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 * 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.

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#ifndef SHARE_VM_GC_IMPLEMENTATION_G1_G1INCSETSTATE_HPP

#define SHARE_VM_GC_IMPLEMENTATION_G1_G1INCSETSTATE_HPP

#include "gc_implementation/g1/g1BiasedArray.hpp"

#include "memory/allocation.hpp"

// Per-region state during garbage collection.

struct InCSetState {

 public:

  // We use different types to represent the state value. Particularly SPARC puts

  // values in structs from "left to right", i.e. MSB to LSB. This results in many

  // unnecessary shift operations when loading and storing values of this type.

  // This degrades performance significantly (>10%) on that platform.

  // Other tested ABIs do not seem to have this problem, and actually tend to

  // favor smaller types, so we use the smallest usable type there.

#ifdef SPARC

  #define CSETSTATE_FORMAT INTPTR_FORMAT

  typedef intptr_t in_cset_state_t;

#else

  #define CSETSTATE_FORMAT "%d"

  typedef int8_t in_cset_state_t;

#endif

 private:

  in_cset_state_t _value;

 public:

  enum {

    // Selection of the values were driven to micro-optimize the encoding and

    // frequency of the checks.

    // The most common check is whether the region is in the collection set or not.

    // This encoding allows us to use an != 0 check which in some architectures

    // (x86*) can be encoded slightly more efficently than a normal comparison

    // against zero.

    // The same situation occurs when checking whether the region is humongous

    // or not, which is encoded by values < 0.

    // The other values are simply encoded in increasing generation order, which

    // makes getting the next generation fast by a simple increment.

    Humongous    = -1,    // The region is humongous - note that actually any value < 0 would be possible here.

    NotInCSet    =  0,    // The region is not in the collection set.

    Young        =  1,    // The region is in the collection set and a young region.

    Old          =  2,    // The region is in the collection set and an old region.

    Num

  };

  InCSetState(in_cset_state_t value = NotInCSet) : _value(value) {

    assert(is_valid(), err_msg("Invalid state %d", _value));

  }

  in_cset_state_t value() const        { return _value; }

  void set_old()                       { _value = Old; }

  bool is_in_cset_or_humongous() const { return _value != NotInCSet; }

  bool is_in_cset() const              { return _value > NotInCSet; }

  bool is_humongous() const            { return _value < NotInCSet; }

  bool is_young() const                { return _value == Young; }

  bool is_old() const                  { return _value == Old; }

#ifdef ASSERT

  bool is_default() const              { return !is_in_cset_or_humongous(); }

  bool is_valid() const                { return (_value >= Humongous) && (_value < Num); }

  bool is_valid_gen() const            { return (_value >= Young && _value <= Old); }

#endif

};

// Instances of this class are used for quick tests on whether a reference points

// into the collection set and into which generation or is a humongous object

//

// Each of the array's elements indicates whether the corresponding region is in

// the collection set and if so in which generation, or a humongous region.

//

// We use this to speed up reference processing during young collection and

// quickly reclaim humongous objects. For the latter, by making a humongous region

// succeed this test, we sort-of add it to the collection set. During the reference

// iteration closures, when we see a humongous region, we then simply mark it as

// referenced, i.e. live.

class G1InCSetStateFastTestBiasedMappedArray : public G1BiasedMappedArray<InCSetState> {

 protected:

  InCSetState default_value() const { return InCSetState::NotInCSet; }

 public:

  void set_humongous(uintptr_t index) {

    assert(get_by_index(index).is_default(),

           err_msg("State at index " INTPTR_FORMAT" should be default but is " CSETSTATE_FORMAT, index, get_by_index(index).value()));

    set_by_index(index, InCSetState::Humongous);

  }

  void clear_humongous(uintptr_t index) {

    set_by_index(index, InCSetState::NotInCSet);

  }

  void set_in_young(uintptr_t index) {

    assert(get_by_index(index).is_default(),

           err_msg("State at index " INTPTR_FORMAT" should be default but is " CSETSTATE_FORMAT, index, get_by_index(index).value()));

    set_by_index(index, InCSetState::Young);

  }

  void set_in_old(uintptr_t index) {

    assert(get_by_index(index).is_default(),

           err_msg("State at index " INTPTR_FORMAT" should be default but is " CSETSTATE_FORMAT, index, get_by_index(index).value()));

    set_by_index(index, InCSetState::Old);

  }

  bool is_in_cset_or_humongous(HeapWord* addr) const { return at(addr).is_in_cset_or_humongous(); }

  bool is_in_cset(HeapWord* addr) const { return at(addr).is_in_cset(); }

  InCSetState at(HeapWord* addr) const { return get_by_address(addr); }

  void clear() { G1BiasedMappedArray<InCSetState>::clear(); }

};

#endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1INCSETSTATE_HPP