\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}
-----------------------------------------------------
Hence the "OR" part of Note [Good arguments] below.
-ALTERNATIVE: pass both boxed and unboxed versions. This no longer saves
+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
rely on CSE to eliminate the duplicate allocation.... This alternative
doesn't look attractive enough to pursue.
+ALTERNATIVE 3: ignore the reboxing problem. The trouble is that
+the conservative reboxing story prevents many useful functions from being
+specialised. Example:
+ foo :: Maybe Int -> Int -> Int
+ foo (Just m) 0 = 0
+ foo x@(Just m) n = foo x (n-m)
+Here the use of 'x' will clearly not require boxing in the specialised function.
+
+The strictness analyser has the same problem, in fact. Example:
+ f p@(a,b) = ...
+If we pass just 'a' and 'b' to the worker, it might need to rebox the
+pair to create (a,b). A more sophisticated analysis might figure out
+precisely the cases in which this could happen, but the strictness
+analyser does no such analysis; it just passes 'a' and 'b', and hopes
+for the best.
+
+So my current choice is to make SpecConstr similarly aggressive, and
+ignore the bad potential of reboxing.
+
Note [Good arguments]
~~~~~~~~~~~~~~~~~~~~~
So we 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]
- cons :: ConstrEnv
+ 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)
+
+ 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 OutExpr = CoreExpr -- _After_ applying the subst
+type OutId = Id
+type OutVar = Var
-type ConstrEnv = IdEnv ConValue
-data ConValue = CV AltCon [CoreArg]
- -- Variables known to be bound to a constructor
- -- in a particular case alternative
+---------------------
+type HowBoundEnv = VarEnv HowBound -- Domain is OutVars
+---------------------
+type ValueEnv = IdEnv Value -- Domain is OutIds
+data Value = ConVal AltCon [CoreArg] -- _Saturated_ constructors
+ -- The AltCon is never DEFAULT
+ | LambdaVal -- Inlinable lambdas or PAPs
-instance Outputable ConValue where
- ppr (CV con args) = ppr con <+> interpp'SP args
+instance Outputable Value where
+ ppr (ConVal con args) = ppr con <+> interpp'SP args
+ ppr LambdaVal = ptext (sLit "<Lambda>")
-emptyScEnv = SCE { scope = emptyVarEnv, cons = emptyVarEnv }
+---------------------
+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
-
-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 con alt_bndrs
- = case con of
- DEFAULT -> env1
- LitAlt lit -> extendCons env1 scrut case_bndr (CV con [])
- DataAlt dc -> extend_data_con dc
+
+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, [Var])
+extendBndrsWith how_bound env bndrs
+ = (env { sc_subst = subst', sc_how_bound = hb_env' }, bndrs')
where
- cur_scope = scope env
- env1 = env { scope = extendVarEnvList cur_scope
- [(b,how_bound) | b <- 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)... }" ]
- how_bound = get_how scrut
- where
- get_how (Var v) = lookupVarEnv cur_scope v `orElse` Other
- get_how (Cast e _) = get_how e
- get_how (Note _ e) = get_how e
- get_how other = Other
-
- extend_data_con data_con =
- extendCons env1 scrut case_bndr (CV con vanilla_args)
- where
- vanilla_args = map Type (tyConAppArgs (idType case_bndr)) ++
- varsToCoreExprs alt_bndrs
-
-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
-
- -- When we encounter a recursive function binding
- -- f = \x y -> ...
- -- we want to extend the scope env with bindings
- -- that record that f is a RecFn and x,y are RecArgs
-extendRecBndr env fn bndrs
- = env { scope = scope env `extendVarEnvList`
- ((fn,RecFun): [(bndr,RecArg) | bndr <- bndrs]) }
+ (subst', bndr') = substBndr (sc_subst env) bndr
+ hb_env' = extendVarEnv (sc_how_bound env) bndr' how_bound
+
+extendRecBndrs :: ScEnv -> [Var] -> (ScEnv, [Var])
+extendRecBndrs env bndrs = (env { sc_subst = subst' }, bndrs')
+ where
+ (subst', bndrs') = substRecBndrs (sc_subst env) bndrs
+
+extendBndr :: ScEnv -> Var -> (ScEnv, Var)
+extendBndr env bndr = (env { sc_subst = subst' }, bndr')
+ where
+ (subst', bndr') = substBndr (sc_subst env) bndr
+
+extendValEnv :: ScEnv -> Id -> Maybe Value -> ScEnv
+extendValEnv env _ Nothing = env
+extendValEnv env id (Just cv) = env { sc_vals = extendVarEnv (sc_vals env) id cv }
+
+extendCaseBndrs :: ScEnv -> Id -> AltCon -> [Var] -> (ScEnv, [Var])
+-- When we encounter
+-- case scrut of b
+-- C x y -> ...
