DsBinds.hs 40.2 KB
Newer Older
Austin Seipp's avatar
Austin Seipp committed
1 2 3 4
{-
(c) The University of Glasgow 2006
(c) The GRASP/AQUA Project, Glasgow University, 1992-1998

Simon Marlow's avatar
Simon Marlow committed
5 6

Pattern-matching bindings (HsBinds and MonoBinds)
7

8 9 10
Handles @HsBinds@; those at the top level require different handling,
in that the @Rec@/@NonRec@/etc structure is thrown away (whereas at
lower levels it is preserved with @let@/@letrec@s).
Austin Seipp's avatar
Austin Seipp committed
11
-}
12

13
{-# LANGUAGE CPP #-}
Ian Lynagh's avatar
Ian Lynagh committed
14

15
module DsBinds ( dsTopLHsBinds, dsLHsBinds, decomposeRuleLhs, dsSpec,
16
                 dsHsWrapper, dsTcEvBinds, dsTcEvBinds_s, dsEvBinds
17
  ) where
18

19 20
#include "HsVersions.h"

21 22
import {-# SOURCE #-}   DsExpr( dsLExpr )
import {-# SOURCE #-}   Match( matchWrapper )
23

24
import DsMonad
Simon Marlow's avatar
Simon Marlow committed
25
import DsGRHSs
26
import DsUtils
27

28 29
import HsSyn            -- lots of things
import CoreSyn          -- lots of things
30
import Literal          ( Literal(MachStr) )
31
import CoreSubst
32
import OccurAnal        ( occurAnalyseExpr )
33
import MkCore
Simon Marlow's avatar
Simon Marlow committed
34
import CoreUtils
35
import CoreArity ( etaExpand )
36
import CoreUnfold
37
import CoreFVs
38 39
import UniqSupply
import Unique( Unique )
40
import Digraph
41

42

43
import TyCon      ( isTupleTyCon, tyConDataCons_maybe )
44
import TcEvidence
45
import TcType
46
import Type
batterseapower's avatar
batterseapower committed
47
import Coercion hiding (substCo)
Joachim Breitner's avatar
Joachim Breitner committed
48
import TysWiredIn ( eqBoxDataCon, coercibleDataCon, tupleCon )
Simon Marlow's avatar
Simon Marlow committed
49
import Id
50
import Class
51
import DataCon  ( dataConWorkId )
52
import Name
53
import MkId     ( seqId )
54
import IdInfo   ( IdDetails(..) )
55
import Var
56
import VarSet
Simon Marlow's avatar
Simon Marlow committed
57
import Rules
58
import VarEnv
59
import Outputable
Simon Marlow's avatar
Simon Marlow committed
60 61
import SrcLoc
import Maybes
62
import OrdList
Simon Marlow's avatar
Simon Marlow committed
63 64
import Bag
import BasicTypes hiding ( TopLevel )
Ian Lynagh's avatar
Ian Lynagh committed
65
import DynFlags
Simon Marlow's avatar
Simon Marlow committed
66
import FastString
67
import ErrUtils( MsgDoc )
68
import ListSetOps( getNth )
69
import Util
70
import Control.Monad( when )
71
import MonadUtils
72
import Control.Monad(liftM)
73

Austin Seipp's avatar
Austin Seipp committed
74 75 76
{-
************************************************************************
*                                                                      *
77
\subsection[dsMonoBinds]{Desugaring a @MonoBinds@}
Austin Seipp's avatar
Austin Seipp committed
78 79 80
*                                                                      *
************************************************************************
-}
81

82 83
dsTopLHsBinds :: LHsBinds Id -> DsM (OrdList (Id,CoreExpr))
dsTopLHsBinds binds = ds_lhs_binds binds
84

85
dsLHsBinds :: LHsBinds Id -> DsM [(Id,CoreExpr)]
86
dsLHsBinds binds = do { binds' <- ds_lhs_binds binds
87
                      ; return (fromOL binds') }
88 89

------------------------
90
ds_lhs_binds :: LHsBinds Id -> DsM (OrdList (Id,CoreExpr))
91

92 93
ds_lhs_binds binds = do { ds_bs <- mapBagM dsLHsBind binds
                        ; return (foldBag appOL id nilOL ds_bs) }
94

95 96
dsLHsBind :: LHsBind Id -> DsM (OrdList (Id,CoreExpr))
dsLHsBind (L loc bind) = putSrcSpanDs loc $ dsHsBind bind
97

98
dsHsBind :: HsBind Id -> DsM (OrdList (Id,CoreExpr))
99

100
dsHsBind (VarBind { var_id = var, var_rhs = expr, var_inline = inline_regardless })
101 102
  = do  { dflags <- getDynFlags
        ; core_expr <- dsLExpr expr
103

104 105
                -- Dictionary bindings are always VarBinds,
                -- so we only need do this here
106
        ; let var' | inline_regardless = var `setIdUnfolding` mkCompulsoryUnfolding core_expr
107
                   | otherwise         = var
108

