[PATCH] vect: Missed opportunity to use [SU]ABD
Richard Sandiford
richard.sandiford@arm.com
Wed May 10 09:01:20 GMT 2023
Oluwatamilore Adebayo <Oluwatamilore.Adebayo@arm.com> writes:
> From 0b5f469171c340ef61a48a31877d495bb77bd35f Mon Sep 17 00:00:00 2001
> From: oluade01 <oluwatamilore.adebayo@arm.com>
> Date: Fri, 14 Apr 2023 10:24:43 +0100
> Subject: [PATCH 1/4] Missed opportunity to use [SU]ABD
>
> This adds a recognition pattern for the non-widening
> absolute difference (ABD).
>
> gcc/ChangeLog:
>
> * doc/md.texi (sabd, uabd): Document them.
> * internal-fn.def (ABD): Use new optab.
> * optabs.def (sabd_optab, uabd_optab): New optabs,
> * tree-vect-patterns.cc (vect_recog_absolute_difference):
> Recognize the following idiom abs (a - b).
> (vect_recog_sad_pattern): Refactor to use
> vect_recog_absolute_difference.
> (vect_recog_abd_pattern): Use patterns found by
> vect_recog_absolute_difference to build a new ABD
> internal call.
> ---
> gcc/doc/md.texi | 10 ++
> gcc/internal-fn.def | 3 +
> gcc/optabs.def | 2 +
> gcc/tree-vect-patterns.cc | 250 +++++++++++++++++++++++++++++++++-----
> 4 files changed, 234 insertions(+), 31 deletions(-)
>
> diff --git a/gcc/doc/md.texi b/gcc/doc/md.texi
> index 07bf8bdebffb2e523f25a41f2b57e43c0276b745..0ad546c63a8deebb4b6db894f437d1e21f0245a8 100644
> --- a/gcc/doc/md.texi
> +++ b/gcc/doc/md.texi
> @@ -5778,6 +5778,16 @@ Other shift and rotate instructions, analogous to the
> Vector shift and rotate instructions that take vectors as operand 2
> instead of a scalar type.
>
> +@cindex @code{uabd@var{m}} instruction pattern
> +@cindex @code{sabd@var{m}} instruction pattern
> +@item @samp{uabd@var{m}}, @samp{sabd@var{m}}
> +Signed and unsigned absolute difference instructions. These
> +instructions find the difference between operands 1 and 2
> +then return the absolute value. A C code equivalent would be:
> +@smallexample
> +op0 = abs (op0 - op1)
op0 = abs (op1 - op2)
But that isn't the correct calculation for unsigned (where abs doesn't
really work). It also doesn't handle some cases correctly for signed.
I think it's more:
op0 = op1 > op2 ? (unsigned type) op1 - op2 : (unsigned type) op2 - op1
or (conceptually) max minus min.
E.g. for 16-bit values, the absolute difference between signed 0x7fff
and signed -0x8000 is 0xffff (reinterpreted as -1 if you cast back
to signed). But, ignoring undefined behaviour:
0x7fff - 0x8000 = -1
abs(-1) = 1
which gives the wrong answer.
We might still be able to fold C abs(a - b) to abd for signed a and b
by relying on undefined behaviour (TYPE_OVERFLOW_UNDEFINED). But we
can't do it for -fwrapv.
Richi knows better than me what would be appropriate here.
