Simplify.lhs 74.8 KB
 keithw committed May 15, 2000 1 %  simonm committed Dec 02, 1998 2 % (c) The AQUA Project, Glasgow University, 1993-1998  partain committed Jan 08, 1996 3 4 5 6 % \section[Simplify]{The main module of the simplifier} \begin{code}  simonpj committed May 18, 1999 7 module Simplify ( simplTopBinds, simplExpr ) where  partain committed Jan 08, 1996 8   simonm committed Jan 08, 1998 9 #include "HsVersions.h"  partain committed Jan 08, 1996 10   simonmar committed Mar 18, 2005 11 import DynFlags ( dopt, DynFlag(Opt_D_dump_inlinings),  simonm committed Dec 02, 1998 12  SimplifierSwitch(..)  sof committed Sep 09, 1997 13  )  simonm committed Dec 02, 1998 14 import SimplMonad  simonpj committed Dec 24, 2004 15 import SimplEnv  simonpj@microsoft.com committed Apr 12, 2006 16 import SimplUtils ( mkCase, mkLam,  simonpj committed Oct 18, 2001 17  SimplCont(..), DupFlag(..), LetRhsFlag(..),  simonpj@microsoft.com committed May 22, 2006 18  mkRhsStop, mkBoringStop, mkLazyArgStop, pushContArgs,  simonpj committed Oct 01, 2001 19  contResultType, countArgs, contIsDupable, contIsRhsOrArg,  simonpj committed Dec 24, 2004 20 21  getContArgs, interestingCallContext, interestingArg, isStrictType, preInlineUnconditionally, postInlineUnconditionally,  simonpj@microsoft.com committed May 22, 2006 22  interestingArgContext, inlineMode, activeInline, activeRule  partain committed Apr 05, 1996 23  )  simonpj committed Feb 12, 2003 24 import Id ( Id, idType, idInfo, idArity, isDataConWorkId,  simonpj@microsoft.com committed Apr 12, 2006 25  idUnfolding, setIdUnfolding, isDeadBinder,  simonpj committed Sep 30, 2004 26  idNewDemandInfo, setIdInfo,  simonpj committed Aug 09, 2005 27  setIdOccInfo, zapLamIdInfo, setOneShotLambda  partain committed Apr 05, 1996 28  )  simonpj committed Sep 30, 2004 29 30 import MkId ( eRROR_ID ) import Literal ( mkStringLit )  simonpj committed Sep 26, 2001 31 import IdInfo ( OccInfo(..), isLoopBreaker,  simonpj committed Sep 23, 2003 32  setArityInfo, zapDemandInfo,  simonpj committed Jul 20, 2001 33  setUnfoldingInfo,  simonmar committed Jul 11, 2000 34  occInfo  simonm committed Dec 02, 1998 35  )  simonpj committed Jul 23, 2001 36 import NewDemand ( isStrictDmd )  simonpj@microsoft.com committed Apr 12, 2006 37 38 39 40 import Unify ( coreRefineTys, dataConCanMatch ) import DataCon ( DataCon, dataConTyCon, dataConRepStrictness, isVanillaDataCon, dataConInstArgTys, dataConTyVars ) import TyCon ( tyConArity, isAlgTyCon, isNewTyCon, tyConDataCons_maybe )  simonm committed Dec 02, 1998 41 import CoreSyn  simonpj committed Jan 11, 2001 42 import PprCore ( pprParendExpr, pprCoreExpr )  simonpj committed Aug 18, 2005 43 import CoreUnfold ( mkUnfolding, callSiteInline )  simonpj committed Sep 26, 2001 44 import CoreUtils ( exprIsDupable, exprIsTrivial, needsCaseBinding,  simonpj committed Nov 01, 2001 45  exprIsConApp_maybe, mkPiTypes, findAlt,  simonpj@microsoft.com committed Apr 12, 2006 46  exprType, exprIsHNF, findDefault, mergeAlts,  simonpj committed Feb 15, 2002 47  exprOkForSpeculation, exprArity,  simonpj committed Sep 30, 2004 48  mkCoerce, mkCoerce2, mkSCC, mkInlineMe, applyTypeToArg  simonm committed Jan 08, 1998 49  )  simonpj committed May 18, 1999 50 import Rules ( lookupRule )  simonpj committed Sep 14, 2001 51 import BasicTypes ( isMarkedStrict )  simonmar committed Jul 11, 2000 52 import CostCentre ( currentCCS )  simonpj committed Oct 04, 2004 53 import Type ( TvSubstEnv, isUnLiftedType, seqType, tyConAppArgs, funArgTy,  simonpj@microsoft.com committed Apr 12, 2006 54 55  splitFunTy_maybe, splitFunTy, coreEqType, splitTyConApp_maybe, isTyVarTy, mkTyVarTys  simonpj committed Dec 18, 1998 56  )  simonpj@microsoft.com committed Apr 12, 2006 57 import Var ( tyVarKind, mkTyVar )  simonpj committed Oct 27, 2005 58 import VarEnv ( elemVarEnv, emptyVarEnv )  simonm committed Dec 02, 1998 59 import TysPrim ( realWorldStatePrimTy )  simonpj committed May 18, 1999 60 import PrelInfo ( realWorldPrimId )  simonpj committed Oct 18, 2001 61 import BasicTypes ( TopLevelFlag(..), isTopLevel,  simonpj committed Sep 26, 2001 62 63  RecFlag(..), isNonRec )  simonpj@microsoft.com committed Apr 12, 2006 64 import Name ( mkSysTvName )  simonpj committed Oct 27, 2005 65 import StaticFlags ( opt_PprStyle_Debug )  simonpj committed Dec 07, 2000 66 import OrdList  simonpj@microsoft.com committed Apr 12, 2006 67 import List ( nub )  simonpj committed Sep 23, 2003 68 import Maybes ( orElse )  simonm committed Dec 02, 1998 69 import Outputable  simonpj@microsoft.com committed Apr 12, 2006 70 import Util ( notNull, filterOut )  partain committed Jan 08, 1996 71 72 73 \end{code}  simonpj committed Sep 26, 2001 74 75 The guts of the simplifier is in this module, but the driver loop for the simplifier is in SimplCore.lhs.  simonpj committed May 18, 1999 76 77   simonpj committed Aug 01, 2000 78 79 80 81 82 83 84 85 ----------------------------------------- *** IMPORTANT NOTE *** ----------------------------------------- The simplifier used to guarantee that the output had no shadowing, but it does not do so any more. (Actually, it never did!) The reason is documented with simplifyArgs.  simonpj committed Sep 26, 2001 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 ----------------------------------------- *** IMPORTANT NOTE *** ----------------------------------------- Many parts of the simplifier return a bunch of "floats" as well as an expression. This is wrapped as a datatype SimplUtils.FloatsWith. All "floats" are let-binds, not case-binds, but some non-rec lets may be unlifted (with RHS ok-for-speculation). ----------------------------------------- ORGANISATION OF FUNCTIONS ----------------------------------------- simplTopBinds - simplify all top-level binders - for NonRec, call simplRecOrTopPair - for Rec, call simplRecBind ------------------------------ simplExpr (applied lambda) ==> simplNonRecBind simplExpr (Let (NonRec ...) ..) ==> simplNonRecBind simplExpr (Let (Rec ...) ..) ==> simplify binders; simplRecBind ------------------------------ simplRecBind [binders already simplfied] - use simplRecOrTopPair on each pair in turn simplRecOrTopPair [binder already simplified] Used for: recursive bindings (top level and nested) top-level non-recursive bindings Returns: - check for PreInlineUnconditionally - simplLazyBind simplNonRecBind Used for: non-top-level non-recursive bindings beta reductions (which amount to the same thing) Because it can deal with strict arts, it takes a "thing-inside" and returns an expression - check for PreInlineUnconditionally - simplify binder, including its IdInfo - if strict binding simplStrictArg mkAtomicArgs completeNonRecX else simplLazyBind addFloats simplNonRecX: [given a *simplified* RHS, but an *unsimplified* binder] Used for: binding case-binder and constr args in a known-constructor case - check for PreInLineUnconditionally - simplify binder - completeNonRecX ------------------------------ simplLazyBind: [binder already simplified, RHS not] Used for: recursive bindings (top level and nested) top-level non-recursive bindings non-top-level, but *lazy* non-recursive bindings [must not be strict or unboxed] Returns floats + an augmented environment, not an expression - substituteIdInfo and add result to in-scope [so that rules are available in rec rhs] - simplify rhs - mkAtomicArgs - float if exposes constructor or PAP - completeLazyBind completeNonRecX: [binder and rhs both simplified] - if the the thing needs case binding (unlifted and not ok-for-spec) build a Case else completeLazyBind addFloats completeLazyBind: [given a simplified RHS] [used for both rec and non-rec bindings, top level and not] - try PostInlineUnconditionally - add unfolding [this is the only place we add an unfolding] - add arity Right hand sides and arguments ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ In many ways we want to treat (a) the right hand side of a let(rec), and (b) a function argument in the same way. But not always! In particular, we would like to leave these arguments exactly as they are, so they will match a RULE more easily. f (g x, h x) g (+ x) It's harder to make the rule match if we ANF-ise the constructor, or eta-expand the PAP: f (let { a = g x; b = h x } in (a,b)) g (\y. + x y) On the other hand if we see the let-defns p = (g x, h x) q = + x then we *do* want to ANF-ise and eta-expand, so that p and q can be safely inlined. Even floating lets out is a bit dubious. For let RHS's we float lets out if that exposes a value, so that the value can be inlined more vigorously. For example r = let x = e in (x,x) Here, if we float the let out we'll expose a nice constructor. We did experiments that showed this to be a generally good thing. But it was a bad thing to float lets out unconditionally, because that meant they got allocated more often. For function arguments, there's less reason to expose a constructor (it won't get inlined). Just possibly it might make a rule match, but I'm pretty skeptical. So for the moment we don't float lets out of function arguments either. Eta expansion ~~~~~~~~~~~~~~ For eta expansion, we want to catch things like case e of (a,b) -> \x -> case a of (p,q) -> \y -> r If the \x was on the RHS of a let, we'd eta expand to bring the two lambdas together. And in general that's a good thing to do. Perhaps we should eta expand wherever we find a (value) lambda? Then the eta expansion at a let RHS can concentrate solely on the PAP case.  simonpj committed Aug 01, 2000 225 226   simonpj committed May 18, 1999 227 228 229 230 231 232 233 %************************************************************************ %* * \subsection{Bindings} %* * %************************************************************************ \begin{code}  simonpj committed Sep 26, 2001 234 simplTopBinds :: SimplEnv -> [InBind] -> SimplM [OutBind]  simonpj committed May 18, 1999 235   simonpj committed Sep 26, 2001 236 simplTopBinds env binds  simonpj committed May 18, 1999 237 238 239 240  = -- Put all the top-level binders into scope at the start -- so that if a transformation rule has unexpectedly brought -- anything into scope, then we don't get a complaint about that. -- It's rather as if the top-level binders were imported.  simonpj@microsoft.com committed Feb 28, 2006 241  simplRecBndrs env (bindersOfBinds binds) thenSmpl \ (env, bndrs') ->  simonpj committed Sep 26, 2001 242 243 244  simpl_binds env binds bndrs' thenSmpl \ (floats, _) -> freeTick SimplifierDone thenSmpl_ returnSmpl (floatBinds floats)  simonpj committed May 18, 1999 245  where  simonpj committed Nov 01, 1999 246 247  -- We need to track the zapped top-level binders, because -- they should have their fragile IdInfo zapped (notably occurrence info)  simonpj committed Sep 26, 2001 248 249 250 251 252 253 254 255 256 257  -- That's why we run down binds and bndrs' simultaneously. simpl_binds :: SimplEnv -> [InBind] -> [OutId] -> SimplM (FloatsWith ()) simpl_binds env [] bs = ASSERT( null bs ) returnSmpl (emptyFloats env, ()) simpl_binds env (bind:binds) bs = simpl_bind env bind bs thenSmpl \ (floats,env) -> addFloats env floats $\env -> simpl_binds env binds (drop_bs bind bs) drop_bs (NonRec _ _) (_ : bs) = bs drop_bs (Rec prs) bs = drop (length prs) bs  simonpj committed Apr 22, 2002 258 259 260 261 262 263 264 265 266  simpl_bind env bind bs = getDOptsSmpl thenSmpl \ dflags -> if dopt Opt_D_dump_inlinings dflags then pprTrace "SimplBind" (ppr (bindersOf bind))$ simpl_bind1 env bind bs else simpl_bind1 env bind bs simpl_bind1 env (NonRec b r) (b':_) = simplRecOrTopPair env TopLevel b b' r simpl_bind1 env (Rec pairs) bs' = simplRecBind env TopLevel pairs bs'  simonpj committed Sep 26, 2001 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 \end{code} %************************************************************************ %* * \subsection{simplNonRec} %* * %************************************************************************ simplNonRecBind is used for * non-top-level non-recursive lets in expressions * beta reduction It takes * An unsimplified (binder, rhs) pair * The env for the RHS. It may not be the same as the current env because the bind might occur via (\x.E) arg It uses the CPS form because the binding might be strict, in which case we might discard the continuation: let x* = error "foo" in (...x...) It needs to turn unlifted bindings into a @case@. They can arise from, say: (\x -> e) (4# + 3#) \begin{code} simplNonRecBind :: SimplEnv -> InId -- Binder -> InExpr -> SimplEnv -- Arg, with its subst-env -> OutType -- Type of thing computed by the context -> (SimplEnv -> SimplM FloatsWithExpr) -- The body -> SimplM FloatsWithExpr #ifdef DEBUG simplNonRecBind env bndr rhs rhs_se cont_ty thing_inside | isTyVar bndr = pprPanic "simplNonRecBind" (ppr bndr <+> ppr rhs) #endif simplNonRecBind env bndr rhs rhs_se cont_ty thing_inside  simonmar committed Aug 03, 2005 306 307 308 309  = simplNonRecBind' env bndr rhs rhs_se cont_ty thing_inside simplNonRecBind' env bndr rhs rhs_se cont_ty thing_inside | preInlineUnconditionally env NotTopLevel bndr rhs  simonpj committed Sep 26, 2001 310  = tick (PreInlineUnconditionally bndr) thenSmpl_  simonpj committed Dec 24, 2004 311  thing_inside (extendIdSubst env bndr (mkContEx rhs_se rhs))  simonpj committed Sep 26, 2001 312   simonmar committed Aug 03, 2005 313  | isStrictDmd (idNewDemandInfo bndr) || isStrictType bndr_ty -- A strict let  simonpj committed Sep 26, 2001 314  = -- Don't use simplBinder because that doesn't keep  simonpj committed Dec 05, 2001 315  -- fragile occurrence info in the