On Fri, 12 May 2023, Richard Sandiford wrote:
> Richard Biener <[email protected]> writes:
> > On Fri, 12 May 2023, Andre Vieira (lists) wrote:
> >
> >> I have dealt with, I think..., most of your comments. There's quite a few
> >> changes, I think it's all a bit simpler now. I made some other changes to
> >> the
> >> costing in tree-inline.cc and gimple-range-op.cc in which I try to preserve
> >> the same behaviour as we had with the tree codes before. Also added some
> >> extra
> >> checks to tree-cfg.cc that made sense to me.
> >>
> >> I am still regression testing the gimple-range-op change, as that was a
> >> last
> >> minute change, but the rest survived a bootstrap and regression test on
> >> aarch64-unknown-linux-gnu.
> >>
> >> cover letter:
> >>
> >> This patch replaces the existing tree_code widen_plus and widen_minus
> >> patterns with internal_fn versions.
> >>
> >> DEF_INTERNAL_OPTAB_WIDENING_HILO_FN and
> >> DEF_INTERNAL_OPTAB_NARROWING_HILO_FN
> >> are like DEF_INTERNAL_SIGNED_OPTAB_FN and DEF_INTERNAL_OPTAB_FN
> >> respectively
> >> except they provide convenience wrappers for defining conversions that
> >> require
> >> a hi/lo split. Each definition for <NAME> will require optabs for _hi and
> >> _lo
> >> and each of those will also require a signed and unsigned version in the
> >> case
> >> of widening. The hi/lo pair is necessary because the widening and narrowing
> >> operations take n narrow elements as inputs and return n/2 wide elements as
> >> outputs. The 'lo' operation operates on the first n/2 elements of input.
> >> The
> >> 'hi' operation operates on the second n/2 elements of input. Defining an
> >> internal_fn along with hi/lo variations allows a single internal function
> >> to
> >> be returned from a vect_recog function that will later be expanded to
> >> hi/lo.
> >>
> >>
> >> For example:
> >> IFN_VEC_WIDEN_PLUS -> IFN_VEC_WIDEN_PLUS_HI, IFN_VEC_WIDEN_PLUS_LO
> >> for aarch64: IFN_VEC_WIDEN_PLUS_HI -> vec_widen_<su>add_hi_<mode> ->
> >> (u/s)addl2
> >> IFN_VEC_WIDEN_PLUS_LO ->
> >> vec_widen_<su>add_lo_<mode>
> >> -> (u/s)addl
> >>
> >> This gives the same functionality as the previous WIDEN_PLUS/WIDEN_MINUS
> >> tree
> >> codes which are expanded into VEC_WIDEN_PLUS_LO, VEC_WIDEN_PLUS_HI.
> >
> > What I still don't understand is how we are so narrowly focused on
> > HI/LO? We need a combined scalar IFN for pattern selection (not
> > sure why that's now called _HILO, I expected no suffix). Then there's
> > three possibilities the target can implement this:
> >
> > 1) with a widen_[su]add<mode> instruction - I _think_ that's what
> > RISCV is going to offer since it is a target where vector modes
> > have "padding" (aka you cannot subreg a V2SI to get V4HI). Instead
> > RVV can do a V4HI to V4SI widening and widening add/subtract
> > using vwadd[u] and vwsub[u] (the HI->SI widening is actually
> > done with a widening add of zero - eh).
> > IIRC GCN is the same here.
>
> SVE currently does this too, but the addition and widening are
> separate operations. E.g. in principle there's no reason why
> you can't sign-extend one operand, zero-extend the other, and
> then add the result together. Or you could extend them from
> different sizes (QI and HI). All of those are supported
> (if the costing allows them).
I see. So why does the target the expose widen_[su]add<mode> at all?
> If the target has operations to do combined extending and adding (or
> whatever), then at the moment we rely on combine to generate them.
>
> So I think this case is separate from Andre's work. The addition
> itself is just an ordinary addition, and any widening happens by
> vectorising a CONVERT/NOP_EXPR.
>
> > 2) with a widen_[su]add{_lo,_hi}<mode> combo - that's what the tree
> > codes currently support (exclusively)
> > 3) similar, but widen_[su]add{_even,_odd}<mode>
> >
> > that said, things like decomposes_to_hilo_fn_p look to paint us into
> > a 2) corner without good reason.
>
> I suppose one question is: how much of the patch is really specific
> to HI/LO, and how much is just grouping two halves together?
Yep, that I don't know for sure.
