> -----Original Message-----
> From: Gcc-patches <gcc-patches-
> bounces+tamar.christina=arm....@gcc.gnu.org> On Behalf Of Richard
> Biener
> Sent: Friday, July 30, 2021 12:34 PM
> To: gcc-patches@gcc.gnu.org
> Cc: Richard Sandiford <richard.sandif...@arm.com>
> Subject: [PATCH] Add emulated gather capability to the vectorizer
>
> This adds a gather vectorization capability to the vectorizer without target
> support by decomposing the offset vector, doing sclar loads and then
> building a vector from the result. This is aimed mainly at cases where
> vectorizing the rest of the loop offsets the cost of vectorizing the gather.
>
> Note it's difficult to avoid vectorizing the offset load, but in some cases
> later
> passes can turn the vector load + extract into scalar loads, see the followup
> patch.
>
> On SPEC CPU 2017 510.parest_r this improves runtime from 250s to 219s on a
> Zen2 CPU which has its native gather instructions disabled (using those the
> runtime instead increases to 254s) using -Ofast -march=znver2 [-flto]. It
> turns out the critical loops in this benchmark all perform gather operations.
>
> Bootstrapped and tested on x86_64-unknown-linux-gnu.
>
> Any comments? I still plan to run this over full SPEC and I have to apply
> TLC to
> the followup patch before I can post it.
>
Interesting patch, I wonder if this can be used to vectorize the first loop
satd in x264,
There the loads look like a gather due to how the dr are detected, you could
transform
It into a linear load and widening operations.
But we could never pattern match it because no SLP tree was ever created
because of the
loads. Maybe this will allow us to then?
Cheers,
Tamar
> I think neither power nor z has gather so I'm curious if the patch helps
> 510.parest_r there, I'm unsure about neon/advsimd.
> Both might need the followup patch - I was surprised about the speedup
> without it on Zen (the followup improves runtime to 198s there).
>
> Thanks,
> Richard.
>
> 2021-07-30 Richard Biener <rguent...@suse.de>
>
> * tree-vect-data-refs.c (vect_check_gather_scatter):
> Include widening conversions only when the result is
> still handed by native gather or the current offset
> size not already matches the data size.
> Also succeed analysis in case there's no native support,
> noted by a IFN_LAST ifn and a NULL decl.
> * tree-vect-patterns.c (vect_recog_gather_scatter_pattern):
> Test for no IFN gather rather than decl gather.
> * tree-vect-stmts.c (vect_model_load_cost): Pass in the
> gather-scatter info and cost emulated gathers accordingly.
> (vect_truncate_gather_scatter_offset): Properly test for
> no IFN gather.
> (vect_use_strided_gather_scatters_p): Likewise.
> (get_load_store_type): Handle emulated gathers and its
> restrictions.
> (vectorizable_load): Likewise. Emulate them by extracting
> scalar offsets, doing scalar loads and a vector construct.
>
> * gcc.target/i386/vect-gather-1.c: New testcase.
> * gfortran.dg/vect/vect-8.f90: Adjust.
> ---
> gcc/testsuite/gcc.target/i386/vect-gather-1.c | 18 ++++
> gcc/testsuite/gfortran.dg/vect/vect-8.f90 | 2 +-
> gcc/tree-vect-data-refs.c | 29 +++--
> gcc/tree-vect-patterns.c | 2 +-
> gcc/tree-vect-stmts.c | 100 ++++++++++++++++--
> 5 files changed, 136 insertions(+), 15 deletions(-) create mode 100644
> gcc/testsuite/gcc.target/i386/vect-gather-1.c
>
> diff --git a/gcc/testsuite/gcc.target/i386/vect-gather-1.c
> b/gcc/testsuite/gcc.target/i386/vect-gather-1.c
