    {-# LANGUAGE CPP #-}

    {-# OPTIONS_GHC -Wno-incomplete-uni-patterns #-}

    {-
    (c) The GRASP/AQUA Project, Glasgow University, 1993-1998

    \section[Specialise]{Stamping out overloading, and (optionally) polymorphism}
    -}

    module GHC.Core.Opt.Specialise ( specProgram, specUnfolding ) where

    #include "HsVersions.h"

    import GHC.Prelude

    import GHC.Driver.Session
    import GHC.Driver.Ppr
    import GHC.Driver.Config
    import GHC.Driver.Env

    import GHC.Tc.Utils.TcType hiding( substTy )

    import GHC.Core.Type  hiding( substTy, extendTvSubstList )
    import GHC.Core.Multiplicity
    import GHC.Core.Predicate
    import GHC.Core.Coercion( Coercion )
    import GHC.Core.Opt.Monad
    import qualified GHC.Core.Subst as Core
    import GHC.Core.Unfold.Make
    import GHC.Core
    import GHC.Core.Rules
    import GHC.Core.Utils     ( exprIsTrivial, getIdFromTrivialExpr_maybe
                              , mkCast, exprType )
    import GHC.Core.FVs
    import GHC.Core.TyCo.Rep (TyCoBinder (..))
    import GHC.Core.Opt.Arity     ( collectBindersPushingCo
                                  , etaExpandToJoinPointRule )

    import GHC.Builtin.Types  ( unboxedUnitTy )

    import GHC.Data.Maybe     ( mapMaybe, maybeToList, isJust )
    import GHC.Data.Bag
    import GHC.Data.FastString

    import GHC.Types.Basic
    import GHC.Types.Unique.Supply
    import GHC.Types.Unique.DFM
    import GHC.Types.Name
    import GHC.Types.Tickish
    import GHC.Types.Id.Make  ( voidArgId, voidPrimId )
    import GHC.Types.Var      ( isLocalVar )
    import GHC.Types.Var.Set
    import GHC.Types.Var.Env
    import GHC.Types.Id

    import GHC.Utils.Monad    ( foldlM )
    import GHC.Utils.Misc
    import GHC.Utils.Outputable
    import GHC.Utils.Panic

    import GHC.Unit.Module( Module )
    import GHC.Unit.Module.ModGuts
    import GHC.Unit.External

    {-
    ************************************************************************
    *                                                                      *
    \subsection[notes-Specialise]{Implementation notes [SLPJ, Aug 18 1993]}
    *                                                                      *
    ************************************************************************

    These notes describe how we implement specialisation to eliminate
    overloading.

    The specialisation pass works on Core
    syntax, complete with all the explicit dictionary application,
    abstraction and construction as added by the type checker.  The
    existing type checker remains largely as it is.

    One important thought: the {\em types} passed to an overloaded
    function, and the {\em dictionaries} passed are mutually redundant.
    If the same function is applied to the same type(s) then it is sure to
    be applied to the same dictionary(s)---or rather to the same {\em
    values}.  (The arguments might look different but they will evaluate
    to the same value.)

    Second important thought: we know that we can make progress by
    treating dictionary arguments as static and worth specialising on.  So
    we can do without binding-time analysis, and instead specialise on
    dictionary arguments and no others.

    The basic idea
    ~~~~~~~~~~~~~~
    Suppose we have

            let f = <f_rhs>
            in <body>

    and suppose f is overloaded.

    STEP 1: CALL-INSTANCE COLLECTION

    We traverse <body>, accumulating all applications of f to types and
    dictionaries.

    (Might there be partial applications, to just some of its types and
    dictionaries?  In principle yes, but in practice the type checker only
    builds applications of f to all its types and dictionaries, so partial
    applications could only arise as a result of transformation, and even
    then I think it's unlikely.  In any case, we simply don't accumulate such
    partial applications.)

    STEP 2: EQUIVALENCES

    So now we have a collection of calls to f:
            f t1 t2 d1 d2
            f t3 t4 d3 d4
            ...
    Notice that f may take several type arguments.  To avoid ambiguity, we
    say that f is called at type t1/t2 and t3/t4.

    We take equivalence classes using equality of the *types* (ignoring
    the dictionary args, which as mentioned previously are redundant).

    STEP 3: SPECIALISATION

    For each equivalence class, choose a representative (f t1 t2 d1 d2),
    and create a local instance of f, defined thus:

            f@t1/t2 = <f_rhs> t1 t2 d1 d2

    f_rhs presumably has some big lambdas and dictionary lambdas, so lots
    of simplification will now result.  However we don't actually *do* that
    simplification.  Rather, we leave it for the simplifier to do.  If we
    *did* do it, though, we'd get more call instances from the specialised
    RHS.  We can work out what they are by instantiating the call-instance
    set from f's RHS with the types t1, t2.

    Add this new id to f's IdInfo, to record that f has a specialised version.

    Before doing any of this, check that f's IdInfo doesn't already
    tell us about an existing instance of f at the required type/s.
    (This might happen if specialisation was applied more than once, or
    it might arise from user SPECIALIZE pragmas.)

    Recursion
    ~~~~~~~~~
    Wait a minute!  What if f is recursive?  Then we can't just plug in
    its right-hand side, can we?

    But it's ok.  The type checker *always* creates non-recursive definitions
    for overloaded recursive functions.  For example:

            f x = f (x+x)           -- Yes I know its silly

    becomes

            f a (d::Num a) = let p = +.sel a d
                             in
                             letrec fl (y::a) = fl (p y y)
                             in
                             fl

    We still have recursion for non-overloaded functions which we
    specialise, but the recursive call should get specialised to the
    same recursive version.

    Polymorphism 1
    ~~~~~~~~~~~~~~

    All this is crystal clear when the function is applied to *constant
    types*; that is, types which have no type variables inside.  But what if
    it is applied to non-constant types?  Suppose we find a call of f at type
    t1/t2.  There are two possibilities:

    (a) The free type variables of t1, t2 are in scope at the definition point
    of f.  In this case there's no problem, we proceed just as before.  A common
    example is as follows.  Here's the Haskell:

            g y = let f x = x+x
                  in f y + f y

    After typechecking we have

            g a (d::Num a) (y::a) = let f b (d'::Num b) (x::b) = +.sel b d' x x
                                    in +.sel a d (f a d y) (f a d y)

    Notice that the call to f is at type type "a"; a non-constant type.
    Both calls to f are at the same type, so we can specialise to give:

            g a (d::Num a) (y::a) = let f@a (x::a) = +.sel a d x x
                                    in +.sel a d (f@a y) (f@a y)

    (b) The other case is when the type variables in the instance types
    are *not* in scope at the definition point of f.  The example we are
    working with above is a good case.  There are two instances of (+.sel a d),
    but "a" is not in scope at the definition of +.sel.  Can we do anything?
    Yes, we can "common them up", a sort of limited common sub-expression deal.
    This would give:

            g a (d::Num a) (y::a) = let +.sel@a = +.sel a d
                                        f@a (x::a) = +.sel@a x x
                                    in +.sel@a (f@a y) (f@a y)

    This can save work, and can't be spotted by the type checker, because
    the two instances of +.sel weren't originally at the same type.

    Further notes on (b)

    * There are quite a few variations here.  For example, the defn of
      +.sel could be floated outside the \y, to attempt to gain laziness.
      It certainly mustn't be floated outside the \d because the d has to
      be in scope too.

    * We don't want to inline f_rhs in this case, because
    that will duplicate code.  Just commoning up the call is the point.

    * Nothing gets added to +.sel's IdInfo.

    * Don't bother unless the equivalence class has more than one item!

    Not clear whether this is all worth it.  It is of course OK to
    simply discard call-instances when passing a big lambda.

    Polymorphism 2 -- Overloading
    ~~~~~~~~~~~~~~
    Consider a function whose most general type is

            f :: forall a b. Ord a => [a] -> b -> b

    There is really no point in making a version of g at Int/Int and another
    at Int/Bool, because it's only instantiating the type variable "a" which
    buys us any efficiency. Since g is completely polymorphic in b there
    ain't much point in making separate versions of g for the different
    b types.

    That suggests that we should identify which of g's type variables
    are constrained (like "a") and which are unconstrained (like "b").
    Then when taking equivalence classes in STEP 2, we ignore the type args
    corresponding to unconstrained type variable.  In STEP 3 we make
    polymorphic versions.  Thus:

            f@t1/ = /\b -> <f_rhs> t1 b d1 d2

    We do this.

    Dictionary floating
    ~~~~~~~~~~~~~~~~~~~
    Consider this

            f a (d::Num a) = let g = ...
                             in
                             ...(let d1::Ord a = Num.Ord.sel a d in g a d1)...

    Here, g is only called at one type, but the dictionary isn't in scope at the
    definition point for g.  Usually the type checker would build a
    definition for d1 which enclosed g, but the transformation system
    might have moved d1's defn inward.  Solution: float dictionary bindings
    outwards along with call instances.

    Consider

            f x = let g p q = p==q
                      h r s = (r+s, g r s)
                  in
                  h x x

    Before specialisation, leaving out type abstractions we have

            f df x = let g :: Eq a => a -> a -> Bool
                         g dg p q = == dg p q
                         h :: Num a => a -> a -> (a, Bool)
                         h dh r s = let deq = eqFromNum dh
                                    in (+ dh r s, g deq r s)
                  in
                  h df x x

    After specialising h we get a specialised version of h, like this:

                        h' r s = let deq = eqFromNum df
                                 in (+ df r s, g deq r s)

    But we can't naively make an instance for g from this, because deq is not in scope
    at the defn of g.  Instead, we have to float out the (new) defn of deq
    to widen its scope.  Notice that this floating can't be done in advance -- it only
    shows up when specialisation is done.

    User SPECIALIZE pragmas
    ~~~~~~~~~~~~~~~~~~~~~~~
    Specialisation pragmas can be digested by the type checker, and implemented
    by adding extra definitions along with that of f, in the same way as before

            f@t1/t2 = <f_rhs> t1 t2 d1 d2

    Indeed the pragmas *have* to be dealt with by the type checker, because
    only it knows how to build the dictionaries d1 and d2!  For example

            g :: Ord a => [a] -> [a]
            {-# SPECIALIZE f :: [Tree Int] -> [Tree Int] #-}

    Here, the specialised version of g is an application of g's rhs to the
    Ord dictionary for (Tree Int), which only the type checker can conjure
    up.  There might not even *be* one, if (Tree Int) is not an instance of
    Ord!  (All the other specialision has suitable dictionaries to hand
    from actual calls.)

    Problem.  The type checker doesn't have to hand a convenient <f_rhs>, because
    it is buried in a complex (as-yet-un-desugared) binding group.
    Maybe we should say

            f@t1/t2 = f* t1 t2 d1 d2

    where f* is the Id f with an IdInfo which says "inline me regardless!".
    Indeed all the specialisation could be done in this way.
    That in turn means that the simplifier has to be prepared to inline absolutely
    any in-scope let-bound thing.

    Again, the pragma should permit polymorphism in unconstrained variables:

            h :: Ord a => [a] -> b -> b
            {-# SPECIALIZE h :: [Int] -> b -> b #-}

    We *insist* that all overloaded type variables are specialised to ground types,
    (and hence there can be no context inside a SPECIALIZE pragma).
    We *permit* unconstrained type variables to be specialised to
            - a ground type
            - or left as a polymorphic type variable
    but nothing in between.  So

            {-# SPECIALIZE h :: [Int] -> [c] -> [c] #-}

    is *illegal*.  (It can be handled, but it adds complication, and gains the
    programmer nothing.)

    SPECIALISING INSTANCE DECLARATIONS
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider

            instance Foo a => Foo [a] where
                    ...
            {-# SPECIALIZE instance Foo [Int] #-}

    The original instance decl creates a dictionary-function
    definition:

            dfun.Foo.List :: forall a. Foo a -> Foo [a]

    The SPECIALIZE pragma just makes a specialised copy, just as for
    ordinary function definitions:

            dfun.Foo.List@Int :: Foo [Int]
            dfun.Foo.List@Int = dfun.Foo.List Int dFooInt

    The information about what instance of the dfun exist gets added to
    the dfun's IdInfo in the same way as a user-defined function too.

    Automatic instance decl specialisation?
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Can instance decls be specialised automatically?  It's tricky.
    We could collect call-instance information for each dfun, but
    then when we specialised their bodies we'd get new call-instances
    for ordinary functions; and when we specialised their bodies, we might get
    new call-instances of the dfuns, and so on.  This all arises because of
    the unrestricted mutual recursion between instance decls and value decls.

    Still, there's no actual problem; it just means that we may not do all
    the specialisation we could theoretically do.

    Furthermore, instance decls are usually exported and used non-locally,
    so we'll want to compile enough to get those specialisations done.

    Lastly, there's no such thing as a local instance decl, so we can
    survive solely by spitting out *usage* information, and then reading that
    back in as a pragma when next compiling the file.  So for now,
    we only specialise instance decls in response to pragmas.

    SPITTING OUT USAGE INFORMATION
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    To spit out usage information we need to traverse the code collecting
    call-instance information for all imported (non-prelude?) functions
    and data types. Then we equivalence-class it and spit it out.

    This is done at the top-level when all the call instances which escape
    must be for imported functions and data types.

    *** Not currently done ***

    Partial specialisation by pragmas
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    What about partial specialisation:

            k :: (Ord a, Eq b) => [a] -> b -> b -> [a]
            {-# SPECIALIZE k :: Eq b => [Int] -> b -> b -> [a] #-}

    or even

            {-# SPECIALIZE k :: Eq b => [Int] -> [b] -> [b] -> [a] #-}

    Seems quite reasonable.  Similar things could be done with instance decls:

            instance (Foo a, Foo b) => Foo (a,b) where
                    ...
            {-# SPECIALIZE instance Foo a => Foo (a,Int) #-}
            {-# SPECIALIZE instance Foo b => Foo (Int,b) #-}

    Ho hum.  Things are complex enough without this.  I pass.

    Requirements for the simplifier
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    The simplifier has to be able to take advantage of the specialisation.

    * When the simplifier finds an application of a polymorphic f, it looks in
    f's IdInfo in case there is a suitable instance to call instead.  This converts

            f t1 t2 d1 d2   ===>   f_t1_t2

    Note that the dictionaries get eaten up too!

    * Dictionary selection operations on constant dictionaries must be
      short-circuited:

            +.sel Int d     ===>  +Int

    The obvious way to do this is in the same way as other specialised
    calls: +.sel has inside it some IdInfo which tells that if it's applied
    to the type Int then it should eat a dictionary and transform to +Int.

    In short, dictionary selectors need IdInfo inside them for constant
    methods.

    * Exactly the same applies if a superclass dictionary is being
      extracted:

            Eq.sel Int d   ===>   dEqInt

    * Something similar applies to dictionary construction too.  Suppose
    dfun.Eq.List is the function taking a dictionary for (Eq a) to
    one for (Eq [a]).  Then we want

            dfun.Eq.List Int d      ===> dEq.List_Int

    Where does the Eq [Int] dictionary come from?  It is built in
    response to a SPECIALIZE pragma on the Eq [a] instance decl.

    In short, dfun Ids need IdInfo with a specialisation for each
    constant instance of their instance declaration.

    All this uses a single mechanism: the SpecEnv inside an Id

    What does the specialisation IdInfo look like?
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    The SpecEnv of an Id maps a list of types (the template) to an expression

            [Type]  |->  Expr

    For example, if f has this RuleInfo:

            [Int, a]  ->  \d:Ord Int. f' a

    it means that we can replace the call

            f Int t  ===>  (\d. f' t)

    This chucks one dictionary away and proceeds with the
    specialised version of f, namely f'.

    What can't be done this way?
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    There is no way, post-typechecker, to get a dictionary for (say)
    Eq a from a dictionary for Eq [a].  So if we find

            ==.sel [t] d

    we can't transform to

            eqList (==.sel t d')

    where
            eqList :: (a->a->Bool) -> [a] -> [a] -> Bool

    Of course, we currently have no way to automatically derive
    eqList, nor to connect it to the Eq [a] instance decl, but you
    can imagine that it might somehow be possible.  Taking advantage
    of this is permanently ruled out.

    Still, this is no great hardship, because we intend to eliminate
    overloading altogether anyway!

    A note about non-tyvar dictionaries
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Some Ids have types like

            forall a,b,c. Eq a -> Ord [a] -> tau

    This seems curious at first, because we usually only have dictionary
    args whose types are of the form (C a) where a is a type variable.
    But this doesn't hold for the functions arising from instance decls,
    which sometimes get arguments with types of form (C (T a)) for some
    type constructor T.

    Should we specialise wrt this compound-type dictionary?  We used to say
    "no", saying:
            "This is a heuristic judgement, as indeed is the fact that we
            specialise wrt only dictionaries.  We choose *not* to specialise
            wrt compound dictionaries because at the moment the only place
            they show up is in instance decls, where they are simply plugged
            into a returned dictionary.  So nothing is gained by specialising
            wrt them."

    But it is simpler and more uniform to specialise wrt these dicts too;
    and in future GHC is likely to support full fledged type signatures
    like
            f :: Eq [(a,b)] => ...

    ************************************************************************
    *                                                                      *
    \subsubsection{The new specialiser}
    *                                                                      *
    ************************************************************************

    Our basic game plan is this.  For let(rec) bound function
            f :: (C a, D c) => (a,b,c,d) -> Bool

    * Find any specialised calls of f, (f ts ds), where
      ts are the type arguments t1 .. t4, and
      ds are the dictionary arguments d1 .. d2.

    * Add a new definition for f1 (say):

            f1 = /\ b d -> (..body of f..) t1 b t3 d d1 d2

      Note that we abstract over the unconstrained type arguments.

    * Add the mapping

            [t1,b,t3,d]  |->  \d1 d2 -> f1 b d

      to the specialisations of f.  This will be used by the
      simplifier to replace calls
                    (f t1 t2 t3 t4) da db
      by
                    (\d1 d1 -> f1 t2 t4) da db

      All the stuff about how many dictionaries to discard, and what types
      to apply the specialised function to, are handled by the fact that the
      SpecEnv contains a template for the result of the specialisation.

    We don't build *partial* specialisations for f.  For example:

      f :: Eq a => a -> a -> Bool
      {-# SPECIALISE f :: (Eq b, Eq c) => (b,c) -> (b,c) -> Bool #-}

    Here, little is gained by making a specialised copy of f.
    There's a distinct danger that the specialised version would
    first build a dictionary for (Eq b, Eq c), and then select the (==)
    method from it!  Even if it didn't, not a great deal is saved.

    We do, however, generate polymorphic, but not overloaded, specialisations:

      f :: Eq a => [a] -> b -> b -> b
      ... SPECIALISE f :: [Int] -> b -> b -> b ...

    Hence, the invariant is this:

            *** no specialised version is overloaded ***

    ************************************************************************
    *                                                                      *
    \subsubsection{The exported function}
    *                                                                      *
    ************************************************************************
    -}

    -- | Specialise calls to type-class overloaded functions occurring in a program.
    specProgram :: ModGuts -> CoreM ModGuts
    specProgram :: ModGuts -> CoreM ModGuts
    specProgram guts :: ModGuts
    guts@(ModGuts { mg_module :: ModGuts -> Module
    mg_module = Module
    this_mod
                              , mg_rules :: ModGuts -> [CoreRule]
    mg_rules = [CoreRule]
    local_rules
                              , mg_binds :: ModGuts -> CoreProgram
    mg_binds = CoreProgram
    binds })
      = do { DynFlags
    dflags <- CoreM DynFlags
    forall (m :: * -> *). HasDynFlags m => m DynFlags
    getDynFlags

                  -- We need to start with a Subst that knows all the things
                  -- that are in scope, so that the substitution engine doesn't
                  -- accidentally re-use a unique that's already in use
                  -- Easiest thing is to do it all at once, as if all the top-level
                  -- decls were mutually recursive
           ; let top_env :: SpecEnv
    top_env = SE { se_subst :: Subst
    se_subst = InScopeSet -> Subst
    Core.mkEmptySubst (InScopeSet -> Subst) -> InScopeSet -> Subst
    forall a b. (a -> b) -> a -> b
    $ VarSet -> InScopeSet
    mkInScopeSet (VarSet -> InScopeSet) -> VarSet -> InScopeSet
    forall a b. (a -> b) -> a -> b
    $ [Id] -> VarSet
    mkVarSet ([Id] -> VarSet) -> [Id] -> VarSet
    forall a b. (a -> b) -> a -> b
    $
                                           CoreProgram -> [Id]
    forall b. [Bind b] -> [b]
    bindersOfBinds CoreProgram
    binds
                              , se_interesting :: VarSet
    se_interesting = VarSet
    emptyVarSet
                              , se_module :: Module
    se_module = Module
    this_mod
                              , se_dflags :: DynFlags
    se_dflags = DynFlags
    dflags }

                 go :: CoreProgram -> UniqSM (CoreProgram, UsageDetails)
    go []           = (CoreProgram, UsageDetails) -> UniqSM (CoreProgram, UsageDetails)
    forall (m :: * -> *) a. Monad m => a -> m a
    return ([], UsageDetails
    emptyUDs)
                 go (CoreBind
    bind:CoreProgram
    binds) = do (CoreProgram
    binds', UsageDetails
    uds) <- CoreProgram -> UniqSM (CoreProgram, UsageDetails)
    go CoreProgram
    binds
                                      (CoreProgram
    bind', UsageDetails
    uds') <- SpecEnv
    -> CoreBind -> UsageDetails -> UniqSM (CoreProgram, UsageDetails)
    specBind SpecEnv
    top_env CoreBind
    bind UsageDetails
    uds
                                      (CoreProgram, UsageDetails) -> UniqSM (CoreProgram, UsageDetails)
    forall (m :: * -> *) a. Monad m => a -> m a
    return (CoreProgram
    bind' CoreProgram -> CoreProgram -> CoreProgram
    forall a. [a] -> [a] -> [a]
    ++ CoreProgram
    binds', UsageDetails
    uds')

                 -- Specialise the bindings of this module
           ; (CoreProgram
    binds', UsageDetails
    uds) <- UniqSM (CoreProgram, UsageDetails)
    -> CoreM (CoreProgram, UsageDetails)
    forall a. SpecM a -> CoreM a
    runSpecM (CoreProgram -> UniqSM (CoreProgram, UsageDetails)
    go CoreProgram
    binds)

           ; ([CoreRule]
    spec_rules, CoreProgram
    spec_binds) <- SpecEnv
    -> [CoreRule] -> UsageDetails -> CoreM ([CoreRule], CoreProgram)
    specImports SpecEnv
    top_env [CoreRule]
    local_rules UsageDetails
    uds

           ; ModGuts -> CoreM ModGuts
    forall (m :: * -> *) a. Monad m => a -> m a
    return (ModGuts
    guts { mg_binds :: CoreProgram
    mg_binds = CoreProgram
    spec_binds CoreProgram -> CoreProgram -> CoreProgram
    forall a. [a] -> [a] -> [a]
    ++ CoreProgram
    binds'
                          , mg_rules :: [CoreRule]
    mg_rules = [CoreRule]
    spec_rules [CoreRule] -> [CoreRule] -> [CoreRule]
    forall a. [a] -> [a] -> [a]
    ++ [CoreRule]
    local_rules }) }

    {-
    Note [Wrap bindings returned by specImports]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    'specImports' returns a set of specialized bindings. However, these are lacking
    necessary floated dictionary bindings, which are returned by
    UsageDetails(ud_binds). These dictionaries need to be brought into scope with
    'wrapDictBinds' before the bindings returned by 'specImports' can be used. See,
    for instance, the 'specImports' call in 'specProgram'.

    Note [Disabling cross-module specialisation]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Since GHC 7.10 we have performed specialisation of INLINABLE bindings living
    in modules outside of the current module. This can sometimes uncover user code
    which explodes in size when aggressively optimized. The
    -fno-cross-module-specialise option was introduced to allow users to being
    bitten by such instances to revert to the pre-7.10 behavior.

