gcc/tracer.c

   1 /* The tracer pass for the GNU compiler.
   2    Contributed by Jan Hubicka, SuSE Labs.
   3    Adapted to work on GIMPLE instead of RTL by Robert Kidd, UIUC.
   4    Copyright (C) 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008
   5    Free Software Foundation, Inc.
   6
   7    This file is part of GCC.
   8
   9    GCC is free software; you can redistribute it and/or modify it
  10    under the terms of the GNU General Public License as published by
  11    the Free Software Foundation; either version 3, or (at your option)
  12    any later version.
  13
  14    GCC is distributed in the hope that it will be useful, but WITHOUT
  15    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  16    or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
  17    License for more details.
  18
  19    You should have received a copy of the GNU General Public License
  20    along with GCC; see the file COPYING3.  If not see
  21    <http://www.gnu.org/licenses/>.  */
  22
  23 /* This pass performs the tail duplication needed for superblock formation.
  24    For more information see:
  25
  26      Design and Analysis of Profile-Based Optimization in Compaq's
  27      Compilation Tools for Alpha; Journal of Instruction-Level
  28      Parallelism 3 (2000) 1-25
  29
  30    Unlike Compaq's implementation we don't do the loop peeling as most
  31    probably a better job can be done by a special pass and we don't
  32    need to worry too much about the code size implications as the tail
  33    duplicates are crossjumped again if optimizations are not
  34    performed.  */
  35
  36
  37 #include "config.h"
  38 #include "system.h"
  39 #include "coretypes.h"
  40 #include "tm.h"
  41 #include "tree.h"
  42 #include "rtl.h"
  43 #include "hard-reg-set.h"
  44 #include "basic-block.h"
  45 #include "output.h"
  46 #include "cfglayout.h"
  47 #include "fibheap.h"
  48 #include "flags.h"
  49 #include "timevar.h"
  50 #include "params.h"
  51 #include "coverage.h"
  52 #include "tree-pass.h"
  53 #include "tree-flow.h"
  54 #include "tree-inline.h"
  55
  56 static int count_insns (basic_block);
  57 static bool ignore_bb_p (const_basic_block);
  58 static bool better_p (const_edge, const_edge);
  59 static edge find_best_successor (basic_block);
  60 static edge find_best_predecessor (basic_block);
  61 static int find_trace (basic_block, basic_block *);
  62 static void tail_duplicate (void);
  63
  64 /* Minimal outgoing edge probability considered for superblock formation.  */
  65 static int probability_cutoff;
  66 static int branch_ratio_cutoff;
  67
  68 /* A bit BB->index is set if BB has already been seen, i.e. it is
  69    connected to some trace already.  */
  70 sbitmap bb_seen;
  71
  72 static inline void
  73 mark_bb_seen (basic_block bb)
  74 {
  75   unsigned int size = SBITMAP_SIZE_BYTES (bb_seen) * 8;
  76
  77   if ((unsigned int)bb->index >= size)
  78     bb_seen = sbitmap_resize (bb_seen, size * 2, 0);
  79
  80   SET_BIT (bb_seen, bb->index);
  81 }
  82
  83 static inline bool
  84 bb_seen_p (basic_block bb)
  85 {
  86   return TEST_BIT (bb_seen, bb->index);
  87 }
  88
  89 /* Return true if we should ignore the basic block for purposes of tracing.  */
  90 static bool
  91 ignore_bb_p (const_basic_block bb)
  92 {
  93   if (bb->index < NUM_FIXED_BLOCKS)
  94     return true;
  95   if (optimize_bb_for_size_p (bb))
  96     return true;
  97   return false;
  98 }
  99
 100 /* Return number of instructions in the block.  */
 101
 102 static int
 103 count_insns (basic_block bb)
 104 {
 105   gimple_stmt_iterator gsi;
 106   gimple stmt;
 107   int n = 0;
 108
 109   for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
 110     {
 111       stmt = gsi_stmt (gsi);
 112       n += estimate_num_insns (stmt, &eni_size_weights);
 113     }
 114   return n;
 115 }
 116
 117 /* Return true if E1 is more frequent than E2.  */
 118 static bool
 119 better_p (const_edge e1, const_edge e2)
 120 {
 121   if (e1->count != e2->count)
 122     return e1->count > e2->count;
 123   if (e1->src->frequency * e1->probability !=
 124       e2->src->frequency * e2->probability)
 125     return (e1->src->frequency * e1->probability
 126             > e2->src->frequency * e2->probability);
 127   /* This is needed to avoid changes in the decision after
 128      CFG is modified.  */
 129   if (e1->src != e2->src)
 130     return e1->src->index > e2->src->index;
 131   return e1->dest->index > e2->dest->index;
 132 }
 133
 134 /* Return most frequent successor of basic block BB.  */
 135
 136 static edge
 137 find_best_successor (basic_block bb)
 138 {
 139   edge e;
 140   edge best = NULL;
 141   edge_iterator ei;
 142
 143   FOR_EACH_EDGE (e, ei, bb->succs)
 144     if (!best || better_p (e, best))
 145       best = e;
 146   if (!best || ignore_bb_p (best->dest))
 147     return NULL;
 148   if (best->probability <= probability_cutoff)
 149     return NULL;
 150   return best;
 151 }
 152
 153 /* Return most frequent predecessor of basic block BB.  */
 154
 155 static edge
 156 find_best_predecessor (basic_block bb)
 157 {
 158   edge e;
 159   edge best = NULL;
 160   edge_iterator ei;
 161
 162   FOR_EACH_EDGE (e, ei, bb->preds)
 163     if (!best || better_p (e, best))
 164       best = e;
 165   if (!best || ignore_bb_p (best->src))
 166     return NULL;
 167   if (EDGE_FREQUENCY (best) * REG_BR_PROB_BASE
 168       < bb->frequency * branch_ratio_cutoff)
 169     return NULL;
 170   return best;
 171 }
 172
 173 /* Find the trace using bb and record it in the TRACE array.