+-- we want to bind b, to (C x y)
+-- NB1: Extends only the sc_vals part of the envt
+-- NB2: Kill the dead-ness info on the pattern binders x,y, since
+-- they are potentially made alive by the [b -> C x y] binding
+extendCaseBndrs env case_bndr con alt_bndrs
+ | isDeadBinder case_bndr
+ = (env, alt_bndrs)
+ | otherwise
+ = (env1, map zap alt_bndrs)
+ -- NB: We used to bind v too, if scrut = (Var v); but
+ -- the simplifer has already done this so it seems
+ -- redundant to do so here
+ -- case scrut of
+ -- Var v -> extendValEnv env1 v cval
+ -- _other -> env1
+ where
+ zap v | isTyCoVar v = v -- See NB2 above
+ | otherwise = zapIdOccInfo v
+ env1 = extendValEnv env case_bndr cval
+ cval = case con of
+ DEFAULT -> Nothing
+ LitAlt {} -> Just (ConVal con [])
+ DataAlt {} -> Just (ConVal con vanilla_args)
+ where
+ vanilla_args = map Type (tyConAppArgs (idType case_bndr)) ++
+ varsToCoreExprs alt_bndrs
+
+
+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 }
-combineUsage u1 u2 = SCU { calls = plusVarEnv_C (++) (calls u1) (calls u2),
- occs = plusVarEnv_C combineOcc (occs u1) (occs u2) }
+combineCalls :: CallEnv -> CallEnv -> CallEnv
+combineCalls = plusVarEnv_C (++)
+combineUsage :: ScUsage -> ScUsage -> ScUsage
+combineUsage u1 u2 = SCU { scu_calls = combineCalls (scu_calls u1) (scu_calls u2),
+ scu_occs = plusVarEnv_C combineOcc (scu_occs u1) (scu_occs u2) }
+
+combineUsages :: [ScUsage] -> ScUsage
combineUsages [] = nullUsage
combineUsages us = foldr1 combineUsage us
-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 vresion of combineOcc makes ScrutOcc "win", so
+-- 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]
+-- 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
- -> 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.
-----------------------
-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))
+At one point I predicated this on the RHS mentioning the outer
+recursive function, but that's not essential and might even be
+harmful. I'm not sure.
+
+
+\begin{code}
+scApp :: ScEnv -> (InExpr, [InExpr]) -> UniqSM (ScUsage, CoreExpr)
+
+scApp env (Var fn, args) -- Function is a variable
+ = ASSERT( not (null args) )
+ do { args_w_usgs <- mapM (scExpr env) args
+ ; let (arg_usgs, args') = unzip args_w_usgs
+ arg_usg = combineUsages arg_usgs
+ ; case scSubstId env fn of
+ fn'@(Lam {}) -> scExpr (zapScSubst env) (doBeta fn' args')
+ -- Do beta-reduction and try again
+
+ Var fn' -> return (arg_usg `combineUsage` fn_usg, mkApps (Var fn') args')
+ where
+ fn_usg = case lookupHowBound env fn' of
+ Just RecFun -> SCU { scu_calls = unitVarEnv fn' [(sc_vals env, args')],
+ scu_occs = emptyVarEnv }
+ Just RecArg -> SCU { scu_calls = emptyVarEnv,
+ scu_occs = unitVarEnv fn' (ScrutOcc emptyUFM) }
+ Nothing -> nullUsage
+
+
+ other_fn' -> return (arg_usg, mkApps other_fn' args') }
+ -- NB: doing this ignores any usage info from the substituted
+ -- function, but I don't think that matters. If it does
+ -- we can fix it.
where
- (bndrs,body) = collectBinders rhs
- val_bndrs = filter isId bndrs
- env_fn_body = extendRecBndr env fn bndrs
+ doBeta :: OutExpr -> [OutExpr] -> OutExpr
+ -- ToDo: adjust for System IF
+ doBeta (Lam bndr body) (arg : args) = Let (NonRec bndr arg) (doBeta body args)
+ doBeta fn args = mkApps fn args
+
+-- The function is almost always a variable, but not always.
