X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2Fspecialise%2FSpecConstr.lhs;h=f214f0cae8d2e1d10f9bdf3fb17c3203407a7a3a;hp=03dd3f55dcbd1ba0ae485c3d86536aff84292265;hb=e95ee1f718c6915c478005aad8af81705357d6ab;hpb=426d9b8565b66eeb7d27725e8823784769cfca48 diff --git a/compiler/specialise/SpecConstr.lhs b/compiler/specialise/SpecConstr.lhs index 03dd3f5..f214f0c 100644 --- a/compiler/specialise/SpecConstr.lhs +++ b/compiler/specialise/SpecConstr.lhs @@ -4,40 +4,54 @@ \section[SpecConstr]{Specialise over constructors} \begin{code} +-- The above warning supression flag is a temporary kludge. +-- While working on this module you are encouraged to remove it and fix +-- any warnings in the module. See +-- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings +-- for details + module SpecConstr( - specConstrProgram + specConstrProgram, SpecConstrAnnotation(..) ) where #include "HsVersions.h" import CoreSyn -import CoreLint ( showPass, endPass ) -import CoreUtils ( exprType, tcEqExpr, mkPiTypes ) +import CoreSubst +import CoreUtils +import CoreUnfold ( couldBeSmallEnoughToInline ) import CoreFVs ( exprsFreeVars ) -import CoreSubst ( Subst, mkSubst, substExpr ) -import CoreTidy ( tidyRules ) -import PprCore ( pprRules ) +import CoreMonad +import HscTypes ( ModGuts(..) ) import WwLib ( mkWorkerArgs ) -import DataCon ( dataConRepArity, isVanillaDataCon ) -import Type ( tyConAppArgs, tyVarsOfTypes ) -import Unify ( coreRefineTys ) -import Id ( Id, idName, idType, isDataConWorkId_maybe, - mkUserLocal, mkSysLocal, idUnfolding ) -import Var ( Var ) +import DataCon ( dataConTyCon, dataConRepArity, dataConUnivTyVars ) +import TyCon ( TyCon ) +import Literal ( literalType ) +import Coercion +import Rules +import Type hiding( substTy ) +import Id +import MkCore ( mkImpossibleExpr ) +import Var import VarEnv import VarSet -import Name ( nameOccName, nameSrcLoc ) -import Rules ( addIdSpecialisations, mkLocalRule, rulesOfBinds ) -import OccName ( mkSpecOcc ) -import ErrUtils ( dumpIfSet_dyn ) -import DynFlags ( DynFlags, DynFlag(..) ) -import BasicTypes ( Activation(..) ) -import Maybes ( orElse ) -import Util ( mapAccumL, lengthAtLeast, notNull ) -import List ( nubBy, partition ) +import Name +import BasicTypes +import DynFlags ( DynFlags(..) ) +import StaticFlags ( opt_PprStyle_Debug ) +import Maybes ( orElse, catMaybes, isJust, isNothing ) +import Demand +import DmdAnal ( both ) +import Serialized ( deserializeWithData ) +import Util import UniqSupply import Outputable import FastString +import UniqFM +import MonadUtils +import Control.Monad ( zipWithM ) +import Data.List +import Data.Data ( Data, Typeable ) \end{code} ----------------------------------------------------- @@ -93,9 +107,55 @@ In Core, by the time we've w/wd (f is strict in i) we get At the call to f, we see that the argument, n is know to be (I# n#), and n is evaluated elsewhere in the body of f, so we can play the same -trick as above. However we don't want to do that if the boxed version -of n is needed (else we'd avoid the eval but pay more for re-boxing n). -So in this case we want that the *only* uses of n are in case statements. +trick as above. + + +Note [Reboxing] +~~~~~~~~~~~~~~~ +We must be careful not to allocate the same constructor twice. Consider + f p = (...(case p of (a,b) -> e)...p..., + ...let t = (r,s) in ...t...(f t)...) +At the recursive call to f, we can see that t is a pair. But we do NOT want +to make a specialised copy: + f' a b = let p = (a,b) in (..., ...) +because now t is allocated by the caller, then r and s are passed to the +recursive call, which allocates the (r,s) pair again. + +This happens if + (a) the argument p is used in other than a case-scrutinsation way. + (b) the argument to the call is not a 'fresh' tuple; you have to + look into its unfolding to see that it's a tuple + +Hence the "OR" part of Note [Good arguments] below. + +ALTERNATIVE 2: pass both boxed and unboxed versions. This no longer saves +allocation, but does perhaps save evals. In the RULE we'd have +something like + + f (I# x#) = f' (I# x#) x# + +If at the call site the (I# x) was an unfolding, then we'd have to +rely on CSE to eliminate the duplicate allocation.... This alternative +doesn't look attractive enough to pursue. + +ALTERNATIVE 3: ignore the reboxing problem. The trouble is that +the conservative reboxing story prevents many useful functions from being +specialised. Example: + foo :: Maybe Int -> Int -> Int + foo (Just m) 0 = 0 + foo x@(Just m) n = foo x (n-m) +Here the use of 'x' will clearly not require boxing in the specialised function. + +The strictness analyser has the same problem, in fact. Example: + f p@(a,b) = ... +If we pass just 'a' and 'b' to the worker, it might need to rebox the +pair to create (a,b). A more sophisticated analysis might figure out +precisely the cases in which this could happen, but the strictness +analyser does no such analysis; it just passes 'a' and 'b', and hopes +for the best. + +So my current choice is to make SpecConstr similarly aggressive, and +ignore the bad potential of reboxing. Note [Good arguments] @@ -121,7 +181,7 @@ So we look for That same parameter is scrutinised by a case somewhere in the RHS of the function AND - Those are the only uses of the parameter + Those are the only uses of the parameter (see Note [Reboxing]) What to abstract over @@ -192,6 +252,171 @@ is to run deShadowBinds before running SpecConstr, but instead we run the simplifier. That gives the simplest possible program for SpecConstr to chew on; and it virtually guarantees no shadowing. +Note [Specialising for constant parameters] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +This one is about specialising on a *constant* (but not necessarily +constructor) argument + + foo :: Int -> (Int -> Int) -> Int + foo 0 f = 0 + foo m f = foo (f m) (+1) + +It produces + + lvl_rmV :: GHC.Base.Int -> GHC.Base.Int + lvl_rmV = + \ (ds_dlk :: GHC.Base.Int) -> + case ds_dlk of wild_alH { GHC.Base.I# x_alG -> + GHC.Base.I# (GHC.Prim.+# x_alG 1) + + T.$wfoo :: GHC.Prim.Int# -> (GHC.Base.Int -> GHC.Base.Int) -> + GHC.Prim.Int# + T.$wfoo = + \ (ww_sme :: GHC.Prim.Int#) (w_smg :: GHC.Base.Int -> GHC.Base.Int) -> + case ww_sme of ds_Xlw { + __DEFAULT -> + case w_smg (GHC.Base.I# ds_Xlw) of w1_Xmo { GHC.Base.I# ww1_Xmz -> + T.$wfoo ww1_Xmz lvl_rmV + }; + 0 -> 0 + } + +The recursive call has lvl_rmV as its argument, so we could create a specialised copy +with that argument baked in; that is, not passed at all. Now it can perhaps be inlined. + +When is this worth it? Call the constant 'lvl' +- If 'lvl' has an unfolding that is a constructor, see if the corresponding + parameter is scrutinised anywhere in the body. + +- If 'lvl' has an unfolding that is a inlinable function, see if the corresponding + parameter is applied (...to enough arguments...?) + + Also do this is if the function has RULES? + +Also + +Note [Specialising for lambda parameters] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + foo :: Int -> (Int -> Int) -> Int + foo 0 f = 0 + foo m f = foo (f m) (\n -> n-m) + +This is subtly different from the previous one in that we get an +explicit lambda as the argument: + + T.$wfoo :: GHC.Prim.Int# -> (GHC.Base.Int -> GHC.Base.Int) -> + GHC.Prim.Int# + T.$wfoo = + \ (ww_sm8 :: GHC.Prim.Int#) (w_sma :: GHC.Base.Int -> GHC.Base.Int) -> + case ww_sm8 of ds_Xlr { + __DEFAULT -> + case w_sma (GHC.Base.I# ds_Xlr) of w1_Xmf { GHC.Base.I# ww1_Xmq -> + T.$wfoo + ww1_Xmq + (\ (n_ad3 :: GHC.Base.Int) -> + case n_ad3 of wild_alB { GHC.Base.I# x_alA -> + GHC.Base.I# (GHC.Prim.