{- (c) The University of Glasgow, 1994-2006 Core pass to saturate constructors and PrimOps -} {-# LANGUAGE BangPatterns, CPP, MultiWayIf #-} module CorePrep ( corePrepPgm, corePrepExpr, cvtLitInteger, lookupMkIntegerName, lookupIntegerSDataConName ) where #include "HsVersions.h" import GhcPrelude import OccurAnal import HscTypes import PrelNames import MkId ( realWorldPrimId ) import CoreUtils import CoreArity import CoreFVs import CoreMonad ( CoreToDo(..) ) import CoreLint ( endPassIO ) import CoreSyn import CoreSubst import MkCore hiding( FloatBind(..) ) -- We use our own FloatBind here import Type import Literal import Coercion import TcEnv import TyCon import Demand import Var import VarSet import VarEnv import Id import IdInfo import TysWiredIn import DataCon import PrimOp import BasicTypes import Module import UniqSupply import Maybes import OrdList import ErrUtils import DynFlags import Util import Pair import Outputable import Platform import FastString import Config import Name ( NamedThing(..), nameSrcSpan ) import SrcLoc ( SrcSpan(..), realSrcLocSpan, mkRealSrcLoc ) import Data.Bits import MonadUtils ( mapAccumLM ) import Data.List ( mapAccumL ) import Control.Monad {- -- --------------------------------------------------------------------------- -- Overview -- --------------------------------------------------------------------------- The goal of this pass is to prepare for code generation. 1. Saturate constructor and primop applications. 2. Convert to A-normal form; that is, function arguments are always variables. * Use case for strict arguments: f E ==> case E of x -> f x (where f is strict) * Use let for non-trivial lazy arguments f E ==> let x = E in f x (were f is lazy and x is non-trivial) 3. Similarly, convert any unboxed lets into cases. [I'm experimenting with leaving 'ok-for-speculation' rhss in let-form right up to this point.] 4. Ensure that *value* lambdas only occur as the RHS of a binding (The code generator can't deal with anything else.) Type lambdas are ok, however, because the code gen discards them. 5. [Not any more; nuked Jun 2002] Do the seq/par munging. 6. Clone all local Ids. This means that all such Ids are unique, rather than the weaker guarantee of no clashes which the simplifier provides. And that is what the code generator needs. We don't clone TyVars or CoVars. The code gen doesn't need that, and doing so would be tiresome because then we'd need to substitute in types and coercions. 7. Give each dynamic CCall occurrence a fresh unique; this is rather like the cloning step above. 8. Inject bindings for the "implicit" Ids: * Constructor wrappers * Constructor workers We want curried definitions for all of these in case they aren't inlined by some caller. 9. Replace (lazy e) by e. See Note [lazyId magic] in MkId.hs Also replace (noinline e) by e. 10. Convert (LitInteger i t) into the core representation for the Integer i. Normally this uses mkInteger, but if we are using the integer-gmp implementation then there is a special case where we use the S# constructor for Integers that are in the range of Int. 11. Uphold tick consistency while doing this: We move ticks out of (non-type) applications where we can, and make sure that we annotate according to scoping rules when floating. This is all done modulo type applications and abstractions, so that when type erasure is done for conversion to STG, we don't end up with any trivial or useless bindings. Note [CorePrep invariants] ~~~~~~~~~~~~~~~~~~~~~~~~~~ Here is the syntax of the Core produced by CorePrep: Trivial expressions arg ::= lit | var | arg ty | /\a. arg | truv co | /\c. arg | arg |> co Applications app ::= lit | var | app arg | app ty | app co | app |> co Expressions body ::= app | let(rec) x = rhs in body -- Boxed only | case body of pat -> body | /\a. body | /\c. body | body |> co Right hand sides (only place where value lambdas can occur) rhs ::= /\a.rhs | \x.rhs | body We define a synonym for each of these non-terminals. Functions with the corresponding name produce a result in that syntax. -} type CpeArg = CoreExpr -- Non-terminal 'arg' type CpeApp = CoreExpr -- Non-terminal 'app' type CpeBody = CoreExpr -- Non-terminal 'body' type CpeRhs = CoreExpr -- Non-terminal 'rhs' {- ************************************************************************ * * Top level stuff * * ************************************************************************ -} corePrepPgm :: HscEnv -> Module -> ModLocation -> CoreProgram -> [TyCon] -> IO CoreProgram corePrepPgm hsc_env this_mod mod_loc binds data_tycons = withTiming (pure dflags) (text "CorePrep"<+>brackets (ppr this_mod)) (const ()) $ do us <- mkSplitUniqSupply 's' initialCorePrepEnv <- mkInitialCorePrepEnv dflags hsc_env let implicit_binds = mkDataConWorkers dflags mod_loc data_tycons -- NB: we must feed mkImplicitBinds through corePrep too -- so that they are suitably cloned and eta-expanded binds_out = initUs_ us $ do floats1 <- corePrepTopBinds initialCorePrepEnv binds floats2 <- corePrepTopBinds initialCorePrepEnv implicit_binds return (deFloatTop (floats1 `appendFloats` floats2)) endPassIO hsc_env alwaysQualify CorePrep binds_out [] return binds_out where dflags = hsc_dflags hsc_env corePrepExpr :: DynFlags -> HscEnv -> CoreExpr -> IO CoreExpr corePrepExpr dflags hsc_env expr = withTiming (pure dflags) (text "CorePrep [expr]") (const ()) $ do us <- mkSplitUniqSupply 's' initialCorePrepEnv <- mkInitialCorePrepEnv dflags hsc_env let new_expr = initUs_ us (cpeBodyNF initialCorePrepEnv expr) dumpIfSet_dyn dflags Opt_D_dump_prep "CorePrep" (ppr new_expr) return new_expr corePrepTopBinds :: CorePrepEnv -> [CoreBind] -> UniqSM Floats -- Note [Floating out of top level bindings] corePrepTopBinds initialCorePrepEnv binds = go initialCorePrepEnv binds where go _ [] = return emptyFloats go env (bind : binds) = do (env', floats, maybe_new_bind) <- cpeBind TopLevel env bind MASSERT(isNothing maybe_new_bind) -- Only join points get returned this way by -- cpeBind, and no join point may float to top floatss <- go env' binds return (floats `appendFloats` floatss) mkDataConWorkers :: DynFlags -> ModLocation -> [TyCon] -> [CoreBind] -- See Note [Data constructor workers] -- c.f. Note [Injecting implicit bindings] in TidyPgm mkDataConWorkers dflags mod_loc data_tycons = [ NonRec id (tick_it (getName data_con) (Var id)) -- The ice is thin here, but it works | tycon <- data_tycons, -- CorePrep will eta-expand it data_con <- tyConDataCons tycon, let id = dataConWorkId data_con ] where -- If we want to generate debug info, we put a source note on the -- worker. This is useful, especially for heap profiling. tick_it name | debugLevel dflags == 0 = id | RealSrcSpan span <- nameSrcSpan name = tick span | Just file <- ml_hs_file mod_loc = tick (span1 file) | otherwise = tick (span1 "???") where tick span = Tick (SourceNote span $ showSDoc dflags (ppr name)) span1 file = realSrcLocSpan $ mkRealSrcLoc (mkFastString file) 1 1 {- Note [Floating out of top level bindings] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ NB: we do need to float out of top-level bindings Consider x = length [True,False] We want to get s1 = False : [] s2 = True : s1 x = length s2 We return a *list* of bindings, because we may start with x* = f (g y) where x is demanded, in which case we want to finish with a = g y x* = f a And then x will actually end up case-bound Note [CafInfo and floating] ~~~~~~~~~~~~~~~~~~~~~~~~~~~ What happens when we try to float bindings to the top level? At this point all the CafInfo is supposed to be correct, and we must make certain that is true of the new top-level bindings. There are two cases to consider a) The top-level binding is marked asCafRefs. In that case we are basically fine. The floated bindings had better all be lazy lets, so they can float to top level, but they'll all have HasCafRefs (the default) which is safe. b) The top-level binding is marked NoCafRefs. This really happens Example. CoreTidy produces $fApplicativeSTM [NoCafRefs] = D:Alternative retry# ...blah... Now CorePrep has to eta-expand to $fApplicativeSTM = let sat = \xy. retry x y in D:Alternative sat ...blah... So what we *want* is sat [NoCafRefs] = \xy. retry x y $fApplicativeSTM [NoCafRefs] = D:Alternative sat ...blah... So, gruesomely, we must set the NoCafRefs flag on the sat bindings, *and* substitute the modified 'sat' into the old RHS. It should be the case that 'sat' is itself [NoCafRefs] (a value, no cafs) else the original top-level binding would not itself have been marked [NoCafRefs]. The DEBUG check in CoreToStg for consistentCafInfo will find this. This is all very gruesome and horrible. It would be better to figure out CafInfo later, after CorePrep. We'll do that in due course. Meanwhile this horrible hack works. Note [Join points and floating] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Join points can float out of other join points but not out of value bindings: let z = let w = ... in -- can float join k = ... in -- can't float ... jump k ... join j x1 ... xn = let y = ... in -- can float (but don't want to) join h = ... in -- can float (but not much point) ... jump h ... in ... Here, the jump to h remains valid if h is floated outward, but the jump to k does not. We don't float *out* of join points. It would only be safe to float out of nullary join points (or ones where the arguments are all either type arguments or dead binders). Nullary join points aren't ever recursive, so they're always effectively one-shot functions, which we don't float out of. We *could* float join points from nullary join points, but there's no clear benefit at this stage. Note [Data constructor workers] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Create any necessary "implicit" bindings for data con workers. We create the rather strange (non-recursive!) binding $wC = \x y -> $wC x y i.e. a curried constructor that allocates. This means that we can treat the worker for a constructor like any other function in the rest of the compiler. The point here is that CoreToStg will generate a StgConApp for the RHS, rather than a call to the worker (which would give a loop). As Lennart says: the ice is thin here, but it works. Hmm. Should we create bindings for dictionary constructors? They are always fully applied, and the bindings are just there to support partial applications. But it's easier to let them through. Note [Dead code in CorePrep] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Imagine that we got an input program like this (see Trac #4962): f :: Show b => Int -> (Int, b -> Maybe Int -> Int) f x = (g True (Just x) + g () (Just x), g) where g :: Show a => a -> Maybe Int -> Int g _ Nothing = x g y (Just z) = if z > 100 then g y (Just (z + length (show y))) else g y unknown After specialisation and SpecConstr, we would get something like this: f :: Show b => Int -> (Int, b -> Maybe Int -> Int) f x = (g$Bool_True_Just x + g$Unit_Unit_Just x, g) where {-# RULES g $dBool = g$Bool g $dUnit = g$Unit #-} g = ... {-# RULES forall x. g$Bool True (Just x) = g$Bool_True_Just x #-} g$Bool = ... {-# RULES forall x. g$Unit () (Just x) = g$Unit_Unit_Just x #-} g$Unit = ... g$Bool_True_Just = ... g$Unit_Unit_Just = ... Note that the g$Bool and g$Unit functions are actually dead code: they are only kept alive by the occurrence analyser because they are referred to by the rules of g, which is being kept alive by the fact that it is used (unspecialised) in the returned pair. However, at the CorePrep stage there is no way that the rules for g will ever fire, and it really seems like a shame to produce an output program that goes to the trouble of allocating a closure for the unreachable g$Bool and g$Unit functions. The way we fix this is to: * In cloneBndr, drop all unfoldings/rules * In deFloatTop, run a simple dead code analyser on each top-level RHS to drop the dead local bindings. For that call to OccAnal, we disable the binder swap, else the occurrence analyser sometimes introduces new let bindings for cased binders, which lead to the bug in #5433. The reason we don't just OccAnal the whole output of CorePrep is that the tidier ensures that all top-level binders are GlobalIds, so they don't show up in the free variables any longer. So if you run the occurrence analyser on the output of CoreTidy (or later) you e.g. turn this program: Rec { f = ... f ... } Into this one: f = ... f ... (Since f is not considered to be free in its own RHS.) ************************************************************************ * * The main code * * ************************************************************************ -} cpeBind :: TopLevelFlag -> CorePrepEnv -> CoreBind -> UniqSM (CorePrepEnv, Floats, -- Floating value bindings Maybe CoreBind) -- Just bind' <=> returned new bind; no float -- Nothing <=> added bind' to floats instead cpeBind top_lvl env (NonRec bndr rhs) | not (isJoinId bndr) = do { (_, bndr1) <- cpCloneBndr env bndr ; let dmd = idDemandInfo bndr is_unlifted = isUnliftedType (idType bndr) ; (floats, bndr2, rhs2) <- cpePair top_lvl NonRecursive dmd is_unlifted env bndr1 rhs -- See Note [Inlining in CorePrep] ; if exprIsTrivial rhs2 && isNotTopLevel top_lvl then return (extendCorePrepEnvExpr env bndr rhs2, floats, Nothing) else do { ; let new_float = mkFloat dmd is_unlifted bndr2 rhs2 -- We want bndr'' in the envt, because it records -- the evaluated-ness of the binder ; return (extendCorePrepEnv env bndr bndr2, addFloat floats new_float, Nothing) }} | otherwise -- See Note [Join points and floating] = ASSERT(not (isTopLevel top_lvl)) -- can't have top-level join point do { (_, bndr1) <- cpCloneBndr