Simplify.lhs 70.8 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}  Ian Lynagh committed Sep 03, 2007 7 {-# OPTIONS -w #-}  Ian Lynagh committed Sep 01, 2007 8 9 10 -- The above warning supression flag is a temporary kludge. -- While working on this module you are encouraged to remove it and fix -- any warnings in the module. See  Ian Lynagh committed Sep 04, 2007 11 -- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings  Ian Lynagh committed Sep 01, 2007 12 13 -- for details  simonpj committed May 18, 1999 14 module Simplify ( simplTopBinds, simplExpr ) where  partain committed Jan 08, 1996 15   simonm committed Jan 08, 1998 16 #include "HsVersions.h"  partain committed Jan 08, 1996 17   simonpj@microsoft.com committed Jan 11, 2007 18 import DynFlags  simonm committed Dec 02, 1998 19 import SimplMonad  simonpj@microsoft.com committed Nov 01, 2006 20 import Type hiding ( substTy, extendTvSubst )  simonpj committed Dec 24, 2004 21 import SimplEnv  simonpj@microsoft.com committed Nov 01, 2006 22 23 import SimplUtils import Id  simonpj@microsoft.com committed Feb 05, 2007 24 import Var  simonpj@microsoft.com committed Nov 01, 2006 25 26 import IdInfo import Coercion  simonpj@microsoft.com committed May 23, 2007 27 import FamInstEnv ( topNormaliseType )  simonpj@microsoft.com committed May 04, 2007 28 import DataCon ( dataConRepStrictness, dataConUnivTyVars )  simonm committed Dec 02, 1998 29 import CoreSyn  simonpj@microsoft.com committed Feb 09, 2007 30 import NewDemand ( isStrictDmd )  simonpj committed Jan 11, 2001 31 import PprCore ( pprParendExpr, pprCoreExpr )  simonpj committed Aug 18, 2005 32 import CoreUnfold ( mkUnfolding, callSiteInline )  simonpj@microsoft.com committed Nov 01, 2006 33 import CoreUtils  simonpj committed May 18, 1999 34 import Rules ( lookupRule )  simonpj committed Sep 14, 2001 35 import BasicTypes ( isMarkedStrict )  simonmar committed Jul 11, 2000 36 import CostCentre ( currentCCS )  simonm committed Dec 02, 1998 37 import TysPrim ( realWorldStatePrimTy )  simonpj committed May 18, 1999 38 import PrelInfo ( realWorldPrimId )  simonpj committed Oct 18, 2001 39 import BasicTypes ( TopLevelFlag(..), isTopLevel,  simonpj@microsoft.com committed Nov 01, 2006 40  RecFlag(..), isNonRuleLoopBreaker )  simonpj committed Sep 23, 2003 41 import Maybes ( orElse )  simonpj@microsoft.com committed Oct 29, 2007 42 import Data.List ( mapAccumL )  simonm committed Dec 02, 1998 43 import Outputable  simonpj@microsoft.com committed Nov 01, 2006 44 import Util  partain committed Jan 08, 1996 45 46 47 \end{code}  simonpj committed Sep 26, 2001 48 49 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 50 51   simonpj committed Aug 01, 2000 52 53 54 55 56 57 58 59 ----------------------------------------- *** 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 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 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 ----------------------------------------- *** 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  simonpj@microsoft.com committed Nov 01, 2006 130  - completeBind  simonpj committed Sep 26, 2001 131 132 133 134 135 136  completeNonRecX: [binder and rhs both simplified] - if the the thing needs case binding (unlifted and not ok-for-spec) build a Case else  simonpj@microsoft.com committed Nov 01, 2006 137  completeBind  simonpj committed Sep 26, 2001 138 139  addFloats  simonpj@microsoft.com committed Nov 01, 2006 140 completeBind: [given a simplified RHS]  simonpj committed Sep 26, 2001 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  [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 199 200   simonpj committed May 18, 1999 201 202 203 204 205 206 207 %************************************************************************ %* * \subsection{Bindings} %* * %************************************************************************ \begin{code}  simonpj committed Sep 26, 2001 208 simplTopBinds :: SimplEnv -> [InBind] -> SimplM [OutBind]  simonpj committed May 18, 1999 209   simonpj committed Sep 26, 2001 210 simplTopBinds env binds  simonpj@microsoft.com committed Nov 01, 2006 211 212 213 214 215 216  = do { -- 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. ; env <- simplRecBndrs env (bindersOfBinds binds) ; dflags <- getDOptsSmpl  simonpj@microsoft.com committed Jan 11, 2007 217 218  ; let dump_flag = dopt Opt_D_dump_inlinings dflags || dopt Opt_D_dump_rule_firings dflags  simonpj@microsoft.com committed Nov 01, 2006 219 220 221  ; env' <- simpl_binds dump_flag env binds ; freeTick SimplifierDone ; return (getFloats env') }  simonpj committed May 18, 1999 222  where  simonpj committed Nov 01, 1999 223 224  -- 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 225  -- That's why we run down binds and bndrs' simultaneously.  simonpj@microsoft.com committed Jan 11, 2007 226 227 228  -- -- The dump-flag emits a trace for each top-level binding, which -- helps to locate the tracing for inlining and rule firing  simonpj@microsoft.com committed Nov 01, 2006 229 230 231 232 233  simpl_binds :: Bool -> SimplEnv -> [InBind] -> SimplM SimplEnv simpl_binds dump env [] = return env simpl_binds dump env (bind:binds) = do { env' <- trace dump bind $simpl_bind env bind ; simpl_binds dump env' binds }  simonpj committed Sep 26, 2001 234   simonpj@microsoft.com committed Nov 01, 2006 235 236  trace True bind = pprTrace "SimplBind" (ppr (bindersOf bind)) trace False bind = \x -> x  simonpj@microsoft.com committed Aug 16, 2006 237   simonpj@microsoft.com committed Oct 29, 2007 238 239 240 241  simpl_bind env (Rec pairs) = simplRecBind env TopLevel pairs simpl_bind env (NonRec b r) = simplRecOrTopPair env' TopLevel b b' r where (env', b') = addLetIdInfo env b (lookupRecBndr env b)  simonpj committed Sep 26, 2001 242 243 244 245 246 247 248 249 250 251 252 253 254 255 \end{code} %************************************************************************ %* * \subsection{Lazy bindings} %* * %************************************************************************ simplRecBind is used for * recursive bindings only \begin{code} simplRecBind :: SimplEnv -> TopLevelFlag  simonpj@microsoft.com committed Nov 01, 2006 256 257 258  -> [(InId, InExpr)] -> SimplM SimplEnv simplRecBind env top_lvl pairs  simonpj@microsoft.com committed Oct 29, 2007 259 260  = do { let (env_with_info, triples) = mapAccumL add_info env pairs ; env' <- go (zapFloats env_with_info) triples  simonpj@microsoft.com committed Nov 