1 /*
2 * Copyright (c) 2005, 2006, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
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
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23 */
24
25 //** Dependencies represent assertions (approximate invariants) within
26 // the class hierarchy. An example is an assertion that a given
27 // method is not overridden; another example is that a type has only
28 // one concrete subtype. Compiled code which relies on such
29 // assertions must be discarded if they are overturned by changes in
30 // the class hierarchy. We can think of these assertions as
31 // approximate invariants, because we expect them to be overturned
32 // very infrequently. We are willing to perform expensive recovery
33 // operations when they are overturned. The benefit, of course, is
34 // performing optimistic optimizations (!) on the object code.
35 //
36 // Changes in the class hierarchy due to dynamic linking or
37 // class evolution can violate dependencies. There is enough
38 // indexing between classes and nmethods to make dependency
39 // checking reasonably efficient.
40
41 class ciEnv;
42 class nmethod;
43 class OopRecorder;
44 class xmlStream;
45 class CompileLog;
46 class DepChange;
47 class No_Safepoint_Verifier;
48
49 class Dependencies: public ResourceObj {
50 public:
51 // Note: In the comments on dependency types, most uses of the terms
52 // subtype and supertype are used in a "non-strict" or "inclusive"
53 // sense, and are starred to remind the reader of this fact.
54 // Strict uses of the terms use the word "proper".
55 //
56 // Specifically, every class is its own subtype* and supertype*.
57 // (This trick is easier than continually saying things like "Y is a
58 // subtype of X or X itself".)
59 //
60 // Sometimes we write X > Y to mean X is a proper supertype of Y.
61 // The notation X > {Y, Z} means X has proper subtypes Y, Z.
62 // The notation X.m > Y means that Y inherits m from X, while
63 // X.m > Y.m means Y overrides X.m. A star denotes abstractness,
64 // as *I > A, meaning (abstract) interface I is a super type of A,
65 // or A.*m > B.m, meaning B.m implements abstract method A.m.
66 //
67 // In this module, the terms "subtype" and "supertype" refer to
68 // Java-level reference type conversions, as detected by
69 // "instanceof" and performed by "checkcast" operations. The method
70 // Klass::is_subtype_of tests these relations. Note that "subtype"
71 // is richer than "subclass" (as tested by Klass::is_subclass_of),
72 // since it takes account of relations involving interface and array
73 // types.
74 //
75 // To avoid needless complexity, dependencies involving array types
76 // are not accepted. If you need to make an assertion about an
77 // array type, make the assertion about its corresponding element
78 // types. Any assertion that might change about an array type can
79 // be converted to an assertion about its element type.
80 //
81 // Most dependencies are evaluated over a "context type" CX, which
82 // stands for the set Subtypes(CX) of every Java type that is a subtype*
83 // of CX. When the system loads a new class or interface N, it is
84 // responsible for re-evaluating changed dependencies whose context
85 // type now includes N, that is, all super types of N.
86 //
87 enum DepType {
88 end_marker = 0,
89
90 // An 'evol' dependency simply notes that the contents of the
91 // method were used. If it evolves (is replaced), the nmethod
92 // must be recompiled. No other dependencies are implied.
93 evol_method,
94 FIRST_TYPE = evol_method,
95
96 // A context type CX is a leaf it if has no proper subtype.
97 leaf_type,
98
99 // An abstract class CX has exactly one concrete subtype CC.
100 abstract_with_unique_concrete_subtype,
101
102 // The type CX is purely abstract, with no concrete subtype* at all.
103 abstract_with_no_concrete_subtype,
104
105 // The concrete CX is free of concrete proper subtypes.
106 concrete_with_no_concrete_subtype,
107
108 // Given a method M1 and a context class CX, the set MM(CX, M1) of
109 // "concrete matching methods" in CX of M1 is the set of every
110 // concrete M2 for which it is possible to create an invokevirtual
111 // or invokeinterface call site that can reach either M1 or M2.
112 // That is, M1 and M2 share a name, signature, and vtable index.
113 // We wish to notice when the set MM(CX, M1) is just {M1}, or
114 // perhaps a set of two {M1,M2}, and issue dependencies on this.
115
116 // The set MM(CX, M1) can be computed by starting with any matching
117 // concrete M2 that is inherited into CX, and then walking the
118 // subtypes* of CX looking for concrete definitions.
