\section[SpecConstr]{Specialise over constructors}
\begin{code}
+-- The above warning supression flag is a temporary kludge.
+-- While working on this module you are encouraged to remove it and fix
+-- any warnings in the module. See
+-- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
+-- for details
+
module SpecConstr(
- specConstrProgram
+ specConstrProgram
+#ifdef GHCI
+ , SpecConstrAnnotation(..)
+#endif
) where
#include "HsVersions.h"
import CoreSyn
-import CoreLint ( showPass, endPass )
-import CoreUtils ( exprType, mkPiTypes )
+import CoreSubst
+import CoreUtils
+import CoreUnfold ( couldBeSmallEnoughToInline )
import CoreFVs ( exprsFreeVars )
-import CoreTidy ( tidyRules )
-import PprCore ( pprRules )
+import CoreMonad
+import HscTypes ( ModGuts(..) )
import WwLib ( mkWorkerArgs )
-import DataCon ( dataConRepArity, dataConUnivTyVars )
-import Type ( Type, tyConAppArgs )
-import Coercion ( coercionKind )
-import Rules ( matchN )
-import Id ( Id, idName, idType, isDataConWorkId_maybe,
- mkUserLocal, mkSysLocal, idUnfolding, isLocalId )
-import Var ( Var )
+import DataCon
+import Coercion
+import Rules
+import Type hiding( substTy )
+import Id
+import MkCore ( mkImpossibleExpr )
+import Var
import VarEnv
import VarSet
-import Name ( nameOccName, nameSrcLoc )
-import Rules ( addIdSpecialisations, mkLocalRule, rulesOfBinds )
-import OccName ( mkSpecOcc )
-import ErrUtils ( dumpIfSet_dyn )
-import DynFlags ( DynFlags, DynFlag(..) )
-import BasicTypes ( Activation(..) )
-import Maybes ( orElse, catMaybes, isJust )
-import Util ( zipWithEqual, lengthAtLeast, notNull )
-import List ( nubBy, partition )
+import Name
+import BasicTypes
+import DynFlags ( DynFlags(..) )
+import StaticFlags ( opt_PprStyle_Debug )
+import Maybes ( orElse, catMaybes, isJust, isNothing )
+import Demand
+import DmdAnal ( both )
+import Serialized ( deserializeWithData )
+import Util
import UniqSupply
import Outputable
import FastString
import UniqFM
+import MonadUtils
+import Control.Monad ( zipWithM )
+import Data.List
+
+
+-- See Note [SpecConstrAnnotation]
+#ifndef GHCI
+type SpecConstrAnnotation = ()
+#else
+import Literal ( literalType )
+import TyCon ( TyCon )
+import GHC.Exts( SpecConstrAnnotation(..) )
+#endif
\end{code}
-----------------------------------------------------
So we want to spot the construtor application inside the cast.
That's why we have the Cast case in argToPat
+Note [Local recursive groups]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+For a *local* recursive group, we can see all the calls to the
+function, so we seed the specialisation loop from the calls in the
+body, not from the calls in the RHS. Consider:
+
+ bar m n = foo n (n,n) (n,n) (n,n) (n,n)
+ where
+ foo n p q r s
+ | n == 0 = m
+ | n > 3000 = case p of { (p1,p2) -> foo (n-1) (p2,p1) q r s }
+ | n > 2000 = case q of { (q1,q2) -> foo (n-1) p (q2,q1) r s }
+ | n > 1000 = case r of { (r1,r2) -> foo (n-1) p q (r2,r1) s }
+ | otherwise = case s of { (s1,s2) -> foo (n-1) p q r (s2,s1) }
+
+If we start with the RHSs of 'foo', we get lots and lots of specialisations,
+most of which are not needed. But if we start with the (single) call
+in the rhs of 'bar' we get exactly one fully-specialised copy, and all
+the recursive calls go to this fully-specialised copy. Indeed, the original
+function is later collected as dead code. This is very important in
+specialising the loops arising from stream fusion, for example in NDP where
+we were getting literally hundreds of (mostly unused) specialisations of
+a local function.
+
+Note [Do not specialise diverging functions]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Specialising a function that just diverges is a waste of code.
+Furthermore, it broke GHC (simpl014) thus:
+ {-# STR Sb #-}
+ f = \x. case x of (a,b) -> f x
+If we specialise f we get
+ f = \x. case x of (a,b) -> fspec a b
+But fspec doesn't have decent strictnes info. As it happened,
+(f x) :: IO t, so the state hack applied and we eta expanded fspec,
+and hence f. But now f's strictness is less than its arity, which
+breaks an invariant.
+
+Note [SpecConstrAnnotation]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+SpecConstrAnnotation is defined in GHC.Exts, and is only guaranteed to
+be available in stage 2 (well, until the bootstrap compiler can be
+guaranteed to have it)
+
+So we define it to be () in stage1 (ie when GHCI is undefined), and
+'#ifdef' out the code that uses it.
+
+See also Note [Forcing specialisation]
+
+Note [Forcing specialisation]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+With stream fusion and in other similar cases, we want to fully specialise
+some (but not necessarily all!) loops regardless of their size and the
+number of specialisations. We allow a library to specify this by annotating
+a type with ForceSpecConstr and then adding a parameter of that type to the
+loop. Here is a (simplified) example from the vector library:
+
+ data SPEC = SPEC | SPEC2
+ {-# ANN type SPEC ForceSpecConstr #-}
+
+ foldl :: (a -> b -> a) -> a -> Stream b -> a
+ {-# INLINE foldl #-}
+ foldl f z (Stream step s _) = foldl_loop SPEC z s
+ where
+ foldl_loop SPEC z s = case step s of
+ Yield x s' -> foldl_loop SPEC (f z x) s'
+ Skip -> foldl_loop SPEC z s'
+ Done -> z
+
+SpecConstr will spot the SPEC parameter and always fully specialise
+foldl_loop. Note that we can't just annotate foldl_loop since it isn't a
+top-level function but even if we could, inlining etc. could easily drop the
+annotation. We also have to prevent the SPEC argument from being removed by
+w/w which is why SPEC is a sum type. This is all quite ugly; we ought to come
+up with a better design.
+
+ForceSpecConstr arguments are spotted in scExpr' and scTopBinds which then set
+force_spec to True when calling specLoop. This flag makes specLoop and
+specialise ignore specConstrCount and specConstrThreshold when deciding
+whether to specialise a function.
-----------------------------------------------------
Stuff not yet handled
a T (I# x) really, because T is strict and Int has one constructor. (We can't
unbox the strict fields, becuase T is polymorphic!)
