From: Matthijs Kooijman Date: Tue, 18 May 2010 09:59:33 +0000 (+0200) Subject: Reorder transformations to match my thesis. X-Git-Url: https://git.stderr.nl/gitweb?p=matthijs%2Fmaster-project%2Fc%CE%BBash.git;a=commitdiff_plain;h=5d58ff471df987d8def34a473103c785890510c6 Reorder transformations to match my thesis. Also add or correct some comments. --- diff --git "a/c\316\273ash/CLasH/Normalize.hs" "b/c\316\273ash/CLasH/Normalize.hs" index dc9606c..1dc20f5 100644 --- "a/c\316\273ash/CLasH/Normalize.hs" +++ "b/c\316\273ash/CLasH/Normalize.hs" @@ -43,26 +43,9 @@ import CLasH.Utils.Core.CoreTools import CLasH.Utils.Core.BinderTools import CLasH.Utils.Pretty --------------------------------- --- Start of transformations --------------------------------- - --------------------------------- --- η expansion --------------------------------- --- Make sure all parameters to the normalized functions are named by top --- level lambda expressions. For this we apply η expansion to the --- function body (possibly enclosed in some lambda abstractions) while --- it has a function type. Eventually this will result in a function --- body consisting of a bunch of nested lambdas containing a --- non-function value (e.g., a complete application). -eta :: Transform -eta c expr | is_fun expr && not (is_lam expr) && all (== LambdaBody) c = do - let arg_ty = (fst . Type.splitFunTy . CoreUtils.exprType) expr - id <- Trans.lift $ mkInternalVar "param" arg_ty - change (Lam id (App expr (Var id))) --- Leave all other expressions unchanged -eta c e = return e +---------------------------------------------------------------- +-- Cleanup transformations +---------------------------------------------------------------- -------------------------------- -- β-reduction @@ -76,58 +59,42 @@ beta c (App (Lam x expr) arg) | CoreSyn.isTyVar x = setChanged >> substitute x a beta c expr = return expr -------------------------------- --- Application propagation +-- Unused let binding removal -------------------------------- -appprop :: Transform --- Propagate the application into the let -appprop c (App (Let binds expr) arg) = change $ Let binds (App expr arg) --- Propagate the application into each of the alternatives -appprop c (App (Case scrut b ty alts) arg) = change $ Case scrut b ty' alts' - where - alts' = map (\(con, bndrs, expr) -> (con, bndrs, (App expr arg))) alts - ty' = CoreUtils.applyTypeToArg ty arg +letremoveunused :: Transform +letremoveunused c expr@(Let (NonRec b bound) res) = do + let used = expr_uses_binders [b] res + if used + then return expr + else change res +letremoveunused c expr@(Let (Rec binds) res) = do + -- Filter out all unused binds. + let binds' = filter dobind binds + -- Only set the changed flag if binds got removed + changeif (length binds' /= length binds) (Let (Rec binds') res) + where + bound_exprs = map snd binds + -- For each bind check if the bind is used by res or any of the bound + -- expressions + dobind (bndr, _) = any (expr_uses_binders [bndr]) (res:bound_exprs) -- Leave all other expressions unchanged -appprop c expr = return expr +letremoveunused c expr = return expr -------------------------------- --- Case of known constructor simplification +-- empty let removal -------------------------------- --- If a case expressions scrutinizes a datacon application, we can --- determine which alternative to use and remove the case alltogether. --- We replace it with a let expression the binds every binder in the --- alternative bound to the corresponding argument of the datacon. We do --- this instead of substituting the binders, to prevent duplication of --- work and preserve sharing wherever appropriate. -knowncase :: Transform -knowncase context expr@(Case scrut@(App _ _) bndr ty alts) | not bndr_used = do - case collectArgs scrut of - (Var f, args) -> case Id.isDataConId_maybe f of - -- Not a dataconstructor? Don't change anything (probably a - -- function, then) - Nothing -> return expr - Just dc -> do - let (altcon, bndrs, res) = case List.find (\(altcon, bndrs, res) -> altcon == (DataAlt dc)) alts of - Just alt -> alt -- Return the alternative found - Nothing -> head alts -- If the datacon is not present, the first must be the default alternative - -- Double check if we have either the correct alternative, or - -- the default. - if altcon /= (DataAlt dc) && altcon /= DEFAULT then error ("Normalize.knowncase: Invalid core, datacon not found in alternatives and DEFAULT alternative is not first? " ++ pprString expr) else return () - -- Find out how many arguments to drop (type variables and - -- predicates like dictionaries). - let (tvs, preds, _, _) = DataCon.dataConSig dc - let count = length tvs + length preds - -- Create a let expression that binds each of the binders in - -- this