Commit ee3654ad authored by simonpj's avatar simonpj
Browse files

[project @ 2001-02-21 12:14:45 by simonpj]

More wibbles
parent a64ef2d0
......@@ -386,10 +386,23 @@ mkNonRec :: Id -> RhsDemand -- Lhs: id with demand
-> OrdList FloatingBind -> CoreExpr -- Rhs: let binds in body
-> UniqSM (OrdList FloatingBind)
mkNonRec bndr dem floats rhs
| exprIsValue rhs -- Notably constructor applications
= ASSERT( allLazy floats ) -- The only floats we can get out of a value are eta expansions
-- e.g. C $wJust ==> let s = \x -> $wJust x in C s
-- Here we want to float the s binding.
| exprIsValue rhs && allLazy floats -- Notably constructor applications
= -- Why the test for allLazy? You might think that the only
-- floats we can get out of a value are eta expansions
-- e.g. C $wJust ==> let s = \x -> $wJust x in C s
-- Here we want to float the s binding.
--
-- But if the programmer writes this:
-- f x = case x of { (a,b) -> \y -> a }
-- then the strictness analyser may say that f has strictness "S"
-- Later the eta expander will transform to
-- f x y = case x of { (a,b) -> a }
-- So now f has arity 2. Now CoreSat may see
-- v = f E
-- so the E argument will turn into a FloatCase.
-- Indeed we should end up with
-- v = case E of { r -> f r }
-- That is, we should not float, even though (f r) is a value
returnUs (floats `snocOL` FloatLet (NonRec bndr rhs))
| isUnLiftedType bndr_rep_ty || isStrictDem dem
......
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