-
-
%************************************************************************
%* *
\subsection{Top level wrapper stuff}
%************************************************************************
\begin{code}
-specConstrProgram :: DynFlags -> UniqSupply -> [CoreBind] -> IO [CoreBind]
-specConstrProgram dflags us binds
+specConstrProgram :: ModGuts -> CoreM ModGuts
+specConstrProgram guts
= do
- showPass dflags "SpecConstr"
-
- let (binds', _) = initUs us (go emptyScEnv binds)
-
- endPass dflags "SpecConstr" Opt_D_dump_spec binds'
-
- dumpIfSet_dyn dflags Opt_D_dump_rules "Top-level specialisations"
- (pprRules (tidyRules emptyTidyEnv (rulesOfBinds binds')))
-
- return binds'
+ dflags <- getDynFlags
+ us <- getUniqueSupplyM
+ annos <- getFirstAnnotations deserializeWithData guts
+ let binds' = fst $ initUs us (go (initScEnv dflags annos) (mg_binds guts))
+ return (guts { mg_binds = binds' })
where
- go env [] = returnUs []
- go env (bind:binds) = scBind env bind `thenUs` \ (env', _, bind') ->
- go env' binds `thenUs` \ binds' ->
- returnUs (bind' : binds')
+ go _ [] = return []
+ go env (bind:binds) = do (env', bind') <- scTopBind env bind
+ binds' <- go env' binds
+ return (bind' : binds')
\end{code}
%************************************************************************
\begin{code}
-data ScEnv = SCE { scope :: InScopeEnv,
- -- Binds all non-top-level variables in scope
+data ScEnv = SCE { sc_size :: Maybe Int, -- Size threshold
+ sc_count :: Maybe Int, -- Max # of specialisations for any one fn
+ -- See Note [Avoiding exponential blowup]
+
+ sc_subst :: Subst, -- Current substitution
+ -- Maps InIds to OutExprs
+
+ 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)
- cons :: ConstrEnv
+ sc_annotations :: UniqFM SpecConstrAnnotation
}
-type InScopeEnv = VarEnv HowBound
+---------------------
+-- As we go, we apply a substitution (sc_subst) to the current term
+type InExpr = CoreExpr -- _Before_ applying the subst
+type InVar = Var
-type ConstrEnv = IdEnv ConValue
-data ConValue = CV AltCon [CoreArg]
- -- Variables known to be bound to a constructor
- -- in a particular case alternative
+type OutExpr = CoreExpr -- _After_ applying the subst
+type OutId = Id
+type OutVar = Var
+---------------------
+type HowBoundEnv = VarEnv HowBound -- Domain is OutVars
-instance Outputable ConValue where
- ppr (CV con args) = ppr con <+> interpp'SP args
+---------------------
+type ValueEnv = IdEnv Value -- Domain is OutIds
+data Value = ConVal AltCon [CoreArg] -- _Saturated_ constructors
+ -- The AltCon is never DEFAULT
+ | 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>")
+
+---------------------
+initScEnv :: DynFlags -> UniqFM SpecConstrAnnotation -> ScEnv
+initScEnv dflags anns
+ = SCE { sc_size = specConstrThreshold dflags,
+ sc_count = specConstrCount dflags,
+ sc_subst = emptySubst,
+ sc_how_bound = emptyVarEnv,
+ sc_vals = emptyVarEnv,
+ sc_annotations = anns }
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
- | 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
-
instance Outputable HowBound where
ppr RecFun = text "RecFun"
ppr RecArg = text "RecArg"
- ppr Other = text "Other"
-lookupScopeEnv env v = lookupVarEnv (scope env) v
+lookupHowBound :: ScEnv -> Id -> Maybe HowBound
+lookupHowBound env id = lookupVarEnv (sc_how_bound env) id
+
+scSubstId :: ScEnv -> Id -> CoreExpr
+scSubstId env v = lookupIdSubst (text "scSubstId") (sc_subst env) v
+
+scSubstTy :: ScEnv -> Type -> Type
+scSubstTy env ty = substTy (sc_subst env) ty
+
+zapScSubst :: ScEnv -> ScEnv
+zapScSubst env = env { sc_subst = zapSubstEnv (sc_subst env) }
+
+extendScInScope :: ScEnv -> [Var] -> ScEnv
+ -- Bring the quantified variables into scope
+extendScInScope env qvars = env { sc_subst = extendInScopeList (sc_subst env) qvars }
+
+ -- Extend the substitution
+extendScSubst :: ScEnv -> Var -> OutExpr -> ScEnv
+extendScSubst env var expr = env { sc_subst = extendSubst (sc_subst env) var expr }
+
+extendScSubstList :: ScEnv -> [(Var,OutExpr)] -> ScEnv
+extendScSubstList env prs = env { sc_subst = extendSubstList (sc_subst env) prs }
+extendHowBound :: ScEnv -> [Var] -> HowBound -> ScEnv
+extendHowBound env bndrs how_bound
+ = env { sc_how_bound = extendVarEnvList (sc_how_bound env)
+ [(bndr,how_bound) | bndr <- bndrs] }
-extendBndrsWith :: HowBound -> ScEnv -> [Var] -> ScEnv
+extendBndrsWith :: HowBound -> ScEnv -> [Var] -> (ScEnv, [Var])
extendBndrsWith how_bound env bndrs
- = env { scope = scope env `extendVarEnvList`
- [(bndr,how_bound) | bndr <- bndrs] }
-
-extendBndrs env bndrs = extendBndrsWith Other env 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 con alt_bndrs
- = case con of
- DEFAULT -> env1
- LitAlt lit -> extendCons env1 scrut case_bndr (CV con [])
- DataAlt dc -> extendCons env1 scrut case_bndr (CV con vanilla_args)
- where
- vanilla_args = map Type (tyConAppArgs (idType case_bndr)) ++
- varsToCoreExprs alt_bndrs
+ = (env { sc_subst = subst', sc_how_bound = hb_env' }, bndrs')
where
- env1 = extendBndrsWith (get_how scrut) env (case_bndr:alt_bndrs)
-
- -- Record RecArg for the components iff the scrutinee is RecArg
- -- I think the only reason for this is to keep the usage envt small
- -- so is it worth it at all?
- -- [This comment looks plain wrong to me, so I'm ignoring it
- -- "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)... }" ]
- get_how (Var v) = lookupVarEnv (scope env) v `orElse` Other
- get_how (Cast e _) = get_how e
- get_how (Note _ e) = get_how e
- get_how other = Other
-
-extendCons :: ScEnv -> CoreExpr -> Id -> ConValue -> ScEnv
-extendCons env scrut case_bndr val
- = case scrut of
- Var v -> env { cons = extendVarEnv cons1 v val }
- other -> env { cons = cons1 }
+ (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
- cons1 = extendVarEnv (cons env) case_bndr val
+ (subst', bndr') = substBndr (sc_subst env) bndr
+ hb_env' = extendVarEnv (sc_how_bound env) bndr' how_bound
+
+extendRecBndrs :: ScEnv -> [Var] -> (ScEnv, [Var])
+extendRecBndrs env bndrs = (env { sc_subst = subst' }, bndrs')
+ where
+ (subst', bndrs') = substRecBndrs (sc_subst env) bndrs
+
+extendBndr :: ScEnv -> Var -> (ScEnv, Var)
+extendBndr env bndr = (env { sc_subst = subst' }, bndr')
+ where
+ (subst', bndr') = substBndr (sc_subst env) bndr
+
+extendValEnv :: ScEnv -> Id -> Maybe Value -> ScEnv
+extendValEnv env _ Nothing = env
+extendValEnv env id (Just cv) = env { sc_vals = extendVarEnv (sc_vals env) id cv }
+
+extendCaseBndrs :: ScEnv -> Id -> AltCon -> [Var] -> (ScEnv, [Var])
+-- When we encounter
+-- case scrut of b
+-- C x y -> ...
+-- we want to bind b, to (C x y)
+-- NB1: Extends only the sc_vals part of the envt
+-- NB2: Kill the dead-ness info on the pattern binders x,y, since
+-- they are potentially made alive by the [b -> C x y] binding
+extendCaseBndrs env case_bndr con alt_bndrs
+ | isDeadBinder case_bndr
+ = (env, alt_bndrs)
+ | otherwise
+ = (env1, map zap alt_bndrs)
+ -- NB: We used to bind v too, if scrut = (Var v); but
+ -- the simplifer has already done this so it seems
+ -- redundant to do so here
+ -- case scrut of
+ -- Var v -> extendValEnv env1 v cval
+ -- _other -> env1
+ where
+ zap v | isTyCoVar v = v -- See NB2 above
+ | otherwise = zapIdOccInfo v
+ env1 = extendValEnv env case_bndr cval
+ cval = case con of
+ DEFAULT -> Nothing
+ LitAlt {} -> Just (ConVal con [])
+ DataAlt {} -> Just (ConVal con vanilla_args)
+ where
+ vanilla_args = map Type (tyConAppArgs (idType case_bndr)) ++
+ varsToCoreExprs alt_bndrs
+
+
+decreaseSpecCount :: ScEnv -> Int -> ScEnv
+-- See Note [Avoiding exponential blowup]
+decreaseSpecCount env n_specs
+ = env { sc_count = case sc_count env of
+ Nothing -> Nothing
+ Just n -> Just (n `div` (n_specs + 1)) }
+ -- The "+1" takes account of the original function;
+ -- See Note [Avoiding exponential blowup]
+
+---------------------------------------------------
+-- See Note [SpecConstrAnnotation]
+ignoreType :: ScEnv -> Type -> Bool
+ignoreAltCon :: ScEnv -> AltCon -> Bool
+forceSpecBndr :: ScEnv -> Var -> Bool
+#ifndef GHCI
+ignoreType _ _ = False
+ignoreAltCon _ _ = False
+forceSpecBndr _ _ = False
+
+#else /* GHCI */
+
+ignoreAltCon env (DataAlt dc) = ignoreTyCon env (dataConTyCon dc)
+ignoreAltCon env (LitAlt lit) = ignoreType env (literalType lit)
+ignoreAltCon _ DEFAULT = panic "ignoreAltCon" -- DEFAULT cannot be in a ConVal
+
+ignoreType env ty
+ = case splitTyConApp_maybe ty of
+ Just (tycon, _) -> ignoreTyCon env tycon
+ _ -> False
+
+ignoreTyCon :: ScEnv -> TyCon -> Bool
+ignoreTyCon env tycon
+ = lookupUFM (sc_annotations env) tycon == Just NoSpecConstr
+
+forceSpecBndr env var = forceSpecFunTy env . snd . splitForAllTys . varType $ var
+
+forceSpecFunTy :: ScEnv -> Type -> Bool
+forceSpecFunTy env = any (forceSpecArgTy env) . fst . splitFunTys
+
+forceSpecArgTy :: ScEnv -> Type -> Bool
+forceSpecArgTy env ty
+ | Just ty' <- coreView ty = forceSpecArgTy env ty'
+
+forceSpecArgTy env ty
+ | Just (tycon, tys) <- splitTyConApp_maybe ty
+ , tycon /= funTyCon
+ = lookupUFM (sc_annotations env) tycon == Just ForceSpecConstr
+ || any (forceSpecArgTy env) tys
+
+forceSpecArgTy _ _ = False
+#endif /* GHCI */
\end{code}
+Note [Avoiding exponential blowup]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The sc_count field of the ScEnv says how many times we are prepared to
+duplicate a single function. But we must take care with recursive
+specialiations. Consider
+
+ let $j1 = let $j2 = let $j3 = ...
