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 /*

  * Copyright (c) 2005, 2014, Oracle and/or its affiliates. All rights reserved.

  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

  *

  * This code is free software; you can redistribute it and/or modify it

  * under the terms of the GNU General Public License version 2 only, as

  * published by the Free Software Foundation.

  *

  * This code is distributed in the hope that it will be useful, but WITHOUT

  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

  * version 2 for more details (a copy is included in the LICENSE file that

  * accompanied this code).

  *

  * You should have received a copy of the GNU General Public License version

  * 2 along with this work; if not, write to the Free Software Foundation,

  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

  *

  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

  * or visit www.oracle.com if you need additional information or have any

  * questions.

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 #ifndef SHARE_VM_CODE_DEPENDENCIES_HPP

 #define SHARE_VM_CODE_DEPENDENCIES_HPP

 #include "ci/ciCallSite.hpp"

 #include "ci/ciKlass.hpp"

 #include "ci/ciMethodHandle.hpp"

 #include "classfile/systemDictionary.hpp"

 #include "code/compressedStream.hpp"

 #include "code/nmethod.hpp"

 #include "utilities/growableArray.hpp"

 //** Dependencies represent assertions (approximate invariants) within

 // the runtime system, e.g. class hierarchy changes.  An example is an

 // assertion that a given method is not overridden; another example is

 // that a type has only one concrete subtype.  Compiled code which

 // relies on such assertions must be discarded if they are overturned

 // by changes in the runtime system.  We can think of these assertions

 // as approximate invariants, because we expect them to be overturned

 // very infrequently.  We are willing to perform expensive recovery

 // operations when they are overturned.  The benefit, of course, is

 // performing optimistic optimizations (!) on the object code.

 //

 // Changes in the class hierarchy due to dynamic linking or

 // class evolution can violate dependencies.  There is enough

 // indexing between classes and nmethods to make dependency

 // checking reasonably efficient.

 class ciEnv;

 class nmethod;

 class OopRecorder;

 class xmlStream;

 class CompileLog;

 class DepChange;

 class   KlassDepChange;

 class   CallSiteDepChange;

 class No_Safepoint_Verifier;

 class Dependencies: public ResourceObj {

  public:

   // Note: In the comments on dependency types, most uses of the terms

   // subtype and supertype are used in a "non-strict" or "inclusive"

   // sense, and are starred to remind the reader of this fact.

   // Strict uses of the terms use the word "proper".

   //

   // Specifically, every class is its own subtype* and supertype*.

   // (This trick is easier than continually saying things like "Y is a

   // subtype of X or X itself".)

   //

   // Sometimes we write X > Y to mean X is a proper supertype of Y.

   // The notation X > {Y, Z} means X has proper subtypes Y, Z.

   // The notation X.m > Y means that Y inherits m from X, while

   // X.m > Y.m means Y overrides X.m.  A star denotes abstractness,

   // as *I > A, meaning (abstract) interface I is a super type of A,

   // or A.*m > B.m, meaning B.m implements abstract method A.m.

   //

   // In this module, the terms "subtype" and "supertype" refer to

   // Java-level reference type conversions, as detected by

   // "instanceof" and performed by "checkcast" operations.  The method

   // Klass::is_subtype_of tests these relations.  Note that "subtype"

   // is richer than "subclass" (as tested by Klass::is_subclass_of),

   // since it takes account of relations involving interface and array

   // types.

   //

   // To avoid needless complexity, dependencies involving array types

   // are not accepted.  If you need to make an assertion about an

   // array type, make the assertion about its corresponding element

   // types.  Any assertion that might change about an array type can

   // be converted to an assertion about its element type.

   //

   // Most dependencies are evaluated over a "context type" CX, which

   // stands for the set Subtypes(CX) of every Java type that is a subtype*

   // of CX.  When the system loads a new class or interface N, it is

   // responsible for re-evaluating changed dependencies whose context

   // type now includes N, that is, all super types of N.

