{- (c) The AQUA Project, Glasgow University, 1993-1998 The simplifier utilities -} module GHC.Core.Opt.Simplify.Utils ( -- Rebuilding rebuildLam, mkCase, prepareAlts, tryEtaExpandRhs, wantEtaExpansion, -- Inlining, preInlineUnconditionally, postInlineUnconditionally, activeUnfolding, activeRule, getUnfoldingInRuleMatch, updModeForStableUnfoldings, updModeForRules, -- The BindContext type BindContext(..), bindContextLevel, -- The continuation type SimplCont(..), DupFlag(..), StaticEnv, isSimplified, contIsStop, contIsDupable, contResultType, contHoleType, contHoleScaling, contIsTrivial, contArgs, contIsRhs, countArgs, mkBoringStop, mkRhsStop, mkLazyArgStop, interestingCallContext, -- ArgInfo ArgInfo(..), ArgSpec(..), RewriteCall(..), mkArgInfo, addValArgTo, addCastTo, addTyArgTo, argInfoExpr, argInfoAppArgs, pushSimplifiedArgs, pushSimplifiedRevArgs, isStrictArgInfo, lazyArgContext, abstractFloats, -- Utilities isExitJoinId ) where import GHC.Prelude hiding (head, init, last, tail) import GHC.Core import GHC.Types.Literal ( isLitRubbish ) import GHC.Core.Opt.Simplify.Env import GHC.Core.Opt.Stats ( Tick(..) ) import qualified GHC.Core.Subst import GHC.Core.Ppr import GHC.Core.TyCo.Ppr ( pprParendType ) import GHC.Core.FVs import GHC.Core.Utils import GHC.Core.Rules( RuleEnv, getRules ) import GHC.Core.Opt.Arity import GHC.Core.Unfold import GHC.Core.Unfold.Make import GHC.Core.Opt.Simplify.Monad import GHC.Core.Type hiding( substTy ) import GHC.Core.Coercion hiding( substCo ) import GHC.Core.DataCon ( dataConWorkId, isNullaryRepDataCon ) import GHC.Core.Multiplicity import GHC.Core.Opt.ConstantFold import GHC.Types.Name import GHC.Types.Id import GHC.Types.Id.Info import GHC.Types.Tickish import GHC.Types.Demand import GHC.Types.Var.Set import GHC.Types.Basic import GHC.Data.OrdList ( isNilOL ) import GHC.Data.FastString ( fsLit ) import GHC.Utils.Misc import GHC.Utils.Monad import GHC.Utils.Outputable import GHC.Utils.Panic import GHC.Utils.Panic.Plain import Control.Monad ( when ) import Data.List ( sortBy ) import qualified Data.List as Partial ( head ) {- ********************************************************************* * * The BindContext type * * ********************************************************************* -} -- What sort of binding is this? A let-binding or a join-binding? data BindContext = BC_Let -- A regular let-binding TopLevelFlag RecFlag | BC_Join -- A join point with continuation k RecFlag -- See Note [Rules and unfolding for join points] SimplCont -- in GHC.Core.Opt.Simplify bindContextLevel :: BindContext -> TopLevelFlag bindContextLevel :: BindContext -> TopLevelFlag bindContextLevel (BC_Let TopLevelFlag top_lvl RecFlag _) = TopLevelFlag top_lvl bindContextLevel (BC_Join {}) = TopLevelFlag NotTopLevel bindContextRec :: BindContext -> RecFlag bindContextRec :: BindContext -> RecFlag bindContextRec (BC_Let TopLevelFlag _ RecFlag rec_flag) = RecFlag rec_flag bindContextRec (BC_Join RecFlag rec_flag SimplCont _) = RecFlag rec_flag isJoinBC :: BindContext -> Bool isJoinBC :: BindContext -> Bool isJoinBC (BC_Let {}) = Bool False isJoinBC (BC_Join {}) = Bool True {- ********************************************************************* * * The SimplCont and DupFlag types * * ************************************************************************ A SimplCont allows the simplifier to traverse the expression in a zipper-like fashion. The SimplCont represents the rest of the expression, "above" the point of interest. You can also think of a SimplCont as an "evaluation context", using that term in the way it is used for operational semantics. This is the way I usually think of it, For example you'll often see a syntax for evaluation context looking like C ::= [] | C e | case C of alts | C `cast` co That's the kind of thing we are doing here, and I use that syntax in the comments. Key points: * A SimplCont describes a *strict* context (just like evaluation contexts do). E.g. Just [] is not a SimplCont * A SimplCont describes a context that *does not* bind any variables. E.g. \x. [] is not a SimplCont -} data SimplCont = Stop -- ^ Stop[e] = e OutType -- ^ Type of the <hole> CallCtxt -- ^ Tells if there is something interesting about -- the syntactic context, and hence the inliner -- should be a bit keener (see interestingCallContext) -- Specifically: -- This is an argument of a function that has RULES -- Inlining the call might allow the rule to fire -- Never ValAppCxt (use ApplyToVal instead) -- or CaseCtxt (use Select instead) SubDemand -- ^ The evaluation context of e. Tells how e is evaluated. -- This fuels eta-expansion or eta-reduction without looking -- at lambda bodies, for example. -- -- See Note [Eta reduction based on evaluation context] -- The evaluation context for other SimplConts can be -- reconstructed with 'contEvalContext' | CastIt -- (CastIt co K)[e] = K[ e `cast` co ] OutCoercion -- The coercion simplified -- Invariant: never an identity coercion SimplCont | ApplyToVal -- (ApplyToVal arg K)[e] = K[ e arg ] { SimplCont -> DupFlag sc_dup :: DupFlag -- See Note [DupFlag invariants] , SimplCont -> OutType sc_hole_ty :: OutType -- Type of the function, presumably (forall a. blah) -- See Note [The hole type in ApplyToTy] , SimplCont -> OutExpr sc_arg :: InExpr -- The argument, , SimplCont -> StaticEnv sc_env :: StaticEnv -- see Note [StaticEnv invariant] , SimplCont -> SimplCont sc_cont :: SimplCont } | ApplyToTy -- (ApplyToTy ty K)[e] = K[ e ty ] { SimplCont -> OutType sc_arg_ty :: OutType -- Argument type , sc_hole_ty :: OutType -- Type of the function, presumably (forall a. blah) -- See Note [The hole type in ApplyToTy] , sc_cont :: SimplCont } | Select -- (Select alts K)[e] = K[ case e of alts ] { sc_dup :: DupFlag -- See Note [DupFlag invariants] , SimplCont -> Id sc_bndr :: InId -- case binder , SimplCont -> [InAlt] sc_alts :: [InAlt] -- Alternatives , sc_env :: StaticEnv -- See Note [StaticEnv invariant] , sc_cont :: SimplCont } -- The two strict forms have no DupFlag, because we never duplicate them | StrictBind -- (StrictBind x b K)[e] = let x = e in K[b] -- or, equivalently, = K[ (\x.b) e ] { sc_dup :: DupFlag -- See Note [DupFlag invariants] , sc_bndr :: InId , SimplCont -> OutExpr sc_body :: InExpr , sc_env :: StaticEnv -- See Note [StaticEnv invariant] , sc_cont :: SimplCont } | StrictArg -- (StrictArg (f e1 ..en) K)[e] = K[ f e1 .. en e ] { sc_dup :: DupFlag -- Always Simplified or OkToDup , SimplCont -> ArgInfo sc_fun :: ArgInfo -- Specifies f, e1..en, Whether f has rules, etc -- plus demands and discount flags for *this* arg -- and further args -- So ai_dmds and ai_discs are never empty , SimplCont -> OutType sc_fun_ty :: OutType -- Type of the function (f e1 .. en), -- presumably (arg_ty -> res_ty) -- where res_ty is expected by sc_cont , sc_cont :: SimplCont } | TickIt -- (TickIt t K)[e] = K[ tick t e ] CoreTickish -- Tick tickish <hole> SimplCont type StaticEnv = SimplEnv -- Just the static part is relevant -- See Note [DupFlag invariants] data DupFlag = NoDup -- Unsimplified, might be big | Simplified -- Simplified | OkToDup -- Simplified and small isSimplified :: DupFlag -> Bool isSimplified :: DupFlag -> Bool isSimplified DupFlag NoDup = Bool False isSimplified DupFlag _ = Bool True -- Invariant: the subst-env is empty perhapsSubstTy :: DupFlag -> StaticEnv -> Type -> Type perhapsSubstTy :: DupFlag -> StaticEnv -> OutType -> OutType perhapsSubstTy DupFlag dup StaticEnv env OutType ty | DupFlag -> Bool isSimplified DupFlag dup = OutType ty | Bool otherwise = HasDebugCallStack => StaticEnv -> OutType -> OutType substTy StaticEnv env OutType ty {- Note [StaticEnv invariant] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We pair up an InExpr or InAlts with a StaticEnv, which establishes the lexical scope for that InExpr. When we simplify that InExpr/InAlts, we use - Its captured StaticEnv - Overriding its InScopeSet with the larger one at the simplification point. Why override the InScopeSet? Example: (let y = ey in f) ex By the time we simplify ex, 'y' will be in scope. However the InScopeSet in the StaticEnv is not irrelevant: it should include all the free vars of applying the substitution to the InExpr. Reason: contHoleType uses perhapsSubstTy to apply the substitution to the expression, and that (rightly) gives ASSERT failures if the InScopeSet isn't big enough. Note [DupFlag invariants] ~~~~~~~~~~~~~~~~~~~~~~~~~ In both ApplyToVal { se_dup = dup, se_env = env, se_cont = k} and Select { se_dup = dup, se_env = env, se_cont = k} the following invariants hold (a) if dup = OkToDup, then continuation k is also ok-to-dup (b) if dup = OkToDup or Simplified, the subst-env is empty, or at least is always ignored; the payload is already an OutThing -} instance Outputable DupFlag where ppr :: DupFlag -> SDoc ppr DupFlag OkToDup = forall doc. IsLine doc => String -> doc text String "ok" ppr DupFlag NoDup = forall doc. IsLine doc => String -> doc text String "nodup" ppr DupFlag Simplified = forall doc. IsLine doc => String -> doc text String "simpl" instance Outputable SimplCont where ppr :: SimplCont -> SDoc ppr (Stop OutType ty CallCtxt interesting SubDemand eval_sd) = forall doc. IsLine doc => String -> doc text String "Stop" forall doc. IsLine doc => doc -> doc -> doc <> forall doc. IsLine doc => doc -> doc brackets (forall doc. IsLine doc => [doc] -> doc sep forall a b. (a -> b) -> a -> b $ forall doc. IsLine doc => doc -> [doc] -> [doc] punctuate forall doc. IsLine doc => doc comma [SDoc] pps) forall doc. IsLine doc => doc -> doc -> doc <+> forall a. Outputable a => a -> SDoc ppr OutType ty where pps :: [SDoc] pps = [forall a. Outputable a => a -> SDoc ppr CallCtxt interesting] forall a. [a] -> [a] -> [a] ++ [forall a. Outputable a => a -> SDoc ppr SubDemand eval_sd | SubDemand eval_sd forall a. Eq a => a -> a -> Bool /= SubDemand topSubDmd] ppr (CastIt OutCoercion co SimplCont cont ) = (forall doc. IsLine doc => String -> doc text String "CastIt" forall doc. IsLine doc => doc -> doc -> doc <+> OutCoercion -> SDoc pprOptCo OutCoercion co) forall doc. IsDoc doc => doc -> doc -> doc $$ forall a. Outputable a => a -> SDoc ppr SimplCont cont ppr (TickIt CoreTickish t SimplCont cont) = (forall doc. IsLine doc => String -> doc text String "TickIt" forall doc. IsLine doc => doc -> doc -> doc <+> forall a. Outputable a => a -> SDoc ppr CoreTickish t) forall doc. IsDoc doc => doc -> doc -> doc $$ forall a. Outputable a => a -> SDoc ppr SimplCont cont ppr (ApplyToTy { sc_arg_ty :: SimplCont -> OutType sc_arg_ty = OutType ty, sc_cont :: SimplCont -> SimplCont sc_cont = SimplCont cont }) = (forall doc. IsLine doc => String -> doc text String "ApplyToTy" forall doc. IsLine doc => doc -> doc -> doc <+> OutType -> SDoc pprParendType OutType ty) forall doc. IsDoc doc => doc -> doc -> doc $$ forall a. Outputable a => a -> SDoc ppr SimplCont cont ppr (ApplyToVal { sc_arg :: SimplCont -> OutExpr sc_arg = OutExpr arg, sc_dup :: SimplCont -> DupFlag sc_dup = DupFlag dup, sc_cont :: SimplCont -> SimplCont sc_cont = SimplCont cont, sc_hole_ty :: SimplCont -> OutType sc_hole_ty = OutType hole_ty }) = (SDoc -> BranchCount -> SDoc -> SDoc hang (forall doc. IsLine doc => String -> doc text String "ApplyToVal" forall doc. IsLine doc => doc -> doc -> doc <+> forall a. Outputable a => a -> SDoc ppr DupFlag dup forall doc. IsLine doc => doc -> doc -> doc <+> forall doc. IsLine doc => String -> doc text String "hole" forall doc. IsLine doc => doc -> doc -> doc <+> forall a. Outputable a => a -> SDoc ppr OutType hole_ty) BranchCount 2 (forall b. OutputableBndr b => Expr b -> SDoc pprParendExpr OutExpr arg)) forall doc. IsDoc doc => doc -> doc -> doc $$ forall a. Outputable a => a -> SDoc ppr SimplCont cont ppr (StrictBind { sc_bndr :: SimplCont -> Id sc_bndr = Id b, sc_cont :: SimplCont -> SimplCont sc_cont = SimplCont cont }) = (forall doc. IsLine doc => String -> doc text String "StrictBind" forall doc. IsLine doc => doc -> doc -> doc <+> forall a. Outputable a => a -> SDoc ppr Id b) forall doc. IsDoc doc => doc -> doc -> doc $$ forall a. Outputable a => a -> SDoc ppr SimplCont cont ppr (StrictArg { sc_fun :: SimplCont -> ArgInfo sc_fun = ArgInfo ai, sc_cont :: SimplCont -> SimplCont sc_cont = SimplCont cont }) = (forall doc. IsLine doc => String -> doc text String "StrictArg" forall doc. IsLine doc => doc -> doc -> doc <+> forall a. Outputable a => a -> SDoc ppr (ArgInfo -> Id ai_fun ArgInfo ai)) forall doc. IsDoc doc => doc -> doc -> doc $$ forall a. Outputable a => a -> SDoc ppr SimplCont cont ppr (Select { sc_dup :: SimplCont -> DupFlag sc_dup = DupFlag dup, sc_bndr :: SimplCont -> Id sc_bndr = Id bndr, sc_alts :: SimplCont -> [InAlt] sc_alts = [InAlt] alts, sc_env :: SimplCont -> StaticEnv sc_env = StaticEnv se, sc_cont :: SimplCont -> SimplCont sc_cont = SimplCont cont }) = (forall doc. IsLine doc => String -> doc text String "Select" forall doc. IsLine doc => doc -> doc -> doc <+> forall a. Outputable a => a -> SDoc ppr DupFlag dup forall doc. IsLine doc => doc -> doc -> doc <+> forall a. Outputable a => a -> SDoc ppr Id bndr) forall doc. IsDoc doc => doc -> doc -> doc $$ forall doc. IsOutput doc => doc -> doc whenPprDebug (BranchCount -> SDoc -> SDoc nest BranchCount 2 forall a b. (a -> b) -> a -> b $ forall doc. IsDoc doc => [doc] -> doc vcat [forall a. Outputable a => a -> SDoc ppr (StaticEnv -> TvSubstEnv seTvSubst StaticEnv se), forall a. Outputable a => a -> SDoc ppr [InAlt] alts]) forall doc. IsDoc doc => doc -> doc -> doc $$ forall a. Outputable a => a -> SDoc ppr SimplCont cont {- Note [The hole type in ApplyToTy] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The sc_hole_ty field of ApplyToTy records the type of the "hole" in the continuation. It is absolutely necessary to compute contHoleType, but it is not used for anything else (and hence may not be evaluated). Why is it necessary for contHoleType? Consider the continuation ApplyToType Int (Stop Int) corresponding to (<hole> @Int) :: Int What is the type of <hole>? It could be (forall a. Int) or (forall a. a), and there is no way to know which, so we must record it. In a chain of applications (f @t1 @t2 @t3) we'll lazily compute exprType for (f @t1) and (f @t1 @t2), which is potentially non-linear; but it probably doesn't matter because we'll never compute them all. ************************************************************************ * * ArgInfo and ArgSpec * * ************************************************************************ -} data ArgInfo = ArgInfo { ArgInfo -> Id ai_fun :: OutId, -- The function ArgInfo -> [ArgSpec] ai_args :: [ArgSpec], -- ...applied to these args (which are in *reverse* order) ArgInfo -> RewriteCall ai_rewrite :: RewriteCall, -- What transformation to try next for this call -- See Note [Rewrite rules and inlining] in GHC.Core.Opt.Simplify.Iteration ArgInfo -> Bool ai_encl :: Bool, -- Flag saying whether this function -- or an enclosing one has rules (recursively) -- True => be keener to inline in all args ArgInfo -> [Demand] ai_dmds :: [Demand], -- Demands on remaining value arguments (beyond ai_args) -- Usually infinite, but if it is finite it guarantees -- that the function diverges after being given -- that number of args ArgInfo -> [BranchCount] ai_discs :: [Int] -- Discounts for remaining value arguments (beyond ai_args) -- non-zero => be keener to inline -- Always infinite } data RewriteCall -- What rewriting to try next for this call -- See Note [Rewrite rules and inlining] in GHC.Core.Opt.Simplify.Iteration = TryRules FullArgCount [CoreRule] | TryInlining | TryNothing data ArgSpec = ValArg { ArgSpec -> Demand as_dmd :: Demand -- Demand placed on this argument , ArgSpec -> OutExpr as_arg :: OutExpr -- Apply to this (coercion or value); c.f. ApplyToVal , ArgSpec -> OutType as_hole_ty :: OutType } -- Type of the function (presumably t1 -> t2) | TyArg { ArgSpec -> OutType as_arg_ty :: OutType -- Apply to this type; c.f. ApplyToTy , as_hole_ty :: OutType } -- Type of the function (presumably forall a. blah) | CastBy OutCoercion -- Cast by this; c.f. CastIt instance Outputable ArgInfo where ppr :: ArgInfo -> SDoc ppr (ArgInfo { ai_fun :: ArgInfo -> Id ai_fun = Id fun, ai_args :: ArgInfo -> [ArgSpec] ai_args = [ArgSpec] args, ai_dmds :: ArgInfo -> [Demand] ai_dmds = [Demand] dmds }) = forall doc. IsLine doc => String -> doc text String "ArgInfo" forall doc. IsLine doc => doc -> doc -> doc <+> forall doc. IsLine doc => doc -> doc braces (forall doc. IsLine doc => [doc] -> doc sep [ forall doc. IsLine doc => String -> doc text String "fun =" forall doc. IsLine doc => doc -> doc -> doc <+> forall a. Outputable a => a -> SDoc ppr Id fun , forall doc. IsLine doc => String -> doc text String "dmds(first 10) =" forall doc. IsLine doc => doc -> doc -> doc <+> forall a. Outputable a => a -> SDoc ppr (forall a. BranchCount -> [a] -> [a] take BranchCount 10 [Demand] dmds) , forall doc. IsLine doc => String -> doc text String "args =" forall doc. IsLine doc => doc -> doc -> doc <+> forall a. Outputable a => a -> SDoc ppr [ArgSpec] args ]) instance Outputable ArgSpec where ppr :: ArgSpec -> SDoc ppr (ValArg { as_arg :: ArgSpec -> OutExpr as_arg = OutExpr arg }) = forall doc. IsLine doc => String -> doc text String "ValArg" forall