109
        ; return (unitOL (makeCorePair dflags var' False 0 core_expr)) }
110

111 112 113
dsHsBind (FunBind { fun_id = L _ fun, fun_matches = matches
                  , fun_co_fn = co_fn, fun_tick = tick
                  , fun_infix = inf })
114
 = do   { dflags <- getDynFlags
115
        ; (args, body) <- matchWrapper (FunRhs (idName fun) inf) matches
116
        ; let body' = mkOptTickBox tick body
117
        ; rhs <- dsHsWrapper co_fn (mkLams args body')
118
        ; {- pprTrace "dsHsBind" (ppr fun <+> ppr (idInlinePragma fun)) $ -}
119
           return (unitOL (makeCorePair dflags fun False 0 rhs)) }
120 121 122

dsHsBind (PatBind { pat_lhs = pat, pat_rhs = grhss, pat_rhs_ty = ty
                  , pat_ticks = (rhs_tick, var_ticks) })
123
  = do  { body_expr <- dsGuarded grhss ty
124 125
        ; let body' = mkOptTickBox rhs_tick body_expr
        ; sel_binds <- mkSelectorBinds var_ticks pat body'
126 127
          -- We silently ignore inline pragmas; no makeCorePair
          -- Not so cool, but really doesn't matter
128
    ; return (toOL sel_binds) }
sof's avatar
sof committed
129

130 131 132 133
        -- A common case: one exported variable
        -- Non-recursive bindings come through this way
        -- So do self-recursive bindings, and recursive bindings
        -- that have been chopped up with type signatures
134 135 136
dsHsBind (AbsBinds { abs_tvs = tyvars, abs_ev_vars = dicts
                   , abs_exports = [export]
                   , abs_ev_binds = ev_binds, abs_binds = binds })
137 138
  | ABE { abe_wrap = wrap, abe_poly = global
        , abe_mono = local, abe_prags = prags } <- export
139
  = do  { dflags <- getDynFlags
140 141 142
        ; bind_prs <- ds_lhs_binds binds
        ; let core_bind = Rec (fromOL bind_prs)
        ; ds_binds <- dsTcEvBinds_s ev_binds
143
        ; rhs <- dsHsWrapper wrap $  -- Usually the identity
144 145
                            mkLams tyvars $ mkLams dicts $
                            mkCoreLets ds_binds $
146 147
                            Let core_bind $
                            Var local
148

149 150 151 152 153 154 155
        ; (spec_binds, rules) <- dsSpecs rhs prags

        ; let   global'   = addIdSpecialisations global rules
                main_bind = makeCorePair dflags global' (isDefaultMethod prags)
                                         (dictArity dicts) rhs

        ; return (main_bind `consOL` spec_binds) }
sof's avatar
sof committed
156

157 158 159
dsHsBind (AbsBinds { abs_tvs = tyvars, abs_ev_vars = dicts
                   , abs_exports = exports, abs_ev_binds = ev_binds
                   , abs_binds = binds })
160
         -- See Note [Desugaring AbsBinds]
161 162 163
  = do  { dflags <- getDynFlags
        ; bind_prs    <- ds_lhs_binds binds
        ; let core_bind = Rec [ makeCorePair dflags (add_inline lcl_id) False 0 rhs
164
                              | (lcl_id, rhs) <- fromOL bind_prs ]
165
                -- Monomorphic recursion possible, hence Rec
166

167 168 169
              locals       = map abe_mono exports
              tup_expr     = mkBigCoreVarTup locals
              tup_ty       = exprType tup_expr
170
        ; ds_binds <- dsTcEvBinds_s ev_binds
171 172 173 174
        ; let poly_tup_rhs = mkLams tyvars $ mkLams dicts $
                             mkCoreLets ds_binds $
                             Let core_bind $
                             tup_expr
175

176
        ; poly_tup_id <- newSysLocalDs (exprType poly_tup_rhs)
177

178
        ; let mk_bind (ABE { abe_wrap = wrap, abe_poly = global
179
                           , abe_mono = local, abe_prags = spec_prags })
180 181
                = do { tup_id  <- newSysLocalDs tup_ty
                     ; rhs <- dsHsWrapper wrap $
182
                                 mkLams tyvars $ mkLams dicts $
183 184
                                 mkTupleSelector locals local tup_id $
                                 mkVarApps (Var poly_tup_id) (tyvars ++ dicts)
185
                     ; let rhs_for_spec = Let (NonRec poly_tup_id poly_tup_rhs) rhs
186 187
                     ; (spec_binds, rules) <- dsSpecs rhs_for_spec spec_prags
                     ; let global' = (global `setInlinePragma` defaultInlinePragma)
188 189 190
                                             `addIdSpecialisations` rules
                           -- Kill the INLINE pragma because it applies to
                           -- the user written (local) function.  The global
191 192
                           -- Id is just the selector.  Hmm.
                     ; return ((global', rhs) `consOL` spec_binds) }
193

194
        ; export_binds_s <- mapM mk_bind exports
195

196 197
        ; return ((poly_tup_id, poly_tup_rhs) `consOL`
                    concatOL export_binds_s) }
198 199 200 201 202 203 204 205 206 207 208
  where
    inline_env :: IdEnv Id   -- Maps a monomorphic local Id to one with
                             -- the inline pragma from the source
                             -- The type checker put the inline pragma
                             -- on the *global* Id, so we need to transfer it
    inline_env = mkVarEnv [ (lcl_id, setInlinePragma lcl_id prag)
                          | ABE { abe_mono = lcl_id, abe_poly = gbl_id } <- exports
                          , let prag = idInlinePragma gbl_id ]

    add_inline :: Id -> Id    -- tran
    add_inline lcl_id = lookupVarEnv inline_env lcl_id `orElse` lcl_id
209

cactus's avatar
cactus committed
210 211
dsHsBind (PatSynBind{}) = panic "dsHsBind: PatSynBind"

212
------------------------
213 214
makeCorePair :: DynFlags -> Id -> Bool -> Arity -> CoreExpr -> (Id, CoreExpr)
makeCorePair dflags gbl_id is_default_method dict_arity rhs
215
  | is_default_method                 -- Default methods are *always* inlined
216 217
  = (gbl_id `setIdUnfolding` mkCompulsoryUnfolding rhs, rhs)