119
120 // The parameters to this dependency are the method M1 and the
121 // context class CX. M1 must be either inherited in CX or defined
122 // in a subtype* of CX. It asserts that MM(CX, M1) is no greater
123 // than {M1}.
124 unique_concrete_method, // one unique concrete method under CX
125
126 // An "exclusive" assertion concerns two methods or subtypes, and
127 // declares that there are at most two (or perhaps later N>2)
128 // specific items that jointly satisfy the restriction.
129 // We list all items explicitly rather than just giving their
130 // count, for robustness in the face of complex schema changes.
131
132 // A context class CX (which may be either abstract or concrete)
133 // has two exclusive concrete subtypes* C1, C2 if every concrete
134 // subtype* of CX is either C1 or C2. Note that if neither C1 or C2
135 // are equal to CX, then CX itself must be abstract. But it is
136 // also possible (for example) that C1 is CX (a concrete class)
137 // and C2 is a proper subtype of C1.
138 abstract_with_exclusive_concrete_subtypes_2,
139
140 // This dependency asserts that MM(CX, M1) is no greater than {M1,M2}.
141 exclusive_concrete_methods_2,
142
143 // This dependency asserts that no instances of class or it's
144 // subclasses require finalization registration.
145 no_finalizable_subclasses,
146
147 TYPE_LIMIT
148 };
149 enum {
150 LG2_TYPE_LIMIT = 4, // assert(TYPE_LIMIT <= (1<<LG2_TYPE_LIMIT))
151
152 // handy categorizations of dependency types:
153 all_types = ((1<<TYPE_LIMIT)-1) & ((-1)<<FIRST_TYPE),
154 non_ctxk_types = (1<<evol_method),
155 ctxk_types = all_types & ~non_ctxk_types,
156
157 max_arg_count = 3, // current maximum number of arguments (incl. ctxk)
158
159 // A "context type" is a class or interface that
160 // provides context for evaluating a dependency.
161 // When present, it is one of the arguments (dep_context_arg).
162 //
163 // If a dependency does not have a context type, there is a
164 // default context, depending on the type of the dependency.
165 // This bit signals that a default context has been compressed away.
166 default_context_type_bit = (1<<LG2_TYPE_LIMIT)
167 };
168
169 static const char* dep_name(DepType dept);
170 static int dep_args(DepType dept);
171 static int dep_context_arg(DepType dept) {
172 return dept_in_mask(dept, ctxk_types)? 0: -1;
173 }
174
175 private:
176 // State for writing a new set of dependencies:
177 GrowableArray<int>* _dep_seen; // (seen[h->ident] & (1<<dept))
178 GrowableArray<ciObject*>* _deps[TYPE_LIMIT];
179
180 static const char* _dep_name[TYPE_LIMIT];
181 static int _dep_args[TYPE_LIMIT];
182
183 static bool dept_in_mask(DepType dept, int mask) {
184 return (int)dept >= 0 && dept < TYPE_LIMIT && ((1<<dept) & mask) != 0;
185 }
186
187 bool note_dep_seen(int dept, ciObject* x) {
188 assert(dept < BitsPerInt, "oob");
189 int x_id = x->ident();
190 assert(_dep_seen != NULL, "deps must be writable");
191 int seen = _dep_seen->at_grow(x_id, 0);
192 _dep_seen->at_put(x_id, seen | (1<<dept));
193 // return true if we've already seen dept/x
194 return (seen & (1<<dept)) != 0;
195 }
196
197 bool maybe_merge_ctxk(GrowableArray<ciObject*>* deps,
198 int ctxk_i, ciKlass* ctxk);
199
200 void sort_all_deps();
201 size_t estimate_size_in_bytes();
202
203 // Initialize _deps, etc.
204 void initialize(ciEnv* env);
205
206 // State for making a new set of dependencies:
207 OopRecorder* _oop_recorder;
208
209 // Logging support
210 CompileLog* _log;
211
212 address _content_bytes; // everything but the oop references, encoded
213 size_t _size_in_bytes;
214
215 public:
216 // Make a new empty dependencies set.
217 Dependencies(ciEnv* env) {
218 initialize(env);
219 }
220
221 private:
222 // Check for a valid context type.
223 // Enforce the restriction against array types.
