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 /* Builds a partial difference equations and inserts them
108 into pointset powerset polyhedron P. Polyhedron is assumed
109 to have the format: T|I|T'|I'|G|S|S'|l1|l2.
111 TIME_DEPTH is the time dimension w.r.t. which we are
113 OFFSET represents the number of dimensions between
114 columns t_{time_depth} and t'_{time_depth}.
115 DIM_SCTR is the number of scattering dimensions. It is
116 essentially the dimensionality of the T vector.
118 The following equations are inserted into the polyhedron P:
121 | t_{time_depth-1} = t'_{time_depth-1}
122 | t_{time_depth} = t'_{time_depth} + 1
123 | t_{time_depth+1} = t'_{time_depth + 1}
125 | t_{dim_sctr} = t'_{dim_sctr}. */
128 build_partial_difference (ppl_Pointset_Powerset_C_Polyhedron_t *p,
129 ppl_dimension_type time_depth,
130 ppl_dimension_type offset,
131 ppl_dimension_type dim_sctr)
133 ppl_Constraint_t new_cstr;
134 ppl_Linear_Expression_t le;
135 ppl_dimension_type i;
136 ppl_dimension_type dim;
137 ppl_Pointset_Powerset_C_Polyhedron_t temp;
139 /* Add the equality: t_{time_depth} = t'_{time_depth} + 1.
140 This is the core part of this alogrithm, since this
141 constraint asks for the memory access stride (difference)
142 between two consecutive points in time dimensions. */
144 ppl_Pointset_Powerset_C_Polyhedron_space_dimension (*p, &dim);
145 ppl_new_Linear_Expression_with_dimension (&le, dim);
146 ppl_set_coef (le, time_depth, 1);
147 ppl_set_coef (le, time_depth + offset, -1);
148 ppl_set_inhomogeneous (le, 1);
149 ppl_new_Constraint (&new_cstr, le, PPL_CONSTRAINT_TYPE_EQUAL);
150 ppl_Pointset_Powerset_C_Polyhedron_add_constraint (*p, new_cstr);
151 ppl_delete_Linear_Expression (le);
152 ppl_delete_Constraint (new_cstr);
157 | t_{time_depth-1} = t'_{time_depth-1}
158 | t_{time_depth+1} = t'_{time_depth+1}
160 | t_{dim_sctr} = t'_{dim_sctr}
162 This means that all the time dimensions are equal except for
163 time_depth, where the constraint is t_{depth} = t'_{depth} + 1
164 step. More to this: we should be carefull not to add equalities
165 to the 'coupled' dimensions, which happens when the one dimension
166 is stripmined dimension, and the other dimension corresponds
167 to the point loop inside stripmined dimension. */
169 ppl_new_Pointset_Powerset_C_Polyhedron_from_Pointset_Powerset_C_Polyhedron (&temp, *p);
171 for (i = 0; i < dim_sctr; i++)
174 ppl_new_Linear_Expression_with_dimension (&le, dim);
175 ppl_set_coef (le, i, 1);
176 ppl_set_coef (le, i + offset, -1);
177 ppl_new_Constraint (&new_cstr, le, PPL_CONSTRAINT_TYPE_EQUAL);
178 ppl_Pointset_Powerset_C_Polyhedron_add_constraint (temp, new_cstr);
180 if (ppl_Pointset_Powerset_C_Polyhedron_is_empty (temp))
182 ppl_delete_Pointset_Powerset_C_Polyhedron (temp);
183 ppl_new_Pointset_Powerset_C_Polyhedron_from_Pointset_Powerset_C_Polyhedron (&temp, *p);
186 ppl_Pointset_Powerset_C_Polyhedron_add_constraint (*p, new_cstr);
187 ppl_delete_Linear_Expression (le);
188 ppl_delete_Constraint (new_cstr);
191 ppl_delete_Pointset_Powerset_C_Polyhedron (temp);
195 /* Set STRIDE to the stride of PDR in memory by advancing by one in
196 the loop at DEPTH. */
