1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
|
/* The tracer pass for the GNU compiler.
Contributed by Jan Hubicka, SuSE Labs.
Adapted to work on GIMPLE instead of RTL by Robert Kidd, UIUC.
Copyright (C) 2001-2019 Free Software Foundation, Inc.
This file is part of GCC.
GCC is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3, or (at your option)
any later version.
GCC is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
License for more details.
You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING3. If not see
<http://www.gnu.org/licenses/>. */
/* This pass performs the tail duplication needed for superblock formation.
For more information see:
Design and Analysis of Profile-Based Optimization in Compaq's
Compilation Tools for Alpha; Journal of Instruction-Level
Parallelism 3 (2000) 1-25
Unlike Compaq's implementation we don't do the loop peeling as most
probably a better job can be done by a special pass and we don't
need to worry too much about the code size implications as the tail
duplicates are crossjumped again if optimizations are not
performed. */
#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "backend.h"
#include "rtl.h"
#include "tree.h"
#include "gimple.h"
#include "cfghooks.h"
#include "tree-pass.h"
#include "profile.h"
#include "cfganal.h"
#include "gimple-iterator.h"
#include "tree-cfg.h"
#include "tree-ssa.h"
#include "tree-inline.h"
#include "cfgloop.h"
#include "fibonacci_heap.h"
#include "tracer.h"
static int count_insns (basic_block);
static bool better_p (const_edge, const_edge);
static edge find_best_successor (basic_block);
static edge find_best_predecessor (basic_block);
static int find_trace (basic_block, basic_block *);
/* Minimal outgoing edge probability considered for superblock formation. */
static int probability_cutoff;
static int branch_ratio_cutoff;
/* A bit BB->index is set if BB has already been seen, i.e. it is
connected to some trace already. */
static sbitmap bb_seen;
static inline void
mark_bb_seen (basic_block bb)
{
unsigned int size = SBITMAP_SIZE (bb_seen);
if ((unsigned int)bb->index >= size)
bb_seen = sbitmap_resize (bb_seen, size * 2, 0);
bitmap_set_bit (bb_seen, bb->index);
}
static inline bool
bb_seen_p (basic_block bb)
{
return bitmap_bit_p (bb_seen, bb->index);
}
/* Return true if we should ignore the basic block for purposes of tracing. */
bool
ignore_bb_p (const_basic_block bb)
{
if (bb->index < NUM_FIXED_BLOCKS)
return true;
if (optimize_bb_for_size_p (bb))
return true;
if (gimple *g = last_stmt (CONST_CAST_BB (bb)))
{
/* A transaction is a single entry multiple exit region. It
must be duplicated in its entirety or not at all. */
if (gimple_code (g) == GIMPLE_TRANSACTION)
return true;
/* An IFN_UNIQUE call must be duplicated as part of its group,
or not at all. */
if (is_gimple_call (g)
&& gimple_call_internal_p (g)
&& gimple_call_internal_unique_p (g))
return true;
}
return false;
}
/* Return number of instructions in the block. */
static int
count_insns (basic_block bb)
{
gimple_stmt_iterator gsi;
gimple *stmt;
int n = 0;
for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
{
stmt = gsi_stmt (gsi);
n += estimate_num_insns (stmt, &eni_size_weights);
}
return n;
}
/* Return true if E1 is more frequent than E2. */
static bool
better_p (const_edge e1, const_edge e2)
{
if ((e1->count () > e2->count ()) || (e1->count () < e2->count ()))
return e1->count () > e2->count ();
/* This is needed to avoid changes in the decision after
CFG is modified. */
if (e1->src != e2->src)
return e1->src->index > e2->src->index;
return e1->dest->index > e2->dest->index;
}
/* Return most frequent successor of basic block BB. */
static edge
find_best_successor (basic_block bb)
{
edge e;
edge best = NULL;
edge_iterator ei;
FOR_EACH_EDGE (e, ei, bb->succs)
{
if (!e->count ().initialized_p ())
return NULL;
if (!best || better_p (e, best))
best = e;
}
if (!best || ignore_bb_p (best->dest))
return NULL;
if (!best->probability.initialized_p ()
|| best->probability.to_reg_br_prob_base () <= probability_cutoff)
return NULL;
return best;
}
/* Return most frequent predecessor of basic block BB. */
static edge
find_best_predecessor (basic_block bb)
{
edge e;
edge best = NULL;
edge_iterator ei;
FOR_EACH_EDGE (e, ei, bb->preds)
{
if (!e->count ().initialized_p ())
return NULL;
if (!best || better_p (e, best))
best = e;
}
if (!best || ignore_bb_p (best->src))
return NULL;
if (bb->count.initialized_p ()
&& (best->count ().to_frequency (cfun) * REG_BR_PROB_BASE
< bb->count.to_frequency (cfun) * branch_ratio_cutoff))
return NULL;
return best;
}
/* Find the trace using bb and record it in the TRACE array.
