import SimplUtils ( findDefault )
import CostCentre ( noCCS )
import Id ( Id, mkSysLocal, idType, getIdStrictness, idUnique, isExportedId,
- externallyVisibleId, setIdUnique, idName, getIdDemandInfo
+ externallyVisibleId, setIdUnique, idName, getIdDemandInfo, setIdType
)
import Var ( Var, varType, modifyIdInfo )
import IdInfo ( setDemandInfo, StrictnessInfo(..) )
import TysPrim ( intPrimTy )
import UniqSupply -- all of it, really
import Util ( lengthExceeds )
-import BasicTypes ( TopLevelFlag(..) )
+import BasicTypes ( TopLevelFlag(..), isNotTopLevel )
+import CmdLineOpts ( opt_D_verbose_stg2stg )
+import UniqSet ( emptyUniqSet )
import Maybes
import Outputable
\end{code}
type StgEnv = IdEnv Id
data StgFloatBind = NoBindF
- | NonRecF Id StgExpr RhsDemand
| RecF [(Id, StgRhs)]
+ | NonRecF
+ Id
+ StgExpr -- *Can* be a StgLam
+ RhsDemand
+ [StgFloatBind]
+
+-- The interesting one is the NonRecF
+-- NonRecF x rhs demand binds
+-- means
+-- x = let binds in rhs
+-- (or possibly case etc if x demand is strict)
+-- The binds are kept separate so they can be floated futher
+-- if appropriate
\end{code}
A @RhsDemand@ gives the demand on an RHS: strict (@isStrictDem@) and
later. For this pass
we use @bOGUS_LVs@ and @bOGUS_FVs@ as placeholders.
+When printing out the Stg we need non-bottom values in these
+locations.
+
\begin{code}
bOGUS_LVs :: StgLiveVars
-bOGUS_LVs = panic "bOGUS_LVs" -- emptyUniqSet (used when pprTracing)
+bOGUS_LVs | opt_D_verbose_stg2stg = emptyUniqSet
+ | otherwise =panic "bOGUS_LVs"
bOGUS_FVs :: [Id]
-bOGUS_FVs = panic "bOGUS_FVs" -- [] (ditto)
+bOGUS_FVs | opt_D_verbose_stg2stg = []
+ | otherwise = panic "bOGUS_FVs"
\end{code}
\begin{code}
coreBindsToStg env (b:bs)
= coreBindToStg TopLevel env b `thenUs` \ (bind_spec, new_env) ->
coreBindsToStg new_env bs `thenUs` \ new_bs ->
- let
- res_bs = case bind_spec of
- NonRecF bndr rhs dem -> ASSERT2( not (isStrictDem dem) && not (isUnLiftedType (idType bndr)),
- ppr b )
- -- No top-level cases!
- StgNonRec bndr (exprToRhs dem rhs) : new_bs
- RecF prs -> StgRec prs : new_bs
- NoBindF -> pprTrace "topCoreBindsToStg" (ppr b) new_bs
- in
- returnUs res_bs
+ case bind_spec of
+ NonRecF bndr rhs dem floats
+ -> ASSERT2( not (isStrictDem dem) &&
+ not (isUnLiftedType (idType bndr)),
+ ppr b ) -- No top-level cases!
+
+ mkStgBinds floats rhs `thenUs` \ new_rhs ->
+ returnUs (StgNonRec bndr (exprToRhs dem TopLevel new_rhs)
+ : new_bs)
+ -- Keep all the floats inside...
+ -- Some might be cases etc
+ -- We might want to revisit this decision
+
+ RecF prs -> returnUs (StgRec prs : new_bs)
+ NoBindF -> pprTrace "topCoreBindsToStg" (ppr b) $
+ returnUs new_bs
\end{code}
coreBindToStg :: TopLevelFlag -> StgEnv -> CoreBind -> UniqSM (StgFloatBind, StgEnv)
coreBindToStg top_lev env (NonRec binder rhs)
- = coreExprToStg env rhs dem `thenUs` \ stg_rhs ->
- case stg_rhs of
- StgApp var [] | not (isExportedId binder)
+ = coreExprToStgFloat env rhs dem `thenUs` \ (floats, stg_rhs) ->
+ case (floats, stg_rhs) of
+ ([], StgApp var []) | not (isExportedId binder)
-> returnUs (NoBindF, extendVarEnv env binder var)
-- A trivial binding let x = y in ...
