Re: [PATCH] PR tree-optimization/108447 - Do not try to logical fold floating point relations.

[Richard Biener <richard.guenther@gmail.com>]

On Thu, Jan 26, 2023 at 8:09 AM Richard Biener
<richard.guenther@gmail.com> wrote:
>
> On Wed, Jan 25, 2023 at 7:05 PM Andrew MacLeod <amacleod@redhat.com> wrote:
> >
> > This boils down to a single place where we are trying to do things with
> > relations in ranger that are simply not safe when we need to honor NANs.
> >
> > I think we can avoid all the other shuffling of relations, and simply
> > not perform this optimization when it comes to floats.
> >
> > The case the routine handles is:
> >
> > c_2 = a_6 > b_7
> > c_3 = a_6 < b_7
> > c_4 = c_2 && c_3
> >
> > c_2 and c_3 can never be true at the same time, Therefore c_4 can always
> > resolve to false based purely on the relations.
> >
> >
> > Range-ops is unable to do this optimization directly as it requires
> > examining things from outside the statement, and is not easily
> > communicated a simple relation to operator_logical_and.
> >
> > This routine proceeds to look at the definitions of c_2 and c_3, tries
> > to determine if there are common operands, and queries for any relations
> > between them.   If it turns out there is something, depending on whether
> > its && or || , we use intersection or union to determine if the result
> > of the logical operation can be folded.  If HONOR_NANS is true for the
> > float type, then we cannot do this optimization, and bail early.
> >
> > At this point I do not think we need to do any of the other things
> > proposed to relations, so we don't need either of the other 2 patches
> > this release.
> >
> > Bootstraps on x86_64-pc-linux-gnu with no regressions.  OK for trunk?
>
> +  if (HONOR_NANS (TREE_TYPE (ssa1_dep1)))
> +    return;
>
> would that rather be !(range-includes-nan (ssa1_dep1) ||
> range-includes-nan (ssa1_dep2) || ..)?

Saw the discussion in the other thread only now, so OK.

> That said, if the other 2 patches fix some latent issues in the new
> frange code I'd
> rather have them fixed.

So do we know bugs in the current code?  You said some buggy
function isn't used, so better delete it.  Are there other latent issues?

Thanks,
Richard.

> Richard.
>
> >
> > Andrew