10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #ifndef SHARE_VM_CODE_DEPENDENCIES_HPP
26 #define SHARE_VM_CODE_DEPENDENCIES_HPP
27
28 #include "ci/ciCallSite.hpp"
29 #include "ci/ciKlass.hpp"
30 #include "ci/ciMethodHandle.hpp"
31 #include "classfile/systemDictionary.hpp"
32 #include "code/compressedStream.hpp"
33 #include "code/nmethod.hpp"
34 #include "utilities/growableArray.hpp"
35
36 //** Dependencies represent assertions (approximate invariants) within
37 // the runtime system, e.g. class hierarchy changes. An example is an
38 // assertion that a given method is not overridden; another example is
39 // that a type has only one concrete subtype. Compiled code which
40 // relies on such assertions must be discarded if they are overturned
41 // by changes in the runtime system. We can think of these assertions
42 // as approximate invariants, because we expect them to be overturned
43 // very infrequently. We are willing to perform expensive recovery
44 // operations when they are overturned. The benefit, of course, is
45 // performing optimistic optimizations (!) on the object code.
46 //
47 // Changes in the class hierarchy due to dynamic linking or
48 // class evolution can violate dependencies. There is enough
49 // indexing between classes and nmethods to make dependency
183 //
184 // If a dependency does not have a context type, there is a
185 // default context, depending on the type of the dependency.
186 // This bit signals that a default context has been compressed away.
187 default_context_type_bit = (1<<LG2_TYPE_LIMIT)
188 };
189
190 static const char* dep_name(DepType dept);
191 static int dep_args(DepType dept);
192
193 static bool is_klass_type( DepType dept) { return dept_in_mask(dept, klass_types ); }
194
195 static bool has_explicit_context_arg(DepType dept) { return dept_in_mask(dept, explicit_ctxk_types); }
196 static bool has_implicit_context_arg(DepType dept) { return dept_in_mask(dept, implicit_ctxk_types); }
197
198 static int dep_context_arg(DepType dept) { return has_explicit_context_arg(dept) ? 0 : -1; }
199 static int dep_implicit_context_arg(DepType dept) { return has_implicit_context_arg(dept) ? 0 : -1; }
200
201 static void check_valid_dependency_type(DepType dept);
202
203 private:
204 // State for writing a new set of dependencies:
205 GrowableArray<int>* _dep_seen; // (seen[h->ident] & (1<<dept))
206 GrowableArray<ciBaseObject*>* _deps[TYPE_LIMIT];
207
208 static const char* _dep_name[TYPE_LIMIT];
209 static int _dep_args[TYPE_LIMIT];
210
211 static bool dept_in_mask(DepType dept, int mask) {
212 return (int)dept >= 0 && dept < TYPE_LIMIT && ((1<<dept) & mask) != 0;
213 }
214
215 bool note_dep_seen(int dept, ciBaseObject* x) {
216 assert(dept < BitsPerInt, "oob");
217 int x_id = x->ident();
218 assert(_dep_seen != NULL, "deps must be writable");
219 int seen = _dep_seen->at_grow(x_id, 0);
220 _dep_seen->at_put(x_id, seen | (1<<dept));
221 // return true if we've already seen dept/x
222 return (seen & (1<<dept)) != 0;
223 }
224
225 bool maybe_merge_ctxk(GrowableArray<ciBaseObject*>* deps,
226 int ctxk_i, ciKlass* ctxk);
227
228 void sort_all_deps();
229 size_t estimate_size_in_bytes();
230
231 // Initialize _deps, etc.
232 void initialize(ciEnv* env);
233
234 // State for making a new set of dependencies:
235 OopRecorder* _oop_recorder;
236
237 // Logging support
238 CompileLog* _log;
239
240 address _content_bytes; // everything but the oop references, encoded
241 size_t _size_in_bytes;
242
243 public:
244 // Make a new empty dependencies set.
245 Dependencies(ciEnv* env) {
246 initialize(env);
247 }
248
249 private:
250 // Check for a valid context type.
251 // Enforce the restriction against array types.
