gcc/graphite-blocking.c

   1 /* Heuristics and transform for loop blocking and strip mining on
   2    polyhedral representation.
   3
   4    Copyright (C) 2009-2013 Free Software Foundation, Inc.
   5    Contributed by Sebastian Pop <sebastian.pop@amd.com> and
   6    Pranav Garg  <pranav.garg2107@gmail.com>.
   7
   8 This file is part of GCC.
   9
  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)
  13 any later version.
  14
  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.
  19
  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/>.  */
  23
  24 #include "config.h"
  25
  26 #ifdef HAVE_cloog
  27 #include <isl/set.h>
  28 #include <isl/map.h>
  29 #include <isl/union_map.h>
  30 #include <isl/constraint.h>
  31 #include <cloog/cloog.h>
  32 #include <cloog/isl/domain.h>
  33 #endif
  34
  35 #include "system.h"
  36 #include "coretypes.h"
  37 #include "tree.h"
  38 #include "basic-block.h"
  39 #include "tree-ssa-alias.h"
  40 #include "internal-fn.h"
  41 #include "gimple-expr.h"
  42 #include "is-a.h"
  43 #include "gimple.h"
  44 #include "gimple-iterator.h"
  45 #include "tree-ssa-loop.h"
  46 #include "dumpfile.h"
  47 #include "cfgloop.h"
  48 #include "tree-chrec.h"
  49 #include "tree-data-ref.h"
  50 #include "sese.h"
  51
  52 #ifdef HAVE_cloog
  53 #include "graphite-poly.h"
  54
  55
  56 /* Strip mines with a factor STRIDE the scattering (time) dimension
  57    around PBB at depth TIME_DEPTH.
  58
  59    The following example comes from the wiki page:
  60    http://gcc.gnu.org/wiki/Graphite/Strip_mine
  61
  62    The strip mine of a loop with a tile of 64 can be obtained with a
  63    scattering function as follows:
  64
  65    $ cat ./albert_strip_mine.cloog
  66    # language: C
  67    c
  68
  69    # parameter {n | n >= 0}
  70    1 3
  71    #  n  1
  72    1  1  0
  73    1
  74    n
  75
  76    1 # Number of statements:
  77
  78    1
  79    # {i | 0 <= i <= n}
  80    2 4
  81    #  i  n   1
  82    1  1  0   0
  83    1 -1  1   0
  84
  85    0  0  0
  86    1
  87    i
  88
  89    1 # Scattering functions
  90
  91    3 6
  92    #  NEW  OLD    i    n    1
  93    1  -64    0    1    0    0
  94    1   64    0   -1    0   63
  95    0    0    1   -1    0    0
  96
  97    1
  98    NEW  OLD
  99
 100    #the output of CLooG is like this:
 101    #$ cloog ./albert_strip_mine.cloog
 102    # for (NEW=0;NEW<=floord(n,64);NEW++) {
 103    #   for (OLD=max(64*NEW,0);OLD<=min(64*NEW+63,n);OLD++) {
 104    #     S1(i = OLD) ;
 105    #   }
 106    # }
 107 */
 108
 109 static void
 110 pbb_strip_mine_time_depth (poly_bb_p pbb, int time_depth, int stride)
 111 {
 112   isl_space *d;
 113   isl_constraint *c;
 114   int iter, strip;
 115   /* STRIP is the dimension that iterates with stride STRIDE.  */
 116   /* ITER is the dimension that enumerates single iterations inside
 117      one strip that has at most STRIDE iterations.  */
 118   strip = time_depth;
 119   iter = strip + 2;
 120
 121   pbb->transformed = isl_map_insert_dims (pbb->transformed, isl_dim_out,
 122                                           strip, 2);
 123
 124   /* Lower bound of the striped loop.  */
 125   d = isl_map_get_space (pbb->transformed);
 126   c = isl_inequality_alloc (isl_local_space_from_space (d));
 127   c = isl_constraint_set_coefficient_si (c, isl_dim_out, strip, -stride);
 128   c = isl_constraint_set_coefficient_si (c, isl_dim_out, iter, 1);
 129   pbb->transformed = isl_map_add_constraint (pbb->transformed, c);
 130
 131   /* Upper bound of the striped loop.  */
 132   d = isl_map_get_space (pbb->transformed);
 133   c = isl_inequality_alloc (isl_local_space_from_space (d));
 134   c = isl_constraint_set_coefficient_si (c, isl_dim_out, strip, stride);
 135   c = isl_constraint_set_coefficient_si (c, isl_dim_out, iter, -1);
 136   c = isl_constraint_set_constant_si (c, stride - 1);
 137   pbb->transformed = isl_map_add_constraint (pbb->transformed, c);
 138
 139   /* Static scheduling for ITER level.
