From: Joost VandeVondele <jv244@hermes.cam.ac.uk>
To: Robert Dewar <dewar@gnat.com>
Cc: gcc@gcc.gnu.org
Subject: Re: (a+b)+c should be replaced by a+(b+c)
Date: Thu, 25 Mar 2004 15:32:00 -0000 [thread overview]
Message-ID: <Pine.SOL.4.58.0403251409340.18567@yellow.csi.cam.ac.uk> (raw)
In-Reply-To: <4062E287.4010007@gnat.com>
>
> > No, I'm only happy there are compilers that make my code 100 times faster
> > without doing a lot of work myself, keeping my code easy to maintain and
> > read.
>
> Well it is fine to have this kind of transformation available as an
> option, though in general it is better to rely on BLAS written by
> competent numerical programmers, than on transformations of unknown
> impact.
>
Obviously, this was an example (and I referred to calling blas
explicitly), to suggest that there exists a wide range of computational
kernels that benefit from (a+b)+c->a+(b+c) being performed by the
compiler. (I realized that there are much better example of this, but
anyway).
I like the name transformation as much as I dislike unsafe-math. FYI the
following warning comes from IBM (at -O3 when optimizing, oops
transforming, expressions in a way that might lead to non-bitwise
identical results), and I think it is not badly worded :
"mytest.f90", 1500-036 (I) The NOSTRICT option (default at OPT(3)) has the
potential to alter the semantics of a program. Please refer to
documentation on the STRICT/NOSTRICT option for more information.
Joost
next prev parent reply other threads:[~2004-03-25 14:21 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-03-25 12:03 Joost VandeVondele
2004-03-25 14:45 ` Robert Dewar
2004-03-25 15:07 ` Joost VandeVondele
2004-03-25 15:18 ` Robert Dewar
2004-03-25 15:32 ` Joost VandeVondele [this message]
2004-03-25 15:59 ` Scott Robert Ladd
2004-03-25 16:18 ` Jakub Jelinek
2004-03-25 16:38 ` Scott Robert Ladd
2004-03-25 19:47 ` Laurent GUERBY
2004-03-25 20:16 ` Scott Robert Ladd
2004-03-26 2:51 ` Gabriel Paubert
2004-03-26 3:17 ` Jakub Jelinek
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