From: Richard Biener <richard.guenther@gmail.com>
To: "Cui, Lili" <lili.cui@intel.com>
Cc: gcc-patches@gcc.gnu.org
Subject: Re: [PATCH] PR gcc/110148:Avoid adding loop-carried ops to long chains
Date: Thu, 29 Jun 2023 08:42:06 +0200 [thread overview]
Message-ID: <CAFiYyc3gGXaLsA0jVm6g8kaP8HozrNVEKm7xbrw65tVKfqb2xw@mail.gmail.com> (raw)
In-Reply-To: <20230629014949.1995621-1-lili.cui@intel.com>
On Thu, Jun 29, 2023 at 3:49 AM Cui, Lili <lili.cui@intel.com> wrote:
>
> From: Lili Cui <lili.cui@intel.com>
>
> Hi Maintainer
>
> This patch is to fix TSVC242 regression related to loop-carried ops.
>
> Bootstrapped and regtested. Ok for trunk?
OK.
Thanks,
Richard.
> Regards
> Lili.
>
> Avoid adding loop-carried ops to long chains, otherwise the whole chain will
> have dependencies across the loop iteration. Just keep loop-carried ops in a
> separate chain.
> E.g.
> x_1 = phi(x_0, x_2)
> y_1 = phi(y_0, y_2)
>
> a + b + c + d + e + x1 + y1
>
> SSA1 = a + b;
> SSA2 = c + d;
> SSA3 = SSA1 + e;
> SSA4 = SSA3 + SSA2;
> SSA5 = x1 + y1;
> SSA6 = SSA4 + SSA5;
>
> With the patch applied, these test cases improved by 32%~100%.
>
> S242:
> for (int i = 1; i < LEN_1D; ++i) {
> a[i] = a[i - 1] + s1 + s2 + b[i] + c[i] + d[i];}
>
> Case 1:
> for (int i = 1; i < LEN_1D; ++i) {
> a[i] = a[i - 1] + s1 + s2 + b[i] + c[i] + d[i] + e[i];}
>
> Case 2:
> for (int i = 1; i < LEN_1D; ++i) {
> a[i] = a[i - 1] + b[i - 1] + s1 + s2 + b[i] + c[i] + d[i] + e[i];}
>
> The value is the execution time
> A: original version
> B: with FMA patch g:e5405f065bace0685cb3b8878d1dfc7a6e7ef409(base on A)
> C: with current patch(base on B)
>
> A B C B/A C/A
> s242 2.859 5.152 2.859 1.802028681 1
> case 1 5.489 5.488 3.511 0.999818 0.64
> case 2 7.216 7.499 4.885 1.039218 0.68
>
> gcc/ChangeLog:
> PR tree-optimization/110148
> * tree-ssa-reassoc.cc (rewrite_expr_tree_parallel): Handle loop-carried
> ops in this function.
> ---
> gcc/tree-ssa-reassoc.cc | 236 ++++++++++++++++++++++++++++------------
> 1 file changed, 167 insertions(+), 69 deletions(-)
>
> diff --git a/gcc/tree-ssa-reassoc.cc b/gcc/tree-ssa-reassoc.cc
> index 96c88ec003e..f5da385e0b2 100644
> --- a/gcc/tree-ssa-reassoc.cc
> +++ b/gcc/tree-ssa-reassoc.cc
> @@ -5471,37 +5471,62 @@ get_reassociation_width (int ops_num, enum tree_code opc,
> return width;
> }
>
> +#define SPECIAL_BIASED_END_STMT 0 /* It is the end stmt of all ops. */
> +#define BIASED_END_STMT 1 /* It is the end stmt of normal or biased ops. */
> +#define NORMAL_END_STMT 2 /* It is the end stmt of normal ops. */
> +
> /* Rewrite statements with dependency chain with regard the chance to generate
> FMA.
> For the chain with FMA: Try to keep fma opportunity as much as possible.