218
  | DFunId is_newtype <- idDetails gbl_id
219 220
  = (mk_dfun_w_stuff is_newtype, rhs)

221 222
  | otherwise
  = case inlinePragmaSpec inline_prag of
223 224 225
          EmptyInlineSpec -> (gbl_id, rhs)
          NoInline        -> (gbl_id, rhs)
          Inlinable       -> (gbl_id `setIdUnfolding` inlinable_unf, rhs)
226
          Inline          -> inline_pair
227

228 229
  where
    inline_prag   = idInlinePragma gbl_id
230
    inlinable_unf = mkInlinableUnfolding dflags rhs
231 232
    inline_pair
       | Just arity <- inlinePragmaSat inline_prag
233 234
        -- Add an Unfolding for an INLINE (but not for NOINLINE)
        -- And eta-expand the RHS; see Note [Eta-expanding INLINE things]
235
       , let real_arity = dict_arity + arity
236
        -- NB: The arity in the InlineRule takes account of the dictionaries
237 238 239 240 241 242
       = ( gbl_id `setIdUnfolding` mkInlineUnfolding (Just real_arity) rhs
         , etaExpand real_arity rhs)

       | otherwise
       = pprTrace "makeCorePair: arity missing" (ppr gbl_id) $
         (gbl_id `setIdUnfolding` mkInlineUnfolding Nothing rhs, rhs)
243

244 245 246
                -- See Note [ClassOp/DFun selection] in TcInstDcls
                -- See Note [Single-method classes]  in TcInstDcls
    mk_dfun_w_stuff is_newtype
Austin Seipp's avatar
Austin Seipp committed
247
       | is_newtype
248 249 250 251 252 253 254 255 256 257 258 259
       = gbl_id `setIdUnfolding`  mkInlineUnfolding (Just 0) rhs
                `setInlinePragma` alwaysInlinePragma { inl_sat = Just 0 }
       | otherwise
       = gbl_id `setIdUnfolding`  mkDFunUnfolding dfun_bndrs dfun_constr dfun_args
                `setInlinePragma` dfunInlinePragma
    (dfun_bndrs, dfun_body) = collectBinders (simpleOptExpr rhs)
    (dfun_con, dfun_args)   = collectArgs dfun_body
    dfun_constr | Var id <- dfun_con
                , DataConWorkId con <- idDetails id
                = con
                | otherwise = pprPanic "makeCorePair: dfun" (ppr rhs)

260 261 262 263

dictArity :: [Var] -> Arity
-- Don't count coercion variables in arity
dictArity dicts = count isId dicts
264

Austin Seipp's avatar
Austin Seipp committed
265
{-
266 267 268 269 270 271 272 273 274 275
[Desugaring AbsBinds]
~~~~~~~~~~~~~~~~~~~~~
In the general AbsBinds case we desugar the binding to this:

       tup a (d:Num a) = let fm = ...gm...
                             gm = ...fm...
                         in (fm,gm)
       f a d = case tup a d of { (fm,gm) -> fm }
       g a d = case tup a d of { (fm,gm) -> fm }

276 277 278 279 280
Note [Rules and inlining]
~~~~~~~~~~~~~~~~~~~~~~~~~
Common special case: no type or dictionary abstraction
This is a bit less trivial than you might suppose
The naive way woudl be to desguar to something like
281 282
        f_lcl = ...f_lcl...     -- The "binds" from AbsBinds
        M.f = f_lcl             -- Generated from "exports"
283
But we don't want that, because if M.f isn't exported,
284 285
it'll be inlined unconditionally at every call site (its rhs is
trivial).  That would be ok unless it has RULES, which would
286 287 288
thereby be completely lost.  Bad, bad, bad.

Instead we want to generate
289 290 291
        M.f = ...f_lcl...
        f_lcl = M.f
Now all is cool. The RULES are attached to M.f (by SimplCore),
292 293 294 295
and f_lcl is rapidly inlined away.

This does not happen in the same way to polymorphic binds,
because they desugar to
296
        M.f = /\a. let f_lcl = ...f_lcl... in f_lcl
297
Although I'm a bit worried about whether full laziness might
298
float the f_lcl binding out and then inline M.f at its call site
299 300 301 302 303 304 305 306 307 308 309 310 311 312 313

Note [Specialising in no-dict case]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Even if there are no tyvars or dicts, we may have specialisation pragmas.
Class methods can generate
      AbsBinds [] [] [( ... spec-prag]
         { AbsBinds [tvs] [dicts] ...blah }
So the overloading is in the nested AbsBinds. A good example is in GHC.Float:

  class  (Real a, Fractional a) => RealFrac a  where
    round :: (Integral b) => a -> b

  instance  RealFrac Float  where
    {-# SPECIALIZE round :: Float -> Int #-}

314
The top-level AbsBinds for $cround has no tyvars or dicts (because the
315 316 317 318 319 320 321
instance does not).  But the method is locally overloaded!

Note [Abstracting over tyvars only]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
When abstracting over type variable only (not dictionaries), we don't really need to
built a tuple and select from it, as we do in the general case. Instead we can take

322 323 324 325 326
        AbsBinds [a,b] [ ([a,b], fg, fl, _),
                         ([b],   gg, gl, _) ]
                { fl = e1
                  gl = e2
                   h = e3 }
327 328 329

and desugar it to

330 331 332
        fg = /\ab. let B in e1
        gg = /\b. let a = () in let B in S(e2)
        h  = /\ab. let B in e3
333 334

where B is the *non-recursive* binding
335 336 337
        fl = fg a b
        gl = gg b
        h  = h a b    -- See (b); note shadowing!
338 339

Notice (a) g has a different number of type variables to f, so we must
340 341
             use the mkArbitraryType thing to fill in the gaps.
             We use a type-let to do that.
342

343 344 345 346
         (b) The local variable h isn't in the exports, and rather than
             clone a fresh copy we simply replace h by (h a b), where
             the two h's have different types!  Shadowing happens here,
             which looks confusing but works fine.
347

348 349 350 351
         (c) The result is *still* quadratic-sized if there are a lot of
             small bindings.  So if there are more than some small
             number (10), we filter the binding set B by the free
             variables of the particular RHS.  Tiresome.
352 353

Why got to this trouble?  It's a common case, and it removes the
354
quadratic-sized tuple desugaring.  Less clutter, hopefully faster
355 356 357 358
compilation, especially in a case where there are a *lot* of
bindings.


359 360 361 362 363 364 365 366
Note [Eta-expanding INLINE things]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider
   foo :: Eq a => a -> a
   {-# INLINE foo #-}
   foo x = ...

If (foo d) ever gets floated out as a common sub-expression (which can
367
happen as a result of method sharing), there's a danger that we never
368 369 370 371
get to do the inlining, which is a Terribly Bad thing given that the
user said "inline"!

To avoid this we pre-emptively eta-expand the definition, so that foo
simonpj@microsoft.com's avatar
simonpj@microsoft.com committed
372
has the arity with which it is declared in the source code.  In this
373
example it has arity 2 (one for the Eq and one for x). Doing this
simonpj@microsoft.com's avatar
simonpj@microsoft.com committed
374
should mean that (foo d) is a PAP and we don't share it.
375 376 377

Note [Nested arities]
~~~~~~~~~~~~~~~~~~~~~
378 379 380 381 382 383 384 385 386 387 388 389 390 391
For reasons that are not entirely clear, method bindings come out looking like
this:

  AbsBinds [] [] [$cfromT <= [] fromT]
    $cfromT [InlPrag=INLINE] :: T Bool -> Bool
    { AbsBinds [] [] [fromT <= [] fromT_1]
        fromT :: T Bool -> Bool
        { fromT_1 ((TBool b)) = not b } } }

Note the nested AbsBind.  The arity for the InlineRule on $cfromT should be
gotten from the binding for fromT_1.

It might be better to have just one level of AbsBinds, but that requires more
thought!
Austin Seipp's avatar
Austin Seipp committed
392
-}
393

394
------------------------
395
dsSpecs :: CoreExpr     -- Its rhs
396
        -> TcSpecPrags
397 398
        -> DsM ( OrdList (Id,CoreExpr)  -- Binding for specialised Ids
               , [CoreRule] )           -- Rules for the Global Ids
399
-- See Note [Handling SPECIALISE pragmas] in TcBinds
400 401 402 403 404 405
dsSpecs _ IsDefaultMethod = return (nilOL, [])
dsSpecs poly_rhs (SpecPrags sps)
  = do { pairs <- mapMaybeM (dsSpec (Just poly_rhs)) sps
       ; let (spec_binds_s, rules) = unzip pairs
       ; return (concatOL spec_binds_s, rules) }

406 407 408
dsSpec :: Maybe CoreExpr        -- Just rhs => RULE is for a local binding
                                -- Nothing => RULE is for an imported Id
                                --            rhs is in the Id's unfolding
409 410 411
       -> Located TcSpecPrag
       -> DsM (Maybe (OrdList (Id,CoreExpr), CoreRule))
dsSpec mb_poly_rhs (L loc (SpecPrag poly_id spec_co spec_inl))
412
  | isJust (isClassOpId_maybe poly_id)
413 414
  = putSrcSpanDs loc $
    do { warnDs (ptext (sLit "Ignoring useless SPECIALISE pragma for class method selector")
415 416
                 <+> quotes (ppr poly_id))
       ; return Nothing  }  -- There is no point in trying to specialise a class op
417 418
                            -- Moreover, classops don't (currently) have an inl_sat arity set
                            -- (it would be Just 0) and that in turn makes makeCorePair bleat
419

420 421
  | no_act_spec && isNeverActive rule_act
  = putSrcSpanDs loc $
422 423 424
    do { warnDs (ptext (sLit "Ignoring useless SPECIALISE pragma for NOINLINE function:")
                 <+> quotes (ppr poly_id))
       ; return Nothing  }  -- Function is NOINLINE, and the specialiation inherits that
425
                            -- See Note [Activation pragmas for SPECIALISE]
426

427
  | otherwise
428
  = putSrcSpanDs loc $
429 430
    do { uniq <- newUnique
       ; let poly_name = idName poly_id
431 432
             spec_occ  = mkSpecOcc (getOccName poly_name)
             spec_name = mkInternalName uniq spec_occ (getSrcSpan poly_name)
433 434 435
       ; (bndrs, ds_lhs) <- liftM collectBinders
                                  (dsHsWrapper spec_co (Var poly_id))
       ; let spec_ty = mkPiTypes bndrs (exprType ds_lhs)
436 437 438 439
       ; -- pprTrace "dsRule" (vcat [ ptext (sLit "Id:") <+> ppr poly_id
         --                         , ptext (sLit "spec_co:") <+> ppr spec_co
         --                         , ptext (sLit "ds_rhs:") <+> ppr ds_lhs ]) $
         case decomposeRuleLhs bndrs ds_lhs of {
440
           Left msg -> do { warnDs msg; return Nothing } ;
441
           Right (rule_bndrs, _fn, args) -> do
442

443
       { dflags <- getDynFlags
Simon Peyton Jones's avatar
Simon Peyton Jones committed
444 445 446 447
       ; let fn_unf    = realIdUnfolding poly_id
             unf_fvs   = stableUnfoldingVars fn_unf `orElse` emptyVarSet
             in_scope  = mkInScopeSet (unf_fvs `unionVarSet` exprsFreeVars args)
             spec_unf  = specUnfolding dflags (mkEmptySubst in_scope) bndrs args fn_unf
448 449 450
             spec_id   = mkLocalId spec_name spec_ty
                            `setInlinePragma` inl_prag
                            `setIdUnfolding`  spec_unf
451
             rule =  mkRule False {- Not auto -} is_local_id
Ian Lynagh's avatar
Ian Lynagh committed
452
                        (mkFastString ("SPEC " ++ showPpr dflags poly_name))
453 454 455
                        rule_act poly_name
                        rule_bndrs args
                        (mkVarApps (Var spec_id) bndrs)
456

457
       ; spec_rhs <- dsHsWrapper spec_co poly_rhs
458

Ian Lynagh's avatar
Ian Lynagh committed
459 460
       ; when (isInlinePragma id_inl && wopt Opt_WarnPointlessPragmas dflags)
              (warnDs (specOnInline poly_name))
Simon Peyton Jones's avatar
Simon Peyton Jones committed
461 462 463 464 465

       ; return (Just (unitOL (spec_id, spec_rhs), rule))
            -- NB: do *not* use makeCorePair on (spec_id,spec_rhs), because
            --     makeCorePair overwrites the unfolding, which we have
            --     just created using specUnfolding
466 467 468 469
       } } }
  where
    is_local_id = isJust mb_poly_rhs
    poly_rhs | Just rhs <-  mb_poly_rhs
470
             = rhs          -- Local Id; this is its rhs
471 472
             | Just unfolding <- maybeUnfoldingTemplate (realIdUnfolding poly_id)
             = unfolding    -- Imported Id; this is its unfolding
473 474 475
                            -- Use realIdUnfolding so we get the unfolding
                            -- even when it is a loop breaker.
                            -- We want to specialise recursive functions!
476
             | otherwise = pprPanic "dsImpSpecs" (ppr poly_id)
477
                            -- The type checker has checked that it *has* an unfolding
478

479 480 481 482 483
    id_inl = idInlinePragma poly_id

    -- See Note [Activation pragmas for SPECIALISE]
    inl_prag | not (isDefaultInlinePragma spec_inl)    = spec_inl
             | not is_local_id  -- See Note [Specialising imported functions]
484
                                 -- in OccurAnal
485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502
             , isStrongLoopBreaker (idOccInfo poly_id) = neverInlinePragma
             | otherwise                               = id_inl
     -- Get the INLINE pragma from SPECIALISE declaration, or,
     -- failing that, from the original Id

    spec_prag_act = inlinePragmaActivation spec_inl

    -- See Note [Activation pragmas for SPECIALISE]
    -- no_act_spec is True if the user didn't write an explicit
    -- phase specification in the SPECIALISE pragma
    no_act_spec = case inlinePragmaSpec spec_inl of
                    NoInline -> isNeverActive  spec_prag_act
                    _        -> isAlwaysActive spec_prag_act
    rule_act | no_act_spec = inlinePragmaActivation id_inl   -- Inherit
             | otherwise   = spec_prag_act                   -- Specified by user


specOnInline :: Name -> MsgDoc
503
specOnInline f = ptext (sLit "SPECIALISE pragma on INLINE function probably won't fire:")
504
                 <+> quotes (ppr f)
505

Austin Seipp's avatar
Austin Seipp committed
506
{-
507 508 509 510 511 512 513 514
Note [Activation pragmas for SPECIALISE]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
From a user SPECIALISE pragma for f, we generate
  a) A top-level binding    spec_fn = rhs
  b) A RULE                 f dOrd = spec_fn

We need two pragma-like things:

515
* spec_fn's inline pragma: inherited from f's inline pragma (ignoring
516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536
                           activation on SPEC), unless overriden by SPEC INLINE

* Activation of RULE: from SPECIALISE pragma (if activation given)
                      otherwise from f's inline pragma

This is not obvious (see Trac #5237)!

Examples      Rule activation   Inline prag on spec'd fn
---------------------------------------------------------------------
SPEC [n] f :: ty            [n]   Always, or NOINLINE [n]
                                  copy f's prag

NOINLINE f
SPEC [n] f :: ty            [n]   NOINLINE
                                  copy f's prag

NOINLINE [k] f
SPEC [n] f :: ty            [n]   NOINLINE [k]
                                  copy f's prag

INLINE [k] f
537
SPEC [n] f :: ty            [n]   INLINE [k]
538 539 540 541 542 543 544 545 546 547
                                  copy f's prag

SPEC INLINE [n] f :: ty     [n]   INLINE [n]
                                  (ignore INLINE prag on f,
                                  same activation for rule and spec'd fn)

NOINLINE [k] f
SPEC f :: ty                [n]   INLINE [k]


Austin Seipp's avatar
Austin Seipp committed
548 549
************************************************************************
*                                                                      *
550
\subsection{Adding inline pragmas}
Austin Seipp's avatar
Austin Seipp committed
551 552 553
*                                                                      *
************************************************************************
-}
554

555
decomposeRuleLhs :: [Var] -> CoreExpr -> Either SDoc ([Var], Id, [CoreExpr])
unknown's avatar
unknown committed
556 557
-- (decomposeRuleLhs bndrs lhs) takes apart the LHS of a RULE,
-- The 'bndrs' are the quantified binders of the rules, but decomposeRuleLhs
558
-- may add some extra dictionary binders (see Note [Free dictionaries])
unknown's avatar
unknown committed
559
--
560
-- Returns Nothing if the LHS isn't of the expected shape
561 562 563 564 565 566 567 568
-- Note [Decomposing the left-hand side of a RULE]
decomposeRuleLhs orig_bndrs orig_lhs
  | not (null unbound)    -- Check for things unbound on LHS
                          -- See Note [Unused spec binders]
  = Left (vcat (map dead_msg unbound))

  | Var fn_var <- fun
  , not (fn_var `elemVarSet` orig_bndr_set)
569 570 571 572 573 574 575
  = -- pprTrace "decmposeRuleLhs" (vcat [ ptext (sLit "orig_bndrs:") <+> ppr orig_bndrs
    --                                  , ptext (sLit "orig_lhs:") <+> ppr orig_lhs
    --                                  , ptext (sLit "lhs1:")     <+> ppr lhs1
    --                                  , ptext (sLit "bndrs1:") <+> ppr bndrs1
    --                                  , ptext (sLit "fn_var:") <+> ppr fn_var
    --                                  , ptext (sLit "args:")   <+> ppr args]) $
    Right (bndrs1, fn_var, args)
576 577

  | Case scrut bndr ty [(DEFAULT, _, body)] <- fun
578
  , isDeadBinder bndr   -- Note [Matching seqId]
579 580 581
  , let args' = [Type (idType bndr), Type ty, scrut, body]
  = Right (bndrs1, seqId, args' ++ args)

582
  | otherwise
583
  = Left bad_shape_msg
584
 where
585 586 587 588 589 590
   lhs1       = drop_dicts orig_lhs
   lhs2       = simpleOptExpr lhs1  -- See Note [Simplify rule LHS]
   (fun,args) = collectArgs lhs2
   lhs_fvs    = exprFreeVars lhs2
   unbound    = filterOut (`elemVarSet` lhs_fvs) orig_bndrs
   bndrs1     = orig_bndrs ++ extra_dict_bndrs
591

592
   orig_bndr_set = mkVarSet orig_bndrs
593

594
        -- Add extra dict binders: Note [Free dictionaries]
595 596 597
   extra_dict_bndrs = [ mkLocalId (localiseName (idName d)) (idType d)
                      | d <- varSetElems (lhs_fvs `delVarSetList` orig_bndrs)
                      , isDictId d ]
598 599

   bad_shape_msg = hang (ptext (sLit "RULE left-hand side too complicated to desugar"))
600 601
                      2 (vcat [ text "Optimised lhs:" <+> ppr lhs2
                              , text "Orig lhs:" <+> ppr orig_lhs])
602
   dead_msg bndr = hang (sep [ ptext (sLit "Forall'd") <+> pp_bndr bndr
603
                             , ptext (sLit "is not bound in RULE lhs")])
604 605 606
                      2 (vcat [ text "Orig bndrs:" <+> ppr orig_bndrs
                              , text "Orig lhs:" <+> ppr orig_lhs
                              , text "optimised lhs:" <+> ppr lhs2 ])
607
   pp_bndr bndr
608 609 610
    | isTyVar bndr                      = ptext (sLit "type variable") <+> quotes (ppr bndr)
    | Just pred <- evVarPred_maybe bndr = ptext (sLit "constraint") <+> quotes (ppr pred)
    | otherwise                         = ptext (sLit "variable") <+> quotes (ppr bndr)
611 612

   drop_dicts :: CoreExpr -> CoreExpr
613
   drop_dicts e
614 615 616
       = wrap_lets needed bnds body
     where
       needed = orig_bndr_set `minusVarSet` exprFreeVars body
617
       (bnds, body) = split_lets (occurAnalyseExpr e)
618
           -- The occurAnalyseExpr drops dead bindings which is
619 620
           -- crucial to ensure that every binding is used later;
           -- which in turn makes wrap_lets work right
621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638

   split_lets :: CoreExpr -> ([(DictId,CoreExpr)], CoreExpr)
   split_lets e
     | Let (NonRec d r) body <- e
     , isDictId d
     , (bs, body') <- split_lets body
     = ((d,r):bs, body')
     | otherwise
     = ([], e)

   wrap_lets :: VarSet -> [(DictId,CoreExpr)] -> CoreExpr -> CoreExpr
   wrap_lets _ [] body = body
   wrap_lets needed ((d, r) : bs) body
     | rhs_fvs `intersectsVarSet` needed = Let (NonRec d r) (wrap_lets needed' bs body)
     | otherwise                         = wrap_lets needed bs body
     where
       rhs_fvs = exprFreeVars r
       needed' = (needed `minusVarSet` rhs_fvs) `extendVarSet` d
639

Austin Seipp's avatar
Austin Seipp committed
640
{-
641
Note [Decomposing the left-hand side of a RULE]
642
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
643
There are several things going on here.
644 645
* drop_dicts: see Note [Drop dictionary bindings on rule LHS]
* simpleOptExpr: see Note [Simplify rule LHS]
646
* extra_dict_bndrs: see Note [Free dictionaries]
647 648 649

Note [Drop dictionary bindings on rule LHS]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
650
drop_dicts drops dictionary bindings on the LHS where possible.
651 652
   E.g.  let d:Eq [Int] = $fEqList $fEqInt in f d
     --> f d
653
   Reasoning here is that there is only one d:Eq [Int], and so we can
654 655 656 657
   quantify over it. That makes 'd' free in the LHS, but that is later
   picked up by extra_dict_bndrs (Note [Dead spec binders]).

   NB 1: We can only drop the binding if the RHS doesn't bind
658
         one of the orig_bndrs, which we assume occur on RHS.
659 660 661 662 663 664
         Example
            f :: (Eq a) => b -> a -> a
            {-# SPECIALISE f :: Eq a => b -> [a] -> [a] #-}
         Here we want to end up with
            RULE forall d:Eq a.  f ($dfEqList d) = f_spec d
         Of course, the ($dfEqlist d) in the pattern makes it less likely
665
         to match, but there is no other way to get d:Eq a
666

667
   NB 2: We do drop_dicts *before* simplOptEpxr, so that we expect all
668 669 670 671 672 673
         the evidence bindings to be wrapped around the outside of the
         LHS.  (After simplOptExpr they'll usually have been inlined.)
         dsHsWrapper does dependency analysis, so that civilised ones
         will be simple NonRec bindings.  We don't handle recursive
         dictionaries!

Gabor Greif's avatar
Gabor Greif committed
674
    NB3: In the common case of a non-overloaded, but perhaps-polymorphic
675 676 677 678 679 680
         specialisation, we don't need to bind *any* dictionaries for use
         in the RHS. For example (Trac #8331)
             {-# SPECIALIZE INLINE useAbstractMonad :: ReaderST s Int #-}
             useAbstractMonad :: MonadAbstractIOST m => m Int
         Here, deriving (MonadAbstractIOST (ReaderST s)) is a lot of code
         but the RHS uses no dictionaries, so we want to end up with
681
             RULE forall s (d :: MonadAbstractIOST (ReaderT s)).
682 683
                useAbstractMonad (ReaderT s) d = $suseAbstractMonad s

684 685 686
   Trac #8848 is a good example of where there are some intersting
   dictionary bindings to discard.

687 688 689 690 691 692 693 694 695 696
The drop_dicts algorithm is based on these observations:

  * Given (let d = rhs in e) where d is a DictId,
    matching 'e' will bind e's free variables.

  * So we want to keep the binding if one of the needed variables (for
    which we need a binding) is in fv(rhs) but not already in fv(e).

  * The "needed variables" are simply the orig_bndrs.  Consider
       f :: (Eq a, Show b) => a -> b -> String
Austin Seipp's avatar
Austin Seipp committed
697
       ... SPECIALISE f :: (Show b) => Int -> b -> String ...
698 699 700 701 702 703
    Then orig_bndrs includes the *quantified* dictionaries of the type
    namely (dsb::Show b), but not the one for Eq Int

So we work inside out, applying the above criterion at each step.


704 705 706 707
Note [Simplify rule LHS]
~~~~~~~~~~~~~~~~~~~~~~~~
simplOptExpr occurrence-analyses and simplifies the LHS:

