class_docstr: A callback to remove empty pad op from the below pattern:
  Pattern:
  %0 = cast(0f, dtype="float16");
  %1 = nn.pad(%inp, %0, pad_width=[[0i64, 0i64], [0i64, 0i64]]);
  nn.matmul(%1, %inp2, units=None)
class_docstr_tok: ["A","callback","to","remove","empty","pad","op","from","the","below","pattern",":","Pattern",":","%","0","=","cast","(","0f",",","dtype=","''","float16","''",")",";","%","1","=","nn.pad","(","%","inp",",","%","0",",","pad_width=","[","[","0i64",",","0i64","]",",","[","0i64",",","0i64","]","]",")",";","nn.matmul","(","%","1",",","%","inp2",",","units=None",")"]
code: def callback(self, pre, post, node_map):
      A = node_map[self.A][0]
      B = node_map[self.B][0]
      return relay.nn.matmul(A, B)
  
imports: import functools
  import numpy
  import tvm
  from tvm import relay
  from tvm.relay.dataflow_pattern import DFPatternCallback, is_constant, is_op, is_tuple, rewrite, wildcard
  from tvm.topi.utils import get_const_tuple
  from tvm.relay.expr import Call
  from tvm.runtime import ndarray
  from ..._ffi.registry import register_func
label_desc: Use image node_id 2 for calling the remove_empty_pad_callback obj's underlying member method code with example usage: obj.callback(pre, post, node_map) and returns: relay