env bndr ; (bndr2, rhs1) <- cpeJoinPair env bndr1 rhs ; return (extendCorePrepEnv env bndr bndr2, emptyFloats, Just (NonRec bndr2 rhs1)) } cpeBind top_lvl env (Rec pairs) | not (isJoinId (head bndrs)) = do { (env', bndrs1) <- cpCloneBndrs env bndrs ; stuff <- zipWithM (cpePair top_lvl Recursive topDmd False env') bndrs1 rhss ; let (floats_s, bndrs2, rhss2) = unzip3 stuff all_pairs = foldrOL add_float (bndrs2 `zip` rhss2) (concatFloats floats_s) ; return (extendCorePrepEnvList env (bndrs `zip` bndrs2), unitFloat (FloatLet (Rec all_pairs)), Nothing) } | otherwise -- See Note [Join points and floating] = do { (env', bndrs1) <- cpCloneBndrs env bndrs ; pairs1 <- zipWithM (cpeJoinPair env') bndrs1 rhss ; let bndrs2 = map fst pairs1 ; return (extendCorePrepEnvList env' (bndrs `zip` bndrs2), emptyFloats, Just (Rec pairs1)) } where (bndrs, rhss) = unzip pairs -- Flatten all the floats, and the current -- group into a single giant Rec add_float (FloatLet (NonRec b r)) prs2 = (b,r) : prs2 add_float (FloatLet (Rec prs1)) prs2 = prs1 ++ prs2 add_float b _ = pprPanic "cpeBind" (ppr b) --------------- cpePair :: TopLevelFlag -> RecFlag -> Demand -> Bool -> CorePrepEnv -> Id -> CoreExpr -> UniqSM (Floats, Id, CpeRhs) -- Used for all bindings cpePair top_lvl is_rec dmd is_unlifted env bndr rhs = ASSERT(not (isJoinId bndr)) -- those should use cpeJoinPair do { (floats1, rhs1) <- cpeRhsE env rhs -- See if we are allowed to float this stuff out of the RHS ; (floats2, rhs2) <- float_from_rhs floats1 rhs1 -- Make the arity match up ; (floats3, rhs3) <- if manifestArity rhs1 <= arity then return (floats2, cpeEtaExpand arity rhs2) else WARN(True, text "CorePrep: silly extra arguments:" <+> ppr bndr) -- Note [Silly extra arguments] (do { v <- newVar (idType bndr) ; let float = mkFloat topDmd False v rhs2 ; return ( addFloat floats2 float , cpeEtaExpand arity (Var v)) }) -- Wrap floating ticks ; let (floats4, rhs4) = wrapTicks floats3 rhs3 -- Record if the binder is evaluated -- and otherwise trim off the unfolding altogether -- It's not used by the code generator; getting rid of it reduces -- heap usage and, since we may be changing uniques, we'd have -- to substitute to keep it right ; let bndr' | exprIsHNF rhs3 = bndr `setIdUnfolding` evaldUnfolding | otherwise = bndr `setIdUnfolding` noUnfolding ; return (floats4, bndr', rhs4) } where platform = targetPlatform (cpe_dynFlags env) arity = idArity bndr -- We must match this arity --------------------- float_from_rhs floats rhs | isEmptyFloats floats = return (emptyFloats, rhs) | isTopLevel top_lvl = float_top floats rhs | otherwise = float_nested floats rhs --------------------- float_nested floats rhs | wantFloatNested is_rec dmd is_unlifted floats rhs = return (floats, rhs) | otherwise = dontFloat floats rhs --------------------- float_top floats rhs -- Urhgh! See Note [CafInfo and floating] | mayHaveCafRefs (idCafInfo bndr) , allLazyTop floats = return (floats, rhs) -- So the top-level binding is marked NoCafRefs | Just (floats', rhs') <- canFloatFromNoCaf platform floats rhs = return (floats', rhs') | otherwise = dontFloat floats rhs dontFloat :: Floats -> CpeRhs -> UniqSM (Floats, CpeBody) -- Non-empty floats, but do not want to float from rhs -- So wrap the rhs in the floats -- But: rhs1 might have lambdas, and we can't -- put them inside a wrapBinds dontFloat floats1 rhs = do { (floats2, body) <- rhsToBody rhs ; return (emptyFloats, wrapBinds floats1 $ wrapBinds floats2 body) } {- Note [Silly extra arguments] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Suppose we had this f{arity=1} = \x\y. e We *must* match the arity on the Id, so we have to generate f' = \x\y. e f = \x. f' x It's a bizarre case: why is the arity on the Id wrong? Reason (in the days of __inline_me__): f{arity=0} = __inline_me__ (let v = expensive in \xy. e) When InlineMe notes go away this won't happen any more. But it seems good for CorePrep to be robust. -} --------------- cpeJoinPair :: CorePrepEnv -> JoinId -> CoreExpr -> UniqSM (JoinId, CpeRhs) -- Used for all join bindings cpeJoinPair env bndr rhs = ASSERT(isJoinId bndr) do { let Just join_arity = isJoinId_maybe bndr (bndrs, body) = collectNBinders join_arity rhs ; (env', bndrs') <- cpCloneBndrs env bndrs ; body' <- cpeBodyNF env' body -- Will let-bind the body if it starts -- with a lambda ; let rhs' = mkCoreLams bndrs' body' bndr' = bndr `setIdUnfolding` evaldUnfolding `setIdArity` count isId bndrs -- See Note [Arity and join points] ; return (bndr', rhs') } {- Note [Arity and join points] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Up to now, we've allowed a join point to have an arity greater than its join arity (minus type arguments), since this is what's useful for eta expansion. However, for code gen purposes, its arity must be exactly the number of value arguments it will be called with, and it must have exactly that many value lambdas. Hence if there are extra lambdas we must let-bind the body of the RHS: join j x y z = \w -> ... in ... => join j x y z = (let f = \w -> ... in f) in ... This is also what happens with Note [Silly extra arguments]. Note that it's okay for us to mess with the arity because a join point is never exported. -} -- --------------------------------------------------------------------------- -- CpeRhs: produces a result satisfying CpeRhs -- --------------------------------------------------------------------------- cpeRhsE :: CorePrepEnv -> CoreExpr -> UniqSM (Floats, CpeRhs) -- If -- e ===> (bs, e') -- then -- e = let bs in e' (semantically, that is!) -- -- For example -- f (g x) ===> ([v = g x], f v) cpeRhsE _env expr@(Type {}) = return (emptyFloats, expr) cpeRhsE _env expr@(Coercion {}) = return (emptyFloats, expr) cpeRhsE env (Lit (LitInteger i _)) = cpeRhsE env (cvtLitInteger (cpe_dynFlags env) (getMkIntegerId env) (cpe_integerSDataCon env) i) cpeRhsE _env expr@(Lit {}) = return (emptyFloats, expr) cpeRhsE env expr@(Var {}) = cpeApp env expr cpeRhsE env expr@(App {}) = cpeApp env expr cpeRhsE env (Let bind body) = do { (env', bind_floats, maybe_bind') <- cpeBind NotTopLevel env bind ; (body_floats, body') <- cpeRhsE env' body ; let expr' = case maybe_bind' of Just bind' -> Let bind' body' Nothing -> body' ; return (bind_floats `appendFloats` body_floats, expr') } cpeRhsE env (Tick tickish expr) | tickishPlace tickish == PlaceNonLam && tickish `tickishScopesLike` SoftScope = do { (floats, body) <- cpeRhsE env expr -- See [Floating Ticks in CorePrep] ; return (unitFloat (FloatTick tickish) `appendFloats` floats, body) } | otherwise = do { body <- cpeBodyNF env expr ; return (emptyFloats, mkTick tickish' body) } where tickish' | Breakpoint n fvs <- tickish -- See also 'substTickish' = Breakpoint n (map (getIdFromTrivialExpr . lookupCorePrepEnv env) fvs) | otherwise = tickish cpeRhsE env (Cast