-# x_alA ds_Xlr) + }) + }; + 0 -> 0 + } + +I wonder if SpecConstr couldn't be extended to handle this? After all, +lambda is a sort of constructor for functions and perhaps it already +has most of the necessary machinery? + +Furthermore, there's an immediate win, because you don't need to allocate the lamda +at the call site; and if perchance it's called in the recursive call, then you +may avoid allocating it altogether. Just like for constructors. + +Looks cool, but probably rare...but it might be easy to implement. + + +Note [SpecConstr for casts] +~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Consider + data family T a :: * + data instance T Int = T Int + + foo n = ... + where + go (T 0) = 0 + go (T n) = go (T (n-1)) + +The recursive call ends up looking like + go (T (I# ...) `cast` g) +So we want to spot the construtor application inside the cast. +That's why we have the Cast case in argToPat + +Note [Local recursive groups] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +For a *local* recursive group, we can see all the calls to the +function, so we seed the specialisation loop from the calls in the +body, not from the calls in the RHS. Consider: + + bar m n = foo n (n,n) (n,n) (n,n) (n,n) + where + foo n p q r s + | n == 0 = m + | n > 3000 = case p of { (p1,p2) -> foo (n-1) (p2,p1) q r s } + | n > 2000 = case q of { (q1,q2) -> foo (n-1) p (q2,q1) r s } + | n > 1000 = case r of { (r1,r2) -> foo (n-1) p q (r2,r1) s } + | otherwise = case s of { (s1,s2) -> foo (n-1) p q r (s2,s1) } + +If we start with the RHSs of 'foo', we get lots and lots of specialisations, +most of which are not needed. But if we start with the (single) call +in the rhs of 'bar' we get exactly one fully-specialised copy, and all +the recursive calls go to this fully-specialised copy. Indeed, the original +function is later collected as dead code. This is very important in +specialising the loops arising from stream fusion, for example in NDP where +we were getting literally hundreds of (mostly unused) specialisations of +a local function. + +Note [Do not specialise diverging functions] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Specialising a function that just diverges is a waste of code. +Furthermore, it broke GHC (simpl014) thus: + {-# STR Sb #-} + f = \x. case x of (a,b) -> f x +If we specialise f we get + f = \x. case x of (a,b) -> fspec a b +But fspec doesn't have decent strictnes info. As it happened, +(f x) :: IO t, so the state hack applied and we eta expanded fspec, +and hence f. But now f's strictness is less than its arity, which +breaks an invariant. + +Note [Forcing specialisation] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +With stream fusion and in other similar cases, we want to fully specialise +some (but not necessarily all!) loops regardless of their size and the +number of specialisations. We allow a library to specify this by annotating +a type with ForceSpecConstr and then adding a parameter of that type to the +loop. Here is a (simplified) example from the vector library: + + data SPEC = SPEC | SPEC2 + {-# ANN type SPEC ForceSpecConstr #-} + + foldl :: (a -> b -> a) -> a -> Stream b -> a + {-# INLINE foldl #-} + foldl f z (Stream step s _) = foldl_loop SPEC z s + where + foldl_loop SPEC z s = case step s of + Yield x s' -> foldl_loop SPEC (f z x) s' + Skip -> foldl_loop SPEC z s' + Done -> z + +SpecConstr will spot the SPEC parameter and always fully specialise +foldl_loop. Note that we can't just annotate foldl_loop since it isn't a +top-level function but even if we could, inlining etc. could easily drop the +annotation. We also have to prevent the SPEC argument from being removed by +w/w which is why SPEC is a sum type. This is all quite ugly; we ought to come +up with a better design. + +ForceSpecConstr arguments are spotted in scExpr' and scTopBinds which then set +force_spec to True when calling specLoop. This flag makes specLoop and +specialise ignore specConstrCount and specConstrThreshold when deciding +whether to specialise a function. + ----------------------------------------------------- Stuff not yet handled ----------------------------------------------------- @@ -264,70 +489,22 @@ We get two specialisations: = Foo.$s$wfoo y_aFp sc_sGC ; But perhaps the first one isn't good. After all, we know that tpl_B2 is -a T (I# x) really! - +a T (I# x) really, because T is strict and Int has one constructor. (We can't +unbox the strict fields, becuase T is polymorphic!) -Example 3 -~~~~~~~~~ -This one is about specialising on a *lambda* argument - - foo :: Int -> (Int -> Int) -> Int - foo 0 f = 0 - foo m f = foo (f m) (+1) - -It produces - - lvl_rmV :: GHC.Base.Int -> GHC.Base.Int - lvl_rmV = - \ (ds_dlk :: GHC.Base.Int) -> - case ds_dlk of wild_alH { GHC.Base.I# x_alG -> - GHC.Base.I# (GHC.Prim.+# x_alG 1) - - T.$wfoo :: GHC.Prim.Int# -> (GHC.Base.Int -> GHC.Base.Int) -> - GHC.Prim.Int# - T.$wfoo = - \ (ww_sme :: GHC.Prim.Int#) (w_smg :: GHC.Base.Int -> GHC.Base.Int) -> - case ww_sme of ds_Xlw { - __DEFAULT -> - case w_smg (GHC.Base.I# ds_Xlw) of w1_Xmo { GHC.Base.I# ww1_Xmz -> - T.$wfoo ww1_Xmz lvl_rmV - }; - 0 -> 0 - } - -Of course, it would be much nicer if the optimiser specialised $wfoo for -when lvl_rmV is passed as the second argument and then inlined it. - -Example 4 -~~~~~~~~~ - foo :: Int -> (Int -> Int) -> Int - foo 0 f = 0 - foo m f = foo (f m) (\n -> n-m) - -This is subtly different from the previous one in that we get an -explicit lambda as the argument: - - T.$wfoo :: GHC.Prim.Int# -> (GHC.Base.Int -> GHC.Base.Int) -> - GHC.Prim.Int# - T.$wfoo = - \ (ww_sm8 :: GHC.Prim.Int#) (w_sma :: GHC.Base.Int -> GHC.Base.Int) -> - case ww_sm8 of ds_Xlr { - __DEFAULT -> - case w_sma (GHC.Base.I# ds_Xlr) of w1_Xmf { GHC.Base.I# ww1_Xmq -> - T.$wfoo - ww1_Xmq - (\ (n_ad3 :: GHC.Base.Int) -> - case n_ad3 of wild_alB { GHC.Base.I# x_alA -> - GHC.Base.I# (GHC.Prim.-# x_alA ds_Xlr) - }) - }; - 0 -> 0 - } +%************************************************************************ +%* * +\subsection{Annotations} +%* * +%************************************************************************ -I wonder if SpecConstr couldn't be extended to handle this? After all, -lambda is a sort of constructor for functions and perhaps it already -has most of the necessary machinery? +Annotating a type with NoSpecConstr will make SpecConstr not specialise +for arguments of that type. +\begin{code} +data SpecConstrAnnotation = NoSpecConstr | ForceSpecConstr + deriving( Data, Typeable, Eq ) +\end{code} %************************************************************************ %* * @@ -336,24 +513,19 @@ has most of the necessary machinery? %************************************************************************ \begin{code} -specConstrProgram :: DynFlags -> UniqSupply -> [CoreBind] -> IO [CoreBind] -specConstrProgram dflags us binds +specConstrProgram :: ModGuts -> CoreM ModGuts +specConstrProgram guts = do - showPass dflags "SpecConstr" - - let (binds', _) = initUs us (go emptyScEnv binds) - - endPass dflags "SpecConstr" Opt_D_dump_spec binds' - - dumpIfSet_dyn dflags Opt_D_dump_rules "Top-level specialisations" - (pprRules (tidyRules emptyTidyEnv (rulesOfBinds binds'))) - - return binds' + dflags <- getDynFlags + us <- getUniqueSupplyM + annos <- getFirstAnnotations deserializeWithData guts + let binds' = fst $ initUs us (go (initScEnv dflags annos) (mg_binds guts)) + return (guts { mg_binds = binds' }) where - go env [] = returnUs [] - go env (bind:binds) = scBind env bind `thenUs` \ (env', _, bind') -> - go env' binds `thenUs` \ binds' -> - returnUs (bind' : binds') + go _ [] = return [] + go env (bind:binds) = do (env', bind') <- scTopBind env bind + binds' <- go env' binds + return (bind' : binds') \end{code} @@ -364,111 +536,218 @@ specConstrProgram dflags us binds %************************************************************************ \begin{code} -data ScEnv = SCE { scope :: VarEnv HowBound, - -- Binds all non-top-level variables in scope +data ScEnv = SCE { sc_size :: Maybe Int, -- Size threshold + sc_count :: Maybe Int, -- Max # of specialisations for any one fn + -- See Note [Avoiding exponential blowup] + + sc_subst :: Subst, -- Current substitution + -- Maps InIds to OutExprs - cons :: ConstrEnv + sc_how_bound :: HowBoundEnv, + -- Binds interesting non-top-level variables + -- Domain is OutVars (*after* applying the substitution) + + sc_vals :: ValueEnv, + -- Domain is OutIds (*after* applying the substitution) + -- Used even for top-level bindings (but not imported ones) + + sc_annotations :: UniqFM SpecConstrAnnotation } -type ConstrEnv = IdEnv ConValue -data ConValue = CV AltCon [CoreArg] - -- Variables known to be bound to a constructor - -- in a particular case alternative +--------------------- +-- As we go, we apply a substitution (sc_subst) to the current term +type InExpr = CoreExpr -- _Before_ applying the subst +type InVar = Var +type OutExpr = CoreExpr -- _After_ applying the subst +type OutId = Id +type OutVar = Var -instance Outputable ConValue where - ppr (CV con args) = ppr con <+> interpp'SP args +--------------------- +type HowBoundEnv = VarEnv HowBound -- Domain is OutVars -refineConstrEnv :: Subst -> ConstrEnv -> ConstrEnv --- The substitution is a type substitution only -refineConstrEnv subst env = mapVarEnv refine_con_value env - where - refine_con_value (CV con args) = CV con (map (substExpr subst) args) +--------------------- +type ValueEnv = IdEnv Value -- Domain is OutIds +data Value = ConVal AltCon [CoreArg] -- _Saturated_ constructors + | LambdaVal -- Inlinable lambdas or PAPs -emptyScEnv = SCE { scope = emptyVarEnv, cons = emptyVarEnv } +instance Outputable Value where + ppr (ConVal con args) = ppr con <+> interpp'SP args + ppr LambdaVal = ptext (sLit "") -data HowBound = RecFun -- These are the recursive functions for which - -- we seek interesting call patterns +--------------------- +initScEnv :: DynFlags -> UniqFM SpecConstrAnnotation -> ScEnv +initScEnv dflags anns + = SCE { sc_size = specConstrThreshold dflags, + sc_count = specConstrCount dflags, + sc_subst = emptySubst, + sc_how_bound = emptyVarEnv, + sc_vals = emptyVarEnv, + sc_annotations = anns } - | RecArg -- These are those functions' arguments; we are - -- interested to see if those arguments are scrutinised +data HowBound = RecFun -- These are the recursive functions for which + -- we seek interesting call patterns - | Other -- We track all others so we know what's in scope - -- This is used in spec_one to check what needs to be - -- passed as a parameter and what is in scope at the - -- function definition site + | RecArg -- These are those functions' arguments, or their sub-components; + -- we gather occurrence information for these instance Outputable HowBound where ppr RecFun = text "RecFun" ppr RecArg = text "RecArg" - ppr Other = text "Other" -lookupScopeEnv env v = lookupVarEnv (scope env) v +lookupHowBound :: ScEnv -> Id -> Maybe HowBound +lookupHowBound env id = lookupVarEnv (sc_how_bound env) id -extendBndrs env bndrs = env { scope = extendVarEnvList (scope env) [(b,Other) | b <- bndrs] } -extendBndr env bndr = env { scope = extendVarEnv (scope env) bndr Other } +scSubstId :: ScEnv -> Id -> CoreExpr +scSubstId env v = lookupIdSubst (text "scSubstId") (sc_subst env) v - -- When we encounter - -- case scrut of b - -- C x y -> ... - -- we want to bind b, and perhaps scrut too, to (C x y) -extendCaseBndrs :: ScEnv -> Id -> CoreExpr -> AltCon -> [Var] -> ScEnv -extendCaseBndrs env case_bndr scrut DEFAULT alt_bndrs - = extendBndrs env (case_bndr : alt_bndrs) +scSubstTy :: ScEnv -> Type -> Type +scSubstTy env ty = substTy (sc_subst env) ty -extendCaseBndrs env case_bndr scrut con@(LitAlt lit) alt_bndrs - = ASSERT( null alt_bndrs ) extendAlt env case_bndr scrut (CV con []) [] +zapScSubst :: ScEnv -> ScEnv +zapScSubst env = env { sc_subst = zapSubstEnv (sc_subst env) } -extendCaseBndrs env case_bndr scrut con@(DataAlt data_con) alt_bndrs - | isVanillaDataCon data_con - = extendAlt env case_bndr scrut (CV con vanilla_args) alt_bndrs - - | otherwise -- GADT - = extendAlt env1 case_bndr scrut (CV con gadt_args) alt_bndrs +extendScInScope :: ScEnv -> [Var] -> ScEnv + -- Bring the quantified variables into scope +extendScInScope env qvars = env { sc_subst = extendInScopeList (sc_subst env) qvars } + + -- Extend the substitution +extendScSubst :: ScEnv -> Var -> OutExpr -> ScEnv +extendScSubst env var expr = env { sc_subst = extendSubst (sc_subst env) var expr } + +extendScSubstList :: ScEnv -> [(Var,OutExpr)] -> ScEnv +extendScSubstList env prs = env { sc_subst = extendSubstList (sc_subst env) prs } + +extendHowBound :: ScEnv -> [Var] -> HowBound -> ScEnv +extendHowBound env bndrs how_bound + = env { sc_how_bound = extendVarEnvList (sc_how_bound env) + [(bndr,how_bound) | bndr <- bndrs] } + +extendBndrsWith :: HowBound -> ScEnv -> [Var] -> (ScEnv, [Var]) +extendBndrsWith how_bound env bndrs + = (env { sc_subst = subst', sc_how_bound = hb_env' }, bndrs') + where + (subst', bndrs') = substBndrs (sc_subst env) bndrs + hb_env' = sc_how_bound env `extendVarEnvList` + [(bndr,how_bound) | bndr <- bndrs'] + +extendBndrWith :: HowBound -> ScEnv -> Var -> (ScEnv, Var) +extendBndrWith how_bound env bndr + = (env { sc_subst = subst', sc_how_bound = hb_env' }, bndr') where - vanilla_args = map Type (tyConAppArgs (idType case_bndr)) ++ - map varToCoreExpr alt_bndrs - - gadt_args = map (substExpr subst . varToCoreExpr) alt_bndrs - -- This call generates some bogus warnings from substExpr, - -- because it's inconvenient to put all the Ids in scope - -- Will be fixed when we move to FC - - (alt_tvs, _) = span isTyVar alt_bndrs - Just (tv_subst, is_local) = coreRefineTys data_con alt_tvs (idType case_bndr) - subst = mkSubst in_scope tv_subst emptyVarEnv -- No Id substitition - in_scope = mkInScopeSet (tyVarsOfTypes (varEnvElts tv_subst)) - - env1 | is_local = env - | otherwise = env { cons = refineConstrEnv subst (cons env) } - - - -extendAlt :: ScEnv -> Id -> CoreExpr -> ConValue -> [Var] -> ScEnv -extendAlt env case_bndr scrut val alt_bndrs - = let - env1 = SCE { scope = extendVarEnvList (scope env) [(b,Other) | b <- case_bndr : alt_bndrs], - cons = extendVarEnv (cons env) case_bndr val } - in - case scrut of - Var v -> -- Bind the scrutinee in the ConstrEnv if it's a variable - -- Also forget if the scrutinee is a RecArg, because we're - -- now in the branch of a case, and we don't want to - -- record a non-scrutinee use of v if we have - -- case v of { (a,b) -> ...(f v)... } - SCE { scope = extendVarEnv (scope env1) v Other, - cons = extendVarEnv (cons env1) v val } - other -> env1 - - -- When we encounter a recursive function binding - -- f = \x y -> ... - -- we want to extend the scope env with bindings - -- that record that f is a RecFn and x,y are RecArgs -extendRecBndr env fn bndrs - = env { scope = scope env `extendVarEnvList` - ((fn,RecFun): [(bndr,RecArg) | bndr <- bndrs]) } + (subst', bndr') = substBndr (sc_subst env) bndr + hb_env' = extendVarEnv (sc_how_bound env) bndr' how_bound + +extendRecBndrs :: ScEnv -> [Var] -> (ScEnv, [Var]) +extendRecBndrs env bndrs = (env { sc_subst = subst' }, bndrs') + where + (subst', bndrs') = substRecBndrs (sc_subst env) bndrs + +extendBndr :: ScEnv -> Var -> (ScEnv, Var) +extendBndr env bndr = (env { sc_subst = subst' }, bndr') + where + (subst', bndr') = substBndr (sc_subst env) bndr + +extendValEnv :: ScEnv -> Id -> Maybe Value -> ScEnv +extendValEnv env _ Nothing = env +extendValEnv env id (Just cv) = env { sc_vals = extendVarEnv (sc_vals env) id cv } + +extendCaseBndrs :: ScEnv -> Id -> AltCon -> [Var] -> (ScEnv, [Var]) +-- When we encounter +-- case scrut of b +-- C x y -> ... +-- we want to bind b, to (C x y) +-- NB1: Extends only the sc_vals part of the envt +-- NB2: Kill the dead-ness info on the pattern binders x,y, since +-- they are potentially made alive by the [b -> C x y] binding +extendCaseBndrs env case_bndr con alt_bndrs + | isDeadBinder case_bndr + = (env, alt_bndrs) + | otherwise + = (env1, map zap alt_bndrs) + -- NB: We used to bind v too, if scrut = (Var v); but + -- the simplifer has already done this so it seems + -- redundant to do so here + -- case scrut of + -- Var v -> extendValEnv env1 v cval + -- _other -> env1 + where + zap v | isTyCoVar v = v -- See NB2 above + | otherwise = zapIdOccInfo v + env1 = extendValEnv env case_bndr cval + cval = case con of + DEFAULT -> Nothing + LitAlt {} -> Just (ConVal con []) + DataAlt {} -> Just (ConVal con vanilla_args) + where + vanilla_args = map Type (tyConAppArgs (idType case_bndr)) ++ + varsToCoreExprs alt_bndrs + +ignoreTyCon :: ScEnv -> TyCon -> Bool +ignoreTyCon env tycon + = lookupUFM (sc_annotations env) tycon == Just NoSpecConstr + +ignoreType :: ScEnv -> Type -> Bool +ignoreType env ty + = case splitTyConApp_maybe ty of + Just (tycon, _) -> ignoreTyCon env tycon + _ -> False + +ignoreAltCon :: ScEnv -> AltCon -> Bool +ignoreAltCon env (DataAlt dc) = ignoreTyCon env (dataConTyCon dc) +ignoreAltCon env (LitAlt lit) = ignoreType env (literalType lit) +ignoreAltCon _ DEFAULT = True + +forceSpecBndr :: ScEnv -> Var -> Bool +forceSpecBndr env var = forceSpecFunTy env . snd . splitForAllTys . varType $ var + +forceSpecFunTy :: ScEnv -> Type -> Bool +forceSpecFunTy env = any (forceSpecArgTy env) . fst . splitFunTys + +forceSpecArgTy :: ScEnv -> Type -> Bool +forceSpecArgTy env ty + | Just ty' <- coreView ty = forceSpecArgTy env ty' + +forceSpecArgTy env ty + | Just (tycon, tys) <- splitTyConApp_maybe ty + , tycon /= funTyCon + = lookupUFM (sc_annotations env) tycon == Just ForceSpecConstr + || any (forceSpecArgTy env) tys + +forceSpecArgTy _ _ = False + +decreaseSpecCount :: ScEnv -> Int -> ScEnv +-- See Note [Avoiding exponential blowup] +decreaseSpecCount env n_specs + = env { sc_count = case sc_count env of + Nothing -> Nothing + Just n -> Just (n `div` (n_specs + 1)) } + -- The "+1" takes account of the original function; + -- See Note [Avoiding exponential blowup] \end{code} +Note [Avoiding exponential blowup] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +The sc_count field of the ScEnv says how many times we are prepared to +duplicate a single function. But we must take care with recursive +specialiations. Consider + + let $j1 = let $j2 = let $j3 = ... + in + ...