%
-% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
+% (c) The GRASP/AQUA Project, Glasgow University, 1993-1998
%
-%************************************************************************
-%* *
-\section[CoreToStg]{Converting core syntax to STG syntax}
-%* *
-%************************************************************************
+\section[CoreToStg]{Converts Core to STG Syntax}
-Convert a @CoreSyntax@ program to a @StgSyntax@ program.
+And, as we have the info in hand, we may convert some lets to
+let-no-escapes.
\begin{code}
-module CoreToStg ( topCoreBindsToStg ) where
+module CoreToStg ( coreToStg, coreExprToStg ) where
#include "HsVersions.h"
-import CoreSyn -- input
-import StgSyn -- output
-
-import CoreUtils ( coreExprType )
-import SimplUtils ( findDefault )
+import CoreSyn
+import CoreFVs
+import CoreUtils
+import SimplUtils
+import StgSyn
+
+import Type
+import TyCon ( isAlgTyCon )
+import Id
+import IdInfo
+import DataCon
import CostCentre ( noCCS )
-import Id ( Id, mkSysLocal, idType, getIdStrictness, idUnique, isExportedId, mkVanillaId,
- externallyVisibleId, setIdUnique, idName, getIdDemandInfo, setIdType
- )
-import Var ( Var, varType, modifyIdInfo )
-import IdInfo ( setDemandInfo, StrictnessInfo(..), zapIdInfoForStg )
-import UsageSPUtils ( primOpUsgTys )
-import DataCon ( DataCon, dataConName, dataConId )
-import Demand ( Demand, isStrict, wwStrict, wwLazy )
-import Name ( Name, nameModule, isLocallyDefinedName, setNameUnique )
-import Module ( isDynamicModule )
-import Const ( Con(..), Literal(..), isLitLitLit, conStrictness, isWHNFCon )
+import VarSet
import VarEnv
-import PrimOp ( PrimOp(..), primOpUsg, primOpSig )
-import Type ( isUnLiftedType, isUnboxedTupleType, Type, splitFunTy_maybe,
- UsageAnn(..), tyUsg, applyTy, mkUsgTy, repType, seqType )
-import TysPrim ( intPrimTy )
-import UniqSupply -- all of it, really
-import Util ( lengthExceeds )
-import BasicTypes ( TopLevelFlag(..), isNotTopLevel )
-import CmdLineOpts ( opt_D_verbose_stg2stg, opt_UsageSPOn )
-import UniqSet ( emptyUniqSet )
-import Maybes
+import DataCon ( dataConWrapId )
+import IdInfo ( OccInfo(..) )
+import PrimOp ( PrimOp(..), ccallMayGC )
+import TysPrim ( foreignObjPrimTyCon )
+import Maybes ( maybeToBool, orElse )
+import Name ( getOccName )
+import Module ( Module )
+import OccName ( occNameUserString )
+import BasicTypes ( TopLevelFlag(..), isNotTopLevel )
+import CmdLineOpts ( DynFlags )
import Outputable
-\end{code}
-
-
- *************************************************
- *************** OVERVIEW *********************
- *************************************************
-
-
-The business of this pass is to convert Core to Stg. On the way it
-does some important transformations:
-
-1. We discard type lambdas and applications. In so doing we discard
- "trivial" bindings such as
- x = y t1 t2
- where t1, t2 are types
-
-2. We get the program into "A-normal form". In particular:
-
- f E ==> let x = E in f x
- OR ==> case E of x -> f x
-
- where E is a non-trivial expression.
- Which transformation is used depends on whether f is strict or not.
- [Previously the transformation to case used to be done by the
- simplifier, but it's better done here. It does mean that f needs
- to have its strictness info correct!.]
-
- Similarly, convert any unboxed let's into cases.
- [I'm experimenting with leaving 'ok-for-speculation' rhss in let-form
- right up to this point.]
-
-3. We clone all local binders. The code generator uses the uniques to
- name chunks of code for thunks, so it's important that the names used
- are globally unique, not simply not-in-scope, which is all that
- the simplifier ensures.
-
-
-NOTE THAT:
-
-* We don't pin on correct arities any more, because they can be mucked up
- by the lambda lifter. In particular, the lambda lifter can take a local
- letrec-bound variable and make it a lambda argument, which shouldn't have
- an arity. So SetStgVarInfo sets arities now.
-
-* We do *not* pin on the correct free/live var info; that's done later.
- Instead we use bOGUS_LVS and _FVS as a placeholder.
-
-[Quite a bit of stuff that used to be here has moved
- to tidyCorePgm (SimplCore.lhs) SLPJ Nov 96]
+import PprCore
+infixr 9 `thenLne`, `thenLne_`
+\end{code}
%************************************************************************
%* *
-\subsection[coreToStg-programs]{Converting a core program and core bindings}
+\subsection[live-vs-free-doc]{Documentation}
%* *
%************************************************************************
-March 98: We keep a small environment to give all locally bound
-Names new unique ids, since the code generator assumes that binders
-are unique across a module. (Simplifier doesn't maintain this
-invariant any longer.)
+(There is other relevant documentation in codeGen/CgLetNoEscape.)
+
+The actual Stg datatype is decorated with {\em live variable}
+information, as well as {\em free variable} information. The two are
+{\em not} the same. Liveness is an operational property rather than a
+semantic one. A variable is live at a particular execution point if
+it can be referred to {\em directly} again. In particular, a dead
+variable's stack slot (if it has one):
+\begin{enumerate}
+\item
+should be stubbed to avoid space leaks, and
+\item
+may be reused for something else.
+\end{enumerate}
+
+There ought to be a better way to say this. Here are some examples:
+\begin{verbatim}
+ let v = [q] \[x] -> e
+ in
+ ...v... (but no q's)
+\end{verbatim}
+
+Just after the `in', v is live, but q is dead. If the whole of that
+let expression was enclosed in a case expression, thus:
+\begin{verbatim}
+ case (let v = [q] \[x] -> e in ...v...) of
+ alts[...q...]
+\end{verbatim}
+(ie @alts@ mention @q@), then @q@ is live even after the `in'; because
+we'll return later to the @alts@ and need it.
+
+Let-no-escapes make this a bit more interesting:
+\begin{verbatim}
+ let-no-escape v = [q] \ [x] -> e
+ in
+ ...v...
+\end{verbatim}
+Here, @q@ is still live at the `in', because @v@ is represented not by
+a closure but by the current stack state. In other words, if @v@ is
+live then so is @q@. Furthermore, if @e@ mentions an enclosing
+let-no-escaped variable, then {\em its} free variables are also live
+if @v@ is.
-A binder to be floated out becomes an @StgFloatBind@.
+%************************************************************************
+%* *
+\subsection[binds-StgVarInfo]{Setting variable info: top-level, binds, RHSs}
+%* *
+%************************************************************************
\begin{code}
-type StgEnv = IdEnv Id
-
-data StgFloatBind = NoBindF
- | 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
+coreToStg :: DynFlags -> Module -> [CoreBind] -> IO [StgBinding]
+coreToStg dflags this_mod pgm
+ = return (fst (initLne (coreTopBindsToStg pgm)))
+
+coreExprToStg :: CoreExpr -> StgExpr
+coreExprToStg expr
+ = new_expr where (new_expr,_,_) = initLne (coreToStgExpr expr)
+
+-- For top-level guys, we basically aren't worried about this
+-- live-variable stuff; we do need to keep adding to the environment
+-- as we step through the bindings (using @extendVarEnv@).