expr co) = do { (floats, expr') <- cpeRhsE env expr ; return (floats, Cast expr' co) } cpeRhsE env expr@(Lam {}) = do { let (bndrs,body) = collectBinders expr ; (env', bndrs') <- cpCloneBndrs env bndrs ; body' <- cpeBodyNF env' body ; return (emptyFloats, mkLams bndrs' body') } cpeRhsE env (Case scrut bndr ty alts) = do { (floats, scrut') <- cpeBody env scrut ; let bndr1 = bndr `setIdUnfolding` evaldUnfolding -- Record that the case binder is evaluated in the alternatives ; (env', bndr2) <- cpCloneBndr env bndr1 ; let alts' -- This flag is intended to aid in debugging strictness -- analysis bugs. These are particularly nasty to chase down as -- they may manifest as segmentation faults. When this flag is -- enabled we instead produce an 'error' expression to catch -- the case where a function we think should bottom -- unexpectedly returns. | gopt Opt_CatchBottoms (cpe_dynFlags env) , not (altsAreExhaustive alts) = addDefault alts (Just err) | otherwise = alts where err = mkRuntimeErrorApp rUNTIME_ERROR_ID ty "Bottoming expression returned" ; alts'' <- mapM (sat_alt env') alts' ; return (floats, Case scrut' bndr2 ty alts'') } where sat_alt env (con, bs, rhs) = do { (env2, bs') <- cpCloneBndrs env bs ; rhs' <- cpeBodyNF env2 rhs ; return (con, bs', rhs') } cvtLitInteger :: DynFlags -> Id -> Maybe DataCon -> Integer -> CoreExpr -- Here we convert a literal Integer to the low-level -- representation. Exactly how we do this depends on the -- library that implements Integer. If it's GMP we -- use the S# data constructor for small literals. -- See Note [Integer literals] in Literal cvtLitInteger dflags _ (Just sdatacon) i | inIntRange dflags i -- Special case for small integers = mkConApp sdatacon [Lit (mkMachInt dflags i)] cvtLitInteger dflags mk_integer _ i = mkApps (Var mk_integer) [isNonNegative, ints] where isNonNegative = if i < 0 then mkConApp falseDataCon [] else mkConApp trueDataCon [] ints = mkListExpr intTy (f (abs i)) f 0 = [] f x = let low = x .&. mask high = x `shiftR` bits in mkConApp intDataCon [Lit (mkMachInt dflags low)] : f high bits = 31 mask = 2 ^ bits - 1 -- --------------------------------------------------------------------------- -- CpeBody: produces a result satisfying CpeBody -- --------------------------------------------------------------------------- -- | Convert a 'CoreExpr' so it satisfies 'CpeBody', without -- producing any floats (any generated floats are immediately -- let-bound using 'wrapBinds'). Generally you want this, esp. -- when you've reached a binding form (e.g., a lambda) and -- floating any further would be incorrect. cpeBodyNF :: CorePrepEnv -> CoreExpr -> UniqSM CpeBody cpeBodyNF env expr = do { (floats, body) <- cpeBody env expr ; return (wrapBinds floats body) } -- | Convert a 'CoreExpr' so it satisfies 'CpeBody'; also produce -- a list of 'Floats' which are being propagated upwards. In -- fact, this function is used in only two cases: to -- implement 'cpeBodyNF' (which is what you usually want), -- and in the case when a let-binding is in a case scrutinee--here, -- we can always float out: -- -- case (let x = y in z) of ... -- ==> let x = y in case z of ... -- cpeBody :: CorePrepEnv -> CoreExpr -> UniqSM (Floats, CpeBody) cpeBody env expr = do { (floats1, rhs) <- cpeRhsE env expr ; (floats2, body) <- rhsToBody rhs ; return (floats1 `appendFloats` floats2, body) } -------- rhsToBody :: CpeRhs -> UniqSM (Floats, CpeBody) -- Remove top level lambdas by let-binding rhsToBody (Tick t expr) | tickishScoped t == NoScope -- only float out of non-scoped annotations = do { (floats, expr') <- rhsToBody expr ; return (floats, mkTick t expr') } rhsToBody (Cast e co) -- You can get things like -- case e of { p -> coerce t (\s -> ...) } = do { (floats, e') <- rhsToBody e ; return (floats, Cast e' co) } rhsToBody expr@(Lam {}) | Just no_lam_result <- tryEtaReducePrep bndrs body = return (emptyFloats, no_lam_result) | all isTyVar bndrs -- Type lambdas are ok = return (emptyFloats, expr) | otherwise -- Some value lambdas = do { fn <- newVar (exprType expr) ; let rhs = cpeEtaExpand (exprArity expr) expr float = FloatLet (NonRec fn rhs) ; return (unitFloat float, Var fn) } where (bndrs,body) = collectBinders expr rhsToBody expr = return (emptyFloats, expr) -- --------------------------------------------------------------------------- -- CpeApp: produces a result satisfying CpeApp -- --------------------------------------------------------------------------- data ArgInfo = CpeApp CoreArg | CpeCast Coercion | CpeTick (Tickish Id) {- Note [runRW arg] ~~~~~~~~~~~~~~~~~~~ If we got, say runRW# (case bot of {}) which happened in Trac #11291, we do /not/ want to turn it into (case bot of {}) realWorldPrimId# because that gives a panic in CoreToStg.myCollectArgs, which expects only variables in function position. But if we are sure to make runRW# strict (which we do in MkId), this can't happen -} cpeApp :: CorePrepEnv -> CoreExpr -> UniqSM (Floats, CpeRhs) -- May return a CpeRhs because of saturating primops cpeApp top_env expr = do { let (terminal, args, depth) = collect_args expr ; cpe_app top_env terminal args depth } where -- We have a nested data structure of the form -- e `App` a1 `App` a2 ... `App` an, convert it into -- (e, [CpeApp a1, CpeApp a2, ..., CpeApp an], depth) -- We use 'ArgInfo' because we may also need to -- record casts and ticks. Depth counts the number -- of arguments that would consume strictness information -- (so, no type or coercion arguments.) collect_args :: CoreExpr -> (CoreExpr, [ArgInfo], Int) collect_args e = go e [] 0 where go (App fun arg) as !depth = go fun (CpeApp arg : as) (if isTyCoArg arg then depth else depth + 1) go (Cast fun co) as depth = go fun (CpeCast co : as) depth go (Tick tickish fun) as depth | tickishPlace tickish == PlaceNonLam && tickish `tickishScopesLike` SoftScope = go fun (CpeTick tickish : as) depth go terminal as depth = (terminal, as, depth) cpe_app :: CorePrepEnv -> CoreExpr -> [ArgInfo] -> Int -> UniqSM (Floats, CpeRhs) cpe_app env (Var f) (CpeApp Type{} : CpeApp arg : args) depth | f `hasKey` lazyIdKey -- Replace (lazy a) with a, and || f `hasKey` noinlineIdKey -- Replace (noinline a) with a -- Consider the code: -- -- lazy (f x) y -- -- We need to make sure that we need to recursively collect arguments on -- "f x", otherwise we'll float "f x" out (it's not a variable) and -- end up with this awful -ddump-prep: -- -- case f x of f_x { -- __DEFAULT -> f_x y -- } -- -- rather than the far superior "f x y". Test case is par01. = let (terminal, args', depth') = collect_args arg in cpe_app env terminal (args' ++ args) (depth + depth' - 1) cpe_app env (Var f) [CpeApp _runtimeRep@Type{}, CpeApp _type@Type{}, CpeApp arg] 1 | f `hasKey` runRWKey -- Replace (runRW# f) by (f realWorld#), beta reducing if possible (this -- is why