% % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 % \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 ) where #include "HsVersions.h" import CoreSyn import CoreSubst import CoreUtils import CoreUnfold ( couldBeSmallEnoughToInline ) import CoreLint ( showPass, endPass ) import CoreFVs ( exprsFreeVars ) import CoreTidy ( tidyRules ) import PprCore ( pprRules ) import WwLib ( mkWorkerArgs ) import DataCon ( dataConRepArity, dataConUnivTyVars ) import Coercion import Type hiding( substTy ) import Id ( Id, idName, idType, isDataConWorkId_maybe, idArity, mkUserLocal, mkSysLocal, idUnfolding, isLocalId ) import Var import VarEnv import VarSet import Name import Rules ( addIdSpecialisations, mkLocalRule, rulesOfBinds ) import OccName ( mkSpecOcc ) import ErrUtils ( dumpIfSet_dyn ) import DynFlags ( DynFlags(..), DynFlag(..) ) import StaticFlags ( opt_SpecInlineJoinPoints ) import BasicTypes ( Activation(..) ) import Maybes ( orElse, catMaybes, isJust, isNothing ) import Util import List ( nubBy, partition ) import UniqSupply import Outputable import FastString import UniqFM import MonadUtils import Control.Monad ( zipWithM ) \end{code} ----------------------------------------------------- Game plan ----------------------------------------------------- Consider drop n [] = [] drop 0 xs = [] drop n (x:xs) = drop (n-1) xs After the first time round, we could pass n unboxed. This happens in numerical code too. Here's what it looks like in Core: drop n xs = case xs of [] -> [] (y:ys) -> case n of I# n# -> case n# of 0 -> [] _ -> drop (I# (n# -# 1#)) xs Notice that the recursive call has an explicit constructor as argument. Noticing this, we can make a specialised version of drop RULE: drop (I# n#) xs ==> drop' n# xs drop' n# xs = let n = I# n# in ...orig RHS... Now the simplifier will apply the specialisation in the rhs of drop', giving drop' n# xs = case xs of [] -> [] (y:ys) -> case n# of 0 -> [] _ -> drop (n# -# 1#) xs Much better! We'd also like to catch cases where a parameter is carried along unchanged, but evaluated each time round the loop: f i n = if i>0 || i>n then i else f (i*2) n Here f isn't strict in n, but we'd like to avoid evaluating it each iteration. In Core, by the time we've w/wd (f is strict in i) we get f i# n = case i# ># 0 of False -> I# i# True -> case n of n' { I# n# -> case i# ># n# of False -> I# i# True -> f (i# *# 2#) n' 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. 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] ~~~~~~~~~~~~~~~~~~~~~ So we look for * A self-recursive function. Ignore mutual recursion for now, because it's less common, and the code is simpler for self-recursion. * EITHER a) At a recursive call, one or more parameters is an explicit constructor application AND That same parameter is scrutinised by a case somewhere in the RHS of the function OR b) At a recursive call, one or more parameters has an unfolding that is an explicit constructor application AND That same parameter is scrutinised by a case somewhere in the RHS of the function AND Those are the only uses of the parameter (see Note [Reboxing]) What to abstract over ~~~~~~~~~~~~~~~~~~~~~ There's a bit of a complication with type arguments. If the call site looks like f p = ...f ((:) [a] x xs)... then our specialised function look like f_spec x xs = let p = (:) [a] x xs in ....as before.... This only makes sense if either a) the type variable 'a' is in scope at the top of f, or b) the type variable 'a' is an argument to f (and hence fs) Actually, (a) may hold for value arguments too, in which case we may not want to pass them. Supose 'x' is in scope at f's defn, but xs is not. Then we'd like f_spec xs = let p = (:) [a] x xs in ....as before.... Similarly (b) may hold too. If x is already an argument at the call, no need to pass it again. Finally, if 'a' is not in scope at the call site, we could abstract it as we do the term variables: f_spec a x xs = let p = (:) [a] x xs in ...as before... So the grand plan is: * abstract the call site to a constructor-only pattern e.g. C x (D (f p) (g