{-
(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 #-}
{-# LANGUAGE BangPatterns #-}

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

module GHC.Core.Unfold (
        Unfolding, UnfoldingGuidance,   -- Abstract types

        UnfoldingOpts (..), defaultUnfoldingOpts,
        updateCreationThreshold, updateUseThreshold,
        updateFunAppDiscount, updateDictDiscount,
        updateVeryAggressive, updateCaseScaling, updateCaseThreshold,

        ArgSummary(..),

        couldBeSmallEnoughToInline, inlineBoringOk,
        certainlyWillInline, smallEnoughToInline,

        callSiteInline, CallCtxt(..),
        calcUnfoldingGuidance
    ) where

#include "HsVersions.h"

import GHC.Prelude

import GHC.Driver.Session
import GHC.Driver.Ppr
import GHC.Core
import GHC.Core.Utils
import GHC.Types.Id
import GHC.Types.Demand ( isDeadEndSig )
import GHC.Core.DataCon
import GHC.Types.Literal
import GHC.Builtin.PrimOps
import GHC.Types.Id.Info
import GHC.Types.Basic  ( Arity, InlineSpec(..), inlinePragmaSpec )
import GHC.Core.Type
import GHC.Builtin.Names
import GHC.Builtin.Types.Prim ( realWorldStatePrimTy )
import GHC.Data.Bag
import GHC.Utils.Logger
import GHC.Utils.Misc
import GHC.Utils.Outputable
import GHC.Types.ForeignCall
import GHC.Types.Name
import GHC.Types.Tickish

import qualified Data.ByteString as BS
import Data.List (isPrefixOf)


-- | Unfolding options
data UnfoldingOpts = UnfoldingOpts
   { UnfoldingOpts -> Int
unfoldingCreationThreshold :: !Int
      -- ^ Threshold above which unfoldings are not *created*

   , UnfoldingOpts -> Int
unfoldingUseThreshold :: !Int
      -- ^ Threshold above which unfoldings are not *inlined*

   , UnfoldingOpts -> Int
unfoldingFunAppDiscount :: !Int
      -- ^ Discount for lambdas that are used (applied)

   , UnfoldingOpts -> Int
unfoldingDictDiscount :: !Int
      -- ^ Discount for dictionaries

   , UnfoldingOpts -> Bool
unfoldingVeryAggressive :: !Bool
      -- ^ Force inlining in many more cases

      -- Don't consider depth up to x
   , UnfoldingOpts -> Int
unfoldingCaseThreshold :: !Int

      -- Penalize depth with 1/x
   , UnfoldingOpts -> Int
unfoldingCaseScaling :: !Int
   }

defaultUnfoldingOpts :: UnfoldingOpts
defaultUnfoldingOpts :: UnfoldingOpts
defaultUnfoldingOpts = UnfoldingOpts
   { unfoldingCreationThreshold :: Int
unfoldingCreationThreshold = Int
750
      -- The unfoldingCreationThreshold threshold must be reasonably high
      -- to take account of possible discounts.
      -- E.g. 450 is not enough in 'fulsom' for Interval.sqr to
      -- inline into Csg.calc (The unfolding for sqr never makes it
      -- into the interface file.)

   , unfoldingUseThreshold :: Int
unfoldingUseThreshold   = Int
90
      -- Last adjusted upwards in #18282, when I reduced
      -- the result discount for constructors.

   , unfoldingFunAppDiscount :: Int
unfoldingFunAppDiscount = Int
60
      -- Be fairly keen to inline a function if that means
      -- we'll be able to pick the right method from a dictionary

   , unfoldingDictDiscount :: Int
unfoldingDictDiscount   = Int
30
      -- Be fairly keen to inline a function if that means
      -- we'll be able to pick the right method from a dictionary

   , unfoldingVeryAggressive :: Bool
unfoldingVeryAggressive = Bool
False

      -- Only apply scaling once we are deeper than threshold cases
      -- in an RHS.
   , unfoldingCaseThreshold :: Int
unfoldingCaseThreshold = Int
2

      -- Penalize depth with (size*depth)/scaling
   , unfoldingCaseScaling :: Int
unfoldingCaseScaling = Int
30
   }

-- Helpers for "GHC.Driver.Session"

updateCreationThreshold :: Int -> UnfoldingOpts -> UnfoldingOpts
updateCreationThreshold :: Int -> UnfoldingOpts -> UnfoldingOpts
updateCreationThreshold Int
n UnfoldingOpts
opts = UnfoldingOpts
opts { unfoldingCreationThreshold :: Int
unfoldingCreationThreshold = Int
n }

updateUseThreshold :: Int -> UnfoldingOpts -> UnfoldingOpts
updateUseThreshold :: Int -> UnfoldingOpts -> UnfoldingOpts
updateUseThreshold Int
n UnfoldingOpts
opts = UnfoldingOpts
opts { unfoldingUseThreshold :: Int
unfoldingUseThreshold = Int
n }

updateFunAppDiscount :: Int -> UnfoldingOpts -> UnfoldingOpts
updateFunAppDiscount :: Int -> UnfoldingOpts -> UnfoldingOpts
updateFunAppDiscount Int
n UnfoldingOpts
opts = UnfoldingOpts
opts { unfoldingFunAppDiscount :: Int
unfoldingFunAppDiscount = Int
n }

updateDictDiscount :: Int -> UnfoldingOpts -> UnfoldingOpts
updateDictDiscount :: Int -> UnfoldingOpts -> UnfoldingOpts
updateDictDiscount Int
n UnfoldingOpts
opts = UnfoldingOpts
opts { unfoldingDictDiscount :: Int
unfoldingDictDiscount = Int
n }

updateVeryAggressive :: Bool -> UnfoldingOpts -> UnfoldingOpts
updateVeryAggressive :: Bool -> UnfoldingOpts -> UnfoldingOpts
updateVeryAggressive Bool
n UnfoldingOpts
opts = UnfoldingOpts
opts { unfoldingVeryAggressive :: Bool
unfoldingVeryAggressive = Bool
n }


updateCaseThreshold :: Int -> UnfoldingOpts -> UnfoldingOpts
updateCaseThreshold :: Int -> UnfoldingOpts -> UnfoldingOpts
updateCaseThreshold Int
n UnfoldingOpts
opts = UnfoldingOpts
opts { unfoldingCaseThreshold :: Int
unfoldingCaseThreshold = Int
n }

updateCaseScaling :: Int -> UnfoldingOpts -> UnfoldingOpts
updateCaseScaling :: Int -> UnfoldingOpts -> UnfoldingOpts
updateCaseScaling Int
n UnfoldingOpts
opts = UnfoldingOpts
opts { unfoldingCaseScaling :: Int
unfoldingCaseScaling = Int
n }

{-
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 actually are.

Note [Calculate unfolding guidance on the non-occ-anal'd expression]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Notice that we give the non-occur-analysed expression to
calcUnfoldingGuidance.  In some ways it'd be better to occur-analyse
first; for example, sometimes during simplification, there's a large
let-bound thing which has been substituted, and so is now dead; so
'expr' contains two copies of the thing while the occurrence-analysed
expression doesn't.

