1 /*
2 * Copyright (c) 2005, 2010, 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
16 * 2 along with this work; if not, write to the Free Software Foundation,
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23 */
24
25 #ifndef SHARE_VM_CODE_DEPENDENCIES_HPP
26 #define SHARE_VM_CODE_DEPENDENCIES_HPP
27
28 #include "ci/ciKlass.hpp"
29 #include "code/compressedStream.hpp"
30 #include "code/nmethod.hpp"
31 #include "utilities/growableArray.hpp"
32
33 //** Dependencies represent assertions (approximate invariants) within
34 // the class hierarchy. An example is an assertion that a given
35 // method is not overridden; another example is that a type has only
36 // one concrete subtype. Compiled code which relies on such
37 // assertions must be discarded if they are overturned by changes in
38 // the class hierarchy. We can think of these assertions as
39 // approximate invariants, because we expect them to be overturned
40 // very infrequently. We are willing to perform expensive recovery
41 // operations when they are overturned. The benefit, of course, is
42 // performing optimistic optimizations (!) on the object code.
43 //
44 // Changes in the class hierarchy due to dynamic linking or
45 // class evolution can violate dependencies. There is enough
46 // indexing between classes and nmethods to make dependency
47 // checking reasonably efficient.
48
49 class ciEnv;
50 class nmethod;
51 class OopRecorder;
52 class xmlStream;
53 class CompileLog;
54 class DepChange;
55 class No_Safepoint_Verifier;
56
57 class Dependencies: public ResourceObj {
58 public:
59 // Note: In the comments on dependency types, most uses of the terms
60 // subtype and supertype are used in a "non-strict" or "inclusive"
61 // sense, and are starred to remind the reader of this fact.
62 // Strict uses of the terms use the word "proper".
63 //
64 // Specifically, every class is its own subtype* and supertype*.
65 // (This trick is easier than continually saying things like "Y is a
66 // subtype of X or X itself".)
67 //
68 // Sometimes we write X > Y to mean X is a proper supertype of Y.
69 // The notation X > {Y, Z} means X has proper subtypes Y, Z.
70 // The notation X.m > Y means that Y inherits m from X, while
71 // X.m > Y.m means Y overrides X.m. A star denotes abstractness,
72 // as *I > A, meaning (abstract) interface I is a super type of A,
73 // or A.*m > B.m, meaning B.m implements abstract method A.m.
74 //
75 // In this module, the terms "subtype" and "supertype" refer to
76 // Java-level reference type conversions, as detected by
77 // "instanceof" and performed by "checkcast" operations. The method
78 // Klass::is_subtype_of tests these relations. Note that "subtype"
79 // is richer than "subclass" (as tested by Klass::is_subclass_of),
80 // since it takes account of relations involving interface and array
81 // types.
82 //
83 // To avoid needless complexity, dependencies involving array types
84 // are not accepted. If you need to make an assertion about an
85 // array type, make the assertion about its corresponding element
86 // types. Any assertion that might change about an array type can
87 // be converted to an assertion about its element type.
88 //
89 // Most dependencies are evaluated over a "context type" CX, which
90 // stands for the set Subtypes(CX) of every Java type that is a subtype*
91 // of CX. When the system loads a new class or interface N, it is
92 // responsible for re-evaluating changed dependencies whose context
93 // type now includes N, that is, all super types of N.
94 //
95 enum DepType {
96 end_marker = 0,
97
98 // An 'evol' dependency simply notes that the contents of the
99 // method were used. If it evolves (is replaced), the nmethod
100 // must be recompiled. No other dependencies are implied.
101 evol_method,
102 FIRST_TYPE = evol_method,
103
104 // A context type CX is a leaf it if has no proper subtype.
105 leaf_type,
106
107 // An abstract class CX has exactly one concrete subtype CC.
108 abstract_with_unique_concrete_subtype,
109
110 // The type CX is purely abstract, with no concrete subtype* at all.
111 abstract_with_no_concrete_subtype,
112
113 // The concrete CX is free of concrete proper subtypes.
114 concrete_with_no_concrete_subtype,
115
116 // Given a method M1 and a context class CX, the set MM(CX, M1) of
117 // "concrete matching methods" in CX of M1 is the set of every
118 // concrete M2 for which it is possible to create an invokevirtual
119 // or invokeinterface call site that can reach either M1 or M2.
120 // That is, M1 and M2 share a name, signature, and vtable index.
