CoreUnfold.lhs 44.4 KB
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 simonpj@microsoft.com committed Dec 11, 2009 1 %  Simon Marlow committed Oct 11, 2006 2 % (c) The University of Glasgow 2006  simonpj committed Jun 08, 1999 3 4 % (c) The AQUA Project, Glasgow University, 1994-1998 %  Simon Marlow committed Oct 11, 2006 5 6  Core-syntax unfoldings  simonpj committed Jun 08, 1999 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 (  simonpj committed Mar 27, 2000 19  Unfolding, UnfoldingGuidance, -- Abstract types  simonpj committed Jun 08, 1999 20   simonpj@microsoft.com committed Oct 29, 2009 21 22 23 24  noUnfolding, mkImplicitUnfolding, mkTopUnfolding, mkUnfolding, mkCoreUnfolding, mkInlineRule, mkWwInlineRule, mkCompulsoryUnfolding, mkDFunUnfolding,  simonpj committed Jun 08, 1999 25   simonpj@microsoft.com committed Apr 03, 2009 26 27  interestingArg, ArgSummary(..),  simonpj committed Jun 08, 1999 28  couldBeSmallEnoughToInline,  simonmar committed Aug 12, 2005 29  certainlyWillInline, smallEnoughToInline,  simonpj committed Jun 08, 1999 30   simonpj@microsoft.com committed Apr 03, 2009 31  callSiteInline, CallCtxt(..),  simonpj@microsoft.com committed Dec 04, 2007 32   simonpj@microsoft.com committed Oct 29, 2009 33 34  exprIsConApp_maybe  simonpj committed Jun 08, 1999 35 36  ) where  simonpj@microsoft.com committed Oct 29, 2009 37 38 #include "HsVersions.h"  Simon Marlow committed Oct 11, 2006 39 40 import StaticFlags import DynFlags  simonpj committed Jun 08, 1999 41 import CoreSyn  simonpj@microsoft.com committed May 04, 2006 42 import PprCore () -- Instances  Simon Marlow committed Oct 11, 2006 43 import OccurAnal  simonpj@microsoft.com committed Oct 29, 2009 44 import CoreSubst hiding( substTy )  simonpj@microsoft.com committed Oct 30, 2009 45 import CoreFVs ( exprFreeVars )  Simon Marlow committed Oct 11, 2006 46 47 48 import CoreUtils import Id import DataCon  simonpj@microsoft.com committed Oct 29, 2009 49 import TyCon  Simon Marlow committed Oct 11, 2006 50 51 52 import Literal import PrimOp import IdInfo  simonpj@microsoft.com committed Oct 29, 2009 53 54 55 56 import BasicTypes ( Arity ) import TcType ( tcSplitDFunTy ) import Type import Coercion  Simon Marlow committed Oct 11, 2006 57 import PrelNames  simonpj@microsoft.com committed Oct 30, 2009 58 import VarEnv ( mkInScopeSet )  simonpj committed Jun 08, 1999 59 import Bag  simonpj@microsoft.com committed Oct 29, 2009 60 import Util  simonmar committed Oct 12, 2000 61 import FastTypes  Ian Lynagh committed Mar 29, 2008 62 import FastString  simonpj committed Jun 08, 1999 63 import Outputable  simonmar committed Sep 06, 1999 64   simonpj committed Jun 08, 1999 65 66 \end{code}  simonpj committed Mar 27, 2000 67   simonpj committed Jun 08, 1999 68 69 %************************************************************************ %* *  simonpj committed Mar 27, 2000 70 \subsection{Making unfoldings}  simonpj committed Jun 08, 1999 71 72 73 74 %* * %************************************************************************ \begin{code}  simonpj@microsoft.com committed Dec 11, 2009 75 76 77 mkTopUnfolding :: Bool -> CoreExpr -> Unfolding mkTopUnfolding is_bottoming expr = mkUnfolding True {- Top level -} is_bottoming expr  simonpj committed Nov 01, 1999 78   simonpj@microsoft.com committed Sep 10, 2008 79 80 mkImplicitUnfolding :: CoreExpr -> Unfolding -- For implicit Ids, do a tiny bit of optimising first  simonpj@microsoft.com committed Dec 11, 2009 81 mkImplicitUnfolding expr = mkTopUnfolding False (simpleOptExpr expr)  Simon Marlow committed Dec 16, 2008 82   simonpj@microsoft.com committed Oct 29, 2009 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.  