Nevertheless, we *don't* and *must not* occ-analyse before computing
the size because

a) The size computation bales out after a while, whereas occurrence
   analysis does not.

b) Residency increases sharply if you occ-anal first.  I'm not
   100% sure why, but it's a large effect.  Compiling Cabal went
   from residency of 534M to over 800M with this one change.

This can occasionally mean that the guidance is very pessimistic;
it gets fixed up next round.  And it should be rare, because large
let-bound things that are dead are usually caught by preInlineUnconditionally


************************************************************************
*                                                                      *
\subsection{The UnfoldingGuidance type}
*                                                                      *
************************************************************************
-}

inlineBoringOk :: CoreExpr -> Bool
-- See Note [INLINE for small functions]
-- True => the result of inlining the expression is
--         no bigger than the expression itself
--     eg      (\x y -> f y x)
-- This is a quick and dirty version. It doesn't attempt
-- to deal with  (\x y z -> x (y z))
-- The really important one is (x `cast` c)
inlineBoringOk :: CoreExpr -> Bool
inlineBoringOk CoreExpr
e
  = Int -> CoreExpr -> Bool
go Int
0 CoreExpr
e
  where
    go :: Int -> CoreExpr -> Bool
    go :: Int -> CoreExpr -> Bool
go Int
credit (Lam Id
x CoreExpr
e) | Id -> Bool
isId Id
x           = Int -> CoreExpr -> Bool
go (Int
creditforall a. Num a => a -> a -> a
+Int
1) CoreExpr
e
                        | Bool
otherwise        = Int -> CoreExpr -> Bool
go Int
credit CoreExpr
e
        -- See Note [Count coercion arguments in boring contexts]
    go Int
credit (App CoreExpr
f (Type {}))            = Int -> CoreExpr -> Bool
go Int
credit CoreExpr
f
    go Int
credit (App CoreExpr
f CoreExpr
a) | Int
credit forall a. Ord a => a -> a -> Bool
> Int
0
                        , CoreExpr -> Bool
exprIsTrivial CoreExpr
a  = Int -> CoreExpr -> Bool
go (Int
creditforall a. Num a => a -> a -> a
-Int
1) CoreExpr
f
    go Int
credit (Tick CoreTickish
_ CoreExpr
e)                   = Int -> CoreExpr -> Bool
go Int
credit CoreExpr
e -- dubious
    go Int
credit (Cast CoreExpr
e CoercionR
_)                   = Int -> CoreExpr -> Bool
go Int
credit CoreExpr
e
    go Int
credit (Case CoreExpr
scrut Id
_ Type
_ [Alt AltCon
_ [Id]
_ CoreExpr
rhs]) -- See Note [Inline unsafeCoerce]
      | CoreExpr -> Bool
isUnsafeEqualityProof CoreExpr
scrut        = Int -> CoreExpr -> Bool
go Int
credit CoreExpr
rhs
    go Int
_      (Var {})                     = Bool
boringCxtOk
    go Int
_      CoreExpr
_                            = Bool
boringCxtNotOk

calcUnfoldingGuidance
        :: UnfoldingOpts
        -> Bool          -- Definitely a top-level, bottoming binding
        -> CoreExpr      -- Expression to look at
        -> UnfoldingGuidance
calcUnfoldingGuidance :: UnfoldingOpts -> Bool -> CoreExpr -> UnfoldingGuidance
calcUnfoldingGuidance UnfoldingOpts
opts Bool
is_top_bottoming (Tick CoreTickish
t CoreExpr
expr)
  | Bool -> Bool
not (forall (pass :: TickishPass). GenTickish pass -> Bool
tickishIsCode CoreTickish
t)  -- non-code ticks don't matter for unfolding
  = UnfoldingOpts -> Bool -> CoreExpr -> UnfoldingGuidance
calcUnfoldingGuidance UnfoldingOpts
opts Bool
is_top_bottoming CoreExpr
expr
calcUnfoldingGuidance UnfoldingOpts
opts Bool
is_top_bottoming CoreExpr
expr
  = case UnfoldingOpts -> Int -> [Id] -> CoreExpr -> ExprSize
sizeExpr UnfoldingOpts
opts Int
bOMB_OUT_SIZE [Id]
val_bndrs CoreExpr
body of
      ExprSize
TooBig -> UnfoldingGuidance
UnfNever
      SizeIs Int
size Bag (Id, Int)
cased_bndrs Int
scrut_discount
        | CoreExpr -> Int -> Int -> Bool
uncondInline CoreExpr
expr Int
n_val_bndrs Int
size
        -> UnfWhen { ug_unsat_ok :: Bool
ug_unsat_ok = Bool
unSaturatedOk
                   , ug_boring_ok :: Bool
ug_boring_ok =  Bool
boringCxtOk
                   , ug_arity :: Int
ug_arity = Int
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
        ->

          -- If you don't force this then we retain all the Ids
          let !discounts :: [Int]
discounts = forall a b. (a -> b) -> [a] -> [b]
strictMap (Bag (Id, Int) -> Id -> Int
mk_discount Bag (Id, Int)
cased_bndrs) [Id]
val_bndrs
          in UnfIfGoodArgs { ug_args :: [Int]
ug_args  = [Int]
discounts
                           , ug_size :: Int
ug_size  = Int
size
                           , ug_res :: Int
ug_res   = Int
scrut_discount }

  where
    ([Id]
bndrs, CoreExpr
body) = forall b. Expr b -> ([b], Expr b)
collectBinders CoreExpr
expr
    bOMB_OUT_SIZE :: Int
bOMB_OUT_SIZE = UnfoldingOpts -> Int
unfoldingCreationThreshold UnfoldingOpts
opts
           -- Bomb out if size gets bigger than this
    val_bndrs :: [Id]
val_bndrs   = forall a. (a -> Bool) -> [a] -> [a]
filter Id -> Bool
isId [Id]
bndrs
    n_val_bndrs :: Int
n_val_bndrs = forall (t :: * -> *) a. Foldable t => t a -> Int
length [Id]
val_bndrs

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

             plus_disc :: Int -> Int -> Int
             plus_disc :: Int -> Int -> Int
plus_disc | Type -> Bool
isFunTy (Id -> Type
idType Id
bndr) = forall a. Ord a => a -> a -> a
max
                       | Bool
otherwise             = forall a. Num a => a -> a -> a
(+)
             -- See Note [Function and non-function discounts]

{- Note [Inline unsafeCoerce]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We really want to inline unsafeCoerce, even when applied to boring
arguments.  It doesn't look as if its RHS is smaller than the call
   unsafeCoerce x = case unsafeEqualityProof @a @b of UnsafeRefl -> x
but that case is discarded -- see Note [Implementing unsafeCoerce]
in base:Unsafe.Coerce.

Moreover, if we /don't/ inline it, we may be left with
          f (unsafeCoerce x)
which will build a thunk -- bad, bad, bad.

Conclusion: we really want inlineBoringOk to be True of the RHS of
unsafeCoerce.  This is (U4) in Note [Implementing unsafeCoerce].

