{-# LANGUAGE CPP #-} #if __GLASGOW_HASKELL__ < 905 {-# LANGUAGE PatternSynonyms #-} #endif {- ToDo [Oct 2013] ~~~~~~~~~~~~~~~ 1. Nuke ForceSpecConstr for good (it is subsumed by GHC.Types.SPEC in ghc-prim) 2. Nuke NoSpecConstr (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 \section[SpecConstr]{Specialise over constructors} -} {-# OPTIONS_GHC -Wno-incomplete-uni-patterns #-} module GHC.Core.Opt.SpecConstr( specConstrProgram, SpecConstrAnnotation(..) ) where import GHC.Prelude import GHC.Driver.Session ( DynFlags(..), GeneralFlag( Opt_SpecConstrKeen ) , gopt, hasPprDebug ) import GHC.Core import GHC.Core.Subst import GHC.Core.Utils import GHC.Core.Unfold import GHC.Core.FVs ( exprsFreeVarsList, exprFreeVars ) import GHC.Core.Opt.Monad import GHC.Core.Opt.WorkWrap.Utils import GHC.Core.Opt.OccurAnal( scrutBinderSwap_maybe ) import GHC.Core.DataCon import GHC.Core.Class( classTyVars ) import GHC.Core.Coercion hiding( substCo ) import GHC.Core.Rules import GHC.Core.Predicate ( typeDeterminesValue ) import GHC.Core.Type hiding ( substTy ) import GHC.Core.TyCon (TyCon, tyConName ) import GHC.Core.Multiplicity import GHC.Core.Ppr ( pprParendExpr ) import GHC.Core.Make ( mkImpossibleExpr ) import GHC.Unit.Module import GHC.Unit.Module.ModGuts import GHC.Types.Literal ( litIsLifted ) import GHC.Types.Id import GHC.Types.Id.Info ( IdDetails(..) ) import GHC.Types.Var.Env import GHC.Types.Var.Set import GHC.Types.Name import GHC.Types.Tickish import GHC.Types.Basic import GHC.Types.Demand import GHC.Types.Cpr import GHC.Types.Unique.Supply import GHC.Types.Unique.FM import GHC.Types.Unique( hasKey ) import GHC.Data.Maybe ( orElse, catMaybes, isJust, isNothing ) import GHC.Data.Pair import GHC.Data.FastString import GHC.Utils.Misc import GHC.Utils.Outputable import GHC.Utils.Panic.Plain import GHC.Utils.Panic import GHC.Utils.Constants (debugIsOn) import GHC.Utils.Monad import GHC.Builtin.Names ( specTyConKey ) import GHC.Exts( SpecConstrAnnotation(..) ) import GHC.Serialized ( deserializeWithData ) import Control.Monad ( zipWithM ) import Data.List (nubBy, sortBy, partition, dropWhileEnd, mapAccumL ) import Data.Maybe( mapMaybe ) import Data.Ord( comparing ) import Data.Tuple {- ----------------------------------------------------- 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 { 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 known 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-scrutinisation 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. Suppose '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 lambda 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 constructor application inside the cast. That's why we have the Cast case in argToPat Note [Seeding recursive groups] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ For a recursive group that is either * nested, or * top-level, but with no exported Ids we can see all the calls to the function, so we seed the specialisation loop from the calls in the body, and /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. In a case like the above we end up never calling the original un-specialised function. (Although we still leave its code around just in case.) Wrinkles * Boring calls. If we find any boring calls in the body, including *unsaturated* ones, such as letrec foo x y = ....foo... in map foo xs then we will end up calling the un-specialised function, so then we *should* use the calls in the un-specialised RHS as seeds. We call these "boring call patterns", and callsToNewPats reports if it finds any of these. Then 'specialise' unleashes the usage info from the un-specialised RHS. * Exported Ids. `specialise` /also/ unleashes `si_mb_unspec` for exported Ids. That way we are sure to generate usage info from the /un-specialised/ RHS of an exported function. More precisely: * Always start from the calls in the body of the let or (for top level) calls in the rest of the module. See the body_calls in the call to `specialise` in `specNonRec`, and to `go` in `specRec`. * si_mb_unspec holds the usage from the unspecialised RHS. See `initSpecInfo`. * `specialise` will unleash si_mb_unspec, if - `callsToNewPats` reports "boring calls found", or - this is a top-level exported Id. Historical note. At an earlier point, if a top-level Id was exported, we used only seeds from the RHS, and /not/from the body. But Dimitrios had an example where using call patterns from the body (the other defns in the module) was crucial. And doing so improved nofib allocation results: multiplier: 4% better minimax: 2.8% better In any case, it is easier to do! 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 strictness 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 do this, in one of two ways (one which is deprecated): 1) Add a parameter of type GHC.Types.SPEC (from ghc-prim) to the loop body. 2) (Deprecated) Annotate a type with ForceSpecConstr from GHC.Exts, and then add *that* type as a parameter to the loop body The reason #2 is deprecated is because it requires GHCi, which isn't available for things like a cross compiler using stage1. Here's a (simplified) example from the `vector` package. You may bring the special 'force specialization' type into scope by saying: import GHC.Types (SPEC(..)) or by defining your own type (again, deprecated): data SPEC = SPEC | SPEC2 {-# ANN type SPEC ForceSpecConstr #-} (Note this is the exact same definition of GHC.Types.SPEC, just without the annotation.) After that, you say: 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 have to prevent the SPEC argument from being removed by w/w which is why (a) SPEC is a sum type, and (b) we have to seq on the SPEC argument. * And lastly, the SPEC argument is ultimately eliminated by SpecConstr itself so there is no runtime overhead. 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 sc_force to True when calling specLoop. This flag does four things: * Ignore specConstrThreshold, to specialise functions of arbitrary size (see scTopBind) * Ignore specConstrCount, to make arbitrary numbers of specialisations (see specialise) * Specialise even for arguments that are not scrutinised in the loop (see argToPat; #4448) * Only specialise on recursive types a finite number of times (see is_too_recursive; #5550; Note [Limit recursive specialisation]) The flag holds only for specialising a single binding group, and NOT for nested bindings. (So really it should be passed around explicitly and not stored in ScEnv.) #14379 turned out to be caused by f SPEC x = let g1 x = ... in ... We force-specialise f (because of the SPEC), but that generates a specialised copy of g1 (as well as the original). Alas g1 has a nested binding g2; and in each copy of g1 we get an unspecialised and specialised copy of g2; and so on. Result, exponential. So the force-spec flag now only applies to one level of bindings at a time. Mechanism for this one-level-only thing: - Switch it on at the call to specRec, in scExpr and scTopBinds - Switch it off when doing the RHSs; this can be done very conveniently in decreaseSpecCount What alternatives did I consider? * Annotating the loop itself doesn't work because (a) it is local and (b) it will be w/w'ed and having w/w propagating annotations somehow doesn't seem like a good idea. The types of the loop arguments really seem to be the most persistent thing. * Annotating the types that make up the loop state doesn't work, either, because (a) it would prevent us from using types like Either or tuples here, (b) we don't want to restrict the set of types that can be used in Stream states and (c) some types are fixed by the user (e.g., the accumulator here) but we still want to specialise as much as possible. Alternatives to ForceSpecConstr ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Instead of giving the loop an extra argument of type SPEC, we also considered *wrapping* arguments in SPEC, thus data SPEC a = SPEC a | SPEC2 loop = \arg -> case arg of SPEC state -> case state of (x,y) -> ... loop (SPEC (x',y')) ... S2 -> error ... The idea is that a SPEC argument says "specialise this argument regardless of whether the function case-analyses it". But this doesn't work well: * SPEC must still be a sum type, else the strictness analyser eliminates it * But that means that 'loop' won't be strict in its real payload This loss of strictness in turn screws up specialisation, because we may end up with calls like loop (SPEC (case z of (p,q) -> (q,p))) Without the SPEC, if 'loop' were strict, the case would move out and we'd see loop applied to a pair. But if 'loop' isn't strict this doesn't look like a specialisable call. Note [Limit recursive specialisation] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ It is possible for ForceSpecConstr to cause an infinite loop of specialisation. Because there is no limit on the number of specialisations, a recursive call with a recursive constructor as an argument (for example, list cons) will generate a specialisation for that constructor. If the resulting specialisation also contains a recursive call with the constructor, this could proceed indefinitely. For example, if ForceSpecConstr is on: loop :: [Int] -> [Int] -> [Int] loop z [] = z