+-- In particular, if this pass follows float-in,
+-- which it may, we can get
+-- (let f = ...f... in f) arg1 arg2
+scApp env (other_fn, args)
+ = do { (fn_usg, fn') <- scExpr env other_fn
+ ; (arg_usgs, args') <- mapAndUnzipM (scExpr env) args
+ ; return (combineUsages arg_usgs `combineUsage` fn_usg, mkApps fn' args') }
-scBind env (Rec prs)
- = mapAndUnzipUs do_one prs `thenUs` \ (usgs, prs') ->
- returnUs (extendBndrs env (map fst prs), combineUsages usgs, Rec prs')
+----------------------
+scTopBind :: ScEnv -> CoreBind -> UniqSM (ScEnv, CoreBind)
+scTopBind env (Rec prs)
+ | Just threshold <- sc_size env
+ , not force_spec
+ , not (all (couldBeSmallEnoughToInline threshold) rhss)
+ -- No specialisation
+ = do { let (rhs_env,bndrs') = extendRecBndrs env bndrs
+ ; (_, rhss') <- mapAndUnzipM (scExpr rhs_env) rhss
+ ; return (rhs_env, Rec (bndrs' `zip` rhss')) }
+ | otherwise -- Do specialisation
+ = do { let (rhs_env1,bndrs') = extendRecBndrs env bndrs
+ rhs_env2 = extendHowBound rhs_env1 bndrs' RecFun
+
+ ; (rhs_usgs, rhs_infos) <- mapAndUnzipM (scRecRhs rhs_env2) (bndrs' `zip` rhss)
+ ; let rhs_usg = combineUsages rhs_usgs
+
+ ; (_, specs) <- specLoop rhs_env2 force_spec
+ (scu_calls rhs_usg) rhs_infos nullUsage
+ [SI [] 0 Nothing | _ <- bndrs]
+
+ ; return (rhs_env1, -- For the body of the letrec, delete the RecFun business
+ Rec (concat (zipWith specInfoBinds rhs_infos specs))) }
where
- do_one (bndr,rhs) = scExpr env rhs `thenUs` \ (usg, rhs') ->
- returnUs (usg, (bndr,rhs'))
+ (bndrs,rhss) = unzip prs
+ force_spec = any (forceSpecBndr env) bndrs
+ -- Note [Forcing specialisation]
-scBind env (NonRec bndr rhs)
- = scExpr env rhs `thenUs` \ (usg, rhs') ->
- returnUs (extendBndr env bndr, usg, NonRec bndr rhs')
+scTopBind env (NonRec bndr rhs)
+ = do { (_, rhs') <- scExpr env rhs
+ ; let (env1, bndr') = extendBndr env bndr
+ env2 = extendValEnv env1 bndr' (isValue (sc_vals env) rhs')
+ ; return (env2, NonRec bndr' rhs') }
----------------------
+scRecRhs :: ScEnv -> (OutId, InExpr) -> UniqSM (ScUsage, RhsInfo)
+scRecRhs env (bndr,rhs)
+ = do { let (arg_bndrs,body) = collectBinders rhs
+ (body_env, arg_bndrs') = extendBndrsWith RecArg env arg_bndrs
+ ; (body_usg, body') <- scExpr body_env body
+ ; let (rhs_usg, arg_occs) = lookupOccs body_usg arg_bndrs'
+ ; return (rhs_usg, RI bndr (mkLams arg_bndrs' body')
+ arg_bndrs body arg_occs) }
+ -- The arg_occs says how the visible,
+ -- lambda-bound binders of the RHS are used
+ -- (including the TyVar binders)
+ -- Two pats are the same if they match both ways
+
+----------------------
+specInfoBinds :: RhsInfo -> SpecInfo -> [(Id,CoreExpr)]
+specInfoBinds (RI fn new_rhs _ _ _) (SI specs _ _)
+ = [(id,rhs) | OS _ _ id rhs <- specs] ++
+ [(fn `addIdSpecialisations` rules, new_rhs)]
+ where
+ rules = [r | OS _ r _ _ <- specs]
+
+----------------------
+varUsage :: ScEnv -> OutVar -> ArgOcc -> ScUsage
varUsage env v use
- | Just RecArg <- lookupScopeEnv env v = SCU { calls = emptyVarEnv,
- occs = unitVarEnv v use }
+ | Just RecArg <- lookupHowBound env v = SCU { scu_calls = emptyVarEnv
+ , scu_occs = unitVarEnv v use }
| otherwise = nullUsage
\end{code}