    See #10491
    -}

    {- *********************************************************************
    *                                                                      *
                       Specialising imported functions
    *                                                                      *
    ********************************************************************* -}

    specImports :: SpecEnv
                -> [CoreRule]
                -> UsageDetails
                -> CoreM ([CoreRule], [CoreBind])
    specImports :: SpecEnv
    -> [CoreRule] -> UsageDetails -> CoreM ([CoreRule], CoreProgram)
    specImports SpecEnv
    top_env [CoreRule]
    local_rules
                (MkUD { ud_binds :: UsageDetails -> Bag DictBind
    ud_binds = Bag DictBind
    dict_binds, ud_calls :: UsageDetails -> CallDetails
    ud_calls = CallDetails
    calls })
      | Bool -> Bool
    not (Bool -> Bool) -> Bool -> Bool
    forall a b. (a -> b) -> a -> b
    $ GeneralFlag -> DynFlags -> Bool
    gopt GeneralFlag
    Opt_CrossModuleSpecialise (SpecEnv -> DynFlags
    se_dflags SpecEnv
    top_env)
        -- See Note [Disabling cross-module specialisation]
      = ([CoreRule], CoreProgram) -> CoreM ([CoreRule], CoreProgram)
    forall (m :: * -> *) a. Monad m => a -> m a
    return ([], Bag DictBind -> CoreProgram -> CoreProgram
    wrapDictBinds Bag DictBind
    dict_binds [])

      | Bool
    otherwise
      = do { RuleBase
    hpt_rules <- CoreM RuleBase
    getRuleBase
           ; let rule_base :: RuleBase
    rule_base = RuleBase -> [CoreRule] -> RuleBase
    extendRuleBaseList RuleBase
    hpt_rules [CoreRule]
    local_rules

           ; ([CoreRule]
    spec_rules, CoreProgram
    spec_binds) <- SpecEnv
    -> [Id]
    -> RuleBase
    -> Bag DictBind
    -> CallDetails
    -> CoreM ([CoreRule], CoreProgram)
    spec_imports SpecEnv
    top_env [] RuleBase
    rule_base
                                                      Bag DictBind
    dict_binds CallDetails
    calls

                 -- Don't forget to wrap the specialized bindings with
                 -- bindings for the needed dictionaries.
                 -- See Note [Wrap bindings returned by specImports]
                 -- and Note [Glom the bindings if imported functions are specialised]
           ; let final_binds :: CoreProgram
    final_binds
                   | CoreProgram -> Bool
    forall (t :: * -> *) a. Foldable t => t a -> Bool
    null CoreProgram
    spec_binds = Bag DictBind -> CoreProgram -> CoreProgram
    wrapDictBinds Bag DictBind
    dict_binds []
                   | Bool
    otherwise       = [[(Id, CoreExpr)] -> CoreBind
    forall b. [(b, Expr b)] -> Bind b
    Rec ([(Id, CoreExpr)] -> CoreBind) -> [(Id, CoreExpr)] -> CoreBind
    forall a b. (a -> b) -> a -> b
    $ CoreProgram -> [(Id, CoreExpr)]
    forall b. [Bind b] -> [(b, Expr b)]
    flattenBinds (CoreProgram -> [(Id, CoreExpr)])
    -> CoreProgram -> [(Id, CoreExpr)]
    forall a b. (a -> b) -> a -> b
    $
                                        Bag DictBind -> CoreProgram -> CoreProgram
    wrapDictBinds Bag DictBind
    dict_binds CoreProgram
    spec_binds]

           ; ([CoreRule], CoreProgram) -> CoreM ([CoreRule], CoreProgram)
    forall (m :: * -> *) a. Monad m => a -> m a
    return ([CoreRule]
    spec_rules, CoreProgram
    final_binds)
        }

    -- | Specialise a set of calls to imported bindings
    spec_imports :: SpecEnv          -- Passed in so that all top-level Ids are in scope
                 -> [Id]             -- Stack of imported functions being specialised
                                     -- See Note [specImport call stack]
                 -> RuleBase         -- Rules from this module and the home package
                                     -- (but not external packages, which can change)
                 -> Bag DictBind     -- Dict bindings, used /only/ for filterCalls
                                     -- See Note [Avoiding loops in specImports]
                 -> CallDetails      -- Calls for imported things
                 -> CoreM ( [CoreRule]   -- New rules
                          , [CoreBind] ) -- Specialised bindings
    spec_imports :: SpecEnv
    -> [Id]
    -> RuleBase
    -> Bag DictBind
    -> CallDetails
    -> CoreM ([CoreRule], CoreProgram)
    spec_imports SpecEnv
    top_env [Id]
    callers RuleBase
    rule_base Bag DictBind
    dict_binds CallDetails
    calls
      = do { let import_calls :: [CallInfoSet]
    import_calls = CallDetails -> [CallInfoSet]
    forall a. DVarEnv a -> [a]
    dVarEnvElts CallDetails
    calls
           -- ; debugTraceMsg (text "specImports {" <+>
           --                  vcat [ text "calls:" <+> ppr import_calls
           --                       , text "dict_binds:" <+> ppr dict_binds ])
           ; ([CoreRule]
    rules, CoreProgram
    spec_binds) <- RuleBase -> [CallInfoSet] -> CoreM ([CoreRule], CoreProgram)
    go RuleBase
    rule_base [CallInfoSet]
    import_calls
           -- ; debugTraceMsg (text "End specImports }" <+> ppr import_calls)

           ; ([CoreRule], CoreProgram) -> CoreM ([CoreRule], CoreProgram)
    forall (m :: * -> *) a. Monad m => a -> m a
    return ([CoreRule]
    rules, CoreProgram
    spec_binds) }
      where
        go :: RuleBase -> [CallInfoSet] -> CoreM ([CoreRule], [CoreBind])
        go :: RuleBase -> [CallInfoSet] -> CoreM ([CoreRule], CoreProgram)
    go RuleBase
    _ [] = ([CoreRule], CoreProgram) -> CoreM ([CoreRule], CoreProgram)
    forall (m :: * -> *) a. Monad m => a -> m a
    return ([], [])
        go RuleBase
    rb (CallInfoSet
    cis : [CallInfoSet]
    other_calls)
          = do { -- debugTraceMsg (text "specImport {" <+> ppr cis)
               ; ([CoreRule]
    rules1, CoreProgram
    spec_binds1) <- SpecEnv
    -> [Id]
    -> RuleBase
    -> Bag DictBind
    -> CallInfoSet
    -> CoreM ([CoreRule], CoreProgram)
    spec_import SpecEnv
    top_env [Id]
    callers RuleBase
    rb Bag DictBind
    dict_binds CallInfoSet
    cis
               -- ; debugTraceMsg (text "specImport }" <+> ppr cis)

               ; ([CoreRule]
    rules2, CoreProgram
    spec_binds2) <- RuleBase -> [CallInfoSet] -> CoreM ([CoreRule], CoreProgram)
    go (RuleBase -> [CoreRule] -> RuleBase
    extendRuleBaseList RuleBase
    rb [CoreRule]
    rules1) [CallInfoSet]
    other_calls
               ; ([CoreRule], CoreProgram) -> CoreM ([CoreRule], CoreProgram)
    forall (m :: * -> *) a. Monad m => a -> m a
    return ([CoreRule]
    rules1 [CoreRule] -> [CoreRule] -> [CoreRule]
    forall a. [a] -> [a] -> [a]
    ++ [CoreRule]
    rules2, CoreProgram
    spec_binds1 CoreProgram -> CoreProgram -> CoreProgram
    forall a. [a] -> [a] -> [a]
    ++ CoreProgram
    spec_binds2) }

    spec_import :: SpecEnv               -- Passed in so that all top-level Ids are in scope
                -> [Id]                  -- Stack of imported functions being specialised
                                         -- See Note [specImport call stack]
                -> RuleBase              -- Rules from this module
                -> Bag DictBind          -- Dict bindings, used /only/ for filterCalls
                                         -- See Note [Avoiding loops in specImports]
                -> CallInfoSet           -- Imported function and calls for it
                -> CoreM ( [CoreRule]    -- New rules
                         , [CoreBind] )  -- Specialised bindings
    spec_import :: SpecEnv
    -> [Id]
    -> RuleBase
    -> Bag DictBind
    -> CallInfoSet
    -> CoreM ([CoreRule], CoreProgram)
    spec_import SpecEnv
    top_env [Id]
    callers RuleBase
    rb Bag DictBind
    dict_binds cis :: CallInfoSet
    cis@(CIS Id
    fn Bag CallInfo
    _)
      | String -> Id -> [Id] -> Bool
    forall a. Eq a => String -> a -> [a] -> Bool
    isIn String
    "specImport" Id
    fn [Id]
    callers
      = ([CoreRule], CoreProgram) -> CoreM ([CoreRule], CoreProgram)
    forall (m :: * -> *) a. Monad m => a -> m a
    return ([], [])     -- No warning.  This actually happens all the time
                            -- when specialising a recursive function, because
                            -- the RHS of the specialised function contains a recursive
                            -- call to the original function

      | [CallInfo] -> Bool
    forall (t :: * -> *) a. Foldable t => t a -> Bool
    null [CallInfo]
    good_calls
      = ([CoreRule], CoreProgram) -> CoreM ([CoreRule], CoreProgram)
    forall (m :: * -> *) a. Monad m => a -> m a
    return ([], [])

      | Just CoreExpr
    rhs <- DynFlags -> Id -> Maybe CoreExpr
    canSpecImport DynFlags
    dflags Id
    fn
      = do {     -- Get rules from the external package state
                 -- We keep doing this in case we "page-fault in"
                 -- more rules as we go along
           ; HscEnv
    hsc_env <- CoreM HscEnv
    getHscEnv
           ; ExternalPackageState
    eps <- IO ExternalPackageState -> CoreM ExternalPackageState
    forall (m :: * -> *) a. MonadIO m => IO a -> m a
    liftIO (IO ExternalPackageState -> CoreM ExternalPackageState)
    -> IO ExternalPackageState -> CoreM ExternalPackageState
    forall a b. (a -> b) -> a -> b
    $ HscEnv -> IO ExternalPackageState
    hscEPS HscEnv
    hsc_env
           ; ModuleSet
    vis_orphs <- CoreM ModuleSet
    getVisibleOrphanMods
           ; let full_rb :: RuleBase
    full_rb = RuleBase -> RuleBase -> RuleBase
    unionRuleBase RuleBase
    rb (ExternalPackageState -> RuleBase
    eps_rule_base ExternalPackageState
    eps)
                 rules_for_fn :: [CoreRule]
    rules_for_fn = RuleEnv -> Id -> [CoreRule]
    getRules (RuleBase -> ModuleSet -> RuleEnv
    RuleEnv RuleBase
    full_rb ModuleSet
    vis_orphs) Id
    fn

           ; ([CoreRule]
    rules1, [(Id, CoreExpr)]
    spec_pairs, MkUD { ud_binds :: UsageDetails -> Bag DictBind
    ud_binds = Bag DictBind
    dict_binds1, ud_calls :: UsageDetails -> CallDetails
    ud_calls = CallDetails
    new_calls })
                <- -- debugTraceMsg (text "specImport1" <+> vcat [ppr fn, ppr good_calls, ppr rhs]) >>
                    (SpecM ([CoreRule], [(Id, CoreExpr)], UsageDetails)
    -> CoreM ([CoreRule], [(Id, CoreExpr)], UsageDetails)
    forall a. SpecM a -> CoreM a
    runSpecM (SpecM ([CoreRule], [(Id, CoreExpr)], UsageDetails)
     -> CoreM ([CoreRule], [(Id, CoreExpr)], UsageDetails))
    -> SpecM ([CoreRule], [(Id, CoreExpr)], UsageDetails)
    -> CoreM ([CoreRule], [(Id, CoreExpr)], UsageDetails)
    forall a b. (a -> b) -> a -> b
    $ Bool
    -> SpecEnv
    -> [CoreRule]
    -> [CallInfo]
    -> Id
    -> CoreExpr
    -> SpecM ([CoreRule], [(Id, CoreExpr)], UsageDetails)
    specCalls Bool
    True SpecEnv
    top_env [CoreRule]
    rules_for_fn [CallInfo]
    good_calls Id
    fn CoreExpr
    rhs)
           ; let spec_binds1 :: CoreProgram
    spec_binds1 = [Id -> CoreExpr -> CoreBind
    forall b. b -> Expr b -> Bind b
    NonRec Id
    b CoreExpr
    r | (Id
    b,CoreExpr
    r) <- [(Id, CoreExpr)]
    spec_pairs]
                 -- After the rules kick in we may get recursion, but
                 -- we rely on a global GlomBinds to sort that out later
                 -- See Note [Glom the bindings if imported functions are specialised]

                  -- Now specialise any cascaded calls
           -- ; debugTraceMsg (text "specImport 2" <+> (ppr fn $$ ppr rules1 $$ ppr spec_binds1))
           ; ([CoreRule]
    rules2, CoreProgram
    spec_binds2) <- SpecEnv
    -> [Id]
    -> RuleBase
    -> Bag DictBind
    -> CallDetails
    -> CoreM ([CoreRule], CoreProgram)
    spec_imports SpecEnv
    top_env
                                                   (Id
    fnId -> [Id] -> [Id]
    forall a. a -> [a] -> [a]
    :[Id]
    callers)
                                                   (RuleBase -> [CoreRule] -> RuleBase
    extendRuleBaseList RuleBase
    rb [CoreRule]
    rules1)
                                                   (Bag DictBind
    dict_binds Bag DictBind -> Bag DictBind -> Bag DictBind
    forall a. Bag a -> Bag a -> Bag a
    `unionBags` Bag DictBind
    dict_binds1)
                                                   CallDetails
    new_calls

           ; let final_binds :: CoreProgram
    final_binds = Bag DictBind -> CoreProgram -> CoreProgram
    wrapDictBinds Bag DictBind
    dict_binds1 (CoreProgram -> CoreProgram) -> CoreProgram -> CoreProgram
    forall a b. (a -> b) -> a -> b
    $
                               CoreProgram
    spec_binds2 CoreProgram -> CoreProgram -> CoreProgram
    forall a. [a] -> [a] -> [a]
    ++ CoreProgram
    spec_binds1

           ; ([CoreRule], CoreProgram) -> CoreM ([CoreRule], CoreProgram)
    forall (m :: * -> *) a. Monad m => a -> m a
    return ([CoreRule]
    rules2 [CoreRule] -> [CoreRule] -> [CoreRule]
    forall a. [a] -> [a] -> [a]
    ++ [CoreRule]
    rules1, CoreProgram
    final_binds) }

      | Bool
    otherwise
      = do { DynFlags -> [Id] -> Id -> [CallInfo] -> CoreM ()
    tryWarnMissingSpecs DynFlags
    dflags [Id]
    callers Id
    fn [CallInfo]
    good_calls
           ; ([CoreRule], CoreProgram) -> CoreM ([CoreRule], CoreProgram)
    forall (m :: * -> *) a. Monad m => a -> m a
    return ([], [])}

      where
        dflags :: DynFlags
    dflags = SpecEnv -> DynFlags
    se_dflags SpecEnv
    top_env
        good_calls :: [CallInfo]
    good_calls = CallInfoSet -> Bag DictBind -> [CallInfo]
    filterCalls CallInfoSet
    cis Bag DictBind
    dict_binds
           -- SUPER IMPORTANT!  Drop calls that (directly or indirectly) refer to fn
           -- See Note [Avoiding loops in specImports]

    canSpecImport :: DynFlags -> Id -> Maybe CoreExpr
    -- See Note [Specialise imported INLINABLE things]
    canSpecImport :: DynFlags -> Id -> Maybe CoreExpr
    canSpecImport DynFlags
    dflags Id
    fn
      | CoreUnfolding { uf_src :: Unfolding -> UnfoldingSource
    uf_src = UnfoldingSource
    src, uf_tmpl :: Unfolding -> CoreExpr
    uf_tmpl = CoreExpr
    rhs } <- Unfolding
    unf
      , UnfoldingSource -> Bool
    isStableSource UnfoldingSource
    src
      = CoreExpr -> Maybe CoreExpr
    forall a. a -> Maybe a
    Just CoreExpr
    rhs   -- By default, specialise only imported things that have a stable
                   -- unfolding; that is, have an INLINE or INLINABLE pragma
                   -- Specialise even INLINE things; it hasn't inlined yet,
                   -- so perhaps it never will.  Moreover it may have calls
                   -- inside it that we want to specialise

        -- CoreUnfolding case does /not/ include DFunUnfoldings;
        -- We only specialise DFunUnfoldings with -fspecialise-aggressively
        -- See Note [Do not specialise imported DFuns]

      | GeneralFlag -> DynFlags -> Bool
    gopt GeneralFlag
    Opt_SpecialiseAggressively DynFlags
    dflags
      = Unfolding -> Maybe CoreExpr
    maybeUnfoldingTemplate Unfolding
    unf  -- With -fspecialise-aggressively, specialise anything
                                    -- with an unfolding, stable or not, DFun or not

      | Bool
    otherwise = Maybe CoreExpr
    forall a. Maybe a
    Nothing
      where
        unf :: Unfolding
    unf = Id -> Unfolding
    realIdUnfolding Id
    fn   -- We want to see the unfolding even for loop breakers

    -- | Returns whether or not to show a missed-spec warning.
    -- If -Wall-missed-specializations is on, show the warning.
    -- Otherwise, if -Wmissed-specializations is on, only show a warning
    -- if there is at least one imported function being specialized,
    -- and if all imported functions are marked with an inline pragma
    -- Use the most specific warning as the reason.
    tryWarnMissingSpecs :: DynFlags -> [Id] -> Id -> [CallInfo] -> CoreM ()
    -- See Note [Warning about missed specialisations]
    tryWarnMissingSpecs :: DynFlags -> [Id] -> Id -> [CallInfo] -> CoreM ()
    tryWarnMissingSpecs DynFlags
    dflags [Id]
    callers Id
    fn [CallInfo]
    calls_for_fn
      | WarningFlag -> DynFlags -> Bool
    wopt WarningFlag
    Opt_WarnMissedSpecs DynFlags
    dflags
        Bool -> Bool -> Bool
    && Bool -> Bool
    not ([Id] -> Bool
    forall (t :: * -> *) a. Foldable t => t a -> Bool
    null [Id]
    callers)
        Bool -> Bool -> Bool
    && Bool
    allCallersInlined                  = WarnReason -> CoreM ()
    doWarn (WarnReason -> CoreM ()) -> WarnReason -> CoreM ()
    forall a b. (a -> b) -> a -> b
    $ WarningFlag -> WarnReason
    Reason WarningFlag
    Opt_WarnMissedSpecs
      | WarningFlag -> DynFlags -> Bool
    wopt WarningFlag
    Opt_WarnAllMissedSpecs DynFlags
    dflags    = WarnReason -> CoreM ()
    doWarn (WarnReason -> CoreM ()) -> WarnReason -> CoreM ()
    forall a b. (a -> b) -> a -> b
    $ WarningFlag -> WarnReason
    Reason WarningFlag
    Opt_WarnAllMissedSpecs
      | Bool
    otherwise                             = () -> CoreM ()
    forall (m :: * -> *) a. Monad m => a -> m a
    return ()
      where
        allCallersInlined :: Bool
    allCallersInlined = (Id -> Bool) -> [Id] -> Bool
    forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
    all (InlinePragma -> Bool
    isAnyInlinePragma (InlinePragma -> Bool) -> (Id -> InlinePragma) -> Id -> Bool
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . Id -> InlinePragma
    idInlinePragma) [Id]
    callers
        doWarn :: WarnReason -> CoreM ()
    doWarn WarnReason
    reason =
          WarnReason -> SDoc -> CoreM ()
    warnMsg WarnReason
    reason
            ([SDoc] -> SDoc
    vcat [ SDoc -> Int -> SDoc -> SDoc
    hang (String -> SDoc
    text (String
    "Could not specialise imported function") SDoc -> SDoc -> SDoc
    <+> SDoc -> SDoc
    quotes (Id -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Id
    fn))
                    Int
    2 ([SDoc] -> SDoc
    vcat [ String -> SDoc
    text String
    "when specialising" SDoc -> SDoc -> SDoc
    <+> SDoc -> SDoc
    quotes (Id -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Id
    caller)
                            | Id
    caller <- [Id]
    callers])
              , SDoc -> SDoc
    whenPprDebug (String -> SDoc
    text String
    "calls:" SDoc -> SDoc -> SDoc
    <+> [SDoc] -> SDoc
    vcat ((CallInfo -> SDoc) -> [CallInfo] -> [SDoc]
    forall a b. (a -> b) -> [a] -> [b]
    map (Id -> CallInfo -> SDoc
    pprCallInfo Id
    fn) [CallInfo]
    calls_for_fn))
              , String -> SDoc
    text String
    "Probable fix: add INLINABLE pragma on" SDoc -> SDoc -> SDoc
    <+> SDoc -> SDoc
    quotes (Id -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Id
    fn) ])

    {- Note [Do not specialise imported DFuns]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Ticket #18223 shows that specialising calls of DFuns is can cause a huge
    and entirely unnecessary blowup in program size.  Consider a call to
        f @[[[[[[[[T]]]]]]]] d1 x
    where df :: C a => C [a]
          d1 :: C [[[[[[[[T]]]]]]]] = dfC[] @[[[[[[[T]]]]]]] d1
          d2 :: C [[[[[[[T]]]]]]]   = dfC[] @[[[[[[T]]]]]] d3
          ...
    Now we'll specialise f's RHS, which may give rise to calls to 'g',
    also overloaded, which we will specialise, and so on.  However, if
    we specialise the calls to dfC[], we'll generate specialised copies of
    all methods of C, at all types; and the same for C's superclasses.

    And many of these specialised functions will never be called.  We are
    going to call the specialised 'f', and the specialised 'g', but DFuns
    group functions into a tuple, many of whose elements may never be used.

    With deeply-nested types this can lead to a simply overwhelming number
    of specialisations: see #18223 for a simple example (from the wild).
    I measured the number of specialisations for various numbers of calls
    of `flip evalStateT ()`, and got this

                           Size after one simplification
      #calls    #SPEC rules    Terms     Types
          5         56          3100     10600
          9        108         13660     77206

    The real tests case has 60+ calls, which blew GHC out of the water.

    Solution: don't specialise DFuns.  The downside is that if we end
    up with (h (dfun d)), /and/ we don't specialise 'h', then we won't
    pass to 'h' a tuple of specialised functions.

    However, the flag -fspecialise-aggressively (experimental, off by default)
    allows DFuns to specialise as well.

    Note [Avoiding loops in specImports]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    We must take great care when specialising instance declarations
    (functions like $fOrdList) lest we accidentally build a recursive
    dictionary. See Note [Avoiding loops].

    The basic strategy of Note [Avoiding loops] is to use filterCalls
    to discard loopy specialisations.  But to do that we must ensure
    that the in-scope dict-binds (passed to filterCalls) contains
    all the needed dictionary bindings.  In particular, in the recursive
    call to spec_imorpts in spec_import, we must include the dict-binds
    from the parent.  Lacking this caused #17151, a really nasty bug.

    Here is what happened.
    * Class structure:
        Source is a superclass of Mut
        Index is a superclass of Source

    * We started with these dict binds
        dSource = $fSourcePix @Int $fIndexInt
        dIndex  = sc_sel dSource
        dMut    = $fMutPix @Int dIndex
      and these calls to specialise
        $fMutPix @Int dIndex
        $fSourcePix @Int $fIndexInt

    * We specialised the call ($fMutPix @Int dIndex)
      ==> new call ($fSourcePix @Int dIndex)
          (because Source is a superclass of Mut)

    * We specialised ($fSourcePix @Int dIndex)
      ==> produces specialised dict $s$fSourcePix,
          a record with dIndex as a field
          plus RULE forall d. ($fSourcePix @Int d) = $s$fSourcePix
      *** This is the bogus step ***

    * Now we decide not to specialise the call
        $fSourcePix @Int $fIndexInt
      because we alredy have a RULE that matches it

    * Finally the simplifer rewrites
        dSource = $fSourcePix @Int $fIndexInt
        ==>  dSource = $s$fSourcePix

    Disaster. Now we have

    Rewrite dSource's RHS to $s$fSourcePix   Disaster
        dSource = $s$fSourcePix
        dIndex  = sc_sel dSource
        $s$fSourcePix = MkSource dIndex ...

    Solution: filterCalls should have stopped the bogus step,
    by seeing that dIndex transitively uses $fSourcePix. But
    it can only do that if it sees all the dict_binds.  Wow.

    --------------
    Here's another example (#13429).  Suppose we have
      class Monoid v => C v a where ...

    We start with a call
       f @ [Integer] @ Integer $fC[]Integer

    Specialising call to 'f' gives dict bindings
       $dMonoid_1 :: Monoid [Integer]
       $dMonoid_1 = M.$p1C @ [Integer] $fC[]Integer

       $dC_1 :: C [Integer] (Node [Integer] Integer)
       $dC_1 = M.$fCvNode @ [Integer] $dMonoid_1

    ...plus a recursive call to
       f @ [Integer] @ (Node [Integer] Integer) $dC_1

    Specialising that call gives
       $dMonoid_2  :: Monoid [Integer]
       $dMonoid_2  = M.$p1C @ [Integer] $dC_1

       $dC_2 :: C [Integer] (Node [Integer] Integer)
       $dC_2 = M.$fCvNode @ [Integer] $dMonoid_2

    Now we have two calls to the imported function
      M.$fCvNode :: Monoid v => C v a
      M.$fCvNode @v @a m = C m some_fun

    But we must /not/ use the call (M.$fCvNode @ [Integer] $dMonoid_2)
    for specialisation, else we get:

      $dC_1 = M.$fCvNode @ [Integer] $dMonoid_1
      $dMonoid_2 = M.$p1C @ [Integer] $dC_1
      $s$fCvNode = C $dMonoid_2 ...
        RULE M.$fCvNode [Integer] _ _ = $s$fCvNode

    Now use the rule to rewrite the call in the RHS of $dC_1
    and we get a loop!

    Note [specImport call stack]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    When specialising an imports function 'f', we may get new calls
    of an imported function 'g', which we want to specialise in turn,
    and similarly specialising 'g' might expose a new call to 'h'.

    We track the stack of enclosing functions. So when specialising 'h' we
    haev a specImport call stack of [g,f]. We do this for two reasons:
    * Note [Warning about missed specialisations]
    * Note [Avoiding recursive specialisation]

    Note [Warning about missed specialisations]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Suppose
     * In module Lib, you carefully mark a function 'foo' INLINABLE
     * Import Lib(foo) into another module M
     * Call 'foo' at some specialised type in M
    Then you jolly well expect it to be specialised in M.  But what if
    'foo' calls another function 'Lib.bar'.  Then you'd like 'bar' to be
    specialised too.  But if 'bar' is not marked INLINABLE it may well
    not be specialised.  The warning Opt_WarnMissedSpecs warns about this.

    It's more noisy to warning about a missed specialisation opportunity
    for /every/ overloaded imported function, but sometimes useful. That
    is what Opt_WarnAllMissedSpecs does.

    ToDo: warn about missed opportunities for local functions.

    Note [Avoiding recursive specialisation]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    When we specialise 'f' we may find new overloaded calls to 'g', 'h' in
    'f's RHS.  So we want to specialise g,h.  But we don't want to
    specialise f any more!  It's possible that f's RHS might have a
    recursive yet-more-specialised call, so we'd diverge in that case.
    And if the call is to the same type, one specialisation is enough.
    Avoiding this recursive specialisation loop is one reason for the
    'callers' stack passed to specImports and specImport.

    Note [Specialise imported INLINABLE things]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    What imported functions do we specialise?  The basic set is
     * DFuns and things with INLINABLE pragmas.
    but with -fspecialise-aggressively we add
     * Anything with an unfolding template

    #8874 has a good example of why we want to auto-specialise DFuns.

    We have the -fspecialise-aggressively flag (usually off), because we
    risk lots of orphan modules from over-vigorous specialisation.
    However it's not a big deal: anything non-recursive with an
    unfolding-template will probably have been inlined already.

    Note [Glom the bindings if imported functions are specialised]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Suppose we have an imported, *recursive*, INLINABLE function
       f :: Eq a => a -> a
       f = /\a \d x. ...(f a d)...
    In the module being compiled we have
       g x = f (x::Int)
    Now we'll make a specialised function
       f_spec :: Int -> Int
       f_spec = \x -> ...(f Int dInt)...
       {-# RULE  f Int _ = f_spec #-}
       g = \x. f Int dInt x
    Note that f_spec doesn't look recursive
    After rewriting with the RULE, we get
       f_spec = \x -> ...(f_spec)...
    BUT since f_spec was non-recursive before it'll *stay* non-recursive.
    The occurrence analyser never turns a NonRec into a Rec.  So we must
    make sure that f_spec is recursive.  Easiest thing is to make all
    the specialisations for imported bindings recursive.

    ************************************************************************
    *                                                                      *
    \subsubsection{@specExpr@: the main function}
    *                                                                      *
    ************************************************************************
    -}

    data SpecEnv
      = SE { SpecEnv -> Subst
    se_subst :: Core.Subst
                 -- We carry a substitution down:
                 -- a) we must clone any binding that might float outwards,
                 --    to avoid name clashes
                 -- b) we carry a type substitution to use when analysing
                 --    the RHS of specialised bindings (no type-let!)

