1 {-# LANGUAGE PackageImports #-}
3 -- Functions to bring a Core expression in normal form. This module provides a
4 -- top level function "normalize", and defines the actual transformation passes that
7 module CLasH.Normalize (getNormalized, normalizeExpr, splitNormalized) where
11 import qualified Maybe
13 import qualified "transformers" Control.Monad.Trans as Trans
14 import qualified Control.Monad as Monad
15 import qualified Control.Monad.Trans.Writer as Writer
16 import qualified Data.Map as Map
17 import qualified Data.Monoid as Monoid
22 import qualified UniqSupply
23 import qualified CoreUtils
25 import qualified TcType
28 import qualified VarSet
29 import qualified NameSet
30 import qualified CoreFVs
31 import qualified CoreUtils
32 import qualified MkCore
33 import qualified HscTypes
34 import Outputable ( showSDoc, ppr, nest )
37 import CLasH.Normalize.NormalizeTypes
38 import CLasH.Translator.TranslatorTypes
39 import CLasH.Normalize.NormalizeTools
40 import CLasH.VHDL.VHDLTypes
41 import qualified CLasH.Utils as Utils
42 import CLasH.Utils.Core.CoreTools
43 import CLasH.Utils.Core.BinderTools
44 import CLasH.Utils.Pretty
46 --------------------------------
47 -- Start of transformations
48 --------------------------------
50 --------------------------------
52 --------------------------------
53 eta, etatop :: Transform
54 eta expr | is_fun expr && not (is_lam expr) = do
55 let arg_ty = (fst . Type.splitFunTy . CoreUtils.exprType) expr
56 id <- Trans.lift $ mkInternalVar "param" arg_ty
57 change (Lam id (App expr (Var id)))
58 -- Leave all other expressions unchanged
60 etatop = notappargs ("eta", eta)
62 --------------------------------
64 --------------------------------
65 beta, betatop :: Transform
66 -- Substitute arg for x in expr
67 beta (App (Lam x expr) arg) = change $ substitute [(x, arg)] expr
68 -- Propagate the application into the let
69 beta (App (Let binds expr) arg) = change $ Let binds (App expr arg)
70 -- Propagate the application into each of the alternatives
71 beta (App (Case scrut b ty alts) arg) = change $ Case scrut b ty' alts'
73 alts' = map (\(con, bndrs, expr) -> (con, bndrs, (App expr arg))) alts
74 ty' = CoreUtils.applyTypeToArg ty arg
75 -- Leave all other expressions unchanged
76 beta expr = return expr
77 -- Perform this transform everywhere
78 betatop = everywhere ("beta", beta)
80 --------------------------------
82 --------------------------------
83 -- Try to move casts as much downward as possible.
84 castprop, castproptop :: Transform
85 castprop (Cast (Let binds expr) ty) = change $ Let binds (Cast expr ty)
86 castprop expr@(Cast (Case scrut b _ alts) ty) = change (Case scrut b ty alts')
88 alts' = map (\(con, bndrs, expr) -> (con, bndrs, (Cast expr ty))) alts
89 -- Leave all other expressions unchanged
90 castprop expr = return expr
91 -- Perform this transform everywhere
92 castproptop = everywhere ("castprop", castprop)
94 --------------------------------
95 -- Cast simplification. Mostly useful for state packing and unpacking, but
96 -- perhaps for others as well.
97 --------------------------------
98 castsimpl, castsimpltop :: Transform
99 castsimpl expr@(Cast val ty) = do
100 -- Don't extract values that are already simpl
101 local_var <- Trans.lift $ is_local_var val
102 -- Don't extract values that are not representable, to prevent loops with
105 if (not local_var) && repr
107 -- Generate a binder for the expression
108 id <- Trans.lift $ mkBinderFor val "castval"
109 -- Extract the expression
110 change $ Let (NonRec id val) (Cast (Var id) ty)
113 -- Leave all other expressions unchanged
114 castsimpl expr = return expr
115 -- Perform this transform everywhere
116 castsimpltop = everywhere ("castsimpl", castsimpl)
118 --------------------------------
119 -- let derecursification
120 --------------------------------
121 letderec, letderectop :: Transform
122 letderec expr@(Let (Rec binds) res) = case liftable of
123 -- Nothing is liftable, just return
125 -- Something can be lifted, generate a new let expression
126 _ -> change $ MkCore.mkCoreLets newbinds res
128 -- Make a list of all the binders bound in this recursive let
129 bndrs = map fst binds
130 -- See which bindings are liftable
131 (liftable, nonliftable) = List.partition canlift binds
132 -- Create nonrec bindings for each liftable binding and a single recursive
133 -- binding for all others
134 newbinds = (map (uncurry NonRec) liftable) ++ [Rec nonliftable]
135 -- Any expression that does not use any of the binders in this recursive let
136 -- can be lifted into a nonrec let. It can't use its own binder either,
137 -- since that would mean the binding is self-recursive and should be in a
138 -- single bind recursive let.
