[commit: ghc] wip/T12357: FastString: Add unpackFSLazy (11f802e)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : wip/T12357
Link       : http://ghc.haskell.org/trac/ghc/changeset/11f802e20c674f5d19b68e95e79cadd2ff1ab600/ghc

>---------------------------------------------------------------

commit 11f802e20c674f5d19b68e95e79cadd2ff1ab600
Author: Ben Gamari <ben at smart-cactus.org>
Date:   Mon Jul 4 21:13:32 2016 -0400

    FastString: Add unpackFSLazy


>---------------------------------------------------------------

11f802e20c674f5d19b68e95e79cadd2ff1ab600
 compiler/utils/FastString.hs | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/compiler/utils/FastString.hs b/compiler/utils/FastString.hs
index f58a5b5..7f29eee 100644
--- a/compiler/utils/FastString.hs
+++ b/compiler/utils/FastString.hs
@@ -52,6 +52,7 @@ module FastString
 
         -- ** Deconstruction
         unpackFS,           -- :: FastString -> String
+        unpackFSLazy,       -- :: FastString -> String
         bytesFS,            -- :: FastString -> [Word8]
 
         -- ** Encoding
@@ -482,7 +483,12 @@ nullFS f = BS.null (fs_bs f)
 
 -- | Unpacks and decodes the FastString
 unpackFS :: FastString -> String
-unpackFS (FastString _ _ bs _) = utf8DecodeStringLazy bs
+unpackFS (FastString _ _ bs _) =
+  inlinePerformIO $ BS.unsafeUseAsCStringLen bs $ \(ptr, len) ->
+        utf8DecodeString (castPtr ptr) len
+
+unpackFSLazy :: FastString -> String
+unpackFSLazy (FastString _ _ bs _) = utf8DecodeStringLazy bs
 {-# INLINEABLE unpackFS #-}
 
 -- | Gives the UTF-8 encoded bytes corresponding to a 'FastString'