           , SpecEnv -> VarSet
    se_interesting :: VarSet
                 -- Dict Ids that we know something about
                 -- and hence may be worth specialising against
                 -- See Note [Interesting dictionary arguments]

           , SpecEnv -> Module
    se_module :: Module
           , SpecEnv -> DynFlags
    se_dflags :: DynFlags
         }

    instance Outputable SpecEnv where
      ppr :: SpecEnv -> SDoc
    ppr (SE { se_subst :: SpecEnv -> Subst
    se_subst = Subst
    subst, se_interesting :: SpecEnv -> VarSet
    se_interesting = VarSet
    interesting })
        = String -> SDoc
    text String
    "SE" SDoc -> SDoc -> SDoc
    <+> SDoc -> SDoc
    braces ([SDoc] -> SDoc
    sep ([SDoc] -> SDoc) -> [SDoc] -> SDoc
    forall a b. (a -> b) -> a -> b
    $ SDoc -> [SDoc] -> [SDoc]
    punctuate SDoc
    comma
            [ String -> SDoc
    text String
    "subst =" SDoc -> SDoc -> SDoc
    <+> Subst -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Subst
    subst
            , String -> SDoc
    text String
    "interesting =" SDoc -> SDoc -> SDoc
    <+> VarSet -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr VarSet
    interesting ])

    specVar :: SpecEnv -> Id -> CoreExpr
    specVar :: SpecEnv -> Id -> CoreExpr
    specVar SpecEnv
    env Id
    v = HasDebugCallStack => Subst -> Id -> CoreExpr
    Subst -> Id -> CoreExpr
    Core.lookupIdSubst (SpecEnv -> Subst
    se_subst SpecEnv
    env) Id
    v

    specExpr :: SpecEnv -> CoreExpr -> SpecM (CoreExpr, UsageDetails)

    ---------------- First the easy cases --------------------
    specExpr :: SpecEnv -> CoreExpr -> SpecM (CoreExpr, UsageDetails)
    specExpr SpecEnv
    env (Type Kind
    ty)     = (CoreExpr, UsageDetails) -> SpecM (CoreExpr, UsageDetails)
    forall (m :: * -> *) a. Monad m => a -> m a
    return (Kind -> CoreExpr
    forall b. Kind -> Expr b
    Type     (SpecEnv -> Kind -> Kind
    substTy SpecEnv
    env Kind
    ty), UsageDetails
    emptyUDs)
    specExpr SpecEnv
    env (Coercion Coercion
    co) = (CoreExpr, UsageDetails) -> SpecM (CoreExpr, UsageDetails)
    forall (m :: * -> *) a. Monad m => a -> m a
    return (Coercion -> CoreExpr
    forall b. Coercion -> Expr b
    Coercion (SpecEnv -> Coercion -> Coercion
    substCo SpecEnv
    env Coercion
    co), UsageDetails
    emptyUDs)
    specExpr SpecEnv
    env (Var Id
    v)       = (CoreExpr, UsageDetails) -> SpecM (CoreExpr, UsageDetails)
    forall (m :: * -> *) a. Monad m => a -> m a
    return (SpecEnv -> Id -> CoreExpr
    specVar SpecEnv
    env Id
    v, UsageDetails
    emptyUDs)
    specExpr SpecEnv
    _   (Lit Literal
    lit)     = (CoreExpr, UsageDetails) -> SpecM (CoreExpr, UsageDetails)
    forall (m :: * -> *) a. Monad m => a -> m a
    return (Literal -> CoreExpr
    forall b. Literal -> Expr b
    Lit Literal
    lit,       UsageDetails
    emptyUDs)
    specExpr SpecEnv
    env (Cast CoreExpr
    e Coercion
    co)
      = do { (CoreExpr
    e', UsageDetails
    uds) <- SpecEnv -> CoreExpr -> SpecM (CoreExpr, UsageDetails)
    specExpr SpecEnv
    env CoreExpr
    e
           ; (CoreExpr, UsageDetails) -> SpecM (CoreExpr, UsageDetails)
    forall (m :: * -> *) a. Monad m => a -> m a
    return ((CoreExpr -> Coercion -> CoreExpr
    mkCast CoreExpr
    e' (SpecEnv -> Coercion -> Coercion
    substCo SpecEnv
    env Coercion
    co)), UsageDetails
    uds) }
    specExpr SpecEnv
    env (Tick CoreTickish
    tickish CoreExpr
    body)
      = do { (CoreExpr
    body', UsageDetails
    uds) <- SpecEnv -> CoreExpr -> SpecM (CoreExpr, UsageDetails)
    specExpr SpecEnv
    env CoreExpr
    body
           ; (CoreExpr, UsageDetails) -> SpecM (CoreExpr, UsageDetails)
    forall (m :: * -> *) a. Monad m => a -> m a
    return (CoreTickish -> CoreExpr -> CoreExpr
    forall b. CoreTickish -> Expr b -> Expr b
    Tick (SpecEnv -> CoreTickish -> CoreTickish
    specTickish SpecEnv
    env CoreTickish
    tickish) CoreExpr
    body', UsageDetails
    uds) }

    ---------------- Applications might generate a call instance --------------------
    specExpr SpecEnv
    env expr :: CoreExpr
    expr@(App {})
      = CoreExpr -> [CoreExpr] -> SpecM (CoreExpr, UsageDetails)
    go CoreExpr
    expr []
      where
        go :: CoreExpr -> [CoreExpr] -> SpecM (CoreExpr, UsageDetails)
    go (App CoreExpr
    fun CoreExpr
    arg) [CoreExpr]
    args = do (CoreExpr
    arg', UsageDetails
    uds_arg) <- SpecEnv -> CoreExpr -> SpecM (CoreExpr, UsageDetails)
    specExpr SpecEnv
    env CoreExpr
    arg
                                   (CoreExpr
    fun', UsageDetails
    uds_app) <- CoreExpr -> [CoreExpr] -> SpecM (CoreExpr, UsageDetails)
    go CoreExpr
    fun (CoreExpr
    arg'CoreExpr -> [CoreExpr] -> [CoreExpr]
    forall a. a -> [a] -> [a]
    :[CoreExpr]
    args)
                                   (CoreExpr, UsageDetails) -> SpecM (CoreExpr, UsageDetails)
    forall (m :: * -> *) a. Monad m => a -> m a
    return (CoreExpr -> CoreExpr -> CoreExpr
    forall b. Expr b -> Expr b -> Expr b
    App CoreExpr
    fun' CoreExpr
    arg', UsageDetails
    uds_arg UsageDetails -> UsageDetails -> UsageDetails
    `plusUDs` UsageDetails
    uds_app)

        go (Var Id
    f)       [CoreExpr]
    args = case SpecEnv -> Id -> CoreExpr
    specVar SpecEnv
    env Id
    f of
                                    Var Id
    f' -> (CoreExpr, UsageDetails) -> SpecM (CoreExpr, UsageDetails)
    forall (m :: * -> *) a. Monad m => a -> m a
    return (Id -> CoreExpr
    forall b. Id -> Expr b
    Var Id
    f', SpecEnv -> Id -> [CoreExpr] -> UsageDetails
    mkCallUDs SpecEnv
    env Id
    f' [CoreExpr]
    args)
                                    CoreExpr
    e'     -> (CoreExpr, UsageDetails) -> SpecM (CoreExpr, UsageDetails)
    forall (m :: * -> *) a. Monad m => a -> m a
    return (CoreExpr
    e', UsageDetails
    emptyUDs) -- I don't expect this!
        go CoreExpr
    other         [CoreExpr]
    _    = SpecEnv -> CoreExpr -> SpecM (CoreExpr, UsageDetails)
    specExpr SpecEnv
    env CoreExpr
    other

    ---------------- Lambda/case require dumping of usage details --------------------
    specExpr SpecEnv
    env e :: CoreExpr
    e@(Lam {})
      = SpecEnv -> [Id] -> CoreExpr -> SpecM (CoreExpr, UsageDetails)
    specLam SpecEnv
    env' [Id]
    bndrs' CoreExpr
    body
      where
        ([Id]
    bndrs, CoreExpr
    body)  = CoreExpr -> ([Id], CoreExpr)
    forall b. Expr b -> ([b], Expr b)
    collectBinders CoreExpr
    e
        (SpecEnv
    env', [Id]
    bndrs') = SpecEnv -> [Id] -> (SpecEnv, [Id])
    substBndrs SpecEnv
    env [Id]
    bndrs
            -- More efficient to collect a group of binders together all at once
            -- and we don't want to split a lambda group with dumped bindings

    specExpr SpecEnv
    env (Case CoreExpr
    scrut Id
    case_bndr Kind
    ty [Alt Id]
    alts)
      = do { (CoreExpr
    scrut', UsageDetails
    scrut_uds) <- SpecEnv -> CoreExpr -> SpecM (CoreExpr, UsageDetails)
    specExpr SpecEnv
    env CoreExpr
    scrut
           ; (CoreExpr
    scrut'', Id
    case_bndr', [Alt Id]
    alts', UsageDetails
    alts_uds)
                 <- SpecEnv
    -> CoreExpr
    -> Id
    -> [Alt Id]
    -> SpecM (CoreExpr, Id, [Alt Id], UsageDetails)
    specCase SpecEnv
    env CoreExpr
    scrut' Id
    case_bndr [Alt Id]
    alts
           ; (CoreExpr, UsageDetails) -> SpecM (CoreExpr, UsageDetails)
    forall (m :: * -> *) a. Monad m => a -> m a
    return (CoreExpr -> Id -> Kind -> [Alt Id] -> CoreExpr
    forall b. Expr b -> b -> Kind -> [Alt b] -> Expr b
    Case CoreExpr
    scrut'' Id
    case_bndr' (SpecEnv -> Kind -> Kind
    substTy SpecEnv
    env Kind
    ty) [Alt Id]
    alts'
                    , UsageDetails
    scrut_uds UsageDetails -> UsageDetails -> UsageDetails
    `plusUDs` UsageDetails
    alts_uds) }

    ---------------- Finally, let is the interesting case --------------------
    specExpr SpecEnv
    env (Let CoreBind
    bind CoreExpr
    body)
      = do { -- Clone binders
             (SpecEnv
    rhs_env, SpecEnv
    body_env, CoreBind
    bind') <- SpecEnv -> CoreBind -> SpecM (SpecEnv, SpecEnv, CoreBind)
    cloneBindSM SpecEnv
    env CoreBind
    bind

             -- Deal with the body
           ; (CoreExpr
    body', UsageDetails
    body_uds) <- SpecEnv -> CoreExpr -> SpecM (CoreExpr, UsageDetails)
    specExpr SpecEnv
    body_env CoreExpr
    body

            -- Deal with the bindings
          ; (CoreProgram
    binds', UsageDetails
    uds) <- SpecEnv
    -> CoreBind -> UsageDetails -> UniqSM (CoreProgram, UsageDetails)
    specBind SpecEnv
    rhs_env CoreBind
    bind' UsageDetails
    body_uds

            -- All done
          ; (CoreExpr, UsageDetails) -> SpecM (CoreExpr, UsageDetails)
    forall (m :: * -> *) a. Monad m => a -> m a
    return ((CoreBind -> CoreExpr -> CoreExpr)
    -> CoreExpr -> CoreProgram -> CoreExpr
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr CoreBind -> CoreExpr -> CoreExpr
    forall b. Bind b -> Expr b -> Expr b
    Let CoreExpr
    body' CoreProgram
    binds', UsageDetails
    uds) }

    --------------
    specLam :: SpecEnv -> [OutBndr] -> InExpr -> SpecM (OutExpr, UsageDetails)
    -- The binders have been substituted, but the body has not
    specLam :: SpecEnv -> [Id] -> CoreExpr -> SpecM (CoreExpr, UsageDetails)
    specLam SpecEnv
    env [Id]
    bndrs CoreExpr
    body
      | [Id] -> Bool
    forall (t :: * -> *) a. Foldable t => t a -> Bool
    null [Id]
    bndrs
      = SpecEnv -> CoreExpr -> SpecM (CoreExpr, UsageDetails)
    specExpr SpecEnv
    env CoreExpr
    body
      | Bool
    otherwise
      = do { (CoreExpr
    body', UsageDetails
    uds) <- SpecEnv -> CoreExpr -> SpecM (CoreExpr, UsageDetails)
    specExpr SpecEnv
    env CoreExpr
    body
           ; let (UsageDetails
    free_uds, Bag DictBind
    dumped_dbs) = [Id] -> UsageDetails -> (UsageDetails, Bag DictBind)
    dumpUDs [Id]
    bndrs UsageDetails
    uds
           ; (CoreExpr, UsageDetails) -> SpecM (CoreExpr, UsageDetails)
    forall (m :: * -> *) a. Monad m => a -> m a
    return ([Id] -> CoreExpr -> CoreExpr
    forall b. [b] -> Expr b -> Expr b
    mkLams [Id]
    bndrs (Bag DictBind -> CoreExpr -> CoreExpr
    wrapDictBindsE Bag DictBind
    dumped_dbs CoreExpr
    body'), UsageDetails
    free_uds) }

    --------------
    specTickish :: SpecEnv -> CoreTickish -> CoreTickish
    specTickish :: SpecEnv -> CoreTickish -> CoreTickish
    specTickish SpecEnv
    env (Breakpoint XBreakpoint 'TickishPassCore
    ext Int
    ix [XTickishId 'TickishPassCore]
    ids)
      = XBreakpoint 'TickishPassCore
    -> Int -> [XTickishId 'TickishPassCore] -> CoreTickish
    forall (pass :: TickishPass).
    XBreakpoint pass -> Int -> [XTickishId pass] -> GenTickish pass
    Breakpoint XBreakpoint 'TickishPassCore
    ext Int
    ix [ Id
    XTickishId 'TickishPassCore
    id' | Id
    id <- [Id]
    [XTickishId 'TickishPassCore]
    ids, Var Id
    id' <- [SpecEnv -> Id -> CoreExpr
    specVar SpecEnv
    env Id
    id]]
      -- drop vars from the list if they have a non-variable substitution.
      -- should never happen, but it's harmless to drop them anyway.
    specTickish SpecEnv
    _ CoreTickish
    other_tickish = CoreTickish
    other_tickish

    --------------
    specCase :: SpecEnv
             -> CoreExpr            -- Scrutinee, already done
             -> Id -> [CoreAlt]
             -> SpecM ( CoreExpr    -- New scrutinee
                      , Id
                      , [CoreAlt]
                      , UsageDetails)
    specCase :: SpecEnv
    -> CoreExpr
    -> Id
    -> [Alt Id]
    -> SpecM (CoreExpr, Id, [Alt Id], UsageDetails)
    specCase SpecEnv
    env CoreExpr
    scrut' Id
    case_bndr [Alt AltCon
    con [Id]
    args CoreExpr
    rhs]
      | Id -> Bool
    isDictId Id
    case_bndr           -- See Note [Floating dictionaries out of cases]
      , SpecEnv -> CoreExpr -> Bool
    interestingDict SpecEnv
    env CoreExpr
    scrut'
      , Bool -> Bool
    not (Id -> Bool
    isDeadBinder Id
    case_bndr Bool -> Bool -> Bool
    && [Id] -> Bool
    forall (t :: * -> *) a. Foldable t => t a -> Bool
    null [Id]
    sc_args')
      = do { (Id
    case_bndr_flt : [Id]
    sc_args_flt) <- (Id -> UniqSM Id) -> [Id] -> UniqSM [Id]
    forall (t :: * -> *) (m :: * -> *) a b.
    (Traversable t, Monad m) =>
    (a -> m b) -> t a -> m (t b)
    mapM Id -> UniqSM Id
    forall {m :: * -> *}. MonadUnique m => Id -> m Id
    clone_me (Id
    case_bndr' Id -> [Id] -> [Id]
    forall a. a -> [a] -> [a]
    : [Id]
    sc_args')

           ; let sc_rhss :: [CoreExpr]
    sc_rhss = [ CoreExpr -> Id -> Kind -> [Alt Id] -> CoreExpr
    forall b. Expr b -> b -> Kind -> [Alt b] -> Expr b
    Case (Id -> CoreExpr
    forall b. Id -> Expr b
    Var Id
    case_bndr_flt) Id
    case_bndr' (Id -> Kind
    idType Id
    sc_arg')
                                  [AltCon -> [Id] -> CoreExpr -> Alt Id
    forall b. AltCon -> [b] -> Expr b -> Alt b
    Alt AltCon
    con [Id]
    args' (Id -> CoreExpr
    forall b. Id -> Expr b
    Var Id
    sc_arg')]
                           | Id
    sc_arg' <- [Id]
    sc_args' ]

                 -- Extend the substitution for RHS to map the *original* binders
                 -- to their floated versions.
                 mb_sc_flts :: [Maybe DictId]
                 mb_sc_flts :: [Maybe Id]
    mb_sc_flts = (Id -> Maybe Id) -> [Id] -> [Maybe Id]
    forall a b. (a -> b) -> [a] -> [b]
    map (VarEnv Id -> Id -> Maybe Id
    forall a. VarEnv a -> Id -> Maybe a
    lookupVarEnv VarEnv Id
    clone_env) [Id]
    args'
                 clone_env :: VarEnv Id
    clone_env  = [Id] -> [Id] -> VarEnv Id
    forall a. [Id] -> [a] -> VarEnv a
    zipVarEnv [Id]
    sc_args' [Id]
    sc_args_flt
                 subst_prs :: [(Id, CoreExpr)]
    subst_prs  = (Id
    case_bndr, Id -> CoreExpr
    forall b. Id -> Expr b
    Var Id
    case_bndr_flt)
                            (Id, CoreExpr) -> [(Id, CoreExpr)] -> [(Id, CoreExpr)]
    forall a. a -> [a] -> [a]
    : [ (Id
    arg, Id -> CoreExpr
    forall b. Id -> Expr b
    Var Id
    sc_flt)
                              | (Id
    arg, Just Id
    sc_flt) <- [Id]
    args [Id] -> [Maybe Id] -> [(Id, Maybe Id)]
    forall a b. [a] -> [b] -> [(a, b)]
    `zip` [Maybe Id]
    mb_sc_flts ]
                 env_rhs' :: SpecEnv
    env_rhs' = SpecEnv
    env_rhs { se_subst :: Subst
    se_subst = Subst -> [(Id, CoreExpr)] -> Subst
    Core.extendIdSubstList (SpecEnv -> Subst
    se_subst SpecEnv
    env_rhs) [(Id, CoreExpr)]
    subst_prs
                                    , se_interesting :: VarSet
    se_interesting = SpecEnv -> VarSet
    se_interesting SpecEnv
    env_rhs VarSet -> [Id] -> VarSet
    `extendVarSetList`
                                                       (Id
    case_bndr_flt Id -> [Id] -> [Id]
    forall a. a -> [a] -> [a]
    : [Id]
    sc_args_flt) }

           ; (CoreExpr
    rhs', UsageDetails
    rhs_uds)   <- SpecEnv -> CoreExpr -> SpecM (CoreExpr, UsageDetails)
    specExpr SpecEnv
    env_rhs' CoreExpr
    rhs
           ; let scrut_bind :: DictBind
    scrut_bind    = CoreBind -> DictBind
    mkDB (Id -> CoreExpr -> CoreBind
    forall b. b -> Expr b -> Bind b
    NonRec Id
    case_bndr_flt CoreExpr
    scrut')
                 case_bndr_set :: VarSet
    case_bndr_set = Id -> VarSet
    unitVarSet Id
    case_bndr_flt
                 sc_binds :: [DictBind]
    sc_binds      = [ DB { db_bind :: CoreBind
    db_bind = Id -> CoreExpr -> CoreBind
    forall b. b -> Expr b -> Bind b
    NonRec Id
    sc_arg_flt CoreExpr
    sc_rhs
                                      , db_fvs :: VarSet
    db_fvs  = VarSet
    case_bndr_set }
                                 | (Id
    sc_arg_flt, CoreExpr
    sc_rhs) <- [Id]
    sc_args_flt [Id] -> [CoreExpr] -> [(Id, CoreExpr)]
    forall a b. [a] -> [b] -> [(a, b)]
    `zip` [CoreExpr]
    sc_rhss ]
                 flt_binds :: [DictBind]
    flt_binds     = DictBind
    scrut_bind DictBind -> [DictBind] -> [DictBind]
    forall a. a -> [a] -> [a]
    : [DictBind]
    sc_binds
                 (UsageDetails
    free_uds, Bag DictBind
    dumped_dbs) = [Id] -> UsageDetails -> (UsageDetails, Bag DictBind)
    dumpUDs (Id
    case_bndr'Id -> [Id] -> [Id]
    forall a. a -> [a] -> [a]
    :[Id]
    args') UsageDetails
    rhs_uds
                 all_uds :: UsageDetails
    all_uds = [DictBind]
    flt_binds [DictBind] -> UsageDetails -> UsageDetails
    `addDictBinds` UsageDetails
    free_uds
                 alt' :: Alt Id
    alt'    = AltCon -> [Id] -> CoreExpr -> Alt Id
    forall b. AltCon -> [b] -> Expr b -> Alt b
    Alt AltCon
    con [Id]
    args' (Bag DictBind -> CoreExpr -> CoreExpr
    wrapDictBindsE Bag DictBind
    dumped_dbs CoreExpr
    rhs')
           ; (CoreExpr, Id, [Alt Id], UsageDetails)
    -> SpecM (CoreExpr, Id, [Alt Id], UsageDetails)
    forall (m :: * -> *) a. Monad m => a -> m a
    return (Id -> CoreExpr
    forall b. Id -> Expr b
    Var Id
    case_bndr_flt, Id
    case_bndr', [Alt Id
    alt'], UsageDetails
    all_uds) }
      where
        (SpecEnv
    env_rhs, (Id
    case_bndr':[Id]
    args')) = SpecEnv -> [Id] -> (SpecEnv, [Id])
    substBndrs SpecEnv
    env (Id
    case_bndrId -> [Id] -> [Id]
    forall a. a -> [a] -> [a]
    :[Id]
    args)
        sc_args' :: [Id]
    sc_args' = (Id -> Bool) -> [Id] -> [Id]
    forall a. (a -> Bool) -> [a] -> [a]
    filter Id -> Bool
    is_flt_sc_arg [Id]
    args'

        clone_me :: Id -> m Id
    clone_me Id
    bndr = do { Unique
    uniq <- m Unique
    forall (m :: * -> *). MonadUnique m => m Unique
    getUniqueM
                           ; Id -> m Id
    forall (m :: * -> *) a. Monad m => a -> m a
    return (OccName -> Unique -> Kind -> Kind -> SrcSpan -> Id
    mkUserLocalOrCoVar OccName
    occ Unique
    uniq Kind
    wght Kind
    ty SrcSpan
    loc) }
           where
             name :: Name
    name = Id -> Name
    idName Id
    bndr
             wght :: Kind
    wght = Id -> Kind
    idMult Id
    bndr
             ty :: Kind
    ty   = Id -> Kind
    idType Id
    bndr
             occ :: OccName
    occ  = Name -> OccName
    nameOccName Name
    name
             loc :: SrcSpan
    loc  = Name -> SrcSpan
    forall a. NamedThing a => a -> SrcSpan
    getSrcSpan Name
    name

        arg_set :: VarSet
    arg_set = [Id] -> VarSet
    mkVarSet [Id]
    args'
        is_flt_sc_arg :: Id -> Bool
    is_flt_sc_arg Id
    var =  Id -> Bool
    isId Id
    var
                          Bool -> Bool -> Bool
    && Bool -> Bool
    not (Id -> Bool
    isDeadBinder Id
    var)
                          Bool -> Bool -> Bool
    && Kind -> Bool
    isDictTy Kind
    var_ty
                          Bool -> Bool -> Bool
    && Kind -> VarSet
    tyCoVarsOfType Kind
    var_ty VarSet -> VarSet -> Bool
    `disjointVarSet` VarSet
    arg_set
           where
             var_ty :: Kind
    var_ty = Id -> Kind
    idType Id
    var

    specCase SpecEnv
    env CoreExpr
    scrut Id
    case_bndr [Alt Id]
    alts
      = do { ([Alt Id]
    alts', UsageDetails
    uds_alts) <- (Alt Id -> SpecM (Alt Id, UsageDetails))
    -> [Alt Id] -> SpecM ([Alt Id], UsageDetails)
    forall a b.
    (a -> SpecM (b, UsageDetails)) -> [a] -> SpecM ([b], UsageDetails)
    mapAndCombineSM Alt Id -> SpecM (Alt Id, UsageDetails)
    spec_alt [Alt Id]
    alts
           ; (CoreExpr, Id, [Alt Id], UsageDetails)
    -> SpecM (CoreExpr, Id, [Alt Id], UsageDetails)
    forall (m :: * -> *) a. Monad m => a -> m a
    return (CoreExpr
    scrut, Id
    case_bndr', [Alt Id]
    alts', UsageDetails
    uds_alts) }
      where
        (SpecEnv
    env_alt, Id
    case_bndr') = SpecEnv -> Id -> (SpecEnv, Id)
    substBndr SpecEnv
    env Id
    case_bndr
        spec_alt :: Alt Id -> SpecM (Alt Id, UsageDetails)
    spec_alt (Alt AltCon
    con [Id]
    args CoreExpr
    rhs) = do
              (CoreExpr
    rhs', UsageDetails
    uds) <- SpecEnv -> CoreExpr -> SpecM (CoreExpr, UsageDetails)
    specExpr SpecEnv
    env_rhs CoreExpr
    rhs
              let (UsageDetails
    free_uds, Bag DictBind
    dumped_dbs) = [Id] -> UsageDetails -> (UsageDetails, Bag DictBind)
    dumpUDs (Id
    case_bndr' Id -> [Id] -> [Id]
    forall a. a -> [a] -> [a]
    : [Id]
    args') UsageDetails
    uds
              (Alt Id, UsageDetails) -> SpecM (Alt Id, UsageDetails)
    forall (m :: * -> *) a. Monad m => a -> m a
    return (AltCon -> [Id] -> CoreExpr -> Alt Id
    forall b. AltCon -> [b] -> Expr b -> Alt b
    Alt AltCon
    con [Id]
    args' (Bag DictBind -> CoreExpr -> CoreExpr
    wrapDictBindsE Bag DictBind
    dumped_dbs CoreExpr
    rhs'), UsageDetails
    free_uds)
            where
              (SpecEnv
    env_rhs, [Id]
    args') = SpecEnv -> [Id] -> (SpecEnv, [Id])
    substBndrs SpecEnv
    env_alt [Id]
    args

    {-
    Note [Floating dictionaries out of cases]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider
       g = \d. case d of { MkD sc ... -> ...(f sc)... }
    Naively we can't float d2's binding out of the case expression,
    because 'sc' is bound by the case, and that in turn means we can't
    specialise f, which seems a pity.

    So we invert the case, by floating out a binding
    for 'sc_flt' thus:
        sc_flt = case d of { MkD sc ... -> sc }
    Now we can float the call instance for 'f'.  Indeed this is just
    what'll happen if 'sc' was originally bound with a let binding,
    but case is more efficient, and necessary with equalities. So it's
    good to work with both.

    You might think that this won't make any difference, because the
    call instance will only get nuked by the \d.  BUT if 'g' itself is
    specialised, then transitively we should be able to specialise f.