> new file mode 100644
> index 00000000000..134aef39666
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/i386/vect-gather-1.c
> @@ -0,0 +1,18 @@
> +/* { dg-do compile } */
> +/* { dg-options "-Ofast -msse2 -fdump-tree-vect-details" } */
> +
> +#ifndef INDEXTYPE
> +#define INDEXTYPE int
> +#endif
> +double vmul(INDEXTYPE *rowstart, INDEXTYPE *rowend,
> + double *luval, double *dst)
> +{
> + double res = 0;
> + for (const INDEXTYPE * col = rowstart; col != rowend; ++col, ++luval)
> + res += *luval * dst[*col];
> + return res;
> +}
> +
> +/* With gather emulation this should be profitable to vectorize
> + even with plain SSE2. */
> +/* { dg-final { scan-tree-dump "loop vectorized" "vect" } } */
> diff --git a/gcc/testsuite/gfortran.dg/vect/vect-8.f90
> b/gcc/testsuite/gfortran.dg/vect/vect-8.f90
> index 9994805d77f..cc1aebfbd84 100644
> --- a/gcc/testsuite/gfortran.dg/vect/vect-8.f90
> +++ b/gcc/testsuite/gfortran.dg/vect/vect-8.f90
> @@ -706,5 +706,5 @@ END SUBROUTINE kernel
>
> ! { dg-final { scan-tree-dump-times "vectorized 24 loops" 1 "vect" { target
> aarch64_sve } } } ! { dg-final { scan-tree-dump-times "vectorized 23 loops" 1
> "vect" { target { aarch64*-*-* && { ! aarch64_sve } } } } } -! { dg-final {
> scan-
> tree-dump-times "vectorized 2\[23\] loops" 1 "vect" { target
> { vect_intdouble_cvt && { ! aarch64*-*-* } } } } }
> +! { dg-final { scan-tree-dump-times "vectorized 2\[234\] loops" 1
> +"vect" { target { vect_intdouble_cvt && { ! aarch64*-*-* } } } } }
> ! { dg-final { scan-tree-dump-times "vectorized 17 loops" 1 "vect" { target
> { { !
> vect_intdouble_cvt } && { ! aarch64*-*-* } } } } } diff --git a/gcc/tree-vect-
> data-refs.c b/gcc/tree-vect-data-refs.c index 6995efba899..0279e75fa8e
> 100644
> --- a/gcc/tree-vect-data-refs.c
> +++ b/gcc/tree-vect-data-refs.c
> @@ -4007,8 +4007,26 @@ vect_check_gather_scatter (stmt_vec_info
> stmt_info, loop_vec_info loop_vinfo,
> continue;
> }
>
> - if (TYPE_PRECISION (TREE_TYPE (op0))
> - < TYPE_PRECISION (TREE_TYPE (off)))
> + /* Include the conversion if it is widening and we're using
> + the IFN path or the target can handle the converted from
> + offset or the current size is not already the same as the
> + data vector element size. */
> + if ((TYPE_PRECISION (TREE_TYPE (op0))
> + < TYPE_PRECISION (TREE_TYPE (off)))
> + && ((!use_ifn_p
> + && (DR_IS_READ (dr)
> + ? (targetm.vectorize.builtin_gather
> + && targetm.vectorize.builtin_gather (vectype,
> + TREE_TYPE (op0),
> + scale))
> + : (targetm.vectorize.builtin_scatter
> + && targetm.vectorize.builtin_scatter (vectype,
> + TREE_TYPE
> (op0),
> + scale))))
> + || (!use_ifn_p
> + && !operand_equal_p (TYPE_SIZE (TREE_TYPE (off)),
> + TYPE_SIZE (TREE_TYPE (vectype)),
> + 0))))
> {
> off = op0;
> offtype = TREE_TYPE (off);
> @@ -4036,7 +4054,8 @@ vect_check_gather_scatter (stmt_vec_info
> stmt_info, loop_vec_info loop_vinfo,
> if (!vect_gather_scatter_fn_p (loop_vinfo, DR_IS_READ (dr), masked_p,
> vectype, memory_type, offtype, scale,
> &ifn, &offset_vectype))
> - return false;
> + ifn = IFN_LAST;
> + decl = NULL_TREE;
> }
> else
> {
> @@ -4050,10 +4069,6 @@ vect_check_gather_scatter (stmt_vec_info
> stmt_info, loop_vec_info loop_vinfo,
> if (targetm.vectorize.builtin_scatter)
> decl = targetm.vectorize.builtin_scatter (vectype, offtype, scale);
> }
> -
> - if (!decl)
> - return false;
> -
> ifn = IFN_LAST;
