8298725: Add BitMap support for reverse iteration

Reviewed-by: stefank, aboldtch, tschatzl

src/hotspot/share/utilities/bitMap.hpp

@@ -264,7 +264,7 @@ class BitMap {
   void verify_range(idx_t beg, idx_t end) const NOT_DEBUG_RETURN;
 
   // Applies an operation to the index of each set bit in [beg, end), in
-  // increasing order.
+  // increasing (decreasing for reverse iteration) order.
   //
   // If i is an index of the bitmap, the operation is either
   // - function(i)
@@ -276,8 +276,8 @@ class BitMap {
   // an operation returning false.
   //
   // If an operation modifies the bitmap, modifications to bits at indices
-  // greater than the current index will affect which further indices the
-  // operation will be applied to.
+  // greater than (less than for reverse iteration) the current index will
+  // affect which further indices the operation will be applied to.
   //
   // precondition: beg and end form a valid range for the bitmap.
   template<typename Function>
@@ -296,6 +296,22 @@ class BitMap {
     return iterate(cl, 0, size());
   }
 
+  template<typename Function>
+  bool reverse_iterate(Function function, idx_t beg, idx_t end) const;
+
+  template<typename BitMapClosureType>
+  bool reverse_iterate(BitMapClosureType* cl, idx_t beg, idx_t end) const;
+
+  template<typename Function>
+  bool reverse_iterate(Function function) const {
+    return reverse_iterate(function, 0, size());
+  }
+
+  template<typename BitMapClosureType>
+  bool reverse_iterate(BitMapClosureType* cl) const {
+    return reverse_iterate(cl, 0, size());
+  }
+
   // 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.

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

@@ -351,6 +351,25 @@ inline bool BitMap::iterate(BitMapClosureType* cl, idx_t beg, idx_t end) const {
   return iterate(function, beg, end);
 }
 
+template <typename Function>
+inline bool BitMap::reverse_iterate(Function function, idx_t beg, idx_t end) const {
+  auto invoke = IterateInvoker<decltype(function(beg))>();
+  for (idx_t index; true; end = index) {
+    index = find_last_set_bit(beg, end);
+    if (index >= end) {
+      return true;
+    } else if (!invoke(function, index)) {
+      return false;
+    }
+  }
+}
+
+template <typename BitMapClosureType>
+inline bool BitMap::reverse_iterate(BitMapClosureType* cl, idx_t beg, idx_t end) const {
+  auto function = [&](idx_t index) { return cl->do_bit(index); };
+  return reverse_iterate(function, beg, end);
+}
+
 // 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

test/hotspot/gtest/utilities/test_bitMap_iterate.cpp

@@ -59,31 +59,81 @@ static void test_iterate_lambda(const BitMap& map,
   ASSERT_EQ(positions_index, positions_size);
 }
 
+static void test_reverse_iterate_lambda(const BitMap& map,
+                                        const idx_t* positions,
+                                        size_t positions_size) {
+  SCOPED_TRACE("reverse iterate with lambda");
+  size_t positions_index = positions_size;
+  auto f = [&](idx_t i) {
+    test_iterate_step(map, i, positions, --positions_index, positions_size);
+  };
+  ASSERT_TRUE(map.reverse_iterate(f));
+  ASSERT_EQ(positions_index, 0u);
+}
+
+
+struct TestBitMapIterationData {
+  const BitMap& _map;
+  const idx_t* _positions;
+  size_t _positions_index;
+  size_t _positions_size;
+
+  TestBitMapIterationData(const BitMap& map,
+                          const idx_t* positions,
+                          size_t positions_index,
+                          size_t positions_size)
+    : _map(map),
+      _positions(positions),
+      _positions_index(positions_index),
+      _positions_size(positions_size)
+  {}
+
+  void test(idx_t index) const {
+    test_iterate_step(_map, index, _positions, _positions_index, _positions_size);
+  }
+};
+
 // Test closure returning bool.  Also tests lambda returning bool.
 static void test_iterate_closure(const BitMap& map,
                                  const idx_t* positions,
                                  size_t positions_size) {
   SCOPED_TRACE("iterate with BitMapClosure");
   struct Closure : public BitMapClosure {
-    const BitMap& _map;
-    const idx_t* _positions;
-    size_t _positions_index;
-    size_t _positions_size;
+    TestBitMapIterationData _data;
 
