From 23b3fda716b92b2545e0bd5e0362ae365022beb3 Mon Sep 17 00:00:00 2001
From: Stefan Behnel <stefan_ml@behnel.de>
Date: Mon, 11 Mar 2013 11:17:47 +0100
Subject: [PATCH] transform empty comprehensions into empty literals

---
 Cython/Compiler/Optimize.py       | 7 +++++++
 tests/run/constant_folding.py     | 8 +++++---
 tests/run/constant_folding_cy.pyx | 3 ++-
 3 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/Cython/Compiler/Optimize.py b/Cython/Compiler/Optimize.py
index a68dc67..6563dfa 100644
--- a/Cython/Compiler/Optimize.py
+++ b/Cython/Compiler/Optimize.py
@@ -3233,6 +3233,13 @@ class ConstantFolding(Visitor.VisitorTransform, SkipDeclarations):
                     return base
         return node
 
+    def visit_ComprehensionNode(self, node):
+        self.visitchildren(node)
+        if isinstance(node.loop, Nodes.StatListNode) and not node.loop.stats:
+            # loop was pruned already => transform into literal
+            return node.target
+        return node
+
     def visit_ForInStatNode(self, node):
         self.visitchildren(node)
         sequence = node.iterator.sequence
diff --git a/tests/run/constant_folding.py b/tests/run/constant_folding.py
index d88978a..2b1ad59 100644
--- a/tests/run/constant_folding.py
+++ b/tests/run/constant_folding.py
@@ -213,10 +213,11 @@ def for_in_empty_else():
 
 
 @cython.test_fail_if_path_exists(
+    "//ComprehensionNode",
     "//ForInStatNode",
 )
 @cython.test_assert_path_exists(
-    "//ComprehensionNode",
+    "//ListNode",
 )
 def for_in_empty_listcomp():
     """
@@ -227,10 +228,11 @@ def for_in_empty_listcomp():
 
 
 @cython.test_fail_if_path_exists(
+    "//ComprehensionNode",
     "//ForInStatNode",
 )
 @cython.test_assert_path_exists(
-    "//ComprehensionNode",
+    "//ListNode",
 )
 def for_in_empty_nested_listcomp():
     """
@@ -242,7 +244,7 @@ def for_in_empty_nested_listcomp():
 
 @cython.test_fail_if_path_exists(
     "//ForInStatNode//ForInStatNode",
-    )
+)
 @cython.test_assert_path_exists(
     "//ForInStatNode",
     "//ComprehensionNode",
diff --git a/tests/run/constant_folding_cy.pyx b/tests/run/constant_folding_cy.pyx
index da9a935..b2ca8ec 100644
--- a/tests/run/constant_folding_cy.pyx
+++ b/tests/run/constant_folding_cy.pyx
@@ -83,10 +83,11 @@ def unicode_slicing_safe_surrogates2():
 
 
 @cython.test_fail_if_path_exists(
+    "//ComprehensionNode",
     "//ForInStatNode",
 )
 @cython.test_assert_path_exists(
-    "//ComprehensionNode",
+    "//SetNode",
 )
 def for_in_empty_setcomp():
     """
-- 
2.7.4