On Mon, Mar 20, 2023 at 5:14 PM Jakub Jelinek <ja...@redhat.com> wrote:
>
> On Mon, Mar 13, 2023 at 09:41:47AM +0100, Aldy Hernandez wrote:
> > On 3/13/23 09:06, Jakub Jelinek wrote:
> > > On Mon, Mar 13, 2023 at 08:59:15AM +0100, Aldy Hernandez wrote:
> > > > > Yes, sure - I just noticed that we're forced to use high-level API for
> > > > > something that's quite low-level and should be internal (a range
> > > > > "breaking" internal consistency checks).
> > > >
> > > > Yeah, let's fix the API. No sense hacking around things if what we
> > > > need is
> > > > to tweak the design.
> > > >
> > > > I don't like hacking around things. It always comes back to bite me
> > > > ;-).
> > >
> > > Sure. The current state is that I think the actual bugs are fixed except
> > > for the !MODE_HAS_INFINITIES case which people rarely use, so fixing up
> > > the
> > > API can wait even to next release.
> > >
> > > For !MODE_HAS_INFINITIES, I wonder if the best fix wouldn't be to change
> > > set and a few other spots, so that if the boundaries are
> > > real_min_representable/real_max_representable, we widen them to -inf and
> > > inf
> > > and change frange_val_min/max to also be dconstninf/dconstinf for
> > > !MODE_HAS_INFINITIES, because the min/max for that case (probably) really
> > > work as
> > > infinities. Whenever we actually round that value to mode, it will become
> > > real_min_representable/real_max_representable again.
> > > But that can also wait a week.
> >
> > That sounds very reasonable. It would remove special casing and would make
> > the code easier to read. For that matter, that was what I had in the
> > original implementation.
>
> I think we don't want to remove the special casing for -ffinite-math-only
> on types which do support infinities.
> Thinking further on it, perhaps for !MODE_HAS_INFINITIES a better fix would
> be to do something like the patch below.
> Consider say having a range of VAX float type:
> #define M0 -FLT_MAX
> #define M1 nextafterf (F0, FLT_MAX)
> #define M2 nextafterf (M1, FLT_MAX)
> [M2, M2] - [M0, M1]
> Or perhaps if one or both of the operands are in such a case a min and max,
> perform real_arithmetic recurse on the argument replaced with
> dconstninf/dconstinf and then depending on inf pick the mininum or maximum
> of the two results (and carefully think about what to do if both operands
> are min/max).
LGTM.
Aldy
>
> 2023-03-20 Jakub Jelinek <ja...@redhat.com>
>
> * range-op-float.cc (frange_arithmetic): For !MODE_HAS_INFINITIES
> types, pretend operands with minimum or maximum values are actually
> infinities.
>
> --- gcc/range-op-float.cc.jj 2023-03-10 12:40:19.673108938 +0100
> +++ gcc/range-op-float.cc 2023-03-20 16:58:36.604981486 +0100
> @@ -313,8 +313,26 @@ frange_arithmetic (enum tree_code code,
> REAL_VALUE_TYPE value;
> enum machine_mode mode = TYPE_MODE (type);
> bool mode_composite = MODE_COMPOSITE_P (mode);
> + const REAL_VALUE_TYPE *pop1 = &op1;
> + const REAL_VALUE_TYPE *pop2 = &op2;
>
> - bool inexact = real_arithmetic (&value, code, &op1, &op2);
> + if (!MODE_HAS_INFINITIES (mode))
> + {
> + // If mode doesn't have infinities, the minimum and maximum
> + // values are saturating. Pretend for real_arithmetic such
> + // values are actual infinities. real_convert will then
> + // canonicalize the result not to be an infinity.
> + if (frange_val_is_min (op1, type))
> + pop1 = &dconstninf;
> + else if (frange_val_is_max (op1, type))
> + pop1 = &dconstinf;
> + if (frange_val_is_min (op2, type))
> + pop2 = &dconstninf;
> + else if (frange_val_is_max (op2, type))
> + pop2 = &dconstinf;
> + }
> +
> + bool inexact = real_arithmetic (&value, code, pop1, pop2);
> real_convert (&result, mode, &value);
>
> // Be extra careful if there may be discrepancies between the
>
>
> Jakub
>
