On Mon, Jun 29, 2020 at 02:29:54PM -0700, Carl Love wrote:
> Segher:
>
> On Thu, 2020-06-25 at 17:39 -0500, Segher Boessenkool wrote:
> > > +;; Return 1 if op is a constant 32-bit floating point value
> > > +(define_predicate "f32bit_const_operand"
> > > + (match_code "const_double")
> > > +{
> > > + if (GET_MODE (op) == SFmode)
> > > + return 1;
> > > +
> > > + else if ((GET_MODE (op) == DFmode) && ((UINTVAL (op) >> 32) ==
> > > 0))
> > > + {
> > > + /* Value fits in 32-bits */
> > > + return 1;
> > > + }
> > > + else
> > > + /* Not the expected mode. */
> > > + return 0;
> > > +})
> >
> > I don't think this is the correct test. What you want to see is if
> > the
> > number in "op" can be converted to an IEEE single-precision number,
> > and
> > back again, losslessly. (And subnormal SP numbers aren't allowed
> > either, but NaNs and infinities are).
>
> The predicate is used with the xxsplitw_v4sf define_expand. The "user"
> claims the given immediate bit pattern is the bit pattern for a single
> precision floating point number. The immediate value is not converted
> to a float. Rather we are splatting a bit pattern that the "user"
> already claims represents a 32-bit floating point value. I just need
> to make sure the immediate value actually fits into 32-bits.
>
> I don't see that I need to check that the value can be converted to
> IEEE float and back.
Ah, okay. Can you please put that in the function comment then? Right
now it says
;; Return 1 if op is a constant 32-bit floating point value
and that is quite misleading.
Segher