 140      This is mandatory to keep the 2d + 1 canonical scheduling format.  */
 141   d = isl_map_get_space (pbb->transformed);
 142   c = isl_equality_alloc (isl_local_space_from_space (d));
 143   c = isl_constraint_set_coefficient_si (c, isl_dim_out, strip + 1, 1);
 144   pbb->transformed = isl_map_add_constraint (pbb->transformed, c);
 145 }
 146
 147 /* Returns true when strip mining with STRIDE of the loop LST is
 148    profitable.  */
 149
 150 static bool
 151 lst_strip_mine_profitable_p (lst_p lst, int stride)
 152 {
 153   mpz_t niter, strip_stride;
 154   bool res;
 155
 156   gcc_assert (LST_LOOP_P (lst));
 157   mpz_init (strip_stride);
 158   mpz_init (niter);
 159
 160   mpz_set_si (strip_stride, stride);
 161   lst_niter_for_loop (lst, niter);
 162   res = (mpz_cmp (niter, strip_stride) > 0);
 163
 164   mpz_clear (strip_stride);
 165   mpz_clear (niter);
 166   return res;
 167 }
 168
 169 /* Strip-mines all the loops of LST with STRIDE.  Return the number of
 170    loops strip-mined.  */
 171
 172 static int
 173 lst_do_strip_mine_loop (lst_p lst, int depth, int stride)
 174 {
 175   int i;
 176   lst_p l;
 177   poly_bb_p pbb;
 178
 179   if (!lst)
 180     return 0;
 181
 182   if (LST_LOOP_P (lst))
 183     {
 184       int res = 0;
 185
 186       FOR_EACH_VEC_ELT (LST_SEQ (lst), i, l)
 187         res += lst_do_strip_mine_loop (l, depth, stride);
 188
 189       return res;
 190     }
 191
 192   pbb = LST_PBB (lst);
 193   pbb_strip_mine_time_depth (pbb, psct_dynamic_dim (pbb, depth), stride);
 194   return 1;
 195 }
 196
 197 /* Strip-mines all the loops of LST with STRIDE.  When STRIDE is zero,
 198    read the stride from the PARAM_LOOP_BLOCK_TILE_SIZE.  Return the
 199    number of strip-mined loops.
 200
 201    Strip mining transforms a loop
 202
 203    | for (i = 0; i < N; i++)
 204    |   S (i);
 205
 206    into the following loop nest:
 207
 208    | for (k = 0; k < N; k += STRIDE)
 209    |   for (j = 0; j < STRIDE; j++)
 210    |     S (i = k + j);
 211 */
 212
 213 static int
 214 lst_do_strip_mine (lst_p lst, int stride)
 215 {
 216   int i;
 217   lst_p l;
 218   int res = 0;
 219   int depth;
 220
 221   if (!stride)
 222     stride = PARAM_VALUE (PARAM_LOOP_BLOCK_TILE_SIZE);
 223
 224   if (!lst
 225       || !LST_LOOP_P (lst))
 226     return false;
 227
 228   FOR_EACH_VEC_ELT (LST_SEQ (lst), i, l)
 229     res += lst_do_strip_mine (l, stride);
 230
 231   depth = lst_depth (lst);
 232   if (depth >= 0
 233       && lst_strip_mine_profitable_p (lst, stride))
 234     {
 235       res += lst_do_strip_mine_loop (lst, lst_depth (lst), stride);
 236       lst_add_loop_under_loop (lst);
 237     }
 238
 239   return res;
 240 }
 241
 242 /* Strip mines all the loops in SCOP.  Returns the number of
 243    strip-mined loops.  */
 244
 245 int
 246 scop_do_strip_mine (scop_p scop, int stride)
 247 {
 248   return lst_do_strip_mine (SCOP_TRANSFORMED_SCHEDULE (scop), stride);
 249 }
 250
 251 /* Loop blocks all the loops in SCOP.  Returns true when we manage to
 252    block some loops.  */
 253
 254 bool
 255 scop_do_block (scop_p scop)
 256 {
 257   store_scattering (scop);
 258
 259   /* If we don't strip mine at least two loops, or not interchange
 260      loops, the strip mine alone will not be profitable, and the
 261      transform is not a loop blocking: so revert the transform.  */
 262   if (lst_do_strip_mine (SCOP_TRANSFORMED_SCHEDULE (scop), 0) < 2
 263       || scop_do_interchange (scop) == 0)
 264     {
 265       restore_scattering (scop);
 266       return false;
 267     }
 268
 269   if (dump_file && (dump_flags & TDF_DETAILS))
 270     fprintf (dump_file, "SCoP will be loop blocked.\n");
 271
 272   return true;
 273 }
 274
 275 #endif