Gabriel Dos Reis wrote:
On Tue, Mar 10, 2009 at 9:45 AM, Sylvain Pion
<sylvain.p...@sophia.inria.fr> wrote:
- Show quoted text -
Joseph S. Myers wrote:
On Mon, 9 Mar 2009, Sylvain Pion wrote:
Later, 1) started to be taken care of, and it was unfortunately
added under the control of the same -frounding-math option.
Which now, makes it harder to come back, since we want different
defaults for these two aspects.
I have already mentioned in a bugzilla PR that it could be nice
to have 2 options, but IIRC, I did not get any reply to this.
Patches to split the option into two *clearly-defined* options are more
likely to be accepted than changing the defaults, given that the fast-math
and related flags have been split more than once before.
My goal is to have interval arithmetic work with the default flags,
without more workarounds in the code (and as efficiently as possible).
So, I'm not going to work on anything if it means only splitting it
in separate flags, if we don't agree a priori on changing the default
for at least one of those sub flags after that.
That would be the opposite of progress for my usage, and so I would
not volunteer.
Currently, typical interval arithmetic code has to work around the fact that
there is no good way to stop constant propagation reliably (so it's using
some volatile or asm, or a big hammer like rounding-math, all these
solutions
having a performance cost).
It is not clear that constant propagation is the evil that needs to
be stopped at all cost. Remember, there is lot under the heading
'constant propagation'.
It would be nice to improve this, but a global flag, be it dedicated,
strikes
me as a clearly suboptimal solution here anyway (and, as has been mentioned,
it causes problems with code which really needs cprop in other places).
For IA, having a __builtin_stop_constant_propagation(expression) would be
OK,
I'm not too sure you really want this, or anybody serious about
scientific computations and performance really wants that.
And how would you reconcile that with constexpr?
I agree.
If you are looking for the Right [tm] solution, please take a look at N2811.
--
Sylvain Pion
INRIA Sophia-Antipolis
Geometrica Project-Team
CGAL, http://cgal.org/