+
+coreTopBindsToStg :: [CoreBind] -> LneM ([StgBinding], FreeVarsInfo)
+
+coreTopBindsToStg [] = returnLne ([], emptyFVInfo)
+coreTopBindsToStg (bind:binds)
+ = let
+ binders = bindersOf bind
+ env_extension = binders `zip` repeat how_bound
+ how_bound = LetrecBound True {- top level -}
+ emptyVarSet
+ in
+
+ extendVarEnvLne env_extension (
+ coreTopBindsToStg binds `thenLne` \ (binds', fv_binds) ->
+ coreTopBindToStg binders fv_binds bind `thenLne` \ (bind', fv_bind) ->
+ returnLne (
+ (bind' : binds'),
+ (fv_binds `unionFVInfo` fv_bind) `minusFVBinders` binders
+ )
+ )
+
+
+coreTopBindToStg
+ :: [Id] -- New binders (with correct arity)
+ -> FreeVarsInfo -- Info about the body
+ -> CoreBind
+ -> LneM (StgBinding, FreeVarsInfo)
+
+coreTopBindToStg [binder] body_fvs (NonRec _ rhs)
+ = coreToStgRhs body_fvs TopLevel (binder,rhs) `thenLne` \ (rhs2, fvs, _) ->
+ returnLne (StgNonRec binder rhs2, fvs)
+
+coreTopBindToStg binders body_fvs (Rec pairs)
+ = fixLne (\ ~(_, rec_rhs_fvs) ->
+ let scope_fvs = unionFVInfo body_fvs rec_rhs_fvs
+ in
+ mapAndUnzip3Lne (coreToStgRhs scope_fvs TopLevel) pairs
+ `thenLne` \ (rhss2, fvss, _) ->
+ let fvs = unionFVInfos fvss
+ in
+ returnLne (StgRec (binders `zip` rhss2), fvs)
+ )
\end{code}
-A @RhsDemand@ gives the demand on an RHS: strict (@isStrictDem@) and
-thus case-bound, or if let-bound, at most once (@isOnceDem@) or
-otherwise.
-
\begin{code}
-data RhsDemand = RhsDemand { isStrictDem :: Bool, -- True => used at least once
- isOnceDem :: Bool -- True => used at most once
- }
-
-mkDem :: Demand -> Bool -> RhsDemand
-mkDem strict once = RhsDemand (isStrict strict) once
-
-mkDemTy :: Demand -> Type -> RhsDemand
-mkDemTy strict ty = RhsDemand (isStrict strict) (isOnceTy ty)
-
-isOnceTy :: Type -> Bool
-isOnceTy ty
- =
-#ifdef USMANY
- opt_UsageSPOn && -- can't expect annotations if -fusagesp is off
+coreToStgRhs
+ :: FreeVarsInfo -- Free var info for the scope of the binding
+ -> TopLevelFlag
+ -> (Id,CoreExpr)
+ -> LneM (StgRhs, FreeVarsInfo, EscVarsSet)
+
+coreToStgRhs scope_fv_info top (binder, rhs)
+ = coreToStgExpr rhs `thenLne` \ (new_rhs, rhs_fvs, rhs_escs) ->
+ case new_rhs of
+
+ StgLam _ bndrs body
+ -> let binder_info = lookupFVInfo scope_fv_info binder
+ in returnLne (StgRhsClosure noCCS
+ binder_info
+ noSRT
+ (getFVs rhs_fvs)
+ ReEntrant
+ bndrs
+ body,
+ rhs_fvs, rhs_escs)
+
+ StgConApp con args
+ | isNotTopLevel top || not (isDllConApp con args)
+ -> returnLne (StgRhsCon noCCS con args, rhs_fvs, rhs_escs)
+
+ _other_expr
+ -> let binder_info = lookupFVInfo scope_fv_info binder
+ in returnLne (StgRhsClosure noCCS
+ binder_info
+ noSRT
+ (getFVs rhs_fvs)
+ (updatable [] new_rhs)
+ []
+ new_rhs,
+ rhs_fvs, rhs_escs
+ )
+
+updatable args body | null args && isPAP body = ReEntrant
+ | otherwise = Updatable
+{- ToDo:
+ upd = if isOnceDem dem
+ then (if isNotTop toplev
+ then SingleEntry -- HA! Paydirt for "dem"
+ else
+#ifdef DEBUG
+ trace "WARNING: SE CAFs unsupported, forcing UPD instead" $
#endif
- case tyUsg ty of
- UsOnce -> True
- UsMany -> False
- UsVar uv -> pprPanic "CoreToStg: unexpected uvar annot:" (ppr uv)
-
-bdrDem :: Id -> RhsDemand
-bdrDem id = mkDem (getIdDemandInfo id) (isOnceTy (idType id))
-
-safeDem, onceDem :: RhsDemand
-safeDem = RhsDemand False False -- always safe to use this
-onceDem = RhsDemand False True -- used at most once
+ Updatable)
+ else Updatable
+ -- For now we forbid SingleEntry CAFs; they tickle the
+ -- ASSERT in rts/Storage.c line 215 at newCAF() re mut_link,
+ -- and I don't understand why. There's only one SE_CAF (well,
+ -- only one that tickled a great gaping bug in an earlier attempt
+ -- at ClosureInfo.getEntryConvention) in the whole of nofib,
+ -- specifically Main.lvl6 in spectral/cryptarithm2.
+ -- So no great loss. KSW 2000-07.
+-}
\end{code}
-No free/live variable information is pinned on in this pass; it's added
-later. For this pass
-we use @bOGUS_LVs@ and @bOGUS_FVs@ as placeholders.
+Detect thunks which will reduce immediately to PAPs, and make them
+non-updatable. This has several advantages:
-When printing out the Stg we need non-bottom values in these
-locations.
+ - the non-updatable thunk behaves exactly like the PAP,
-\begin{code}
-bOGUS_LVs :: StgLiveVars
-bOGUS_LVs | opt_D_verbose_stg2stg = emptyUniqSet
- | otherwise =panic "bOGUS_LVs"
+ - the thunk is more efficient to enter, because it is
+ specialised to the task.
-bOGUS_FVs :: [Id]
-bOGUS_FVs | opt_D_verbose_stg2stg = []
- | otherwise = panic "bOGUS_FVs"
-\end{code}
-
-\begin{code}
-topCoreBindsToStg :: UniqSupply -- name supply
- -> [CoreBind] -- input
- -> [StgBinding] -- output
-
-topCoreBindsToStg us core_binds
- = initUs_ us (coreBindsToStg emptyVarEnv core_binds)
- where
- coreBindsToStg :: StgEnv -> [CoreBind] -> UniqSM [StgBinding]
-
- coreBindsToStg env [] = returnUs []
- coreBindsToStg env (b:bs)
- = coreBindToStg TopLevel env b `thenUs` \ (bind_spec, new_env) ->
- coreBindsToStg new_env bs `thenUs` \ new_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}
+ - we save one update frame, one stg_update_PAP, one update
+ and lots of PAP_enters.
+ - in the case where the thunk is top-level, we save building
+ a black hole and futhermore the thunk isn't considered to
+ be a CAF any more, so it doesn't appear in any SRTs.
-%************************************************************************
-%* *
-\subsection[coreToStg-binds]{Converting bindings}
-%* *
-%************************************************************************
+We do it here, because the arity information is accurate, and we need
+to do it before the SRT pass to save the SRT entries associated with
+any top-level PAPs.
\begin{code}
-coreBindToStg :: TopLevelFlag -> StgEnv -> CoreBind -> UniqSM (StgFloatBind, StgEnv)
-
-coreBindToStg top_lev env (NonRec binder rhs)
- = 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
- -- so it seems sensible to deal with it well.
