docs: @Override
      public void visitJumpInsn(final int opcode, final Label lbl) {
          super.visitJumpInsn(opcode, lbl);
          LabelNode ln = ((JumpInsnNode) instructions.getLast()).label;
          if (opcode == JSR && !subroutineHeads.containsKey(ln)) {
              subroutineHeads.put(ln, new BitSet());
          }
      }