* First pass a defining a non-recursive Graph Vistor and Rewriter

autoformat

remove a currently empty test until testing is solidfied

* Make CalcDep from Dead Code Elimination non-recursive

* Partially working, not passing all tests yet

passes tests when disabling GetExprRefCount, I think I have a bug in visit counting

fix GetExprRefCount

Fix a subtle bug with nested recursive/non-recursive scopes

* Refactor

* improve comments

* respond to review comments on comments

* Fix a problem with default recursion for dataflow nodes

mark DataflowVisitor methods as override

* implement ScopeMutator

* convert forward_rewrite to ScopeMutator, remove DataflowMutator

* rewrite ExprRewriter and convert fast_math to use it

* switch BiasAddSimplifier to ExprRewriter

fix a clang warning

fix cpp lint

fix doc param error

* respond to review comments

* fix a typo in the iterative looping

* add a regression test for GetExprRefCount issue

* Normalize naming

* fix lint

* First pass a defining a non-recursive Graph Vistor and Rewriter

autoformat

remove a currently empty test until testing is solidfied

* Make CalcDep from Dead Code Elimination non-recursive

* Partially working, not passing all tests yet

passes tests when disabling GetExprRefCount, I think I have a bug in visit counting

fix GetExprRefCount

Fix a subtle bug with nested recursive/non-recursive scopes

* Refactor

* improve comments

* respond to review comments on comments

* Fix a problem with default recursion for dataflow nodes

mark DataflowVisitor methods as override

* implement ScopeMutator

* convert forward_rewrite to ScopeMutator, remove DataflowMutator

* rewrite ExprRewriter and convert fast_math to use it

* switch BiasAddSimplifier to ExprRewriter

fix a clang warning

fix cpp lint

fix doc param error

* respond to review comments

* fix a typo in the iterative looping

* add a regression test for GetExprRefCount issue

* Normalize naming

* fix lint

* respond to review comments