On 6/2/2021 4:43 PM, Segher Boessenkool wrote:
Hi!
On Wed, Jun 02, 2021 at 06:07:28PM +0100, Richard Sandiford wrote:
Segher Boessenkool <seg...@kernel.crashing.org> writes:
Since times immemorial there has been const_int_rtx for all values from
-64 to 64, but only constm1_rtx..const2_rtx have been available for
convenient use. Change this, so that we can use all values in
{-64,...,64} in RTL easily. This matters, because then we we just say
if (XEXP (x, 1) == const16_rtx)
and things like that, since all const_int in that range are unique. We
already do for -1, 0, 1, 2, but we could for everything.
No strong objection, but personally I'd rather not add something
that is very specific to VOIDmode CONST_INTs. I realise it's very
unlikely that we'll ever be able to give CONST_INTs their proper mode
(no-one has the kind of time needed to do that), but I don't think we
should make the switch actively harder either.
How does this make that harder?
Having no mode for CONST_INTs makes some things significantly *easier*
btw. Well you know that, that is what makes any conversion away from
this so much harder :-)
We have has const0_rtx etc. since forever, this patch just increases the
range (to those values that have had guaranteed unique RTXes since
decades as well).
Yea, but often what you really want is CONST0_RTX (mode) instead of
const0_rtx. It's easily goof'd and often the cause minor missed
optimizations.
jeff
