LLVM OpenMP* Runtime Library
kmp_taskdeps.cpp
1 /*
2  * kmp_taskdeps.cpp
3  */
4 
5 //===----------------------------------------------------------------------===//
6 //
7 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
8 // See https://llvm.org/LICENSE.txt for license information.
9 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
10 //
11 //===----------------------------------------------------------------------===//
12 
13 //#define KMP_SUPPORT_GRAPH_OUTPUT 1
14 
15 #include "kmp.h"
16 #include "kmp_io.h"
17 #include "kmp_wait_release.h"
18 #include "kmp_taskdeps.h"
19 #if OMPT_SUPPORT
20 #include "ompt-specific.h"
21 #endif
22 
23 // TODO: Improve memory allocation? keep a list of pre-allocated structures?
24 // allocate in blocks? re-use list finished list entries?
25 // TODO: don't use atomic ref counters for stack-allocated nodes.
26 // TODO: find an alternate to atomic refs for heap-allocated nodes?
27 // TODO: Finish graph output support
28 // TODO: kmp_lock_t seems a tad to big (and heavy weight) for this. Check other
29 // runtime locks
30 // TODO: Any ITT support needed?
31 
32 #ifdef KMP_SUPPORT_GRAPH_OUTPUT
33 static std::atomic<kmp_int32> kmp_node_id_seed = 0;
34 #endif
35 
36 static void __kmp_init_node(kmp_depnode_t *node, bool on_stack) {
37  node->dn.successors = NULL;
38  node->dn.task = NULL; // will point to the right task
39  // once dependences have been processed
40  for (int i = 0; i < MAX_MTX_DEPS; ++i)
41  node->dn.mtx_locks[i] = NULL;
42  node->dn.mtx_num_locks = 0;
43  __kmp_init_lock(&node->dn.lock);
44  // Init creates the first reference. Bit 0 indicates that this node
45  // resides on the stack. The refcount is incremented and decremented in
46  // steps of two, maintaining use of even numbers for heap nodes and odd
47  // numbers for stack nodes.
48  KMP_ATOMIC_ST_RLX(&node->dn.nrefs, on_stack ? 3 : 2);
49 #ifdef KMP_SUPPORT_GRAPH_OUTPUT
50  node->dn.id = KMP_ATOMIC_INC(&kmp_node_id_seed);
51 #endif
52 #if USE_ITT_BUILD && USE_ITT_NOTIFY
53  __itt_sync_create(node, "OMP task dep node", NULL, 0);
54 #endif
55 }
56 
57 static inline kmp_depnode_t *__kmp_node_ref(kmp_depnode_t *node) {
58  KMP_ATOMIC_ADD(&node->dn.nrefs, 2);
59  return node;
60 }
61 
62 enum { KMP_DEPHASH_OTHER_SIZE = 97, KMP_DEPHASH_MASTER_SIZE = 997 };
63 
64 size_t sizes[] = {997, 2003, 4001, 8191, 16001, 32003, 64007, 131071, 270029};
65 const size_t MAX_GEN = 8;
66 
67 static inline size_t __kmp_dephash_hash(kmp_intptr_t addr, size_t hsize) {
68  // TODO alternate to try: set = (((Addr64)(addrUsefulBits * 9.618)) %
69  // m_num_sets );
70  return ((addr >> 6) ^ (addr >> 2)) % hsize;
71 }
72 
73 static kmp_dephash_t *__kmp_dephash_extend(kmp_info_t *thread,
74  kmp_dephash_t *current_dephash) {
75  kmp_dephash_t *h;
76 
77  size_t gen = current_dephash->generation + 1;
78  if (gen >= MAX_GEN)
79  return current_dephash;
80  size_t new_size = sizes[gen];
81 
82  size_t size_to_allocate =
83  new_size * sizeof(kmp_dephash_entry_t *) + sizeof(kmp_dephash_t);
84 
85 #if USE_FAST_MEMORY
86  h = (kmp_dephash_t *)__kmp_fast_allocate(thread, size_to_allocate);
87 #else
88  h = (kmp_dephash_t *)__kmp_thread_malloc(thread, size_to_allocate);
89 #endif
90 
91  h->size = new_size;
92  h->nelements = current_dephash->nelements;
93  h->buckets = (kmp_dephash_entry **)(h + 1);
94  h->generation = gen;
95  h->nconflicts = 0;
96  h->last_all = current_dephash->last_all;
97 
98  // make sure buckets are properly initialized
99  for (size_t i = 0; i < new_size; i++) {
100  h->buckets[i] = NULL;
101  }
102 
103  // insert existing elements in the new table
104  for (size_t i = 0; i < current_dephash->size; i++) {
105  kmp_dephash_entry_t *next, *entry;
106  for (entry = current_dephash->buckets[i]; entry; entry = next) {
107  next = entry->next_in_bucket;
108  // Compute the new hash using the new size, and insert the entry in
109  // the new bucket.
