PR gcc/98350:Handle FMA friendly in reassoc pass
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Commit Message
From: Lili Cui <lili.cui@intel.com>
Make some changes in reassoc pass to make it more friendly to fma pass later.
Using FMA instead of mult + add reduces register pressure and insruction
retired.
There are mainly two changes
1. Put no-mult ops and mult ops alternately at the end of the queue, which is
conducive to generating more fma and reducing the loss of FMA when breaking
the chain.
2. Rewrite the rewrite_expr_tree_parallel function to try to build parallel
chains according to the given correlation width, keeping the FMA chance as
much as possible.
TEST1:
float
foo (float a, float b, float c, float d, float *e)
{
return *e + a * b + c * d ;
}
For "-Ofast -mfpmath=sse -mfma" GCC generates:
vmulss %xmm3, %xmm2, %xmm2
vfmadd132ss %xmm1, %xmm2, %xmm0
vaddss (%rdi), %xmm0, %xmm0
ret
With this patch GCC generates:
vfmadd213ss (%rdi), %xmm1, %xmm0
vfmadd231ss %xmm2, %xmm3, %xmm0
ret
TEST2:
for (int i = 0; i < N; i++)
{
a[i] += b[i]* c[i] + d[i] * e[i] + f[i] * g[i] + h[i] * j[i] + k[i] * l[i] + m[i]* o[i] + p[i];
}
For "-Ofast -mfpmath=sse -mfma" GCC generates:
vmovapd e(%rax), %ymm4
vmulpd d(%rax), %ymm4, %ymm3
addq $32, %rax
vmovapd c-32(%rax), %ymm5
vmovapd j-32(%rax), %ymm6
vmulpd h-32(%rax), %ymm6, %ymm2
vmovapd a-32(%rax), %ymm6
vaddpd p-32(%rax), %ymm6, %ymm0
vmovapd g-32(%rax), %ymm7
vfmadd231pd b-32(%rax), %ymm5, %ymm3
vmovapd o-32(%rax), %ymm4
vmulpd m-32(%rax), %ymm4, %ymm1
vmovapd l-32(%rax), %ymm5
vfmadd231pd f-32(%rax), %ymm7, %ymm2
vfmadd231pd k-32(%rax), %ymm5, %ymm1
vaddpd %ymm3, %ymm0, %ymm0
vaddpd %ymm2, %ymm0, %ymm0
vaddpd %ymm1, %ymm0, %ymm0
vmovapd %ymm0, a-32(%rax)
cmpq $8192, %rax
jne .L4
vzeroupper
ret
with this patch applied GCC breaks the chain with width = 2 and generates 6 fma:
vmovapd a(%rax), %ymm2
vmovapd c(%rax), %ymm0
addq $32, %rax
vmovapd e-32(%rax), %ymm1
vmovapd p-32(%rax), %ymm5
vmovapd g-32(%rax), %ymm3
vmovapd j-32(%rax), %ymm6
vmovapd l-32(%rax), %ymm4
vmovapd o-32(%rax), %ymm7
vfmadd132pd b-32(%rax), %ymm2, %ymm0
vfmadd132pd d-32(%rax), %ymm5, %ymm1
vfmadd231pd f-32(%rax), %ymm3, %ymm0
vfmadd231pd h-32(%rax), %ymm6, %ymm1
vfmadd231pd k-32(%rax), %ymm4, %ymm0
vfmadd231pd m-32(%rax), %ymm7, %ymm1
vaddpd %ymm1, %ymm0, %ymm0
vmovapd %ymm0, a-32(%rax)
cmpq $8192, %rax
jne .L2
vzeroupper
ret
gcc/ChangeLog:
PR gcc/98350
* tree-ssa-reassoc.cc
(rewrite_expr_tree_parallel): Rewrite this function.
(rank_ops_for_fma): New.
(reassociate_bb): Handle new function.
gcc/testsuite/ChangeLog:
PR gcc/98350
* gcc.dg/pr98350-1.c: New test.
* gcc.dg/pr98350-2.c: Ditto.
---
gcc/testsuite/gcc.dg/pr98350-1.c | 31 ++++
gcc/testsuite/gcc.dg/pr98350-2.c | 11 ++
gcc/tree-ssa-reassoc.cc | 256 +++++++++++++++++++++----------
3 files changed, 215 insertions(+), 83 deletions(-)
create mode 100644 gcc/testsuite/gcc.dg/pr98350-1.c
create mode 100644 gcc/testsuite/gcc.dg/pr98350-2.c
Comments
Attach CPU2017 3 run results:
On ICX:
507.cactuBSSN_r: Improved by 1.7% for multi-copy .
503.bwaves_r : Improved by 0.60% for single copy .
507.cactuBSSN_r : Improved by 1.10% for single copy .
519.lbm_r : Improved by 2.21% for single copy .
no measurable changes for other benchmarks.
On aarch64
507.cactuBSSN_r: Improved by 1.7% for multi-copy.
503.bwaves_r : Improved by 6.00% for single-copy.
no measurable changes for other benchmarks.
> -----Original Message-----
> From: Cui, Lili <lili.cui@intel.com>
> Sent: Wednesday, May 17, 2023 9:02 PM
> To: gcc-patches@gcc.gnu.org
> Cc: richard.guenther@gmail.com; Cui, Lili <lili.cui@intel.com>
> Subject: [PATCH] PR gcc/98350:Handle FMA friendly in reassoc pass
>
> From: Lili Cui <lili.cui@intel.com>
>
> Make some changes in reassoc pass to make it more friendly to fma pass
> later.
> Using FMA instead of mult + add reduces register pressure and insruction
> retired.
>
> There are mainly two changes
> 1. Put no-mult ops and mult ops alternately at the end of the queue, which is
> conducive to generating more fma and reducing the loss of FMA when
> breaking the chain.
> 2. Rewrite the rewrite_expr_tree_parallel function to try to build parallel
> chains according to the given correlation width, keeping the FMA chance as
> much as possible.
>
> TEST1:
>
> float
> foo (float a, float b, float c, float d, float *e) {
> return *e + a * b + c * d ;
> }
>
> For "-Ofast -mfpmath=sse -mfma" GCC generates:
> vmulss %xmm3, %xmm2, %xmm2
> vfmadd132ss %xmm1, %xmm2, %xmm0
> vaddss (%rdi), %xmm0, %xmm0
> ret
>
> With this patch GCC generates:
> vfmadd213ss (%rdi), %xmm1, %xmm0
> vfmadd231ss %xmm2, %xmm3, %xmm0
> ret
>
> TEST2:
>
> for (int i = 0; i < N; i++)
> {
> a[i] += b[i]* c[i] + d[i] * e[i] + f[i] * g[i] + h[i] * j[i] + k[i] * l[i] + m[i]* o[i] +
> p[i]; }
>
> For "-Ofast -mfpmath=sse -mfma" GCC generates:
> vmovapd e(%rax), %ymm4
> vmulpd d(%rax), %ymm4, %ymm3
> addq $32, %rax
> vmovapd c-32(%rax), %ymm5
> vmovapd j-32(%rax), %ymm6
> vmulpd h-32(%rax), %ymm6, %ymm2
> vmovapd a-32(%rax), %ymm6
> vaddpd p-32(%rax), %ymm6, %ymm0
> vmovapd g-32(%rax), %ymm7
> vfmadd231pd b-32(%rax), %ymm5, %ymm3
> vmovapd o-32(%rax), %ymm4
> vmulpd m-32(%rax), %ymm4, %ymm1
> vmovapd l-32(%rax), %ymm5
> vfmadd231pd f-32(%rax), %ymm7, %ymm2
> vfmadd231pd k-32(%rax), %ymm5, %ymm1
> vaddpd %ymm3, %ymm0, %ymm0
> vaddpd %ymm2, %ymm0, %ymm0
> vaddpd %ymm1, %ymm0, %ymm0
> vmovapd %ymm0, a-32(%rax)
> cmpq $8192, %rax
> jne .L4
> vzeroupper
> ret
>
> with this patch applied GCC breaks the chain with width = 2 and generates 6
> fma:
>
> vmovapd a(%rax), %ymm2
> vmovapd c(%rax), %ymm0
> addq $32, %rax
> vmovapd e-32(%rax), %ymm1
> vmovapd p-32(%rax), %ymm5
> vmovapd g-32(%rax), %ymm3
> vmovapd j-32(%rax), %ymm6
> vmovapd l-32(%rax), %ymm4
> vmovapd o-32(%rax), %ymm7
> vfmadd132pd b-32(%rax), %ymm2, %ymm0
> vfmadd132pd d-32(%rax), %ymm5, %ymm1
> vfmadd231pd f-32(%rax), %ymm3, %ymm0
> vfmadd231pd h-32(%rax), %ymm6, %ymm1
> vfmadd231pd k-32(%rax), %ymm4, %ymm0
> vfmadd231pd m-32(%rax), %ymm7, %ymm1
> vaddpd %ymm1, %ymm0, %ymm0
> vmovapd %ymm0, a-32(%rax)
> cmpq $8192, %rax
> jne .L2
> vzeroupper
> ret
>
> gcc/ChangeLog:
>
> PR gcc/98350
> * tree-ssa-reassoc.cc
> (rewrite_expr_tree_parallel): Rewrite this function.