alternative to the corresponding argument of the data - -- constructor. - let binds = zip bndrs (drop count args) - change $ Let (Rec binds) res - _ -> return expr -- Scrutinee is not an application of a var - where - is_used (_, _, expr) = expr_uses_binders [bndr] expr - bndr_used = or $ map is_used alts - +-- Remove empty (recursive) lets +letremove :: Transform +letremove c (Let (Rec []) res) = change res -- Leave all other expressions unchanged -knowncase c expr = return expr +letremove c expr = return expr + +-------------------------------- +-- Simple let binding removal +-------------------------------- +-- Remove a = b bindings from let expressions everywhere +letremovesimple :: Transform +letremovesimple = inlinebind (\(b, e) -> Trans.lift $ is_local_var e) -------------------------------- -- Cast propagation @@ -163,168 +130,6 @@ castsimpl c expr@(Cast val ty) = do -- Leave all other expressions unchanged castsimpl c expr = return expr --------------------------------- --- Return value simplification --------------------------------- --- Ensure the return value of a function follows proper normal form. eta --- expansion ensures the body starts with lambda abstractions, this --- transformation ensures that the lambda abstractions always contain a --- recursive let and that, when the return value is representable, the --- let contains a local variable reference in its body. -retvalsimpl c expr | all (== LambdaBody) c && not (is_lam expr) && not (is_let expr) = do - local_var <- Trans.lift $ is_local_var expr - repr <- isRepr expr - if not local_var && repr - then do - id <- Trans.lift $ mkBinderFor expr "res" - change $ Let (Rec [(id, expr)]) (Var id) - else - return expr - -retvalsimpl c expr@(Let (Rec binds) body) | all (== LambdaBody) c = do - -- Don't extract values that are already a local variable, to prevent - -- loops with ourselves. - local_var <- Trans.lift $ is_local_var body - -- Don't extract values that are not representable, to prevent loops with - -- inlinenonrep - repr <- isRepr body - if not local_var && repr - then do - id <- Trans.lift $ mkBinderFor body "res" - change $ Let (Rec ((id, body):binds)) (Var id) - else - return expr - - --- Leave all other expressions unchanged -retvalsimpl c expr = return expr - --------------------------------- --- let derecursification --------------------------------- -letrec :: Transform -letrec c expr@(Let (NonRec bndr val) res) = - change $ Let (Rec [(bndr, val)]) res - --- Leave all other expressions unchanged -letrec c expr = return expr - --------------------------------- --- let flattening --------------------------------- --- Takes a let that binds another let, and turns that into two nested lets. --- e.g., from: --- let b = (let b' = expr' in res') in res --- to: --- let b' = expr' in (let b = res' in res) -letflat :: Transform --- Turn a nonrec let that binds a let into two nested lets. -letflat c (Let (NonRec b (Let binds res')) res) = - change $ Let binds (Let (NonRec b res') res) -letflat c (Let (Rec binds) expr) = do - -- Flatten each binding. - binds' <- Utils.concatM $ Monad.mapM flatbind binds - -- Return the new let. We don't use change here, since possibly nothing has - -- changed. If anything has changed, flatbind has already flagged that - -- change. - return $ Let (Rec binds') expr - where - -- Turns a binding of a let into a multiple bindings, or any other binding - -- into a list with just that binding - flatbind :: (CoreBndr, CoreExpr) -> TransformMonad [(CoreBndr, CoreExpr)] - flatbind (b, Let (Rec binds) expr) = change ((b, expr):binds) - flatbind (b, Let (NonRec b' expr') expr) = change [(b, expr), (b', expr')] - flatbind (b, expr) = return [(b, expr)] --- Leave all other expressions unchanged -letflat c expr = return expr - --------------------------------- --- empty let removal --------------------------------- --- Remove empty (recursive) lets -letremove :: Transform -letremove c (Let (Rec []) res) = change res --- Leave all other expressions unchanged -letremove c expr = return expr - --------------------------------- --- Simple let binding removal --------------------------------- --- Remove a = b bindings from let expressions everywhere -letremovesimple :: Transform -letremovesimple = inlinebind (\(b, e) -> Trans.lift $ is_local_var e) - --------------------------------- --- Unused let binding removal --------------------------------- -letremoveunused :: Transform -letremoveunused c expr@(Let (NonRec b bound) res) = do - let used = expr_uses_binders [b] res - if used - then return expr - else change res -letremoveunused c expr@(Let (Rec binds) res) = do - -- Filter out all unused binds. - let binds' = filter dobind binds - -- Only set the changed flag if binds got removed - changeif (length binds' /= length binds) (Let (Rec binds') res) - where - bound_exprs = map snd binds - -- For each bind check if the bind is used by res or any of the bound - -- expressions - dobind (bndr, _) = any (expr_uses_binders [bndr]) (res:bound_exprs) --- Leave all other expressions unchanged -letremoveunused c expr = return expr - -{- --------------------------------- --- Identical let binding merging --------------------------------- --- Merge two bindings in a let if they are identical --- TODO: We would very much like to use GHC's CSE module for this, but that --- doesn't track if something changed or not, so we can't use it properly. -letmerge :: Transform -letmerge c expr@(Let _ _) = do - let (binds, res) = flattenLets expr - binds' <- domerge binds - return $ mkNonRecLets binds' res - where - domerge :: [(CoreBndr, CoreExpr)] -> TransformMonad [(CoreBndr, CoreExpr)] - domerge [] = return [] - domerge (e:es) = do - es' <- mapM (mergebinds e) es - es'' <- domerge es' - return (e:es'') - - -- Uses the second bind to simplify the second bind, if applicable. - mergebinds :: (CoreBndr, CoreExpr) -> (CoreBndr, CoreExpr) -> TransformMonad (CoreBndr, CoreExpr) - mergebinds (b1, e1) (b2, e2) - -- Identical expressions? Replace the second binding with a reference to - -- the first binder. - | CoreUtils.cheapEqExpr e1 e2 = change $ (b2, Var b1) - -- Different expressions? Don't change - | otherwise = return (b2, e2) --- Leave all other expressions unchanged -letmerge c expr = return expr --} - --------------------------------- --- Non-representable binding inlining --------------------------------- --- Remove a = B bindings, with B of a non-representable type, from let --- expressions everywhere. This means that any value that we can't generate a --- signal for, will be inlined and hopefully turned into something we can --- represent. --- --- This is a tricky function, which is prone to create loops in the --- transformations. To fix this, we make sure that no transformation will --- create a new let binding with a non-representable type. These other --- transformations will just not work on those function-typed values at first, --- but the other transformations (in particular β-reduction) should make sure --- that the type of those values eventually becomes representable. -inlinenonrep :: Transform -inlinenonrep = inlinebind ((Monad.liftM not) . isRepr . snd) - -------------------------------- -- Top level function inlining -------------------------------- @@ -397,97 +202,209 @@ needsInline f = do -- More complicated function, don't inline _ -> return Nothing + +---------------------------------------------------------------- +-- Program structure transformations +---------------------------------------------------------------- + -------------------------------- --- Dictionary inlining +-- η expansion -------------------------------- --- Inline all top level dictionaries, that are in a position where --- classopresolution can actually resolve them. This makes this --- transformation look similar to classoperesolution below, but we'll --- keep them separated for clarity. By not inlining other dictionaries, --- we prevent expression sizes exploding when huge type level integer --- dictionaries are inlined which can never be expanded (in casts, for --- example). -inlinedict c expr@(App (App (Var sel) ty) (Var dict)) | not is_builtin && is_classop = do - body_maybe <- Trans.lift $ getGlobalBind dict - case body_maybe of - -- No body available (no source available, or a local variable / - -- argument) - Nothing -> return expr - Just body -> change (App (App (Var sel) ty) body) +-- Make sure all parameters to the normalized functions are named by top +-- level lambda expressions. For this we apply η expansion to the +-- function body (possibly enclosed in some lambda abstractions) while +-- it has a function type. Eventually this will result in a function +-- body consisting of a bunch of nested lambdas containing a +-- non-function value (e.g., a complete application). +eta :: Transform +eta c expr | is_fun expr && not (is_lam expr) && all (== LambdaBody) c = do + let arg_ty = (fst . Type.splitFunTy . CoreUtils.exprType) expr + id <- Trans.lift $ mkInternalVar "param" arg_ty + change (Lam id (App expr (Var id))) +-- Leave all other expressions unchanged +eta c e = return e + +-------------------------------- +-- Application propagation +-------------------------------- +-- Move applications into let and case expressions. +appprop :: Transform +-- Propagate the application into the let +appprop c (App (Let binds expr) arg) = change $ Let binds (App expr arg) +-- Propagate the application into each of the alternatives +appprop c (App (Case scrut b ty alts) arg) = change $ Case scrut b