{-
(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 CoreUnfold (
        Unfolding, UnfoldingGuidance,   -- Abstract types

        noUnfolding, mkImplicitUnfolding,
        mkUnfolding, mkCoreUnfolding,
        mkTopUnfolding, mkSimpleUnfolding, mkWorkerUnfolding,
        mkInlineUnfolding, mkInlineUnfoldingWithArity,
        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 GhcPrelude

import DynFlags
import CoreSyn
import OccurAnal        ( occurAnalyseExpr_NoBinderSwap )
import CoreOpt
import CoreArity       ( manifestArity )
import CoreUtils
import Id
import Demand          ( isBottomingSig )
import DataCon
import Literal
import PrimOp
import IdInfo
import BasicTypes       ( Arity, InlineSpec(..), inlinePragmaSpec )
import Type
import PrelNames
import TysPrim          ( realWorldStatePrimTy )
import Bag
import Util
import Outputable
import ForeignCall
import Name

import qualified Data.ByteString as BS
import Data.List

{-
************************************************************************
*                                                                      *
\subsection{Making unfoldings}
*                                                                      *
************************************************************************
-}

mkTopUnfolding :: DynFlags -> Bool -> CoreExpr -> Unfolding
mkTopUnfolding :: DynFlags -> Bool -> CoreExpr -> Unfolding
mkTopUnfolding DynFlags
dflags Bool
is_bottoming CoreExpr
rhs
  = DynFlags
-> UnfoldingSource -> Bool -> Bool -> CoreExpr -> Unfolding
mkUnfolding DynFlags
dflags UnfoldingSource
InlineRhs Bool
True Bool
is_bottoming CoreExpr
rhs

mkImplicitUnfolding :: DynFlags -> CoreExpr -> Unfolding
-- For implicit Ids, do a tiny bit of optimising first
mkImplicitUnfolding :: DynFlags -> CoreExpr -> Unfolding
mkImplicitUnfolding DynFlags
dflags CoreExpr
expr
  = DynFlags -> Bool -> CoreExpr -> Unfolding
mkTopUnfolding DynFlags
dflags Bool
False (DynFlags -> CoreExpr -> CoreExpr
simpleOptExpr DynFlags
dflags CoreExpr
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 :: DynFlags -> CoreExpr -> Unfolding
mkSimpleUnfolding DynFlags
dflags CoreExpr
rhs
  = DynFlags
-> UnfoldingSource -> Bool -> Bool -> CoreExpr -> Unfolding
mkUnfolding DynFlags
dflags UnfoldingSource
InlineRhs Bool
False Bool
False CoreExpr
rhs

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

mkWwInlineRule :: DynFlags -> CoreExpr -> Arity -> Unfolding
mkWwInlineRule :: DynFlags -> CoreExpr -> Arity -> Unfolding
mkWwInlineRule DynFlags
dflags CoreExpr
expr Arity
arity
  = UnfoldingSource
-> Bool -> CoreExpr -> UnfoldingGuidance -> Unfolding
mkCoreUnfolding UnfoldingSource
InlineStable Bool
True
                   (DynFlags -> CoreExpr -> CoreExpr
simpleOptExpr DynFlags
dflags CoreExpr
expr)
                   (UnfWhen :: Arity -> Bool -> Bool -> UnfoldingGuidance
UnfWhen { ug_arity :: Arity
ug_arity = Arity
arity, ug_unsat_ok :: Bool
ug_unsat_ok = Bool
unSaturatedOk
                            , ug_boring_ok :: Bool
ug_boring_ok = Bool
boringCxtNotOk })

mkCompulsoryUnfolding :: CoreExpr -> Unfolding
mkCompulsoryUnfolding :: CoreExpr -> Unfolding
mkCompulsoryUnfolding CoreExpr
expr         -- Used for things that absolutely must be unfolded
  = UnfoldingSource
-> Bool -> CoreExpr -> UnfoldingGuidance -> Unfolding
mkCoreUnfolding UnfoldingSource
InlineCompulsory Bool
True
                    (DynFlags -> CoreExpr -> CoreExpr
simpleOptExpr DynFlags
unsafeGlobalDynFlags CoreExpr
expr)
                    (UnfWhen :: Arity -> Bool -> Bool -> UnfoldingGuidance
UnfWhen { ug_arity :: Arity
ug_arity = Arity
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 })

mkWorkerUnfolding :: DynFlags -> (CoreExpr -> CoreExpr) -> Unfolding -> Unfolding
-- See Note [Worker-wrapper for INLINABLE functions] in WorkWrap
mkWorkerUnfolding :: DynFlags -> (CoreExpr -> CoreExpr) -> Unfolding -> Unfolding
mkWorkerUnfolding DynFlags
dflags CoreExpr -> CoreExpr
work_fn
                  (CoreUnfolding { uf_src :: Unfolding -> UnfoldingSource
uf_src = UnfoldingSource
src, uf_tmpl :: Unfolding -> CoreExpr
uf_tmpl = CoreExpr
tmpl
                                 , uf_is_top :: Unfolding -> Bool
uf_is_top = Bool
top_lvl })
  | UnfoldingSource -> Bool
isStableSource UnfoldingSource
src
  = UnfoldingSource
-> Bool -> CoreExpr -> UnfoldingGuidance -> Unfolding
mkCoreUnfolding UnfoldingSource
src Bool
top_lvl CoreExpr
new_tmpl UnfoldingGuidance
guidance
  where
    new_tmpl :: CoreExpr
new_tmpl = DynFlags -> CoreExpr -> CoreExpr
simpleOptExpr DynFlags
dflags (CoreExpr -> CoreExpr
work_fn CoreExpr
tmpl)
    guidance :: UnfoldingGuidance
guidance = DynFlags -> Bool -> CoreExpr -> UnfoldingGuidance
calcUnfoldingGuidance DynFlags
dflags Bool
False CoreExpr
new_tmpl

mkWorkerUnfolding DynFlags
_ CoreExpr -> CoreExpr
_ Unfolding
_ = Unfolding
noUnfolding

-- | Make an 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).
mkInlineUnfolding :: CoreExpr -> Unfolding
mkInlineUnfolding :: CoreExpr -> Unfolding
mkInlineUnfolding CoreExpr
expr
  = UnfoldingSource
-> Bool -> CoreExpr -> UnfoldingGuidance -> Unfolding
mkCoreUnfolding UnfoldingSource
InlineStable
                    Bool
True         -- Note [Top-level flag on inline rules]
                    CoreExpr
expr' UnfoldingGuidance
guide
  where
    expr' :: CoreExpr
expr' = DynFlags -> CoreExpr -> CoreExpr
simpleOptExpr DynFlags
unsafeGlobalDynFlags CoreExpr
expr
    guide :: UnfoldingGuidance
guide = UnfWhen :: Arity -> Bool -> Bool -> UnfoldingGuidance
UnfWhen { ug_arity :: Arity
ug_arity = CoreExpr -> Arity
manifestArity CoreExpr
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 = CoreExpr -> Bool
inlineBoringOk CoreExpr
expr'

-- | Make an unfolding that will be used once the RHS has been saturated
-- to the given arity.
mkInlineUnfoldingWithArity :: Arity -> CoreExpr -> Unfolding
mkInlineUnfoldingWithArity :: Arity -> CoreExpr -> Unfolding
mkInlineUnfoldingWithArity Arity
arity CoreExpr
expr
  = UnfoldingSource
-> Bool -> CoreExpr -> UnfoldingGuidance -> Unfolding
mkCoreUnfolding UnfoldingSource
InlineStable
                    Bool
True         -- Note [Top-level flag on inline rules]
                    CoreExpr
expr' UnfoldingGuidance
guide
  where
    expr' :: CoreExpr
expr' = DynFlags -> CoreExpr -> CoreExpr
simpleOptExpr DynFlags
unsafeGlobalDynFlags CoreExpr
expr
    guide :: UnfoldingGuidance
guide = UnfWhen :: Arity -> Bool -> Bool -> UnfoldingGuidance
UnfWhen { ug_arity :: Arity
ug_arity = Arity
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 | Arity
arity Arity -> Arity -> Bool
forall a. Eq a => a -> a -> Bool
== Arity
0 = Bool
True
              | Bool
otherwise  = CoreExpr -> Bool
inlineBoringOk CoreExpr
expr'

mkInlinableUnfolding :: DynFlags -> CoreExpr -> Unfolding
mkInlinableUnfolding :: DynFlags -> CoreExpr -> Unfolding
mkInlinableUnfolding DynFlags
dflags CoreExpr
expr
  = DynFlags
-> UnfoldingSource -> Bool -> Bool -> CoreExpr -> Unfolding
mkUnfolding DynFlags
dflags UnfoldingSource
InlineStable Bool
False Bool
False CoreExpr
expr'
  where
    expr' :: CoreExpr
expr' = DynFlags -> CoreExpr -> CoreExpr
simpleOptExpr DynFlags
dflags CoreExpr
expr

specUnfolding :: DynFlags
              -> [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 :: DynFlags
-> [Var]
-> (CoreExpr -> CoreExpr)
-> [CoreExpr]
-> Unfolding
-> Unfolding
specUnfolding DynFlags
dflags [Var]
spec_bndrs CoreExpr -> CoreExpr
spec_app [CoreExpr]
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 -> [CoreExpr]
df_args = [CoreExpr]
args })
  = ASSERT2( rule_lhs_args `equalLength` old_bndrs
           , ppr df $$ ppr rule_lhs_args )
           -- For this ASSERT see Note [DFunUnfoldings] in GHC.Core.Opt.Specialise
    [Var] -> DataCon -> [CoreExpr] -> Unfolding
mkDFunUnfolding [Var]
spec_bndrs DataCon
con ((CoreExpr -> CoreExpr) -> [CoreExpr] -> [CoreExpr]
forall a b. (a -> b) -> [a] -> [b]
map CoreExpr -> CoreExpr
spec_arg [CoreExpr]
args)
      -- For DFunUnfoldings we transform
      --       \obs. MkD <op1> ... <opn>
      -- to
      --       \sbs. MkD ((\obs. <op1>) spec_args) ... ditto <opn>
  where
    spec_arg :: CoreExpr -> CoreExpr
spec_arg CoreExpr
arg = DynFlags -> CoreExpr -> CoreExpr
simpleOptExpr DynFlags
dflags (CoreExpr -> CoreExpr) -> CoreExpr -> CoreExpr
forall a b. (a -> b) -> a -> b
$
                   CoreExpr -> CoreExpr
spec_app ([Var] -> CoreExpr -> CoreExpr
forall b. [b] -> Expr b -> Expr b
mkLams [Var]
old_bndrs CoreExpr
arg)
                   -- The beta-redexes created by spec_app will be
                   -- simplified away by simplOptExpr