 174    Return number of basic blocks recorded.  */
 175
 176 static int
 177 find_trace (basic_block bb, basic_block *trace)
 178 {
 179   int i = 0;
 180   edge e;
 181
 182   if (dump_file)
 183     fprintf (dump_file, "Trace seed %i [%i]", bb->index, bb->frequency);
 184
 185   while ((e = find_best_predecessor (bb)) != NULL)
 186     {
 187       basic_block bb2 = e->src;
 188       if (bb_seen_p (bb2) || (e->flags & (EDGE_DFS_BACK | EDGE_COMPLEX))
 189           || find_best_successor (bb2) != e)
 190         break;
 191       if (dump_file)
 192         fprintf (dump_file, ",%i [%i]", bb->index, bb->frequency);
 193       bb = bb2;
 194     }
 195   if (dump_file)
 196     fprintf (dump_file, " forward %i [%i]", bb->index, bb->frequency);
 197   trace[i++] = bb;
 198
 199   /* Follow the trace in forward direction.  */
 200   while ((e = find_best_successor (bb)) != NULL)
 201     {
 202       bb = e->dest;
 203       if (bb_seen_p (bb) || (e->flags & (EDGE_DFS_BACK | EDGE_COMPLEX))
 204           || find_best_predecessor (bb) != e)
 205         break;
 206       if (dump_file)
 207         fprintf (dump_file, ",%i [%i]", bb->index, bb->frequency);
 208       trace[i++] = bb;
 209     }
 210   if (dump_file)
 211     fprintf (dump_file, "\n");
 212   return i;
 213 }
 214
 215 /* Look for basic blocks in frequency order, construct traces and tail duplicate
 216    if profitable.  */
 217
 218 static void
 219 tail_duplicate (void)
 220 {
 221   fibnode_t *blocks = XCNEWVEC (fibnode_t, last_basic_block);
 222   basic_block *trace = XNEWVEC (basic_block, n_basic_blocks);
 223   int *counts = XNEWVEC (int, last_basic_block);
 224   int ninsns = 0, nduplicated = 0;
 225   gcov_type weighted_insns = 0, traced_insns = 0;
 226   fibheap_t heap = fibheap_new ();
 227   gcov_type cover_insns;
 228   int max_dup_insns;
 229   basic_block bb;
 230
 231   /* Create an oversized sbitmap to reduce the chance that we need to
 232      resize it.  */
 233   bb_seen = sbitmap_alloc (last_basic_block * 2);
 234   sbitmap_zero (bb_seen);
 235   initialize_original_copy_tables ();
 236
 237   if (profile_info && flag_branch_probabilities)
 238     probability_cutoff = PARAM_VALUE (TRACER_MIN_BRANCH_PROBABILITY_FEEDBACK);
 239   else
 240     probability_cutoff = PARAM_VALUE (TRACER_MIN_BRANCH_PROBABILITY);
 241   probability_cutoff = REG_BR_PROB_BASE / 100 * probability_cutoff;
 242
 243   branch_ratio_cutoff =
 244     (REG_BR_PROB_BASE / 100 * PARAM_VALUE (TRACER_MIN_BRANCH_RATIO));
 245
 246   FOR_EACH_BB (bb)
 247     {
 248       int n = count_insns (bb);
 249       if (!ignore_bb_p (bb))
 250         blocks[bb->index] = fibheap_insert (heap, -bb->frequency,
 251                                             bb);
 252
 253       counts [bb->index] = n;
 254       ninsns += n;
 255       weighted_insns += n * bb->frequency;
 256     }
 257
 258   if (profile_info && flag_branch_probabilities)
 259     cover_insns = PARAM_VALUE (TRACER_DYNAMIC_COVERAGE_FEEDBACK);
 260   else
 261     cover_insns = PARAM_VALUE (TRACER_DYNAMIC_COVERAGE);
 262   cover_insns = (weighted_insns * cover_insns + 50) / 100;
 263   max_dup_insns = (ninsns * PARAM_VALUE (TRACER_MAX_CODE_GROWTH) + 50) / 100;
 264
 265   while (traced_insns < cover_insns && nduplicated < max_dup_insns
 266          && !fibheap_empty (heap))
 267     {
 268       basic_block bb = (basic_block) fibheap_extract_min (heap);
 269       int n, pos;
 270
 271       if (!bb)
 272         break;
 273
 274       blocks[bb->index] = NULL;
 275
 276       if (ignore_bb_p (bb))
 277         continue;
 278       gcc_assert (!bb_seen_p (bb));
 279
 280       n = find_trace (bb, trace);
 281
 282       bb = trace[0];
 283       traced_insns += bb->frequency * counts [bb->index];
 284       if (blocks[bb->index])
 285         {
 286           fibheap_delete_node (heap, blocks[bb->index]);
