CoreUnfold.lhs 44.4 KB
Newer Older
1
%
Simon Marlow's avatar
Simon Marlow committed
2
% (c) The University of Glasgow 2006
3 4
% (c) The AQUA Project, Glasgow University, 1994-1998
%
Simon Marlow's avatar
Simon Marlow committed
5 6

Core-syntax unfoldings
7 8 9 10 11 12 13 14 15 16 17 18

Unfoldings (which can travel across module boundaries) are in Core
syntax (namely @CoreExpr@s).

The type @Unfolding@ sits ``above'' simply-Core-expressions
unfoldings, capturing ``higher-level'' things we know about a binding,
usually things that the simplifier found out (e.g., ``it's a
literal'').  In the corner of a @CoreUnfolding@ unfolding, you will
find, unsurprisingly, a Core expression.

\begin{code}
module CoreUnfold (
19
	Unfolding, UnfoldingGuidance,	-- Abstract types
20

21 22 23 24
	noUnfolding, mkImplicitUnfolding, 
	mkTopUnfolding, mkUnfolding, mkCoreUnfolding,
	mkInlineRule, mkWwInlineRule,
	mkCompulsoryUnfolding, mkDFunUnfolding,
25

26 27
	interestingArg, ArgSummary(..),

28
	couldBeSmallEnoughToInline, 
29
	certainlyWillInline, smallEnoughToInline,
30

31
	callSiteInline, CallCtxt(..), 
32

33 34
	exprIsConApp_maybe

35 36
    ) where

37 38
#include "HsVersions.h"

Simon Marlow's avatar
Simon Marlow committed
39 40
import StaticFlags
import DynFlags
41
import CoreSyn
42
import PprCore		()	-- Instances
Simon Marlow's avatar
Simon Marlow committed
43
import OccurAnal
44
import CoreSubst hiding( substTy )
45
import CoreFVs         ( exprFreeVars )
Simon Marlow's avatar
Simon Marlow committed
46 47 48
import CoreUtils
import Id
import DataCon
49
import TyCon
Simon Marlow's avatar
Simon Marlow committed
50 51 52
import Literal
import PrimOp
import IdInfo
53 54 55 56
import BasicTypes	( Arity )
import TcType		( tcSplitDFunTy )
import Type 
import Coercion
Simon Marlow's avatar
Simon Marlow committed
57
import PrelNames
58
import VarEnv           ( mkInScopeSet )
59
import Bag
60
import Util
61
import FastTypes
62
import FastString
63
import Outputable
64

65 66
\end{code}

67

68 69
%************************************************************************
%*									*
70
\subsection{Making unfoldings}
71 72 73 74
%*									*
%************************************************************************

\begin{code}
75 76 77
mkTopUnfolding :: Bool -> CoreExpr -> Unfolding
mkTopUnfolding is_bottoming expr 
  = mkUnfolding True {- Top level -} is_bottoming expr
78

79 80
mkImplicitUnfolding :: CoreExpr -> Unfolding
-- For implicit Ids, do a tiny bit of optimising first
81
mkImplicitUnfolding expr = mkTopUnfolding False (simpleOptExpr expr) 
Simon Marlow's avatar
Simon Marlow committed
82

83 84 85 86 87
-- Note [Top-level flag on inline rules]
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-- Slight hack: note that mk_inline_rules conservatively sets the
-- top-level flag to True.  It gets set more accurately by the simplifier
-- Simplify.simplUnfolding.
88

89 90
mkUnfolding :: Bool -> Bool -> CoreExpr -> Unfolding
mkUnfolding top_lvl is_bottoming expr
91 92 93 94 95 96 97 98 99
  = CoreUnfolding { uf_tmpl   	  = occurAnalyseExpr expr,
    		    uf_src        = InlineRhs,
    		    uf_arity      = arity,
		    uf_is_top 	  = top_lvl,
		    uf_is_value   = exprIsHNF        expr,
                    uf_is_conlike = exprIsConLike    expr,
		    uf_expandable = exprIsExpandable expr,
		    uf_is_cheap   = is_cheap,
		    uf_guidance   = guidance }
100
  where
101
    is_cheap = exprIsCheap expr
102 103
    (arity, guidance) = calcUnfoldingGuidance is_cheap (top_lvl && is_bottoming) 
                                              opt_UF_CreationThreshold expr
104 105 106
	-- Sometimes during simplification, there's a large let-bound thing	
	-- which has been substituted, and so is now dead; so 'expr' contains
	-- two copies of the thing while the occurrence-analysed expression doesn't
107
	-- Nevertheless, we *don't* occ-analyse before computing the size because the
108 109 110
	-- size computation bales out after a while, whereas occurrence analysis does not.
	--
	-- This can occasionally mean that the guidance is very pessimistic;
111 112
	-- it gets fixed up next round.  And it should be rare, because large
	-- let-bound things that are dead are usually caught by preInlineUnconditionally
113

114 115
mkCoreUnfolding :: Bool -> UnfoldingSource -> CoreExpr
                -> Arity -> UnfoldingGuidance -> Unfolding
116
-- Occurrence-analyses the expression before capturing it
117
mkCoreUnfolding top_lvl src expr arity guidance 
118
  = CoreUnfolding { uf_tmpl   	  = occurAnalyseExpr expr,
119
    		    uf_src        = src,
120 121
    		    uf_arity      = arity,
		    uf_is_top 	  = top_lvl,
122 123 124
		    uf_is_value   = exprIsHNF        expr,
                    uf_is_conlike = exprIsConLike    expr,
		    uf_is_cheap   = exprIsCheap      expr,
125 126 127 128 129
		    uf_expandable = exprIsExpandable expr,
		    uf_guidance   = guidance }

mkDFunUnfolding :: DataCon -> [Id] -> Unfolding
mkDFunUnfolding con ops = DFunUnfolding con (map Var ops)
Simon Marlow's avatar
Simon Marlow committed
130

131 132
mkWwInlineRule :: Id -> CoreExpr -> Arity -> Unfolding
mkWwInlineRule id expr arity
133 134 135
  = mkCoreUnfolding True (InlineWrapper id) 
                   (simpleOptExpr expr) arity
                   (UnfWhen unSaturatedOk boringCxtNotOk)
136

twanvl's avatar
twanvl committed
137
mkCompulsoryUnfolding :: CoreExpr -> Unfolding
138
mkCompulsoryUnfolding expr	   -- Used for things that absolutely must be unfolded
139 140 141
  = mkCoreUnfolding True InlineCompulsory
                    expr 0    -- Arity of unfolding doesn't matter
                    (UnfWhen unSaturatedOk boringCxtOk)
142

