%
-% (c) The GRASP/AQUA Project, Glasgow University, 1992-1996
+% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
%************************************************************************
%* *
Convert a @CoreSyntax@ program to a @StgSyntax@ program.
-
\begin{code}
-#include "HsVersions.h"
-
module CoreToStg ( topCoreBindsToStg ) where
-import Ubiq{-uitous-}
+#include "HsVersions.h"
import CoreSyn -- input
import StgSyn -- output
-import Bag ( emptyBag, unitBag, unionBags, unionManyBags, bagToList )
-import CoreUtils ( coreExprType )
-import CostCentre ( noCostCentre )
-import Id ( mkSysLocal, idType, isBottomingId,
- nullIdEnv, addOneToIdEnv, lookupIdEnv,
- IdEnv(..), GenId{-instance NamedThing-}
+import PprCore ( {- instance Outputable Bind/Expr -} )
+import CoreUtils ( exprType )
+import SimplUtils ( findDefault )
+import CostCentre ( noCCS )
+import Id ( Id, mkSysLocal, idType, idStrictness, idUnique, isExportedId, mkVanillaId,
+ externallyVisibleId, setIdUnique, idName,
+ idDemandInfo, idArity, setIdType, idFlavour
)
-import Literal ( mkMachInt, Literal(..) )
-import Name ( isExported )
-import PrelInfo ( unpackCStringId, unpackCString2Id, stringTy,
- integerTy, rationalTy, ratioDataCon,
- integerZeroId, integerPlusOneId,
- integerPlusTwoId, integerMinusOneId
+import Var ( Var, varType, modifyIdInfo )
+import IdInfo ( setDemandInfo, StrictnessInfo(..), IdFlavour(..) )
+import UsageSPUtils ( primOpUsgTys )
+import DataCon ( DataCon, dataConName, dataConWrapId )
+import Demand ( Demand, isStrict, wwStrict, wwLazy )
+import Name ( Name, nameModule, isLocallyDefinedName, setNameUnique )
+import Literal ( Literal(..) )
+import VarEnv
+import PrimOp ( PrimOp(..), CCall(..), CCallTarget(..), primOpUsg )
+import Type ( isUnLiftedType, isUnboxedTupleType, Type, splitFunTy_maybe,
+ UsageAnn(..), tyUsg, applyTy, mkUsgTy, repType, seqType,
+ splitRepFunTys, mkFunTys
)
-import PrimOp ( PrimOp(..) )
-import SpecUtils ( mkSpecialisedCon )
-import SrcLoc ( mkUnknownSrcLoc )
-import Type ( getAppDataTyCon )
+import TysPrim ( intPrimTy )
import UniqSupply -- all of it, really
-import Util ( panic )
-
-isLeakFreeType = panic "CoreToStg.isLeakFreeType (ToDo)"
+import Util ( lengthExceeds )
+import BasicTypes ( TopLevelFlag(..), isNotTopLevel, Arity )
+import CmdLineOpts ( opt_D_verbose_stg2stg, opt_UsageSPOn )
+import UniqSet ( emptyUniqSet )
+import Maybes
+import Outputable
\end{code}
+ *************************************************
*************** OVERVIEW *********************
+ *************************************************
-The business of this pass is to convert Core to Stg. On the way:
+The business of this pass is to convert Core to Stg. On the way it
+does some important transformations:
-* We discard type lambdas and applications. In so doing we discard
- "trivial" bindings such as
+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
+ 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.]
-* We make the representation of NoRep literals explicit, and
- float their bindings to the top level
+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.
-* We convert case x of {...; x' -> ...x'...}
- to
- case x of {...; _ -> ...x... }
-
- See notes in SimplCase.lhs, near simplDefault for the reasoning here.
+[Quite a bit of stuff that used to be here has moved
+ to tidyCorePgm (SimplCore.lhs) SLPJ Nov 96]
%************************************************************************
%* *
%************************************************************************
-Because we're going to come across ``boring'' bindings like
-\tr{let x = /\ tyvars -> y in ...}, we want to keep a small
-environment, so we can just replace all occurrences of \tr{x}
-with \tr{y}.
+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.)
+
+A binder to be floated out becomes an @StgFloatBind@.
\begin{code}
-type StgEnv = IdEnv StgArg
+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
+\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
+#endif
+ case tyUsg ty of
+ UsOnce -> True
+ UsMany -> False
+ UsVar uv -> pprPanic "CoreToStg: unexpected uvar annot:" (ppr uv)
+
+bdrDem :: Id -> RhsDemand
+bdrDem id = mkDem (idDemandInfo id) (isOnceTy (idType id))
+
+safeDem, onceDem :: RhsDemand
+safeDem = RhsDemand False False -- always safe to use this
+onceDem = RhsDemand False True -- used at most once
\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.
