\section[SpecConstr]{Specialise over constructors}
\begin{code}
+{-# OPTIONS -w #-}
+-- The above warning supression flag is a temporary kludge.
+-- While working on this module you are encouraged to remove it and fix
+-- any warnings in the module. See
+-- http://hackage.haskell.org/trac/ghc/wiki/CodingStyle#Warnings
+-- for details
+
module SpecConstr(
specConstrProgram
) where
#include "HsVersions.h"
import CoreSyn
+import CoreSubst
+import CoreUtils
+import CoreUnfold ( couldBeSmallEnoughToInline )
import CoreLint ( showPass, endPass )
-import CoreUtils ( exprType, tcEqExpr, mkPiTypes )
import CoreFVs ( exprsFreeVars )
-import CoreSubst ( Subst, mkSubst, substExpr )
import CoreTidy ( tidyRules )
import PprCore ( pprRules )
import WwLib ( mkWorkerArgs )
-import DataCon ( dataConRepArity, isVanillaDataCon )
-import Type ( tyConAppArgs, tyVarsOfTypes )
-import Unify ( coreRefineTys )
-import Id ( Id, idName, idType, isDataConWorkId_maybe,
- mkUserLocal, mkSysLocal, idUnfolding )
+import DataCon ( dataConRepArity, dataConUnivTyVars )
+import Type ( Type, tyConAppArgs )
+import Coercion ( coercionKind )
+import Id ( Id, idName, idType, isDataConWorkId_maybe, idArity,
+ mkUserLocal, mkSysLocal, idUnfolding, isLocalId )
import Var ( Var )
import VarEnv
import VarSet
-import Name ( nameOccName, nameSrcLoc )
+import Name
import Rules ( addIdSpecialisations, mkLocalRule, rulesOfBinds )
import OccName ( mkSpecOcc )
import ErrUtils ( dumpIfSet_dyn )
-import DynFlags ( DynFlags, DynFlag(..) )
+import DynFlags ( DynFlags(..), DynFlag(..) )
import BasicTypes ( Activation(..) )
-import Maybes ( orElse )
-import Util ( mapAccumL, lengthAtLeast, notNull )
+import Maybes ( orElse, catMaybes, isJust )
+import Util
import List ( nubBy, partition )
import UniqSupply
import Outputable
import FastString
+import UniqFM
\end{code}
-----------------------------------------------------
At the call to f, we see that the argument, n is know to be (I# n#),
and n is evaluated elsewhere in the body of f, so we can play the same
-trick as above. However we don't want to do that if the boxed version
-of n is needed (else we'd avoid the eval but pay more for re-boxing n).
-So in this case we want that the *only* uses of n are in case statements.
+trick as above.
+
+
+Note [Reboxing]
+~~~~~~~~~~~~~~~
+We must be careful not to allocate the same constructor twice. Consider
+ f p = (...(case p of (a,b) -> e)...p...,
+ ...let t = (r,s) in ...t...(f t)...)
+At the recursive call to f, we can see that t is a pair. But we do NOT want
+to make a specialised copy:
+ f' a b = let p = (a,b) in (..., ...)
+because now t is allocated by the caller, then r and s are passed to the
+recursive call, which allocates the (r,s) pair again.
+
+This happens if
+ (a) the argument p is used in other than a case-scrutinsation way.
+ (b) the argument to the call is not a 'fresh' tuple; you have to
+ look into its unfolding to see that it's a tuple
+
+Hence the "OR" part of Note [Good arguments] below.
+
+ALTERNATIVE 2: pass both boxed and unboxed versions. This no longer saves
+allocation, but does perhaps save evals. In the RULE we'd have
+something like
+
+ f (I# x#) = f' (I# x#) x#
+
+If at the call site the (I# x) was an unfolding, then we'd have to
+rely on CSE to eliminate the duplicate allocation.... This alternative
+doesn't look attractive enough to pursue.
+
+ALTERNATIVE 3: ignore the reboxing problem. The trouble is that
+the conservative reboxing story prevents many useful functions from being
+specialised. Example:
+ foo :: Maybe Int -> Int -> Int
+ foo (Just m) 0 = 0
+ foo x@(Just m) n = foo x (n-m)
+Here the use of 'x' will clearly not require boxing in the specialised function.
+
+The strictness analyser has the same problem, in fact. Example:
+ f p@(a,b) = ...
+If we pass just 'a' and 'b' to the worker, it might need to rebox the
+pair to create (a,b). A more sophisticated analysis might figure out
+precisely the cases in which this could happen, but the strictness
+analyser does no such analysis; it just passes 'a' and 'b', and hopes
+for the best.
+
+So my current choice is to make SpecConstr similarly aggressive, and
+ignore the bad potential of reboxing.
Note [Good arguments]
That same parameter is scrutinised by a case somewhere in
the RHS of the function
AND
- Those are the only uses of the parameter
+ Those are the only uses of the parameter (see Note [Reboxing])
What to abstract over
simplifier. That gives the simplest possible program for SpecConstr to
chew on; and it virtually guarantees no shadowing.
+Note [Specialising for constant parameters]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+This one is about specialising on a *constant* (but not necessarily
+constructor) argument
+
+ foo :: Int -> (Int -> Int) -> Int
+ foo 0 f = 0
+ foo m f = foo (f m) (+1)
+
+It produces
+
+ lvl_rmV :: GHC.Base.Int -> GHC.Base.Int
+ lvl_rmV =
+ \ (ds_dlk :: GHC.Base.Int) ->
+ case ds_dlk of wild_alH { GHC.Base.I# x_alG ->
+ GHC.Base.I# (GHC.Prim.+# x_alG 1)
+
+ T.$wfoo :: GHC.Prim.Int# -> (GHC.Base.Int -> GHC.Base.Int) ->
+ GHC.Prim.Int#
+ T.$wfoo =
+ \ (ww_sme :: GHC.Prim.Int#) (w_smg :: GHC.Base.Int -> GHC.Base.Int) ->
+ case ww_sme of ds_Xlw {
+ __DEFAULT ->
+ case w_smg (GHC.Base.I# ds_Xlw) of w1_Xmo { GHC.Base.I# ww1_Xmz ->
+ T.$wfoo ww1_Xmz lvl_rmV
+ };
+ 0 -> 0
+ }
+
+The recursive call has lvl_rmV as its argument, so we could create a specialised copy
+with that argument baked in; that is, not passed at all. Now it can perhaps be inlined.
+
+When is this worth it? Call the constant 'lvl'
+- If 'lvl' has an unfolding that is a constructor, see if the corresponding
+ parameter is scrutinised anywhere in the body.
+
+- If 'lvl' has an unfolding that is a inlinable function, see if the corresponding
+ parameter is applied (...to enough arguments...?)
+
+ Also do this is if the function has RULES?
+
+Also
+
+Note [Specialising for lambda parameters]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ foo :: Int -> (Int -> Int) -> Int
+ foo 0 f = 0
+ foo m f = foo (f m) (\n -> n-m)
+
+This is subtly different from the previous one in that we get an
+explicit lambda as the argument:
+
+ T.$wfoo :: GHC.Prim.Int# -> (GHC.Base.Int -> GHC.Base.Int) ->
+ GHC.Prim.Int#
+ T.$wfoo =
+ \ (ww_sm8 :: GHC.Prim.Int#) (w_sma :: GHC.Base.Int -> GHC.Base.Int) ->
+ case ww_sm8 of ds_Xlr {
+ __DEFAULT ->
+ case w_sma (GHC.Base.I# ds_Xlr) of w1_Xmf { GHC.Base.I# ww1_Xmq ->
+ T.$wfoo
+ ww1_Xmq
+ (\ (n_ad3 :: GHC.Base.Int) ->
+ case n_ad3 of wild_alB { GHC.Base.I# x_alA ->
+ GHC.Base.I# (GHC.Prim.-# x_alA ds_Xlr)
+ })
+ };
+ 0 -> 0
+ }
+
+I wonder if SpecConstr couldn't be extended to handle this? After all,
+lambda is a sort of constructor for functions and perhaps it already
+has most of the necessary machinery?
