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Introducing a datatype for WorkLists that properly prioritizes equali…

…ties.

We were not prioritizing the interaction of equalities in the worklist, because
pre-canonicalization solved the constraints one by one, in their arrival order.
This patch fixes this, so it's a generally useful improvement, mainly for
efficiency. It makes #4981 go away, although it's not a definite answer to the
cause of the problem. See discussion on Trac.
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commit 5cfe9e92a92201043d5dbb1c4e10fef0ed0d9f49 1 parent 2d72a85
dimitris@microsoft.com authored
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81 compiler/typecheck/TcCanonical.lhs
@@ -1,7 +1,7 @@
\begin{code}
module TcCanonical(
- mkCanonical, mkCanonicals, mkCanonicalFEV, canWanteds, canGivens,
- canOccursCheck, canEq,
+ mkCanonical, mkCanonicals, mkCanonicalFEV, mkCanonicalFEVs, canWanteds, canGivens,
+ canOccursCheck, canEqToWorkList,
rewriteWithFunDeps
) where
@@ -218,28 +218,35 @@ flattenPred ctxt (EqPred ty1 ty2)
%************************************************************************
\begin{code}
-canWanteds :: [WantedEvVar] -> TcS CanonicalCts
-canWanteds = fmap andCCans . mapM (\(EvVarX ev loc) -> mkCanonical (Wanted loc) ev)
+canWanteds :: [WantedEvVar] -> TcS WorkList
+canWanteds = fmap unionWorkLists . mapM (\(EvVarX ev loc) -> mkCanonical (Wanted loc) ev)
-canGivens :: GivenLoc -> [EvVar] -> TcS CanonicalCts
+canGivens :: GivenLoc -> [EvVar] -> TcS WorkList
canGivens loc givens = do { ccs <- mapM (mkCanonical (Given loc)) givens
- ; return (andCCans ccs) }
+ ; return (unionWorkLists ccs) }
-mkCanonicals :: CtFlavor -> [EvVar] -> TcS CanonicalCts
-mkCanonicals fl vs = fmap andCCans (mapM (mkCanonical fl) vs)
+mkCanonicals :: CtFlavor -> [EvVar] -> TcS WorkList
+mkCanonicals fl vs = fmap unionWorkLists (mapM (mkCanonical fl) vs)
-mkCanonicalFEV :: FlavoredEvVar -> TcS CanonicalCts
+mkCanonicalFEV :: FlavoredEvVar -> TcS WorkList
mkCanonicalFEV (EvVarX ev fl) = mkCanonical fl ev
-mkCanonical :: CtFlavor -> EvVar -> TcS CanonicalCts
+mkCanonicalFEVs :: Bag FlavoredEvVar -> TcS WorkList
+mkCanonicalFEVs = foldrBagM canon_one emptyWorkList
+ where -- Preserves order (shouldn't be important, but curently
+ -- is important for the vectoriser)
+ canon_one fev wl = do { wl' <- mkCanonicalFEV fev
+ ; return (unionWorkList wl' wl) }
+
+mkCanonical :: CtFlavor -> EvVar -> TcS WorkList
mkCanonical fl ev = case evVarPred ev of
- ClassP clas tys -> canClass fl ev clas tys
- IParam ip ty -> canIP fl ev ip ty
- EqPred ty1 ty2 -> canEq fl ev ty1 ty2
+ ClassP clas tys -> canClassToWorkList fl ev clas tys
+ IParam ip ty -> canIPToWorkList fl ev ip ty
+ EqPred ty1 ty2 -> canEqToWorkList fl ev ty1 ty2
-canClass :: CtFlavor -> EvVar -> Class -> [TcType] -> TcS CanonicalCts
-canClass fl v cn tys
+canClassToWorkList :: CtFlavor -> EvVar -> Class -> [TcType] -> TcS WorkList
+canClassToWorkList fl v cn tys
= do { (xis,cos,ccs) <- flattenMany fl tys -- cos :: xis ~ tys
; let no_flattening_happened = isEmptyCCan ccs
dict_co = mkTyConCoercion (classTyCon cn) cos
@@ -256,13 +263,15 @@ canClass fl v cn tys
-- Add the superclasses of this one here, See Note [Adding superclasses].