- -- But we don't want to discard exported things. They can
- -- 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 floats, new_env)
- where
- dem = bdrDem binder
-
-coreBindToStg top_lev env (Rec pairs)
- = newLocalIds top_lev env binders `thenUs` \ (env', binders') ->
- mapUs (do_rhs env') pairs `thenUs` \ stg_rhss ->
- returnUs (RecF (binders' `zip` stg_rhss), env')
+isPAP (StgApp f args) = idArity f > length args
+isPAP _ = False
+
+-- ---------------------------------------------------------------------------
+-- Atoms
+-- ---------------------------------------------------------------------------
+
+coreToStgAtoms :: [CoreArg] -> LneM ([StgArg], FreeVarsInfo)
+coreToStgAtoms atoms
+ = let val_atoms = filter isValArg atoms in
+ mapAndUnzipLne coreToStgAtom val_atoms `thenLne` \ (args', fvs_lists) ->
+ returnLne (args', unionFVInfos fvs_lists)
where
- binders = map fst pairs
- 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}
-
-
-%************************************************************************
-%* *
-\subsection[coreToStg-rhss]{Converting right hand sides}
-%* *
-%************************************************************************
-
-\begin{code}
-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
+ coreToStgAtom e
+ = coreToStgExpr e `thenLne` \ (expr, fvs, escs) ->
+ case expr of
+ StgApp v [] -> returnLne (StgVarArg v, fvs)
+ StgConApp con [] -> returnLne (StgVarArg (dataConWrapId con), fvs)
+ StgLit lit -> returnLne (StgLitArg lit, fvs)
+ _ -> pprPanic "coreToStgAtom" (ppr expr)
+
+-- ---------------------------------------------------------------------------
+-- Expressions
+-- ---------------------------------------------------------------------------
{-
- We reject the following candidates for 'static constructor'dom:
-
- - any dcon that takes a lit-lit as an arg.
- - [Win32 DLLs only]: any dcon that resides in a DLL
- (or takes as arg something that is.)
-
- These constraints are necessary to ensure that the code
- generated in the end for the static constructors, which
- live in the data segment, remain valid - i.e., it has to
- be constant. For obvious reasons, that's hard to guarantee
- with lit-lits. The second case of a constructor referring
- to static closures hiding out in some DLL is an artifact
- of the way Win32 DLLs handle global DLL variables. A (data)
- symbol exported from a DLL has to be accessed through a
- level of indirection at the site of use, so whereas
-
- extern StgClosure y_closure;
- extern StgClosure z_closure;
- x = { ..., &y_closure, &z_closure };
-
- is legal when the symbols are in scope at link-time, it is
- not when y_closure is in a DLL. So, any potential static
- closures that refers to stuff that's residing in a DLL
- will be put in an (updateable) thunk instead.
-
- An alternative strategy is to support the generation of
- constructors (ala C++ static class constructors) which will
- then be run at load time to fix up static closures.
+@varsExpr@ carries in a monad-ised environment, which binds each
+let(rec) variable (ie non top level, not imported, not lambda bound,
+not case-alternative bound) to:
+ - its STG arity, and
+ - its set of live vars.
+For normal variables the set of live vars is just the variable
+itself. For let-no-escaped variables, the set of live vars is the set
+live at the moment the variable is entered. The set is guaranteed to
+have no further let-no-escaped vars in it.
-}
-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
-
- is_lit_lit (StgVarArg _) = False
- is_lit_lit (StgConArg x) =
- case x of
- Literal l -> isLitLitLit l
- _ -> False
-
-exprToRhs dem _ expr
- = upd `seq`
- StgRhsClosure noCCS -- No cost centre (ToDo?)
- stgArgOcc -- safe
- noSRT -- figure out later
- bOGUS_FVs
- upd
- []
- expr
- where
- upd = if isOnceDem dem then SingleEntry else Updatable
- -- HA! Paydirt for "dem"
-
-isDynCon :: DataCon -> Bool
-isDynCon con = isDynName (dataConName con)
-
-isDynArg :: StgArg -> Bool
-isDynArg (StgVarArg v) = isDynName (idName v)
-isDynArg (StgConArg con) =
- case con of
- DataCon dc -> isDynCon dc
- Literal l -> isLitLitLit l
- _ -> False
-
-isDynName :: Name -> Bool
-isDynName nm =
- not (isLocallyDefinedName nm) &&
- isDynamicModule (nameModule nm)
+
+coreToStgExpr
+ :: CoreExpr
+ -> LneM (StgExpr, -- Decorated STG expr
+ FreeVarsInfo, -- Its free vars (NB free, not live)
+ EscVarsSet) -- Its escapees, a subset of its free vars;
+ -- also a subset of the domain of the envt
+ -- because we are only interested in the escapees
+ -- for vars which might be turned into
+ -- let-no-escaped ones.
\end{code}
-
-%************************************************************************
-%* *
-\subsection[coreToStg-atoms{Converting atoms}
-%* *
-%************************************************************************
+The second and third components can be derived in a simple bottom up pass, not
+dependent on any decisions about which variables will be let-no-escaped or
+not. The first component, that is, the decorated expression, may then depend
+on these components, but it in turn is not scrutinised as the basis for any
+decisions. Hence no black holes.
\begin{code}
-coreArgsToStg :: StgEnv -> [(CoreArg,RhsDemand)] -> UniqSM ([StgFloatBind], [StgArg])
--- Arguments are all value arguments (tyargs already removed), paired with their demand
+coreToStgExpr (Lit l) = returnLne (StgLit l, emptyFVInfo, emptyVarSet)
-coreArgsToStg env []
- = returnUs ([], [])
+coreToStgExpr (Var v)
+ = coreToStgApp Nothing v []
-coreArgsToStg env (ad:ads)
- = coreArgToStg env ad `thenUs` \ (bs1, a') ->
- coreArgsToStg env ads `thenUs` \ (bs2, as') ->
- returnUs (bs1 ++ bs2, a' : as')
+coreToStgExpr expr@(App _ _)
+ = let (f, args) = myCollectArgs expr
+ in
+ coreToStgApp Nothing (shouldBeVar f) args
+coreToStgExpr expr@(Lam _ _)
+ = let (args, body) = myCollectBinders expr
+ args' = filter isId args
+ in
+ extendVarEnvLne [ (a, LambdaBound) | a <- args' ] $
+ coreToStgExpr body `thenLne` \ (body, body_fvs, body_escs) ->
+ let
+ set_of_args = mkVarSet args'
+ fvs = body_fvs `minusFVBinders` args'
+ escs = body_escs `minusVarSet` set_of_args
+ in
+ if null args'
+ then returnLne (body, fvs, escs)
+ else returnLne (StgLam (exprType expr) args' body, fvs, escs)
-coreArgToStg :: StgEnv -> (CoreArg,RhsDemand) -> UniqSM ([StgFloatBind], StgArg)
--- This is where we arrange that a non-trivial argument is let-bound
+coreToStgExpr (Note (SCC cc) expr)
+ = coreToStgExpr expr `thenLne` ( \ (expr2, fvs, escs) ->
+ returnLne (StgSCC cc expr2, fvs, escs) )
-coreArgToStg env (arg,dem)
- = coreExprToStgFloat env arg dem `thenUs` \ (floats, arg') ->
- case arg' of
- 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}
+coreToStgExpr (Note other_note expr)
+ = coreToStgExpr expr
-%************************************************************************
-%* *
-\subsection[coreToStg-exprs]{Converting core expressions}
-%* *
-%************************************************************************
+-- Cases require a little more real work.