139 canlift (bndr, e) = not $ expr_uses_binders bndrs e
140 -- Leave all other expressions unchanged
141 letderec expr = return expr
142 -- Perform this transform everywhere
143 letderectop = everywhere ("letderec", letderec)
145 --------------------------------
146 -- let simplification
147 --------------------------------
148 letsimpl, letsimpltop :: Transform
149 -- Put the "in ..." value of a let in its own binding, but not when the
150 -- expression is already a local variable, or not representable (to prevent loops with inlinenonrep).
151 letsimpl expr@(Let binds res) = do
153 local_var <- Trans.lift $ is_local_var res
154 if not local_var && repr
156 -- If the result is not a local var already (to prevent loops with
157 -- ourselves), extract it.
158 id <- Trans.lift $ mkBinderFor res "foo"
159 change $ Let binds (Let (NonRec id res) (Var id))
161 -- If the result is already a local var, don't extract it.
164 -- Leave all other expressions unchanged
165 letsimpl expr = return expr
166 -- Perform this transform everywhere
167 letsimpltop = everywhere ("letsimpl", letsimpl)
169 --------------------------------
171 --------------------------------
172 -- Takes a let that binds another let, and turns that into two nested lets.
174 -- let b = (let b' = expr' in res') in res
176 -- let b' = expr' in (let b = res' in res)
177 letflat, letflattop :: Transform
178 letflat (Let (NonRec b (Let (NonRec b' expr') res')) res) =
179 change $ Let (NonRec b' expr') (Let (NonRec b res') res)
180 -- Leave all other expressions unchanged
181 letflat expr = return expr
182 -- Perform this transform everywhere
183 letflattop = everywhere ("letflat", letflat)
185 --------------------------------
186 -- Simple let binding removal
187 --------------------------------
188 -- Remove a = b bindings from let expressions everywhere
189 letremovetop :: Transform
190 letremovetop = everywhere ("letremove", inlinebind (\(b, e) -> Trans.lift $ is_local_var e))
192 --------------------------------
193 -- Unused let binding removal
194 --------------------------------
195 letremoveunused, letremoveunusedtop :: Transform
196 letremoveunused expr@(Let (Rec binds) res) = do
197 -- Filter out all unused binds.
198 let binds' = filter dobind binds
199 -- Only set the changed flag if binds got removed
200 changeif (length binds' /= length binds) (Let (Rec binds') res)
202 bound_exprs = map snd binds
203 -- For each bind check if the bind is used by res or any of the bound
205 dobind (bndr, _) = any (expr_uses_binders [bndr]) (res:bound_exprs)
206 -- Leave all other expressions unchanged
207 letremoveunused expr = return expr
208 letremoveunusedtop = everywhere ("letremoveunused", letremoveunused)
210 --------------------------------
211 -- Identical let binding merging
212 --------------------------------
213 -- Merge two bindings in a let if they are identical
214 -- TODO: We would very much like to use GHC's CSE module for this, but that
215 -- doesn't track if something changed or not, so we can't use it properly.
216 letmerge, letmergetop :: Transform
217 letmerge expr@(Let (Rec binds) res) = do
218 binds' <- domerge binds
219 return (Let (Rec binds') res)
221 domerge :: [(CoreBndr, CoreExpr)] -> TransformMonad [(CoreBndr, CoreExpr)]
222 domerge [] = return []
224 es' <- mapM (mergebinds e) es
228 -- Uses the second bind to simplify the second bind, if applicable.
