+++ /dev/null
-%
-% (c) The GRASP/AQUA Project, Glasgow University, 1992-1995
-%
-\section[Cyclic]{Knot tying}
-
->#include "HsVersions.h"
->
-> module Cyclic (
-> mkLoops, fixupFreeVars
-> ) where
-
-> import DefSyn
-> import DefUtils
-> import Def2Core ( d2c, defPanic )
-
-> import Type ( glueTyArgs, quantifyTy, mkForallTy, mkTyVarTys,
-> TyVarTemplate
-> )
-> import Digraph ( dfs )
-> import Id ( idType, updateIdType,
-> addIdDeforestInfo, eqId, Id
-> )
-> import IdInfo
-> import Outputable
-> import Pretty
-> import UniqSupply
-> import Util
-
------------------------------------------------------------------------------
-A more efficient representation for lists that are extended multiple
-times, but only examined once.
-
-> type FList a = [a] -> [a]
-> append = (.)
-> singleton x = (x:)
-> cons x xs = \ys -> x:(xs ys)
-> list x = (x++)
-> emptylist = id
-
------------------------------------------------------------------------------
-Monad for the knot-tier.
-
-> type Lbl a = UniqSM (
-> [(Id)], -- loops used
-> [(Id,DefExpr,[Id],DefExpr)], -- bindings floating upwards
-> [(Id,DefExpr)], -- back loops
-> a) -- computation result
->
-> thenLbl :: Lbl a -> (a -> Lbl b) -> Lbl b
-> thenLbl a k
-> = a `thenUs` \(ls, bs, bls, a) ->
-> k a `thenUs` \(ls',bs',bls', b) ->
-> returnUs (ls ++ ls', bs ++ bs', bls ++ bls', b)
->
-> returnLbl :: a -> Lbl a
-> returnLbl a = returnUs ([],[],[],a)
->
-> mapLbl :: (a -> Lbl b) -> [a] -> Lbl [b]
-> mapLbl f [] = returnLbl []
-> mapLbl f (x:xs)
-> = f x `thenLbl` \x ->
-> mapLbl f xs `thenLbl` \xs ->
-> returnLbl (x:xs)
-
------------------------------------------------------------------------------
-
-This is terribly inefficient.
-
-> mkLoops :: DefExpr -> UniqSM ([(Id,DefExpr)],DefExpr)
-> mkLoops e =
-> error "mkLoops"
->{- LATER:
-> loop [] e `thenUs` \(ls,bs,bls,e) ->
-
-Throw away all the extracted bindings that can't be reached. These
-can occur as the result of some forward loops being short-circuited by
-back-loops. We find out which bindings can be reached by a
-depth-first search of the call graph starting with the free variables
-of the expression being returned.
-
-> let
-> loops_out = filter deforestable (freeVars e)
-> (_,reachable) = dfs (==) r ([],[]) loops_out
-> r f = lookup f bs
->
-> lookup f [] = []
-> lookup f ((g,out,_):xs) | f == g = out
-> | otherwise = lookup f xs
->
-> isReachable (f,_,_) = f `elem` reachable
-> in
-> returnUs (map (\(f,_,e) -> (f,e)) (filter isReachable bs),e)
-> where
-
-> loop :: [(Id,DefExpr,[Id],[TyVar])] -> DefExpr -> Lbl DefExpr
-
-> loop ls (Var (Label e e1))
-> =
-> d2c e `thenUs` \core_e ->
->-- trace ("loop:\n" ++ show (ppr PprDebug core_e)) $
-
-> mapUs (\(f,e',val_args,ty_args) ->
-> renameExprs e' e `thenUs` \r ->
-> returnUs (f,val_args,ty_args,r)) ls `thenUs` \results ->
-> let
-> loops =
-> [ (f,val_args,ty_args,r) |
-> (f,val_args,ty_args,IsRenaming r) <- results ]
-> inconsistent_renamings =
-> [ (f,r) |
-> (f,val_args,ty_args,InconsistentRenaming r)
-> <- results ]
-> in
->
-> (case loops of
-> [] ->
-
-Ok, there are no loops (i.e. this expression hasn't occurred before).
-Prepare for a possible re-occurrence of *this* expression, by making
-up a new function name and type (laziness ensures that this isn't
-actually done unless the function is required).
-
-The type of a new function, if one is generated at this point, is
-constructed as follows:
-
- \/ a1 ... \/ an . b1 -> ... -> bn -> t
-
-where a1...an are the free type variables in the expression, b1...bn
-are the types of the free variables in the expression, and t is the
-type of the expression itself.
-
-> let
->
-> -- Collect the value/type arguments for the function
-> fvs = freeVars e
-> val_args = filter isArgId fvs
-> ty_args = freeTyVars e
->
-> -- Now to make up the type...
