1 /*
   2  * Copyright (c) 2005, 2019, 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,
  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_CODE_DEPENDENCIES_HPP
  26 #define SHARE_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 "memory/resourceArea.hpp"
  36 #include "runtime/safepointVerifiers.hpp"
  37 #include "utilities/growableArray.hpp"
  38 #include "utilities/hashtable.hpp"
  39 
  40 //** Dependencies represent assertions (approximate invariants) within
  41 // the runtime system, e.g. class hierarchy changes.  An example is an
  42 // assertion that a given method is not overridden; another example is
  43 // that a type has only one concrete subtype.  Compiled code which
  44 // relies on such assertions must be discarded if they are overturned
  45 // by changes in the runtime system.  We can think of these assertions
  46 // as approximate invariants, because we expect them to be overturned
  47 // very infrequently.  We are willing to perform expensive recovery
  48 // operations when they are overturned.  The benefit, of course, is
  49 // performing optimistic optimizations (!) on the object code.
  50 //
  51 // Changes in the class hierarchy due to dynamic linking or
  52 // class evolution can violate dependencies.  There is enough
  53 // indexing between classes and nmethods to make dependency
  54 // checking reasonably efficient.
  55 
  56 class ciEnv;
  57 class nmethod;
  58 class OopRecorder;
  59 class xmlStream;
  60 class CompileLog;
  61 class DepChange;
  62 class   KlassDepChange;
  63 class   CallSiteDepChange;
  64 class NoSafepointVerifier;
  65 
  66 class Dependencies: public ResourceObj {
  67  public:
  68   // Note: In the comments on dependency types, most uses of the terms
  69   // subtype and supertype are used in a "non-strict" or "inclusive"
  70   // sense, and are starred to remind the reader of this fact.
  71   // Strict uses of the terms use the word "proper".
  72   //
  73   // Specifically, every class is its own subtype* and supertype*.
  74   // (This trick is easier than continually saying things like "Y is a
  75   // subtype of X or X itself".)
  76   //
  77   // Sometimes we write X > Y to mean X is a proper supertype of Y.
  78   // The notation X > {Y, Z} means X has proper subtypes Y, Z.
  79   // The notation X.m > Y means that Y inherits m from X, while
  80   // X.m > Y.m means Y overrides X.m.  A star denotes abstractness,
  81   // as *I > A, meaning (abstract) interface I is a super type of A,
  82   // or A.*m > B.m, meaning B.m implements abstract method A.m.
  83   //
  84   // In this module, the terms "subtype" and "supertype" refer to
  85   // Java-level reference type conversions, as detected by
  86   // "instanceof" and performed by "checkcast" operations.  The method
  87   // Klass::is_subtype_of tests these relations.  Note that "subtype"
  88   // is richer than "subclass" (as tested by Klass::is_subclass_of),
  89   // since it takes account of relations involving interface and array
  90   // types.
  91   //
  92   // To avoid needless complexity, dependencies involving array types
  93   // are not accepted.  If you need to make an assertion about an
  94   // array type, make the assertion about its corresponding element
  95   // types.  Any assertion that might change about an array type can
  96   // be converted to an assertion about its element type.
  97   //
  98   // Most dependencies are evaluated over a "context type" CX, which
  99   // stands for the set Subtypes(CX) of every Java type that is a subtype*
 100   // of CX.  When the system loads a new class or interface N, it is
 101   // responsible for re-evaluating changed dependencies whose context
 102   // type now includes N, that is, all super types of N.
 103   //
 104   enum DepType {
 105     end_marker = 0,
 106 
 107     // An 'evol' dependency simply notes that the contents of the
 108     // method were used.  If it evolves (is replaced), the nmethod
 109     // must be recompiled.  No other dependencies are implied.
 110     evol_method,
 111     FIRST_TYPE = evol_method,
 112 
 113     // A context type CX is a leaf it if has no proper subtype.
 114     leaf_type,
 115 
 116     // An abstract class CX has exactly one concrete subtype CC.
 117     abstract_with_unique_concrete_subtype,
 118 
 119     // The type CX is purely abstract, with no concrete subtype* at all.
 120     abstract_with_no_concrete_subtype,
 121 
 122     // The concrete CX is free of concrete proper subtypes.
 123     concrete_with_no_concrete_subtype,
 124 
 125     // Given a method M1 and a context class CX, the set MM(CX, M1) of
 126     // "concrete matching methods" in CX of M1 is the set of every
 127     // concrete M2 for which it is possible to create an invokevirtual
 128     // or invokeinterface call site that can reach either M1 or M2.