specUnfolding DynFlags
dflags [Var]
spec_bndrs CoreExpr -> CoreExpr
spec_app [CoreExpr]
rule_lhs_args
              (CoreUnfolding { uf_src :: Unfolding -> UnfoldingSource
uf_src = UnfoldingSource
src, uf_tmpl :: Unfolding -> CoreExpr
uf_tmpl = CoreExpr
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 -> Arity
ug_arity     = Arity
old_arity } <- UnfoldingGuidance
old_guidance
 = UnfoldingSource
-> Bool -> CoreExpr -> UnfoldingGuidance -> Unfolding
mkCoreUnfolding UnfoldingSource
src Bool
top_lvl CoreExpr
new_tmpl
                   (UnfoldingGuidance
old_guidance { ug_arity :: Arity
ug_arity = Arity
old_arity Arity -> Arity -> Arity
forall a. Num a => a -> a -> a
- Arity
arity_decrease })
 where
   new_tmpl :: CoreExpr
new_tmpl = DynFlags -> CoreExpr -> CoreExpr
simpleOptExpr DynFlags
dflags (CoreExpr -> CoreExpr) -> CoreExpr -> CoreExpr
forall a b. (a -> b) -> a -> b
$
              [Var] -> CoreExpr -> CoreExpr
forall b. [b] -> Expr b -> Expr b
mkLams [Var]
spec_bndrs    (CoreExpr -> CoreExpr) -> CoreExpr -> CoreExpr
forall a b. (a -> b) -> a -> b
$
              CoreExpr -> CoreExpr
spec_app CoreExpr
tmpl  -- The beta-redexes created by spec_app
                             -- will besimplified away by simplOptExpr
   arity_decrease :: Arity
arity_decrease = (CoreExpr -> Bool) -> [CoreExpr] -> Arity
forall a. (a -> Bool) -> [a] -> Arity
count CoreExpr -> Bool
forall b. Expr b -> Bool
isValArg [CoreExpr]
rule_lhs_args Arity -> Arity -> Arity
forall a. Num a => a -> a -> a
- (Var -> Bool) -> [Var] -> Arity
forall a. (a -> Bool) -> [a] -> Arity
count Var -> Bool
isId [Var]
spec_bndrs


specUnfolding DynFlags
_ [Var]
_ CoreExpr -> CoreExpr
_ [CoreExpr]
_ 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

* There is a bit of hack for INLINABLE functions:
     f :: Ord a => ....
     f = <big-rhs>
     {- INLINABLE f #-}
  Now if we specialise f, should the specialised version still have
  an INLINABLE 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 INLINABLE 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 INLINABLE), we discard it

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 soure-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.
-}

mkCoreUnfolding :: UnfoldingSource -> Bool -> CoreExpr
                -> UnfoldingGuidance -> Unfolding
-- Occurrence-analyses the expression before capturing it
mkCoreUnfolding :: UnfoldingSource
-> Bool -> CoreExpr -> UnfoldingGuidance -> Unfolding
mkCoreUnfolding UnfoldingSource
src Bool
top_lvl CoreExpr
expr UnfoldingGuidance
guidance
  = CoreUnfolding :: CoreExpr
-> UnfoldingSource
-> Bool
-> Bool
-> Bool
-> Bool
-> Bool
-> UnfoldingGuidance
-> Unfolding
CoreUnfolding { uf_tmpl :: CoreExpr
uf_tmpl         = CoreExpr -> CoreExpr
occurAnalyseExpr_NoBinderSwap CoreExpr
expr,
                      -- See Note [Occurrence analysis of unfoldings]
                    uf_src :: UnfoldingSource
uf_src          = UnfoldingSource
src,
                    uf_is_top :: Bool
uf_is_top       = Bool
top_lvl,
                    uf_is_value :: Bool
uf_is_value     = CoreExpr -> Bool
exprIsHNF        CoreExpr
expr,
                    uf_is_conlike :: Bool
uf_is_conlike   = CoreExpr -> Bool
exprIsConLike    CoreExpr
expr,
                    uf_is_work_free :: Bool
uf_is_work_free = CoreExpr -> Bool
exprIsWorkFree   CoreExpr
expr,
                    uf_expandable :: Bool
uf_expandable   = CoreExpr -> Bool
exprIsExpandable CoreExpr
expr,
                    uf_guidance :: UnfoldingGuidance
uf_guidance     = UnfoldingGuidance
guidance }

mkUnfolding :: DynFlags -> UnfoldingSource
            -> Bool       -- Is top-level
            -> Bool       -- Definitely a bottoming binding
                          -- (only relevant for top-level bindings)
            -> CoreExpr
            -> Unfolding
-- Calculates unfolding guidance
-- Occurrence-analyses the expression before capturing it
mkUnfolding :: DynFlags
-> UnfoldingSource -> Bool -> Bool -> CoreExpr -> Unfolding
mkUnfolding DynFlags
dflags UnfoldingSource
src Bool
is_top_lvl Bool
is_bottoming CoreExpr
expr
  = CoreUnfolding :: CoreExpr
-> UnfoldingSource
-> Bool
-> Bool
-> Bool
-> Bool
-> Bool
-> UnfoldingGuidance
-> Unfolding
CoreUnfolding { uf_tmpl :: CoreExpr
uf_tmpl         = CoreExpr -> CoreExpr
occurAnalyseExpr_NoBinderSwap CoreExpr
expr,
                      -- See Note [Occurrence analysis of unfoldings]
                    uf_src :: UnfoldingSource
uf_src          = UnfoldingSource
src,
                    uf_is_top :: Bool
uf_is_top       = Bool
is_top_lvl,
                    uf_is_value :: Bool
uf_is_value     = CoreExpr -> Bool
exprIsHNF        CoreExpr
expr,
                    uf_is_conlike :: Bool
uf_is_conlike   = CoreExpr -> Bool
exprIsConLike    CoreExpr
expr,
                    uf_expandable :: Bool
uf_expandable   = CoreExpr -> Bool
exprIsExpandable CoreExpr
expr,
                    uf_is_work_free :: Bool
uf_is_work_free = CoreExpr -> Bool
exprIsWorkFree   CoreExpr
expr,
                    uf_guidance :: UnfoldingGuidance
uf_guidance     = UnfoldingGuidance
guidance }
  where
    is_top_bottoming :: Bool
is_top_bottoming = Bool
is_top_lvl Bool -> Bool -> Bool
&& Bool
is_bottoming
    guidance :: UnfoldingGuidance
guidance         = DynFlags -> Bool -> CoreExpr -> UnfoldingGuidance
calcUnfoldingGuidance DynFlags
dflags Bool
is_top_bottoming CoreExpr
expr
        -- NB: *not* (calcUnfoldingGuidance (occurAnalyseExpr_NoBinderSwap 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 #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.

We use occurAnalyseExpr_NoBinderSwap instead of occurAnalyseExpr;
see Note [No binder swap in unfoldings].

Note [No binder swap in unfoldings]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The binder swap can temporarily violate Core Lint, by assinging
a LocalId binding to a GlobalId. For example, if A.foo{r872}
is a GlobalId with unique r872, then

 case A.foo{r872} of bar {
   K x -> ...(A.foo{r872})...
 }

gets transformed to

  case A.foo{r872} of bar {
    K x -> let foo{r872} = bar
           in ...(A.foo{r872})...

This is usually not a problem, because the simplifier will transform
this to:

  case A.foo{r872} of bar {
    K x -> ...(bar)...

However, after occurrence analysis but before simplification, this extra 'let'
violates the Core Lint invariant that we do not have local 'let' bindings for
GlobalIds.  That seems (just) tolerable for the occurrence analysis that happens
just before the Simplifier, but not for unfoldings, which are Linted
independently.
As a quick workaround, we disable binder swap in this module.
See #16288 and #16296 for further plans.

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 :: CoreExpr -> Bool
inlineBoringOk CoreExpr
e
  = Arity -> CoreExpr -> Bool
go Arity
0 CoreExpr
e
  where
    go :: Int -> CoreExpr -> Bool
    go :: Arity -> CoreExpr -> Bool
go Arity
credit (Lam Var
x CoreExpr
e) | Var -> Bool
isId Var
x           = Arity -> CoreExpr -> Bool
go (Arity
creditArity -> Arity -> Arity
forall a. Num a => a -> a -> a
+Arity
1) CoreExpr
e
                        | Bool
otherwise        = Arity -> CoreExpr -> Bool
go Arity
credit CoreExpr
e
        -- See Note [Count coercion arguments in boring contexts]
    go Arity
credit (App CoreExpr
f (Type {}))            = Arity -> CoreExpr -> Bool
go Arity
credit CoreExpr
f
    go Arity
credit (App CoreExpr
f CoreExpr
a) | Arity
credit Arity -> Arity -> Bool
forall a. Ord a => a -> a -> Bool
> Arity
0
                        , CoreExpr -> Bool
exprIsTrivial CoreExpr
a  = Arity -> CoreExpr -> Bool
go (Arity
creditArity -> Arity -> Arity
forall a. Num a => a -> a -> a
-Arity
1) CoreExpr
f
    go Arity
credit (Tick Tickish Var
_ CoreExpr
e)                   = Arity -> CoreExpr -> Bool
go Arity
credit CoreExpr
e -- dubious
    go Arity
credit (Cast CoreExpr
e Coercion
_)                   = Arity -> CoreExpr -> Bool
go Arity
credit CoreExpr
e
    go Arity
_      (Var {})                     = Bool
boringCxtOk
    go Arity
_      CoreExpr
_                            = Bool
boringCxtNotOk

