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

-- | Unfolding creation
module GHC.Core.Unfold.Make
   ( noUnfolding
   , mkUnfolding
   , mkCoreUnfolding
   , mkFinalUnfolding
   , mkFinalUnfolding'
   , mkSimpleUnfolding
   , mkWorkerUnfolding
   , mkInlineUnfoldingWithArity, mkInlineUnfoldingNoArity
   , mkInlinableUnfolding
   , mkWrapperUnfolding
   , mkCompulsoryUnfolding, mkCompulsoryUnfolding'
   , mkDFunUnfolding
   , mkDataConUnfolding
   , specUnfolding
   , certainlyWillInline
   )
where

import GHC.Prelude
import GHC.Core
import GHC.Core.Unfold
import GHC.Core.Opt.OccurAnal ( occurAnalyseExpr )
import GHC.Core.Opt.Arity   ( manifestArity )
import GHC.Core.DataCon
import GHC.Core.Utils
import GHC.Types.Basic
import GHC.Types.Id
import GHC.Types.Id.Info
import GHC.Types.Demand ( DmdSig, isDeadEndSig )

import GHC.Utils.Outputable
import GHC.Utils.Misc
import GHC.Utils.Panic

import Data.Maybe ( fromMaybe )

-- the very simple optimiser is used to optimise unfoldings
import {-# SOURCE #-} GHC.Core.SimpleOpt



mkFinalUnfolding :: UnfoldingOpts -> UnfoldingSource -> DmdSig -> CoreExpr -> Unfolding
-- "Final" in the sense that this is a GlobalId that will not be further
-- simplified; so the unfolding should be occurrence-analysed
mkFinalUnfolding :: UnfoldingOpts -> UnfoldingSource -> DmdSig -> CoreArg -> Unfolding
mkFinalUnfolding UnfoldingOpts
opts UnfoldingSource
src DmdSig
strict_sig CoreArg
expr = UnfoldingOpts
-> UnfoldingSource
-> DmdSig
-> CoreArg
-> Maybe UnfoldingCache
-> Unfolding
mkFinalUnfolding' UnfoldingOpts
opts UnfoldingSource
src DmdSig
strict_sig CoreArg
expr Maybe UnfoldingCache
forall a. Maybe a
Nothing

-- See Note [Tying the 'CoreUnfolding' knot] for why interfaces need
-- to pass a precomputed 'UnfoldingCache'
mkFinalUnfolding' :: UnfoldingOpts -> UnfoldingSource -> DmdSig -> CoreExpr -> Maybe UnfoldingCache -> Unfolding
-- "Final" in the sense that this is a GlobalId that will not be further
-- simplified; so the unfolding should be occurrence-analysed
mkFinalUnfolding' :: UnfoldingOpts
-> UnfoldingSource
-> DmdSig
-> CoreArg
-> Maybe UnfoldingCache
-> Unfolding
mkFinalUnfolding' UnfoldingOpts
opts UnfoldingSource
src DmdSig
strict_sig CoreArg
expr
  = UnfoldingOpts
-> UnfoldingSource
-> Bool
-> Bool
-> CoreArg
-> Maybe UnfoldingCache
-> Unfolding
mkUnfolding UnfoldingOpts
opts UnfoldingSource
src
                Bool
True {- Top level -}
                (DmdSig -> Bool
isDeadEndSig DmdSig
strict_sig)
                CoreArg
expr

-- | Same as 'mkCompulsoryUnfolding' but simplifies the unfolding first
mkCompulsoryUnfolding' :: SimpleOpts -> CoreExpr -> Unfolding
mkCompulsoryUnfolding' :: SimpleOpts -> CoreArg -> Unfolding
mkCompulsoryUnfolding' SimpleOpts
opts CoreArg
expr = CoreArg -> Unfolding
mkCompulsoryUnfolding (HasDebugCallStack => SimpleOpts -> CoreArg -> CoreArg
SimpleOpts -> CoreArg -> CoreArg
simpleOptExpr SimpleOpts
opts CoreArg
expr)

-- | Used for things that absolutely must be unfolded
mkCompulsoryUnfolding :: CoreExpr -> Unfolding
mkCompulsoryUnfolding :: CoreArg -> Unfolding
mkCompulsoryUnfolding CoreArg
expr
  = UnfoldingSource
-> Bool
-> CoreArg
-> Maybe UnfoldingCache
-> UnfoldingGuidance
-> Unfolding
mkCoreUnfolding UnfoldingSource
CompulsorySrc Bool
True
                    CoreArg
expr Maybe UnfoldingCache
forall a. Maybe a
Nothing
                    (UnfWhen { ug_arity :: ArityInfo
ug_arity = ArityInfo
0    -- Arity of unfolding doesn't matter
                             , ug_unsat_ok :: Bool
ug_unsat_ok = Bool
unSaturatedOk, ug_boring_ok :: Bool
ug_boring_ok = Bool
boringCxtOk })

