code: private void opNullCheckEndMemSTPush() {
          int mem = code[ip++];   /* mem: null check id */
  
          int isNull;
          if (Config.USE_MONOMANIAC_CHECK_CAPTURES_IN_ENDLESS_REPEAT) {
              isNull = nullCheckMemStRec(mem, s);
          } else {
              isNull = nullCheckRec(mem, s);
          }
  
          if (isNull != 0) {
              if (Config.DEBUG_MATCH) {
                  Config.log.println("NULL_CHECK_END_MEMST_PUSH: skip  id:" + mem + ", s:" + s);
              }
  
              if (isNull == -1) {opFail(); return;}
              nullCheckFound();
          } else {
              pushNullCheckEnd(mem);
          }
      }
docs: USE_SUBEXP_CALL