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   gimple g;
  94
  95   if (bb->index < NUM_FIXED_BLOCKS)
  96     return true;
  97   if (optimize_bb_for_size_p (bb))
  98     return true;
  99
 100   /* A transaction is a single entry multiple exit region.  It must be
 101      duplicated in its entirety or not at all.  */
 102   g = last_stmt (CONST_CAST_BB (bb));
 103   if (g && gimple_code (g) == GIMPLE_TRANSACTION)
 104     return true;
 105
 106   return false;
 107 }
 108
 109 /* Return number of instructions in the block.  */
 110
 111 static int
 112 count_insns (basic_block bb)
 113 {
 114   gimple_stmt_iterator gsi;
 115   gimple stmt;
 116   int n = 0;
 117
 118   for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
 119     {
 120       stmt = gsi_stmt (gsi);
 121       n += estimate_num_insns (stmt, &eni_size_weights);
 122     }
 123   return n;
 124 }
 125
 126 /* Return true if E1 is more frequent than E2.  */
 127 static bool
 128 better_p (const_edge e1, const_edge e2)
 129 {
 130   if (e1->count != e2->count)
 131     return e1->count > e2->count;
 132   if (e1->src->frequency * e1->probability !=
 133       e2->src->frequency * e2->probability)
 134     return (e1->src->frequency * e1->probability
 135             > e2->src->frequency * e2->probability);
 136   /* This is needed to avoid changes in the decision after
 137      CFG is modified.  */
 138   if (e1->src != e2->src)
 139     return e1->src->index > e2->src->index;
 140   return e1->dest->index > e2->dest->index;
 141 }
 142
 143 /* Return most frequent successor of basic block BB.  */
 144
 145 static edge
 146 find_best_successor (basic_block bb)
 147 {
 148   edge e;
 149   edge best = NULL;
 150   edge_iterator ei;
 151
 152   FOR_EACH_EDGE (e, ei, bb->succs)
 153     if (!best || better_p (e, best))
 154       best = e;
 155   if (!best || ignore_bb_p (best->dest))
 156     return NULL;
 157   if (best->probability <= probability_cutoff)
 158     return NULL;
 159   return best;
 160 }
 161
 162 /* Return most frequent predecessor of basic block BB.  */
 163
 164 static edge
 165 find_best_predecessor (basic_block bb)
 166 {
 167   edge e;
 168   edge best = NULL;
 169   edge_iterator ei;
 170
 171   FOR_EACH_EDGE (e, ei, bb->preds)
 172     if (!best || better_p (e, best))
 173       best = e;
 174   if (!best || ignore_bb_p (best->src))
 175     return NULL;
 176   if (EDGE_FREQUENCY (best) * REG_BR_PROB_BASE
 177       < bb->frequency * branch_ratio_cutoff)
 178     return NULL;
 179   return best;
 180 }
 181
 182 /* Find the trace using bb and record it in the TRACE array.
 183    Return number of basic blocks recorded.  */
 184
 185 static int
 186 find_trace (basic_block bb, basic_block *trace)
 187 {
 188   int i = 0;
 189   edge e;
 190
 191   if (dump_file)
 192     fprintf (dump_file, "Trace seed %i [%i]", bb->index, bb->frequency);
 193
 194   while ((e = find_best_predecessor (bb)) != NULL)
 195     {
 196       basic_block bb2 = e->src;
 197       if (bb_seen_p (bb2) || (e->flags & (EDGE_DFS_BACK | EDGE_COMPLEX))
 198           || find_best_successor (bb2) != e)
 199         break;
 200       if (dump_file)
 201         fprintf (dump_file, ",%i [%i]", bb->index, bb->frequency);
 202       bb = bb2;
 203     }
 204   if (dump_file)
 205     fprintf (dump_file, " forward %i [%i]", bb->index, bb->frequency);
 206   trace[i++] = bb;
 207
 208   /* Follow the trace in forward direction.  */
 209   while ((e = find_best_successor (bb)) != NULL)
 210     {
 211       bb = e->dest;
 212       if (bb_seen_p (bb) || (e->flags & (EDGE_DFS_BACK | EDGE_COMPLEX))
 213           || find_best_predecessor (bb) != e)
 214         break;
 215       if (dump_file)
 216         fprintf (dump_file, ",%i [%i]", bb->index, bb->frequency);
 217       trace[i++] = bb;
 218     }
 219   if (dump_file)
 220     fprintf (dump_file, "\n");
 221   return i;
 222 }
 223
 224 /* Look for basic blocks in frequency order, construct traces and tail duplicate
 225    if profitable.  */
 226
 227 static void
 228 tail_duplicate (void)
 229 {
 230   fibnode_t *blocks = XCNEWVEC (fibnode_t, last_basic_block);
 231   basic_block *trace = XNEWVEC (basic_block, n_basic_blocks);
 232   int *counts = XNEWVEC (int, last_basic_block);
 233   int ninsns = 0, nduplicated = 0;
 234   gcov_type weighted_insns = 0, traced_insns = 0;
 235   fibheap_t heap = fibheap_new ();
 236   gcov_type cover_insns;
 237   int max_dup_insns;
 238   basic_block bb;
 239
 240   /* Create an oversized sbitmap to reduce the chance that we need to
 241      resize it.  */
 242   bb_seen = sbitmap_alloc (last_basic_block * 2);
 243   sbitmap_zero (bb_seen);
 244   initialize_original_copy_tables ();
 245
 246   if (profile_info && flag_branch_probabilities)
 247     probability_cutoff = PARAM_VALUE (TRACER_MIN_BRANCH_PROBABILITY_FEEDBACK);
 248   else
 249     probability_cutoff = PARAM_VALUE (TRACER_MIN_BRANCH_PROBABILITY);
 250   probability_cutoff = REG_BR_PROB_BASE / 100 * probability_cutoff;
 251
 252   branch_ratio_cutoff =
 253     (REG_BR_PROB_BASE / 100 * PARAM_VALUE (TRACER_MIN_BRANCH_RATIO));
 254
 255   FOR_EACH_BB (bb)