143 144 145
mkInlineRule :: Bool -> CoreExpr -> Arity -> Unfolding
mkInlineRule unsat_ok expr arity 
  = mkCoreUnfolding True InlineRule 	 -- Note [Top-level flag on inline rules]
146
    		    expr' arity 
147
		    (UnfWhen unsat_ok boring_ok)
148 149
  where
    expr' = simpleOptExpr expr
150
    boring_ok = case calcUnfoldingGuidance True    -- Treat as cheap
151
    	      	     			   False   -- But not bottoming
152 153 154 155
                                           (arity+1) expr' of
              	  (_, UnfWhen _ boring_ok) -> boring_ok
              	  _other                   -> boringCxtNotOk
     -- See Note [INLINE for small functions]
156
\end{code}
157

158

159 160 161 162 163
%************************************************************************
%*									*
\subsection{The UnfoldingGuidance type}
%*									*
%************************************************************************
164 165 166

\begin{code}
calcUnfoldingGuidance
167 168
	:: Bool		-- True <=> the rhs is cheap, or we want to treat it
	   		--          as cheap (INLINE things)	 
169 170
        -> Bool		-- True <=> this is a top-level unfolding for a
	                --          diverging function; don't inline this
171 172
        -> Int		-- Bomb out if size gets bigger than this
	-> CoreExpr    	-- Expression to look at
173
	-> (Arity, UnfoldingGuidance)
174
calcUnfoldingGuidance expr_is_cheap top_bot bOMB_OUT_SIZE expr
175
  = case collectBinders expr of { (bndrs, body) ->
176
    let
177 178 179 180 181 182 183 184 185 186
        val_bndrs   = filter isId bndrs
	n_val_bndrs = length val_bndrs

    	guidance 
          = case (sizeExpr (iUnbox bOMB_OUT_SIZE) val_bndrs body) of
      	      TooBig -> UnfNever
      	      SizeIs size cased_bndrs scrut_discount
      	        | uncondInline n_val_bndrs (iBox size) && expr_is_cheap
      	        -> UnfWhen needSaturated boringCxtOk

187 188 189
		| top_bot  -- See Note [Do not inline top-level bottoming functions]
		-> UnfNever

190 191 192 193 194 195 196 197
	        | otherwise
      	        -> UnfIfGoodArgs { ug_args  = map (discount cased_bndrs) val_bndrs
      	                         , ug_size  = iBox size
      	        	  	 , ug_res   = iBox scrut_discount }

        discount cbs bndr
           = foldlBag (\acc (b',n) -> if bndr==b' then acc+n else acc) 
		      0 cbs
198
    in
199
    (n_val_bndrs, guidance) }
200 201
\end{code}

202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223
Note [Computing the size of an expression]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The basic idea of sizeExpr is obvious enough: count nodes.  But getting the
heuristics right has taken a long time.  Here's the basic strategy:

    * Variables, literals: 0
      (Exception for string literals, see litSize.)

    * Function applications (f e1 .. en): 1 + #value args

    * Constructor applications: 1, regardless of #args

    * Let(rec): 1 + size of components

    * Note, cast: 0

Examples

  Size	Term
  --------------
    0	  42#
    0	  x
224
    0     True
225 226 227 228 229 230 231 232
    2	  f x
    1	  Just x
    4 	  f (g x)

Notice that 'x' counts 0, while (f x) counts 2.  That's deliberate: there's
a function call to account for.  Notice also that constructor applications 
are very cheap, because exposing them to a caller is so valuable.

233 234 235 236 237 238 239 240 241

Note [Do not inline top-level bottoming functions]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The FloatOut pass has gone to some trouble to float out calls to 'error' 
and similar friends.  See Note [Bottoming floats] in SetLevels.
Do not re-inline them!  But we *do* still inline if they are very small
(the uncondInline stuff).


242 243 244 245
Note [Unconditional inlining]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We inline *unconditionally* if inlined thing is smaller (using sizeExpr)
than the thing it's replacing.  Notice that
246 247 248 249 250 251
      (f x) --> (g 3) 		  -- YES, unconditionally
      (f x) --> x : []		  -- YES, *even though* there are two
      	    	    		  --      arguments to the cons
      x     --> g 3		  -- NO
      x	    --> Just v		  -- NO

252 253 254 255 256 257 258 259 260 261 262 263
It's very important not to unconditionally replace a variable by
a non-atomic term.

\begin{code}
uncondInline :: Arity -> Int -> Bool
-- Inline unconditionally if there no size increase
-- Size of call is arity (+1 for the function)
-- See Note [Unconditional inlining]
uncondInline arity size 
  | arity == 0 = size == 0
  | otherwise  = size <= arity + 1
\end{code}
264 265


266
\begin{code}
267
sizeExpr :: FastInt 	    -- Bomb out if it gets bigger than this
268 269 270 271 272
	 -> [Id]	    -- Arguments; we're interested in which of these
			    -- get case'd
	 -> CoreExpr
	 -> ExprSize

273 274
-- Note [Computing the size of an expression]

275
sizeExpr bOMB_OUT_SIZE top_args expr
276 277
  = size_up expr
  where
278 279
    size_up (Cast e _) = size_up e
    size_up (Note _ e) = size_up e
280 281
    size_up (Type _)   = sizeZero           -- Types cost nothing
    size_up (Lit lit)  = sizeN (litSize lit)
282
    size_up (Var f)    = size_up_call f []  -- Make sure we get constructor
283
    	    	       	 	      	    -- discounts even on nullary constructors
Simon Marlow's avatar
Simon Marlow committed
284

twanvl's avatar
twanvl committed
285
    size_up (App fun (Type _)) = size_up fun
286 287
    size_up (App fun arg)      = size_up arg  `addSizeNSD`
                                 size_up_app fun [arg]
288

289
    size_up (Lam b e) | isId b    = lamScrutDiscount (size_up e `addSizeN` 1)
290 291 292
		      | otherwise = size_up e

    size_up (Let (NonRec binder rhs) body)
293 294
      = size_up rhs		`addSizeNSD`
	size_up body		`addSizeN`
295 296 297
	(if isUnLiftedType (idType binder) then 0 else 1)
		-- For the allocation
		-- If the binder has an unlifted type there is no allocation
298 299

    size_up (Let (Rec pairs) body)
300 301 302
      = foldr (addSizeNSD . size_up . snd) 
              (size_up body `addSizeN` length pairs)	-- (length pairs) for the allocation
              pairs
303

304
    size_up (Case (Var v) _ _ alts) 
305
	| v `elem` top_args		-- We are scrutinising an argument variable
306
	= alts_size (foldr1 addAltSize alt_sizes)
307
		    (foldr1 maxSize alt_sizes)
308 309 310 311 312 313
		-- Good to inline if an arg is scrutinised, because
		-- that may eliminate allocation in the caller
		-- And it eliminates the case itself
	where
	  alt_sizes = map size_up_alt alts

314 315
		-- alts_size tries to compute a good discount for
		-- the case when we are scrutinising an argument variable
316 317 318
	  alts_size (SizeIs tot tot_disc tot_scrut)  -- Size of all alternatives
		    (SizeIs max _        _)          -- Size of biggest alternative
	 	= SizeIs tot (unitBag (v, iBox (_ILIT(2) +# tot -# max)) `unionBags` tot_disc) tot_scrut
319
			-- If the variable is known, we produce a discount that
320
			-- will take us back to 'max', the size of the largest alternative
321
			-- The 1+ is a little discount for reduced allocation in the caller
322 323 324 325
			--
			-- Notice though, that we return tot_disc, the total discount from 
			-- all branches.  I think that's right.