252 static void check_ctxk(ciKlass* ctxk) {
253 assert(ctxk->is_instance_klass(), "java types only");
254 }
255 static void check_ctxk_concrete(ciKlass* ctxk) {
256 assert(is_concrete_klass(ctxk->as_instance_klass()), "must be concrete");
257 }
258 static void check_ctxk_abstract(ciKlass* ctxk) {
259 check_ctxk(ctxk);
260 assert(!is_concrete_klass(ctxk->as_instance_klass()), "must be abstract");
261 }
262
263 void assert_common_1(DepType dept, ciBaseObject* x);
264 void assert_common_2(DepType dept, ciBaseObject* x0, ciBaseObject* x1);
265 void assert_common_3(DepType dept, ciKlass* ctxk, ciBaseObject* x1, ciBaseObject* x2);
266
267 public:
268 // Adding assertions to a new dependency set at compile time:
269 void assert_evol_method(ciMethod* m);
270 void assert_leaf_type(ciKlass* ctxk);
271 void assert_abstract_with_unique_concrete_subtype(ciKlass* ctxk, ciKlass* conck);
272 void assert_abstract_with_no_concrete_subtype(ciKlass* ctxk);
273 void assert_concrete_with_no_concrete_subtype(ciKlass* ctxk);
274 void assert_unique_concrete_method(ciKlass* ctxk, ciMethod* uniqm);
275 void assert_abstract_with_exclusive_concrete_subtypes(ciKlass* ctxk, ciKlass* k1, ciKlass* k2);
276 void assert_exclusive_concrete_methods(ciKlass* ctxk, ciMethod* m1, ciMethod* m2);
277 void assert_has_no_finalizable_subclasses(ciKlass* ctxk);
278 void assert_call_site_target_value(ciCallSite* call_site, ciMethodHandle* method_handle);
279
280 // Define whether a given method or type is concrete.
281 // These methods define the term "concrete" as used in this module.
282 // For this module, an "abstract" class is one which is non-concrete.
283 //
284 // Future optimizations may allow some classes to remain
285 // non-concrete until their first instantiation, and allow some
286 // methods to remain non-concrete until their first invocation.
287 // In that case, there would be a middle ground between concrete
288 // and abstract (as defined by the Java language and VM).
289 static bool is_concrete_klass(Klass* k); // k is instantiable
290 static bool is_concrete_method(Method* m); // m is invocable
291 static Klass* find_finalizable_subclass(Klass* k);
292
293 // These versions of the concreteness queries work through the CI.
294 // The CI versions are allowed to skew sometimes from the VM
295 // (oop-based) versions. The cost of such a difference is a
296 // (safely) aborted compilation, or a deoptimization, or a missed
297 // optimization opportunity.
298 //
351 static int find_exclusive_concrete_methods(Klass* ctxk, int mlen, Method* m[]);
352
353 // Create the encoding which will be stored in an nmethod.
354 void encode_content_bytes();
355
356 address content_bytes() {
357 assert(_content_bytes != NULL, "encode it first");
358 return _content_bytes;
359 }
360 size_t size_in_bytes() {
361 assert(_content_bytes != NULL, "encode it first");
362 return _size_in_bytes;
363 }
364
365 OopRecorder* oop_recorder() { return _oop_recorder; }
366 CompileLog* log() { return _log; }
367
368 void copy_to(nmethod* nm);
369
370 void log_all_dependencies();
371 void log_dependency(DepType dept, int nargs, ciBaseObject* args[]) {
372 write_dependency_to(log(), dept, nargs, args);
373 }
374 void log_dependency(DepType dept,
375 ciBaseObject* x0,
376 ciBaseObject* x1 = NULL,
377 ciBaseObject* x2 = NULL) {
378 if (log() == NULL) return;
379 ciBaseObject* args[max_arg_count];
380 args[0] = x0;
381 args[1] = x1;
382 args[2] = x2;
383 assert(2 < max_arg_count, "");
384 log_dependency(dept, dep_args(dept), args);
385 }
386
387 class DepArgument : public ResourceObj {
388 private:
389 bool _is_oop;
