-----------------
\begin{code}
-{-# OPTIONS -w #-}
--- The above warning supression flag is a temporary kludge.
--- While working on this module you are encouraged to remove it and fix
--- any warnings in the module. See
--- http://hackage.haskell.org/trac/ghc/wiki/CodingStyle#Warnings
--- for details
-
module DmdAnal ( dmdAnalPgm, dmdAnalTopRhs,
both {- needed by WwLib -}
) where
#include "HsVersions.h"
-import DynFlags ( DynFlags, DynFlag(..) )
+import DynFlags ( DynFlags )
import StaticFlags ( opt_MaxWorkerArgs )
-import NewDemand -- All of it
+import Demand -- All of it
import CoreSyn
import PprCore
-import CoreUtils ( exprIsHNF, exprIsTrivial, exprArity )
-import DataCon ( dataConTyCon )
+import Coercion ( isCoVarType )
+import CoreUtils ( exprIsHNF, exprIsTrivial )
+import CoreArity ( exprArity )
+import DataCon ( dataConTyCon, dataConRepStrictness )
import TyCon ( isProductTyCon, isRecursiveTyCon )
-import Id ( Id, idType, idInlinePragma,
+import Id ( Id, idType, idInlineActivation,
isDataConWorkId, isGlobalId, idArity,
-#ifdef OLD_STRICTNESS
- idDemandInfo, idStrictness, idCprInfo, idName,
-#endif
- idNewStrictness, idNewStrictness_maybe,
- setIdNewStrictness, idNewDemandInfo,
- idNewDemandInfo_maybe,
- setIdNewDemandInfo
+ idStrictness,
+ setIdStrictness, idDemandInfo, idUnfolding,
+ idDemandInfo_maybe, setIdDemandInfo
)
-#ifdef OLD_STRICTNESS
-import IdInfo ( newStrictnessFromOld, newDemand )
-#endif
-import Var ( Var )
+import Var ( Var, isTyVar )
import VarEnv
import TysWiredIn ( unboxedPairDataCon )
import TysPrim ( realWorldStatePrimTy )
-import UniqFM ( plusUFM_C, addToUFM_Directly, lookupUFM_Directly,
- keysUFM, minusUFM, ufmToList, filterUFM )
-import Type ( isUnLiftedType, coreEqType, splitTyConApp_maybe )
+import UniqFM ( addToUFM_Directly, lookupUFM_Directly,
+ minusUFM, filterUFM )
+import Type ( isUnLiftedType, eqType, splitTyConApp_maybe )
import Coercion ( coercionKind )
-import CoreLint ( showPass, endPass )
-import Util ( mapAndUnzip, lengthIs )
+import Util ( mapAndUnzip, lengthIs, zipEqual )
import BasicTypes ( Arity, TopLevelFlag(..), isTopLevel, isNeverActive,
- RecFlag(..), isRec )
+ RecFlag(..), isRec, isMarkedStrict )
import Maybes ( orElse, expectJust )
import Outputable
-
+import Pair
import Data.List
+import FastString
\end{code}
To think about
\begin{code}
dmdAnalPgm :: DynFlags -> [CoreBind] -> IO [CoreBind]
-dmdAnalPgm dflags binds
+dmdAnalPgm _ binds
= do {
- showPass dflags "Demand analysis" ;
let { binds_plus_dmds = do_prog binds } ;
-
- endPass dflags "Demand analysis"
- Opt_D_dump_stranal binds_plus_dmds ;
-#ifdef OLD_STRICTNESS
- -- Only if OLD_STRICTNESS is on, because only then is the old
- -- strictness analyser run
- let { dmd_changes = get_changes binds_plus_dmds } ;
- printDump (text "Changes in demands" $$ dmd_changes) ;
-#endif
return binds_plus_dmds
}
where
-> CoreBind
-> (SigEnv, CoreBind)
dmdAnalTopBind sigs (NonRec id rhs)
- = let
- ( _, _, (_, rhs1)) = dmdAnalRhs TopLevel NonRecursive sigs (id, rhs)
- (sigs2, _, (id2, rhs2)) = dmdAnalRhs TopLevel NonRecursive sigs (id, rhs1)
- -- Do two passes to improve CPR information
- -- See comments with ignore_cpr_info in mk_sig_ty
- -- and with extendSigsWithLam
- in
- (sigs2, NonRec id2 rhs2)
+ = (sigs2, NonRec id2 rhs2)
+ where
+ ( _, _, (_, rhs1)) = dmdAnalRhs TopLevel NonRecursive (virgin sigs) (id, rhs)
+ (sigs2, _, (id2, rhs2)) = dmdAnalRhs TopLevel NonRecursive (nonVirgin sigs) (id, rhs1)
+ -- Do two passes to improve CPR information
+ -- See comments with ignore_cpr_info in mk_sig_ty
+ -- and with extendSigsWithLam
dmdAnalTopBind sigs (Rec pairs)
- = let
- (sigs', _, pairs') = dmdFix TopLevel sigs pairs
+ = (sigs', Rec pairs')
+ where
+ (sigs', _, pairs') = dmdFix TopLevel (virgin sigs) pairs
-- We get two iterations automatically
-- c.f. the NonRec case above
- in
- (sigs', Rec pairs')
\end{code}
\begin{code}
dmdAnalTopRhs :: CoreExpr -> (StrictSig, CoreExpr)
-- Analyse the RHS and return
-- a) appropriate strictness info
--- b) the unfolding (decorated with stricntess info)
+-- b) the unfolding (decorated with strictness info)
dmdAnalTopRhs rhs
= (sig, rhs2)
where
call_dmd = vanillaCall (exprArity rhs)
- (_, rhs1) = dmdAnal emptySigEnv call_dmd rhs
- (rhs_ty, rhs2) = dmdAnal emptySigEnv call_dmd rhs1
+ (_, rhs1) = dmdAnal (virgin emptySigEnv) call_dmd rhs
+ (rhs_ty, rhs2) = dmdAnal (nonVirgin emptySigEnv) call_dmd rhs1
sig = mkTopSigTy rhs rhs_ty
-- Do two passes; see notes with extendSigsWithLam
-- Otherwise we get bogus CPR info for constructors like
%************************************************************************
\begin{code}
-dmdAnal :: SigEnv -> Demand -> CoreExpr -> (DmdType, CoreExpr)
+dmdAnal :: AnalEnv -> Demand -> CoreExpr -> (DmdType, CoreExpr)
-dmdAnal sigs Abs e = (topDmdType, e)
+dmdAnal _ Abs e = (topDmdType, e)
-dmdAnal sigs dmd e
+dmdAnal env dmd e
| not (isStrictDmd dmd)
= let
- (res_ty, e') = dmdAnal sigs evalDmd e
+ (res_ty, e') = dmdAnal env evalDmd e
in
(deferType res_ty, e')
-- It's important not to analyse e with a lazy demand because
-- evaluation of f in a C(L) demand!