    In general, given
       case e of cb { MkD sc ... -> ...(f sc)... }
    we transform to
       let cb_flt = e
           sc_flt = case cb_flt of { MkD sc ... -> sc }
       in
       case cb_flt of bg { MkD sc ... -> ....(f sc_flt)... }

    The "_flt" things are the floated binds; we use the current substitution
    to substitute sc -> sc_flt in the RHS

    ************************************************************************
    *                                                                      *
                         Dealing with a binding
    *                                                                      *
    ************************************************************************
    -}

    specBind :: SpecEnv                     -- Use this for RHSs
             -> CoreBind                    -- Binders are already cloned by cloneBindSM,
                                            -- but RHSs are un-processed
             -> UsageDetails                -- Info on how the scope of the binding
             -> SpecM ([CoreBind],          -- New bindings
                       UsageDetails)        -- And info to pass upstream

    -- Returned UsageDetails:
    --    No calls for binders of this bind
    specBind :: SpecEnv
    -> CoreBind -> UsageDetails -> UniqSM (CoreProgram, UsageDetails)
    specBind SpecEnv
    rhs_env (NonRec Id
    fn CoreExpr
    rhs) UsageDetails
    body_uds
      = do { (CoreExpr
    rhs', UsageDetails
    rhs_uds) <- SpecEnv -> CoreExpr -> SpecM (CoreExpr, UsageDetails)
    specExpr SpecEnv
    rhs_env CoreExpr
    rhs

            ; let zapped_fn :: Id
    zapped_fn = Id -> Id
    zapIdDemandInfo Id
    fn
                  -- We zap the demand info because the binding may float,
                  -- which would invaidate the demand info (see #17810 for example).
                  -- Destroying demand info is not terrible; specialisation is
                  -- always followed soon by demand analysis.
          ; (Id
    fn', [(Id, CoreExpr)]
    spec_defns, UsageDetails
    body_uds1) <- SpecEnv
    -> UsageDetails
    -> Id
    -> CoreExpr
    -> SpecM (Id, [(Id, CoreExpr)], UsageDetails)
    specDefn SpecEnv
    rhs_env UsageDetails
    body_uds Id
    zapped_fn CoreExpr
    rhs

           ; let pairs :: [(Id, CoreExpr)]
    pairs = [(Id, CoreExpr)]
    spec_defns [(Id, CoreExpr)] -> [(Id, CoreExpr)] -> [(Id, CoreExpr)]
    forall a. [a] -> [a] -> [a]
    ++ [(Id
    fn', CoreExpr
    rhs')]
                            -- fn' mentions the spec_defns in its rules,
                            -- so put the latter first

                 combined_uds :: UsageDetails
    combined_uds = UsageDetails
    body_uds1 UsageDetails -> UsageDetails -> UsageDetails
    `plusUDs` UsageDetails
    rhs_uds

                 (UsageDetails
    free_uds, Bag DictBind
    dump_dbs, Bool
    float_all) = [Id] -> UsageDetails -> (UsageDetails, Bag DictBind, Bool)
    dumpBindUDs [Id
    fn] UsageDetails
    combined_uds

                 final_binds :: [DictBind]
                 -- See Note [From non-recursive to recursive]
                 final_binds :: [DictBind]
    final_binds
                   | Bool -> Bool
    not (Bag DictBind -> Bool
    forall a. Bag a -> Bool
    isEmptyBag Bag DictBind
    dump_dbs)
                   , Bool -> Bool
    not ([(Id, CoreExpr)] -> Bool
    forall (t :: * -> *) a. Foldable t => t a -> Bool
    null [(Id, CoreExpr)]
    spec_defns)
                   = [[(Id, CoreExpr)] -> Bag DictBind -> DictBind
    recWithDumpedDicts [(Id, CoreExpr)]
    pairs Bag DictBind
    dump_dbs]
                   | Bool
    otherwise
                   = [CoreBind -> DictBind
    mkDB (CoreBind -> DictBind) -> CoreBind -> DictBind
    forall a b. (a -> b) -> a -> b
    $ Id -> CoreExpr -> CoreBind
    forall b. b -> Expr b -> Bind b
    NonRec Id
    b CoreExpr
    r | (Id
    b,CoreExpr
    r) <- [(Id, CoreExpr)]
    pairs]
                     [DictBind] -> [DictBind] -> [DictBind]
    forall a. [a] -> [a] -> [a]
    ++ Bag DictBind -> [DictBind]
    forall a. Bag a -> [a]
    bagToList Bag DictBind
    dump_dbs

           ; if Bool
    float_all then
                 -- Rather than discard the calls mentioning the bound variables
                 -- we float this (dictionary) binding along with the others
                  (CoreProgram, UsageDetails) -> UniqSM (CoreProgram, UsageDetails)
    forall (m :: * -> *) a. Monad m => a -> m a
    return ([], UsageDetails
    free_uds UsageDetails -> [DictBind] -> UsageDetails
    `snocDictBinds` [DictBind]
    final_binds)
             else
                 -- No call in final_uds mentions bound variables,
                 -- so we can just leave the binding here
                  (CoreProgram, UsageDetails) -> UniqSM (CoreProgram, UsageDetails)
    forall (m :: * -> *) a. Monad m => a -> m a
    return ((DictBind -> CoreBind) -> [DictBind] -> CoreProgram
    forall a b. (a -> b) -> [a] -> [b]
    map DictBind -> CoreBind
    db_bind [DictBind]
    final_binds, UsageDetails
    free_uds) }

    specBind SpecEnv
    rhs_env (Rec [(Id, CoreExpr)]
    pairs) UsageDetails
    body_uds
           -- Note [Specialising a recursive group]
      = do { let ([Id]
    bndrs,[CoreExpr]
    rhss) = [(Id, CoreExpr)] -> ([Id], [CoreExpr])
    forall a b. [(a, b)] -> ([a], [b])
    unzip [(Id, CoreExpr)]
    pairs
           ; ([CoreExpr]
    rhss', UsageDetails
    rhs_uds) <- (CoreExpr -> SpecM (CoreExpr, UsageDetails))
    -> [CoreExpr] -> SpecM ([CoreExpr], UsageDetails)
    forall a b.
    (a -> SpecM (b, UsageDetails)) -> [a] -> SpecM ([b], UsageDetails)
    mapAndCombineSM (SpecEnv -> CoreExpr -> SpecM (CoreExpr, UsageDetails)
    specExpr SpecEnv
    rhs_env) [CoreExpr]
    rhss
           ; let scope_uds :: UsageDetails
    scope_uds = UsageDetails
    body_uds UsageDetails -> UsageDetails -> UsageDetails
    `plusUDs` UsageDetails
    rhs_uds
                           -- Includes binds and calls arising from rhss

           ; ([Id]
    bndrs1, [(Id, CoreExpr)]
    spec_defns1, UsageDetails
    uds1) <- SpecEnv
    -> UsageDetails
    -> [(Id, CoreExpr)]
    -> SpecM ([Id], [(Id, CoreExpr)], UsageDetails)
    specDefns SpecEnv
    rhs_env UsageDetails
    scope_uds [(Id, CoreExpr)]
    pairs

           ; ([Id]
    bndrs3, [(Id, CoreExpr)]
    spec_defns3, UsageDetails
    uds3)
                 <- if [(Id, CoreExpr)] -> Bool
    forall (t :: * -> *) a. Foldable t => t a -> Bool
    null [(Id, CoreExpr)]
    spec_defns1  -- Common case: no specialisation
                    then ([Id], [(Id, CoreExpr)], UsageDetails)
    -> SpecM ([Id], [(Id, CoreExpr)], UsageDetails)
    forall (m :: * -> *) a. Monad m => a -> m a
    return ([Id]
    bndrs1, [], UsageDetails
    uds1)
                    else do {            -- Specialisation occurred; do it again
                              ([Id]
    bndrs2, [(Id, CoreExpr)]
    spec_defns2, UsageDetails
    uds2)
                                  <- SpecEnv
    -> UsageDetails
    -> [(Id, CoreExpr)]
    -> SpecM ([Id], [(Id, CoreExpr)], UsageDetails)
    specDefns SpecEnv
    rhs_env UsageDetails
    uds1 ([Id]
    bndrs1 [Id] -> [CoreExpr] -> [(Id, CoreExpr)]
    forall a b. [a] -> [b] -> [(a, b)]
    `zip` [CoreExpr]
    rhss)
                            ; ([Id], [(Id, CoreExpr)], UsageDetails)
    -> SpecM ([Id], [(Id, CoreExpr)], UsageDetails)
    forall (m :: * -> *) a. Monad m => a -> m a
    return ([Id]
    bndrs2, [(Id, CoreExpr)]
    spec_defns2 [(Id, CoreExpr)] -> [(Id, CoreExpr)] -> [(Id, CoreExpr)]
    forall a. [a] -> [a] -> [a]
    ++ [(Id, CoreExpr)]
    spec_defns1, UsageDetails
    uds2) }

           ; let (UsageDetails
    final_uds, Bag DictBind
    dumped_dbs, Bool
    float_all) = [Id] -> UsageDetails -> (UsageDetails, Bag DictBind, Bool)
    dumpBindUDs [Id]
    bndrs UsageDetails
    uds3
                 final_bind :: DictBind
    final_bind = [(Id, CoreExpr)] -> Bag DictBind -> DictBind
    recWithDumpedDicts ([(Id, CoreExpr)]
    spec_defns3 [(Id, CoreExpr)] -> [(Id, CoreExpr)] -> [(Id, CoreExpr)]
    forall a. [a] -> [a] -> [a]
    ++ [Id] -> [CoreExpr] -> [(Id, CoreExpr)]
    forall a b. [a] -> [b] -> [(a, b)]
    zip [Id]
    bndrs3 [CoreExpr]
    rhss')
                                                 Bag DictBind
    dumped_dbs

           ; if Bool
    float_all then
                  (CoreProgram, UsageDetails) -> UniqSM (CoreProgram, UsageDetails)
    forall (m :: * -> *) a. Monad m => a -> m a
    return ([], UsageDetails
    final_uds UsageDetails -> DictBind -> UsageDetails
    `snocDictBind` DictBind
    final_bind)
             else
                  (CoreProgram, UsageDetails) -> UniqSM (CoreProgram, UsageDetails)
    forall (m :: * -> *) a. Monad m => a -> m a
    return ([DictBind -> CoreBind
    db_bind DictBind
    final_bind], UsageDetails
    final_uds) }

    ---------------------------
    specDefns :: SpecEnv
              -> UsageDetails               -- Info on how it is used in its scope
              -> [(OutId,InExpr)]           -- The things being bound and their un-processed RHS
              -> SpecM ([OutId],            -- Original Ids with RULES added
                        [(OutId,OutExpr)],  -- Extra, specialised bindings
                        UsageDetails)       -- Stuff to fling upwards from the specialised versions

    -- Specialise a list of bindings (the contents of a Rec), but flowing usages
    -- upwards binding by binding.  Example: { f = ...g ...; g = ...f .... }
    -- Then if the input CallDetails has a specialised call for 'g', whose specialisation
    -- in turn generates a specialised call for 'f', we catch that in this one sweep.
    -- But not vice versa (it's a fixpoint problem).

    specDefns :: SpecEnv
    -> UsageDetails
    -> [(Id, CoreExpr)]
    -> SpecM ([Id], [(Id, CoreExpr)], UsageDetails)
    specDefns SpecEnv
    _env UsageDetails
    uds []
      = ([Id], [(Id, CoreExpr)], UsageDetails)
    -> SpecM ([Id], [(Id, CoreExpr)], UsageDetails)
    forall (m :: * -> *) a. Monad m => a -> m a
    return ([], [], UsageDetails
    uds)
    specDefns SpecEnv
    env UsageDetails
    uds ((Id
    bndr,CoreExpr
    rhs):[(Id, CoreExpr)]
    pairs)
      = do { ([Id]
    bndrs1, [(Id, CoreExpr)]
    spec_defns1, UsageDetails
    uds1) <- SpecEnv
    -> UsageDetails
    -> [(Id, CoreExpr)]
    -> SpecM ([Id], [(Id, CoreExpr)], UsageDetails)
    specDefns SpecEnv
    env UsageDetails
    uds [(Id, CoreExpr)]
    pairs
           ; (Id
    bndr1, [(Id, CoreExpr)]
    spec_defns2, UsageDetails
    uds2)  <- SpecEnv
    -> UsageDetails
    -> Id
    -> CoreExpr
    -> SpecM (Id, [(Id, CoreExpr)], UsageDetails)
    specDefn SpecEnv
    env UsageDetails
    uds1 Id
    bndr CoreExpr
    rhs
           ; ([Id], [(Id, CoreExpr)], UsageDetails)
    -> SpecM ([Id], [(Id, CoreExpr)], UsageDetails)
    forall (m :: * -> *) a. Monad m => a -> m a
    return (Id
    bndr1 Id -> [Id] -> [Id]
    forall a. a -> [a] -> [a]
    : [Id]
    bndrs1, [(Id, CoreExpr)]
    spec_defns1 [(Id, CoreExpr)] -> [(Id, CoreExpr)] -> [(Id, CoreExpr)]
    forall a. [a] -> [a] -> [a]
    ++ [(Id, CoreExpr)]
    spec_defns2, UsageDetails
    uds2) }

    ---------------------------
    specDefn :: SpecEnv
             -> UsageDetails                -- Info on how it is used in its scope
             -> OutId -> InExpr             -- The thing being bound and its un-processed RHS
             -> SpecM (Id,                  -- Original Id with added RULES
                       [(Id,CoreExpr)],     -- Extra, specialised bindings
                       UsageDetails)        -- Stuff to fling upwards from the specialised versions

    specDefn :: SpecEnv
    -> UsageDetails
    -> Id
    -> CoreExpr
    -> SpecM (Id, [(Id, CoreExpr)], UsageDetails)
    specDefn SpecEnv
    env UsageDetails
    body_uds Id
    fn CoreExpr
    rhs
      = do { let (UsageDetails
    body_uds_without_me, [CallInfo]
    calls_for_me) = Id -> UsageDetails -> (UsageDetails, [CallInfo])
    callsForMe Id
    fn UsageDetails
    body_uds
                 rules_for_me :: [CoreRule]
    rules_for_me = Id -> [CoreRule]
    idCoreRules Id
    fn
           ; ([CoreRule]
    rules, [(Id, CoreExpr)]
    spec_defns, UsageDetails
    spec_uds) <- Bool
    -> SpecEnv
    -> [CoreRule]
    -> [CallInfo]
    -> Id
    -> CoreExpr
    -> SpecM ([CoreRule], [(Id, CoreExpr)], UsageDetails)
    specCalls Bool
    False SpecEnv
    env [CoreRule]
    rules_for_me
                                                        [CallInfo]
    calls_for_me Id
    fn CoreExpr
    rhs
           ; (Id, [(Id, CoreExpr)], UsageDetails)
    -> SpecM (Id, [(Id, CoreExpr)], UsageDetails)
    forall (m :: * -> *) a. Monad m => a -> m a
    return ( Id
    fn Id -> [CoreRule] -> Id
    `addIdSpecialisations` [CoreRule]
    rules
                    , [(Id, CoreExpr)]
    spec_defns
                    , UsageDetails
    body_uds_without_me UsageDetails -> UsageDetails -> UsageDetails
    `plusUDs` UsageDetails
    spec_uds) }
                    -- It's important that the `plusUDs` is this way
                    -- round, because body_uds_without_me may bind
                    -- dictionaries that are used in calls_for_me passed
                    -- to specDefn.  So the dictionary bindings in
                    -- spec_uds may mention dictionaries bound in
                    -- body_uds_without_me

    ---------------------------
    specCalls :: Bool              -- True  =>  specialising imported fn
                                   -- False =>  specialising local fn
              -> SpecEnv
              -> [CoreRule]        -- Existing RULES for the fn
              -> [CallInfo]
              -> OutId -> InExpr
              -> SpecM SpecInfo    -- New rules, specialised bindings, and usage details

    -- This function checks existing rules, and does not create
    -- duplicate ones. So the caller does not need to do this filtering.
    -- See 'already_covered'

    type SpecInfo = ( [CoreRule]       -- Specialisation rules
                    , [(Id,CoreExpr)]  -- Specialised definition
                    , UsageDetails )   -- Usage details from specialised RHSs

    specCalls :: Bool
    -> SpecEnv
    -> [CoreRule]
    -> [CallInfo]
    -> Id
    -> CoreExpr
    -> SpecM ([CoreRule], [(Id, CoreExpr)], UsageDetails)
    specCalls Bool
    spec_imp SpecEnv
    env [CoreRule]
    existing_rules [CallInfo]
    calls_for_me Id
    fn CoreExpr
    rhs
            -- The first case is the interesting one
      |  [CallInfo] -> Bool
    forall (f :: * -> *) a. Foldable f => f a -> Bool
    notNull [CallInfo]
    calls_for_me               -- And there are some calls to specialise
      Bool -> Bool -> Bool
    && Bool -> Bool
    not (Activation -> Bool
    isNeverActive (Id -> Activation
    idInlineActivation Id
    fn))
            -- Don't specialise NOINLINE things
            -- See Note [Auto-specialisation and RULES]

    --   && not (certainlyWillInline (idUnfolding fn))      -- And it's not small
    --      See Note [Inline specialisation] for why we do not
    --      switch off specialisation for inline functions

      = -- pprTrace "specDefn: some" (ppr fn $$ ppr calls_for_me $$ ppr existing_rules) $
        (([CoreRule], [(Id, CoreExpr)], UsageDetails)
     -> CallInfo -> SpecM ([CoreRule], [(Id, CoreExpr)], UsageDetails))
    -> ([CoreRule], [(Id, CoreExpr)], UsageDetails)
    -> [CallInfo]
    -> SpecM ([CoreRule], [(Id, CoreExpr)], UsageDetails)
    forall (t :: * -> *) (m :: * -> *) b a.
    (Foldable t, Monad m) =>
    (b -> a -> m b) -> b -> t a -> m b
    foldlM ([CoreRule], [(Id, CoreExpr)], UsageDetails)
    -> CallInfo -> SpecM ([CoreRule], [(Id, CoreExpr)], UsageDetails)
    spec_call ([], [], UsageDetails
    emptyUDs) [CallInfo]
    calls_for_me

      | Bool
    otherwise   -- No calls or RHS doesn't fit our preconceptions
      = String -> SDoc
    WARN( not (exprIsTrivial rhs(SpecM ([CoreRule], [(Id, CoreExpr)], UsageDetails)
     -> SpecM ([CoreRule], [(Id, CoreExpr)], UsageDetails))
    -> SpecM ([CoreRule], [(Id, CoreExpr)], UsageDetails)
    -> SpecM ([CoreRule], [(Id, CoreExpr)], UsageDetails)
    forall a b. (a -> b) -> a -> b
    ) && notNull calls_for_me,
              text "Missed specialisation opportunity for"
                                     <+> ppr fn $$ _trace_doc )
              -- Note [Specialisation shape]
        -- pprTrace "specDefn: none" (ppr fn <+> ppr calls_for_me) $
        ([CoreRule], [(Id, CoreExpr)], UsageDetails)
    -> SpecM ([CoreRule], [(Id, CoreExpr)], UsageDetails)
    forall (m :: * -> *) a. Monad m => a -> m a
    return ([], [], UsageDetails
    emptyUDs)
      where
        _trace_doc :: SDoc
    _trace_doc = [SDoc] -> SDoc
    sep [ [Id] -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr [Id]
    rhs_bndrs, Activation -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr (Id -> Activation
    idInlineActivation Id
    fn) ]

        fn_type :: Kind
    fn_type   = Id -> Kind
    idType Id
    fn
        fn_arity :: Int
    fn_arity  = Id -> Int
    idArity Id
    fn
        fn_unf :: Unfolding
    fn_unf    = Id -> Unfolding
    realIdUnfolding Id
    fn  -- Ignore loop-breaker-ness here
        inl_prag :: InlinePragma
    inl_prag  = Id -> InlinePragma
    idInlinePragma Id
    fn
        inl_act :: Activation
    inl_act   = InlinePragma -> Activation
    inlinePragmaActivation InlinePragma
    inl_prag
        is_local :: Bool
    is_local  = Id -> Bool
    isLocalId Id
    fn
        is_dfun :: Bool
    is_dfun   = Id -> Bool
    isDFunId Id
    fn
        dflags :: DynFlags
    dflags    = SpecEnv -> DynFlags
    se_dflags SpecEnv
    env
        ropts :: RuleOpts
    ropts     = DynFlags -> RuleOpts
    initRuleOpts DynFlags
    dflags
        this_mod :: Module
    this_mod  = SpecEnv -> Module
    se_module SpecEnv
    env
            -- Figure out whether the function has an INLINE pragma
            -- See Note [Inline specialisations]

        ([Id]
    rhs_bndrs, CoreExpr
    rhs_body) = CoreExpr -> ([Id], CoreExpr)
    collectBindersPushingCo CoreExpr
    rhs
                                -- See Note [Account for casts in binding]

        in_scope :: InScopeSet
    in_scope = Subst -> InScopeSet
    Core.substInScope (SpecEnv -> Subst
    se_subst SpecEnv
    env)

        already_covered :: RuleOpts -> [CoreRule] -> [CoreExpr] -> Bool
        already_covered :: RuleOpts -> [CoreRule] -> [CoreExpr] -> Bool
    already_covered RuleOpts
    ropts [CoreRule]
    new_rules [CoreExpr]
    args      -- Note [Specialisations already covered]
           = Maybe (CoreRule, CoreExpr) -> Bool
    forall a. Maybe a -> Bool
    isJust (RuleOpts
    -> InScopeEnv
    -> (Activation -> Bool)
    -> Id
    -> [CoreExpr]
    -> [CoreRule]
    -> Maybe (CoreRule, CoreExpr)
    lookupRule RuleOpts
    ropts (InScopeSet
    in_scope, Id -> Unfolding
    realIdUnfolding)
                                (Bool -> Activation -> Bool
    forall a b. a -> b -> a
    const Bool
    True) Id
    fn [CoreExpr]
    args
                                ([CoreRule]
    new_rules [CoreRule] -> [CoreRule] -> [CoreRule]
    forall a. [a] -> [a] -> [a]
    ++ [CoreRule]
    existing_rules))
             -- NB: we look both in the new_rules (generated by this invocation
             --     of specCalls), and in existing_rules (passed in to specCalls)

        ----------------------------------------------------------
            -- Specialise to one particular call pattern
        spec_call :: SpecInfo                         -- Accumulating parameter
                  -> CallInfo                         -- Call instance
                  -> SpecM SpecInfo
        spec_call :: ([CoreRule], [(Id, CoreExpr)], UsageDetails)
    -> CallInfo -> SpecM ([CoreRule], [(Id, CoreExpr)], UsageDetails)
    spec_call spec_acc :: ([CoreRule], [(Id, CoreExpr)], UsageDetails)
    spec_acc@([CoreRule]
    rules_acc, [(Id, CoreExpr)]
    pairs_acc, UsageDetails
    uds_acc) _ci :: CallInfo
    _ci@(CI { ci_key :: CallInfo -> [SpecArg]
    ci_key = [SpecArg]
    call_args })
          = -- See Note [Specialising Calls]
            do { let all_call_args :: [SpecArg]
    all_call_args | Bool
    is_dfun   = [SpecArg]
    call_args [SpecArg] -> [SpecArg] -> [SpecArg]
    forall a. [a] -> [a] -> [a]
    ++ SpecArg -> [SpecArg]
    forall a. a -> [a]
    repeat SpecArg
    UnspecArg
                                   | Bool
    otherwise = [SpecArg]
    call_args
                                   -- See Note [Specialising DFuns]
               ; ( Bool
    useful, SpecEnv
    rhs_env2, [Id]
    leftover_bndrs
                 , [Id]
    rule_bndrs, [CoreExpr]
    rule_lhs_args
                 , [Id]
    spec_bndrs1, [DictBind]
    dx_binds, [CoreExpr]
    spec_args) <- SpecEnv
    -> [Id]
    -> [SpecArg]
    -> SpecM
         (Bool, SpecEnv, [Id], [Id], [CoreExpr], [Id], [DictBind],
          [CoreExpr])
    specHeader SpecEnv
    env [Id]
    rhs_bndrs [SpecArg]
    all_call_args

    --           ; pprTrace "spec_call" (vcat [ text "call info: " <+> ppr _ci
    --                                        , text "useful:    " <+> ppr useful
    --                                        , text "rule_bndrs:" <+> ppr rule_bndrs
    --                                        , text "lhs_args:  " <+> ppr rule_lhs_args
    --                                        , text "spec_bndrs:" <+> ppr spec_bndrs1
    --                                        , text "spec_args: " <+> ppr spec_args
    --                                        , text "dx_binds:  " <+> ppr dx_binds
    --                                        , text "rhs_env2:  " <+> ppr (se_subst rhs_env2)
    --                                        , ppr dx_binds ]) $
    --             return ()

               ; if Bool -> Bool
    not Bool
    useful  -- No useful specialisation
                    Bool -> Bool -> Bool
    || RuleOpts -> [CoreRule] -> [CoreExpr] -> Bool
    already_covered RuleOpts
    ropts [CoreRule]
    rules_acc [CoreExpr]
    rule_lhs_args
                 then ([CoreRule], [(Id, CoreExpr)], UsageDetails)
    -> SpecM ([CoreRule], [(Id, CoreExpr)], UsageDetails)
    forall (m :: * -> *) a. Monad m => a -> m a
    return ([CoreRule], [(Id, CoreExpr)], UsageDetails)
    spec_acc
                 else
            do { -- Run the specialiser on the specialised RHS
                 -- The "1" suffix is before we maybe add the void arg
               ; (CoreExpr
    spec_rhs1, UsageDetails
    rhs_uds) <- SpecEnv -> [Id] -> CoreExpr -> SpecM (CoreExpr, UsageDetails)
    specLam SpecEnv
    rhs_env2 ([Id]
    spec_bndrs1 [Id] -> [Id] -> [Id]
    forall a. [a] -> [a] -> [a]
    ++ [Id]
    leftover_bndrs) CoreExpr
    rhs_body
               ; let spec_fn_ty1 :: Kind
    spec_fn_ty1 = CoreExpr -> Kind
    exprType CoreExpr
    spec_rhs1

                     -- Maybe add a void arg to the specialised function,
                     -- to avoid unlifted bindings
                     -- See Note [Specialisations Must Be Lifted]
                     -- C.f. GHC.Core.Opt.WorkWrap.Utils.mkWorkerArgs
                     add_void_arg :: Bool
    add_void_arg = HasDebugCallStack => Kind -> Bool
    Kind -> Bool
    isUnliftedType Kind
    spec_fn_ty1 Bool -> Bool -> Bool
    && Bool -> Bool
    not (Id -> Bool
    isJoinId Id
    fn)
                     ([Id]
    spec_bndrs, CoreExpr
    spec_rhs, Kind
    spec_fn_ty)
                       | Bool
    add_void_arg = ( Id
    voidPrimId Id -> [Id] -> [Id]
    forall a. a -> [a] -> [a]
    : [Id]
    spec_bndrs1
                                        , Id -> CoreExpr -> CoreExpr
    forall b. b -> Expr b -> Expr b
    Lam        Id
    voidArgId  CoreExpr
    spec_rhs1
                                        , Kind -> Kind -> Kind
    mkVisFunTyMany Kind
    unboxedUnitTy Kind
    spec_fn_ty1)
                       | Bool
    otherwise   = ([Id]
    spec_bndrs1, CoreExpr
    spec_rhs1, Kind
    spec_fn_ty1)

                     join_arity_decr :: Int
    join_arity_decr = [CoreExpr] -> Int
    forall (t :: * -> *) a. Foldable t => t a -> Int
    length [CoreExpr]
    rule_lhs_args Int -> Int -> Int
    forall a. Num a => a -> a -> a
    - [Id] -> Int
    forall (t :: * -> *) a. Foldable t => t a -> Int
    length [Id]
    spec_bndrs
                     spec_join_arity :: Maybe Int
    spec_join_arity | Just Int
    orig_join_arity <- Id -> Maybe Int
    isJoinId_maybe Id
    fn
                                     = Int -> Maybe Int
    forall a. a -> Maybe a
    Just (Int
    orig_join_arity Int -> Int -> Int
    forall a. Num a => a -> a -> a
    - Int
    join_arity_decr)
                                     | Bool
    otherwise
                                     = Maybe Int
    forall a. Maybe a
    Nothing

