Implement the core of the generator functions. (#3368)

Some things are missing:
 - yield* support
 - generator definition in object literal
 - the hidden GeneratorFunction

JerryScript-DCO-1.0-Signed-off-by: Zoltan Herczeg zherczeg.u-szeged@partner.samsung.com

jerry-core/ecma/base/ecma-helpers-value.c

@@ -855,10 +855,10 @@ ecma_fast_copy_value (ecma_value_t value)  /**< value description */
  *
  * @return copy of the given value
  */
-ecma_value_t
+inline ecma_value_t JERRY_ATTR_ALWAYS_INLINE
 ecma_copy_value_if_not_object (ecma_value_t value) /**< value description */
 {
-  if (ecma_get_value_type_field (value) != ECMA_TYPE_OBJECT)
+  if (!ecma_is_value_object (value))
   {
     return ecma_copy_value (value);
   }
@@ -866,6 +866,30 @@ ecma_copy_value_if_not_object (ecma_value_t value) /**< value description */
   return value;
 } /* ecma_copy_value_if_not_object */
 
+/**
+ * Increase reference counter of a value if it is an object.
+ */
+inline void JERRY_ATTR_ALWAYS_INLINE
+ecma_ref_if_object (ecma_value_t value) /**< value description */
+{
+  if (ecma_is_value_object (value))
+  {
+    ecma_ref_object (ecma_get_object_from_value (value));
+  }
+} /* ecma_ref_if_object */
+
+/**
+ * Decrease reference counter of a value if it is an object.
+ */
+inline void JERRY_ATTR_ALWAYS_INLINE
+ecma_deref_if_object (ecma_value_t value) /**< value description */
+{
+  if (ecma_is_value_object (value))
+  {
+    ecma_deref_object (ecma_get_object_from_value (value));
+  }
+} /* ecma_deref_if_object */
+
 /**
  * Assign a new value to an ecma-value
  *