+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}
topCoreBindsToStg :: UniqSupply -- name supply
- -> [CoreBinding] -- input
+ -> [CoreBind] -- input
-> [StgBinding] -- output
topCoreBindsToStg us core_binds
- = case (initUs us (binds_to_stg nullIdEnv core_binds)) of
- (_, stuff) -> stuff
+ = initUs_ us (coreBindsToStg emptyVarEnv core_binds)
where
- binds_to_stg :: StgEnv -> [CoreBinding] -> UniqSM [StgBinding]
-
- binds_to_stg env [] = returnUs []
- binds_to_stg env (b:bs)
- = do_top_bind env b `thenUs` \ (new_b, new_env, float_binds) ->
- binds_to_stg new_env bs `thenUs` \ new_bs ->
- returnUs (bagToList float_binds ++ -- Literals
- new_b ++
- new_bs)
-
- do_top_bind env bind@(Rec pairs)
- = coreBindToStg env bind
-
- do_top_bind env bind@(NonRec var rhs)
- = coreBindToStg env bind `thenUs` \ (stg_binds, new_env, float_binds) ->
-{- TESTING:
- let
- ppr_blah xs = ppInterleave ppComma (map pp_x xs)
- pp_x (u,x) = ppBesides [pprUnique u, ppStr ": ", ppr PprDebug x]
- in
- pprTrace "do_top_bind:" (ppAbove (ppr PprDebug stg_binds) (ppr_blah (ufmToList new_env))) $
--}
- case stg_binds of
- [StgNonRec var (StgRhsClosure cc bi fvs u [] rhs_body)] ->
- -- Mega-special case; there's still a binding there
- -- no fvs (of course), *no args*, "let" rhs
- let
- (extra_float_binds, rhs_body') = seek_liftable [] rhs_body
- in
- returnUs (extra_float_binds ++
- [StgNonRec var (StgRhsClosure cc bi fvs u [] rhs_body')],
- new_env,
- float_binds)
-
- other -> returnUs (stg_binds, new_env, float_binds)
-
- --------------------
- -- HACK: look for very simple, obviously-liftable bindings
- -- that can come up to the top level; those that couldn't
- -- 'cause they were big-lambda constrained in the Core world.
-
- seek_liftable :: [StgBinding] -- accumulator...
- -> StgExpr -- look for top-lev liftables
- -> ([StgBinding], StgExpr) -- result
-
- seek_liftable acc expr@(StgLet inner_bind body)
- | is_liftable inner_bind
- = seek_liftable (inner_bind : acc) body
-
- seek_liftable acc other_expr = (reverse acc, other_expr) -- Finished
-
- --------------------
- is_liftable (StgNonRec binder (StgRhsClosure _ _ _ _ args body))
- = not (null args) -- it's manifestly a function...
- || isLeakFreeType [] (idType binder)
- || is_whnf body
- -- ToDo: use a decent manifestlyWHNF function for STG?
- where
- is_whnf (StgCon _ _ _) = True
- is_whnf (StgApp (StgVarArg v) _ _) = isBottomingId v
- is_whnf other = False
-
- is_liftable (StgRec [(_, StgRhsClosure _ _ _ _ args body)])
- = not (null args) -- it's manifestly a (recursive) function...
-
- is_liftable anything_else = False
+ 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}
+
%************************************************************************
%* *
\subsection[coreToStg-binds]{Converting bindings}
%************************************************************************
\begin{code}
-coreBindToStg :: StgEnv
- -> CoreBinding
- -> UniqSM ([StgBinding], -- Empty or singleton
- StgEnv, -- New envt
- Bag StgBinding) -- Floats
+coreBindToStg :: TopLevelFlag -> StgEnv -> CoreBind -> UniqSM (StgFloatBind, StgEnv)
+
+coreBindToStg top_lev env (NonRec binder rhs)
+ = coreExprToStgFloat env rhs `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 env (NonRec binder rhs)
- = coreRhsToStg env rhs `thenUs` \ (stg_rhs, rhs_binds) ->
- let
- -- Binds to return if RHS is trivial
- triv_binds = if isExported binder then
- [StgNonRec binder stg_rhs] -- Retain it
- else
- [] -- Discard it
- in
- case stg_rhs of
- StgRhsClosure cc bi fvs upd [] (StgApp atom [] lvs) ->
- -- Trivial RHS, so augment envt, and ditch the binding
- returnUs (triv_binds, new_env, rhs_binds)
- where
- new_env = addOneToIdEnv env binder atom
-
- StgRhsCon cc con_id [] ->
- -- Trivial RHS, so augment envt, and ditch the binding
- returnUs (triv_binds, new_env, rhs_binds)
- where
- new_env = addOneToIdEnv env binder (StgVarArg con_id)
-
- other -> -- Non-trivial RHS, so don't augment envt
- returnUs ([StgNonRec binder stg_rhs], env, rhs_binds)
-
-coreBindToStg env (Rec pairs)
- = -- NB: *** WE DO NOT CHECK FOR TRIV_BINDS in REC BIND ****
- -- (possibly ToDo)
- let
- (binders, rhss) = unzip pairs
- in
- mapAndUnzipUs (coreRhsToStg env) rhss `thenUs` \ (stg_rhss, rhs_binds) ->
- returnUs ([StgRec (binders `zip` stg_rhss)], env, unionManyBags rhs_binds)
+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')
+ where
+ binders = map fst pairs
+ do_rhs env (bndr,rhs) = coreExprToStgFloat env rhs `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 (bdrDem bndr) top_lev stg_expr')
\end{code}
%************************************************************************
\begin{code}
-coreRhsToStg :: StgEnv -> CoreExpr -> UniqSM (StgRhs, Bag StgBinding)
-
-coreRhsToStg env core_rhs
- = coreExprToStg env core_rhs `thenUs` \ (stg_expr, stg_binds) ->
-
- let stg_rhs = case stg_expr of
- StgLet (StgNonRec var1 rhs) (StgApp (StgVarArg 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
-
- StgCon con args _ -> StgRhsCon noCostCentre con args
-
- other -> StgRhsClosure noCostCentre -- No cost centre (ToDo?)