loop z (x:xs) = loop (x:z) xs this example will create a specialisation for the pattern loop (a:b) c = loop' a b c loop' a b [] = (a:b) loop' a b (x:xs) = loop (x:(a:b)) xs and a new pattern is found: loop (a:(b:c)) d = loop'' a b c d which can continue indefinitely. Roman's suggestion to fix this was to stop after a couple of times on recursive types, but still specialising on non-recursive types as much as possible. To implement this, we count the number of times we have gone round the "specialise recursively" loop ('go' in 'specRec'). Once have gone round more than N times (controlled by -fspec-constr-recursive=N) we check - If sc_force is off, and sc_count is (Just max) then we don't need to do anything: trim_pats will limit the number of specs - Otherwise check if any function has now got more than (sc_count env) specialisations. If sc_count is "no limit" then we arbitrarily choose 10 as the limit (ugh). See #5550. Also #13623, where this test had become over-aggressive, and we lost a wonderful specialisation that we really wanted! Note [NoSpecConstr] ~~~~~~~~~~~~~~~~~~~ The ignoreDataCon stuff allows you to say {-# ANN type T NoSpecConstr #-} to mean "don't specialise on arguments of this type". It was added before we had ForceSpecConstr. Lacking ForceSpecConstr we specialised regardless of size; and then we needed a way to turn that *off*. Now that we have ForceSpecConstr, this NoSpecConstr is probably redundant. (Used only for PArray, TODO: remove?) Note [SpecConstr and strict fields] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We treat strict fields in SpecConstr the same way we do in W/W. That is we make the specialized function strict in arguments representing strict fields. See Note [Call-by-value for worker args] for why we do this. Note [Specialising on dictionaries] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ In #21386, SpecConstr saw this call: $wgo 100# @.. ($fMonadStateT @.. @.. $fMonadIdentity) where $wgo :: Int# -> forall m. Monad m => blah You might think that the type-class Specialiser would have specialised this, but there are good reasons why not: the Specialiser ran too early. But regardless, SpecConstr can and should! It's easy: * isValue: treat ($fblah d1 .. dn) like a constructor application. * scApp: treat (op_sel d), a class method selection, like a case expression * Float that dictionary application to top level, thus lvl = $fMonadStateT @.. @.. $fMonadIdentity so the call looks like ($wgo 100# @.. lvl) Why? This way dictionaries will appear as top level binders which we can trivially match in rules. (CSE runs before SpecConstr, so we may hope to common-up duplicate top-level dictionaries.) For the floating part, see the "Arguments" case of Note [Floating to the top] in GHC.Core.Opt.SetLevels. We could be more clever, perhaps, and generate a RULE like $wgo _ @.. ($fMonadStateT @.. @.. $fMonadIdentity) = $s$wgo ... but that would mean making argToPat able to spot dfun applications as well as constructor applications. Wrinkles: * This should all work perfectly fine for newtype classes. Mind you, currently newtype classes are inlined fairly agressively, but we may change that. And it would take extra code to exclude them, as well as being unnecessary. * In isValue, we (mis-) use LambdaVal for this ($fblah d1 .. dn) because ConVal requires us to list the data constructor and fields, and that is (a) inconvenient and (b) unnecessary for class methods. ----------------------------------------------------- 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, because T is polymorphic!) ************************************************************************ * * \subsection{Top level wrapper stuff} * * ************************************************************************ -} specConstrProgram :: ModGuts -> CoreM ModGuts specConstrProgram guts = do { env0 <- initScEnv guts ; us <- getUniqueSupplyM ; let (_usg, binds') = initUs_ us $ scTopBinds env0 (mg_binds guts) ; return (guts { mg_binds = binds' }) } scTopBinds :: ScEnv -> [InBind] -> UniqSM (ScUsage, [OutBind]) scTopBinds _env [] = return (nullUsage, []) scTopBinds env (b:bs) = do { (usg, b', bs') <- scBind TopLevel env b $ (\env -> scTopBinds env bs) ; return (usg, b' ++ bs') } {- ************************************************************************ * * \subsection{Environment: goes downwards} * * ************************************************************************ Note [Work-free values only in environment] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The sc_vals field keeps track of in-scope value bindings, so that if we come across (case x of Just y ->...) we can reduce the case from knowing that x is bound to a pair. But only *work-free* values are ok here. For example if the envt had x -> Just (expensive v) then we do NOT want to expand to let y = expensive v in ... because the x-binding still exists and we've now duplicated (expensive v). This seldom happens because let-bound constructor applications are ANF-ised, but it can happen as a result of on-the-fly transformations in SpecConstr itself. Here is #7865: let { a'_shr = case xs_af8 of _ { [] -> acc_af6; : ds_dgt [Dmd=] ds_dgu [Dmd=] -> (expensive x_af7, x_af7 } } in let { ds_sht = case a'_shr of _ { (p'_afd, q'_afe) -> TSpecConstr_DoubleInline.recursive (GHC.Types.: @ GHC.Types.Int x_af7 wild_X6) (q'_afe, p'_afd) } } in When processed knowing that xs_af8 was bound to a cons, we simplify to a'_shr = (expensive x_af7, x_af7) and we do NOT want to inline that at the occurrence of a'_shr in ds_sht. (There are other occurrences of a'_shr.) No no no. It would be possible to do some on-the-fly ANF-ising, so that a'_shr turned into a work-free value again, thus a1 = expensive x_af7 a'_shr = (a1, x_af7) but that's more work, so until its shown to be important I'm going to leave it for now. Note [Making SpecConstr keener] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider this, in (perf/should_run/T9339) last (filter odd [1..1000]) After optimisation, including SpecConstr, we get: f :: Int# -> Int -> Int f x y = case remInt# x 2# of __DEFAULT -> case x of __DEFAULT -> f (+# wild_Xp 1#) (I# x) 1000000# -> ... 0# -> case x of __DEFAULT -> f (+# wild_Xp 1#) y 1000000# -> y Not good! We build an (I# x) box every time around the loop. SpecConstr (as described in the paper) does not specialise f, despite the call (f ... (I# x)) because 'y' is not scrutinised in the body. But it is much better to specialise f for the case where the argument is of form (I# x); then we build the box only when returning y, which is on the cold path. Another example: f x = ...(g x).... Here 'x' is not scrutinised in f's body; but if we did specialise 'f' then the call (g x) might allow 'g' to be specialised in turn. So sc_keen controls whether or not we take account of whether argument is scrutinised in the body. True <=> ignore that, and specialise whenever the function is applied to a data constructor. -} -- | Options for Specializing over constructors in Core. data SpecConstrOpts = SpecConstrOpts { sc_max_args :: !Int -- ^ The threshold at which a worker-wrapper transformation used as part of -- this pass will no longer happen, measured in the number of arguments. , sc_debug :: !Bool -- ^ Whether to print debug information , sc_uf_opts :: !UnfoldingOpts -- ^ Unfolding options , sc_module :: !Module -- ^ The name of the module being processed , sc_size :: !(Maybe Int) -- ^ Size threshold: Nothing => no limit , sc_count :: !(Maybe Int) -- ^ Max # of specialisations for any one function. Nothing => no limit. -- See Note [Avoiding exponential blowup] and decreaseSpecCount , sc_recursive :: !Int -- ^ Max # of specialisations over recursive type. Stops -- ForceSpecConstr from diverging. , sc_keen :: !Bool -- ^ Specialise on arguments that are known constructors, even if they are -- not scrutinised in the body. See Note [Making SpecConstr keener]. } data ScEnv = SCE { sc_opts :: !SpecConstrOpts, sc_force :: Bool, -- Force specialisation? -- See Note [Forcing specialisation] 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) -- The range of the ValueEnv is *work-free* values -- such as (\x. blah), or (Just v) -- but NOT (Just (expensive v)) -- See Note [Work-free values only in environment] sc_annotations :: UniqFM Name SpecConstrAnnotation } --------------------- type HowBoundEnv = VarEnv HowBound -- Domain is OutVars --------------------- type ValueEnv = IdEnv Value -- Domain is OutIds data Value = ConVal AltCon [CoreArg] -- _Saturated_ constructors -- The AltCon is never DEFAULT | LambdaVal -- Inlinable lambdas or PAPs instance Outputable Value where ppr (ConVal con args) = ppr con <+> interpp'SP args ppr LambdaVal = text "" --------------------- initScOpts :: DynFlags -> Module -> SpecConstrOpts initScOpts dflags this_mod = SpecConstrOpts { sc_max_args = maxWorkerArgs dflags, sc_debug = hasPprDebug dflags, sc_uf_opts = unfoldingOpts dflags, sc_module = this_mod, sc_size = specConstrThreshold dflags, sc_count = specConstrCount dflags, sc_recursive = specConstrRecursive dflags, sc_keen = gopt Opt_SpecConstrKeen dflags } initScEnv :: ModGuts -> CoreM ScEnv initScEnv guts = do { dflags <- getDynFlags ; (_, anns) <- getFirstAnnotations deserializeWithData guts ; this_mod <- getModule ; return (SCE { sc_opts = initScOpts dflags this_mod, sc_force = False, sc_subst = init_subst, sc_how_bound = emptyVarEnv, sc_vals = emptyVarEnv, sc_annotations = anns }) } where init_subst = mkEmptySubst $ mkInScopeSetBndrs (mg_binds guts) -- Acccount for top-level bindings that are not in dependency order; -- see Note [Glomming] in GHC.Core.Opt.OccurAnal -- Easiest thing is to bring all the top level binders into scope at once, -- as if at once, as if all the top-level decls were mutually recursive. 