A couple of platform compatibility issues...

Jeremy Herbison herbie at autobotcity.net
Sun Jan 5 19:54:44 PST 2003


fair enough, I know for instance UW IMAP still uses the -O9 flag, which
AFAIK hasn't done anything since we used egcs-1.2 or so.

My experience with openssl was with the old gcc, so what you're saying could
be pretty relevant. I would just bring it up with the maintainers of the
respective packages rather than this list, unless of course compile errors
are occuring.


"Greg Schafer" <gschafer at zip.com.au> wrote in message
news:20030105234814.GA26602 at tigers-lfs.nsw.bigpond.net.au...
> On Sun, Jan 05, 2003 at 04:08:08PM -0700, Jeremy Herbison wrote:
> > The difference between -O3 and -O2 is mostly that -O3 unrolls all loops
of
> > known length at compile time, resulting in larger but sometimes faster
>
> yes, we all know that :) But that is not the issue. The issue is that
> starting with the gcc-3 series of compilers, code compiled with -O3 is
often
> slower than -O2, not always, but often. gcc hackers acknowledge this. Even
> our very own MSB has proven it. (see blfs-dev archives)
>
> > binaries. The thing is, most well-written software (such as the linux
kernel
> > for instance) tends to use inline functions where necessary anyhow, so
even
> > with -O2 those functions are inlined as the developers intend. My
assumption
> > is that some packages do not use any inline funtions in the source code,
so
> > they often benefit from -O3, and many of these infact use -O3 by default
(I
> > know for a fact that openssl is like this and runs MUCH faster with -O3.
>
> I dispute that. I played around with the openssl speed benchmarking option
> recently and did not see any significant speed increase (using gcc-3.2.1)
>
> > mysql also recommends compiling with -O3). As a rule I therefore
personally
> > compile with -O2 unless a package defaults to -O3.
> >
> > Since we don't recommend anything other than default compile flags
though,
> > lets just not mess with this one k? :)
>
> Nobody is suggesting that. I just mentioned it coz this is a classic
example
> of an older package where the compiler options were composed long before
> gcc-3 came into existence and therefore may not be appropriate anymore.
>
> k? :)
>
> Greg
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