we return a CorePrepEnv as well) = case arg of Lam s body -> cpe_app (extendCorePrepEnv env s realWorldPrimId) body [] 0 _ -> cpe_app env arg [CpeApp (Var realWorldPrimId)] 1 cpe_app env (Var v) args depth = do { v1 <- fiddleCCall v ; let e2 = lookupCorePrepEnv env v1 hd = getIdFromTrivialExpr_maybe e2 -- NB: depth from collect_args is right, because e2 is a trivial expression -- and thus its embedded Id *must* be at the same depth as any -- Apps it is under are type applications only (c.f. -- exprIsTrivial). But note that we need the type of the -- expression, not the id. ; (app, floats) <- rebuild_app args e2 (exprType e2) emptyFloats stricts ; mb_saturate hd app floats depth } where stricts = case idStrictness v of StrictSig (DmdType _ demands _) | listLengthCmp demands depth /= GT -> demands -- length demands <= depth | otherwise -> [] -- If depth < length demands, then we have too few args to -- satisfy strictness info so we have to ignore all the -- strictness info, e.g. + (error "urk") -- Here, we can't evaluate the arg strictly, because this -- partial application might be seq'd -- We inlined into something that's not a var and has no args. -- Bounce it back up to cpeRhsE. cpe_app env fun [] _ = cpeRhsE env fun -- N-variable fun, better let-bind it cpe_app env fun args depth = do { (fun_floats, fun') <- cpeArg env evalDmd fun ty -- The evalDmd says that it's sure to be evaluated, -- so we'll end up case-binding it ; (app, floats) <- rebuild_app args fun' ty fun_floats [] ; mb_saturate Nothing app floats depth } where ty = exprType fun -- Saturate if necessary mb_saturate head app floats depth = case head of Just fn_id -> do { sat_app <- maybeSaturate fn_id app depth ; return (floats, sat_app) } _other -> return (floats, app) -- Deconstruct and rebuild the application, floating any non-atomic -- arguments to the outside. We collect the type of the expression, -- the head of the application, and the number of actual value arguments, -- all of which are used to possibly saturate this application if it -- has a constructor or primop at the head. rebuild_app :: [ArgInfo] -- The arguments (inner to outer) -> CpeApp -> Type -> Floats -> [Demand] -> UniqSM (CpeApp, Floats) rebuild_app [] app _ floats ss = do MASSERT(null ss) -- make sure we used all the strictness info return (app, floats) rebuild_app (a : as) fun' fun_ty floats ss = case a of CpeApp arg@(Type arg_ty) -> rebuild_app as (App fun' arg) (piResultTy fun_ty arg_ty) floats ss CpeApp arg@(Coercion {}) -> rebuild_app as (App fun' arg) (funResultTy fun_ty) floats ss CpeApp arg -> do let (ss1, ss_rest) -- See Note [lazyId magic] in MkId = case (ss, isLazyExpr arg) of (_ : ss_rest, True) -> (topDmd, ss_rest) (ss1 : ss_rest, False) -> (ss1, ss_rest) ([], _) -> (topDmd, []) (arg_ty, res_ty) = expectJust "cpeBody:collect_args" $ splitFunTy_maybe fun_ty (fs, arg') <- cpeArg top_env ss1 arg arg_ty rebuild_app as (App fun' arg') res_ty (fs `appendFloats` floats) ss_rest CpeCast co -> let Pair _ty1 ty2 = coercionKind co in rebuild_app as (Cast fun' co) ty2 floats ss CpeTick tickish -> -- See [Floating Ticks in CorePrep] rebuild_app as fun' fun_ty (addFloat floats (FloatTick tickish)) ss isLazyExpr :: CoreExpr -> Bool -- See Note [lazyId magic] in MkId isLazyExpr (Cast e _) = isLazyExpr e isLazyExpr (Tick _ e) = isLazyExpr e isLazyExpr (Var f `App` _ `App` _) = f `hasKey` lazyIdKey isLazyExpr _ = False -- --------------------------------------------------------------------------- -- CpeArg: produces a result satisfying CpeArg -- --------------------------------------------------------------------------- {- Note [ANF-ising literal string arguments] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider a program like, data Foo = Foo Addr# foo = Foo "turtle"# When we go to ANFise this we might think that we want to float the string literal like we do any other non-trivial argument. This would look like, foo = u\ [] case "turtle"# of s { __DEFAULT__ -> Foo s } However, this 1) isn't necessary since strings are in a sense "trivial"; and 2) wreaks havoc on the CAF annotations that we produce here since we the result above is caffy since it is updateable. Ideally at some point in the future we would like to just float the literal to the top level as suggested in #11312, s = "turtle"# foo = Foo s However, until then we simply add a special case excluding literals from the floating done by cpeArg. -} -- | Is an argument okay to CPE? okCpeArg :: CoreExpr -> Bool -- Don't float literals. See Note [ANF-ising literal string arguments]. okCpeArg (Lit _) = False -- Do not eta expand a trivial argument okCpeArg expr = not (exprIsTrivial expr) -- This is where we arrange that a non-trivial argument is let-bound cpeArg :: CorePrepEnv -> Demand -> CoreArg -> Type -> UniqSM (Floats, CpeArg) cpeArg env dmd arg arg_ty = do { (floats1, arg1) <- cpeRhsE env arg -- arg1 can be a lambda ; (floats2, arg2) <- if want_float floats1 arg1 then return (floats1, arg1) else dontFloat floats1 arg1 -- Else case: arg1 might have lambdas, and we can't -- put them inside a wrapBinds ; if okCpeArg arg2 then do { v <- newVar arg_ty ; let arg3 = cpeEtaExpand (exprArity arg2) arg2 arg_float = mkFloat dmd is_unlifted v arg3 ; return (addFloat floats2 arg_float, varToCoreExpr v) } else return (floats2, arg2) } where is_unlifted = isUnliftedType arg_ty want_float = wantFloatNested NonRecursive dmd is_unlifted {- Note [Floating unlifted arguments] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider C (let v* = expensive in v) where the "*" indicates "will be demanded". Usually v will have been inlined by now, but let's suppose it hasn't (see Trac #2756). Then we do *not* want to get let v* = expensive in C v because that has different strictness. Hence the use of 'allLazy'. (NB: the let v* turns into a FloatCase, in mkLocalNonRec.) ------------------------------------------------------------------------------ -- Building the saturated syntax -- --------------------------------------------------------------------------- maybeSaturate deals with saturating primops and constructors The type is the type of the entire application -} maybeSaturate :: Id -> CpeApp -> Int -> UniqSM CpeRhs maybeSaturate fn expr n_args | Just DataToTagOp <- isPrimOpId_maybe fn -- DataToTag must have an evaluated arg -- A gruesome special case = saturateDataToTag sat_expr | hasNoBinding fn -- There's no binding = return sat_expr | otherwise = return expr where fn_arity = idArity fn excess_arity = fn_arity - n_args sat_expr = cpeEtaExpand excess_arity expr ------------- saturateDataToTag :: CpeApp -> UniqSM CpeApp -- See Note [dataToTag magic] saturateDataToTag sat_expr = do { let (eta_bndrs, eta_body) = collectBinders sat_expr ; eta_body' <- eval_data2tag_arg eta_body ; return (mkLams eta_bndrs eta_body') } where