01, 2006 261 262 263  ; return (env addRecFloats env') } -- addFloats adds the floats from env', -- *and* updates env with the in-scope set from env'  simonpj committed May 18, 1999 264  where  simonpj@microsoft.com committed Oct 29, 2007 265 266 267 268 269 270  add_info :: SimplEnv -> (InBndr,InExpr) -> (SimplEnv, (InBndr, OutBndr, InExpr)) -- Substitute in IdInfo, agument envt add_info env (bndr, rhs) = (env, (bndr, bndr', rhs)) where (env', bndr') = addLetIdInfo env bndr (lookupRecBndr env bndr)  simonpj@microsoft.com committed Nov 01, 2006 271  go env [] = return env  simonpj committed May 18, 1999 272   simonpj@microsoft.com committed Oct 29, 2007 273 274  go env ((old_bndr, new_bndr, rhs) : pairs) = do { env <- simplRecOrTopPair env top_lvl old_bndr new_bndr rhs  simonpj@microsoft.com committed Nov 01, 2006 275  ; go env pairs }  simonpj committed Sep 26, 2001 276 277 \end{code}  simonpj@microsoft.com committed Nov 01, 2006 278 simplOrTopPair is used for  simonpj committed Sep 26, 2001 279 280 281 282 283 284 285 286  * 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  simonpj@microsoft.com committed Oct 29, 2007 287  -> InId -> OutBndr -> InExpr -- Binder and rhs  simonpj@microsoft.com committed Nov 01, 2006 288  -> SimplM SimplEnv -- Returns an env that includes the binding  simonpj committed Sep 26, 2001 289   simonpj@microsoft.com committed Oct 29, 2007 290 291 292 293 simplRecOrTopPair env top_lvl old_bndr new_bndr rhs | preInlineUnconditionally env top_lvl old_bndr rhs -- Check for unconditional inline = do { tick (PreInlineUnconditionally old_bndr) ; return (extendIdSubst env old_bndr (mkContEx env rhs)) }  simonpj committed Sep 26, 2001 294 295  | otherwise  simonpj@microsoft.com committed Oct 29, 2007 296  = simplLazyBind env top_lvl Recursive old_bndr new_bndr rhs env  simonpj committed Sep 26, 2001 297 298 299 300 301  -- May not actually be recursive, but it doesn't matter \end{code} simplLazyBind is used for  simonpj@microsoft.com committed Nov 01, 2006 302 303 304  * [simplRecOrTopPair] recursive bindings (whether top level or not) * [simplRecOrTopPair] top-level non-recursive bindings * [simplNonRecE] non-top-level *lazy* non-recursive bindings  simonpj committed Sep 26, 2001 305 306 307  Nota bene: 1. It assumes that the binder is *already* simplified,  simonpj@microsoft.com committed Nov 01, 2006 308  and is in scope, and its IdInfo too, except unfolding  simonpj committed Sep 26, 2001 309 310 311 312 313 314 315 316 317 318  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  simonpj@microsoft.com committed Nov 01, 2006 319  -- The OutId has IdInfo, except arity, unfolding  simonpj committed Sep 26, 2001 320  -> InExpr -> SimplEnv -- The RHS and its environment  simonpj@microsoft.com committed Nov 01, 2006 321  -> SimplM SimplEnv  simonpj committed Sep 26, 2001 322   simonpj@microsoft.com committed Mar 01, 2006 323 simplLazyBind env top_lvl is_rec bndr bndr1 rhs rhs_se  simonpj@microsoft.com committed May 07, 2007 324 325 326 327 328  = do { let rhs_env = rhs_se setInScope env (tvs, body) = collectTyBinders rhs ; (body_env, tvs') <- simplBinders rhs_env tvs -- See Note [Floating and type abstraction] -- in SimplUtils  simonpj@microsoft.com committed Nov 01, 2006 329   simonpj committed Sep 30, 2004 330  -- Simplify the RHS; note the mkRhsStop, which tells  simonpj committed Sep 26, 2001 331  -- the simplifier that this is the RHS of a let.  simonpj@microsoft.com committed May 07, 2007 332 333 334  ; let rhs_cont = mkRhsStop (applyTys (idType bndr1) (mkTyVarTys tvs')) ; (body_env1, body1) <- simplExprF body_env body rhs_cont  simonpj committed Sep 26, 2001 335  -- ANF-ise a constructor or PAP rhs  simonpj@microsoft.com committed May 07, 2007 336  ; (body_env2, body2) <- prepareRhs body_env1 body1  simonpj@microsoft.com committed Nov 01, 2006 337   simonpj@microsoft.com committed May 07, 2007 338 339 340 341 342  ; (env', rhs') <- if not (doFloatFromRhs top_lvl is_rec False body2 body_env2) then -- No floating, just wrap up! do { rhs' <- mkLam tvs' (wrapFloats body_env2 body2) ; return (env, rhs') }  simonpj@microsoft.com committed Nov 01, 2006 343   simonpj@microsoft.com committed May 07, 2007 344 345 346 347 348 349  else if null tvs then -- Simple floating do { tick LetFloatFromLet ; return (addFloats env body_env2, body2) } else -- Do type-abstraction first do { tick LetFloatFromLet  simonpj@microsoft.com committed May 09, 2007 350  ; (poly_binds, body3) <- abstractFloats tvs' body_env2 body2  simonpj@microsoft.com committed May 07, 2007 351 352 353 354 355  ; rhs' <- mkLam tvs' body3 ; return (extendFloats env poly_binds, rhs') } ; completeBind env' top_lvl bndr bndr1 rhs' } \end{code}  simonpj@microsoft.com committed Nov 01, 2006 356 357 358 359 360 361 362 363 364 365 366 367 368  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 -> SimplM SimplEnv simplNonRecX env bndr new_rhs = do { (env, bndr') <- simplBinder env bndr ; completeNonRecX env NotTopLevel NonRecursive  simonpj@microsoft.com committed Jan 31, 2007 369  (isStrictId bndr) bndr bndr' new_rhs }  simonpj@microsoft.com committed Nov 01, 2006 370 371 372 373 374 375 376 377 378 379  completeNonRecX :: SimplEnv -> TopLevelFlag -> RecFlag -> Bool -> InId -- Old binder -> OutId -- New binder -> OutExpr -- Simplified RHS -> SimplM SimplEnv completeNonRecX env top_lvl is_rec is_strict old_bndr new_bndr new_rhs = do { (env1, rhs1) <- prepareRhs (zapFloats env) new_rhs  simonpj@microsoft.com committed May 07, 2007 380 381 382 383 384  ; (env2, rhs2) <- if doFloatFromRhs top_lvl is_rec is_strict rhs1 env1 then do { tick LetFloatFromLet ; return (addFloats env env1, rhs1) } -- Add the floats to the main env else return (env, wrapFloats env1 rhs1) -- Wrap the floats around the RHS  simonpj@microsoft.com committed Nov 01, 2006 385 386 387 388 389 390 391 392 393 394 395  ; completeBind env2 NotTopLevel old_bndr new_bndr rhs2 } \end{code} {- No, no, no! Do not try preInlineUnconditionally in completeNonRecX 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. -- 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 ...  simonpj committed Sep 11, 2003 396  --  simonpj@microsoft.com committed Nov 01, 2006 397 398 399  -- 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 committed Sep 26, 2001 400   simonpj@microsoft.com committed Nov 01, 2006 401 402 403 404 405 406 407  Furthermore in the case-binding case preInlineUnconditionally risks extra thunks -- 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.  