110  size_t new_bucket = __kmp_dephash_hash(entry->addr, h->size);
111  entry->next_in_bucket = h->buckets[new_bucket];
112  if (entry->next_in_bucket) {
113  h->nconflicts++;
114  }
115  h->buckets[new_bucket] = entry;
116  }
117  }
118 
119  // Free old hash table
120 #if USE_FAST_MEMORY
121  __kmp_fast_free(thread, current_dephash);
122 #else
123  __kmp_thread_free(thread, current_dephash);
124 #endif
125 
126  return h;
127 }
128 
129 static kmp_dephash_t *__kmp_dephash_create(kmp_info_t *thread,
130  kmp_taskdata_t *current_task) {
131  kmp_dephash_t *h;
132 
133  size_t h_size;
134 
135  if (current_task->td_flags.tasktype == TASK_IMPLICIT)
136  h_size = KMP_DEPHASH_MASTER_SIZE;
137  else
138  h_size = KMP_DEPHASH_OTHER_SIZE;
139 
140  size_t size = h_size * sizeof(kmp_dephash_entry_t *) + sizeof(kmp_dephash_t);
141 
142 #if USE_FAST_MEMORY
143  h = (kmp_dephash_t *)__kmp_fast_allocate(thread, size);
144 #else
145  h = (kmp_dephash_t *)__kmp_thread_malloc(thread, size);
146 #endif
147  h->size = h_size;
148 
149  h->generation = 0;
150  h->nelements = 0;
151  h->nconflicts = 0;
152  h->buckets = (kmp_dephash_entry **)(h + 1);
153  h->last_all = NULL;
154 
155  for (size_t i = 0; i < h_size; i++)
156  h->buckets[i] = 0;
157 
158  return h;
159 }
160 
161 static kmp_dephash_entry *__kmp_dephash_find(kmp_info_t *thread,
162  kmp_dephash_t **hash,
163  kmp_intptr_t addr) {
164  kmp_dephash_t *h = *hash;
165  if (h->nelements != 0 && h->nconflicts / h->size >= 1) {
166  *hash = __kmp_dephash_extend(thread, h);
167  h = *hash;
168  }
169  size_t bucket = __kmp_dephash_hash(addr, h->size);
170 
171  kmp_dephash_entry_t *entry;
172  for (entry = h->buckets[bucket]; entry; entry = entry->next_in_bucket)
173  if (entry->addr == addr)
174  break;
175 
176  if (entry == NULL) {
177 // create entry. This is only done by one thread so no locking required
178 #if USE_FAST_MEMORY
179  entry = (kmp_dephash_entry_t *)__kmp_fast_allocate(
180  thread, sizeof(kmp_dephash_entry_t));
181 #else
182  entry = (kmp_dephash_entry_t *)__kmp_thread_malloc(
183  thread, sizeof(kmp_dephash_entry_t));
184 #endif
185  entry->addr = addr;
186  if (!h->last_all) // no predecessor task with omp_all_memory dependence
187  entry->last_out = NULL;
188  else // else link the omp_all_memory depnode to the new entry
189  entry->last_out = __kmp_node_ref(h->last_all);
190  entry->last_set = NULL;
191  entry->prev_set = NULL;
192  entry->last_flag = 0;
193  entry->mtx_lock = NULL;
194  entry->next_in_bucket = h->buckets[bucket];
195  h->buckets[bucket] = entry;
196  h->nelements++;
197  if (entry->next_in_bucket)
198  h->nconflicts++;
199  }
200  return entry;
201 }
202 
203 static kmp_depnode_list_t *__kmp_add_node(kmp_info_t *thread,
204  kmp_depnode_list_t *list,
205  kmp_depnode_t *node) {
206  kmp_depnode_list_t *new_head;
207 
208 #if USE_FAST_MEMORY
209  new_head = (kmp_depnode_list_t *)__kmp_fast_allocate(
210  thread, sizeof(kmp_depnode_list_t));
211 #else
212  new_head = (kmp_depnode_list_t *)__kmp_thread_malloc(
213  thread, sizeof(kmp_depnode_list_t));
214 #endif
215 
216  new_head->node = __kmp_node_ref(node);
217  new_head->next = list;
218 
219  return new_head;
220 }
221 
222 static inline void __kmp_track_dependence(kmp_int32 gtid, kmp_depnode_t *source,
223  kmp_depnode_t *sink,
224  kmp_task_t *sink_task) {
225 #if OMPX_TASKGRAPH
226  kmp_taskdata_t *task_source = KMP_TASK_TO_TASKDATA(source->dn.task);
227  kmp_taskdata_t *task_sink = KMP_TASK_TO_TASKDATA(sink_task);
228  if (source->dn.task && sink_task) {
229  // Not supporting dependency between two tasks that one is within the TDG
230  // and the other is not
231  KMP_ASSERT(task_source->is_taskgraph == task_sink->is_taskgraph);
232  }
233  if (task_sink->is_taskgraph &&
234  __kmp_tdg_is_recording(task_sink->tdg->tdg_status)) {
235  kmp_node_info_t *source_info =
236  &task_sink->tdg->record_map[task_source->td_tdg_task_id];
237  bool exists = false;
238  for (int i = 0; i < source_info->nsuccessors; i++) {
239  if (source_info->successors[i] == task_sink->td_tdg_task_id) {
240  exists = true;
241  break;
242  }
243  }
244  if (!exists) {
245  if (source_info->nsuccessors >= source_info->successors_size) {
246  kmp_uint old_size = source_info->successors_size;
247  source_info->successors_size = 2 * source_info->successors_size;
248  kmp_int32 *old_succ_ids = source_info->successors;
249  kmp_int32 *new_succ_ids = (kmp_int32 *)__kmp_allocate(
250  source_info->successors_size * sizeof(kmp_int32));
251  KMP_MEMCPY(new_succ_ids, old_succ_ids, old_size * sizeof(kmp_int32));
252  source_info->successors = new_succ_ids;
253  __kmp_free(old_succ_ids);
254  }
255 
256  source_info->successors[source_info->nsuccessors] =
257  task_sink->td_tdg_task_id;
258  source_info->nsuccessors++;
259 
260  kmp_node_info_t *sink_info =
261  &(task_sink->tdg->record_map[task_sink->td_tdg_task_id]);
262  sink_info->npredecessors++;
263  }
264  }
265 #endif
266 #ifdef KMP_SUPPORT_GRAPH_OUTPUT
267  kmp_taskdata_t *task_source = KMP_TASK_TO_TASKDATA(source->dn.task);
268  // do not use sink->dn.task as that is only filled after the dependences
269  // are already processed!
