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) 2001-2018 Free Software Foundation, Inc.
   5
   6    This file is part of GCC.
   7
   8    GCC is free software; you can redistribute it and/or modify it
   9    under the terms of the GNU General Public License as published by
  10    the Free Software Foundation; either version 3, or (at your option)
  11    any later version.
  12
  13    GCC is distributed in the hope that it will be useful, but WITHOUT
  14    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  15    or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
  16    License for more details.
  17
  18    You should have received a copy of the GNU General Public License
  19    along with GCC; see the file COPYING3.  If not see
  20    <http://www.gnu.org/licenses/>.  */
  21
  22 /* This pass performs the tail duplication needed for superblock formation.
  23    For more information see:
  24
  25      Design and Analysis of Profile-Based Optimization in Compaq's
  26      Compilation Tools for Alpha; Journal of Instruction-Level
  27      Parallelism 3 (2000) 1-25
  28
  29    Unlike Compaq's implementation we don't do the loop peeling as most
  30    probably a better job can be done by a special pass and we don't
  31    need to worry too much about the code size implications as the tail
  32    duplicates are crossjumped again if optimizations are not
  33    performed.  */
  34
  35
  36 #include "config.h"
  37 #include "system.h"
  38 #include "coretypes.h"
  39 #include "backend.h"
  40 #include "rtl.h"
  41 #include "tree.h"
  42 #include "gimple.h"
  43 #include "cfghooks.h"
  44 #include "tree-pass.h"
  45 #include "profile.h"
  46 #include "cfganal.h"
  47 #include "params.h"
  48 #include "gimple-iterator.h"
  49 #include "tree-cfg.h"
  50 #include "tree-ssa.h"
  51 #include "tree-inline.h"
  52 #include "cfgloop.h"
  53 #include "fibonacci_heap.h"
  54 #include "tracer.h"
  55
  56 static int count_insns (basic_block);
  57 static bool better_p (const_edge, const_edge);
  58 static edge find_best_successor (basic_block);
  59 static edge find_best_predecessor (basic_block);
  60 static int find_trace (basic_block, basic_block *);
  61
  62 /* Minimal outgoing edge probability considered for superblock formation.  */
  63 static int probability_cutoff;
  64 static int branch_ratio_cutoff;
  65
  66 /* A bit BB->index is set if BB has already been seen, i.e. it is
  67    connected to some trace already.  */
  68 static sbitmap bb_seen;
  69
  70 static inline void
  71 mark_bb_seen (basic_block bb)
  72 {
  73   unsigned int size = SBITMAP_SIZE (bb_seen);
  74
  75   if ((unsigned int)bb->index >= size)
  76     bb_seen = sbitmap_resize (bb_seen, size * 2, 0);
  77
  78   bitmap_set_bit (bb_seen, bb->index);
  79 }
  80
  81 static inline bool
  82 bb_seen_p (basic_block bb)
  83 {
  84   return bitmap_bit_p (bb_seen, bb->index);
  85 }
  86
  87 /* Return true if we should ignore the basic block for purposes of tracing.  */
  88 bool
  89 ignore_bb_p (const_basic_block bb)
  90 {
  91   if (bb->index < NUM_FIXED_BLOCKS)
  92     return true;
  93   if (optimize_bb_for_size_p (bb))
  94     return true;
  95
  96   if (gimple *g = last_stmt (CONST_CAST_BB (bb)))
  97     {
  98       /* A transaction is a single entry multiple exit region.  It
  99          must be duplicated in its entirety or not at all.  */
 100       if (gimple_code (g) == GIMPLE_TRANSACTION)
 101         return true;
 102
 103       /* An IFN_UNIQUE call must be duplicated as part of its group,
 104          or not at all.  */
 105       if (is_gimple_call (g)
 106           && gimple_call_internal_p (g)
 107           && gimple_call_internal_unique_p (g))
 108         return true;
 109     }
 110
 111   return false;
 112 }
 113
 114 /* Return number of instructions in the block.  */
