Bug Summary

File:build/gcc/tracer.cc
Warning:line 392, column 25
Division by zero

Annotated Source Code

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clang -cc1 -cc1 -triple x86_64-suse-linux -analyze -disable-free -clear-ast-before-backend -disable-llvm-verifier -discard-value-names -main-file-name tracer.cc -analyzer-checker=core -analyzer-checker=apiModeling -analyzer-checker=unix -analyzer-checker=deadcode -analyzer-checker=cplusplus -analyzer-checker=security.insecureAPI.UncheckedReturn -analyzer-checker=security.insecureAPI.getpw -analyzer-checker=security.insecureAPI.gets -analyzer-checker=security.insecureAPI.mktemp -analyzer-checker=security.insecureAPI.mkstemp -analyzer-checker=security.insecureAPI.vfork -analyzer-checker=nullability.NullPassedToNonnull -analyzer-checker=nullability.NullReturnedFromNonnull -analyzer-output plist -w -setup-static-analyzer -analyzer-config-compatibility-mode=true -mrelocation-model static -mframe-pointer=none -fmath-errno -ffp-contract=on -fno-rounding-math -mconstructor-aliases -funwind-tables=2 -target-cpu x86-64 -tune-cpu generic -debugger-tuning=gdb -fcoverage-compilation-dir=/buildworker/marxinbox-gcc-clang-static-analyzer/objdir/gcc -resource-dir /usr/lib64/clang/15.0.7 -D IN_GCC -D HAVE_CONFIG_H -I . -I . -I /buildworker/marxinbox-gcc-clang-static-analyzer/build/gcc -I /buildworker/marxinbox-gcc-clang-static-analyzer/build/gcc/. -I /buildworker/marxinbox-gcc-clang-static-analyzer/build/gcc/../include -I /buildworker/marxinbox-gcc-clang-static-analyzer/build/gcc/../libcpp/include -I /buildworker/marxinbox-gcc-clang-static-analyzer/build/gcc/../libcody -I /buildworker/marxinbox-gcc-clang-static-analyzer/build/gcc/../libdecnumber -I /buildworker/marxinbox-gcc-clang-static-analyzer/build/gcc/../libdecnumber/bid -I ../libdecnumber -I /buildworker/marxinbox-gcc-clang-static-analyzer/build/gcc/../libbacktrace -internal-isystem /usr/bin/../lib64/gcc/x86_64-suse-linux/13/../../../../include/c++/13 -internal-isystem /usr/bin/../lib64/gcc/x86_64-suse-linux/13/../../../../include/c++/13/x86_64-suse-linux -internal-isystem /usr/bin/../lib64/gcc/x86_64-suse-linux/13/../../../../include/c++/13/backward -internal-isystem /usr/lib64/clang/15.0.7/include -internal-isystem /usr/local/include -internal-isystem /usr/bin/../lib64/gcc/x86_64-suse-linux/13/../../../../x86_64-suse-linux/include -internal-externc-isystem /include -internal-externc-isystem /usr/include -O2 -Wno-narrowing -Wwrite-strings -Wno-long-long -Wno-variadic-macros -Wno-overlength-strings -fdeprecated-macro -fdebug-compilation-dir=/buildworker/marxinbox-gcc-clang-static-analyzer/objdir/gcc -ferror-limit 19 -fno-rtti -fgnuc-version=4.2.1 -vectorize-loops -vectorize-slp -analyzer-output=plist-html -analyzer-config silence-checkers=core.NullDereference -faddrsig -D__GCC_HAVE_DWARF2_CFI_ASM=1 -o /buildworker/marxinbox-gcc-clang-static-analyzer/objdir/clang-static-analyzer/2023-03-27-141847-20772-1/report-3MIA3X.plist -x c++ /buildworker/marxinbox-gcc-clang-static-analyzer/build/gcc/tracer.cc
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) 2001-2023 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 "backend.h"
40#include "rtl.h"
41#include "tree.h"
42#include "gimple.h"
43#include "cfghooks.h"
44#include "tree-pass.h"
45#include "profile.h"
46#include "cfganal.h"
47#include "gimple-iterator.h"
48#include "tree-cfg.h"
49#include "tree-ssa.h"
50#include "tree-inline.h"
51#include "cfgloop.h"
52#include "alloc-pool.h"
53#include "fibonacci_heap.h"
54#include "tracer.h"
55
56static void analyze_bb (basic_block, int *);
57static bool better_p (const_edge, const_edge);
58static edge find_best_successor (basic_block);
59static edge find_best_predecessor (basic_block);
60static int find_trace (basic_block, basic_block *);
61
62/* Minimal outgoing edge probability considered for superblock formation. */