doc. IsLine doc => doc -> doc -> doc <+> forall a. Outputable a => a -> SDoc ppr OutExpr arg ppr (TyArg { as_arg_ty :: ArgSpec -> OutType as_arg_ty = OutType ty }) = forall doc. IsLine doc => String -> doc text String "TyArg" forall doc. IsLine doc => doc -> doc -> doc <+> forall a. Outputable a => a -> SDoc ppr OutType ty ppr (CastBy OutCoercion c) = forall doc. IsLine doc => String -> doc text String "CastBy" forall doc. IsLine doc => doc -> doc -> doc <+> forall a. Outputable a => a -> SDoc ppr OutCoercion c addValArgTo :: ArgInfo -> OutExpr -> OutType -> ArgInfo addValArgTo :: ArgInfo -> OutExpr -> OutType -> ArgInfo addValArgTo ArgInfo ai OutExpr arg OutType hole_ty | ArgInfo { ai_dmds :: ArgInfo -> [Demand] ai_dmds = Demand dmd:[Demand] dmds, ai_discs :: ArgInfo -> [BranchCount] ai_discs = BranchCount _:[BranchCount] discs, ai_rewrite :: ArgInfo -> RewriteCall ai_rewrite = RewriteCall rew } <- ArgInfo ai -- Pop the top demand and and discounts off , let arg_spec :: ArgSpec arg_spec = ValArg { as_arg :: OutExpr as_arg = OutExpr arg, as_hole_ty :: OutType as_hole_ty = OutType hole_ty, as_dmd :: Demand as_dmd = Demand dmd } = ArgInfo ai { ai_args :: [ArgSpec] ai_args = ArgSpec arg_spec forall a. a -> [a] -> [a] : ArgInfo -> [ArgSpec] ai_args ArgInfo ai , ai_dmds :: [Demand] ai_dmds = [Demand] dmds , ai_discs :: [BranchCount] ai_discs = [BranchCount] discs , ai_rewrite :: RewriteCall ai_rewrite = RewriteCall -> RewriteCall decArgCount RewriteCall rew } | Bool otherwise = forall a. HasCallStack => String -> SDoc -> a pprPanic String "addValArgTo" (forall a. Outputable a => a -> SDoc ppr ArgInfo ai forall doc. IsDoc doc => doc -> doc -> doc $$ forall a. Outputable a => a -> SDoc ppr OutExpr arg) -- There should always be enough demands and discounts addTyArgTo :: ArgInfo -> OutType -> OutType -> ArgInfo addTyArgTo :: ArgInfo -> OutType -> OutType -> ArgInfo addTyArgTo ArgInfo ai OutType arg_ty OutType hole_ty = ArgInfo ai { ai_args :: [ArgSpec] ai_args = ArgSpec arg_spec forall a. a -> [a] -> [a] : ArgInfo -> [ArgSpec] ai_args ArgInfo ai , ai_rewrite :: RewriteCall ai_rewrite = RewriteCall -> RewriteCall decArgCount (ArgInfo -> RewriteCall ai_rewrite ArgInfo ai) } where arg_spec :: ArgSpec arg_spec = TyArg { as_arg_ty :: OutType as_arg_ty = OutType arg_ty, as_hole_ty :: OutType as_hole_ty = OutType hole_ty } addCastTo :: ArgInfo -> OutCoercion -> ArgInfo addCastTo :: ArgInfo -> OutCoercion -> ArgInfo addCastTo ArgInfo ai OutCoercion co = ArgInfo ai { ai_args :: [ArgSpec] ai_args = OutCoercion -> ArgSpec CastBy OutCoercion co forall a. a -> [a] -> [a] : ArgInfo -> [ArgSpec] ai_args ArgInfo ai } isStrictArgInfo :: ArgInfo -> Bool -- True if the function is strict in the next argument isStrictArgInfo :: ArgInfo -> Bool isStrictArgInfo (ArgInfo { ai_dmds :: ArgInfo -> [Demand] ai_dmds = [Demand] dmds }) | Demand dmd:[Demand] _ <- [Demand] dmds = Demand -> Bool isStrUsedDmd Demand dmd | Bool otherwise = Bool False argInfoAppArgs :: [ArgSpec] -> [OutExpr] argInfoAppArgs :: [ArgSpec] -> [OutExpr] argInfoAppArgs [] = [] argInfoAppArgs (CastBy {} : [ArgSpec] _) = [] -- Stop at a cast argInfoAppArgs (ValArg { as_arg :: ArgSpec -> OutExpr as_arg = OutExpr arg } : [ArgSpec] as) = OutExpr arg forall a. a -> [a] -> [a] : [ArgSpec] -> [OutExpr] argInfoAppArgs [ArgSpec] as argInfoAppArgs (TyArg { as_arg_ty :: ArgSpec -> OutType as_arg_ty = OutType ty } : [ArgSpec] as) = forall b. OutType -> Expr b Type OutType ty forall a. a -> [a] -> [a] : [ArgSpec] -> [OutExpr] argInfoAppArgs [ArgSpec] as pushSimplifiedArgs, pushSimplifiedRevArgs :: SimplEnv -> [ArgSpec] -- In normal, forward order for pushSimplifiedArgs, -- in /reverse/ order for pushSimplifiedRevArgs -> SimplCont -> SimplCont pushSimplifiedArgs :: StaticEnv -> [ArgSpec] -> SimplCont -> SimplCont pushSimplifiedArgs StaticEnv env [ArgSpec] args SimplCont cont = forall (t :: * -> *) a b. Foldable t => (a -> b -> b) -> b -> t a -> b foldr (StaticEnv -> ArgSpec -> SimplCont -> SimplCont pushSimplifiedArg StaticEnv env) SimplCont cont [ArgSpec] args pushSimplifiedRevArgs :: StaticEnv -> [ArgSpec] -> SimplCont -> SimplCont pushSimplifiedRevArgs StaticEnv env [ArgSpec] args SimplCont cont = forall (t :: * -> *) b a. Foldable t => (b -> a -> b) -> b -> t a -> b foldl' (\SimplCont k ArgSpec a -> StaticEnv -> ArgSpec -> SimplCont -> SimplCont pushSimplifiedArg StaticEnv env ArgSpec a SimplCont k) SimplCont cont [ArgSpec] args pushSimplifiedArg :: SimplEnv -> ArgSpec -> SimplCont -> SimplCont pushSimplifiedArg :: StaticEnv -> ArgSpec -> SimplCont -> SimplCont pushSimplifiedArg StaticEnv _env (TyArg { as_arg_ty :: ArgSpec -> OutType as_arg_ty = OutType arg_ty, as_hole_ty :: ArgSpec -> OutType as_hole_ty = OutType hole_ty }) SimplCont cont = ApplyToTy { sc_arg_ty :: OutType sc_arg_ty = OutType arg_ty, sc_hole_ty :: OutType sc_hole_ty = OutType hole_ty, sc_cont :: SimplCont sc_cont = SimplCont cont } pushSimplifiedArg StaticEnv env (ValArg { as_arg :: ArgSpec -> OutExpr as_arg = OutExpr arg, as_hole_ty :: ArgSpec -> OutType as_hole_ty = OutType hole_ty }) SimplCont cont = ApplyToVal { sc_arg :: OutExpr sc_arg = OutExpr arg, sc_env :: StaticEnv sc_env = StaticEnv env, sc_dup :: DupFlag sc_dup = DupFlag Simplified -- The SubstEnv will be ignored since sc_dup=Simplified , sc_hole_ty :: OutType sc_hole_ty = OutType hole_ty, sc_cont :: SimplCont sc_cont = SimplCont cont } pushSimplifiedArg StaticEnv _ (CastBy OutCoercion c) SimplCont cont = OutCoercion -> SimplCont -> SimplCont CastIt OutCoercion c SimplCont cont argInfoExpr :: OutId -> [ArgSpec] -> OutExpr -- NB: the [ArgSpec] is reversed so that the first arg -- in the list is the last one in the application argInfoExpr :: Id -> [ArgSpec] -> OutExpr argInfoExpr Id fun [ArgSpec] rev_args = [ArgSpec] -> OutExpr go [ArgSpec] rev_args where go :: [ArgSpec] -> OutExpr go [] = forall b. Id -> Expr b Var Id fun go (ValArg { as_arg :: ArgSpec -> OutExpr as_arg = OutExpr arg } : [ArgSpec] as) = [ArgSpec] -> OutExpr go [ArgSpec] as forall b. Expr b -> Expr b -> Expr b `App` OutExpr arg go (TyArg { as_arg_ty :: ArgSpec -> OutType as_arg_ty = OutType ty } : [ArgSpec] as) = [ArgSpec] -> OutExpr go [ArgSpec] as forall b. Expr b -> Expr b -> Expr b `App` forall b. OutType -> Expr b Type OutType ty go (CastBy OutCoercion co : [ArgSpec] as) = HasDebugCallStack => OutExpr -> OutCoercion -> OutExpr mkCast ([ArgSpec] -> OutExpr go [ArgSpec] as) OutCoercion co decArgCount :: RewriteCall -> RewriteCall decArgCount :: RewriteCall -> RewriteCall decArgCount (TryRules BranchCount n [CoreRule] rules) = BranchCount -> [CoreRule] -> RewriteCall TryRules (BranchCount nforall a. Num a => a -> a -> a -BranchCount 1) [CoreRule] rules decArgCount RewriteCall rew = RewriteCall rew mkRewriteCall :: Id -> RuleEnv -> RewriteCall -- See Note [Rewrite rules and inlining] in GHC.Core.Opt.Simplify.Iteration -- We try to skip any unnecessary stages: -- No rules => skip TryRules -- No unfolding => skip TryInlining -- This skipping is "just" for efficiency. But rebuildCall is -- quite a heavy hammer, so skipping stages is a good plan. -- And it's extremely simple to do. mkRewriteCall :: Id -> RuleEnv -> RewriteCall mkRewriteCall Id fun RuleEnv rule_env | Bool -> Bool not (forall (t :: * -> *) a. Foldable t => t a -> Bool null [CoreRule] rules) = BranchCount -> [CoreRule] -> RewriteCall TryRules BranchCount n_required [CoreRule] rules | Unfolding -> Bool canUnfold Unfolding unf = RewriteCall TryInlining | Bool otherwise = RewriteCall TryNothing where n_required :: BranchCount n_required = forall (t :: * -> *) a. (Foldable t, Ord a) => t a -> a maximum (forall a b. (a -> b) -> [a] -> [b] map CoreRule -> BranchCount ruleArity [CoreRule] rules) rules :: [CoreRule] rules = RuleEnv -> Id -> [CoreRule] getRules RuleEnv rule_env Id fun unf :: Unfolding unf = Id -> Unfolding idUnfolding Id fun {- ************************************************************************ * * Functions on SimplCont * * ************************************************************************ -} mkBoringStop :: OutType -> SimplCont mkBoringStop :: OutType -> SimplCont mkBoringStop OutType ty = OutType -> CallCtxt -> SubDemand -> SimplCont Stop OutType ty CallCtxt BoringCtxt SubDemand topSubDmd mkRhsStop :: OutType -> RecFlag -> Demand -> SimplCont -- See Note [RHS of lets] in GHC.Core.Unfold mkRhsStop :: OutType -> RecFlag -> Demand -> SimplCont mkRhsStop OutType ty RecFlag is_rec Demand bndr_dmd = OutType -> CallCtxt -> SubDemand -> SimplCont Stop OutType ty (RecFlag -> CallCtxt RhsCtxt RecFlag is_rec) (Demand -> SubDemand subDemandIfEvaluated Demand bndr_dmd) mkLazyArgStop :: OutType -> ArgInfo -> SimplCont mkLazyArgStop :: OutType -> ArgInfo -> SimplCont mkLazyArgStop OutType ty ArgInfo fun_info = OutType -> CallCtxt -> SubDemand -> SimplCont Stop OutType ty (ArgInfo -> CallCtxt lazyArgContext ArgInfo fun_info) SubDemand arg_sd where arg_sd :: SubDemand arg_sd = Demand -> SubDemand subDemandIfEvaluated (forall a. [a] -> a Partial.head (ArgInfo -> [Demand] ai_dmds ArgInfo fun_info)) ------------------- contIsRhs :: SimplCont -> Maybe RecFlag contIsRhs :: SimplCont -> Maybe RecFlag contIsRhs (Stop OutType _ (RhsCtxt RecFlag is_rec) SubDemand _) = forall a. a -> Maybe a Just RecFlag is_rec contIsRhs (CastIt OutCoercion _ SimplCont k) = SimplCont -> Maybe RecFlag contIsRhs SimplCont k -- For f = e |> co, treat e as Rhs context contIsRhs SimplCont _ = forall a. Maybe a Nothing ------------------- contIsStop :: SimplCont -> Bool contIsStop :: SimplCont -> Bool contIsStop (Stop {}) = Bool True contIsStop SimplCont _ = Bool False contIsDupable :: SimplCont -> Bool contIsDupable :: SimplCont -> Bool contIsDupable (Stop {}) = Bool True contIsDupable (ApplyToTy { sc_cont :: SimplCont -> SimplCont sc_cont = SimplCont k }) = SimplCont -> Bool contIsDupable SimplCont k contIsDupable (ApplyToVal { sc_dup :: SimplCont -> DupFlag sc_dup = DupFlag OkToDup }) = Bool True -- See Note [DupFlag invariants] contIsDupable (Select { sc_dup :: SimplCont -> DupFlag sc_dup = DupFlag OkToDup }) = Bool True -- ...ditto... contIsDupable (StrictArg { sc_dup :: SimplCont -> DupFlag sc_dup = DupFlag OkToDup }) = Bool True -- ...ditto... contIsDupable (CastIt OutCoercion _ SimplCont k) = SimplCont -> Bool contIsDupable SimplCont k contIsDupable SimplCont _ = Bool False ------------------- contIsTrivial :: SimplCont -> Bool contIsTrivial :: SimplCont -> Bool contIsTrivial (Stop {}) = Bool True contIsTrivial (ApplyToTy { sc_cont :: SimplCont -> SimplCont sc_cont = SimplCont k }) = SimplCont -> Bool contIsTrivial SimplCont k -- This one doesn't look right. A value application is not trivial -- contIsTrivial (ApplyToVal { sc_arg = Coercion _, sc_cont = k }) = contIsTrivial k contIsTrivial (CastIt OutCoercion _ SimplCont k) = SimplCont -> Bool contIsTrivial SimplCont k contIsTrivial SimplCont _ = Bool False ------------------- contResultType :: SimplCont -> OutType contResultType :: SimplCont -> OutType contResultType (Stop OutType ty CallCtxt _ SubDemand _) = OutType ty contResultType (CastIt OutCoercion _ SimplCont k) = SimplCont -> OutType contResultType SimplCont k contResultType (StrictBind { sc_cont :: SimplCont -> SimplCont sc_cont = SimplCont k }) = SimplCont -> OutType contResultType SimplCont k contResultType (StrictArg { sc_cont :: SimplCont -> SimplCont sc_cont = SimplCont k }) = SimplCont -> OutType contResultType SimplCont k contResultType (Select { sc_cont :: SimplCont -> SimplCont sc_cont = SimplCont k }) = SimplCont -> OutType contResultType SimplCont k contResultType (ApplyToTy { sc_cont :: SimplCont -> SimplCont sc_cont = SimplCont k }) = SimplCont -> OutType contResultType SimplCont k contResultType (ApplyToVal { sc_cont :: SimplCont -> SimplCont sc_cont = SimplCont k }) = SimplCont -> OutType contResultType SimplCont k contResultType (TickIt CoreTickish _ SimplCont k) = SimplCont -> OutType contResultType SimplCont k contHoleType :: SimplCont -> OutType contHoleType :: SimplCont -> OutType contHoleType (Stop OutType ty CallCtxt _ SubDemand _) = OutType ty contHoleType (TickIt CoreTickish _ SimplCont k) = SimplCont -> OutType contHoleType SimplCont k contHoleType (CastIt OutCoercion co SimplCont _) = OutCoercion -> OutType coercionLKind OutCoercion co contHoleType (StrictBind { sc_bndr :: SimplCont -> Id sc_bndr = Id b, sc_dup :: SimplCont -> DupFlag sc_dup = DupFlag dup, sc_env :: SimplCont -> StaticEnv sc_env = StaticEnv se }) = DupFlag -> StaticEnv -> OutType -> OutType perhapsSubstTy DupFlag dup StaticEnv se (Id -> OutType idType Id b) contHoleType (StrictArg { sc_fun_ty :: SimplCont -> OutType sc_fun_ty = OutType ty }) = OutType -> OutType funArgTy OutType ty contHoleType (ApplyToTy { sc_hole_ty :: SimplCont -> OutType sc_hole_ty = OutType ty }) = OutType ty -- See Note [The hole type in ApplyToTy] contHoleType (ApplyToVal { sc_hole_ty :: SimplCont -> OutType sc_hole_ty = OutType ty }) = OutType ty -- See Note [The hole type in ApplyToTy] contHoleType (Select { sc_dup :: SimplCont -> DupFlag sc_dup = DupFlag d, sc_bndr :: SimplCont -> Id sc_bndr = Id b, sc_env :: SimplCont -> StaticEnv sc_env = StaticEnv se }) = DupFlag -> StaticEnv -> OutType -> OutType perhapsSubstTy DupFlag d StaticEnv se (Id -> OutType idType Id b) -- Computes the multiplicity scaling factor at the hole. That is, in (case [] of -- x ::(p) _ { … }) (respectively for arguments of functions), the scaling -- factor is p. And in E[G[]], the scaling factor is the product of the scaling -- factor of E and that of G. -- -- The scaling factor at the hole of E[] is used to determine how a binder -- should be scaled if it commutes with E. This appears, in particular, in the -- case-of-case transformation. contHoleScaling :: SimplCont -> Mult contHoleScaling :: SimplCont -> OutType contHoleScaling (Stop OutType _ CallCtxt _ SubDemand _) = OutType OneTy contHoleScaling (CastIt OutCoercion _ SimplCont k) = SimplCont -> OutType contHoleScaling SimplCont k contHoleScaling (StrictBind { sc_bndr :: SimplCont -> Id sc_bndr = Id id, sc_cont :: SimplCont -> SimplCont sc_cont = SimplCont k }) = Id -> OutType idMult Id id OutType -> OutType -> OutType `mkMultMul` SimplCont -> OutType contHoleScaling SimplCont k contHoleScaling (Select { sc_bndr :: SimplCont -> Id sc_bndr = Id id, sc_cont :: SimplCont -> SimplCont sc_cont = SimplCont k }) = Id -> OutType idMult Id id OutType -> OutType -> OutType `mkMultMul` SimplCont -> OutType contHoleScaling SimplCont k contHoleScaling (StrictArg { sc_fun_ty :: SimplCont -> OutType sc_fun_ty = OutType fun_ty, sc_cont :: SimplCont -> SimplCont sc_cont = SimplCont k }) = OutType w OutType -> OutType -> OutType `mkMultMul` SimplCont -> OutType contHoleScaling SimplCont k where (OutType w, OutType _, OutType _) = OutType -> (OutType, OutType, OutType) splitFunTy OutType fun_ty contHoleScaling (ApplyToTy { sc_cont :: SimplCont -> SimplCont sc_cont = SimplCont k }) = SimplCont -> OutType contHoleScaling SimplCont k contHoleScaling (ApplyToVal { sc_cont :: SimplCont -> SimplCont sc_cont = SimplCont k }) = SimplCont -> OutType contHoleScaling SimplCont k contHoleScaling (TickIt CoreTickish _ SimplCont k) = SimplCont -> OutType contHoleScaling SimplCont k ------------------- countArgs :: SimplCont -> Int -- Count all arguments, including types, coercions, -- and other values; skipping over casts. countArgs :: SimplCont -> BranchCount countArgs (ApplyToTy { sc_cont :: SimplCont -> SimplCont sc_cont = SimplCont cont }) = BranchCount 1 forall a. Num a => a -> a -> a + SimplCont -> BranchCount countArgs SimplCont cont countArgs (ApplyToVal { sc_cont :: SimplCont -> SimplCont sc_cont = SimplCont cont }) = BranchCount 1 forall a. Num a => a -> a -> a + SimplCont -> BranchCount countArgs SimplCont cont countArgs (CastIt OutCoercion _ SimplCont cont) = SimplCont -> BranchCount countArgs SimplCont cont countArgs SimplCont _ = BranchCount 0 countValArgs :: SimplCont -> Int -- Count value arguments only countValArgs :: SimplCont -> BranchCount countValArgs (ApplyToTy { sc_cont :: SimplCont -> SimplCont sc_cont = SimplCont cont }) = BranchCount 1 forall a. Num a => a -> a -> a + SimplCont -> BranchCount countValArgs SimplCont cont countValArgs (ApplyToVal { sc_cont :: SimplCont -> SimplCont sc_cont = SimplCont cont }) = BranchCount 1 forall a. Num a => a -> a -> a + SimplCont -> BranchCount countValArgs SimplCont cont countValArgs (CastIt OutCoercion _ SimplCont cont) = SimplCont -> BranchCount countValArgs SimplCont cont countValArgs SimplCont _ = BranchCount 0 ------------------- contArgs :: SimplCont -> (Bool, [ArgSummary], SimplCont) -- Summarises value args, discards type args and coercions -- The returned continuation of the call is only used to -- answer questions like "are you interesting?" contArgs :: SimplCont -> (Bool, [ArgSummary], SimplCont) contArgs SimplCont cont | SimplCont -> Bool lone SimplCont cont = (Bool True, [], SimplCont cont) | Bool otherwise = [ArgSummary] -> SimplCont -> (Bool, [ArgSummary], SimplCont) go [] SimplCont cont where lone :: SimplCont -> Bool lone (ApplyToTy {}) = Bool False -- See Note [Lone variables] in GHC.Core.Unfold lone (ApplyToVal {}) = Bool False -- NB: even a type application or cast lone (CastIt {}) = Bool False -- stops it being "lone" lone SimplCont _ = Bool True go :: [ArgSummary] -> SimplCont -> (Bool, [ArgSummary], SimplCont) go [ArgSummary] args (ApplyToVal { sc_arg :: SimplCont -> OutExpr sc_arg = OutExpr arg, sc_env :: SimplCont -> StaticEnv sc_env = StaticEnv se, sc_cont :: SimplCont -> SimplCont sc_cont = SimplCont k }) = [ArgSummary] -> SimplCont -> (Bool, [ArgSummary], SimplCont) go (OutExpr -> StaticEnv -> ArgSummary is_interesting OutExpr arg StaticEnv se forall a. a -> [a] -> [a] : [ArgSummary] args) SimplCont k go [ArgSummary] args (ApplyToTy { sc_cont :: SimplCont -> SimplCont sc_cont = SimplCont k }) = [ArgSummary] -> SimplCont -> (Bool, [ArgSummary], SimplCont) go [ArgSummary] args SimplCont k go [ArgSummary] args (CastIt OutCoercion _ SimplCont k) = [ArgSummary] -> SimplCont -> (Bool, [ArgSummary], SimplCont) go [ArgSummary] args SimplCont k go [ArgSummary] args SimplCont k = (Bool False, forall a. [a] -> [a] reverse [ArgSummary] args, SimplCont k) is_interesting :: OutExpr -> StaticEnv -> ArgSummary is_interesting OutExpr arg StaticEnv se = StaticEnv -> OutExpr -> ArgSummary interestingArg StaticEnv se OutExpr arg -- Do *not* use short-cutting substitution here -- because we want to get as much IdInfo as possible -- | Describes how the 'SimplCont' will evaluate the hole as a 'SubDemand'. -- This can be more insightful than the limited syntactic context that -- 'SimplCont' provides, because the 'Stop' constructor might carry a useful -- 'SubDemand'. -- For example, when simplifying the argument `e` in `f e` and `f` has the -- demand signature `<MP(S,A)>`, this function will give you back `P(S,A)` when -- simplifying `e`. -- -- PRECONDITION: Don't call with 'ApplyToVal'. We haven't thoroughly thought -- about what to do then and no call sites so far seem to care. contEvalContext :: SimplCont -> SubDemand contEvalContext :: SimplCont -> SubDemand contEvalContext SimplCont k = case SimplCont k of (Stop OutType _ CallCtxt _ SubDemand sd) -> SubDemand sd (TickIt CoreTickish _ SimplCont k) -> SimplCont -> SubDemand contEvalContext SimplCont k (CastIt OutCoercion _ SimplCont k) -> SimplCont -> SubDemand contEvalContext SimplCont k ApplyToTy{sc_cont :: SimplCont -> SimplCont sc_cont=SimplCont k} -> SimplCont -> SubDemand contEvalContext SimplCont k -- ApplyToVal{sc_cont=k} -> mkCalledOnceDmd $ contEvalContext k -- Not 100% sure that's correct, . Here's an example: -- f (e x) and f :: <SC(S,C(1,L))> -- then what is the evaluation context of 'e' when we simplify it? E.g., -- simpl e (ApplyToVal x $ Stop "C(S,C(1,L))") -- then it *should* be "C(1,C(S,C(1,L))", so perhaps correct after all. -- But for now we just panic: ApplyToVal{} -> forall a. HasCallStack => String -> SDoc -> a pprPanic String "contEvalContext" (forall a. Outputable a => a -> SDoc ppr SimplCont k) StrictArg{sc_fun :: SimplCont -> ArgInfo sc_fun=ArgInfo fun_info} -> Demand -> SubDemand subDemandIfEvaluated (forall a. [a] -> a Partial.head (ArgInfo -> [Demand] ai_dmds ArgInfo fun_info)) StrictBind{sc_bndr :: SimplCont -> Id sc_bndr=Id bndr} -> Demand -> SubDemand subDemandIfEvaluated (Id -> Demand idDemandInfo Id bndr) Select{} -> SubDemand topSubDmd -- Perhaps reconstruct the demand on the scrutinee by looking at field -- and case binder dmds, see addCaseBndrDmd. No priority right now. ------------------- mkArgInfo :: SimplEnv -> RuleEnv -> Id -> SimplCont -> ArgInfo mkArgInfo :: StaticEnv -> RuleEnv -> Id -> SimplCont -> ArgInfo mkArgInfo StaticEnv env RuleEnv rule_base Id fun SimplCont cont | BranchCount n_val_args forall a. Ord a => a -> a -> Bool < Id -> BranchCount idArity Id fun -- Note [Unsaturated functions] = ArgInfo { ai_fun :: Id ai_fun = Id fun, ai_args :: [ArgSpec] ai_args = [] , ai_rewrite :: RewriteCall ai_rewrite = RewriteCall fun_rewrite , ai_encl :: Bool ai_encl = Bool False , ai_dmds :: [Demand] ai_dmds = [Demand] vanilla_dmds , ai_discs :: [BranchCount] ai_discs = [BranchCount] vanilla_discounts } | Bool otherwise = ArgInfo { ai_fun :: Id ai_fun = Id fun , ai_args :: [ArgSpec] ai_args = [] , ai_rewrite :: RewriteCall ai_rewrite = RewriteCall fun_rewrite , ai_encl :: Bool ai_encl = Bool fun_has_rules Bool -> Bool -> Bool || SimplCont -> Bool contHasRules SimplCont cont , ai_dmds :: [Demand] ai_dmds = OutType -> [Demand] -> [Demand] add_type_strictness (Id -> OutType idType Id fun) [Demand] arg_dmds , ai_discs :: [BranchCount] ai_discs = [BranchCount] arg_discounts } where n_val_args :: BranchCount n_val_args = SimplCont -> BranchCount countValArgs SimplCont cont fun_rewrite :: RewriteCall fun_rewrite = Id -> RuleEnv -> RewriteCall mkRewriteCall Id fun RuleEnv rule_base fun_has_rules :: Bool fun_has_rules = case RewriteCall fun_rewrite of TryRules {} -> Bool True RewriteCall _ -> Bool False vanilla_discounts, arg_discounts :: [Int] vanilla_discounts :: [BranchCount] vanilla_discounts = forall a. a -> [a] repeat BranchCount 0 arg_discounts :: [BranchCount] arg_discounts = case Id -> Unfolding idUnfolding Id fun of CoreUnfolding {uf_guidance :: Unfolding -> UnfoldingGuidance uf_guidance = UnfIfGoodArgs {ug_args :: UnfoldingGuidance -> [BranchCount] ug_args = [BranchCount] discounts}} -> [BranchCount] discounts forall a. [a] -> [a] -> [a] ++ [BranchCount] vanilla_discounts Unfolding _ -> [BranchCount] vanilla_discounts vanilla_dmds, arg_dmds :: [Demand] vanilla_dmds :: [Demand] vanilla_dmds = forall a. a -> [a] repeat Demand topDmd arg_dmds :: [Demand] arg_dmds | Bool -> Bool not (StaticEnv -> Bool seInline StaticEnv env) = [Demand] vanilla_dmds -- See Note [Do not expose strictness if sm_inline=False] | Bool otherwise = -- add_type_str fun_ty $ case DmdSig -> ([Demand], Divergence) splitDmdSig (Id -> DmdSig idDmdSig Id fun) of ([Demand] demands, Divergence result_info) | Bool -> Bool not ([Demand] demands forall a. [a] -> BranchCount -> Bool `lengthExceeds` BranchCount n_val_args) -> -- Enough args, use the strictness given. -- For bottoming functions we used to pretend that the arg -- is lazy, so that we don't treat the arg as an -- interesting context. This avoids substituting -- top-level bindings for (say) strings into -- calls to error. But now we are more careful about -- inlining lone variables, so its ok -- (see GHC.Core.Op.Simplify.Utils.analyseCont) if Divergence -> Bool isDeadEndDiv Divergence result_info then [Demand] demands -- Finite => result is bottom else [Demand] demands forall a. [a] -> [a] -> [a] ++ [Demand] vanilla_dmds | Bool otherwise -> forall a. HasCallStack => Bool -> String -> SDoc -> a -> a warnPprTrace Bool True String "More demands than arity" (forall a. Outputable a => a -> SDoc ppr Id fun forall doc. IsLine doc => doc -> doc -> doc <+> forall a. Outputable a => a -> SDoc ppr (Id -> BranchCount idArity Id fun) forall doc. IsLine doc => doc -> doc -> doc <+> forall a. Outputable a => a -> SDoc ppr BranchCount n_val_args forall doc. IsLine doc => doc -> doc -> doc <+> forall a. Outputable a => a -> SDoc ppr [Demand] demands) forall a b. (a -> b) -> a -> b $ [Demand] vanilla_dmds -- Not enough args, or no strictness add_type_strictness :: Type -> [Demand] -> [Demand] -- If the function arg types are strict, record that in the 'strictness bits' -- No need to instantiate because unboxed types (which dominate the strict -- types) can't instantiate type variables. -- add_type_strictness is done repeatedly (for each call); -- might be better once-for-all in the function -- But beware primops/datacons with no strictness add_type_strictness :: OutType -> [Demand] -> [Demand] add_type_strictness OutType fun_ty [Demand] dmds | forall (t :: * -> *) a. Foldable t => t a -> Bool null [Demand] dmds = [] | Just (Id _, OutType fun_ty') <- OutType -> Maybe (Id, OutType) splitForAllTyCoVar_maybe OutType fun_ty = OutType -> [Demand] -> [Demand] add_type_strictness OutType fun_ty' [Demand] dmds -- Look through foralls | Just (FunTyFlag _, OutType _, OutType arg_ty, OutType fun_ty') <- OutType -> Maybe (FunTyFlag, OutType, OutType, OutType) splitFunTy_maybe OutType fun_ty -- Add strict-type info , Demand dmd : [Demand] rest_dmds <- [Demand] dmds , let dmd' :: Demand dmd' | Just Levity Unlifted <- HasDebugCallStack => OutType -> Maybe Levity typeLevity_maybe OutType arg_ty = Demand -> Demand strictifyDmd Demand dmd | Bool otherwise -- Something that's not definitely unlifted. -- If the type is representation-polymorphic, we can't know whether -- it's strict. = Demand dmd = Demand dmd' forall a. a -> [a] -> [a] : OutType -> [Demand] -> [Demand] add_type_strictness OutType fun_ty' [Demand] rest_dmds | Bool otherwise = [Demand] dmds {- Note [Unsaturated functions] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider (test eyeball/inline4) x = a:as y = f x where f has arity 2. Then we do not want to inline 'x', because it'll just be floated out again. Even if f has lots of discounts on its first argument -- it must be saturated for these to kick in Note [Do not expose strictness if sm_inline=False] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ #15163 showed a case in which we had {-# INLINE [1] zip #-} zip = undefined {-# RULES "foo" forall as bs. stream (zip as bs) = ..blah... #-} If we expose zip's bottoming nature when simplifying the LHS of the RULE we get {-# RULES "foo" forall as bs. stream (case zip of {}) = ..blah... #-} discarding the arguments to zip. Usually this is fine, but on the LHS of a rule it's not, because 'as' and 'bs' are now not bound on the LHS. This is a pretty pathological example, so I'm not losing sleep over it, but the simplest solution was to check sm_inline; if it is False, which it is on the LHS of a rule (see updModeForRules), then don't make use of the strictness info for the function. -} {- ************************************************************************ * * Interesting arguments * * ************************************************************************ Note [Interesting call context] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We want to avoid inlining an expression where there can't possibly be any gain, such as in an argument position. Hence, if the continuation is interesting (eg. a case scrutinee that isn't just a seq, application etc.) then we inline, otherwise we don't. Previously some_benefit used to return True only if the variable was applied to some value arguments. This didn't work: let x = _coerce_ (T Int) Int (I# 3) in case _coerce_ Int (T Int) x of I# y -> .... we want to inline x, but can't see that it's a constructor in a case scrutinee position, and some_benefit is False. Another example: dMonadST = _/\_ t -> :Monad (g1 _@_ t, g2 _@_ t, g3 _@_ t) .... case dMonadST _@_ x0 of (a,b,c) -> .... we'd really like to inline dMonadST here, but we *don't* want to inline if the case expression is just case x of y { DEFAULT -> ... } since we can just eliminate this case instead (x is in WHNF). Similar applies when x is bound to a lambda expression. Hence contIsInteresting looks for case expressions with just a single default case. Note [No case of case is boring] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ If we see case f x of <alts> we'd usually treat the context as interesting, to encourage 'f' to inline. But if case-of-case is off, it's really not so interesting after all, because we are unlikely to be able to push the case expression into the branches of any case in f's unfolding. So, to reduce unnecessary code expansion, we just make the context look boring. This made a small compile-time perf improvement in perf/compiler/T6048, and it looks plausible to me. Note [Seq is boring] ~~~~~~~~~~~~~~~~~~~~ Suppose f x = case v of True -> Just x False -> Just (x-1) Now consider these cases: 1. case f x of b{-dead-} { DEFAULT -> blah[no b] } Inlining (f x) will allow us to avoid ever allocating (Just x), since the case binder `b` is dead. We will end up with a join point for blah, thus join j = blah in case v of { True -> j; False -> j } which will turn into (case v of DEFAULT -> blah All good 2. case f x of b { DEFAULT -> blah[b] } Inlining (f x) will still mean we allocate (Just x). We'd get: join j b = blah[b] case v of { True -> j (Just x); False -> j (Just (x-1)) } No new optimisations are revealed. Nothing is gained. (This is the situation in T22317.) 2a. case g x of b { (x{-dead-}, x{-dead-}) -> blah[b, no x, no y] } Instead of DEFAULT we have a single constructor alternative with all dead binders. This is just a variant of (2); no gain from inlining (f x) 3. case f x of b { Just y -> blah[y,b] } Inlining (f x) will mean we still allocate (Just x), but we also get to bind `y` without fetching it out of the Just, thus join j y b = blah[y,b] case v of { True -> j x (Just x) ; False -> let y = x-1 in j y (Just y) } Inlining (f x) has a small benefit, perhaps. (To T14955 it makes a surprisingly large difference of ~30% to inline here.) Conclusion: if the case expression * Has a non-dead case-binder * Has one alternative * All the binders in the alternative are dead then the `case` is just a strict let-binding, and the scrutinee is BoringCtxt (don't inline). Otherwise CaseCtxt. -} lazyArgContext :: ArgInfo -> CallCtxt -- Use this for lazy arguments lazyArgContext :: ArgInfo -> CallCtxt lazyArgContext (ArgInfo { ai_encl :: ArgInfo -> Bool ai_encl = Bool encl_rules, ai_discs :: ArgInfo -> [BranchCount] ai_discs = [BranchCount] discs }) | Bool encl_rules = CallCtxt RuleArgCtxt | BranchCount disc:[BranchCount] _ <- [BranchCount] discs, BranchCount disc forall a. Ord a => a -> a -> Bool > BranchCount 0 = CallCtxt DiscArgCtxt -- Be keener here | Bool otherwise = CallCtxt BoringCtxt -- Nothing interesting strictArgContext :: ArgInfo -> CallCtxt strictArgContext :: ArgInfo -> CallCtxt strictArgContext (ArgInfo { ai_encl :: ArgInfo -> Bool ai_encl = Bool encl_rules, ai_discs :: ArgInfo -> [BranchCount] ai_discs = [BranchCount] discs }) -- Use this for strict arguments | Bool encl_rules = CallCtxt RuleArgCtxt | BranchCount disc:[BranchCount] _ <- [BranchCount] discs, BranchCount disc forall a. Ord a => a -> a -> Bool > BranchCount 0 = CallCtxt DiscArgCtxt -- Be keener here | Bool otherwise = RecFlag -> CallCtxt RhsCtxt RecFlag NonRecursive -- Why RhsCtxt? if we see f (g x), and f is strict, we -- want to be a bit more eager to inline g, because it may -- expose an eval (on x perhaps) that can be eliminated or -- shared. I saw this in nofib 'boyer2', RewriteFuns.onewayunify1 -- It's worth an 18% improvement in allocation for this -- particular benchmark; 5% on 'mate' and 1.3% on 'multiplier' -- -- Why NonRecursive? Becuase it's a bit like -- let a = g x in f a interestingCallContext :: SimplEnv -> SimplCont -> CallCtxt -- See Note [Interesting call context] interestingCallContext :: StaticEnv -> SimplCont -> CallCtxt interestingCallContext StaticEnv env SimplCont cont = SimplCont -> CallCtxt interesting SimplCont cont where interesting :: SimplCont -> CallCtxt interesting (Select {sc_alts :: SimplCont -> [InAlt] sc_alts=[InAlt] alts, sc_bndr :: SimplCont -> Id sc_bndr=Id case_bndr}) | Bool -> Bool not (StaticEnv -> Bool seCaseCase StaticEnv env) = CallCtxt BoringCtxt -- See Note [No case of case is boring] | [Alt AltCon _ [Id] bs OutExpr _] <- [InAlt] alts , forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool all Id -> Bool isDeadBinder [Id] bs , Bool -> Bool not (Id -> Bool isDeadBinder Id case_bndr) = CallCtxt BoringCtxt -- See Note [Seq is boring] | Bool otherwise = CallCtxt CaseCtxt interesting (ApplyToVal {}) = CallCtxt ValAppCtxt -- Can happen if we have (f Int |> co) y -- If f has an INLINE prag we need to give it some -- motivation to inline. See Note [Cast then apply] -- in GHC.Core.Unfold interesting (StrictArg { sc_fun :: SimplCont -> ArgInfo sc_fun = ArgInfo fun }) = ArgInfo -> CallCtxt strictArgContext ArgInfo fun interesting (StrictBind {}) = CallCtxt BoringCtxt interesting (Stop OutType _ CallCtxt cci SubDemand _) = CallCtxt cci interesting (TickIt CoreTickish _ SimplCont k) = SimplCont -> CallCtxt interesting SimplCont k interesting (ApplyToTy { sc_cont :: SimplCont -> SimplCont sc_cont = SimplCont k }) = SimplCont -> CallCtxt interesting SimplCont k interesting (CastIt OutCoercion _ SimplCont k) = SimplCont -> CallCtxt interesting SimplCont k -- If this call is the arg of a strict function, the context -- is a bit interesting. If we inline here, we may get useful -- evaluation information to avoid repeated evals: e.g. -- x + (y * z) -- Here the contIsInteresting makes the '*' keener to inline, -- which in turn exposes a constructor which makes the '+' inline. -- Assuming that +,* aren't small enough to inline regardless. -- -- It's also very important to inline in a strict context for things -- like -- foldr k z (f x) -- Here, the context of (f x) is strict, and if f's unfolding is -- a build it's *great* to inline it here. So we must ensure that -- the context for (f x) is not totally uninteresting. contHasRules :: SimplCont -> Bool -- If the argument has form (f x y), where x,y are boring, -- and f is marked INLINE, then we don't want to inline f. -- But if the context of the argument is -- g (f x y) -- where g has rules, then we *do* want to inline f, in case it -- exposes a rule that might fire. Similarly, if the context is -- h (g (f x x)) -- where h has rules, then we do want to inline f. So contHasRules -- tries to see if the context of the f-call is a call to a function -- with rules. -- -- The ai_encl flag makes this happen; if it's -- set, the inliner gets just enough keener to inline f -- regardless of how boring f's arguments are, if it's marked INLINE -- -- The alternative would be to *always* inline an INLINE function, -- regardless of how boring its context is; but that seems overkill -- For example, it'd mean that wrapper functions were always inlined contHasRules :: SimplCont -> Bool contHasRules SimplCont cont = SimplCont -> Bool go SimplCont cont where go :: SimplCont -> Bool go (ApplyToVal { sc_cont :: SimplCont -> SimplCont sc_cont = SimplCont cont }) = SimplCont -> Bool go SimplCont cont go (ApplyToTy { sc_cont :: SimplCont -> SimplCont sc_cont = SimplCont cont }) = SimplCont -> Bool go SimplCont cont go (CastIt OutCoercion _ SimplCont cont) = SimplCont -> Bool go SimplCont cont go (StrictArg { sc_fun :: SimplCont -> ArgInfo sc_fun = ArgInfo fun }) = ArgInfo -> Bool ai_encl ArgInfo fun go (Stop OutType _ CallCtxt RuleArgCtxt SubDemand _) = Bool True go (TickIt CoreTickish _ SimplCont c) = SimplCont -> Bool go SimplCont c go (Select {}) = Bool False go (StrictBind {}) = Bool False -- ?? go (Stop OutType _ CallCtxt _ SubDemand _) = Bool False {- Note [Interesting arguments] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ An argument is interesting if it deserves a discount for unfoldings with a discount in that argument position. The idea is to avoid unfolding a function that is applied only to variables that have no unfolding (i.e. they are probably lambda bound): f x y z There is little point in inlining f here. Generally, *values* (like (C a b) and (\x.e)) deserve discounts. But we must look through lets, eg (let x = e in C a b), because the let will float, exposing the value, if we inline. That makes it different to exprIsHNF. Before 2009 we said it was interesting if the argument had *any* structure at all; i.e. (hasSomeUnfolding v). But does too much inlining; see #3016. But we don't regard (f x y) as interesting, unless f is unsaturated. If it's saturated and f hasn't inlined, then it's probably not going to now! Note [Conlike is interesting] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider f d = ...