+
+Furthermore, there's an immediate win, because you don't need to allocate the lamda
+at the call site; and if perchance it's called in the recursive call, then you
+may avoid allocating it altogether. Just like for constructors.
+
+Looks cool, but probably rare...but it might be easy to implement.
+
+
+Note [SpecConstr for casts]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Consider
+ data family T a :: *
+ data instance T Int = T Int
+
+ foo n = ...
+ where
+ go (T 0) = 0
+ go (T n) = go (T (n-1))
+
+The recursive call ends up looking like
+ go (T (I# ...) `cast` g)
+So we want to spot the construtor application inside the cast.
+That's why we have the Cast case in argToPat
+
+
+-----------------------------------------------------
+ Stuff not yet handled
+-----------------------------------------------------
+
+Here are notes arising from Roman's work that I don't want to lose.
+
+Example 1
+~~~~~~~~~
+ data T a = T !a
+
+ foo :: Int -> T Int -> Int
+ foo 0 t = 0
+ foo x t | even x = case t of { T n -> foo (x-n) t }
+ | otherwise = foo (x-1) t
+
+SpecConstr does no specialisation, because the second recursive call
+looks like a boxed use of the argument. A pity.
+
+ $wfoo_sFw :: GHC.Prim.Int# -> T.T GHC.Base.Int -> GHC.Prim.Int#
+ $wfoo_sFw =
+ \ (ww_sFo [Just L] :: GHC.Prim.Int#) (w_sFq [Just L] :: T.T GHC.Base.Int) ->
+ case ww_sFo of ds_Xw6 [Just L] {
+ __DEFAULT ->
+ case GHC.Prim.remInt# ds_Xw6 2 of wild1_aEF [Dead Just A] {
+ __DEFAULT -> $wfoo_sFw (GHC.Prim.-# ds_Xw6 1) w_sFq;
+ 0 ->
+ case w_sFq of wild_Xy [Just L] { T.T n_ad5 [Just U(L)] ->
+ case n_ad5 of wild1_aET [Just A] { GHC.Base.I# y_aES [Just L] ->
+ $wfoo_sFw (GHC.Prim.-# ds_Xw6 y_aES) wild_Xy
+ } } };
+ 0 -> 0
+
+Example 2
+~~~~~~~~~
+ data a :*: b = !a :*: !b
+ data T a = T !a
+
+ foo :: (Int :*: T Int) -> Int
+ foo (0 :*: t) = 0
+ foo (x :*: t) | even x = case t of { T n -> foo ((x-n) :*: t) }
+ | otherwise = foo ((x-1) :*: t)
+
+Very similar to the previous one, except that the parameters are now in
+a strict tuple. Before SpecConstr, we have
+
+ $wfoo_sG3 :: GHC.Prim.Int# -> T.T GHC.Base.Int -> GHC.Prim.Int#
+ $wfoo_sG3 =
+ \ (ww_sFU [Just L] :: GHC.Prim.Int#) (ww_sFW [Just L] :: T.T
+ GHC.Base.Int) ->
+ case ww_sFU of ds_Xws [Just L] {
+ __DEFAULT ->
+ case GHC.Prim.remInt# ds_Xws 2 of wild1_aEZ [Dead Just A] {
+ __DEFAULT ->
+ case ww_sFW of tpl_B2 [Just L] { T.T a_sFo [Just A] ->
+ $wfoo_sG3 (GHC.Prim.-# ds_Xws 1) tpl_B2 -- $wfoo1
+ };
+ 0 ->
+ case ww_sFW of wild_XB [Just A] { T.T n_ad7 [Just S(L)] ->
+ case n_ad7 of wild1_aFd [Just L] { GHC.Base.I# y_aFc [Just L] ->
+ $wfoo_sG3 (GHC.Prim.-# ds_Xws y_aFc) wild_XB -- $wfoo2
+ } } };
+ 0 -> 0 }
+
+We get two specialisations:
+"SC:$wfoo1" [0] __forall {a_sFB :: GHC.Base.Int sc_sGC :: GHC.Prim.Int#}
+ Foo.$wfoo sc_sGC (Foo.T @ GHC.Base.Int a_sFB)
+ = Foo.$s$wfoo1 a_sFB sc_sGC ;
+"SC:$wfoo2" [0] __forall {y_aFp :: GHC.Prim.Int# sc_sGC :: GHC.Prim.Int#}
+ Foo.$wfoo sc_sGC (Foo.T @ GHC.Base.Int (GHC.Base.I# y_aFp))
+ = Foo.$s$wfoo y_aFp sc_sGC ;
+
+But perhaps the first one isn't good. After all, we know that tpl_B2 is
+a T (I# x) really, because T is strict and Int has one constructor. (We can't
+unbox the strict fields, becuase T is polymorphic!)
+
+
%************************************************************************
%* *
= do
showPass dflags "SpecConstr"
- let (binds', _) = initUs us (go emptyScEnv binds)
+ let (binds', _) = initUs us (go (initScEnv dflags) binds)
endPass dflags "SpecConstr" Opt_D_dump_spec binds'
%************************************************************************
\begin{code}
-data ScEnv = SCE { scope :: VarEnv HowBound,
- -- Binds all non-top-level variables in scope
+data ScEnv = SCE { sc_size :: Int, -- Size threshold
- cons :: ConstrEnv
+ sc_subst :: Subst, -- Current substitution
+
+ 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)
}
-type ConstrEnv = IdEnv ConValue
-data ConValue = CV AltCon [CoreArg]
- -- Variables known to be bound to a constructor
- -- in a particular case alternative
+---------------------
+-- As we go, we apply a substitution (sc_subst) to the current term
+type InExpr = CoreExpr -- *Before* applying the subst
+type OutExpr = CoreExpr -- *After* applying the subst
+type OutId = Id
+type OutVar = Var
-instance Outputable ConValue where
- ppr (CV con args) = ppr con <+> interpp'SP args
+---------------------
+type HowBoundEnv = VarEnv HowBound -- Domain is OutVars
-refineConstrEnv :: Subst -> ConstrEnv -> ConstrEnv
--- The substitution is a type substitution only
-refineConstrEnv subst env = mapVarEnv refine_con_value env
- where
- refine_con_value (CV con args) = CV con (map (substExpr subst) args)
+---------------------
+type ValueEnv = IdEnv Value -- Domain is OutIds
+data Value = ConVal AltCon [CoreArg] -- *Saturated* constructors
+ | LambdaVal -- Inlinable lambdas or PAPs
-emptyScEnv = SCE { scope = emptyVarEnv, cons = emptyVarEnv }
+instance Outputable Value where
+ ppr (ConVal con args) = ppr con <+> interpp'SP args
+ ppr LambdaVal = ptext SLIT("<Lambda>")
-data HowBound = RecFun -- These are the recursive functions for which
- -- we seek interesting call patterns
+---------------------
+initScEnv dflags
+ = SCE { sc_size = specThreshold dflags,
+ sc_subst = emptySubst,
+ sc_how_bound = emptyVarEnv,
+ sc_vals = emptyVarEnv }
- | RecArg -- These are those functions' arguments; we are
- -- interested to see if those arguments are scrutinised
+data HowBound = RecFun -- These are the recursive functions for which
+ -- we seek interesting call patterns
- | Other -- We track all others so we know what's in scope
- -- This is used in spec_one to check what needs to be
- -- passed as a parameter and what is in scope at the
- -- function definition site
+ | RecArg -- These are those functions' arguments, or their sub-components;
+ -- we gather occurrence information for these
instance Outputable HowBound where
ppr RecFun = text "RecFun"
ppr RecArg = text "RecArg"
- ppr Other = text "Other"
-
-lookupScopeEnv env v = lookupVarEnv (scope env) v
-
-extendBndrs env bndrs = env { scope = extendVarEnvList (scope env) [(b,Other) | b <- bndrs] }
-extendBndr env bndr = env { scope = extendVarEnv (scope env) bndr Other }
-
- -- When we encounter
- -- case scrut of b
- -- C x y -> ...