simonpj committed Sep 26, 2001 408   simonpj@microsoft.com committed Nov 01, 2006 409 410 411 412  | preInlineUnconditionally env NotTopLevel bndr new_rhs = thing_inside (extendIdSubst env bndr (DoneEx new_rhs)) -}  simonpj@microsoft.com committed Feb 05, 2007 413 ----------------------------------  simonpj@microsoft.com committed Nov 01, 2006 414 415 416 417 418 419 420 421 422 prepareRhs 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)  simonpj@microsoft.com committed Feb 05, 2007 423 424 425 426 427 428 We also want to deal well cases like this v = (f e1 cast co) e2 Here we want to make e1,e2 trivial and get x1 = e1; x2 = e2; v = (f x1 cast co) v2 That's what the 'go' loop in prepareRhs does  simonpj@microsoft.com committed Nov 01, 2006 429 430 431 \begin{code} prepareRhs :: SimplEnv -> OutExpr -> SimplM (SimplEnv, OutExpr) -- Adds new floats to the env iff that allows us to return a good RHS  simonpj@microsoft.com committed Jan 10, 2007 432 prepareRhs env (Cast rhs co) -- Note [Float coercions]  simonpj@microsoft.com committed Sep 20, 2007 433 434  | (ty1, ty2) <- coercionKind co -- Do *not* do this if rhs has an unlifted type , not (isUnLiftedType ty1) -- see Note [Float coercions (unlifted)]  simonpj@microsoft.com committed Nov 01, 2006 435 436 437 438  = do { (env', rhs') <- makeTrivial env rhs ; return (env', Cast rhs' co) } prepareRhs env rhs  simonpj@microsoft.com committed Feb 05, 2007 439 440  = do { (is_val, env', rhs') <- go 0 env rhs ; return (env', rhs') }  simonpj@microsoft.com committed Nov 01, 2006 441  where  simonpj@microsoft.com committed Feb 05, 2007 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461  go n_val_args env (Cast rhs co) = do { (is_val, env', rhs') <- go n_val_args env rhs ; return (is_val, env', Cast rhs' co) } go n_val_args env (App fun (Type ty)) = do { (is_val, env', rhs') <- go n_val_args env fun ; return (is_val, env', App rhs' (Type ty)) } go n_val_args env (App fun arg) = do { (is_val, env', fun') <- go (n_val_args+1) env fun ; case is_val of True -> do { (env'', arg') <- makeTrivial env' arg ; return (True, env'', App fun' arg') } False -> return (False, env, App fun arg) } go n_val_args env (Var fun) = return (is_val, env, Var fun) where is_val = n_val_args > 0 -- There is at least one arg -- ...and the fun a constructor or PAP && (isDataConWorkId fun || n_val_args < idArity fun) go n_val_args env other = return (False, env, other)  simonpj@microsoft.com committed Nov 01, 2006 462 463 \end{code}  simonpj@microsoft.com committed May 07, 2007 464   simonpj@microsoft.com committed Nov 01, 2006 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 Note [Float coercions] ~~~~~~~~~~~~~~~~~~~~~~ When we find the binding x = e cast co we'd like to transform it to x' = e x = x cast co -- A trivial binding There's a chance that e will be a constructor application or function, or something like that, so moving the coerion to the usage site may well cancel the coersions and lead to further optimisation. Example: data family T a :: * data instance T Int = T Int foo :: Int -> Int -> Int foo m n = ... where x = T m go 0 = 0 go n = case x of { T m -> go (n-m) } -- This case should optimise  simonpj@microsoft.com committed Sep 20, 2007 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 Note [Float coercions (unlifted)] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ BUT don't do [Float coercions] if 'e' has an unlifted type. This *can* happen: foo :: Int = (error (# Int,Int #) "urk") cast CoUnsafe (# Int,Int #) Int If do the makeTrivial thing to the error call, we'll get foo = case error (# Int,Int #) "urk" of v -> v cast ... But 'v' isn't in scope! These strange casts can happen as a result of case-of-case bar = case (case x of { T -> (# 2,3 #); F -> error "urk" }) of (# p,q #) -> p+q  simonpj@microsoft.com committed Nov 01, 2006 503 504 505 506 507 508 509 510 511 512 513 514  \begin{code} makeTrivial :: SimplEnv -> OutExpr -> SimplM (SimplEnv, OutExpr) -- Binds the expression to a variable, if it's not trivial, returning the variable makeTrivial env expr | exprIsTrivial expr = return (env, expr) | otherwise -- See Note [Take care] below = do { var <- newId FSLIT("a") (exprType expr) ; env <- completeNonRecX env NotTopLevel NonRecursive False var var expr ; return (env, substExpr env (Var var)) }  simonpj committed May 18, 1999 515 \end{code}  partain committed Jan 08, 1996 516 517   simonpj committed Sep 26, 2001 518 519 520 521 522 523 %************************************************************************ %* * \subsection{Completing a lazy binding} %* * %************************************************************************  simonpj@microsoft.com committed Nov 01, 2006 524 525 526 527 528 completeBind * 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  simonpj committed Sep 26, 2001 529 530 531 532 533 534 535 536  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  simonpj@microsoft.com committed Nov 01, 2006 537 538  - top-level bindings (when let-to-case is impossible) - many situations where the "rhs" is known to be a WHNF  simonpj committed Sep 26, 2001 539 540  (so let-to-case is inappropriate).  simonpj@microsoft.com committed Nov 01, 2006 541 542 Nor does it do the atomic-argument thing  simonpj committed Sep 26, 2001 543 \begin{code}  simonpj@microsoft.com committed Nov 01, 2006 544 545 546 547 548 549 550 551 552 553 completeBind :: SimplEnv -> TopLevelFlag -- Flag stuck into unfolding -> InId -- Old binder -> OutId -> OutExpr -- New binder and RHS -> SimplM SimplEnv -- completeBind may choose to do its work -- * by extending the substitution (e.g. let x = y in ...) -- * or by adding to the floats in the envt completeBind env top_lvl old_bndr new_bndr new_rhs  simonmar committed Aug 12, 2005 554  | postInlineUnconditionally env top_lvl new_bndr occ_info new_rhs unfolding  simonpj@microsoft.com committed Nov 01, 2006 555 556 557 558 559 560  -- Inline and discard the binding = do { tick (PostInlineUnconditionally old_bndr) ; -- pprTrace "postInlineUnconditionally" (ppr old_bndr <+> ppr new_bndr <+> ppr new_rhs)$ return (extendIdSubst env old_bndr (DoneEx new_rhs)) } -- Use the substitution to make quite, quite sure that the -- substitution will happen, since we are going to discard the binding  simonpj committed Sep 26, 2001 561 562 563  | otherwise = let  simonpj@microsoft.com committed Oct 04, 2006 564  -- Arity info  simonpj committed Sep 26, 2001 565 566  new_bndr_info = idInfo new_bndr setArityInfo exprArity new_rhs  simonpj@microsoft.com committed Oct 04, 2006 567  -- Unfolding info  simonpj committed Sep 23, 2003 568 569 570 571 572  -- 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  simonpj@microsoft.com committed Oct 04, 2006 573 574  -- Demand info  simonpj committed Sep 23, 2003 575 576 577 578 579 580 581 582 583 584  -- 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...  