From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugs-return-405400-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 13153 invoked by alias); 1 Nov 2012 19:34:39 -0000
Received: (qmail 6732 invoked by uid 48); 1 Nov 2012 19:34:24 -0000
From: "chri.snell at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/55169] New: std::discrete_distribution::operator(generator&) makes unnecessary copy of parameter vector
Date: Thu, 01 Nov 2012 19:34:00 -0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: libstdc++
X-Bugzilla-Keywords:
X-Bugzilla-Severity: normal
X-Bugzilla-Who: chri.snell at gmail dot com
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Changed-Fields:
Message-ID: <bug-55169-4@http.gcc.gnu.org/bugzilla/>
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
Content-Type: text/plain; charset="UTF-8"
MIME-Version: 1.0
Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm
Precedence: bulk
List-Id: <gcc-bugs.gcc.gnu.org>
List-Archive: <http://gcc.gnu.org/ml/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-help@gcc.gnu.org>
Sender: gcc-bugs-owner@gcc.gnu.org
X-SW-Source: 2012-11/txt/msg00062.txt.bz2


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.