> /* The offset vector type will be read from DECL when needed. */
> offset_vectype = NULL_TREE;
> diff --git a/gcc/tree-vect-patterns.c b/gcc/tree-vect-patterns.c index
> 743fd3f5414..25de97bd9b0 100644
> --- a/gcc/tree-vect-patterns.c
> +++ b/gcc/tree-vect-patterns.c
> @@ -4811,7 +4811,7 @@ vect_recog_gather_scatter_pattern (vec_info
> *vinfo,
> function for the gather/scatter operation. */
> gather_scatter_info gs_info;
> if (!vect_check_gather_scatter (stmt_info, loop_vinfo, &gs_info)
> - || gs_info.decl)
> + || gs_info.ifn == IFN_LAST)
> return NULL;
>
> /* Convert the mask to the right form. */ diff --git
> a/gcc/tree-vect-stmts.c
> b/gcc/tree-vect-stmts.c index 05085e1b110..9d51b476db6 100644
> --- a/gcc/tree-vect-stmts.c
> +++ b/gcc/tree-vect-stmts.c
> @@ -1084,6 +1084,7 @@ static void
> vect_model_load_cost (vec_info *vinfo,
> stmt_vec_info stmt_info, unsigned ncopies, poly_uint64
> vf,
> vect_memory_access_type memory_access_type,
> + gather_scatter_info *gs_info,
> slp_tree slp_node,
> stmt_vector_for_cost *cost_vec) { @@ -1172,9 +1173,17
> @@ vect_model_load_cost (vec_info *vinfo,
> if (memory_access_type == VMAT_ELEMENTWISE
> || memory_access_type == VMAT_GATHER_SCATTER)
> {
> - /* N scalar loads plus gathering them into a vector. */
> tree vectype = STMT_VINFO_VECTYPE (stmt_info);
> unsigned int assumed_nunits = vect_nunits_for_cost (vectype);
> + if (memory_access_type == VMAT_GATHER_SCATTER
> + && gs_info->ifn == IFN_LAST && !gs_info->decl)
> + /* For emulated gathers N offset vector element extracts
> + (we assume the scalar scaling and ptr + offset add is consumed by
> + the load). */
> + inside_cost += record_stmt_cost (cost_vec, ncopies *
> assumed_nunits,
> + vec_to_scalar, stmt_info, 0,
> + vect_body);
> + /* N scalar loads plus gathering them into a vector. */
> inside_cost += record_stmt_cost (cost_vec,
> ncopies * assumed_nunits,
> scalar_load, stmt_info, 0, vect_body);
> @@ -1184,7 +1193,9 @@ vect_model_load_cost (vec_info *vinfo,
> &inside_cost, &prologue_cost,
> cost_vec, cost_vec, true);
> if (memory_access_type == VMAT_ELEMENTWISE
> - || memory_access_type == VMAT_STRIDED_SLP)
> + || memory_access_type == VMAT_STRIDED_SLP
> + || (memory_access_type == VMAT_GATHER_SCATTER
> + && gs_info->ifn == IFN_LAST && !gs_info->decl))
> inside_cost += record_stmt_cost (cost_vec, ncopies, vec_construct,
> stmt_info, 0, vect_body);
>
> @@ -1866,7 +1877,8 @@ vect_truncate_gather_scatter_offset
> (stmt_vec_info stmt_info,
> tree memory_type = TREE_TYPE (DR_REF (dr));
> if (!vect_gather_scatter_fn_p (loop_vinfo, DR_IS_READ (dr), masked_p,
> vectype, memory_type, offset_type, scale,
> - &gs_info->ifn, &gs_info->offset_vectype))
> + &gs_info->ifn, &gs_info->offset_vectype)
> + || gs_info->ifn == IFN_LAST)
> continue;
>
> gs_info->decl = NULL_TREE;
> @@ -1901,7 +1913,7 @@ vect_use_strided_gather_scatters_p
> (stmt_vec_info stmt_info,
> gather_scatter_info *gs_info)
> {
> if (!vect_check_gather_scatter (stmt_info, loop_vinfo, gs_info)
> - || gs_info->decl)
> + || gs_info->ifn == IFN_LAST)
> return vect_truncate_gather_scatter_offset (stmt_info, loop_vinfo,
> masked_p, gs_info);
>
> @@ -2355,6 +2367,27 @@ get_load_store_type (vec_info *vinfo,
> stmt_vec_info stmt_info,
> vls_type == VLS_LOAD ? "gather" : "scatter");
> return false;
> }
> + else if (gs_info->ifn == IFN_LAST && !gs_info->decl)
> + {
> + if (vls_type != VLS_LOAD)
> + {
> + if (dump_enabled_p ())
> + dump_printf_loc (MSG_MISSED_OPTIMIZATION,