199 memory_stride_in_loop (Value stride, graphite_dim_t depth, poly_dr_p pdr)
201 ppl_dimension_type time_depth;
202 ppl_Linear_Expression_t le, lma;
203 ppl_Constraint_t new_cstr;
204 ppl_dimension_type i, *map;
205 ppl_Pointset_Powerset_C_Polyhedron_t p1, p2, sctr;
206 graphite_dim_t nb_subscripts = PDR_NB_SUBSCRIPTS (pdr) + 1;
207 poly_bb_p pbb = PDR_PBB (pdr);
208 ppl_dimension_type offset = pbb_nb_scattering_transform (pbb)
209 + pbb_nb_local_vars (pbb)
210 + pbb_dim_iter_domain (pbb);
211 ppl_dimension_type offsetg = offset + pbb_nb_params (pbb);
212 ppl_dimension_type dim_sctr = pbb_nb_scattering_transform (pbb)
213 + pbb_nb_local_vars (pbb);
214 ppl_dimension_type dim_L1 = offset + offsetg + 2 * nb_subscripts;
215 ppl_dimension_type dim_L2 = offset + offsetg + 2 * nb_subscripts + 1;
216 ppl_dimension_type new_dim = offset + offsetg + 2 * nb_subscripts + 2;
218 /* The resulting polyhedron should have the following format:
219 T|I|T'|I'|G|S|S'|l1|l2
221 | T = t_1..t_{dim_sctr}
222 | I = i_1..i_{dim_iter_domain}
223 | T'= t'_1..t'_{dim_sctr}
224 | I'= i'_1..i'_{dim_iter_domain}
225 | G = g_1..g_{nb_params}
226 | S = s_1..s_{nb_subscripts}
227 | S'= s'_1..s'_{nb_subscripts}
228 | l1 and l2 are scalars.
231 offset = dim_sctr + dim_iter_domain + nb_local_vars
232 offsetg = dim_sctr + dim_iter_domain + nb_local_vars + nb_params. */
234 /* Construct the T|I|0|0|G|0|0|0|0 part. */
236 ppl_new_Pointset_Powerset_C_Polyhedron_from_C_Polyhedron
237 (&sctr, PBB_TRANSFORMED_SCATTERING (pbb));
238 ppl_Pointset_Powerset_C_Polyhedron_add_space_dimensions_and_embed
239 (sctr, 2 * nb_subscripts + 2);
240 ppl_insert_dimensions_pointset (sctr, offset, offset);
243 /* Construct the 0|I|0|0|G|S|0|0|0 part. */
245 ppl_new_Pointset_Powerset_C_Polyhedron_from_Pointset_Powerset_C_Polyhedron
246 (&p1, PDR_ACCESSES (pdr));
247 ppl_Pointset_Powerset_C_Polyhedron_add_space_dimensions_and_embed
248 (p1, nb_subscripts + 2);
249 ppl_insert_dimensions_pointset (p1, 0, dim_sctr);
250 ppl_insert_dimensions_pointset (p1, offset, offset);
253 /* Construct the 0|0|0|0|0|S|0|l1|0 part. */
255 lma = build_linearized_memory_access (offset + dim_sctr, pdr);
256 ppl_set_coef (lma, dim_L1, -1);
257 ppl_new_Constraint (&new_cstr, lma, PPL_CONSTRAINT_TYPE_EQUAL);
258 ppl_Pointset_Powerset_C_Polyhedron_add_constraint (p1, new_cstr);
259 ppl_delete_Linear_Expression (lma);
260 ppl_delete_Constraint (new_cstr);
263 /* Now intersect all the parts to get the polyhedron P1:
268 T|I|0|0|G|S|0|l1|0. */
270 ppl_Pointset_Powerset_C_Polyhedron_intersection_assign (p1, sctr);
271 ppl_delete_Pointset_Powerset_C_Polyhedron (sctr);
273 /* Build P2, which would have the following form:
274 0|0|T'|I'|G|0|S'|0|l2
276 P2 is built, by remapping the P1 polyhedron:
279 using the following mapping:
285 ppl_new_Pointset_Powerset_C_Polyhedron_from_Pointset_Powerset_C_Polyhedron
288 map = ppl_new_id_map (new_dim);
291 for (i = 0; i < offset; i++)
292 ppl_interchange (map, i, i + offset);
295 ppl_interchange (map, dim_L1, dim_L2);
298 for (i = 0; i < nb_subscripts; i++)
299 ppl_interchange (map, offset + offsetg + i,
300 offset + offsetg + nb_subscripts + i);
