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, 2002, 2003, 2004, 2005, 2006, 2007, 2008
5 Free Software Foundation, Inc.
7 This file is part of GCC.
9 GCC is free software; you can redistribute it and/or modify it
10 under the terms of the GNU General Public License as published by
11 the Free Software Foundation; either version 3, or (at your option)
14 GCC is distributed in the hope that it will be useful, but WITHOUT
15 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
16 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
17 License for more details.
19 You should have received a copy of the GNU General Public License
20 along with GCC; see the file COPYING3. If not see
21 <http://www.gnu.org/licenses/>. */
23 /* This pass performs the tail duplication needed for superblock formation.
24 For more information see:
26 Design and Analysis of Profile-Based Optimization in Compaq's
27 Compilation Tools for Alpha; Journal of Instruction-Level
28 Parallelism 3 (2000) 1-25
30 Unlike Compaq's implementation we don't do the loop peeling as most
31 probably a better job can be done by a special pass and we don't
32 need to worry too much about the code size implications as the tail
33 duplicates are crossjumped again if optimizations are not
39 #include "coretypes.h"
43 #include "hard-reg-set.h"
44 #include "basic-block.h"
46 #include "cfglayout.h"
52 #include "tree-pass.h"
53 #include "tree-flow.h"
54 #include "tree-inline.h"
56 static int count_insns (basic_block);
57 static bool ignore_bb_p (const_basic_block);
58 static bool better_p (const_edge, const_edge);
59 static edge find_best_successor (basic_block);
60 static edge find_best_predecessor (basic_block);
61 static int find_trace (basic_block, basic_block *);
62 static void tail_duplicate (void);
64 /* Minimal outgoing edge probability considered for superblock formation. */
65 static int probability_cutoff;
66 static int branch_ratio_cutoff;
68 /* A bit BB->index is set if BB has already been seen, i.e. it is
69 connected to some trace already. */
73 mark_bb_seen (basic_block bb)
75 unsigned int size = SBITMAP_SIZE_BYTES (bb_seen) * 8;
77 if ((unsigned int)bb->index >= size)
78 bb_seen = sbitmap_resize (bb_seen, size * 2, 0);
80 SET_BIT (bb_seen, bb->index);
84 bb_seen_p (basic_block bb)
86 return TEST_BIT (bb_seen, bb->index);
89 /* Return true if we should ignore the basic block for purposes of tracing. */
91 ignore_bb_p (const_basic_block bb)
95 if (bb->index < NUM_FIXED_BLOCKS)
97 if (optimize_bb_for_size_p (bb))
100 /* A transaction is a single entry multiple exit region. It must be
101 duplicated in its entirety or not at all. */
102 g = last_stmt (CONST_CAST_BB (bb));
103 if (g && gimple_code (g) == GIMPLE_TRANSACTION)
109 /* Return number of instructions in the block. */
112 count_insns (basic_block bb)
114 gimple_stmt_iterator gsi;
118 for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
120 stmt = gsi_stmt (gsi);
121 n += estimate_num_insns (stmt, &eni_size_weights);
126 /* Return true if E1 is more frequent than E2. */
128 better_p (const_edge e1, const_edge e2)
130 if (e1->count != e2->count)
131 return e1->count > e2->count;
132 if (e1->src->frequency * e1->probability !=
133 e2->src->frequency * e2->probability)
134 return (e1->src->frequency * e1->probability
135 > e2->src->frequency * e2->probability);
136 /* This is needed to avoid changes in the decision after
138 if (e1->src != e2->src)
139 return e1->src->index > e2->src->index;
140 return e1->dest->index > e2->dest->index;
143 /* Return most frequent successor of basic block BB. */
146 find_best_successor (basic_block bb)
152 FOR_EACH_EDGE (e, ei, bb->succs)
153 if (!best || better_p (e, best))
155 if (!best || ignore_bb_p (best->dest))
157 if (best->probability <= probability_cutoff)
162 /* Return most frequent predecessor of basic block BB. */
165 find_best_predecessor (basic_block bb)
171 FOR_EACH_EDGE (e, ei, bb->preds)
172 if (!best || better_p (e, best))
174 if (!best || ignore_bb_p (best->src))
176 if (EDGE_FREQUENCY (best) * REG_BR_PROB_BASE
177 < bb->frequency * branch_ratio_cutoff)
182 /* Find the trace using bb and record it in the TRACE array.
