[PATCH] move x86 to use gather/scatter internal functions

Hongtao Liu crazylht@gmail.com
Wed Aug 18 03:29:47 GMT 2021


On Wed, Aug 18, 2021 at 11:24 AM Hongtao Liu <crazylht@gmail.com> wrote:
>
> On Tue, Aug 17, 2021 at 10:43 PM Richard Biener via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
> >
> > On Tue, Aug 17, 2021 at 3:29 PM Richard Biener via Gcc-patches
> > <gcc-patches@gcc.gnu.org> wrote:
> > >
> > > This is an attempt to start moving the x86 backend to use
> > > standard pattern names for [mask_]gather_load and [mask_]scatter_store
> > > rather than using the builtin_{gather,scatter} target hooks.
> > >
> > > I've started with AVX2 gathers and given x86 only supports masked
> > > gather I only implemented mask_gather_load.  Note while for
> > > the builtin_gather case the vectorizer will provide an all-true
> > > mask operand for non-masked gathers this capability does not
> > > exist for the IFN path yet, so only testcases with actual masked
> > > gathers will work.
> > >
> > > If this looks reasonable on the backend side I'll see to first
> > > complete the vectorizer part, ripping out the target hook and
> > > arranging for the missing pieces.  Another one is the support
> > > for SImode indices with DFmode data which requires unpacking
> > > the index vector and actually recognizing the IFN.
> > >
> > > 2021-08-17  Richard Biener  <rguenther@suse.de>
> > >
> > >         * tree-vect-data-refs.c (vect_check_gather_scatter):
> > >         Always use internal functions.
> > >         * config/i386/sse.md
> > >         (mask_gather_load<mode><vec_gather_idxsi>): New expander.
> > >         (mask_gather_load<mode><vec_gather_idxdi>): Likewise.
> > > ---
> > >  gcc/config/i386/sse.md    | 56 +++++++++++++++++++++++++++++++++++++++
> > >  gcc/tree-vect-data-refs.c |  4 +--
> > >  2 files changed, 57 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/gcc/config/i386/sse.md b/gcc/config/i386/sse.md
> > > index 3957c86c3df..40bec98d9f7 100644
> > > --- a/gcc/config/i386/sse.md
> > > +++ b/gcc/config/i386/sse.md
> > > @@ -23232,12 +23232,22 @@
> > >                        (V2DF "V4SI") (V4DF "V4SI") (V8DF "V8SI")
> > >                        (V4SI "V4SI") (V8SI "V8SI") (V16SI "V16SI")
> > >                        (V4SF "V4SI") (V8SF "V8SI") (V16SF "V16SI")])
> > > +(define_mode_attr vec_gather_idxsi
> > > +                     [(V2DI "v4si") (V4DI "v4si") (V8DI "v8si")
> > > +                      (V2DF "v4si") (V4DF "v4si") (V8DF "v8si")
> > > +                      (V4SI "v4si") (V8SI "v8si") (V16SI "v16si")
> > > +                      (V4SF "v4si") (V8SF "v8si") (V16SF "v16si")])
> > >
> > >  (define_mode_attr VEC_GATHER_IDXDI
> > >                       [(V2DI "V2DI") (V4DI "V4DI") (V8DI "V8DI")
> > >                        (V2DF "V2DI") (V4DF "V4DI") (V8DF "V8DI")
> > >                        (V4SI "V2DI") (V8SI "V4DI") (V16SI "V8DI")
> > >                        (V4SF "V2DI") (V8SF "V4DI") (V16SF "V8DI")])
> > > +(define_mode_attr vec_gather_idxdi
> > > +                     [(V2DI "v2di") (V4DI "v4di") (V8DI "v8di")
> > > +                      (V2DF "v2di") (V4DF "v4di") (V8DF "v8di")
> > > +                      (V4SI "v2di") (V8SI "v4di") (V16SI "v8di")
> > > +                      (V4SF "v2di") (V8SF "v4di") (V16SF "v8di")])
> > >
> > >  (define_mode_attr VEC_GATHER_SRCDI
> > >                       [(V2DI "V2DI") (V4DI "V4DI") (V8DI "V8DI")
> > > @@ -23245,6 +23255,29 @@
> > >                        (V4SI "V4SI") (V8SI "V4SI") (V16SI "V8SI")
> > >                        (V4SF "V4SF") (V8SF "V4SF") (V16SF "V8SF")])
> > >
> > > +(define_expand "mask_gather_load<mode><vec_gather_idxsi>"
> > > +  [(parallel [(set (match_operand:VEC_GATHER_MODE 0 "register_operand")
> > > +                  (unspec:VEC_GATHER_MODE
> > > +                    [(pc)
> > > +                     (mem:<ssescalarmode>
> > > +                       (match_par_dup 6
> > > +                         [(match_operand 1 "vsib_address_operand")
> > > +                          (match_operand:<VEC_GATHER_IDXSI>
> > > +                             2 "register_operand")
> > > +                          (match_operand:SI 4 "const1248_operand")
> > > +                          (match_operand:SI 3 "const0_operand")]))
