Silence CF warnings when taking address of C variable, fix ticket #714

Cython/Compiler/FlowControl.py

@@ -1106,3 +1106,10 @@ class CreateControlFlowGraph(CythonTransform):
         self.flow.nextblock()
         self.env = self.env_stack.pop()
         return node
+
+    def visit_AmpersandNode(self, node):
+        if node.operand.is_name:
+            # Fake assignment to silence warning
+            self.mark_assignment(node.operand)
+        self.visitchildren(node)
+        return node

tests/run/ptr_warning_T714.pyx

+# mode: run
+# tag: werror
+# ticket: 714
+
+def test_ptr():
+    """
+    >>> test_ptr()
+    123
+    """
+    cdef int a
+    cdef int *ptr
+
+    ptr = &a
+    ptr[0] = 123
+    return a