This is the mail archive of the
gcc@gcc.gnu.org
mailing list for the GCC project.
Re: [lno] [RFC] if-conversion and auto vectorizer
- From: Richard Henderson <rth at redhat dot com>
- To: Robert Dewar <dewar at gnat dot com>
- Cc: alexr at spies dot com, gcc at gcc dot gnu dot org
- Date: Mon, 15 Mar 2004 15:08:36 -0800
- Subject: Re: [lno] [RFC] if-conversion and auto vectorizer
- References: <20040315224228.4F44BF2DAF@nile.gnat.com>
On Mon, Mar 15, 2004 at 05:42:28PM -0500, Robert Dewar wrote:
> > (1) MIN/MAX have better floating-point properties than conditional move.
> > Consider
> >
> > a = 0; b = NaN;
> >
> > c = a < b ? b : a; // 0
> > vs
> > c = a > b ? a : b; // NaN
> > vs
> > c = max(a, b); // Undefined
>
> Does the C standard really specify that the < and > here are unordered
> comparisons?
No. C99 added isgreater etc that are defined to dtrt with NaN.
However, if fp exceptions are disabled (as they ususally are),
then the above will work as shown for almost all targets.
r~