    {-# LANGUAGE BangPatterns #-}
    {-# LANGUAGE CPP          #-}
    {-# LANGUAGE ViewPatterns #-}

    {-# OPTIONS_GHC -Wno-incomplete-record-updates #-}

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

    ************************************************************************
    *                                                                      *
    \section[OccurAnal]{Occurrence analysis pass}
    *                                                                      *
    ************************************************************************

    The occurrence analyser re-typechecks a core expression, returning a new
    core expression with (hopefully) improved usage information.
    -}

    module GHC.Core.Opt.OccurAnal ( occurAnalysePgm, occurAnalyseExpr ) where

    #include "HsVersions.h"

    import GHC.Prelude

    import GHC.Driver.Ppr

    import GHC.Core
    import GHC.Core.FVs
    import GHC.Core.Utils   ( exprIsTrivial, isDefaultAlt, isExpandableApp,
                              stripTicksTopE, mkTicks )
    import GHC.Core.Opt.Arity   ( joinRhsArity )
    import GHC.Types.Id
    import GHC.Types.Id.Info
    import GHC.Types.Basic
    import GHC.Types.Tickish
    import GHC.Unit.Module( Module )
    import GHC.Core.Coercion
    import GHC.Core.Type
    import GHC.Core.TyCo.FVs( tyCoVarsOfMCo )

    import GHC.Types.Var.Set
    import GHC.Types.Var.Env
    import GHC.Types.Var
    import GHC.Types.Demand ( argOneShots, argsOneShots )
    import GHC.Data.Graph.Directed ( SCC(..), Node(..)
                                   , stronglyConnCompFromEdgedVerticesUniq
                                   , stronglyConnCompFromEdgedVerticesUniqR )
    import GHC.Builtin.Names( runRWKey )
    import GHC.Types.Unique
    import GHC.Types.Unique.FM
    import GHC.Types.Unique.Set
    import GHC.Utils.Misc
    import GHC.Data.Maybe( isJust )
    import GHC.Utils.Outputable
    import GHC.Utils.Panic
    import Data.List (mapAccumL, mapAccumR)

    {-
    ************************************************************************
    *                                                                      *
        occurAnalysePgm, occurAnalyseExpr
    *                                                                      *
    ************************************************************************

    Here's the externally-callable interface:
    -}

    occurAnalyseExpr :: CoreExpr -> CoreExpr
    -- Do occurrence analysis, and discard occurrence info returned
    occurAnalyseExpr :: CoreExpr -> CoreExpr
    occurAnalyseExpr CoreExpr
    expr
      = (UsageDetails, CoreExpr) -> CoreExpr
    forall a b. (a, b) -> b
    snd (OccEnv -> CoreExpr -> (UsageDetails, CoreExpr)
    occAnal OccEnv
    initOccEnv CoreExpr
    expr)

    occurAnalysePgm :: Module         -- Used only in debug output
                    -> (Id -> Bool)         -- Active unfoldings
                    -> (Activation -> Bool) -- Active rules
                    -> [CoreRule]           -- Local rules for imported Ids
                    -> CoreProgram -> CoreProgram
    occurAnalysePgm :: Module
    -> (CoreBndr -> Bool)
    -> (Activation -> Bool)
    -> [CoreRule]
    -> CoreProgram
    -> CoreProgram
    occurAnalysePgm Module
    this_mod CoreBndr -> Bool
    active_unf Activation -> Bool
    active_rule [CoreRule]
    imp_rules CoreProgram
    binds
      | UsageDetails -> Bool
    isEmptyDetails UsageDetails
    final_usage
      = CoreProgram
    occ_anald_binds

      | Bool
    otherwise   -- See Note [Glomming]
      = WARN( True, hang (text "Glomming in" <+> ppr this_mod <> colon)
                       2 (ppr final_usage ) )
        CoreProgram
    occ_anald_glommed_binds
      where
        init_env :: OccEnv
    init_env = OccEnv
    initOccEnv { occ_rule_act :: Activation -> Bool
    occ_rule_act = Activation -> Bool
    active_rule
                              , occ_unf_act :: CoreBndr -> Bool
    occ_unf_act  = CoreBndr -> Bool
    active_unf }

        (UsageDetails
    final_usage, CoreProgram
    occ_anald_binds) = OccEnv -> CoreProgram -> (UsageDetails, CoreProgram)
    go OccEnv
    init_env CoreProgram
    binds
        (UsageDetails
    _, CoreProgram
    occ_anald_glommed_binds)   = OccEnv
    -> TopLevelFlag
    -> ImpRuleEdges
    -> [(CoreBndr, CoreExpr)]
    -> UsageDetails
    -> (UsageDetails, CoreProgram)
    occAnalRecBind OccEnv
    init_env TopLevelFlag
    TopLevel
                                                        ImpRuleEdges
    imp_rule_edges
                                                        (CoreProgram -> [(CoreBndr, CoreExpr)]
    forall b. [Bind b] -> [(b, Expr b)]
    flattenBinds CoreProgram
    binds)
                                                        UsageDetails
    initial_uds
              -- It's crucial to re-analyse the glommed-together bindings
              -- so that we establish the right loop breakers. Otherwise
              -- we can easily create an infinite loop (#9583 is an example)
              --
              -- Also crucial to re-analyse the /original/ bindings
              -- in case the first pass accidentally discarded as dead code
              -- a binding that was actually needed (albeit before its
              -- definition site).  #17724 threw this up.

        initial_uds :: UsageDetails
    initial_uds = UsageDetails -> VarSet -> UsageDetails
    addManyOccs UsageDetails
    emptyDetails ([CoreRule] -> VarSet
    rulesFreeVars [CoreRule]
    imp_rules)
        -- The RULES declarations keep things alive!

        -- imp_rule_edges maps a top-level local binder 'f' to the
        -- RHS free vars of any IMP-RULE, a local RULE for an imported function,
        -- where 'f' appears on the LHS
        --   e.g.  RULE foldr f = blah
        --         imp_rule_edges contains f :-> fvs(blah)
        -- We treat such RULES as extra rules for 'f'
        -- See Note [Preventing loops due to imported functions rules]
        imp_rule_edges :: ImpRuleEdges
        imp_rule_edges :: ImpRuleEdges
    imp_rule_edges = (ImpRuleEdges -> ImpRuleEdges -> ImpRuleEdges)
    -> ImpRuleEdges -> [ImpRuleEdges] -> ImpRuleEdges
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr (([(Activation, VarSet)]
     -> [(Activation, VarSet)] -> [(Activation, VarSet)])
    -> ImpRuleEdges -> ImpRuleEdges -> ImpRuleEdges
    forall a. (a -> a -> a) -> VarEnv a -> VarEnv a -> VarEnv a
    plusVarEnv_C [(Activation, VarSet)]
    -> [(Activation, VarSet)] -> [(Activation, VarSet)]
    forall a. [a] -> [a] -> [a]
    (++)) ImpRuleEdges
    forall a. VarEnv a
    emptyVarEnv
                               [ (CoreBndr -> [(Activation, VarSet)])
    -> VarEnv CoreBndr -> ImpRuleEdges
    forall a b. (a -> b) -> VarEnv a -> VarEnv b
    mapVarEnv ([(Activation, VarSet)] -> CoreBndr -> [(Activation, VarSet)]
    forall a b. a -> b -> a
    const [(Activation
    act,VarSet
    rhs_fvs)]) (VarEnv CoreBndr -> ImpRuleEdges)
    -> VarEnv CoreBndr -> ImpRuleEdges
    forall a b. (a -> b) -> a -> b
    $ VarSet -> VarEnv CoreBndr
    forall a. UniqSet a -> UniqFM a a
    getUniqSet (VarSet -> VarEnv CoreBndr) -> VarSet -> VarEnv CoreBndr
    forall a b. (a -> b) -> a -> b
    $
                                 [CoreExpr] -> VarSet
    exprsFreeIds [CoreExpr]
    args VarSet -> [CoreBndr] -> VarSet
    `delVarSetList` [CoreBndr]
    bndrs
                               | Rule { ru_act :: CoreRule -> Activation
    ru_act = Activation
    act, ru_bndrs :: CoreRule -> [CoreBndr]
    ru_bndrs = [CoreBndr]
    bndrs
                                       , ru_args :: CoreRule -> [CoreExpr]
    ru_args = [CoreExpr]
    args, ru_rhs :: CoreRule -> CoreExpr
    ru_rhs = CoreExpr
    rhs } <- [CoreRule]
    imp_rules
                                       -- Not BuiltinRules; see Note [Plugin rules]
                               , let rhs_fvs :: VarSet
    rhs_fvs = CoreExpr -> VarSet
    exprFreeIds CoreExpr
    rhs VarSet -> [CoreBndr] -> VarSet
    `delVarSetList` [CoreBndr]
    bndrs ]

        go :: OccEnv -> [CoreBind] -> (UsageDetails, [CoreBind])
        go :: OccEnv -> CoreProgram -> (UsageDetails, CoreProgram)
    go OccEnv
    _ []
            = (UsageDetails
    initial_uds, [])
        go OccEnv
    env (CoreBind
    bind:CoreProgram
    binds)
            = (UsageDetails
    final_usage, CoreProgram
    bind' CoreProgram -> CoreProgram -> CoreProgram
    forall a. [a] -> [a] -> [a]
    ++ CoreProgram
    binds')
            where
               (UsageDetails
    bs_usage, CoreProgram
    binds')   = OccEnv -> CoreProgram -> (UsageDetails, CoreProgram)
    go OccEnv
    env CoreProgram
    binds
               (UsageDetails
    final_usage, CoreProgram
    bind') = OccEnv
    -> TopLevelFlag
    -> ImpRuleEdges
    -> CoreBind
    -> UsageDetails
    -> (UsageDetails, CoreProgram)
    occAnalBind OccEnv
    env TopLevelFlag
    TopLevel ImpRuleEdges
    imp_rule_edges CoreBind
    bind
                                                  UsageDetails
    bs_usage

    {- *********************************************************************
    *                                                                      *
                    IMP-RULES
             Local rules for imported functions
    *                                                                      *
    ********************************************************************* -}

    type ImpRuleEdges = IdEnv [(Activation, VarSet)]
        -- Mapping from a local Id 'f' to info about its IMP-RULES,
        -- i.e. /local/ rules for an imported Id that mention 'f' on the LHS
        -- We record (a) its Activation and (b) the RHS free vars
        -- See Note [IMP-RULES: local rules for imported functions]

    noImpRuleEdges :: ImpRuleEdges
    noImpRuleEdges :: ImpRuleEdges
    noImpRuleEdges = ImpRuleEdges
    forall a. VarEnv a
    emptyVarEnv

    lookupImpRules :: ImpRuleEdges -> Id -> [(Activation,VarSet)]
    lookupImpRules :: ImpRuleEdges -> CoreBndr -> [(Activation, VarSet)]
    lookupImpRules ImpRuleEdges
    imp_rule_edges CoreBndr
    bndr
      = case ImpRuleEdges -> CoreBndr -> Maybe [(Activation, VarSet)]
    forall a. VarEnv a -> CoreBndr -> Maybe a
    lookupVarEnv ImpRuleEdges
    imp_rule_edges CoreBndr
    bndr of
          Maybe [(Activation, VarSet)]
    Nothing -> []
          Just [(Activation, VarSet)]
    vs -> [(Activation, VarSet)]
    vs

    impRulesScopeUsage :: [(Activation,VarSet)] -> UsageDetails
    -- Variable mentioned in RHS of an IMP-RULE for the bndr,
    -- whether active or not
    impRulesScopeUsage :: [(Activation, VarSet)] -> UsageDetails
    impRulesScopeUsage [(Activation, VarSet)]
    imp_rules_info
      = ((Activation, VarSet) -> UsageDetails -> UsageDetails)
    -> UsageDetails -> [(Activation, VarSet)] -> UsageDetails
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr (Activation, VarSet) -> UsageDetails -> UsageDetails
    forall {a}. (a, VarSet) -> UsageDetails -> UsageDetails
    add UsageDetails
    emptyDetails [(Activation, VarSet)]
    imp_rules_info
      where
        add :: (a, VarSet) -> UsageDetails -> UsageDetails
    add (a
    _,VarSet
    vs) UsageDetails
    usage = UsageDetails -> VarSet -> UsageDetails
    addManyOccs UsageDetails
    usage VarSet
    vs

    impRulesActiveFvs :: (Activation -> Bool) -> VarSet
                      -> [(Activation,VarSet)] -> VarSet
    impRulesActiveFvs :: (Activation -> Bool) -> VarSet -> [(Activation, VarSet)] -> VarSet
    impRulesActiveFvs Activation -> Bool
    is_active VarSet
    bndr_set [(Activation, VarSet)]
    vs
      = ((Activation, VarSet) -> VarSet -> VarSet)
    -> VarSet -> [(Activation, VarSet)] -> VarSet
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr (Activation, VarSet) -> VarSet -> VarSet
    add VarSet
    emptyVarSet [(Activation, VarSet)]
    vs VarSet -> VarSet -> VarSet
    `intersectVarSet` VarSet
    bndr_set
      where
        add :: (Activation, VarSet) -> VarSet -> VarSet
    add (Activation
    act,VarSet
    vs) VarSet
    acc | Activation -> Bool
    is_active Activation
    act = VarSet
    vs VarSet -> VarSet -> VarSet
    `unionVarSet` VarSet
    acc
                         | Bool
    otherwise     = VarSet
    acc

    {- Note [IMP-RULES: local rules for imported functions]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    We quite often have
      * A /local/ rule
      * for an /imported/ function
    like this:
      foo x = blah
      {-# RULE "map/foo" forall xs. map foo xs = xs #-}
    We call them IMP-RULES.  They are important in practice, and occur a
    lot in the libraries.

    IMP-RULES are held in mg_rules of ModGuts, and passed in to
    occurAnalysePgm.

    Main Invariant:

    * Throughout, we treat an IMP-RULE that mentions 'f' on its LHS
      just like a RULE for f.

    Note [IMP-RULES: unavoidable loops]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider this
       f = /\a. B.g a
       RULE B.g Int = 1 + f Int
    Note that
      * The RULE is for an imported function.
      * f is non-recursive
    Now we
    can get
       f Int --> B.g Int      Inlining f
             --> 1 + f Int    Firing RULE
    and so the simplifier goes into an infinite loop. This
    would not happen if the RULE was for a local function,
    because we keep track of dependencies through rules.  But
    that is pretty much impossible to do for imported Ids.  Suppose
    f's definition had been
       f = /\a. C.h a
    where (by some long and devious process), C.h eventually inlines to
    B.g.  We could only spot such loops by exhaustively following
    unfoldings of C.h etc, in case we reach B.g, and hence (via the RULE)
    f.

    We regard this potential infinite loop as a *programmer* error.
    It's up the programmer not to write silly rules like
         RULE f x = f x
    and the example above is just a more complicated version.

    Note [Specialising imported functions] (referred to from Specialise)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    For *automatically-generated* rules, the programmer can't be
    responsible for the "programmer error" in Note [IMP-RULES: unavoidable
    loops].  In particular, consider specialising a recursive function
    defined in another module.  If we specialise a recursive function B.g,
    we get
      g_spec = .....(B.g Int).....
      RULE B.g Int = g_spec
    Here, g_spec doesn't look recursive, but when the rule fires, it
    becomes so.  And if B.g was mutually recursive, the loop might not be
    as obvious as it is here.

    To avoid this,
     * When specialising a function that is a loop breaker,
       give a NOINLINE pragma to the specialised function

    Note [Preventing loops due to imported functions rules]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider:
      import GHC.Base (foldr)

      {-# RULES "filterList" forall p. foldr (filterFB (:) p) [] = filter p #-}
      filter p xs = build (\c n -> foldr (filterFB c p) n xs)
      filterFB c p = ...

      f = filter p xs

    Note that filter is not a loop-breaker, so what happens is:
      f =          filter p xs
        = {inline} build (\c n -> foldr (filterFB c p) n xs)
        = {inline} foldr (filterFB (:) p) [] xs
        = {RULE}   filter p xs

    We are in an infinite loop.

    A more elaborate example (that I actually saw in practice when I went to
    mark GHC.List.filter as INLINABLE) is as follows. Say I have this module:
      {-# LANGUAGE RankNTypes #-}
      module GHCList where

      import Prelude hiding (filter)
      import GHC.Base (build)

      {-# INLINABLE filter #-}
      filter :: (a -> Bool) -> [a] -> [a]
      filter p [] = []
      filter p (x:xs) = if p x then x : filter p xs else filter p xs

      {-# NOINLINE [0] filterFB #-}
      filterFB :: (a -> b -> b) -> (a -> Bool) -> a -> b -> b
      filterFB c p x r | p x       = x `c` r
                       | otherwise = r

      {-# RULES
      "filter"     [~1] forall p xs.  filter p xs = build (\c n -> foldr
      (filterFB c p) n xs)
      "filterList" [1]  forall p.     foldr (filterFB (:) p) [] = filter p
       #-}

    Then (because RULES are applied inside INLINABLE unfoldings, but inlinings
    are not), the unfolding given to "filter" in the interface file will be:
      filter p []     = []
      filter p (x:xs) = if p x then x : build (\c n -> foldr (filterFB c p) n xs)
                               else     build (\c n -> foldr (filterFB c p) n xs

    Note that because this unfolding does not mention "filter", filter is not
    marked as a strong loop breaker. Therefore at a use site in another module:
      filter p xs
        = {inline}
          case xs of []     -> []
                     (x:xs) -> if p x then x : build (\c n -> foldr (filterFB c p) n xs)
                                      else     build (\c n -> foldr (filterFB c p) n xs)

      build (\c n -> foldr (filterFB c p) n xs)
        = {inline} foldr (filterFB (:) p) [] xs
        = {RULE}   filter p xs

    And we are in an infinite loop again, except that this time the loop is producing an
    infinitely large *term* (an unrolling of filter) and so the simplifier finally
    dies with "ticks exhausted"

    SOLUTION: we treat the rule "filterList" as an extra rule for 'filterFB'
    because it mentions 'filterFB' on the LHS.  This is the Main Invariant
    in Note [IMP-RULES: local rules for imported functions].

    So, during loop-breaker analysis:

    - for each active RULE for a local function 'f' we add an edge between
      'f' and the local FVs of the rule RHS

    - for each active RULE for an *imported* function we add dependency
      edges between the *local* FVS of the rule LHS and the *local* FVS of
      the rule RHS.

    Even with this extra hack we aren't always going to get things
    right. For example, it might be that the rule LHS mentions an imported
    Id, and another module has a RULE that can rewrite that imported Id to
    one of our local Ids.

    Note [Plugin rules]
    ~~~~~~~~~~~~~~~~~~~
    Conal Elliott (#11651) built a GHC plugin that added some
    BuiltinRules (for imported Ids) to the mg_rules field of ModGuts, to
    do some domain-specific transformations that could not be expressed
    with an ordinary pattern-matching CoreRule.  But then we can't extract
    the dependencies (in imp_rule_edges) from ru_rhs etc, because a
    BuiltinRule doesn't have any of that stuff.

    So we simply assume that BuiltinRules have no dependencies, and filter
    them out from the imp_rule_edges comprehension.

    Note [Glomming]
    ~~~~~~~~~~~~~~~
    RULES for imported Ids can make something at the top refer to
    something at the bottom:

            foo = ...(B.f @Int)...
            $sf = blah
            RULE:  B.f @Int = $sf

    Applying this rule makes foo refer to $sf, although foo doesn't appear to
    depend on $sf.  (And, as in Note [Rules for imported functions], the
    dependency might be more indirect. For example, foo might mention C.t
    rather than B.f, where C.t eventually inlines to B.f.)

    NOTICE that this cannot happen for rules whose head is a
    locally-defined function, because we accurately track dependencies
    through RULES.  It only happens for rules whose head is an imported
    function (B.f in the example above).

    Solution:
      - When simplifying, bring all top level identifiers into
        scope at the start, ignoring the Rec/NonRec structure, so
        that when 'h' pops up in f's rhs, we find it in the in-scope set
        (as the simplifier generally expects). This happens in simplTopBinds.

      - In the occurrence analyser, if there are any out-of-scope
        occurrences that pop out of the top, which will happen after
        firing the rule:      f = \x -> h x
                              h = \y -> 3
        then just glom all the bindings into a single Rec, so that
        the *next* iteration of the occurrence analyser will sort
        them all out.   This part happens in occurAnalysePgm.
    -}

    {-
    ************************************************************************
    *                                                                      *
                    Bindings
    *                                                                      *
    ************************************************************************

    Note [Recursive bindings: the grand plan]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Loop breaking is surprisingly subtle.  First read the section 4 of
    "Secrets of the GHC inliner".  This describes our basic plan.  We
    avoid infinite inlinings by choosing loop breakers, and ensuring that
    a loop breaker cuts each loop.

    See also Note [Inlining and hs-boot files] in GHC.Core.ToIface, which
    deals with a closely related source of infinite loops.

    When we come across a binding group
      Rec { x1 = r1; ...; xn = rn }
    we treat it like this (occAnalRecBind):

    1. Note [Forming Rec groups]
       Occurrence-analyse each right hand side, and build a
       "Details" for each binding to capture the results.
       Wrap the details in a LetrecNode, ready for SCC analysis.
       All this is done by makeNode.

       The edges of this graph are the "scope edges".

    2. Do SCC-analysis on these Nodes:
       - Each CyclicSCC will become a new Rec
       - Each AcyclicSCC will become a new NonRec

       The key property is that every free variable of a binding is
       accounted for by the scope edges, so that when we are done
       everything is still in scope.

    3. For each AcyclicSCC, just make a NonRec binding.

    4. For each CyclicSCC of the scope-edge SCC-analysis in (2), we
       identify suitable loop-breakers to ensure that inlining terminates.
       This is done by occAnalRec.

       To do so, form the loop-breaker graph, do SCC analysis. For each
       CyclicSCC we choose a loop breaker, delete all edges to that node,
       re-analyse the SCC, and iterate. See Note [Choosing loop breakers]
       for the details

    Note [Dead code]
    ~~~~~~~~~~~~~~~~
    Dropping dead code for a cyclic Strongly Connected Component is done
    in a very simple way:

            the entire SCC is dropped if none of its binders are mentioned
            in the body; otherwise the whole thing is kept.

    The key observation is that dead code elimination happens after
    dependency analysis: so 'occAnalBind' processes SCCs instead of the
    original term's binding groups.

    Thus 'occAnalBind' does indeed drop 'f' in an example like

            letrec f = ...g...
                   g = ...(...g...)...
            in
               ...g...

    when 'g' no longer uses 'f' at all (eg 'f' does not occur in a RULE in
    'g'). 'occAnalBind' first consumes 'CyclicSCC g' and then it consumes
    'AcyclicSCC f', where 'body_usage' won't contain 'f'.

    Note [Forming Rec groups]
    ~~~~~~~~~~~~~~~~~~~~~~~~~
    The key point about the "Forming Rec groups" step is that it /preserves
    scoping/.  If 'x' is mentioned, it had better be bound somewhere.  So if
    we start with
      Rec { f = ...h...
          ; g = ...f...
          ; h = ...f... }
    we can split into SCCs
      Rec { f = ...h...
          ; h = ..f... }
      NonRec { g = ...f... }

    We put bindings {f = ef; g = eg } in a Rec group if "f uses g" and "g
    uses f", no matter how indirectly.  We do a SCC analysis with an edge
    f -> g if "f mentions g". That is, g is free in:
      a) the rhs 'ef'
      b) or the RHS of a rule for f, whether active or inactive
           Note [Rules are extra RHSs]
      c) or the LHS or a rule for f, whether active or inactive
           Note [Rule dependency info]
      d) the RHS of an /active/ local IMP-RULE
           Note [IMP-RULES: local rules for imported functions]

    (b) and (c) apply regardless of the activation of the RULE, because even if
    the rule is inactive its free variables must be bound.  But (d) doesn't need
    to worry about this because IMP-RULES are always notionally at the bottom
    of the file.

      * Note [Rules are extra RHSs]
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~
        A RULE for 'f' is like an extra RHS for 'f'. That way the "parent"
        keeps the specialised "children" alive.  If the parent dies
        (because it isn't referenced any more), then the children will die
        too (unless they are already referenced directly).

        So in Example [eftInt], eftInt and eftIntFB will be put in the
        same Rec, even though their 'main' RHSs are both non-recursive.

        We must also include inactive rules, so that their free vars
        remain in scope.

      * Note [Rule dependency info]
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~
        The VarSet in a RuleInfo is used for dependency analysis in the
        occurrence analyser.  We must track free vars in *both* lhs and rhs.
        Hence use of idRuleVars, rather than idRuleRhsVars in occAnalBind.
        Why both? Consider
            x = y
            RULE f x = v+4
        Then if we substitute y for x, we'd better do so in the
        rule's LHS too, so we'd better ensure the RULE appears to mention 'x'
        as well as 'v'

      * Note [Rules are visible in their own rec group]
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
        We want the rules for 'f' to be visible in f's right-hand side.
        And we'd like them to be visible in other functions in f's Rec
        group.  E.g. in Note [Specialisation rules] we want f' rule
        to be visible in both f's RHS, and fs's RHS.

        This means that we must simplify the RULEs first, before looking
        at any of the definitions.  This is done by Simplify.simplRecBind,
        when it calls addLetIdInfo.

    Note [Stable unfoldings]
    ~~~~~~~~~~~~~~~~~~~~~~~~
    None of the above stuff about RULES applies to a stable unfolding
    stored in a CoreUnfolding.  The unfolding, if any, is simplified
    at the same time as the regular RHS of the function (ie *not* like
    Note [Rules are visible in their own rec group]), so it should be
    treated *exactly* like an extra RHS.

    Or, rather, when computing loop-breaker edges,
      * If f has an INLINE pragma, and it is active, we treat the
        INLINE rhs as f's rhs
      * If it's inactive, we treat f as having no rhs
      * If it has no INLINE pragma, we look at f's actual rhs

    There is a danger that we'll be sub-optimal if we see this
         f = ...f...
         [INLINE f = ..no f...]
    where f is recursive, but the INLINE is not. This can just about
    happen with a sufficiently odd set of rules; eg

            foo :: Int -> Int
            {-# INLINE [1] foo #-}
            foo x = x+1

            bar :: Int -> Int
            {-# INLINE [1] bar #-}
            bar x = foo x + 1

            {-# RULES "foo" [~1] forall x. foo x = bar x #-}

    Here the RULE makes bar recursive; but it's INLINE pragma remains
    non-recursive. It's tempting to then say that 'bar' should not be
    a loop breaker, but an attempt to do so goes wrong in two ways:
       a) We may get
             $df = ...$cfoo...
             $cfoo = ...$df....
             [INLINE $cfoo = ...no-$df...]
          But we want $cfoo to depend on $df explicitly so that we
          put the bindings in the right order to inline $df in $cfoo
          and perhaps break the loop altogether.  (Maybe this
       b)

    Example [eftInt]
    ~~~~~~~~~~~~~~~
    Example (from GHC.Enum):

      eftInt :: Int# -> Int# -> [Int]
      eftInt x y = ...(non-recursive)...

      {-# INLINE [0] eftIntFB #-}
      eftIntFB :: (Int -> r -> r) -> r -> Int# -> Int# -> r
      eftIntFB c n x y = ...(non-recursive)...

      {-# RULES
      "eftInt"  [~1] forall x y. eftInt x y = build (\ c n -> eftIntFB c n x y)
      "eftIntList"  [1] eftIntFB  (:) [] = eftInt
       #-}

    Note [Specialisation rules]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider this group, which is typical of what SpecConstr builds:

       fs a = ....f (C a)....
       f  x = ....f (C a)....
       {-# RULE f (C a) = fs a #-}

    So 'f' and 'fs' are in the same Rec group (since f refers to fs via its RULE).

    But watch out!  If 'fs' is not chosen as a loop breaker, we may get an infinite loop:
      - the RULE is applied in f's RHS (see Note [Self-recursive rules] in GHC.Core.Opt.Simplify
      - fs is inlined (say it's small)
      - now there's another opportunity to apply the RULE

    This showed up when compiling Control.Concurrent.Chan.getChanContents.
    Hence the transitive rule_fv_env stuff described in
    Note [Rules and  loop breakers].

    ------------------------------------------------------------
    Note [Finding join points]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~
    It's the occurrence analyser's job to find bindings that we can turn into join
    points, but it doesn't perform that transformation right away. Rather, it marks
    the eligible bindings as part of their occurrence data, leaving it to the
    simplifier (or to simpleOptPgm) to actually change the binder's 'IdDetails'.
    The simplifier then eta-expands the RHS if needed and then updates the
    occurrence sites. Dividing the work this way means that the occurrence analyser
    still only takes one pass, yet one can always tell the difference between a
    function call and a jump by looking at the occurrence (because the same pass
    changes the 'IdDetails' and propagates the binders to their occurrence sites).

    To track potential join points, we use the 'occ_tail' field of OccInfo. A value
    of `AlwaysTailCalled n` indicates that every occurrence of the variable is a
    tail call with `n` arguments (counting both value and type arguments). Otherwise
    'occ_tail' will be 'NoTailCallInfo'. The tail call info flows bottom-up with the
    rest of 'OccInfo' until it goes on the binder.

    Note [Join points and unfoldings/rules]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider
       let j2 y = blah
       let j x = j2 (x+x)
           {-# INLINE [2] j #-}
       in case e of { A -> j 1; B -> ...; C -> j 2 }

    Before j is inlined, we'll have occurrences of j2 in
    both j's RHS and in its stable unfolding.  We want to discover
    j2 as a join point.  So we must do the adjustRhsUsage thing
    on j's RHS.  That's why we pass mb_join_arity to calcUnfolding.

    Aame with rules. Suppose we have:

      let j :: Int -> Int
          j y = 2 * y
      let k :: Int -> Int -> Int
          {-# RULES "SPEC k 0" k 0 y = j y #-}
          k x y = x + 2 * y
      in case e of { A -> k 1 2; B -> k 3 5; C -> blah }

    We identify k as a join point, and we want j to be a join point too.
    Without the RULE it would be, and we don't want the RULE to mess it
    up.  So provided the join-point arity of k matches the args of the
    rule we can allow the tail-cal info from the RHS of the rule to
    propagate.

    * Wrinkle for Rec case. In the recursive case we don't know the
      join-point arity in advance, when calling occAnalUnfolding and
      occAnalRules.  (See makeNode.)  We don't want to pass Nothing,
      because then a recursive joinrec might lose its join-poin-hood
      when SpecConstr adds a RULE.  So we just make do with the
      *current* join-poin-hood, stored in the Id.

      In the non-recursive case things are simple: see occAnalNonRecBind

    * Wrinkle for RULES.  Suppose the example was a bit different:
          let j :: Int -> Int
              j y = 2 * y
              k :: Int -> Int -> Int
              {-# RULES "SPEC k 0" k 0 = j #-}
              k x y = x + 2 * y
          in ...
      If we eta-expanded the rule all would be well, but as it stands the
      one arg of the rule don't match the join-point arity of 2.

      Conceivably we could notice that a potential join point would have
      an "undersaturated" rule and account for it. This would mean we
      could make something that's been specialised a join point, for
      instance. But local bindings are rarely specialised, and being
      overly cautious about rules only costs us anything when, for some `j`:

      * Before specialisation, `j` has non-tail calls, so it can't be a join point.
      * During specialisation, `j` gets specialised and thus acquires rules.
      * Sometime afterward, the non-tail calls to `j` disappear (as dead code, say),
        and so now `j` *could* become a join point.

      This appears to be very rare in practice. TODO Perhaps we should gather
      statistics to be sure.

    Note [Unfoldings and join points]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    We assume that anything in an unfolding occurs multiple times, since
    unfoldings are often copied (that's the whole point!). But we still
    need to track tail calls for the purpose of finding join points.

    ------------------------------------------------------------
    Note [Adjusting right-hand sides]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    There's a bit of a dance we need to do after analysing a lambda expression or
    a right-hand side. In particular, we need to

      a) call 'markAllInsideLam' *unless* the binding is for a thunk, a one-shot
         lambda, or a non-recursive join point; and
      b) call 'markAllNonTail' *unless* the binding is for a join point.

    Some examples, with how the free occurrences in e (assumed not to be a value
    lambda) get marked:

                                 inside lam    non-tail-called
      ------------------------------------------------------------
      let x = e                  No            Yes
      let f = \x -> e            Yes           Yes
      let f = \x{OneShot} -> e   No            Yes
      \x -> e                    Yes           Yes
      join j x = e               No            No
      joinrec j x = e            Yes           No

    There are a few other caveats; most importantly, if we're marking a binding as
    'AlwaysTailCalled', it's *going* to be a join point, so we treat it as one so
    that the effect cascades properly. Consequently, at the time the RHS is
    analysed, we won't know what adjustments to make; thus 'occAnalLamOrRhs' must
    return the unadjusted 'UsageDetails', to be adjusted by 'adjustRhsUsage' once
    join-point-hood has been decided.

    Thus the overall sequence taking place in 'occAnalNonRecBind' and
    'occAnalRecBind' is as follows:

      1. Call 'occAnalLamOrRhs' to find usage information for the RHS.
      2. Call 'tagNonRecBinder' or 'tagRecBinders', which decides whether to make
         the binding a join point.
      3. Call 'adjustRhsUsage' accordingly. (Done as part of 'tagRecBinders' when
         recursive.)

    (In the recursive case, this logic is spread between 'makeNode' and
    'occAnalRec'.)
    -}

    ------------------------------------------------------------------
    --                 occAnalBind
    ------------------------------------------------------------------

    occAnalBind :: OccEnv           -- The incoming OccEnv
                -> TopLevelFlag
                -> ImpRuleEdges
                -> CoreBind
                -> UsageDetails             -- Usage details of scope
                -> (UsageDetails,           -- Of the whole let(rec)
                    [CoreBind])

    occAnalBind :: OccEnv
    -> TopLevelFlag
    -> ImpRuleEdges
    -> CoreBind
    -> UsageDetails
    -> (UsageDetails, CoreProgram)
    occAnalBind OccEnv
    env TopLevelFlag
    lvl ImpRuleEdges
    top_env (NonRec CoreBndr
    binder CoreExpr
    rhs) UsageDetails
    body_usage
      = OccEnv
    -> TopLevelFlag
    -> ImpRuleEdges
    -> CoreBndr
    -> CoreExpr
    -> UsageDetails
    -> (UsageDetails, CoreProgram)
    occAnalNonRecBind OccEnv
    env TopLevelFlag
    lvl ImpRuleEdges
    top_env CoreBndr
    binder CoreExpr
    rhs UsageDetails
    body_usage
    occAnalBind OccEnv
    env TopLevelFlag
    lvl ImpRuleEdges
    top_env (Rec [(CoreBndr, CoreExpr)]
    pairs) UsageDetails
    body_usage
      = OccEnv
    -> TopLevelFlag
    -> ImpRuleEdges
    -> [(CoreBndr, CoreExpr)]
    -> UsageDetails
    -> (UsageDetails, CoreProgram)
    occAnalRecBind OccEnv
    env TopLevelFlag
    lvl ImpRuleEdges
    top_env [(CoreBndr, CoreExpr)]
    pairs UsageDetails
    body_usage

    -----------------
    occAnalNonRecBind :: OccEnv -> TopLevelFlag -> ImpRuleEdges -> Var -> CoreExpr
                      -> UsageDetails -> (UsageDetails, [CoreBind])
    occAnalNonRecBind :: OccEnv
    -> TopLevelFlag
    -> ImpRuleEdges
    -> CoreBndr
    -> CoreExpr
    -> UsageDetails
    -> (UsageDetails, CoreProgram)
    occAnalNonRecBind OccEnv
    env TopLevelFlag
    lvl ImpRuleEdges
    imp_rule_edges CoreBndr
    bndr CoreExpr
    rhs UsageDetails
    body_usage
      | CoreBndr -> Bool
    isTyVar CoreBndr
    bndr      -- A type let; we don't gather usage info
      = (UsageDetails
    body_usage, [CoreBndr -> CoreExpr -> CoreBind
    forall b. b -> Expr b -> Bind b
    NonRec CoreBndr
    bndr CoreExpr
    rhs])

      | Bool -> Bool
    not (CoreBndr
    bndr CoreBndr -> UsageDetails -> Bool
    `usedIn` UsageDetails
    body_usage)    -- It's not mentioned
      = (UsageDetails
    body_usage, [])

      | Bool
    otherwise                   -- It's mentioned in the body
      = (UsageDetails
    body_usage' UsageDetails -> UsageDetails -> UsageDetails
    `andUDs` UsageDetails
    rhs_usage, [CoreBndr -> CoreExpr -> CoreBind
    forall b. b -> Expr b -> Bind b
    NonRec CoreBndr
    final_bndr CoreExpr
    rhs'])
      where
        (UsageDetails
    body_usage', CoreBndr
    tagged_bndr) = TopLevelFlag
    -> UsageDetails -> CoreBndr -> (UsageDetails, CoreBndr)
    tagNonRecBinder TopLevelFlag
    lvl UsageDetails
    body_usage CoreBndr
    bndr
        final_bndr :: CoreBndr
    final_bndr = CoreBndr
    tagged_bndr CoreBndr -> Unfolding -> CoreBndr
    `setIdUnfolding` Unfolding
    unf'
                                 CoreBndr -> RuleInfo -> CoreBndr
    `setIdSpecialisation` [CoreRule] -> RuleInfo
    mkRuleInfo [CoreRule]
    rules'
        rhs_usage :: UsageDetails
    rhs_usage = UsageDetails
    rhs_uds UsageDetails -> UsageDetails -> UsageDetails
    `andUDs` UsageDetails
    unf_uds UsageDetails -> UsageDetails -> UsageDetails
    `andUDs` UsageDetails
    rule_uds

        -- Get the join info from the *new* decision
        -- See Note [Join points and unfoldings/rules]
        mb_join_arity :: Maybe JoinArity
    mb_join_arity = CoreBndr -> Maybe JoinArity
    willBeJoinId_maybe CoreBndr
    tagged_bndr
        is_join_point :: Bool
    is_join_point = Maybe JoinArity -> Bool
    forall a. Maybe a -> Bool
    isJust Maybe JoinArity
    mb_join_arity

        --------- Right hand side ---------
        env1 :: OccEnv
    env1 | Bool
    is_join_point    = OccEnv
    env  -- See Note [Join point RHSs]
             | Bool
    certainly_inline = OccEnv
    env  -- See Note [Cascading inlines]
             | Bool
    otherwise        = OccEnv -> OccEnv
    rhsCtxt OccEnv
    env

        -- See Note [Sources of one-shot information]
        rhs_env :: OccEnv
    rhs_env = OccEnv
    env1 { occ_one_shots :: OneShots
    occ_one_shots = Demand -> OneShots
    argOneShots Demand
    dmd }
        (UsageDetails
    rhs_uds, CoreExpr
    rhs') = OccEnv
    -> RecFlag
    -> Maybe JoinArity
    -> CoreExpr
    -> (UsageDetails, CoreExpr)
    occAnalRhs OccEnv
    rhs_env RecFlag
    NonRecursive Maybe JoinArity
    mb_join_arity CoreExpr
    rhs

        --------- Unfolding ---------
        -- See Note [Unfoldings and join points]
        unf :: Unfolding
    unf = CoreBndr -> Unfolding
    idUnfolding CoreBndr
    bndr
        (UsageDetails
    unf_uds, Unfolding
    unf') = OccEnv
    -> RecFlag
    -> Maybe JoinArity
    -> Unfolding
    -> (UsageDetails, Unfolding)
    occAnalUnfolding OccEnv
    rhs_env RecFlag
    NonRecursive Maybe JoinArity
    mb_join_arity Unfolding
    unf

        --------- Rules ---------
        -- See Note [Rules are extra RHSs] and Note [Rule dependency info]
        rules_w_uds :: [(CoreRule, UsageDetails, UsageDetails)]
    rules_w_uds  = OccEnv
    -> Maybe JoinArity
    -> CoreBndr
    -> [(CoreRule, UsageDetails, UsageDetails)]
    occAnalRules OccEnv
    rhs_env Maybe JoinArity
    mb_join_arity CoreBndr
    bndr
        rules' :: [CoreRule]
    rules'       = ((CoreRule, UsageDetails, UsageDetails) -> CoreRule)
    -> [(CoreRule, UsageDetails, UsageDetails)] -> [CoreRule]
    forall a b. (a -> b) -> [a] -> [b]
    map (CoreRule, UsageDetails, UsageDetails) -> CoreRule
    forall a b c. (a, b, c) -> a
    fstOf3 [(CoreRule, UsageDetails, UsageDetails)]
    rules_w_uds
        imp_rule_uds :: UsageDetails
    imp_rule_uds = [(Activation, VarSet)] -> UsageDetails
    impRulesScopeUsage (ImpRuleEdges -> CoreBndr -> [(Activation, VarSet)]
    lookupImpRules ImpRuleEdges
    imp_rule_edges CoreBndr
    bndr)
             -- imp_rule_uds: consider
             --     h = ...
             --     g = ...
             --     RULE map g = h
             -- Then we want to ensure that h is in scope everwhere
             -- that g is (since the RULE might turn g into h), so
             -- we make g mention h.

        rule_uds :: UsageDetails
    rule_uds = ((CoreRule, UsageDetails, UsageDetails)
     -> UsageDetails -> UsageDetails)
    -> UsageDetails
    -> [(CoreRule, UsageDetails, UsageDetails)]
    -> UsageDetails
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr (CoreRule, UsageDetails, UsageDetails)
    -> UsageDetails -> UsageDetails
    forall {a}.
    (a, UsageDetails, UsageDetails) -> UsageDetails -> UsageDetails
    add_rule_uds UsageDetails
    imp_rule_uds [(CoreRule, UsageDetails, UsageDetails)]
    rules_w_uds
        add_rule_uds :: (a, UsageDetails, UsageDetails) -> UsageDetails -> UsageDetails
    add_rule_uds (a
    _, UsageDetails
    l, UsageDetails
    r) UsageDetails
    uds = UsageDetails
    l UsageDetails -> UsageDetails -> UsageDetails
    `andUDs` UsageDetails
    r UsageDetails -> UsageDetails -> UsageDetails
    `andUDs` UsageDetails
    uds

        ----------
        occ :: OccInfo
    occ = CoreBndr -> OccInfo
    idOccInfo CoreBndr
    tagged_bndr
        certainly_inline :: Bool
    certainly_inline -- See Note [Cascading inlines]
          = case OccInfo
    occ of
              OneOcc { occ_in_lam :: OccInfo -> InsideLam
    occ_in_lam = InsideLam
    NotInsideLam, occ_n_br :: OccInfo -> JoinArity
    occ_n_br = JoinArity
    1 }
                -> Bool
    active Bool -> Bool -> Bool
    && Bool
    not_stable
              OccInfo
    _ -> Bool
    False

        dmd :: Demand
    dmd        = CoreBndr -> Demand
    idDemandInfo CoreBndr
    bndr
        active :: Bool
    active     = Activation -> Bool
    isAlwaysActive (CoreBndr -> Activation
    idInlineActivation CoreBndr
    bndr)
        not_stable :: Bool
    not_stable = Bool -> Bool
    not (Unfolding -> Bool
    isStableUnfolding (CoreBndr -> Unfolding
    idUnfolding CoreBndr
    bndr))

    -----------------
    occAnalRecBind :: OccEnv -> TopLevelFlag -> ImpRuleEdges -> [(Var,CoreExpr)]
                   -> UsageDetails -> (UsageDetails, [CoreBind])
    -- For a recursive group, we
    --      * occ-analyse all the RHSs
    --      * compute strongly-connected components
    --      * feed those components to occAnalRec
    -- See Note [Recursive bindings: the grand plan]
    occAnalRecBind :: OccEnv
    -> TopLevelFlag
    -> ImpRuleEdges
    -> [(CoreBndr, CoreExpr)]
    -> UsageDetails
    -> (UsageDetails, CoreProgram)
    occAnalRecBind OccEnv
    env TopLevelFlag
    lvl ImpRuleEdges
    imp_rule_edges [(CoreBndr, CoreExpr)]
    pairs UsageDetails
    body_usage
      = (SCC Details
     -> (UsageDetails, CoreProgram) -> (UsageDetails, CoreProgram))
    -> (UsageDetails, CoreProgram)
    -> [SCC Details]
    -> (UsageDetails, CoreProgram)
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr (OccEnv
    -> TopLevelFlag
    -> SCC Details
    -> (UsageDetails, CoreProgram)
    -> (UsageDetails, CoreProgram)
    occAnalRec OccEnv
    rhs_env TopLevelFlag
    lvl) (UsageDetails
    body_usage, []) [SCC Details]
    sccs
      where
        sccs :: [SCC Details]
        sccs :: [SCC Details]
    sccs = {-# SCC "occAnalBind.scc" #-}
               [Node Unique Details] -> [SCC Details]
    forall key payload.
    Uniquable key =>
    [Node key payload] -> [SCC payload]
    stronglyConnCompFromEdgedVerticesUniq [Node Unique Details]
    nodes

        nodes :: [LetrecNode]
        nodes :: [Node Unique Details]
    nodes = {-# SCC "occAnalBind.assoc" #-}
                ((CoreBndr, CoreExpr) -> Node Unique Details)
    -> [(CoreBndr, CoreExpr)] -> [Node Unique Details]
    forall a b. (a -> b) -> [a] -> [b]
    map (OccEnv
    -> ImpRuleEdges
    -> VarSet
    -> (CoreBndr, CoreExpr)
    -> Node Unique Details
    makeNode OccEnv
    rhs_env ImpRuleEdges
    imp_rule_edges VarSet
    bndr_set) [(CoreBndr, CoreExpr)]
    pairs

        bndrs :: [CoreBndr]
    bndrs    = ((CoreBndr, CoreExpr) -> CoreBndr)
    -> [(CoreBndr, CoreExpr)] -> [CoreBndr]
    forall a b. (a -> b) -> [a] -> [b]
    map (CoreBndr, CoreExpr) -> CoreBndr
    forall a b. (a, b) -> a
    fst [(CoreBndr, CoreExpr)]
    pairs
        bndr_set :: VarSet
    bndr_set = [CoreBndr] -> VarSet
    mkVarSet [CoreBndr]
    bndrs
        rhs_env :: OccEnv
    rhs_env  = OccEnv
    env OccEnv -> [CoreBndr] -> OccEnv
    `addInScope` [CoreBndr]
    bndrs

    -----------------------------
    occAnalRec :: OccEnv -> TopLevelFlag
               -> SCC Details
               -> (UsageDetails, [CoreBind])
               -> (UsageDetails, [CoreBind])

            -- The NonRec case is just like a Let (NonRec ...) above
    occAnalRec :: OccEnv
    -> TopLevelFlag
    -> SCC Details
    -> (UsageDetails, CoreProgram)
    -> (UsageDetails, CoreProgram)
    occAnalRec OccEnv
    _ TopLevelFlag
    lvl (AcyclicSCC (ND { nd_bndr :: Details -> CoreBndr
    nd_bndr = CoreBndr
    bndr, nd_rhs :: Details -> CoreExpr
    nd_rhs = CoreExpr
    rhs
                                     , nd_uds :: Details -> UsageDetails
    nd_uds = UsageDetails
    rhs_uds, nd_rhs_bndrs :: Details -> [CoreBndr]
    nd_rhs_bndrs = [CoreBndr]
    rhs_bndrs }))
               (UsageDetails
    body_uds, CoreProgram
    binds)
      | Bool -> Bool
    not (CoreBndr
    bndr CoreBndr -> UsageDetails -> Bool
    `usedIn` UsageDetails
    body_uds)
      = (UsageDetails
    body_uds, CoreProgram
    binds)           -- See Note [Dead code]

      | Bool
    otherwise                   -- It's mentioned in the body
      = (UsageDetails
    body_uds' UsageDetails -> UsageDetails -> UsageDetails
    `andUDs` UsageDetails
    rhs_uds',
         CoreBndr -> CoreExpr -> CoreBind
    forall b. b -> Expr b -> Bind b
    NonRec CoreBndr
    tagged_bndr CoreExpr
    rhs CoreBind -> CoreProgram -> CoreProgram
    forall a. a -> [a] -> [a]
    : CoreProgram
    binds)
      where
        (UsageDetails
    body_uds', CoreBndr
    tagged_bndr) = TopLevelFlag
    -> UsageDetails -> CoreBndr -> (UsageDetails, CoreBndr)
    tagNonRecBinder TopLevelFlag
    lvl UsageDetails
    body_uds CoreBndr
    bndr
        rhs_uds' :: UsageDetails
    rhs_uds'   = RecFlag
    -> Maybe JoinArity -> [CoreBndr] -> UsageDetails -> UsageDetails
    adjustRhsUsage RecFlag
    NonRecursive (CoreBndr -> Maybe JoinArity
    willBeJoinId_maybe CoreBndr
    tagged_bndr)
                                    [CoreBndr]
    rhs_bndrs UsageDetails
    rhs_uds

            -- The Rec case is the interesting one
            -- See Note [Recursive bindings: the grand plan]
            -- See Note [Loop breaking]
    occAnalRec OccEnv
    env TopLevelFlag
    lvl (CyclicSCC [Details]
    details_s) (UsageDetails
    body_uds, CoreProgram
    binds)
      | Bool -> Bool
    not ((CoreBndr -> Bool) -> [CoreBndr] -> Bool
    forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
    any (CoreBndr -> UsageDetails -> Bool
    `usedIn` UsageDetails
    body_uds) [CoreBndr]
    bndrs) -- NB: look at body_uds, not total_uds
      = (UsageDetails
    body_uds, CoreProgram
    binds)                   -- See Note [Dead code]

      | Bool
    otherwise   -- At this point we always build a single Rec
      = -- pprTrace "occAnalRec" (ppr loop_breaker_nodes)
        (UsageDetails
    final_uds, [(CoreBndr, CoreExpr)] -> CoreBind
    forall b. [(b, Expr b)] -> Bind b
    Rec [(CoreBndr, CoreExpr)]
    pairs CoreBind -> CoreProgram -> CoreProgram
    forall a. a -> [a] -> [a]
    : CoreProgram
    binds)

      where
        bndrs :: [CoreBndr]
    bndrs      = (Details -> CoreBndr) -> [Details] -> [CoreBndr]
    forall a b. (a -> b) -> [a] -> [b]
    map Details -> CoreBndr
    nd_bndr [Details]
    details_s
        all_simple :: Bool
    all_simple = (Details -> Bool) -> [Details] -> Bool
    forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
    all Details -> Bool
    nd_simple [Details]
    details_s

        ------------------------------
        -- Make the nodes for the loop-breaker analysis
        -- See Note [Choosing loop breakers] for loop_breaker_nodes
        final_uds :: UsageDetails
        loop_breaker_nodes :: [LetrecNode]
        (UsageDetails
    final_uds, [Node Unique Details]
    loop_breaker_nodes) = OccEnv
    -> TopLevelFlag
    -> UsageDetails
    -> [Details]
    -> (UsageDetails, [Node Unique Details])
    mkLoopBreakerNodes OccEnv
    env TopLevelFlag
    lvl UsageDetails
    body_uds [Details]
    details_s

        ------------------------------
        active_rule_fvs :: VarSet
        active_rule_fvs :: VarSet
    active_rule_fvs = (Details -> VarSet) -> [Details] -> VarSet
    forall a. (a -> VarSet) -> [a] -> VarSet
    mapUnionVarSet Details -> VarSet
    nd_active_rule_fvs [Details]
    details_s

        ---------------------------
        -- Now reconstruct the cycle
        pairs :: [(Id,CoreExpr)]
        pairs :: [(CoreBndr, CoreExpr)]
    pairs | Bool
    all_simple = JoinArity
    -> VarSet
    -> [Node Unique Details]
    -> [(CoreBndr, CoreExpr)]
    -> [(CoreBndr, CoreExpr)]
    reOrderNodes   JoinArity
    0 VarSet
    active_rule_fvs [Node Unique Details]
    loop_breaker_nodes []
              | Bool
    otherwise  = JoinArity
    -> VarSet
    -> [Node Unique Details]
    -> [(CoreBndr, CoreExpr)]
    -> [(CoreBndr, CoreExpr)]
    loopBreakNodes JoinArity
    0 VarSet
    active_rule_fvs [Node Unique Details]
    loop_breaker_nodes []
              -- In the common case when all are "simple" (no rules at all)
              -- the loop_breaker_nodes will include all the scope edges
              -- so a SCC computation would yield a single CyclicSCC result;
              -- and reOrderNodes deals with exactly that case.
              -- Saves a SCC analysis in a common case

    {- *********************************************************************
    *                                                                      *
                    Loop breaking
    *                                                                      *
    ********************************************************************* -}

    {- Note [Choosing loop breakers]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    In Step 4 in Note [Recursive bindings: the grand plan]), occAnalRec does
    loop-breaking on each CyclicSCC of the original program:

    * mkLoopBreakerNodes: Form the loop-breaker graph for that CyclicSCC

    * loopBreakNodes: Do SCC analysis on it

    * reOrderNodes: For each CyclicSCC, pick a loop breaker
        * Delete edges to that loop breaker
        * Do another SCC analysis on that reduced SCC
        * Repeat

    To form the loop-breaker graph, we construct a new set of Nodes, the
    "loop-breaker nodes", with the same details but different edges, the
    "loop-breaker edges".  The loop-breaker nodes have both more and fewer
    dependencies than the scope edges:

      More edges:
         If f calls g, and g has an active rule that mentions h then
         we add an edge from f -> h.  See Note [Rules and loop breakers].

      Fewer edges: we only include dependencies
         * only on /active/ rules,
         * on rule /RHSs/ (not LHSs)

    The scope edges, by contrast, must be much more inclusive.

    The nd_simple flag tracks the common case when a binding has no RULES
    at all, in which case the loop-breaker edges will be identical to the
    scope edges.

    Note that in Example [eftInt], *neither* eftInt *nor* eftIntFB is
    chosen as a loop breaker, because their RHSs don't mention each other.
    And indeed both can be inlined safely.

    Note [inl_fvs]
    ~~~~~~~~~~~~~~
    Note that the loop-breaker graph includes edges for occurrences in
    /both/ the RHS /and/ the stable unfolding.  Consider this, which actually
    occurred when compiling BooleanFormula.hs in GHC:

      Rec { lvl1 = go
          ; lvl2[StableUnf = go] = lvl1
          ; go = ...go...lvl2... }

    From the point of view of infinite inlining, we need only these edges:
       lvl1 :-> go
       lvl2 :-> go       -- The RHS lvl1 will never be used for inlining
       go   :-> go, lvl2

    But the danger is that, lacking any edge to lvl1, we'll put it at the
    end thus
      Rec { lvl2[ StableUnf = go] = lvl1
          ; go[LoopBreaker] = ...go...lvl2... }
          ; lvl1[Occ=Once]  = go }

    And now the Simplifer will try to use PreInlineUnconditionally on lvl1
    (which occurs just once), but because it is last we won't actually
    substitute in lvl2.  Sigh.

    To avoid this possiblity, we include edges from lvl2 to /both/ its
    stable unfolding /and/ its RHS.  Hence the defn of inl_fvs in
    makeNode.  Maybe we could be more clever, but it's very much a corner
    case.

    Note [Weak loop breakers]
    ~~~~~~~~~~~~~~~~~~~~~~~~~
    There is a last nasty wrinkle.  Suppose we have

        Rec { f = f_rhs
              RULE f [] = g

              h = h_rhs
              g = h
              ...more...
        }

    Remember that we simplify the RULES before any RHS (see Note
    [Rules are visible in their own rec group] above).

    So we must *not* postInlineUnconditionally 'g', even though
    its RHS turns out to be trivial.  (I'm assuming that 'g' is
    not chosen as a loop breaker.)  Why not?  Because then we
    drop the binding for 'g', which leaves it out of scope in the
    RULE!

    Here's a somewhat different example of the same thing
        Rec { q = r
            ; r = ...p...
            ; p = p_rhs
              RULE p [] = q }
    Here the RULE is "below" q, but we *still* can't postInlineUnconditionally
    q, because the RULE for p is active throughout.  So the RHS of r
    might rewrite to     r = ...q...
    So q must remain in scope in the output program!

    We "solve" this by:

        Make q a "weak" loop breaker (OccInfo = IAmLoopBreaker True)
        iff q is a mentioned in the RHS of an active RULE in the Rec group

    A normal "strong" loop breaker has IAmLoopBreaker False.  So:

                                    Inline  postInlineUnconditionally
    strong   IAmLoopBreaker False    no      no
    weak     IAmLoopBreaker True     yes     no
             other                   yes     yes

    The **sole** reason for this kind of loop breaker is so that
    postInlineUnconditionally does not fire.  Ugh.

    Annoyingly, since we simplify the rules *first* we'll never inline
    q into p's RULE.  That trivial binding for q will hang around until
    we discard the rule.  Yuk.  But it's rare.

     Note [Rules and loop breakers]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    When we form the loop-breaker graph (Step 4 in Note [Recursive
    bindings: the grand plan]), we must be careful about RULEs.

    For a start, we want a loop breaker to cut every cycle, so inactive
    rules play no part; we need only consider /active/ rules.
    See Note [Finding rule RHS free vars]

    The second point is more subtle.  A RULE is like an equation for
    'f' that is *always* inlined if it is applicable.  We do *not* disable
    rules for loop-breakers.  It's up to whoever makes the rules to make
    sure that the rules themselves always terminate.  See Note [Rules for
    recursive functions] in GHC.Core.Opt.Simplify

    Hence, if
        f's RHS (or its stable unfolding if it has one) mentions g, and
        g has a RULE that mentions h, and
        h has a RULE that mentions f

    then we *must* choose f to be a loop breaker.  Example: see Note
    [Specialisation rules]. So out plan is this:

       Take the free variables of f's RHS, and augment it with all the
       variables reachable by a transitive sequence RULES from those
       starting points.

    That is the whole reason for computing rule_fv_env in mkLoopBreakerNodes.
    Wrinkles:

    * We only consider /active/ rules. See Note [Finding rule RHS free vars]

    * We need only consider free vars that are also binders in this Rec
      group.  See also Note [Finding rule RHS free vars]

    * We only consider variables free in the *RHS* of the rule, in
      contrast to the way we build the Rec group in the first place (Note
      [Rule dependency info])

    * Why "transitive sequence of rules"?  Because active rules apply
      unconditionally, without checking loop-breaker-ness.
     See Note [Loop breaker dependencies].

    Note [Finding rule RHS free vars]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider this real example from Data Parallel Haskell
         tagZero :: Array Int -> Array Tag
         {-# INLINE [1] tagZeroes #-}
         tagZero xs = pmap (\x -> fromBool (x==0)) xs

         {-# RULES "tagZero" [~1] forall xs n.
             pmap fromBool <blah blah> = tagZero xs #-}
    So tagZero's RHS mentions pmap, and pmap's RULE mentions tagZero.
    However, tagZero can only be inlined in phase 1 and later, while
    the RULE is only active *before* phase 1.  So there's no problem.

    To make this work, we look for the RHS free vars only for
    *active* rules. That's the reason for the occ_rule_act field
    of the OccEnv.

    Note [loopBreakNodes]
    ~~~~~~~~~~~~~~~~~~~~~
    loopBreakNodes is applied to the list of nodes for a cyclic strongly
    connected component (there's guaranteed to be a cycle).  It returns
    the same nodes, but
            a) in a better order,
            b) with some of the Ids having a IAmALoopBreaker pragma

    The "loop-breaker" Ids are sufficient to break all cycles in the SCC.  This means
    that the simplifier can guarantee not to loop provided it never records an inlining
    for these no-inline guys.

    Furthermore, the order of the binds is such that if we neglect dependencies
    on the no-inline Ids then the binds are topologically sorted.  This means
    that the simplifier will generally do a good job if it works from top bottom,
    recording inlinings for any Ids which aren't marked as "no-inline" as it goes.
    -}

    type Binding = (Id,CoreExpr)

    -- See Note [loopBreakNodes]
    loopBreakNodes :: Int
                   -> VarSet        -- Binders whose dependencies may be "missing"
                                    -- See Note [Weak loop breakers]
                   -> [LetrecNode]
                   -> [Binding]             -- Append these to the end
                   -> [Binding]

    -- Return the bindings sorted into a plausible order, and marked with loop breakers.
    -- See Note [loopBreakNodes]
    loopBreakNodes :: JoinArity
    -> VarSet
    -> [Node Unique Details]
    -> [(CoreBndr, CoreExpr)]
    -> [(CoreBndr, CoreExpr)]
    loopBreakNodes JoinArity
    depth VarSet
    weak_fvs [Node Unique Details]
    nodes [(CoreBndr, CoreExpr)]
    binds
      = -- pprTrace "loopBreakNodes" (ppr nodes) $
        [SCC (Node Unique Details)] -> [(CoreBndr, CoreExpr)]
    go ([Node Unique Details] -> [SCC (Node Unique Details)]
    forall key payload.
    Uniquable key =>
    [Node key payload] -> [SCC (Node key payload)]
    stronglyConnCompFromEdgedVerticesUniqR [Node Unique Details]
    nodes)
      where
        go :: [SCC (Node Unique Details)] -> [(CoreBndr, CoreExpr)]
    go []         = [(CoreBndr, CoreExpr)]
    binds
        go (SCC (Node Unique Details)
    scc:[SCC (Node Unique Details)]
    sccs) = SCC (Node Unique Details)
    -> [(CoreBndr, CoreExpr)] -> [(CoreBndr, CoreExpr)]
    loop_break_scc SCC (Node Unique Details)
    scc ([SCC (Node Unique Details)] -> [(CoreBndr, CoreExpr)]
    go [SCC (Node Unique Details)]
    sccs)

        loop_break_scc :: SCC (Node Unique Details)
    -> [(CoreBndr, CoreExpr)] -> [(CoreBndr, CoreExpr)]
    loop_break_scc SCC (Node Unique Details)
    scc [(CoreBndr, CoreExpr)]
    binds
          = case SCC (Node Unique Details)
    scc of
              AcyclicSCC Node Unique Details
    node  -> (CoreBndr -> CoreBndr)
    -> Node Unique Details -> (CoreBndr, CoreExpr)
    nodeBinding (VarSet -> CoreBndr -> CoreBndr
    mk_non_loop_breaker VarSet
    weak_fvs) Node Unique Details
    node (CoreBndr, CoreExpr)
    -> [(CoreBndr, CoreExpr)] -> [(CoreBndr, CoreExpr)]
    forall a. a -> [a] -> [a]
    : [(CoreBndr, CoreExpr)]
    binds
              CyclicSCC [Node Unique Details]
    nodes  -> JoinArity
    -> VarSet
    -> [Node Unique Details]
    -> [(CoreBndr, CoreExpr)]
    -> [(CoreBndr, CoreExpr)]
    reOrderNodes JoinArity
    depth VarSet
    weak_fvs [Node Unique Details]
    nodes [(CoreBndr, CoreExpr)]
    binds

    ----------------------------------
    reOrderNodes :: Int -> VarSet -> [LetrecNode] -> [Binding] -> [Binding]
        -- Choose a loop breaker, mark it no-inline,
        -- and call loopBreakNodes on the rest
    reOrderNodes :: JoinArity
    -> VarSet
    -> [Node Unique Details]
    -> [(CoreBndr, CoreExpr)]
    -> [(CoreBndr, CoreExpr)]
    reOrderNodes JoinArity
    _ VarSet
    _ []     [(CoreBndr, CoreExpr)]
    _     = String -> [(CoreBndr, CoreExpr)]
    forall a. String -> a
    panic String
    "reOrderNodes"
    reOrderNodes JoinArity
    _ VarSet
    _ [Node Unique Details
    node] [(CoreBndr, CoreExpr)]
    binds = (CoreBndr -> CoreBndr)
    -> Node Unique Details -> (CoreBndr, CoreExpr)
    nodeBinding CoreBndr -> CoreBndr
    mk_loop_breaker Node Unique Details
    node (CoreBndr, CoreExpr)
    -> [(CoreBndr, CoreExpr)] -> [(CoreBndr, CoreExpr)]
    forall a. a -> [a] -> [a]
    : [(CoreBndr, CoreExpr)]
    binds
    reOrderNodes JoinArity
    depth VarSet
    weak_fvs (Node Unique Details
    node : [Node Unique Details]
    nodes) [(CoreBndr, CoreExpr)]
    binds
      = -- pprTrace "reOrderNodes" (vcat [ text "unchosen" <+> ppr unchosen
        --                               , text "chosen" <+> ppr chosen_nodes ]) $
        JoinArity
    -> VarSet
    -> [Node Unique Details]
    -> [(CoreBndr, CoreExpr)]
    -> [(CoreBndr, CoreExpr)]
    loopBreakNodes JoinArity
    new_depth VarSet
    weak_fvs [Node Unique Details]
    unchosen ([(CoreBndr, CoreExpr)] -> [(CoreBndr, CoreExpr)])
    -> [(CoreBndr, CoreExpr)] -> [(CoreBndr, CoreExpr)]
    forall a b. (a -> b) -> a -> b
    $
        ((Node Unique Details -> (CoreBndr, CoreExpr))
    -> [Node Unique Details] -> [(CoreBndr, CoreExpr)]
    forall a b. (a -> b) -> [a] -> [b]
    map ((CoreBndr -> CoreBndr)
    -> Node Unique Details -> (CoreBndr, CoreExpr)
    nodeBinding CoreBndr -> CoreBndr
    mk_loop_breaker) [Node Unique Details]
    chosen_nodes [(CoreBndr, CoreExpr)]
    -> [(CoreBndr, CoreExpr)] -> [(CoreBndr, CoreExpr)]
    forall a. [a] -> [a] -> [a]
    ++ [(CoreBndr, CoreExpr)]
    binds)
      where
        ([Node Unique Details]
    chosen_nodes, [Node Unique Details]
    unchosen) = Bool
    -> NodeScore
    -> [Node Unique Details]
    -> [Node Unique Details]
    -> [Node Unique Details]
    -> ([Node Unique Details], [Node Unique Details])
    chooseLoopBreaker Bool
    approximate_lb
                                                     (Details -> NodeScore
    nd_score (Node Unique Details -> Details
    forall key payload. Node key payload -> payload
    node_payload Node Unique Details
    node))
                                                     [Node Unique Details
    node] [] [Node Unique Details]
    nodes

        approximate_lb :: Bool
    approximate_lb = JoinArity
    depth JoinArity -> JoinArity -> Bool
    forall a. Ord a => a -> a -> Bool
    >= JoinArity
    2
        new_depth :: JoinArity
    new_depth | Bool
    approximate_lb = JoinArity
    0
                  | Bool
    otherwise      = JoinArity
    depthJoinArity -> JoinArity -> JoinArity
    forall a. Num a => a -> a -> a
    +JoinArity
    1
            -- After two iterations (d=0, d=1) give up
            -- and approximate, returning to d=0

    nodeBinding :: (Id -> Id) -> LetrecNode -> Binding
    nodeBinding :: (CoreBndr -> CoreBndr)
    -> Node Unique Details -> (CoreBndr, CoreExpr)
    nodeBinding CoreBndr -> CoreBndr
    set_id_occ (Node Unique Details -> Details
    forall key payload. Node key payload -> payload
    node_payload -> ND { nd_bndr :: Details -> CoreBndr
    nd_bndr = CoreBndr
    bndr, nd_rhs :: Details -> CoreExpr
    nd_rhs = CoreExpr
    rhs})
      = (CoreBndr -> CoreBndr
    set_id_occ CoreBndr
    bndr, CoreExpr
    rhs)

    mk_loop_breaker :: Id -> Id
    mk_loop_breaker :: CoreBndr -> CoreBndr
    mk_loop_breaker CoreBndr
    bndr
      = CoreBndr
    bndr CoreBndr -> OccInfo -> CoreBndr
    `setIdOccInfo` OccInfo
    occ'
      where
        occ' :: OccInfo
    occ'      = OccInfo
    strongLoopBreaker { occ_tail :: TailCallInfo
    occ_tail = TailCallInfo
    tail_info }
        tail_info :: TailCallInfo
    tail_info = OccInfo -> TailCallInfo
    tailCallInfo (CoreBndr -> OccInfo
    idOccInfo CoreBndr
    bndr)

    mk_non_loop_breaker :: VarSet -> Id -> Id
    -- See Note [Weak loop breakers]
    mk_non_loop_breaker :: VarSet -> CoreBndr -> CoreBndr
    mk_non_loop_breaker VarSet
    weak_fvs CoreBndr
    bndr
      | CoreBndr
    bndr CoreBndr -> VarSet -> Bool
    `elemVarSet` VarSet
    weak_fvs = CoreBndr -> OccInfo -> CoreBndr
    setIdOccInfo CoreBndr
    bndr OccInfo
    occ'
      | Bool
    otherwise                  = CoreBndr
    bndr
      where
        occ' :: OccInfo
    occ'      = OccInfo
    weakLoopBreaker { occ_tail :: TailCallInfo
    occ_tail = TailCallInfo
    tail_info }
        tail_info :: TailCallInfo
    tail_info = OccInfo -> TailCallInfo
    tailCallInfo (CoreBndr -> OccInfo
    idOccInfo CoreBndr
    bndr)

    ----------------------------------
    chooseLoopBreaker :: Bool             -- True <=> Too many iterations,
                                          --          so approximate
                      -> NodeScore            -- Best score so far
                      -> [LetrecNode]       -- Nodes with this score
                      -> [LetrecNode]       -- Nodes with higher scores
                      -> [LetrecNode]       -- Unprocessed nodes
                      -> ([LetrecNode], [LetrecNode])
        -- This loop looks for the bind with the lowest score
        -- to pick as the loop  breaker.  The rest accumulate in
    chooseLoopBreaker :: Bool
    -> NodeScore
    -> [Node Unique Details]
    -> [Node Unique Details]
    -> [Node Unique Details]
    -> ([Node Unique Details], [Node Unique Details])
    chooseLoopBreaker Bool
    _ NodeScore
    _ [Node Unique Details]
    loop_nodes [Node Unique Details]
    acc []
      = ([Node Unique Details]
    loop_nodes, [Node Unique Details]
    acc)        -- Done

        -- If approximate_loop_breaker is True, we pick *all*
        -- nodes with lowest score, else just one
        -- See Note [Complexity of loop breaking]
    chooseLoopBreaker Bool
    approx_lb NodeScore
    loop_sc [Node Unique Details]
    loop_nodes [Node Unique Details]
    acc (Node Unique Details
    node : [Node Unique Details]
    nodes)
      | Bool
    approx_lb
      , NodeScore -> JoinArity
    rank NodeScore
    sc JoinArity -> JoinArity -> Bool
    forall a. Eq a => a -> a -> Bool
    == NodeScore -> JoinArity
    rank NodeScore
    loop_sc
      = Bool
    -> NodeScore
    -> [Node Unique Details]
    -> [Node Unique Details]
    -> [Node Unique Details]
    -> ([Node Unique Details], [Node Unique Details])
    chooseLoopBreaker Bool
    approx_lb NodeScore
    loop_sc (Node Unique Details
    node Node Unique Details
    -> [Node Unique Details] -> [Node Unique Details]
    forall a. a -> [a] -> [a]
    : [Node Unique Details]
    loop_nodes) [Node Unique Details]
    acc [Node Unique Details]
    nodes

      | NodeScore
    sc NodeScore -> NodeScore -> Bool
    `betterLB` NodeScore
    loop_sc  -- Better score so pick this new one
      = Bool
    -> NodeScore
    -> [Node Unique Details]
    -> [Node Unique Details]
    -> [Node Unique Details]
    -> ([Node Unique Details], [Node Unique Details])
    chooseLoopBreaker Bool
    approx_lb NodeScore
    sc [Node Unique Details
    node] ([Node Unique Details]
    loop_nodes [Node Unique Details]
    -> [Node Unique Details] -> [Node Unique Details]
    forall a. [a] -> [a] -> [a]
    ++ [Node Unique Details]
    acc) [Node Unique Details]
    nodes

      | Bool
    otherwise              -- Worse score so don't pick it
      = Bool
    -> NodeScore
    -> [Node Unique Details]
    -> [Node Unique Details]
    -> [Node Unique Details]
    -> ([Node Unique Details], [Node Unique Details])
    chooseLoopBreaker Bool
    approx_lb NodeScore
    loop_sc [Node Unique Details]
    loop_nodes (Node Unique Details
    node Node Unique Details
    -> [Node Unique Details] -> [Node Unique Details]
    forall a. a -> [a] -> [a]
    : [Node Unique Details]
    acc) [Node Unique Details]
    nodes
      where
        sc :: NodeScore
    sc = Details -> NodeScore
    nd_score (Node Unique Details -> Details
    forall key payload. Node key payload -> payload
    node_payload Node Unique Details
    node)

    {-
    Note [Complexity of loop breaking]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    The loop-breaking algorithm knocks out one binder at a time, and
    performs a new SCC analysis on the remaining binders.  That can
    behave very badly in tightly-coupled groups of bindings; in the
    worst case it can be (N**2)*log N, because it does a full SCC
    on N, then N-1, then N-2 and so on.

    To avoid this, we switch plans after 2 (or whatever) attempts:
      Plan A: pick one binder with the lowest score, make it
              a loop breaker, and try again
      Plan B: pick *all* binders with the lowest score, make them
              all loop breakers, and try again
    Since there are only a small finite number of scores, this will
    terminate in a constant number of iterations, rather than O(N)
    iterations.

    You might thing that it's very unlikely, but RULES make it much
    more likely.  Here's a real example from #1969:
      Rec { $dm = \d.\x. op d
            {-# RULES forall d. $dm Int d  = $s$dm1
                      forall d. $dm Bool d = $s$dm2 #-}

            dInt = MkD .... opInt ...
            dInt = MkD .... opBool ...
            opInt  = $dm dInt
            opBool = $dm dBool

            $s$dm1 = \x. op dInt
            $s$dm2 = \x. op dBool }
    The RULES stuff means that we can't choose $dm as a loop breaker
    (Note [Choosing loop breakers]), so we must choose at least (say)
    opInt *and* opBool, and so on.  The number of loop breakders is
    linear in the number of instance declarations.

    Note [Loop breakers and INLINE/INLINABLE pragmas]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Avoid choosing a function with an INLINE pramga as the loop breaker!
    If such a function is mutually-recursive with a non-INLINE thing,
    then the latter should be the loop-breaker.

    It's vital to distinguish between INLINE and INLINABLE (the
    Bool returned by hasStableCoreUnfolding_maybe).  If we start with
       Rec { {-# INLINABLE f #-}
             f x = ...f... }
    and then worker/wrapper it through strictness analysis, we'll get
       Rec { {-# INLINABLE $wf #-}
             $wf p q = let x = (p,q) in ...f...

             {-# INLINE f #-}
             f x = case x of (p,q) -> $wf p q }

    Now it is vital that we choose $wf as the loop breaker, so we can
    inline 'f' in '$wf'.

    Note [DFuns should not be loop breakers]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    It's particularly bad to make a DFun into a loop breaker.  See
    Note [How instance declarations are translated] in GHC.Tc.TyCl.Instance

    We give DFuns a higher score than ordinary CONLIKE things because
    if there's a choice we want the DFun to be the non-loop breaker. Eg

    rec { sc = /\ a \$dC. $fBWrap (T a) ($fCT @ a $dC)

          $fCT :: forall a_afE. (Roman.C a_afE) => Roman.C (Roman.T a_afE)
          {-# DFUN #-}
          $fCT = /\a \$dC. MkD (T a) ((sc @ a $dC) |> blah) ($ctoF @ a $dC)
        }

    Here 'sc' (the superclass) looks CONLIKE, but we'll never get to it
    if we can't unravel the DFun first.

    Note [Constructor applications]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    It's really really important to inline dictionaries.  Real
    example (the Enum Ordering instance from GHC.Base):

         rec     f = \ x -> case d of (p,q,r) -> p x
                 g = \ x -> case d of (p,q,r) -> q x
                 d = (v, f, g)

    Here, f and g occur just once; but we can't inline them into d.
    On the other hand we *could* simplify those case expressions if
    we didn't stupidly choose d as the loop breaker.
    But we won't because constructor args are marked "Many".
    Inlining dictionaries is really essential to unravelling
    the loops in static numeric dictionaries, see GHC.Float.

    Note [Closure conversion]
    ~~~~~~~~~~~~~~~~~~~~~~~~~
    We treat (\x. C p q) as a high-score candidate in the letrec scoring algorithm.
    The immediate motivation came from the result of a closure-conversion transformation
    which generated code like this:

        data Clo a b = forall c. Clo (c -> a -> b) c

        ($:) :: Clo a b -> a -> b
        Clo f env $: x = f env x

        rec { plus = Clo plus1 ()

            ; plus1 _ n = Clo plus2 n

            ; plus2 Zero     n = n
            ; plus2 (Succ m) n = Succ (plus $: m $: n) }

    If we inline 'plus' and 'plus1', everything unravels nicely.  But if
    we choose 'plus1' as the loop breaker (which is entirely possible
    otherwise), the loop does not unravel nicely.

    @occAnalUnfolding@ deals with the question of bindings where the Id is marked
    by an INLINE pragma.  For these we record that anything which occurs
    in its RHS occurs many times.  This pessimistically assumes that this
    inlined binder also occurs many times in its scope, but if it doesn't
    we'll catch it next time round.  At worst this costs an extra simplifier pass.
    ToDo: try using the occurrence info for the inline'd binder.

    [March 97] We do the same for atomic RHSs.  Reason: see notes with loopBreakSCC.
    [June 98, SLPJ]  I've undone this change; I don't understand it.  See notes with loopBreakSCC.

    ************************************************************************
    *                                                                      *
                       Making nodes
    *                                                                      *
    ************************************************************************
    -}

    type LetrecNode = Node Unique Details  -- Node comes from Digraph
                                           -- The Unique key is gotten from the Id
    data Details
      = ND { Details -> CoreBndr
    nd_bndr :: Id          -- Binder

           , Details -> CoreExpr
    nd_rhs  :: CoreExpr    -- RHS, already occ-analysed

           , Details -> [CoreBndr]
    nd_rhs_bndrs :: [CoreBndr] -- Outer lambdas of RHS
                                        -- INVARIANT: (nd_rhs_bndrs nd, _) ==
                                        --              collectBinders (nd_rhs nd)

           , Details -> UsageDetails
    nd_uds  :: UsageDetails  -- Usage from RHS, and RULES, and stable unfoldings
                                      -- ignoring phase (ie assuming all are active)
                                      -- See Note [Forming Rec groups]

           , Details -> VarSet
    nd_inl  :: IdSet       -- Free variables of the stable unfolding and the RHS
                                    -- but excluding any RULES
                                    -- This is the IdSet that may be used if the Id is inlined

           , Details -> Bool
    nd_simple :: Bool      -- True iff this binding has no local RULES
                                    -- If all nodes are simple we don't need a loop-breaker
                                    -- dep-anal before reconstructing.

           , Details -> VarSet
    nd_active_rule_fvs :: IdSet    -- Variables bound in this Rec group that are free
                                            -- in the RHS of an active rule for this bndr

           , Details -> NodeScore
    nd_score :: NodeScore
      }

    instance Outputable Details where
       ppr :: Details -> SDoc
    ppr Details
    nd = String -> SDoc
    text String
    "ND" SDoc -> SDoc -> SDoc
    <> SDoc -> SDoc
    braces
                 ([SDoc] -> SDoc
    sep [ String -> SDoc
    text String
    "bndr =" SDoc -> SDoc -> SDoc
    <+> CoreBndr -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr (Details -> CoreBndr
    nd_bndr Details
    nd)
                      , String -> SDoc
    text String
    "uds =" SDoc -> SDoc -> SDoc
    <+> UsageDetails -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr (Details -> UsageDetails
    nd_uds Details
    nd)
                      , String -> SDoc
    text String
    "inl =" SDoc -> SDoc -> SDoc
    <+> VarSet -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr (Details -> VarSet
    nd_inl Details
    nd)
                      , String -> SDoc
    text String
    "simple =" SDoc -> SDoc -> SDoc
    <+> Bool -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr (Details -> Bool
    nd_simple Details
    nd)
                      , String -> SDoc
    text String
    "active_rule_fvs =" SDoc -> SDoc -> SDoc
    <+> VarSet -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr (Details -> VarSet
    nd_active_rule_fvs Details
    nd)
                      , String -> SDoc
    text String
    "score =" SDoc -> SDoc -> SDoc
    <+> NodeScore -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr (Details -> NodeScore
    nd_score Details
    nd)
                 ])

    -- The NodeScore is compared lexicographically;
    --      e.g. lower rank wins regardless of size
    type NodeScore = ( Int     -- Rank: lower => more likely to be picked as loop breaker
                     , Int     -- Size of rhs: higher => more likely to be picked as LB
                               -- Maxes out at maxExprSize; we just use it to prioritise
                               -- small functions
                     , Bool )  -- Was it a loop breaker before?
                               -- True => more likely to be picked
                               -- Note [Loop breakers, node scoring, and stability]

    rank :: NodeScore -> Int
    rank :: NodeScore -> JoinArity
    rank (JoinArity
    r, JoinArity
    _, Bool
    _) = JoinArity
    r

    makeNode :: OccEnv -> ImpRuleEdges -> VarSet
             -> (Var, CoreExpr) -> LetrecNode
    -- See Note [Recursive bindings: the grand plan]
    makeNode :: OccEnv
    -> ImpRuleEdges
    -> VarSet
    -> (CoreBndr, CoreExpr)
    -> Node Unique Details
    makeNode OccEnv
    env ImpRuleEdges
    imp_rule_edges VarSet
    bndr_set (CoreBndr
    bndr, CoreExpr
    rhs)
      = DigraphNode { node_payload :: Details
    node_payload      = Details
    details
                    , node_key :: Unique
    node_key          = CoreBndr -> Unique
    varUnique CoreBndr
    bndr
                    , node_dependencies :: [Unique]
    node_dependencies = VarSet -> [Unique]
    forall elt. UniqSet elt -> [Unique]
    nonDetKeysUniqSet VarSet
    scope_fvs }
        -- It's OK to use nonDetKeysUniqSet here as stronglyConnCompFromEdgedVerticesR
        -- is still deterministic with edges in nondeterministic order as
        -- explained in Note [Deterministic SCC] in GHC.Data.Graph.Directed.
      where
        details :: Details
    details = ND { nd_bndr :: CoreBndr
    nd_bndr            = CoreBndr
    bndr'
                     , nd_rhs :: CoreExpr
    nd_rhs             = CoreExpr
    rhs'
                     , nd_rhs_bndrs :: [CoreBndr]
    nd_rhs_bndrs       = [CoreBndr]
    bndrs'
                     , nd_uds :: UsageDetails
    nd_uds             = UsageDetails
    scope_uds
                     , nd_inl :: VarSet
    nd_inl             = VarSet
    inl_fvs
                     , nd_simple :: Bool
    nd_simple          = [(CoreRule, UsageDetails, UsageDetails)] -> Bool
    forall (t :: * -> *) a. Foldable t => t a -> Bool
    null [(CoreRule, UsageDetails, UsageDetails)]
    rules_w_uds Bool -> Bool -> Bool
    && [(Activation, VarSet)] -> Bool
    forall (t :: * -> *) a. Foldable t => t a -> Bool
    null [(Activation, VarSet)]
    imp_rule_info
                     , nd_active_rule_fvs :: VarSet
    nd_active_rule_fvs = VarSet
    active_rule_fvs
                     , nd_score :: NodeScore
    nd_score           = String -> SDoc -> NodeScore
    forall a. HasCallStack => String -> SDoc -> a
    pprPanic String
    "makeNodeDetails" (CoreBndr -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr CoreBndr
    bndr) }

        bndr' :: CoreBndr
    bndr' = CoreBndr
    bndr CoreBndr -> Unfolding -> CoreBndr
    `setIdUnfolding`      Unfolding
    unf'
                     CoreBndr -> RuleInfo -> CoreBndr
    `setIdSpecialisation` [CoreRule] -> RuleInfo
    mkRuleInfo [CoreRule]
    rules'

        inl_uds :: UsageDetails
    inl_uds = UsageDetails
    rhs_uds UsageDetails -> UsageDetails -> UsageDetails
    `andUDs` UsageDetails
    unf_uds
        scope_uds :: UsageDetails
    scope_uds = UsageDetails
    inl_uds UsageDetails -> UsageDetails -> UsageDetails
    `andUDs` UsageDetails
    rule_uds
                       -- Note [Rules are extra RHSs]
                       -- Note [Rule dependency info]
        scope_fvs :: VarSet
    scope_fvs = VarSet -> UsageDetails -> VarSet
    udFreeVars VarSet
    bndr_set UsageDetails
    scope_uds
        -- scope_fvs: all occurrences from this binder: RHS, unfolding,
        --            and RULES, both LHS and RHS thereof, active or inactive

        inl_fvs :: VarSet
    inl_fvs  = VarSet -> UsageDetails -> VarSet
    udFreeVars VarSet
    bndr_set UsageDetails
    inl_uds
        -- inl_fvs: vars that would become free if the function was inlined.
        -- We conservatively approximate that by thefree vars from the RHS
        -- and the unfolding together.
        -- See Note [inl_fvs]

        mb_join_arity :: Maybe JoinArity
    mb_join_arity = CoreBndr -> Maybe JoinArity
    isJoinId_maybe CoreBndr
    bndr
        -- Get join point info from the *current* decision
        -- We don't know what the new decision will be!
        -- Using the old decision at least allows us to
        -- preserve existing join point, even RULEs are added
        -- See Note [Join points and unfoldings/rules]

        --------- Right hand side ---------
        -- Constructing the edges for the main Rec computation
        -- See Note [Forming Rec groups]
        -- Do not use occAnalRhs because we don't yet know
        -- the final answer for mb_join_arity
        ([CoreBndr]
    bndrs, CoreExpr
    body)            = CoreExpr -> ([CoreBndr], CoreExpr)
    forall b. Expr b -> ([b], Expr b)
    collectBinders CoreExpr
    rhs
        rhs_env :: OccEnv
    rhs_env                  = OccEnv -> OccEnv
    rhsCtxt OccEnv
    env
        (UsageDetails
    rhs_uds, [CoreBndr]
    bndrs', CoreExpr
    body') = OccEnv
    -> [CoreBndr] -> CoreExpr -> (UsageDetails, [CoreBndr], CoreExpr)
    occAnalLamOrRhs OccEnv
    rhs_env [CoreBndr]
    bndrs CoreExpr
    body
        rhs' :: CoreExpr
    rhs'                     = [CoreBndr] -> CoreExpr -> CoreExpr
    forall b. [b] -> Expr b -> Expr b
    mkLams [CoreBndr]
    bndrs' CoreExpr
    body'

        --------- Unfolding ---------
        -- See Note [Unfoldings and join points]
        unf :: Unfolding
    unf = CoreBndr -> Unfolding
    realIdUnfolding CoreBndr
    bndr -- realIdUnfolding: Ignore loop-breaker-ness
                                   -- here because that is what we are setting!
        (UsageDetails
    unf_uds, Unfolding
    unf') = OccEnv
    -> RecFlag
    -> Maybe JoinArity
    -> Unfolding
    -> (UsageDetails, Unfolding)
    occAnalUnfolding OccEnv
    rhs_env RecFlag
    Recursive Maybe JoinArity
    mb_join_arity Unfolding
    unf

        --------- IMP-RULES --------
        is_active :: Activation -> Bool
    is_active     = OccEnv -> Activation -> Bool
    occ_rule_act OccEnv
    env :: Activation -> Bool
        imp_rule_info :: [(Activation, VarSet)]
    imp_rule_info = ImpRuleEdges -> CoreBndr -> [(Activation, VarSet)]
    lookupImpRules ImpRuleEdges
    imp_rule_edges CoreBndr
    bndr
        imp_rule_uds :: UsageDetails
    imp_rule_uds  = [(Activation, VarSet)] -> UsageDetails
    impRulesScopeUsage [(Activation, VarSet)]
    imp_rule_info
        imp_rule_fvs :: VarSet
    imp_rule_fvs  = (Activation -> Bool) -> VarSet -> [(Activation, VarSet)] -> VarSet
    impRulesActiveFvs Activation -> Bool
    is_active VarSet
    bndr_set [(Activation, VarSet)]
    imp_rule_info

        --------- All rules --------
        rules_w_uds :: [(CoreRule, UsageDetails, UsageDetails)]
        rules_w_uds :: [(CoreRule, UsageDetails, UsageDetails)]
    rules_w_uds = OccEnv
    -> Maybe JoinArity
    -> CoreBndr
    -> [(CoreRule, UsageDetails, UsageDetails)]
    occAnalRules OccEnv
    rhs_env Maybe JoinArity
    mb_join_arity CoreBndr
    bndr
        rules' :: [CoreRule]
    rules'      = ((CoreRule, UsageDetails, UsageDetails) -> CoreRule)
    -> [(CoreRule, UsageDetails, UsageDetails)] -> [CoreRule]
    forall a b. (a -> b) -> [a] -> [b]
    map (CoreRule, UsageDetails, UsageDetails) -> CoreRule
    forall a b c. (a, b, c) -> a
    fstOf3 [(CoreRule, UsageDetails, UsageDetails)]
    rules_w_uds

        rule_uds :: UsageDetails
    rule_uds = ((CoreRule, UsageDetails, UsageDetails)
     -> UsageDetails -> UsageDetails)
    -> UsageDetails
    -> [(CoreRule, UsageDetails, UsageDetails)]
    -> UsageDetails
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr (CoreRule, UsageDetails, UsageDetails)
    -> UsageDetails -> UsageDetails
    forall {a}.
    (a, UsageDetails, UsageDetails) -> UsageDetails -> UsageDetails
    add_rule_uds UsageDetails
    imp_rule_uds [(CoreRule, UsageDetails, UsageDetails)]
    rules_w_uds
        add_rule_uds :: (a, UsageDetails, UsageDetails) -> UsageDetails -> UsageDetails
    add_rule_uds (a
    _, UsageDetails
    l, UsageDetails
    r) UsageDetails
    uds = UsageDetails
    l UsageDetails -> UsageDetails -> UsageDetails
    `andUDs` UsageDetails
    r UsageDetails -> UsageDetails -> UsageDetails
    `andUDs` UsageDetails
    uds

        active_rule_fvs :: VarSet
    active_rule_fvs = ((CoreRule, UsageDetails, UsageDetails) -> VarSet -> VarSet)
    -> VarSet -> [(CoreRule, UsageDetails, UsageDetails)] -> VarSet
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr (CoreRule, UsageDetails, UsageDetails) -> VarSet -> VarSet
    add_active_rule VarSet
    imp_rule_fvs [(CoreRule, UsageDetails, UsageDetails)]
    rules_w_uds
        add_active_rule :: (CoreRule, UsageDetails, UsageDetails) -> VarSet -> VarSet
    add_active_rule (CoreRule
    rule, UsageDetails
    _, UsageDetails
    rhs_uds) VarSet
    fvs
          | Activation -> Bool
    is_active (CoreRule -> Activation
    ruleActivation CoreRule
    rule)
          = VarSet -> UsageDetails -> VarSet
    udFreeVars VarSet
    bndr_set UsageDetails
    rhs_uds VarSet -> VarSet -> VarSet
    `unionVarSet` VarSet
    fvs
          | Bool
    otherwise
          = VarSet
    fvs

    mkLoopBreakerNodes :: OccEnv -> TopLevelFlag
                       -> UsageDetails   -- for BODY of let
                       -> [Details]
                       -> (UsageDetails, -- adjusted
                           [LetrecNode])
    -- See Note [Choosing loop breakers]
    -- This function primarily creates the Nodes for the
    -- loop-breaker SCC analysis.  More specifically:
    --   a) tag each binder with its occurrence info
    --   b) add a NodeScore to each node
    --   c) make a Node with the right dependency edges for
    --      the loop-breaker SCC analysis
    --   d) adjust each RHS's usage details according to
    --      the binder's (new) shotness and join-point-hood
    mkLoopBreakerNodes :: OccEnv
    -> TopLevelFlag
    -> UsageDetails
    -> [Details]
    -> (UsageDetails, [Node Unique Details])
    mkLoopBreakerNodes OccEnv
    env TopLevelFlag
    lvl UsageDetails
    body_uds [Details]
    details_s
      = (UsageDetails
    final_uds, String
    -> (Details -> CoreBndr -> Node Unique Details)
    -> [Details]
    -> [CoreBndr]
    -> [Node Unique Details]
    forall a b c. String -> (a -> b -> c) -> [a] -> [b] -> [c]
    zipWithEqual String
    "mkLoopBreakerNodes" Details -> CoreBndr -> Node Unique Details
    mk_lb_node [Details]
    details_s [CoreBndr]
    bndrs')
      where
        (UsageDetails
    final_uds, [CoreBndr]
    bndrs')
           = TopLevelFlag
    -> UsageDetails
    -> [(CoreBndr, UsageDetails, [CoreBndr])]
    -> (UsageDetails, [CoreBndr])
    tagRecBinders TopLevelFlag
    lvl UsageDetails
    body_uds
                [ (CoreBndr
    bndr, UsageDetails
    uds, [CoreBndr]
    rhs_bndrs)
                | ND { nd_bndr :: Details -> CoreBndr
    nd_bndr = CoreBndr
    bndr, nd_uds :: Details -> UsageDetails
    nd_uds = UsageDetails
    uds, nd_rhs_bndrs :: Details -> [CoreBndr]
    nd_rhs_bndrs = [CoreBndr]
    rhs_bndrs }
                     <- [Details]
    details_s ]

        mk_lb_node :: Details -> CoreBndr -> Node Unique Details
    mk_lb_node nd :: Details
    nd@(ND { nd_bndr :: Details -> CoreBndr
    nd_bndr = CoreBndr
    old_bndr, nd_inl :: Details -> VarSet
    nd_inl = VarSet
    inl_fvs }) CoreBndr
    new_bndr
          = DigraphNode { node_payload :: Details
    node_payload      = Details
    new_nd
                        , node_key :: Unique
    node_key          = CoreBndr -> Unique
    varUnique CoreBndr
    old_bndr
                        , node_dependencies :: [Unique]
    node_dependencies = VarSet -> [Unique]
    forall elt. UniqSet elt -> [Unique]
    nonDetKeysUniqSet VarSet
    lb_deps }
                  -- It's OK to use nonDetKeysUniqSet here as
                  -- stronglyConnCompFromEdgedVerticesR is still deterministic with edges
                  -- in nondeterministic order as explained in
                  -- Note [Deterministic SCC] in GHC.Data.Graph.Directed.
          where
            new_nd :: Details
    new_nd = Details
    nd { nd_bndr :: CoreBndr
    nd_bndr = CoreBndr
    new_bndr, nd_score :: NodeScore
    nd_score = NodeScore
    score }
            score :: NodeScore
    score  = OccEnv -> CoreBndr -> VarSet -> Details -> NodeScore
    nodeScore OccEnv
    env CoreBndr
    new_bndr VarSet
    lb_deps Details
    nd
            lb_deps :: VarSet
    lb_deps = VarEnv VarSet -> VarSet -> VarSet
    extendFvs_ VarEnv VarSet
    rule_fv_env VarSet
    inl_fvs
            -- See Note [Loop breaker dependencies]

        rule_fv_env :: IdEnv IdSet
        -- Maps a variable f to the variables from this group
        --      reachable by a sequence of RULES starting with f
        -- Domain is *subset* of bound vars (others have no rule fvs)
        -- See Note [Finding rule RHS free vars]
        -- Why transClosureFV?  See Note [Loop breaker dependencies]
        rule_fv_env :: VarEnv VarSet
    rule_fv_env = VarEnv VarSet -> VarEnv VarSet
    transClosureFV (VarEnv VarSet -> VarEnv VarSet) -> VarEnv VarSet -> VarEnv VarSet
    forall a b. (a -> b) -> a -> b
    $ [(CoreBndr, VarSet)] -> VarEnv VarSet
    forall a. [(CoreBndr, a)] -> VarEnv a
    mkVarEnv ([(CoreBndr, VarSet)] -> VarEnv VarSet)
    -> [(CoreBndr, VarSet)] -> VarEnv VarSet
    forall a b. (a -> b) -> a -> b
    $
                      [ (CoreBndr
    b, VarSet
    rule_fvs)
                      | ND { nd_bndr :: Details -> CoreBndr
    nd_bndr = CoreBndr
    b, nd_active_rule_fvs :: Details -> VarSet
    nd_active_rule_fvs = VarSet
    rule_fvs } <- [Details]
    details_s
                      , Bool -> Bool
    not (VarSet -> Bool
    isEmptyVarSet VarSet
    rule_fvs) ]

    {- Note [Loop breaker dependencies]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    The loop breaker dependencies of x in a recursive
    group { f1 = e1; ...; fn = en } are:

    - The "inline free variables" of f: the fi free in
      f's stable unfolding and RHS; see Note [inl_fvs]

    - Any fi reachable from those inline free variables by a sequence
      of RULE rewrites.  Remember, rule rewriting is not affected
      by fi being a loop breaker, so we have to take the transitive
      closure in case f is the only possible loop breaker in the loop.

      Hence rule_fv_env.  We need only account for /active/ rules.
    -}

    ------------------------------------------
    nodeScore :: OccEnv
              -> Id        -- Binder with new occ-info
              -> VarSet    -- Loop-breaker dependencies
              -> Details
              -> NodeScore
    nodeScore :: OccEnv -> CoreBndr -> VarSet -> Details -> NodeScore
    nodeScore OccEnv
    env CoreBndr
    new_bndr VarSet
    lb_deps
              (ND { nd_bndr :: Details -> CoreBndr
    nd_bndr = CoreBndr
    old_bndr, nd_rhs :: Details -> CoreExpr
    nd_rhs = CoreExpr
    bind_rhs })

      | Bool -> Bool
    not (CoreBndr -> Bool
    isId CoreBndr
    old_bndr)     -- A type or coercion variable is never a loop breaker
      = (JoinArity
    100, JoinArity
    0, Bool
    False)

      | CoreBndr
    old_bndr CoreBndr -> VarSet -> Bool
    `elemVarSet` VarSet
    lb_deps  -- Self-recursive things are great loop breakers
      = (JoinArity
    0, JoinArity
    0, Bool
    True)                   -- See Note [Self-recursion and loop breakers]

      | Bool -> Bool
    not (OccEnv -> CoreBndr -> Bool
    occ_unf_act OccEnv
    env CoreBndr
    old_bndr) -- A binder whose inlining is inactive (e.g. has
      = (JoinArity
    0, JoinArity
    0, Bool
    True)                   -- a NOINLINE pragma) makes a great loop breaker

      | CoreExpr -> Bool
    exprIsTrivial CoreExpr
    rhs
      = JoinArity -> NodeScore
    mk_score JoinArity
    10  -- Practically certain to be inlined
        -- Used to have also: && not (isExportedId bndr)
        -- But I found this sometimes cost an extra iteration when we have
        --      rec { d = (a,b); a = ...df...; b = ...df...; df = d }
        -- where df is the exported dictionary. Then df makes a really
        -- bad choice for loop breaker

      | DFunUnfolding { df_args :: Unfolding -> [CoreExpr]
    df_args = [CoreExpr]
    args } <- Unfolding
    old_unf
        -- Never choose a DFun as a loop breaker
        -- Note [DFuns should not be loop breakers]
      = (JoinArity
    9, [CoreExpr] -> JoinArity
    forall (t :: * -> *) a. Foldable t => t a -> JoinArity
    length [CoreExpr]
    args, Bool
    is_lb)

        -- Data structures are more important than INLINE pragmas
        -- so that dictionary/method recursion unravels

      | CoreUnfolding { uf_guidance :: Unfolding -> UnfoldingGuidance
    uf_guidance = UnfWhen {} } <- Unfolding
    old_unf
      = JoinArity -> NodeScore
    mk_score JoinArity
    6

      | CoreExpr -> Bool
    forall {b}. Expr b -> Bool
    is_con_app CoreExpr
    rhs   -- Data types help with cases:
      = JoinArity -> NodeScore
    mk_score JoinArity
    5       -- Note [Constructor applications]

      | Unfolding -> Bool
    isStableUnfolding Unfolding
    old_unf
      , Bool
    can_unfold
      = JoinArity -> NodeScore
    mk_score JoinArity
    3

      | OccInfo -> Bool
    isOneOcc (CoreBndr -> OccInfo
    idOccInfo CoreBndr
    new_bndr)
      = JoinArity -> NodeScore
    mk_score JoinArity
    2  -- Likely to be inlined

      | Bool
    can_unfold  -- The Id has some kind of unfolding
      = JoinArity -> NodeScore
    mk_score JoinArity
    1

      | Bool
    otherwise
      = (JoinArity
    0, JoinArity
    0, Bool
    is_lb)

      where
        mk_score :: Int -> NodeScore
        mk_score :: JoinArity -> NodeScore
    mk_score JoinArity
    rank = (JoinArity
    rank, JoinArity
    rhs_size, Bool
    is_lb)

        -- is_lb: see Note [Loop breakers, node scoring, and stability]
        is_lb :: Bool
    is_lb = OccInfo -> Bool
    isStrongLoopBreaker (CoreBndr -> OccInfo
    idOccInfo CoreBndr
    old_bndr)

        old_unf :: Unfolding
    old_unf = CoreBndr -> Unfolding
    realIdUnfolding CoreBndr
    old_bndr
        can_unfold :: Bool
    can_unfold = Unfolding -> Bool
    canUnfold Unfolding
    old_unf
        rhs :: CoreExpr
    rhs        = case Unfolding
    old_unf of
                       CoreUnfolding { uf_src :: Unfolding -> UnfoldingSource
    uf_src = UnfoldingSource
    src, uf_tmpl :: Unfolding -> CoreExpr
    uf_tmpl = CoreExpr
    unf_rhs }
                         | UnfoldingSource -> Bool
    isStableSource UnfoldingSource
    src
                         -> CoreExpr
    unf_rhs
                       Unfolding
    _ -> CoreExpr
    bind_rhs
           -- 'bind_rhs' is irrelevant for inlining things with a stable unfolding
        rhs_size :: JoinArity
    rhs_size = case Unfolding
    old_unf of
                     CoreUnfolding { uf_guidance :: Unfolding -> UnfoldingGuidance
    uf_guidance = UnfoldingGuidance
    guidance }
                        | UnfIfGoodArgs { ug_size :: UnfoldingGuidance -> JoinArity
    ug_size = JoinArity
    size } <- UnfoldingGuidance
    guidance
                        -> JoinArity
    size
                     Unfolding
    _  -> CoreExpr -> JoinArity
    cheapExprSize CoreExpr
    rhs

            -- Checking for a constructor application
            -- Cheap and cheerful; the simplifier moves casts out of the way
            -- The lambda case is important to spot x = /\a. C (f a)
            -- which comes up when C is a dictionary constructor and
            -- f is a default method.
            -- Example: the instance for Show (ST s a) in GHC.ST
            --
            -- However we *also* treat (\x. C p q) as a con-app-like thing,
            --      Note [Closure conversion]
        is_con_app :: Expr b -> Bool
    is_con_app (Var CoreBndr
    v)    = CoreBndr -> Bool
    isConLikeId CoreBndr
    v
        is_con_app (App Expr b
    f Expr b
    _)  = Expr b -> Bool
    is_con_app Expr b
    f
        is_con_app (Lam b
    _ Expr b
    e)  = Expr b -> Bool
    is_con_app Expr b
    e
        is_con_app (Tick CoreTickish
    _ Expr b
    e) = Expr b -> Bool
    is_con_app Expr b
    e
        is_con_app Expr b
    _          = Bool
    False

    maxExprSize :: Int
    maxExprSize :: JoinArity
    maxExprSize = JoinArity
    20  -- Rather arbitrary

    cheapExprSize :: CoreExpr -> Int
    -- Maxes out at maxExprSize
    cheapExprSize :: CoreExpr -> JoinArity
    cheapExprSize CoreExpr
    e
      = JoinArity -> CoreExpr -> JoinArity
    go JoinArity
    0 CoreExpr
    e
      where
        go :: JoinArity -> CoreExpr -> JoinArity
    go JoinArity
    n CoreExpr
    e | JoinArity
    n JoinArity -> JoinArity -> Bool
    forall a. Ord a => a -> a -> Bool
    >= JoinArity
    maxExprSize = JoinArity
    n
               | Bool
    otherwise        = JoinArity -> CoreExpr -> JoinArity
    go1 JoinArity
    n CoreExpr
    e

        go1 :: JoinArity -> CoreExpr -> JoinArity
    go1 JoinArity
    n (Var {})        = JoinArity
    nJoinArity -> JoinArity -> JoinArity
    forall a. Num a => a -> a -> a
    +JoinArity
    1
        go1 JoinArity
    n (Lit {})        = JoinArity
    nJoinArity -> JoinArity -> JoinArity
    forall a. Num a => a -> a -> a
    +JoinArity
    1
        go1 JoinArity
    n (Type {})       = JoinArity
    n
        go1 JoinArity
    n (Coercion {})   = JoinArity
    n
        go1 JoinArity
    n (Tick CoreTickish
    _ CoreExpr
    e)      = JoinArity -> CoreExpr -> JoinArity
    go1 JoinArity
    n CoreExpr
    e
        go1 JoinArity
    n (Cast CoreExpr
    e CoercionR
    _)      = JoinArity -> CoreExpr -> JoinArity
    go1 JoinArity
    n CoreExpr
    e
        go1 JoinArity
    n (App CoreExpr
    f CoreExpr
    a)       = JoinArity -> CoreExpr -> JoinArity
    go (JoinArity -> CoreExpr -> JoinArity
    go1 JoinArity
    n CoreExpr
    f) CoreExpr
    a
        go1 JoinArity
    n (Lam CoreBndr
    b CoreExpr
    e)
          | CoreBndr -> Bool
    isTyVar CoreBndr
    b         = JoinArity -> CoreExpr -> JoinArity
    go1 JoinArity
    n CoreExpr
    e
          | Bool
    otherwise         = JoinArity -> CoreExpr -> JoinArity
    go (JoinArity
    nJoinArity -> JoinArity -> JoinArity
    forall a. Num a => a -> a -> a
    +JoinArity
    1) CoreExpr
    e
        go1 JoinArity
    n (Let CoreBind
    b CoreExpr
    e)       = JoinArity -> [CoreExpr] -> JoinArity
    gos (JoinArity -> CoreExpr -> JoinArity
    go1 JoinArity
    n CoreExpr
    e) (CoreBind -> [CoreExpr]
    forall b. Bind b -> [Expr b]
    rhssOfBind CoreBind
    b)
        go1 JoinArity
    n (Case CoreExpr
    e CoreBndr
    _ Type
    _ [Alt CoreBndr]
    as) = JoinArity -> [CoreExpr] -> JoinArity
    gos (JoinArity -> CoreExpr -> JoinArity
    go1 JoinArity
    n CoreExpr
    e) ([Alt CoreBndr] -> [CoreExpr]
    forall b. [Alt b] -> [Expr b]
    rhssOfAlts [Alt CoreBndr]
    as)

        gos :: JoinArity -> [CoreExpr] -> JoinArity
    gos JoinArity
    n [] = JoinArity
    n
        gos JoinArity
    n (CoreExpr
    e:[CoreExpr]
    es) | JoinArity
    n JoinArity -> JoinArity -> Bool
    forall a. Ord a => a -> a -> Bool
    >= JoinArity
    maxExprSize = JoinArity
    n
                     | Bool
    otherwise        = JoinArity -> [CoreExpr] -> JoinArity
    gos (JoinArity -> CoreExpr -> JoinArity
    go1 JoinArity
    n CoreExpr
    e) [CoreExpr]
    es

    betterLB :: NodeScore -> NodeScore -> Bool
    -- If  n1 `betterLB` n2  then choose n1 as the loop breaker
    betterLB :: NodeScore -> NodeScore -> Bool
    betterLB (JoinArity
    rank1, JoinArity
    size1, Bool
    lb1) (JoinArity
    rank2, JoinArity
    size2, Bool
    _)
      | JoinArity
    rank1 JoinArity -> JoinArity -> Bool
    forall a. Ord a => a -> a -> Bool
    < JoinArity
    rank2 = Bool
    True
      | JoinArity
    rank1 JoinArity -> JoinArity -> Bool
    forall a. Ord a => a -> a -> Bool
    > JoinArity
    rank2 = Bool
    False
      | JoinArity
    size1 JoinArity -> JoinArity -> Bool
    forall a. Ord a => a -> a -> Bool
    < JoinArity
    size2 = Bool
    False   -- Make the bigger n2 into the loop breaker
      | JoinArity
    size1 JoinArity -> JoinArity -> Bool
    forall a. Ord a => a -> a -> Bool
    > JoinArity
    size2 = Bool
    True
      | Bool
    lb1           = Bool
    True    -- Tie-break: if n1 was a loop breaker before, choose it
      | Bool
    otherwise     = Bool
    False   -- See Note [Loop breakers, node scoring, and stability]

    {- Note [Self-recursion and loop breakers]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    If we have
       rec { f = ...f...g...
           ; g = .....f...   }
    then 'f' has to be a loop breaker anyway, so we may as well choose it
    right away, so that g can inline freely.

    This is really just a cheap hack. Consider
       rec { f = ...g...
           ; g = ..f..h...
          ;  h = ...f....}
    Here f or g are better loop breakers than h; but we might accidentally
    choose h.  Finding the minimal set of loop breakers is hard.

    Note [Loop breakers, node scoring, and stability]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    To choose a loop breaker, we give a NodeScore to each node in the SCC,
    and pick the one with the best score (according to 'betterLB').

    We need to be jolly careful (#12425, #12234) about the stability
    of this choice. Suppose we have

        let rec { f = ...g...g...
                ; g = ...f...f... }
        in
        case x of
          True  -> ...f..
          False -> ..f...

    In each iteration of the simplifier the occurrence analyser OccAnal
    chooses a loop breaker. Suppose in iteration 1 it choose g as the loop
    breaker. That means it is free to inline f.

    Suppose that GHC decides to inline f in the branches of the case, but
    (for some reason; eg it is not saturated) in the rhs of g. So we get

        let rec { f = ...g...g...
                ; g = ...f...f... }
        in
        case x of
          True  -> ...g...g.....
          False -> ..g..g....

    Now suppose that, for some reason, in the next iteration the occurrence
    analyser chooses f as the loop breaker, so it can freely inline g. And
    again for some reason the simplifier inlines g at its calls in the case
    branches, but not in the RHS of f. Then we get

        let rec { f = ...g...g...
                ; g = ...f...f... }
        in
        case x of
          True  -> ...(...f...f...)...(...f..f..).....
          False -> ..(...f...f...)...(..f..f...)....

    You can see where this is going! Each iteration of the simplifier
    doubles the number of calls to f or g. No wonder GHC is slow!

    (In the particular example in comment:3 of #12425, f and g are the two
    mutually recursive fmap instances for CondT and Result. They are both
    marked INLINE which, oddly, is why they don't inline in each other's
    RHS, because the call there is not saturated.)

    The root cause is that we flip-flop on our choice of loop breaker. I
    always thought it didn't matter, and indeed for any single iteration
    to terminate, it doesn't matter. But when we iterate, it matters a
    lot!!

    So The Plan is this:
       If there is a tie, choose the node that
       was a loop breaker last time round

    Hence the is_lb field of NodeScore

    ************************************************************************
    *                                                                      *
                       Right hand sides
    *                                                                      *
    ************************************************************************
    -}

    occAnalRhs :: OccEnv -> RecFlag -> Maybe JoinArity
               -> CoreExpr   -- RHS
               -> (UsageDetails, CoreExpr)
    occAnalRhs :: OccEnv
    -> RecFlag
    -> Maybe JoinArity
    -> CoreExpr
    -> (UsageDetails, CoreExpr)
    occAnalRhs OccEnv
    env RecFlag
    is_rec Maybe JoinArity
    mb_join_arity CoreExpr
    rhs
      = case OccEnv
    -> [CoreBndr] -> CoreExpr -> (UsageDetails, [CoreBndr], CoreExpr)
    occAnalLamOrRhs OccEnv
    env [CoreBndr]
    bndrs CoreExpr
    body of { (UsageDetails
    body_usage, [CoreBndr]
    bndrs', CoreExpr
    body') ->
        let final_bndrs :: [CoreBndr]
    final_bndrs | RecFlag -> Bool
    isRec RecFlag
    is_rec = [CoreBndr]
    bndrs'
                        | Bool
    otherwise    = Maybe JoinArity -> [CoreBndr] -> [CoreBndr]
    markJoinOneShots Maybe JoinArity
    mb_join_arity [CoreBndr]
    bndrs'
                   -- For a /non-recursive/ join point we can mark all
                   -- its join-lambda as one-shot; and it's a good idea to do so

            -- Final adjustment
            rhs_usage :: UsageDetails
    rhs_usage = RecFlag
    -> Maybe JoinArity -> [CoreBndr] -> UsageDetails -> UsageDetails
    adjustRhsUsage RecFlag
    is_rec Maybe JoinArity
    mb_join_arity [CoreBndr]
    final_bndrs UsageDetails
    body_usage

        in (UsageDetails
    rhs_usage, [CoreBndr] -> CoreExpr -> CoreExpr
    forall b. [b] -> Expr b -> Expr b
    mkLams [CoreBndr]
    final_bndrs CoreExpr
    body') }
      where
        ([CoreBndr]
    bndrs, CoreExpr
    body) = CoreExpr -> ([CoreBndr], CoreExpr)
    forall b. Expr b -> ([b], Expr b)
    collectBinders CoreExpr
    rhs

    occAnalUnfolding :: OccEnv
                     -> RecFlag
                     -> Maybe JoinArity   -- See Note [Join points and unfoldings/rules]
                     -> Unfolding
                     -> (UsageDetails, Unfolding)
    -- Occurrence-analyse a stable unfolding;
    -- discard a non-stable one altogether.
    occAnalUnfolding :: OccEnv
    -> RecFlag
    -> Maybe JoinArity
    -> Unfolding
    -> (UsageDetails, Unfolding)
    occAnalUnfolding OccEnv
    env RecFlag
    is_rec Maybe JoinArity
    mb_join_arity Unfolding
    unf
      = case Unfolding
    unf of
          unf :: Unfolding
    unf@(CoreUnfolding { uf_tmpl :: Unfolding -> CoreExpr
    uf_tmpl = CoreExpr
    rhs, uf_src :: Unfolding -> UnfoldingSource
    uf_src = UnfoldingSource
    src })
            | UnfoldingSource -> Bool
    isStableSource UnfoldingSource
    src -> (UsageDetails -> UsageDetails
    markAllMany UsageDetails
    usage, Unfolding
    unf')
                  -- markAllMany: see Note [Occurrences in stable unfoldings]
            | Bool
    otherwise          -> (UsageDetails
    emptyDetails,      Unfolding
    unf)
                  -- For non-Stable unfoldings we leave them undisturbed, but
                  -- don't count their usage because the simplifier will discard them.
                  -- We leave them undisturbed because nodeScore uses their size info
                  -- to guide its decisions.  It's ok to leave un-substituted
                  -- expressions in the tree because all the variables that were in
                  -- scope remain in scope; there is no cloning etc.
            where
              (UsageDetails
    usage, CoreExpr
    rhs') = OccEnv
    -> RecFlag
    -> Maybe JoinArity
    -> CoreExpr
    -> (UsageDetails, CoreExpr)
    occAnalRhs OccEnv
    env RecFlag
    is_rec Maybe JoinArity
    mb_join_arity CoreExpr
    rhs

              unf' :: Unfolding
    unf' | OccEnv -> Bool
    noBinderSwaps OccEnv
    env = Unfolding
    unf -- Note [Unfoldings and rules]
                   | Bool
    otherwise         = Unfolding
    unf { uf_tmpl :: CoreExpr
    uf_tmpl = CoreExpr
    rhs' }

          unf :: Unfolding
    unf@(DFunUnfolding { df_bndrs :: Unfolding -> [CoreBndr]
    df_bndrs = [CoreBndr]
    bndrs, df_args :: Unfolding -> [CoreExpr]
    df_args = [CoreExpr]
    args })
            -> ( UsageDetails
    final_usage, Unfolding
    unf { df_args :: [CoreExpr]
    df_args = [CoreExpr]
    args' } )
            where
              env' :: OccEnv
    env'            = OccEnv
    env OccEnv -> [CoreBndr] -> OccEnv
    `addInScope` [CoreBndr]
    bndrs
              (UsageDetails
    usage, [CoreExpr]
    args')  = OccEnv -> [CoreExpr] -> (UsageDetails, [CoreExpr])
    occAnalList OccEnv
    env' [CoreExpr]
    args
              final_usage :: UsageDetails
    final_usage     = UsageDetails -> UsageDetails
    markAllManyNonTail (UsageDetails -> [CoreBndr] -> UsageDetails
    delDetailsList UsageDetails
    usage [CoreBndr]
    bndrs)

          Unfolding
    unf -> (UsageDetails
    emptyDetails, Unfolding
    unf)

    occAnalRules :: OccEnv
                 -> Maybe JoinArity  -- See Note [Join points and unfoldings/rules]
                 -> Id               -- Get rules from here
                 -> [(CoreRule,      -- Each (non-built-in) rule
                      UsageDetails,  -- Usage details for LHS
                      UsageDetails)] -- Usage details for RHS
    occAnalRules :: OccEnv
    -> Maybe JoinArity
    -> CoreBndr
    -> [(CoreRule, UsageDetails, UsageDetails)]
    occAnalRules OccEnv
    env Maybe JoinArity
    mb_join_arity CoreBndr
    bndr
      = (CoreRule -> (CoreRule, UsageDetails, UsageDetails))
    -> [CoreRule] -> [(CoreRule, UsageDetails, UsageDetails)]
    forall a b. (a -> b) -> [a] -> [b]
    map CoreRule -> (CoreRule, UsageDetails, UsageDetails)
    occ_anal_rule (CoreBndr -> [CoreRule]
    idCoreRules CoreBndr
    bndr)
      where
        occ_anal_rule :: CoreRule -> (CoreRule, UsageDetails, UsageDetails)
    occ_anal_rule rule :: CoreRule
    rule@(Rule { ru_bndrs :: CoreRule -> [CoreBndr]
    ru_bndrs = [CoreBndr]
    bndrs, ru_args :: CoreRule -> [CoreExpr]
    ru_args = [CoreExpr]
    args, ru_rhs :: CoreRule -> CoreExpr
    ru_rhs = CoreExpr
    rhs })
          = (CoreRule
    rule', UsageDetails
    lhs_uds', UsageDetails
    rhs_uds')
          where
            env' :: OccEnv
    env' = OccEnv
    env OccEnv -> [CoreBndr] -> OccEnv
    `addInScope` [CoreBndr]
    bndrs
            rule' :: CoreRule
    rule' | OccEnv -> Bool
    noBinderSwaps OccEnv
    env = CoreRule
    rule  -- Note [Unfoldings and rules]
                  | Bool
    otherwise         = CoreRule
    rule { ru_args :: [CoreExpr]
    ru_args = [CoreExpr]
    args', ru_rhs :: CoreExpr
    ru_rhs = CoreExpr
    rhs' }

            (UsageDetails
    lhs_uds, [CoreExpr]
    args') = OccEnv -> [CoreExpr] -> (UsageDetails, [CoreExpr])
    occAnalList OccEnv
    env' [CoreExpr]
    args
            lhs_uds' :: UsageDetails
    lhs_uds'         = UsageDetails -> UsageDetails
    markAllManyNonTail (UsageDetails -> UsageDetails) -> UsageDetails -> UsageDetails
    forall a b. (a -> b) -> a -> b
    $
                               UsageDetails
    lhs_uds UsageDetails -> [CoreBndr] -> UsageDetails
    `delDetailsList` [CoreBndr]
    bndrs

            (UsageDetails
    rhs_uds, CoreExpr
    rhs') = OccEnv -> CoreExpr -> (UsageDetails, CoreExpr)
    occAnal OccEnv
    env' CoreExpr
    rhs
                                -- Note [Rules are extra RHSs]
                                -- Note [Rule dependency info]
            rhs_uds' :: UsageDetails
    rhs_uds' = Bool -> UsageDetails -> UsageDetails
    markAllNonTailIf (Bool -> Bool
    not Bool
    exact_join) (UsageDetails -> UsageDetails) -> UsageDetails -> UsageDetails
    forall a b. (a -> b) -> a -> b
    $
                       UsageDetails -> UsageDetails
    markAllMany                             (UsageDetails -> UsageDetails) -> UsageDetails -> UsageDetails
    forall a b. (a -> b) -> a -> b
    $
                       UsageDetails
    rhs_uds UsageDetails -> [CoreBndr] -> UsageDetails
    `delDetailsList` [CoreBndr]
    bndrs

            exact_join :: Bool
    exact_join = Maybe JoinArity -> [CoreExpr] -> Bool
    forall a. Maybe JoinArity -> [a] -> Bool
    exactJoin Maybe JoinArity
    mb_join_arity [CoreExpr]
    args
                         -- See Note [Join points and unfoldings/rules]

        occ_anal_rule CoreRule
    other_rule = (CoreRule
    other_rule, UsageDetails
    emptyDetails, UsageDetails
    emptyDetails)

    {- Note [Join point RHSs]
    ~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider
       x = e
       join j = Just x

    We want to inline x into j right away, so we don't want to give
    the join point a RhsCtxt (#14137).  It's not a huge deal, because
    the FloatIn pass knows to float into join point RHSs; and the simplifier
    does not float things out of join point RHSs.  But it's a simple, cheap
    thing to do.  See #14137.

    Note [Occurrences in stable unfoldings]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider
        f p = BIG
        {-# INLINE g #-}
        g y = not (f y)
    where this is the /only/ occurrence of 'f'.  So 'g' will get a stable
    unfolding.  Now suppose that g's RHS gets optimised (perhaps by a rule
    or inlining f) so that it doesn't mention 'f' any more.  Now the last
    remaining call to f is in g's Stable unfolding. But, even though there
    is only one syntactic occurrence of f, we do /not/ want to do
    preinlineUnconditionally here!

    The INLINE pragma says "inline exactly this RHS"; perhaps the
    programmer wants to expose that 'not', say. If we inline f that will make
    the Stable unfoldign big, and that wasn't what the programmer wanted.

    Another way to think about it: if we inlined g as-is into multiple
    call sites, now there's be multiple calls to f.

    Bottom line: treat all occurrences in a stable unfolding as "Many".

    Note [Unfoldings and rules]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Generally unfoldings and rules are already occurrence-analysed, so we
    don't want to reconstruct their trees; we just want to analyse them to
    find how they use their free variables.

    EXCEPT if there is a binder-swap going on, in which case we do want to
    produce a new tree.

    So we have a fast-path that keeps the old tree if the occ_bs_env is
    empty.   This just saves a bit of allocation and reconstruction; not
    a big deal.

    Note [Cascading inlines]
    ~~~~~~~~~~~~~~~~~~~~~~~~
    By default we use an rhsCtxt for the RHS of a binding.  This tells the
    occ anal n that it's looking at an RHS, which has an effect in
    occAnalApp.  In particular, for constructor applications, it makes
    the arguments appear to have NoOccInfo, so that we don't inline into
    them. Thus    x = f y
                  k = Just x
    we do not want to inline x.

    But there's a problem.  Consider
         x1 = a0 : []
         x2 = a1 : x1
         x3 = a2 : x2
         g  = f x3
    First time round, it looks as if x1 and x2 occur as an arg of a
    let-bound constructor ==> give them a many-occurrence.
    But then x3 is inlined (unconditionally as it happens) and
    next time round, x2 will be, and the next time round x1 will be
    Result: multiple simplifier iterations.  Sigh.

    So, when analysing the RHS of x3 we notice that x3 will itself
    definitely inline the next time round, and so we analyse x3's rhs in
    an ordinary context, not rhsCtxt.  Hence the "certainly_inline" stuff.

    Annoyingly, we have to approximate GHC.Core.Opt.Simplify.Utils.preInlineUnconditionally.
    If (a) the RHS is expandable (see isExpandableApp in occAnalApp), and
       (b) certainly_inline says "yes" when preInlineUnconditionally says "no"
    then the simplifier iterates indefinitely:
            x = f y
            k = Just x   -- We decide that k is 'certainly_inline'
            v = ...k...  -- but preInlineUnconditionally doesn't inline it
    inline ==>
            k = Just (f y)
            v = ...k...
    float ==>
            x1 = f y
            k = Just x1
            v = ...k...

    This is worse than the slow cascade, so we only want to say "certainly_inline"
    if it really is certain.  Look at the note with preInlineUnconditionally
    for the various clauses.

    ************************************************************************
    *                                                                      *
                    Expressions
    *                                                                      *
    ************************************************************************
    -}

    occAnalList :: OccEnv -> [CoreExpr] -> (UsageDetails, [CoreExpr])
    occAnalList :: OccEnv -> [CoreExpr] -> (UsageDetails, [CoreExpr])
    occAnalList OccEnv
    _   []     = (UsageDetails
    emptyDetails, [])
    occAnalList OccEnv
    env (CoreExpr
    e:[CoreExpr]
    es) = case OccEnv -> CoreExpr -> (UsageDetails, CoreExpr)
    occAnal OccEnv
    env CoreExpr
    e      of { (UsageDetails
    uds1, CoreExpr
    e')  ->
                             case OccEnv -> [CoreExpr] -> (UsageDetails, [CoreExpr])
    occAnalList OccEnv
    env [CoreExpr]
    es of { (UsageDetails
    uds2, [CoreExpr]
    es') ->
                             (UsageDetails
    uds1 UsageDetails -> UsageDetails -> UsageDetails
    `andUDs` UsageDetails
    uds2, CoreExpr
    e' CoreExpr -> [CoreExpr] -> [CoreExpr]
    forall a. a -> [a] -> [a]
    : [CoreExpr]
    es') } }

    occAnal :: OccEnv
            -> CoreExpr
            -> (UsageDetails,       -- Gives info only about the "interesting" Ids
                CoreExpr)

    occAnal :: OccEnv -> CoreExpr -> (UsageDetails, CoreExpr)
    occAnal OccEnv
    _   expr :: CoreExpr
    expr@(Type Type
    _) = (UsageDetails
    emptyDetails,         CoreExpr
    expr)
    occAnal OccEnv
    _   expr :: CoreExpr
    expr@(Lit Literal
    _)  = (UsageDetails
    emptyDetails,         CoreExpr
    expr)
    occAnal OccEnv
    env expr :: CoreExpr
    expr@(Var CoreBndr
    _)  = OccEnv
    -> (CoreExpr, [CoreExpr], [CoreTickish])
    -> (UsageDetails, CoreExpr)
    occAnalApp OccEnv
    env (CoreExpr
    expr, [], [])
        -- At one stage, I gathered the idRuleVars for the variable here too,
        -- which in a way is the right thing to do.
        -- But that went wrong right after specialisation, when
        -- the *occurrences* of the overloaded function didn't have any
        -- rules in them, so the *specialised* versions looked as if they
        -- weren't used at all.

    occAnal OccEnv
    _ (Coercion CoercionR
    co)
      = (UsageDetails -> VarSet -> UsageDetails
    addManyOccs UsageDetails
    emptyDetails (CoercionR -> VarSet
    coVarsOfCo CoercionR
    co), CoercionR -> CoreExpr
    forall b. CoercionR -> Expr b
    Coercion CoercionR
    co)
            -- See Note [Gather occurrences of coercion variables]

    {-
    Note [Gather occurrences of coercion variables]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    We need to gather info about what coercion variables appear, so that
    we can sort them into the right place when doing dependency analysis.
    -}

    occAnal OccEnv
    env (Tick CoreTickish
    tickish CoreExpr
    body)
      | SourceNote{} <- CoreTickish
    tickish
      = (UsageDetails
    usage, CoreTickish -> CoreExpr -> CoreExpr
    forall b. CoreTickish -> Expr b -> Expr b
    Tick CoreTickish
    tickish CoreExpr
    body')
                      -- SourceNotes are best-effort; so we just proceed as usual.
                      -- If we drop a tick due to the issues described below it's
                      -- not the end of the world.

      | CoreTickish
    tickish CoreTickish -> TickishScoping -> Bool
    forall (pass :: TickishPass).
    GenTickish pass -> TickishScoping -> Bool
    `tickishScopesLike` TickishScoping
    SoftScope
      = (UsageDetails -> UsageDetails
    markAllNonTail UsageDetails
    usage, CoreTickish -> CoreExpr -> CoreExpr
    forall b. CoreTickish -> Expr b -> Expr b
    Tick CoreTickish
    tickish CoreExpr
    body')

      | Breakpoint XBreakpoint 'TickishPassCore
    _ JoinArity
    _ [XTickishId 'TickishPassCore]
    ids <- CoreTickish
    tickish
      = (UsageDetails
    usage_lam UsageDetails -> UsageDetails -> UsageDetails
    `andUDs` (CoreBndr -> UsageDetails -> UsageDetails)
    -> UsageDetails -> [CoreBndr] -> UsageDetails
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr CoreBndr -> UsageDetails -> UsageDetails
    addManyOcc UsageDetails
    emptyDetails [CoreBndr]
    [XTickishId 'TickishPassCore]
    ids, CoreTickish -> CoreExpr -> CoreExpr
    forall b. CoreTickish -> Expr b -> Expr b
    Tick CoreTickish
    tickish CoreExpr
    body')
        -- never substitute for any of the Ids in a Breakpoint

      | Bool
    otherwise
      = (UsageDetails
    usage_lam, CoreTickish -> CoreExpr -> CoreExpr
    forall b. CoreTickish -> Expr b -> Expr b
    Tick CoreTickish
    tickish CoreExpr
    body')
      where
        !(UsageDetails
    usage,CoreExpr
    body') = OccEnv -> CoreExpr -> (UsageDetails, CoreExpr)
    occAnal OccEnv
    env CoreExpr
    body
        -- for a non-soft tick scope, we can inline lambdas only
        usage_lam :: UsageDetails
    usage_lam = UsageDetails -> UsageDetails
    markAllNonTail (UsageDetails -> UsageDetails
    markAllInsideLam UsageDetails
    usage)
                      -- TODO There may be ways to make ticks and join points play
                      -- nicer together, but right now there are problems:
                      --   let j x = ... in tick<t> (j 1)
                      -- Making j a join point may cause the simplifier to drop t
                      -- (if the tick is put into the continuation). So we don't
                      -- count j 1 as a tail call.
                      -- See #14242.

    occAnal OccEnv
    env (Cast CoreExpr
    expr CoercionR
    co)
      = case OccEnv -> CoreExpr -> (UsageDetails, CoreExpr)
    occAnal OccEnv
    env CoreExpr
    expr of { (UsageDetails
    usage, CoreExpr
    expr') ->
        let usage1 :: UsageDetails
    usage1 = Bool -> UsageDetails -> UsageDetails
    markAllManyNonTailIf (OccEnv -> Bool
    isRhsEnv OccEnv
    env) UsageDetails
    usage
              -- usage1: if we see let x = y `cast` co
              -- then mark y as 'Many' so that we don't
              -- immediately inline y again.
            usage2 :: UsageDetails
    usage2 = UsageDetails -> VarSet -> UsageDetails
    addManyOccs UsageDetails
    usage1 (CoercionR -> VarSet
    coVarsOfCo CoercionR
    co)
              -- usage2: see Note [Gather occurrences of coercion variables]
        in (UsageDetails -> UsageDetails
    markAllNonTail UsageDetails
    usage2, CoreExpr -> CoercionR -> CoreExpr
    forall b. Expr b -> CoercionR -> Expr b
    Cast CoreExpr
    expr' CoercionR
    co)
        }

    occAnal OccEnv
    env app :: CoreExpr
    app@(App CoreExpr
    _ CoreExpr
    _)
      = OccEnv
    -> (CoreExpr, [CoreExpr], [CoreTickish])
    -> (UsageDetails, CoreExpr)
    occAnalApp OccEnv
    env ((CoreTickish -> Bool)
    -> CoreExpr -> (CoreExpr, [CoreExpr], [CoreTickish])
    forall b.
    (CoreTickish -> Bool)
    -> Expr b -> (Expr b, [Expr b], [CoreTickish])
    collectArgsTicks CoreTickish -> Bool
    forall (pass :: TickishPass). GenTickish pass -> Bool
    tickishFloatable CoreExpr
    app)

    -- Ignore type variables altogether
    --   (a) occurrences inside type lambdas only not marked as InsideLam
    --   (b) type variables not in environment

    occAnal OccEnv
    env (Lam CoreBndr
    x CoreExpr
    body)
      | CoreBndr -> Bool
    isTyVar CoreBndr
    x
      = case OccEnv -> CoreExpr -> (UsageDetails, CoreExpr)
    occAnal OccEnv
    env CoreExpr
    body of { (UsageDetails
    body_usage, CoreExpr
    body') ->
        (UsageDetails -> UsageDetails
    markAllNonTail UsageDetails
    body_usage, CoreBndr -> CoreExpr -> CoreExpr
    forall b. b -> Expr b -> Expr b
    Lam CoreBndr
    x CoreExpr
    body')
        }

    {- Note [Occurrence analysis for lambda binders]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    For value lambdas we do a special hack.  Consider
         (\x. \y. ...x...)
    If we did nothing, x is used inside the \y, so would be marked
    as dangerous to dup.  But in the common case where the abstraction
    is applied to two arguments this is over-pessimistic, which delays
    inlining x, which forces more simplifier iterations.

    So instead, we just mark each binder with its occurrence info in the
    *body* of the multiple lambda.  Then, the simplifier is careful when
    partially applying lambdas. See the calls to zapLamBndrs in
      GHC.Core.Opt.Simplify.simplExprF1
      GHC.Core.SimpleOpt.simple_app
    -}

    occAnal OccEnv
    env expr :: CoreExpr
    expr@(Lam CoreBndr
    _ CoreExpr
    _)
      = -- See Note [Occurrence analysis for lambda binders]
        case OccEnv
    -> [CoreBndr] -> CoreExpr -> (UsageDetails, [CoreBndr], CoreExpr)
    occAnalLamOrRhs OccEnv
    env [CoreBndr]
    bndrs CoreExpr
    body of { (UsageDetails
    usage, [CoreBndr]
    tagged_bndrs, CoreExpr
    body') ->
        let
            expr' :: CoreExpr
    expr'       = [CoreBndr] -> CoreExpr -> CoreExpr
    forall b. [b] -> Expr b -> Expr b
    mkLams [CoreBndr]
    tagged_bndrs CoreExpr
    body'
            usage1 :: UsageDetails
    usage1      = UsageDetails -> UsageDetails
    markAllNonTail UsageDetails
    usage
            one_shot_gp :: Bool
    one_shot_gp = (CoreBndr -> Bool) -> [CoreBndr] -> Bool
    forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
    all CoreBndr -> Bool
    isOneShotBndr [CoreBndr]
    tagged_bndrs
            final_usage :: UsageDetails
    final_usage = Bool -> UsageDetails -> UsageDetails
    markAllInsideLamIf (Bool -> Bool
    not Bool
    one_shot_gp) UsageDetails
    usage1
        in
        (UsageDetails
    final_usage, CoreExpr
    expr') }
      where
        ([CoreBndr]
    bndrs, CoreExpr
    body) = CoreExpr -> ([CoreBndr], CoreExpr)
    forall b. Expr b -> ([b], Expr b)
    collectBinders CoreExpr
    expr

    occAnal OccEnv
    env (Case CoreExpr
    scrut CoreBndr
    bndr Type
    ty [Alt CoreBndr]
    alts)
      = case OccEnv -> CoreExpr -> (UsageDetails, CoreExpr)
    occAnal (OccEnv -> [Alt CoreBndr] -> OccEnv
    scrutCtxt OccEnv
    env [Alt CoreBndr]
    alts) CoreExpr
    scrut of { (UsageDetails
    scrut_usage, CoreExpr
    scrut') ->
        let alt_env :: OccEnv
    alt_env = CoreExpr -> CoreBndr -> OccEnv -> OccEnv
    addBndrSwap CoreExpr
    scrut' CoreBndr
    bndr (OccEnv -> OccEnv) -> OccEnv -> OccEnv
    forall a b. (a -> b) -> a -> b
    $
                      OccEnv
    env { occ_encl :: OccEncl
    occ_encl = OccEncl
    OccVanilla } OccEnv -> [CoreBndr] -> OccEnv
    `addInScope` [CoreBndr
    bndr]
        in
        case (Alt CoreBndr -> (UsageDetails, Alt CoreBndr))
    -> [Alt CoreBndr] -> ([UsageDetails], [Alt CoreBndr])
    forall a b c. (a -> (b, c)) -> [a] -> ([b], [c])
    mapAndUnzip (OccEnv -> Alt CoreBndr -> (UsageDetails, Alt CoreBndr)
    occAnalAlt OccEnv
    alt_env) [Alt CoreBndr]
    alts of { ([UsageDetails]
    alts_usage_s, [Alt CoreBndr]
    alts')   ->
        let
            alts_usage :: UsageDetails
    alts_usage  = (UsageDetails -> UsageDetails -> UsageDetails)
    -> UsageDetails -> [UsageDetails] -> UsageDetails
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr UsageDetails -> UsageDetails -> UsageDetails
    orUDs UsageDetails
    emptyDetails [UsageDetails]
    alts_usage_s
            (UsageDetails
    alts_usage1, CoreBndr
    tagged_bndr) = UsageDetails -> CoreBndr -> (UsageDetails, CoreBndr)
    tagLamBinder UsageDetails
    alts_usage CoreBndr
    bndr
            total_usage :: UsageDetails
    total_usage = UsageDetails -> UsageDetails
    markAllNonTail UsageDetails
    scrut_usage UsageDetails -> UsageDetails -> UsageDetails
    `andUDs` UsageDetails
    alts_usage1
                            -- Alts can have tail calls, but the scrutinee can't
        in
        UsageDetails
    total_usage UsageDetails
    -> (UsageDetails, CoreExpr) -> (UsageDetails, CoreExpr)
    `seq` (UsageDetails
    total_usage, CoreExpr -> CoreBndr -> Type -> [Alt CoreBndr] -> CoreExpr
    forall b. Expr b -> b -> Type -> [Alt b] -> Expr b
    Case CoreExpr
    scrut' CoreBndr
    tagged_bndr Type
    ty [Alt CoreBndr]
    alts') }}

    occAnal OccEnv
    env (Let CoreBind
    bind CoreExpr
    body)
      = case OccEnv -> CoreExpr -> (UsageDetails, CoreExpr)
    occAnal (OccEnv
    env OccEnv -> [CoreBndr] -> OccEnv
    `addInScope` CoreBind -> [CoreBndr]
    forall b. Bind b -> [b]
    bindersOf CoreBind
    bind)
                     CoreExpr
    body                    of { (UsageDetails
    body_usage, CoreExpr
    body') ->
        case OccEnv
    -> TopLevelFlag
    -> ImpRuleEdges
    -> CoreBind
    -> UsageDetails
    -> (UsageDetails, CoreProgram)
    occAnalBind OccEnv
    env TopLevelFlag
    NotTopLevel
                         ImpRuleEdges
    noImpRuleEdges CoreBind
    bind
                         UsageDetails
    body_usage          of { (UsageDetails
    final_usage, CoreProgram
    new_binds) ->
           (UsageDetails
    final_usage, CoreProgram -> CoreExpr -> CoreExpr
    forall b. [Bind b] -> Expr b -> Expr b
    mkLets CoreProgram
    new_binds CoreExpr
    body') }}

    occAnalArgs :: OccEnv -> [CoreExpr] -> [OneShots] -> (UsageDetails, [CoreExpr])
    occAnalArgs :: OccEnv -> [CoreExpr] -> [OneShots] -> (UsageDetails, [CoreExpr])
    occAnalArgs OccEnv
    _ [] [OneShots]
    _
      = (UsageDetails
    emptyDetails, [])

    occAnalArgs OccEnv
    env (CoreExpr
    arg:[CoreExpr]
    args) [OneShots]
    one_shots
      | CoreExpr -> Bool
    forall {b}. Expr b -> Bool
    isTypeArg CoreExpr
    arg
      = case OccEnv -> [CoreExpr] -> [OneShots] -> (UsageDetails, [CoreExpr])
    occAnalArgs OccEnv
    env [CoreExpr]
    args [OneShots]
    one_shots of { (UsageDetails
    uds, [CoreExpr]
    args') ->
        (UsageDetails
    uds, CoreExpr
    argCoreExpr -> [CoreExpr] -> [CoreExpr]
    forall a. a -> [a] -> [a]
    :[CoreExpr]
    args') }

      | Bool
    otherwise
      = case OccEnv -> [OneShots] -> (OccEnv, [OneShots])
    argCtxt OccEnv
    env [OneShots]
    one_shots           of { (OccEnv
    arg_env, [OneShots]
    one_shots') ->
        case OccEnv -> CoreExpr -> (UsageDetails, CoreExpr)
    occAnal OccEnv
    arg_env CoreExpr
    arg             of { (UsageDetails
    uds1, CoreExpr
    arg') ->
        case OccEnv -> [CoreExpr] -> [OneShots] -> (UsageDetails, [CoreExpr])
    occAnalArgs OccEnv
    env [CoreExpr]
    args [OneShots]
    one_shots' of { (UsageDetails
    uds2, [CoreExpr]
    args') ->
        (UsageDetails
    uds1 UsageDetails -> UsageDetails -> UsageDetails
    `andUDs` UsageDetails
    uds2, CoreExpr
    arg'CoreExpr -> [CoreExpr] -> [CoreExpr]
    forall a. a -> [a] -> [a]
    :[CoreExpr]
    args') }}}

    {-
    Applications are dealt with specially because we want
    the "build hack" to work.

    Note [Arguments of let-bound constructors]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider
        f x = let y = expensive x in
              let z = (True,y) in
              (case z of {(p,q)->q}, case z of {(p,q)->q})
    We feel free to duplicate the WHNF (True,y), but that means
    that y may be duplicated thereby.

    If we aren't careful we duplicate the (expensive x) call!
    Constructors are rather like lambdas in this way.
    -}

    occAnalApp :: OccEnv
               -> (Expr CoreBndr, [Arg CoreBndr], [CoreTickish])
               -> (UsageDetails, Expr CoreBndr)
    -- Naked variables (not applied) end up here too
    occAnalApp :: OccEnv
    -> (CoreExpr, [CoreExpr], [CoreTickish])
    -> (UsageDetails, CoreExpr)
    occAnalApp OccEnv
    env (Var CoreBndr
    fun, [CoreExpr]
    args, [CoreTickish]
    ticks)
      -- Account for join arity of runRW# continuation
      -- See Note [Simplification of runRW#]
      --
      -- NB: Do not be tempted to make the next (Var fun, args, tick)
      --     equation into an 'otherwise' clause for this equation
      --     The former has a bang-pattern to occ-anal the args, and
      --     we don't want to occ-anal them twice in the runRW# case!
      --     This caused #18296
      | CoreBndr
    fun CoreBndr -> Unique -> Bool
    forall a. Uniquable a => a -> Unique -> Bool
    `hasKey` Unique
    runRWKey
      , [CoreExpr
    t1, CoreExpr
    t2, CoreExpr
    arg]  <- [CoreExpr]
    args
      , let (UsageDetails
    usage, CoreExpr
    arg') = OccEnv
    -> RecFlag
    -> Maybe JoinArity
    -> CoreExpr
    -> (UsageDetails, CoreExpr)
    occAnalRhs OccEnv
    env RecFlag
    NonRecursive (JoinArity -> Maybe JoinArity
    forall a. a -> Maybe a
    Just JoinArity
    1) CoreExpr
    arg
      = (UsageDetails
    usage, [CoreTickish] -> CoreExpr -> CoreExpr
    mkTicks [CoreTickish]
    ticks (CoreExpr -> CoreExpr) -> CoreExpr -> CoreExpr
    forall a b. (a -> b) -> a -> b
    $ CoreExpr -> [CoreExpr] -> CoreExpr
    forall b. Expr b -> [Expr b] -> Expr b
    mkApps (CoreBndr -> CoreExpr
    forall b. CoreBndr -> Expr b
    Var CoreBndr
    fun) [CoreExpr
    t1, CoreExpr
    t2, CoreExpr
    arg'])

    occAnalApp OccEnv
    env (Var CoreBndr
    fun_id, [CoreExpr]
    args, [CoreTickish]
    ticks)
      = (UsageDetails
    all_uds, [CoreTickish] -> CoreExpr -> CoreExpr
    mkTicks [CoreTickish]
    ticks (CoreExpr -> CoreExpr) -> CoreExpr -> CoreExpr
    forall a b. (a -> b) -> a -> b
    $ CoreExpr -> [CoreExpr] -> CoreExpr
    forall b. Expr b -> [Expr b] -> Expr b
    mkApps CoreExpr
    fun' [CoreExpr]
    args')
      where
        (CoreExpr
    fun', CoreBndr
    fun_id') = OccEnv -> CoreBndr -> (CoreExpr, CoreBndr)
    lookupBndrSwap OccEnv
    env CoreBndr
    fun_id

        fun_uds :: UsageDetails
    fun_uds = CoreBndr -> InterestingCxt -> JoinArity -> UsageDetails
    mkOneOcc CoreBndr
    fun_id' InterestingCxt
    int_cxt JoinArity
    n_args
           -- NB: fun_uds is computed for fun_id', not fun_id
           -- See (BS1) in Note [The binder-swap substitution]

        all_uds :: UsageDetails
    all_uds = UsageDetails
    fun_uds UsageDetails -> UsageDetails -> UsageDetails
    `andUDs` UsageDetails
    final_args_uds

        !(UsageDetails
    args_uds, [CoreExpr]
    args') = OccEnv -> [CoreExpr] -> [OneShots] -> (UsageDetails, [CoreExpr])
    occAnalArgs OccEnv
    env [CoreExpr]
    args [OneShots]
    one_shots
        !final_args_uds :: UsageDetails
    final_args_uds = UsageDetails -> UsageDetails
    markAllNonTail                        (UsageDetails -> UsageDetails) -> UsageDetails -> UsageDetails
    forall a b. (a -> b) -> a -> b
    $
                          Bool -> UsageDetails -> UsageDetails
    markAllInsideLamIf (OccEnv -> Bool
    isRhsEnv OccEnv
    env Bool -> Bool -> Bool
    && Bool
    is_exp) (UsageDetails -> UsageDetails) -> UsageDetails -> UsageDetails
    forall a b. (a -> b) -> a -> b
    $
                          UsageDetails
    args_uds
           -- We mark the free vars of the argument of a constructor or PAP
           -- as "inside-lambda", if it is the RHS of a let(rec).
           -- This means that nothing gets inlined into a constructor or PAP
           -- argument position, which is what we want.  Typically those
           -- constructor arguments are just variables, or trivial expressions.
           -- We use inside-lam because it's like eta-expanding the PAP.
           --
           -- This is the *whole point* of the isRhsEnv predicate
           -- See Note [Arguments of let-bound constructors]

        n_val_args :: JoinArity
    n_val_args = [CoreExpr] -> JoinArity
    forall b. [Arg b] -> JoinArity
    valArgCount [CoreExpr]
    args
        n_args :: JoinArity
    n_args     = [CoreExpr] -> JoinArity
    forall (t :: * -> *) a. Foldable t => t a -> JoinArity
    length [CoreExpr]
    args
        int_cxt :: InterestingCxt
    int_cxt    = case OccEnv -> OccEncl
    occ_encl OccEnv
    env of
                       OccEncl
    OccScrut -> InterestingCxt
    IsInteresting
                       OccEncl
    _other   | JoinArity
    n_val_args JoinArity -> JoinArity -> Bool
    forall a. Ord a => a -> a -> Bool
    > JoinArity
    0 -> InterestingCxt
    IsInteresting
                                | Bool
    otherwise      -> InterestingCxt
    NotInteresting

        is_exp :: Bool
    is_exp     = CheapAppFun
    isExpandableApp CoreBndr
    fun_id JoinArity
    n_val_args
            -- See Note [CONLIKE pragma] in GHC.Types.Basic
            -- The definition of is_exp should match that in GHC.Core.Opt.Simplify.prepareRhs

        one_shots :: [OneShots]
    one_shots  = StrictSig -> JoinArity -> [OneShots]
    argsOneShots (CoreBndr -> StrictSig
    idStrictness CoreBndr
    fun_id) JoinArity
    guaranteed_val_args
        guaranteed_val_args :: JoinArity
    guaranteed_val_args = JoinArity
    n_val_args JoinArity -> JoinArity -> JoinArity
    forall a. Num a => a -> a -> a
    + OneShots -> JoinArity
    forall (t :: * -> *) a. Foldable t => t a -> JoinArity
    length ((OneShotInfo -> Bool) -> OneShots -> OneShots
    forall a. (a -> Bool) -> [a] -> [a]
    takeWhile OneShotInfo -> Bool
    isOneShotInfo
                                                             (OccEnv -> OneShots
    occ_one_shots OccEnv
    env))
            -- See Note [Sources of one-shot information], bullet point A']

    occAnalApp OccEnv
    env (CoreExpr
    fun, [CoreExpr]
    args, [CoreTickish]
    ticks)
      = (UsageDetails -> UsageDetails
    markAllNonTail (UsageDetails
    fun_uds UsageDetails -> UsageDetails -> UsageDetails
    `andUDs` UsageDetails
    args_uds),
         [CoreTickish] -> CoreExpr -> CoreExpr
    mkTicks [CoreTickish]
    ticks (CoreExpr -> CoreExpr) -> CoreExpr -> CoreExpr
    forall a b. (a -> b) -> a -> b
    $ CoreExpr -> [CoreExpr] -> CoreExpr
    forall b. Expr b -> [Expr b] -> Expr b
    mkApps CoreExpr
    fun' [CoreExpr]
    args')
      where
        !(UsageDetails
    fun_uds, CoreExpr
    fun') = OccEnv -> CoreExpr -> (UsageDetails, CoreExpr)
    occAnal (OccEnv -> [CoreExpr] -> OccEnv
    addAppCtxt OccEnv
    env [CoreExpr]
    args) CoreExpr
    fun
            -- The addAppCtxt is a bit cunning.  One iteration of the simplifier
            -- often leaves behind beta redexs like
            --      (\x y -> e) a1 a2
            -- Here we would like to mark x,y as one-shot, and treat the whole
            -- thing much like a let.  We do this by pushing some True items
            -- onto the context stack.
        !(UsageDetails
    args_uds, [CoreExpr]
    args') = OccEnv -> [CoreExpr] -> [OneShots] -> (UsageDetails, [CoreExpr])
    occAnalArgs OccEnv
    env [CoreExpr]
    args []

    {-
    Note [Sources of one-shot information]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    The occurrence analyser obtains one-shot-lambda information from two sources:

    A:  Saturated applications:  eg   f e1 .. en

        In general, given a call (f e1 .. en) we can propagate one-shot info from
        f's strictness signature into e1 .. en, but /only/ if n is enough to
        saturate the strictness signature. A strictness signature like

              f :: C1(C1(L))LS

        means that *if f is applied to three arguments* then it will guarantee to
        call its first argument at most once, and to call the result of that at
        most once. But if f has fewer than three arguments, all bets are off; e.g.

              map (f (\x y. expensive) e2) xs

        Here the \x y abstraction may be called many times (once for each element of
        xs) so we should not mark x and y as one-shot. But if it was

              map (f (\x y. expensive) 3 2) xs

        then the first argument of f will be called at most once.

        The one-shot info, derived from f's strictness signature, is
        computed by 'argsOneShots', called in occAnalApp.

    A': Non-obviously saturated applications: eg    build (f (\x y -> expensive))
        where f is as above.

        In this case, f is only manifestly applied to one argument, so it does not
        look saturated. So by the previous point, we should not use its strictness
        signature to learn about the one-shotness of \x y. But in this case we can:
        build is fully applied, so we may use its strictness signature; and from
        that we learn that build calls its argument with two arguments *at most once*.

        So there is really only one call to f, and it will have three arguments. In
        that sense, f is saturated, and we may proceed as described above.

        Hence the computation of 'guaranteed_val_args' in occAnalApp, using
        '(occ_one_shots env)'.  See also #13227, comment:9

    B:  Let-bindings:  eg   let f = \c. let ... in \n -> blah
                            in (build f, build f)

        Propagate one-shot info from the demanand-info on 'f' to the
        lambdas in its RHS (which may not be syntactically at the top)

        This information must have come from a previous run of the demanand
        analyser.

    Previously, the demand analyser would *also* set the one-shot information, but
    that code was buggy (see #11770), so doing it only in on place, namely here, is
    saner.

    Note [OneShots]
    ~~~~~~~~~~~~~~~
    When analysing an expression, the occ_one_shots argument contains information
    about how the function is being used. The length of the list indicates
    how many arguments will eventually be passed to the analysed expression,
    and the OneShotInfo indicates whether this application is once or multiple times.

    Example:

     Context of f                occ_one_shots when analysing f

     f 1 2                       [OneShot, OneShot]
     map (f 1)                   [OneShot, NoOneShotInfo]
     build f                     [OneShot, OneShot]
     f 1 2 `seq` f 2 1           [NoOneShotInfo, OneShot]

    Note [Binders in case alternatives]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider
        case x of y { (a,b) -> f y }
    We treat 'a', 'b' as dead, because they don't physically occur in the
    case alternative.  (Indeed, a variable is dead iff it doesn't occur in
    its scope in the output of OccAnal.)  It really helps to know when
    binders are unused.  See esp the call to isDeadBinder in
    Simplify.mkDupableAlt

    In this example, though, the Simplifier will bring 'a' and 'b' back to
    life, because it binds 'y' to (a,b) (imagine got inlined and
    scrutinised y).
    -}

    occAnalLamOrRhs :: OccEnv -> [CoreBndr] -> CoreExpr
                    -> (UsageDetails, [CoreBndr], CoreExpr)
    -- Tags the returned binders with their OccInfo, but does
    -- not do any markInsideLam to the returned usage details
    occAnalLamOrRhs :: OccEnv
    -> [CoreBndr] -> CoreExpr -> (UsageDetails, [CoreBndr], CoreExpr)
    occAnalLamOrRhs OccEnv
    env [] CoreExpr
    body
      = case OccEnv -> CoreExpr -> (UsageDetails, CoreExpr)
    occAnal OccEnv
    env CoreExpr
    body of (UsageDetails
    body_usage, CoreExpr
    body') -> (UsageDetails
    body_usage, [], CoreExpr
    body')
          -- RHS of thunk or nullary join point

    occAnalLamOrRhs OccEnv
    env (CoreBndr
    bndr:[CoreBndr]
    bndrs) CoreExpr
    body
      | CoreBndr -> Bool
    isTyVar CoreBndr
    bndr
      = -- Important: Keep the environment so that we don't inline into an RHS like
        --   \(@ x) -> C @x (f @x)
        -- (see the beginning of Note [Cascading inlines]).
        case OccEnv
    -> [CoreBndr] -> CoreExpr -> (UsageDetails, [CoreBndr], CoreExpr)
    occAnalLamOrRhs OccEnv
    env [CoreBndr]
    bndrs CoreExpr
    body of
          (UsageDetails
    body_usage, [CoreBndr]
    bndrs', CoreExpr
    body') -> (UsageDetails
    body_usage, CoreBndr
    bndrCoreBndr -> [CoreBndr] -> [CoreBndr]
    forall a. a -> [a] -> [a]
    :[CoreBndr]
    bndrs', CoreExpr
    body')

    occAnalLamOrRhs OccEnv
    env [CoreBndr]
    binders CoreExpr
    body
      = case OccEnv -> CoreExpr -> (UsageDetails, CoreExpr)
    occAnal OccEnv
    env_body CoreExpr
    body of { (UsageDetails
    body_usage, CoreExpr
    body') ->
        let
            (UsageDetails
    final_usage, [CoreBndr]
    tagged_binders) = UsageDetails -> [CoreBndr] -> (UsageDetails, [CoreBndr])
    tagLamBinders UsageDetails
    body_usage [CoreBndr]
    binders'
                          -- Use binders' to put one-shot info on the lambdas
        in
        (UsageDetails
    final_usage, [CoreBndr]
    tagged_binders, CoreExpr
    body') }
      where
        env1 :: OccEnv
    env1 = OccEnv
    env OccEnv -> [CoreBndr] -> OccEnv
    `addInScope` [CoreBndr]
    binders
        (OccEnv
    env_body, [CoreBndr]
    binders') = OccEnv -> [CoreBndr] -> (OccEnv, [CoreBndr])
    oneShotGroup OccEnv
    env1 [CoreBndr]
    binders

    occAnalAlt :: OccEnv
               -> CoreAlt -> (UsageDetails, Alt IdWithOccInfo)
    occAnalAlt :: OccEnv -> Alt CoreBndr -> (UsageDetails, Alt CoreBndr)
    occAnalAlt OccEnv
    env (Alt AltCon
    con [CoreBndr]
    bndrs CoreExpr
    rhs)
      = case OccEnv -> CoreExpr -> (UsageDetails, CoreExpr)
    occAnal (OccEnv
    env OccEnv -> [CoreBndr] -> OccEnv
    `addInScope` [CoreBndr]
    bndrs) CoreExpr
    rhs of { (UsageDetails
    rhs_usage1, CoreExpr
    rhs1) ->
        let
          (UsageDetails
    alt_usg, [CoreBndr]
    tagged_bndrs) = UsageDetails -> [CoreBndr] -> (UsageDetails, [CoreBndr])
    tagLamBinders UsageDetails
    rhs_usage1 [CoreBndr]
    bndrs
        in                          -- See Note [Binders in case alternatives]
        (UsageDetails
    alt_usg, AltCon -> [CoreBndr] -> CoreExpr -> Alt CoreBndr
    forall b. AltCon -> [b] -> Expr b -> Alt b
    Alt AltCon
    con [CoreBndr]
    tagged_bndrs CoreExpr
    rhs1) }

    {-
    ************************************************************************
    *                                                                      *
                        OccEnv
    *                                                                      *
    ************************************************************************
    -}

    data OccEnv
      = OccEnv { OccEnv -> OccEncl
    occ_encl       :: !OccEncl      -- Enclosing context information
               , OccEnv -> OneShots
    occ_one_shots  :: !OneShots     -- See Note [OneShots]
               , OccEnv -> CoreBndr -> Bool
    occ_unf_act    :: Id -> Bool          -- Which Id unfoldings are active
               , OccEnv -> Activation -> Bool
    occ_rule_act   :: Activation -> Bool  -- Which rules are active
                 -- See Note [Finding rule RHS free vars]

               -- See Note [The binder-swap substitution]
               -- If  x :-> (y, co)  is in the env,
               -- then please replace x by (y |> sym mco)
               -- Invariant of course: idType x = exprType (y |> sym mco)
               , OccEnv -> VarEnv (CoreBndr, MCoercion)
    occ_bs_env  :: VarEnv (OutId, MCoercion)
               , OccEnv -> VarSet
    occ_bs_rng  :: VarSet   -- Vars free in the range of occ_bs_env
                       -- Domain is Global and Local Ids
                       -- Range is just Local Ids
        }

    -----------------------------
    -- OccEncl is used to control whether to inline into constructor arguments
    -- For example:
    --      x = (p,q)               -- Don't inline p or q
    --      y = /\a -> (p a, q a)   -- Still don't inline p or q
    --      z = f (p,q)             -- Do inline p,q; it may make a rule fire
    -- So OccEncl tells enough about the context to know what to do when
    -- we encounter a constructor application or PAP.
    --
    -- OccScrut is used to set the "interesting context" field of OncOcc

    data OccEncl
      = OccRhs         -- RHS of let(rec), albeit perhaps inside a type lambda
                       -- Don't inline into constructor args here

      | OccScrut       -- Scrutintee of a case
                       -- Can inline into constructor args

      | OccVanilla     -- Argument of function, body of lambda, etc
                       -- Do inline into constructor args here

    instance Outputable OccEncl where
      ppr :: OccEncl -> SDoc
    ppr OccEncl
    OccRhs     = String -> SDoc
    text String
    "occRhs"
      ppr OccEncl
    OccScrut   = String -> SDoc
    text String
    "occScrut"
      ppr OccEncl
    OccVanilla = String -> SDoc
    text String
    "occVanilla"

    -- See note [OneShots]
    type OneShots = [OneShotInfo]

    initOccEnv :: OccEnv
    initOccEnv :: OccEnv
    initOccEnv
      = OccEnv { occ_encl :: OccEncl
    occ_encl      = OccEncl
    OccVanilla
               , occ_one_shots :: OneShots
    occ_one_shots = []

                     -- To be conservative, we say that all
                     -- inlines and rules are active
               , occ_unf_act :: CoreBndr -> Bool
    occ_unf_act   = \CoreBndr
    _ -> Bool
    True
               , occ_rule_act :: Activation -> Bool
    occ_rule_act  = \Activation
    _ -> Bool
    True

               , occ_bs_env :: VarEnv (CoreBndr, MCoercion)
    occ_bs_env = VarEnv (CoreBndr, MCoercion)
    forall a. VarEnv a
    emptyVarEnv
               , occ_bs_rng :: VarSet
    occ_bs_rng = VarSet
    emptyVarSet }

    noBinderSwaps :: OccEnv -> Bool
    noBinderSwaps :: OccEnv -> Bool
    noBinderSwaps (OccEnv { occ_bs_env :: OccEnv -> VarEnv (CoreBndr, MCoercion)
    occ_bs_env = VarEnv (CoreBndr, MCoercion)
    bs_env }) = VarEnv (CoreBndr, MCoercion) -> Bool
    forall a. VarEnv a -> Bool
    isEmptyVarEnv VarEnv (CoreBndr, MCoercion)
    bs_env

    scrutCtxt :: OccEnv -> [CoreAlt] -> OccEnv
    scrutCtxt :: OccEnv -> [Alt CoreBndr] -> OccEnv
    scrutCtxt OccEnv
    env [Alt CoreBndr]
    alts
      | Bool
    interesting_alts =  OccEnv
    env { occ_encl :: OccEncl
    occ_encl = OccEncl
    OccScrut,   occ_one_shots :: OneShots
    occ_one_shots = [] }
      | Bool
    otherwise        =  OccEnv
    env { occ_encl :: OccEncl
    occ_encl = OccEncl
    OccVanilla, occ_one_shots :: OneShots
    occ_one_shots = [] }
      where
        interesting_alts :: Bool
    interesting_alts = case [Alt CoreBndr]
    alts of
                             []    -> Bool
    False
                             [Alt CoreBndr
    alt] -> Bool -> Bool
    not (Alt CoreBndr -> Bool
    forall b. Alt b -> Bool
    isDefaultAlt Alt CoreBndr
    alt)
                             [Alt CoreBndr]
    _     -> Bool
    True
         -- 'interesting_alts' is True if the case has at least one
         -- non-default alternative.  That in turn influences
         -- pre/postInlineUnconditionally.  Grep for "occ_int_cxt"!

    rhsCtxt :: OccEnv -> OccEnv
    rhsCtxt :: OccEnv -> OccEnv
    rhsCtxt OccEnv
    env = OccEnv
    env { occ_encl :: OccEncl
    occ_encl = OccEncl
    OccRhs, occ_one_shots :: OneShots
    occ_one_shots = [] }

    argCtxt :: OccEnv -> [OneShots] -> (OccEnv, [OneShots])
    argCtxt :: OccEnv -> [OneShots] -> (OccEnv, [OneShots])
    argCtxt OccEnv
    env []
      = (OccEnv
    env { occ_encl :: OccEncl
    occ_encl = OccEncl
    OccVanilla, occ_one_shots :: OneShots
    occ_one_shots = [] }, [])
    argCtxt OccEnv
    env (OneShots
    one_shots:[OneShots]
    one_shots_s)
      = (OccEnv
    env { occ_encl :: OccEncl
    occ_encl = OccEncl
    OccVanilla, occ_one_shots :: OneShots
    occ_one_shots = OneShots
    one_shots }, [OneShots]
    one_shots_s)

    isRhsEnv :: OccEnv -> Bool
    isRhsEnv :: OccEnv -> Bool
    isRhsEnv (OccEnv { occ_encl :: OccEnv -> OccEncl
    occ_encl = OccEncl
    cxt }) = case OccEncl
    cxt of
                                              OccEncl
    OccRhs -> Bool
    True
                                              OccEncl
    _      -> Bool
    False

    addInScope :: OccEnv -> [Var] -> OccEnv
    -- See Note [The binder-swap substitution]
    addInScope :: OccEnv -> [CoreBndr] -> OccEnv
    addInScope env :: OccEnv
    env@(OccEnv { occ_bs_env :: OccEnv -> VarEnv (CoreBndr, MCoercion)
    occ_bs_env = VarEnv (CoreBndr, MCoercion)
    swap_env, occ_bs_rng :: OccEnv -> VarSet
    occ_bs_rng = VarSet
    rng_vars }) [CoreBndr]
    bndrs
      | (CoreBndr -> Bool) -> [CoreBndr] -> Bool
    forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
    any (CoreBndr -> VarSet -> Bool
    `elemVarSet` VarSet
    rng_vars) [CoreBndr]
    bndrs = OccEnv
    env { occ_bs_env :: VarEnv (CoreBndr, MCoercion)
    occ_bs_env = VarEnv (CoreBndr, MCoercion)
    forall a. VarEnv a
    emptyVarEnv, occ_bs_rng :: VarSet
    occ_bs_rng = VarSet
    emptyVarSet }
      | Bool
    otherwise                         = OccEnv
    env { occ_bs_env :: VarEnv (CoreBndr, MCoercion)
    occ_bs_env = VarEnv (CoreBndr, MCoercion)
    swap_env VarEnv (CoreBndr, MCoercion)
    -> [CoreBndr] -> VarEnv (CoreBndr, MCoercion)
    forall a. VarEnv a -> [CoreBndr] -> VarEnv a
    `delVarEnvList` [CoreBndr]
    bndrs }

    oneShotGroup :: OccEnv -> [CoreBndr]
                 -> ( OccEnv
                    , [CoreBndr] )
            -- The result binders have one-shot-ness set that they might not have had originally.
            -- This happens in (build (\c n -> e)).  Here the occurrence analyser
            -- linearity context knows that c,n are one-shot, and it records that fact in
            -- the binder. This is useful to guide subsequent float-in/float-out transformations

    oneShotGroup :: OccEnv -> [CoreBndr] -> (OccEnv, [CoreBndr])
    oneShotGroup env :: OccEnv
    env@(OccEnv { occ_one_shots :: OccEnv -> OneShots
    occ_one_shots = OneShots
    ctxt }) [CoreBndr]
    bndrs
      = OneShots -> [CoreBndr] -> [CoreBndr] -> (OccEnv, [CoreBndr])
    go OneShots
    ctxt [CoreBndr]
    bndrs []
      where
        go :: OneShots -> [CoreBndr] -> [CoreBndr] -> (OccEnv, [CoreBndr])
    go OneShots
    ctxt [] [CoreBndr]
    rev_bndrs
          = ( OccEnv
    env { occ_one_shots :: OneShots
    occ_one_shots = OneShots
    ctxt, occ_encl :: OccEncl
    occ_encl = OccEncl
    OccVanilla }
            , [CoreBndr] -> [CoreBndr]
    forall a. [a] -> [a]
    reverse [CoreBndr]
    rev_bndrs )

        go [] [CoreBndr]
    bndrs [CoreBndr]
    rev_bndrs
          = ( OccEnv
    env { occ_one_shots :: OneShots
    occ_one_shots = [], occ_encl :: OccEncl
    occ_encl = OccEncl
    OccVanilla }
            , [CoreBndr] -> [CoreBndr]
    forall a. [a] -> [a]
    reverse [CoreBndr]
    rev_bndrs [CoreBndr] -> [CoreBndr] -> [CoreBndr]
    forall a. [a] -> [a] -> [a]
    ++ [CoreBndr]
    bndrs )

        go ctxt :: OneShots
    ctxt@(OneShotInfo
    one_shot : OneShots
    ctxt') (CoreBndr
    bndr : [CoreBndr]
    bndrs) [CoreBndr]
    rev_bndrs
          | CoreBndr -> Bool
    isId CoreBndr
    bndr = OneShots -> [CoreBndr] -> [CoreBndr] -> (OccEnv, [CoreBndr])
    go OneShots
    ctxt' [CoreBndr]
    bndrs (CoreBndr
    bndr'CoreBndr -> [CoreBndr] -> [CoreBndr]
    forall a. a -> [a] -> [a]
    : [CoreBndr]
    rev_bndrs)
          | Bool
    otherwise = OneShots -> [CoreBndr] -> [CoreBndr] -> (OccEnv, [CoreBndr])
    go OneShots
    ctxt  [CoreBndr]
    bndrs (CoreBndr
    bndr CoreBndr -> [CoreBndr] -> [CoreBndr]
    forall a. a -> [a] -> [a]
    : [CoreBndr]
    rev_bndrs)
          where
            bndr' :: CoreBndr
    bndr' = CoreBndr -> OneShotInfo -> CoreBndr
    updOneShotInfo CoreBndr
    bndr OneShotInfo
    one_shot
                   -- Use updOneShotInfo, not setOneShotInfo, as pre-existing
                   -- one-shot info might be better than what we can infer, e.g.
                   -- due to explicit use of the magic 'oneShot' function.
                   -- See Note [The oneShot function]

    markJoinOneShots :: Maybe JoinArity -> [Var] -> [Var]
    -- Mark the lambdas of a non-recursive join point as one-shot.
    -- This is good to prevent gratuitous float-out etc
    markJoinOneShots :: Maybe JoinArity -> [CoreBndr] -> [CoreBndr]
    markJoinOneShots Maybe JoinArity
    mb_join_arity [CoreBndr]
    bndrs
      = case Maybe JoinArity
    mb_join_arity of
          Maybe JoinArity
    Nothing -> [CoreBndr]
    bndrs
          Just JoinArity
    n  -> JoinArity -> [CoreBndr] -> [CoreBndr]
    forall {t}. (Eq t, Num t) => t -> [CoreBndr] -> [CoreBndr]
    go JoinArity
    n [CoreBndr]
    bndrs
     where
       go :: t -> [CoreBndr] -> [CoreBndr]
    go t
    0 [CoreBndr]
    bndrs  = [CoreBndr]
    bndrs
       go t
    _ []     = [] -- This can legitimately happen.
                        -- e.g.    let j = case ... in j True
                        -- This will become an arity-1 join point after the
                        -- simplifier has eta-expanded it; but it may not have
                        -- enough lambdas /yet/. (Lint checks that JoinIds do
                        -- have enough lambdas.)
       go t
    n (CoreBndr
    b:[CoreBndr]
    bs) = CoreBndr
    b' CoreBndr -> [CoreBndr] -> [CoreBndr]
    forall a. a -> [a] -> [a]
    : t -> [CoreBndr] -> [CoreBndr]
    go (t
    nt -> t -> t
    forall a. Num a => a -> a -> a
    -t
    1) [CoreBndr]
    bs
         where
           b' :: CoreBndr
    b' | CoreBndr -> Bool
    isId CoreBndr
    b    = CoreBndr -> CoreBndr
    setOneShotLambda CoreBndr
    b
              | Bool
    otherwise = CoreBndr
    b

    addAppCtxt :: OccEnv -> [Arg CoreBndr] -> OccEnv
    addAppCtxt :: OccEnv -> [CoreExpr] -> OccEnv
    addAppCtxt env :: OccEnv
    env@(OccEnv { occ_one_shots :: OccEnv -> OneShots
    occ_one_shots = OneShots
    ctxt }) [CoreExpr]
    args
      = OccEnv
    env { occ_one_shots :: OneShots
    occ_one_shots = JoinArity -> OneShotInfo -> OneShots
    forall a. JoinArity -> a -> [a]
    replicate ([CoreExpr] -> JoinArity
    forall b. [Arg b] -> JoinArity
    valArgCount [CoreExpr]
    args) OneShotInfo
    OneShotLam OneShots -> OneShots -> OneShots
    forall a. [a] -> [a] -> [a]
    ++ OneShots
    ctxt }

    --------------------
    transClosureFV :: VarEnv VarSet -> VarEnv VarSet
    -- If (f,g), (g,h) are in the input, then (f,h) is in the output
    --                                   as well as (f,g), (g,h)
    transClosureFV :: VarEnv VarSet -> VarEnv VarSet
    transClosureFV VarEnv VarSet
    env
      | Bool
    no_change = VarEnv VarSet
    env
      | Bool
    otherwise = VarEnv VarSet -> VarEnv VarSet
    transClosureFV ([(Unique, VarSet)] -> VarEnv VarSet
    forall elt key. [(Unique, elt)] -> UniqFM key elt
    listToUFM_Directly [(Unique, VarSet)]
    new_fv_list)
      where
        (Bool
    no_change, [(Unique, VarSet)]
    new_fv_list) = (Bool -> (Unique, VarSet) -> (Bool, (Unique, VarSet)))
    -> Bool -> [(Unique, VarSet)] -> (Bool, [(Unique, VarSet)])
    forall (t :: * -> *) a b c.
    Traversable t =>
    (a -> b -> (a, c)) -> a -> t b -> (a, t c)
    mapAccumL Bool -> (Unique, VarSet) -> (Bool, (Unique, VarSet))
    bump Bool
    True (VarEnv VarSet -> [(Unique, VarSet)]
    forall key elt. UniqFM key elt -> [(Unique, elt)]
    nonDetUFMToList VarEnv VarSet
    env)
          -- It's OK to use nonDetUFMToList here because we'll forget the
          -- ordering by creating a new set with listToUFM
        bump :: Bool -> (Unique, VarSet) -> (Bool, (Unique, VarSet))
    bump Bool
    no_change (Unique
    b,VarSet
    fvs)
          | Bool
    no_change_here = (Bool
    no_change, (Unique
    b,VarSet
    fvs))
          | Bool
    otherwise      = (Bool
    False,     (Unique
    b,VarSet
    new_fvs))
          where
            (VarSet
    new_fvs, Bool
    no_change_here) = VarEnv VarSet -> VarSet -> (VarSet, Bool)
    extendFvs VarEnv VarSet
    env VarSet
    fvs

    -------------
    extendFvs_ :: VarEnv VarSet -> VarSet -> VarSet
    extendFvs_ :: VarEnv VarSet -> VarSet -> VarSet
    extendFvs_ VarEnv VarSet
    env VarSet
    s = (VarSet, Bool) -> VarSet
    forall a b. (a, b) -> a
    fst (VarEnv VarSet -> VarSet -> (VarSet, Bool)
    extendFvs VarEnv VarSet
    env VarSet
    s)   -- Discard the Bool flag

    extendFvs :: VarEnv VarSet -> VarSet -> (VarSet, Bool)
    -- (extendFVs env s) returns
    --     (s `union` env(s), env(s) `subset` s)
    extendFvs :: VarEnv VarSet -> VarSet -> (VarSet, Bool)
    extendFvs VarEnv VarSet
    env VarSet
    s
      | VarEnv VarSet -> Bool
    forall key elt. UniqFM key elt -> Bool
    isNullUFM VarEnv VarSet
    env
      = (VarSet
    s, Bool
    True)
      | Bool
    otherwise
      = (VarSet
    s VarSet -> VarSet -> VarSet
    `unionVarSet` VarSet
    extras, VarSet
    extras VarSet -> VarSet -> Bool
    `subVarSet` VarSet
    s)
      where
        extras :: VarSet    -- env(s)
        extras :: VarSet
    extras = (VarSet -> VarSet -> VarSet) -> VarSet -> VarEnv VarSet -> VarSet
    forall elt a key. (elt -> a -> a) -> a -> UniqFM key elt -> a
    nonDetStrictFoldUFM VarSet -> VarSet -> VarSet
    unionVarSet VarSet
    emptyVarSet (VarEnv VarSet -> VarSet) -> VarEnv VarSet -> VarSet
    forall a b. (a -> b) -> a -> b
    $
          -- It's OK to use nonDetStrictFoldUFM here because unionVarSet commutes
                 (VarSet -> CoreBndr -> VarSet)
    -> VarEnv VarSet -> VarEnv CoreBndr -> VarEnv VarSet
    forall elt1 elt2 elt3 key.
    (elt1 -> elt2 -> elt3)
    -> UniqFM key elt1 -> UniqFM key elt2 -> UniqFM key elt3
    intersectUFM_C (\VarSet
    x CoreBndr
    _ -> VarSet
    x) VarEnv VarSet
    env (VarSet -> VarEnv CoreBndr
    forall a. UniqSet a -> UniqFM a a
    getUniqSet VarSet
    s)

    {-
    ************************************************************************
    *                                                                      *
                        Binder swap
    *                                                                      *
    ************************************************************************

    Note [Binder swap]
    ~~~~~~~~~~~~~~~~~~
    The "binder swap" transformation swaps occurrence of the
    scrutinee of a case for occurrences of the case-binder:

     (1)  case x of b { pi -> ri }
             ==>
          case x of b { pi -> ri[b/x] }

     (2)  case (x |> co) of b { pi -> ri }
            ==>
          case (x |> co) of b { pi -> ri[b |> sym co/x] }

    The substitution ri[b/x] etc is done by the occurrence analyser.
    See Note [The binder-swap substitution].

    There are two reasons for making this swap:

    (A) It reduces the number of occurrences of the scrutinee, x.
        That in turn might reduce its occurrences to one, so we
        can inline it and save an allocation.  E.g.
          let x = factorial y in case x of b { I# v -> ...x... }
        If we replace 'x' by 'b' in the alternative we get
          let x = factorial y in case x of b { I# v -> ...b... }
        and now we can inline 'x', thus
          case (factorial y) of b { I# v -> ...b... }

    (B) The case-binder b has unfolding information; in the
        example above we know that b = I# v. That in turn allows
        nested cases to simplify.  Consider
           case x of b { I# v ->
           ...(case x of b2 { I# v2 -> rhs })...
        If we replace 'x' by 'b' in the alternative we get
           case x of b { I# v ->
           ...(case b of b2 { I# v2 -> rhs })...
        and now it is trivial to simplify the inner case:
           case x of b { I# v ->
           ...(let b2 = b in rhs)...

        The same can happen even if the scrutinee is a variable
        with a cast: see Note [Case of cast]

    The reason for doing these transformations /here in the occurrence
    analyser/ is because it allows us to adjust the OccInfo for 'x' and
    'b' as we go.

      * Suppose the only occurrences of 'x' are the scrutinee and in the
        ri; then this transformation makes it occur just once, and hence
        get inlined right away.

      * If instead the Simplifier replaces occurrences of x with
        occurrences of b, that will mess up b's occurrence info. That in
        turn might have consequences.

    There is a danger though.  Consider
          let v = x +# y
          in case (f v) of w -> ...v...v...
    And suppose that (f v) expands to just v.  Then we'd like to
    use 'w' instead of 'v' in the alternative.  But it may be too
    late; we may have substituted the (cheap) x+#y for v in the
    same simplifier pass that reduced (f v) to v.

    I think this is just too bad.  CSE will recover some of it.

    Note [The binder-swap substitution]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    The binder-swap is implemented by the occ_bs_env field of OccEnv.
    There are two main pieces:

    * Given    case x |> co of b { alts }
      we add [x :-> (b, co)] to the occ_bs_env environment; this is
      done by addBndrSwap.

    * Then, at an occurrence of a variable, we look up in the occ_bs_env
      to perform the swap. This is done by lookupBndrSwap.

    Some tricky corners:

    (BS1) We do the substitution before gathering occurrence info. So in
          the above example, an occurrence of x turns into an occurrence
          of b, and that's what we gather in the UsageDetails.  It's as
          if the binder-swap occurred before occurrence analysis. See
          the computation of fun_uds in occAnalApp.

    (BS2) When doing a lookup in occ_bs_env, we may need to iterate,
          as you can see implemented in lookupBndrSwap.  Why?
          Consider   case x of a { 1# -> e1; DEFAULT ->
                     case x of b { 2# -> e2; DEFAULT ->
                     case x of c { 3# -> e3; DEFAULT -> ..x..a..b.. }}}
          At the first case addBndrSwap will extend occ_bs_env with
              [x :-> a]
          At the second case we occ-anal the scrutinee 'x', which looks up
            'x in occ_bs_env, returning 'a', as it should.
          Then addBndrSwap will add [a :-> b] to occ_bs_env, yielding
             occ_bs_env = [x :-> a, a :-> b]
          At the third case we'll again look up 'x' which returns 'a'.
          But we don't want to stop the lookup there, else we'll end up with
                     case x of a { 1# -> e1; DEFAULT ->
                     case a of b { 2# -> e2; DEFAULT ->
                     case a of c { 3# -> e3; DEFAULT -> ..a..b..c.. }}}
          Instead, we want iterate the lookup in addBndrSwap, to give
                     case x of a { 1# -> e1; DEFAULT ->
                     case a of b { 2# -> e2; DEFAULT ->
                     case b of c { 3# -> e3; DEFAULT -> ..c..c..c.. }}}
          This makes a particular difference for case-merge, which works
          only if the scrutinee is the case-binder of the immediately enclosing
          case (Note [Merge Nested Cases] in GHC.Core.Opt.Simplify.Utils
          See #19581 for the bug report that showed this up.

    (BS3) We need care when shadowing.  Suppose [x :-> b] is in occ_bs_env,
          and we encounter:
             - \x. blah
               Here we want to delete the x-binding from occ_bs_env

             - \b. blah
               This is harder: we really want to delete all bindings that
               have 'b' free in the range.  That is a bit tiresome to implement,
               so we compromise.  We keep occ_bs_rng, which is the set of
               free vars of rng(occc_bs_env).  If a binder shadows any of these
               variables, we discard all of occ_bs_env.  Safe, if a bit
               brutal.  NB, however: the simplifer de-shadows the code, so the
               next time around this won't happen.

          These checks are implemented in addInScope.

          The occurrence analyser itself does /not/ do cloning. It could, in
          principle, but it'd make it a bit more complicated and there is no
          great benefit. The simplifer uses cloning to get a no-shadowing
          situation, the care-when-shadowing behaviour above isn't needed for
          long.

    (BS4) The domain of occ_bs_env can include GlobaIds.  Eg
             case M.foo of b { alts }
          We extend occ_bs_env with [M.foo :-> b].  That's fine.

    (BS5) We have to apply the occ_bs_env substitution uniformly,
          including to (local) rules and unfoldings.

    Historical note
    ---------------
    We used to do the binder-swap transformation by introducing
    a proxy let-binding, thus;

       case x of b { pi -> ri }
          ==>
       case x of b { pi -> let x = b in ri }

    But that had two problems:

    1. If 'x' is an imported GlobalId, we'd end up with a GlobalId
       on the LHS of a let-binding which isn't allowed.  We worked
       around this for a while by "localising" x, but it turned
       out to be very painful #16296,

    2. In CorePrep we use the occurrence analyser to do dead-code
       elimination (see Note [Dead code in CorePrep]).  But that
       occasionally led to an unlifted let-binding
           case x of b { DEFAULT -> let x::Int# = b in ... }
       which disobeys one of CorePrep's output invariants (no unlifted
       let-bindings) -- see #5433.

    Doing a substitution (via occ_bs_env) is much better.

    Note [Case of cast]
    ~~~~~~~~~~~~~~~~~~~
    Consider        case (x `cast` co) of b { I# ->
                    ... (case (x `cast` co) of {...}) ...
    We'd like to eliminate the inner case.  That is the motivation for
    equation (2) in Note [Binder swap].  When we get to the inner case, we
    inline x, cancel the casts, and away we go.

    Note [Zap case binders in proxy bindings]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    From the original
         case x of cb(dead) { p -> ...x... }
    we will get
         case x of cb(live) { p -> ...cb... }

    Core Lint never expects to find an *occurrence* of an Id marked
    as Dead, so we must zap the OccInfo on cb before making the
    binding x = cb.  See #5028.

    NB: the OccInfo on /occurrences/ really doesn't matter much; the simplifier
    doesn't use it. So this is only to satisfy the perhaps-over-picky Lint.

    Historical note [no-case-of-case]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    We *used* to suppress the binder-swap in case expressions when
    -fno-case-of-case is on.  Old remarks:
        "This happens in the first simplifier pass,
        and enhances full laziness.  Here's the bad case:
                f = \ y -> ...(case x of I# v -> ...(case x of ...) ... )
        If we eliminate the inner case, we trap it inside the I# v -> arm,
        which might prevent some full laziness happening.  I've seen this
        in action in spectral/cichelli/Prog.hs:
                 [(m,n) | m <- [1..max], n <- [1..max]]
        Hence the check for NoCaseOfCase."
    However, now the full-laziness pass itself reverses the binder-swap, so this
    check is no longer necessary.

    Historical note [Suppressing the case binder-swap]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    This old note describes a problem that is also fixed by doing the
    binder-swap in OccAnal:

        There is another situation when it might make sense to suppress the
        case-expression binde-swap. If we have

            case x of w1 { DEFAULT -> case x of w2 { A -> e1; B -> e2 }
                           ...other cases .... }

        We'll perform the binder-swap for the outer case, giving

            case x of w1 { DEFAULT -> case w1 of w2 { A -> e1; B -> e2 }
                           ...other cases .... }

        But there is no point in doing it for the inner case, because w1 can't
        be inlined anyway.  Furthermore, doing the case-swapping involves
        zapping w2's occurrence info (see paragraphs that follow), and that
        forces us to bind w2 when doing case merging.  So we get

            case x of w1 { A -> let w2 = w1 in e1
                           B -> let w2 = w1 in e2
                           ...other cases .... }

        This is plain silly in the common case where w2 is dead.

        Even so, I can't see a good way to implement this idea.  I tried
        not doing the binder-swap if the scrutinee was already evaluated
        but that failed big-time:

                data T = MkT !Int

                case v of w  { MkT x ->
                case x of x1 { I# y1 ->
                case x of x2 { I# y2 -> ...

        Notice that because MkT is strict, x is marked "evaluated".  But to
        eliminate the last case, we must either make sure that x (as well as
        x1) has unfolding MkT y1.  The straightforward thing to do is to do
        the binder-swap.  So this whole note is a no-op.

    It's fixed by doing the binder-swap in OccAnal because we can do the
    binder-swap unconditionally and still get occurrence analysis
    information right.
    -}

    addBndrSwap :: OutExpr -> Id -> OccEnv -> OccEnv
    -- See Note [The binder-swap substitution]
    addBndrSwap :: CoreExpr -> CoreBndr -> OccEnv -> OccEnv
    addBndrSwap CoreExpr
    scrut CoreBndr
    case_bndr
                env :: OccEnv
    env@(OccEnv { occ_bs_env :: OccEnv -> VarEnv (CoreBndr, MCoercion)
    occ_bs_env = VarEnv (CoreBndr, MCoercion)
    swap_env, occ_bs_rng :: OccEnv -> VarSet
    occ_bs_rng = VarSet
    rng_vars })
      | Just (CoreBndr
    scrut_var, MCoercion
    mco) <- CoreExpr -> Maybe (CoreBndr, MCoercion)
    get_scrut_var ((CoreTickish -> Bool) -> CoreExpr -> CoreExpr
    forall b. (CoreTickish -> Bool) -> Expr b -> Expr b
    stripTicksTopE (Bool -> CoreTickish -> Bool
    forall a b. a -> b -> a
    const Bool
    True) CoreExpr
    scrut)
      , CoreBndr
    scrut_var CoreBndr -> CoreBndr -> Bool
    forall a. Eq a => a -> a -> Bool
    /= CoreBndr
    case_bndr
          -- Consider: case x of x { ... }
          -- Do not add [x :-> x] to occ_bs_env, else lookupBndrSwap will loop
      = OccEnv
    env { occ_bs_env :: VarEnv (CoreBndr, MCoercion)
    occ_bs_env = VarEnv (CoreBndr, MCoercion)
    -> CoreBndr
    -> (CoreBndr, MCoercion)
    -> VarEnv (CoreBndr, MCoercion)
    forall a. VarEnv a -> CoreBndr -> a -> VarEnv a
    extendVarEnv VarEnv (CoreBndr, MCoercion)
    swap_env CoreBndr
    scrut_var (CoreBndr
    case_bndr', MCoercion
    mco)
            , occ_bs_rng :: VarSet
    occ_bs_rng = VarSet
    rng_vars VarSet -> CoreBndr -> VarSet
    `extendVarSet` CoreBndr
    case_bndr'
                           VarSet -> VarSet -> VarSet
    `unionVarSet` MCoercion -> VarSet
    tyCoVarsOfMCo MCoercion
    mco }

      | Bool
    otherwise
      = OccEnv
    env
      where
        get_scrut_var :: OutExpr -> Maybe (OutVar, MCoercion)
        get_scrut_var :: CoreExpr -> Maybe (CoreBndr, MCoercion)
    get_scrut_var (Var CoreBndr
    v)           = (CoreBndr, MCoercion) -> Maybe (CoreBndr, MCoercion)
    forall a. a -> Maybe a
    Just (CoreBndr
    v, MCoercion
    MRefl)
        get_scrut_var (Cast (Var CoreBndr
    v) CoercionR
    co) = (CoreBndr, MCoercion) -> Maybe (CoreBndr, MCoercion)
    forall a. a -> Maybe a
    Just (CoreBndr
    v, CoercionR -> MCoercion
    MCo CoercionR
    co) -- See Note [Case of cast]
        get_scrut_var CoreExpr
    _                 = Maybe (CoreBndr, MCoercion)
    forall a. Maybe a
    Nothing

        case_bndr' :: CoreBndr
    case_bndr' = CoreBndr -> CoreBndr
    zapIdOccInfo CoreBndr
    case_bndr
                     -- See Note [Zap case binders in proxy bindings]

    lookupBndrSwap :: OccEnv -> Id -> (CoreExpr, Id)
    -- See Note [The binder-swap substitution]
    -- Returns an expression of the same type as Id
    lookupBndrSwap :: OccEnv -> CoreBndr -> (CoreExpr, CoreBndr)
    lookupBndrSwap env :: OccEnv
    env@(OccEnv { occ_bs_env :: OccEnv -> VarEnv (CoreBndr, MCoercion)
    occ_bs_env = VarEnv (CoreBndr, MCoercion)
    bs_env })  CoreBndr
    bndr
      = case VarEnv (CoreBndr, MCoercion)
    -> CoreBndr -> Maybe (CoreBndr, MCoercion)
    forall a. VarEnv a -> CoreBndr -> Maybe a
    lookupVarEnv VarEnv (CoreBndr, MCoercion)
    bs_env CoreBndr
    bndr of {
           Maybe (CoreBndr, MCoercion)
    Nothing           -> (CoreBndr -> CoreExpr
    forall b. CoreBndr -> Expr b
    Var CoreBndr
    bndr, CoreBndr
    bndr) ;
           Just (CoreBndr
    bndr1, MCoercion
    mco) ->

        -- Why do we iterate here?
        -- See (BS2) in Note [The binder-swap substitution]
        case OccEnv -> CoreBndr -> (CoreExpr, CoreBndr)
    lookupBndrSwap OccEnv
    env CoreBndr
    bndr1 of
          (CoreExpr
    fun, CoreBndr
    fun_id) -> (CoreExpr -> MCoercion -> CoreExpr
    forall {b}. Expr b -> MCoercion -> Expr b
    add_cast CoreExpr
    fun MCoercion
    mco, CoreBndr
    fun_id) }

      where
        add_cast :: Expr b -> MCoercion -> Expr b
    add_cast Expr b
    fun MCoercion
    MRefl    = Expr b
    fun
        add_cast Expr b
    fun (MCo CoercionR
    co) = Expr b -> CoercionR -> Expr b
    forall b. Expr b -> CoercionR -> Expr b
    Cast Expr b
    fun (CoercionR -> CoercionR
    mkSymCo CoercionR
    co)
        -- We must switch that 'co' to 'sym co';
        -- see the comment with occ_bs_env
        -- No need to test for isReflCo, because 'co' came from
        -- a (Cast e co) and hence is unlikely to be Refl

    {-
    ************************************************************************
    *                                                                      *
    \subsection[OccurAnal-types]{OccEnv}
    *                                                                      *
    ************************************************************************

    Note [UsageDetails and zapping]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    On many occasions, we must modify all gathered occurrence data at once. For
    instance, all occurrences underneath a (non-one-shot) lambda set the
    'occ_in_lam' flag to become 'True'. We could use 'mapVarEnv' to do this, but
    that takes O(n) time and we will do this often---in particular, there are many
    places where tail calls are not allowed, and each of these causes all variables
    to get marked with 'NoTailCallInfo'.

    Instead of relying on `mapVarEnv`, then, we carry three 'IdEnv's around along
    with the 'OccInfoEnv'. Each of these extra environments is a "zapped set"
    recording which variables have been zapped in some way. Zapping all occurrence
    info then simply means setting the corresponding zapped set to the whole
    'OccInfoEnv', a fast O(1) operation.
    -}

    type OccInfoEnv = IdEnv OccInfo -- A finite map from ids to their usage
                    -- INVARIANT: never IAmDead
                    -- (Deadness is signalled by not being in the map at all)

    type ZappedSet = OccInfoEnv -- Values are ignored

    data UsageDetails
      = UD { UsageDetails -> OccInfoEnv
    ud_env       :: !OccInfoEnv
           , UsageDetails -> OccInfoEnv
    ud_z_many    :: ZappedSet   -- apply 'markMany' to these
           , UsageDetails -> OccInfoEnv
    ud_z_in_lam  :: ZappedSet   -- apply 'markInsideLam' to these
           , UsageDetails -> OccInfoEnv
    ud_z_no_tail :: ZappedSet } -- apply 'markNonTail' to these
      -- INVARIANT: All three zapped sets are subsets of the OccInfoEnv

    instance Outputable UsageDetails where
      ppr :: UsageDetails -> SDoc
    ppr UsageDetails
    ud = OccInfoEnv -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr (UsageDetails -> OccInfoEnv
    ud_env (UsageDetails -> UsageDetails
    flattenUsageDetails UsageDetails
    ud))

    -------------------
    -- UsageDetails API

    andUDs, orUDs
            :: UsageDetails -> UsageDetails -> UsageDetails
    andUDs :: UsageDetails -> UsageDetails -> UsageDetails
    andUDs = (OccInfo -> OccInfo -> OccInfo)
    -> UsageDetails -> UsageDetails -> UsageDetails
    combineUsageDetailsWith OccInfo -> OccInfo -> OccInfo
    addOccInfo
    orUDs :: UsageDetails -> UsageDetails -> UsageDetails
    orUDs  = (OccInfo -> OccInfo -> OccInfo)
    -> UsageDetails -> UsageDetails -> UsageDetails
    combineUsageDetailsWith OccInfo -> OccInfo -> OccInfo
    orOccInfo

    mkOneOcc ::Id -> InterestingCxt -> JoinArity -> UsageDetails
    mkOneOcc :: CoreBndr -> InterestingCxt -> JoinArity -> UsageDetails
    mkOneOcc CoreBndr
    id InterestingCxt
    int_cxt JoinArity
    arity
      | CoreBndr -> Bool
    isLocalId CoreBndr
    id
      = UsageDetails
    emptyDetails { ud_env :: OccInfoEnv
    ud_env = CoreBndr -> OccInfo -> OccInfoEnv
    forall a. CoreBndr -> a -> VarEnv a
    unitVarEnv CoreBndr
    id OccInfo
    occ_info }
      | Bool
    otherwise
      = UsageDetails
    emptyDetails
      where
        occ_info :: OccInfo
    occ_info = OneOcc { occ_in_lam :: InsideLam
    occ_in_lam  = InsideLam
    NotInsideLam
                          , occ_n_br :: JoinArity
    occ_n_br    = JoinArity
    oneBranch
                          , occ_int_cxt :: InterestingCxt
    occ_int_cxt = InterestingCxt
    int_cxt
                          , occ_tail :: TailCallInfo
    occ_tail    = JoinArity -> TailCallInfo
    AlwaysTailCalled JoinArity
    arity }

    addManyOccId :: UsageDetails -> Id -> UsageDetails
    -- Add the non-committal (id :-> noOccInfo) to the usage details
    addManyOccId :: UsageDetails -> CoreBndr -> UsageDetails
    addManyOccId UsageDetails
    ud CoreBndr
    id = UsageDetails
    ud { ud_env :: OccInfoEnv
    ud_env = OccInfoEnv -> CoreBndr -> OccInfo -> OccInfoEnv
    forall a. VarEnv a -> CoreBndr -> a -> VarEnv a
    extendVarEnv (UsageDetails -> OccInfoEnv
    ud_env UsageDetails
    ud) CoreBndr
    id OccInfo
    noOccInfo }

    -- Add several occurrences, assumed not to be tail calls
    addManyOcc :: Var -> UsageDetails -> UsageDetails
    addManyOcc :: CoreBndr -> UsageDetails -> UsageDetails
    addManyOcc CoreBndr
    v UsageDetails
    u | CoreBndr -> Bool
    isId CoreBndr
    v    = UsageDetails -> CoreBndr -> UsageDetails
    addManyOccId UsageDetails
    u CoreBndr
    v
                   | Bool
    otherwise = UsageDetails
    u
            -- Give a non-committal binder info (i.e noOccInfo) because
            --   a) Many copies of the specialised thing can appear
            --   b) We don't want to substitute a BIG expression inside a RULE
            --      even if that's the only occurrence of the thing
            --      (Same goes for INLINE.)

    addManyOccs :: UsageDetails -> VarSet -> UsageDetails
    addManyOccs :: UsageDetails -> VarSet -> UsageDetails
    addManyOccs UsageDetails
    usage VarSet
    id_set = (CoreBndr -> UsageDetails -> UsageDetails)
    -> UsageDetails -> VarSet -> UsageDetails
    forall elt a. (elt -> a -> a) -> a -> UniqSet elt -> a
    nonDetStrictFoldUniqSet CoreBndr -> UsageDetails -> UsageDetails
    addManyOcc UsageDetails
    usage VarSet
    id_set
      -- It's OK to use nonDetStrictFoldUniqSet here because addManyOcc commutes

    delDetails :: UsageDetails -> Id -> UsageDetails
    delDetails :: UsageDetails -> CoreBndr -> UsageDetails
    delDetails UsageDetails
    ud CoreBndr
    bndr
      = UsageDetails
    ud UsageDetails -> (OccInfoEnv -> OccInfoEnv) -> UsageDetails
    `alterUsageDetails` (OccInfoEnv -> CoreBndr -> OccInfoEnv
    forall a. VarEnv a -> CoreBndr -> VarEnv a
    `delVarEnv` CoreBndr
    bndr)

    delDetailsList :: UsageDetails -> [Id] -> UsageDetails
    delDetailsList :: UsageDetails -> [CoreBndr] -> UsageDetails
    delDetailsList UsageDetails
    ud [CoreBndr]
    bndrs
      = UsageDetails
    ud UsageDetails -> (OccInfoEnv -> OccInfoEnv) -> UsageDetails
    `alterUsageDetails` (OccInfoEnv -> [CoreBndr] -> OccInfoEnv
    forall a. VarEnv a -> [CoreBndr] -> VarEnv a
    `delVarEnvList` [CoreBndr]
    bndrs)

    emptyDetails :: UsageDetails
    emptyDetails :: UsageDetails
    emptyDetails = UD { ud_env :: OccInfoEnv
    ud_env       = OccInfoEnv
    forall a. VarEnv a
    emptyVarEnv
                      , ud_z_many :: OccInfoEnv
    ud_z_many    = OccInfoEnv
    forall a. VarEnv a
    emptyVarEnv
                      , ud_z_in_lam :: OccInfoEnv
    ud_z_in_lam  = OccInfoEnv
    forall a. VarEnv a
    emptyVarEnv
                      , ud_z_no_tail :: OccInfoEnv
    ud_z_no_tail = OccInfoEnv
    forall a. VarEnv a
    emptyVarEnv }

    isEmptyDetails :: UsageDetails -> Bool
    isEmptyDetails :: UsageDetails -> Bool
    isEmptyDetails = OccInfoEnv -> Bool
    forall a. VarEnv a -> Bool
    isEmptyVarEnv (OccInfoEnv -> Bool)
    -> (UsageDetails -> OccInfoEnv) -> UsageDetails -> Bool
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . UsageDetails -> OccInfoEnv
    ud_env

    markAllMany, markAllInsideLam, markAllNonTail, markAllManyNonTail
      :: UsageDetails -> UsageDetails
    markAllMany :: UsageDetails -> UsageDetails
    markAllMany          UsageDetails
    ud = UsageDetails
    ud { ud_z_many :: OccInfoEnv
    ud_z_many    = UsageDetails -> OccInfoEnv
    ud_env UsageDetails
    ud }
    markAllInsideLam :: UsageDetails -> UsageDetails
    markAllInsideLam     UsageDetails
    ud = UsageDetails
    ud { ud_z_in_lam :: OccInfoEnv
    ud_z_in_lam  = UsageDetails -> OccInfoEnv
    ud_env UsageDetails
    ud }
    markAllNonTail :: UsageDetails -> UsageDetails
    markAllNonTail UsageDetails
    ud = UsageDetails
    ud { ud_z_no_tail :: OccInfoEnv
    ud_z_no_tail = UsageDetails -> OccInfoEnv
    ud_env UsageDetails
    ud }

    markAllInsideLamIf, markAllNonTailIf :: Bool -> UsageDetails -> UsageDetails

    markAllInsideLamIf :: Bool -> UsageDetails -> UsageDetails
    markAllInsideLamIf  Bool
    True  UsageDetails
    ud = UsageDetails -> UsageDetails
    markAllInsideLam UsageDetails
    ud
    markAllInsideLamIf  Bool
    False UsageDetails
    ud = UsageDetails
    ud

    markAllNonTailIf :: Bool -> UsageDetails -> UsageDetails
    markAllNonTailIf Bool
    True  UsageDetails
    ud = UsageDetails -> UsageDetails
    markAllNonTail UsageDetails
    ud
    markAllNonTailIf Bool
    False UsageDetails
    ud = UsageDetails
    ud

    markAllManyNonTail :: UsageDetails -> UsageDetails
    markAllManyNonTail = UsageDetails -> UsageDetails
    markAllMany (UsageDetails -> UsageDetails)
    -> (UsageDetails -> UsageDetails) -> UsageDetails -> UsageDetails
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . UsageDetails -> UsageDetails
    markAllNonTail -- effectively sets to noOccInfo

    markAllManyNonTailIf :: Bool              -- If this is true
                 -> UsageDetails      -- Then do markAllManyNonTail on this
                 -> UsageDetails
    markAllManyNonTailIf :: Bool -> UsageDetails -> UsageDetails
    markAllManyNonTailIf Bool
    True  UsageDetails
    uds = UsageDetails -> UsageDetails
    markAllManyNonTail UsageDetails
    uds
    markAllManyNonTailIf Bool
    False UsageDetails
    uds = UsageDetails
    uds

    lookupDetails :: UsageDetails -> Id -> OccInfo
    lookupDetails :: UsageDetails -> CoreBndr -> OccInfo
    lookupDetails UsageDetails
    ud CoreBndr
    id
      | CoreBndr -> Bool
    isCoVar CoreBndr
    id  -- We do not currently gather occurrence info (from types)
      = OccInfo
    noOccInfo   -- for CoVars, so we must conservatively mark them as used
                    -- See Note [DoO not mark CoVars as dead]
      | Bool
    otherwise
      = case OccInfoEnv -> CoreBndr -> Maybe OccInfo
    forall a. VarEnv a -> CoreBndr -> Maybe a
    lookupVarEnv (UsageDetails -> OccInfoEnv
    ud_env UsageDetails
    ud) CoreBndr
    id of
          Just OccInfo
    occ -> UsageDetails -> CoreBndr -> OccInfo -> OccInfo
    doZapping UsageDetails
    ud CoreBndr
    id OccInfo
    occ
          Maybe OccInfo
    Nothing  -> OccInfo
    IAmDead

    usedIn :: Id -> UsageDetails -> Bool
    CoreBndr
    v usedIn :: CoreBndr -> UsageDetails -> Bool
    `usedIn` UsageDetails
    ud = CoreBndr -> Bool
    isExportedId CoreBndr
    v Bool -> Bool -> Bool
    || CoreBndr
    v CoreBndr -> OccInfoEnv -> Bool
    forall a. CoreBndr -> VarEnv a -> Bool
    `elemVarEnv` UsageDetails -> OccInfoEnv
    ud_env UsageDetails
    ud

    udFreeVars :: VarSet -> UsageDetails -> VarSet
    -- Find the subset of bndrs that are mentioned in uds
    udFreeVars :: VarSet -> UsageDetails -> VarSet
    udFreeVars VarSet
    bndrs UsageDetails
    ud = VarSet -> OccInfoEnv -> VarSet
    restrictFreeVars VarSet
    bndrs (UsageDetails -> OccInfoEnv
    ud_env UsageDetails
    ud)

    restrictFreeVars :: VarSet -> OccInfoEnv -> VarSet
    restrictFreeVars :: VarSet -> OccInfoEnv -> VarSet
    restrictFreeVars VarSet
    bndrs OccInfoEnv
    fvs = VarSet -> OccInfoEnv -> VarSet
    forall key b. UniqSet key -> UniqFM key b -> UniqSet key
    restrictUniqSetToUFM VarSet
    bndrs OccInfoEnv
    fvs

    {- Note [Do not mark CoVars as dead]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    It's obviously wrong to mark CoVars as dead if they are used.
    Currently we don't traverse types to gather usase info for CoVars,
    so we had better treat them as having noOccInfo.

    This showed up in #15696 we had something like
      case eq_sel d of co -> ...(typeError @(...co...) "urk")...

    Then 'd' was substituted by a dictionary, so the expression
    simpified to
      case (Coercion <blah>) of co -> ...(typeError @(...co...) "urk")...

    But then the "drop the case altogether" equation of rebuildCase
    thought that 'co' was dead, and discarded the entire case. Urk!

    I have no idea how we managed to avoid this pitfall for so long!
    -}

    -------------------
    -- Auxiliary functions for UsageDetails implementation

    combineUsageDetailsWith :: (OccInfo -> OccInfo -> OccInfo)
                            -> UsageDetails -> UsageDetails -> UsageDetails
    combineUsageDetailsWith :: (OccInfo -> OccInfo -> OccInfo)
    -> UsageDetails -> UsageDetails -> UsageDetails
    combineUsageDetailsWith OccInfo -> OccInfo -> OccInfo
    plus_occ_info UsageDetails
    ud1 UsageDetails
    ud2
      | UsageDetails -> Bool
    isEmptyDetails UsageDetails
    ud1 = UsageDetails
    ud2
      | UsageDetails -> Bool
    isEmptyDetails UsageDetails
    ud2 = UsageDetails
    ud1
      | Bool
    otherwise
      = UD { ud_env :: OccInfoEnv
    ud_env       = (OccInfo -> OccInfo -> OccInfo)
    -> OccInfoEnv -> OccInfoEnv -> OccInfoEnv
    forall a. (a -> a -> a) -> VarEnv a -> VarEnv a -> VarEnv a
    plusVarEnv_C OccInfo -> OccInfo -> OccInfo
    plus_occ_info (UsageDetails -> OccInfoEnv
    ud_env UsageDetails
    ud1) (UsageDetails -> OccInfoEnv
    ud_env UsageDetails
    ud2)
           , ud_z_many :: OccInfoEnv
    ud_z_many    = OccInfoEnv -> OccInfoEnv -> OccInfoEnv
    forall a. VarEnv a -> VarEnv a -> VarEnv a
    plusVarEnv (UsageDetails -> OccInfoEnv
    ud_z_many    UsageDetails
    ud1) (UsageDetails -> OccInfoEnv
    ud_z_many    UsageDetails
    ud2)
           , ud_z_in_lam :: OccInfoEnv
    ud_z_in_lam  = OccInfoEnv -> OccInfoEnv -> OccInfoEnv
    forall a. VarEnv a -> VarEnv a -> VarEnv a
    plusVarEnv (UsageDetails -> OccInfoEnv
    ud_z_in_lam  UsageDetails
    ud1) (UsageDetails -> OccInfoEnv
    ud_z_in_lam  UsageDetails
    ud2)
           , ud_z_no_tail :: OccInfoEnv
    ud_z_no_tail = OccInfoEnv -> OccInfoEnv -> OccInfoEnv
    forall a. VarEnv a -> VarEnv a -> VarEnv a
    plusVarEnv (UsageDetails -> OccInfoEnv
    ud_z_no_tail UsageDetails
    ud1) (UsageDetails -> OccInfoEnv
    ud_z_no_tail UsageDetails
    ud2) }

    doZapping :: UsageDetails -> Var -> OccInfo -> OccInfo
    doZapping :: UsageDetails -> CoreBndr -> OccInfo -> OccInfo
    doZapping UsageDetails
    ud CoreBndr
    var OccInfo
    occ
      = UsageDetails -> Unique -> OccInfo -> OccInfo
    doZappingByUnique UsageDetails
    ud (CoreBndr -> Unique
    varUnique CoreBndr
    var) OccInfo
    occ

    doZappingByUnique :: UsageDetails -> Unique -> OccInfo -> OccInfo
    doZappingByUnique :: UsageDetails -> Unique -> OccInfo -> OccInfo
    doZappingByUnique (UD { ud_z_many :: UsageDetails -> OccInfoEnv
    ud_z_many = OccInfoEnv
    many
                          , ud_z_in_lam :: UsageDetails -> OccInfoEnv
    ud_z_in_lam = OccInfoEnv
    in_lam
                          , ud_z_no_tail :: UsageDetails -> OccInfoEnv
    ud_z_no_tail = OccInfoEnv
    no_tail })
                      Unique
    uniq OccInfo
    occ
      = OccInfo
    occ2
      where
        occ1 :: OccInfo
    occ1 | Unique
    uniq Unique -> OccInfoEnv -> Bool
    forall a. Unique -> VarEnv a -> Bool
    `elemVarEnvByKey` OccInfoEnv
    many    = OccInfo -> OccInfo
    markMany OccInfo
    occ
             | Unique
    uniq Unique -> OccInfoEnv -> Bool
    forall a. Unique -> VarEnv a -> Bool
    `elemVarEnvByKey` OccInfoEnv
    in_lam  = OccInfo -> OccInfo
    markInsideLam OccInfo
    occ
             | Bool
    otherwise                      = OccInfo
    occ
        occ2 :: OccInfo
    occ2 | Unique
    uniq Unique -> OccInfoEnv -> Bool
    forall a. Unique -> VarEnv a -> Bool
    `elemVarEnvByKey` OccInfoEnv
    no_tail = OccInfo -> OccInfo
    markNonTail OccInfo
    occ1
             | Bool
    otherwise                      = OccInfo
    occ1

    alterZappedSets :: UsageDetails -> (ZappedSet -> ZappedSet) -> UsageDetails
    alterZappedSets :: UsageDetails -> (OccInfoEnv -> OccInfoEnv) -> UsageDetails
    alterZappedSets UsageDetails
    ud OccInfoEnv -> OccInfoEnv
    f
      = UsageDetails
    ud { ud_z_many :: OccInfoEnv
    ud_z_many    = OccInfoEnv -> OccInfoEnv
    f (UsageDetails -> OccInfoEnv
    ud_z_many    UsageDetails
    ud)
           , ud_z_in_lam :: OccInfoEnv
    ud_z_in_lam  = OccInfoEnv -> OccInfoEnv
    f (UsageDetails -> OccInfoEnv
    ud_z_in_lam  UsageDetails
    ud)
           , ud_z_no_tail :: OccInfoEnv
    ud_z_no_tail = OccInfoEnv -> OccInfoEnv
    f (UsageDetails -> OccInfoEnv
    ud_z_no_tail UsageDetails
    ud) }

    alterUsageDetails :: UsageDetails -> (OccInfoEnv -> OccInfoEnv) -> UsageDetails
    alterUsageDetails :: UsageDetails -> (OccInfoEnv -> OccInfoEnv) -> UsageDetails
    alterUsageDetails UsageDetails
    ud OccInfoEnv -> OccInfoEnv
    f
      = UsageDetails
    ud { ud_env :: OccInfoEnv
    ud_env = OccInfoEnv -> OccInfoEnv
    f (UsageDetails -> OccInfoEnv
    ud_env UsageDetails
    ud) } UsageDetails -> (OccInfoEnv -> OccInfoEnv) -> UsageDetails
    `alterZappedSets` OccInfoEnv -> OccInfoEnv
    f

    flattenUsageDetails :: UsageDetails -> UsageDetails
    flattenUsageDetails :: UsageDetails -> UsageDetails
    flattenUsageDetails UsageDetails
    ud
      = UsageDetails
    ud { ud_env :: OccInfoEnv
    ud_env = (Unique -> OccInfo -> OccInfo) -> OccInfoEnv -> OccInfoEnv
    forall elt1 elt2 key.
    (Unique -> elt1 -> elt2) -> UniqFM key elt1 -> UniqFM key elt2
    mapUFM_Directly (UsageDetails -> Unique -> OccInfo -> OccInfo
    doZappingByUnique UsageDetails
    ud) (UsageDetails -> OccInfoEnv
    ud_env UsageDetails
    ud) }
          UsageDetails -> (OccInfoEnv -> OccInfoEnv) -> UsageDetails
    `alterZappedSets` OccInfoEnv -> OccInfoEnv -> OccInfoEnv
    forall a b. a -> b -> a
    const OccInfoEnv
    forall a. VarEnv a
    emptyVarEnv

    -------------------
    -- See Note [Adjusting right-hand sides]
    adjustRhsUsage :: RecFlag -> Maybe JoinArity
                   -> [CoreBndr]     -- Outer lambdas, AFTER occ anal
                   -> UsageDetails   -- From body of lambda
                   -> UsageDetails
    adjustRhsUsage :: RecFlag
    -> Maybe JoinArity -> [CoreBndr] -> UsageDetails -> UsageDetails
    adjustRhsUsage RecFlag
    is_rec Maybe JoinArity
    mb_join_arity [CoreBndr]
    bndrs UsageDetails
    usage
      = Bool -> UsageDetails -> UsageDetails
    markAllInsideLamIf (Bool -> Bool
    not Bool
    one_shot) (UsageDetails -> UsageDetails) -> UsageDetails -> UsageDetails
    forall a b. (a -> b) -> a -> b
    $
        Bool -> UsageDetails -> UsageDetails
    markAllNonTailIf (Bool -> Bool
    not Bool
    exact_join) (UsageDetails -> UsageDetails) -> UsageDetails -> UsageDetails
    forall a b. (a -> b) -> a -> b
    $
        UsageDetails
    usage
      where
        one_shot :: Bool
    one_shot = case Maybe JoinArity
    mb_join_arity of
                     Just JoinArity
    join_arity
                       | RecFlag -> Bool
    isRec RecFlag
    is_rec -> Bool
    False
                       | Bool
    otherwise    -> (CoreBndr -> Bool) -> [CoreBndr] -> Bool
    forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
    all CoreBndr -> Bool
    isOneShotBndr (JoinArity -> [CoreBndr] -> [CoreBndr]
    forall a. JoinArity -> [a] -> [a]
    drop JoinArity
    join_arity [CoreBndr]
    bndrs)
                     Maybe JoinArity
    Nothing          -> (CoreBndr -> Bool) -> [CoreBndr] -> Bool
    forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
    all CoreBndr -> Bool
    isOneShotBndr [CoreBndr]
    bndrs

        exact_join :: Bool
    exact_join = Maybe JoinArity -> [CoreBndr] -> Bool
    forall a. Maybe JoinArity -> [a] -> Bool
    exactJoin Maybe JoinArity
    mb_join_arity [CoreBndr]
    bndrs

    exactJoin :: Maybe JoinArity -> [a] -> Bool
    exactJoin :: forall a. Maybe JoinArity -> [a] -> Bool
    exactJoin Maybe JoinArity
    Nothing           [a]
    _    = Bool
    False
    exactJoin (Just JoinArity
    join_arity) [a]
    args = [a]
    args [a] -> JoinArity -> Bool
    forall a. [a] -> JoinArity -> Bool
    `lengthIs` JoinArity
    join_arity
      -- Remember join_arity includes type binders

    type IdWithOccInfo = Id

    tagLamBinders :: UsageDetails          -- Of scope
                  -> [Id]                  -- Binders
                  -> (UsageDetails,        -- Details with binders removed
                     [IdWithOccInfo])    -- Tagged binders
    tagLamBinders :: UsageDetails -> [CoreBndr] -> (UsageDetails, [CoreBndr])
    tagLamBinders UsageDetails
    usage [CoreBndr]
    binders
      = UsageDetails
    usage' UsageDetails
    -> (UsageDetails, [CoreBndr]) -> (UsageDetails, [CoreBndr])
    `seq` (UsageDetails
    usage', [CoreBndr]
    bndrs')
      where
        (UsageDetails
    usage', [CoreBndr]
    bndrs') = (UsageDetails -> CoreBndr -> (UsageDetails, CoreBndr))
    -> UsageDetails -> [CoreBndr] -> (UsageDetails, [CoreBndr])
    forall (t :: * -> *) a b c.
    Traversable t =>
    (a -> b -> (a, c)) -> a -> t b -> (a, t c)
    mapAccumR UsageDetails -> CoreBndr -> (UsageDetails, CoreBndr)
    tagLamBinder UsageDetails
    usage [CoreBndr]
    binders

    tagLamBinder :: UsageDetails       -- Of scope
                 -> Id                 -- Binder
                 -> (UsageDetails,     -- Details with binder removed
                     IdWithOccInfo)    -- Tagged binders
    -- Used for lambda and case binders
    -- It copes with the fact that lambda bindings can have a
    -- stable unfolding, used for join points
    tagLamBinder :: UsageDetails -> CoreBndr -> (UsageDetails, CoreBndr)
    tagLamBinder UsageDetails
    usage CoreBndr
    bndr
      = (UsageDetails
    usage2, CoreBndr
    bndr')
      where
            occ :: OccInfo
    occ    = UsageDetails -> CoreBndr -> OccInfo
    lookupDetails UsageDetails
    usage CoreBndr
    bndr
            bndr' :: CoreBndr
    bndr'  = OccInfo -> CoreBndr -> CoreBndr
    setBinderOcc (OccInfo -> OccInfo
    markNonTail OccInfo
    occ) CoreBndr
    bndr
                       -- Don't try to make an argument into a join point
            usage1 :: UsageDetails
    usage1 = UsageDetails
    usage UsageDetails -> CoreBndr -> UsageDetails
    `delDetails` CoreBndr
    bndr
            usage2 :: UsageDetails
    usage2 | CoreBndr -> Bool
    isId CoreBndr
    bndr = UsageDetails -> VarSet -> UsageDetails
    addManyOccs UsageDetails
    usage1 (CoreBndr -> VarSet
    idUnfoldingVars CoreBndr
    bndr)
                                   -- This is effectively the RHS of a
                                   -- non-join-point binding, so it's okay to use
                                   -- addManyOccsSet, which assumes no tail calls
                   | Bool
    otherwise = UsageDetails
    usage1

    tagNonRecBinder :: TopLevelFlag           -- At top level?
                    -> UsageDetails           -- Of scope
                    -> CoreBndr               -- Binder
                    -> (UsageDetails,         -- Details with binder removed
                        IdWithOccInfo)        -- Tagged binder

    tagNonRecBinder :: TopLevelFlag
    -> UsageDetails -> CoreBndr -> (UsageDetails, CoreBndr)
    tagNonRecBinder TopLevelFlag
    lvl UsageDetails
    usage CoreBndr
    binder
     = let
         occ :: OccInfo
    occ     = UsageDetails -> CoreBndr -> OccInfo
    lookupDetails UsageDetails
    usage CoreBndr
    binder
         will_be_join :: Bool
    will_be_join = TopLevelFlag -> UsageDetails -> [CoreBndr] -> Bool
    decideJoinPointHood TopLevelFlag
    lvl UsageDetails
    usage [CoreBndr
    binder]
         occ' :: OccInfo
    occ'    | Bool
    will_be_join = -- must already be marked AlwaysTailCalled
                                  ASSERT(isAlwaysTailCalled occ) occ
                 | Bool
    otherwise    = OccInfo -> OccInfo
    markNonTail OccInfo
    occ
         binder' :: CoreBndr
    binder' = OccInfo -> CoreBndr -> CoreBndr
    setBinderOcc OccInfo
    occ' CoreBndr
    binder
         usage' :: UsageDetails
    usage'  = UsageDetails
    usage UsageDetails -> CoreBndr -> UsageDetails
    `delDetails` CoreBndr
    binder
       in
       UsageDetails
    usage' UsageDetails
    -> (UsageDetails, CoreBndr) -> (UsageDetails, CoreBndr)
    `seq` (UsageDetails
    usage', CoreBndr
    binder')

    tagRecBinders :: TopLevelFlag           -- At top level?
                  -> UsageDetails           -- Of body of let ONLY
                  -> [(CoreBndr,            -- Binder
                       UsageDetails,        -- RHS usage details
                       [CoreBndr])]         -- Lambdas in new RHS
                  -> (UsageDetails,         -- Adjusted details for whole scope,
                                            -- with binders removed
                      [IdWithOccInfo])      -- Tagged binders
    -- Substantially more complicated than non-recursive case. Need to adjust RHS
    -- details *before* tagging binders (because the tags depend on the RHSes).
    tagRecBinders :: TopLevelFlag
    -> UsageDetails
    -> [(CoreBndr, UsageDetails, [CoreBndr])]
    -> (UsageDetails, [CoreBndr])
    tagRecBinders TopLevelFlag
    lvl UsageDetails
    body_uds [(CoreBndr, UsageDetails, [CoreBndr])]
    triples
     = let
         ([CoreBndr]
    bndrs, [UsageDetails]
    rhs_udss, [[CoreBndr]]
    _) = [(CoreBndr, UsageDetails, [CoreBndr])]
    -> ([CoreBndr], [UsageDetails], [[CoreBndr]])
    forall a b c. [(a, b, c)] -> ([a], [b], [c])
    unzip3 [(CoreBndr, UsageDetails, [CoreBndr])]
    triples

         -- 1. Determine join-point-hood of whole group, as determined by
         --    the *unadjusted* usage details
         unadj_uds :: UsageDetails
    unadj_uds     = (UsageDetails -> UsageDetails -> UsageDetails)
    -> UsageDetails -> [UsageDetails] -> UsageDetails
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr UsageDetails -> UsageDetails -> UsageDetails
    andUDs UsageDetails
    body_uds [UsageDetails]
    rhs_udss
         will_be_joins :: Bool
    will_be_joins = TopLevelFlag -> UsageDetails -> [CoreBndr] -> Bool
    decideJoinPointHood TopLevelFlag
    lvl UsageDetails
    unadj_uds [CoreBndr]
    bndrs

         -- 2. Adjust usage details of each RHS, taking into account the
         --    join-point-hood decision
         rhs_udss' :: [UsageDetails]
    rhs_udss' = ((CoreBndr, UsageDetails, [CoreBndr]) -> UsageDetails)
    -> [(CoreBndr, UsageDetails, [CoreBndr])] -> [UsageDetails]
    forall a b. (a -> b) -> [a] -> [b]
    map (CoreBndr, UsageDetails, [CoreBndr]) -> UsageDetails
    adjust [(CoreBndr, UsageDetails, [CoreBndr])]
    triples
         adjust :: (CoreBndr, UsageDetails, [CoreBndr]) -> UsageDetails
    adjust (CoreBndr
    bndr, UsageDetails
    rhs_uds, [CoreBndr]
    rhs_bndrs)
           = RecFlag
    -> Maybe JoinArity -> [CoreBndr] -> UsageDetails -> UsageDetails
    adjustRhsUsage RecFlag
    Recursive Maybe JoinArity
    mb_join_arity [CoreBndr]
    rhs_bndrs UsageDetails
    rhs_uds
           where
             -- Can't use willBeJoinId_maybe here because we haven't tagged the
             -- binder yet (the tag depends on these adjustments!)
             mb_join_arity :: Maybe JoinArity
    mb_join_arity
               | Bool
    will_be_joins
               , let occ :: OccInfo
    occ = UsageDetails -> CoreBndr -> OccInfo
    lookupDetails UsageDetails
    unadj_uds CoreBndr
    bndr
               , AlwaysTailCalled JoinArity
    arity <- OccInfo -> TailCallInfo
    tailCallInfo OccInfo
    occ
               = JoinArity -> Maybe JoinArity
    forall a. a -> Maybe a
    Just JoinArity
    arity
               | Bool
    otherwise
               = ASSERT(not will_be_joins) -- Should be AlwaysTailCalled if
                 Maybe JoinArity
    forall a. Maybe a
    Nothing                   -- we are making join points!

         -- 3. Compute final usage details from adjusted RHS details
         adj_uds :: UsageDetails
    adj_uds   = (UsageDetails -> UsageDetails -> UsageDetails)
    -> UsageDetails -> [UsageDetails] -> UsageDetails
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr UsageDetails -> UsageDetails -> UsageDetails
    andUDs UsageDetails
    body_uds [UsageDetails]
    rhs_udss'

         -- 4. Tag each binder with its adjusted details
         bndrs' :: [CoreBndr]
    bndrs'    = [ OccInfo -> CoreBndr -> CoreBndr
    setBinderOcc (UsageDetails -> CoreBndr -> OccInfo
    lookupDetails UsageDetails
    adj_uds CoreBndr
    bndr) CoreBndr
    bndr
                     | CoreBndr
    bndr <- [CoreBndr]
    bndrs ]

         -- 5. Drop the binders from the adjusted details and return
         usage' :: UsageDetails
    usage'    = UsageDetails
    adj_uds UsageDetails -> [CoreBndr] -> UsageDetails
    `delDetailsList` [CoreBndr]
    bndrs
       in
       (UsageDetails
    usage', [CoreBndr]
    bndrs')

    setBinderOcc :: OccInfo -> CoreBndr -> CoreBndr
    setBinderOcc :: OccInfo -> CoreBndr -> CoreBndr
    setBinderOcc OccInfo
    occ_info CoreBndr
    bndr
      | CoreBndr -> Bool
    isTyVar CoreBndr
    bndr      = CoreBndr
    bndr
      | CoreBndr -> Bool
    isExportedId CoreBndr
    bndr = if OccInfo -> Bool
    isManyOccs (CoreBndr -> OccInfo
    idOccInfo CoreBndr
    bndr)
                              then CoreBndr
    bndr
                              else CoreBndr -> OccInfo -> CoreBndr
    setIdOccInfo CoreBndr
    bndr OccInfo
    noOccInfo
                -- Don't use local usage info for visible-elsewhere things
                -- BUT *do* erase any IAmALoopBreaker annotation, because we're
                -- about to re-generate it and it shouldn't be "sticky"

      | Bool
    otherwise = CoreBndr -> OccInfo -> CoreBndr
    setIdOccInfo CoreBndr
    bndr OccInfo
    occ_info

    -- | Decide whether some bindings should be made into join points or not.
    -- Returns `False` if they can't be join points. Note that it's an
    -- all-or-nothing decision, as if multiple binders are given, they're
    -- assumed to be mutually recursive.
    --
    -- It must, however, be a final decision. If we say "True" for 'f',
    -- and then subsequently decide /not/ make 'f' into a join point, then
    -- the decision about another binding 'g' might be invalidated if (say)
    -- 'f' tail-calls 'g'.
    --
    -- See Note [Invariants on join points] in "GHC.Core".
    decideJoinPointHood :: TopLevelFlag -> UsageDetails
                        -> [CoreBndr]
                        -> Bool
    decideJoinPointHood :: TopLevelFlag -> UsageDetails -> [CoreBndr] -> Bool
    decideJoinPointHood TopLevelFlag
    TopLevel UsageDetails
    _ [CoreBndr]
    _
      = Bool
    False
    decideJoinPointHood TopLevelFlag
    NotTopLevel UsageDetails
    usage [CoreBndr]
    bndrs
      | CoreBndr -> Bool
    isJoinId ([CoreBndr] -> CoreBndr
    forall a. [a] -> a
    head [CoreBndr]
    bndrs)
      = WARN(not all_ok, text "OccurAnal failed to rediscover join point(s):" <+>
                           ppr bndrs)
        Bool
    all_ok
      | Bool
    otherwise
      = Bool
    all_ok
      where
        -- See Note [Invariants on join points]; invariants cited by number below.
        -- Invariant 2 is always satisfiable by the simplifier by eta expansion.
        all_ok :: Bool
    all_ok = -- Invariant 3: Either all are join points or none are
                 (CoreBndr -> Bool) -> [CoreBndr] -> Bool
    forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
    all CoreBndr -> Bool
    ok [CoreBndr]
    bndrs

        ok :: CoreBndr -> Bool
    ok CoreBndr
    bndr
          | -- Invariant 1: Only tail calls, all same join arity
            AlwaysTailCalled JoinArity
    arity <- OccInfo -> TailCallInfo
    tailCallInfo (UsageDetails -> CoreBndr -> OccInfo
    lookupDetails UsageDetails
    usage CoreBndr
    bndr)

          , -- Invariant 1 as applied to LHSes of rules
            (CoreRule -> Bool) -> [CoreRule] -> Bool
    forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
    all (JoinArity -> CoreRule -> Bool
    ok_rule JoinArity
    arity) (CoreBndr -> [CoreRule]
    idCoreRules CoreBndr
    bndr)

            -- Invariant 2a: stable unfoldings
            -- See Note [Join points and INLINE pragmas]
          , JoinArity -> Unfolding -> Bool
    ok_unfolding JoinArity
    arity (CoreBndr -> Unfolding
    realIdUnfolding CoreBndr
    bndr)

            -- Invariant 4: Satisfies polymorphism rule
          , JoinArity -> Type -> Bool
    isValidJoinPointType JoinArity
    arity (CoreBndr -> Type
    idType CoreBndr
    bndr)
          = Bool
    True

          | Bool
    otherwise
          = Bool
    False

        ok_rule :: JoinArity -> CoreRule -> Bool
    ok_rule JoinArity
    _ BuiltinRule{} = Bool
    False -- only possible with plugin shenanigans
        ok_rule JoinArity
    join_arity (Rule { ru_args :: CoreRule -> [CoreExpr]
    ru_args = [CoreExpr]
    args })
          = [CoreExpr]
    args [CoreExpr] -> JoinArity -> Bool
    forall a. [a] -> JoinArity -> Bool
    `lengthIs` JoinArity
    join_arity
            -- Invariant 1 as applied to LHSes of rules

        -- ok_unfolding returns False if we should /not/ convert a non-join-id
        -- into a join-id, even though it is AlwaysTailCalled
        ok_unfolding :: JoinArity -> Unfolding -> Bool
    ok_unfolding JoinArity
    join_arity (CoreUnfolding { uf_src :: Unfolding -> UnfoldingSource
    uf_src = UnfoldingSource
    src, uf_tmpl :: Unfolding -> CoreExpr
    uf_tmpl = CoreExpr
    rhs })
          = Bool -> Bool
    not (UnfoldingSource -> Bool
    isStableSource UnfoldingSource
    src Bool -> Bool -> Bool
    && JoinArity
    join_arity JoinArity -> JoinArity -> Bool
    forall a. Ord a => a -> a -> Bool
    > CoreExpr -> JoinArity
    joinRhsArity CoreExpr
    rhs)
        ok_unfolding JoinArity
    _ (DFunUnfolding {})
          = Bool
    False
        ok_unfolding JoinArity
    _ Unfolding
    _
          = Bool
    True

    willBeJoinId_maybe :: CoreBndr -> Maybe JoinArity
    willBeJoinId_maybe :: CoreBndr -> Maybe JoinArity
    willBeJoinId_maybe CoreBndr
    bndr
      = case OccInfo -> TailCallInfo
    tailCallInfo (CoreBndr -> OccInfo
    idOccInfo CoreBndr
    bndr) of
          AlwaysTailCalled JoinArity
    arity -> JoinArity -> Maybe JoinArity
    forall a. a -> Maybe a
    Just JoinArity
    arity
          TailCallInfo
    _                      -> CoreBndr -> Maybe JoinArity
    isJoinId_maybe CoreBndr
    bndr

    {- Note [Join points and INLINE pragmas]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider
       f x = let g = \x. not  -- Arity 1
                 {-# INLINE g #-}
             in case x of
                  A -> g True True
                  B -> g True False
                  C -> blah2

    Here 'g' is always tail-called applied to 2 args, but the stable
    unfolding captured by the INLINE pragma has arity 1.  If we try to
    convert g to be a join point, its unfolding will still have arity 1
    (since it is stable, and we don't meddle with stable unfoldings), and
    Lint will complain (see Note [Invariants on join points], (2a), in
    GHC.Core.  #13413.

    Moreover, since g is going to be inlined anyway, there is no benefit
    from making it a join point.

    If it is recursive, and uselessly marked INLINE, this will stop us
    making it a join point, which is annoying.  But occasionally
    (notably in class methods; see Note [Instances and loop breakers] in
    GHC.Tc.TyCl.Instance) we mark recursive things as INLINE but the recursion
    unravels; so ignoring INLINE pragmas on recursive things isn't good
    either.

    See Invariant 2a of Note [Invariants on join points] in GHC.Core

    ************************************************************************
    *                                                                      *
    \subsection{Operations over OccInfo}
    *                                                                      *
    ************************************************************************
    -}

    markMany, markInsideLam, markNonTail :: OccInfo -> OccInfo

    markMany :: OccInfo -> OccInfo
    markMany OccInfo
    IAmDead = OccInfo
    IAmDead
    markMany OccInfo
    occ     = ManyOccs { occ_tail :: TailCallInfo
    occ_tail = OccInfo -> TailCallInfo
    occ_tail OccInfo
    occ }

    markInsideLam :: OccInfo -> OccInfo
    markInsideLam occ :: OccInfo
    occ@(OneOcc {}) = OccInfo
    occ { occ_in_lam :: InsideLam
    occ_in_lam = InsideLam
    IsInsideLam }
    markInsideLam OccInfo
    occ             = OccInfo
    occ

    markNonTail :: OccInfo -> OccInfo
    markNonTail OccInfo
    IAmDead = OccInfo
    IAmDead
    markNonTail OccInfo
    occ     = OccInfo
    occ { occ_tail :: TailCallInfo
    occ_tail = TailCallInfo
    NoTailCallInfo }

    addOccInfo, orOccInfo :: OccInfo -> OccInfo -> OccInfo

    addOccInfo :: OccInfo -> OccInfo -> OccInfo
    addOccInfo OccInfo
    a1 OccInfo
    a2  = ASSERT( not (isDeadOcc a1 || isDeadOcc a2) )
                        ManyOccs { occ_tail :: TailCallInfo
    occ_tail = OccInfo -> TailCallInfo
    tailCallInfo OccInfo
    a1 TailCallInfo -> TailCallInfo -> TailCallInfo
    `andTailCallInfo`
                                              OccInfo -> TailCallInfo
    tailCallInfo OccInfo
    a2 }
                                    -- Both branches are at least One
                                    -- (Argument is never IAmDead)

    -- (orOccInfo orig new) is used
    -- when combining occurrence info from branches of a case

    orOccInfo :: OccInfo -> OccInfo -> OccInfo
    orOccInfo (OneOcc { occ_in_lam :: OccInfo -> InsideLam
    occ_in_lam  = InsideLam
    in_lam1
                      , occ_n_br :: OccInfo -> JoinArity
    occ_n_br    = JoinArity
    nbr1
                      , occ_int_cxt :: OccInfo -> InterestingCxt
    occ_int_cxt = InterestingCxt
    int_cxt1
                      , occ_tail :: OccInfo -> TailCallInfo
    occ_tail    = TailCallInfo
    tail1 })
              (OneOcc { occ_in_lam :: OccInfo -> InsideLam
    occ_in_lam  = InsideLam
    in_lam2
                      , occ_n_br :: OccInfo -> JoinArity
    occ_n_br    = JoinArity
    nbr2
                      , occ_int_cxt :: OccInfo -> InterestingCxt
    occ_int_cxt = InterestingCxt
    int_cxt2
                      , occ_tail :: OccInfo -> TailCallInfo
    occ_tail    = TailCallInfo
    tail2 })
      = OneOcc { occ_n_br :: JoinArity
    occ_n_br    = JoinArity
    nbr1 JoinArity -> JoinArity -> JoinArity
    forall a. Num a => a -> a -> a
    + JoinArity
    nbr2
               , occ_in_lam :: InsideLam
    occ_in_lam  = InsideLam
    in_lam1 InsideLam -> InsideLam -> InsideLam
    forall a. Monoid a => a -> a -> a
    `mappend` InsideLam
    in_lam2
               , occ_int_cxt :: InterestingCxt
    occ_int_cxt = InterestingCxt
    int_cxt1 InterestingCxt -> InterestingCxt -> InterestingCxt
    forall a. Monoid a => a -> a -> a
    `mappend` InterestingCxt
    int_cxt2
               , occ_tail :: TailCallInfo
    occ_tail    = TailCallInfo
    tail1 TailCallInfo -> TailCallInfo -> TailCallInfo
    `andTailCallInfo` TailCallInfo
    tail2 }

    orOccInfo OccInfo
    a1 OccInfo
    a2 = ASSERT( not (isDeadOcc a1 || isDeadOcc a2) )
                      ManyOccs { occ_tail :: TailCallInfo
    occ_tail = OccInfo -> TailCallInfo
    tailCallInfo OccInfo
    a1 TailCallInfo -> TailCallInfo -> TailCallInfo
    `andTailCallInfo`
                                            OccInfo -> TailCallInfo
    tailCallInfo OccInfo
    a2 }

    andTailCallInfo :: TailCallInfo -> TailCallInfo -> TailCallInfo
    andTailCallInfo :: TailCallInfo -> TailCallInfo -> TailCallInfo
    andTailCallInfo info :: TailCallInfo
    info@(AlwaysTailCalled JoinArity
    arity1) (AlwaysTailCalled JoinArity
    arity2)
      | JoinArity
    arity1 JoinArity -> JoinArity -> Bool
    forall a. Eq a => a -> a -> Bool
    == JoinArity
    arity2 = TailCallInfo
    info
    andTailCallInfo TailCallInfo
    _ TailCallInfo
    _  = TailCallInfo
    NoTailCallInfo