https://gcc.gnu.org/g:db3c8c9726d0bafbb9f85b6d7027fe83602643e7
commit r15-2097-gdb3c8c9726d0bafbb9f85b6d7027fe83602643e7
Author: Feng Xue <f...@os.amperecomputing.com>
Date: Wed May 29 17:28:14 2024 +0800
vect: Optimize order of lane-reducing operations in loop def-use cycles
When transforming multiple lane-reducing operations in a loop reduction
chain,
originally, corresponding vectorized statements are generated into def-use
cycles starting from 0. The def-use cycle with smaller index, would contain
more statements, which means more instruction dependency. For example:
int sum = 1;
for (i)
{
sum += d0[i] * d1[i]; // dot-prod <vector(16) char>
sum += w[i]; // widen-sum <vector(16) char>
sum += abs(s0[i] - s1[i]); // sad <vector(8) short>
sum += n[i]; // normal <vector(4) int>
}
Original transformation result:
for (i / 16)
{
sum_v0 = DOT_PROD (d0_v0[i: 0 ~ 15], d1_v0[i: 0 ~ 15], sum_v0);
sum_v1 = sum_v1; // copy
sum_v2 = sum_v2; // copy
sum_v3 = sum_v3; // copy
sum_v0 = WIDEN_SUM (w_v0[i: 0 ~ 15], sum_v0);
sum_v1 = sum_v1; // copy
sum_v2 = sum_v2; // copy
sum_v3 = sum_v3; // copy
sum_v0 = SAD (s0_v0[i: 0 ~ 7 ], s1_v0[i: 0 ~ 7 ], sum_v0);
sum_v1 = SAD (s0_v1[i: 8 ~ 15], s1_v1[i: 8 ~ 15], sum_v1);
sum_v2 = sum_v2; // copy
sum_v3 = sum_v3; // copy
...
}
For a higher instruction parallelism in final vectorized loop, an optimal
means is to make those effective vector lane-reducing ops be distributed
evenly among all def-use cycles. Transformed as the below, DOT_PROD,
WIDEN_SUM and SADs are generated into disparate cycles, instruction
dependency among them could be eliminated.
for (i / 16)
{
sum_v0 = DOT_PROD (d0_v0[i: 0 ~ 15], d1_v0[i: 0 ~ 15], sum_v0);
sum_v1 = sum_v1; // copy
sum_v2 = sum_v2; // copy
sum_v3 = sum_v3; // copy
sum_v0 = sum_v0; // copy
sum_v1 = WIDEN_SUM (w_v1[i: 0 ~ 15], sum_v1);
sum_v2 = sum_v2; // copy
sum_v3 = sum_v3; // copy
sum_v0 = sum_v0; // copy
sum_v1 = sum_v1; // copy
sum_v2 = SAD (s0_v2[i: 0 ~ 7 ], s1_v2[i: 0 ~ 7 ], sum_v2);
sum_v3 = SAD (s0_v3[i: 8 ~ 15], s1_v3[i: 8 ~ 15], sum_v3);
...
}
2024-03-22 Feng Xue <f...@os.amperecomputing.com>
gcc/
PR tree-optimization/114440
* tree-vectorizer.h (struct _stmt_vec_info): Add a new field
reduc_result_pos.
* tree-vect-loop.cc (vect_transform_reduction): Generate
lane-reducing
statements in an optimized order.