((*) d x y)... ... f (df d')... where df is con-like. Then we'd really like to inline 'f' so that the rule for (*) (df d) can fire. To do this a) we give a discount for being an argument of a class-op (eg (*) d) b) we say that a con-like argument (eg (df d)) is interesting -} interestingArg :: SimplEnv -> CoreExpr -> ArgSummary -- See Note [Interesting arguments] interestingArg :: StaticEnv -> OutExpr -> ArgSummary interestingArg StaticEnv env OutExpr e = StaticEnv -> BranchCount -> OutExpr -> ArgSummary go StaticEnv env BranchCount 0 OutExpr e where -- n is # value args to which the expression is applied go :: StaticEnv -> BranchCount -> OutExpr -> ArgSummary go StaticEnv env BranchCount n (Var Id v) = case StaticEnv -> Id -> SimplSR substId StaticEnv env Id v of DoneId Id v' -> BranchCount -> Id -> ArgSummary go_var BranchCount n Id v' DoneEx OutExpr e Maybe BranchCount _ -> StaticEnv -> BranchCount -> OutExpr -> ArgSummary go (StaticEnv -> StaticEnv zapSubstEnv StaticEnv env) BranchCount n OutExpr e ContEx TvSubstEnv tvs CvSubstEnv cvs SimplIdSubst ids OutExpr e -> StaticEnv -> BranchCount -> OutExpr -> ArgSummary go (StaticEnv -> TvSubstEnv -> CvSubstEnv -> SimplIdSubst -> StaticEnv setSubstEnv StaticEnv env TvSubstEnv tvs CvSubstEnv cvs SimplIdSubst ids) BranchCount n OutExpr e go StaticEnv _ BranchCount _ (Lit Literal l) | Literal -> Bool isLitRubbish Literal l = ArgSummary TrivArg -- Leads to unproductive inlining in WWRec, #20035 | Bool otherwise = ArgSummary ValueArg go StaticEnv _ BranchCount _ (Type OutType _) = ArgSummary TrivArg go StaticEnv _ BranchCount _ (Coercion OutCoercion _) = ArgSummary TrivArg go StaticEnv env BranchCount n (App OutExpr fn (Type OutType _)) = StaticEnv -> BranchCount -> OutExpr -> ArgSummary go StaticEnv env BranchCount n OutExpr fn go StaticEnv env BranchCount n (App OutExpr fn OutExpr _) = StaticEnv -> BranchCount -> OutExpr -> ArgSummary go StaticEnv env (BranchCount nforall a. Num a => a -> a -> a +BranchCount 1) OutExpr fn go StaticEnv env BranchCount n (Tick CoreTickish _ OutExpr a) = StaticEnv -> BranchCount -> OutExpr -> ArgSummary go StaticEnv env BranchCount n OutExpr a go StaticEnv env BranchCount n (Cast OutExpr e OutCoercion _) = StaticEnv -> BranchCount -> OutExpr -> ArgSummary go StaticEnv env BranchCount n OutExpr e go StaticEnv env BranchCount n (Lam Id v OutExpr e) | Id -> Bool isTyVar Id v = StaticEnv -> BranchCount -> OutExpr -> ArgSummary go StaticEnv env BranchCount n OutExpr e | BranchCount nforall a. Ord a => a -> a -> Bool >BranchCount 0 = ArgSummary NonTrivArg -- (\x.b) e is NonTriv | Bool otherwise = ArgSummary ValueArg go StaticEnv _ BranchCount _ (Case {}) = ArgSummary NonTrivArg go StaticEnv env BranchCount n (Let Bind Id b OutExpr e) = case StaticEnv -> BranchCount -> OutExpr -> ArgSummary go StaticEnv env' BranchCount n OutExpr e of ArgSummary ValueArg -> ArgSummary ValueArg ArgSummary _ -> ArgSummary NonTrivArg where env' :: StaticEnv env' = StaticEnv env StaticEnv -> [Id] -> StaticEnv `addNewInScopeIds` forall b. Bind b -> [b] bindersOf Bind Id b go_var :: BranchCount -> Id -> ArgSummary go_var BranchCount n Id v | Id -> Bool isConLikeId Id v = ArgSummary ValueArg -- Experimenting with 'conlike' rather that -- data constructors here | Id -> BranchCount idArity Id v forall a. Ord a => a -> a -> Bool > BranchCount n = ArgSummary ValueArg -- Catches (eg) primops with arity but no unfolding | BranchCount n forall a. Ord a => a -> a -> Bool > BranchCount 0 = ArgSummary NonTrivArg -- Saturated or unknown call | Bool conlike_unfolding = ArgSummary ValueArg -- n==0; look for an interesting unfolding -- See Note [Conlike is interesting] | Bool otherwise = ArgSummary TrivArg -- n==0, no useful unfolding where conlike_unfolding :: Bool conlike_unfolding = Unfolding -> Bool isConLikeUnfolding (Id -> Unfolding idUnfolding Id v) {- ************************************************************************ * * SimplMode * * ************************************************************************ -} updModeForStableUnfoldings :: Activation -> SimplMode -> SimplMode -- See Note [The environments of the Simplify pass] updModeForStableUnfoldings :: Activation -> SimplMode -> SimplMode updModeForStableUnfoldings Activation unf_act SimplMode current_mode = SimplMode current_mode { sm_phase :: CompilerPhase sm_phase = Activation -> CompilerPhase phaseFromActivation Activation unf_act , sm_eta_expand :: Bool sm_eta_expand = Bool False , sm_inline :: Bool sm_inline = Bool True } -- sm_eta_expand: see Note [Eta expansion in stable unfoldings and rules] -- sm_rules: just inherit; sm_rules might be "off" -- because of -fno-enable-rewrite-rules where phaseFromActivation :: Activation -> CompilerPhase phaseFromActivation (ActiveAfter SourceText _ BranchCount n) = BranchCount -> CompilerPhase Phase BranchCount n phaseFromActivation Activation _ = CompilerPhase InitialPhase updModeForRules :: SimplMode -> SimplMode -- See Note [Simplifying rules] -- See Note [The environments of the Simplify pass] updModeForRules :: SimplMode -> SimplMode updModeForRules SimplMode current_mode = SimplMode current_mode { sm_phase :: CompilerPhase sm_phase = CompilerPhase InitialPhase , sm_inline :: Bool sm_inline = Bool False -- See Note [Do not expose strictness if sm_inline=False] , sm_rules :: Bool sm_rules = Bool False , sm_cast_swizzle :: Bool sm_cast_swizzle = Bool False -- See Note [Cast swizzling on rule LHSs] , sm_eta_expand :: Bool sm_eta_expand = Bool False } {- Note [Simplifying rules] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ When simplifying a rule LHS, refrain from /any/ inlining or applying of other RULES. Doing anything to the LHS is plain confusing, because it means that what the rule matches is not what the user wrote. c.f. #10595, and #10528. * sm_inline, sm_rules: inlining (or applying rules) on rule LHSs risks introducing Ticks into the LHS, which makes matching trickier. #10665, #10745. Doing this to either side confounds tools like HERMIT, which seek to reason about and apply the RULES as originally written. See #10829. See also Note [Do not expose strictness if sm_inline=False] * sm_eta_expand: the template (LHS) of a rule must only mention coercion /variables/ not arbitrary coercions. See Note [Casts in the template] in GHC.Core.Rules. Eta expansion can create new coercions; so we switch it off. There is, however, one case where we are pretty much /forced/ to transform the LHS of a rule: postInlineUnconditionally. For instance, in the case of let f = g @Int in f We very much want to inline f into the body of the let. However, to do so (and be able to safely drop f's binding) we must inline into all occurrences of f, including those in the LHS of rules. This can cause somewhat surprising results; for instance, in #18162 we found that a rule template contained ticks in its arguments, because postInlineUnconditionally substituted in a trivial expression that contains ticks. See Note [Tick annotations in RULE matching] in GHC.Core.Rules for details. Note [Cast swizzling on rule LHSs] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ In the LHS of a RULE we may have (\x. blah |> CoVar cv) where `cv` is a coercion variable. Critically, we really only want coercion /variables/, not general coercions, on the LHS of a RULE. So we don't want to swizzle this to (\x. blah) |> (Refl xty `FunCo` CoVar cv) So we switch off cast swizzling in updModeForRules. Note [Eta expansion in stable unfoldings and rules] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ SPJ Jul 22: whether or not eta-expansion is switched on in a stable unfolding, or the RHS of a RULE, seems to be a bit moot. But switching it on adds clutter, so I'm experimenting with switching off eta-expansion in such places. In the olden days, we really /wanted/ to switch it off. Old note: If we have a stable unfolding f :: Ord a => a -> IO () -- Unfolding template -- = /\a \(d:Ord a) (x:a). bla we do not want to eta-expand to f :: Ord a => a -> IO () -- Unfolding template -- = (/\a \(d:Ord a) (x:a) (eta:State#). bla eta) |> co because now specialisation of the overloading doesn't work properly (see Note [Specialisation shape] in GHC.Core.Opt.Specialise), #9509. So we disable eta-expansion in stable unfoldings. But this old note is no longer relevant because the specialiser has improved: see Note [Account for casts in binding] in GHC.Core.Opt.Specialise. So we seem to have a free choice. Note [Inlining in gentle mode] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Something is inlined if (i) the sm_inline flag is on, AND (ii) the thing has an INLINE pragma, AND (iii) the thing is inlinable in the earliest phase. Example of why (iii) is important: {-# INLINE [~1] g #-} g = ... {-# INLINE f #-} f x = g (g x) If we were to inline g into f's inlining, then an importing module would never be able to do f e --> g (g e) ---> RULE fires because the stable unfolding for f has had g inlined into it. On the other hand, it is bad not to do ANY inlining into an stable unfolding, because then recursive knots in instance declarations don't get unravelled. However, *sometimes* SimplGently must do no call-site inlining at all (hence sm_inline = False). Before full laziness we must be careful not to inline wrappers, because doing so inhibits floating e.g. ...(case f x of ...)... ==> ...(case (case x of I# x# -> fw x#) of ...)... ==> ...(case x of I# x# -> case fw x# of ...)... and now the redex (f x) isn't floatable any more. The no-inlining thing is also important for Template Haskell. You might be compiling in one-shot mode with -O2; but when TH compiles a splice before running it, we don't want to use -O2. Indeed, we don't want to inline anything, because the byte-code interpreter might get confused about unboxed tuples and suchlike. Note [Simplifying inside stable unfoldings] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We must take care with simplification inside stable unfoldings (which come from INLINE pragmas). First, consider the following example let f = \pq -> BIG in let g = \y -> f y y {-# INLINE g #-} in ...g...g...g...g...g... Now, if that's the ONLY occurrence of f, it might be inlined inside g, and thence copied multiple times when g is inlined. HENCE we treat any occurrence in a stable unfolding as a multiple occurrence, not a single one; see OccurAnal.addRuleUsage. Second, we do want *do* to some modest rules/inlining stuff in stable unfoldings, partly to eliminate senseless crap, and partly to break the recursive knots generated by instance declarations. However, suppose we have {-# INLINE <act> f #-} f = <rhs> meaning "inline f in phases p where activation <act>(p) holds". Then what inlinings/rules can we apply to the copy of <rhs> captured in f's stable unfolding? Our model is that literally <rhs> is substituted for f when it is inlined. So our conservative plan (implemented by updModeForStableUnfoldings) is this: ------------------------------------------------------------- When simplifying the RHS of a stable unfolding, set the phase to the phase in which the stable unfolding first becomes active ------------------------------------------------------------- That ensures that a) Rules/inlinings that *cease* being active before p will not apply to the stable unfolding, consistent with it being inlined in its *original* form in phase p. b) Rules/inlinings that only become active *after* p will not apply to the stable unfolding, again to be consistent with inlining the *original* rhs in phase p. For example, {-# INLINE f #-} f x = ...g... {-# NOINLINE [1] g #-} g y = ... {-# RULE h g = ... #-} Here we must not inline g into f's RHS, even when we get to phase 0, because when f is later inlined into some other module we want the rule for h to fire. Similarly, consider {-# INLINE f #-} f x = ...g... g y = ... and suppose that there are auto-generated specialisations and a strictness wrapper for g. The specialisations get activation AlwaysActive, and the strictness wrapper get activation (ActiveAfter 0). So the strictness wrepper fails the test and won't be inlined into f's stable unfolding. That means f can inline, expose the specialised call to g, so the specialisation rules can fire. A note about wrappers ~~~~~~~~~~~~~~~~~~~~~ It's also important not to inline a worker back into a wrapper. A wrapper looks like wraper = inline_me (\x -> ...worker... ) Normally, the inline_me prevents the worker getting inlined into the wrapper (initially, the worker's only call site!). But, if the wrapper is sure to be called, the strictness analyser will mark it 'demanded', so when the RHS is simplified, it'll get an ArgOf continuation. -} activeUnfolding :: SimplMode -> Id -> Bool activeUnfolding :: SimplMode -> Id -> Bool activeUnfolding SimplMode mode Id id | Unfolding -> Bool isCompulsoryUnfolding (Id -> Unfolding realIdUnfolding Id id) = Bool True -- Even sm_inline can't override compulsory unfoldings | Bool otherwise = CompilerPhase -> Activation -> Bool isActive (SimplMode -> CompilerPhase sm_phase SimplMode mode) (Id -> Activation idInlineActivation Id id) Bool -> Bool -> Bool && SimplMode -> Bool sm_inline SimplMode mode -- `or` isStableUnfolding (realIdUnfolding id) -- Inline things when -- (a) they are active -- (b) sm_inline says so, except that for stable unfoldings -- (ie pragmas) we inline anyway getUnfoldingInRuleMatch :: SimplEnv -> InScopeEnv -- When matching in RULE, we want to "look through" an unfolding -- (to see a constructor) if *rules* are on, even if *inlinings* -- are not. A notable example is DFuns, which really we want to -- match in rules like (op dfun) in gentle mode. Another example -- is 'otherwise' which we want exprIsConApp_maybe to be able to -- see very early on getUnfoldingInRuleMatch :: StaticEnv -> InScopeEnv getUnfoldingInRuleMatch StaticEnv env = (InScopeSet in_scope, Id -> Unfolding id_unf) where in_scope :: InScopeSet in_scope = StaticEnv -> InScopeSet seInScope StaticEnv env id_unf :: Id -> Unfolding id_unf Id id | Id -> Bool unf_is_active Id id = Id -> Unfolding idUnfolding Id id | Bool otherwise = Unfolding NoUnfolding unf_is_active :: Id -> Bool unf_is_active Id id = CompilerPhase -> Activation -> Bool isActive (StaticEnv -> CompilerPhase sePhase StaticEnv env) (Id -> Activation idInlineActivation Id id) -- When sm_rules was off we used to test for a /stable/ unfolding, -- but that seems wrong (#20941) ---------------------- activeRule :: SimplMode -> Activation -> Bool -- Nothing => No rules at all activeRule :: SimplMode -> Activation -> Bool activeRule SimplMode mode | Bool -> Bool not (SimplMode -> Bool sm_rules SimplMode mode) = \Activation _ -> Bool False -- Rewriting is off | Bool otherwise = CompilerPhase -> Activation -> Bool isActive (SimplMode -> CompilerPhase sm_phase SimplMode mode) {- ************************************************************************ * * preInlineUnconditionally * * ************************************************************************ preInlineUnconditionally ~~~~~~~~~~~~~~~~~~~~~~~~ @preInlineUnconditionally@ examines a bndr to see if it is used just once in a completely safe way, so that it is safe to discard the binding inline its RHS at the (unique) usage site, REGARDLESS of how big the RHS might be. If this is the case we don't simplify the RHS first, but just inline it un-simplified. This is much better than first simplifying a perhaps-huge RHS and then inlining and re-simplifying it. Indeed, it can be at least quadratically better. Consider x1 = e1 x2 = e2[x1] x3 = e3[x2] ...etc... xN = eN[xN-1] We may end up simplifying e1 N times, e2 N-1 times, e3 N-3 times etc. This can happen with cascades of functions too: f1 = \x1.e1 f2 = \xs.e2[f1] f3 = \xs.e3[f3] ...etc... THE MAIN INVARIANT is this: ---- preInlineUnconditionally invariant ----- IF preInlineUnconditionally chooses to inline x = <rhs> THEN doing the inlining should not change the occurrence info for the free vars of <rhs> ---------------------------------------------- For example, it's tempting to look at trivial binding like x = y and inline it unconditionally. But suppose x is used many times, but this is the unique occurrence of y. Then inlining x would change y's occurrence info, which breaks the invariant. It matters: y might have a BIG rhs, which will now be dup'd at every occurrence of x. Even RHSs labelled InlineMe aren't caught here, because there might be no benefit from inlining at the call site. [Sept 01] Don't unconditionally inline a top-level thing, because that can simply make a static thing into something built dynamically. E.g. x = (a,b) main = \s -> h x [Remember that we treat \s as a one-shot lambda.] No point in inlining x unless there is something interesting about the call site. But watch out: if you aren't careful, some useful foldr/build fusion can be lost (most notably in spectral/hartel/parstof) because the foldr didn't see the build. Doing the dynamic allocation isn't a big deal, in fact, but losing the fusion can be. But the right thing here seems to be to do a callSiteInline based on the fact that there is something interesting about the call site (it's strict). Hmm. That seems a bit fragile. Conclusion: inline top level things gaily until FinalPhase (the last phase), at which point don't. Note [pre/postInlineUnconditionally in gentle mode] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Even in gentle mode we want to do preInlineUnconditionally. The reason is that too little clean-up happens if you don't inline use-once things. Also a bit of inlining is *good* for full laziness; it can expose constant sub-expressions. Example in spectral/mandel/Mandel.hs, where the mandelset function gets a useful let-float if you inline windowToViewport However, as usual for Gentle mode, do not inline things that are inactive in the initial stages. See Note [Gentle mode]. Note [Stable unfoldings and preInlineUnconditionally] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Surprisingly, do not pre-inline-unconditionally Ids with INLINE pragmas! Example {-# INLINE f #-} f :: Eq a => a -> a f x = ... fInt :: Int -> Int fInt = f Int dEqInt ...fInt...fInt...fInt... Here f occurs just once, in the RHS of fInt. But if we inline it there it might make fInt look big, and we'll lose the opportunity to inline f at each of fInt's call sites. The INLINE pragma will only inline when the application is saturated for exactly this reason; and we don't want PreInlineUnconditionally to second-guess it. A live example is #3736. c.f. Note [Stable unfoldings and postInlineUnconditionally] NB: this only applies for INLINE things. Do /not/ switch off preInlineUnconditionally for * INLINABLE. It just says to GHC "inline this if you like". If there is a unique occurrence, we want to inline the stable unfolding, not the RHS. * NONLINE[n] just switches off inlining until phase n. We should respect that, but after phase n, just behave as usual. * NoUserInlinePrag. There is no pragma at all. This ends up on wrappers. (See #18815.) Note [Top-level bottoming Ids] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Don't inline top-level Ids that are bottoming, even if they are used just once, because FloatOut has gone to some trouble to extract them out. Inlining them won't make the program run faster! Note [Do not inline CoVars unconditionally] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Coercion variables appear inside coercions, and the RHS of a let-binding is a term (not a coercion) so we can't necessarily inline the latter in the former. -} preInlineUnconditionally :: SimplEnv -> TopLevelFlag -> InId -> InExpr -> StaticEnv -- These two go together -> Maybe SimplEnv -- Returned env has extended substitution -- Precondition: rhs satisfies the let-can-float invariant -- See Note [Core let-can-float invariant] in GHC.Core -- Reason: we don't want to inline single uses, or discard dead bindings, -- for unlifted, side-effect-ful bindings preInlineUnconditionally :: StaticEnv -> TopLevelFlag -> Id -> OutExpr -> StaticEnv -> Maybe StaticEnv preInlineUnconditionally StaticEnv env TopLevelFlag top_lvl Id bndr OutExpr rhs StaticEnv rhs_env | Bool -> Bool not Bool pre_inline = forall a. Maybe a Nothing | Bool -> Bool not Bool active = forall a. Maybe a Nothing | TopLevelFlag -> Bool isTopLevel TopLevelFlag top_lvl Bool -> Bool -> Bool && Id -> Bool isDeadEndId Id bndr = forall a. Maybe a Nothing -- Note [Top-level bottoming Ids] | Id -> Bool isCoVar Id bndr = forall a. Maybe a Nothing -- Note [Do not inline CoVars unconditionally] | Bool keep_exits, Id -> Bool isExitJoinId Id bndr = forall a. Maybe a Nothing -- Note [Do not inline exit join points] -- in module Exitify | Bool -> Bool not (OccInfo -> Bool one_occ (Id -> OccInfo idOccInfo Id bndr)) = forall a. Maybe a Nothing | Bool -> Bool not (Unfolding -> Bool isStableUnfolding Unfolding unf) = forall a. a -> Maybe a Just forall a b. (a -> b) -> a -> b $! (OutExpr -> StaticEnv extend_subst_with OutExpr rhs) -- See Note [Stable unfoldings and preInlineUnconditionally] | Bool -> Bool not (InlinePragma -> Bool isInlinePragma InlinePragma inline_prag) , Just OutExpr inl <- Unfolding -> Maybe OutExpr maybeUnfoldingTemplate Unfolding unf = forall a. a -> Maybe a Just forall a b. (a -> b) -> a -> b $! (OutExpr -> StaticEnv extend_subst_with OutExpr inl) | Bool otherwise = forall a. Maybe a Nothing where mode :: SimplMode mode = StaticEnv -> SimplMode seMode StaticEnv env phase :: CompilerPhase phase = SimplMode -> CompilerPhase sm_phase SimplMode mode keep_exits :: Bool keep_exits = SimplMode -> Bool sm_keep_exits SimplMode mode pre_inline :: Bool pre_inline = SimplMode -> Bool sm_pre_inline SimplMode mode unf :: Unfolding unf = Id -> Unfolding idUnfolding Id bndr extend_subst_with :: OutExpr -> StaticEnv extend_subst_with OutExpr inl_rhs = StaticEnv -> Id -> SimplSR -> StaticEnv extendIdSubst StaticEnv env Id bndr forall a b. (a -> b) -> a -> b $! (StaticEnv -> OutExpr -> SimplSR mkContEx StaticEnv rhs_env OutExpr inl_rhs) one_occ :: OccInfo -> Bool one_occ OccInfo IAmDead = Bool True -- Happens in ((\x.1) v) one_occ OneOcc{ occ_n_br :: OccInfo -> BranchCount occ_n_br = BranchCount 1 , occ_in_lam :: OccInfo -> InsideLam occ_in_lam = InsideLam NotInsideLam } = TopLevelFlag -> Bool isNotTopLevel TopLevelFlag top_lvl Bool -> Bool -> Bool || Bool early_phase one_occ OneOcc{ occ_n_br :: OccInfo -> BranchCount occ_n_br = BranchCount 1 , occ_in_lam :: OccInfo -> InsideLam occ_in_lam = InsideLam IsInsideLam , occ_int_cxt :: OccInfo -> InterestingCxt occ_int_cxt = InterestingCxt IsInteresting } = OutExpr -> Bool canInlineInLam OutExpr rhs one_occ OneOcc{ occ_n_br :: OccInfo -> BranchCount occ_n_br = BranchCount 1 } -- Inline join point that are used once, even inside | Id -> Bool isJoinId Id bndr = Bool True -- lambdas (which are presumably other join points) -- E.g. join j x = rhs in -- joinrec k y = ....j x.... -- Here j must be an exit for k, and we can safely inline it under the lambda -- This includes the case where j is nullary: a nullary join point is just the -- same as an arity-1 one. So we don't look at occ_int_cxt. -- All of this only applies if keep_exits is False, otherwise the -- earlier guard on preInlineUnconditionally would have fired one_occ OccInfo _ = Bool False active :: Bool active = CompilerPhase -> Activation -> Bool isActive CompilerPhase phase (InlinePragma -> Activation inlinePragmaActivation InlinePragma inline_prag) -- See Note [pre/postInlineUnconditionally in gentle mode] inline_prag :: InlinePragma inline_prag = Id -> InlinePragma idInlinePragma Id bndr -- Be very careful before inlining inside a lambda, because (a) we must not -- invalidate occurrence information, and (b) we want to avoid pushing a -- single allocation (here) into multiple allocations (inside lambda). -- Inlining a *function* with a single *saturated* call would be ok, mind you. -- || (if is_cheap && not (canInlineInLam rhs) then pprTrace "preinline" (ppr bndr <+> ppr rhs) ok else ok) -- where -- is_cheap = exprIsCheap rhs -- ok = is_cheap && int_cxt -- int_cxt The context isn't totally boring -- E.g. let f = \ab.BIG in \y. map f xs -- Don't want to substitute for f, because then we allocate -- its closure every time the \y is called -- But: let f = \ab.BIG in \y. map (f y) xs -- Now we do want to substitute for f, even though it's not -- saturated, because we're going to allocate a closure for -- (f y) every time round the loop anyhow. -- canInlineInLam => free vars of rhs are (Once in_lam) or Many, -- so substituting rhs inside a lambda doesn't change the occ info. -- Sadly, not quite the same as exprIsHNF. canInlineInLam :: OutExpr -> Bool canInlineInLam (Lit Literal _) = Bool True canInlineInLam (Lam Id b OutExpr e) = Id -> Bool isRuntimeVar Id b Bool -> Bool -> Bool || OutExpr -> Bool canInlineInLam OutExpr e canInlineInLam (Tick CoreTickish t OutExpr e) = Bool -> Bool not (forall (pass :: TickishPass). GenTickish pass -> Bool tickishIsCode CoreTickish t) Bool -> Bool -> Bool && OutExpr -> Bool canInlineInLam OutExpr e canInlineInLam OutExpr _ = Bool False -- not ticks. Counting ticks cannot be duplicated, and non-counting -- ticks around a Lam will disappear anyway. early_phase :: Bool early_phase = CompilerPhase phase forall a. Eq a => a -> a -> Bool /= CompilerPhase FinalPhase -- If we don't have this early_phase test, consider -- x = length [1,2,3] -- The full laziness pass carefully floats all the cons cells to -- top level, and preInlineUnconditionally floats them all back in. -- Result is (a) static allocation replaced by dynamic allocation -- (b) many simplifier iterations because this tickles -- a related problem; only one inlining per pass -- -- On the other hand, I have seen cases where top-level fusion is -- lost if we don't inline top level thing (e.g. string constants) -- Hence the test for phase zero (which is the phase for all the final -- simplifications). Until phase zero we take no special notice of -- top level things, but then we become more leery about inlining -- them. {- ************************************************************************ * * postInlineUnconditionally * * ************************************************************************ postInlineUnconditionally ~~~~~~~~~~~~~~~~~~~~~~~~~ @postInlineUnconditionally@ decides whether to unconditionally inline a thing based on the form of its RHS; in particular if it has a trivial RHS. If so, we can inline and discard the binding altogether. NB: a loop breaker has must_keep_binding = True and non-loop-breakers only have *forward* references. Hence, it's safe to discard the binding NOTE: This isn't our last opportunity to inline. We're at the binding site right now, and we'll get another opportunity when we get to the occurrence(s) Note that we do this unconditional inlining only for trivial RHSs. Don't inline even WHNFs inside lambdas; doing so may simply increase allocation when the function is called. This isn't the last chance; see NOTE above. NB: Even inline pragmas (e.g. IMustBeINLINEd) are ignored here Why? Because we don't even want to inline them into the RHS of constructor arguments. See NOTE above NB: At one time even NOINLINE was ignored here: if the rhs is trivial it's best to inline it anyway. We often get a=E; b=a from desugaring, with both a and b marked NOINLINE. But that seems incompatible with our new view that inlining is like a RULE, so I'm sticking to the 'active' story for now. NB: unconditional inlining of this sort can introduce ticks in places that may seem surprising; for instance, the LHS of rules. See Note [Simplifying rules] for details. -} postInlineUnconditionally :: SimplEnv -> BindContext -> OutId -- The binder (*not* a CoVar), including its unfolding -> OccInfo -- From the InId -> OutExpr -> Bool -- Precondition: rhs satisfies the let-can-float invariant -- See Note [Core let-can-float invariant] in GHC.Core -- Reason: we don't want to inline single uses, or discard dead bindings, -- for unlifted, side-effect-ful bindings postInlineUnconditionally :: StaticEnv -> BindContext -> Id -> OccInfo -> OutExpr -> Bool postInlineUnconditionally StaticEnv env BindContext bind_cxt Id bndr OccInfo occ_info OutExpr rhs | Bool -> Bool not Bool active = Bool False | OccInfo -> Bool isWeakLoopBreaker OccInfo occ_info = Bool False -- If it's a loop-breaker of any kind, don't inline -- because it might be referred to "earlier" | Unfolding -> Bool isStableUnfolding Unfolding unfolding = Bool False -- Note [Stable unfoldings and postInlineUnconditionally] | TopLevelFlag -> Bool isTopLevel (BindContext -> TopLevelFlag bindContextLevel BindContext bind_cxt) = Bool False -- Note [Top level and postInlineUnconditionally] | OutExpr -> Bool exprIsTrivial OutExpr rhs = Bool True | BC_Join {} <- BindContext bind_cxt -- See point (1) of Note [Duplicating join points] , Bool -> Bool not (CompilerPhase phase forall a. Eq a => a -> a -> Bool == CompilerPhase FinalPhase) = Bool False -- in Simplify.hs | Bool otherwise = case OccInfo occ_info of OneOcc { occ_in_lam :: OccInfo -> InsideLam occ_in_lam = InsideLam in_lam, occ_int_cxt :: OccInfo -> InterestingCxt occ_int_cxt = InterestingCxt int_cxt, occ_n_br :: OccInfo -> BranchCount occ_n_br = BranchCount n_br } -- See Note [Inline small things to avoid creating a thunk] -> BranchCount n_br forall a. Ord a => a -> a -> Bool < BranchCount 100 -- See Note [Suppress exponential blowup] Bool -> Bool -> Bool && UnfoldingOpts -> Unfolding -> Bool smallEnoughToInline UnfoldingOpts uf_opts Unfolding unfolding -- Small enough to dup -- ToDo: consider discount on smallEnoughToInline if int_cxt is true -- -- NB: Do NOT inline arbitrarily big things, even if occ_n_br=1 -- Reason: doing so risks exponential behaviour. We simplify a big -- expression, inline it, and simplify it again. But if the -- very same thing happens in the big expression, we get -- exponential cost! -- PRINCIPLE: when we've already simplified an expression once, -- make sure that we only inline it if it's reasonably small. Bool -> Bool -> Bool && (InsideLam in_lam forall a. Eq a => a -> a -> Bool == InsideLam NotInsideLam Bool -> Bool -> Bool || -- Outside a lambda, we want to be reasonably aggressive -- about inlining into multiple branches of case -- e.g. let x = <non-value> -- in case y of { C1 -> ..x..; C2 -> ..x..; C3 -> ... } -- Inlining can be a big win if C3 is the hot-spot, even if -- the uses in C1, C2 are not 'interesting' -- An example that gets worse if you add int_cxt here is 'clausify' (Unfolding -> Bool isCheapUnfolding Unfolding unfolding Bool -> Bool -> Bool && InterestingCxt int_cxt forall a. Eq a => a -> a -> Bool == InterestingCxt IsInteresting)) -- isCheap => acceptable work duplication; in_lam may be true -- int_cxt to prevent us inlining inside a lambda without some -- good reason. See the notes on int_cxt in preInlineUnconditionally OccInfo IAmDead -> Bool True -- This happens; for example, the case_bndr during case of -- known constructor: case (a,b) of x { (p,q) -> ... } -- Here x isn't mentioned in the RHS, so we don't want to -- create the (dead) let-binding let x = (a,b) in ... OccInfo _ -> Bool False -- Here's an example that we don't handle well: -- let f = if b then Left (\x.BIG) else Right (\y.BIG) -- in \y. ....case f of {...} .... -- Here f is used just once, and duplicating the case work is fine (exprIsCheap). -- But -- - We can't preInlineUnconditionally because that would invalidate -- the occ info for b. -- - We can't postInlineUnconditionally because the RHS is big, and -- that risks exponential behaviour -- - We can't call-site inline, because the rhs is big -- Alas! where unfolding :: Unfolding unfolding = Id -> Unfolding idUnfolding Id bndr uf_opts :: UnfoldingOpts uf_opts = StaticEnv -> UnfoldingOpts seUnfoldingOpts StaticEnv env phase :: CompilerPhase phase = StaticEnv -> CompilerPhase sePhase StaticEnv env active :: Bool active = CompilerPhase -> Activation -> Bool isActive CompilerPhase phase (Id -> Activation idInlineActivation Id bndr) -- See Note [pre/postInlineUnconditionally in gentle mode] {- Note [Inline small things to avoid creating a thunk] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The point of examining occ_info here is that for *non-values* that occur outside a lambda, the call-site inliner won't have a chance (because it doesn't know that the thing only occurs once). The pre-inliner won't have gotten it either, if the thing occurs in more than one branch So the main target is things like let x = f y in case v of True -> case x of ... False -> case x of ... This is very important in practice; e.g. wheel-seive1 doubles in allocation if you miss this out. And bits of GHC itself start to allocate more. An egregious example is test perf/compiler/T14697, where GHC.Driver.CmdLine.