ty' alts' + where + alts' = map (\(con, bndrs, expr) -> (con, bndrs, (App expr arg))) alts + ty' = CoreUtils.applyTypeToArg ty arg +-- Leave all other expressions unchanged +appprop c expr = return expr + +-------------------------------- +-- Let recursification +-------------------------------- +-- Make all lets recursive, so other transformations don't need to +-- handle non-recursive lets +letrec :: Transform +letrec c expr@(Let (NonRec bndr val) res) = + change $ Let (Rec [(bndr, val)]) res + +-- Leave all other expressions unchanged +letrec c expr = return expr + +-------------------------------- +-- let flattening +-------------------------------- +-- Takes a let that binds another let, and turns that into two nested lets. +-- e.g., from: +-- let b = (let b' = expr' in res') in res +-- to: +-- let b' = expr' in (let b = res' in res) +letflat :: Transform +-- Turn a nonrec let that binds a let into two nested lets. +letflat c (Let (NonRec b (Let binds res')) res) = + change $ Let binds (Let (NonRec b res') res) +letflat c (Let (Rec binds) expr) = do + -- Flatten each binding. + binds' <- Utils.concatM $ Monad.mapM flatbind binds + -- Return the new let. We don't use change here, since possibly nothing has + -- changed. If anything has changed, flatbind has already flagged that + -- change. + return $ Let (Rec binds') expr where - -- Is this a builtin function / method? - is_builtin = elem (Name.getOccString sel) builtinIds - -- Are we dealing with a class operation selector? - is_classop = Maybe.isJust (Id.isClassOpId_maybe sel) + -- Turns a binding of a let into a multiple bindings, or any other binding + -- into a list with just that binding + flatbind :: (CoreBndr, CoreExpr) -> TransformMonad [(CoreBndr, CoreExpr)] + flatbind (b, Let (Rec binds) expr) = change ((b, expr):binds) + flatbind (b, Let (NonRec b' expr') expr) = change [(b, expr), (b', expr')] + flatbind (b, expr) = return [(b, expr)] +-- Leave all other expressions unchanged +letflat c expr = return expr + +-------------------------------- +-- Return value simplification +-------------------------------- +-- Ensure the return value of a function follows proper normal form. eta +-- expansion ensures the body starts with lambda abstractions, this +-- transformation ensures that the lambda abstractions always contain a +-- recursive let and that, when the return value is representable, the +-- let contains a local variable reference in its body. + +-- Extract the return value from the body of the top level lambdas (of +-- which ther could be zero), unless it is a let expression (in which +-- case the next clause applies). +retvalsimpl c expr | all (== LambdaBody) c && not (is_lam expr) && not (is_let expr) = do + local_var <- Trans.lift $ is_local_var expr + repr <- isRepr expr + if not local_var && repr + then do + id <- Trans.lift $ mkBinderFor expr "res" + change $ Let (Rec [(id, expr)]) (Var id) + else + return expr +-- Extract the return value from the body of a let expression, which is +-- itself the body of the top level lambdas (of which there could be +-- zero). +retvalsimpl c expr@(Let (Rec binds) body) | all (== LambdaBody) c = do + -- Don't extract values that are already a local variable, to prevent + -- loops with ourselves. + local_var <- Trans.lift $ is_local_var body + -- Don't extract values that are not representable, to prevent loops with + -- inlinenonrep + repr <- isRepr body + if not local_var && repr + then do + id <- Trans.lift $ mkBinderFor body "res" + change $ Let (Rec ((id, body):binds)) (Var id) + else + return expr +-- Leave all other expressions unchanged +retvalsimpl c expr = return expr +-------------------------------- +-- Representable arguments simplification +-------------------------------- +-- Make sure that all arguments of a representable type are simple variables. +appsimpl :: Transform +-- Simplify all representable arguments. Do this by introducing a new Let +-- that binds the argument and passing the new binder in the application. +appsimpl c expr@(App f arg) = do + -- Check runtime representability + repr <- isRepr arg + local_var <- Trans.lift $ is_local_var arg + if repr && not local_var + then do -- Extract representable arguments + id <- Trans.lift $ mkBinderFor arg "arg" + change $ Let (NonRec id arg) (App f (Var id)) + else -- Leave non-representable arguments unchanged + return expr -- Leave all other expressions unchanged -inlinedict c expr = return expr +appsimpl c expr = return expr + +---------------------------------------------------------------- +-- Built-in function transformations +---------------------------------------------------------------- -------------------------------- --- ClassOp resolution +-- Function-typed argument extraction -------------------------------- --- Resolves any class operation to the actual operation whenever --- possible. Class methods (as well as parent dictionary selectors) are --- special "functions" that take a type and a dictionary and evaluate to --- the corresponding method. A dictionary is nothing more than a --- special dataconstructor applied to the type the dictionary is for, --- each of the superclasses and all of the class method definitions for --- that particular type. Since dictionaries all always inlined (top --- levels dictionaries are inlined by inlinedict, local dictionaries are --- inlined by inlinenonrep), we will eventually have something like: --- --- baz --- @ CLasH.HardwareTypes.Bit --- (D:Baz @ CLasH.HardwareTypes.Bit bitbaz) --- --- Here, baz is the method selector for the baz method, while --- D:Baz is the dictionary constructor for the Baz and bitbaz is the baz --- method defined in the Baz Bit instance declaration. --- --- To resolve this, we can look at the ClassOp IdInfo from the baz Id, --- which contains the Class it is defined for. From the Class, we can --- get a list of all selectors (both parent class selectors as well as --- method selectors). Since the arguments to D:Baz (after the type --- argument) correspond exactly to this list, we then look up baz in --- that list and replace the entire expression by the corresponding --- argument to D:Baz. --- --- We don't resolve methods that have a builtin translation (such as --- ==), since the actual implementation is not always (easily) --- translateable. For example, when deriving ==, GHC generates code --- using $con2tag functions to translate a datacon to an int and compare --- that with GHC.Prim.==# . Better to avoid that for now. -classopresolution :: Transform -classopresolution c expr@(App (App (Var sel) ty) dict) | not is_builtin = - case Id.isClassOpId_maybe sel of - -- Not a class op selector - Nothing -> return expr - Just cls -> case collectArgs dict of - (_, []) -> return expr -- Dict is not an application (e.g., not inlined yet) - (Var dictdc, (ty':selectors)) | not (Maybe.isJust (Id.isDataConId_maybe dictdc)) -> return expr -- Dictionary is not a datacon yet (but e.g., a top level binder) - | tyargs_neq ty ty' -> error $ "Normalize.classopresolution: Applying class selector to dictionary without matching type?\n" ++ pprString expr - | otherwise -> - let selector_ids = Class.classSelIds cls in - -- Find the selector used in the class' list of selectors - case List.elemIndex sel selector_ids of - Nothing -> error $ "Normalize.classopresolution: Selector not found in class' selector list? This should not happen!\nExpression: " ++ pprString expr ++ "\nClass: " ++ show cls ++ "\nSelectors: " ++ show selector_ids - -- Get the corresponding argument from the dictionary - Just n -> change (selectors!!n) - (_, _) -> return expr -- Not applying a variable? Don't touch +-- This transform takes any function-typed argument that cannot be propagated +-- (because the function that is applied to it is a builtin function), and +-- puts it in a brand new top level binder. This allows us to for example +-- apply map to a lambda expression This will not conflict with inlinenonrep, +-- since that only inlines local let bindings, not top level bindings. +funextract :: Transform +funextract c expr@(App _ _) | is_var fexpr = do + body_maybe <- Trans.lift $ getGlobalBind f + case body_maybe of + -- We don't have a function body for f, so we can perform this transform. + Nothing -> do + -- Find the new arguments + args' <- mapM doarg args + -- And update the arguments. We use return instead of changed, so the + -- changed flag doesn't get set if none of the args got changed. + return $ MkCore.mkCoreApps fexpr args' + -- We have a function body for f, leave this application to funprop + Just _ -> return expr where - -- Compare two type arguments, returning True if they are _not_ - -- equal - tyargs_neq (Type ty1) (Type ty2) = not $ Type.coreEqType ty1 ty2 - tyargs_neq _ _ = True - -- Is this a builtin function / method? - is_builtin = elem (Name.getOccString sel) builtinIds + -- Find the function called and the arguments + (fexpr, args) = collectArgs expr + Var f = fexpr + -- Change any arguments that have a function type, but are not simple yet + -- (ie, a variable or application). This means to create a new function + -- for map (\f -> ...) b, but not for map (foo a) b. + -- + -- We could use is_applicable here instead of is_fun, but I think + -- arguments to functions could only have forall typing when existential + -- typing is enabled. Not sure, though. + doarg arg | not (is_simple arg) && is_fun arg = do + -- Create a new top level binding that binds the argument. Its body will + -- be extended with lambda expressions, to take any