-- 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 :: UnfoldingOpts -> CoreExpr -> Unfolding
mkSimpleUnfolding :: UnfoldingOpts -> CoreArg -> Unfolding
mkSimpleUnfolding !UnfoldingOpts
opts CoreArg
rhs
  = UnfoldingOpts
-> UnfoldingSource
-> Bool
-> Bool
-> CoreArg
-> Maybe UnfoldingCache
-> Unfolding
mkUnfolding UnfoldingOpts
opts UnfoldingSource
VanillaSrc Bool
False Bool
False CoreArg
rhs Maybe UnfoldingCache
forall a. Maybe a
Nothing

mkDFunUnfolding :: [Var] -> DataCon -> [CoreExpr] -> Unfolding
mkDFunUnfolding :: [Var] -> DataCon -> [CoreArg] -> Unfolding
mkDFunUnfolding [Var]
bndrs DataCon
con [CoreArg]
ops
  = DFunUnfolding { df_bndrs :: [Var]
df_bndrs = [Var]
bndrs
                  , df_con :: DataCon
df_con = DataCon
con
                  , df_args :: [CoreArg]
df_args = (CoreArg -> CoreArg) -> [CoreArg] -> [CoreArg]
forall a b. (a -> b) -> [a] -> [b]
map CoreArg -> CoreArg
occurAnalyseExpr [CoreArg]
ops }
                  -- See Note [Occurrence analysis of unfoldings]

mkDataConUnfolding :: CoreExpr -> Unfolding
-- Used for non-newtype data constructors with non-trivial wrappers
mkDataConUnfolding :: CoreArg -> Unfolding
mkDataConUnfolding CoreArg
expr
  = UnfoldingSource
-> Bool
-> CoreArg
-> Maybe UnfoldingCache
-> UnfoldingGuidance
-> Unfolding
mkCoreUnfolding UnfoldingSource
StableSystemSrc Bool
True CoreArg
expr Maybe UnfoldingCache
forall a. Maybe a
Nothing UnfoldingGuidance
guide
    -- No need to simplify the expression
  where
    guide :: UnfoldingGuidance
guide = UnfWhen { ug_arity :: ArityInfo
ug_arity     = CoreArg -> ArityInfo
manifestArity CoreArg
expr
                    , ug_unsat_ok :: Bool
ug_unsat_ok  = Bool
unSaturatedOk
                    , ug_boring_ok :: Bool
ug_boring_ok = Bool
False }

mkWrapperUnfolding :: SimpleOpts -> CoreExpr -> Arity -> Unfolding
-- Make the unfolding for the wrapper in a worker/wrapper split
-- after demand/CPR analysis
mkWrapperUnfolding :: SimpleOpts -> CoreArg -> ArityInfo -> Unfolding
mkWrapperUnfolding SimpleOpts
opts CoreArg
expr ArityInfo
arity
  = UnfoldingSource
-> Bool
-> CoreArg
-> Maybe UnfoldingCache
-> UnfoldingGuidance
-> Unfolding
mkCoreUnfolding UnfoldingSource
StableSystemSrc Bool
True
                    (HasDebugCallStack => SimpleOpts -> CoreArg -> CoreArg
SimpleOpts -> CoreArg -> CoreArg
simpleOptExpr SimpleOpts
opts CoreArg
expr) Maybe UnfoldingCache
forall a. Maybe a
Nothing
                    (UnfWhen { ug_arity :: ArityInfo
ug_arity     = ArityInfo
arity
                             , ug_unsat_ok :: Bool
ug_unsat_ok  = Bool
unSaturatedOk
                             , ug_boring_ok :: Bool
ug_boring_ok = Bool
boringCxtNotOk })

