{-
(c) The University of Glasgow 2006
(c) The GRASP/AQUA Project, Glasgow University, 1992-1998
-}
{-# LANGUAGE CPP, DeriveDataTypeable, FlexibleContexts #-}
{-# LANGUAGE NamedFieldPuns #-}
{-# LANGUAGE BangPatterns #-}
{-# OPTIONS_GHC -Wno-incomplete-uni-patterns #-}
{-# OPTIONS_GHC -Wno-incomplete-record-updates #-}
-- | 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,
Tickish(..), TickishScoping(..), TickishPlacement(..),
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, mkIntLitInt,
mkWordLit, mkWordLitWord,
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,
collectBinders, collectTyBinders, collectTyAndValBinders,
collectNBinders,
collectArgs, stripNArgs, collectArgsTicks, flattenBinds,
exprToType, exprToCoercion_maybe,
applyTypeToArg,
isValArg, isTypeArg, isCoArg, isTyCoArg, valArgCount, valBndrCount,
isRuntimeArg, isRuntimeVar,
-- * Tick-related functions
tickishCounts, tickishScoped, tickishScopesLike, tickishFloatable,
tickishCanSplit, mkNoCount, mkNoScope,
tickishIsCode, tickishPlace,
tickishContains,
-- * Unfolding data types
Unfolding(..), 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, hasCoreUnfolding, hasSomeUnfolding,
isBootUnfolding,
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(..), RuleBase,
RuleName, RuleFun, IdUnfoldingFun, InScopeEnv,
RuleEnv(..), RuleOpts(..), mkRuleEnv, emptyRuleEnv,
-- ** Operations on 'CoreRule's
ruleArity, ruleName, ruleIdName, ruleActivation,
setRuleIdName, ruleModule,
isBuiltinRule, isLocalRule, isAutoRule,
) where
#include "HsVersions.h"
import GHC.Prelude
import GHC.Platform
import GHC.Types.CostCentre
import GHC.Types.Var.Env( InScopeSet )
import GHC.Types.Var
import GHC.Core.Type
import GHC.Core.Coercion
import GHC.Types.Name
import GHC.Types.Name.Set
import GHC.Types.Name.Env( NameEnv, emptyNameEnv )
import GHC.Types.Literal
import GHC.Core.DataCon
import GHC.Unit.Module
import GHC.Types.Basic
import GHC.Utils.Outputable
import GHC.Utils.Misc
import GHC.Types.Unique.Set
import GHC.Types.SrcLoc ( RealSrcSpan, containsSpan )
import GHC.Utils.Binary
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 'RdrName.RdrNames'
--
-- 2. This syntax tree is /renamed/, which attaches a 'Unique.Unique' to every 'RdrName.RdrName'
-- (yielding a '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 '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 [Core let/app invariant]
-- See Note [Levity polymorphism invariants]
--
-- * Lambda abstraction
-- See Note [Levity 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/app invariant]
-- See Note [Levity 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.
--
-- * Notes. These allow general information to be added to expressions
-- in the syntax tree
--
-- * 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) Coercion
| Tick (Tickish Id) (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
type Alt b = (AltCon, [b], Expr b)
-- | 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
S# x -> ...
J# _ _ -> ...
(where S#, J# 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/app invariant]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The let/app invariant
the right hand side of a non-recursive 'Let', and
the argument of an 'App',
/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/app invariant is initially enforced by mkCoreLet and mkCoreApp in
GHC.Core.Make.
For discussion of some implications of the let/app invariant primops see
Note [Checking versus non-checking primops] in GHC.Builtin.PrimOps.
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 isFloatingTy.
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.
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 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 [Levity polymorphism invariants]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The levity-polymorphism invariants are these (as per "Levity Polymorphism",
PLDI '17):
* The type of a term-binder must not be levity-polymorphic,
unless it is a let(rec)-bound join point
(see Note [Invariants on join points])
* The type of the argument of an App must not be levity-polymorphic.
A type (t::TYPE r) is "levity polymorphic" if 'r' has any free variables.
For example
\(r::RuntimeRep). \(a::TYPE r). \(x::a). e
is illegal because x's type has kind (TYPE r), which has 'r' free.
See Note [Levity polymorphism checking] in GHC.HsToCore.Monad to see where these
invariants are established for user-written code.
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 [Type let]
~~~~~~~~~~~~~~~
See #type_let#
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 is the number of value
binders in the top n lambdas, where n is the join arity.