simonpj@microsoft.com committed Oct 05, 2006 585  -- After inlining f at some of its call sites the original binding may  simonpj committed Sep 23, 2003 586 587 588 589 590 591 592 593  -- (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 594 595 596 597  in -- These seqs forces the Id, and hence its IdInfo, -- and hence any inner substitutions final_id seq  simonpj@microsoft.com committed Aug 16, 2006 598  -- pprTrace "Binding" (ppr final_id <+> ppr unfolding) $ simonpj@microsoft.com committed Nov 01, 2006 599  return (addNonRec env final_id new_rhs)  simonpj committed Sep 26, 2001 600  where  simonmar committed Aug 03, 2005 601  unfolding = mkUnfolding (isTopLevel top_lvl) new_rhs  simonpj@microsoft.com committed Oct 04, 2006 602  loop_breaker = isNonRuleLoopBreaker occ_info  simonpj committed Sep 26, 2001 603 604  old_info = idInfo old_bndr occ_info = occInfo old_info  SamB committed Nov 10, 2006 605 \end{code}  simonpj committed Sep 26, 2001 606 607 608   partain committed Jan 08, 1996 609 610 611 612 613 614 %************************************************************************ %* * \subsection[Simplify-simplExpr]{The main function: simplExpr} %* * %************************************************************************  simonpj committed Dec 18, 1998 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 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 653 \begin{code}  simonpj committed Sep 26, 2001 654 simplExpr :: SimplEnv -> CoreExpr -> SimplM CoreExpr  simonpj committed Sep 30, 2004 655 simplExpr env expr = simplExprC env expr (mkBoringStop expr_ty')  simonpj committed Sep 26, 2001 656  where  simonpj committed Dec 24, 2004 657  expr_ty' = substTy env (exprType expr)  simonpj committed Sep 26, 2001 658  -- The type in the Stop continuation, expr_ty', is usually not used  simonpj committed May 18, 1999 659  -- It's only needed when discarding continuations after finding  simonpj committed Jul 14, 1999 660 661  -- a function that returns bottom. -- Hence the lazy substitution  partain committed Jan 08, 1996 662   simonpj committed Dec 18, 1998 663   simonpj committed Sep 26, 2001 664 665 666 simplExprC :: SimplEnv -> CoreExpr -> SimplCont -> SimplM CoreExpr -- Simplify an expression, given a continuation simplExprC env expr cont  simonpj@microsoft.com committed Nov 01, 2006 667 668 669 670 671 672 673 674 675 676 677  = -- pprTrace "simplExprC" (ppr expr $$ppr cont {-$$ ppr (seIdSubst env) -} $$ppr (seFloats env) ) do { (env', expr') <- simplExprF (zapFloats env) expr cont ; -- pprTrace "simplExprC ret" (ppr expr$$ ppr expr')$ -- pprTrace "simplExprC ret3" (ppr (seInScope env')) $-- pprTrace "simplExprC ret4" (ppr (seFloats env'))$ return (wrapFloats env' expr') } -------------------------------------------------- simplExprF :: SimplEnv -> InExpr -> SimplCont -> SimplM (SimplEnv, OutExpr)  simonpj@microsoft.com committed Nov 06, 2006 678 679 680 simplExprF env e cont = -- pprTrace "simplExprF" (ppr e $$ppr cont$$ ppr (seTvSubst env) $$ppr (seIdSubst env) {-$$ ppr (seFloats env) -} ) $simplExprF' env e cont  simonpj@microsoft.com committed Nov 01, 2006 681   simonpj@microsoft.com committed Jan 03, 2007 682 simplExprF' env (Var v) cont = simplVar env v cont  simonpj@microsoft.com committed Nov 01, 2006 683 684 685 686 simplExprF' env (Lit lit) cont = rebuild env (Lit lit) cont simplExprF' env (Note n expr) cont = simplNote env n expr cont simplExprF' env (Cast body co) cont = simplCast env body co cont simplExprF' env (App fun arg) cont = simplExprF env fun$  simonpj@microsoft.com committed Jan 03, 2007 687  ApplyTo NoDup arg env cont  simonpj@microsoft.com committed Nov 01, 2006 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705  simplExprF' env expr@(Lam _ _) cont = simplLam env (map zap bndrs) body cont -- The main issue here is under-saturated lambdas -- (\x1. \x2. e) arg1 -- Here x1 might have "occurs-once" occ-info, because occ-info -- is computed assuming that a group of lambdas is applied -- all at once. If there are too few args, we must zap the -- occ-info. where n_args = countArgs cont n_params = length bndrs (bndrs, body) = collectBinders expr zap | n_args >= n_params = \b -> b | otherwise = \b -> if isTyVar b then b else zapLamIdInfo b -- NB: we count all the args incl type args -- so we must count all the binders (incl type lambdas)  simonm committed Dec 02, 1998 706   simonpj@microsoft.com committed Nov 01, 2006 707 simplExprF' env (Type ty) cont  simonpj committed Sep 26, 2001 708  = ASSERT( contIsRhsOrArg cont )  simonpj@microsoft.com committed Nov 01, 2006 709 710  do { ty' <- simplType env ty ; rebuild env (Type ty') cont }  simonpj committed Mar 08, 2001 711   simonpj@microsoft.com committed Nov 01, 2006 712 simplExprF' env (Case scrut bndr case_ty alts) cont  simonpj committed Sep 26, 2001 713 714 715  | 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 716   simonpj committed Sep 26, 2001 717 718  | otherwise = -- If case-of-case is off, simply simplify the case expression  simonpj committed Mar 24, 2000 719  -- in a vanilla Stop context, and rebuild the result around it  simonpj@microsoft.com committed Nov 01, 2006 720 721  do { case_expr' <- simplExprC env scrut case_cont ; rebuild env case_expr' cont }  simonpj committed Sep 26, 2001 722  where  simonpj committed Sep 30, 2004 723  case_cont = Select NoDup bndr alts env (mkBoringStop case_ty')  simonpj committed Dec 24, 2004 724  case_ty' = substTy env case_ty -- c.f. defn of simplExpr  simonpj committed May 18, 1999 725   simonpj@microsoft.com committed Nov 01, 2006 726 727 728 729 simplExprF' env (Let (Rec pairs) body) cont = do { env <- simplRecBndrs env (map fst pairs) -- NB: bndrs' don't have unfoldings or rules -- We add them as we go down  simonm committed Dec 02, 1998 730   simonpj@microsoft.com committed Nov 01, 2006 731 732  ; env <- simplRecBind env NotTopLevel pairs ; simplExprF env body cont }  simonpj committed May 18, 1999 733   simonpj@microsoft.com committed Nov 01, 2006 734 735 simplExprF' env (Let (NonRec bndr rhs) body) cont = simplNonRecE env bndr (rhs, env) ([], body) cont  simonpj committed May 18, 1999 736 737  ---------------------------------  simonpj committed Sep 26, 2001 738 739 740 simplType :: SimplEnv -> InType -> SimplM OutType -- Kept monadic just so we can do the seqType simplType env ty  simonpj@microsoft.com committed Nov 01, 2006 741 742  = -- pprTrace "simplType" (ppr ty $$ppr (seTvSubst env))  seqType new_ty seq returnSmpl new_ty  simonpj committed Sep 26, 2001 743  where  simonpj committed Dec 24, 2004 744  new_ty = substTy env ty  simonpj committed Mar 08, 2001 745 746 747 \end{code}  simonpj@microsoft.com committed Nov 01, 2006 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 %************************************************************************ %* * \subsection{The main rebuilder} %* * %************************************************************************ \begin{code} rebuild :: SimplEnv -> OutExpr -> SimplCont -> SimplM (SimplEnv, OutExpr) -- At this point the substitution in the SimplEnv should be irrelevant -- only the in-scope set and floats should matter rebuild env expr cont = -- pprTrace "rebuild" (ppr expr$$ ppr cont $$ppr (seFloats env))  case cont of Stop {} -> return (env, expr) CoerceIt co cont -> rebuild env (mkCoerce co expr) cont Select _ bndr alts se cont -> rebuildCase (se setFloats env) expr bndr alts cont StrictArg fun ty info cont -> rebuildCall env (fun App expr) (funResultTy ty) info cont StrictBind b bs body se cont -> do { env' <- simplNonRecX (se setFloats env) b expr ; simplLam env' bs body cont } ApplyTo _ arg se cont -> do { arg' <- simplExpr (se setInScope env) arg ; rebuild env (App expr arg') cont } \end{code}  chak@cse.unsw.edu.au. committed Sep 15, 2006 772 773 774 775 776 777 778 %************************************************************************ %* * \subsection{Lambdas} %* * %************************************************************************ \begin{code}  simonpj@microsoft.com committed Nov 01, 2006 779 780 simplCast :: SimplEnv -> InExpr -> Coercion -> SimplCont -> SimplM (SimplEnv, OutExpr)  chak@cse.unsw.edu.au. committed Sep 15, 2006 781 simplCast env body co cont  simonpj@microsoft.com committed Nov 01, 2006 782 783 784  = do { co' <- simplType env co ; simplExprF env body (addCoerce co' cont) } where  simonpj@microsoft.com committed Jan 03, 2007 785 786  addCoerce co cont = add_coerce co (coercionKind co) cont  simonpj@microsoft.com committed Jan 11, 2007 787 788 789  add_coerce co (s1, k1) cont -- co :: ty~ty | s1 coreEqType k1 = cont -- is a no-op  simonpj@microsoft.com committed Jan 03, 2007 790 791  add_coerce co1 (s1, k2) (CoerceIt co2 cont) | (l1, t1) <- coercionKind co2  chak@cse.unsw.edu.au. committed Sep 15, 2006 792 793 794 795 796 797 798 799 800 801 802 803  -- 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 , s1 coreEqType t1 = cont -- The coerces cancel out | otherwise = CoerceIt (mkTransCoercion co1 co2) cont  simonpj@microsoft.com committed Feb 05, 2007 804 805 806 807 808 809 810 811 812 813 814  add_coerce co (s1s2, t1t2) (ApplyTo dup (Type arg_ty) arg_se cont) -- (f cast g) ty ---> (f ty) cast (g @ ty) -- This implements the PushT rule from the paper | Just (tyvar,_) <- splitForAllTy_maybe s1s2 , not (isCoVar tyvar) = ApplyTo dup (Type ty') (zapSubstEnv env) (addCoerce (mkInstCoercion co ty') cont) where ty' = substTy arg_se arg_ty -- ToDo: the PushC rule is not implemented at all  simonpj@microsoft.com committed Jan 03, 2007 815  add_coerce co (s1s2, t1t2) (ApplyTo dup arg arg_se cont)  simonpj@microsoft.com committed Feb 05, 2007 816  | not (isTypeArg arg) -- This implements the Push rule from the paper  simonpj@microsoft.com committed Jan 03, 2007 817  , isFunTy s1s2 -- t1t2 must be a function type, becuase it's applied  chak@cse.unsw.edu.au. committed Sep 15, 2006 818 819 820 821 822 823 824 825 826 827 828 829  -- co : s1s2 :=: t1t2 -- (coerce (T1->T2) (S1->S2) F) E -- ===> -- coerce T2 S2 (F (coerce S1 T1 E)) -- -- t1t2 must be a function type, T1->T2, because it's applied -- to something 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 -- to make it all consistent. It's a bit messy. -- But it isn't a common case.  simonpj@microsoft.com committed Jan 03, 2007 830 831  -- -- Example of use: Trac #995  simonpj@microsoft.com committed Nov 01, 2006 832  = ApplyTo dup new_arg (zapSubstEnv env) (addCoerce co2 cont)  chak@cse.unsw.edu.au. committed Sep 15, 2006 833 834 835 836 837  where -- we split coercion t1->t2 :=: s1->s2 into t1 :=: s1 and -- t2 :=: s2 with left and right on the curried form: -- (->) t1 t2 :=: (->) s1 s2 [co1, co2] = decomposeCo 2 co  chak@cse.unsw.edu.au. committed Sep 19, 2006 838  new_arg = mkCoerce (mkSymCoercion co1) arg'  simonpj@microsoft.com committed Nov 01, 2006 839 840  arg' = substExpr arg_se arg  simonpj@microsoft.com committed Jan 03, 2007 841  add_coerce co _ cont = CoerceIt co cont  chak@cse.unsw.edu.au. committed Sep 15, 2006 842 843 \end{code}  simonpj@microsoft.com committed Nov 01, 2006 844   simonpj committed Mar 08, 2001 845 846 847 848 849 %************************************************************************ %* * \subsection{Lambdas} %* * %************************************************************************  simonpj committed May 18, 1999 850 851  \begin{code}  simonpj@microsoft.com committed Nov 01, 2006 852 853 854 855 simplLam :: SimplEnv -> [InId] -> InExpr -> SimplCont -> SimplM (SimplEnv, OutExpr) simplLam env [] body cont = simplExprF env body cont  simonpj committed May 18, 1999 856 857  -- Type-beta reduction  simonpj@microsoft.com committed Nov 01, 2006 858 859 860 861 862 simplLam env (bndr:bndrs) body (ApplyTo _ (Type ty_arg) arg_se cont) = ASSERT( isTyVar bndr ) do { tick (BetaReduction bndr) ; ty_arg' <- simplType (arg_se setInScope env) ty_arg ; simplLam (extendTvSubst env bndr ty_arg') bndrs body cont }  simonpj committed May 18, 1999 863 864  -- Ordinary beta reduction  simonpj@microsoft.com committed Nov 01, 2006 865 866 867 simplLam env (bndr:bndrs) body (ApplyTo _ arg arg_se cont) = do { tick (BetaReduction bndr) ; simplNonRecE env bndr (arg, arg_se) (bndrs, body) cont }  simonpj committed May 18, 1999 868   simonpj committed Sep 26, 2001 869  -- Not enough args, so there are real lambdas left to put in the result  simonpj@microsoft.com committed Nov 01, 2006 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 simplLam env bndrs body cont = do { (env, bndrs') <- simplLamBndrs env bndrs ; body' <- simplExpr env