Hi!
On Wed, Oct 14, 2020 at 01:43:45PM +0800, Hongtao Liu wrote:
> On Wed, Oct 14, 2020 at 4:01 AM Segher Boessenkool
> <seg...@kernel.crashing.org> wrote:
> > On Tue, Oct 13, 2020 at 04:40:53PM +0800, Hongtao Liu wrote:
> > > For rtx like
> > > (vec_select:V2SI (subreg:V4SI (inner:V2SI) 0)
> > > (parallel [(const_int 0) (const_int 1)]))
> > > it could be simplified as inner.
> >
> > You could even simplify any vec_select of a subreg of X to just a
> > vec_select of X, by changing the selection vector a bit (well, only do
>
> Yes, when SUBREG_BYTE of trueop0 is not 0, we need to add offset to selection.
Exactly.
> > this if that is a constant vector, I suppose). Not just for paradoxical
> > subregs either, just for *all* subregs.
>
> Yes, and only when X has the same inner mode and more elements.
No, for *all*. The mode of the first argument of vec_select does not
have to equal its result mode.
Any (constant indices) vec_select of a subreg can be written as just a
vec_select.
> + /* Simplify vec_select of a subreg of X to just a vec_select of X
> + when available. */
What does "when available" mean here?
> + int l2;
> + if (GET_CODE (trueop0) == SUBREG
> + && (GET_MODE_INNER (mode)
> + == GET_MODE_INNER (GET_MODE (XEXP (trueop0, 0))))
Don't use unnecessary parens here please, it makes it harder to read
(there are quite enough parens already :-) )
> + gcc_assert (can_div_trunc_p (SUBREG_BYTE (trueop0),
> + GET_MODE_SIZE (GET_MODE_INNER
> (mode)),
> + &subreg_offset));
Why is this needed?
> + bool success = true;
> + for (int i = 0;i != l1; i++)
(space after ; )
> + {
> + rtx j = XVECEXP (trueop1, 0, i);
(i and j and k ususally are integers, not rtx)
> + if (!CONST_INT_P (j)
> + || known_ge (UINTVAL (j), l2 - subreg_offset))
> + {
> + success = false;
> + break;
> + }
> + }
You don't have to test if the input RTL is valid. You can assume it is.
> + if (success)
> + {
> + rtx par = trueop1;
> + if (subreg_offset)
> + {
> + rtvec vec = rtvec_alloc (l1);
> + for (int i = 0; i < l1; i++)
> + RTVEC_ELT (vec, i)
> + = GEN_INT (INTVAL (XVECEXP (trueop1, 0, i)
> + + subreg_offset));
> + par = gen_rtx_PARALLEL (VOIDmode, vec);
> + }
> + return gen_rtx_VEC_SELECT (mode, XEXP (trueop0, 0), par);
> + }
> + }
subreg_offset will differ in meaning if big-endian; is this correct
there, do all the stars align so this code works out fine there as well?
Looks fine otherwise, thanks :-)
Segher
