1 /* Interchange heuristics and transform for loop interchange on
2 polyhedral representation.
4 Copyright (C) 2009 Free Software Foundation, Inc.
5 Contributed by Sebastian Pop <sebastian.pop@amd.com> and
6 Harsha Jagasia <harsha.jagasia@amd.com>.
8 This file is part of GCC.
10 GCC is free software; you can redistribute it and/or modify
11 it under the terms of the GNU General Public License as published by
12 the Free Software Foundation; either version 3, or (at your option)
15 GCC is distributed in the hope that it will be useful,
16 but WITHOUT ANY WARRANTY; without even the implied warranty of
17 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
18 GNU General Public License for more details.
20 You should have received a copy of the GNU General Public License
21 along with GCC; see the file COPYING3. If not see
22 <http://www.gnu.org/licenses/>. */
25 #include "coretypes.h"
31 #include "basic-block.h"
32 #include "diagnostic.h"
33 #include "tree-flow.h"
35 #include "tree-dump.h"
38 #include "tree-chrec.h"
39 #include "tree-data-ref.h"
40 #include "tree-scalar-evolution.h"
41 #include "tree-pass.h"
43 #include "value-prof.h"
44 #include "pointer-set.h"
49 #include "cloog/cloog.h"
52 #include "graphite-ppl.h"
54 #include "graphite-poly.h"
56 /* Builds a linear expression, of dimension DIM, representing PDR's
59 L = r_{n}*r_{n-1}*...*r_{1}*s_{0} + ... + r_{n}*s_{n-1} + s_{n}.
61 For an array A[10][20] with two subscript locations s0 and s1, the
62 linear memory access is 20 * s0 + s1: a stride of 1 in subscript s0
63 corresponds to a memory stride of 20.
65 OFFSET is a number of dimensions to prepend before the
66 subscript dimensions: s_0, s_1, ..., s_n.
68 Thus, the final linear expression has the following format:
69 0 .. 0_{offset} | 0 .. 0_{nit} | 0 .. 0_{gd} | 0 | c_0 c_1 ... c_n
70 where the expression itself is:
71 c_0 * s_0 + c_1 * s_1 + ... c_n * s_n. */
73 static ppl_Linear_Expression_t
74 build_linearized_memory_access (ppl_dimension_type offset, poly_dr_p pdr)
76 ppl_Linear_Expression_t res;
77 ppl_Linear_Expression_t le;
79 ppl_dimension_type first = pdr_subscript_dim (pdr, 0);
80 ppl_dimension_type last = pdr_subscript_dim (pdr, PDR_NB_SUBSCRIPTS (pdr));
82 graphite_dim_t dim = offset + pdr_dim (pdr);
84 ppl_new_Linear_Expression_with_dimension (&res, dim);
87 value_set_si (size, 1);
88 value_init (sub_size);
89 value_set_si (sub_size, 1);
91 for (i = last - 1; i >= first; i--)
93 ppl_set_coef_gmp (res, i + offset, size);
95 ppl_new_Linear_Expression_with_dimension (&le, dim - offset);
96 ppl_set_coef (le, i, 1);
97 ppl_max_for_le_pointset (PDR_ACCESSES (pdr), le, sub_size);
98 value_multiply (size, size, sub_size);
99 ppl_delete_Linear_Expression (le);
102 value_clear (sub_size);
107 /* Set STRIDE to the stride of PDR in memory by advancing by one in
108 time dimension DEPTH. */
111 memory_stride_in_loop (Value stride, graphite_dim_t depth, poly_dr_p pdr)
113 ppl_dimension_type time_depth;
114 ppl_Linear_Expression_t le, lma;
115 ppl_Constraint_t new_cstr;
116 ppl_dimension_type i, *map;
117 ppl_Pointset_Powerset_C_Polyhedron_t p1, p2, sctr;
118 graphite_dim_t nb_subscripts = PDR_NB_SUBSCRIPTS (pdr) + 1;
119 poly_bb_p pbb = PDR_PBB (pdr);
120 ppl_dimension_type offset = pbb_nb_scattering_transform (pbb)
121 + pbb_nb_local_vars (pbb)
122 + pbb_dim_iter_domain (pbb);
123 ppl_dimension_type offsetg = offset + pbb_nb_params (pbb);
124 ppl_dimension_type dim_sctr = pbb_nb_scattering_transform (pbb)
125 + pbb_nb_local_vars (pbb);
126 ppl_dimension_type dim_L1 = offset + offsetg + 2 * nb_subscripts;
127 ppl_dimension_type dim_L2 = offset + offsetg + 2 * nb_subscripts + 1;
128 ppl_dimension_type new_dim = offset + offsetg + 2 * nb_subscripts + 2;
130 /* The resulting polyhedron should have the following format:
131 T|I|T'|I'|G|S|S'|l1|l2
133 | T = t_1..t_{dim_sctr}
134 | I = i_1..i_{dim_iter_domain}
135 | T'= t'_1..t'_{dim_sctr}
136 | I'= i'_1..i'_{dim_iter_domain}
137 | G = g_1..g_{nb_params}
138 | S = s_1..s_{nb_subscripts}
139 | S'= s'_1..s'_{nb_subscripts}
140 | l1 and l2 are scalars.
143 offset = dim_sctr + dim_iter_domain + nb_local_vars
144 offsetg = dim_sctr + dim_iter_domain + nb_local_vars + nb_params. */
146 /* Construct the T|I|0|0|G|0|0|0|0 part. */
148 ppl_new_Pointset_Powerset_C_Polyhedron_from_C_Polyhedron
149 (&sctr, PBB_TRANSFORMED_SCATTERING (pbb));
150 ppl_Pointset_Powerset_C_Polyhedron_add_space_dimensions_and_embed
151 (sctr, 2 * nb_subscripts + 2);
152 ppl_insert_dimensions_pointset (sctr, offset, offset);
155 /* Construct the 0|I|0|0|G|S|0|0|0 part. */
157 ppl_new_Pointset_Powerset_C_Polyhedron_from_Pointset_Powerset_C_Polyhedron
158 (&p1, PDR_ACCESSES (pdr));
159 ppl_Pointset_Powerset_C_Polyhedron_add_space_dimensions_and_embed
160 (p1, nb_subscripts + 2);
161 ppl_insert_dimensions_pointset (p1, 0, dim_sctr);
162 ppl_insert_dimensions_pointset (p1, offset, offset);
165 /* Construct the 0|0|0|0|0|S|0|l1|0 part. */
167 lma = build_linearized_memory_access (offset + dim_sctr, pdr);
168 ppl_set_coef (lma, dim_L1, -1);
169 ppl_new_Constraint (&new_cstr, lma, PPL_CONSTRAINT_TYPE_EQUAL);
170 ppl_Pointset_Powerset_C_Polyhedron_add_constraint (p1, new_cstr);
173 /* Now intersect all the parts to get the polyhedron P1:
178 T|I|0|0|G|S|0|l1|0. */
180 ppl_Pointset_Powerset_C_Polyhedron_intersection_assign (p1, sctr);
181 ppl_delete_Pointset_Powerset_C_Polyhedron (sctr);
183 /* Build P2, which would have the following form:
184 0|0|T'|I'|G|0|S'|0|l2
186 P2 is built, by remapping the P1 polyhedron:
189 using the following mapping:
195 ppl_new_Pointset_Powerset_C_Polyhedron_from_Pointset_Powerset_C_Polyhedron
198 map = ppl_new_id_map (new_dim);
201 for (i = 0; i < offset; i++)
202 ppl_interchange (map, i, i + offset);
205 ppl_interchange (map, dim_L1, dim_L2);
208 for (i = 0; i < nb_subscripts; i++)
209 ppl_interchange (map, offset + offsetg + i,
210 offset + offsetg + nb_subscripts + i);
212 ppl_Pointset_Powerset_C_Polyhedron_map_space_dimensions (p2, map, new_dim);
219 | t_{depth-1} = t'_{depth-1}
220 | t_{depth+1} = t'_{depth+1}
222 | t_{dim_sctr} = t'_{dim_sctr}
224 This means that all the time dimensions are equal except for
225 depth, where we will add t_{depth} = t'_{depth} + 1 in the next
228 time_depth = psct_dynamic_dim (pbb, depth);
229 for (i = 0; i < dim_sctr; i++)
232 ppl_new_Linear_Expression_with_dimension (&le, new_dim);
233 ppl_set_coef (le, i, 1);
234 ppl_set_coef (le, i + offset, -1);
235 ppl_new_Constraint (&new_cstr, le, PPL_CONSTRAINT_TYPE_EQUAL);
236 ppl_Pointset_Powerset_C_Polyhedron_add_constraint (p2, new_cstr);
237 ppl_delete_Linear_Expression (le);
238 ppl_delete_Constraint (new_cstr);
241 /* Add equality : t_{depth} = t'_{depth} + 1.