simonpj@microsoft.com committed Mar 18, 2009 88   simonpj@microsoft.com committed Dec 11, 2009 89 90 mkUnfolding :: Bool -> Bool -> CoreExpr -> Unfolding mkUnfolding top_lvl is_bottoming expr  simonpj@microsoft.com committed Dec 02, 2009 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 }  simonpj@microsoft.com committed Oct 29, 2009 100  where  simonpj@microsoft.com committed Dec 02, 2009 101  is_cheap = exprIsCheap expr  simonpj@microsoft.com committed Dec 11, 2009 102 103  (arity, guidance) = calcUnfoldingGuidance is_cheap (top_lvl && is_bottoming) opt_UF_CreationThreshold expr  simonpj committed Mar 23, 2000 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  simonpj@microsoft.com committed Nov 19, 2009 107  -- Nevertheless, we *don't* occ-analyse before computing the size because the  simonpj committed Mar 23, 2000 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;  simonpj@microsoft.com committed Nov 19, 2009 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  simonpj committed Jun 22, 1999 113   simonpj@microsoft.com committed Dec 02, 2009 114 115 mkCoreUnfolding :: Bool -> UnfoldingSource -> CoreExpr -> Arity -> UnfoldingGuidance -> Unfolding  simonpj@microsoft.com committed Oct 29, 2009 116 -- Occurrence-analyses the expression before capturing it  simonpj@microsoft.com committed Dec 02, 2009 117 mkCoreUnfolding top_lvl src expr arity guidance  simonpj@microsoft.com committed Oct 29, 2009 118  = CoreUnfolding { uf_tmpl = occurAnalyseExpr expr,  simonpj@microsoft.com committed Dec 02, 2009 119  uf_src = src,  simonpj@microsoft.com committed Oct 29, 2009 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,  simonpj@microsoft.com committed Oct 29, 2009 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 committed Dec 16, 2008 130   simonpj@microsoft.com committed Nov 05, 2009 131 132 mkWwInlineRule :: Id -> CoreExpr -> Arity -> Unfolding mkWwInlineRule id expr arity  simonpj@microsoft.com committed Dec 02, 2009 133 134 135  = mkCoreUnfolding True (InlineWrapper id) (simpleOptExpr expr) arity (UnfWhen unSaturatedOk boringCxtNotOk)  simonpj@microsoft.com committed Nov 05, 2009 136   twanvl committed Jan 25, 2008 137 mkCompulsoryUnfolding :: CoreExpr -> Unfolding  simonpj@microsoft.com committed Nov 05, 2009 138 mkCompulsoryUnfolding expr -- Used for things that absolutely must be unfolded  simonpj@microsoft.com committed Dec 02, 2009 139 140 141  = mkCoreUnfolding True InlineCompulsory expr 0 -- Arity of unfolding doesn't matter (UnfWhen unSaturatedOk boringCxtOk)  simonpj@microsoft.com committed Nov 05, 2009 142   simonpj@microsoft.com committed Dec 02, 2009 143 144 145 mkInlineRule :: Bool -> CoreExpr -> Arity -> Unfolding mkInlineRule unsat_ok expr arity = mkCoreUnfolding True InlineRule -- Note [Top-level flag on inline rules]  simonpj@microsoft.com committed Nov 05, 2009 146  expr' arity  simonpj@microsoft.com committed Dec 02, 2009 147  (UnfWhen unsat_ok boring_ok)  simonpj@microsoft.com committed Nov 05, 2009 148 149  where expr' = simpleOptExpr expr  simonpj@microsoft.com committed Dec 02, 2009 150  boring_ok = case calcUnfoldingGuidance True -- Treat as cheap  simonpj@microsoft.com committed Dec 11, 2009 151  False -- But not bottoming  simonpj@microsoft.com committed Dec 02, 2009 152 153 154 155  (arity+1) expr' of (_, UnfWhen _ boring_ok) -> boring_ok _other -> boringCxtNotOk -- See Note [INLINE for small functions]  simonpj committed Mar 27, 2000 156 \end{code}  simonpj committed Nov 01, 1999 157   simonpj committed Jul 14, 1999 158   simonpj committed Mar 27, 2000 159 160 161 162 163 %************************************************************************ %* * \subsection{The UnfoldingGuidance type} %* * %************************************************************************  simonpj committed Jun 08, 1999 164 165 166  \begin{code} calcUnfoldingGuidance  simonpj@microsoft.com committed Dec 02, 2009 167 168  :: Bool -- True <=> the rhs is cheap, or we want to treat it -- as cheap (INLINE things)  simonpj@microsoft.com committed Dec 11, 2009 169 170  -> Bool -- True <=> this is a top-level unfolding for a -- diverging function; don't inline this  simonpj@microsoft.com committed Dec 02, 2009 171 172  -> Int -- Bomb out if size gets bigger than this -> CoreExpr -- Expression to look at  simonpj@microsoft.com committed Oct 29, 2009 173  -> (Arity, UnfoldingGuidance)  simonpj@microsoft.com committed Dec 11, 2009 174 calcUnfoldingGuidance expr_is_cheap