> vect_location,
> + "unsupported emulated scatter.\n");
> + return false;
> + }
> + else if (!TYPE_VECTOR_SUBPARTS (vectype).is_constant ()
> + || !known_eq (TYPE_VECTOR_SUBPARTS (vectype),
> + TYPE_VECTOR_SUBPARTS
> + (gs_info->offset_vectype)))
> + {
> + if (dump_enabled_p ())
> + dump_printf_loc (MSG_MISSED_OPTIMIZATION,
> vect_location,
> + "unsupported vector types for emulated "
> + "gather.\n");
> + return false;
> + }
> + }
> /* Gather-scatter accesses perform only component accesses, alignment
> is irrelevant for them. */
> *alignment_support_scheme = dr_unaligned_supported; @@ -8692,6
> +8725,15 @@ vectorizable_load (vec_info *vinfo,
> "unsupported access type for masked load.\n");
> return false;
> }
> + else if (memory_access_type == VMAT_GATHER_SCATTER
> + && gs_info.ifn == IFN_LAST
> + && !gs_info.decl)
> + {
> + if (dump_enabled_p ())
> + dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
> + "unsupported masked emulated gather.\n");
> + return false;
> + }
> }
>
> if (!vec_stmt) /* transformation not required. */ @@ -8725,7 +8767,7 @@
> vectorizable_load (vec_info *vinfo,
>
> STMT_VINFO_TYPE (orig_stmt_info) = load_vec_info_type;
> vect_model_load_cost (vinfo, stmt_info, ncopies, vf,
> memory_access_type,
> - slp_node, cost_vec);
> + &gs_info, slp_node, cost_vec);
> return true;
> }
>
> @@ -9438,7 +9480,8 @@ vectorizable_load (vec_info *vinfo,
> unsigned int misalign;
> unsigned HOST_WIDE_INT align;
>
> - if (memory_access_type == VMAT_GATHER_SCATTER)
> + if (memory_access_type == VMAT_GATHER_SCATTER
> + && gs_info.ifn != IFN_LAST)
> {
> tree zero = build_zero_cst (vectype);
> tree scale = size_int (gs_info.scale); @@ -9456,6
> +9499,51 @@ vectorizable_load (vec_info *vinfo,
> data_ref = NULL_TREE;
> break;
> }
> + else if (memory_access_type == VMAT_GATHER_SCATTER)
> + {
> + /* Emulated gather-scatter. */
> + gcc_assert (!final_mask);
> + unsigned HOST_WIDE_INT const_nunits
> + = nunits.to_constant ();
> + vec<constructor_elt, va_gc> *ctor_elts;
> + vec_alloc (ctor_elts, const_nunits);
> + gimple_seq stmts = NULL;
> + tree idx_type = TREE_TYPE (TREE_TYPE (vec_offset));
> + tree scale = size_int (gs_info.scale);
> + align
> + = get_object_alignment (DR_REF (first_dr_info-
> >dr));
> + tree ltype = build_aligned_type (TREE_TYPE
> (vectype),
> + align);
> + for (unsigned k = 0; k < const_nunits; ++k)
> + {
> + tree boff = size_binop (MULT_EXPR,
> + TYPE_SIZE (idx_type),
> + bitsize_int (k));
> + tree idx = gimple_build (&stmts, BIT_FIELD_REF,
> + idx_type, vec_offset,
> + TYPE_SIZE (idx_type),
> + boff);
> + idx = gimple_convert (&stmts, sizetype, idx);
> + idx = gimple_build (&stmts, MULT_EXPR,
> + sizetype, idx, scale);
> + tree ptr = gimple_build (&stmts, PLUS_EXPR,
> + TREE_TYPE (dataref_ptr),
> + dataref_ptr, idx);
> + ptr = gimple_convert (&stmts, ptr_type_node, ptr);
> + tree elt = make_ssa_name (TREE_TYPE (vectype));
> + tree ref = build2 (MEM_REF, ltype, ptr,
> + build_int_cst (ref_type, 0));
> + new_stmt = gimple_build_assign (elt, ref);
> + gimple_seq_add_stmt (&stmts, new_stmt);
> + CONSTRUCTOR_APPEND_ELT (ctor_elts,
> NULL_TREE, elt);
> + }
> + gsi_insert_seq_before (gsi, stmts, GSI_SAME_STMT);
> + new_stmt = gimple_build_assign (NULL_TREE,
> + build_constructor
> + (vectype, ctor_elts));
> + data_ref = NULL_TREE;
> + break;
> + }
>
> align =
> known_alignment (DR_TARGET_ALIGNMENT
> (first_dr_info));
> --
> 2.31.1
