[Bug libstdc++/33488] New: parallel v3: std::accumulate uses accumulator of wrong type

[Bug libstdc++/33488] New: parallel v3: std::accumulate uses accumulator of wrong type

[bangerth at dealii dot org]

This little program
----------------------
#include <numeric>
void f () {
  bool *p, *q;
  std::accumulate (p, q, 0U);
}
----------------------
counts the 'true's in the range [p,q) but this doesn't work in parallel mode, 
the compiler says that it can't resolve a function call. It should as per 
26.4.1.

In particular, the error message is this:

4.3.0/parallel/par_loop.h: In function 'Op
__gnu_parallel::for_each_template_random_access_ed(RandomAccessIterator,
RandomAccessIterator, Op, Fu&, Red, Result, Result&, typename
std::iterator_traits<_Iterator>::difference_type) [with RandomAccessIterator =
bool*, Op = __gnu_parallel::nothing, Fu =
__gnu_parallel::accumulate_selector<bool*>, Red =
__gnu_parallel::accumulate_binop_reduct<std::plus<bool> >, Result = unsigned
int]':
4.3.0/parallel/for_each.h:73:   instantiated from 'UserOp
__gnu_parallel::for_each_template_random_access(InputIterator, InputIterator,
UserOp, Functionality&, Red, Result, Result&, typename
std::iterator_traits<_Iterator>::difference_type, __gnu_parallel::parallelism)
[with InputIterator = bool*, UserOp = __gnu_parallel::nothing, Functionality =
__gnu_parallel::accumulate_selector<bool*>, Red =
__gnu_parallel::accumulate_binop_reduct<std::plus<bool> >, Result = unsigned
int]'
4.3.0/parallel/numeric:103:   instantiated from 'T
std::__parallel::accumulate_switch(_RAIter, _RAIter, T, _BinaryOper,
std::random_access_iterator_tag, __gnu_parallel::parallelism) [with _RAIter =
bool*, T = unsigned int, _BinaryOper = std::plus<bool>]'
4.3.0/parallel/numeric:83:   instantiated from 'T
std::__parallel::accumulate(_IIter, _IIter, T, __gnu_parallel::parallelism)
[with _IIter = bool*, T = unsigned int]'
x.cc:4:   instantiated from here
4.3.0/parallel/par_loop.h:103: error: no match for call to
'(__gnu_parallel::accumulate_binop_reduct<std::plus<bool> >) (unsigned int&,
bool)'
4.3.0/parallel/omp_loop.h: In function 'Op
__gnu_parallel::for_each_template_random_access_omp_loop(RandomAccessIterator,
RandomAccessIterator, Op, Fu&, Red, Result, Result&, typename
std::iterator_traits<_Iterator>::difference_type) [with RandomAccessIterator =
bool*, Op = __gnu_parallel::nothing, Fu =
__gnu_parallel::accumulate_selector<bool*>, Red =
__gnu_parallel::accumulate_binop_reduct<std::plus<bool> >, Result = unsigned
int]':
4.3.0/parallel/for_each.h:75:   instantiated from 'UserOp
__gnu_parallel::for_each_template_random_access(InputIterator, InputIterator,
UserOp, Functionality&, Red, Result, Result&, typename
std::iterator_traits<_Iterator>::difference_type, __gnu_parallel::parallelism)
[with InputIterator = bool*, UserOp = __gnu_parallel::nothing, Functionality =
__gnu_parallel::accumulate_selector<bool*>, Red =
__gnu_parallel::accumulate_binop_reduct<std::plus<bool> >, Result = unsigned
int]'
4.3.0/parallel/numeric:103:   instantiated from 'T
std::__parallel::accumulate_switch(_RAIter, _RAIter, T, _BinaryOper,
std::random_access_iterator_tag, __gnu_parallel::parallelism) [with _RAIter =
bool*, T = unsigned int, _BinaryOper = std::plus<bool>]'
4.3.0/parallel/numeric:83:   instantiated from 'T
std::__parallel::accumulate(_IIter, _IIter, T, __gnu_parallel::parallelism)
[with _IIter = bool*, T = unsigned int]'
x.cc:4:   instantiated from here
4.3.0/parallel/omp_loop.h:78: error: no match for call to
'(__gnu_parallel::accumulate_binop_reduct<std::plus<bool> >) (unsigned int&,
bool)'
4.3.0/parallel/omp_loop.h:86: error: no match for call to
'(__gnu_parallel::accumulate_binop_reduct<std::plus<bool> >) (unsigned int&,
bool)'
4.3.0/parallel/workstealing.h: In function 'Op
__gnu_parallel::for_each_template_random_access_workstealing(RandomAccessIterator,
RandomAccessIterator, Op, Fu&, Red, Result, Result&, typename
std::iterator_traits<_Iterator>::difference_type) [with RandomAccessIterator =
bool*, Op = __gnu_parallel::nothing, Fu =
__gnu_parallel::accumulate_selector<bool*>, Red =
__gnu_parallel::accumulate_binop_reduct<std::plus<bool> >, Result = unsigned
int]':
4.3.0/parallel/for_each.h:79:   instantiated from 'UserOp
__gnu_parallel::for_each_template_random_access(InputIterator, InputIterator,
UserOp, Functionality&, Red, Result, Result&, typename
std::iterator_traits<_Iterator>::difference_type, __gnu_parallel::parallelism)
[with InputIterator = bool*, UserOp = __gnu_parallel::nothing, Functionality =
__gnu_parallel::accumulate_selector<bool*>, Red =
__gnu_parallel::accumulate_binop_reduct<std::plus<bool> >, Result = unsigned
int]'
4.3.0/parallel/numeric:103:   instantiated from 'T
std::__parallel::accumulate_switch(_RAIter, _RAIter, T, _BinaryOper,
std::random_access_iterator_tag, __gnu_parallel::parallelism) [with _RAIter =
bool*, T = unsigned int, _BinaryOper = std::plus<bool>]'
4.3.0/parallel/numeric:83:   instantiated from 'T
std::__parallel::accumulate(_IIter, _IIter, T, __gnu_parallel::parallelism)
[with _IIter = bool*, T = unsigned int]'
x.cc:4:   instantiated from here
4.3.0/parallel/workstealing.h:204: error: no match for call to
'(__gnu_parallel::accumulate_binop_reduct<std::plus<bool> >) (unsigned int&,
bool)'


