Add a Common Sub-Expression Elimination optimization for the AST.
Add a Common Sub-Expression Elimination optimization for the AST.

This optimization pass walks through the node list and finds references to
nodes for which there are string representations and replaces them with
the first node found that has the same string representation.

eXhausted/Ovale,Xeltor/ovale,ultijlam/ovale,eXhausted/Ovale,ultijlam/ovale,eXhausted/Ovale,ultijlam/ovale