top_bot bOMB_OUT_SIZE expr  simonpj@microsoft.com committed Dec 02, 2009 175  = case collectBinders expr of { (bndrs, body) ->  simonpj committed Nov 01, 1999 176  let  simonpj@microsoft.com committed Dec 02, 2009 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  simonpj@microsoft.com committed Dec 11, 2009 187 188 189  | top_bot -- See Note [Do not inline top-level bottoming functions] -> UnfNever  simonpj@microsoft.com committed Dec 02, 2009 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  simonpj committed Nov 01, 1999 198  in  simonpj@microsoft.com committed Dec 02, 2009 199  (n_val_bndrs, guidance) }  simonpj committed Jun 08, 1999 200 201 \end{code}  simonpj@microsoft.com committed Apr 03, 2009 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  simonpj@microsoft.com committed Nov 19, 2009 224  0 True  simonpj@microsoft.com committed Apr 03, 2009 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.  simonpj@microsoft.com committed Dec 11, 2009 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).  simonpj@microsoft.com committed Oct 29, 2009 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  simonpj@microsoft.com committed Apr 03, 2009 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  simonpj@microsoft.com committed Oct 29, 2009 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}  simonpj@microsoft.com committed Apr 03, 2009 264 265   simonpj committed Jun 08, 1999 266 \begin{code}  Isaac Dupree committed Jan 17, 2008 267 sizeExpr :: FastInt -- Bomb out if it gets bigger than this  simonpj committed Jun 08, 1999 268 269 270 271 272  -> [Id] -- Arguments; we're interested in which of these -- get case'd -> CoreExpr -> ExprSize  simonpj@microsoft.com committed Apr 03, 2009 273 274 -- Note [Computing the size of an expression]  simonmar committed Oct 12, 2000 275 sizeExpr bOMB_OUT_SIZE top_args expr  simonpj committed Jun 08, 1999 276 277  = size_up expr where  simonpj@microsoft.com committed Oct 29, 2009 278 279  size_up (Cast e _) = size_up e size_up (Note _ e) = size_up e  simonpj@microsoft.com committed Apr 03, 2009 280 281  size_up (Type _) = sizeZero -- Types cost nothing size_up (Lit lit) = sizeN (litSize lit)  simonpj@microsoft.com committed Oct 29, 2009 282  size_up (Var f) = size_up_call f [] -- Make sure we get constructor  simonpj@microsoft.com committed Apr 03, 2009 283  -- discounts even on nullary constructors  Simon Marlow committed Dec 16, 2008 284   twanvl committed Jan 25, 2008 285  size_up (App fun (Type _)) = size_up fun  simonpj@microsoft.com committed Dec 14, 2009 286 287  size_up (App fun arg) = size_up arg addSizeNSD size_up_app fun [arg]  simonpj committed Jun 08, 1999 288   simonpj committed Mar 23, 2000 289  size_up (Lam b e) | isId b = lamScrutDiscount (size_up e addSizeN 1)  simonpj committed Jun 08, 1999 290 291 292  | otherwise = size_up e size_up (Let (NonRec binder rhs) body)  simonpj@microsoft.com committed Dec 14, 2009 293 294  = size_up rhs addSizeNSD size_up body addSizeN  simonpj committed Jun 22, 1999 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  simonpj committed Jun 08, 1999 298 299  size_up (Let (Rec pairs) body)  simonpj@microsoft.com committed Dec 14, 2009 300 301 302  = foldr (addSizeNSD . size_up . snd) (size_up body addSizeN length pairs) -- (length pairs) for the allocation pairs  simonpj committed Jun 08, 1999 303   simonpj committed Sep 30, 2004 304  size_up (Case (Var v) _ _ alts)  simonpj committed Aug 01, 2000 305  | v elem top_args -- We are scrutinising an argument variable  simonpj@microsoft.com committed Dec 14, 2009 306  = alts_size (foldr1 addAltSize alt_sizes)  simonpj@microsoft.com committed Apr 03, 2009 307  (foldr1 maxSize alt_sizes)  simonpj committed Mar 23, 2000 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  simonpj committed Aug 01, 2000 314 315  -- alts_size tries to compute a good discount for -- the case when we are scrutinising an argument variable  simonpj@microsoft.com committed Dec 14, 2009 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  simonpj committed Mar 23, 2000 319  -- If the variable is known, we produce a discount that  simonpj@microsoft.com committed Apr 03, 2009 320  -- will take us back to 'max', the size of the largest alternative  simonpj committed Mar 23, 2000 321  -- The 1+ is a little discount for reduced allocation in the caller  simonpj@microsoft.com committed Apr 03, 2009 322 323 324 325  -- -- Notice though, that we return tot_disc, the total discount from -- all branches. I think that's right.  