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).
> How about adding a new inline helper function that tests whether an
> rtx is a CONST_INT with a given value? Then we could have a
> __builtin_constant_p shortcut for the [-64, 64] case. That would
> also avoid hard-coding the range.
Currently you have to write the example as
if (XEXP (x, 1) == const_int_rtx[MAX_SAVED_CONST_INT + 16])
and with your suggestion it will be
if (is_const_int_with_value (XEXP (x, 1), 16))
I like
if (XEXP (x, 1) == const16_rtx)
better: it is shorter and clearer (often you have something like this is
more complex conditionals, it matters), and this pattern is already very
well known (for -1, 0, 1, 2).
Do you like this patch a bit better if I also add such an
is_const_int_with_value function?
Segher