326 327
	  alts_size tot_size _ = tot_size

328 329
    size_up (Case e _ _ alts) = size_up e  `addSizeNSD` 
                                foldr (addAltSize . size_up_alt) sizeZero alts
330 331 332 333 334
	  	-- We don't charge for the case itself
		-- It's a strict thing, and the price of the call
		-- is paid by scrut.  Also consider
		--	case f x of DEFAULT -> e
		-- This is just ';'!  Don't charge for it.
335 336
		--
		-- Moreover, we charge one per alternative.
337 338

    ------------ 
339 340 341
    -- size_up_app is used when there's ONE OR MORE value args
    size_up_app (App fun arg) args 
	| isTypeArg arg		   = size_up_app fun args
342 343
	| otherwise		   = size_up arg  `addSizeNSD`
                                     size_up_app fun (arg:args)
344
    size_up_app (Var fun)     args = size_up_call fun args
345 346 347
    size_up_app other         args = size_up other `addSizeN` length args

    ------------ 
348 349
    size_up_call :: Id -> [CoreExpr] -> ExprSize
    size_up_call fun val_args
350 351
       = case idDetails fun of
           FCallId _        -> sizeN opt_UF_DearOp
352 353 354 355
           DataConWorkId dc -> conSize    dc (length val_args)
           PrimOpId op      -> primOpSize op (length val_args)
	   ClassOpId _ 	    -> classOpSize top_args val_args
	   _     	    -> funSize top_args fun (length val_args)
356 357

    ------------ 
358
    size_up_alt (_con, _bndrs, rhs) = size_up rhs `addSizeN` 1
359 360
 	-- Don't charge for args, so that wrappers look cheap
	-- (See comments about wrappers with Case)
361 362 363 364
	--
	-- IMPORATANT: *do* charge 1 for the alternative, else we 
	-- find that giant case nests are treated as practically free
	-- A good example is Foreign.C.Error.errrnoToIOError
365 366 367 368

    ------------
	-- These addSize things have to be here because
	-- I don't want to give them bOMB_OUT_SIZE as an argument
369 370
    addSizeN TooBig          _  = TooBig
    addSizeN (SizeIs n xs d) m 	= mkSizeIs bOMB_OUT_SIZE (n +# iUnbox m) xs d
371
    
372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387
        -- addAltSize is used to add the sizes of case alternatives
    addAltSize TooBig	         _	= TooBig
    addAltSize _		 TooBig	= TooBig
    addAltSize (SizeIs n1 xs d1) (SizeIs n2 ys d2) 
	= mkSizeIs bOMB_OUT_SIZE (n1 +# n2) 
                                 (xs `unionBags` ys) 
                                 (d1 +# d2)   -- Note [addAltSize result discounts]

        -- This variant ignores the result discount from its LEFT argument
	-- It's used when the second argument isn't part of the result
    addSizeNSD TooBig	         _	= TooBig
    addSizeNSD _		 TooBig	= TooBig
    addSizeNSD (SizeIs n1 xs _) (SizeIs n2 ys d2) 
	= mkSizeIs bOMB_OUT_SIZE (n1 +# n2) 
                                 (xs `unionBags` ys) 
                                 d2  -- Ignore d1
388 389 390
\end{code}

\begin{code}
391 392 393 394 395 396 397 398 399 400 401
-- | Finds a nominal size of a string literal.
litSize :: Literal -> Int
-- Used by CoreUnfold.sizeExpr
litSize (MachStr str) = 1 + ((lengthFS str + 3) `div` 4)
	-- If size could be 0 then @f "x"@ might be too small
	-- [Sept03: make literal strings a bit bigger to avoid fruitless 
	--  duplication of little strings]
litSize _other = 0    -- Must match size of nullary constructors
	       	      -- Key point: if  x |-> 4, then x must inline unconditionally
		      --     	    (eg via case binding)

402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417
classOpSize :: [Id] -> [CoreExpr] -> ExprSize
-- See Note [Conlike is interesting]
classOpSize _ [] 
  = sizeZero
classOpSize top_args (arg1 : other_args)
  = SizeIs (iUnbox size) arg_discount (_ILIT(0))
  where
    size = 2 + length other_args
    -- If the class op is scrutinising a lambda bound dictionary then
    -- give it a discount, to encourage the inlining of this function
    -- The actual discount is rather arbitrarily chosen
    arg_discount = case arg1 of
    		     Var dict | dict `elem` top_args 
		     	      -> unitBag (dict, opt_UF_DictDiscount)
		     _other   -> emptyBag
    		     
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
funSize :: [Id] -> Id -> Int -> ExprSize
-- Size for functions that are not constructors or primops
-- Note [Function applications]
funSize top_args fun n_val_args
  | fun `hasKey` buildIdKey   = buildSize
  | fun `hasKey` augmentIdKey = augmentSize
  | otherwise = SizeIs (iUnbox size) arg_discount (iUnbox res_discount)
  where
    some_val_args = n_val_args > 0

    arg_discount | some_val_args && fun `elem` top_args
    		 = unitBag (fun, opt_UF_FunAppDiscount)
		 | otherwise = emptyBag
	-- If the function is an argument and is applied
	-- to some values, give it an arg-discount

    res_discount | idArity fun > n_val_args = opt_UF_FunAppDiscount
    		 | otherwise   	 	    = 0
        -- If the function is partially applied, show a result discount

    size | some_val_args = 1 + n_val_args
         | otherwise     = 0
	-- The 1+ is for the function itself
	-- Add 1 for each non-trivial arg;
	-- the allocation cost, as in let(rec)
  

conSize :: DataCon -> Int -> ExprSize
conSize dc n_val_args
447
  | n_val_args == 0      = SizeIs (_ILIT(0)) emptyBag (_ILIT(1))	-- Like variables
448 449 450 451
  | isUnboxedTupleCon dc = SizeIs (_ILIT(0)) emptyBag (iUnbox n_val_args +# _ILIT(1))
  | otherwise		 = SizeIs (_ILIT(1)) emptyBag (iUnbox n_val_args +# _ILIT(1))
	-- Treat a constructors application as size 1, regardless of how
	-- many arguments it has; we are keen to expose them
452
	-- (and we charge separately for their args).  We can't treat
453
	-- them as size zero, else we find that (Just x) has size 0,
454
	-- which is the same as a lone variable; and hence 'v' will 
455
	-- always be replaced by (Just x), where v is bound to Just x.
456 457 458 459 460
	--
	-- However, unboxed tuples count as size zero
	-- I found occasions where we had 
	--	f x y z = case op# x y z of { s -> (# s, () #) }
	-- and f wasn't getting inlined
461