> The nice
> thing about the internal-fn grouping macros is that, if (3) is
> implemented in future, the structure will strongly encourage even/odd
> pairs to be supported for all operations that support hi/lo. That is,
> I would expect the grouping macros to be extended to define even/odd
> ifns alongside hi/lo ones, rather than adding separate definitions
> for even/odd functions.
>
> If so, at least from the internal-fn.* side of things, I think the question
> is whether it's OK to stick with hilo names for now, or whether we should
> use more forward-looking names.
I think for parts that are independent we could use a more
forward-looking name. Maybe _halves? But I'm also not sure
how much of that is really needed (it seems to be tied around
optimizing optabs space?)
Richard.
> Thanks,
> Richard
>
> >
> > Richard.
> >
> >> gcc/ChangeLog:
> >>
> >> 2023-05-12 Andre Vieira <[email protected]>
> >> Joel Hutton <[email protected]>
> >> Tamar Christina <[email protected]>
> >>
> >> * config/aarch64/aarch64-simd.md (vec_widen_<su>addl_lo_<mode>):
> >> Rename
> >> this ...
> >> (vec_widen_<su>add_lo_<mode>): ... to this.
> >> (vec_widen_<su>addl_hi_<mode>): Rename this ...
> >> (vec_widen_<su>add_hi_<mode>): ... to this.
> >> (vec_widen_<su>subl_lo_<mode>): Rename this ...
> >> (vec_widen_<su>sub_lo_<mode>): ... to this.
> >> (vec_widen_<su>subl_hi_<mode>): Rename this ...
> >> (vec_widen_<su>sub_hi_<mode>): ...to this.
> >> * doc/generic.texi: Document new IFN codes.
> >> * internal-fn.cc (DEF_INTERNAL_OPTAB_WIDENING_HILO_FN): Macro to
> >> define an
> >> internal_fn that expands into multiple internal_fns for widening.
> >> (DEF_INTERNAL_OPTAB_NARROWING_HILO_FN): Likewise but for narrowing.
> >> (ifn_cmp): Function to compare ifn's for sorting/searching.
> >> (lookup_hilo_internal_fn): Add lookup function.
> >> (commutative_binary_fn_p): Add widen_plus fn's.
> >> (widening_fn_p): New function.
> >> (narrowing_fn_p): New function.
> >> (decomposes_to_hilo_fn_p): New function.
> >> (direct_internal_fn_optab): Change visibility.
> >> * internal-fn.def (DEF_INTERNAL_OPTAB_WIDENING_HILO_FN): Define
> >> widening
> >> plus,minus functions.
> >> (VEC_WIDEN_PLUS): Replacement for VEC_WIDEN_PLUS_EXPR tree code.
> >> (VEC_WIDEN_MINUS): Replacement for VEC_WIDEN_MINUS_EXPR tree code.
> >> * internal-fn.h (GCC_INTERNAL_FN_H): Add headers.
> >> (direct_internal_fn_optab): Declare new prototype.
> >> (lookup_hilo_internal_fn): Likewise.
> >> (widening_fn_p): Likewise.
> >> (Narrowing_fn_p): Likewise.
> >> (decomposes_to_hilo_fn_p): Likewise.
> >> * optabs.cc (commutative_optab_p): Add widening plus optabs.
> >> * optabs.def (OPTAB_D): Define widen add, sub optabs.
> >> * tree-cfg.cc (verify_gimple_call): Add checks for new widen
> >> add and sub IFNs.
> >> * tree-inline.cc (estimate_num_insns): Return same
> >> cost for widen add and sub IFNs as previous tree_codes.
> >> * tree-vect-patterns.cc (vect_recog_widen_op_pattern): Support
> >> patterns with a hi/lo split.
> >> (vect_recog_sad_pattern): Refactor to use new IFN codes.
> >> (vect_recog_widen_plus_pattern): Likewise.
> >> (vect_recog_widen_minus_pattern): Likewise.
> >> (vect_recog_average_pattern): Likewise.
> >> * tree-vect-stmts.cc (vectorizable_conversion): Add support for
> >> _HILO IFNs.
> >> (supportable_widening_operation): Likewise.
> >> * tree.def (WIDEN_SUM_EXPR): Update example to use new IFNs.
> >>
> >> gcc/testsuite/ChangeLog:
> >>
> >> * gcc.target/aarch64/vect-widen-add.c: Test that new
> >> IFN_VEC_WIDEN_PLUS is being used.
> >> * gcc.target/aarch64/vect-widen-sub.c: Test that new
> >> IFN_VEC_WIDEN_MINUS is being used.
> >>
>
--
Richard Biener <[email protected]>
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