simonpj committed Mar 23, 2000 326 327  alts_size tot_size _ = tot_size  simonpj@microsoft.com committed Dec 14, 2009 328 329  size_up (Case e _ _ alts) = size_up e addSizeNSD foldr (addAltSize . size_up_alt) sizeZero alts  simonpj committed Mar 23, 2000 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.  simonpj@microsoft.com committed Dec 02, 2009 335 336  -- -- Moreover, we charge one per alternative.  simonpj committed Jun 08, 1999 337 338  ------------  simonpj@microsoft.com committed Apr 03, 2009 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  simonpj@microsoft.com committed Dec 14, 2009 342 343  | otherwise = size_up arg addSizeNSD size_up_app fun (arg:args)  simonpj@microsoft.com committed Oct 29, 2009 344  size_up_app (Var fun) args = size_up_call fun args  simonpj@microsoft.com committed Apr 03, 2009 345 346 347  size_up_app other args = size_up other addSizeN length args ------------  simonpj@microsoft.com committed Oct 29, 2009 348 349  size_up_call :: Id -> [CoreExpr] -> ExprSize size_up_call fun val_args  simonpj@microsoft.com committed Apr 03, 2009 350 351  = case idDetails fun of FCallId _ -> sizeN opt_UF_DearOp  simonpj@microsoft.com committed Oct 29, 2009 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)  simonpj committed Jun 08, 1999 356 357  ------------  simonpj@microsoft.com committed Nov 19, 2009 358  size_up_alt (_con, _bndrs, rhs) = size_up rhs addSizeN 1  simonpj committed Sep 07, 2000 359 360  -- Don't charge for args, so that wrappers look cheap -- (See comments about wrappers with Case)  simonpj@microsoft.com committed Nov 19, 2009 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  simonpj committed Jun 08, 1999 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  simonpj committed Oct 03, 2001 369 370  addSizeN TooBig _ = TooBig addSizeN (SizeIs n xs d) m = mkSizeIs bOMB_OUT_SIZE (n +# iUnbox m) xs d  simonpj committed Jun 08, 1999 371   simonpj@microsoft.com committed Dec 14, 2009 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  simonpj committed Jun 08, 1999 388 389 390 \end{code} \begin{code}  simonpj@microsoft.com committed Apr 03, 2009 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)  simonpj@microsoft.com committed Oct 29, 2009 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  simonpj@microsoft.com committed Apr 03, 2009 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  simonpj@microsoft.com committed Nov 19, 2009 447  | n_val_args == 0 = SizeIs (_ILIT(0)) emptyBag (_ILIT(1)) -- Like variables  simonpj@microsoft.com committed Apr 03, 2009 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  simonpj committed Mar 23, 2000 452  -- (and we charge separately for their args). We can't treat  simonpj@microsoft.com committed Apr 03, 2009 453  -- them as size zero, else we find that (Just x) has size 0,  simonpj committed Mar 23, 2000 454  -- which is the same as a lone variable; and hence 'v' will  simonpj@microsoft.com committed Apr 03, 2009 455  -- always be replaced by (Just x), where v is bound to Just x.  simonpj committed Sep 26, 2001 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  simonpj committed Mar 23, 2000 461   twanvl committed Jan 25, 2008 462 primOpSize :: PrimOp -> Int -> ExprSize  simonpj@microsoft.com committed Apr 03, 2009 463 primOpSize op n_val_args  simonpj committed Mar 23, 2000 464  | not (primOpIsDupable op) = sizeN opt_UF_DearOp  simonpj@microsoft.com committed Apr 03, 2009 465  | not (primOpOutOfLine op) = sizeN 1  simonpj committed Dec 07, 2000 466  -- Be very keen to inline simple primops.  simonpj committed Sep 26, 2001 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!  