body ; new_lam <- mkLam bndrs' body' ; rebuild env new_lam cont } ------------------ simplNonRecE :: SimplEnv -> InId -- The binder -> (InExpr, SimplEnv) -- Rhs of binding (or arg of lambda) -> ([InId], InExpr) -- Body of the let/lambda -- \xs.e -> SimplCont -> SimplM (SimplEnv, OutExpr) -- simplNonRecE is used for -- * non-top-level non-recursive lets in expressions -- * beta reduction -- -- It deals with strict bindings, via the StrictBind continuation, -- which may abort the whole process -- -- The "body" of the binding comes as a pair of ([InId],InExpr) -- representing a lambda; so we recurse back to simplLam -- Why? Because of the binder-occ-info-zapping done before -- the call to simplLam in simplExprF (Lam ...) simplNonRecE env bndr (rhs, rhs_se) (bndrs, body) cont | preInlineUnconditionally env NotTopLevel bndr rhs = do { tick (PreInlineUnconditionally bndr) ; simplLam (extendIdSubst env bndr (mkContEx rhs_se rhs)) bndrs body cont }  simonpj@microsoft.com committed Jan 31, 2007 902  | isStrictId bndr  simonpj@microsoft.com committed Nov 01, 2006 903 904 905 906  = do { simplExprF (rhs_se setFloats env) rhs (StrictBind bndr bndrs body env cont) } | otherwise  simonpj@microsoft.com committed Oct 29, 2007 907 908 909 910  = do { (env1, bndr1) <- simplNonRecBndr env bndr ; let (env2, bndr2) = addLetIdInfo env1 bndr bndr1 ; env3 <- simplLazyBind env2 NotTopLevel NonRecursive bndr bndr2 rhs rhs_se ; simplLam env3 bndrs body cont }  partain committed Jan 08, 1996 911 912 \end{code}  simonpj committed May 18, 1999 913   simonpj committed Mar 08, 2001 914 915 916 917 918 919 %************************************************************************ %* * \subsection{Notes} %* * %************************************************************************  sof committed May 18, 1997 920 \begin{code}  simonpj@microsoft.com committed Nov 01, 2006 921 922 -- Hack alert: we only distinguish subsumed cost centre stacks for the -- purposes of inlining. All other CCCSs are mapped to currentCCS.  simonpj committed Sep 26, 2001 923 simplNote env (SCC cc) e cont  simonpj@microsoft.com committed Nov 01, 2006 924 925  = do { e' <- simplExpr (setEnclosingCC env currentCCS) e ; rebuild env (mkSCC cc e') cont }  simonpj committed Sep 26, 2001 926 927 928  -- See notes with SimplMonad.inlineMode simplNote env InlineMe e cont  929  | Just (inside, outside) <- splitInlineCont cont -- Boring boring continuation; see notes above  simonpj@microsoft.com committed Nov 01, 2006 930  = do { -- Don't inline inside an INLINE expression  931 932  e' <- simplExprC (setMode inlineMode env) e inside ; rebuild env (mkInlineMe e') outside }  simonpj committed Mar 08, 2001 933 934 935 936  | 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 937  = simplExprF env e cont  simonpj committed Feb 20, 2003 938 939  simplNote env (CoreNote s) e cont  andy@galois.com committed Nov 29, 2006 940 941  = simplExpr env e thenSmpl \ e' -> rebuild env (Note (CoreNote s) e') cont  partain committed Jan 08, 1996 942 943 944 \end{code}  simonm committed Dec 02, 1998 945 946 %************************************************************************ %* *  simonpj committed Sep 26, 2001 947 \subsection{Dealing with calls}  simonm committed Dec 02, 1998 948 949 %* * %************************************************************************  partain committed Jan 08, 1996 950   simonpj committed May 18, 1999 951 \begin{code}  simonpj committed Sep 26, 2001 952 simplVar env var cont  simonpj committed Dec 24, 2004 953 954 955  = case substId env var of DoneEx e -> simplExprF (zapSubstEnv env) e cont ContEx tvs ids e -> simplExprF (setSubstEnv env tvs ids) e cont  simonpj@microsoft.com committed Oct 05, 2006 956  DoneId var1 -> completeCall (zapSubstEnv env) var1 cont  simonpj committed Sep 30, 2004 957  -- Note [zapSubstEnv]  simonpj committed Jun 22, 1999 958 959 960 961 962 963 964 965  -- 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 966   simonpj committed Mar 23, 2000 967 ---------------------------------------------------------  simonpj committed Oct 01, 2001 968 -- Dealing with a call site  simonpj committed Mar 23, 2000 969   simonpj@microsoft.com committed Oct 05, 2006 970 completeCall env var cont  simonpj@microsoft.com committed Nov 01, 2006 971 972 973 974 975 976 977 978 979 980 981 982  = do { dflags <- getDOptsSmpl ; let (args,call_cont) = contArgs cont -- The args are OutExprs, obtained by *lazily* substituting -- in the args found in cont. These args are only examined -- to limited depth (unless a rule fires). But we must do -- the substitution; rule matching on un-simplified args would -- be bogus ------------- First try rules ---------------- -- Do this before trying inlining. Some functions have -- rules *and* are strict; in this case, we don't want to -- inline the wrapper of the non-specialised thing; better  simonpj committed Sep 17, 1999 983  -- to call the specialised thing instead.  simonpj@microsoft.com committed Nov 01, 2006 984  --  simonpj committed Oct 01, 2001 985 986 987  -- 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 988  --  simonpj@microsoft.com committed Oct 29, 2007 989 990  -- Note [Rules for recursive functions] -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  simonpj committed Jan 04, 2001 991 992 993 994 995 996 997 998 999 1000 1001  -- 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@microsoft.com committed May 23, 2007 1002  ; rules <- getRules  simonpj@microsoft.com committed Nov 01, 2006 1003  ; let in_scope = getInScope env  simonpj@microsoft.com committed May 04, 2007 1004  maybe_rule = case activeRule dflags env of  simonpj@microsoft.com committed Nov 01, 2006 1005 1006 1007 1008 1009 1010  Nothing -> Nothing -- No rules apply Just act_fn -> lookupRule act_fn in_scope rules var args ; case maybe_rule of { Just (rule, rule_rhs) -> tick (RuleFired (ru_name rule)) thenSmpl_  simonpj@microsoft.com committed Jan 11, 2007 1011  (if dopt Opt_D_dump_rule_firings dflags then  simonpj committed Jan 11, 2001 1012  pprTrace "Rule fired" (vcat [  simonpj@microsoft.com committed Nov 01, 2006 1013  text "Rule:" <+> ftext (ru_name rule),  simonpj committed Oct 01, 2001 1014  text "Before:" <+> ppr var <+> sep (map pprParendExpr args),  simonpj committed Nov 19, 2001 1015 1016  text "After: " <+> pprCoreExpr rule_rhs, text "Cont: " <+> ppr call_cont])  simonpj committed Jan 11, 2001 1017 1018  else id)   simonpj@microsoft.com committed Nov 01, 2006 1019 1020  simplExprF env