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) 2001-2017 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 "tree-pass.h"
48 #include "gimple-iterator.h"
51 #include "tree-inline.h"
53 #include "fibonacci_heap.h"
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
*);
62 /* Minimal outgoing edge probability considered for superblock formation. */
63 static int probability_cutoff
;
64 static int branch_ratio_cutoff
;
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
;
71 mark_bb_seen (basic_block bb
)
73 unsigned int size
= SBITMAP_SIZE (bb_seen
);
75 if ((unsigned int)bb
->index
>= size
)
76 bb_seen
= sbitmap_resize (bb_seen
, size
* 2, 0);
78 bitmap_set_bit (bb_seen
, bb
->index
);
82 bb_seen_p (basic_block bb
)
84 return bitmap_bit_p (bb_seen
, bb
->index
);
87 /* Return true if we should ignore the basic block for purposes of tracing. */
89 ignore_bb_p (const_basic_block bb
)
91 if (bb
->index
< NUM_FIXED_BLOCKS
)
93 if (optimize_bb_for_size_p (bb
))
96 if (gimple
*g
= last_stmt (CONST_CAST_BB (bb
)))
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
)
103 /* An IFN_UNIQUE call must be duplicated as part of its group,
105 if (is_gimple_call (g
)
106 && gimple_call_internal_p (g
)
107 && gimple_call_internal_unique_p (g
))
114 /* Return number of instructions in the block. */
117 count_insns (basic_block bb
)
119 gimple_stmt_iterator gsi
;
123 for (gsi
= gsi_start_bb (bb
); !gsi_end_p (gsi
); gsi_next (&gsi
))
125 stmt
= gsi_stmt (gsi
);
126 n
+= estimate_num_insns (stmt
, &eni_size_weights
);
131 /* Return true if E1 is more frequent than E2. */
133 better_p (const_edge e1
, const_edge e2
)
135 if (e1
->count
.initialized_p () && e2
->count
.initialized_p ()
136 && !(e1
->count
== e2
->count
))
137 return e1
->count
> e2
->count
;
138 if (e1
->src
->frequency
* e1
->probability
!=
139 e2
->src
->frequency
* e2
->probability
)
140 return (e1
->src
->frequency
* e1
->probability
141 > e2
->src
->frequency
* e2
->probability
);
142 /* This is needed to avoid changes in the decision after
144 if (e1
->src
!= e2
->src
)
145 return e1
->src
->index
> e2
->src
->index
;
146 return e1
->dest
->index
> e2
->dest
->index
;
149 /* Return most frequent successor of basic block BB. */
152 find_best_successor (basic_block bb
)
158 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
159 if (!best
|| better_p (e
, best
))
161 if (!best
|| ignore_bb_p (best
->dest
))
163 if (best
->probability
<= probability_cutoff
)
168 /* Return most frequent predecessor of basic block BB. */
171 find_best_predecessor (basic_block bb
)
177 FOR_EACH_EDGE (e
, ei
, bb
->preds
)
178 if (!best
|| better_p (e
, best
))
180 if (!best
|| ignore_bb_p (best
->src
))
182 if (EDGE_FREQUENCY (best
) * REG_BR_PROB_BASE
183 < bb
->frequency
* branch_ratio_cutoff
)
188 /* Find the trace using bb and record it in the TRACE array.
189 Return number of basic blocks recorded. */
192 find_trace (basic_block bb
, basic_block
*trace
)
198 fprintf (dump_file
, "Trace seed %i [%i]", bb
->index
, bb
->frequency
);
200 while ((e
= find_best_predecessor (bb
)) != NULL
)
202 basic_block bb2
= e
->src
;
203 if (bb_seen_p (bb2
) || (e
->flags
& (EDGE_DFS_BACK
| EDGE_COMPLEX
))
204 || find_best_successor (bb2
) != e
)
207 fprintf (dump_file
, ",%i [%i]", bb
->index
, bb
->frequency
);
211 fprintf (dump_file
, " forward %i [%i]", bb
->index
, bb
->frequency
);
214 /* Follow the trace in forward direction. */
215 while ((e
= find_best_successor (bb
)) != NULL
)
218 if (bb_seen_p (bb
) || (e
->flags
& (EDGE_DFS_BACK
| EDGE_COMPLEX
))
219 || find_best_predecessor (bb
) != e
)
222 fprintf (dump_file
, ",%i [%i]", bb
->index
, bb
->frequency
);
226 fprintf (dump_file
, "\n");
230 /* Duplicate block BB2, placing it after BB in the CFG. Return the
231 newly created block. */
233 transform_duplicate (basic_block bb
, basic_block bb2
)
238 e
= find_edge (bb
, bb2
);
240 copy
= duplicate_block (bb2
, e
, bb
);
241 flush_pending_stmts (e
);
243 add_phi_args_after_copy (©
, 1, NULL
);
248 /* Look for basic blocks in frequency order, construct traces and tail duplicate
252 tail_duplicate (void)
254 auto_vec
<fibonacci_node
<long, basic_block_def
>*> blocks
;
255 blocks
.safe_grow_cleared (last_basic_block_for_fn (cfun
));
257 basic_block
*trace
= XNEWVEC (basic_block
, n_basic_blocks_for_fn (cfun
));
258 int *counts