mkWorkerUnfolding :: SimpleOpts -> (CoreExpr -> CoreExpr) -> Unfolding -> Unfolding
-- See Note [Worker/wrapper for INLINABLE functions] in GHC.Core.Opt.WorkWrap
mkWorkerUnfolding :: SimpleOpts -> (CoreArg -> CoreArg) -> Unfolding -> Unfolding
mkWorkerUnfolding SimpleOpts
opts CoreArg -> CoreArg
work_fn
                  (CoreUnfolding { uf_src :: Unfolding -> UnfoldingSource
uf_src = UnfoldingSource
src, uf_tmpl :: Unfolding -> CoreArg
uf_tmpl = CoreArg
tmpl
                                 , uf_is_top :: Unfolding -> Bool
uf_is_top = Bool
top_lvl })
  | UnfoldingSource -> Bool
isStableSource UnfoldingSource
src
  = UnfoldingSource
-> Bool
-> CoreArg
-> Maybe UnfoldingCache
-> UnfoldingGuidance
-> Unfolding
mkCoreUnfolding UnfoldingSource
src Bool
top_lvl CoreArg
new_tmpl Maybe UnfoldingCache
forall a. Maybe a
Nothing UnfoldingGuidance
guidance
  where
    new_tmpl :: CoreArg
new_tmpl = HasDebugCallStack => SimpleOpts -> CoreArg -> CoreArg
SimpleOpts -> CoreArg -> CoreArg
simpleOptExpr SimpleOpts
opts (CoreArg -> CoreArg
work_fn CoreArg
tmpl)
    guidance :: UnfoldingGuidance
guidance = UnfoldingOpts -> Bool -> CoreArg -> UnfoldingGuidance
calcUnfoldingGuidance (SimpleOpts -> UnfoldingOpts
so_uf_opts SimpleOpts
opts) Bool
False CoreArg
new_tmpl

mkWorkerUnfolding SimpleOpts
_ CoreArg -> CoreArg
_ Unfolding
_ = Unfolding
noUnfolding

-- | Make an INLINE unfolding that may be used unsaturated
-- (ug_unsat_ok = unSaturatedOk) and that is reported as having its
-- manifest arity (the number of outer lambdas applications will
-- resolve before doing any work).
mkInlineUnfoldingNoArity :: SimpleOpts -> UnfoldingSource -> CoreExpr -> Unfolding
mkInlineUnfoldingNoArity :: SimpleOpts -> UnfoldingSource -> CoreArg -> Unfolding
mkInlineUnfoldingNoArity SimpleOpts
opts UnfoldingSource
src CoreArg
expr
  = UnfoldingSource
-> Bool
-> CoreArg
-> Maybe UnfoldingCache
-> UnfoldingGuidance
-> Unfolding
mkCoreUnfolding UnfoldingSource
src
                    Bool
True         -- Note [Top-level flag on inline rules]
                    CoreArg
expr' Maybe UnfoldingCache
forall a. Maybe a
Nothing UnfoldingGuidance
guide
  where
    expr' :: CoreArg
expr' = HasDebugCallStack => SimpleOpts -> CoreArg -> CoreArg
SimpleOpts -> CoreArg -> CoreArg
simpleOptExpr SimpleOpts
opts CoreArg
expr
    guide :: UnfoldingGuidance
guide = UnfWhen { ug_arity :: ArityInfo
ug_arity = CoreArg -> ArityInfo
manifestArity CoreArg
expr'
                    , ug_unsat_ok :: Bool
ug_unsat_ok = Bool
unSaturatedOk
                    , ug_boring_ok :: Bool
ug_boring_ok = Bool
boring_ok }
    boring_ok :: Bool
boring_ok = CoreArg -> Bool
inlineBoringOk CoreArg
expr'

-- | Make an INLINE unfolding that will be used once the RHS has been saturated
-- to the given arity.
mkInlineUnfoldingWithArity :: SimpleOpts -> UnfoldingSource -> Arity -> CoreExpr -> Unfolding
mkInlineUnfoldingWithArity :: SimpleOpts -> UnfoldingSource -> ArityInfo -> CoreArg -> Unfolding
mkInlineUnfoldingWithArity SimpleOpts
opts UnfoldingSource
src ArityInfo
arity CoreArg
expr
  = UnfoldingSource
-> Bool
-> CoreArg
-> Maybe UnfoldingCache
-> UnfoldingGuidance
-> Unfolding
mkCoreUnfolding UnfoldingSource
src
                    Bool
True         -- Note [Top-level flag on inline rules]
                    CoreArg
expr' Maybe UnfoldingCache
forall a. Maybe a
Nothing UnfoldingGuidance
guide
  where
    expr' :: CoreArg
expr' = HasDebugCallStack => SimpleOpts -> CoreArg -> CoreArg
SimpleOpts -> CoreArg -> CoreArg
simpleOptExpr SimpleOpts
opts CoreArg
expr
    guide :: UnfoldingGuidance
guide = UnfWhen { ug_arity :: ArityInfo
ug_arity = ArityInfo
arity
                    , ug_unsat_ok :: Bool
ug_unsat_ok = Bool
needSaturated
                    , ug_boring_ok :: Bool
ug_boring_ok = Bool
boring_ok }
    -- See Note [INLINE pragmas and boring contexts] as to why we need to look
    -- at the arity here.
    boring_ok :: Bool
boring_ok | ArityInfo
arity ArityInfo -> ArityInfo -> Bool
forall a. Eq a => a -> a -> Bool
== ArityInfo
0 = Bool
True
              | Bool
otherwise  = CoreArg -> Bool
inlineBoringOk CoreArg
expr'