%************************************************************************
%* *
-\subsection{The specialiser}
+ The specialiser itself
%* *
%************************************************************************
\begin{code}
-specialise :: ScEnv
- -> Id -- Functionn
- -> [CoreBndr] -> CoreExpr -- Its RHS
- -> ScUsage -- Info on usage
- -> UniqSM ([CoreRule], -- Rules
- [(Id,CoreExpr)]) -- Bindings
-
-specialise env fn bndrs body body_usg
- = do { let (_, bndr_occs) = lookupOccs body_usg bndrs
- all_calls = lookupVarEnv (calls body_usg) fn `orElse` []
-
- ; mb_pats <- mapM (callToPats (scope env) bndr_occs) all_calls
-
- ; let good_pats :: [([Var], [CoreArg])]
- good_pats = catMaybes mb_pats
- in_scope = mkInScopeSet $ unionVarSets $
- [ exprsFreeVars pats `delVarSetList` vs
- | (vs,pats) <- good_pats ]
- uniq_pats = nubBy (same_pat in_scope) good_pats
- ; -- pprTrace "specialise" (vcat [ppr fn <+> ppr bndrs <+> ppr bndr_occs,
- -- text "calls" <+> ppr all_calls,
- -- text "good pats" <+> ppr good_pats,
- -- text "uniq pats" <+> ppr uniq_pats]) $
- mapAndUnzipUs (spec_one env fn (mkLams bndrs body))
- (uniq_pats `zip` [1..]) }
- 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
+data RhsInfo = RI OutId -- The binder
+ OutExpr -- The new RHS
+ [InVar] InExpr -- The *original* RHS (\xs.body)
+ -- Note [Specialise original body]
+ [ArgOcc] -- Info on how the xs occur in body
+
+data SpecInfo = SI [OneSpec] -- The specialisations we have generated
+
+ Int -- Length of specs; used for numbering them
+
+ (Maybe ScUsage) -- Nothing => we have generated specialisations
+ -- from calls in the *original* RHS
+ -- Just cs => we haven't, and this is the usage
+ -- of the original RHS
+ -- See Note [Local recursive groups]
+
+ -- One specialisation: Rule plus definition
+data OneSpec = OS CallPat -- Call pattern that generated this specialisation
+ CoreRule -- Rule connecting original id with the specialisation
+ OutId OutExpr -- Spec id + its rhs
+
+
+specLoop :: ScEnv
+ -> Bool -- force specialisation?
+ -- Note [Forcing specialisation]
+ -> CallEnv
+ -> [RhsInfo]
+ -> ScUsage -> [SpecInfo] -- One per binder; acccumulating parameter
+ -> UniqSM (ScUsage, [SpecInfo]) -- ...ditto...
+specLoop env force_spec all_calls rhs_infos usg_so_far specs_so_far
+ = do { specs_w_usg <- zipWithM (specialise env force_spec all_calls) rhs_infos specs_so_far
+ ; let (new_usg_s, all_specs) = unzip specs_w_usg
+ new_usg = combineUsages new_usg_s
+ new_calls = scu_calls new_usg
+ all_usg = usg_so_far `combineUsage` new_usg
+ ; if isEmptyVarEnv new_calls then
+ return (all_usg, all_specs)
+ else
+ specLoop env force_spec new_calls rhs_infos all_usg all_specs }
+
+specialise
+ :: ScEnv
+ -> Bool -- force specialisation?
+ -- Note [Forcing specialisation]
+ -> CallEnv -- Info on calls
+ -> RhsInfo
+ -> SpecInfo -- Original RHS plus patterns dealt with
+ -> UniqSM (ScUsage, SpecInfo) -- New specialised versions and their usage
+
+-- Note: the rhs here is the optimised version of the original rhs
+-- So when we make a specialised copy of the RHS, we're starting
+-- from an RHS whose nested functions have been optimised already.