390 bool _valid;
391 void* _value;
392 public:
393 DepArgument() : _is_oop(false), _value(NULL), _valid(false) {}
394 DepArgument(oop v): _is_oop(true), _value(v), _valid(true) {}
395 DepArgument(Metadata* v): _is_oop(false), _value(v), _valid(true) {}
396
397 bool is_null() const { return _value == NULL; }
398 bool is_oop() const { return _is_oop; }
399 bool is_metadata() const { return !_is_oop; }
400 bool is_klass() const { return is_metadata() && metadata_value()->is_klass(); }
401 bool is_method() const { return is_metadata() && metadata_value()->is_method(); }
402
403 oop oop_value() const { assert(_is_oop && _valid, "must be"); return (oop) _value; }
404 Metadata* metadata_value() const { assert(!_is_oop && _valid, "must be"); return (Metadata*) _value; }
405 };
406
407 static void write_dependency_to(CompileLog* log,
408 DepType dept,
409 int nargs, ciBaseObject* args[],
410 Klass* witness = NULL);
411 static void write_dependency_to(CompileLog* log,
412 DepType dept,
413 int nargs, DepArgument args[],
414 Klass* witness = NULL);
415 static void write_dependency_to(xmlStream* xtty,
416 DepType dept,
417 int nargs, DepArgument args[],
418 Klass* witness = NULL);
419 static void print_dependency(DepType dept,
420 int nargs, DepArgument args[],
421 Klass* witness = NULL);
422
423 private:
424 // helper for encoding common context types as zero:
425 static ciKlass* ctxk_encoded_as_null(DepType dept, ciBaseObject* x);
426
427 static Klass* ctxk_encoded_as_null(DepType dept, Metadata* x);
428
429 public:
430 // Use this to iterate over an nmethod's dependency set.
431 // Works on new and old dependency sets.
432 // Usage:
433 //
434 // ;
435 // Dependencies::DepType dept;
436 // for (Dependencies::DepStream deps(nm); deps.next(); ) {
437 // ...
438 // }
439 //
440 // The caller must be in the VM, since oops are not wrapped in handles.
441 class DepStream {
442 private:
443 nmethod* _code; // null if in a compiler thread
444 Dependencies* _deps; // null if not in a compiler thread
445 CompressedReadStream _bytes;
|
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #ifndef SHARE_VM_CODE_DEPENDENCIES_HPP
26 #define SHARE_VM_CODE_DEPENDENCIES_HPP
27
28 #include "ci/ciCallSite.hpp"
29 #include "ci/ciKlass.hpp"
30 #include "ci/ciMethod.hpp"
31 #include "ci/ciMethodHandle.hpp"
32 #include "classfile/systemDictionary.hpp"
33 #include "code/compressedStream.hpp"
34 #include "code/nmethod.hpp"
35 #include "utilities/growableArray.hpp"
36
37 //** Dependencies represent assertions (approximate invariants) within
38 // the runtime system, e.g. class hierarchy changes. An example is an
39 // assertion that a given method is not overridden; another example is
40 // that a type has only one concrete subtype. Compiled code which
41 // relies on such assertions must be discarded if they are overturned
42 // by changes in the runtime system. We can think of these assertions
43 // as approximate invariants, because we expect them to be overturned
44 // very infrequently. We are willing to perform expensive recovery
45 // operations when they are overturned. The benefit, of course, is
46 // performing optimistic optimizations (!) on the object code.
47 //
48 // Changes in the class hierarchy due to dynamic linking or
49 // class evolution can violate dependencies. There is enough
50 // indexing between classes and nmethods to make dependency
184 //
185 // If a dependency does not have a context type, there is a
186 // default context, depending on the type of the dependency.
187 // This bit signals that a default context has been compressed away.
