The structure of evaluate::Expr is highly customized for the specific
operation or entity that it represents. The different cases are
expressed with different types, which makes the traversal and
modifications somewhat complicated. There exists a framework for
read-only traversal (traverse.h), but there is nothing that helps with
modifying evaluate::Expr.
It's rare that evaluate::Expr needs to be modified, but for the cases
where it needs to be, this code will make it easier.
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Co-authored-by: Tom Eccles <tom.eccles@arm.com>
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