+
+specialise env force_spec bind_calls (RI fn _ arg_bndrs body arg_occs)
+ spec_info@(SI specs spec_count mb_unspec)
+ | not (isBottomingId fn) -- Note [Do not specialise diverging functions]
+ , not (isNeverActive (idInlineActivation fn)) -- See Note [Transfer activation]
+ , notNull arg_bndrs -- Only specialise functions
+ , Just all_calls <- lookupVarEnv bind_calls fn
+ = do { (boring_call, pats) <- callsToPats env specs arg_occs all_calls
+-- ; pprTrace "specialise" (vcat [ ppr fn <+> text "with" <+> int (length pats) <+> text "good patterns"
+-- , text "arg_occs" <+> ppr arg_occs
+-- , text "calls" <+> ppr all_calls
+-- , text "good pats" <+> ppr pats]) $
+-- return ()
+
+ -- Bale out if too many specialisations
+ ; let n_pats = length pats
+ spec_count' = n_pats + spec_count
+ ; case sc_count env of
+ Just max | not force_spec && spec_count' > max
+ -> pprTrace "SpecConstr" msg $
+ return (nullUsage, spec_info)
+ where
+ msg = vcat [ sep [ ptext (sLit "Function") <+> quotes (ppr fn)
+ , nest 2 (ptext (sLit "has") <+>
+ speakNOf spec_count' (ptext (sLit "call pattern")) <> comma <+>
+ ptext (sLit "but the limit is") <+> int max) ]
+ , ptext (sLit "Use -fspec-constr-count=n to set the bound")
+ , extra ]
+ extra | not opt_PprStyle_Debug = ptext (sLit "Use -dppr-debug to see specialisations")
+ | otherwise = ptext (sLit "Specialisations:") <+> ppr (pats ++ [p | OS p _ _ _ <- specs])
+
+ _normal_case -> do {
+
+ let spec_env = decreaseSpecCount env n_pats
+ ; (spec_usgs, new_specs) <- mapAndUnzipM (spec_one spec_env fn arg_bndrs body)
+ (pats `zip` [spec_count..])
+ -- See Note [Specialise original body]
+
+ ; let spec_usg = combineUsages spec_usgs
+ (new_usg, mb_unspec')
+ = case mb_unspec of
+ Just rhs_usg | boring_call -> (spec_usg `combineUsage` rhs_usg, Nothing)
+ _ -> (spec_usg, mb_unspec)
+
+ ; return (new_usg, SI (new_specs ++ specs) spec_count' mb_unspec') } }
| otherwise
- = 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 :: ScEnv
- -> Id -- Function
- -> CoreExpr -- Rhs of the original function
- -> (([Var], [CoreArg]), Int)
- -> UniqSM (CoreRule, (Id,CoreExpr)) -- Rule and binding
+ -> OutId -- Function
+ -> [InVar] -- Lambda-binders of RHS; should match patterns
+ -> InExpr -- Body of the original function
+ -> (CallPat, Int)
+ -> UniqSM (ScUsage, OneSpec) -- Rule and binding
-- spec_one creates a specialised copy of the function, together
-- with a rule for using it. I'm very proud of how short this
[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 ((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 (Var v) arg_occ
- | not (isLocalId v) || v `elemVarEnv` in_scope
- = -- The recursive call passes 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
- if (case arg_occ of { UnkOcc -> False; other -> True }) -- (a)
- && isValueUnfolding (idUnfolding v) -- (b)
- then return (True, Var v)
- else wildCardPat (idType v)
-
-argToPat in_scope con_env (Let _ 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
+ -- Perhaps we should not ignore profiling notes, but I'm going to
+ -- ride roughshod over them all for now.
+ --- See Note [Notes in RULE matching] in Rules
+
+argToPat env in_scope val_env (Let _ arg) arg_occ
+ = argToPat env in_scope val_env arg arg_occ
+ -- See Note [Matching lets] in Rule.lhs
-- Look through let expressions
- -- e.g. f (let v = rhs in \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
+-}
-argToPat in_scope con_env arg arg_occ
- | Just (CV dc args) <- is_con_app_maybe con_env arg
+ -- Check for a constructor application
+ -- NB: this *precedes* the Var case, so that we catch nullary constrs
+argToPat env in_scope val_env arg arg_occ
+ | Just (ConVal dc args) <- isValue val_env arg
+ , not (ignoreAltCon env dc)
, case arg_occ of
ScrutOcc _ -> True -- Used only by case scrutinee
BothOcc -> case arg of -- Used elsewhere
App {} -> True -- see Note [Reboxing]
- other -> False
- other -> False -- No point; the arg is not decomposed
- = do { args' <- argsToPats 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')) }
-argToPat in_scope con_env (Var v) arg_occ
- = -- 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!!