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 universally 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 GHC.Core.Opt.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 GHC.Core.Opt.Simplify.Utils
    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 "GHC.CoreToStg"). 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 -> Int -> Int -> Bool
uncondInline CoreExpr
rhs Int
arity Int
size
  | Int
arity forall a. Ord a => a -> a -> Bool
> Int
0 = Int
size forall a. Ord a => a -> a -> Bool
<= Int
10 forall a. Num a => a -> a -> a
* (Int
arity forall a. Num a => a -> a -> a
+ Int
1) -- See Note [INLINE for small functions] (1)
  | Bool
otherwise = CoreExpr -> Bool
exprIsTrivial CoreExpr
rhs        -- See Note [INLINE for small functions] (4)

sizeExpr :: UnfoldingOpts
         -> 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]

-- Forcing bOMB_OUT_SIZE early prevents repeated
-- unboxing of the Int argument.
sizeExpr :: UnfoldingOpts -> Int -> [Id] -> CoreExpr -> ExprSize
sizeExpr UnfoldingOpts
opts !Int
bOMB_OUT_SIZE [Id]
top_args CoreExpr
expr
  = CoreExpr -> ExprSize
size_up CoreExpr
expr
  where
    size_up :: CoreExpr -> ExprSize
size_up (Cast CoreExpr
e CoercionR
_) = CoreExpr -> ExprSize
size_up CoreExpr
e
    size_up (Tick CoreTickish
_ CoreExpr
e) = CoreExpr -> ExprSize
size_up CoreExpr
e
    size_up (Type Type
_)   = ExprSize
sizeZero           -- Types cost nothing
    size_up (Coercion CoercionR
_) = ExprSize
sizeZero
    size_up (Lit Literal
lit)  = Int -> ExprSize
sizeN (Literal -> Int
litSize Literal
lit)
    size_up (Var Id
f) | Id -> Bool
isRealWorldId Id
f = ExprSize
sizeZero
                      -- Make sure we get constructor discounts even
                      -- on nullary constructors
                    | Bool
otherwise       = Id -> [CoreExpr] -> Int -> ExprSize
size_up_call Id
f [] Int
0

    size_up (App CoreExpr
fun CoreExpr
arg)
      | 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] -> Int -> ExprSize
size_up_app CoreExpr
fun [CoreExpr
arg] (if forall b. Expr b -> Bool
isRealWorldExpr CoreExpr
arg then Int
1 else Int
0)

    size_up (Lam Id
b CoreExpr
e)
      | Id -> Bool
isId Id
b Bool -> Bool -> Bool
&& Bool -> Bool
not (Id -> Bool
isRealWorldId Id
b) = UnfoldingOpts -> ExprSize -> ExprSize
lamScrutDiscount UnfoldingOpts
opts (CoreExpr -> ExprSize
size_up CoreExpr
e ExprSize -> Int -> ExprSize
`addSizeN` Int
10)
      | Bool
otherwise = CoreExpr -> ExprSize
size_up CoreExpr
e

    size_up (Let (NonRec Id
binder CoreExpr
rhs) CoreExpr
body)
      = (Id, CoreExpr) -> ExprSize
size_up_rhs (Id
binder, CoreExpr
rhs) ExprSize -> ExprSize -> ExprSize
`addSizeNSD`
        CoreExpr -> ExprSize
size_up CoreExpr
body              ExprSize -> Int -> ExprSize
`addSizeN`
        forall {a}. Num a => Id -> a
size_up_alloc Id
binder

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

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

    size_up (Case CoreExpr
e Id
_ Type
_ [Alt Id]
alts)
        -- Now alts is non-empty
        | Just Id
v <- CoreExpr -> Maybe Id
is_top_arg CoreExpr
e -- We are scrutinising an argument variable
        = let
            alt_sizes :: [ExprSize]
alt_sizes = forall a b. (a -> b) -> [a] -> [b]
map Alt Id -> ExprSize
size_up_alt [Alt Id]
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 Int
tot Bag (Id, Int)
tot_disc Int
tot_scrut)
                          -- Size of all alternatives
                      (SizeIs Int
max Bag (Id, Int)
_        Int
_)
                          -- Size of biggest alternative
                  = Int -> Bag (Id, Int) -> Int -> ExprSize
SizeIs Int
tot (forall a. a -> Bag a
unitBag (Id
v, Int
20 forall a. Num a => a -> a -> a
+ Int
tot forall a. Num a => a -> a -> a
- Int
max)
                      forall a. Bag a -> Bag a -> Bag a
`unionBags` Bag (Id, Int)
tot_disc) Int
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 (forall (t :: * -> *) a. Foldable t => (a -> a -> a) -> t a -> a
foldr1 ExprSize -> ExprSize -> ExprSize
addAltSize [ExprSize]
alt_sizes)  -- alts is non-empty
                    (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 :: CoreExpr -> Maybe Id
is_top_arg (Var Id
v) | Id
v forall (t :: * -> *) a. (Foldable t, Eq a) => a -> t a -> Bool
`elem` [Id]
top_args = forall a. a -> Maybe a
Just Id
v
          is_top_arg (Cast CoreExpr
e CoercionR
_) = CoreExpr -> Maybe Id
is_top_arg CoreExpr
e
          is_top_arg CoreExpr
_ = forall a. Maybe a
Nothing


