8304759: Add BitMap iterators

src/hotspot/share/utilities/bitMap.cpp

@@ -654,6 +654,12 @@ void BitMap::write_to(bm_word_t* buffer, size_t buffer_size_in_bytes) const {
   memcpy(buffer, _map, size_in_bytes());
 }
 
+#ifdef ASSERT
+void BitMap::IteratorImpl::assert_not_empty() const {
+  assert(!is_empty(), "empty iterator");
+}
+#endif
+
 #ifndef PRODUCT
 
 void BitMap::print_on(outputStream* st) const {

src/hotspot/share/utilities/bitMap.hpp

@@ -116,6 +116,8 @@ class BitMap {
 
   template<typename ReturnType> struct IterateInvoker;
 
+  struct IteratorImpl;
+
   // Threshold for performing small range operation, even when large range
   // operation was requested. Measured in words.
   static const size_t small_range_words = 32;
@@ -279,6 +281,8 @@ class BitMap {
   // greater than (less than for reverse iteration) the current index will
   // affect which further indices the operation will be applied to.
   //
+  // See also the Iterator and ReverseIterator classes.
+  //
   // precondition: beg and end form a valid range for the bitmap.
   template<typename Function>
   bool iterate(Function function, idx_t beg, idx_t end) const;
@@ -312,6 +316,11 @@ class BitMap {
     return reverse_iterate(cl, 0, size());
   }
 
+  class Iterator;
+  class ReverseIterator;
+  class RBFIterator;
+  class ReverseRBFIterator;
+
   // Return the index of the first set (or clear) bit in the range [beg, end),
   // or end if none found.
   // precondition: beg and end form a valid range for the bitmap.
@@ -385,6 +394,167 @@ class BitMap {
 #endif
 };
 
