Old compiler optimizations in installed headers

[Richard Henderson]

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?


r~