242 This is the core part of this alogrithm, since this
243 constraint asks for the memory access stride (difference)
244 between two consecutive points in time dimensions. */
246 ppl_new_Linear_Expression_with_dimension (&le, new_dim);
247 ppl_set_coef (le, time_depth, 1);
248 ppl_set_coef (le, time_depth + offset, -1);
249 ppl_set_inhomogeneous (le, 1);
250 ppl_new_Constraint (&new_cstr, le, PPL_CONSTRAINT_TYPE_EQUAL);
251 ppl_Pointset_Powerset_C_Polyhedron_add_constraint (p2, new_cstr);
252 ppl_delete_Linear_Expression (le);
253 ppl_delete_Constraint (new_cstr);
256 /* P1 = P1 inter P2. */
258 ppl_Pointset_Powerset_C_Polyhedron_intersection_assign (p1, p2);
259 ppl_delete_Pointset_Powerset_C_Polyhedron (p2);
262 /* Maximise the expression L2 - L1. */
264 ppl_new_Linear_Expression_with_dimension (&le, new_dim);
265 ppl_set_coef (le, dim_L2, 1);
266 ppl_set_coef (le, dim_L1, -1);
267 ppl_max_for_le_pointset (p1, le, stride);
268 ppl_delete_Linear_Expression (le);
272 /* Returns true when it is profitable to interchange time dimensions DEPTH1
273 and DEPTH2 with DEPTH1 < DEPTH2 for PBB.
285 | for (i = 0; i < N; i++)
286 | for (j = 0; j < N; j++)
292 The data access A[j][i] is described like this:
300 | 0 0 0 0 -1 0 100 >= 0
301 | 0 0 0 0 0 -1 100 >= 0
303 The linearized memory access L to A[100][100] is:
308 TODO: the shown format is not valid as it does not show the fact
309 that the iteration domain "i j" is transformed using the scattering.
311 Next, to measure the impact of iterating once in loop "i", we build
312 a maximization problem: first, we add to DR accesses the dimensions
313 k, s2, s3, L1 = 100 * s0 + s1, L2, and D1: polyhedron P1.
315 | i j N a s0 s1 k s2 s3 L1 L2 D1 1
316 | 0 0 0 1 0 0 0 0 0 0 0 0 -5 = 0 alias = 5
317 | 0 -1 0 0 1 0 0 0 0 0 0 0 0 = 0 s0 = j
318 |-2 0 0 0 0 1 0 0 0 0 0 0 0 = 0 s1 = 2 * i
319 | 0 0 0 0 1 0 0 0 0 0 0 0 0 >= 0
320 | 0 0 0 0 0 1 0 0 0 0 0 0 0 >= 0
321 | 0 0 0 0 -1 0 0 0 0 0 0 0 100 >= 0
322 | 0 0 0 0 0 -1 0 0 0 0 0 0 100 >= 0
323 | 0 0 0 0 100 1 0 0 0 -1 0 0 0 = 0 L1 = 100 * s0 + s1
325 Then, we generate the polyhedron P2 by interchanging the dimensions
326 (s0, s2), (s1, s3), (L1, L2), (k, i)
328 | i j N a s0 s1 k s2 s3 L1 L2 D1 1
329 | 0 0 0 1 0 0 0 0 0 0 0 0 -5 = 0 alias = 5
330 | 0 -1 0 0 0 0 0 1 0 0 0 0 0 = 0 s2 = j
331 | 0 0 0 0 0 0 -2 0 1 0 0 0 0 = 0 s3 = 2 * k
332 | 0 0 0 0 0 0 0 1 0 0 0 0 0 >= 0
333 | 0 0 0 0 0 0 0 0 1 0 0 0 0 >= 0
334 | 0 0 0 0 0 0 0 -1 0 0 0 0 100 >= 0
335 | 0 0 0 0 0 0 0 0 -1 0 0 0 100 >= 0
336 | 0 0 0 0 0 0 0 100 1 0 -1 0 0 = 0 L2 = 100 * s2 + s3
338 then we add to P2 the equality k = i + 1:
340 |-1 0 0 0 0 0 1 0 0 0 0 0 -1 = 0 k = i + 1
342 and finally we maximize the expression "D1 = max (P1 inter P2, L2 - L1)".
344 Similarly, to determine the impact of one iteration on loop "j", we
345 interchange (k, j), we add "k = j + 1", and we compute D2 the
346 maximal value of the difference.
