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pre/post traversal expression transformers #4891

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pre/post traversal expression transformers #4891

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57 changes: 57 additions & 0 deletions src/util/expr.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -287,6 +287,63 @@ void exprt::visit_post(std::function<void(const exprt &)> visitor) const
visit_post_template(visitor, this);
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Commit message: "Transformers for expressions that offer an interface similar to that offered
by the goto-program API." There isn't enough context available to understand why what looks like a comparison of apples and oranges is useful to the reader.

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Fixed

}

optionalt<exprt>
exprt::transform_pre(std::function<optionalt<exprt>(exprt)> visitor) const
{
auto visitor_result = visitor(*this);

// make a copy
exprt tmp = visitor_result.value_or(*this);

bool op_changed = false;

for(auto &op : tmp.operands()) // this breaks sharing of the copy
{
auto op_result = op.transform_pre(visitor);
if(op_result.has_value())
{
op = std::move(op_result.value());
op_changed = true;
}
}

if(op_changed)
return std::move(tmp);
else
return visitor_result;
}

optionalt<exprt>
exprt::transform_post(std::function<optionalt<exprt>(exprt)> visitor) const
{
// make a copy
exprt tmp = *this;

bool op_changed = false;

for(auto &op : tmp.operands()) // this breaks sharing of the copy
{
auto op_result = op.transform_post(visitor);
if(op_result.has_value())
{
op = std::move(op_result.value());
op_changed = true;
}
}

if(op_changed)
{
auto visitor_result = visitor(tmp);

if(visitor_result.has_value())
return std::move(visitor_result.value());
else
return std::move(tmp);
}
else
return visitor(*this);
}

template <typename T>
static void visit_pre_template(std::function<void(T &)> visitor, T *_expr)
{
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2 changes: 2 additions & 0 deletions src/util/expr.h
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Original file line number Diff line number Diff line change
Expand Up @@ -332,12 +332,14 @@ class exprt:public irept
void visit(class const_expr_visitort &visitor) const;
void visit_pre(std::function<void(exprt &)>);
void visit_pre(std::function<void(const exprt &)>) const;
optionalt<exprt> transform_pre(std::function<optionalt<exprt>(exprt)>) const;

/// These are post-order traversal visitors, i.e.,
/// the visitor is executed on a node _after_ its children
/// have been visited.
void visit_post(std::function<void(exprt &)>);
void visit_post(std::function<void(const exprt &)>) const;
optionalt<exprt> transform_post(std::function<optionalt<exprt>(exprt)>) const;

depth_iteratort depth_begin();
depth_iteratort depth_end();
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