708
   (a) Inline any remaining dictionary bindings (which hopefully
709 710 711
       occur just once)

   (b) Substitute trivial lets so that they don't get in the way
712
       Note that we substitute the function too; we might
713 714
       have this as a LHS:  let f71 = M.f Int in f71

715
   (c) Do eta reduction.  To see why, consider the fold/build rule,
716 717 718 719
       which without simplification looked like:
          fold k z (build (/\a. g a))  ==>  ...
       This doesn't match unless you do eta reduction on the build argument.
       Similarly for a LHS like
720
         augment g (build h)
721
       we do not want to get
722
         augment (\a. g a) (build h)
723 724
       otherwise we don't match when given an argument like
          augment (\a. h a a) (build h)
725

726
Note [Matching seqId]
727 728
~~~~~~~~~~~~~~~~~~~
The desugarer turns (seq e r) into (case e of _ -> r), via a special-case hack
729
and this code turns it back into an application of seq!
730 731
See Note [Rules for seq] in MkId for the details.

732 733 734
Note [Unused spec binders]
~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider
735
        f :: a -> a
Austin Seipp's avatar
Austin Seipp committed
736
        ... SPECIALISE f :: Eq a => a -> a ...
737 738
It's true that this *is* a more specialised type, but the rule
we get is something like this:
739 740
        f_spec d = f
        RULE: f = f_spec d
Gabor Greif's avatar
typos  
Gabor Greif committed
741 742
Note that the rule is bogus, because it mentions a 'd' that is
not bound on the LHS!  But it's a silly specialisation anyway, because
743 744 745 746
the constraint is unused.  We could bind 'd' to (error "unused")
but it seems better to reject the program because it's almost certainly
a mistake.  That's what the isDeadBinder call detects.

747 748
Note [Free dictionaries]
~~~~~~~~~~~~~~~~~~~~~~~~
749 750
When the LHS of a specialisation rule, (/\as\ds. f es) has a free dict,
which is presumably in scope at the function definition site, we can quantify
751 752 753
over it too.  *Any* dict with that type will do.

So for example when you have
754 755
        f :: Eq a => a -> a
        f = <rhs>
Austin Seipp's avatar
Austin Seipp committed
756
        ... SPECIALISE f :: Int -> Int ...
757 758

Then we get the SpecPrag
759
        SpecPrag (f Int dInt)
760 761

And from that we want the rule
762 763 764

        RULE forall dInt. f Int dInt = f_spec
        f_spec = let f = <rhs> in f Int dInt
765 766 767 768 769 770 771

But be careful!  That dInt might be GHC.Base.$fOrdInt, which is an External
Name, and you can't bind them in a lambda or forall without getting things
confused.   Likewise it might have an InlineRule or something, which would be
utterly bogus. So we really make a fresh Id, with the same unique and type
as the old one, but with an Internal name and no IdInfo.