 129     // That is, M1 and M2 share a name, signature, and vtable index.
 130     // We wish to notice when the set MM(CX, M1) is just {M1}, or
 131     // perhaps a set of two {M1,M2}, and issue dependencies on this.
 132 
 133     // The set MM(CX, M1) can be computed by starting with any matching
 134     // concrete M2 that is inherited into CX, and then walking the
 135     // subtypes* of CX looking for concrete definitions.
 136 
 137     // The parameters to this dependency are the method M1 and the
 138     // context class CX.  M1 must be either inherited in CX or defined
 139     // in a subtype* of CX.  It asserts that MM(CX, M1) is no greater
 140     // than {M1}.
 141     unique_concrete_method,       // one unique concrete method under CX
 142 
 143     // An "exclusive" assertion concerns two methods or subtypes, and
 144     // declares that there are at most two (or perhaps later N>2)
 145     // specific items that jointly satisfy the restriction.
 146     // We list all items explicitly rather than just giving their
 147     // count, for robustness in the face of complex schema changes.
 148 
 149     // A context class CX (which may be either abstract or concrete)
 150     // has two exclusive concrete subtypes* C1, C2 if every concrete
 151     // subtype* of CX is either C1 or C2.  Note that if neither C1 or C2
 152     // are equal to CX, then CX itself must be abstract.  But it is
 153     // also possible (for example) that C1 is CX (a concrete class)
 154     // and C2 is a proper subtype of C1.
 155     abstract_with_exclusive_concrete_subtypes_2,
 156 
 157     // This dependency asserts that MM(CX, M1) is no greater than {M1,M2}.
 158     exclusive_concrete_methods_2,
 159 
 160     // This dependency asserts that no instances of class or it's
 161     // subclasses require finalization registration.
 162     no_finalizable_subclasses,
 163 
 164     // This dependency asserts when the CallSite.target value changed.
 165     call_site_target_value,
 166 
 167     TYPE_LIMIT
 168   };
 169   enum {
 170     LG2_TYPE_LIMIT = 4,  // assert(TYPE_LIMIT <= (1<<LG2_TYPE_LIMIT))
 171 
 172     // handy categorizations of dependency types:
 173     all_types           = ((1 << TYPE_LIMIT) - 1) & ((~0u) << FIRST_TYPE),
 174 
 175     non_klass_types     = (1 << call_site_target_value),
 176     klass_types         = all_types & ~non_klass_types,
 177 
 178     non_ctxk_types      = (1 << evol_method) | (1 << call_site_target_value),
 179     implicit_ctxk_types = 0,
 180     explicit_ctxk_types = all_types & ~(non_ctxk_types | implicit_ctxk_types),
 181 
 182     max_arg_count = 3,   // current maximum number of arguments (incl. ctxk)
 183 
 184     // A "context type" is a class or interface that
 185     // provides context for evaluating a dependency.
 186     // When present, it is one of the arguments (dep_context_arg).
 187     //
 188     // If a dependency does not have a context type, there is a
 189     // default context, depending on the type of the dependency.
 190     // This bit signals that a default context has been compressed away.
