src/hotspot/share/ci/ciObject.cpp

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
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 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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#include "ci/ciObject.hpp"
#include "ci/ciUtilities.inline.hpp"
#include "gc/shared/collectedHeap.inline.hpp"
#include "oops/oop.inline.hpp"
#include "runtime/jniHandles.inline.hpp"

// ciObject
//
// This class represents an oop in the HotSpot virtual machine.
// Its subclasses are structured in a hierarchy which mirrors
// an aggregate of the VM's oop and klass hierarchies (see
// oopHierarchy.hpp).  Each instance of ciObject holds a handle
// to a corresponding oop on the VM side and provides routines
// for accessing the information in its oop.  By using the ciObject
// hierarchy for accessing oops in the VM, the compiler ensures
// that it is safe with respect to garbage collection; that is,
// GC and compilation can proceed independently without
// interference.
//
// Within the VM, the oop and klass hierarchies are separate.
// The compiler interface does not preserve this separation --
// the distinction between `Klass*' and `Klass' are not
// reflected in the interface and instead the Klass hierarchy
// is directly modeled as the subclasses of ciKlass.

// ------------------------------------------------------------------
// ciObject::ciObject
ciObject::ciObject(oop o) {
  ASSERT_IN_VM;
  if (ciObjectFactory::is_initialized()) {
    _handle = JNIHandles::make_local(o);
  } else {
    Handle obj(Thread::current(), o);
    _handle = JNIHandles::make_global(obj);
  }
  _klass = nullptr;
  assert(oopDesc::is_oop_or_null(o), "Checking");
}

// ------------------------------------------------------------------
// ciObject::ciObject
//
ciObject::ciObject(Handle h) {
  ASSERT_IN_VM;
  if (ciObjectFactory::is_initialized()) {
    _handle = JNIHandles::make_local(h());
  } else {
    _handle = JNIHandles::make_global(h);
  }
  _klass = nullptr;
  assert(oopDesc::is_oop_or_null(h()), "Checking");
}

// ------------------------------------------------------------------
// ciObject::ciObject
//
// Unloaded klass/method variant.  `klass' is the klass of the unloaded
// klass/method, if that makes sense.
ciObject::ciObject(ciKlass* klass) {
  ASSERT_IN_VM;
  assert(klass != nullptr, "must supply klass");
  _handle = nullptr;
  _klass = klass;
}

// ------------------------------------------------------------------
// ciObject::ciObject
//
// null variant.  Used only by ciNullObject.
ciObject::ciObject() {
  ASSERT_IN_VM;
  _handle = nullptr;
  _klass = nullptr;
}

// ------------------------------------------------------------------
// ciObject::get_oop
//
// Get the oop of this ciObject.
oop ciObject::get_oop() const {
  return JNIHandles::resolve_non_null(_handle);
}

// ------------------------------------------------------------------
// ciObject::klass
//
// Get the ciKlass of this ciObject.
ciKlass* ciObject::klass() {
  if (_klass == nullptr) {
    if (_handle == nullptr) {
      // When both _klass and _handle are null, we are dealing
      // with the distinguished instance of ciNullObject.
      // No one should ask it for its klass.
      assert(is_null_object(), "must be null object");
      ShouldNotReachHere();
      return nullptr;
    }

    GUARDED_VM_ENTRY(
      oop o = get_oop();
      _klass = CURRENT_ENV->get_klass(o->klass());
    );
  }
  return _klass;
}

// ------------------------------------------------------------------
// ciObject::equals
//
// Are two ciObjects equal?
bool ciObject::equals(ciObject* obj) {
  return (this == obj);
}

// ------------------------------------------------------------------
// ciObject::hash
//
// A hash value for the convenience of compilers.
//
// Implementation note: we use the address of the ciObject as the
// basis for the hash.  Use the _ident field, which is well-behaved.
uint ciObject::hash() {
  return ident() * 31;
}

// ------------------------------------------------------------------
// ciObject::constant_encoding
//
// The address which the compiler should embed into the
// generated code to represent this oop.  This address
// is not the true address of the oop -- it will get patched
// during nmethod creation.
//
//
//
// Implementation note: we use the handle as the encoding.  The
// nmethod constructor resolves the handle and patches in the oop.
//
// This method should be changed to return an generified address
// to discourage use of the JNI handle.
jobject ciObject::constant_encoding() {
  assert(is_null_object() || handle() != nullptr, "cannot embed null pointer");
  return handle();
}

// ------------------------------------------------------------------
// ciObject::check_constant_value_cache()
//
// Cache constant value lookups to ensure that consistent values are observed
// during compilation because fields may be (re-)initialized concurrently.
ciConstant ciObject::check_constant_value_cache(int off, BasicType bt) {
  if (_constant_values != nullptr) {
    for (int i = 0; i < _constant_values->length(); ++i) {
      ConstantValue cached_val = _constant_values->at(i);
      if (cached_val.off() == off) {
        assert(cached_val.value().basic_type() == bt, "unexpected type");
        return cached_val.value();
      }
    }
  }
  return ciConstant();
}

// ------------------------------------------------------------------
// ciObject::add_to_constant_value_cache()
//
// Add a constant value to the cache.
void ciObject::add_to_constant_value_cache(int off, ciConstant val) {
  assert(val.is_valid(), "value must be valid");
  assert(!check_constant_value_cache(off, val.basic_type()).is_valid(), "duplicate");
  if (_constant_values == nullptr) {
    Arena* arena = CURRENT_ENV->arena();
    _constant_values = new (arena) GrowableArray<ConstantValue>(arena, 1, 0, ConstantValue());
  }
  _constant_values->append(ConstantValue(off, val));
}

// ------------------------------------------------------------------
// ciObject::should_be_constant()
bool ciObject::should_be_constant() {
  if (ScavengeRootsInCode >= 2)  return true;  // force everybody to be a constant
  if (is_null_object()) return true;

  ciEnv* env = CURRENT_ENV;

    // We want Strings and Classes to be embeddable by default since
    // they used to be in the perm world.  Not all Strings used to be
    // embeddable but there's no easy way to distinguish the interned
    // from the regulars ones so just treat them all that way.
    if (klass() == env->String_klass() || klass() == env->Class_klass()) {
      return true;
    }
  if (klass()->is_subclass_of(env->MethodHandle_klass()) ||
      klass()->is_subclass_of(env->CallSite_klass())) {
    // We want to treat these aggressively.
    return true;
  }

  return handle() == nullptr;
}

// ------------------------------------------------------------------
// ciObject::print
//
// Print debugging output about this ciObject.
//
// Implementation note: dispatch to the virtual print_impl behavior
// for this ciObject.
void ciObject::print(outputStream* st) {
  st->print("<%s", type_string());
  GUARDED_VM_ENTRY(print_impl(st);)
  st->print(" ident=%d address=" INTPTR_FORMAT ">", ident(), p2i(this));
}

// ------------------------------------------------------------------
// ciObject::print_oop
//
// Print debugging output about the oop this ciObject represents.
void ciObject::print_oop(outputStream* st) {
  if (is_null_object()) {
    st->print_cr("nullptr");
  } else if (!is_loaded()) {
    st->print_cr("UNLOADED");
  } else {
    GUARDED_VM_ENTRY(get_oop()->print_on(st);)
  }
}