Add implementation of arithmetic operator bvadd.

Also add tests for the data structure itself and the conversion of
`plus_exprt` to `smt_bit_vector_theoryt::addition`.

Author: NlightNFotis

src/solvers/smt2_incremental/convert_expr_to_smt.cpp

@@ -326,8 +326,19 @@ static optionalt<smt_termt> try_relational_conversion(const exprt &expr)
 
 static smt_termt convert_expr_to_smt(const plus_exprt &plus)
 {
-  UNIMPLEMENTED_FEATURE(
-    "Generation of SMT formula for plus expression: " + plus.pretty());
+  if(std::all_of(
+       plus.operands().cbegin(), plus.operands().cend(), [](exprt operand) {
+         return can_cast_type<integer_bitvector_typet>(operand.type());
+       }))
+  {
+    return convert_multiary_operator_to_terms(
+      plus, smt_bit_vector_theoryt::add);
+  }
+  else
+  {
+    UNIMPLEMENTED_FEATURE(
+      "Generation of SMT formula for plus expression: " + plus.pretty());
+  }
 }
 
 static smt_termt convert_expr_to_smt(const minus_exprt &minus)

src/solvers/smt2_incremental/smt_bit_vector_theory.cpp

@@ -205,3 +205,25 @@ void smt_bit_vector_theoryt::signed_greater_than_or_equalt::validate(
 const smt_function_application_termt::factoryt<
   smt_bit_vector_theoryt::signed_greater_than_or_equalt>
   smt_bit_vector_theoryt::signed_greater_than_or_equal{};
+
+const char *smt_bit_vector_theoryt::addt::identifier()
+{
+  return "bvadd";
+}
+
+smt_sortt smt_bit_vector_theoryt::addt::return_sort(
+  const smt_termt &lhs,
+  const smt_termt &rhs)
+{
+  return lhs.get_sort();
+}
+
+void smt_bit_vector_theoryt::addt::validate(
+  const smt_termt &lhs,
+  const smt_termt &rhs)
+{
+  validate_bit_vector_predicate_arguments(lhs, rhs);
+}
+
+const smt_function_application_termt::factoryt<smt_bit_vector_theoryt::addt>
+  smt_bit_vector_theoryt::add{};

src/solvers/smt2_incremental/smt_bit_vector_theory.h

@@ -84,6 +84,14 @@ class smt_bit_vector_theoryt
   static const smt_function_application_termt::factoryt<
     signed_greater_than_or_equalt>
     signed_greater_than_or_equal;
+
+  struct addt final
+  {
+    static const char *identifier();
+    static smt_sortt return_sort(const smt_termt &lhs, const smt_termt &rhs);
+    static void validate(const smt_termt &lhs, const smt_termt &rhs);
+  };
+  static const smt_function_application_termt::factoryt<addt> add;
 };
 