   //

   enum DepType {

     end_marker = 0,

     // An 'evol' dependency simply notes that the contents of the

     // method were used.  If it evolves (is replaced), the nmethod

     // must be recompiled.  No other dependencies are implied.

     evol_method,

     FIRST_TYPE = evol_method,

     // A context type CX is a leaf it if has no proper subtype.

     leaf_type,

     // An abstract class CX has exactly one concrete subtype CC.

     abstract_with_unique_concrete_subtype,

     // The type CX is purely abstract, with no concrete subtype* at all.

     abstract_with_no_concrete_subtype,

     // The concrete CX is free of concrete proper subtypes.

     concrete_with_no_concrete_subtype,

     // Given a method M1 and a context class CX, the set MM(CX, M1) of

     // "concrete matching methods" in CX of M1 is the set of every

     // concrete M2 for which it is possible to create an invokevirtual

     // or invokeinterface call site that can reach either M1 or M2.

     // That is, M1 and M2 share a name, signature, and vtable index.

     // We wish to notice when the set MM(CX, M1) is just {M1}, or

     // perhaps a set of two {M1,M2}, and issue dependencies on this.

     // The set MM(CX, M1) can be computed by starting with any matching

     // concrete M2 that is inherited into CX, and then walking the

     // subtypes* of CX looking for concrete definitions.

     // The parameters to this dependency are the method M1 and the

     // context class CX.  M1 must be either inherited in CX or defined

     // in a subtype* of CX.  It asserts that MM(CX, M1) is no greater

     // than {M1}.

     unique_concrete_method,       // one unique concrete method under CX

     // An "exclusive" assertion concerns two methods or subtypes, and

     // declares that there are at most two (or perhaps later N>2)

     // specific items that jointly satisfy the restriction.

     // We list all items explicitly rather than just giving their

     // count, for robustness in the face of complex schema changes.

     // A context class CX (which may be either abstract or concrete)

     // has two exclusive concrete subtypes* C1, C2 if every concrete

     // subtype* of CX is either C1 or C2.  Note that if neither C1 or C2

     // are equal to CX, then CX itself must be abstract.  But it is

     // also possible (for example) that C1 is CX (a concrete class)

     // and C2 is a proper subtype of C1.

     abstract_with_exclusive_concrete_subtypes_2,

     // This dependency asserts that MM(CX, M1) is no greater than {M1,M2}.

     exclusive_concrete_methods_2,

     // This dependency asserts that no instances of class or it's

     // subclasses require finalization registration.

     no_finalizable_subclasses,

     // This dependency asserts when the CallSite.target value changed.

     call_site_target_value,

     TYPE_LIMIT

   };

   enum {

     LG2_TYPE_LIMIT = 4,  // assert(TYPE_LIMIT <= (1<<LG2_TYPE_LIMIT))

     // handy categorizations of dependency types:

     all_types           = ((1 << TYPE_LIMIT) - 1) & ((-1) << FIRST_TYPE),

     non_klass_types     = (1 << call_site_target_value),

     klass_types         = all_types & ~non_klass_types,

     non_ctxk_types      = (1 << evol_method),

     implicit_ctxk_types = (1 << call_site_target_value),

     explicit_ctxk_types = all_types & ~(non_ctxk_types | implicit_ctxk_types),

     max_arg_count = 3,   // current maximum number of arguments (incl. ctxk)

     // A "context type" is a class or interface that

     // provides context for evaluating a dependency.

     // When present, it is one of the arguments (dep_context_arg).

     //

     // If a dependency does not have a context type, there is a

     // default context, depending on the type of the dependency.

     // This bit signals that a default context has been compressed away.

     default_context_type_bit = (1<<LG2_TYPE_LIMIT)

   };

   static const char* dep_name(DepType dept);

   static int         dep_args(DepType dept);

   static bool is_klass_type(           DepType dept) { return dept_in_mask(dept, klass_types        ); }

   static bool has_explicit_context_arg(DepType dept) { return dept_in_mask(dept, explicit_ctxk_types); }

   static bool has_implicit_context_arg(DepType dept) { return dept_in_mask(dept, implicit_ctxk_types); }

   static int           dep_context_arg(DepType dept) { return has_explicit_context_arg(dept) ? 0 : -1; }

   static int  dep_implicit_context_arg(DepType dept) { return has_implicit_context_arg(dept) ? 0 : -1; }

   static void check_valid_dependency_type(DepType dept);

  private:

   // State for writing a new set of dependencies:

   GrowableArray<int>*       _dep_seen;  // (seen[h->ident] & (1<<dept))