> For the chain without FMA: Putting the computation in rank order and trying
> to allow operations to be executed in parallel.
> E.g.
> - e + f + g + a * b + c * d;
> + e + f + a * b + c * d;
>
> - ssa1 = e + f;
> - ssa2 = g + a * b;
> - ssa3 = ssa1 + c * d;
> - ssa4 = ssa2 + ssa3;
> + ssa1 = e + a * b;
> + ssa2 = f + c * d;
> + ssa3 = ssa1 + ssa2;
>
> This reassociation approach preserves the chance of fma generation as much
> - as possible. */
> + as possible.
> +
> + Another thing is to avoid adding loop-carried ops to long chains, otherwise
> + the whole chain will have dependencies across the loop iteration. Just keep
> + loop-carried ops in a separate chain.
> + E.g.
> + x_1 = phi(x_0, x_2)
> + y_1 = phi(y_0, y_2)
> +
> + a + b + c + d + e + x1 + y1
> +
> + SSA1 = a + b;
> + SSA2 = c + d;
> + SSA3 = SSA1 + e;
> + SSA4 = SSA3 + SSA2;
> + SSA5 = x1 + y1;
> + SSA6 = SSA4 + SSA5;
> + */
> static void
> rewrite_expr_tree_parallel (gassign *stmt, int width, bool has_fma,
> - const vec<operand_entry *> &ops)
> + const vec<operand_entry *> &ops)
> {
> enum tree_code opcode = gimple_assign_rhs_code (stmt);
> int op_num = ops.length ();
> + int op_normal_num = op_num;
> gcc_assert (op_num > 0);
> int stmt_num = op_num - 1;
> gimple **stmts = XALLOCAVEC (gimple *, stmt_num);
> - int op_index = op_num - 1;
> - int width_count = width;
> int i = 0, j = 0;
> tree tmp_op[2], op1;
> operand_entry *oe;
> gimple *stmt1 = NULL;
> tree last_rhs1 = gimple_assign_rhs1 (stmt);
> + int last_rhs1_stmt_index = 0, last_rhs2_stmt_index = 0;
> + int width_active = 0, width_count = 0;
> + bool has_biased = false, ops_changed = false;
> + auto_vec<operand_entry *> ops_normal;
> + auto_vec<operand_entry *> ops_biased;
> + vec<operand_entry *> *ops1;
>
> /* We start expression rewriting from the top statements.
> So, in this loop we create a full list of statements
> @@ -5510,83 +5535,155 @@ rewrite_expr_tree_parallel (gassign *stmt, int width, bool has_fma,
> for (i = stmt_num - 2; i >= 0; i--)
> stmts[i] = SSA_NAME_DEF_STMT (gimple_assign_rhs1 (stmts[i+1]));
>
> - /* Width should not be larger than op_num / 2, since we can not create
> + /* Avoid adding loop-carried ops to long chains, first filter out the
> + loop-carried. But we need to make sure that the length of the remainder
> + is not less than 4, which is the smallest ops length we can break the
> + dependency. */
> + FOR_EACH_VEC_ELT (ops, i, oe)
> + {
> + if (TREE_CODE (oe->op) == SSA_NAME
> + && bitmap_bit_p (biased_names, SSA_NAME_VERSION (oe->op))
> + && op_normal_num > 4)
> + {
> + ops_biased.safe_push (oe);
> + has_biased = true;
> + op_normal_num --;
> + }
> + else
> + ops_normal.safe_push (oe);
> + }
> +
> + /* Width should not be larger than ops length / 2, since we can not create
> more parallel dependency chains that exceeds such value. */
> - width = width <= op_num / 2 ? width : op_num / 2;
> + int width_normal = op_normal_num / 2;
> + int width_biased = (op_num - op_normal_num) / 2;
> + width_normal = width <= width_normal ? width : width_normal;