-- But only if we are not simplifying the LHS of a rule.
; sctx <- getTcSContext
- ; sc_cts <- if simplEqsOnly sctx then return emptyCCan
+ ; sc_cts <- if simplEqsOnly sctx then return emptyWorkList
else newSCWorkFromFlavored v_new fl cn xis
- ; return (sc_cts `andCCan` ccs `extendCCans` CDictCan { cc_id = v_new
- , cc_flavor = fl
- , cc_class = cn
- , cc_tyargs = xis }) }
+ ; return (sc_cts `unionWorkList`
+ workListFromEqs ccs `unionWorkList`
+ workListFromNonEq CDictCan { cc_id = v_new
+ , cc_flavor = fl
+ , cc_class = cn
+ , cc_tyargs = xis }) }
\end{code}
Note [Adding superclasses]
@@ -330,12 +339,12 @@ happen.
\begin{code}
-newSCWorkFromFlavored :: EvVar -> CtFlavor -> Class -> [Xi] -> TcS CanonicalCts
+newSCWorkFromFlavored :: EvVar -> CtFlavor -> Class -> [Xi] -> TcS WorkList
-- Returns superclasses, see Note [Adding superclasses]
newSCWorkFromFlavored ev orig_flavor cls xis
| isDerived orig_flavor
- = return emptyCCan -- Deriveds don't yield more superclasses because we will
- -- add them transitively in the case of wanteds.
+ = return emptyWorkList -- Deriveds don't yield more superclasses because we will
+ -- add them transitively in the case of wanteds.
| isGiven orig_flavor
= do { let sc_theta = immSuperClasses cls xis
@@ -345,8 +354,8 @@ newSCWorkFromFlavored ev orig_flavor cls xis
; mkCanonicals flavor sc_vars }
| isEmptyVarSet (tyVarsOfTypes xis)
- = return emptyCCan -- Wanteds with no variables yield no deriveds.
- -- See Note [Improvement from Ground Wanteds]
+ = return emptyWorkList -- Wanteds with no variables yield no deriveds.
+ -- See Note [Improvement from Ground Wanteds]
| otherwise -- Wanted case, just add those SC that can lead to improvement.
= do { let sc_rec_theta = transSuperClasses cls xis
@@ -366,16 +375,20 @@ is_improvement_pty _ = False
-canIP :: CtFlavor -> EvVar -> IPName Name -> TcType -> TcS CanonicalCts
+canIPToWorkList :: CtFlavor -> EvVar -> IPName Name -> TcType -> TcS WorkList
-- See Note [Canonical implicit parameter constraints] to see why we don't
-- immediately canonicalize (flatten) IP constraints.
-canIP fl v nm ty
- = return $ singleCCan $ CIPCan { cc_id = v
- , cc_flavor = fl
- , cc_ip_nm = nm
- , cc_ip_ty = ty }
+canIPToWorkList fl v nm ty
+ = return $ workListFromNonEq (CIPCan { cc_id = v
+ , cc_flavor = fl
+ , cc_ip_nm = nm
+ , cc_ip_ty = ty })
-----------------
+canEqToWorkList :: CtFlavor -> EvVar -> Type -> Type -> TcS WorkList
+canEqToWorkList fl cv ty1 ty2 = do { cts <- canEq fl cv ty1 ty2
+ ; return $ workListFromEqs cts }
+
canEq :: CtFlavor -> EvVar -> Type -> Type -> TcS CanonicalCts
canEq fl cv ty1 ty2
| tcEqType ty1 ty2 -- Dealing with equality here avoids
@@ -1020,15 +1033,15 @@ now!).