q)) ==> C s1 (D s2 s3) * Find the free variables of the abstracted pattern * Pass these variables, less any that are in scope at the fn defn. But see Note [Shadowing] below. NOTICE that we only abstract over variables that are not in scope, so we're in no danger of shadowing variables used in "higher up" in f_spec's RHS. Note [Shadowing] ~~~~~~~~~~~~~~~~ In this pass we gather up usage information that may mention variables that are bound between the usage site and the definition site; or (more seriously) may be bound to something different at the definition site. For example: f x = letrec g y v = let x = ... in ...(g (a,b) x)... Since 'x' is in scope at the call site, we may make a rewrite rule that looks like RULE forall a,b. g (a,b) x = ... But this rule will never match, because it's really a different 'x' at the call site -- and that difference will be manifest by the time the simplifier gets to it. [A worry: the simplifier doesn't *guarantee* no-shadowing, so perhaps it may not be distinct?] Anyway, the rule isn't actually wrong, it's just not useful. One possibility 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. ----------------------------------------------------- Stuff not yet handled ----------------------------------------------------- Here are notes arising from Roman's work that I don't want to lose. Example 1 ~~~~~~~~~ data T a = T !a foo :: Int -> T Int -> Int foo 0 t = 0 foo x t | even x = case t of { T n -> foo (x-n) t } | otherwise = foo (x-1) t SpecConstr does no specialisation, because the second recursive call looks like a boxed use of the argument. A pity. $wfoo_sFw :: GHC.Prim.Int# -> T.T GHC.Base.Int -> GHC.Prim.Int# $wfoo_sFw = \ (ww_sFo [Just L] :: GHC.Prim.Int#) (w_sFq [Just L] :: T.T GHC.Base.Int) -> case ww_sFo of ds_Xw6 [Just L] { __DEFAULT -> case GHC.Prim.remInt# ds_Xw6 2 of wild1_aEF [Dead Just A] { __DEFAULT -> $wfoo_sFw (GHC.Prim.-# ds_Xw6 1) w_sFq; 0 -> case w_sFq of wild_Xy [Just L] { T.T n_ad5 [Just U(L)] -> case n_ad5 of wild1_aET [Just A] { GHC.Base.I# y_aES [Just L] -> $wfoo_sFw (GHC.Prim.-# ds_Xw6 y_aES) wild_Xy } } }; 0 -> 0 Example 2 ~~~~~~~~~ data a :*: b = !a :*: !b data T a = T !a foo :: (Int :*: T Int) -> Int foo (0 :*: t) = 0 foo (x :*: t) | even x = case t of { T n -> foo ((x-n) :*: t) } | otherwise = foo ((x-1) :*: t) Very similar to the previous one, except that the parameters are now in a strict tuple. Before SpecConstr, we have $wfoo_sG3 :: GHC.Prim.Int# -> T.T GHC.Base.Int -> GHC.Prim.Int# $wfoo_sG3 = \ (ww_sFU [Just L] :: GHC.Prim.Int#) (ww_sFW [Just L] :: T.T GHC.Base.Int) -> case ww_sFU of ds_Xws [Just L] { __DEFAULT -> case GHC.Prim.remInt# ds_Xws 2 of wild1_aEZ [Dead Just A] { __DEFAULT -> case ww_sFW of tpl_B2 [Just L] { T.T a_sFo [Just A] -> $wfoo_sG3 (GHC.Prim.-# ds_Xws 1) tpl_B2 -- $wfoo1 }; 0 -> case ww_sFW of wild_XB [Just A] { T.T n_ad7 [Just S(L)] -> case n_ad7 of wild1_aFd [Just L] { GHC.Base.I# y_aFc [Just L] -> $wfoo_sG3 (GHC.Prim.-# ds_Xws y_aFc) wild_XB -- $wfoo2 } } }; 0 -> 0 } We get two specialisations: "SC:$wfoo1" [0] __forall {a_sFB :: GHC.Base.Int sc_sGC :: GHC.Prim.Int#} Foo.$wfoo sc_sGC (Foo.T @ GHC.Base.Int a_sFB) = Foo.$s$wfoo1 a_sFB sc_sGC ; "SC:$wfoo2" [0] __forall {y_aFp :: GHC.Prim.Int# sc_sGC :: GHC.Prim.Int#} Foo.$wfoo sc_sGC (Foo.T @ GHC.Base.Int (GHC.Base.I# y_aFp)) = Foo.$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, because T is strict and Int has one constructor. (We can't unbox the strict fields, becuase T is polymorphic!) %************************************************************************ %* * \subsection{Top level wrapper stuff} %* * %************************************************************************ \begin{code} specConstrProgram :: DynFlags -> UniqSupply -> [CoreBind] -> IO [CoreBind] specConstrProgram dflags us binds = do showPass dflags "SpecConstr" let (binds', _) = initUs us (go (initScEnv dflags) 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' where go _ [] = return [] go env (bind:binds) = do (env', bind') <- scTopBind env bind binds' <- go env' binds return (bind' : binds') \end{code} %************************************************************************ %* * \subsection{Environment: goes downwards} %* * %************************************************************************ \begin{code} data ScEnv = SCE { sc_size :: Maybe Int, -- Size threshold sc_count :: Maybe Int, -- Max # of specialisations for any one fn sc_subst :: Subst, -- Current substitution -- Maps InIds to OutExprs 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) } --------------------- -- As we go, we apply a substitution (sc_subst) to the current term type InExpr = CoreExpr -- *Before* applying the subst type OutExpr = CoreExpr -- *After* applying the subst type OutId = Id type OutVar = Var --------------------- type HowBoundEnv = VarEnv HowBound -- Domain is OutVars --------------------- type ValueEnv = IdEnv Value -- Domain is OutIds data Value = ConVal AltCon [CoreArg] -- *Saturated* constructors | LambdaVal -- Inlinable lambdas or PAPs instance Outputable Value where ppr (ConVal con args) = ppr con <+> interpp'SP args ppr LambdaVal = ptext SLIT("") --------------------- initScEnv :: DynFlags -> ScEnv initScEnv dflags = SCE { sc_size = specConstrThreshold dflags, sc_count = specConstrCount dflags, sc_subst = emptySubst, sc_how_bound = emptyVarEnv, sc_vals = emptyVarEnv } data HowBound = RecFun -- These are the recursive functions for which -- we seek interesting call patterns | 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" lookupHowBound :: ScEnv -> Id -> Maybe HowBound lookupHowBound env id = lookupVarEnv (sc_how_bound env) id scSubstId :: ScEnv -> Id -> CoreExpr scSubstId env v = lookupIdSubst (sc_subst env) v scSubstTy :: ScEnv -> Type -> Type scSubstTy env ty = substTy (sc_subst env) ty zapScSubst :: ScEnv -> ScEnv zapScSubst env = env { sc_subst = zapSubstEnv (sc_subst env) } 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 (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 -> CoreExpr -> Id -> AltCon -> [Var] -> ScEnv -- When we encounter -- case scrut of b -- C x y -> ... -- we want to bind b, and perhaps scrut too, to (C x y) -- NB: Extends only the sc_vals part of the envt extendCaseBndrs env scrut case_bndr con alt_bndrs = case scrut of Var v -> extendValEnv env1 v cval _other -> env1 where 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 \end{code} %************************************************************************ %* * \subsection{Usage information: flows upwards} %* * %************************************************************************ \begin{code} data ScUsage = SCU { scu_calls :: CallEnv, -- Calls -- The functions are a subset of the -- RecFuns in the ScEnv scu_occs :: !(IdEnv ArgOcc) -- Information on argument occurrences } -- The domain is OutIds 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 :: ScUsage nullUsage = SCU { scu_calls = emptyVarEnv, scu_occs = emptyVarEnv } 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 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) 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]) 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} %************************************************************************ %* * \subsection{The main recursive function} %* * %************************************************************************ The main recursive function gathers up usage information, and creates specialised versions of functions. \begin{code} 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 = 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_con_app con args scrut' -- Known constructor; simplify = do { let (_, bs, rhs) = findAlt con 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, bs') = extendBndrsWith RecArg env bs env2 = extendCaseBndrs env1 scrut' b' con bs' ; (usg,rhs') <- scExpr env2 rhs ; let (usg', arg_occs) = lookupOccs usg bs' scrut_occ = case con of DataAlt dc -> ScrutOcc (unitUFM dc arg_occs) _ofther -> ScrutOcc emptyUFM ; return (usg', scrut_occ, (con,bs',rhs')) } scExpr' env (Let (NonRec bndr rhs) body) | isTyVar bndr -- Type-lets may be created by doBeta = scExpr' (extendScSubst env bndr rhs) body | otherwise = do { let (body_env, bndr') = extendBndr env bndr ; (rhs_usg, (_, args', rhs_body', _)) <- scRecRhs env (bndr',rhs) ; let rhs' = mkLams args' rhs_body' ; if not opt_SpecInlineJoinPoints || null args' || isEmptyVarEnv (scu_calls rhs_usg) then do do { -- Vanilla case let body_env2 = extendValEnv body_env bndr' (isValue (sc_vals env) rhs') -- Record if the RHS is a value ; (body_usg, body') <- scExpr body_env2 body ; return (body_usg `combineUsage` rhs_usg, Let (NonRec bndr' rhs') body') } else -- For now, just brutally inline the join point do { let body_env2 = extendScSubst env bndr rhs' ; scExpr body_env2 body } } {- Old code do { -- Join-point case let body_env2 = extendHowBound body_env [bndr'] RecFun -- If the RHS of this 'let' contains calls -- to recursive functions that we're trying -- to specialise, then treat this let too -- as one to specialise ; (body_usg, body') <- scExpr body_env2 body ; (spec_usg, _, specs) <- specialise env (scu_calls body_usg) ([], rhs_info) ; return (body_usg { scu_calls = scu_calls body_usg `delVarEnv` bndr' } `combineUsage` rhs_usg `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 ; (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 (scu_calls body_usg) rhs_infos nullUsage [SI [] 0 (Just usg) | usg <- rhs_usgs] ; 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') } ----------------------------------- 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 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') } ---------------------- scTopBind :: ScEnv -> CoreBind -> UniqSM (ScEnv, CoreBind) scTopBind env (Rec prs) | Just threshold <- sc_size env , 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 (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 (bndrs,rhss) = unzip prs 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') } ---------------------- 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, (bndr, 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 (fn, args, body, _) (SI specs _ _) = [(id,rhs) | OS _ _ id rhs <- specs] ++ [(fn `addIdSpecialisations` rules, mkLams args body)] where rules = [r | OS _ r _ _ <- specs] ---------------------- varUsage :: ScEnv -> OutVar -> ArgOcc -> ScUsage varUsage env v use | Just RecArg <- lookupHowBound env v = SCU { scu_calls = emptyVarEnv , scu_occs = unitVarEnv v use } | otherwise = nullUsage \end{code} %************************************************************************ %* * The specialiser itself %* * %************************************************************************ \begin{code} type RhsInfo = (OutId, [OutVar], OutExpr, [ArgOcc]) -- Info about the *original* RHS of a binding we are specialising -- Original binding f = \xs.body -- Plus info about usage of arguments 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 -- 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 -> CallEnv -> [RhsInfo] -> ScUsage -> [SpecInfo] -- One per binder; acccumulating parameter -> UniqSM (ScUsage, [SpecInfo]) -- ...ditto... specLoop env all_calls rhs_infos usg_so_far specs_so_far = do { specs_w_usg <- zipWithM (specialise env 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 new_calls rhs_infos all_usg all_specs } specialise :: ScEnv -> 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 bind_calls (fn, arg_bndrs, body, arg_occs) spec_info@(SI specs spec_count mb_unspec) | 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 <+> ppr arg_occs, -- text "calls" <+> ppr all_calls, -- text "good pats" <+> ppr pats]) $ -- return () -- Bale out if too many specialisations -- Rather a hacky way to do so, but it'll do for now ; let spec_count' = length pats + spec_count ; case sc_count env of Just max | spec_count' > max -> pprTrace "SpecConstr: too many specialisations for one function (see -fspec-constr-count):" (vcat [ptext SLIT("Function:") <+> ppr fn, ptext SLIT("Specialisations:") <+> ppr (pats ++ [p | OS p _ _ _ <- specs])]) return (nullUsage, spec_info) _normal_case -> do { (spec_usgs, new_specs) <- mapAndUnzipM (spec_one env fn arg_bndrs body) (pats `zip` [spec_count..]) ; 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 --------------------- spec_one :: ScEnv -> OutId -- Function -> [Var] -- Lambda-binders of RHS; should match patterns -> CoreExpr -- 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 -- function is, considering what it does :-). {- Example In-scope: a, x::a f = /\b \y::[(a,b)] -> ....f (b,c) ((:) (a,(b,c)) (x,v) (h w))... [c::*, v::(b,c) are presumably bound by the (...) part] ==> f_spec = /\ b c \ v::(b,c) hw::[(a,(b,c))] -> (...