Fix nasty recompilation bug in MkIface.computeChangedOccs

	MERGE to 6.8 branch

In computeChangedOccs we look up the old version of a Name.
But a WiredIn Name doesn't have an old version, because WiredIn things
don't appear in interface files at all.

Result: ghc-6.9: panic! (the 'impossible' happened)
  (GHC version 6.9 for x86_64-unknown-linux):
	lookupVers1 base:GHC.Prim chr#{v}

This fixes the problem.  The patch should merge easily onto the branch.

diff --git a/compiler/iface/MkIface.lhs b/compiler/iface/MkIface.lhs
index f972a91..1521069 100644 (file)
--- a/compiler/iface/MkIface.lhs
+++ b/compiler/iface/MkIface.lhs
@@ -708,6 +708,8 @@ computeChangedOccs ver_fn this_module old_usages eq_info
     -- return True if an external name has changed
     name_changed :: Name -> Bool
     name_changed nm
     -- return True if an external name has changed
     name_changed :: Name -> Bool
     name_changed nm

+       | isWiredInName nm      -- Wired-in things don't get into interface
+       = False                 -- files and hence don't get into the ver_fn

         | Just ents <- lookupUFM usg_modmap (moduleName mod),
           Just v    <- lookupUFM ents parent_occ
         = v < new_version
         | Just ents <- lookupUFM usg_modmap (moduleName mod),
           Just v    <- lookupUFM ents parent_occ
         = v < new_version