rule_rhs (dropArgs (ruleArity rule) cont) -- The ruleArity says how many args the rule consumed  simonpj committed Sep 17, 1999 1021   simonpj@microsoft.com committed Nov 01, 2006 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031  ; Nothing -> do -- No rules ------------- Next try inlining ---------------- { let arg_infos = [interestingArg arg | arg <- args, isValArg arg] n_val_args = length arg_infos interesting_cont = interestingCallContext (notNull args) (notNull arg_infos) call_cont active_inline = activeInline env var maybe_inline = callSiteInline dflags active_inline  simonpj committed Oct 01, 2001 1032  var arg_infos interesting_cont  simonpj@microsoft.com committed Nov 01, 2006 1033 1034 1035 1036  ; case maybe_inline of { Just unfolding -- There is an inlining! -> do { tick (UnfoldingDone var) ; (if dopt Opt_D_dump_inlinings dflags then  simonpj@microsoft.com committed Oct 16, 2007 1037  pprTrace ("Inlining done" ++ showSDoc (ppr var)) (vcat [  simonpj@microsoft.com committed Nov 01, 2006 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052  text "Before:" <+> ppr var <+> sep (map pprParendExpr args), text "Inlined fn: " <+> nest 2 (ppr unfolding), text "Cont: " <+> ppr call_cont]) else id) simplExprF env unfolding cont } ; Nothing -> -- No inlining! ------------- No inlining! ---------------- -- Next, look for rules or specialisations that match -- rebuildCall env (Var var) (idType var) (mkArgInfo var n_val_args call_cont) cont }}}}  simonpj committed Dec 22, 1998 1053   simonpj@microsoft.com committed Nov 01, 2006 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 rebuildCall :: SimplEnv -> OutExpr -> OutType -- Function and its type -> (Bool, [Bool]) -- See SimplUtils.mkArgInfo -> SimplCont -> SimplM (SimplEnv, OutExpr) rebuildCall env fun fun_ty (has_rules, []) cont -- When we run out of strictness args, it means -- that the call is definitely bottom; see SimplUtils.mkArgInfo -- Then we want to discard the entire strict continuation. E.g. -- * case (error "hello") of { ... } -- * (error "Hello") arg -- * f (error "Hello") where f is strict -- etc -- Then, especially in the first of these cases, we'd like to discard -- the continuation, leaving just the bottoming expression. But the -- type might not be right, so we may have to add a coerce.  simonpj@microsoft.com committed May 23, 2007 1070  | not (contIsTrivial cont) -- Only do this if there is a non-trivial  simonpj@microsoft.com committed Nov 01, 2006 1071 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096  = return (env, mk_coerce fun) -- contination to discard, else we do it where -- again and again! cont_ty = contResultType cont co = mkUnsafeCoercion fun_ty cont_ty mk_coerce expr | cont_ty coreEqType fun_ty = fun | otherwise = mkCoerce co fun rebuildCall env fun fun_ty info (ApplyTo _ (Type arg_ty) se cont) = do { ty' <- simplType (se setInScope env) arg_ty ; rebuildCall env (fun App Type ty') (applyTy fun_ty ty') info cont } rebuildCall env fun fun_ty (has_rules, str:strs) (ApplyTo _ arg arg_se cont) | str || isStrictType arg_ty -- Strict argument = -- pprTrace "Strict Arg" (ppr arg$$ ppr (seIdSubst env)  ppr (seInScope env)) \$ simplExprF (arg_se setFloats env) arg (StrictArg fun fun_ty (has_rules, strs) cont) -- Note [Shadowing] | 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. = do { arg' <- simplExprC (arg_se setInScope env) arg (mkLazyArgStop arg_ty has_rules) ; rebuildCall env (fun App arg') res_ty (has_rules, strs) cont }  simonpj committed Sep 26, 2001 1097  where  simonpj@microsoft.com committed Nov 01, 2006 1098  (arg_ty, res_ty) = splitFunTy fun_ty  simonpj committed Dec 22, 1998 1099   simonpj@microsoft.com committed Nov 01, 2006 1100 1101 rebuildCall env fun fun_ty info cont = rebuild env fun cont  simonpj committed Sep 26, 2001 1102 \end{code}  simonpj committed Dec 18, 1998 1103   simonpj@microsoft.com committed Nov 01, 2006 1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 Note [Shadowing] ~~~~~~~~~~~~~~~~ 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 committed Dec 22, 1998 1127   simonpj committed Sep 26, 2001 1128 1129 %************************************************************************ %* *  simonpj@microsoft.com committed Nov 01, 2006 1130  Rebuilding a cse expression  simonpj committed Sep 26, 2001 1131 1132 %* * %************************************************************************  simonpj committed Dec 22, 1998 1133   simonpj committed Dec 18, 1998 1134 1135 1136 Blob of helper functions for the "case-of-something-else" situation. \begin{code}  simonpj committed Jan 04, 2000 1137 ---------------------------------------------------------  simonpj committed Mar 23, 2000 1138 -- Eliminate the case if possible  simonpj committed Jan 04, 2000 1139   simonpj committed Sep 26, 2001 1140 1141 1142 rebuildCase :: SimplEnv -> OutExpr -- Scrutinee -> InId -- Case binder  simonpj committed Dec 22, 2004 1143  -> [InAlt] -- Alternatives (inceasing order)  simonpj committed Sep 26, 2001 1144  -> SimplCont  simonpj@microsoft.com committed Nov 01, 2006 1145  -> SimplM (SimplEnv, OutExpr)  simonpj committed Mar 23, 2000 1146   simonpj@microsoft.com committed Feb 09, 2007 1147 1148 1149 1150 -------------------------------------------------- -- 1. Eliminate the case if there's a known constructor --------------------------------------------------  simonpj committed Sep 26, 2001 1151 1152 1153 1154 rebuildCase env scrut case_bndr alts cont | Just (con,args) <- exprIsConApp_maybe scrut -- Works when the scrutinee is a variable with a known unfolding -- as well as when it's an explicit constructor application  simonpj@microsoft.com committed Aug 16, 2006 1155  = knownCon env scrut (DataAlt con) args case_bndr alts cont  simonpj committed Jan 04, 2000 1156   simonpj committed Sep 26, 2001 1157 1158  | Lit lit <- scrut -- No need for same treatment as constructors -- because literals are inlined more vigorously  simonpj@microsoft.com committed Aug 16, 2006 1159  = knownCon env scrut (LitAlt lit) [] case_bndr alts cont  simonpj committed Mar 23, 2000 1160   simonpj@microsoft.com committed Feb 09, 2007 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184 1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200  -------------------------------------------------- -- 2. Eliminate the case if scrutinee is evaluated -------------------------------------------------- rebuildCase env scrut case_bndr [(con,bndrs,rhs)] cont -- See if we can get rid of the case