Old compiler optimizations in installed headers

[Ondřej Bílka]

On Wed, May 27, 2015 at 08:15:51AM -0700, Richard Henderson wrote:
> On 05/24/2015 06:31 AM, Ondřej Bílka wrote:
> > While good idea in general I would be wary of signbit et al. macros.
> > Using gcc will cause performance regression in some cases as they
> > generate suboptimal branchless code. Adding branches is correct as
> > performance savings from branchless code are in branch misprediction
> > which doesn't happen. If you have more than 5% inputs NaN to offset
> > single cycle penalty of going branchless your problem is that you are
> > producing garbage instead performance.
> 
> I beg your pardon?  Why would you *ever* have a branch implementing signbit?
> 
Sorry, I meant that you must be careful with others like isinf. Not signbit
thats ok.