import CoreUtils ( coreExprType )
import SimplUtils ( findDefault )
import CostCentre ( noCCS )
-import Id ( Id, mkSysLocal, idType,
- externallyVisibleId, setIdUnique, idName
+import Id ( Id, mkSysLocal, idType, getIdStrictness, idUnique, isExportedId,
+ externallyVisibleId, setIdUnique, idName, getIdDemandInfo, setIdType
)
+import Var ( Var, varType, modifyIdInfo )
+import IdInfo ( setDemandInfo, StrictnessInfo(..) )
+import UsageSPUtils ( primOpUsgTys )
import DataCon ( DataCon, dataConName, dataConId )
+import Demand ( Demand, isStrict, wwStrict, wwLazy )
import Name ( Name, nameModule, isLocallyDefinedName )
import Module ( isDynamicModule )
-import Const ( Con(..), Literal, isLitLitLit )
+import Const ( Con(..), Literal(..), isLitLitLit, conStrictness, isWHNFCon )
import VarEnv
-import Const ( Con(..), isWHNFCon, Literal(..) )
-import PrimOp ( PrimOp(..) )
-import Type ( isUnLiftedType, isUnboxedTupleType, Type )
-import Unique ( Unique, Uniquable(..) )
+import PrimOp ( PrimOp(..), primOpUsg, primOpSig )
+import Type ( isUnLiftedType, isUnboxedTupleType, Type, splitFunTy_maybe,
+ UsageAnn(..), tyUsg, applyTy, mkUsgTy )
+import TysPrim ( intPrimTy )
import UniqSupply -- all of it, really
+import Util ( lengthExceeds )
+import BasicTypes ( TopLevelFlag(..), isNotTopLevel )
+import CmdLineOpts ( opt_D_verbose_stg2stg )
+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.]
+
+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
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 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 = case tyUsg ty of
+ UsOnce -> True
+ UsMany -> False
+
+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
\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}
-> [StgBinding] -- output
topCoreBindsToStg us core_binds
- = initUs us (coreBindsToStg emptyVarEnv core_binds)
+ = initUs_ us (coreBindsToStg emptyVarEnv core_binds)
where
coreBindsToStg :: StgEnv -> [CoreBind] -> UniqSM [StgBinding]
coreBindsToStg env [] = returnUs []
coreBindsToStg env (b:bs)
- = coreBindToStg env b `thenUs` \ (new_b, new_env) ->
+ = coreBindToStg TopLevel env b `thenUs` \ (bind_spec, new_env) ->
coreBindsToStg new_env bs `thenUs` \ new_bs ->
- returnUs (new_b ++ 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
- -> CoreBind
- -> UniqSM ([StgBinding], -- Empty or singleton
- StgEnv) -- Floats
-
-coreBindToStg env (NonRec binder rhs)
- = coreRhsToStg env rhs `thenUs` \ stg_rhs ->
- newLocalId env binder `thenUs` \ (new_env, new_binder) ->
- returnUs ([StgNonRec new_binder stg_rhs], new_env)
-
-coreBindToStg env (Rec pairs)
- = newLocalIds env binders `thenUs` \ (env', binders') ->
- mapUs (coreRhsToStg env') rhss `thenUs` \ stg_rhss ->
- returnUs ([StgRec (binders' `zip` stg_rhss)], env')
+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')
where
- (binders, rhss) = unzip pairs
+ 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}
%************************************************************************
\begin{code}
-coreRhsToStg :: StgEnv -> CoreExpr -> UniqSM StgRhs
-
-coreRhsToStg env core_rhs
- = coreExprToStg env core_rhs `thenUs` \ stg_expr ->
- returnUs (exprToRhs stg_expr)
-
-exprToRhs (StgLet (StgNonRec var1 rhs) (StgApp var2 []))
- | var1 == var2
- = rhs
- -- This curious stuff is to unravel what a lambda turns into
- -- We have to do it this way, rather than spot a lambda in the
- -- incoming rhs. Why? Because trivial bindings might conceal
- -- what the rhs is actually like.
+exprToRhs :: RhsDemand -> TopLevelFlag -> StgExpr -> StgRhs
+exprToRhs dem _ (StgLam _ bndrs body)
+ = ASSERT( not (null bndrs) )
+ StgRhsClosure noCCS
+ stgArgOcc
+ noSRT
+ bOGUS_FVs
+ ReEntrant -- binders is non-empty
+ bndrs
+ body
{-
We reject the following candidates for 'static constructor'dom:
constructors (ala C++ static class constructors) which will
then be run at load time to fix up static closures.