-dmdAnal sigs dmd (Lit lit)
- = (topDmdType, Lit lit)
+dmdAnal _ _ (Lit lit) = (topDmdType, Lit lit)
+dmdAnal _ _ (Type ty) = (topDmdType, Type ty) -- Doesn't happen, in fact
+dmdAnal _ _ (Coercion co) = (topDmdType, Coercion co)
-dmdAnal sigs dmd (Var var)
- = (dmdTransform sigs var dmd, Var var)
+dmdAnal env dmd (Var var)
+ = (dmdTransform env var dmd, Var var)
-dmdAnal sigs dmd (Cast e co)
+dmdAnal env dmd (Cast e co)
= (dmd_ty, Cast e' co)
where
- (dmd_ty, e') = dmdAnal sigs dmd' e
- to_co = snd (coercionKind co)
+ (dmd_ty, e') = dmdAnal env dmd' e
+ to_co = pSnd (coercionKind co)
dmd'
- | Just (tc, args) <- splitTyConApp_maybe to_co
+ | Just (tc, _) <- splitTyConApp_maybe to_co
, isRecursiveTyCon tc = evalDmd
| otherwise = dmd
-- This coerce usually arises from a recursive
-- inside recursive products -- we might not reach
-- a fixpoint. So revert to a vanilla Eval demand
-dmdAnal sigs dmd (Note n e)
+dmdAnal env dmd (Note n e)
= (dmd_ty, Note n e')
where
- (dmd_ty, e') = dmdAnal sigs dmd e
+ (dmd_ty, e') = dmdAnal env dmd e
-dmdAnal sigs dmd (App fun (Type ty))
+dmdAnal env dmd (App fun (Type ty))
= (fun_ty, App fun' (Type ty))
where
+ (fun_ty, fun') = dmdAnal env dmd fun
+
+dmdAnal sigs dmd (App fun (Coercion co))
+ = (fun_ty, App fun' (Coercion co))
+ where
(fun_ty, fun') = dmdAnal sigs dmd fun
-- Lots of the other code is there to make this
-- beautiful, compositional, application rule :-)
-dmdAnal sigs dmd e@(App fun arg) -- Non-type arguments
+dmdAnal env dmd (App fun arg) -- Non-type arguments
= let -- [Type arg handled above]
- (fun_ty, fun') = dmdAnal sigs (Call dmd) fun
- (arg_ty, arg') = dmdAnal sigs arg_dmd arg
+ (fun_ty, fun') = dmdAnal env (Call dmd) fun
+ (arg_ty, arg') = dmdAnal env arg_dmd arg
(arg_dmd, res_ty) = splitDmdTy fun_ty
in
(res_ty `bothType` arg_ty, App fun' arg')
-dmdAnal sigs dmd (Lam var body)
+dmdAnal env dmd (Lam var body)
| isTyVar var
= let
- (body_ty, body') = dmdAnal sigs dmd body
+ (body_ty, body') = dmdAnal env dmd body
in
(body_ty, Lam var body')
| Call body_dmd <- dmd -- A call demand: good!
= let
- sigs' = extendSigsWithLam sigs var
- (body_ty, body') = dmdAnal sigs' body_dmd body
- (lam_ty, var') = annotateLamIdBndr body_ty var
+ env' = extendSigsWithLam env var
+ (body_ty, body') = dmdAnal env' body_dmd body
+ (lam_ty, var') = annotateLamIdBndr env body_ty var
in
(lam_ty, Lam var' body')
| otherwise -- Not enough demand on the lambda; but do the body
= let -- anyway to annotate it and gather free var info
- (body_ty, body') = dmdAnal sigs evalDmd body
- (lam_ty, var') = annotateLamIdBndr body_ty var
+ (body_ty, body') = dmdAnal env evalDmd body
+ (lam_ty, var') = annotateLamIdBndr env body_ty var
in
(deferType lam_ty, Lam var' body')
-dmdAnal sigs dmd (Case scrut case_bndr ty [alt@(DataAlt dc,bndrs,rhs)])
- | let tycon = dataConTyCon dc,
- isProductTyCon tycon,
- not (isRecursiveTyCon tycon)
+dmdAnal env dmd (Case scrut case_bndr ty [alt@(DataAlt dc, _, _)])
+ | let tycon = dataConTyCon dc
+ , isProductTyCon tycon
+ , not (isRecursiveTyCon tycon)
= let
- sigs_alt = extendSigEnv NotTopLevel sigs case_bndr case_bndr_sig
- (alt_ty, alt') = dmdAnalAlt sigs_alt dmd alt
+ env_alt = extendAnalEnv NotTopLevel env case_bndr case_bndr_sig
+ (alt_ty, alt') = dmdAnalAlt env_alt dmd alt
(alt_ty1, case_bndr') = annotateBndr alt_ty case_bndr
(_, bndrs', _) = alt'
case_bndr_sig = cprSig
-- x = (a, absent-error)
-- and that'll crash.
-- So at one stage I had:
- -- dead_case_bndr = isAbsentDmd (idNewDemandInfo case_bndr')
+ -- dead_case_bndr = isAbsentDmd (idDemandInfo case_bndr')
-- keepity | dead_case_bndr = Drop
-- | otherwise = Keep
--
-- The insight is, of course, that a demand on y is a demand on the
-- scrutinee, so we need to `both` it with the scrut demand
- alt_dmd = Eval (Prod [idNewDemandInfo b | b <- bndrs', isId b])
+ alt_dmd = Eval (Prod [idDemandInfo b | b <- bndrs', isId b])
scrut_dmd = alt_dmd `both`
- idNewDemandInfo case_bndr'
+ idDemandInfo case_bndr'
- (scrut_ty, scrut') = dmdAnal sigs scrut_dmd scrut
+ (scrut_ty, scrut') = dmdAnal env scrut_dmd scrut
in
(alt_ty1 `bothType` scrut_ty, Case scrut' case_bndr' ty [alt'])
-dmdAnal sigs dmd (Case scrut case_bndr ty alts)
+dmdAnal env dmd (Case scrut case_bndr ty alts)
= let
- (alt_tys, alts') = mapAndUnzip (dmdAnalAlt sigs dmd) alts
- (scrut_ty, scrut') = dmdAnal sigs evalDmd scrut
+ (alt_tys, alts') = mapAndUnzip (dmdAnalAlt env dmd) alts
+ (scrut_ty, scrut') = dmdAnal env evalDmd scrut
(alt_ty, case_bndr') = annotateBndr (foldr1 lubType alt_tys) case_bndr
in
-- pprTrace "dmdAnal:Case" (ppr alts $$ ppr alt_tys)
(alt_ty `bothType` scrut_ty, Case scrut' case_bndr' ty alts')
-dmdAnal sigs dmd (Let (NonRec id rhs) body)
+dmdAnal env dmd (Let (NonRec id rhs) body)
= let
- (sigs', lazy_fv, (id1, rhs')) = dmdAnalRhs NotTopLevel NonRecursive sigs (id, rhs)
- (body_ty, body') = dmdAnal sigs' dmd body
+ (sigs', lazy_fv, (id1, rhs')) = dmdAnalRhs NotTopLevel NonRecursive env (id, rhs)
+ (body_ty, body') = dmdAnal (updSigEnv env sigs') dmd body
(body_ty1, id2) = annotateBndr body_ty id1
body_ty2 = addLazyFVs body_ty1 lazy_fv
in
-- bother to re-analyse the RHS.