substitution  simonpj@microsoft.com committed Mar 01, 2006 316 317  simplNonRecBndr env bndr thenSmpl \ (env, bndr1) -> simplStrictArg AnRhs env rhs rhs_se (idType bndr1) cont_ty $\ env1 rhs1 ->  simonpj committed Apr 10, 2003 318 319  -- Now complete the binding and simplify the body  simonpj@microsoft.com committed Mar 01, 2006 320 321 322  let (env2,bndr2) = addLetIdInfo env1 bndr bndr1 in  simonmar committed Aug 03, 2005 323 324 325 326 327 328 329  if needsCaseBinding bndr_ty rhs1 then thing_inside env2 thenSmpl \ (floats, body) -> returnSmpl (emptyFloats env2, Case rhs1 bndr2 (exprType body) [(DEFAULT, [], wrapFloats floats body)]) else completeNonRecX env2 True {- strict -} bndr bndr2 rhs1 thing_inside  simonpj committed Sep 26, 2001 330 331 332  | otherwise -- Normal, lazy case = -- Don't use simplBinder because that doesn't keep  simonpj committed Dec 05, 2001 333  -- fragile occurrence info in the substitution  simonpj@microsoft.com committed Feb 28, 2006 334  simplNonRecBndr env bndr thenSmpl \ (env, bndr') ->  simonpj committed Sep 26, 2001 335 336 337  simplLazyBind env NotTopLevel NonRecursive bndr bndr' rhs rhs_se thenSmpl \ (floats, env) -> addFloats env floats thing_inside  simonmar committed Aug 03, 2005 338 339 340  where bndr_ty = idType bndr  simonpj committed Sep 26, 2001 341 342 343 344 345 346 347 348 349 350 351 352 353 \end{code} A specialised variant of simplNonRec used when the RHS is already simplified, notably in knownCon. It uses case-binding where necessary. \begin{code} simplNonRecX :: SimplEnv -> InId -- Old binder -> OutExpr -- Simplified RHS -> (SimplEnv -> SimplM FloatsWithExpr) -> SimplM FloatsWithExpr simplNonRecX env bndr new_rhs thing_inside  simonpj committed Dec 14, 2001 354 355 356 357 358 359 360 361 362 363  | needsCaseBinding (idType bndr) new_rhs -- Make this test *before* the preInlineUnconditionally -- Consider case I# (quotInt# x y) of -- I# v -> let w = J# v in ... -- If we gaily inline (quotInt# x y) for v, we end up building an -- extra thunk: -- let w = J# (quotInt# x y) in ... -- because quotInt# can fail. = simplBinder env bndr thenSmpl \ (env, bndr') -> thing_inside env thenSmpl \ (floats, body) ->  simonpj committed Sep 30, 2004 364 365  let body' = wrapFloats floats body in returnSmpl (emptyFloats env, Case new_rhs bndr' (exprType body') [(DEFAULT, [], body')])  simonpj committed Dec 14, 2001 366   simonpj@microsoft.com committed Aug 10, 2006 367 {- No, no, no! Do not try preInlineUnconditionally  simonpj@microsoft.com committed Aug 10, 2006 368 369 370  Doing so risks exponential behaviour, because new_rhs has been simplified once already In the cases described by the folowing commment, postInlineUnconditionally will catch many of the relevant cases.  simonpj committed Sep 26, 2001 371 372 373 374 375 376 377 378  -- This happens; for example, the case_bndr during case of -- known constructor: case (a,b) of x { (p,q) -> ... } -- Here x isn't mentioned in the RHS, so we don't want to -- create the (dead) let-binding let x = (a,b) in ... -- -- Similarly, single occurrences can be inlined vigourously -- e.g. case (f x, g y) of (a,b) -> .... -- If a,b occur once we can avoid constructing the let binding for them.  simonpj@microsoft.com committed Aug 10, 2006 379  | preInlineUnconditionally env NotTopLevel bndr new_rhs  simonpj committed Dec 24, 2004 380  = thing_inside (extendIdSubst env bndr (DoneEx new_rhs))  simonpj@microsoft.com committed Aug 16, 2006 381 382  -- NB: completeLazyBind uses postInlineUnconditionally; no need to do that here  simonpj@microsoft.com committed Aug 10, 2006 383 -}  simonpj committed Sep 26, 2001 384 385 386  | otherwise = simplBinder env bndr thenSmpl \ (env, bndr') ->  simonpj committed Oct 01, 2001 387 388  completeNonRecX env False {- Non-strict; pessimistic -} bndr bndr' new_rhs thing_inside  simonpj committed Sep 26, 2001 389   simonpj committed Oct 01, 2001 390 391 392 393 394 395 396 completeNonRecX env is_strict old_bndr new_bndr new_rhs thing_inside = mkAtomicArgs is_strict True {- OK to float unlifted -} new_rhs thenSmpl \ (aux_binds, rhs2) -> -- Make the arguments atomic if necessary, -- adding suitable bindings  simonpj committed Oct 24, 2001 397  addAtomicBindsE env (fromOL aux_binds)$ \ env ->  simonpj committed Oct 01, 2001 398 399  completeLazyBind env NotTopLevel old_bndr new_bndr rhs2 thenSmpl \ (floats, env) ->  simonpj committed Sep 26, 2001 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419  addFloats env floats thing_inside \end{code} %************************************************************************ %* * \subsection{Lazy bindings} %* * %************************************************************************ simplRecBind is used for * recursive bindings only \begin{code} simplRecBind :: SimplEnv -> TopLevelFlag -> [(InId, InExpr)] -> [OutId] -> SimplM (FloatsWith SimplEnv) simplRecBind env top_lvl pairs bndrs' = go env pairs bndrs' thenSmpl \ (floats, env) -> returnSmpl (flattenFloats floats, env)  simonpj committed May 18, 1999 420  where  simonpj committed Sep 26, 2001 421  go env [] _ = returnSmpl (emptyFloats env, env)  simonpj committed May 18, 1999 422   simonpj committed Sep 26, 2001 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442  go env ((bndr, rhs) : pairs) (bndr' : bndrs') = simplRecOrTopPair env top_lvl bndr bndr' rhs thenSmpl \ (floats, env) -> addFloats env floats (\env -> go env pairs bndrs') \end{code} simplRecOrTopPair is used for * recursive bindings (whether top level or not) * top-level non-recursive bindings It assumes the binder has already been simplified, but not its IdInfo. \begin{code} simplRecOrTopPair :: SimplEnv -> TopLevelFlag -> InId -> OutId -- Binder, both pre-and post simpl -> InExpr -- The RHS and its environment -> SimplM (FloatsWith SimplEnv) simplRecOrTopPair env top_lvl bndr bndr' rhs  simonmar committed Aug 03, 2005 443 444  | preInlineUnconditionally env top_lvl bndr rhs -- Check for unconditional inline = tick (PreInlineUnconditionally bndr) thenSmpl_  simonpj committed Dec 24, 2004 445  returnSmpl (emptyFloats env, extendIdSubst env bndr (mkContEx env rhs))  simonpj committed Sep 26, 2001 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476  | otherwise = simplLazyBind env top_lvl Recursive bndr bndr' rhs env -- May not actually be recursive, but it doesn't matter \end{code} simplLazyBind is used for * recursive bindings (whether top level or not) * top-level non-recursive bindings * non-top-level *lazy* non-recursive bindings [Thus it deals with the lazy cases from simplNonRecBind, and all cases from SimplRecOrTopBind] Nota bene: 1. It assumes that the binder is *already* simplified, and is in scope, but not its IdInfo 2. It assumes that the binder type is lifted. 