> (rank_ops_for_fma): New.
> (reassociate_bb): Handle new function.
>
> gcc/testsuite/ChangeLog:
>
> PR gcc/98350
> * gcc.dg/pr98350-1.c: New test.
> * gcc.dg/pr98350-2.c: Ditto.
> ---
> gcc/testsuite/gcc.dg/pr98350-1.c | 31 ++++ gcc/testsuite/gcc.dg/pr98350-2.c
> | 11 ++
> gcc/tree-ssa-reassoc.cc | 256 +++++++++++++++++++++----------
> 3 files changed, 215 insertions(+), 83 deletions(-) create mode 100644
> gcc/testsuite/gcc.dg/pr98350-1.c create mode 100644
> gcc/testsuite/gcc.dg/pr98350-2.c
>
> diff --git a/gcc/testsuite/gcc.dg/pr98350-1.c b/gcc/testsuite/gcc.dg/pr98350-
> 1.c
> new file mode 100644
> index 00000000000..185511c5e0a
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/pr98350-1.c
> @@ -0,0 +1,31 @@
> +/* { dg-do compile } */
> +/* { dg-options "-Ofast -mfpmath=sse -mfma -Wno-attributes " } */
> +
> +/* Test that the compiler properly optimizes multiply and add
> + to generate more FMA instructions. */ #define N 1024 double a[N];
> +double b[N]; double c[N]; double d[N]; double e[N]; double f[N]; double
> +g[N]; double h[N]; double j[N]; double k[N]; double l[N]; double m[N];
> +double o[N]; double p[N];
> +
> +
> +void
> +foo (void)
> +{
> + for (int i = 0; i < N; i++)
> + {
> + a[i] += b[i] * c[i] + d[i] * e[i] + f[i] * g[i] + h[i] * j[i] +
> +k[i] * l[i] + m[i]* o[i] + p[i];
> + }
> +}
> +/* { dg-final { scan-assembler-times "vfm" 6 } } */
> diff --git a/gcc/testsuite/gcc.dg/pr98350-2.c b/gcc/testsuite/gcc.dg/pr98350-
> 2.c
> new file mode 100644
> index 00000000000..b35d88aead9
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/pr98350-2.c
> @@ -0,0 +1,11 @@
> +/* { dg-do compile } */
> +/* { dg-options "-Ofast -mfpmath=sse -mfma -Wno-attributes " } */
> +
> +/* Test that the compiler rearrange the ops to generate more FMA. */
> +
> +float
> +foo1 (float a, float b, float c, float d, float *e) {
> + return *e + a * b + c * d ;
> +}
> +/* { dg-final { scan-assembler-times "vfm" 2 } } */
> diff --git a/gcc/tree-ssa-reassoc.cc b/gcc/tree-ssa-reassoc.cc index
> 067a3f07f7e..52c8aab6033 100644
> --- a/gcc/tree-ssa-reassoc.cc
> +++ b/gcc/tree-ssa-reassoc.cc
> @@ -54,6 +54,7 @@ along with GCC; see the file COPYING3. If not see
> #include "tree-ssa-reassoc.h"
> #include "tree-ssa-math-opts.h"
> #include "gimple-range.h"
> +#include "internal-fn.h"
>
> /* This is a simple global reassociation pass. It is, in part, based
> on the LLVM pass of the same name (They do some things more/less @@
> -5468,14 +5469,24 @@ get_reassociation_width (int ops_num, enum
> tree_code opc,
> return width;
> }
>
> -/* Recursively rewrite our linearized statements so that the operators
> - match those in OPS[OPINDEX], putting the computation in rank
> - order and trying to allow operations to be executed in
> - parallel. */
> +/* Rewrite statements with dependency chain with regard to 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;
>
> + ssa1 = e + f;
> + ssa2 = g + a * b;
> + ssa3 = ssa1 + c * d;
> + ssa4 = ssa2 + ssa3;
> +
> + This reassociation approach preserves the chance of fma generation as
> much
> + as possible. */
> static void
> -rewrite_expr_tree_parallel (gassign *stmt, int width,
> - const vec<operand_entry *> &ops)
> +rewrite_expr_tree_parallel (gassign *stmt, int width, bool has_fma,
> + const vec<operand_entry *> &ops)
> {
> enum tree_code opcode = gimple_assign_rhs_code (stmt);
> int op_num = ops.length ();
> @@ -5483,10 +5494,11 @@ rewrite_expr_tree_parallel (gassign *stmt, int
> width,
> int stmt_num = op_num - 1;
> gimple **stmts = XALLOCAVEC (gimple *, stmt_num);
> int op_index = op_num - 1;
> - int stmt_index = 0;
> - int ready_stmts_end = 0;
> - int i = 0;
> - gimple *stmt1 = NULL, *stmt2 = NULL;
> + 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);
>
> /* We start expression rewriting from the top statements.
