Using throw(): continue with "simple code"...

["Maxim Dementiev" <max at e-soft dot ru>]

-----Original Message-----
From: Joe Buck [mailto:jbuck@synopsys.com]
Sent: Thursday, November 29, 2001 8:35 PM
To: Maxim Dementiev
Cc: gcc@gcc.gnu.org
Subject: Re: Using throw(): to use or not to use?
>
> This seems surprising, but you haven't specified what platform you are
> using and you haven't provided sample code, so it's hard to figure out
> why you are seeing a slowdown.
>
> Specififying throw() should, if anything, make it possible to generate
> slightly faster code.  If the code is instead slower, I'd call it a bug,
> but we'd need a full bug report.

Oh, I'm sorry!

Linux 2.2.19 (Slackware 8.0), Intel Celeron (Mendocino).
gcc 3.0.2 was builded with gcc 2.95.3 (from slackware).
Here is "simple code" (this is modification of
http://cpp3.virtualave.net/cpp3comm/043).
This code with "throw()". Just cancel out "throw()" and try again with same
argument.


-=-=-=-=-=-=-=-=- start -=-=-=-=-=-=-=-=-

#include <stdio.h>
#include <stdlib.h>
#include <time.h>


long Var=0, Count=0;


void some_func() throw();


class A
{
public:
    A() throw();
    ~A() throw();
};


void ACon() throw();
void ADes() throw();
void f1() throw();
void f2() throw();


int main( int argc, char** argv )
{
    if (argc>1) Count=atol(argv[1]);

    clock_t c1,c2;
    {
        c1=clock();

        for( long i=0; i<Count; i++ )
            for( long j=0; j<1000000; j++ )
                f1();

        c2=clock();

        printf( "f1(): %ld mlns calls per %.1f sec\n",
                Count,
                double(c2-c1)/CLOCKS_PER_SEC );
    }

    {
        c1=clock();

        for( long i=0; i<Count; i++ )
            for( long j=0; j<1000000; j++ )
                f2();

        c2=clock();

        printf( "f2(): %ld mlns calls per %.1f sec\n",
                Count,
                double(c2-c1)/CLOCKS_PER_SEC );
    }

    return 0;
}


void f1() throw()
{
    A a;
}


void f2() throw()
{
    ACon();
    ADes();
}


A::A() throw()
{
    some_func();
}


A::~A() throw()
{
    some_func();
}


void ACon() throw()
{
    some_func();
}


void ADes() throw()
{
    some_func();
}


void some_func() throw()
{
    Var++;
}

-=-=-=-=-=-=-=-=- end -=-=-=-=-=-=-=-=-

My test results (with 500 iteration X 1 mlns):
-----------------------------------------------------
                   -O0       -O1       -O2
-----------------------------------------------------
with
throw()  53.2/45.2  50.6/42.0  45.5/43.1
-----------------------------------------------------
without
throw()  50.9/45.5  48.8/41.2  44.4/40.8
-----------------------------------------------------

Maxim Dementiev