$wprocessArgs allocated hugely more. Note [Suppress exponential blowup] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ In #13253, and several related tickets, we got an exponential blowup in code size from postInlineUnconditionally. The trouble comes when we have let j1a = case f y of { True -> p; False -> q } j1b = case f y of { True -> q; False -> p } j2a = case f (y+1) of { True -> j1a; False -> j1b } j2b = case f (y+1) of { True -> j1b; False -> j1a } ... in case f (y+10) of { True -> j10a; False -> j10b } when there are many branches. In pass 1, postInlineUnconditionally inlines j10a and j10b (they are both small). Now we have two calls to j9a and two to j9b. In pass 2, postInlineUnconditionally inlines all four of these calls, leaving four calls to j8a and j8b. Etc. Yikes! This is exponential! A possible plan: stop doing postInlineUnconditionally for some fixed, smallish number of branches, say 4. But that turned out to be bad: see Note [Inline small things to avoid creating a thunk]. And, as it happened, the problem with #13253 was solved in a different way (Note [Duplicating StrictArg] in Simplify). So I just set an arbitrary, high limit of 100, to stop any totally exponential behaviour. This still leaves the nasty possibility that /ordinary/ inlining (not postInlineUnconditionally) might inline these join points, each of which is individually quiet small. I'm still not sure what to do about this (e.g. see #15488). Note [Top level and postInlineUnconditionally] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We don't do postInlineUnconditionally for top-level things (even for ones that are trivial): * Doing so will inline top-level error expressions that have been carefully floated out by FloatOut. More generally, it might replace static allocation with dynamic. * Even for trivial expressions there's a problem. Consider {-# RULE "foo" forall (xs::[T]). reverse xs = ruggle xs #-} blah xs = reverse xs ruggle = sort In one simplifier pass we might fire the rule, getting blah xs = ruggle xs but in *that* simplifier pass we must not do postInlineUnconditionally on 'ruggle' because then we'll have an unbound occurrence of 'ruggle' If the rhs is trivial it'll be inlined by callSiteInline, and then the binding will be dead and discarded by the next use of OccurAnal * There is less point, because the main goal is to get rid of local bindings used in multiple case branches. * The inliner should inline trivial things at call sites anyway. * The Id might be exported. We could check for that separately, but since we aren't going to postInlineUnconditionally /any/ top-level bindings, we don't need to test. Note [Stable unfoldings and postInlineUnconditionally] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Do not do postInlineUnconditionally if the Id has a stable unfolding, otherwise we lose the unfolding. Example -- f has stable unfolding with rhs (e |> co) -- where 'e' is big f = e |> co Then there's a danger we'll optimise to f' = e f = f' |> co and now postInlineUnconditionally, losing the stable unfolding on f. Now f' won't inline because 'e' is too big. c.f. Note [Stable unfoldings and preInlineUnconditionally] ************************************************************************ * * Rebuilding a lambda * * ************************************************************************ -} rebuildLam :: SimplEnv -> [OutBndr] -> OutExpr -> SimplCont -> SimplM OutExpr -- (rebuildLam env bndrs body cont) -- returns expr which means the same as \bndrs. body -- -- But it tries -- a) eta reduction, if that gives a trivial expression -- b) eta expansion [only if there are some value lambdas] -- -- NB: the SimplEnv already includes the [OutBndr] in its in-scope set rebuildLam :: StaticEnv -> [Id] -> OutExpr -> SimplCont -> SimplM OutExpr rebuildLam StaticEnv _env [] OutExpr body SimplCont _cont = forall (m :: * -> *) a. Monad m => a -> m a return OutExpr body rebuildLam StaticEnv env bndrs :: [Id] bndrs@(Id bndr:[Id] _) OutExpr body SimplCont cont = {-# SCC "rebuildLam" #-} [Id] -> OutExpr -> SimplM OutExpr try_eta [Id] bndrs OutExpr body where rec_ids :: UnVarSet rec_ids = StaticEnv -> UnVarSet seRecIds StaticEnv env in_scope :: InScopeSet in_scope = StaticEnv -> InScopeSet getInScope StaticEnv env -- Includes 'bndrs' mb_rhs :: Maybe RecFlag mb_rhs = SimplCont -> Maybe RecFlag contIsRhs SimplCont cont -- See Note [Eta reduction based on evaluation context] eval_sd :: SubDemand eval_sd = SimplCont -> SubDemand contEvalContext SimplCont cont -- NB: cont is never ApplyToVal, because beta-reduction would -- have happened. So contEvalContext can panic on ApplyToVal. try_eta :: [OutBndr] -> OutExpr -> SimplM OutExpr try_eta :: [Id] -> OutExpr -> SimplM OutExpr try_eta [Id] bndrs OutExpr body | -- Try eta reduction StaticEnv -> Bool seDoEtaReduction StaticEnv env , Just OutExpr etad_lam <- UnVarSet -> [Id] -> OutExpr -> SubDemand -> Maybe OutExpr tryEtaReduce UnVarSet rec_ids [Id] bndrs OutExpr body SubDemand eval_sd = do { Tick -> SimplM () tick (Id -> Tick EtaReduction Id bndr) ; forall (m :: * -> *) a. Monad m => a -> m a return OutExpr etad_lam } | -- Try eta expansion Maybe RecFlag Nothing <- Maybe RecFlag mb_rhs -- See Note [Eta expanding lambdas] , StaticEnv -> Bool seEtaExpand StaticEnv env , forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool any Id -> Bool isRuntimeVar [Id] bndrs -- Only when there is at least one value lambda already , Just SafeArityType body_arity <- ArityOpts -> OutExpr -> Maybe SafeArityType exprEtaExpandArity (StaticEnv -> ArityOpts seArityOpts StaticEnv env) OutExpr body = do { Tick -> SimplM () tick (Id -> Tick EtaExpansion Id bndr) ; let body' :: OutExpr body' = InScopeSet -> SafeArityType -> OutExpr -> OutExpr etaExpandAT InScopeSet in_scope SafeArityType body_arity OutExpr body ; String -> SDoc -> SimplM () traceSmpl String "eta expand" (forall doc. IsDoc doc => [doc] -> doc vcat [forall doc. IsLine doc => String -> doc text String "before" forall doc. IsLine doc => doc -> doc -> doc <+> forall a. Outputable a => a -> SDoc ppr OutExpr body , forall doc. IsLine doc => String -> doc text String "after" forall doc. IsLine doc => doc -> doc -> doc <+> forall a. Outputable a => a -> SDoc ppr OutExpr body']) -- NB: body' might have an outer Cast, but if so -- mk_lams will pull it further out, past 'bndrs' to the top ; forall (m :: * -> *) a. Monad m => a -> m a return ([Id] -> OutExpr -> OutExpr mk_lams [Id] bndrs OutExpr body') } | Bool otherwise = forall (m :: * -> *) a. Monad m => a -> m a return ([Id] -> OutExpr -> OutExpr mk_lams [Id] bndrs OutExpr body) mk_lams :: [OutBndr] -> OutExpr -> OutExpr -- mk_lams pulls casts and ticks to the top mk_lams :: [Id] -> OutExpr -> OutExpr mk_lams [Id] bndrs body :: OutExpr body@(Lam {}) = [Id] -> OutExpr -> OutExpr mk_lams ([Id] bndrs forall a. [a] -> [a] -> [a] ++ [Id] bndrs1) OutExpr body1 where ([Id] bndrs1, OutExpr body1) = forall b. Expr b -> ([b], Expr b) collectBinders OutExpr body mk_lams [Id] bndrs (Tick CoreTickish t OutExpr expr) | forall (pass :: TickishPass). GenTickish pass -> Bool tickishFloatable CoreTickish t = CoreTickish -> OutExpr -> OutExpr mkTick CoreTickish t ([Id] -> OutExpr -> OutExpr mk_lams [Id] bndrs OutExpr expr) mk_lams [Id] bndrs (Cast OutExpr body OutCoercion co) | -- Note [Casts and lambdas] StaticEnv -> Bool seCastSwizzle StaticEnv env , Bool -> Bool not (forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool any Id -> Bool bad [Id] bndrs) = HasDebugCallStack => OutExpr -> OutCoercion -> OutExpr mkCast ([Id] -> OutExpr -> OutExpr mk_lams [Id] bndrs OutExpr body) (Role -> [Id] -> OutCoercion -> OutCoercion mkPiCos Role Representational [Id] bndrs OutCoercion co) where co_vars :: TyCoVarSet co_vars = OutCoercion -> TyCoVarSet tyCoVarsOfCo OutCoercion co bad :: Id -> Bool bad Id bndr = Id -> Bool isCoVar Id bndr Bool -> Bool -> Bool && Id bndr Id -> TyCoVarSet -> Bool `elemVarSet` TyCoVarSet co_vars mk_lams [Id] bndrs OutExpr body = forall b. [b] -> Expr b -> Expr b mkLams [Id] bndrs OutExpr body {- Note [Eta expanding lambdas] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ In general we *do* want to eta-expand lambdas. Consider f (\x -> case x of (a,b) -> \s -> blah) where 's' is a state token, and hence can be eta expanded. This showed up in the code for GHc.IO.Handle.Text.hPutChar, a rather important function! The eta-expansion will never happen unless we do it now. (Well, it's possible that CorePrep will do it, but CorePrep only has a half-baked eta-expander that can't deal with casts. So it's much better to do it here.) However, when the lambda is let-bound, as the RHS of a let, we have a better eta-expander (in the form of tryEtaExpandRhs), so we don't bother to try expansion in mkLam in that case; hence the contIsRhs guard. Note [Casts and lambdas] ~~~~~~~~~~~~~~~~~~~~~~~~ Consider (\(x:tx). (\(y:ty). e) `cast` co) We float the cast out, thus (\(x:tx) (y:ty). e) `cast` (tx -> co) We do this for at least three reasons: 1. There is a danger here that the two lambdas look separated, and the full laziness pass might float an expression to between the two. 2. The occurrence analyser will mark x as InsideLam if the Lam nodes are separated (see the Lam case of occAnal). By floating the cast out we put the two Lams together, so x can get a vanilla Once annotation. If this lambda is the RHS of a let, which we inline, we can do preInlineUnconditionally on that x=arg binding. With the InsideLam OccInfo, we can't do that, which results in an extra iteration of the Simplifier. 3. It may cancel with another cast. E.g (\x. e |> co1) |> co2 If we float out co1 it might cancel with co2. Similarly let f = (\x. e |> co1) in ... If we float out co1, and then do cast worker/wrapper, we get let f1 = \x.e; f = f1 |> co1 in ... and now we can inline f, hoping that co1 may cancel at a call site. TL;DR: put the lambdas together if at all possible. In general, here's the transformation: \x. e `cast` co ===> (\x. e) `cast` (tx -> co) /\a. e `cast` co ===> (/\a. e) `cast` (/\a. co) /\g. e `cast` co ===> (/\g. e) `cast` (/\g. co) (if not (g `in` co)) We call this "cast swizzling". It is controlled by sm_cast_swizzle. See also Note [Cast swizzling on rule LHSs] Wrinkles * Notice that it works regardless of 'e'. Originally it worked only if 'e' was itself a lambda, but in some cases that resulted in fruitless iteration in the simplifier. A good example was when compiling Text.ParserCombinators.ReadPrec, where we had a definition like (\x. Get `cast` g) where Get is a constructor with nonzero arity. Then mkLam eta-expanded the Get, and the next iteration eta-reduced it, and then eta-expanded it again. * Note also the side condition for the case of coercion binders, namely not (any bad bndrs). It does not make sense to transform /\g. e `cast` g ==> (/\g.e) `cast` (/\g.g) because the latter is not well-kinded. ************************************************************************ * * Eta expansion * * ************************************************************************ -} tryEtaExpandRhs :: SimplEnv -> BindContext -> OutId -> OutExpr -> SimplM (ArityType, OutExpr) -- See Note [Eta-expanding at let bindings] tryEtaExpandRhs :: StaticEnv -> BindContext -> Id -> OutExpr -> SimplM (SafeArityType, OutExpr) tryEtaExpandRhs StaticEnv env BindContext bind_cxt Id bndr OutExpr rhs | Bool do_eta_expand -- If the current manifest arity isn't enough -- (never true for join points) , StaticEnv -> Bool seEtaExpand StaticEnv env -- and eta-expansion is on , OutExpr -> Bool wantEtaExpansion OutExpr rhs = -- Do eta-expansion. forall a. HasCallStack => Bool -> SDoc -> a -> a assertPpr( Bool -> Bool not (BindContext -> Bool isJoinBC BindContext bind_cxt) ) (forall a. Outputable a => a -> SDoc ppr Id bndr) forall a b. (a -> b) -> a -> b $ -- assert: this never happens for join points; see GHC.Core.Opt.Arity -- Note [Do not eta-expand join points] do { Tick -> SimplM () tick (Id -> Tick EtaExpansion Id bndr) ; forall (m :: * -> *) a. Monad m => a -> m a return (SafeArityType arity_type, InScopeSet -> SafeArityType -> OutExpr -> OutExpr etaExpandAT InScopeSet in_scope SafeArityType arity_type OutExpr rhs) } | Bool otherwise = forall (m :: * -> *) a. Monad m => a -> m a return (SafeArityType arity_type, OutExpr rhs) where in_scope :: InScopeSet in_scope = StaticEnv -> InScopeSet getInScope StaticEnv env arity_opts :: ArityOpts arity_opts = StaticEnv -> ArityOpts seArityOpts StaticEnv env is_rec :: RecFlag is_rec = BindContext -> RecFlag bindContextRec BindContext bind_cxt (Bool do_eta_expand, SafeArityType arity_type) = ArityOpts -> RecFlag -> Id -> OutExpr -> (Bool, SafeArityType) findRhsArity ArityOpts arity_opts RecFlag is_rec Id bndr OutExpr rhs wantEtaExpansion :: CoreExpr -> Bool -- Mostly True; but False of PAPs which will immediately eta-reduce again -- See Note [Which RHSs do we eta-expand?] wantEtaExpansion :: OutExpr -> Bool wantEtaExpansion (Cast OutExpr e OutCoercion _) = OutExpr -> Bool wantEtaExpansion OutExpr e wantEtaExpansion (Tick CoreTickish _ OutExpr e) = OutExpr -> Bool wantEtaExpansion OutExpr e wantEtaExpansion (Lam Id b OutExpr e) | Id -> Bool isTyVar Id b = OutExpr -> Bool wantEtaExpansion OutExpr e wantEtaExpansion (App OutExpr e OutExpr _) = OutExpr -> Bool wantEtaExpansion OutExpr e wantEtaExpansion (Var {}) = Bool False wantEtaExpansion (Lit {}) = Bool False wantEtaExpansion OutExpr _ = Bool True {- Note [Eta-expanding at let bindings] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We now eta expand at let-bindings, which is where the payoff comes. The most significant thing is that we can do a simple arity analysis (in GHC.Core.Opt.Arity.findRhsArity), which we can't do for free-floating lambdas One useful consequence of not eta-expanding lambdas is this example: genMap :: C a => ... {-# INLINE genMap #-} genMap f xs = ... myMap :: D a => ... {-# INLINE myMap #-} myMap = genMap Notice that 'genMap' should only inline if applied to two arguments. In the stable unfolding for myMap we'll have the unfolding (\d -> genMap Int (..d..)) We do not want to eta-expand to (\d f xs -> genMap Int (..d..) f xs) because then 'genMap' will inline, and it really shouldn't: at least as far as the programmer is concerned, it's not applied to two arguments! Note [Which RHSs do we eta-expand?] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We don't eta-expand: * Trivial RHSs, e.g. f = g If we eta expand do f = \x. g x we'll just eta-reduce again, and so on; so the simplifier never terminates. * PAPs: see Note [Do not eta-expand PAPs] What about things like this? f = case y of p -> \x -> blah Here we do eta-expand. This is a change (Jun 20), but if we have really decided that f has arity 1, then putting that lambda at the top seems like a Good idea. Note [Do not eta-expand PAPs] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We used to have old_arity = manifestArity rhs, which meant that we would eta-expand even PAPs. But this gives no particular advantage, and can lead to a massive blow-up in code size, exhibited by #9020. Suppose we have a PAP foo :: IO () foo = returnIO () Then we can eta-expand to foo = (\eta. (returnIO () |> sym g) eta) |> g where g :: IO () ~ State# RealWorld -> (# State# RealWorld, () #) But there is really no point in doing this, and it generates masses of coercions and whatnot that eventually disappear again. For T9020, GHC allocated 6.6G before, and 0.8G afterwards; and residency dropped from 1.8G to 45M. Moreover, if we eta expand f = g d ==> f = \x. g d x that might in turn make g inline (if it has an inline pragma), which we might not want. After all, INLINE pragmas say "inline only when saturated" so we don't want to be too gung-ho about saturating! But note that this won't eta-expand, say f = \g -> map g Does it matter not eta-expanding such functions? I'm not sure. Perhaps strictness analysis will have less to bite on? ************************************************************************ * * \subsection{Floating lets out of big lambdas} * * ************************************************************************ Note [Floating and type abstraction] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider this: x = /\a. C e1 e2 We'd like to float this to y1 = /\a. e1 y2 = /\a. e2 x = /\a. C (y1 a) (y2 a) for the usual reasons: we want to inline x rather vigorously. You may think that this kind of thing is rare. But in some programs it is common. For example, if you do closure conversion you might get: data a :-> b = forall e. (e -> a -> b) :$ e f_cc :: forall a. a :-> a f_cc = /\a. (\e. id a) :$ () Now we really want to inline that f_cc thing so that the construction of the closure goes away. So I have elaborated simplLazyBind to understand right-hand sides that look like /\ a1..an. body and treat them specially. The real work is done in GHC.Core.Opt.Simplify.Utils.abstractFloats, but there is quite a bit of plumbing in simplLazyBind as well. The same transformation is good when there are lets in the body: /\abc -> let(rec) x = e in b ==> let(rec) x' = /\abc -> let x = x' a b c in e in /\abc -> let x = x' a b c in b This is good because it can turn things like: let f = /\a -> letrec g = ... g ... in g into letrec g' = /\a -> ... g' a ... in let f = /\ a -> g' a which is better. In effect, it means that big lambdas don't impede let-floating. This optimisation is CRUCIAL in eliminating the junk introduced by desugaring mutually recursive definitions. Don't eliminate it lightly! [May 1999] If we do this transformation *regardless* then we can end up with some pretty silly stuff. For example, let st = /\ s -> let { x1=r1 ; x2=r2 } in ... in .. becomes let y1 = /\s -> r1 y2 = /\s -> r2 st = /\s -> ...