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" scForce :: ScEnv -> Bool -> ScEnv scForce env b = env { sc_force = b } lookupHowBound :: ScEnv -> OutId -> Maybe HowBound lookupHowBound env id = lookupVarEnv (sc_how_bound env) id scSubstId :: ScEnv -> InId -> OutExpr scSubstId env v = lookupIdSubst (sc_subst env) v -- Solo is only defined in base starting from ghc-9.2 #if !(MIN_VERSION_base(4, 16, 0)) data Solo a = Solo a #endif -- The Solo constructor was renamed to MkSolo in ghc 9.5 #if __GLASGOW_HASKELL__ < 905 pattern MkSolo :: a -> Solo a pattern MkSolo a = Solo a #endif -- The !subst ensures that we force the selection `(sc_subst env)`, which avoids -- retaining all of `env` when we only need `subst`. The `Solo` means that the -- substitution itself is lazy, because that type is often discarded. -- The callers of `scSubstTy` always force the result (to unpack the `Solo`) -- so we get the desired effect: we leave a thunk, but retain only the subst, -- not the whole env. -- -- Fully forcing the result of `scSubstTy` regresses performance (#22102) scSubstTy :: ScEnv -> InType -> Solo OutType scSubstTy env ty = let !subst = sc_subst env in MkSolo (substTyUnchecked subst ty) scSubstCo :: ScEnv -> Coercion -> Coercion scSubstCo env co = substCo (sc_subst env) co zapScSubst :: ScEnv -> ScEnv zapScSubst env = env { sc_subst = zapSubst (sc_subst env) } extendScInScope :: ScEnv -> [Var] -> ScEnv -- Bring the quantified variables into scope extendScInScope env qvars = env { sc_subst = extendSubstInScopeList (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 extendBndrs :: ScEnv -> [Var] -> (ScEnv, [Var]) extendBndrs env bndrs = mapAccumL extendBndr 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) | valueIsWorkFree cv -- Don't duplicate work!! #7865 = env { sc_vals = extendVarEnv (sc_vals env) id cv } extendValEnv env _ _ = env extendCaseBndrs :: ScEnv -> OutExpr -> OutId -> 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 scrut case_bndr con alt_bndrs = (env2, alt_bndrs') where live_case_bndr = not (isDeadBinder case_bndr) env1 | Just (v, mco) <- scrutBinderSwap_maybe scrut , isReflMCo mco = extendValEnv env v cval | otherwise = env -- See Note [Add scrutinee to ValueEnv too] env2 | live_case_bndr = extendValEnv env1 case_bndr cval | otherwise = env1 alt_bndrs' | case scrut of { Var {} -> True; _ -> live_case_bndr } = map zap alt_bndrs | otherwise = alt_bndrs 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 zap v | isTyVar v = v -- See NB2 above | otherwise = zapIdOccInfo v decreaseSpecCount :: ScEnv -> Int -> ScEnv -- See Note [Avoiding exponential blowup] decreaseSpecCount env _n_specs = env { sc_force = False -- See Note [Forcing specialisation] , sc_opts = opts { sc_count = case sc_count opts of Nothing -> Nothing Just n -> Just $! dec n } } where opts = sc_opts env dec n = n `div` 2 -- See Note [Avoiding exponential blowup] -- Or: n `div` (n_specs + 1) -- See the historical note part of Note [Avoiding exponential blowup] -- The "+1" takes account of the original function; --------------------------------------------------- -- See Note [Forcing specialisation] ignoreType :: ScEnv -> Type -> Bool ignoreDataCon :: ScEnv -> DataCon -> Bool forceSpecBndr :: ScEnv -> Var -> Bool ignoreDataCon env dc = ignoreTyCon env (dataConTyCon dc) ignoreType env ty = case tyConAppTyCon_maybe ty of Just tycon -> ignoreTyCon env tycon _ -> False ignoreTyCon :: ScEnv -> TyCon -> Bool ignoreTyCon env tycon = lookupUFM (sc_annotations env) (tyConName tycon) == Just NoSpecConstr forceSpecBndr env var = forceSpecFunTy env . snd . splitForAllTyCoVars . varType $ var forceSpecFunTy :: ScEnv -> Type -> Bool forceSpecFunTy env = any (forceSpecArgTy env) . map scaledThing . fst . splitFunTys forceSpecArgTy :: ScEnv -> Type -> Bool forceSpecArgTy env ty | isFunTy ty = False | Just (tycon, tys) <- splitTyConApp_maybe ty = tycon `hasKey` specTyConKey || lookupUFM (sc_annotations env) (tyConName tycon) == Just ForceSpecConstr || any (forceSpecArgTy env) tys forceSpecArgTy _ _ = False {- Note [Add scrutinee to ValueEnv too] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider this: case x of y (a,b) -> case b of c I# v -> ...(f y)... By the time we get to the call (f y), the ValueEnv will have a binding for y, and for c y -> (a,b) c -> I# v BUT that's not enough! Looking at the call (f y) we see that y is pair (a,b), but we also need to know what 'b' is. So in extendCaseBndrs we must *also* add the binding b -> I# v else we lose a useful specialisation for f. This is necessary even though the simplifier has systematically replaced uses of 'x' with 'y' and 'b' with 'c' in the code. The use of 'b' in the ValueEnv came from outside the case. See #4908 for the live example. It's very like the binder-swap story, so we use scrutBinderSwap_maybe to identify suitable scrutinees -- but only if there is no cast (isReflMCo) because that's all that the ValueEnv allows. 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 specialisations. 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, because 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 (the maximum number of specialisations, in the ScEnv) by two. You might think that gives us n*(n/2)*(n/4)... copies of the innnermost thing, which is still exponential the depth. But we use integer division, rounding down, so if the starting sc_count is 3, we'll get 3 -> 1 -> 0, and stop. In fact, simply subtracting 1 would be good enough, for the same reason. Historical note: in the past we divided by (n_specs+1), where n_specs is the number of specialisations at this level; but that gets us down to zero jolly quickly, which I found led to some regressions. (An example is nofib/spectral/fibheaps, the getMin' function inside the outer function $sfibToList, which has several interesting call patterns.) ************************************************************************ * * \subsection{Usage information: flows upwards} * * ************************************************************************ -} 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] -- Domain is OutIds data Call = Call OutId [CoreArg] ValueEnv -- The arguments of the call, together with the -- env giving the constructor bindings at the call site -- We keep the function mainly for debug output -- -- The call is not necessarily saturated; we just put -- in however many args are visible at the call site instance Outputable ScUsage where ppr (SCU { scu_calls = calls, scu_occs = occs }) = text "SCU" <+> braces (sep [ text "calls =" <+> ppr calls , text "occs =" <+> ppr occs ]) instance Outputable Call where ppr (Call fn args _) = ppr fn <+> fsep (map pprParendExpr args) nullUsage :: ScUsage nullUsage = SCU { scu_calls = emptyVarEnv, scu_occs = emptyVarEnv } combineCalls :: CallEnv -> CallEnv -> CallEnv combineCalls = plusVarEnv_C (++) delCallsFor :: ScUsage -> [Var] -> ScUsage delCallsFor env bndrs = env { scu_calls = scu_calls env `delVarEnvList` bndrs } 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 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 -- See Note [ScrutOcc] (DataConEnv [ArgOcc]) -- [ArgOcc]: how the sub-components are used deadArgOcc :: ArgOcc -> Bool deadArgOcc (ScrutOcc {}) = False deadArgOcc UnkOcc = False deadArgOcc NoOcc = True specialisableArgOcc :: ArgOcc -> Bool -- | Does this occurence represent one worth specializing for. specialisableArgOcc UnkOcc = False specialisableArgOcc NoOcc = False specialisableArgOcc (ScrutOcc {}) = True {- 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) = text "scrut-occ" <> ppr xs ppr UnkOcc = text "unk-occ" ppr NoOcc = text "no-occ" evalScrutOcc :: ArgOcc -- We use evalScrutOcc for -- - mkVarUsage: applied functions -- - scApp: dicts that are the argument of a classop evalScrutOcc = ScrutOcc emptyUFM -- Experimentally, this version 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 aggressive; 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 UnkOcc (ScrutOcc ys) = ScrutOcc ys combineOcc (ScrutOcc xs) UnkOcc = ScrutOcc xs combineOcc UnkOcc UnkOcc = UnkOcc 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 (Tick _ 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 {- ************************************************************************ * * \subsection{The main recursive function} * * ************************************************************************ The main recursive function gathers up usage information, and creates specialised versions of functions. -} scBind :: TopLevelFlag -> ScEnv -> InBind -> (ScEnv -> UniqSM (ScUsage, a)) -- Specialise the scope of the binding -> UniqSM (ScUsage, [OutBind], a) scBind top_lvl env (NonRec bndr rhs) do_body | isTyVar bndr -- Type-lets may be created by doBeta = do { (final_usage, body') <- do_body (extendScSubst env bndr rhs) ; return (final_usage, [], body') } | not (isTopLevel top_lvl) -- Nested non-recursive value binding -- See Note [Specialising local let bindings] = do { let (body_env, bndr') = extendBndr env bndr -- Not necessary at top level; but here we are nested ; rhs_info <- scRecRhs env (bndr',rhs) ; let body_env2 = extendHowBound body_env [bndr'] RecFun rhs' = ri_new_rhs rhs_info body_env3 = extendValEnv body_env2 bndr' (isValue (sc_vals env) rhs') ; (body_usg, body') <- do_body body_env3 -- Now make specialised copies of the binding, -- based on calls in body_usg ; (spec_usg, specs) <- specNonRec env (scu_calls body_usg) rhs_info -- NB: For non-recursive bindings we inherit sc_force flag from -- the parent function (see Note [Forcing specialisation]) -- Specialized + original binding ; let spec_bnds = [NonRec b r | (b,r) <- ruleInfoBinds rhs_info specs] bind_usage = (body_usg `delCallsFor` [bndr']) `combineUsage` spec_usg -- Note [spec_usg includes rhs_usg] ; return (bind_usage, spec_bnds, body') } | otherwise -- Top-level, non-recursive value binding -- At top level we do not specialise non-recursive bindings; that -- is, we do not call specNonRec, passing the calls from the body. -- The original paper only specialised /recursive/ bindings, but -- we later started specialising nested non-recursive bindings: -- see Note [Specialising local let bindings] -- -- I tried always specialising non-recursive top-level bindings too, -- but found some regressions (see !8135). So I backed off. = do { (rhs_usage, rhs') <- scExpr env rhs -- At top level, we've already put all binders into scope; see initScEnv -- Hence no need to call `extendBndr`. But we still want to -- extend the `ValueEnv` to record the value of this binder. ; let body_env = extendValEnv env bndr (isValue (sc_vals env) rhs') ; (body_usage, body') <- do_body body_env ; return (rhs_usage `combineUsage` body_usage, [NonRec bndr rhs'], body') } scBind top_lvl env (Rec prs) do_body | isTopLevel top_lvl , Just threshold <- sc_size (sc_opts env) , not force_spec , not (all (couldBeSmallEnoughToInline (sc_uf_opts (sc_opts env)) threshold) rhss) = -- Do no specialisation if the RHSs are too big -- ToDo: I'm honestly not sure of the rationale of this size-testing, nor -- why it only applies at top level. But that's the way it has been -- for a while. See #21456. do { (body_usg, body') <- do_body rhs_env2 ; (rhs_usgs, rhss') <- mapAndUnzipM (scExpr env) rhss ; let all_usg = (combineUsages rhs_usgs `combineUsage` body_usg) `delCallsFor` bndrs' bind' = Rec (bndrs' `zip` rhss') ; return (all_usg, [bind'], body') } | otherwise = do { rhs_infos <- mapM (scRecRhs rhs_env2) (bndrs' `zip` rhss) ; (body_usg, body') <- do_body rhs_env2 ; (spec_usg, specs) <- specRec (scForce rhs_env2 force_spec) (scu_calls body_usg) rhs_infos -- Do not unconditionally generate specialisations from rhs_usgs -- Instead use them only if we find an unspecialised call -- See Note [Seeding recursive groups] ; let all_usg = (spec_usg `combineUsage` body_usg) -- Note [spec_usg includes rhs_usg] `delCallsFor` bndrs' bind' = Rec (concat (zipWithEqual "scExpr'" ruleInfoBinds rhs_infos specs)) -- zipWithEqual: length of returned [SpecInfo] -- should be the same as incoming [RhsInfo] ; return (all_usg, [bind'], body') } where (bndrs,rhss) = unzip prs force_spec = any (forceSpecBndr env) bndrs -- Note [Forcing specialisation] (rhs_env1,bndrs') | isTopLevel top_lvl = (env, bndrs) | otherwise = extendRecBndrs env bndrs -- At top level, we've already put all binders into scope; see initScEnv rhs_env2 = extendHowBound rhs_env1 bndrs' RecFun {- Note [Specialising local let bindings] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ It is not uncommon to find this 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. -} ------------------------ 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 (mkVarUsage env v' [], Var v') e' -> scExpr (zapScSubst env) e' scExpr' env (Type t) = let !(MkSolo ty') = scSubstTy env t in return (nullUsage, Type ty') scExpr' env (Coercion c) = return (nullUsage, Coercion (scSubstCo env c)) scExpr' _ e@(Lit {}) = return (nullUsage, e) scExpr' env (Tick t e) = do (usg, e') <- scExpr env e return (usg, Tick t e') scExpr' env (Cast e co) = do (usg, e') <- scExpr env e return (usg, mkCast e' (scSubstCo env co)) -- Important to use mkCast here -- See Note [SpecConstr call patterns] 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 (Let bind body) = do { (final_usage, binds', body') <- scBind NotTopLevel env bind $ (\env -> scExpr env body) ; return (final_usage, mkLets binds' body') } 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 Alt _ bs rhs = findAlt con alts `orElse` Alt DEFAULT [] (mkImpossibleExpr ty "SpecConstr") 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 scrut_occ = foldr combineOcc NoOcc 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 setScrutOcc, which -- in turn treats a bare-variable scrutinee specially ; let !(MkSolo ty') = scSubstTy env ty ; return (foldr combineUsage scrut_usg' alt_usgs, Case scrut' b' ty' alts') } single_alt = isSingleton alts sc_alt env scrut' b' (Alt con bs rhs) = do { let (env1, bs1) = extendBndrsWith RecArg env bs (env2, bs2) = extendCaseBndrs env1 scrut' b' con bs1 ; (usg, rhs') <- scExpr env2 rhs ; let (usg', b_occ:arg_occs) = lookupOccs usg (b':bs2) scrut_occ = case con of DataAlt dc -- See Note [Do not specialise evals] | not (single_alt && all deadArgOcc arg_occs) -> -- pprTrace "sc_alt1" (ppr b' $$ ppr con $$ ppr bs $$ ppr arg_occs) $ ScrutOcc (unitUFM dc arg_occs) _ -> -- pprTrace "sc_alt1" (ppr b' $$ ppr con $$ ppr bs $$ ppr arg_occs) $ UnkOcc ; return (usg', b_occ `combineOcc` scrut_occ, Alt con bs2 rhs') } {- Note [Do not specialise evals] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider f x y = case x of I# _ -> if y>1 then f x (y-1) else x Here `x` is scrutinised by a case, but only in an eval-like way; the /component/ of the I# is unused. We don't want to specialise this function, even if we find a call (f (I# z)), because nothing is gained * No case branches are discarded * No allocation in removed The specialised version would take an unboxed Int#, pass it along, and rebox it at the end. In fact this can cause significant regression. In #21763 we had: like f = ... case x of x' { I# n -> join j y = rhs in ...jump j x'... Now if we specialise `j` for the argument `I# n`, we'll end up reboxing it in `j`, without even removing an allocation from the call site. Reboxing is always a worry. But here we can ameliorate the problem as follows. * In scExpr (Case ...), for a /single-alternative/ case expression, in which the pattern binders are all unused, we build a UnkOcc for the scrutinee, not one that maps the data constructor; we don't treat this occurrence as a reason for specialisation. * Conveniently, SpecConstr is doing its own occurrence analysis, so the "unused" bit is just looking for NoOcc * Note that if we have f x = case x of { True -> e1; False -> e2 } then even though the pattern binders are unused (there are none), it is still worth specialising on x. Hence the /single-alternative/ guard. -} 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` mkVarUsage env fn' args', mkApps (Var fn') args') where -- arg_usg': see Note [Specialising on dictionaries] arg_usg' | Just cls <- isClassOpId_maybe fn' , dict_arg : _ <- dropList (classTyVars cls) args' = setScrutOcc env arg_usg dict_arg evalScrutOcc | otherwise = arg_usg 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 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') } ---------------------- mkVarUsage :: ScEnv -> Id -> [CoreExpr] -> ScUsage mkVarUsage env fn args = case lookupHowBound env fn of Just RecFun -> SCU { scu_calls = unitVarEnv fn [Call fn args (sc_vals env)] , scu_occs = emptyVarEnv } Just RecArg -> SCU { scu_calls = emptyVarEnv , scu_occs = unitVarEnv fn arg_occ } Nothing -> nullUsage where arg_occ | null args = UnkOcc | otherwise = evalScrutOcc ---------------------- scRecRhs :: ScEnv -> (OutId, InExpr) -> UniqSM 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 (RI { ri_rhs_usg = rhs_usg , ri_fn = bndr, ri_new_rhs = mkLams arg_bndrs' body' , ri_lam_bndrs = arg_bndrs, ri_lam_body = body , ri_arg_occs = 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 ---------------------- ruleInfoBinds :: RhsInfo -> SpecInfo -> [(Id,CoreExpr)] ruleInfoBinds (RI { ri_fn = fn, ri_new_rhs = new_rhs }) (SI { si_specs = specs }) = [(id,rhs) | OS { os_id = id, os_rhs = rhs } <- specs] ++ -- First the specialised bindings [(fn `addIdSpecialisations` rules, new_rhs)] -- And now the original binding where rules = [r | OS { os_rule = r } <- specs] {- ************************************************************************ * * The specialiser itself * * ************************************************************************ -} data RhsInfo = RI { ri_fn :: OutId -- The binder , ri_new_rhs :: OutExpr -- The specialised RHS (in current envt) , ri_rhs_usg :: ScUsage -- Usage