{- (c) The University of Glasgow 2006 (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 -} {-# LANGUAGE DeriveDataTypeable, FlexibleContexts #-} {-# LANGUAGE NamedFieldPuns #-} {-# LANGUAGE BangPatterns #-} -- | GHC.Core holds all the main data types for use by for the Glasgow Haskell Compiler midsection module GHC.Core ( -- * Main data types Expr(..), Alt(..), Bind(..), AltCon(..), Arg, CoreProgram, CoreExpr, CoreAlt, CoreBind, CoreArg, CoreBndr, TaggedExpr, TaggedAlt, TaggedBind, TaggedArg, TaggedBndr(..), deTagExpr, -- * In/Out type synonyms InId, InBind, InExpr, InAlt, InArg, InType, InKind, InBndr, InVar, InCoercion, InTyVar, InCoVar, OutId, OutBind, OutExpr, OutAlt, OutArg, OutType, OutKind, OutBndr, OutVar, OutCoercion, OutTyVar, OutCoVar, MOutCoercion, -- ** 'Expr' construction mkLet, mkLets, mkLetNonRec, mkLetRec, mkLams, mkApps, mkTyApps, mkCoApps, mkVarApps, mkTyArg, mkIntLit, mkIntLitWrap, mkWordLit, mkWordLitWrap, mkWord8Lit, mkWord64LitWord64, mkInt64LitInt64, mkCharLit, mkStringLit, mkFloatLit, mkFloatLitFloat, mkDoubleLit, mkDoubleLitDouble, mkConApp, mkConApp2, mkTyBind, mkCoBind, varToCoreExpr, varsToCoreExprs, isId, cmpAltCon, cmpAlt, ltAlt, -- ** Simple 'Expr' access functions and predicates bindersOf, bindersOfBinds, rhssOfBind, rhssOfAlts, foldBindersOfBindStrict, foldBindersOfBindsStrict, collectBinders, collectTyBinders, collectTyAndValBinders, collectNBinders, collectNValBinders_maybe, collectArgs, stripNArgs, collectArgsTicks, flattenBinds, collectFunSimple, exprToType, wrapLamBody, isValArg, isTypeArg, isCoArg, isTyCoArg, valArgCount, valBndrCount, isRuntimeArg, isRuntimeVar, -- * Unfolding data types Unfolding(..), UnfoldingCache(..), UnfoldingGuidance(..), UnfoldingSource(..), -- ** Constructing 'Unfolding's noUnfolding, bootUnfolding, evaldUnfolding, mkOtherCon, unSaturatedOk, needSaturated, boringCxtOk, boringCxtNotOk, -- ** Predicates and deconstruction on 'Unfolding' unfoldingTemplate, expandUnfolding_maybe, maybeUnfoldingTemplate, otherCons, isValueUnfolding, isEvaldUnfolding, isCheapUnfolding, isExpandableUnfolding, isConLikeUnfolding, isCompulsoryUnfolding, isStableUnfolding, isStableUserUnfolding, isStableSystemUnfolding, isInlineUnfolding, isBootUnfolding, hasCoreUnfolding, hasSomeUnfolding, canUnfold, neverUnfoldGuidance, isStableSource, -- * Annotated expression data types AnnExpr, AnnExpr'(..), AnnBind(..), AnnAlt(..), -- ** Operations on annotated expressions collectAnnArgs, collectAnnArgsTicks, -- ** Operations on annotations deAnnotate, deAnnotate', deAnnAlt, deAnnBind, collectAnnBndrs, collectNAnnBndrs, -- * Orphanhood IsOrphan(..), isOrphan, notOrphan, chooseOrphanAnchor, -- * Core rule data types CoreRule(..), RuleName, RuleFun, IdUnfoldingFun, InScopeEnv, RuleOpts, -- ** Operations on 'CoreRule's ruleArity, ruleName, ruleIdName, ruleActivation, setRuleIdName, ruleModule, isBuiltinRule, isLocalRule, isAutoRule, ) where import GHC.Prelude import GHC.Platform import GHC.Types.Var.Env( InScopeSet ) import GHC.Types.Var import GHC.Core.Type import GHC.Core.Coercion import GHC.Core.Rules.Config ( RuleOpts ) import GHC.Types.Name import GHC.Types.Name.Set import GHC.Types.Literal import GHC.Types.Tickish import GHC.Core.DataCon import GHC.Unit.Module import GHC.Types.Basic import GHC.Types.Unique.Set import GHC.Utils.Binary import GHC.Utils.Misc import GHC.Utils.Outputable import GHC.Utils.Panic import GHC.Utils.Panic.Plain import Data.Data hiding (TyCon) import Data.Int import Data.Word infixl 4 `mkApps`, `mkTyApps`, `mkVarApps`, `App`, `mkCoApps` -- Left associative, so that we can say (f `mkTyApps` xs `mkVarApps` ys) {- ************************************************************************ * * \subsection{The main data types} * * ************************************************************************ These data types are the heart of the compiler -} -- | This is the data type that represents GHCs core intermediate language. Currently -- GHC uses System FC for this purpose, -- which is closely related to the simpler and better known System F . -- -- We get from Haskell source to this Core language in a number of stages: -- -- 1. The source code is parsed into an abstract syntax tree, which is represented -- by the data type 'GHC.Hs.Expr.HsExpr' with the names being 'GHC.Types.Name.Reader.RdrNames' -- -- 2. This syntax tree is /renamed/, which attaches a 'GHC.Types.Unique.Unique' to every 'GHC.Types.Name.Reader.RdrName' -- (yielding a 'GHC.Types.Name.Name') to disambiguate identifiers which are lexically identical. -- For example, this program: -- -- @ -- f x = let f x = x + 1 -- in f (x - 2) -- @ -- -- Would be renamed by having 'Unique's attached so it looked something like this: -- -- @ -- f_1 x_2 = let f_3 x_4 = x_4 + 1 -- in f_3 (x_2 - 2) -- @ -- But see Note [Shadowing] below. -- -- 3. The resulting syntax tree undergoes type checking (which also deals with instantiating -- type class arguments) to yield a 'GHC.Hs.Expr.HsExpr' type that has 'GHC.Types.Id.Id' as it's names. -- -- 4. Finally the syntax tree is /desugared/ from the expressive 'GHC.Hs.Expr.HsExpr' type into -- this 'Expr' type, which has far fewer constructors and hence is easier to perform -- optimization, analysis and code generation on. -- -- The type parameter @b@ is for the type of binders in the expression tree. -- -- The language consists of the following elements: -- -- * Variables -- See Note [Variable occurrences in Core] -- -- * Primitive literals -- -- * Applications: note that the argument may be a 'Type'. -- See Note [Representation polymorphism invariants] -- -- * Lambda abstraction -- See Note [Representation polymorphism invariants] -- -- * Recursive and non recursive @let@s. Operationally -- this corresponds to allocating a thunk for the things -- bound and then executing the sub-expression. -- -- See Note [Core letrec invariant] -- See Note [Core let-can-float invariant] -- See Note [Representation polymorphism invariants] -- See Note [Core type and coercion invariant] -- -- * Case expression. Operationally this corresponds to evaluating -- the scrutinee (expression examined) to weak head normal form -- and then examining at most one level of resulting constructor (i.e. you -- cannot do nested pattern matching directly with this). -- -- The binder gets bound to the value of the scrutinee, -- and the 'Type' must be that of all the case alternatives -- -- IMPORTANT: see Note [Case expression invariants] -- -- * Cast an expression to a particular type. -- This is used to implement @newtype@s (a @newtype@ constructor or -- destructor just becomes a 'Cast' in Core) and GADTs. -- -- * Ticks. These are used to represent all the source annotation we -- support: profiling SCCs, HPC ticks, and GHCi breakpoints. -- -- * A type: this should only show up at the top level of an Arg -- -- * A coercion {- Note [Why does Case have a 'Type' field?] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The obvious alternative is exprType (Case scrut bndr alts) | (_,_,rhs1):_ <- alts = exprType rhs1 But caching the type in the Case constructor exprType (Case scrut bndr ty alts) = ty is better for at least three reasons: * It works when there are no alternatives (see case invariant 1 above) * It might be faster in deeply-nested situations. * It might not be quite the same as (exprType rhs) for one of the RHSs in alts. Consider a phantom type synonym type S a = Int and we want to form the case expression case x of { K (a::*) -> (e :: S a) } Then exprType of the RHS is (S a), but we cannot make that be the 'ty' in the Case constructor because 'a' is simply not in scope there. Instead we must expand the synonym to Int before putting it in the Case constructor. See GHC.Core.Utils.mkSingleAltCase. So we'd have to do synonym expansion in exprType which would be inefficient. * The type stored in the case is checked with lintInTy. This checks (among other things) that it does not mention any variables that are not in scope. If we did not have the type there, it would be a bit harder for Core Lint to reject case blah of Ex x -> x where data Ex = forall a. Ex a. -} -- If you edit this type, you may need to update the GHC formalism -- See Note [GHC Formalism] in GHC.Core.Lint data Expr b = Var Id | Lit Literal | App (Expr b) (Arg b) | Lam b (Expr b) | Let (Bind b) (Expr b) | Case (Expr b) b Type [Alt b] -- See Note [Case expression invariants] -- and Note [Why does Case have a 'Type' field?] | Cast (Expr b) CoercionR -- The Coercion has Representational role | Tick CoreTickish (Expr b) | Type Type | Coercion Coercion deriving Data -- | Type synonym for expressions that occur in function argument positions. -- Only 'Arg' should contain a 'Type' at top level, general 'Expr' should not type Arg b = Expr b -- | A case split alternative. Consists of the constructor leading to the alternative, -- the variables bound from the constructor, and the expression to be executed given that binding. -- The default alternative is @(DEFAULT, [], rhs)@ -- If you edit this type, you may need to update the GHC formalism -- See Note [GHC Formalism] in GHC.Core.Lint data Alt b = Alt AltCon [b] (Expr b) deriving (Data) -- | A case alternative constructor (i.e. pattern match) -- If you edit this type, you may need to update the GHC formalism -- See Note [GHC Formalism] in GHC.Core.Lint data AltCon = DataAlt DataCon -- ^ A plain data constructor: @case e of { Foo x -> ... }@. -- Invariant: the 'DataCon' is always from a @data@ type, and never from a @newtype@ | LitAlt Literal -- ^ A literal: @case e of { 1 -> ... }@ -- Invariant: always an *unlifted* literal -- See Note [Literal alternatives] | DEFAULT -- ^ Trivial alternative: @case e of { _ -> ... }@ deriving (Eq, Data) -- This instance is a bit shady. It can only be used to compare AltCons for -- a single type constructor. Fortunately, it seems quite unlikely that we'll -- ever need to