> -----Original Message-----
> From: Tamar Christina <tamar.christ...@arm.com>
> Sent: Thursday, August 1, 2024 9:51 AM
> To: Richard Sandiford <richard.sandif...@arm.com>
> Cc: Kyrylo Tkachov <ktkac...@nvidia.com>; gcc-patches@gcc.gnu.org; nd
> <n...@arm.com>; Richard Earnshaw <richard.earns...@arm.com>; Marcus
> Shawcroft <marcus.shawcr...@arm.com>; ktkac...@gcc.gnu.org
> Subject: RE: [PATCH 8/8]AArch64: take gather/scatter decode overhead into
> account
>
> > -----Original Message-----
> > From: Richard Sandiford <richard.sandif...@arm.com>
> > Sent: Wednesday, July 31, 2024 7:17 PM
> > To: Tamar Christina <tamar.christ...@arm.com>
> > Cc: Kyrylo Tkachov <ktkac...@nvidia.com>; gcc-patches@gcc.gnu.org; nd
> > <n...@arm.com>; Richard Earnshaw <richard.earns...@arm.com>; Marcus
> > Shawcroft <marcus.shawcr...@arm.com>; ktkac...@gcc.gnu.org
> > Subject: Re: [PATCH 8/8]AArch64: take gather/scatter decode overhead into
> > account
> >
> > Tamar Christina <tamar.christ...@arm.com> writes:
> > > @@ -289,6 +293,12 @@ struct sve_vec_cost : simd_vec_cost
> > > const int gather_load_x32_cost;
> > > const int gather_load_x64_cost;
> > >
> > > + /* Additional loop initialization cost of using a gather load
> > > instruction. The
> x32
> >
> > Sorry for the trivia, but: long line.
>
> Yeah, noticed it after I sent out the patch 😊
>
> >
> > > + value is for loads of 32-bit elements and the x64 value is for
> > > loads of
> > > + 64-bit elements. */
> > > + const int gather_load_x32_init_cost;
> > > + const int gather_load_x64_init_cost;
> > > +
> > > /* The per-element cost of a scatter store. */
> > > const int scatter_store_elt_cost;
> > > };
> > > [...]
> > > @@ -17291,6 +17295,20 @@ aarch64_vector_costs::add_stmt_cost (int
> count,
> > vect_cost_for_stmt kind,
> > > stmt_cost = aarch64_detect_vector_stmt_subtype (m_vinfo, kind,
> > > stmt_info, vectype,
> > > where, stmt_cost);
> > > +
> > > + /* Check if we've seen an SVE gather/scatter operation and which
> > > size. */
> > > + if (kind == scalar_load
> > > + && aarch64_sve_mode_p (TYPE_MODE (vectype))
> > > + && STMT_VINFO_MEMORY_ACCESS_TYPE (stmt_info) ==
> > VMAT_GATHER_SCATTER)
> > > + {
> > > + const sve_vec_cost *sve_costs = aarch64_tune_params.vec_costs->sve;
> >
> > I think we need to check whether this is nonnull, since not all tuning
> > targets provide SVE costs.
>
> Will do, but I thought since this was in a block that checked
> aarch64_use_new_vector_costs_p ()
> that the SVE costs were required. What does that predicate mean then?
Ah nevermind, just realized it just means to apply the new vector cost routines,
I hadn't realized that we supported new costing for non-SVE models as well.
Will add the check.
Thanks,
Tamar
>
> Cheers,
> Tamar
> >
> > > + if (GET_MODE_UNIT_BITSIZE (TYPE_MODE (vectype)) == 64)
> > > + m_sve_gather_scatter_init_cost
> > > + += sve_costs->gather_load_x64_init_cost;
> > > + else
> > > + m_sve_gather_scatter_init_cost
> > > + += sve_costs->gather_load_x32_init_cost;
> > > + }
> > > }
> > >
> > > /* Do any SVE-specific adjustments to the cost. */
> > > @@ -17676,6 +17694,12 @@ aarch64_vector_costs::finish_cost (const
> > vector_costs *uncast_scalar_costs)
> > > m_costs[vect_body] = adjust_body_cost (loop_vinfo, scalar_costs,
> > > m_costs[vect_body]);
> > > m_suggested_unroll_factor = determine_suggested_unroll_factor ();
> > > +
> > > + /* For gather and scatters there's an additional overhead for the
> > > first
> > > + iteration. For low count loops they're not beneficial so model the
> > > + overhead as loop prologue costs. */
> > > + if (m_sve_gather_scatter_init_cost)
> > > + m_costs[vect_prologue] += m_sve_gather_scatter_init_cost;
> >
> > Might as well make this unconditional now.
