CoreUnfold.lhs 49.4 KB
 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  noUnfolding, mkImplicitUnfolding,  simonpj@microsoft.com committed Sep 15, 2010 22 23 24  mkUnfolding, mkCoreUnfolding, mkTopUnfolding, mkSimpleUnfolding, mkInlineUnfolding, mkInlinableUnfolding, mkWwInlineRule,  simonpj@microsoft.com committed Oct 29, 2009 25  mkCompulsoryUnfolding, mkDFunUnfolding,  simonpj committed Jun 08, 1999 26   simonpj@microsoft.com committed Apr 03, 2009 27 28  interestingArg, ArgSummary(..),  simonpj@microsoft.com committed Dec 21, 2010 29  couldBeSmallEnoughToInline, inlineBoringOk,  simonmar committed Aug 12, 2005 30  certainlyWillInline, smallEnoughToInline,  simonpj committed Jun 08, 1999 31   simonpj@microsoft.com committed Apr 03, 2009 32  callSiteInline, CallCtxt(..),  simonpj@microsoft.com committed Dec 04, 2007 33   simonpj@microsoft.com committed Oct 29, 2009 34 35  exprIsConApp_maybe  simonpj committed Jun 08, 1999 36 37  ) where  simonpj@microsoft.com committed Oct 29, 2009 38 39 #include "HsVersions.h"  Simon Marlow committed Oct 11, 2006 40 41 import StaticFlags import DynFlags  simonpj committed Jun 08, 1999 42 import CoreSyn  simonpj@microsoft.com committed May 04, 2006 43 import PprCore () -- Instances  simonpj@microsoft.com committed Dec 22, 2010 44 45 import TcType ( tcSplitDFunTy ) import OccurAnal ( occurAnalyseExpr )  simonpj@microsoft.com committed Oct 29, 2009 46 import CoreSubst hiding( substTy )  simonpj@microsoft.com committed Oct 30, 2009 47 import CoreFVs ( exprFreeVars )  simonpj@microsoft.com committed Sep 15, 2010 48 import CoreArity ( manifestArity, exprBotStrictness_maybe )  Simon Marlow committed Oct 11, 2006 49 50 51 import CoreUtils import Id import DataCon  simonpj@microsoft.com committed Oct 29, 2009 52 import TyCon  Simon Marlow committed Oct 11, 2006 53 54 55 import Literal import PrimOp import IdInfo  simonpj@microsoft.com committed Oct 29, 2009 56 import BasicTypes ( Arity )  simonpj@microsoft.com committed Dec 22, 2010 57 import Type  simonpj@microsoft.com committed Oct 29, 2009 58 import Coercion  Simon Marlow committed Oct 11, 2006 59 import PrelNames  simonpj@microsoft.com committed Oct 30, 2009 60 import VarEnv ( mkInScopeSet )  simonpj committed Jun 08, 1999 61 import Bag  simonpj@microsoft.com committed Oct 29, 2009 62 import Util  simonmar committed Oct 12, 2000 63 import FastTypes  Ian Lynagh committed Mar 29, 2008 64 import FastString  simonpj committed Jun 08, 1999 65 import Outputable  simonpj@microsoft.com committed Sep 15, 2010 66 import Data.Maybe  simonpj committed Jun 08, 1999 67 68 \end{code}  simonpj committed Mar 27, 2000 69   simonpj committed Jun 08, 1999 70 71 %************************************************************************ %* *  simonpj committed Mar 27, 2000 72 \subsection{Making unfoldings}  simonpj committed Jun 08, 1999 73 74 75 76 %* * %************************************************************************ \begin{code}  simonpj@microsoft.com committed Dec 11, 2009 77 mkTopUnfolding :: Bool -> CoreExpr -> Unfolding  simonpj@microsoft.com committed Sep 15, 2010 78 mkTopUnfolding = mkUnfolding InlineRhs True {- Top level -}  simonpj committed Nov 01, 1999 79   simonpj@microsoft.com committed Sep 10, 2008 80 81 mkImplicitUnfolding :: CoreExpr -> Unfolding -- For implicit Ids, do a tiny bit of optimising first  simonpj@microsoft.com committed Dec 11, 2009 82 mkImplicitUnfolding expr = mkTopUnfolding False (simpleOptExpr expr)  Simon Marlow committed Dec 16, 2008 83   simonpj@microsoft.com committed Oct 29, 2009 84 85 86 87 88 -- 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 89   simonpj@microsoft.com committed Sep 15, 2010 90 91 mkSimpleUnfolding :: CoreExpr -> Unfolding mkSimpleUnfolding = mkUnfolding InlineRhs False False  simonpj@microsoft.com committed Oct 29, 2009 92   simonpj@microsoft.com committed Dec 13, 2010 93 mkDFunUnfolding :: Type -> [DFunArg CoreExpr] -> Unfolding  simonpj@microsoft.com committed May 31, 2010 94 95 96 mkDFunUnfolding dfun_ty ops = DFunUnfolding dfun_nargs data_con ops where  simonpj@microsoft.com committed Dec 22, 2010 97 98  (tvs, n_theta, cls, _) = tcSplitDFunTy dfun_ty dfun_nargs = length tvs + n_theta  simonpj@microsoft.com committed May 31, 2010 99  data_con = classDataCon cls  Simon Marlow committed Dec 16, 2008 100   simonpj@microsoft.com committed Nov 05, 2009 101 102 mkWwInlineRule :: Id -> CoreExpr -> Arity -> Unfolding mkWwInlineRule id expr arity  Simon Marlow committed Oct 15, 2010 103  = mkCoreUnfolding (InlineWrapper id) True  simonpj@microsoft.com committed Dec 02, 2009 104 105  (simpleOptExpr expr) arity (UnfWhen unSaturatedOk boringCxtNotOk)  simonpj@microsoft.com committed Nov 05, 2009 106   twanvl committed Jan 25, 2008 107 mkCompulsoryUnfolding :: CoreExpr -> Unfolding  simonpj@microsoft.com committed Nov 05, 2009 108 mkCompulsoryUnfolding expr -- Used for things that absolutely must be unfolded  Simon Marlow committed Oct 15, 2010 109  = mkCoreUnfolding InlineCompulsory True  simonpj@microsoft.com committed Dec 02, 2009 110 111  expr 0 -- Arity of unfolding doesn't matter (UnfWhen unSaturatedOk boringCxtOk)  simonpj@microsoft.com committed Nov 05, 2009 112   simonpj@microsoft.com