[Bug c/51360] New: spurious unused-but-set-variable warning for var used in OpenMP pragma

[Bug c/51360] New: spurious unused-but-set-variable warning for var used in OpenMP pragma

[kmccarty at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51360

             Bug #: 51360
           Summary: spurious unused-but-set-variable warning for var used
                    in OpenMP pragma
    Classification: Unclassified
           Product: gcc
           Version: 4.6.2
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: kmccarty@gmail.com


Hi,

gcc 4.6.2 produces a spurious unused variable warning for the following code. 
The variable 'num' is used in setting the number of threads within an OpenMP
parallel region but the compiler does not realize this.

The warning is:

% /usr/local/gcc46/bin/gcc -Wall -fopenmp omp.c
omp.c: In function ‘main’:
omp.c:12:12: warning: variable ‘num’ set but not used
[-Wunused-but-set-variable]

% cat omp.c
#include <omp.h>
#include <stdlib.h>
#include <stdio.h>

// Compile with: gcc -Wall -fopenmp omp.c
// Run with:     ./a.out <num_threads> e.g. "./a.out 4"

int main(int argc, char ** argv) {
    if (argc != 2) return EXIT_FAILURE;

    int vec[20] = { 0, };
    int i, num = atoi(argv[1]);

    #pragma omp parallel for num_threads(num)
    for (i = 0; i < 20; ++i) {
        #pragma omp critical
        {
            printf("thread %d\n", (int)omp_get_thread_num());
            fflush(stdout);
        }

        vec[i] *= 5;
    }

    return 0;
}


Running the generated binary (RHEL 4 update 6 on x86_64) with a specified value
for argv[1] indicates that the value of 'num' is being used as expected.

gcc 4.2.4 and 4.4.3 do not warn with the same compiler flags.

Thanks,
- Kevin B. McCarty

[Bug c/51360] [4.6/4.7 Regression] spurious unused-but-set-variable warning for var used in OpenMP pragma

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51360

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
           Keywords|                            |diagnostic
   Last reconfirmed|                            |2011-12-14
     Ever Confirmed|0                           |1
            Summary|spurious                    |[4.6/4.7 Regression]
                   |unused-but-set-variable     |spurious
                   |warning for var used in     |unused-but-set-variable
                   |OpenMP pragma               |warning for var used in
                   |                            |OpenMP pragma
   Target Milestone|---                         |4.6.3

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> 2011-12-14 23:46:31 UTC ---
Confirmed.

[Bug c/51360] [4.6/4.7 Regression] spurious unused-but-set-variable warning for var used in OpenMP pragma

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51360

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

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

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-12-15 13:27:29 UTC ---
Created attachment 26101
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=26101
gcc47-pr51360.patch

Untested fix.

[Bug c/51360] [4.6/4.7 Regression] spurious unused-but-set-variable warning for var used in OpenMP pragma

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51360

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-12-15 17:29:29 UTC ---
Author: jakub
Date: Thu Dec 15 17:29:25 2011
New Revision: 182381

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=182381
Log:
    PR c/51360
    * c-parser.c (c_parser_omp_clause_num_threads,
    c_parser_omp_clause_schedule): Call mark_exp_read.

    * semantics.c (finish_omp_clauses): For OMP_CLAUSE_NUM_THREADS_EXPR
    and OMP_CLAUSE_SCHEDULE_CHUNK_EXPR call mark_rvalue_use.

    * c-c++-common/gomp/pr51360.c: New test.
    * g++.dg/gomp/pr51360.C: New test.

Added:
    trunk/gcc/testsuite/c-c++-common/gomp/pr51360.c
    trunk/gcc/testsuite/g++.dg/gomp/pr51360.C
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/c-parser.c
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/semantics.c
    trunk/gcc/testsuite/ChangeLog

[Bug c/51360] [4.6 Regression] spurious unused-but-set-variable warning for var used in OpenMP pragma

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51360

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[4.6/4.7 Regression]        |[4.6 Regression] spurious
                   |spurious                    |unused-but-set-variable
                   |unused-but-set-variable     |warning for var used in
                   |warning for var used in     |OpenMP pragma
                   |OpenMP pragma               |

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-12-15 20:51:03 UTC ---
Fixed on the trunk so far.

[Bug c/51360] [4.6 Regression] spurious unused-but-set-variable warning for var used in OpenMP pragma

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51360

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> 2012-02-09 17:15:39 UTC ---
Author: jakub
Date: Thu Feb  9 17:15:29 2012
New Revision: 184049

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=184049
Log:
    Backported from mainline
    2011-12-15  Jakub Jelinek  <jakub@redhat.com>

    PR c/51360
    * c-parser.c (c_parser_omp_clause_num_threads,
    c_parser_omp_clause_schedule): Call mark_exp_read.

    * semantics.c (finish_omp_clauses): For OMP_CLAUSE_NUM_THREADS_EXPR
    and OMP_CLAUSE_SCHEDULE_CHUNK_EXPR call mark_rvalue_use.

    * gcc.dg/gomp/pr51360.c: New test.
    * g++.dg/gomp/pr51360.C: New test.
    * g++.dg/gomp/pr51360-2.C: New test.

Added:
    branches/gcc-4_6-branch/gcc/testsuite/g++.dg/gomp/pr51360-2.C
    branches/gcc-4_6-branch/gcc/testsuite/g++.dg/gomp/pr51360.C
    branches/gcc-4_6-branch/gcc/testsuite/gcc.dg/gomp/pr51360.c
Modified:
    branches/gcc-4_6-branch/gcc/ChangeLog
    branches/gcc-4_6-branch/gcc/c-parser.c
    branches/gcc-4_6-branch/gcc/cp/ChangeLog
    branches/gcc-4_6-branch/gcc/cp/semantics.c
    branches/gcc-4_6-branch/gcc/testsuite/ChangeLog

[Bug c/51360] [4.6 Regression] spurious unused-but-set-variable warning for var used in OpenMP pragma

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51360

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> 2012-02-09 17:39:48 UTC ---
Fixed.