diff -r fd5166fdb978 Lib/test/test_list.py
--- a/Lib/test/test_list.py	Mon Jul 30 19:59:53 2012 +0300
+++ b/Lib/test/test_list.py	Tue Jul 31 23:55:09 2012 +0200
@@ -70,6 +70,14 @@
         check(1000000)
 
 
+    def test_no_comdat_folding(self):
+        # Issue 8847: In the PGO build, the MSVC linker's COMDAT folding
+        # optimization causes failures in code that relies on distinct
+        # function addresses.
+        class L(list): pass
+        with self.assertRaises(TypeError):
+            (3,) + L([1,2])
+
 def test_main(verbose=None):
     support.run_unittest(ListTest)
 
diff -r fd5166fdb978 Lib/test/test_tuple.py
--- a/Lib/test/test_tuple.py	Mon Jul 30 19:59:53 2012 +0300
+++ b/Lib/test/test_tuple.py	Tue Jul 31 23:55:09 2012 +0200
@@ -164,6 +164,14 @@
         check(10)       # check our checking code
         check(1000000)
 
+    def test_no_comdat_folding(self):
+        # Issue 8847: In the PGO build, the MSVC linker's COMDAT folding
+        # optimization causes failures in code that relies on distinct
+        # function addresses.
+        class T(tuple): pass
+        with self.assertRaises(TypeError):
+            [3,] + T((1,2))
+
 def test_main():
     support.run_unittest(TupleTest)
 
diff -r fd5166fdb978 PCbuild/pginstrument.vsprops
--- a/PCbuild/pginstrument.vsprops	Mon Jul 30 19:59:53 2012 +0300
+++ b/PCbuild/pginstrument.vsprops	Tue Jul 31 23:55:09 2012 +0200
@@ -22,7 +22,7 @@
 	<Tool
 		Name="VCLinkerTool"
 		OptimizeReferences="2"
-		EnableCOMDATFolding="2"
+		EnableCOMDATFolding="1"
 		LinkTimeCodeGeneration="2"
 		ProfileGuidedDatabase="$(SolutionDir)$(PlatformName)-pgi\$(TargetName).pgd"
 		ImportLibrary="$(OutDirPGI)\$(TargetName).lib"