compare AltCons for different type constructors. -- The instance adheres to the order described in [Core case invariants] instance Ord AltCon where compare (DataAlt con1) (DataAlt con2) = assert (dataConTyCon con1 == dataConTyCon con2) $ compare (dataConTag con1) (dataConTag con2) compare (DataAlt _) _ = GT compare _ (DataAlt _) = LT compare (LitAlt l1) (LitAlt l2) = compare l1 l2 compare (LitAlt _) DEFAULT = GT compare DEFAULT DEFAULT = EQ compare DEFAULT _ = LT -- | Binding, used for top level bindings in a module and local bindings in a @let@. -- If you edit this type, you may need to update the GHC formalism -- See Note [GHC Formalism] in GHC.Core.Lint data Bind b = NonRec b (Expr b) | Rec [(b, (Expr b))] deriving Data {- Note [Shadowing] ~~~~~~~~~~~~~~~~ While various passes attempt to rename on-the-fly in a manner that avoids "shadowing" (thereby simplifying downstream optimizations), neither the simplifier nor any other pass GUARANTEES that shadowing is avoided. Thus, all passes SHOULD work fine even in the presence of arbitrary shadowing in their inputs. In particular, scrutinee variables `x` in expressions of the form `Case e x t` are often renamed to variables with a prefix "wild_". These "wild" variables may appear in the body of the case-expression, and further, may be shadowed within the body. So the Unique in a Var is not really unique at all. Still, it's very useful to give a constant-time equality/ordering for Vars, and to give a key that can be used to make sets of Vars (VarSet), or mappings from Vars to other things (VarEnv). Moreover, if you do want to eliminate shadowing, you can give a new Unique to an Id without changing its printable name, which makes debugging easier. Note [Literal alternatives] ~~~~~~~~~~~~~~~~~~~~~~~~~~~ Literal alternatives (LitAlt lit) are always for *un-lifted* literals. We have one literal, a literal Integer, that is lifted, and we don't allow in a LitAlt, because LitAlt cases don't do any evaluation. Also (see #5603) if you say case 3 of IS x -> ... IP _ -> ... IN _ -> ... (where IS, IP, IN are the constructors for Integer) we don't want the simplifier calling findAlt with argument (LitAlt 3). No no. Integer literals are an opaque encoding of an algebraic data type, not of an unlifted literal, like all the others. Also, we do not permit case analysis with literal patterns on floating-point types. See #9238 and Note [Rules for floating-point comparisons] in GHC.Core.Opt.ConstantFold for the rationale for this restriction. -------------------------- GHC.Core INVARIANTS --------------------------- Note [Variable occurrences in Core] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Variable /occurrences/ are never CoVars, though /bindings/ can be. All CoVars appear in Coercions. For example \(c :: Age~#Int) (d::Int). d |> (sym c) Here 'c' is a CoVar, which is lambda-bound, but it /occurs/ in a Coercion, (sym c). Note [Core letrec invariant] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The right hand sides of all top-level and recursive @let@s /must/ be of lifted type (see "Type#type_classification" for the meaning of /lifted/ vs. /unlifted/). There is one exception to this rule, top-level @let@s are allowed to bind primitive string literals: see Note [Core top-level string literals]. Note [Core top-level string literals] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ As an exception to the usual rule that top-level binders must be lifted, we allow binding primitive string literals (of type Addr#) of type Addr# at the top level. This allows us to share string literals earlier in the pipeline and crucially allows other optimizations in the Core2Core pipeline to fire. Consider, f n = let a::Addr# = "foo"# in \x -> blah In order to be able to inline `f`, we would like to float `a` to the top. Another option would be to inline `a`, but that would lead to duplicating string literals, which we want to avoid. See #8472. The solution is simply to allow top-level unlifted binders. We can't allow arbitrary unlifted expression at the top-level though, unlifted binders cannot be thunks, so we just allow string literals. We allow the top-level primitive string literals to be wrapped in Ticks in the same way they can be wrapped when nested in an expression. CoreToSTG currently discards Ticks around top-level primitive string literals. See #14779. Also see Note [Compilation plan for top-level string literals]. Note [Compilation plan for top-level string literals] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Here is a summary on how top-level string literals are handled by various parts of the compilation pipeline. * In the source language, there is no way to bind a primitive string literal at the top level. * In Core, we have a special rule that permits top-level Addr# bindings. See Note [Core top-level string literals]. Core-to-core passes may introduce new top-level string literals. * In STG, top-level string literals are explicitly represented in the syntax tree. * A top-level string literal may end up exported from a module. In this case, in the object file, the content of the exported literal is given a label with the _bytes suffix. Note [Core let-can-float invariant] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The let-can-float invariant: The right hand side of a non-recursive 'Let' /may/ be of unlifted type, but only if the expression is ok-for-speculation or the 'Let' is for a join point. This means that the let can be floated around without difficulty. For example, this is OK: y::Int# = x +# 1# But this is not, as it may affect termination if the expression is floated out: y::Int# = fac 4# In this situation you should use @case@ rather than a @let@. The function 'GHC.Core.Utils.needsCaseBinding' can help you determine which to generate, or alternatively use 'GHC.Core.Make.mkCoreLet' rather than this constructor directly, which will generate a @case@ if necessary The let-can-float invariant is initially enforced by mkCoreLet in GHC.Core.Make. For discussion of some implications of the let-can-float invariant primops see Note [Checking versus non-checking primops] in GHC.Builtin.PrimOps. Historical Note [The let/app invariant] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Before 2022 GHC used the "let/app invariant", which applied the let-can-float rules to the argument of an application, as well as to the RHS of a let. This made some kind of sense, because 'let' can always be encoded as application: let x=rhs in b = (\x.b) rhs But the let/app invariant got in the way of RULES; see #19313. For example up :: Int# -> Int# {-# RULES "up/down" forall x. up (down x) = x #-} The LHS of this rule doesn't satisfy the let/app invariant. Indeed RULES is a big reason that GHC doesn't use ANF, where the argument of an application is always a variable or a constant. To allow RULES to work nicely we need to allow lots of things in the arguments of a call. TL;DR: we relaxed the let/app invariant to become the let-can-float invariant. Note [Case expression invariants] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Case expressions are one of the more complicated elements of the Core language, and come with a number of invariants. All of them should be checked by Core Lint. 1. The list of alternatives may be empty; See Note [Empty case alternatives] 2. The 'DEFAULT' case alternative must be first in the list, if it occurs at all. Checked in GHC.Core.Lint.checkCaseAlts. 3. The remaining cases are in order of (strictly) increasing tag (for 'DataAlts') or lit (for 'LitAlts'). This makes finding the relevant constructor easy, and makes comparison easier too. Checked in GHC.Core.Lint.checkCaseAlts. 4. The list of alternatives must be exhaustive. An /exhaustive/ case does not necessarily mention all constructors: @ data Foo = Red | Green | Blue ... case x of Red -> True other -> f (case x of Green -> ... Blue -> ... ) ... @ The inner case does not need a @Red@ alternative, because @x@ can't be @Red@ at that program point. This is not checked by Core Lint -- it's very hard to do so. E.g. suppose that inner case was floated out, thus: let a = case x of Green -> ... Blue -> ... ) case x of Red -> True other -> f a Now it's really hard to see that the Green/Blue case is exhaustive. But it is. If you have a case-expression that really /isn't/ exhaustive, we may generate seg-faults. Consider the Green/Blue case above. Since there are only two branches we may generate code that tests for Green, and if not Green simply /assumes/ Blue (since, if the case is exhaustive, that's all that remains). Of course, if it's not Blue and we start fetching fields that should be in a Blue constructor, we may die horribly. See also Note [Core Lint guarantee] in GHC.Core.Lint. 5. Floating-point values must not be scrutinised against literals. See #9238 and Note [Rules for floating-point comparisons] in GHC.Core.Opt.ConstantFold for rationale. Checked in lintCaseExpr; see the call to isFloatingPrimTy. 6. The 'ty' field of (Case scrut bndr ty alts) is the type of the /entire/ case expression. Checked in lintAltExpr. See also Note [Why does Case have a 'Type' field?]. 7. The type of the scrutinee must be the same as the type of the case binder, obviously. Checked in lintCaseExpr. 