-}
-exprToRhs (StgCon (DataCon con) args _)
- | not is_dynamic &&
- all (not.is_lit_lit) args = StgRhsCon noCCS con args
+exprToRhs dem toplev (StgCon (DataCon con) args _)
+ | isNotTopLevel toplev ||
+ (not is_dynamic &&
+ all (not.is_lit_lit) args) = StgRhsCon noCCS con args
where
is_dynamic = isDynCon con || any (isDynArg) args
Literal l -> isLitLitLit l
_ -> False
-exprToRhs expr
+exprToRhs dem _ expr
= StgRhsClosure noCCS -- No cost centre (ToDo?)
stgArgOcc -- safe
noSRT -- figure out later
bOGUS_FVs
-
- Updatable -- Be pessimistic
+ (if isOnceDem dem then SingleEntry else Updatable)
+ -- HA! Paydirt for "dem"
[]
expr
isDynName nm =
not (isLocallyDefinedName nm) &&
isDynamicModule (nameModule nm)
-
-
\end{code}
%************************************************************************
\begin{code}
-coreArgsToStg :: StgEnv -> [CoreArg]
- -> UniqSM ([(Id,StgExpr)], [StgArg])
+coreArgsToStg :: StgEnv -> [(CoreArg,RhsDemand)] -> UniqSM ([StgFloatBind], [StgArg])
+-- Arguments are all value arguments (tyargs already removed), paired with their demand
coreArgsToStg env []
= returnUs ([], [])
-coreArgsToStg env (Type ty : as) -- Discard type arguments
- = coreArgsToStg env as
-
-coreArgsToStg env (a:as)
- = coreArgToStg env a `thenUs` \ (bs1, a') ->
- coreArgsToStg env as `thenUs` \ (bs2, as') ->
+coreArgsToStg env (ad:ads)
+ = coreArgToStg env ad `thenUs` \ (bs1, a') ->
+ coreArgsToStg env ads `thenUs` \ (bs2, as') ->
returnUs (bs1 ++ bs2, a' : as')
--- This is where we arrange that a non-trivial argument is let-bound
-
-coreArgToStg :: StgEnv -> CoreArg -> UniqSM ([(Id,StgExpr)], StgArg)
-coreArgToStg env arg
- = coreExprToStgFloat env arg `thenUs` \ (binds, arg') ->
- case (binds, arg') of
- ([], StgCon con [] _) | isWHNFCon con -> returnUs ([], StgConArg con)
- ([], StgApp v []) -> returnUs ([], StgVarArg v)
-
- -- A non-trivial argument: we must let (or case-bind)
- -- We don't do the case part here... we leave that to mkStgLets
-
- -- Further complication: if we're converting this binding into
- -- a case, then try to avoid generating any case-of-case
- -- expressions by pulling out the floats.
- (_, other) ->
- newStgVar ty `thenUs` \ v ->
- if isUnLiftedType ty
- then returnUs (binds ++ [(v,arg')], StgVarArg v)
- else returnUs ([(v, mkStgLets binds arg')], StgVarArg v)
- where
- ty = coreExprType arg
+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 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}
%************************************************************************
\begin{code}
-coreExprToStg :: StgEnv -> CoreExpr -> UniqSM StgExpr
-
-coreExprToStg env (Var var)
- = returnUs (StgApp (stgLookup env var) [])
-
+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}
%************************************************************************
%* *
-\subsubsection[coreToStg-lambdas]{Lambda abstractions}
+\subsubsection[coreToStg-let(rec)]{Let and letrec expressions}
%* *
%************************************************************************
\begin{code}
-coreExprToStg env expr@(Lam _ _)
- = let
- (binders, body) = collectBinders expr
- id_binders = filter isId binders
- in
- newLocalIds env id_binders `thenUs` \ (env', binders') ->
- coreExprToStg env' body `thenUs` \ stg_body ->
+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}
- if null id_binders then -- it was all type/usage binders; tossed
- returnUs stg_body
- else
- case stg_body of
-
- -- if the body reduced to a lambda too...