229 mergebinds :: (CoreBndr, CoreExpr) -> (CoreBndr, CoreExpr) -> TransformMonad (CoreBndr, CoreExpr)
230 mergebinds (b1, e1) (b2, e2)
231 -- Identical expressions? Replace the second binding with a reference to
233 | CoreUtils.cheapEqExpr e1 e2 = change $ (b2, Var b1)
234 -- Different expressions? Don't change
235 | otherwise = return (b2, e2)
236 -- Leave all other expressions unchanged
237 letmerge expr = return expr
238 letmergetop = everywhere ("letmerge", letmerge)
240 --------------------------------
242 --------------------------------
243 -- Remove a = B bindings, with B :: a -> b, or B :: forall x . T, from let
244 -- expressions everywhere. This means that any value that still needs to be
245 -- applied to something else (polymorphic values need to be applied to a
246 -- Type) will be inlined, and will eventually be applied to all their
249 -- This is a tricky function, which is prone to create loops in the
250 -- transformations. To fix this, we make sure that no transformation will
251 -- create a new let binding with a function type. These other transformations
252 -- will just not work on those function-typed values at first, but the other
253 -- transformations (in particular β-reduction) should make sure that the type
254 -- of those values eventually becomes primitive.
255 inlinenonreptop :: Transform
256 inlinenonreptop = everywhere ("inlinenonrep", inlinebind ((Monad.liftM not) . isRepr . snd))
258 --------------------------------
259 -- Scrutinee simplification
260 --------------------------------
261 scrutsimpl,scrutsimpltop :: Transform
262 -- Don't touch scrutinees that are already simple
263 scrutsimpl expr@(Case (Var _) _ _ _) = return expr
264 -- Replace all other cases with a let that binds the scrutinee and a new
265 -- simple scrutinee, but only when the scrutinee is representable (to prevent
266 -- loops with inlinenonrep, though I don't think a non-representable scrutinee
267 -- will be supported anyway...)
268 scrutsimpl expr@(Case scrut b ty alts) = do
272 id <- Trans.lift $ mkBinderFor scrut "scrut"
273 change $ Let (NonRec id scrut) (Case (Var id) b ty alts)
276 -- Leave all other expressions unchanged
277 scrutsimpl expr = return expr
278 -- Perform this transform everywhere
279 scrutsimpltop = everywhere ("scrutsimpl", scrutsimpl)
281 --------------------------------
282 -- Case binder wildening
283 --------------------------------
284 casesimpl, casesimpltop :: Transform
285 -- This is already a selector case (or, if x does not appear in bndrs, a very
286 -- simple case statement that will be removed by caseremove below). Just leave
288 casesimpl expr@(Case scrut b ty [(con, bndrs, Var x)]) = return expr
289 -- Make sure that all case alternatives have only wild binders and simple
291 -- This is done by creating a new let binding for each non-wild binder, which
292 -- is bound to a new simple selector case statement and for each complex
293 -- expression. We do this only for representable types, to prevent loops with
295 casesimpl expr@(Case scrut b ty alts) = do
296 (bindingss, alts') <- (Monad.liftM unzip) $ mapM doalt alts
297 let bindings = concat bindingss
298 -- Replace the case with a let with bindings and a case
299 let newlet = (Let (Rec bindings) (Case scrut b ty alts'))
300 -- If there are no non-wild binders, or this case is already a simple
301 -- selector (i.e., a single alt with exactly one binding), already a simple
302 -- selector altan no bindings (i.e., no wild binders in the original case),
303 -- don't change anything, otherwise, replace the case.
304 if null bindings then return expr else change newlet
306 -- Generate a single wild binder, since they are all the same
307 wild = MkCore.mkWildBinder
308 -- Wilden the binders of one alt, producing a list of bindings as a
310 doalt :: CoreAlt -> TransformMonad ([(CoreBndr, CoreExpr)], CoreAlt)
311 doalt (con, bndrs, expr) = do
312 -- Make each binder wild, if possible
313 bndrs_res <- Monad.zipWithM dobndr bndrs [0..]
314 let (newbndrs, bindings_maybe) = unzip bndrs_res
315 -- Extract a complex expression, if possible. For this we check if any of
316 -- the new list of bndrs are used by expr. We can't use free_vars here,
317 -- since that looks at the old bndrs.
