2 % (c) The University of Glasgow, 1994-2000
4 \section{Core pass to saturate constructors and PrimOps}
8 coreSatPgm, coreSatExpr
11 #include "HsVersions.h"
19 import Var ( TyVar, setTyVarUnique )
31 -- ---------------------------------------------------------------------------
33 -- ---------------------------------------------------------------------------
35 Most of the contents of this pass used to be in CoreToStg. The
36 primary goals here are:
38 1. Get the program into "A-normal form". In particular:
40 f E ==> let x = E in f x
41 OR ==> case E of x -> f x
44 if E is a non-trivial expression.
45 Which transformation is used depends on whether f is strict or not.
46 [Previously the transformation to case used to be done by the
47 simplifier, but it's better done here. It does mean that f needs
48 to have its strictness info correct!.]
50 2. Similarly, convert any unboxed lets into cases.
51 [I'm experimenting with leaving 'ok-for-speculation' rhss in let-form
52 right up to this point.]
54 This is all done modulo type applications and abstractions, so that
55 when type erasure is done for conversion to STG, we don't end up with
56 any trivial or useless bindings.
58 3. Ensure that lambdas only occur as the RHS of a binding
59 (The code generator can't deal with anything else.)
61 4. Saturate constructor and primop applications.
65 -- -----------------------------------------------------------------------------
67 -- -----------------------------------------------------------------------------
70 coreSatPgm :: DynFlags -> [CoreBind] -> IO [CoreBind]
71 coreSatPgm dflags binds
72 = do showPass dflags "CoreSat"
73 us <- mkSplitUniqSupply 's'
74 let new_binds = initUs_ us (coreSatBinds binds)
75 endPass dflags "CoreSat" Opt_D_dump_sat new_binds
77 coreSatExpr :: DynFlags -> CoreExpr -> IO CoreExpr
78 coreSatExpr dflags expr
79 = do showPass dflags "CoreSat"
80 us <- mkSplitUniqSupply 's'
81 let new_expr = initUs_ us (coreSatAnExpr expr)
82 dumpIfSet_dyn dflags Opt_D_dump_sat "Saturated/Normal form syntax:"
86 -- ---------------------------------------------------------------------------
87 -- Dealing with bindings
88 -- ---------------------------------------------------------------------------
91 = RecF [(Id, CoreExpr)]
93 CoreExpr -- *Can* be a Lam
97 coreSatBinds :: [CoreBind] -> UniqSM [CoreBind]
98 coreSatBinds [] = returnUs []
100 = coreSatBind b `thenUs` \ float ->
101 coreSatBinds bs `thenUs` \ new_bs ->
103 NonRecF bndr rhs dem floats
104 -> ASSERT2( not (isStrictDem dem) &&
105 not (isUnLiftedType (idType bndr)),
106 ppr b ) -- No top-level cases!
108 mkBinds floats rhs `thenUs` \ new_rhs ->
109 returnUs (NonRec bndr new_rhs : new_bs)
110 -- Keep all the floats inside...
111 -- Some might be cases etc
112 -- We might want to revisit this decision
114 RecF prs -> returnUs (Rec prs : new_bs)
116 coreSatBind :: CoreBind -> UniqSM FloatingBind
117 coreSatBind (NonRec binder rhs)
118 = coreSatExprFloat rhs `thenUs` \ (floats, new_rhs) ->
119 returnUs (NonRecF binder new_rhs (bdrDem binder) floats)
120 coreSatBind (Rec pairs)
121 = mapUs do_rhs pairs `thenUs` \ new_rhss ->
122 returnUs (RecF (binders `zip` new_rhss))
124 binders = map fst pairs
126 coreSatExprFloat rhs `thenUs` \ (floats, new_rhs) ->
127 mkBinds floats new_rhs `thenUs` \ new_rhs' ->
128 -- NB: new_rhs' might still be a Lam (and we want that)
131 -- ---------------------------------------------------------------------------
132 -- Making arguments atomic (function args & constructor args)
133 -- ---------------------------------------------------------------------------
135 -- This is where we arrange that a non-trivial argument is let-bound
136 coreSatArg :: CoreArg -> RhsDemand -> UniqSM ([FloatingBind], CoreArg)
138 = coreSatExprFloat arg `thenUs` \ (floats, arg') ->
139 if exprIsTrivial arg'
140 then returnUs (floats, arg')
141 else newVar (exprType arg') `thenUs` \ v ->
142 returnUs ([NonRecF v arg' dem floats], Var v)
144 -- ---------------------------------------------------------------------------
145 -- Dealing with expressions
146 -- ---------------------------------------------------------------------------
148 coreSatAnExpr :: CoreExpr -> UniqSM CoreExpr
150 = coreSatExprFloat expr `thenUs` \ (floats, expr) ->
154 coreSatExprFloat :: CoreExpr -> UniqSM ([FloatingBind], CoreExpr)
158 -- e = let bs in e' (semantically, that is!)