- stgArgOcc -- safe
- bOGUS_FVs
- Updatable -- Be pessimistic
- []
- stg_expr
- in
- returnUs (stg_rhs, stg_binds)
+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:
+
+ - 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.
+-}
+exprToRhs dem toplev (StgConApp con args)
+ | isNotTopLevel toplev || not (isDllConApp con args)
+ -- isDllConApp checks for LitLit args too
+ = StgRhsCon noCCS con args
+
+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"
\end{code}
%************************************************************************
%* *
-\subsection[coreToStg-lits]{Converting literals}
+\subsection[coreToStg-atoms{Converting atoms}
%* *
%************************************************************************
-Literals: the NoRep kind need to be de-no-rep'd.
-We always replace them with a simple variable, and float a suitable
-binding out to the top level.
+\begin{code}
+coreArgsToStg :: StgEnv -> [(CoreArg,RhsDemand)] -> UniqSM ([StgFloatBind], [StgArg])
+-- Arguments are all value arguments (tyargs already removed), paired with their demand
-If an Integer is small enough (Haskell implementations must support
-Ints in the range $[-2^29+1, 2^29-1]$), wrap it up in @int2Integer@;
-otherwise, wrap with @litString2Integer@.
+coreArgsToStg env []
+ = returnUs ([], [])
-\begin{code}
-tARGET_MIN_INT, tARGET_MAX_INT :: Integer
-tARGET_MIN_INT = -536870912
-tARGET_MAX_INT = 536870912
+coreArgsToStg env (ad:ads)
+ = coreArgToStg env ad `thenUs` \ (bs1, a') ->
+ coreArgsToStg env ads `thenUs` \ (bs2, as') ->
+ returnUs (bs1 ++ bs2, a' : as')
-litToStgArg :: Literal -> UniqSM (StgArg, Bag StgBinding)
-litToStgArg (NoRepStr s)
- = newStgVar stringTy `thenUs` \ var ->
- let
- rhs = StgRhsClosure noCostCentre -- No cost centre (ToDo?)
- stgArgOcc -- safe
- bOGUS_FVs
- Updatable -- WAS: ReEntrant (see note below)
- [] -- No arguments
- val
-
--- We used not to update strings, so that they wouldn't clog up the heap,
--- but instead be unpacked each time. But on some programs that costs a lot
--- [eg hpg], so now we update them.
-
- val = if (any is_NUL (_UNPK_ s)) then -- must cater for NULs in literal string
- StgApp (StgVarArg unpackCString2Id)
- [StgLitArg (MachStr s),
- StgLitArg (mkMachInt (toInteger (_LENGTH_ s)))]
- bOGUS_LVs
- else
- StgApp (StgVarArg unpackCStringId)
- [StgLitArg (MachStr s)]
- bOGUS_LVs
- in
- returnUs (StgVarArg var, unitBag (StgNonRec var rhs))
+coreArgToStg :: StgEnv -> (CoreArg,RhsDemand) -> UniqSM ([StgFloatBind], StgArg)
+-- This is where we arrange that a non-trivial argument is let-bound
+
+coreArgToStg env (arg,dem)
+ = coreExprToStgFloat env arg `thenUs` \ (floats, arg') ->
+ case arg' of
+ StgApp v [] -> returnUs (floats, StgVarArg v)
+ StgLit lit -> returnUs (floats, StgLitArg lit)
+
+ StgConApp con [] -> returnUs (floats, StgVarArg (dataConWrapId con))
+ -- A nullary constructor can be replaced with
+ -- a ``call'' to its wrapper
+
+ other -> newStgVar arg_ty `thenUs` \ v ->
+ returnUs ([NonRecF v arg' dem floats], StgVarArg v)
where
- is_NUL c = c == '\0'
-
-litToStgArg (NoRepInteger i)
- -- extremely convenient to look out for a few very common
- -- Integer literals!