+ in
+ ...$j3...
+ in
+ ...$j2...
+ in
+ ...$j1...
+
+If we specialise $j1 then in each specialisation (as well as the original)
+we can specialise $j2, and similarly $j3. Even if we make just *one*
+specialisation of each, becuase we also have the original we'll get 2^n
+copies of $j3, which is not good.
+
+So when recursively specialising we divide the sc_count by the number of
+copies we are making at this level, including the original.
+
%************************************************************************
%* *
\begin{code}
data ScUsage
= SCU {
- calls :: !(IdEnv [Call]), -- Calls
+ scu_calls :: CallEnv, -- Calls
-- The functions are a subset of the
-- RecFuns in the ScEnv
- occs :: !(IdEnv ArgOcc) -- Information on argument occurrences
- } -- The variables are a subset of the
- -- RecArg in the ScEnv
+ scu_occs :: !(IdEnv ArgOcc) -- Information on argument occurrences
+ } -- The domain is OutIds
-type Call = (ConstrEnv, [CoreArg])
+type CallEnv = IdEnv [Call]
+type Call = (ValueEnv, [CoreArg])
-- The arguments of the call, together with the
-- env giving the constructor bindings at the call site
-nullUsage = SCU { calls = emptyVarEnv, occs = emptyVarEnv }
+nullUsage :: ScUsage
+nullUsage = SCU { scu_calls = emptyVarEnv, scu_occs = emptyVarEnv }
+
+combineCalls :: CallEnv -> CallEnv -> CallEnv
+combineCalls = plusVarEnv_C (++)
-combineUsage u1 u2 = SCU { calls = plusVarEnv_C (++) (calls u1) (calls u2),
- occs = plusVarEnv_C combineOcc (occs u1) (occs u2) }
+combineUsage :: ScUsage -> ScUsage -> ScUsage
+combineUsage u1 u2 = SCU { scu_calls = combineCalls (scu_calls u1) (scu_calls u2),
+ scu_occs = plusVarEnv_C combineOcc (scu_occs u1) (scu_occs u2) }
+combineUsages :: [ScUsage] -> ScUsage
combineUsages [] = nullUsage
combineUsages us = foldr1 combineUsage us
-lookupOcc :: ScUsage -> Var -> (ScUsage, ArgOcc)
-lookupOcc (SCU { calls = sc_calls, occs = sc_occs }) bndr
- = (SCU {calls = sc_calls, occs = delVarEnv sc_occs bndr},
+lookupOcc :: ScUsage -> OutVar -> (ScUsage, ArgOcc)
+lookupOcc (SCU { scu_calls = sc_calls, scu_occs = sc_occs }) bndr
+ = (SCU {scu_calls = sc_calls, scu_occs = delVarEnv sc_occs bndr},
lookupVarEnv sc_occs bndr `orElse` NoOcc)
-lookupOccs :: ScUsage -> [Var] -> (ScUsage, [ArgOcc])
-lookupOccs (SCU { calls = sc_calls, occs = sc_occs }) bndrs
- = (SCU {calls = sc_calls, occs = delVarEnvList sc_occs bndrs},
+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
-}
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")
+ ppr (ScrutOcc xs) = ptext (sLit "scrut-occ") <> ppr xs
+ ppr UnkOcc = ptext (sLit "unk-occ")
+ ppr BothOcc = ptext (sLit "both-occ")
+ ppr NoOcc = ptext (sLit "no-occ")
-- Experimentally, this vesion of combineOcc makes ScrutOcc "win", so
-- that if the thing is scrutinised anywhere then we get to see that
-- in the overall result, even if it's also used in a boxed way
-- This might be too agressive; see Note [Reboxing] Alternative 3
+combineOcc :: ArgOcc -> ArgOcc -> ArgOcc
combineOcc NoOcc occ = occ
combineOcc occ NoOcc = occ
combineOcc (ScrutOcc xs) (ScrutOcc ys) = ScrutOcc (plusUFM_C combineOccs xs ys)
-combineOcc occ (ScrutOcc ys) = ScrutOcc ys
-combineOcc (ScrutOcc xs) occ = ScrutOcc xs
+combineOcc _occ (ScrutOcc ys) = ScrutOcc ys
+combineOcc (ScrutOcc xs) _occ = ScrutOcc xs
combineOcc UnkOcc UnkOcc = UnkOcc
combineOcc _ _ = BothOcc
combineOccs :: [ArgOcc] -> [ArgOcc] -> [ArgOcc]
combineOccs xs ys = zipWithEqual "combineOccs" combineOcc xs ys
+setScrutOcc :: ScEnv -> ScUsage -> OutExpr -> ArgOcc -> ScUsage
+-- _Overwrite_ the occurrence info for the scrutinee, if the scrutinee
+-- is a variable, and an interesting variable
+setScrutOcc env usg (Cast e _) occ = setScrutOcc env usg e occ
+setScrutOcc env usg (Note _ e) occ = setScrutOcc env usg e occ
+setScrutOcc env usg (Var v) occ
+ | Just RecArg <- lookupHowBound env v = usg { scu_occs = extendVarEnv (scu_occs usg) v occ }
+ | otherwise = usg
+setScrutOcc _env usg _other _occ -- Catch-all
+ = usg
+
conArgOccs :: ArgOcc -> AltCon -> [ArgOcc]
-- Find usage of components of data con; returns [UnkOcc...] if unknown
-- See Note [ScrutOcc] for the extra UnkOccs in the vanilla datacon case
conArgOccs (ScrutOcc fm) (DataAlt dc)
| Just pat_arg_occs <- lookupUFM fm dc
- = [UnkOcc | tv <- dataConUnivTyVars dc] ++ pat_arg_occs
+ = [UnkOcc | _ <- dataConUnivTyVars dc] ++ pat_arg_occs
-conArgOccs other con = repeat UnkOcc
+conArgOccs _other _con = repeat UnkOcc
\end{code}
-
%************************************************************************
%* *
\subsection{The main recursive function}
creates specialised versions of functions.