Diff:
---
gcc/tree-vect-loop.cc | 64 +++++++++++++++++++++++++++++++++++++++++++++------
gcc/tree-vectorizer.h | 6 +++++
2 files changed, 63 insertions(+), 7 deletions(-)
diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
index 1c3dbf4bc71b..d7d628efa60f 100644
--- a/gcc/tree-vect-loop.cc
+++ b/gcc/tree-vect-loop.cc
@@ -8844,6 +8844,7 @@ vect_transform_reduction (loop_vec_info loop_vinfo,
sum += d0[i] * d1[i]; // dot-prod <vector(16) char>
sum += w[i]; // widen-sum <vector(16) char>
sum += abs(s0[i] - s1[i]); // sad <vector(8) short>
+ sum += n[i]; // normal <vector(4) int>
}
The vector size is 128-bit，vectorization factor is 16. Reduction
@@ -8861,19 +8862,27 @@ vect_transform_reduction (loop_vec_info loop_vinfo,
sum_v2 = sum_v2; // copy
sum_v3 = sum_v3; // copy
- sum_v0 = WIDEN_SUM (w_v0[i: 0 ~ 15], sum_v0);
- sum_v1 = sum_v1; // copy
+ sum_v0 = sum_v0; // copy
+ sum_v1 = WIDEN_SUM (w_v1[i: 0 ~ 15], sum_v1);
sum_v2 = sum_v2; // copy
sum_v3 = sum_v3; // copy
- sum_v0 = SAD (s0_v0[i: 0 ~ 7 ], s1_v0[i: 0 ~ 7 ], sum_v0);
- sum_v1 = SAD (s0_v1[i: 8 ~ 15], s1_v1[i: 8 ~ 15], sum_v1);
- sum_v2 = sum_v2; // copy
+ sum_v0 = sum_v0; // copy
+ sum_v1 = SAD (s0_v1[i: 0 ~ 7 ], s1_v1[i: 0 ~ 7 ], sum_v1);
+ sum_v2 = SAD (s0_v2[i: 8 ~ 15], s1_v2[i: 8 ~ 15], sum_v2);
sum_v3 = sum_v3; // copy
+
+ sum_v0 += n_v0[i: 0 ~ 3 ];
+ sum_v1 += n_v1[i: 4 ~ 7 ];
+ sum_v2 += n_v2[i: 8 ~ 11];
+ sum_v3 += n_v3[i: 12 ~ 15];
}
- sum_v = sum_v0 + sum_v1 + sum_v2 + sum_v3; // = sum_v0 + sum_v1
- */
+ Moreover, for a higher instruction parallelism in final vectorized
+ loop, it is considered to make those effective vector lane-reducing
+ ops be distributed evenly among all def-use cycles. In the above
+ example, DOT_PROD, WIDEN_SUM and SADs are generated into disparate
+ cycles, instruction dependency among them could be eliminated. */
unsigned effec_ncopies = vec_oprnds[0].length ();
unsigned total_ncopies = vec_oprnds[reduc_index].length ();
@@ -8887,6 +8896,47 @@ vect_transform_reduction (loop_vec_info loop_vinfo,
vec_oprnds[i].safe_grow_cleared (total_ncopies);
}
}
+
+ tree reduc_vectype_in = STMT_VINFO_REDUC_VECTYPE_IN (reduc_info);
+ gcc_assert (reduc_vectype_in);
+
+ unsigned effec_reduc_ncopies
+ = vect_get_num_copies (loop_vinfo, slp_node, reduc_vectype_in);
+
+ gcc_assert (effec_ncopies <= effec_reduc_ncopies);
+
+ if (effec_ncopies < effec_reduc_ncopies)
+ {
+ /* Find suitable def-use cycles to generate vectorized statements
+ into, and reorder operands based on the selection. */
+ unsigned curr_pos = reduc_info->reduc_result_pos;
+ unsigned next_pos = (curr_pos + effec_ncopies) % effec_reduc_ncopies;
+
+ gcc_assert (curr_pos < effec_reduc_ncopies);
+ reduc_info->reduc_result_pos = next_pos;
+
+ if (curr_pos)
+ {
+ unsigned count = effec_reduc_ncopies - effec_ncopies;
+ unsigned start = curr_pos - count;
+
+ if ((int) start < 0)
+ {
+ count = curr_pos;
+ start = 0;
+ }
+
+ for (unsigned i = 0; i < op.num_ops - 1; i++)
+ {
+ for (unsigned j = effec_ncopies; j > start; j--)
+ {
+ unsigned k = j - 1;
+ std::swap (vec_oprnds[i][k], vec_oprnds[i][k + count]);
+ gcc_assert (!vec_oprnds[i][k]);
+ }
+ }
+ }
+ }
}
bool emulated_mixed_dot_prod = vect_is_emulated_mixed_dot_prod (stmt_info);
diff --git a/gcc/tree-vectorizer.h b/gcc/tree-vectorizer.h
index d8be89c37891..df6c8ada2f78 100644
--- a/gcc/tree-vectorizer.h
+++ b/gcc/tree-vectorizer.h
@@ -1402,6 +1402,12 @@ public:
/* The vector type for performing the actual reduction. */
tree reduc_vectype;
+ /* For loop reduction with multiple vectorized results (ncopies > 1), a
+ lane-reducing operation participating in it may not use all of those
+ results, this field specifies result index starting from which any
+ following land-reducing operation would be assigned to. */
+ unsigned int reduc_result_pos;
+
/* If IS_REDUC_INFO is true and if the vector code is performing
N scalar reductions in parallel, this variable gives the initial
scalar values of those N reductions. */
