speed of g++ v3

speed of g++ v3

[Wei Qin]

Hi,

	I compile my code with g++ v3.0.4 with -O3. But the code is
running 20% slower than the code compiled with g++ v2.96 -O3.
	Why is there such huge speed difference and is there any way for
me to regain speed?

thanks in advance,

Wei

Re: speed of g++ v3

[Oscar Fuentes]

Wei Qin <wqin@EE.Princeton.EDU> writes:

> Hi,
> 
> 	I compile my code with g++ v3.0.4 with -O3. But the code is
> running 20% slower than the code compiled with g++ v2.96 -O3.
> 	Why is there such huge speed difference and is there any way for
> me to regain speed?

IIRC, gcc 3.0.x have some issues with -O3 and inlining. Compile your
code with -O2 and the performance will improve. However, there are
certain cases where gcc 3.0 performance is worse than gcc 2.95 no
matter what optimization level you use for gcc 3.0.x. Those cases are
rare.

-- 
Oscar

Re: speed of g++ v3

[Wei Qin]

Thanks for the reply. Now I try with -O2, but see no difference.
The code is as slow. My platform is x86 linux.

Wei


> Wei Qin <wqin@EE.Princeton.EDU> writes:
>
> > Hi,
> >
> > 	I compile my code with g++ v3.0.4 with -O3. But the code is
> > running 20% slower than the code compiled with g++ v2.96 -O3.
> > 	Why is there such huge speed difference and is there any way for
> > me to regain speed?
>
> IIRC, gcc 3.0.x have some issues with -O3 and inlining. Compile your
> code with -O2 and the performance will improve. However, there are
> certain cases where gcc 3.0 performance is worse than gcc 2.95 no
> matter what optimization level you use for gcc 3.0.x. Those cases are
> rare.
>
> --
> Oscar
>
>