- | i == 0 = returnUs (StgVarArg integerZeroId, emptyBag)
- | i == 1 = returnUs (StgVarArg integerPlusOneId, emptyBag)
- | i == 2 = returnUs (StgVarArg integerPlusTwoId, emptyBag)
- | i == (-1) = returnUs (StgVarArg integerMinusOneId, emptyBag)
-
- | otherwise
- = newStgVar integerTy `thenUs` \ var ->
- let
- rhs = StgRhsClosure noCostCentre -- No cost centre (ToDo?)
- stgArgOcc -- safe
- bOGUS_FVs
- Updatable -- Update an integer
- [] -- No arguments
- val
-
- val
- | i > tARGET_MIN_INT && i < tARGET_MAX_INT
- = -- Start from an Int
- StgPrim Int2IntegerOp [StgLitArg (mkMachInt i)] bOGUS_LVs
-
- | otherwise
- = -- Start from a string
- StgPrim Addr2IntegerOp [StgLitArg (MachStr (_PK_ (show i)))] bOGUS_LVs
- in
- returnUs (StgVarArg var, unitBag (StgNonRec var rhs))
-
-litToStgArg (NoRepRational r)
- = litToStgArg (NoRepInteger (numerator r)) `thenUs` \ (num_atom, binds1) ->
- litToStgArg (NoRepInteger (denominator r)) `thenUs` \ (denom_atom, binds2) ->
- newStgVar rationalTy `thenUs` \ var ->
- let
- rhs = StgRhsCon noCostCentre -- No cost centre (ToDo?)
- ratioDataCon -- Constructor
- [num_atom, denom_atom]
- in
- returnUs (StgVarArg var, binds1 `unionBags`
- binds2 `unionBags`
- unitBag (StgNonRec var rhs))
-
-litToStgArg other_lit = returnUs (StgLitArg other_lit, emptyBag)
+ arg_ty = exprType arg
\end{code}
%************************************************************************
%* *
-\subsection[coreToStg-atoms{Converting atoms}
+\subsection[coreToStg-exprs]{Converting core expressions}
%* *
%************************************************************************
\begin{code}
-coreArgsToStg :: StgEnv -> [CoreArg] -> UniqSM ([Type], [StgArg], Bag StgBinding)
-
-coreArgsToStg env [] = returnUs ([], [], emptyBag)
-coreArgsToStg env (a:as)
- = coreArgsToStg env as `thenUs` \ (tys, args, binds) ->
- do_arg a tys args binds
- where
- do_arg a trest vrest binds
- = case a of
- TyArg t -> returnUs (t:trest, vrest, binds)
- UsageArg u -> returnUs (trest, vrest, binds)
- VarArg v -> returnUs (trest, stgLookup env v : vrest, binds)
- LitArg i -> litToStgArg i `thenUs` \ (v, bs) ->
- returnUs (trest, v:vrest, bs `unionBags` binds)
-\end{code}
-
-There's not anything interesting we can ASSERT about \tr{var} if it
-isn't in the StgEnv. (WDP 94/06)
-\begin{code}
-stgLookup :: StgEnv -> Id -> StgArg
-
-stgLookup env var = case (lookupIdEnv env var) of
- Nothing -> StgVarArg var
- Just atom -> atom
+coreExprToStg :: StgEnv -> CoreExpr -> UniqSM StgExpr
+coreExprToStg env expr
+ = coreExprToStgFloat env expr `thenUs` \ (binds,stg_expr) ->
+ mkStgBinds binds stg_expr `thenUs` \ stg_expr' ->
+ deStgLam stg_expr'
\end{code}
%************************************************************************
%* *
-\subsection[coreToStg-exprs]{Converting core expressions}
+\subsubsection[coreToStg-let(rec)]{Let and letrec expressions}
%* *
%************************************************************************
\begin{code}
-coreExprToStg :: StgEnv
- -> CoreExpr
- -> UniqSM (StgExpr, -- Result
- Bag StgBinding) -- Float these to top level
+coreExprToStgFloat :: StgEnv -> CoreExpr
+ -> UniqSM ([StgFloatBind], StgExpr)
+-- Transform an expression to STG. The 'floats' are
+-- any bindings we had to create for function arguments.
\end{code}
+Simple cases first
+
\begin{code}
-coreExprToStg env (Lit lit)
- = litToStgArg lit `thenUs` \ (atom, binds) ->
- returnUs (StgApp atom [] bOGUS_LVs, binds)
+coreExprToStgFloat env (Var var)
+ = mkStgApp env var [] (idType var) `thenUs` \ app ->
+ returnUs ([], app)
-coreExprToStg env (Var var)
- = returnUs (StgApp (stgLookup env var) [] bOGUS_LVs, emptyBag)
+coreExprToStgFloat env (Lit lit)
+ = returnUs ([], StgLit lit)
-coreExprToStg env (Con con args)
- = coreArgsToStg env args `thenUs` \ (types, stg_atoms, stg_binds) ->
- let
- spec_con = mkSpecialisedCon con types
- in
- returnUs (StgCon spec_con stg_atoms bOGUS_LVs, stg_binds)
+coreExprToStgFloat env (Let bind body)
+ = coreBindToStg NotTopLevel env bind `thenUs` \ (new_bind, new_env) ->
+ coreExprToStgFloat new_env body `thenUs` \ (floats, stg_body) ->
+ returnUs (new_bind:floats, stg_body)
+\end{code}
-coreExprToStg env (Prim op args)
- = coreArgsToStg env args `thenUs` \ (_, stg_atoms, stg_binds) ->
- returnUs (StgPrim op stg_atoms bOGUS_LVs, stg_binds)
+Convert core @scc@ expression directly to STG @scc@ expression.