318 let uses_bndrs = not $ VarSet.isEmptyVarSet $ CoreFVs.exprSomeFreeVars (`elem` newbndrs) $ expr
319 (exprbinding_maybe, expr') <- doexpr expr uses_bndrs
320 -- Create a new alternative
321 let newalt = (con, newbndrs, expr')
322 let bindings = Maybe.catMaybes (exprbinding_maybe : bindings_maybe)
323 return (bindings, newalt)
325 -- Make wild alternatives for each binder
326 wildbndrs = map (\bndr -> MkCore.mkWildBinder (Id.idType bndr)) bndrs
327 -- A set of all the binders that are used by the expression
328 free_vars = CoreFVs.exprSomeFreeVars (`elem` bndrs) expr
329 -- Look at the ith binder in the case alternative. Return a new binder
330 -- for it (either the same one, or a wild one) and optionally a let
331 -- binding containing a case expression.
332 dobndr :: CoreBndr -> Int -> TransformMonad (CoreBndr, Maybe (CoreBndr, CoreExpr))
334 repr <- isRepr (Var b)
335 -- Is b wild (e.g., not a free var of expr. Since b is only in scope
336 -- in expr, this means that b is unused if expr does not use it.)
337 let wild = not (VarSet.elemVarSet b free_vars)
338 -- Create a new binding for any representable binder that is not
339 -- already wild and is representable (to prevent loops with
341 if (not wild) && repr
343 -- Create on new binder that will actually capture a value in this
344 -- case statement, and return it.
345 let bty = (Id.idType b)
346 id <- Trans.lift $ mkInternalVar "sel" bty
347 let binders = take i wildbndrs ++ [id] ++ drop (i+1) wildbndrs
348 let caseexpr = Case scrut b bty [(con, binders, Var id)]
349 return (wildbndrs!!i, Just (b, caseexpr))
351 -- Just leave the original binder in place, and don't generate an
352 -- extra selector case.
354 -- Process the expression of a case alternative. Accepts an expression
355 -- and whether this expression uses any of the binders in the
356 -- alternative. Returns an optional new binding and a new expression.
357 doexpr :: CoreExpr -> Bool -> TransformMonad (Maybe (CoreBndr, CoreExpr), CoreExpr)
358 doexpr expr uses_bndrs = do
359 local_var <- Trans.lift $ is_local_var expr
361 -- Extract any expressions that do not use any binders from this
362 -- alternative, is not a local var already and is representable (to
363 -- prevent loops with inlinenonrep).
364 if (not uses_bndrs) && (not local_var) && repr
366 id <- Trans.lift $ mkBinderFor expr "caseval"
367 -- We don't flag a change here, since casevalsimpl will do that above
368 -- based on Just we return here.
369 return $ (Just (id, expr), Var id)
371 -- Don't simplify anything else
372 return (Nothing, expr)
373 -- Leave all other expressions unchanged
374 casesimpl expr = return expr
375 -- Perform this transform everywhere
376 casesimpltop = everywhere ("casesimpl", casesimpl)
378 --------------------------------
380 --------------------------------
381 -- Remove case statements that have only a single alternative and only wild
383 caseremove, caseremovetop :: Transform
384 -- Replace a useless case by the value of its single alternative
385 caseremove (Case scrut b ty [(con, bndrs, expr)]) | not usesvars = change expr
386 -- Find if any of the binders are used by expr
387 where usesvars = (not . VarSet.isEmptyVarSet . (CoreFVs.exprSomeFreeVars (`elem` bndrs))) expr
388 -- Leave all other expressions unchanged
389 caseremove expr = return expr
390 -- Perform this transform everywhere
391 caseremovetop = everywhere ("caseremove", caseremove)
393 --------------------------------
394 -- Argument extraction
395 --------------------------------
396 -- Make sure that all arguments of a representable type are simple variables.
397 appsimpl, appsimpltop :: Transform
398 -- Simplify all representable arguments. Do this by introducing a new Let
399 -- that binds the argument and passing the new binder in the application.
400 appsimpl expr@(App f arg) = do
401 -- Check runtime representability
403 local_var <- Trans.lift $ is_local_var arg
404 if repr && not local_var
405 then do -- Extract representable arguments
406 id <- Trans.lift $ mkBinderFor arg "arg"
407 change $ Let (NonRec id arg) (App f (Var id))
408 else -- Leave non-representable arguments unchanged
410 -- Leave all other expressions unchanged
411 appsimpl expr = return expr
412 -- Perform this transform everywhere
413 appsimpltop = everywhere ("appsimpl", appsimpl)
415 --------------------------------
416 -- Function-typed argument propagation
417 --------------------------------
418 -- Remove all applications to function-typed arguments, by duplication the
419 -- function called with the function-typed parameter replaced by the free
420 -- variables of the argument passed in.