3. It does not check for pre-inline-unconditionallly; that should have been done already. \begin{code} simplLazyBind :: SimplEnv -> TopLevelFlag -> RecFlag -> InId -> OutId -- Binder, both pre-and post simpl -> InExpr -> SimplEnv -- The RHS and its environment -> SimplM (FloatsWith SimplEnv)  simonpj@microsoft.com committed Mar 01, 2006 477 simplLazyBind env top_lvl is_rec bndr bndr1 rhs rhs_se  simonpj@microsoft.com committed Feb 28, 2006 478  = let  simonpj@microsoft.com committed Mar 01, 2006 479 480  (env1,bndr2) = addLetIdInfo env bndr bndr1 rhs_env = setInScope rhs_se env1  simonpj committed Dec 05, 2001 481  is_top_level = isTopLevel top_lvl  simonpj committed Oct 18, 2001 482  ok_float_unlifted = not is_top_level && isNonRec is_rec  simonpj@microsoft.com committed Feb 28, 2006 483  rhs_cont = mkRhsStop (idType bndr2)  simonpj committed Sep 26, 2001 484  in  simonpj committed Sep 30, 2004 485  -- Simplify the RHS; note the mkRhsStop, which tells  simonpj committed Sep 26, 2001 486 487 488 489 490 491  -- the simplifier that this is the RHS of a let. simplExprF rhs_env rhs rhs_cont thenSmpl \ (floats, rhs1) -> -- If any of the floats can't be floated, give up now -- (The allLifted predicate says True for empty floats.) if (not ok_float_unlifted && not (allLifted floats)) then  simonpj@microsoft.com committed Mar 01, 2006 492  completeLazyBind env1 top_lvl bndr bndr2  simonpj committed Sep 26, 2001 493 494 495 496 497 498 499 500 501  (wrapFloats floats rhs1) else -- ANF-ise a constructor or PAP rhs mkAtomicArgs False {- Not strict -} ok_float_unlifted rhs1 thenSmpl \ (aux_binds, rhs2) -> -- If the result is a PAP, float the floats out, else wrap them -- By this time it's already been ANF-ised (if necessary)  simonpj committed Oct 24, 2001 502  if isEmptyFloats floats && isNilOL aux_binds then -- Shortcut a common case  simonpj@microsoft.com committed Mar 01, 2006 503  completeLazyBind env1 top_lvl bndr bndr2 rhs2  simonpj committed Sep 26, 2001 504   simonpj committed Aug 10, 2005 505  else if is_top_level || exprIsTrivial rhs2 || exprIsHNF rhs2 then  simonpj committed Sep 11, 2003 506 507 508  -- WARNING: long dodgy argument coming up -- WANTED: a better way to do this --  simonpj committed Aug 10, 2005 509  -- We can't use "exprIsCheap" instead of exprIsHNF,  simonpj committed Sep 11, 2003 510  -- because that causes a strictness bug.  simonpj committed Sep 26, 2001 511 512 513 514  -- x = let y* = E in case (scc y) of { T -> F; F -> T} -- The case expression is 'cheap', but it's wrong to transform to -- y* = E; x = case (scc y) of {...} -- Either we must be careful not to float demanded non-values, or  simonpj committed Aug 10, 2005 515 516  -- we must use exprIsHNF for the test, which ensures that the -- thing is non-strict. So exprIsHNF => bindings are non-strict  simonpj committed Sep 11, 2003 517 518 519 520 521  -- I think. The WARN below tests for this. -- -- We use exprIsTrivial here because we want to reveal lone variables. -- E.g. let { x = letrec { y = E } in y } in ... -- Here we definitely want to float the y=E defn.  simonpj committed Aug 10, 2005 522  -- exprIsHNF definitely isn't right for that.  simonpj committed Sep 11, 2003 523 524 525 526 527 528 529 530 531 532  -- -- Again, the floated binding can't be strict; if it's recursive it'll -- be non-strict; if it's non-recursive it'd be inlined. -- -- Note [SCC-and-exprIsTrivial] -- If we have -- y = let { x* = E } in scc "foo" x -- then we do *not* want to float out the x binding, because -- it's strict! Fortunately, exprIsTrivial replies False to -- (scc "foo" x).  simonpj committed Oct 18, 2001 533   simonpj committed Sep 26, 2001 534 535 536  -- There's a subtlety here. There may be a binding (x* = e) in the -- floats, where the '*' means 'will be demanded'. So is it safe -- to float it out? Answer no, but it won't matter because  simonpj committed Nov 19, 2002 537  -- we only float if (a) arg' is a WHNF, or (b) it's going to top level  simonpj committed Sep 26, 2001 538  -- and so there can't be any 'will be demanded' bindings in the floats.  simonpj committed Nov 19, 2002 539  -- Hence the warning  simonpj committed Sep 11, 2003 540 541  ASSERT2( is_top_level || not (any demanded_float (floatBinds floats)), ppr (filter demanded_float (floatBinds floats)) )  simonpj committed Sep 26, 2001 542 543  tick LetFloatFromLet thenSmpl_ (  simonpj@microsoft.com committed Mar 01, 2006 544  addFloats env1 floats $\ env2 ->  simonpj committed Oct 24, 2001 545  addAtomicBinds env2 (fromOL aux_binds)$ \ env3 ->  simonpj committed Apr 10, 2003 546  completeLazyBind env3 top_lvl bndr bndr2 rhs2)  simonpj committed Sep 26, 2001 547 548  else  simonpj@microsoft.com committed Mar 01, 2006 549  completeLazyBind env1 top_lvl bndr bndr2 (wrapFloats floats rhs1)  simonpj committed Sep 26, 2001 550 551 552 553 554 555  #ifdef DEBUG demanded_float (NonRec b r) = isStrictDmd (idNewDemandInfo b) && not (isUnLiftedType (idType b)) -- Unlifted-type (cheap-eagerness) lets may well have a demanded flag on them demanded_float (Rec _) = False #endif  simonpj committed May 18, 1999 556 \end{code}  partain committed Jan 08, 1996 557 558   simonpj committed Sep 26, 2001 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 %************************************************************************ %* * \subsection{Completing a lazy binding} %* * %************************************************************************ completeLazyBind * deals only with Ids, not TyVars * takes an already-simplified binder and RHS * is used for both recursive and non-recursive bindings * is used for both top-level and non-top-level bindings It does the following: - tries discarding a dead binding - tries PostInlineUnconditionally - add unfolding [this is the only place we add an unfolding] - add arity It does *not* attempt to do let-to-case. Why? Because it is used for - top-level bindings (when let-to-case is impossible) - many situations where the "rhs" is known to be a WHNF (so let-to-case is inappropriate). \begin{code} completeLazyBind :: SimplEnv -> TopLevelFlag -- Flag stuck into unfolding -> InId -- Old binder -> OutId -- New binder -> OutExpr -- Simplified RHS -> SimplM (FloatsWith SimplEnv) -- We return a new SimplEnv, because completeLazyBind may choose to do its work -- by extending the substitution (e.g. let x = y in ...) -- The new binding (if any) is returned as part of the floats. -- NB: the returned SimplEnv has the right SubstEnv, but you should -- (as usual) use the in-scope-env from the floats completeLazyBind env top_lvl old_bndr new_bndr new_rhs  simonmar committed Aug 12, 2005 596  | postInlineUnconditionally env top_lvl new_bndr occ_info new_rhs unfolding  simonpj committed Sep 26, 2001 597 598  = -- Drop the binding tick (PostInlineUnconditionally old_bndr) thenSmpl_  simonpj committed Sep 30, 2004 599  returnSmpl (emptyFloats env, extendIdSubst env old_bndr (DoneEx new_rhs))  simonpj committed Sep 26, 2001 600 601 602 603 604 605 606 607  -- Use the substitution to make quite, quite sure that the substitution -- will happen, since we are going to discard the binding | otherwise = let -- Add arity info new_bndr_info = idInfo new_bndr setArityInfo exprArity new_rhs  simonpj committed Sep 23, 2003 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632  -- Add the unfolding *only* for non-loop-breakers -- Making loop breakers not have an unfolding at all -- means that we can avoid tests in exprIsConApp, for example. -- This is important: if exprIsConApp says 'yes' for a recursive -- thing, then we can get into an infinite loop -- If the unfolding is a value, the demand info may -- go pear-shaped, so we nuke it. Example: -- let x = (a,b) in -- case x of (p,q) -> h p q x -- Here x is certainly demanded. But after we've nuked -- the case, we'll get just -- let x = (a,b) in h a b x -- and now x is not demanded (I'm assuming h is lazy) -- This really happens. Similarly -- let f = \x -> e in ...f..f... -- After inling f at some of its call sites the original binding may -- (for example) be no longer strictly demanded. -- The solution here is a bit ad hoc... info_w_unf = new_bndr_info setUnfoldingInfo unfolding final_info | loop_breaker = new_bndr_info | isEvaldUnfolding unfolding = zapDemandInfo info_w_unf orElse info_w_unf | otherwise = info_w_unf final_id = new_bndr setIdInfo final_info  simonpj committed Sep 26, 2001 633 634 635 636 637 638 639  in -- These seqs forces the Id, and hence its IdInfo, -- and hence any inner substitutions final_id seq returnSmpl (unitFloat env final_id new_rhs, env) where  simonmar committed Aug 03, 2005 640  unfolding = mkUnfolding (isTopLevel top_lvl) new_rhs  simonpj committed Sep 26, 2001 641 642 643 644 645 646 647  loop_breaker = isLoopBreaker occ_info old_info = idInfo old_bndr occ_info = occInfo old_info \end{code}  partain committed Jan 08, 1996 648 649 650 651 652 653 %************************************************************************ %* * \subsection[Simplify-simplExpr]{The main function: simplExpr} %* * %************************************************************************  simonpj committed Dec 18, 1998 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 The reason for this OutExprStuff stuff is that we want to float *after* simplifying a RHS, not before. If we do so naively we get quadratic behaviour as things float out. To see why it's important to do it after, consider this (real) example: let t = f x in fst t ==> let t = let a = e1 b = e2 in (a,b) in fst t ==> let a = e1 b = e2 t = (a,b) in a -- Can't inline a this round, cos it appears twice ==> e1 Each of the ==> steps is a round of simplification. We'd save a whole round if we float first. This can cascade. Consider let f = g d in \x -> ...f... ==> let f = let d1 = ..d.. in \y -> e in \x -> ...f... ==> let d1 = ..d.. in \x -> ...(\y ->e)... Only in this second round can the \y be applied, and it might do the same again.  partain committed Jan 08, 1996 692 \begin{code}  simonpj committed Sep 26, 2001 693 simplExpr :: SimplEnv -> CoreExpr -> SimplM CoreExpr  simonpj committed Sep 30, 2004 694 simplExpr env expr = simplExprC env expr (mkBoringStop expr_ty')  simonpj committed Sep 26, 2001 695  where  simonpj committed Dec 24, 2004 696  expr_ty' = substTy env (exprType expr)  simonpj committed Sep 26, 2001 697  -- The type in the Stop continuation, expr_ty', is usually not used  simonpj committed May 18, 1999 698  -- It's only needed when discarding continuations after finding  simonpj committed Jul 14, 1999 699 700  -- a function that returns bottom. -- Hence the lazy substitution  partain committed Jan 08, 1996 701   simonpj committed Dec 18, 1998 702   simonpj committed Sep 26, 2001 703 704 705 706 707 simplExprC :: SimplEnv -> CoreExpr -> SimplCont -> SimplM CoreExpr -- Simplify an expression, given a continuation simplExprC env expr cont = simplExprF env expr cont thenSmpl \ (floats, expr) -> returnSmpl (wrapFloats floats expr)  partain committed Jan 08, 1996 708   simonpj committed Sep 26, 2001 709 simplExprF :: SimplEnv -> InExpr -> SimplCont -> SimplM FloatsWithExpr  simonpj committed May 18, 1999 710  -- Simplify an expression, returning floated binds  partain committed Jan 08, 1996 711   simonpj committed Sep 26, 2001 712 713 714 715 simplExprF env (Var v) cont = simplVar env v cont simplExprF env (Lit lit) cont = rebuild env (Lit lit) cont simplExprF env expr@(Lam _ _) cont = simplLam env expr cont simplExprF env (Note note expr) cont = simplNote env note expr cont  simonpj@microsoft.com committed Aug 10, 2006 716 simplExprF env (App fun arg) cont = simplExprF env fun (ApplyTo NoDup arg (Just env) cont)  simonm committed Dec 02, 1998 717   simonpj committed Sep 26, 2001 718 719 720 721 simplExprF env (Type ty) cont = ASSERT( contIsRhsOrArg cont ) simplType env ty thenSmpl \ ty' -> rebuild env (Type ty') cont  simonpj committed Mar 08, 2001 722   simonpj committed Sep 30, 2004 723 simplExprF env (Case scrut bndr case_ty alts) cont  simonpj committed Sep 26, 2001 724 725 726  | not (switchIsOn (getSwitchChecker env) NoCaseOfCase) = -- Simplify the scrutinee with a Select continuation simplExprF env scrut (Select NoDup bndr alts env cont)  simonpj committed Mar 24, 2000 727   simonpj committed Sep 26, 2001 728 729  | otherwise = -- If case-of-case is off, simply simplify the case expression  simonpj committed Mar 24, 2000 730  -- in a vanilla Stop context, and rebuild the result around it  simonpj committed Sep 26, 2001 731 732 733  simplExprC env scrut case_cont thenSmpl \ case_expr' -> rebuild env case_expr' cont where  simonpj committed Sep 30, 2004 734  case_cont = Select NoDup bndr alts env (mkBoringStop case_ty')  simonpj committed Dec 24, 2004 735  case_ty' = substTy env case_ty -- c.f. defn of simplExpr  simonpj committed May 18, 1999 736   simonpj committed Sep 26, 2001 737 simplExprF env (Let (Rec pairs) body) cont  simonpj@microsoft.com committed Feb 28, 2006 738  = simplRecBndrs env (map fst pairs) thenSmpl \ (env, bndrs') ->  simonpj committed Apr 10, 2003 739 740  -- NB: bndrs' don't have unfoldings or rules -- We add them as we go down  simonm committed Dec 02, 1998 741   simonpj committed Sep 26, 2001 742 743 744  simplRecBind env NotTopLevel pairs bndrs' thenSmpl \ (floats, env) -> addFloats env floats $\ env -> simplExprF env body cont  simonpj committed May 18, 1999 745   simonpj committed Mar 01, 2001 746 -- A non-recursive let is dealt with by simplNonRecBind  simonpj committed Sep 26, 2001 747 748 749 simplExprF env (Let (NonRec bndr rhs) body) cont = simplNonRecBind env bndr rhs env (contResultType cont)$ \ env -> simplExprF