121 // We wish to notice when the set MM(CX, M1) is just {M1}, or
122 // perhaps a set of two {M1,M2}, and issue dependencies on this.
123
124 // The set MM(CX, M1) can be computed by starting with any matching
125 // concrete M2 that is inherited into CX, and then walking the
126 // subtypes* of CX looking for concrete definitions.
127
128 // The parameters to this dependency are the method M1 and the
129 // context class CX. M1 must be either inherited in CX or defined
130 // in a subtype* of CX. It asserts that MM(CX, M1) is no greater
131 // than {M1}.
132 unique_concrete_method, // one unique concrete method under CX
133
134 // An "exclusive" assertion concerns two methods or subtypes, and
135 // declares that there are at most two (or perhaps later N>2)
136 // specific items that jointly satisfy the restriction.
137 // We list all items explicitly rather than just giving their
138 // count, for robustness in the face of complex schema changes.
139
140 // A context class CX (which may be either abstract or concrete)
141 // has two exclusive concrete subtypes* C1, C2 if every concrete
142 // subtype* of CX is either C1 or C2. Note that if neither C1 or C2
143 // are equal to CX, then CX itself must be abstract. But it is
144 // also possible (for example) that C1 is CX (a concrete class)
145 // and C2 is a proper subtype of C1.
146 abstract_with_exclusive_concrete_subtypes_2,
147
148 // This dependency asserts that MM(CX, M1) is no greater than {M1,M2}.
149 exclusive_concrete_methods_2,
150
151 // This dependency asserts that no instances of class or it's
152 // subclasses require finalization registration.
153 no_finalizable_subclasses,
154
155 TYPE_LIMIT
156 };
157 enum {
158 LG2_TYPE_LIMIT = 4, // assert(TYPE_LIMIT <= (1<<LG2_TYPE_LIMIT))
159
160 // handy categorizations of dependency types:
161 all_types = ((1<<TYPE_LIMIT)-1) & ((-1)<<FIRST_TYPE),
162 non_ctxk_types = (1<<evol_method),
163 ctxk_types = all_types & ~non_ctxk_types,
164
165 max_arg_count = 3, // current maximum number of arguments (incl. ctxk)
166
167 // A "context type" is a class or interface that
168 // provides context for evaluating a dependency.
169 // When present, it is one of the arguments (dep_context_arg).
170 //
171 // If a dependency does not have a context type, there is a
172 // default context, depending on the type of the dependency.
173 // This bit signals that a default context has been compressed away.
174 default_context_type_bit = (1<<LG2_TYPE_LIMIT)
175 };
176
177 static const char* dep_name(DepType dept);
178 static int dep_args(DepType dept);
179 static int dep_context_arg(DepType dept) {
180 return dept_in_mask(dept, ctxk_types)? 0: -1;
181 }
182
183 private:
184 // State for writing a new set of dependencies:
185 GrowableArray<int>* _dep_seen; // (seen[h->ident] & (1<<dept))
186 GrowableArray<ciObject*>* _deps[TYPE_LIMIT];
187
188 static const char* _dep_name[TYPE_LIMIT];
189 static int _dep_args[TYPE_LIMIT];
190
191 static bool dept_in_mask(DepType dept, int mask) {
192 return (int)dept >= 0 && dept < TYPE_LIMIT && ((1<<dept) & mask) != 0;
193 }
194
195 bool note_dep_seen(int dept, ciObject* x) {
196 assert(dept < BitsPerInt, "oob");
197 int x_id = x->ident();
198 assert(_dep_seen != NULL, "deps must be writable");
199 int seen = _dep_seen->at_grow(x_id, 0);
200 _dep_seen->at_put(x_id, seen | (1<<dept));
201 // return true if we've already seen dept/x
202 return (seen & (1<<dept)) != 0;
203 }
204
205 bool maybe_merge_ctxk(GrowableArray<ciObject*>* deps,
206 int ctxk_i, ciKlass* ctxk);
207
208 void sort_all_deps();
209 size_t estimate_size_in_bytes();
210
211 // Initialize _deps, etc.
212 void initialize(ciEnv* env);
213
214 // State for making a new set of dependencies:
215 OopRecorder* _oop_recorder;
216
217 // Logging support
218 CompileLog* _log;
219
220 address _content_bytes; // everything but the oop references, encoded
221 size_t _size_in_bytes;
222
223 public:
224 // Make a new empty dependencies set.