- (StgLet (StgNonRec var (StgRhsClosure cc bi srt fvs uf args body))
- (StgApp var' []))
- | var == var' ->
- returnUs (StgLet (StgNonRec var
- (StgRhsClosure noCCS
- stgArgOcc
- noSRT
- bOGUS_FVs
- ReEntrant
- (binders' ++ args)
- body))
- (StgApp var []))
-
- other ->
+Simple cases first
- -- We must let-bind the lambda
- newStgVar (coreExprType expr) `thenUs` \ var ->
- returnUs
- (StgLet (StgNonRec var (StgRhsClosure noCCS
- stgArgOcc
- noSRT
- bOGUS_FVs
- ReEntrant -- binders is non-empty
- binders'
- stg_body))
- (StgApp var []))
+\begin{code}
+coreExprToStgFloat env (Var var) dem
+ = returnUs ([], StgApp (stgLookup env var) [])
+
+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)
\end{code}
-%************************************************************************
-%* *
-\subsubsection[coreToStg-let(rec)]{Let and letrec expressions}
-%* *
-%************************************************************************
+Convert core @scc@ expression directly to STG @scc@ expression.
+
+\begin{code}
+coreExprToStgFloat env (Note (SCC cc) expr) dem
+ = coreExprToStg env expr dem `thenUs` \ stg_expr ->
+ returnUs ([], StgSCC cc stg_expr)
+
+coreExprToStgFloat env (Note other_note expr) dem
+ = coreExprToStgFloat env expr dem
+\end{code}
\begin{code}
-coreExprToStg env (Let bind body)
- = coreBindToStg env bind `thenUs` \ (stg_binds, new_env) ->
- coreExprToStg new_env body `thenUs` \ stg_body ->
- returnUs (foldr StgLet stg_body stg_binds)
+coreExprToStgFloat env expr@(Type _) dem
+ = pprPanic "coreExprToStgFloat: tyarg unexpected:" $ ppr expr
\end{code}
%************************************************************************
%* *
-\subsubsection[coreToStg-scc]{SCC expressions}
+\subsubsection[coreToStg-lambdas]{Lambda abstractions}
%* *
%************************************************************************
-Covert core @scc@ expression directly to STG @scc@ expression.
-\begin{code}
-coreExprToStg env (Note (SCC cc) expr)
- = coreExprToStg env expr `thenUs` \ stg_expr ->
- returnUs (StgSCC cc stg_expr)
-\end{code}
-
\begin{code}
-coreExprToStg env (Note other_note expr) = coreExprToStg env expr
-\end{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' ->
-The rest are handled by coreExprStgFloat.
+ case stg_body' of
+ StgLam ty lam_bndrs lam_body ->
+ -- If the body reduced to a lambda too, join them up
+ returnUs ([], StgLam expr_ty (binders' ++ lam_bndrs) lam_body)
-\begin{code}
-coreExprToStg env expr
- = coreExprToStgFloat env expr `thenUs` \ (binds,stg_expr) ->
- returnUs (mkStgLets binds stg_expr)
+ other ->
+ -- Body didn't reduce to a lambda, so return one
+ returnUs ([], StgLam expr_ty binders' stg_body')
\end{code}
+
%************************************************************************
%* *
\subsubsection[coreToStg-applications]{Applications}
%************************************************************************
\begin{code}
-coreExprToStgFloat env expr@(App _ _)
+coreExprToStgFloat env expr@(App _ _) dem
= let
- (fun,args) = collect_args expr []
+ (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 args `thenUs` \ (binds, stg_args) ->
+ coreArgsToStg env final_ads `thenUs` \ (arg_floats, stg_args) ->
-- Now deal with the function
case (fun, stg_args) of
(Var fun_id, _) -> -- A function Id, so do an StgApp; it's ok if
-- there are no arguments.
- returnUs (binds,
- StgApp (stgLookup env fun_id) stg_args)
+ returnUs (arg_floats,
+ StgApp (stgLookup env fun_id) stg_args)
(non_var_fun, []) -> -- No value args, so recurse into the function
- ASSERT( null binds )
- coreExprToStg env non_var_fun `thenUs` \e ->
- returnUs ([], e)
+ ASSERT( null arg_floats )
+ coreExprToStgFloat env non_var_fun dem
other -> -- A non-variable applied to things; better let-bind it.
- newStgVar (coreExprType fun) `thenUs` \ fun_id ->
- coreExprToStg env fun `thenUs` \ (stg_fun) ->
- let
- fun_rhs = StgRhsClosure noCCS -- No cost centre (ToDo?)
- stgArgOcc
- noSRT
- bOGUS_FVs
- SingleEntry -- Only entered once
- []
- stg_fun
- in
- returnUs (binds,
- StgLet (StgNonRec fun_id fun_rhs) $
+ newStgVar (coreExprType fun) `thenUs` \ fun_id ->
+ coreExprToStgFloat env fun onceDem `thenUs` \ (fun_floats, stg_fun) ->
+ returnUs (NonRecF fun_id stg_fun onceDem fun_floats : arg_floats,
StgApp fun_id stg_args)
+
where
- -- Collect arguments
- collect_args (App fun arg) args = collect_args fun (arg:args)
- collect_args (Note (Coerce _ _) expr) args = collect_args expr args
- collect_args (Note InlineCall expr) args = collect_args expr args
- collect_args fun args = (fun, args)
+ -- 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
+
+ collect_args fun = (fun, [], coreExprType 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-con]{Constructors}
+\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.