So arity <= join arity; the former counts only value binders
while the latter counts all binders.
e.g. Suppose $j has join arity 1
let j = \x y. e in case x of { A -> j 1; B -> j 2 }
Then its ordinary arity is also 1, not 2.
The arity of a join point isn't very important; but short of setting
it to zero, it is helpful to have an invariant. E.g. #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/app invariant)
e.g. let j :: Int# = factorial x in ...
6. A join point can have a levity-polymorphic RHS
e.g. let j :: r :: TYPE l = fail void# 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. 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.
This 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
{- *********************************************************************
* *
Ticks
* *
************************************************************************
-}
-- | Allows attaching extra information to points in expressions
-- If you edit this type, you may need to update the GHC formalism
-- See Note [GHC Formalism] in GHC.Core.Lint
data Tickish id =
-- | An @{-# SCC #-}@ profiling annotation, either automatically
-- added by the desugarer as a result of -auto-all, or added by
-- the user.
ProfNote {
profNoteCC :: CostCentre, -- ^ the cost centre
profNoteCount :: !Bool, -- ^ bump the entry count?
profNoteScope :: !Bool -- ^ scopes over the enclosed expression
-- (i.e. not just a tick)
}
-- | A "tick" used by HPC to track the execution of each
-- subexpression in the original source code.
| HpcTick {
tickModule :: Module,
tickId :: !Int
}
-- | A breakpoint for the GHCi debugger. This behaves like an HPC
-- tick, but has a list of free variables which will be available
-- for inspection in GHCi when the program stops at the breakpoint.
--
-- NB. we must take account of these Ids when (a) counting free variables,
-- and (b) substituting (don't substitute for them)
| Breakpoint
{ breakpointId :: !Int
, breakpointFVs :: [id] -- ^ the order of this list is important:
-- it matches the order of the lists in the
-- appropriate entry in GHC.Driver.Types.ModBreaks.
--
-- Careful about substitution! See
-- Note [substTickish] in GHC.Core.Subst.
}
-- | A source note.
--
-- Source notes are pure annotations: Their presence should neither
-- influence compilation nor execution. The semantics are given by
-- causality: The presence of a source note means that a local
-- change in the referenced source code span will possibly provoke
-- the generated code to change. On the flip-side, the functionality
-- of annotated code *must* be invariant against changes to all
-- source code *except* the spans referenced in the source notes
-- (see "Causality of optimized Haskell" paper for details).
--
-- Therefore extending the scope of any given source note is always
-- valid. Note that it is still undesirable though, as this reduces
-- their usefulness for debugging and profiling. Therefore we will
-- generally try only to make use of this property where it is
-- necessary to enable optimizations.
| SourceNote
{ sourceSpan :: RealSrcSpan -- ^ Source covered
, sourceName :: String -- ^ Name for source location
-- (uses same names as CCs)
}
deriving (Eq, Ord, Data)
-- | A "counting tick" (where tickishCounts is True) is one that
-- counts evaluations in some way. We cannot discard a counting tick,
-- and the compiler should preserve the number of counting ticks as
-- far as possible.
--
-- However, we still allow the simplifier to increase or decrease
-- sharing, so in practice the actual number of ticks may vary, except
-- that we never change the value from zero to non-zero or vice versa.
tickishCounts :: Tickish id -> Bool
tickishCounts n@ProfNote{} = profNoteCount n
tickishCounts HpcTick{} = True
tickishCounts Breakpoint{} = True
tickishCounts _ = False
-- | Specifies the scoping behaviour of ticks. This governs the
-- behaviour of ticks that care about the covered code and the cost
-- associated with it. Important for ticks relating to profiling.
data TickishScoping =
-- | No scoping: The tick does not care about what code it
-- covers. Transformations can freely move code inside as well as
-- outside without any additional annotation obligations
NoScope
-- | Soft scoping: We want all code that is covered to stay
-- covered. Note that this scope type does not forbid
-- transformations from happening, as long as all results of
-- the transformations are still covered by this tick or a copy of
-- it. For example
--
-- let x = tick<...> (let y = foo in bar) in baz
-- ===>
-- let x = tick<...> bar; y = tick<...> foo in baz
--
-- Is a valid transformation as far as "bar" and "foo" is
-- concerned, because both still are scoped over by the tick.