(body_ty2, Let (NonRec id2 rhs') body')
-dmdAnal sigs dmd (Let (Rec pairs) body)
+dmdAnal env dmd (Let (Rec pairs) body)
= let
bndrs = map fst pairs
- (sigs', lazy_fv, pairs') = dmdFix NotTopLevel sigs pairs
- (body_ty, body') = dmdAnal sigs' dmd body
+ (sigs', lazy_fv, pairs') = dmdFix NotTopLevel env pairs
+ (body_ty, body') = dmdAnal (updSigEnv env sigs') dmd body
body_ty1 = addLazyFVs body_ty lazy_fv
in
sigs' `seq` body_ty `seq`
(body_ty2, Let (Rec pairs') body')
-dmdAnalAlt sigs dmd (con,bndrs,rhs)
+dmdAnalAlt :: AnalEnv -> Demand -> Alt Var -> (DmdType, Alt Var)
+dmdAnalAlt env dmd (con,bndrs,rhs)
= let
- (rhs_ty, rhs') = dmdAnal sigs dmd rhs
- (alt_ty, bndrs') = annotateBndrs rhs_ty bndrs
+ (rhs_ty, rhs') = dmdAnal env dmd rhs
+ rhs_ty' = addDataConPatDmds con bndrs rhs_ty
+ (alt_ty, bndrs') = annotateBndrs rhs_ty' bndrs
final_alt_ty | io_hack_reqd = alt_ty `lubType` topDmdType
| otherwise = alt_ty
-- ; print len }
io_hack_reqd = con == DataAlt unboxedPairDataCon &&
- idType (head bndrs) `coreEqType` realWorldStatePrimTy
+ idType (head bndrs) `eqType` realWorldStatePrimTy
in
(final_alt_ty, (con, bndrs', rhs'))
+
+addDataConPatDmds :: AltCon -> [Var] -> DmdType -> DmdType
+-- See Note [Add demands for strict constructors]
+addDataConPatDmds DEFAULT _ dmd_ty = dmd_ty
+addDataConPatDmds (LitAlt _) _ dmd_ty = dmd_ty
+addDataConPatDmds (DataAlt con) bndrs dmd_ty
+ = foldr add dmd_ty str_bndrs
+ where
+ add bndr dmd_ty = addVarDmd dmd_ty bndr seqDmd
+ str_bndrs = [ b | (b,s) <- zipEqual "addDataConPatBndrs"
+ (filter isId bndrs)
+ (dataConRepStrictness con)
+ , isMarkedStrict s ]
+\end{code}
+
+Note [Add demands for strict constructors]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Consider this program (due to Roman):
+
+ data X a = X !a
+
+ foo :: X Int -> Int -> Int
+ foo (X a) n = go 0
+ where
+ go i | i < n = a + go (i+1)
+ | otherwise = 0
+
+We want the worker for 'foo' too look like this:
+
+ $wfoo :: Int# -> Int# -> Int#
+
+with the first argument unboxed, so that it is not eval'd each time
+around the loop (which would otherwise happen, since 'foo' is not
+strict in 'a'. It is sound for the wrapper to pass an unboxed arg
+because X is strict, so its argument must be evaluated. And if we
+*don't* pass an unboxed argument, we can't even repair it by adding a
+`seq` thus:
+
+ foo (X a) n = a `seq` go 0
+
+because the seq is discarded (very early) since X is strict!
+
+There is the usual danger of reboxing, which as usual we ignore. But
+if X is monomorphic, and has an UNPACK pragma, then this optimisation
+is even more important. We don't want the wrapper to rebox an unboxed
+argument, and pass an Int to $wfoo!
+
+
+%************************************************************************
+%* *
+ Demand transformer
+%* *
+%************************************************************************
+
+\begin{code}
+dmdTransform :: AnalEnv -- The strictness environment
+ -> Id -- The function
+ -> Demand -- The demand on the function
+ -> DmdType -- The demand type of the function in this context
+ -- Returned DmdEnv includes the demand on
+ -- this function plus demand on its free variables
+
+dmdTransform env var dmd
+
+------ DATA CONSTRUCTOR
+ | isDataConWorkId var -- Data constructor
+ = let
+ StrictSig dmd_ty = idStrictness var -- It must have a strictness sig
+ DmdType _ _ con_res = dmd_ty
+ arity = idArity var
+ in
+ if arity == call_depth then -- Saturated, so unleash the demand
+ let
+ -- Important! If we Keep the constructor application, then
+ -- we need the demands the constructor places (always lazy)
+ -- If not, we don't need to. For example:
+ -- f p@(x,y) = (p,y) -- S(AL)
+ -- g a b = f (a,b)
+ -- It's vital that we don't calculate Absent for a!
+ dmd_ds = case res_dmd of
+ Box (Eval ds) -> mapDmds box ds
+ Eval ds -> ds
+ _ -> Poly Top
+
+ -- ds can be empty, when we are just seq'ing the thing
+ -- If so we must make up a suitable bunch of demands
+ arg_ds = case dmd_ds of
+ Poly d -> replicate arity d
+ Prod ds -> ASSERT( ds `lengthIs` arity ) ds
+
+ in
+ mkDmdType emptyDmdEnv arg_ds con_res
+ -- Must remember whether it's a product, hence con_res, not TopRes
+ else
+ topDmdType
+
+------ IMPORTED FUNCTION
+ | isGlobalId var, -- Imported function
+ let StrictSig dmd_ty = idStrictness var
+ = -- pprTrace "strict-sig" (ppr var $$ ppr dmd_ty) $
+ if dmdTypeDepth dmd_ty <= call_depth then -- Saturated, so unleash the demand
+ dmd_ty
+ else
+ topDmdType
+
+------ LOCAL LET/REC BOUND THING
+ | Just (StrictSig dmd_ty, top_lvl) <- lookupSigEnv env var
+ = let
+ fn_ty | dmdTypeDepth dmd_ty <= call_depth = dmd_ty
+ | otherwise = deferType dmd_ty
+ -- NB: it's important to use deferType, and not just return topDmdType
+ -- Consider let { f x y = p + x } in f 1
+ -- The application isn't saturated, but we must nevertheless propagate
+ -- a lazy demand for p!