+// Implementation support for bitmap iteration.  While it could be used to
+// support bi-directional iteration, it is only intended to be used for
+// uni-directional iteration.  The directionality is determined by the using
+// class.
+struct BitMap::IteratorImpl {
+  const BitMap* _map;
+  idx_t _cur_beg;
+  idx_t _cur_end;
+
+  void assert_not_empty() const NOT_DEBUG_RETURN;
+
+  // Constructs an empty iterator.
+  IteratorImpl();
+
+  // Constructs an iterator for map, over the range [beg, end).
+  // May be constructed for one of forward or reverse iteration.
+  // precondition: beg and end form a valid range for map.
+  // precondition: either beg == end or
+  // (1) if for forward iteration, then beg must designate a set bit,
+  // (2) if for reverse iteration, then end-1 must designate a set bit.
+  IteratorImpl(const BitMap* map, idx_t beg, idx_t end);
+
+  // Returns true if the remaining iteration range is empty.
+  bool is_empty() const;
+
+  // Returns the index of the first set bit in the remaining iteration range.
+  // precondition: !is_empty()
+  // precondition: constructed for forward iteration.
+  idx_t first() const;
+
+  // Returns the index of the last set bit in the remaining iteration range.
+  // precondition: !is_empty()
+  // precondition: constructed for reverse iteration.
+  idx_t last() const;
+
+  // Updates first() to the position of the first set bit in the range
+  // [first() + 1, last()]. The iterator instead becomes empty if there
+  // aren't any set bits in that range.
+  // precondition: !is_empty()
+  // precondition: constructed for forward iteration.
+  void step_first();
+
+  // Updates last() to the position of the last set bit in the range
+  // [first(), last()). The iterator instead becomes empty if there aren't
+  // any set bits in that range.
+  // precondition: !is_empty()
+  // precondition: constructed for reverse iteration.
+  void step_last();
+};
+
+// Provides iteration over the indices of the set bits in a range of a bitmap,
+// in increasing order. This is an alternative to the iterate() function.
+class BitMap::Iterator {
+  IteratorImpl _impl;
+
+public:
+  // Constructs an empty iterator.
+  Iterator();
+
+  // Constructs an iterator for map, over the range [0, map.size()).
+  explicit Iterator(const BitMap& map);
+
+  // Constructs an iterator for map, over the range [beg, end).
+  // If there are no set bits in that range, the resulting iterator is empty.
+  // Otherwise, index() is initially the position of the first set bit in
+  // that range.
+  // precondition: beg and end form a valid range for map.
+  Iterator(const BitMap& map, idx_t beg, idx_t end);
+
+  // Returns true if the remaining iteration range is empty.
+  bool is_empty() const;
+
+  // Returns the index of the first set bit in the remaining iteration range.
+  // precondition: !is_empty()
+  idx_t index() const;
+
+  // Updates index() to the position of the first set bit in the range
+  // [index(), end), where end was the corresponding constructor argument.
+  // The iterator instead becomes empty if there aren't any set bits in
+  // that range.
+  // precondition: !is_empty()
+  void step();
+
+  // Range-based for loop support.
+  RBFIterator begin() const;
+  RBFIterator end() const;
+};
+
+// Provides iteration over the indices of the set bits in a range of a bitmap,
+// in decreasing order. This is an alternative to the reverse_iterate() function.
+class BitMap::ReverseIterator {
+  IteratorImpl _impl;
+
+  static idx_t initial_end(const BitMap& map, idx_t beg, idx_t end);
+
+public:
+  // Constructs an empty iterator.
+  ReverseIterator();
+
+  // Constructs a reverse iterator for map, over the range [0, map.size()).
+  explicit ReverseIterator(const BitMap& map);
+
+  // Constructs a reverse iterator for map, over the range [beg, end).
+  // If there are no set bits in that range, the resulting iterator is empty.
+  // Otherwise, index() is initially the position of the last set bit in
+  // that range.
+  // precondition: beg and end form a valid range for map.
+  ReverseIterator(const BitMap& map, idx_t beg, idx_t end);
+
+  // Returns true if the remaining iteration range is empty.
+  bool is_empty() const;
+
+  // Returns the index of the last set bit in the remaining iteration range.
+  // precondition: !is_empty()
+  idx_t index() const;
+
+  // Updates index() to the position of the last set bit in the range
+  // [beg, index()), where beg was the corresponding constructor argument.
+  // The iterator instead becomes empty if there aren't any set bits in
+  // that range.
+  // precondition: !is_empty()
+  void step();
+
+  // Range-based for loop support.
+  ReverseRBFIterator begin() const;
+  ReverseRBFIterator end() const;
+};
+
+// Provides range-based for loop iteration support.  This class is not
+// intended for direct use by an application.  It provides the functionality
+// required by a range-based for loop with an Iterator as the range.
+class BitMap::RBFIterator {
+  friend class Iterator;
+
+  IteratorImpl _impl;
+
+  RBFIterator(const BitMap* map, idx_t beg, idx_t end);
+
+public:
+  bool operator!=(const RBFIterator& i) const;
+  idx_t operator*() const;
+  RBFIterator& operator++();
+};
+
+// Provides range-based for loop reverse iteration support.  This class is
+// not intended for direct use by an application.  It provides the
+// functionality required by a range-based for loop with a ReverseIterator
+// as the range.
+class BitMap::ReverseRBFIterator {
+  friend class ReverseIterator;
+
+  IteratorImpl _impl;
+
+  ReverseRBFIterator(const BitMap* map, idx_t beg, idx_t end);
+
+public:
+  bool operator!=(const ReverseRBFIterator& i) const;
+  idx_t operator*() const;
+  ReverseRBFIterator& operator++();
+};
+
 // CRTP: BitmapWithAllocator exposes the following Allocator interfaces upward to GrowableBitMap.
 //
 //  bm_word_t* allocate(idx_t size_in_words) const;

src/hotspot/share/utilities/bitMap.inline.hpp

@@ -370,6 +370,161 @@ inline bool BitMap::reverse_iterate(BitMapClosureType* cl, idx_t beg, idx_t end)
   return reverse_iterate(function, beg, end);
 }
 