+
\begin{code}
-coreExprToStgFloat env expr@(Con (PrimOp (CCallOp (Right _) a b c)) args)
- = getUniqueUs `thenUs` \ u ->
- coreArgsToStg env args `thenUs` \ (binds, stg_atoms) ->
- let con' = PrimOp (CCallOp (Right u) a b c) in
- returnUs (binds, StgCon con' stg_atoms (coreExprType expr))
-
-coreExprToStgFloat env expr@(Con con args)
- = coreArgsToStg env args `thenUs` \ (binds, stg_atoms) ->
- returnUs (binds, StgCon con stg_atoms (coreExprType expr))
+coreExprToStgFloat env expr@(Con con args) dem
+ = let
+ (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, StgCon con' stg_atoms (coreExprType expr))
\end{code}
+
%************************************************************************
%* *
\subsubsection[coreToStg-cases]{Case expressions}
%* *
%************************************************************************
+First, two special cases. We mangle cases involving
+ par# and seq#
+inthe scrutinee.
+
+Up to this point, seq# will appear like this:
+
+ case seq# e of
+ 0# -> seqError#
+ _ -> <stuff>
+
+This code comes from an unfolding for 'seq' in Prelude.hs.
+The 0# branch is purely to bamboozle the strictness analyser.
+For example, if <stuff> is strict in x, and there was no seqError#
+branch, the strictness analyser would conclude that the whole expression
+was strict in x, and perhaps evaluate x first -- but that would be a DISASTER.
+
+Now that the evaluation order is safe, we translate this into
+
+ case e of
+ _ -> ...
+
+This used to be done in the post-simplification phase, but we need
+unfoldings involving seq# to appear unmangled in the interface file,
+hence we do this mangling here.
+
+Similarly, par# has an unfolding in PrelConc.lhs that makes it show
+up like this:
+
+ case par# e of
+ 0# -> rhs
+ _ -> parError#
+
+
+ ==>
+ case par# e of
+ _ -> rhs
+
+fork# isn't handled like this - it's an explicit IO operation now.
+The reason is that fork# returns a ThreadId#, which gets in the
+way of the above scheme. And anyway, IO is the only guaranteed
+way to enforce ordering --SDM.
+
+
\begin{code}
-coreExprToStgFloat env expr@(Case scrut bndr alts)
- = coreExprToStgFloat env scrut `thenUs` \ (binds, scrut') ->
- newLocalId env bndr `thenUs` \ (env', bndr') ->
+coreExprToStgFloat env
+ (Case scrut@(Con (PrimOp SeqOp) [Type ty, e]) bndr alts) dem
+ = coreExprToStgFloat env (Case e new_bndr [(DEFAULT,[],default_rhs)]) dem
+ where
+ new_bndr = setIdType bndr ty
+ (other_alts, maybe_default) = findDefault alts
+ Just default_rhs = maybe_default
+
+coreExprToStgFloat env
+ (Case scrut@(Con (PrimOp ParOp) args) bndr alts) dem
+ | maybeToBool maybe_default
+ = coreExprToStgFloat env scrut (bdrDem bndr) `thenUs` \ (binds, scrut') ->
+ newEvaldLocalId env bndr `thenUs` \ (env', bndr') ->
+ coreExprToStg env' default_rhs dem `thenUs` \ default_rhs' ->
+ returnUs (binds, mkStgCase scrut' bndr' (StgPrimAlts (idType bndr) [] (StgBindDefault default_rhs')))
+ where
+ (other_alts, maybe_default) = findDefault alts
+ Just default_rhs = maybe_default
+\end{code}
+
+Now for normal case expressions...