-- can arise if postSimplExpr floats a NoRep literal out
-- occur; e.g. an exported user binding f = g
other -> newLocalId top_lev env binder `thenUs` \ (new_env, new_binder) ->
- returnUs (NonRecF new_binder stg_rhs dem, new_env)
+ returnUs (NonRecF new_binder stg_rhs dem floats, new_env)
where
dem = bdrDem binder
returnUs (RecF (binders' `zip` stg_rhss), env')
where
binders = map fst pairs
- do_rhs env (bndr,rhs) = coreRhsToStg env rhs (bdrDem bndr)
+ do_rhs env (bndr,rhs) = coreExprToStgFloat env rhs dem `thenUs` \ (floats, stg_expr) ->
+ mkStgBinds floats stg_expr `thenUs` \ stg_expr' ->
+ -- NB: stg_expr' might still be a StgLam (and we want that)
+ returnUs (exprToRhs dem top_lev stg_expr')
+ where
+ dem = bdrDem bndr
\end{code}
%************************************************************************
\begin{code}
-coreRhsToStg :: StgEnv -> CoreExpr -> RhsDemand -> UniqSM StgRhs
-coreRhsToStg env rhs dem
- = coreExprToStg env rhs dem `thenUs` \ stg_expr ->
- returnUs (exprToRhs dem stg_expr)
-
-exprToRhs :: RhsDemand -> StgExpr -> StgRhs
-exprToRhs dem (StgLet (StgNonRec var1 rhs) (StgApp var2 []))
- | var1 == var2
- = rhs
- -- This curious stuff is to unravel what a lambda turns into
- -- We have to do it this way, rather than spot a lambda in the
- -- incoming rhs. Why? Because trivial bindings might conceal
- -- what the rhs is actually like.
+exprToRhs :: RhsDemand -> TopLevelFlag -> StgExpr -> StgRhs
+exprToRhs dem _ (StgLam _ bndrs body)
+ = ASSERT( not (null bndrs) )
+ StgRhsClosure noCCS
+ stgArgOcc
+ noSRT
+ bOGUS_FVs
+ ReEntrant -- binders is non-empty
+ bndrs
+ body
{-
We reject the following candidates for 'static constructor'dom:
constructors (ala C++ static class constructors) which will
then be run at load time to fix up static closures.
-}
-exprToRhs dem (StgCon (DataCon con) args _)
- | not is_dynamic &&
- all (not.is_lit_lit) args = StgRhsCon noCCS con args
+exprToRhs dem toplev (StgCon (DataCon con) args _)
+ | isNotTopLevel toplev ||
+ (not is_dynamic &&
+ all (not.is_lit_lit) args) = StgRhsCon noCCS con args
where
is_dynamic = isDynCon con || any (isDynArg) args
Literal l -> isLitLitLit l
_ -> False
-exprToRhs dem expr
+exprToRhs dem _ expr
= StgRhsClosure noCCS -- No cost centre (ToDo?)
