Re: C++: EGCS perf. vs GCC

[Alex Maranda <amaranda at spider dot com>]

> > Date: Mon, 7 Dec 1998 13:34:14 +0000 (GMT)
> > From: Alex Maranda <amaranda@spider.com>
> 
> > Multiple runs were performed for each combination, to average out
> > the variations induced by the OS scheduling The best result was
> > kept, as the standard deviation was very small.
> 
> I wouldn't use the term `average' to describe the selection of the
> `best' time.  When given, 10 11 12, average means 11, and `best' means
> 10.  It is confusing if you use both words.
You are definitely right, it is poor wording, but hopefully not procedure
:-) What I actually meant was: Initially I wanted to present the results
in a nice statistical form, averaging them and presenting also the
standard deviation. as the latter was very small (under 0.5%), I changed
my mind and chose the best result in each case - I suppose it is even more
relevant as I was trying to measure the compiler's instruction scheduler
performance, without taking into account the non-determinism introduced by
the OS task switching.

> 
> > -O3 -fno-rtti -mcpu=i386         46636    100          781263    100
> > -O3 -fno-rtti -mcpu=i486         50200    107.6        716301    91.6
> > -O3 -fno-rtti -mcpu=pentium      47392    101.6        777032    99.4
> > -O3 -fno-rtti -mcpu=pentiumpro   47344    101.5        725632    92.8
> 
> I'd try -fno-excetions, and -O2 and maybe even -O1.
I said I'm not using exceptions, I guess what you're implying is that even
so there is a constant overhead in the generated code which can be
eliminated by -fno-exceptions. I'll give it a try. The latter suggestions
don't make a lot of sense to me, each -Ox turns on an increasingly large
-f<stuff> pack (you can see it when compiling with gcc -v -Q -O<optlevel>)
and is my understanding that a greater <optlevel> is meant for speed. BTW,
did you know there are undocumented levels -O4...-O8?

Cheers,
Alex