> + width_biased = width <= width_biased ? width : width_biased;
> +
> + ops1 = &ops_normal;
> + width_count = width_active = width_normal;
>
> /* Build parallel dependency chain according to width. */
> - for (i = 0; i < width; i++)
> + for (i = 0; i < stmt_num; i++)
> {
> - /* If the chain has FAM, we do not swap two operands. */
> - if (op_index > 1 && !has_fma)
> - swap_ops_for_binary_stmt (ops, op_index - 2);
> -
> - for (j = 0; j < 2; j++)
> + if (dump_file && (dump_flags & TDF_DETAILS))
> {
> - gcc_assert (op_index >= 0);
> - oe = ops[op_index--];
> - tmp_op[j] = oe->op;
> - /* If the stmt that defines operand has to be inserted, insert it
> - before the use. */
> - stmt1 = oe->stmt_to_insert;
> - if (stmt1)
> - insert_stmt_before_use (stmts[i], stmt1);
> - stmt1 = NULL;
> + fprintf (dump_file, "Transforming ");
> + print_gimple_stmt (dump_file, stmts[i], 0);
> }
> - stmts[i] = build_and_add_sum (TREE_TYPE (last_rhs1),
> - tmp_op[1],
> - tmp_op[0],
> - opcode);
> - gimple_set_visited (stmts[i], true);
>
> - if (dump_file && (dump_flags & TDF_DETAILS))
> + /* When the work of normal ops is over, but the loop is not over,
> + continue to do biased ops. */
> + if (width_count == 0 && ops1 == &ops_normal)
> {
> - fprintf (dump_file, " into ");
> - print_gimple_stmt (dump_file, stmts[i], 0);
> + ops1 = &ops_biased;
> + width_count = width_active = width_biased;
> + ops_changed = true;
> }
> - }
>
> - for (i = width; i < stmt_num; i++)
> - {
> - /* We keep original statement only for the last one. All others are
> - recreated. */
> - if ( op_index < 0)
> + /* Swap the operands if no FMA in the chain. */
> + if (ops1->length () > 2 && !has_fma)
> + swap_ops_for_binary_stmt (*ops1, ops1->length () - 3);
> +
> + if (i < width_active
> + || (ops_changed && i <= (last_rhs1_stmt_index + width_active)))
> {
> - if (width_count == 2)
> + for (j = 0; j < 2; j++)
> {
> -
> - /* We keep original statement only for the last one. All
> - others are recreated. */
> - gimple_assign_set_rhs1 (stmts[i], gimple_assign_lhs (stmts[i-1]));
> - gimple_assign_set_rhs2 (stmts[i], gimple_assign_lhs (stmts[i-2]));
> - update_stmt (stmts[i]);
> + oe = ops1->pop ();
> + tmp_op[j] = oe->op;
> + /* If the stmt that defines operand has to be inserted, insert it
> + before the use. */
> + stmt1 = oe->stmt_to_insert;
> + if (stmt1)
> + insert_stmt_before_use (stmts[i], stmt1);
> + stmt1 = NULL;
> }
> - else
> - {
> + stmts[i] = build_and_add_sum (TREE_TYPE (last_rhs1),
> + tmp_op[1],
> + tmp_op[0],
> + opcode);
> + gimple_set_visited (stmts[i], true);
>
> - stmts[i] =
> - build_and_add_sum (TREE_TYPE (last_rhs1),
> - gimple_assign_lhs (stmts[i-width_count]),
> - gimple_assign_lhs (stmts[i-width_count+1]),
> - opcode);
> - gimple_set_visited (stmts[i], true);
> - width_count--;
> - }
> }
> else
> {
> - /* Attach the rest of the ops to the parallel dependency chain. */
> - oe = ops[op_index--];
> - op1 = oe->op;
> - stmt1 = oe->stmt_to_insert;
> - if (stmt1)
> - insert_stmt_before_use (stmts[i], stmt1);