- return (False, Var v)
-
--- The default case: make a wild-card
-argToPat in_scope con_env arg arg_occ = wildCardPat (exprType arg)
+ -- Check if the argument is a variable that
+ -- is in scope at the function definition site
+ -- It's worth specialising on this if
+ -- (a) it's used in an interesting way in the body
+ -- (b) we know what its value is
+argToPat env in_scope val_env (Var v) arg_occ
+ | case arg_occ of { UnkOcc -> False; _other -> True }, -- (a)
+ is_value, -- (b)
+ not (ignoreType env (varType v))
+ = return (True, Var v)
+ where
+ is_value
+ | isLocalId v = v `elemInScopeSet` in_scope
+ && isJust (lookupVarEnv val_env v)
+ -- Local variables have values in val_env
+ | otherwise = isValueUnfolding (idUnfolding v)
+ -- Imports have unfoldings
+
+-- I'm really not sure what this comment means
+-- And by not wild-carding we tend to get forall'd
+-- variables that are in soope, which in turn can
+-- expose the weakness in let-matching
+-- See Note [Matching lets] in Rules
+
+ -- Check for a variable bound inside the function.
+ -- Don't make a wild-card, because we may usefully share
+ -- e.g. f a = let x = ... in f (x,x)
+ -- NB: this case follows the lambda and con-app cases!!
+-- argToPat _in_scope _val_env (Var v) _arg_occ
+-- = return (False, Var v)
+ -- SLPJ : disabling this to avoid proliferation of versions
+ -- also works badly when thinking about seeding the loop
+ -- from the body of the let
+ -- f x y = letrec g z = ... in g (x,y)
+ -- We don't want to specialise for that *particular* x,y
+
+ -- The default case: make a wild-card
+argToPat _env _in_scope _val_env arg _arg_occ
+ = wildCardPat (exprType arg)
wildCardPat :: Type -> UniqSM (Bool, CoreArg)
wildCardPat ty = do { uniq <- getUniqueUs
- ; let id = mkSysLocal FSLIT("sc") uniq ty
+ ; 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 (Var v)
- = case lookupVarEnv env v of
- Just stuff -> Just stuff
- -- You might think we could look in the idUnfolding here
+isValue :: ValueEnv -> CoreExpr -> Maybe Value
+isValue _env (Lit lit)
+ = Just (ConVal (LitAlt lit) [])
+
+isValue env (Var v)
+ | Just stuff <- lookupVarEnv env v
+ = Just stuff -- You might think we could look in the idUnfolding here
-- but that doesn't take account of which branch of a
-- case we are in, which is the whole point
- Nothing | isCheapUnfolding unf
- -> is_con_app_maybe env (unfoldingTemplate unf)
- where
- unf = idUnfolding v
- -- However we do want to consult the unfolding
- -- as well, for let-bound constructors!
+ | not (isLocalId v) && isCheapUnfolding unf
+ = isValue env (unfoldingTemplate unf)
+ where
+ unf = idUnfolding v
+ -- However we do want to consult the unfolding
+ -- as well, for let-bound constructors!
+
+isValue env (Lam b e)
+ | isTyCoVar b = case isValue env e of
+ Just _ -> Just LambdaVal
+ Nothing -> Nothing
+ | otherwise = Just LambdaVal
- other -> Nothing
+isValue _env expr -- Maybe it's a constructor application
+ | (Var fun, args) <- collectArgs expr
+ = case isDataConWorkId_maybe fun of
-is_con_app_maybe env (Lit lit)
- = Just (CV (LitAlt lit) [])
+ Just con | args `lengthAtLeast` dataConRepArity con
+ -- Check saturated; might be > because the
+ -- arity excludes type args
+ -> Just (ConVal (DataAlt con) args)
-is_con_app_maybe env expr
- = case collectArgs expr of
- (Var fun, args) | Just con <- isDataConWorkId_maybe fun,
- args `lengthAtLeast` dataConRepArity con
- -- Might be > because the arity excludes type args
- -> Just (CV (DataAlt con) args)
+ _other | valArgCount args < idArity fun
+ -- Under-applied function
+ -> Just LambdaVal -- Partial application
- other -> Nothing
+ _other -> Nothing
+
+isValue _env _expr = Nothing
mk_con_app :: AltCon -> [CoreArg] -> CoreExpr
mk_con_app (LitAlt lit) [] = Lit lit
mk_con_app (DataAlt con) args = mkConApp con args
-mk_con_app other args = panic "SpecConstr.mk_con_app"
+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.
+
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