63static int probability_cutoff;
64static int branch_ratio_cutoff;
65
66/* A bit BB->index is set if BB has already been seen, i.e. it is
67 connected to some trace already. */
68static sbitmap bb_seen;
69
70static inline void
71mark_bb_seen (basic_block bb)
72{
73 unsigned int size = SBITMAP_SIZE (bb_seen)((bb_seen)->n_bits);
74
75 if ((unsigned int)bb->index >= size)
76 bb_seen = sbitmap_resize (bb_seen, size * 2, 0);
77
78 bitmap_set_bit (bb_seen, bb->index);
79}
80
81static inline bool
82bb_seen_p (basic_block bb)
83{
84 return bitmap_bit_p (bb_seen, bb->index);
85}
86
87static sbitmap can_duplicate_bb;
88
89/* Cache VAL as value of can_duplicate_bb_p for BB. */
90static inline void
91cache_can_duplicate_bb_p (const_basic_block bb, bool val)
92{
93 if (val)
94 bitmap_set_bit (can_duplicate_bb, bb->index);
95}
96
97/* Return cached value of can_duplicate_bb_p for BB. */
98static bool
99cached_can_duplicate_bb_p (const_basic_block bb)
100{
101 if (can_duplicate_bb)
102 {
103 unsigned int size = SBITMAP_SIZE (can_duplicate_bb)((can_duplicate_bb)->n_bits);
104 if ((unsigned int)bb->index < size)
105 return bitmap_bit_p (can_duplicate_bb, bb->index);
106
107 /* Assume added bb's should not be duplicated. */
108 return false;
109 }
110
111 return can_duplicate_block_p (bb);
112}
113
114/* Return true if we should ignore the basic block for purposes of tracing. */
115bool
116ignore_bb_p (const_basic_block bb)
117{
118 if (bb->index < NUM_FIXED_BLOCKS(2))
119 return true;
120 if (optimize_bb_for_size_p (bb))
121 return true;
122
123 return !cached_can_duplicate_bb_p (bb);
124}
125
126/* Return number of instructions in the block. */
127
128static void
129analyze_bb (basic_block bb, int *count)
130{
131 gimple_stmt_iterator gsi;
132 gimple *stmt;
133 int n = 0;
134
135 for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
136 {
137 stmt = gsi_stmt (gsi);
138 n += estimate_num_insns (stmt, &eni_size_weights);
139 }
140 *count = n;
141
142 cache_can_duplicate_bb_p (bb, can_duplicate_block_p (CONST_CAST_BB (bb)(const_cast<struct basic_block_def *> (((bb))))));
143}
144
145/* Return true if E1 is more frequent than E2. */
146static bool
147better_p (const_edge e1, const_edge e2)
148{
149 if ((e1->count () > e2->count ()) || (e1->count () < e2->count ()))
150 return e1->count () > e2->count ();
151 /* This is needed to avoid changes in the decision after
152 CFG is modified. */
153 if (e1->src != e2->src)
154 return e1->src->index > e2->src->index;
155 return e1->dest->index > e2->dest->index;
156}
157
158/* Return most frequent successor of basic block BB. */
159
160static edge
161find_best_successor (basic_block bb)
162{
163 edge e;
164 edge best = NULLnullptr;
165 edge_iterator ei;
166
167 FOR_EACH_EDGE (e, ei, bb->succs)for ((ei) = ei_start_1 (&((bb->succs))); ei_cond ((ei)
, &(e)); ei_next (&(ei)))
168 {
169 if (!e->count ().initialized_p ())
170 return NULLnullptr;
171 if (!best || better_p (e, best))
172 best = e;
173 }
174 if (!best || ignore_bb_p (best->dest))
175 return NULLnullptr;
176 if (!best->probability.initialized_p ()
177 || best->probability.to_reg_br_prob_base () <= probability_cutoff)
178 return NULLnullptr;
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 = NULLnullptr;
189 edge_iterator ei;
190
191 FOR_EACH_EDGE (e, ei, bb->preds)for ((ei) = ei_start_1 (&((bb->preds))); ei_cond ((ei)
, &(e)); ei_next (&(ei)))
192 {
193 if (!e->count ().initialized_p ())
194 return NULLnullptr;
195 if (!best || better_p (e, best))
196 best = e;
197 }
198 if (!best || ignore_bb_p (best->src))
199 return NULLnullptr;
200 if (bb->count.initialized_p ()
201 && (best->count ().to_frequency (cfun(cfun + 0)) * REG_BR_PROB_BASE10000
202 < bb->count.to_frequency (cfun(cfun + 0)) * branch_ratio_cutoff))
203 return NULLnullptr;
204 return best;
205}
206
207/* Find the trace using bb and record it in the TRACE array.