$j3... + in + ...$j2... + in + ...$j1... + +If we specialise $j1 then in each specialisation (as well as the original) +we can specialise $j2, and similarly $j3. Even if we make just *one* +specialisation of each, becuase we also have the original we'll get 2^n +copies of $j3, which is not good. + +So when recursively specialising we divide the sc_count by the number of +copies we are making at this level, including the original. + %************************************************************************ %* * @@ -479,40 +758,110 @@ extendRecBndr env fn bndrs \begin{code} data ScUsage = SCU { - calls :: !(IdEnv ([Call])), -- Calls + scu_calls :: CallEnv, -- Calls -- The functions are a subset of the -- RecFuns in the ScEnv - occs :: !(IdEnv ArgOcc) -- Information on argument occurrences - } -- The variables are a subset of the - -- RecArg in the ScEnv + scu_occs :: !(IdEnv ArgOcc) -- Information on argument occurrences + } -- The domain is OutIds -type Call = (ConstrEnv, [CoreArg]) +type CallEnv = IdEnv [Call] +type Call = (ValueEnv, [CoreArg]) -- The arguments of the call, together with the -- env giving the constructor bindings at the call site -nullUsage = SCU { calls = emptyVarEnv, occs = emptyVarEnv } +nullUsage :: ScUsage +nullUsage = SCU { scu_calls = emptyVarEnv, scu_occs = emptyVarEnv } -combineUsage u1 u2 = SCU { calls = plusVarEnv_C (++) (calls u1) (calls u2), - occs = plusVarEnv_C combineOcc (occs u1) (occs u2) } +combineCalls :: CallEnv -> CallEnv -> CallEnv +combineCalls = plusVarEnv_C (++) +combineUsage :: ScUsage -> ScUsage -> ScUsage +combineUsage u1 u2 = SCU { scu_calls = combineCalls (scu_calls u1) (scu_calls u2), + scu_occs = plusVarEnv_C combineOcc (scu_occs u1) (scu_occs u2) } + +combineUsages :: [ScUsage] -> ScUsage combineUsages [] = nullUsage combineUsages us = foldr1 combineUsage us -data ArgOcc = CaseScrut - | OtherOcc - | Both +lookupOcc :: ScUsage -> OutVar -> (ScUsage, ArgOcc) +lookupOcc (SCU { scu_calls = sc_calls, scu_occs = sc_occs }) bndr + = (SCU {scu_calls = sc_calls, scu_occs = delVarEnv sc_occs bndr}, + lookupVarEnv sc_occs bndr `orElse` NoOcc) -instance Outputable ArgOcc where - ppr CaseScrut = ptext SLIT("case-scrut") - ppr OtherOcc = ptext SLIT("other-occ") - ppr Both = ptext SLIT("case-scrut and other") +lookupOccs :: ScUsage -> [OutVar] -> (ScUsage, [ArgOcc]) +lookupOccs (SCU { scu_calls = sc_calls, scu_occs = sc_occs }) bndrs + = (SCU {scu_calls = sc_calls, scu_occs = delVarEnvList sc_occs bndrs}, + [lookupVarEnv sc_occs b `orElse` NoOcc | b <- bndrs]) -combineOcc CaseScrut CaseScrut = CaseScrut -combineOcc OtherOcc OtherOcc = OtherOcc -combineOcc _ _ = Both -\end{code} +data ArgOcc = NoOcc -- Doesn't occur at all; or a type argument + | UnkOcc -- Used in some unknown way + | ScrutOcc (UniqFM [ArgOcc]) -- See Note [ScrutOcc] + + | BothOcc -- Definitely taken apart, *and* perhaps used in some other way + +{- Note [ScrutOcc] + +An occurrence of ScrutOcc indicates that the thing, or a `cast` version of the thing, +is *only* taken apart or applied. + + Functions, literal: ScrutOcc emptyUFM + Data constructors: ScrutOcc subs, + +where (subs :: UniqFM [ArgOcc]) gives usage of the *pattern-bound* components, +The domain of the UniqFM is the Unique of the data constructor + +The [ArgOcc] is the occurrences of the *pattern-bound* components +of the data structure. E.g. + data T a = forall b. MkT a b (b->a) +A pattern binds b, x::a, y::b, z::b->a, but not 'a'! + +-} + +instance Outputable ArgOcc where + ppr (ScrutOcc xs) = ptext (sLit "scrut-occ") <> ppr xs + ppr UnkOcc = ptext (sLit "unk-occ") + ppr BothOcc = ptext (sLit "both-occ") + ppr NoOcc = ptext (sLit "no-occ") + +-- Experimentally, this vesion of combineOcc makes ScrutOcc "win", so +-- that if the thing is scrutinised anywhere then we get to see that +-- in the overall result, even if it's also used in a boxed way +-- This might be too agressive; see Note [Reboxing] Alternative 3 +combineOcc :: ArgOcc -> ArgOcc -> ArgOcc +combineOcc NoOcc occ = occ +combineOcc occ NoOcc = occ +combineOcc (ScrutOcc xs) (ScrutOcc ys) = ScrutOcc (plusUFM_C combineOccs xs ys) +combineOcc _occ (ScrutOcc ys) = ScrutOcc ys +combineOcc (ScrutOcc xs) _occ = ScrutOcc xs +combineOcc UnkOcc UnkOcc = UnkOcc +combineOcc _ _ = BothOcc + +combineOccs :: [ArgOcc] -> [ArgOcc] -> [ArgOcc] +combineOccs xs ys = zipWithEqual "combineOccs" combineOcc xs ys + +setScrutOcc :: ScEnv -> ScUsage -> OutExpr -> ArgOcc -> ScUsage +-- _Overwrite_ the occurrence info for the scrutinee, if the scrutinee +-- is a variable, and an interesting variable +setScrutOcc env usg (Cast e _) occ = setScrutOcc env usg e occ +setScrutOcc env usg (Note _ e) occ = setScrutOcc env usg e occ +setScrutOcc env usg (Var v) occ + | Just RecArg <- lookupHowBound env v = usg { scu_occs = extendVarEnv (scu_occs usg) v occ } + | otherwise = usg +setScrutOcc _env usg _other _occ -- Catch-all + = usg + +conArgOccs :: ArgOcc -> AltCon -> [ArgOcc] +-- Find usage of components of data con; returns [UnkOcc...] if unknown +-- See Note [ScrutOcc] for the extra UnkOccs in the vanilla datacon case + +conArgOccs (ScrutOcc fm) (DataAlt dc) + | Just pat_arg_occs <- lookupUFM fm dc + = [UnkOcc | _ <- dataConUnivTyVars dc] ++ pat_arg_occs + +conArgOccs _other _con = repeat UnkOcc +\end{code} %************************************************************************ %* * @@ -524,155 +873,358 @@ The main recursive function gathers up usage information, and creates specialised versions of functions. \begin{code} -scExpr :: ScEnv -> CoreExpr -> UniqSM (ScUsage, CoreExpr) +scExpr, scExpr' :: ScEnv -> CoreExpr -> UniqSM (ScUsage, CoreExpr) -- The unique supply is needed when we invent -- a new name for the specialised function and its args -scExpr env e@(Type t) = returnUs (nullUsage, e) -scExpr env e@(Lit l) = returnUs (nullUsage, e) -scExpr env e@(Var v) = returnUs (varUsage env v OtherOcc, e) -scExpr env (Note n e) = scExpr env e `thenUs` \ (usg,e') -> - returnUs (usg, Note n e') -scExpr env (Lam b e) = scExpr (extendBndr env b) e `thenUs` \ (usg,e') -> - returnUs (usg, Lam b e') - -scExpr env (Case scrut b ty alts) - = sc_scrut scrut `thenUs` \ (scrut_usg, scrut') -> - mapAndUnzipUs sc_alt alts `thenUs` \ (alts_usgs, alts') -> - returnUs (combineUsages alts_usgs `combineUsage` scrut_usg, - Case scrut' b ty alts') +scExpr env e = scExpr' env e + + +scExpr' env (Var v) = case scSubstId env v of + Var v' -> return (varUsage env v' UnkOcc, Var v') + e' -> scExpr (zapScSubst env) e' + +scExpr' env (Type t) = return (nullUsage, Type (scSubstTy env t)) +scExpr' _ e@(Lit {}) = return (nullUsage, e) +scExpr' env (Note n e) = do (usg,e') <- scExpr env e + return (usg, Note n e') +scExpr' env (Cast e co) = do (usg, e') <- scExpr env e + return (usg, Cast e' (scSubstTy env co)) +scExpr' env e@(App _ _) = scApp env (collectArgs e) +scExpr' env (Lam b e) = do let (env', b') = extendBndr env b + (usg, e') <- scExpr env' e + return (usg, Lam b' e') + +scExpr' env (Case scrut b ty alts) + = do { (scrut_usg, scrut') <- scExpr env scrut + ; case isValue (sc_vals env) scrut' of + Just (ConVal con args) -> sc_con_app con args scrut' + _other -> sc_vanilla scrut_usg scrut' + } where - sc_scrut e@(Var v) = returnUs (varUsage env v CaseScrut, e) - sc_scrut e = scExpr env e - - sc_alt (con,bs,rhs) = scExpr env1 rhs `thenUs` \ (usg,rhs') -> - returnUs (usg, (con,bs,rhs')) - where - env1 = extendCaseBndrs env b scrut con bs - -scExpr env (Let bind body) - = scBind env bind `thenUs` \ (env', bind_usg, bind') -> - scExpr env' body `thenUs` \ (body_usg, body') -> - returnUs (bind_usg `combineUsage` body_usg, Let bind' body') - -scExpr env e@(App _ _) - = let - (fn, args) = collectArgs e - in - mapAndUnzipUs (scExpr env) (fn:args) `thenUs` \ (usgs, (fn':args')) -> - -- Process the function too. It's almost always a variable, - -- but not always. In particular, if this pass follows float-in, - -- which it may, we can get - -- (let f = ...f... in f) arg1 arg2 - let - call_usg = case fn of - Var f | Just RecFun <- lookupScopeEnv env f - -> SCU { calls = unitVarEnv f [(cons env, args)], - occs = emptyVarEnv } - other -> nullUsage - in - returnUs (combineUsages usgs `combineUsage` call_usg, mkApps fn' args') + sc_con_app con args scrut' -- Known constructor; simplify + = do { let (_, bs, rhs) = findAlt con alts + `orElse` (DEFAULT, [], mkImpossibleExpr (coreAltsType alts)) + alt_env' = extendScSubstList env ((b,scrut') : bs `zip` trimConArgs con args) + ; scExpr alt_env' rhs } + + sc_vanilla scrut_usg scrut' -- Normal case + = do { let (alt_env,b') = extendBndrWith RecArg env b + -- Record RecArg for the components + + ; (alt_usgs, alt_occs, alts') + <- mapAndUnzip3M (sc_alt alt_env scrut' b') alts + + ; let (alt_usg, b_occ) = lookupOcc (combineUsages alt_usgs) b' + scrut_occ = foldr combineOcc b_occ alt_occs + scrut_usg' = setScrutOcc env scrut_usg scrut' scrut_occ + -- The combined usage of the scrutinee is given + -- by scrut_occ, which is passed to scScrut, which + -- in turn treats a bare-variable scrutinee specially + + ; return (alt_usg `combineUsage` scrut_usg', + Case scrut' b' (scSubstTy env ty) alts') } + + sc_alt env _scrut' b' (con,bs,rhs) + = do { let (env1, bs1) = extendBndrsWith RecArg env bs + (env2, bs2) = extendCaseBndrs env1 b' con bs1 + ; (usg,rhs') <- scExpr env2 rhs + ; let (usg', arg_occs) = lookupOccs usg bs2 + scrut_occ = case con of + DataAlt dc -> ScrutOcc (unitUFM dc arg_occs) + _ -> ScrutOcc emptyUFM + ; return (usg', scrut_occ, (con, bs2, rhs')) } + +scExpr' env (Let (NonRec bndr rhs) body) + | isTyCoVar bndr -- Type-lets may be created by doBeta + = scExpr' (extendScSubst env bndr rhs) body + + | otherwise -- Note [Local let bindings] + = do { let (body_env, bndr') = extendBndr env bndr + body_env2 = extendHowBound body_env [bndr'] RecFun + ; (body_usg, body') <- scExpr body_env2 body + + ; (rhs_usg, rhs_info) <- scRecRhs env (bndr',rhs) + + -- NB: We don't use the ForceSpecConstr mechanism (see + -- Note [Forcing specialisation]) for non-recursive bindings + -- at the moment. I'm not sure if this is the right thing to do. + ; let force_spec = False + ; (spec_usg, specs) <- specialise env force_spec + (scu_calls body_usg) + rhs_info + (SI [] 0 (Just rhs_usg)) + + ; return (body_usg { scu_calls = scu_calls body_usg `delVarEnv` bndr' } + `combineUsage` spec_usg, + mkLets [NonRec b r | (b,r) <- specInfoBinds rhs_info specs] body') + } + + +-- A *local* recursive group: see Note [Local recursive groups] +scExpr' env (Let (Rec prs) body) + = do { let (bndrs,rhss) = unzip prs + (rhs_env1,bndrs') = extendRecBndrs env bndrs + rhs_env2 = extendHowBound rhs_env1 bndrs' RecFun + force_spec = any (forceSpecBndr env) bndrs' + -- Note [Forcing specialisation] + + ; (rhs_usgs, rhs_infos) <- mapAndUnzipM (scRecRhs rhs_env2) (bndrs' `zip` rhss) + ; (body_usg, body') <- scExpr rhs_env2 body + + -- NB: start specLoop from body_usg + ; (spec_usg, specs) <- specLoop rhs_env2 force_spec + (scu_calls body_usg) rhs_infos nullUsage + [SI [] 0 (Just usg) | usg <- rhs_usgs] + -- Do not unconditionally use rhs_usgs. + -- Instead use them only if we find an unspecialised call + -- See Note [Local recursive groups] + + ; let all_usg = spec_usg `combineUsage` body_usg + bind' = Rec (concat (zipWith specInfoBinds rhs_infos specs)) + + ; return (all_usg { scu_calls = scu_calls all_usg `delVarEnvList` bndrs' }, + Let bind' body') } +\end{code} +Note [Local let bindings] +~~~~~~~~~~~~~~~~~~~~~~~~~ +It is not uncommon to find this ----------------------- -scBind :: ScEnv -> CoreBind -> UniqSM (ScEnv, ScUsage, CoreBind) -scBind env (Rec [(fn,rhs)]) - | notNull val_bndrs - = scExpr env_fn_body body `thenUs` \ (usg, body') -> - specialise env fn bndrs body' usg `thenUs` \ (rules, spec_prs) -> - -- Note body': the specialised copies should be based on the - -- optimised version of the body, in case there were - -- nested functions inside. - let - SCU { calls = calls, occs = occs } = usg - in - returnUs (extendBndr env fn, -- For the body of the letrec, just - -- extend the env with Other to record - -- that it's in scope; no funny RecFun business - SCU { calls = calls `delVarEnv` fn, occs = occs `delVarEnvList` val_bndrs}, - Rec ((fn `addIdSpecialisations` rules, mkLams bndrs body') : spec_prs)) + let $j = \x. in ...$j True...$j True... + +Here $j is an arbitrary let-bound function, but it often comes up for +join points. We might like to specialise $j for its call patterns. +Notice the difference from a letrec, where we look for call patterns +in the *RHS* of the function. Here we look for call patterns in the +*body* of the let. + +At one point I predicated this on the RHS mentioning the outer +recursive function, but that's not essential and might even be +harmful. I'm not sure. + + +\begin{code} +scApp :: ScEnv -> (InExpr, [InExpr]) -> UniqSM (ScUsage, CoreExpr) + +scApp env (Var fn, args) -- Function is a variable + = ASSERT( not (null args) ) + do { args_w_usgs <- mapM (scExpr env) args + ; let (arg_usgs, args') = unzip args_w_usgs + arg_usg = combineUsages arg_usgs + ; case scSubstId env fn of + fn'@(Lam {}) -> scExpr (zapScSubst env) (doBeta fn' args') + -- Do beta-reduction and try again + + Var fn' -> return (arg_usg `combineUsage` fn_usg, mkApps (Var fn') args') + where + fn_usg = case lookupHowBound env fn' of + Just RecFun -> SCU { scu_calls = unitVarEnv fn' [(sc_vals env, args')], + scu_occs = emptyVarEnv } + Just RecArg -> SCU { scu_calls = emptyVarEnv, + scu_occs = unitVarEnv fn' (ScrutOcc emptyUFM) } + Nothing -> nullUsage + + + other_fn' -> return (arg_usg, mkApps other_fn' args') } + -- NB: doing this ignores any usage info from the substituted + -- function, but I don't think that matters. If it does + -- we can fix it. where - (bndrs,body) = collectBinders rhs - val_bndrs = filter isId bndrs - env_fn_body = extendRecBndr env fn bndrs + doBeta :: OutExpr -> [OutExpr] -> OutExpr + -- ToDo: adjust for System IF + doBeta (Lam bndr body) (arg : args) = Let (NonRec bndr arg) (doBeta body args) + doBeta fn args = mkApps fn args + +-- The function is almost always a variable, but not always. +-- In particular, if this pass follows float-in, +-- which it may, we can get +-- (let f = ...f... in f) arg1 arg2 +scApp env (other_fn, args) + = do { (fn_usg, fn') <- scExpr env other_fn + ; (arg_usgs, args') <- mapAndUnzipM (scExpr env) args + ; return (combineUsages arg_usgs `combineUsage` fn_usg, mkApps fn' args') } -scBind env (Rec prs) - = mapAndUnzipUs do_one prs `thenUs` \ (usgs, prs') -> - returnUs (extendBndrs env (map fst prs), combineUsages usgs, Rec prs') +---------------------- +scTopBind :: ScEnv -> CoreBind -> UniqSM (ScEnv, CoreBind) +scTopBind env (Rec prs) + | Just threshold <- sc_size env + , not force_spec + , not (all (couldBeSmallEnoughToInline threshold) rhss) + -- No specialisation + = do { let (rhs_env,bndrs') = extendRecBndrs env bndrs + ; (_, rhss') <- mapAndUnzipM (scExpr rhs_env) rhss + ; return (rhs_env, Rec (bndrs' `zip` rhss')) } + | otherwise -- Do specialisation + = do { let (rhs_env1,bndrs') = extendRecBndrs env bndrs + rhs_env2 = extendHowBound rhs_env1 bndrs' RecFun + + ; (rhs_usgs, rhs_infos) <- mapAndUnzipM (scRecRhs rhs_env2) (bndrs' `zip` rhss) + ; let rhs_usg = combineUsages rhs_usgs + + ; (_, specs) <- specLoop rhs_env2 force_spec + (scu_calls rhs_usg) rhs_infos nullUsage + [SI [] 0 Nothing | _ <- bndrs] + + ; return (rhs_env1, -- For the body of the letrec, delete the RecFun business + Rec (concat (zipWith specInfoBinds rhs_infos specs))) } where - do_one (bndr,rhs) = scExpr env rhs `thenUs` \ (usg, rhs') -> - returnUs (usg, (bndr,rhs')) + (bndrs,rhss) = unzip prs + force_spec = any (forceSpecBndr env) bndrs + -- Note [Forcing specialisation] + +scTopBind env (NonRec bndr