stgArgOcc -- safe
noSRT -- figure out later
-- This is where we arrange that a non-trivial argument is let-bound
coreArgToStg env (arg,dem)
- | isStrictDem dem || isUnLiftedType arg_ty
- -- Strict, so float all the binds out
- = coreExprToStgFloat env arg dem `thenUs` \ (binds, arg') ->
+ = coreExprToStgFloat env arg dem `thenUs` \ (floats, arg') ->
case arg' of
- StgCon con [] _ | isWHNFCon con -> returnUs (binds, StgConArg con)
- StgApp v [] -> returnUs (binds, StgVarArg v)
- other -> newStgVar arg_ty `thenUs` \ v ->
- returnUs (binds ++ [NonRecF v arg' dem], StgVarArg v)
- | otherwise
- -- Lazy
- = coreExprToStgFloat env arg dem `thenUs` \ (binds, arg') ->
- case (binds, arg') of
- ([], StgCon con [] _) | isWHNFCon con -> returnUs ([], StgConArg con)
- ([], StgApp v []) -> returnUs ([], StgVarArg v)
-
- -- A non-trivial argument: we must let-bind it
- -- We don't do the case part here... we leave that to mkStgLets
- (_, other) -> newStgVar arg_ty `thenUs` \ v ->
- returnUs ([NonRecF v (mkStgBinds binds arg') dem], StgVarArg v)
+ StgCon con [] _ -> returnUs (floats, StgConArg con)
+ StgApp v [] -> returnUs (floats, StgVarArg v)
+ other -> newStgVar arg_ty `thenUs` \ v ->
+ returnUs ([NonRecF v arg' dem floats], StgVarArg v)
where
arg_ty = coreExprType arg
\end{code}
\begin{code}
coreExprToStg :: StgEnv -> CoreExpr -> RhsDemand -> UniqSM StgExpr
coreExprToStg env expr dem
- = coreExprToStgFloat env expr dem `thenUs` \ (binds,stg_expr) ->
- returnUs (mkStgBinds binds stg_expr)
+ = coreExprToStgFloat env expr dem `thenUs` \ (binds,stg_expr) ->
+ mkStgBinds binds stg_expr `thenUs` \ stg_expr' ->
+ deStgLam stg_expr'
\end{code}
%************************************************************************
-- given by RhsDemand, and is solely used ot figure out the usage
-- of constructor args: if the constructor is used once, then so are
-- its arguments. The strictness info in RhsDemand isn't used.
+
+-- The StgExpr returned *can* be an StgLam
\end{code}
Simple cases first
returnUs (new_bind:floats, stg_body)
\end{code}
-Covert core @scc@ expression directly to STG @scc@ expression.
+Convert core @scc@ expression directly to STG @scc@ expression.
\begin{code}
coreExprToStgFloat env (Note (SCC cc) expr) dem
\begin{code}
coreExprToStgFloat env expr@(Lam _ _) dem
= let
+ expr_ty = coreExprType expr
(binders, body) = collectBinders expr
id_binders = filter isId binders
body_dem = trace "coreExprToStg: approximating body_dem in Lam"
safeDem
in
- newLocalIds NotTopLevel env id_binders `thenUs` \ (env', binders') ->
- coreExprToStg env' body body_dem `thenUs` \ stg_body ->
-
if null id_binders then -- It was all type/usage binders; tossed
- returnUs ([], stg_body)
+ coreExprToStgFloat env body dem
else
- case stg_body of
-
- -- if the body reduced to a lambda too...
- (StgLet (StgNonRec var (StgRhsClosure cc bi srt fvs uf args body))
- (StgApp var' []))
- | var == var' ->
- returnUs ([],
- -- ToDo: make this a float, but we need
- -- a lambda form for that! Sigh
- StgLet (StgNonRec var (StgRhsClosure noCCS
- stgArgOcc
- noSRT
- bOGUS_FVs
- ReEntrant
- (binders' ++ args)
- body))
- (StgApp var []))
-
- other ->
+ -- At least some value binders
+ newLocalIds NotTopLevel env id_binders `thenUs` \ (env', binders') ->
+ coreExprToStgFloat env' body body_dem `thenUs` \ (floats, stg_body) ->
+ mkStgBinds floats stg_body `thenUs` \ stg_body' ->
+