183 Return number of basic blocks recorded. */
186 find_trace (basic_block bb, basic_block *trace)
192 fprintf (dump_file, "Trace seed %i [%i]", bb->index, bb->frequency);
194 while ((e = find_best_predecessor (bb)) != NULL)
196 basic_block bb2 = e->src;
197 if (bb_seen_p (bb2) || (e->flags & (EDGE_DFS_BACK | EDGE_COMPLEX))
198 || find_best_successor (bb2) != e)
201 fprintf (dump_file, ",%i [%i]", bb->index, bb->frequency);
205 fprintf (dump_file, " forward %i [%i]", bb->index, bb->frequency);
208 /* Follow the trace in forward direction. */
209 while ((e = find_best_successor (bb)) != NULL)
212 if (bb_seen_p (bb) || (e->flags & (EDGE_DFS_BACK | EDGE_COMPLEX))
213 || find_best_predecessor (bb) != e)
216 fprintf (dump_file, ",%i [%i]", bb->index, bb->frequency);
220 fprintf (dump_file, "\n");
224 /* Look for basic blocks in frequency order, construct traces and tail duplicate
228 tail_duplicate (void)
230 fibnode_t *blocks = XCNEWVEC (fibnode_t, last_basic_block);
231 basic_block *trace = XNEWVEC (basic_block, n_basic_blocks);
232 int *counts = XNEWVEC (int, last_basic_block);
233 int ninsns = 0, nduplicated = 0;
234 gcov_type weighted_insns = 0, traced_insns = 0;
235 fibheap_t heap = fibheap_new ();
236 gcov_type cover_insns;
240 /* Create an oversized sbitmap to reduce the chance that we need to
242 bb_seen = sbitmap_alloc (last_basic_block * 2);
243 sbitmap_zero (bb_seen);
244 initialize_original_copy_tables ();
246 if (profile_info && flag_branch_probabilities)
247 probability_cutoff = PARAM_VALUE (TRACER_MIN_BRANCH_PROBABILITY_FEEDBACK);
249 probability_cutoff = PARAM_VALUE (TRACER_MIN_BRANCH_PROBABILITY);
250 probability_cutoff = REG_BR_PROB_BASE / 100 * probability_cutoff;
252 branch_ratio_cutoff =
253 (REG_BR_PROB_BASE / 100 * PARAM_VALUE (TRACER_MIN_BRANCH_RATIO));
257 int n = count_insns (bb);
258 if (!ignore_bb_p (bb))
259 blocks[bb->index] = fibheap_insert (heap, -bb->frequency,
262 counts [bb->index] = n;
264 weighted_insns += n * bb->frequency;
267 if (profile_info && flag_branch_probabilities)
268 cover_insns = PARAM_VALUE (TRACER_DYNAMIC_COVERAGE_FEEDBACK);
270 cover_insns = PARAM_VALUE (TRACER_DYNAMIC_COVERAGE);
271 cover_insns = (weighted_insns * cover_insns + 50) / 100;
272 max_dup_insns = (ninsns * PARAM_VALUE (TRACER_MAX_CODE_GROWTH) + 50) / 100;
274 while (traced_insns < cover_insns && nduplicated < max_dup_insns
275 && !fibheap_empty (heap))
277 basic_block bb = (basic_block) fibheap_extract_min (heap);
283 blocks[bb->index] = NULL;
285 if (ignore_bb_p (bb))
287 gcc_assert (!bb_seen_p (bb));
289 n = find_trace (bb, trace);
292 traced_insns += bb->frequency * counts [bb->index];
293 if (blocks[bb->index])
295 fibheap_delete_node (heap, blocks[bb->index]);
296 blocks[bb->index] = NULL;
299 for (pos = 1; pos < n; pos++)
301 basic_block bb2 = trace[pos];
303 if (blocks[bb2->index])
305 fibheap_delete_node (heap, blocks[bb2->index]);
306 blocks[bb2->index] = NULL;
308 traced_insns += bb2->frequency * counts [bb2->index];
309 if (EDGE_COUNT (bb2->preds) > 1
310 && can_duplicate_block_p (bb2))
315 nduplicated += counts [bb2->index];
317 e = find_edge (bb, bb2);
319 copy = duplicate_block (bb2, e, bb);
320 flush_pending_stmts (e);
322 add_phi_args_after_copy (©, 1, NULL);
324 /* Reconsider the original copy of block we've duplicated.
325 Removing the most common predecessor may make it to be
328 fibheap_insert (heap, -bb2->frequency, bb2);
331 fprintf (dump_file, "Duplicated %i as %i [%i]\n",
332 bb2->index, copy->index, copy->frequency);
338 /* In case the trace became infrequent, stop duplicating. */
339 if (ignore_bb_p (bb))
343 fprintf (dump_file, " covered now %.1f\n\n",
344 traced_insns * 100.0 / weighted_insns);
347 fprintf (dump_file, "Duplicated %i insns (%i%%)\n", nduplicated,
348 nduplicated * 100 / ninsns);
350 free_original_copy_tables ();
351 sbitmap_free (bb_seen);
355 fibheap_delete (heap);
358 /* Main entry point to this file. */
363 gcc_assert (current_ir_type () == IR_GIMPLE);
365 if (n_basic_blocks <= NUM_FIXED_BLOCKS + 1)
368 mark_dfs_back_edges ();
370 dump_flow_info (dump_file, dump_flags);
372 /* Trace formation is done on the fly inside tail_duplicate */
375 /* FIXME: We really only need to do this when we know tail duplication
376 has altered the CFG. */
377 free_dominance_info (CDI_DOMINATORS);
379 dump_flow_info (dump_file, dump_flags);
387 return (optimize > 0 && flag_tracer && flag_reorder_blocks);
390 struct gimple_opt_pass pass_tracer =
395 gate_tracer, /* gate */
396 tracer, /* execute */
399 0, /* static_pass_number */
400 TV_TRACER, /* tv_id */
401 0, /* properties_required */
402 0, /* properties_provided */
403 0, /* properties_destroyed */
404 0, /* todo_flags_start */
406 | TODO_verify_ssa /* todo_flags_finish */