-\begin{code}
-coreExprToStg :: StgEnv -> CoreExpr -> RhsDemand -> UniqSM StgExpr
-coreExprToStg env expr dem
- = coreExprToStgFloat env expr dem `thenUs` \ (binds,stg_expr) ->
- mkStgBinds binds stg_expr `thenUs` \ stg_expr' ->
- deStgLam stg_expr'
-\end{code}
+coreToStgExpr (Case scrut bndr alts)
+ = getVarsLiveInCont `thenLne` \ live_in_cont ->
+ extendVarEnvLne [(bndr, CaseBound)] $
+ vars_alts (findDefault alts) `thenLne` \ (alts2, alts_fvs, alts_escs) ->
+ lookupLiveVarsForSet alts_fvs `thenLne` \ alts_lvs ->
+ let
+ -- determine whether the default binder is dead or not
+ bndr'= if (bndr `elementOfFVInfo` alts_fvs)
+ then bndr `setIdOccInfo` NoOccInfo
+ else bndr `setIdOccInfo` IAmDead
+
+ -- for a _ccall_GC_, some of the *arguments* need to live across the
+ -- call (see findLiveArgs comments.), so we annotate them as being live
+ -- in the alts to achieve the desired effect.
+ mb_live_across_case =
+ case scrut of
+ -- ToDo: Notes?
+ e@(App _ _) | (Var v, args) <- myCollectArgs e,
+ PrimOpId (CCallOp ccall) <- idFlavour v,
+ ccallMayGC ccall
+ -> Just (filterVarSet isForeignObjArg (exprFreeVars e))
+ _ -> Nothing
+
+ -- Don't consider the default binder as being 'live in alts',
+ -- since this is from the point of view of the case expr, where
+ -- the default binder is not free.
+ live_in_alts = orElse (FMAP unionVarSet mb_live_across_case) id $
+ live_in_cont `unionVarSet`
+ (alts_lvs `minusVarSet` unitVarSet bndr)
+ in
+ -- we tell the scrutinee that everything live in the alts
+ -- is live in it, too.
+ setVarsLiveInCont live_in_alts (
+ coreToStgExpr scrut
+ ) `thenLne` \ (scrut2, scrut_fvs, scrut_escs) ->
-%************************************************************************
-%* *
-\subsubsection[coreToStg-let(rec)]{Let and letrec expressions}
-%* *
-%************************************************************************
+ lookupLiveVarsForSet scrut_fvs `thenLne` \ scrut_lvs ->
+ let
+ live_in_whole_case = live_in_alts `unionVarSet` scrut_lvs
+ in
+ returnLne (
+ mkStgCase scrut2 live_in_whole_case live_in_alts bndr' noSRT alts2,
+ (scrut_fvs `unionFVInfo` alts_fvs) `minusFVBinders` [bndr],
+ (alts_escs `minusVarSet` unitVarSet bndr) `unionVarSet` getFVSet scrut_fvs
+ -- You might think we should have scrut_escs, not (getFVSet scrut_fvs),
+ -- but actually we can't call, and then return from, a let-no-escape thing.
+ )
+ where
+ scrut_ty = idType bndr
+ prim_case = isUnLiftedType scrut_ty && not (isUnboxedTupleType scrut_ty)
+
+ vars_alts (alts,deflt)
+ | prim_case
+ = mapAndUnzip3Lne vars_prim_alt alts
+ `thenLne` \ (alts2, alts_fvs_list, alts_escs_list) ->
+ let
+ alts_fvs = unionFVInfos alts_fvs_list
+ alts_escs = unionVarSets alts_escs_list
+ in
+ vars_deflt deflt `thenLne` \ (deflt2, deflt_fvs, deflt_escs) ->
+ returnLne (
+ mkStgPrimAlts scrut_ty alts2 deflt2,
+ alts_fvs `unionFVInfo` deflt_fvs,
+ alts_escs `unionVarSet` deflt_escs
+ )
+
+ | otherwise
+ = mapAndUnzip3Lne vars_alg_alt alts
+ `thenLne` \ (alts2, alts_fvs_list, alts_escs_list) ->
+ let
+ alts_fvs = unionFVInfos alts_fvs_list
+ alts_escs = unionVarSets alts_escs_list
+ in
+ vars_deflt deflt `thenLne` \ (deflt2, deflt_fvs, deflt_escs) ->
+ returnLne (
+ mkStgAlgAlts scrut_ty alts2 deflt2,
+ alts_fvs `unionFVInfo` deflt_fvs,
+ alts_escs `unionVarSet` deflt_escs
+ )
+
+ where
+ vars_prim_alt (LitAlt lit, _, rhs)
+ = coreToStgExpr rhs `thenLne` \ (rhs2, rhs_fvs, rhs_escs) ->
+ returnLne ((lit, rhs2), rhs_fvs, rhs_escs)
+
+ vars_alg_alt (DataAlt con, binders, rhs)
+ = let
+ -- remove type variables
+ binders' = filter isId binders
+ in
+ extendVarEnvLne [(b, CaseBound) | b <- binders'] $
+ coreToStgExpr rhs `thenLne` \ (rhs2, rhs_fvs, rhs_escs) ->
+ let
+ good_use_mask = [ b `elementOfFVInfo` rhs_fvs | b <- binders' ]
+ -- records whether each param is used in the RHS
+ in
+ returnLne (
+ (con, binders', good_use_mask, rhs2),
+ rhs_fvs `minusFVBinders` binders',
+ rhs_escs `minusVarSet` mkVarSet binders'
+ -- ToDo: remove the minusVarSet;
+ -- since escs won't include any of these binders
+ )
+
+ vars_deflt Nothing
+ = returnLne (StgNoDefault, emptyFVInfo, emptyVarSet)
+
+ vars_deflt (Just rhs)
+ = coreToStgExpr rhs `thenLne` \ (rhs2, rhs_fvs, rhs_escs) ->
+ returnLne (StgBindDefault rhs2, rhs_fvs, rhs_escs)
-\begin{code}
-coreExprToStgFloat :: StgEnv -> CoreExpr
- -> RhsDemand
- -> UniqSM ([StgFloatBind], StgExpr)
--- Transform an expression to STG. The demand on the expression is
--- 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
+Lets not only take quite a bit of work, but this is where we convert
+then to let-no-escapes, if we wish.
+(Meanwhile, we don't expect to see let-no-escapes...)
\begin{code}
-coreExprToStgFloat env (Var var) dem
- = returnUs ([], mkStgApp (stgLookup env var) [])
+coreToStgExpr (Let bind body)
+ = fixLne (\ ~(_, _, _, no_binder_escapes) ->
+ coreToStgLet no_binder_escapes bind body
+ ) `thenLne` \ (new_let, fvs, escs, _) ->
-coreExprToStgFloat env (Let bind body) dem
- = coreBindToStg NotTopLevel env bind `thenUs` \ (new_bind, new_env) ->
- coreExprToStgFloat new_env body dem `thenUs` \ (floats, stg_body) ->
- returnUs (new_bind:floats, stg_body)
+ returnLne (new_let, fvs, escs)
\end{code}
-Convert core @scc@ expression directly to STG @scc@ expression.