free variables used + -- by the argument expression. + let free_vars = VarSet.varSetElems $ CoreFVs.exprFreeVars arg + let body = MkCore.mkCoreLams free_vars arg + id <- Trans.lift $ mkBinderFor body "fun" + Trans.lift $ addGlobalBind id body + -- Replace the argument with a reference to the new function, applied to + -- all vars it uses. + change $ MkCore.mkCoreApps (Var id) (map Var free_vars) + -- Leave all other arguments untouched + doarg arg = return arg -- Leave all other expressions unchanged -classopresolution c expr = return expr +funextract c expr = return expr + + + + +---------------------------------------------------------------- +-- Case normalization transformations +---------------------------------------------------------------- -------------------------------- -- Scrutinee simplification -------------------------------- +-- Make sure the scrutinee of a case expression is a local variable +-- reference. scrutsimpl :: Transform -- Don't touch scrutinees that are already simple scrutsimpl c expr@(Case (Var _) _ _ _) = return expr @@ -531,8 +448,14 @@ scrutbndrremove c (Case (Var scrut) bndr ty alts) | bndr_used = do scrutbndrremove c expr = return expr -------------------------------- --- Case binder wildening +-- Case normalization -------------------------------- +-- Turn a case expression with any number of alternatives with any +-- number of non-wild binders into as set of case and let expressions, +-- all of which are in normal form (e.g., a bunch of extractor case +-- expressions to extract all fields from the scrutinee, a number of let +-- bindings to bind each alternative and a single selector case to +-- select the right value. casesimpl :: Transform -- This is already a selector case (or, if x does not appear in bndrs, a very -- simple case statement that will be removed by caseremove below). Just leave @@ -639,30 +562,74 @@ caseremove c (Case scrut b ty [(con, bndrs, expr)]) | not usesvars = change expr caseremove c expr = return expr -------------------------------- --- Argument extraction +-- Case of known constructor simplification -------------------------------- --- Make sure that all arguments of a representable type are simple variables. -appsimpl :: Transform --- Simplify all representable arguments. Do this by introducing a new Let --- that binds the argument and passing the new binder in the application. -appsimpl c expr@(App f arg) = do - -- Check runtime representability - repr <- isRepr arg - local_var <- Trans.lift $ is_local_var arg - if repr && not local_var - then do -- Extract representable arguments - id <- Trans.lift $ mkBinderFor arg "arg" - change $ Let (NonRec id arg) (App f (Var id)) - else -- Leave non-representable arguments unchanged - return expr +-- If a case expressions scrutinizes a datacon application, we can +-- determine which alternative to use and remove the case alltogether. +-- We replace it with a let expression the binds every binder in the +-- alternative bound to the corresponding argument of the datacon. We do +-- this instead of substituting the binders, to prevent duplication of +-- work and preserve sharing wherever appropriate. +knowncase :: Transform +knowncase context expr@(Case scrut@(App _ _) bndr ty alts) | not bndr_used = do + case collectArgs scrut of + (Var f, args) -> case Id.isDataConId_maybe f of + -- Not a dataconstructor? Don't change anything (probably a + -- function, then) + Nothing -> return expr + Just dc -> do + let (altcon, bndrs, res) = case List.find (\(altcon, bndrs, res) -> altcon == (DataAlt dc)) alts of + Just alt -> alt -- Return the alternative found + Nothing -> head alts -- If the datacon is not present, the first must be the default alternative + -- Double check if we have either the correct alternative, or + -- the default. + if altcon /= (DataAlt dc) && altcon /= DEFAULT then error ("Normalize.knowncase: Invalid core, datacon not found in alternatives and DEFAULT alternative is not first? " ++ pprString expr) else return () + -- Find out how many arguments to drop (type variables and + -- predicates like dictionaries). + let (tvs, preds, _, _) = DataCon.dataConSig dc + let count = length tvs + length preds + -- Create a let expression that binds each of the binders in + -- this alternative to the corresponding argument of the data + -- constructor. + let binds = zip bndrs (drop count args) + change $ Let (Rec binds) res + _ -> return expr -- Scrutinee is not an application of a var + where + is_used (_, _, expr) = expr_uses_binders [bndr] expr + bndr_used = or $ map is_used alts + -- Leave all other expressions unchanged -appsimpl c expr = return expr +knowncase c expr = return expr + + + + +---------------------------------------------------------------- +-- Unrepresentable