-> base_type = coreExprType core_e
-> fun_type = glueTyArgs (map idType val_args) base_type
-> (_, type_of_f) = quantifyTy ty_args fun_type
-> in
->
-> newDefId type_of_f `thenUs` \f' ->
-> let
-> f = addIdDeforestInfo f' DoDeforest
-> in
-> loop ((f,e,val_args,ty_args):ls) e1
-> `thenUs` \res@(ls',bs,bls,e') ->
-
-Key: ls = loops, bs = bindings, bls = back loops, e = expression.
-
-If we are in a back-loop (i.e. we found a label somewhere below which
-this expression is a renaming of), then just insert the expression
-here.
-
-Comment the next section out to disable back-loops.
-
-(NB. I've seen this panic too - investigate?)
-
-> let back_loops = reverse [ e | (f',e) <- bls, f' == f ] in
-> if not (null back_loops){- && not (f `elem` ls')-} then
-> --if length back_loops > 1 then panic "barf!" else
-> d2c (head back_loops) `thenUs` \core_e ->
-> pprTrace "Back Loop:\n" (ppr PprDebug core_e) $
-
-If we find a back-loop that also occurs where we would normally make a
-new function...
-
-> if f `elem` ls' then
-> d2c e' `thenUs` \core_e' ->
-> trace ("In Forward Loop " ++
-> show (ppr PprDebug f) ++ "\n" ++
-> show (ppr PprDebug core_e')) $
-> if f `notElem` (freeVars (head back_loops)) then
-> returnUs (ls', bs, bls, head back_loops)
-> else
-> panic "hello"
-> else
-
-> returnUs (ls', bs, bls, head back_loops)
-> else
-
-If we are in a forward-loop (i.e. we found a label somewhere below
-which is a renaming of this one), then make a new function definition.
-
-> if f `elem` ls' then
->
-> rebindExpr (mkLam ty_args val_args e')
-> `thenUs` \rhs ->
-> returnUs
-> (ls',
-> (f,filter deforestable (freeVars e'),e,rhs) : bs,
-> bls,
-> mkLoopFunApp val_args ty_args f)
-
-otherwise, forget about it
-
-> else returnUs res
-
-This is a loop, just make a call to the function which we
-will create on the way back up the tree.
-
-(NB: it appears that sometimes we do get more than one loop matching,
-investigate this?)
-
-> ((f,val_args,ty_args,r):_) ->
->
-> returnUs
-> ([f], -- found a loop, propagate it back
-> [], -- no bindings
-> [], -- no back loops
-> mkLoopFunApp (applyRenaming r val_args) ty_args f)
->
-> ) `thenUs` \res@(ls',bs,bls,e') ->
-
-If this expression reoccurs, record the binding and replace the cycle
-with a call to the new function. We also rebind all the free
-variables in the new function to avoid name clashes later.
-
-> let
-> findBackLoops (g,r) bls
-> | consistent r' = subst s e' `thenUs` \e' ->
-> returnUs ((g,e') : bls)
-> | otherwise = returnUs bls
-> where
-> r' = map swap r
-> s = map (\(x,y) -> (x, Var (DefArgVar y))) (nub r')
-> in
-
-We just want the first one (ie. furthest up the tree), so reverse the
-list of inconsistent renamings.
-
-> foldrSUs findBackLoops [] (reverse inconsistent_renamings)
-> `thenUs` \back_loops ->
-
-Comment out the next block to disable back-loops. ToDo: trace all of them.
-
-> if not (null back_loops) then
-> d2c e' `thenUs` \core_e ->
-> trace ("Floating back loop:\n"
-> ++ show (ppr PprDebug core_e))
-> returnUs (ls', bs, back_loops ++ bls, e')
-> else
-> returnUs res
-
-> loop ls e@(Var (DefArgVar v))
-> = returnLbl e
-> loop ls e@(Lit l)
-> = returnLbl e
-> loop ls (Con c ts es)
-> = mapLbl (loopAtom ls) es `thenLbl` \es ->
-> returnLbl (Con c ts es)
-> loop ls (Prim op ts es)
-> = mapLbl (loopAtom ls) es `thenLbl` \es ->
-> returnLbl (Prim op ts es)
-> loop ls (Lam vs e)
-> = loop ls e `thenLbl` \e ->
-> returnLbl (Lam vs e)
-> loop ls (CoTyLam alpha e)
-> = loop ls e `thenLbl` \e ->
-> returnLbl (CoTyLam alpha e)
-> loop ls (App e v)
-> = loop ls e `thenLbl` \e ->
-> loopAtom ls v `thenLbl` \v ->
-> returnLbl (App e v)
-> loop ls (CoTyApp e t)
-> = loop ls e `thenLbl` \e ->
-> returnLbl (CoTyApp e t)
-> loop ls (Case e ps)
-> = loop ls e `thenLbl` \e ->
-> loopCaseAlts ls ps `thenLbl` \ps ->
-> returnLbl (Case e ps)
-> loop ls (Let (NonRec v e) e')