 191     default_context_type_bit = (1<<LG2_TYPE_LIMIT)
 192   };
 193 
 194   static const char* dep_name(DepType dept);
 195   static int         dep_args(DepType dept);
 196 
 197   static bool is_klass_type(           DepType dept) { return dept_in_mask(dept, klass_types        ); }
 198 
 199   static bool has_explicit_context_arg(DepType dept) { return dept_in_mask(dept, explicit_ctxk_types); }
 200   static bool has_implicit_context_arg(DepType dept) { return dept_in_mask(dept, implicit_ctxk_types); }
 201 
 202   static int           dep_context_arg(DepType dept) { return has_explicit_context_arg(dept) ? 0 : -1; }
 203   static int  dep_implicit_context_arg(DepType dept) { return has_implicit_context_arg(dept) ? 0 : -1; }
 204 
 205   static void check_valid_dependency_type(DepType dept);
 206 
 207 #if INCLUDE_JVMCI
 208   // A Metadata* or object value recorded in an OopRecorder
 209   class DepValue {
 210    private:
 211     // Unique identifier of the value within the associated OopRecorder that
 212     // encodes both the category of the value (0: invalid, positive: metadata, negative: object)
 213     // and the index within a category specific array (metadata: index + 1, object: -(index + 1))
 214     int _id;
 215 
 216    public:
 217     DepValue() : _id(0) {}
 218     DepValue(OopRecorder* rec, Metadata* metadata, DepValue* candidate = NULL) {
 219       assert(candidate == NULL || candidate->is_metadata(), "oops");
 220       if (candidate != NULL && candidate->as_metadata(rec) == metadata) {
 221         _id = candidate->_id;
 222       } else {
 223         _id = rec->find_index(metadata) + 1;
 224       }
 225     }
 226     DepValue(OopRecorder* rec, jobject obj, DepValue* candidate = NULL) {
 227       assert(candidate == NULL || candidate->is_object(), "oops");
 228       if (candidate != NULL && candidate->as_object(rec) == obj) {
 229         _id = candidate->_id;
 230       } else {
 231         _id = -(rec->find_index(obj) + 1);
 232       }
 233     }
 234 
 235     // Used to sort values in ascending order of index() with metadata values preceding object values
 236     int sort_key() const { return -_id; }
 237 
 238     bool operator == (const DepValue& other) const   { return other._id == _id; }
 239 
 240     bool is_valid() const             { return _id != 0; }
 241     int  index() const                { assert(is_valid(), "oops"); return _id < 0 ? -(_id + 1) : _id - 1; }
 242     bool is_metadata() const          { assert(is_valid(), "oops"); return _id > 0; }
 243     bool is_object() const            { assert(is_valid(), "oops"); return _id < 0; }
 244 
 245     Metadata*  as_metadata(OopRecorder* rec) const    { assert(is_metadata(), "oops"); return rec->metadata_at(index()); }
 246     Klass*     as_klass(OopRecorder* rec) const {
 247       Metadata* m = as_metadata(rec);
 248       assert(m != NULL, "as_metadata returned NULL");
 249       assert(m->is_klass(), "oops");
 250       return (Klass*) m;
 251     }
 252     Method*    as_method(OopRecorder* rec) const {
 253       Metadata* m = as_metadata(rec);
 254       assert(m != NULL, "as_metadata returned NULL");
 255       assert(m->is_method(), "oops");
 256       return (Method*) m;
 257     }
 258     jobject    as_object(OopRecorder* rec) const      { assert(is_object(), "oops"); return rec->oop_at(index()); }
 259   };
 260 #endif // INCLUDE_JVMCI
 261 
 262  private:
 263   // State for writing a new set of dependencies:
 264   GrowableArray<int>*       _dep_seen;  // (seen[h->ident] & (1<<dept))
 265   GrowableArray<ciBaseObject*>*  _deps[TYPE_LIMIT];
 266 #if INCLUDE_JVMCI
 267   bool _using_dep_values;
 268   GrowableArray<DepValue>*  _dep_values[TYPE_LIMIT];
 269 #endif
 270 
 271   static const char* _dep_name[TYPE_LIMIT];
 272   static int         _dep_args[TYPE_LIMIT];
 273 
 274   static bool dept_in_mask(DepType dept, int mask) {
 275     return (int)dept >= 0 && dept < TYPE_LIMIT && ((1<<dept) & mask) != 0;
 276   }
 277 
 278   bool note_dep_seen(int dept, ciBaseObject* x) {
 279     assert(dept < BitsPerInt, "oob");
 280     int x_id = x->ident();
 281     assert(_dep_seen != NULL, "deps must be writable");
 282     int seen = _dep_seen->at_grow(x_id, 0);
 283     _dep_seen->at_put(x_id, seen | (1<<dept));
 284     // return true if we've already seen dept/x
 285     return (seen & (1<<dept)) != 0;
 286   }
 287 
 288 #if INCLUDE_JVMCI
 289   bool note_dep_seen(int dept, DepValue x) {
 290     assert(dept < BitsPerInt, "oops");
 291     // place metadata deps at even indexes, object deps at odd indexes
 292     int x_id = x.is_metadata() ? x.index() * 2 : (x.index() * 2) + 1;
 293     assert(_dep_seen != NULL, "deps must be writable");
 294     int seen = _dep_seen->at_grow(x_id, 0);
 295     _dep_seen->at_put(x_id, seen | (1<<dept));
 296     // return true if we've already seen dept/x
 297     return (seen & (1<<dept)) != 0;
 298   }
 299 #endif
 300 
 301   bool maybe_merge_ctxk(GrowableArray<ciBaseObject*>* deps,
 302                         int ctxk_i, ciKlass* ctxk);
 303 #if INCLUDE_JVMCI
 304   bool maybe_merge_ctxk(GrowableArray<DepValue>* deps,
 305                         int ctxk_i, DepValue ctxk);
 306 #endif
 307 
 308   void sort_all_deps();
 309   size_t estimate_size_in_bytes();
 310 
 311   // Initialize _deps, etc.
