[commit: ghc] master: doc tweak: mention that UNPACK doesn't work without -O (a9256c7)

[Simon Marlow]

Repository : ssh://darcs.haskell.org//srv/darcs/ghc

On branch  : master

http://hackage.haskell.org/trac/ghc/changeset/a9256c75141b0b5ff616da9b5194267a72ae889c

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

commit a9256c75141b0b5ff616da9b5194267a72ae889c
Author: Simon Marlow <marlowsd at gmail.com>
Date:   Tue Jun 28 13:42:00 2011 +0100

    doc tweak: mention that UNPACK doesn't work without -O

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

 docs/users_guide/glasgow_exts.xml |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)

diff --git a/docs/users_guide/glasgow_exts.xml b/docs/users_guide/glasgow_exts.xml
index 16cc760..54b7a0f 100644
--- a/docs/users_guide/glasgow_exts.xml
+++ b/docs/users_guide/glasgow_exts.xml
@@ -8416,7 +8416,11 @@ data T = T {-# UNPACK #-} !Float
       compiler).</para>
 
       <para>Unpacking constructor fields should only be used in
-      conjunction with <option>-O</option>, in order to expose
+      conjunction with <option>-O</option><footnote>in fact, UNPACK
+          has no effect without <option>-O</option>, for technical
+          reasons
+      (see <ulink url="http://hackage.haskell.org/trac/ghc/ticket/5252">tick
+            5252</ulink>)</footnote>, in order to expose
       unfoldings to the compiler so the reboxing can be removed as
       often as possible.  For example:</para>