- -- we want to bind b, and perhaps scrut too, to (C x y)
-extendCaseBndrs :: ScEnv -> Id -> CoreExpr -> AltCon -> [Var] -> ScEnv
-extendCaseBndrs env case_bndr scrut DEFAULT alt_bndrs
- = extendBndrs env (case_bndr : alt_bndrs)
-
-extendCaseBndrs env case_bndr scrut con@(LitAlt lit) alt_bndrs
- = ASSERT( null alt_bndrs ) extendAlt env case_bndr scrut (CV con []) []
-
-extendCaseBndrs env case_bndr scrut con@(DataAlt data_con) alt_bndrs
- | isVanillaDataCon data_con
- = extendAlt env case_bndr scrut (CV con vanilla_args) alt_bndrs
-
- | otherwise -- GADT
- = extendAlt env1 case_bndr scrut (CV con gadt_args) alt_bndrs
+
+lookupHowBound :: ScEnv -> Id -> Maybe HowBound
+lookupHowBound env id = lookupVarEnv (sc_how_bound env) id
+
+scSubstId :: ScEnv -> Id -> CoreExpr
+scSubstId env v = lookupIdSubst (sc_subst env) v
+
+scSubstTy :: ScEnv -> Type -> Type
+scSubstTy env ty = substTy (sc_subst env) ty
+
+zapScSubst :: ScEnv -> ScEnv
+zapScSubst env = env { sc_subst = zapSubstEnv (sc_subst env) }
+
+extendScInScope :: ScEnv -> [Var] -> ScEnv
+ -- Bring the quantified variables into scope
+extendScInScope env qvars = env { sc_subst = extendInScopeList (sc_subst env) qvars }
+
+extendScSubst :: ScEnv -> [(Var,CoreArg)] -> ScEnv
+ -- Extend the substitution
+extendScSubst 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
- vanilla_args = map Type (tyConAppArgs (idType case_bndr)) ++
- map varToCoreExpr alt_bndrs
-
- gadt_args = map (substExpr subst . varToCoreExpr) alt_bndrs
- -- This call generates some bogus warnings from substExpr,
- -- because it's inconvenient to put all the Ids in scope
- -- Will be fixed when we move to FC
-
- (alt_tvs, _) = span isTyVar alt_bndrs
- Just (tv_subst, is_local) = coreRefineTys data_con alt_tvs (idType case_bndr)
- subst = mkSubst in_scope tv_subst emptyVarEnv -- No Id substitition
- in_scope = mkInScopeSet (tyVarsOfTypes (varEnvElts tv_subst))
-
- env1 | is_local = env
- | otherwise = env { cons = refineConstrEnv subst (cons env) }
-
-
-
-extendAlt :: ScEnv -> Id -> CoreExpr -> ConValue -> [Var] -> ScEnv
-extendAlt env case_bndr scrut val alt_bndrs
- = let
- env1 = SCE { scope = extendVarEnvList (scope env) [(b,Other) | b <- case_bndr : alt_bndrs],
- cons = extendVarEnv (cons env) case_bndr val }
- in
- case scrut of
- Var v -> -- Bind the scrutinee in the ConstrEnv if it's a variable
- -- Also forget if the scrutinee is a RecArg, because we're
- -- now in the branch of a case, and we don't want to
- -- record a non-scrutinee use of v if we have
- -- case v of { (a,b) -> ...(f v)... }
- SCE { scope = extendVarEnv (scope env1) v Other,
- cons = extendVarEnv (cons env1) v val }
- other -> env1
+ (subst', bndrs') = substBndrs (sc_subst env) bndrs
+ hb_env' = sc_how_bound env `extendVarEnvList`
+ [(bndr,how_bound) | bndr <- bndrs']
- -- When we encounter a recursive function binding
- -- f = \x y -> ...
- -- we want to extend the scope env with bindings
- -- that record that f is a RecFn and x,y are RecArgs
-extendRecBndr env fn bndrs
- = env { scope = scope env `extendVarEnvList`
- ((fn,RecFun): [(bndr,RecArg) | bndr <- bndrs]) }
+extendBndrWith :: HowBound -> ScEnv -> Var -> (ScEnv, Var)
+extendBndrWith how_bound env bndr
+ = (env { sc_subst = subst', sc_how_bound = hb_env' }, bndr')
+ where
+ (subst', bndr') = substBndr (sc_subst env) bndr
+ hb_env' = extendVarEnv (sc_how_bound env) bndr' how_bound
+
+extendRecBndrs :: ScEnv -> [Var] -> (ScEnv, [Var])
+extendRecBndrs env bndrs = (env { sc_subst = subst' }, bndrs')
+ where
+ (subst', bndrs') = substRecBndrs (sc_subst env) bndrs
+
+extendBndr :: ScEnv -> Var -> (ScEnv, Var)
+extendBndr env bndr = (env { sc_subst = subst' }, bndr')
+ where
+ (subst', bndr') = substBndr (sc_subst env) bndr
+
+extendValEnv :: ScEnv -> Id -> Maybe Value -> ScEnv
+extendValEnv env id Nothing = env
+extendValEnv env id (Just cv) = env { sc_vals = extendVarEnv (sc_vals env) id cv }
+
+extendCaseBndrs :: ScEnv -> CoreExpr -> Id -> AltCon -> [Var] -> ScEnv
+-- When we encounter
+-- case scrut of b
+-- C x y -> ...