calcUnfoldingGuidance
        :: DynFlags
        -> Bool          -- Definitely a top-level, bottoming binding
        -> CoreExpr      -- Expression to look at
        -> UnfoldingGuidance
calcUnfoldingGuidance :: DynFlags -> Bool -> CoreExpr -> UnfoldingGuidance
calcUnfoldingGuidance DynFlags
dflags Bool
is_top_bottoming (Tick Tickish Var
t CoreExpr
expr)
  | Bool -> Bool
not (Tickish Var -> Bool
forall id. Tickish id -> Bool
tickishIsCode Tickish Var
t)  -- non-code ticks don't matter for unfolding
  = DynFlags -> Bool -> CoreExpr -> UnfoldingGuidance
calcUnfoldingGuidance DynFlags
dflags Bool
is_top_bottoming CoreExpr
expr
calcUnfoldingGuidance DynFlags
dflags Bool
is_top_bottoming CoreExpr
expr
  = case DynFlags -> Arity -> [Var] -> CoreExpr -> ExprSize
sizeExpr DynFlags
dflags Arity
bOMB_OUT_SIZE [Var]
val_bndrs CoreExpr
body of
      ExprSize
TooBig -> UnfoldingGuidance
UnfNever
      SizeIs Arity
size Bag (Var, Arity)
cased_bndrs Arity
scrut_discount
        | CoreExpr -> Arity -> Arity -> Bool
uncondInline CoreExpr
expr Arity
n_val_bndrs Arity
size
        -> UnfWhen :: Arity -> Bool -> Bool -> UnfoldingGuidance
UnfWhen { ug_unsat_ok :: Bool
ug_unsat_ok = Bool
unSaturatedOk
                   , ug_boring_ok :: Bool
ug_boring_ok =  Bool
boringCxtOk
                   , ug_arity :: Arity
ug_arity = Arity
n_val_bndrs }   -- Note [INLINE for small functions]

        | Bool
is_top_bottoming
        -> UnfoldingGuidance
UnfNever   -- See Note [Do not inline top-level bottoming functions]

        | Bool
otherwise
        -> UnfIfGoodArgs :: [Arity] -> Arity -> Arity -> UnfoldingGuidance
UnfIfGoodArgs { ug_args :: [Arity]
ug_args  = (Var -> Arity) -> [Var] -> [Arity]
forall a b. (a -> b) -> [a] -> [b]
map (Bag (Var, Arity) -> Var -> Arity
mk_discount Bag (Var, Arity)
cased_bndrs) [Var]
val_bndrs
                         , ug_size :: Arity
ug_size  = Arity
size
                         , ug_res :: Arity
ug_res   = Arity
scrut_discount }

  where
    ([Var]
bndrs, CoreExpr
body) = CoreExpr -> ([Var], CoreExpr)
forall b. Expr b -> ([b], Expr b)
collectBinders CoreExpr
expr
    bOMB_OUT_SIZE :: Arity
bOMB_OUT_SIZE = DynFlags -> Arity
ufCreationThreshold DynFlags
dflags
           -- Bomb out if size gets bigger than this
    val_bndrs :: [Var]
val_bndrs   = (Var -> Bool) -> [Var] -> [Var]
forall a. (a -> Bool) -> [a] -> [a]
filter Var -> Bool
isId [Var]
bndrs
    n_val_bndrs :: Arity
n_val_bndrs = [Var] -> Arity
forall (t :: * -> *) a. Foldable t => t a -> Arity
length [Var]
val_bndrs

    mk_discount :: Bag (Id,Int) -> Id -> Int
    mk_discount :: Bag (Var, Arity) -> Var -> Arity
mk_discount Bag (Var, Arity)
cbs Var
bndr = (Arity -> (Var, Arity) -> Arity)
-> Arity -> Bag (Var, Arity) -> Arity
forall (t :: * -> *) b a.
Foldable t =>
(b -> a -> b) -> b -> t a -> b
foldl' Arity -> (Var, Arity) -> Arity
combine Arity
0 Bag (Var, Arity)
cbs
           where
             combine :: Arity -> (Var, Arity) -> Arity
combine Arity
acc (Var
bndr', Arity
disc)
               | Var
bndr Var -> Var -> Bool
forall a. Eq a => a -> a -> Bool
== Var
bndr' = Arity
acc Arity -> Arity -> Arity
`plus_disc` Arity
disc
               | Bool
otherwise     = Arity
acc

             plus_disc :: Int -> Int -> Int
             plus_disc :: Arity -> Arity -> Arity
plus_disc | Type -> Bool
isFunTy (Var -> Type
idType Var
bndr) = Arity -> Arity -> Arity
forall a. Ord a => a -> a -> a
max
                       | Bool
otherwise             = Arity -> Arity -> Arity
forall a. Num a => a -> a -> a
(+)
             -- 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]

Note [Count coercion arguments in boring contexts]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In inlineBoringOK, we ignore type arguments when deciding whether an
expression is okay to inline into boring contexts. This is good, since
if we have a definition like

  let y = x @Int in f y y

there’s no reason not to inline y at both use sites — no work is
actually duplicated. It may seem like the same reasoning applies to
coercion arguments, and indeed, in #17182 we changed inlineBoringOK to
treat coercions the same way.

However, this isn’t a good idea: unlike type arguments, which have
no runtime representation, coercion arguments *do* have a runtime
representation (albeit the zero-width VoidRep, see Note [Coercion tokens]
in CoreToStg.hs). This caused trouble in #17787 for DataCon wrappers for
nullary GADT constructors: the wrappers would be inlined and each use of
the constructor would lead to a separate allocation instead of just
sharing the wrapper closure.

The solution: don’t ignore coercion arguments after all.
-}

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 :: CoreExpr -> Arity -> Arity -> Bool
uncondInline CoreExpr
rhs Arity
arity Arity
size
  | Arity
arity Arity -> Arity -> Bool
forall a. Ord a => a -> a -> Bool
> Arity
0 = Arity
size Arity -> Arity -> Bool
forall a. Ord a => a -> a -> Bool
<= Arity
10 Arity -> Arity -> Arity
forall a. Num a => a -> a -> a
* (Arity
arity Arity -> Arity -> Arity
forall a. Num a => a -> a -> a
+ Arity
1) -- See Note [INLINE for small functions] (1)
  | Bool
otherwise = CoreExpr -> Bool
exprIsTrivial CoreExpr
rhs        -- See Note [INLINE for small functions] (4)

sizeExpr :: DynFlags
         -> Int             -- 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 :: DynFlags -> Arity -> [Var] -> CoreExpr -> ExprSize
sizeExpr DynFlags
dflags Arity
bOMB_OUT_SIZE [Var]
top_args CoreExpr
expr
  = CoreExpr -> ExprSize
size_up CoreExpr
expr
  where
    size_up :: CoreExpr -> ExprSize
size_up (Cast CoreExpr
e Coercion
_) = CoreExpr -> ExprSize
size_up CoreExpr
e
    size_up (Tick Tickish Var
_ CoreExpr
e) = CoreExpr -> ExprSize
size_up CoreExpr
e
    size_up (Type Type
_)   = ExprSize
sizeZero           -- Types cost nothing
    size_up (Coercion Coercion
_) = ExprSize
sizeZero
    size_up (Lit Literal
lit)  = Arity -> ExprSize
sizeN (Literal -> Arity
litSize Literal
lit)
    size_up (Var Var
f) | Var -> Bool
isRealWorldId Var
f = ExprSize
sizeZero
                      -- Make sure we get constructor discounts even
                      -- on nullary constructors
                    | Bool
otherwise       = Var -> [CoreExpr] -> Arity -> ExprSize
size_up_call Var
f [] Arity
0

    size_up (App CoreExpr
fun CoreExpr
arg)
      | CoreExpr -> Bool
forall b. Expr b -> Bool
isTyCoArg CoreExpr
arg = CoreExpr -> ExprSize
size_up CoreExpr
fun
      | Bool
otherwise     = CoreExpr -> ExprSize
size_up CoreExpr
arg  ExprSize -> ExprSize -> ExprSize
`addSizeNSD`
                        CoreExpr -> [CoreExpr] -> Arity -> ExprSize
size_up_app CoreExpr
fun [CoreExpr
arg] (if CoreExpr -> Bool
forall b. Expr b -> Bool
isRealWorldExpr CoreExpr
arg then Arity
1 else Arity
0)

    size_up (Lam Var
b CoreExpr
e)
      | Var -> Bool
isId Var
b Bool -> Bool -> Bool
&& Bool -> Bool
not (Var -> Bool
isRealWorldId Var
b) = DynFlags -> ExprSize -> ExprSize
lamScrutDiscount DynFlags
dflags (CoreExpr -> ExprSize
size_up CoreExpr
e ExprSize -> Arity -> ExprSize
`addSizeN` Arity
10)
      | Bool
otherwise = CoreExpr -> ExprSize
size_up CoreExpr
e

    size_up (Let (NonRec Var
binder CoreExpr
rhs) CoreExpr
body)
      = (Var, CoreExpr) -> ExprSize
size_up_rhs (Var
binder, CoreExpr
rhs) ExprSize -> ExprSize -> ExprSize
`addSizeNSD`
        CoreExpr -> ExprSize
size_up CoreExpr
body              ExprSize -> Arity -> ExprSize
`addSizeN`
        Var -> Arity
forall p. Num p => Var -> p
size_up_alloc Var
binder

    size_up (Let (Rec [(Var, CoreExpr)]
pairs) CoreExpr
body)
      = ((Var, CoreExpr) -> ExprSize -> ExprSize)
-> ExprSize -> [(Var, CoreExpr)] -> ExprSize
forall (t :: * -> *) a b.
Foldable t =>
(a -> b -> b) -> b -> t a -> b
foldr (ExprSize -> ExprSize -> ExprSize
addSizeNSD (ExprSize -> ExprSize -> ExprSize)
-> ((Var, CoreExpr) -> ExprSize)
-> (Var, CoreExpr)
-> ExprSize
-> ExprSize
forall b c a. (b -> c) -> (a -> b) -> a -> c
. (Var, CoreExpr) -> ExprSize
size_up_rhs)
              (CoreExpr -> ExprSize
size_up CoreExpr
body ExprSize -> Arity -> ExprSize
`addSizeN` [Arity] -> Arity
forall (t :: * -> *) a. (Foldable t, Num a) => t a -> a
sum (((Var, CoreExpr) -> Arity) -> [(Var, CoreExpr)] -> [Arity]
forall a b. (a -> b) -> [a] -> [b]
map (Var -> Arity
forall p. Num p => Var -> p
size_up_alloc (Var -> Arity)
-> ((Var, CoreExpr) -> Var) -> (Var, CoreExpr) -> Arity
forall b c a. (b -> c) -> (a -> b) -> a -> c
. (Var, CoreExpr) -> Var
forall a b. (a, b) -> a
fst) [(Var, CoreExpr)]
pairs))
              [(Var, CoreExpr)]
pairs

    size_up (Case CoreExpr
e Var
_ Type
_ [Alt Var]
alts)
        | [Alt Var] -> Bool
forall (t :: * -> *) a. Foldable t => t a -> Bool
null [Alt Var]
alts
        = CoreExpr -> ExprSize
size_up CoreExpr
e    -- case e of {} never returns, so take size of scrutinee

    size_up (Case CoreExpr
e Var
_ Type
_ [Alt Var]
alts)
        -- Now alts is non-empty
        | Just Var
v <- CoreExpr -> Maybe Var
forall b. Expr b -> Maybe Var
is_top_arg CoreExpr
e -- We are scrutinising an argument variable
        = let
            alt_sizes :: [ExprSize]
alt_sizes = (Alt Var -> ExprSize) -> [Alt Var] -> [ExprSize]
forall a b. (a -> b) -> [a] -> [b]
map Alt Var -> ExprSize
size_up_alt [Alt Var]
alts