+ case stg_body' of
+ StgLam ty lam_bndrs lam_body ->
+ -- If the body reduced to a lambda too, join them up
+ returnUs ([], StgLam expr_ty (binders' ++ lam_bndrs) lam_body)
- -- We must let-bind the lambda
- newStgVar (coreExprType expr) `thenUs` \ var ->
- returnUs ([],
- -- Ditto
- StgLet (StgNonRec var (StgRhsClosure noCCS
- stgArgOcc
- noSRT
- bOGUS_FVs
- ReEntrant -- binders is non-empty
- binders'
- stg_body))
- (StgApp var []))
+ other ->
+ -- Body didn't reduce to a lambda, so return one
+ returnUs ([], StgLam expr_ty binders' stg_body')
\end{code}
+
%************************************************************************
%* *
\subsubsection[coreToStg-applications]{Applications}
\begin{code}
coreExprToStgFloat env expr@(App _ _) dem
= let
- (fun,rads,_,_) = collect_args expr
- ads = reverse rads
+ (fun,rads,_,ss) = collect_args expr
+ ads = reverse rads
+ final_ads | null ss = ads
+ | otherwise = zap ads -- Too few args to satisfy strictness info
+ -- so we have to ignore all the strictness info
+ -- e.g. + (error "urk")
+ -- Here, we can't evaluate the arg strictly,
+ -- because this partial application might be seq'd
in
- coreArgsToStg env ads `thenUs` \ (binds, stg_args) ->
+ coreArgsToStg env final_ads `thenUs` \ (arg_floats, stg_args) ->
-- Now deal with the function
case (fun, stg_args) of
(Var fun_id, _) -> -- A function Id, so do an StgApp; it's ok if
-- there are no arguments.
- returnUs (binds,
+ returnUs (arg_floats,
StgApp (stgLookup env fun_id) stg_args)
(non_var_fun, []) -> -- No value args, so recurse into the function
- ASSERT( null binds )
+ ASSERT( null arg_floats )
coreExprToStgFloat env non_var_fun dem
other -> -- A non-variable applied to things; better let-bind it.
- newStgVar (coreExprType fun) `thenUs` \ fun_id ->
- coreExprToStg env fun onceDem `thenUs` \ stg_fun ->
- returnUs (NonRecF fun_id stg_fun onceDem : binds,
+ newStgVar (coreExprType fun) `thenUs` \ fun_id ->
+ coreExprToStgFloat env fun onceDem `thenUs` \ (fun_floats, stg_fun) ->
+ returnUs (NonRecF fun_id stg_fun onceDem fun_floats : arg_floats,
StgApp fun_id stg_args)
where
collect_args (App fun (Type tyarg)) = let (the_fun,ads,fun_ty,ss) = collect_args fun
in (the_fun,ads,applyTy fun_ty tyarg,ss)
collect_args (App fun arg)
- = case ss of
- [] -> -- Strictness info has run out
- (the_fun, (arg, mkDemTy wwLazy arg_ty) : zap ads, res_ty, repeat wwLazy)
- (ss1:ss_rest) -> -- Enough strictness info
- (the_fun, (arg, mkDemTy ss1 arg_ty) : ads, res_ty, ss_rest)
+ = (the_fun, (arg, mkDemTy ss1 arg_ty) : ads, res_ty, ss_rest)
where
+ (ss1, ss_rest) = case ss of
+ (ss1:ss_rest) -> (ss1, ss_rest)
+ [] -> (wwLazy, [])
(the_fun, ads, fun_ty, ss) = collect_args fun
(arg_ty, res_ty) = expectJust "coreExprToStgFloat:collect_args" $
splitFunTy_maybe fun_ty
dems' = zipWith mkDem stricts onces
args' = filter isValArg args
in
- coreArgsToStg env (zip args' dems') `thenUs` \ (binds, stg_atoms) ->
+ coreArgsToStg env (zip args' dems') `thenUs` \ (arg_floats, stg_atoms) ->
-- YUK YUK: must unique if present
(case con of
_ -> returnUs con
) `thenUs` \ con' ->
- returnUs (binds, StgCon con' stg_atoms (coreExprType expr))
+ returnUs (arg_floats, StgCon con' stg_atoms (coreExprType expr))
\end{code}
%* *
%************************************************************************
+First, two special cases. We mangle cases involving
+ par# and seq#
+inthe scrutinee.