270  kmp_taskdata_t *task_sink = KMP_TASK_TO_TASKDATA(sink_task);
271 
272  __kmp_printf("%d(%s) -> %d(%s)\n", source->dn.id,
273  task_source->td_ident->psource, sink->dn.id,
274  task_sink->td_ident->psource);
275 #endif
276 #if OMPT_SUPPORT && OMPT_OPTIONAL
277  /* OMPT tracks dependences between task (a=source, b=sink) in which
278  task a blocks the execution of b through the ompt_new_dependence_callback
279  */
280  if (ompt_enabled.ompt_callback_task_dependence) {
281  kmp_taskdata_t *task_source = KMP_TASK_TO_TASKDATA(source->dn.task);
282  ompt_data_t *sink_data;
283  if (sink_task)
284  sink_data = &(KMP_TASK_TO_TASKDATA(sink_task)->ompt_task_info.task_data);
285  else
286  sink_data = &__kmp_threads[gtid]->th.ompt_thread_info.task_data;
287 
288  ompt_callbacks.ompt_callback(ompt_callback_task_dependence)(
289  &(task_source->ompt_task_info.task_data), sink_data);
290  }
291 #endif /* OMPT_SUPPORT && OMPT_OPTIONAL */
292 }
293 
294 kmp_base_depnode_t *__kmpc_task_get_depnode(kmp_task_t *task) {
295  kmp_taskdata_t *td = KMP_TASK_TO_TASKDATA(task);
296  return td->td_depnode ? &(td->td_depnode->dn) : NULL;
297 }
298 
299 kmp_depnode_list_t *__kmpc_task_get_successors(kmp_task_t *task) {
300  kmp_taskdata_t *td = KMP_TASK_TO_TASKDATA(task);
301  return td->td_depnode->dn.successors;
302 }
303 
304 static inline kmp_int32
305 __kmp_depnode_link_successor(kmp_int32 gtid, kmp_info_t *thread,
306  kmp_task_t *task, kmp_depnode_t *node,
307  kmp_depnode_list_t *plist) {
308  if (!plist)
309  return 0;
310  kmp_int32 npredecessors = 0;
311  // link node as successor of list elements
312  for (kmp_depnode_list_t *p = plist; p; p = p->next) {
313  kmp_depnode_t *dep = p->node;
314 #if OMPX_TASKGRAPH
315  kmp_tdg_status tdg_status = KMP_TDG_NONE;
316  if (task) {
317  kmp_taskdata_t *td = KMP_TASK_TO_TASKDATA(task);
318  if (td->is_taskgraph)
319  tdg_status = KMP_TASK_TO_TASKDATA(task)->tdg->tdg_status;
320  if (__kmp_tdg_is_recording(tdg_status))
321  __kmp_track_dependence(gtid, dep, node, task);
322  }
323 #endif
324  if (dep->dn.task) {
325  KMP_ACQUIRE_DEPNODE(gtid, dep);
326  if (dep->dn.task) {
327  if (!dep->dn.successors || dep->dn.successors->node != node) {
328 #if OMPX_TASKGRAPH
329  if (!(__kmp_tdg_is_recording(tdg_status)) && task)
330 #endif
331  __kmp_track_dependence(gtid, dep, node, task);
332  dep->dn.successors = __kmp_add_node(thread, dep->dn.successors, node);
333  KA_TRACE(40, ("__kmp_process_deps: T#%d adding dependence from %p to "
334  "%p\n",
335  gtid, KMP_TASK_TO_TASKDATA(dep->dn.task),
336  KMP_TASK_TO_TASKDATA(task)));
337  npredecessors++;
338  }
339  }
340  KMP_RELEASE_DEPNODE(gtid, dep);
341  }
342  }
343  return npredecessors;
344 }
345 
346 // Add the edge 'sink' -> 'source' in the task dependency graph
347 static inline kmp_int32 __kmp_depnode_link_successor(kmp_int32 gtid,
348  kmp_info_t *thread,
349  kmp_task_t *task,
350  kmp_depnode_t *source,
351  kmp_depnode_t *sink) {
352  if (!sink)
353  return 0;
354  kmp_int32 npredecessors = 0;
355 #if OMPX_TASKGRAPH
356  kmp_tdg_status tdg_status = KMP_TDG_NONE;
357  kmp_taskdata_t *td = KMP_TASK_TO_TASKDATA(task);
358  if (task) {
359  if (td->is_taskgraph)
360  tdg_status = KMP_TASK_TO_TASKDATA(task)->tdg->tdg_status;
361  if (__kmp_tdg_is_recording(tdg_status) && sink->dn.task)
362  __kmp_track_dependence(gtid, sink, source, task);
363  }
364 #endif
365  if (sink->dn.task) {
366  // synchronously add source to sink' list of successors
367  KMP_ACQUIRE_DEPNODE(gtid, sink);
368  if (sink->dn.task) {
369  if (!sink->dn.successors || sink->dn.successors->node != source) {
370 #if OMPX_TASKGRAPH
371  if (!(__kmp_tdg_is_recording(tdg_status)) && task)
372 #endif
373  __kmp_track_dependence(gtid, sink, source, task);
374  sink->dn.successors = __kmp_add_node(thread, sink->dn.successors, source);
375  KA_TRACE(40, ("__kmp_process_deps: T#%d adding dependence from %p to "
376  "%p\n",
377  gtid, KMP_TASK_TO_TASKDATA(sink->dn.task),
378  KMP_TASK_TO_TASKDATA(task)));
379 #if OMPX_TASKGRAPH
380  if (__kmp_tdg_is_recording(tdg_status)) {
381  kmp_taskdata_t *tdd = KMP_TASK_TO_TASKDATA(sink->dn.task);
382  if (tdd->is_taskgraph) {
383  if (tdd->td_flags.onced)
384  // decrement npredecessors if sink->dn.task belongs to a taskgraph
385  // and
386  // 1) the task is reset to its initial state (by kmp_free_task) or
387  // 2) the task is complete but not yet reset
388  npredecessors--;
389  }
390  }
391 #endif
392  npredecessors++;
393  }
394  }
395  KMP_RELEASE_DEPNODE(gtid, sink);
396  }
397  return npredecessors;
398 }
399 
400 static inline kmp_int32
401 __kmp_process_dep_all(kmp_int32 gtid, kmp_depnode_t *node, kmp_dephash_t *h,
402  bool dep_barrier, kmp_task_t *task) {
403  KA_TRACE(30, ("__kmp_process_dep_all: T#%d processing dep_all, "
404  "dep_barrier = %d\n",
405  gtid, dep_barrier));
406  kmp_info_t *thread = __kmp_threads[gtid];
407  kmp_int32 npredecessors = 0;
408 
409  // process previous omp_all_memory node if any
410  npredecessors +=
411  __kmp_depnode_link_successor(gtid, thread, task, node, h->last_all);
412  __kmp_node_deref(thread, h->last_all);
413  if (!dep_barrier) {
414  h->last_all = __kmp_node_ref(node);
415  } else {
416  // if this is a sync point in the serial sequence, then the previous
417  // outputs are guaranteed to be completed after the execution of this
418  // task so the previous output nodes can be cleared.