               ; Id
    spec_fn <- Id -> Kind -> Maybe Int -> UniqSM Id
    newSpecIdSM Id
    fn Kind
    spec_fn_ty Maybe Int
    spec_join_arity
               ; let
                    -- The rule to put in the function's specialisation is:
                    --      forall x @b d1' d2'.
                    --          f x @T1 @b @T2 d1' d2' = f1 x @b
                    -- See Note [Specialising Calls]
                    herald :: SDoc
    herald | Bool
    spec_imp  = -- Specialising imported fn
                                         String -> SDoc
    text String
    "SPEC/" SDoc -> SDoc -> SDoc
    <> Module -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Module
    this_mod
                           | Bool
    otherwise = -- Specialising local fn
                                         String -> SDoc
    text String
    "SPEC"

                    rule_name :: FastString
    rule_name = String -> FastString
    mkFastString (String -> FastString) -> String -> FastString
    forall a b. (a -> b) -> a -> b
    $ DynFlags -> SDoc -> String
    showSDoc DynFlags
    dflags (SDoc -> String) -> SDoc -> String
    forall a b. (a -> b) -> a -> b
    $
                                SDoc
    herald SDoc -> SDoc -> SDoc
    <+> FastString -> SDoc
    ftext (OccName -> FastString
    occNameFS (Id -> OccName
    forall a. NamedThing a => a -> OccName
    getOccName Id
    fn))
                                       SDoc -> SDoc -> SDoc
    <+> [SDoc] -> SDoc
    hsep ((SpecArg -> Maybe SDoc) -> [SpecArg] -> [SDoc]
    forall a b. (a -> Maybe b) -> [a] -> [b]
    mapMaybe SpecArg -> Maybe SDoc
    ppr_call_key_ty [SpecArg]
    call_args)
                                -- This name ends up in interface files, so use occNameString.
                                -- Otherwise uniques end up there, making builds
                                -- less deterministic (See #4012 comment:61 ff)

                    rule_wout_eta :: CoreRule
    rule_wout_eta = Module
    -> Bool
    -> Bool
    -> FastString
    -> Activation
    -> Name
    -> [Id]
    -> [CoreExpr]
    -> CoreExpr
    -> CoreRule
    mkRule
                                      Module
    this_mod
                                      Bool
    True {- Auto generated -}
                                      Bool
    is_local
                                      FastString
    rule_name
                                      Activation
    inl_act       -- Note [Auto-specialisation and RULES]
                                      (Id -> Name
    idName Id
    fn)
                                      [Id]
    rule_bndrs
                                      [CoreExpr]
    rule_lhs_args
                                      (CoreExpr -> [Id] -> CoreExpr
    forall b. Expr b -> [Id] -> Expr b
    mkVarApps (Id -> CoreExpr
    forall b. Id -> Expr b
    Var Id
    spec_fn) [Id]
    spec_bndrs)

                    spec_rule :: CoreRule
    spec_rule
                      = case Id -> Maybe Int
    isJoinId_maybe Id
    fn of
                          Just Int
    join_arity -> Int -> CoreRule -> CoreRule
    etaExpandToJoinPointRule Int
    join_arity CoreRule
    rule_wout_eta
                          Maybe Int
    Nothing -> CoreRule
    rule_wout_eta

                    -- Add the { d1' = dx1; d2' = dx2 } usage stuff
                    -- See Note [Specialising Calls]
                    spec_uds :: UsageDetails
    spec_uds = (DictBind -> UsageDetails -> UsageDetails)
    -> UsageDetails -> [DictBind] -> UsageDetails
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr DictBind -> UsageDetails -> UsageDetails
    consDictBind UsageDetails
    rhs_uds [DictBind]
    dx_binds

                    simpl_opts :: SimpleOpts
    simpl_opts = DynFlags -> SimpleOpts
    initSimpleOpts DynFlags
    dflags

                    --------------------------------------
                    -- Add a suitable unfolding if the spec_inl_prag says so
                    -- See Note [Inline specialisations]
                    (InlinePragma
    spec_inl_prag, Unfolding
    spec_unf)
                      | Bool -> Bool
    not Bool
    is_local Bool -> Bool -> Bool
    && OccInfo -> Bool
    isStrongLoopBreaker (Id -> OccInfo
    idOccInfo Id
    fn)
                      = (InlinePragma
    neverInlinePragma, Unfolding
    noUnfolding)
                            -- See Note [Specialising imported functions] in "GHC.Core.Opt.OccurAnal"

                      | InlinePragma { inl_inline :: InlinePragma -> InlineSpec
    inl_inline = InlineSpec
    Inlinable } <- InlinePragma
    inl_prag
                      = (InlinePragma
    inl_prag { inl_inline :: InlineSpec
    inl_inline = InlineSpec
    NoUserInlinePrag }, Unfolding
    noUnfolding)

                      | Bool
    otherwise
                      = (InlinePragma
    inl_prag, SimpleOpts
    -> [Id]
    -> (CoreExpr -> CoreExpr)
    -> [CoreExpr]
    -> Unfolding
    -> Unfolding
    specUnfolding SimpleOpts
    simpl_opts [Id]
    spec_bndrs (CoreExpr -> [CoreExpr] -> CoreExpr
    forall b. Expr b -> [Expr b] -> Expr b
    `mkApps` [CoreExpr]
    spec_args)
                                                 [CoreExpr]
    rule_lhs_args Unfolding
    fn_unf)

                    --------------------------------------
                    -- Adding arity information just propagates it a bit faster
                    --      See Note [Arity decrease] in GHC.Core.Opt.Simplify
                    -- Copy InlinePragma information from the parent Id.
                    -- So if f has INLINE[1] so does spec_fn
                    arity_decr :: Int
    arity_decr     = (CoreExpr -> Bool) -> [CoreExpr] -> Int
    forall a. (a -> Bool) -> [a] -> Int
    count CoreExpr -> Bool
    forall b. Expr b -> Bool
    isValArg [CoreExpr]
    rule_lhs_args Int -> Int -> Int
    forall a. Num a => a -> a -> a
    - (Id -> Bool) -> [Id] -> Int
    forall a. (a -> Bool) -> [a] -> Int
    count Id -> Bool
    isId [Id]
    spec_bndrs
                    spec_f_w_arity :: Id
    spec_f_w_arity = Id
    spec_fn Id -> Int -> Id
    `setIdArity`      Int -> Int -> Int
    forall a. Ord a => a -> a -> a
    max Int
    0 (Int
    fn_arity Int -> Int -> Int
    forall a. Num a => a -> a -> a
    - Int
    arity_decr)
                                             Id -> InlinePragma -> Id
    `setInlinePragma` InlinePragma
    spec_inl_prag
                                             Id -> Unfolding -> Id
    `setIdUnfolding`  Unfolding
    spec_unf
                                             Id -> Maybe Int -> Id
    `asJoinId_maybe`  Maybe Int
    spec_join_arity

                    _rule_trace_doc :: SDoc
    _rule_trace_doc = [SDoc] -> SDoc
    vcat [ Id -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Id
    fn SDoc -> SDoc -> SDoc
    <+> SDoc
    dcolon SDoc -> SDoc -> SDoc
    <+> Kind -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Kind
    fn_type
                                           , Id -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Id
    spec_fn  SDoc -> SDoc -> SDoc
    <+> SDoc
    dcolon SDoc -> SDoc -> SDoc
    <+> Kind -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Kind
    spec_fn_ty
                                           , [Id] -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr [Id]
    rhs_bndrs, [SpecArg] -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr [SpecArg]
    call_args
                                           , CoreRule -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr CoreRule
    spec_rule
                                           ]

               ; -- pprTrace "spec_call: rule" _rule_trace_doc
                 ([CoreRule], [(Id, CoreExpr)], UsageDetails)
    -> SpecM ([CoreRule], [(Id, CoreExpr)], UsageDetails)
    forall (m :: * -> *) a. Monad m => a -> m a
    return ( CoreRule
    spec_rule                  CoreRule -> [CoreRule] -> [CoreRule]
    forall a. a -> [a] -> [a]
    : [CoreRule]
    rules_acc
                        , (Id
    spec_f_w_arity, CoreExpr
    spec_rhs) (Id, CoreExpr) -> [(Id, CoreExpr)] -> [(Id, CoreExpr)]
    forall a. a -> [a] -> [a]
    : [(Id, CoreExpr)]
    pairs_acc
                        , UsageDetails
    spec_uds           UsageDetails -> UsageDetails -> UsageDetails
    `plusUDs` UsageDetails
    uds_acc
                        ) } }

    {- Note [Specialising DFuns]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    DFuns have a special sort of unfolding (DFunUnfolding), and these are
    hard to specialise a DFunUnfolding to give another DFunUnfolding
    unless the DFun is fully applied (#18120).  So, in the case of DFunIds
    we simply extend the CallKey with trailing UnspecArgs, so we'll
    generate a rule that completely saturates the DFun.

    There is an ASSERT that checks this, in the DFunUnfolding case of
    GHC.Core.Unfold.specUnfolding.

    Note [Specialisation Must Preserve Sharing]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider a function:

        f :: forall a. Eq a => a -> blah
        f =
          if expensive
             then f1
             else f2

    As written, all calls to 'f' will share 'expensive'. But if we specialise 'f'
    at 'Int', eg:

        $sfInt = SUBST[a->Int,dict->dEqInt] (if expensive then f1 else f2)

        RULE "SPEC f"
          forall (d :: Eq Int).
            f Int _ = $sfIntf

    We've now lost sharing between 'f' and '$sfInt' for 'expensive'. Yikes!

    To avoid this, we only generate specialisations for functions whose arity is
    enough to bind all of the arguments we need to specialise.  This ensures our
    specialised functions don't do any work before receiving all of their dicts,
    and thus avoids the 'f' case above.

    Note [Specialisations Must Be Lifted]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider a function 'f':

        f = forall a. Eq a => Array# a

    used like

        case x of
          True -> ...f @Int dEqInt...
          False -> 0

    Naively, we might generate an (expensive) specialisation

        $sfInt :: Array# Int

    even in the case that @x = False@! Instead, we add a dummy 'Void#' argument to
    the specialisation '$sfInt' ($sfInt :: Void# -> Array# Int) in order to
    preserve laziness.

    Note [Specialising Calls]
    ~~~~~~~~~~~~~~~~~~~~~~~~~
    Suppose we have a function with a complicated type:

        f :: forall a b c. Int -> Eq a => Show b => c -> Blah
        f @a @b @c i dEqA dShowA x = blah

    and suppose it is called at:

        f 7 @T1 @T2 @T3 dEqT1 ($dfShow dShowT2) t3

    This call is described as a 'CallInfo' whose 'ci_key' is:

        [ SpecType T1, SpecType T2, UnspecType, UnspecArg, SpecDict dEqT1
        , SpecDict ($dfShow dShowT2), UnspecArg ]

    Why are 'a' and 'b' identified as 'SpecType', while 'c' is 'UnspecType'?
    Because we must specialise the function on type variables that appear
    free in its *dictionary* arguments; but not on type variables that do not
    appear in any dictionaries, i.e. are fully polymorphic.

    Because this call has dictionaries applied, we'd like to specialise
    the call on any type argument that appears free in those dictionaries.
    In this case, those are [a :-> T1, b :-> T2].

    We also need to substitute the dictionary binders with their
    specialised dictionaries. The simplest substitution would be
    [dEqA :-> dEqT1, dShowA :-> $dfShow dShowT2], but this duplicates
    work, since `$dfShow dShowT2` is a function application. Therefore, we
    also want to *float the dictionary out* (via bindAuxiliaryDict),
    creating a new dict binding

        dShow1 = $dfShow dShowT2

    and the substitution [dEqA :-> dEqT1, dShowA :-> dShow1].

    With the substitutions in hand, we can generate a specialised function:

        $sf :: forall c. Int -> c -> Blah
        $sf = SUBST[a :-> T1, b :-> T2, dEqA :-> dEqT1, dShowA :-> dShow1] (\@c i x -> blah)

    Note that the substitution is applied to the whole thing.  This is
    convenient, but just slightly fragile.  Notably:
      * There had better be no name clashes in a/b/c

    We must construct a rewrite rule:

        RULE "SPEC f @T1 @T2 _"
          forall (@c :: Type) (i :: Int) (d1 :: Eq T1) (d2 :: Show T2).
            f @T1 @T2 @c i d1 d2 = $sf @c i

    In the rule, d1 and d2 are just wildcards, not used in the RHS.  Note
    additionally that 'x' isn't captured by this rule --- we bind only
    enough etas in order to capture all of the *specialised* arguments.

    Note [Drop dead args from specialisations]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    When specialising a function, it’s possible some of the arguments may
    actually be dead. For example, consider:

        f :: forall a. () -> Show a => a -> String
        f x y = show y ++ "!"

    We might generate the following CallInfo for `f @Int`:

        [SpecType Int, UnspecArg, SpecDict $dShowInt, UnspecArg]

    Normally we’d include both the x and y arguments in the
    specialisation, since we’re not specialising on either of them. But
    that’s silly, since x is actually unused! So we might as well drop it
    in the specialisation:

        $sf :: Int -> String
        $sf y = show y ++ "!"

        {-# RULE "SPEC f @Int" forall x. f @Int x $dShow = $sf #-}

    This doesn’t save us much, since the arg would be removed later by
    worker/wrapper, anyway, but it’s easy to do. Note, however, that we
    only drop dead arguments if:

      1. We don’t specialise on them.
      2. They come before an argument we do specialise on.

    Doing the latter would require eta-expanding the RULE, which could
    make it match less often, so it’s not worth it. Doing the former could
    be more useful --- it would stop us from generating pointless
    specialisations --- but it’s more involved to implement and unclear if
    it actually provides much benefit in practice.

    Note [Zap occ info in rule binders]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    When we generate a specialisation RULE, we need to drop occurrence
    info on the binders. If we don’t, things go wrong when we specialise a
    function like

        f :: forall a. () -> Show a => a -> String
        f x y = show y ++ "!"

    since we’ll generate a RULE like

        RULE "SPEC f @Int" forall x [Occ=Dead].
          f @Int x $dShow = $sf

    and Core Lint complains, even though x only appears on the LHS (due to
    Note [Drop dead args from specialisations]).

    Why is that a Lint error? Because the arguments on the LHS of a rule
    are syntactically expressions, not patterns, so Lint treats the
    appearance of x as a use rather than a binding. Fortunately, the
    solution is simple: we just make sure to zap the occ info before
    using ids as wildcard binders in a rule.

    Note [Account for casts in binding]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider
       f :: Eq a => a -> IO ()
       {-# INLINABLE f
           StableUnf = (/\a \(d:Eq a) (x:a). blah) |> g
         #-}
       f = ...

    In f's stable unfolding we have done some modest simplification which
    has pushed the cast to the outside.  (I wonder if this is the Right
    Thing, but it's what happens now; see GHC.Core.Opt.Simplify.Utils Note [Casts and
    lambdas].)  Now that stable unfolding must be specialised, so we want
    to push the cast back inside. It would be terrible if the cast
    defeated specialisation!  Hence the use of collectBindersPushingCo.

    Note [Evidence foralls]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~
    Suppose (#12212) that we are specialising
       f :: forall a b. (Num a, F a ~ F b) => blah
    with a=b=Int. Then the RULE will be something like
       RULE forall (d:Num Int) (g :: F Int ~ F Int).
            f Int Int d g = f_spec
    But both varToCoreExpr (when constructing the LHS args), and the
    simplifier (when simplifying the LHS args), will transform to
       RULE forall (d:Num Int) (g :: F Int ~ F Int).
            f Int Int d <F Int> = f_spec
    by replacing g with Refl.  So now 'g' is unbound, which results in a later
    crash. So we use Refl right off the bat, and do not forall-quantify 'g':
     * varToCoreExpr generates a Refl
     * exprsFreeIdsList returns the Ids bound by the args,
       which won't include g

    You might wonder if this will match as often, but the simplifier replaces
    complicated Refl coercions with Refl pretty aggressively.

    Note [Orphans and auto-generated rules]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    When we specialise an INLINABLE function, or when we have
    -fspecialise-aggressively, we auto-generate RULES that are orphans.
    We don't want to warn about these, or we'd generate a lot of warnings.
    Thus, we only warn about user-specified orphan rules.

    Indeed, we don't even treat the module as an orphan module if it has
    auto-generated *rule* orphans.  Orphan modules are read every time we
    compile, so they are pretty obtrusive and slow down every compilation,
    even non-optimised ones.  (Reason: for type class instances it's a
    type correctness issue.)  But specialisation rules are strictly for
    *optimisation* only so it's fine not to read the interface.

    What this means is that a SPEC rules from auto-specialisation in
    module M will be used in other modules only if M.hi has been read for
    some other reason, which is actually pretty likely.

    Note [From non-recursive to recursive]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Even in the non-recursive case, if any dict-binds depend on 'fn' we might
    have built a recursive knot

          f a d x = <blah>
          MkUD { ud_binds = NonRec d7  (MkD ..f..)
               , ud_calls = ...(f T d7)... }

    The we generate

         Rec { fs x = <blah>[T/a, d7/d]
               f a d x = <blah>
                   RULE f T _ = fs
               d7 = ...f... }

    Here the recursion is only through the RULE.

    However we definitely should /not/ make the Rec in this wildly common
    case:
          d = ...
          MkUD { ud_binds = NonRec d7 (...d...)
               , ud_calls = ...(f T d7)... }

    Here we want simply to add d to the floats, giving
          MkUD { ud_binds = NonRec d (...)
                            NonRec d7 (...d...)
               , ud_calls = ...(f T d7)... }

    In general, we need only make this Rec if
      - there are some specialisations (spec_binds non-empty)
      - there are some dict_binds that depend on f (dump_dbs non-empty)

    Note [Avoiding loops]
    ~~~~~~~~~~~~~~~~~~~~~
    When specialising /dictionary functions/ we must be very careful to
    avoid building loops. Here is an example that bit us badly, on
    several distinct occasions.

    Here is one: #3591
         class Eq a => C a
         instance Eq [a] => C [a]

    This translates to
         dfun :: Eq [a] -> C [a]
         dfun a d = MkD a d (meth d)

         d4 :: Eq [T] = <blah>
         d2 ::  C [T] = dfun T d4
         d1 :: Eq [T] = $p1 d2
         d3 ::  C [T] = dfun T d1

    None of these definitions is recursive. What happened was that we
    generated a specialisation:
         RULE forall d. dfun T d = dT  :: C [T]
         dT = (MkD a d (meth d)) [T/a, d1/d]
            = MkD T d1 (meth d1)

    But now we use the RULE on the RHS of d2, to get
        d2 = dT = MkD d1 (meth d1)
        d1 = $p1 d2

    and now d1 is bottom!  The problem is that when specialising 'dfun' we
    should first dump "below" the binding all floated dictionary bindings
    that mention 'dfun' itself.  So d2 and d3 (and hence d1) must be
    placed below 'dfun', and thus unavailable to it when specialising
    'dfun'.  That in turn means that the call (dfun T d1) must be
    discarded.  On the other hand, the call (dfun T d4) is fine, assuming
    d4 doesn't mention dfun.

    Solution:
      Discard all calls that mention dictionaries that depend
      (directly or indirectly) on the dfun we are specialising.
      This is done by 'filterCalls'

    --------------
    Here's yet another example

      class C a where { foo,bar :: [a] -> [a] }

      instance C Int where
         foo x = r_bar x
         bar xs = reverse xs

      r_bar :: C a => [a] -> [a]
      r_bar xs = bar (xs ++ xs)

    That translates to:

        r_bar a (c::C a) (xs::[a]) = bar a d (xs ++ xs)

        Rec { $fCInt :: C Int = MkC foo_help reverse
              foo_help (xs::[Int]) = r_bar Int $fCInt xs }

    The call (r_bar $fCInt) mentions $fCInt,
                            which mentions foo_help,
                            which mentions r_bar
    But we DO want to specialise r_bar at Int:

        Rec { $fCInt :: C Int = MkC foo_help reverse
              foo_help (xs::[Int]) = r_bar Int $fCInt xs

              r_bar a (c::C a) (xs::[a]) = bar a d (xs ++ xs)
                RULE r_bar Int _ = r_bar_Int

              r_bar_Int xs = bar Int $fCInt (xs ++ xs)
               }

    Note that, because of its RULE, r_bar joins the recursive
    group.  (In this case it'll unravel a short moment later.)

    Note [Specialising a recursive group]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider
        let rec { f x = ...g x'...
                ; g y = ...f y'.... }
        in f 'a'
    Here we specialise 'f' at Char; but that is very likely to lead to
    a specialisation of 'g' at Char.  We must do the latter, else the
    whole point of specialisation is lost.

    But we do not want to keep iterating to a fixpoint, because in the
    presence of polymorphic recursion we might generate an infinite number
    of specialisations.

    So we use the following heuristic:
      * Arrange the rec block in dependency order, so far as possible
        (the occurrence analyser already does this)

      * Specialise it much like a sequence of lets

      * Then go through the block a second time, feeding call-info from
        the RHSs back in the bottom, as it were

    In effect, the ordering maxmimises the effectiveness of each sweep,
    and we do just two sweeps.   This should catch almost every case of
    monomorphic recursion -- the exception could be a very knotted-up
    recursion with multiple cycles tied up together.

    This plan is implemented in the Rec case of specBindItself.

    Note [Specialisations already covered]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    We obviously don't want to generate two specialisations for the same
    argument pattern.  There are two wrinkles

    1. We do the already-covered test in specDefn, not when we generate
    the CallInfo in mkCallUDs.  We used to test in the latter place, but
    we now iterate the specialiser somewhat, and the Id at the call site
    might therefore not have all the RULES that we can see in specDefn

    2. What about two specialisations where the second is an *instance*
    of the first?  If the more specific one shows up first, we'll generate
    specialisations for both.  If the *less* specific one shows up first,
    we *don't* currently generate a specialisation for the more specific
    one.  (See the call to lookupRule in already_covered.)  Reasons:
      (a) lookupRule doesn't say which matches are exact (bad reason)
      (b) if the earlier specialisation is user-provided, it's
          far from clear that we should auto-specialise further

    Note [Auto-specialisation and RULES]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider:
       g :: Num a => a -> a
       g = ...

       f :: (Int -> Int) -> Int
       f w = ...
       {-# RULE f g = 0 #-}

    Suppose that auto-specialisation makes a specialised version of
    g::Int->Int That version won't appear in the LHS of the RULE for f.
    So if the specialisation rule fires too early, the rule for f may
    never fire.

    It might be possible to add new rules, to "complete" the rewrite system.
    Thus when adding
            RULE forall d. g Int d = g_spec
    also add
            RULE f g_spec = 0

    But that's a bit complicated.  For now we ask the programmer's help,
    by *copying the INLINE activation pragma* to the auto-specialised
    rule.  So if g says {-# NOINLINE[2] g #-}, then the auto-spec rule
    will also not be active until phase 2.  And that's what programmers
    should jolly well do anyway, even aside from specialisation, to ensure
    that g doesn't inline too early.

    This in turn means that the RULE would never fire for a NOINLINE
    thing so not much point in generating a specialisation at all.

    Note [Specialisation shape]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~
    We only specialise a function if it has visible top-level lambdas
    corresponding to its overloading.  E.g. if
            f :: forall a. Eq a => ....
    then its body must look like
            f = /\a. \d. ...

    Reason: when specialising the body for a call (f ty dexp), we want to
    substitute dexp for d, and pick up specialised calls in the body of f.

    This doesn't always work.  One example I came across was this:
            newtype Gen a = MkGen{ unGen :: Int -> a }

            choose :: Eq a => a -> Gen a
            choose n = MkGen (\r -> n)

            oneof = choose (1::Int)

    It's a silly example, but we get
            choose = /\a. g `cast` co
    where choose doesn't have any dict arguments.  Thus far I have not
    tried to fix this (wait till there's a real example).

    Mind you, then 'choose' will be inlined (since RHS is trivial) so
    it doesn't matter.  This comes up with single-method classes

       class C a where { op :: a -> a }
       instance C a => C [a] where ....
    ==>
       $fCList :: C a => C [a]
       $fCList = $copList |> (...coercion>...)
       ....(uses of $fCList at particular types)...

    So we suppress the WARN if the rhs is trivial.

    Note [Inline specialisations]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Here is what we do with the InlinePragma of the original function
      * Activation/RuleMatchInfo: both transferred to the
                                  specialised function
      * InlineSpec:
           (a) An INLINE pragma is transferred
           (b) An INLINABLE pragma is *not* transferred

    Why (a): transfer INLINE pragmas? The point of INLINE was precisely to
    specialise the function at its call site, and arguably that's not so
    important for the specialised copies.  BUT *pragma-directed*
    specialisation now takes place in the typechecker/desugarer, with
    manually specified INLINEs.  The specialisation here is automatic.
    It'd be very odd if a function marked INLINE was specialised (because
    of some local use), and then forever after (including importing
    modules) the specialised version wasn't INLINEd.  After all, the
    programmer said INLINE!

    You might wonder why we specialise INLINE functions at all.  After
    all they should be inlined, right?  Two reasons:

     * Even INLINE functions are sometimes not inlined, when they aren't
       applied to interesting arguments.  But perhaps the type arguments
       alone are enough to specialise (even though the args are too boring
       to trigger inlining), and it's certainly better to call the
       specialised version.

     * The RHS of an INLINE function might call another overloaded function,
       and we'd like to generate a specialised version of that function too.
       This actually happens a lot. Consider
          replicateM_ :: (Monad m) => Int -> m a -> m ()
          {-# INLINABLE replicateM_ #-}
          replicateM_ d x ma = ...
       The strictness analyser may transform to
          replicateM_ :: (Monad m) => Int -> m a -> m ()
          {-# INLINE replicateM_ #-}
          replicateM_ d x ma = case x of I# x' -> $wreplicateM_ d x' ma

          $wreplicateM_ :: (Monad m) => Int# -> m a -> m ()
          {-# INLINABLE $wreplicateM_ #-}
          $wreplicateM_ = ...
       Now an importing module has a specialised call to replicateM_, say
       (replicateM_ dMonadIO).  We certainly want to specialise $wreplicateM_!
       This particular example had a huge effect on the call to replicateM_
       in nofib/shootout/n-body.

    Why (b): discard INLINABLE pragmas? See #4874 for persuasive examples.
    Suppose we have
        {-# INLINABLE f #-}
        f :: Ord a => [a] -> Int
        f xs = letrec f' = ...f'... in f'
    Then, when f is specialised and optimised we might get
        wgo :: [Int] -> Int#
        wgo = ...wgo...
        f_spec :: [Int] -> Int
        f_spec xs = case wgo xs of { r -> I# r }
    and we clearly want to inline f_spec at call sites.  But if we still
    have the big, un-optimised of f (albeit specialised) captured in an
    INLINABLE pragma for f_spec, we won't get that optimisation.

