Eliminate redundant subexpressions (#3047)
* Eliminate redundant subexpressions
Apply local value numbering to merge graph nodes that will always
evaluate to the same value.
* Rename cpp->cc
* Handle optional arguments
* Add test models
* Add more tests with optional arguments
* Fix processing of subgraphs
Also, be resilient to possible mixture of optional and variadic
parameters
* Fix random operators
* Address PR comments
* Minor changes and a test
* Move CSE before constant folding
* Random* operators are always non-deterministic
Even when seed is provided.
* Fix a CSE test
* Reuse the list of non-deterministic operators with constant folding pass
* Address PR comments
* Fix formatting
* Address PR comment
* Minor cleanup / comments
* Fix build failure in Linux
* Reuse existing optimizer/utils file.
Also, check for graph outputs when removing a node.
* Add a test
* Fix compiler warnings
* Fix build in older compilers
* More compatibility with old STL versions
