[Bug tree-optimization/107591] range-op{,-float}.cc for x * x

["amacleod at redhat dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107591

--- Comment #13 from Andrew Macleod <amacleod at redhat dot com> ---
(In reply to Jakub Jelinek from comment #12)
> (In reply to Andrew Macleod from comment #11)
> > no, I meant in addition to the VREL_EQ.  so 
> >   if (rel == VREL_EQ && op1_range != op2_range)
> >      then you know you have something like  if (x == y) z=x*y and may have
> > to check for various signed zero cobinations in each range, 
> > whereas is op1_range == op2_range in this case, it should be perfectly safe..
> 
> I don't understand.  Let's modify the testcase to:

> I'd expect that fold_range on the x * y should see trio.op1_op2 () == VREL_EQ
> because of the guarding x == y condition.  And the ranges of both are
> [-13.f, 26.f] +-NAN too.  Still, x could be -0.0f and y 0.0f or vice versa,
> and so
> x * y could be -0.0f, so we need [-0.f, 676.f] +-NAN.  While if it is x * x,
> we know the result will have always sign bit of 0 (except if NAN), so [0.f,
> 676.f] +-NAN.

gah. Clearly it is I who does not understand. -0.0 and +0.0 interactions remind
me of all the signed single bit crud we (ie Aldy) went thru.  The same team
must have come up with both concepts :-P  At least they deserve the same award.

Move along and ignore me.