8. The multiplicity of the binders in constructor patterns must be the multiplicity of the corresponding field /scaled by the multiplicity of the case binder/. Checked in lintCoreAlt. Note [Core type and coercion invariant] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We allow a /non-recursive/, /non-top-level/ let to bind type and coercion variables. These can be very convenient for postponing type substitutions until the next run of the simplifier. * A type variable binding must have a RHS of (Type ty) * A coercion variable binding must have a RHS of (Coercion co) It is possible to have terms that return a coercion, but we use case-binding for those; e.g. case (eq_sel d) of (co :: a ~# b) -> blah where eq_sel :: (a~b) -> (a~#b) Or even case (df @Int) of (co :: a ~# b) -> blah Which is very exotic, and I think never encountered; but see Note [Equality superclasses in quantified constraints] in GHC.Tc.Solver.Canonical Note [Core case invariants] ~~~~~~~~~~~~~~~~~~~~~~~~~~~ See Note [Case expression invariants] Note [Representation polymorphism invariants] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ GHC allows us to abstract over calling conventions using **representation polymorphism**. For example, we have: ($) :: forall (r :: RuntimeRep) (a :: Type) (b :: TYPE r). a -> b -> b In this example, the type `b` is representation-polymorphic: it has kind `TYPE r`, where the type variable `r :: RuntimeRep` abstracts over the runtime representation of values of type `b`. To ensure that programs containing representation-polymorphism remain compilable, we enforce the following representation-polymorphism invariants: The paper "Levity Polymorphism" [PLDI'17] states the first two invariants: I1. The type of a bound variable must have a fixed runtime representation (except for join points: See Note [Invariants on join points]) I2. The type of a function argument must have a fixed runtime representation. On top of these two invariants, GHC's internal eta-expansion mechanism also requires: I3. In any partial application `f e_1 .. e_n`, where `f` is `hasNoBinding`, it must be the case that the application can be eta-expanded to match the arity of `f`. See Note [checkCanEtaExpand] in GHC.Core.Lint for more details. Example of I1: \(r::RuntimeRep). \(a::TYPE r). \(x::a). e This contravenes I1 because x's type has kind (TYPE r), which has 'r' free. We thus wouldn't know how to compile this lambda abstraction. Example of I2: f (undefined :: (a :: TYPE r)) This contravenes I2: we are applying the function `f` to a value with an unknown runtime representation. Examples of I3: myUnsafeCoerce# :: forall {r1} (a :: TYPE r1) {r2} (b :: TYPE r2). a -> b myUnsafeCoerce# = unsafeCoerce# This contravenes I3: we are instantiating `unsafeCoerce#` without any value arguments, and with a remaining argument type, `a`, which does not have a fixed runtime representation. But `unsafeCorce#` has no binding (see Note [Wiring in unsafeCoerce#] in GHC.HsToCore). So before code-generation we must saturate it by eta-expansion (see GHC.CoreToStg.Prep.maybeSaturate), thus myUnsafeCoerce# = \x. unsafeCoerce# x But we can't do that because now the \x binding would violate I1. bar :: forall (a :: TYPE) r (b :: TYPE r). a -> b bar = unsafeCoerce# OK: eta expand to `\ (x :: Type) -> unsafeCoerce# x`, and `x` has a fixed RuntimeRep. Note that we currently require something slightly stronger than a fixed runtime representation: we check whether bound variables and function arguments have a /fixed RuntimeRep/ in the sense of Note [Fixed RuntimeRep] in GHC.Tc.Utils.Concrete. See Note [Representation polymorphism checking] in GHC.Tc.Utils.Concrete for an overview of how we enforce these invariants in the typechecker. Note [Core let goal] ~~~~~~~~~~~~~~~~~~~~ * The simplifier tries to ensure that if the RHS of a let is a constructor application, its arguments are trivial, so that the constructor can be inlined vigorously. Note [Empty case alternatives] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The alternatives of a case expression should be exhaustive. But this exhaustive list can be empty! * A case expression can have empty alternatives if (and only if) the scrutinee is bound to raise an exception or diverge. When do we know this? See Note [Bottoming expressions] in GHC.Core.Utils. * The possibility of empty alternatives is one reason we need a type on the case expression: if the alternatives are empty we can't get the type from the alternatives! * In the case of empty types (see Note [Bottoming expressions]), say data T we do NOT want to replace case (x::T) of Bool {} --> error Bool "Inaccessible case" because x might raise an exception, and *that*'s what we want to see! (#6067 is an example.) To preserve semantics we'd have to say x `seq` error Bool "Inaccessible case" but the 'seq' is just such a case, so we are back to square 1. * We can use the empty-alternative construct to coerce error values from one type to another. For example f :: Int -> Int f n = error "urk" g :: Int -> (# Char, Bool #) g x = case f x of { 0 -> ..., n -> ... } Then if we inline f in g's RHS we get case (error Int "urk") of (# Char, Bool #) { ... } and we can discard the alternatives since the scrutinee is bottom to give case (error Int "urk") of (# Char, Bool #) {} This is nicer than using an unsafe coerce between Int ~ (# Char,Bool #), if for no other reason that we don't need to instantiate the (~) at an unboxed type. * We treat a case expression with empty alternatives as trivial iff its scrutinee is (see GHC.Core.Utils.exprIsTrivial). This is actually important; see Note [Empty case is trivial] in GHC.Core.Utils * An empty case is replaced by its scrutinee during the CoreToStg conversion; remember STG is un-typed, so there is no need for the empty case to do the type conversion. Note [Join points] ~~~~~~~~~~~~~~~~~~ In Core, a *join point* is a specially tagged function whose only occurrences are saturated tail calls. A tail call can appear in these places: 1. In the branches (not the scrutinee) of a case 2. Underneath a let (value or join point) 3. Inside another join point We write a join-point declaration as join j @a @b x y = e1 in e2, like a let binding but with "join" instead (or "join rec" for "let rec"). Note that we put the parameters before the = rather than using lambdas; this is because it's relevant how many parameters the join point takes *as a join point.* This number is called the *join arity,* distinct from arity because it counts types as well as values. Note that a join point may return a lambda! So join j x = x + 1 is different from join j = \x -> x + 1 The former has join arity 1, while the latter has join arity 0. The identifier for a join point is called a join id or a *label.* An invocation is called a *jump.* We write a jump using the jump keyword: jump j 3 The words *label* and *jump* are evocative of assembly code (or Cmm) for a reason: join points are indeed compiled as labeled blocks, and jumps become actual jumps (plus argument passing and stack adjustment). There is no closure allocated and only a fraction of the function-call overhead. Hence we would like as many functions as possible to become join points (see OccurAnal) and the type rules for join points ensure we preserve the properties that make them efficient. In the actual AST, a join point is indicated by the IdDetails of the binder: a local value binding gets 'VanillaId' but a join point gets a 'JoinId' with its join arity. For more details, see the paper: Luke Maurer, Paul Downen, Zena Ariola, and Simon Peyton Jones. "Compiling without continuations." Submitted to PLDI'17. https://www.microsoft.com/en-us/research/publication/compiling-without-continuations/ Note [Invariants on join points] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Join points must follow these invariants: 1. All occurrences must be tail calls. Each of these tail calls must pass the same number of arguments, counting both types and values; we call this the "join arity" (to distinguish from regular arity, which only counts values). See Note [Join points are less general than the paper] 2. For join arity n, the right-hand side must begin with at least n lambdas. No ticks, no casts, just lambdas! C.f. GHC.Core.Utils.joinRhsArity. 2a. Moreover, this same constraint applies to any unfolding of the binder. Reason: if we want to push a continuation into the RHS we must push it into the unfolding as well. 2b. The Arity (in the IdInfo) of a join point varies independently of the join-arity. For example, we could have j x = case x of { T -> \y.y; F -> \y.3 } Its join-arity is 1, but its idArity is 2; and we do not eta-expand join points: see Note [Do not eta-expand join points] in GHC.Core.Opt.Simplify.Utils. Allowing the idArity to be bigger than the join-arity is important in arityType; see GHC.Core.Opt.Arity Note [Arity for recursive join bindings] Historical note: see #17294. 3. If the binding is recursive, then all other bindings in the recursive group must also be join points. 4. The binding's type must not be polymorphic in its return type (as defined in Note [The polymorphism rule of join points]). However, join points have simpler invariants in other ways 5. A join point can have an unboxed type without the RHS being ok-for-speculation (i.e. drop the let-can-float invariant) e.g. let j :: Int# = factorial x in ... 