 115
 116 static int
 117 count_insns (basic_block bb)
 118 {
 119   gimple_stmt_iterator gsi;
 120   gimple *stmt;
 121   int n = 0;
 122
 123   for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
 124     {
 125       stmt = gsi_stmt (gsi);
 126       n += estimate_num_insns (stmt, &eni_size_weights);
 127     }
 128   return n;
 129 }
 130
 131 /* Return true if E1 is more frequent than E2.  */
 132 static bool
 133 better_p (const_edge e1, const_edge e2)
 134 {
 135   if (e1->count ().initialized_p () && e2->count ().initialized_p ()
 136       && ((e1->count () > e2->count ()) || (e1->count () < e2->count  ())))
 137     return e1->count () > e2->count ();
 138   /* This is needed to avoid changes in the decision after
 139      CFG is modified.  */
 140   if (e1->src != e2->src)
 141     return e1->src->index > e2->src->index;
 142   return e1->dest->index > e2->dest->index;
 143 }
 144
 145 /* Return most frequent successor of basic block BB.  */
 146
 147 static edge
 148 find_best_successor (basic_block bb)
 149 {
 150   edge e;
 151   edge best = NULL;
 152   edge_iterator ei;
 153
 154   FOR_EACH_EDGE (e, ei, bb->succs)
 155     if (!best || better_p (e, best))
 156       best = e;
 157   if (!best || ignore_bb_p (best->dest))
 158     return NULL;
 159   if (best->probability.initialized_p ()
 160       && best->probability.to_reg_br_prob_base () <= probability_cutoff)
 161     return NULL;
 162   return best;
 163 }
 164
 165 /* Return most frequent predecessor of basic block BB.  */
 166
 167 static edge
 168 find_best_predecessor (basic_block bb)
 169 {
 170   edge e;
 171   edge best = NULL;
 172   edge_iterator ei;
 173
 174   FOR_EACH_EDGE (e, ei, bb->preds)
 175     if (!best || better_p (e, best))
 176       best = e;
 177   if (!best || ignore_bb_p (best->src))
 178     return NULL;
 179   if (EDGE_FREQUENCY (best) * REG_BR_PROB_BASE
 180       < bb->count.to_frequency (cfun) * branch_ratio_cutoff)
 181     return NULL;
 182   return best;
 183 }
 184
 185 /* Find the trace using bb and record it in the TRACE array.
 186    Return number of basic blocks recorded.  */
 187
 188 static int
 189 find_trace (basic_block bb, basic_block *trace)
 190 {
 191   int i = 0;
 192   edge e;
 193
 194   if (dump_file)
 195     fprintf (dump_file, "Trace seed %i [%i]", bb->index, bb->count.to_frequency (cfun));
 196
 197   while ((e = find_best_predecessor (bb)) != NULL)
 198     {
 199       basic_block bb2 = e->src;
 200       if (bb_seen_p (bb2) || (e->flags & (EDGE_DFS_BACK | EDGE_COMPLEX))
 201           || find_best_successor (bb2) != e)
 202         break;
 203       if (dump_file)
 204         fprintf (dump_file, ",%i [%i]", bb->index, bb->count.to_frequency (cfun));
 205       bb = bb2;
 206     }
 207   if (dump_file)
 208     fprintf (dump_file, " forward %i [%i]", bb->index, bb->count.to_frequency (cfun));
 209   trace[i++] = bb;
 210
 211   /* Follow the trace in forward direction.  */
 212   while ((e = find_best_successor (bb)) != NULL)
 213     {
 214       bb = e->dest;
 215       if (bb_seen_p (bb) || (e->flags & (EDGE_DFS_BACK | EDGE_COMPLEX))
 216           || find_best_predecessor (bb) != e)
 217         break;
 218       if (dump_file)
 219         fprintf (dump_file, ",%i [%i]", bb->index, bb->count.to_frequency (cfun));
 220       trace[i++] = bb;
 221     }
 222   if (dump_file)
 223     fprintf (dump_file, "\n");
 224   return i;
 225 }
 226
 227 /* Duplicate block BB2, placing it after BB in the CFG.  Return the
 228    newly created block.  */
 229 basic_block
 230 transform_duplicate (basic_block bb, basic_block bb2)
 231 {
 232   edge e;
 233   basic_block copy;
 234
 235   e = find_edge (bb, bb2);
 236
 237   copy = duplicate_block (bb2, e, bb);
 238   flush_pending_stmts (e);
 239
 240   add_phi_args_after_copy (&copy, 1, NULL);
 241
 242   return (copy);