+/// BitMap::IteratorImpl
+
+inline BitMap::IteratorImpl::IteratorImpl()
+  : _map(nullptr), _cur_beg(0), _cur_end(0)
+{}
+
+inline BitMap::IteratorImpl::IteratorImpl(const BitMap* map, idx_t beg, idx_t end)
+  : _map(map), _cur_beg(beg), _cur_end(end)
+{}
+
+inline bool BitMap::IteratorImpl::is_empty() const {
+  return _cur_beg == _cur_end;
+}
+
+inline BitMap::idx_t BitMap::IteratorImpl::first() const {
+  assert_not_empty();
+  return _cur_beg;
+}
+
+inline BitMap::idx_t BitMap::IteratorImpl::last() const {
+  assert_not_empty();
+  return _cur_end - 1;
+}
+
+inline void BitMap::IteratorImpl::step_first() {
+  assert_not_empty();
+  _cur_beg = _map->find_first_set_bit(_cur_beg + 1, _cur_end);
+}
+
+inline void BitMap::IteratorImpl::step_last() {
+  assert_not_empty();
+  idx_t lastpos = last();
+  idx_t pos = _map->find_last_set_bit(_cur_beg, lastpos);
+  _cur_end = (pos < lastpos) ? (pos + 1) : _cur_beg;
+}
+
+/// BitMap::Iterator
+
+inline BitMap::Iterator::Iterator() : _impl() {}
+
+inline BitMap::Iterator::Iterator(const BitMap& map)
+  : Iterator(map, 0, map.size())
+{}
+
+inline BitMap::Iterator::Iterator(const BitMap& map, idx_t beg, idx_t end)
+  : _impl(&map, map.find_first_set_bit(beg, end), end)
+{}
+
+inline bool BitMap::Iterator::is_empty() const {
+  return _impl.is_empty();
+}
+
+inline BitMap::idx_t BitMap::Iterator::index() const {
+  return _impl.first();
+}
+
+inline void BitMap::Iterator::step() {
+  _impl.step_first();
+}
+
+inline BitMap::RBFIterator BitMap::Iterator::begin() const {
+  return RBFIterator(_impl._map, _impl._cur_beg, _impl._cur_end);
+}
+
+inline BitMap::RBFIterator BitMap::Iterator::end() const {
+  return RBFIterator(_impl._map, _impl._cur_end, _impl._cur_end);
+}
+
+/// BitMap::ReverseIterator
+
+inline BitMap::idx_t BitMap::ReverseIterator::initial_end(const BitMap& map,
+                                                          idx_t beg,
+                                                          idx_t end) {
+  idx_t pos = map.find_last_set_bit(beg, end);
+  return (pos < end) ? (pos + 1) : beg;
+}
+
+inline BitMap::ReverseIterator::ReverseIterator() : _impl() {}
+
+inline BitMap::ReverseIterator::ReverseIterator(const BitMap& map)
+  : ReverseIterator(map, 0, map.size())
+{}
+
+inline BitMap::ReverseIterator::ReverseIterator(const BitMap& map,
+                                                idx_t beg,
+                                                idx_t end)
+  : _impl(&map, beg, initial_end(map, beg, end))
+{}
+
+inline bool BitMap::ReverseIterator::is_empty() const {
+  return _impl.is_empty();
+}
+
+inline BitMap::idx_t BitMap::ReverseIterator::index() const {
+  return _impl.last();
+}
+
+inline void BitMap::ReverseIterator::step() {
+  _impl.step_last();
+}
+
+inline BitMap::ReverseRBFIterator BitMap::ReverseIterator::begin() const {
+  return ReverseRBFIterator(_impl._map, _impl._cur_beg, _impl._cur_end);
+}
+
+inline BitMap::ReverseRBFIterator BitMap::ReverseIterator::end() const {
+  return ReverseRBFIterator(_impl._map, _impl._cur_beg, _impl._cur_beg);
+}
+
+/// BitMap::RBFIterator
+
+inline BitMap::RBFIterator::RBFIterator(const BitMap* map, idx_t beg, idx_t end)
+  : _impl(map, beg, end)
+{}
+
+inline bool BitMap::RBFIterator::operator!=(const RBFIterator& i) const {
+  // Shouldn't be comparing RBF iterators from different contexts.
+  assert(_impl._map == i._impl._map, "mismatched range-based for iterators");
+  assert(_impl._cur_end == i._impl._cur_end, "mismatched range-based for iterators");
+  return _impl._cur_beg != i._impl._cur_beg;
+}
+
+inline BitMap::idx_t BitMap::RBFIterator::operator*() const {
+  return _impl.first();
+}
+
+inline BitMap::RBFIterator& BitMap::RBFIterator::operator++() {
+  _impl.step_first();
+  return *this;
+}
+
+/// BitMap::ReverseRBFIterator
+
+inline BitMap::ReverseRBFIterator::ReverseRBFIterator(const BitMap* map,
+                                                      idx_t beg,
+                                                      idx_t end)
+  : _impl(map, beg, end)
+{}
+
+inline bool BitMap::ReverseRBFIterator::operator!=(const ReverseRBFIterator& i) const {
+  // Shouldn't be comparing RBF iterators from different contexts.
+  assert(_impl._map == i._impl._map, "mismatched range-based for iterators");
+  assert(_impl._cur_beg == i._impl._cur_beg, "mismatched range-based for iterators");
+  return _impl._cur_end != i._impl._cur_end;
+}
+
+inline BitMap::idx_t BitMap::ReverseRBFIterator::operator*() const {
+  return _impl.last();
+}
+
+inline BitMap::ReverseRBFIterator& BitMap::ReverseRBFIterator::operator++() {
+  _impl.step_last();
+  return *this;
+}
+
 // Returns a bit mask for a range of bits [beg, end) within a single word.  Each
 // bit in the mask is 0 if the bit is in the range, 1 if not in the range.  The
 // returned mask can be used directly to clear the range, or inverted to set the