+ in
+ if isTopLevel top_lvl then fn_ty -- Don't record top level things
+ else addVarDmd fn_ty var dmd
+
+------ LOCAL NON-LET/REC BOUND THING
+ | otherwise -- Default case
+ = unitVarDmd var dmd
+
+ where
+ (call_depth, res_dmd) = splitCallDmd dmd
\end{code}
%************************************************************************
\begin{code}
dmdFix :: TopLevelFlag
- -> SigEnv -- Does not include bindings for this binding
+ -> AnalEnv -- Does not include bindings for this binding
-> [(Id,CoreExpr)]
-> (SigEnv, DmdEnv,
[(Id,CoreExpr)]) -- Binders annotated with stricness info
-dmdFix top_lvl sigs orig_pairs
- = loop 1 initial_sigs orig_pairs
+dmdFix top_lvl env orig_pairs
+ = loop 1 initial_env orig_pairs
where
bndrs = map fst orig_pairs
- initial_sigs = extendSigEnvList sigs [(id, (initialSig id, top_lvl)) | id <- bndrs]
+ initial_env = addInitialSigs top_lvl env bndrs
loop :: Int
- -> SigEnv -- Already contains the current sigs
+ -> AnalEnv -- Already contains the current sigs
-> [(Id,CoreExpr)]
-> (SigEnv, DmdEnv, [(Id,CoreExpr)])
- loop n sigs pairs
+ loop n env pairs
+ = -- pprTrace "dmd loop" (ppr n <+> ppr bndrs $$ ppr env) $
+ loop' n env pairs
+
+ loop' n env pairs
| found_fixpoint
= (sigs', lazy_fv, pairs')
- -- Note: use pairs', not pairs. pairs' is the result of
+ -- Note: return pairs', not pairs. pairs' is the result of
-- processing the RHSs with sigs (= sigs'), whereas pairs
-- is the result of processing the RHSs with the *previous*
-- iteration of sigs.
- | n >= 10 = pprTrace "dmdFix loop" (ppr n <+> (vcat
- [ text "Sigs:" <+> ppr [(id,lookup sigs id, lookup sigs' id) | (id,_) <- pairs],
- text "env:" <+> ppr (ufmToList sigs),
- text "binds:" <+> pprCoreBinding (Rec pairs)]))
- (emptySigEnv, lazy_fv, orig_pairs) -- Safe output
- -- The lazy_fv part is really important! orig_pairs has no strictness
- -- info, including nothing about free vars. But if we have
- -- letrec f = ....y..... in ...f...
- -- where 'y' is free in f, we must record that y is mentioned,
- -- otherwise y will get recorded as absent altogether
-
- | otherwise = loop (n+1) sigs' pairs'
+ | n >= 10
+ = pprTrace "dmdFix loop" (ppr n <+> (vcat
+ [ text "Sigs:" <+> ppr [ (id,lookupVarEnv sigs id, lookupVarEnv sigs' id)
+ | (id,_) <- pairs],
+ text "env:" <+> ppr env,
+ text "binds:" <+> pprCoreBinding (Rec pairs)]))
+ (sigEnv env, lazy_fv, orig_pairs) -- Safe output
+ -- The lazy_fv part is really important! orig_pairs has no strictness
+ -- info, including nothing about free vars. But if we have
+ -- letrec f = ....y..... in ...f...
+ -- where 'y' is free in f, we must record that y is mentioned,
+ -- otherwise y will get recorded as absent altogether
+
+ | otherwise
+ = loop (n+1) (nonVirgin sigs') pairs'
where
+ sigs = sigEnv env
found_fixpoint = all (same_sig sigs sigs') bndrs
- -- Use the new signature to do the next pair
+
+ ((sigs',lazy_fv), pairs') = mapAccumL my_downRhs (sigs, emptyDmdEnv) pairs
+ -- mapAccumL: Use the new signature to do the next pair
-- The occurrence analyser has arranged them in a good order
-- so this can significantly reduce the number of iterations needed
- ((sigs',lazy_fv), pairs') = mapAccumL (my_downRhs top_lvl) (sigs, emptyDmdEnv) pairs
- my_downRhs top_lvl (sigs,lazy_fv) (id,rhs)
- = -- pprTrace "downRhs {" (ppr id <+> (ppr old_sig))
- -- (new_sig `seq`
- -- pprTrace "downRhsEnd" (ppr id <+> ppr new_sig <+> char '}' )
- ((sigs', lazy_fv'), pair')
- -- )
- where
- (sigs', lazy_fv1, pair') = dmdAnalRhs top_lvl Recursive sigs (id,rhs)
- lazy_fv' = plusUFM_C both lazy_fv lazy_fv1
- -- old_sig = lookup sigs id
- -- new_sig = lookup sigs' id
+ my_downRhs (sigs,lazy_fv) (id,rhs)
+ = ((sigs', lazy_fv'), pair')
+ where
+ (sigs', lazy_fv1, pair') = dmdAnalRhs top_lvl Recursive (updSigEnv env sigs) (id,rhs)
+ lazy_fv' = plusVarEnv_C both lazy_fv lazy_fv1
same_sig sigs sigs' var = lookup sigs var == lookup sigs' var
lookup sigs var = case lookupVarEnv sigs var of
Just (sig,_) -> sig
-
- -- Get an initial strictness signature from the Id
- -- itself. That way we make use of earlier iterations
- -- of the fixpoint algorithm. (Cunning plan.)
- -- Note that the cunning plan extends to the DmdEnv too,
- -- since it is part of the strictness signature
-initialSig id = idNewStrictness_maybe id `orElse` botSig
+ Nothing -> pprPanic "dmdFix" (ppr var)
dmdAnalRhs :: TopLevelFlag -> RecFlag
- -> SigEnv -> (Id, CoreExpr)
+ -> AnalEnv -> (Id, CoreExpr)
-> (SigEnv, DmdEnv, (Id, CoreExpr))
-- Process the RHS of the binding, add the strictness signature
-- to the Id, and augment the environment with the signature as well.
-dmdAnalRhs top_lvl rec_flag sigs (id, rhs)
+dmdAnalRhs top_lvl rec_flag env (id, rhs)
= (sigs', lazy_fv, (id', rhs'))
where
arity = idArity id -- The idArity should be up to date
-- The simplifier was run just beforehand
- (rhs_dmd_ty, rhs') = dmdAnal sigs (vanillaCall arity) rhs
+ (rhs_dmd_ty, rhs') = dmdAnal env (vanillaCall arity) rhs
(lazy_fv, sig_ty) = WARN( arity /= dmdTypeDepth rhs_dmd_ty && not (exprIsTrivial rhs), ppr id )
-- The RHS can be eta-reduced to just a variable,
-- in which case we should not complain.
mkSigTy top_lvl rec_flag id rhs rhs_dmd_ty
- id' = id `setIdNewStrictness` sig_ty
- sigs' = extendSigEnv top_lvl sigs id sig_ty
+ id' = id `setIdStrictness` sig_ty
+ sigs' = extendSigEnv top_lvl (sigEnv env) id sig_ty
\end{code}
+
%************************************************************************
%* *
\subsection{Strictness signatures and types}
mkSigTy top_lvl rec_flag id rhs dmd_ty
= mk_sig_ty never_inline thunk_cpr_ok rhs dmd_ty
where
- never_inline = isNeverActive (idInlinePragma id)
- maybe_id_dmd = idNewDemandInfo_maybe id
+ never_inline = isNeverActive (idInlineActivation id)
+ maybe_id_dmd = idDemandInfo_maybe id
-- Is Nothing the first time round
thunk_cpr_ok
by dmdAnalTopBind.
+Note [NOINLINE and strictness]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The strictness analyser used to have a HACK which ensured that NOINLNE
+things were not strictness-analysed. The reason was unsafePerformIO.