> > > +                     (mem:BLK (scratch))
> > > +                     (match_operand:<sseintvecmode> 5 "register_operand")]
> >
> > One problem of these is that when AVX512[VL] is enabled we get a AVX512 mask
> > mode here and while the internal function expansion check succeeds (it
> > never checks
> > the mask operand!), RTL expansion fails unexpectedly because of this mismatch.
> >
> > I suppose a more complicated define_mode_attr might do the trick or do I
> I don't think define_mode_attr supports conditional selection based on
> target feature.
> > need to add && !TARGET_AVX512F to these expanders?
> There'll be a duplicated definition of  mask_loadv8sfv8si for avx512
> and no-avx512 versions.
Note gather_loadmn can be shared by avx512 and non-avx512 version, we
can handle mask mode in the preparation statements based on target
feature.
> >
> The best way is like maskloadmn to accept different mask modes in its
> name, but that may create too much complexity in the middle-end to
> choose between avx2 mask_gather_load and avx512 mask_gather_load.
>
> > I've meanwhile posted a patch to make the vectorizer fall back to
> > masked_ when non-masked_ variants are not available and that seems to work
> > fine at least.
> >
> > Richard.
> >
> > > +                    UNSPEC_GATHER))
> > > +             (clobber (match_scratch:VEC_GATHER_MODE 7))])]
> > > +  "TARGET_AVX2 && TARGET_USE_GATHER"
> > > +{
> > > +  operands[5] = gen_lowpart_SUBREG (<MODE>mode, operands[5]);
> > > +  operands[6]
> > > +    = gen_rtx_UNSPEC (Pmode, gen_rtvec (3, operands[2], operands[3],
> > > +                                       operands[5]), UNSPEC_VSIBADDR);
> > > +})
> > > +
> > >  (define_expand "avx2_gathersi<mode>"
> > >    [(parallel [(set (match_operand:VEC_GATHER_MODE 0 "register_operand")
> > >                    (unspec:VEC_GATHER_MODE
> > > @@ -23306,6 +23339,29 @@
> > >     (set_attr "prefix" "vex")
> > >     (set_attr "mode" "<sseinsnmode>")])
> > >
> > > +(define_expand "mask_gather_load<mode><vec_gather_idxdi>"
> > > +  [(parallel [(set (match_operand:VEC_GATHER_MODE 0 "register_operand")
> > > +                  (unspec:VEC_GATHER_MODE
> > > +                    [(pc)
> > > +                     (mem:<ssescalarmode>
> > > +                       (match_par_dup 6
> > > +                         [(match_operand 1 "vsib_address_operand")
> > > +                          (match_operand:<VEC_GATHER_IDXDI>
> > > +                             2 "register_operand")
> > > +                          (match_operand:SI 4 "const1248_operand ")
> > > +                          (match_operand:SI 3 "const0_operand")]))
> > > +                     (mem:BLK (scratch))
> > > +                     (match_operand:<sseintvecmode> 5 "register_operand")]
> > > +                    UNSPEC_GATHER))
> > > +             (clobber (match_scratch:VEC_GATHER_MODE 7))])]
> > > +  "TARGET_AVX2 && TARGET_USE_GATHER"
> > > +{
> > > +  operands[5] = gen_lowpart_SUBREG (<VEC_GATHER_SRCDI>mode, operands[5]);
> > > +  operands[6]
> > > +    = gen_rtx_UNSPEC (Pmode, gen_rtvec (3, operands[1], operands[2],
> > > +                                       operands[4]), UNSPEC_VSIBADDR);
> > > +})
> > > +
> > >  (define_expand "avx2_gatherdi<mode>"
> > >    [(parallel [(set (match_operand:VEC_GATHER_MODE 0 "register_operand")
> > >                    (unspec:VEC_GATHER_MODE
> > > diff --git a/gcc/tree-vect-data-refs.c b/gcc/tree-vect-data-refs.c
> > > index d594c0a1b1e..67564b45c32 100644
> > > --- a/gcc/tree-vect-data-refs.c
> > > +++ b/gcc/tree-vect-data-refs.c
> > > @@ -3824,9 +3824,7 @@ vect_check_gather_scatter (stmt_vec_info stmt_info, loop_vec_info loop_vinfo,
> > >
> > >    /* True if we should aim to use internal functions rather than
> > >       built-in functions.  */
> > > -  bool use_ifn_p = (DR_IS_READ (dr)
> > > -                   ? supports_vec_gather_load_p ()
> > > -                   : supports_vec_scatter_store_p ());
> > > +  bool use_ifn_p = true;
> > >
> > >    base = DR_REF (dr);
> > >    /* For masked loads/stores, DR_REF (dr) is an artificial MEM_REF,
> > > --
> > > 2.31.1
>
>
>
> --
> BR,
> Hongtao



-- 
BR,
Hongtao


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