302 ppl_Pointset_Powerset_C_Polyhedron_map_space_dimensions (p2, map, new_dim);
306 time_depth = psct_dynamic_dim (pbb, depth);
308 /* P1 = P1 inter P2. */
309 ppl_Pointset_Powerset_C_Polyhedron_intersection_assign (p1, p2);
310 build_partial_difference (&p1, time_depth, offset, dim_sctr);
312 /* Maximise the expression L2 - L1. */
314 ppl_new_Linear_Expression_with_dimension (&le, new_dim);
315 ppl_set_coef (le, dim_L2, 1);
316 ppl_set_coef (le, dim_L1, -1);
317 ppl_max_for_le_pointset (p1, le, stride);
320 if (dump_file && (dump_flags & TDF_DETAILS))
322 fprintf (dump_file, "\nStride in BB_%d, DR_%d, depth %d:",
323 pbb_index (pbb), PDR_ID (pdr), (int) depth);
324 value_print (dump_file, " %s ", stride);
327 ppl_delete_Pointset_Powerset_C_Polyhedron (p1);
328 ppl_delete_Pointset_Powerset_C_Polyhedron (p2);
329 ppl_delete_Linear_Expression (le);
332 /* Sets STRIDES to the sum of all the strides of the data references
333 accessed in LOOP at DEPTH. */
336 memory_strides_in_loop (lst_p loop, graphite_dim_t depth, Value strides)
346 for (j = 0; VEC_iterate (lst_p, LST_SEQ (loop), j, l); j++)
348 memory_strides_in_loop (l, depth, strides);
350 for (i = 0; VEC_iterate (poly_dr_p, PBB_DRS (LST_PBB (l)), i, pdr); i++)
352 memory_stride_in_loop (s, depth, pdr);
353 value_set_si (n, PDR_NB_REFS (pdr));
354 value_multiply (s, s, n);
355 value_addto (strides, strides, s);
362 /* Return true when the interchange of loops LOOP1 and LOOP2 is
375 | for (i = 0; i < N; i++)
376 | for (j = 0; j < N; j++)
382 The data access A[j][i] is described like this:
390 | 0 0 0 0 -1 0 100 >= 0
391 | 0 0 0 0 0 -1 100 >= 0
393 The linearized memory access L to A[100][100] is:
398 TODO: the shown format is not valid as it does not show the fact
399 that the iteration domain "i j" is transformed using the scattering.
401 Next, to measure the impact of iterating once in loop "i", we build
402 a maximization problem: first, we add to DR accesses the dimensions
403 k, s2, s3, L1 = 100 * s0 + s1, L2, and D1: this is the polyhedron P1.
404 L1 and L2 are the linearized memory access functions.
406 | i j N a s0 s1 k s2 s3 L1 L2 D1 1
407 | 0 0 0 1 0 0 0 0 0 0 0 0 -5 = 0 alias = 5
408 | 0 -1 0 0 1 0 0 0 0 0 0 0 0 = 0 s0 = j
409 |-2 0 0 0 0 1 0 0 0 0 0 0 0 = 0 s1 = 2 * i
410 | 0 0 0 0 1 0 0 0 0 0 0 0 0 >= 0
411 | 0 0 0 0 0 1 0 0 0 0 0 0 0 >= 0
412 | 0 0 0 0 -1 0 0 0 0 0 0 0 100 >= 0
413 | 0 0 0 0 0 -1 0 0 0 0 0 0 100 >= 0
414 | 0 0 0 0 100 1 0 0 0 -1 0 0 0 = 0 L1 = 100 * s0 + s1
416 Then, we generate the polyhedron P2 by interchanging the dimensions
417 (s0, s2), (s1, s3), (L1, L2), (k, i)
419 | i j N a s0 s1 k s2 s3 L1 L2 D1 1
420 | 0 0 0 1 0 0 0 0 0 0 0 0 -5 = 0 alias = 5
421 | 0 -1 0 0 0 0 0 1 0 0 0 0 0 = 0 s2 = j
422 | 0 0 0 0 0 0 -2 0 1 0 0 0 0 = 0 s3 = 2 * k
423 | 0 0 0 0 0 0 0 1 0 0 0 0 0 >= 0
424 | 0 0 0 0 0 0 0 0 1 0 0 0 0 >= 0
425 | 0 0 0 0 0 0 0 -1 0 0 0 0 100 >= 0
426 | 0 0 0 0 0 0 0 0 -1 0 0 0 100 >= 0
427 | 0 0 0 0 0 0 0 100 1 0 -1 0 0 = 0 L2 = 100 * s2 + s3
429 then we add to P2 the equality k = i + 1:
431 |-1 0 0 0 0 0 1 0 0 0 0 0 -1 = 0 k = i + 1
433 and finally we maximize the expression "D1 = max (P1 inter P2, L2 - L1)".
