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.
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 "tm.h"
40#include "hash-set.h"
41#include "machmode.h"
42#include "vec.h"
43#include "double-int.h"
44#include "input.h"
45#include "alias.h"
46#include "symtab.h"
47#include "wide-int.h"
48#include "inchash.h"
49#include "tree.h"
50#include "fold-const.h"
51#include "rtl.h"
52#include "hard-reg-set.h"
53#include "profile.h"
54#include "predict.h"
55#include "input.h"
56#include "function.h"
57#include "dominance.h"
58#include "cfg.h"
59#include "cfganal.h"
60#include "basic-block.h"
61#include "flags.h"
62#include "params.h"
63#include "coverage.h"
64#include "tree-pass.h"
65#include "tree-ssa-alias.h"
66#include "internal-fn.h"
67#include "gimple-expr.h"
68#include "is-a.h"
69#include "gimple.h"
70#include "gimple-iterator.h"
71#include "tree-cfg.h"
72#include "tree-ssa.h"
73#include "tree-inline.h"
74#include "cfgloop.h"
75#include "fibonacci_heap.h"
76
77static int count_insns (basic_block);
78static bool ignore_bb_p (const_basic_block);
79static bool better_p (const_edge, const_edge);
80static edge find_best_successor (basic_block);
81static edge find_best_predecessor (basic_block);
82static int find_trace (basic_block, basic_block *);
83
84/* Minimal outgoing edge probability considered for superblock formation.  */
85static int probability_cutoff;
86static int branch_ratio_cutoff;
87
88/* A bit BB->index is set if BB has already been seen, i.e. it is
89   connected to some trace already.  */
90sbitmap bb_seen;
91
92static inline void
93mark_bb_seen (basic_block bb)
94{
95  unsigned int size = SBITMAP_SIZE (bb_seen);
96
97  if ((unsigned int)bb->index >= size)
98    bb_seen = sbitmap_resize (bb_seen, size * 2, 0);
99
100  bitmap_set_bit (bb_seen, bb->index);
101}
102
103static inline bool
104bb_seen_p (basic_block bb)
105{
106  return bitmap_bit_p (bb_seen, bb->index);
107}
108
109/* Return true if we should ignore the basic block for purposes of tracing.  */
110static bool
111ignore_bb_p (const_basic_block bb)
112{
113  gimple g;
114
115  if (bb->index < NUM_FIXED_BLOCKS)
116    return true;
117  if (optimize_bb_for_size_p (bb))
118    return true;
119
120  /* A transaction is a single entry multiple exit region.  It must be
121     duplicated in its entirety or not at all.  */
122  g = last_stmt (CONST_CAST_BB (bb));
123  if (g && gimple_code (g) == GIMPLE_TRANSACTION)
124    return true;
125
126  return false;
127}
128
129/* Return number of instructions in the block.  */
130
131static int
132count_insns (basic_block bb)
133{
134  gimple_stmt_iterator gsi;
135  gimple stmt;
136  int n = 0;
137
138  for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
139    {
140      stmt = gsi_stmt (gsi);
141      n += estimate_num_insns (stmt, &eni_size_weights);
142    }
143  return n;
144}
145
146/* Return true if E1 is more frequent than E2.  */
147static bool
148better_p (const_edge e1, const_edge e2)
149{
150  if (e1->count != e2->count)
151    return e1->count > e2->count;
152  if (e1->src->frequency * e1->probability !=
153      e2->src->frequency * e2->probability)
154    return (e1->src->frequency * e1->probability
155	    > e2->src->frequency * e2->probability);
156  /* This is needed to avoid changes in the decision after
157     CFG is modified.  */
158  if (e1->src != e2->src)
159    return e1->src->index > e2->src->index;
160  return e1->dest->index > e2->dest->index;
161}
162
163/* Return most frequent successor of basic block BB.  */
164
165static edge
166find_best_successor (basic_block bb)
167{
168  edge e;
169  edge best = NULL;
170  edge_iterator ei;
171
172  FOR_EACH_EDGE (e, ei, bb->succs)
173    if (!best || better_p (e, best))
174      best = e;
175  if (!best || ignore_bb_p (best->dest))
176    return NULL;
177  if (best->probability <= probability_cutoff)
178    return NULL;
179  return best;
180}
181
182/* Return most frequent predecessor of basic block BB.  */
183
184static edge
185find_best_predecessor (basic_block bb)
186{
187  edge e;
188  edge best = NULL;
189  edge_iterator ei;
190
191  FOR_EACH_EDGE (e, ei, bb->preds)
192    if (!best || better_p (e, best))
193      best = e;
194  if (!best || ignore_bb_p (best->src))
195    return NULL;
196  if (EDGE_FREQUENCY (best) * REG_BR_PROB_BASE
197      < bb->frequency * branch_ratio_cutoff)
198    return NULL;
199  return best;
200}
201
202/* Find the trace using bb and record it in the TRACE array.