+Left to itself, the strictness analyser would discover this strictness
+for unsafePerformIO:
+ unsafePerformIO: C(U(AV))
+But then consider this sub-expression
+ unsafePerformIO (\s -> let r = f x in
+ case writeIORef v r s of (# s1, _ #) ->
+ (# s1, r #)
+The strictness analyser will now find that r is sure to be eval'd,
+and may then hoist it out. This makes tests/lib/should_run/memo002
+deadlock.
+
+Solving this by making all NOINLINE things have no strictness info is overkill.
+In particular, it's overkill for runST, which is perfectly respectable.
+Consider
+ f x = runST (return x)
+This should be strict in x.
+
+So the new plan is to define unsafePerformIO using the 'lazy' combinator:
+
+ unsafePerformIO (IO m) = lazy (case m realWorld# of (# _, r #) -> r)
+
+Remember, 'lazy' is a wired-in identity-function Id, of type a->a, which is
+magically NON-STRICT, and is inlined after strictness analysis. So
+unsafePerformIO will look non-strict, and that's what we want.
+
+Now we don't need the hack in the strictness analyser. HOWEVER, this
+decision does mean that even a NOINLINE function is not entirely
+opaque: some aspect of its implementation leaks out, notably its
+strictness. For example, if you have a function implemented by an
+error stub, but which has RULES, you may want it not to be eliminated
+in favour of error!
+
+
\begin{code}
-mk_sig_ty never_inline thunk_cpr_ok rhs (DmdType fv dmds res)
+mk_sig_ty :: Bool -> Bool -> CoreExpr
+ -> DmdType -> (DmdEnv, StrictSig)
+mk_sig_ty _never_inline thunk_cpr_ok rhs (DmdType fv dmds res)
= (lazy_fv, mkStrictSig dmd_ty)
+ -- Re unused never_inline, see Note [NOINLINE and strictness]
where
dmd_ty = DmdType strict_fv final_dmds res'
res' = case res of
RetCPR | ignore_cpr_info -> TopRes
- other -> res
+ _ -> res
ignore_cpr_info = not (exprIsHNF rhs || thunk_cpr_ok)
\end{code}
nonAbsentArgs :: [Demand] -> Int
nonAbsentArgs [] = 0
nonAbsentArgs (Abs : ds) = nonAbsentArgs ds
-nonAbsentArgs (d : ds) = 1 + nonAbsentArgs ds
+nonAbsentArgs (_ : ds) = 1 + nonAbsentArgs ds
\end{code}
%************************************************************************
\begin{code}
-splitDmdTy :: DmdType -> (Demand, DmdType)
--- Split off one function argument
--- We already have a suitable demand on all
--- free vars, so no need to add more!
-splitDmdTy (DmdType fv (dmd:dmds) res_ty) = (dmd, DmdType fv dmds res_ty)
-splitDmdTy ty@(DmdType fv [] res_ty) = (resTypeArgDmd res_ty, ty)
-\end{code}
-
-\begin{code}
+unitVarDmd :: Var -> Demand -> DmdType
unitVarDmd var dmd = DmdType (unitVarEnv var dmd) [] TopRes
-addVarDmd top_lvl dmd_ty@(DmdType fv ds res) var dmd
- | isTopLevel top_lvl = dmd_ty -- Don't record top level things
- | otherwise = DmdType (extendVarEnv fv var dmd) ds res
+addVarDmd :: DmdType -> Var -> Demand -> DmdType
+addVarDmd (DmdType fv ds res) var dmd
+ = DmdType (extendVarEnv_C both fv var dmd) ds res
+addLazyFVs :: DmdType -> DmdEnv -> DmdType
addLazyFVs (DmdType fv ds res) lazy_fvs
= DmdType both_fv1 ds res
where
- both_fv = (plusUFM_C both fv lazy_fvs)
+ both_fv = plusVarEnv_C both fv lazy_fvs
both_fv1 = modifyEnv (isBotRes res) (`both` Bot) lazy_fvs fv both_fv
-- This modifyEnv is vital. Consider
-- let f = \x -> (x,y)
-- No effect on the argument demands
annotateBndr dmd_ty@(DmdType fv ds res) var
| isTyVar var = (dmd_ty, var)
- | otherwise = (DmdType fv' ds res, setIdNewDemandInfo var dmd)
+ | otherwise = (DmdType fv' ds res, setIdDemandInfo var dmd)
where
(fv', dmd) = removeFV fv var res
+annotateBndrs :: DmdType -> [Var] -> (DmdType, [Var])
annotateBndrs = mapAccumR annotateBndr
-annotateLamIdBndr dmd_ty@(DmdType fv ds res) id
+annotateLamIdBndr :: AnalEnv
+ -> DmdType -- Demand type of body
+ -> Id -- Lambda binder
+ -> (DmdType, -- Demand type of lambda
+ Id) -- and binder annotated with demand
+
+annotateLamIdBndr env (DmdType fv ds res) id
-- For lambdas we add the demand to the argument demands
-- Only called for Ids
= ASSERT( isId id )
- (DmdType fv' (hacked_dmd:ds) res, setIdNewDemandInfo id hacked_dmd)
+ (final_ty, setIdDemandInfo id hacked_dmd)
where
+ -- Watch out! See note [Lambda-bound unfoldings]
+ final_ty = case maybeUnfoldingTemplate (idUnfolding id) of
+ Nothing -> main_ty
+ Just unf -> main_ty `bothType` unf_ty
+ where
+ (unf_ty, _) = dmdAnal env dmd unf
+
+ main_ty = DmdType fv' (hacked_dmd:ds) res
+
(fv', dmd) = removeFV fv id res
hacked_dmd = argDemand dmd
-- This call to argDemand is vital, because otherwise we label
-- And then the simplifier things the 'B' is a strict demand
-- and evaluates the (error "oops"). Sigh
+removeFV :: DmdEnv -> Var -> DmdResult -> (DmdEnv, Demand)
removeFV fv id res = (fv', zapUnlifted id dmd)
where
fv' = fv `delVarEnv` id
deflt | isBotRes res = Bot
| otherwise = Abs
+zapUnlifted :: Id -> Demand -> Demand
-- For unlifted-type variables, we are only
-- interested in Bot/Abs/Box Abs
-zapUnlifted is Bot = Bot
-zapUnlifted id Abs = Abs
-zapUnlifted id dmd | isUnLiftedType (idType id) = lazyDmd
- | otherwise = dmd
+zapUnlifted id dmd
+ = case dmd of
+ _ | isCoVarType ty -> lazyDmd -- For coercions, ignore str/abs totally
+ Bot -> Bot
+ Abs -> Abs
+ _ | isUnLiftedType ty -> lazyDmd -- For unlifted types, ignore strictness
+ | otherwise -> dmd
+ where
+ ty = idType id
\end{code}
+Note [Lamba-bound unfoldings]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+We allow a lambda-bound variable to carry an unfolding, a facility that is used
+exclusively for join points; see Note [Case binders and join points]. If so,
+we must be careful to demand-analyse the RHS of the unfolding! Example
+ \x. \y{=Just x}. <body>
+Then if <body> uses 'y', then transitively it uses 'x', and we must not
+forget that fact, otherwise we might make 'x' absent when it isn't.
