1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
|
%
% (c) The GRASP/AQUA Project, Glasgow University, 1993-1998
%
\section[StrictAnal]{``Simple'' Mycroft-style strictness analyser}
The original version(s) of all strictness-analyser code (except the
Semantique analyser) was written by Andy Gill.
\begin{code}
#ifndef OLD_STRICTNESS
module StrictAnal ( ) where
#else
module StrictAnal ( saBinds ) where
#include "HsVersions.h"
import DynFlags ( DynFlags, DynFlag(..) )
import CoreSyn
import Id ( setIdStrictness, setInlinePragma,
idDemandInfo, setIdDemandInfo, isBottomingId,
Id
)
import CoreLint ( showPass, endPass )
import ErrUtils ( dumpIfSet_dyn )
import SaAbsInt
import SaLib
import Demand ( Demand, wwStrict, isStrict, isLazy )
import Util ( zipWith3Equal, stretchZipWith, compareLength )
import BasicTypes ( Activation( NeverActive ) )
import Outputable
import FastTypes
\end{code}
%************************************************************************
%* *
\subsection[Thoughts]{Random thoughts}
%* *
%************************************************************************
A note about worker-wrappering. If we have
f :: Int -> Int
f = let v = <expensive>
in \x -> <body>
and we deduce that f is strict, it is nevertheless NOT safe to worker-wapper to
f = \x -> case x of Int x# -> fw x#
fw = \x# -> let x = Int x#
in
let v = <expensive>
in <body>
because this obviously loses laziness, since now <expensive>
is done each time. Alas.
WATCH OUT! This can mean that something is unboxed only to be
boxed again. For example
g x y = f x
Here g is strict, and *will* split into worker-wrapper. A call to
g, with the wrapper inlined will then be
case arg of Int a# -> gw a#
Now g calls f, which has no wrapper, so it has to box it.
gw = \a# -> f (Int a#)
Alas and alack.
%************************************************************************
%* *
\subsection[iface-StrictAnal]{Interface to the outside world}
%* *
%************************************************************************
@saBinds@ decorates bindings with strictness info. A later
worker-wrapper pass can use this info to create wrappers and
strict workers.
\begin{code}
saBinds :: DynFlags -> [CoreBind] -> IO [CoreBind]
saBinds dflags binds
= do {
showPass dflags "Strictness analysis";
-- Mark each binder with its strictness
#ifndef OMIT_STRANAL_STATS
let { (binds_w_strictness, sa_stats) = saTopBinds binds nullSaStats };
dumpIfSet_dyn dflags Opt_D_dump_simpl_stats "Strictness analysis statistics"
(pp_stats sa_stats);
#else
let { binds_w_strictness = saTopBindsBinds binds };
#endif
endPass dflags "Strictness analysis" Opt_D_dump_stranal
binds_w_strictness
}
\end{code}
%************************************************************************
%* *
\subsection[saBinds]{Strictness analysis of bindings}
%* *
%************************************************************************
[Some of the documentation about types, etc., in \tr{SaLib} may be
helpful for understanding this module.]
@saTopBinds@ tags each binder in the program with its @Demand@.
That tells how each binder is {\em used}; if @Strict@, then the binder
is sure to be evaluated to HNF; if @NonStrict@ it may or may not be;
if @Absent@, then it certainly is not used. [DATED; ToDo: update]
(The above info is actually recorded for posterity in each binder's
IdInfo, notably its @DemandInfo@.)
We proceed by analysing the bindings top-to-bottom, building up an
environment which maps @Id@s to their abstract values (i.e., an
@AbsValEnv@ maps an @Id@ to its @AbsVal@).
\begin{code}
saTopBinds :: [CoreBind] -> SaM [CoreBind] -- not exported
saTopBinds binds
= let
starting_abs_env = nullAbsValEnv
in
do_it starting_abs_env starting_abs_env binds
where
do_it _ _ [] = returnSa []
do_it senv aenv (b:bs)
= saTopBind senv aenv b `thenSa` \ (senv2, aenv2, new_b) ->
do_it senv2 aenv2 bs `thenSa` \ new_bs ->
returnSa (new_b : new_bs)
\end{code}
@saTopBind@ is only used for the top level. We don't add any demand
info to these ids because we can't work it out. In any case, it
doesn't do us any good to know whether top-level binders are sure to
be used; we can't turn top-level @let@s into @case@s.
\begin{code}
saTopBind :: StrictEnv -> AbsenceEnv
-> CoreBind
-> SaM (StrictEnv, AbsenceEnv, CoreBind)
saTopBind str_env abs_env (NonRec binder rhs)
= saExpr minDemand str_env abs_env rhs `thenSa` \ new_rhs ->
let
str_rhs = absEval StrAnal rhs str_env
abs_rhs = absEval AbsAnal rhs abs_env
widened_str_rhs = widen StrAnal str_rhs
widened_abs_rhs = widen AbsAnal abs_rhs
-- The widening above is done for efficiency reasons.
-- See notes on Let case in SaAbsInt.lhs
new_binder
= addStrictnessInfoToTopId
widened_str_rhs widened_abs_rhs
binder
-- Augment environments with a mapping of the
-- binder to its abstract values, computed by absEval
new_str_env = addOneToAbsValEnv str_env binder widened_str_rhs
new_abs_env = addOneToAbsValEnv abs_env binder widened_abs_rhs
in
returnSa (new_str_env, new_abs_env, NonRec new_binder new_rhs)
saTopBind str_env abs_env (Rec pairs)
= let
(binders,rhss) = unzip pairs
str_rhss = fixpoint StrAnal binders rhss str_env
abs_rhss = fixpoint AbsAnal binders rhss abs_env
-- fixpoint returns widened values
new_str_env = growAbsValEnvList str_env (binders `zip` str_rhss)
new_abs_env = growAbsValEnvList abs_env (binders `zip` abs_rhss)
new_binders = zipWith3Equal "saTopBind" addStrictnessInfoToTopId
str_rhss abs_rhss binders
in
mapSa (saExpr minDemand new_str_env new_abs_env) rhss `thenSa` \ new_rhss ->
let
new_pairs = new_binders `zip` new_rhss
in
returnSa (new_str_env, new_abs_env, Rec new_pairs)
-- Hack alert!
-- Top level divergent bindings are marked NOINLINE
-- This avoids fruitless inlining of top level error functions
addStrictnessInfoToTopId str_val abs_val bndr
= if isBottomingId new_id then
new_id `setInlinePragma` NeverActive
else
new_id
where
new_id = addStrictnessInfoToId str_val abs_val bndr
\end{code}
%************************************************************************
%* *
\subsection[saExpr]{Strictness analysis of an expression}
%* *
%************************************************************************
@saExpr@ computes the strictness of an expression within a given
environment.
\begin{code}
saExpr :: Demand -> StrictEnv -> AbsenceEnv -> CoreExpr -> SaM CoreExpr
-- The demand is the least demand we expect on the
-- expression. WwStrict is the least, because we're only
-- interested in the expression at all if it's being evaluated,
-- but the demand may be more. E.g.
-- f E
-- where f has strictness u(LL), will evaluate E with demand u(LL)
minDemand = wwStrict
minDemands = repeat minDemand
-- When we find an application, do the arguments
-- with demands gotten from the function
saApp str_env abs_env (fun, args)
= sequenceSa sa_args `thenSa` \ args' ->
saExpr minDemand str_env abs_env fun `thenSa` \ fun' ->
returnSa (mkApps fun' args')
where
arg_dmds = case fun of
Var var -> case lookupAbsValEnv str_env var of
Just (AbsApproxFun ds _)
| compareLength ds args /= LT
-- 'ds' is at least as long as 'args'.
-> ds ++ minDemands
other -> minDemands
other -> minDemands
sa_args = stretchZipWith isTypeArg (error "saApp:dmd")
sa_arg args arg_dmds
-- The arg_dmds are for value args only, we need to skip
-- over the type args when pairing up with the demands
-- Hence the stretchZipWith
sa_arg arg dmd = saExpr dmd' str_env abs_env arg
where
-- Bring arg demand up to minDemand
dmd' | isLazy dmd = minDemand
| otherwise = dmd
saExpr _ _ _ e@(Var _) = returnSa e
saExpr _ _ _ e@(Lit _) = returnSa e
saExpr _ _ _ e@(Type _) = returnSa e
saExpr dmd str_env abs_env (Lam bndr body)
= -- Don't bother to set the demand-info on a lambda binder
-- We do that only for let(rec)-bound functions
saExpr minDemand str_env abs_env body `thenSa` \ new_body ->
returnSa (Lam bndr new_body)
saExpr dmd str_env abs_env e@(App fun arg)
= saApp str_env abs_env (collectArgs e)
saExpr dmd str_env abs_env (Note note expr)
= saExpr dmd str_env abs_env expr `thenSa` \ new_expr ->
returnSa (Note note new_expr)
saExpr dmd str_env abs_env (Case expr case_bndr alts)
= saExpr minDemand str_env abs_env expr `thenSa` \ new_expr ->
mapSa sa_alt alts `thenSa` \ new_alts ->
let
new_case_bndr = addDemandInfoToCaseBndr dmd str_env abs_env alts case_bndr
in
returnSa (Case new_expr new_case_bndr new_alts)
where
sa_alt (con, binders, rhs)
= saExpr dmd str_env abs_env rhs `thenSa` \ new_rhs ->
let
new_binders = map add_demand_info binders
add_demand_info bndr | isTyVar bndr = bndr
| otherwise = addDemandInfoToId dmd str_env abs_env rhs bndr
in
tickCases new_binders `thenSa_` -- stats
returnSa (con, new_binders, new_rhs)
saExpr dmd str_env abs_env (Let (NonRec binder rhs) body)
= -- Analyse the RHS in the environment at hand
let
-- Find the demand on the RHS
rhs_dmd = findDemand dmd str_env abs_env body binder
-- Bind this binder to the abstract value of the RHS; analyse
-- the body of the `let' in the extended environment.
str_rhs_val = absEval StrAnal rhs str_env
abs_rhs_val = absEval AbsAnal rhs abs_env
widened_str_rhs = widen StrAnal str_rhs_val
widened_abs_rhs = widen AbsAnal abs_rhs_val
-- The widening above is done for efficiency reasons.
-- See notes on Let case in SaAbsInt.lhs
new_str_env = addOneToAbsValEnv str_env binder widened_str_rhs
new_abs_env = addOneToAbsValEnv abs_env binder widened_abs_rhs
-- Now determine the strictness of this binder; use that info
-- to record DemandInfo/StrictnessInfo in the binder.
new_binder = addStrictnessInfoToId
widened_str_rhs widened_abs_rhs
(binder `setIdDemandInfo` rhs_dmd)
in
tickLet new_binder `thenSa_` -- stats
saExpr rhs_dmd str_env abs_env rhs `thenSa` \ new_rhs ->
saExpr dmd new_str_env new_abs_env body `thenSa` \ new_body ->
returnSa (Let (NonRec new_binder new_rhs) new_body)
saExpr dmd str_env abs_env (Let (Rec pairs) body)
= let
(binders,rhss) = unzip pairs
str_vals = fixpoint StrAnal binders rhss str_env
abs_vals = fixpoint AbsAnal binders rhss abs_env
-- fixpoint returns widened values
new_str_env = growAbsValEnvList str_env (binders `zip` str_vals)
new_abs_env = growAbsValEnvList abs_env (binders `zip` abs_vals)
in
saExpr dmd new_str_env new_abs_env body `thenSa` \ new_body ->
mapSa (saExpr minDemand new_str_env new_abs_env) rhss `thenSa` \ new_rhss ->
let
-- DON'T add demand info in a Rec!
-- a) it's useless: we can't do let-to-case
-- b) it's incorrect. Consider
-- letrec x = ...y...
-- y = ...x...
-- in ...x...
-- When we ask whether y is demanded we'll bind y to bottom and
-- evaluate the body of the letrec. But that will result in our
-- deciding that y is absent, which is plain wrong!
-- It's much easier simply not to do this.
improved_binders = zipWith3Equal "saExpr" addStrictnessInfoToId
str_vals abs_vals binders
new_pairs = improved_binders `zip` new_rhss
in
returnSa (Let (Rec new_pairs) new_body)
\end{code}
%************************************************************************
%* *
\subsection[computeInfos]{Add computed info to binders}
%* *
%************************************************************************
Important note (Sept 93). @addStrictnessInfoToId@ is used only for
let(rec) bound variables, and is use to attach the strictness (not
demand) info to the binder. We are careful to restrict this
strictness info to the lambda-bound arguments which are actually
visible, at the top level, lest we accidentally lose laziness by
eagerly looking for an "extra" argument. So we "dig for lambdas" in a
rather syntactic way.