 312   void initialize(ciEnv* env);
 313 
 314   // State for making a new set of dependencies:
 315   OopRecorder* _oop_recorder;
 316 
 317   // Logging support
 318   CompileLog* _log;
 319 
 320   address  _content_bytes;  // everything but the oop references, encoded
 321   size_t   _size_in_bytes;
 322 
 323  public:
 324   // Make a new empty dependencies set.
 325   Dependencies(ciEnv* env) {
 326     initialize(env);
 327   }
 328 #if INCLUDE_JVMCI
 329   Dependencies(Arena* arena, OopRecorder* oop_recorder, CompileLog* log);
 330 #endif
 331 
 332  private:
 333   // Check for a valid context type.
 334   // Enforce the restriction against array types.
 335   static void check_ctxk(ciKlass* ctxk) {
 336     assert(ctxk->is_instance_klass(), "java types only");
 337   }
 338   static void check_ctxk_concrete(ciKlass* ctxk) {
 339     assert(is_concrete_klass(ctxk->as_instance_klass()), "must be concrete");
 340   }
 341   static void check_ctxk_abstract(ciKlass* ctxk) {
 342     check_ctxk(ctxk);
 343     assert(!is_concrete_klass(ctxk->as_instance_klass()), "must be abstract");
 344   }
 345   static void check_unique_method(ciKlass* ctxk, ciMethod* m) {
 346     assert(!m->can_be_statically_bound(ctxk->as_instance_klass()), "redundant");
 347   }
 348 
 349   void assert_common_1(DepType dept, ciBaseObject* x);
 350   void assert_common_2(DepType dept, ciBaseObject* x0, ciBaseObject* x1);
 351   void assert_common_3(DepType dept, ciKlass* ctxk, ciBaseObject* x1, ciBaseObject* x2);
 352 
 353  public:
 354   // Adding assertions to a new dependency set at compile time:
 355   void assert_evol_method(ciMethod* m);
 356   void assert_leaf_type(ciKlass* ctxk);
 357   void assert_abstract_with_unique_concrete_subtype(ciKlass* ctxk, ciKlass* conck);
 358   void assert_abstract_with_no_concrete_subtype(ciKlass* ctxk);
 359   void assert_concrete_with_no_concrete_subtype(ciKlass* ctxk);
 360   void assert_unique_concrete_method(ciKlass* ctxk, ciMethod* uniqm);
 361   void assert_abstract_with_exclusive_concrete_subtypes(ciKlass* ctxk, ciKlass* k1, ciKlass* k2);
 362   void assert_exclusive_concrete_methods(ciKlass* ctxk, ciMethod* m1, ciMethod* m2);
 363   void assert_has_no_finalizable_subclasses(ciKlass* ctxk);
 364   void assert_call_site_target_value(ciCallSite* call_site, ciMethodHandle* method_handle);
 365 
 366 #if INCLUDE_JVMCI
 367  private:
 368   static void check_ctxk(Klass* ctxk) {
 369     assert(ctxk->is_instance_klass(), "java types only");
 370   }
 371   static void check_ctxk_abstract(Klass* ctxk) {
 372     check_ctxk(ctxk);
 373     assert(ctxk->is_abstract(), "must be abstract");
 374   }
 375   static void check_unique_method(Klass* ctxk, Method* m) {
 376     assert(!m->can_be_statically_bound(InstanceKlass::cast(ctxk)), "redundant");
 377   }
 378 
 379   void assert_common_1(DepType dept, DepValue x);
 380   void assert_common_2(DepType dept, DepValue x0, DepValue x1);
 381 
 382  public:
 383   void assert_evol_method(Method* m);
 384   void assert_has_no_finalizable_subclasses(Klass* ctxk);
 385   void assert_leaf_type(Klass* ctxk);
 386   void assert_unique_concrete_method(Klass* ctxk, Method* uniqm);
 387   void assert_abstract_with_unique_concrete_subtype(Klass* ctxk, Klass* conck);
 388   void assert_call_site_target_value(oop callSite, oop methodHandle);
 389 #endif // INCLUDE_JVMCI
 390 
 391   // Define whether a given method or type is concrete.
