Make sure that `all`, `any`, `and`, and `or` fuse (#9848)

Test Plan: validate

Reviewers: hvr, austin, bgamari, simonpj

Reviewed By: simonpj

Subscribers: simonpj, thomie

Differential Revision: https://phabricator.haskell.org/D1126

GHC Trac Issues: #9848

4 files changed, 25 insertions, 0 deletions

diff --git a/libraries/base/Data/Foldable.hs b/libraries/base/Data/Foldable.hs
index 1f20261943..24b6dd18c2 100644
--- a/libraries/base/Data/Foldable.hs
+++ b/libraries/base/Data/Foldable.hs
@@ -119,6 +119,8 @@ class Foldable t where
     -- | Map each element of the structure to a monoid,
     -- and combine the results.
     foldMap :: Monoid m => (a -> m) -> t a -> m
+    {-# INLINE foldMap #-}
+    -- This INLINE allows more list functions to fuse. See Trac #9848.
     foldMap f = foldr (mappend . f) mempty
 
     -- | Right-associative fold of a structure.
diff --git a/libraries/base/tests/T9848.hs b/libraries/base/tests/T9848.hs
new file mode 100644
index 0000000000..d473f93c31
--- /dev/null
+++ b/libraries/base/tests/T9848.hs
@@ -0,0 +1,14 @@
+import Data.IORef
+
+foo :: Int -> Bool
+foo n = all (<10000000) [1..n]
+
+bar :: Int -> Bool
+bar n = and $ map (<10000000) [1..n]
+
+main :: IO ()
+main = do
+  ref <- newIORef 1000000
+  val <- readIORef ref
+  print $ foo val
+  print $ bar val
diff --git a/libraries/base/tests/T9848.stdout b/libraries/base/tests/T9848.stdout
new file mode 100644
index 0000000000..dbde422651
--- /dev/null
+++ b/libraries/base/tests/T9848.stdout
@@ -0,0 +1,2 @@
+True
+True
diff --git a/libraries/base/tests/all.T b/libraries/base/tests/all.T
index 34176d0153..1b065a33e9 100644
--- a/libraries/base/tests/all.T
+++ b/libraries/base/tests/all.T
@@ -191,3 +191,10 @@ test('T9681', normal, compile_fail, [''])
 test('T8089', [exit_code(99), run_timeout_multiplier(0.01)],
               compile_and_run, [''])
 test('T9826',normal, compile_and_run,[''])
+test('T9848',
+        [ stats_num_field('bytes allocated',
+                          [ (wordsize(64), 51840, 20)
+                          , (wordsize(32), 47348, 20) ])
+        , only_ways(['normal'])],
+      compile_and_run,
+      ['-O'])