Add case_exprt to std_expr.h and refactor code to use it

Introduces `case_exprt` for improved type safety.

Fixes: #3037

Author: tautschnig

src/solvers/flattening/boolbv.cpp

@@ -123,7 +123,7 @@ bvt boolbvt::convert_bitvector(const exprt &expr)
   else if(expr.id() == ID_update_bit)
     return convert_update_bit(to_update_bit_expr(expr));
   else if(expr.id()==ID_case)
-    return convert_case(expr);
+    return convert_case(to_case_expr(expr));
   else if(expr.id()==ID_cond)
     return convert_cond(to_cond_expr(expr));
   else if(expr.id()==ID_if)
@@ -390,7 +390,7 @@ literalt boolbvt::convert_rest(const exprt &expr)
   }
   else if(expr.id()==ID_case)
   {
-    bvt bv=convert_case(expr);
+    bvt bv = convert_case(to_case_expr(expr));
     CHECK_RETURN(bv.size() == 1);
     return bv[0];
   }

src/solvers/flattening/boolbv.h

@@ -185,7 +185,7 @@ class boolbvt:public arrayst
   virtual bvt convert_update(const update_exprt &);
   virtual bvt convert_update_bit(const update_bit_exprt &);
   virtual bvt convert_update_bits(const update_bits_exprt &);
-  virtual bvt convert_case(const exprt &expr);
+  virtual bvt convert_case(const case_exprt &expr);
   virtual bvt convert_cond(const cond_exprt &);
   virtual bvt convert_shift(const binary_exprt &expr);
   virtual bvt convert_bitwise(const exprt &expr);

src/solvers/flattening/boolbv_case.cpp

@@ -6,14 +6,13 @@ Author: Daniel Kroening, [email protected]
 
 \*******************************************************************/
 
-#include "boolbv.h"
-
 #include <util/invariant.h>
+#include <util/std_expr.h>
 
-bvt boolbvt::convert_case(const exprt &expr)
-{
-  PRECONDITION(expr.id() == ID_case);
+#include "boolbv.h"
 
+bvt boolbvt::convert_case(const case_exprt &expr)
+{
   const std::vector<exprt> &operands=expr.operands();
 
   std::size_t width=boolbv_width(expr.type());

src/util/std_expr.h

@@ -3578,6 +3578,123 @@ inline cond_exprt &to_cond_expr(exprt &expr)
   return ret;
 }
 
