import UniqSupply ( UniqSupply )
import List ( partition )
import Outputable
-import Util ( notNull )
\end{code}
-----------------
pp_not True = empty
pp_not False = text "not"
-floatTopBind bind@(NonRec _ _)
- = case (floatBind bind) of { (fs, floats, bind') ->
- (fs, floatsToBinds floats ++ [bind'])
+floatTopBind bind
+ = case (floatBind bind) of { (fs, floats) ->
+ (fs, floatsToBinds floats)
}
-
-floatTopBind bind@(Rec _)
- = case (floatBind bind) of { (fs, floats, Rec pairs') ->
- WARN( notNull floats, ppr bind $$ ppr floats )
- (fs, [Rec (floatsToBindPairs floats ++ pairs')]) }
\end{code}
%************************************************************************
\begin{code}
-floatBind :: LevelledBind
- -> (FloatStats, FloatBinds, CoreBind)
+floatBind :: LevelledBind -> (FloatStats, FloatBinds)
floatBind (NonRec (TB name level) rhs)
- = case (floatNonRecRhs level rhs) of { (fs, rhs_floats, rhs') ->
- (fs, rhs_floats, NonRec name rhs') }
+ = case (floatRhs level rhs) of { (fs, rhs_floats, rhs') ->
+ (fs, rhs_floats ++ [(level, NonRec name rhs')]) }
floatBind bind@(Rec pairs)
= case (unzip3 (map do_pair pairs)) of { (fss, rhss_floats, new_pairs) ->
-
- if not (isTopLvl bind_dest_level) then
- -- Standard case; the floated bindings can't mention the
- -- binders, because they couldn't be escaping a major level
- -- if so.
- (sum_stats fss, concat rhss_floats, Rec new_pairs)
+ let rhs_floats = concat rhss_floats in
+
+ if not (isTopLvl bind_dest_lvl) then
+ -- Find which bindings float out at least one lambda beyond this one
+ -- These ones can't mention the binders, because they couldn't
+ -- be escaping a major level if so.
+ -- The ones that are not going further can join the letrec;
+ -- they may not be mutually recursive but the occurrence analyser will
+ -- find that out.
+ case (partitionByMajorLevel bind_dest_lvl rhs_floats) of { (floats', heres) ->
+ (sum_stats fss, floats' ++ [(bind_dest_lvl, Rec (floatsToBindPairs heres ++ new_pairs))]) }
else
-- In a recursive binding, *destined for* the top level
-- (only), the rhs floats may contain references to the
-- This can only happen for bindings destined for the top level,
-- because only then will partitionByMajorLevel allow through a binding
-- that only differs in its minor level
- (sum_stats fss, [],
- Rec (new_pairs ++ floatsToBindPairs (concat rhss_floats)))
+ (sum_stats fss, [(bind_dest_lvl, Rec (new_pairs ++ floatsToBindPairs rhs_floats))])
}
where
- bind_dest_level = getBindLevel bind
+ bind_dest_lvl = getBindLevel bind
do_pair (TB name level, rhs)
= case (floatRhs level rhs) of { (fs, rhs_floats, rhs') ->
%************************************************************************
\begin{code}
-floatExpr, floatRhs, floatNonRecRhs
+floatExpr, floatRhs, floatCaseAlt
:: Level
-> LevelledExpr
-> (FloatStats, FloatBinds, CoreExpr)
-floatRhs lvl arg -- Used rec rhss, and case-alternative rhss
+floatCaseAlt lvl arg -- Used rec rhss, and case-alternative rhss
= case (floatExpr lvl arg) of { (fsa, floats, arg') ->
case (partitionByMajorLevel lvl floats) of { (floats', heres) ->
-- Dump bindings that aren't going to escape from a lambda;
-- the rec or case alternative
(fsa, floats', install heres arg') }}
-floatNonRecRhs lvl arg -- Used for nested non-rec rhss, and fn args
+floatRhs lvl arg -- Used for nested non-rec rhss, and fn args
+ -- See Note [Floating out of RHS]
= case (floatExpr lvl arg) of { (fsa, floats, arg') ->
- -- Dump bindings that aren't going to escape from a lambda
- -- This isn't a scoping issue (the binder isn't in scope in the RHS of a non-rec binding)
- -- Rather, it is to avoid floating the x binding out of
- -- f (let x = e in b)
- -- unnecessarily. But we first test for values or trival rhss,
- -- because (in particular) we don't want to insert new bindings between
- -- the "=" and the "\". E.g.