env body cont  simonpj committed May 18, 1999 750 751 752  ---------------------------------  simonpj committed Sep 26, 2001 753 754 755 756 757 simplType :: SimplEnv -> InType -> SimplM OutType -- Kept monadic just so we can do the seqType simplType env ty = seqType new_ty seq returnSmpl new_ty where  simonpj committed Dec 24, 2004 758  new_ty = substTy env ty  simonpj committed Mar 08, 2001 759 760 761 762 763 764 765 766 \end{code} %************************************************************************ %* * \subsection{Lambdas} %* * %************************************************************************  simonpj committed May 18, 1999 767 768  \begin{code}  simonpj committed Sep 26, 2001 769 770 simplLam env fun cont = go env fun cont  partain committed Jan 08, 1996 771  where  simonpj committed Oct 01, 2001 772  zap_it = mkLamBndrZapper fun (countArgs cont)  simonpj committed May 18, 1999 773 774 775  cont_ty = contResultType cont -- Type-beta reduction  simonpj@microsoft.com committed Aug 10, 2006 776  go env (Lam bndr body) (ApplyTo _ (Type ty_arg) mb_arg_se body_cont)  simonpj committed May 18, 1999 777  = ASSERT( isTyVar bndr )  simonpj@microsoft.com committed Aug 10, 2006 778 779 780 781 782  do { tick (BetaReduction bndr) ; ty_arg' <- case mb_arg_se of Just arg_se -> simplType (setInScope arg_se env) ty_arg Nothing -> return ty_arg ; go (extendTvSubst env bndr ty_arg') body body_cont }  simonpj committed May 18, 1999 783 784  -- Ordinary beta reduction  simonpj@microsoft.com committed Aug 10, 2006 785 786 787 788 789 790 791 792 793  go env (Lam bndr body) cont@(ApplyTo _ arg (Just arg_se) body_cont) = do { tick (BetaReduction bndr) ; simplNonRecBind env (zap_it bndr) arg arg_se cont_ty $\ env -> go env body body_cont } go env (Lam bndr body) cont@(ApplyTo _ arg Nothing body_cont) = do { tick (BetaReduction bndr) ; simplNonRecX env (zap_it bndr) arg$ \ env -> go env body body_cont }  simonpj committed May 18, 1999 794   simonpj committed Sep 26, 2001 795 796  -- Not enough args, so there are real lambdas left to put in the result go env lam@(Lam _ _) cont  simonpj@microsoft.com committed Aug 10, 2006 797 798 799 800 801  = do { (env, bndrs') <- simplLamBndrs env bndrs ; body' <- simplExpr env body ; (floats, new_lam) <- mkLam env bndrs' body' cont ; addFloats env floats $\ env -> rebuild env new_lam cont }  simonpj committed Sep 26, 2001 802 803  where (bndrs,body) = collectBinders lam  simonpj committed May 18, 1999 804 805  -- Exactly enough args  simonpj committed Sep 26, 2001 806  go env expr cont = simplExprF env expr cont  simonpj committed May 18, 1999 807 808  mkLamBndrZapper :: CoreExpr -- Function  simonpj committed Oct 01, 2001 809  -> Int -- Number of args supplied, *including* type args  simonpj committed May 18, 1999 810  -> Id -> Id -- Use this to zap the binders  simonpj committed Oct 01, 2001 811 mkLamBndrZapper fun n_args  simonmar committed May 26, 1999 812  | n_args >= n_params fun = \b -> b -- Enough args  simonpj committed Nov 01, 1999 813  | otherwise = \b -> zapLamIdInfo b  simonpj committed May 18, 1999 814  where  simonpj committed Nov 01, 1999 815 816 817 818 819  -- NB: we count all the args incl type args -- so we must count all the binders (incl type lambdas) n_params (Note _ e) = n_params e n_params (Lam b e) = 1 + n_params e n_params other = 0::Int  partain committed Jan 08, 1996 820 821 \end{code}  simonpj committed May 18, 1999 822   simonpj committed Mar 08, 2001 823 824 825 826 827 828 %************************************************************************ %* * \subsection{Notes} %* * %************************************************************************  sof committed May 18, 1997 829 \begin{code}  simonpj committed Sep 26, 2001 830 831 simplNote env (Coerce to from) body cont = let  simonpj committed Aug 18, 2005 832 833 834 835 836  addCoerce s1 k1 cont -- Drop redundant coerces. This can happen if a polymoprhic -- (coerce a b e) is instantiated with a=ty1 b=ty2 and the -- two are the same. This happens a lot in Happy-generated parsers | s1 coreEqType k1 = cont  simonpj committed Mar 08, 2001 837 838 839 840 841 842 843 844 845 846  addCoerce s1 k1 (CoerceIt t1 cont) -- coerce T1 S1 (coerce S1 K1 e) -- ==> -- e, if T1=K1 -- coerce T1 K1 e, otherwise -- -- For example, in the initial form of a worker -- we may find (coerce T (coerce S (\x.e))) y -- and we'd like it to simplify to e[y/x] in one round -- of simplification  simonpj committed Aug 18, 2005 847 848 849  | t1 coreEqType k1 = cont -- The coerces cancel out | otherwise = CoerceIt t1 cont -- They don't cancel, but -- the inner one is redundant  simonpj committed Mar 08, 2001 850   simonpj@microsoft.com committed Aug 10, 2006 851  addCoerce t1t2 s1s2 (ApplyTo dup arg mb_arg_se cont)  simonpj committed Sep 02, 2002 852 853 854  | not (isTypeArg arg), -- This whole case only works for value args -- Could upgrade to have equiv thing for type apps too Just (s1, s2) <- splitFunTy_maybe s1s2  simonpj committed Mar 08, 2001 855 856 857 858  -- (coerce (T1->T2) (S1->S2) F) E -- ===> -- coerce T2 S2 (F (coerce S1 T1 E)) --  simonpj committed Sep 02, 2002 859  -- t1t2 must be a function type, T1->T2, because it's applied to something  simonpj committed Mar 08, 2001 860 861 862 863  -- but s1s2 might conceivably not be -- -- When we build the ApplyTo we can't mix the out-types -- with the InExpr in the argument, so we simply substitute  simonpj committed Sep 26, 2001 864 865  -- to make it all consistent. It's a bit messy. -- But it isn't a common case.  simonpj committed Mar 08, 2001 866 867  = let (t1,t2) = splitFunTy t1t2  simonpj@microsoft.com committed Aug 10, 2006 868 869 870 871  new_arg = mkCoerce2 s1 t1 arg' arg' = case mb_arg_se of Nothing -> arg Just arg_se -> substExpr (setInScope arg_se env) arg  simonpj committed Mar 08, 2001 872  in  simonpj@microsoft.com committed Aug 10, 2006 873  ApplyTo dup new_arg Nothing (addCoerce t2 s2 cont)  simonpj committed Mar 08, 2001 874 875  addCoerce to' _ cont = CoerceIt to' cont  simonpj committed Jul 14, 1999 876  in  simonpj committed Sep 26, 2001 877 878 879  simplType env to thenSmpl \ to' -> simplType env from thenSmpl \ from' -> simplExprF env body (addCoerce to' from' cont)  simonpj committed Mar 08, 2001 880 881 882 883  -- Hack: we only distinguish subsumed cost centre stacks for the purposes of -- inlining. All other CCCSs are mapped to currentCCS.  