419  h->last_all = NULL;
420  }
421 
422  // process all regular dependences
423  for (size_t i = 0; i < h->size; i++) {
424  kmp_dephash_entry_t *info = h->buckets[i];
425  if (!info) // skip empty slots in dephash
426  continue;
427  for (; info; info = info->next_in_bucket) {
428  // for each entry the omp_all_memory works as OUT dependence
429  kmp_depnode_t *last_out = info->last_out;
430  kmp_depnode_list_t *last_set = info->last_set;
431  kmp_depnode_list_t *prev_set = info->prev_set;
432  if (last_set) {
433  npredecessors +=
434  __kmp_depnode_link_successor(gtid, thread, task, node, last_set);
435  __kmp_depnode_list_free(thread, last_set);
436  __kmp_depnode_list_free(thread, prev_set);
437  info->last_set = NULL;
438  info->prev_set = NULL;
439  info->last_flag = 0; // no sets in this dephash entry
440  } else {
441  npredecessors +=
442  __kmp_depnode_link_successor(gtid, thread, task, node, last_out);
443  }
444  __kmp_node_deref(thread, last_out);
445  if (!dep_barrier) {
446  info->last_out = __kmp_node_ref(node);
447  } else {
448  info->last_out = NULL;
449  }
450  }
451  }
452  KA_TRACE(30, ("__kmp_process_dep_all: T#%d found %d predecessors\n", gtid,
453  npredecessors));
454  return npredecessors;
455 }
456 
457 template <bool filter>
458 static inline kmp_int32
459 __kmp_process_deps(kmp_int32 gtid, kmp_depnode_t *node, kmp_dephash_t **hash,
460  bool dep_barrier, kmp_int32 ndeps,
461  kmp_depend_info_t *dep_list, kmp_task_t *task) {
462  KA_TRACE(30, ("__kmp_process_deps<%d>: T#%d processing %d dependences : "
463  "dep_barrier = %d\n",
464  filter, gtid, ndeps, dep_barrier));
465 
466  kmp_info_t *thread = __kmp_threads[gtid];
467  kmp_int32 npredecessors = 0;
468  for (kmp_int32 i = 0; i < ndeps; i++) {
469  const kmp_depend_info_t *dep = &dep_list[i];
470 
471  if (filter && dep->base_addr == 0)
472  continue; // skip filtered entries
473 
474  kmp_dephash_entry_t *info =
475  __kmp_dephash_find(thread, hash, dep->base_addr);
476  kmp_depnode_t *last_out = info->last_out;
477  kmp_depnode_list_t *last_set = info->last_set;
478  kmp_depnode_list_t *prev_set = info->prev_set;
479 
480  if (dep->flags.out) { // out or inout --> clean lists if any
481  if (last_set) {
482  npredecessors +=
483  __kmp_depnode_link_successor(gtid, thread, task, node, last_set);
484  __kmp_depnode_list_free(thread, last_set);
485  __kmp_depnode_list_free(thread, prev_set);
486  info->last_set = NULL;
487  info->prev_set = NULL;
488  info->last_flag = 0; // no sets in this dephash entry
489  } else {
490  npredecessors +=
491  __kmp_depnode_link_successor(gtid, thread, task, node, last_out);
492  }
493  __kmp_node_deref(thread, last_out);
494  if (!dep_barrier) {
495  info->last_out = __kmp_node_ref(node);
496  } else {
497  // if this is a sync point in the serial sequence, then the previous
498  // outputs are guaranteed to be completed after the execution of this
499  // task so the previous output nodes can be cleared.
500  info->last_out = NULL;
501  }
502  } else { // either IN or MTX or SET
503  if (info->last_flag == 0 || info->last_flag == dep->flag) {
504  // last_set either didn't exist or of same dep kind
505  // link node as successor of the last_out if any
506  npredecessors +=
507  __kmp_depnode_link_successor(gtid, thread, task, node, last_out);
508  // link node as successor of all nodes in the prev_set if any
509  npredecessors +=
510  __kmp_depnode_link_successor(gtid, thread, task, node, prev_set);
511  if (dep_barrier) {
512  // clean last_out and prev_set if any; don't touch last_set
513  __kmp_node_deref(thread, last_out);
514  info->last_out = NULL;
515  __kmp_depnode_list_free(thread, prev_set);
516  info->prev_set = NULL;
517  }
518  } else { // last_set is of different dep kind, make it prev_set
519  // link node as successor of all nodes in the last_set
520  npredecessors +=
521  __kmp_depnode_link_successor(gtid, thread, task, node, last_set);
522  // clean last_out if any
523  __kmp_node_deref(thread, last_out);
524  info->last_out = NULL;
525  // clean prev_set if any
526  __kmp_depnode_list_free(thread, prev_set);
527  if (!dep_barrier) {
528  // move last_set to prev_set, new last_set will be allocated
529  info->prev_set = last_set;
530  } else {
531  info->prev_set = NULL;
532  info->last_flag = 0;
533  }
534  info->last_set = NULL;
535  }
536  // for dep_barrier last_flag value should remain:
537  // 0 if last_set is empty, unchanged otherwise
538  if (!dep_barrier) {
539  info->last_flag = dep->flag; // store dep kind of the last_set
540  info->last_set = __kmp_add_node(thread, info->last_set, node);
541  }
542  // check if we are processing MTX dependency
543  if (dep->flag == KMP_DEP_MTX) {