--
-- Note though that one might object to the "let" not being
-- covered by the tick any more. However, we are generally lax
-- with this - constant costs don't matter too much, and given
-- that the "let" was effectively merged we can view it as having
-- lost its identity anyway.
--
-- Also note that this scoping behaviour allows floating a tick
-- "upwards" in pretty much any situation. For example:
--
-- case foo of x -> tick<...> bar
-- ==>
-- tick<...> case foo of x -> bar
--
-- While this is always legal, we want to make a best effort to
-- only make us of this where it exposes transformation
-- opportunities.
| SoftScope
-- | Cost centre scoping: We don't want any costs to move to other
-- cost-centre stacks. This means we not only want no code or cost
-- to get moved out of their cost centres, but we also object to
-- code getting associated with new cost-centre ticks - or
-- changing the order in which they get applied.
--
-- A rule of thumb is that we don't want any code to gain new
-- annotations. However, there are notable exceptions, for
-- example:
--
-- let f = \y -> foo in tick<...> ... (f x) ...
-- ==>
-- tick<...> ... foo[x/y] ...
--
-- In-lining lambdas like this is always legal, because inlining a
-- function does not change the cost-centre stack when the
-- function is called.
| CostCentreScope
deriving (Eq)
-- | Returns the intended scoping rule for a Tickish
tickishScoped :: Tickish id -> TickishScoping
tickishScoped n@ProfNote{}
| profNoteScope n = CostCentreScope
| otherwise = NoScope
tickishScoped HpcTick{} = NoScope
tickishScoped Breakpoint{} = CostCentreScope
-- Breakpoints are scoped: eventually we're going to do call
-- stacks, but also this helps prevent the simplifier from moving
-- breakpoints around and changing their result type (see #1531).
tickishScoped SourceNote{} = SoftScope
-- | Returns whether the tick scoping rule is at least as permissive
-- as the given scoping rule.
tickishScopesLike :: Tickish id -> TickishScoping -> Bool
tickishScopesLike t scope = tickishScoped t `like` scope
where NoScope `like` _ = True
_ `like` NoScope = False
SoftScope `like` _ = True
_ `like` SoftScope = False
CostCentreScope `like` _ = True
-- | Returns @True@ for ticks that can be floated upwards easily even
-- where it might change execution counts, such as:
--
-- Just (tick<...> foo)
-- ==>
-- tick<...> (Just foo)
--
-- This is a combination of @tickishSoftScope@ and
-- @tickishCounts@. Note that in principle splittable ticks can become
-- floatable using @mkNoTick@ -- even though there's currently no
-- tickish for which that is the case.
tickishFloatable :: Tickish id -> Bool
tickishFloatable t = t `tickishScopesLike` SoftScope && not (tickishCounts t)
-- | Returns @True@ for a tick that is both counting /and/ scoping and
-- can be split into its (tick, scope) parts using 'mkNoScope' and
-- 'mkNoTick' respectively.
tickishCanSplit :: Tickish id -> Bool
tickishCanSplit ProfNote{profNoteScope = True, profNoteCount = True}
= True
tickishCanSplit _ = False
mkNoCount :: Tickish id -> Tickish id
mkNoCount n | not (tickishCounts n) = n
| not (tickishCanSplit n) = panic "mkNoCount: Cannot split!"
mkNoCount n@ProfNote{} = n {profNoteCount = False}
mkNoCount _ = panic "mkNoCount: Undefined split!"
mkNoScope :: Tickish id -> Tickish id
mkNoScope n | tickishScoped n == NoScope = n
| not (tickishCanSplit n) = panic "mkNoScope: Cannot split!"
mkNoScope n@ProfNote{} = n {profNoteScope = False}
mkNoScope _ = panic "mkNoScope: Undefined split!"
-- | Return @True@ if this source annotation compiles to some backend
-- code. Without this flag, the tickish is seen as a simple annotation
-- that does not have any associated evaluation code.
--
-- What this means that we are allowed to disregard the tick if doing
-- so means that we can skip generating any code in the first place. A
-- typical example is top-level bindings:
--
-- foo = tick<...> \y -> ...
-- ==>
-- foo = \y -> tick<...> ...