twanvl's avatar
twanvl committed
462
primOpSize :: PrimOp -> Int -> ExprSize
463
primOpSize op n_val_args
464
 | not (primOpIsDupable op) = sizeN opt_UF_DearOp
465
 | not (primOpOutOfLine op) = sizeN 1
466
	-- Be very keen to inline simple primops.
467 468 469 470 471 472 473 474
	-- We give a discount of 1 for each arg so that (op# x y z) costs 2.
	-- We can't make it cost 1, else we'll inline let v = (op# x y z) 
	-- at every use of v, which is excessive.
	--
	-- A good example is:
	--	let x = +# p q in C {x}
	-- Even though x get's an occurrence of 'many', its RHS looks cheap,
	-- and there's a good chance it'll get inlined back into C's RHS. Urgh!
475 476 477

 | otherwise = sizeN n_val_args

478

twanvl's avatar
twanvl committed
479
buildSize :: ExprSize
480
buildSize = SizeIs (_ILIT(0)) emptyBag (_ILIT(4))
481 482 483 484
	-- We really want to inline applications of build
	-- build t (\cn -> e) should cost only the cost of e (because build will be inlined later)
	-- Indeed, we should add a result_discount becuause build is 
	-- very like a constructor.  We don't bother to check that the
485
	-- build is saturated (it usually is).  The "-2" discounts for the \c n, 
486
	-- The "4" is rather arbitrary.
487

twanvl's avatar
twanvl committed
488
augmentSize :: ExprSize
489
augmentSize = SizeIs (_ILIT(0)) emptyBag (_ILIT(4))
490 491
	-- Ditto (augment t (\cn -> e) ys) should cost only the cost of
	-- e plus ys. The -2 accounts for the \cn 
twanvl's avatar
twanvl committed
492

493
-- When we return a lambda, give a discount if it's used (applied)
twanvl's avatar
twanvl committed
494
lamScrutDiscount :: ExprSize -> ExprSize
495
lamScrutDiscount (SizeIs n vs _) = SizeIs n vs (iUnbox opt_UF_FunAppDiscount)
twanvl's avatar
twanvl committed
496
lamScrutDiscount TooBig          = TooBig
497 498
\end{code}

499 500 501 502 503 504 505 506 507
Note [addAltSize result discounts]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
When adding the size of alternatives, we *add* the result discounts
too, rather than take the *maximum*.  For a multi-branch case, this
gives a discount for each branch that returns a constructor, making us
keener to inline.  I did try using 'max' instead, but it makes nofib 
'rewrite' and 'puzzle' allocate significantly more, and didn't make
binary sizes shrink significantly either.

508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536
Note [Discounts and thresholds]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Constants for discounts and thesholds are defined in main/StaticFlags,
all of form opt_UF_xxxx.   They are:

opt_UF_CreationThreshold (45)
     At a definition site, if the unfolding is bigger than this, we
     may discard it altogether

opt_UF_UseThreshold (6)
     At a call site, if the unfolding, less discounts, is smaller than
     this, then it's small enough inline

opt_UF_KeennessFactor (1.5)
     Factor by which the discounts are multiplied before 
     subtracting from size

opt_UF_DictDiscount (1)
     The discount for each occurrence of a dictionary argument
     as an argument of a class method.  Should be pretty small
     else big functions may get inlined

opt_UF_FunAppDiscount (6)
     Discount for a function argument that is applied.  Quite
     large, because if we inline we avoid the higher-order call.

opt_UF_DearOp (4)
     The size of a foreign call or not-dupable PrimOp

537

538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577
Note [Function applications]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In a function application (f a b)

  - If 'f' is an argument to the function being analysed, 
    and there's at least one value arg, record a FunAppDiscount for f

  - If the application if a PAP (arity > 2 in this example)
    record a *result* discount (because inlining
    with "extra" args in the call may mean that we now 
    get a saturated application)

Code for manipulating sizes

\begin{code}
data ExprSize = TooBig
	      | SizeIs FastInt		-- Size found
		       (Bag (Id,Int))	-- Arguments cased herein, and discount for each such
		       FastInt		-- Size to subtract if result is scrutinised 
					-- by a case expression

instance Outputable ExprSize where
  ppr TooBig         = ptext (sLit "TooBig")
  ppr (SizeIs a _ c) = brackets (int (iBox a) <+> int (iBox c))

-- subtract the discount before deciding whether to bale out. eg. we
-- want to inline a large constructor application into a selector:
--  	tup = (a_1, ..., a_99)
--  	x = case tup of ...
--
mkSizeIs :: FastInt -> FastInt -> Bag (Id, Int) -> FastInt -> ExprSize
mkSizeIs max n xs d | (n -# d) ># max = TooBig
		    | otherwise	      = SizeIs n xs d
 
maxSize :: ExprSize -> ExprSize -> ExprSize
maxSize TooBig         _ 				  = TooBig
maxSize _              TooBig				  = TooBig
maxSize s1@(SizeIs n1 _ _) s2@(SizeIs n2 _ _) | n1 ># n2  = s1
					      | otherwise = s2

578
sizeZero :: ExprSize
579 580 581 582 583 584 585
sizeN :: Int -> ExprSize

sizeZero = SizeIs (_ILIT(0))  emptyBag (_ILIT(0))
sizeN n  = SizeIs (iUnbox n) emptyBag (_ILIT(0))
\end{code}


586 587 588 589 590 591
%************************************************************************
%*									*
\subsection[considerUnfolding]{Given all the info, do (not) do the unfolding}
%*									*
%************************************************************************

592 593 594 595
We use 'couldBeSmallEnoughToInline' to avoid exporting inlinings that
we ``couldn't possibly use'' on the other side.  Can be overridden w/
flaggery.  Just the same as smallEnoughToInline, except that it has no
actual arguments.
596 597

\begin{code}
598
couldBeSmallEnoughToInline :: Int -> CoreExpr -> Bool
599
couldBeSmallEnoughToInline threshold rhs 
600
  = case calcUnfoldingGuidance False False threshold rhs of
601 602
       (_, UnfNever) -> False
       _             -> True
603

604
----------------
605
smallEnoughToInline :: Unfolding -> Bool
606
smallEnoughToInline (CoreUnfolding {uf_guidance = UnfIfGoodArgs {ug_size = size}})
607
  = size <= opt_UF_UseThreshold
twanvl's avatar
twanvl committed
608
smallEnoughToInline _
609
  = False
610 611 612 613 614 615