6. The RHS of join point is not required to have a fixed runtime representation, e.g. let j :: r :: TYPE l = fail (##) in ... This happened in an intermediate program #13394 Examples: join j1 x = 1 + x in jump j (jump j x) -- Fails 1: non-tail call join j1' x = 1 + x in if even a then jump j1 a else jump j1 a b -- Fails 1: inconsistent calls join j2 x = flip (+) x in j2 1 2 -- Fails 2: not enough lambdas join j2' x = \y -> x + y in j3 1 -- Passes: extra lams ok join j @a (x :: a) = x -- Fails 4: polymorphic in ret type Invariant 1 applies to left-hand sides of rewrite rules, so a rule for a join point must have an exact call as its LHS. Strictly speaking, invariant 3 is redundant, since a call from inside a lazy binding isn't a tail call. Since a let-bound value can't invoke a free join point, then, they can't be mutually recursive. (A Core binding group *can* include spurious extra bindings if the occurrence analyser hasn't run, so invariant 3 does still need to be checked.) For the rigorous definition of "tail call", see Section 3 of the paper (Note [Join points]). Invariant 4 is subtle; see Note [The polymorphism rule of join points]. Invariant 6 is to enable code like this: f = \(r :: RuntimeRep) (a :: TYPE r) (x :: T). join j :: a j = error @r @a "bloop" in case x of A -> j B -> j C -> error @r @a "blurp" Core Lint will check these invariants, anticipating that any binder whose OccInfo is marked AlwaysTailCalled will become a join point as soon as the simplifier (or simpleOptPgm) runs. Note [Join points are less general than the paper] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ In the paper "Compiling without continuations", this expression is perfectly valid: join { j = \_ -> e } in (case blah of ) ( True -> j void# ) arg ( False -> blah ) assuming 'j' has arity 1. Here the call to 'j' does not look like a tail call, but actually everything is fine. See Section 3, "Managing \Delta" in the paper. In GHC, however, we adopt a slightly more restrictive subset, in which join point calls must be tail calls. I think we /could/ loosen it up, but in fact the simplifier ensures that we always get tail calls, and it makes the back end a bit easier I think. Generally, just less to think about; nothing deeper than that. Note [The type of a join point] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ A join point has the same type it would have as a function. That is, if it takes an Int and a Bool and its body produces a String, its type is `Int -> Bool -> String`. Natural as this may seem, it can be awkward. A join point shouldn't be thought to "return" in the same sense a function does---a jump is one-way. This is crucial for understanding how case-of-case interacts with join points: case (join j :: Int -> Bool -> String j x y = ... in jump j z w) of "" -> True _ -> False The simplifier will pull the case into the join point (see Note [Join points and case-of-case] in GHC.Core.Opt.Simplify): join j :: Int -> Bool -> Bool -- changed! j x y = case ... of "" -> True _ -> False in jump j z w The body of the join point now returns a Bool, so the label `j` has to have its type updated accordingly, which is done by GHC.Core.Opt.Simplify.Env.adjustJoinPointType. Inconvenient though this may be, it has the advantage that 'GHC.Core.Utils.exprType' can still return a type for any expression, including a jump. Relationship to the paper This plan differs from the paper (see Note [Invariants on join points]). In the paper, we instead give j the type `Int -> Bool -> forall a. a`. Then each jump carries the "return type" as a parameter, exactly the way other non-returning functions like `error` work: case (join j :: Int -> Bool -> forall a. a j x y = ... in jump j z w @String) of "" -> True _ -> False Now we can move the case inward and we only have to change the jump: join j :: Int -> Bool -> forall a. a j x y = case ... of "" -> True _ -> False in jump j z w @Bool (Core Lint would still check that the body of the join point has the right type; that type would simply not be reflected in the join id.) Note [The polymorphism rule of join points] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Invariant 4 of Note [Invariants on join points] forbids a join point to be polymorphic in its return type. That is, if its type is forall a1 ... ak. t1 -> ... -> tn -> r where its join arity is k+n, none of the type parameters ai may occur free in r. In some way, this falls out of the fact that given join j @a1 ... @ak x1 ... xn = e1 in e2 then all calls to `j` are in tail-call positions of `e`, and expressions in tail-call positions in `e` have the same type as `e`. Therefore the type of `e1` -- the return type of the join point -- must be the same as the type of e2. Since the type variables aren't bound in `e2`, its type can't include them, and thus neither can the type of `e1`. This unfortunately prevents the `go` in the following code from being a join-point: iter :: forall a. Int -> (a -> a) -> a -> a iter @a n f x = go @a n f x where go :: forall a. Int -> (a -> a) -> a -> a go @a 0 _ x = x go @a n f x = go @a (n-1) f (f x) In this case, a static argument transformation would fix that (see ticket #14620): iter :: forall a. Int -> (a -> a) -> a -> a iter @a n f x = go' @a n f x where go' :: Int -> (a -> a) -> a -> a go' 0 _ x = x go' n f x = go' (n-1) f (f x) In general, loopification could be employed to do that (see #14068.) Can we simply drop the requirement, and allow `go` to be a join-point? We could, and it would work. But we could not longer apply the case-of-join-point transformation universally. This transformation would do: case (join go @a n f x = case n of 0 -> x n -> go @a (n-1) f (f x) in go @Bool n neg True) of True -> e1; False -> e2 ===> join go @a n f x = case n of 0 -> case x of True -> e1; False -> e2 n -> go @a (n-1) f (f x) in go @Bool n neg True but that is ill-typed, as `x` is type `a`, not `Bool`. This also justifies why we do not consider the `e` in `e |> co` to be in tail position: A cast changes the type, but the type must be the same. But operationally, casts are vacuous, so this is a bit unfortunate! See #14610 for ideas how to fix this. ************************************************************************ * * In/Out type synonyms * * ********************************************************************* -} {- Many passes apply a substitution, and it's very handy to have type synonyms to remind us whether or not the substitution has been applied -} -- Pre-cloning or substitution type InBndr = CoreBndr type InType = Type type InKind = Kind type InBind = CoreBind type InExpr = CoreExpr type InAlt = CoreAlt type InArg = CoreArg type InCoercion = Coercion -- Post-cloning or substitution type OutBndr = CoreBndr type OutType = Type type OutKind = Kind type OutCoercion = Coercion type OutBind = CoreBind type OutExpr = CoreExpr type OutAlt = CoreAlt type OutArg = CoreArg type MOutCoercion = MCoercion {- ************************************************************************ * * Orphans * * ************************************************************************ -} -- | Is this instance an orphan? If it is not an orphan, contains an 'OccName' -- witnessing the instance's non-orphanhood. -- See Note [Orphans] data IsOrphan = IsOrphan | NotOrphan !OccName -- The OccName 'n' witnesses the instance's non-orphanhood -- In that case, the instance is fingerprinted as part -- of the definition of 'n's definition deriving Data -- | Returns true if 'IsOrphan' is orphan. isOrphan :: IsOrphan -> Bool isOrphan IsOrphan = True isOrphan _ = False -- | Returns true if 'IsOrphan' is not an orphan. notOrphan :: IsOrphan -> Bool notOrphan NotOrphan{} = True notOrphan _ = False chooseOrphanAnchor :: NameSet -> IsOrphan -- Something (rule, instance) is relate to all the Names in this -- list. Choose one of them to be an "anchor" for the orphan. We make -- the choice deterministic to avoid gratuitous changes in the ABI -- hash (#4012). Specifically, use lexicographic comparison of -- OccName rather than comparing Uniques -- -- NB: 'minimum' use Ord, and (Ord OccName) works lexicographically -- chooseOrphanAnchor local_names | isEmptyNameSet local_names = IsOrphan | otherwise = NotOrphan (minimum occs) where occs = map nameOccName $ nonDetEltsUniqSet local_names -- It's OK to use nonDetEltsUFM here, see comments above instance Binary IsOrphan where put_ bh IsOrphan = putByte bh 0 put_ bh (NotOrphan n) = do putByte bh 1 put_ bh n get bh = do h <- getByte bh case h of 0 -> return IsOrphan _ -> do n <- get bh return $ NotOrphan n {- Note [Orphans] ~~~~~~~~~~~~~~ Class instances, rules, and family instances are divided into orphans and non-orphans. Roughly speaking, an instance/rule is an orphan if its left hand side mentions nothing defined in this module. Orphan-hood has two major consequences * A module that contains orphans is called an "orphan module". If the module being compiled depends (transitively) on an orphan module M, then M.hi is read in regardless of whether M is otherwise needed. This is to ensure that we don't miss any instance decls in M. But it's painful, because it means we need to keep track of all the orphan modules below us. * The "visible orphan modules" are all the orphan module in the transitive closure of the imports of this module. * During instance lookup, we filter orphan instances depending on whether or not the instance is in a visible orphan module. * A non-orphan is not finger-printed separately. Instead, for fingerprinting purposes it is treated as part of the entity it mentions on the LHS. For example data T = T1 | T2 instance Eq T where .... The instance (Eq T) is incorporated as part of T's fingerprint. In contrast, orphans are all fingerprinted together in the mi_orph_hash field of the ModIface. See GHC.Iface.Recomp.addFingerprints. Orphan-hood is computed * For class instances: when we make a ClsInst in GHC.Core.InstEnv.mkLocalInstance (because it is needed during instance lookup) See Note [When exactly is an instance decl an orphan?] in GHC.Core.InstEnv * For rules when we generate a CoreRule (GHC.Core.Rules.mkRule) * For family instances: when we generate an IfaceFamInst (GHC.Iface.Make.instanceToIfaceInst) Orphan-hood is persisted into interface files, in ClsInst, FamInst, and CoreRules. -} {- ************************************************************************ * * \subsection{Rewrite rules} * * ************************************************************************ The CoreRule type and its friends are dealt with mainly in GHC.Core.Rules, but GHC.Core.FVs, GHC.Core.Subst, GHC.Core.Ppr, GHC.Core.Tidy also inspect the representation. -} -- | A 'CoreRule' is: -- -- * \"Local\" if the function it is a rule for is defined in the -- same module as the rule itself. -- -- * \"Orphan\" if nothing on the LHS is defined in the same module -- as the rule itself data CoreRule = Rule { ru_name :: RuleName, -- ^ Name of the rule, for communication with the user ru_act :: Activation, -- ^ When the rule is active -- Rough-matching stuff -- see comments with InstEnv.ClsInst( is_cls, is_rough ) ru_fn :: !Name, -- ^ Name of the 'GHC.Types.Id.Id' at the head of this rule ru_rough :: [Maybe Name], -- ^ Name at the head of each argument to the left hand side -- Proper-matching stuff -- see comments with InstEnv.ClsInst( is_tvs, is_tys ) ru_bndrs :: [CoreBndr], -- ^ Variables quantified over ru_args :: [CoreExpr], -- ^ Left hand side arguments -- And the right-hand side ru_rhs :: CoreExpr, -- ^ Right hand side of the rule -- Occurrence info is guaranteed correct -- See Note [OccInfo in unfoldings and rules] -- Locality ru_auto :: Bool, -- ^ @True@ <=> this rule is auto-generated -- (notably by Specialise or SpecConstr) -- @False@ <=> generated at the user's behest -- See Note [Trimming auto-rules] in "GHC.Iface.Tidy" -- for the sole purpose of this field. ru_origin :: !Module, -- ^ 'Module' the rule was defined in, used -- to test if we should see an orphan rule. ru_orphan :: !IsOrphan, -- ^ Whether or not the rule is an orphan. ru_local :: Bool -- ^ @True@ iff the fn at the head of the rule is -- defined in the same module as the rule -- and is not an implicit 'Id' (like a record selector, -- class operation, or data constructor). This -- is different from 'ru_orphan', where a rule -- can avoid being an orphan if *any* Name in -- LHS of the rule was defined in the same -- module as the rule. } -- | Built-in rules are used for constant folding -- and suchlike. They have no free variables. -- A built-in rule is always visible (there is no such thing as -- an orphan built-in rule.) | BuiltinRule { ru_name :: RuleName, -- ^ As above ru_fn :: Name, -- ^ As above ru_nargs :: Int, -- ^ Number of arguments that 'ru_try' consumes, -- if it fires, including type arguments ru_try :: RuleFun -- ^ This function does the rewrite. It given too many -- arguments, it simply discards them; the returned 'CoreExpr' -- is just the rewrite of 'ru_fn' applied to the first 'ru_nargs' args } -- See Note [Extra args in the target] in GHC.Core.Rules -- | The 'InScopeSet' in the 'InScopeEnv' is a /superset/ of variables that are -- currently in scope. See Note [The InScopeSet invariant]. type RuleFun = RuleOpts -> InScopeEnv -> Id -> [CoreExpr] -> Maybe CoreExpr type InScopeEnv = (InScopeSet, IdUnfoldingFun) type IdUnfoldingFun = Id -> Unfolding -- A function that embodies how to unfold an Id if you need -- to do that in the Rule. The reason we need to pass this info in -- is that whether an Id is unfoldable depends on the simplifier phase isBuiltinRule :: CoreRule -> Bool isBuiltinRule (BuiltinRule {}) = True isBuiltinRule _ = False isAutoRule :: CoreRule -> Bool isAutoRule (BuiltinRule {}) = False isAutoRule (Rule { ru_auto = is_auto }) = is_auto -- | The number of arguments the 'ru_fn' must be applied -- to before the rule can match on it ruleArity :: CoreRule -> Int ruleArity (BuiltinRule {ru_nargs = n}) = n ruleArity (Rule {ru_args = args}) = length args ruleName :: CoreRule -> RuleName ruleName = ru_name ruleModule :: CoreRule -> Maybe Module ruleModule Rule { ru_origin } = Just ru_origin ruleModule BuiltinRule {} = Nothing ruleActivation :: CoreRule -> Activation ruleActivation (BuiltinRule { }) = AlwaysActive ruleActivation (Rule { ru_act = act }) = act -- | The 'Name' of the 'GHC.Types.Id.Id' at the head of the rule left hand side ruleIdName :: CoreRule -> Name ruleIdName = ru_fn isLocalRule :: CoreRule -> Bool isLocalRule = ru_local -- | Set the 'Name' of the 'GHC.Types.Id.Id' at the head of the rule left hand side setRuleIdName :: Name -> CoreRule -> CoreRule setRuleIdName nm ru = ru { ru_fn = nm } {- ************************************************************************ * * Unfoldings * * ************************************************************************ The @Unfolding@ type is declared here to avoid numerous loops Note [Never put `OtherCon` unfoldings on lambda binders] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Based on #21496 we never attach unfoldings of any kind to lambda binders. It's just too easy for the call site to change and invalidate the unfolding. E.g. the caller of the lambda drops a seq (e.g. because the lambda is strict in it's binder) which in turn makes the OtherCon[] unfolding a lie. So unfoldings on lambda binders can never really be trusted when on lambda binders if there is the chance of the call site to change. So it's easiest to just never attach any to lambda binders to begin with, as well as stripping them off if we e.g. float out and expression while abstracting over some arguments. -} -- | Records the /unfolding/ of an identifier, which is approximately the form the -- identifier would have if we substituted its definition in for the identifier. -- This type should be treated as abstract everywhere except in "GHC.Core.Unfold" data Unfolding = NoUnfolding -- ^ We have no information about the unfolding. | BootUnfolding -- ^ We have no information about the unfolding, because -- this 'Id' came from an @hi-boot@ file. -- See Note [Inlining and hs-boot files] in "GHC.CoreToIface" -- for what this is used for. | OtherCon [AltCon] -- ^ It ain't one of these constructors. -- @OtherCon xs@ also indicates that something has been evaluated -- and hence there's no point in re-evaluating it. -- @OtherCon []@ is used even for non-data-type values -- to indicated evaluated-ness. Notably: -- -- > data C = C !(Int -> Int) -- > case x of { C f -> ... } -- -- Here, @f@ gets an @OtherCon []@ unfolding. | DFunUnfolding { -- The Unfolding of a DFunId -- See Note [DFun unfoldings] -- df = /\a1..am. \d1..dn. MkD t1 .. tk -- (op1 a1..am d1..dn) -- (op2 a1..am d1..dn) df_bndrs :: [Var], -- The bound variables [a1..m],[d1..dn] df_con :: DataCon, -- The dictionary data constructor (never a newtype datacon) df_args :: [CoreExpr] -- Args of the data con: types, superclasses and methods, } -- in positional order | CoreUnfolding { -- An unfolding for an Id with no pragma, -- or perhaps a NOINLINE pragma -- (For NOINLINE, the phase, if any, is in the -- InlinePragInfo for this Id.) uf_tmpl :: CoreExpr, -- Template; occurrence info is correct uf_src :: UnfoldingSource, -- Where the unfolding came from uf_is_top :: Bool, -- True <=> top level binding uf_cache :: UnfoldingCache, -- Cache of flags computable from the expr -- See Note [Tying the 'CoreUnfolding' knot] uf_guidance :: UnfoldingGuidance -- Tells about the *size* of the template. } -- ^ An unfolding with redundant cached information. Parameters: -- -- uf_tmpl: Template used to perform unfolding; -- NB: Occurrence info is guaranteed correct: -- see Note [OccInfo in unfoldings and rules] -- -- uf_is_top: Is this a top level binding? -- -- uf_is_value: 'exprIsHNF' template (cached); it is ok to discard a 'seq' on -- this variable -- -- uf_is_work_free: Does this waste only a little work if we expand it inside an inlining? -- Basically this is a cached version of 'exprIsWorkFree' -- -- uf_guidance: Tells us about the /size/ of the unfolding template -- | Properties of a 'CoreUnfolding' that could be computed on-demand from its template. -- See Note [UnfoldingCache] data UnfoldingCache = UnfoldingCache { uf_is_value :: !Bool, -- exprIsHNF template (cached); it is ok to discard -- a `seq` on this variable uf_is_conlike :: !Bool, -- True <=> applicn of constructor or CONLIKE function -- Cached version of exprIsConLike uf_is_work_free :: !Bool, -- True <=> doesn't waste (much) work to expand -- inside an inlining -- Cached version of exprIsCheap uf_expandable :: !Bool -- True <=> can expand in RULE matching -- Cached version of exprIsExpandable } deriving (Eq) -- | 'UnfoldingGuidance' says when unfolding should take place data UnfoldingGuidance = UnfWhen { -- Inline without thinking about the *size* of the uf_tmpl -- Used (a) for small *and* cheap unfoldings -- (b) for INLINE functions -- See Note [INLINE for small functions] in GHC.Core.Unfold ug_arity :: Arity, -- Number of value arguments expected ug_unsat_ok :: Bool, -- True <=> ok to inline even if unsaturated ug_boring_ok :: Bool -- True <=> ok to inline even if the context is boring -- So True,True means "always" } | UnfIfGoodArgs { -- Arose from a normal Id; the info here is the -- result of a simple analysis of the RHS ug_args :: [Int], -- Discount if the argument is evaluated. -- (i.e., a simplification will definitely -- be possible). One elt of the list per *value* arg. ug_size :: Int, -- The "size" of the unfolding. ug_res :: Int -- Scrutinee discount: the discount to subtract if the thing is in } -- a context (case (thing args) of ...), -- (where there are the right number of arguments.) | UnfNever -- The RHS is big, so don't inline it deriving (Eq) {- Note [UnfoldingCache] ~~~~~~~~~~~~~~~~~~~~~~~~ The UnfoldingCache field of an Unfolding holds four (strict) booleans, all derived from the uf_tmpl field of the unfolding. * We serialise the UnfoldingCache to and from interface files, for reasons described in Note [Tying the 'CoreUnfolding' knot] in GHC.IfaceToCore * Because it is a strict data type, we must be careful not to pattern-match on it until we actually want its values. E.g GHC.Core.Unfold.callSiteInline/tryUnfolding are careful not to force it unnecessarily. Just saves a bit of work. * When `seq`ing Core to eliminate space leaks, to suffices to `seq` on the cache, but not its fields, because it is strict in all fields. Note [Historical note: unfoldings for wrappers] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We used to have a nice clever scheme in interface files for wrappers. A wrapper's unfolding can be reconstructed from its worker's id and its strictness. This decreased .hi file size (sometimes significantly, for modules like GHC.Classes with many high-arity w/w splits) and had a slight corresponding effect on compile times. However, when we added the second demand analysis, this scheme lead to some Core lint errors. The second analysis could change the strictness signatures, which sometimes resulted in a wrapper's regenerated unfolding applying the wrapper to too many arguments. Instead of repairing the clever .hi scheme, we abandoned it in favor of simplicity. The .hi sizes are usually insignificant (excluding the +1M for base libraries), and compile time barely increases (~+1% for nofib). The nicer upshot is that the UnfoldingSource no longer mentions an Id, so, eg, substitutions need not traverse them. Note [DFun unfoldings] ~~~~~~~~~~~~~~~~~~~~~~ The Arity in a DFunUnfolding is total number of args (type and value) that the DFun needs to produce a dictionary. That's not necessarily related to the ordinary arity of the dfun Id, esp if the class has one method, so the dictionary is represented by a newtype. Example class C a where { op :: a -> Int } instance C a -> C [a] where op xs = op (head xs) The instance translates to $dfCList :: forall a. C a => C [a] -- Arity 2! $dfCList = /\a.