- Comment #5 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:2dcceedb3c121f2498ae58d8414e7b8454b7bf55

commit r13-1888-g2dcceedb3c121f2498ae58d8414e7b8454b7bf55
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Fri Jul 29 09:59:19 2022 +0200

    openmp: Reject invalid forms of C++ #pragma omp atomic compare [PR106448]

    The allowed syntaxes of atomic compare don't allow ()s around the condition
    of ?:, but we were accepting it in one case for C++.

    Fixed thusly.

    2022-07-29  Jakub Jelinek  <jakub@redhat.com>

            PR c++/106448
            * parser.cc (cp_parser_omp_atomic): For simple cast followed by
            CPP_QUERY token, don't try cp_parser_binary_operation if compare
            is true.

            * c-c++-common/gomp/atomic-32.c: New test.

[Bug c++/106448] [OpenMP] atomic compare – g++ wrongly accepts parenthesized condition

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106448

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

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

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Fixed on the trunk.  Not going to be backported, as it is accepts-invalid.