 256     {
 257       int n = count_insns (bb);
 258       if (!ignore_bb_p (bb))
 259         blocks[bb->index] = fibheap_insert (heap, -bb->frequency,
 260                                             bb);
 261
 262       counts [bb->index] = n;
 263       ninsns += n;
 264       weighted_insns += n * bb->frequency;
 265     }
 266
 267   if (profile_info && flag_branch_probabilities)
 268     cover_insns = PARAM_VALUE (TRACER_DYNAMIC_COVERAGE_FEEDBACK);
 269   else
 270     cover_insns = PARAM_VALUE (TRACER_DYNAMIC_COVERAGE);
 271   cover_insns = (weighted_insns * cover_insns + 50) / 100;
 272   max_dup_insns = (ninsns * PARAM_VALUE (TRACER_MAX_CODE_GROWTH) + 50) / 100;
 273
 274   while (traced_insns < cover_insns && nduplicated < max_dup_insns
 275          && !fibheap_empty (heap))
 276     {
 277       basic_block bb = (basic_block) fibheap_extract_min (heap);
 278       int n, pos;
 279
 280       if (!bb)
 281         break;
 282
 283       blocks[bb->index] = NULL;
 284
 285       if (ignore_bb_p (bb))
 286         continue;
 287       gcc_assert (!bb_seen_p (bb));
 288
 289       n = find_trace (bb, trace);
 290
 291       bb = trace[0];
 292       traced_insns += bb->frequency * counts [bb->index];
 293       if (blocks[bb->index])
 294         {
 295           fibheap_delete_node (heap, blocks[bb->index]);
 296           blocks[bb->index] = NULL;
 297         }
 298
 299       for (pos = 1; pos < n; pos++)
 300         {
 301           basic_block bb2 = trace[pos];
 302
 303           if (blocks[bb2->index])
 304             {
 305               fibheap_delete_node (heap, blocks[bb2->index]);
 306               blocks[bb2->index] = NULL;
 307             }
 308           traced_insns += bb2->frequency * counts [bb2->index];
 309           if (EDGE_COUNT (bb2->preds) > 1
 310               && can_duplicate_block_p (bb2))
 311             {
 312               edge e;
 313               basic_block copy;
 314
 315               nduplicated += counts [bb2->index];
 316
 317               e = find_edge (bb, bb2);
 318
 319               copy = duplicate_block (bb2, e, bb);
 320               flush_pending_stmts (e);
 321
 322               add_phi_args_after_copy (&copy, 1, NULL);
 323
 324               /* Reconsider the original copy of block we've duplicated.
 325                  Removing the most common predecessor may make it to be
 326                  head.  */
 327               blocks[bb2->index] =
 328                 fibheap_insert (heap, -bb2->frequency, bb2);
 329
 330               if (dump_file)
 331                 fprintf (dump_file, "Duplicated %i as %i [%i]\n",
 332                          bb2->index, copy->index, copy->frequency);
 333
 334               bb2 = copy;
 335             }
 336           mark_bb_seen (bb2);
 337           bb = bb2;
 338           /* In case the trace became infrequent, stop duplicating.  */
 339           if (ignore_bb_p (bb))
 340             break;
 341         }
 342       if (dump_file)
 343         fprintf (dump_file, " covered now %.1f\n\n",
 344                  traced_insns * 100.0 / weighted_insns);
 345     }
 346   if (dump_file)
 347     fprintf (dump_file, "Duplicated %i insns (%i%%)\n", nduplicated,
 348              nduplicated * 100 / ninsns);
 349
 350   free_original_copy_tables ();
 351   sbitmap_free (bb_seen);
 352   free (blocks);
 353   free (trace);
 354   free (counts);
 355   fibheap_delete (heap);
 356 }
 357
 358 /* Main entry point to this file.  */
 359
 360 static unsigned int
 361 tracer (void)
 362 {
 363   gcc_assert (current_ir_type () == IR_GIMPLE);
 364
 365   if (n_basic_blocks <= NUM_FIXED_BLOCKS + 1)
 366     return 0;
 367
 368   mark_dfs_back_edges ();
 369   if (dump_file)
 370     dump_flow_info (dump_file, dump_flags);
 371
 372   /* Trace formation is done on the fly inside tail_duplicate */
 373   tail_duplicate ();
 374
 375   /* FIXME: We really only need to do this when we know tail duplication
 376             has altered the CFG. */
 377   free_dominance_info (CDI_DOMINATORS);
 378   if (dump_file)
 379     dump_flow_info (dump_file, dump_flags);
 380
 381   return 0;
 382 }
 383 \f
 384 static bool
 385 gate_tracer (void)
 386 {
 387   return (optimize > 0 && flag_tracer && flag_reorder_blocks);
 388 }
 389
 390 struct gimple_opt_pass pass_tracer =
 391 {
 392  {
 393   GIMPLE_PASS,
 394   "tracer",                             /* name */
 395   gate_tracer,                          /* gate */
 396   tracer,                               /* execute */
 397   NULL,                                 /* sub */
 398   NULL,                                 /* next */
 399   0,                                    /* static_pass_number */
 400   TV_TRACER,                            /* tv_id */
 401   0,                                    /* properties_required */
 402   0,                                    /* properties_provided */
 403   0,                                    /* properties_destroyed */
 404   0,                                    /* todo_flags_start */
 405   TODO_update_ssa
 406     | TODO_verify_ssa                   /* todo_flags_finish */
 407  }
 408 };