421 argprop, argproptop :: Transform
422 -- Transform any application of a named function (i.e., skip applications of
423 -- lambda's). Also skip applications that have arguments with free type
424 -- variables, since we can't inline those.
425 argprop expr@(App _ _) | is_var fexpr = do
426 -- Find the body of the function called
427 body_maybe <- Trans.lift $ getGlobalBind f
430 -- Process each of the arguments in turn
431 (args', changed) <- Writer.listen $ mapM doarg args
432 -- See if any of the arguments changed
433 case Monoid.getAny changed of
435 let (newargs', newparams', oldargs) = unzip3 args'
436 let newargs = concat newargs'
437 let newparams = concat newparams'
438 -- Create a new body that consists of a lambda for all new arguments and
439 -- the old body applied to some arguments.
440 let newbody = MkCore.mkCoreLams newparams (MkCore.mkCoreApps body oldargs)
441 -- Create a new function with the same name but a new body
442 newf <- Trans.lift $ mkFunction f newbody
443 -- Replace the original application with one of the new function to the
445 change $ MkCore.mkCoreApps (Var newf) newargs
447 -- Don't change the expression if none of the arguments changed
450 -- If we don't have a body for the function called, leave it unchanged (it
451 -- should be a primitive function then).
452 Nothing -> return expr
454 -- Find the function called and the arguments
455 (fexpr, args) = collectArgs expr
458 -- Process a single argument and return (args, bndrs, arg), where args are
459 -- the arguments to replace the given argument in the original
460 -- application, bndrs are the binders to include in the top-level lambda
461 -- in the new function body, and arg is the argument to apply to the old
463 doarg :: CoreExpr -> TransformMonad ([CoreExpr], [CoreBndr], CoreExpr)
466 bndrs <- Trans.lift getGlobalBinders
467 let interesting var = Var.isLocalVar var && (not $ var `elem` bndrs)
468 if not repr && not (is_var arg && interesting (exprToVar arg)) && not (has_free_tyvars arg)
470 -- Propagate all complex arguments that are not representable, but not
471 -- arguments with free type variables (since those would require types
472 -- not known yet, which will always be known eventually).
473 -- Find interesting free variables, each of which should be passed to
474 -- the new function instead of the original function argument.
476 -- Interesting vars are those that are local, but not available from the
477 -- top level scope (functions from this module are defined as local, but
478 -- they're not local to this function, so we can freely move references
479 -- to them into another function).
480 let free_vars = VarSet.varSetElems $ CoreFVs.exprSomeFreeVars interesting arg
481 -- Mark the current expression as changed
483 return (map Var free_vars, free_vars, arg)
485 -- Representable types will not be propagated, and arguments with free
486 -- type variables will be propagated later.
487 -- TODO: preserve original naming?
488 id <- Trans.lift $ mkBinderFor arg "param"
489 -- Just pass the original argument to the new function, which binds it
490 -- to a new id and just pass that new id to the old function body.
491 return ([arg], [id], mkReferenceTo id)
492 -- Leave all other expressions unchanged
493 argprop expr = return expr
494 -- Perform this transform everywhere
495 argproptop = everywhere ("argprop", argprop)
497 --------------------------------
498 -- Function-typed argument extraction
499 --------------------------------
500 -- This transform takes any function-typed argument that cannot be propagated
501 -- (because the function that is applied to it is a builtin function), and
502 -- puts it in a brand new top level binder. This allows us to for example
503 -- apply map to a lambda expression This will not conflict with inlinenonrep,
504 -- since that only inlines local let bindings, not top level bindings.
505 funextract, funextracttop :: Transform
506 funextract expr@(App _ _) | is_var fexpr = do
507 body_maybe <- Trans.lift $ getGlobalBind f
509 -- We don't have a function body for f, so we can perform this transform.
511 -- Find the new arguments
512 args' <- mapM doarg args
513 -- And update the arguments. We use return instead of changed, so the
514 -- changed flag doesn't get set if none of the args got changed.
515 return $ MkCore.mkCoreApps fexpr args'
516 -- We have a function body for f, leave this application to funprop
517 Just _ -> return expr
519 -- Find the function called and the arguments
520 (fexpr, args) = collectArgs expr
522 -- Change any arguments that have a function type, but are not simple yet
523 -- (ie, a variable or application). This means to create a new function
524 -- for map (\f -> ...) b, but not for map (foo a) b.
