Re: program executin times differ between gcc versions

[Tim Prince <tprince at computer dot org>]

Joel Dice wrote:
> On Thu, 1 Nov 2007, Paul Moore wrote:
>
> > Dear List,
>
> <snip>
>
> > Using optimization flags is not possible due to the fact that large
> > parts of the application failed in -O test runs and would need to be
> > fixed/tested extensively first. Profiling with -pg/gprof has not been
> > produced usable results as shared libraries are not being tracked.
>
> In my experience, OProfile (oprofile.sourceforge.net) is much better 
> than gprof at revealing the hotspots in my programs, including time 
> spent in shared libraries.  I strongly recommend it.
When hotspots occur in libraries, gprof is satisfactory only with static 
linking.  Library questions seem unlikely to be relevant in this thread.
> OTOH, I would worry more about correctness than performance at this 
> point if the code breaks with optimization turned on.
That's for sure. gcc is unlikely to break reliable code with 
optimization, unless -ffast-math is set.


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