203   Return number of basic blocks recorded.  */
204
205static int
206find_trace (basic_block bb, basic_block *trace)
207{
208  int i = 0;
209  edge e;
210
211  if (dump_file)
212    fprintf (dump_file, "Trace seed %i [%i]", bb->index, bb->frequency);
213
214  while ((e = find_best_predecessor (bb)) != NULL)
215    {
216      basic_block bb2 = e->src;
217      if (bb_seen_p (bb2) || (e->flags & (EDGE_DFS_BACK | EDGE_COMPLEX))
218	  || find_best_successor (bb2) != e)
219	break;
220      if (dump_file)
221	fprintf (dump_file, ",%i [%i]", bb->index, bb->frequency);
222      bb = bb2;
223    }
224  if (dump_file)
225    fprintf (dump_file, " forward %i [%i]", bb->index, bb->frequency);
226  trace[i++] = bb;
227
228  /* Follow the trace in forward direction.  */
229  while ((e = find_best_successor (bb)) != NULL)
230    {
231      bb = e->dest;
232      if (bb_seen_p (bb) || (e->flags & (EDGE_DFS_BACK | EDGE_COMPLEX))
233	  || find_best_predecessor (bb) != e)
234	break;
235      if (dump_file)
236	fprintf (dump_file, ",%i [%i]", bb->index, bb->frequency);
237      trace[i++] = bb;
238    }
239  if (dump_file)
240    fprintf (dump_file, "\n");
241  return i;
242}
243
244/* Look for basic blocks in frequency order, construct traces and tail duplicate
245   if profitable.  */
246
247static bool
248tail_duplicate (void)
249{
250  auto_vec<fibonacci_node<long, basic_block_def>*> blocks;
251  blocks.safe_grow_cleared (last_basic_block_for_fn (cfun));
252
253  basic_block *trace = XNEWVEC (basic_block, n_basic_blocks_for_fn (cfun));
254  int *counts = XNEWVEC (int, last_basic_block_for_fn (cfun));
255  int ninsns = 0, nduplicated = 0;
256  gcov_type weighted_insns = 0, traced_insns = 0;
257  fibonacci_heap<long, basic_block_def> heap (LONG_MIN);
258  gcov_type cover_insns;
259  int max_dup_insns;
260  basic_block bb;
261  bool changed = false;
262
263  /* Create an oversized sbitmap to reduce the chance that we need to
264     resize it.  */
265  bb_seen = sbitmap_alloc (last_basic_block_for_fn (cfun) * 2);
266  bitmap_clear (bb_seen);
267  initialize_original_copy_tables ();
268
269  if (profile_info && flag_branch_probabilities)
270    probability_cutoff = PARAM_VALUE (TRACER_MIN_BRANCH_PROBABILITY_FEEDBACK);
271  else
272    probability_cutoff = PARAM_VALUE (TRACER_MIN_BRANCH_PROBABILITY);
273  probability_cutoff = REG_BR_PROB_BASE / 100 * probability_cutoff;
274
275  branch_ratio_cutoff =
276    (REG_BR_PROB_BASE / 100 * PARAM_VALUE (TRACER_MIN_BRANCH_RATIO));
277
278  FOR_EACH_BB_FN (bb, cfun)
279    {
280      int n = count_insns (bb);
281      if (!ignore_bb_p (bb))
282	blocks[bb->index] = heap.insert (-bb->frequency, bb);
283
284      counts [bb->index] = n;
285      ninsns += n;
286      weighted_insns += n * bb->frequency;
287    }
288
289  if (profile_info && flag_branch_probabilities)
290    cover_insns = PARAM_VALUE (TRACER_DYNAMIC_COVERAGE_FEEDBACK);
291  else
292    cover_insns = PARAM_VALUE (TRACER_DYNAMIC_COVERAGE);
293  cover_insns = (weighted_insns * cover_insns + 50) / 100;
294  max_dup_insns = (ninsns * PARAM_VALUE (TRACER_MAX_CODE_GROWTH) + 50) / 100;
295
296  while (traced_insns < cover_insns && nduplicated < max_dup_insns
297         && !heap.empty ())
298    {
299      basic_block bb = heap.extract_min ();
300      int n, pos;
301
302      if (!bb)
303	break;
304
305      blocks[bb->index] = NULL;
306
307      if (ignore_bb_p (bb))
308	continue;
309      gcc_assert (!bb_seen_p (bb));
310
311      n = find_trace (bb, trace);
312
313      bb = trace[0];
314      traced_insns += bb->frequency * counts [bb->index];
315      if (blocks[bb->index])