rhs) + = do { (_, rhs') <- scExpr env rhs + ; let (env1, bndr') = extendBndr env bndr + env2 = extendValEnv env1 bndr' (isValue (sc_vals env) rhs') + ; return (env2, NonRec bndr' rhs') } -scBind env (NonRec bndr rhs) - = scExpr env rhs `thenUs` \ (usg, rhs') -> - returnUs (extendBndr env bndr, usg, NonRec bndr rhs') +---------------------- +scRecRhs :: ScEnv -> (OutId, InExpr) -> UniqSM (ScUsage, RhsInfo) +scRecRhs env (bndr,rhs) + = do { let (arg_bndrs,body) = collectBinders rhs + (body_env, arg_bndrs') = extendBndrsWith RecArg env arg_bndrs + ; (body_usg, body') <- scExpr body_env body + ; let (rhs_usg, arg_occs) = lookupOccs body_usg arg_bndrs' + ; return (rhs_usg, RI bndr (mkLams arg_bndrs' body') + arg_bndrs body arg_occs) } + -- The arg_occs says how the visible, + -- lambda-bound binders of the RHS are used + -- (including the TyVar binders) + -- Two pats are the same if they match both ways + +---------------------- +specInfoBinds :: RhsInfo -> SpecInfo -> [(Id,CoreExpr)] +specInfoBinds (RI fn new_rhs _ _ _) (SI specs _ _) + = [(id,rhs) | OS _ _ id rhs <- specs] ++ + [(fn `addIdSpecialisations` rules, new_rhs)] + where + rules = [r | OS _ r _ _ <- specs] ---------------------- +varUsage :: ScEnv -> OutVar -> ArgOcc -> ScUsage varUsage env v use - | Just RecArg <- lookupScopeEnv env v = SCU { calls = emptyVarEnv, - occs = unitVarEnv v use } + | Just RecArg <- lookupHowBound env v = SCU { scu_calls = emptyVarEnv + , scu_occs = unitVarEnv v use } | otherwise = nullUsage \end{code} %************************************************************************ %* * -\subsection{The specialiser} + The specialiser itself %* * %************************************************************************ \begin{code} -specialise :: ScEnv - -> Id -- Functionn - -> [CoreBndr] -> CoreExpr -- Its RHS - -> ScUsage -- Info on usage - -> UniqSM ([CoreRule], -- Rules - [(Id,CoreExpr)]) -- Bindings - -specialise env fn bndrs body (SCU {calls=calls, occs=occs}) - = getUs `thenUs` \ us -> - let - all_calls = lookupVarEnv calls fn `orElse` [] - - good_calls :: [[CoreArg]] - good_calls = [ pats - | (con_env, call_args) <- all_calls, - call_args `lengthAtLeast` n_bndrs, -- App is saturated - let call = bndrs `zip` call_args, - any (good_arg con_env occs) call, -- At least one arg is a constr app - let (_, pats) = argsToPats con_env us call_args - ] - in - mapAndUnzipUs (spec_one env fn (mkLams bndrs body)) - (nubBy same_call good_calls `zip` [1..]) - where - n_bndrs = length bndrs - same_call as1 as2 = and (zipWith tcEqExpr as1 as2) +data RhsInfo = RI OutId -- The binder + OutExpr -- The new RHS + [InVar] InExpr -- The *original* RHS (\xs.body) + -- Note [Specialise original body] + [ArgOcc] -- Info on how the xs occur in body + +data SpecInfo = SI [OneSpec] -- The specialisations we have generated + + Int -- Length of specs; used for numbering them + + (Maybe ScUsage) -- Nothing => we have generated specialisations + -- from calls in the *original* RHS + -- Just cs => we haven't, and this is the usage + -- of the original RHS + -- See Note [Local recursive groups] + + -- One specialisation: Rule plus definition +data OneSpec = OS CallPat -- Call pattern that generated this specialisation + CoreRule -- Rule connecting original id with the specialisation + OutId OutExpr -- Spec id + its rhs + + +specLoop :: ScEnv + -> Bool -- force specialisation? + -- Note [Forcing specialisation] + -> CallEnv + -> [RhsInfo] + -> ScUsage -> [SpecInfo] -- One per binder; acccumulating parameter + -> UniqSM (ScUsage, [SpecInfo]) -- ...ditto... +specLoop env force_spec all_calls rhs_infos usg_so_far specs_so_far + = do { specs_w_usg <- zipWithM (specialise env force_spec all_calls) rhs_infos specs_so_far + ; let (new_usg_s, all_specs) = unzip specs_w_usg + new_usg = combineUsages new_usg_s + new_calls = scu_calls new_usg + all_usg = usg_so_far `combineUsage` new_usg + ; if isEmptyVarEnv new_calls then + return (all_usg, all_specs) + else + specLoop env force_spec new_calls rhs_infos all_usg all_specs } + +specialise + :: ScEnv + -> Bool -- force specialisation? + -- Note [Forcing specialisation] + -> CallEnv -- Info on calls + -> RhsInfo + -> SpecInfo -- Original RHS plus patterns dealt with + -> UniqSM (ScUsage, SpecInfo) -- New specialised versions and their usage + +-- Note: the rhs here is the optimised version of the original rhs +-- So when we make a specialised copy of the RHS, we're starting +-- from an RHS whose nested functions have been optimised already. + +specialise env force_spec bind_calls (RI fn _ arg_bndrs body arg_occs) + spec_info@(SI specs spec_count mb_unspec) + | not (isBottomingId fn) -- Note [Do not specialise diverging functions] + , not (isNeverActive (idInlineActivation fn)) -- See Note [Transfer activation] + , notNull arg_bndrs -- Only specialise functions + , Just all_calls <- lookupVarEnv bind_calls fn + = do { (boring_call, pats) <- callsToPats env specs arg_occs all_calls +-- ; pprTrace "specialise" (vcat [ ppr fn <+> text "with" <+> int (length pats) <+> text "good patterns" +-- , text "arg_occs" <+> ppr arg_occs +-- , text "calls" <+> ppr all_calls +-- , text "good pats" <+> ppr pats]) $ +-- return () + + -- Bale out if too many specialisations + ; let n_pats = length pats + spec_count' = n_pats + spec_count + ; case sc_count env of + Just max | not force_spec && spec_count' > max + -> pprTrace "SpecConstr" msg $ + return (nullUsage, spec_info) + where + msg = vcat [ sep [ ptext (sLit "Function") <+> quotes (ppr fn) + , nest 2 (ptext (sLit "has") <+> + speakNOf spec_count' (ptext (sLit "call pattern")) <> comma <+> + ptext (sLit "but the limit is") <+> int max) ] + , ptext (sLit "Use -fspec-constr-count=n to set the bound") + , extra ] + extra | not opt_PprStyle_Debug = ptext (sLit "Use -dppr-debug to see specialisations") + | otherwise = ptext (sLit "Specialisations:") <+> ppr (pats ++ [p | OS p _ _ _ <- specs]) + + _normal_case -> do { + + let spec_env = decreaseSpecCount env n_pats + ; (spec_usgs, new_specs) <- mapAndUnzipM (spec_one spec_env fn arg_bndrs body) + (pats `zip` [spec_count..]) + -- See Note [Specialise original body] + + ; let spec_usg = combineUsages spec_usgs + (new_usg, mb_unspec') + = case mb_unspec of + Just rhs_usg | boring_call -> (spec_usg `combineUsage` rhs_usg, Nothing) + _ -> (spec_usg, mb_unspec) + + ; return (new_usg, SI (new_specs ++ specs) spec_count' mb_unspec') } } + | otherwise + = return (nullUsage, spec_info) -- The boring case ---------------------- -good_arg :: ConstrEnv -> IdEnv ArgOcc -> (CoreBndr, CoreArg) -> Bool --- See Note [Good arguments] above -good_arg con_env arg_occs (bndr, arg) - = case is_con_app_maybe con_env arg of - Just _ -> bndr_usg_ok arg_occs bndr arg - other -> False - -bndr_usg_ok :: IdEnv ArgOcc -> Var -> CoreArg -> Bool -bndr_usg_ok arg_occs bndr arg - = case lookupVarEnv arg_occs bndr of - Just CaseScrut -> True -- Used only by case scrutiny - Just Both -> case arg of -- Used by case and elsewhere - App _ _ -> True -- so the arg should be an explicit con app - other -> False - other -> False -- Not used, or used wonkily - --------------------- spec_one :: ScEnv - -> Id -- Function - -> CoreExpr -- Rhs of the original function - -> ([CoreArg], Int) - -> UniqSM (CoreRule, (Id,CoreExpr)) -- Rule and binding + -> OutId -- Function + -> [InVar] -- Lambda-binders of RHS; should match patterns + -> InExpr -- Body of the original function + -> (CallPat, Int) + -> UniqSM (ScUsage, OneSpec) -- Rule and binding -- spec_one creates a specialised copy of the function, together -- with a rule for using it. I'm very proud of how short this @@ -686,7 +1238,8 @@ spec_one :: ScEnv [c::*, v::(b,c) are presumably bound by the (...) part] ==> f_spec = /\ b c \ v::(b,c) hw::[(a,(b,c))] -> - (...entire RHS of f...) (b,c) ((:) (a,(b,c)) (x,v) hw) + (...entire body of f...) [b -> (b,c), + y -> ((:) (a,(b,c)) (x,v) hw)] RULE: forall b::* c::*, -- Note, *not* forall a, x v::(b,c), @@ -695,48 +1248,109 @@ spec_one :: ScEnv f (b,c) ((:) (a,(b,c)) (x,v) hw) = f_spec b c v hw -} -spec_one env fn rhs (pats, rule_number) - = getUniqueUs `thenUs` \ spec_uniq -> - let - fn_name = idName fn - fn_loc = nameSrcLoc fn_name - spec_occ = mkSpecOcc (nameOccName fn_name) - pat_fvs = varSetElems (exprsFreeVars pats) - vars_to_bind = filter not_avail pat_fvs - -- See Note [Shadowing] at the top +spec_one env fn arg_bndrs body (call_pat@(qvars, pats), rule_number) + = do { spec_uniq <- getUniqueUs + ; let spec_env = extendScSubstList (extendScInScope env qvars) + (arg_bndrs `zip` pats) + fn_name = idName fn + fn_loc = nameSrcSpan fn_name + spec_occ = mkSpecOcc (nameOccName fn_name) + rule_name = mkFastString ("SC:" ++ showSDoc (ppr fn <> int rule_number)) + spec_name = mkInternalName spec_uniq spec_occ fn_loc +-- ; pprTrace "{spec_one" (ppr (sc_count env) <+> ppr fn <+> ppr pats <+> text "-->" <+> ppr spec_name) $ +-- return () + + -- Specialise the body + ; (spec_usg, spec_body) <- scExpr spec_env body + +-- ; pprTrace "done spec_one}" (ppr fn) $ +-- return () + + -- And build the results + ; let spec_id = mkLocalId spec_name (mkPiTypes spec_lam_args body_ty) + `setIdStrictness` spec_str -- See Note [Transfer strictness] + `setIdArity` count isId spec_lam_args + spec_str = calcSpecStrictness fn spec_lam_args pats + (spec_lam_args, spec_call_args) = mkWorkerArgs qvars body_ty + -- Usual w/w hack to avoid generating + -- a spec_rhs of unlifted type and no args + + spec_rhs = mkLams spec_lam_args spec_body + body_ty = exprType spec_body + rule_rhs = mkVarApps (Var spec_id) spec_call_args + inline_act = idInlineActivation fn + rule = mkLocalRule rule_name inline_act fn_name qvars pats rule_rhs + -- See Note [Transfer activation] + ; return (spec_usg, OS call_pat rule spec_id spec_rhs) } + +calcSpecStrictness :: Id -- The original function + -> [Var] -> [CoreExpr] -- Call pattern + -> StrictSig -- Strictness of specialised thing +-- See Note [Transfer strictness] +calcSpecStrictness fn qvars pats + = StrictSig (mkTopDmdType spec_dmds TopRes) + where + spec_dmds = [ lookupVarEnv dmd_env qv `orElse` lazyDmd | qv <- qvars, isId qv ] + StrictSig (DmdType _ dmds _) = idStrictness fn + + dmd_env = go emptyVarEnv dmds pats + + go env ds (Type {} : pats) = go env ds pats + go env (d:ds) (pat : pats) = go (go_one env d pat) ds pats + go env _ _ = env + + go_one env d (Var v) = extendVarEnv_C both env v d + go_one env (Box d) e = go_one env d e + go_one env (Eval (Prod ds)) e + | (Var _, args) <- collectArgs e = go env ds args + go_one env _ _ = env - not_avail v = not (v `elemVarEnv` scope env) - -- Put the type variables first; the type of a term - -- variable may mention a type variable - (tvs, ids) = partition isTyVar vars_to_bind - bndrs = tvs ++ ids - spec_body = mkApps rhs pats - body_ty = exprType spec_body - - (spec_lam_args, spec_call_args) = mkWorkerArgs bndrs body_ty - -- Usual w/w hack to avoid generating - -- a spec_rhs of unlifted type and no args - - rule_name = mkFastString ("SC:" ++ showSDoc (ppr fn <> int rule_number)) - spec_rhs = mkLams spec_lam_args spec_body - spec_id = mkUserLocal spec_occ spec_uniq (mkPiTypes spec_lam_args body_ty) fn_loc - rule_rhs = mkVarApps (Var spec_id) spec_call_args - rule = mkLocalRule rule_name specConstrActivation fn_name bndrs pats rule_rhs - in - returnUs (rule, (spec_id, spec_rhs)) - --- In which phase should the specialise-constructor rules be active? --- Originally I made them always-active, but Manuel found that --- this defeated some clever user-written rules. So Plan B --- is to make them active only in Phase 0; after all, currently, --- the specConstr transformation is only run after the simplifier --- has reached Phase 0. In general one would want it to be --- flag-controllable, but for now I'm leaving it baked in --- [SLPJ Oct 01] -specConstrActivation :: Activation -specConstrActivation = ActiveAfter 0 -- Baked in; see comments above \end{code} +Note [Specialise original body] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +The RhsInfo for a binding keeps the *original* body of the binding. We +must specialise that, *not* the result of applying specExpr to the RHS +(which is also kept in RhsInfo). Otherwise we end up specialising a +specialised RHS, and that can lead directly to exponential behaviour. + +Note [Transfer activation] +~~~~~~~~~~~~~~~~~~~~~~~~~~ + This note is for SpecConstr, but exactly the same thing + happens in the overloading specialiser; see + Note [Auto-specialisation and RULES] in Specialise. + +In which phase should the specialise-constructor rules be active? +Originally I made them always-active, but Manuel found that this +defeated some clever user-written rules. Then I made them active only +in Phase 0; after all, currently, the specConstr transformation is +only run after the simplifier has reached Phase 0, but that meant +that specialisations didn't fire inside wrappers; see test +simplCore/should_compile/spec-inline. + +So now I just use the inline-activation of the parent Id, as the +activation for the specialiation RULE, just like the main specialiser; + +This in turn means there is no point in specialising NOINLINE things, +so we test for that. + +Note [Transfer strictness] +~~~~~~~~~~~~~~~~~~~~~~~~~~ +We must transfer strictness information from the original function to +the specialised one. Suppose, for example + + f has strictness SS + and a RULE f (a:as) b = f_spec a as b + +Now we want f_spec to have strictess LLS, otherwise we'll use call-by-need +when calling f_spec instead of call-by-value. And that can result in +unbounded worsening in space (cf the classic foldl vs foldl') + +See Trac #3437 for a good example. + +The function calcSpecStrictness performs the calculation. + + %************************************************************************ %* * \subsection{Argument analysis} @@ -746,68 +1360,276 @@ specConstrActivation = ActiveAfter 0 -- Baked in; see comments above This code deals with analysing call-site arguments to see whether they are constructor applications. + \begin{code} +type CallPat = ([Var], [CoreExpr]) -- Quantified variables and arguments + + +callsToPats :: ScEnv -> [OneSpec] -> [ArgOcc] -> [Call] -> UniqSM (Bool, [CallPat]) + -- Result has no duplicate patterns, + -- nor ones mentioned in done_pats + -- Bool indicates that there was at least one boring pattern +callsToPats env done_specs bndr_occs calls + = do { mb_pats <- mapM (callToPats env bndr_occs) calls + + ; let good_pats :: [([Var], [CoreArg])] + good_pats = catMaybes mb_pats + done_pats = [p | OS p _ _ _ <- done_specs] + is_done p = any (samePat p) done_pats + + ; return (any isNothing mb_pats, + filterOut is_done (nubBy samePat good_pats)) } + +callToPats :: ScEnv -> [ArgOcc] -> Call -> UniqSM (Maybe CallPat) + -- The [Var] is the variables to quantify over in the rule + -- Type variables come first, since they may scope + -- over the following term variables + -- The [CoreExpr] are the argument patterns for the rule +callToPats env bndr_occs (con_env, args) + | length args < length bndr_occs -- Check saturated + = return Nothing + | otherwise + = do { let in_scope = substInScope (sc_subst env) + ; prs <- argsToPats env in_scope con_env (args `zip` bndr_occs) + ; let (interesting_s, pats) = unzip prs + pat_fvs = varSetElems (exprsFreeVars pats) + qvars = filterOut (`elemInScopeSet` in_scope) pat_fvs + -- Quantify over variables that are not in sccpe + -- at the call site + -- See Note [Shadowing] at the top + + (tvs, ids) = partition isTyCoVar qvars + qvars' = tvs ++ ids + -- Put the type variables first; the type of a term + -- variable may mention a type variable + + ; -- pprTrace "callToPats" (ppr args $$ ppr prs $$ ppr bndr_occs) $ + if or interesting_s + then return (Just (qvars', pats)) + else return Nothing } + -- argToPat takes an actual argument, and returns an abstracted -- version, consisting of just the "constructor skeleton" of the -- argument, with non-constructor sub-expression replaced by new -- placeholder variables. For example: -- C a (D (f x) (g y)) ==> C p1 (D p2 p3) -argToPat :: ConstrEnv -> UniqSupply -> CoreArg -> (UniqSupply, CoreExpr) -argToPat env us (Type ty) - = (us, Type ty) +argToPat :: ScEnv + -> InScopeSet -- What's in scope at the fn defn site + -> ValueEnv -- ValueEnv at the call site + -> CoreArg -- A call arg (or component thereof) + -> ArgOcc + -> UniqSM (Bool, CoreArg) +-- Returns (interesting, pat), +-- where pat is the pattern derived from the argument +-- intersting=True if the pattern is non-trivial (not a variable or type) +-- E.g. x:xs --> (True, x:xs) +-- f xs --> (False, w) where w is a fresh wildcard +-- (f xs, 'c') --> (True, (w, 