- -- f = \x -> let <bind> in <body>
- -- We do not want
- -- f = let <bind> in \x -> <body>
- -- (a) The simplifier will immediately float it further out, so we may
- -- as well do so right now; in general, keeping rhss as manifest
- -- values is good
- -- (b) If a float-in pass follows immediately, it might add yet more
- -- bindings just after the '='. And some of them might (correctly)
- -- be strict even though the 'let f' is lazy, because f, being a value,
- -- gets its demand-info zapped by the simplifier.
if exprIsHNF arg' || exprIsTrivial arg' then
(fsa, floats, arg')
else
case (partitionByMajorLevel lvl floats) of { (floats', heres) ->
(fsa, floats', install heres arg') }}
+-- Note [Floating out of RHSs]
+-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~
+-- Dump bindings that aren't going to escape from a lambda
+-- This isn't a scoping issue (the binder isn't in scope in the RHS
+-- of a non-rec binding)
+-- Rather, it is to avoid floating the x binding out of
+-- f (let x = e in b)
+-- unnecessarily. But we first test for values or trival rhss,
+-- because (in particular) we don't want to insert new bindings between
+-- the "=" and the "\". E.g.
+-- f = \x -> let <bind> in <body>
+-- We do not want
+-- f = let <bind> in \x -> <body>
+-- (a) The simplifier will immediately float it further out, so we may
+-- as well do so right now; in general, keeping rhss as manifest
+-- values is good
+-- (b) If a float-in pass follows immediately, it might add yet more
+-- bindings just after the '='. And some of them might (correctly)
+-- be strict even though the 'let f' is lazy, because f, being a value,
+-- gets its demand-info zapped by the simplifier.
+
floatExpr _ (Var v) = (zeroStats, [], Var v)
floatExpr _ (Type ty) = (zeroStats, [], Type ty)
floatExpr _ (Lit lit) = (zeroStats, [], Lit lit)
floatExpr lvl (App e a)
= case (floatExpr lvl e) of { (fse, floats_e, e') ->
- case (floatNonRecRhs lvl a) of { (fsa, floats_a, a') ->
+ case (floatRhs lvl a) of { (fsa, floats_a, a') ->
(fse `add_stats` fsa, floats_e ++ floats_a, App e' a') }}
floatExpr lvl lam@(Lam _ _)
(fs, rhs_floats ++ body_floats, Let (NonRec bndr rhs') body') }}
floatExpr lvl (Let bind body)
- = case (floatBind bind) of { (fsb, rhs_floats, bind') ->
+ = case (floatBind bind) of { (fsb, bind_floats) ->
case (floatExpr lvl body) of { (fse, body_floats, body') ->
(add_stats fsb fse,
- rhs_floats ++ [(bind_lvl, bind')] ++ body_floats,
+ bind_floats ++ body_floats,
body') }}
- where
- bind_lvl = getBindLevel bind
floatExpr lvl (Case scrut (TB case_bndr case_lvl) ty alts)
= case floatExpr lvl scrut of { (fse, fde, scrut') ->
(add_stats fse fsa, fda ++ fde, Case scrut' case_bndr ty alts')
}}
where
- -- Use floatRhs for the alternatives, so that we
+ -- Use floatCaseAlt for the alternatives, so that we
-- don't gratuitiously float bindings out of the RHSs
float_alt (con, bs, rhs)
- = case (floatRhs case_lvl rhs) of { (fs, rhs_floats, rhs') ->
+ = case (floatCaseAlt case_lvl rhs) of { (fs, rhs_floats, rhs') ->
(fs, rhs_floats, (con, [b | TB b _ <- bs], rhs')) }
projects / ghc-hetmet.git / commitdiff