+ !Bool -- True <=> This loop breaker occurs only the RHS of a RULE
+\end{code}
+
+Note [RulesOnly]
+~~~~~~~~~~~~~~~~
+The RulesOnly constructor records if an Id occurs only in the RHS of a Rule.
+Similarly, the boolean in IAmLoopbreaker True if the only reason the Id is a
+loop-breaker only because of recursion through a RULE. In that case,
+we can ignore the loop-breaker-ness for inlining purposes. Example
+(from GHC.Enum):
+
+ eftInt :: Int# -> Int# -> [Int]
+ eftInt x y = ...(non-recursive)...
+
+ {-# INLINE [0] eftIntFB #-}
+ eftIntFB :: (Int -> r -> r) -> r -> Int# -> Int# -> r
+ eftIntFB c n x y = ...(non-recursive)...