[commit: ghc] wip/nested-cpr: Leave singleton (# . #) in place if they were already there (6729a76)

[git at git.haskell.org]

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

On branch  : wip/nested-cpr
Link       : http://ghc.haskell.org/trac/ghc/changeset/6729a76e0250d2dd8c5b458a825aabf2c2de204d/ghc

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

commit 6729a76e0250d2dd8c5b458a825aabf2c2de204d
Author: Joachim Breitner <mail at joachim-breitner.de>
Date:   Thu Dec 5 11:49:14 2013 +0000

    Leave singleton (# . #) in place if they were already there


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

6729a76e0250d2dd8c5b458a825aabf2c2de204d
 compiler/stranal/WwLib.lhs |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/compiler/stranal/WwLib.lhs b/compiler/stranal/WwLib.lhs
index ba56060..b79dc05 100644
--- a/compiler/stranal/WwLib.lhs
+++ b/compiler/stranal/WwLib.lhs
@@ -536,13 +536,16 @@ mkWWcpr :: Type                              -- function body type
 mkWWcpr body_ty res
   = do (arg_vars, con_app, decon) <- mkWWcpr_help False body_ty res
        case arg_vars of
+         -- Do leave things alone if it is a non-nested unboxed tuple.
+         -- How does this relates to the next case? Seems to make a difference
+         -- in Text.Read.Lex, for example.
+         _ | isWWUseless body_ty res -> return (id, id, body_ty)
+
          -- When we have to wrap only on argument, skip the (# .. #)
          [arg_var] -> do
            return ( \ wkr_call -> mkRename wkr_call arg_var con_app
                   , \ body     -> decon body (Var arg_var)
                   , idType arg_var )
-
-         _ | isWWUseless body_ty res -> return (id, id, body_ty)
          _ -> do
            wrap_wild_uniq <- getUniqueM