[y1 s/x1, y2 s/x2] in .. Unless the "..." is a WHNF there is really no point in doing this. Indeed it can make things worse. Suppose x1 is used strictly, and is of the form x1* = case f y of { (a,b) -> e } If we abstract this wrt the tyvar we then can't do the case inline as we would normally do. That's why the whole transformation is part of the same process that floats let-bindings and constructor arguments out of RHSs. In particular, it is guarded by the doFloatFromRhs call in simplLazyBind. Note [Which type variables to abstract over] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Abstract only over the type variables free in the rhs wrt which the new binding is abstracted. Note that * The naive approach of abstracting wrt the tyvars free in the Id's /type/ fails. Consider: /\ a b -> let t :: (a,b) = (e1, e2) x :: a = fst t in ... Here, b isn't free in x's type, but we must nevertheless abstract wrt b as well, because t's type mentions b. Since t is floated too, we'd end up with the bogus: poly_t = /\ a b -> (e1, e2) poly_x = /\ a -> fst (poly_t a *b*) * We must do closeOverKinds. Example (#10934): f = /\k (f:k->*) (a:k). let t = AccFailure @ (f a) in ... Here we want to float 't', but we must remember to abstract over 'k' as well, even though it is not explicitly mentioned in the RHS, otherwise we get t = /\ (f:k->*) (a:k). AccFailure @ (f a) which is obviously bogus. * We get the variables to abstract over by filtering down the the main_tvs for the original function, picking only ones mentioned in the abstracted body. This means: - they are automatically in dependency order, because main_tvs is - there is no issue about non-determinism - we don't gratuitously change order, which may help (in a tiny way) with CSE and/or the compiler-debugging experience -} abstractFloats :: UnfoldingOpts -> TopLevelFlag -> [OutTyVar] -> SimplFloats -> OutExpr -> SimplM ([OutBind], OutExpr) abstractFloats :: UnfoldingOpts -> TopLevelFlag -> [Id] -> SimplFloats -> OutExpr -> SimplM ([Bind Id], OutExpr) abstractFloats UnfoldingOpts uf_opts TopLevelFlag top_lvl [Id] main_tvs SimplFloats floats OutExpr body = forall a. HasCallStack => Bool -> a -> a assert (forall (f :: * -> *) a. Foldable f => f a -> Bool notNull [Bind Id] body_floats) forall a b. (a -> b) -> a -> b $ forall a. HasCallStack => Bool -> a -> a assert (forall a. OrdList a -> Bool isNilOL (SimplFloats -> JoinFloats sfJoinFloats SimplFloats floats)) forall a b. (a -> b) -> a -> b $ do { (Subst subst, [Bind Id] float_binds) <- forall (m :: * -> *) (t :: * -> *) acc x y. (Monad m, Traversable t) => (acc -> x -> m (acc, y)) -> acc -> t x -> m (acc, t y) mapAccumLM Subst -> Bind Id -> SimplM (Subst, Bind Id) abstract Subst empty_subst [Bind Id] body_floats ; forall (m :: * -> *) a. Monad m => a -> m a return ([Bind Id] float_binds, HasDebugCallStack => Subst -> OutExpr -> OutExpr GHC.Core.Subst.substExpr Subst subst OutExpr body) } where is_top_lvl :: Bool is_top_lvl = TopLevelFlag -> Bool isTopLevel TopLevelFlag top_lvl body_floats :: [Bind Id] body_floats = LetFloats -> [Bind Id] letFloatBinds (SimplFloats -> LetFloats sfLetFloats SimplFloats floats) empty_subst :: Subst empty_subst = InScopeSet -> Subst GHC.Core.Subst.mkEmptySubst (SimplFloats -> InScopeSet sfInScope SimplFloats floats) abstract :: GHC.Core.Subst.Subst -> OutBind -> SimplM (GHC.Core.Subst.Subst, OutBind) abstract :: Subst -> Bind Id -> SimplM (Subst, Bind Id) abstract Subst subst (NonRec Id id OutExpr rhs) = do { (Id poly_id1, OutExpr poly_app) <- [Id] -> Id -> SimplM (Id, OutExpr) mk_poly1 [Id] tvs_here Id id ; let (Id poly_id2, OutExpr poly_rhs) = Id -> [Id] -> OutExpr -> (Id, OutExpr) mk_poly2 Id poly_id1 [Id] tvs_here OutExpr rhs' !subst' :: Subst subst' = Subst -> Id -> OutExpr -> Subst GHC.Core.Subst.extendIdSubst Subst subst Id id OutExpr poly_app ; forall (m :: * -> *) a. Monad m => a -> m a return (Subst subst', forall b. b -> Expr b -> Bind b NonRec Id poly_id2 OutExpr poly_rhs) } where rhs' :: OutExpr rhs' = HasDebugCallStack => Subst -> OutExpr -> OutExpr GHC.Core.Subst.substExpr Subst subst OutExpr rhs -- tvs_here: see Note [Which type variables to abstract over] tvs_here :: [Id] tvs_here = forall a. (a -> Bool) -> [a] -> [a] filter (Id -> TyCoVarSet -> Bool `elemVarSet` TyCoVarSet free_tvs) [Id] main_tvs free_tvs :: TyCoVarSet free_tvs = TyCoVarSet -> TyCoVarSet closeOverKinds forall a b. (a -> b) -> a -> b $ (Id -> Bool) -> OutExpr -> TyCoVarSet exprSomeFreeVars Id -> Bool isTyVar OutExpr rhs' abstract Subst subst (Rec [(Id, OutExpr)] prs) = do { ([Id] poly_ids, [OutExpr] poly_apps) <- forall (m :: * -> *) a b c. Applicative m => (a -> m (b, c)) -> [a] -> m ([b], [c]) mapAndUnzipM ([Id] -> Id -> SimplM (Id, OutExpr) mk_poly1 [Id] tvs_here) [Id] ids ; let subst' :: Subst subst' = Subst -> [(Id, OutExpr)] -> Subst GHC.Core.Subst.extendSubstList Subst subst ([Id] ids forall a b. [a] -> [b] -> [(a, b)] `zip` [OutExpr] poly_apps) poly_pairs :: [(Id, OutExpr)] poly_pairs = [ Id -> [Id] -> OutExpr -> (Id, OutExpr) mk_poly2 Id poly_id [Id] tvs_here OutExpr rhs' | (Id poly_id, OutExpr rhs) <- [Id] poly_ids forall a b. [a] -> [b] -> [(a, b)] `zip` [OutExpr] rhss , let rhs' :: OutExpr rhs' = HasDebugCallStack => Subst -> OutExpr -> OutExpr GHC.Core.Subst.substExpr Subst subst' OutExpr rhs ] ; forall (m :: * -> *) a. Monad m => a -> m a return (Subst subst', forall b. [(b, Expr b)] -> Bind b Rec [(Id, OutExpr)] poly_pairs) } where ([Id] ids,[OutExpr] rhss) = forall a b. [(a, b)] -> ([a], [b]) unzip [(Id, OutExpr)] prs -- For a recursive group, it's a bit of a pain to work out the minimal -- set of tyvars over which to abstract: -- /\ a b c. let x = ...a... in -- letrec { p = ...x...q... -- q = .....p...b... } in -- ... -- Since 'x' is abstracted over 'a', the {p,q} group must be abstracted -- over 'a' (because x is replaced by (poly_x a)) as well as 'b'. -- Since it's a pain, we just use the whole set, which is always safe -- -- If you ever want to be more selective, remember this bizarre case too: -- x::a = x -- Here, we must abstract 'x' over 'a'. tvs_here :: [Id] tvs_here = [Id] -> [Id] scopedSort [Id] main_tvs mk_poly1 :: [TyVar] -> Id -> SimplM (Id, CoreExpr) mk_poly1 :: [Id] -> Id -> SimplM (Id, OutExpr) mk_poly1 [Id] tvs_here Id var = do { Unique uniq <- forall (m :: * -> *). MonadUnique m => m Unique getUniqueM ; let poly_name :: Name poly_name = Name -> Unique -> Name setNameUnique (Id -> Name idName Id var) Unique uniq -- Keep same name poly_ty :: OutType poly_ty = [Id] -> OutType -> OutType mkInfForAllTys [Id] tvs_here (Id -> OutType idType Id var) -- But new type of course poly_id :: Id poly_id = Id -> [Id] -> Id -> Id transferPolyIdInfo Id var [Id] tvs_here forall a b. (a -> b) -> a -> b $ -- Note [transferPolyIdInfo] in GHC.Types.Id HasDebugCallStack => Name -> OutType -> OutType -> Id mkLocalId Name poly_name (Id -> OutType idMult Id var) OutType poly_ty ; forall (m :: * -> *) a. Monad m => a -> m a return (Id poly_id, forall b. Expr b -> [OutType] -> Expr b mkTyApps (forall b. Id -> Expr b Var Id poly_id) ([Id] -> [OutType] mkTyVarTys [Id] tvs_here)) } -- In the olden days, it was crucial to copy the occInfo of the original var, -- because we were looking at occurrence-analysed but as yet unsimplified code! -- In particular, we mustn't lose the loop breakers. BUT NOW we are looking -- at already simplified code, so it doesn't matter -- -- It's even right to retain single-occurrence or dead-var info: -- Suppose we started with /\a -> let x = E in B -- where x occurs once in B. Then we transform to: -- let x' = /\a -> E in /\a -> let x* = x' a in B -- where x* has an INLINE prag on it. Now, once x* is inlined, -- the occurrences of x' will be just the occurrences originally -- pinned on x. mk_poly2 :: Id -> [TyVar] -> CoreExpr -> (Id, CoreExpr) mk_poly2 :: Id -> [Id] -> OutExpr -> (Id, OutExpr) mk_poly2 Id poly_id [Id] tvs_here OutExpr rhs = (Id poly_id Id -> Unfolding -> Id `setIdUnfolding` Unfolding unf, OutExpr poly_rhs) where poly_rhs :: OutExpr poly_rhs = forall b. [b] -> Expr b -> Expr b mkLams [Id] tvs_here OutExpr rhs unf :: Unfolding unf = UnfoldingOpts -> UnfoldingSource -> Bool -> Bool -> OutExpr -> Unfolding mkUnfolding UnfoldingOpts uf_opts UnfoldingSource VanillaSrc Bool is_top_lvl Bool False OutExpr poly_rhs -- We want the unfolding. Consider -- let -- x = /\a. let y = ... in Just y -- in body -- Then we float the y-binding out (via abstractFloats and addPolyBind) -- but 'x' may well then be inlined in 'body' in which case we'd like the -- opportunity to inline 'y' too. {- Note [Abstract over coercions] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ If a coercion variable (g :: a ~ Int) is free in the RHS, then so is the type variable a. Rather than sort this mess out, we simply bale out and abstract wrt all the type variables if any of them are coercion variables. Historical note: if you use let-bindings instead of a substitution, beware of this: -- Suppose we start with: -- -- x = /\ a -> let g = G in E -- -- Then we'll float to get -- -- x = let poly_g = /\ a -> G -- in /\ a -> let g = poly_g a in E -- -- But now the occurrence analyser will see just one occurrence -- of poly_g, not inside a lambda, so the simplifier will -- PreInlineUnconditionally poly_g back into g! Badk to square 1! -- (I used to think that the "don't inline lone occurrences" stuff -- would stop this happening, but since it's the *only* occurrence, -- PreInlineUnconditionally kicks in first!) -- -- Solution: put an INLINE note on g's RHS, so that poly_g seems -- to appear many times. (NB: mkInlineMe eliminates -- such notes on trivial RHSs, so do it manually.) ************************************************************************ * * prepareAlts * * ************************************************************************ prepareAlts tries these things: 1. filterAlts: eliminate alternatives that cannot match, including the DEFAULT alternative. Here "cannot match" includes knowledge from GADTs 2. refineDefaultAlt: if the DEFAULT alternative can match only one possible constructor, then make that constructor explicit. e.g. case e of x { DEFAULT -> rhs } ===> case e of x { (a,b) -> rhs } where the type is a single constructor type. This gives better code when rhs also scrutinises x or e. See GHC.Core.Utils Note [Refine DEFAULT case alternatives] 3. combineIdenticalAlts: combine identical alternatives into a DEFAULT. See CoreUtils Note [Combine identical alternatives], which also says why we do this on InAlts not on OutAlts 4. Returns a list of the constructors that cannot holds in the DEFAULT alternative (if there is one) It's a good idea to do this stuff before simplifying the alternatives, to avoid simplifying alternatives we know can't happen, and to come up with the list of constructors that are handled, to put into the IdInfo of the case binder, for use when simplifying the alternatives. Eliminating the default alternative in (1) isn't so obvious, but it can happen: data Colour = Red | Green | Blue f x = case x of Red -> .. Green -> .. DEFAULT -> h x h y = case y of Blue -> .. DEFAULT -> [ case y of ... ] If we inline h into f, the default case of the inlined h can't happen. If we don't notice this, we may end up filtering out *all* the cases of the inner case y, which give us nowhere to go! -} prepareAlts :: OutExpr -> OutId -> [InAlt] -> SimplM ([AltCon], [InAlt]) -- The returned alternatives can be empty, none are possible prepareAlts :: OutExpr -> Id -> [InAlt] -> SimplM ([AltCon], [InAlt]) prepareAlts OutExpr scrut Id case_bndr' [InAlt] alts | Just (TyCon tc, [OutType] tys) <- HasDebugCallStack => OutType -> Maybe (TyCon, [OutType]) splitTyConApp_maybe (Id -> OutType varType Id case_bndr') -- Case binder is needed just for its type. Note that as an -- OutId, it has maximum information; this is important. -- Test simpl013 is an example = do { [Unique] us <- forall (m :: * -> *). MonadUnique m => m [Unique] getUniquesM ; let ([AltCon] idcs1, [InAlt] alts1) = forall b. TyCon -> [OutType] -> [AltCon] -> [Alt b] -> ([AltCon], [Alt b]) filterAlts TyCon tc [OutType] tys [AltCon] imposs_cons [InAlt] alts (Bool yes2, [InAlt] alts2) = [Unique] -> OutType -> TyCon -> [OutType] -> [AltCon] -> [InAlt] -> (Bool, [InAlt]) refineDefaultAlt [Unique] us (Id -> OutType idMult Id case_bndr') TyCon tc [OutType] tys [AltCon] idcs1 [InAlt] alts1 -- the multiplicity on case_bndr's is the multiplicity of the -- case expression The newly introduced patterns in -- refineDefaultAlt must be scaled by this multiplicity (Bool yes3, [AltCon] idcs3, [InAlt] alts3) = [AltCon] -> [InAlt] -> (Bool, [AltCon], [InAlt]) combineIdenticalAlts [AltCon] idcs1 [InAlt] alts2 -- "idcs" stands for "impossible default data constructors" -- i.e. the constructors that can't match the default case ; forall (f :: * -> *). Applicative f => Bool -> f () -> f () when Bool yes2 forall a b. (a -> b) -> a -> b $ Tick -> SimplM () tick (Id -> Tick FillInCaseDefault Id case_bndr') ; forall (f :: * -> *). Applicative f => Bool -> f () -> f () when Bool yes3 forall a b. (a -> b) -> a -> b $ Tick -> SimplM () tick (Id -> Tick AltMerge Id case_bndr') ; forall (m :: * -> *) a. Monad m => a -> m a return ([AltCon] idcs3, [InAlt] alts3) } | Bool otherwise -- Not a data type, so nothing interesting happens = forall (m :: * -> *) a. Monad m => a -> m a return ([], [InAlt] alts) where imposs_cons :: [AltCon] imposs_cons = case OutExpr scrut of Var Id v -> Unfolding -> [AltCon] otherCons (Id -> Unfolding idUnfolding Id v) OutExpr _ -> [] {- ************************************************************************ * * mkCase * * ************************************************************************ mkCase tries these things * Note [Merge Nested Cases] * Note [Eliminate Identity Case] * Note [Scrutinee Constant Folding] Note [Merge Nested Cases] ~~~~~~~~~~~~~~~~~~~~~~~~~ case e of b { ==> case e of b { p1 -> rhs1 p1 -> rhs1 ... ... pm -> rhsm pm -> rhsm _ -> case b of b' { pn -> let b'=b in rhsn pn -> rhsn ... ... po -> let b'=b in rhso po -> rhso _ -> let b'=b in rhsd _ -> rhsd } which merges two cases in one case when -- the default alternative of the outer case scrutinises the same variable as the outer case. This transformation is called Case Merging. It avoids that the same variable is scrutinised multiple times. Note [Eliminate Identity Case] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ case e of ===> e True -> True; False -> False and similar friends. Note [Scrutinee Constant Folding] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ case x op# k# of _ { ===> case x of _ { a1# -> e1 (a1# inv_op# k#) -> e1 a2# -> e2 (a2# inv_op# k#) -> e2 ... ... DEFAULT -> ed DEFAULT -> ed where (x op# k#) inv_op# k# == x And similarly for commuted arguments and for some unary operations. The purpose of this transformation is not only to avoid an arithmetic operation at runtime but to allow other transformations to apply in cascade. Example with the "Merge Nested Cases" optimization (from #12877): main = case t of t0 0## -> ... DEFAULT -> case t0 `minusWord#` 1## of t1 0## -> ... DEFAULT -> case t1 `minusWord#` 1## of t2 0## -> ... DEFAULT -> case t2 `minusWord#` 1## of _ 0## -> ... DEFAULT -> ... becomes: main = case t of _ 0## -> ... 1## -> ... 2## -> ... 