committed Sep 15, 2010 113 114 mkInlineUnfolding :: Maybe Arity -> CoreExpr -> Unfolding mkInlineUnfolding mb_arity expr  Simon Marlow committed Oct 15, 2010 115 116  = mkCoreUnfolding InlineStable True -- Note [Top-level flag on inline rules]  simonpj@microsoft.com committed Sep 15, 2010 117  expr' arity  simonpj@microsoft.com committed Dec 02, 2009 118  (UnfWhen unsat_ok boring_ok)  simonpj@microsoft.com committed Nov 05, 2009 119 120  where expr' = simpleOptExpr expr  simonpj@microsoft.com committed Jan 06, 2010 121 122 123 124  (unsat_ok, arity) = case mb_arity of Nothing -> (unSaturatedOk, manifestArity expr') Just ar -> (needSaturated, ar)  simonpj@microsoft.com committed Dec 21, 2010 125  boring_ok = inlineBoringOk expr'  simonpj@microsoft.com committed Sep 15, 2010 126 127 128  mkInlinableUnfolding :: CoreExpr -> Unfolding mkInlinableUnfolding expr  Simon Marlow committed Oct 15, 2010 129  = mkUnfolding InlineStable True is_bot expr'  simonpj@microsoft.com committed Sep 15, 2010 130  where  Simon Marlow committed Oct 15, 2010 131 132  expr' = simpleOptExpr expr is_bot = isJust (exprBotStrictness_maybe expr')  simonpj committed Mar 27, 2000 133 \end{code}  simonpj committed Nov 01, 1999 134   simonpj@microsoft.com committed Sep 15, 2010 135 136 137 Internal functions \begin{code}  Simon Marlow committed Oct 15, 2010 138 mkCoreUnfolding :: UnfoldingSource -> Bool -> CoreExpr  simonpj@microsoft.com committed Sep 15, 2010 139 140  -> Arity -> UnfoldingGuidance -> Unfolding -- Occurrence-analyses the expression before capturing it  Simon Marlow committed Oct 15, 2010 141 mkCoreUnfolding src top_lvl expr arity guidance  simonpj@microsoft.com committed Sep 15, 2010 142 143 144 145 146 147 148 149 150 151 152 153 154 155  = CoreUnfolding { uf_tmpl = occurAnalyseExpr expr, uf_src = src, uf_arity = arity, uf_is_top = top_lvl, uf_is_value = exprIsHNF expr, uf_is_conlike = exprIsConLike expr, uf_is_cheap = exprIsCheap expr, uf_expandable = exprIsExpandable expr, uf_guidance = guidance } mkUnfolding :: UnfoldingSource -> Bool -> Bool -> CoreExpr -> Unfolding -- Calculates unfolding guidance -- Occurrence-analyses the expression before capturing it mkUnfolding src top_lvl is_bottoming expr  simonpj@microsoft.com committed Dec 21, 2010 156 157 158 159  | top_lvl && is_bottoming , not (exprIsTrivial expr) = NoUnfolding -- See Note [Do not inline top-level bottoming functions] | otherwise  simonpj@microsoft.com committed Sep 15, 2010 160 161 162 163 164 165 166 167 168 169 170  = CoreUnfolding { uf_tmpl = occurAnalyseExpr expr, uf_src = src, 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 } where is_cheap = exprIsCheap expr  simonpj@microsoft.com committed Dec 21, 2010 171  (arity, guidance) = calcUnfoldingGuidance is_cheap  simonpj@microsoft.com committed Sep 15, 2010 172 173 174 175 176 177 178 179 180 181 182  opt_UF_CreationThreshold expr -- 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 -- Nevertheless, we *don't* occ-analyse before computing the size because the -- size computation bales out after a while, whereas occurrence analysis does not. -- -- This can occasionally mean that the guidance is very pessimistic; -- it gets fixed up next round. And it should be rare, because large -- let-bound things that are dead are usually caught by preInlineUnconditionally \end{code}  simonpj committed Jul 14, 1999 183   simonpj committed Mar 27, 2000 184 185 186 187 188 %************************************************************************ %* * \subsection{The UnfoldingGuidance type} %* * %************************************************************************  simonpj committed Jun 08, 1999 189 190  \begin{code}  simonpj@microsoft.com committed Dec 21, 2010 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 inlineBoringOk :: CoreExpr -> Bool -- See Note [INLINE for small functions] -- True => the result of inlining the expression is -- no bigger than the expression itself -- eg (\x y -> f y x) -- This is a quick and dirty version. It doesn't attempt -- to deal with (\x y z -> x (y z)) -- The really important one is (x cast c) inlineBoringOk e = go 0 e where go :: Int -> CoreExpr -> Bool go credit (Lam x e) | isId x = go (credit+1) e | otherwise = go credit e go credit (App f (Type {})) = go credit f go credit (App f a) | credit > 0 , exprIsTrivial a = go (credit-1) f go credit (Note _ e) = go credit e go credit (Cast e _) = go credit e go _ (Var {}) = boringCxtOk go _ _ = boringCxtNotOk  simonpj committed Jun 08, 1999 213 calcUnfoldingGuidance  simonpj@microsoft.com committed Dec 02, 2009 214 215 216 217  :: Bool -- True <=> the rhs is cheap, or we want to treat it -- as cheap (INLINE things) -> Int -- Bomb out if size gets bigger than this -> CoreExpr -- Expression to look at  simonpj@microsoft.com committed Oct 29, 2009 218  -> (Arity, UnfoldingGuidance)  simonpj@microsoft.com committed Dec 21, 2010 219 calcUnfoldingGuidance expr_is_cheap bOMB_OUT_SIZE expr  simonpj@microsoft.com committed Dec 02, 2009 220  = case collectBinders expr of { (bndrs, body) ->  simonpj committed Nov 01, 1999 221  let  simonpj@microsoft.com committed Dec 02, 2009 222 223 224 225 226 227 228  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  