+
+\begin{code}
+coreExprToStgFloat env (Note (SCC cc) expr)
+ = coreExprToStg env expr `thenUs` \ stg_expr ->
+ returnUs ([], StgSCC cc stg_expr)
+
+coreExprToStgFloat env (Note other_note expr)
+ = coreExprToStgFloat env expr
+\end{code}
+
+\begin{code}
+coreExprToStgFloat env expr@(Type _)
+ = pprPanic "coreExprToStgFloat: tyarg unexpected:" $ ppr expr
\end{code}
+
%************************************************************************
%* *
\subsubsection[coreToStg-lambdas]{Lambda abstractions}
%************************************************************************
\begin{code}
-coreExprToStg env expr@(Lam _ _)
+coreExprToStgFloat env expr@(Lam _ _)
= let
- (_,_, binders, body) = collectBinders expr
+ expr_ty = exprType expr
+ (binders, body) = collectBinders expr
+ id_binders = filter isId binders
in
- coreExprToStg env body `thenUs` \ (stg_body, binds) ->
- newStgVar (coreExprType expr) `thenUs` \ var ->
- returnUs
- (StgLet (StgNonRec var (StgRhsClosure noCostCentre
- stgArgOcc
- bOGUS_FVs
- ReEntrant -- binders is non-empty
- binders
- stg_body))
- (StgApp (StgVarArg var) [] bOGUS_LVs),
- binds)
+ if null id_binders then -- It was all type/usage binders; tossed
+ coreExprToStgFloat env body
+ else
+ -- At least some value binders
+ newLocalIds NotTopLevel env id_binders `thenUs` \ (env', binders') ->
+ coreExprToStgFloat env' body `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}
%************************************************************************
\begin{code}
-coreExprToStg env expr@(App _ _)
+coreExprToStgFloat env expr@(App _ _)
= let
- (fun, _, _, args) = collectArgs expr
+ (fun,rads,ty,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
- -- Deal with the arguments
- coreArgsToStg env args `thenUs` \ (_, stg_args, arg_binds) ->
+ coreArgsToStg env final_ads `thenUs` \ (arg_floats, stg_args) ->
-- Now deal with the function
- case fun of
- Var fun_id -> returnUs (StgApp (stgLookup env fun_id) stg_args bOGUS_LVs, arg_binds)
+ case (fun, stg_args) of
+ (Var fn_id, _) -> -- A function Id, so do an StgApp; it's ok if
+ -- there are no arguments.
+ mkStgApp env fn_id stg_args ty `thenUs` \ app ->
+ returnUs (arg_floats, app)
+
+ (non_var_fun, []) -> -- No value args, so recurse into the function
+ ASSERT( null arg_floats )
+ coreExprToStgFloat env non_var_fun
other -> -- A non-variable applied to things; better let-bind it.
- newStgVar (coreExprType fun) `thenUs` \ fun_id ->
- coreExprToStg env fun `thenUs` \ (stg_fun, fun_binds) ->
- let
- fun_rhs = StgRhsClosure noCostCentre -- No cost centre (ToDo?)