3## -> ... DEFAULT -> ... There are some wrinkles. Wrinkle 1: Do not apply caseRules if there is just a single DEFAULT alternative, unless the case-binder is dead. Example: case e +# 3# of b { DEFAULT -> rhs } If we applied the transformation here we would (stupidly) get case e of b' { DEFAULT -> let b = b' +# 3# in rhs } and now the process may repeat, because that let will really be a case. But if the original case binder b is dead, we instead get case e of b' { DEFAULT -> rhs } and there is no such problem. See Note [Example of case-merging and caseRules] for a compelling example of why this dead-binder business can be really important. Wrinkle 2: The type of the scrutinee might change. E.g. case tagToEnum (x :: Int#) of (b::Bool) False -> e1 True -> e2 ==> case x of (b'::Int#) DEFAULT -> e1 1# -> e2 Wrinkle 3: The case binder may be used in the right hand sides, so we need to make a local binding for it, if it is alive. e.g. case e +# 10# of b DEFAULT -> blah...b... 44# -> blah2...b... ===> case e of b' DEFAULT -> let b = b' +# 10# in blah...b... 34# -> let b = 44# in blah2...b... Note that in the non-DEFAULT cases we know what to bind 'b' to, whereas in the DEFAULT case we must reconstruct the original value. But NB: we use b'; we do not duplicate 'e'. Wrinkle 4: In dataToTag we might need to make up some fake binders; see Note [caseRules for dataToTag] in GHC.Core.Opt.ConstantFold Note [Example of case-merging and caseRules] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The case-transformation rules are quite powerful. Here's a subtle example from #22375. We start with data T = A | B | ... deriving Eq f :: T -> String f x = if | x==A -> "one" | x==B -> "two" | ... In Core after a bit of simplification we get: f x = case dataToTag# x of a# { _DEFAULT -> case a# of _DEFAULT -> case dataToTag# x of b# { _DEFAULT -> case b# of _DEFAULT -> ... 1# -> "two" } 0# -> "one" } Now consider what mkCase does to these case expressions. The case-merge transformation Note [Merge Nested Cases] does this (affecting both pairs of cases): f x = case dataToTag# x of a# { _DEFAULT -> case dataToTag# x of b# { _DEFAULT -> ... 1# -> "two" } 0# -> "one" } Now Note [caseRules for dataToTag] does its work, again on both dataToTag# cases: f x = case x of x1 { _DEFAULT -> case dataToTag# x1 of a# { _DEFAULT -> case x of x2 { _DEFAULT -> case dataToTag# x2 of b# { _DEFAULT -> ... } B -> "two" }} A -> "one" } The new dataToTag# calls come from the "reconstruct scrutinee" part of caseRules (note that a# and b# were not dead in the original program before all this merging). However, since a# and b# /are/ in fact dead in the resulting program, we are left with redundant dataToTag# calls. But they are easily eliminated by doing caseRules again, in the next Simplifier iteration, this time noticing that a# and b# are dead. Hence the "dead-binder" sub-case of Wrinkle 1 of Note [Scrutinee Constant Folding] above. Once we do this we get f x = case x of x1 { _DEFAULT -> case x1 of x2 { _DEFAULT -> case x1 of x2 { _DEFAULT -> case x2 of x3 { _DEFAULT -> ... } B -> "two" }} A -> "one" } and now we can do case-merge again, getting the desired f x = case x of A -> "one" B -> "two" ... -} mkCase, mkCase1, mkCase2, mkCase3 :: SimplMode -> OutExpr -> OutId -> OutType -> [OutAlt] -- Alternatives in standard (increasing) order -> SimplM OutExpr -------------------------------------------------- -- 1. Merge Nested Cases -------------------------------------------------- mkCase :: SimplMode -> OutExpr -> Id -> OutType -> [InAlt] -> SimplM OutExpr mkCase SimplMode mode OutExpr scrut Id outer_bndr OutType alts_ty (Alt AltCon DEFAULT [Id] _ OutExpr deflt_rhs : [InAlt] outer_alts) | SimplMode -> Bool sm_case_merge SimplMode mode , ([CoreTickish] ticks, Case (Var Id inner_scrut_var) Id inner_bndr OutType _ [InAlt] inner_alts) <- forall b. (CoreTickish -> Bool) -> Expr b -> ([CoreTickish], Expr b) stripTicksTop forall (pass :: TickishPass). GenTickish pass -> Bool tickishFloatable OutExpr deflt_rhs , Id inner_scrut_var forall a. Eq a => a -> a -> Bool == Id outer_bndr = do { Tick -> SimplM () tick (Id -> Tick CaseMerge Id outer_bndr) ; let wrap_alt :: InAlt -> InAlt wrap_alt (Alt AltCon con [Id] args OutExpr rhs) = forall a. HasCallStack => Bool -> a -> a assert (Id outer_bndr forall (t :: * -> *) a. (Foldable t, Eq a) => a -> t a -> Bool `notElem` [Id] args) (forall b. AltCon -> [b] -> Expr b -> Alt b Alt AltCon con [Id] args (OutExpr -> OutExpr wrap_rhs OutExpr rhs)) -- Simplifier's no-shadowing invariant should ensure -- that outer_bndr is not shadowed by the inner patterns wrap_rhs :: OutExpr -> OutExpr wrap_rhs OutExpr rhs = forall b. Bind b -> Expr b -> Expr b Let (forall b. b -> Expr b -> Bind b NonRec Id inner_bndr (forall b. Id -> Expr b Var Id outer_bndr)) OutExpr rhs -- The let is OK even for unboxed binders, wrapped_alts :: [InAlt] wrapped_alts | Id -> Bool isDeadBinder Id inner_bndr = [InAlt] inner_alts | Bool otherwise = forall a b. (a -> b) -> [a] -> [b] map InAlt -> InAlt wrap_alt [InAlt] inner_alts merged_alts :: [InAlt] merged_alts = forall a. [Alt a] -> [Alt a] -> [Alt a] mergeAlts [InAlt] outer_alts [InAlt] wrapped_alts -- NB: mergeAlts gives priority to the left -- case x of -- A -> e1 -- DEFAULT -> case x of -- A -> e2 -- B -> e3 -- When we merge, we must ensure that e1 takes -- precedence over e2 as the value for A! ; forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b fmap ([CoreTickish] -> OutExpr -> OutExpr mkTicks [CoreTickish] ticks) forall a b. (a -> b) -> a -> b $ SimplMode -> OutExpr -> Id -> OutType -> [InAlt] -> SimplM OutExpr mkCase1 SimplMode mode OutExpr scrut Id outer_bndr OutType alts_ty [InAlt] merged_alts } -- Warning: don't call mkCase recursively! -- Firstly, there's no point, because inner alts have already had -- mkCase applied to them, so they won't have a case in their default -- Secondly, if you do, you get an infinite loop, because the bindCaseBndr -- in munge_rhs may put a case into the DEFAULT branch! mkCase SimplMode mode OutExpr scrut Id bndr OutType alts_ty [InAlt] alts = SimplMode -> OutExpr -> Id -> OutType -> [InAlt] -> SimplM OutExpr mkCase1 SimplMode mode OutExpr scrut Id bndr OutType alts_ty [InAlt] alts -------------------------------------------------- -- 2. Eliminate Identity Case -------------------------------------------------- mkCase1 :: SimplMode -> OutExpr -> Id -> OutType -> [InAlt] -> SimplM OutExpr mkCase1 SimplMode _mode OutExpr scrut Id case_bndr OutType _ alts :: [InAlt] alts@(Alt AltCon _ [Id] _ OutExpr rhs1 : [InAlt] alts') -- Identity case | forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool all InAlt -> Bool identity_alt [InAlt] alts = do { Tick -> SimplM () tick (Id -> Tick CaseIdentity Id case_bndr) ; forall (m :: * -> *) a. Monad m => a -> m a return ([CoreTickish] -> OutExpr -> OutExpr mkTicks [CoreTickish] ticks forall a b. (a -> b) -> a -> b $ forall {b} {b}. Expr b -> Expr b -> Expr b re_cast OutExpr scrut OutExpr rhs1) } where ticks :: [CoreTickish] ticks = forall (t :: * -> *) a b. Foldable t => (a -> [b]) -> t a -> [b] concatMap (\(Alt AltCon _ [Id] _ OutExpr rhs) -> forall b. (CoreTickish -> Bool) -> Expr b -> [CoreTickish] stripTicksT forall (pass :: TickishPass). GenTickish pass -> Bool tickishFloatable OutExpr rhs) [InAlt] alts' identity_alt :: InAlt -> Bool identity_alt (Alt AltCon con [Id] args OutExpr rhs) = OutExpr -> AltCon -> [Id] -> Bool check_eq OutExpr rhs AltCon con [Id] args check_eq :: OutExpr -> AltCon -> [Id] -> Bool check_eq (Cast OutExpr rhs OutCoercion co) AltCon con [Id] args -- See Note [RHS casts] = Bool -> Bool not (forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool any (Id -> TyCoVarSet -> Bool `elemVarSet` OutCoercion -> TyCoVarSet tyCoVarsOfCo OutCoercion co) [Id] args) Bool -> Bool -> Bool && OutExpr -> AltCon -> [Id] -> Bool check_eq OutExpr rhs AltCon con [Id] args check_eq (Tick CoreTickish t OutExpr e) AltCon alt [Id] args = forall (pass :: TickishPass). GenTickish pass -> Bool tickishFloatable CoreTickish t Bool -> Bool -> Bool && OutExpr -> AltCon -> [Id] -> Bool check_eq OutExpr e AltCon alt [Id] args check_eq (Lit Literal lit) (LitAlt Literal lit') [Id] _ = Literal lit forall a. Eq a => a -> a -> Bool == Literal lit' check_eq (Var Id v) AltCon _ [Id] _ | Id v forall a. Eq a => a -> a -> Bool == Id case_bndr = Bool True check_eq (Var Id v) (DataAlt DataCon con) [Id] args | forall (t :: * -> *) a. Foldable t => t a -> Bool null [OutType] arg_tys, forall (t :: * -> *) a. Foldable t => t a -> Bool null [Id] args = Id v forall a. Eq a => a -> a -> Bool == DataCon -> Id dataConWorkId DataCon con -- Optimisation only check_eq OutExpr rhs (DataAlt DataCon con) [Id] args = forall b. (CoreTickish -> Bool) -> Expr b -> Expr b -> Bool cheapEqExpr' forall (pass :: TickishPass). GenTickish pass -> Bool tickishFloatable OutExpr rhs forall a b. (a -> b) -> a -> b $ forall b. DataCon -> [OutType] -> [Id] -> Expr b mkConApp2 DataCon con [OutType] arg_tys [Id] args check_eq OutExpr _ AltCon _ [Id] _ = Bool False arg_tys :: [OutType] arg_tys = HasCallStack => OutType -> [OutType] tyConAppArgs (Id -> OutType idType Id case_bndr) -- Note [RHS casts] -- ~~~~~~~~~~~~~~~~ -- We've seen this: -- case e of x { _ -> x `cast` c } -- And we definitely want to eliminate this case, to give -- e `cast` c -- So we throw away the cast from the RHS, and reconstruct -- it at the other end. All the RHS casts must be the same -- if (all identity_alt alts) holds. -- -- Don't worry about nested casts, because the simplifier combines them re_cast :: Expr b -> Expr b -> Expr b re_cast Expr b scrut (Cast Expr b rhs OutCoercion co) = forall b. Expr b -> OutCoercion -> Expr b Cast (Expr b -> Expr b -> Expr b re_cast Expr b scrut Expr b rhs) OutCoercion co re_cast Expr b scrut Expr b _ = Expr b scrut mkCase1 SimplMode mode OutExpr scrut Id bndr OutType alts_ty [InAlt] alts = SimplMode -> OutExpr -> Id -> OutType -> [InAlt] -> SimplM OutExpr mkCase2 SimplMode mode OutExpr scrut Id bndr OutType alts_ty [InAlt] alts -------------------------------------------------- -- 2. Scrutinee Constant Folding -------------------------------------------------- mkCase2 :: SimplMode -> OutExpr -> Id -> OutType -> [InAlt] -> SimplM OutExpr mkCase2 SimplMode mode OutExpr scrut Id bndr OutType alts_ty [InAlt] alts | -- See Note [Scrutinee Constant Folding] case [InAlt] alts of [Alt AltCon DEFAULT [Id] _ OutExpr _] -> Id -> Bool isDeadBinder Id bndr -- see wrinkle 1 [InAlt] _ -> Bool True , SimplMode -> Bool sm_case_folding SimplMode mode , Just (OutExpr scrut', AltCon -> Maybe AltCon tx_con, Id -> OutExpr mk_orig) <- Platform -> OutExpr -> Maybe (OutExpr, AltCon -> Maybe AltCon, Id -> OutExpr) caseRules (SimplMode -> Platform smPlatform SimplMode mode) OutExpr scrut = do { Id bndr' <- FastString -> OutType -> OutType -> SimplM Id newId (String -> FastString fsLit String "lwild") OutType ManyTy (HasDebugCallStack => OutExpr -> OutType exprType OutExpr scrut') ; [InAlt] alts' <- forall (m :: * -> *) a b. Applicative m => (a -> m (Maybe b)) -> [a] -> m [b] mapMaybeM ((AltCon -> Maybe AltCon) -> (Id -> OutExpr) -> Id -> InAlt -> SimplM (Maybe InAlt) tx_alt AltCon -> Maybe AltCon tx_con Id -> OutExpr mk_orig Id bndr') [InAlt] alts -- mapMaybeM: discard unreachable alternatives -- See Note [Unreachable caseRules alternatives] -- in GHC.Core.Opt.ConstantFold ; SimplMode -> OutExpr -> Id -> OutType -> [InAlt] -> SimplM OutExpr mkCase3 SimplMode mode OutExpr scrut' Id bndr' OutType alts_ty forall a b. (a -> b) -> a -> b $ [InAlt] -> [InAlt] add_default ([InAlt] -> [InAlt] re_sort [InAlt] alts') } | Bool otherwise = SimplMode -> OutExpr -> Id -> OutType -> [InAlt] -> SimplM OutExpr mkCase3 SimplMode mode OutExpr scrut Id bndr OutType alts_ty [InAlt] alts where -- We need to keep the correct association between the scrutinee and its -- binder if the latter isn't dead. Hence we wrap rhs of alternatives with -- "let bndr = ... in": -- -- case v + 10 of y =====> case v of y' -- 20 -> e1 10 -> let y = 20 in e1 -- DEFAULT -> e2 DEFAULT -> let y = y' + 10 in e2 -- -- This wrapping is done in tx_alt; we use mk_orig, returned by caseRules, -- to construct an expression equivalent to the original one, for use -- in the DEFAULT case tx_alt :: (AltCon -> Maybe AltCon) -> (Id -> CoreExpr) -> Id -> CoreAlt -> SimplM (Maybe CoreAlt) tx_alt :: (AltCon -> Maybe AltCon) -> (Id -> OutExpr) -> Id -> InAlt -> SimplM (Maybe InAlt) tx_alt AltCon -> Maybe AltCon tx_con Id -> OutExpr mk_orig Id new_bndr (Alt AltCon con [Id] bs OutExpr rhs) = case AltCon -> Maybe AltCon tx_con AltCon con of Maybe AltCon Nothing -> forall (m :: * -> *) a. Monad m => a -> m a return forall a. Maybe a Nothing Just AltCon con' -> do { [Id] bs' <- forall {m :: * -> *}. MonadUnique m => Id -> AltCon -> m [Id] mk_new_bndrs Id new_bndr AltCon con' ; forall (m :: * -> *) a. Monad m => a -> m a return (forall a. a -> Maybe a Just (forall b. AltCon -> [b] -> Expr b -> Alt b Alt AltCon con' [Id] bs' OutExpr rhs')) } where rhs' :: OutExpr rhs' | Id -> Bool isDeadBinder Id bndr = OutExpr rhs | Bool otherwise = HasDebugCallStack => Id -> OutExpr -> OutExpr -> OutExpr bindNonRec Id bndr OutExpr orig_val OutExpr rhs orig_val :: OutExpr orig_val = case AltCon con of AltCon DEFAULT -> Id -> OutExpr mk_orig Id new_bndr LitAlt Literal l -> forall b. Literal -> Expr b Lit Literal l DataAlt DataCon dc -> forall b. DataCon -> [OutType] -> [Id] -> Expr b mkConApp2 DataCon dc (HasCallStack => OutType -> [OutType] tyConAppArgs (Id -> OutType idType Id bndr)) [Id] bs mk_new_bndrs :: Id -> AltCon -> m [Id] mk_new_bndrs Id new_bndr (DataAlt DataCon dc) | Bool -> Bool not (DataCon -> Bool isNullaryRepDataCon DataCon dc) = -- For non-nullary data cons we must invent some fake binders -- See Note [caseRules for dataToTag] in GHC.Core.Opt.ConstantFold do { [Unique] us <- forall (m :: * -> *). MonadUnique m => m [Unique] getUniquesM ; let ([Id] ex_tvs, [Id] arg_ids) = [Unique] -> OutType -> DataCon -> [OutType] -> ([Id], [Id]) dataConRepInstPat [Unique] us (Id -> OutType idMult Id new_bndr) DataCon dc (HasCallStack => OutType -> [OutType] tyConAppArgs (Id -> OutType idType Id new_bndr)) ; forall (m :: * -> *) a. Monad m => a -> m a return ([Id] ex_tvs forall a. [a] -> [a] -> [a] ++ [Id] arg_ids) } mk_new_bndrs Id _ AltCon _ = forall (m :: * -> *) a. Monad m => a -> m a return [] re_sort :: [CoreAlt] -> [CoreAlt] -- Sort the alternatives to re-establish -- GHC.Core Note [Case expression invariants] re_sort :: [InAlt] -> [InAlt] re_sort [InAlt] alts = forall a. (a -> a -> Ordering) -> [a] -> [a] sortBy forall a. Alt a -> Alt a -> Ordering cmpAlt [InAlt] alts add_default :: [CoreAlt] -> [CoreAlt] -- See Note [Literal cases] add_default :: [InAlt] -> [InAlt] add_default (Alt (LitAlt {}) [Id] bs OutExpr rhs : [InAlt] alts) = forall b. AltCon -> [b] -> Expr b -> Alt b Alt AltCon DEFAULT [Id] bs OutExpr rhs forall a. a -> [a] -> [a] : [InAlt] alts add_default [InAlt] alts = [InAlt] alts {- Note [Literal cases] ~~~~~~~~~~~~~~~~~~~~~~~ If we have case tagToEnum (a ># b) of False -> e1 True -> e2 then caseRules for TagToEnum will turn it into case tagToEnum (a ># b) of 0# -> e1 1# -> e2 Since the case is exhaustive (all cases are) we can convert it to case tagToEnum (a ># b) of DEFAULT -> e1 1# -> e2 This may generate slightly better code (although it should not, since all cases are exhaustive) and/or optimise better. I'm not certain that it's necessary, but currently we do make this change. We do it here, NOT in the TagToEnum rules (see "Beware" in Note [caseRules for tagToEnum] in GHC.Core.Opt.ConstantFold) -} -------------------------------------------------- -- Catch-all -------------------------------------------------- mkCase3 :: SimplMode -> OutExpr -> Id -> OutType -> [InAlt] -> SimplM OutExpr mkCase3 SimplMode _mode OutExpr scrut Id bndr OutType alts_ty [InAlt] alts = forall (m :: * -> *) a. Monad m => a -> m a return (forall b. Expr b -> b -> OutType -> [Alt b] -> Expr b Case OutExpr scrut Id bndr OutType alts_ty [InAlt] alts) -- See Note [Exitification] and Note [Do not inline exit join points] in -- GHC.Core.Opt.Exitify -- This lives here (and not in Id) because occurrence info is only valid on -- InIds, so it's crucial that isExitJoinId is only called on freshly -- occ-analysed code. It's not a generic function you can call anywhere. isExitJoinId :: Var -> Bool isExitJoinId :: Id -> Bool isExitJoinId Id id = Id -> Bool isJoinId Id id Bool -> Bool -> Bool && OccInfo -> Bool isOneOcc (Id -> OccInfo idOccInfo Id id) Bool -> Bool -> Bool && OccInfo -> InsideLam occ_in_lam (Id -> OccInfo idOccInfo Id id) forall a. Eq a => a -> a -> Bool == InsideLam IsInsideLam {- Note [Dead binders] ~~~~~~~~~~~~~~~~~~~~ Note that dead-ness is maintained by the simplifier, so that it is accurate after simplification as well as before. Note [Cascading case merge] ~~~~~~~~~~~~~~~~~~~~~~~~~~~ Case merging should cascade in one sweep, because it happens bottom-up case e of a { DEFAULT -> case a of b DEFAULT -> case b of c { DEFAULT -> e A -> ea B -> eb C -> ec ==> case e of a { DEFAULT -> case a of b DEFAULT -> let c = b in e A -> let c = b in ea B -> eb C -> ec ==> case e of a { DEFAULT -> let b = a in let c = b in e A -> let b = a in let c = b in ea B -> let b = a in eb C -> ec However here's a tricky case that we still don't catch, and I don't see how to catch it in one pass: case x of c1 { I# a1 -> case a1 of c2 -> 0 -> ... DEFAULT -> case x of c3 { I# a2 -> case a2 of ... After occurrence analysis (and its binder-swap) we get this case x of c1 { I# a1 -> let x = c1 in -- Binder-swap addition case a1 of c2 -> 0 -> ... DEFAULT -> case x of c3 { I# a2 -> case a2 of ... When we simplify the inner case x, we'll see that x=c1=I# a1. So we'll bind a2 to a1, and get case x of c1 { I# a1 -> case a1 of c2 -> 0 -> ... DEFAULT -> case a1 of ... This is correct, but we can't do a case merge in this sweep because c2 /= a1. Reason: the binding c1=I# a1 went inwards without getting changed to c1=I# c2. I don't think this is worth fixing, even if I knew how. It'll all come out in the next pass anyway. -}