Re: [match.pd PATCH] PR tree-optimization/126467: 0.0-x -> -x vs. signed zeros.

On Fri, Aug 7, 2026 at 9:31 AM Alexander Monakov <[email protected]> wrote:
>
>
> On Wed, 5 Aug 2026, Roger Sayle wrote:
>
> > Likewise when x is NaN, 0.0 - x
> > may change the payload, but -x is guaranteed not to.
>
> Not saying you should drop the condition in your patch, but do we care
> about NaN payload propagation anywhere else? The HONOR_NANS et al. only
> seem to cover presence/absence of NaNs, not observability of payloads.

I think we don't.  -x will still turn sNaN into qNaN?

> > gcc/ChangeLog
> >         PR tree-optimization/126467
> >         * match.pd (0.0 - x -> -x): Update the conditions under which
> >         the transformation is performed, disallowing x = +0.0 when we
> >         honor signed zeros.
>
> (this doesn't seem to mention NaNs)
>
> Alexander