> - stmt1 = NULL;
> - stmts[i] = build_and_add_sum (TREE_TYPE (last_rhs1),
> - gimple_assign_lhs (stmts[i-width]),
> - op1,
> - opcode);
> - gimple_set_visited (stmts[i], true);
> + /* We keep original statement only for the last one. All others are
> + recreated. */
> + if (!ops1->length ())
> + {
> + /* For biased length equal to 2. */
> + if (width_count == BIASED_END_STMT && !last_rhs2_stmt_index)
> + last_rhs2_stmt_index = i - 1;
> +
> + /* When width_count == 2 and there is no biased, just finish. */
> + if (width_count == NORMAL_END_STMT && !has_biased)
> + {
> + last_rhs1_stmt_index = i - 1;
> + last_rhs2_stmt_index = i - 2;
> + }
> + if (last_rhs1_stmt_index && (last_rhs2_stmt_index || !has_biased))
> + {
> + /* We keep original statement only for the last one. All
> + others are recreated. */
> + gimple_assign_set_rhs1 (stmts[i], gimple_assign_lhs (stmts[last_rhs1_stmt_index]));
> + gimple_assign_set_rhs2 (stmts[i], gimple_assign_lhs (stmts[last_rhs2_stmt_index]));
> + update_stmt (stmts[i]);
> + }
> + else
> + {
> + stmts[i] =
> + build_and_add_sum (TREE_TYPE (last_rhs1),
> + gimple_assign_lhs (stmts[i-width_count]),
> + gimple_assign_lhs (stmts[i-width_count+1]),
> + opcode);
> + gimple_set_visited (stmts[i], true);
> + width_count--;
> +
> + /* It is the end of normal or biased ops.
> + last_rhs1_stmt_index used to record the last stmt index
> + for normal ops. last_rhs2_stmt_index used to record the
> + last stmt index for biased ops. */
> + if (width_count == BIASED_END_STMT)
> + {
> + gcc_assert (has_biased);
> + if (ops_biased.length ())
> + last_rhs1_stmt_index = i;
> + else
> + last_rhs2_stmt_index = i;
> + width_count--;
> + }
> + }
> + }
> + else
> + {
> + /* Attach the rest of the ops to the parallel dependency chain. */
> + oe = ops1->pop ();
> + op1 = oe->op;
> + stmt1 = oe->stmt_to_insert;
> + if (stmt1)
> + insert_stmt_before_use (stmts[i], stmt1);
> + stmt1 = NULL;
> +
> + /* For only one biased ops. */
> + if (width_count == SPECIAL_BIASED_END_STMT)
> + {
> + /* We keep original statement only for the last one. All
> + others are recreated. */
> + gcc_assert (has_biased);
> + gimple_assign_set_rhs1 (stmts[i], gimple_assign_lhs (stmts[last_rhs1_stmt_index]));
> + gimple_assign_set_rhs2 (stmts[i], op1);
> + update_stmt (stmts[i]);
> + }
> + else
> + {
> + stmts[i] = build_and_add_sum (TREE_TYPE (last_rhs1),
> + gimple_assign_lhs (stmts[i-width_active]),
> + op1,
> + opcode);
> + gimple_set_visited (stmts[i], true);
> + }
> + }
> }
>
> if (dump_file && (dump_flags & TDF_DETAILS))
> @@ -5595,6 +5692,7 @@ rewrite_expr_tree_parallel (gassign *stmt, int width, bool has_fma,
> print_gimple_stmt (dump_file, stmts[i], 0);
> }
> }
> +
> remove_visited_stmt_chain (last_rhs1);
> }
>
> --
> 2.25.1
>
next prev parent reply other threads:[~2023-06-29 6:45 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-29 1:49 Cui, Lili
2023-06-29 6:42 ` Richard Biener [this message]
2023-06-29 9:35 ` Cui, Lili
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