 243 }
 244
 245 /* Look for basic blocks in frequency order, construct traces and tail duplicate
 246    if profitable.  */
 247
 248 static bool
 249 tail_duplicate (void)
 250 {
 251   auto_vec<fibonacci_node<long, basic_block_def>*> blocks;
 252   blocks.safe_grow_cleared (last_basic_block_for_fn (cfun));
 253
 254   basic_block *trace = XNEWVEC (basic_block, n_basic_blocks_for_fn (cfun));
 255   int *counts = XNEWVEC (int, last_basic_block_for_fn (cfun));
 256   int ninsns = 0, nduplicated = 0;
 257   gcov_type weighted_insns = 0, traced_insns = 0;
 258   fibonacci_heap<long, basic_block_def> heap (LONG_MIN);
 259   gcov_type cover_insns;
 260   int max_dup_insns;
 261   basic_block bb;
 262   bool changed = false;
 263
 264   /* Create an oversized sbitmap to reduce the chance that we need to
 265      resize it.  */
 266   bb_seen = sbitmap_alloc (last_basic_block_for_fn (cfun) * 2);
 267   bitmap_clear (bb_seen);
 268   initialize_original_copy_tables ();
 269
 270   if (profile_info && profile_status_for_fn (cfun) == PROFILE_READ)
 271     probability_cutoff = PARAM_VALUE (TRACER_MIN_BRANCH_PROBABILITY_FEEDBACK);
 272   else
 273     probability_cutoff = PARAM_VALUE (TRACER_MIN_BRANCH_PROBABILITY);
 274   probability_cutoff = REG_BR_PROB_BASE / 100 * probability_cutoff;
 275
 276   branch_ratio_cutoff =
 277     (REG_BR_PROB_BASE / 100 * PARAM_VALUE (TRACER_MIN_BRANCH_RATIO));
 278
 279   FOR_EACH_BB_FN (bb, cfun)
 280     {
 281       int n = count_insns (bb);
 282       if (!ignore_bb_p (bb))
 283         blocks[bb->index] = heap.insert (-bb->count.to_frequency (cfun), bb);
 284
 285       counts [bb->index] = n;
 286       ninsns += n;
 287       weighted_insns += n * bb->count.to_frequency (cfun);
 288     }
 289
 290   if (profile_info && profile_status_for_fn (cfun) == PROFILE_READ)
 291     cover_insns = PARAM_VALUE (TRACER_DYNAMIC_COVERAGE_FEEDBACK);
 292   else
 293     cover_insns = PARAM_VALUE (TRACER_DYNAMIC_COVERAGE);
 294   cover_insns = (weighted_insns * cover_insns + 50) / 100;
 295   max_dup_insns = (ninsns * PARAM_VALUE (TRACER_MAX_CODE_GROWTH) + 50) / 100;
 296
 297   while (traced_insns < cover_insns && nduplicated < max_dup_insns
 298          && !heap.empty ())
 299     {
 300       basic_block bb = heap.extract_min ();
 301       int n, pos;
 302
 303       if (!bb)
 304         break;
 305
 306       blocks[bb->index] = NULL;
 307
 308       if (ignore_bb_p (bb))
 309         continue;
 310       gcc_assert (!bb_seen_p (bb));
 311
 312       n = find_trace (bb, trace);
 313
 314       bb = trace[0];
 315       traced_insns += bb->count.to_frequency (cfun) * counts [bb->index];
 316       if (blocks[bb->index])
 317         {
 318           heap.delete_node (blocks[bb->index]);
 319           blocks[bb->index] = NULL;
 320         }
 321
 322       for (pos = 1; pos < n; pos++)
 323         {
 324           basic_block bb2 = trace[pos];
 325
 326           if (blocks[bb2->index])
 327             {
 328               heap.delete_node (blocks[bb2->index]);
 329               blocks[bb2->index] = NULL;
 330             }
 331           traced_insns += bb2->count.to_frequency (cfun) * counts [bb2->index];
 332           if (EDGE_COUNT (bb2->preds) > 1
 333               && can_duplicate_block_p (bb2)
 334               /* We have the tendency to duplicate the loop header
 335                  of all do { } while loops.  Do not do that - it is
 336                  not profitable and it might create a loop with multiple
 337                  entries or at least rotate the loop.  */
 338               && bb2->loop_father->header != bb2)
 339             {
 340               nduplicated += counts [bb2->index];
 341               basic_block copy = transform_duplicate (bb, bb2);
 342
 343               /* Reconsider the original copy of block we've duplicated.