\begin{code}
-scExpr :: ScEnv -> CoreExpr -> UniqSM (ScUsage, CoreExpr)
+scExpr, scExpr' :: ScEnv -> CoreExpr -> UniqSM (ScUsage, CoreExpr)
-- The unique supply is needed when we invent
-- a new name for the specialised function and its args
-scExpr env e@(Type t) = returnUs (nullUsage, e)
-scExpr env e@(Lit l) = returnUs (nullUsage, e)
-scExpr env e@(Var v) = returnUs (varUsage env v UnkOcc, e)
-scExpr env (Note n e) = scExpr env e `thenUs` \ (usg,e') ->
- returnUs (usg, Note n e')
-scExpr env (Cast e co)= scExpr env e `thenUs` \ (usg,e') ->
- returnUs (usg, Cast e' co)
-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)
- = do { (alt_usgs, alt_occs, alts') <- mapAndUnzip3Us sc_alt alts
- ; let (alt_usg, b_occ) = lookupOcc (combineUsages alt_usgs) b
- scrut_occ = foldr combineOcc b_occ alt_occs
- -- 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
- ; (scrut_usg, scrut') <- scScrut env scrut scrut_occ
- ; return (alt_usg `combineUsage` scrut_usg,
- Case scrut' b ty alts') }
+scExpr env e = scExpr' env e
+
+
+scExpr' env (Var v) = case scSubstId env v of
+ Var v' -> return (varUsage env v' UnkOcc, Var v')
+ e' -> scExpr (zapScSubst env) e'
+
+scExpr' env (Type t) = return (nullUsage, Type (scSubstTy env t))
+scExpr' _ e@(Lit {}) = return (nullUsage, e)
+scExpr' env (Note n e) = do (usg,e') <- scExpr env e
+ return (usg, Note n e')
+scExpr' env (Cast e co) = do (usg, e') <- scExpr env e
+ return (usg, Cast e' (scSubstTy env co))
+scExpr' env e@(App _ _) = scApp env (collectArgs e)
+scExpr' env (Lam b e) = do let (env', b') = extendBndr env b
+ (usg, e') <- scExpr env' e
+ return (usg, Lam b' e')
+
+scExpr' env (Case scrut b ty alts)
+ = do { (scrut_usg, scrut') <- scExpr env scrut
+ ; case isValue (sc_vals env) scrut' of
+ Just (ConVal con args) -> sc_con_app con args scrut'
+ _other -> sc_vanilla scrut_usg scrut'
+ }
where
- sc_alt (con,bs,rhs)
- = do { let env1 = extendCaseBndrs env b scrut con bs
- ; (usg,rhs') <- scExpr env1 rhs
- ; let (usg', arg_occs) = lookupOccs usg bs
+ sc_con_app con args scrut' -- Known constructor; simplify
+ = do { let (_, bs, rhs) = findAlt con alts
+ `orElse` (DEFAULT, [], mkImpossibleExpr (coreAltsType alts))
+ alt_env' = extendScSubstList env ((b,scrut') : bs `zip` trimConArgs con args)
+ ; scExpr alt_env' rhs }
+
+ sc_vanilla scrut_usg scrut' -- Normal case
+ = do { let (alt_env,b') = extendBndrWith RecArg env b
+ -- Record RecArg for the components
+
+ ; (alt_usgs, alt_occs, alts')
+ <- mapAndUnzip3M (sc_alt alt_env scrut' b') alts
+
+ ; let (alt_usg, b_occ) = lookupOcc (combineUsages alt_usgs) b'
+ scrut_occ = foldr combineOcc b_occ alt_occs
+ scrut_usg' = setScrutOcc env scrut_usg scrut' scrut_occ
+ -- The combined usage of the scrutinee is given
+ -- by scrut_occ, which is passed to scScrut, which
+ -- in turn treats a bare-variable scrutinee specially
+
+ ; return (alt_usg `combineUsage` scrut_usg',
+ Case scrut' b' (scSubstTy env ty) alts') }
+
+ sc_alt env _scrut' b' (con,bs,rhs)
+ = do { let (env1, bs1) = extendBndrsWith RecArg env bs
+ (env2, bs2) = extendCaseBndrs env1 b' con bs1
+ ; (usg,rhs') <- scExpr env2 rhs
+ ; let (usg', arg_occs) = lookupOccs usg bs2
scrut_occ = case con of
DataAlt dc -> ScrutOcc (unitUFM dc arg_occs)
- other -> ScrutOcc emptyUFM
- ; return (usg', scrut_occ, (con,bs,rhs')) }
-
-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 _ _)
- = do { let (fn, args) = collectArgs e
- ; (fn_usg, fn') <- scScrut env fn (ScrutOcc emptyUFM)
- -- 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
- -- We use scScrut to record the fact that the function is called
- -- Perhpas 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 <- lookupScopeEnv env f
- , not (null args) -- Not a proper call!
- -> SCU { calls = unitVarEnv f [(cons env, args)],
- occs = emptyVarEnv }
- other -> nullUsage
- ; return (combineUsages arg_usgs `combineUsage` fn_usg
- `combineUsage` call_usg,
- mkApps fn' args') }
+ _ -> ScrutOcc emptyUFM
+ ; return (usg', scrut_occ, (con, bs2, rhs')) }
+
+scExpr' env (Let (NonRec bndr rhs) body)
+ | isTyCoVar bndr -- Type-lets may be created by doBeta
+ = scExpr' (extendScSubst env bndr rhs) body
+
+ | otherwise
+ = do { let (body_env, bndr') = extendBndr env bndr
+ ; (rhs_usg, rhs_info) <- scRecRhs env (bndr',rhs)
+
+ ; let body_env2 = extendHowBound body_env [bndr'] RecFun
+ -- Note [Local let bindings]
+ RI _ rhs' _ _ _ = rhs_info
+ body_env3 = extendValEnv body_env2 bndr' (isValue (sc_vals env) rhs')
+
+ ; (body_usg, body') <- scExpr body_env3 body
+
+ -- NB: We don't use the ForceSpecConstr mechanism (see
+ -- Note [Forcing specialisation]) for non-recursive bindings
+ -- at the moment. I'm not sure if this is the right thing to do.
+ ; let force_spec = False
+ ; (spec_usg, specs) <- specialise env force_spec
+ (scu_calls body_usg)
+ rhs_info
+ (SI [] 0 (Just rhs_usg))
+
+ ; return (body_usg { scu_calls = scu_calls body_usg `delVarEnv` bndr' }
+ `combineUsage` spec_usg,
+ mkLets [NonRec b r | (b,r) <- specInfoBinds rhs_info specs] body')
+ }
+
+
+-- A *local* recursive group: see Note [Local recursive groups]
+scExpr' env (Let (Rec prs) body)
+ = do { let (bndrs,rhss) = unzip prs
+ (rhs_env1,bndrs') = extendRecBndrs env bndrs
+ rhs_env2 = extendHowBound rhs_env1 bndrs' RecFun
+ force_spec = any (forceSpecBndr env) bndrs'
+ -- Note [Forcing specialisation]
+
+ ; (rhs_usgs, rhs_infos) <- mapAndUnzipM (scRecRhs rhs_env2) (bndrs' `zip` rhss)
+ ; (body_usg, body') <- scExpr rhs_env2 body
+
+ -- NB: start specLoop from body_usg
+ ; (spec_usg, specs) <- specLoop rhs_env2 force_spec
+ (scu_calls body_usg) rhs_infos nullUsage
+ [SI [] 0 (Just usg) | usg <- rhs_usgs]
+ -- Do not unconditionally use rhs_usgs.
+ -- Instead use them only if we find an unspecialised call
+ -- See Note [Local recursive groups]
+
+ ; let all_usg = spec_usg `combineUsage` body_usg
+ bind' = Rec (concat (zipWith specInfoBinds rhs_infos specs))
+
+ ; return (all_usg { scu_calls = scu_calls all_usg `delVarEnvList` bndrs' },
+ Let bind' body') }
+\end{code}
+Note [Local let bindings]
+~~~~~~~~~~~~~~~~~~~~~~~~~
+It is not uncommon to find this
-----------------------
-scScrut :: ScEnv -> CoreExpr -> ArgOcc -> UniqSM (ScUsage, CoreExpr)
--- Used for the scrutinee of a case,
--- or the function of an application.
--- Remember to look through casts
-scScrut env e@(Var v) occ = returnUs (varUsage env v occ, e)
-scScrut env (Cast e co) occ = do { (usg, e') <- scScrut env e occ
- ; returnUs (usg, Cast e' co) }
-scScrut env e occ = scExpr env e
+ let $j = \x. <blah> in ...$j True...$j True...
+Here $j is an arbitrary let-bound function, but it often comes up for
+join points. We might like to specialise $j for its call patterns.
+Notice the difference from a letrec, where we look for call patterns
+in the *RHS* of the function. Here we look for call patterns in the
+*body* of the let.
+
+At one point I predicated this on the RHS mentioning the outer
+recursive function, but that's not essential and might even be
+harmful. I'm not sure.