> >
> > LGTM with those changes, but please wait for Kyrill's review too.
> >
> > Thanks,
> > Richard
> >
> > > }
> > >
> > > /* Apply the heuristic described above m_stp_sequence_cost. Prefer
> > > diff --git a/gcc/config/aarch64/tuning_models/a64fx.h
> > b/gcc/config/aarch64/tuning_models/a64fx.h
> > > index
> >
> 6091289d4c3c66f01d7e4dbf97a85c1f8c40bb0b..378a1b3889ee265859786c1
> > ff6525fce2305b615 100644
> > > --- a/gcc/config/aarch64/tuning_models/a64fx.h
> > > +++ b/gcc/config/aarch64/tuning_models/a64fx.h
> > > @@ -104,6 +104,8 @@ static const sve_vec_cost a64fx_sve_vector_cost =
> > > 13, /* fadda_f64_cost */
> > > 64, /* gather_load_x32_cost */
> > > 32, /* gather_load_x64_cost */
> > > + 0, /* gather_load_x32_init_cost */
> > > + 0, /* gather_load_x64_init_cost */
> > > 1 /* scatter_store_elt_cost */
> > > };
> > >
> > > diff --git a/gcc/config/aarch64/tuning_models/cortexx925.h
> > b/gcc/config/aarch64/tuning_models/cortexx925.h
> > > index
> >
> 6cae5b7de5ca7ffad8a0f683e1285039bb55d159..b509cae758419a415d9067ec
> > 751ef1e6528eb09a 100644
> > > --- a/gcc/config/aarch64/tuning_models/cortexx925.h
> > > +++ b/gcc/config/aarch64/tuning_models/cortexx925.h
> > > @@ -135,6 +135,8 @@ static const sve_vec_cost cortexx925_sve_vector_cost
> =
> > > operation more than a 64-bit gather. */
> > > 14, /* gather_load_x32_cost */
> > > 12, /* gather_load_x64_cost */
> > > + 42, /* gather_load_x32_init_cost */
> > > + 24, /* gather_load_x64_init_cost */
> > > 1 /* scatter_store_elt_cost */
> > > };
> > >
> > > diff --git a/gcc/config/aarch64/tuning_models/generic.h
> > b/gcc/config/aarch64/tuning_models/generic.h
> > > index
> >
> 2b1f68b3052117814161a32f426422736ad6462b..101969bdbb9ccf7eafbd9a1c
> > d6e25f0b584fb261 100644
> > > --- a/gcc/config/aarch64/tuning_models/generic.h
> > > +++ b/gcc/config/aarch64/tuning_models/generic.h
> > > @@ -105,6 +105,8 @@ static const sve_vec_cost generic_sve_vector_cost =
> > > 2, /* fadda_f64_cost */
> > > 4, /* gather_load_x32_cost */
> > > 2, /* gather_load_x64_cost */
> > > + 12, /* gather_load_x32_init_cost */
> > > + 4, /* gather_load_x64_init_cost */
> > > 1 /* scatter_store_elt_cost */
> > > };
> > >
> > > diff --git a/gcc/config/aarch64/tuning_models/generic_armv8_a.h
> > b/gcc/config/aarch64/tuning_models/generic_armv8_a.h
> > > index
> >
> b38b9a8c5cad7d12aa38afdb610a14a25e755010..b5088afe068aa4be7f9dd614
> > cfdd2a51fa96e524 100644
> > > --- a/gcc/config/aarch64/tuning_models/generic_armv8_a.h
> > > +++ b/gcc/config/aarch64/tuning_models/generic_armv8_a.h
> > > @@ -106,6 +106,8 @@ static const sve_vec_cost
> > generic_armv8_a_sve_vector_cost =
> > > 2, /* fadda_f64_cost */
> > > 4, /* gather_load_x32_cost */
> > > 2, /* gather_load_x64_cost */
> > > + 12, /* gather_load_x32_init_cost */
> > > + 4, /* gather_load_x64_init_cost */
