Re: Setting -frounding-math by default

[Sylvain Pion <Sylvain dot Pion at sophia dot inria dot fr>]

Paolo Bonzini wrote:
> Sylvain Pion wrote:
> > Andrew Thomas Pinski wrote:
> > > > The fact is that Roger's patch introduced a regression (this word
> > > > should be clear enough here), in that some users now have their old
> > > > code broken, and they are forced to add the -frounding-math option
> > > > (after having lost some time finding about this non trivial issue).
> > > > This is a long term hindrance.
> > > Actually before roger's patch the default is the same. Just there was
> > > no way to turn it off.
> > Actually, there are 2 things controlled by -frounding-math :
> > 1) constant propagation of FP operations
> > 2) generic transformations like (-a)*b <-> -(a*b)
>
> I think 2) is taken care of by -fassociative-math, or it should at least.

I don't think it is (I haven't checked), and I don't see why it should.
This transformation has nothing to do with associativity : unless I'm
mistaken, it is always valid when rounding is to the nearest or towards
zero.

--
Sylvain Pion
INRIA Sophia-Antipolis
Geometrica Project-Team
CGAL, http://cgal.org/