                  -- alts_size tries to compute a good discount for
                  -- the case when we are scrutinising an argument variable
            alts_size :: ExprSize -> ExprSize -> ExprSize
alts_size (SizeIs Arity
tot Bag (Var, Arity)
tot_disc Arity
tot_scrut)
                          -- Size of all alternatives
                      (SizeIs Arity
max Bag (Var, Arity)
_        Arity
_)
                          -- Size of biggest alternative
                  = Arity -> Bag (Var, Arity) -> Arity -> ExprSize
SizeIs Arity
tot ((Var, Arity) -> Bag (Var, Arity)
forall a. a -> Bag a
unitBag (Var
v, Arity
20 Arity -> Arity -> Arity
forall a. Num a => a -> a -> a
+ Arity
tot Arity -> Arity -> Arity
forall a. Num a => a -> a -> a
- Arity
max)
                      Bag (Var, Arity) -> Bag (Var, Arity) -> Bag (Var, Arity)
forall a. Bag a -> Bag a -> Bag a
`unionBags` Bag (Var, Arity)
tot_disc) Arity
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 ExprSize
tot_size ExprSize
_ = ExprSize
tot_size
          in
          ExprSize -> ExprSize -> ExprSize
alts_size ((ExprSize -> ExprSize -> ExprSize) -> [ExprSize] -> ExprSize
forall (t :: * -> *) a. Foldable t => (a -> a -> a) -> t a -> a
foldr1 ExprSize -> ExprSize -> ExprSize
addAltSize [ExprSize]
alt_sizes)  -- alts is non-empty
                    ((ExprSize -> ExprSize -> ExprSize) -> [ExprSize] -> ExprSize
forall (t :: * -> *) a. Foldable t => (a -> a -> a) -> t a -> a
foldr1 ExprSize -> ExprSize -> ExprSize
maxSize    [ExprSize]
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
          is_top_arg :: Expr b -> Maybe Var
is_top_arg (Var Var
v) | Var
v Var -> [Var] -> Bool
forall (t :: * -> *) a. (Foldable t, Eq a) => a -> t a -> Bool
`elem` [Var]
top_args = Var -> Maybe Var
forall a. a -> Maybe a
Just Var
v
          is_top_arg (Cast Expr b
e Coercion
_) = Expr b -> Maybe Var
is_top_arg Expr b
e
          is_top_arg Expr b
_ = Maybe Var
forall a. Maybe a
Nothing


    size_up (Case CoreExpr
e Var
_ Type
_ [Alt Var]
alts) = CoreExpr -> ExprSize
size_up CoreExpr
e  ExprSize -> ExprSize -> ExprSize
`addSizeNSD`
                                (Alt Var -> ExprSize -> ExprSize)
-> ExprSize -> [Alt Var] -> ExprSize
forall (t :: * -> *) a b.
Foldable t =>
(a -> b -> b) -> b -> t a -> b
foldr (ExprSize -> ExprSize -> ExprSize
addAltSize (ExprSize -> ExprSize -> ExprSize)
-> (Alt Var -> ExprSize) -> Alt Var -> ExprSize -> ExprSize
forall b c a. (b -> c) -> (a -> b) -> a -> c
. Alt Var -> ExprSize
size_up_alt) ExprSize
case_size [Alt Var]
alts
      where
          case_size :: ExprSize
case_size
           | CoreExpr -> Bool
forall b. Expr b -> Bool
is_inline_scrut CoreExpr
e, [Alt Var] -> Arity -> Bool
forall a. [a] -> Arity -> Bool
lengthAtMost [Alt Var]
alts Arity
1 = Arity -> ExprSize
sizeN (-Arity
10)
           | Bool
otherwise = ExprSize
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 "lengthAtMost 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 :: Expr b -> Bool
is_inline_scrut (Var Var
v) = HasDebugCallStack => Type -> Bool
Type -> Bool
isUnliftedType (Var -> Type
idType Var
v)
          is_inline_scrut Expr b
scrut
              | (Var Var
f, [Expr b]
_) <- Expr b -> (Expr b, [Expr b])
forall b. Expr b -> (Expr b, [Expr b])
collectArgs Expr b
scrut
                = case Var -> IdDetails
idDetails Var
f of
                    FCallId ForeignCall
fc  -> Bool -> Bool
not (ForeignCall -> Bool
isSafeForeignCall ForeignCall
fc)
                    PrimOpId PrimOp
op -> Bool -> Bool
not (PrimOp -> Bool
primOpOutOfLine PrimOp
op)
                    IdDetails
_other      -> Bool
False
              | Bool
otherwise
                = Bool
False

    size_up_rhs :: (Var, CoreExpr) -> ExprSize
size_up_rhs (Var
bndr, CoreExpr
rhs)
      | Just Arity
join_arity <- Var -> Maybe Arity
isJoinId_maybe Var
bndr
        -- Skip arguments to join point
      , ([Var]
_bndrs, CoreExpr
body) <- Arity -> CoreExpr -> ([Var], CoreExpr)
forall b. Arity -> Expr b -> ([b], Expr b)
collectNBinders Arity
join_arity CoreExpr
rhs
      = CoreExpr -> ExprSize
size_up CoreExpr
body
      | Bool
otherwise
      = CoreExpr -> ExprSize
size_up CoreExpr
rhs

    ------------
    -- size_up_app is used when there's ONE OR MORE value args
    size_up_app :: CoreExpr -> [CoreExpr] -> Arity -> ExprSize
size_up_app (App CoreExpr
fun CoreExpr
arg) [CoreExpr]
args Arity
voids
        | CoreExpr -> Bool
forall b. Expr b -> Bool
isTyCoArg CoreExpr
arg                  = CoreExpr -> [CoreExpr] -> Arity -> ExprSize
size_up_app CoreExpr
fun [CoreExpr]
args Arity
voids
        | CoreExpr -> Bool
forall b. Expr b -> Bool
isRealWorldExpr CoreExpr
arg            = CoreExpr -> [CoreExpr] -> Arity -> ExprSize
size_up_app CoreExpr
fun (CoreExpr
argCoreExpr -> [CoreExpr] -> [CoreExpr]
forall a. a -> [a] -> [a]
:[CoreExpr]
args) (Arity
voids Arity -> Arity -> Arity
forall a. Num a => a -> a -> a
+ Arity
1)
        | Bool
otherwise                      = CoreExpr -> ExprSize
size_up CoreExpr
arg  ExprSize -> ExprSize -> ExprSize
`addSizeNSD`
                                           CoreExpr -> [CoreExpr] -> Arity -> ExprSize
size_up_app CoreExpr
fun (CoreExpr
argCoreExpr -> [CoreExpr] -> [CoreExpr]
forall a. a -> [a] -> [a]
:[CoreExpr]
args) Arity
voids
    size_up_app (Var Var
fun)     [CoreExpr]
args Arity
voids = Var -> [CoreExpr] -> Arity -> ExprSize
size_up_call Var
fun [CoreExpr]
args Arity
voids
    size_up_app (Tick Tickish Var
_ CoreExpr
expr) [CoreExpr]
args Arity
voids = CoreExpr -> [CoreExpr] -> Arity -> ExprSize
size_up_app CoreExpr
expr [CoreExpr]
args Arity
voids
    size_up_app (Cast CoreExpr
expr Coercion
_) [CoreExpr]
args Arity
voids = CoreExpr -> [CoreExpr] -> Arity -> ExprSize
size_up_app CoreExpr
expr [CoreExpr]
args Arity
voids
    size_up_app CoreExpr
other         [CoreExpr]
args Arity
voids = CoreExpr -> ExprSize
size_up CoreExpr
other ExprSize -> Arity -> ExprSize
`addSizeN`
                                           Arity -> Arity -> Arity
callSize ([CoreExpr] -> Arity
forall (t :: * -> *) a. Foldable t => t a -> Arity
length [CoreExpr]
args) Arity
voids
       -- if the lhs is not an App or a Var, or an invisible thing like a
       -- Tick or Cast, then we should charge for a complete call plus the
       -- size of the lhs itself.

    ------------
    size_up_call :: Id -> [CoreExpr] -> Int -> ExprSize
    size_up_call :: Var -> [CoreExpr] -> Arity -> ExprSize
size_up_call Var
fun [CoreExpr]
val_args Arity
voids
       = case Var -> IdDetails
idDetails Var
fun of
           FCallId ForeignCall
_        -> Arity -> ExprSize
sizeN (Arity -> Arity -> Arity
callSize ([CoreExpr] -> Arity
forall (t :: * -> *) a. Foldable t => t a -> Arity
length [CoreExpr]
val_args) Arity
voids)
           DataConWorkId DataCon
dc -> DataCon -> Arity -> ExprSize
conSize    DataCon
dc ([CoreExpr] -> Arity
forall (t :: * -> *) a. Foldable t => t a -> Arity
length [CoreExpr]
val_args)
           PrimOpId PrimOp
op      -> PrimOp -> Arity -> ExprSize
primOpSize PrimOp
op ([CoreExpr] -> Arity
forall (t :: * -> *) a. Foldable t => t a -> Arity
length [CoreExpr]
val_args)
           ClassOpId Class
_      -> DynFlags -> [Var] -> [CoreExpr] -> ExprSize
classOpSize DynFlags
dflags [Var]
top_args [CoreExpr]
val_args
           IdDetails
_                -> DynFlags -> [Var] -> Var -> Arity -> Arity -> ExprSize
funSize DynFlags
dflags [Var]
top_args Var
fun ([CoreExpr] -> Arity
forall (t :: * -> *) a. Foldable t => t a -> Arity
length [CoreExpr]
val_args) Arity
voids

    ------------
    size_up_alt :: Alt Var -> ExprSize
size_up_alt (AltCon
_con, [Var]
_bndrs, CoreExpr
rhs) = CoreExpr -> ExprSize
size_up CoreExpr
rhs ExprSize -> Arity -> ExprSize
`addSizeN` Arity
10
        -- Don't charge for args, so that wrappers look cheap
        -- (See comments about wrappers with Case)
        --
        -- IMPORTANT: *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.errnoToIOError