mkInlinableUnfolding :: SimpleOpts -> UnfoldingSource -> CoreExpr -> Unfolding
mkInlinableUnfolding :: SimpleOpts -> UnfoldingSource -> CoreArg -> Unfolding
mkInlinableUnfolding SimpleOpts
opts UnfoldingSource
src CoreArg
expr
  = UnfoldingOpts
-> UnfoldingSource
-> Bool
-> Bool
-> CoreArg
-> Maybe UnfoldingCache
-> Unfolding
mkUnfolding (SimpleOpts -> UnfoldingOpts
so_uf_opts SimpleOpts
opts) UnfoldingSource
src Bool
False Bool
False CoreArg
expr' Maybe UnfoldingCache
forall a. Maybe a
Nothing
  where
    expr' :: CoreArg
expr' = HasDebugCallStack => SimpleOpts -> CoreArg -> CoreArg
SimpleOpts -> CoreArg -> CoreArg
simpleOptExpr SimpleOpts
opts CoreArg
expr

specUnfolding :: SimpleOpts
              -> [Var] -> (CoreExpr -> CoreExpr)
              -> [CoreArg]   -- LHS arguments in the RULE
              -> Unfolding -> Unfolding
-- See Note [Specialising unfoldings]
-- specUnfolding spec_bndrs spec_args unf
--   = \spec_bndrs. unf spec_args
--
specUnfolding :: SimpleOpts
-> [Var]
-> (CoreArg -> CoreArg)
-> [CoreArg]
-> Unfolding
-> Unfolding
specUnfolding SimpleOpts
opts [Var]
spec_bndrs CoreArg -> CoreArg
spec_app [CoreArg]
rule_lhs_args
              df :: Unfolding
df@(DFunUnfolding { df_bndrs :: Unfolding -> [Var]
df_bndrs = [Var]
old_bndrs, df_con :: Unfolding -> DataCon
df_con = DataCon
con, df_args :: Unfolding -> [CoreArg]
df_args = [CoreArg]
args })
  = Bool -> SDoc -> Unfolding -> Unfolding
forall a. HasCallStack => Bool -> SDoc -> a -> a
assertPpr ([CoreArg]
rule_lhs_args [CoreArg] -> [Var] -> Bool
forall a b. [a] -> [b] -> Bool
`equalLength` [Var]
old_bndrs)
              (Unfolding -> SDoc
forall a. Outputable a => a -> SDoc
ppr Unfolding
df SDoc -> SDoc -> SDoc
forall doc. IsDoc doc => doc -> doc -> doc
$$ [CoreArg] -> SDoc
forall a. Outputable a => a -> SDoc
ppr [CoreArg]
rule_lhs_args) (Unfolding -> Unfolding) -> Unfolding -> Unfolding
forall a b. (a -> b) -> a -> b
$
           -- For this ASSERT see Note [Specialising DFuns] in GHC.Core.Opt.Specialise
    [Var] -> DataCon -> [CoreArg] -> Unfolding
mkDFunUnfolding [Var]
spec_bndrs DataCon
con ((CoreArg -> CoreArg) -> [CoreArg] -> [CoreArg]
forall a b. (a -> b) -> [a] -> [b]
map CoreArg -> CoreArg
spec_arg [CoreArg]
args)
      -- For DFunUnfoldings we transform
      --       \obs. MkD <op1> ... <opn>
      -- to
      --       \sbs. MkD ((\obs. <op1>) spec_args) ... ditto <opn>
  where
    spec_arg :: CoreArg -> CoreArg
spec_arg CoreArg
arg = HasDebugCallStack => SimpleOpts -> CoreArg -> CoreArg
SimpleOpts -> CoreArg -> CoreArg
simpleOptExpr SimpleOpts
opts (CoreArg -> CoreArg) -> CoreArg -> CoreArg
forall a b. (a -> b) -> a -> b
$
                   CoreArg -> CoreArg
spec_app ([Var] -> CoreArg -> CoreArg
forall b. [b] -> Expr b -> Expr b
mkLams [Var]
old_bndrs CoreArg
arg)
                   -- The beta-redexes created by spec_app will be
                   -- simplified away by simplOptExpr

