2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 %************************************************************************
6 \section[CoreToStg]{Converting core syntax to STG syntax}
8 %************************************************************************
10 Convert a @CoreSyntax@ program to a @StgSyntax@ program.
13 module CoreToStg ( topCoreBindsToStg ) where
15 #include "HsVersions.h"
17 import CoreSyn -- input
18 import StgSyn -- output
20 import CoreUtils ( exprType )
21 import SimplUtils ( findDefault )
22 import CostCentre ( noCCS )
23 import Id ( Id, mkSysLocal, idType, idStrictness, isExportedId,
24 mkVanillaId, idName, idDemandInfo, idArity, setIdType,
27 import IdInfo ( StrictnessInfo(..), IdFlavour(..) )
28 import DataCon ( dataConWrapId )
29 import Demand ( Demand, isStrict, wwLazy )
30 import Name ( setNameUnique )
32 import PrimOp ( PrimOp(..), setCCallUnique )
33 import Type ( isUnLiftedType, isUnboxedTupleType, Type, splitFunTy_maybe,
34 UsageAnn(..), tyUsg, applyTy, repType, seqType,
35 splitRepFunTys, mkFunTys
37 import UniqSupply -- all of it, really
38 import BasicTypes ( TopLevelFlag(..), isNotTopLevel )
39 import CmdLineOpts ( opt_D_verbose_stg2stg )
40 import UniqSet ( emptyUniqSet )
46 *************************************************
47 *************** OVERVIEW *********************
48 *************************************************
51 The business of this pass is to convert Core to Stg. On the way it
52 does some important transformations:
54 1. We discard type lambdas and applications. In so doing we discard
55 "trivial" bindings such as
57 where t1, t2 are types
59 2. We get the program into "A-normal form". In particular:
61 f E ==> let x = E in f x
62 OR ==> case E of x -> f x
64 where E is a non-trivial expression.
65 Which transformation is used depends on whether f is strict or not.
66 [Previously the transformation to case used to be done by the
67 simplifier, but it's better done here. It does mean that f needs
68 to have its strictness info correct!.]
70 Similarly, convert any unboxed let's into cases.
71 [I'm experimenting with leaving 'ok-for-speculation' rhss in let-form
72 right up to this point.]
74 3. We clone all local binders. The code generator uses the uniques to
75 name chunks of code for thunks, so it's important that the names used
76 are globally unique, not simply not-in-scope, which is all that
77 the simplifier ensures.
82 * We don't pin on correct arities any more, because they can be mucked up
83 by the lambda lifter. In particular, the lambda lifter can take a local
84 letrec-bound variable and make it a lambda argument, which shouldn't have
85 an arity. So SetStgVarInfo sets arities now.
87 * We do *not* pin on the correct free/live var info; that's done later.
88 Instead we use bOGUS_LVS and _FVS as a placeholder.
90 [Quite a bit of stuff that used to be here has moved
91 to tidyCorePgm (SimplCore.lhs) SLPJ Nov 96]
94 %************************************************************************
96 \subsection[coreToStg-programs]{Converting a core program and core bindings}
98 %************************************************************************
100 March 98: We keep a small environment to give all locally bound
101 Names new unique ids, since the code generator assumes that binders
102 are unique across a module. (Simplifier doesn't maintain this
103 invariant any longer.)