    size_up (Case CoreExpr
e Id
_ Type
_ [Alt Id]
alts) = CoreExpr -> ExprSize
size_up CoreExpr
e  ExprSize -> ExprSize -> ExprSize
`addSizeNSD`
                                forall (t :: * -> *) a b.
Foldable t =>
(a -> b -> b) -> b -> t a -> b
foldr (ExprSize -> ExprSize -> ExprSize
addAltSize forall b c a. (b -> c) -> (a -> b) -> a -> c
. Alt Id -> ExprSize
size_up_alt) ExprSize
case_size [Alt Id]
alts
      where
          case_size :: ExprSize
case_size
           | forall b. Expr b -> Bool
is_inline_scrut CoreExpr
e, forall a. [a] -> Int -> Bool
lengthAtMost [Alt Id]
alts Int
1 = Int -> ExprSize
sizeN (-Int
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 Id
v) = HasDebugCallStack => Type -> Bool
isUnliftedType (Id -> Type
idType Id
v)
          is_inline_scrut Expr b
scrut
              | (Var Id
f, [Expr b]
_) <- forall b. Expr b -> (Expr b, [Expr b])
collectArgs Expr b
scrut
                = case Id -> IdDetails
idDetails Id
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 :: (Id, CoreExpr) -> ExprSize
size_up_rhs (Id
bndr, CoreExpr
rhs)
      | Just Int
join_arity <- Id -> Maybe Int
isJoinId_maybe Id
bndr
        -- Skip arguments to join point
      , ([Id]
_bndrs, CoreExpr
body) <- forall b. Int -> Expr b -> ([b], Expr b)
collectNBinders Int
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] -> Int -> ExprSize
size_up_app (App CoreExpr
fun CoreExpr
arg) [CoreExpr]
args Int
voids
        | forall b. Expr b -> Bool
isTyCoArg CoreExpr
arg                  = CoreExpr -> [CoreExpr] -> Int -> ExprSize
size_up_app CoreExpr
fun [CoreExpr]
args Int
voids
        | forall b. Expr b -> Bool
isRealWorldExpr CoreExpr
arg            = CoreExpr -> [CoreExpr] -> Int -> ExprSize
size_up_app CoreExpr
fun (CoreExpr
argforall a. a -> [a] -> [a]
:[CoreExpr]
args) (Int
voids forall a. Num a => a -> a -> a
+ Int
1)
        | Bool
otherwise                      = CoreExpr -> ExprSize
size_up CoreExpr
arg  ExprSize -> ExprSize -> ExprSize
`addSizeNSD`
                                           CoreExpr -> [CoreExpr] -> Int -> ExprSize
size_up_app CoreExpr
fun (CoreExpr
argforall a. a -> [a] -> [a]
:[CoreExpr]
args) Int
voids
    size_up_app (Var Id
fun)     [CoreExpr]
args Int
voids = Id -> [CoreExpr] -> Int -> ExprSize
size_up_call Id
fun [CoreExpr]
args Int
voids
    size_up_app (Tick CoreTickish
_ CoreExpr
expr) [CoreExpr]
args Int
voids = CoreExpr -> [CoreExpr] -> Int -> ExprSize
size_up_app CoreExpr
expr [CoreExpr]
args Int
voids
    size_up_app (Cast CoreExpr
expr CoercionR
_) [CoreExpr]
args Int
voids = CoreExpr -> [CoreExpr] -> Int -> ExprSize
size_up_app CoreExpr
expr [CoreExpr]
args Int
voids
    size_up_app CoreExpr
other         [CoreExpr]
args Int
voids = CoreExpr -> ExprSize
size_up CoreExpr
other ExprSize -> Int -> ExprSize
`addSizeN`
                                           Int -> Int -> Int
callSize (forall (t :: * -> *) a. Foldable t => t a -> Int
length [CoreExpr]
args) Int
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 :: Id -> [CoreExpr] -> Int -> ExprSize
size_up_call Id
fun [CoreExpr]
val_args Int
voids
       = case Id -> IdDetails
idDetails Id
fun of
           FCallId ForeignCall
_        -> Int -> ExprSize
sizeN (Int -> Int -> Int
callSize (forall (t :: * -> *) a. Foldable t => t a -> Int
length [CoreExpr]
val_args) Int
voids)
           DataConWorkId DataCon
dc -> DataCon -> Int -> ExprSize
conSize    DataCon
dc (forall (t :: * -> *) a. Foldable t => t a -> Int
length [CoreExpr]
val_args)
           PrimOpId PrimOp
op      -> PrimOp -> Int -> ExprSize
primOpSize PrimOp
op (forall (t :: * -> *) a. Foldable t => t a -> Int
length [CoreExpr]
val_args)
           ClassOpId Class
_      -> UnfoldingOpts -> [Id] -> [CoreExpr] -> ExprSize
classOpSize UnfoldingOpts
opts [Id]
top_args [CoreExpr]
val_args
           IdDetails
_                -> UnfoldingOpts -> [Id] -> Id -> Int -> Int -> ExprSize
funSize UnfoldingOpts
opts [Id]
top_args Id
fun (forall (t :: * -> *) a. Foldable t => t a -> Int
length [CoreExpr]
val_args) Int
voids

    ------------
    size_up_alt :: Alt Id -> ExprSize
size_up_alt (Alt AltCon
_con [Id]
_bndrs CoreExpr
rhs) = CoreExpr -> ExprSize
size_up CoreExpr
rhs ExprSize -> Int -> ExprSize
`addSizeN` Int
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 :: Id -> a
size_up_alloc Id
bndr
      |  Id -> Bool
isTyVar Id
bndr                 -- Doesn't exist at runtime
      Bool -> Bool -> Bool
|| Id -> Bool
isJoinId Id
bndr                -- Not allocated at all
      Bool -> Bool -> Bool
|| HasDebugCallStack => Type -> Bool
isUnliftedType (Id -> Type
idType Id
bndr) -- Doesn't live in heap
      = a
0
      | Bool
otherwise
      = a
10

    ------------
        -- These addSize things have to be here because
        -- I don't want to give them bOMB_OUT_SIZE as an argument
    addSizeN :: ExprSize -> Int -> ExprSize
addSizeN ExprSize
TooBig          Int
_  = ExprSize
TooBig
    addSizeN (SizeIs Int
n Bag (Id, Int)
xs Int
d) Int
m  = Int -> Int -> Bag (Id, Int) -> Int -> ExprSize
mkSizeIs Int
bOMB_OUT_SIZE (Int
n forall a. Num a => a -> a -> a
+ Int
m) Bag (Id, Int)
xs Int
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 Int
n1 Bag (Id, Int)
xs Int
d1) (SizeIs Int
n2 Bag (Id, Int)
ys Int
d2)
        = Int -> Int -> Bag (Id, Int) -> Int -> ExprSize
mkSizeIs Int
bOMB_OUT_SIZE (Int
n1 forall a. Num a => a -> a -> a
+ Int
n2)
                                 (Bag (Id, Int)
xs forall a. Bag a -> Bag a -> Bag a
`unionBags` Bag (Id, Int)
ys)
                                 (Int
d1 forall a. Num a => a -> a -> a
+ Int
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 Int
n1 Bag (Id, Int)
xs Int
_) (SizeIs Int
n2 Bag (Id, Int)
ys Int
d2)
        = Int -> Int -> Bag (Id, Int) -> Int -> ExprSize
mkSizeIs Int
bOMB_OUT_SIZE (Int
n1 forall a. Num a => a -> a -> a
+ Int
n2)
                                 (Bag (Id, Int)
xs forall a. Bag a -> Bag a -> Bag a
`unionBags` Bag (Id, Int)
ys)
                                 Int
d2  -- Ignore d1

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

    -- an expression of type State# RealWorld must be a variable
    isRealWorldExpr :: Expr b -> Bool
isRealWorldExpr (Var Id
id)   = Id -> Bool
isRealWorldId Id
id
    isRealWorldExpr (Tick CoreTickish
_ 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 GHC.Core.Unfold.sizeExpr
litSize :: Literal -> Int
litSize (LitNumber LitNumType
LitNumInteger Integer
_) = Int
100   -- Note [Size of literal integers]
litSize (LitNumber LitNumType
LitNumNatural Integer
_) = Int
100
litSize (LitString ByteString
str) = Int
10 forall a. Num a => a -> a -> a
+ Int
10 forall a. Num a => a -> a -> a
* ((ByteString -> Int
BS.length ByteString
str forall a. Num a => a -> a -> a
+ Int
3) forall a. Integral a => a -> a -> a
`div` Int
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 = Int
0    -- Must match size of nullary constructors
                      -- Key point: if  x |-> 4, then x must inline unconditionally
                      --            (eg via case binding)

