Reduce the memory allocations while getting a string's length property (#2736)

This patch reduces the number of string to string object conversion during property managing operations,
via access the length property directly from the string instead of the newly created string object.

JerryScript-DCO-1.0-Signed-off-by: Robert Fancsik frobert@inf.u-szeged.hu

jerry-core/ecma/operations/ecma-get-put-value.c

@@ -99,6 +99,15 @@ ecma_op_get_value_object_base (ecma_value_t base_value, /**< base value */
                 || ECMA_ASSERT_VALUE_IS_SYMBOL (base_value)
                 || ecma_is_value_string (base_value));
 
+  /* Fast path for the strings length property. The length of the string
+     can be obtained directly from the ecma-string. */
+  if (ecma_is_value_string (base_value) && ecma_string_is_length (property_name_p))
+  {
+    ecma_string_t *string_p = ecma_get_string_from_value (base_value);
+
+    return ecma_make_uint32_value (ecma_string_get_length (string_p));
+  }
+
   ecma_value_t object_base = ecma_op_to_object (base_value);
   JERRY_ASSERT (!ECMA_IS_VALUE_ERROR (object_base));