+If we've got a case containing a _ccall_GC_ primop, we need to
+ensure that the arguments are kept live for the duration of the
+call. This only an issue
\begin{code}
-coreExprToStgFloat env (Note (SCC cc) expr) dem
- = coreExprToStg env expr dem `thenUs` \ stg_expr ->
- returnUs ([], StgSCC cc stg_expr)
+isForeignObjArg :: Id -> Bool
+isForeignObjArg x = isId x && isForeignObjPrimTy (idType x)
-coreExprToStgFloat env (Note other_note expr) dem
- = coreExprToStgFloat env expr dem
+isForeignObjPrimTy ty
+ = case splitTyConApp_maybe ty of
+ Just (tycon, _) -> tycon == foreignObjPrimTyCon
+ Nothing -> False
\end{code}
\begin{code}
-coreExprToStgFloat env expr@(Type _) dem
- = pprPanic "coreExprToStgFloat: tyarg unexpected:" $ ppr expr
-\end{code}
-
+mkStgCase scrut@(StgPrimApp ParOp _ _) lvs1 lvs2 bndr srt
+ (StgPrimAlts tycon _ deflt@(StgBindDefault _))
+ = StgCase scrut lvs1 lvs2 bndr srt (StgPrimAlts tycon [] deflt)
-%************************************************************************
-%* *
-\subsubsection[coreToStg-lambdas]{Lambda abstractions}
-%* *
-%************************************************************************
-
-\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
- if null id_binders then -- It was all type/usage binders; tossed
- coreExprToStgFloat env body dem
- else
- -- 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 ([], mkStgLam expr_ty (binders' ++ lam_bndrs) lam_body)
-
- other ->
- -- Body didn't reduce to a lambda, so return one
- returnUs ([], mkStgLam expr_ty binders' stg_body')
-\end{code}
-
-
-%************************************************************************
-%* *
-\subsubsection[coreToStg-applications]{Applications}
-%* *
-%************************************************************************
+mkStgCase (StgPrimApp SeqOp [scrut] _) lvs1 lvs2 bndr srt
+ (StgPrimAlts _ _ deflt@(StgBindDefault rhs))
+ = StgCase scrut_expr lvs1 lvs2 new_bndr srt new_alts
+ where
+ new_alts
+ | isUnLiftedType scrut_ty = WARN( True, text "mkStgCase" )
+ mkStgPrimAlts scrut_ty [] deflt
+ | otherwise = mkStgAlgAlts scrut_ty [] deflt
-\begin{code}
-coreExprToStgFloat env expr@(App _ _) dem
- = let
- (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 final_ads `thenUs` \ (arg_floats, stg_args) ->
+ scrut_ty = stgArgType scrut
+ new_bndr = setIdType bndr scrut_ty
+ -- NB: SeqOp :: forall a. a -> Int#
+ -- So bndr has type Int#
+ -- But now we are going to scrutinise the SeqOp's argument directly,
+ -- so we must change the type of the case binder to match that
+ -- of the argument expression e.
- -- 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 (arg_floats,
- mkStgApp (stgLookup env fun_id) stg_args)
+ scrut_expr = case scrut of
+ StgVarArg v -> StgApp v []
+ -- Others should not happen because
+ -- seq of a value should have disappeared
+ StgLitArg l -> WARN( True, text "seq on" <+> ppr l ) StgLit l
- (non_var_fun, []) -> -- No value args, so recurse into the function
- ASSERT( null arg_floats )
- coreExprToStgFloat env non_var_fun dem
+mkStgCase scrut lvs1 lvs2 bndr srt alts
+ = StgCase scrut lvs1 lvs2 bndr srt alts
- other -> -- A non-variable applied to things; better let-bind it.
- 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,
- mkStgApp fun_id stg_args)
- where
- -- Collect arguments and demands (*in reverse order*)
- -- collect_args e = (f, args_w_demands, ty, stricts)
- -- => e = f tys args, (i.e. args are just the value args)
- -- e :: ty
- -- stricts is the leftover demands of e on its further args
- -- If stricts runs out, we zap all the demands in args_w_demands
- -- because partial applications are lazy
-
- collect_args :: CoreExpr -> (CoreExpr, [(CoreExpr,RhsDemand)], Type, [Demand])
-
- collect_args (Note (Coerce ty _) e) = let (the_fun,ads,_,ss) = collect_args e
- in (the_fun,ads,ty,ss)
- collect_args (Note InlineCall e) = collect_args e
- collect_args (Note (TermUsg _) e) = collect_args e
-
- 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)
- = (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
-
- collect_args (Var v)
- = (Var v, [], idType v, stricts)
- where
- stricts = case getIdStrictness v of
- StrictnessInfo demands _ -> demands
- other -> repeat wwLazy
+mkStgAlgAlts ty alts deflt
+ = case alts of
+ -- Get the tycon from the data con
+ (dc, _, _, _) : _rest
+ -> StgAlgAlts (Just (dataConTyCon dc)) alts deflt
- collect_args fun = (fun, [], coreExprType fun, repeat wwLazy)
+ -- Otherwise just do your best
+ [] -> case splitTyConApp_maybe (repType ty) of
+ Just (tc,_) | isAlgTyCon tc
+ -> StgAlgAlts (Just tc) alts deflt
+ other
+ -> StgAlgAlts Nothing alts deflt
- -- "zap" nukes the strictness info for a partial application
- zap ads = [(arg, RhsDemand False once) | (arg, RhsDemand _ once) <- ads]
+mkStgPrimAlts ty alts deflt
+ = StgPrimAlts (tyConAppTyCon ty) alts deflt
\end{code}
-%************************************************************************
-%* *
-\subsubsection[coreToStg-con]{Constructors and primops}
-%* *
-%************************************************************************
-
-For data constructors, the demand on an argument is the demand on the
-constructor as a whole (see module UsageSPInf). For primops, the
-demand is derived from the type of the primop.
-
-If usage inference is off, we simply make all bindings updatable for
-speed.
+Applications:
\begin{code}
-coreExprToStgFloat env expr@(Con con args) dem
- = let
- expr_ty = coreExprType expr
- (stricts,_) = conStrictness con
- onces = case con of
- DEFAULT -> panic "coreExprToStgFloat: DEFAULT"
-
- Literal _ -> ASSERT( null args' {-'cpp-} ) []
-
- DataCon c -> repeat (isOnceDem dem)
- -- HA! This is the sole reason we propagate
- -- dem all the way down
-
- PrimOp p -> let tyargs = map (\ (Type ty) -> ty) $
- takeWhile isTypeArg args
- (arg_tys,_) = primOpUsgTys p tyargs
- in ASSERT( length arg_tys == length args' {-'cpp-} )
- -- primops always fully applied, so == not >=
- map isOnceTy arg_tys
-
- dems' = zipWith mkDem stricts onces
- args' = filter isValArg args
- in
- coreArgsToStg env (zip args' dems') `thenUs` \ (arg_floats, stg_atoms) ->
-
- -- YUK YUK: must unique if present
- (case con of
- PrimOp (CCallOp (Right _) a b c) -> getUniqueUs `thenUs` \ u ->
- returnUs (PrimOp (CCallOp (Right u) a b c))
- _ -> returnUs con
- ) `thenUs` \ con' ->
-
- returnUs (arg_floats, mkStgCon con' stg_atoms expr_ty)
-\end{code}
-
+coreToStgApp
+ :: Maybe UpdateFlag -- Just upd <=> this application is
+ -- the rhs of a thunk binding
+ -- x = [...] \upd [] -> the_app
+ -- with specified update flag
+ -> Id -- Function
+ -> [CoreArg] -- Arguments
+ -> LneM (StgExpr, FreeVarsInfo, EscVarsSet)
+
+coreToStgApp maybe_thunk_body f args
+ = getVarsLiveInCont `thenLne` \ live_in_cont ->
+ coreToStgAtoms args `thenLne` \ (args', args_fvs) ->
+ lookupVarLne f `thenLne` \ how_bound ->
-%************************************************************************
-%* *
-\subsubsection[coreToStg-cases]{Case expressions}
-%* *
-%************************************************************************
+ let
+ n_args = length args
+ not_letrec_bound = not (isLetrecBound how_bound)
+ f_arity = idArity f
+ fun_fvs = singletonFVInfo f how_bound fun_occ
+
+ fun_occ
+ | not_letrec_bound = NoStgBinderInfo -- Uninteresting variable
+
+ -- Otherwise it is letrec bound; must have its arity
+ | n_args == 0 = stgFakeFunAppOcc -- Function Application
+ -- with no arguments.
+ -- used by the lambda lifter.