\begin{code}
rewriteWithFunDeps :: [Equation]
-> [Xi] -> CtFlavor
- -> TcS (Maybe ([Xi], [Coercion], CanonicalCts))
+ -> TcS (Maybe ([Xi], [Coercion], WorkList))
rewriteWithFunDeps eqn_pred_locs xis fl
= do { fd_ev_poss <- mapM (instFunDepEqn fl) eqn_pred_locs
; let fd_ev_pos :: [(Int,FlavoredEvVar)]
fd_ev_pos = concat fd_ev_poss
(rewritten_xis, cos) = unzip (rewriteDictParams fd_ev_pos xis)
; fds <- mapM (\(_,fev) -> mkCanonicalFEV fev) fd_ev_pos
- ; let fd_work = unionManyBags fds
- ; if isEmptyBag fd_work
+ ; let fd_work = unionWorkLists fds
+ ; if isEmptyWorkList fd_work
then return Nothing
else return (Just (rewritten_xis, cos, fd_work)) }
View
82 compiler/typecheck/TcInteract.lhs
@@ -225,22 +225,6 @@ Note [Basic plan]
type AtomicInert = CanonicalCt -- constraint pulled from InertSet
type WorkItem = CanonicalCt -- constraint pulled from WorkList
--- A mixture of Given, Wanted, and Derived constraints.
--- We split between equalities and the rest to process equalities first.
-type WorkList = CanonicalCts
-
-unionWorkLists :: WorkList -> WorkList -> WorkList
-unionWorkLists = andCCan
-
-isEmptyWorkList :: WorkList -> Bool
-isEmptyWorkList = isEmptyCCan
-
-emptyWorkList :: WorkList
-emptyWorkList = emptyCCan
-
-workListFromCCan :: CanonicalCt -> WorkList
-workListFromCCan = singleCCan
-
------------------------
data StopOrContinue
= Stop -- Work item is consumed
@@ -305,7 +289,7 @@ runSolverPipeline depth pipeline inerts workItem
, sr_stop = ContinueWith work_item })
= do { itr <- stage depth work_item inerts
; traceTcS ("Stage result (" ++ name ++ ")") (ppr itr)
- ; let itr' = itr { sr_new_work = accum_work `unionWorkLists` sr_new_work itr }
+ ; let itr' = itr { sr_new_work = accum_work `unionWorkList` sr_new_work itr }
; run_pipeline stages itr' }
\end{code}
@@ -365,8 +349,10 @@ solveInteract inert ws
-> (ct,evVarPred ev)) ws)
, text "inert = " <+> ppr inert ]
- ; (flag, inert_ret) <- foldrBagM (tryPreSolveAndInteract sctx dyn_flags) (True,inert) ws
- -- use foldr to preserve the order
+ ; can_ws <- mkCanonicalFEVs ws
+
+ ; (flag, inert_ret)
+ <- foldrWorkListM (tryPreSolveAndInteract sctx dyn_flags) (True,inert) can_ws
; traceTcS "solveInteract, after clever canonicalization (and interaction):" $
vcat [ text "No interaction happened = " <+> ppr flag
@@ -374,27 +360,32 @@ solveInteract inert ws
; return (flag, inert_ret) }
-
tryPreSolveAndInteract :: SimplContext
-> DynFlags
- -> FlavoredEvVar
+ -> CanonicalCt
-> (Bool, InertSet)
-> TcS (Bool, InertSet)
-- Returns: True if it was able to discharge this constraint AND all previous ones
-tryPreSolveAndInteract sctx dyn_flags flavev@(EvVarX ev_var fl) (all_previous_discharged, inert)
+tryPreSolveAndInteract sctx dyn_flags ct (all_previous_discharged, inert)
= do { let inert_cts = get_inert_cts (evVarPred ev_var)
- ; this_one_discharged <- dischargeFromCCans inert_cts flavev
+ ; this_one_discharged <-
+ if isCFrozenErr ct then
+ return False
+ else
+ dischargeFromCCans inert_cts ev_var fl
; if this_one_discharged
then return (all_previous_discharged, inert)
else do
- { extra_cts <- mkCanonical fl ev_var
- ; inert_ret <- solveInteractWithDepth (ctxtStkDepth dyn_flags,0,[]) extra_cts inert
+ { inert_ret <- solveOneWithDepth (ctxtStkDepth dyn_flags,0,[]) ct inert
; return (False, inert_ret) } }
where
+ ev_var = cc_id ct
+ fl = cc_flavor ct
+
get_inert_cts (ClassP clas _)
| simplEqsOnly sctx = emptyCCan
| otherwise = fst (getRelevantCts clas (inert_dicts inert))
@@ -405,12 +396,12 @@ tryPreSolveAndInteract sctx dyn_flags flavev@(EvVarX ev_var fl) (all_previous_di
get_inert_cts (EqPred {})