A better idea might be to have some kind of arity analysis to
tell how many args could safely be grabbed.
\begin{code}
addStrictnessInfoToId
:: AbsVal -- Abstract strictness value
-> AbsVal -- Ditto absence
-> Id -- The id
-> Id -- Augmented with strictness
addStrictnessInfoToId str_val abs_val binder
= binder `setIdStrictness` findStrictness binder str_val abs_val
\end{code}
\begin{code}
addDemandInfoToId :: Demand -> StrictEnv -> AbsenceEnv
-> CoreExpr -- The scope of the id
-> Id
-> Id -- Id augmented with Demand info
addDemandInfoToId dmd str_env abs_env expr binder
= binder `setIdDemandInfo` (findDemand dmd str_env abs_env expr binder)
addDemandInfoToCaseBndr dmd str_env abs_env alts binder
= binder `setIdDemandInfo` (findDemandAlts dmd str_env abs_env alts binder)
\end{code}
%************************************************************************
%* *
\subsection{Monad used herein for stats}
%* *
%************************************************************************
\begin{code}
data SaStats
= SaStats FastInt FastInt -- total/marked-demanded lambda-bound
FastInt FastInt -- total/marked-demanded case-bound
FastInt FastInt -- total/marked-demanded let-bound
-- (excl. top-level; excl. letrecs)
nullSaStats = SaStats (_ILIT 0) (_ILIT 0) (_ILIT 0) (_ILIT 0) (_ILIT 0) (_ILIT 0)
thenSa :: SaM a -> (a -> SaM b) -> SaM b
thenSa_ :: SaM a -> SaM b -> SaM b
returnSa :: a -> SaM a
{-# INLINE thenSa #-}
{-# INLINE thenSa_ #-}
{-# INLINE returnSa #-}
tickLambda :: Id -> SaM ()
tickCases :: [CoreBndr] -> SaM ()
tickLet :: Id -> SaM ()
#ifndef OMIT_STRANAL_STATS
type SaM a = SaStats -> (a, SaStats)
thenSa expr cont stats
= case (expr stats) of { (result, stats1) ->
cont result stats1 }
thenSa_ expr cont stats
= case (expr stats) of { (_, stats1) ->
cont stats1 }
returnSa x stats = (x, stats)
tickLambda var (SaStats tlam dlam tc dc tlet dlet)
= case (tick_demanded var (0,0)) of { (totB, demandedB) ->
let tot = iUnbox totB ; demanded = iUnbox demandedB
in
((), SaStats (tlam +# tot) (dlam +# demanded) tc dc tlet dlet) }
tickCases vars (SaStats tlam dlam tc dc tlet dlet)
= case (foldr tick_demanded (0,0) vars) of { (totB, demandedB) ->
let tot = iUnbox totB ; demanded = iUnbox demandedB
in
((), SaStats tlam dlam (tc +# tot) (dc +# demanded) tlet dlet) }
tickLet var (SaStats tlam dlam tc dc tlet dlet)
= case (tick_demanded var (0,0)) of { (totB, demandedB) ->
let tot = iUnbox totB ; demanded = iUnbox demandedB
in
((), SaStats tlam dlam tc dc (tlet +# tot) (dlet +# demanded)) }
tick_demanded var (tot, demanded)
| isTyVar var = (tot, demanded)
| otherwise
= (tot + 1,
if (isStrict (idDemandInfo var))
then demanded + 1
else demanded)
pp_stats (SaStats tlam dlam tc dc tlet dlet)
= hcat [ptext SLIT("Lambda vars: "), int (iBox dlam), char '/', int (iBox tlam),
ptext SLIT("; Case vars: "), int (iBox dc), char '/', int (iBox tc),
ptext SLIT("; Let vars: "), int (iBox dlet), char '/', int (iBox tlet)
]
#else /* OMIT_STRANAL_STATS */
-- identity monad
type SaM a = a
thenSa expr cont = cont expr
thenSa_ expr cont = cont
returnSa x = x
tickLambda var = panic "OMIT_STRANAL_STATS: tickLambda"
tickCases vars = panic "OMIT_STRANAL_STATS: tickCases"
tickLet var = panic "OMIT_STRANAL_STATS: tickLet"
#endif /* OMIT_STRANAL_STATS */
mapSa :: (a -> SaM b) -> [a] -> SaM [b]
mapSa f [] = returnSa []
mapSa f (x:xs) = f x `thenSa` \ r ->
mapSa f xs `thenSa` \ rs ->
returnSa (r:rs)
sequenceSa :: [SaM a] -> SaM [a]
sequenceSa [] = returnSa []
sequenceSa (m:ms) = m `thenSa` \ r ->
sequenceSa ms `thenSa` \ rs ->
returnSa (r:rs)
#endif /* OLD_STRICTNESS */
\end{code}
|