simonpj@microsoft.com committed Dec 22, 2009 229 230 231  | uncondInline n_val_bndrs (iBox size) , expr_is_cheap -> UnfWhen unSaturatedOk boringCxtOk -- Note [INLINE for small functions]  simonpj@microsoft.com committed Dec 02, 2009 232 233 234 235 236 237 238 239  | 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 240  in  simonpj@microsoft.com committed Dec 02, 2009 241  (n_val_bndrs, guidance) }  simonpj committed Jun 08, 1999 242 243 \end{code}  simonpj@microsoft.com committed Apr 03, 2009 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 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 266  0 True  simonpj@microsoft.com committed Apr 03, 2009 267 268 269 270 271 272 273 274  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 275 276 277 278 279 280 281 282 283  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 Dec 22, 2009 284 285 286 287 288 289 290 291 292 293 294 295 296 297 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. In general, f the function is sufficiently small that its body is as small as the call itself, the inline unconditionally, regardless of how boring the context is. Things to note: * 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 298 299 300 301 302 303  (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 Dec 22, 2009 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323  It's very important not to unconditionally replace a variable by a non-atomic term. * We do this even if the thing isn't saturated, else we end up with the silly situation that f x y = x ...map (f 3)... doesn't inline. Even in a boring context, inlining without being saturated will give a lambda instead of a PAP, and will be more efficient at runtime. * However, when the function's arity > 0, we do insist that it has at least one value argument at the call site. Otherwise we find this: f = /\a \x:a. x d = /\b. MkD (f b) If we inline f here we get d = /\b. MkD (\x:b. x) and then prepareRhs floats out the argument, abstracting the type variables, so we end up with the original again!  simonpj@microsoft.com committed Oct 29, 2009 324 325 326 327 328  \begin{code} uncondInline :: Arity -> Int -> Bool -- Inline unconditionally if there no size increase -- Size of call is arity (+1 for the function)  simonpj@microsoft.com committed Dec 22, 2009 329 -- See Note [INLINE for small functions]  simonpj@microsoft.com committed Oct 29, 2009 330 331 332 333 uncondInline arity size | arity == 0 = size == 0 | otherwise = size <= arity + 1 \end{code}  simonpj@microsoft.com committed Apr 03, 2009 334 335   simonpj committed Jun 08, 1999 336 \begin{code}  Isaac Dupree committed Jan 17, 2008 337 sizeExpr :: FastInt -- Bomb out if it gets bigger than this  simonpj committed Jun 08, 1999 338 339 340 341 342  -> [Id] -- Arguments; we're interested in which of these -- get case'd -> CoreExpr -> ExprSize  simonpj@microsoft.com committed Apr 03, 2009 343 344 -- Note [Computing the size of an expression]  simonmar committed Oct 12, 2000 345 sizeExpr bOMB_OUT_SIZE top_args expr  simonpj committed Jun 08, 1999 346 347  = size_up expr where  simonpj@microsoft.com committed Oct 29, 2009 348 349  size_up (Cast e _) = size_up e size_up (Note _ e) = size_up e  simonpj@microsoft.com committed Apr 03, 2009 350 351  size_up (Type _) = sizeZero -- Types cost nothing size_up (Lit lit) = sizeN (litSize lit)  simonpj@microsoft.com committed Oct 29, 2009 352  size_up (Var f) = size_up_call f [] -- Make sure we get constructor  simonpj@microsoft.com committed Apr 03, 2009 353  -- discounts even on nullary constructors  Simon Marlow committed Dec 16, 2008 354   twanvl committed Jan 25, 2008 355  size_up (App fun (Type _)) = size_up fun  simonpj@microsoft.com committed Dec 14, 2009 356 357  size_up (App fun arg) = size_up arg addSizeNSD size_up_app fun [arg]  simonpj committed Jun 08, 1999 358   simonpj committed Mar 23, 2000 359  size_up (Lam b e) | isId b = lamScrutDiscount (size_up e addSizeN 1)  simonpj committed Jun 08, 1999 360 361 362  | otherwise = size_up e size_up (Let (NonRec binder rhs) body)  simonpj@microsoft.com committed Dec 14, 2009 363 364  = size_up rhs addSizeNSD size_up body addSizeN  simonpj committed Jun 22, 1999 365 366 367  (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 368 369  size_up (Let (Rec pairs) body)  simonpj@microsoft.com committed Dec 14, 2009 370 371 372  = foldr (addSizeNSD . size_up . snd) (size_up body addSizeN length pairs) -- (length pairs) for the allocation pairs  simonpj committed Jun 08, 1999 373   simonpj committed Sep 30, 2004 374  size_up (Case (Var v) _ _ alts)  simonpj committed Aug 01, 2000 375  | v elem top_args -- We are scrutinising an argument variable  simonpj@microsoft.com committed Dec 14, 2009 376  = alts_size (foldr1 addAltSize alt_sizes)  simonpj@microsoft.com committed Apr 03, 2009 377  (foldr1 maxSize alt_sizes)  simonpj committed Mar 23, 2000 378 379 380 381 382 383  -- 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 384 385  -- 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 386 387 388  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 389  -- If the variable is known, we produce a discount that  simonpj@microsoft.com committed Apr 03, 2009 390  -- will take us back to 'max', the size of the largest alternative  simonpj committed Mar 23, 2000 391  -- The 1+ is a little discount for reduced allocation in the caller  simonpj@microsoft.com committed Apr 03, 2009 392 393 394 395  -- -- Notice though, that we return tot_disc, the total discount from -- all branches. I think that's right.  