    ------------
    -- Cost to allocate binding with given binder
    size_up_alloc :: Var -> p
size_up_alloc Var
bndr
      |  Var -> Bool
isTyVar Var
bndr                 -- Doesn't exist at runtime
      Bool -> Bool -> Bool
|| Var -> Bool
isJoinId Var
bndr                -- Not allocated at all
      Bool -> Bool -> Bool
|| HasDebugCallStack => Type -> Bool
Type -> Bool
isUnliftedType (Var -> Type
idType Var
bndr) -- Doesn't live in heap
      = p
0
      | Bool
otherwise
      = p
10

    ------------
        -- These addSize things have to be here because
        -- I don't want to give them bOMB_OUT_SIZE as an argument
    addSizeN :: ExprSize -> Arity -> ExprSize
addSizeN ExprSize
TooBig          Arity
_  = ExprSize
TooBig
    addSizeN (SizeIs Arity
n Bag (Var, Arity)
xs Arity
d) Arity
m  = Arity -> Arity -> Bag (Var, Arity) -> Arity -> ExprSize
mkSizeIs Arity
bOMB_OUT_SIZE (Arity
n Arity -> Arity -> Arity
forall a. Num a => a -> a -> a
+ Arity
m) Bag (Var, Arity)
xs Arity
d

        -- addAltSize is used to add the sizes of case alternatives
    addAltSize :: ExprSize -> ExprSize -> ExprSize
addAltSize ExprSize
TooBig            ExprSize
_      = ExprSize
TooBig
    addAltSize ExprSize
_                 ExprSize
TooBig = ExprSize
TooBig
    addAltSize (SizeIs Arity
n1 Bag (Var, Arity)
xs Arity
d1) (SizeIs Arity
n2 Bag (Var, Arity)
ys Arity
d2)
        = Arity -> Arity -> Bag (Var, Arity) -> Arity -> ExprSize
mkSizeIs Arity
bOMB_OUT_SIZE (Arity
n1 Arity -> Arity -> Arity
forall a. Num a => a -> a -> a
+ Arity
n2)
                                 (Bag (Var, Arity)
xs Bag (Var, Arity) -> Bag (Var, Arity) -> Bag (Var, Arity)
forall a. Bag a -> Bag a -> Bag a
`unionBags` Bag (Var, Arity)
ys)
                                 (Arity
d1 Arity -> Arity -> Arity
forall a. Num a => a -> a -> a
+ Arity
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 :: ExprSize -> ExprSize -> ExprSize
addSizeNSD ExprSize
TooBig            ExprSize
_      = ExprSize
TooBig
    addSizeNSD ExprSize
_                 ExprSize
TooBig = ExprSize
TooBig
    addSizeNSD (SizeIs Arity
n1 Bag (Var, Arity)
xs Arity
_) (SizeIs Arity
n2 Bag (Var, Arity)
ys Arity
d2)
        = Arity -> Arity -> Bag (Var, Arity) -> Arity -> ExprSize
mkSizeIs Arity
bOMB_OUT_SIZE (Arity
n1 Arity -> Arity -> Arity
forall a. Num a => a -> a -> a
+ Arity
n2)
                                 (Bag (Var, Arity)
xs Bag (Var, Arity) -> Bag (Var, Arity) -> Bag (Var, Arity)
forall a. Bag a -> Bag a -> Bag a
`unionBags` Bag (Var, Arity)
ys)
                                 Arity
d2  -- Ignore d1

    isRealWorldId :: Var -> Bool
isRealWorldId Var
id = Var -> Type
idType Var
id Type -> Type -> Bool
`eqType` Type
realWorldStatePrimTy

    -- an expression of type State# RealWorld must be a variable
    isRealWorldExpr :: Expr b -> Bool
isRealWorldExpr (Var Var
id)   = Var -> Bool
isRealWorldId Var
id
    isRealWorldExpr (Tick Tickish Var
_ Expr b
e) = Expr b -> Bool
isRealWorldExpr Expr b
e
    isRealWorldExpr Expr b
_          = Bool
False

-- | Finds a nominal size of a string literal.
litSize :: Literal -> Int
-- Used by CoreUnfold.sizeExpr
litSize :: Literal -> Arity
litSize (LitNumber LitNumType
LitNumInteger Integer
_ Type
_) = Arity
100   -- Note [Size of literal integers]
litSize (LitNumber LitNumType
LitNumNatural Integer
_ Type
_) = Arity
100
litSize (LitString ByteString
str) = Arity
10 Arity -> Arity -> Arity
forall a. Num a => a -> a -> a
+ Arity
10 Arity -> Arity -> Arity
forall a. Num a => a -> a -> a
* ((ByteString -> Arity
BS.length ByteString
str Arity -> Arity -> Arity
forall a. Num a => a -> a -> a
+ Arity
3) Arity -> Arity -> Arity
forall a. Integral a => a -> a -> a
`div` Arity
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 Literal
_other = Arity
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 :: DynFlags -> [Var] -> [CoreExpr] -> ExprSize
classOpSize DynFlags
_ [Var]
_ []
  = ExprSize
sizeZero
classOpSize DynFlags
dflags [Var]
top_args (CoreExpr
arg1 : [CoreExpr]
other_args)
  = Arity -> Bag (Var, Arity) -> Arity -> ExprSize
SizeIs Arity
size Bag (Var, Arity)
arg_discount Arity
0
  where
    size :: Arity
size = Arity
20 Arity -> Arity -> Arity
forall a. Num a => a -> a -> a
+ (Arity
10 Arity -> Arity -> Arity
forall a. Num a => a -> a -> a
* [CoreExpr] -> Arity
forall (t :: * -> *) a. Foldable t => t a -> Arity
length [CoreExpr]
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 :: Bag (Var, Arity)
arg_discount = case CoreExpr
arg1 of
                     Var Var
dict | Var
dict Var -> [Var] -> Bool
forall (t :: * -> *) a. (Foldable t, Eq a) => a -> t a -> Bool
`elem` [Var]
top_args
                              -> (Var, Arity) -> Bag (Var, Arity)
forall a. a -> Bag a
unitBag (Var
dict, DynFlags -> Arity
ufDictDiscount DynFlags
dflags)
                     CoreExpr
_other   -> Bag (Var, Arity)
forall a. Bag a
emptyBag

-- | The size of a function call
callSize
 :: Int  -- ^ number of value args
 -> Int  -- ^ number of value args that are void
 -> Int
callSize :: Arity -> Arity -> Arity
callSize Arity
n_val_args Arity
voids = Arity
10 Arity -> Arity -> Arity
forall a. Num a => a -> a -> a
* (Arity
1 Arity -> Arity -> Arity
forall a. Num a => a -> a -> a
+ Arity
n_val_args Arity -> Arity -> Arity
forall a. Num a => a -> a -> a
- Arity
voids)
        -- The 1+ is for the function itself
        -- Add 1 for each non-trivial arg;
        -- the allocation cost, as in let(rec)

-- | The size of a jump to a join point
jumpSize
 :: Int  -- ^ number of value args
 -> Int  -- ^ number of value args that are void
 -> Int
jumpSize :: Arity -> Arity -> Arity
jumpSize Arity
n_val_args Arity
voids = Arity
2 Arity -> Arity -> Arity
forall a. Num a => a -> a -> a
* (Arity
1 Arity -> Arity -> Arity
forall a. Num a => a -> a -> a
+ Arity
n_val_args Arity -> Arity -> Arity
forall a. Num a => a -> a -> a
- Arity
voids)
  -- A jump is 20% the size of a function call. Making jumps free reopens
  -- bug #6048, but making them any more expensive loses a 21% improvement in
  -- spectral/puzzle. TODO Perhaps adjusting the default threshold would be a
  -- better solution?

funSize :: DynFlags -> [Id] -> Id -> Int -> Int -> ExprSize
-- Size for functions that are not constructors or primops
-- Note [Function applications]
funSize :: DynFlags -> [Var] -> Var -> Arity -> Arity -> ExprSize
funSize DynFlags
dflags [Var]
top_args Var
fun Arity
n_val_args Arity
voids
  | Var
fun Var -> Unique -> Bool
forall a. Uniquable a => a -> Unique -> Bool
`hasKey` Unique
buildIdKey   = ExprSize
buildSize
  | Var
fun Var -> Unique -> Bool
forall a. Uniquable a => a -> Unique -> Bool
`hasKey` Unique
augmentIdKey = ExprSize
augmentSize
  | Bool
otherwise = Arity -> Bag (Var, Arity) -> Arity -> ExprSize
SizeIs Arity
size Bag (Var, Arity)
arg_discount Arity
res_discount
  where
    some_val_args :: Bool
some_val_args = Arity
n_val_args Arity -> Arity -> Bool
forall a. Ord a => a -> a -> Bool
> Arity
0
    is_join :: Bool
is_join = Var -> Bool
isJoinId Var
fun

    size :: Arity
size | Bool
is_join              = Arity -> Arity -> Arity
jumpSize Arity
n_val_args Arity
voids
         | Bool -> Bool
not Bool
some_val_args    = Arity
0
         | Bool
otherwise            = Arity -> Arity -> Arity
callSize Arity
n_val_args Arity
voids

        --                  DISCOUNTS
        --  See Note [Function and non-function discounts]
    arg_discount :: Bag (Var, Arity)
arg_discount | Bool
some_val_args Bool -> Bool -> Bool
&& Var
fun Var -> [Var] -> Bool
forall (t :: * -> *) a. (Foldable t, Eq a) => a -> t a -> Bool
`elem` [Var]
top_args
                 = (Var, Arity) -> Bag (Var, Arity)
forall a. a -> Bag a
unitBag (Var
fun, DynFlags -> Arity
ufFunAppDiscount DynFlags
dflags)
                 | Bool
otherwise = Bag (Var, Arity)
forall a. Bag a
emptyBag
        -- If the function is an argument and is applied
        -- to some values, give it an arg-discount

    res_discount :: Arity
res_discount | Var -> Arity
idArity Var
fun Arity -> Arity -> Bool
forall a. Ord a => a -> a -> Bool
> Arity
n_val_args = DynFlags -> Arity
ufFunAppDiscount DynFlags
dflags
                 | Bool
otherwise                = Arity
0
        -- If the function is partially applied, show a result discount
-- XXX maybe behave like ConSize for eval'd variable

conSize :: DataCon -> Int -> ExprSize
conSize :: DataCon -> Arity -> ExprSize
conSize DataCon
dc Arity
n_val_args
  | Arity
n_val_args Arity -> Arity -> Bool
forall a. Eq a => a -> a -> Bool
== Arity
0 = Arity -> Bag (Var, Arity) -> Arity -> ExprSize
SizeIs Arity
0 Bag (Var, Arity)
forall a. Bag a
emptyBag Arity
10    -- Like variables