 392   // These methods define the term "concrete" as used in this module.
 393   // For this module, an "abstract" class is one which is non-concrete.
 394   //
 395   // Future optimizations may allow some classes to remain
 396   // non-concrete until their first instantiation, and allow some
 397   // methods to remain non-concrete until their first invocation.
 398   // In that case, there would be a middle ground between concrete
 399   // and abstract (as defined by the Java language and VM).
 400   static bool is_concrete_klass(Klass* k);    // k is instantiable
 401   static bool is_concrete_method(Method* m, Klass* k);  // m is invocable
 402   static Klass* find_finalizable_subclass(Klass* k);
 403 
 404   // These versions of the concreteness queries work through the CI.
 405   // The CI versions are allowed to skew sometimes from the VM
 406   // (oop-based) versions.  The cost of such a difference is a
 407   // (safely) aborted compilation, or a deoptimization, or a missed
 408   // optimization opportunity.
 409   //
 410   // In order to prevent spurious assertions, query results must
 411   // remain stable within any single ciEnv instance.  (I.e., they must
 412   // not go back into the VM to get their value; they must cache the
 413   // bit in the CI, either eagerly or lazily.)
 414   static bool is_concrete_klass(ciInstanceKlass* k); // k appears instantiable
 415   static bool has_finalizable_subclass(ciInstanceKlass* k);
 416 
 417   // As a general rule, it is OK to compile under the assumption that
 418   // a given type or method is concrete, even if it at some future
 419   // point becomes abstract.  So dependency checking is one-sided, in
 420   // that it permits supposedly concrete classes or methods to turn up
 421   // as really abstract.  (This shouldn't happen, except during class
 422   // evolution, but that's the logic of the checking.)  However, if a
 423   // supposedly abstract class or method suddenly becomes concrete, a
 424   // dependency on it must fail.
 425 
 426   // Checking old assertions at run-time (in the VM only):
 427   static Klass* check_evol_method(Method* m);
 428   static Klass* check_leaf_type(Klass* ctxk);
 429   static Klass* check_abstract_with_unique_concrete_subtype(Klass* ctxk, Klass* conck,
 430                                                               KlassDepChange* changes = NULL);
 431   static Klass* check_abstract_with_no_concrete_subtype(Klass* ctxk,
 432                                                           KlassDepChange* changes = NULL);
 433   static Klass* check_concrete_with_no_concrete_subtype(Klass* ctxk,
 434                                                           KlassDepChange* changes = NULL);
 435   static Klass* check_unique_concrete_method(Klass* ctxk, Method* uniqm,
 436                                                KlassDepChange* changes = NULL);
 437   static Klass* check_abstract_with_exclusive_concrete_subtypes(Klass* ctxk, Klass* k1, Klass* k2,
 438                                                                   KlassDepChange* changes = NULL);
 439   static Klass* check_exclusive_concrete_methods(Klass* ctxk, Method* m1, Method* m2,
 440                                                    KlassDepChange* changes = NULL);
 441   static Klass* check_has_no_finalizable_subclasses(Klass* ctxk, KlassDepChange* changes = NULL);
 442   static Klass* check_call_site_target_value(oop call_site, oop method_handle, CallSiteDepChange* changes = NULL);
 443   // A returned Klass* is NULL if the dependency assertion is still
 444   // valid.  A non-NULL Klass* is a 'witness' to the assertion
 445   // failure, a point in the class hierarchy where the assertion has
 446   // been proven false.  For example, if check_leaf_type returns
 447   // non-NULL, the value is a subtype of the supposed leaf type.  This
 448   // witness value may be useful for logging the dependency failure.
 449   // Note that, when a dependency fails, there may be several possible
 450   // witnesses to the failure.  The value returned from the check_foo
 451   // method is chosen arbitrarily.
 452 
 453   // The 'changes' value, if non-null, requests a limited spot-check
 454   // near the indicated recent changes in the class hierarchy.
 455   // It is used by DepStream::spot_check_dependency_at.
