Add the notion of "constructor-like" Ids for rule-matching

This patch adds an optional CONLIKE modifier to INLINE/NOINLINE pragmas, 
   {-# NOINLINE CONLIKE [1] f #-}
The effect is to allow applications of 'f' to be expanded in a potential
rule match.  Example
  {-# RULE "r/f" forall v. r (f v) = f (v+1) #-}

Consider the term
     let x = f v in ..x...x...(r x)...
Normally the (r x) would not match the rule, because GHC would be scared
about duplicating the redex (f v). However the CONLIKE modifier says to
treat 'f' like a constructor in this situation, and "look through" the
unfolding for x.  So (r x) fires, yielding (f (v+1)).

The main changes are:
  - Syntax

  - The inlinePragInfo field of an IdInfo has a RuleMatchInfo
    component, which records whether or not the Id is CONLIKE.
    Of course, this needs to be serialised in interface files too.

  - The occurrence analyser (OccAnal) and simplifier (Simplify) treat
    CONLIKE thing like constructors, by ANF-ing them

  - New function coreUtils.exprIsExpandable is like exprIsCheap, but
    additionally spots applications of CONLIKE functions

  - A CoreUnfolding has a field that caches exprIsExpandable

  - The rule matcher consults this field.  See 
    Note [Expanding variables] in Rules.lhs.

On the way I fixed a lurking variable bug in the way variables are
expanded.  See Note [Do not expand locally-bound variables] in
Rule.lhs.  I also did a bit of reformatting and refactoring in
Rules.lhs, so the module has more lines changed than are really
different.

3 files changed, 27 insertions, 7 deletions

diff --git a/compiler/iface/BinIface.hs b/compiler/iface/BinIface.hs
index 7a274011b7..1a4a65a290 100644
--- a/compiler/iface/BinIface.hs
+++ b/compiler/iface/BinIface.hs
@@ -578,6 +578,24 @@ instance Binary Activation where
 	      _ -> do ab <- get bh
 		      return (ActiveAfter ab)
 
+instance Binary RuleMatchInfo where
+    put_ bh FunLike = putByte bh 0
+    put_ bh ConLike = putByte bh 1
+    get bh = do
+            h <- getByte bh
+            if h == 1 then return ConLike
+                      else return FunLike
+
+instance Binary InlinePragma where
+    put_ bh (InlinePragma activation match_info) = do
+            put_ bh activation
+            put_ bh match_info
+
+    get bh = do
+           act  <- get bh
+           info <- get bh
+           return (InlinePragma act info)
+
 instance Binary StrictnessMark where
     put_ bh MarkedStrict    = putByte bh 0
     put_ bh MarkedUnboxed   = putByte bh 1
diff --git a/compiler/iface/IfaceSyn.lhs b/compiler/iface/IfaceSyn.lhs
index b679cf68c1..51e5f8a231 100644
--- a/compiler/iface/IfaceSyn.lhs
+++ b/compiler/iface/IfaceSyn.lhs
@@ -203,7 +203,7 @@ data IfaceIdInfo
 data IfaceInfoItem
   = HsArity	 Arity
   | HsStrictness StrictSig
-  | HsInline     Activation
+  | HsInline     InlinePragma
   | HsUnfold	 IfaceExpr
   | HsNoCafRefs
   | HsWorker	 Name Arity	-- Worker, if any see IdInfo.WorkerInfo
@@ -660,7 +660,7 @@ instance Outputable IfaceIdInfo where
 instance Outputable IfaceInfoItem where
   ppr (HsUnfold unf)  	 = ptext (sLit "Unfolding:") <+>
 				  	parens (pprIfaceExpr noParens unf)
-  ppr (HsInline act)     = ptext (sLit "Inline:") <+> ppr act
+  ppr (HsInline prag)    = ptext (sLit "Inline:") <+> ppr prag
   ppr (HsArity arity)    = ptext (sLit "Arity:") <+> int arity
   ppr (HsStrictness str) = ptext (sLit "Strictness:") <+> pprIfaceStrictSig str
   ppr HsNoCafRefs	 = ptext (sLit "HasNoCafRefs")
diff --git a/compiler/iface/MkIface.lhs b/compiler/iface/MkIface.lhs
index 22c1756e00..8cfc08f329 100644
--- a/compiler/iface/MkIface.lhs
+++ b/compiler/iface/MkIface.lhs
@@ -1440,8 +1440,8 @@ toIfaceLetBndr id  = IfLetBndr (occNameFS (getOccName id))
 	-- See Note [IdInfo on nested let-bindings] in IfaceSyn
     id_info = idInfo id
     inline_prag = inlinePragInfo id_info
-    prag_info | isAlwaysActive inline_prag = NoInfo
-	      | otherwise		   = HasInfo [HsInline inline_prag]
+    prag_info | isDefaultInlinePragma inline_prag = NoInfo
+	      | otherwise		          = HasInfo [HsInline inline_prag]
 
 --------------------------
 toIfaceIdDetails :: IdDetails -> IfaceIdDetails
@@ -1495,11 +1495,13 @@ toIfaceIdInfo id_info
 					
     ------------  Inline prag  --------------
     inline_prag = inlinePragInfo id_info
-    inline_hsinfo | isAlwaysActive inline_prag     = Nothing
-		  | no_unfolding && not has_worker = Nothing
+    inline_hsinfo | isDefaultInlinePragma inline_prag = Nothing
+		  | no_unfolding && not has_worker 
+                      && isFunLike (inlinePragmaRuleMatchInfo inline_prag)
+                                                      = Nothing
 			-- If the iface file give no unfolding info, we 
 			-- don't need to say when inlining is OK!
-		  | otherwise			   = Just (HsInline inline_prag)
+		  | otherwise			      = Just (HsInline inline_prag)
 
 --------------------------
 coreRuleToIfaceRule :: Module -> CoreRule -> IfaceRule