1 /* Heuristics and transform for loop blocking and strip mining on
2 polyhedral representation.
4 Copyright (C) 2009, 2010 Free Software Foundation, Inc.
5 Contributed by Sebastian Pop <sebastian.pop@amd.com> and
6 Pranav Garg <pranav.garg2107@gmail.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"
26 #include "tree-flow.h"
27 #include "tree-dump.h"
29 #include "tree-chrec.h"
30 #include "tree-data-ref.h"
35 #include "graphite-ppl.h"
36 #include "graphite-poly.h"
39 /* Strip mines with a factor STRIDE the scattering (time) dimension
40 around PBB at depth TIME_DEPTH.
42 The following example comes from the wiki page:
43 http://gcc.gnu.org/wiki/Graphite/Strip_mine
45 The strip mine of a loop with a tile of 64 can be obtained with a
46 scattering function as follows:
48 $ cat ./albert_strip_mine.cloog
52 # parameter {n | n >= 0}
59 1 # Number of statements:
72 1 # Scattering functions
83 #the output of CLooG is like this:
84 #$ cloog ./albert_strip_mine.cloog
85 # for (NEW=0;NEW<=floord(n,64);NEW++) {
86 # for (OLD=max(64*NEW,0);OLD<=min(64*NEW+63,n);OLD++) {
93 pbb_strip_mine_time_depth (poly_bb_p pbb, int time_depth, int stride)
95 ppl_dimension_type iter, dim, strip;
96 ppl_Polyhedron_t res = PBB_TRANSFORMED_SCATTERING (pbb);
97 /* STRIP is the dimension that iterates with stride STRIDE. */
98 /* ITER is the dimension that enumerates single iterations inside
99 one strip that has at most STRIDE iterations. */
103 psct_add_scattering_dimension (pbb, strip);
104 psct_add_scattering_dimension (pbb, strip + 1);
106 ppl_Polyhedron_space_dimension (res, &dim);
108 /* Lower bound of the striped loop. */
110 ppl_Constraint_t new_cstr;
111 ppl_Linear_Expression_t expr;
113 ppl_new_Linear_Expression_with_dimension (&expr, dim);
114 ppl_set_coef (expr, strip, -1 * stride);
115 ppl_set_coef (expr, iter, 1);
117 ppl_new_Constraint (&new_cstr, expr, PPL_CONSTRAINT_TYPE_GREATER_OR_EQUAL);
118 ppl_delete_Linear_Expression (expr);
119 ppl_Polyhedron_add_constraint (res, new_cstr);
120 ppl_delete_Constraint (new_cstr);
123 /* Upper bound of the striped loop. */
125 ppl_Constraint_t new_cstr;
126 ppl_Linear_Expression_t expr;
128 ppl_new_Linear_Expression_with_dimension (&expr, dim);
129 ppl_set_coef (expr, strip, stride);
130 ppl_set_coef (expr, iter, -1);
131 ppl_set_inhomogeneous (expr, stride - 1);
133 ppl_new_Constraint (&new_cstr, expr, PPL_CONSTRAINT_TYPE_GREATER_OR_EQUAL);
134 ppl_delete_Linear_Expression (expr);
135 ppl_Polyhedron_add_constraint (res, new_cstr);
136 ppl_delete_Constraint (new_cstr);
139 /* Static scheduling for ITER level.
140 This is mandatory to keep the 2d + 1 canonical scheduling format. */
142 ppl_Constraint_t new_cstr;
143 ppl_Linear_Expression_t expr;
145 ppl_new_Linear_Expression_with_dimension (&expr, dim);
146 ppl_set_coef (expr, strip + 1, 1);
147 ppl_set_inhomogeneous (expr, 0);
149 ppl_new_Constraint (&new_cstr, expr, PPL_CONSTRAINT_TYPE_EQUAL);
150 ppl_delete_Linear_Expression (expr);
151 ppl_Polyhedron_add_constraint (res, new_cstr);
152 ppl_delete_Constraint (new_cstr);
158 /* Returns true when strip mining with STRIDE of the loop LST is
162 lst_strip_mine_profitable_p (lst_p lst, int stride)
164 mpz_t niter, strip_stride;
167 gcc_assert (LST_LOOP_P (lst));
168 mpz_init (strip_stride);
171 mpz_set_si (strip_stride, stride);
172 lst_niter_for_loop (lst, niter);
173 res = (mpz_cmp (niter, strip_stride) > 0);
175 mpz_clear (strip_stride);
180 /* Strip-mines all the loops of LST with STRIDE. Return true if it
181 did strip-mined some loops. */
184 lst_do_strip_mine_loop (lst_p lst, int depth, int stride)
193 if (LST_LOOP_P (lst))
197 FOR_EACH_VEC_ELT (lst_p, LST_SEQ (lst), i, l)
198 res |= lst_do_strip_mine_loop (l, depth, stride);
204 return pbb_strip_mine_time_depth (pbb, psct_dynamic_dim (pbb, depth),
208 /* Strip-mines all the loops of LST with STRIDE. When STRIDE is zero,
209 read the stride from the PARAM_LOOP_BLOCK_TILE_SIZE. Return true
210 if it did strip-mined some loops.
212 Strip mining transforms a loop
214 | for (i = 0; i < N; i++)
217 into the following loop nest:
219 | for (k = 0; k < N; k += STRIDE)
220 | for (j = 0; j < STRIDE; j++)
225 lst_do_strip_mine (lst_p lst, int stride)
233 stride = PARAM_VALUE (PARAM_LOOP_BLOCK_TILE_SIZE);
236 || !LST_LOOP_P (lst))
239 FOR_EACH_VEC_ELT (lst_p, LST_SEQ (lst), i, l)
240 res |= lst_do_strip_mine (l, stride);
242 depth = lst_depth (lst);
244 && lst_strip_mine_profitable_p (lst, stride))
246 res |= lst_do_strip_mine_loop (lst, lst_depth (lst), stride);
247 lst_add_loop_under_loop (lst);
253 /* Strip mines all the loops in SCOP. Returns true when some loops
254 have been strip-mined. */
257 scop_do_strip_mine (scop_p scop, int stride)
259 return lst_do_strip_mine (SCOP_TRANSFORMED_SCHEDULE (scop), stride);
262 /* Loop blocks all the loops in SCOP. Returns true when we manage to
266 scop_do_block (scop_p scop)
268 bool strip_mined = false;
269 bool interchanged = false;
271 store_scattering (scop);
273 strip_mined = lst_do_strip_mine (SCOP_TRANSFORMED_SCHEDULE (scop), 0);
274 interchanged = scop_do_interchange (scop);
276 /* If we don't interchange loops, the strip mine alone will not be
277 profitable, and the transform is not a loop blocking: so revert
281 restore_scattering (scop);
284 else if (strip_mined && interchanged
285 && dump_file && (dump_flags & TDF_DETAILS))
286 fprintf (dump_file, "SCoP will be loop blocked.\n");
288 return strip_mined || interchanged;