= XNEWVEC (int, last_basic_block_for_fn (cfun
));
259 int ninsns
= 0, nduplicated
= 0;
260 gcov_type weighted_insns
= 0, traced_insns
= 0;
261 fibonacci_heap
<long, basic_block_def
> heap (LONG_MIN
);
262 gcov_type cover_insns
;
265 bool changed
= false;
267 /* Create an oversized sbitmap to reduce the chance that we need to
269 bb_seen
= sbitmap_alloc (last_basic_block_for_fn (cfun
) * 2);
270 bitmap_clear (bb_seen
);
271 initialize_original_copy_tables ();
273 if (profile_info
&& flag_branch_probabilities
)
274 probability_cutoff
= PARAM_VALUE (TRACER_MIN_BRANCH_PROBABILITY_FEEDBACK
);
276 probability_cutoff
= PARAM_VALUE (TRACER_MIN_BRANCH_PROBABILITY
);
277 probability_cutoff
= REG_BR_PROB_BASE
/ 100 * probability_cutoff
;
279 branch_ratio_cutoff
=
280 (REG_BR_PROB_BASE
/ 100 * PARAM_VALUE (TRACER_MIN_BRANCH_RATIO
));
282 FOR_EACH_BB_FN (bb
, cfun
)
284 int n
= count_insns (bb
);
285 if (!ignore_bb_p (bb
))
286 blocks
[bb
->index
] = heap
.insert (-bb
->frequency
, bb
);
288 counts
[bb
->index
] = n
;
290 weighted_insns
+= n
* bb
->frequency
;
293 if (profile_info
&& flag_branch_probabilities
)
294 cover_insns
= PARAM_VALUE (TRACER_DYNAMIC_COVERAGE_FEEDBACK
);
296 cover_insns
= PARAM_VALUE (TRACER_DYNAMIC_COVERAGE
);
297 cover_insns
= (weighted_insns
* cover_insns
+ 50) / 100;
298 max_dup_insns
= (ninsns
* PARAM_VALUE (TRACER_MAX_CODE_GROWTH
) + 50) / 100;
300 while (traced_insns
< cover_insns
&& nduplicated
< max_dup_insns
303 basic_block bb
= heap
.extract_min ();
309 blocks
[bb
->index
] = NULL
;
311 if (ignore_bb_p (bb
))
313 gcc_assert (!bb_seen_p (bb
));
315 n
= find_trace (bb
, trace
);
318 traced_insns
+= bb
->frequency
* counts
[bb
->index
];
319 if (blocks
[bb
->index
])
321 heap
.delete_node (blocks
[bb
->index
]);
322 blocks
[bb
->index
] = NULL
;
325 for (pos
= 1; pos
< n
; pos
++)
327 basic_block bb2
= trace
[pos
];
329 if (blocks
[bb2
->index
])
331 heap
.delete_node (blocks
[bb2
->index
]);
332 blocks
[bb2
->index
] = NULL
;
334 traced_insns
+= bb2
->frequency
* counts
[bb2
->index
];
335 if (EDGE_COUNT (bb2
->preds
) > 1
336 && can_duplicate_block_p (bb2
)
337 /* We have the tendency to duplicate the loop header
338 of all do { } while loops. Do not do that - it is
339 not profitable and it might create a loop with multiple
340 entries or at least rotate the loop. */
341 && bb2
->loop_father
->header
!= bb2
)
343 nduplicated
+= counts
[bb2
->index
];
344 basic_block copy
= transform_duplicate (bb
, bb2
);
346 /* Reconsider the original copy of block we've duplicated.
347 Removing the most common predecessor may make it to be
349 blocks
[bb2
->index
] = heap
.insert (-bb2
->frequency
, bb2
);
352 fprintf (dump_file
, "Duplicated %i as %i [%i]\n",
353 bb2
->index
, copy
->index
, copy
->frequency
);
360 /* In case the trace became infrequent, stop duplicating. */
361 if (ignore_bb_p (bb
))
365 fprintf (dump_file
, " covered now %.1f\n\n",
366 traced_insns
* 100.0 / weighted_insns
);
369 fprintf (dump_file
, "Duplicated %i insns (%i%%)\n", nduplicated
,
370 nduplicated
* 100 / ninsns
);
372 free_original_copy_tables ();
373 sbitmap_free (bb_seen
);
382 const pass_data pass_data_tracer
=
384 GIMPLE_PASS
, /* type */
386 OPTGROUP_NONE
, /* optinfo_flags */
387 TV_TRACER
, /* tv_id */
388 0, /* properties_required */
389 0, /* properties_provided */
390 0, /* properties_destroyed */
391 0, /* todo_flags_start */
392 TODO_update_ssa
, /* todo_flags_finish */
395 class pass_tracer
: public gimple_opt_pass
398 pass_tracer (gcc::context
*ctxt
)
399 : gimple_opt_pass (pass_data_tracer
, ctxt
)
402 /* opt_pass methods: */
403 virtual bool gate (function
*)
405 return (optimize
> 0 && flag_tracer
&& flag_reorder_blocks
);
408 virtual unsigned int execute (function
*);
410 }; // class pass_tracer
413 pass_tracer::execute (function
*fun
)
417 if (n_basic_blocks_for_fn (fun
) <= NUM_FIXED_BLOCKS
+ 1)
420 mark_dfs_back_edges ();
422 brief_dump_cfg (dump_file
, dump_flags
);
424 /* Trace formation is done on the fly inside tail_duplicate */
425 changed
= tail_duplicate ();
428 free_dominance_info (CDI_DOMINATORS
);
429 /* If we changed the CFG schedule loops for fixup by cleanup_cfg. */
430 loops_state_set (LOOPS_NEED_FIXUP
);
434 brief_dump_cfg (dump_file
, dump_flags
);
436 return changed
? TODO_cleanup_cfg
: 0;
441 make_pass_tracer (gcc::context
*ctxt
)
443 return new pass_tracer (ctxt
);