simonpj@microsoft.com committed Apr 03, 2009 475 476 477  | otherwise = sizeN n_val_args  simonpj committed Jun 08, 1999 478   twanvl committed Jan 25, 2008 479 buildSize :: ExprSize  simonpj@microsoft.com committed Apr 03, 2009 480 buildSize = SizeIs (_ILIT(0)) emptyBag (_ILIT(4))  simonpj committed Jun 08, 1999 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  simonpj committed Jun 22, 1999 485  -- build is saturated (it usually is). The "-2" discounts for the \c n,  simonpj committed Jun 08, 1999 486  -- The "4" is rather arbitrary.  simonpj committed Jun 22, 1999 487   twanvl committed Jan 25, 2008 488 augmentSize :: ExprSize  simonpj@microsoft.com committed Apr 03, 2009 489 augmentSize = SizeIs (_ILIT(0)) emptyBag (_ILIT(4))  simonpj committed Jun 22, 1999 490 491  -- Ditto (augment t (\cn -> e) ys) should cost only the cost of -- e plus ys. The -2 accounts for the \cn  twanvl committed Jan 25, 2008 492   simonpj committed Mar 23, 2000 493 -- When we return a lambda, give a discount if it's used (applied)  twanvl committed Jan 25, 2008 494 lamScrutDiscount :: ExprSize -> ExprSize  simonpj@microsoft.com committed Apr 03, 2009 495 lamScrutDiscount (SizeIs n vs _) = SizeIs n vs (iUnbox opt_UF_FunAppDiscount)  twanvl committed Jan 25, 2008 496 lamScrutDiscount TooBig = TooBig  simonpj committed Jun 08, 1999 497 498 \end{code}  simonpj@microsoft.com committed Dec 14, 2009 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.  simonpj@microsoft.com committed Oct 29, 2009 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  simonpj committed Jun 08, 1999 537   simonpj@microsoft.com committed Apr 03, 2009 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  simonpj@microsoft.com committed Dec 02, 2009 578 sizeZero :: ExprSize  simonpj@microsoft.com committed Apr 03, 2009 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}  simonpj committed Jun 08, 1999 586 587 588 589 590 591 %************************************************************************ %* * \subsection[considerUnfolding]{Given all the info, do (not) do the unfolding} %* * %************************************************************************  simonpj@microsoft.com committed Oct 29, 2009 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.  simonpj committed Jun 08, 1999 596 597  \begin{code}  simonpj committed Mar 23, 2000 598 couldBeSmallEnoughToInline :: Int -> CoreExpr -> Bool  simonpj@microsoft.com committed Oct 29, 2009 599 couldBeSmallEnoughToInline threshold rhs  simonpj@microsoft.com committed Dec 11, 2009 600  = case calcUnfoldingGuidance False False threshold rhs of  simonpj@microsoft.com committed Dec 02, 2009 601 602  (_, UnfNever) -> False _ -> True  simonmar committed Aug 12, 2005 603   simonpj@microsoft.com committed Oct 29, 2009 604 ----------------  simonmar committed Aug 12, 2005 605 smallEnoughToInline :: Unfolding -> Bool  simonpj@microsoft.com committed Dec 02, 2009 606 smallEnoughToInline (CoreUnfolding {uf_guidance = UnfIfGoodArgs {ug_size = size}})  simonmar committed Aug 12, 2005 607  = size <= opt_UF_UseThreshold  twanvl committed Jan 25, 2008 608 smallEnoughToInline _  simonmar committed Aug 12, 2005 609  = False  simonpj@microsoft.com committed Oct 29, 2009 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  simonpj@microsoft.com committed Dec 02, 2009 616 617 618  UnfNever -> False UnfWhen {} -> True UnfIfGoodArgs { ug_size = size}  simonpj@microsoft.com committed Oct 29, 2009 619 620 621 622  -> is_cheap && size - (n_vals +1) <= opt_UF_UseThreshold certainlyWillInline _ = False  simonpj committed Jun 08, 1999 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  simonpj committed Mar 23, 2000 642 NOTE: we don't want to inline top-level functions that always diverge.  