specUnfolding SimpleOpts
opts [Var]
spec_bndrs CoreArg -> CoreArg
spec_app [CoreArg]
rule_lhs_args
              (CoreUnfolding { uf_src :: Unfolding -> UnfoldingSource
uf_src = UnfoldingSource
src, uf_tmpl :: Unfolding -> CoreArg
uf_tmpl = CoreArg
tmpl
                             , uf_is_top :: Unfolding -> Bool
uf_is_top = Bool
top_lvl
                             , uf_guidance :: Unfolding -> UnfoldingGuidance
uf_guidance = UnfoldingGuidance
old_guidance })
 | UnfoldingSource -> Bool
isStableSource UnfoldingSource
src  -- See Note [Specialising unfoldings]
 , UnfWhen { ug_arity :: UnfoldingGuidance -> ArityInfo
ug_arity = ArityInfo
old_arity } <- UnfoldingGuidance
old_guidance
 = UnfoldingSource
-> Bool
-> CoreArg
-> Maybe UnfoldingCache
-> UnfoldingGuidance
-> Unfolding
mkCoreUnfolding UnfoldingSource
src Bool
top_lvl CoreArg
new_tmpl Maybe UnfoldingCache
forall a. Maybe a
Nothing
                   (UnfoldingGuidance
old_guidance { ug_arity = old_arity - arity_decrease })
 where
   new_tmpl :: CoreArg
new_tmpl = HasDebugCallStack => SimpleOpts -> CoreArg -> CoreArg
SimpleOpts -> CoreArg -> CoreArg
simpleOptExpr SimpleOpts
opts (CoreArg -> CoreArg) -> CoreArg -> CoreArg
forall a b. (a -> b) -> a -> b
$
              [Var] -> CoreArg -> CoreArg
forall b. [b] -> Expr b -> Expr b
mkLams [Var]
spec_bndrs  (CoreArg -> CoreArg) -> CoreArg -> CoreArg
forall a b. (a -> b) -> a -> b
$
              CoreArg -> CoreArg
spec_app CoreArg
tmpl  -- The beta-redexes created by spec_app
                             -- will be simplified away by simplOptExpr
   arity_decrease :: ArityInfo
arity_decrease = (CoreArg -> Bool) -> [CoreArg] -> ArityInfo
forall a. (a -> Bool) -> [a] -> ArityInfo
count CoreArg -> Bool
forall b. Expr b -> Bool
isValArg [CoreArg]
rule_lhs_args ArityInfo -> ArityInfo -> ArityInfo
forall a. Num a => a -> a -> a
- (Var -> Bool) -> [Var] -> ArityInfo
forall a. (a -> Bool) -> [a] -> ArityInfo
count Var -> Bool
isId [Var]
spec_bndrs


specUnfolding SimpleOpts
_ [Var]
_ CoreArg -> CoreArg
_ [CoreArg]
_ Unfolding
_ = Unfolding
noUnfolding

{- 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

* For a /stable/ CoreUnfolding, we specialise the unfolding, no matter
  how big, iff it has UnfWhen guidance.  This happens for INLINE
  functions, and for wrappers.  For these, it would be very odd if a
  function marked INLINE was specialised (because of some local use),
  and then forever after (including importing modules) the specialised
  version wasn't INLINEd!  After all, the programmer said INLINE.

* However, for a stable CoreUnfolding with guidance UnfoldIfGoodArgs,
  which arises from INLINABLE functions, we drop the unfolding.
  See #4874 for persuasive examples.  Suppose we have
    {-# INLINABLE f #-}
    f :: Ord a => [a] -> Int f xs = letrec f' = ...f'... in f'

  Then, when f is specialised and optimised we might get
    wgo :: [Int] -> Int#
    wgo = ...wgo...
    f_spec :: [Int] -> Int
    f_spec xs = case wgo xs of { r -> I# r }

  and we clearly want to inline f_spec at call sites.  But if we still
  have the big, un-optimised of f (albeit specialised) captured in the
  stable unfolding for f_spec, we won't get that optimisation.

  This happens with Control.Monad.liftM3, and can cause a lot more
  allocation as a result (nofib n-body shows this).

  Moreover, keeping the stable unfolding isn't much help, because
  the specialised function (probably) isn't overloaded any more.

  TL;DR: we simply drop the stable unfolding when specialising. It's not
  really a complete solution; ignoring specialisation for now, INLINABLE
  functions don't get properly strictness analysed, for example.
  Moreover, it means that the specialised function has an INLINEABLE
  pragma, but no stable unfolding. But it works well for examples
  involving specialisation, which is the dominant use of INLINABLE.

Note [Honour INLINE on 0-ary bindings]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider

   x = <expensive>
   {-# INLINE x #-}

   f y = ...x...

The semantics of an INLINE pragma is

  inline x at every call site, provided it is saturated;
  that is, applied to at least as many arguments as appear
  on the LHS of the Haskell source definition.

(This source-code-derived arity is stored in the `ug_arity` field of
the `UnfoldingGuidance`.)

In the example, x's ug_arity is 0, so we should inline it at every use
site.  It's rare to have such an INLINE pragma (usually INLINE is on
functions), but it's occasionally very important (#15578, #15519).
In #15519 we had something like
   x = case (g a b) of I# r -> T r
   {-# INLINE x #-}
   f y = ...(h x)....

where h is strict.  So we got
   f y = ...(case g a b of I# r -> h (T r))...

and that in turn allowed SpecConstr to ramp up performance.

How do we deliver on this?  By adjusting the ug_boring_ok
flag in mkInlineUnfoldingWithArity; see
Note [INLINE pragmas and boring contexts]

NB: there is a real risk that full laziness will float it right back
out again. Consider again
  x = factorial 200
  {-# INLINE x #-}
  f y = ...x...

After inlining we get
  f y = ...(factorial 200)...

but it's entirely possible that full laziness will do
  lvl23 = factorial 200
  f y = ...lvl23...

That's a problem for another day.

Note [INLINE pragmas and boring contexts]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
An INLINE pragma uses mkInlineUnfoldingWithArity to build the
unfolding.  That sets the ug_boring_ok flag to False if the function
is not tiny (inlineBoringOK), so that even INLINE functions are not
inlined in an utterly boring context.  E.g.
     \x y. Just (f y x)
Nothing is gained by inlining f here, even if it has an INLINE
pragma.

But for 0-ary bindings, we want to inline regardless; see
Note [Honour INLINE on 0-ary bindings].

I'm a bit worried that it's possible for the same kind of problem
to arise for non-0-ary functions too, but let's wait and see.
-}

mkUnfolding :: UnfoldingOpts
            -> UnfoldingSource
            -> Bool       -- Is top-level
            -> Bool       -- Definitely a bottoming binding
                          -- (only relevant for top-level bindings)
            -> CoreExpr
            -> Maybe UnfoldingCache
            -> Unfolding
-- Calculates unfolding guidance
-- Occurrence-analyses the expression before capturing it
mkUnfolding :: UnfoldingOpts
-> UnfoldingSource
-> Bool
-> Bool
-> CoreArg
-> Maybe UnfoldingCache
-> Unfolding
mkUnfolding UnfoldingOpts
opts UnfoldingSource
src Bool
top_lvl Bool
is_bottoming CoreArg
expr Maybe UnfoldingCache
cache
  = UnfoldingSource
-> Bool
-> CoreArg
-> Maybe UnfoldingCache
-> UnfoldingGuidance
-> Unfolding
mkCoreUnfolding UnfoldingSource
src Bool
top_lvl CoreArg
expr Maybe UnfoldingCache
cache UnfoldingGuidance
guidance
  where
    is_top_bottoming :: Bool
is_top_bottoming = Bool
top_lvl Bool -> Bool -> Bool
&& Bool
is_bottoming
    guidance :: UnfoldingGuidance
guidance         = UnfoldingOpts -> Bool -> CoreArg -> UnfoldingGuidance
calcUnfoldingGuidance UnfoldingOpts
opts Bool
is_top_bottoming CoreArg
expr
        -- NB: *not* (calcUnfoldingGuidance (occurAnalyseExpr expr))!
        -- See Note [Calculate unfolding guidance on the non-occ-anal'd expression]

mkCoreUnfolding :: UnfoldingSource -> Bool -> CoreExpr
                -> Maybe UnfoldingCache -> UnfoldingGuidance -> Unfolding
-- Occurrence-analyses the expression before capturing it
mkCoreUnfolding :: UnfoldingSource
-> Bool
-> CoreArg
-> Maybe UnfoldingCache
-> UnfoldingGuidance
-> Unfolding
mkCoreUnfolding UnfoldingSource
src Bool
top_lvl CoreArg
expr Maybe UnfoldingCache
precomputed_cache UnfoldingGuidance
guidance
  = CoreUnfolding { uf_tmpl :: CoreArg
uf_tmpl = UnfoldingCache
cache UnfoldingCache -> CoreArg -> CoreArg
forall a b. a -> b -> b
`seq`
                              CoreArg -> CoreArg
occurAnalyseExpr CoreArg
expr
      -- occAnalyseExpr: see Note [Occurrence analysis of unfoldings]
      -- See #20905 for what a discussion of this 'seq'.
      -- We are careful to make sure we only
      -- have one copy of an unfolding around at once.
      -- Note [Thoughtful forcing in mkCoreUnfolding]