> > > 1 /* scatter_store_elt_cost */
> > > };
> > >
> > > diff --git a/gcc/config/aarch64/tuning_models/generic_armv9_a.h
> > b/gcc/config/aarch64/tuning_models/generic_armv9_a.h
> > > index
> >
> 7156dbe5787e831bc4343deb7d7b88e9823fc1bc..999985ed40f694f2681779d
> > 940bdb282f289b8e3 100644
> > > --- a/gcc/config/aarch64/tuning_models/generic_armv9_a.h
> > > +++ b/gcc/config/aarch64/tuning_models/generic_armv9_a.h
> > > @@ -136,6 +136,8 @@ static const sve_vec_cost
> > generic_armv9_a_sve_vector_cost =
> > > operation more than a 64-bit gather. */
> > > 14, /* gather_load_x32_cost */
> > > 12, /* gather_load_x64_cost */
> > > + 42, /* gather_load_x32_init_cost */
> > > + 24, /* gather_load_x64_init_cost */
> > > 3 /* scatter_store_elt_cost */
> > > };
> > >
> > > diff --git a/gcc/config/aarch64/tuning_models/neoverse512tvb.h
> > b/gcc/config/aarch64/tuning_models/neoverse512tvb.h
> > > index
> >
> 825c6a64990b72cda3641737957dc94d75db1509..d2a0b647791de8fca6d7684
> > 849d2ab1e9104b045 100644
> > > --- a/gcc/config/aarch64/tuning_models/neoverse512tvb.h
> > > +++ b/gcc/config/aarch64/tuning_models/neoverse512tvb.h
> > > @@ -79,6 +79,8 @@ static const sve_vec_cost
> > neoverse512tvb_sve_vector_cost =
> > > operation more than a 64-bit gather. */
> > > 14, /* gather_load_x32_cost */
> > > 12, /* gather_load_x64_cost */
> > > + 42, /* gather_load_x32_init_cost */
> > > + 24, /* gather_load_x64_init_cost */
> > > 3 /* scatter_store_elt_cost */
> > > };
> > >
> > > diff --git a/gcc/config/aarch64/tuning_models/neoversen2.h
> > b/gcc/config/aarch64/tuning_models/neoversen2.h
> > > index
> >
> d41e714aa045266ecae62a36ed02dfbfb7597c3a..1a5b66901b5c3fb78f87fee40
> > 236957139644585 100644
> > > --- a/gcc/config/aarch64/tuning_models/neoversen2.h
> > > +++ b/gcc/config/aarch64/tuning_models/neoversen2.h
> > > @@ -135,6 +135,8 @@ static const sve_vec_cost neoversen2_sve_vector_cost
> =
> > > operation more than a 64-bit gather. */
> > > 14, /* gather_load_x32_cost */
> > > 12, /* gather_load_x64_cost */
> > > + 42, /* gather_load_x32_init_cost */
> > > + 24, /* gather_load_x64_init_cost */
> > > 3 /* scatter_store_elt_cost */
> > > };
> > >
> > > diff --git a/gcc/config/aarch64/tuning_models/neoversen3.h
> > b/gcc/config/aarch64/tuning_models/neoversen3.h
> > > index
> >
> 36f770c0a14fc127c75a60cd37048d46c3b069c7..cfd5060e6b64a0433de41b03c
> > de886da119d9a1c 100644
> > > --- a/gcc/config/aarch64/tuning_models/neoversen3.h
> > > +++ b/gcc/config/aarch64/tuning_models/neoversen3.h
> > > @@ -135,6 +135,8 @@ static const sve_vec_cost neoversen3_sve_vector_cost
> =
> > > operation more than a 64-bit gather. */
> > > 14, /* gather_load_x32_cost */
> > > 12, /* gather_load_x64_cost */
> > > + 42, /* gather_load_x32_init_cost */
> > > + 24, /* gather_load_x64_init_cost */