Thanks,
Richard
> +@end smallexample
> +
> @cindex @code{avg@var{m}3_floor} instruction pattern
> @cindex @code{uavg@var{m}3_floor} instruction pattern
> @item @samp{avg@var{m}3_floor}
> diff --git a/gcc/internal-fn.def b/gcc/internal-fn.def
> index 7fe742c2ae713e7152ab05cfdfba86e4e0aa3456..0f1724ecf37a31c231572edf90b5577e2d82f468 100644
> --- a/gcc/internal-fn.def
> +++ b/gcc/internal-fn.def
> @@ -167,6 +167,9 @@ DEF_INTERNAL_OPTAB_FN (FMS, ECF_CONST, fms, ternary)
> DEF_INTERNAL_OPTAB_FN (FNMA, ECF_CONST, fnma, ternary)
> DEF_INTERNAL_OPTAB_FN (FNMS, ECF_CONST, fnms, ternary)
>
> +DEF_INTERNAL_SIGNED_OPTAB_FN (ABD, ECF_CONST | ECF_NOTHROW, first,
> + sabd, uabd, binary)
> +
> DEF_INTERNAL_SIGNED_OPTAB_FN (AVG_FLOOR, ECF_CONST | ECF_NOTHROW, first,
> savg_floor, uavg_floor, binary)
> DEF_INTERNAL_SIGNED_OPTAB_FN (AVG_CEIL, ECF_CONST | ECF_NOTHROW, first,
> diff --git a/gcc/optabs.def b/gcc/optabs.def
> index 695f5911b300c9ca5737de9be809fa01aabe5e01..29bc92281a2175f898634cbe6af63c18021e5268 100644
> --- a/gcc/optabs.def
> +++ b/gcc/optabs.def
> @@ -359,6 +359,8 @@ OPTAB_D (mask_fold_left_plus_optab, "mask_fold_left_plus_$a")
> OPTAB_D (extract_last_optab, "extract_last_$a")
> OPTAB_D (fold_extract_last_optab, "fold_extract_last_$a")
>
> +OPTAB_D (uabd_optab, "uabd$a3")
> +OPTAB_D (sabd_optab, "sabd$a3")
> OPTAB_D (savg_floor_optab, "avg$a3_floor")
> OPTAB_D (uavg_floor_optab, "uavg$a3_floor")
> OPTAB_D (savg_ceil_optab, "avg$a3_ceil")
> diff --git a/gcc/tree-vect-patterns.cc b/gcc/tree-vect-patterns.cc
> index a49b09539776c0056e77f99b10365d0a8747fbc5..91e1f9d4b610275dd833ec56dc77f76367ee7886 100644
> --- a/gcc/tree-vect-patterns.cc
> +++ b/gcc/tree-vect-patterns.cc
> @@ -770,6 +770,89 @@ vect_split_statement (vec_info *vinfo, stmt_vec_info stmt2_info, tree new_rhs,
> }
> }
>
> +/* Look for the following pattern
> + X = x[i]
> + Y = y[i]
> + DIFF = X - Y
> + DAD = ABS_EXPR<DIFF>
> + */
> +static bool
> +vect_recog_absolute_difference (vec_info *vinfo, gassign *abs_stmt,
> + tree *half_type, bool reject_unsigned,
> + vect_unpromoted_value unprom[2],
> + tree diff_oprnds[2])
> +{
> + if (!abs_stmt)
> + return false;
> +
> + /* FORNOW. Can continue analyzing the def-use chain when this stmt in a phi
> + inside the loop (in case we are analyzing an outer-loop). */
> + enum tree_code code = gimple_assign_rhs_code (abs_stmt);
> + if (code != ABS_EXPR && code != ABSU_EXPR)
> + return false;
> +
> + tree abs_oprnd = gimple_assign_rhs1 (abs_stmt);
> + tree abs_type = TREE_TYPE (abs_oprnd);
> + if (!abs_oprnd)
> + return false;
> + if (reject_unsigned && TYPE_UNSIGNED (abs_type))
> + return false;
> + if (!ANY_INTEGRAL_TYPE_P (abs_type) || TYPE_OVERFLOW_WRAPS (abs_type))
> + return false;
> +
> + /* Peel off conversions from the ABS input. This can involve sign
> + changes (e.g. from an unsigned subtraction to a signed ABS input)
> + or signed promotion, but it can't include unsigned promotion.
> + (Note that ABS of an unsigned promotion should have been folded
> + away before now anyway.) */
> + vect_unpromoted_value unprom_diff;
> + abs_oprnd = vect_look_through_possible_promotion (vinfo, abs_oprnd,
> + &unprom_diff);
> + if (!abs_oprnd)
> + return false;
> + if (TYPE_PRECISION (unprom_diff.type) != TYPE_PRECISION (abs_type)
> + && TYPE_UNSIGNED (unprom_diff.type))
> + if (!reject_unsigned)
> + return false;
> +
> + /* We then detect if the operand of abs_expr is defined by a minus_expr. */
> + stmt_vec_info diff_stmt_vinfo = vect_get_internal_def (vinfo, abs_oprnd);
> + if (!diff_stmt_vinfo)
> + return false;
> +
> + bool assigned_oprnds = false;
> + gassign *diff = dyn_cast <gassign *> (STMT_VINFO_STMT (diff_stmt_vinfo));
> + if (diff_oprnds && diff && gimple_assign_rhs_code (diff) == MINUS_EXPR)
> + {
> + assigned_oprnds = true;
> + diff_oprnds[0] = gimple_assign_rhs1 (diff);
> + diff_oprnds[1] = gimple_assign_rhs2 (diff);
> + }
> +
> + /* FORNOW. Can continue analyzing the def-use chain when this stmt in a phi
> + inside the loop (in case we are analyzing an outer-loop). */
> + if (vect_widened_op_tree (vinfo, diff_stmt_vinfo, MINUS_EXPR,
> + WIDEN_MINUS_EXPR,
> + false, 2, unprom, half_type))
> + {
> + if (diff_oprnds && !assigned_oprnds)
> + {
> + diff_oprnds[0] = unprom[0].op;
> + diff_oprnds[1] = unprom[1].op;
> + }
> + }
> + else if (!assigned_oprnds)
> + {
> + return false;
> + }
> + else
> + {
> + *half_type = NULL_TREE;
> + }
> +
> + return true;
> +}
> +
> /* Convert UNPROM to TYPE and return the result, adding new statements
> to STMT_INFO's pattern definition statements if no better way is
> available. VECTYPE is the vector form of TYPE.
