[petsc-dev] CFLAGS and COPTFLAGS

[Matthew Knepley]

On Sun, Jan 19, 2014 at 2:05 PM, Jed Brown <jed at jedbrown.org> wrote:

> Barry Smith <bsmith at mcs.anl.gov> writes:
>
> >    Summary
> >
> >    The reason for the current model is that in the original plan
> >    —with-debugging=0 would providing good compiler optimization flags
> >    (for each system) without the user having to set them; if the user
> >    set them via COPTFLAGS then we did set them ourselves.
> >
> >    Observations
> >
> >     1) The “standard” for passing optimization flags to ./configure is
> >     CFLAGS=“-O3 crap” we don’t support this and this confuses users
> >
> >     2) If we followed the standard and the user only set
> >     non-optimization flags with CFLAGS we would not turn on
> >     optimization when user might expect it (does this ever happen?)
>
> Does it happen and would it be confusing?  I think it is not confusing,
> especially since it's what everyone else does.
>
> >     3) We provide a different, “better" way of providing optimization
> >     flags and other CFLAGS, but know one knows about it.
> >
> >     4) Our —with-debugging=0 optimization flags are pretty bad, we
> >     should improve them
> >
> >     So choices are
> >
> >      A) follow standard
>
> I'm inclined to do this because it's less code and simpler logic, thus
> the easiest to explain.  If they don't set CFLAGS, of course we have to
> automatically choose reasonable defaults based on --with-debugging.
>

I think changing to this is worse than what we currently have.

   Matt

-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
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