105 A binder to be floated out becomes an @StgFloatBind@.
108 type StgEnv = IdEnv Id
110 data StgFloatBind = NoBindF
111 | RecF [(Id, StgRhs)]
114 StgExpr -- *Can* be a StgLam
118 -- The interesting one is the NonRecF
119 -- NonRecF x rhs demand binds
121 -- x = let binds in rhs
122 -- (or possibly case etc if x demand is strict)
123 -- The binds are kept separate so they can be floated futher
127 A @RhsDemand@ gives the demand on an RHS: strict (@isStrictDem@) and
128 thus case-bound, or if let-bound, at most once (@isOnceDem@) or
132 data RhsDemand = RhsDemand { isStrictDem :: Bool, -- True => used at least once
133 isOnceDem :: Bool -- True => used at most once
136 mkDem :: Demand -> Bool -> RhsDemand
137 mkDem strict once = RhsDemand (isStrict strict) once
139 mkDemTy :: Demand -> Type -> RhsDemand
140 mkDemTy strict ty = RhsDemand (isStrict strict) (isOnceTy ty)
142 isOnceTy :: Type -> Bool
146 opt_UsageSPOn && -- can't expect annotations if -fusagesp is off
151 UsVar uv -> pprPanic "CoreToStg: unexpected uvar annot:" (ppr uv)
153 bdrDem :: Id -> RhsDemand
154 bdrDem id = mkDem (idDemandInfo id) (isOnceTy (idType id))
156 safeDem, onceDem :: RhsDemand
157 safeDem = RhsDemand False False -- always safe to use this
158 onceDem = RhsDemand False True -- used at most once
161 No free/live variable information is pinned on in this pass; it's added
163 we use @bOGUS_LVs@ and @bOGUS_FVs@ as placeholders.
165 When printing out the Stg we need non-bottom values in these
169 bOGUS_LVs :: StgLiveVars
170 bOGUS_LVs | opt_D_verbose_stg2stg = emptyUniqSet
171 | otherwise =panic "bOGUS_LVs"
174 bOGUS_FVs | opt_D_verbose_stg2stg = []
175 | otherwise = panic "bOGUS_FVs"
179 topCoreBindsToStg :: UniqSupply -- name supply
180 -> [CoreBind] -- input
181 -> [StgBinding] -- output
183 topCoreBindsToStg us core_binds
184 = initUs_ us (coreBindsToStg emptyVarEnv core_binds)
186 coreBindsToStg :: StgEnv -> [CoreBind] -> UniqSM [StgBinding]
188 coreBindsToStg env [] = returnUs []
189 coreBindsToStg env (b:bs)
190 = coreBindToStg TopLevel env b `thenUs` \ (bind_spec, new_env) ->
191 coreBindsToStg new_env bs `thenUs` \ new_bs ->
193 NonRecF bndr rhs dem floats
194 -> ASSERT2( not (isStrictDem dem) &&
195 not (isUnLiftedType (idType bndr)),
196 ppr b ) -- No top-level cases!
198 mkStgBinds floats rhs `thenUs` \ new_rhs ->
199 returnUs (StgNonRec bndr (exprToRhs dem TopLevel new_rhs)
201 -- Keep all the floats inside...
202 -- Some might be cases etc
203 -- We might want to revisit this decision
205 RecF prs -> returnUs (StgRec prs : new_bs)
206 NoBindF -> pprTrace "topCoreBindsToStg" (ppr b) $
211 %************************************************************************
213 \subsection[coreToStg-binds]{Converting bindings}
215 %************************************************************************
218 coreBindToStg :: TopLevelFlag -> StgEnv -> CoreBind -> UniqSM (StgFloatBind, StgEnv)
220 coreBindToStg top_lev env (NonRec binder rhs)
221 = coreExprToStgFloat env rhs `thenUs` \ (floats, stg_rhs) ->
222 case (floats, stg_rhs) of
223 ([], StgApp var []) | not (isExportedId binder)
224 -> returnUs (NoBindF, extendVarEnv env binder var)
225 -- A trivial binding let x = y in ...
226 -- can arise if postSimplExpr floats a NoRep literal out
227 -- so it seems sensible to deal with it well.