435 Similarly, to determine the impact of one iteration on loop "j", we
436 interchange (k, j), we add "k = j + 1", and we compute D2 the
437 maximal value of the difference.
439 Finally, the profitability test is D1 < D2: if in the outer loop
440 the strides are smaller than in the inner loop, then it is
441 profitable to interchange the loops at DEPTH1 and DEPTH2. */
444 lst_interchange_profitable_p (lst_p loop1, lst_p loop2)
449 gcc_assert (loop1 && loop2
450 && LST_LOOP_P (loop1) && LST_LOOP_P (loop2)
451 && lst_depth (loop1) < lst_depth (loop2));
455 value_set_si (d1, 0);
456 value_set_si (d2, 0);
458 memory_strides_in_loop (loop1, lst_depth (loop1), d1);
459 memory_strides_in_loop (loop2, lst_depth (loop2), d2);
461 res = value_lt (d1, d2);
469 /* Interchanges the loops at DEPTH1 and DEPTH2 of the original
470 scattering and assigns the resulting polyhedron to the transformed
474 pbb_interchange_loop_depths (graphite_dim_t depth1, graphite_dim_t depth2,
477 ppl_dimension_type i, dim;
478 ppl_dimension_type *map;
479 ppl_Polyhedron_t poly = PBB_TRANSFORMED_SCATTERING (pbb);
480 ppl_dimension_type dim1 = psct_dynamic_dim (pbb, depth1);
481 ppl_dimension_type dim2 = psct_dynamic_dim (pbb, depth2);
483 ppl_Polyhedron_space_dimension (poly, &dim);
484 map = (ppl_dimension_type *) XNEWVEC (ppl_dimension_type, dim);
486 for (i = 0; i < dim; i++)
492 ppl_Polyhedron_map_space_dimensions (poly, map, dim);
496 /* Apply the interchange of loops at depths DEPTH1 and DEPTH2 to all
497 the statements below LST. */
500 lst_apply_interchange (lst_p lst, int depth1, int depth2)
505 if (LST_LOOP_P (lst))
510 for (i = 0; VEC_iterate (lst_p, LST_SEQ (lst), i, l); i++)
511 lst_apply_interchange (l, depth1, depth2);
514 pbb_interchange_loop_depths (depth1, depth2, LST_PBB (lst));
517 /* Return true when the nest starting at LOOP1 and ending on LOOP2 is
518 perfect: i.e. there are no sequence of statements. */
521 lst_perfectly_nested_p (lst_p loop1, lst_p loop2)
526 if (!LST_LOOP_P (loop1))
529 return VEC_length (lst_p, LST_SEQ (loop1)) == 1
530 && lst_perfectly_nested_p (VEC_index (lst_p, LST_SEQ (loop1), 0), loop2);
533 /* Transform the loop nest between LOOP1 and LOOP2 into a perfect
534 nest. To continue the naming tradition, this function is called
535 after perfect_nestify. NEST is set to the perfectly nested loop
536 that is created. BEFORE/AFTER are set to the loops distributed
537 before/after the loop NEST. */
540 lst_perfect_nestify (lst_p loop1, lst_p loop2, lst_p *before,
541 lst_p *nest, lst_p *after)
543 poly_bb_p first, last;
545 gcc_assert (loop1 && loop2
547 && LST_LOOP_P (loop1) && LST_LOOP_P (loop2));
549 first = LST_PBB (lst_find_first_pbb (loop2));
550 last = LST_PBB (lst_find_last_pbb (loop2));
552 *before = copy_lst (loop1);
553 *nest = copy_lst (loop1);
554 *after = copy_lst (loop1);
556 lst_remove_all_before_including_pbb (*before, first, false);
557 lst_remove_all_before_including_pbb (*after, last, true);
559 lst_remove_all_before_excluding_pbb (*nest, first, true);
560 lst_remove_all_before_excluding_pbb (*nest, last, false);