+-- we want to bind b, and perhaps scrut too, to (C x y)
+-- NB: Extends only the sc_vals part of the envt
+extendCaseBndrs env scrut case_bndr con alt_bndrs
+ = case scrut of
+ Var v -> extendValEnv env1 v cval
+ other -> env1
+ where
+ env1 = extendValEnv env case_bndr cval
+ cval = case con of
+ DEFAULT -> Nothing
+ LitAlt lit -> Just (ConVal con [])
+ DataAlt dc -> Just (ConVal con vanilla_args)
+ where
+ vanilla_args = map Type (tyConAppArgs (idType case_bndr)) ++
+ varsToCoreExprs alt_bndrs
\end{code}
\begin{code}
data ScUsage
= SCU {
- calls :: !(IdEnv ([Call])), -- Calls
+ calls :: CallEnv, -- Calls
-- The functions are a subset of the
-- RecFuns in the ScEnv
} -- The variables are a subset of the
-- RecArg in the ScEnv
-type Call = (ConstrEnv, [CoreArg])
+type CallEnv = IdEnv [Call]
+type Call = (ValueEnv, [CoreArg])
-- The arguments of the call, together with the
-- env giving the constructor bindings at the call site
nullUsage = SCU { calls = emptyVarEnv, occs = emptyVarEnv }
-combineUsage u1 u2 = SCU { calls = plusVarEnv_C (++) (calls u1) (calls u2),
+combineCalls :: CallEnv -> CallEnv -> CallEnv
+combineCalls = plusVarEnv_C (++)
+
+combineUsage u1 u2 = SCU { calls = combineCalls (calls u1) (calls u2),
occs = plusVarEnv_C combineOcc (occs u1) (occs u2) }
combineUsages [] = nullUsage
combineUsages us = foldr1 combineUsage us
-data ArgOcc = CaseScrut
- | OtherOcc
- | Both
+lookupOcc :: ScUsage -> Var -> (ScUsage, ArgOcc)
+lookupOcc (SCU { calls = sc_calls, occs = sc_occs }) bndr
+ = (SCU {calls = sc_calls, occs = delVarEnv sc_occs bndr},
+ lookupVarEnv sc_occs bndr `orElse` NoOcc)
-instance Outputable ArgOcc where
- ppr CaseScrut = ptext SLIT("case-scrut")
- ppr OtherOcc = ptext SLIT("other-occ")
- ppr Both = ptext SLIT("case-scrut and other")
+lookupOccs :: ScUsage -> [Var] -> (ScUsage, [ArgOcc])
+lookupOccs (SCU { calls = sc_calls, occs = sc_occs }) bndrs
+ = (SCU {calls = sc_calls, occs = delVarEnvList sc_occs bndrs},
+ [lookupVarEnv sc_occs b `orElse` NoOcc | b <- bndrs])
-combineOcc CaseScrut CaseScrut = CaseScrut
-combineOcc OtherOcc OtherOcc = OtherOcc
-combineOcc _ _ = Both
-\end{code}
+data ArgOcc = NoOcc -- Doesn't occur at all; or a type argument
+ | UnkOcc -- Used in some unknown way
+
+ | ScrutOcc (UniqFM [ArgOcc]) -- See Note [ScrutOcc]
+
+ | BothOcc -- Definitely taken apart, *and* perhaps used in some other way
+
+{- Note [ScrutOcc]
+An occurrence of ScrutOcc indicates that the thing, or a `cast` version of the thing,
+is *only* taken apart or applied.
+
+ Functions, literal: ScrutOcc emptyUFM
+ Data constructors: ScrutOcc subs,
+
+where (subs :: UniqFM [ArgOcc]) gives usage of the *pattern-bound* components,
+The domain of the UniqFM is the Unique of the data constructor
+
+The [ArgOcc] is the occurrences of the *pattern-bound* components
+of the data structure. E.g.
+ data T a = forall b. MkT a b (b->a)
+A pattern binds b, x::a, y::b, z::b->a, but not 'a'!
+
+-}
+
+instance Outputable ArgOcc where
+ ppr (ScrutOcc xs) = ptext SLIT("scrut-occ") <> ppr xs
+ ppr UnkOcc = ptext SLIT("unk-occ")
+ ppr BothOcc = ptext SLIT("both-occ")
+ ppr NoOcc = ptext SLIT("no-occ")
+
+-- Experimentally, this vesion of combineOcc makes ScrutOcc "win", so
+-- that if the thing is scrutinised anywhere then we get to see that
+-- in the overall result, even if it's also used in a boxed way
+-- This might be too agressive; see Note [Reboxing] Alternative 3
+combineOcc NoOcc occ = occ
+combineOcc occ NoOcc = occ
+combineOcc (ScrutOcc xs) (ScrutOcc ys) = ScrutOcc (plusUFM_C combineOccs xs ys)
+combineOcc occ (ScrutOcc ys) = ScrutOcc ys
+combineOcc (ScrutOcc xs) occ = ScrutOcc xs
+combineOcc UnkOcc UnkOcc = UnkOcc
+combineOcc _ _ = BothOcc
+
+combineOccs :: [ArgOcc] -> [ArgOcc] -> [ArgOcc]
+combineOccs xs ys = zipWithEqual "combineOccs" combineOcc xs ys
+
+setScrutOcc :: ScEnv -> ScUsage -> CoreExpr -> ArgOcc -> ScUsage
+-- *Overwrite* the occurrence info for the scrutinee, if the scrutinee
+-- is a variable, and an interesting variable
+setScrutOcc env usg (Cast e _) occ = setScrutOcc env usg e occ
+setScrutOcc env usg (Note _ e) occ = setScrutOcc env usg e occ
+setScrutOcc env usg (Var v) occ
+ | Just RecArg <- lookupHowBound env v = usg { occs = extendVarEnv (occs usg) v occ }
+ | otherwise = usg
+setScrutOcc env usg other occ -- Catch-all
+ = usg
+
+conArgOccs :: ArgOcc -> AltCon -> [ArgOcc]
+-- Find usage of components of data con; returns [UnkOcc...] if unknown
+-- See Note [ScrutOcc] for the extra UnkOccs in the vanilla datacon case
+
+conArgOccs (ScrutOcc fm) (DataAlt dc)
+ | Just pat_arg_occs <- lookupUFM fm dc
+ = [UnkOcc | tv <- dataConUnivTyVars dc] ++ pat_arg_occs
+
+conArgOccs other con = repeat UnkOcc
+\end{code}
%************************************************************************
%* *
-- The unique supply is needed when we invent
-- a new name for the specialised function and its args
-scExpr env e@(Type t) = returnUs (nullUsage, e)
-scExpr env e@(Lit l) = returnUs (nullUsage, e)
-scExpr env e@(Var v) = returnUs (varUsage env v OtherOcc, e)
-scExpr env (Note n e) = scExpr env e `thenUs` \ (usg,e') ->
- returnUs (usg, Note n e')
-scExpr env (Lam b e) = scExpr (extendBndr env b) e `thenUs` \ (usg,e') ->
- returnUs (usg, Lam b e')
-
-scExpr env (Case scrut b ty alts)
- = sc_scrut scrut `thenUs` \ (scrut_usg, scrut') ->
- mapAndUnzipUs sc_alt alts `thenUs` \ (alts_usgs, alts') ->
- returnUs (combineUsages alts_usgs `combineUsage` scrut_usg,