simonpj committed Mar 23, 2000 396 397  alts_size tot_size _ = tot_size  simonpj@microsoft.com committed Dec 14, 2009 398 399  size_up (Case e _ _ alts) = size_up e addSizeNSD foldr (addAltSize . size_up_alt) sizeZero alts  simonpj committed Mar 23, 2000 400 401 402 403 404  -- 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 405 406  -- -- Moreover, we charge one per alternative.  simonpj committed Jun 08, 1999 407 408  ------------  simonpj@microsoft.com committed Apr 03, 2009 409 410 411  -- 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 412 413  | otherwise = size_up arg addSizeNSD size_up_app fun (arg:args)  simonpj@microsoft.com committed Oct 29, 2009 414  size_up_app (Var fun) args = size_up_call fun args  simonpj@microsoft.com committed Apr 03, 2009 415 416 417  size_up_app other args = size_up other addSizeN length args ------------  simonpj@microsoft.com committed Oct 29, 2009 418 419  size_up_call :: Id -> [CoreExpr] -> ExprSize size_up_call fun val_args  simonpj@microsoft.com committed Apr 03, 2009 420 421  = case idDetails fun of FCallId _ -> sizeN opt_UF_DearOp  simonpj@microsoft.com committed Oct 29, 2009 422 423 424 425  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 426 427  ------------  simonpj@microsoft.com committed Nov 19, 2009 428  size_up_alt (_con, _bndrs, rhs) = size_up rhs addSizeN 1  simonpj committed Sep 07, 2000 429 430  -- Don't charge for args, so that wrappers look cheap -- (See comments about wrappers with Case)  simonpj@microsoft.com committed Nov 19, 2009 431 432 433 434  -- -- 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 435 436 437 438  ------------ -- 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 439 440  addSizeN TooBig _ = TooBig addSizeN (SizeIs n xs d) m = mkSizeIs bOMB_OUT_SIZE (n +# iUnbox m) xs d  simonpj committed Jun 08, 1999 441   simonpj@microsoft.com committed Dec 14, 2009 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457  -- 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 458 459 460 \end{code} \begin{code}  simonpj@microsoft.com committed Apr 03, 2009 461 462 463 464 465 466 467 468 469 470 471 -- | 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 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 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 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 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 Jan 07, 2010 517 518 519  | n_val_args == 0 = SizeIs (_ILIT(0)) emptyBag (_ILIT(1)) -- Like variables -- See Note [Constructor size]  simonpj@microsoft.com committed Apr 03, 2009 520  | isUnboxedTupleCon dc = SizeIs (_ILIT(0)) emptyBag (iUnbox n_val_args +# _ILIT(1))  simonpj committed Mar 23, 2000 521   simonpj@microsoft.com committed Jan 07, 2010 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 -- See Note [Unboxed tuple result discount] -- | isUnboxedTupleCon dc = SizeIs (_ILIT(0)) emptyBag (_ILIT(0)) -- See Note [Constructor size] | otherwise = SizeIs (_ILIT(1)) emptyBag (iUnbox n_val_args +# _ILIT(1)) \end{code} Note [Constructor size] ~~~~~~~~~~~~~~~~~~~~~~~ Treat a constructors application as size 1, regardless of how many arguments it has; we are keen to expose them (and we charge separately for their args). We can't treat them as size zero, else we find that (Just x) has size 0, which is the same as a lone variable; and hence 'v' will always be replaced by (Just x), where v is bound to Just x. 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. Note [Unboxed tuple result discount] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ I tried giving unboxed tuples a *result discount* of zero (see the commented-out line). Why? When returned as a result they do not allocate, so maybe we don't want to charge so much for them If you have a non-zero discount here, we find that workers often get inlined back into wrappers, because it look like f x = case $wf x of (# a,b #) -> (a,b) and we are keener because of the case. However while this change shrank binary sizes by 0.5% it also made spectral/boyer allocate 5% more. All other changes were very small. So it's not a big deal but I didn't adopt the idea. \begin{code}  twanvl committed Jan 25, 2008 555 primOpSize :: PrimOp -> Int -> ExprSize  simonpj@microsoft.com committed Apr 03, 2009 556 primOpSize op n_val_args  simonpj committed Mar 23, 2000 557  | not (primOpIsDupable op) = sizeN opt_UF_DearOp  simonpj@microsoft.com committed Apr 03, 2009 558  | not (primOpOutOfLine op) = sizeN 1  simonpj committed Dec 07, 2000 559  -- Be very keen to inline simple primops.  