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.
Carl