- Case scrut' b ty alts')
+scExpr env e = scExpr' env e
+
+
+scExpr' env (Var v) = case scSubstId env v of
+ Var v' -> returnUs (varUsage env v UnkOcc, Var v')
+ e' -> scExpr (zapScSubst env) e'
+
+scExpr' env e@(Type t) = returnUs (nullUsage, Type (scSubstTy env t))
+scExpr' env e@(Lit l) = returnUs (nullUsage, e)
+scExpr' env (Note n e) = do { (usg,e') <- scExpr env e
+ ; return (usg, Note n e') }
+scExpr' env (Cast e co) = do { (usg, e') <- scExpr env e
+ ; return (usg, Cast e' (scSubstTy env co)) }
+scExpr' env (Lam b e) = do { let (env', b') = extendBndr env b
+ ; (usg, e') <- scExpr env' e
+ ; return (usg, Lam b' e') }
+
+scExpr' env (Case scrut b ty alts)
+ = do { (scrut_usg, scrut') <- scExpr env scrut
+ ; case isValue (sc_vals env) scrut' of
+ Just (ConVal con args) -> sc_con_app con args scrut'
+ other -> sc_vanilla scrut_usg scrut'
+ }
where
- sc_scrut e@(Var v) = returnUs (varUsage env v CaseScrut, e)
- sc_scrut e = scExpr env e
-
- sc_alt (con,bs,rhs) = scExpr env1 rhs `thenUs` \ (usg,rhs') ->
- returnUs (usg, (con,bs,rhs'))
- where
- env1 = extendCaseBndrs env b scrut con bs
-
-scExpr env (Let bind body)
- = scBind env bind `thenUs` \ (env', bind_usg, bind') ->
- scExpr env' body `thenUs` \ (body_usg, body') ->
- returnUs (bind_usg `combineUsage` body_usg, Let bind' body')
-
-scExpr env e@(App _ _)
- = let
- (fn, args) = collectArgs e
- in
- mapAndUnzipUs (scExpr env) (fn:args) `thenUs` \ (usgs, (fn':args')) ->
+ sc_con_app con args scrut' -- Known constructor; simplify
+ = do { let (_, bs, rhs) = findAlt con alts
+ alt_env' = extendScSubst 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')
+ <- mapAndUnzip3Us (sc_alt alt_env scrut' b') alts
+
+ ; let (alt_usg, b_occ) = lookupOcc (combineUsages alt_usgs) b
+ scrut_occ = foldr combineOcc b_occ alt_occs
+ scrut_usg' = setScrutOcc env scrut_usg scrut' scrut_occ
+ -- The combined usage of the scrutinee is given
+ -- by scrut_occ, which is passed to scScrut, which
+ -- in turn treats a bare-variable scrutinee specially
+
+ ; return (alt_usg `combineUsage` scrut_usg',
+ Case scrut' b' (scSubstTy env ty) alts') }
+
+ sc_alt env scrut' b' (con,bs,rhs)
+ = do { let (env1, bs') = extendBndrsWith RecArg env bs
+ env2 = extendCaseBndrs env1 scrut' b' con bs'
+ ; (usg,rhs') <- scExpr env2 rhs
+ ; let (usg', arg_occs) = lookupOccs usg bs
+ scrut_occ = case con of
+ DataAlt dc -> ScrutOcc (unitUFM dc arg_occs)
+ other -> ScrutOcc emptyUFM
+ ; return (usg', scrut_occ, (con,bs',rhs')) }
+
+scExpr' env (Let (NonRec bndr rhs) body)
+ = do { let (body_env, bndr') = extendBndr env bndr
+ ; (rhs_usg, rhs_info@(_, args', rhs_body', _)) <- scRecRhs env (bndr',rhs)
+
+ ; if null args' || isEmptyVarEnv (calls rhs_usg) then do
+ do { -- Vanilla case
+ let rhs' = mkLams args' rhs_body'
+ body_env2 = extendValEnv body_env bndr' (isValue (sc_vals env) rhs')
+ -- Record if the RHS is a value
+ ; (body_usg, body') <- scExpr body_env2 body
+ ; return (body_usg `combineUsage` rhs_usg, Let (NonRec bndr' rhs') body') }
+ else
+ do { -- Join-point case
+ let body_env2 = extendHowBound body_env [bndr'] RecFun
+ -- If the RHS of this 'let' contains calls
+ -- to recursive functions that we're trying
+ -- to specialise, then treat this let too
+ -- as one to specialise
+ ; (body_usg, body') <- scExpr body_env2 body
+
+ ; (spec_usg, _, specs) <- specialise env (calls body_usg) ([], rhs_info)
+
+ ; return (body_usg { calls = calls body_usg `delVarEnv` bndr' }
+ `combineUsage` rhs_usg `combineUsage` spec_usg,
+ mkLets [NonRec b r | (b,r) <- addRules rhs_info specs] body')
+ } }
+
+scExpr' env (Let (Rec prs) body)
+ = do { (env', bind_usg, bind') <- scBind env (Rec prs)
+ ; (body_usg, body') <- scExpr env' body
+ ; return (bind_usg `combineUsage` body_usg, Let bind' body') }
+
+scExpr' env e@(App _ _)
+ = do { let (fn, args) = collectArgs e
+ ; (fn_usg, fn') <- scExpr env fn
-- Process the function too. It's almost always a variable,
-- but not always. In particular, if this pass follows float-in,
-- which it may, we can get
-- (let f = ...f... in f) arg1 arg2
- let
- call_usg = case fn of
- Var f | Just RecFun <- lookupScopeEnv env f
- -> SCU { calls = unitVarEnv f [(cons env, args)],
- occs = emptyVarEnv }
- other -> nullUsage
- in
- returnUs (combineUsages usgs `combineUsage` call_usg, mkApps fn' args')
+ -- Also the substitution may replace a variable by a non-variable
+
+ ; let fn_usg' = setScrutOcc env fn_usg fn' (ScrutOcc emptyUFM)
+ -- We use setScrutOcc to record the fact that the function is called
+ -- Perhaps we should check that it has at least one value arg,
+ -- but currently we don't bother
+
+ ; (arg_usgs, args') <- mapAndUnzipUs (scExpr env) args
+ ; let call_usg = case fn' of
+ Var f | Just RecFun <- lookupHowBound env f
+ , not (null args) -- Not a proper call!
+ -> SCU { calls = unitVarEnv f [(sc_vals env, args')],
+ occs = emptyVarEnv }
+ other -> nullUsage
+ ; return (combineUsages arg_usgs `combineUsage` fn_usg'
+ `combineUsage` call_usg,
+ mkApps fn' args') }
----------------------
scBind :: ScEnv -> CoreBind -> UniqSM (ScEnv, ScUsage, CoreBind)
-scBind env (Rec [(fn,rhs)])
- | notNull val_bndrs
- = scExpr env_fn_body body `thenUs` \ (usg, body') ->
- specialise env fn bndrs body' usg `thenUs` \ (rules, spec_prs) ->
- -- Note body': the specialised copies should be based on the
- -- optimised version of the body, in case there were
- -- nested functions inside.