classOpSize :: UnfoldingOpts -> [Id] -> [CoreExpr] -> ExprSize
-- See Note [Conlike is interesting]
classOpSize :: UnfoldingOpts -> [Id] -> [CoreExpr] -> ExprSize
classOpSize UnfoldingOpts
_ [Id]
_ []
  = ExprSize
sizeZero
classOpSize UnfoldingOpts
opts [Id]
top_args (CoreExpr
arg1 : [CoreExpr]
other_args)
  = Int -> Bag (Id, Int) -> Int -> ExprSize
SizeIs Int
size Bag (Id, Int)
arg_discount Int
0
  where
    size :: Int
size = Int
20 forall a. Num a => a -> a -> a
+ (Int
10 forall a. Num a => a -> a -> a
* forall (t :: * -> *) a. Foldable t => t a -> Int
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 (Id, Int)
arg_discount = case CoreExpr
arg1 of
                     Var Id
dict | Id
dict forall (t :: * -> *) a. (Foldable t, Eq a) => a -> t a -> Bool
`elem` [Id]
top_args
                              -> forall a. a -> Bag a
unitBag (Id
dict, UnfoldingOpts -> Int
unfoldingDictDiscount UnfoldingOpts
opts)
                     CoreExpr
_other   -> 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 :: Int -> Int -> Int
callSize Int
n_val_args Int
voids = Int
10 forall a. Num a => a -> a -> a
* (Int
1 forall a. Num a => a -> a -> a
+ Int
n_val_args forall a. Num a => a -> a -> a
- Int
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 :: Int -> Int -> Int
jumpSize Int
n_val_args Int
voids = Int
2 forall a. Num a => a -> a -> a
* (Int
1 forall a. Num a => a -> a -> a
+ Int
n_val_args forall a. Num a => a -> a -> a
- Int
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 :: UnfoldingOpts -> [Id] -> Id -> Int -> Int -> ExprSize
-- Size for functions that are not constructors or primops
-- Note [Function applications]
funSize :: UnfoldingOpts -> [Id] -> Id -> Int -> Int -> ExprSize
funSize UnfoldingOpts
opts [Id]
top_args Id
fun Int
n_val_args Int
voids
  | Id
fun forall a. Uniquable a => a -> Unique -> Bool
`hasKey` Unique
buildIdKey   = ExprSize
buildSize
  | Id
fun forall a. Uniquable a => a -> Unique -> Bool
`hasKey` Unique
augmentIdKey = ExprSize
augmentSize
  | Bool
otherwise = Int -> Bag (Id, Int) -> Int -> ExprSize
SizeIs Int
size Bag (Id, Int)
arg_discount Int
res_discount
  where
    some_val_args :: Bool
some_val_args = Int
n_val_args forall a. Ord a => a -> a -> Bool
> Int
0
    is_join :: Bool
is_join = Id -> Bool
isJoinId Id
fun

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

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

    res_discount :: Int
res_discount | Id -> Int
idArity Id
fun forall a. Ord a => a -> a -> Bool
> Int
n_val_args = UnfoldingOpts -> Int
unfoldingFunAppDiscount UnfoldingOpts
opts
                 | Bool
otherwise                = Int
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 -> Int -> ExprSize
conSize DataCon
dc Int
n_val_args
  | Int
n_val_args forall a. Eq a => a -> a -> Bool
== Int
0 = Int -> Bag (Id, Int) -> Int -> ExprSize
SizeIs Int
0 forall a. Bag a
emptyBag Int
10    -- Like variables

-- See Note [Unboxed tuple size and result discount]
  | DataCon -> Bool
isUnboxedTupleDataCon DataCon
dc = Int -> Bag (Id, Int) -> Int -> ExprSize
SizeIs Int
0 forall a. Bag a
emptyBag Int
10

-- See Note [Constructor size and result discount]
  | Bool
otherwise = Int -> Bag (Id, Int) -> Int -> ExprSize
SizeIs Int
10 forall a. Bag a
emptyBag Int
10

{- 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.

Historical note 1: Until Jun 2020 we gave it a "bit of extra
incentive" via a discount of 10*(1 + n_val_args), but that was FAR too
much (#18282).  In particular, consider a huge case tree like

   let r = case y1 of
          Nothing -> B1 a b c
          Just v1 -> case y2 of
                      Nothing -> B1 c b a
                      Just v2 -> ...

If conSize gives a cost of 10 (regardless of n_val_args) and a
discount of 10, that'll make each alternative RHS cost zero.  We
charge 10 for each case alternative (see size_up_alt).  If we give a
bigger discount (say 20) in conSize, we'll make the case expression
cost *nothing*, and that can make a huge case tree cost nothing. This
leads to massive, sometimes exponenial inlinings (#18282).  In short,
don't give a discount that give a negative size to a sub-expression!

Historical note 2: Much longer ago, 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.

When fixing #18282 (see Note [Constructor size and result discount])
I changed the result discount to be just 10, not 10*(1+n_val_args).

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 (IS n).  We just use an arbitrary big-ish constant here
so that, in particular, we don't inline top-level defns like
   n = IS 5
There's no point in doing so -- any optimisations will see the IS
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 -> Int -> ExprSize
primOpSize PrimOp
op Int
n_val_args
 = if PrimOp -> Bool
primOpOutOfLine PrimOp
op
      then Int -> ExprSize
sizeN (Int
op_size forall a. Num a => a -> a -> a
+ Int
n_val_args)
      else Int -> ExprSize
sizeN Int
op_size
 where
   op_size :: Int
op_size = PrimOp -> Int
primOpCodeSize PrimOp
op


buildSize :: ExprSize
buildSize :: ExprSize
buildSize = Int -> Bag (Id, Int) -> Int -> ExprSize
SizeIs Int
0 forall a. Bag a
emptyBag Int
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 = Int -> Bag (Id, Int) -> Int -> ExprSize
SizeIs Int
0 forall a. Bag a
emptyBag Int
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 :: UnfoldingOpts -> ExprSize -> ExprSize
lamScrutDiscount :: UnfoldingOpts -> ExprSize -> ExprSize
lamScrutDiscount UnfoldingOpts
opts (SizeIs Int
n Bag (Id, Int)
vs Int
_) = Int -> Bag (Id, Int) -> Int -> ExprSize
SizeIs Int
n Bag (Id, Int)
vs (UnfoldingOpts -> Int
unfoldingFunAppDiscount UnfoldingOpts
opts)
lamScrutDiscount UnfoldingOpts
_      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 thresholds are defined in 'UnfoldingOpts'. They are:

unfoldingCreationThreshold
     At a definition site, if the unfolding is bigger than this, we
     may discard it altogether

unfoldingUseThreshold
     At a call site, if the unfolding, less discounts, is smaller than
     this, then it's small enough inline

unfoldingDictDiscount
     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

unfoldingFunAppDiscount
     Discount for a function argument that is applied.  Quite
     large, because if we inline we avoid the higher-order call.

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


Historical Note: Before April 2020 we had another factor,
ufKeenessFactor, which would scale the discounts before they were subtracted
from the size. This was justified with the following comment:

  -- We multiply 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.

However, this is highly suspect since it means that we subtract a *scaled* size
from an absolute size, resulting in crazy (e.g. negative) scores in some cases
(#15304). We consequently killed off ufKeenessFactor and bumped up the
ufUseThreshold to compensate.