value removal transformations +---------------------------------------------------------------- + +-------------------------------- +-- Non-representable binding inlining +-------------------------------- +-- Remove a = B bindings, with B of a non-representable type, from let +-- expressions everywhere. This means that any value that we can't generate a +-- signal for, will be inlined and hopefully turned into something we can +-- represent. +-- +-- This is a tricky function, which is prone to create loops in the +-- transformations. To fix this, we make sure that no transformation will +-- create a new let binding with a non-representable type. These other +-- transformations will just not work on those function-typed values at first, +-- but the other transformations (in particular β-reduction) should make sure +-- that the type of those values eventually becomes representable. +inlinenonrep :: Transform +inlinenonrep = inlinebind ((Monad.liftM not) . isRepr . snd) -------------------------------- --- Function-typed argument propagation +-- Function specialization -------------------------------- --- Remove all applications to function-typed arguments, by duplication the --- function called with the function-typed parameter replaced by the free +-- Remove all applications to non-representable arguments, by duplicating the +-- function called with the non-representable parameter replaced by the free -- variables of the argument passed in. argprop :: Transform -- Transform any application of a named function (i.e., skip applications of @@ -850,55 +817,126 @@ inlinenonrepresult context expr | not (is_fun expr) = -- Leave all other expressions unchanged inlinenonrepresult c expr = return expr +-------------------------------- +-- ClassOp resolution +-------------------------------- +-- Resolves any class operation to the actual operation whenever +-- possible. Class methods (as well as parent dictionary selectors) are +-- special "functions" that take a type and a dictionary and evaluate to +-- the corresponding method. A dictionary is nothing more than a +-- special dataconstructor applied to the type the dictionary is for, +-- each of the superclasses and all of the class method definitions for +-- that particular type. Since dictionaries all always inlined (top +-- levels dictionaries are inlined by inlinedict, local dictionaries are +-- inlined by inlinenonrep), we will eventually have something like: +-- +-- baz +-- @ CLasH.HardwareTypes.Bit +-- (D:Baz @ CLasH.HardwareTypes.Bit bitbaz) +-- +-- Here, baz is the method selector for the baz method, while +-- D:Baz is the dictionary constructor for the Baz and bitbaz is the baz +-- method defined in the Baz Bit instance declaration. +-- +-- To resolve this, we can look at the ClassOp IdInfo from the baz Id, +-- which contains the Class it is defined for. From the Class, we can +-- get a list of all selectors (both parent class selectors as well as +-- method selectors). Since the arguments to D:Baz (after the type +-- argument) correspond exactly to this list, we then look up baz in +-- that list and replace the entire expression by the corresponding +-- argument to D:Baz. +-- +-- We don't resolve methods that have a builtin translation (such as +-- ==), since the actual implementation is not always (easily) +-- translateable. For example, when deriving ==, GHC generates code +-- using $con2tag functions to translate a datacon to an int and compare +-- that with GHC.Prim.==# . Better to avoid that for now. +classopresolution :: Transform +classopresolution c expr@(App (App (Var sel) ty) dict) | not is_builtin = + case Id.isClassOpId_maybe sel of + -- Not a class op selector + Nothing -> return expr + Just cls -> case collectArgs dict of + (_, []) -> return expr -- Dict is not an application (e.g., not inlined yet) + (Var dictdc, (ty':selectors)) | not (Maybe.isJust (Id.isDataConId_maybe dictdc)) -> return expr -- Dictionary is not a datacon yet (but e.g., a top level binder) + | tyargs_neq ty ty' -> error $ "Normalize.classopresolution: Applying class selector to dictionary without matching type?\n" ++ pprString expr + | otherwise -> + let selector_ids = Class.classSelIds cls in + -- Find the selector used in the class' list of selectors + case List.elemIndex sel selector_ids of + Nothing -> error $ "Normalize.classopresolution: Selector not found in class' selector list? This should not happen!