 456 
 457   // Detecting possible new assertions:
 458   static Klass*    find_unique_concrete_subtype(Klass* ctxk);
 459   static Method*   find_unique_concrete_method(Klass* ctxk, Method* m);
 460   static int       find_exclusive_concrete_subtypes(Klass* ctxk, int klen, Klass* k[]);
 461 
 462   // Create the encoding which will be stored in an nmethod.
 463   void encode_content_bytes();
 464 
 465   address content_bytes() {
 466     assert(_content_bytes != NULL, "encode it first");
 467     return _content_bytes;
 468   }
 469   size_t size_in_bytes() {
 470     assert(_content_bytes != NULL, "encode it first");
 471     return _size_in_bytes;
 472   }
 473 
 474   OopRecorder* oop_recorder() { return _oop_recorder; }
 475   CompileLog*  log()          { return _log; }
 476 
 477   void copy_to(nmethod* nm);
 478 
 479   DepType validate_dependencies(CompileTask* task, bool counter_changed, char** failure_detail = NULL);
 480 
 481   void log_all_dependencies();
 482 
 483   void log_dependency(DepType dept, GrowableArray<ciBaseObject*>* args) {
 484     ResourceMark rm;
 485     int argslen = args->length();
 486     write_dependency_to(log(), dept, args);
 487     guarantee(argslen == args->length(),
 488               "args array cannot grow inside nested ResoureMark scope");
 489   }
 490 
 491   void log_dependency(DepType dept,
 492                       ciBaseObject* x0,
 493                       ciBaseObject* x1 = NULL,
 494                       ciBaseObject* x2 = NULL) {
 495     if (log() == NULL) {
 496       return;
 497     }
 498     ResourceMark rm;
 499     GrowableArray<ciBaseObject*>* ciargs =
 500                 new GrowableArray<ciBaseObject*>(dep_args(dept));
 501     assert (x0 != NULL, "no log x0");
 502     ciargs->push(x0);
 503 
 504     if (x1 != NULL) {
 505       ciargs->push(x1);
 506     }
 507     if (x2 != NULL) {
 508       ciargs->push(x2);
 509     }
 510     assert(ciargs->length() == dep_args(dept), "");
 511     log_dependency(dept, ciargs);
 512   }
 513 
 514   class DepArgument : public ResourceObj {
 515    private:
 516     bool  _is_oop;
 517     bool  _valid;
 518     void* _value;
 519    public:
 520     DepArgument() : _is_oop(false), _valid(false), _value(NULL) {}
 521     DepArgument(oop v): _is_oop(true), _valid(true), _value(v) {}
 522     DepArgument(Metadata* v): _is_oop(false), _valid(true), _value(v) {}
 523 
 524     bool is_null() const               { return _value == NULL; }
 525     bool is_oop() const                { return _is_oop; }
 526     bool is_metadata() const           { return !_is_oop; }
 527     bool is_klass() const              { return is_metadata() && metadata_value()->is_klass(); }
 528     bool is_method() const              { return is_metadata() && metadata_value()->is_method(); }
 529 
 530     oop oop_value() const              { assert(_is_oop && _valid, "must be"); return (oop) _value; }
 531     Metadata* metadata_value() const { assert(!_is_oop && _valid, "must be"); return (Metadata*) _value; }
 532   };
 533 
 534   static void print_dependency(DepType dept,
 535                                GrowableArray<DepArgument>* args,
 536                                Klass* witness = NULL, outputStream* st = tty);
 537 
 538  private:
 539   // helper for encoding common context types as zero:
 540   static ciKlass* ctxk_encoded_as_null(DepType dept, ciBaseObject* x);
 541 
 542   static Klass* ctxk_encoded_as_null(DepType dept, Metadata* x);
 543 
 544   static void write_dependency_to(CompileLog* log,
 545                                   DepType dept,
 546                                   GrowableArray<ciBaseObject*>* args,
 547                                   Klass* witness = NULL);
 548   static void write_dependency_to(CompileLog* log,
 549                                   DepType dept,
 550                                   GrowableArray<DepArgument>* args,
 551                                   Klass* witness = NULL);
 552   static void write_dependency_to(xmlStream* xtty,
 553                                   DepType dept,
 554                                   GrowableArray<DepArgument>* args,
 555                                   Klass* witness = NULL);
 556  public:
 557   // Use this to iterate over an nmethod's dependency set.
 558   // Works on new and old dependency sets.
 559   // Usage:
 560   //
 561   // ;
 562   // Dependencies::DepType dept;
 563   // for (Dependencies::DepStream deps(nm); deps.next(); ) {
 564   //   ...
