------- Comment #57 from pinskia at physics dot uc dot edu 2006-08-09 21:46 ------- Subject: Re: [4.0/4.1 Regression] gcc 4 produces worse x87 code on all platforms than gcc 3
> > > > ------- Comment #56 from whaley at cs dot utsa dot edu 2006-08-09 21:33 > ------- > Dorit, > > >This flag is needed in order to allow vectorization of reduction (summation > >in your case) of floating-point data. > > OK, but this is a baaaad flag to require. From the computational scientist's > point of view, there is a *vast* difference between reordering (which many > aggressive optimizations imply) and failing to have IEEE compliance. Almost > no > computational scientist will use non-IEEE code (because you have essentially > no > idea if your answer is correct), but almost all will allow reordering. So, it > is really important to separate the non-IEEE optimizations from the IEEE > compliant ones. Except for the fact IEEE compliant fp does not allow for reordering at all except in some small cases. For an example is (a + b) + (-a) is not the same as (a + (-a)) + b, so reordering will invalid IEEE fp for larger a and small b. Yes maybe we should split out the option for unsafe math fp op for reordering but that is different issue. -- Pinski -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27827