 287           blocks[bb->index] = NULL;
 288         }
 289
 290       for (pos = 1; pos < n; pos++)
 291         {
 292           basic_block bb2 = trace[pos];
 293
 294           if (blocks[bb2->index])
 295             {
 296               fibheap_delete_node (heap, blocks[bb2->index]);
 297               blocks[bb2->index] = NULL;
 298             }
 299           traced_insns += bb2->frequency * counts [bb2->index];
 300           if (EDGE_COUNT (bb2->preds) > 1
 301               && can_duplicate_block_p (bb2))
 302             {
 303               edge e;
 304               basic_block copy;
 305
 306               nduplicated += counts [bb2->index];
 307
 308               e = find_edge (bb, bb2);
 309
 310               copy = duplicate_block (bb2, e, bb);
 311               flush_pending_stmts (e);
 312
 313               add_phi_args_after_copy (&copy, 1, NULL);
 314
 315               /* Reconsider the original copy of block we've duplicated.
 316                  Removing the most common predecessor may make it to be
 317                  head.  */
 318               blocks[bb2->index] =
 319                 fibheap_insert (heap, -bb2->frequency, bb2);
 320
 321               if (dump_file)
 322                 fprintf (dump_file, "Duplicated %i as %i [%i]\n",
 323                          bb2->index, copy->index, copy->frequency);
 324
 325               bb2 = copy;
 326             }
 327           mark_bb_seen (bb2);
 328           bb = bb2;
 329           /* In case the trace became infrequent, stop duplicating.  */
 330           if (ignore_bb_p (bb))
 331             break;
 332         }
 333       if (dump_file)
 334         fprintf (dump_file, " covered now %.1f\n\n",
 335                  traced_insns * 100.0 / weighted_insns);
 336     }
 337   if (dump_file)
 338     fprintf (dump_file, "Duplicated %i insns (%i%%)\n", nduplicated,
 339              nduplicated * 100 / ninsns);
 340
 341   free_original_copy_tables ();
 342   sbitmap_free (bb_seen);
 343   free (blocks);
 344   free (trace);
 345   free (counts);
 346   fibheap_delete (heap);
 347 }
 348
 349 /* Main entry point to this file.  */
 350
 351 static unsigned int
 352 tracer (void)
 353 {
 354   gcc_assert (current_ir_type () == IR_GIMPLE);
 355
 356   if (n_basic_blocks <= NUM_FIXED_BLOCKS + 1)
 357     return 0;
 358
 359   mark_dfs_back_edges ();
 360   if (dump_file)
 361     dump_flow_info (dump_file, dump_flags);
 362
 363   /* Trace formation is done on the fly inside tail_duplicate */
 364   tail_duplicate ();
 365
 366   /* FIXME: We really only need to do this when we know tail duplication
 367             has altered the CFG. */
 368   free_dominance_info (CDI_DOMINATORS);
 369   if (dump_file)
 370     dump_flow_info (dump_file, dump_flags);
 371
 372   return 0;
 373 }
 374 \f
 375 static bool
 376 gate_tracer (void)
 377 {
 378   return (optimize > 0 && flag_tracer && flag_reorder_blocks);
 379 }
 380
 381 struct gimple_opt_pass pass_tracer =
 382 {
 383  {
 384   GIMPLE_PASS,
 385   "tracer",                             /* name */
 386   gate_tracer,                          /* gate */
 387   tracer,                               /* execute */
 388   NULL,                                 /* sub */
 389   NULL,                                 /* next */
 390   0,                                    /* static_pass_number */
 391   TV_TRACER,                            /* tv_id */
 392   0,                                    /* properties_required */
 393   0,                                    /* properties_provided */
 394   0,                                    /* properties_destroyed */
 395   0,                                    /* todo_flags_start */
 396   TODO_update_ssa
 397     | TODO_verify_ssa                   /* todo_flags_finish */
 398  }
 399 };