   GrowableArray<ciBaseObject*>*  _deps[TYPE_LIMIT];

   static const char* _dep_name[TYPE_LIMIT];

   static int         _dep_args[TYPE_LIMIT];

   static bool dept_in_mask(DepType dept, int mask) {

     return (int)dept >= 0 && dept < TYPE_LIMIT && ((1<<dept) & mask) != 0;

   }

   bool note_dep_seen(int dept, ciBaseObject* x) {

     assert(dept < BitsPerInt, "oob");

     int x_id = x->ident();

     assert(_dep_seen != NULL, "deps must be writable");

     int seen = _dep_seen->at_grow(x_id, 0);

     _dep_seen->at_put(x_id, seen | (1<<dept));

     // return true if we've already seen dept/x

     return (seen & (1<<dept)) != 0;

   }

   bool maybe_merge_ctxk(GrowableArray<ciBaseObject*>* deps,

                         int ctxk_i, ciKlass* ctxk);

   void sort_all_deps();

   size_t estimate_size_in_bytes();

   // Initialize _deps, etc.

   void initialize(ciEnv* env);

   // State for making a new set of dependencies:

   OopRecorder* _oop_recorder;

   // Logging support

   CompileLog* _log;

   address  _content_bytes;  // everything but the oop references, encoded

   size_t   _size_in_bytes;

  public:

   // Make a new empty dependencies set.

   Dependencies(ciEnv* env) {

     initialize(env);

   }

  private:

   // Check for a valid context type.

   // Enforce the restriction against array types.

   static void check_ctxk(ciKlass* ctxk) {

     assert(ctxk->is_instance_klass(), "java types only");

   }

   static void check_ctxk_concrete(ciKlass* ctxk) {

     assert(is_concrete_klass(ctxk->as_instance_klass()), "must be concrete");

   }

   static void check_ctxk_abstract(ciKlass* ctxk) {

     check_ctxk(ctxk);

     assert(!is_concrete_klass(ctxk->as_instance_klass()), "must be abstract");

   }

   void assert_common_1(DepType dept, ciBaseObject* x);

   void assert_common_2(DepType dept, ciBaseObject* x0, ciBaseObject* x1);

   void assert_common_3(DepType dept, ciKlass* ctxk, ciBaseObject* x1, ciBaseObject* x2);

  public:

   // Adding assertions to a new dependency set at compile time:

   void assert_evol_method(ciMethod* m);

   void assert_leaf_type(ciKlass* ctxk);

   void assert_abstract_with_unique_concrete_subtype(ciKlass* ctxk, ciKlass* conck);

   void assert_abstract_with_no_concrete_subtype(ciKlass* ctxk);

   void assert_concrete_with_no_concrete_subtype(ciKlass* ctxk);

   void assert_unique_concrete_method(ciKlass* ctxk, ciMethod* uniqm);

   void assert_abstract_with_exclusive_concrete_subtypes(ciKlass* ctxk, ciKlass* k1, ciKlass* k2);

   void assert_exclusive_concrete_methods(ciKlass* ctxk, ciMethod* m1, ciMethod* m2);

   void assert_has_no_finalizable_subclasses(ciKlass* ctxk);

   void assert_call_site_target_value(ciCallSite* call_site, ciMethodHandle* method_handle);

   // Define whether a given method or type is concrete.

   // These methods define the term "concrete" as used in this module.

   // For this module, an "abstract" class is one which is non-concrete.

   //

   // Future optimizations may allow some classes to remain

   // non-concrete until their first instantiation, and allow some

   // methods to remain non-concrete until their first invocation.

   // In that case, there would be a middle ground between concrete

   // and abstract (as defined by the Java language and VM).

   static bool is_concrete_klass(Klass* k);    // k is instantiable

   static bool is_concrete_method(Method* m, Klass* k);  // m is invocable

   static Klass* find_finalizable_subclass(Klass* k);

   // These versions of the concreteness queries work through the CI.

   // The CI versions are allowed to skew sometimes from the VM

   // (oop-based) versions.  The cost of such a difference is a

   // (safely) aborted compilation, or a deoptimization, or a missed

   // optimization opportunity.