-- See Note [Unboxed tuple size and result discount]
  | DataCon -> Bool
isUnboxedTupleCon DataCon
dc = Arity -> Bag (Var, Arity) -> Arity -> ExprSize
SizeIs Arity
0 Bag (Var, Arity)
forall a. Bag a
emptyBag (Arity
10 Arity -> Arity -> Arity
forall a. Num a => a -> a -> a
* (Arity
1 Arity -> Arity -> Arity
forall a. Num a => a -> a -> a
+ Arity
n_val_args))

-- See Note [Constructor size and result discount]
  | Bool
otherwise = Arity -> Bag (Var, Arity) -> Arity -> ExprSize
SizeIs Arity
10 Bag (Var, Arity)
forall a. Bag a
emptyBag (Arity
10 Arity -> Arity -> Arity
forall a. Num a => a -> a -> a
* (Arity
1 Arity -> Arity -> Arity
forall a. Num a => a -> a -> a
+ Arity
n_val_args))

-- XXX still looks to large to me

{-
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 function with many many case branches, each finishing with
a constructor, can have an arbitrarily large discount.  This led to
terrible code bloat: see #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 #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
#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 arbitrary 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 :: PrimOp -> Arity -> ExprSize
primOpSize PrimOp
op Arity
n_val_args
 = if PrimOp -> Bool
primOpOutOfLine PrimOp
op
      then Arity -> ExprSize
sizeN (Arity
op_size Arity -> Arity -> Arity
forall a. Num a => a -> a -> a
+ Arity
n_val_args)
      else Arity -> ExprSize
sizeN Arity
op_size
 where
   op_size :: Arity
op_size = PrimOp -> Arity
primOpCodeSize PrimOp
op


buildSize :: ExprSize
buildSize :: ExprSize
buildSize = Arity -> Bag (Var, Arity) -> Arity -> ExprSize
SizeIs Arity
0 Bag (Var, Arity)
forall a. Bag a
emptyBag Arity
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 because 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 :: ExprSize
augmentSize = Arity -> Bag (Var, Arity) -> Arity -> ExprSize
SizeIs Arity
0 Bag (Var, Arity)
forall a. Bag a
emptyBag Arity
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 :: DynFlags -> ExprSize -> ExprSize
lamScrutDiscount DynFlags
dflags (SizeIs Arity
n Bag (Var, Arity)
vs Arity
_) = Arity -> Bag (Var, Arity) -> Arity -> ExprSize
SizeIs Arity
n Bag (Var, Arity)
vs (DynFlags -> Arity
ufFunAppDiscount DynFlags
dflags)
lamScrutDiscount DynFlags
_      ExprSize
TooBig          = ExprSize
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

ufVeryAggressive
     If True, the compiler ignores all the thresholds and inlines very
     aggressively. It still adheres to arity, simplifier phase control and
     loop breakers.


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
-}

-- | The size of a candidate expression for unfolding
data ExprSize
    = TooBig
    | SizeIs { ExprSize -> Arity
_es_size_is  :: {-# UNPACK #-} !Int -- ^ Size found
             , ExprSize -> Bag (Var, Arity)
_es_args     :: !(Bag (Id,Int))
               -- ^ Arguments cased herein, and discount for each such
             , ExprSize -> Arity
_es_discount :: {-# UNPACK #-} !Int
               -- ^ Size to subtract if result is scrutinised by a case
               -- expression
             }

instance Outputable ExprSize where
  ppr :: ExprSize -> SDoc
ppr ExprSize
TooBig         = String -> SDoc
text String
"TooBig"
  ppr (SizeIs Arity
a Bag (Var, Arity)
_ Arity
c) = SDoc -> SDoc
brackets (Arity -> SDoc
int Arity
a SDoc -> SDoc -> SDoc
<+> Arity -> SDoc
int Arity
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 :: Int -> Int -> Bag (Id, Int) -> Int -> ExprSize
mkSizeIs :: Arity -> Arity -> Bag (Var, Arity) -> Arity -> ExprSize
mkSizeIs Arity
max Arity
n Bag (Var, Arity)
xs Arity
d | (Arity
n Arity -> Arity -> Arity
forall a. Num a => a -> a -> a
- Arity
d) Arity -> Arity -> Bool
forall a. Ord a => a -> a -> Bool
> Arity
max = ExprSize
TooBig
                    | Bool
otherwise     = Arity -> Bag (Var, Arity) -> Arity -> ExprSize
SizeIs Arity
n Bag (Var, Arity)
xs Arity
d

maxSize :: ExprSize -> ExprSize -> ExprSize
maxSize :: ExprSize -> ExprSize -> ExprSize
maxSize ExprSize
TooBig         ExprSize
_                                  = ExprSize
TooBig
maxSize ExprSize
_              ExprSize
TooBig                             = ExprSize
TooBig
maxSize s1 :: ExprSize
s1@(SizeIs Arity
n1 Bag (Var, Arity)
_ Arity
_) s2 :: ExprSize
s2@(SizeIs Arity
n2 Bag (Var, Arity)
_ Arity
_) | Arity
n1 Arity -> Arity -> Bool
forall a. Ord a => a -> a -> Bool
> Arity
n2   = ExprSize
s1
                                              | Bool
otherwise = ExprSize
s2

sizeZero :: ExprSize
sizeN :: Int -> ExprSize

sizeZero :: ExprSize
sizeZero = Arity -> Bag (Var, Arity) -> Arity -> ExprSize
SizeIs Arity
0 Bag (Var, Arity)
forall a. Bag a
emptyBag Arity
0
sizeN :: Arity -> ExprSize
sizeN Arity
n  = Arity -> Bag (Var, Arity) -> Arity -> ExprSize
SizeIs Arity
n Bag (Var, Arity)
forall a. Bag a
emptyBag Arity
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 :: DynFlags -> Arity -> CoreExpr -> Bool
couldBeSmallEnoughToInline DynFlags
dflags Arity
threshold CoreExpr
rhs
  = case DynFlags -> Arity -> [Var] -> CoreExpr -> ExprSize
sizeExpr DynFlags
dflags Arity
threshold [] CoreExpr
body of
       ExprSize
TooBig -> Bool
False
       ExprSize
_      -> Bool
True
  where
    ([Var]
_, CoreExpr
body) = CoreExpr -> ([Var], CoreExpr)
forall b. Expr b -> ([b], Expr b)
collectBinders CoreExpr
rhs

----------------
smallEnoughToInline :: DynFlags -> Unfolding -> Bool
smallEnoughToInline :: DynFlags -> Unfolding -> Bool
smallEnoughToInline DynFlags
dflags (CoreUnfolding {uf_guidance :: Unfolding -> UnfoldingGuidance
uf_guidance = UnfIfGoodArgs {ug_size :: UnfoldingGuidance -> Arity
ug_size = Arity
size}})
  = Arity
size Arity -> Arity -> Bool
forall a. Ord a => a -> a -> Bool
<= DynFlags -> Arity
ufUseThreshold DynFlags
dflags
smallEnoughToInline DynFlags
_ Unfolding
_
  = Bool
False

----------------

certainlyWillInline :: DynFlags -> IdInfo -> Maybe Unfolding
-- ^ Sees if the unfolding is pretty certain to inline.
-- If so, return a *stable* unfolding for it, that will always inline.
certainlyWillInline :: DynFlags -> IdInfo -> Maybe Unfolding
certainlyWillInline DynFlags
dflags IdInfo
fn_info
  = case IdInfo -> Unfolding
unfoldingInfo IdInfo
fn_info of
      CoreUnfolding { uf_tmpl :: Unfolding -> CoreExpr
uf_tmpl = CoreExpr
e, uf_guidance :: Unfolding -> UnfoldingGuidance
uf_guidance = UnfoldingGuidance
g }
        | Bool
loop_breaker -> Maybe Unfolding
forall a. Maybe a
Nothing      -- Won't inline, so try w/w
        | Bool
noinline     -> Maybe Unfolding
forall a. Maybe a
Nothing      -- See Note [Worker-wrapper for NOINLINE functions]
        | Bool
otherwise    -> CoreExpr -> UnfoldingGuidance -> Maybe Unfolding
do_cunf CoreExpr
e UnfoldingGuidance
g  -- Depends on size, so look at that

      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
    loop_breaker :: Bool
loop_breaker = OccInfo -> Bool
isStrongLoopBreaker (IdInfo -> OccInfo
occInfo IdInfo
fn_info)
    noinline :: Bool
noinline     = InlinePragma -> InlineSpec
inlinePragmaSpec (IdInfo -> InlinePragma
inlinePragInfo IdInfo
fn_info) InlineSpec -> InlineSpec -> Bool
forall a. Eq a => a -> a -> Bool
== InlineSpec
NoInline
    fn_unf :: Unfolding
fn_unf       = IdInfo -> Unfolding
unfoldingInfo IdInfo
fn_info

    do_cunf :: CoreExpr -> UnfoldingGuidance -> Maybe Unfolding
    do_cunf :: CoreExpr -> UnfoldingGuidance -> Maybe Unfolding
do_cunf CoreExpr
_ UnfoldingGuidance
UnfNever     = Maybe Unfolding
forall a. Maybe a
Nothing
    do_cunf CoreExpr
_ (UnfWhen {}) = Unfolding -> Maybe Unfolding
forall a. a -> Maybe a
Just (Unfolding
fn_unf { uf_src :: UnfoldingSource
uf_src = UnfoldingSource
InlineStable })
                             -- INLINE functions have UnfWhen