\d. $copList {a} d |> co $copList :: forall a. C a => [a] -> Int -- Arity 2! $copList = /\a.\d.\xs. op {a} d (head xs) Now we might encounter (op (dfCList {ty} d) a1 a2) and we want the (op (dfList {ty} d)) rule to fire, because $dfCList has all its arguments, even though its (value) arity is 2. That's why we record the number of expected arguments in the DFunUnfolding. Note that although it's an Arity, it's most convenient for it to give the *total* number of arguments, both type and value. See the use site in exprIsConApp_maybe. -} -- Constants for the UnfWhen constructor needSaturated, unSaturatedOk :: Bool needSaturated = False unSaturatedOk = True boringCxtNotOk, boringCxtOk :: Bool boringCxtOk = True boringCxtNotOk = False ------------------------------------------------ noUnfolding :: Unfolding -- ^ There is no known 'Unfolding' evaldUnfolding :: Unfolding -- ^ This unfolding marks the associated thing as being evaluated noUnfolding = NoUnfolding evaldUnfolding = OtherCon [] -- | There is no known 'Unfolding', because this came from an -- hi-boot file. bootUnfolding :: Unfolding bootUnfolding = BootUnfolding mkOtherCon :: [AltCon] -> Unfolding mkOtherCon = OtherCon -- | Retrieves the template of an unfolding: panics if none is known unfoldingTemplate :: Unfolding -> CoreExpr unfoldingTemplate = uf_tmpl -- | Retrieves the template of an unfolding if possible -- maybeUnfoldingTemplate is used mainly when specialising, and we do -- want to specialise DFuns, so it's important to return a template -- for DFunUnfoldings maybeUnfoldingTemplate :: Unfolding -> Maybe CoreExpr maybeUnfoldingTemplate (CoreUnfolding { uf_tmpl = expr }) = Just expr maybeUnfoldingTemplate (DFunUnfolding { df_bndrs = bndrs, df_con = con, df_args = args }) = Just (mkLams bndrs (mkApps (Var (dataConWorkId con)) args)) maybeUnfoldingTemplate _ = Nothing -- | The constructors that the unfolding could never be: -- returns @[]@ if no information is available otherCons :: Unfolding -> [AltCon] otherCons (OtherCon cons) = cons otherCons _ = [] -- | Determines if it is certainly the case that the unfolding will -- yield a value (something in HNF): returns @False@ if unsure isValueUnfolding :: Unfolding -> Bool -- Returns False for OtherCon isValueUnfolding (CoreUnfolding { uf_cache = cache }) = uf_is_value cache isValueUnfolding (DFunUnfolding {}) = True isValueUnfolding _ = False -- | Determines if it possibly the case that the unfolding will -- yield a value. Unlike 'isValueUnfolding' it returns @True@ -- for 'OtherCon' isEvaldUnfolding :: Unfolding -> Bool -- Returns True for OtherCon isEvaldUnfolding (OtherCon _) = True isEvaldUnfolding (DFunUnfolding {}) = True isEvaldUnfolding (CoreUnfolding { uf_cache = cache }) = uf_is_value cache isEvaldUnfolding _ = False -- | @True@ if the unfolding is a constructor application, the application -- of a CONLIKE function or 'OtherCon' isConLikeUnfolding :: Unfolding -> Bool isConLikeUnfolding (OtherCon _) = True isConLikeUnfolding (CoreUnfolding { uf_cache = cache }) = uf_is_conlike cache isConLikeUnfolding _ = False -- | Is the thing we will unfold into certainly cheap? isCheapUnfolding :: Unfolding -> Bool isCheapUnfolding (CoreUnfolding { uf_cache = cache }) = uf_is_work_free cache isCheapUnfolding _ = False isExpandableUnfolding :: Unfolding -> Bool isExpandableUnfolding (CoreUnfolding { uf_cache = cache }) = uf_expandable cache isExpandableUnfolding _ = False expandUnfolding_maybe :: Unfolding -> Maybe CoreExpr -- Expand an expandable unfolding; this is used in rule matching -- See Note [Expanding variables] in GHC.Core.Rules -- The key point here is that CONLIKE things can be expanded expandUnfolding_maybe (CoreUnfolding { uf_cache = cache, uf_tmpl = rhs }) | uf_expandable cache = Just rhs expandUnfolding_maybe _ = Nothing isCompulsoryUnfolding :: Unfolding -> Bool isCompulsoryUnfolding (CoreUnfolding { uf_src = src }) = isCompulsorySource src isCompulsoryUnfolding _ = False isStableUnfolding :: Unfolding -> Bool -- True of unfoldings that should not be overwritten -- by a CoreUnfolding for the RHS of a let-binding isStableUnfolding (CoreUnfolding { uf_src = src }) = isStableSource src isStableUnfolding (DFunUnfolding {}) = True isStableUnfolding _ = False isStableUserUnfolding :: Unfolding -> Bool -- True of unfoldings that arise from an INLINE or INLINEABLE pragma isStableUserUnfolding (CoreUnfolding { uf_src = src }) = isStableUserSource src isStableUserUnfolding _ = False isStableSystemUnfolding :: Unfolding -> Bool -- True of unfoldings that arise from an INLINE or INLINEABLE pragma isStableSystemUnfolding (CoreUnfolding { uf_src = src }) = isStableSystemSource src isStableSystemUnfolding _ = False isInlineUnfolding :: Unfolding -> Bool -- ^ True of a /stable/ unfolding that is -- (a) always inlined; that is, with an `UnfWhen` guidance, or -- (b) a DFunUnfolding which never needs to be inlined isInlineUnfolding (CoreUnfolding { uf_src = src, uf_guidance = guidance }) | isStableSource src , UnfWhen {} <- guidance = True isInlineUnfolding (DFunUnfolding {}) = True -- Default case isInlineUnfolding _ = False -- | Only returns False if there is no unfolding information available at all hasSomeUnfolding :: Unfolding -> Bool hasSomeUnfolding NoUnfolding = False hasSomeUnfolding BootUnfolding = False hasSomeUnfolding _ = True isBootUnfolding :: Unfolding -> Bool isBootUnfolding BootUnfolding = True isBootUnfolding _ = False neverUnfoldGuidance :: UnfoldingGuidance -> Bool neverUnfoldGuidance UnfNever = True neverUnfoldGuidance _ = False hasCoreUnfolding :: Unfolding -> Bool -- An unfolding "has Core" if it contains a Core expression, which -- may mention free variables. See Note [Fragile unfoldings] hasCoreUnfolding (CoreUnfolding {}) = True hasCoreUnfolding (DFunUnfolding {}) = True hasCoreUnfolding _ = False -- NoUnfolding, BootUnfolding, OtherCon have no Core canUnfold :: Unfolding -> Bool canUnfold (CoreUnfolding { uf_guidance = g }) = not (neverUnfoldGuidance g) canUnfold _ = False {- Note [Fragile unfoldings] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ An unfolding is "fragile" if it mentions free variables (and hence would need substitution) or might be affected by optimisation. The non-fragile ones are NoUnfolding, BootUnfolding OtherCon {} If we know this binder (say a lambda binder) will be bound to an evaluated thing, we want to retain that info in simpleOptExpr; see #13077. We consider even a StableUnfolding as fragile, because it needs substitution. Note [Stable unfoldings] ~~~~~~~~~~~~~~~~~~~~~~~~ When you say {-# INLINE f #-} f x = you intend that calls (f e) are replaced by [e/x] So we should capture (\x.) in the Unfolding of 'f', and never meddle with it. Meanwhile, we can optimise to our heart's content, leaving the original unfolding intact in Unfolding of 'f'. For example all xs = foldr (&&) True xs any p = all . map p {-# INLINE any #-} We optimise any's RHS fully, but leave the stable unfolding for `any` saying "all . map p", which deforests well at the call site. So INLINE pragma gives rise to a stable unfolding, which captures the original RHS. Moreover, it's only used when 'f' is applied to the specified number of arguments; that is, the number of argument on the LHS of the '=' sign in the original source definition. For example, (.) is now defined in the libraries like this {-# INLINE (.) #-} (.) f g = \x -> f (g x) so that it'll inline when applied to two arguments. If 'x' appeared on the left, thus (.) f g x = f (g x) it'd only inline when applied to three arguments. This slightly-experimental change was requested by Roman, but it seems to make sense. Note [OccInfo in unfoldings and rules] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ In unfoldings and rules, we guarantee that the template is occ-analysed, so that the occurrence info on the binders is correct. This is important, because the Simplifier does not re-analyse the template when using it. If the occurrence info is wrong - We may get more simplifier iterations than necessary, because once-occ info isn't there - More seriously, we may get an infinite loop if there's a Rec without a loop breaker marked ************************************************************************ * * AltCon * * ************************************************************************ -} -- The Ord is needed for the FiniteMap used in the lookForConstructor -- in GHC.Core.Opt.Simplify.Env. If you declared that lookForConstructor -- *ignores* constructor-applications with LitArg args, then you could get rid -- of this Ord. instance Outputable AltCon where ppr (DataAlt dc) = ppr dc ppr (LitAlt lit) = ppr lit ppr DEFAULT = text "__DEFAULT" cmpAlt :: Alt a -> Alt a -> Ordering cmpAlt (Alt con1 _ _) (Alt con2 _ _) = con1 `cmpAltCon` con2 ltAlt :: Alt a -> Alt a -> Bool ltAlt a1 a2 = (a1 `cmpAlt` a2) == LT cmpAltCon :: AltCon -> AltCon -> Ordering -- ^ Compares 'AltCon's within a single list of alternatives -- DEFAULT comes out smallest, so that sorting by AltCon puts -- alternatives in the order required: see Note [Case expression invariants] cmpAltCon DEFAULT DEFAULT = EQ cmpAltCon DEFAULT _ = LT cmpAltCon (DataAlt d1) (DataAlt d2) = dataConTag d1 `compare` dataConTag d2 cmpAltCon (DataAlt _) DEFAULT = GT cmpAltCon (LitAlt l1) (LitAlt l2) = l1 `compare` l2 cmpAltCon (LitAlt _) DEFAULT = GT cmpAltCon con1 con2 = pprPanic "cmpAltCon" (ppr con1 $$ ppr con2) {- ************************************************************************ * * \subsection{Useful synonyms} * * ************************************************************************ Note [CoreProgram] ~~~~~~~~~~~~~~~~~~ The top level bindings of a program, a CoreProgram, are represented as a list of CoreBind * Later bindings in the list can refer to earlier ones, but not vice versa. So this is OK NonRec { x = 4 } Rec { p = ...q...x... ; q = ...p...x } Rec { f = ...p..x..f.. } NonRec { g = ..f..q...x.. } But it would NOT be ok for 'f' to refer to 'g'. * The occurrence analyser does strongly-connected component analysis on each Rec binding, and splits it into a sequence of smaller bindings where possible. So the program typically starts life as a single giant Rec, which is then dependency-analysed into smaller chunks. -} -- If you edit this type, you may need to update the GHC formalism -- See Note [GHC Formalism] in GHC.Core.Lint type CoreProgram = [CoreBind] -- See Note [CoreProgram] -- | The common case for the type of binders and variables when -- we are manipulating the Core language within GHC type CoreBndr = Var -- | Expressions where binders are 'CoreBndr's type CoreExpr = Expr CoreBndr -- | Argument expressions where binders are 'CoreBndr's type CoreArg = Arg CoreBndr -- | Binding groups where binders are 'CoreBndr's type CoreBind = Bind CoreBndr -- | Case alternatives where binders are 'CoreBndr's type CoreAlt = Alt CoreBndr {- ************************************************************************ * * \subsection{Tagging} * * ************************************************************************ -} -- | Binders are /tagged/ with a t data TaggedBndr t = TB CoreBndr t -- TB for "tagged binder" type TaggedBind t = Bind (TaggedBndr t) type TaggedExpr t = Expr (TaggedBndr t) type TaggedArg t = Arg (TaggedBndr t) type TaggedAlt t = Alt (TaggedBndr t) instance Outputable b => Outputable (TaggedBndr b) where ppr (TB b l) = char '<' <> ppr b <> comma <> ppr l <> char '>' deTagExpr :: TaggedExpr t -> CoreExpr deTagExpr (Var v) = Var v deTagExpr (Lit l) = Lit l deTagExpr (Type ty) = Type ty deTagExpr (Coercion co) = Coercion co deTagExpr (App e1 e2) = App (deTagExpr e1) (deTagExpr e2) deTagExpr (Lam (TB b _) e) = Lam b (deTagExpr e) deTagExpr (Let bind body) = Let (deTagBind bind) (deTagExpr body) deTagExpr (Case e (TB b _) ty alts) = Case (deTagExpr e) b ty (map deTagAlt alts) deTagExpr (Tick t e) = Tick t (deTagExpr e) deTagExpr (Cast e co) = Cast (deTagExpr e) co deTagBind :: TaggedBind t -> CoreBind deTagBind (NonRec (TB b _) rhs) = NonRec b (deTagExpr rhs) deTagBind (Rec prs) = Rec [(b, deTagExpr rhs) | (TB b _, rhs) <- prs] deTagAlt :: TaggedAlt t -> CoreAlt deTagAlt (Alt con bndrs rhs) = Alt con [b | TB b _ <- bndrs] (deTagExpr rhs) {- ************************************************************************ * * \subsection{Core-constructing functions with checking} * * ************************************************************************ -} -- | Apply a list of argument expressions to a function expression in a nested fashion. Prefer to -- use 'GHC.Core.Make.mkCoreApps' if possible mkApps :: Expr b -> [Arg b] -> Expr b -- | Apply a list of type argument expressions to a function expression in a nested fashion mkTyApps :: Expr b -> [Type] -> Expr b -- | Apply a list of coercion argument expressions to a function expression in a nested fashion mkCoApps :: Expr b -> [Coercion] -> Expr b -- | Apply a list of type or value variables to a function expression in a nested fashion mkVarApps :: Expr b -> [Var] -> Expr b -- | Apply a list of argument expressions to a data constructor in a nested fashion. Prefer to -- use 'GHC.Core.Make.mkCoreConApps' if possible mkConApp :: DataCon -> [Arg b] -> Expr b mkApps f args = foldl' App f args mkCoApps f args = foldl' (\ e a -> App e (Coercion a)) f args mkVarApps f vars = foldl' (\ e a -> App e (varToCoreExpr a)) f vars mkConApp con args = mkApps (Var (dataConWorkId con)) args mkTyApps f args = foldl' (\ e a -> App e (mkTyArg a)) f args mkConApp2 :: DataCon -> [Type] -> [Var] -> Expr b mkConApp2 con tys arg_ids = Var (dataConWorkId con) `mkApps` map Type tys `mkApps` map varToCoreExpr arg_ids mkTyArg :: Type -> Expr b mkTyArg ty | Just co <- isCoercionTy_maybe ty = Coercion co | otherwise = Type ty -- | Create a machine integer literal expression of type @Int#@ from an @Integer@. -- If you want an expression of type @Int@ use 'GHC.Core.Make.mkIntExpr' mkIntLit :: Platform -> Integer -> Expr b mkIntLit platform n = Lit (mkLitInt platform n) -- | Create a machine integer literal expression of type @Int#@ from an -- @Integer@, wrapping if necessary. -- If you want an expression of type @Int@ use 'GHC.Core.Make.mkIntExpr' mkIntLitWrap :: Platform -> Integer -> Expr b mkIntLitWrap platform n = Lit (mkLitIntWrap platform n) -- | Create a machine word literal expression of type @Word#@ from an @Integer@. -- If you want an expression of type @Word@ use 'GHC.Core.Make.mkWordExpr' mkWordLit :: Platform -> Integer -> Expr b mkWordLit platform w = Lit (mkLitWord platform w) -- | Create a machine word literal expression of type @Word#@ from an -- @Integer@, wrapping if necessary. -- If you want an expression of type @Word@ use 'GHC.Core.Make.mkWordExpr' mkWordLitWrap :: Platform -> Integer -> Expr b mkWordLitWrap platform w = Lit (mkLitWordWrap platform w) mkWord8Lit :: Integer -> Expr b mkWord8Lit w = Lit (mkLitWord8 w) mkWord64LitWord64 :: Word64 -> Expr b mkWord64LitWord64 w = Lit (mkLitWord64 (toInteger w)) mkInt64LitInt64 :: Int64 -> Expr b mkInt64LitInt64 w = Lit (mkLitInt64 (toInteger w)) -- | Create a machine character literal expression of type @Char#@. -- If you want an expression of type @Char@ use 'GHC.Core.Make.mkCharExpr' mkCharLit :: Char -> Expr b -- | Create a machine string literal expression of type @Addr#@. -- If you want an expression of type @String@ use 'GHC.Core.Make.mkStringExpr' mkStringLit :: String -> Expr b mkCharLit c = Lit (mkLitChar c) mkStringLit s = Lit (mkLitString s) -- | Create a machine single precision literal expression of type @Float#@ from a @Rational@. -- If you want an expression of type @Float@ use 'GHC.Core.Make.mkFloatExpr' mkFloatLit :: Rational -> Expr b -- | Create a machine single precision literal expression of type @Float#@ from a @Float@. -- If you want an expression of type @Float@ use 'GHC.Core.Make.mkFloatExpr' mkFloatLitFloat :: Float -> Expr b mkFloatLit f = Lit (mkLitFloat f) mkFloatLitFloat f = Lit (mkLitFloat (toRational f)) -- | Create a machine double precision literal expression of type @Double#@ from a @Rational@. -- If you want an expression of type @Double@ use 'GHC.Core.Make.mkDoubleExpr' mkDoubleLit :: Rational -> Expr b -- | Create a machine double precision literal expression of type @Double#@ from a @Double@. -- If you want an expression of type @Double@ use 'GHC.Core.Make.mkDoubleExpr' mkDoubleLitDouble :: Double -> Expr b mkDoubleLit d = Lit (mkLitDouble d) mkDoubleLitDouble d = Lit (mkLitDouble (toRational d)) -- | Bind all supplied binding groups over an expression in a nested let expression. Assumes -- that the rhs satisfies the let-can-float invariant. Prefer to use -- 'GHC.Core.Make.mkCoreLets' if possible, which does guarantee the invariant mkLets :: [Bind b] -> Expr b -> Expr b -- | Bind all supplied binders over an expression in a nested lambda expression. Prefer to -- use 'GHC.Core.Make.mkCoreLams' if possible mkLams :: [b] -> Expr b -> Expr b mkLams binders body = foldr Lam body binders mkLets binds body = foldr mkLet body binds mkLet :: Bind b -> Expr b -> Expr b -- The desugarer sometimes generates an empty Rec group -- which Lint rejects, so we kill it off right away mkLet (Rec []) body = body mkLet bind body = Let bind body -- | @mkLetNonRec bndr rhs body@ wraps @body@ in a @let@ binding @bndr@. mkLetNonRec :: b -> Expr b -> Expr b -> Expr b mkLetNonRec b rhs body = Let (NonRec b rhs) body -- | @mkLetRec binds body@ wraps @body@ in a @let rec@ with the given set of -- @binds@ if binds is non-empty. mkLetRec :: [(b, Expr b)] -> Expr b -> Expr b mkLetRec [] body = body mkLetRec bs body = Let (Rec bs) body -- | Create a binding group where a type variable is bound to a type. -- Per Note [Core type and coercion invariant], -- this can only be used to bind something in a non-recursive @let@ expression mkTyBind :: TyVar -> Type -> CoreBind mkTyBind tv ty = NonRec tv (Type ty) -- | Create a binding group where a type variable is bound to a type. -- Per Note [Core type and coercion invariant], -- this can only be used to bind something in a non-recursive @let@ expression mkCoBind :: CoVar -> Coercion -> CoreBind mkCoBind cv co = NonRec cv (Coercion co) -- | Convert a binder into either a 'Var' or 'Type' 'Expr' appropriately varToCoreExpr :: CoreBndr -> Expr b varToCoreExpr v | isTyVar v = Type (mkTyVarTy v) | isCoVar v = Coercion (mkCoVarCo v) | otherwise = assert (isId v) $ Var v varsToCoreExprs :: [CoreBndr] -> [Expr b] varsToCoreExprs vs = map varToCoreExpr vs {- ************************************************************************ * * Getting a result type * * ************************************************************************ These are defined here to avoid a module loop between GHC.Core.Utils and GHC.Core.FVs -} -- | If the expression is a 'Type', converts. Otherwise, -- panics. NB: This does /not/ convert 'Coercion' to 'CoercionTy'. exprToType :: CoreExpr -> Type exprToType (Type ty) = ty exprToType _bad = pprPanic "exprToType" empty {- ************************************************************************ * * \subsection{Simple access functions} * * ************************************************************************ -} -- | Extract every variable by this group bindersOf :: Bind b -> [b] -- If you edit this function, you may need to update the GHC formalism -- See Note [GHC Formalism] in GHC.Core.Lint bindersOf (NonRec binder _) = [binder] bindersOf (Rec pairs) = [binder | (binder, _) <- pairs] -- | 'bindersOf' applied to a list of binding groups bindersOfBinds :: [Bind b] -> [b] bindersOfBinds binds = foldr ((++) . bindersOf) [] binds -- We inline this to avoid unknown function calls. {-# INLINE foldBindersOfBindStrict #-} foldBindersOfBindStrict :: (a -> b -> a) -> a -> Bind b -> a foldBindersOfBindStrict f = \z bind -> case bind of NonRec b _rhs -> f z b Rec pairs -> foldl' f z $ map fst pairs {-# INLINE foldBindersOfBindsStrict #-} foldBindersOfBindsStrict :: (a -> b -> a) -> a -> [Bind b] -> a foldBindersOfBindsStrict f = \z binds -> foldl' fold_bind z binds where fold_bind = (foldBindersOfBindStrict f) rhssOfBind :: Bind b -> [Expr b] rhssOfBind (NonRec _ rhs) = [rhs] rhssOfBind (Rec pairs) = [rhs | (_,rhs) <- pairs] rhssOfAlts :: [Alt b] -> [Expr b] rhssOfAlts alts = [e | Alt _ _ e <- alts] -- | Collapse all the bindings in the supplied groups into a single -- list of lhs\/rhs pairs suitable for binding in a 'Rec' binding group flattenBinds :: [Bind b] -> [(b, Expr b)] flattenBinds (NonRec b r : binds) = (b,r) : flattenBinds binds flattenBinds (Rec prs1 : binds) = prs1 ++ flattenBinds binds flattenBinds [] = [] -- | We often want to strip off leading lambdas before getting down to -- business. Variants are 'collectTyBinders', 'collectValBinders', -- and 'collectTyAndValBinders' collectBinders :: Expr b -> ([b], Expr b) collectTyBinders :: CoreExpr -> ([TyVar], CoreExpr) collectValBinders :: CoreExpr -> ([Id], CoreExpr) collectTyAndValBinders :: CoreExpr -> ([TyVar], [Id], CoreExpr) -- | Strip off exactly N leading lambdas (type or value). -- Good for use with join points. -- Panic if there aren't enough collectNBinders :: JoinArity -> Expr b -> ([b], Expr b) collectBinders expr = go [] expr where go bs (Lam b e) = go (b:bs) e go bs e = (reverse bs, e) collectTyBinders expr = go [] expr where go tvs (Lam b e) | isTyVar b = go (b:tvs) e go tvs e = (reverse tvs, e) collectValBinders expr = go [] expr where go ids (Lam b e) | isId b = go (b:ids) e go ids body = (reverse ids, body) collectTyAndValBinders expr = (tvs, ids, body) where (tvs, body1) = collectTyBinders expr (ids, body) = collectValBinders body1 collectNBinders orig_n orig_expr = go orig_n [] orig_expr where go 0 bs expr = (reverse bs, expr) go n bs (Lam b e) = go (n-1) (b:bs) e go _ _ _ = pprPanic "collectNBinders" $ int orig_n -- | Strip off exactly N leading value lambdas -- returning all the binders found up to that point -- Return Nothing if there aren't enough collectNValBinders_maybe :: Arity -> CoreExpr -> Maybe ([Var], CoreExpr) collectNValBinders_maybe orig_n orig_expr = go orig_n [] orig_expr where go 0 bs expr = Just (reverse bs, expr) go n bs (Lam b e) | isId b = go (n-1) (b:bs) e | otherwise = go n (b:bs) e go _ _ _ = Nothing -- | Takes a nested application expression and returns the function -- being applied and the arguments to which it is applied collectArgs :: Expr b -> (Expr b, [Arg b]) collectArgs expr = go expr [] where go (App f a) as = go f (a:as) go e as = (e, as) -- | Takes a nested application expression and returns the function -- being applied. Looking through casts and ticks to find it. collectFunSimple :: Expr b -> Expr b collectFunSimple expr = go expr where go expr' = case expr' of App f _a -> go f Tick _t e -> go e Cast e _co -> go e e -> e -- | fmap on the body of a lambda. -- wrapLamBody f (\x -> body) == (\x -> f body) wrapLamBody :: (CoreExpr -> CoreExpr) -> CoreExpr -> CoreExpr wrapLamBody f expr = go expr where go (Lam v body) = Lam v $ go body go expr = f expr -- | Attempt to remove the last N arguments of a function call. -- Strip off any ticks or coercions encountered along the way and any -- at the end. stripNArgs :: Word -> Expr a -> Maybe (Expr a) stripNArgs !n (Tick _ e) = stripNArgs n e stripNArgs n (Cast f _) = stripNArgs n f stripNArgs 0 e = Just e stripNArgs n (App f _) = stripNArgs (n - 1) f stripNArgs _ _ = Nothing -- | Like @collectArgs@, but also collects looks through floatable -- ticks if it means that we can find more arguments. collectArgsTicks :: (CoreTickish -> Bool) -> Expr b -> (Expr b, [Arg b], [CoreTickish]) collectArgsTicks skipTick expr = go expr [] [] where go (App f a) as ts = go f (a:as) ts go (Tick t e) as ts | skipTick t = go e as (t:ts) go e as ts = (e, as, reverse ts) {- ************************************************************************ * * \subsection{Predicates} * * ************************************************************************ At one time we optionally carried type arguments through to runtime. @isRuntimeVar v@ returns if (Lam v _) really becomes a lambda at runtime, i.e. if type applications are actual lambdas because types are kept around at runtime. Similarly isRuntimeArg. -} -- | Will this variable exist at runtime? isRuntimeVar :: Var -> Bool isRuntimeVar = isId -- | Will this argument expression exist at runtime? isRuntimeArg :: CoreExpr -> Bool isRuntimeArg = isValArg -- | Returns @True@ for value arguments, false for type args -- NB: coercions are value arguments (zero width, to be sure, -- like State#, but still value args). isValArg :: Expr b -> Bool isValArg e = not (isTypeArg e) -- | Returns @True@ iff the expression is a 'Type' or 'Coercion' -- expression at its top level isTyCoArg :: Expr b -> Bool isTyCoArg (Type {}) = True isTyCoArg (Coercion {}) = True isTyCoArg _ = False -- | Returns @True@ iff the expression is a 'Coercion' -- expression at its top level isCoArg :: Expr b -> Bool isCoArg (Coercion {}) = True isCoArg _ = False -- | Returns @True@ iff the expression is a 'Type' expression at its -- top level. Note this does NOT include 'Coercion's. isTypeArg :: Expr b -> Bool isTypeArg (Type {}) = True isTypeArg _ = False -- | The number of binders that bind values rather than types valBndrCount :: [CoreBndr] -> Int valBndrCount = count isId -- | The number of argument expressions that are values rather than types at their top level valArgCount :: [Arg b] -> Int valArgCount = count isValArg {- ************************************************************************ * * \subsection{Annotated core} * * ************************************************************************ -} -- | Annotated core: allows annotation at every node in the tree type AnnExpr bndr annot = (annot, AnnExpr' bndr annot) -- | A clone of the 'Expr' type but allowing annotation at every tree node data AnnExpr' bndr annot = AnnVar Id | AnnLit Literal | AnnLam bndr (AnnExpr bndr annot) | AnnApp (AnnExpr bndr annot) (AnnExpr bndr annot) | AnnCase (AnnExpr bndr annot) bndr Type [AnnAlt bndr annot] | AnnLet (AnnBind bndr annot) (AnnExpr bndr annot) | AnnCast (AnnExpr bndr annot) (annot, Coercion) -- Put an annotation on the (root of) the coercion | AnnTick CoreTickish (AnnExpr bndr annot) | AnnType Type | AnnCoercion Coercion -- | A clone of the 'Alt' type but allowing annotation at every tree node data AnnAlt bndr annot = AnnAlt AltCon [bndr] (AnnExpr bndr annot) -- | A clone of the 'Bind' type but allowing annotation at every tree node data AnnBind bndr annot = AnnNonRec bndr (AnnExpr bndr annot) | AnnRec [(bndr, AnnExpr bndr annot)] -- | Takes a nested application expression and returns the function -- being applied and the arguments to which it is applied collectAnnArgs :: AnnExpr b a -> (AnnExpr b a, [AnnExpr b a]) collectAnnArgs expr = go expr [] where go (_, AnnApp f a) as = go f (a:as) go e as = (e, as) collectAnnArgsTicks :: (CoreTickish -> Bool) -> AnnExpr b a -> (AnnExpr b a, [AnnExpr b a], [CoreTickish]) collectAnnArgsTicks tickishOk expr = go expr [] [] where go (_, AnnApp f a) as ts = go f (a:as) ts go (_, AnnTick t e) as ts | tickishOk t = go e as (t:ts) go e as ts = (e, as, reverse ts) deAnnotate :: AnnExpr bndr annot -> Expr bndr deAnnotate (_, e) = deAnnotate' e deAnnotate' :: AnnExpr' bndr annot -> Expr bndr deAnnotate' (AnnType t) = Type t deAnnotate' (AnnCoercion co) = Coercion co deAnnotate' (AnnVar v) = Var v deAnnotate' (AnnLit lit) = Lit lit deAnnotate' (AnnLam binder body) = Lam binder (deAnnotate body) deAnnotate' (AnnApp fun arg) = App (deAnnotate fun) (deAnnotate arg) deAnnotate' (AnnCast e (_,co)) = Cast (deAnnotate e) co deAnnotate' (AnnTick tick body) = Tick tick (deAnnotate body) deAnnotate' (AnnLet bind body) = Let (deAnnBind bind) (deAnnotate body) deAnnotate' (AnnCase scrut v t alts) = Case (deAnnotate scrut) v t (map deAnnAlt alts) deAnnAlt :: AnnAlt bndr annot -> Alt bndr deAnnAlt (AnnAlt con args rhs) = Alt con args (deAnnotate rhs) deAnnBind :: AnnBind b annot -> Bind b deAnnBind (AnnNonRec var rhs) = NonRec var (deAnnotate rhs) deAnnBind (AnnRec pairs) = Rec [(v,deAnnotate rhs) | (v,rhs) <- pairs] -- | As 'collectBinders' but for 'AnnExpr' rather than 'Expr' collectAnnBndrs :: AnnExpr bndr annot -> ([bndr], AnnExpr bndr annot) collectAnnBndrs e = collect [] e where collect bs (_, AnnLam b body) = collect (b:bs) body collect bs body = (reverse bs, body) -- | As 'collectNBinders' but for 'AnnExpr' rather than 'Expr' collectNAnnBndrs :: Int -> AnnExpr bndr annot -> ([bndr], AnnExpr bndr annot) collectNAnnBndrs orig_n e = collect orig_n [] e where collect 0 bs body = (reverse bs, body) collect n bs (_, AnnLam b body) = collect (n-1) (b:bs) body collect _ _ _ = pprPanic "collectNBinders" $ int orig_n