 565   // }
 566   //
 567   // The caller must be in the VM, since oops are not wrapped in handles.
 568   class DepStream {
 569   private:
 570     nmethod*              _code;   // null if in a compiler thread
 571     Dependencies*         _deps;   // null if not in a compiler thread
 572     CompressedReadStream  _bytes;
 573 #ifdef ASSERT
 574     size_t                _byte_limit;
 575 #endif
 576 
 577     // iteration variables:
 578     DepType               _type;
 579     int                   _xi[max_arg_count+1];
 580 
 581     void initial_asserts(size_t byte_limit) NOT_DEBUG({});
 582 
 583     inline Metadata* recorded_metadata_at(int i);
 584     inline oop recorded_oop_at(int i);
 585 
 586     Klass* check_klass_dependency(KlassDepChange* changes);
 587     Klass* check_call_site_dependency(CallSiteDepChange* changes);
 588 
 589     void trace_and_log_witness(Klass* witness);
 590 
 591   public:
 592     DepStream(Dependencies* deps)
 593       : _code(NULL),
 594         _deps(deps),
 595         _bytes(deps->content_bytes())
 596     {
 597       initial_asserts(deps->size_in_bytes());
 598     }
 599     DepStream(nmethod* code)
 600       : _code(code),
 601         _deps(NULL),
 602         _bytes(code->dependencies_begin())
 603     {
 604       initial_asserts(code->dependencies_size());
 605     }
 606 
 607     bool next();
 608 
 609     DepType type()               { return _type; }
 610     bool is_oop_argument(int i)  { return type() == call_site_target_value; }
 611     uintptr_t get_identifier(int i);
 612 
 613     int argument_count()         { return dep_args(type()); }
 614     int argument_index(int i)    { assert(0 <= i && i < argument_count(), "oob");
 615                                    return _xi[i]; }
 616     Metadata* argument(int i);     // => recorded_oop_at(argument_index(i))
 617     oop argument_oop(int i);         // => recorded_oop_at(argument_index(i))
 618     Klass* context_type();
 619 
 620     bool is_klass_type()         { return Dependencies::is_klass_type(type()); }
 621 
 622     Method* method_argument(int i) {
 623       Metadata* x = argument(i);
 624       assert(x->is_method(), "type");
 625       return (Method*) x;
 626     }
 627     Klass* type_argument(int i) {
 628       Metadata* x = argument(i);
 629       assert(x->is_klass(), "type");
 630       return (Klass*) x;
 631     }
 632 
 633     // The point of the whole exercise:  Is this dep still OK?
 634     Klass* check_dependency() {
 635       Klass* result = check_klass_dependency(NULL);
 636       if (result != NULL)  return result;
 637       return check_call_site_dependency(NULL);
 638     }
 639 
 640     // A lighter version:  Checks only around recent changes in a class
 641     // hierarchy.  (See Universe::flush_dependents_on.)
 642     Klass* spot_check_dependency_at(DepChange& changes);
 643 
 644     // Log the current dependency to xtty or compilation log.
 645     void log_dependency(Klass* witness = NULL);
 646 
 647     // Print the current dependency to tty.
 648     void print_dependency(Klass* witness = NULL, bool verbose = false, outputStream* st = tty);
 649   };
 650   friend class Dependencies::DepStream;
 651 
 652   static void print_statistics() PRODUCT_RETURN;
 653 };
 654 
 655 
 656 class DependencySignature : public ResourceObj {
 657  private:
 658   int                   _args_count;
 659   uintptr_t             _argument_hash[Dependencies::max_arg_count];
 660   Dependencies::DepType _type;
 661 
 662  public:
 663   DependencySignature(Dependencies::DepStream& dep) {
 664     _args_count = dep.argument_count();
 665     _type = dep.type();
 666     for (int i = 0; i < _args_count; i++) {
 667       _argument_hash[i] = dep.get_identifier(i);
 668     }
 669   }
 670 
 671   static bool     equals(DependencySignature const& s1, DependencySignature const& s2);
 672   static unsigned hash  (DependencySignature const& s1) { return s1.arg(0) >> 2; }
 673 
 674   int args_count()             const { return _args_count; }
 675   uintptr_t arg(int idx)       const { return _argument_hash[idx]; }
 676   Dependencies::DepType type() const { return _type; }
 677 
 678 };
 679 
 680 
 681 // Every particular DepChange is a sub-class of this class.