Simon Marlow committed Feb 01, 2008 643 It just makes the code bigger. Tt turns out that the convenient way to prevent  simonpj committed Mar 23, 2000 644 645 646 them inlining is to give them a NOINLINE pragma, which we do in StrictAnal.addStrictnessInfoToTopId  simonpj committed Jun 08, 1999 647 \begin{code}  sewardj committed Oct 12, 2000 648 callSiteInline :: DynFlags  simonpj committed Jun 08, 1999 649  -> Id -- The Id  simonpj@microsoft.com committed Dec 02, 2009 650  -> Unfolding -- Its unfolding (if active)  simonpj@microsoft.com committed Dec 04, 2007 651  -> Bool -- True if there are are no arguments at all (incl type args)  simonpj@microsoft.com committed Apr 03, 2009 652  -> [ArgSummary] -- One for each value arg; True if it is interesting  simonpj@microsoft.com committed Feb 07, 2008 653  -> CallCtxt -- True <=> continuation is interesting  simonpj committed Jun 08, 1999 654 655 656  -> Maybe CoreExpr -- Unfolding, if any  simonpj@microsoft.com committed Apr 03, 2009 657 658 659 660 661 instance Outputable ArgSummary where ppr TrivArg = ptext (sLit "TrivArg") ppr NonTrivArg = ptext (sLit "NonTrivArg") ppr ValueArg = ptext (sLit "ValueArg")  simonpj@microsoft.com committed Feb 07, 2008 662 data CallCtxt = BoringCtxt  simonpj@microsoft.com committed Dec 04, 2007 663   simonpj@microsoft.com committed Nov 05, 2009 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  simonpj@microsoft.com committed Feb 07, 2008 671   simonpj@microsoft.com committed Oct 28, 2008 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  simonpj@microsoft.com committed Feb 07, 2008 676 677 678 679  | CaseCtxt -- We're the scrutinee of a case -- that decomposes its scrutinee instance Outputable CallCtxt where  simonpj@microsoft.com committed Nov 05, 2009 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")  simonpj@microsoft.com committed Dec 04, 2007 684   simonpj@microsoft.com committed Dec 02, 2009 685 686 callSiteInline dflags id unfolding lone_variable arg_infos cont_info = case unfolding of {  simonpj@microsoft.com committed Oct 29, 2009 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  simonpj committed Jun 08, 1999 694  let  simonpj@microsoft.com committed Dec 02, 2009 695 696  n_val_args = length arg_infos saturated = n_val_args >= uf_arity  simonpj@microsoft.com committed Nov 19, 2009 697   simonpj committed Jun 08, 1999 698 699 700  result | yes_or_no = Just unf_template | otherwise = Nothing  simonpj@microsoft.com committed Oct 29, 2009 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  simonpj@microsoft.com committed Dec 02, 2009 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  simonpj@microsoft.com committed Oct 29, 2009 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]  simonpj@microsoft.com committed Dec 02, 2009 725  (yes_or_no, extra_doc)  simonpj committed Jun 08, 1999 726  = case guidance of  simonpj@microsoft.com committed Dec 02, 2009 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]  simonpj@microsoft.com committed Oct 29, 2009 733   simonpj@microsoft.com committed Dec 02, 2009 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) )  simonpj@microsoft.com committed Oct 29, 2009 737  where  simonpj@microsoft.com committed Dec 02, 2009 738 739  discounted_size = size - discount small_enough = discounted_size <= opt_UF_UseThreshold  simonpj@microsoft.com committed Oct 29, 2009 740 741  discount = computeDiscount uf_arity arg_discounts res_discount arg_infos cont_info  simonpj committed Nov 01, 1999 742   simonpj committed Jun 08, 1999 743  in  simonmar committed Oct 17, 2000 744  if dopt Opt_D_dump_inlinings dflags then  simonpj@microsoft.com committed Jan 13, 2009 745  pprTrace ("Considering inlining: " ++ showSDoc (ppr id))  simonpj@microsoft.com committed Dec 02, 2009 746 747  (vcat [text "arg infos" <+> ppr arg_infos, text "uf arity" <+> ppr uf_arity,  simonpj@microsoft.com committed Jan 13, 2009 748  text "interesting continuation" <+> ppr cont_info,  simonpj@microsoft.com committed Dec 02, 2009 749  text "some_benefit" <+> ppr some_benefit,  simonpj@microsoft.com committed Jan 13, 2009 750  text "is value:" <+> ppr is_value,  simonpj@microsoft.com committed Mar 18, 2009 751  text "is cheap:" <+> ppr is_cheap,  simonpj@microsoft.com committed Jan 13, 2009 752  text "guidance" <+> ppr guidance,  simonpj@microsoft.com committed Dec 02, 2009 753  extra_doc,  simonpj@microsoft.com committed Jan 13, 2009 754  text "ANSWER =" <+> if yes_or_no then text "YES" else text "NO"])  simonpj committed Jun 08, 1999 755 756 757 758  result else result }  simonpj@microsoft.com committed Dec 04, 2007 759 760 \end{code}  simonpj@microsoft.com committed Nov 05, 2009 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.  