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diff --git a/testsuite/tests/indexed-types/should_compile/ATLoop.hs b/testsuite/tests/indexed-types/should_compile/ATLoop.hs
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+++ b/testsuite/tests/indexed-types/should_compile/ATLoop.hs
@@ -0,0 +1,22 @@
+{-# OPTIONS_GHC -O2 #-}
+
+-- Reading the interface file caused a black hole
+-- in earlier versions of GHC
+
+-- Also, foo should compile to very tight code with -O2
+-- (The O2 was nothing to do with the black hole though.)
+
+module ShouldCompile where
+
+import ATLoop_help
+
+foo :: FooT Int -> Int -> Int
+foo t n = t `seq` bar n
+   where
+     bar 0 = 0
+     bar n | even n = bar (n `div` 2)
+     bar n          = bar (n - int t)
+
+
+
+