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 | n_remaining >= 0 &&
338 and (zipWith ok bndrs last_args) &&
339 not (any (`elemVarSet` fvs_remaining) bndrs)
340 = Just remaining_expr
342 (f, args) = collectArgs expr
343 remaining_expr = mkApps f remaining_args
344 fvs_remaining = exprFreeVars remaining_expr
345 (remaining_args, last_args) = splitAt n_remaining args
346 n_remaining = length args - length bndrs
348 ok bndr (Var arg) = bndr == arg
349 ok bndr other = False
351 eta (Let bind@(NonRec b r) body)
352 | not (any (`elemVarSet` fvs) bndrs)
354 Just e -> Just (Let bind e)
356 where fvs = exprFreeVars r
360 deLam expr = returnUs expr
362 -- ---------------------------------------------------------------------------
363 -- Precipitating the floating bindings
364 -- ---------------------------------------------------------------------------
366 mkBinds :: [FloatingBind] -> CoreExpr -> UniqSM CoreExpr
367 mkBinds [] body = returnUs body
369 = deLam body `thenUs` \ body' ->
372 go [] body = returnUs body
373 go (b:bs) body = go bs body `thenUs` \ body' ->
377 mkBind (RecF prs) body = returnUs (Let (Rec prs) body)
379 mkBind (NonRecF bndr rhs dem floats) body
381 -- We shouldn't get let or case of the form v=w
382 = if exprIsTrivial rhs
383 then pprTrace "mkBind" (ppr bndr <+> ppr rhs)
384 (mk_let bndr rhs dem floats body)
385 else mk_let bndr rhs dem floats body
387 mk_let bndr rhs dem floats body
389 | isUnLiftedType bndr_rep_ty
390 = ASSERT( not (isUnboxedTupleType bndr_rep_ty) )
391 mkBinds floats (Case rhs bndr [(DEFAULT, [], body)])
395 -- Strict let with WHNF rhs
397 Let (NonRec bndr rhs) body
399 -- Lazy let with WHNF rhs; float until we find a strict binding
401 (floats_out, floats_in) = splitFloats floats
403 mkBinds floats_in rhs `thenUs` \ new_rhs ->
405 Let (NonRec bndr new_rhs) body
407 | otherwise -- Not WHNF
409 -- Strict let with non-WHNF rhs
410 mkBinds floats (Case rhs bndr [(DEFAULT, [], body)])
412 -- Lazy let with non-WHNF rhs, so keep the floats in the RHS
413 mkBinds floats rhs `thenUs` \ new_rhs ->
414 returnUs (Let (NonRec bndr new_rhs) body)
417 bndr_rep_ty = repType (idType bndr)
418 is_strict = isStrictDem dem
419 is_whnf = exprIsValue rhs
421 splitFloats fs@(NonRecF _ _ dem _ : _)
422 | isStrictDem dem = ([], fs)
424 splitFloats (f : fs) = case splitFloats fs of
425 (fs_out, fs_in) -> (f : fs_out, fs_in)
427 splitFloats [] = ([], [])
429 -- -----------------------------------------------------------------------------
431 -- -----------------------------------------------------------------------------
434 = RhsDemand { isStrictDem :: Bool, -- True => used at least once
435 isOnceDem :: Bool -- True => used at most once
438 mkDem :: Demand -> Bool -> RhsDemand
439 mkDem strict once = RhsDemand (isStrict strict) once
441 mkDemTy :: Demand -> Type -> RhsDemand
442 mkDemTy strict ty = RhsDemand (isStrict strict) (isOnceTy ty)
444 isOnceTy :: Type -> Bool
448 opt_UsageSPOn && -- can't expect annotations if -fusagesp is off
453 once | u == usOnce = True
454 | u == usMany = False
455 | isTyVarTy u = False -- if unknown at compile-time, is Top ie usMany
457 bdrDem :: Id -> RhsDemand
458 bdrDem id = mkDem (idDemandInfo id) (isOnceTy (idType id))
460 safeDem, onceDem :: RhsDemand
461 safeDem = RhsDemand False False -- always safe to use this
462 onceDem = RhsDemand False True -- used at most once