   //

   // In order to prevent spurious assertions, query results must

   // remain stable within any single ciEnv instance.  (I.e., they must

   // not go back into the VM to get their value; they must cache the

   // bit in the CI, either eagerly or lazily.)

   static bool is_concrete_klass(ciInstanceKlass* k); // k appears instantiable

   static bool has_finalizable_subclass(ciInstanceKlass* k);

   // As a general rule, it is OK to compile under the assumption that

   // a given type or method is concrete, even if it at some future

   // point becomes abstract.  So dependency checking is one-sided, in

   // that it permits supposedly concrete classes or methods to turn up

   // as really abstract.  (This shouldn't happen, except during class

   // evolution, but that's the logic of the checking.)  However, if a

   // supposedly abstract class or method suddenly becomes concrete, a

   // dependency on it must fail.

   // Checking old assertions at run-time (in the VM only):

   static Klass* check_evol_method(Method* m);

   static Klass* check_leaf_type(Klass* ctxk);

   static Klass* check_abstract_with_unique_concrete_subtype(Klass* ctxk, Klass* conck,

                                                               KlassDepChange* changes = NULL);

   static Klass* check_abstract_with_no_concrete_subtype(Klass* ctxk,

                                                           KlassDepChange* changes = NULL);

   static Klass* check_concrete_with_no_concrete_subtype(Klass* ctxk,

                                                           KlassDepChange* changes = NULL);

   static Klass* check_unique_concrete_method(Klass* ctxk, Method* uniqm,

                                                KlassDepChange* changes = NULL);

   static Klass* check_abstract_with_exclusive_concrete_subtypes(Klass* ctxk, Klass* k1, Klass* k2,

                                                                   KlassDepChange* changes = NULL);

   static Klass* check_exclusive_concrete_methods(Klass* ctxk, Method* m1, Method* m2,

                                                    KlassDepChange* changes = NULL);

   static Klass* check_has_no_finalizable_subclasses(Klass* ctxk, KlassDepChange* changes = NULL);

   static Klass* check_call_site_target_value(oop call_site, oop method_handle, CallSiteDepChange* changes = NULL);

   // A returned Klass* is NULL if the dependency assertion is still

   // valid.  A non-NULL Klass* is a 'witness' to the assertion

   // failure, a point in the class hierarchy where the assertion has

   // been proven false.  For example, if check_leaf_type returns

   // non-NULL, the value is a subtype of the supposed leaf type.  This

   // witness value may be useful for logging the dependency failure.

   // Note that, when a dependency fails, there may be several possible

   // witnesses to the failure.  The value returned from the check_foo

   // method is chosen arbitrarily.

   // The 'changes' value, if non-null, requests a limited spot-check

   // near the indicated recent changes in the class hierarchy.

   // It is used by DepStream::spot_check_dependency_at.

   // Detecting possible new assertions:

   static Klass*    find_unique_concrete_subtype(Klass* ctxk);

   static Method*   find_unique_concrete_method(Klass* ctxk, Method* m);

   static int       find_exclusive_concrete_subtypes(Klass* ctxk, int klen, Klass* k[]);

   // Create the encoding which will be stored in an nmethod.

   void encode_content_bytes();

   address content_bytes() {

     assert(_content_bytes != NULL, "encode it first");

     return _content_bytes;

   }

   size_t size_in_bytes() {

     assert(_content_bytes != NULL, "encode it first");

     return _size_in_bytes;

   }

   OopRecorder* oop_recorder() { return _oop_recorder; }

   CompileLog*  log()          { return _log; }

   void copy_to(nmethod* nm);

   void log_all_dependencies();

   void log_dependency(DepType dept, GrowableArray<ciBaseObject*>* args) {

     ResourceMark rm;

     int argslen = args->length();

     write_dependency_to(log(), dept, args);

     guarantee(argslen == args->length(),

               "args array cannot grow inside nested ResoureMark scope");

   }

   void log_dependency(DepType dept,

                       ciBaseObject* x0,

                       ciBaseObject* x1 = NULL,

                       ciBaseObject* x2 = NULL) {

     if (log() == NULL) {

       return;

     }

     ResourceMark rm;

     GrowableArray<ciBaseObject*>* ciargs =

                 new GrowableArray<ciBaseObject*>(dep_args(dept));

     assert (x0 != NULL, "no log x0");

     ciargs->push(x0);

     if (x1 != NULL) {

       ciargs->push(x1);