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 -> Int
_es_size_is  :: {-# UNPACK #-} !Int -- ^ Size found
             , ExprSize -> Bag (Id, Int)
_es_args     :: !(Bag (Id,Int))
               -- ^ Arguments cased herein, and discount for each such
             , ExprSize -> Int
_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 Int
a Bag (Id, Int)
_ Int
c) = SDoc -> SDoc
brackets (Int -> SDoc
int Int
a SDoc -> SDoc -> SDoc
<+> Int -> SDoc
int Int
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 :: Int -> Int -> Bag (Id, Int) -> Int -> ExprSize
mkSizeIs Int
max Int
n Bag (Id, Int)
xs Int
d | (Int
n forall a. Num a => a -> a -> a
- Int
d) forall a. Ord a => a -> a -> Bool
> Int
max = ExprSize
TooBig
                    | Bool
otherwise     = Int -> Bag (Id, Int) -> Int -> ExprSize
SizeIs Int
n Bag (Id, Int)
xs Int
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 Int
n1 Bag (Id, Int)
_ Int
_) s2 :: ExprSize
s2@(SizeIs Int
n2 Bag (Id, Int)
_ Int
_) | Int
n1 forall a. Ord a => a -> a -> Bool
> Int
n2   = ExprSize
s1
                                              | Bool
otherwise = ExprSize
s2

sizeZero :: ExprSize
sizeN :: Int -> ExprSize

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

----------------
smallEnoughToInline :: UnfoldingOpts -> Unfolding -> Bool
smallEnoughToInline :: UnfoldingOpts -> Unfolding -> Bool
smallEnoughToInline UnfoldingOpts
opts (CoreUnfolding {uf_guidance :: Unfolding -> UnfoldingGuidance
uf_guidance = UnfIfGoodArgs {ug_size :: UnfoldingGuidance -> Int
ug_size = Int
size}})
  = Int
size forall a. Ord a => a -> a -> Bool
<= UnfoldingOpts -> Int
unfoldingUseThreshold UnfoldingOpts
opts
smallEnoughToInline UnfoldingOpts
_ Unfolding
_
  = Bool
False

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

certainlyWillInline :: UnfoldingOpts -> 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 :: UnfoldingOpts -> IdInfo -> Maybe Unfolding
certainlyWillInline UnfoldingOpts
opts IdInfo
fn_info
  = case Unfolding
fn_unf of
      CoreUnfolding { uf_tmpl :: Unfolding -> CoreExpr
uf_tmpl = CoreExpr
expr, uf_guidance :: Unfolding -> UnfoldingGuidance
uf_guidance = UnfoldingGuidance
guidance, uf_src :: Unfolding -> UnfoldingSource
uf_src = UnfoldingSource
src }
        | Bool
loop_breaker -> forall a. Maybe a
Nothing       -- Won't inline, so try w/w
        | Bool
noinline     -> forall a. Maybe a
Nothing       -- See Note [Worker-wrapper for NOINLINE functions]
        | Bool
otherwise
        -> case UnfoldingGuidance
guidance of
             UnfoldingGuidance
UnfNever  -> forall a. Maybe a
Nothing
             UnfWhen {} -> forall a. a -> Maybe a
Just (Unfolding
fn_unf { uf_src :: UnfoldingSource
uf_src = UnfoldingSource
src' })
                             -- INLINE functions have UnfWhen
             UnfIfGoodArgs { ug_size :: UnfoldingGuidance -> Int
ug_size = Int
size, ug_args :: UnfoldingGuidance -> [Int]
ug_args = [Int]
args }
               -> CoreExpr -> Int -> [Int] -> UnfoldingSource -> Maybe Unfolding
do_cunf CoreExpr
expr Int
size [Int]
args UnfoldingSource
src'
        where
          src' :: UnfoldingSource
src' = case UnfoldingSource
src of
                   UnfoldingSource
InlineRhs -> UnfoldingSource
InlineStable
                   UnfoldingSource
_         -> UnfoldingSource
src  -- Do not change InlineCompulsory!

      DFunUnfolding {} -> 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       -> 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) forall a. Eq a => a -> a -> Bool
== InlineSpec
NoInline
    fn_unf :: Unfolding
fn_unf       = IdInfo -> Unfolding
unfoldingInfo IdInfo
fn_info

        -- 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 -> Int -> [Int] -> UnfoldingSource -> Maybe Unfolding
do_cunf CoreExpr
expr Int
size [Int]
args UnfoldingSource
src'
      | IdInfo -> Int
arityInfo IdInfo
fn_info forall a. Ord a => a -> a -> Bool
> Int
0  -- See Note [certainlyWillInline: be careful of thunks]
      , Bool -> Bool
not (StrictSig -> Bool
isDeadEndSig (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 :: Int
unf_arity = forall (t :: * -> *) a. Foldable t => t a -> Int
length [Int]
args
      , Int
size forall a. Num a => a -> a -> a
- (Int
10 forall a. Num a => a -> a -> a
* (Int
unf_arity forall a. Num a => a -> a -> a
+ Int
1)) forall a. Ord a => a -> a -> Bool
<= UnfoldingOpts -> Int
unfoldingUseThreshold UnfoldingOpts
opts
      = forall a. a -> Maybe a
Just (Unfolding
fn_unf { uf_src :: UnfoldingSource
uf_src      = UnfoldingSource
src'
                     , uf_guidance :: UnfoldingGuidance
uf_guidance = UnfWhen { ug_arity :: Int
ug_arity     = Int
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
      = 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 :: Logger
               -> DynFlags
               -> Int                   -- Case depth
               -> 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 :: Logger
-> DynFlags
-> Int
-> Id
-> Bool
-> Bool
-> [ArgSummary]
-> CallCtxt
-> Maybe CoreExpr
callSiteInline Logger
logger DynFlags
dflags !Int
case_depth Id
id Bool
active_unfolding Bool
lone_variable [ArgSummary]
arg_infos CallCtxt
cont_info
  = case Id -> Unfolding
idUnfolding Id
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 -> Logger
-> DynFlags
-> Int
-> Id
-> Bool
-> [ArgSummary]
-> CallCtxt
-> CoreExpr
-> Bool
-> Bool
-> UnfoldingGuidance
-> Maybe CoreExpr
tryUnfolding Logger
logger DynFlags
dflags Int
case_depth Id
id Bool
lone_variable
                                    [ArgSummary]
arg_infos CallCtxt
cont_info CoreExpr
unf_template
                                    Bool
is_wf Bool
is_exp UnfoldingGuidance
guidance
          | Bool
otherwise -> forall a. Logger -> DynFlags -> Id -> String -> SDoc -> a -> a
traceInline Logger
logger DynFlags
dflags Id
id String
"Inactive unfolding:" (forall a. Outputable a => a -> SDoc
ppr Id
id) forall a. Maybe a
Nothing
        Unfolding
NoUnfolding      -> forall a. Maybe a
Nothing
        Unfolding
BootUnfolding    -> forall a. Maybe a
Nothing
        OtherCon {}      -> forall a. Maybe a
Nothing
        DFunUnfolding {} -> forall a. Maybe a
Nothing     -- Never unfold a DFun

