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Date: Sat, 16 May 2020 00:59:59 -0000
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comaniac opened a new issue #5605:
URL: https://github.com/apache/incubator-tvm/issues/5605


   I was trying the new merged pattern language. Specifically, my goal is to create a function for the matched pattern and rewrite the pattern with a function call, which is very similar to fusion.
   
   However, the following example encounters segmentation fault. I breifly located the position and found that it was in dominator analysis. Specifically in `LeastCommonAncestor`. It crashes when visiting an input node with null parent.
   
   Here is the code snippet to reproduce the problem. I am not sure if I wrote the pattern in the right way, but it works fine with `pattern.match`.
   
   cc @mbrookhart 
   
   ```python
   import tvm
   from tvm import relay
   from tvm.relay.dataflow_pattern import *
   
   class PatternCallback(DFPatternCallback):
       def __init__(self, pattern):
           self.pattern = pattern
   
       def callback(self, pre, post, node_map):
           return post
   
   def gen():
       x = relay.var('x')
       y = relay.var('y')
       y_add = relay.add(y, y)
       n0 = relay.add(x, y_add)
       n1 = relay.add(x, n0)
       return relay.add(n1, n0)
   
   def pattern():
       a = wildcard()
       b = wildcard()
       n0 = is_op('add')(a, b)
       n1 = is_op('add')(n0, a)
       return is_op('add')(n0, n1)
   
   out = gen()
   pat = pattern()
   print(pat.match(out))
   new_out = rewrite(PatternCallback(pat), out)
   print(new_out)
   ```


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