Implement -fexpose-all-unfoldings, and fix a non-termination bug

The -fexpose-all-unfoldings flag arranges to put unfoldings for *everything*
in the interface file.  Of course,  this makes the file a lot bigger, but
it also makes it complete, and that's great for supercompilation; or indeed
any whole-program work.

Consequences:
  * Interface files need to record loop-breaker-hood.  (Previously,
    loop breakers were never exposed, so that info wasn't necessary.)
    Hence a small interface file format change. 

  * When inlining, must check loop-breaker-hood. (Previously, loop
    breakers didn't have an unfolding at all, so no need to check.)

  * Ditto in exprIsConApp_maybe.  Roman actually tripped this bug, 
    because a DFun, which had an unfolding, was also a loop breaker

  * TidyPgm.tidyIdInfo must be careful to preserve loop-breaker-hood

So Id.idUnfolding checks for loop-breaker-hood and returns NoUnfolding
if so. When you want the unfolding regardless of loop-breaker-hood, 
use Id.realIdUnfolding.

I have not documented the flag yet, because it's experimental.  Nor
have I tested it thoroughly.  But with the flag off (the normal case)
everything should work.

1 files changed, 1 insertions, 1 deletions

diff --git a/compiler/specialise/Specialise.lhs b/compiler/specialise/Specialise.lhs
index b772a3f25c..6d071e22b6 100644
--- a/compiler/specialise/Specialise.lhs
+++ b/compiler/specialise/Specialise.lhs
@@ -800,7 +800,7 @@ specDefn subst body_uds fn rhs
   where
     fn_type	       = idType fn
     fn_arity	       = idArity fn
-    fn_unf             = idUnfolding fn
+    fn_unf             = realIdUnfolding fn	-- Ignore loop-breaker-ness here
     (tyvars, theta, _) = tcSplitSigmaTy fn_type
     n_tyvars	       = length tyvars
     n_dicts	       = length theta