eval_data2tag_arg :: CpeApp -> UniqSM CpeBody eval_data2tag_arg app@(fun `App` arg) | exprIsHNF arg -- Includes nullary constructors = return app -- The arg is evaluated | otherwise -- Arg not evaluated, so evaluate it = do { arg_id <- newVar (exprType arg) ; let arg_id1 = setIdUnfolding arg_id evaldUnfolding ; return (Case arg arg_id1 (exprType app) [(DEFAULT, [], fun `App` Var arg_id1)]) } eval_data2tag_arg (Tick t app) -- Scc notes can appear = do { app' <- eval_data2tag_arg app ; return (Tick t app') } eval_data2tag_arg other -- Should not happen = pprPanic "eval_data2tag" (ppr other) {- Note [dataToTag magic] ~~~~~~~~~~~~~~~~~~~~~~ Horrid: we must ensure that the arg of data2TagOp is evaluated (data2tag x) --> (case x of y -> data2tag y) (yuk yuk) take into account the lambdas we've now introduced How might it not be evaluated? Well, we might have floated it out of the scope of a `seq`, or dropped the `seq` altogether. ************************************************************************ * * Simple CoreSyn operations * * ************************************************************************ -} {- -- ----------------------------------------------------------------------------- -- Eta reduction -- ----------------------------------------------------------------------------- Note [Eta expansion] ~~~~~~~~~~~~~~~~~~~~~ Eta expand to match the arity claimed by the binder Remember, CorePrep must not change arity Eta expansion might not have happened already, because it is done by the simplifier only when there at least one lambda already. NB1:we could refrain when the RHS is trivial (which can happen for exported things). This would reduce the amount of code generated (a little) and make things a little words for code compiled without -O. The case in point is data constructor wrappers. NB2: we have to be careful that the result of etaExpand doesn't invalidate any of the assumptions that CorePrep is attempting to establish. One possible cause is eta expanding inside of an SCC note - we're now careful in etaExpand to make sure the SCC is pushed inside any new lambdas that are generated. Note [Eta expansion and the CorePrep invariants] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ It turns out to be much much easier to do eta expansion *after* the main CorePrep stuff. But that places constraints on the eta expander: given a CpeRhs, it must return a CpeRhs. For example here is what we do not want: f = /\a -> g (h 3) -- h has arity 2 After ANFing we get f = /\a -> let s = h 3 in g s and now we do NOT want eta expansion to give f = /\a -> \ y -> (let s = h 3 in g s) y Instead CoreArity.etaExpand gives f = /\a -> \y -> let s = h 3 in g s y -} cpeEtaExpand :: Arity -> CpeRhs -> CpeRhs cpeEtaExpand arity expr | arity == 0 = expr | otherwise = etaExpand arity expr {- -- ----------------------------------------------------------------------------- -- Eta reduction -- ----------------------------------------------------------------------------- Why try eta reduction? Hasn't the simplifier already done eta? But the simplifier only eta reduces if that leaves something trivial (like f, or f Int). But for deLam it would be enough to get to a partial application: case x of { p -> \xs. map f xs } ==> case x of { p -> map f } -} tryEtaReducePrep :: [CoreBndr] -> CoreExpr -> Maybe CoreExpr tryEtaReducePrep bndrs expr@(App _ _) | ok_to_eta_reduce f , n_remaining >= 0 , and (zipWith ok bndrs last_args) , not (any (`elemVarSet` fvs_remaining) bndrs) , exprIsHNF remaining_expr -- Don't turn value into a non-value -- else the behaviour with 'seq' changes = Just remaining_expr where (f, args) = collectArgs expr remaining_expr = mkApps f remaining_args fvs_remaining = exprFreeVars remaining_expr (remaining_args, last_args) = splitAt n_remaining args n_remaining = length args - length bndrs ok bndr (Var arg) = bndr == arg ok _ _ = False -- We can't eta reduce something which must be saturated. ok_to_eta_reduce (Var f) = not (hasNoBinding f) ok_to_eta_reduce _ = False -- Safe. ToDo: generalise tryEtaReducePrep bndrs (Let bind@(NonRec _ r) body) | not (any (`elemVarSet` fvs) bndrs) = case tryEtaReducePrep bndrs body of Just e -> Just (Let bind e) Nothing -> Nothing where fvs = exprFreeVars r -- NB: do not attempt to eta-reduce across ticks -- Otherwise we risk reducing -- \x. (Tick (Breakpoint {x}) f x) -- ==> Tick (breakpoint {x}) f -- which is bogus (Trac #17228) -- tryEtaReducePrep bndrs (Tick tickish e) -- = fmap (mkTick tickish) $ tryEtaReducePrep bndrs e tryEtaReducePrep _ _ = Nothing {- ************************************************************************ * * Floats * * ************************************************************************ Note [Pin demand info on floats] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We pin demand info on floated lets, so that we can see the one-shot thunks. -} data FloatingBind = FloatLet CoreBind -- Rhs of bindings are CpeRhss -- They are always of lifted type; -- unlifted ones are done with FloatCase | FloatCase Id CpeBody Bool -- The bool indicates "ok-for-speculation" -- | See Note [Floating Ticks in CorePrep] | FloatTick (Tickish Id) data Floats = Floats OkToSpec (OrdList FloatingBind) instance Outputable FloatingBind where ppr (FloatLet b) = ppr b ppr (FloatCase b r ok) = brackets (ppr ok) <+> ppr b <+> equals <+> ppr r ppr (FloatTick t) = ppr t instance Outputable Floats where ppr (Floats flag fs) = text "Floats" <> brackets (ppr flag) <+> braces (vcat (map ppr (fromOL fs))) instance Outputable OkToSpec where ppr OkToSpec = text "OkToSpec" ppr IfUnboxedOk = text "IfUnboxedOk" ppr NotOkToSpec = text "NotOkToSpec" -- Can we float these binds out of the rhs of a let? We cache this decision -- to avoid having to recompute it in a non-linear way when there are -- deeply nested lets. data OkToSpec = OkToSpec -- Lazy bindings of lifted type | IfUnboxedOk -- A mixture of lazy lifted bindings and n -- ok-to-speculate unlifted bindings | NotOkToSpec -- Some not-ok-to-speculate unlifted bindings mkFloat :: Demand -> Bool -> Id -> CpeRhs -> FloatingBind mkFloat dmd is_unlifted bndr rhs | use_case = FloatCase bndr rhs (exprOkForSpeculation rhs) | is_hnf = FloatLet (NonRec bndr rhs) | otherwise = FloatLet (NonRec (setIdDemandInfo bndr dmd) rhs) -- See Note [Pin demand info on floats] where is_hnf = exprIsHNF rhs is_strict = isStrictDmd dmd use_case = is_unlifted || is_strict && not is_hnf -- Don't make a case for a value binding, -- even if it's strict. Otherwise we get -- case (\x -> e) of ...! emptyFloats :: Floats emptyFloats = Floats OkToSpec nilOL isEmptyFloats :: Floats -> Bool isEmptyFloats (Floats _ bs) = isNilOL bs wrapBinds :: Floats -> CpeBody -> CpeBody wrapBinds (Floats _ binds) body = foldrOL mk_bind body binds where mk_bind (FloatCase bndr rhs _) body = Case