Bug#102193: gcc-3.0: compiled code with gcc 3.0 is slow and big

[Daniel Jacobowitz <dan@debian.org>]

On Sat, Jan 05, 2002 at 02:17:21AM +0100, Morten Brix Pedersen wrote:
> Package: gcc-3.0
> Version: 1:3.0.3-1
> 
> I don't know if it's valid for this bug report, but all code I have tried is
> slower in g++ 3, here's a simple example:

There's lots of reasons for this.  The biggest one is that the
conforming libstdc++ v3.0 is muchlarger and more complicated.

> (numbers first, code in the bottom)
> mbp:~$ g++ benchmark.cpp ; ls -l a.out ; time a.out ; g++-3.0 benchmark.cpp
> ; ls -l a.out ; time a.out
> -rwxr-xr-x    1 mbp      mbp         42840  5 jan 02:14 a.out*
> 
> real    0m13.542s
> user    0m6.200s
> sys     0m0.220s
> -rwxr-xr-x    1 mbp      mbp         38016  5 jan 02:14 a.out*
> 
> real    0m20.882s
> user    0m9.950s
> sys     0m0.080s

The default for G++ is, and has always been, to compile without
optimization.  Try with -O2 (or -Os if size is your concern) (or -O3 in
some cases).  It may still be slower, but probably much less so.

-- 
Daniel Jacobowitz                           Carnegie Mellon University
MontaVista Software                         Debian GNU/Linux Developer