208 Return number of basic blocks recorded. */
209
210static int
211find_trace (basic_block bb, basic_block *trace)
212{
213 int i = 0;
214 edge e;
215
216 if (dump_file)
217 fprintf (dump_file, "Trace seed %i [%i]", bb->index, bb->count.to_frequency (cfun(cfun + 0)));
218
219 while ((e = find_best_predecessor (bb)) != NULLnullptr)
220 {
221 basic_block bb2 = e->src;
222 if (bb_seen_p (bb2) || (e->flags & (EDGE_DFS_BACK | EDGE_COMPLEX(EDGE_ABNORMAL | EDGE_ABNORMAL_CALL | EDGE_EH | EDGE_PRESERVE
)))
223 || find_best_successor (bb2) != e)
224 break;
225 if (dump_file)
226 fprintf (dump_file, ",%i [%i]", bb->index, bb->count.to_frequency (cfun(cfun + 0)));
227 bb = bb2;
228 }
229 if (dump_file)
230 fprintf (dump_file, " forward %i [%i]", bb->index, bb->count.to_frequency (cfun(cfun + 0)));
231 trace[i++] = bb;
232
233 /* Follow the trace in forward direction. */
234 while ((e = find_best_successor (bb)) != NULLnullptr)
235 {
236 bb = e->dest;
237 if (bb_seen_p (bb) || (e->flags & (EDGE_DFS_BACK | EDGE_COMPLEX(EDGE_ABNORMAL | EDGE_ABNORMAL_CALL | EDGE_EH | EDGE_PRESERVE
)))
238 || find_best_predecessor (bb) != e)
239 break;
240 if (dump_file)
241 fprintf (dump_file, ",%i [%i]", bb->index, bb->count.to_frequency (cfun(cfun + 0)));
242 trace[i++] = bb;
243 }
244 if (dump_file)
245 fprintf (dump_file, "\n");
246 return i;
247}
248
249/* Duplicate block BB2, placing it after BB in the CFG. Return the
250 newly created block. */
251basic_block
252transform_duplicate (basic_block bb, basic_block bb2)
253{
254 edge e;
255 basic_block copy;
256
257 e = find_edge (bb, bb2);
258
259 copy = duplicate_block (bb2, e, bb);
260 flush_pending_stmts (e);
261
262 add_phi_args_after_copy (&copy, 1, NULLnullptr);
263
264 return (copy);
265}
266
267/* Look for basic blocks in frequency order, construct traces and tail duplicate
268 if profitable. */
269
270static bool
271tail_duplicate (void)
272{
273 auto_vec<fibonacci_node<long, basic_block_def>*> blocks;
274 blocks.safe_grow_cleared (last_basic_block_for_fn (cfun)(((cfun + 0))->cfg->x_last_basic_block), true);
275
276 basic_block *trace = XNEWVEC (basic_block, n_basic_blocks_for_fn (cfun))((basic_block *) xmalloc (sizeof (basic_block) * ((((cfun + 0
))->cfg->x_n_basic_blocks))));
277 int *counts = XNEWVEC (int, last_basic_block_for_fn (cfun))((int *) xmalloc (sizeof (int) * ((((cfun + 0))->cfg->x_last_basic_block
))));
278 int ninsns = 0, nduplicated = 0;
6
←
'ninsns' initialized to 0
→
279 gcov_type weighted_insns = 0, traced_insns = 0;
280 fibonacci_heap<long, basic_block_def> heap (LONG_MIN(-9223372036854775807L -1L));
281 gcov_type cover_insns;
282 int max_dup_insns;
283 basic_block bb;
284 bool changed = false;
285
286 /* Create an oversized sbitmap to reduce the chance that we need to
287 resize it. */
288 bb_seen = sbitmap_alloc (last_basic_block_for_fn (cfun)(((cfun + 0))->cfg->x_last_basic_block) * 2);
289 bitmap_clear (bb_seen);
290 can_duplicate_bb = sbitmap_alloc (last_basic_block_for_fn (cfun)(((cfun + 0))->cfg->x_last_basic_block));
291 bitmap_clear (can_duplicate_bb);
292 initialize_original_copy_tables ();
293