> @@ -1308,40 +1391,13 @@ vect_recog_sad_pattern (vec_info *vinfo,
> /* FORNOW. Can continue analyzing the def-use chain when this stmt in a phi
> inside the loop (in case we are analyzing an outer-loop). */
> gassign *abs_stmt = dyn_cast <gassign *> (abs_stmt_vinfo->stmt);
> - if (!abs_stmt
> - || (gimple_assign_rhs_code (abs_stmt) != ABS_EXPR
> - && gimple_assign_rhs_code (abs_stmt) != ABSU_EXPR))
> - return NULL;
> -
> - tree abs_oprnd = gimple_assign_rhs1 (abs_stmt);
> - tree abs_type = TREE_TYPE (abs_oprnd);
> - if (TYPE_UNSIGNED (abs_type))
> - return NULL;
> -
> - /* Peel off conversions from the ABS input. This can involve sign
> - changes (e.g. from an unsigned subtraction to a signed ABS input)
> - or signed promotion, but it can't include unsigned promotion.
> - (Note that ABS of an unsigned promotion should have been folded
> - away before now anyway.) */
> - vect_unpromoted_value unprom_diff;
> - abs_oprnd = vect_look_through_possible_promotion (vinfo, abs_oprnd,
> - &unprom_diff);
> - if (!abs_oprnd)
> - return NULL;
> - if (TYPE_PRECISION (unprom_diff.type) != TYPE_PRECISION (abs_type)
> - && TYPE_UNSIGNED (unprom_diff.type))
> - return NULL;
>
> - /* We then detect if the operand of abs_expr is defined by a minus_expr. */
> - stmt_vec_info diff_stmt_vinfo = vect_get_internal_def (vinfo, abs_oprnd);
> - if (!diff_stmt_vinfo)
> + vect_unpromoted_value unprom[2];
> + if (!vect_recog_absolute_difference (vinfo, abs_stmt, &half_type,
> + true, unprom, NULL))
> return NULL;
>
> - /* FORNOW. Can continue analyzing the def-use chain when this stmt in a phi
> - inside the loop (in case we are analyzing an outer-loop). */
> - vect_unpromoted_value unprom[2];
> - if (!vect_widened_op_tree (vinfo, diff_stmt_vinfo, MINUS_EXPR, WIDEN_MINUS_EXPR,
> - false, 2, unprom, &half_type))
> + if (!half_type)
> return NULL;
>
> vect_pattern_detected ("vect_recog_sad_pattern", last_stmt);
> @@ -1363,6 +1419,137 @@ vect_recog_sad_pattern (vec_info *vinfo,
> return pattern_stmt;
> }
>
> +/* Function vect_recog_abd_pattern
> +
> + Try to find the following ABsolute Difference (ABD) pattern:
> +
> + VTYPE x, y, out;
> + type diff;
> + loop i in range:
> + S1 diff = x[i] - y[i]
> + S2 out[i] = ABS_EXPR <diff>;
> +
> + where 'type' is a integer and 'VTYPE' is a vector of integers
> + the same size as 'type'
> +
> + Input:
> +
> + * STMT_VINFO: The stmt from which the pattern search begins
> +
> + Output:
> +
> + * TYPE_out: The type of the output of this pattern
> +
> + * Return value: A new stmt that will be used to replace the sequence of
> + stmts that constitute the pattern; either SABD or UABD:
> + SABD_EXPR<x, y, out>
> + UABD_EXPR<x, y, out>
> +
> + UABD expressions are used when the input types are
> + narrower than the output types or the output type is narrower
> + than 32 bits
> + */
> +
> +static gimple *
> +vect_recog_abd_pattern (vec_info *vinfo,
> + stmt_vec_info stmt_vinfo, tree *type_out)
> +{
> + /* Look for the following patterns
> + X = x[i]
> + Y = y[i]
> + DIFF = X - Y
> + DAD = ABS_EXPR<DIFF>
> + out[i] = DAD
> +
> + In which
> + - X, Y, DIFF, DAD all have the same type
> + - x, y, out are all vectors of the same type
