fix warning about unused temp variable when both FlattenInListTransform and...

fix warning about unused temp variable when both FlattenInListTransform and SwitchTransform are applied

Cython/Compiler/Optimize.py

-
 import cython
 cython.declare(UtilityCode=object, EncodedString=object, BytesLiteral=object,
                Nodes=object, ExprNodes=object, PyrexTypes=object, Builtin=object,
@@ -977,7 +976,19 @@ class SwitchTransform(Visitor.VisitorTransform):
                                            test = common_var,
                                            cases = cases,
                                            else_clause = false_body)
-        return UtilNodes.TempResultFromStatNode(result_ref, switch_node)
+        replacement = UtilNodes.TempResultFromStatNode(result_ref, switch_node)
+        return replacement
+
+    def visit_EvalWithTempExprNode(self, node):
+        # drop unused expression temp from FlattenInListTransform
+        orig_expr = node.subexpression
+        temp_ref = node.lazy_temp
+        self.visitchildren(node)
+        if node.subexpression is not orig_expr:
+            # node was restructured => check if temp is still used
+            if not Visitor.tree_contains(node.subexpression, temp_ref):
+                return node.subexpression
+        return node
 
     visit_Node = Visitor.VisitorTransform.recurse_to_children
 

Cython/Compiler/Visitor.pxd

@@ -35,3 +35,7 @@ cdef class MethodDispatcherTransform(EnvTransform):
 cdef class RecursiveNodeReplacer(VisitorTransform):
      cdef public orig_node
      cdef public new_node
+
+cdef class NodeFinder(TreeVisitor):
+    cdef node
+    cdef public bint found

Cython/Compiler/Visitor.py

@@ -488,6 +488,27 @@ def recursively_replace_node(tree, old_node, new_node):
     replace_in(tree)
 
 
+class NodeFinder(TreeVisitor):
+    """
+    Find out if a node appears in a subtree.
+    """
+    def __init__(self, node):
+        super(NodeFinder, self).__init__()
+        self.node = node
+        self.found = False
+
+    def visit_Node(self, node):
+        if node is self.node:
+            self.found = True
+        else:
+            self.visitchildren(node)
+
+def tree_contains(tree, node):
+    finder = NodeFinder(node)
+    finder.visit(tree)
+    return finder.found
+
+
 # Utils
 def replace_node(ptr, value):
     """Replaces a node. ptr is of the form used on the access path stack