Add INLINABLE pragmas to `generic*` functions in Data.OldListwip/generic-inlinable

These functions are

* recursive
* overloaded

So it's important to add an `INLINABLE` pragma to each so that they can be
specialised at the use site when the specific numeric type is known.
Adding these pragmas improves the LazyText replicate benchmark (see https://gitlab.haskell.org/ghc/ghc/-/issues/22886#note_481020)

https://github.com/haskell/core-libraries-committee/issues/129

2 files changed, 7 insertions, 0 deletions

diff --git a/libraries/base/Data/OldList.hs b/libraries/base/Data/OldList.hs
index 211978dadd..ef5960542d 100644
--- a/libraries/base/Data/OldList.hs
+++ b/libraries/base/Data/OldList.hs
@@ -842,6 +842,7 @@ strictGenericLength l   =  gl l 0
                         where
                            gl [] a     = a
                            gl (_:xs) a = let a' = a + 1 in a' `seq` gl xs a'
+{-# INLINABLE strictGenericLength #-}
 
 -- | The 'genericTake' function is an overloaded version of 'take', which
 -- accepts any 'Integral' value as the number of elements to take.
@@ -849,6 +850,7 @@ genericTake             :: (Integral i) => i -> [a] -> [a]
 genericTake n _ | n <= 0 = []
 genericTake _ []        =  []
 genericTake n (x:xs)    =  x : genericTake (n-1) xs
+{-# INLINABLE genericTake #-}
 
 -- | The 'genericDrop' function is an overloaded version of 'drop', which
 -- accepts any 'Integral' value as the number of elements to drop.
@@ -856,6 +858,7 @@ genericDrop             :: (Integral i) => i -> [a] -> [a]
 genericDrop n xs | n <= 0 = xs
 genericDrop _ []        =  []
 genericDrop n (_:xs)    =  genericDrop (n-1) xs
+{-# INLINABLE genericDrop #-}
 
 
 -- | The 'genericSplitAt' function is an overloaded version of 'splitAt', which
@@ -865,6 +868,7 @@ genericSplitAt n xs | n <= 0 =  ([],xs)
 genericSplitAt _ []     =  ([],[])
 genericSplitAt n (x:xs) =  (x:xs',xs'') where
     (xs',xs'') = genericSplitAt (n-1) xs
+{-# INLINABLE genericSplitAt #-}
 
 -- | The 'genericIndex' function is an overloaded version of '!!', which
 -- accepts any 'Integral' value as the index.
@@ -874,11 +878,13 @@ genericIndex (_:xs) n
  | n > 0     = genericIndex xs (n-1)
  | otherwise = errorWithoutStackTrace "List.genericIndex: negative argument."
 genericIndex _ _      = errorWithoutStackTrace "List.genericIndex: index too large."
+{-# INLINABLE genericIndex #-}
 
 -- | The 'genericReplicate' function is an overloaded version of 'replicate',
 -- which accepts any 'Integral' value as the number of repetitions to make.
 genericReplicate        :: (Integral i) => i -> a -> [a]
 genericReplicate n x    =  genericTake n (repeat x)
+{-# INLINABLE genericReplicate #-}
 
 -- | The 'zip4' function takes four lists and returns a list of
 -- quadruples, analogous to 'zip'.
diff --git a/libraries/base/changelog.md b/libraries/base/changelog.md
index b102de449c..bef533f263 100644
--- a/libraries/base/changelog.md
+++ b/libraries/base/changelog.md
@@ -6,6 +6,7 @@
     types significantly.
   * Refactor `generalCategory` to stop very large literal string being inlined to call-sites.
       ([CLC proposal #130](https://github.com/haskell/core-libraries-committee/issues/130))
+  * Add INLINABLE pragmas to `generic*` functions in Data.OldList ([CLC proposal #129](https://github.com/haskell/core-libraries-committee/issues/130))
 
 ## 4.18.0.0 *TBA*