+ | f_arity > n_args = stgUnsatOcc -- Unsaturated
+
+ | f_arity == n_args &&
+ maybeToBool maybe_thunk_body -- Exactly saturated,
+ -- and rhs of thunk
+ = case maybe_thunk_body of
+ Just Updatable -> stgStdHeapOcc
+ Just SingleEntry -> stgNoUpdHeapOcc
+ other -> panic "coreToStgApp"
+
+ | otherwise = stgNormalOcc
+ -- Record only that it occurs free
+
+ myself = unitVarSet f
+
+ fun_escs | not_letrec_bound = emptyVarSet
+ -- Only letrec-bound escapees are interesting
+ | f_arity == n_args = emptyVarSet
+ -- Function doesn't escape
+ | otherwise = myself
+ -- Inexact application; it does escape
+
+ -- At the moment of the call:
+
+ -- either the function is *not* let-no-escaped, in which case
+ -- nothing is live except live_in_cont
+ -- or the function *is* let-no-escaped in which case the
+ -- variables it uses are live, but still the function
+ -- itself is not. PS. In this case, the function's
+ -- live vars should already include those of the
+ -- continuation, but it does no harm to just union the
+ -- two regardless.
+
+ -- XXX not needed?
+ -- live_at_call
+ -- = live_in_cont `unionVarSet` case how_bound of
+ -- LetrecBound _ lvs -> lvs `minusVarSet` myself
+ -- other -> emptyVarSet
+
+ app = case idFlavour f of
+ DataConId dc -> StgConApp dc args'
+ PrimOpId op -> StgPrimApp op args' (exprType (mkApps (Var f) args))
+ _other -> StgApp f args'
-First, two special cases. We mangle cases involving
- par# and seq#
-inthe scrutinee.
+ in
+ returnLne (
+ app,
+ fun_fvs `unionFVInfo` args_fvs,
+ fun_escs `unionVarSet` (getFVSet args_fvs)
+ -- All the free vars of the args are disqualified
+ -- from being let-no-escaped.
+ )
+
+
+-- ---------------------------------------------------------------------------
+-- The magic for lets:
+-- ---------------------------------------------------------------------------
+
+coreToStgLet
+ :: Bool -- True <=> yes, we are let-no-escaping this let
+ -> CoreBind -- bindings
+ -> CoreExpr -- body
+ -> LneM (StgExpr, -- new let
+ FreeVarsInfo, -- variables free in the whole let
+ EscVarsSet, -- variables that escape from the whole let
+ Bool) -- True <=> none of the binders in the bindings
+ -- is among the escaping vars
+
+coreToStgLet let_no_escape bind body
+ = fixLne (\ ~(_, _, _, rec_bind_lvs, _, rec_body_fvs, _, _) ->
+
+ -- Do the bindings, setting live_in_cont to empty if
+ -- we ain't in a let-no-escape world
+ getVarsLiveInCont `thenLne` \ live_in_cont ->
+ setVarsLiveInCont
+ (if let_no_escape then live_in_cont else emptyVarSet)
+ (vars_bind rec_bind_lvs rec_body_fvs bind)
+ `thenLne` \ (bind2, bind_fvs, bind_escs, env_ext) ->
+
+ -- The live variables of this binding are the ones which are live
+ -- by virtue of being accessible via the free vars of the binding (lvs_from_fvs)
+ -- together with the live_in_cont ones
+ lookupLiveVarsForSet (bind_fvs `minusFVBinders` binders)
+ `thenLne` \ lvs_from_fvs ->
+ let
+ bind_lvs = lvs_from_fvs `unionVarSet` live_in_cont
+ in
-Up to this point, seq# will appear like this:
+ -- bind_fvs and bind_escs still include the binders of the let(rec)
+ -- but bind_lvs does not
- case seq# e of
- 0# -> seqError#
- _ -> <stuff>
+ -- Do the body
+ extendVarEnvLne env_ext (
+ coreToStgExpr body `thenLne` \ (body2, body_fvs, body_escs) ->
+ lookupLiveVarsForSet body_fvs `thenLne` \ body_lvs ->
-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.
+ returnLne (bind2, bind_fvs, bind_escs, bind_lvs,
+ body2, body_fvs, body_escs, body_lvs)
-Now that the evaluation order is safe, we translate this into
+ )) `thenLne` (\ (bind2, bind_fvs, bind_escs, bind_lvs,
+ body2, body_fvs, body_escs, body_lvs) ->
- 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.
+ -- Compute the new let-expression
+ let
+ new_let | let_no_escape = StgLetNoEscape live_in_whole_let bind_lvs bind2 body2
+ | otherwise = StgLet bind2 body2
-Similarly, par# has an unfolding in PrelConc.lhs that makes it show
-up like this:
+ free_in_whole_let
+ = (bind_fvs `unionFVInfo` body_fvs) `minusFVBinders` binders
- case par# e of
- 0# -> rhs
- _ -> parError#
+ live_in_whole_let
+ = bind_lvs `unionVarSet` (body_lvs `minusVarSet` set_of_binders)
+ real_bind_escs = if let_no_escape then
+ bind_escs
+ else
+ getFVSet bind_fvs
+ -- Everything escapes which is free in the bindings
- ==>
- case par# e of
- _ -> rhs
+ let_escs = (real_bind_escs `unionVarSet` body_escs) `minusVarSet` set_of_binders
-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.
+ all_escs = bind_escs `unionVarSet` body_escs -- Still includes binders of
+ -- this let(rec)
+ no_binder_escapes = isEmptyVarSet (set_of_binders `intersectVarSet` all_escs)
-\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
- (other_alts, maybe_default) = findDefault alts
- Just default_rhs = maybe_default
- new_bndr = setIdType bndr ty
- -- NB: SeqOp :: forall a. a -> Int#
- -- So bndr has type Int#
- -- But now we are going to scrutinise the SeqOp's argument directly,
- -- so we must change the type of the case binder to match that
- -- of the argument expression e. We can get this type from the argument
- -- type of the SeqOp.
-
-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')))
+#ifdef DEBUG
+ -- Debugging code as requested by Andrew Kennedy
+ checked_no_binder_escapes
+ | not no_binder_escapes && any is_join_var binders
+ = pprTrace "Interesting! A join var that isn't let-no-escaped" (ppr binders)
+ False
+ | otherwise = no_binder_escapes
+#else
+ checked_no_binder_escapes = no_binder_escapes
+#endif
+
+ -- Mustn't depend on the passed-in let_no_escape flag, since
+ -- no_binder_escapes is used by the caller to derive the flag!
+ in
+ returnLne (
+ new_let,
+ free_in_whole_let,
+ let_escs,
+ checked_no_binder_escapes
+ ))
where
- (other_alts, maybe_default) = findDefault alts
- Just default_rhs = maybe_default
-\end{code}
-
-Now for normal case expressions...