simonpj@microsoft.com committed Oct 29, 2009 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  simonpj@microsoft.com committed Dec 02, 2009 805 pragma!)  simonpj@microsoft.com committed Oct 29, 2009 806 807   simonpj@microsoft.com committed Apr 03, 2009 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.  simonpj@microsoft.com committed Oct 29, 2009 819 820 821 Note [Inlining an InlineRule] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ An InlineRules is used for  simonpj@microsoft.com committed Dec 02, 2009 822  (a) programmer INLINE pragmas  simonpj@microsoft.com committed Oct 29, 2009 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.  simonpj@microsoft.com committed Dec 04, 2007 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.  simonpj@microsoft.com committed Oct 28, 2008 846 847 848 849 850 851 852 853 854 855 Note [Cast then apply] ~~~~~~~~~~~~~~~~~~~~~~ Consider myIndex = __inline_me ( (/\a. ) |> 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] ~~~~~~~~~~~~~~~~~~~~~~~~~~  simonpj@microsoft.com committed Oct 29, 2009 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.  simonpj@microsoft.com committed Nov 05, 2009 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).  simonpj@microsoft.com committed Dec 04, 2007 874 Note [Lone variables]  simonpj@microsoft.com committed Jan 02, 2009 875 ~~~~~~~~~~~~~~~~~~~~~  simonpj@microsoft.com committed Dec 04, 2007 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  simonpj@microsoft.com committed Oct 29, 2009 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  simonpj@microsoft.com committed Dec 04, 2007 883 884 AND it is bound to a value  simonpj@microsoft.com committed Oct 29, 2009 885   simonpj@microsoft.com committed Dec 04, 2007 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.  simonpj@microsoft.com committed Oct 29, 2009 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.  simonpj@microsoft.com committed Dec 04, 2007 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  simonpj committed Jun 08, 1999 935   simonpj@microsoft.com committed Dec 04, 2007 936 \begin{code}  simonpj@microsoft.com committed Apr 03, 2009 937 938 computeDiscount :: Int -> [Int] -> Int -> [ArgSummary] -> CallCtxt -> Int computeDiscount n_vals_wanted arg_discounts res_discount arg_infos cont_info  simonpj committed Jun 08, 1999 939 940  -- We multiple the raw discounts (args_discount and result_discount) -- ty opt_UnfoldingKeenessFactor because the former have to do with  simonmar committed Mar 31, 2005 941 942  -- *size* whereas the discounts imply that there's some extra -- *efficiency* to be gained (e.g. beta reductions, case reductions)  simonpj committed Jun 08, 1999 943 944  -- by inlining.  simonpj@microsoft.com committed Apr 03, 2009 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'))  simonpj committed Jun 08, 1999 954 955 956  where arg_discount = sum (zipWith mk_arg_discount arg_discounts arg_infos)  simonpj@microsoft.com committed Apr 03, 2009 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  simonpj@microsoft.com committed Nov 05, 2009 966  -- constructors; but we only want to invoke that large discount  simonpj@microsoft.com committed Apr 03, 2009 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"  simonpj committed Jun 08, 1999 971 \end{code}  simonpj@microsoft.com committed Sep 10, 2008 972   simonpj@microsoft.com committed Apr 03, 2009 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!  