224 static void check_ctxk(ciKlass* ctxk) {
225 assert(ctxk->is_instance_klass(), "java types only");
226 }
227 static void check_ctxk_concrete(ciKlass* ctxk) {
228 assert(is_concrete_klass(ctxk->as_instance_klass()), "must be concrete");
229 }
230 static void check_ctxk_abstract(ciKlass* ctxk) {
231 check_ctxk(ctxk);
232 assert(!is_concrete_klass(ctxk->as_instance_klass()), "must be abstract");
233 }
234
235 void assert_common_1(DepType dept, ciObject* x);
236 void assert_common_2(DepType dept, ciKlass* ctxk, ciObject* x);
237 void assert_common_3(DepType dept, ciKlass* ctxk, ciObject* x, ciObject* x2);
238
239 public:
240 // Adding assertions to a new dependency set at compile time:
241 void assert_evol_method(ciMethod* m);
242 void assert_leaf_type(ciKlass* ctxk);
243 void assert_abstract_with_unique_concrete_subtype(ciKlass* ctxk, ciKlass* conck);
244 void assert_abstract_with_no_concrete_subtype(ciKlass* ctxk);
245 void assert_concrete_with_no_concrete_subtype(ciKlass* ctxk);
246 void assert_unique_concrete_method(ciKlass* ctxk, ciMethod* uniqm);
247 void assert_abstract_with_exclusive_concrete_subtypes(ciKlass* ctxk, ciKlass* k1, ciKlass* k2);
248 void assert_exclusive_concrete_methods(ciKlass* ctxk, ciMethod* m1, ciMethod* m2);
249 void assert_has_no_finalizable_subclasses(ciKlass* ctxk);
250
251 // Define whether a given method or type is concrete.
252 // These methods define the term "concrete" as used in this module.
253 // For this module, an "abstract" class is one which is non-concrete.
254 //
255 // Future optimizations may allow some classes to remain
256 // non-concrete until their first instantiation, and allow some
257 // methods to remain non-concrete until their first invocation.
258 // In that case, there would be a middle ground between concrete
259 // and abstract (as defined by the Java language and VM).
260 static bool is_concrete_klass(klassOop k); // k is instantiable
261 static bool is_concrete_method(methodOop m); // m is invocable
262 static Klass* find_finalizable_subclass(Klass* k);
263
264 // These versions of the concreteness queries work through the CI.
265 // The CI versions are allowed to skew sometimes from the VM
266 // (oop-based) versions. The cost of such a difference is a
267 // (safely) aborted compilation, or a deoptimization, or a missed
268 // optimization opportunity.
269 //
270 // In order to prevent spurious assertions, query results must
271 // remain stable within any single ciEnv instance. (I.e., they must
272 // not go back into the VM to get their value; they must cache the
273 // bit in the CI, either eagerly or lazily.)
274 static bool is_concrete_klass(ciInstanceKlass* k); // k appears instantiable
275 static bool is_concrete_method(ciMethod* m); // m appears invocable
276 static bool has_finalizable_subclass(ciInstanceKlass* k);
277
278 // As a general rule, it is OK to compile under the assumption that
279 // a given type or method is concrete, even if it at some future
280 // point becomes abstract. So dependency checking is one-sided, in
281 // that it permits supposedly concrete classes or methods to turn up
282 // as really abstract. (This shouldn't happen, except during class
283 // evolution, but that's the logic of the checking.) However, if a
284 // supposedly abstract class or method suddenly becomes concrete, a
285 // dependency on it must fail.
286
287 // Checking old assertions at run-time (in the VM only):
288 static klassOop check_evol_method(methodOop m);
289 static klassOop check_leaf_type(klassOop ctxk);
290 static klassOop check_abstract_with_unique_concrete_subtype(klassOop ctxk, klassOop conck,
291 DepChange* changes = NULL);
292 static klassOop check_abstract_with_no_concrete_subtype(klassOop ctxk,
293 DepChange* changes = NULL);
294 static klassOop check_concrete_with_no_concrete_subtype(klassOop ctxk,
295 DepChange* changes = NULL);
296 static klassOop check_unique_concrete_method(klassOop ctxk, methodOop uniqm,
297 DepChange* changes = NULL);
298 static klassOop check_abstract_with_exclusive_concrete_subtypes(klassOop ctxk, klassOop k1, klassOop k2,
299 DepChange* changes = NULL);
300 static klassOop check_exclusive_concrete_methods(klassOop ctxk, methodOop m1, methodOop m2,
301 DepChange* changes = NULL);
302 static klassOop check_has_no_finalizable_subclasses(klassOop ctxk,
303 DepChange* changes = NULL);
304 // A returned klassOop is NULL if the dependency assertion is still
305 // valid. A non-NULL klassOop is a 'witness' to the assertion
306 // failure, a point in the class hierarchy where the assertion has
307 // been proven false. For example, if check_leaf_type returns
308 // non-NULL, the value is a subtype of the supposed leaf type. This
309 // witness value may be useful for logging the dependency failure.