188 default_context_type_bit = (1<<LG2_TYPE_LIMIT)
189 };
190
191 static const char* dep_name(DepType dept);
192 static int dep_args(DepType dept);
193
194 static bool is_klass_type( DepType dept) { return dept_in_mask(dept, klass_types ); }
195
196 static bool has_explicit_context_arg(DepType dept) { return dept_in_mask(dept, explicit_ctxk_types); }
197 static bool has_implicit_context_arg(DepType dept) { return dept_in_mask(dept, implicit_ctxk_types); }
198
199 static int dep_context_arg(DepType dept) { return has_explicit_context_arg(dept) ? 0 : -1; }
200 static int dep_implicit_context_arg(DepType dept) { return has_implicit_context_arg(dept) ? 0 : -1; }
201
202 static void check_valid_dependency_type(DepType dept);
203
204 // A Metadata* or object value recorded in an OopRecorder
205 class DepValue VALUE_OBJ_CLASS_SPEC {
206 private:
207 // Unique identifier of the value within the associated OopRecorder that
208 // encodes both the category of the value (0: invalid, positive: metadata, negative: object)
209 // and the index within a category specific array (metadata: index + 1, object: -(index + 1))
210 int _id;
211
212 public:
213 DepValue() : _id(0) {}
214 DepValue(OopRecorder* rec, Metadata* metadata, DepValue* candidate = NULL) {
215 assert(candidate == NULL || candidate->is_metadata(), "oops");
216 if (candidate != NULL && candidate->as_metadata(rec) == metadata) {
217 _id = candidate->_id;
218 } else {
219 _id = rec->find_index(metadata) + 1;
220 }
221 }
222 DepValue(OopRecorder* rec, jobject obj, DepValue* candidate = NULL) {
223 assert(candidate == NULL || candidate->is_object(), "oops");
224 if (candidate != NULL && candidate->as_object(rec) == obj) {
225 _id = candidate->_id;
226 } else {
227 _id = -(rec->find_index(obj) + 1);
228 }
229 }
230
231 // Used to sort values in ascending order of index() with metadata values preceding object values
232 int sort_key() const { return -_id; }
233
234 bool operator == (const DepValue& other) const { return other._id == _id; }
235
236 bool is_valid() const { return _id != 0; }
237 int index() const { assert(is_valid(), "oops"); return _id < 0 ? -(_id + 1) : _id - 1; }
238 bool is_metadata() const { assert(is_valid(), "oops"); return _id > 0; }
239 bool is_object() const { assert(is_valid(), "oops"); return _id < 0; }
240
241 Metadata* as_metadata(OopRecorder* rec) const { assert(is_metadata(), "oops"); return rec->metadata_at(index()); }
242 Klass* as_klass(OopRecorder* rec) const { assert(as_metadata(rec)->is_klass(), "oops"); return (Klass*) as_metadata(rec); }
243 Method* as_method(OopRecorder* rec) const { assert(as_metadata(rec)->is_method(), "oops"); return (Method*) as_metadata(rec); }
244 jobject as_object(OopRecorder* rec) const { assert(is_object(), "oops"); return rec->oop_at(index()); }
245 };
246
247 private:
248 // State for writing a new set of dependencies:
249 GrowableArray<int>* _dep_seen; // (seen[h->ident] & (1<<dept))
250 GrowableArray<DepValue>* _deps[TYPE_LIMIT];
251
252 static const char* _dep_name[TYPE_LIMIT];
253 static int _dep_args[TYPE_LIMIT];
254
255 static bool dept_in_mask(DepType dept, int mask) {
256 return (int)dept >= 0 && dept < TYPE_LIMIT && ((1<<dept) & mask) != 0;
257 }
258
259 bool note_dep_seen(int dept, DepValue x) {
260 assert(dept < BitsPerInt, "oops");
261 // place metadata deps at even indexes, object deps at odd indexes
262 int x_id = x.is_metadata() ? x.index() * 2 : (x.index() * 2) + 1;
263 assert(_dep_seen != NULL, "deps must be writable");
264 int seen = _dep_seen->at_grow(x_id, 0);
265 _dep_seen->at_put(x_id, seen | (1<<dept));
266 // return true if we've already seen dept/x
267 return (seen & (1<<dept)) != 0;
268 }
269
270 bool maybe_merge_ctxk(GrowableArray<DepValue>* deps,
271 int ctxk_i, Klass* ctxk);
272
273 void sort_all_deps();
274 size_t estimate_size_in_bytes();
275
276 // Initialize _deps, etc.
277 void initialize(ciEnv* env);
278
279 // State for making a new set of dependencies:
280 OopRecorder* _oop_recorder;
281
282 // Logging support
283 CompileLog* _log;
284
285 address _content_bytes; // everything but the oop references, encoded
286 size_t _size_in_bytes;
287
288 public:
289 // Make a new empty dependencies set.
290 Dependencies(ciEnv* env) {
291 initialize(env);
292 }
293
294 private:
295 // Check for a valid context type.