228 -- But we don't want to discard exported things. They can
229 -- occur; e.g. an exported user binding f = g
231 other -> newLocalId top_lev env binder `thenUs` \ (new_env, new_binder) ->
232 returnUs (NonRecF new_binder stg_rhs dem floats, new_env)
237 coreBindToStg top_lev env (Rec pairs)
238 = newLocalIds top_lev env binders `thenUs` \ (env', binders') ->
239 mapUs (do_rhs env') pairs `thenUs` \ stg_rhss ->
240 returnUs (RecF (binders' `zip` stg_rhss), env')
242 binders = map fst pairs
243 do_rhs env (bndr,rhs) = coreExprToStgFloat env rhs `thenUs` \ (floats, stg_expr) ->
244 mkStgBinds floats stg_expr `thenUs` \ stg_expr' ->
245 -- NB: stg_expr' might still be a StgLam (and we want that)
246 returnUs (exprToRhs (bdrDem bndr) top_lev stg_expr')
250 %************************************************************************
252 \subsection[coreToStg-rhss]{Converting right hand sides}
254 %************************************************************************
257 exprToRhs :: RhsDemand -> TopLevelFlag -> StgExpr -> StgRhs
258 exprToRhs dem _ (StgLam _ bndrs body)
259 = ASSERT( not (null bndrs) )
264 ReEntrant -- binders is non-empty
269 We reject the following candidates for 'static constructor'dom:
271 - any dcon that takes a lit-lit as an arg.
272 - [Win32 DLLs only]: any dcon that resides in a DLL
273 (or takes as arg something that is.)
275 These constraints are necessary to ensure that the code
276 generated in the end for the static constructors, which
277 live in the data segment, remain valid - i.e., it has to
278 be constant. For obvious reasons, that's hard to guarantee
279 with lit-lits. The second case of a constructor referring
280 to static closures hiding out in some DLL is an artifact
281 of the way Win32 DLLs handle global DLL variables. A (data)
282 symbol exported from a DLL has to be accessed through a
283 level of indirection at the site of use, so whereas
285 extern StgClosure y_closure;
286 extern StgClosure z_closure;
287 x = { ..., &y_closure, &z_closure };
289 is legal when the symbols are in scope at link-time, it is
290 not when y_closure is in a DLL. So, any potential static
291 closures that refers to stuff that's residing in a DLL
292 will be put in an (updateable) thunk instead.
294 An alternative strategy is to support the generation of
295 constructors (ala C++ static class constructors) which will
296 then be run at load time to fix up static closures.
298 exprToRhs dem toplev (StgConApp con args)
299 | isNotTopLevel toplev || not (isDllConApp con args)
300 -- isDllConApp checks for LitLit args too
301 = StgRhsCon noCCS con args
305 StgRhsClosure noCCS -- No cost centre (ToDo?)
307 noSRT -- figure out later
313 upd = if isOnceDem dem then SingleEntry else Updatable
314 -- HA! Paydirt for "dem"
318 %************************************************************************
320 \subsection[coreToStg-atoms{Converting atoms}
322 %************************************************************************
325 coreArgsToStg :: StgEnv -> [(CoreArg,RhsDemand)] -> UniqSM ([StgFloatBind], [StgArg])
326 -- Arguments are all value arguments (tyargs already removed), paired with their demand
331 coreArgsToStg env (ad:ads)
332 = coreArgToStg env ad `thenUs` \ (bs1, a') ->
333 coreArgsToStg env ads `thenUs` \ (bs2, as') ->
334 returnUs (bs1 ++ bs2, a' : as')
337 coreArgToStg :: StgEnv -> (CoreArg,RhsDemand) -> UniqSM ([StgFloatBind], StgArg)
338 -- This is where we arrange that a non-trivial argument is let-bound
340 coreArgToStg env (arg,dem)
341 = coreExprToStgFloat env arg `thenUs` \ (floats, arg') ->
343 StgApp v [] -> returnUs (floats, StgVarArg v)
344 StgLit lit -> returnUs (floats, StgLitArg lit)
346 StgConApp con [] -> returnUs (floats, StgVarArg (dataConWrapId con))
347 -- A nullary constructor can be replaced with
348 -- a ``call'' to its wrapper
350 other -> newStgVar arg_ty `thenUs` \ v ->
351 returnUs ([NonRecF v arg' dem floats], StgVarArg v)
353 arg_ty = exprType arg
357 %************************************************************************
359 \subsection[coreToStg-exprs]{Converting core expressions}
361 %************************************************************************
364 coreExprToStg :: StgEnv -> CoreExpr -> UniqSM StgExpr
365 coreExprToStg env expr
366 = coreExprToStgFloat env expr `thenUs` \ (binds,stg_expr) ->
367 mkStgBinds binds stg_expr `thenUs` \ stg_expr' ->
371 %************************************************************************
373 \subsubsection[coreToStg-let(rec)]{Let and letrec expressions}
375 %************************************************************************
378 coreExprToStgFloat :: StgEnv -> CoreExpr
379 -> UniqSM ([StgFloatBind], StgExpr)
380 -- Transform an expression to STG. The 'floats' are
381 -- any bindings we had to create for function arguments.
