content: {-
  (c) The University of Glasgow 2006
  (c) The AQUA Project, Glasgow University, 1994-1998
  
  
  Core-syntax unfoldings
  
  Unfoldings (which can travel across module boundaries) are in Core
  syntax (namely @CoreExpr@s).
  
  The type @Unfolding@ sits ``above'' simply-Core-expressions
  unfoldings, capturing ``higher-level'' things we know about a binding,
  usually things that the simplifier found out (e.g., ``it's a
  literal'').  In the corner of a @CoreUnfolding@ unfolding, you will
  find, unsurprisingly, a Core expression.
  -}
  
  {-# LANGUAGE CPP #-}
  
  module Eta.Core.CoreUnfold (
          Unfolding, UnfoldingGuidance,   -- Abstract types
  
          noUnfolding, mkImplicitUnfolding,
          mkUnfolding, mkCoreUnfolding,
          mkTopUnfolding, mkSimpleUnfolding, mkWorkerUnfolding,
          mkInlineUnfolding, mkInlinableUnfolding, mkWwInlineRule,
          mkCompulsoryUnfolding, mkDFunUnfolding,
          specUnfolding,
  
          ArgSummary(..),
  
          couldBeSmallEnoughToInline, inlineBoringOk,
          certainlyWillInline, smallEnoughToInline,
  
          callSiteInline, CallCtxt(..),
  
          -- Reexport from CoreSubst (it only live there so it can be used
          -- by the Very Simple Optimiser)
          exprIsConApp_maybe, exprIsLiteral_maybe
      ) where
  
  #include "HsVersions.h"
  
  import Eta.Main.DynFlags
  import Eta.Core.CoreSyn
  import Eta.Core.PprCore          ()      -- Instances
  import Eta.SimplCore.OccurAnal        ( occurAnalyseExpr )
  import Eta.Core.CoreSubst hiding( substTy )
  import Eta.Core.CoreArity       ( manifestArity, exprBotStrictness_maybe )
  import Eta.Core.CoreUtils
  import Eta.BasicTypes.Id
  import Eta.BasicTypes.DataCon
  import Eta.BasicTypes.Literal
  import Eta.Prelude.PrimOp
  import Eta.BasicTypes.IdInfo
  import Eta.BasicTypes.BasicTypes       ( Arity )
  import Eta.Types.Type
  import Eta.Prelude.PrelNames
  import Eta.Prelude.TysPrim          ( realWorldStatePrimTy )
  import Eta.Utils.Bag
  import Eta.Utils.Util
  import Eta.Utils.FastTypes
  import Eta.Utils.FastString
  import Eta.Utils.Outputable
  import Eta.Prelude.ForeignCall
  
  import qualified Data.ByteString as BS
  import Data.Maybe
  
  {-
  ************************************************************************
  *                                                                      *
  \subsection{Making unfoldings}
  *                                                                      *
  ************************************************************************
  -}
  
  mkTopUnfolding :: DynFlags -> Bool -> CoreExpr -> Unfolding
  mkTopUnfolding dflags = mkUnfolding dflags InlineRhs True {- Top level -}
  
  mkImplicitUnfolding :: DynFlags -> CoreExpr -> Unfolding
  -- For implicit Ids, do a tiny bit of optimising first
  mkImplicitUnfolding dflags expr
      = mkTopUnfolding dflags False (simpleOptExpr expr)
  
  -- Note [Top-level flag on inline rules]
  -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  -- Slight hack: note that mk_inline_rules conservatively sets the
  -- top-level flag to True.  It gets set more accurately by the simplifier
  -- Simplify.simplUnfolding.
  
  mkSimpleUnfolding :: DynFlags -> CoreExpr -> Unfolding
  mkSimpleUnfolding dflags = mkUnfolding dflags InlineRhs False False
  
  mkDFunUnfolding :: [Var] -> DataCon -> [CoreExpr] -> Unfolding
  mkDFunUnfolding bndrs con ops
    = DFunUnfolding { df_bndrs = bndrs
                    , df_con = con
                    , df_args = map occurAnalyseExpr ops }
                    -- See Note [Occurrrence analysis of unfoldings]
  
  mkWwInlineRule :: CoreExpr -> Arity -> Unfolding
  mkWwInlineRule expr arity
    = mkCoreUnfolding InlineStable True
                     (simpleOptExpr expr)
                     (UnfWhen { ug_arity = arity, ug_unsat_ok = unSaturatedOk
                              , ug_boring_ok = boringCxtNotOk })
  
  mkCompulsoryUnfolding :: CoreExpr -> Unfolding
  mkCompulsoryUnfolding expr         -- Used for things that absolutely must be unfolded
    = mkCoreUnfolding InlineCompulsory True
                      (simpleOptExpr expr)
                      (UnfWhen { ug_arity = 0    -- Arity of unfolding doesn't matter
                               , ug_unsat_ok = unSaturatedOk, ug_boring_ok = boringCxtOk })
  
  mkWorkerUnfolding :: DynFlags -> (CoreExpr -> CoreExpr) -> Unfolding -> Unfolding
  -- See Note [Worker-wrapper for INLINABLE functions] in WorkWrap
  mkWorkerUnfolding dflags work_fn
                    (CoreUnfolding { uf_src = src, uf_tmpl = tmpl
                                   , uf_is_top = top_lvl })
    | isStableSource src
    = mkCoreUnfolding src top_lvl new_tmpl guidance
    where
      new_tmpl = simpleOptExpr (work_fn tmpl)
      guidance = calcUnfoldingGuidance dflags new_tmpl
  
  mkWorkerUnfolding _ _ _ = noUnfolding
  
  mkInlineUnfolding :: Maybe Arity -> CoreExpr -> Unfolding
  mkInlineUnfolding mb_arity expr
    = mkCoreUnfolding InlineStable
                      True         -- Note [Top-level flag on inline rules]
                      expr' guide
    where
      expr' = simpleOptExpr expr
      guide = case mb_arity of
                Nothing    -> UnfWhen { ug_arity = manifestArity expr'
                                      , ug_unsat_ok = unSaturatedOk
                                      , ug_boring_ok = boring_ok }
                Just arity -> UnfWhen { ug_arity = arity
                                      , ug_unsat_ok = needSaturated
                                      , ug_boring_ok = boring_ok }
      boring_ok = inlineBoringOk expr'
  
  mkInlinableUnfolding :: DynFlags -> CoreExpr -> Unfolding
  mkInlinableUnfolding dflags expr
    = mkUnfolding dflags InlineStable True is_bot expr'
    where
      expr' = simpleOptExpr expr
      is_bot = isJust (exprBotStrictness_maybe expr')
  
  specUnfolding :: DynFlags -> Subst -> [Var] -> [CoreExpr] -> Unfolding -> Unfolding
  -- See Note [Specialising unfoldings]
  specUnfolding _ subst new_bndrs spec_args
                df@(DFunUnfolding { df_bndrs = bndrs, df_con = con , df_args = args })
    = ASSERT2( length bndrs >= length spec_args, ppr df $$ ppr spec_args $$ ppr new_bndrs )
      mkDFunUnfolding (new_bndrs ++ extra_bndrs) con
                      (map (substExpr spec_doc subst2) args)
    where
      subst1 = extendSubstList subst (bndrs `zip` spec_args)
      (subst2, extra_bndrs) = substBndrs subst1 (dropList spec_args bndrs)
  
  specUnfolding _dflags subst new_bndrs spec_args
                (CoreUnfolding { uf_src = src, uf_tmpl = tmpl
                               , uf_is_top = top_lvl
                               , uf_guidance = old_guidance })
   | isStableSource src  -- See Note [Specialising unfoldings]
   , UnfWhen { ug_arity = old_arity
             , ug_unsat_ok = unsat_ok
             , ug_boring_ok = boring_ok } <- old_guidance
   = let guidance = UnfWhen { ug_arity = old_arity - count isValArg spec_args
                                       + count isId new_bndrs
                            , ug_unsat_ok = unsat_ok
                            , ug_boring_ok = boring_ok }
         new_tmpl = simpleOptExpr $ mkLams new_bndrs $
                    mkApps (substExpr spec_doc subst tmpl) spec_args
                     -- The beta-redexes created here will be simplified
                     -- away by simplOptExpr in mkUnfolding
  
     in mkCoreUnfolding src top_lvl new_tmpl guidance
  
  specUnfolding _ _ _ _ _ = noUnfolding
  
  spec_doc :: SDoc
  spec_doc = ptext (sLit "specUnfolding")
  
  {-
  Note [Specialising unfoldings]
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  When we specialise a function for some given type-class arguments, we use
  specUnfolding to specialise its unfolding.  Some important points:
  
  * If the original function has a DFunUnfolding, the specialised one
    must do so too!  Otherwise we lose the magic rules that make it
    interact with ClassOps
  
  * There is a bit of hack for INLINABLE functions:
       f :: Ord a => ....
       f = <big-rhs>
       {- INLINEABLE f #-}
    Now if we specialise f, should the specialised version still have
    an INLINEABLE pragma?  If it does, we'll capture a specialised copy
    of <big-rhs> as its unfolding, and that probaby won't inline.  But
    if we don't, the specialised version of <big-rhs> might be small
    enough to inline at a call site. This happens with Control.Monad.liftM3,
    and can cause a lot more allocation as a result (nofib n-body shows this).
  
    Moreover, keeping the INLINEABLE thing isn't much help, because
    the specialised function (probaby) isn't overloaded any more.
  
    Conclusion: drop the INLINEALE pragma.  In practice what this means is:
       if a stable unfolding has UnfoldingGuidance of UnfWhen,
          we keep it (so the specialised thing too will always inline)
       if a stable unfolding has UnfoldingGuidance of UnfIfGoodArgs
          (which arises from INLINEABLE), we discard it
  -}
  
  mkCoreUnfolding :: UnfoldingSource -> Bool -> CoreExpr
                  -> UnfoldingGuidance -> Unfolding
  -- Occurrence-analyses the expression before capturing it
  mkCoreUnfolding src top_lvl expr guidance
    = CoreUnfolding { uf_tmpl         = occurAnalyseExpr expr,
                        -- See Note [Occurrrence analysis of unfoldings]
                      uf_src          = src,
                      uf_is_top       = top_lvl,
                      uf_is_value     = exprIsHNF        expr,
                      uf_is_conlike   = exprIsConLike    expr,
                      uf_is_work_free = exprIsWorkFree   expr,
                      uf_expandable   = exprIsExpandable expr,
                      uf_guidance     = guidance }
  
  mkUnfolding :: DynFlags -> UnfoldingSource -> Bool -> Bool -> CoreExpr
              -> Unfolding
  -- Calculates unfolding guidance
  -- Occurrence-analyses the expression before capturing it
  mkUnfolding dflags src top_lvl is_bottoming expr
    | top_lvl && is_bottoming
    , not (exprIsTrivial expr)
    = NoUnfolding    -- See Note [Do not inline top-level bottoming functions]
    | otherwise
    = CoreUnfolding { uf_tmpl         = occurAnalyseExpr expr,
                        -- See Note [Occurrrence analysis of unfoldings]
                      uf_src          = src,
                      uf_is_top       = top_lvl,
                      uf_is_value     = exprIsHNF        expr,
                      uf_is_conlike   = exprIsConLike    expr,
                      uf_expandable   = exprIsExpandable expr,
                      uf_is_work_free = exprIsWorkFree   expr,
                      uf_guidance     = guidance }
    where
      guidance = calcUnfoldingGuidance dflags expr
          -- NB: *not* (calcUnfoldingGuidance (occurAnalyseExpr expr))!
          -- See Note [Calculate unfolding guidance on the non-occ-anal'd expression]
  
  {-
  Note [Occurrence analysis of unfoldings]
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  We do occurrence-analysis of unfoldings once and for all, when the
  unfolding is built, rather than each time we inline them.
  
  But given this decision it's vital that we do
  *always* do it.  Consider this unfolding
      \x -> letrec { f = ...g...; g* = f } in body
  where g* is (for some strange reason) the loop breaker.  If we don't
  occ-anal it when reading it in, we won't mark g as a loop breaker, and
  we may inline g entirely in body, dropping its binding, and leaving
  the occurrence in f out of scope. This happened in Trac #8892, where
  the unfolding in question was a DFun unfolding.
  
  But more generally, the simplifier is designed on the
  basis that it is looking at occurrence-analysed expressions, so better
  ensure that they acutally are.
  
  Note [Calculate unfolding guidance on the non-occ-anal'd expression]
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  Notice that we give the non-occur-analysed expression to
  calcUnfoldingGuidance.  In some ways it'd be better to occur-analyse
  first; for example, sometimes during simplification, there's a large
  let-bound thing which has been substituted, and so is now dead; so
  'expr' contains two copies of the thing while the occurrence-analysed
  expression doesn't.
  
  Nevertheless, we *don't* and *must not* occ-analyse before computing
  the size because
  
  a) The size computation bales out after a while, whereas occurrence
     analysis does not.
  
  b) Residency increases sharply if you occ-anal first.  I'm not
     100% sure why, but it's a large effect.  Compiling Cabal went
     from residency of 534M to over 800M with this one change.
  
  This can occasionally mean that the guidance is very pessimistic;
  it gets fixed up next round.  And it should be rare, because large
  let-bound things that are dead are usually caught by preInlineUnconditionally
  
  
  ************************************************************************
  *                                                                      *
  \subsection{The UnfoldingGuidance type}
  *                                                                      *
  ************************************************************************
  -}
  
  inlineBoringOk :: CoreExpr -> Bool
  -- See Note [INLINE for small functions]
  -- True => the result of inlining the expression is
  --         no bigger than the expression itself
  --     eg      (\x y -> f y x)
  -- This is a quick and dirty version. It doesn't attempt
  -- to deal with  (\x y z -> x (y z))
  -- The really important one is (x `cast` c)
  inlineBoringOk e
    = go 0 e
    where
      go :: Int -> CoreExpr -> Bool
      go credit (Lam x e) | isId x           = go (credit+1) e
                          | otherwise        = go credit e
      go credit (App f (Type {}))            = go credit f
      go credit (App f a) | credit > 0
                          , exprIsTrivial a  = go (credit-1) f
      go credit (Tick _ e)                 = go credit e -- dubious
      go credit (Cast e _)                   = go credit e
      go _      (Var {})                     = boringCxtOk
      go _      _                            = boringCxtNotOk
  
  calcUnfoldingGuidance
          :: DynFlags
          -> CoreExpr    -- Expression to look at
          -> UnfoldingGuidance
  calcUnfoldingGuidance dflags (Tick t expr)
    | not (tickishIsCode t)  -- non-code ticks don't matter for unfolding
    = calcUnfoldingGuidance dflags expr
  calcUnfoldingGuidance dflags expr
    = case sizeExpr dflags (iUnbox bOMB_OUT_SIZE) val_bndrs body of
        TooBig -> UnfNever
        SizeIs size cased_bndrs scrut_discount
          | uncondInline expr n_val_bndrs (iBox size)
          -> UnfWhen { ug_unsat_ok = unSaturatedOk
                     , ug_boring_ok =  boringCxtOk
                     , ug_arity = n_val_bndrs }   -- Note [INLINE for small functions]
          | otherwise
          -> UnfIfGoodArgs { ug_args  = map (mk_discount cased_bndrs) val_bndrs
                           , ug_size  = iBox size
                           , ug_res   = iBox scrut_discount }
  
    where
      (bndrs, body) = collectBinders expr
      bOMB_OUT_SIZE = ufCreationThreshold dflags
             -- Bomb out if size gets bigger than this
      val_bndrs   = filter isId bndrs
      n_val_bndrs = length val_bndrs
  
      mk_discount :: Bag (Id,Int) -> Id -> Int
      mk_discount cbs bndr = foldlBag combine 0 cbs
             where
               combine acc (bndr', disc)
                 | bndr == bndr' = acc `plus_disc` disc
                 | otherwise     = acc
  
               plus_disc :: Int -> Int -> Int
               plus_disc | isFunTy (idType bndr) = max
                         | otherwise             = (+)
               -- See Note [Function and non-function discounts]
  
  {-
  Note [Computing the size of an expression]
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  The basic idea of sizeExpr is obvious enough: count nodes.  But getting the
  heuristics right has taken a long time.  Here's the basic strategy:
  
      * Variables, literals: 0
        (Exception for string literals, see litSize.)
  
      * Function applications (f e1 .. en): 1 + #value args
  
      * Constructor applications: 1, regardless of #args
  
      * Let(rec): 1 + size of components
  
      * Note, cast: 0
  
  Examples
  
    Size  Term
    --------------
      0     42#
      0     x
      0     True
      2     f x
      1     Just x
      4     f (g x)
  
  Notice that 'x' counts 0, while (f x) counts 2.  That's deliberate: there's
  a function call to account for.  Notice also that constructor applications
  are very cheap, because exposing them to a caller is so valuable.
  
  [25/5/11] All sizes are now multiplied by 10, except for primops
  (which have sizes like 1 or 4.  This makes primops look fantastically
  cheap, and seems to be almost unversally beneficial.  Done partly as a
  result of #4978.
  
  Note [Do not inline top-level bottoming functions]
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  The FloatOut pass has gone to some trouble to float out calls to 'error'
  and similar friends.  See Note [Bottoming floats] in SetLevels.
  Do not re-inline them!  But we *do* still inline if they are very small
  (the uncondInline stuff).
  
  Note [INLINE for small functions]
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  Consider        {-# INLINE f #-}
                  f x = Just x
                  g y = f y
  Then f's RHS is no larger than its LHS, so we should inline it into
  even the most boring context.  In general, f the function is
  sufficiently small that its body is as small as the call itself, the
  inline unconditionally, regardless of how boring the context is.
  
  Things to note:
  
  (1) We inline *unconditionally* if inlined thing is smaller (using sizeExpr)
      than the thing it's replacing.  Notice that
        (f x) --> (g 3)             -- YES, unconditionally
        (f x) --> x : []            -- YES, *even though* there are two
                                    --      arguments to the cons
        x     --> g 3               -- NO
        x     --> Just v            -- NO
  
      It's very important not to unconditionally replace a variable by
      a non-atomic term.
  
  (2) We do this even if the thing isn't saturated, else we end up with the
      silly situation that
         f x y = x
         ...map (f 3)...
      doesn't inline.  Even in a boring context, inlining without being
      saturated will give a lambda instead of a PAP, and will be more
      efficient at runtime.
  
  (3) However, when the function's arity > 0, we do insist that it
      has at least one value argument at the call site.  (This check is
      made in the UnfWhen case of callSiteInline.) Otherwise we find this:
           f = /\a \x:a. x
           d = /\b. MkD (f b)
      If we inline f here we get
           d = /\b. MkD (\x:b. x)
      and then prepareRhs floats out the argument, abstracting the type
      variables, so we end up with the original again!
  
  (4) We must be much more cautious about arity-zero things. Consider
         let x = y +# z in ...
      In *size* terms primops look very small, because the generate a
      single instruction, but we do not want to unconditionally replace
      every occurrence of x with (y +# z).  So we only do the
      unconditional-inline thing for *trivial* expressions.
  
      NB: you might think that PostInlineUnconditionally would do this
      but it doesn't fire for top-level things; see SimplUtils
      Note [Top level and postInlineUnconditionally]
  -}
  
  uncondInline :: CoreExpr -> Arity -> Int -> Bool
  -- Inline unconditionally if there no size increase
  -- Size of call is arity (+1 for the function)
  -- See Note [INLINE for small functions]
  uncondInline rhs arity size
    | arity > 0 = size <= 10 * (arity + 1) -- See Note [INLINE for small functions] (1)
    | otherwise = exprIsTrivial rhs        -- See Note [INLINE for small functions] (4)
  
  sizeExpr :: DynFlags
           -> FastInt         -- Bomb out if it gets bigger than this
           -> [Id]            -- Arguments; we're interested in which of these
                              -- get case'd
           -> CoreExpr
           -> ExprSize
  
  -- Note [Computing the size of an expression]
  
  sizeExpr dflags bOMB_OUT_SIZE top_args expr
    = size_up expr
    where
      size_up (Cast e _) = size_up e
      size_up (Tick _ e) = size_up e
      size_up (Type _)   = sizeZero           -- Types cost nothing
      size_up (Coercion _) = sizeZero
      size_up (Lit lit)  = sizeN (litSize lit)
      size_up (Var f) | isRealWorldId f = sizeZero
                        -- Make sure we get constructor discounts even
                        -- on nullary constructors
                      | otherwise       = size_up_call f [] 0
  
      size_up (App fun arg)
        | isTyCoArg arg = size_up fun
        | otherwise     = size_up arg  `addSizeNSD`
                          size_up_app fun [arg] (if isRealWorldExpr arg then 1 else 0)
  
      size_up (Lam b e)
        | isId b && not (isRealWorldId b) = lamScrutDiscount dflags (size_up e `addSizeN` 10)
        | otherwise = size_up e
  
      size_up (Let (NonRec binder rhs) body)
        = size_up rhs             `addSizeNSD`
          size_up body            `addSizeN`
          (if isUnLiftedType (idType binder) then 0 else 10)
                  -- For the allocation
                  -- If the binder has an unlifted type there is no allocation
  
      size_up (Let (Rec pairs) body)
        = foldr (addSizeNSD . size_up . snd)
                (size_up body `addSizeN` (10 * length pairs))     -- (length pairs) for the allocation
                pairs
  
      size_up (Case (Var v) _ _ alts)
          | v `elem` top_args             -- We are scrutinising an argument variable
          = alts_size (foldr addAltSize sizeZero alt_sizes)
                      (foldr maxSize    sizeZero alt_sizes)
                  -- Good to inline if an arg is scrutinised, because
                  -- that may eliminate allocation in the caller
                  -- And it eliminates the case itself
          where
            alt_sizes = map size_up_alt alts
  
                  -- alts_size tries to compute a good discount for
                  -- the case when we are scrutinising an argument variable
            alts_size (SizeIs tot tot_disc tot_scrut)  -- Size of all alternatives
                      (SizeIs max _        _)          -- Size of biggest alternative
                  = SizeIs tot (unitBag (v, iBox (_ILIT(20) +# tot -# max)) `unionBags` tot_disc) tot_scrut
                          -- If the variable is known, we produce a discount that
                          -- will take us back to 'max', the size of the largest alternative
                          -- The 1+ is a little discount for reduced allocation in the caller
                          --
                          -- Notice though, that we return tot_disc, the total discount from
                          -- all branches.  I think that's right.
  
            alts_size tot_size _ = tot_size
  
      size_up (Case e _ _ alts) = size_up e  `addSizeNSD`
                                  foldr (addAltSize . size_up_alt) case_size alts
        where
            case_size
             | is_inline_scrut e, not (lengthExceeds alts 1)  = sizeN (-10)
             | otherwise = sizeZero
                  -- Normally we don't charge for the case itself, but
                  -- we charge one per alternative (see size_up_alt,
                  -- below) to account for the cost of the info table
                  -- and comparisons.
                  --
                  -- However, in certain cases (see is_inline_scrut
                  -- below), no code is generated for the case unless
                  -- there are multiple alts.  In these cases we
                  -- subtract one, making the first alt free.
                  -- e.g. case x# +# y# of _ -> ...   should cost 1
                  --      case touch# x# of _ -> ...  should cost 0
                  -- (see #4978)
                  --
                  -- I would like to not have the "not (lengthExceeds alts 1)"
                  -- condition above, but without that some programs got worse
                  -- (spectral/hartel/event and spectral/para).  I don't fully
                  -- understand why. (SDM 24/5/11)
  
                  -- unboxed variables, inline primops and unsafe foreign calls
                  -- are all "inline" things:
            is_inline_scrut (Var v) = isUnLiftedType (idType v)
            is_inline_scrut scrut
                | (Var f, _) <- collectArgs scrut
                  = case idDetails f of
                      FCallId fc  -> not (isSafeForeignCall fc)
                      PrimOpId op -> not (primOpOutOfLine op)
                      _other      -> False
                | otherwise
                  = False
  
      ------------
      -- size_up_app is used when there's ONE OR MORE value args
      size_up_app (App fun arg) args voids
          | isTyCoArg arg                  = size_up_app fun args voids
          | isRealWorldExpr arg            = size_up_app fun (arg:args) (voids + 1)
          | otherwise                      = size_up arg  `addSizeNSD`
                                             size_up_app fun (arg:args) voids
      size_up_app (Var fun)     args voids = size_up_call fun args voids
      size_up_app (Tick _ expr) args voids = size_up_app expr args voids
      size_up_app other         args voids = size_up other `addSizeN` (length args - voids)
  
      ------------
      size_up_call :: Id -> [CoreExpr] -> Int -> ExprSize
      size_up_call fun val_args voids
         = case idDetails fun of
             FCallId _        -> sizeN (10 * (1 + length val_args))
             DataConWorkId dc -> conSize    dc (length val_args)
             PrimOpId op      -> primOpSize op (length val_args)
             ClassOpId _      -> classOpSize dflags top_args val_args
             _                -> funSize dflags top_args fun (length val_args) voids
  
      ------------
      size_up_alt (_con, _bndrs, rhs) = size_up rhs `addSizeN` 10
          -- Don't charge for args, so that wrappers look cheap
          -- (See comments about wrappers with Case)
          --
          -- IMPORATANT: *do* charge 1 for the alternative, else we
          -- find that giant case nests are treated as practically free
          -- A good example is Foreign.C.Error.errrnoToIOError
  
      ------------
          -- These addSize things have to be here because
          -- I don't want to give them bOMB_OUT_SIZE as an argument
      addSizeN TooBig          _  = TooBig
      addSizeN (SizeIs n xs d) m  = mkSizeIs bOMB_OUT_SIZE (n +# iUnbox m) xs d
  
          -- addAltSize is used to add the sizes of case alternatives
      addAltSize TooBig            _      = TooBig
      addAltSize _                 TooBig = TooBig
      addAltSize (SizeIs n1 xs d1) (SizeIs n2 ys d2)
          = mkSizeIs bOMB_OUT_SIZE (n1 +# n2)
                                   (xs `unionBags` ys)
                                   (d1 +# d2)   -- Note [addAltSize result discounts]
  
          -- This variant ignores the result discount from its LEFT argument
          -- It's used when the second argument isn't part of the result
      addSizeNSD TooBig            _      = TooBig
      addSizeNSD _                 TooBig = TooBig
      addSizeNSD (SizeIs n1 xs _) (SizeIs n2 ys d2)
          = mkSizeIs bOMB_OUT_SIZE (n1 +# n2)
                                   (xs `unionBags` ys)
                                   d2  -- Ignore d1
  
      isRealWorldId id = idType id `eqType` realWorldStatePrimTy
  
      -- an expression of type State# RealWorld must be a variable
      isRealWorldExpr (Var id)   = isRealWorldId id
      isRealWorldExpr (Tick _ e) = isRealWorldExpr e
      isRealWorldExpr _          = False
  
  -- | Finds a nominal size of a string literal.
  litSize :: Literal -> Int
  -- Used by CoreUnfold.sizeExpr
  litSize (LitInteger {}) = 100   -- Note [Size of literal integers]
  litSize (MachStr str)   = 10 + 10 * ((BS.length str + 3) `div` 4)
          -- If size could be 0 then @f "x"@ might be too small
          -- [Sept03: make literal strings a bit bigger to avoid fruitless
          --  duplication of little strings]
  litSize _other = 0    -- Must match size of nullary constructors
                        -- Key point: if  x |-> 4, then x must inline unconditionally
                        --            (eg via case binding)
  
  classOpSize :: DynFlags -> [Id] -> [CoreExpr] -> ExprSize
  -- See Note [Conlike is interesting]
  classOpSize _ _ []
    = sizeZero
  classOpSize dflags top_args (arg1 : other_args)
    = SizeIs (iUnbox size) arg_discount (_ILIT(0))
    where
      size = 20 + (10 * length other_args)
      -- If the class op is scrutinising a lambda bound dictionary then
      -- give it a discount, to encourage the inlining of this function
      -- The actual discount is rather arbitrarily chosen
      arg_discount = case arg1 of
                       Var dict | dict `elem` top_args
                                -> unitBag (dict, ufDictDiscount dflags)
                       _other   -> emptyBag
  
  funSize :: DynFlags -> [Id] -> Id -> Int -> Int -> ExprSize
  -- Size for functions that are not constructors or primops
  -- Note [Function applications]
  funSize dflags top_args fun n_val_args voids
    | fun `hasKey` buildIdKey   = buildSize
    | fun `hasKey` augmentIdKey = augmentSize
    | otherwise = SizeIs (iUnbox size) arg_discount (iUnbox res_discount)
    where
      some_val_args = n_val_args > 0
  
      size | some_val_args = 10 * (1 + n_val_args - voids)
           | otherwise     = 0
          -- The 1+ is for the function itself
          -- Add 1 for each non-trivial arg;
          -- the allocation cost, as in let(rec)
  
          --                  DISCOUNTS
          --  See Note [Function and non-function discounts]
      arg_discount | some_val_args && fun `elem` top_args
                   = unitBag (fun, ufFunAppDiscount dflags)
                   | otherwise = emptyBag
          -- If the function is an argument and is applied
          -- to some values, give it an arg-discount
  
      res_discount | idArity fun > n_val_args = ufFunAppDiscount dflags
                   | otherwise                = 0
          -- If the function is partially applied, show a result discount
  
  conSize :: DataCon -> Int -> ExprSize
  conSize dc n_val_args
    | n_val_args == 0 = SizeIs (_ILIT(0)) emptyBag (_ILIT(10))    -- Like variables
  
  -- See Note [Unboxed tuple size and result discount]
    | isUnboxedTupleCon dc = SizeIs (_ILIT(0)) emptyBag (iUnbox (10 * (1 + n_val_args)))
  
  -- See Note [Constructor size and result discount]
    | otherwise = SizeIs (_ILIT(10)) emptyBag (iUnbox (10 * (1 + n_val_args)))
  
  {-
  Note [Constructor size and result discount]
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  Treat a constructors application as size 10, regardless of how many
  arguments it has; we are keen to expose them (and we charge separately
  for their args).  We can't treat them as size zero, else we find that
  (Just x) has size 0, which is the same as a lone variable; and hence
  'v' will always be replaced by (Just x), where v is bound to Just x.
  
  The "result discount" is applied if the result of the call is
  scrutinised (say by a case).  For a constructor application that will
  mean the constructor application will disappear, so we don't need to
  charge it to the function.  So the discount should at least match the
  cost of the constructor application, namely 10.  But to give a bit
  of extra incentive we give a discount of 10*(1 + n_val_args).
  
  Simon M tried a MUCH bigger discount: (10 * (10 + n_val_args)),
  and said it was an "unambiguous win", but its terribly dangerous
  because a fuction with many many case branches, each finishing with
  a constructor, can have an arbitrarily large discount.  This led to
  terrible code bloat: see Trac #6099.
  
  Note [Unboxed tuple size and result discount]
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  However, unboxed tuples count as size zero. I found occasions where we had
          f x y z = case op# x y z of { s -> (# s, () #) }
  and f wasn't getting inlined.
  
  I tried giving unboxed tuples a *result discount* of zero (see the
  commented-out line).  Why?  When returned as a result they do not
  allocate, so maybe we don't want to charge so much for them If you
  have a non-zero discount here, we find that workers often get inlined
  back into wrappers, because it look like
      f x = case $wf x of (# a,b #) -> (a,b)
  and we are keener because of the case.  However while this change
  shrank binary sizes by 0.5% it also made spectral/boyer allocate 5%
  more. All other changes were very small. So it's not a big deal but I
  didn't adopt the idea.
  
  Note [Function and non-function discounts]
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  We want a discount if the function is applied. A good example is
  monadic combinators with continuation arguments, where inlining is
  quite important.
  
  But we don't want a big discount when a function is called many times
  (see the detailed comments with Trac #6048) because if the function is
  big it won't be inlined at its many call sites and no benefit results.
  Indeed, we can get exponentially big inlinings this way; that is what
  Trac #6048 is about.
  
  On the other hand, for data-valued arguments, if there are lots of
  case expressions in the body, each one will get smaller if we apply
  the function to a constructor application, so we *want* a big discount
  if the argument is scrutinised by many case expressions.
  
  Conclusion:
    - For functions, take the max of the discounts
    - For data values, take the sum of the discounts
  
  
  Note [Literal integer size]
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~
  Literal integers *can* be big (mkInteger [...coefficients...]), but
  need not be (S# n).  We just use an aribitrary big-ish constant here
  so that, in particular, we don't inline top-level defns like
     n = S# 5
  There's no point in doing so -- any optimisations will see the S#
  through n's unfolding.  Nor will a big size inhibit unfoldings functions
  that mention a literal Integer, because the float-out pass will float
  all those constants to top level.
  -}
  
  primOpSize :: PrimOp -> Int -> ExprSize
  primOpSize op n_val_args
   = if primOpOutOfLine op
        then sizeN (op_size + n_val_args)
        else sizeN op_size
   where
     op_size = primOpCodeSize op
  
  
  buildSize :: ExprSize
  buildSize = SizeIs (_ILIT(0)) emptyBag (_ILIT(40))
          -- We really want to inline applications of build
          -- build t (\cn -> e) should cost only the cost of e (because build will be inlined later)
          -- Indeed, we should add a result_discount becuause build is
          -- very like a constructor.  We don't bother to check that the
          -- build is saturated (it usually is).  The "-2" discounts for the \c n,
          -- The "4" is rather arbitrary.
  
  augmentSize :: ExprSize
  augmentSize = SizeIs (_ILIT(0)) emptyBag (_ILIT(40))
          -- Ditto (augment t (\cn -> e) ys) should cost only the cost of
          -- e plus ys. The -2 accounts for the \cn
  
  -- When we return a lambda, give a discount if it's used (applied)
  lamScrutDiscount :: DynFlags -> ExprSize -> ExprSize
  lamScrutDiscount dflags (SizeIs n vs _) = SizeIs n vs (iUnbox (ufFunAppDiscount dflags))
  lamScrutDiscount _      TooBig          = TooBig
  
  {-
  Note [addAltSize result discounts]
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  When adding the size of alternatives, we *add* the result discounts
  too, rather than take the *maximum*.  For a multi-branch case, this
  gives a discount for each branch that returns a constructor, making us
  keener to inline.  I did try using 'max' instead, but it makes nofib
  'rewrite' and 'puzzle' allocate significantly more, and didn't make
  binary sizes shrink significantly either.
  
  Note [Discounts and thresholds]
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  Constants for discounts and thesholds are defined in main/DynFlags,
  all of form ufXxxx.   They are:
  
  ufCreationThreshold
       At a definition site, if the unfolding is bigger than this, we
       may discard it altogether
  
  ufUseThreshold
       At a call site, if the unfolding, less discounts, is smaller than
       this, then it's small enough inline
  
  ufKeenessFactor
       Factor by which the discounts are multiplied before
       subtracting from size
  
  ufDictDiscount
       The discount for each occurrence of a dictionary argument
       as an argument of a class method.  Should be pretty small
       else big functions may get inlined
  
  ufFunAppDiscount
       Discount for a function argument that is applied.  Quite
       large, because if we inline we avoid the higher-order call.
  
  ufDearOp
       The size of a foreign call or not-dupable PrimOp
  
  
  Note [Function applications]
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  In a function application (f a b)
  
    - If 'f' is an argument to the function being analysed,
      and there's at least one value arg, record a FunAppDiscount for f
  
    - If the application if a PAP (arity > 2 in this example)
      record a *result* discount (because inlining
      with "extra" args in the call may mean that we now
      get a saturated application)
  
  Code for manipulating sizes
  -}
  
  data ExprSize = TooBig
                | SizeIs FastInt          -- Size found
                         !(Bag (Id,Int))  -- Arguments cased herein, and discount for each such
                         FastInt          -- Size to subtract if result is scrutinised
                                          -- by a case expression
  
  instance Outputable ExprSize where
    ppr TooBig         = ptext (sLit "TooBig")
    ppr (SizeIs a _ c) = brackets (int (iBox a) <+> int (iBox c))
  
  -- subtract the discount before deciding whether to bale out. eg. we
  -- want to inline a large constructor application into a selector:
  --      tup = (a_1, ..., a_99)
  --      x = case tup of ...
  --
  mkSizeIs :: FastInt -> FastInt -> Bag (Id, Int) -> FastInt -> ExprSize
  mkSizeIs max n xs d | (n -# d) ># max = TooBig
                      | otherwise       = SizeIs n xs d
  
  maxSize :: ExprSize -> ExprSize -> ExprSize
  maxSize TooBig         _                                  = TooBig
  maxSize _              TooBig                             = TooBig
  maxSize s1@(SizeIs n1 _ _) s2@(SizeIs n2 _ _) | n1 ># n2  = s1
                                                | otherwise = s2
  
  sizeZero :: ExprSize
  sizeN :: Int -> ExprSize
  
  sizeZero = SizeIs (_ILIT(0))  emptyBag (_ILIT(0))
  sizeN n  = SizeIs (iUnbox n) emptyBag (_ILIT(0))
  
  {-
  ************************************************************************
  *                                                                      *
  \subsection[considerUnfolding]{Given all the info, do (not) do the unfolding}
  *                                                                      *
  ************************************************************************
  
  We use 'couldBeSmallEnoughToInline' to avoid exporting inlinings that
  we ``couldn't possibly use'' on the other side.  Can be overridden w/
  flaggery.  Just the same as smallEnoughToInline, except that it has no
  actual arguments.
  -}
  
  couldBeSmallEnoughToInline :: DynFlags -> Int -> CoreExpr -> Bool
  couldBeSmallEnoughToInline dflags threshold rhs
    = case sizeExpr dflags (iUnbox threshold) [] body of
         TooBig -> False
         _      -> True
    where
      (_, body) = collectBinders rhs
  
  ----------------
  smallEnoughToInline :: DynFlags -> Unfolding -> Bool
  smallEnoughToInline dflags (CoreUnfolding {uf_guidance = UnfIfGoodArgs {ug_size = size}})
    = size <= ufUseThreshold dflags
  smallEnoughToInline _ _
    = False
  
  ----------------
  certainlyWillInline :: DynFlags -> Unfolding -> Maybe Unfolding
  -- Sees if the unfolding is pretty certain to inline
  -- If so, return a *stable* unfolding for it, that will always inline
  certainlyWillInline dflags unf@(CoreUnfolding { uf_guidance = guidance, uf_tmpl = expr })
    = case guidance of
        UnfNever   -> Nothing
        UnfWhen {} -> Just (unf { uf_src = InlineStable })
  
        -- The UnfIfGoodArgs case seems important.  If we w/w small functions
        -- binary sizes go up by 10%!  (This is with SplitObjs.)  I'm not totally
        -- sure whyy.
        UnfIfGoodArgs { ug_size = size, ug_args = args }
           | not (null args)  -- See Note [certainlyWillInline: be careful of thunks]
           , let arity = length args
           , size - (10 * (arity + 1)) <= ufUseThreshold dflags
           -> Just (unf { uf_src      = InlineStable
                        , uf_guidance = UnfWhen { ug_arity     = arity
                                                , ug_unsat_ok  = unSaturatedOk
                                                , ug_boring_ok = inlineBoringOk expr } })
                  -- Note the "unsaturatedOk". A function like  f = \ab. a
                  -- will certainly inline, even if partially applied (f e), so we'd
                  -- better make sure that the transformed inlining has the same property
  
        _  -> Nothing
  
  certainlyWillInline _ unf@(DFunUnfolding {})
    = Just unf
  
  certainlyWillInline _ _
    = Nothing
  
  {-
  Note [certainlyWillInline: be careful of thunks]
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  Don't claim that thunks will certainly inline, because that risks work
  duplication.  Even if the work duplication is not great (eg is_cheap
  holds), it can make a big difference in an inner loop In Trac #5623 we
  found that the WorkWrap phase thought that
         y = case x of F# v -> F# (v +# v)
  was certainlyWillInline, so the addition got duplicated.
  
  
  ************************************************************************
  *                                                                      *
  \subsection{callSiteInline}
  *                                                                      *
  ************************************************************************
  
  This is the key function.  It decides whether to inline a variable at a call site
  
  callSiteInline is used at call sites, so it is a bit more generous.
  It's a very important function that embodies lots of heuristics.
  A non-WHNF can be inlined if it doesn't occur inside a lambda,
  and occurs exactly once or
      occurs once in each branch of a case and is small
  
  If the thing is in WHNF, there's no danger of duplicating work,
  so we can inline if it occurs once, or is small
  
  NOTE: we don't want to inline top-level functions that always diverge.
  It just makes the code bigger.  Tt turns out that the convenient way to prevent
  them inlining is to give them a NOINLINE pragma, which we do in
  StrictAnal.addStrictnessInfoToTopId
  -}
  
  callSiteInline :: DynFlags
                 -> Id                    -- The Id
                 -> Bool                  -- True <=> unfolding is active
                 -> Bool                  -- True if there are are no arguments at all (incl type args)
                 -> [ArgSummary]          -- One for each value arg; True if it is interesting
                 -> CallCtxt              -- True <=> continuation is interesting
                 -> Maybe CoreExpr        -- Unfolding, if any
  
  data ArgSummary = TrivArg       -- Nothing interesting
                  | NonTrivArg    -- Arg has structure
                  | ValueArg      -- Arg is a con-app or PAP
                                  -- ..or con-like. Note [Conlike is interesting]
  
  instance Outputable ArgSummary where
    ppr TrivArg    = ptext (sLit "TrivArg")
    ppr NonTrivArg = ptext (sLit "NonTrivArg")
    ppr ValueArg   = ptext (sLit "ValueArg")
  
  nonTriv ::  ArgSummary -> Bool
  nonTriv TrivArg = False
  nonTriv _       = True
  
  data CallCtxt
    = BoringCtxt
    | RhsCtxt             -- Rhs of a let-binding; see Note [RHS of lets]
    | DiscArgCtxt         -- Argument of a fuction with non-zero arg discount
    | RuleArgCtxt         -- We are somewhere in the argument of a function with rules
  
    | ValAppCtxt          -- We're applied to at least one value arg
                          -- This arises when we have ((f x |> co) y)
                          -- Then the (f x) has argument 'x' but in a ValAppCtxt
  
    | CaseCtxt            -- We're the scrutinee of a case
                          -- that decomposes its scrutinee
  
  instance Outputable CallCtxt where
    ppr CaseCtxt    = ptext (sLit "CaseCtxt")
    ppr ValAppCtxt  = ptext (sLit "ValAppCtxt")
    ppr BoringCtxt  = ptext (sLit "BoringCtxt")
    ppr RhsCtxt     = ptext (sLit "RhsCtxt")
    ppr DiscArgCtxt = ptext (sLit "DiscArgCtxt")
    ppr RuleArgCtxt = ptext (sLit "RuleArgCtxt")
  
  callSiteInline dflags id active_unfolding lone_variable arg_infos cont_info
    = case idUnfolding id of
        -- idUnfolding checks for loop-breakers, returning NoUnfolding
        -- Things with an INLINE pragma may have an unfolding *and*
        -- be a loop breaker  (maybe the knot is not yet untied)
          CoreUnfolding { uf_tmpl = unf_template, uf_is_top = is_top
                        , uf_is_work_free = is_wf
                        , uf_guidance = guidance, uf_expandable = is_exp }
            | active_unfolding -> tryUnfolding dflags id lone_variable
                                      arg_infos cont_info unf_template is_top
                                      is_wf is_exp guidance
            | otherwise -> traceInline dflags "Inactive unfolding:" (ppr id) Nothing
          NoUnfolding      -> Nothing
          OtherCon {}      -> Nothing
          DFunUnfolding {} -> Nothing     -- Never unfold a DFun
  
  traceInline :: DynFlags -> String -> SDoc -> a -> a
  traceInline dflags str doc result
   | dopt Opt_D_dump_inlinings dflags && dopt Opt_D_verbose_core2core dflags
   = pprTrace str doc result
   | otherwise
   = result
  
  tryUnfolding :: DynFlags -> Id -> Bool -> [ArgSummary] -> CallCtxt
               -> CoreExpr -> Bool -> Bool -> Bool -> UnfoldingGuidance
               -> Maybe CoreExpr
  tryUnfolding dflags id lone_variable
               arg_infos cont_info unf_template is_top
               is_wf is_exp guidance
   = case guidance of
       UnfNever -> traceInline dflags str (ptext (sLit "UnfNever")) Nothing
  
       UnfWhen { ug_arity = uf_arity, ug_unsat_ok = unsat_ok, ug_boring_ok = boring_ok }
          | enough_args && (boring_ok || some_benefit)
                  -- See Note [INLINE for small functions (3)]
          -> traceInline dflags str (mk_doc some_benefit empty True) (Just unf_template)
          | otherwise
          -> traceInline dflags str (mk_doc some_benefit empty False) Nothing
          where
            some_benefit = calc_some_benefit uf_arity
            enough_args = (n_val_args >= uf_arity) || (unsat_ok && n_val_args > 0)
  
       UnfIfGoodArgs { ug_args = arg_discounts, ug_res = res_discount, ug_size = size }
          | is_wf && some_benefit && small_enough
          -> traceInline dflags str (mk_doc some_benefit extra_doc True) (Just unf_template)
          | otherwise
          -> traceInline dflags str (mk_doc some_benefit extra_doc False) Nothing
          where
            some_benefit = calc_some_benefit (length arg_discounts)
            extra_doc = text "discounted size =" <+> int discounted_size
            discounted_size = size - discount
            small_enough = discounted_size <= ufUseThreshold dflags
            discount = computeDiscount dflags arg_discounts
                                       res_discount arg_infos cont_info
  
    where
      mk_doc some_benefit extra_doc yes_or_no
        = vcat [ text "arg infos" <+> ppr arg_infos
               , text "interesting continuation" <+> ppr cont_info
               , text "some_benefit" <+> ppr some_benefit
               , text "is exp:" <+> ppr is_exp
               , text "is work-free:" <+> ppr is_wf
               , text "guidance" <+> ppr guidance
               , extra_doc
               , text "ANSWER =" <+> if yes_or_no then text "YES" else text "NO"]
  
      str = "Considering inlining: " ++ showSDocDump dflags (ppr id)
      n_val_args = length arg_infos
  
             -- some_benefit is used when the RHS is small enough
             -- and the call has enough (or too many) value
             -- arguments (ie n_val_args >= arity). But there must
             -- be *something* interesting about some argument, or the
             -- result context, to make it worth inlining
      calc_some_benefit :: Arity -> Bool   -- The Arity is the number of args
                                           -- expected by the unfolding
      calc_some_benefit uf_arity
         | not saturated = interesting_args       -- Under-saturated
                                          -- Note [Unsaturated applications]
         | otherwise = interesting_args   -- Saturated or over-saturated
                    || interesting_call
        where
          saturated      = n_val_args >= uf_arity
          over_saturated = n_val_args > uf_arity
          interesting_args = any nonTriv arg_infos
                  -- NB: (any nonTriv arg_infos) looks at the
                  -- over-saturated args too which is "wrong";
                  -- but if over-saturated we inline anyway.
  
          interesting_call
            | over_saturated
            = True
            | otherwise
            = case cont_info of
                CaseCtxt   -> not (lone_variable && is_wf)  -- Note [Lone variables]
                ValAppCtxt -> True                              -- Note [Cast then apply]
                RuleArgCtxt -> uf_arity > 0  -- See Note [Unfold info lazy contexts]
                DiscArgCtxt -> uf_arity > 0  --
                RhsCtxt     -> uf_arity > 0  --
                _           -> not is_top && uf_arity > 0   -- Note [Nested functions]
                                                        -- Note [Inlining in ArgCtxt]
  
  {-
  Note [Unfold into lazy contexts], Note [RHS of lets]
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  When the call is the argument of a function with a RULE, or the RHS of a let,
  we are a little bit keener to inline.  For example
       f y = (y,y,y)
       g y = let x = f y in ...(case x of (a,b,c) -> ...) ...
  We'd inline 'f' if the call was in a case context, and it kind-of-is,
  only we can't see it.  Also
       x = f v
  could be expensive whereas
       x = case v of (a,b) -> a
  is patently cheap and may allow more eta expansion.
  So we treat the RHS of a let as not-totally-boring.
  
  Note [Unsaturated applications]
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  When a call is not saturated, we *still* inline if one of the
  arguments has interesting structure.  That's sometimes very important.
  A good example is the Ord instance for Bool in Base:
  
   Rec {
      $fOrdBool =GHC.Classes.D:Ord
                   @ Bool
                   ...
                   $cmin_ajX
  
      $cmin_ajX [Occ=LoopBreaker] :: Bool -> Bool -> Bool
      $cmin_ajX = GHC.Classes.$dmmin @ Bool $fOrdBool
    }
  
  But the defn of GHC.Classes.$dmmin is:
  
    $dmmin :: forall a. GHC.Classes.Ord a => a -> a -> a
      {- Arity: 3, HasNoCafRefs, Strictness: SLL,
         Unfolding: (\ @ a $dOrd :: GHC.Classes.Ord a x :: a y :: a ->
                     case @ a GHC.Classes.<= @ a $dOrd x y of wild {
                       GHC.Types.False -> y GHC.Types.True -> x }) -}
  
  We *really* want to inline $dmmin, even though it has arity 3, in
  order to unravel the recursion.
  
  
  Note [Things to watch]
  ~~~~~~~~~~~~~~~~~~~~~~
  *   { y = I# 3; x = y `cast` co; ...case (x `cast` co) of ... }
      Assume x is exported, so not inlined unconditionally.
      Then we want x to inline unconditionally; no reason for it
      not to, and doing so avoids an indirection.
  
  *   { x = I# 3; ....f x.... }
      Make sure that x does not inline unconditionally!
      Lest we get extra allocation.
  
  Note [Inlining an InlineRule]
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  An InlineRules is used for
    (a) programmer INLINE pragmas
    (b) inlinings from worker/wrapper
  
  For (a) the RHS may be large, and our contract is that we *only* inline
  when the function is applied to all the arguments on the LHS of the
  source-code defn.  (The uf_arity in the rule.)
  
  However for worker/wrapper it may be worth inlining even if the
  arity is not satisfied (as we do in the CoreUnfolding case) so we don't
  require saturation.
  
  
  Note [Nested functions]
  ~~~~~~~~~~~~~~~~~~~~~~~
  If a function has a nested defn we also record some-benefit, on the
  grounds that we are often able to eliminate the binding, and hence the
  allocation, for the function altogether; this is good for join points.
  But this only makes sense for *functions*; inlining a constructor
  doesn't help allocation unless the result is scrutinised.  UNLESS the
  constructor occurs just once, albeit possibly in multiple case
  branches.  Then inlining it doesn't increase allocation, but it does
  increase the chance that the constructor won't be allocated at all in
  the branches that don't use it.
  
  Note [Cast then apply]
  ~~~~~~~~~~~~~~~~~~~~~~
  Consider
     myIndex = __inline_me ( (/\a. <blah>) |> co )
     co :: (forall a. a -> a) ~ (forall a. T a)
       ... /\a.\x. case ((myIndex a) |> sym co) x of { ... } ...
  
  We need to inline myIndex to unravel this; but the actual call (myIndex a) has
  no value arguments.  The ValAppCtxt gives it enough incentive to inline.
  
  Note [Inlining in ArgCtxt]
  ~~~~~~~~~~~~~~~~~~~~~~~~~~
  The condition (arity > 0) here is very important, because otherwise
  we end up inlining top-level stuff into useless places; eg
     x = I# 3#
     f = \y.  g x
  This can make a very big difference: it adds 16% to nofib 'integer' allocs,
  and 20% to 'power'.
  
  At one stage I replaced this condition by 'True' (leading to the above
  slow-down).  The motivation was test eyeball/inline1.hs; but that seems
  to work ok now.
  
  NOTE: arguably, we should inline in ArgCtxt only if the result of the
  call is at least CONLIKE.  At least for the cases where we use ArgCtxt
  for the RHS of a 'let', we only profit from the inlining if we get a
  CONLIKE thing (modulo lets).
  
  Note [Lone variables]   See also Note [Interaction of exprIsWorkFree and lone variables]
  ~~~~~~~~~~~~~~~~~~~~~   which appears below
  The "lone-variable" case is important.  I spent ages messing about
  with unsatisfactory varaints, but this is nice.  The idea is that if a
  variable appears all alone
  
          as an arg of lazy fn, or rhs    BoringCtxt
          as scrutinee of a case          CaseCtxt
          as arg of a fn                  ArgCtxt
  AND
          it is bound to a cheap expression
  
  then we should not inline it (unless there is some other reason,
  e.g. is is the sole occurrence).  That is what is happening at
  the use of 'lone_variable' in 'interesting_call'.
  
  Why?  At least in the case-scrutinee situation, turning
          let x = (a,b) in case x of y -> ...
  into
          let x = (a,b) in case (a,b) of y -> ...
  and thence to
          let x = (a,b) in let y = (a,b) in ...
  is bad if the binding for x will remain.
  
  Another example: I discovered that strings
  were getting inlined straight back into applications of 'error'
  because the latter is strict.
          s = "foo"
          f = \x -> ...(error s)...
  
  Fundamentally such contexts should not encourage inlining because the
  context can ``see'' the unfolding of the variable (e.g. case or a
  RULE) so there's no gain.  If the thing is bound to a value.
  
  However, watch out:
  
   * Consider this:
          foo = _inline_ (\n. [n])
          bar = _inline_ (foo 20)
          baz = \n. case bar of { (m:_) -> m + n }
     Here we really want to inline 'bar' so that we can inline 'foo'
     and the whole thing unravels as it should obviously do.  This is
     important: in the NDP project, 'bar' generates a closure data
     structure rather than a list.
  
     So the non-inlining of lone_variables should only apply if the
     unfolding is regarded as cheap; because that is when exprIsConApp_maybe
     looks through the unfolding.  Hence the "&& is_wf" in the
     InlineRule branch.
  
   * Even a type application or coercion isn't a lone variable.
     Consider
          case $fMonadST @ RealWorld of { :DMonad a b c -> c }
     We had better inline that sucker!  The case won't see through it.
  
     For now, I'm treating treating a variable applied to types
     in a *lazy* context "lone". The motivating example was
          f = /\a. \x. BIG
          g = /\a. \y.  h (f a)
     There's no advantage in inlining f here, and perhaps
     a significant disadvantage.  Hence some_val_args in the Stop case
  
  Note [Interaction of exprIsWorkFree and lone variables]
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  The lone-variable test says "don't inline if a case expression
  scrutines a lone variable whose unfolding is cheap".  It's very
  important that, under these circumstances, exprIsConApp_maybe
  can spot a constructor application. So, for example, we don't
  consider
          let x = e in (x,x)
  to be cheap, and that's good because exprIsConApp_maybe doesn't
  think that expression is a constructor application.
  
  In the 'not (lone_variable && is_wf)' test, I used to test is_value
  rather than is_wf, which was utterly wrong, because the above
  expression responds True to exprIsHNF, which is what sets is_value.
  
  This kind of thing can occur if you have
  
          {-# INLINE foo #-}
          foo = let x = e in (x,x)
  
  which Roman did.
  -}
  
  computeDiscount :: DynFlags -> [Int] -> Int -> [ArgSummary] -> CallCtxt
                  -> Int
  computeDiscount dflags arg_discounts res_discount arg_infos cont_info
          -- We multiple the raw discounts (args_discount and result_discount)
          -- ty opt_UnfoldingKeenessFactor because the former have to do with
          --  *size* whereas the discounts imply that there's some extra
          --  *efficiency* to be gained (e.g. beta reductions, case reductions)
          -- by inlining.
  
    = 10          -- Discount of 10 because the result replaces the call
                  -- so we count 10 for the function itself
  
      + 10 * length actual_arg_discounts
                 -- Discount of 10 for each arg supplied,
                 -- because the result replaces the call
  
      + round (ufKeenessFactor dflags *
               fromIntegral (total_arg_discount + res_discount'))
    where
      actual_arg_discounts = zipWith mk_arg_discount arg_discounts arg_infos
      total_arg_discount   = sum actual_arg_discounts
  
      mk_arg_discount _        TrivArg    = 0
      mk_arg_discount _        NonTrivArg = 10
      mk_arg_discount discount ValueArg   = discount
  
      res_discount'
        | LT <- arg_discounts `compareLength` arg_infos
        = res_discount   -- Over-saturated
        | otherwise
        = case cont_info of
                          BoringCtxt  -> 0
                          CaseCtxt    -> res_discount  -- Presumably a constructor
                          ValAppCtxt  -> res_discount  -- Presumably a function
                          _           -> 40 `min` res_discount
                  -- ToDo: this 40 `min` res_discount doesn't seem right
                  --   for DiscArgCtxt it shouldn't matter because the function will
                  --    get the arg discount for any non-triv arg
                  --   for RuleArgCtxt we do want to be keener to inline; but not only
                  --    constructor results
                  --   for RhsCtxt I suppose that exposing a data con is good in general
                  --   And 40 seems very arbitrary
                  --
                  -- res_discount can be very large when a function returns
                  -- constructors; but we only want to invoke that large discount
                  -- when there's a case continuation.
                  -- Otherwise we, rather arbitrarily, threshold it.  Yuk.
                  -- But we want to aovid inlining large functions that return
                  -- constructors into contexts that are simply "interesting"
  
  