info from specialising RHS , ri_lam_bndrs :: [InVar] -- The *original* RHS (\xs.body) , ri_lam_body :: InExpr -- Note [Specialise original body] , ri_arg_occs :: [ArgOcc] -- Info on how the xs occur in body } data SpecInfo -- Info about specialisations for a particular Id = SI { si_specs :: [OneSpec] -- The specialisations we have -- generated for this function , si_n_specs :: Int -- Length of si_specs; used for numbering them , si_mb_unspec :: Maybe ScUsage -- Just cs => we have not yet used calls in the } -- from calls in the *original* RHS as -- seeds for new specialisations; -- if you decide to do so, here is the -- RHS usage (which has not yet been -- unleashed) -- Nothing => we have -- See Note [Seeding recursive groups] -- See Note [spec_usg includes rhs_usg] -- One specialisation: Rule plus definition data OneSpec = OS { os_pat :: CallPat -- Call pattern that generated this specialisation , os_rule :: CoreRule -- Rule connecting original id with the specialisation , os_id :: OutId -- Spec id , os_rhs :: OutExpr } -- Spec rhs initSpecInfo :: RhsInfo -> SpecInfo initSpecInfo (RI { ri_rhs_usg = rhs_usg }) = SI { si_specs = [], si_n_specs = 0, si_mb_unspec = Just rhs_usg } -- si_mb_unspec: add in rhs_usg if there are any boring calls, -- or if the bndr is exported ---------------------- specNonRec :: ScEnv -> CallEnv -- Calls in body -> RhsInfo -- Structure info usage info for un-specialised RHS -> UniqSM (ScUsage, SpecInfo) -- Usage from RHSs (specialised and not) -- plus details of specialisations specNonRec env body_calls rhs_info = specialise env body_calls rhs_info (initSpecInfo rhs_info) ---------------------- specRec :: ScEnv -> CallEnv -- Calls in body -> [RhsInfo] -- Structure info and usage info for un-specialised RHSs -> UniqSM (ScUsage, [SpecInfo]) -- Usage from all RHSs (specialised and not) -- plus details of specialisations specRec env body_calls rhs_infos = go 1 body_calls nullUsage (map initSpecInfo rhs_infos) -- body_calls: see Note [Seeding recursive groups] -- NB: 'go' always calls 'specialise' once, which in turn unleashes -- si_mb_unspec if there are any boring calls in body_calls, -- or if any of the Id(s) are exported where opts = sc_opts env -- Loop, specialising, until you get no new specialisations go, go_again :: Int -- Which iteration of the "until no new specialisations" -- loop we are on; first iteration is 1 -> CallEnv -- Seed calls -- Two accumulating parameters: -> ScUsage -- Usage from earlier specialisations -> [SpecInfo] -- Details of specialisations so far -> UniqSM (ScUsage, [SpecInfo]) go n_iter seed_calls usg_so_far spec_infos = -- pprTrace "specRec3" (vcat [ text "bndrs" <+> ppr (map ri_fn rhs_infos) -- , text "iteration" <+> int n_iter -- , text "spec_infos" <+> ppr (map (map os_pat . si_specs) spec_infos) -- ]) $ do { specs_w_usg <- zipWithM (specialise env seed_calls) rhs_infos spec_infos ; let (extra_usg_s, all_spec_infos) = unzip specs_w_usg extra_usg = combineUsages extra_usg_s all_usg = usg_so_far `combineUsage` extra_usg new_calls = scu_calls extra_usg ; go_again n_iter new_calls all_usg all_spec_infos } -- go_again deals with termination go_again n_iter seed_calls usg_so_far spec_infos | isEmptyVarEnv seed_calls = return (usg_so_far, spec_infos) -- Limit recursive specialisation -- See Note [Limit recursive specialisation] | n_iter > sc_recursive opts -- Too many iterations of the 'go' loop , sc_force env || isNothing (sc_count opts) -- If both of these are false, the sc_count -- threshold will prevent non-termination , any ((> the_limit) . si_n_specs) spec_infos = -- Give up on specialisation, but don't forget to include the rhs_usg -- for the unspecialised function, since it may now be called -- pprTrace "specRec2" (ppr (map (map os_pat . si_specs) spec_infos)) $ let rhs_usgs = combineUsages (mapMaybe si_mb_unspec spec_infos) in return (usg_so_far `combineUsage` rhs_usgs, spec_infos) | otherwise = go (n_iter + 1) seed_calls usg_so_far spec_infos -- See Note [Limit recursive specialisation] the_limit = case sc_count opts of Nothing -> 10 -- Ugh! Just max -> max ---------------------- specialise :: ScEnv -> CallEnv -- Info on newly-discovered calls to this function -> RhsInfo -> SpecInfo -- Original RHS plus patterns dealt with -> UniqSM (ScUsage, SpecInfo) -- New specialised versions and their usage -- See Note [spec_usg includes rhs_usg] -- Note: this only generates *specialised* bindings -- The original binding is added by ruleInfoBinds -- -- 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 (RI { ri_fn = fn, ri_lam_bndrs = arg_bndrs , ri_lam_body = body, ri_arg_occs = arg_occs }) spec_info@(SI { si_specs = specs, si_n_specs = spec_count , si_mb_unspec = mb_unspec }) | isDeadEndId fn -- Note [Do not specialise diverging functions] -- /and/ do not generate specialisation seeds from its RHS = -- pprTrace "specialise bot" (ppr fn) $ return (nullUsage, spec_info) | not (isNeverActive (idInlineActivation fn)) -- See Note [Transfer activation] -- Don't specialise OPAQUE things, see Note [OPAQUE pragma]. -- Since OPAQUE things are always never-active (see -- GHC.Parser.PostProcess.mkOpaquePragma) this guard never fires for -- OPAQUE things. , not (null arg_bndrs) -- Only specialise functions , Just all_calls <- lookupVarEnv bind_calls fn -- Some calls to it = -- pprTrace "specialise entry {" (ppr fn <+> ppr all_calls) $ do { (boring_call, pats_discarded, new_pats) <- callsToNewPats env fn spec_info arg_occs all_calls ; let n_pats = length new_pats -- ; when (not (null new_pats) || isJust mb_unspec) $ -- pprTraceM "specialise" (vcat [ ppr fn <+> text "with" <+> int n_pats <+> text "good patterns" -- , text "boring_call:" <+> ppr boring_call -- , text "pats_discarded:" <+> ppr pats_discarded -- , text "old spec_count" <+> ppr spec_count -- , text "spec count limit" <+> ppr (sc_count (sc_opts env)) -- , text "mb_unspec" <+> ppr (isJust mb_unspec) -- , text "arg_occs" <+> ppr arg_occs -- , text "new_pats" <+> ppr new_pats]) ; let spec_env = decreaseSpecCount env n_pats ; (spec_usgs, new_specs) <- mapAndUnzipM (spec_one spec_env fn arg_bndrs body) (new_pats `zip` [spec_count..]) -- See Note [Specialise original body] ; let spec_usg = combineUsages spec_usgs unspec_rhs_needed = pats_discarded || boring_call || isExportedId fn -- If there were any boring calls among the seeds (= all_calls), then those -- calls will call the un-specialised function. So we should use the seeds -- from the _unspecialised_ function's RHS, which are in mb_unspec, by returning -- then in new_usg. (new_usg, mb_unspec') = case mb_unspec of Just rhs_usg | unspec_rhs_needed -> (spec_usg `combineUsage` rhs_usg, Nothing) _ -> (spec_usg, mb_unspec) -- ; pprTraceM "specialise return }" $ -- vcat [ ppr fn -- , text "unspec_rhs_needed:" <+> ppr unspec_rhs_needed -- , text "new calls:" <+> ppr (scu_calls new_usg)] ; return (new_usg, SI { si_specs = new_specs ++ specs , si_n_specs = spec_count + n_pats , si_mb_unspec = mb_unspec' }) } | otherwise -- No calls, inactive, or not a function -- Behave as if there was a single, boring call = -- pprTrace "specialise inactive" (ppr fn $$ ppr mb_unspec) $ case mb_unspec of -- Behave as if there was a single, boring call Just rhs_usg -> return (rhs_usg, spec_info { si_mb_unspec = Nothing }) -- See Note [spec_usg includes rhs_usg] Nothing -> return (nullUsage, spec_info) --------------------- spec_one :: ScEnv -> 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 -- 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, rule_number) | CP { cp_qvars = qvars, cp_args = pats, cp_strict_args = cbv_args } <- call_pat = do { -- pprTraceM "spec_one {" (ppr fn <+> ppr pats) ; spec_uniq <- getUniqueM ; let env1 = extendScSubstList (extendScInScope env qvars) (arg_bndrs `zip` pats) (body_env, extra_bndrs) = extendBndrs env1 (dropList pats arg_bndrs) -- Remember, there may be fewer pats than arg_bndrs -- See Note [SpecConstr call patterns] -- extra_bndrs will then be arguments in the specialized version -- which are *not* applied to arguments immediately at the call sites. -- e.g. let f x y = ... in map (f True) xs -- will result in y becoming an extra_bndr fn_name = idName fn fn_loc = nameSrcSpan fn_name fn_occ = nameOccName fn_name spec_occ = mkSpecOcc fn_occ -- We use fn_occ rather than fn in the rule_name string -- as we don't want the uniq to end up in the rule, and -- hence in the ABI, as that can cause spurious ABI -- changes (#4012). rule_name = mkFastString ("SC:" ++ occNameString fn_occ ++ show rule_number) spec_name = mkInternalName spec_uniq spec_occ fn_loc -- Specialise the body -- ; pprTraceM "body_subst_for" $ ppr (spec_occ) $$ ppr (sc_subst body_env) ; (spec_usg, spec_body) <- scExpr body_env body -- And build the results ; (qvars', pats') <- generaliseDictPats qvars pats ; let spec_body_ty = exprType spec_body (spec_lam_args1, spec_sig, spec_arity1, spec_join_arity1) = calcSpecInfo fn call_pat extra_bndrs -- Annotate the variables with the strictness information from -- the function (see Note [Strictness information in worker binders]) add_void_arg = needsVoidWorkerArg fn arg_bndrs spec_lam_args1 (spec_lam_args, spec_call_args, spec_arity, spec_join_arity) | add_void_arg -- See Note [SpecConstr needs to add void args first] , (spec_lam_args, spec_call_args, _) <- addVoidWorkerArg spec_lam_args1 [] -- needsVoidWorkerArg: usual w/w hack to avoid generating -- a spec_rhs of unlifted type and no args. , !spec_arity <- spec_arity1 + 1 , !spec_join_arity <- fmap (+ 1) spec_join_arity1 = (spec_lam_args, spec_call_args, spec_arity, spec_join_arity) | otherwise = (spec_lam_args1, spec_lam_args1, spec_arity1, spec_join_arity1) spec_id = asWorkerLikeId $ mkLocalId spec_name ManyTy (mkLamTypes spec_lam_args spec_body_ty) -- See Note [Transfer strictness] `setIdDmdSig` spec_sig `setIdCprSig` topCprSig `setIdArity` spec_arity `asJoinId_maybe` spec_join_arity -- Conditionally use result of new worker-wrapper transform spec_rhs = mkLams spec_lam_args (mkSeqs cbv_args spec_body_ty spec_body) rule_rhs = mkVarApps (Var spec_id) $ -- This will give us all the arguments we quantify over -- in the rule plus the void argument if present -- since `length(qvars) + void + length(extra_bndrs) = length spec_call_args` dropTail (length extra_bndrs) spec_call_args inline_act = idInlineActivation fn this_mod = sc_module $ sc_opts env rule = mkRule this_mod True {- Auto -} True {- Local -} rule_name inline_act fn_name qvars' pats' rule_rhs -- See Note [Transfer activation] -- ; pprTraceM "spec_one end }" $ -- vcat [ text "function:" <+> ppr fn <+> braces (ppr (idUnique fn)) -- , text "pats:" <+> ppr pats -- , text "call_pat:" <+> ppr call_pat -- , text "-->" <+> ppr spec_name -- , text "bndrs" <+> ppr arg_bndrs -- , text "extra_bndrs" <+> ppr extra_bndrs -- , text "cbv_args" <+> ppr cbv_args -- , text "spec_lam_args" <+> ppr spec_lam_args -- , text "spec_call_args" <+> ppr spec_call_args -- , text "rule_rhs" <+> ppr rule_rhs -- , text "adds_void_worker_arg" <+> ppr add_void_arg ---- , text "body" <+> ppr body ---- , text "spec_rhs" <+> ppr spec_rhs ---- , text "how_bound" <+> ppr (sc_how_bound env) ] -- ] ; return (spec_usg, OS { os_pat = call_pat, os_rule = rule , os_id = spec_id , os_rhs = spec_rhs }) } generaliseDictPats :: [Var] -> [CoreExpr] -- Quantified vars and pats -> UniqSM ([Var], [CoreExpr]) -- New quantified vars and pats -- See Note [generaliseDictPats] generaliseDictPats qvars pats = do { (extra_qvars, pats') <- mapAccumLM go [] pats ; case extra_qvars of [] -> return (qvars, pats) _ -> return (qvars ++ extra_qvars, pats') } where qvar_set = mkVarSet qvars go :: [Id] -> CoreExpr -> UniqSM ([Id], CoreExpr) go extra_qvs pat | not (isTyCoArg pat) , let pat_ty = exprType pat , typeDeterminesValue pat_ty , exprFreeVars pat `disjointVarSet` qvar_set = do { id <- mkSysLocalOrCoVarM (fsLit "dict") ManyTy pat_ty ; return (id:extra_qvs, Var id) } | otherwise = return (extra_qvs, pat) -- See Note [SpecConstr and strict fields] mkSeqs :: [Var] -> Type -> CoreExpr -> CoreExpr mkSeqs seqees res_ty rhs = foldr addEval rhs seqees where addEval :: Var -> CoreExpr -> CoreExpr addEval arg_id rhs -- Argument representing strict field and it's worth passing via cbv | shouldStrictifyIdForCbv arg_id = Case (Var arg_id) arg_id res_ty ([Alt DEFAULT [] rhs]) | otherwise = rhs {- Note [SpecConstr needs to add void args first] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider a function f start @t = e We want to specialize for a partially applied call `f True`. See also Note [SpecConstr call patterns], second Wrinkle. Naively we would expect to get $sf @t = $se RULE: f True = $sf The specialized function only takes a single type argument so we add a void argument to prevent it from turning into a thunk. See Note [Protecting the last value argument] for details why. Normally we would add the void argument after the type argument giving us: $sf :: forall t. Void# -> bla $sf @t void = $se RULE: f True = $sf void# (wrong) But if you look closely this wouldn't typecheck! If we substitute `f True` with `$sf void#` we expect the type argument to be applied first but we apply void# first. The easiest fix seems to be just to add the void argument to the front of the arguments. Now we get: $sf :: Void# -> forall t. bla $sf void @t = $se RULE: f True = $sf void# And now we can substitute `f True` with `$sf void#` with everything working out nicely! Note [generaliseDictPats] ~~~~~~~~~~~~~~~~~~~~~~~~~ Consider these two rules (#21831, item 2): RULE "SPEC:foo" forall d1 d2. foo @Int @Integer d1 d2 = $sfoo1 RULE "SC:foo" forall a. foo @Int @a $fNumInteger = $sfoo2 @a The former comes from the type class specialiser, the latter from SpecConstr. Note that $fNumInteger is a top-level binding for Num Integer. The trouble is that neither is more general than the other. In a call (foo @Int @Integer $fNumInteger d) it isn't clear which rule to fire. The trouble is that the SpecConstr rule fires on a /specific/ dict, $fNumInteger, but actually /could/ fire regardless. That is, it could be RULE "SC:foo" forall a d. foo @Int @a d = $sfoo2 @a Now, it is clear that SPEC:foo is more specific. But GHC can't tell that, because SpecConstr doesn't know that dictionary arguments are singleton types! So generaliseDictPats teaches it this fact. It spots such patterns (using typeDeterminesValue), and quantifies over the dictionary. Now we get RULE "SC:foo" forall a d. foo @Int @a d = $sfoo2 @a And /now/ "SPEC:foo" is clearly more specific: we can instantiate the new "SC:foo" to match the (prefix of) "SPEC:foo". -} calcSpecInfo :: Id -- The original function -> CallPat -- Call pattern -> [Var] -- Extra bndrs -> ( [Var] -- Demand-decorated binders , DmdSig -- Strictness of specialised thing , Arity, Maybe JoinArity ) -- Arities of specialised thing -- Calculate bits of IdInfo for the specialised function -- See Note [Transfer strictness] -- See Note [Strictness information in worker binders] calcSpecInfo fn (CP { cp_qvars = qvars, cp_args = pats }) extra_bndrs | isJoinId fn -- Join points have strictness and arity for LHS only = ( bndrs_w_dmds , mkClosedDmdSig qvar_dmds div , count isId qvars , Just (length qvars) ) | otherwise = ( bndrs_w_dmds , mkClosedDmdSig (qvar_dmds ++ extra_dmds) div , count isId qvars + count isId extra_bndrs , Nothing ) where DmdSig (DmdType _ fn_dmds div) = idDmdSig fn val_pats = filterOut isTypeArg pats -- value args at call sites, used to determine how many demands to drop -- from the original functions demand and for setting up dmd_env. qvar_dmds = [ lookupVarEnv dmd_env qv `orElse` topDmd | qv <- qvars, isId qv ] extra_dmds = dropList val_pats fn_dmds bndrs_w_dmds = set_dmds qvars qvar_dmds ++ set_dmds extra_bndrs extra_dmds set_dmds :: [Var] -> [Demand] -> [Var] set_dmds [] _ = [] set_dmds vs [] = vs -- Run out of demands set_dmds (v:vs) ds@(d:ds') | isTyVar v = v : set_dmds vs ds | otherwise = setIdDemandInfo v d : set_dmds vs ds' dmd_env = go emptyVarEnv fn_dmds val_pats go :: DmdEnv -> [Demand] -> [CoreExpr] -> DmdEnv -- We've filtered out all the type patterns already go env (d:ds) (pat : pats) = go (go_one env d pat) ds pats go env _ _ = env go_one :: DmdEnv -> Demand -> CoreExpr -> DmdEnv go_one env d (Var v) = extendVarEnv_C plusDmd env v d go_one env (_n :* cd) e -- NB: _n does not have to be strict | (Var _, args) <- collectArgs e , Just (_b, ds) <- viewProd (length args) cd -- TODO: We may want to look at boxity _b, though... = go env ds args go_one env _ _ = env {- Note [spec_usg includes rhs_usg] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ In calls to 'specialise', the returned ScUsage must include the rhs_usg in the passed-in SpecInfo in si_mb_unspec, unless there are no calls at all to the function. The caller can, indeed must, assume this. They should not combine in rhs_usg themselves, or they'll get rhs_usg twice -- and that can lead to an exponential blowup of duplicates in the CallEnv. This is what gave rise to the massive performance loss in #8852. 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 GHC.Core.Opt.