387 coreExprToStgFloat env (Var var)
388 = mkStgApp env var [] (idType var) `thenUs` \ app ->
391 coreExprToStgFloat env (Lit lit)
392 = returnUs ([], StgLit lit)
394 coreExprToStgFloat env (Let bind body)
395 = coreBindToStg NotTopLevel env bind `thenUs` \ (new_bind, new_env) ->
396 coreExprToStgFloat new_env body `thenUs` \ (floats, stg_body) ->
397 returnUs (new_bind:floats, stg_body)
400 Convert core @scc@ expression directly to STG @scc@ expression.
403 coreExprToStgFloat env (Note (SCC cc) expr)
404 = coreExprToStg env expr `thenUs` \ stg_expr ->
405 returnUs ([], StgSCC cc stg_expr)
407 coreExprToStgFloat env (Note other_note expr)
408 = coreExprToStgFloat env expr
412 coreExprToStgFloat env expr@(Type _)
413 = pprPanic "coreExprToStgFloat: tyarg unexpected:" $ ppr expr
417 %************************************************************************
419 \subsubsection[coreToStg-lambdas]{Lambda abstractions}
421 %************************************************************************
424 coreExprToStgFloat env expr@(Lam _ _)
426 expr_ty = exprType expr
427 (binders, body) = collectBinders expr
428 id_binders = filter isId binders
430 if null id_binders then -- It was all type/usage binders; tossed
431 coreExprToStgFloat env body
433 -- At least some value binders
434 newLocalIds NotTopLevel env id_binders `thenUs` \ (env', binders') ->
435 coreExprToStgFloat env' body `thenUs` \ (floats, stg_body) ->
436 mkStgBinds floats stg_body `thenUs` \ stg_body' ->
439 StgLam ty lam_bndrs lam_body ->
440 -- If the body reduced to a lambda too, join them up
441 returnUs ([], mkStgLam expr_ty (binders' ++ lam_bndrs) lam_body)
444 -- Body didn't reduce to a lambda, so return one
445 returnUs ([], mkStgLam expr_ty binders' stg_body')
449 %************************************************************************
451 \subsubsection[coreToStg-applications]{Applications}
453 %************************************************************************
456 coreExprToStgFloat env expr@(App _ _)
458 (fun,rads,ty,ss) = collect_args expr
460 final_ads | null ss = ads
461 | otherwise = zap ads -- Too few args to satisfy strictness info
462 -- so we have to ignore all the strictness info
463 -- e.g. + (error "urk")
464 -- Here, we can't evaluate the arg strictly,
465 -- because this partial application might be seq'd
467 coreArgsToStg env final_ads `thenUs` \ (arg_floats, stg_args) ->
469 -- Now deal with the function
470 case (fun, stg_args) of
471 (Var fn_id, _) -> -- A function Id, so do an StgApp; it's ok if
472 -- there are no arguments.
473 mkStgApp env fn_id stg_args ty `thenUs` \ app ->
474 returnUs (arg_floats, app)
476 (non_var_fun, []) -> -- No value args, so recurse into the function
477 ASSERT( null arg_floats )
478 coreExprToStgFloat env non_var_fun
480 other -> -- A non-variable applied to things; better let-bind it.
