1 files changed, 30 insertions, 0 deletions
diff --git a/testsuite/tests/perf/should_run/T19347.hs b/testsuite/tests/perf/should_run/T19347.hs
new file mode 100644
index 0000000000..c885eac724
--- /dev/null
+++ b/testsuite/tests/perf/should_run/T19347.hs
@@ -0,0 +1,30 @@
+{-# LANGUAGE UnboxedTuples #-}
+
+module Main where
+
+data T = MkT !Int Int
+
+-- An expensive recursive function
+g :: Int -> Int -> (# Int, Int #)
+g x 0 = (# x, 33 #)
+g x n = g (x+n) (n-1)
+
+-- 'foo' calls 'h' often
+foo h 0 = 0
+foo h n = h n `seq` foo h (n-1)
+
+main = print (foo (MkT (case g 1 200 of (# a,b #) -> a))
+                  200)
+
+{- In main, we don't want to eta-expand the MkT to
+  (\x. MkT (case g 1 200 of (# a,b #) -> a) x)
+because then that call to g may be made more often
+The faffing with unboxed tuples is to defeat full
+laziness which would otherwise lift the call to g
+out to top level
+
+Before fixing #19347, running this program gave
+       2,012,096 bytes allocated in the heap
+after it gave
+         101,712 bytes allocated in the heap
+-}