8214377: ZGC: Don't use memset to initialize array of ZForwardingTableEntry

Reviewed-by: rkennke, eosterlund

src/hotspot/share/gc/z/zForwardingTable.cpp

@@ -38,11 +38,18 @@ void ZForwardingTable::setup(size_t live_objects) {
   _size = ZUtils::round_up_power_of_2(live_objects * 2);
   _table = MallocArrayAllocator<ZForwardingTableEntry>::allocate(_size, mtGC);
 
-  // Clear table
+  // Construct table entries
-  memset(_table, ZForwardingTableEntry::empty(), _size * sizeof(ZForwardingTableEntry));
+  for (size_t i = 0; i < _size; i++) {
+    ::new (_table + i) ZForwardingTableEntry();
+  }
 }
 
 void ZForwardingTable::reset() {
+  // Destruct table entries
+  for (size_t i = 0; i < _size; i++) {
+    (_table + i)->~ZForwardingTableEntry();
+  }
+
   // Free table
   MallocArrayAllocator<ZForwardingTableEntry>::free(_table);
   _table = NULL;

src/hotspot/share/gc/z/zForwardingTableEntry.hpp

@@ -52,6 +52,10 @@ private:
 
   uint64_t _entry;
 
+  static uintptr_t empty() {
+    return (uintptr_t)-1;
+  }
+
 public:
   ZForwardingTableEntry() :
       _entry(empty()) {}
@@ -60,10 +64,6 @@ public:
       _entry(field_from_index::encode(from_index) |
              field_to_offset::encode(to_offset)) {}
 
-  static uintptr_t empty() {
-    return (uintptr_t)-1;
-  }
-
   bool is_empty() const {
     return _entry == empty();
   }