 #endif // CPROVER_SOLVERS_SMT2_INCREMENTAL_SMT_BIT_VECTOR_THEORY_H

unit/solvers/smt2_incremental/convert_expr_to_smt.cpp

@@ -239,3 +239,75 @@ TEST_CASE(
       smt_bit_vector_theoryt::unsigned_less_than_or_equal(one_term, two_term));
   }
 }
+
+TEST_CASE(
+  "expr to smt conversion for arithmetic operators",
+  "[core][smt2_incremental]")
+{
+  const smt_termt smt_term_one = smt_bit_vector_constant_termt{1, 8};
+  const smt_termt smt_term_two = smt_bit_vector_constant_termt{2, 8};
+
+  // Just regular (bit-vector) integers, to be used for the comparison
+  const auto one_bvint = from_integer({1}, signedbv_typet{8});
+  const auto two_bvint = from_integer({2}, signedbv_typet{8});
+  const auto one_bvint_unsigned = from_integer({1}, unsignedbv_typet{8});
+  const auto two_bvint_unsigned = from_integer({2}, unsignedbv_typet{8});
+
+  SECTION("Addition of two constant size bit-vectors")
+  {
+    const auto constructed_term =
+      convert_expr_to_smt(plus_exprt{one_bvint, two_bvint});
+    const auto expected_term =
+      smt_bit_vector_theoryt::add(smt_term_one, smt_term_two);
+    CHECK(constructed_term == expected_term);
+  }
+
+  SECTION(
+    "Addition of four constant size bit-vectors - testing multi-ary handling "
+    "of plus_exprt")
+  {
+    const auto three_bv_int = from_integer({3}, signedbv_typet{8});
+    const auto four_bv_int = from_integer({4}, signedbv_typet{8});
+
+    const auto three_smt_term = smt_bit_vector_constant_termt{3, 8};
+    const auto four_smt_term = smt_bit_vector_constant_termt{4, 8};
+
+    const exprt::operandst plus_operands{
+      one_bvint, two_bvint, three_bv_int, four_bv_int};
+    const auto constructed_term =
+      convert_expr_to_smt(plus_exprt{plus_operands, signedbv_typet{8}});
+    const auto expected_term = smt_bit_vector_theoryt::add(
+      smt_bit_vector_theoryt::add(
+        smt_bit_vector_theoryt::add(smt_term_one, smt_term_two),
+        three_smt_term),
+      four_smt_term);
+
+    CHECK(constructed_term == expected_term);
+  }
+
+  SECTION(
+    "Ensure that addition node conversion fails if the operands are not "
+    "bit-vector based")
+  {
+    const cbmc_invariants_should_throwt invariants_throw;
+    REQUIRE_THROWS(
+      convert_expr_to_smt(plus_exprt{true_exprt{}, false_exprt{}}));
+  }
+
+  SECTION(
+    "Ensure that addition node conversion fails if it has a malformed "
+    "expression")
+  {
+    const cbmc_invariants_should_throwt invariants_throw;
+    // No operands to expression
+    exprt::operandst zero_operands;
+    REQUIRE_THROWS(
+      convert_expr_to_smt(plus_exprt{zero_operands, signedbv_typet{8}}));
+
+    // One operand to expression
+    const auto four_bv_int = from_integer({4}, signedbv_typet{8});
+    exprt::operandst one_operand{four_bv_int};
+    REQUIRE_THROWS(
+      convert_expr_to_smt(plus_exprt{one_operand, signedbv_typet{8}}));
+  }
+}

unit/solvers/smt2_incremental/smt_bit_vector_theory.cpp

@@ -166,3 +166,31 @@ TEST_CASE("SMT bit vector predicates", "[core][smt2_incremental]")
       smt_bit_vector_theoryt::signed_greater_than_or_equal(two, wider));
   }
 }
+
+TEST_CASE(
+  "SMT bit vector arithmetic operator implementation tests",
+  "[core][smt2_incremental]")
+{
+  const smt_bit_vector_constant_termt two{2, 8};
+  const smt_bit_vector_constant_termt three{3, 8};
+  const smt_bit_vector_constant_termt four{4, 16};
+  const smt_bool_literal_termt true_val{true};
+
+  SECTION("Addition")
+  {
+    const auto function_application = smt_bit_vector_theoryt::add(two, three);
+    REQUIRE(
+      function_application.function_identifier() ==
+      smt_identifier_termt("bvadd", smt_bit_vector_sortt{8}));
+    REQUIRE(function_application.get_sort() == smt_bit_vector_sortt{8});
+    REQUIRE(function_application.arguments().size() == 2);
+    REQUIRE(function_application.arguments()[0].get() == two);
+    REQUIRE(function_application.arguments()[1].get() == three);
+
+    cbmc_invariants_should_throwt invariants_throw;
+    // Bit-vectors of mismatched sorts are going to hit an invariant violation.
+    REQUIRE_THROWS(smt_bit_vector_theoryt::add(three, four));
+    // An addition of a bool and a bitvector should hit an invariant violation.
+    REQUIRE_THROWS(smt_bit_vector_theoryt::add(three, true_val));
+  }
+}