rhs bndr (exprType body) [(DEFAULT, [], body)] mk_bind (FloatLet bind) body = Let bind body mk_bind (FloatTick tickish) body = mkTick tickish body addFloat :: Floats -> FloatingBind -> Floats addFloat (Floats ok_to_spec floats) new_float = Floats (combine ok_to_spec (check new_float)) (floats `snocOL` new_float) where check (FloatLet _) = OkToSpec check (FloatCase _ _ ok_for_spec) | ok_for_spec = IfUnboxedOk | otherwise = NotOkToSpec check FloatTick{} = OkToSpec -- The ok-for-speculation flag says that it's safe to -- float this Case out of a let, and thereby do it more eagerly -- We need the top-level flag because it's never ok to float -- an unboxed binding to the top level unitFloat :: FloatingBind -> Floats unitFloat = addFloat emptyFloats appendFloats :: Floats -> Floats -> Floats appendFloats (Floats spec1 floats1) (Floats spec2 floats2) = Floats (combine spec1 spec2) (floats1 `appOL` floats2) concatFloats :: [Floats] -> OrdList FloatingBind concatFloats = foldr (\ (Floats _ bs1) bs2 -> appOL bs1 bs2) nilOL combine :: OkToSpec -> OkToSpec -> OkToSpec combine NotOkToSpec _ = NotOkToSpec combine _ NotOkToSpec = NotOkToSpec combine IfUnboxedOk _ = IfUnboxedOk combine _ IfUnboxedOk = IfUnboxedOk combine _ _ = OkToSpec deFloatTop :: Floats -> [CoreBind] -- For top level only; we don't expect any FloatCases deFloatTop (Floats _ floats) = foldrOL get [] floats where get (FloatLet b) bs = occurAnalyseRHSs b : bs get (FloatCase var body _) bs = occurAnalyseRHSs (NonRec var body) : bs get b _ = pprPanic "corePrepPgm" (ppr b) -- See Note [Dead code in CorePrep] occurAnalyseRHSs (NonRec x e) = NonRec x (occurAnalyseExpr_NoBinderSwap e) occurAnalyseRHSs (Rec xes) = Rec [(x, occurAnalyseExpr_NoBinderSwap e) | (x, e) <- xes] --------------------------------------------------------------------------- canFloatFromNoCaf :: Platform -> Floats -> CpeRhs -> Maybe (Floats, CpeRhs) -- Note [CafInfo and floating] canFloatFromNoCaf platform (Floats ok_to_spec fs) rhs | OkToSpec <- ok_to_spec -- Worth trying , Just (subst, fs') <- go (emptySubst, nilOL) (fromOL fs) = Just (Floats OkToSpec fs', subst_expr subst rhs) | otherwise = Nothing where subst_expr = substExpr (text "CorePrep") go :: (Subst, OrdList FloatingBind) -> [FloatingBind] -> Maybe (Subst, OrdList FloatingBind) go (subst, fbs_out) [] = Just (subst, fbs_out) go (subst, fbs_out) (FloatLet (NonRec b r) : fbs_in) | rhs_ok r = go (subst', fbs_out `snocOL` new_fb) fbs_in where (subst', b') = set_nocaf_bndr subst b new_fb = FloatLet (NonRec b' (subst_expr subst r)) go (subst, fbs_out) (FloatLet (Rec prs) : fbs_in) | all rhs_ok rs = go (subst', fbs_out `snocOL` new_fb) fbs_in where (bs,rs) = unzip prs (subst', bs') = mapAccumL set_nocaf_bndr subst bs rs' = map (subst_expr subst') rs new_fb = FloatLet (Rec (bs' `zip` rs')) go (subst, fbs_out) (ft@FloatTick{} : fbs_in) = go (subst, fbs_out `snocOL` ft) fbs_in go _ _ = Nothing -- Encountered a caffy binding ------------ set_nocaf_bndr subst bndr = (extendIdSubst subst bndr (Var bndr'), bndr') where bndr' = bndr `setIdCafInfo` NoCafRefs ------------ rhs_ok :: CoreExpr -> Bool -- We can only float to top level from a NoCaf thing if -- the new binding is static. However it can't mention -- any non-static things or it would *already* be Caffy rhs_ok = rhsIsStatic platform (\_ -> False) (\i -> pprPanic "rhsIsStatic" (integer i)) -- Integer literals should not show up wantFloatNested :: RecFlag -> Demand -> Bool -> Floats -> CpeRhs -> Bool wantFloatNested is_rec dmd is_unlifted floats rhs = isEmptyFloats floats || isStrictDmd dmd || is_unlifted || (allLazyNested is_rec floats && exprIsHNF rhs) -- Why the test for allLazyNested? -- v = f (x `divInt#` y) -- we don't want to float the case, even if f has arity 2, -- because floating the case would make it evaluated too early allLazyTop :: Floats -> Bool allLazyTop (Floats OkToSpec _) = True allLazyTop _ = False allLazyNested :: RecFlag -> Floats -> Bool allLazyNested _ (Floats OkToSpec _) = True allLazyNested _ (Floats NotOkToSpec _) = False allLazyNested is_rec (Floats IfUnboxedOk _) = isNonRec is_rec {- ************************************************************************ * * Cloning * * ************************************************************************ -} -- --------------------------------------------------------------------------- -- The environment -- --------------------------------------------------------------------------- -- Note [Inlining in CorePrep] -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~ -- There is a subtle but important invariant that must be upheld in the output -- of CorePrep: there are no "trivial" updatable thunks. Thus, this Core -- is impermissible: -- -- let x :: () -- x = y -- -- (where y is a reference to a GLOBAL variable). Thunks like this are silly: -- they can always be profitably replaced by inlining x with y. Consequently, -- the code generator/runtime does not bother implementing this properly -- (specifically, there is no implementation of stg_ap_0_upd_info, which is the -- stack frame that would be used to update this thunk. The "0" means it has -- zero free variables.) -- -- In general, the inliner is good at eliminating these let-bindings. However, -- there is one case where these trivial updatable thunks can arise: when -- we are optimizing away 'lazy' (see Note [lazyId magic], and also -- 'cpeRhsE'.) Then, we could have started with: -- -- let x :: () -- x = lazy @ () y -- -- which is a perfectly fine, non-trivial thunk, but then CorePrep will -- drop 'lazy', giving us 'x = y' which is trivial and impermissible. -- The solution is CorePrep to have a miniature inlining pass which deals -- with cases like this. We can then drop the let-binding altogether. -- -- Why does the removal of 'lazy' have to occur in CorePrep? -- The gory details are in Note [lazyId magic] in MkId, but the -- main reason is that lazy must appear in unfoldings (optimizer -- output) and it must prevent call-by-value for catch# (which -- is implemented by CorePrep.) -- -- An alternate strategy for solving this problem is to have the -- inliner treat 'lazy e' as a trivial expression if 'e' is trivial. -- We decided not to adopt this solution to keep the definition -- of 'exprIsTrivial' simple. -- -- There is ONE caveat however: for top-level bindings we have -- to preserve the binding so that we float the (hacky) non-recursive -- binding for data constructors; see Note [Data constructor workers]. -- -- Note [CorePrep inlines trivial CoreExpr not Id] -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -- Why does cpe_env need to be an IdEnv CoreExpr, as opposed to an -- IdEnv Id? Naively, we might conjecture that trivial updatable thunks -- as per Note [Inlining in CorePrep] always have the form -- 'lazy @ SomeType gbl_id'. But this is not true: the following is -- perfectly reasonable Core: -- -- let x :: () -- x = lazy @ (forall a. a) y @ Bool -- -- When we inline 'x' after eliminating 'lazy', we need to replace -- occurrences of 'x' with 'y @ bool', not just 'y'. Situations like -- this can easily arise with higher-rank types; thus, cpe_env must -- map to CoreExprs, not Ids. data CorePrepEnv = CPE { cpe_dynFlags :: DynFlags , cpe_env :: IdEnv CoreExpr -- Clone local Ids -- ^ This environment is used for three operations: -- -- 1. To support cloning of local Ids so that they are -- all unique (see item (6) of CorePrep overview). -- -- 2. To support beta-reduction of runRW, see -- Note [runRW magic] and Note [runRW arg]. -- -- 3. To let us inline trivial RHSs of non top-level let-bindings, -- see Note [lazyId magic], Note [Inlining in CorePrep] -- and Note [CorePrep inlines trivial CoreExpr not Id] (#12076) , cpe_mkIntegerId :: Id , cpe_integerSDataCon :: Maybe DataCon } lookupMkIntegerName :: DynFlags -> HscEnv -> IO Id lookupMkIntegerName dflags hsc_env = guardIntegerUse dflags $ liftM tyThingId $ lookupGlobal hsc_env mkIntegerName lookupIntegerSDataConName :: DynFlags -> HscEnv -> IO (Maybe DataCon) lookupIntegerSDataConName dflags hsc_env = case cIntegerLibraryType of IntegerGMP -> guardIntegerUse dflags $ liftM (Just . tyThingDataCon) $ lookupGlobal hsc_env integerSDataConName IntegerSimple -> return Nothing -- | Helper for 'lookupMkIntegerName' and 'lookupIntegerSDataConName' guardIntegerUse :: DynFlags -> IO a -> IO a guardIntegerUse dflags act | thisPackage dflags == primUnitId = return $ panic "Can't use Integer in ghc-prim" | thisPackage dflags == integerUnitId = return $ panic "Can't use Integer in integer-*" | otherwise = act mkInitialCorePrepEnv :: DynFlags -> HscEnv -> IO CorePrepEnv mkInitialCorePrepEnv dflags hsc_env = do mkIntegerId <- lookupMkIntegerName dflags hsc_env integerSDataCon <- lookupIntegerSDataConName dflags hsc_env return $ CPE { cpe_dynFlags = dflags, cpe_env = emptyVarEnv, cpe_mkIntegerId = mkIntegerId, cpe_integerSDataCon = integerSDataCon } extendCorePrepEnv :: CorePrepEnv -> Id -> Id -> CorePrepEnv extendCorePrepEnv cpe id id' = cpe { cpe_env = extendVarEnv (cpe_env cpe) id (Var id') } extendCorePrepEnvExpr :: CorePrepEnv -> Id -> CoreExpr -> CorePrepEnv extendCorePrepEnvExpr cpe id expr = cpe { cpe_env = extendVarEnv (cpe_env cpe) id expr } extendCorePrepEnvList :: CorePrepEnv -> [(Id,Id)] -> CorePrepEnv extendCorePrepEnvList cpe prs = cpe { cpe_env = extendVarEnvList (cpe_env cpe) (map (\(id, id') -> (id, Var id')) prs) } lookupCorePrepEnv :: CorePrepEnv -> Id -> CoreExpr lookupCorePrepEnv cpe id = case lookupVarEnv (cpe_env cpe) id of Nothing -> Var id Just exp -> exp getMkIntegerId :: CorePrepEnv -> Id getMkIntegerId = cpe_mkIntegerId ------------------------------------------------------------------------------ -- Cloning binders -- --------------------------------------------------------------------------- cpCloneBndrs :: CorePrepEnv -> [Var] -> UniqSM (CorePrepEnv, [Var]) cpCloneBndrs env bs = mapAccumLM cpCloneBndr env bs cpCloneBndr :: CorePrepEnv -> Var -> UniqSM (CorePrepEnv, Var) cpCloneBndr env bndr | isLocalId bndr, not (isCoVar bndr) = do bndr' <- setVarUnique bndr <$> getUniqueM -- We are going to OccAnal soon, so drop (now-useless) rules/unfoldings -- so that we can drop more stuff as dead code. -- See also Note [Dead code in CorePrep] let bndr'' = bndr' `setIdUnfolding` noUnfolding `setIdSpecialisation` emptyRuleInfo return (extendCorePrepEnv env bndr bndr'', bndr'') | otherwise -- Top level things, which we don't want -- to clone, have become GlobalIds by now -- And we don't clone tyvars, or coercion variables = return (env, bndr) ------------------------------------------------------------------------------ -- Cloning ccall Ids; each must have a unique name, -- to give the code generator a handle to hang it on -- --------------------------------------------------------------------------- fiddleCCall :: Id -> UniqSM Id fiddleCCall id | isFCallId id = (id `setVarUnique`) <$> getUniqueM | otherwise = return id ------------------------------------------------------------------------------ -- Generating new binders -- --------------------------------------------------------------------------- newVar :: Type -> UniqSM Id newVar ty = seqType ty `seq` do uniq <- getUniqueM return (mkSysLocalOrCoVar (fsLit "sat") uniq ty) ------------------------------------------------------------------------------ -- Floating ticks -- --------------------------------------------------------------------------- -- -- Note [Floating Ticks in CorePrep] -- -- It might seem counter-intuitive to float ticks by default, given -- that we don't actually want to move them if we can help it. On the -- other hand, nothing gets very far in CorePrep anyway, and we want -- to preserve the order of let bindings and tick annotations in -- relation to each other. For example, if we just wrapped let floats -- when they pass through ticks, we might end up performing the -- following transformation: -- -- src<...> let foo = bar in baz -- ==> let foo = src<...> bar in src<...> baz -- -- Because the let-binding would float through the tick, and then -- immediately materialize, achieving nothing but decreasing tick -- accuracy. The only special case is the following scenario: -- -- let foo = src<...> (let a = b in bar) in baz -- ==> let foo = src<...> bar; a = src<...> b in baz -- -- Here we would not want the source tick to end up covering "baz" and -- therefore refrain from pushing ticks outside. Instead, we copy them -- into the floating binds (here "a") in cpePair. Note that where "b" -- or "bar" are (value) lambdas we have to push the annotations -- further inside in order to uphold our rules. -- -- All of this is implemented below in @wrapTicks@. -- | Like wrapFloats, but only wraps tick floats wrapTicks :: Floats -> CoreExpr -> (Floats, CoreExpr) wrapTicks (Floats flag floats0) expr = (Floats flag (toOL $ reverse floats1), foldr mkTick expr (reverse ticks1)) where (floats1, ticks1) = foldlOL go ([], []) $ floats0 -- Deeply nested constructors will produce long lists of -- redundant source note floats here. We need to eliminate -- those early, as relying on mkTick to spot it after the fact -- can yield O(n^3) complexity [#11095] go (floats, ticks) (FloatTick t) = ASSERT(tickishPlace t == PlaceNonLam) (floats, if any (flip tickishContains t) ticks then ticks else t:ticks) go (floats, ticks) f = (foldr wrap f (reverse ticks):floats, ticks) wrap t (FloatLet bind) = FloatLet (wrapBind t bind) wrap t (FloatCase b r ok) = FloatCase b (mkTick t r) ok wrap _ other = pprPanic "wrapTicks: unexpected float!" (ppr other) wrapBind t (NonRec binder rhs) = NonRec binder (mkTick t rhs) wrapBind t (Rec pairs) = Rec (mapSnd (mkTick t) pairs)