On October 14, 2020 7:35:32 PM GMT+02:00, Segher Boessenkool
<seg...@kernel.crashing.org> wrote:
>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.
But IIRC the component mode needs to match.
>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
