Decompose if_expr when adding dependencies

We add the dependencies on atomic string expressions, instead of the
if_expr directly.

Author: romainbrenguier

src/solvers/refinement/string_refinement_util.cpp

@@ -434,12 +434,30 @@ void string_dependenciest::add_dependency(
   const array_string_exprt &e,
   const builtin_function_nodet &builtin_function_node)
 {
+  if(e.id() == ID_if)
+  {
+    const auto if_expr = to_if_expr(e);
+    const auto &true_case = to_array_string_expr(if_expr.true_case());
+    const auto &false_case = to_array_string_expr(if_expr.false_case());
+    add_dependency(true_case, builtin_function_node);
+    add_dependency(false_case, builtin_function_node);
+    return;
+  }
   string_nodet &string_node = get_node(e);
   string_node.dependencies.push_back(builtin_function_node);
 }
 
 void string_dependenciest::add_unknown_dependency(const array_string_exprt &e)
 {
+  if(e.id() == ID_if)
+  {
+    const auto if_expr = to_if_expr(e);
+    const auto &true_case = to_array_string_expr(if_expr.true_case());
+    const auto &false_case = to_array_string_expr(if_expr.false_case());
+    add_unknown_dependency(true_case);
+    add_unknown_dependency(false_case);
+    return;
+  }
   string_nodet &string_node = get_node(e);
   string_node.depends_on_unknown_builtin_function = true;
 }

src/solvers/refinement/string_refinement_util.h

@@ -343,7 +343,9 @@ class string_dependenciest
   const string_builtin_functiont &
   get_builtin_function(const builtin_function_nodet &node) const;
 
-  /// Add edge from node for `e` to node for `builtin_function`
+  /// Add edge from node for `e` to node for `builtin_function` if `e` is a
+  /// simple array expression. If it is an `if_exprt` we add the sub-expressions
+  /// that are not `if_exprt`s instead.
   void add_dependency(
     const array_string_exprt &e,
     const builtin_function_nodet &builtin_function);