[commit: ghc] master: Give the Unique generated by strings a tag '$', fixes #9413. (4855be0)

[git at git.haskell.org]

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

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/4855be0d0d1ac90f836a6fb54f4034f478e38fd8/ghc

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

commit 4855be0d0d1ac90f836a6fb54f4034f478e38fd8
Author: Edward Z. Yang <ezyang at cs.stanford.edu>
Date:   Wed Aug 6 11:55:06 2014 +0100

    Give the Unique generated by strings a tag '$', fixes #9413.
    
    Summary:
    Previously, we allocated uniques for strings starting at zero, which
    means the tag bits in the unique are zero, which means that printing a
    Unique for a string will start with a null byte.  This is bad.  So
    instead, start our numbering with the tag byte as '$' (as in $tring).
    This is hard coded so we don't have to worry about the optimizer
    reducing the expression.
    
    Signed-off-by: Edward Z. Yang <ezyang at cs.stanford.edu>
    
    Test Plan: validate
    
    Reviewers: hvr, simonmar, austin
    
    Subscribers: simonmar, relrod, ezyang, carter
    
    Differential Revision: https://phabricator.haskell.org/D123
    
    GHC Trac Issues: #9413


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4855be0d0d1ac90f836a6fb54f4034f478e38fd8
 compiler/utils/FastString.lhs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/compiler/utils/FastString.lhs b/compiler/utils/FastString.lhs
index 0396c02..157e5f0 100644
--- a/compiler/utils/FastString.lhs
+++ b/compiler/utils/FastString.lhs
@@ -239,7 +239,7 @@ data FastStringTable =
 string_table :: FastStringTable
 {-# NOINLINE string_table #-}
 string_table = unsafePerformIO $ do
-  uid <- newIORef 0
+  uid <- newIORef 603979776 -- ord '$' * 0x01000000
   tab <- IO $ \s1# -> case newArray# hASH_TBL_SIZE_UNBOXED (panic "string_table") s1# of
                           (# s2#, arr# #) ->
                               (# s2#, FastStringTable uid arr# #)