_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
-- 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
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....
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