> + */
> + gassign *last_stmt = dyn_cast <gassign *> (STMT_VINFO_STMT (stmt_vinfo));
> + if (!last_stmt)
> + return NULL;
> +
> + tree out_type = TREE_TYPE (gimple_assign_lhs (last_stmt));
> +
> + gassign *abs_stmt = last_stmt;
> + if (gimple_assign_cast_p (last_stmt))
> + {
> + tree last_rhs = gimple_assign_rhs1 (last_stmt);
> + if (!SSA_VAR_P (last_rhs))
> + return NULL;
> +
> + abs_stmt = dyn_cast <gassign *> (SSA_NAME_DEF_STMT (last_rhs));
> + if (!abs_stmt)
> + return NULL;
> + }
> +
> + vect_unpromoted_value unprom[2];
> + tree diff_oprnds[2];
> + tree half_type;
> + if (!vect_recog_absolute_difference (vinfo, abs_stmt, &half_type,
> + false, unprom, diff_oprnds))
> + return NULL;
> +
> +#define SAME_TYPE(A, B) (TYPE_PRECISION (A) == TYPE_PRECISION (B))
> +
> + tree abd_oprnds[2];
> + if (half_type)
> + {
> + if (!SAME_TYPE (unprom[0].type, unprom[1].type))
> + return NULL;
> +
> + tree diff_type = TREE_TYPE (diff_oprnds[0]);
> + if (TYPE_PRECISION (out_type) != TYPE_PRECISION (diff_type))
> + {
> + vect_convert_inputs (vinfo, stmt_vinfo, 2, abd_oprnds, half_type, unprom,
> + get_vectype_for_scalar_type (vinfo, half_type));
> + }
> + else
> + {
> + abd_oprnds[0] = diff_oprnds[0];
> + abd_oprnds[1] = diff_oprnds[1];
> + }
> + }
> + else
> + {
> + if (unprom[0].op && unprom[1].op
> + && (!SAME_TYPE (unprom[0].type, unprom[1].type)
> + || !SAME_TYPE (unprom[0].type, out_type)))
> + return NULL;
> +
> + unprom[0].op = diff_oprnds[0];
> + unprom[1].op = diff_oprnds[1];
> + tree signed_out = signed_type_for (out_type);
> + tree signed_out_vectype = get_vectype_for_scalar_type (vinfo, signed_out);
> + vect_convert_inputs (vinfo, stmt_vinfo, 2, abd_oprnds,
> + signed_out, unprom, signed_out_vectype);
> +
> + if (!SAME_TYPE (TREE_TYPE (diff_oprnds[0]), TREE_TYPE (abd_oprnds[0])))
> + return NULL;
> + }
> +
> + if (!SAME_TYPE (TREE_TYPE (abd_oprnds[0]), TREE_TYPE (abd_oprnds[1]))
> + || !SAME_TYPE (TREE_TYPE (abd_oprnds[0]), out_type))
> + return NULL;
> +
> + vect_pattern_detected ("vect_recog_abd_pattern", last_stmt);
> +
> + tree vectype = get_vectype_for_scalar_type (vinfo, out_type);
> + if (!vectype
> + || !direct_internal_fn_supported_p (IFN_ABD, vectype,
> + OPTIMIZE_FOR_SPEED))
> + return NULL;
> +
> + *type_out = STMT_VINFO_VECTYPE (stmt_vinfo);
> +
> + tree var = vect_recog_temp_ssa_var (out_type, NULL);
> + gcall *abd_stmt = gimple_build_call_internal (IFN_ABD, 2,
> + abd_oprnds[0], abd_oprnds[1]);
> + gimple_call_set_lhs (abd_stmt, var);
> + gimple_set_location (abd_stmt, gimple_location (last_stmt));
> + return abd_stmt;
> +}
> +
> /* Recognize an operation that performs ORIG_CODE on widened inputs,
> so that it can be treated as though it had the form:
>
> @@ -6439,6 +6626,7 @@ struct vect_recog_func
> static vect_recog_func vect_vect_recog_func_ptrs[] = {
> { vect_recog_bitfield_ref_pattern, "bitfield_ref" },
> { vect_recog_bit_insert_pattern, "bit_insert" },
> + { vect_recog_abd_pattern, "abd" },
> { vect_recog_over_widening_pattern, "over_widening" },
> /* Must come after over_widening, which narrows the shift as much as
> possible beforehand. */
> --
> 2.25.1
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