> @@ -5496,91 +5508,84 @@ rewrite_expr_tree_parallel (gassign *stmt, int
> width,
> for (i = stmt_num - 2; i >= 0; i--)
> stmts[i] = SSA_NAME_DEF_STMT (gimple_assign_rhs1 (stmts[i+1]));
>
> - for (i = 0; i < stmt_num; i++)
> + /* Build parallel dependency chain according to width. */ for (i =
> + 0; i < width; i++)
> {
> - tree op1, op2;
> -
> - /* Determine whether we should use results of
> - already handled statements or not. */
> - if (ready_stmts_end == 0
> - && (i - stmt_index >= width || op_index < 1))
> - ready_stmts_end = i;
> -
> - /* Now we choose operands for the next statement. Non zero
> - value in ready_stmts_end means here that we should use
> - the result of already generated statements as new operand. */
> - if (ready_stmts_end > 0)
> - {
> - op1 = gimple_assign_lhs (stmts[stmt_index++]);
> - if (ready_stmts_end > stmt_index)
> - op2 = gimple_assign_lhs (stmts[stmt_index++]);
> - else if (op_index >= 0)
> - {
> - operand_entry *oe = ops[op_index--];
> - stmt2 = oe->stmt_to_insert;
> - op2 = oe->op;
> - }
> - else
> - {
> - gcc_assert (stmt_index < i);
> - op2 = gimple_assign_lhs (stmts[stmt_index++]);
> - }
> + /* */
> + if (op_index > 1 && !has_fma)
> + swap_ops_for_binary_stmt (ops, op_index - 2);
>
> - if (stmt_index >= ready_stmts_end)
> - ready_stmts_end = 0;
> - }
> - else
> + for (j = 0; j < 2; j++)
> {
> - if (op_index > 1)
> - swap_ops_for_binary_stmt (ops, op_index - 2);
> - operand_entry *oe2 = ops[op_index--];
> - operand_entry *oe1 = ops[op_index--];
> - op2 = oe2->op;
> - stmt2 = oe2->stmt_to_insert;
> - op1 = oe1->op;
> - stmt1 = oe1->stmt_to_insert;
> + 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;
> }
> -
> - /* If we emit the last statement then we should put
> - operands into the last statement. It will also
> - break the loop. */
> - if (op_index < 0 && stmt_index == i)
> - i = stmt_num - 1;
> + 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))
> {
> - fprintf (dump_file, "Transforming ");
> + fprintf (dump_file, " into ");
> print_gimple_stmt (dump_file, stmts[i], 0);
> }
> + }
>
> - /* If the stmt that defines operand has to be inserted, insert it
> - before the use. */
> - if (stmt1)
> - insert_stmt_before_use (stmts[i], stmt1);
> - if (stmt2)
> - insert_stmt_before_use (stmts[i], stmt2);
> - stmt1 = stmt2 = NULL;
> -
> - /* We keep original statement only for the last one. All
> - others are recreated. */
> - if (i == stmt_num - 1)
> + for (i = width; i < stmt_num; i++)
> + {
> + /* We keep original statement only for the last one. All others are
> + recreated. */
> + if ( op_index < 0)
> {
> - gimple_assign_set_rhs1 (stmts[i], op1);
> - gimple_assign_set_rhs2 (stmts[i], op2);
> - update_stmt (stmts[i]);
> + if (width_count == 2)
> + {
> +
> + /* 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]);
> + }
> + 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--;
> + }
> }
> else
> {
> - stmts[i] = build_and_add_sum (TREE_TYPE (last_rhs1), op1, op2,
> opcode);
> + /* 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);
> }
> +
> if (dump_file && (dump_flags & TDF_DETAILS))
> {
> fprintf (dump_file, " into ");
> print_gimple_stmt (dump_file, stmts[i], 0);
> }
> }
> -
> remove_visited_stmt_chain (last_rhs1); }
>
> @@ -6649,6 +6654,76 @@ transform_stmt_to_multiply
> (gimple_stmt_iterator *gsi, gimple *stmt,
> }
> }
>
> +/* Rearrange ops to generate more FMA when the chain may has more
> than 2 fmas.
> + Put no-mult ops and mult ops alternately at the end of the queue, which is
> + conducive to generating more fma and reducing the loss of FMA when
> breaking
> + the chain.
> + E.g.
> + a * b + c * d + e generates:
> +
> + _4 = c_9(D) * d_10(D);
> + _12 = .FMA (a_7(D), b_8(D), _4);
> + _11 = e_6(D) + _12;
> +
> + Rtearrange ops to -> e + a * b + c * d generates:
> +
> + _4 = .FMA (c_7(D), d_8(D), _3);
> + _11 = .FMA (a_5(D), b_6(D), _4);
> + */
> +static bool
> +rank_ops_for_fma (vec<operand_entry *> *ops) {
> + operand_entry *oe;
> + unsigned int i;
> + unsigned int ops_length = ops->length ();
> + auto_vec<operand_entry *> ops_mult;
> + auto_vec<operand_entry *> ops_others;
> +
> + FOR_EACH_VEC_ELT (*ops, i, oe)
> + {
> + if (TREE_CODE (oe->op) == SSA_NAME)
> + {
> + gimple *def_stmt = SSA_NAME_DEF_STMT (oe->op);
> + if (is_gimple_assign (def_stmt)
> + && gimple_assign_rhs_code (def_stmt) == MULT_EXPR)
> + ops_mult.safe_push (oe);
> + else
> + ops_others.safe_push (oe);
> + }
> + else
> + ops_others.safe_push (oe);
> + }
> + /* When ops_mult.length == 2, like the following case,
> +
> + a * b + c * d + e.
> +
> + we need to rearrange the ops.
> +
> + Putting ops that not def from mult in front can generate more
> +fmas. */
> + if (ops_mult.length () >= 2)
> + {
> + /* If all ops are defined with mult, we don't need to rearrange them. */
> + if (ops_mult.length () != ops_length)
> + {
> + /* Put no-mult ops and mult ops alternately at the end of the
> + queue, which is conducive to generating more fma and reducing
> the
> + loss of FMA when breaking the chain. */
> + ops->truncate (0);
> + ops->splice (ops_mult);
> + int j, opindex = ops->length ();
> + int others_length = ops_others.length();
> + for (j = 0; j < others_length; j++)
> + {
> + oe = ops_others.pop ();
> + ops->safe_insert (opindex, oe);
> + if (opindex > 0)
> + opindex--;
> + }
> + }
> + return true;
> + }
> + return false;
> +}
> /* Reassociate expressions in basic block BB and its post-dominator as
> children.
>
> @@ -6813,6 +6888,7 @@ reassociate_bb (basic_block bb)
> machine_mode mode = TYPE_MODE (TREE_TYPE (lhs));
> int ops_num = ops.length ();
> int width;
> + bool has_fma = false;
>
> /* For binary bit operations, if there are at least 3
> operands and the last operand in OPS is a constant, @@ -
> 6821,11 +6897,23 @@ reassociate_bb (basic_block bb)
> often match a canonical bit test when we get to RTL. */
> if (ops.length () > 2
> && (rhs_code == BIT_AND_EXPR
> - || rhs_code == BIT_IOR_EXPR
> - || rhs_code == BIT_XOR_EXPR)
> + || rhs_code == BIT_IOR_EXPR
> + || rhs_code == BIT_XOR_EXPR)
> && TREE_CODE (ops.last ()->op) == INTEGER_CST)
> std::swap (*ops[0], *ops[ops_num - 1]);
>
> + optimization_type opt_type = bb_optimization_type (bb);
> +
> + /* If the target support FMA, rank_ops_for_fma will detect
> if
> + the chain has fmas and rearrange the ops if so. */
> + if (direct_internal_fn_supported_p (IFN_FMA,
> + TREE_TYPE (lhs),
> + opt_type)
> + && (rhs_code == PLUS_EXPR || rhs_code == MINUS_EXPR))
> + {
> + has_fma = rank_ops_for_fma(&ops);
> + }
> +
> /* Only rewrite the expression tree to parallel in the
> last reassoc pass to avoid useless work back-and-forth
> with initial linearization. */
> @@ -6839,22 +6927,24 @@ reassociate_bb (basic_block bb)
> "Width = %d was chosen for
> reassociation\n",
> width);
> rewrite_expr_tree_parallel (as_a <gassign *> (stmt),
> - width, ops);
> + width,
> + has_fma,
> + ops);
> }
> else
> - {
> - /* When there are three operands left, we want
> - to make sure the ones that get the double
> - binary op are chosen wisely. */
> - int len = ops.length ();
> - if (len >= 3)
> + {
> + /* When there are three operands left, we want
> + to make sure the ones that get the double
> + binary op are chosen wisely. */
> + int len = ops.length ();
> + if (len >= 3 && !has_fma)
> swap_ops_for_binary_stmt (ops, len - 3);
>
> new_lhs = rewrite_expr_tree (stmt, rhs_code, 0, ops,
> powi_result != NULL
> || negate_result,
> len != orig_len);
> - }
> + }
>
> /* If we combined some repeated factors into a
> __builtin_powi call, multiply that result by the
> --
> 2.25.1
On Wed, May 17, 2023 at 3:02 PM Cui, Lili <lili.cui@intel.com> wrote:
>
> From: Lili Cui <lili.cui@intel.com>
>
> Make some changes in reassoc pass to make it more friendly to fma pass later.