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), hw::[(a,(b,c))] . f (b,c) ((:) (a,(b,c)) (x,v) hw) = f_spec b c v hw -} spec_one env fn arg_bndrs body (call_pat@(qvars, pats), rule_number) = do { -- Specialise the body let spec_env = extendScSubstList (extendScInScope env qvars) (arg_bndrs `zip` pats) ; (spec_usg, spec_body) <- scExpr spec_env body -- ; pprTrace "spec_one" (ppr fn <+> vcat [text "pats" <+> ppr pats, -- text "calls" <+> (ppr (scu_calls spec_usg))]) -- (return ()) -- And build the results ; spec_uniq <- getUniqueUs ; let (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 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_rhs = mkLams spec_lam_args spec_body spec_id = mkUserLocal spec_occ spec_uniq (mkPiTypes spec_lam_args body_ty) fn_loc body_ty = exprType spec_body rule_rhs = mkVarApps (Var spec_id) spec_call_args rule = mkLocalRule rule_name specConstrActivation fn_name qvars pats rule_rhs ; return (spec_usg, OS call_pat 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} %************************************************************************ %* * \subsection{Argument analysis} %* * %************************************************************************ 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 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 isTyVar 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 :: 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 _in_scope _val_env arg@(Type {}) _arg_occ = return (False, arg) argToPat in_scope val_env (Note _ arg) arg_occ = argToPat 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 in_scope val_env (Let _ arg) arg_occ = argToPat in_scope val_env arg arg_occ -- Look through let expressions -- e.g. f (let v = rhs in \y -> ...v...) -- Here we can specialise for f (\y -> ...) -- because the rule-matcher will look through the let. argToPat in_scope val_env (Cast arg co) arg_occ = do { (interesting, arg') <- argToPat in_scope val_env arg arg_occ ; let (ty1,ty2) = coercionKind co ; 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)) } } {- 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 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 -} -- Check for a constructor application -- NB: this *precedes* the Var case, so that we catch nullary constrs argToPat in_scope val_env arg arg_occ | Just (ConVal dc args) <- isValue val_env arg , 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 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 in_scope val_env (Var v) arg_occ | case arg_occ of { UnkOcc -> False; _other -> True }, -- (a) is_value -- (b) = 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 _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 :: InScopeSet -> ValueEnv -> [(CoreArg, ArgOcc)] -> UniqSM [(Bool, CoreArg)] argsToPats in_scope val_env args = mapM do_one args where do_one (arg,occ) = argToPat in_scope val_env arg occ \end{code} \begin{code} 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 | 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) | isTyVar b = isValue env e | otherwise = Just LambdaVal isValue _env expr -- Maybe it's a constructor application | (Var fun, args) <- collectArgs expr = case isDataConWorkId_maybe fun of Just con | args `lengthAtLeast` dataConRepArity con -- Check saturated; might be > because the -- arity excludes type args -> Just (ConVal (DataAlt con) args) _other | valArgCount args < idArity fun -- Under-applied function -> Just LambdaVal -- Partial application _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.