= inert_eqs inert `unionBags` cCanMapToBag (inert_funeqs inert)
-dischargeFromCCans :: CanonicalCts -> FlavoredEvVar -> TcS Bool
+dischargeFromCCans :: CanonicalCts -> EvVar -> CtFlavor -> TcS Bool
-- See if this (pre-canonicalised) work-item is identical to a
-- one already in the inert set. Reasons:
-- a) Avoid creating superclass constraints for millions of incoming (Num a) constraints
-- b) Termination for improve_eqs in TcSimplify.simpl_loop
-dischargeFromCCans cans (EvVarX ev fl)
+dischargeFromCCans cans ev fl
= Bag.foldrBag discharge_ct (return False) cans
where
the_pred = evVarPred ev
@@ -469,11 +460,9 @@ solveInteractWithDepth ctxt@(max_depth,n,stack) ws inert
, text "Max depth =" <+> ppr max_depth
, text "ws =" <+> ppr ws ]
- -- Solve equalities first
- ; let (eqs, non_eqs) = Bag.partitionBag isCTyEqCan ws
- ; is_from_eqs <- Bag.foldrBagM (solveOneWithDepth ctxt) inert eqs
- ; Bag.foldrBagM (solveOneWithDepth ctxt) is_from_eqs non_eqs }
- -- use foldr to preserve the order
+
+ ; foldrWorkListM (solveOneWithDepth ctxt) inert ws }
+ -- use foldr to preserve the order
------------------
-- Fully interact the given work item with an inert set, and return a
@@ -834,7 +823,7 @@ data WhichComesFromInert = LeftComesFromInert | RightComesFromInert
interactWithInertEqsStage :: SimplifierStage
interactWithInertEqsStage depth workItem inert
= Bag.foldrBagM (interactNext depth) initITR (inert_eqs inert)
- -- use foldr to preserve the order
+ -- use foldr to preserve the order
where
initITR = SR { sr_inerts = inert { inert_eqs = emptyCCan }
, sr_new_work = emptyWorkList
@@ -893,7 +882,7 @@ interactNext depth inert it
= text rule <+> keep_doc
<+> vcat [ ptext (sLit "Inert =") <+> ppr inert
, ptext (sLit "Work =") <+> ppr work_item
- , ppUnless (isEmptyBag new_work) $
+ , ppUnless (isEmptyWorkList new_work) $
ptext (sLit "New =") <+> ppr new_work ]
keep_doc = case inert_action of
KeepInert -> ptext (sLit "[keep]")
@@ -909,7 +898,7 @@ interactNext depth inert it
DropInert -> inerts
; return $ SR { sr_inerts = inerts_new
- , sr_new_work = sr_new_work it `unionWorkLists` new_work
+ , sr_new_work = sr_new_work it `unionWorkList` new_work
, sr_stop = stop } }
| otherwise
= return $ it { sr_inerts = (sr_inerts it) `updInertSet` inert }
@@ -971,8 +960,8 @@ doInteractWithInert
-- and put it back into the work-list
-- Maybe rather than starting again, we could *replace* the
-- inert item, but its safe and simple to restart
- ; mkIRStopD "Cls/Cls fundep (solved)" (inert_w `consBag` fd_work) }
-
+ ; mkIRStopD "Cls/Cls fundep (solved)" $
+ workListFromNonEq inert_w `unionWorkList` fd_work }
| otherwise
-> do { setDictBind d2 (EvCast d1 dict_co)
; mkIRStopK "Cls/Cls fundep (solved)" fd_work }
@@ -998,7 +987,8 @@ doInteractWithInert
Wanted {} -> setDictBind d2 (EvCast d2' dict_co)
Derived {} -> return ()
; let workItem' = workItem { cc_id = d2', cc_tyargs = rewritten_tys2 }
- ; mkIRStopK "Cls/Cls fundep (partial)" (workItem' `consBag` fd_work) }
+ ; mkIRStopK "Cls/Cls fundep (partial)" $
+ workListFromNonEq workItem' `unionWorkList` fd_work }
where
dict_co = mkTyConCoercion (classTyCon cls1) cos2
@@ -1020,7 +1010,7 @@ doInteractWithInert (CDictCan { cc_id = dv, cc_flavor = ifl, cc_class = cl, cc_t
| wfl `canRewrite` ifl
, tv `elemVarSet` tyVarsOfTypes xis
= do { rewritten_dict <- rewriteDict (cv,tv,xi) (dv,ifl,cl,xis)
- ; mkIRContinue "Cls/Eq" workItem DropInert (workListFromCCan rewritten_dict) }
+ ; mkIRContinue "Cls/Eq" workItem DropInert (workListFromNonEq rewritten_dict) }
-- Class constraint and given equality: use the equality to rewrite
-- the class constraint.