     }

     if (x2 != NULL) {

       ciargs->push(x2);

     }

     assert(ciargs->length() == dep_args(dept), "");

     log_dependency(dept, ciargs);

   }

   class DepArgument : public ResourceObj {

    private:

     bool  _is_oop;

     bool  _valid;

     void* _value;

    public:

     DepArgument() : _is_oop(false), _value(NULL), _valid(false) {}

     DepArgument(oop v): _is_oop(true), _value(v), _valid(true) {}

     DepArgument(Metadata* v): _is_oop(false), _value(v), _valid(true) {}

     bool is_null() const               { return _value == NULL; }

     bool is_oop() const                { return _is_oop; }

     bool is_metadata() const           { return !_is_oop; }

     bool is_klass() const              { return is_metadata() && metadata_value()->is_klass(); }

     bool is_method() const              { return is_metadata() && metadata_value()->is_method(); }

     oop oop_value() const              { assert(_is_oop && _valid, "must be"); return (oop) _value; }

     Metadata* metadata_value() const { assert(!_is_oop && _valid, "must be"); return (Metadata*) _value; }

   };

   static void print_dependency(DepType dept,

                                GrowableArray<DepArgument>* args,

                                Klass* witness = NULL);

  private:

   // helper for encoding common context types as zero:

   static ciKlass* ctxk_encoded_as_null(DepType dept, ciBaseObject* x);

   static Klass* ctxk_encoded_as_null(DepType dept, Metadata* x);

   static void write_dependency_to(CompileLog* log,

                                   DepType dept,

                                   GrowableArray<ciBaseObject*>* args,

                                   Klass* witness = NULL);

   static void write_dependency_to(CompileLog* log,

                                   DepType dept,

                                   GrowableArray<DepArgument>* args,

                                   Klass* witness = NULL);

   static void write_dependency_to(xmlStream* xtty,

                                   DepType dept,

                                   GrowableArray<DepArgument>* args,

                                   Klass* witness = NULL);

  public:

   // Use this to iterate over an nmethod's dependency set.

   // Works on new and old dependency sets.

   // Usage:

   //

   // ;

   // Dependencies::DepType dept;

   // for (Dependencies::DepStream deps(nm); deps.next(); ) {

   //   ...

   // }

   //

   // The caller must be in the VM, since oops are not wrapped in handles.

   class DepStream {

   private:

     nmethod*              _code;   // null if in a compiler thread

     Dependencies*         _deps;   // null if not in a compiler thread

     CompressedReadStream  _bytes;

 #ifdef ASSERT

     size_t                _byte_limit;

 #endif

     // iteration variables:

     DepType               _type;

     int                   _xi[max_arg_count+1];

     void initial_asserts(size_t byte_limit) NOT_DEBUG({});

     inline Metadata* recorded_metadata_at(int i);

     inline oop recorded_oop_at(int i);

     Klass* check_klass_dependency(KlassDepChange* changes);

     Klass* check_call_site_dependency(CallSiteDepChange* changes);

     void trace_and_log_witness(Klass* witness);

   public:

     DepStream(Dependencies* deps)

       : _deps(deps),

         _code(NULL),

         _bytes(deps->content_bytes())

     {

       initial_asserts(deps->size_in_bytes());

     }

     DepStream(nmethod* code)

       : _deps(NULL),

         _code(code),

         _bytes(code->dependencies_begin())

     {

       initial_asserts(code->dependencies_size());

     }

     bool next();

     DepType type()               { return _type; }

     int argument_count()         { return dep_args(type()); }

     int argument_index(int i)    { assert(0 <= i && i < argument_count(), "oob");

                                    return _xi[i]; }

     Metadata* argument(int i);     // => recorded_oop_at(argument_index(i))

     oop argument_oop(int i);         // => recorded_oop_at(argument_index(i))

     Klass* context_type();

     bool is_klass_type()         { return Dependencies::is_klass_type(type()); }

     Method* method_argument(int i) {

       Metadata* x = argument(i);

       assert(x->is_method(), "type");

       return (Method*) x;

     }

     Klass* type_argument(int i) {

       Metadata* x = argument(i);

       assert(x->is_klass(), "type");

       return (Klass*) x;

     }

     // The point of the whole exercise:  Is this dep still OK?