161 -- f (g x) ===> ([v = g x], f v)
163 coreSatExprFloat (Var v)
164 = maybeSaturate v (Var v) 0 (idType v) `thenUs` \ app ->
167 coreSatExprFloat (Lit lit)
168 = returnUs ([], Lit lit)
170 coreSatExprFloat (Let bind body)
171 = coreSatBind bind `thenUs` \ new_bind ->
172 coreSatExprFloat body `thenUs` \ (floats, new_body) ->
173 returnUs (new_bind:floats, new_body)
175 coreSatExprFloat (Note other_note expr)
176 = coreSatExprFloat expr `thenUs` \ (floats, expr) ->
177 returnUs (floats, Note other_note expr)
179 coreSatExprFloat expr@(Type _)
180 = returnUs ([], expr)
182 coreSatExprFloat (Lam v e)
183 = coreSatAnExpr e `thenUs` \ e' ->
184 returnUs ([], Lam v e')
186 coreSatExprFloat (Case scrut bndr alts)
187 = coreSatExprFloat scrut `thenUs` \ (floats, scrut) ->
188 mapUs sat_alt alts `thenUs` \ alts ->
189 returnUs (floats, Case scrut bndr alts)
191 sat_alt (con, bs, rhs)
192 = coreSatAnExpr rhs `thenUs` \ rhs ->
193 deLam rhs `thenUs` \ rhs ->
194 returnUs (con, bs, rhs)
196 coreSatExprFloat expr@(App _ _)
197 = collect_args expr 0 `thenUs` \ (app,(head,depth),ty,floats,ss) ->
198 ASSERT(null ss) -- make sure we used all the strictness info
200 -- Now deal with the function
202 Var fn_id -> maybeSaturate fn_id app depth ty `thenUs` \ app' ->
203 returnUs (floats, app')
205 _other -> returnUs (floats, app)
209 -- Deconstruct and rebuild the application, floating any non-atomic
210 -- arguments to the outside. We collect the type of the expression,
211 -- the head of the applicaiton, and the number of actual value arguments,
212 -- all of which are used to possibly saturate this application if it
213 -- has a constructor or primop at the head.
