Attempt compile time encoding/decoding when using str.encode() on lit…

…erals.

Cython/Compiler/Optimize.py

@@ -3868,29 +3868,29 @@ def _handle_simple_method_unicode_encode(self, node, function, args, is_unbound_
 
         string_node = args[0]
 
-        if len(args) == 1:
-            null_node = ExprNodes.NullNode(node.pos)
-            return self._substitute_method_call(
-                node, function, "PyUnicode_AsEncodedString",
-                self.PyUnicode_AsEncodedString_func_type,
-                'encode', is_unbound_method, [string_node, null_node, null_node])
-
         parameters = self._unpack_encoding_and_error_mode(node.pos, args)
         if parameters is None:
             return node
         encoding, encoding_node, error_handling, error_handling_node = parameters
 
-        if encoding and isinstance(string_node, ExprNodes.UnicodeNode):
+        if string_node.has_constant_result():
             # constant, so try to do the encoding at compile time
             try:
-                value = string_node.value.encode(encoding, error_handling)
+                value = string_node.constant_result.encode(encoding, error_handling)
             except:
                 # well, looks like we can't
                 pass
             else:
-                value = bytes_literal(value, encoding)
+                value = bytes_literal(value, encoding or 'UTF-8')
                 return ExprNodes.BytesNode(string_node.pos, value=value, type=Builtin.bytes_type)
 
+        if len(args) == 1:
+            null_node = ExprNodes.NullNode(node.pos)
+            return self._substitute_method_call(
+                node, function, "PyUnicode_AsEncodedString",
+                self.PyUnicode_AsEncodedString_func_type,
+                'encode', is_unbound_method, [string_node, null_node, null_node])
+
         if encoding and error_handling == 'strict':
             # try to find a specific encoder function
             codec_name = self._find_special_codec_name(encoding)
@@ -3944,6 +3944,20 @@ def _handle_simple_method_bytes_decode(self, node, function, args, is_unbound_me
             self._error_wrong_arg_count('bytes.decode', node, args, '1-3')
             return node
 
+        # Try to extract encoding parameters and attempt constant decode.
+        parameters = self._unpack_encoding_and_error_mode(node.pos, args)
+        if parameters is None:
+            return node
+        encoding, encoding_node, error_handling, error_handling_node = parameters
+
+        if args[0].has_constant_result():
+            try:
+                constant_result = args[0].constant_result.decode(encoding, error_handling)
+            except (AttributeError, ValueError, UnicodeDecodeError):
+                pass
+            else:
+                return UnicodeNode(args[0].pos, value=encoded_string(constant_result, encoding))
+
         # normalise input nodes
         string_node = args[0]
         start = stop = None
@@ -3971,11 +3985,6 @@ def _handle_simple_method_bytes_decode(self, node, function, args, is_unbound_me
             # nothing to optimise here
             return node
 
-        parameters = self._unpack_encoding_and_error_mode(node.pos, args)
-        if parameters is None:
-            return node
-        encoding, encoding_node, error_handling, error_handling_node = parameters
-
         if not start:
             start = ExprNodes.IntNode(node.pos, value='0', constant_result=0)
         elif not start.type.is_int: