Implement union values

Reuse get_struct_member for unions (copy-paste).

Author: petr-bauch

src/memory-analyzer/analyze_symbol.cpp

@@ -421,7 +421,11 @@ exprt gdb_value_extractort::get_expr_value(
 
     return get_pointer_value(expr, zero_expr, location);
   }
-  UNIMPLEMENTED;
+  else if(type.id() == ID_union_tag)
+  {
+    return get_union_value(expr, zero_expr, location);
+  }
+  UNREACHABLE;
 }
 
 exprt gdb_value_extractort::get_struct_value(
@@ -457,6 +461,28 @@ exprt gdb_value_extractort::get_struct_value(
   return new_expr;
 }
 
+exprt gdb_value_extractort::get_union_value(
+  const exprt &expr,
+  const exprt &zero_expr,
+  const source_locationt &location)
+{
+  PRECONDITION(zero_expr.id() == ID_union);
+
+  PRECONDITION(expr.type().id() == ID_union_tag);
+  PRECONDITION(expr.type() == zero_expr.type());
+
+  exprt new_expr(zero_expr);
+
+  const union_tag_typet &union_tag_type = to_union_tag_type(expr.type());
+  const union_typet &union_type = ns.follow_tag(union_tag_type);
+
+  CHECK_RETURN(new_expr.operands().size() == 1);
+  const union_typet::componentt &component = union_type.components()[0];
+  auto &operand = new_expr.operands()[0];
+  operand = get_expr_value(member_exprt{expr, component}, operand, location);
+  return new_expr;
+}
+
 void gdb_value_extractort::process_outstanding_assignments()
 {
   for(const auto &pair : outstanding_assignments)

src/memory-analyzer/analyze_symbol.h

@@ -138,6 +138,16 @@ class gdb_value_extractort
     const exprt &zero_expr,
     const source_locationt &location);
 
+  /// For each of the members of the struct: call \ref get_expr_value
+  /// \param expr: struct expression to be analysed
+  /// \param zero_expr: struct with zero-initialised members
+  /// \param location: the source location
+  /// \return the value of the struct from \ref gdb_apit
+  exprt get_union_value(
+    const exprt &expr,
+    const exprt &zero_expr,
+    const source_locationt &location);
+
   /// Call \ref gdb_apit::get_memory on \p expr then split based on the
   ///   points-to type being `char` type or not. These have dedicated functions.
   /// \param expr: the input pointer expression