217 -> Int -- current app depth
218 -> UniqSM (CoreExpr, -- the rebuilt expression
219 (CoreExpr,Int), -- the head of the application,
220 -- and no. of args it was applied to
221 Type, -- type of the whole expr
222 [FloatingBind], -- any floats we pulled out
223 [Demand]) -- remaining argument demands
225 collect_args (App fun arg@(Type arg_ty)) depth
226 = collect_args fun depth `thenUs` \ (fun',hd,fun_ty,floats,ss) ->
227 returnUs (App fun' arg, hd, applyTy fun_ty arg_ty, floats, ss)
229 collect_args (App fun arg) depth
230 = collect_args fun (depth+1) `thenUs` \ (fun',hd,fun_ty,floats,ss) ->
232 (ss1, ss_rest) = case ss of
233 (ss1:ss_rest) -> (ss1, ss_rest)
235 (arg_ty, res_ty) = expectJust "coreSatExprFloat:collect_args" $
236 splitFunTy_maybe fun_ty
238 coreSatArg arg (mkDemTy ss1 arg_ty) `thenUs` \ (fs, arg') ->
239 returnUs (App fun' arg', hd, res_ty, fs ++ floats, ss_rest)
241 collect_args (Var v) depth
242 = returnUs (Var v, (Var v, depth), idType v, [], stricts)
244 stricts = case idStrictness v of
245 StrictnessInfo demands _
246 | depth >= length demands -> demands
249 -- If depth < length demands, then we have too few args to
250 -- satisfy strictness info so we have to ignore all the
251 -- strictness info, e.g. + (error "urk")
252 -- Here, we can't evaluate the arg strictly, because this
253 -- partial application might be seq'd
255 collect_args (Note (Coerce ty1 ty2) fun) depth
256 = collect_args fun depth `thenUs` \ (fun', hd, fun_ty, floats, ss) ->
257 returnUs (Note (Coerce ty1 ty2) fun', hd, ty1, floats, ss)
259 collect_args (Note note fun) depth
261 = collect_args fun depth `thenUs` \ (fun', hd, fun_ty, floats, ss) ->
262 returnUs (Note note fun', hd, fun_ty, floats, ss)
264 -- non-variable fun, better let-bind it
265 collect_args fun depth
266 = newVar ty `thenUs` \ fn_id ->
267 coreSatExprFloat fun `thenUs` \ (fun_floats, fun) ->
268 returnUs (Var fn_id, (Var fn_id, depth), ty,
269 [NonRecF fn_id fun onceDem fun_floats], [])
270 where ty = exprType fun
272 ignore_note InlineCall = True
273 ignore_note InlineMe = True
274 ignore_note _other = False
275 -- we don't ignore SCCs, since they require some code generation
277 ------------------------------------------------------------------------------
278 -- Generating new binders
279 -- ---------------------------------------------------------------------------
281 newVar :: Type -> UniqSM Id
283 = getUniqueUs `thenUs` \ uniq ->
285 returnUs (mkSysLocal SLIT("sat") uniq ty)
287 cloneTyVar :: TyVar -> UniqSM TyVar
289 = getUniqueUs `thenUs` \ uniq ->
290 returnUs (setTyVarUnique tv uniq)
292 ------------------------------------------------------------------------------
293 -- Building the saturated syntax
294 -- ---------------------------------------------------------------------------
296 -- maybeSaturate deals with saturating primops and constructors
297 -- The type is the type of the entire application
298 maybeSaturate :: Id -> CoreExpr -> Int -> Type -> UniqSM CoreExpr
299 maybeSaturate fn expr n_args ty
300 = case idFlavour fn of
301 PrimOpId op -> saturate_it
302 DataConId dc -> saturate_it
303 other -> returnUs expr
305 fn_arity = idArity fn
306 excess_arity = fn_arity - n_args
307 saturate_it = getUs `thenUs` \ us ->
308 returnUs (etaExpand excess_arity us expr ty)
310 -- ---------------------------------------------------------------------------
311 -- Eliminate Lam as a non-rhs (STG doesn't have such a thing)
312 -- ---------------------------------------------------------------------------
315 = deLam e `thenUs` \ e ->
318 -- types will all disappear, so that's ok
319 deLam (Lam x e) | isTyVar x
320 = deLam e `thenUs` \ e ->
324 -- Try for eta reduction
328 -- Eta failed, so let-bind the lambda
330 = newVar (exprType expr) `thenUs` \ fn ->
331 returnUs (Let (NonRec fn expr) (Var fn))
334 (bndrs, body) = collectBinders expr
337 | ok_to_eta_reduce f &&
339 and (zipWith ok bndrs last_args) &&
340 not (any (`elemVarSet` fvs_remaining) bndrs)
341 = Just remaining_expr
343 (f, args) = collectArgs expr
344 remaining_expr = mkApps f remaining_args
345 fvs_remaining = exprFreeVars remaining_expr
346 (remaining_args, last_args) = splitAt n_remaining args
347 n_remaining = length args - length bndrs
349 ok bndr (Var arg) = bndr == arg
350 ok bndr other = False
352 -- we can't eta reduce something which must be saturated.