+
+
+\begin{code}
+scApp :: ScEnv -> (InExpr, [InExpr]) -> UniqSM (ScUsage, CoreExpr)
+
+scApp env (Var fn, args) -- Function is a variable
+ = ASSERT( not (null args) )
+ do { args_w_usgs <- mapM (scExpr env) args
+ ; let (arg_usgs, args') = unzip args_w_usgs
+ arg_usg = combineUsages arg_usgs
+ ; case scSubstId env fn of
+ fn'@(Lam {}) -> scExpr (zapScSubst env) (doBeta fn' args')
+ -- Do beta-reduction and try again
+
+ Var fn' -> return (arg_usg `combineUsage` fn_usg, mkApps (Var fn') args')
+ where
+ fn_usg = case lookupHowBound env fn' of
+ Just RecFun -> SCU { scu_calls = unitVarEnv fn' [(sc_vals env, args')],
+ scu_occs = emptyVarEnv }
+ Just RecArg -> SCU { scu_calls = emptyVarEnv,
+ scu_occs = unitVarEnv fn' (ScrutOcc emptyUFM) }
+ Nothing -> nullUsage
+
+
+ other_fn' -> return (arg_usg, mkApps other_fn' args') }
+ -- NB: doing this ignores any usage info from the substituted
+ -- function, but I don't think that matters. If it does
+ -- we can fix it.
+ where
+ doBeta :: OutExpr -> [OutExpr] -> OutExpr
+ -- ToDo: adjust for System IF
+ doBeta (Lam bndr body) (arg : args) = Let (NonRec bndr arg) (doBeta body args)
+ doBeta fn args = mkApps fn args
+
+-- The function is almost always a variable, but not always.
+-- In particular, if this pass follows float-in,
+-- which it may, we can get
+-- (let f = ...f... in f) arg1 arg2
+scApp env (other_fn, args)
+ = do { (fn_usg, fn') <- scExpr env other_fn
+ ; (arg_usgs, args') <- mapAndUnzipM (scExpr env) args
+ ; return (combineUsages arg_usgs `combineUsage` fn_usg, mkApps fn' args') }
----------------------
-scBind :: ScEnv -> CoreBind -> UniqSM (ScEnv, ScUsage, CoreBind)
-scBind env (Rec prs)
- = do { let bndrs = map fst prs
- rhs_env = extendBndrsWith RecFun env bndrs
-
- ; (rhs_usgs, prs_w_occs) <- mapAndUnzipUs (scRecRhs rhs_env) prs
- ; let rhs_usg = combineUsages rhs_usgs
- rhs_calls = calls rhs_usg
-
- ; prs_s <- mapUs (specialise env rhs_calls) prs_w_occs
- ; return (extendBndrs env bndrs,
- -- For the body of the letrec, just
- -- extend the env with Other to record
- -- that it's in scope; no funny RecFun business
- rhs_usg { calls = calls rhs_usg `delVarEnvList` bndrs },
- Rec (concat prs_s)) }
-
-scBind env (NonRec bndr rhs)
- = do { (usg, rhs') <- scExpr env rhs
- ; return (extendBndr env bndr, usg, NonRec bndr rhs') }
+scTopBind :: ScEnv -> CoreBind -> UniqSM (ScEnv, CoreBind)
+scTopBind env (Rec prs)
+ | Just threshold <- sc_size env
+ , not force_spec
+ , not (all (couldBeSmallEnoughToInline threshold) rhss)
+ -- No specialisation
+ = do { let (rhs_env,bndrs') = extendRecBndrs env bndrs
+ ; (_, rhss') <- mapAndUnzipM (scExpr rhs_env) rhss
+ ; return (rhs_env, Rec (bndrs' `zip` rhss')) }
+ | otherwise -- Do specialisation
+ = do { let (rhs_env1,bndrs') = extendRecBndrs env bndrs
+ rhs_env2 = extendHowBound rhs_env1 bndrs' RecFun
+
+ ; (rhs_usgs, rhs_infos) <- mapAndUnzipM (scRecRhs rhs_env2) (bndrs' `zip` rhss)
+ ; let rhs_usg = combineUsages rhs_usgs
+
+ ; (_, specs) <- specLoop rhs_env2 force_spec
+ (scu_calls rhs_usg) rhs_infos nullUsage
+ [SI [] 0 Nothing | _ <- bndrs]
+
+ ; return (rhs_env1, -- For the body of the letrec, delete the RecFun business
+ Rec (concat (zipWith specInfoBinds rhs_infos specs))) }
+ where
+ (bndrs,rhss) = unzip prs
+ force_spec = any (forceSpecBndr env) bndrs
+ -- Note [Forcing specialisation]
+
+scTopBind env (NonRec bndr rhs)
+ = do { (_, rhs') <- scExpr env rhs
+ ; let (env1, bndr') = extendBndr env bndr
+ env2 = extendValEnv env1 bndr' (isValue (sc_vals env) rhs')
+ ; return (env2, NonRec bndr' rhs') }
----------------------
-scRecRhs :: ScEnv -> (Id,CoreExpr)
- -> UniqSM (ScUsage, (Id, CoreExpr, [ArgOcc]))
--- The returned [ArgOcc] says how the visible,
--- lambda-bound binders of the RHS are used
--- (including the TyVar binders)
+scRecRhs :: ScEnv -> (OutId, InExpr) -> UniqSM (ScUsage, RhsInfo)
scRecRhs env (bndr,rhs)
= do { let (arg_bndrs,body) = collectBinders rhs
- body_env = extendBndrsWith RecArg env arg_bndrs
+ (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, mkLams arg_bndrs body', arg_occs)) }
+ ; let (rhs_usg, arg_occs) = lookupOccs body_usg arg_bndrs'
+ ; return (rhs_usg, RI bndr (mkLams arg_bndrs' body')
+ arg_bndrs body arg_occs) }
+ -- The arg_occs says how the visible,
+ -- lambda-bound binders of the RHS are used
+ -- (including the TyVar binders)
+ -- Two pats are the same if they match both ways
+
+----------------------
+specInfoBinds :: RhsInfo -> SpecInfo -> [(Id,CoreExpr)]
+specInfoBinds (RI fn new_rhs _ _ _) (SI specs _ _)
+ = [(id,rhs) | OS _ _ id rhs <- specs] ++
+ [(fn `addIdSpecialisations` rules, new_rhs)]
+ where
+ rules = [r | OS _ r _ _ <- specs]
----------------------
+varUsage :: ScEnv -> OutVar -> ArgOcc -> ScUsage
varUsage env v use
- | Just RecArg <- lookupScopeEnv env v = SCU { calls = emptyVarEnv,
- occs = unitVarEnv v use }
+ | Just RecArg <- lookupHowBound env v = SCU { scu_calls = emptyVarEnv
+ , scu_occs = unitVarEnv v use }
| otherwise = nullUsage
\end{code}
%************************************************************************
%* *
-\subsection{The specialiser}
+ The specialiser itself
%* *
%************************************************************************
\begin{code}
+data RhsInfo = RI OutId -- The binder
+ OutExpr -- The new RHS
+ [InVar] InExpr -- The *original* RHS (\xs.body)
+ -- Note [Specialise original body]
+ [ArgOcc] -- Info on how the xs occur in body
+
+data SpecInfo = SI [OneSpec] -- The specialisations we have generated
+
+ Int -- Length of specs; used for numbering them
+
+ (Maybe ScUsage) -- Nothing => we have generated specialisations
+ -- from calls in the *original* RHS
+ -- Just cs => we haven't, and this is the usage
+ -- of the original RHS
+ -- See Note [Local recursive groups]
+
+ -- One specialisation: Rule plus definition
+data OneSpec = OS CallPat -- Call pattern that generated this specialisation
+ CoreRule -- Rule connecting original id with the specialisation
+ OutId OutExpr -- Spec id + its rhs
+
+
+specLoop :: ScEnv
+ -> Bool -- force specialisation?
+ -- Note [Forcing specialisation]
+ -> CallEnv
+ -> [RhsInfo]
+ -> ScUsage -> [SpecInfo] -- One per binder; acccumulating parameter
+ -> UniqSM (ScUsage, [SpecInfo]) -- ...ditto...