+
+\begin{code}
+coreExprToStgFloat env (Case scrut bndr alts) dem
+ = coreExprToStgFloat env scrut (bdrDem bndr) `thenUs` \ (binds, scrut') ->
+ newEvaldLocalId env bndr `thenUs` \ (env', bndr') ->
alts_to_stg env' (findDefault alts) `thenUs` \ alts' ->
returnUs (binds, mkStgCase scrut' bndr' alts')
where
returnUs (StgAlgAlts scrut_ty alts' deflt')
alg_alt_to_stg env (DataCon con, bs, rhs)
- = coreExprToStg env rhs `thenUs` \ stg_rhs ->
+ = coreExprToStg env rhs dem `thenUs` \ stg_rhs ->
returnUs (con, filter isId bs, [ True | b <- 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 `thenUs` \ stg_rhs ->
+ 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 `thenUs` \ stg_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)
\end{code}
-\begin{code}
-coreExprToStgFloat env expr
- = coreExprToStg env expr `thenUs` \stg_expr ->
- returnUs ([], stg_expr)
-\end{code}
%************************************************************************
%* *
\end{code}
\begin{code}
-newLocalId env id
- | externallyVisibleId id
+-- 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')
+
+
+newLocalId TopLevel env id
= returnUs (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.
- | otherwise
+newLocalId NotTopLevel env id
= -- Local binder, give it a new unique Id.
getUniqueUs `thenUs` \ uniq ->
let
in
returnUs (new_env, id')
-newLocalIds :: StgEnv -> [Id] -> UniqSM (StgEnv, [Id])
-newLocalIds env []
+newLocalIds :: TopLevelFlag -> StgEnv -> [Id] -> UniqSM (StgEnv, [Id])
+newLocalIds top_lev env []
= returnUs (env, [])
-newLocalIds env (b:bs)
- = newLocalId env b `thenUs` \ (env', b') ->
- newLocalIds env' bs `thenUs` \ (env'', bs') ->
+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}
\begin{code}
-mkStgLets :: [(Id,StgExpr)] -> StgExpr -> StgExpr
-mkStgLets binds body = foldr mkStgLet body binds
+-- Stg doesn't have a lambda *expression*,
+deStgLam (StgLam ty bndrs body) = mkStgLamExpr ty bndrs body
+deStgLam expr = returnUs expr
+
+mkStgLamExpr ty bndrs body
+ = ASSERT( not (null bndrs) )
+ newStgVar ty `thenUs` \ fn ->
+ returnUs (StgLet (StgNonRec fn lam_closure) (StgApp fn []))
+ where
+ lam_closure = StgRhsClosure noCCS
+ stgArgOcc
+ noSRT
+ bOGUS_FVs
+ ReEntrant -- binders is non-empty
+ bndrs
+ body
+
+mkStgBinds :: [StgFloatBind]
+ -> StgExpr -- *Can* be a StgLam
+ -> UniqSM StgExpr -- *Can* be a StgLam
+
+mkStgBinds [] body = returnUs body
+mkStgBinds (b:bs) body
+ = deStgLam body `thenUs` \ body' ->
+ go (b:bs) body'
+ where
+ go [] body = returnUs body
+ go (b:bs) body = go bs body `thenUs` \ body' ->
+ mkStgBind b body'
+
+-- 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_ty -- Use a case/PrimAlts
+ = ASSERT( not (isUnboxedTupleType bndr_ty) )
+ mkStgBinds floats $
+ mkStgCase rhs bndr (StgPrimAlts bndr_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_ty [] (StgBindDefault body))
+ else
+ -- Lazy let with non-WHNF rhs, so keep the floats in the RHS
+ mkStgBinds floats rhs `thenUs` \ new_rhs ->
+ returnUs (StgLet (StgNonRec bndr (exprToRhs dem NotTopLevel new_rhs)) body)
+
+ where
+ bndr_ty = idType bndr
+ is_strict = isStrictDem dem
+ is_whnf = case rhs of
+ StgCon _ _ _ -> True
+ StgLam _ _ _ -> True
+ other -> False
-mkStgLet (bndr, rhs) body
- | isUnboxedTupleType bndr_ty
- = panic "mkStgLets: unboxed tuple"
- | isUnLiftedType bndr_ty
- = mkStgCase rhs bndr (StgPrimAlts bndr_ty [] (StgBindDefault body))
+-- 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 [] = ([], [])
- | otherwise
- = StgLet (StgNonRec bndr (exprToRhs rhs)) body
- where
- bndr_ty = idType bndr
-mkStgCase (StgLet bind expr) bndr alts
- = StgLet bind (mkStgCase expr bndr alts)
mkStgCase scrut bndr alts
- = StgCase scrut bOGUS_LVs bOGUS_LVs bndr noSRT alts
+ = ASSERT( case scrut of { StgLam _ _ _ -> False; other -> True } )
+ -- We should never find
+ -- case (\x->e) of { ... }
+ -- The simplifier eliminates such things
+ StgCase scrut bOGUS_LVs bOGUS_LVs bndr noSRT alts
\end{code}
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