481 newStgVar (exprType fun) `thenUs` \ fn_id ->
482 coreExprToStgFloat env fun `thenUs` \ (fun_floats, stg_fun) ->
483 mkStgApp env fn_id stg_args ty `thenUs` \ app ->
484 returnUs (NonRecF fn_id stg_fun onceDem fun_floats : arg_floats,
488 -- Collect arguments and demands (*in reverse order*)
489 -- collect_args e = (f, args_w_demands, ty, stricts)
490 -- => e = f tys args, (i.e. args are just the value args)
492 -- stricts is the leftover demands of e on its further args
493 -- If stricts runs out, we zap all the demands in args_w_demands
494 -- because partial applications are lazy
496 collect_args :: CoreExpr -> (CoreExpr, [(CoreExpr,RhsDemand)], Type, [Demand])
498 collect_args (Note (Coerce ty _) e) = let (the_fun,ads,_,ss) = collect_args e
499 in (the_fun,ads,ty,ss)
500 collect_args (Note InlineCall e) = collect_args e
501 collect_args (Note (TermUsg _) e) = collect_args e
503 collect_args (App fun (Type tyarg)) = let (the_fun,ads,fun_ty,ss) = collect_args fun
504 in (the_fun,ads,applyTy fun_ty tyarg,ss)
505 collect_args (App fun arg)
506 = (the_fun, (arg, mkDemTy ss1 arg_ty) : ads, res_ty, ss_rest)
508 (ss1, ss_rest) = case ss of
509 (ss1:ss_rest) -> (ss1, ss_rest)
511 (the_fun, ads, fun_ty, ss) = collect_args fun
512 (arg_ty, res_ty) = expectJust "coreExprToStgFloat:collect_args" $
513 splitFunTy_maybe fun_ty
516 = (Var v, [], idType v, stricts)
518 stricts = case idStrictness v of
519 StrictnessInfo demands _ -> demands
520 other -> repeat wwLazy
522 collect_args fun = (fun, [], exprType fun, repeat wwLazy)
524 -- "zap" nukes the strictness info for a partial application
525 zap ads = [(arg, RhsDemand False once) | (arg, RhsDemand _ once) <- ads]
529 %************************************************************************
531 \subsubsection[coreToStg-cases]{Case expressions}
533 %************************************************************************
536 coreExprToStgFloat env (Case scrut bndr alts)
537 = coreExprToStgFloat env scrut `thenUs` \ (binds, scrut') ->
538 newLocalId NotTopLevel env bndr `thenUs` \ (env', bndr') ->
539 alts_to_stg env' (findDefault alts) `thenUs` \ alts' ->
540 mkStgCase scrut' bndr' alts' `thenUs` \ expr' ->
541 returnUs (binds, expr')
543 scrut_ty = idType bndr
544 prim_case = isUnLiftedType scrut_ty && not (isUnboxedTupleType scrut_ty)
546 alts_to_stg env (alts, deflt)
548 = default_to_stg env deflt `thenUs` \ deflt' ->
549 mapUs (prim_alt_to_stg env) alts `thenUs` \ alts' ->
550 returnUs (mkStgPrimAlts scrut_ty alts' deflt')
553 = default_to_stg env deflt `thenUs` \ deflt' ->
554 mapUs (alg_alt_to_stg env) alts `thenUs` \ alts' ->
555 returnUs (mkStgAlgAlts scrut_ty alts' deflt')
557 alg_alt_to_stg env (DataAlt con, bs, rhs)
558 = newLocalIds NotTopLevel env (filter isId bs) `thenUs` \ (env', stg_bs) ->
559 coreExprToStg env' rhs `thenUs` \ stg_rhs ->
560 returnUs (con, stg_bs, [ True | b <- stg_bs ]{-bogus use mask-}, stg_rhs)
561 -- NB the filter isId. Some of the binders may be
562 -- existential type variables, which STG doesn't care about
564 prim_alt_to_stg env (LitAlt lit, args, rhs)
565 = ASSERT( null args )
566 coreExprToStg env rhs `thenUs` \ stg_rhs ->
567 returnUs (lit, stg_rhs)
569 default_to_stg env Nothing
570 = returnUs StgNoDefault
572 default_to_stg env (Just rhs)
573 = coreExprToStg env rhs `thenUs` \ stg_rhs ->
574 returnUs (StgBindDefault stg_rhs)
575 -- The binder is used for prim cases and not otherwise
576 -- (hack for old code gen)
580 %************************************************************************
582 \subsection[coreToStg-misc]{Miscellaneous helping functions}
584 %************************************************************************
586 There's not anything interesting we can ASSERT about \tr{var} if it
587 isn't in the StgEnv. (WDP 94/06)
591 newStgVar :: Type -> UniqSM Id
593 = getUniqueUs `thenUs` \ uniq ->
595 returnUs (mkSysLocal SLIT("stg") uniq ty)
599 newLocalId TopLevel env id
600 -- Don't clone top-level binders. MkIface relies on their
601 -- uniques staying the same, so it can snaffle IdInfo off the
602 -- STG ids to put in interface files.