     Closure(const BitMap& map, const idx_t* positions, size_t positions_size)
-      : _map(map),
-        _positions(positions),
-        _positions_index(0),
-        _positions_size(positions_size)
+      : _data(map, positions, 0, positions_size)
     {}
 
     bool do_bit(idx_t i) override {
-      test_iterate_step(_map, i, _positions, _positions_index++, _positions_size);
+      _data.test(i);
+      _data._positions_index += 1;
       return true;
     }
   } closure{map, positions, positions_size};
   ASSERT_TRUE(map.iterate(&closure));
-  ASSERT_EQ(closure._positions_index, positions_size);
+  ASSERT_EQ(closure._data._positions_index, positions_size);
+}
+
+static void test_reverse_iterate_closure(const BitMap& map,
+                                         const idx_t* positions,
+                                         size_t positions_size) {
+  SCOPED_TRACE("reverse iterate with BitMapClosure");
+  struct Closure : public BitMapClosure {
+    TestBitMapIterationData _data;
+
+    Closure(const BitMap& map, const idx_t* positions, size_t positions_size)
+      : _data(map, positions, positions_size, positions_size)
+    {}
+
+    bool do_bit(idx_t i) override {
+      _data._positions_index -= 1;
+      _data.test(i);
+      return true;
+    }
+  } closure{map, positions, positions_size};
+  ASSERT_TRUE(map.reverse_iterate(&closure));
+  ASSERT_EQ(closure._data._positions_index, 0u);
 }
 
 // Test closure returning void.  Also tests lambda returning bool.
@@ -92,24 +142,37 @@ static void test_iterate_non_closure(const BitMap& map,
                                      size_t positions_size) {
   SCOPED_TRACE("iterate with non-BitMapClosure");
   struct Closure {
-    const BitMap& _map;
-    const idx_t* _positions;
-    size_t _positions_index;
-    size_t _positions_size;
-
+    TestBitMapIterationData _data;
     Closure(const BitMap& map, const idx_t* positions, size_t positions_size)
-      : _map(map),
-        _positions(positions),
-        _positions_index(0),
-        _positions_size(positions_size)
+      : _data(map, positions, 0, positions_size)
     {}
 
     void do_bit(idx_t i) {
-      test_iterate_step(_map, i, _positions, _positions_index++, _positions_size);
+      _data.test(i);
+      _data._positions_index += 1;
     }
   } closure{map, positions, positions_size};
   ASSERT_TRUE(map.iterate(&closure));
-  ASSERT_EQ(closure._positions_index, positions_size);
+  ASSERT_EQ(closure._data._positions_index, positions_size);
+}
+
+static void test_reverse_iterate_non_closure(const BitMap& map,
+                                             const idx_t* positions,
+                                             size_t positions_size) {
+  SCOPED_TRACE("reverse iterate with non-BitMapClosure");
+  struct Closure {
+    TestBitMapIterationData _data;
+    Closure(const BitMap& map, const idx_t* positions, size_t positions_size)
+      : _data(map, positions, positions_size, positions_size)
+    {}
+
+    void do_bit(idx_t i) {
+      _data._positions_index -= 1;
+      _data.test(i);
+    }
+  } closure{map, positions, positions_size};
+  ASSERT_TRUE(map.reverse_iterate(&closure));
+  ASSERT_EQ(closure._data._positions_index, 0u);
 }
 
 static void fill_iterate_map(BitMap& map,
@@ -125,9 +188,14 @@ static void test_iterate(BitMap& map,
                          const idx_t* positions,
                          size_t positions_size) {
   fill_iterate_map(map, positions, positions_size);
+
   test_iterate_lambda(map, positions, positions_size);
   test_iterate_closure(map, positions, positions_size);
   test_iterate_non_closure(map, positions, positions_size);
+
+  test_reverse_iterate_lambda(map, positions, positions_size);
+  test_reverse_iterate_closure(map, positions, positions_size);
+  test_reverse_iterate_non_closure(map, positions, positions_size);
 }
 
 TEST(BitMap, iterate_empty) {