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 FinalPhase; after all, currently, the specConstr transformation is only run after the simplifier has reached FinalPhase, 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 specialisation 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 SSx and a RULE f (a:as) b = f_spec a as b Now we want f_spec to have strictness LLSx, 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 #3437 for a good example. The function calcSpecStrictness performs the calculation. Note [Strictness information in worker binders] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ After having calculated the strictness annotation for the worker (see Note [Transfer strictness] above), we also want to have this information attached to the worker’s arguments, for the benefit of later passes. The function handOutStrictnessInformation decomposes the strictness annotation calculated by calcSpecStrictness and attaches them to the variables. ************************************************************************ * * \subsection{Argument analysis} * * ************************************************************************ This code deals with analysing call-site arguments to see whether they are constructor applications. Note [Free type variables of the qvar types] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ In a call (f @a x True), that we want to specialise, what variables should we quantify over. Clearly over 'a' and 'x', but what about any type variables free in x's type? In fact we don't need to worry about them because (f @a) can only be a well-typed application if its type is compatible with x, so any variables free in x's type must be free in (f @a), and hence either be gathered via 'a' itself, or be in scope at f's defn. Hence we just take (exprsFreeVars pats). BUT phantom type synonyms can mess this reasoning up, eg x::T b with type T b = Int So we apply expandTypeSynonyms to the bound Ids. See # 5458. Yuk. Note [SpecConstr call patterns] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ A "call patterns" that we collect is going to become the LHS of a RULE. Wrinkles: * The list of argument patterns, cp_args, is no longer than the visible lambdas of the binding, ri_arg_occs. This is done via the zipWithM in callToPats. * The list of argument patterns can certainly be shorter than the lambdas in the function definition (under-saturated). For example f x y = case x of { True -> e1; False -> e2 } ....map (f True) e... We want to specialise `f` for `f True`. * In fact we deliberately shrink the list of argument patterns, cp_args, by trimming off all the boring ones at the end (see `dropWhileEnd is_boring` in callToPats). Since the RULE only applies when it is saturated, this shrinking makes the RULE more applicable. But it does mean that the argument patterns do not necessarily saturate the lambdas of the function. * It's important that the pattern arguments do not look like e |> Refl or e |> g1 |> g2 because both of these will be optimised by Simplify.simplRule. In the former case such optimisation benign, because the rule will match more terms; but in the latter we may lose a binding of 'g1' or 'g2', and end up with a rule LHS that doesn't bind the template variables (#10602). The simplifier eliminates such things, but SpecConstr itself constructs new terms by substituting. So the 'mkCast' in the Cast case of scExpr is very important! Note [Choosing patterns] ~~~~~~~~~~~~~~~~~~~~~~~~ If we get lots of patterns we may not want to make a specialisation for each of them (code bloat), so we choose as follows, implemented by trim_pats. * The flag -fspec-constr-count-N sets the sc_count field of the ScEnv to (Just n). This limits the total number of specialisations for a given function to N. * -fno-spec-constr-count sets the sc_count field to Nothing, which switches of the limit. * The ghastly ForceSpecConstr trick also switches of the limit for a particular function * Otherwise we sort the patterns to choose the most general ones first; more general => more widely applicable. Note [SpecConstr and casts] ~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider (#14270) a call like let f = e in ... f (K @(a |> co)) ... where 'co' is a coercion variable not in scope at f's definition site. If we aren't careful we'll get let $sf a co = e (K @(a |> co)) RULE "SC:f" forall a co. f (K @(a |> co)) = $sf a co f = e in ... But alas, when we match the call we won't bind 'co', because type-matching (for good reasons) discards casts). I don't know how to solve this, so for now I'm just discarding any call patterns that * Mentions a coercion variable in a type argument * That is not in scope at the binding of the function I think this is very rare. It is important (e.g. #14936) that this /only/ applies to coercions mentioned in casts. We don't want to be discombobulated by casts in terms! For example, consider f ((e1,e2) |> sym co) where, say, f :: Foo -> blah co :: Foo ~R (Int,Int) Here we definitely do want to specialise for that pair! We do not match on the structure of the coercion; instead we just match on a coercion variable, so the RULE looks like forall (x::Int, y::Int, co :: (Int,Int) ~R Foo) f ((x,y) |> co) = $sf x y co Often the body of f looks like f arg = ...(case arg |> co' of (x,y) -> blah)... so that the specialised f will turn into $sf x y co = let arg = (x,y) |> co in ...(case arg>| co' of (x,y) -> blah).... which will simplify to not use 'co' at all. But we can't guarantee that co will end up unused, so we still pass it. Absence analysis may remove it later. Note that this /also/ discards the call pattern if we have a cast in a /term/, although in fact Rules.match does make a very flaky and fragile attempt to match coercions. e.g. a call like f (Maybe Age) (Nothing |> co) blah where co :: Maybe Int ~ Maybe Age will be discarded. It's extremely fragile to match on the form of a coercion, so I think it's better just not to try. A more complicated alternative would be to discard calls that mention coercion variables only in kind-casts, but I'm doing the simple thing for now. -} data CallPat = CP { cp_qvars :: [Var] -- Quantified variables , cp_args :: [CoreExpr] -- Arguments , cp_strict_args :: [Var] } -- Arguments we want to pass unlifted even if they are boxed -- See Note [SpecConstr call patterns] instance Outputable CallPat where ppr (CP { cp_qvars = qvars, cp_args = args, cp_strict_args = strict }) = text "CP" <> braces (sep [ text "cp_qvars =" <+> ppr qvars <> comma , text "cp_args =" <+> ppr args , text "cp_strict_args = " <> ppr strict ]) callsToNewPats :: ScEnv -> Id -> SpecInfo -> [ArgOcc] -> [Call] -> UniqSM ( Bool -- At least one boring call , Bool -- Patterns were discarded , [CallPat] ) -- Patterns to specialise -- Result has no duplicate patterns, -- nor ones mentioned in si_specs (hence "new" patterns) -- Bool indicates that there was at least one boring pattern -- The "New" in the name means "patterns that are not already covered -- by an existing specialisation" callsToNewPats env fn spec_info@(SI { si_specs = done_specs }) bndr_occs calls = do { mb_pats <- mapM (callToPats env bndr_occs) calls ; let have_boring_call = any isNothing mb_pats good_pats :: [CallPat] good_pats = catMaybes mb_pats -- Remove patterns we have already done new_pats = filterOut is_done good_pats is_done p = any (samePat p . os_pat) done_specs -- Remove duplicates non_dups = nubBy samePat new_pats -- Remove ones that have too many worker variables small_pats = filterOut too_big non_dups too_big (CP { cp_qvars = vars, cp_args = args }) = not (isWorkerSmallEnough (sc_max_args $ sc_opts env) (valArgCount args) vars) -- We are about to construct w/w pair in 'spec_one'. -- Omit specialisation leading to high arity workers. -- See Note [Limit w/w arity] in GHC.Core.Opt.WorkWrap.Utils -- Discard specialisations if there are too many of them (pats_were_discarded, trimmed_pats) = trim_pats env fn spec_info small_pats -- ; pprTraceM "callsToPats" (vcat [ text "calls to" <+> ppr fn <> colon <+> ppr calls -- , text "done_specs:" <+> ppr (map os_pat done_specs) -- , text "trimmed_pats:" <+> ppr trimmed_pats ]) ; return (have_boring_call, pats_were_discarded, trimmed_pats) } -- If any of the calls does not give rise to a specialisation, either -- because it is boring, or because there are too many specialisations, -- return a flag to say so, so that we know to keep the original function. trim_pats :: ScEnv -> Id -> SpecInfo -> [CallPat] -> (Bool, [CallPat]) -- True <=> some patterns were discarded -- See Note [Choosing patterns] trim_pats env fn (SI { si_n_specs = done_spec_count }) pats | sc_force env || isNothing mb_scc || n_remaining >= n_pats = -- pprTrace "trim_pats: no-trim" (ppr (sc_force env) $$ ppr mb_scc $$ ppr n_remaining $$ ppr n_pats) (False, pats) -- No need to trim | otherwise = emit_trace $ -- Need to trim, so keep the best ones (True, take n_remaining sorted_pats) where n_pats = length pats spec_count' = n_pats + done_spec_count n_remaining = max_specs - done_spec_count mb_scc = sc_count $ sc_opts env Just max_specs = mb_scc sorted_pats = map fst $ sortBy (comparing snd) $ [(pat, pat_cons pat) | pat <- pats] -- Sort in order of increasing number of constructors -- (i.e. decreasing generality) and pick the initial -- segment of this list pat_cons :: CallPat -> Int -- How many data constructors of literals are in -- the pattern. More data-cons => less general pat_cons (CP { cp_qvars = qs, cp_args = ps }) = foldr ((+) . n_cons) 0 ps where q_set = mkVarSet qs n_cons (Var v) | v `elemVarSet` q_set = 0 | otherwise = 1 n_cons (Cast e _) = n_cons e n_cons (App e1 e2) = n_cons e1 + n_cons e2 n_cons (Lit {}) = 1 n_cons _ = 0 emit_trace result | debugIsOn || sc_debug (sc_opts env) -- Suppress this scary message for ordinary users! #5125 = pprTrace "SpecConstr" msg result | otherwise = result msg = vcat [ sep [ text "Function" <+> quotes (ppr fn) , nest 2 (text "has" <+> speakNOf spec_count' (text "call pattern") <> comma <+> text "but the limit is" <+> int max_specs) ] , text "Use -fspec-constr-count=n to set the bound" , text "done_spec_count =" <+> int done_spec_count , text "Keeping " <+> int n_remaining <> text ", out of" <+> int n_pats , text "Discarding:" <+> ppr (drop n_remaining sorted_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 call@(Call fn args con_env) = do { let in_scope = getSubstInScope (sc_subst env) ; arg_tripples <- zipWith3M (argToPat env in_scope con_env) args bndr_occs (map (const