> Using FMA instead of mult + add reduces register pressure and insruction
> retired.
>
> There are mainly two changes
> 1. Put no-mult ops and mult ops alternately at the end of the queue, which is
> conducive to generating more fma and reducing the loss of FMA when breaking
> the chain.
> 2. Rewrite the rewrite_expr_tree_parallel function to try to build parallel
> chains according to the given correlation width, keeping the FMA chance as
> much as possible.
>
> TEST1:
>
> float
> foo (float a, float b, float c, float d, float *e)
> {
> return *e + a * b + c * d ;
> }
>
> For "-Ofast -mfpmath=sse -mfma" GCC generates:
> vmulss %xmm3, %xmm2, %xmm2
> vfmadd132ss %xmm1, %xmm2, %xmm0
> vaddss (%rdi), %xmm0, %xmm0
> ret
>
> With this patch GCC generates:
> vfmadd213ss (%rdi), %xmm1, %xmm0
> vfmadd231ss %xmm2, %xmm3, %xmm0
> ret
>
> TEST2:
>
> for (int i = 0; i < N; i++)
> {
> a[i] += b[i]* c[i] + d[i] * e[i] + f[i] * g[i] + h[i] * j[i] + k[i] * l[i] + m[i]* o[i] + p[i];
> }
>
> For "-Ofast -mfpmath=sse -mfma" GCC generates:
> vmovapd e(%rax), %ymm4
> vmulpd d(%rax), %ymm4, %ymm3
> addq $32, %rax
> vmovapd c-32(%rax), %ymm5
> vmovapd j-32(%rax), %ymm6
> vmulpd h-32(%rax), %ymm6, %ymm2
> vmovapd a-32(%rax), %ymm6
> vaddpd p-32(%rax), %ymm6, %ymm0
> vmovapd g-32(%rax), %ymm7
> vfmadd231pd b-32(%rax), %ymm5, %ymm3
> vmovapd o-32(%rax), %ymm4
> vmulpd m-32(%rax), %ymm4, %ymm1
> vmovapd l-32(%rax), %ymm5
> vfmadd231pd f-32(%rax), %ymm7, %ymm2
> vfmadd231pd k-32(%rax), %ymm5, %ymm1
> vaddpd %ymm3, %ymm0, %ymm0
> vaddpd %ymm2, %ymm0, %ymm0
> vaddpd %ymm1, %ymm0, %ymm0
> vmovapd %ymm0, a-32(%rax)
> cmpq $8192, %rax
> jne .L4
> vzeroupper
> ret
>
> with this patch applied GCC breaks the chain with width = 2 and generates 6 fma:
>
> vmovapd a(%rax), %ymm2
> vmovapd c(%rax), %ymm0
> addq $32, %rax
> vmovapd e-32(%rax), %ymm1
> vmovapd p-32(%rax), %ymm5
> vmovapd g-32(%rax), %ymm3
> vmovapd j-32(%rax), %ymm6
> vmovapd l-32(%rax), %ymm4
> vmovapd o-32(%rax), %ymm7
> vfmadd132pd b-32(%rax), %ymm2, %ymm0
> vfmadd132pd d-32(%rax), %ymm5, %ymm1
> vfmadd231pd f-32(%rax), %ymm3, %ymm0
> vfmadd231pd h-32(%rax), %ymm6, %ymm1
> vfmadd231pd k-32(%rax), %ymm4, %ymm0
> vfmadd231pd m-32(%rax), %ymm7, %ymm1
> vaddpd %ymm1, %ymm0, %ymm0
> vmovapd %ymm0, a-32(%rax)
> cmpq $8192, %rax
> jne .L2
> vzeroupper
> ret
>
> gcc/ChangeLog:
>
> PR gcc/98350
> * tree-ssa-reassoc.cc
> (rewrite_expr_tree_parallel): Rewrite this function.
> (rank_ops_for_fma): New.
> (reassociate_bb): Handle new function.
>
> gcc/testsuite/ChangeLog:
>
> PR gcc/98350
> * gcc.dg/pr98350-1.c: New test.
> * gcc.dg/pr98350-2.c: Ditto.
> ---
> gcc/testsuite/gcc.dg/pr98350-1.c | 31 ++++
> gcc/testsuite/gcc.dg/pr98350-2.c | 11 ++
> gcc/tree-ssa-reassoc.cc | 256 +++++++++++++++++++++----------
> 3 files changed, 215 insertions(+), 83 deletions(-)
> create mode 100644 gcc/testsuite/gcc.dg/pr98350-1.c
> create mode 100644 gcc/testsuite/gcc.dg/pr98350-2.c
>
> diff --git a/gcc/testsuite/gcc.dg/pr98350-1.c b/gcc/testsuite/gcc.dg/pr98350-1.c
> new file mode 100644
> index 00000000000..185511c5e0a
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/pr98350-1.c
> @@ -0,0 +1,31 @@
> +/* { dg-do compile } */
> +/* { dg-options "-Ofast -mfpmath=sse -mfma -Wno-attributes " } */
> +
> +/* Test that the compiler properly optimizes multiply and add
> + to generate more FMA instructions. */
> +#define N 1024
> +double a[N];
> +double b[N];
> +double c[N];
> +double d[N];
> +double e[N];
> +double f[N];
> +double g[N];
> +double h[N];
> +double j[N];
> +double k[N];
> +double l[N];
> +double m[N];
> +double o[N];
> +double p[N];
> +
> +
> +void
> +foo (void)
> +{
> + for (int i = 0; i < N; i++)
> + {
> + a[i] += b[i] * c[i] + d[i] * e[i] + f[i] * g[i] + h[i] * j[i] + k[i] * l[i] + m[i]* o[i] + p[i];
> + }
> +}
> +/* { dg-final { scan-assembler-times "vfm" 6 } } */
> diff --git a/gcc/testsuite/gcc.dg/pr98350-2.c b/gcc/testsuite/gcc.dg/pr98350-2.c
> new file mode 100644
> index 00000000000..b35d88aead9
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/pr98350-2.c
> @@ -0,0 +1,11 @@
> +/* { dg-do compile } */
> +/* { dg-options "-Ofast -mfpmath=sse -mfma -Wno-attributes " } */
> +
> +/* Test that the compiler rearrange the ops to generate more FMA. */
> +
> +float
> +foo1 (float a, float b, float c, float d, float *e)
> +{
> + return *e + a * b + c * d ;
> +}
> +/* { dg-final { scan-assembler-times "vfm" 2 } } */
> diff --git a/gcc/tree-ssa-reassoc.cc b/gcc/tree-ssa-reassoc.cc
> index 067a3f07f7e..52c8aab6033 100644
> --- a/gcc/tree-ssa-reassoc.cc
> +++ b/gcc/tree-ssa-reassoc.cc
> @@ -54,6 +54,7 @@ along with GCC; see the file COPYING3. If not see
> #include "tree-ssa-reassoc.h"
> #include "tree-ssa-math-opts.h"
> #include "gimple-range.h"
> +#include "internal-fn.h"
>
> /* This is a simple global reassociation pass. It is, in part, based
> on the LLVM pass of the same name (They do some things more/less
> @@ -5468,14 +5469,24 @@ get_reassociation_width (int ops_num, enum tree_code opc,
> return width;
> }
>
> -/* Recursively rewrite our linearized statements so that the operators
> - match those in OPS[OPINDEX], putting the computation in rank
> - order and trying to allow operations to be executed in
> - parallel. */
> +/* Rewrite statements with dependency chain with regard to 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;
>
> + ssa1 = e + f;
> + ssa2 = g + a * b;
> + ssa3 = ssa1 + c * d;
> + ssa4 = ssa2 + ssa3;
> +
> + This reassociation approach preserves the chance of fma generation as much
> + as possible. */
> static void
> -rewrite_expr_tree_parallel (gassign *stmt, int width,
> - const vec<operand_entry *> &ops)
> +rewrite_expr_tree_parallel (gassign *stmt, int width, bool has_fma,
> + const vec<operand_entry *> &ops)
> {
> enum tree_code opcode = gimple_assign_rhs_code (stmt);
> int op_num = ops.length ();
> @@ -5483,10 +5494,11 @@ rewrite_expr_tree_parallel (gassign *stmt, int width,
> int stmt_num = op_num - 1;
> gimple **stmts = XALLOCAVEC (gimple *, stmt_num);
> int op_index = op_num - 1;
> - int stmt_index = 0;
> - int ready_stmts_end = 0;
> - int i = 0;
> - gimple *stmt1 = NULL, *stmt2 = NULL;
> + 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);
>
> /* We start expression rewriting from the top statements.
