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Subject: Re: [OMPI users] open-mpi behaviour on Fedora, Ubuntu, Debian and CentOS
From: Dave Love (d.love_at_[hidden])
Date: 2010-04-28 19:25:14

Fabian Hänsel <fabtagon_at_[hidden]> writes:

> You could try to set optimizations more fine-grained. Every
> -Osomething stands for a certain set of optimizations. Start with
> e.g. "gcc -Q -O2 --help=optimizers" to see all available optimizations
> and which are enabled at -O2. Read about them on the gcc
> manpage. Disable those that decrease accuracy.

There are none which `decrease accuracy' or violate the IEEE floating
point rules (modulo rather rare bugs). I was willing to take bets on
problems being in the user's code rather than GCC when I was a
maintainer. -ffast-math, for instance, is chosen explicitly. This
surely isn't the place to talk about it, though.