X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=Data%2FBits.hs;h=8eaec9c63f900959b1552483dbda5cb0db5a71a6;hb=e0d697e559faf32d4b9f034c0968c1a299dd74c5;hp=8f6776f37dc7e83421508bd06350dbc04f50c0d9;hpb=72e4fe7801d2d8ab5b243cbb430272b45010f59d;p=ghc-base.git

diff --git a/Data/Bits.hs b/Data/Bits.hs
index 8f6776f..8eaec9c 100644
--- a/Data/Bits.hs
+++ b/Data/Bits.hs
@@ -1,4 +1,4 @@
-{-# OPTIONS_GHC -fno-implicit-prelude #-}
+{-# OPTIONS_GHC -XNoImplicitPrelude #-}
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Data.Bits
@@ -202,20 +202,30 @@ instance Bits Int where
 
 #ifdef __GLASGOW_HASKELL__
     (I# x#) .&.   (I# y#)  = I# (word2Int# (int2Word# x# `and#` int2Word# y#))
+
     (I# x#) .|.   (I# y#)  = I# (word2Int# (int2Word# x# `or#`  int2Word# y#))
+
     (I# x#) `xor` (I# y#)  = I# (word2Int# (int2Word# x# `xor#` int2Word# y#))
+
     complement (I# x#)     = I# (word2Int# (int2Word# x# `xor#` int2Word# (-1#)))
+
     (I# x#) `shift` (I# i#)
         | i# >=# 0#        = I# (x# `iShiftL#` i#)
         | otherwise        = I# (x# `iShiftRA#` negateInt# i#)
+
+    {-# INLINE rotate #-} 	-- See Note [Constant folding for rotate]
     (I# x#) `rotate` (I# i#) =
         I# (word2Int# ((x'# `uncheckedShiftL#` i'#) `or#`
                        (x'# `uncheckedShiftRL#` (wsib -# i'#))))
-        where
+      where
         x'# = int2Word# x#
         i'# = word2Int# (int2Word# i# `and#` int2Word# (wsib -# 1#))
         wsib = WORD_SIZE_IN_BITS#   {- work around preprocessor problem (??) -}
     bitSize  _             = WORD_SIZE_IN_BITS
+
+    {-# INLINE shiftR #-}
+    -- same as the default definition, but we want it inlined (#2376)
+    x `shiftR`  i = x `shift`  (-i)
 #else /* !__GLASGOW_HASKELL__ */
 
 #ifdef __HUGS__
@@ -321,3 +331,30 @@ fromInts = foldr catInt 0
 
 numInts = toInteger (maxBound::Int) - toInteger (minBound::Int) + 1
 #endif /* !__GLASGOW_HASKELL__ */
+
+{- 	Note [Constant folding for rotate]
+	~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The INLINE on the Int instance of rotate enables it to be constant
+folded.  For example:
+     sumU . mapU (`rotate` 3) . replicateU 10000000 $ (7 :: Int)
+goes to:
+   Main.$wfold =
+     \ (ww_sO7 :: Int#) (ww1_sOb :: Int#) ->
+       case ww1_sOb of wild_XM {
+         __DEFAULT -> Main.$wfold (+# ww_sO7 56) (+# wild_XM 1);
+         10000000 -> ww_sO7
+whereas before it was left as a call to $wrotate.
+
+All other Bits instances seem to inline well enough on their
+own to enable constant folding; for example 'shift':
+     sumU . mapU (`shift` 3) . replicateU 10000000 $ (7 :: Int)
+ goes to:
+     Main.$wfold =
+       \ (ww_sOb :: Int#) (ww1_sOf :: Int#) ->
+         case ww1_sOf of wild_XM {
+           __DEFAULT -> Main.$wfold (+# ww_sOb 56) (+# wild_XM 1);
+           10000000 -> ww_sOb
+         }
+-} 
+     
+