+/// \brief Case expression: evaluates to the value corresponding to the first
+/// matching case. The first operand is the value to compare against. Subsequent
+/// operands alternate between compare values and result values.
+/// The syntax is: case(select_value, case1_value, result1, case2_value, result2, ...)
+class case_exprt : public multi_ary_exprt
+{
+public:
+  case_exprt(operandst _operands, typet _type)
+    : multi_ary_exprt(ID_case, std::move(_operands), std::move(_type))
+  {
+  }
+
+  /// Constructor with select value
+  case_exprt(exprt _select_value, typet _type)
+    : multi_ary_exprt(ID_case, {std::move(_select_value)}, std::move(_type))
+  {
+  }
+
+  /// Get the value that is being compared against
+  const exprt &select_value() const
+  {
+    PRECONDITION(!operands().empty());
+    return operands()[0];
+  }
+
+  /// Get the value that is being compared against
+  exprt &select_value()
+  {
+    PRECONDITION(!operands().empty());
+    return operands()[0];
+  }
+
+  /// Add a case: value to compare and corresponding result
+  /// \param case_value: the value to compare against select_value
+  /// \param result_value: the value to return if case_value matches select_value
+  void add_case(const exprt &case_value, const exprt &result_value)
+  {
+    operands().reserve(operands().size() + 2);
+    operands().push_back(case_value);
+    operands().push_back(result_value);
+  }
+
+  /// Get the number of cases (excluding the select value)
+  std::size_t number_of_cases() const
+  {
+    PRECONDITION(operands().size() >= 1);
+    return (operands().size() - 1) / 2;
+  }
+
+  /// Get the case value for the i-th case
+  const exprt &case_value(std::size_t i) const
+  {
+    PRECONDITION(i < number_of_cases());
+    return operands()[1 + 2 * i];
+  }
+
+  /// Get the case value for the i-th case
+  exprt &case_value(std::size_t i)
+  {
+    PRECONDITION(i < number_of_cases());
+    return operands()[1 + 2 * i];
+  }
+
+  /// Get the result value for the i-th case
+  const exprt &result_value(std::size_t i) const
+  {
+    PRECONDITION(i < number_of_cases());
+    return operands()[1 + 2 * i + 1];
+  }
+
+  /// Get the result value for the i-th case
+  exprt &result_value(std::size_t i)
+  {
+    PRECONDITION(i < number_of_cases());
+    return operands()[1 + 2 * i + 1];
+  }
+};
+
+template <>
+inline bool can_cast_expr<case_exprt>(const exprt &base)
+{
+  return base.id() == ID_case;
+}
+
+inline void validate_expr(const case_exprt &value)
+{
+  DATA_INVARIANT(
+    value.operands().size() >= 1,
+    "case expression must have at least one operand");
+  DATA_INVARIANT(
+    value.operands().size() % 2 == 1,
+    "case expression must have odd number of operands");
+}
+
+/// \brief Cast an exprt to a \ref case_exprt
+///
+/// \a expr must be known to be \ref case_exprt.
+///
+/// \param expr: Source expression
+/// \return Object of type \ref case_exprt
+inline const case_exprt &to_case_expr(const exprt &expr)
+{
+  PRECONDITION(expr.id() == ID_case);
+  const case_exprt &ret = static_cast<const case_exprt &>(expr);
+  validate_expr(ret);
+  return ret;
+}
+
+/// \copydoc to_case_expr(const exprt &)
+inline case_exprt &to_case_expr(exprt &expr)
+{
+  PRECONDITION(expr.id() == ID_case);
+  case_exprt &ret = static_cast<case_exprt &>(expr);
+  validate_expr(ret);
+  return ret;
+}
+
 /// \brief Expression to define a mapping from an argument (index) to elements.
 /// This enables constructing an array via an anonymous function.
 /// Not all kinds of array comprehension can be expressed, only those of the

test_case_expr_example.cpp

@@ -0,0 +1,57 @@
+/*******************************************************************\
+
+Example: Demonstrating the new case_exprt usage
+
+Author: Example
+
+\*******************************************************************/
+
+#include <util/arith_tools.h>
+#include <util/bitvector_types.h>
+#include <util/std_expr.h>
+
+#include <iostream>
+
+int main()
+{
+  // Create integer type
+  const signedbv_typet int_type(32);
+
+  // Create select value (the variable being matched)
+  const symbol_exprt x("x", int_type);
+
+  // Create a case expression: case(x, 1, 10, 2, 20, 3, 30)
+  // This means: if x==1 return 10, if x==2 return 20, if x==3 return 30
+  case_exprt case_expr(x, int_type);
+
+  // Add cases
+  case_expr.add_case(from_integer(1, int_type), from_integer(10, int_type));
+  case_expr.add_case(from_integer(2, int_type), from_integer(20, int_type));
+  case_expr.add_case(from_integer(3, int_type), from_integer(30, int_type));
+
+  // Demonstrate usage
+  std::cout << "Expression ID: " << case_expr.id() << std::endl;
+  std::cout << "Number of cases: " << case_expr.number_of_cases() << std::endl;
+  std::cout << "Total operands: " << case_expr.operands().size() << std::endl;
+
+  // Show each case
+  for(std::size_t i = 0; i < case_expr.number_of_cases(); ++i)
+  {
+    auto case_val = to_constant_expr(case_expr.case_value(i));
+    auto result_val = to_constant_expr(case_expr.result_value(i));
+    std::cout << "Case " << i << ": when x==" << case_val.get_value()
+              << " return " << result_val.get_value() << std::endl;
+  }
+
+  // Demonstrate conversion
+  exprt &base_expr = case_expr;
+  if(can_cast_expr<case_exprt>(base_expr))
+  {
+    case_exprt &converted = to_case_expr(base_expr);
+    std::cout << "Successfully converted back to case_exprt" << std::endl;
+    std::cout << "Converted has " << converted.number_of_cases() << " cases"
+              << std::endl;
+  }
+
+  return 0;
+}