348 Finally, the profitability test is D1 < D2: if in the outer loop
349 the strides are smaller than in the inner loop, then it is
350 profitable to interchange the loops at DEPTH1 and DEPTH2. */
353 pbb_interchange_profitable_p (graphite_dim_t depth1, graphite_dim_t depth2,
361 gcc_assert (depth1 < depth2);
364 value_set_si (d1, 0);
366 value_set_si (d2, 0);
370 for (i = 0; VEC_iterate (poly_dr_p, PBB_DRS (pbb), i, pdr); i++)
372 value_set_si (n, PDR_NB_REFS (pdr));
374 memory_stride_in_loop (s, depth1, pdr);
375 value_multiply (s, s, n);
376 value_addto (d1, d1, s);
378 memory_stride_in_loop (s, depth2, pdr);
379 value_multiply (s, s, n);
380 value_addto (d2, d2, s);
383 res = value_lt (d1, d2);
393 /* Interchanges the loops at DEPTH1 and DEPTH2 of the original
394 scattering and assigns the resulting polyhedron to the transformed
398 pbb_interchange_loop_depths (graphite_dim_t depth1, graphite_dim_t depth2,
401 ppl_dimension_type i, dim;
402 ppl_dimension_type *map;
403 ppl_Polyhedron_t poly = PBB_TRANSFORMED_SCATTERING (pbb);
404 ppl_dimension_type dim1 = psct_dynamic_dim (pbb, depth1);
405 ppl_dimension_type dim2 = psct_dynamic_dim (pbb, depth2);
407 ppl_Polyhedron_space_dimension (poly, &dim);
408 map = (ppl_dimension_type *) XNEWVEC (ppl_dimension_type, dim);
410 for (i = 0; i < dim; i++)
416 ppl_Polyhedron_map_space_dimensions (poly, map, dim);
420 /* Apply the interchange of loops at depths DEPTH1 and DEPTH2 to all
421 the statements below LST. */
424 lst_apply_interchange (lst_p lst, int depth1, int depth2)
429 if (LST_LOOP_P (lst))
434 for (i = 0; VEC_iterate (lst_p, LST_SEQ (lst), i, l); i++)
435 lst_apply_interchange (l, depth1, depth2);
438 pbb_interchange_loop_depths (depth1, depth2, LST_PBB (lst));
441 /* Return true when the interchange of loops at depths DEPTH1 and
442 DEPTH2 to all the statements below LST is profitable. */
445 lst_interchange_profitable_p (lst_p lst, int depth1, int depth2)
450 if (LST_LOOP_P (lst))
456 for (i = 0; VEC_iterate (lst_p, LST_SEQ (lst), i, l); i++)
458 bool profitable = lst_interchange_profitable_p (l, depth1, depth2);
460 if (profitable && !LST_LOOP_P (lst)
461 && dump_file && (dump_flags & TDF_DETAILS))
463 "Interchanging loops at depths %d and %d is profitable for stmt_%d.\n",
464 depth1, depth2, pbb_index (LST_PBB (lst)));
472 return pbb_interchange_profitable_p (depth1, depth2, LST_PBB (lst));
476 /* Try to interchange LOOP1 with LOOP2 for all the statements of the
477 body of LOOP2. LOOP1 contains LOOP2. Return true if it did the
481 lst_try_interchange_loops (scop_p scop, lst_p loop1, lst_p loop2)
483 int depth1 = lst_depth (loop1);
484 int depth2 = lst_depth (loop2);
486 if (!lst_interchange_profitable_p (loop2, depth1, depth2))
489 lst_apply_interchange (loop2, depth1, depth2);
491 if (graphite_legal_transform (scop))
493 if (dump_file && (dump_flags & TDF_DETAILS))
495 "Loops at depths %d and %d will be interchanged.\n",
501 /* Undo the transform. */
502 lst_apply_interchange (loop2, depth2, depth1);
506 /* Try to interchange LOOP with all the loops contained in the body of
507 LST. Return true if it did interchanged some loops. */
510 lst_try_interchange (scop_p scop, lst_p loop, lst_p lst)
515 if (LST_LOOP_P (lst))
519 bool res = lst_try_interchange_loops (scop, loop, lst);
521 for (i = 0; VEC_iterate (lst_p, LST_SEQ (lst), i, l); i++)
522 res |= lst_try_interchange (scop, loop, l);
530 /* Interchanges all the loops of LST that are considered profitable to
531 interchange. Return true if it did interchanged some loops. */
534 lst_do_interchange (scop_p scop, lst_p lst)
539 if (LST_LOOP_P (lst))
545 if (lst_depth (lst) >= 0)
546 for (i = 0; VEC_iterate (lst_p, LST_SEQ (lst), i, l); i++)
547 res |= lst_try_interchange (scop, lst, l);
549 for (i = 0; VEC_iterate (lst_p, LST_SEQ (lst), i, l); i++)
550 res |= lst_do_interchange (scop, l);
558 /* Interchanges all the loop depths that are considered profitable for SCOP. */
561 scop_do_interchange (scop_p scop)
563 bool transform_done = false;
565 store_scattering (scop);
567 transform_done = lst_do_interchange (scop, SCOP_TRANSFORMED_SCHEDULE (scop));
572 if (!graphite_legal_transform (scop))
574 restore_scattering (scop);
578 return transform_done;