-> = loop ls e `thenLbl` \e ->
-> loop ls e' `thenLbl` \e' ->
-> returnLbl (Let (NonRec v e) e')
-> loop ls (Let (Rec bs) e)
-> = mapLbl loopRecBind bs `thenLbl` \bs ->
-> loop ls e `thenLbl` \e ->
-> returnLbl (Let (Rec bs) e)
-> where
-> vs = map fst bs
-> loopRecBind (v, e)
-> = loop ls e `thenLbl` \e ->
-> returnLbl (v, e)
-> loop ls e
-> = defPanic "Cyclic" "loop" e
-
-> loopAtom ls (VarArg (DefArgExpr e))
-> = loop ls e `thenLbl` \e ->
-> returnLbl (VarArg (DefArgExpr e))
-> loopAtom ls (VarArg e@(DefArgVar v))
-> = defPanic "Cyclic" "loopAtom" (Var e)
-> loopAtom ls (VarArg e@(Label _ _))
-> = defPanic "Cyclic" "loopAtom" (Var e)
-> loopAtom ls e@(LitArg l)
-> = returnLbl e
->
-> loopCaseAlts ls (AlgAlts as def) =
-> mapLbl loopAlgAlt as `thenLbl` \as ->
-> loopDefault ls def `thenLbl` \def ->
-> returnLbl (AlgAlts as def)
-> where
-> loopAlgAlt (c, vs, e) =
-> loop ls e `thenLbl` \e ->
-> returnLbl (c, vs, e)
-
-> loopCaseAlts ls (PrimAlts as def) =
-> mapLbl loopPrimAlt as `thenLbl` \as ->
-> loopDefault ls def `thenLbl` \def ->
-> returnLbl (PrimAlts as def)
-> where
-> loopPrimAlt (l, e) =
-> loop ls e `thenLbl` \e ->
-> returnLbl (l, e)
-
-> loopDefault ls NoDefault =
-> returnLbl NoDefault
-> loopDefault ls (BindDefault v e) =
-> loop ls e `thenLbl` \e ->
-> returnLbl (BindDefault v e)
-> -}
-
-> mkVar v = VarArg (DefArgExpr (Var (DefArgVar v)))
-
------------------------------------------------------------------------------
-The next function is applied to all deforestable functions which are
-placed in the environment. Given a list of free variables in the
-recursive set of which the function is a member, this funciton
-abstracts those variables, generates a new Id with the new type, and
-returns a substitution element which can be applied to all other
-expressions and function right hand sides that call this function.
-
- (freeVars e) \subseteq (freeVars l)
-
-> fixupFreeVars :: [Id] -> Id -> DefExpr -> ((Id,DefExpr),[(Id,DefExpr)])
-> fixupFreeVars total_fvs id e =
-> case fvs of
-> [] -> ((id,e),[])
-> _ -> let new_type =
-> glueTyArgs (map idType fvs)
-> (idType id)
-> new_id =
-> updateIdType id new_type
-> in
-> let
-> t = foldl App (Var (DefArgVar new_id))
-> (map mkVar fvs)
-> in
-> trace ("adding " ++ show (length fvs) ++ " args to " ++ show (ppr PprDebug id)) $
-> ((new_id, mkValLam fvs e), [(id,t)])
-> where
-> fvs = case e of
-> Lam bvs e -> filter (`notElem` bvs) total_fvs
-> _ -> total_fvs
-
-> swap (x,y) = (y,x)
-
-> applyRenaming :: [(Id,Id)] -> [Id] -> [Id]
-> applyRenaming r ids = map rename ids
-> where
-> rename x = case [ y | (x',y) <- r, x' `eqId` x ] of
-> [] -> panic "Cyclic(rename): no match in rename"
-> (y:_) -> y
-
-> mkLoopFunApp :: [Id] -> [TyVar] -> Id -> DefExpr
-> mkLoopFunApp val_args ty_args f =
-> foldl App
-> (foldl CoTyApp (Var (DefArgVar f))
-> (mkTyVarTys ty_args))
-> (map mkVar val_args)
-
------------------------------------------------------------------------------
-Removing duplicates from a list of definitions.
-
-> removeDuplicateDefinitions
-> :: [(DefExpr,(Id,DefExpr))] -- (label,(id,rhs))
-> -> UniqSM [(Id,DefExpr)]
-
-> removeDuplicateDefinitions defs =
-> foldrSUs rem ([],[]) defs `thenUs` \(newdefs,s) ->
-> mapUs (\(l,(f,e)) -> subst s e `thenUs` \e ->
-> returnUs (f, e)) newdefs
-> where
-
-> rem d@(l,(f,e)) (defs,s) =
-> findDup l defs `thenUs` \maybe ->
-> case maybe of
-> Nothing -> returnUs (d:defs,s)
-> Just g -> returnUs (defs, (f,(Var.DefArgVar) g):s)
-
-We insist that labels rename in both directions, is this necessary?
-
-> findDup l [] = returnUs Nothing
-> findDup l ((l',(f,e)):defs) =
-> renameExprs l l' `thenUs` \r ->
-> case r of
-> IsRenaming _ -> renameExprs l' l `thenUs` \r ->
-> case r of
-> IsRenaming r -> returnUs (Just f)
-> _ -> findDup l defs
-> _ -> findDup l defs
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