simonpj@microsoft.com committed Oct 29, 2009 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  simonpj@microsoft.com committed Oct 29, 2009 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  simonpj@microsoft.com committed Apr 03, 2009 1009 1010 1011 1012 \begin{code} data ArgSummary = TrivArg -- Nothing interesting | NonTrivArg -- Arg has structure | ValueArg -- Arg is a con-app or PAP  simonpj@microsoft.com committed Oct 29, 2009 1013  -- ..or con-like. Note [Conlike is interesting]  simonpj@microsoft.com committed Apr 03, 2009 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  simonpj@microsoft.com committed Oct 29, 2009 1022 1023  | isConLikeId v = ValueArg -- Experimenting with 'conlike' rather that -- data constructors here  simonpj@microsoft.com committed Apr 03, 2009 1024 1025  | idArity v > n = ValueArg -- Catches (eg) primops with arity but no unfolding | n > 0 = NonTrivArg -- Saturated or unknown call  rl@cse.unsw.edu.au committed Nov 04, 2009 1026  | conlike_unfolding = ValueArg -- n==0; look for an interesting unfolding  1027  -- See Note [Conlike is interesting]  simonpj@microsoft.com committed Apr 03, 2009 1028 1029  | otherwise = TrivArg -- n==0, no useful unfolding where  rl@cse.unsw.edu.au committed Nov 04, 2009 1030  conlike_unfolding = isConLikeUnfolding (idUnfolding v)  simonpj@microsoft.com committed Apr 03, 2009 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 committed Dec 16, 2008 1049 1050 %************************************************************************ %* *  simonpj@microsoft.com committed Oct 29, 2009 1051  exprIsConApp_maybe  Simon Marlow committed Dec 16, 2008 1052 1053 1054 %* * %************************************************************************  simonpj@microsoft.com committed Oct 29, 2009 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 committed Dec 16, 2008 1066 1067  \begin{code}  simonpj@microsoft.com committed Oct 29, 2009 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'  simonpj@microsoft.com committed Dec 02, 2009 1071 exprIsConApp_maybe :: IdUnfoldingFun -> CoreExpr -> Maybe (DataCon, [Type], [CoreExpr])  simonpj@microsoft.com committed Oct 29, 2009 1072   simonpj@microsoft.com committed Dec 02, 2009 1073 1074 exprIsConApp_maybe id_unf (Note _ expr) = exprIsConApp_maybe id_unf expr  simonpj@microsoft.com committed Oct 29, 2009 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.  simonpj@microsoft.com committed Dec 02, 2009 1081 exprIsConApp_maybe id_unf (Cast expr co)  simonpj@microsoft.com committed Oct 29, 2009 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.)  simonpj@microsoft.com committed Dec 02, 2009 1089  case exprIsConApp_maybe id_unf expr of {  simonpj@microsoft.com committed Oct 29, 2009 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]  simonpj@microsoft.com committed Oct 30, 2009 1141 1142  in ASSERT2( coreEqType _from_ty (mkTyConApp dc_tc _dc_univ_args), dump_doc )  simonpj@microsoft.com committed Oct 29, 2009 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) }}  simonpj@microsoft.com committed Dec 02, 2009 1150 exprIsConApp_maybe id_unf expr  simonpj@microsoft.com committed Oct 29, 2009 1151  = analyse expr []  Simon Marlow committed Dec 16, 2008 1152  where  simonpj@microsoft.com committed Oct 29, 2009 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  simonpj@microsoft.com committed Dec 02, 2009 1177  unfolding = id_unf fun -- Does not look through loop breakers  simonpj@microsoft.com committed Nov 19, 2009 1178 1179  -- ToDo: we *may* look through variables that are NOINLINE -- in this phase, and that is really not right  simonpj@microsoft.com committed Oct 29, 2009 1180 1181 1182  analyse _ _ = Nothing  simonpj@microsoft.com committed Oct 30, 2009 1183 1184 1185  ----------- in_scope = mkInScopeSet (exprFreeVars expr)  simonpj@microsoft.com committed Oct 29, 2009 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  simonpj@microsoft.com committed Oct 30, 2009 1195  = case analyse (substExpr subst fun) args of  simonpj@microsoft.com committed Oct 29, 2009 1196 1197 1198 1199 1200  Nothing -> -- pprTrace "Bale out! exprIsConApp_maybe" doc $Nothing Just ans -> -- pprTrace "Woo-hoo! exprIsConApp_maybe" doc$ Just ans where  simonpj@microsoft.com committed Oct 30, 2009 1201  subst = mkOpenSubst in_scope pairs  simonpj@microsoft.com committed Oct 29, 2009 1202 1203 1204 1205 1206