NotMarkedStrict) args) -- This zip trims the args to be no longer than -- the lambdas in the function definition (bndr_occs) -- Drop boring patterns from the end -- See Note [SpecConstr call patterns] ; let arg_tripples' | isJoinId fn = arg_tripples | otherwise = dropWhileEnd is_boring arg_tripples is_boring (interesting, _,_) = not interesting (interesting_s, pats, cbv_ids) = unzip3 arg_tripples' interesting = or interesting_s ; let pat_fvs = exprsFreeVarsList pats -- To get determinism we need the list of free variables in -- deterministic order. Otherwise we end up creating -- lambdas with different argument orders. See -- determinism/simplCore/should_compile/spec-inline-determ.hs -- for an example. For explanation of determinism -- considerations See Note [Unique Determinism] in GHC.Types.Unique. in_scope_vars = getInScopeVars in_scope is_in_scope v = v `elemVarSet` in_scope_vars qvars = filterOut is_in_scope pat_fvs -- Quantify over variables that are not in scope -- at the call site -- See Note [Free type variables of the qvar types] -- See Note [Shadowing] at the top (ktvs, ids) = partition isTyVar qvars qvars' = scopedSort ktvs ++ map sanitise ids -- Order into kind variables, type variables, term variables -- The kind of a type variable may mention a kind variable -- and the type of a term variable may mention a type variable sanitise id = updateIdTypeAndMult expandTypeSynonyms id -- See Note [Free type variables of the qvar types] -- Check for bad coercion variables: see Note [SpecConstr and casts] ; let bad_covars :: CoVarSet bad_covars = mapUnionVarSet get_bad_covars pats get_bad_covars :: CoreArg -> CoVarSet get_bad_covars (Type ty) = filterVarSet bad_covar (tyCoVarsOfType ty) get_bad_covars _ = emptyVarSet bad_covar v = isId v && not (is_in_scope v) ; warnPprTrace (not (isEmptyVarSet bad_covars)) "SpecConstr: bad covars" (ppr bad_covars $$ ppr call) $ if interesting && isEmptyVarSet bad_covars then do { let cp_res = CP { cp_qvars = qvars', cp_args = pats , cp_strict_args = concat cbv_ids } -- ; pprTraceM "callToPatsOut" $ -- vcat [ text "fn:" <+> ppr fn -- , text "args:" <+> ppr args -- , text "bndr_occs:" <+> ppr bndr_occs -- , text "pat_fvs:" <+> ppr pat_fvs -- , text "cp_res:" <+> ppr cp_res ] ; return (Just cp_res) } 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 :: 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 -> StrictnessMark -- Tells us if this argument is a strict field of a data constructor -- See Note [SpecConstr and strict fields] -> UniqSM (Bool, CoreArg, [Id]) -- Returns (interesting, pat), -- where pat is the pattern derived from the argument -- interesting=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 arg_occ arg_str = do -- pprTraceM "argToPatIn" (ppr arg) !res <- argToPat1 env in_scope val_env arg arg_occ arg_str -- pprTraceM "argToPatOut" (ppr res) return res argToPat1 :: ScEnv -> InScopeSet -> ValueEnv -> Expr CoreBndr -> ArgOcc -> StrictnessMark -> UniqSM (Bool, Expr CoreBndr, [Id]) argToPat1 _env _in_scope _val_env arg@(Type {}) _arg_occ _arg_str = return (False, arg, []) argToPat1 env in_scope val_env (Tick _ arg) arg_occ arg_str = argToPat env in_scope val_env arg arg_occ arg_str -- Note [Tick annotations 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 [Tick annotations in RULE matching] in GHC.Core.Rules argToPat1 env in_scope val_env (Let _ arg) arg_occ arg_str = argToPat env in_scope val_env arg arg_occ arg_str -- See Note [Matching lets] in "GHC.Core.Rules" -- 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 "GHC.Core.Rules" argToPat env in_scope val_env (Case scrut _ _ [(_, _, rhs)]) arg_occ | exprOkForSpeculation scrut -- See Note [Matching cases] in "GHC.Core.Rules" = argToPat env in_scope val_env rhs arg_occ -} argToPat1 env in_scope val_env (Cast arg co) arg_occ arg_str | not (ignoreType env ty2) = do { (interesting, arg', strict_args) <- argToPat env in_scope val_env arg arg_occ arg_str ; if not interesting then wildCardPat ty2 arg_str else do { -- Make a wild-card pattern for the coercion uniq <- getUniqueM ; let co_name = mkSysTvName uniq (fsLit "sg") co_var = mkCoVar co_name (mkCoercionType Representational ty1 ty2) ; return (interesting, Cast arg' (mkCoVarCo co_var), strict_args) } } where Pair ty1 ty2 = coercionKind co {- 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 argToPat1 env in_scope val_env arg arg_occ _arg_str | Just (ConVal (DataAlt dc) args) <- isValue val_env arg , not (ignoreDataCon env dc) -- See Note [NoSpecConstr] , Just arg_occs <- mb_scrut dc = do { let (ty_args, rest_args) = splitAtList (dataConUnivTyVars dc) args con_str, matched_str :: [StrictnessMark] -- con_str corresponds 1-1 with the /value/ arguments -- matched_str corresponds 1-1 with /all/ arguments con_str = dataConRepStrictness dc matched_str = match_vals con_str rest_args -- ; pprTraceM "bangs" (ppr (length rest_args == length con_str) $$ -- ppr dc $$ -- ppr con_str $$ -- ppr rest_args $$ -- ppr (map isTypeArg rest_args)) ; prs <- zipWith3M (argToPat env in_scope val_env) rest_args arg_occs matched_str ; let args' = map sndOf3 prs :: [CoreArg] ; assertPpr (length con_str == length (filter isRuntimeArg rest_args)) ( ppr con_str $$ ppr rest_args $$ ppr (length con_str) $$ ppr (length rest_args) ) $ return () ; return (True, mkConApp dc (ty_args ++ args'), concat (map thdOf3 prs)) } where mb_scrut dc = case arg_occ of ScrutOcc bs | Just occs <- lookupUFM bs dc -> Just (occs) -- See Note [Reboxing] _other | sc_force env || sc_keen (sc_opts env) -> Just (repeat UnkOcc) | otherwise -> Nothing match_vals bangs (arg:args) | isTypeArg arg = NotMarkedStrict : match_vals bangs args | (b:bs) <- bangs = b : match_vals bs args match_vals [] [] = [] match_vals as bs = pprPanic "spec-constr:argToPat - Bangs don't match value arguments" (text "arg:" <> ppr arg $$ text "remaining args:" <> ppr as $$ text "remaining bangs:" <> ppr bs) -- Check if the argument is a variable that -- (a) is used in an interesting way in the function body --- i.e. ScrutOcc. UnkOcc and NoOcc are not interesting -- (NoOcc means we could drop the argument, but that's the -- business of absence analysis, not SpecConstr.) -- (b) we know what its value is -- In that case it counts as "interesting" argToPat1 env in_scope val_env (Var v) arg_occ arg_str | sc_force env || specialisableArgOcc arg_occ -- (a) , is_value -- (b) -- Ignoring sc_keen here to avoid gratuitously incurring Note [Reboxing] -- So sc_keen focused just on f (I# x), where we have freshly-allocated -- box that we can eliminate in the caller , not (ignoreType env (varType v)) -- See Note [SpecConstr and strict fields] = return (True, Var v, if isMarkedStrict arg_str then [v] else mempty) 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 scope, which in turn can -- expose the weakness in let-matching -- See Note [Matching lets] in GHC.Core.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 -- We use this for coercions too argToPat1 _env _in_scope _val_env arg _arg_occ arg_str = wildCardPat (exprType arg) arg_str -- | wildCardPats are always boring wildCardPat :: Type -> StrictnessMark -> UniqSM (Bool, CoreArg, [Id]) wildCardPat ty str = do { id <- mkSysLocalOrCoVarM (fsLit "sc") ManyTy ty -- ; pprTraceM "wildCardPat" (ppr id' <+> ppr (idUnfolding id')) ; return (False, varToCoreExpr id, if isMarkedStrict str then [id] else []) } isValue :: ValueEnv -> CoreExpr -> Maybe Value isValue _env (Lit lit) | litIsLifted lit = Nothing | otherwise = Just (ConVal (LitAlt lit) []) isValue env (Var v) | Just cval <- lookupVarEnv env v = Just cval -- 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 = case isValue env e of Just _ -> Just LambdaVal Nothing -> Nothing | otherwise = Just LambdaVal isValue env (Tick t e) | not (tickishIsCode t) = isValue env e isValue _env expr -- Maybe it's a constructor application | (Var fun, args, _) <- collectArgsTicks (not . tickishIsCode) expr = case idDetails fun of DataConWorkId con | args `lengthAtLeast` dataConRepArity con -- Check saturated; might be > because the -- arity excludes type args -> Just (ConVal (DataAlt con) args) DFunId {} -> Just LambdaVal -- DFunId: see Note [Specialising on dictionaries] _other | valArgCount args < idArity fun -- Under-applied function -> Just LambdaVal -- Partial application _other -> Nothing isValue _env _expr = Nothing valueIsWorkFree :: Value -> Bool valueIsWorkFree LambdaVal = True valueIsWorkFree (ConVal _ args) = all exprIsWorkFree args samePat :: CallPat -> CallPat -> Bool samePat (CP { cp_qvars = vs1, cp_args = as1 }) (CP { cp_qvars = vs2, cp_args = as2 }) = all2 same as1 as2 where -- If the args are the same, their strictness marks will be too so we don't compare those. 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 (Coercion {}) (Coercion {}) = True same (Tick _ e1) e2 = same e1 e2 -- Ignore casts and notes same (Cast e1 _) e2 = same e1 e2 same e1 (Tick _ e2) = same e1 e2 same e1 (Cast e2 _) = same e1 e2 same e1 e2 = warnPprTrace (bad e1 || bad e2) "samePat" (ppr e1 $$ ppr e2) $ False -- Let, lambda, case should not occur bad (Case {}) = True bad (Let {}) = True bad (Lam {}) = True bad _other = False {- 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. -}