Use quotRemWord in showWord

Using the following high-quality benchmark (with -O2):

  main :: IO ()
  main = do
    let
      go 0         = ""
      go n@(W# n#) = showWord n# (go (n -1))
    print $ length (go 10000000)

I get the following performance results:

- remWord+quotRem: 0,76s user 0,00s system 99% cpu 0,762 total
- quotRemWord:     0,45s user 0,01s system 99% cpu 0,456 total

Note that showSignedInt already uses quotRemInt.

1 files changed, 5 insertions, 3 deletions

diff --git a/libraries/base/GHC/Show.hs b/libraries/base/GHC/Show.hs
index 0d90006432..04fbcb6112 100644
--- a/libraries/base/GHC/Show.hs
+++ b/libraries/base/GHC/Show.hs
@@ -202,9 +202,11 @@ instance Show Word where
 showWord :: Word# -> ShowS
 showWord w# cs
  | isTrue# (w# `ltWord#` 10##) = C# (chr# (ord# '0'# +# word2Int# w#)) : cs
- | otherwise = case chr# (ord# '0'# +# word2Int# (w# `remWord#` 10##)) of
-               c# ->
-                   showWord (w# `quotWord#` 10##) (C# c# : cs)
+ | otherwise =
+    let
+      !(# q, r #) = quotRemWord# w# 10##
+      !c#         = chr# (ord# '0'# +# word2Int# r)
+    in showWord q (C# c# : cs)
 
 -- | @since 2.01
 deriving instance Show a => Show (Maybe a)