@@ -1036,7 +1026,7 @@ doInteractWithInert (CIPCan { cc_id = ipid, cc_flavor = ifl, cc_ip_nm = nm, cc_i
| wfl `canRewrite` ifl
, tv `elemVarSet` tyVarsOfType ty
= do { rewritten_ip <- rewriteIP (cv,tv,xi) (ipid,ifl,nm,ty)
- ; mkIRContinue "IP/Eq" workItem DropInert (workListFromCCan rewritten_ip) }
+ ; mkIRContinue "IP/Eq" workItem DropInert (workListFromNonEq rewritten_ip) }
-- Two implicit parameter constraints. If the names are the same,
-- but their types are not, we generate a wanted type equality
@@ -1075,7 +1065,7 @@ doInteractWithInert (CTyEqCan { cc_id = cv1, cc_flavor = ifl, cc_tyvar = tv, cc_
| ifl `canRewrite` wfl
, tv `elemVarSet` tyVarsOfTypes (xi2:args) -- Rewrite RHS as well
= do { rewritten_funeq <- rewriteFunEq (cv1,tv,xi1) (cv2,wfl,tc,args,xi2)
- ; mkIRStopK "Eq/FunEq" (workListFromCCan rewritten_funeq) }
+ ; mkIRStopK "Eq/FunEq" (workListFromEq rewritten_funeq) }
-- Must Stop here, because we may no longer be inert after the rewritting.
-- Inert: function equality, work item: equality
@@ -1085,7 +1075,7 @@ doInteractWithInert (CFunEqCan {cc_id = cv1, cc_flavor = ifl, cc_fun = tc
| wfl `canRewrite` ifl
, tv `elemVarSet` tyVarsOfTypes (xi1:args) -- Rewrite RHS as well
= do { rewritten_funeq <- rewriteFunEq (cv2,tv,xi2) (cv1,ifl,tc,args,xi1)
- ; mkIRContinue "FunEq/Eq" workItem DropInert (workListFromCCan rewritten_funeq) }
+ ; mkIRContinue "FunEq/Eq" workItem DropInert (workListFromEq rewritten_funeq) }
-- One may think that we could (KeepTransformedInert rewritten_funeq)
-- but that is wrong, because it may end up not being inert with respect
-- to future inerts. Example:
@@ -1214,7 +1204,7 @@ rewriteEqRHS (cv1,tv1,xi1) (cv2,gw,tv2,xi2)
| Just tv2' <- tcGetTyVar_maybe xi2'
, tv2 == tv2' -- In this case xi2[xi1/tv1] = tv2, so we have tv2~tv2
= do { when (isWanted gw) (setCoBind cv2 (mkSymCoercion co2'))
- ; return emptyCCan }
+ ; return emptyWorkList }
| otherwise
= do { cv2' <- newCoVar (mkTyVarTy tv2) xi2'
; case gw of
@@ -1223,7 +1213,7 @@ rewriteEqRHS (cv1,tv1,xi1) (cv2,gw,tv2,xi2)
Given {} -> setCoBind cv2' $ mkCoVarCoercion cv2 `mkTransCoercion`
co2'
Derived {} -> return ()
- ; canEq gw cv2' (mkTyVarTy tv2) xi2' }
+ ; canEqToWorkList gw cv2' (mkTyVarTy tv2) xi2' }
where
xi2' = substTyWith [tv1] [xi1] xi2
co2' = substTyWith [tv1] [mkCoVarCoercion cv1] xi2 -- xi2 ~ xi2[xi1/tv1]
@@ -1269,7 +1259,7 @@ rewriteFrozen (cv1, tv1, xi1) (cv2, fl2)
Derived {} -> return ()
- ; return (singleCCan $ CFrozenErr { cc_id = cv2', cc_flavor = fl2 }) }
+ ; return (workListFromNonEq $ CFrozenErr { cc_id = cv2', cc_flavor = fl2 }) }
where
(ty2a, ty2b) = coVarKind cv2 -- cv2 : ty2a ~ ty2b
ty2a' = substTyWith [tv1] [xi1] ty2a
