class_docstr: This is used to create external functions for ccompiler.
  A simple annotator that creates the following program:
         |
    -- begin --
         |
        add
         |
      subtract
         |
      multiply
         |
     -- end --
         |
code: def visit_call(self, call):
      if call.op.name == "add":  # Annotate begin at args
          if self.in_compiler == 1:
              lhs = compiler_begin(
                  super().visit(call.args[0]), "ccompiler"
              )
              rhs = compiler_begin(
                  super().visit(call.args[1]), "ccompiler"
              )
              op = relay.add(lhs, rhs)
              self.in_compiler = 2
              return op
      elif call.op.name == "subtract":
          if self.in_compiler == 1:
              lhs = super().visit(call.args[0])
              rhs = super().visit(call.args[1])
              if isinstance(lhs, relay.expr.Var):
                  lhs = compiler_begin(lhs, "ccompiler")
              if isinstance(rhs, relay.expr.Var):
                  rhs = compiler_begin(rhs, "ccompiler")
              return relay.subtract(lhs, rhs)
      elif call.op.name == "multiply":  # Annotate end at output
          self.in_compiler = 1
          lhs = super().visit(call.args[0])
          rhs = super().visit(call.args[1])
          if isinstance(lhs, relay.expr.Var):
              lhs = compiler_begin(lhs, "ccompiler")
          if isinstance(rhs, relay.expr.Var):
              rhs = compiler_begin(rhs, "ccompiler")
          op = relay.multiply(lhs, rhs)
          if self.in_compiler == 2:
              op = compiler_end(op, "ccompiler")
          self.in_compiler = 0
          return op
      return super().visit_call(call)
  
imports: from tvm import relay
  from tvm.relay.expr_functor import ExprMutator
  from tvm.relay.op.annotation import compiler_begin, compiler_end
label_desc: Use image node_id 2 for calling the CcompilerAnnotator obj's underlying member method code with example usage: obj.visit_call(call) and returns: super, op, relay, op