8156207: Resource allocated BitMaps are often cleared unnecessarily

Summary: Removed unnecessary clearing of BitMap.
Reviewed-by: kbarrett, kvn, thartmann
Contributed-by: NChristian Hagedorn <christian.hagedorn@oracle.com>

src/hotspot/share/compiler/methodLiveness.cpp

@@ -994,8 +994,8 @@ MethodLivenessResult MethodLiveness::BasicBlock::get_liveness_at(ciMethod* metho
 
 #ifdef ASSERT
   ResourceMark rm;
-  ResourceBitMap g(_gen.size()); g.set_from(_gen);
-  ResourceBitMap k(_kill.size()); k.set_from(_kill);
+  ResourceBitMap g(_gen.size(), false); g.set_from(_gen);
+  ResourceBitMap k(_kill.size(), false); k.set_from(_kill);
 #endif
   if (_last_bci != bci || trueInDebug) {
     ciBytecodeStream bytes(method);

src/hotspot/share/utilities/bitMap.cpp

@@ -133,8 +133,8 @@ void BitMap::reinitialize(const Allocator& allocator, idx_t new_size_in_bits) {
   initialize(allocator, new_size_in_bits);
 }
 
-ResourceBitMap::ResourceBitMap(idx_t size_in_bits)
-    : BitMap(allocate(ResourceBitMapAllocator(), size_in_bits), size_in_bits) {
+ResourceBitMap::ResourceBitMap(idx_t size_in_bits, bool clear)
+    : BitMap(allocate(ResourceBitMapAllocator(), size_in_bits, clear), size_in_bits) {
 }
 
 void ResourceBitMap::resize(idx_t new_size_in_bits) {

src/hotspot/share/utilities/bitMap.hpp

@@ -319,8 +319,8 @@ class ResourceBitMap : public BitMap {
 
  public:
   ResourceBitMap() : BitMap(NULL, 0) {}
-  // Clears the bitmap memory.
-  ResourceBitMap(idx_t size_in_bits);
+  // Conditionally clears the bitmap memory.
+  ResourceBitMap(idx_t size_in_bits, bool clear = true);
 
   // Resize the backing bitmap memory.
   //