294 if (profile_info && profile_status_for_fn (cfun)(((cfun + 0))->cfg->x_profile_status) == PROFILE_READ)
7
←
Assuming 'profile_info' is null
→
295 probability_cutoff = param_tracer_min_branch_probability_feedbackglobal_options.x_param_tracer_min_branch_probability_feedback;
296 else
297 probability_cutoff = param_tracer_min_branch_probabilityglobal_options.x_param_tracer_min_branch_probability;
298 probability_cutoff = REG_BR_PROB_BASE10000 / 100 * probability_cutoff;
299
300 branch_ratio_cutoff =
301 (REG_BR_PROB_BASE10000 / 100 * param_tracer_min_branch_ratioglobal_options.x_param_tracer_min_branch_ratio);
302
303 FOR_EACH_BB_FN (bb, cfun)for (bb = ((cfun + 0))->cfg->x_entry_block_ptr->next_bb
; bb != ((cfun + 0))->cfg->x_exit_block_ptr; bb = bb->
next_bb)
8
←
Assuming 'bb' is equal to field 'x_exit_block_ptr'
→
304 {
305 int n;
306 analyze_bb (bb, &n);
307 if (!ignore_bb_p (bb))
308 blocks[bb->index] = heap.insert (-bb->count.to_frequency (cfun(cfun + 0)), bb);
309
310 counts [bb->index] = n;
311 ninsns += n;
312 weighted_insns += n * bb->count.to_frequency (cfun(cfun + 0));
313 }
314
315 if (profile_info
8.1
'profile_info' is null
 && profile_status_for_fn (cfun)(((cfun + 0))->cfg->x_profile_status) == PROFILE_READ)
316 cover_insns = param_tracer_dynamic_coverage_feedbackglobal_options.x_param_tracer_dynamic_coverage_feedback;
317 else
318 cover_insns = param_tracer_dynamic_coverageglobal_options.x_param_tracer_dynamic_coverage;
319 cover_insns = (weighted_insns * cover_insns + 50) / 100;
320 max_dup_insns = (ninsns * param_tracer_max_code_growthglobal_options.x_param_tracer_max_code_growth + 50) / 100;
321
322 while (traced_insns
8.2
'traced_insns' is >= 'cover_insns'
 < cover_insns && nduplicated < max_dup_insns
323 && !heap.empty ())
324 {
325 basic_block bb = heap.extract_min ();
326 int n, pos;
327
328 if (!bb)
329 break;
330
331 blocks[bb->index] = NULLnullptr;
332
333 if (ignore_bb_p (bb))
334 continue;
335 gcc_assert (!bb_seen_p (bb))((void)(!(!bb_seen_p (bb)) ? fancy_abort ("/buildworker/marxinbox-gcc-clang-static-analyzer/build/gcc/tracer.cc"
, 335, __FUNCTION__), 0 : 0));
336
337 n = find_trace (bb, trace);
338
339 bb = trace[0];
340 traced_insns += bb->count.to_frequency (cfun(cfun + 0)) * counts [bb->index];
341 if (blocks[bb->index])
342 {
343 heap.delete_node (blocks[bb->index]);
344 blocks[bb->index] = NULLnullptr;
345 }
346
347 for (pos = 1; pos < n; pos++)
348 {
349 basic_block bb2 = trace[pos];
350
351 if (blocks[bb2->index])
352 {
353 heap.delete_node (blocks[bb2->index]);
354 blocks[bb2->index] = NULLnullptr;
355 }
356 traced_insns += bb2->count.to_frequency (cfun(cfun + 0)) * counts [bb2->index];
357 if (EDGE_COUNT (bb2->preds)vec_safe_length (bb2->preds) > 1
358 && can_duplicate_block_p (bb2)
359 /* We have the tendency to duplicate the loop header
360 of all do { } while loops. Do not do that - it is
361 not profitable and it might create a loop with multiple
362 entries or at least rotate the loop. */
363 && bb2->loop_father->header != bb2)
364 {
365 nduplicated += counts [bb2->index];
366 basic_block copy = transform_duplicate (bb, bb2);
367
368 /* Reconsider the original copy of block we've duplicated.