simonpj committed Sep 26, 2001 560 561 562 563 564 565 566 567  -- 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 568 569 570  | otherwise = sizeN n_val_args  simonpj committed Jun 08, 1999 571   twanvl committed Jan 25, 2008 572 buildSize :: ExprSize  simonpj@microsoft.com committed Apr 03, 2009 573 buildSize = SizeIs (_ILIT(0)) emptyBag (_ILIT(4))  simonpj committed Jun 08, 1999 574 575 576 577  -- 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 578  -- build is saturated (it usually is). The "-2" discounts for the \c n,  simonpj committed Jun 08, 1999 579  -- The "4" is rather arbitrary.  simonpj committed Jun 22, 1999 580   twanvl committed Jan 25, 2008 581 augmentSize :: ExprSize  simonpj@microsoft.com committed Apr 03, 2009 582 augmentSize = SizeIs (_ILIT(0)) emptyBag (_ILIT(4))  simonpj committed Jun 22, 1999 583 584  -- 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 585   simonpj committed Mar 23, 2000 586 -- When we return a lambda, give a discount if it's used (applied)  twanvl committed Jan 25, 2008 587 lamScrutDiscount :: ExprSize -> ExprSize  simonpj@microsoft.com committed Apr 03, 2009 588 lamScrutDiscount (SizeIs n vs _) = SizeIs n vs (iUnbox opt_UF_FunAppDiscount)  twanvl committed Jan 25, 2008 589 lamScrutDiscount TooBig = TooBig  simonpj committed Jun 08, 1999 590 591 \end{code}  simonpj@microsoft.com committed Dec 14, 2009 592 593 594 595 596 597 598 599 600 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 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 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 630   simonpj@microsoft.com committed Apr 03, 2009 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 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 671 sizeZero :: ExprSize  simonpj@microsoft.com committed Apr 03, 2009 672 673 674 675 676 677 678 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 679 680 681 682 683 684 %************************************************************************ %* * \subsection[considerUnfolding]{Given all the info, do (not) do the unfolding} %* * %************************************************************************  simonpj@microsoft.com committed Oct 29, 2009 685 686 687 688 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 689 690  \begin{code}  simonpj committed Mar 23, 2000 691 couldBeSmallEnoughToInline :: Int -> CoreExpr -> Bool  simonpj@microsoft.com committed Oct 29, 2009 692 couldBeSmallEnoughToInline threshold rhs  simonpj@microsoft.com committed Jan 06, 2010 693 694 695 696 697  = case sizeExpr (iUnbox threshold) [] body of TooBig -> False _ -> True where (_, body) = collectBinders rhs  simonmar committed Aug 12, 2005 698   simonpj@microsoft.com committed Oct 29, 2009 699 ----------------  simonmar committed Aug 12, 2005 700 smallEnoughToInline :: Unfolding -> Bool  simonpj@microsoft.com committed Dec 02, 2009 701 smallEnoughToInline (CoreUnfolding {uf_guidance = UnfIfGoodArgs {ug_size = size}})  simonmar committed Aug 12, 2005 702  = size <= opt_UF_UseThreshold  twanvl committed Jan 25, 2008 703 smallEnoughToInline _  simonmar committed Aug 12, 2005 704  = False  simonpj@microsoft.com committed Oct 29, 2009 705 706 707 708 709 710  ---------------- 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 711 712 713  UnfNever -> False UnfWhen {} -> True UnfIfGoodArgs { ug_size = size}  simonpj@microsoft.com committed Oct 29, 2009 714 715 716 717  -> is_cheap && size - (n_vals +1) <= opt_UF_UseThreshold certainlyWillInline _ = False  simonpj committed Jun 08, 1999 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 \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 737 NOTE: we don't want to inline top-level functions that always diverge.  Simon Marlow committed Feb 01, 2008 738 It just makes the code bigger. Tt turns out that the convenient way to prevent  simonpj committed Mar 23, 2000 739 740 741 them inlining is to give them a NOINLINE pragma, which we do in StrictAnal.addStrictnessInfoToTopId  simonpj committed Jun 08, 1999 742 \begin{code}  sewardj committed Oct 12, 2000 743 callSiteInline :: DynFlags  simonpj committed Jun 08, 1999 744  -> Id -- The Id  simonpj@microsoft.com committed Nov 16, 2010 745  -> Bool -- True <=> unfolding is active  simonpj@microsoft.com committed Dec 04, 2007 746  -> Bool -- True if there are are no arguments at all (incl type args)  simonpj@microsoft.com committed Apr 03, 2009 747  -> [ArgSummary] -- One for each value arg; True if it is interesting  simonpj@microsoft.com committed Feb 07, 2008 748  -> CallCtxt -- True <=> continuation is interesting  simonpj committed Jun 08, 1999 749 750  -> Maybe CoreExpr -- Unfolding, if any  simonpj@microsoft.com committed Apr 03, 2009 751 752 753 754 755 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 756 data CallCtxt = BoringCtxt  simonpj@microsoft.com committed Dec 04, 2007 757   simonpj@microsoft.com committed Nov 05, 2009 758 759 760 761 762 763 764  | 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 765   simonpj@microsoft.com committed Oct 28, 2008 766 767 768 769  | 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 770 771 772 773  | CaseCtxt -- We're the scrutinee of a case -- that decomposes its scrutinee instance Outputable CallCtxt where  simonpj@microsoft.com committed Nov 05, 2009 774 775 776 777  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 778   simonpj@microsoft.com committed Nov 16, 2010 779 780 781 782 783 784 785 callSiteInline dflags id