225 Dependencies(ciEnv* env) {
226 initialize(env);
227 }
228
229 private:
230 // Check for a valid context type.
231 // Enforce the restriction against array types.
232 static void check_ctxk(ciKlass* ctxk) {
233 assert(ctxk->is_instance_klass(), "java types only");
234 }
235 static void check_ctxk_concrete(ciKlass* ctxk) {
236 assert(is_concrete_klass(ctxk->as_instance_klass()), "must be concrete");
237 }
238 static void check_ctxk_abstract(ciKlass* ctxk) {
239 check_ctxk(ctxk);
240 assert(!is_concrete_klass(ctxk->as_instance_klass()), "must be abstract");
241 }
242
243 void assert_common_1(DepType dept, ciObject* x);
244 void assert_common_2(DepType dept, ciKlass* ctxk, ciObject* x);
245 void assert_common_3(DepType dept, ciKlass* ctxk, ciObject* x, ciObject* x2);
246
247 public:
248 // Adding assertions to a new dependency set at compile time:
249 void assert_evol_method(ciMethod* m);
250 void assert_leaf_type(ciKlass* ctxk);
251 void assert_abstract_with_unique_concrete_subtype(ciKlass* ctxk, ciKlass* conck);
252 void assert_abstract_with_no_concrete_subtype(ciKlass* ctxk);
253 void assert_concrete_with_no_concrete_subtype(ciKlass* ctxk);
254 void assert_unique_concrete_method(ciKlass* ctxk, ciMethod* uniqm);
255 void assert_abstract_with_exclusive_concrete_subtypes(ciKlass* ctxk, ciKlass* k1, ciKlass* k2);
256 void assert_exclusive_concrete_methods(ciKlass* ctxk, ciMethod* m1, ciMethod* m2);
257 void assert_has_no_finalizable_subclasses(ciKlass* ctxk);
258
259 // Define whether a given method or type is concrete.
260 // These methods define the term "concrete" as used in this module.
261 // For this module, an "abstract" class is one which is non-concrete.
262 //
263 // Future optimizations may allow some classes to remain
264 // non-concrete until their first instantiation, and allow some
265 // methods to remain non-concrete until their first invocation.
266 // In that case, there would be a middle ground between concrete
267 // and abstract (as defined by the Java language and VM).
268 static bool is_concrete_klass(klassOop k); // k is instantiable
269 static bool is_concrete_method(methodOop m); // m is invocable
270 static Klass* find_finalizable_subclass(Klass* k);
271
272 // These versions of the concreteness queries work through the CI.
273 // The CI versions are allowed to skew sometimes from the VM
274 // (oop-based) versions. The cost of such a difference is a
275 // (safely) aborted compilation, or a deoptimization, or a missed
276 // optimization opportunity.
277 //
278 // In order to prevent spurious assertions, query results must
279 // remain stable within any single ciEnv instance. (I.e., they must
280 // not go back into the VM to get their value; they must cache the
281 // bit in the CI, either eagerly or lazily.)
282 static bool is_concrete_klass(ciInstanceKlass* k); // k appears instantiable
283 static bool is_concrete_method(ciMethod* m); // m appears invocable
284 static bool has_finalizable_subclass(ciInstanceKlass* k);
285
286 // As a general rule, it is OK to compile under the assumption that
287 // a given type or method is concrete, even if it at some future
288 // point becomes abstract. So dependency checking is one-sided, in
289 // that it permits supposedly concrete classes or methods to turn up
290 // as really abstract. (This shouldn't happen, except during class
291 // evolution, but that's the logic of the checking.) However, if a
292 // supposedly abstract class or method suddenly becomes concrete, a
293 // dependency on it must fail.
294
295 // Checking old assertions at run-time (in the VM only):
296 static klassOop check_evol_method(methodOop m);
297 static klassOop check_leaf_type(klassOop ctxk);
298 static klassOop check_abstract_with_unique_concrete_subtype(klassOop ctxk, klassOop conck,
299 DepChange* changes = NULL);
300 static klassOop check_abstract_with_no_concrete_subtype(klassOop ctxk,
301 DepChange* changes = NULL);
302 static klassOop check_concrete_with_no_concrete_subtype(klassOop ctxk,
303 DepChange* changes = NULL);
304 static klassOop check_unique_concrete_method(klassOop ctxk, methodOop uniqm,
305 DepChange* changes = NULL);
306 static klassOop check_abstract_with_exclusive_concrete_subtypes(klassOop ctxk, klassOop k1, klassOop k2,
307 DepChange* changes = NULL);
308 static klassOop check_exclusive_concrete_methods(klassOop ctxk, methodOop m1, methodOop m2,
309 DepChange* changes = NULL);
310 static klassOop check_has_no_finalizable_subclasses(klassOop ctxk,
311 DepChange* changes = NULL);
312 // A returned klassOop is NULL if the dependency assertion is still
313 // valid. A non-NULL klassOop is a 'witness' to the assertion
314 // failure, a point in the class hierarchy where the assertion has
315 // been proven false. For example, if check_leaf_type returns
316 // non-NULL, the value is a subtype of the supposed leaf type. This
317 // witness value may be useful for logging the dependency failure.