- stgArgOcc
- bOGUS_FVs
- SingleEntry -- Only entered once
- []
- stg_fun
- in
- returnUs (StgLet (StgNonRec fun_id fun_rhs)
- (StgApp (StgVarArg fun_id) stg_args bOGUS_LVs),
- arg_binds `unionBags` fun_binds)
+ newStgVar (exprType fun) `thenUs` \ fn_id ->
+ coreExprToStgFloat env fun `thenUs` \ (fun_floats, stg_fun) ->
+ mkStgApp env fn_id stg_args ty `thenUs` \ app ->
+ returnUs (NonRecF fn_id stg_fun onceDem fun_floats : arg_floats,
+ app)
+
+ 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 idStrictness v of
+ StrictnessInfo demands _ -> demands
+ other -> repeat wwLazy
+
+ collect_args fun = (fun, [], exprType fun, repeat wwLazy)
+
+ -- "zap" nukes the strictness info for a partial application
+ zap ads = [(arg, RhsDemand False once) | (arg, RhsDemand _ once) <- ads]
\end{code}
+
%************************************************************************
%* *
\subsubsection[coreToStg-cases]{Case expressions}
%* *
%************************************************************************
-At this point, we *mangle* cases involving fork# and par# in the
-discriminant. The original templates for these primops (see
-@PrelVals.lhs@) constructed case expressions with boolean results
-solely to fool the strictness analyzer, the simplifier, and anyone
-else who might want to fool with the evaluation order. Now, we
-believe that once the translation to STG code is performed, our
-evaluation order is safe. Therefore, we convert expressions of the
-form:
-
- case par# e of
- True -> rhs
- False -> parError#
-
-to
-
- case par# e of
- _ -> rhs
-
\begin{code}
-
-coreExprToStg env (Case discrim@(Prim op _) alts)
- | funnyParallelOp op
- = getUnique `thenUs` \ uniq ->
- coreExprToStg env discrim `thenUs` \ (stg_discrim, discrim_binds) ->
- alts_to_stg alts `thenUs` \ (stg_alts, alts_binds) ->
- returnUs (
- StgCase stg_discrim
- bOGUS_LVs
- bOGUS_LVs
- uniq
- stg_alts,
- discrim_binds `unionBags` alts_binds
- )
+coreExprToStgFloat env (Case scrut bndr alts)
+ = coreExprToStgFloat env scrut `thenUs` \ (binds, scrut') ->
+ newLocalId NotTopLevel env bndr `thenUs` \ (env', bndr') ->
+ alts_to_stg env' (findDefault alts) `thenUs` \ alts' ->
+ mkStgCase scrut' bndr' alts' `thenUs` \ expr' ->
+ returnUs (binds, expr')
where
- funnyParallelOp SeqOp = True
- funnyParallelOp ParOp = True
- funnyParallelOp ForkOp = True
- funnyParallelOp _ = False
-
- discrim_ty = coreExprType discrim
-
- alts_to_stg (PrimAlts _ (BindDefault binder rhs))
- = coreExprToStg env rhs `thenUs` \ (stg_rhs, rhs_binds) ->
- let
- stg_deflt = StgBindDefault binder False stg_rhs
- in
- returnUs (StgPrimAlts discrim_ty [] stg_deflt, rhs_binds)
-
--- OK, back to real life...
-
-coreExprToStg env (Case discrim alts)
- = coreExprToStg env discrim `thenUs` \ (stg_discrim, discrim_binds) ->
- alts_to_stg discrim alts `thenUs` \ (stg_alts, alts_binds) ->
- getUnique `thenUs` \ uniq ->
- returnUs (
- StgCase stg_discrim
- bOGUS_LVs
- bOGUS_LVs
- uniq
- stg_alts,
- discrim_binds `unionBags` alts_binds
- )
- where
- discrim_ty = coreExprType discrim
- (_, discrim_ty_args, _) = getAppDataTyCon discrim_ty
-
- alts_to_stg discrim (AlgAlts alts deflt)
- = default_to_stg discrim deflt `thenUs` \ (stg_deflt, deflt_binds) ->
- mapAndUnzipUs boxed_alt_to_stg alts `thenUs` \ (stg_alts, alts_binds) ->
- returnUs (StgAlgAlts discrim_ty stg_alts stg_deflt,
- deflt_binds `unionBags` unionManyBags alts_binds)
- where
- boxed_alt_to_stg (con, bs, rhs)
- = coreExprToStg env rhs `thenUs` \ (stg_rhs, rhs_binds) ->
- returnUs ((spec_con, bs, [ True | b <- bs ]{-bogus use mask-}, stg_rhs),
- rhs_binds)
- where
- spec_con = mkSpecialisedCon con discrim_ty_args
-
- alts_to_stg discrim (PrimAlts alts deflt)
- = default_to_stg discrim deflt `thenUs` \ (stg_deflt,deflt_binds) ->
- mapAndUnzipUs unboxed_alt_to_stg alts `thenUs` \ (stg_alts, alts_binds) ->
- returnUs (StgPrimAlts discrim_ty stg_alts stg_deflt,
- deflt_binds `unionBags` unionManyBags alts_binds)
- where
- unboxed_alt_to_stg (lit, rhs)
- = coreExprToStg env rhs `thenUs` \ (stg_rhs, rhs_binds) ->
- returnUs ((lit, stg_rhs), rhs_binds)
-
- default_to_stg discrim NoDefault
- = returnUs (StgNoDefault, emptyBag)
-
- default_to_stg discrim (BindDefault binder rhs)
- = coreExprToStg new_env rhs `thenUs` \ (stg_rhs, rhs_binds) ->
- returnUs (StgBindDefault binder True{-used? no it is lying-} stg_rhs,
- rhs_binds)
- where
- --
- -- We convert case x of {...; x' -> ...x'...}
- -- to
- -- case x of {...; _ -> ...x... }
- --
- -- See notes in SimplCase.lhs, near simplDefault for the reasoning.
- -- It's quite easily done: simply extend the environment to bind the
- -- default binder to the scrutinee.