 344                  Removing the most common predecessor may make it to be
 345                  head.  */
 346               blocks[bb2->index] = heap.insert (-bb2->count.to_frequency (cfun), bb2);
 347
 348               if (dump_file)
 349                 fprintf (dump_file, "Duplicated %i as %i [%i]\n",
 350                          bb2->index, copy->index, copy->count.to_frequency (cfun));
 351
 352               bb2 = copy;
 353               changed = true;
 354             }
 355           mark_bb_seen (bb2);
 356           bb = bb2;
 357           /* In case the trace became infrequent, stop duplicating.  */
 358           if (ignore_bb_p (bb))
 359             break;
 360         }
 361       if (dump_file)
 362         fprintf (dump_file, " covered now %.1f\n\n",
 363                  traced_insns * 100.0 / weighted_insns);
 364     }
 365   if (dump_file)
 366     fprintf (dump_file, "Duplicated %i insns (%i%%)\n", nduplicated,
 367              nduplicated * 100 / ninsns);
 368
 369   free_original_copy_tables ();
 370   sbitmap_free (bb_seen);
 371   free (trace);
 372   free (counts);
 373
 374   return changed;
 375 }
 376 \f
 377 namespace {
 378
 379 const pass_data pass_data_tracer =
 380 {
 381   GIMPLE_PASS, /* type */
 382   "tracer", /* name */
 383   OPTGROUP_NONE, /* optinfo_flags */
 384   TV_TRACER, /* tv_id */
 385   0, /* properties_required */
 386   0, /* properties_provided */
 387   0, /* properties_destroyed */
 388   0, /* todo_flags_start */
 389   TODO_update_ssa, /* todo_flags_finish */
 390 };
 391
 392 class pass_tracer : public gimple_opt_pass
 393 {
 394 public:
 395   pass_tracer (gcc::context *ctxt)
 396     : gimple_opt_pass (pass_data_tracer, ctxt)
 397   {}
 398
 399   /* opt_pass methods: */
 400   virtual bool gate (function *)
 401     {
 402       return (optimize > 0 && flag_tracer && flag_reorder_blocks);
 403     }
 404
 405   virtual unsigned int execute (function *);
 406
 407 }; // class pass_tracer
 408
 409 unsigned int
 410 pass_tracer::execute (function *fun)
 411 {
 412   bool changed;
 413
 414   if (n_basic_blocks_for_fn (fun) <= NUM_FIXED_BLOCKS + 1)
 415     return 0;
 416
 417   mark_dfs_back_edges ();
 418   if (dump_file)
 419     brief_dump_cfg (dump_file, dump_flags);
 420
 421   /* Trace formation is done on the fly inside tail_duplicate */
 422   changed = tail_duplicate ();
 423   if (changed)
 424     {
 425       free_dominance_info (CDI_DOMINATORS);
 426       /* If we changed the CFG schedule loops for fixup by cleanup_cfg.  */
 427       loops_state_set (LOOPS_NEED_FIXUP);
 428     }
 429
 430   if (dump_file)
 431     brief_dump_cfg (dump_file, dump_flags);
 432
 433   return changed ? TODO_cleanup_cfg : 0;
 434 }
 435 } // anon namespace
 436
 437 gimple_opt_pass *
 438 make_pass_tracer (gcc::context *ctxt)
 439 {
 440   return new pass_tracer (ctxt);
 441 }