        -- 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 CoreExpr
expr (UnfIfGoodArgs { ug_size :: UnfoldingGuidance -> Arity
ug_size = Arity
size, ug_args :: UnfoldingGuidance -> [Arity]
ug_args = [Arity]
args })
      | IdInfo -> Arity
arityInfo IdInfo
fn_info Arity -> Arity -> Bool
forall a. Ord a => a -> a -> Bool
> Arity
0  -- See Note [certainlyWillInline: be careful of thunks]
      , Bool -> Bool
not (StrictSig -> Bool
isBottomingSig (IdInfo -> StrictSig
strictnessInfo 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 :: Arity
unf_arity = [Arity] -> Arity
forall (t :: * -> *) a. Foldable t => t a -> Arity
length [Arity]
args
      , Arity
size Arity -> Arity -> Arity
forall a. Num a => a -> a -> a
- (Arity
10 Arity -> Arity -> Arity
forall a. Num a => a -> a -> a
* (Arity
unf_arity Arity -> Arity -> Arity
forall a. Num a => a -> a -> a
+ Arity
1)) Arity -> Arity -> Bool
forall a. Ord a => a -> a -> Bool
<= DynFlags -> Arity
ufUseThreshold DynFlags
dflags
      = Unfolding -> Maybe Unfolding
forall a. a -> Maybe a
Just (Unfolding
fn_unf { uf_src :: UnfoldingSource
uf_src      = UnfoldingSource
InlineStable
                     , uf_guidance :: UnfoldingGuidance
uf_guidance = UnfWhen :: Arity -> Bool -> Bool -> UnfoldingGuidance
UnfWhen { ug_arity :: Arity
ug_arity     = Arity
unf_arity
                                             , ug_unsat_ok :: Bool
ug_unsat_ok  = Bool
unSaturatedOk
                                             , ug_boring_ok :: Bool
ug_boring_ok = CoreExpr -> Bool
inlineBoringOk CoreExpr
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
      | 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]

************************************************************************
*                                                                      *
\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 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 :: ArgSummary -> SDoc
ppr ArgSummary
TrivArg    = String -> SDoc
text String
"TrivArg"
  ppr ArgSummary
NonTrivArg = String -> SDoc
text String
"NonTrivArg"
  ppr ArgSummary
ValueArg   = String -> SDoc
text String
"ValueArg"

nonTriv ::  ArgSummary -> Bool
nonTriv :: ArgSummary -> Bool
nonTriv ArgSummary
TrivArg = Bool
False
nonTriv ArgSummary
_       = Bool
True

data CallCtxt
  = BoringCtxt
  | RhsCtxt             -- Rhs of a let-binding; see Note [RHS of lets]
  | DiscArgCtxt         -- Argument of a function 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 :: CallCtxt -> SDoc
ppr CallCtxt
CaseCtxt    = String -> SDoc
text String
"CaseCtxt"
  ppr CallCtxt
ValAppCtxt  = String -> SDoc
text String
"ValAppCtxt"
  ppr CallCtxt
BoringCtxt  = String -> SDoc
text String
"BoringCtxt"
  ppr CallCtxt
RhsCtxt     = String -> SDoc
text String
"RhsCtxt"
  ppr CallCtxt
DiscArgCtxt = String -> SDoc
text String
"DiscArgCtxt"
  ppr CallCtxt
RuleArgCtxt = String -> SDoc
text String
"RuleArgCtxt"

callSiteInline :: DynFlags
-> Var
-> Bool
-> Bool
-> [ArgSummary]
-> CallCtxt
-> Maybe CoreExpr
callSiteInline DynFlags
dflags Var
id Bool
active_unfolding Bool
lone_variable [ArgSummary]
arg_infos CallCtxt
cont_info
  = case Var -> Unfolding
idUnfolding Var
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 :: Unfolding -> CoreExpr
uf_tmpl = CoreExpr
unf_template
                      , uf_is_work_free :: Unfolding -> Bool
uf_is_work_free = Bool
is_wf
                      , uf_guidance :: Unfolding -> UnfoldingGuidance
uf_guidance = UnfoldingGuidance
guidance, uf_expandable :: Unfolding -> Bool
uf_expandable = Bool
is_exp }
          | Bool
active_unfolding -> DynFlags
-> Var
-> Bool
-> [ArgSummary]
-> CallCtxt
-> CoreExpr
-> Bool
-> Bool
-> UnfoldingGuidance
-> Maybe CoreExpr
tryUnfolding DynFlags
dflags Var
id Bool
lone_variable
                                    [ArgSummary]
arg_infos CallCtxt
cont_info CoreExpr
unf_template
                                    Bool
is_wf Bool
is_exp UnfoldingGuidance
guidance
          | Bool
otherwise -> DynFlags
-> Var -> String -> SDoc -> Maybe CoreExpr -> Maybe CoreExpr
forall a. DynFlags -> Var -> String -> SDoc -> a -> a
traceInline DynFlags
dflags Var
id String
"Inactive unfolding:" (Var -> SDoc
forall a. Outputable a => a -> SDoc
ppr Var
id) Maybe CoreExpr
forall a. Maybe a
Nothing
        Unfolding
NoUnfolding      -> Maybe CoreExpr
forall a. Maybe a
Nothing
        Unfolding
BootUnfolding    -> Maybe CoreExpr
forall a. Maybe a
Nothing
        OtherCon {}      -> Maybe CoreExpr
forall a. Maybe a
Nothing
        DFunUnfolding {} -> Maybe CoreExpr
forall a. Maybe a
Nothing     -- Never unfold a DFun

traceInline :: DynFlags -> Id -> String -> SDoc -> a -> a
traceInline :: DynFlags -> Var -> String -> SDoc -> a -> a
traceInline DynFlags
dflags Var
inline_id String
str SDoc
doc a
result
 | Just String
prefix <- DynFlags -> Maybe String
inlineCheck DynFlags
dflags
 =  if String
prefix String -> String -> Bool
forall a. Eq a => [a] -> [a] -> Bool
`isPrefixOf` OccName -> String
occNameString (Var -> OccName
forall a. NamedThing a => a -> OccName
getOccName Var
inline_id)
      then String -> SDoc -> a -> a
forall a. String -> SDoc -> a -> a
pprTrace String
str SDoc
doc a
result
      else a
result
 | DumpFlag -> DynFlags -> Bool
dopt DumpFlag
Opt_D_dump_inlinings DynFlags
dflags Bool -> Bool -> Bool
&& DumpFlag -> DynFlags -> Bool
dopt DumpFlag
Opt_D_verbose_core2core DynFlags
dflags
 = String -> SDoc -> a -> a
forall a. String -> SDoc -> a -> a
pprTrace String
str SDoc
doc a
result
 | Bool
otherwise
 = a
result

-- | This is an awful but temporary workaround for #17615, where the
-- case analysis from the 'ufVeryAggressive' selector causes the entire
-- 'DynFlags' to be unpacked into local bindings (due to binder swap). This
-- results in a tremendous amount of stack spillage, severely bloating the code
-- generated for 'callSiteInline'.
--
-- The right solution here is likely to fix binder swap to avoid this terrible
-- behavior (since there are likely other instances of this as well) but this
-- case was serious enough that it showed up in a CPU profile and consequently
-- I wanted to fix it for 8.10.
very_aggressive :: DynFlags -> Bool
very_aggressive :: DynFlags -> Bool
very_aggressive = DynFlags -> Bool
ufVeryAggressive
{-# NOINLINE very_aggressive #-}

tryUnfolding :: DynFlags -> Id -> Bool -> [ArgSummary] -> CallCtxt
             -> CoreExpr -> Bool -> Bool -> UnfoldingGuidance
             -> Maybe CoreExpr
tryUnfolding :: DynFlags
-> Var
-> Bool
-> [ArgSummary]
-> CallCtxt
-> CoreExpr
-> Bool
-> Bool
-> UnfoldingGuidance
-> Maybe CoreExpr
tryUnfolding DynFlags
dflags Var
id Bool
lone_variable
             [ArgSummary]
arg_infos CallCtxt
cont_info CoreExpr
unf_template
             Bool
is_wf Bool
is_exp UnfoldingGuidance
guidance
 = case UnfoldingGuidance
guidance of
     UnfoldingGuidance
UnfNever -> DynFlags
-> Var -> String -> SDoc -> Maybe CoreExpr -> Maybe CoreExpr
forall a. DynFlags -> Var -> String -> SDoc -> a -> a
traceInline DynFlags
dflags Var
id String
str (String -> SDoc
text String
"UnfNever") Maybe CoreExpr
forall a. Maybe a
Nothing

     UnfWhen { ug_arity :: UnfoldingGuidance -> Arity
ug_arity = Arity
uf_arity, ug_unsat_ok :: UnfoldingGuidance -> Bool
ug_unsat_ok = Bool
unsat_ok, ug_boring_ok :: UnfoldingGuidance -> Bool
ug_boring_ok = Bool
boring_ok }
        | Bool
enough_args Bool -> Bool -> Bool
&& (Bool
boring_ok Bool -> Bool -> Bool
|| Bool
some_benefit Bool -> Bool -> Bool
|| DynFlags -> Bool
very_aggressive DynFlags
dflags)
                -- See Note [INLINE for small functions (3)]
        -> DynFlags
-> Var -> String -> SDoc -> Maybe CoreExpr -> Maybe CoreExpr
forall a. DynFlags -> Var -> String -> SDoc -> a -> a
traceInline DynFlags
dflags Var
id String
str (Bool -> SDoc -> Bool -> SDoc
forall a. Outputable a => a -> SDoc -> Bool -> SDoc
mk_doc Bool
some_benefit SDoc
empty Bool
True) (CoreExpr -> Maybe CoreExpr
forall a. a -> Maybe a
Just CoreExpr
unf_template)
        | Bool
otherwise
        -> DynFlags
-> Var -> String -> SDoc -> Maybe CoreExpr -> Maybe CoreExpr
forall a. DynFlags -> Var -> String -> SDoc -> a -> a
traceInline DynFlags
dflags Var
id String
str (Bool -> SDoc -> Bool -> SDoc
forall a. Outputable a => a -> SDoc -> Bool -> SDoc
mk_doc Bool
some_benefit SDoc
empty Bool
False) Maybe CoreExpr
forall a. Maybe a
Nothing
        where
          some_benefit :: Bool
some_benefit = Arity -> Bool
calc_some_benefit Arity
uf_arity
          enough_args :: Bool
enough_args = (Arity
n_val_args Arity -> Arity -> Bool
forall a. Ord a => a -> a -> Bool
>= Arity
uf_arity) Bool -> Bool -> Bool
|| (Bool
unsat_ok Bool -> Bool -> Bool
&& Arity
n_val_args Arity -> Arity -> Bool
forall a. Ord a => a -> a -> Bool
> Arity
0)