    So we simply drop INLINABLE pragmas when specialising. It's not really
    a complete solution; ignoring specialisation for now, INLINABLE functions
    don't get properly strictness analysed, for example. But it works well
    for examples involving specialisation, which is the dominant use of
    INLINABLE.  See #4874.
    -}

    {- *********************************************************************
    *                                                                      *
                       SpecArg, and specHeader
    *                                                                      *
    ********************************************************************* -}

    -- | An argument that we might want to specialise.
    -- See Note [Specialising Calls] for the nitty gritty details.
    data SpecArg
      =
        -- | Type arguments that should be specialised, due to appearing
        -- free in the type of a 'SpecDict'.
        SpecType Type

        -- | Type arguments that should remain polymorphic.
      | UnspecType

        -- | Dictionaries that should be specialised. mkCallUDs ensures
        -- that only "interesting" dictionary arguments get a SpecDict;
        -- see Note [Interesting dictionary arguments]
      | SpecDict DictExpr

        -- | Value arguments that should not be specialised.
      | UnspecArg

    instance Outputable SpecArg where
      ppr :: SpecArg -> SDoc
    ppr (SpecType Kind
    t) = String -> SDoc
    text String
    "SpecType" SDoc -> SDoc -> SDoc
    <+> Kind -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Kind
    t
      ppr SpecArg
    UnspecType   = String -> SDoc
    text String
    "UnspecType"
      ppr (SpecDict CoreExpr
    d) = String -> SDoc
    text String
    "SpecDict" SDoc -> SDoc -> SDoc
    <+> CoreExpr -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr CoreExpr
    d
      ppr SpecArg
    UnspecArg    = String -> SDoc
    text String
    "UnspecArg"

    specArgFreeVars :: SpecArg -> VarSet
    specArgFreeVars :: SpecArg -> VarSet
    specArgFreeVars (SpecType Kind
    ty) = Kind -> VarSet
    tyCoVarsOfType Kind
    ty
    specArgFreeVars (SpecDict CoreExpr
    dx) = CoreExpr -> VarSet
    exprFreeVars CoreExpr
    dx
    specArgFreeVars SpecArg
    UnspecType    = VarSet
    emptyVarSet
    specArgFreeVars SpecArg
    UnspecArg     = VarSet
    emptyVarSet

    isSpecDict :: SpecArg -> Bool
    isSpecDict :: SpecArg -> Bool
    isSpecDict (SpecDict {}) = Bool
    True
    isSpecDict SpecArg
    _             = Bool
    False

    -- | Given binders from an original function 'f', and the 'SpecArg's
    -- corresponding to its usage, compute everything necessary to build
    -- a specialisation.
    --
    -- We will use the running example from Note [Specialising Calls]:
    --
    --     f :: forall a b c. Int -> Eq a => Show b => c -> Blah
    --     f @a @b @c i dEqA dShowA x = blah
    --
    -- Suppose we decide to specialise it at the following pattern:
    --
    --     [ SpecType T1, SpecType T2, UnspecType, UnspecArg
    --     , SpecDict dEqT1, SpecDict ($dfShow dShowT2), UnspecArg ]
    --
    -- We'd eventually like to build the RULE
    --
    --     RULE "SPEC f @T1 @T2 _"
    --       forall (@c :: Type) (i :: Int) (d1 :: Eq T1) (d2 :: Show T2).
    --         f @T1 @T2 @c i d1 d2 = $sf @c i
    --
    -- and the specialisation '$sf'
    --
    --     $sf :: forall c. Int -> c -> Blah
    --     $sf = SUBST[a :-> T1, b :-> T2, dEqA :-> dEqT1, dShowA :-> dShow1] (\@c i x -> blah)
    --
    -- where dShow1 is a floated binding created by bindAuxiliaryDict.
    --
    -- The cases for 'specHeader' below are presented in the same order as this
    -- running example. The result of 'specHeader' for this example is as follows:
    --
    --    ( -- Returned arguments
    --      env + [a :-> T1, b :-> T2, dEqA :-> dEqT1, dShowA :-> dShow1]
    --    , [x]
    --
    --      -- RULE helpers
    --    , [c, i, d1, d2]
    --    , [T1, T2, c, i, d1, d2]
    --
    --      -- Specialised function helpers
    --    , [c, i, x]
    --    , [dShow1 = $dfShow dShowT2]
    --    , [T1, T2, c, i, dEqT1, dShow1]
    --    )
    specHeader
         :: SpecEnv
         -> [InBndr]    -- The binders from the original function 'f'
         -> [SpecArg]   -- From the CallInfo
         -> SpecM ( Bool     -- True <=> some useful specialisation happened
                             -- Not the same as any (isSpecDict args) because
                             -- the args might be longer than bndrs

                    -- Returned arguments
                  , SpecEnv      -- Substitution to apply to the body of 'f'
                  , [OutBndr]    -- Leftover binders from the original function 'f'
                                 --   that don’t have a corresponding SpecArg

                    -- RULE helpers
                  , [OutBndr]    -- Binders for the RULE
                  , [OutExpr]    -- Args for the LHS of the rule

                    -- Specialised function helpers
                  , [OutBndr]    -- Binders for $sf
                  , [DictBind]   -- Auxiliary dictionary bindings
                  , [OutExpr]    -- Specialised arguments for unfolding
                                 -- Same length as "args for LHS of rule"
                  )

    -- We want to specialise on type 'T1', and so we must construct a substitution
    -- 'a->T1', as well as a LHS argument for the resulting RULE and unfolding
    -- details.
    specHeader :: SpecEnv
    -> [Id]
    -> [SpecArg]
    -> SpecM
         (Bool, SpecEnv, [Id], [Id], [CoreExpr], [Id], [DictBind],
          [CoreExpr])
    specHeader SpecEnv
    env (Id
    bndr : [Id]
    bndrs) (SpecType Kind
    t : [SpecArg]
    args)
      = do { let env' :: SpecEnv
    env' = SpecEnv -> [(Id, Kind)] -> SpecEnv
    extendTvSubstList SpecEnv
    env [(Id
    bndr, Kind
    t)]
           ; (Bool
    useful, SpecEnv
    env'', [Id]
    leftover_bndrs, [Id]
    rule_bs, [CoreExpr]
    rule_es, [Id]
    bs', [DictBind]
    dx, [CoreExpr]
    spec_args)
                <- SpecEnv
    -> [Id]
    -> [SpecArg]
    -> SpecM
         (Bool, SpecEnv, [Id], [Id], [CoreExpr], [Id], [DictBind],
          [CoreExpr])
    specHeader SpecEnv
    env' [Id]
    bndrs [SpecArg]
    args
           ; (Bool, SpecEnv, [Id], [Id], [CoreExpr], [Id], [DictBind],
     [CoreExpr])
    -> SpecM
         (Bool, SpecEnv, [Id], [Id], [CoreExpr], [Id], [DictBind],
          [CoreExpr])
    forall (f :: * -> *) a. Applicative f => a -> f a
    pure ( Bool
    useful
                  , SpecEnv
    env''
                  , [Id]
    leftover_bndrs
                  , [Id]
    rule_bs
                  , Kind -> CoreExpr
    forall b. Kind -> Expr b
    Type Kind
    t CoreExpr -> [CoreExpr] -> [CoreExpr]
    forall a. a -> [a] -> [a]
    : [CoreExpr]
    rule_es
                  , [Id]
    bs'
                  , [DictBind]
    dx
                  , Kind -> CoreExpr
    forall b. Kind -> Expr b
    Type Kind
    t CoreExpr -> [CoreExpr] -> [CoreExpr]
    forall a. a -> [a] -> [a]
    : [CoreExpr]
    spec_args
                  )
           }

    -- Next we have a type that we don't want to specialise. We need to perform
    -- a substitution on it (in case the type refers to 'a'). Additionally, we need
    -- to produce a binder, LHS argument and RHS argument for the resulting rule,
    -- /and/ a binder for the specialised body.
    specHeader SpecEnv
    env (Id
    bndr : [Id]
    bndrs) (SpecArg
    UnspecType : [SpecArg]
    args)
      = do { let (SpecEnv
    env', Id
    bndr') = SpecEnv -> Id -> (SpecEnv, Id)
    substBndr SpecEnv
    env Id
    bndr
           ; (Bool
    useful, SpecEnv
    env'', [Id]
    leftover_bndrs, [Id]
    rule_bs, [CoreExpr]
    rule_es, [Id]
    bs', [DictBind]
    dx, [CoreExpr]
    spec_args)
                <- SpecEnv
    -> [Id]
    -> [SpecArg]
    -> SpecM
         (Bool, SpecEnv, [Id], [Id], [CoreExpr], [Id], [DictBind],
          [CoreExpr])
    specHeader SpecEnv
    env' [Id]
    bndrs [SpecArg]
    args
           ; (Bool, SpecEnv, [Id], [Id], [CoreExpr], [Id], [DictBind],
     [CoreExpr])
    -> SpecM
         (Bool, SpecEnv, [Id], [Id], [CoreExpr], [Id], [DictBind],
          [CoreExpr])
    forall (f :: * -> *) a. Applicative f => a -> f a
    pure ( Bool
    useful
                  , SpecEnv
    env''
                  , [Id]
    leftover_bndrs
                  , Id
    bndr' Id -> [Id] -> [Id]
    forall a. a -> [a] -> [a]
    : [Id]
    rule_bs
                  , Id -> CoreExpr
    forall b. Id -> Expr b
    varToCoreExpr Id
    bndr' CoreExpr -> [CoreExpr] -> [CoreExpr]
    forall a. a -> [a] -> [a]
    : [CoreExpr]
    rule_es
                  , Id
    bndr' Id -> [Id] -> [Id]
    forall a. a -> [a] -> [a]
    : [Id]
    bs'
                  , [DictBind]
    dx
                  , Id -> CoreExpr
    forall b. Id -> Expr b
    varToCoreExpr Id
    bndr' CoreExpr -> [CoreExpr] -> [CoreExpr]
    forall a. a -> [a] -> [a]
    : [CoreExpr]
    spec_args
                  )
           }

    -- Next we want to specialise the 'Eq a' dict away. We need to construct
    -- a wildcard binder to match the dictionary (See Note [Specialising Calls] for
    -- the nitty-gritty), as a LHS rule and unfolding details.
    specHeader SpecEnv
    env (Id
    bndr : [Id]
    bndrs) (SpecDict CoreExpr
    d : [SpecArg]
    args)
      = do { Id
    bndr' <- SpecEnv -> Id -> UniqSM Id
    newDictBndr SpecEnv
    env Id
    bndr -- See Note [Zap occ info in rule binders]
           ; let (SpecEnv
    env', Maybe DictBind
    dx_bind, CoreExpr
    spec_dict) = SpecEnv
    -> Id -> Id -> CoreExpr -> (SpecEnv, Maybe DictBind, CoreExpr)
    bindAuxiliaryDict SpecEnv
    env Id
    bndr Id
    bndr' CoreExpr
    d
           ; (Bool
    _, SpecEnv
    env'', [Id]
    leftover_bndrs, [Id]
    rule_bs, [CoreExpr]
    rule_es, [Id]
    bs', [DictBind]
    dx, [CoreExpr]
    spec_args)
                 <- SpecEnv
    -> [Id]
    -> [SpecArg]
    -> SpecM
         (Bool, SpecEnv, [Id], [Id], [CoreExpr], [Id], [DictBind],
          [CoreExpr])
    specHeader SpecEnv
    env' [Id]
    bndrs [SpecArg]
    args
           ; (Bool, SpecEnv, [Id], [Id], [CoreExpr], [Id], [DictBind],
     [CoreExpr])
    -> SpecM
         (Bool, SpecEnv, [Id], [Id], [CoreExpr], [Id], [DictBind],
          [CoreExpr])
    forall (f :: * -> *) a. Applicative f => a -> f a
    pure ( Bool
    True      -- Ha!  A useful specialisation!
                  , SpecEnv
    env''
                  , [Id]
    leftover_bndrs
                  -- See Note [Evidence foralls]
                  , CoreExpr -> [Id]
    exprFreeIdsList (Id -> CoreExpr
    forall b. Id -> Expr b
    varToCoreExpr Id
    bndr') [Id] -> [Id] -> [Id]
    forall a. [a] -> [a] -> [a]
    ++ [Id]
    rule_bs
                  , Id -> CoreExpr
    forall b. Id -> Expr b
    varToCoreExpr Id
    bndr' CoreExpr -> [CoreExpr] -> [CoreExpr]
    forall a. a -> [a] -> [a]
    : [CoreExpr]
    rule_es
                  , [Id]
    bs'
                  , Maybe DictBind -> [DictBind]
    forall a. Maybe a -> [a]
    maybeToList Maybe DictBind
    dx_bind [DictBind] -> [DictBind] -> [DictBind]
    forall a. [a] -> [a] -> [a]
    ++ [DictBind]
    dx
                  , CoreExpr
    spec_dict CoreExpr -> [CoreExpr] -> [CoreExpr]
    forall a. a -> [a] -> [a]
    : [CoreExpr]
    spec_args
                  )
           }

    -- Finally, we have the unspecialised argument 'i'. We need to produce
    -- a binder, LHS and RHS argument for the RULE, and a binder for the
    -- specialised body.
    --
    -- NB: Calls to 'specHeader' will trim off any trailing 'UnspecArg's, which is
    -- why 'i' doesn't appear in our RULE above. But we have no guarantee that
    -- there aren't 'UnspecArg's which come /before/ all of the dictionaries, so
    -- this case must be here.
    specHeader SpecEnv
    env (Id
    bndr : [Id]
    bndrs) (SpecArg
    UnspecArg : [SpecArg]
    args)
      = do { -- see Note [Zap occ info in rule binders]
             let (SpecEnv
    env', Id
    bndr') = SpecEnv -> Id -> (SpecEnv, Id)
    substBndr SpecEnv
    env (Id -> Id
    zapIdOccInfo Id
    bndr)
           ; (Bool
    useful, SpecEnv
    env'', [Id]
    leftover_bndrs, [Id]
    rule_bs, [CoreExpr]
    rule_es, [Id]
    bs', [DictBind]
    dx, [CoreExpr]
    spec_args)
                 <- SpecEnv
    -> [Id]
    -> [SpecArg]
    -> SpecM
         (Bool, SpecEnv, [Id], [Id], [CoreExpr], [Id], [DictBind],
          [CoreExpr])
    specHeader SpecEnv
    env' [Id]
    bndrs [SpecArg]
    args
           ; (Bool, SpecEnv, [Id], [Id], [CoreExpr], [Id], [DictBind],
     [CoreExpr])
    -> SpecM
         (Bool, SpecEnv, [Id], [Id], [CoreExpr], [Id], [DictBind],
          [CoreExpr])
    forall (f :: * -> *) a. Applicative f => a -> f a
    pure ( Bool
    useful
                  , SpecEnv
    env''
                  , [Id]
    leftover_bndrs
                  , Id
    bndr' Id -> [Id] -> [Id]
    forall a. a -> [a] -> [a]
    : [Id]
    rule_bs
                  , Id -> CoreExpr
    forall b. Id -> Expr b
    varToCoreExpr Id
    bndr' CoreExpr -> [CoreExpr] -> [CoreExpr]
    forall a. a -> [a] -> [a]
    : [CoreExpr]
    rule_es
                  , if Id -> Bool
    isDeadBinder Id
    bndr
                      then [Id]
    bs' -- see Note [Drop dead args from specialisations]
                      else Id
    bndr' Id -> [Id] -> [Id]
    forall a. a -> [a] -> [a]
    : [Id]
    bs'
                  , [DictBind]
    dx
                  , Id -> CoreExpr
    forall b. Id -> Expr b
    varToCoreExpr Id
    bndr' CoreExpr -> [CoreExpr] -> [CoreExpr]
    forall a. a -> [a] -> [a]
    : [CoreExpr]
    spec_args
                  )
           }

    -- If we run out of binders, stop immediately
    -- See Note [Specialisation Must Preserve Sharing]
    specHeader SpecEnv
    env [] [SpecArg]
    _ = (Bool, SpecEnv, [Id], [Id], [CoreExpr], [Id], [DictBind],
     [CoreExpr])
    -> SpecM
         (Bool, SpecEnv, [Id], [Id], [CoreExpr], [Id], [DictBind],
          [CoreExpr])
    forall (f :: * -> *) a. Applicative f => a -> f a
    pure (Bool
    False, SpecEnv
    env, [], [], [], [], [], [])

    -- Return all remaining binders from the original function. These have the
    -- invariant that they should all correspond to unspecialised arguments, so
    -- it's safe to stop processing at this point.
    specHeader SpecEnv
    env [Id]
    bndrs []
      = (Bool, SpecEnv, [Id], [Id], [CoreExpr], [Id], [DictBind],
     [CoreExpr])
    -> SpecM
         (Bool, SpecEnv, [Id], [Id], [CoreExpr], [Id], [DictBind],
          [CoreExpr])
    forall (f :: * -> *) a. Applicative f => a -> f a
    pure (Bool
    False, SpecEnv
    env', [Id]
    bndrs', [], [], [], [], [])
      where
        (SpecEnv
    env', [Id]
    bndrs') = SpecEnv -> [Id] -> (SpecEnv, [Id])
    substBndrs SpecEnv
    env [Id]
    bndrs

    -- | Binds a dictionary argument to a fresh name, to preserve sharing
    bindAuxiliaryDict
      :: SpecEnv
      -> InId -> OutId -> OutExpr -- Original dict binder, and the witnessing expression
      -> ( SpecEnv        -- Substitute for orig_dict_id
         , Maybe DictBind -- Auxiliary dict binding, if any
         , OutExpr)        -- Witnessing expression (always trivial)
    bindAuxiliaryDict :: SpecEnv
    -> Id -> Id -> CoreExpr -> (SpecEnv, Maybe DictBind, CoreExpr)
    bindAuxiliaryDict env :: SpecEnv
    env@(SE { se_subst :: SpecEnv -> Subst
    se_subst = Subst
    subst, se_interesting :: SpecEnv -> VarSet
    se_interesting = VarSet
    interesting })
                      Id
    orig_dict_id Id
    fresh_dict_id CoreExpr
    dict_expr

      -- If the dictionary argument is trivial,
      -- don’t bother creating a new dict binding; just substitute
      | Just Id
    dict_id <- CoreExpr -> Maybe Id
    getIdFromTrivialExpr_maybe CoreExpr
    dict_expr
      = let env' :: SpecEnv
    env' = SpecEnv
    env { se_subst :: Subst
    se_subst = Subst -> Id -> CoreExpr -> Subst
    Core.extendSubst Subst
    subst Id
    orig_dict_id CoreExpr
    dict_expr
                                    Subst -> Id -> Subst
    `Core.extendInScope` Id
    dict_id
                              -- See Note [Keep the old dictionaries interesting]
                       , se_interesting :: VarSet
    se_interesting = VarSet
    interesting VarSet -> Id -> VarSet
    `extendVarSet` Id
    dict_id }
        in (SpecEnv
    env', Maybe DictBind
    forall a. Maybe a
    Nothing, CoreExpr
    dict_expr)

      | Bool
    otherwise  -- Non-trivial dictionary arg; make an auxiliary binding
      = let dict_bind :: DictBind
    dict_bind = CoreBind -> DictBind
    mkDB (Id -> CoreExpr -> CoreBind
    forall b. b -> Expr b -> Bind b
    NonRec Id
    fresh_dict_id CoreExpr
    dict_expr)
            env' :: SpecEnv
    env' = SpecEnv
    env { se_subst :: Subst
    se_subst = Subst -> Id -> CoreExpr -> Subst
    Core.extendSubst Subst
    subst Id
    orig_dict_id (Id -> CoreExpr
    forall b. Id -> Expr b
    Var Id
    fresh_dict_id)
                                    Subst -> Id -> Subst
    `Core.extendInScope` Id
    fresh_dict_id
                          -- See Note [Make the new dictionaries interesting]
                       , se_interesting :: VarSet
    se_interesting = VarSet
    interesting VarSet -> Id -> VarSet
    `extendVarSet` Id
    fresh_dict_id }
        in (SpecEnv
    env', DictBind -> Maybe DictBind
    forall a. a -> Maybe a
    Just DictBind
    dict_bind, Id -> CoreExpr
    forall b. Id -> Expr b
    Var Id
    fresh_dict_id)

    {-
    Note [Make the new dictionaries interesting]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Important!  We're going to substitute dx_id1 for d
    and we want it to look "interesting", else we won't gather *any*
    consequential calls. E.g.
        f d = ...g d....
    If we specialise f for a call (f (dfun dNumInt)), we'll get
    a consequent call (g d') with an auxiliary definition
        d' = df dNumInt
    We want that consequent call to look interesting

    Note [Keep the old dictionaries interesting]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    In bindAuxiliaryDict, we don’t bother creating a new dict binding if
    the dict expression is trivial. For example, if we have

        f = \ @m1 (d1 :: Monad m1) -> ...

    and we specialize it at the pattern

        [SpecType IO, SpecArg $dMonadIO]

    it would be silly to create a new binding for $dMonadIO; it’s already
    a binding! So we just extend the substitution directly:

        m1 :-> IO
        d1 :-> $dMonadIO

    But this creates a new subtlety: the dict expression might be a dict
    binding we floated out while specializing another function. For
    example, we might have

        d2 = $p1Monad $dMonadIO -- floated out by bindAuxiliaryDict
        $sg = h @IO d2
        h = \ @m2 (d2 :: Applicative m2) -> ...

    and end up specializing h at the following pattern:

        [SpecType IO, SpecArg d2]

    When we created the d2 binding in the first place, we locally marked
    it as interesting while specializing g as described above by
    Note [Make the new dictionaries interesting]. But when we go to
    specialize h, it isn’t in the SpecEnv anymore, so we’ve lost the
    knowledge that we should specialize on it.

    To fix this, we have to explicitly add d2 *back* to the interesting
    set. That way, it will still be considered interesting while
    specializing the body of h. See !2913.
    -}

    {- *********************************************************************
    *                                                                      *
                UsageDetails and suchlike
    *                                                                      *
    ********************************************************************* -}

    data UsageDetails
      = MkUD {
          UsageDetails -> Bag DictBind
    ud_binds :: !(Bag DictBind),
                   -- See Note [Floated dictionary bindings]
                   -- The order is important;
                   -- in ds1 `union` ds2, bindings in ds2 can depend on those in ds1
                   -- (Remember, Bags preserve order in GHC.)

          UsageDetails -> CallDetails
    ud_calls :: !CallDetails

          -- INVARIANT: suppose bs = bindersOf ud_binds
          -- Then 'calls' may *mention* 'bs',
          -- but there should be no calls *for* bs
        }

    -- | A 'DictBind' is a binding along with a cached set containing its free
    -- variables (both type variables and dictionaries)
    data DictBind = DB { DictBind -> CoreBind
    db_bind :: CoreBind, DictBind -> VarSet
    db_fvs :: VarSet }

    {- Note [Floated dictionary bindings]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    We float out dictionary bindings for the reasons described under
    "Dictionary floating" above.  But not /just/ dictionary bindings.
    Consider

       f :: Eq a => blah
       f a d = rhs

       $c== :: T -> T -> Bool
       $c== x y = ...

       $df :: Eq T
       $df = Eq $c== ...

       gurgle = ...(f @T $df)...

    We gather the call info for (f @T $df), and we don't want to drop it
    when we come across the binding for $df.  So we add $df to the floats
    and continue.  But then we have to add $c== to the floats, and so on.
    These all float above the binding for 'f', and now we can
    successfully specialise 'f'.

    So the DictBinds in (ud_binds :: Bag DictBind) may contain
    non-dictionary bindings too.
    -}

    instance Outputable DictBind where
      ppr :: DictBind -> SDoc
    ppr (DB { db_bind :: DictBind -> CoreBind
    db_bind = CoreBind
    bind, db_fvs :: DictBind -> VarSet
    db_fvs = VarSet
    fvs })
        = String -> SDoc
    text String
    "DB" SDoc -> SDoc -> SDoc
    <+> SDoc -> SDoc
    braces ([SDoc] -> SDoc
    sep [ String -> SDoc
    text String
    "bind:" SDoc -> SDoc -> SDoc
    <+> CoreBind -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr CoreBind
    bind
                                    , String -> SDoc
    text String
    "fvs: " SDoc -> SDoc -> SDoc
    <+> VarSet -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr VarSet
    fvs ])

    instance Outputable UsageDetails where
      ppr :: UsageDetails -> SDoc
    ppr (MkUD { ud_binds :: UsageDetails -> Bag DictBind
    ud_binds = Bag DictBind
    dbs, ud_calls :: UsageDetails -> CallDetails
    ud_calls = CallDetails
    calls })
            = String -> SDoc
    text String
    "MkUD" SDoc -> SDoc -> SDoc
    <+> SDoc -> SDoc
    braces ([SDoc] -> SDoc
    sep (SDoc -> [SDoc] -> [SDoc]
    punctuate SDoc
    comma
                    [String -> SDoc
    text String
    "binds" SDoc -> SDoc -> SDoc
    <+> SDoc
    equals SDoc -> SDoc -> SDoc
    <+> Bag DictBind -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Bag DictBind
    dbs,
                     String -> SDoc
    text String
    "calls" SDoc -> SDoc -> SDoc
    <+> SDoc
    equals SDoc -> SDoc -> SDoc
    <+> CallDetails -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr CallDetails
    calls]))

    emptyUDs :: UsageDetails
    emptyUDs :: UsageDetails
    emptyUDs = MkUD { ud_binds :: Bag DictBind
    ud_binds = Bag DictBind
    forall a. Bag a
    emptyBag, ud_calls :: CallDetails
    ud_calls = CallDetails
    forall a. DVarEnv a
    emptyDVarEnv }

    ------------------------------------------------------------
    type CallDetails  = DIdEnv CallInfoSet
      -- The order of specialized binds and rules depends on how we linearize
      -- CallDetails, so to get determinism we must use a deterministic set here.
      -- See Note [Deterministic UniqFM] in GHC.Types.Unique.DFM

    data CallInfoSet = CIS Id (Bag CallInfo)
      -- The list of types and dictionaries is guaranteed to
      -- match the type of f
      -- The Bag may contain duplicate calls (i.e. f @T and another f @T)
      -- These dups are eliminated by already_covered in specCalls

    data CallInfo
      = CI { CallInfo -> [SpecArg]
    ci_key  :: [SpecArg]   -- All arguments
           , CallInfo -> VarSet
    ci_fvs  :: VarSet      -- Free vars of the ci_key
                                    -- call (including tyvars)
                                    -- [*not* include the main id itself, of course]
        }

    type DictExpr = CoreExpr

    ciSetFilter :: (CallInfo -> Bool) -> CallInfoSet -> CallInfoSet
    ciSetFilter :: (CallInfo -> Bool) -> CallInfoSet -> CallInfoSet
    ciSetFilter CallInfo -> Bool
    p (CIS Id
    id Bag CallInfo
    a) = Id -> Bag CallInfo -> CallInfoSet
    CIS Id
    id ((CallInfo -> Bool) -> Bag CallInfo -> Bag CallInfo
    forall a. (a -> Bool) -> Bag a -> Bag a
    filterBag CallInfo -> Bool
    p Bag CallInfo
    a)

    instance Outputable CallInfoSet where
      ppr :: CallInfoSet -> SDoc
    ppr (CIS Id
    fn Bag CallInfo
    map) = SDoc -> Int -> SDoc -> SDoc
    hang (String -> SDoc
    text String
    "CIS" SDoc -> SDoc -> SDoc
    <+> Id -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Id
    fn)
                            Int
    2 (Bag CallInfo -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Bag CallInfo
    map)

    pprCallInfo :: Id -> CallInfo -> SDoc
    pprCallInfo :: Id -> CallInfo -> SDoc
    pprCallInfo Id
    fn (CI { ci_key :: CallInfo -> [SpecArg]
    ci_key = [SpecArg]
    key })
      = Id -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Id
    fn SDoc -> SDoc -> SDoc
    <+> [SpecArg] -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr [SpecArg]
    key

    ppr_call_key_ty :: SpecArg -> Maybe SDoc
    ppr_call_key_ty :: SpecArg -> Maybe SDoc
    ppr_call_key_ty (SpecType Kind
    ty) = SDoc -> Maybe SDoc
    forall a. a -> Maybe a
    Just (SDoc -> Maybe SDoc) -> SDoc -> Maybe SDoc
    forall a b. (a -> b) -> a -> b
    $ Char -> SDoc
    char Char
    '@' SDoc -> SDoc -> SDoc
    <> Kind -> SDoc
    pprParendType Kind
    ty
    ppr_call_key_ty SpecArg
    UnspecType    = SDoc -> Maybe SDoc
    forall a. a -> Maybe a
    Just (SDoc -> Maybe SDoc) -> SDoc -> Maybe SDoc
    forall a b. (a -> b) -> a -> b
    $ Char -> SDoc
    char Char
    '_'
    ppr_call_key_ty (SpecDict CoreExpr
    _)  = Maybe SDoc
    forall a. Maybe a
    Nothing
    ppr_call_key_ty SpecArg
    UnspecArg     = Maybe SDoc
    forall a. Maybe a
    Nothing

    instance Outputable CallInfo where
      ppr :: CallInfo -> SDoc
    ppr (CI { ci_key :: CallInfo -> [SpecArg]
    ci_key = [SpecArg]
    key, ci_fvs :: CallInfo -> VarSet
    ci_fvs = VarSet
    _fvs })
        = String -> SDoc
    text String
    "CI" SDoc -> SDoc -> SDoc
    <> SDoc -> SDoc
    braces ([SDoc] -> SDoc
    sep ((SpecArg -> SDoc) -> [SpecArg] -> [SDoc]
    forall a b. (a -> b) -> [a] -> [b]
    map SpecArg -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr [SpecArg]
    key))

    unionCalls :: CallDetails -> CallDetails -> CallDetails
    unionCalls :: CallDetails -> CallDetails -> CallDetails
    unionCalls CallDetails
    c1 CallDetails
    c2 = (CallInfoSet -> CallInfoSet -> CallInfoSet)
    -> CallDetails -> CallDetails -> CallDetails
    forall a. (a -> a -> a) -> DVarEnv a -> DVarEnv a -> DVarEnv a
    plusDVarEnv_C CallInfoSet -> CallInfoSet -> CallInfoSet
    unionCallInfoSet CallDetails
    c1 CallDetails
    c2

    unionCallInfoSet :: CallInfoSet -> CallInfoSet -> CallInfoSet
    unionCallInfoSet :: CallInfoSet -> CallInfoSet -> CallInfoSet
    unionCallInfoSet (CIS Id
    f Bag CallInfo
    calls1) (CIS Id
    _ Bag CallInfo
    calls2) =
      Id -> Bag CallInfo -> CallInfoSet
    CIS Id
    f (Bag CallInfo
    calls1 Bag CallInfo -> Bag CallInfo -> Bag CallInfo
    forall a. Bag a -> Bag a -> Bag a
    `unionBags` Bag CallInfo
    calls2)

    callDetailsFVs :: CallDetails -> VarSet
    callDetailsFVs :: CallDetails -> VarSet
    callDetailsFVs CallDetails
    calls =
      (CallInfoSet -> VarSet -> VarSet)
    -> VarSet -> CallDetails -> VarSet
    forall elt a key. (elt -> a -> a) -> a -> UniqDFM key elt -> a
    nonDetStrictFoldUDFM (VarSet -> VarSet -> VarSet
    unionVarSet (VarSet -> VarSet -> VarSet)
    -> (CallInfoSet -> VarSet) -> CallInfoSet -> VarSet -> VarSet
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . CallInfoSet -> VarSet
    callInfoFVs) VarSet
    emptyVarSet CallDetails
    calls
      -- It's OK to use nonDetStrictFoldUDFM here because we forget the ordering
      -- immediately by converting to a nondeterministic set.

    callInfoFVs :: CallInfoSet -> VarSet
    callInfoFVs :: CallInfoSet -> VarSet
    callInfoFVs (CIS Id
    _ Bag CallInfo
    call_info) =
      (CallInfo -> VarSet -> VarSet) -> VarSet -> Bag CallInfo -> VarSet
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr (\(CI { ci_fvs :: CallInfo -> VarSet
    ci_fvs = VarSet
    fv }) VarSet
    vs -> VarSet -> VarSet -> VarSet
    unionVarSet VarSet
    fv VarSet
    vs) VarSet
    emptyVarSet Bag CallInfo
    call_info

    getTheta :: [TyCoBinder] -> [PredType]
    getTheta :: [TyCoBinder] -> [Kind]
    getTheta = (TyCoBinder -> Kind) -> [TyCoBinder] -> [Kind]
    forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
    fmap TyCoBinder -> Kind
    tyBinderType ([TyCoBinder] -> [Kind])
    -> ([TyCoBinder] -> [TyCoBinder]) -> [TyCoBinder] -> [Kind]
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . (TyCoBinder -> Bool) -> [TyCoBinder] -> [TyCoBinder]
    forall a. (a -> Bool) -> [a] -> [a]
    filter TyCoBinder -> Bool
    isInvisibleBinder ([TyCoBinder] -> [TyCoBinder])
    -> ([TyCoBinder] -> [TyCoBinder]) -> [TyCoBinder] -> [TyCoBinder]
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . (TyCoBinder -> Bool) -> [TyCoBinder] -> [TyCoBinder]
    forall a. (a -> Bool) -> [a] -> [a]
    filter (Bool -> Bool
    not (Bool -> Bool) -> (TyCoBinder -> Bool) -> TyCoBinder -> Bool
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . TyCoBinder -> Bool
    isNamedBinder)

    ------------------------------------------------------------
    singleCall :: Id -> [SpecArg] -> UsageDetails
    singleCall :: Id -> [SpecArg] -> UsageDetails
    singleCall Id
    id [SpecArg]
    args
      = MkUD {ud_binds :: Bag DictBind
    ud_binds = Bag DictBind
    forall a. Bag a
    emptyBag,
              ud_calls :: CallDetails
    ud_calls = Id -> CallInfoSet -> CallDetails
    forall a. Id -> a -> DVarEnv a
    unitDVarEnv Id
    id (CallInfoSet -> CallDetails) -> CallInfoSet -> CallDetails
    forall a b. (a -> b) -> a -> b
    $ Id -> Bag CallInfo -> CallInfoSet
    CIS Id
    id (Bag CallInfo -> CallInfoSet) -> Bag CallInfo -> CallInfoSet
    forall a b. (a -> b) -> a -> b
    $
                         CallInfo -> Bag CallInfo
    forall a. a -> Bag a
    unitBag (CI { ci_key :: [SpecArg]
    ci_key  = [SpecArg]
    args -- used to be tys
                                     , ci_fvs :: VarSet
    ci_fvs  = VarSet
    call_fvs }) }
      where
        call_fvs :: VarSet
    call_fvs = (SpecArg -> VarSet -> VarSet) -> VarSet -> [SpecArg] -> VarSet
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr (VarSet -> VarSet -> VarSet
    unionVarSet (VarSet -> VarSet -> VarSet)
    -> (SpecArg -> VarSet) -> SpecArg -> VarSet -> VarSet
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . SpecArg -> VarSet
    specArgFreeVars) VarSet
    emptyVarSet [SpecArg]
    args
            -- The type args (tys) are guaranteed to be part of the dictionary
            -- types, because they are just the constrained types,
            -- and the dictionary is therefore sure to be bound
            -- inside the binding for any type variables free in the type;
            -- hence it's safe to neglect tyvars free in tys when making
            -- the free-var set for this call
            -- BUT I don't trust this reasoning; play safe and include tys_fvs
            --
            -- We don't include the 'id' itself.

    mkCallUDs, mkCallUDs' :: SpecEnv -> Id -> [CoreExpr] -> UsageDetails
    mkCallUDs :: SpecEnv -> Id -> [CoreExpr] -> UsageDetails
    mkCallUDs SpecEnv
    env Id
    f [CoreExpr]
    args
      = -- pprTrace "mkCallUDs" (vcat [ ppr f, ppr args, ppr res ])
        UsageDetails
    res
      where
        res :: UsageDetails
    res = SpecEnv -> Id -> [CoreExpr] -> UsageDetails
    mkCallUDs' SpecEnv
    env Id
    f [CoreExpr]
    args

    mkCallUDs' :: SpecEnv -> Id -> [CoreExpr] -> UsageDetails
    mkCallUDs' SpecEnv
    env Id
    f [CoreExpr]
    args
      | SpecEnv -> Id -> Bool
    wantCallsFor SpecEnv
    env Id
    f    -- We want it, and...
      , Bool -> Bool
    not ([SpecArg] -> Bool
    forall (t :: * -> *) a. Foldable t => t a -> Bool
    null [SpecArg]
    ci_key)     -- this call site has a useful specialisation
      = -- pprTrace "mkCallUDs: keeping" _trace_doc
        Id -> [SpecArg] -> UsageDetails
    singleCall Id
    f [SpecArg]
    ci_key

      | Bool
    otherwise  -- See also Note [Specialisations already covered]
      = -- pprTrace "mkCallUDs: discarding" _trace_doc
        UsageDetails
    emptyUDs

      where
        _trace_doc :: SDoc
    _trace_doc = [SDoc] -> SDoc
    vcat [Id -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Id
    f, [CoreExpr] -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr [CoreExpr]
    args, [SpecArg] -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr [SpecArg]
    ci_key]
        pis :: [TyCoBinder]
    pis                = ([TyCoBinder], Kind) -> [TyCoBinder]
    forall a b. (a, b) -> a
    fst (([TyCoBinder], Kind) -> [TyCoBinder])
    -> ([TyCoBinder], Kind) -> [TyCoBinder]
    forall a b. (a -> b) -> a -> b
    $ Kind -> ([TyCoBinder], Kind)
    splitPiTys (Kind -> ([TyCoBinder], Kind)) -> Kind -> ([TyCoBinder], Kind)
    forall a b. (a -> b) -> a -> b
    $ Id -> Kind
    idType Id
    f
        constrained_tyvars :: VarSet
    constrained_tyvars = [Kind] -> VarSet
    tyCoVarsOfTypes ([Kind] -> VarSet) -> [Kind] -> VarSet
    forall a b. (a -> b) -> a -> b
    $ [TyCoBinder] -> [Kind]
    getTheta [TyCoBinder]
    pis

        ci_key :: [SpecArg]
        ci_key :: [SpecArg]
    ci_key = (SpecArg -> Bool) -> [SpecArg] -> [SpecArg]
    forall a. (a -> Bool) -> [a] -> [a]
    dropWhileEndLE (Bool -> Bool
    not (Bool -> Bool) -> (SpecArg -> Bool) -> SpecArg -> Bool
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . SpecArg -> Bool
    isSpecDict) ([SpecArg] -> [SpecArg]) -> [SpecArg] -> [SpecArg]
    forall a b. (a -> b) -> a -> b
    $
                 (CoreExpr -> TyCoBinder -> SpecArg)
    -> [CoreExpr] -> [TyCoBinder] -> [SpecArg]
    forall a b c. (a -> b -> c) -> [a] -> [b] -> [c]
    zipWith CoreExpr -> TyCoBinder -> SpecArg
    mk_spec_arg [CoreExpr]
    args [TyCoBinder]
    pis
                 -- Drop trailing args until we get to a SpecDict
                 -- In this way the RULE has as few args as possible,
                 -- which broadens its applicability, since rules only
                 -- fire when saturated

        mk_spec_arg :: CoreExpr -> TyCoBinder -> SpecArg
        mk_spec_arg :: CoreExpr -> TyCoBinder -> SpecArg
    mk_spec_arg CoreExpr
    arg (Named TyCoVarBinder
    bndr)
          |  TyCoVarBinder -> Id
    forall tv argf. VarBndr tv argf -> tv
    binderVar TyCoVarBinder
    bndr Id -> VarSet -> Bool
    `elemVarSet` VarSet
    constrained_tyvars
          = case CoreExpr
    arg of
              Type Kind
    ty -> Kind -> SpecArg
    SpecType Kind
    ty
              CoreExpr
    _       -> String -> SDoc -> SpecArg
    forall a. HasCallStack => String -> SDoc -> a
    pprPanic String
    "ci_key" (SDoc -> SpecArg) -> SDoc -> SpecArg
    forall a b. (a -> b) -> a -> b
    $ CoreExpr -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr CoreExpr
    arg
          |  Bool
    otherwise = SpecArg
    UnspecType

        -- For "InvisArg", which are the type-class dictionaries,
        -- we decide on a case by case basis if we want to specialise
        -- on this argument; if so, SpecDict, if not UnspecArg
        mk_spec_arg CoreExpr
    arg (Anon AnonArgFlag
    InvisArg Scaled Kind
    pred)
          | Bool -> Bool
    not (Kind -> Bool
    isIPLikePred (Scaled Kind -> Kind
    forall a. Scaled a -> a
    scaledThing Scaled Kind
    pred))
                  -- See Note [Type determines value]
          , SpecEnv -> CoreExpr -> Bool
    interestingDict SpecEnv
    env CoreExpr
    arg
                  -- See Note [Interesting dictionary arguments]
          = CoreExpr -> SpecArg
    SpecDict CoreExpr
    arg

          | Bool
    otherwise = SpecArg
    UnspecArg

        mk_spec_arg CoreExpr
    _ (Anon AnonArgFlag
    VisArg Scaled Kind
    _)
          = SpecArg
    UnspecArg

    wantCallsFor :: SpecEnv -> Id -> Bool
    wantCallsFor :: SpecEnv -> Id -> Bool
    wantCallsFor SpecEnv
    _env Id
    _f = Bool
    True
     -- We could reduce the size of the UsageDetails by being less eager
     -- about collecting calls for LocalIds: there is no point for
     -- ones that are lambda-bound.  We can't decide this by looking at
     -- the (absence of an) unfolding, because unfoldings for local
     -- functions are discarded by cloneBindSM, so no local binder will
     -- have an unfolding at this stage.  We'd have to keep a candidate
     -- set of let-binders.
     --
     -- Not many lambda-bound variables have dictionary arguments, so
     -- this would make little difference anyway.
     --
     -- For imported Ids we could check for an unfolding, but we have to
     -- do so anyway in canSpecImport, and it seems better to have it
     -- all in one place.  So we simply collect usage info for imported
     -- overloaded functions.

    {- Note [Type determines value]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Only specialise on non-impicit-parameter predicates, because these
    are the ones whose *type* determines their *value*.  In particular,
    with implicit params, the type args *don't* say what the value of the
    implicit param is!  See #7101.

    So we treat implicit params just like ordinary arguments for the
    purposes of specialisation.  Note that we still want to specialise
    functions with implicit params if they have *other* dicts which are
    class params; see #17930.

    Note [Interesting dictionary arguments]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider this
             \a.\d:Eq a.  let f = ... in ...(f d)...
    There really is not much point in specialising f wrt the dictionary d,
    because the code for the specialised f is not improved at all, because
    d is lambda-bound.  We simply get junk specialisations.

    What is "interesting"?  Just that it has *some* structure.  But what about
    variables?

     * A variable might be imported, in which case its unfolding
       will tell us whether it has useful structure

     * Local variables are cloned on the way down (to avoid clashes when
       we float dictionaries), and cloning drops the unfolding
       (cloneIdBndr).  Moreover, we make up some new bindings, and it's a
       nuisance to give them unfoldings.  So we keep track of the
       "interesting" dictionaries as a VarSet in SpecEnv.
       We have to take care to put any new interesting dictionary
       bindings in the set.

    We accidentally lost accurate tracking of local variables for a long
    time, because cloned variables don't have unfoldings. But makes a
    massive difference in a few cases, eg #5113. For nofib as a
    whole it's only a small win: 2.2% improvement in allocation for ansi,
    1.2% for bspt, but mostly 0.0!  Average 0.1% increase in binary size.
    -}

    interestingDict :: SpecEnv -> CoreExpr -> Bool
    -- A dictionary argument is interesting if it has *some* structure
    -- NB: "dictionary" arguments include constraints of all sorts,
    --     including equality constraints; hence the Coercion case
    interestingDict :: SpecEnv -> CoreExpr -> Bool
    interestingDict SpecEnv
    env (Var Id
    v) =  Unfolding -> Bool
    hasSomeUnfolding (Id -> Unfolding
    idUnfolding Id
    v)
                                Bool -> Bool -> Bool
    || Id -> Bool
    isDataConWorkId Id
    v
                                Bool -> Bool -> Bool
    || Id
    v Id -> VarSet -> Bool
    `elemVarSet` SpecEnv -> VarSet
    se_interesting SpecEnv
    env
    interestingDict SpecEnv
    _ (Type Kind
    _)                = Bool
    False
    interestingDict SpecEnv
    _ (Coercion Coercion
    _)            = Bool
    False
    interestingDict SpecEnv
    env (App CoreExpr
    fn (Type Kind
    _))     = SpecEnv -> CoreExpr -> Bool
    interestingDict SpecEnv
    env CoreExpr
    fn
    interestingDict SpecEnv
    env (App CoreExpr
    fn (Coercion Coercion
    _)) = SpecEnv -> CoreExpr -> Bool
    interestingDict SpecEnv
    env CoreExpr
    fn
    interestingDict SpecEnv
    env (Tick CoreTickish
    _ CoreExpr
    a)            = SpecEnv -> CoreExpr -> Bool
    interestingDict SpecEnv
    env CoreExpr
    a
    interestingDict SpecEnv
    env (Cast CoreExpr
    e Coercion
    _)            = SpecEnv -> CoreExpr -> Bool
    interestingDict SpecEnv
    env CoreExpr
    e
    interestingDict SpecEnv
    _ CoreExpr
    _                       = Bool
    True

    plusUDs :: UsageDetails -> UsageDetails -> UsageDetails
    plusUDs :: UsageDetails -> UsageDetails -> UsageDetails
    plusUDs (MkUD {ud_binds :: UsageDetails -> Bag DictBind
    ud_binds = Bag DictBind
    db1, ud_calls :: UsageDetails -> CallDetails
    ud_calls = CallDetails
    calls1})
            (MkUD {ud_binds :: UsageDetails -> Bag DictBind
    ud_binds = Bag DictBind
    db2, ud_calls :: UsageDetails -> CallDetails
    ud_calls = CallDetails
    calls2})
      = MkUD { ud_binds :: Bag DictBind
    ud_binds = Bag DictBind
    db1    Bag DictBind -> Bag DictBind -> Bag DictBind
    forall a. Bag a -> Bag a -> Bag a
    `unionBags`   Bag DictBind
    db2
             , ud_calls :: CallDetails
    ud_calls = CallDetails
    calls1 CallDetails -> CallDetails -> CallDetails
    `unionCalls`  CallDetails
    calls2 }

    -----------------------------
    _dictBindBndrs :: Bag DictBind -> [Id]
    _dictBindBndrs :: Bag DictBind -> [Id]
    _dictBindBndrs Bag DictBind
    dbs = (DictBind -> [Id] -> [Id]) -> [Id] -> Bag DictBind -> [Id]
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr ([Id] -> [Id] -> [Id]
    forall a. [a] -> [a] -> [a]
    (++) ([Id] -> [Id] -> [Id])
    -> (DictBind -> [Id]) -> DictBind -> [Id] -> [Id]
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . CoreBind -> [Id]
    forall b. Bind b -> [b]
    bindersOf (CoreBind -> [Id]) -> (DictBind -> CoreBind) -> DictBind -> [Id]
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . DictBind -> CoreBind
    db_bind) [] Bag DictBind
    dbs

    -- | Construct a 'DictBind' from a 'CoreBind'
    mkDB :: CoreBind -> DictBind
    mkDB :: CoreBind -> DictBind
    mkDB CoreBind
    bind = DB { db_bind :: CoreBind
    db_bind = CoreBind
    bind, db_fvs :: VarSet
    db_fvs = CoreBind -> VarSet
    bind_fvs CoreBind
    bind }

    -- | Identify the free variables of a 'CoreBind'
    bind_fvs :: CoreBind -> VarSet
    bind_fvs :: CoreBind -> VarSet
    bind_fvs (NonRec Id
    bndr CoreExpr
    rhs) = (Id, CoreExpr) -> VarSet
    pair_fvs (Id
    bndr,CoreExpr
    rhs)
    bind_fvs (Rec [(Id, CoreExpr)]
    prs)         = (VarSet -> Id -> VarSet) -> VarSet -> [Id] -> VarSet
    forall (t :: * -> *) b a.
    Foldable t =>
    (b -> a -> b) -> b -> t a -> b
    foldl' VarSet -> Id -> VarSet
    delVarSet VarSet
    rhs_fvs [Id]
    bndrs
                               where
                                 bndrs :: [Id]
    bndrs = ((Id, CoreExpr) -> Id) -> [(Id, CoreExpr)] -> [Id]
    forall a b. (a -> b) -> [a] -> [b]
    map (Id, CoreExpr) -> Id
    forall a b. (a, b) -> a
    fst [(Id, CoreExpr)]
    prs
                                 rhs_fvs :: VarSet
    rhs_fvs = [VarSet] -> VarSet
    unionVarSets (((Id, CoreExpr) -> VarSet) -> [(Id, CoreExpr)] -> [VarSet]
    forall a b. (a -> b) -> [a] -> [b]
    map (Id, CoreExpr) -> VarSet
    pair_fvs [(Id, CoreExpr)]
    prs)

    pair_fvs :: (Id, CoreExpr) -> VarSet
    pair_fvs :: (Id, CoreExpr) -> VarSet
    pair_fvs (Id
    bndr, CoreExpr
    rhs) = (Id -> Bool) -> CoreExpr -> VarSet
    exprSomeFreeVars Id -> Bool
    interesting CoreExpr
    rhs
                           VarSet -> VarSet -> VarSet
    `unionVarSet` Id -> VarSet
    idFreeVars Id
    bndr
            -- idFreeVars: don't forget variables mentioned in
            -- the rules of the bndr.  C.f. OccAnal.addRuleUsage
            -- Also tyvars mentioned in its type; they may not appear
            -- in the RHS
            --      type T a = Int
            --      x :: T a = 3
      where
        interesting :: InterestingVarFun
        interesting :: Id -> Bool
    interesting Id
    v = Id -> Bool
    isLocalVar Id
    v Bool -> Bool -> Bool
    || (Id -> Bool
    isId Id
    v Bool -> Bool -> Bool
    && Id -> Bool
    isDFunId Id
    v)
            -- Very important: include DFunIds /even/ if it is imported
            -- Reason: See Note [Avoiding loops], the second example
            --         involving an imported dfun.  We must know whether
            --         a dictionary binding depends on an imported dfun,
            --         in case we try to specialise that imported dfun
            --         #13429 illustrates

    -- | Flatten a set of "dumped" 'DictBind's, and some other binding
    -- pairs, into a single recursive binding.
    recWithDumpedDicts :: [(Id,CoreExpr)] -> Bag DictBind -> DictBind
    recWithDumpedDicts :: [(Id, CoreExpr)] -> Bag DictBind -> DictBind
    recWithDumpedDicts [(Id, CoreExpr)]
    pairs Bag DictBind
    dbs
      = DB { db_bind :: CoreBind
    db_bind = [(Id, CoreExpr)] -> CoreBind
    forall b. [(b, Expr b)] -> Bind b
    Rec [(Id, CoreExpr)]
    bindings, db_fvs :: VarSet
    db_fvs = VarSet
    fvs }
      where
        ([(Id, CoreExpr)]
    bindings, VarSet
    fvs) = (DictBind
     -> ([(Id, CoreExpr)], VarSet) -> ([(Id, CoreExpr)], VarSet))
    -> ([(Id, CoreExpr)], VarSet)
    -> Bag DictBind
    -> ([(Id, CoreExpr)], VarSet)
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr DictBind
    -> ([(Id, CoreExpr)], VarSet) -> ([(Id, CoreExpr)], VarSet)
    add ([], VarSet
    emptyVarSet)
                                    (Bag DictBind
    dbs Bag DictBind -> DictBind -> Bag DictBind
    forall a. Bag a -> a -> Bag a
    `snocBag` CoreBind -> DictBind
    mkDB ([(Id, CoreExpr)] -> CoreBind
    forall b. [(b, Expr b)] -> Bind b
    Rec [(Id, CoreExpr)]
    pairs))
        add :: DictBind
    -> ([(Id, CoreExpr)], VarSet) -> ([(Id, CoreExpr)], VarSet)
    add (DB { db_bind :: DictBind -> CoreBind
    db_bind = CoreBind
    bind, db_fvs :: DictBind -> VarSet
    db_fvs = VarSet
    fvs }) ([(Id, CoreExpr)]
    prs_acc, VarSet
    fvs_acc)
          = case CoreBind
    bind of
              NonRec Id
    b CoreExpr
    r -> ((Id
    b,CoreExpr
    r) (Id, CoreExpr) -> [(Id, CoreExpr)] -> [(Id, CoreExpr)]
    forall a. a -> [a] -> [a]
    : [(Id, CoreExpr)]
    prs_acc, VarSet
    fvs')
              Rec [(Id, CoreExpr)]
    prs1   -> ([(Id, CoreExpr)]
    prs1 [(Id, CoreExpr)] -> [(Id, CoreExpr)] -> [(Id, CoreExpr)]
    forall a. [a] -> [a] -> [a]
    ++ [(Id, CoreExpr)]
    prs_acc, VarSet
    fvs')
          where
            fvs' :: VarSet
    fvs' = VarSet
    fvs_acc VarSet -> VarSet -> VarSet
    `unionVarSet` VarSet
    fvs

    snocDictBinds :: UsageDetails -> [DictBind] -> UsageDetails
    -- Add ud_binds to the tail end of the bindings in uds
    snocDictBinds :: UsageDetails -> [DictBind] -> UsageDetails
    snocDictBinds UsageDetails
    uds [DictBind]
    dbs
      = UsageDetails
    uds { ud_binds :: Bag DictBind
    ud_binds = UsageDetails -> Bag DictBind
    ud_binds UsageDetails
    uds Bag DictBind -> Bag DictBind -> Bag DictBind
    forall a. Bag a -> Bag a -> Bag a
    `unionBags` [DictBind] -> Bag DictBind
    forall a. [a] -> Bag a
    listToBag [DictBind]
    dbs }

    consDictBind :: DictBind -> UsageDetails -> UsageDetails
    consDictBind :: DictBind -> UsageDetails -> UsageDetails
    consDictBind DictBind
    bind UsageDetails
    uds = UsageDetails
    uds { ud_binds :: Bag DictBind
    ud_binds = DictBind
    bind DictBind -> Bag DictBind -> Bag DictBind
    forall a. a -> Bag a -> Bag a
    `consBag` UsageDetails -> Bag DictBind
    ud_binds UsageDetails
    uds }

    addDictBinds :: [DictBind] -> UsageDetails -> UsageDetails
    addDictBinds :: [DictBind] -> UsageDetails -> UsageDetails
    addDictBinds [DictBind]
    binds UsageDetails
    uds = UsageDetails
    uds { ud_binds :: Bag DictBind
    ud_binds = [DictBind] -> Bag DictBind
    forall a. [a] -> Bag a
    listToBag [DictBind]
    binds Bag DictBind -> Bag DictBind -> Bag DictBind
    forall a. Bag a -> Bag a -> Bag a
    `unionBags` UsageDetails -> Bag DictBind
    ud_binds UsageDetails
    uds }

    snocDictBind :: UsageDetails -> DictBind -> UsageDetails
    snocDictBind :: UsageDetails -> DictBind -> UsageDetails
    snocDictBind UsageDetails
    uds DictBind
    bind = UsageDetails
    uds { ud_binds :: Bag DictBind
    ud_binds = UsageDetails -> Bag DictBind
    ud_binds UsageDetails
    uds Bag DictBind -> DictBind -> Bag DictBind
    forall a. Bag a -> a -> Bag a
    `snocBag` DictBind
    bind }

    wrapDictBinds :: Bag DictBind -> [CoreBind] -> [CoreBind]
    wrapDictBinds :: Bag DictBind -> CoreProgram -> CoreProgram
    wrapDictBinds Bag DictBind
    dbs CoreProgram
    binds
      = (DictBind -> CoreProgram -> CoreProgram)
    -> CoreProgram -> Bag DictBind -> CoreProgram
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr DictBind -> CoreProgram -> CoreProgram
    add CoreProgram
    binds Bag DictBind
    dbs
      where
        add :: DictBind -> CoreProgram -> CoreProgram
    add (DB { db_bind :: DictBind -> CoreBind
    db_bind = CoreBind
    bind }) CoreProgram
    binds = CoreBind
    bind CoreBind -> CoreProgram -> CoreProgram
    forall a. a -> [a] -> [a]
    : CoreProgram
    binds

    wrapDictBindsE :: Bag DictBind -> CoreExpr -> CoreExpr
    wrapDictBindsE :: Bag DictBind -> CoreExpr -> CoreExpr
    wrapDictBindsE Bag DictBind
    dbs CoreExpr
    expr
      = (DictBind -> CoreExpr -> CoreExpr)
    -> CoreExpr -> Bag DictBind -> CoreExpr
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr DictBind -> CoreExpr -> CoreExpr
    add CoreExpr
    expr Bag DictBind
    dbs
      where
        add :: DictBind -> CoreExpr -> CoreExpr
    add (DB { db_bind :: DictBind -> CoreBind
    db_bind = CoreBind
    bind }) CoreExpr
    expr = CoreBind -> CoreExpr -> CoreExpr
    forall b. Bind b -> Expr b -> Expr b
    Let CoreBind
    bind CoreExpr
    expr

    ----------------------
    dumpUDs :: [CoreBndr] -> UsageDetails -> (UsageDetails, Bag DictBind)
    -- Used at a lambda or case binder; just dump anything mentioning the binder
    dumpUDs :: [Id] -> UsageDetails -> (UsageDetails, Bag DictBind)
    dumpUDs [Id]
    bndrs uds :: UsageDetails
    uds@(MkUD { ud_binds :: UsageDetails -> Bag DictBind
    ud_binds = Bag DictBind
    orig_dbs, ud_calls :: UsageDetails -> CallDetails
    ud_calls = CallDetails
    orig_calls })
      | [Id] -> Bool
    forall (t :: * -> *) a. Foldable t => t a -> Bool
    null [Id]
    bndrs = (UsageDetails
    uds, Bag DictBind
    forall a. Bag a
    emptyBag)  -- Common in case alternatives
      | Bool
    otherwise  = -- pprTrace "dumpUDs" (ppr bndrs $$ ppr free_uds $$ ppr dump_dbs) $
                     (UsageDetails
    free_uds, Bag DictBind
    dump_dbs)
      where
        free_uds :: UsageDetails
    free_uds = MkUD { ud_binds :: Bag DictBind
    ud_binds = Bag DictBind
    free_dbs, ud_calls :: CallDetails
    ud_calls = CallDetails
    free_calls }
        bndr_set :: VarSet
    bndr_set = [Id] -> VarSet
    mkVarSet [Id]
    bndrs
        (Bag DictBind
    free_dbs, Bag DictBind
    dump_dbs, VarSet
    dump_set) = Bag DictBind -> VarSet -> (Bag DictBind, Bag DictBind, VarSet)
    splitDictBinds Bag DictBind
    orig_dbs VarSet
    bndr_set
        free_calls :: CallDetails
    free_calls = VarSet -> CallDetails -> CallDetails
    deleteCallsMentioning VarSet
    dump_set (CallDetails -> CallDetails) -> CallDetails -> CallDetails
    forall a b. (a -> b) -> a -> b
    $   -- Drop calls mentioning bndr_set on the floor
                     [Id] -> CallDetails -> CallDetails
    deleteCallsFor [Id]
    bndrs CallDetails
    orig_calls    -- Discard calls for bndr_set; there should be
                                                        -- no calls for any of the dicts in dump_dbs

    dumpBindUDs :: [CoreBndr] -> UsageDetails -> (UsageDetails, Bag DictBind, Bool)
    -- Used at a let(rec) binding.
    -- We return a boolean indicating whether the binding itself is mentioned,
    -- directly or indirectly, by any of the ud_calls; in that case we want to
    -- float the binding itself;
    -- See Note [Floated dictionary bindings]
    dumpBindUDs :: [Id] -> UsageDetails -> (UsageDetails, Bag DictBind, Bool)
    dumpBindUDs [Id]
    bndrs (MkUD { ud_binds :: UsageDetails -> Bag DictBind
    ud_binds = Bag DictBind
    orig_dbs, ud_calls :: UsageDetails -> CallDetails
    ud_calls = CallDetails
    orig_calls })
      = -- pprTrace "dumpBindUDs" (ppr bndrs $$ ppr free_uds $$ ppr dump_dbs) $
        (UsageDetails
    free_uds, Bag DictBind
    dump_dbs, Bool
    float_all)
      where
        free_uds :: UsageDetails
    free_uds = MkUD { ud_binds :: Bag DictBind
    ud_binds = Bag DictBind
    free_dbs, ud_calls :: CallDetails
    ud_calls = CallDetails
    free_calls }
        bndr_set :: VarSet
    bndr_set = [Id] -> VarSet
    mkVarSet [Id]
    bndrs
        (Bag DictBind
    free_dbs, Bag DictBind
    dump_dbs, VarSet
    dump_set) = Bag DictBind -> VarSet -> (Bag DictBind, Bag DictBind, VarSet)
    splitDictBinds Bag DictBind
    orig_dbs VarSet
    bndr_set
        free_calls :: CallDetails
    free_calls = [Id] -> CallDetails -> CallDetails
    deleteCallsFor [Id]
    bndrs CallDetails
    orig_calls
        float_all :: Bool
    float_all = VarSet
    dump_set VarSet -> VarSet -> Bool
    `intersectsVarSet` CallDetails -> VarSet
    callDetailsFVs CallDetails
    free_calls

    callsForMe :: Id -> UsageDetails -> (UsageDetails, [CallInfo])
    callsForMe :: Id -> UsageDetails -> (UsageDetails, [CallInfo])
    callsForMe Id
    fn (MkUD { ud_binds :: UsageDetails -> Bag DictBind
    ud_binds = Bag DictBind
    orig_dbs, ud_calls :: UsageDetails -> CallDetails
    ud_calls = CallDetails
    orig_calls })
      = -- pprTrace ("callsForMe")
        --          (vcat [ppr fn,
        --                 text "Orig dbs ="     <+> ppr (_dictBindBndrs orig_dbs),
        --                 text "Orig calls ="   <+> ppr orig_calls,
        --                 text "Dep set ="      <+> ppr dep_set,
        --                 text "Calls for me =" <+> ppr calls_for_me]) $
        (UsageDetails
    uds_without_me, [CallInfo]
    calls_for_me)
      where
        uds_without_me :: UsageDetails
    uds_without_me = MkUD { ud_binds :: Bag DictBind
    ud_binds = Bag DictBind
    orig_dbs
                              , ud_calls :: CallDetails
    ud_calls = CallDetails -> Id -> CallDetails
    forall a. DVarEnv a -> Id -> DVarEnv a
    delDVarEnv CallDetails
    orig_calls Id
    fn }
        calls_for_me :: [CallInfo]
    calls_for_me = case CallDetails -> Id -> Maybe CallInfoSet
    forall a. DVarEnv a -> Id -> Maybe a
    lookupDVarEnv CallDetails
    orig_calls Id
    fn of
                            Maybe CallInfoSet
    Nothing -> []
                            Just CallInfoSet
    cis -> CallInfoSet -> Bag DictBind -> [CallInfo]
    filterCalls CallInfoSet
    cis Bag DictBind
    orig_dbs
             -- filterCalls: drop calls that (directly or indirectly)
             -- refer to fn.  See Note [Avoiding loops]

    ----------------------
    filterCalls :: CallInfoSet -> Bag DictBind -> [CallInfo]
    -- See Note [Avoiding loops]
    filterCalls :: CallInfoSet -> Bag DictBind -> [CallInfo]
    filterCalls (CIS Id
    fn Bag CallInfo
    call_bag) Bag DictBind
    dbs
      = (CallInfo -> Bool) -> [CallInfo] -> [CallInfo]
    forall a. (a -> Bool) -> [a] -> [a]
    filter CallInfo -> Bool
    ok_call (Bag CallInfo -> [CallInfo]
    forall a. Bag a -> [a]
    bagToList Bag CallInfo
    call_bag)
      where
        dump_set :: VarSet
    dump_set = (VarSet -> DictBind -> VarSet) -> VarSet -> Bag DictBind -> VarSet
    forall (t :: * -> *) b a.
    Foldable t =>
    (b -> a -> b) -> b -> t a -> b
    foldl' VarSet -> DictBind -> VarSet
    go (Id -> VarSet
    unitVarSet Id
    fn) Bag DictBind
    dbs
          -- This dump-set could also be computed by splitDictBinds
          --   (_,_,dump_set) = splitDictBinds dbs {fn}
          -- But this variant is shorter

        go :: VarSet -> DictBind -> VarSet
    go VarSet
    so_far (DB { db_bind :: DictBind -> CoreBind
    db_bind = CoreBind
    bind, db_fvs :: DictBind -> VarSet
    db_fvs = VarSet
    fvs })
           | VarSet
    fvs VarSet -> VarSet -> Bool
    `intersectsVarSet` VarSet
    so_far
           = VarSet -> [Id] -> VarSet
    extendVarSetList VarSet
    so_far (CoreBind -> [Id]
    forall b. Bind b -> [b]
    bindersOf CoreBind
    bind)
           | Bool
    otherwise = VarSet
    so_far

        ok_call :: CallInfo -> Bool
    ok_call (CI { ci_fvs :: CallInfo -> VarSet
    ci_fvs = VarSet
    fvs }) = VarSet
    fvs VarSet -> VarSet -> Bool
    `disjointVarSet` VarSet
    dump_set

    ----------------------
    splitDictBinds :: Bag DictBind -> IdSet -> (Bag DictBind, Bag DictBind, IdSet)
    -- splitDictBinds dbs bndrs returns
    --   (free_dbs, dump_dbs, dump_set)
    -- where
    --   * dump_dbs depends, transitively on bndrs
    --   * free_dbs does not depend on bndrs
    --   * dump_set = bndrs `union` bndrs(dump_dbs)
    splitDictBinds :: Bag DictBind -> VarSet -> (Bag DictBind, Bag DictBind, VarSet)
    splitDictBinds Bag DictBind
    dbs VarSet
    bndr_set
       = ((Bag DictBind, Bag DictBind, VarSet)
     -> DictBind -> (Bag DictBind, Bag DictBind, VarSet))
    -> (Bag DictBind, Bag DictBind, VarSet)
    -> Bag DictBind
    -> (Bag DictBind, Bag DictBind, VarSet)
    forall (t :: * -> *) b a.
    Foldable t =>
    (b -> a -> b) -> b -> t a -> b
    foldl' (Bag DictBind, Bag DictBind, VarSet)
    -> DictBind -> (Bag DictBind, Bag DictBind, VarSet)
    split_db (Bag DictBind
    forall a. Bag a
    emptyBag, Bag DictBind
    forall a. Bag a
    emptyBag, VarSet
    bndr_set) Bag DictBind
    dbs
                    -- Important that it's foldl' not foldr;
                    -- we're accumulating the set of dumped ids in dump_set
       where
        split_db :: (Bag DictBind, Bag DictBind, VarSet)
    -> DictBind -> (Bag DictBind, Bag DictBind, VarSet)
    split_db (Bag DictBind
    free_dbs, Bag DictBind
    dump_dbs, VarSet
    dump_idset) DictBind
    db
            | DB { db_bind :: DictBind -> CoreBind
    db_bind = CoreBind
    bind, db_fvs :: DictBind -> VarSet
    db_fvs = VarSet
    fvs } <- DictBind
    db
            , VarSet
    dump_idset VarSet -> VarSet -> Bool
    `intersectsVarSet` VarSet
    fvs     -- Dump it
            = (Bag DictBind
    free_dbs, Bag DictBind
    dump_dbs Bag DictBind -> DictBind -> Bag DictBind
    forall a. Bag a -> a -> Bag a
    `snocBag` DictBind
    db,
               VarSet -> [Id] -> VarSet
    extendVarSetList VarSet
    dump_idset (CoreBind -> [Id]
    forall b. Bind b -> [b]
    bindersOf CoreBind
    bind))

            | Bool
    otherwise     -- Don't dump it
            = (Bag DictBind
    free_dbs Bag DictBind -> DictBind -> Bag DictBind
    forall a. Bag a -> a -> Bag a
    `snocBag` DictBind
    db, Bag DictBind
    dump_dbs, VarSet
    dump_idset)

    ----------------------
    deleteCallsMentioning :: VarSet -> CallDetails -> CallDetails
    -- Remove calls *mentioning* bs in any way
    deleteCallsMentioning :: VarSet -> CallDetails -> CallDetails
    deleteCallsMentioning VarSet
    bs CallDetails
    calls
      = (CallInfoSet -> CallInfoSet) -> CallDetails -> CallDetails
    forall a b. (a -> b) -> DVarEnv a -> DVarEnv b
    mapDVarEnv ((CallInfo -> Bool) -> CallInfoSet -> CallInfoSet
    ciSetFilter CallInfo -> Bool
    keep_call) CallDetails
    calls
      where
        keep_call :: CallInfo -> Bool
    keep_call (CI { ci_fvs :: CallInfo -> VarSet
    ci_fvs = VarSet
    fvs }) = VarSet
    fvs VarSet -> VarSet -> Bool
    `disjointVarSet` VarSet
    bs

    deleteCallsFor :: [Id] -> CallDetails -> CallDetails
    -- Remove calls *for* bs
    deleteCallsFor :: [Id] -> CallDetails -> CallDetails
    deleteCallsFor [Id]
    bs CallDetails
    calls = CallDetails -> [Id] -> CallDetails
    forall a. DVarEnv a -> [Id] -> DVarEnv a
    delDVarEnvList CallDetails
    calls [Id]
    bs

    {-
    ************************************************************************
    *                                                                      *
    \subsubsection{Boring helper functions}
    *                                                                      *
    ************************************************************************
    -}

    type SpecM a = UniqSM a

    runSpecM :: SpecM a -> CoreM a
    runSpecM :: forall a. SpecM a -> CoreM a
    runSpecM SpecM a
    thing_inside
      = do { UniqSupply
    us <- CoreM UniqSupply
    forall (m :: * -> *). MonadUnique m => m UniqSupply
    getUniqueSupplyM
           ; a -> CoreM a
    forall (m :: * -> *) a. Monad m => a -> m a
    return (UniqSupply -> SpecM a -> a
    forall a. UniqSupply -> UniqSM a -> a
    initUs_ UniqSupply
    us SpecM a
    thing_inside) }

    mapAndCombineSM :: (a -> SpecM (b, UsageDetails)) -> [a] -> SpecM ([b], UsageDetails)
    mapAndCombineSM :: forall a b.
    (a -> SpecM (b, UsageDetails)) -> [a] -> SpecM ([b], UsageDetails)
    mapAndCombineSM a -> SpecM (b, UsageDetails)
    _ []     = ([b], UsageDetails) -> UniqSM ([b], UsageDetails)
    forall (m :: * -> *) a. Monad m => a -> m a
    return ([], UsageDetails
    emptyUDs)
    mapAndCombineSM a -> SpecM (b, UsageDetails)
    f (a
    x:[a]
    xs) = do (b
    y, UsageDetails
    uds1) <- a -> SpecM (b, UsageDetails)
    f a
    x
                                  ([b]
    ys, UsageDetails
    uds2) <- (a -> SpecM (b, UsageDetails)) -> [a] -> UniqSM ([b], UsageDetails)
    forall a b.
    (a -> SpecM (b, UsageDetails)) -> [a] -> SpecM ([b], UsageDetails)
    mapAndCombineSM a -> SpecM (b, UsageDetails)
    f [a]
    xs
                                  ([b], UsageDetails) -> UniqSM ([b], UsageDetails)
    forall (m :: * -> *) a. Monad m => a -> m a
    return (b
    yb -> [b] -> [b]
    forall a. a -> [a] -> [a]
    :[b]
    ys, UsageDetails
    uds1 UsageDetails -> UsageDetails -> UsageDetails
    `plusUDs` UsageDetails
    uds2)

    extendTvSubstList :: SpecEnv -> [(TyVar,Type)] -> SpecEnv
    extendTvSubstList :: SpecEnv -> [(Id, Kind)] -> SpecEnv
    extendTvSubstList SpecEnv
    env [(Id, Kind)]
    tv_binds
      = SpecEnv
    env { se_subst :: Subst
    se_subst = Subst -> [(Id, Kind)] -> Subst
    Core.extendTvSubstList (SpecEnv -> Subst
    se_subst SpecEnv
    env) [(Id, Kind)]
    tv_binds }

    substTy :: SpecEnv -> Type -> Type
    substTy :: SpecEnv -> Kind -> Kind
    substTy SpecEnv
    env Kind
    ty = Subst -> Kind -> Kind
    Core.substTy (SpecEnv -> Subst
    se_subst SpecEnv
    env) Kind
    ty

    substCo :: SpecEnv -> Coercion -> Coercion
    substCo :: SpecEnv -> Coercion -> Coercion
    substCo SpecEnv
    env Coercion
    co = HasCallStack => Subst -> Coercion -> Coercion
    Subst -> Coercion -> Coercion
    Core.substCo (SpecEnv -> Subst
    se_subst SpecEnv
    env) Coercion
    co

    substBndr :: SpecEnv -> CoreBndr -> (SpecEnv, CoreBndr)
    substBndr :: SpecEnv -> Id -> (SpecEnv, Id)
    substBndr SpecEnv
    env Id
    bs = case Subst -> Id -> (Subst, Id)
    Core.substBndr (SpecEnv -> Subst
    se_subst SpecEnv
    env) Id
    bs of
                          (Subst
    subst', Id
    bs') -> (SpecEnv
    env { se_subst :: Subst
    se_subst = Subst
    subst' }, Id
    bs')

    substBndrs :: SpecEnv -> [CoreBndr] -> (SpecEnv, [CoreBndr])
    substBndrs :: SpecEnv -> [Id] -> (SpecEnv, [Id])
    substBndrs SpecEnv
    env [Id]
    bs = case Subst -> [Id] -> (Subst, [Id])
    Core.substBndrs (SpecEnv -> Subst
    se_subst SpecEnv
    env) [Id]
    bs of
                          (Subst
    subst', [Id]
    bs') -> (SpecEnv
    env { se_subst :: Subst
    se_subst = Subst
    subst' }, [Id]
    bs')

    cloneBindSM :: SpecEnv -> CoreBind -> SpecM (SpecEnv, SpecEnv, CoreBind)
    -- Clone the binders of the bind; return new bind with the cloned binders
    -- Return the substitution to use for RHSs, and the one to use for the body
    cloneBindSM :: SpecEnv -> CoreBind -> SpecM (SpecEnv, SpecEnv, CoreBind)
    cloneBindSM env :: SpecEnv
    env@(SE { se_subst :: SpecEnv -> Subst
    se_subst = Subst
    subst, se_interesting :: SpecEnv -> VarSet
    se_interesting = VarSet
    interesting }) (NonRec Id
    bndr CoreExpr
    rhs)
      = do { UniqSupply
    us <- UniqSM UniqSupply
    forall (m :: * -> *). MonadUnique m => m UniqSupply
    getUniqueSupplyM
           ; let (Subst
    subst', Id
    bndr') = Subst -> UniqSupply -> Id -> (Subst, Id)
    Core.cloneIdBndr Subst
    subst UniqSupply
    us Id
    bndr
                 interesting' :: VarSet
    interesting' | SpecEnv -> CoreExpr -> Bool
    interestingDict SpecEnv
    env CoreExpr
    rhs
                              = VarSet
    interesting VarSet -> Id -> VarSet
    `extendVarSet` Id
    bndr'
                              | Bool
    otherwise = VarSet
    interesting
           ; (SpecEnv, SpecEnv, CoreBind) -> SpecM (SpecEnv, SpecEnv, CoreBind)
    forall (m :: * -> *) a. Monad m => a -> m a
    return (SpecEnv
    env, SpecEnv
    env { se_subst :: Subst
    se_subst = Subst
    subst', se_interesting :: VarSet
    se_interesting = VarSet
    interesting' }
                    , Id -> CoreExpr -> CoreBind
    forall b. b -> Expr b -> Bind b
    NonRec Id
    bndr' CoreExpr
    rhs) }

    cloneBindSM env :: SpecEnv
    env@(SE { se_subst :: SpecEnv -> Subst
    se_subst = Subst
    subst, se_interesting :: SpecEnv -> VarSet
    se_interesting = VarSet
    interesting }) (Rec [(Id, CoreExpr)]
    pairs)
      = do { UniqSupply
    us <- UniqSM UniqSupply
    forall (m :: * -> *). MonadUnique m => m UniqSupply
    getUniqueSupplyM
           ; let (Subst
    subst', [Id]
    bndrs') = Subst -> UniqSupply -> [Id] -> (Subst, [Id])
    Core.cloneRecIdBndrs Subst
    subst UniqSupply
    us (((Id, CoreExpr) -> Id) -> [(Id, CoreExpr)] -> [Id]
    forall a b. (a -> b) -> [a] -> [b]
    map (Id, CoreExpr) -> Id
    forall a b. (a, b) -> a
    fst [(Id, CoreExpr)]
    pairs)
                 env' :: SpecEnv
    env' = SpecEnv
    env { se_subst :: Subst
    se_subst = Subst
    subst'
                            , se_interesting :: VarSet
    se_interesting = VarSet
    interesting VarSet -> [Id] -> VarSet
    `extendVarSetList`
                                               [ Id
    v | (Id
    v,CoreExpr
    r) <- [(Id, CoreExpr)]
    pairs, SpecEnv -> CoreExpr -> Bool
    interestingDict SpecEnv
    env CoreExpr
    r ] }
           ; (SpecEnv, SpecEnv, CoreBind) -> SpecM (SpecEnv, SpecEnv, CoreBind)
    forall (m :: * -> *) a. Monad m => a -> m a
    return (SpecEnv
    env', SpecEnv
    env', [(Id, CoreExpr)] -> CoreBind
    forall b. [(b, Expr b)] -> Bind b
    Rec ([Id]
    bndrs' [Id] -> [CoreExpr] -> [(Id, CoreExpr)]
    forall a b. [a] -> [b] -> [(a, b)]
    `zip` ((Id, CoreExpr) -> CoreExpr) -> [(Id, CoreExpr)] -> [CoreExpr]
    forall a b. (a -> b) -> [a] -> [b]
    map (Id, CoreExpr) -> CoreExpr
    forall a b. (a, b) -> b
    snd [(Id, CoreExpr)]
    pairs)) }

    newDictBndr :: SpecEnv -> CoreBndr -> SpecM CoreBndr
    -- Make up completely fresh binders for the dictionaries
    -- Their bindings are going to float outwards
    newDictBndr :: SpecEnv -> Id -> UniqSM Id
    newDictBndr SpecEnv
    env Id
    b = do { Unique
    uniq <- UniqSM Unique
    forall (m :: * -> *). MonadUnique m => m Unique
    getUniqueM
                            ; let n :: Name
    n   = Id -> Name
    idName Id
    b
                                  ty' :: Kind
    ty' = SpecEnv -> Kind -> Kind
    substTy SpecEnv
    env (Id -> Kind
    idType Id
    b)
                            ; Id -> UniqSM Id
    forall (m :: * -> *) a. Monad m => a -> m a
    return (OccName -> Unique -> Kind -> Kind -> SrcSpan -> Id
    mkUserLocal (Name -> OccName
    nameOccName Name
    n) Unique
    uniq Kind
    Many Kind
    ty' (Name -> SrcSpan
    forall a. NamedThing a => a -> SrcSpan
    getSrcSpan Name
    n)) }

    newSpecIdSM :: Id -> Type -> Maybe JoinArity -> SpecM Id
        -- Give the new Id a similar occurrence name to the old one
    newSpecIdSM :: Id -> Kind -> Maybe Int -> UniqSM Id
    newSpecIdSM Id
    old_id Kind
    new_ty Maybe Int
    join_arity_maybe
      = do  { Unique
    uniq <- UniqSM Unique
    forall (m :: * -> *). MonadUnique m => m Unique
    getUniqueM
            ; let name :: Name
    name    = Id -> Name
    idName Id
    old_id
                  new_occ :: OccName
    new_occ = OccName -> OccName
    mkSpecOcc (Name -> OccName
    nameOccName Name
    name)
                  new_id :: Id
    new_id  = OccName -> Unique -> Kind -> Kind -> SrcSpan -> Id
    mkUserLocal OccName
    new_occ Unique
    uniq Kind
    Many Kind
    new_ty (Name -> SrcSpan
    forall a. NamedThing a => a -> SrcSpan
    getSrcSpan Name
    name)
                              Id -> Maybe Int -> Id
    `asJoinId_maybe` Maybe Int
    join_arity_maybe
            ; Id -> UniqSM Id
    forall (m :: * -> *) a. Monad m => a -> m a
    return Id
    new_id }

    {-
                    Old (but interesting) stuff about unboxed bindings
                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    What should we do when a value is specialised to a *strict* unboxed value?

            map_*_* f (x:xs) = let h = f x
                                   t = map f xs
                               in h:t

    Could convert let to case:

            map_*_Int# f (x:xs) = case f x of h# ->
                                  let t = map f xs
                                  in h#:t

    This may be undesirable since it forces evaluation here, but the value
    may not be used in all branches of the body. In the general case this
    transformation is impossible since the mutual recursion in a letrec
    cannot be expressed as a case.

    There is also a problem with top-level unboxed values, since our
    implementation cannot handle unboxed values at the top level.

    Solution: Lift the binding of the unboxed value and extract it when it
    is used:

            map_*_Int# f (x:xs) = let h = case (f x) of h# -> _Lift h#
                                      t = map f xs
                                  in case h of
                                     _Lift h# -> h#:t

    Now give it to the simplifier and the _Lifting will be optimised away.

    The benefit is that we have given the specialised "unboxed" values a
    very simple lifted semantics and then leave it up to the simplifier to
    optimise it --- knowing that the overheads will be removed in nearly
    all cases.

    In particular, the value will only be evaluated in the branches of the
    program which use it, rather than being forced at the point where the
    value is bound. For example:

            filtermap_*_* p f (x:xs)
              = let h = f x
                    t = ...
                in case p x of
                    True  -> h:t
                    False -> t
       ==>
            filtermap_*_Int# p f (x:xs)
              = let h = case (f x) of h# -> _Lift h#
                    t = ...
                in case p x of
                    True  -> case h of _Lift h#
                               -> h#:t
                    False -> t

    The binding for h can still be inlined in the one branch and the
    _Lifting eliminated.

    Question: When won't the _Lifting be eliminated?

    Answer: When they at the top-level (where it is necessary) or when
    inlining would duplicate work (or possibly code depending on
    options). However, the _Lifting will still be eliminated if the
    strictness analyser deems the lifted binding strict.
    -}