- --
- new_env = case discrim of
- Var v -> addOneToIdEnv env binder (stgLookup env v)
- other -> env
+ 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 (DataAlt con, bs, rhs)
+ = newLocalIds NotTopLevel env (filter isId bs) `thenUs` \ (env', stg_bs) ->
+ coreExprToStg env' rhs `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 (LitAlt lit, args, rhs)
+ = ASSERT( null args )
+ coreExprToStg env rhs `thenUs` \ stg_rhs ->
+ returnUs (lit, stg_rhs)
+
+ default_to_stg env Nothing
+ = returnUs StgNoDefault
+
+ default_to_stg env (Just rhs)
+ = coreExprToStg env rhs `thenUs` \ stg_rhs ->
+ returnUs (StgBindDefault stg_rhs)
+ -- The binder is used for prim cases and not otherwise
+ -- (hack for old code gen)
\end{code}
+
%************************************************************************
%* *
-\subsubsection[coreToStg-let(rec)]{Let and letrec expressions}
+\subsection[coreToStg-misc]{Miscellaneous helping functions}
%* *
%************************************************************************
+There's not anything interesting we can ASSERT about \tr{var} if it
+isn't in the StgEnv. (WDP 94/06)
+
+Invent a fresh @Id@:
\begin{code}
-coreExprToStg env (Let bind body)
- = coreBindToStg env bind `thenUs` \ (stg_binds, new_env, float_binds1) ->
- coreExprToStg new_env body `thenUs` \ (stg_body, float_binds2) ->
- returnUs (mkStgLets stg_binds stg_body, float_binds1 `unionBags` float_binds2)
+newStgVar :: Type -> UniqSM Id
+newStgVar ty
+ = getUniqueUs `thenUs` \ uniq ->
+ seqType ty `seq`
+ returnUs (mkSysLocal SLIT("stg") uniq ty)
\end{code}
+\begin{code}
+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)
-%************************************************************************
-%* *
-\subsubsection[coreToStg-scc]{SCC expressions}
-%* *
-%************************************************************************
-Covert core @scc@ expression directly to STG @scc@ expression.
-\begin{code}
-coreExprToStg env (SCC cc expr)
- = coreExprToStg env expr `thenUs` \ (stg_expr, binds) ->
- returnUs (StgSCC (coreExprType expr) cc stg_expr, binds)
+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')
\end{code}
%************************************************************************
%* *
-\subsection[coreToStg-misc]{Miscellaneous helping functions}
+\subsection{Building STG syn}
%* *
%************************************************************************
-Utilities.
-
-Invent a fresh @Id@:
\begin{code}
-newStgVar :: Type -> UniqSM Id
-newStgVar ty
- = getUnique `thenUs` \ uniq ->
- returnUs (mkSysLocal SLIT("stg") uniq ty mkUnknownSrcLoc)
+mkStgAlgAlts ty alts deflt = seqType ty `seq` StgAlgAlts ty alts deflt
+mkStgPrimAlts ty alts deflt = seqType ty `seq` StgPrimAlts ty alts deflt
+mkStgLam ty bndrs body = seqType ty `seq` StgLam ty bndrs body
+
+mkStgApp :: StgEnv -> Id -> [StgArg] -> Type -> UniqSM StgExpr
+ -- The type is the type of the entire application
+mkStgApp env fn args ty
+ = case idFlavour fn_alias of
+ DataConId dc
+ -> saturate fn_alias args ty $ \ args' ty' ->
+ returnUs (StgConApp dc args')
+
+ PrimOpId (CCallOp (CCall (DynamicTarget _) a b c))
+ -- Sigh...make a guaranteed unique name for a dynamic ccall
+ -> saturate fn_alias args ty $ \ args' ty' ->
+ getUniqueUs `thenUs` \ u ->
+ returnUs (StgPrimApp (CCallOp (CCall (DynamicTarget u) a b c)) args' ty')
+
+ PrimOpId op
+ -> saturate fn_alias args ty $ \ args' ty' ->
+ returnUs (StgPrimApp op args' ty')
+
+ other -> returnUs (StgApp fn_alias args)
+ -- Force the lookup
+ where
+ fn_alias = case (lookupVarEnv env fn) of -- In case it's been cloned
+ Nothing -> fn
+ Just fn' -> fn'
+
+saturate :: Id -> [StgArg] -> Type -> ([StgArg] -> Type -> UniqSM StgExpr) -> UniqSM StgExpr
+ -- The type should be the type of (id args)
+saturate fn args ty thing_inside
+ | excess_arity == 0 -- Saturated, so nothing to do
+ = thing_inside args ty
+
+ | otherwise -- An unsaturated constructor or primop; eta expand it
+ = ASSERT2( excess_arity > 0 && excess_arity <= length arg_tys,
+ ppr fn <+> ppr args <+> ppr excess_arity <+> parens (ppr ty) <+> ppr arg_tys )