\nExpression: " ++ pprString expr ++ "\nClass: " ++ show cls ++ "\nSelectors: " ++ show selector_ids + -- Get the corresponding argument from the dictionary + Just n -> change (selectors!!n) + (_, _) -> return expr -- Not applying a variable? Don't touch + where + -- Compare two type arguments, returning True if they are _not_ + -- equal + tyargs_neq (Type ty1) (Type ty2) = not $ Type.coreEqType ty1 ty2 + tyargs_neq _ _ = True + -- Is this a builtin function / method? + is_builtin = elem (Name.getOccString sel) builtinIds + +-- Leave all other expressions unchanged +classopresolution c expr = return expr -------------------------------- --- Function-typed argument extraction +-- Dictionary inlining -------------------------------- --- This transform takes any function-typed argument that cannot be propagated --- (because the function that is applied to it is a builtin function), and --- puts it in a brand new top level binder. This allows us to for example --- apply map to a lambda expression This will not conflict with inlinenonrep, --- since that only inlines local let bindings, not top level bindings. -funextract :: Transform -funextract c expr@(App _ _) | is_var fexpr = do - body_maybe <- Trans.lift $ getGlobalBind f +-- Inline all top level dictionaries, that are in a position where +-- classopresolution can actually resolve them. This makes this +-- transformation look similar to classoperesolution below, but we'll +-- keep them separated for clarity. By not inlining other dictionaries, +-- we prevent expression sizes exploding when huge type level integer +-- dictionaries are inlined which can never be expanded (in casts, for +-- example). +inlinedict c expr@(App (App (Var sel) ty) (Var dict)) | not is_builtin && is_classop = do + body_maybe <- Trans.lift $ getGlobalBind dict case body_maybe of - -- We don't have a function body for f, so we can perform this transform. - Nothing -> do - -- Find the new arguments - args' <- mapM doarg args - -- And update the arguments. We use return instead of changed, so the - -- changed flag doesn't get set if none of the args got changed. - return $ MkCore.mkCoreApps fexpr args' - -- We have a function body for f, leave this application to funprop - Just _ -> return expr + -- No body available (no source available, or a local variable / + -- argument) + Nothing -> return expr + Just body -> change (App (App (Var sel) ty) body) where - -- Find the function called and the arguments - (fexpr, args) = collectArgs expr - Var f = fexpr - -- Change any arguments that have a function type, but are not simple yet - -- (ie, a variable or application). This means to create a new function - -- for map (\f -> ...) b, but not for map (foo a) b. - -- - -- We could use is_applicable here instead of is_fun, but I think - -- arguments to functions could only have forall typing when existential - -- typing is enabled. Not sure, though. - doarg arg | not (is_simple arg) && is_fun arg = do - -- Create a new top level binding that binds the argument. Its body will - -- be extended with lambda expressions, to take any free variables used - -- by the argument expression. - let free_vars = VarSet.varSetElems $ CoreFVs.exprFreeVars arg - let body = MkCore.mkCoreLams free_vars arg - id <- Trans.lift $ mkBinderFor body "fun" - Trans.lift $ addGlobalBind id body - -- Replace the argument with a reference to the new function, applied to - -- all vars it uses. - change $ MkCore.mkCoreApps (Var id) (map Var free_vars) - -- Leave all other arguments untouched - doarg arg = return arg + -- Is this a builtin function / method? + is_builtin = elem (Name.getOccString sel) builtinIds + -- Are we dealing with a class operation selector? + is_classop = Maybe.isJust (Id.isClassOpId_maybe sel) -- Leave all other expressions unchanged -funextract c expr = return expr +inlinedict c expr = return expr + + +{- +-------------------------------- +-- Identical let binding merging +-------------------------------- +-- Merge two bindings in a let if they are identical +-- TODO: We would very much like to use GHC's CSE module for this, but that +-- doesn't track if something changed or not, so we can't use it properly. +letmerge :: Transform +letmerge c expr@(Let _ _) = do + let (binds, res) = flattenLets expr + binds' <- domerge binds + return $ mkNonRecLets binds' res + where + domerge :: [(CoreBndr, CoreExpr)] -> TransformMonad [(CoreBndr, CoreExpr)] + domerge [] = return [] + domerge (e:es) = do + es' <- mapM (mergebinds e) es + es'' <- domerge es' + return (e:es'') + + -- Uses the second bind to simplify the second bind, if applicable. + mergebinds :: (CoreBndr, CoreExpr) -> (CoreBndr, CoreExpr) -> TransformMonad (CoreBndr, CoreExpr) + mergebinds (b1, e1) (b2, e2) + -- Identical expressions? Replace the second binding with a reference to + -- the first binder. + | CoreUtils.cheapEqExpr e1 e2 = change $ (b2, Var b1) + -- Different expressions? Don't change + | otherwise = return (b2, e2) +-- Leave all other expressions unchanged +letmerge c expr = return expr +-} -------------------------------- -- End of transformations