unit/util/case_expr.cpp

@@ -0,0 +1,97 @@
+/*******************************************************************\
+
+Module: Unit tests for case_exprt
+
+Author: Unit test
+
+\*******************************************************************/
+
+#include <util/arith_tools.h>
+#include <util/bitvector_types.h>
+#include <util/std_expr.h>
+
+#include <testing-utils/use_catch.h>
+
+TEST_CASE("case_exprt construction and access", "[core][util][case_expr]")
+{
+  const signedbv_typet int_type(32);
+  const symbol_exprt select_value("x", int_type);
+
+  SECTION("Basic construction")
+  {
+    case_exprt case_expr(select_value, int_type);
+
+    REQUIRE(case_expr.id() == ID_case);
+    REQUIRE(case_expr.select_value() == select_value);
+    REQUIRE(case_expr.number_of_cases() == 0);
+  }
+
+  SECTION("Adding cases")
+  {
+    case_exprt case_expr(select_value, int_type);
+
+    const constant_exprt case1_value = from_integer(1, int_type);
+    const constant_exprt result1_value = from_integer(10, int_type);
+
+    const constant_exprt case2_value = from_integer(2, int_type);
+    const constant_exprt result2_value = from_integer(20, int_type);
+
+    case_expr.add_case(case1_value, result1_value);
+    REQUIRE(case_expr.number_of_cases() == 1);
+    REQUIRE(case_expr.case_value(0) == case1_value);
+    REQUIRE(case_expr.result_value(0) == result1_value);
+
+    case_expr.add_case(case2_value, result2_value);
+    REQUIRE(case_expr.number_of_cases() == 2);
+    REQUIRE(case_expr.case_value(1) == case2_value);
+    REQUIRE(case_expr.result_value(1) == result2_value);
+
+    // Verify operands structure: 1 select + 2*2 case/result pairs = 5
+    REQUIRE(case_expr.operands().size() == 5);
+    // Verify odd number of operands
+    REQUIRE(case_expr.operands().size() % 2 == 1);
+  }
+
+  SECTION("to_case_expr conversion")
+  {
+    case_exprt case_expr(select_value, int_type);
+    const constant_exprt case_value = from_integer(1, int_type);
+    const constant_exprt result_value = from_integer(10, int_type);
+    case_expr.add_case(case_value, result_value);
+
+    exprt &base = case_expr;
+    case_exprt &converted = to_case_expr(base);
+
+    REQUIRE(&converted == &case_expr);
+    REQUIRE(converted.number_of_cases() == 1);
+    REQUIRE(converted.case_value(0) == case_value);
+  }
+
+  SECTION("can_cast_expr")
+  {
+    case_exprt case_expr(select_value, int_type);
+    exprt &base = case_expr;
+
+    REQUIRE(can_cast_expr<case_exprt>(base));
+    REQUIRE_FALSE(can_cast_expr<if_exprt>(base));
+  }
+
+  SECTION("Construction with operands")
+  {
+    const constant_exprt case_value = from_integer(1, int_type);
+    const constant_exprt result_value = from_integer(10, int_type);
+
+    case_exprt::operandst ops;
+    ops.push_back(select_value);
+    ops.push_back(case_value);
+    ops.push_back(result_value);
+
+    case_exprt case_expr(std::move(ops), int_type);
+
+    REQUIRE(case_expr.id() == ID_case);
+    REQUIRE(case_expr.number_of_cases() == 1);
+    REQUIRE(case_expr.select_value() == select_value);
+    REQUIRE(case_expr.case_value(0) == case_value);
+    REQUIRE(case_expr.result_value(0) == result_value);
+  }
+}