Improvements in the code for String.toCharArray in String preprocessing

regression/strings-smoke-tests/java_char_array/test.desc

@@ -1,7 +1,13 @@
 CORE
 test_char_array.class
 --refine-strings
-^EXIT=0$
+^EXIT=10$
 ^SIGNAL=0$
-^VERIFICATION SUCCESSFUL$
+.*assertion.* test_char_array.java line 9 .* SUCCESS$
+.*assertion.* test_char_array.java line 10 .* SUCCESS$
+.*assertion.* test_char_array.java line 11 .* SUCCESS$
+.*assertion.* test_char_array.java line 13 .* FAILURE$
+.*assertion.* test_char_array.java line 15 .* FAILURE$
+.*assertion.* test_char_array.java line 17 .* FAILURE$
+^VERIFICATION FAILED$
 --

regression/strings-smoke-tests/java_char_array/test_char_array.java

@@ -1,6 +1,6 @@
 public class test_char_array
 {
-   public static void main(/*String[] argv*/)
+   public static void main(int i)
    {
       String s = "abc";
       char [] str = s.toCharArray();
@@ -9,5 +9,11 @@ public static void main(/*String[] argv*/)
       assert(str.length == 3);
       assert(a == 'a');
       assert(c == 'c');
+      if(i==0)
+          assert(str.length != 3);
+      if(i==2)
+          assert(a != 'a');
+      if(i==3)
+          assert(c != 'c');
    }
 }

src/java_bytecode/java_string_library_preprocess.cpp

@@ -1138,12 +1138,20 @@ codet java_string_library_preprocesst::make_assign_function_from_call(
 }
 
 /// Used to provide our own implementation of the
-/// java.lang.String.toCharArray:()[C function.
+/// `java.lang.String.toCharArray:()[C` function.
 /// \param type: type of the function called
 /// \param loc: location in the source
 /// \param symbol_table: the symbol table
-/// \return Code corresponding to > return_tmp0 = malloc(array[char]); >
-///   return_tmp0->data=&((s->data)[0]) > return_tmp0->length=s->length
+/// \return Code corresponding to
+/// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/// lhs = new java::array[char]
+/// string_expr = {length=this->length, content=*(this->data)}
+/// data = new char[]
+/// *data = string_expr.content
+/// lhs->data = &data[0]
+/// lhs->length = string_expr.length
+/// return lhs
+/// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 codet java_string_library_preprocesst::make_string_to_char_array_code(
     const code_typet &type,
     const source_locationt &loc,
@@ -1154,29 +1162,37 @@ codet java_string_library_preprocesst::make_string_to_char_array_code(
   const code_typet::parametert &p=type.parameters()[0];
   symbol_exprt string_argument(p.get_identifier(), p.type());
   assert(implements_java_char_sequence(string_argument.type()));
-  dereference_exprt deref(string_argument, string_argument.type().subtype());
 
-  // lhs <- malloc(array[char])
-  exprt lhs=fresh_array(type.return_type(), loc, symbol_table);
-  allocate_dynamic_object_with_decl(
-    lhs, lhs.type().subtype(), symbol_table, loc, code);
+  // lhs = new java::array[char]
+  exprt lhs=allocate_fresh_array(
+    type.return_type(), loc, symbol_table, code);
 
-  // first_element_address is `&((string_argument->data)[0])`
-  exprt data=get_data(deref, symbol_table);
+  // string_expr = {this->length, this->data}
+  string_exprt string_expr=fresh_string_expr(loc, symbol_table, code);
+  code.add(code_assign_java_string_to_string_expr(
+    string_expr, string_argument, symbol_table));
+  exprt string_expr_sym=fresh_string_expr_symbol(
+    loc, symbol_table, code);
+  code.add(code_assignt(string_expr_sym, string_expr));
+
+  // data = new char[]
+  exprt data=allocate_fresh_array(
+    pointer_typet(string_expr.content().type()), loc, symbol_table, code);
+
+  // *data = string_expr.content
   dereference_exprt deref_data(data, data.type().subtype());
-  exprt first_index=from_integer(0, string_length_type());
-  index_exprt first_element(deref_data, first_index, java_char_type());
-  address_of_exprt first_element_address(first_element);
+  code.add(code_assignt(deref_data, string_expr.content()));
 
-  // lhs->data <- &((string_argument->data)[0])
+  // lhs->data = &data[0]
   dereference_exprt deref_lhs(lhs, lhs.type().subtype());
   exprt lhs_data=get_data(deref_lhs, symbol_table);
-  code.add(code_assignt(lhs_data, first_element_address));
+  index_exprt first_elt(
+    deref_data, from_integer(0, java_int_type()), java_char_type());
+  code.add(code_assignt(lhs_data, address_of_exprt(first_elt)));
 
-  // lhs->length <- s->length
-  exprt rhs_length=get_length(deref, symbol_table);
+  // lhs->length = string_expr.length
   exprt lhs_length=get_length(deref_lhs, symbol_table);
-  code.add(code_assignt(lhs_length, rhs_length));
+  code.add(code_assignt(lhs_length, string_expr.length()));
 
   // return lhs
   code.add(code_returnt(lhs));