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) 2001-2015 Free Software Foundation, Inc.
6 This file is part of GCC.
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)
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.
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/>. */
22 /* This pass performs the tail duplication needed for superblock formation.
23 For more information see:
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
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
38 #include "coretypes.h"
44 #include "fold-const.h"
46 #include "hard-reg-set.h"
51 #include "dominance.h"
54 #include "basic-block.h"
58 #include "tree-pass.h"
59 #include "tree-ssa-alias.h"
60 #include "internal-fn.h"
61 #include "gimple-expr.h"
64 #include "gimple-iterator.h"
67 #include "tree-inline.h"
69 #include "fibonacci_heap.h"
71 static int count_insns (basic_block);
72 static bool ignore_bb_p (const_basic_block);
73 static bool better_p (const_edge, const_edge);
74 static edge find_best_successor (basic_block);
75 static edge find_best_predecessor (basic_block);
76 static int find_trace (basic_block, basic_block *);
78 /* Minimal outgoing edge probability considered for superblock formation. */
79 static int probability_cutoff;
80 static int branch_ratio_cutoff;
82 /* A bit BB->index is set if BB has already been seen, i.e. it is
83 connected to some trace already. */
87 mark_bb_seen (basic_block bb)
89 unsigned int size = SBITMAP_SIZE (bb_seen);
91 if ((unsigned int)bb->index >= size)
92 bb_seen = sbitmap_resize (bb_seen, size * 2, 0);
94 bitmap_set_bit (bb_seen, bb->index);
98 bb_seen_p (basic_block bb)
100 return bitmap_bit_p (bb_seen, bb->index);
103 /* Return true if we should ignore the basic block for purposes of tracing. */
105 ignore_bb_p (const_basic_block bb)
109 if (bb->index < NUM_FIXED_BLOCKS)
111 if (optimize_bb_for_size_p (bb))
114 /* A transaction is a single entry multiple exit region. It must be
115 duplicated in its entirety or not at all. */
116 g = last_stmt (CONST_CAST_BB (bb));
117 if (g && gimple_code (g) == GIMPLE_TRANSACTION)
123 /* Return number of instructions in the block. */
126 count_insns (basic_block bb)
128 gimple_stmt_iterator gsi;
132 for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
134 stmt = gsi_stmt (gsi);
135 n += estimate_num_insns (stmt, &eni_size_weights);
140 /* Return true if E1 is more frequent than E2. */
142 better_p (const_edge e1, const_edge e2)
144 if (e1->count != e2->count)
145 return e1->count > e2->count;
146 if (e1->src->frequency * e1->probability !=
147 e2->src->frequency * e2->probability)
148 return (e1->src->frequency * e1->probability
149 > e2->src->frequency * e2->probability);
150 /* This is needed to avoid changes in the decision after
152 if (e1->src != e2->src)
153 return e1->src->index > e2->src->index;
154 return e1->dest->index > e2->dest->index;
157 /* Return most frequent successor of basic block BB. */
160 find_best_successor (basic_block bb)
166 FOR_EACH_EDGE (e, ei, bb->succs)
167 if (!best || better_p (e, best))
169 if (!best || ignore_bb_p (best->dest))
171 if (best->probability <= probability_cutoff)
176 /* Return most frequent predecessor of basic block BB. */
179 find_best_predecessor (basic_block bb)
185 FOR_EACH_EDGE (e, ei, bb->preds)
186 if (!best || better_p (e, best))
188 if (!best || ignore_bb_p (best->src))
190 if (EDGE_FREQUENCY (best) * REG_BR_PROB_BASE
191 < bb->frequency * branch_ratio_cutoff)
196 /* Find the trace using bb and record it in the TRACE array.
197 Return number of basic blocks recorded. */
200 find_trace (basic_block bb, basic_block *trace)
206 fprintf (dump_file, "Trace seed %i [%i]", bb->index, bb->frequency);
208 while ((e = find_best_predecessor (bb)) != NULL)
210 basic_block bb2 = e->src;
211 if (bb_seen_p (bb2) || (e->flags & (EDGE_DFS_BACK | EDGE_COMPLEX))
212 || find_best_successor (bb2) != e)
215 fprintf (dump_file, ",%i [%i]", bb->index, bb->frequency);
219 fprintf (dump_file, " forward %i [%i]", bb->index, bb->frequency);
222 /* Follow the trace in forward direction. */
223 while ((e = find_best_successor (bb)) != NULL)
226 if (bb_seen_p (bb) || (e->flags & (EDGE_DFS_BACK | EDGE_COMPLEX))
227 || find_best_predecessor (bb) != e)
230 fprintf (dump_file, ",%i [%i]", bb->index, bb->frequency);
234 fprintf (dump_file, "\n");
238 /* Look for basic blocks in frequency order, construct traces and tail duplicate
242 tail_duplicate (void)
244 auto_vec<fibonacci_node<long, basic_block_def>*> blocks;