- let
- SCU { calls = calls, occs = occs } = usg
- in
- returnUs (extendBndr env fn, -- For the body of the letrec, just
- -- extend the env with Other to record
- -- that it's in scope; no funny RecFun business
- SCU { calls = calls `delVarEnv` fn, occs = occs `delVarEnvList` val_bndrs},
- Rec ((fn `addIdSpecialisations` rules, mkLams bndrs body') : spec_prs))
- where
- (bndrs,body) = collectBinders rhs
- val_bndrs = filter isId bndrs
- env_fn_body = extendRecBndr env fn bndrs
-
scBind env (Rec prs)
- = mapAndUnzipUs do_one prs `thenUs` \ (usgs, prs') ->
- returnUs (extendBndrs env (map fst prs), combineUsages usgs, Rec prs')
+ | not (all (couldBeSmallEnoughToInline (sc_size env)) rhss)
+ -- No specialisation
+ = do { let (rhs_env,bndrs') = extendRecBndrs env bndrs
+ ; (rhs_usgs, rhss') <- mapAndUnzipUs (scExpr rhs_env) rhss
+ ; return (rhs_env, combineUsages rhs_usgs, Rec (bndrs' `zip` rhss')) }
+ | otherwise -- Do specialisation
+ = do { let (rhs_env1,bndrs') = extendRecBndrs env bndrs
+ rhs_env2 = extendHowBound rhs_env1 bndrs' RecFun
+
+ ; (rhs_usgs, rhs_infos) <- mapAndUnzipUs (scRecRhs rhs_env2) (bndrs' `zip` rhss)
+ ; let rhs_usg = combineUsages rhs_usgs
+
+ ; (spec_usg, specs) <- spec_loop rhs_env2 (calls rhs_usg)
+ (repeat [] `zip` rhs_infos)
+
+ ; let all_usg = rhs_usg `combineUsage` spec_usg
+
+ ; return (rhs_env1, -- For the body of the letrec, delete the RecFun business
+ all_usg { calls = calls rhs_usg `delVarEnvList` bndrs' },
+ Rec (concat (zipWith addRules rhs_infos specs))) }
where
- do_one (bndr,rhs) = scExpr env rhs `thenUs` \ (usg, rhs') ->
- returnUs (usg, (bndr,rhs'))
+ (bndrs,rhss) = unzip prs
+
+ spec_loop :: ScEnv
+ -> CallEnv
+ -> [([CallPat], RhsInfo)] -- One per binder
+ -> UniqSM (ScUsage, [[SpecInfo]]) -- One list per binder
+ spec_loop env all_calls rhs_stuff
+ = do { (spec_usg_s, new_pats_s, specs) <- mapAndUnzip3Us (specialise env all_calls) rhs_stuff
+ ; let spec_usg = combineUsages spec_usg_s
+ ; if all null new_pats_s then
+ return (spec_usg, specs) else do
+ { (spec_usg1, specs1) <- spec_loop env (calls spec_usg)
+ (zipWith add_pats new_pats_s rhs_stuff)
+ ; return (spec_usg `combineUsage` spec_usg1, zipWith (++) specs specs1) } }
+
+ add_pats :: [CallPat] -> ([CallPat], RhsInfo) -> ([CallPat], RhsInfo)
+ add_pats new_pats (done_pats, rhs_info) = (done_pats ++ new_pats, rhs_info)
scBind env (NonRec bndr rhs)
- = scExpr env rhs `thenUs` \ (usg, rhs') ->
- returnUs (extendBndr env bndr, usg, NonRec bndr rhs')
+ = do { (usg, rhs') <- scExpr env rhs
+ ; let (env1, bndr') = extendBndr env bndr
+ env2 = extendValEnv env1 bndr' (isValue (sc_vals env) rhs')
+ ; return (env2, usg, NonRec bndr' rhs') }
+
+----------------------
+scRecRhs :: ScEnv -> (OutId, InExpr) -> UniqSM (ScUsage, RhsInfo)
+scRecRhs env (bndr,rhs)
+ = do { let (arg_bndrs,body) = collectBinders rhs
+ (body_env, arg_bndrs') = extendBndrsWith RecArg env arg_bndrs
+ ; (body_usg, body') <- scExpr body_env body
+ ; let (rhs_usg, arg_occs) = lookupOccs body_usg arg_bndrs'
+ ; return (rhs_usg, (bndr, arg_bndrs', body', arg_occs)) }
+
+ -- The arg_occs says how the visible,
+ -- lambda-bound binders of the RHS are used
+ -- (including the TyVar binders)
+ -- Two pats are the same if they match both ways
+
+----------------------
+addRules :: RhsInfo -> [SpecInfo] -> [(Id,CoreExpr)]
+addRules (fn, args, body, _) specs
+ = [(id,rhs) | (_,id,rhs) <- specs] ++
+ [(fn `addIdSpecialisations` rules, mkLams args body)]
+ where
+ rules = [r | (r,_,_) <- specs]
----------------------
varUsage env v use
- | Just RecArg <- lookupScopeEnv env v = SCU { calls = emptyVarEnv,
+ | Just RecArg <- lookupHowBound env v = SCU { calls = emptyVarEnv,
occs = unitVarEnv v use }
| otherwise = nullUsage
\end{code}
%************************************************************************
%* *
-\subsection{The specialiser}
+ The specialiser itself
%* *
%************************************************************************
\begin{code}
-specialise :: ScEnv
- -> Id -- Functionn
- -> [CoreBndr] -> CoreExpr -- Its RHS
- -> ScUsage -- Info on usage
- -> UniqSM ([CoreRule], -- Rules
- [(Id,CoreExpr)]) -- Bindings
-
-specialise env fn bndrs body (SCU {calls=calls, occs=occs})
- = getUs `thenUs` \ us ->
- let
- all_calls = lookupVarEnv calls fn `orElse` []
-
- good_calls :: [[CoreArg]]
- good_calls = [ pats
- | (con_env, call_args) <- all_calls,
- call_args `lengthAtLeast` n_bndrs, -- App is saturated
- let call = bndrs `zip` call_args,
- any (good_arg con_env occs) call, -- At least one arg is a constr app
- let (_, pats) = argsToPats con_env us call_args
- ]
- in
- mapAndUnzipUs (spec_one env fn (mkLams bndrs body))
- (nubBy same_call good_calls `zip` [1..])
- where
- n_bndrs = length bndrs
- same_call as1 as2 = and (zipWith tcEqExpr as1 as2)
+type RhsInfo = (OutId, [OutVar], OutExpr, [ArgOcc])
+ -- Info about the *original* RHS of a binding we are specialising
+ -- Original binding f = \xs.body
+ -- Plus info about usage of arguments
+
+type SpecInfo = (CoreRule, OutId, OutExpr)
+ -- One specialisation: Rule plus definition
+
+
+specialise
+ :: ScEnv
+ -> CallEnv -- Info on calls
+ -> ([CallPat], RhsInfo) -- Original RHS plus patterns dealt with
+ -> UniqSM (ScUsage, [CallPat], [SpecInfo]) -- Specialised calls
+
+-- 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 (done_pats, (fn, arg_bndrs, body, arg_occs))
+ | notNull arg_bndrs, -- Only specialise functions
+ Just all_calls <- lookupVarEnv bind_calls fn
+ = do { pats <- callsToPats env done_pats arg_occs all_calls
+-- ; pprTrace "specialise" (vcat [ppr fn <+> ppr arg_occs,
+-- text "calls" <+> ppr all_calls,
+-- text "good pats" <+> ppr pats]) $
+-- return ()
+
+ ; (spec_usgs, specs) <- mapAndUnzipUs (spec_one env fn arg_bndrs body)
+ (pats `zip` [length done_pats..])
