8331626: unsafe.cpp:162:38: runtime error in index_oop_from_field_off…

…set_long - applying non-zero offset 4563897424 to null pointer

Backport-of: 23a72a1f2f651d5e8e9a0eb1e75e2b44572a13da

src/hotspot/share/prims/unsafe.cpp

@@ -131,13 +131,9 @@ static inline void assert_field_offset_sane(oop p, jlong field_offset) {
 
 static inline void* index_oop_from_field_offset_long(oop p, jlong field_offset) {
   assert_field_offset_sane(p, field_offset);
-  jlong byte_offset = field_offset_to_byte_offset(field_offset);
-
-  if (sizeof(char*) == sizeof(jint)) {   // (this constant folds!)
-    return cast_from_oop<address>(p) + (jint) byte_offset;
-  } else {
-    return cast_from_oop<address>(p) +        byte_offset;
-  }
+  uintptr_t base_address = cast_from_oop<uintptr_t>(p);
+  uintptr_t byte_offset  = (uintptr_t)field_offset_to_byte_offset(field_offset);
+  return (void*)(base_address + byte_offset);
 }
 
 // Externally callable versions: