Re: [COMMITTED] [range-op-float] Abstract out binary operator code out of PLUS_EXPR entry.

[Aldy Hernandez <aldyh@redhat.com>]

On Wed, Nov 9, 2022 at 1:48 PM Jakub Jelinek <jakub@redhat.com> wrote:
>
> On Wed, Nov 09, 2022 at 08:07:57AM +0100, Aldy Hernandez wrote:
> > The PLUS_EXPR was always meant to be a template for further
> > development, since most of the binary operators will share a similar
> > structure.  This patch abstracts out the common bits into the default
> > definition for range_operator_float::fold_range() and provides an
> > rv_fold() to be implemented by the individual entries wishing to use
> > the generic folder.  This is akin to what we do with fold_range() and
> > wi_fold() in the integer version of range-ops.
>
> Shouldn't foperator_mult be very similar to this (except that until
> division is done op[12]_range can't be implemented), with the exception
> that the invalid case isn't -INF + INF or INF + -INF, but
> 0 * +/-INF or +/-INF * 0?

Multiplication and division are tricky because you have to keep track
of signs to order the resulting range.  It's the most annoying pattern
we have for integers:

// Multiplications, divisions and shifts are a bit tricky to handle,
// depending on the mix of signs we have in the two ranges, we need to
// operate on different values to get the minimum and maximum values
// for the new range.  One approach is to figure out all the
// variations of range combinations and do the operations.
//
// However, this involves several calls to compare_values and it is
// pretty convoluted.  It's simpler to do the 4 operations (MIN0 OP
// MIN1, MIN0 OP MAX1, MAX0 OP MIN1 and MAX0 OP MAX0 OP MAX1) and then
// figure the smallest and largest values to form the new range.

But if you have a simpler approach, have at it.  I may have to bail on
multiplication and division for this cycle, cause I'm running out of
cycles :-/.

Hmmm...even if we don't get to implement mult/div in this cycle,
perhaps we could at least figure out if we'll NAN as you've suggested
above.  So, set [-INF,+INF] but without a NAN when applicable.

Aldy