X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2FsimplCore%2FOccurAnal.lhs;h=2e07e089ed001833d69b0f901c4cadab0539c3ba;hb=f07f25fdbac2b885aea6aa62c0326840c85f7b59;hp=91e34f879e48e75a2025fc78ebed6187555a536a;hpb=72462499b891d5779c19f3bda03f96e24f9554ae;p=ghc-hetmet.git

diff --git a/compiler/simplCore/OccurAnal.lhs b/compiler/simplCore/OccurAnal.lhs
index 91e34f8..2e07e08 100644
--- a/compiler/simplCore/OccurAnal.lhs
+++ b/compiler/simplCore/OccurAnal.lhs
@@ -177,7 +177,7 @@ However things are made quite a bit more complicated by RULES.  Remember
     "loop"?  In particular, a RULE is like an equation for 'f' that
     is *always* inlined if it is applicable.  We do *not* disable
     rules for loop-breakers.  It's up to whoever makes the rules to
-    make sure that the rules themselves alwasys terminate.  See Note
+    make sure that the rules themselves always terminate.  See Note
     [Rules for recursive functions] in Simplify.lhs
 
     Hence, if
@@ -533,15 +533,15 @@ reOrderCycle depth (bind : binds) pairs
                 -- where df is the exported dictionary. Then df makes a really
                 -- bad choice for loop breaker
 
-        | Just inl_rule_info <- isInlineRule_maybe (idUnfolding bndr)
+        | Just (inl_rule_info, _) <- isInlineRule_maybe (idUnfolding bndr)
 	= case inl_rule_info of
 	     InlWrapper {} -> 10  -- Note [INLINE pragmas]
 	     _other	   ->  3  -- Data structures are more important than this
 	     		          -- so that dictionary/method recursion unravels
                 
-        | is_con_app rhs = 5    -- Data types help with cases
-	  	     	   	-- Includes dict funs
-                -- Note [Constructor applictions]
+        | is_con_app rhs = 5  -- Data types help with cases: Note [Constructor applications]
+	   	     	      -- Includes dict funs: Note [DFuns should not be loop breakers]
+                
 
 -- If an Id is marked "never inline" then it makes a great loop breaker
 -- The only reason for not checking that here is that it is rare
@@ -555,8 +555,6 @@ reOrderCycle depth (bind : binds) pairs
                 -- the Id has some kind of unfolding
 
         | otherwise = 0
-        where
-	  
 
 	-- Checking for a constructor application
         -- Cheap and cheerful; the simplifer moves casts out of the way
@@ -615,13 +613,14 @@ linear in the number of instance declarations.
 
 Note [INLINE pragmas]
 ~~~~~~~~~~~~~~~~~~~~~
-Never choose a function with an INLINE pramga as the loop breaker!  
+Avoid choosing a function with an INLINE pramga as the loop breaker!  
 If such a function is mutually-recursive with a non-INLINE thing,
 then the latter should be the loop-breaker.
 
-A particular case is wrappers generated by the demand analyser.
-If you make then into a loop breaker you may get an infinite 
-inlining loop.  For example:
+Usually this is just a question of optimisation. But a particularly
+bad case is wrappers generated by the demand analyser: if you make
+then into a loop breaker you may get an infinite inlining loop.  For
+example:
   rec {
         $wfoo x = ....foo x....
 
@@ -645,6 +644,11 @@ happened when we gave is_con_app a lower score than inline candidates:
 
 Here we do *not* want to choose 'repTree' as the loop breaker.
 
+Note [DFuns should not be loop breakers]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+It's particularly bad to make a DFun into a loop breaker.  See
+Note [How instance declarations are translated] in TcInstDcls
+
 Note [Constructor applications]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 It's really really important to inline dictionaries.  Real