+
+
%************************************************************************
%* *
\subsection{Strictness signatures}
%************************************************************************
\begin{code}
-type SigEnv = VarEnv (StrictSig, TopLevelFlag)
- -- We use the SigEnv to tell us whether to
+data AnalEnv
+ = AE { ae_sigs :: SigEnv
+ , ae_virgin :: Bool } -- True on first iteration only
+ -- See Note [Initialising strictness]
+ -- We use the se_env to tell us whether to
-- record info about a variable in the DmdEnv
-- We do so if it's a LocalId, but not top-level
--
-- The DmdEnv gives the demand on the free vars of the function
-- when it is given enough args to satisfy the strictness signature
-emptySigEnv = emptyVarEnv
+type SigEnv = VarEnv (StrictSig, TopLevelFlag)
+
+instance Outputable AnalEnv where
+ ppr (AE { ae_sigs = env, ae_virgin = virgin })
+ = ptext (sLit "AE") <+> braces (vcat
+ [ ptext (sLit "ae_virgin =") <+> ppr virgin
+ , ptext (sLit "ae_sigs =") <+> ppr env ])
+
+emptySigEnv :: SigEnv
+emptySigEnv = emptyVarEnv
+
+sigEnv :: AnalEnv -> SigEnv
+sigEnv = ae_sigs
+
+updSigEnv :: AnalEnv -> SigEnv -> AnalEnv
+updSigEnv env sigs = env { ae_sigs = sigs }
+
+extendAnalEnv :: TopLevelFlag -> AnalEnv -> Id -> StrictSig -> AnalEnv
+extendAnalEnv top_lvl env var sig
+ = env { ae_sigs = extendSigEnv top_lvl (ae_sigs env) var sig }
extendSigEnv :: TopLevelFlag -> SigEnv -> Id -> StrictSig -> SigEnv
-extendSigEnv top_lvl env var sig = extendVarEnv env var (sig, top_lvl)
+extendSigEnv top_lvl sigs var sig = extendVarEnv sigs var (sig, top_lvl)
+
+lookupSigEnv :: AnalEnv -> Id -> Maybe (StrictSig, TopLevelFlag)
+lookupSigEnv env id = lookupVarEnv (ae_sigs env) id
+
+addInitialSigs :: TopLevelFlag -> AnalEnv -> [Id] -> AnalEnv
+-- See Note [Initialising strictness]
+addInitialSigs top_lvl env@(AE { ae_sigs = sigs, ae_virgin = virgin }) ids
+ = env { ae_sigs = extendVarEnvList sigs [ (id, (init_sig id, top_lvl))
+ | id <- ids ] }
+ where
+ init_sig | virgin = \_ -> botSig
+ | otherwise = idStrictness
-extendSigEnvList = extendVarEnvList
+virgin, nonVirgin :: SigEnv -> AnalEnv
+virgin sigs = AE { ae_sigs = sigs, ae_virgin = True }
+nonVirgin sigs = AE { ae_sigs = sigs, ae_virgin = False }
-extendSigsWithLam :: SigEnv -> Id -> SigEnv
--- Extend the SigEnv when we meet a lambda binder
+extendSigsWithLam :: AnalEnv -> Id -> AnalEnv
+-- Extend the AnalEnv when we meet a lambda binder
-- If the binder is marked demanded with a product demand, then give it a CPR
-- signature, because in the likely event that this is a lambda on a fn defn
-- [we only use this when the lambda is being consumed with a call demand],
-- definitely has product type, else we may get over-optimistic
-- CPR results (e.g. from \x -> x!).
-extendSigsWithLam sigs id
- = case idNewDemandInfo_maybe id of
- Nothing -> extendVarEnv sigs id (cprSig, NotTopLevel)
+extendSigsWithLam env id
+ = case idDemandInfo_maybe id of
+ Nothing -> extendAnalEnv NotTopLevel env id cprSig
-- Optimistic in the Nothing case;
-- See notes [CPR-AND-STRICTNESS]
- Just (Eval (Prod ds)) -> extendVarEnv sigs id (cprSig, NotTopLevel)
- other -> sigs
-
-
-dmdTransform :: SigEnv -- The strictness environment
- -> Id -- The function
- -> Demand -- The demand on the function
- -> DmdType -- The demand type of the function in this context
- -- Returned DmdEnv includes the demand on
- -- this function plus demand on its free variables
-
-dmdTransform sigs var dmd
-
------- DATA CONSTRUCTOR
- | isDataConWorkId var -- Data constructor
- = let
- StrictSig dmd_ty = idNewStrictness var -- It must have a strictness sig
- DmdType _ _ con_res = dmd_ty
- arity = idArity var
- in
- if arity == call_depth then -- Saturated, so unleash the demand
- let
- -- Important! If we Keep the constructor application, then
- -- we need the demands the constructor places (always lazy)
- -- If not, we don't need to. For example:
- -- f p@(x,y) = (p,y) -- S(AL)
- -- g a b = f (a,b)
- -- It's vital that we don't calculate Absent for a!
- dmd_ds = case res_dmd of
- Box (Eval ds) -> mapDmds box ds
- Eval ds -> ds
- other -> Poly Top
-
- -- ds can be empty, when we are just seq'ing the thing
- -- If so we must make up a suitable bunch of demands
- arg_ds = case dmd_ds of
- Poly d -> replicate arity d
- Prod ds -> ASSERT( ds `lengthIs` arity ) ds
-
- in
- mkDmdType emptyDmdEnv arg_ds con_res
- -- Must remember whether it's a product, hence con_res, not TopRes
- else
- topDmdType
-
------- IMPORTED FUNCTION
- | isGlobalId var, -- Imported function
- let StrictSig dmd_ty = idNewStrictness var
- = if dmdTypeDepth dmd_ty <= call_depth then -- Saturated, so unleash the demand
- dmd_ty
- else
- topDmdType
+ Just (Eval (Prod _)) -> extendAnalEnv NotTopLevel env id cprSig
+ _ -> env
+\end{code}
------- LOCAL LET/REC BOUND THING
- | Just (StrictSig dmd_ty, top_lvl) <- lookupVarEnv sigs var
- = let
- fn_ty | dmdTypeDepth dmd_ty <= call_depth = dmd_ty
- | otherwise = deferType dmd_ty
- -- NB: it's important to use deferType, and not just return topDmdType
- -- Consider let { f x y = p + x } in f 1
- -- The application isn't saturated, but we must nevertheless propagate
- -- a lazy demand for p!
- in
- addVarDmd top_lvl fn_ty var dmd
+Note [Initialising strictness]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Our basic plan is to initialise the strictness of each Id in
+a recursive group to "bottom", and find a fixpoint from there.
+However, this group A might be inside an *enclosing* recursive
+group B, in which case we'll do the entire fixpoint shebang on A
+for each iteration of B.
------- LOCAL NON-LET/REC BOUND THING
- | otherwise -- Default case
- = unitVarDmd var dmd
+To speed things up, we initialise each iteration of B from the result
+of the last one, which is neatly recorded in each binder. That way we
+make use of earlier iterations of the fixpoint algorithm. (Cunning
+plan.)
