[Bug c/69389] New: bit field incompatible with OpenMP atomic update

[weeks at iastate dot edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69389

            Bug ID: 69389
           Summary: bit field incompatible with OpenMP atomic update
           Product: gcc
           Version: 5.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: weeks at iastate dot edu
  Target Milestone: ---

gcc 5.2.0 cannot utilize bit fields within an OpenMP atomic update.

Consider the following code (atomic_bitwise_or.c):

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#include <stdio.h>

struct BGZF {
    unsigned errcode:16, is_write:2, is_be:2;
};

int main(void) {
   struct BGZF A = {0};

#pragma omp parallel
#pragma omp master
#pragma omp atomic update
   A.errcode |= 1;

   if (A.errcode != 1) {
       printf("failed\n");
       return 1;
   } else {
       printf("success\n");
       return 0;
   }
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

When compiled without OpenMP, it produces the expected result:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
$ gcc atomic_bitwise_or.c
$ ./a.out
success
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

However, it fails to compile when OpenMP is enabled:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
$ gcc -fopenmp atomic_bitwise_or.c
atomic_bitwise_or.c: In function 'main':
atomic_bitwise_or.c:13:4: error: cannot take address of bit-field 'errcode'
    A.errcode |= 1;
    ^
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

gcc version info:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
$ gcc -v
Using built-in specs.
COLLECT_GCC=/opt/gcc/5.2.0/bin/../snos/bin/gcc
COLLECT_LTO_WRAPPER=/opt/gcc/5.2.0/snos/libexec/gcc/x86_64-suse-linux/5.2.0/lto-wrapper
Target: x86_64-suse-linux
Configured with: ../cray-gcc-5.2.0/configure --prefix=/opt/gcc/5.2.0/snos
--disable-nls --libdir=/opt/gcc/5.2.0/snos/lib --enable-languages=c,c++,fortran
--with-gxx-include-dir=/opt/gcc/5.2.0/snos/include/g++
--with-slibdir=/opt/gcc/5.2.0/snos/lib --with-system-zlib --enable-shared
--enable-__cxa_atexit --build=x86_64-suse-linux --with-ppl --with-cloog
Thread model: posix
gcc version 5.2.0 20150716 (Cray Inc.) (GCC)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~