+specLoop env force_spec all_calls rhs_infos usg_so_far specs_so_far
+ = do { specs_w_usg <- zipWithM (specialise env force_spec all_calls) rhs_infos specs_so_far
+ ; let (new_usg_s, all_specs) = unzip specs_w_usg
+ new_usg = combineUsages new_usg_s
+ new_calls = scu_calls new_usg
+ all_usg = usg_so_far `combineUsage` new_usg
+ ; if isEmptyVarEnv new_calls then
+ return (all_usg, all_specs)
+ else
+ specLoop env force_spec new_calls rhs_infos all_usg all_specs }
+
specialise
:: ScEnv
- -> IdEnv [Call] -- Info on usage
- -> (Id, CoreExpr, [ArgOcc]) -- Original binding, plus info on how the rhs's
- -- lambda-binders are used (includes TyVar bndrs)
- -> UniqSM [(Id,CoreExpr)] -- Original binding (decorated with rules)
- -- plus specialised bindings
+ -> Bool -- force specialisation?
+ -- Note [Forcing specialisation]
+ -> CallEnv -- Info on calls
+ -> RhsInfo
+ -> SpecInfo -- Original RHS plus patterns dealt with
+ -> UniqSM (ScUsage, SpecInfo) -- New specialised versions and their usage
-- Note: the rhs here is the optimised version of the original rhs
-- So when we make a specialised copy of the RHS, we're starting
-- from an RHS whose nested functions have been optimised already.
-specialise env calls (fn, rhs, arg_occs)
- | notNull arg_occs, -- Only specialise functions
- Just all_calls <- lookupVarEnv calls fn
- = do { mb_pats <- mapM (callToPats (scope env) arg_occs) all_calls
-
- ; let good_pats :: [([Var], [CoreArg])]
- good_pats = catMaybes mb_pats
- in_scope = mkInScopeSet $ unionVarSets $
- [ exprsFreeVars pats
- | (vs,pats) <- good_pats ]
- -- This in-scope set is used when matching to see if
- -- we have identical patterns. We want to treat the
- -- forall'd variables of each pattern as "in scope",
- -- because each in turn serves as the match target for
- -- a matchN call. So don't remove the 'vs' from the free vars!
- uniq_pats = nubBy (same_pat in_scope) good_pats
--- ; pprTrace "specialise" (vcat [ppr fn <+> ppr arg_occs,
--- text "calls" <+> ppr all_calls,
--- text "good pats" <+> ppr good_pats,
--- text "uniq pats" <+> ppr uniq_pats]) $
+specialise env force_spec bind_calls (RI fn _ arg_bndrs body arg_occs)
+ spec_info@(SI specs spec_count mb_unspec)
+ | not (isBottomingId fn) -- Note [Do not specialise diverging functions]
+ , not (isNeverActive (idInlineActivation fn)) -- See Note [Transfer activation]
+ , notNull arg_bndrs -- Only specialise functions
+ , Just all_calls <- lookupVarEnv bind_calls fn
+ = do { (boring_call, pats) <- callsToPats env specs arg_occs all_calls
+-- ; pprTrace "specialise" (vcat [ ppr fn <+> text "with" <+> int (length pats) <+> text "good patterns"
+-- , text "arg_occs" <+> ppr arg_occs
+-- , text "calls" <+> ppr all_calls
+-- , text "good pats" <+> ppr pats]) $
-- return ()
- ; (rules, spec_prs) <- mapAndUnzipUs (spec_one fn rhs)
- (uniq_pats `zip` [1..])
-
- ; return ((fn `addIdSpecialisations` rules, rhs) : spec_prs) }
-
+ -- Bale out if too many specialisations
+ ; let n_pats = length pats
+ spec_count' = n_pats + spec_count
+ ; case sc_count env of
+ Just max | not force_spec && spec_count' > max
+ -> pprTrace "SpecConstr" msg $
+ return (nullUsage, spec_info)
+ where
+ msg = vcat [ sep [ ptext (sLit "Function") <+> quotes (ppr fn)
+ , nest 2 (ptext (sLit "has") <+>
+ speakNOf spec_count' (ptext (sLit "call pattern")) <> comma <+>
+ ptext (sLit "but the limit is") <+> int max) ]
+ , ptext (sLit "Use -fspec-constr-count=n to set the bound")
+ , extra ]
+ extra | not opt_PprStyle_Debug = ptext (sLit "Use -dppr-debug to see specialisations")
+ | otherwise = ptext (sLit "Specialisations:") <+> ppr (pats ++ [p | OS p _ _ _ <- specs])
+
+ _normal_case -> do {
+
+ let spec_env = decreaseSpecCount env n_pats
+ ; (spec_usgs, new_specs) <- mapAndUnzipM (spec_one spec_env fn arg_bndrs body)
+ (pats `zip` [spec_count..])
+ -- See Note [Specialise original body]
+
+ ; let spec_usg = combineUsages spec_usgs
+ (new_usg, mb_unspec')
+ = case mb_unspec of
+ Just rhs_usg | boring_call -> (spec_usg `combineUsage` rhs_usg, Nothing)
+ _ -> (spec_usg, mb_unspec)
+
+ ; return (new_usg, SI (new_specs ++ specs) spec_count' mb_unspec') } }
| otherwise
- = return [(fn,rhs)] -- The boring case
- where
- -- Two pats are the same if they match both ways
- same_pat in_scope (vs1,as1)(vs2,as2)
- = isJust (matchN in_scope vs1 as1 as2)
- && isJust (matchN in_scope vs2 as2 as1)
-
-callToPats :: InScopeEnv -> [ArgOcc] -> Call
- -> UniqSM (Maybe ([Var], [CoreExpr]))
- -- The VarSet is the variables to quantify over in the rule
- -- The [CoreExpr] are the argument patterns for the rule
-callToPats in_scope bndr_occs (con_env, args)
- | length args < length bndr_occs -- Check saturated
- = return Nothing
- | otherwise
- = do { prs <- argsToPats in_scope con_env (args `zip` bndr_occs)
- ; let (good_pats, pats) = unzip prs
- pat_fvs = varSetElems (exprsFreeVars pats)
- qvars = filter (not . (`elemVarEnv` in_scope)) pat_fvs
- -- Quantify over variables that are not in sccpe
- -- See Note [Shadowing] at the top
-
- ; -- pprTrace "callToPats" (ppr args $$ ppr prs $$ ppr bndr_occs) $
- if or good_pats
- then return (Just (qvars, pats))
- else return Nothing }
+ = return (nullUsage, spec_info) -- The boring case
+
---------------------
-spec_one :: Id -- Function
- -> CoreExpr -- Rhs of the original function
- -> (([Var], [CoreArg]), Int)
- -> UniqSM (CoreRule, (Id,CoreExpr)) -- Rule and binding
+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
[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 fn rhs ((vars_to_bind, pats), rule_number)
- = getUniqueUs `thenUs` \ spec_uniq ->
- let
- fn_name = idName fn
- fn_loc = nameSrcLoc fn_name
- spec_occ = mkSpecOcc (nameOccName fn_name)
+spec_one env fn arg_bndrs body (call_pat@(qvars, pats), rule_number)
+ = do { spec_uniq <- getUniqueUs
+ ; let spec_env = extendScSubstList (extendScInScope env qvars)
+ (arg_bndrs `zip` pats)
+ fn_name = idName fn
+ fn_loc = nameSrcSpan fn_name
+ spec_occ = mkSpecOcc (nameOccName fn_name)
+ rule_name = mkFastString ("SC:" ++ showSDoc (ppr fn <> int rule_number))
+ spec_name = mkInternalName spec_uniq spec_occ fn_loc
+-- ; pprTrace "{spec_one" (ppr (sc_count env) <+> ppr fn <+> ppr pats <+> text "-->" <+> ppr spec_name) $
+-- return ()
+
+ -- Specialise the body
+ ; (spec_usg, spec_body) <- scExpr spec_env body
+
+-- ; pprTrace "done spec_one}" (ppr fn) $
+-- return ()
+
+ -- And build the results
+ ; let spec_id = mkLocalId spec_name (mkPiTypes spec_lam_args body_ty)
+ `setIdStrictness` spec_str -- See Note [Transfer strictness]
+ `setIdArity` count isId spec_lam_args
+ spec_str = calcSpecStrictness fn spec_lam_args pats
+ (spec_lam_args, spec_call_args) = mkWorkerArgs qvars body_ty
+ -- Usual w/w hack to avoid generating
+ -- a spec_rhs of unlifted type and no args
+
+ spec_rhs = mkLams spec_lam_args spec_body
+ body_ty = exprType spec_body
+ rule_rhs = mkVarApps (Var spec_id) spec_call_args
+ inline_act = idInlineActivation fn
+ rule = mkRule True {- Auto -} True {- Local -}
+ rule_name inline_act fn_name qvars pats rule_rhs
+ -- See Note [Transfer activation]
+ ; return (spec_usg, OS call_pat rule spec_id spec_rhs) }
+
+calcSpecStrictness :: Id -- The original function
+ -> [Var] -> [CoreExpr] -- Call pattern
+ -> StrictSig -- Strictness of specialised thing
+-- See Note [Transfer strictness]
+calcSpecStrictness fn qvars pats
+ = StrictSig (mkTopDmdType spec_dmds TopRes)
+ where
+ spec_dmds = [ lookupVarEnv dmd_env qv `orElse` lazyDmd | qv <- qvars, isId qv ]
+ StrictSig (DmdType _ dmds _) = idStrictness fn
+
+ dmd_env = go emptyVarEnv dmds pats
+
+ go env ds (Type {} : pats) = go env ds pats
+ go env (d:ds) (pat : pats) = go (go_one env d pat) ds pats
+ go env _ _ = env
+
+ go_one env d (Var v) = extendVarEnv_C both env v d
+ go_one env (Box d) e = go_one env d e
+ go_one env (Eval (Prod ds)) e
+ | (Var _, args) <- collectArgs e = go env ds args
+ go_one env _ _ = env
- -- Put the type variables first; the type of a term
- -- variable may mention a type variable
- (tvs, ids) = partition isTyVar vars_to_bind
- bndrs = tvs ++ ids
- spec_body = mkApps rhs pats
- body_ty = exprType spec_body
-
- (spec_lam_args, spec_call_args) = mkWorkerArgs bndrs body_ty
- -- Usual w/w hack to avoid generating
- -- a spec_rhs of unlifted type and no args
-
- rule_name = mkFastString ("SC:" ++ showSDoc (ppr fn <> int rule_number))
- spec_rhs = mkLams spec_lam_args spec_body
- spec_id = mkUserLocal spec_occ spec_uniq (mkPiTypes spec_lam_args body_ty) fn_loc
- rule_rhs = mkVarApps (Var spec_id) spec_call_args
- rule = mkLocalRule rule_name specConstrActivation fn_name bndrs pats rule_rhs
- in
- returnUs (rule, (spec_id, spec_rhs))
-
--- In which phase should the specialise-constructor rules be active?