318 // Note that, when a dependency fails, there may be several possible
319 // witnesses to the failure. The value returned from the check_foo
320 // method is chosen arbitrarily.
321
322 // The 'changes' value, if non-null, requests a limited spot-check
323 // near the indicated recent changes in the class hierarchy.
324 // It is used by DepStream::spot_check_dependency_at.
325
326 // Detecting possible new assertions:
327 static klassOop find_unique_concrete_subtype(klassOop ctxk);
328 static methodOop find_unique_concrete_method(klassOop ctxk, methodOop m);
329 static int find_exclusive_concrete_subtypes(klassOop ctxk, int klen, klassOop k[]);
330 static int find_exclusive_concrete_methods(klassOop ctxk, int mlen, methodOop m[]);
331
332 // Create the encoding which will be stored in an nmethod.
333 void encode_content_bytes();
334
335 address content_bytes() {
336 assert(_content_bytes != NULL, "encode it first");
337 return _content_bytes;
338 }
339 size_t size_in_bytes() {
340 assert(_content_bytes != NULL, "encode it first");
341 return _size_in_bytes;
342 }
343
344 OopRecorder* oop_recorder() { return _oop_recorder; }
345 CompileLog* log() { return _log; }
346
347 void copy_to(nmethod* nm);
348
349 void log_all_dependencies();
350 void log_dependency(DepType dept, int nargs, ciObject* args[]) {
351 write_dependency_to(log(), dept, nargs, args);
352 }
353 void log_dependency(DepType dept,
354 ciObject* x0,
355 ciObject* x1 = NULL,
356 ciObject* x2 = NULL) {
357 if (log() == NULL) return;
358 ciObject* args[max_arg_count];
359 args[0] = x0;
360 args[1] = x1;
361 args[2] = x2;
362 assert(2 < max_arg_count, "");
363 log_dependency(dept, dep_args(dept), args);
364 }
365
366 static void write_dependency_to(CompileLog* log,
367 DepType dept,
368 int nargs, ciObject* args[],
369 klassOop witness = NULL);
370 static void write_dependency_to(CompileLog* log,
371 DepType dept,
372 int nargs, oop args[],
373 klassOop witness = NULL);
374 static void write_dependency_to(xmlStream* xtty,
375 DepType dept,
376 int nargs, oop args[],
377 klassOop witness = NULL);
378 static void print_dependency(DepType dept,
379 int nargs, oop args[],
380 klassOop witness = NULL);
381
382 private:
383 // helper for encoding common context types as zero:
384 static ciKlass* ctxk_encoded_as_null(DepType dept, ciObject* x);
385
386 static klassOop ctxk_encoded_as_null(DepType dept, oop x);
387
388 public:
389 // Use this to iterate over an nmethod's dependency set.
390 // Works on new and old dependency sets.
391 // Usage:
392 //
393 // ;
394 // Dependencies::DepType dept;
395 // for (Dependencies::DepStream deps(nm); deps.next(); ) {
396 // ...
397 // }
398 //
399 // The caller must be in the VM, since oops are not wrapped in handles.