353 ok_to_eta_reduce (Var f)
354 = case idFlavour f of
356 DataConId dc -> False
358 ok_to_eta_reduce _ = False --safe. ToDo: generalise
360 eta (Let bind@(NonRec b r) body)
361 | not (any (`elemVarSet` fvs) bndrs)
363 Just e -> Just (Let bind e)
365 where fvs = exprFreeVars r
369 deLam expr = returnUs expr
371 -- ---------------------------------------------------------------------------
372 -- Precipitating the floating bindings
373 -- ---------------------------------------------------------------------------
375 mkBinds :: [FloatingBind] -> CoreExpr -> UniqSM CoreExpr
376 mkBinds [] body = returnUs body
378 = deLam body `thenUs` \ body' ->
381 go [] body = returnUs body
382 go (b:bs) body = go bs body `thenUs` \ body' ->
386 mkBind (RecF prs) body = returnUs (Let (Rec prs) body)
388 mkBind (NonRecF bndr rhs dem floats) body
390 -- We shouldn't get let or case of the form v=w
391 = if exprIsTrivial rhs
392 then pprTrace "mkBind" (ppr bndr <+> ppr rhs)
393 (mk_let bndr rhs dem floats body)
394 else mk_let bndr rhs dem floats body
396 mk_let bndr rhs dem floats body
398 | isUnLiftedType bndr_rep_ty
399 = ASSERT( not (isUnboxedTupleType bndr_rep_ty) )
400 mkBinds floats (Case rhs bndr [(DEFAULT, [], body)])
404 -- Strict let with WHNF rhs
406 Let (NonRec bndr rhs) body
408 -- Lazy let with WHNF rhs; float until we find a strict binding
410 (floats_out, floats_in) = splitFloats floats
412 mkBinds floats_in rhs `thenUs` \ new_rhs ->
414 Let (NonRec bndr new_rhs) body
416 | otherwise -- Not WHNF
418 -- Strict let with non-WHNF rhs
419 mkBinds floats (Case rhs bndr [(DEFAULT, [], body)])
421 -- Lazy let with non-WHNF rhs, so keep the floats in the RHS
422 mkBinds floats rhs `thenUs` \ new_rhs ->
423 returnUs (Let (NonRec bndr new_rhs) body)
426 bndr_rep_ty = repType (idType bndr)
427 is_strict = isStrictDem dem
428 is_whnf = exprIsValue rhs
430 splitFloats fs@(NonRecF _ _ dem _ : _)
431 | isStrictDem dem = ([], fs)
433 splitFloats (f : fs) = case splitFloats fs of
434 (fs_out, fs_in) -> (f : fs_out, fs_in)
436 splitFloats [] = ([], [])
438 -- -----------------------------------------------------------------------------
440 -- -----------------------------------------------------------------------------
443 = RhsDemand { isStrictDem :: Bool, -- True => used at least once
444 isOnceDem :: Bool -- True => used at most once
447 mkDem :: Demand -> Bool -> RhsDemand
448 mkDem strict once = RhsDemand (isStrict strict) once
450 mkDemTy :: Demand -> Type -> RhsDemand
451 mkDemTy strict ty = RhsDemand (isStrict strict) (isOnceTy ty)
453 isOnceTy :: Type -> Bool
457 opt_UsageSPOn && -- can't expect annotations if -fusagesp is off
462 once | u == usOnce = True
463 | u == usMany = False
464 | isTyVarTy u = False -- if unknown at compile-time, is Top ie usMany
466 bdrDem :: Id -> RhsDemand
467 bdrDem id = mkDem (idDemandInfo id) (isOnceTy (idType id))
469 safeDem, onceDem :: RhsDemand
470 safeDem = RhsDemand False False -- always safe to use this
471 onceDem = RhsDemand False True -- used at most once