609 returnUs (env, mkVanillaId name ty)
612 newLocalId NotTopLevel env id
613 = -- Local binder, give it a new unique Id.
614 getUniqueUs `thenUs` \ uniq ->
618 new_id = mkVanillaId (setNameUnique name uniq) ty
619 new_env = extendVarEnv env id new_id
623 returnUs (new_env, new_id)
625 newLocalIds :: TopLevelFlag -> StgEnv -> [Id] -> UniqSM (StgEnv, [Id])
626 newLocalIds top_lev env []
628 newLocalIds top_lev env (b:bs)
629 = newLocalId top_lev env b `thenUs` \ (env', b') ->
630 newLocalIds top_lev env' bs `thenUs` \ (env'', bs') ->
631 returnUs (env'', b':bs')
635 %************************************************************************
637 \subsection{Building STG syn}
639 %************************************************************************
642 mkStgAlgAlts ty alts deflt = seqType ty `seq` StgAlgAlts ty alts deflt
643 mkStgPrimAlts ty alts deflt = seqType ty `seq` StgPrimAlts ty alts deflt
644 mkStgLam ty bndrs body = seqType ty `seq` StgLam ty bndrs body
646 mkStgApp :: StgEnv -> Id -> [StgArg] -> Type -> UniqSM StgExpr
647 -- The type is the type of the entire application
648 mkStgApp env fn args ty
649 = case idFlavour fn_alias of
651 -> saturate fn_alias args ty $ \ args' ty' ->
652 returnUs (StgConApp dc args')
654 PrimOpId (CCallOp ccall)
655 -- Sigh...make a guaranteed unique name for a dynamic ccall
656 -- Done here, not earlier, because it's a code-gen thing
657 -> saturate fn_alias args ty $ \ args' ty' ->
658 getUniqueUs `thenUs` \ uniq ->
659 let ccall' = setCCallUnique ccall uniq in
660 returnUs (StgPrimApp (CCallOp ccall') args' ty')
664 -> saturate fn_alias args ty $ \ args' ty' ->
665 returnUs (StgPrimApp op args' ty')
667 other -> returnUs (StgApp fn_alias args)
670 fn_alias = case (lookupVarEnv env fn) of -- In case it's been cloned
674 saturate :: Id -> [StgArg] -> Type -> ([StgArg] -> Type -> UniqSM StgExpr) -> UniqSM StgExpr
675 -- The type should be the type of (id args)
676 saturate fn args ty thing_inside
677 | excess_arity == 0 -- Saturated, so nothing to do
678 = thing_inside args ty
680 | otherwise -- An unsaturated constructor or primop; eta expand it
681 = ASSERT2( excess_arity > 0 && excess_arity <= length arg_tys,
682 ppr fn <+> ppr args <+> ppr excess_arity <+> parens (ppr ty) <+> ppr arg_tys )
683 mapUs newStgVar extra_arg_tys `thenUs` \ arg_vars ->
684 thing_inside (args ++ map StgVarArg arg_vars) final_res_ty `thenUs` \ body ->
685 returnUs (StgLam ty arg_vars body)
687 fn_arity = idArity fn
688 excess_arity = fn_arity - length args
689 (arg_tys, res_ty) = splitRepFunTys ty
690 extra_arg_tys = take excess_arity arg_tys
691 final_res_ty = mkFunTys (drop excess_arity arg_tys) res_ty
695 -- Stg doesn't have a lambda *expression*
696 deStgLam (StgLam ty bndrs body)
697 -- Try for eta reduction
698 = ASSERT( not (null bndrs) )
700 Just e -> -- Eta succeeded
703 Nothing -> -- Eta failed, so let-bind the lambda
704 newStgVar ty `thenUs` \ fn ->
705 returnUs (StgLet (StgNonRec fn lam_closure) (StgApp fn []))
