> -----Original Message-----
> From: Richard Biener <richard.guent...@gmail.com>
> Sent: Thursday, June 29, 2023 2:42 PM
> To: Cui, Lili <lili....@intel.com>
> Cc: gcc-patches@gcc.gnu.org
> Subject: Re: [PATCH] PR gcc/110148:Avoid adding loop-carried ops to long
> chains
>
> On Thu, Jun 29, 2023 at 3:49 AM Cui, Lili <lili....@intel.com> wrote:
> >
> > From: Lili Cui <lili....@intel.com>
> >
> > Hi Maintainer
> >
> > This patch is to fix TSVC242 regression related to loop-carried ops.
> >
> > Bootstrapped and regtested. Ok for trunk?
>
> OK.
>
Committed, thanks Richard.
Regards,
Lili.
> 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
> >