+ mapUs newStgVar extra_arg_tys `thenUs` \ arg_vars ->
+ thing_inside (args ++ map StgVarArg arg_vars) final_res_ty `thenUs` \ body ->
+ returnUs (StgLam ty arg_vars body)
+ where
+ fn_arity = idArity fn
+ excess_arity = fn_arity - length args
+ (arg_tys, res_ty) = splitRepFunTys ty
+ extra_arg_tys = take excess_arity arg_tys
+ final_res_ty = mkFunTys (drop excess_arity arg_tys) res_ty
\end{code}
\begin{code}
-mkStgLets :: [StgBinding]
- -> StgExpr -- body of let
- -> StgExpr
+-- Stg doesn't have a lambda *expression*
+deStgLam (StgLam ty bndrs body)
+ -- Try for eta reduction
+ = ASSERT( not (null bndrs) )
+ case eta body of
+ Just e -> -- Eta succeeded
+ returnUs e
+
+ Nothing -> -- Eta failed, so let-bind the lambda
+ 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
+
+ eta (StgApp f args)
+ | n_remaining >= 0 &&
+ and (zipWith ok bndrs last_args) &&
+ notInExpr bndrs remaining_expr
+ = Just remaining_expr
+ where
+ remaining_expr = StgApp f remaining_args
+ (remaining_args, last_args) = splitAt n_remaining args
+ n_remaining = length args - length bndrs
+
+ eta (StgLet bind@(StgNonRec b r) body)
+ | notInRhs bndrs r = case eta body of
+ Just e -> Just (StgLet bind e)
+ Nothing -> Nothing
+
+ eta _ = Nothing
+
+ ok bndr (StgVarArg arg) = bndr == arg
+ ok bndr other = False
+
+deStgLam expr = returnUs expr
+
+
+--------------------------------------------------
+notInExpr :: [Id] -> StgExpr -> Bool
+notInExpr vs (StgApp f args) = notInId vs f && notInArgs vs args
+notInExpr vs (StgLet (StgNonRec b r) body) = notInRhs vs r && notInExpr vs body
+notInExpr vs other = False -- Safe
+
+notInRhs :: [Id] -> StgRhs -> Bool
+notInRhs vs (StgRhsCon _ _ args) = notInArgs vs args
+notInRhs vs (StgRhsClosure _ _ _ _ _ _ body) = notInExpr vs body
+ -- Conservative: we could delete the binders from vs, but
+ -- cloning means this will never help
+
+notInArgs :: [Id] -> [StgArg] -> Bool
+notInArgs vs args = all ok args
+ where
+ ok (StgVarArg v) = notInId vs v
+ ok (StgLitArg l) = True
+
+notInId :: [Id] -> Id -> Bool
+notInId vs v = not (v `elem` vs)
+
+
+
+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'
+
+-- 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 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
+
+mk_stg_let bndr rhs dem floats body
+#endif
+ | isUnLiftedType bndr_rep_ty -- Use a case/PrimAlts
+ = ASSERT( not (isUnboxedTupleType bndr_rep_ty) )
+ mkStgCase rhs bndr (StgPrimAlts bndr_rep_ty [] (StgBindDefault body)) `thenUs` \ expr' ->
+ mkStgBinds floats expr'
+
+ | 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
+ mkStgCase rhs bndr (StgAlgAlts bndr_rep_ty [] (StgBindDefault body)) `thenUs` \ expr' ->
+ mkStgBinds floats expr'
+ 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
+ StgConApp _ _ -> 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 [] = ([], [])
+\end{code}
+
-mkStgLets binds body = foldr StgLet body binds
+Making an STG case
+~~~~~~~~~~~~~~~~~~
+
+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}
+-- Discard alernatives in case (par# ..) of
+mkStgCase scrut@(StgPrimApp ParOp _ _) bndr
+ (StgPrimAlts ty _ deflt@(StgBindDefault _))
+ = returnUs (StgCase scrut bOGUS_LVs bOGUS_LVs bndr noSRT (StgPrimAlts ty [] deflt))
+
+mkStgCase (StgPrimApp SeqOp [scrut] _) bndr
+ (StgPrimAlts _ _ deflt@(StgBindDefault rhs))
+ = mkStgCase scrut_expr new_bndr new_alts
+ where
+ new_alts | isUnLiftedType scrut_ty = WARN( True, text "mkStgCase" ) StgPrimAlts scrut_ty [] deflt
+ | otherwise = StgAlgAlts scrut_ty [] deflt
+ 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.
+
+ 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
+
+mkStgCase scrut bndr alts
+ = deStgLam scrut `thenUs` \ scrut' ->
+ -- It is (just) possible to get a lambda as a srutinee here
+ -- Namely: fromDyn (toDyn ((+1)::Int->Int)) False)
+ -- gives: case ...Bool == Int->Int... of
+ -- True -> case coerce Bool (\x -> + 1 x) of
+ -- True -> ...
+ -- False -> ...
+ -- False -> ...
+ -- The True branch of the outer case will never happen, of course.
+
+ returnUs (StgCase scrut' bOGUS_LVs bOGUS_LVs bndr noSRT alts)
\end{code}
projects / ghc-hetmet.git / blobdiff