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"
31 #include "basic-block.h"
32 #include "diagnostic.h"
33 #include "tree-flow.h"
34 #include "tree-dump.h"
37 #include "tree-chrec.h"
38 #include "tree-data-ref.h"
39 #include "tree-scalar-evolution.h"
40 #include "tree-pass.h"
42 #include "value-prof.h"
43 #include "pointer-set.h"
50 #include "graphite-ppl.h"
52 #include "graphite-poly.h"
55 /* Strip mines with a factor STRIDE the scattering (time) dimension
56 around PBB at depth TIME_DEPTH.
58 The following example comes from the wiki page:
59 http://gcc.gnu.org/wiki/Graphite/Strip_mine
61 The strip mine of a loop with a tile of 64 can be obtained with a
62 scattering function as follows:
64 $ cat ./albert_strip_mine.cloog
68 # parameter {n | n >= 0}
75 1 # Number of statements:
88 1 # Scattering functions
99 #the output of CLooG is like this:
100 #$ cloog ./albert_strip_mine.cloog
101 # for (NEW=0;NEW<=floord(n,64);NEW++) {
102 # for (OLD=max(64*NEW,0);OLD<=min(64*NEW+63,n);OLD++) {
109 pbb_strip_mine_time_depth (poly_bb_p pbb, int time_depth, int stride)
111 ppl_dimension_type iter, dim, strip;
112 ppl_Polyhedron_t res = PBB_TRANSFORMED_SCATTERING (pbb);
113 /* STRIP is the dimension that iterates with stride STRIDE. */
114 /* ITER is the dimension that enumerates single iterations inside
115 one strip that has at most STRIDE iterations. */
119 psct_add_scattering_dimension (pbb, strip);
120 psct_add_scattering_dimension (pbb, strip + 1);
122 ppl_Polyhedron_space_dimension (res, &dim);
124 /* Lower bound of the striped loop. */
126 ppl_Constraint_t new_cstr;
127 ppl_Linear_Expression_t expr;
129 ppl_new_Linear_Expression_with_dimension (&expr, dim);
130 ppl_set_coef (expr, strip, -1 * stride);
131 ppl_set_coef (expr, iter, 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 /* Upper bound of the striped loop. */
141 ppl_Constraint_t new_cstr;
142 ppl_Linear_Expression_t expr;
144 ppl_new_Linear_Expression_with_dimension (&expr, dim);
145 ppl_set_coef (expr, strip, stride);
146 ppl_set_coef (expr, iter, -1);
147 ppl_set_inhomogeneous (expr, stride - 1);
149 ppl_new_Constraint (&new_cstr, expr, PPL_CONSTRAINT_TYPE_GREATER_OR_EQUAL);
150 ppl_delete_Linear_Expression (expr);
151 ppl_Polyhedron_add_constraint (res, new_cstr);
152 ppl_delete_Constraint (new_cstr);
155 /* Static scheduling for ITER level.
156 This is mandatory to keep the 2d + 1 canonical scheduling format. */
158 ppl_Constraint_t new_cstr;
159 ppl_Linear_Expression_t expr;
161 ppl_new_Linear_Expression_with_dimension (&expr, dim);
162 ppl_set_coef (expr, strip + 1, 1);
163 ppl_set_inhomogeneous (expr, 0);
165 ppl_new_Constraint (&new_cstr, expr, PPL_CONSTRAINT_TYPE_EQUAL);
166 ppl_delete_Linear_Expression (expr);
167 ppl_Polyhedron_add_constraint (res, new_cstr);
168 ppl_delete_Constraint (new_cstr);
174 /* Returns true when strip mining with STRIDE of the loop LST is
178 lst_strip_mine_profitable_p (lst_p lst, int stride)
180 mpz_t niter, strip_stride;
183 gcc_assert (LST_LOOP_P (lst));
184 mpz_init (strip_stride);
187 mpz_set_si (strip_stride, stride);
188 lst_niter_for_loop (lst, niter);
189 res = (mpz_cmp (niter, strip_stride) > 0);
191 mpz_clear (strip_stride);
196 /* Strip-mines all the loops of LST with STRIDE. Return true if it
197 did strip-mined some loops. */
200 lst_do_strip_mine_loop (lst_p lst, int depth, int stride)
209 if (LST_LOOP_P (lst))
213 FOR_EACH_VEC_ELT (lst_p, LST_SEQ (lst), i, l)
214 res |= lst_do_strip_mine_loop (l, depth, stride);
220 return pbb_strip_mine_time_depth (pbb, psct_dynamic_dim (pbb, depth),
224 /* Strip-mines all the loops of LST with STRIDE. When STRIDE is zero,
225 read the stride from the PARAM_LOOP_BLOCK_TILE_SIZE. Return true
226 if it did strip-mined some loops.
228 Strip mining transforms a loop
230 | for (i = 0; i < N; i++)
233 into the following loop nest:
235 | for (k = 0; k < N; k += STRIDE)
236 | for (j = 0; j < STRIDE; j++)
241 lst_do_strip_mine (lst_p lst, int stride)
249 stride = PARAM_VALUE (PARAM_LOOP_BLOCK_TILE_SIZE);
252 || !LST_LOOP_P (lst))
255 FOR_EACH_VEC_ELT (lst_p, LST_SEQ (lst), i, l)
256 res |= lst_do_strip_mine (l, stride);
258 depth = lst_depth (lst);
260 && lst_strip_mine_profitable_p (lst, stride))
262 res |= lst_do_strip_mine_loop (lst, lst_depth (lst), stride);
263 lst_add_loop_under_loop (lst);
269 /* Strip mines all the loops in SCOP. Returns true when some loops
270 have been strip-mined. */
273 scop_do_strip_mine (scop_p scop, int stride)
275 return lst_do_strip_mine (SCOP_TRANSFORMED_SCHEDULE (scop), stride);
278 /* Loop blocks all the loops in SCOP. Returns true when we manage to
282 scop_do_block (scop_p scop)
284 bool strip_mined = false;
285 bool interchanged = false;
287 store_scattering (scop);
289 strip_mined = lst_do_strip_mine (SCOP_TRANSFORMED_SCHEDULE (scop), 0);
290 interchanged = scop_do_interchange (scop);
292 /* If we don't interchange loops, the strip mine alone will not be
293 profitable, and the transform is not a loop blocking: so revert
297 restore_scattering (scop);
300 else if (strip_mined && interchanged
301 && dump_file && (dump_flags & TDF_DETAILS))
302 fprintf (dump_file, "SCoP will be loop blocked.\n");
304 return strip_mined || interchanged;