Re: libstdc++/7076: iostreams very slow compared with earlier gcc versions

Re: libstdc++/7076: iostreams very slow compared with earlier gcc versions

[bkoz]

Synopsis: iostreams very slow compared with earlier gcc versions

Responsible-Changed-From-To: unassigned->bkoz
Responsible-Changed-By: bkoz
Responsible-Changed-When: Thu Feb 20 18:28:44 2003
Responsible-Changed-Why:
    Mine.
State-Changed-From-To: open->feedback
State-Changed-By: bkoz
State-Changed-When: Thu Feb 20 18:28:44 2003
State-Changed-Why:
    This specific example has been fixed in gcc-3.4. I hope to back port these fixes into the gcc-3.3 and gcc-3.2 compilers in the near future.
    
    Performance improvement, and optimization work, continues. Please be patient.
    
    -benjamin

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=7076

Re: libstdc++/7076: iostreams very slow compared with earlier gcc versions

[Joe Buck]

The following reply was made to PR libstdc++/7076; it has been noted by GNATS.

From: Joe Buck <jbuck@synopsys.com>
To: gcc-gnats@gcc.gnu.org, gcc-bugs@gcc.gnu.org, morten@wtf.dk
Cc:  
Subject: Re: libstdc++/7076: iostreams very slow compared with earlier gcc
 versions
Date: Thu, 06 Feb 2003 18:48:06 -0800

 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=7076
 
 It seems that snprintf is being called now, while it wasn't in libstdc++ 
 version 2,
 making things about 8x to more than 20x slower depending on details.
 
 

libstdc++/7076: iostreams very slow compared with earlier gcc versions

[morten]

>Number:         7076
>Category:       libstdc++
>Synopsis:       iostreams very slow compared with earlier gcc versions
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Jun 19 05:46:00 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator:     Morten Brix Pedersen
>Release:        gcc-3.1
>Organization:
>Environment:

>Description:
'cout' is very slow in g++ 3.1 compared with g++ 2.95.4 (Debian prerelease).

My results with 'time', gcc 2.95.4:

mbp:~/testcode$ time ./stream > /dev/null

real    0m1.886s
user    0m0.940s
sys     0m0.000s

My results with gcc 3.1.0:

mbp:~/testcode$ time ./stream-3.1 > /dev/null

real    0m37.636s
user    0m18.520s
sys     0m0.010s


>How-To-Repeat:
#include <iostream>

int main(int argc, char** argv) 
{
    for(int i=0; i< 1500000; i++)
        std::cout << i << '\n';
} 
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted: