    {-
    (c) The GRASP/AQUA Project, Glasgow University, 1992-1998

    ************************************************************************
    *                                                                      *
    \section[FloatIn]{Floating Inwards pass}
    *                                                                      *
    ************************************************************************

    The main purpose of @floatInwards@ is floating into branches of a
    case, so that we don't allocate things, save them on the stack, and
    then discover that they aren't needed in the chosen branch.
    -}

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

    module GHC.Core.Opt.FloatIn ( floatInwards ) where

    import GHC.Prelude
    import GHC.Platform

    import GHC.Core
    import GHC.Core.Make hiding ( wrapFloats )
    import GHC.Core.Utils
    import GHC.Core.FVs
    import GHC.Core.Type

    import GHC.Types.Basic      ( RecFlag(..), isRec, Levity(Unlifted) )
    import GHC.Types.Id         ( isOneShotBndr, idType, isJoinId, isJoinId_maybe )
    import GHC.Types.Tickish
    import GHC.Types.Var
    import GHC.Types.Var.Set

    import GHC.Utils.Misc
    import GHC.Utils.Panic
    import GHC.Utils.Panic.Plain

    {-
    Top-level interface function, @floatInwards@.  Note that we do not
    actually float any bindings downwards from the top-level.
    -}

    floatInwards :: Platform -> CoreProgram -> CoreProgram
    floatInwards :: Platform -> CoreProgram -> CoreProgram
    floatInwards Platform
    platform CoreProgram
    binds = (Bind CoreBndr -> Bind CoreBndr) -> CoreProgram -> CoreProgram
    forall a b. (a -> b) -> [a] -> [b]
    map (Platform -> Bind CoreBndr -> Bind CoreBndr
    fi_top_bind Platform
    platform) CoreProgram
    binds
      where
        fi_top_bind :: Platform -> Bind CoreBndr -> Bind CoreBndr
    fi_top_bind Platform
    platform (NonRec CoreBndr
    binder Expr CoreBndr
    rhs)
          = CoreBndr -> Expr CoreBndr -> Bind CoreBndr
    forall b. b -> Expr b -> Bind b
    NonRec CoreBndr
    binder (Platform -> FloatInBinds -> CoreExprWithFVs -> Expr CoreBndr
    fiExpr Platform
    platform [] (Expr CoreBndr -> CoreExprWithFVs
    freeVars Expr CoreBndr
    rhs))
        fi_top_bind Platform
    platform (Rec [(CoreBndr, Expr CoreBndr)]
    pairs)
          = [(CoreBndr, Expr CoreBndr)] -> Bind CoreBndr
    forall b. [(b, Expr b)] -> Bind b
    Rec [ (CoreBndr
    b, Platform -> FloatInBinds -> CoreExprWithFVs -> Expr CoreBndr
    fiExpr Platform
    platform [] (Expr CoreBndr -> CoreExprWithFVs
    freeVars Expr CoreBndr
    rhs)) | (CoreBndr
    b, Expr CoreBndr
    rhs) <- [(CoreBndr, Expr CoreBndr)]
    pairs ]

    {-
    ************************************************************************
    *                                                                      *
    \subsection{Mail from Andr\'e [edited]}
    *                                                                      *
    ************************************************************************

    {\em Will wrote: What??? I thought the idea was to float as far
    inwards as possible, no matter what.  This is dropping all bindings
    every time it sees a lambda of any kind.  Help! }

    You are assuming we DO DO full laziness AFTER floating inwards!  We
    have to [not float inside lambdas] if we don't.

    If we indeed do full laziness after the floating inwards (we could
    check the compilation flags for that) then I agree we could be more
    aggressive and do float inwards past lambdas.

    Actually we are not doing a proper full laziness (see below), which
    was another reason for not floating inwards past a lambda.

    This can easily be fixed.  The problem is that we float lets outwards,
    but there are a few expressions which are not let bound, like case
    scrutinees and case alternatives.  After floating inwards the
    simplifier could decide to inline the let and the laziness would be
    lost, e.g.

    \begin{verbatim}
    let a = expensive             ==> \b -> case expensive of ...
    in \ b -> case a of ...
    \end{verbatim}
    The fix is
    \begin{enumerate}
    \item
    to let bind the algebraic case scrutinees (done, I think) and
    the case alternatives (except the ones with an
    unboxed type)(not done, I think). This is best done in the
    GHC.Core.Opt.SetLevels module, which tags things with their level numbers.
    \item
    do the full laziness pass (floating lets outwards).
    \item
    simplify. The simplifier inlines the (trivial) lets that were
     created but were not floated outwards.
    \end{enumerate}

    With the fix I think Will's suggestion that we can gain even more from
    strictness by floating inwards past lambdas makes sense.

    We still gain even without going past lambdas, as things may be
    strict in the (new) context of a branch (where it was floated to) or
    of a let rhs, e.g.
    \begin{verbatim}
    let a = something            case x of
    in case x of                   alt1 -> case something of a -> a + a
         alt1 -> a + a      ==>    alt2 -> b
         alt2 -> b

    let a = something           let b = case something of a -> a + a
    in let b = a + a        ==> in (b,b)
    in (b,b)
    \end{verbatim}
    Also, even if a is not found to be strict in the new context and is
    still left as a let, if the branch is not taken (or b is not entered)
    the closure for a is not built.

    ************************************************************************
    *                                                                      *
    \subsection{Main floating-inwards code}
    *                                                                      *
    ************************************************************************
    -}

    type FreeVarSet  = DIdSet
    type BoundVarSet = DIdSet

    data FloatInBind = FB BoundVarSet FreeVarSet FloatBind
            -- The FreeVarSet is the free variables of the binding.  In the case
            -- of recursive bindings, the set doesn't include the bound
            -- variables.

    type FloatInBinds = [FloatInBind]
            -- In reverse dependency order (innermost binder first)

    fiExpr :: Platform
           -> FloatInBinds      -- Binds we're trying to drop
                                -- as far "inwards" as possible
           -> CoreExprWithFVs   -- Input expr
           -> CoreExpr          -- Result

    fiExpr :: Platform -> FloatInBinds -> CoreExprWithFVs -> Expr CoreBndr
    fiExpr Platform
    _ FloatInBinds
    to_drop (FVAnn
    _, AnnLit Literal
    lit)     = FloatInBinds -> Expr CoreBndr -> Expr CoreBndr
    wrapFloats FloatInBinds
    to_drop (Literal -> Expr CoreBndr
    forall b. Literal -> Expr b
    Lit Literal
    lit)
                                           -- See Note [Dead bindings]
    fiExpr Platform
    _ FloatInBinds
    to_drop (FVAnn
    _, AnnType Type
    ty)     = Bool -> Expr CoreBndr -> Expr CoreBndr
    forall a. HasCallStack => Bool -> a -> a
    assert (FloatInBinds -> Bool
    forall a. [a] -> Bool
    forall (t :: * -> *) a. Foldable t => t a -> Bool
    null FloatInBinds
    to_drop) (Expr CoreBndr -> Expr CoreBndr) -> Expr CoreBndr -> Expr CoreBndr
    forall a b. (a -> b) -> a -> b
    $ Type -> Expr CoreBndr
    forall b. Type -> Expr b
    Type Type
    ty
    fiExpr Platform
    _ FloatInBinds
    to_drop (FVAnn
    _, AnnVar CoreBndr
    v)       = FloatInBinds -> Expr CoreBndr -> Expr CoreBndr
    wrapFloats FloatInBinds
    to_drop (CoreBndr -> Expr CoreBndr
    forall b. CoreBndr -> Expr b
    Var CoreBndr
    v)
    fiExpr Platform
    _ FloatInBinds
    to_drop (FVAnn
    _, AnnCoercion Coercion
    co) = FloatInBinds -> Expr CoreBndr -> Expr CoreBndr
    wrapFloats FloatInBinds
    to_drop (Coercion -> Expr CoreBndr
    forall b. Coercion -> Expr b
    Coercion Coercion
    co)
    fiExpr Platform
    platform FloatInBinds
    to_drop (FVAnn
    _, AnnCast CoreExprWithFVs
    expr (FVAnn
    co_ann, Coercion
    co))
      = FloatInBinds -> Expr CoreBndr -> Expr CoreBndr
    wrapFloats (FloatInBinds
    drop_here FloatInBinds -> FloatInBinds -> FloatInBinds
    forall a. [a] -> [a] -> [a]
    ++ FloatInBinds
    co_drop) (Expr CoreBndr -> Expr CoreBndr) -> Expr CoreBndr -> Expr CoreBndr
    forall a b. (a -> b) -> a -> b
    $
        Expr CoreBndr -> Coercion -> Expr CoreBndr
    forall b. Expr b -> Coercion -> Expr b
    Cast (Platform -> FloatInBinds -> CoreExprWithFVs -> Expr CoreBndr
    fiExpr Platform
    platform FloatInBinds
    e_drop CoreExprWithFVs
    expr) Coercion
    co
      where
        [FloatInBinds
    drop_here, FloatInBinds
    e_drop, FloatInBinds
    co_drop]
          = Platform -> Bool -> [FVAnn] -> FloatInBinds -> [FloatInBinds]
    sepBindsByDropPoint Platform
    platform Bool
    False
              [CoreExprWithFVs -> FVAnn
    freeVarsOf CoreExprWithFVs
    expr, FVAnn -> FVAnn
    freeVarsOfAnn FVAnn
    co_ann]
              FloatInBinds
    to_drop

    {-
    Applications: we do float inside applications, mainly because we
    need to get at all the arguments.  The next simplifier run will
    pull out any silly ones.
    -}

    fiExpr Platform
    platform FloatInBinds
    to_drop ann_expr :: CoreExprWithFVs
    ann_expr@(FVAnn
    _,AnnApp {})
      = FloatInBinds -> Expr CoreBndr -> Expr CoreBndr
    wrapFloats FloatInBinds
    drop_here (Expr CoreBndr -> Expr CoreBndr) -> Expr CoreBndr -> Expr CoreBndr
    forall a b. (a -> b) -> a -> b
    $ FloatInBinds -> Expr CoreBndr -> Expr CoreBndr
    wrapFloats FloatInBinds
    extra_drop (Expr CoreBndr -> Expr CoreBndr) -> Expr CoreBndr -> Expr CoreBndr
    forall a b. (a -> b) -> a -> b
    $
        [CoreTickish] -> Expr CoreBndr -> Expr CoreBndr
    mkTicks [CoreTickish]
    ticks (Expr CoreBndr -> Expr CoreBndr) -> Expr CoreBndr -> Expr CoreBndr
    forall a b. (a -> b) -> a -> b
    $
        Expr CoreBndr -> [Expr CoreBndr] -> Expr CoreBndr
    forall b. Expr b -> [Expr b] -> Expr b
    mkApps (Platform -> FloatInBinds -> CoreExprWithFVs -> Expr CoreBndr
    fiExpr Platform
    platform FloatInBinds
    fun_drop CoreExprWithFVs
    ann_fun)
               (String
    -> (FloatInBinds -> CoreExprWithFVs -> Expr CoreBndr)
    -> [FloatInBinds]
    -> [CoreExprWithFVs]
    -> [Expr CoreBndr]
    forall a b c. String -> (a -> b -> c) -> [a] -> [b] -> [c]
    zipWithEqual String
    "fiExpr" (Platform -> FloatInBinds -> CoreExprWithFVs -> Expr CoreBndr
    fiExpr Platform
    platform) [FloatInBinds]
    arg_drops [CoreExprWithFVs]
    ann_args)
               -- use zipWithEqual, we should have
               -- length ann_args = length arg_fvs = length arg_drops
      where
        (CoreExprWithFVs
    ann_fun, [CoreExprWithFVs]
    ann_args, [CoreTickish]
    ticks) = (CoreTickish -> Bool)
    -> CoreExprWithFVs
    -> (CoreExprWithFVs, [CoreExprWithFVs], [CoreTickish])
    forall b a.
    (CoreTickish -> Bool)
    -> AnnExpr b a -> (AnnExpr b a, [AnnExpr b a], [CoreTickish])
    collectAnnArgsTicks CoreTickish -> Bool
    forall (pass :: TickishPass). GenTickish pass -> Bool
    tickishFloatable CoreExprWithFVs
    ann_expr
        fun_ty :: Type
    fun_ty  = (() :: Constraint) => Expr CoreBndr -> Type
    Expr CoreBndr -> Type
    exprType (CoreExprWithFVs -> Expr CoreBndr
    forall bndr annot. AnnExpr bndr annot -> Expr bndr
    deAnnotate CoreExprWithFVs
    ann_fun)
        fun_fvs :: FVAnn
    fun_fvs = CoreExprWithFVs -> FVAnn
    freeVarsOf CoreExprWithFVs
    ann_fun
        arg_fvs :: [FVAnn]
    arg_fvs = (CoreExprWithFVs -> FVAnn) -> [CoreExprWithFVs] -> [FVAnn]
    forall a b. (a -> b) -> [a] -> [b]
    map CoreExprWithFVs -> FVAnn
    freeVarsOf [CoreExprWithFVs]
    ann_args

        (FloatInBinds
    drop_here : FloatInBinds
    extra_drop : FloatInBinds
    fun_drop : [FloatInBinds]
    arg_drops)
           = Platform -> Bool -> [FVAnn] -> FloatInBinds -> [FloatInBinds]
    sepBindsByDropPoint Platform
    platform Bool
    False
                                 (FVAnn
    extra_fvs FVAnn -> [FVAnn] -> [FVAnn]
    forall a. a -> [a] -> [a]
    : FVAnn
    fun_fvs FVAnn -> [FVAnn] -> [FVAnn]
    forall a. a -> [a] -> [a]
    : [FVAnn]
    arg_fvs)
                                 FloatInBinds
    to_drop
             -- Shortcut behaviour: if to_drop is empty,
             -- sepBindsByDropPoint returns a suitable bunch of empty
             -- lists without evaluating extra_fvs, and hence without
             -- peering into each argument

        (Type
    _, FVAnn
    extra_fvs) = ((Type, FVAnn) -> CoreExprWithFVs -> (Type, FVAnn))
    -> (Type, FVAnn) -> [CoreExprWithFVs] -> (Type, FVAnn)
    forall b a. (b -> a -> b) -> b -> [a] -> b
    forall (t :: * -> *) b a.
    Foldable t =>
    (b -> a -> b) -> b -> t a -> b
    foldl' (Type, FVAnn) -> CoreExprWithFVs -> (Type, FVAnn)
    add_arg (Type
    fun_ty, FVAnn
    extra_fvs0) [CoreExprWithFVs]
    ann_args
        extra_fvs0 :: FVAnn
    extra_fvs0 = case CoreExprWithFVs
    ann_fun of
                       (FVAnn
    _, AnnVar CoreBndr
    _) -> FVAnn
    fun_fvs
                       CoreExprWithFVs
    _             -> FVAnn
    emptyDVarSet
              -- Don't float the binding for f into f x y z; see Note [Join points]
              -- for why we *can't* do it when f is a join point. (If f isn't a
              -- join point, floating it in isn't especially harmful but it's
              -- useless since the simplifier will immediately float it back out.)

        add_arg :: (Type,FreeVarSet) -> CoreExprWithFVs -> (Type,FreeVarSet)
        add_arg :: (Type, FVAnn) -> CoreExprWithFVs -> (Type, FVAnn)
    add_arg (Type
    fun_ty, FVAnn
    extra_fvs) (FVAnn
    _, AnnType Type
    ty)
          = ((() :: Constraint) => Type -> Type -> Type
    Type -> Type -> Type
    piResultTy Type
    fun_ty Type
    ty, FVAnn
    extra_fvs)

        add_arg (Type
    fun_ty, FVAnn
    extra_fvs) (FVAnn
    arg_fvs, AnnExpr' CoreBndr FVAnn
    arg)
          | AnnExpr' CoreBndr FVAnn -> Type -> Bool
    noFloatIntoArg AnnExpr' CoreBndr FVAnn
    arg Type
    arg_ty
          = (Type
    res_ty, FVAnn
    extra_fvs FVAnn -> FVAnn -> FVAnn
    `unionDVarSet` FVAnn
    arg_fvs)
          | Bool
    otherwise
          = (Type
    res_ty, FVAnn
    extra_fvs)
          where
           (Type
    _, Type
    arg_ty, Type
    res_ty) = Type -> (Type, Type, Type)
    splitFunTy Type
    fun_ty

    {- Note [Dead bindings]
    ~~~~~~~~~~~~~~~~~~~~~~~
    At a literal we won't usually have any floated bindings; the
    only way that can happen is if the binding wrapped the literal
    /in the original input program/.  e.g.
       case x of { DEFAULT -> 1# }
    But, while this may be unusual it is not actually wrong, and it did
    once happen (#15696).

    Note [Do not destroy the let/app invariant]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Watch out for
       f (x +# y)
    We don't want to float bindings into here
       f (case ... of { x -> x +# y })
    because that might destroy the let/app invariant, which requires
    unlifted function arguments to be ok-for-speculation.

    Note [Join points]
    ~~~~~~~~~~~~~~~~~~
    Generally, we don't need to worry about join points - there are places we're
    not allowed to float them, but since they can't have occurrences in those
    places, we're not tempted.

    We do need to be careful about jumps, however:

      joinrec j x y z = ... in
      jump j a b c

    Previous versions often floated the definition of a recursive function into its
    only non-recursive occurrence. But for a join point, this is a disaster:

      (joinrec j x y z = ... in
      jump j) a b c -- wrong!

    Every jump must be exact, so the jump to j must have three arguments. Hence
    we're careful not to float into the target of a jump (though we can float into
    the arguments just fine).

    Note [Floating in past a lambda group]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    * We must be careful about floating inside a value lambda.
      That risks losing laziness.
      The float-out pass might rescue us, but then again it might not.

    * We must be careful about type lambdas too.  At one time we did, and
      there is no risk of duplicating work thereby, but we do need to be
      careful.  In particular, here is a bad case (it happened in the
      cichelli benchmark:
            let v = ...
            in let f = /\t -> \a -> ...
               ==>
            let f = /\t -> let v = ... in \a -> ...
      This is bad as now f is an updatable closure (update PAP)
      and has arity 0.

    * Hack alert!  We only float in through one-shot lambdas,
      not (as you might guess) through lone big lambdas.
      Reason: we float *out* past big lambdas (see the test in the Lam
      case of FloatOut.floatExpr) and we don't want to float straight
      back in again.

      It *is* important to float into one-shot lambdas, however;
      see the remarks with noFloatIntoRhs.

    So we treat lambda in groups, using the following rule:

     Float in if (a) there is at least one Id,
             and (b) there are no non-one-shot Ids

     Otherwise drop all the bindings outside the group.

    This is what the 'go' function in the AnnLam case is doing.

    (Join points are handled similarly: a join point is considered one-shot iff
    it's non-recursive, so we float only into non-recursive join points.)

    Urk! if all are tyvars, and we don't float in, we may miss an
          opportunity to float inside a nested case branch

    Note [Floating coercions]
    ~~~~~~~~~~~~~~~~~~~~~~~~~
    We could, in principle, have a coercion binding like
       case f x of co { DEFAULT -> e1 e2 }
    It's not common to have a function that returns a coercion, but nothing
    in Core prohibits it.  If so, 'co' might be mentioned in e1 or e2
    /only in a type/.  E.g. suppose e1 was
      let (x :: Int |> co) = blah in blah2

    But, with coercions appearing in types, there is a complication: we
    might be floating in a "strict let" -- that is, a case. Case expressions
    mention their return type. We absolutely can't float a coercion binding
    inward to the point that the type of the expression it's about to wrap
    mentions the coercion. So we include the union of the sets of free variables
    of the types of all the drop points involved. If any of the floaters
    bind a coercion variable mentioned in any of the types, that binder must
    be dropped right away.

    -}

    fiExpr Platform
    platform FloatInBinds
    to_drop lam :: CoreExprWithFVs
    lam@(FVAnn
    _, AnnLam CoreBndr
    _ CoreExprWithFVs
    _)
      | [CoreBndr] -> Bool
    noFloatIntoLam [CoreBndr]
    bndrs       -- Dump it all here
         -- NB: Must line up with noFloatIntoRhs (AnnLam...); see #7088
      = FloatInBinds -> Expr CoreBndr -> Expr CoreBndr
    wrapFloats FloatInBinds
    to_drop ([CoreBndr] -> Expr CoreBndr -> Expr CoreBndr
    forall b. [b] -> Expr b -> Expr b
    mkLams [CoreBndr]
    bndrs (Platform -> FloatInBinds -> CoreExprWithFVs -> Expr CoreBndr
    fiExpr Platform
    platform [] CoreExprWithFVs
    body))

      | Bool
    otherwise           -- Float inside
      = [CoreBndr] -> Expr CoreBndr -> Expr CoreBndr
    forall b. [b] -> Expr b -> Expr b
    mkLams [CoreBndr]
    bndrs (Platform -> FloatInBinds -> CoreExprWithFVs -> Expr CoreBndr
    fiExpr Platform
    platform FloatInBinds
    to_drop CoreExprWithFVs
    body)

      where
        ([CoreBndr]
    bndrs, CoreExprWithFVs
    body) = CoreExprWithFVs -> ([CoreBndr], CoreExprWithFVs)
    forall bndr annot.
    AnnExpr bndr annot -> ([bndr], AnnExpr bndr annot)
    collectAnnBndrs CoreExprWithFVs
    lam

    {-
    We don't float lets inwards past an SCC.
            ToDo: keep info on current cc, and when passing
            one, if it is not the same, annotate all lets in binds with current
            cc, change current cc to the new one and float binds into expr.
    -}

    fiExpr Platform
    platform FloatInBinds
    to_drop (FVAnn
    _, AnnTick CoreTickish
    tickish CoreExprWithFVs
    expr)
      | CoreTickish
    tickish CoreTickish -> TickishScoping -> Bool
    forall (pass :: TickishPass).
    GenTickish pass -> TickishScoping -> Bool
    `tickishScopesLike` TickishScoping
    SoftScope
      = CoreTickish -> Expr CoreBndr -> Expr CoreBndr
    forall b. CoreTickish -> Expr b -> Expr b
    Tick CoreTickish
    tickish (Platform -> FloatInBinds -> CoreExprWithFVs -> Expr CoreBndr
    fiExpr Platform
    platform FloatInBinds
    to_drop CoreExprWithFVs
    expr)

      | Bool
    otherwise -- Wimp out for now - we could push values in
      = FloatInBinds -> Expr CoreBndr -> Expr CoreBndr
    wrapFloats FloatInBinds
    to_drop (CoreTickish -> Expr CoreBndr -> Expr CoreBndr
    forall b. CoreTickish -> Expr b -> Expr b
    Tick CoreTickish
    tickish (Platform -> FloatInBinds -> CoreExprWithFVs -> Expr CoreBndr
    fiExpr Platform
    platform [] CoreExprWithFVs
    expr))

    {-
    For @Lets@, the possible ``drop points'' for the \tr{to_drop}
    bindings are: (a)~in the body, (b1)~in the RHS of a NonRec binding,
    or~(b2), in each of the RHSs of the pairs of a @Rec@.

    Note that we do {\em weird things} with this let's binding.  Consider:
    \begin{verbatim}
    let
        w = ...
    in {
        let v = ... w ...
        in ... v .. w ...
    }
    \end{verbatim}
    Look at the inner \tr{let}.  As \tr{w} is used in both the bind and
    body of the inner let, we could panic and leave \tr{w}'s binding where
    it is.  But \tr{v} is floatable further into the body of the inner let, and
    {\em then} \tr{w} will also be only in the body of that inner let.

    So: rather than drop \tr{w}'s binding here, we add it onto the list of
    things to drop in the outer let's body, and let nature take its
    course.

    Note [extra_fvs (1)]: avoid floating into RHS
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider let x=\y....t... in body.  We do not necessarily want to float
    a binding for t into the RHS, because it'll immediately be floated out
    again.  (It won't go inside the lambda else we risk losing work.)
    In letrec, we need to be more careful still. We don't want to transform
            let x# = y# +# 1#
            in
            letrec f = \z. ...x#...f...
            in ...
    into
            letrec f = let x# = y# +# 1# in \z. ...x#...f... in ...
    because now we can't float the let out again, because a letrec
    can't have unboxed bindings.

    So we make "extra_fvs" which is the rhs_fvs of such bindings, and
    arrange to dump bindings that bind extra_fvs before the entire let.

    Note [extra_fvs (2)]: free variables of rules
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider
      let x{rule mentioning y} = rhs in body
    Here y is not free in rhs or body; but we still want to dump bindings
    that bind y outside the let.  So we augment extra_fvs with the
    idRuleAndUnfoldingVars of x.  No need for type variables, hence not using
    idFreeVars.
    -}

    fiExpr Platform
    platform FloatInBinds
    to_drop (FVAnn
    _,AnnLet AnnBind CoreBndr FVAnn
    bind CoreExprWithFVs
    body)
      = Platform -> FloatInBinds -> CoreExprWithFVs -> Expr CoreBndr
    fiExpr Platform
    platform (FloatInBinds
    after FloatInBinds -> FloatInBinds -> FloatInBinds
    forall a. [a] -> [a] -> [a]
    ++ FloatInBind
    new_float FloatInBind -> FloatInBinds -> FloatInBinds
    forall a. a -> [a] -> [a]
    : FloatInBinds
    before) CoreExprWithFVs
    body
               -- to_drop is in reverse dependency order
      where
        (FloatInBinds
    before, FloatInBind
    new_float, FloatInBinds
    after) = Platform
    -> FloatInBinds
    -> AnnBind CoreBndr FVAnn
    -> FVAnn
    -> (FloatInBinds, FloatInBind, FloatInBinds)
    fiBind Platform
    platform FloatInBinds
    to_drop AnnBind CoreBndr FVAnn
    bind FVAnn
    body_fvs
        body_fvs :: FVAnn
    body_fvs    = CoreExprWithFVs -> FVAnn
    freeVarsOf CoreExprWithFVs
    body

    {- Note [Floating primops]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~
    We try to float-in a case expression over an unlifted type.  The
    motivating example was #5658: in particular, this change allows
    array indexing operations, which have a single DEFAULT alternative
    without any binders, to be floated inward.

    SIMD primops for unpacking SIMD vectors into an unboxed tuple of unboxed
    scalars also need to be floated inward, but unpacks have a single non-DEFAULT
    alternative that binds the elements of the tuple. We now therefore also support
    floating in cases with a single alternative that may bind values.

    But there are wrinkles

    * Which unlifted cases do we float?
      See Note [PrimOp can_fail and has_side_effects] in GHC.Builtin.PrimOps which
      explains:
       - We can float in can_fail primops (which concerns imprecise exceptions),
         but we can't float them out.
       - But we can float a has_side_effects primop, but NOT inside a lambda,
         so for now we don't float them at all. Hence exprOkForSideEffects.
       - Throwing precise exceptions is a special case of the previous point: We
         may /never/ float in a call to (something that ultimately calls)
         'raiseIO#'.
         See Note [Precise exceptions and strictness analysis] in GHC.Types.Demand.

    * Because we can float can-fail primops (array indexing, division) inwards
      but not outwards, we must be careful not to transform
         case a /# b of r -> f (F# r)
      ===>
        f (case a /# b of r -> F# r)
      because that creates a new thunk that wasn't there before.  And
      because it can't be floated out (can_fail), the thunk will stay
      there.  Disaster!  (This happened in nofib 'simple' and 'scs'.)

      Solution: only float cases into the branches of other cases, and
      not into the arguments of an application, or the RHS of a let. This
      is somewhat conservative, but it's simple.  And it still hits the
      cases like #5658.   This is implemented in sepBindsByJoinPoint;
      if is_case is False we dump all floating cases right here.

    * #14511 is another example of why we want to restrict float-in
      of case-expressions.  Consider
         case indexArray# a n of (# r #) -> writeArray# ma i (f r)
      Now, floating that indexing operation into the (f r) thunk will
      not create any new thunks, but it will keep the array 'a' alive
      for much longer than the programmer expected.

      So again, not floating a case into a let or argument seems like
      the Right Thing

    For @Case@, the possible drop points for the 'to_drop'
    bindings are:
      (a) inside the scrutinee
      (b) inside one of the alternatives/default (default FVs always /first/!).

    -}

    fiExpr Platform
    platform FloatInBinds
    to_drop (FVAnn
    _, AnnCase CoreExprWithFVs
    scrut CoreBndr
    case_bndr Type
    _ [AnnAlt AltCon
    con [CoreBndr]
    alt_bndrs CoreExprWithFVs
    rhs])
      | (() :: Constraint) => Type -> Bool
    Type -> Bool
    isUnliftedType (CoreBndr -> Type
    idType CoreBndr
    case_bndr)
         -- binders have a fixed RuntimeRep so it's OK to call isUnliftedType
      , Expr CoreBndr -> Bool
    exprOkForSideEffects (CoreExprWithFVs -> Expr CoreBndr
    forall bndr annot. AnnExpr bndr annot -> Expr bndr
    deAnnotate CoreExprWithFVs
    scrut)
          -- See Note [Floating primops]
      = FloatInBinds -> Expr CoreBndr -> Expr CoreBndr
    wrapFloats FloatInBinds
    shared_binds (Expr CoreBndr -> Expr CoreBndr) -> Expr CoreBndr -> Expr CoreBndr
    forall a b. (a -> b) -> a -> b
    $
        Platform -> FloatInBinds -> CoreExprWithFVs -> Expr CoreBndr
    fiExpr Platform
    platform (FloatInBind
    case_float FloatInBind -> FloatInBinds -> FloatInBinds
    forall a. a -> [a] -> [a]
    : FloatInBinds
    rhs_binds) CoreExprWithFVs
    rhs
      where
        case_float :: FloatInBind
    case_float = FVAnn -> FVAnn -> FloatBind -> FloatInBind
    FB ([CoreBndr] -> FVAnn
    mkDVarSet (CoreBndr
    case_bndr CoreBndr -> [CoreBndr] -> [CoreBndr]
    forall a. a -> [a] -> [a]
    : [CoreBndr]
    alt_bndrs)) FVAnn
    scrut_fvs
                        (Expr CoreBndr -> CoreBndr -> AltCon -> [CoreBndr] -> FloatBind
    FloatCase Expr CoreBndr
    scrut' CoreBndr
    case_bndr AltCon
    con [CoreBndr]
    alt_bndrs)
        scrut' :: Expr CoreBndr
    scrut'     = Platform -> FloatInBinds -> CoreExprWithFVs -> Expr CoreBndr
    fiExpr Platform
    platform FloatInBinds
    scrut_binds CoreExprWithFVs
    scrut
        rhs_fvs :: FVAnn
    rhs_fvs    = CoreExprWithFVs -> FVAnn
    freeVarsOf CoreExprWithFVs
    rhs FVAnn -> [CoreBndr] -> FVAnn
    `delDVarSetList` (CoreBndr
    case_bndr CoreBndr -> [CoreBndr] -> [CoreBndr]
    forall a. a -> [a] -> [a]
    : [CoreBndr]
    alt_bndrs)
        scrut_fvs :: FVAnn
    scrut_fvs  = CoreExprWithFVs -> FVAnn
    freeVarsOf CoreExprWithFVs
    scrut

        [FloatInBinds
    shared_binds, FloatInBinds
    scrut_binds, FloatInBinds
    rhs_binds]
           = Platform -> Bool -> [FVAnn] -> FloatInBinds -> [FloatInBinds]
    sepBindsByDropPoint Platform
    platform Bool
    False
               [FVAnn
    scrut_fvs, FVAnn
    rhs_fvs]
               FloatInBinds
    to_drop

    fiExpr Platform
    platform FloatInBinds
    to_drop (FVAnn
    _, AnnCase CoreExprWithFVs
    scrut CoreBndr
    case_bndr Type
    ty [AnnAlt CoreBndr FVAnn]
    alts)
      = FloatInBinds -> Expr CoreBndr -> Expr CoreBndr
    wrapFloats FloatInBinds
    drop_here1 (Expr CoreBndr -> Expr CoreBndr) -> Expr CoreBndr -> Expr CoreBndr
    forall a b. (a -> b) -> a -> b
    $
        FloatInBinds -> Expr CoreBndr -> Expr CoreBndr
    wrapFloats FloatInBinds
    drop_here2 (Expr CoreBndr -> Expr CoreBndr) -> Expr CoreBndr -> Expr CoreBndr
    forall a b. (a -> b) -> a -> b
    $
        Expr CoreBndr
    -> CoreBndr -> Type -> [Alt CoreBndr] -> Expr CoreBndr
    forall b. Expr b -> b -> Type -> [Alt b] -> Expr b
    Case (Platform -> FloatInBinds -> CoreExprWithFVs -> Expr CoreBndr
    fiExpr Platform
    platform FloatInBinds
    scrut_drops CoreExprWithFVs
    scrut) CoreBndr
    case_bndr Type
    ty
             (String
    -> (FloatInBinds -> AnnAlt CoreBndr FVAnn -> Alt CoreBndr)
    -> [FloatInBinds]
    -> [AnnAlt CoreBndr FVAnn]
    -> [Alt CoreBndr]
    forall a b c. String -> (a -> b -> c) -> [a] -> [b] -> [c]
    zipWithEqual String
    "fiExpr" FloatInBinds -> AnnAlt CoreBndr FVAnn -> Alt CoreBndr
    fi_alt [FloatInBinds]
    alts_drops_s [AnnAlt CoreBndr FVAnn]
    alts)
             -- use zipWithEqual, we should have length alts_drops_s = length alts
      where
            -- Float into the scrut and alts-considered-together just like App
        [FloatInBinds
    drop_here1, FloatInBinds
    scrut_drops, FloatInBinds
    alts_drops]
           = Platform -> Bool -> [FVAnn] -> FloatInBinds -> [FloatInBinds]
    sepBindsByDropPoint Platform
    platform Bool
    False
               [FVAnn
    scrut_fvs, FVAnn
    all_alts_fvs]
               FloatInBinds
    to_drop

            -- Float into the alts with the is_case flag set
        (FloatInBinds
    drop_here2 : [FloatInBinds]
    alts_drops_s)
          | [ AnnAlt CoreBndr FVAnn
    _ ] <- [AnnAlt CoreBndr FVAnn]
    alts = [] FloatInBinds -> [FloatInBinds] -> [FloatInBinds]
    forall a. a -> [a] -> [a]
    : [FloatInBinds
    alts_drops]
          | Bool
    otherwise     = Platform -> Bool -> [FVAnn] -> FloatInBinds -> [FloatInBinds]
    sepBindsByDropPoint Platform
    platform Bool
    True [FVAnn]
    alts_fvs FloatInBinds
    alts_drops

        scrut_fvs :: FVAnn
    scrut_fvs    = CoreExprWithFVs -> FVAnn
    freeVarsOf CoreExprWithFVs
    scrut
        alts_fvs :: [FVAnn]
    alts_fvs     = (AnnAlt CoreBndr FVAnn -> FVAnn)
    -> [AnnAlt CoreBndr FVAnn] -> [FVAnn]
    forall a b. (a -> b) -> [a] -> [b]
    map AnnAlt CoreBndr FVAnn -> FVAnn
    alt_fvs [AnnAlt CoreBndr FVAnn]
    alts
        all_alts_fvs :: FVAnn
    all_alts_fvs = [FVAnn] -> FVAnn
    unionDVarSets [FVAnn]
    alts_fvs
        alt_fvs :: AnnAlt CoreBndr FVAnn -> FVAnn
    alt_fvs (AnnAlt AltCon
    _con [CoreBndr]
    args CoreExprWithFVs
    rhs)
          = (FVAnn -> CoreBndr -> FVAnn) -> FVAnn -> [CoreBndr] -> FVAnn
    forall b a. (b -> a -> b) -> b -> [a] -> b
    forall (t :: * -> *) b a.
    Foldable t =>
    (b -> a -> b) -> b -> t a -> b
    foldl' FVAnn -> CoreBndr -> FVAnn
    delDVarSet (CoreExprWithFVs -> FVAnn
    freeVarsOf CoreExprWithFVs
    rhs) (CoreBndr
    case_bndrCoreBndr -> [CoreBndr] -> [CoreBndr]
    forall a. a -> [a] -> [a]
    :[CoreBndr]
    args)
               -- Delete case_bndr and args from free vars of rhs
               -- to get free vars of alt

        fi_alt :: FloatInBinds -> AnnAlt CoreBndr FVAnn -> Alt CoreBndr
    fi_alt FloatInBinds
    to_drop (AnnAlt AltCon
    con [CoreBndr]
    args CoreExprWithFVs
    rhs) = AltCon -> [CoreBndr] -> Expr CoreBndr -> Alt CoreBndr
    forall b. AltCon -> [b] -> Expr b -> Alt b
    Alt AltCon
    con [CoreBndr]
    args (Platform -> FloatInBinds -> CoreExprWithFVs -> Expr CoreBndr
    fiExpr Platform
    platform FloatInBinds
    to_drop CoreExprWithFVs
    rhs)

    ------------------
    fiBind :: Platform
           -> FloatInBinds      -- Binds we're trying to drop
                                -- as far "inwards" as possible
           -> CoreBindWithFVs   -- Input binding
           -> DVarSet           -- Free in scope of binding
           -> ( FloatInBinds    -- Land these before
              , FloatInBind     -- The binding itself
              , FloatInBinds)   -- Land these after

    fiBind :: Platform
    -> FloatInBinds
    -> AnnBind CoreBndr FVAnn
    -> FVAnn
    -> (FloatInBinds, FloatInBind, FloatInBinds)
    fiBind Platform
    platform FloatInBinds
    to_drop (AnnNonRec CoreBndr
    id ann_rhs :: CoreExprWithFVs
    ann_rhs@(FVAnn
    rhs_fvs, AnnExpr' CoreBndr FVAnn
    rhs)) FVAnn
    body_fvs
      = ( FloatInBinds
    extra_binds FloatInBinds -> FloatInBinds -> FloatInBinds
    forall a. [a] -> [a] -> [a]
    ++ FloatInBinds
    shared_binds          -- Land these before
                                               -- See Note [extra_fvs (1)] and Note [extra_fvs (2)]
        , FVAnn -> FVAnn -> FloatBind -> FloatInBind
    FB (CoreBndr -> FVAnn
    unitDVarSet CoreBndr
    id) FVAnn
    rhs_fvs'         -- The new binding itself
              (Bind CoreBndr -> FloatBind
    FloatLet (CoreBndr -> Expr CoreBndr -> Bind CoreBndr
    forall b. b -> Expr b -> Bind b
    NonRec CoreBndr
    id Expr CoreBndr
    rhs'))
        , FloatInBinds
    body_binds )                         -- Land these after

      where
        body_fvs2 :: FVAnn
    body_fvs2 = FVAnn
    body_fvs FVAnn -> CoreBndr -> FVAnn
    `delDVarSet` CoreBndr
    id

        rule_fvs :: FVAnn
    rule_fvs = CoreBndr -> FVAnn
    bndrRuleAndUnfoldingVarsDSet CoreBndr
    id        -- See Note [extra_fvs (2)]
        extra_fvs :: FVAnn
    extra_fvs | RecFlag -> CoreBndr -> AnnExpr' CoreBndr FVAnn -> Bool
    noFloatIntoRhs RecFlag
    NonRecursive CoreBndr
    id AnnExpr' CoreBndr FVAnn
    rhs
                  = FVAnn
    rule_fvs FVAnn -> FVAnn -> FVAnn
    `unionDVarSet` FVAnn
    rhs_fvs
                  | Bool
    otherwise
                  = FVAnn
    rule_fvs
            -- See Note [extra_fvs (1)]
            -- No point in floating in only to float straight out again
            -- We *can't* float into ok-for-speculation unlifted RHSs
            -- But do float into join points

        [FloatInBinds
    shared_binds, FloatInBinds
    extra_binds, FloatInBinds
    rhs_binds, FloatInBinds
    body_binds]
            = Platform -> Bool -> [FVAnn] -> FloatInBinds -> [FloatInBinds]
    sepBindsByDropPoint Platform
    platform Bool
    False
                [FVAnn
    extra_fvs, FVAnn
    rhs_fvs, FVAnn
    body_fvs2]
                FloatInBinds
    to_drop

            -- Push rhs_binds into the right hand side of the binding
        rhs' :: Expr CoreBndr
    rhs'     = Platform
    -> FloatInBinds -> CoreBndr -> CoreExprWithFVs -> Expr CoreBndr
    fiRhs Platform
    platform FloatInBinds
    rhs_binds CoreBndr
    id CoreExprWithFVs
    ann_rhs
        rhs_fvs' :: FVAnn
    rhs_fvs' = FVAnn
    rhs_fvs FVAnn -> FVAnn -> FVAnn
    `unionDVarSet` FloatInBinds -> FVAnn
    floatedBindsFVs FloatInBinds
    rhs_binds FVAnn -> FVAnn -> FVAnn
    `unionDVarSet` FVAnn
    rule_fvs
                            -- Don't forget the rule_fvs; the binding mentions them!

    fiBind Platform
    platform FloatInBinds
    to_drop (AnnRec [(CoreBndr, CoreExprWithFVs)]
    bindings) FVAnn
    body_fvs
      = ( FloatInBinds
    extra_binds FloatInBinds -> FloatInBinds -> FloatInBinds
    forall a. [a] -> [a] -> [a]
    ++ FloatInBinds
    shared_binds
        , FVAnn -> FVAnn -> FloatBind -> FloatInBind
    FB ([CoreBndr] -> FVAnn
    mkDVarSet [CoreBndr]
    ids) FVAnn
    rhs_fvs'
             (Bind CoreBndr -> FloatBind
    FloatLet ([(CoreBndr, Expr CoreBndr)] -> Bind CoreBndr
    forall b. [(b, Expr b)] -> Bind b
    Rec ([FloatInBinds]
    -> [(CoreBndr, CoreExprWithFVs)] -> [(CoreBndr, Expr CoreBndr)]
    fi_bind [FloatInBinds]
    rhss_binds [(CoreBndr, CoreExprWithFVs)]
    bindings)))
        , FloatInBinds
    body_binds )
      where
        ([CoreBndr]
    ids, [CoreExprWithFVs]
    rhss) = [(CoreBndr, CoreExprWithFVs)] -> ([CoreBndr], [CoreExprWithFVs])
    forall a b. [(a, b)] -> ([a], [b])
    unzip [(CoreBndr, CoreExprWithFVs)]
    bindings
        rhss_fvs :: [FVAnn]
    rhss_fvs = (CoreExprWithFVs -> FVAnn) -> [CoreExprWithFVs] -> [FVAnn]
    forall a b. (a -> b) -> [a] -> [b]
    map CoreExprWithFVs -> FVAnn
    freeVarsOf [CoreExprWithFVs]
    rhss

            -- See Note [extra_fvs (1)] and Note [extra_fvs (2)]
        rule_fvs :: FVAnn
    rule_fvs = (CoreBndr -> FVAnn) -> [CoreBndr] -> FVAnn
    forall a. (a -> FVAnn) -> [a] -> FVAnn
    mapUnionDVarSet CoreBndr -> FVAnn
    bndrRuleAndUnfoldingVarsDSet [CoreBndr]
    ids
        extra_fvs :: FVAnn
    extra_fvs = FVAnn
    rule_fvs FVAnn -> FVAnn -> FVAnn
    `unionDVarSet`
                    [FVAnn] -> FVAnn
    unionDVarSets [ FVAnn
    rhs_fvs | (CoreBndr
    bndr, (FVAnn
    rhs_fvs, AnnExpr' CoreBndr FVAnn
    rhs)) <- [(CoreBndr, CoreExprWithFVs)]
    bindings
                                  , RecFlag -> CoreBndr -> AnnExpr' CoreBndr FVAnn -> Bool
    noFloatIntoRhs RecFlag
    Recursive CoreBndr
    bndr AnnExpr' CoreBndr FVAnn
    rhs ]

        (FloatInBinds
    shared_binds:FloatInBinds
    extra_binds:FloatInBinds
    body_binds:[FloatInBinds]
    rhss_binds)
            = Platform -> Bool -> [FVAnn] -> FloatInBinds -> [FloatInBinds]
    sepBindsByDropPoint Platform
    platform Bool
    False
                (FVAnn
    extra_fvsFVAnn -> [FVAnn] -> [FVAnn]
    forall a. a -> [a] -> [a]
    :FVAnn
    body_fvsFVAnn -> [FVAnn] -> [FVAnn]
    forall a. a -> [a] -> [a]
    :[FVAnn]
    rhss_fvs)
                FloatInBinds
    to_drop

        rhs_fvs' :: FVAnn
    rhs_fvs' = [FVAnn] -> FVAnn
    unionDVarSets [FVAnn]
    rhss_fvs FVAnn -> FVAnn -> FVAnn
    `unionDVarSet`
                   [FVAnn] -> FVAnn
    unionDVarSets ((FloatInBinds -> FVAnn) -> [FloatInBinds] -> [FVAnn]
    forall a b. (a -> b) -> [a] -> [b]
    map FloatInBinds -> FVAnn
    floatedBindsFVs [FloatInBinds]
    rhss_binds) FVAnn -> FVAnn -> FVAnn
    `unionDVarSet`
                   FVAnn
    rule_fvs         -- Don't forget the rule variables!

        -- Push rhs_binds into the right hand side of the binding
        fi_bind :: [FloatInBinds]       -- one per "drop pt" conjured w/ fvs_of_rhss
                -> [(Id, CoreExprWithFVs)]
                -> [(Id, CoreExpr)]

        fi_bind :: [FloatInBinds]
    -> [(CoreBndr, CoreExprWithFVs)] -> [(CoreBndr, Expr CoreBndr)]
    fi_bind [FloatInBinds]
    to_drops [(CoreBndr, CoreExprWithFVs)]
    pairs
          = [ (CoreBndr
    binder, Platform
    -> FloatInBinds -> CoreBndr -> CoreExprWithFVs -> Expr CoreBndr
    fiRhs Platform
    platform FloatInBinds
    to_drop CoreBndr
    binder CoreExprWithFVs
    rhs)
            | ((CoreBndr
    binder, CoreExprWithFVs
    rhs), FloatInBinds
    to_drop) <- String
    -> [(CoreBndr, CoreExprWithFVs)]
    -> [FloatInBinds]
    -> [((CoreBndr, CoreExprWithFVs), FloatInBinds)]
    forall a b. String -> [a] -> [b] -> [(a, b)]
    zipEqual String
    "fi_bind" [(CoreBndr, CoreExprWithFVs)]
    pairs [FloatInBinds]
    to_drops ]

    ------------------
    fiRhs :: Platform -> FloatInBinds -> CoreBndr -> CoreExprWithFVs -> CoreExpr
    fiRhs :: Platform
    -> FloatInBinds -> CoreBndr -> CoreExprWithFVs -> Expr CoreBndr
    fiRhs Platform
    platform FloatInBinds
    to_drop CoreBndr
    bndr CoreExprWithFVs
    rhs
      | Just Int
    join_arity <- CoreBndr -> Maybe Int
    isJoinId_maybe CoreBndr
    bndr
      , let ([CoreBndr]
    bndrs, CoreExprWithFVs
    body) = Int -> CoreExprWithFVs -> ([CoreBndr], CoreExprWithFVs)
    forall bndr annot.
    Int -> AnnExpr bndr annot -> ([bndr], AnnExpr bndr annot)
    collectNAnnBndrs Int
    join_arity CoreExprWithFVs
    rhs
      = [CoreBndr] -> Expr CoreBndr -> Expr CoreBndr
    forall b. [b] -> Expr b -> Expr b
    mkLams [CoreBndr]
    bndrs (Platform -> FloatInBinds -> CoreExprWithFVs -> Expr CoreBndr
    fiExpr Platform
    platform FloatInBinds
    to_drop CoreExprWithFVs
    body)
      | Bool
    otherwise
      = Platform -> FloatInBinds -> CoreExprWithFVs -> Expr CoreBndr
    fiExpr Platform
    platform FloatInBinds
    to_drop CoreExprWithFVs
    rhs

    ------------------
    noFloatIntoLam :: [Var] -> Bool
    noFloatIntoLam :: [CoreBndr] -> Bool
    noFloatIntoLam [CoreBndr]
    bndrs = (CoreBndr -> Bool) -> [CoreBndr] -> Bool
    forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
    any CoreBndr -> Bool
    bad [CoreBndr]
    bndrs
      where
        bad :: CoreBndr -> Bool
    bad CoreBndr
    b = CoreBndr -> Bool
    isId CoreBndr
    b Bool -> Bool -> Bool
    && Bool -> Bool
    not (CoreBndr -> Bool
    isOneShotBndr CoreBndr
    b)
        -- Don't float inside a non-one-shot lambda

    noFloatIntoRhs :: RecFlag -> Id -> CoreExprWithFVs' -> Bool
    -- ^ True if it's a bad idea to float bindings into this RHS
    noFloatIntoRhs :: RecFlag -> CoreBndr -> AnnExpr' CoreBndr FVAnn -> Bool
    noFloatIntoRhs RecFlag
    is_rec CoreBndr
    bndr AnnExpr' CoreBndr FVAnn
    rhs
      | CoreBndr -> Bool
    isJoinId CoreBndr
    bndr
      = RecFlag -> Bool
    isRec RecFlag
    is_rec -- Joins are one-shot iff non-recursive

      | Bool
    otherwise
      = AnnExpr' CoreBndr FVAnn -> Type -> Bool
    noFloatIntoArg AnnExpr' CoreBndr FVAnn
    rhs (CoreBndr -> Type
    idType CoreBndr
    bndr)

    noFloatIntoArg :: CoreExprWithFVs' -> Type -> Bool
    noFloatIntoArg :: AnnExpr' CoreBndr FVAnn -> Type -> Bool
    noFloatIntoArg AnnExpr' CoreBndr FVAnn
    expr Type
    expr_ty
      | Just Levity
    Unlifted <- (() :: Constraint) => Type -> Maybe Levity
    Type -> Maybe Levity
    typeLevity_maybe Type
    expr_ty
      = Bool
    True  -- See Note [Do not destroy the let/app invariant]

       | AnnLam CoreBndr
    bndr CoreExprWithFVs
    e <- AnnExpr' CoreBndr FVAnn
    expr
       , ([CoreBndr]
    bndrs, CoreExprWithFVs
    _) <- CoreExprWithFVs -> ([CoreBndr], CoreExprWithFVs)
    forall bndr annot.
    AnnExpr bndr annot -> ([bndr], AnnExpr bndr annot)
    collectAnnBndrs CoreExprWithFVs
    e
       =  [CoreBndr] -> Bool
    noFloatIntoLam (CoreBndr
    bndrCoreBndr -> [CoreBndr] -> [CoreBndr]
    forall a. a -> [a] -> [a]
    :[CoreBndr]
    bndrs)  -- Wrinkle 1 (a)
       Bool -> Bool -> Bool
    || (CoreBndr -> Bool) -> [CoreBndr] -> Bool
    forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
    all CoreBndr -> Bool
    isTyVar (CoreBndr
    bndrCoreBndr -> [CoreBndr] -> [CoreBndr]
    forall a. a -> [a] -> [a]
    :[CoreBndr]
    bndrs)     -- Wrinkle 1 (b)
          -- See Note [noFloatInto considerations] wrinkle 2

      | Bool
    otherwise  -- See Note [noFloatInto considerations] wrinkle 2
      = Expr CoreBndr -> Bool
    exprIsTrivial Expr CoreBndr
    deann_expr Bool -> Bool -> Bool
    || Expr CoreBndr -> Bool
    exprIsHNF Expr CoreBndr
    deann_expr
      where
        deann_expr :: Expr CoreBndr
    deann_expr = AnnExpr' CoreBndr FVAnn -> Expr CoreBndr
    forall bndr annot. AnnExpr' bndr annot -> Expr bndr
    deAnnotate' AnnExpr' CoreBndr FVAnn
    expr

    {- Note [noFloatInto considerations]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    When do we want to float bindings into
       - noFloatIntoRHs: the RHS of a let-binding
       - noFloatIntoArg: the argument of a function application

    Definitely don't float in if it has unlifted type; that
    would destroy the let/app invariant.

    * Wrinkle 1: do not float in if
         (a) any non-one-shot value lambdas
      or (b) all type lambdas
      In both cases we'll float straight back out again
      NB: Must line up with fiExpr (AnnLam...); see #7088

      (a) is important: we /must/ float into a one-shot lambda group
      (which includes join points). This makes a big difference
      for things like
         f x# = let x = I# x#
                in let j = \() -> ...x...
                   in if <condition> then normal-path else j ()
      If x is used only in the error case join point, j, we must float the
      boxing constructor into it, else we box it every time which is very
      bad news indeed.

    * Wrinkle 2: for RHSs, do not float into a HNF; we'll just float right
      back out again... not tragic, but a waste of time.

      For function arguments we will still end up with this
      in-then-out stuff; consider
        letrec x = e in f x
      Here x is not a HNF, so we'll produce
        f (letrec x = e in x)
      which is OK... it's not that common, and we'll end up
      floating out again, in CorePrep if not earlier.
      Still, we use exprIsTrivial to catch this case (sigh)

    ************************************************************************
    *                                                                      *
    \subsection{@sepBindsByDropPoint@}
    *                                                                      *
    ************************************************************************

    This is the crucial function.  The idea is: We have a wad of bindings
    that we'd like to distribute inside a collection of {\em drop points};
    insides the alternatives of a \tr{case} would be one example of some
    drop points; the RHS and body of a non-recursive \tr{let} binding
    would be another (2-element) collection.

    So: We're given a list of sets-of-free-variables, one per drop point,
    and a list of floating-inwards bindings.  If a binding can go into
    only one drop point (without suddenly making something out-of-scope),
    in it goes.  If a binding is used inside {\em multiple} drop points,
    then it has to go in a you-must-drop-it-above-all-these-drop-points
    point.

    We have to maintain the order on these drop-point-related lists.
    -}

    -- pprFIB :: FloatInBinds -> SDoc
    -- pprFIB fibs = text "FIB:" <+> ppr [b | FB _ _ b <- fibs]

    sepBindsByDropPoint
        :: Platform
        -> Bool                -- True <=> is case expression
        -> [FreeVarSet]        -- One set of FVs per drop point
                               -- Always at least two long!
        -> FloatInBinds        -- Candidate floaters
        -> [FloatInBinds]      -- FIRST one is bindings which must not be floated
                               -- inside any drop point; the rest correspond
                               -- one-to-one with the input list of FV sets

    -- Every input floater is returned somewhere in the result;
    -- none are dropped, not even ones which don't seem to be
    -- free in *any* of the drop-point fvs.  Why?  Because, for example,
    -- a binding (let x = E in B) might have a specialised version of
    -- x (say x') stored inside x, but x' isn't free in E or B.

    type DropBox = (FreeVarSet, FloatInBinds)

    sepBindsByDropPoint :: Platform -> Bool -> [FVAnn] -> FloatInBinds -> [FloatInBinds]
    sepBindsByDropPoint Platform
    platform Bool
    is_case [FVAnn]
    drop_pts FloatInBinds
    floaters
      | FloatInBinds -> Bool
    forall a. [a] -> Bool
    forall (t :: * -> *) a. Foldable t => t a -> Bool
    null FloatInBinds
    floaters  -- Shortcut common case
      = [] FloatInBinds -> [FloatInBinds] -> [FloatInBinds]
    forall a. a -> [a] -> [a]
    : [[] | FVAnn
    _ <- [FVAnn]
    drop_pts]

      | Bool
    otherwise
      = Bool -> [FloatInBinds] -> [FloatInBinds]
    forall a. HasCallStack => Bool -> a -> a
    assert ([FVAnn]
    drop_pts [FVAnn] -> Int -> Bool
    forall a. [a] -> Int -> Bool
    `lengthAtLeast` Int
    2) ([FloatInBinds] -> [FloatInBinds])
    -> [FloatInBinds] -> [FloatInBinds]
    forall a b. (a -> b) -> a -> b
    $
        FloatInBinds -> [DropBox] -> [FloatInBinds]
    go FloatInBinds
    floaters ((FVAnn -> DropBox) -> [FVAnn] -> [DropBox]
    forall a b. (a -> b) -> [a] -> [b]
    map (\FVAnn
    fvs -> (FVAnn
    fvs, [])) (FVAnn
    emptyDVarSet FVAnn -> [FVAnn] -> [FVAnn]
    forall a. a -> [a] -> [a]
    : [FVAnn]
    drop_pts))
      where
        n_alts :: Int
    n_alts = [FVAnn] -> Int
    forall a. [a] -> Int
    forall (t :: * -> *) a. Foldable t => t a -> Int
    length [FVAnn]
    drop_pts

        go :: FloatInBinds -> [DropBox] -> [FloatInBinds]
            -- The *first* one in the argument list is the drop_here set
            -- The FloatInBinds in the lists are in the reverse of
            -- the normal FloatInBinds order; that is, they are the right way round!