> @@ -5496,91 +5508,84 @@ rewrite_expr_tree_parallel (gassign *stmt, int width,
> for (i = stmt_num - 2; i >= 0; i--)
> stmts[i] = SSA_NAME_DEF_STMT (gimple_assign_rhs1 (stmts[i+1]));
>
> - for (i = 0; i < stmt_num; i++)
> + /* Build parallel dependency chain according to width. */
> + for (i = 0; i < width; i++)
> {
> - tree op1, op2;
> -
> - /* Determine whether we should use results of
> - already handled statements or not. */
> - if (ready_stmts_end == 0
> - && (i - stmt_index >= width || op_index < 1))
> - ready_stmts_end = i;
> -
> - /* Now we choose operands for the next statement. Non zero
> - value in ready_stmts_end means here that we should use
> - the result of already generated statements as new operand. */
> - if (ready_stmts_end > 0)
> - {
> - op1 = gimple_assign_lhs (stmts[stmt_index++]);
> - if (ready_stmts_end > stmt_index)
> - op2 = gimple_assign_lhs (stmts[stmt_index++]);
> - else if (op_index >= 0)
> - {
> - operand_entry *oe = ops[op_index--];
> - stmt2 = oe->stmt_to_insert;
> - op2 = oe->op;
> - }
> - else
> - {
> - gcc_assert (stmt_index < i);
> - op2 = gimple_assign_lhs (stmts[stmt_index++]);
> - }
> + /* */
empty comment?
> + if (op_index > 1 && !has_fma)
> + swap_ops_for_binary_stmt (ops, op_index - 2);
>
> - if (stmt_index >= ready_stmts_end)
> - ready_stmts_end = 0;
> - }
> - else
> + for (j = 0; j < 2; j++)
> {
> - if (op_index > 1)
> - swap_ops_for_binary_stmt (ops, op_index - 2);
> - operand_entry *oe2 = ops[op_index--];
> - operand_entry *oe1 = ops[op_index--];
> - op2 = oe2->op;
> - stmt2 = oe2->stmt_to_insert;
> - op1 = oe1->op;
> - stmt1 = oe1->stmt_to_insert;
> + 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;
> }
> -
> - /* If we emit the last statement then we should put
> - operands into the last statement. It will also
> - break the loop. */
> - if (op_index < 0 && stmt_index == i)
> - i = stmt_num - 1;
> + 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))
> {
> - fprintf (dump_file, "Transforming ");
> + fprintf (dump_file, " into ");
> print_gimple_stmt (dump_file, stmts[i], 0);
> }
> + }
>
> - /* If the stmt that defines operand has to be inserted, insert it
> - before the use. */
> - if (stmt1)
> - insert_stmt_before_use (stmts[i], stmt1);
> - if (stmt2)
> - insert_stmt_before_use (stmts[i], stmt2);
> - stmt1 = stmt2 = NULL;
> -
> - /* We keep original statement only for the last one. All
> - others are recreated. */
> - if (i == stmt_num - 1)
> + for (i = width; i < stmt_num; i++)
> + {
> + /* We keep original statement only for the last one. All others are
> + recreated. */
> + if ( op_index < 0)
> {
> - gimple_assign_set_rhs1 (stmts[i], op1);
> - gimple_assign_set_rhs2 (stmts[i], op2);
> - update_stmt (stmts[i]);
> + if (width_count == 2)
> + {
> +
> + /* 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]);
> + }
> + 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--;
> + }
> }
> else
> {
> - stmts[i] = build_and_add_sum (TREE_TYPE (last_rhs1), op1, op2, opcode);
> + /* 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);
> }
> +
> if (dump_file && (dump_flags & TDF_DETAILS))
> {
> fprintf (dump_file, " into ");
> print_gimple_stmt (dump_file, stmts[i], 0);
> }
> }
> -
I've looked three times but didn't find a use of 'has_fma'?
> remove_visited_stmt_chain (last_rhs1);
> }
>
> @@ -6649,6 +6654,76 @@ transform_stmt_to_multiply (gimple_stmt_iterator *gsi, gimple *stmt,
> }
> }
>
> +/* Rearrange ops to generate more FMA when the chain may has more than 2 fmas.
may have
> + Put no-mult ops and mult ops alternately at the end of the queue, which is
> + conducive to generating more fma and reducing the loss of FMA when breaking
> + the chain.
> + E.g.
> + a * b + c * d + e generates:
> +
> + _4 = c_9(D) * d_10(D);
> + _12 = .FMA (a_7(D), b_8(D), _4);
> + _11 = e_6(D) + _12;
> +
> + Rtearrange ops to -> e + a * b + c * d generates:
Rearrange
> +
> + _4 = .FMA (c_7(D), d_8(D), _3);
> + _11 = .FMA (a_5(D), b_6(D), _4);
> + */
> +static bool
> +rank_ops_for_fma (vec<operand_entry *> *ops)
> +{
> + operand_entry *oe;
> + unsigned int i;
> + unsigned int ops_length = ops->length ();
> + auto_vec<operand_entry *> ops_mult;
> + auto_vec<operand_entry *> ops_others;
> +
> + FOR_EACH_VEC_ELT (*ops, i, oe)
> + {
> + if (TREE_CODE (oe->op) == SSA_NAME)
> + {
> + gimple *def_stmt = SSA_NAME_DEF_STMT (oe->op);
> + if (is_gimple_assign (def_stmt)
> + && gimple_assign_rhs_code (def_stmt) == MULT_EXPR)
> + ops_mult.safe_push (oe);
> + else
> + ops_others.safe_push (oe);
> + }
> + else
> + ops_others.safe_push (oe);
> + }
> + /* When ops_mult.length == 2, like the following case,
> +
> + a * b + c * d + e.
> +
> + we need to rearrange the ops.
> +
> + Putting ops that not def from mult in front can generate more fmas. */
> + if (ops_mult.length () >= 2)
> + {
> + /* If all ops are defined with mult, we don't need to rearrange them. */
> + if (ops_mult.length () != ops_length)
use && with the previous condition.