                  , uf_src :: UnfoldingSource
uf_src          = UnfoldingSource
src
                  , uf_is_top :: Bool
uf_is_top       = Bool
top_lvl
                  , uf_cache :: UnfoldingCache
uf_cache        = UnfoldingCache
cache
                  , uf_guidance :: UnfoldingGuidance
uf_guidance     = UnfoldingGuidance
guidance }
  where
    is_value :: Bool
is_value      = CoreArg -> Bool
exprIsHNF CoreArg
expr
    is_conlike :: Bool
is_conlike    = CoreArg -> Bool
exprIsConLike CoreArg
expr
    is_work_free :: Bool
is_work_free  = CoreArg -> Bool
exprIsWorkFree CoreArg
expr
    is_expandable :: Bool
is_expandable = CoreArg -> Bool
exprIsExpandable CoreArg
expr

    recomputed_cache :: UnfoldingCache
recomputed_cache = UnfoldingCache { uf_is_value :: Bool
uf_is_value = Bool
is_value
                                      , uf_is_conlike :: Bool
uf_is_conlike = Bool
is_conlike
                                      , uf_is_work_free :: Bool
uf_is_work_free = Bool
is_work_free
                                      , uf_expandable :: Bool
uf_expandable = Bool
is_expandable }

    cache :: UnfoldingCache
cache = UnfoldingCache -> Maybe UnfoldingCache -> UnfoldingCache
forall a. a -> Maybe a -> a
fromMaybe UnfoldingCache
recomputed_cache Maybe UnfoldingCache
precomputed_cache

----------------
certainlyWillInline :: UnfoldingOpts -> IdInfo -> CoreExpr -> Maybe Unfolding
-- ^ Sees if the unfolding is pretty certain to inline.
-- If so, return a *stable* unfolding for it, that will always inline.
-- The CoreExpr is the WW'd and simplified RHS. In contrast, the unfolding
-- template might not have been WW'd yet.
certainlyWillInline :: UnfoldingOpts -> IdInfo -> CoreArg -> Maybe Unfolding
certainlyWillInline UnfoldingOpts
opts IdInfo
fn_info CoreArg
rhs'
  = case Unfolding
fn_unf of
      CoreUnfolding { uf_guidance :: Unfolding -> UnfoldingGuidance
uf_guidance = UnfoldingGuidance
guidance, uf_src :: Unfolding -> UnfoldingSource
uf_src = UnfoldingSource
src }
        | Bool
noinline -> Maybe Unfolding
forall a. Maybe a
Nothing       -- See Note [Worker/wrapper for NOINLINE functions]
        | Bool
otherwise
        -> case UnfoldingGuidance
guidance of
             UnfoldingGuidance
UnfNever   -> Maybe Unfolding
forall a. Maybe a
Nothing
             UnfWhen {} -> Unfolding -> Maybe Unfolding
forall a. a -> Maybe a
Just (Unfolding
fn_unf { uf_src = src', uf_tmpl = tmpl' })
                             -- INLINE functions have UnfWhen
             UnfIfGoodArgs { ug_size :: UnfoldingGuidance -> ArityInfo
ug_size = ArityInfo
size, ug_args :: UnfoldingGuidance -> [ArityInfo]
ug_args = [ArityInfo]
args }
                        -> ArityInfo
-> [ArityInfo] -> UnfoldingSource -> CoreArg -> Maybe Unfolding
do_cunf ArityInfo
size [ArityInfo]
args UnfoldingSource
src' CoreArg
tmpl'
        where
          src' :: UnfoldingSource
src' | UnfoldingSource -> Bool
isCompulsorySource UnfoldingSource
src = UnfoldingSource
src  -- Do not change InlineCompulsory!
               | Bool
otherwise              = UnfoldingSource
StableSystemSrc

          tmpl' :: CoreArg
tmpl' | UnfoldingSource -> Bool
isStableSource UnfoldingSource
src = Unfolding -> CoreArg
uf_tmpl Unfolding
fn_unf
                | Bool
otherwise          = CoreArg -> CoreArg
occurAnalyseExpr CoreArg
rhs'
                -- Do not overwrite stable unfoldings!

      DFunUnfolding {} -> Unfolding -> Maybe Unfolding
forall a. a -> Maybe a
Just Unfolding
fn_unf  -- Don't w/w DFuns; it never makes sense
                                       -- to do so, and even if it is currently a
                                       -- loop breaker, it may not be later

      Unfolding
_other_unf       -> Maybe Unfolding
forall a. Maybe a
Nothing

  where
    noinline :: Bool
noinline = InlinePragma -> Bool
isNoInlinePragma (IdInfo -> InlinePragma
inlinePragInfo IdInfo
fn_info)
    fn_unf :: Unfolding
fn_unf   = IdInfo -> Unfolding
unfoldingInfo IdInfo
fn_info -- NB: loop-breakers never inline