310 // Note that, when a dependency fails, there may be several possible
311 // witnesses to the failure. The value returned from the check_foo
312 // method is chosen arbitrarily.
313
314 // The 'changes' value, if non-null, requests a limited spot-check
315 // near the indicated recent changes in the class hierarchy.
316 // It is used by DepStream::spot_check_dependency_at.
317
318 // Detecting possible new assertions:
319 static klassOop find_unique_concrete_subtype(klassOop ctxk);
320 static methodOop find_unique_concrete_method(klassOop ctxk, methodOop m);
321 static int find_exclusive_concrete_subtypes(klassOop ctxk, int klen, klassOop k[]);
322 static int find_exclusive_concrete_methods(klassOop ctxk, int mlen, methodOop m[]);
323
324 // Create the encoding which will be stored in an nmethod.
325 void encode_content_bytes();
326
327 address content_bytes() {
328 assert(_content_bytes != NULL, "encode it first");
329 return _content_bytes;
330 }
331 size_t size_in_bytes() {
332 assert(_content_bytes != NULL, "encode it first");
333 return _size_in_bytes;
334 }
335
336 OopRecorder* oop_recorder() { return _oop_recorder; }
337 CompileLog* log() { return _log; }
338
339 void copy_to(nmethod* nm);
340
341 void log_all_dependencies();
342 void log_dependency(DepType dept, int nargs, ciObject* args[]) {
343 write_dependency_to(log(), dept, nargs, args);
344 }
345 void log_dependency(DepType dept,
346 ciObject* x0,
347 ciObject* x1 = NULL,
348 ciObject* x2 = NULL) {
349 if (log() == NULL) return;
350 ciObject* args[max_arg_count];
351 args[0] = x0;
352 args[1] = x1;
353 args[2] = x2;
354 assert(2 < max_arg_count, "");
355 log_dependency(dept, dep_args(dept), args);
356 }
357
358 static void write_dependency_to(CompileLog* log,
359 DepType dept,
360 int nargs, ciObject* args[],
361 klassOop witness = NULL);
362 static void write_dependency_to(CompileLog* log,
363 DepType dept,
364 int nargs, oop args[],
365 klassOop witness = NULL);
366 static void write_dependency_to(xmlStream* xtty,
367 DepType dept,
368 int nargs, oop args[],
369 klassOop witness = NULL);
370 static void print_dependency(DepType dept,
371 int nargs, oop args[],
372 klassOop witness = NULL);
373
374 private:
375 // helper for encoding common context types as zero:
376 static ciKlass* ctxk_encoded_as_null(DepType dept, ciObject* x);
377
378 static klassOop ctxk_encoded_as_null(DepType dept, oop x);
379
380 public:
381 // Use this to iterate over an nmethod's dependency set.
382 // Works on new and old dependency sets.
383 // Usage:
384 //
385 // ;
386 // Dependencies::DepType dept;
387 // for (Dependencies::DepStream deps(nm); deps.next(); ) {
388 // ...
389 // }
390 //
391 // The caller must be in the VM, since oops are not wrapped in handles.