active_unfolding lone_variable arg_infos cont_info = case idUnfolding id of -- idUnfolding checks for loop-breakers, returning NoUnfolding -- Things with an INLINE pragma may have an unfolding *and* -- be a loop breaker (maybe the knot is not yet untied) CoreUnfolding { uf_tmpl = unf_template, uf_is_top = is_top , uf_is_cheap = is_cheap, uf_arity = uf_arity  simonpj@microsoft.com committed Jan 26, 2011 786  , uf_guidance = guidance, uf_expandable = is_exp }  simonpj@microsoft.com committed Nov 16, 2010 787 788  | active_unfolding -> tryUnfolding dflags id lone_variable arg_infos cont_info unf_template is_top  simonpj@microsoft.com committed Jan 26, 2011 789  is_cheap is_exp uf_arity guidance  simonpj@microsoft.com committed Nov 16, 2010 790 791 792 793 794 795  | otherwise -> Nothing NoUnfolding -> Nothing OtherCon {} -> Nothing DFunUnfolding {} -> Nothing -- Never unfold a DFun tryUnfolding :: DynFlags -> Id -> Bool -> [ArgSummary] -> CallCtxt  simonpj@microsoft.com committed Jan 26, 2011 796  -> CoreExpr -> Bool -> Bool -> Bool -> Arity -> UnfoldingGuidance  simonpj@microsoft.com committed Nov 16, 2010 797 798 799  -> Maybe CoreExpr tryUnfolding dflags id lone_variable arg_infos cont_info unf_template is_top  simonpj@microsoft.com committed Jan 26, 2011 800  is_cheap is_exp uf_arity guidance  simonpj@microsoft.com committed Oct 29, 2009 801 802  -- uf_arity will typically be equal to (idArity id), -- but may be less for InlineRules  simonpj@microsoft.com committed Nov 16, 2010 803 804  | dopt Opt_D_dump_inlinings dflags && dopt Opt_D_verbose_core2core dflags = pprTrace ("Considering inlining: " ++ showSDoc (ppr id))  simonpj@microsoft.com committed Dec 02, 2009 805 806  (vcat [text "arg infos" <+> ppr arg_infos, text "uf arity" <+> ppr uf_arity,  simonpj@microsoft.com committed Jan 13, 2009 807  text "interesting continuation" <+> ppr cont_info,  simonpj@microsoft.com committed Dec 02, 2009 808  text "some_benefit" <+> ppr some_benefit,  simonpj@microsoft.com committed Jan 26, 2011 809  text "is exp:" <+> ppr is_exp,  simonpj@microsoft.com committed Mar 18, 2009 810  text "is cheap:" <+> ppr is_cheap,  simonpj@microsoft.com committed Jan 13, 2009 811  text "guidance" <+> ppr guidance,  simonpj@microsoft.com committed Dec 02, 2009 812  extra_doc,  simonpj@microsoft.com committed Jan 13, 2009 813  text "ANSWER =" <+> if yes_or_no then text "YES" else text "NO"])  simonpj@microsoft.com committed Nov 16, 2010 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842  result | otherwise = result where n_val_args = length arg_infos saturated = n_val_args >= uf_arity result | yes_or_no = Just unf_template | otherwise = Nothing 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 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 interesting_saturated_call = case cont_info of  simonpj@microsoft.com committed Jan 26, 2011 843  BoringCtxt -> not is_top && uf_arity > 0 -- Note [Nested functions]  simonpj@microsoft.com committed Nov 16, 2010 844  CaseCtxt -> not (lone_variable && is_cheap) -- Note [Lone variables]  simonpj@microsoft.com committed Jan 26, 2011 845 846  ArgCtxt {} -> uf_arity > 0 -- Note [Inlining in ArgCtxt] ValAppCtxt -> True -- Note [Cast then apply]  simonpj@microsoft.com committed Nov 16, 2010 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864  (yes_or_no, extra_doc) = case guidance of UnfNever -> (False, empty) UnfWhen unsat_ok boring_ok -> (enough_args && (boring_ok || some_benefit), empty ) where -- See Note [INLINE for small functions] enough_args = saturated || (unsat_ok && n_val_args > 0) UnfIfGoodArgs { ug_args = arg_discounts, ug_res = res_discount, ug_size = size } -> ( is_cheap && some_benefit && small_enough , (text "discounted size =" <+> int discounted_size) ) where discounted_size = size - discount small_enough = discounted_size <= opt_UF_UseThreshold discount = computeDiscount uf_arity arg_discounts res_discount arg_infos cont_info  simonpj@microsoft.com committed Dec 04, 2007 865 866 \end{code}  simonpj@microsoft.com committed Nov 05, 2009 867 868 869 870 871 872 873 874 875 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 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 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 $dOrd x y of wild {  Ian Lynagh committed Oct 23, 2010 898  GHC.Types.False -> y GHC.Types.True -> x }) -}  simonpj@microsoft.com committed Oct 29, 2009 899 900 901 902 903  We *really* want to inline$dmmin, even though it has arity 3, in order to unravel the recursion.  simonpj@microsoft.com committed Apr 03, 2009 904 905 906 907 908 909 910 911 912 913 914 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 915 916 917 Note [Inlining an InlineRule] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ An InlineRules is used for  simonpj@microsoft.com committed Dec 02, 2009 918  (a) programmer INLINE pragmas  simonpj@microsoft.com committed Oct 29, 2009 919 920 921 922 923 924 925 926 927 928 929  (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 930 931 932 933 934 935 936 937 938 939 940 941 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 942 943 944 945 946 947 948 949 950 951 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.  