        -- 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 why.
        -- INLINABLE functions come via this path
        --    See Note [certainlyWillInline: INLINABLE]
    do_cunf :: ArityInfo
-> [ArityInfo] -> UnfoldingSource -> CoreArg -> Maybe Unfolding
do_cunf ArityInfo
size [ArityInfo]
args UnfoldingSource
src' CoreArg
tmpl'
      | IdInfo -> ArityInfo
arityInfo IdInfo
fn_info ArityInfo -> ArityInfo -> Bool
forall a. Ord a => a -> a -> Bool
> ArityInfo
0  -- See Note [certainlyWillInline: be careful of thunks]
      , Bool -> Bool
not (DmdSig -> Bool
isDeadEndSig (IdInfo -> DmdSig
dmdSigInfo IdInfo
fn_info))
              -- Do not unconditionally inline a bottoming functions even if
              -- it seems smallish. We've carefully lifted it out to top level,
              -- so we don't want to re-inline it.
      , let unf_arity :: ArityInfo
unf_arity = [ArityInfo] -> ArityInfo
forall a. [a] -> ArityInfo
forall (t :: * -> *) a. Foldable t => t a -> ArityInfo
length [ArityInfo]
args
      , ArityInfo
size ArityInfo -> ArityInfo -> ArityInfo
forall a. Num a => a -> a -> a
- (ArityInfo
10 ArityInfo -> ArityInfo -> ArityInfo
forall a. Num a => a -> a -> a
* (ArityInfo
unf_arity ArityInfo -> ArityInfo -> ArityInfo
forall a. Num a => a -> a -> a
+ ArityInfo
1)) ArityInfo -> ArityInfo -> Bool
forall a. Ord a => a -> a -> Bool
<= UnfoldingOpts -> ArityInfo
unfoldingUseThreshold UnfoldingOpts
opts
      = Unfolding -> Maybe Unfolding
forall a. a -> Maybe a
Just (Unfolding
fn_unf { uf_src      = src'
                     , uf_tmpl     = tmpl'
                     , uf_guidance = UnfWhen { ug_arity     = unf_arity
                                             , ug_unsat_ok  = unSaturatedOk
                                             , ug_boring_ok = inlineBoringOk tmpl' } })
             -- 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
      | Bool
otherwise
      = Maybe Unfolding
forall a. Maybe a
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 #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.

Note that we check arityInfo instead of the arity of the unfolding to detect
this case. This is so that we don't accidentally fail to inline small partial
applications, like `f = g 42` (where `g` recurses into `f`) where g has arity 2
(say). Here there is no risk of work duplication, and the RHS is tiny, so
certainlyWillInline should return True. But `unf_arity` is zero! However f's
arity, gotten from `arityInfo fn_info`, is 1.

Failing to say that `f` will inline forces W/W to generate a potentially huge
worker for f that will immediately cancel with `g`'s wrapper anyway, causing
unnecessary churn in the Simplifier while arriving at the same result.

Note [certainlyWillInline: INLINABLE]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
certainlyWillInline /must/ return Nothing for a large INLINABLE thing,
even though we have a stable inlining, so that strictness w/w takes
place.  It makes a big difference to efficiency, and the w/w pass knows
how to transfer the INLINABLE info to the worker; see WorkWrap
Note [Worker/wrapper for INLINABLE functions]

Note [Thoughtful forcing in mkCoreUnfolding]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Core expressions retained in unfoldings is one of biggest uses of memory when compiling
a program. Therefore we have to be careful about retaining copies of old or redundant
templates (see !6202 for a particularly bad case).

With that in mind we want to maintain the invariant that each unfolding only references
a single CoreExpr. One place where we have to be careful is in mkCoreUnfolding.

* The template of the unfolding is the result of performing occurrence analysis
  (Note [Occurrence analysis of unfoldings])
* Predicates are applied to the unanalysed expression

Therefore if we are not thoughtful about forcing you can end up in a situation where the
template is forced but not all the predicates are forced so the unfolding will retain
both the old and analysed expressions.

I investigated this using ghc-debug and it was clear this situation did often arise:

```
(["ghc:GHC.Core:Lam","ghc-prim:GHC.Types:True","THUNK_1_0","THUNK_1_0","THUNK_1_0"],Count 4307)
```

Here the predicates are unforced but the template is forced.

Therefore we basically had two options in order to fix this:

1. Perform the predicates on the analysed expression.
2. Force the predicates to remove retainer to the old expression if we force the template.

Option 1 is bad because occurrence analysis is expensive and destroys any sharing of the unfolding
with the actual program. (Testing this approach showed peak 25G memory usage)

Therefore we got for Option 2 which performs a little more work but compensates by
reducing memory pressure.

The result of fixing this led to a 1G reduction in peak memory usage (12G -> 11G) when
compiling a very large module (peak 3 million terms). For more discussion see #20905.
-}