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Re: Change x86 default arch for 4.5?
On Sun, 21 Feb 2010, Geert Bosch wrote:
> On Feb 21, 2010, at 17:42, Erik Trulsson wrote:
> > Newer compilers usually have better generic optimizations that are not
> > CPU-dependent. Newer compilers also typically have improved support
> > for new language-features (and new languages for that matter.)
>
> This is exactly where CPU dependence comes into play. I'd like
> for example take advantage of IEEE floating point semantics in
> our Ada compiler. Fifteen years ago, we had to face the fact that
It's up to the Ada maintainers what is or is not considered floating-point
behavior expected to be stable between versions, and so whether making Ada
use -mfpmath=sse when SSE2 is available would be appropriate.
> So, I'd like to be able to put all this behind me, and only
> have to think about fully IEEE compliant systems. Similarly,
> there is no way to fully implement C99 Annex F without using
> SSE2.
I know some people have claimed (e.g. glibc bug 6981) that you can't
conform to Annex F when you have excess precision, but this does not
appear to be the view of WG14.
A proper implementation of Annex F is also likely to result in generating
slower floating-point code if we keep the present default of
-ftrapping-math being on by default (I think it would end up inhibiting
optimizations as much as -frounding-math to ensure exactly the right set
of exceptions is raised).
--
Joseph S. Myers
joseph@codesourcery.com