316	{
317	  heap.delete_node (blocks[bb->index]);
318	  blocks[bb->index] = NULL;
319	}
320
321      for (pos = 1; pos < n; pos++)
322	{
323	  basic_block bb2 = trace[pos];
324
325	  if (blocks[bb2->index])
326	    {
327	      heap.delete_node (blocks[bb2->index]);
328	      blocks[bb2->index] = NULL;
329	    }
330	  traced_insns += bb2->frequency * counts [bb2->index];
331	  if (EDGE_COUNT (bb2->preds) > 1
332	      && can_duplicate_block_p (bb2)
333	      /* We have the tendency to duplicate the loop header
334	         of all do { } while loops.  Do not do that - it is
335		 not profitable and it might create a loop with multiple
336		 entries or at least rotate the loop.  */
337	      && bb2->loop_father->header != bb2)
338	    {
339	      edge e;
340	      basic_block copy;
341
342	      nduplicated += counts [bb2->index];
343
344	      e = find_edge (bb, bb2);
345
346	      copy = duplicate_block (bb2, e, bb);
347	      flush_pending_stmts (e);
348
349	      add_phi_args_after_copy (&copy, 1, NULL);
350
351	      /* Reconsider the original copy of block we've duplicated.
352	         Removing the most common predecessor may make it to be
353	         head.  */
354	      blocks[bb2->index] = heap.insert (-bb2->frequency, bb2);
355
356	      if (dump_file)
357		fprintf (dump_file, "Duplicated %i as %i [%i]\n",
358			 bb2->index, copy->index, copy->frequency);
359
360	      bb2 = copy;
361	      changed = true;
362	    }
363	  mark_bb_seen (bb2);
364	  bb = bb2;
365	  /* In case the trace became infrequent, stop duplicating.  */
366	  if (ignore_bb_p (bb))
367	    break;
368	}
369      if (dump_file)
370	fprintf (dump_file, " covered now %.1f\n\n",
371		 traced_insns * 100.0 / weighted_insns);
372    }
373  if (dump_file)
374    fprintf (dump_file, "Duplicated %i insns (%i%%)\n", nduplicated,
375	     nduplicated * 100 / ninsns);
376
377  free_original_copy_tables ();
378  sbitmap_free (bb_seen);
379  free (trace);
380  free (counts);
381
382  return changed;
383}
384
385namespace {
386
387const pass_data pass_data_tracer =
388{
389  GIMPLE_PASS, /* type */
390  "tracer", /* name */
391  OPTGROUP_NONE, /* optinfo_flags */
392  TV_TRACER, /* tv_id */
393  0, /* properties_required */
394  0, /* properties_provided */
395  0, /* properties_destroyed */
396  0, /* todo_flags_start */
397  TODO_update_ssa, /* todo_flags_finish */
398};
399
400class pass_tracer : public gimple_opt_pass
401{
402public:
403  pass_tracer (gcc::context *ctxt)
404    : gimple_opt_pass (pass_data_tracer, ctxt)
405  {}
406
407  /* opt_pass methods: */
408  virtual bool gate (function *)
409    {
410      return (optimize > 0 && flag_tracer && flag_reorder_blocks);
411    }
412
413  virtual unsigned int execute (function *);
414
415}; // class pass_tracer
416
417unsigned int
418pass_tracer::execute (function *fun)
419{
420  bool changed;
421
422  if (n_basic_blocks_for_fn (fun) <= NUM_FIXED_BLOCKS + 1)
423    return 0;
424
425  mark_dfs_back_edges ();
426  if (dump_file)
427    brief_dump_cfg (dump_file, dump_flags);
428
429  /* Trace formation is done on the fly inside tail_duplicate */
430  changed = tail_duplicate ();
431  if (changed)
432    {
433      free_dominance_info (CDI_DOMINATORS);
434      /* If we changed the CFG schedule loops for fixup by cleanup_cfg.  */
435      loops_state_set (LOOPS_NEED_FIXUP);
436    }
437
438  if (dump_file)
439    brief_dump_cfg (dump_file, dump_flags);
440
441  return changed ? TODO_cleanup_cfg : 0;
442}
443} // anon namespace
444
445gimple_opt_pass *
446make_pass_tracer (gcc::context *ctxt)
447{
448  return new pass_tracer (ctxt);
449}
450