     UnfIfGoodArgs { ug_args :: UnfoldingGuidance -> [Arity]
ug_args = [Arity]
arg_discounts, ug_res :: UnfoldingGuidance -> Arity
ug_res = Arity
res_discount, ug_size :: UnfoldingGuidance -> Arity
ug_size = Arity
size }
        | DynFlags -> Bool
very_aggressive DynFlags
dflags
        -> DynFlags
-> Var -> String -> SDoc -> Maybe CoreExpr -> Maybe CoreExpr
forall a. DynFlags -> Var -> String -> SDoc -> a -> a
traceInline DynFlags
dflags Var
id String
str (Bool -> SDoc -> Bool -> SDoc
forall a. Outputable a => a -> SDoc -> Bool -> SDoc
mk_doc Bool
some_benefit SDoc
extra_doc Bool
True) (CoreExpr -> Maybe CoreExpr
forall a. a -> Maybe a
Just CoreExpr
unf_template)
        | Bool
is_wf Bool -> Bool -> Bool
&& Bool
some_benefit Bool -> Bool -> Bool
&& Bool
small_enough
        -> DynFlags
-> Var -> String -> SDoc -> Maybe CoreExpr -> Maybe CoreExpr
forall a. DynFlags -> Var -> String -> SDoc -> a -> a
traceInline DynFlags
dflags Var
id String
str (Bool -> SDoc -> Bool -> SDoc
forall a. Outputable a => a -> SDoc -> Bool -> SDoc
mk_doc Bool
some_benefit SDoc
extra_doc Bool
True) (CoreExpr -> Maybe CoreExpr
forall a. a -> Maybe a
Just CoreExpr
unf_template)
        | Bool
otherwise
        -> DynFlags
-> Var -> String -> SDoc -> Maybe CoreExpr -> Maybe CoreExpr
forall a. DynFlags -> Var -> String -> SDoc -> a -> a
traceInline DynFlags
dflags Var
id String
str (Bool -> SDoc -> Bool -> SDoc
forall a. Outputable a => a -> SDoc -> Bool -> SDoc
mk_doc Bool
some_benefit SDoc
extra_doc Bool
False) Maybe CoreExpr
forall a. Maybe a
Nothing
        where
          some_benefit :: Bool
some_benefit = Arity -> Bool
calc_some_benefit ([Arity] -> Arity
forall (t :: * -> *) a. Foldable t => t a -> Arity
length [Arity]
arg_discounts)
          extra_doc :: SDoc
extra_doc = String -> SDoc
text String
"discounted size =" SDoc -> SDoc -> SDoc
<+> Arity -> SDoc
int Arity
discounted_size
          discounted_size :: Arity
discounted_size = Arity
size Arity -> Arity -> Arity
forall a. Num a => a -> a -> a
- Arity
discount
          small_enough :: Bool
small_enough = Arity
discounted_size Arity -> Arity -> Bool
forall a. Ord a => a -> a -> Bool
<= DynFlags -> Arity
ufUseThreshold DynFlags
dflags
          discount :: Arity
discount = DynFlags -> [Arity] -> Arity -> [ArgSummary] -> CallCtxt -> Arity
computeDiscount DynFlags
dflags [Arity]
arg_discounts
                                     Arity
res_discount [ArgSummary]
arg_infos CallCtxt
cont_info

  where
    mk_doc :: a -> SDoc -> Bool -> SDoc
mk_doc a
some_benefit SDoc
extra_doc Bool
yes_or_no
      = [SDoc] -> SDoc
vcat [ String -> SDoc
text String
"arg infos" SDoc -> SDoc -> SDoc
<+> [ArgSummary] -> SDoc
forall a. Outputable a => a -> SDoc
ppr [ArgSummary]
arg_infos
             , String -> SDoc
text String
"interesting continuation" SDoc -> SDoc -> SDoc
<+> CallCtxt -> SDoc
forall a. Outputable a => a -> SDoc
ppr CallCtxt
cont_info
             , String -> SDoc
text String
"some_benefit" SDoc -> SDoc -> SDoc
<+> a -> SDoc
forall a. Outputable a => a -> SDoc
ppr a
some_benefit
             , String -> SDoc
text String
"is exp:" SDoc -> SDoc -> SDoc
<+> Bool -> SDoc
forall a. Outputable a => a -> SDoc
ppr Bool
is_exp
             , String -> SDoc
text String
"is work-free:" SDoc -> SDoc -> SDoc
<+> Bool -> SDoc
forall a. Outputable a => a -> SDoc
ppr Bool
is_wf
             , String -> SDoc
text String
"guidance" SDoc -> SDoc -> SDoc
<+> UnfoldingGuidance -> SDoc
forall a. Outputable a => a -> SDoc
ppr UnfoldingGuidance
guidance
             , SDoc
extra_doc
             , String -> SDoc
text String
"ANSWER =" SDoc -> SDoc -> SDoc
<+> if Bool
yes_or_no then String -> SDoc
text String
"YES" else String -> SDoc
text String
"NO"]

    str :: String
str = String
"Considering inlining: " String -> String -> String
forall a. [a] -> [a] -> [a]
++ DynFlags -> SDoc -> String
showSDocDump DynFlags
dflags (Var -> SDoc
forall a. Outputable a => a -> SDoc
ppr Var
id)
    n_val_args :: Arity
n_val_args = [ArgSummary] -> Arity
forall (t :: * -> *) a. Foldable t => t a -> Arity
length [ArgSummary]
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 :: Arity -> Bool
calc_some_benefit Arity
uf_arity
       | Bool -> Bool
not Bool
saturated = Bool
interesting_args       -- Under-saturated
                                        -- Note [Unsaturated applications]
       | Bool
otherwise = Bool
interesting_args   -- Saturated or over-saturated
                  Bool -> Bool -> Bool
|| Bool
interesting_call
      where
        saturated :: Bool
saturated      = Arity
n_val_args Arity -> Arity -> Bool
forall a. Ord a => a -> a -> Bool
>= Arity
uf_arity
        over_saturated :: Bool
over_saturated = Arity
n_val_args Arity -> Arity -> Bool
forall a. Ord a => a -> a -> Bool
> Arity
uf_arity
        interesting_args :: Bool
interesting_args = (ArgSummary -> Bool) -> [ArgSummary] -> Bool
forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
any ArgSummary -> Bool
nonTriv [ArgSummary]
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 :: Bool
interesting_call
          | Bool
over_saturated
          = Bool
True
          | Bool
otherwise
          = case CallCtxt
cont_info of
              CallCtxt
CaseCtxt   -> Bool -> Bool
not (Bool
lone_variable Bool -> Bool -> Bool
&& Bool
is_exp)  -- Note [Lone variables]
              CallCtxt
ValAppCtxt -> Bool
True                           -- Note [Cast then apply]
              CallCtxt
RuleArgCtxt -> Arity
uf_arity Arity -> Arity -> Bool
forall a. Ord a => a -> a -> Bool
> Arity
0  -- See Note [Unfold info lazy contexts]
              CallCtxt
DiscArgCtxt -> Arity
uf_arity Arity -> Arity -> Bool
forall a. Ord a => a -> a -> Bool
> Arity
0  -- Note [Inlining in ArgCtxt]
              CallCtxt
RhsCtxt     -> Arity
uf_arity Arity -> Arity -> Bool
forall a. Ord a => a -> a -> Bool
> Arity
0  --
              CallCtxt
_other      -> Bool
False         -- See Note [Nested functions]


{-
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]
~~~~~~~~~~~~~~~~~~~~~~~
At one time we treated a call of a non-top-level function as
"interesting" (regardless of how boring the context) in the hope
that inlining it would eliminate the binding, and its allocation.
Specifically, in the default case of interesting_call we had
   _other -> not is_top && uf_arity > 0

But actually postInlineUnconditionally does some of this and overall
it makes virtually no difference to nofib.  So I simplified away this
special case

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 variants, 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. it 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, provided
the RHS is "expandable" (see Note [exprIsExpandable] in CoreUtils) the
context can ``see'' the unfolding of the variable (e.g. case or a
RULE) so there's no gain.

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
scrutinises 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 :: DynFlags -> [Arity] -> Arity -> [ArgSummary] -> CallCtxt -> Arity
computeDiscount DynFlags
dflags [Arity]
arg_discounts Arity
res_discount [ArgSummary]
arg_infos CallCtxt
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.

  = Arity
10          -- Discount of 10 because the result replaces the call
                -- so we count 10 for the function itself

    Arity -> Arity -> Arity
forall a. Num a => a -> a -> a
+ Arity
10 Arity -> Arity -> Arity
forall a. Num a => a -> a -> a
* [Arity] -> Arity
forall (t :: * -> *) a. Foldable t => t a -> Arity
length [Arity]
actual_arg_discounts
               -- Discount of 10 for each arg supplied,
               -- because the result replaces the call

    Arity -> Arity -> Arity
forall a. Num a => a -> a -> a
+ Float -> Arity
forall a b. (RealFrac a, Integral b) => a -> b
round (DynFlags -> Float
ufKeenessFactor DynFlags
dflags Float -> Float -> Float
forall a. Num a => a -> a -> a
*
             Arity -> Float
forall a b. (Integral a, Num b) => a -> b
fromIntegral (Arity
total_arg_discount Arity -> Arity -> Arity
forall a. Num a => a -> a -> a
+ Arity
res_discount'))
  where
    actual_arg_discounts :: [Arity]
actual_arg_discounts = (Arity -> ArgSummary -> Arity)
-> [Arity] -> [ArgSummary] -> [Arity]
forall a b c. (a -> b -> c) -> [a] -> [b] -> [c]
zipWith Arity -> ArgSummary -> Arity
forall p. Num p => p -> ArgSummary -> p
mk_arg_discount [Arity]
arg_discounts [ArgSummary]
arg_infos
    total_arg_discount :: Arity
total_arg_discount   = [Arity] -> Arity
forall (t :: * -> *) a. (Foldable t, Num a) => t a -> a
sum [Arity]
actual_arg_discounts

    mk_arg_discount :: p -> ArgSummary -> p
mk_arg_discount p
_        ArgSummary
TrivArg    = p
0
    mk_arg_discount p
_        ArgSummary
NonTrivArg = p
10
    mk_arg_discount p
discount ArgSummary
ValueArg   = p
discount

    res_discount' :: Arity
res_discount'
      | Ordering
LT <- [Arity]
arg_discounts [Arity] -> [ArgSummary] -> Ordering
forall a b. [a] -> [b] -> Ordering
`compareLength` [ArgSummary]
arg_infos
      = Arity
res_discount   -- Over-saturated
      | Bool
otherwise
      = case CallCtxt
cont_info of
           CallCtxt
BoringCtxt  -> Arity
0
           CallCtxt
CaseCtxt    -> Arity
res_discount  -- Presumably a constructor
           CallCtxt
ValAppCtxt  -> Arity
res_discount  -- Presumably a function
           CallCtxt
_           -> Arity
40 Arity -> Arity -> Arity
forall a. Ord a => a -> a -> a
`min` Arity
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"