- where
- (call_depth, res_dmd) = splitCallDmd dmd
-\end{code}
+But on the *first* iteration we want to *ignore* the current strictness
+of the Id, and start from "bottom". Nowadays the Id can have a current
+strictness, because interface files record strictness for nested bindings.
+To know when we are in the first iteration, we look at the ae_virgin
+field of the AnalEnv.
%************************************************************************
%* *
-\subsection{Demands}
+ Demands
%* *
%************************************************************************
\begin{code}
+splitDmdTy :: DmdType -> (Demand, DmdType)
+-- Split off one function argument
+-- We already have a suitable demand on all
+-- free vars, so no need to add more!
+splitDmdTy (DmdType fv (dmd:dmds) res_ty) = (dmd, DmdType fv dmds res_ty)
+splitDmdTy ty@(DmdType _ [] res_ty) = (resTypeArgDmd res_ty, ty)
+
splitCallDmd :: Demand -> (Int, Demand)
splitCallDmd (Call d) = case splitCallDmd d of
(n, r) -> (n+1, r)
-- Notice that we throw away info about both arguments and results
-- For example, f = let ... in \x -> x
-- We don't want to get a stricness type V->T for f.
- -- Peter??
deferEnv :: DmdEnv -> DmdEnv
deferEnv fv = mapVarEnv defer fv
-- The 'Defer' demands are just Lazy at function boundaries
-- Ugly! Ask John how to improve it.
argDemand Top = lazyDmd
-argDemand (Defer d) = lazyDmd
+argDemand (Defer _) = lazyDmd
argDemand (Eval ds) = Eval (mapDmds argDemand ds)
argDemand (Box Bot) = evalDmd
argDemand (Box d) = box (argDemand d)
\begin{code}
-------------------------
+lubType :: DmdType -> DmdType -> DmdType
-- Consider (if x then y else []) with demand V
-- Then the first branch gives {y->V} and the second
-- *implicitly* has {y->A}. So we must put {y->(V `lub` A)}
lubType (DmdType fv1 ds1 r1) (DmdType fv2 ds2 r2)
= DmdType lub_fv2 (lub_ds ds1 ds2) (r1 `lubRes` r2)
where
- lub_fv = plusUFM_C lub fv1 fv2
+ lub_fv = plusVarEnv_C lub fv1 fv2
lub_fv1 = modifyEnv (not (isBotRes r1)) absLub fv2 fv1 lub_fv
lub_fv2 = modifyEnv (not (isBotRes r2)) absLub fv1 fv2 lub_fv1
-- lub is the identity for Bot
lub_ds [] ds2 = map (resTypeArgDmd r1 `lub`) ds2
-----------------------------------
+bothType :: DmdType -> DmdType -> DmdType
-- (t1 `bothType` t2) takes the argument/result info from t1,
-- using t2 just for its free-var info
-- NB: Don't forget about r2! It might be BotRes, which is
-- a bottom demand on all the in-scope variables.
-- Peter: can this be done more neatly?
-bothType (DmdType fv1 ds1 r1) (DmdType fv2 ds2 r2)
+bothType (DmdType fv1 ds1 r1) (DmdType fv2 _ r2)
= DmdType both_fv2 ds1 (r1 `bothRes` r2)
where
- both_fv = plusUFM_C both fv1 fv2
+ both_fv = plusVarEnv_C both fv1 fv2
both_fv1 = modifyEnv (isBotRes r1) (`both` Bot) fv2 fv1 both_fv
both_fv2 = modifyEnv (isBotRes r2) (`both` Bot) fv1 fv2 both_fv1
-- both is the identity for Abs
\begin{code}
+lubRes :: DmdResult -> DmdResult -> DmdResult
lubRes BotRes r = r
lubRes r BotRes = r
lubRes RetCPR RetCPR = RetCPR
-lubRes r1 r2 = TopRes
+lubRes _ _ = TopRes
+bothRes :: DmdResult -> DmdResult -> DmdResult
-- If either diverges, the whole thing does
-- Otherwise take CPR info from the first
-bothRes r1 BotRes = BotRes
-bothRes r1 r2 = r1
+bothRes _ BotRes = BotRes
+bothRes r1 _ = r1
\end{code}
\begin{code}
-- Assume: dom(env) includes dom(Env1) and dom(Env2)
modifyEnv need_to_modify zapper env1 env2 env
- | need_to_modify = foldr zap env (keysUFM (env1 `minusUFM` env2))
+ | need_to_modify = foldr zap env (varEnvKeys (env1 `minusUFM` env2))
| otherwise = env
where
zap uniq env = addToUFM_Directly env uniq (zapper current_val)
lub Bot d2 = d2
lub Abs d2 = absLub d2
-lub Top d2 = Top
+lub Top _ = Top
lub (Defer ds1) d2 = defer (Eval ds1 `lub` d2)
lub (Call d1) (Call d2) = Call (d1 `lub` d2)
lub d1@(Call _) (Box d2) = d1 `lub` d2 -- Just strip the box
-lub d1@(Call _) d2@(Eval _) = d2 -- Presumably seq or vanilla eval
+lub (Call _) d2@(Eval _) = d2 -- Presumably seq or vanilla eval
lub d1@(Call _) d2 = d2 `lub` d1 -- Bot, Abs, Top
-- For the Eval case, we use these approximation rules
lub (Box d1) (Box d2) = box (d1 `lub` d2)
lub d1@(Box _) d2 = d2 `lub` d1
+lubs :: Demands -> Demands -> Demands
lubs ds1 ds2 = zipWithDmds lub ds1 ds2
---------------------
+box :: Demand -> Demand
-- box is the smart constructor for Box
-- It computes <B,bot> & d
-- INVARIANT: (Box d) => d = Bot, Abs, Eval
defer (Defer ds) = Defer ds
defer (Eval ds) = deferEval ds
+deferEval :: Demands -> Demand
-- deferEval ds = defer (Eval ds)
deferEval ds | allTop ds = Top
| otherwise = Defer ds
absLub (Eval ds) = Defer (absLubs ds) -- Or (Defer ds)?
absLub (Defer ds) = Defer (absLubs ds) -- Or (Defer ds)?
+absLubs :: Demands -> Demands
absLubs = mapDmds absLub
---------------
both Abs d2 = d2
-both Bot Bot = Bot
-both Bot Abs = Bot
-both Bot (Eval ds) = Eval (mapDmds (`both` Bot) ds)
- -- Consider
- -- f x = error x
- -- From 'error' itself we get demand Bot on x
- -- From the arg demand on x we get
- -- x :-> evalDmd = Box (Eval (Poly Abs))
- -- So we get Bot `both` Box (Eval (Poly Abs))
- -- = Seq Keep (Poly Bot)
- --
- -- Consider also
- -- f x = if ... then error (fst x) else fst x
- -- Then we get (Eval (Box Bot, Bot) `lub` Eval (SA))
- -- = Eval (SA)
- -- which is what we want.
