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

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 *

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

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

// the class hierarchy.  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 class hierarchy.  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 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,

    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_ctxk_types = (1<<evol_method),

    ctxk_types     = all_types & ~non_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 int  dep_context_arg(DepType dept) {

    return dept_in_mask(dept, ctxk_types)? 0: -1;

  }

 private:

  // State for writing a new set of dependencies:

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

  GrowableArray<ciObject*>* _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, ciObject* 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<ciObject*>* 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, ciObject* x);

  void assert_common_2(DepType dept, ciKlass* ctxk, ciObject* x);

  void assert_common_3(DepType dept, ciKlass* ctxk, ciObject* x, ciObject* 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);

  // 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(klassOop k);    // k is instantiable

  static bool is_concrete_method(methodOop m);  // 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 is_concrete_method(ciMethod* m);       // m appears invocable

  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 klassOop check_evol_method(methodOop m);

  static klassOop check_leaf_type(klassOop ctxk);

  static klassOop check_abstract_with_unique_concrete_subtype(klassOop ctxk, klassOop conck,

                                                              DepChange* changes = NULL);

  static klassOop check_abstract_with_no_concrete_subtype(klassOop ctxk,

                                                          DepChange* changes = NULL);

  static klassOop check_concrete_with_no_concrete_subtype(klassOop ctxk,

                                                          DepChange* changes = NULL);

  static klassOop check_unique_concrete_method(klassOop ctxk, methodOop uniqm,

                                               DepChange* changes = NULL);

  static klassOop check_abstract_with_exclusive_concrete_subtypes(klassOop ctxk, klassOop k1, klassOop k2,

                                                                  DepChange* changes = NULL);

  static klassOop check_exclusive_concrete_methods(klassOop ctxk, methodOop m1, methodOop m2,

                                                   DepChange* changes = NULL);

  static klassOop check_has_no_finalizable_subclasses(klassOop ctxk,

                                                      DepChange* changes = NULL);

  // A returned klassOop is NULL if the dependency assertion is still

  // valid.  A non-NULL klassOop 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 klassOop  find_unique_concrete_subtype(klassOop ctxk);

  static methodOop find_unique_concrete_method(klassOop ctxk, methodOop m);

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

  static int       find_exclusive_concrete_methods(klassOop ctxk, int mlen, methodOop m[]);

  // 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, int nargs, ciObject* args[]) {

    write_dependency_to(log(), dept, nargs, args);

  }

  void log_dependency(DepType dept,

                      ciObject* x0,

                      ciObject* x1 = NULL,

                      ciObject* x2 = NULL) {

    if (log() == NULL)  return;

    ciObject* args[max_arg_count];

    args[0] = x0;

    args[1] = x1;

    args[2] = x2;

    assert(2 < max_arg_count, "");

    log_dependency(dept, dep_args(dept), args);

  }

  static void write_dependency_to(CompileLog* log,

                                  DepType dept,

                                  int nargs, ciObject* args[],

                                  klassOop witness = NULL);

  static void write_dependency_to(CompileLog* log,

                                  DepType dept,

                                  int nargs, oop args[],

                                  klassOop witness = NULL);

  static void write_dependency_to(xmlStream* xtty,

                                  DepType dept,

                                  int nargs, oop args[],

                                  klassOop witness = NULL);

  static void print_dependency(DepType dept,

                               int nargs, oop args[],

                               klassOop witness = NULL);

 private:

  // helper for encoding common context types as zero:

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

  static klassOop ctxk_encoded_as_null(DepType dept, oop x);

 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 oop recorded_oop_at(int i);

        // => _code? _code->oop_at(i): *_deps->_oop_recorder->handle_at(i)

    klassOop check_dependency_impl(DepChange* changes);

  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]; }

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

    klassOop context_type();

    methodOop method_argument(int i) {

      oop x = argument(i);

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

      return (methodOop) x;

    }

    klassOop type_argument(int i) {

      oop x = argument(i);

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

      return (klassOop) x;

    }

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

    klassOop check_dependency() {

      return check_dependency_impl(NULL);

    }

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

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

    klassOop spot_check_dependency_at(DepChange& changes);

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

    void log_dependency(klassOop witness = NULL);

    // Print the current dependency to tty.

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

  };

  friend class Dependencies::DepStream;

  static void print_statistics() PRODUCT_RETURN;

};

// 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 DepChange : public StackObj {

 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

  };

 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

  DepChange(KlassHandle new_type)

    : _new_type(new_type)

  {

    initialize();

  }

  // cleans up the marks

  ~DepChange();

  klassOop new_type()                   { return _new_type(); }

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

  bool involves_context(klassOop k);

  // Usage:

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

  //   klassOop k = str.klass();

  //   switch (str.change_type()) {

  //     ...

  //   }

  // }

  class ContextStream : public StackObj {

   private:

    DepChange&  _changes;

    friend class DepChange;

    // iteration variables:

    ChangeType  _change_type;