--- Originally I made them always-active, but Manuel found that
--- this defeated some clever user-written rules. So Plan B
--- is to make them active only in Phase 0; after all, currently,
--- the specConstr transformation is only run after the simplifier
--- has reached Phase 0. In general one would want it to be
--- flag-controllable, but for now I'm leaving it baked in
--- [SLPJ Oct 01]
-specConstrActivation :: Activation
-specConstrActivation = ActiveAfter 0 -- Baked in; see comments above
\end{code}
+Note [Specialise original body]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The RhsInfo for a binding keeps the *original* body of the binding. We
+must specialise that, *not* the result of applying specExpr to the RHS
+(which is also kept in RhsInfo). Otherwise we end up specialising a
+specialised RHS, and that can lead directly to exponential behaviour.
+
+Note [Transfer activation]
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+ This note is for SpecConstr, but exactly the same thing
+ happens in the overloading specialiser; see
+ Note [Auto-specialisation and RULES] in Specialise.
+
+In which phase should the specialise-constructor rules be active?
+Originally I made them always-active, but Manuel found that this
+defeated some clever user-written rules. Then I made them active only
+in Phase 0; after all, currently, the specConstr transformation is
+only run after the simplifier has reached Phase 0, but that meant
+that specialisations didn't fire inside wrappers; see test
+simplCore/should_compile/spec-inline.
+
+So now I just use the inline-activation of the parent Id, as the
+activation for the specialiation RULE, just like the main specialiser;
+
+This in turn means there is no point in specialising NOINLINE things,
+so we test for that.
+
+Note [Transfer strictness]
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+We must transfer strictness information from the original function to
+the specialised one. Suppose, for example
+
+ f has strictness SS
+ and a RULE f (a:as) b = f_spec a as b
+
+Now we want f_spec to have strictess LLS, otherwise we'll use call-by-need
+when calling f_spec instead of call-by-value. And that can result in
+unbounded worsening in space (cf the classic foldl vs foldl')
+
+See Trac #3437 for a good example.
+
+The function calcSpecStrictness performs the calculation.
+
+
%************************************************************************
%* *
\subsection{Argument analysis}
\begin{code}
+type CallPat = ([Var], [CoreExpr]) -- Quantified variables and arguments
+
+
+callsToPats :: ScEnv -> [OneSpec] -> [ArgOcc] -> [Call] -> UniqSM (Bool, [CallPat])
+ -- Result has no duplicate patterns,
+ -- nor ones mentioned in done_pats
+ -- Bool indicates that there was at least one boring pattern
+callsToPats env done_specs bndr_occs calls
+ = do { mb_pats <- mapM (callToPats env bndr_occs) calls
+
+ ; let good_pats :: [([Var], [CoreArg])]
+ good_pats = catMaybes mb_pats
+ done_pats = [p | OS p _ _ _ <- done_specs]
+ is_done p = any (samePat p) done_pats
+
+ ; return (any isNothing mb_pats,
+ filterOut is_done (nubBy samePat good_pats)) }
+
+callToPats :: ScEnv -> [ArgOcc] -> Call -> UniqSM (Maybe CallPat)
+ -- The [Var] is the variables to quantify over in the rule
+ -- Type variables come first, since they may scope
+ -- over the following term variables
+ -- The [CoreExpr] are the argument patterns for the rule
+callToPats env bndr_occs (con_env, args)
+ | length args < length bndr_occs -- Check saturated
+ = return Nothing
+ | otherwise
+ = do { let in_scope = substInScope (sc_subst env)
+ ; prs <- argsToPats env in_scope con_env (args `zip` bndr_occs)
+ ; let (interesting_s, pats) = unzip prs
+ pat_fvs = varSetElems (exprsFreeVars pats)
+ qvars = filterOut (`elemInScopeSet` in_scope) pat_fvs
+ -- Quantify over variables that are not in sccpe
+ -- at the call site
+ -- See Note [Shadowing] at the top
+
+ (tvs, ids) = partition isTyCoVar qvars
+ qvars' = tvs ++ ids
+ -- Put the type variables first; the type of a term
+ -- variable may mention a type variable
+
+ ; -- pprTrace "callToPats" (ppr args $$ ppr prs $$ ppr bndr_occs) $
+ if or interesting_s
+ then return (Just (qvars', pats))
+ else return Nothing }
+
-- argToPat takes an actual argument, and returns an abstracted
-- version, consisting of just the "constructor skeleton" of the
-- argument, with non-constructor sub-expression replaced by new
-- placeholder variables. For example:
-- C a (D (f x) (g y)) ==> C p1 (D p2 p3)
-argToPat :: InScopeEnv -- What's in scope at the fn defn site
- -> ConstrEnv -- ConstrEnv at the call site
+argToPat :: ScEnv
+ -> InScopeSet -- What's in scope at the fn defn site
+ -> ValueEnv -- ValueEnv at the call site
-> CoreArg -- A call arg (or component thereof)
-> ArgOcc
-> UniqSM (Bool, CoreArg)
-- lvl7 --> (True, lvl7) if lvl7 is bound
-- somewhere further out
-argToPat in_scope con_env arg@(Type ty) arg_occ
+argToPat _env _in_scope _val_env arg@(Type {}) _arg_occ
= return (False, arg)
-argToPat in_scope con_env (Note n arg) arg_occ
- = argToPat in_scope con_env arg arg_occ
+argToPat env in_scope val_env (Note _ arg) arg_occ
+ = argToPat env in_scope val_env arg arg_occ
-- Note [Notes in call patterns]
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-- Ignore Notes. In particular, we want to ignore any InlineMe notes
-- ride roughshod over them all for now.
--- See Note [Notes in RULE matching] in Rules
-argToPat in_scope con_env (Let _ arg) arg_occ
- = argToPat in_scope con_env arg arg_occ
+argToPat env in_scope val_env (Let _ arg) arg_occ
+ = argToPat env in_scope val_env arg arg_occ
+ -- See Note [Matching lets] in Rule.lhs
-- Look through let expressions
- -- e.g. f (let v = rhs in \y -> ...v...)