        go :: FloatInBinds -> [DropBox] -> [FloatInBinds]
    go [] [DropBox]
    drop_boxes = (DropBox -> FloatInBinds) -> [DropBox] -> [FloatInBinds]
    forall a b. (a -> b) -> [a] -> [b]
    map (FloatInBinds -> FloatInBinds
    forall a. [a] -> [a]
    reverse (FloatInBinds -> FloatInBinds)
    -> (DropBox -> FloatInBinds) -> DropBox -> FloatInBinds
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . DropBox -> FloatInBinds
    forall a b. (a, b) -> b
    snd) [DropBox]
    drop_boxes

        go (bind_w_fvs :: FloatInBind
    bind_w_fvs@(FB FVAnn
    bndrs FVAnn
    bind_fvs FloatBind
    bind) : FloatInBinds
    binds) drop_boxes :: [DropBox]
    drop_boxes@(DropBox
    here_box : [DropBox]
    fork_boxes)
            = FloatInBinds -> [DropBox] -> [FloatInBinds]
    go FloatInBinds
    binds [DropBox]
    new_boxes
            where
              -- "here" means the group of bindings dropped at the top of the fork

              (Bool
    used_here : [Bool]
    used_in_flags) = [ FVAnn
    fvs FVAnn -> FVAnn -> Bool
    `intersectsDVarSet` FVAnn
    bndrs
                                            | (FVAnn
    fvs, FloatInBinds
    _) <- [DropBox]
    drop_boxes]

              drop_here :: Bool
    drop_here = Bool
    used_here Bool -> Bool -> Bool
    || Bool
    cant_push

              n_used_alts :: Int
    n_used_alts = (Bool -> Bool) -> [Bool] -> Int
    forall a. (a -> Bool) -> [a] -> Int
    count Bool -> Bool
    forall a. a -> a
    id [Bool]
    used_in_flags -- returns number of Trues in list.

              cant_push :: Bool
    cant_push
                | Bool
    is_case   = Int
    n_used_alts Int -> Int -> Bool
    forall a. Eq a => a -> a -> Bool
    == Int
    n_alts   -- Used in all, don't push
                                                      -- Remember n_alts > 1
                              Bool -> Bool -> Bool
    || (Int
    n_used_alts Int -> Int -> Bool
    forall a. Ord a => a -> a -> Bool
    > Int
    1 Bool -> Bool -> Bool
    && Bool -> Bool
    not (Platform -> FloatBind -> Bool
    floatIsDupable Platform
    platform FloatBind
    bind))
                                 -- floatIsDupable: see Note [Duplicating floats]

                | Bool
    otherwise = FloatBind -> Bool
    floatIsCase FloatBind
    bind Bool -> Bool -> Bool
    || Int
    n_used_alts Int -> Int -> Bool
    forall a. Ord a => a -> a -> Bool
    > Int
    1
                                 -- floatIsCase: see Note [Floating primops]

              new_boxes :: [DropBox]
    new_boxes | Bool
    drop_here = (DropBox -> DropBox
    insert DropBox
    here_box DropBox -> [DropBox] -> [DropBox]
    forall a. a -> [a] -> [a]
    : [DropBox]
    fork_boxes)
                        | Bool
    otherwise = (DropBox
    here_box DropBox -> [DropBox] -> [DropBox]
    forall a. a -> [a] -> [a]
    : [DropBox]
    new_fork_boxes)

              new_fork_boxes :: [DropBox]
    new_fork_boxes = String
    -> (DropBox -> Bool -> DropBox) -> [DropBox] -> [Bool] -> [DropBox]
    forall a b c. String -> (a -> b -> c) -> [a] -> [b] -> [c]
    zipWithEqual String
    "FloatIn.sepBinds" DropBox -> Bool -> DropBox
    insert_maybe
                                            [DropBox]
    fork_boxes [Bool]
    used_in_flags

              insert :: DropBox -> DropBox
              insert :: DropBox -> DropBox
    insert (FVAnn
    fvs,FloatInBinds
    drops) = (FVAnn
    fvs FVAnn -> FVAnn -> FVAnn
    `unionDVarSet` FVAnn
    bind_fvs, FloatInBind
    bind_w_fvsFloatInBind -> FloatInBinds -> FloatInBinds
    forall a. a -> [a] -> [a]
    :FloatInBinds
    drops)

              insert_maybe :: DropBox -> Bool -> DropBox
    insert_maybe DropBox
    box Bool
    True  = DropBox -> DropBox
    insert DropBox
    box
              insert_maybe DropBox
    box Bool
    False = DropBox
    box

        go FloatInBinds
    _ [DropBox]
    _ = String -> [FloatInBinds]
    forall a. String -> a
    panic String
    "sepBindsByDropPoint/go"

    {- Note [Duplicating floats]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    For case expressions we duplicate the binding if it is reasonably
    small, and if it is not used in all the RHSs This is good for
    situations like
         let x = I# y in
         case e of
           C -> error x
           D -> error x
           E -> ...not mentioning x...

    If the thing is used in all RHSs there is nothing gained,
    so we don't duplicate then.
    -}

    floatedBindsFVs :: FloatInBinds -> FreeVarSet
    floatedBindsFVs :: FloatInBinds -> FVAnn
    floatedBindsFVs FloatInBinds
    binds = (FloatInBind -> FVAnn) -> FloatInBinds -> FVAnn
    forall a. (a -> FVAnn) -> [a] -> FVAnn
    mapUnionDVarSet FloatInBind -> FVAnn
    fbFVs FloatInBinds
    binds

    fbFVs :: FloatInBind -> DVarSet
    fbFVs :: FloatInBind -> FVAnn
    fbFVs (FB FVAnn
    _ FVAnn
    fvs FloatBind
    _) = FVAnn
    fvs

    wrapFloats :: FloatInBinds -> CoreExpr -> CoreExpr
    -- Remember FloatInBinds is in *reverse* dependency order
    wrapFloats :: FloatInBinds -> Expr CoreBndr -> Expr CoreBndr
    wrapFloats []               Expr CoreBndr
    e = Expr CoreBndr
    e
    wrapFloats (FB FVAnn
    _ FVAnn
    _ FloatBind
    fl : FloatInBinds
    bs) Expr CoreBndr
    e = FloatInBinds -> Expr CoreBndr -> Expr CoreBndr
    wrapFloats FloatInBinds
    bs (FloatBind -> Expr CoreBndr -> Expr CoreBndr
    wrapFloat FloatBind
    fl Expr CoreBndr
    e)

    floatIsDupable :: Platform -> FloatBind -> Bool
    floatIsDupable :: Platform -> FloatBind -> Bool
    floatIsDupable Platform
    platform (FloatCase Expr CoreBndr
    scrut CoreBndr
    _ AltCon
    _ [CoreBndr]
    _) = Platform -> Expr CoreBndr -> Bool
    exprIsDupable Platform
    platform Expr CoreBndr
    scrut
    floatIsDupable Platform
    platform (FloatLet (Rec [(CoreBndr, Expr CoreBndr)]
    prs))    = ((CoreBndr, Expr CoreBndr) -> Bool)
    -> [(CoreBndr, Expr CoreBndr)] -> Bool
    forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
    all (Platform -> Expr CoreBndr -> Bool
    exprIsDupable Platform
    platform (Expr CoreBndr -> Bool)
    -> ((CoreBndr, Expr CoreBndr) -> Expr CoreBndr)
    -> (CoreBndr, Expr CoreBndr)
    -> Bool
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . (CoreBndr, Expr CoreBndr) -> Expr CoreBndr
    forall a b. (a, b) -> b
    snd) [(CoreBndr, Expr CoreBndr)]
    prs
    floatIsDupable Platform
    platform (FloatLet (NonRec CoreBndr
    _ Expr CoreBndr
    r)) = Platform -> Expr CoreBndr -> Bool
    exprIsDupable Platform
    platform Expr CoreBndr
    r

    floatIsCase :: FloatBind -> Bool
    floatIsCase :: FloatBind -> Bool
    floatIsCase (FloatCase {}) = Bool
    True
    floatIsCase (FloatLet {})  = Bool
    False