'c')) where w is a fresh wildcard +-- \x. x+y --> (True, \x. x+y) +-- lvl7 --> (True, lvl7) if lvl7 is bound +-- somewhere further out + +argToPat _env _in_scope _val_env arg@(Type {}) _arg_occ + = return (False, arg) + +argToPat env in_scope val_env (Note _ arg) arg_occ + = argToPat env in_scope val_env arg arg_occ + -- Note [Notes in call patterns] + -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + -- Ignore Notes. In particular, we want to ignore any InlineMe notes + -- Perhaps we should not ignore profiling notes, but I'm going to + -- ride roughshod over them all for now. + --- See Note [Notes in RULE matching] in Rules + +argToPat env in_scope val_env (Let _ arg) arg_occ + = argToPat env in_scope val_env arg arg_occ + -- See Note [Matching lets] in Rule.lhs + -- Look through let expressions + -- e.g. f (let v = rhs in (v,w)) + -- Here we can specialise for f (v,w) + -- because the rule-matcher will look through the let. + +{- Disabled; see Note [Matching cases] in Rule.lhs +argToPat env in_scope val_env (Case scrut _ _ [(_, _, rhs)]) arg_occ + | exprOkForSpeculation scrut -- See Note [Matching cases] in Rule.hhs + = argToPat env in_scope val_env rhs arg_occ +-} -argToPat env us arg - | Just (CV dc args) <- is_con_app_maybe env arg - = let - (us',args') = argsToPats env us args - in - (us', mk_con_app dc args') +argToPat env in_scope val_env (Cast arg co) arg_occ + | not (ignoreType env ty2) + = do { (interesting, arg') <- argToPat env in_scope val_env arg arg_occ + ; if not interesting then + wildCardPat ty2 + else do + { -- Make a wild-card pattern for the coercion + uniq <- getUniqueUs + ; let co_name = mkSysTvName uniq (fsLit "sg") + co_var = mkCoVar co_name (mkCoKind ty1 ty2) + ; return (interesting, Cast arg' (mkTyVarTy co_var)) } } + where + (ty1, ty2) = coercionKind co -argToPat env us (Var v) -- Don't uniqify existing vars, - = (us, Var v) -- so that we can spot when we pass them twice + -argToPat env us arg - = (us1, Var (mkSysLocal FSLIT("sc") (uniqFromSupply us2) (exprType arg))) +{- Disabling lambda specialisation for now + It's fragile, and the spec_loop can be infinite +argToPat in_scope val_env arg arg_occ + | is_value_lam arg + = return (True, arg) where - (us1,us2) = splitUniqSupply us + is_value_lam (Lam v e) -- Spot a value lambda, even if + | isId v = True -- it is inside a type lambda + | otherwise = is_value_lam e + is_value_lam other = False +-} -argsToPats :: ConstrEnv -> UniqSupply -> [CoreArg] -> (UniqSupply, [CoreExpr]) -argsToPats env us args = mapAccumL (argToPat env) us args + -- Check for a constructor application + -- NB: this *precedes* the Var case, so that we catch nullary constrs +argToPat env in_scope val_env arg arg_occ + | Just (ConVal dc args) <- isValue val_env arg + , not (ignoreAltCon env dc) + , case arg_occ of + ScrutOcc _ -> True -- Used only by case scrutinee + BothOcc -> case arg of -- Used elsewhere + App {} -> True -- see Note [Reboxing] + _other -> False + _other -> False -- No point; the arg is not decomposed + = do { args' <- argsToPats env in_scope val_env (args `zip` conArgOccs arg_occ dc) + ; return (True, mk_con_app dc (map snd args')) } + + -- Check if the argument is a variable that + -- is in scope at the function definition site + -- It's worth specialising on this if + -- (a) it's used in an interesting way in the body + -- (b) we know what its value is +argToPat env in_scope val_env (Var v) arg_occ + | case arg_occ of { UnkOcc -> False; _other -> True }, -- (a) + is_value, -- (b) + not (ignoreType env (varType v)) + = return (True, Var v) + where + is_value + | isLocalId v = v `elemInScopeSet` in_scope + && isJust (lookupVarEnv val_env v) + -- Local variables have values in val_env + | otherwise = isValueUnfolding (idUnfolding v) + -- Imports have unfoldings + +-- I'm really not sure what this comment means +-- And by not wild-carding we tend to get forall'd +-- variables that are in soope, which in turn can +-- expose the weakness in let-matching +-- See Note [Matching lets] in Rules + + -- Check for a variable bound inside the function. + -- Don't make a wild-card, because we may usefully share + -- e.g. f a = let x = ... in f (x,x) + -- NB: this case follows the lambda and con-app cases!! +-- argToPat _in_scope _val_env (Var v) _arg_occ +-- = return (False, Var v) + -- SLPJ : disabling this to avoid proliferation of versions + -- also works badly when thinking about seeding the loop + -- from the body of the let + -- f x y = letrec g z = ... in g (x,y) + -- We don't want to specialise for that *particular* x,y + + -- The default case: make a wild-card +argToPat _env _in_scope _val_env arg _arg_occ + = wildCardPat (exprType arg) + +wildCardPat :: Type -> UniqSM (Bool, CoreArg) +wildCardPat ty = do { uniq <- getUniqueUs + ; let id = mkSysLocal (fsLit "sc") uniq ty + ; return (False, Var id) } + +argsToPats :: ScEnv -> InScopeSet -> ValueEnv + -> [(CoreArg, ArgOcc)] + -> UniqSM [(Bool, CoreArg)] +argsToPats env in_scope val_env args + = mapM do_one args + where + do_one (arg,occ) = argToPat env in_scope val_env arg occ \end{code} \begin{code} -is_con_app_maybe :: ConstrEnv -> CoreExpr -> Maybe ConValue -is_con_app_maybe env (Var v) - = case lookupVarEnv env v of - Just stuff -> Just stuff - -- You might think we could look in the idUnfolding here +isValue :: ValueEnv -> CoreExpr -> Maybe Value +isValue _env (Lit lit) + = Just (ConVal (LitAlt lit) []) + +isValue env (Var v) + | Just stuff <- lookupVarEnv env v + = Just stuff -- You might think we could look in the idUnfolding here -- but that doesn't take account of which branch of a -- case we are in, which is the whole point - Nothing | isCheapUnfolding unf - -> is_con_app_maybe env (unfoldingTemplate unf) - where - unf = idUnfolding v - -- However we do want to consult the unfolding as well, - -- for let-bound constructors! + | not (isLocalId v) && isCheapUnfolding unf + = isValue env (unfoldingTemplate unf) + where + unf = idUnfolding v + -- However we do want to consult the unfolding + -- as well, for let-bound constructors! + +isValue env (Lam b e) + | isTyCoVar b = case isValue env e of + Just _ -> Just LambdaVal + Nothing -> Nothing + | otherwise = Just LambdaVal - other -> Nothing +isValue _env expr -- Maybe it's a constructor application + | (Var fun, args) <- collectArgs expr + = case isDataConWorkId_maybe fun of -is_con_app_maybe env (Lit lit) - = Just (CV (LitAlt lit) []) + Just con | args `lengthAtLeast` dataConRepArity con + -- Check saturated; might be > because the + -- arity excludes type args + -> Just (ConVal (DataAlt con) args) -is_con_app_maybe env expr - = case collectArgs expr of - (Var fun, args) | Just con <- isDataConWorkId_maybe fun, - args `lengthAtLeast` dataConRepArity con - -- Might be > because the arity excludes type args - -> Just (CV (DataAlt con) args) + _other | valArgCount args < idArity fun + -- Under-applied function + -> Just LambdaVal -- Partial application - other -> Nothing + _other -> Nothing + +isValue _env _expr = Nothing mk_con_app :: AltCon -> [CoreArg] -> CoreExpr mk_con_app (LitAlt lit) [] = Lit lit mk_con_app (DataAlt con) args = mkConApp con args +mk_con_app _other _args = panic "SpecConstr.mk_con_app" + +samePat :: CallPat -> CallPat -> Bool +samePat (vs1, as1) (vs2, as2) + = all2 same as1 as2 + where + same (Var v1) (Var v2) + | v1 `elem` vs1 = v2 `elem` vs2 + | v2 `elem` vs2 = False + | otherwise = v1 == v2 + + same (Lit l1) (Lit l2) = l1==l2 + same (App f1 a1) (App f2 a2) = same f1 f2 && same a1 a2 + + same (Type {}) (Type {}) = True -- Note [Ignore type differences] + same (Note _ e1) e2 = same e1 e2 -- Ignore casts and notes + same (Cast e1 _) e2 = same e1 e2 + same e1 (Note _ e2) = same e1 e2 + same e1 (Cast e2 _) = same e1 e2 + + same e1 e2 = WARN( bad e1 || bad e2, ppr e1 $$ ppr e2) + False -- Let, lambda, case should not occur + bad (Case {}) = True + bad (Let {}) = True + bad (Lam {}) = True + bad _other = False \end{code} + +Note [Ignore type differences] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +We do not want to generate specialisations where the call patterns +differ only in their type arguments! Not only is it utterly useless, +but it also means that (with polymorphic recursion) we can generate +an infinite number of specialisations. Example is Data.Sequence.adjustTree, +I think. +