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

["burnus at gcc dot gnu.org" <gcc-bugzilla@gcc.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
}