On Mon, May 13, 2013 at 7:23 PM, DJ Delorie <d...@redhat.com> wrote:
>
>> Can you add that (partial int modes have fewer bits than int modes)
>> as verification to genmodes.c:make_partial_integer_mode?
>
> I could, but it would be a no-op for PARTIAL_INT_MODE()
>
>> I wonder if this should not use GET_MODE_PRECISION - after all it is
>> the precision that determines whether we have to extend / truncate?
>> Or is precision a so much unused term on RTL that this would cause
>> problems?
>
> The problem is, the precision of PSImode *is* the same as SImode,
> if you just use PARTIAL_INT_MODE() in *-modes.def
How can you then ever "truncate" from SImode to PSImode? That is,
currently we have
if (GET_MODE_BITSIZE (GET_MODE (op0)) < GET_MODE_BITSIZE
(GET_MODE (op1)))
op1 = simplify_gen_unary (TRUNCATE, GET_MODE (op0), op1,
GET_MODE (op1));
else
/* We always sign-extend, regardless of the signedness of
the operand, because the operand is always unsigned
here even if the original C expression is signed. */
op1 = simplify_gen_unary (SIGN_EXTEND, GET_MODE (op0), op1,
GET_MODE (op1));
but the case of same precision/bitsize is not handled here. So, shouldn't it
be then
if (GET_MODE_BITSIZE (GET_MODE (op0)) == GET_MODE_BITSIZE
(GET_MODE (op1)))
op1 = convert_move (GET_MODE (op0), op1);
else if (....
?
That said, special casing PARTIAL_INT_MODEs anywhere looks bogus to me.
Which might mean that PARTIAL_INT_MODEs are bogus... what are they
useful for if they do not even have a precision and share the same bitsize
as their base mode? Do they even have a "precision"?
> grep PARTIAL_INT_MODE config/*/*.def
config/bfin/bfin-modes.def:PARTIAL_INT_MODE (DI);
config/m32c/m32c-modes.def:PARTIAL_INT_MODE (SI);
config/rs6000/rs6000-modes.def:PARTIAL_INT_MODE (TI);
config/sh/sh-modes.def:PARTIAL_INT_MODE (SI);
config/sh/sh-modes.def:PARTIAL_INT_MODE (DI);
so it shouldn't be difficult to fix that precision thing by adjusting genmodes.c
and the few occurences above? Make it
config/bfin/bfin-modes.def:PARTIAL_INT_MODE (DI, 40);
btw, what's the relation to fractional int modes?
Richard.