 682 class DepChange : public StackObj {
 683  public:
 684   // What kind of DepChange is this?
 685   virtual bool is_klass_change()     const { return false; }
 686   virtual bool is_call_site_change() const { return false; }
 687 
 688   virtual void mark_for_deoptimization(nmethod* nm) = 0;
 689 
 690   // Subclass casting with assertions.
 691   KlassDepChange*    as_klass_change() {
 692     assert(is_klass_change(), "bad cast");
 693     return (KlassDepChange*) this;
 694   }
 695   CallSiteDepChange* as_call_site_change() {
 696     assert(is_call_site_change(), "bad cast");
 697     return (CallSiteDepChange*) this;
 698   }
 699 
 700   void print();
 701 
 702  public:
 703   enum ChangeType {
 704     NO_CHANGE = 0,              // an uninvolved klass
 705     Change_new_type,            // a newly loaded type
 706     Change_new_sub,             // a super with a new subtype
 707     Change_new_impl,            // an interface with a new implementation
 708     CHANGE_LIMIT,
 709     Start_Klass = CHANGE_LIMIT  // internal indicator for ContextStream
 710   };
 711 
 712   // Usage:
 713   // for (DepChange::ContextStream str(changes); str.next(); ) {
 714   //   Klass* k = str.klass();
 715   //   switch (str.change_type()) {
 716   //     ...
 717   //   }
 718   // }
 719   class ContextStream : public StackObj {
 720    private:
 721     DepChange&  _changes;
 722     friend class DepChange;
 723 
 724     // iteration variables:
 725     ChangeType  _change_type;
 726     Klass*      _klass;
 727     Array<InstanceKlass*>* _ti_base;    // i.e., transitive_interfaces
 728     int         _ti_index;
 729     int         _ti_limit;
 730 
 731     // start at the beginning:
 732     void start();
 733 
 734    public:
 735     ContextStream(DepChange& changes)
 736       : _changes(changes)
 737     { start(); }
 738 
 739     ContextStream(DepChange& changes, NoSafepointVerifier& nsv)
 740       : _changes(changes)
 741       // the nsv argument makes it safe to hold oops like _klass
 742     { start(); }
 743 
 744     bool next();
 745 
 746     ChangeType change_type()     { return _change_type; }
 747     Klass*     klass()           { return _klass; }
 748   };
 749   friend class DepChange::ContextStream;
 750 };
 751 
 752 
 753 // A class hierarchy change coming through the VM (under the Compile_lock).
 754 // The change is structured as a single new type with any number of supers
 755 // and implemented interface types.  Other than the new type, any of the
 756 // super types can be context types for a relevant dependency, which the
 757 // new type could invalidate.
 758 class KlassDepChange : public DepChange {
 759  private:
 760   // each change set is rooted in exactly one new type (at present):
 761   Klass* _new_type;
 762 
 763   void initialize();
 764 
 765  public:
 766   // notes the new type, marks it and all its super-types
 767   KlassDepChange(Klass* new_type)
 768     : _new_type(new_type)
 769   {
 770     initialize();
 771   }
 772 
 773   // cleans up the marks
 774   ~KlassDepChange();
 775 
 776   // What kind of DepChange is this?
 777   virtual bool is_klass_change() const { return true; }
 778 
 779   virtual void mark_for_deoptimization(nmethod* nm) {
 780     nm->mark_for_deoptimization(/*inc_recompile_counts=*/true);
 781   }
 782 
 783   Klass* new_type() { return _new_type; }
 784 
 785   // involves_context(k) is true if k is new_type or any of the super types
 786   bool involves_context(Klass* k);
 787 };
 788 
 789 
 790 // A CallSite has changed its target.
 791 class CallSiteDepChange : public DepChange {
 792  private:
 793   Handle _call_site;
 794   Handle _method_handle;
 795 
 796  public:
 797   CallSiteDepChange(Handle call_site, Handle method_handle);
 798 
 799   // What kind of DepChange is this?
 800   virtual bool is_call_site_change() const { return true; }
 801 
 802   virtual void mark_for_deoptimization(nmethod* nm) {
 803     nm->mark_for_deoptimization(/*inc_recompile_counts=*/false);
 804   }
 805 
 806   oop call_site()     const { return _call_site();     }
 807   oop method_handle() const { return _method_handle(); }
 808 };
 809 
 810 #endif // SHARE_CODE_DEPENDENCIES_HPP