Make Data.List.foldr1 inline

Previously, foldr1 would be defiend recursively and thus not inline.
This is bad, for example, when maximumBy has a strict comparison
function: Before the BBP, it was implemented via foldl1, which inlined
and yielded good code. With BBP, it goes via foldr1, so we better inline
this as well. Fixes #10830.

Differential Revision: https://phabricator.haskell.org/D1205

libraries/base/GHC/List.hs

@@ -355,9 +355,11 @@ match on everything past the :, which is just the tail of scanl.
 -- and thus must be applied to non-empty lists.
 
 foldr1                  :: (a -> a -> a) -> [a] -> a
-foldr1 _ [x]            =  x
-foldr1 f (x:xs)         =  f x (foldr1 f xs)
-foldr1 _ []             =  errorEmptyList "foldr1"
+foldr1 f = go
+  where go [x]            =  x
+        go (x:xs)         =  f x (go xs)
+        go []             =  errorEmptyList "foldr1"
+{-# INLINE [0] foldr1 #-}
 
 -- | 'scanr' is the right-to-left dual of 'scanl'.
 -- Note that

testsuite/tests/simplCore/should_run/T10830.hs

+import GHC.OldList
+main :: IO ()
+main = maximumBy compare [1..10000] `seq` return ()

testsuite/tests/simplCore/should_run/all.T

@@ -69,3 +69,4 @@ test('T457', [ only_ways(['normal','optasm']), exit_code(1) ], compile_and_run,
 
 test('T9128', normal, compile_and_run, [''])
 test('T9390', normal, compile_and_run, [''])
+test('T10830', extra_run_opts('+RTS -K100k -RTS'), compile_and_run, [''])