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Re: Fortran flags


From: Daniel Kraft
Subject: Re: Fortran flags
Date: Wed, 11 May 2011 11:06:50 +0200
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On 05/11/11 02:16, Jordi Gutiérrez Hermoso wrote:
On 10 May 2011 15:08, Dmitri A. Sergatskov<address@hidden>  wrote:
2011/5/10 Thomas Weber<address@hidden>:
On Tue, May 10, 2011 at 11:20:45AM -0500, Jordi Gutiérrez Hermoso wrote:
On 10 May 2011 10:12, Daniel Kraft<address@hidden>  wrote:

Usually, -O2 should be a good thing for gfortran.  And in general, please
report any "problems" -O2 causes as gfortran bug.

I was wondering why it's not enabled in the default Fortran flags.
Instead we merely use -O. I thought the option enabled other
optimisation flags that caused problems. Red Hat for example broke ABI
compatibility by compiling with -O2:

      https://bugzilla.redhat.com/show_bug.cgi?id=478856

Maybe I don't get it, but I don't see anything in that bug report that
even says someting about optimization flags?

        Thomas


I suspect he meant this bug:

https://bugzilla.redhat.com/show_bug.cgi?id=520518#c0

(and few ones related)
which showed up in all other distributions as well...
(It was not really RedHat specific).

Yes, thank you, about compilation Fortran flags. I read the first
report too quickly.

Daniel, this was Dmitri's original report on the matter:

     
http://octave.1599824.n4.nabble.com/help-with-compiling-octave-3-3-51-tp2272804p2282648.html

Do you think this is a gcc bug?

I did not look at it in detail, but gfortran 4.1 is already quite old; and I think, at this stage gfortran just started to being somewhat useful. So I strongly suppose that this bug (if it is one) has been fixed long since.

So, my opinion is that -O2 should be really fine (and should help with performance at least a little) -- unless some new problems explicitely come up.

Yours,
Daniel

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