----------------
certainlyWillInline :: Unfolding -> Bool
  -- Sees if the unfolding is pretty certain to inline	
certainlyWillInline (CoreUnfolding { uf_is_cheap = is_cheap, uf_arity = n_vals, uf_guidance = guidance })
  = case guidance of
616 617 618
      UnfNever      -> False
      UnfWhen {}    -> True
      UnfIfGoodArgs { ug_size = size} 
619 620 621 622
                    -> is_cheap && size - (n_vals +1) <= opt_UF_UseThreshold

certainlyWillInline _
  = False
623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641
\end{code}

%************************************************************************
%*									*
\subsection{callSiteInline}
%*									*
%************************************************************************

This is the key function.  It decides whether to inline a variable at a call site

callSiteInline is used at call sites, so it is a bit more generous.
It's a very important function that embodies lots of heuristics.
A non-WHNF can be inlined if it doesn't occur inside a lambda,
and occurs exactly once or 
    occurs once in each branch of a case and is small

If the thing is in WHNF, there's no danger of duplicating work, 
so we can inline if it occurs once, or is small

642
NOTE: we don't want to inline top-level functions that always diverge.
643
It just makes the code bigger.  Tt turns out that the convenient way to prevent
644 645 646
them inlining is to give them a NOINLINE pragma, which we do in 
StrictAnal.addStrictnessInfoToTopId

647
\begin{code}
648
callSiteInline :: DynFlags
649
	       -> Id			-- The Id
650
	       -> Unfolding		-- Its unfolding (if active)
651
	       -> Bool			-- True if there are are no arguments at all (incl type args)
652
	       -> [ArgSummary]		-- One for each value arg; True if it is interesting
653
	       -> CallCtxt		-- True <=> continuation is interesting
654 655 656
	       -> Maybe CoreExpr	-- Unfolding, if any


657 658 659 660 661
instance Outputable ArgSummary where
  ppr TrivArg    = ptext (sLit "TrivArg")
  ppr NonTrivArg = ptext (sLit "NonTrivArg")
  ppr ValueArg   = ptext (sLit "ValueArg")

662
data CallCtxt = BoringCtxt
663

664 665 666 667 668 669 670
	      | ArgCtxt		-- We are somewhere in the argument of a function
                        Bool	-- True  <=> we're somewhere in the RHS of function with rules
				-- False <=> we *are* the argument of a function with non-zero
				-- 	     arg discount
                                --        OR 
                                --           we *are* the RHS of a let  Note [RHS of lets]
                                -- In both cases, be a little keener to inline
671

672 673 674 675
	      | ValAppCtxt 	-- We're applied to at least one value arg
				-- This arises when we have ((f x |> co) y)
				-- Then the (f x) has argument 'x' but in a ValAppCtxt

676 677 678 679
	      | CaseCtxt	-- We're the scrutinee of a case
				-- that decomposes its scrutinee

instance Outputable CallCtxt where
680 681 682 683
  ppr BoringCtxt      = ptext (sLit "BoringCtxt")
  ppr (ArgCtxt rules) = ptext (sLit "ArgCtxt") <+> ppr rules
  ppr CaseCtxt 	      = ptext (sLit "CaseCtxt")
  ppr ValAppCtxt      = ptext (sLit "ValAppCtxt")
684

685 686
callSiteInline dflags id unfolding lone_variable arg_infos cont_info
  = case unfolding of {
687 688 689 690 691 692 693
	NoUnfolding 	 -> Nothing ;
	OtherCon _  	 -> Nothing ;
	DFunUnfolding {} -> Nothing ;	-- Never unfold a DFun
	CoreUnfolding { uf_tmpl = unf_template, uf_is_top = is_top, uf_is_value = is_value,
		        uf_is_cheap = is_cheap, uf_arity = uf_arity, uf_guidance = guidance } ->
			-- uf_arity will typically be equal to (idArity id), 
			-- but may be less for InlineRules
694
    let
695 696
	n_val_args = length arg_infos
        saturated  = n_val_args >= uf_arity
697

698 699 700
	result | yes_or_no = Just unf_template
	       | otherwise = Nothing

701 702 703 704 705 706 707 708 709 710
	interesting_args = any nonTriv arg_infos 
 		-- NB: (any nonTriv arg_infos) looks at the
 		-- over-saturated args too which is "wrong"; 
 		-- but if over-saturated we inline anyway.

	       -- some_benefit is used when the RHS is small enough
	       -- and the call has enough (or too many) value
	       -- arguments (ie n_val_args >= arity). But there must
	       -- be *something* interesting about some argument, or the
	       -- result context, to make it worth inlining
711 712 713 714 715 716
	some_benefit 
           | not saturated = interesting_args	-- Under-saturated
		   	      		     	-- Note [Unsaturated applications]
	   | n_val_args > uf_arity = True	-- Over-saturated
           | otherwise = interesting_args	-- Saturated
                      || interesting_saturated_call 
717 718 719 720 721 722 723 724

	interesting_saturated_call 
	  = case cont_info of
	      BoringCtxt -> not is_top && uf_arity > 0		-- Note [Nested functions]
	      CaseCtxt   -> not (lone_variable && is_value)	-- Note [Lone variables]
	      ArgCtxt {} -> uf_arity > 0     			-- Note [Inlining in ArgCtxt]
	      ValAppCtxt -> True				-- Note [Cast then apply]

725
	(yes_or_no, extra_doc)
726
	  = case guidance of
727 728 729 730 731 732
	      UnfNever -> (False, empty)

	      UnfWhen unsat_ok boring_ok -> ( (unsat_ok  || saturated)
                                           && (boring_ok || some_benefit)
                                            , empty )
		   -- For the boring_ok part see Note [INLINE for small functions]
733

734 735 736
	      UnfIfGoodArgs { ug_args = arg_discounts, ug_res = res_discount, ug_size = size }
	  	 -> ( is_cheap && some_benefit && small_enough
                    , (text "discounted size =" <+> int discounted_size) )
737
		 where
738 739
		   discounted_size = size - discount
		   small_enough = discounted_size <= opt_UF_UseThreshold
740 741
		   discount = computeDiscount uf_arity arg_discounts 
				              res_discount arg_infos cont_info
742
		