@@ -1750,7 +1740,7 @@ doTopReact workItem@(CDictCan { cc_id = dv, cc_flavor = fl@(Wanted loc)
; let workItem' = CDictCan { cc_id = dv', cc_flavor = fl,
cc_class = cls, cc_tyargs = xis' }
; return $
- SomeTopInt { tir_new_work = singleCCan workItem' `andCCan` fd_work
+ SomeTopInt { tir_new_work = workListFromNonEq workItem' `unionWorkList` fd_work
, tir_new_inert = Stop } } }
GenInst wtvs ev_term -- Solved
View
54 compiler/typecheck/TcSMonad.lhs
@@ -8,6 +8,10 @@ module TcSMonad (
isCDictCan_Maybe, isCIPCan_Maybe, isCFunEqCan_Maybe,
isCFrozenErr,
+ WorkList, unionWorkList, unionWorkLists, isEmptyWorkList, emptyWorkList,
+ workListFromEq, workListFromNonEq,
+ workListFromEqs, workListFromNonEqs, foldrWorkListM,
+
CanonicalCt(..), Xi, tyVarsOfCanonical, tyVarsOfCanonicals, tyVarsOfCDicts,
deCanonicalise, mkFrozenError,
@@ -257,8 +261,58 @@ isCFunEqCan_Maybe _ = Nothing
isCFrozenErr :: CanonicalCt -> Bool
isCFrozenErr (CFrozenErr {}) = True
isCFrozenErr _ = False
+
+
+-- A mixture of Given, Wanted, and Derived constraints.
+-- We split between equalities and the rest to process equalities first.
+data WorkList = WorkList { weqs :: CanonicalCts
+ -- NB: weqs includes equalities /and/ family equalities
+ , wrest :: CanonicalCts }
+
+unionWorkList :: WorkList -> WorkList -> WorkList
+unionWorkList wl1 wl2
+ = WorkList { weqs = weqs wl1 `andCCan` weqs wl2
+ , wrest = wrest wl1 `andCCan` wrest wl2 }
+
+unionWorkLists :: [WorkList] -> WorkList
+unionWorkLists = foldr unionWorkList emptyWorkList
+
+isEmptyWorkList :: WorkList -> Bool
+isEmptyWorkList wl = isEmptyCCan (weqs wl) && isEmptyCCan (wrest wl)
+
+emptyWorkList :: WorkList
+emptyWorkList
+ = WorkList { weqs = emptyBag, wrest = emptyBag }
+
+workListFromEq :: CanonicalCt -> WorkList
+workListFromEq = workListFromEqs . singleCCan
+
+workListFromNonEq :: CanonicalCt -> WorkList
+workListFromNonEq = workListFromNonEqs . singleCCan
+
+workListFromNonEqs :: CanonicalCts -> WorkList
+workListFromNonEqs cts
+ = WorkList { weqs = emptyCCan, wrest = cts }
+
+workListFromEqs :: CanonicalCts -> WorkList
+workListFromEqs cts
+ = WorkList { weqs = cts, wrest = emptyCCan }
+
+foldrWorkListM :: (Monad m) => (CanonicalCt -> r -> m r)
+ -> r -> WorkList -> m r
+-- Prioritizes equalities
+foldrWorkListM on_ct r (WorkList {weqs = eqs, wrest = rest })
+ = do { r1 <- foldrBagM on_ct r eqs
+ ; foldrBagM on_ct r1 rest }
+
+instance Outputable WorkList where
+ ppr wl = vcat [ text "WorkList (Equalities) = " <+> ppr (weqs wl)
+ , text "WorkList (Other) = " <+> ppr (wrest wl) ]
+
\end{code}
+
+
%************************************************************************
%* *
CtFlavor
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