+
+ ; return (combineUsages spec_usgs, pats, specs) }
+ | otherwise
+ = return (nullUsage, [], []) -- The boring case
----------------------
-good_arg :: ConstrEnv -> IdEnv ArgOcc -> (CoreBndr, CoreArg) -> Bool
--- See Note [Good arguments] above
-good_arg con_env arg_occs (bndr, arg)
- = case is_con_app_maybe con_env arg of
- Just _ -> bndr_usg_ok arg_occs bndr arg
- other -> False
-
-bndr_usg_ok :: IdEnv ArgOcc -> Var -> CoreArg -> Bool
-bndr_usg_ok arg_occs bndr arg
- = case lookupVarEnv arg_occs bndr of
- Just CaseScrut -> True -- Used only by case scrutiny
- Just Both -> case arg of -- Used by case and elsewhere
- App _ _ -> True -- so the arg should be an explicit con app
- other -> False
- other -> False -- Not used, or used wonkily
-
---------------------
spec_one :: ScEnv
- -> Id -- Function
- -> CoreExpr -- Rhs of the original function
- -> ([CoreArg], Int)
- -> UniqSM (CoreRule, (Id,CoreExpr)) -- Rule and binding
+ -> OutId -- Function
+ -> [Var] -- Lambda-binders of RHS; should match patterns
+ -> CoreExpr -- Body of the original function
+ -> (([Var], [CoreArg]), Int)
+ -> UniqSM (ScUsage, SpecInfo) -- 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
[c::*, v::(b,c) are presumably bound by the (...) part]
==>
f_spec = /\ b c \ v::(b,c) hw::[(a,(b,c))] ->
- (...entire RHS of f...) (b,c) ((:) (a,(b,c)) (x,v) hw)
+ (...entire body of f...) [b -> (b,c),
+ y -> ((:) (a,(b,c)) (x,v) hw)]
RULE: forall b::* c::*, -- Note, *not* forall a, x
v::(b,c),
f (b,c) ((:) (a,(b,c)) (x,v) hw) = f_spec b c v hw
-}
-spec_one env fn rhs (pats, rule_number)
- = getUniqueUs `thenUs` \ spec_uniq ->
- let
- fn_name = idName fn
- fn_loc = nameSrcLoc fn_name
- spec_occ = mkSpecOcc (nameOccName fn_name)
- pat_fvs = varSetElems (exprsFreeVars pats)
- vars_to_bind = filter not_avail pat_fvs
- -- See Note [Shadowing] at the top
-
- not_avail v = not (v `elemVarEnv` scope env)
- -- Put the type variables first; the type of a term
- -- variable may mention a type variable
- (tvs, ids) = partition isTyVar vars_to_bind
- bndrs = tvs ++ ids
- spec_body = mkApps rhs pats
- body_ty = exprType spec_body
-
- (spec_lam_args, spec_call_args) = mkWorkerArgs bndrs body_ty
- -- Usual w/w hack to avoid generating
- -- a spec_rhs of unlifted type and no args
+spec_one env fn arg_bndrs body ((qvars, pats), rule_number)
+ = do { -- Specialise the body
+ let spec_env = extendScSubst (extendScInScope env qvars)
+ (arg_bndrs `zip` pats)
+ ; (spec_usg, spec_body) <- scExpr spec_env body
+
+-- ; pprTrace "spec_one" (ppr fn <+> vcat [text "pats" <+> ppr pats,
+-- text "calls" <+> (ppr (calls spec_usg))])
+-- (return ())
+
+ -- And build the results
+ ; spec_uniq <- getUniqueUs
+ ; let (spec_lam_args, spec_call_args) = mkWorkerArgs qvars body_ty
+ -- Usual w/w hack to avoid generating
+ -- a spec_rhs of unlifted type and no args
- rule_name = mkFastString ("SC:" ++ showSDoc (ppr fn <> int rule_number))
- spec_rhs = mkLams spec_lam_args spec_body
- spec_id = mkUserLocal spec_occ spec_uniq (mkPiTypes spec_lam_args body_ty) fn_loc
- rule_rhs = mkVarApps (Var spec_id) spec_call_args
- rule = mkLocalRule rule_name specConstrActivation fn_name bndrs pats rule_rhs
- in
- returnUs (rule, (spec_id, spec_rhs))
+ fn_name = idName fn
+ fn_loc = nameSrcSpan fn_name
+ spec_occ = mkSpecOcc (nameOccName fn_name)
+ rule_name = mkFastString ("SC:" ++ showSDoc (ppr fn <> int rule_number))
+ spec_rhs = mkLams spec_lam_args spec_body
+ spec_id = mkUserLocal spec_occ spec_uniq (mkPiTypes spec_lam_args body_ty) fn_loc
+ body_ty = exprType spec_body
+ rule_rhs = mkVarApps (Var spec_id) spec_call_args
+ rule = mkLocalRule rule_name specConstrActivation fn_name qvars pats rule_rhs
+ ; return (spec_usg, (rule, spec_id, spec_rhs)) }
-- In which phase should the specialise-constructor rules be active?
-- Originally I made them always-active, but Manuel found that
This code deals with analysing call-site arguments to see whether
they are constructor applications.
+
\begin{code}
+type CallPat = ([Var], [CoreExpr]) -- Quantified variables and arguments
+
+
+callsToPats :: ScEnv -> [CallPat] -> [ArgOcc] -> [Call] -> UniqSM [CallPat]
+ -- Result has no duplicate patterns,
+ -- nor ones mentioned in done_pats
+callsToPats env done_pats bndr_occs calls
+ = do { mb_pats <- mapM (callToPats env bndr_occs) calls
+
+ ; let good_pats :: [([Var], [CoreArg])]
+ good_pats = catMaybes mb_pats
+ is_done p = any (samePat p) done_pats
+
+ ; return (filterOut is_done (nubBy samePat good_pats)) }
+
+callToPats :: ScEnv -> [ArgOcc] -> Call -> UniqSM (Maybe CallPat)
+ -- The [Var] is the variables to quantify over in the rule
+ -- Type variables come first, since they may scope
+ -- over the following term variables
+ -- The [CoreExpr] are the argument patterns for the rule
+callToPats env bndr_occs (con_env, args)
+ | length args < length bndr_occs -- Check saturated
+ = return Nothing
+ | otherwise
+ = do { let in_scope = substInScope (sc_subst env)
+ ; prs <- argsToPats in_scope con_env (args `zip` bndr_occs)
+ ; let (good_pats, pats) = unzip prs
+ pat_fvs = varSetElems (exprsFreeVars pats)
+ qvars = filterOut (`elemInScopeSet` in_scope) pat_fvs
+ -- Quantify over variables that are not in sccpe
+ -- at the call site
+ -- See Note [Shadowing] at the top
+
+ (tvs, ids) = partition isTyVar qvars
+ qvars' = tvs ++ ids
+ -- Put the type variables first; the type of a term
+ -- variable may mention a type variable
+
+ ; -- pprTrace "callToPats" (ppr args $$ ppr prs $$ ppr bndr_occs) $
+ if or good_pats
+ then return (Just (qvars', pats))
+ else return Nothing }
+
-- argToPat takes an actual argument, and returns an abstracted
-- version, consisting of just the "constructor skeleton" of the
-- argument, with non-constructor sub-expression replaced by new
-- placeholder variables. For example:
-- C a (D (f x) (g y)) ==> C p1 (D p2 p3)
-argToPat :: ConstrEnv -> UniqSupply -> CoreArg -> (UniqSupply, CoreExpr)
-argToPat env us (Type ty)
- = (us, Type ty)
-
-argToPat env us arg
- | Just (CV dc args) <- is_con_app_maybe env arg
- = let
- (us',args') = argsToPats env us args
- in
- (us', mk_con_app dc args')
-
-argToPat env us (Var v) -- Don't uniqify existing vars,
- = (us, Var v) -- so that we can spot when we pass them twice
-
-argToPat env us arg
- = (us1, Var (mkSysLocal FSLIT("sc") (uniqFromSupply us2) (exprType arg)))
+argToPat :: InScopeSet -- What's in scope at the fn defn site
+ -> ValueEnv -- ValueEnv at the call site
+ -> CoreArg -- A call arg (or component thereof)
+ -> ArgOcc
+ -> UniqSM (Bool, CoreArg)
+-- Returns (interesting, pat),
+-- where pat is the pattern derived from the argument
+-- intersting=True if the pattern is non-trivial (not a variable or type)
+-- E.g. x:xs --> (True, x:xs)
+-- f xs --> (False, w) where w is a fresh wildcard
+-- (f xs, 'c') --> (True, (w, 'c')) where w is a fresh wildcard
+-- \x. x+y --> (True, \x. x+y)
+-- lvl7 --> (True, lvl7) if lvl7 is bound
+-- somewhere further out
+
+argToPat in_scope val_env arg@(Type ty) arg_occ
+ = return (False, arg)
+
+argToPat in_scope val_env (Note n arg) arg_occ
+ = argToPat in_scope val_env arg arg_occ
+ -- Note [Notes in call patterns]
+ -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ -- Ignore Notes. In particular, we want to ignore any InlineMe notes
+ -- Perhaps we should not ignore profiling notes, but I'm going to
+ -- ride roughshod over them all for now.
