On Fri, Apr 19, 2024 at 3:29 PM Tamar Christina <tamar.christ...@arm.com> wrote:
>
> Hi All,
>
> As the reporter in PR114769 points out the control flow for the abd detection
> is hard to follow. This is because vect_recog_absolute_difference has two
> different ways it can return true.
>
> 1. It can return true when the widening operation is matched, in which case
> unprom is set, half_type is not NULL and diff_stmt is not set.
>
> 2. It can return true when the widening operation is not matched, but the stmt
> being checked is a minus. In this case unprom is not set, half_type is set
> to NULL and diff_stmt is set. This because to get to diff_stmt you have to
> dig through the abs statement and any possible promotions.
>
> This however leads to complicated uses of the function at the call sites as
> the
> exact semantic needs to be known to use it safely.
>
> vect_recog_absolute_difference has two callers:
>
> 1. vect_recog_sad_pattern where if you return true with unprom not set, then
> *half_type will be NULL. The call to vect_supportable_direct_optab_p will
> always reject it since there's no vector mode for NULL. Note that if
> looking
> at the dump files, the convention in the dump files have always been that
> we
> first indicate that a pattern could possibly be recognize and then check
> that
> it's supported.
>
> This change somewhat incorrectly makes the diagnostic message get printed
> for
> "invalid" patterns.
>
> 2. vect_recog_abd_pattern, where if half_type is NULL, it then uses diff_stmt
> to
> set them.
>
> So while the note in the dump file is misleading, the code is safe.
>
> This refactors the code, it now only has 1 success condition, and diff_stmt is
> always set to the minus statement in the abs if there is one.
>
> The function now only returns success if the widening minus is found, in which
> case unprom and half_type set.
>
> This then leaves it up to the caller to decide if they want to do anything
> with
> diff_stmt.
>
> Bootstrapped Regtested on aarch64-none-linux-gnu and no issues.
>
> Ok for master?
OK.
Thanks,
Richard.
> Thanks,
> Tamar
>
> gcc/ChangeLog:
>
> PR tree-optimization/114769
> * tree-vect-patterns.cc:
> (vect_recog_absolute_difference): Have only one success condition.
> (vect_recog_abd_pattern): Handle further checks if
> vect_recog_absolute_difference fails.
>
> ---
> diff --git a/gcc/tree-vect-patterns.cc b/gcc/tree-vect-patterns.cc
> index
> 4f491c6b8336f8710c3519dec1fa7e0f49387d2b..87c2acff386d91d22a3b2d6e6443d1f2f2326ea6
> 100644
> --- a/gcc/tree-vect-patterns.cc
> +++ b/gcc/tree-vect-patterns.cc
> @@ -797,8 +797,7 @@ vect_split_statement (vec_info *vinfo, stmt_vec_info
> stmt2_info, tree new_rhs,
> HALF_TYPE and UNPROM will be set should the statement be found to
> be a widened operation.
> DIFF_STMT will be set to the MINUS_EXPR
> - statement that precedes the ABS_STMT unless vect_widened_op_tree
> - succeeds.
> + statement that precedes the ABS_STMT if it is a MINUS_EXPR..
> */
> static bool
> vect_recog_absolute_difference (vec_info *vinfo, gassign *abs_stmt,
> @@ -843,6 +842,12 @@ vect_recog_absolute_difference (vec_info *vinfo, gassign
> *abs_stmt,
> if (!diff_stmt_vinfo)
> return false;
>
> + gassign *diff = dyn_cast <gassign *> (STMT_VINFO_STMT (diff_stmt_vinfo));
> + if (diff_stmt && diff
> + && gimple_assign_rhs_code (diff) == MINUS_EXPR
> + && TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (abs_oprnd)))
> + *diff_stmt = 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,
> @@ -850,17 +855,6 @@ vect_recog_absolute_difference (vec_info *vinfo, gassign
> *abs_stmt,
> false, 2, unprom, half_type))
> return true;
>
> - /* Failed to find a widen operation so we check for a regular MINUS_EXPR.
> */
> - gassign *diff = dyn_cast <gassign *> (STMT_VINFO_STMT (diff_stmt_vinfo));
> - if (diff_stmt && diff
> - && gimple_assign_rhs_code (diff) == MINUS_EXPR
> - && TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (abs_oprnd)))
> - {
> - *diff_stmt = diff;
> - *half_type = NULL_TREE;
> - return true;
> - }
> -
> return false;
> }
>
> @@ -1499,27 +1493,22 @@ vect_recog_abd_pattern (vec_info *vinfo,
> tree out_type = TREE_TYPE (gimple_assign_lhs (last_stmt));
>
> vect_unpromoted_value unprom[2];
> - gassign *diff_stmt;
> - tree half_type;
> - if (!vect_recog_absolute_difference (vinfo, last_stmt, &half_type,
> + gassign *diff_stmt = NULL;
> + tree abd_in_type;
> + if (!vect_recog_absolute_difference (vinfo, last_stmt, &abd_in_type,
> unprom, &diff_stmt))
> - return NULL;
> -
> - tree abd_in_type, abd_out_type;
> -
> - if (half_type)
> - {
> - abd_in_type = half_type;
> - abd_out_type = abd_in_type;
> - }
> - else
> {
> + /* We cannot try further without having a non-widening MINUS. */
> + if (!diff_stmt)
> + return NULL;
> +
> unprom[0].op = gimple_assign_rhs1 (diff_stmt);
> unprom[1].op = gimple_assign_rhs2 (diff_stmt);
> abd_in_type = signed_type_for (out_type);
> - abd_out_type = abd_in_type;
> }
>
> + tree abd_out_type = abd_in_type;
> +
> tree vectype_in = get_vectype_for_scalar_type (vinfo, abd_in_type);
> if (!vectype_in)
> return NULL;
>
>
>
>
> --
