1 /* Heuristics and transform for loop blocking and strip mining on
2 polyhedral representation.
4 Copyright (C) 2009, 2010, 2011 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/>. */
29 #include <isl/union_map.h>
30 #include <isl/constraint.h>
31 #include <cloog/cloog.h>
32 #include <cloog/isl/domain.h>
36 #include "coretypes.h"
37 #include "tree-flow.h"
38 #include "tree-dump.h"
40 #include "tree-chrec.h"
41 #include "tree-data-ref.h"
45 #include "graphite-poly.h"
48 /* Strip mines with a factor STRIDE the scattering (time) dimension
49 around PBB at depth TIME_DEPTH.
51 The following example comes from the wiki page:
52 http://gcc.gnu.org/wiki/Graphite/Strip_mine
54 The strip mine of a loop with a tile of 64 can be obtained with a
55 scattering function as follows:
57 $ cat ./albert_strip_mine.cloog
61 # parameter {n | n >= 0}
68 1 # Number of statements:
81 1 # Scattering functions
92 #the output of CLooG is like this:
93 #$ cloog ./albert_strip_mine.cloog
94 # for (NEW=0;NEW<=floord(n,64);NEW++) {
95 # for (OLD=max(64*NEW,0);OLD<=min(64*NEW+63,n);OLD++) {
102 pbb_strip_mine_time_depth (poly_bb_p pbb
, int time_depth
, int stride
)
107 /* STRIP is the dimension that iterates with stride STRIDE. */
108 /* ITER is the dimension that enumerates single iterations inside
109 one strip that has at most STRIDE iterations. */
113 pbb
->transformed
= isl_map_insert_dims (pbb
->transformed
, isl_dim_out
,
116 /* Lower bound of the striped loop. */
117 d
= isl_map_get_space (pbb
->transformed
);
118 c
= isl_inequality_alloc (isl_local_space_from_space (d
));
119 c
= isl_constraint_set_coefficient_si (c
, isl_dim_out
, strip
, -stride
);
120 c
= isl_constraint_set_coefficient_si (c
, isl_dim_out
, iter
, 1);
121 pbb
->transformed
= isl_map_add_constraint (pbb
->transformed
, c
);
123 /* Upper bound of the striped loop. */
124 d
= isl_map_get_space (pbb
->transformed
);
125 c
= isl_inequality_alloc (isl_local_space_from_space (d
));
126 c
= isl_constraint_set_coefficient_si (c
, isl_dim_out
, strip
, stride
);
127 c
= isl_constraint_set_coefficient_si (c
, isl_dim_out
, iter
, -1);
128 c
= isl_constraint_set_constant_si (c
, stride
- 1);
129 pbb
->transformed
= isl_map_add_constraint (pbb
->transformed
, c
);
131 /* Static scheduling for ITER level.
132 This is mandatory to keep the 2d + 1 canonical scheduling format. */
133 d
= isl_map_get_space (pbb
->transformed
);
134 c
= isl_equality_alloc (isl_local_space_from_space (d
));
135 c
= isl_constraint_set_coefficient_si (c
, isl_dim_out
, strip
+ 1, 1);
136 pbb
->transformed
= isl_map_add_constraint (pbb
->transformed
, c
);
139 /* Returns true when strip mining with STRIDE of the loop LST is
143 lst_strip_mine_profitable_p (lst_p lst
, int stride
)
145 mpz_t niter
, strip_stride
;
148 gcc_assert (LST_LOOP_P (lst
));
149 mpz_init (strip_stride
);
152 mpz_set_si (strip_stride
, stride
);
153 lst_niter_for_loop (lst
, niter
);
154 res
= (mpz_cmp (niter
, strip_stride
) > 0);
156 mpz_clear (strip_stride
);
161 /* Strip-mines all the loops of LST with STRIDE. Return the number of
162 loops strip-mined. */
165 lst_do_strip_mine_loop (lst_p lst
, int depth
, int stride
)
174 if (LST_LOOP_P (lst
))
178 FOR_EACH_VEC_ELT (lst_p
, LST_SEQ (lst
), i
, l
)
179 res
+= lst_do_strip_mine_loop (l
, depth
, stride
);
185 pbb_strip_mine_time_depth (pbb
, psct_dynamic_dim (pbb
, depth
), stride
);
189 /* Strip-mines all the loops of LST with STRIDE. When STRIDE is zero,
190 read the stride from the PARAM_LOOP_BLOCK_TILE_SIZE. Return the
191 number of strip-mined loops.
193 Strip mining transforms a loop
195 | for (i = 0; i < N; i++)
198 into the following loop nest:
200 | for (k = 0; k < N; k += STRIDE)
201 | for (j = 0; j < STRIDE; j++)
206 lst_do_strip_mine (lst_p lst
, int stride
)
214 stride
= PARAM_VALUE (PARAM_LOOP_BLOCK_TILE_SIZE
);
217 || !LST_LOOP_P (lst
))
220 FOR_EACH_VEC_ELT (lst_p
, LST_SEQ (lst
), i
, l
)
221 res
+= lst_do_strip_mine (l
, stride
);
223 depth
= lst_depth (lst
);
225 && lst_strip_mine_profitable_p (lst
, stride
))
227 res
+= lst_do_strip_mine_loop (lst
, lst_depth (lst
), stride
);
228 lst_add_loop_under_loop (lst
);
234 /* Strip mines all the loops in SCOP. Returns the number of
235 strip-mined loops. */
238 scop_do_strip_mine (scop_p scop
, int stride
)
240 return lst_do_strip_mine (SCOP_TRANSFORMED_SCHEDULE (scop
), stride
);
243 /* Loop blocks all the loops in SCOP. Returns true when we manage to
247 scop_do_block (scop_p scop
)
249 store_scattering (scop
);
251 /* If we don't strip mine at least two loops, or not interchange
252 loops, the strip mine alone will not be profitable, and the
253 transform is not a loop blocking: so revert the transform. */
254 if (lst_do_strip_mine (SCOP_TRANSFORMED_SCHEDULE (scop
), 0) < 2
255 || scop_do_interchange (scop
) == 0)
257 restore_scattering (scop
);
261 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
262 fprintf (dump_file
, "SCoP will be loop blocked.\n");