> + {
> + /* Put no-mult ops and mult ops alternately at the end of the
> + queue, which is conducive to generating more fma and reducing the
> + loss of FMA when breaking the chain. */
> + ops->truncate (0);
> + ops->splice (ops_mult);
> + int j, opindex = ops->length ();
> + int others_length = ops_others.length();
> + for (j = 0; j < others_length; j++)
> + {
> + oe = ops_others.pop ();
> + ops->safe_insert (opindex, oe);
that's quadratic as it needs to move ops. As said previously
we know that 'ops' has enough room and you can use the
quick_ (or non-safe_) variants of the APIs on it.
Otherwise looks good to me.
Thanks,
Richard.
> + if (opindex > 0)
> + opindex--;
> + }
> + }
> + return true;
> + }
> + return false;
> +}
> /* Reassociate expressions in basic block BB and its post-dominator as
> children.
>
> @@ -6813,6 +6888,7 @@ reassociate_bb (basic_block bb)
> machine_mode mode = TYPE_MODE (TREE_TYPE (lhs));
> int ops_num = ops.length ();
> int width;
> + bool has_fma = false;
>
> /* For binary bit operations, if there are at least 3
> operands and the last operand in OPS is a constant,
> @@ -6821,11 +6897,23 @@ reassociate_bb (basic_block bb)
> often match a canonical bit test when we get to RTL. */
> if (ops.length () > 2
> && (rhs_code == BIT_AND_EXPR
> - || rhs_code == BIT_IOR_EXPR
> - || rhs_code == BIT_XOR_EXPR)
> + || rhs_code == BIT_IOR_EXPR
> + || rhs_code == BIT_XOR_EXPR)
> && TREE_CODE (ops.last ()->op) == INTEGER_CST)
> std::swap (*ops[0], *ops[ops_num - 1]);
>
> + optimization_type opt_type = bb_optimization_type (bb);
> +
> + /* If the target support FMA, rank_ops_for_fma will detect if
> + the chain has fmas and rearrange the ops if so. */
> + if (direct_internal_fn_supported_p (IFN_FMA,
> + TREE_TYPE (lhs),
> + opt_type)
> + && (rhs_code == PLUS_EXPR || rhs_code == MINUS_EXPR))
> + {
> + has_fma = rank_ops_for_fma(&ops);
> + }
> +
> /* Only rewrite the expression tree to parallel in the
> last reassoc pass to avoid useless work back-and-forth
> with initial linearization. */
> @@ -6839,22 +6927,24 @@ reassociate_bb (basic_block bb)
> "Width = %d was chosen for reassociation\n",
> width);
> rewrite_expr_tree_parallel (as_a <gassign *> (stmt),
> - width, ops);
> + width,
> + has_fma,
> + ops);
> }
> else
> - {
> - /* When there are three operands left, we want
> - to make sure the ones that get the double
> - binary op are chosen wisely. */
> - int len = ops.length ();
> - if (len >= 3)
> + {
> + /* When there are three operands left, we want
> + to make sure the ones that get the double
> + binary op are chosen wisely. */
> + int len = ops.length ();
> + if (len >= 3 && !has_fma)
> swap_ops_for_binary_stmt (ops, len - 3);
>
> new_lhs = rewrite_expr_tree (stmt, rhs_code, 0, ops,
> powi_result != NULL
> || negate_result,
> len != orig_len);
> - }
> + }
>
> /* If we combined some repeated factors into a
> __builtin_powi call, multiply that result by the
> --
> 2.25.1
>
> > +rewrite_expr_tree_parallel (gassign *stmt, int width, bool has_fma,
> > + const vec<operand_entry *>
> > +&ops)
> > {
> > enum tree_code opcode = gimple_assign_rhs_code (stmt);
> > int op_num = ops.length ();
> > @@ -5483,10 +5494,11 @@ rewrite_expr_tree_parallel (gassign *stmt, int
> width,
> > int stmt_num = op_num - 1;
> > gimple **stmts = XALLOCAVEC (gimple *, stmt_num);
> > int op_index = op_num - 1;
> > - int stmt_index = 0;
> > - int ready_stmts_end = 0;
> > - int i = 0;
> > - gimple *stmt1 = NULL, *stmt2 = NULL;
> > + 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);
> >
> > /* We start expression rewriting from the top statements.
> > @@ -5496,91 +5508,84 @@ rewrite_expr_tree_parallel (gassign *stmt, int
> width,
> > for (i = stmt_num - 2; i >= 0; i--)
> > stmts[i] = SSA_NAME_DEF_STMT (gimple_assign_rhs1 (stmts[i+1]));
> >
> > - for (i = 0; i < stmt_num; i++)
> > + /* Build parallel dependency chain according to width. */ for (i
> > + = 0; i < width; i++)
> > {
> > - tree op1, op2;
> > -
> > - /* Determine whether we should use results of
> > - already handled statements or not. */
> > - if (ready_stmts_end == 0
> > - && (i - stmt_index >= width || op_index < 1))
> > - ready_stmts_end = i;
> > -
> > - /* Now we choose operands for the next statement. Non zero
> > - value in ready_stmts_end means here that we should use
> > - the result of already generated statements as new operand. */
> > - if (ready_stmts_end > 0)
> > - {
> > - op1 = gimple_assign_lhs (stmts[stmt_index++]);
> > - if (ready_stmts_end > stmt_index)
> > - op2 = gimple_assign_lhs (stmts[stmt_index++]);
> > - else if (op_index >= 0)
> > - {
> > - operand_entry *oe = ops[op_index--];
> > - stmt2 = oe->stmt_to_insert;
> > - op2 = oe->op;
> > - }
> > - else
> > - {
> > - gcc_assert (stmt_index < i);
> > - op2 = gimple_assign_lhs (stmts[stmt_index++]);
> > - }
> > + /* */
>
> empty comment?
Added it, thanks.
>
> > + if (op_index > 1 && !has_fma)
> > + swap_ops_for_binary_stmt (ops, op_index - 2);
> >
> > - if (stmt_index >= ready_stmts_end)
> > - ready_stmts_end = 0;
> > - }
> > - else
> > + for (j = 0; j < 2; j++)
> > {
> > - if (op_index > 1)
> > - swap_ops_for_binary_stmt (ops, op_index - 2);
> > - operand_entry *oe2 = ops[op_index--];
> > - operand_entry *oe1 = ops[op_index--];
> > - op2 = oe2->op;
> > - stmt2 = oe2->stmt_to_insert;
> > - op1 = oe1->op;
> > - stmt1 = oe1->stmt_to_insert;
> > + 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;
> > }
> > -
> > - /* If we emit the last statement then we should put
> > - operands into the last statement. It will also
> > - break the loop. */
> > - if (op_index < 0 && stmt_index == i)
> > - i = stmt_num - 1;
> > + 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))
> > {
> > - fprintf (dump_file, "Transforming ");
> > + fprintf (dump_file, " into ");
> > print_gimple_stmt (dump_file, stmts[i], 0);
> > }
> > + }
> >
> > - /* If the stmt that defines operand has to be inserted, insert it
> > - before the use. */
> > - if (stmt1)
> > - insert_stmt_before_use (stmts[i], stmt1);
> > - if (stmt2)
> > - insert_stmt_before_use (stmts[i], stmt2);
> > - stmt1 = stmt2 = NULL;
> > -
> > - /* We keep original statement only for the last one. All
> > - others are recreated. */
> > - if (i == stmt_num - 1)
> > + for (i = width; i < stmt_num; i++)
> > + {
> > + /* We keep original statement only for the last one. All others are
> > + recreated. */
> > + if ( op_index < 0)
> > {
> > - gimple_assign_set_rhs1 (stmts[i], op1);
> > - gimple_assign_set_rhs2 (stmts[i], op2);
> > - update_stmt (stmts[i]);
> > + if (width_count == 2)
> > + {
> > +
> > + /* 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]);
> > + }
> > + 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--;
> > + }
> > }
> > else
> > {
> > - stmts[i] = build_and_add_sum (TREE_TYPE (last_rhs1), op1, op2,
> opcode);
> > + /* 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);
> > }
> > +
> > if (dump_file && (dump_flags & TDF_DETAILS))
> > {
> > fprintf (dump_file, " into ");
> > print_gimple_stmt (dump_file, stmts[i], 0);
> > }
> > }
> > -
>
> I've looked three times but didn't find a use of 'has_fma'?