-both Bot d = errDmd
-
-both Top Bot = errDmd
-both Top Abs = Top
-both Top Top = Top
+-- Note [Bottom demands]
+both Bot Bot = Bot
+both Bot Abs = Bot
+both Bot (Eval ds) = Eval (mapDmds (`both` Bot) ds)
+both Bot (Defer ds) = Eval (mapDmds (`both` Bot) ds)
+both Bot _ = errDmd
+
+both Top Bot = errDmd
+both Top Abs = Top
+both Top Top = Top
both Top (Box d) = Box d
both Top (Call d) = Call d
both Top (Eval ds) = Eval (mapDmds (`both` Top) ds)
both (Box d1) (Box d2) = box (d1 `both` d2)
both (Box d1) d2@(Call _) = box (d1 `both` d2)
both (Box d1) d2@(Eval _) = box (d1 `both` d2)
-both (Box d1) (Defer d2) = Box d1
+both (Box d1) (Defer _) = Box d1
both d1@(Box _) d2 = d2 `both` d1
both (Call d1) (Call d2) = Call (d1 `both` d2)
-both (Call d1) (Eval ds2) = Call d1 -- Could do better for (Poly Bot)?
-both (Call d1) (Defer ds2) = Call d1 -- Ditto
-both d1@(Call _) d2 = d1 `both` d1
+both (Call d1) (Eval _) = Call d1 -- Could do better for (Poly Bot)?
+both (Call d1) (Defer _) = Call d1 -- Ditto
+both d1@(Call _) d2 = d2 `both` d1
-both (Eval ds1) (Eval ds2) = Eval (ds1 `boths` ds2)
-both (Eval ds1) (Defer ds2) = Eval (ds1 `boths` mapDmds defer ds2)
-both d1@(Eval ds1) d2 = d2 `both` d1
+both (Eval ds1) (Eval ds2) = Eval (ds1 `boths` ds2)
+both (Eval ds1) (Defer ds2) = Eval (ds1 `boths` mapDmds defer ds2)
+both d1@(Eval _) d2 = d2 `both` d1
-both (Defer ds1) (Defer ds2) = deferEval (ds1 `boths` ds2)
-both d1@(Defer ds1) d2 = d2 `both` d1
+both (Defer ds1) (Defer ds2) = deferEval (ds1 `boths` ds2)
+both d1@(Defer _) d2 = d2 `both` d1
+boths :: Demands -> Demands -> Demands
boths ds1 ds2 = zipWithDmds both ds1 ds2
\end{code}
+Note [Bottom demands]
+~~~~~~~~~~~~~~~~~~~~~
+Consider
+ f x = error x
+From 'error' itself we get demand Bot on x
+From the arg demand on x we get
+ x :-> evalDmd = Box (Eval (Poly Abs))
+So we get Bot `both` Box (Eval (Poly Abs))
+ = Seq Keep (Poly Bot)
+
+Consider also
+ f x = if ... then error (fst x) else fst x
+Then we get (Eval (Box Bot, Bot) `lub` Eval (SA))
+ = Eval (SA)
+which is what we want.
+
+Consider also
+ f x = error [fst x]
+Then we get
+ x :-> Bot `both` Defer [SA]
+and we want the Bot demand to cancel out the Defer
+so that we get Eval [SA]. Otherwise we'd have the odd
+situation that
+ f x = error (fst x) -- Strictness U(SA)b
+ g x = error ('y':fst x) -- Strictness Tb
-
-%************************************************************************
-%* *
-\subsection{Miscellaneous
-%* *
-%************************************************************************
-
-
-\begin{code}
-#ifdef OLD_STRICTNESS
-get_changes binds = vcat (map get_changes_bind binds)
-
-get_changes_bind (Rec pairs) = vcat (map get_changes_pr pairs)
-get_changes_bind (NonRec id rhs) = get_changes_pr (id,rhs)
-
-get_changes_pr (id,rhs)
- = get_changes_var id $$ get_changes_expr rhs
-
-get_changes_var var
- | isId var = get_changes_str var $$ get_changes_dmd var
- | otherwise = empty
-
-get_changes_expr (Type t) = empty
-get_changes_expr (Var v) = empty
-get_changes_expr (Lit l) = empty
-get_changes_expr (Note n e) = get_changes_expr e
-get_changes_expr (App e1 e2) = get_changes_expr e1 $$ get_changes_expr e2
-get_changes_expr (Lam b e) = {- get_changes_var b $$ -} get_changes_expr e
-get_changes_expr (Let b e) = get_changes_bind b $$ get_changes_expr e
-get_changes_expr (Case e b a) = get_changes_expr e $$ {- get_changes_var b $$ -} vcat (map get_changes_alt a)
-
-get_changes_alt (con,bs,rhs) = {- vcat (map get_changes_var bs) $$ -} get_changes_expr rhs
-
-get_changes_str id
- | new_better && old_better = empty
- | new_better = message "BETTER"
- | old_better = message "WORSE"
- | otherwise = message "INCOMPARABLE"
- where
- message word = text word <+> text "strictness for" <+> ppr id <+> info
- info = (text "Old" <+> ppr old) $$ (text "New" <+> ppr new)
- new = squashSig (idNewStrictness id) -- Don't report spurious diffs that the old
- -- strictness analyser can't track
- old = newStrictnessFromOld (idName id) (idArity id) (idStrictness id) (idCprInfo id)
- old_better = old `betterStrictness` new
- new_better = new `betterStrictness` old
-
-get_changes_dmd id
- | isUnLiftedType (idType id) = empty -- Not useful
- | new_better && old_better = empty
- | new_better = message "BETTER"
- | old_better = message "WORSE"
- | otherwise = message "INCOMPARABLE"
- where
- message word = text word <+> text "demand for" <+> ppr id <+> info
- info = (text "Old" <+> ppr old) $$ (text "New" <+> ppr new)
- new = squashDmd (argDemand (idNewDemandInfo id)) -- To avoid spurious improvements
- -- A bit of a hack
- old = newDemand (idDemandInfo id)
- new_better = new `betterDemand` old
- old_better = old `betterDemand` new
-
-betterStrictness :: StrictSig -> StrictSig -> Bool
-betterStrictness (StrictSig t1) (StrictSig t2) = betterDmdType t1 t2
-
-betterDmdType t1 t2 = (t1 `lubType` t2) == t2
-
-betterDemand :: Demand -> Demand -> Bool
--- If d1 `better` d2, and d2 `better` d2, then d1==d2
-betterDemand d1 d2 = (d1 `lub` d2) == d2
-
-squashSig (StrictSig (DmdType fv ds res))
- = StrictSig (DmdType emptyDmdEnv (map squashDmd ds) res)
- where
- -- squash just gets rid of call demands
- -- which the old analyser doesn't track
-squashDmd (Call d) = evalDmd
-squashDmd (Box d) = Box (squashDmd d)
-squashDmd (Eval ds) = Eval (mapDmds squashDmd ds)
-squashDmd (Defer ds) = Defer (mapDmds squashDmd ds)
-squashDmd d = d
-#endif
-\end{code}
projects / ghc-hetmet.git / blobdiff