Simplify overflow-result: preserve sizeof annotation

We already did this for various other expressions, but failed to do so
for overflow-result simplification. Consequently, calls to our modelled
calloc (which uses overflow-result multiplication) failed to pick up the
sizeof information, which in turn yields byte arrays even when more type
information would have been available.

Author: tautschnig

regression/cbmc-library/calloc-01/main.c

@@ -3,7 +3,7 @@
 
 int main()
 {
-  int *x = calloc(sizeof(int), 1);
+  int *x = calloc(sizeof(int), 2);
   assert(*x == 0);
   return 0;
 }

regression/cbmc-library/calloc-01/program-only.desc

@@ -0,0 +1,12 @@
+CORE
+main.c
+--program-only
+dynamic_object#1 == \{ 0, 0 \}
+^EXIT=0$
+^SIGNAL=0$
+--
+^warning: ignoring
+dynamic_object#1 == \{ 0, (0, )+0 \}
+--
+calloc with a sizeof argument (over a type larger than a byte) should not result
+in a byte array being generated by symex.

src/util/simplify_expr.cpp

@@ -2645,6 +2645,19 @@ simplify_exprt::simplify_overflow_result(const overflow_result_exprt &expr)
     if(!expr.op0().is_constant() || !expr.op1().is_constant())
       return unchanged(expr);
 
+    // preserve the sizeof type annotation
+    optionalt<typet> c_sizeof_type;
+    for(const auto &op : expr.operands())
+    {
+      const typet &sizeof_type =
+        static_cast<const typet &>(op.find(ID_C_c_sizeof_type));
+      if(sizeof_type.is_not_nil())
+      {
+        c_sizeof_type = sizeof_type;
+        break;
+      }
+    }
+
     const auto op0_value = numeric_cast<mp_integer>(expr.op0());
     const auto op1_value = numeric_cast<mp_integer>(expr.op1());
     if(!op0_value.has_value() || !op1_value.has_value())
@@ -2662,21 +2675,24 @@ simplify_exprt::simplify_overflow_result(const overflow_result_exprt &expr)
     else
       UNREACHABLE;
 
+    exprt no_overflow_result_expr =
+      from_integer(no_overflow_result, expr.op0().type());
+    if(c_sizeof_type.has_value())
+      no_overflow_result_expr.set(ID_C_c_sizeof_type, *c_sizeof_type);
+
     const std::size_t width = to_bitvector_type(expr.op0().type()).get_width();
     const integer_bitvector_typet bv_type{op_type_id, width};
     if(
       no_overflow_result < bv_type.smallest() ||
       no_overflow_result > bv_type.largest())
     {
       return struct_exprt{
-        {from_integer(no_overflow_result, expr.op0().type()), true_exprt{}},
-        expr.type()};
+        {std::move(no_overflow_result_expr), true_exprt{}}, expr.type()};
     }
     else
     {
       return struct_exprt{
-        {from_integer(no_overflow_result, expr.op0().type()), false_exprt{}},
-        expr.type()};
+        {std::move(no_overflow_result_expr), false_exprt{}}, expr.type()};
     }
   }
 }