fix FlattenInListTransform for the trivial case

Cython/Compiler/Main.py

@@ -114,7 +114,7 @@ class Context:
             _specific_post_parse,
             InterpretCompilerDirectives(self, self.pragma_overrides),
             _align_function_definitions,
-#            FlattenInListTransform(),
+            FlattenInListTransform(),
             WithTransform(self),
             DecoratorTransform(self),
             AnalyseDeclarationsTransform(self),

Cython/Compiler/Optimize.py

@@ -311,8 +311,13 @@ class FlattenInListTransform(Visitor.VisitorTransform):
             args = node.operand2.args
             if len(args) == 0:
                 return ExprNodes.BoolNode(pos = node.pos, value = node.operator == 'not_in')
+
+            if node.operand1.is_temp or node.operand1.is_simple():
+                lhs = node.operand1
             else:
-                lhs = ExprNodes.PersistentNode(node.operand1, len(args))
+                # FIXME: allocate temp for evaluated node.operand1
+                return node
+
             conds = []
             for arg in args:
                 cond = ExprNodes.PrimaryCmpNode(
@@ -331,6 +336,7 @@ class FlattenInListTransform(Visitor.VisitorTransform):
                                     operator = conjunction,
                                     operand1 = left,
                                     operand2 = right)
+
             return reduce(concat, conds)
         else:
             return node