gcc/graphite-blocking.c

   1 /* Heuristics and transform for loop blocking and strip mining on
   2    polyhedral representation.
   3
   4    Copyright (C) 2009 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 #include "config.h"
  24 #include "system.h"
  25 #include "coretypes.h"
  26 #include "tm.h"
  27 #include "ggc.h"
  28 #include "tree.h"
  29 #include "rtl.h"
  30 #include "output.h"
  31 #include "basic-block.h"
  32 #include "diagnostic.h"
  33 #include "tree-flow.h"
  34 #include "toplev.h"
  35 #include "tree-dump.h"
  36 #include "timevar.h"
  37 #include "cfgloop.h"
  38 #include "tree-chrec.h"
  39 #include "tree-data-ref.h"
  40 #include "tree-scalar-evolution.h"
  41 #include "tree-pass.h"
  42 #include "domwalk.h"
  43 #include "value-prof.h"
  44 #include "pointer-set.h"
  45 #include "gimple.h"
  46 #include "params.h"
  47
  48 #ifdef HAVE_cloog
  49 #include "cloog/cloog.h"
  50 #include "ppl_c.h"
  51 #include "sese.h"
  52 #include "graphite-ppl.h"
  53 #include "graphite.h"
  54 #include "graphite-poly.h"
  55
  56
  57 /* Strip mines with a factor STRIDE the scattering (time) dimension
  58    around PBB at depth TIME_DEPTH.
  59
  60    The following example comes from the wiki page:
  61    http://gcc.gnu.org/wiki/Graphite/Strip_mine
  62
  63    The strip mine of a loop with a tile of 64 can be obtained with a
  64    scattering function as follows:
  65
  66    $ cat ./albert_strip_mine.cloog
  67    # language: C
  68    c
  69
  70    # parameter {n | n >= 0}
  71    1 3
  72    #  n  1
  73    1  1  0
  74    1
  75    n
  76
  77    1 # Number of statements:
  78
  79    1
  80    # {i | 0 <= i <= n}
  81    2 4
  82    #  i  n   1
  83    1  1  0   0
  84    1 -1  1   0
  85
  86    0  0  0
  87    1
  88    i
  89
  90    1 # Scattering functions
  91
  92    3 6
  93    #  NEW  OLD    i    n    1
  94    1  -64    0    1    0    0
  95    1   64    0   -1    0   63
  96    0    0    1   -1    0    0
  97
  98    1
  99    NEW  OLD
 100
 101    #the output of CLooG is like this:
 102    #$ cloog ./albert_strip_mine.cloog
 103    # for (NEW=0;NEW<=floord(n,64);NEW++) {
 104    #   for (OLD=max(64*NEW,0);OLD<=min(64*NEW+63,n);OLD++) {
 105    #     S1(i = OLD) ;
 106    #   }
 107    # }
 108 */
 109
 110 static bool
 111 pbb_strip_mine_time_depth (poly_bb_p pbb, int time_depth, int stride)
 112 {
 113   ppl_dimension_type iter, dim, strip;
 114   ppl_Polyhedron_t res = PBB_TRANSFORMED_SCATTERING (pbb);
 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   psct_add_scattering_dimension (pbb, strip);
 122   psct_add_scattering_dimension (pbb, strip + 1);
 123
 124   ppl_Polyhedron_space_dimension (res, &dim);
 125
 126   /* Lower bound of the striped loop.  */
 127   {
 128     ppl_Constraint_t new_cstr;
 129     ppl_Linear_Expression_t expr;
 130
 131     ppl_new_Linear_Expression_with_dimension (&expr, dim);
 132     ppl_set_coef (expr, strip, -1 * stride);
 133     ppl_set_coef (expr, iter, 1);
 134
 135     ppl_new_Constraint (&new_cstr, expr, PPL_CONSTRAINT_TYPE_GREATER_OR_EQUAL);
 136     ppl_delete_Linear_Expression (expr);
 137     ppl_Polyhedron_add_constraint (res, new_cstr);
 138     ppl_delete_Constraint (new_cstr);
 139   }
 140
 141   /* Upper bound of the striped loop.  */
 142   {
 143     ppl_Constraint_t new_cstr;
 144     ppl_Linear_Expression_t expr;
 145
 146     ppl_new_Linear_Expression_with_dimension (&expr, dim);
 147     ppl_set_coef (expr, strip, stride);
 148     ppl_set_coef (expr, iter, -1);
 149     ppl_set_inhomogeneous (expr, stride - 1);
 150
 151     ppl_new_Constraint (&new_cstr, expr, PPL_CONSTRAINT_TYPE_GREATER_OR_EQUAL);
 152     ppl_delete_Linear_Expression (expr);
 153     ppl_Polyhedron_add_constraint (res, new_cstr);
 154     ppl_delete_Constraint (new_cstr);
 155   }
 156
 157   /* Static scheduling for ITER level.
 158      This is mandatory to keep the 2d + 1 canonical scheduling format.  */
 159   {
 160     ppl_Constraint_t new_cstr;
 161     ppl_Linear_Expression_t expr;
 162
 163     ppl_new_Linear_Expression_with_dimension (&expr, dim);
 164     ppl_set_coef (expr, strip + 1, 1);
 165     ppl_set_inhomogeneous (expr, 0);
 166
 167     ppl_new_Constraint (&new_cstr, expr, PPL_CONSTRAINT_TYPE_EQUAL);
 168     ppl_delete_Linear_Expression (expr);
 169     ppl_Polyhedron_add_constraint (res, new_cstr);
 170     ppl_delete_Constraint (new_cstr);
 171   }
 172
 173   return true;
 174 }
 175
 176 /* Returns true when strip mining with STRIDE of the loop around PBB
 177    at scattering time TIME_DEPTH is profitable.  */
 178
 179 static bool
 180 pbb_strip_mine_profitable_p (poly_bb_p pbb,
 181                              graphite_dim_t time_depth,
 182                              int stride)
 183 {
 184   Value niter, strip_stride;
 185   bool res;
 186
 187   value_init (strip_stride);
 188   value_init (niter);
 189   value_set_si (strip_stride, stride);
 190   pbb_number_of_iterations_at_time (pbb, time_depth, niter);
 191   res = value_gt (niter, strip_stride);
 192   value_clear (strip_stride);
 193   value_clear (niter);
 194
 195   return res;
 196 }
 197
 198 /* Strip mines all the loops around PBB.  Nothing profitable in all this:
 199    this is just a driver function.  */
 200
 201 static bool
 202 pbb_do_strip_mine (poly_bb_p pbb)
 203 {
 204   graphite_dim_t s_dim;
 205   int stride = 64;
 206   bool transform_done = false;
 207
 208   for (s_dim = 0; s_dim < pbb_nb_dynamic_scattering_transform (pbb); s_dim++)
 209     if (pbb_strip_mine_profitable_p (pbb, psct_dynamic_dim (pbb, s_dim),
 210                                      stride))
 211       {
 212         ppl_dimension_type d = psct_dynamic_dim (pbb, s_dim);
 213         transform_done |= pbb_strip_mine_time_depth (pbb, d, stride);
 214         s_dim++;
 215       }
 216
 217   return transform_done;
 218 }
 219
 220 /* Strip mines all the loops in SCOP.  Nothing profitable in all this:
 221    this is just a driver function.  */
 222
 223 bool
 224 scop_do_strip_mine (scop_p scop)
 225 {
 226   poly_bb_p pbb;
 227   int i;
 228   bool transform_done = false;
 229
 230   store_scattering (scop);
 231
 232   for (i = 0; VEC_iterate (poly_bb_p, SCOP_BBS (scop), i, pbb); i++)
 233     transform_done |= pbb_do_strip_mine (pbb);
 234
 235   if (!transform_done)
 236     return false;
 237
 238   if (!graphite_legal_transform (scop))
 239     {
 240       restore_scattering (scop);
 241       return false;
 242     }
 243
 244   return true;
 245 }
 246
 247 #endif