It's located after your first comment, 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);
> > remove_visited_stmt_chain (last_rhs1); }
> >
> > @@ -6649,6 +6654,76 @@ transform_stmt_to_multiply
> (gimple_stmt_iterator *gsi, gimple *stmt,
> > }
> > }
> >
> > +/* Rearrange ops to generate more FMA when the chain may has more
> than 2 fmas.
>
> may have
>
Done.
> > + Put no-mult ops and mult ops alternately at the end of the queue, which
> is
> > + conducive to generating more fma and reducing the loss of FMA when
> breaking
> > + the chain.
> > + E.g.
> > + a * b + c * d + e generates:
> > +
> > + _4 = c_9(D) * d_10(D);
> > + _12 = .FMA (a_7(D), b_8(D), _4);
> > + _11 = e_6(D) + _12;
> > +
> > + Rtearrange ops to -> e + a * b + c * d generates:
>
> Rearrange
>
Done.
> > +
> > + _4 = .FMA (c_7(D), d_8(D), _3);
> > + _11 = .FMA (a_5(D), b_6(D), _4);
> > + */
> > +static bool
> > +rank_ops_for_fma (vec<operand_entry *> *ops) {
> > + operand_entry *oe;
> > + unsigned int i;
> > + unsigned int ops_length = ops->length ();
> > + auto_vec<operand_entry *> ops_mult;
> > + auto_vec<operand_entry *> ops_others;
> > +
> > + FOR_EACH_VEC_ELT (*ops, i, oe)
> > + {
> > + if (TREE_CODE (oe->op) == SSA_NAME)
> > + {
> > + gimple *def_stmt = SSA_NAME_DEF_STMT (oe->op);
> > + if (is_gimple_assign (def_stmt)
> > + && gimple_assign_rhs_code (def_stmt) == MULT_EXPR)
> > + ops_mult.safe_push (oe);
> > + else
> > + ops_others.safe_push (oe);
> > + }
> > + else
> > + ops_others.safe_push (oe);
> > + }
> > + /* When ops_mult.length == 2, like the following case,
> > +
> > + a * b + c * d + e.
> > +
> > + we need to rearrange the ops.
> > +
> > + Putting ops that not def from mult in front can generate more
> > + fmas. */ if (ops_mult.length () >= 2)
> > + {
> > + /* If all ops are defined with mult, we don't need to rearrange them.
> */
> > + if (ops_mult.length () != ops_length)
>
> use && with the previous condition.
>
Done.
> > + {
> > + /* Put no-mult ops and mult ops alternately at the end of the
> > + queue, which is conducive to generating more fma and reducing
> the
> > + loss of FMA when breaking the chain. */
> > + ops->truncate (0);
> > + ops->splice (ops_mult);
> > + int j, opindex = ops->length ();
> > + int others_length = ops_others.length();
> > + for (j = 0; j < others_length; j++)
> > + {
> > + oe = ops_others.pop ();
> > + ops->safe_insert (opindex, oe);
>
> that's quadratic as it needs to move ops. As said previously we know that
> 'ops' has enough room and you can use the quick_ (or non-safe_) variants of
> the APIs on it.
>
Done, thanks.
Regards,
Lili.
> Otherwise looks good to me.
>
> Thanks,
> Richard.
>
new file mode 100644
@@ -0,0 +1,31 @@
+/* { dg-do compile } */
+/* { dg-options "-Ofast -mfpmath=sse -mfma -Wno-attributes " } */
+
+/* Test that the compiler properly optimizes multiply and add
+ to generate more FMA instructions. */
+#define N 1024
+double a[N];
+double b[N];
+double c[N];
+double d[N];
+double e[N];
+double f[N];
+double g[N];
+double h[N];
+double j[N];
+double k[N];
+double l[N];
+double m[N];
+double o[N];
+double p[N];
+
+
+void
+foo (void)
+{
+ for (int i = 0; i < N; i++)
+ {
+ a[i] += b[i] * c[i] + d[i] * e[i] + f[i] * g[i] + h[i] * j[i] + k[i] * l[i] + m[i]* o[i] + p[i];
+ }
+}
+/* { dg-final { scan-assembler-times "vfm" 6 } } */
new file mode 100644
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-Ofast -mfpmath=sse -mfma -Wno-attributes " } */
+
+/* Test that the compiler rearrange the ops to generate more FMA. */
+
+float
+foo1 (float a, float b, float c, float d, float *e)
+{
+ return *e + a * b + c * d ;
+}
+/* { dg-final { scan-assembler-times "vfm" 2 } } */
@@ -54,6 +54,7 @@ along with GCC; see the file COPYING3. If not see
#include "tree-ssa-reassoc.h"
#include "tree-ssa-math-opts.h"
#include "gimple-range.h"
+#include "internal-fn.h"
/* This is a simple global reassociation pass. It is, in part, based
on the LLVM pass of the same name (They do some things more/less
@@ -5468,14 +5469,24 @@ get_reassociation_width (int ops_num, enum tree_code opc,
return width;
}
-/* Recursively rewrite our linearized statements so that the operators
- match those in OPS[OPINDEX], putting the computation in rank
- order and trying to allow operations to be executed in
- parallel. */
+/* Rewrite statements with dependency chain with regard to 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;
+ ssa1 = e + f;
+ ssa2 = g + a * b;
+ ssa3 = ssa1 + c * d;
+ ssa4 = ssa2 + ssa3;
+
+ This reassociation approach preserves the chance of fma generation as much
+ as possible. */
static void
-rewrite_expr_tree_parallel (gassign *stmt, int width,
- const vec<operand_entry *> &ops)
+rewrite_expr_tree_parallel (gassign *stmt, int width, bool has_fma,
+ const vec<operand_entry *> &ops)
{
enum tree_code opcode = gimple_assign_rhs_code (stmt);
int op_num = ops.length ();
@@ -5483,10 +5494,11 @@ rewrite_expr_tree_parallel (gassign *stmt, int width,
int stmt_num = op_num - 1;
gimple **stmts = XALLOCAVEC (gimple *, stmt_num);
int op_index = op_num - 1;
- int stmt_index = 0;
- int ready_stmts_end = 0;
- int i = 0;
- gimple *stmt1 = NULL, *stmt2 = NULL;
+ 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);
/* We start expression rewriting from the top statements.
