simplify constant folded comparison code a little and extend the test for it

Cython/Compiler/Optimize.py

@@ -3307,19 +3307,13 @@ class ConstantFolding(Visitor.VisitorTransform, SkipDeclarations):
 
         # collect partial cascades: [[value, CmpNode...], [value, CmpNode, ...], ...]
         cascades = [[node.operand1]]
+        final_result = [True]
 
         def split_cascades(cmp_node):
             if cmp_node.has_constant_result():
                 if not cmp_node.constant_result:
                     # False => short-circuit
-                    cascades.append([
-                        self._bool_node(cmp_node, True),
-                        ExprNodes.CascadedCmpNode(
-                            cmp_node.pos,
-                            operator='==',
-                            operand2=self._bool_node(cmp_node, False),
-                            constant_result=False)
-                    ])
+                    final_result[0] = False
                     return
                 else:
                     # True => discard and start new cascade
@@ -3351,7 +3345,10 @@ class ConstantFolding(Visitor.VisitorTransform, SkipDeclarations):
                 last_cmp_node = cmp_node
             last_cmp_node.cascade = None
 
-        if not cmp_nodes:
+        if not final_result[0]:
+            # last cascade was constant False
+            cmp_nodes.append(self._bool_node(cmp_node, False))
+        elif not cmp_nodes:
             # only constants, but no False result
             return self._bool_node(node, True)
         node = cmp_nodes[0]

tests/run/constant_folding.py

@@ -361,3 +361,70 @@ def combined():
     True
     """
     return 5 in 100 * [1, 2] * 0  or  5 not in 100 * [] * 10
+
+
+@cython.test_assert_path_exists(
+    '//IntNode[@value = "2"]',
+    '//IntNode[@value = "4"]',
+    '//IntNode[@value = "5"]',
+    '//IntNode[@value = "7"]',
+    '//BoolBinopNode//PrimaryCmpNode',
+    '//BoolBinopNode[.//PrimaryCmpNode//IntNode[@value = "4"] and .//PrimaryCmpNode//IntNode[@value = "5"]]',
+    '//PrimaryCmpNode[.//IntNode[@value = "2"] and .//IntNode[@value = "4"]]',
+    '//PrimaryCmpNode[.//IntNode[@value = "5"] and .//IntNode[@value = "7"]]',
+)
+@cython.test_fail_if_path_exists(
+    '//IntNode[@value = "1"]',
+    '//IntNode[@value = "8"]',
+    '//PrimaryCmpNode[.//IntNode[@value = "4"] and .//IntNode[@value = "5"]]',
+    '//PrimaryCmpNode[.//IntNode[@value = "2"] and .//IntNode[@value = "7"]]',
+    '//BoolNode',
+)
+def cascaded_cmp_with_partial_constants(a, b):
+    """
+    >>> cascaded_cmp_with_partial_constants(3, 6)
+    True
+    >>> cascaded_cmp_with_partial_constants(1, 6)
+    False
+    >>> cascaded_cmp_with_partial_constants(4, 6)
+    False
+    >>> cascaded_cmp_with_partial_constants(3, 7)
+    False
+    >>> cascaded_cmp_with_partial_constants(3, 6)
+    True
+    """
+    return 1 < 2 < a < 4 < 5 < b < 7 < 8
+
+
+@cython.test_assert_path_exists(
+    '//IntNode[@value = "2"]',
+    '//IntNode[@value = "4"]',
+    '//IntNode[@value = "5"]',
+    '//IntNode[@value = "7"]',
+    '//BoolBinopNode',
+    '//SingleAssignmentNode//BoolBinopNode',
+    '//SingleAssignmentNode//BoolBinopNode//NameNode[@name = "a"]',
+    '//SingleAssignmentNode//BoolBinopNode//NameNode[@name = "b"]',
+    '//BoolBinopNode[.//PrimaryCmpNode//IntNode[@value = "4"] and .//PrimaryCmpNode//IntNode[@value = "5"]]',
+    '//BoolNode[@value = False]',
+)
+@cython.test_fail_if_path_exists(
+    '//SingleAssignmentNode//NameNode[@name = "c"]',
+    '//IntNode[@value = "1"]',
+    '//PrimaryCmpNode[.//IntNode[@value = "4"] and .//IntNode[@value = "5"]]',
+    '//PrimaryCmpNode[.//IntNode[@value = "2"] and .//IntNode[@value = "7"]]',
+    '//BoolNode[@value = True]',
+)
+def cascaded_cmp_with_partial_constants_and_false_end(a, b, c):
+    """
+    >>> cascaded_cmp_with_partial_constants_and_false_end(3, 6, 8)
+    False
+    >>> cascaded_cmp_with_partial_constants_and_false_end(1, 6, 8)
+    False
+    >>> cascaded_cmp_with_partial_constants_and_false_end(4, 6, 8)
+    False
+    >>> cascaded_cmp_with_partial_constants_and_false_end(3, 7, 8)
+    False
+    """
+    x = 1 < 2 < a < 4 < 5 < b < 7 < 7 < c
+    return x