544  if (info->mtx_lock == NULL) {
545  info->mtx_lock = (kmp_lock_t *)__kmp_allocate(sizeof(kmp_lock_t));
546  __kmp_init_lock(info->mtx_lock);
547  }
548  KMP_DEBUG_ASSERT(node->dn.mtx_num_locks < MAX_MTX_DEPS);
549  kmp_int32 m;
550  // Save lock in node's array
551  for (m = 0; m < MAX_MTX_DEPS; ++m) {
552  // sort pointers in decreasing order to avoid potential livelock
553  if (node->dn.mtx_locks[m] < info->mtx_lock) {
554  KMP_DEBUG_ASSERT(!node->dn.mtx_locks[node->dn.mtx_num_locks]);
555  for (int n = node->dn.mtx_num_locks; n > m; --n) {
556  // shift right all lesser non-NULL pointers
557  KMP_DEBUG_ASSERT(node->dn.mtx_locks[n - 1] != NULL);
558  node->dn.mtx_locks[n] = node->dn.mtx_locks[n - 1];
559  }
560  node->dn.mtx_locks[m] = info->mtx_lock;
561  break;
562  }
563  }
564  KMP_DEBUG_ASSERT(m < MAX_MTX_DEPS); // must break from loop
565  node->dn.mtx_num_locks++;
566  }
567  }
568  }
569  KA_TRACE(30, ("__kmp_process_deps<%d>: T#%d found %d predecessors\n", filter,
570  gtid, npredecessors));
571  return npredecessors;
572 }
573 
574 #define NO_DEP_BARRIER (false)
575 #define DEP_BARRIER (true)
576 
577 // returns true if the task has any outstanding dependence
578 static bool __kmp_check_deps(kmp_int32 gtid, kmp_depnode_t *node,
579  kmp_task_t *task, kmp_dephash_t **hash,
580  bool dep_barrier, kmp_int32 ndeps,
581  kmp_depend_info_t *dep_list,
582  kmp_int32 ndeps_noalias,
583  kmp_depend_info_t *noalias_dep_list) {
584  int i, n_mtxs = 0, dep_all = 0;
585 #if KMP_DEBUG
586  kmp_taskdata_t *taskdata = KMP_TASK_TO_TASKDATA(task);
587 #endif
588  KA_TRACE(20, ("__kmp_check_deps: T#%d checking dependences for task %p : %d "
589  "possibly aliased dependences, %d non-aliased dependences : "
590  "dep_barrier=%d .\n",
591  gtid, taskdata, ndeps, ndeps_noalias, dep_barrier));
592 
593  // Filter deps in dep_list
594  // TODO: Different algorithm for large dep_list ( > 10 ? )
595  for (i = 0; i < ndeps; i++) {
596  if (dep_list[i].base_addr != 0 &&
597  dep_list[i].base_addr != (kmp_intptr_t)KMP_SIZE_T_MAX) {
598  KMP_DEBUG_ASSERT(
599  dep_list[i].flag == KMP_DEP_IN || dep_list[i].flag == KMP_DEP_OUT ||
600  dep_list[i].flag == KMP_DEP_INOUT ||
601  dep_list[i].flag == KMP_DEP_MTX || dep_list[i].flag == KMP_DEP_SET);
602  for (int j = i + 1; j < ndeps; j++) {
603  if (dep_list[i].base_addr == dep_list[j].base_addr) {
604  if (dep_list[i].flag != dep_list[j].flag) {
605  // two different dependences on same address work identical to OUT
606  dep_list[i].flag = KMP_DEP_OUT;
607  }
608  dep_list[j].base_addr = 0; // Mark j element as void
609  }
610  }
611  if (dep_list[i].flag == KMP_DEP_MTX) {
612  // limit number of mtx deps to MAX_MTX_DEPS per node
613  if (n_mtxs < MAX_MTX_DEPS && task != NULL) {
614  ++n_mtxs;
615  } else {
616  dep_list[i].flag = KMP_DEP_OUT; // downgrade mutexinoutset to inout
617  }
618  }
619  } else if (dep_list[i].flag == KMP_DEP_ALL ||
620  dep_list[i].base_addr == (kmp_intptr_t)KMP_SIZE_T_MAX) {
621  // omp_all_memory dependence can be marked by compiler by either
622  // (addr=0 && flag=0x80) (flag KMP_DEP_ALL), or (addr=-1).
623  // omp_all_memory overrides all other dependences if any
624  dep_all = 1;
625  break;
626  }
627  }
628 
629  // doesn't need to be atomic as no other thread is going to be accessing this
630  // node just yet.
631  // npredecessors is set -1 to ensure that none of the releasing tasks queues
632  // this task before we have finished processing all the dependences
633  node->dn.npredecessors = -1;
634 
635  // used to pack all npredecessors additions into a single atomic operation at
636  // the end
637  int npredecessors;
638 
639  if (!dep_all) { // regular dependences
640  npredecessors = __kmp_process_deps<true>(gtid, node, hash, dep_barrier,
641  ndeps, dep_list, task);
642  npredecessors += __kmp_process_deps<false>(
643  gtid, node, hash, dep_barrier, ndeps_noalias, noalias_dep_list, task);
644  } else { // omp_all_memory dependence
645  npredecessors = __kmp_process_dep_all(gtid, node, *hash, dep_barrier, task);
646  }
647 
648  node->dn.task = task;
649  KMP_MB();
650 
651  // Account for our initial fake value
652  npredecessors++;
653 
654  // Update predecessors and obtain current value to check if there are still
655  // any outstanding dependences (some tasks may have finished while we
656  // processed the dependences)
657  npredecessors =
658  node->dn.npredecessors.fetch_add(npredecessors) + npredecessors;
659 
660  KA_TRACE(20, ("__kmp_check_deps: T#%d found %d predecessors for task %p \n",
661  gtid, npredecessors, taskdata));
662 
663  // beyond this point the task could be queued (and executed) by a releasing
664  // task...