707 lam_closure = StgRhsClosure noCCS
711 ReEntrant -- binders is non-empty
716 | n_remaining >= 0 &&
717 and (zipWith ok bndrs last_args) &&
718 notInExpr bndrs remaining_expr
719 = Just remaining_expr
721 remaining_expr = StgApp f remaining_args
722 (remaining_args, last_args) = splitAt n_remaining args
723 n_remaining = length args - length bndrs
725 eta (StgLet bind@(StgNonRec b r) body)
726 | notInRhs bndrs r = case eta body of
727 Just e -> Just (StgLet bind e)
732 ok bndr (StgVarArg arg) = bndr == arg
733 ok bndr other = False
735 deStgLam expr = returnUs expr
738 --------------------------------------------------
739 notInExpr :: [Id] -> StgExpr -> Bool
740 notInExpr vs (StgApp f args) = notInId vs f && notInArgs vs args
741 notInExpr vs (StgLet (StgNonRec b r) body) = notInRhs vs r && notInExpr vs body
742 notInExpr vs other = False -- Safe
744 notInRhs :: [Id] -> StgRhs -> Bool
745 notInRhs vs (StgRhsCon _ _ args) = notInArgs vs args
746 notInRhs vs (StgRhsClosure _ _ _ _ _ _ body) = notInExpr vs body
747 -- Conservative: we could delete the binders from vs, but
748 -- cloning means this will never help
750 notInArgs :: [Id] -> [StgArg] -> Bool
751 notInArgs vs args = all ok args
753 ok (StgVarArg v) = notInId vs v
754 ok (StgLitArg l) = True
756 notInId :: [Id] -> Id -> Bool
757 notInId vs v = not (v `elem` vs)
761 mkStgBinds :: [StgFloatBind]
762 -> StgExpr -- *Can* be a StgLam
763 -> UniqSM StgExpr -- *Can* be a StgLam
765 mkStgBinds [] body = returnUs body
766 mkStgBinds (b:bs) body
767 = deStgLam body `thenUs` \ body' ->
770 go [] body = returnUs body
771 go (b:bs) body = go bs body `thenUs` \ body' ->
774 -- The 'body' arg of mkStgBind can't be a StgLam
775 mkStgBind NoBindF body = returnUs body
776 mkStgBind (RecF prs) body = returnUs (StgLet (StgRec prs) body)
778 mkStgBind (NonRecF bndr rhs dem floats) body
780 -- We shouldn't get let or case of the form v=w
782 StgApp v [] -> pprTrace "mkStgLet" (ppr bndr <+> ppr v)
783 (mk_stg_let bndr rhs dem floats body)
784 other -> mk_stg_let bndr rhs dem floats body
786 mk_stg_let bndr rhs dem floats body
788 | isUnLiftedType bndr_rep_ty -- Use a case/PrimAlts
789 = ASSERT( not (isUnboxedTupleType bndr_rep_ty) )
790 mkStgCase rhs bndr (StgPrimAlts bndr_rep_ty [] (StgBindDefault body)) `thenUs` \ expr' ->
791 mkStgBinds floats expr'
795 -- Strict let with WHNF rhs
797 StgLet (StgNonRec bndr (exprToRhs dem NotTopLevel rhs)) body
799 -- Lazy let with WHNF rhs; float until we find a strict binding
801 (floats_out, floats_in) = splitFloats floats
803 mkStgBinds floats_in rhs `thenUs` \ new_rhs ->
804 mkStgBinds floats_out $
805 StgLet (StgNonRec bndr (exprToRhs dem NotTopLevel new_rhs)) body
807 | otherwise -- Not WHNF
809 -- Strict let with non-WHNF rhs
810 mkStgCase rhs bndr (StgAlgAlts bndr_rep_ty [] (StgBindDefault body)) `thenUs` \ expr' ->
811 mkStgBinds floats expr'
813 -- Lazy let with non-WHNF rhs, so keep the floats in the RHS