772

Austin Seipp's avatar
Austin Seipp committed
773 774
************************************************************************
*                                                                      *
775
                Desugaring evidence
Austin Seipp's avatar
Austin Seipp committed
776 777
*                                                                      *
************************************************************************
778

Austin Seipp's avatar
Austin Seipp committed
779
-}
780

781
dsHsWrapper :: HsWrapper -> CoreExpr -> DsM CoreExpr
782
dsHsWrapper WpHole            e = return e
783 784 785
dsHsWrapper (WpTyApp ty)      e = return $ App e (Type ty)
dsHsWrapper (WpLet ev_binds)  e = do bs <- dsTcEvBinds ev_binds
                                     return (mkCoreLets bs e)
786 787 788 789 790 791
dsHsWrapper (WpCompose c1 c2) e = do { e1 <- dsHsWrapper c2 e
                                     ; dsHsWrapper c1 e1 }
dsHsWrapper (WpFun c1 c2 t1 _) e = do { x <- newSysLocalDs t1
                                      ; e1 <- dsHsWrapper c1 (Var x)
                                      ; e2 <- dsHsWrapper c2 (e `mkCoreAppDs` e1)
                                      ; return (Lam x e2) }
792
dsHsWrapper (WpCast co)       e = ASSERT(tcCoercionRole co == Representational)
Joachim Breitner's avatar
Joachim Breitner committed
793
                                  dsTcCoercion co (mkCast e)
794 795
dsHsWrapper (WpEvLam ev)      e = return $ Lam ev e
dsHsWrapper (WpTyLam tv)      e = return $ Lam tv e
796
dsHsWrapper (WpEvApp    tm)   e = liftM (App e) (dsEvTerm tm)
797 798

--------------------------------------
799 800 801 802 803
dsTcEvBinds_s :: [TcEvBinds] -> DsM [CoreBind]
dsTcEvBinds_s []       = return []
dsTcEvBinds_s (b:rest) = ASSERT( null rest )  -- Zonker ensures null
                         dsTcEvBinds b

804
dsTcEvBinds :: TcEvBinds -> DsM [CoreBind]
805
dsTcEvBinds (TcEvBinds {}) = panic "dsEvBinds"    -- Zonker has got rid of this
806 807
dsTcEvBinds (EvBinds bs)   = dsEvBinds bs

808
dsEvBinds :: Bag EvBind -> DsM [CoreBind]
809
dsEvBinds bs = mapM ds_scc (sccEvBinds bs)
810
  where
811 812 813
    ds_scc (AcyclicSCC (EvBind { eb_lhs = v, eb_rhs = r }))
                          = liftM (NonRec v) (dsEvTerm r)
    ds_scc (CyclicSCC bs) = liftM Rec (mapM ds_pair bs)
814

815
    ds_pair (EvBind { eb_lhs = v, eb_rhs = r }) = liftM ((,) v) (dsEvTerm r)
816 817 818 819 820

sccEvBinds :: Bag EvBind -> [SCC EvBind]
sccEvBinds bs = stronglyConnCompFromEdgedVertices edges
  where
    edges :: [(EvBind, EvVar, [EvVar])]
821
    edges = foldrBag ((:) . mk_node) [] bs
822 823

    mk_node :: EvBind -> (EvBind, EvVar, [EvVar])
824 825
    mk_node b@(EvBind { eb_lhs = var, eb_rhs = term })
       = (b, var, varSetElems (evVarsOfTerm term))
826 827 828


---------------------------------------
829
dsEvTerm :: EvTerm -> DsM CoreExpr
830
dsEvTerm (EvId v) = return (Var v)
831

832
dsEvTerm (EvCast tm co)
833
  = do { tm' <- dsEvTerm tm
834
       ; dsTcCoercion co $ mkCast tm' }
835 836 837 838 839
                        -- 'v' is always a lifted evidence variable so it is
                        -- unnecessary to call varToCoreExpr v here.

dsEvTerm (EvDFunApp df tys tms) = do { tms' <- mapM dsEvTerm tms
                                     ; return (Var df `mkTyApps` tys `mkApps` tms') }
840 841

dsEvTerm (EvCoercion (TcCoVarCo v)) = return (Var v)  -- See Note [Simple coercions]
Joachim Breitner's avatar
Joachim Breitner committed
842
dsEvTerm (EvCoercion co)            = dsTcCoercion co mkEqBox
843

844
dsEvTerm (EvTupleSel v n)
845 846 847
   = do { tm' <- dsEvTerm v
        ; let scrut_ty = exprType tm'
              (tc, tys) = splitTyConApp scrut_ty
848 849
              Just [dc] = tyConDataCons_maybe tc
              xs = mkTemplateLocals tys
850
              the_x = getNth xs n
851 852 853 854
        ; ASSERT( isTupleTyCon tc )
          return $
          Case tm' (mkWildValBinder scrut_ty) (idType the_x) [(DataAlt dc, xs, Var the_x)] }

855
dsEvTerm (EvTupleMk tms)
856 857 858
  = do { tms' <- mapM dsEvTerm tms
       ; let tys = map exprType tms'
       ; return $ Var (dataConWorkId dc) `mkTyApps` tys `mkApps` tms' }
859
  where
860 861
    dc = tupleCon ConstraintTuple (length tms)

862
dsEvTerm (EvSuperClass d n)
863 864
  = do { d' <- dsEvTerm d
       ; let (cls, tys) = getClassPredTys (exprType d')
865
             sc_sel_id  = classSCSelId cls n    -- Zero-indexed
866
       ; return $ Var sc_sel_id `mkTyApps` tys `App` d' }
867
  where
868

869
dsEvTerm (EvDelayedError ty msg) = return $ Var errorId `mkTyApps` [ty] `mkApps