@@ -5496,91 +5508,84 @@ rewrite_expr_tree_parallel (gassign *stmt, int width,
for (i = stmt_num - 2; i >= 0; i--)
stmts[i] = SSA_NAME_DEF_STMT (gimple_assign_rhs1 (stmts[i+1]));
- for (i = 0; i < stmt_num; i++)
+ /* Build parallel dependency chain according to width. */
+ for (i = 0; i < width; i++)
{
- tree op1, op2;
-
- /* Determine whether we should use results of
- already handled statements or not. */
- if (ready_stmts_end == 0
- && (i - stmt_index >= width || op_index < 1))
- ready_stmts_end = i;
-
- /* Now we choose operands for the next statement. Non zero
- value in ready_stmts_end means here that we should use
- the result of already generated statements as new operand. */
- if (ready_stmts_end > 0)
- {
- op1 = gimple_assign_lhs (stmts[stmt_index++]);
- if (ready_stmts_end > stmt_index)
- op2 = gimple_assign_lhs (stmts[stmt_index++]);
- else if (op_index >= 0)
- {
- operand_entry *oe = ops[op_index--];
- stmt2 = oe->stmt_to_insert;
- op2 = oe->op;
- }
- else
- {
- gcc_assert (stmt_index < i);
- op2 = gimple_assign_lhs (stmts[stmt_index++]);
- }
+ /* */
+ if (op_index > 1 && !has_fma)
+ swap_ops_for_binary_stmt (ops, op_index - 2);
- if (stmt_index >= ready_stmts_end)
- ready_stmts_end = 0;
- }
- else
+ for (j = 0; j < 2; j++)
{
- if (op_index > 1)
- swap_ops_for_binary_stmt (ops, op_index - 2);
- operand_entry *oe2 = ops[op_index--];
- operand_entry *oe1 = ops[op_index--];
- op2 = oe2->op;
- stmt2 = oe2->stmt_to_insert;
- op1 = oe1->op;
- stmt1 = oe1->stmt_to_insert;
+ 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;
}
-
- /* If we emit the last statement then we should put
- operands into the last statement. It will also
- break the loop. */
- if (op_index < 0 && stmt_index == i)
- i = stmt_num - 1;
+ 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))
{
- fprintf (dump_file, "Transforming ");
+ fprintf (dump_file, " into ");
print_gimple_stmt (dump_file, stmts[i], 0);
}
+ }
- /* If the stmt that defines operand has to be inserted, insert it
- before the use. */
- if (stmt1)
- insert_stmt_before_use (stmts[i], stmt1);
- if (stmt2)
- insert_stmt_before_use (stmts[i], stmt2);
- stmt1 = stmt2 = NULL;
-
- /* We keep original statement only for the last one. All
- others are recreated. */
- if (i == stmt_num - 1)
+ for (i = width; i < stmt_num; i++)
+ {
+ /* We keep original statement only for the last one. All others are
+ recreated. */
+ if ( op_index < 0)
{
- gimple_assign_set_rhs1 (stmts[i], op1);
- gimple_assign_set_rhs2 (stmts[i], op2);
- update_stmt (stmts[i]);
+ if (width_count == 2)
+ {
+
+ /* 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]);
+ }
+ 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--;
+ }
}
else
{
- stmts[i] = build_and_add_sum (TREE_TYPE (last_rhs1), op1, op2, opcode);
+ /* 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);
}
+
if (dump_file && (dump_flags & TDF_DETAILS))
{
fprintf (dump_file, " into ");
print_gimple_stmt (dump_file, stmts[i], 0);
}
}
-
remove_visited_stmt_chain (last_rhs1);
}
@@ -6649,6 +6654,76 @@ transform_stmt_to_multiply (gimple_stmt_iterator *gsi, gimple *stmt,
}
}
+/* Rearrange ops to generate more FMA when the chain may has more than 2 fmas.
+ Put no-mult ops and mult ops alternately at the end of the queue, which is
+ conducive to generating more fma and reducing the loss of FMA when breaking
+ the chain.
+ E.g.
+ a * b + c * d + e generates:
+
+ _4 = c_9(D) * d_10(D);
+ _12 = .FMA (a_7(D), b_8(D), _4);
+ _11 = e_6(D) + _12;
+
+ Rtearrange ops to -> e + a * b + c * d generates:
+
+ _4 = .FMA (c_7(D), d_8(D), _3);
+ _11 = .FMA (a_5(D), b_6(D), _4);
+ */
+static bool
+rank_ops_for_fma (vec<operand_entry *> *ops)
+{
+ operand_entry *oe;
+ unsigned int i;
+ unsigned int ops_length = ops->length ();
+ auto_vec<operand_entry *> ops_mult;
+ auto_vec<operand_entry *> ops_others;
+
+ FOR_EACH_VEC_ELT (*ops, i, oe)
+ {
+ if (TREE_CODE (oe->op) == SSA_NAME)
+ {
+ gimple *def_stmt = SSA_NAME_DEF_STMT (oe->op);
+ if (is_gimple_assign (def_stmt)
+ && gimple_assign_rhs_code (def_stmt) == MULT_EXPR)
+ ops_mult.safe_push (oe);
+ else
+ ops_others.safe_push (oe);
+ }
+ else
+ ops_others.safe_push (oe);
+ }
+ /* When ops_mult.length == 2, like the following case,
+
+ a * b + c * d + e.
+
+ we need to rearrange the ops.
+
+ Putting ops that not def from mult in front can generate more fmas. */
+ if (ops_mult.length () >= 2)
+ {
+ /* If all ops are defined with mult, we don't need to rearrange them. */
+ if (ops_mult.length () != ops_length)
+ {
+ /* Put no-mult ops and mult ops alternately at the end of the
+ queue, which is conducive to generating more fma and reducing the
+ loss of FMA when breaking the chain. */
+ ops->truncate (0);
+ ops->splice (ops_mult);
+ int j, opindex = ops->length ();
+ int others_length = ops_others.length();
+ for (j = 0; j < others_length; j++)
+ {
+ oe = ops_others.pop ();
+ ops->safe_insert (opindex, oe);
+ if (opindex > 0)
+ opindex--;
+ }
+ }
+ return true;
+ }
+ return false;
+}
/* Reassociate expressions in basic block BB and its post-dominator as
children.
@@ -6813,6 +6888,7 @@ reassociate_bb (basic_block bb)
machine_mode mode = TYPE_MODE (TREE_TYPE (lhs));
int ops_num = ops.length ();
int width;
+ bool has_fma = false;
/* For binary bit operations, if there are at least 3
operands and the last operand in OPS is a constant,
@@ -6821,11 +6897,23 @@ reassociate_bb (basic_block bb)
often match a canonical bit test when we get to RTL. */
if (ops.length () > 2
&& (rhs_code == BIT_AND_EXPR
- || rhs_code == BIT_IOR_EXPR
- || rhs_code == BIT_XOR_EXPR)
+ || rhs_code == BIT_IOR_EXPR
+ || rhs_code == BIT_XOR_EXPR)
&& TREE_CODE (ops.last ()->op) == INTEGER_CST)
std::swap (*ops[0], *ops[ops_num - 1]);
+ optimization_type opt_type = bb_optimization_type (bb);
+
+ /* If the target support FMA, rank_ops_for_fma will detect if
+ the chain has fmas and rearrange the ops if so. */
+ if (direct_internal_fn_supported_p (IFN_FMA,
+ TREE_TYPE (lhs),
+ opt_type)
+ && (rhs_code == PLUS_EXPR || rhs_code == MINUS_EXPR))
+ {
+ has_fma = rank_ops_for_fma(&ops);
+ }
+
/* Only rewrite the expression tree to parallel in the
last reassoc pass to avoid useless work back-and-forth
with initial linearization. */
@@ -6839,22 +6927,24 @@ reassociate_bb (basic_block bb)
"Width = %d was chosen for reassociation\n",
width);
rewrite_expr_tree_parallel (as_a <gassign *> (stmt),
- width, ops);
+ width,
+ has_fma,
+ ops);
}
else
- {
- /* When there are three operands left, we want
- to make sure the ones that get the double
- binary op are chosen wisely. */
- int len = ops.length ();
- if (len >= 3)
+ {
+ /* When there are three operands left, we want
+ to make sure the ones that get the double
+ binary op are chosen wisely. */
+ int len = ops.length ();
+ if (len >= 3 && !has_fma)
swap_ops_for_binary_stmt (ops, len - 3);
new_lhs = rewrite_expr_tree (stmt, rhs_code, 0, ops,
powi_result != NULL
|| negate_result,
len != orig_len);
- }
+ }
/* If we combined some repeated factors into a
__builtin_powi call, multiply that result by the