665  return npredecessors > 0 ? true : false;
666 }
667 
684 kmp_int32 __kmpc_omp_task_with_deps(ident_t *loc_ref, kmp_int32 gtid,
685  kmp_task_t *new_task, kmp_int32 ndeps,
686  kmp_depend_info_t *dep_list,
687  kmp_int32 ndeps_noalias,
688  kmp_depend_info_t *noalias_dep_list) {
689 
690  kmp_taskdata_t *new_taskdata = KMP_TASK_TO_TASKDATA(new_task);
691  KA_TRACE(10, ("__kmpc_omp_task_with_deps(enter): T#%d loc=%p task=%p\n", gtid,
692  loc_ref, new_taskdata));
693  __kmp_assert_valid_gtid(gtid);
694  kmp_info_t *thread = __kmp_threads[gtid];
695  kmp_taskdata_t *current_task = thread->th.th_current_task;
696 
697 #if OMPX_TASKGRAPH
698  // record TDG with deps
699  if (new_taskdata->is_taskgraph &&
700  __kmp_tdg_is_recording(new_taskdata->tdg->tdg_status)) {
701  kmp_tdg_info_t *tdg = new_taskdata->tdg;
702  // extend record_map if needed
703  if (new_taskdata->td_tdg_task_id >= tdg->map_size) {
704  __kmp_acquire_bootstrap_lock(&tdg->graph_lock);
705  if (new_taskdata->td_tdg_task_id >= tdg->map_size) {
706  kmp_uint old_size = tdg->map_size;
707  kmp_uint new_size = old_size * 2;
708  kmp_node_info_t *old_record = tdg->record_map;
709  kmp_node_info_t *new_record = (kmp_node_info_t *)__kmp_allocate(
710  new_size * sizeof(kmp_node_info_t));
711  KMP_MEMCPY(new_record, tdg->record_map,
712  old_size * sizeof(kmp_node_info_t));
713  tdg->record_map = new_record;
714 
715  __kmp_free(old_record);
716 
717  for (kmp_int i = old_size; i < new_size; i++) {
718  kmp_int32 *successorsList = (kmp_int32 *)__kmp_allocate(
719  __kmp_successors_size * sizeof(kmp_int32));
720  new_record[i].task = nullptr;
721  new_record[i].successors = successorsList;
722  new_record[i].nsuccessors = 0;
723  new_record[i].npredecessors = 0;
724  new_record[i].successors_size = __kmp_successors_size;
725  KMP_ATOMIC_ST_REL(&new_record[i].npredecessors_counter, 0);
726  }
727  // update the size at the end, so that we avoid other
728  // threads use old_record while map_size is already updated
729  tdg->map_size = new_size;
730  }
731  __kmp_release_bootstrap_lock(&tdg->graph_lock);
732  }
733  tdg->record_map[new_taskdata->td_tdg_task_id].task = new_task;
734  tdg->record_map[new_taskdata->td_tdg_task_id].parent_task =
735  new_taskdata->td_parent;
736  KMP_ATOMIC_INC(&tdg->num_tasks);
737  }
738 #endif
739 #if OMPT_SUPPORT
740  if (ompt_enabled.enabled) {
741  if (!current_task->ompt_task_info.frame.enter_frame.ptr)
742  current_task->ompt_task_info.frame.enter_frame.ptr =
743  OMPT_GET_FRAME_ADDRESS(0);
744  if (ompt_enabled.ompt_callback_task_create) {
745  ompt_callbacks.ompt_callback(ompt_callback_task_create)(
746  &(current_task->ompt_task_info.task_data),
747  &(current_task->ompt_task_info.frame),
748  &(new_taskdata->ompt_task_info.task_data),
749  TASK_TYPE_DETAILS_FORMAT(new_taskdata), 1,
750  OMPT_LOAD_OR_GET_RETURN_ADDRESS(gtid));
751  }
752 
753  new_taskdata->ompt_task_info.frame.enter_frame.ptr =
754  OMPT_GET_FRAME_ADDRESS(0);
755  }
756 
757 #if OMPT_OPTIONAL
758  /* OMPT grab all dependences if requested by the tool */
759  if (ndeps + ndeps_noalias > 0 && ompt_enabled.ompt_callback_dependences) {
760  kmp_int32 i;
761 
762  int ompt_ndeps = ndeps + ndeps_noalias;
763  ompt_dependence_t *ompt_deps = (ompt_dependence_t *)KMP_OMPT_DEPS_ALLOC(
764  thread, (ndeps + ndeps_noalias) * sizeof(ompt_dependence_t));
765 
766  KMP_ASSERT(ompt_deps != NULL);
767 
768  for (i = 0; i < ndeps; i++) {
769  ompt_deps[i].variable.ptr = (void *)dep_list[i].base_addr;
770  if (dep_list[i].base_addr == (kmp_intptr_t)KMP_SIZE_T_MAX)
771  ompt_deps[i].dependence_type = ompt_dependence_type_out_all_memory;
772  else if (dep_list[i].flags.in && dep_list[i].flags.out)
773  ompt_deps[i].dependence_type = ompt_dependence_type_inout;
774  else if (dep_list[i].flags.out)
775  ompt_deps[i].dependence_type = ompt_dependence_type_out;
776  else if (dep_list[i].flags.in)
777  ompt_deps[i].dependence_type = ompt_dependence_type_in;
778  else if (dep_list[i].flags.mtx)
779  ompt_deps[i].dependence_type = ompt_dependence_type_mutexinoutset;
780  else if (dep_list[i].flags.set)
781  ompt_deps[i].dependence_type = ompt_dependence_type_inoutset;
782  else if (dep_list[i].flags.all)
783  ompt_deps[i].dependence_type = ompt_dependence_type_out_all_memory;
784  }
785  for (i = 0; i < ndeps_noalias; i++) {
786  ompt_deps[ndeps + i].variable.ptr = (void *)noalias_dep_list[i].base_addr;
787  if (noalias_dep_list[i].base_addr == (kmp_intptr_t)KMP_SIZE_T_MAX)
788  ompt_deps[ndeps + i].dependence_type =
789  ompt_dependence_type_out_all_memory;
790  else if (noalias_dep_list[i].flags.in && noalias_dep_list[i].flags.out)
791  ompt_deps[ndeps + i].dependence_type = ompt_dependence_type_inout;
792  else if (noalias_dep_list[i].flags.out)
793  ompt_deps[ndeps + i].dependence_type = ompt_dependence_type_out;
794  else if (noalias_dep_list[i].flags.in)
795  ompt_deps[ndeps + i].dependence_type = ompt_dependence_type_in;
796  else if (noalias_dep_list[i].flags.mtx)
797  ompt_deps[ndeps + i].dependence_type =
798  ompt_dependence_type_mutexinoutset;
799  else if (noalias_dep_list[i].flags.set)
800  ompt_deps[ndeps + i].dependence_type = ompt_dependence_type_inoutset;
801  else if (noalias_dep_list[i].flags.all)
802  ompt_deps[ndeps + i].dependence_type =