526 -- We could use is_applicable here instead of is_fun, but I think
527 -- arguments to functions could only have forall typing when existential
528 -- typing is enabled. Not sure, though.
529 doarg arg | not (is_simple arg) && is_fun arg = do
530 -- Create a new top level binding that binds the argument. Its body will
531 -- be extended with lambda expressions, to take any free variables used
532 -- by the argument expression.
533 let free_vars = VarSet.varSetElems $ CoreFVs.exprFreeVars arg
534 let body = MkCore.mkCoreLams free_vars arg
535 id <- Trans.lift $ mkBinderFor body "fun"
536 Trans.lift $ addGlobalBind id body
537 -- Replace the argument with a reference to the new function, applied to
539 change $ MkCore.mkCoreApps (Var id) (map Var free_vars)
540 -- Leave all other arguments untouched
541 doarg arg = return arg
543 -- Leave all other expressions unchanged
544 funextract expr = return expr
545 -- Perform this transform everywhere
546 funextracttop = everywhere ("funextract", funextract)
548 --------------------------------
549 -- End of transformations
550 --------------------------------
555 -- What transforms to run?
556 transforms = [argproptop, funextracttop, etatop, betatop, castproptop, letremovetop, letderectop, letsimpltop, letflattop, scrutsimpltop, casesimpltop, caseremovetop, inlinenonreptop, appsimpltop, letmergetop, letremoveunusedtop, castsimpltop]
558 -- | Returns the normalized version of the given function.
560 CoreBndr -- ^ The function to get
561 -> TranslatorSession CoreExpr -- The normalized function body
563 getNormalized bndr = Utils.makeCached bndr tsNormalized $ do
564 if is_poly (Var bndr)
566 -- This should really only happen at the top level... TODO: Give
567 -- a different error if this happens down in the recursion.
568 error $ "\nNormalize.normalizeBind: Function " ++ show bndr ++ " is polymorphic, can't normalize"
570 expr <- getBinding bndr
571 normalizeExpr (show bndr) expr
573 -- | Normalize an expression
575 String -- ^ What are we normalizing? For debug output only.
576 -> CoreSyn.CoreExpr -- ^ The expression to normalize
577 -> TranslatorSession CoreSyn.CoreExpr -- ^ The normalized expression
579 normalizeExpr what expr = do
580 -- Normalize this expression
581 trace (what ++ " before normalization:\n\n" ++ showSDoc ( ppr expr ) ++ "\n") $ return ()
582 expr' <- dotransforms transforms expr
583 trace ("\n" ++ what ++ " after normalization:\n\n" ++ showSDoc ( ppr expr')) $ return ()
586 -- | Get the value that is bound to the given binder at top level. Fails when
587 -- there is no such binding.
589 CoreBndr -- ^ The binder to get the expression for
590 -> TranslatorSession CoreExpr -- ^ The value bound to the binder
592 getBinding bndr = Utils.makeCached bndr tsBindings $ do
593 -- If the binding isn't in the "cache" (bindings map), then we can't create
594 -- it out of thin air, so return an error.
595 error $ "Normalize.getBinding: Unknown function requested: " ++ show bndr
597 -- | Split a normalized expression into the argument binders, top level
598 -- bindings and the result binder.
600 CoreExpr -- ^ The normalized expression
601 -> ([CoreBndr], [Binding], CoreBndr)
602 splitNormalized expr = (args, binds, res)
604 (args, letexpr) = CoreSyn.collectBinders expr
605 (binds, resexpr) = flattenLets letexpr
606 res = case resexpr of
608 _ -> error $ "Normalize.splitNormalized: Not in normal form: " ++ pprString expr ++ "\n"
610 -- | Flattens nested lets into a single list of bindings. The expression
611 -- passed does not have to be a let expression, if it isn't an empty list of
612 -- bindings is returned.
614 CoreExpr -- ^ The expression to flatten.
615 -> ([Binding], CoreExpr) -- ^ The bindings and resulting expression.
616 flattenLets (Let binds expr) =
617 (bindings ++ bindings', expr')
619 -- Recursively flatten the contained expression
620 (bindings', expr') =flattenLets expr
621 -- Flatten our own bindings to remove the Rec / NonRec constructors
622 bindings = CoreSyn.flattenBinds [binds]
623 flattenLets expr = ([], expr)