400 class DepStream {
401 private:
402 nmethod* _code; // null if in a compiler thread
403 Dependencies* _deps; // null if not in a compiler thread
404 CompressedReadStream _bytes;
405 #ifdef ASSERT
406 size_t _byte_limit;
407 #endif
408
409 // iteration variables:
410 DepType _type;
411 int _xi[max_arg_count+1];
412
413 void initial_asserts(size_t byte_limit) NOT_DEBUG({});
414
415 inline oop recorded_oop_at(int i);
416 // => _code? _code->oop_at(i): *_deps->_oop_recorder->handle_at(i)
417
418 klassOop check_dependency_impl(DepChange* changes);
419
420 public:
421 DepStream(Dependencies* deps)
422 : _deps(deps),
423 _code(NULL),
424 _bytes(deps->content_bytes())
425 {
426 initial_asserts(deps->size_in_bytes());
427 }
428 DepStream(nmethod* code)
429 : _deps(NULL),
430 _code(code),
431 _bytes(code->dependencies_begin())
432 {
433 initial_asserts(code->dependencies_size());
434 }
435
436 bool next();
437
438 DepType type() { return _type; }
439 int argument_count() { return dep_args(type()); }
440 int argument_index(int i) { assert(0 <= i && i < argument_count(), "oob");
441 return _xi[i]; }
442 oop argument(int i); // => recorded_oop_at(argument_index(i))
443 klassOop context_type();
444
445 methodOop method_argument(int i) {
446 oop x = argument(i);
447 assert(x->is_method(), "type");
448 return (methodOop) x;
449 }
450 klassOop type_argument(int i) {
451 oop x = argument(i);
452 assert(x->is_klass(), "type");
453 return (klassOop) x;
454 }
455
456 // The point of the whole exercise: Is this dep is still OK?
457 klassOop check_dependency() {
458 return check_dependency_impl(NULL);
459 }
460 // A lighter version: Checks only around recent changes in a class
461 // hierarchy. (See Universe::flush_dependents_on.)
462 klassOop spot_check_dependency_at(DepChange& changes);
463
464 // Log the current dependency to xtty or compilation log.
465 void log_dependency(klassOop witness = NULL);
466
467 // Print the current dependency to tty.
468 void print_dependency(klassOop witness = NULL, bool verbose = false);
469 };
470 friend class Dependencies::DepStream;
471
472 static void print_statistics() PRODUCT_RETURN;
473 };
474
475 // A class hierarchy change coming through the VM (under the Compile_lock).
476 // The change is structured as a single new type with any number of supers
477 // and implemented interface types. Other than the new type, any of the
478 // super types can be context types for a relevant dependency, which the
479 // new type could invalidate.
480 class DepChange : public StackObj {
481 public:
482 enum ChangeType {
483 NO_CHANGE = 0, // an uninvolved klass
484 Change_new_type, // a newly loaded type
485 Change_new_sub, // a super with a new subtype
486 Change_new_impl, // an interface with a new implementation
487 CHANGE_LIMIT,
488 Start_Klass = CHANGE_LIMIT // internal indicator for ContextStream
489 };
490
491 private:
492 // each change set is rooted in exactly one new type (at present):
493 KlassHandle _new_type;
494
495 void initialize();
496
497 public:
498 // notes the new type, marks it and all its super-types
499 DepChange(KlassHandle new_type)
500 : _new_type(new_type)
501 {
502 initialize();
503 }
504
505 // cleans up the marks
506 ~DepChange();
507
508 klassOop new_type() { return _new_type(); }
509
510 // involves_context(k) is true if k is new_type or any of the super types
511 bool involves_context(klassOop k);
512
513 // Usage:
514 // for (DepChange::ContextStream str(changes); str.next(); ) {
515 // klassOop k = str.klass();
516 // switch (str.change_type()) {
517 // ...
518 // }
519 // }
520 class ContextStream : public StackObj {
521 private:
522 DepChange& _changes;
523 friend class DepChange;
524
525 // iteration variables:
526 ChangeType _change_type;
527 klassOop _klass;
528 objArrayOop _ti_base; // i.e., transitive_interfaces
529 int _ti_index;
530 int _ti_limit;
531
532 // start at the beginning:
533 void start() {
534 klassOop new_type = _changes.new_type();
535 _change_type = (new_type == NULL ? NO_CHANGE: Start_Klass);
536 _klass = new_type;
537 _ti_base = NULL;
538 _ti_index = 0;
539 _ti_limit = 0;
540 }
541
542 public:
543 ContextStream(DepChange& changes)
544 : _changes(changes)
545 { start(); }
546
547 ContextStream(DepChange& changes, No_Safepoint_Verifier& nsv)
548 : _changes(changes)
549 // the nsv argument makes it safe to hold oops like _klass
550 { start(); }
551
552 bool next();
553
554 ChangeType change_type() { return _change_type; }
555 klassOop klass() { return _klass; }
556 };
557 friend class DepChange::ContextStream;
558
559 void print();
560 };
561
562 #endif // SHARE_VM_CODE_DEPENDENCIES_HPP