If-branch inline makes exponential explosion

name	about	labels
Bug Report	Use this template for reporting a bug	kind/bug

Environment

Uncomment only one /device <> line, hit enter to put that in a new line, and remove leading whitespaces from that line:

/device ascend

/device gpu
/device cpu

Software Environment:
-- MindSpore version (source or binary):r0.3
-- Python version (e.g., Python 3.7.5):3.7.5
-- OS platform and distribution (e.g., Linux Ubuntu 16.04):any
-- GCC/Compiler version (if compiled from source): 7.3.0

tests/st/control/test_multigraph_sink.py::test_if_by_if

       root
        |
      /   \ 
     t     f
    /  \ /  \
  tt  tf ft  ff

   root
    |
  /   \ 
true  false
  \   /  
    |
  /   \ 
true  false
  \   /  
    |
   end

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