803  ompt_dependence_type_out_all_memory;
804  }
805  ompt_callbacks.ompt_callback(ompt_callback_dependences)(
806  &(new_taskdata->ompt_task_info.task_data), ompt_deps, ompt_ndeps);
807  /* We can now free the allocated memory for the dependences */
808  /* For OMPD we might want to delay the free until end of this function */
809  KMP_OMPT_DEPS_FREE(thread, ompt_deps);
810  }
811 #endif /* OMPT_OPTIONAL */
812 #endif /* OMPT_SUPPORT */
813 
814  bool serial = current_task->td_flags.team_serial ||
815  current_task->td_flags.tasking_ser ||
816  current_task->td_flags.final;
817  kmp_task_team_t *task_team = thread->th.th_task_team;
818  serial = serial &&
819  !(task_team && (task_team->tt.tt_found_proxy_tasks ||
820  task_team->tt.tt_hidden_helper_task_encountered));
821 
822  if (!serial && (ndeps > 0 || ndeps_noalias > 0)) {
823  /* if no dependences have been tracked yet, create the dependence hash */
824  if (current_task->td_dephash == NULL)
825  current_task->td_dephash = __kmp_dephash_create(thread, current_task);
826 
827 #if USE_FAST_MEMORY
828  kmp_depnode_t *node =
829  (kmp_depnode_t *)__kmp_fast_allocate(thread, sizeof(kmp_depnode_t));
830 #else
831  kmp_depnode_t *node =
832  (kmp_depnode_t *)__kmp_thread_malloc(thread, sizeof(kmp_depnode_t));
833 #endif
834 
835  __kmp_init_node(node, /*on_stack=*/false);
836  new_taskdata->td_depnode = node;
837 
838  if (__kmp_check_deps(gtid, node, new_task, &current_task->td_dephash,
839  NO_DEP_BARRIER, ndeps, dep_list, ndeps_noalias,
840  noalias_dep_list)) {
841  KA_TRACE(10, ("__kmpc_omp_task_with_deps(exit): T#%d task had blocking "
842  "dependences: "
843  "loc=%p task=%p, return: TASK_CURRENT_NOT_QUEUED\n",
844  gtid, loc_ref, new_taskdata));
845 #if OMPT_SUPPORT
846  if (ompt_enabled.enabled) {
847  current_task->ompt_task_info.frame.enter_frame = ompt_data_none;
848  }
849 #endif
850  return TASK_CURRENT_NOT_QUEUED;
851  }
852  } else {
853  KA_TRACE(10, ("__kmpc_omp_task_with_deps(exit): T#%d ignored dependences "
854  "for task (serialized) loc=%p task=%p\n",
855  gtid, loc_ref, new_taskdata));
856  }
857 
858  KA_TRACE(10, ("__kmpc_omp_task_with_deps(exit): T#%d task had no blocking "
859  "dependences : "
860  "loc=%p task=%p, transferring to __kmp_omp_task\n",
861  gtid, loc_ref, new_taskdata));
862 
863  kmp_int32 ret = __kmp_omp_task(gtid, new_task, true);
864 #if OMPT_SUPPORT
865  if (ompt_enabled.enabled) {
866  current_task->ompt_task_info.frame.enter_frame = ompt_data_none;
867  }
868 #endif
869  return ret;
870 }
871 
872 #if OMPT_SUPPORT
873 void __ompt_taskwait_dep_finish(kmp_taskdata_t *current_task,
874  ompt_data_t *taskwait_task_data) {
875  if (ompt_enabled.ompt_callback_task_schedule) {
876  ompt_callbacks.ompt_callback(ompt_callback_task_schedule)(
877  taskwait_task_data, ompt_taskwait_complete, NULL);
878  }
879  current_task->ompt_task_info.frame.enter_frame.ptr = NULL;
880  *taskwait_task_data = ompt_data_none;
881 }
882 #endif /* OMPT_SUPPORT */
883 
895 void __kmpc_omp_wait_deps(ident_t *loc_ref, kmp_int32 gtid, kmp_int32 ndeps,
896  kmp_depend_info_t *dep_list, kmp_int32 ndeps_noalias,
897  kmp_depend_info_t *noalias_dep_list) {
898  __kmpc_omp_taskwait_deps_51(loc_ref, gtid, ndeps, dep_list, ndeps_noalias,
899  noalias_dep_list, false);
900 }
901 
902 /* __kmpc_omp_taskwait_deps_51 : Function for OpenMP 5.1 nowait clause.
903  Placeholder for taskwait with nowait clause.
904  Earlier code of __kmpc_omp_wait_deps() is now
905  in this function.
906 */
907 void __kmpc_omp_taskwait_deps_51(ident_t *loc_ref, kmp_int32 gtid,
908  kmp_int32 ndeps, kmp_depend_info_t *dep_list,
909  kmp_int32 ndeps_noalias,
910  kmp_depend_info_t *noalias_dep_list,
911  kmp_int32 has_no_wait) {
912  KA_TRACE(10, ("__kmpc_omp_taskwait_deps(enter): T#%d loc=%p nowait#%d\n",
913  gtid, loc_ref, has_no_wait));
914  if (ndeps == 0 && ndeps_noalias == 0) {
915  KA_TRACE(10, ("__kmpc_omp_taskwait_deps(exit): T#%d has no dependences to "
916  "wait upon : loc=%p\n",
917  gtid, loc_ref));
918  return;
919  }
920  __kmp_assert_valid_gtid(gtid);
921  kmp_info_t *thread = __kmp_threads[gtid];
922  kmp_taskdata_t *current_task = thread->th.th_current_task;
923 
924 #if OMPT_SUPPORT
925  // this function represents a taskwait construct with depend clause
926  // We signal 4 events:
927  // - creation of the taskwait task
928  // - dependences of the taskwait task
929  // - schedule and finish of the taskwait task
930  ompt_data_t *taskwait_task_data = &thread->th.ompt_thread_info.task_data;
931  KMP_ASSERT(taskwait_task_data->ptr == NULL);
932  if (ompt_enabled.enabled) {
933  if (!current_task->ompt_task_info.frame.enter_frame.ptr)
934  current_task->ompt_task_info.frame.enter_frame.ptr =
935  OMPT_GET_FRAME_ADDRESS(0);
936  if (ompt_enabled.ompt_callback_task_create) {
937  ompt_callbacks.ompt_callback(ompt_callback_task_create)(
938  &(current_task->ompt_task_info.task_data),
939  &(current_task->ompt_task_info.frame), taskwait_task_data,
940  ompt_task_taskwait | ompt_task_undeferred | ompt_task_mergeable, 1,
941  OMPT_LOAD_OR_GET_RETURN_ADDRESS(gtid));
942  }
943  }
944 
945 #if OMPT_OPTIONAL
946  /* OMPT grab all dependences if requested by the tool */
947  if (ndeps + ndeps_noalias > 0 && ompt_enabled.ompt_callback_dependences) {