altogether -- See the extensive notes on case-elimination above -- mkCase made sure that if all the alternatives are equal, -- then there is now only one (DEFAULT) rhs | all isDeadBinder bndrs -- bndrs are [InId] -- Check that the scrutinee can be let-bound instead of case-bound , exprOkForSpeculation scrut -- OK not to evaluate it -- This includes things like (==# a# b#)::Bool -- so that we simplify -- case ==# a# b# of { True -> x; False -> x } -- to just -- x -- This particular example shows up in default methods for -- comparision operations (e.g. in (>=) for Int.Int32) || exprIsHNF scrut -- It's already evaluated || var_demanded_later scrut -- It'll be demanded later -- || not opt_SimplPedanticBottoms) -- Or we don't care! -- We used to allow improving termination by discarding cases, unless -fpedantic-bottoms was on, -- but that breaks badly for the dataToTag# primop, which relies on a case to evaluate -- its argument: case x of { y -> dataToTag# y } -- Here we must *not* discard the case, because dataToTag# just fetches the tag from -- the info pointer. So we'll be pedantic all the time, and see if that gives any -- other problems -- Also we don't want to discard 'seq's = do { tick (CaseElim case_bndr) ; env <- simplNonRecX env case_bndr scrut ; simplExprF env rhs cont } where -- The case binder is going to be evaluated later, -- and the scrutinee is a simple variable var_demanded_later (Var v) = isStrictDmd (idNewDemandInfo case_bndr)  andy@galois.com committed May 01, 2007 1201 1202 1203  && not (isTickBoxOp v) -- ugly hack; covering this case is what -- exprOkForSpeculation was intended for.  simonpj@microsoft.com committed Feb 09, 2007 1204 1205 1206 1207 1208 1209 1210 1211  var_demanded_later other = False -------------------------------------------------- -- 3. Catch-all case -------------------------------------------------- rebuildCase env scrut case_bndr alts cont  simonpj@microsoft.com committed Nov 01, 2006 1212 1213 1214  = do { -- Prepare the continuation; -- The new subst_env is in place (env, dup_cont, nodup_cont) <- prepareCaseCont env alts cont  simonpj committed Sep 30, 2004 1215   simonpj@microsoft.com committed Nov 01, 2006 1216  -- Simplify the alternatives  simonpj@microsoft.com committed May 23, 2007 1217  ; (scrut', case_bndr', alts') <- simplAlts env scrut case_bndr alts dup_cont  simonpj@microsoft.com committed Nov 01, 2006 1218  ; let res_ty' = contResultType dup_cont  simonpj@microsoft.com committed May 23, 2007 1219  ; case_expr <- mkCase scrut' case_bndr' res_ty' alts'  sof committed Sep 04, 1997 1220   simonpj committed Sep 26, 2001 1221 1222  -- Notice that rebuildDone returns the in-scope set from env, not alt_env -- The case binder *not* scope over the whole returned case-expression  simonpj@microsoft.com committed Nov 01, 2006 1223  ; rebuild env case_expr nodup_cont }  simonm committed Dec 02, 1998 1224 \end{code}  partain committed Jan 08, 1996 1225   simonpj committed Jun 18, 2000 1226 1227 1228 1229 1230 simplCaseBinder checks whether the scrutinee is a variable, v. If so, try to eliminate uses of v in the RHSs in favour of case_bndr; that way, there's a chance that v will now only be used once, and hence inlined.  simonpj@microsoft.com committed Oct 04, 2006 1231 1232 Note [no-case-of-case] ~~~~~~~~~~~~~~~~~~~~~~  simonpj committed Jun 18, 2000 1233 1234 1235 There is a time we *don't* want to do that, namely when -fno-case-of-case is on. This happens in the first simplifier pass, and enhances full laziness. Here's the bad case:  simonpj committed Mar 23, 2000 1236 1237 1238 1239 1240  f = \ y -> ...(case x of I# v -> ...(case x of ...) ... ) If we eliminate the inner case, we trap it inside the I# v -> arm, which might prevent some full laziness happening. I've seen this in action in spectral/cichelli/Prog.hs: [(m,n) | m <- [1..max], n <- [1..max]]  simonpj committed Sep 26, 2001 1241 1242 Hence the check for NoCaseOfCase.  simonpj@microsoft.com committed Jan 11, 2007 1243 1244 1245 1246 Note [Suppressing the case binder-swap] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ There is another situation when it might make sense to suppress the case-expression binde-swap. If we have  simonpj committed Sep 26, 2001 1247 1248 1249 1250 1251 1252 1253 1254 1255  case x of w1 { DEFAULT -> case x of w2 { A -> e1; B -> e2 } ...other cases .... } We'll perform the binder-swap for the outer case, giving case x of w1 { DEFAULT -> case w1 of w2 { A -> e1; B -> e2 } ...other cases .... }  simonpj committed Dec 14, 2001 1256 1257 1258 1259 But there is no point in doing it for the inner case, because w1 can't be inlined anyway. Furthermore, doing the case-swapping involves zapping w2's occurrence info (see paragraphs that follow), and that forces us to bind w2 when doing case merging. So we get  simonpj committed Sep 26, 2001 1260 1261 1262 1263 1264 1265 1266 1267 1268 1269 1270 1271  case x of w1 { A -> let w2 = w1 in e1 B -> let w2 = w1 in e2 ...other cases .... } This is plain silly in the common case where w2 is dead. Even so, I can't see a good way to implement this idea. I tried not doing the binder-swap if the scrutinee was already evaluated but that failed big-time: data T = MkT !Int  simonpj committed Mar 23, 2000 1272   simonpj committed Sep 26, 2001 1273 1274 1275  case v of w { MkT x -> case x of x1 { I# y1 -> case x of x2 { I# y2 -> ...  simonpj committed Mar 23, 2000 1276   simonpj committed Sep 26, 2001 1277 1278 1279 1280 1281 Notice that because MkT is strict, x is marked "evaluated". But to eliminate the last case, we must either make sure that x (as well as x1) has unfolding MkT y1. THe straightforward thing to do is to do the binder-swap. So this whole note is a no-op.  simonpj@microsoft.com committed Oct 04, 2006 1282 1283 Note [zapOccInfo] ~~~~~~~~~~~~~~~~~  simonpj committed Sep 26, 2001 1284 1285 1286 1287 If we replace the scrutinee, v, by tbe case binder, then we have to nuke any occurrence info (eg IAmDead) in the case binder, because the case-binder now effectively occurs whenever v does. AND we have to do the same for the pattern-bound variables! Example:  simonpj committed Sep 26, 1997 1288   simonm committed Dec 02, 1998 1289  (case x of { (a,b) -> a }) (case x of { (p,q) -> q })  simonpj committed Sep 26, 1997 1290   simonm committed Dec 02, 1998 1291 1292 Here, b and p are dead. But when we move the argment inside the first case RHS, and eliminate the second case, we get  simonpj committed Sep 26, 1997 1293