> > > 1 /* scatter_store_elt_cost */
> > > };
> > >
> > > diff --git a/gcc/config/aarch64/tuning_models/neoversev1.h
> > b/gcc/config/aarch64/tuning_models/neoversev1.h
> > > index
> >
> 0fc41ce6a41b3135fa06d2bda1f517fdf4f8dbcf..705ed025730f6683109a4796c6
> > eefa55b437cec9 100644
> > > --- a/gcc/config/aarch64/tuning_models/neoversev1.h
> > > +++ b/gcc/config/aarch64/tuning_models/neoversev1.h
> > > @@ -126,6 +126,8 @@ static const sve_vec_cost neoversev1_sve_vector_cost
> =
> > > 8, /* fadda_f64_cost */
> > > 32, /* gather_load_x32_cost */
> > > 16, /* gather_load_x64_cost */
> > > + 96, /* gather_load_x32_init_cost */
> > > + 32, /* gather_load_x64_init_cost */
> > > 3 /* scatter_store_elt_cost */
> > > };
> > >
> > > diff --git a/gcc/config/aarch64/tuning_models/neoversev2.h
> > b/gcc/config/aarch64/tuning_models/neoversev2.h
> > > index
> >
> c9c3019dd01a98bc20a76e8455fb59ff24a9ff6c..47908636b0f4c3eadd5848b59
> > 0fd079c1c04aa10 100644
> > > --- a/gcc/config/aarch64/tuning_models/neoversev2.h
> > > +++ b/gcc/config/aarch64/tuning_models/neoversev2.h
> > > @@ -135,6 +135,8 @@ static const sve_vec_cost neoversev2_sve_vector_cost
> =
> > > operation more than a 64-bit gather. */
> > > 14, /* gather_load_x32_cost */
> > > 12, /* gather_load_x64_cost */
> > > + 42, /* gather_load_x32_init_cost */
> > > + 24, /* gather_load_x64_init_cost */
> > > 3 /* scatter_store_elt_cost */
> > > };
> > >
> > > diff --git a/gcc/config/aarch64/tuning_models/neoversev3.h
> > b/gcc/config/aarch64/tuning_models/neoversev3.h
> > > index
> >
> c602d067c7116cf6b081caeae8d36f9969e06d8d..c91e8c829532f9236de01027
> > 70e5c6b94e83da9a 100644
> > > --- a/gcc/config/aarch64/tuning_models/neoversev3.h
> > > +++ b/gcc/config/aarch64/tuning_models/neoversev3.h
> > > @@ -135,6 +135,8 @@ static const sve_vec_cost neoversev3_sve_vector_cost
> =
> > > operation more than a 64-bit gather. */
> > > 14, /* gather_load_x32_cost */
> > > 12, /* gather_load_x64_cost */
> > > + 42, /* gather_load_x32_init_cost */
> > > + 24, /* gather_load_x64_init_cost */
> > > 1 /* scatter_store_elt_cost */
> > > };
> > >
> > > diff --git a/gcc/config/aarch64/tuning_models/neoversev3ae.h
> > b/gcc/config/aarch64/tuning_models/neoversev3ae.h
> > > index
> >
> 96d7ccf03cd96056d09676d908c63a25e3da6765..61e439326eb6f983abf8574e
> > 657cfbb0c2f9bb33 100644
> > > --- a/gcc/config/aarch64/tuning_models/neoversev3ae.h
> > > +++ b/gcc/config/aarch64/tuning_models/neoversev3ae.h
> > > @@ -135,6 +135,8 @@ static const sve_vec_cost
> > neoversev3ae_sve_vector_cost =
> > > operation more than a 64-bit gather. */
> > > 14, /* gather_load_x32_cost */
> > > 12, /* gather_load_x64_cost */
> > > + 42, /* gather_load_x32_init_cost */
> > > + 24, /* gather_load_x64_init_cost */
> > > 1 /* scatter_store_elt_cost */
> > > };
