range-op: Implement op[12]_range operators for {PLUS,MINUS,MULT,RDIV}_EXPR

range-op: Implement op[12]_range operators for {PLUS,MINUS,MULT,RDIV}_EXPR

On Wed, Nov 09, 2022 at 04:43:56PM +0100, Aldy Hernandez wrote:
> On Wed, Nov 9, 2022 at 3:58 PM Jakub Jelinek <jakub@redhat.com> wrote:
> >
> > On Wed, Nov 09, 2022 at 10:02:46AM +0100, Aldy Hernandez wrote:
> > > We can implement the op[12]_range entries for plus and minus in terms
> > > of each other.  These are adapted from the integer versions.
> >
> > I think for NANs the op[12]_range shouldn't act this way.
> > For the forward binary operations, we have the (maybe/known) NAN handling
> > of one or both NAN operands resulting in VARYING sign (maybe/known) NAN
> > result, that is the somehow the case for the reverse binary operations too,
> > if result is (maybe/known) NAN and the other op is not NAN, op is
> > VARYING sign (maybe/known) NAN, if other op is (maybe/known) NAN,
> > then op is VARYING sign maybe NAN (always maybe, never known).
> > But then for + we have the -INF + INF or vice versa into NAN, and that
> > is something that shouldn't be considered.  If result isn't NAN, then
> > neither operand can be NAN, regardless of whether result can be
> > +/- INF and the other op -/+ INF.
>
> Heh.  I just ran into this while debugging the problem reported by Xi.
>
> We are solving NAN = op1 - VARYING, and trying to do it with op1 = NAN
> + VARYING, which returns op1 = NAN (incorrectly).
>
> I suppose in the above case op1 should ideally be
> [-INF,-INF][+INF,+INF]+-NAN, but since we can't represent that then
> [-INF,+INF] +-NAN, which is actually VARYING.  Do you agree?
>
> I'm reverting this patch as attached, while I sort this out.

Here is a patch which reinstalls your change, add the fixups I've talked
about and also hooks up reverse operators for MULT_EXPR/RDIV_EXPR.

2022-11-12  Aldy Hernandez  <aldyh@redhat.com>
	    Jakub Jelinek  <jakub@redhat.com>

	* range-op-float.cc (float_binary_op_range_finish): New function.
	(foperator_plus::op1_range): New.
	(foperator_plus::op2_range): New.
	(foperator_minus::op1_range): New.
	(foperator_minus::op2_range): New.
	(foperator_mult::op1_range): New.
	(foperator_mult::op2_range): New.
	(foperator_div::op1_range): New.
	(foperator_div::op2_range): New.

	* gcc.c-torture/execute/ieee/inf-4.c: New test.