296 // Enforce the restriction against array types.
297 static void check_ctxk(Klass* ctxk) {
298 assert(ctxk->oop_is_instance(), "java types only");
299 }
300 static void check_ctxk_concrete(Klass* ctxk) {
301 check_ctxk(ctxk);
302 assert(!ctxk->is_abstract(), "must be abstract");
303 }
304 static void check_ctxk_abstract(Klass* ctxk) {
305 check_ctxk(ctxk);
306 assert(ctxk->is_abstract(), "must be abstract");
307 }
308
309 void assert_common_1(DepType dept, DepValue x);
310 void assert_common_2(DepType dept, DepValue x0, DepValue x1);
311 void assert_common_3(DepType dept, Klass* ctxk, DepValue x1, DepValue x2);
312
313 public:
314 // Adding assertions to a new dependency set at compile time:
315 void assert_evol_method(Method* m);
316 void assert_leaf_type(Klass* ctxk);
317 void assert_abstract_with_unique_concrete_subtype(Klass* ctxk, Klass* conck);
318 void assert_abstract_with_no_concrete_subtype(Klass* ctxk);
319 void assert_concrete_with_no_concrete_subtype(Klass* ctxk);
320 void assert_unique_concrete_method(Klass* ctxk, Method* uniqm);
321 void assert_abstract_with_exclusive_concrete_subtypes(Klass* ctxk, Klass* k1, Klass* k2);
322 void assert_exclusive_concrete_methods(Klass* ctxk, Method* m1, Method* m2);
323 void assert_has_no_finalizable_subclasses(Klass* ctxk);
324 void assert_call_site_target_value(jobject call_site, jobject method_handle);
325
326 // Wrappers for the above in terms of ci classes:
327 void assert_evol_method(ciMethod* m) {
328 assert_evol_method(m->get_Method());
329 }
330 void assert_leaf_type(ciKlass* ctxk) {
331 assert_leaf_type(ctxk->get_Klass());
332 }
333 void assert_abstract_with_unique_concrete_subtype(ciKlass* ctxk, ciKlass* conck) {
334 assert_abstract_with_unique_concrete_subtype(ctxk->get_Klass(), conck->get_Klass());
335 }
336 void assert_abstract_with_no_concrete_subtype(ciKlass* ctxk) {
337 assert_abstract_with_no_concrete_subtype(ctxk->get_Klass());
338 }
339 void assert_concrete_with_no_concrete_subtype(ciKlass* ctxk) {
340 assert_concrete_with_no_concrete_subtype(ctxk->get_Klass());
341 }
342 void assert_unique_concrete_method(ciKlass* ctxk, ciMethod* uniqm) {
343 assert_unique_concrete_method(ctxk->get_Klass(), uniqm->get_Method());
344 }
345 void assert_abstract_with_exclusive_concrete_subtypes(ciKlass* ctxk, ciKlass* k1, ciKlass* k2) {
346 assert_abstract_with_exclusive_concrete_subtypes(ctxk->get_Klass(), k1->get_Klass(), k2->get_Klass());
347 }
348 void assert_exclusive_concrete_methods(ciKlass* ctxk, ciMethod* m1, ciMethod* m2) {
349 assert_exclusive_concrete_methods(ctxk->get_Klass(), m1->get_Method(), m2->get_Method());
350 }
351 void assert_has_no_finalizable_subclasses(ciKlass* ctxk) {
352 assert_has_no_finalizable_subclasses(ctxk->get_Klass());
353 }
354 void assert_call_site_target_value(ciCallSite* call_site, ciMethodHandle* method_handle) {
355 assert_call_site_target_value(call_site->constant_encoding(), method_handle->constant_encoding());
356 }
357
358 // Define whether a given method or type is concrete.
359 // These methods define the term "concrete" as used in this module.
360 // For this module, an "abstract" class is one which is non-concrete.
361 //
362 // Future optimizations may allow some classes to remain
363 // non-concrete until their first instantiation, and allow some
364 // methods to remain non-concrete until their first invocation.
365 // In that case, there would be a middle ground between concrete
366 // and abstract (as defined by the Java language and VM).