+ --- See Note [Notes in RULE matching] in Rules
+
+argToPat in_scope val_env (Let _ arg) arg_occ
+ = argToPat in_scope val_env arg arg_occ
+ -- Look through let expressions
+ -- e.g. f (let v = rhs in \y -> ...v...)
+ -- Here we can specialise for f (\y -> ...)
+ -- because the rule-matcher will look through the let.
+
+argToPat in_scope val_env (Cast arg co) arg_occ
+ = do { (interesting, arg') <- argToPat in_scope val_env arg arg_occ
+ ; if interesting then
+ return (interesting, Cast arg' co)
+ else
+ wildCardPat (snd (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
- (us1,us2) = splitUniqSupply us
+ is_value_lam (Lam v e) -- Spot a value lambda, even if
+ | isId v = True -- it is inside a type lambda
+ | otherwise = is_value_lam e
+ is_value_lam other = False
+-}
-argsToPats :: ConstrEnv -> UniqSupply -> [CoreArg] -> (UniqSupply, [CoreExpr])
-argsToPats env us args = mapAccumL (argToPat env) us args
+ -- Check for a constructor application
+ -- NB: this *precedes* the Var case, so that we catch nullary constrs
+argToPat in_scope val_env arg arg_occ
+ | Just (ConVal dc args) <- isValue val_env arg
+ , case arg_occ of
+ ScrutOcc _ -> True -- Used only by case scrutinee
+ BothOcc -> case arg of -- Used elsewhere
+ App {} -> True -- see Note [Reboxing]
+ other -> False
+ other -> False -- No point; the arg is not decomposed
+ = do { args' <- argsToPats in_scope val_env (args `zip` conArgOccs arg_occ dc)
+ ; return (True, mk_con_app dc (map snd args')) }
+
+ -- Check if the argument is a variable that
+ -- is in scope at the function definition site
+ -- It's worth specialising on this if
+ -- (a) it's used in an interesting way in the body
+ -- (b) we know what its value is
+argToPat in_scope val_env (Var v) arg_occ
+ | case arg_occ of { UnkOcc -> False; other -> True }, -- (a)
+ is_value -- (b)
+ = return (True, Var v)
+ where
+ is_value
+ | isLocalId v = v `elemInScopeSet` in_scope
+ && isJust (lookupVarEnv val_env v)
+ -- Local variables have values in val_env
+ | otherwise = isValueUnfolding (idUnfolding v)
+ -- Imports have unfoldings
+
+-- I'm really not sure what this comment means
+-- And by not wild-carding we tend to get forall'd
+-- variables that are in soope, which in turn can
+-- expose the weakness in let-matching
+-- See Note [Matching lets] in Rules
+ -- Check for a variable bound inside the function.
+ -- Don't make a wild-card, because we may usefully share
+ -- e.g. f a = let x = ... in f (x,x)
+ -- NB: this case follows the lambda and con-app cases!!
+argToPat in_scope val_env (Var v) arg_occ
+ = return (False, Var v)
+
+ -- The default case: make a wild-card
+argToPat in_scope val_env arg arg_occ
+ = wildCardPat (exprType arg)
+
+wildCardPat :: Type -> UniqSM (Bool, CoreArg)
+wildCardPat ty = do { uniq <- getUniqueUs
+ ; let id = mkSysLocal FSLIT("sc") uniq ty
+ ; return (False, Var id) }
+
+argsToPats :: InScopeSet -> ValueEnv
+ -> [(CoreArg, ArgOcc)]
+ -> UniqSM [(Bool, CoreArg)]
+argsToPats in_scope val_env args
+ = mapUs do_one args
+ where
+ do_one (arg,occ) = argToPat in_scope val_env arg occ
\end{code}
\begin{code}
-is_con_app_maybe :: ConstrEnv -> CoreExpr -> Maybe ConValue
-is_con_app_maybe env (Var v)
- = case lookupVarEnv env v of
- Just stuff -> Just stuff
- -- You might think we could look in the idUnfolding here
+isValue :: ValueEnv -> CoreExpr -> Maybe Value
+isValue env (Lit lit)
+ = Just (ConVal (LitAlt lit) [])
+
+isValue env (Var v)
+ | Just stuff <- lookupVarEnv env v
+ = Just stuff -- You might think we could look in the idUnfolding here
-- but that doesn't take account of which branch of a
-- case we are in, which is the whole point
- Nothing | isCheapUnfolding unf
- -> is_con_app_maybe env (unfoldingTemplate unf)
- where
- unf = idUnfolding v
- -- However we do want to consult the unfolding as well,
- -- for let-bound constructors!
+ | not (isLocalId v) && isCheapUnfolding unf
+ = isValue env (unfoldingTemplate unf)
+ where
+ unf = idUnfolding v
+ -- However we do want to consult the unfolding
+ -- as well, for let-bound constructors!
+
+isValue env (Lam b e)
+ | isTyVar b = isValue env e
+ | otherwise = Just LambdaVal
- other -> Nothing
+isValue env expr -- Maybe it's a constructor application
+ | (Var fun, args) <- collectArgs expr
+ = case isDataConWorkId_maybe fun of
-is_con_app_maybe env (Lit lit)
- = Just (CV (LitAlt lit) [])
+ Just con | args `lengthAtLeast` dataConRepArity con
+ -- Check saturated; might be > because the
+ -- arity excludes type args
+ -> Just (ConVal (DataAlt con) args)
-is_con_app_maybe env expr
- = case collectArgs expr of
- (Var fun, args) | Just con <- isDataConWorkId_maybe fun,
- args `lengthAtLeast` dataConRepArity con
- -- Might be > because the arity excludes type args
- -> Just (CV (DataAlt con) args)
+ other | valArgCount args < idArity fun
+ -- Under-applied function
+ -> Just LambdaVal -- Partial application
other -> Nothing
+isValue env expr = Nothing
+
mk_con_app :: AltCon -> [CoreArg] -> CoreExpr
mk_con_app (LitAlt lit) [] = Lit lit
mk_con_app (DataAlt con) args = mkConApp con args
+mk_con_app other args = panic "SpecConstr.mk_con_app"
+
+samePat :: CallPat -> CallPat -> Bool
+samePat (vs1, as1) (vs2, as2)
+ = all2 same as1 as2
+ where
+ same (Var v1) (Var v2)
+ | v1 `elem` vs1 = v2 `elem` vs2
+ | v2 `elem` vs2 = False
+ | otherwise = v1 == v2
+
+ same (Lit l1) (Lit l2) = l1==l2
+ same (App f1 a1) (App f2 a2) = same f1 f2 && same a1 a2
+
+ same (Type t1) (Type t2) = True -- Note [Ignore type differences]
+ same (Note _ e1) e2 = same e1 e2 -- Ignore casts and notes
+ same (Cast e1 _) e2 = same e1 e2
+ same e1 (Note _ e2) = same e1 e2
+ same e1 (Cast e2 _) = same e1 e2
+
+ same e1 e2 = WARN( bad e1 || bad e2, ppr e1 $$ ppr e2)
+ False -- Let, lambda, case should not occur
+#ifdef DEBUG
+ bad (Case {}) = True
+ bad (Let {}) = True
+ bad (Lam {}) = True
+ bad other = False
+#endif
\end{code}
+
+Note [Ignore type differences]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+We do not want to generate specialisations where the call patterns
+differ only in their type arguments! Not only is it utterly useless,
+but it also means that (with polymorphic recursion) we can generate
+an infinite number of specialisations. Example is Data.Sequence.adjustTree,
+I think.
+
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