[Bug libstdc++/55169] New: std::discrete_distribution::operator(generator&) makes unnecessary copy of parameter vector

[Bug libstdc++/55169] New: std::discrete_distribution::operator(generator&) makes unnecessary copy of parameter vector

[chri.snell at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55169

             Bug #: 55169
           Summary: std::discrete_distribution::operator(generator&) makes
                    unnecessary copy of parameter vector
    Classification: Unclassified
           Product: gcc
           Version: 4.7.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: chri.snell@gmail.com


Created attachment 28592
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=28592
demonstration of slow std::discrete_distribution in GCC

std::discrete_distribution::operator()(generator&) is significantly slower than
directly calling operator()(generator&, const param_type&), which it delegates
to.  This is because, on random.h:4805, this->param() returns a copy rather
than a const reference.

The attached file is a simple test demonstrating this inefficient behaviour.

[Bug libstdc++/55169] std::discrete_distribution::operator(generator&) makes unnecessary copy of parameter vector

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55169

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2012-11-01
         AssignedTo|unassigned at gcc dot       |paolo.carlini at oracle dot
                   |gnu.org                     |com
     Ever Confirmed|0                           |1

--- Comment #1 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-11-01 19:38:51 UTC ---
Yes, seems easy to fix.

[Bug libstdc++/55169] std::discrete_distribution::operator(generator&) makes unnecessary copy of parameter vector

[chri.snell at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55169

--- Comment #2 from Chris Nell <chri.snell at gmail dot com> 2012-11-01 19:48:43 UTC ---
After a bit more poking, it appears that param() returns a copy (not a const
reference) for all distributions, not just discrete_distribution.  As such, it
might we worth looking into whether other implementations of
operator(generator&) suffer from the same bug.

[Bug libstdc++/55169] std::discrete_distribution::operator(generator&) makes unnecessary copy of parameter vector

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55169

--- Comment #3 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-11-01 19:59:48 UTC ---
Of course, of course. But in 4_7-branch we are going to change only the three
distributions using std::vectors

[Bug libstdc++/55169] std::discrete_distribution::operator(generator&) makes unnecessary copy of parameter vector

[paolo at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55169

--- Comment #4 from paolo at gcc dot gnu.org <paolo at gcc dot gnu.org> 2012-11-02 10:45:40 UTC ---
Author: paolo
Date: Fri Nov  2 10:45:25 2012
New Revision: 193092

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=193092
Log:
2012-11-02  Paolo Carlini  <paolo.carlini@oracle.com>

    PR libstdc++/55169
    * include/bits/random.h: Remove all uses of param().
    (chi_squared_distribution<>::__generate_impl(_ForwardIterator,
    _ForwardIterator, _UniformRandomNumberGenerator&): Declare
    * include/bits/random.tcc: ... define.
    * include/ext/random: Remove all uses of param().

Modified:
    trunk/libstdc++-v3/ChangeLog
    trunk/libstdc++-v3/include/bits/random.h
    trunk/libstdc++-v3/include/bits/random.tcc
    trunk/libstdc++-v3/include/ext/random

[Bug libstdc++/55169] std::discrete_distribution::operator(generator&) makes unnecessary copy of parameter vector

[paolo at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55169

--- Comment #5 from paolo at gcc dot gnu.org <paolo at gcc dot gnu.org> 2012-11-02 11:18:22 UTC ---
Author: paolo
Date: Fri Nov  2 11:18:13 2012
New Revision: 193093

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=193093
Log:
2012-11-02  Paolo Carlini  <paolo.carlini@oracle.com>

    PR libstdc++/55169
    * include/bits/random.h: Remove all uses of param().

Modified:
    branches/gcc-4_7-branch/libstdc++-v3/ChangeLog
    branches/gcc-4_7-branch/libstdc++-v3/include/bits/random.h

[Bug libstdc++/55169] std::discrete_distribution::operator(generator&) makes unnecessary copy of parameter vector

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55169

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.7.3

--- Comment #6 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-11-02 11:19:37 UTC ---
Fixed mainline and 4.7.3.