Return number of basic blocks recorded. */
static int
find_trace (basic_block bb, basic_block *trace)
{
int i = 0;
edge e;
if (dump_file)
fprintf (dump_file, "Trace seed %i [%i]", bb->index, bb->count.to_frequency (cfun));
while ((e = find_best_predecessor (bb)) != NULL)
{
basic_block bb2 = e->src;
if (bb_seen_p (bb2) || (e->flags & (EDGE_DFS_BACK | EDGE_COMPLEX))
|| find_best_successor (bb2) != e)
break;
if (dump_file)
fprintf (dump_file, ",%i [%i]", bb->index, bb->count.to_frequency (cfun));
bb = bb2;
}
if (dump_file)
fprintf (dump_file, " forward %i [%i]", bb->index, bb->count.to_frequency (cfun));
trace[i++] = bb;
/* Follow the trace in forward direction. */
while ((e = find_best_successor (bb)) != NULL)
{
bb = e->dest;
if (bb_seen_p (bb) || (e->flags & (EDGE_DFS_BACK | EDGE_COMPLEX))
|| find_best_predecessor (bb) != e)
break;
if (dump_file)
fprintf (dump_file, ",%i [%i]", bb->index, bb->count.to_frequency (cfun));
trace[i++] = bb;
}
if (dump_file)
fprintf (dump_file, "\n");
return i;
}
/* Duplicate block BB2, placing it after BB in the CFG. Return the
newly created block. */
basic_block
transform_duplicate (basic_block bb, basic_block bb2)
{
edge e;
basic_block copy;
e = find_edge (bb, bb2);
copy = duplicate_block (bb2, e, bb);
flush_pending_stmts (e);
add_phi_args_after_copy (©, 1, NULL);
return (copy);
}
/* Look for basic blocks in frequency order, construct traces and tail duplicate
if profitable. */
static bool
tail_duplicate (void)
{
auto_vec<fibonacci_node<long, basic_block_def>*> blocks;
blocks.safe_grow_cleared (last_basic_block_for_fn (cfun));
basic_block *trace = XNEWVEC (basic_block, n_basic_blocks_for_fn (cfun));
int *counts = XNEWVEC (int, last_basic_block_for_fn (cfun));
int ninsns = 0, nduplicated = 0;
gcov_type weighted_insns = 0, traced_insns = 0;
fibonacci_heap<long, basic_block_def> heap (LONG_MIN);
gcov_type cover_insns;
int max_dup_insns;
basic_block bb;
bool changed = false;
/* Create an oversized sbitmap to reduce the chance that we need to
resize it. */
bb_seen = sbitmap_alloc (last_basic_block_for_fn (cfun) * 2);
bitmap_clear (bb_seen);
initialize_original_copy_tables ();
if (profile_info && profile_status_for_fn (cfun) == PROFILE_READ)
probability_cutoff = param_tracer_min_branch_probability_feedback;
else
probability_cutoff = param_tracer_min_branch_probability;
probability_cutoff = REG_BR_PROB_BASE / 100 * probability_cutoff;
branch_ratio_cutoff =
(REG_BR_PROB_BASE / 100 * param_tracer_min_branch_ratio);
FOR_EACH_BB_FN (bb, cfun)
{
int n = count_insns (bb);
if (!ignore_bb_p (bb))
blocks[bb->index] = heap.insert (-bb->count.to_frequency (cfun), bb);
counts [bb->index] = n;
ninsns += n;
weighted_insns += n * bb->count.to_frequency (cfun);
}
if (profile_info && profile_status_for_fn (cfun) == PROFILE_READ)
cover_insns = param_tracer_dynamic_coverage_feedback;
else
cover_insns = param_tracer_dynamic_coverage;
cover_insns = (weighted_insns * cover_insns + 50) / 100;
max_dup_insns = (ninsns * param_tracer_max_code_growth + 50) / 100;
while (traced_insns < cover_insns && nduplicated < max_dup_insns