- -- Here we can specialise for f (\y -> ...)
+ -- 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.
-argToPat in_scope con_env (Cast arg co) arg_occ
- = do { (interesting, arg') <- argToPat in_scope con_env arg arg_occ
- ; if interesting then
- return (interesting, Cast arg' co)
- else
- wildCardPat (snd (coercionKind co)) }
+{- Disabled; see Note [Matching cases] in Rule.lhs
+argToPat env in_scope val_env (Case scrut _ _ [(_, _, rhs)]) arg_occ
+ | exprOkForSpeculation scrut -- See Note [Matching cases] in Rule.hhs
+ = argToPat env in_scope val_env rhs arg_occ
+-}
-argToPat in_scope con_env arg arg_occ
+argToPat env in_scope val_env (Cast arg co) arg_occ
+ | not (ignoreType env ty2)
+ = do { (interesting, arg') <- argToPat env in_scope val_env arg arg_occ
+ ; if not interesting then
+ wildCardPat ty2
+ else do
+ { -- Make a wild-card pattern for the coercion
+ uniq <- getUniqueUs
+ ; let co_name = mkSysTvName uniq (fsLit "sg")
+ co_var = mkCoVar co_name (mkCoKind ty1 ty2)
+ ; return (interesting, Cast arg' (mkTyVarTy co_var)) } }
+ where
+ (ty1, ty2) = coercionKind co
+
+
+
+{- 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
| isId v = True -- it is inside a type lambda
| otherwise = is_value_lam e
is_value_lam other = False
+-}
-- Check for a constructor application
-- NB: this *precedes* the Var case, so that we catch nullary constrs
-argToPat in_scope con_env arg arg_occ
- | Just (CV dc args) <- is_con_app_maybe con_env arg
+argToPat env in_scope val_env arg arg_occ
+ | Just (ConVal dc args) <- isValue val_env arg
+ , not (ignoreAltCon env dc)
, case arg_occ of
ScrutOcc _ -> True -- Used only by case scrutinee
BothOcc -> case arg of -- Used elsewhere
App {} -> True -- see Note [Reboxing]
- other -> False
- other -> False -- No point; the arg is not decomposed
- = do { args' <- argsToPats in_scope con_env (args `zip` conArgOccs arg_occ dc)
+ _other -> False
+ _other -> False -- No point; the arg is not decomposed
+ = do { args' <- argsToPats env in_scope val_env (args `zip` conArgOccs arg_occ dc)
; return (True, mk_con_app dc (map snd args')) }
-- Check if the argument is a variable that
-- 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 con_env (Var v) arg_occ
- | not (isLocalId v) || v `elemVarEnv` in_scope,
- case arg_occ of { UnkOcc -> False; other -> True }, -- (a)
- isValueUnfolding (idUnfolding v) -- (b)
+argToPat env in_scope val_env (Var v) arg_occ
+ | case arg_occ of { UnkOcc -> False; _other -> True }, -- (a)
+ is_value, -- (b)
+ not (ignoreType env (varType v))
= return (True, Var v)
+ where
+ is_value
+ | isLocalId v = v `elemInScopeSet` in_scope
+ && isJust (lookupVarEnv val_env v)
+ -- Local variables have values in val_env
+ | otherwise = isValueUnfolding (idUnfolding v)
+ -- Imports have unfoldings
+
+-- I'm really not sure what this comment means
+-- And by not wild-carding we tend to get forall'd
+-- variables that are in soope, which in turn can
+-- expose the weakness in let-matching
+-- See Note [Matching lets] in Rules
-- Check for a variable bound inside the function.
-- Don't make a wild-card, because we may usefully share
-- e.g. f a = let x = ... in f (x,x)
-- NB: this case follows the lambda and con-app cases!!
-argToPat in_scope con_env (Var v) arg_occ
- = return (False, Var v)
+-- argToPat _in_scope _val_env (Var v) _arg_occ
+-- = return (False, Var v)
+ -- SLPJ : disabling this to avoid proliferation of versions
+ -- also works badly when thinking about seeding the loop
+ -- from the body of the let
+ -- f x y = letrec g z = ... in g (x,y)
+ -- We don't want to specialise for that *particular* x,y
-- The default case: make a wild-card
-argToPat in_scope con_env arg arg_occ
+argToPat _env _in_scope _val_env arg _arg_occ
= wildCardPat (exprType arg)
wildCardPat :: Type -> UniqSM (Bool, CoreArg)
wildCardPat ty = do { uniq <- getUniqueUs
- ; let id = mkSysLocal FSLIT("sc") uniq ty
+ ; let id = mkSysLocal (fsLit "sc") uniq ty
; return (False, Var id) }
-argsToPats :: InScopeEnv -> ConstrEnv
+argsToPats :: ScEnv -> InScopeSet -> ValueEnv
-> [(CoreArg, ArgOcc)]
-> UniqSM [(Bool, CoreArg)]
-argsToPats in_scope con_env args
- = mapUs do_one args
+argsToPats env in_scope val_env args
+ = mapM do_one args
where
- do_one (arg,occ) = argToPat in_scope con_env arg occ
+ do_one (arg,occ) = argToPat env in_scope val_env arg occ
\end{code}
\begin{code}
-is_con_app_maybe :: ConstrEnv -> CoreExpr -> Maybe ConValue
-is_con_app_maybe env (Lit lit)
- = Just (CV (LitAlt lit) [])
-
-is_con_app_maybe env expr -- Maybe it's a constructor application
- | (Var fun, args) <- collectArgs expr,
- Just con <- isDataConWorkId_maybe fun,
- args `lengthAtLeast` dataConRepArity con
- -- Might be > because the arity excludes type args
- = Just (CV (DataAlt con) args)
-
-is_con_app_maybe env (Var v)
+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
- | isCheapUnfolding unf
- = is_con_app_maybe env (unfoldingTemplate unf)
+ | 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!
-is_con_app_maybe env expr = Nothing
+isValue env (Lam b e)
+ | isTyCoVar b = case isValue env e of
+ Just _ -> Just LambdaVal
+ Nothing -> Nothing
+ | otherwise = Just LambdaVal
+
+isValue _env expr -- Maybe it's a constructor application
+ | (Var fun, args) <- collectArgs expr
+ = case isDataConWorkId_maybe fun of
+
+ Just con | args `lengthAtLeast` dataConRepArity con
+ -- Check saturated; might be > because the
+ -- arity excludes type args
+ -> Just (ConVal (DataAlt con) args)
+
+ _other | valArgCount args < idArity fun
+ -- Under-applied function
+ -> Just LambdaVal -- Partial application
+
+ _other -> Nothing
+
+isValue _env _expr = Nothing
mk_con_app :: AltCon -> [CoreArg] -> CoreExpr
mk_con_app (LitAlt lit) [] = Lit lit
mk_con_app (DataAlt con) args = mkConApp con args
-mk_con_app other args = panic "SpecConstr.mk_con_app"
+mk_con_app _other _args = panic "SpecConstr.mk_con_app"
+
+samePat :: CallPat -> CallPat -> Bool
+samePat (vs1, as1) (vs2, as2)
+ = all2 same as1 as2
+ where
+ same (Var v1) (Var v2)
+ | v1 `elem` vs1 = v2 `elem` vs2
+ | v2 `elem` vs2 = False
+ | otherwise = v1 == v2
+
+ same (Lit l1) (Lit l2) = l1==l2
+ same (App f1 a1) (App f2 a2) = same f1 f2 && same a1 a2
+
+ same (Type {}) (Type {}) = True -- Note [Ignore type differences]
+ same (Note _ e1) e2 = same e1 e2 -- Ignore casts and notes
+ same (Cast e1 _) e2 = same e1 e2
+ same e1 (Note _ e2) = same e1 e2
+ same e1 (Cast e2 _) = same e1 e2
+
+ same e1 e2 = WARN( bad e1 || bad e2, ppr e1 $$ ppr e2)
+ False -- Let, lambda, case should not occur
+ bad (Case {}) = True
+ bad (Let {}) = True
+ bad (Lam {}) = True
+ bad _other = False
\end{code}
+
+Note [Ignore type differences]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+We do not want to generate specialisations where the call patterns
+differ only in their type arguments! Not only is it utterly useless,
+but it also means that (with polymorphic recursion) we can generate
+an infinite number of specialisations. Example is Data.Sequence.adjustTree,
+I think.
+