562 if (lst_empty_p (*before))
567 if (lst_empty_p (*after))
572 if (lst_empty_p (*nest))
579 /* Try to interchange LOOP1 with LOOP2 for all the statements of the
580 body of LOOP2. LOOP1 contains LOOP2. Return true if it did the
584 lst_try_interchange_loops (scop_p scop, lst_p loop1, lst_p loop2)
586 int depth1 = lst_depth (loop1);
587 int depth2 = lst_depth (loop2);
590 lst_p before = NULL, nest = NULL, after = NULL;
592 if (!lst_interchange_profitable_p (loop1, loop2))
595 if (!lst_perfectly_nested_p (loop1, loop2))
596 lst_perfect_nestify (loop1, loop2, &before, &nest, &after);
598 lst_apply_interchange (loop2, depth1, depth2);
600 /* Sync the transformed LST information and the PBB scatterings
601 before using the scatterings in the data dependence analysis. */
602 if (before || nest || after)
604 transformed = lst_substitute_3 (SCOP_TRANSFORMED_SCHEDULE (scop), loop1,
605 before, nest, after);
606 lst_update_scattering (transformed);
607 free_lst (transformed);
610 if (graphite_legal_transform (scop))
612 if (dump_file && (dump_flags & TDF_DETAILS))
614 "Loops at depths %d and %d will be interchanged.\n",
617 /* Transform the SCOP_TRANSFORMED_SCHEDULE of the SCOP. */
618 lst_insert_in_sequence (before, loop1, true);
619 lst_insert_in_sequence (after, loop1, false);
623 lst_replace (loop1, nest);
630 /* Undo the transform. */
634 lst_apply_interchange (loop2, depth2, depth1);
638 /* Selects the inner loop in LST_SEQ (INNER_FATHER) to be interchanged
639 with the loop OUTER in LST_SEQ (OUTER_FATHER). */
642 lst_interchange_select_inner (scop_p scop, lst_p outer_father, int outer,
648 gcc_assert (outer_father
649 && LST_LOOP_P (outer_father)
650 && LST_LOOP_P (VEC_index (lst_p, LST_SEQ (outer_father), outer))
652 && LST_LOOP_P (inner_father));
654 loop1 = VEC_index (lst_p, LST_SEQ (outer_father), outer);
656 for (inner = 0; VEC_iterate (lst_p, LST_SEQ (inner_father), inner, loop2); inner++)
657 if (LST_LOOP_P (loop2)
658 && (lst_try_interchange_loops (scop, loop1, loop2)
659 || lst_interchange_select_inner (scop, outer_father, outer, loop2)))
665 /* Interchanges all the loops of LOOP and the loops of its body that
666 are considered profitable to interchange. Return true if it did
667 interchanged some loops. OUTER is the index in LST_SEQ (LOOP) that
668 points to the next outer loop to be considered for interchange. */
671 lst_interchange_select_outer (scop_p scop, lst_p loop, int outer)
678 if (!loop || !LST_LOOP_P (loop))
681 father = LST_LOOP_FATHER (loop);
684 while (lst_interchange_select_inner (scop, father, outer, loop))
687 loop = VEC_index (lst_p, LST_SEQ (father), outer);
691 if (LST_LOOP_P (loop))
692 for (i = 0; VEC_iterate (lst_p, LST_SEQ (loop), i, l); i++)
694 res |= lst_interchange_select_outer (scop, l, i);
699 /* Interchanges all the loop depths that are considered profitable for SCOP. */
702 scop_do_interchange (scop_p scop)
704 bool res = lst_interchange_select_outer
705 (scop, SCOP_TRANSFORMED_SCHEDULE (scop), 0);
707 lst_update_scattering (SCOP_TRANSFORMED_SCHEDULE (scop));