     Klass* check_dependency() {

       Klass* result = check_klass_dependency(NULL);

       if (result != NULL)  return result;

       return check_call_site_dependency(NULL);

     }

     // A lighter version:  Checks only around recent changes in a class

     // hierarchy.  (See Universe::flush_dependents_on.)

     Klass* spot_check_dependency_at(DepChange& changes);

     // Log the current dependency to xtty or compilation log.

     void log_dependency(Klass* witness = NULL);

     // Print the current dependency to tty.

     void print_dependency(Klass* witness = NULL, bool verbose = false);

   };

   friend class Dependencies::DepStream;

   static void print_statistics() PRODUCT_RETURN;

 };

 // Every particular DepChange is a sub-class of this class.

 class DepChange : public StackObj {

  public:

   // What kind of DepChange is this?

   virtual bool is_klass_change()     const { return false; }

   virtual bool is_call_site_change() const { return false; }

   // Subclass casting with assertions.

   KlassDepChange*    as_klass_change() {

     assert(is_klass_change(), "bad cast");

     return (KlassDepChange*) this;

   }

   CallSiteDepChange* as_call_site_change() {

     assert(is_call_site_change(), "bad cast");

     return (CallSiteDepChange*) this;

   }

   void print();

  public:

   enum ChangeType {

     NO_CHANGE = 0,              // an uninvolved klass

     Change_new_type,            // a newly loaded type

     Change_new_sub,             // a super with a new subtype

     Change_new_impl,            // an interface with a new implementation

     CHANGE_LIMIT,

     Start_Klass = CHANGE_LIMIT  // internal indicator for ContextStream

   };

   // Usage:

   // for (DepChange::ContextStream str(changes); str.next(); ) {

   //   Klass* k = str.klass();

   //   switch (str.change_type()) {

   //     ...

   //   }

   // }

   class ContextStream : public StackObj {

    private:

     DepChange&  _changes;

     friend class DepChange;

     // iteration variables:

     ChangeType  _change_type;

     Klass*      _klass;

     Array<Klass*>* _ti_base;    // i.e., transitive_interfaces

     int         _ti_index;

     int         _ti_limit;

     // start at the beginning:

     void start();

    public:

     ContextStream(DepChange& changes)

       : _changes(changes)

     { start(); }

     ContextStream(DepChange& changes, No_Safepoint_Verifier& nsv)

       : _changes(changes)

       // the nsv argument makes it safe to hold oops like _klass

     { start(); }

     bool next();

     ChangeType change_type()     { return _change_type; }

     Klass*     klass()           { return _klass; }

   };

   friend class DepChange::ContextStream;

 };

 // A class hierarchy change coming through the VM (under the Compile_lock).

 // The change is structured as a single new type with any number of supers

 // and implemented interface types.  Other than the new type, any of the

 // super types can be context types for a relevant dependency, which the

 // new type could invalidate.

 class KlassDepChange : public DepChange {

  private:

   // each change set is rooted in exactly one new type (at present):

   KlassHandle _new_type;

   void initialize();

  public:

   // notes the new type, marks it and all its super-types

   KlassDepChange(KlassHandle new_type)

     : _new_type(new_type)

   {

     initialize();

   }

   // cleans up the marks

   ~KlassDepChange();

   // What kind of DepChange is this?

   virtual bool is_klass_change() const { return true; }

   Klass* new_type() { return _new_type(); }

   // involves_context(k) is true if k is new_type or any of the super types

   bool involves_context(Klass* k);

 };

 // A CallSite has changed its target.

 class CallSiteDepChange : public DepChange {

  private:

   Handle _call_site;

   Handle _method_handle;

  public:

   CallSiteDepChange(Handle call_site, Handle method_handle)

     : _call_site(call_site),

       _method_handle(method_handle)

   {

     assert(_call_site()    ->is_a(SystemDictionary::CallSite_klass()),     "must be");

     assert(_method_handle()->is_a(SystemDictionary::MethodHandle_klass()), "must be");

   }

   // What kind of DepChange is this?

   virtual bool is_call_site_change() const { return true; }

   oop call_site()     const { return _call_site();     }

   oop method_handle() const { return _method_handle(); }

 };

 #endif // SHARE_VM_CODE_DEPENDENCIES_HPP