where
(final_body_usage, tagged_binder) = tagBinder body_usage binder
- (rhs_usage, rhs') = occAnalRhs env binder rhs
+ (rhs_usage, rhs') = occAnalRhs env tagged_binder rhs
\end{code}
Dropping dead code for recursive bindings is done in a very simple way:
\begin{code}
occAnalRhs :: OccEnv
-> Id -> CoreExpr -- Binder and rhs
+ -- For non-recs the binder is alrady tagged
+ -- with occurrence info
-> (UsageDetails, CoreExpr)
occAnalRhs env id rhs
= (final_usage, rhs')
where
- (rhs_usage, rhs') = occAnal (rhsCtxt env) rhs
- -- Note that we use an rhsCtxt. This tells the occ anal that it's
- -- looking at an RHS, which has an effect in occAnalApp
+ (rhs_usage, rhs') = occAnal ctxt rhs
+ ctxt | certainly_inline id = env
+ | otherwise = rhsCtxt env
+ -- Note that we generally use an rhsCtxt. This tells the occ anal n
+ -- that it's looking at an RHS, which has an effect in occAnalApp
--
-- But there's a problem. Consider
-- x1 = a0 : []
-- x2 = a1 : x1
-- x3 = a2 : x2
- -- g = f x2
+ -- g = f x3
-- First time round, it looks as if x1 and x2 occur as an arg of a
-- let-bound constructor ==> give them a many-occurrence.
-- But then x3 is inlined (unconditionally as it happens) and
-- next time round, x2 will be, and the next time round x1 will be
-- Result: multiple simplifier iterations. Sigh.
- -- Possible solution: use rhsCtxt for things that occur just once...
+ -- Crude solution: use rhsCtxt for things that occur just once...
+
+ certainly_inline id = case idOccInfo id of
+ OneOcc in_lam one_br -> not in_lam && one_br
+ other -> False
-- [March 98] A new wrinkle is that if the binder has specialisations inside
-- it then we count the specialised Ids as "extra rhs's". That way
add v u = addOneOcc u v NoOccInfo -- Give a non-committal binder info
-- (i.e manyOcc) because many copies
-- of the specialised thing can appear
+
\end{code}
Expressions