--
-- Here there is just no operational difference between the first and
-- the second version. Therefore code generation should simply
-- translate the code as if it found the latter.
tickishIsCode :: Tickish id -> Bool
tickishIsCode SourceNote{} = False
tickishIsCode _tickish = True -- all the rest for now
-- | Governs the kind of expression that the tick gets placed on when
-- annotating for example using @mkTick@. If we find that we want to
-- put a tickish on an expression ruled out here, we try to float it
-- inwards until we find a suitable expression.
data TickishPlacement =
-- | Place ticks exactly on run-time expressions. We can still
-- move the tick through pure compile-time constructs such as
-- other ticks, casts or type lambdas. This is the most
-- restrictive placement rule for ticks, as all tickishs have in
-- common that they want to track runtime processes. The only
-- legal placement rule for counting ticks.
PlaceRuntime
-- | As @PlaceRuntime@, but we float the tick through all
-- lambdas. This makes sense where there is little difference
-- between annotating the lambda and annotating the lambda's code.
| PlaceNonLam
-- | In addition to floating through lambdas, cost-centre style
-- tickishs can also be moved from constructors, non-function
-- variables and literals. For example:
--
-- let x = scc<...> C (scc<...> y) (scc<...> 3) in ...
--
-- Neither the constructor application, the variable or the
-- literal are likely to have any cost worth mentioning. And even
-- if y names a thunk, the call would not care about the
-- evaluation context. Therefore removing all annotations in the
-- above example is safe.
| PlaceCostCentre
deriving (Eq)
-- | Placement behaviour we want for the ticks
tickishPlace :: Tickish id -> TickishPlacement
tickishPlace n@ProfNote{}
| profNoteCount n = PlaceRuntime
| otherwise = PlaceCostCentre
tickishPlace HpcTick{} = PlaceRuntime
tickishPlace Breakpoint{} = PlaceRuntime
tickishPlace SourceNote{} = PlaceNonLam
-- | Returns whether one tick "contains" the other one, therefore
-- making the second tick redundant.
tickishContains :: Eq b => Tickish b -> Tickish b -> Bool
tickishContains (SourceNote sp1 n1) (SourceNote sp2 n2)
= containsSpan sp1 sp2 && n1 == n2
-- compare the String last
tickishContains t1 t2
= t1 == t2
{-
************************************************************************
* *
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.
* 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
(because it is needed during instance lookup)
* For rules and family instances:
when we generate an IfaceRule (GHC.Iface.Make.coreRuleToIfaceRule)
or IfaceFamInst (GHC.Iface.Make.instanceToIfaceInst)
-}
{-
************************************************************************
* *
\subsection{Transformation 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.
-}
-- | Gathers a collection of 'CoreRule's. Maps (the name of) an 'Id' to its rules
type RuleBase = NameEnv [CoreRule]
-- The rules are unordered;
-- we sort out any overlaps on lookup
-- | A full rule environment which we can apply rules from. Like a 'RuleBase',
-- but it also includes the set of visible orphans we use to filter out orphan
-- rules which are not visible (even though we can see them...)
data RuleEnv
= RuleEnv { re_base :: RuleBase
, re_visible_orphs :: ModuleSet
}
mkRuleEnv :: RuleBase -> [Module] -> RuleEnv
mkRuleEnv rules vis_orphs = RuleEnv rules (mkModuleSet vis_orphs)
emptyRuleEnv :: RuleEnv
emptyRuleEnv = RuleEnv emptyNameEnv emptyModuleSet
-- | 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 '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 rule matching] in GHC.Core.Rules
-- | Rule options
data RuleOpts = RuleOpts
{ roPlatform :: !Platform -- ^ Target platform
, roNumConstantFolding :: !Bool -- ^ Enable more advanced numeric constant folding
, roExcessRationalPrecision :: !Bool -- ^ Cut down precision of Rational values to that of Float/Double if disabled
}
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 '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 '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
-}
-- | 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_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
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
------------------------------------------------
data UnfoldingSource
= -- See also Note [Historical note: unfoldings for wrappers]
InlineRhs -- The current rhs of the function
-- Replace uf_tmpl each time around
| InlineStable -- From an INLINE or INLINABLE pragma
-- INLINE if guidance is UnfWhen
-- INLINABLE if guidance is UnfIfGoodArgs/UnfoldNever
-- (well, technically an INLINABLE might be made
-- UnfWhen if it was small enough, and then
-- it will behave like INLINE outside the current
-- module, but that is the way automatic unfoldings
-- work so it is consistent with the intended
-- meaning of INLINABLE).
--
-- uf_tmpl may change, but only as a result of
-- gentle simplification, it doesn't get updated
-- to the current RHS during compilation as with
-- InlineRhs.