simonpj committed Sep 26, 2001 884 885 886 887 888 889 890 simplNote env (SCC cc) e cont = simplExpr (setEnclosingCC env currentCCS) e thenSmpl \ e' -> rebuild env (mkSCC cc e') cont -- See notes with SimplMonad.inlineMode simplNote env InlineMe e cont | contIsRhsOrArg cont -- Totally boring continuation; see notes above  simonpj committed Mar 08, 2001 891  = -- Don't inline inside an INLINE expression  simonpj committed Sep 26, 2001 892 893  simplExpr (setMode inlineMode env ) e thenSmpl \ e' -> rebuild env (mkInlineMe e') cont  simonpj committed Mar 08, 2001 894 895 896 897  | otherwise -- Dissolve the InlineMe note if there's -- an interesting context of any kind to combine with -- (even a type application -- anything except Stop)  simonpj committed Sep 26, 2001 898  = simplExprF env e cont  simonpj committed Feb 20, 2003 899 900 901 902  simplNote env (CoreNote s) e cont = simplExpr env e thenSmpl \ e' -> rebuild env (Note (CoreNote s) e') cont  partain committed Jan 08, 1996 903 904 905 \end{code}  simonm committed Dec 02, 1998 906 907 %************************************************************************ %* *  simonpj committed Sep 26, 2001 908 \subsection{Dealing with calls}  simonm committed Dec 02, 1998 909 910 %* * %************************************************************************  partain committed Jan 08, 1996 911   simonpj committed May 18, 1999 912 \begin{code}  simonpj committed Sep 26, 2001 913 simplVar env var cont  simonpj committed Dec 24, 2004 914 915 916 917  = case substId env var of DoneEx e -> simplExprF (zapSubstEnv env) e cont ContEx tvs ids e -> simplExprF (setSubstEnv env tvs ids) e cont DoneId var1 occ -> completeCall (zapSubstEnv env) var1 occ cont  simonpj committed Sep 30, 2004 918  -- Note [zapSubstEnv]  simonpj committed Jun 22, 1999 919 920 921 922 923 924 925 926  -- The template is already simplified, so don't re-substitute. -- This is VITAL. Consider -- let x = e in -- let y = \z -> ...x... in -- \ x -> ...y... -- We'll clone the inner \x, adding x->x' in the id_subst -- Then when we inline y, we must *not* replace x by x' in -- the inlined copy!!  simonpj committed Sep 17, 1999 927   simonpj committed Mar 23, 2000 928 ---------------------------------------------------------  simonpj committed Oct 01, 2001 929 -- Dealing with a call site  simonpj committed Mar 23, 2000 930   simonpj committed Sep 26, 2001 931 completeCall env var occ_info cont  simonpj committed Oct 01, 2001 932 933  = -- Simplify the arguments getDOptsSmpl thenSmpl \ dflags ->  simonpj committed Mar 23, 2000 934  let  simonpj@microsoft.com committed Jun 05, 2006 935 936 937  chkr = getSwitchChecker env (args, call_cont) = getContArgs chkr var cont fn_ty = idType var  simonpj committed Mar 23, 2000 938  in  simonpj@microsoft.com committed May 22, 2006 939 940  simplifyArgs env fn_ty (interestingArgContext var call_cont) args (contResultType call_cont)$ \ env args ->  simonpj committed Aug 01, 2000 941   simonpj committed Mar 23, 2000 942  -- Next, look for rules or specialisations that match  simonpj committed Sep 17, 1999 943 944 945 946 947 948 949 950 951  -- -- It's important to simplify the args first, because the rule-matcher -- doesn't do substitution as it goes. We don't want to use subst_args -- (defined in the 'where') because that throws away useful occurrence info, -- and perhaps-very-important specialisations. -- -- Some functions have specialisations *and* are strict; in this case, -- we don't want to inline the wrapper of the non-specialised thing; better -- to call the specialised thing instead.  simonpj committed Oct 01, 2001 952 953 954  -- We used to use the black-listing mechanism to ensure that inlining of -- the wrapper didn't occur for things that have specialisations till a -- later phase, so but now we just try RULES first  simonpj committed Jan 03, 2001 955  --  simonpj committed Jan 04, 2001 956 957 958 959 960 961 962 963 964 965 966  -- You might think that we shouldn't apply rules for a loop breaker: -- doing so might give rise to an infinite loop, because a RULE is -- rather like an extra equation for the function: -- RULE: f (g x) y = x+y -- Eqn: f a y = a-y -- -- But it's too drastic to disable rules for loop breakers. -- Even the foldr/build rule would be disabled, because foldr -- is recursive, and hence a loop breaker: -- foldr k z (build g) = g k z -- So it's up to the programmer: rules can cause divergence  simonpj committed Mar 23, 2000 967 968  let  simonpj committed Oct 01, 2001 969  in_scope = getInScope env  simonpj committed Dec 24, 2004 970  rules = getRules env  simonpj committed Sep 26, 2001 971 972  maybe_rule = case activeRule env of Nothing -> Nothing -- No rules apply  simonpj committed Dec 24, 2004 973  Just act_fn -> lookupRule act_fn in_scope rules var args  simonpj committed Mar 23, 2000 974 975  in case maybe_rule of {  simonpj committed Jan 04, 2000 976  Just (rule_name, rule_rhs) ->  simonpj committed Sep 17, 1999 977  tick (RuleFired rule_name) thenSmpl_  simonpj committed Jan 11, 2001 978 979  (if dopt Opt_D_dump_inlinings dflags then pprTrace "Rule fired" (vcat [  simonmar committed Apr 29, 2002 980  text "Rule:" <+> ftext rule_name,  simonpj committed Oct 01, 2001 981  text "Before:" <+> ppr var <+> sep (map pprParendExpr args),  simonpj committed Nov 19, 2001 982 983  text "After: " <+> pprCoreExpr rule_rhs, text "Cont: " <+> ppr call_cont])  simonpj committed Jan 11, 2001 984 985  else id) $ simonpj committed Sep 26, 2001 986  simplExprF env rule_rhs call_cont ;  simonpj committed Sep 17, 1999 987   simonpj committed Mar 23, 2000 988  Nothing -> -- No rules  simonpj committed Mar 19, 1998 989   simonpj committed Oct 01, 2001 990 991 992  -- Next, look for an inlining let arg_infos = [ interestingArg arg | arg <- args, isValArg arg]  sof committed Apr 05, 2002 993 994  interesting_cont = interestingCallContext (notNull args) (notNull arg_infos)  simonpj committed Oct 01, 2001 995  call_cont  simonpj committed Oct 22, 2001 996  active_inline = activeInline env var occ_info  simonpj@microsoft.com committed Jun 05, 2006 997  maybe_inline = callSiteInline dflags active_inline occ_info  simonpj committed Oct 01, 2001 998 999 1000 1001 1002  var arg_infos interesting_cont in case maybe_inline of { Just unfolding -- There is an inlining! -> tick (UnfoldingDone var) thenSmpl_  simonpj committed May 16, 2005 1003 1004 1005 1006 1007 1008 1009  (if dopt Opt_D_dump_inlinings dflags then pprTrace "Inlining done" (vcat [ text "Before:" <+> ppr var <+> sep (map pprParendExpr args), text "Inlined fn: " <+> ppr unfolding, text "Cont: " <+> ppr call_cont]) else id)$  simonpj@microsoft.com committed Aug 10, 2006 1010  simplExprF env unfolding (pushContArgs args call_cont)  simonpj committed Oct 01, 2001 1011 1012 1013 1014  ; Nothing -> -- No inlining!  