948  kmp_int32 i;
949 
950  int ompt_ndeps = ndeps + ndeps_noalias;
951  ompt_dependence_t *ompt_deps = (ompt_dependence_t *)KMP_OMPT_DEPS_ALLOC(
952  thread, (ndeps + ndeps_noalias) * sizeof(ompt_dependence_t));
953 
954  KMP_ASSERT(ompt_deps != NULL);
955 
956  for (i = 0; i < ndeps; i++) {
957  ompt_deps[i].variable.ptr = (void *)dep_list[i].base_addr;
958  if (dep_list[i].flags.in && dep_list[i].flags.out)
959  ompt_deps[i].dependence_type = ompt_dependence_type_inout;
960  else if (dep_list[i].flags.out)
961  ompt_deps[i].dependence_type = ompt_dependence_type_out;
962  else if (dep_list[i].flags.in)
963  ompt_deps[i].dependence_type = ompt_dependence_type_in;
964  else if (dep_list[i].flags.mtx)
965  ompt_deps[ndeps + i].dependence_type =
966  ompt_dependence_type_mutexinoutset;
967  else if (dep_list[i].flags.set)
968  ompt_deps[ndeps + i].dependence_type = ompt_dependence_type_inoutset;
969  }
970  for (i = 0; i < ndeps_noalias; i++) {
971  ompt_deps[ndeps + i].variable.ptr = (void *)noalias_dep_list[i].base_addr;
972  if (noalias_dep_list[i].flags.in && noalias_dep_list[i].flags.out)
973  ompt_deps[ndeps + i].dependence_type = ompt_dependence_type_inout;
974  else if (noalias_dep_list[i].flags.out)
975  ompt_deps[ndeps + i].dependence_type = ompt_dependence_type_out;
976  else if (noalias_dep_list[i].flags.in)
977  ompt_deps[ndeps + i].dependence_type = ompt_dependence_type_in;
978  else if (noalias_dep_list[i].flags.mtx)
979  ompt_deps[ndeps + i].dependence_type =
980  ompt_dependence_type_mutexinoutset;
981  else if (noalias_dep_list[i].flags.set)
982  ompt_deps[ndeps + i].dependence_type = ompt_dependence_type_inoutset;
983  }
984  ompt_callbacks.ompt_callback(ompt_callback_dependences)(
985  taskwait_task_data, ompt_deps, ompt_ndeps);
986  /* We can now free the allocated memory for the dependences */
987  /* For OMPD we might want to delay the free until end of this function */
988  KMP_OMPT_DEPS_FREE(thread, ompt_deps);
989  ompt_deps = NULL;
990  }
991 #endif /* OMPT_OPTIONAL */
992 #endif /* OMPT_SUPPORT */
993 
994  // We can return immediately as:
995  // - dependences are not computed in serial teams (except with proxy tasks)
996  // - if the dephash is not yet created it means we have nothing to wait for
997  bool ignore = current_task->td_flags.team_serial ||
998  current_task->td_flags.tasking_ser ||
999  current_task->td_flags.final;
1000  ignore =
1001  ignore && thread->th.th_task_team != NULL &&
1002  thread->th.th_task_team->tt.tt_found_proxy_tasks == FALSE &&
1003  thread->th.th_task_team->tt.tt_hidden_helper_task_encountered == FALSE;
1004  ignore = ignore || current_task->td_dephash == NULL;
1005 
1006  if (ignore) {
1007  KA_TRACE(10, ("__kmpc_omp_taskwait_deps(exit): T#%d has no blocking "
1008  "dependences : loc=%p\n",
1009  gtid, loc_ref));
1010 #if OMPT_SUPPORT
1011  __ompt_taskwait_dep_finish(current_task, taskwait_task_data);
1012 #endif /* OMPT_SUPPORT */
1013  return;
1014  }
1015 
1016  kmp_depnode_t node = {0};
1017  __kmp_init_node(&node, /*on_stack=*/true);
1018 
1019  if (!__kmp_check_deps(gtid, &node, NULL, &current_task->td_dephash,
1020  DEP_BARRIER, ndeps, dep_list, ndeps_noalias,
1021  noalias_dep_list)) {
1022  KA_TRACE(10, ("__kmpc_omp_taskwait_deps(exit): T#%d has no blocking "
1023  "dependences : loc=%p\n",
1024  gtid, loc_ref));
1025 #if OMPT_SUPPORT
1026  __ompt_taskwait_dep_finish(current_task, taskwait_task_data);
1027 #endif /* OMPT_SUPPORT */
1028 
1029  // There may still be references to this node here, due to task stealing.
1030  // Wait for them to be released.
1031  kmp_int32 nrefs;
1032  while ((nrefs = node.dn.nrefs) > 3) {
1033  KMP_DEBUG_ASSERT((nrefs & 1) == 1);
1034  KMP_YIELD(TRUE);
1035  }
1036  KMP_DEBUG_ASSERT(nrefs == 3);
1037 
1038  return;
1039  }
1040 
1041  int thread_finished = FALSE;
1042  kmp_flag_32<false, false> flag(
1043  (std::atomic<kmp_uint32> *)&node.dn.npredecessors, 0U);
1044  while (node.dn.npredecessors > 0) {
1045  flag.execute_tasks(thread, gtid, FALSE,
1046  &thread_finished USE_ITT_BUILD_ARG(NULL),
1047  __kmp_task_stealing_constraint);
1048  }
1049 
1050  // Wait until the last __kmp_release_deps is finished before we free the
1051  // current stack frame holding the "node" variable; once its nrefs count
1052  // reaches 3 (meaning 1, since bit zero of the refcount indicates a stack
1053  // rather than a heap address), we're sure nobody else can try to reference
1054  // it again.
1055  kmp_int32 nrefs;
1056  while ((nrefs = node.dn.nrefs) > 3) {
1057  KMP_DEBUG_ASSERT((nrefs & 1) == 1);
1058  KMP_YIELD(TRUE);
1059  }
1060  KMP_DEBUG_ASSERT(nrefs == 3);
1061 
1062 #if OMPT_SUPPORT
1063  __ompt_taskwait_dep_finish(current_task, taskwait_task_data);
1064 #endif /* OMPT_SUPPORT */
1065  KA_TRACE(10, ("__kmpc_omp_taskwait_deps(exit): T#%d finished waiting : loc=%p\
1066  \n",
1067  gtid, loc_ref));
1068 }
kmp_int32 __kmpc_omp_task_with_deps(ident_t *loc_ref, kmp_int32 gtid, kmp_task_t *new_task, kmp_int32 ndeps, kmp_depend_info_t *dep_list, kmp_int32 ndeps_noalias, kmp_depend_info_t *noalias_dep_list)
void __kmpc_omp_wait_deps(ident_t *loc_ref, kmp_int32 gtid, kmp_int32 ndeps, kmp_depend_info_t *dep_list, kmp_int32 ndeps_noalias, kmp_depend_info_t *noalias_dep_list)
Definition: kmp.h:227