392 class DepStream {
393 private:
394 nmethod* _code; // null if in a compiler thread
395 Dependencies* _deps; // null if not in a compiler thread
396 CompressedReadStream _bytes;
397 #ifdef ASSERT
398 size_t _byte_limit;
399 #endif
400
401 // iteration variables:
402 DepType _type;
403 int _xi[max_arg_count+1];
404
405 void initial_asserts(size_t byte_limit) NOT_DEBUG({});
406
407 inline oop recorded_oop_at(int i);
408 // => _code? _code->oop_at(i): *_deps->_oop_recorder->handle_at(i)
409
410 klassOop check_dependency_impl(DepChange* changes);
411
412 public:
413 DepStream(Dependencies* deps)
414 : _deps(deps),
415 _code(NULL),
416 _bytes(deps->content_bytes())
417 {
418 initial_asserts(deps->size_in_bytes());
419 }
420 DepStream(nmethod* code)
421 : _deps(NULL),
422 _code(code),
423 _bytes(code->dependencies_begin())
424 {
425 initial_asserts(code->dependencies_size());
426 }
427
428 bool next();
429
430 DepType type() { return _type; }
431 int argument_count() { return dep_args(type()); }
432 int argument_index(int i) { assert(0 <= i && i < argument_count(), "oob");
433 return _xi[i]; }
434 oop argument(int i); // => recorded_oop_at(argument_index(i))
435 klassOop context_type();
436
437 methodOop method_argument(int i) {
438 oop x = argument(i);
439 assert(x->is_method(), "type");
440 return (methodOop) x;
441 }
442 klassOop type_argument(int i) {
443 oop x = argument(i);
444 assert(x->is_klass(), "type");
445 return (klassOop) x;
446 }
447
448 // The point of the whole exercise: Is this dep is still OK?
449 klassOop check_dependency() {
450 return check_dependency_impl(NULL);
451 }
452 // A lighter version: Checks only around recent changes in a class
453 // hierarchy. (See Universe::flush_dependents_on.)
454 klassOop spot_check_dependency_at(DepChange& changes);
455
456 // Log the current dependency to xtty or compilation log.
457 void log_dependency(klassOop witness = NULL);
458
459 // Print the current dependency to tty.
460 void print_dependency(klassOop witness = NULL, bool verbose = false);
461 };
462 friend class Dependencies::DepStream;
463
464 static void print_statistics() PRODUCT_RETURN;
465 };
466
467 // A class hierarchy change coming through the VM (under the Compile_lock).
468 // The change is structured as a single new type with any number of supers
469 // and implemented interface types. Other than the new type, any of the
470 // super types can be context types for a relevant dependency, which the
471 // new type could invalidate.
472 class DepChange : public StackObj {
473 public:
474 enum ChangeType {
475 NO_CHANGE = 0, // an uninvolved klass
476 Change_new_type, // a newly loaded type
477 Change_new_sub, // a super with a new subtype
478 Change_new_impl, // an interface with a new implementation
479 CHANGE_LIMIT,
480 Start_Klass = CHANGE_LIMIT // internal indicator for ContextStream
481 };
482
483 private:
484 // each change set is rooted in exactly one new type (at present):
485 KlassHandle _new_type;
486
487 void initialize();
488
489 public:
490 // notes the new type, marks it and all its super-types
491 DepChange(KlassHandle new_type)
492 : _new_type(new_type)
493 {
494 initialize();
495 }
496
497 // cleans up the marks
498 ~DepChange();
499
500 klassOop new_type() { return _new_type(); }
501
502 // involves_context(k) is true if k is new_type or any of the super types
503 bool involves_context(klassOop k);
504
505 // Usage:
506 // for (DepChange::ContextStream str(changes); str.next(); ) {
507 // klassOop k = str.klass();
508 // switch (str.change_type()) {
509 // ...
510 // }
511 // }
512 class ContextStream : public StackObj {
513 private:
514 DepChange& _changes;
515 friend class DepChange;
516
517 // iteration variables:
518 ChangeType _change_type;
519 klassOop _klass;
520 objArrayOop _ti_base; // i.e., transitive_interfaces
521 int _ti_index;
522 int _ti_limit;
523
524 // start at the beginning:
525 void start() {
526 klassOop new_type = _changes.new_type();
527 _change_type = (new_type == NULL ? NO_CHANGE: Start_Klass);
528 _klass = new_type;
529 _ti_base = NULL;
530 _ti_index = 0;
531 _ti_limit = 0;
532 }
533
534 public:
535 ContextStream(DepChange& changes)
536 : _changes(changes)
537 { start(); }
538
539 ContextStream(DepChange& changes, No_Safepoint_Verifier& nsv)
540 : _changes(changes)
541 // the nsv argument makes it safe to hold oops like _klass
542 { start(); }
543
544 bool next();
545
546 ChangeType change_type() { return _change_type; }
547 klassOop klass() { return _klass; }
548 };
549 friend class DepChange::ContextStream;
550
551 void print();
552 };