743
    in    
744
    if dopt Opt_D_dump_inlinings dflags then
simonpj@microsoft.com's avatar
simonpj@microsoft.com committed
745
	pprTrace ("Considering inlining: " ++ showSDoc (ppr id))
746 747
		 (vcat [text "arg infos" <+> ppr arg_infos,
			text "uf arity" <+> ppr uf_arity,
simonpj@microsoft.com's avatar
simonpj@microsoft.com committed
748
			text "interesting continuation" <+> ppr cont_info,
749
			text "some_benefit" <+> ppr some_benefit,
simonpj@microsoft.com's avatar
simonpj@microsoft.com committed
750
			text "is value:" <+> ppr is_value,
751
                        text "is cheap:" <+> ppr is_cheap,
simonpj@microsoft.com's avatar
simonpj@microsoft.com committed
752
			text "guidance" <+> ppr guidance,
753
			extra_doc,
simonpj@microsoft.com's avatar
simonpj@microsoft.com committed
754
			text "ANSWER =" <+> if yes_or_no then text "YES" else text "NO"])
755 756 757 758
		  result
    else
    result
    }
759 760
\end{code}

761 762 763 764 765 766 767 768 769
Note [RHS of lets]
~~~~~~~~~~~~~~~~~~
Be a tiny bit keener to inline in the RHS of a let, because that might
lead to good thing later
     f y = (y,y,y)
     g y = let x = f y in ...(case x of (a,b,c) -> ...) ...
We'd inline 'f' if the call was in a case context, and it kind-of-is,
only we can't see it.  So we treat the RHS of a let as not-totally-boring.
    
770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804
Note [Unsaturated applications]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
When a call is not saturated, we *still* inline if one of the
arguments has interesting structure.  That's sometimes very important.
A good example is the Ord instance for Bool in Base:

 Rec {
    $fOrdBool =GHC.Classes.D:Ord
        	 @ Bool
      		 ...
      		 $cmin_ajX

    $cmin_ajX [Occ=LoopBreaker] :: Bool -> Bool -> Bool
    $cmin_ajX = GHC.Classes.$dmmin @ Bool $fOrdBool
  }

But the defn of GHC.Classes.$dmmin is:

  $dmmin :: forall a. GHC.Classes.Ord a => a -> a -> a
    {- Arity: 3, HasNoCafRefs, Strictness: SLL,
       Unfolding: (\ @ a $dOrd :: GHC.Classes.Ord a x :: a y :: a ->
                   case @ a GHC.Classes.<= @ a $dOrd x y of wild {
                     GHC.Bool.False -> y GHC.Bool.True -> x }) -}

We *really* want to inline $dmmin, even though it has arity 3, in
order to unravel the recursion.


Note [INLINE for small functions]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider	{-# INLINE f #-}
                f x = Just x
                g y = f y
Then f's RHS is no larger than its LHS, so we should inline it
into even the most boring context.  (We do so if there is no INLINE
805
pragma!)  
806 807


808 809 810 811 812 813 814 815 816 817 818
Note [Things to watch]
~~~~~~~~~~~~~~~~~~~~~~
*   { y = I# 3; x = y `cast` co; ...case (x `cast` co) of ... }
    Assume x is exported, so not inlined unconditionally.
    Then we want x to inline unconditionally; no reason for it 
    not to, and doing so avoids an indirection.

*   { x = I# 3; ....f x.... }
    Make sure that x does not inline unconditionally!  
    Lest we get extra allocation.

819 820 821
Note [Inlining an InlineRule]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
An InlineRules is used for
822
  (a) programmer INLINE pragmas
823 824 825 826 827 828 829 830 831 832 833
  (b) inlinings from worker/wrapper

For (a) the RHS may be large, and our contract is that we *only* inline
when the function is applied to all the arguments on the LHS of the
source-code defn.  (The uf_arity in the rule.)

However for worker/wrapper it may be worth inlining even if the 
arity is not satisfied (as we do in the CoreUnfolding case) so we don't
require saturation.


834 835 836 837 838 839 840 841 842 843 844 845
Note [Nested functions]
~~~~~~~~~~~~~~~~~~~~~~~
If a function has a nested defn we also record some-benefit, on the
grounds that we are often able to eliminate the binding, and hence the
allocation, for the function altogether; this is good for join points.
But this only makes sense for *functions*; inlining a constructor
doesn't help allocation unless the result is scrutinised.  UNLESS the
constructor occurs just once, albeit possibly in multiple case
branches.  Then inlining it doesn't increase allocation, but it does
increase the chance that the constructor won't be allocated at all in
the branches that don't use it.

846 847 848 849 850 851 852 853 854 855
Note [Cast then apply]
~~~~~~~~~~~~~~~~~~~~~~
Consider
   myIndex = __inline_me ( (/\a. <blah>) |> co )
   co :: (forall a. a -> a) ~ (forall a. T a)
     ... /\a.\x. case ((myIndex a) |> sym co) x of { ... } ...

We need to inline myIndex to unravel this; but the actual call (myIndex a) has
no value arguments.  The ValAppCtxt gives it enough incentive to inline.

856 857
Note [Inlining in ArgCtxt]
~~~~~~~~~~~~~~~~~~~~~~~~~~
858
The condition (arity > 0) here is very important, because otherwise
859 860 861 862 863 864 865 866 867 868
we end up inlining top-level stuff into useless places; eg
   x = I# 3#
   f = \y.  g x
This can make a very big difference: it adds 16% to nofib 'integer' allocs,
and 20% to 'power'.

At one stage I replaced this condition by 'True' (leading to the above 
slow-down).  The motivation was test eyeball/inline1.hs; but that seems
to work ok now.

869 870 871 872 873
NOTE: arguably, we should inline in ArgCtxt only if the result of the
call is at least CONLIKE.  At least for the cases where we use ArgCtxt
for the RHS of a 'let', we only profit from the inlining if we get a 
CONLIKE thing (modulo lets).

874
Note [Lone variables]
875
~~~~~~~~~~~~~~~~~~~~~
876 877 878
The "lone-variable" case is important.  I spent ages messing about
with unsatisfactory varaints, but this is nice.  The idea is that if a
variable appears all alone
879 880 881 882

	as an arg of lazy fn, or rhs	BoringCtxt
	as scrutinee of a case		CaseCtxt
	as arg of a fn			ArgCtxt
883 884
AND
	it is bound to a value
885

886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918
then we should not inline it (unless there is some other reason,
e.g. is is the sole occurrence).  That is what is happening at 
the use of 'lone_variable' in 'interesting_saturated_call'.

Why?  At least in the case-scrutinee situation, turning
	let x = (a,b) in case x of y -> ...
into
	let x = (a,b) in case (a,b) of y -> ...
and thence to 
	let x = (a,b) in let y = (a,b) in ...
is bad if the binding for x will remain.

Another example: I discovered that strings
were getting inlined straight back into applications of 'error'
because the latter is strict.
	s = "foo"
	f = \x -> ...(error s)...

Fundamentally such contexts should not encourage inlining because the
context can ``see'' the unfolding of the variable (e.g. case or a
RULE) so there's no gain.  If the thing is bound to a value.

However, watch out:

 * Consider this:
	foo = _inline_ (\n. [n])
	bar = _inline_ (foo 20)
	baz = \n. case bar of { (m:_) -> m + n }
   Here we really want to inline 'bar' so that we can inline 'foo'
   and the whole thing unravels as it should obviously do.  This is 
   important: in the NDP project, 'bar' generates a closure data
   structure rather than a list. 

919 920 921 922 923
   So the non-inlining of lone_variables should only apply if the
   unfolding is regarded as cheap; because that is when exprIsConApp_maybe
   looks through the unfolding.  Hence the "&& is_cheap" in the
   InlineRule branch.

924 925 926 927 928 929 930 931 932 933 934
 * Even a type application or coercion isn't a lone variable.
   Consider
	case $fMonadST @ RealWorld of { :DMonad a b c -> c }
   We had better inline that sucker!  The case won't see through it.

   For now, I'm treating treating a variable applied to types 
   in a *lazy* context "lone". The motivating example was
	f = /\a. \x. BIG
	g = /\a. \y.  h (f a)
   There's no advantage in inlining f here, and perhaps
   a significant disadvantage.  Hence some_val_args in the Stop case
935

936
\begin{code}
937 938
computeDiscount :: Int -> [Int] -> Int -> [ArgSummary] -> CallCtxt -> Int
computeDiscount n_vals_wanted arg_discounts res_discount arg_infos cont_info
939 940
 	-- We multiple the raw discounts (args_discount and result_discount)
	-- ty opt_UnfoldingKeenessFactor because the former have to do with
941 942
	--  *size* whereas the discounts imply that there's some extra 
	--  *efficiency* to be gained (e.g. beta reductions, case reductions) 
943 944
	-- by inlining.

945 946 947 948 949 950 951 952 953
  = 1 		-- Discount of 1 because the result replaces the call
		-- so we count 1 for the function itself

    + length (take n_vals_wanted arg_infos)
      	       -- Discount of (un-scaled) 1 for each arg supplied, 
   	       -- because the result replaces the call

    + round (opt_UF_KeenessFactor * 
	     fromIntegral (arg_discount + res_discount'))
954 955 956
  where
    arg_discount = sum (zipWith mk_arg_discount arg_discounts arg_infos)

957 958 959 960 961 962 963 964 965
    mk_arg_discount _ 	     TrivArg    = 0 
    mk_arg_discount _ 	     NonTrivArg = 1   
    mk_arg_discount discount ValueArg   = discount 

    res_discount' = case cont_info of
			BoringCtxt  -> 0
			CaseCtxt    -> res_discount
			_other      -> 4 `min` res_discount
		-- res_discount can be very large when a function returns
966
		-- constructors; but we only want to invoke that large discount
967 968 969 970
		-- when there's a case continuation.
		-- Otherwise we, rather arbitrarily, threshold it.  Yuk.
		-- But we want to aovid inlining large functions that return 
		-- constructors into contexts that are simply "interesting"
971
\end{code}
972

973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998
%************************************************************************
%*									*
	Interesting arguments
%*									*
%************************************************************************

Note [Interesting arguments]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
An argument is interesting if it deserves a discount for unfoldings
with a discount in that argument position.  The idea is to avoid
unfolding a function that is applied only to variables that have no
unfolding (i.e. they are probably lambda bound): f x y z There is
little point in inlining f here.

Generally, *values* (like (C a b) and (\x.e)) deserve discounts.  But
we must look through lets, eg (let x = e in C a b), because the let will
float, exposing the value, if we inline.  That makes it different to
exprIsHNF.

Before 2009 we said it was interesting if the argument had *any* structure
at all; i.e. (hasSomeUnfolding v).  But does too much inlining; see Trac #3016.

But we don't regard (f x y) as interesting, unless f is unsaturated.
If it's saturated and f hasn't inlined, then it's probably not going
to now!

999 1000 1001 1002 1003
Note [Conlike is interesting]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider
	f d = ...((*) d x y)...
	... f (df d')...
1004
where df is con-like. Then we'd really like to inline 'f' so that the
1005 1006 1007 1008
rule for (*) (df d) can fire.  To do this 
  a) we give a discount for being an argument of a class-op (eg (*) d)
  b) we say that a con-like argument (eg (df d)) is interesting

1009 1010 1011 1012
\begin{code}
data ArgSummary = TrivArg	-- Nothing interesting
     		| NonTrivArg	-- Arg has structure
		| ValueArg	-- Arg is a con-app or PAP
1013
		  		-- ..or con-like. Note [Conlike is interesting]
1014 1015 1016 1017 1018 1019 1020 1021

interestingArg :: CoreExpr -> ArgSummary
-- See Note [Interesting arguments]
interestingArg e = go e 0
  where
    -- n is # value args to which the expression is applied
    go (Lit {}) _   	   = ValueArg
    go (Var v)  n
1022 1023
       | isConLikeId v     = ValueArg	-- Experimenting with 'conlike' rather that
       	 	     	     		--    data constructors here
1024 1025
       | idArity v > n	   = ValueArg	-- Catches (eg) primops with arity but no unfolding
       | n > 0	           = NonTrivArg	-- Saturated or unknown call
1026
       | conlike_unfolding = ValueArg	-- n==0; look for an interesting unfolding
1027
                                        -- See Note [Conlike is interesting]
1028 1029
       | otherwise	   = TrivArg	-- n==0, no useful unfolding
       where
1030
         conlike_unfolding = isConLikeUnfolding (idUnfolding v)
1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048

    go (Type _)          _ = TrivArg
    go (App fn (Type _)) n = go fn n    
    go (App fn _)        n = go fn (n+1)
    go (Note _ a) 	 n = go a n
    go (Cast e _) 	 n = go e n
    go (Lam v e)  	 n 
       | isTyVar v	   = go e n
       | n>0	 	   = go e (n-1)
       | otherwise	   = ValueArg
    go (Let _ e)  	 n = case go e n of { ValueArg -> ValueArg; _ -> NonTrivArg }
    go (Case {})  	 _ = NonTrivArg

nonTriv ::  ArgSummary -> Bool
nonTriv TrivArg = False
nonTriv _       = True
\end{code}

Simon Marlow's avatar
Simon Marlow committed
1049 1050
%************************************************************************
%*									*
1051
         exprIsConApp_maybe
Simon Marlow's avatar
Simon Marlow committed
1052 1053 1054
%*									*
%************************************************************************