simonpj committed Mar 23, 2000 1015  -- Done  simonpj committed Oct 01, 2001 1016  rebuild env (mkApps (Var var) args) call_cont  simonpj committed Mar 23, 2000 1017  }}  simonpj@microsoft.com committed Aug 10, 2006 1018 \end{code}  simonpj committed Jun 22, 1999 1019   simonpj committed Sep 26, 2001 1020 1021 1022 1023 1024 1025 1026 %************************************************************************ %* * \subsection{Arguments} %* * %************************************************************************ \begin{code}  simonpj committed May 18, 1999 1027 ---------------------------------------------------------  simonpj committed Aug 01, 2000 1028 1029 -- Simplifying the arguments of a call  simonpj committed Sep 26, 2001 1030 simplifyArgs :: SimplEnv  simonpj committed Nov 16, 2001 1031  -> OutType -- Type of the function  simonpj@microsoft.com committed May 22, 2006 1032  -> Bool -- True if the fn has RULES  simonpj@microsoft.com committed Aug 10, 2006 1033  -> [(InExpr, Maybe SimplEnv, Bool)] -- Details of the arguments  simonpj committed Aug 01, 2000 1034  -> OutType -- Type of the continuation  simonpj committed Sep 26, 2001 1035 1036 1037 1038  -> (SimplEnv -> [OutExpr] -> SimplM FloatsWithExpr) -> SimplM FloatsWithExpr -- [CPS-like because of strict arguments]  simonpj committed Aug 01, 2000 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062  -- Simplify the arguments to a call. -- This part of the simplifier may break the no-shadowing invariant -- Consider -- f (...(\a -> e)...) (case y of (a,b) -> e') -- where f is strict in its second arg -- If we simplify the innermost one first we get (...(\a -> e)...) -- Simplifying the second arg makes us float the case out, so we end up with -- case y of (a,b) -> f (...(\a -> e)...) e' -- So the output does not have the no-shadowing invariant. However, there is -- no danger of getting name-capture, because when the first arg was simplified -- we used an in-scope set that at least mentioned all the variables free in its -- static environment, and that is enough. -- -- We can't just do innermost first, or we'd end up with a dual problem: -- case x of (a,b) -> f e (...(\a -> e')...) -- -- I spent hours trying to recover the no-shadowing invariant, but I just could -- not think of an elegant way to do it. The simplifier is already knee-deep in -- continuations. We have to keep the right in-scope set around; AND we have -- to get the effect that finding (error "foo") in a strict arg position will -- discard the entire application and replace it with (error "foo"). Getting -- all this at once is TOO HARD!  simonpj@microsoft.com committed May 22, 2006 1063 simplifyArgs env fn_ty has_rules args cont_ty thing_inside  simonpj committed Nov 16, 2001 1064  = go env fn_ty args thing_inside  simonpj committed Aug 01, 2000 1065  where  simonpj committed Nov 16, 2001 1066  go env fn_ty [] thing_inside = thing_inside env []  simonpj@microsoft.com committed May 22, 2006 1067  go env fn_ty (arg:args) thing_inside = simplifyArg env fn_ty has_rules arg cont_ty $\ env arg' ->  simonpj committed Nov 16, 2001 1068 1069  go env (applyTypeToArg fn_ty arg') args$ \ env args' -> thing_inside env (arg':args')  simonpj committed Aug 01, 2000 1070   simonpj@microsoft.com committed Aug 10, 2006 1071 1072 1073 1074 simplifyArg env fn_ty has_rules (arg, Nothing, _) cont_ty thing_inside = thing_inside env arg -- Already simplified simplifyArg env fn_ty has_rules (Type ty_arg, Just se, _) cont_ty thing_inside  simonpj committed Sep 26, 2001 1075 1076  = simplType (setInScope se env) ty_arg thenSmpl \ new_ty_arg -> thing_inside env (Type new_ty_arg)  simonpj committed Aug 01, 2000 1077   simonpj@microsoft.com committed Aug 10, 2006 1078 simplifyArg env fn_ty has_rules (val_arg, Just arg_se, is_strict) cont_ty thing_inside  simonpj committed Sep 26, 2001 1079  | is_strict  simonpj committed Nov 16, 2001 1080  = simplStrictArg AnArg env val_arg arg_se arg_ty cont_ty thing_inside  simonpj committed May 18, 1999 1081   simonpj committed Nov 19, 2002 1082 1083 1084 1085 1086 1087  | otherwise -- Lazy argument -- DO NOT float anything outside, hence simplExprC -- There is no benefit (unlike in a let-binding), and we'd -- have to be very careful about bogus strictness through -- floating a demanded let. = simplExprC (setInScope arg_se env) val_arg  simonpj@microsoft.com committed May 22, 2006 1088 1089  (mkLazyArgStop arg_ty has_rules) thenSmpl \ arg1 -> thing_inside env arg1  simonpj committed Nov 16, 2001 1090 1091  where arg_ty = funArgTy fn_ty  simonpj committed Sep 26, 2001 1092 1093   simonpj committed Nov 16, 2001 1094 1095 1096 1097 simplStrictArg :: LetRhsFlag -> SimplEnv -- The env of the call -> InExpr -> SimplEnv -- The arg plus its env -> OutType -- arg_ty: type of the argument  simonpj committed Sep 26, 2001 1098 1099 1100 1101 1102 1103 1104 1105  -> OutType -- cont_ty: Type of thing computed by the context -> (SimplEnv -> OutExpr -> SimplM FloatsWithExpr) -- Takes an expression of type rhs_ty, -- returns an expression of type cont_ty -- The env passed to this continuation is the -- env of the call, plus any new in-scope variables -> SimplM FloatsWithExpr -- An expression of type cont_ty  simonpj committed Nov 16, 2001 1106 simplStrictArg is_rhs call_env arg arg_env arg_ty cont_ty thing_inside  simonpj committed Sep 26, 2001 1107  = simplExprF (setInScope arg_env call_env) arg  simonpj committed Nov 16, 2001 1108  (ArgOf is_rhs arg_ty cont_ty (\ new_env -> thing_inside (setInScope call_env new_env)))  simonpj committed Sep 26, 2001 1109 1110 1111  -- Notice the way we use arg_env (augmented with in-scope vars from call_env) -- to simplify the argument -- and call-env (augmented with in-scope vars from the arg) to pass to the continuation  simonpj committed May 18, 1999 1112 \end{code}  simonm committed Dec 02, 1998 1113   partain committed Jan 08, 1996 1114   simonm committed Dec 02, 1998 1115 1116 %************************************************************************ %* *  simonpj committed Sep 26, 2001 1117 \subsection{mkAtomicArgs}  simonm committed Dec 02, 1998 1118 1119 %* * %************************************************************************  partain committed Jan 08, 1996 1120   simonpj committed Sep 26, 2001 1121 1122 1123 1124 1125 1126 1127 1128 mkAtomicArgs takes a putative RHS, checks whether it's a PAP or constructor application and, if so, converts it to ANF, so that the resulting thing can be inlined more easily. Thus x = (f a, g b) becomes t1 = f a t2 = g b x = (t1,t2)  sof committed Sep 04, 1997 1129   simonpj committed Sep 26, 2001 1130 1131 There are three sorts of binding context, specified by the two boolean arguments  sof committed Sep 04, 1997 1132   simonpj committed Sep 26, 2001 1133 1134 Strict OK-unlifted  simonpj committed Dec 18, 1998 1135   simonpj committed Sep 26, 2001 1136 N N Top-level or recursive Only bind args of lifted type  simonm committed Dec 02, 1998 1137   simonpj committed Sep 26, 2001 1138 1139 N Y Non-top-level and non-recursive, Bind args of lifted type, or but lazy unlifted-and-ok-for-speculation  simonm committed Dec 02, 1998 1140