952 953 Note [Inlining in ArgCtxt] ~~~~~~~~~~~~~~~~~~~~~~~~~~  simonpj@microsoft.com committed Oct 29, 2009 954 The condition (arity > 0) here is very important, because otherwise  955 956 957 958 959 960 961 962 963 964 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 965 966 967 968 969 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 May 05, 2010 970 971 Note [Lone variables] See also Note [Interaction of exprIsCheap and lone variables] ~~~~~~~~~~~~~~~~~~~~~ which appears below  simonpj@microsoft.com committed Dec 04, 2007 972 973 974 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 975 976 977 978  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 979 AND  simonpj@microsoft.com committed May 05, 2010 980  it is bound to a cheap expression  simonpj@microsoft.com committed Oct 29, 2009 981   simonpj@microsoft.com committed Dec 04, 2007 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 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 1015 1016 1017 1018 1019  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 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030  * 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 1031   simonpj@microsoft.com committed May 05, 2010 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 Note [Interaction of exprIsCheap and lone variables] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The lone-variable test says "don't inline if a case expression scrutines a lone variable whose unfolding is cheap". It's very important that, under these circumstances, exprIsConApp_maybe can spot a constructor application. So, for example, we don't consider let x = e in (x,x) to be cheap, and that's good because exprIsConApp_maybe doesn't think that expression is a constructor application. I used to test is_value rather than is_cheap, which was utterly wrong, because the above expression responds True to exprIsHNF. This kind of thing can occur if you have {-# INLINE foo #-} foo = let x = e in (x,x) which Roman did.  simonpj@microsoft.com committed Dec 04, 2007 1053 \begin{code}  simonpj@microsoft.com committed Apr 03, 2009 1054 1055 computeDiscount :: Int -> [Int] -> Int -> [ArgSummary] -> CallCtxt -> Int computeDiscount n_vals_wanted arg_discounts res_discount arg_infos cont_info  simonpj committed Jun 08, 1999 1056 1057  -- 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 1058 1059  -- *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 1060 1061  -- by inlining.  simonpj@microsoft.com committed Apr 03, 2009 1062 1063 1064 1065 1066 1067 1068 1069 1070  = 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 1071 1072 1073  where arg_discount = sum (zipWith mk_arg_discount arg_discounts arg_infos)  simonpj@microsoft.com committed Apr 03, 2009 1074 1075 1076 1077 1078 1079 1080 1081 1082  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 1083  -- constructors; but we only want to invoke that large discount  simonpj@microsoft.com committed Apr 03, 2009 1084 1085 1086 1087  -- 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 1088 \end{code}  simonpj@microsoft.com committed Sep 10, 2008 1089   simonpj@microsoft.com committed Apr 03, 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 %************************************************************************ %* * 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 1116 1117 1118 1119 1120 Note [Conlike is interesting] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider f d = ...((*) d x y)... ... f (df d')...  1121 where df is con-like. Then we'd really like to inline 'f' so that the  simonpj@microsoft.com committed Oct 29, 2009 1122 1123 1124 1125 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 1126 1127 1128 1129 \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 1130  -- ..or con-like. Note [Conlike is interesting]  simonpj@microsoft.com committed Apr 03, 2009 1131 1132 1133 1134 1135 1136 1137 1138  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 1139 1140  | isConLikeId v = ValueArg -- Experimenting with 'conlike' rather that -- data constructors here  simonpj@microsoft.com committed Apr 03, 2009 1141 1142  | 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 1143  | conlike_unfolding = ValueArg -- n==0; look for an interesting unfolding  1144  -- See Note [Conlike is interesting]  simonpj@microsoft.com committed Apr 03, 2009 1145 1146  | otherwise = TrivArg -- n==0, no useful unfolding where  rl@cse.unsw.edu.au committed Nov 04, 2009 1147  conlike_unfolding = isConLikeUnfolding (idUnfolding v)  simonpj@microsoft.com committed Apr 03, 2009 1148 1149 1150 1151 1152 1153 1154  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  simonpj@microsoft.com committed Sep 13, 2010 1155  | isTyCoVar v = go e n  simonpj@microsoft.com committed Apr 03, 2009 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165  | 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 1166 1167 %************************************************************************ %* *  simonpj@microsoft.com committed Oct 29, 2009 1168  exprIsConApp_maybe  Simon Marlow committed Dec 16, 2008 1169 1170 1171 %* * %************************************************************************  simonpj@microsoft.com committed