&& !heap.empty ())
{
basic_block bb = heap.extract_min ();
int n, pos;
if (!bb)
break;
blocks[bb->index] = NULL;
if (ignore_bb_p (bb))
continue;
gcc_assert (!bb_seen_p (bb));
n = find_trace (bb, trace);
bb = trace[0];
traced_insns += bb->count.to_frequency (cfun) * counts [bb->index];
if (blocks[bb->index])
{
heap.delete_node (blocks[bb->index]);
blocks[bb->index] = NULL;
}
for (pos = 1; pos < n; pos++)
{
basic_block bb2 = trace[pos];
if (blocks[bb2->index])
{
heap.delete_node (blocks[bb2->index]);
blocks[bb2->index] = NULL;
}
traced_insns += bb2->count.to_frequency (cfun) * counts [bb2->index];
if (EDGE_COUNT (bb2->preds) > 1
&& can_duplicate_block_p (bb2)
/* We have the tendency to duplicate the loop header
of all do { } while loops. Do not do that - it is
not profitable and it might create a loop with multiple
entries or at least rotate the loop. */
&& bb2->loop_father->header != bb2)
{
nduplicated += counts [bb2->index];
basic_block copy = transform_duplicate (bb, bb2);
/* Reconsider the original copy of block we've duplicated.
Removing the most common predecessor may make it to be
head. */
blocks[bb2->index] = heap.insert (-bb2->count.to_frequency (cfun), bb2);
if (dump_file)
fprintf (dump_file, "Duplicated %i as %i [%i]\n",
bb2->index, copy->index, copy->count.to_frequency (cfun));
bb2 = copy;
changed = true;
}
mark_bb_seen (bb2);
bb = bb2;
/* In case the trace became infrequent, stop duplicating. */
if (ignore_bb_p (bb))
break;
}
if (dump_file)
fprintf (dump_file, " covered now %.1f\n\n",
traced_insns * 100.0 / weighted_insns);
}
if (dump_file)
fprintf (dump_file, "Duplicated %i insns (%i%%)\n", nduplicated,
nduplicated * 100 / ninsns);
free_original_copy_tables ();
sbitmap_free (bb_seen);
free (trace);
free (counts);
return changed;
}
namespace {
const pass_data pass_data_tracer =
{
GIMPLE_PASS, /* type */
"tracer", /* name */
OPTGROUP_NONE, /* optinfo_flags */
TV_TRACER, /* tv_id */
0, /* properties_required */
0, /* properties_provided */
0, /* properties_destroyed */
0, /* todo_flags_start */
TODO_update_ssa, /* todo_flags_finish */
};
class pass_tracer : public gimple_opt_pass
{
public:
pass_tracer (gcc::context *ctxt)
: gimple_opt_pass (pass_data_tracer, ctxt)
{}
/* opt_pass methods: */
virtual bool gate (function *)
{
return (optimize > 0 && flag_tracer && flag_reorder_blocks);
}
virtual unsigned int execute (function *);
}; // class pass_tracer
unsigned int
pass_tracer::execute (function *fun)
{
bool changed;
if (n_basic_blocks_for_fn (fun) <= NUM_FIXED_BLOCKS + 1)
return 0;
mark_dfs_back_edges ();
if (dump_file)
brief_dump_cfg (dump_file, dump_flags);
/* Trace formation is done on the fly inside tail_duplicate */
changed = tail_duplicate ();
if (changed)
{
free_dominance_info (CDI_DOMINATORS);
/* If we changed the CFG schedule loops for fixup by cleanup_cfg. */
loops_state_set (LOOPS_NEED_FIXUP);
}
if (dump_file)
brief_dump_cfg (dump_file, dump_flags);
return changed ? TODO_cleanup_cfg : 0;
}
} // anon namespace
gimple_opt_pass *
make_pass_tracer (gcc::context *ctxt)
{
return new pass_tracer (ctxt);
}
|