+ set_of_binders = mkVarSet binders
+ binders = case bind of
+ NonRec binder rhs -> [binder]
+ Rec pairs -> map fst pairs
+
+ mk_binding bind_lvs binder
+ = (binder, LetrecBound False -- Not top level
+ live_vars
+ )
+ where
+ live_vars = if let_no_escape then
+ extendVarSet bind_lvs binder
+ else
+ unitVarSet binder
+
+ vars_bind :: StgLiveVars
+ -> FreeVarsInfo -- Free var info for body of binding
+ -> CoreBind
+ -> LneM (StgBinding,
+ FreeVarsInfo, EscVarsSet, -- free vars; escapee vars
+ [(Id, HowBound)])
+ -- extension to environment
+
+ vars_bind rec_bind_lvs rec_body_fvs (NonRec binder rhs)
+ = coreToStgRhs rec_body_fvs NotTopLevel (binder,rhs)
+ `thenLne` \ (rhs2, fvs, escs) ->
+ let
+ env_ext_item@(binder', _) = mk_binding rec_bind_lvs binder
+ in
+ returnLne (StgNonRec binder' rhs2, fvs, escs, [env_ext_item])
-\begin{code}
-coreExprToStgFloat env (Case scrut bndr alts) dem
- = coreExprToStgFloat env scrut (bdrDem bndr) `thenUs` \ (binds, scrut') ->
- newEvaldLocalId env bndr `thenUs` \ (env', bndr') ->
- alts_to_stg env' (findDefault alts) `thenUs` \ alts' ->
- returnUs (binds, mkStgCase scrut' bndr' alts')
- where
- scrut_ty = idType bndr
- prim_case = isUnLiftedType scrut_ty && not (isUnboxedTupleType scrut_ty)
-
- alts_to_stg env (alts, deflt)
- | prim_case
- = default_to_stg env deflt `thenUs` \ deflt' ->
- mapUs (prim_alt_to_stg env) alts `thenUs` \ alts' ->
- returnUs (mkStgPrimAlts scrut_ty alts' deflt')
-
- | otherwise
- = default_to_stg env deflt `thenUs` \ deflt' ->
- mapUs (alg_alt_to_stg env) alts `thenUs` \ alts' ->
- returnUs (mkStgAlgAlts scrut_ty alts' deflt')
-
- alg_alt_to_stg env (DataCon con, bs, rhs)
- = newLocalIds NotTopLevel env (filter isId bs) `thenUs` \ (env', stg_bs) ->
- coreExprToStg env' rhs dem `thenUs` \ stg_rhs ->
- returnUs (con, stg_bs, [ True | b <- stg_bs ]{-bogus use mask-}, stg_rhs)
- -- NB the filter isId. Some of the binders may be
- -- existential type variables, which STG doesn't care about
-
- prim_alt_to_stg env (Literal lit, args, rhs)
- = ASSERT( null args )
- coreExprToStg env rhs dem `thenUs` \ stg_rhs ->
- returnUs (lit, stg_rhs)
-
- default_to_stg env Nothing
- = returnUs StgNoDefault
-
- default_to_stg env (Just rhs)
- = coreExprToStg env rhs dem `thenUs` \ stg_rhs ->
- returnUs (StgBindDefault stg_rhs)
- -- The binder is used for prim cases and not otherwise
- -- (hack for old code gen)
+ vars_bind rec_bind_lvs rec_body_fvs (Rec pairs)
+ = let
+ binders = map fst pairs
+ env_ext = map (mk_binding rec_bind_lvs) binders
+ in
+ extendVarEnvLne env_ext (
+ fixLne (\ ~(_, rec_rhs_fvs, _, _) ->
+ let
+ rec_scope_fvs = unionFVInfo rec_body_fvs rec_rhs_fvs
+ in
+ mapAndUnzip3Lne (coreToStgRhs rec_scope_fvs NotTopLevel) pairs
+ `thenLne` \ (rhss2, fvss, escss) ->
+ let
+ fvs = unionFVInfos fvss
+ escs = unionVarSets escss
+ in
+ returnLne (StgRec (binders `zip` rhss2), fvs, escs, env_ext)
+ ))
+
+is_join_var :: Id -> Bool
+-- A hack (used only for compiler debuggging) to tell if
+-- a variable started life as a join point ($j)
+is_join_var j = occNameUserString (getOccName j) == "$j"
\end{code}
-
%************************************************************************
%* *
-\subsection[coreToStg-misc]{Miscellaneous helping functions}
+\subsection[LNE-monad]{A little monad for this let-no-escaping pass}
%* *
%************************************************************************
-There's not anything interesting we can ASSERT about \tr{var} if it
-isn't in the StgEnv. (WDP 94/06)
+There's a lot of stuff to pass around, so we use this @LneM@ monad to
+help. All the stuff here is only passed {\em down}.
\begin{code}
-stgLookup :: StgEnv -> Id -> Id
-stgLookup env var = case (lookupVarEnv env var) of
- Nothing -> var
- Just var -> var
+type LneM a = IdEnv HowBound
+ -> StgLiveVars -- vars live in continuation
+ -> a
+
+data HowBound
+ = ImportBound
+ | CaseBound
+ | LambdaBound
+ | LetrecBound
+ Bool -- True <=> bound at top level
+ StgLiveVars -- Live vars... see notes below
+
+isLetrecBound (LetrecBound _ _) = True
+isLetrecBound other = False
\end{code}
-Invent a fresh @Id@:
+For a let(rec)-bound variable, x, we record what varibles are live if
+x is live. For "normal" variables that is just x alone. If x is
+a let-no-escaped variable then x is represented by a code pointer and
+a stack pointer (well, one for each stack). So all of the variables
+needed in the execution of x are live if x is, and are therefore recorded
+in the LetrecBound constructor; x itself *is* included.
+
+The std monad functions:
\begin{code}
-newStgVar :: Type -> UniqSM Id
-newStgVar ty
- = getUniqueUs `thenUs` \ uniq ->
- seqType ty `seq`
- returnUs (mkSysLocal SLIT("stg") uniq ty)
+initLne :: LneM a -> a
+initLne m = m emptyVarEnv emptyVarSet
+
+{-# INLINE thenLne #-}
+{-# INLINE thenLne_ #-}
+{-# INLINE returnLne #-}
+
+returnLne :: a -> LneM a
+returnLne e env lvs_cont = e
+
+thenLne :: LneM a -> (a -> LneM b) -> LneM b
+thenLne m k env lvs_cont
+ = case (m env lvs_cont) of
+ m_result -> k m_result env lvs_cont
+
+thenLne_ :: LneM a -> LneM b -> LneM b
+thenLne_ m k env lvs_cont
+ = case (m env lvs_cont) of
+ _ -> k env lvs_cont
+
+mapLne :: (a -> LneM b) -> [a] -> LneM [b]
+mapLne f [] = returnLne []
+mapLne f (x:xs)
+ = f x `thenLne` \ r ->
+ mapLne f xs `thenLne` \ rs ->
+ returnLne (r:rs)
+
+mapAndUnzipLne :: (a -> LneM (b,c)) -> [a] -> LneM ([b],[c])
+
+mapAndUnzipLne f [] = returnLne ([],[])
+mapAndUnzipLne f (x:xs)
+ = f x `thenLne` \ (r1, r2) ->
+ mapAndUnzipLne f xs `thenLne` \ (rs1, rs2) ->
+ returnLne (r1:rs1, r2:rs2)
+
+mapAndUnzip3Lne :: (a -> LneM (b,c,d)) -> [a] -> LneM ([b],[c],[d])
+
+mapAndUnzip3Lne f [] = returnLne ([],[],[])
+mapAndUnzip3Lne f (x:xs)
+ = f x `thenLne` \ (r1, r2, r3) ->
+ mapAndUnzip3Lne f xs `thenLne` \ (rs1, rs2, rs3) ->
+ returnLne (r1:rs1, r2:rs2, r3:rs3)
+
+fixLne :: (a -> LneM a) -> LneM a
+fixLne expr env lvs_cont = result
+ where
+ result = expr result env lvs_cont
+-- ^^^^^^ ------ ^^^^^^
\end{code}
+Functions specific to this monad:
\begin{code}
-{- Now redundant, I believe
--- we overload the demandInfo field of an Id to indicate whether the Id is definitely
--- evaluated or not (i.e. whether it is a case binder). This can be used to eliminate
--- some redundant cases (c.f. dataToTag# above).
-
-newEvaldLocalId env id
- = getUniqueUs `thenUs` \ uniq ->
- let
- id' = modifyIdInfo (`setDemandInfo` wwStrict) (setIdUnique id uniq)
- new_env = extendVarEnv env id id'
- in
- returnUs (new_env, id')
--}
-
-newEvaldLocalId env id = newLocalId NotTopLevel env id
-
-newLocalId TopLevel env id
- -- Don't clone top-level binders. MkIface relies on their
- -- uniques staying the same, so it can snaffle IdInfo off the
- -- STG ids to put in interface files.