1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065
Note [exprIsConApp_maybe]
~~~~~~~~~~~~~~~~~~~~~~~~~
exprIsConApp_maybe is a very important function.  There are two principal
uses:
  * case e of { .... }
  * cls_op e, where cls_op is a class operation

In both cases you want to know if e is of form (C e1..en) where C is
a data constructor.

However e might not *look* as if 
Simon Marlow's avatar
Simon Marlow committed
1066 1067

\begin{code}
1068 1069 1070
-- | Returns @Just (dc, [t1..tk], [x1..xn])@ if the argument expression is 
-- a *saturated* constructor application of the form @dc t1..tk x1 .. xn@,
-- where t1..tk are the *universally-qantified* type args of 'dc'
1071
exprIsConApp_maybe :: IdUnfoldingFun -> CoreExpr -> Maybe (DataCon, [Type], [CoreExpr])
1072

1073 1074
exprIsConApp_maybe id_unf (Note _ expr)
  = exprIsConApp_maybe id_unf expr
1075 1076 1077 1078 1079 1080
	-- We ignore all notes.  For example,
	--  	case _scc_ "foo" (C a b) of
	--			C a b -> e
	-- should be optimised away, but it will be only if we look
	-- through the SCC note.

1081
exprIsConApp_maybe id_unf (Cast expr co)
1082 1083 1084 1085 1086 1087 1088
  =     -- Here we do the KPush reduction rule as described in the FC paper
	-- The transformation applies iff we have
	--	(C e1 ... en) `cast` co
	-- where co :: (T t1 .. tn) ~ to_ty
	-- The left-hand one must be a T, because exprIsConApp returned True
	-- but the right-hand one might not be.  (Though it usually will.)

1089
    case exprIsConApp_maybe id_unf expr of {
1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140
	Nothing 	                 -> Nothing ;
	Just (dc, _dc_univ_args, dc_args) -> 

    let (_from_ty, to_ty) = coercionKind co
	dc_tc = dataConTyCon dc
    in
    case splitTyConApp_maybe to_ty of {
	Nothing -> Nothing ;
	Just (to_tc, to_tc_arg_tys) 
		| dc_tc /= to_tc -> Nothing
		-- These two Nothing cases are possible; we might see 
		--	(C x y) `cast` (g :: T a ~ S [a]),
		-- where S is a type function.  In fact, exprIsConApp
		-- will probably not be called in such circumstances,
		-- but there't nothing wrong with it 

	 	| otherwise  ->
    let
	tc_arity       = tyConArity dc_tc
	dc_univ_tyvars = dataConUnivTyVars dc
        dc_ex_tyvars   = dataConExTyVars dc
        arg_tys        = dataConRepArgTys dc

        dc_eqs :: [(Type,Type)]	  -- All equalities from the DataCon
        dc_eqs = [(mkTyVarTy tv, ty)   | (tv,ty) <- dataConEqSpec dc] ++
                 [getEqPredTys eq_pred | eq_pred <- dataConEqTheta dc]

        (ex_args, rest1)    = splitAtList dc_ex_tyvars dc_args
	(co_args, val_args) = splitAtList dc_eqs rest1

	-- Make the "theta" from Fig 3 of the paper
        gammas = decomposeCo tc_arity co
        theta  = zipOpenTvSubst (dc_univ_tyvars ++ dc_ex_tyvars)
                                (gammas         ++ stripTypeArgs ex_args)

          -- Cast the existential coercion arguments
        cast_co (ty1, ty2) (Type co) 
          = Type $ mkSymCoercion (substTy theta ty1)
		   `mkTransCoercion` co
		   `mkTransCoercion` (substTy theta ty2)
        cast_co _ other_arg = pprPanic "cast_co" (ppr other_arg)
        new_co_args = zipWith cast_co dc_eqs co_args
  
          -- Cast the value arguments (which include dictionaries)
	new_val_args = zipWith cast_arg arg_tys val_args
	cast_arg arg_ty arg = mkCoerce (substTy theta arg_ty) arg
    in
#ifdef DEBUG
    let dump_doc = vcat [ppr dc,      ppr dc_univ_tyvars, ppr dc_ex_tyvars,
                         ppr arg_tys, ppr dc_args,        ppr _dc_univ_args,
                         ppr ex_args, ppr val_args]
1141 1142
    in
    ASSERT2( coreEqType _from_ty (mkTyConApp dc_tc _dc_univ_args), dump_doc )
1143 1144 1145 1146 1147 1148 1149
    ASSERT2( all isTypeArg (ex_args ++ co_args), dump_doc )
    ASSERT2( equalLength val_args arg_tys, dump_doc )
#endif

    Just (dc, to_tc_arg_tys, ex_args ++ new_co_args ++ new_val_args)
    }}

1150
exprIsConApp_maybe id_unf expr 
1151
  = analyse expr [] 
Simon Marlow's avatar
Simon Marlow committed
1152
  where
1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176
    analyse (App fun arg) args = analyse fun (arg:args)
    analyse fun@(Lam {})  args = beta fun [] args 

    analyse (Var fun) args
	| Just con <- isDataConWorkId_maybe fun
        , is_saturated
	, let (univ_ty_args, rest_args) = splitAtList (dataConUnivTyVars con) args
	= Just (con, stripTypeArgs univ_ty_args, rest_args)

	-- Look through dictionary functions; see Note [Unfolding DFuns]
        | DFunUnfolding con ops <- unfolding
        , is_saturated
        , let (dfun_tvs, _cls, dfun_res_tys) = tcSplitDFunTy (idType fun)
	      subst = zipOpenTvSubst dfun_tvs (stripTypeArgs (takeList dfun_tvs args))
        = Just (con, substTys subst dfun_res_tys, 
                     [mkApps op args | op <- ops])

	-- Look through unfoldings, but only cheap ones, because
	-- we are effectively duplicating the unfolding
	| CoreUnfolding { uf_expandable = expand_me, uf_tmpl = rhs } <- unfolding
	, expand_me = -- pprTrace "expanding" (ppr fun $$ ppr rhs) $
                      analyse rhs args
        where
	  is_saturated = count isValArg args == idArity fun
1177
          unfolding = id_unf fun    -- Does not look through loop breakers
1178 1179
		    -- ToDo: we *may* look through variables that are NOINLINE
		    --       in this phase, and that is really not right
1180 1181 1182

    analyse _ _ = Nothing

1183 1184 1185
    -----------
    in_scope = mkInScopeSet (exprFreeVars expr)

1186 1187 1188 1189 1190 1191 1192 1193 1194
    -----------
    beta (Lam v body) pairs (arg : args) 
        | isTypeArg arg
        = beta body ((v,arg):pairs) args 

    beta (Lam {}) _ _    -- Un-saturated, or not a type lambda
	= Nothing

    beta fun pairs args
1195
        = case analyse (substExpr subst fun) args of
1196 1197 1198 1199 1200
	    Nothing  -> -- pprTrace "Bale out! exprIsConApp_maybe" doc $
	    	        Nothing
	    Just ans -> -- pprTrace "Woo-hoo! exprIsConApp_maybe" doc $
                        Just ans
        where
1201
          subst = mkOpenSubst in_scope pairs
1202 1203 1204 1205 1206