[Bug c++/54729] New: __compare_and_swap does not return on all paths

[cvoica at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54729

             Bug #: 54729
           Summary: __compare_and_swap does not return on all paths
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: cvoica@gmail.com


I had wrongly used the __compare_and_swap with a "volatile bool" variable and
without the _GLIBCXX_DEBUG and _GLIBCXX_PARALLEL being defined.

Analyzing the function I would like to suggest to return false before leaving
the function, otherwise the user belive that the CAS was successful while he is
actually using it incorrectly.

Possible solution is something like this.

  template<typename _Tp>
  inline bool
  __compare_and_swap(volatile _Tp* __ptr, _Tp __comparand, _Tp __replacement)
  {
    if (sizeof(_Tp) == sizeof(int32_t))
      return __compare_and_swap_32((volatile int32_t*) __ptr,
                                   (int32_t)__comparand,
                                   (int32_t)__replacement);
    else if (sizeof(_Tp) == sizeof(int64_t))
      return __compare_and_swap_64((volatile int64_t*) __ptr,
                                   (int64_t)__comparand,
                                   (int64_t)__replacement);
    else
      _GLIBCXX_PARALLEL_ASSERT(false);

    return false;
  }