- = let
- name = idName id
- ty = idType id
- in
- name `seq`
- seqType ty `seq`
- returnUs (env, mkVanillaId name ty)
-
-
-newLocalId NotTopLevel env id
- = -- Local binder, give it a new unique Id.
- getUniqueUs `thenUs` \ uniq ->
- let
- name = idName id
- ty = idType id
- new_id = mkVanillaId (setNameUnique name uniq) ty
- new_env = extendVarEnv env id new_id
- in
- name `seq`
- seqType ty `seq`
- returnUs (new_env, new_id)
-
-newLocalIds :: TopLevelFlag -> StgEnv -> [Id] -> UniqSM (StgEnv, [Id])
-newLocalIds top_lev env []
- = returnUs (env, [])
-newLocalIds top_lev env (b:bs)
- = newLocalId top_lev env b `thenUs` \ (env', b') ->
- newLocalIds top_lev env' bs `thenUs` \ (env'', bs') ->
- returnUs (env'', b':bs')
+getVarsLiveInCont :: LneM StgLiveVars
+getVarsLiveInCont env lvs_cont = lvs_cont
+
+setVarsLiveInCont :: StgLiveVars -> LneM a -> LneM a
+setVarsLiveInCont new_lvs_cont expr env lvs_cont
+ = expr env new_lvs_cont
+
+extendVarEnvLne :: [(Id, HowBound)] -> LneM a -> LneM a
+extendVarEnvLne ids_w_howbound expr env lvs_cont
+ = expr (extendVarEnvList env ids_w_howbound) lvs_cont
+
+lookupVarLne :: Id -> LneM HowBound
+lookupVarLne v env lvs_cont
+ = returnLne (
+ case (lookupVarEnv env v) of
+ Just xx -> xx
+ Nothing -> ImportBound
+ ) env lvs_cont
+
+-- The result of lookupLiveVarsForSet, a set of live variables, is
+-- only ever tacked onto a decorated expression. It is never used as
+-- the basis of a control decision, which might give a black hole.
+
+lookupLiveVarsForSet :: FreeVarsInfo -> LneM StgLiveVars
+
+lookupLiveVarsForSet fvs env lvs_cont
+ = returnLne (unionVarSets (map do_one (getFVs fvs)))
+ env lvs_cont
+ where
+ do_one v
+ = if isLocalId v then
+ case (lookupVarEnv env v) of
+ Just (LetrecBound _ lvs) -> extendVarSet lvs v
+ Just _ -> unitVarSet v
+ Nothing -> pprPanic "lookupVarEnv/do_one:" (ppr v)
+ else
+ emptyVarSet
\end{code}
%************************************************************************
%* *
-\subsection{Building STG syn}
+\subsection[Free-var info]{Free variable information}
%* *
%************************************************************************
\begin{code}
-mkStgAlgAlts ty alts deflt = seqType ty `seq` StgAlgAlts ty alts deflt
-mkStgPrimAlts ty alts deflt = seqType ty `seq` StgPrimAlts ty alts deflt
-mkStgCon con args ty = seqType ty `seq` StgCon con args ty
-mkStgLam ty bndrs body = seqType ty `seq` StgLam ty bndrs body
-
-mkStgApp :: Id -> [StgArg] -> StgExpr
-mkStgApp fn args = fn `seq` StgApp fn args
- -- Force the lookup
+type FreeVarsInfo = IdEnv (Id, Bool, StgBinderInfo)
+ -- If f is mapped to NoStgBinderInfo, that means
+ -- that f *is* mentioned (else it wouldn't be in the
+ -- IdEnv at all), but only in a saturated applications.
+ --
+ -- All case/lambda-bound things are also mapped to
+ -- NoStgBinderInfo, since we aren't interested in their
+ -- occurence info.
+ --
+ -- The Bool is True <=> the Id is top level letrec bound
+
+type EscVarsSet = IdSet
\end{code}
\begin{code}
--- 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) (mkStgApp 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'
+emptyFVInfo :: FreeVarsInfo
+emptyFVInfo = emptyVarEnv
--- The 'body' arg of mkStgBind can't be a StgLam
-mkStgBind NoBindF body = returnUs body
-mkStgBind (RecF prs) body = returnUs (StgLet (StgRec prs) body)
+singletonFVInfo :: Id -> HowBound -> StgBinderInfo -> FreeVarsInfo
+singletonFVInfo id ImportBound info = emptyVarEnv
+singletonFVInfo id (LetrecBound top_level _) info = unitVarEnv id (id, top_level, info)
+singletonFVInfo id other info = unitVarEnv id (id, False, info)
-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 floats body)
- other -> mk_stg_let bndr rhs dem floats body
+unionFVInfo :: FreeVarsInfo -> FreeVarsInfo -> FreeVarsInfo
+unionFVInfo fv1 fv2 = plusVarEnv_C plusFVInfo fv1 fv2
-mk_stg_let bndr rhs dem floats body
-#endif
- | isUnLiftedType bndr_rep_ty -- Use a case/PrimAlts
- = ASSERT( not (isUnboxedTupleType bndr_rep_ty) )
- mkStgBinds floats $
- mkStgCase rhs bndr (StgPrimAlts bndr_rep_ty [] (StgBindDefault 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_rep_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_rep_ty = repType (idType bndr)
- is_strict = isStrictDem dem
- is_whnf = case rhs of
- StgCon _ _ _ -> True
- StgLam _ _ _ -> True
- other -> False
+unionFVInfos :: [FreeVarsInfo] -> FreeVarsInfo
+unionFVInfos fvs = foldr unionFVInfo emptyFVInfo fvs
--- Split at the first strict binding
-splitFloats fs@(NonRecF _ _ dem _ : _)
- | isStrictDem dem = ([], fs)
+minusFVBinders :: FreeVarsInfo -> [Id] -> FreeVarsInfo
+minusFVBinders fv ids = fv `delVarEnvList` ids
-splitFloats (f : fs) = case splitFloats fs of
- (fs_out, fs_in) -> (f : fs_out, fs_in)
+elementOfFVInfo :: Id -> FreeVarsInfo -> Bool
+elementOfFVInfo id fvs = maybeToBool (lookupVarEnv fvs id)
-splitFloats [] = ([], [])
+lookupFVInfo :: FreeVarsInfo -> Id -> StgBinderInfo
+lookupFVInfo fvs id = case lookupVarEnv fvs id of
+ Nothing -> NoStgBinderInfo
+ Just (_,_,info) -> info
+getFVs :: FreeVarsInfo -> [Id] -- Non-top-level things only
+getFVs fvs = [id | (id,False,_) <- rngVarEnv fvs]
+
+getFVSet :: FreeVarsInfo -> IdSet
+getFVSet fvs = mkVarSet (getFVs fvs)
+
+plusFVInfo (id1,top1,info1) (id2,top2,info2)
+ = ASSERT (id1 == id2 && top1 == top2)
+ (id1, top1, combineStgBinderInfo info1 info2)
+\end{code}
-mkStgCase scrut bndr 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
+Misc.
+
+\begin{code}
+shouldBeVar (Note _ e) = shouldBeVar e
+shouldBeVar (Var v) = v
+shouldBeVar e = pprPanic "shouldBeVar" (ppr e)
+
+-- ignore all notes except SCC
+myCollectBinders expr
+ = go [] expr
+ where
+ go bs (Lam b e) = go (b:bs) e
+ go bs e@(Note (SCC _) _) = (reverse bs, e)
+ go bs (Note _ e) = go bs e
+ go bs e = (reverse bs, e)
+
+myCollectArgs :: Expr b -> (Expr b, [Arg b])
+myCollectArgs expr
+ = go expr []
+ where
+ go (App f a) as = go f (a:as)
+ go (Note (SCC _) e) as = panic "CoreToStg.myCollectArgs"
+ go (Note n e) as = go e as
+ go e as = (e, as)
\end{code}
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