[GitHub] [incubator-mxnet] ptrendx opened a new pull request #15657: Eliminate common expressions

[GitBox <gi...@apache.org>]

ptrendx opened a new pull request #15657: Eliminate common expressions
URL: https://github.com/apache/incubator-mxnet/pull/15657
 
 
   ## Description ##
   This PR introduces a graph pass that eliminates redundant common expressions in the graph. 
   
   For example, let's look at the graph created from a following Python code:
   ```
   a = mx.sym.Variable()
   out = (a + 5) * (a + 5)
   ```
   This graph will compute `a+5` twice, which is wasteful. After the pass introduced in this PR, the actual executed graph will be equivalent to
   ```
   a = mx.sym.Variable()
   b = a + 5
   out = b * b
   ```
   which computes the `a+5` only once.
   
   @eric-haibin-lin FYI
   
   ## Checklist ##
   ### Essentials ###
   Please feel free to remove inapplicable items for your PR.
   - [x] Changes are complete (i.e. I finished coding on this PR)
   - [ ] All changes have test coverage:
   - Unit tests are added for small changes to verify correctness (e.g. adding a new operator)
   - [x] Code is well-documented: 
   - For new C++ functions in header files, their functionalities and arguments are documented. 
   - [x] To the my best knowledge, examples are either not affected by this change, or have been fixed to be compatible with this change
   
   ### Changes ###
   - [ ] Feature1, tests, (and when applicable, API doc)
   - [ ] Feature2, tests, (and when applicable, API doc)
   
   ## Comments ##
   

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