[RFC] Fix PR28684

[Richard Guenther]

On Thu, 16 Nov 2006, Geert Bosch wrote:

> On Nov 16, 2006, at 09:30, Revital1 Eres wrote:
> > > I believe we may also inhibit or create underflow or overflow with
> > > re-ordering for example
> > > (X + C1) - C2 to X + (C1 - C2)
> > > for X near FLT_MAX and C1 sufficiently large.
> >
> > Right.
> >
> > > Even transforming
> > > X + Y - Y to X
> > > may fail to propagate a NaN Y to the result.
> > >
> >
> > Is transforming X + Y - Y to X is allowed by our flag?
> > Isn't it like x * 0 -> 0?
> 
> It seems we really need a table with a row for each transformation,
> and columns indicating which flags allow or inhibit the compiler
> to perform the transformation. Shall I start such a page on the Wiki?
> When we converge to a list that people can agree with, this would
> then be moved to the regular documentation.

That's a good plan.  I think we (at least I) are enough confused with
the existing options already ;)  [not to mention the meta-options
HONOR_* in flags.h]

Richard.

--
Richard Guenther <rguenther@suse.de>
Novell / SUSE Labs