814 mkStgBinds floats rhs `thenUs` \ new_rhs ->
815 returnUs (StgLet (StgNonRec bndr (exprToRhs dem NotTopLevel new_rhs)) body)
818 bndr_rep_ty = repType (idType bndr)
819 is_strict = isStrictDem dem
820 is_whnf = case rhs of
821 StgConApp _ _ -> True
825 -- Split at the first strict binding
826 splitFloats fs@(NonRecF _ _ dem _ : _)
827 | isStrictDem dem = ([], fs)
829 splitFloats (f : fs) = case splitFloats fs of
830 (fs_out, fs_in) -> (f : fs_out, fs_in)
832 splitFloats [] = ([], [])
839 First, two special cases. We mangle cases involving
843 Up to this point, seq# will appear like this:
849 This code comes from an unfolding for 'seq' in Prelude.hs.
850 The 0# branch is purely to bamboozle the strictness analyser.
851 For example, if <stuff> is strict in x, and there was no seqError#
852 branch, the strictness analyser would conclude that the whole expression
853 was strict in x, and perhaps evaluate x first -- but that would be a DISASTER.
855 Now that the evaluation order is safe, we translate this into
860 This used to be done in the post-simplification phase, but we need
861 unfoldings involving seq# to appear unmangled in the interface file,
862 hence we do this mangling here.
864 Similarly, par# has an unfolding in PrelConc.lhs that makes it show
876 fork# isn't handled like this - it's an explicit IO operation now.
877 The reason is that fork# returns a ThreadId#, which gets in the
878 way of the above scheme. And anyway, IO is the only guaranteed
879 way to enforce ordering --SDM.
883 -- Discard alernatives in case (par# ..) of
884 mkStgCase scrut@(StgPrimApp ParOp _ _) bndr
885 (StgPrimAlts ty _ deflt@(StgBindDefault _))
886 = returnUs (StgCase scrut bOGUS_LVs bOGUS_LVs bndr noSRT (StgPrimAlts ty [] deflt))
888 mkStgCase (StgPrimApp SeqOp [scrut] _) bndr
889 (StgPrimAlts _ _ deflt@(StgBindDefault rhs))
890 = mkStgCase scrut_expr new_bndr new_alts
892 new_alts | isUnLiftedType scrut_ty = WARN( True, text "mkStgCase" ) StgPrimAlts scrut_ty [] deflt
893 | otherwise = StgAlgAlts scrut_ty [] deflt
894 scrut_ty = stgArgType scrut
895 new_bndr = setIdType bndr scrut_ty
896 -- NB: SeqOp :: forall a. a -> Int#
897 -- So bndr has type Int#
898 -- But now we are going to scrutinise the SeqOp's argument directly,
899 -- so we must change the type of the case binder to match that
900 -- of the argument expression e.
902 scrut_expr = case scrut of
903 StgVarArg v -> StgApp v []
904 -- Others should not happen because
905 -- seq of a value should have disappeared
906 StgLitArg l -> WARN( True, text "seq on" <+> ppr l ) StgLit l
908 mkStgCase scrut bndr alts
909 = deStgLam scrut `thenUs` \ scrut' ->
910 -- It is (just) possible to get a lambda as a srutinee here
911 -- Namely: fromDyn (toDyn ((+1)::Int->Int)) False)
912 -- gives: case ...Bool == Int->Int... of
913 -- True -> case coerce Bool (\x -> + 1 x) of
917 -- The True branch of the outer case will never happen, of course.
919 returnUs (StgCase scrut' bOGUS_LVs bOGUS_LVs bndr noSRT alts)