+
+Up to this point, seq# will appear like this:
+
+ case seq# e of
+ 0# -> seqError#
+ _ -> <stuff>
+
+This code comes from an unfolding for 'seq' in Prelude.hs.
+The 0# branch is purely to bamboozle the strictness analyser.
+For example, if <stuff> is strict in x, and there was no seqError#
+branch, the strictness analyser would conclude that the whole expression
+was strict in x, and perhaps evaluate x first -- but that would be a DISASTER.
+
+Now that the evaluation order is safe, we translate this into
+
+ case e of
+ _ -> ...
+
+This used to be done in the post-simplification phase, but we need
+unfoldings involving seq# to appear unmangled in the interface file,
+hence we do this mangling here.
+
+Similarly, par# has an unfolding in PrelConc.lhs that makes it show
+up like this:
+
+ case par# e of
+ 0# -> rhs
+ _ -> parError#
+
+
+ ==>
+ case par# e of
+ _ -> rhs
+
+fork# isn't handled like this - it's an explicit IO operation now.
+The reason is that fork# returns a ThreadId#, which gets in the
+way of the above scheme. And anyway, IO is the only guaranteed
+way to enforce ordering --SDM.
+
+
+\begin{code}
+coreExprToStgFloat env
+ (Case scrut@(Con (PrimOp SeqOp) [Type ty, e]) bndr alts) dem
+ = coreExprToStgFloat env (Case e new_bndr [(DEFAULT,[],default_rhs)]) dem
+ where
+ new_bndr = setIdType bndr ty
+ (other_alts, maybe_default) = findDefault alts
+ Just default_rhs = maybe_default
+
+coreExprToStgFloat env
+ (Case scrut@(Con (PrimOp ParOp) args) bndr alts) dem
+ | maybeToBool maybe_default
+ = coreExprToStgFloat env scrut (bdrDem bndr) `thenUs` \ (binds, scrut') ->
+ newEvaldLocalId env bndr `thenUs` \ (env', bndr') ->
+ coreExprToStg env' default_rhs dem `thenUs` \ default_rhs' ->
+ returnUs (binds, mkStgCase scrut' bndr' (StgPrimAlts (idType bndr) [] (StgBindDefault default_rhs')))
+ where
+ (other_alts, maybe_default) = findDefault alts
+ Just default_rhs = maybe_default
+\end{code}
+
+Now for normal case expressions...
+
\begin{code}
coreExprToStgFloat env (Case scrut bndr alts) dem
= coreExprToStgFloat env scrut (bdrDem bndr) `thenUs` \ (binds, scrut') ->
\begin{code}
-mkStgBinds :: [StgFloatBind] -> StgExpr -> StgExpr
-mkStgBinds binds body = foldr mkStgBind body binds
+-- Stg doesn't have a lambda *expression*,
+deStgLam (StgLam ty bndrs body) = mkStgLamExpr ty bndrs body
+deStgLam expr = returnUs expr
+
+mkStgLamExpr ty bndrs body
+ = ASSERT( not (null bndrs) )
+ newStgVar ty `thenUs` \ fn ->
+ returnUs (StgLet (StgNonRec fn lam_closure) (StgApp fn []))
+ where
+ lam_closure = StgRhsClosure noCCS
+ stgArgOcc
+ noSRT
+ bOGUS_FVs
+ ReEntrant -- binders is non-empty
+ bndrs
+ body
+
+mkStgBinds :: [StgFloatBind]
+ -> StgExpr -- *Can* be a StgLam
+ -> UniqSM StgExpr -- *Can* be a StgLam
+
+mkStgBinds [] body = returnUs body
+mkStgBinds (b:bs) body
+ = deStgLam body `thenUs` \ body' ->
+ go (b:bs) body'
+ where
+ go [] body = returnUs body
+ go (b:bs) body = go bs body `thenUs` \ body' ->