--
-- See Note [InlineStable]
| InlineCompulsory -- Something that *has* no binding, so you *must* inline it
-- Only a few primop-like things have this property
-- (see MkId.hs, calls to mkCompulsoryUnfolding).
-- Inline absolutely always, however boring the context.
-- | '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 [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
isStableSource :: UnfoldingSource -> Bool
-- Keep the unfolding template
isStableSource InlineCompulsory = True
isStableSource InlineStable = True
isStableSource InlineRhs = False
-- | 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 wnen 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_is_value = is_evald }) = is_evald
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 (CoreUnfolding { uf_is_value = is_evald }) = is_evald
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_is_conlike = con }) = con
isConLikeUnfolding _ = False
-- | Is the thing we will unfold into certainly cheap?
isCheapUnfolding :: Unfolding -> Bool
isCheapUnfolding (CoreUnfolding { uf_is_work_free = is_wf }) = is_wf
isCheapUnfolding _ = False
isExpandableUnfolding :: Unfolding -> Bool
isExpandableUnfolding (CoreUnfolding { uf_expandable = is_expable }) = is_expable
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_expandable = True, uf_tmpl = rhs }) = Just rhs
expandUnfolding_maybe _ = Nothing
isCompulsoryUnfolding :: Unfolding -> Bool
isCompulsoryUnfolding (CoreUnfolding { uf_src = InlineCompulsory }) = True
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
-- | 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 [InlineStable]
~~~~~~~~~~~~~~~~~
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 InlineRule saying "all . map p",
which deforests well at the call site.
So INLINE pragma gives rise to an InlineRule, 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.
See also Note [Inlining an InlineRule] in GHC.Core.Unfold.
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 :: (AltCon, a, b) -> (AltCon, a, b) -> Ordering
cmpAlt (con1, _, _) (con2, _, _) = con1 `cmpAltCon` con2
ltAlt :: (AltCon, a, b) -> (AltCon, a, b) -> 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 = WARN( True, text "Comparing incomparable AltCons" <+>
ppr con1 <+> ppr con2 )
LT
{-
************************************************************************
* *
\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 (con, bndrs, rhs) = (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
-- | Create a machine integer literal expression of type @Int#@ from an @Int@.
-- If you want an expression of type @Int@ use 'GHC.Core.Make.mkIntExpr'
mkIntLitInt :: Platform -> Int -> Expr b
mkIntLit platform n = Lit (mkLitInt platform n)
mkIntLitInt platform n = Lit (mkLitInt platform (toInteger 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
-- | Create a machine word literal expression of type @Word#@ from a @Word@.
-- If you want an expression of type @Word@ use 'GHC.Core.Make.mkWordExpr'
mkWordLitWord :: Platform -> Word -> Expr b
mkWordLit platform w = Lit (mkLitWord platform w)
mkWordLitWord platform w = Lit (mkLitWord platform (toInteger 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/app 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 "GHC.Core#type_let",
-- 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 "GHC.Core#type_let",
-- 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
-}
applyTypeToArg :: Type -> CoreExpr -> Type
-- ^ Determines the type resulting from applying an expression with given type
-- to a given argument expression
applyTypeToArg fun_ty arg = piResultTy fun_ty (exprToType arg)
-- | 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
-- | If the expression is a 'Coercion', converts.
exprToCoercion_maybe :: CoreExpr -> Maybe Coercion
exprToCoercion_maybe (Coercion co) = Just co
exprToCoercion_maybe _ = Nothing
{-
************************************************************************
* *
\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
rhssOfBind :: Bind b -> [Expr b]
rhssOfBind (NonRec _ rhs) = [rhs]
rhssOfBind (Rec pairs) = [rhs | (_,rhs) <- pairs]
rhssOfAlts :: [Alt b] -> [Expr b]
rhssOfAlts alts = [e | (_,_,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.
collectNBinders :: Int -> 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
-- | 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)
-- | 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 :: (Tickish Id -> Bool) -> Expr b
-> (Expr b, [Arg b], [Tickish Id])
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 (Tickish Id) (AnnExpr bndr annot)
| AnnType Type
| AnnCoercion Coercion
-- | A clone of the 'Alt' type but allowing annotation at every tree node
type AnnAlt bndr annot = (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 :: (Tickish Var -> Bool) -> AnnExpr b a
-> (AnnExpr b a, [AnnExpr b a], [Tickish Var])
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 (con,args,rhs) = (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