Oct 29, 2009 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 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 1183 1184  \begin{code}  simonpj@microsoft.com committed Oct 29, 2009 1185 1186 1187 -- | 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 1188 exprIsConApp_maybe :: IdUnfoldingFun -> CoreExpr -> Maybe (DataCon, [Type], [CoreExpr])  simonpj@microsoft.com committed Oct 29, 2009 1189   simonpj@microsoft.com committed Oct 26, 2010 1190 1191 exprIsConApp_maybe id_unf (Note note expr) | notSccNote note  simonpj@microsoft.com committed Dec 02, 2009 1192  = exprIsConApp_maybe id_unf expr  simonpj@microsoft.com committed Oct 26, 2010 1193  -- We ignore all notes except SCCs. For example,  simonpj@microsoft.com committed Oct 29, 2009 1194 1195  -- case _scc_ "foo" (C a b) of -- C a b -> e  simonpj@microsoft.com committed Oct 26, 2010 1196 1197  -- should not be optimised away, because we'll lose the -- entry count on 'foo'; see Trac #4414  simonpj@microsoft.com committed Oct 29, 2009 1198   simonpj@microsoft.com committed Dec 02, 2009 1199 exprIsConApp_maybe id_unf (Cast expr co)  simonpj@microsoft.com committed Oct 29, 2009 1200 1201 1202 1203 1204 1205 1206  = -- 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 1207  case exprIsConApp_maybe id_unf expr of {  simonpj@microsoft.com committed Oct 29, 2009 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217 1218 1219 1220 1221 1222 1223 1224 1225 1226 1227 1228 1229 1230 1231 1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 1245 1246 1247 1248 1249 1250 1251 1252 1253 1254 1255 1256 1257 1258  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 1259 1260  in ASSERT2( coreEqType _from_ty (mkTyConApp dc_tc _dc_univ_args), dump_doc )  simonpj@microsoft.com committed Oct 29, 2009 1261 1262 1263 1264 1265 1266 1267  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 1268 exprIsConApp_maybe id_unf expr  simonpj@microsoft.com committed Oct 29, 2009 1269  = analyse expr []  Simon Marlow committed Dec 16, 2008 1270  where  simonpj@microsoft.com committed Oct 29, 2009 1271 1272 1273 1274 1275  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  simonpj@microsoft.com committed May 31, 2010 1276  , count isValArg args == idArity fun  simonpj@microsoft.com committed Oct 29, 2009 1277 1278 1279 1280  , 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]  simonpj@microsoft.com committed May 31, 2010 1281 1282 1283 1284  | DFunUnfolding dfun_nargs con ops <- unfolding , let sat = length args == dfun_nargs -- See Note [DFun arity check] in if sat then True else pprTrace "Unsaturated dfun" (ppr fun <+> int dfun_nargs $$ppr args) False  simonpj@microsoft.com committed Dec 22, 2010 1285  , let (dfun_tvs, _n_theta, _cls, dfun_res_tys) = tcSplitDFunTy (idType fun)  simonpj@microsoft.com committed Dec 13, 2010 1286 1287 1288 1289 1290  subst = zipOpenTvSubst dfun_tvs (stripTypeArgs (takeList dfun_tvs args)) mk_arg (DFunConstArg e) = e mk_arg (DFunLamArg i) = args !! i mk_arg (DFunPolyArg e) = mkApps e args = Just (con, substTys subst dfun_res_tys, map mk_arg ops)  simonpj@microsoft.com committed Oct 29, 2009 1291 1292 1293  -- Look through unfoldings, but only cheap ones, because -- we are effectively duplicating the unfolding  simonpj@microsoft.com committed Dec 16, 2009 1294 1295 1296  | Just rhs <- expandUnfolding_maybe unfolding = -- pprTrace "expanding" (ppr fun$$ ppr rhs) $analyse rhs args  simonpj@microsoft.com committed Oct 29, 2009 1297  where  simonpj@microsoft.com committed Dec 16, 2009 1298  unfolding = id_unf fun  simonpj@microsoft.com committed Oct 29, 2009 1299 1300 1301 1302 1303 1304 1305 1306 1307 1308 1309 1310  analyse _ _ = Nothing ----------- beta (Lam v body) pairs (arg : args) | isTypeArg arg = beta body ((v,arg):pairs) args beta (Lam {}) _ _ -- Un-saturated, or not a type lambda = Nothing beta fun pairs args  simonpj@microsoft.com committed Jun 01, 2010 1311  = analyse (substExpr (text "subst-expr-is-con-app") subst fun) args  simonpj@microsoft.com committed Oct 29, 2009 1312  where  simonpj@microsoft.com committed Dec 15, 2009 1313  subst = mkOpenSubst (mkInScopeSet (exprFreeVars fun)) pairs  simonpj@microsoft.com committed Oct 29, 2009 1314 1315 1316 1317 1318 1319 1320 1321 1322 1323 1324 1325 1326 1327 1328 1329 1330 1331 1332 1333  -- doc = vcat [ppr fun, ppr expr, ppr pairs, ppr args] stripTypeArgs :: [CoreExpr] -> [Type] stripTypeArgs args = ASSERT2( all isTypeArg args, ppr args ) [ty | Type ty <- args] \end{code} Note [Unfolding DFuns] ~~~~~~~~~~~~~~~~~~~~~~ DFuns look like df :: forall a b. (Eq a, Eq b) -> Eq (a,b) df a b d_a d_b = MkEqD (a,b) ($c1 a b d_a d_b) ($c2 a b d_a d_b) So to split it up we just need to apply the ops$c1, \$c2 etc to the very same args as the dfun. It takes a little more work to compute the type arguments to the dictionary constructor.  simonpj@microsoft.com committed May 31, 2010 1334 1335 1336 1337 Note [DFun arity check] ~~~~~~~~~~~~~~~~~~~~~~~ Here we check that the total number of supplied arguments (inclding type args) matches what the dfun is expecting. This may be *less*  Simon Marlow committed Oct 15, 2010 1338 than the ordinary arity of the dfun: see Note [DFun unfoldings] in CoreSyn