369 Removing the most common predecessor may make it to be
370 head. */
371 blocks[bb2->index] = heap.insert (-bb2->count.to_frequency (cfun(cfun + 0)), bb2);
372
373 if (dump_file)
374 fprintf (dump_file, "Duplicated %i as %i [%i]\n",
375 bb2->index, copy->index, copy->count.to_frequency (cfun(cfun + 0)));
376
377 bb2 = copy;
378 changed = true;
379 }
380 mark_bb_seen (bb2);
381 bb = bb2;
382 /* In case the trace became infrequent, stop duplicating. */
383 if (ignore_bb_p (bb))
384 break;
385 }
386 if (dump_file)
387 fprintf (dump_file, " covered now %.1f\n\n",
388 traced_insns * 100.0 / weighted_insns);
389 }
390 if (dump_file)
9
←
Assuming 'dump_file' is non-null
→
10
←
Taking true branch
→
391 fprintf (dump_file, "Duplicated %i insns (%i%%)\n", nduplicated,
392 nduplicated * 100 / ninsns);
11
←
Division by zero
393
394 free_original_copy_tables ();
395 sbitmap_free (bb_seen);
396 sbitmap_free (can_duplicate_bb);
397 can_duplicate_bb = NULLnullptr;
398 free (trace);
399 free (counts);
400
401 return changed;
402}
403
404namespace {
405
406const pass_data pass_data_tracer =
407{
408 GIMPLE_PASS, /* type */
409 "tracer", /* name */
410 OPTGROUP_NONE, /* optinfo_flags */
411 TV_TRACER, /* tv_id */
412 0, /* properties_required */
413 0, /* properties_provided */
414 0, /* properties_destroyed */
415 0, /* todo_flags_start */
416 TODO_update_ssa(1 << 11), /* todo_flags_finish */
417};
418
419class pass_tracer : public gimple_opt_pass
420{
421public:
422 pass_tracer (gcc::context *ctxt)
423 : gimple_opt_pass (pass_data_tracer, ctxt)
424 {}
425
426 /* opt_pass methods: */
427 bool gate (function *) final override
428 {
429 return (optimizeglobal_options.x_optimize > 0 && flag_tracerglobal_options.x_flag_tracer && flag_reorder_blocksglobal_options.x_flag_reorder_blocks);
430 }
431
432 unsigned int execute (function *) final override;
433
434}; // class pass_tracer
435
436unsigned int
437pass_tracer::execute (function *fun)
438{
439 bool changed;
440
441 if (n_basic_blocks_for_fn (fun)((fun)->cfg->x_n_basic_blocks) <= NUM_FIXED_BLOCKS(2) + 1)
1
Assuming the condition is false
→
2
←
Taking false branch
→
442 return 0;
443
444 mark_dfs_back_edges ();
445 if (dump_file)
3
←
Assuming 'dump_file' is null
→
4
←
Taking false branch
→
446 brief_dump_cfg (dump_file, dump_flags);
447
448 /* Trace formation is done on the fly inside tail_duplicate */
449 changed = tail_duplicate ();
5
←
Calling 'tail_duplicate'
→
450 if (changed)
451 {
452 free_dominance_info (CDI_DOMINATORS);
453 /* If we changed the CFG schedule loops for fixup by cleanup_cfg. */
454 loops_state_set (LOOPS_NEED_FIXUP);
455 }
456
457 if (dump_file)
458 brief_dump_cfg (dump_file, dump_flags);
459
460 return changed ? TODO_cleanup_cfg(1 << 5) : 0;
461}
462} // anon namespace
463
464gimple_opt_pass *
465make_pass_tracer (gcc::context *ctxt)
466{
467 return new pass_tracer (ctxt);
468}