367 static bool is_concrete_klass(Klass* k); // k is instantiable
368 static bool is_concrete_method(Method* m); // m is invocable
369 static Klass* find_finalizable_subclass(Klass* k);
370
371 // These versions of the concreteness queries work through the CI.
372 // The CI versions are allowed to skew sometimes from the VM
373 // (oop-based) versions. The cost of such a difference is a
374 // (safely) aborted compilation, or a deoptimization, or a missed
375 // optimization opportunity.
376 //
429 static int find_exclusive_concrete_methods(Klass* ctxk, int mlen, Method* m[]);
430
431 // Create the encoding which will be stored in an nmethod.
432 void encode_content_bytes();
433
434 address content_bytes() {
435 assert(_content_bytes != NULL, "encode it first");
436 return _content_bytes;
437 }
438 size_t size_in_bytes() {
439 assert(_content_bytes != NULL, "encode it first");
440 return _size_in_bytes;
441 }
442
443 OopRecorder* oop_recorder() { return _oop_recorder; }
444 CompileLog* log() { return _log; }
445
446 void copy_to(nmethod* nm);
447
448 void log_all_dependencies();
449 void log_dependency(DepType dept, int nargs, DepValue args[]) {
450 write_dependency_to(log(), dept, nargs, args);
451 }
452 void log_dependency(DepType dept,
453 DepValue x0,
454 DepValue x1 = DepValue(),
455 DepValue x2 = DepValue()) {
456 if (log() == NULL) return;
457 DepValue args[max_arg_count];
458 args[0] = x0;
459 args[1] = x1;
460 args[2] = x2;
461 assert(2 < max_arg_count, "");
462 log_dependency(dept, dep_args(dept), args);
463 }
464
465 class DepArgument : public ResourceObj {
466 private:
467 bool _is_oop;
468 bool _valid;
469 void* _value;
470 public:
471 DepArgument() : _is_oop(false), _value(NULL), _valid(false) {}
472 DepArgument(oop v): _is_oop(true), _value(v), _valid(true) {}
473 DepArgument(Metadata* v): _is_oop(false), _value(v), _valid(true) {}
474
475 bool is_null() const { return _value == NULL; }
476 bool is_oop() const { return _is_oop; }
477 bool is_metadata() const { return !_is_oop; }
478 bool is_klass() const { return is_metadata() && metadata_value()->is_klass(); }
479 bool is_method() const { return is_metadata() && metadata_value()->is_method(); }
480
481 oop oop_value() const { assert(_is_oop && _valid, "must be"); return (oop) _value; }
482 Metadata* metadata_value() const { assert(!_is_oop && _valid, "must be"); return (Metadata*) _value; }
483 };
484
485 static void write_dependency_to(CompileLog* log,
486 DepType dept,
487 int nargs, ciBaseObject* args[],
488 Klass* witness = NULL);
489 static void write_dependency_to(CompileLog* log,
490 DepType dept,
491 int nargs, DepArgument args[],
492 Klass* witness = NULL);
493 void write_dependency_to(CompileLog* log,
494 DepType dept,
495 int nargs, DepValue args[],
496 Klass* witness = NULL);
497 static void write_dependency_to(xmlStream* xtty,
498 DepType dept,
499 int nargs, DepArgument args[],
500 Klass* witness = NULL);
501 static void print_dependency(DepType dept,
502 int nargs, DepArgument args[],
503 Klass* witness = NULL);
504
505 private:
506 // helper for encoding common context types as zero:
507 static Klass* ctxk_encoded_as_null(OopRecorder* oop_recorder, DepType dept, DepValue x);
508
509 static Klass* ctxk_encoded_as_null(DepType dept, Metadata* x);
510
511 public:
512 // Use this to iterate over an nmethod's dependency set.
513 // Works on new and old dependency sets.
514 // Usage:
515 //
516 // ;
517 // Dependencies::DepType dept;
518 // for (Dependencies::DepStream deps(nm); deps.next(); ) {
519 // ...
520 // }
521 //
522 // The caller must be in the VM, since oops are not wrapped in handles.
523 class DepStream {
524 private:
525 nmethod* _code; // null if in a compiler thread
526 Dependencies* _deps; // null if not in a compiler thread
527 CompressedReadStream _bytes;
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