While 26.4.1 doesn't spell this out explicitly, one can only deduce that
what is mean is that the accumulator variable has the same type as
the initializer, which in the example is 'unsigned int'. Consequently,
the function should do something like
  while (p!=q)
    acc += *p++;
in which case the rhs is converted to int. The current implementation
attempts to use an accumulator of type 'bool'.

W.


-- 
           Summary: parallel v3: std::accumulate uses accumulator of wrong
                    type
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Keywords: rejects-valid
          Severity: normal
          Priority: P3
         Component: libstdc++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: bangerth at dealii dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33488

[Bug libstdc++/33488] parallel v3: std::accumulate uses accumulator of wrong type

[bkoz at gcc dot gnu dot org]

-- 

bkoz at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2007-09-19 17:06:52
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33488

[Bug libstdc++/33488] parallel v3: std::accumulate uses accumulator of wrong type

[singler at ira dot uka dot de]

------- Comment #1 from singler at ira dot uka dot de  2007-09-19 18:34 -------
Instead of std::plus, a functor should be used that accepts two different types
for LHS and RHS, Result and
std::iterator_traits<RandomAccessIterator>::value_type, respectively.


-- 

singler at ira dot uka dot de changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |singler at ira dot uka dot
                   |                            |de


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33488

[Bug libstdc++/33488] parallel v3: std::accumulate uses accumulator of wrong type

[bangerth at dealii dot org]

------- Comment #2 from bangerth at dealii dot org  2007-09-19 19:04 -------
As I've said in the other report, I believe you shouldn't rely on the
existence of iterator_traits for the iterator type. You should use the
return type of dereferencing the iterator.

W.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33488

[Bug libstdc++/33488] parallel v3: std::accumulate uses accumulator of wrong type

[bkoz at gcc dot gnu dot org]

------- Comment #3 from bkoz at gcc dot gnu dot org  2007-10-09 20:52 -------

Wolfgang, I think some of this is fixed, and for the rest (comment #2), there
is another bug report (33490) that is focused just on that.

Is my understanding correct?

-benjamin


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33488

[Bug libstdc++/33488] parallel v3: std::accumulate uses accumulator of wrong type

[bangerth at dealii dot org]

------- Comment #5 from bangerth at dealii dot org  2007-10-10 01:13 -------
I meant to close this one, as it appears fixed.


-- 

bangerth at dealii dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33488

[Bug libstdc++/33488] parallel v3: std::accumulate uses accumulator of wrong type

[bangerth at dealii dot org]

------- Comment #4 from bangerth at dealii dot org  2007-10-10 01:12 -------
(In reply to comment #3)
> Wolfgang, I think some of this is fixed, and for the rest (comment #2), there
> is another bug report (33490) that is focused just on that.
> 
> Is my understanding correct?

I believe so. In any case, by adding a few std:: to my call (which works
around PR 33486) I can now build my code. I'll see if it also works...

Thanks for your prompt work on all this!

Best
 W.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33488