--- a/src/hotspot/share/utilities/bitMap.cpp	Mon Apr 15 11:47:46 2019 +0200
+++ b/src/hotspot/share/utilities/bitMap.cpp	Thu May 02 10:32:14 2019 +0200
@@ -111,26 +111,26 @@
 }
 
 template <class Allocator>
-void BitMap::resize(const Allocator& allocator, idx_t new_size_in_bits) {
-  bm_word_t* new_map = reallocate(allocator, map(), size(), new_size_in_bits);
+void BitMap::resize(const Allocator& allocator, idx_t new_size_in_bits, bool clear) {
+  bm_word_t* new_map = reallocate(allocator, map(), size(), new_size_in_bits, clear);
 
   update(new_map, new_size_in_bits);
 }
 
 template <class Allocator>
-void BitMap::initialize(const Allocator& allocator, idx_t size_in_bits) {
+void BitMap::initialize(const Allocator& allocator, idx_t size_in_bits, bool clear) {
   assert(map() == NULL, "precondition");
   assert(size() == 0,   "precondition");
 
-  resize(allocator, size_in_bits);
+  resize(allocator, size_in_bits, clear);
 }
 
 template <class Allocator>
-void BitMap::reinitialize(const Allocator& allocator, idx_t new_size_in_bits) {
-  // Remove previous bits.
-  resize(allocator, 0);
+void BitMap::reinitialize(const Allocator& allocator, idx_t new_size_in_bits, bool clear) {
+  // Remove previous bits - no need to clear
+  resize(allocator, 0, false /* clear */);
 
-  initialize(allocator, new_size_in_bits);
+  initialize(allocator, new_size_in_bits, clear);
 }
 
 ResourceBitMap::ResourceBitMap(idx_t size_in_bits)
@@ -138,15 +138,15 @@
 }
 
 void ResourceBitMap::resize(idx_t new_size_in_bits) {
-  BitMap::resize(ResourceBitMapAllocator(), new_size_in_bits);
+  BitMap::resize(ResourceBitMapAllocator(), new_size_in_bits, true /* clear */);
 }
 
 void ResourceBitMap::initialize(idx_t size_in_bits) {
-  BitMap::initialize(ResourceBitMapAllocator(), size_in_bits);
+  BitMap::initialize(ResourceBitMapAllocator(), size_in_bits, true /* clear */);
 }
 
 void ResourceBitMap::reinitialize(idx_t size_in_bits) {
-  BitMap::reinitialize(ResourceBitMapAllocator(), size_in_bits);
+  BitMap::reinitialize(ResourceBitMapAllocator(), size_in_bits, true /* clear */);
 }
 
 ArenaBitMap::ArenaBitMap(Arena* arena, idx_t size_in_bits)
@@ -161,16 +161,16 @@
   free(CHeapBitMapAllocator(_flags), map(), size());
 }
 
-void CHeapBitMap::resize(idx_t new_size_in_bits) {
-  BitMap::resize(CHeapBitMapAllocator(_flags), new_size_in_bits);
+void CHeapBitMap::resize(idx_t new_size_in_bits, bool clear) {
+  BitMap::resize(CHeapBitMapAllocator(_flags), new_size_in_bits, clear);
 }
 
-void CHeapBitMap::initialize(idx_t size_in_bits) {
-  BitMap::initialize(CHeapBitMapAllocator(_flags), size_in_bits);
+void CHeapBitMap::initialize(idx_t size_in_bits, bool clear) {
+  BitMap::initialize(CHeapBitMapAllocator(_flags), size_in_bits, clear);
 }
 
-void CHeapBitMap::reinitialize(idx_t size_in_bits) {
-  BitMap::reinitialize(CHeapBitMapAllocator(_flags), size_in_bits);
+void CHeapBitMap::reinitialize(idx_t size_in_bits, bool clear) {
+  BitMap::reinitialize(CHeapBitMapAllocator(_flags), size_in_bits, clear);
 }
 
 #ifdef ASSERT

--- a/src/hotspot/share/utilities/bitMap.hpp	Mon Apr 15 11:47:46 2019 +0200
+++ b/src/hotspot/share/utilities/bitMap.hpp	Thu May 02 10:32:14 2019 +0200
@@ -157,20 +157,20 @@
   // Old bits are transfered to the new memory
   // and the extended memory is cleared.
   template <class Allocator>
-  void resize(const Allocator& allocator, idx_t new_size_in_bits);
+  void resize(const Allocator& allocator, idx_t new_size_in_bits, bool clear);
 
   // Set up and clear the bitmap memory.
   //
   // Precondition: The bitmap was default constructed and has
   // not yet had memory allocated via resize or (re)initialize.
   template <class Allocator>
-  void initialize(const Allocator& allocator, idx_t size_in_bits);
+  void initialize(const Allocator& allocator, idx_t size_in_bits, bool clear);
 
   // Set up and clear the bitmap memory.
   //
   // Can be called on previously initialized bitmaps.
   template <class Allocator>
-  void reinitialize(const Allocator& allocator, idx_t new_size_in_bits);
+  void reinitialize(const Allocator& allocator, idx_t new_size_in_bits, bool clear);
 
   // Set the map and size.
   void update(bm_word_t* map, idx_t size) {
@@ -384,18 +384,18 @@
   //
   // Old bits are transfered to the new memory
   // and the extended memory is cleared.
-  void resize(idx_t new_size_in_bits);
+  void resize(idx_t new_size_in_bits, bool clear = true);
 
   // Set up and clear the bitmap memory.
   //
   // Precondition: The bitmap was default constructed and has
   // not yet had memory allocated via resize or initialize.
-  void initialize(idx_t size_in_bits);
+  void initialize(idx_t size_in_bits, bool clear = true);
 
   // Set up and clear the bitmap memory.
   //
   // Can be called on previously initialized bitmaps.
-  void reinitialize(idx_t size_in_bits);
+  void reinitialize(idx_t size_in_bits, bool clear = true);
 };
 
 // Convenience class wrapping BitMap which provides multiple bits per slot.