245 blocks.safe_grow_cleared (last_basic_block_for_fn (cfun));
247 basic_block *trace = XNEWVEC (basic_block, n_basic_blocks_for_fn (cfun));
248 int *counts = XNEWVEC (int, last_basic_block_for_fn (cfun));
249 int ninsns = 0, nduplicated = 0;
250 gcov_type weighted_insns = 0, traced_insns = 0;
251 fibonacci_heap<long, basic_block_def> heap (LONG_MIN);
252 gcov_type cover_insns;
255 bool changed = false;
257 /* Create an oversized sbitmap to reduce the chance that we need to
259 bb_seen = sbitmap_alloc (last_basic_block_for_fn (cfun) * 2);
260 bitmap_clear (bb_seen);
261 initialize_original_copy_tables ();
263 if (profile_info && flag_branch_probabilities)
264 probability_cutoff = PARAM_VALUE (TRACER_MIN_BRANCH_PROBABILITY_FEEDBACK);
266 probability_cutoff = PARAM_VALUE (TRACER_MIN_BRANCH_PROBABILITY);
267 probability_cutoff = REG_BR_PROB_BASE / 100 * probability_cutoff;
269 branch_ratio_cutoff =
270 (REG_BR_PROB_BASE / 100 * PARAM_VALUE (TRACER_MIN_BRANCH_RATIO));
272 FOR_EACH_BB_FN (bb, cfun)
274 int n = count_insns (bb);
275 if (!ignore_bb_p (bb))
276 blocks[bb->index] = heap.insert (-bb->frequency, bb);
278 counts [bb->index] = n;
280 weighted_insns += n * bb->frequency;
283 if (profile_info && flag_branch_probabilities)
284 cover_insns = PARAM_VALUE (TRACER_DYNAMIC_COVERAGE_FEEDBACK);
286 cover_insns = PARAM_VALUE (TRACER_DYNAMIC_COVERAGE);
287 cover_insns = (weighted_insns * cover_insns + 50) / 100;
288 max_dup_insns = (ninsns * PARAM_VALUE (TRACER_MAX_CODE_GROWTH) + 50) / 100;
290 while (traced_insns < cover_insns && nduplicated < max_dup_insns
293 basic_block bb = heap.extract_min ();
299 blocks[bb->index] = NULL;
301 if (ignore_bb_p (bb))
303 gcc_assert (!bb_seen_p (bb));
305 n = find_trace (bb, trace);
308 traced_insns += bb->frequency * counts [bb->index];
309 if (blocks[bb->index])
311 heap.delete_node (blocks[bb->index]);
312 blocks[bb->index] = NULL;
315 for (pos = 1; pos < n; pos++)
317 basic_block bb2 = trace[pos];
319 if (blocks[bb2->index])
321 heap.delete_node (blocks[bb2->index]);
322 blocks[bb2->index] = NULL;
324 traced_insns += bb2->frequency * counts [bb2->index];
325 if (EDGE_COUNT (bb2->preds) > 1
326 && can_duplicate_block_p (bb2)
327 /* We have the tendency to duplicate the loop header
328 of all do { } while loops. Do not do that - it is
329 not profitable and it might create a loop with multiple
330 entries or at least rotate the loop. */
331 && bb2->loop_father->header != bb2)
336 nduplicated += counts [bb2->index];
338 e = find_edge (bb, bb2);
340 copy = duplicate_block (bb2, e, bb);
341 flush_pending_stmts (e);
343 add_phi_args_after_copy (©, 1, NULL);
345 /* Reconsider the original copy of block we've duplicated.
346 Removing the most common predecessor may make it to be
348 blocks[bb2->index] = heap.insert (-bb2->frequency, bb2);
351 fprintf (dump_file, "Duplicated %i as %i [%i]\n",
352 bb2->index, copy->index, copy->frequency);
359 /* In case the trace became infrequent, stop duplicating. */
360 if (ignore_bb_p (bb))
364 fprintf (dump_file, " covered now %.1f\n\n",
365 traced_insns * 100.0 / weighted_insns);
368 fprintf (dump_file, "Duplicated %i insns (%i%%)\n", nduplicated,
369 nduplicated * 100 / ninsns);
371 free_original_copy_tables ();
372 sbitmap_free (bb_seen);
381 const pass_data pass_data_tracer =
383 GIMPLE_PASS, /* type */
385 OPTGROUP_NONE, /* optinfo_flags */
386 TV_TRACER, /* tv_id */
387 0, /* properties_required */
388 0, /* properties_provided */
389 0, /* properties_destroyed */
390 0, /* todo_flags_start */
391 TODO_update_ssa, /* todo_flags_finish */
394 class pass_tracer : public gimple_opt_pass
397 pass_tracer (gcc::context *ctxt)
398 : gimple_opt_pass (pass_data_tracer, ctxt)
401 /* opt_pass methods: */
402 virtual bool gate (function *)
404 return (optimize > 0 && flag_tracer && flag_reorder_blocks);
407 virtual unsigned int execute (function *);
409 }; // class pass_tracer
412 pass_tracer::execute (function *fun)
416 if (n_basic_blocks_for_fn (fun) <= NUM_FIXED_BLOCKS + 1)
419 mark_dfs_back_edges ();
421 brief_dump_cfg (dump_file, dump_flags);
423 /* Trace formation is done on the fly inside tail_duplicate */
424 changed = tail_duplicate ();
427 free_dominance_info (CDI_DOMINATORS);
428 /* If we changed the CFG schedule loops for fixup by cleanup_cfg. */
429 loops_state_set (LOOPS_NEED_FIXUP);
433 brief_dump_cfg (dump_file, dump_flags);
435 return changed ? TODO_cleanup_cfg : 0;
440 make_pass_tracer (gcc::context *ctxt)
442 return new pass_tracer (ctxt);