-- | Report the inlining of an identifier's RHS to the user, if requested.
traceInline :: Logger -> DynFlags -> Id -> String -> SDoc -> a -> a
traceInline :: forall a. Logger -> DynFlags -> Id -> String -> SDoc -> a -> a
traceInline Logger
logger DynFlags
dflags Id
inline_id String
str SDoc
doc a
result
  -- We take care to ensure that doc is used in only one branch, ensuring that
  -- the simplifier can push its allocation into the branch. See Note [INLINE
  -- conditional tracing utilities].
  | Bool
enable    = forall a. Logger -> TraceAction a
putTraceMsg Logger
logger DynFlags
dflags String
str SDoc
doc a
result
  | Bool
otherwise = a
result
  where
    enable :: Bool
enable
      | 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
      = Bool
True
      | Just String
prefix <- DynFlags -> Maybe String
inlineCheck DynFlags
dflags
      = String
prefix forall a. Eq a => [a] -> [a] -> Bool
`isPrefixOf` OccName -> String
occNameString (forall a. NamedThing a => a -> OccName
getOccName Id
inline_id)
      | Bool
otherwise
      = Bool
False
{-# INLINE traceInline #-} -- see Note [INLINE conditional tracing utilities]

{- Note [Avoid inlining into deeply nested cases]
   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Consider a function f like this:

  f arg1 arg2 =
    case ...
      ... -> g arg1
      ... -> g arg2

This function is small. So should be safe to inline.
However sometimes this doesn't quite work out like that.
Consider this code:

f1 arg1 arg2 ... = ...
    case _foo of
      alt1 -> ... f2 arg1 ...
      alt2 -> ... f2 arg2 ...

f2 arg1 arg2 ... = ...
    case _foo of
      alt1 -> ... f3 arg1 ...
      alt2 -> ... f3 arg2 ...

f3 arg1 arg2 ... = ...

... repeats up to n times. And then f1 is
applied to some arguments:

foo = ... f1 <interestingArgs> ...

Initially f2..fn are not interesting to inline so we don't.
However we see that f1 is applied to interesting args.
So it's an obvious choice to inline those:

foo =
    ...
      case _foo of
        alt1 -> ... f2 <interestingArg> ...
        alt2 -> ... f2 <interestingArg> ...

As a result we go and inline f2 both mentions of f2 in turn are now applied to interesting
arguments and f2 is small:

foo =
    ...
      case _foo of
        alt1 -> ... case _foo of
            alt1 -> ... f3 <interestingArg> ...
            alt2 -> ... f3 <interestingArg> ...

        alt2 -> ... case _foo of
            alt1 -> ... f3 <interestingArg> ...
            alt2 -> ... f3 <interestingArg> ...

The same thing happens for each binding up to f_n, duplicating the amount of inlining
done in each step. Until at some point we are either done or run out of simplifier
ticks/RAM. This pattern happened #18730.

To combat this we introduce one more heuristic when weighing inlining decision.
We keep track of a "case-depth". Which increases each time we look inside a case
expression with more than one alternative.

We then apply a penalty to inlinings based on the case-depth at which they would
be inlined. Bounding the number of inlinings in such a scenario.

The heuristic can be tuned in two ways:

* We can ignore the first n levels of case nestings for inlining decisions using
  -funfolding-case-threshold.
* The penalty grows linear with the depth. It's computed as size*(depth-threshold)/scaling.
  Scaling can be set with -funfolding-case-scaling.

Some guidance on setting these defaults:

* A low treshold (<= 2) is needed to prevent exponential cases from spiraling out of
  control. We picked 2 for no particular reason.
* Scaling the penalty by any more than 30 means the reproducer from
  T18730 won't compile even with reasonably small values of n. Instead
  it will run out of runs/ticks. This means to positively affect the reproducer
  a scaling <= 30 is required.
* A scaling of >= 15 still causes a few very large regressions on some nofib benchmarks.
  (+80% for gc/fulsom, +90% for real/ben-raytrace, +20% for spectral/fibheaps)
* A scaling of >= 25 showed no regressions on nofib. However it showed a number of
  (small) regression for compiler perf benchmarks.

The end result is that we are settling for a scaling of 30, with a threshold of 2.
This gives us minimal compiler perf regressions. No nofib runtime regressions and
will still avoid this pattern sometimes. This is a "safe" default, where we err on
the side of compiler blowup instead of risking runtime regressions.

For cases where the default falls short the flag can be changed to allow more/less inlining as
needed on a per-module basis.

-}

tryUnfolding :: Logger -> DynFlags -> Int -> Id -> Bool -> [ArgSummary] -> CallCtxt
             -> CoreExpr -> Bool -> Bool -> UnfoldingGuidance
             -> Maybe CoreExpr
tryUnfolding :: Logger
-> DynFlags
-> Int
-> Id
-> Bool
-> [ArgSummary]
-> CallCtxt
-> CoreExpr
-> Bool
-> Bool
-> UnfoldingGuidance
-> Maybe CoreExpr
tryUnfolding Logger
logger DynFlags
dflags !Int
case_depth Id
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 -> forall a. Logger -> DynFlags -> Id -> String -> SDoc -> a -> a
traceInline Logger
logger DynFlags
dflags Id
id String
str (String -> SDoc
text String
"UnfNever") forall a. Maybe a
Nothing

     UnfWhen { ug_arity :: UnfoldingGuidance -> Int
ug_arity = Int
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
|| UnfoldingOpts -> Bool
unfoldingVeryAggressive UnfoldingOpts
uf_opts)
                -- See Note [INLINE for small functions (3)]
        -> forall a. Logger -> DynFlags -> Id -> String -> SDoc -> a -> a
traceInline Logger
logger DynFlags
dflags Id
id String
str (Bool -> SDoc -> Bool -> SDoc
mk_doc Bool
some_benefit SDoc
empty Bool
True) (forall a. a -> Maybe a
Just CoreExpr
unf_template)
        | Bool
otherwise
        -> forall a. Logger -> DynFlags -> Id -> String -> SDoc -> a -> a
traceInline Logger
logger DynFlags
dflags Id
id String
str (Bool -> SDoc -> Bool -> SDoc
mk_doc Bool
some_benefit SDoc
empty Bool
False) forall a. Maybe a
Nothing
        where
          some_benefit :: Bool
some_benefit = Int -> Bool
calc_some_benefit Int
uf_arity
          enough_args :: Bool
enough_args = (Int
n_val_args forall a. Ord a => a -> a -> Bool
>= Int
uf_arity) Bool -> Bool -> Bool
|| (Bool
unsat_ok Bool -> Bool -> Bool
&& Int
n_val_args forall a. Ord a => a -> a -> Bool
> Int
0)

     UnfIfGoodArgs { ug_args :: UnfoldingGuidance -> [Int]
ug_args = [Int]
arg_discounts, ug_res :: UnfoldingGuidance -> Int
ug_res = Int
res_discount, ug_size :: UnfoldingGuidance -> Int
ug_size = Int
size }
        | UnfoldingOpts -> Bool
unfoldingVeryAggressive UnfoldingOpts
uf_opts
        -> forall a. Logger -> DynFlags -> Id -> String -> SDoc -> a -> a
traceInline Logger
logger DynFlags
dflags Id
id String
str (Bool -> SDoc -> Bool -> SDoc
mk_doc Bool
some_benefit SDoc
extra_doc Bool
True) (forall a. a -> Maybe a
Just CoreExpr
unf_template)
        | Bool
is_wf Bool -> Bool -> Bool
&& Bool
some_benefit Bool -> Bool -> Bool
&& Bool
small_enough
        -> forall a. Logger -> DynFlags -> Id -> String -> SDoc -> a -> a
traceInline Logger
logger DynFlags
dflags Id
id String
str (Bool -> SDoc -> Bool -> SDoc
mk_doc Bool
some_benefit SDoc
extra_doc Bool
True) (forall a. a -> Maybe a
Just CoreExpr
unf_template)
        | Bool
otherwise
        -> forall a. Logger -> DynFlags -> Id -> String -> SDoc -> a -> a
traceInline Logger
logger DynFlags
dflags Id
id String
str (Bool -> SDoc -> Bool -> SDoc
mk_doc Bool
some_benefit SDoc
extra_doc Bool
False) forall a. Maybe a
Nothing
        where
          some_benefit :: Bool
some_benefit = Int -> Bool
calc_some_benefit (forall (t :: * -> *) a. Foldable t => t a -> Int
length [Int]
arg_discounts)
          extra_doc :: SDoc
extra_doc = [SDoc] -> SDoc
vcat [ String -> SDoc
text String
"case depth =" SDoc -> SDoc -> SDoc
<+> Int -> SDoc
int Int
case_depth
                           , String -> SDoc
text String
"depth based penalty =" SDoc -> SDoc -> SDoc
<+> Int -> SDoc
int Int
depth_penalty
                           , String -> SDoc
text String
"discounted size =" SDoc -> SDoc -> SDoc
<+> Int -> SDoc
int Int
adjusted_size ]
          -- See Note [Avoid inlining into deeply nested cases]
          depth_treshold :: Int
depth_treshold = UnfoldingOpts -> Int
unfoldingCaseThreshold UnfoldingOpts
uf_opts
          depth_scaling :: Int
depth_scaling = UnfoldingOpts -> Int
unfoldingCaseScaling UnfoldingOpts
uf_opts
          depth_penalty :: Int
depth_penalty | Int
case_depth forall a. Ord a => a -> a -> Bool
<= Int
depth_treshold = Int
0
                        | Bool
otherwise       = (Int
size forall a. Num a => a -> a -> a
* (Int
case_depth forall a. Num a => a -> a -> a
- Int
depth_treshold)) forall a. Integral a => a -> a -> a
`div` Int
depth_scaling
          adjusted_size :: Int
adjusted_size = Int
size forall a. Num a => a -> a -> a
+ Int
depth_penalty forall a. Num a => a -> a -> a
- Int
discount
          small_enough :: Bool
small_enough = Int
adjusted_size forall a. Ord a => a -> a -> Bool
<= UnfoldingOpts -> Int
unfoldingUseThreshold UnfoldingOpts
uf_opts
          discount :: Int
discount = [Int] -> Int -> [ArgSummary] -> CallCtxt -> Int
computeDiscount [Int]
arg_discounts Int
res_discount [ArgSummary]
arg_infos CallCtxt
cont_info

  where
    uf_opts :: UnfoldingOpts
uf_opts = DynFlags -> UnfoldingOpts
unfoldingOpts DynFlags
dflags
    mk_doc :: Bool -> SDoc -> Bool -> SDoc
mk_doc Bool
some_benefit SDoc
extra_doc Bool
yes_or_no
      = [SDoc] -> SDoc
vcat [ String -> SDoc
text String
"arg infos" SDoc -> SDoc -> SDoc
<+> forall a. Outputable a => a -> SDoc
ppr [ArgSummary]
arg_infos
             , String -> SDoc
text String
"interesting continuation" SDoc -> SDoc -> SDoc
<+> forall a. Outputable a => a -> SDoc
ppr CallCtxt
cont_info
             , String -> SDoc
text String
"some_benefit" SDoc -> SDoc -> SDoc
<+> forall a. Outputable a => a -> SDoc
ppr Bool
some_benefit
             , String -> SDoc
text String
"is exp:" SDoc -> SDoc -> SDoc
<+> forall a. Outputable a => a -> SDoc
ppr Bool
is_exp
             , String -> SDoc
text String
"is work-free:" SDoc -> SDoc -> SDoc
<+> forall a. Outputable a => a -> SDoc
ppr Bool
is_wf
             , String -> SDoc
text String
"guidance" SDoc -> SDoc -> 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"]

    ctx :: SDocContext
ctx = DynFlags -> PprStyle -> SDocContext
initSDocContext DynFlags
dflags PprStyle
defaultDumpStyle
    str :: String
str = String
"Considering inlining: " forall a. [a] -> [a] -> [a]
++ SDocContext -> SDoc -> String
showSDocDump SDocContext
ctx (forall a. Outputable a => a -> SDoc
ppr Id
id)
    n_val_args :: Int
n_val_args = forall (t :: * -> *) a. Foldable t => t a -> Int
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 :: Int -> Bool
calc_some_benefit Int
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      = Int
n_val_args forall a. Ord a => a -> a -> Bool
>= Int
uf_arity
        over_saturated :: Bool
over_saturated = Int
n_val_args forall a. Ord a => a -> a -> Bool
> Int
uf_arity
        interesting_args :: Bool
interesting_args = 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 -> Int
uf_arity forall a. Ord a => a -> a -> Bool
> Int
0  -- See Note [Unfold info lazy contexts]
              CallCtxt
DiscArgCtxt -> Int
uf_arity forall a. Ord a => a -> a -> Bool
> Int
0  -- Note [Inlining in ArgCtxt]
              CallCtxt
RhsCtxt     -> Int
uf_arity forall a. Ord a => a -> a -> Bool
> Int
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 GHC.Core.Utils) 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 :: [Int] -> Int -> [ArgSummary] -> CallCtxt
                -> Int
computeDiscount :: [Int] -> Int -> [ArgSummary] -> CallCtxt -> Int
computeDiscount [Int]
arg_discounts Int
res_discount [ArgSummary]
arg_infos CallCtxt
cont_info

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

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

    forall a. Num a => a -> a -> a
+ Int
total_arg_discount forall a. Num a => a -> a -> a
+ Int
res_discount'
  where
    actual_arg_discounts :: [Int]
actual_arg_discounts = forall a b c. (a -> b -> c) -> [a] -> [b] -> [c]
zipWith forall {a}. Num a => a -> ArgSummary -> a
mk_arg_discount [Int]
arg_discounts [ArgSummary]
arg_infos
    total_arg_discount :: Int
total_arg_discount   = forall (t :: * -> *) a. (Foldable t, Num a) => t a -> a
sum [Int]
actual_arg_discounts

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

    res_discount' :: Int
res_discount'
      | Ordering
LT <- [Int]
arg_discounts forall a b. [a] -> [b] -> Ordering
`compareLength` [ArgSummary]
arg_infos
      = Int
res_discount   -- Over-saturated
      | Bool
otherwise
      = case CallCtxt
cont_info of
           CallCtxt
BoringCtxt  -> Int
0
           CallCtxt
CaseCtxt    -> Int
res_discount  -- Presumably a constructor
           CallCtxt
ValAppCtxt  -> Int
res_discount  -- Presumably a function
           CallCtxt
_           -> Int
40 forall a. Ord a => a -> a -> a
`min` Int
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 avoid inlining large functions that return
                -- constructors into contexts that are simply "interesting"