+ mkStgBind b body'
-mkStgBind NoBindF body = body
-mkStgBind (RecF prs) body = StgLet (StgRec prs) body
+-- The 'body' arg of mkStgBind can't be a StgLam
+mkStgBind NoBindF body = returnUs body
+mkStgBind (RecF prs) body = returnUs (StgLet (StgRec prs) body)
-mkStgBind (NonRecF bndr rhs dem) body
+mkStgBind (NonRecF bndr rhs dem floats) body
#ifdef DEBUG
-- We shouldn't get let or case of the form v=w
= case rhs of
StgApp v [] -> pprTrace "mkStgLet" (ppr bndr <+> ppr v)
- (mk_stg_let bndr rhs dem body)
- other -> mk_stg_let bndr rhs dem body
+ (mk_stg_let bndr rhs dem floats body)
+ other -> mk_stg_let bndr rhs dem floats body
-mk_stg_let bndr rhs dem body
+mk_stg_let bndr rhs dem floats body
#endif
- | isUnLiftedType bndr_ty -- Use a case/PrimAlts
+ | isUnLiftedType bndr_ty -- Use a case/PrimAlts
= ASSERT( not (isUnboxedTupleType bndr_ty) )
+ mkStgBinds floats $
mkStgCase rhs bndr (StgPrimAlts bndr_ty [] (StgBindDefault body))
- | isStrictDem dem && not_whnf -- Use an case/AlgAlts
- = mkStgCase rhs bndr (StgAlgAlts bndr_ty [] (StgBindDefault body))
-
- | otherwise
- = ASSERT( not (isUnLiftedType bndr_ty) )
- StgLet (StgNonRec bndr expr_rhs) body
+ | is_whnf
+ = if is_strict then
+ -- Strict let with WHNF rhs
+ mkStgBinds floats $
+ StgLet (StgNonRec bndr (exprToRhs dem NotTopLevel rhs)) body
+ else
+ -- Lazy let with WHNF rhs; float until we find a strict binding
+ let
+ (floats_out, floats_in) = splitFloats floats
+ in
+ mkStgBinds floats_in rhs `thenUs` \ new_rhs ->
+ mkStgBinds floats_out $
+ StgLet (StgNonRec bndr (exprToRhs dem NotTopLevel new_rhs)) body
+
+ | otherwise -- Not WHNF
+ = if is_strict then
+ -- Strict let with non-WHNF rhs
+ mkStgBinds floats $
+ mkStgCase rhs bndr (StgAlgAlts bndr_ty [] (StgBindDefault body))
+ else
+ -- Lazy let with non-WHNF rhs, so keep the floats in the RHS
+ mkStgBinds floats rhs `thenUs` \ new_rhs ->
+ returnUs (StgLet (StgNonRec bndr (exprToRhs dem NotTopLevel new_rhs)) body)
+
where
- bndr_ty = idType bndr
- expr_rhs = exprToRhs dem rhs
- not_whnf = case expr_rhs of
- StgRhsClosure _ _ _ _ _ args _ -> null args
- StgRhsCon _ _ _ -> False
-
-mkStgCase (StgLet bind expr) bndr alts
- = StgLet bind (mkStgCase expr bndr alts)
+ bndr_ty = idType bndr
+ is_strict = isStrictDem dem
+ is_whnf = case rhs of
+ StgCon _ _ _ -> True
+ StgLam _ _ _ -> True
+ other -> False
+
+-- Split at the first strict binding
+splitFloats fs@(NonRecF _ _ dem _ : _)
+ | isStrictDem dem = ([], fs)
+
+splitFloats (f : fs) = case splitFloats fs of
+ (fs_out, fs_in) -> (f : fs_out, fs_in)
+
+splitFloats [] = ([], [])
+
+
mkStgCase scrut bndr alts
- = StgCase scrut bOGUS_LVs bOGUS_LVs bndr noSRT alts
+ = ASSERT( case scrut of { StgLam _ _ _ -> False; other -> True } )
+ -- We should never find
+ -- case (\x->e) of { ... }
+ -- The simplifier eliminates such things
+ StgCase scrut bOGUS_LVs bOGUS_LVs bndr noSRT alts
\end{code}
projects / ghc-hetmet.git / blobdiff