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

************************************************************************
*                                                                      *
\section[FloatIn]{Floating Inwards pass}
*                                                                      *
************************************************************************

The main purpose of @floatInwards@ is floating into branches of a
case, so that we don't allocate things, save them on the stack, and
then discover that they aren't needed in the chosen branch.
-}

{-# LANGUAGE CPP #-}
{-# OPTIONS_GHC -fprof-auto #-}

module FloatIn ( floatInwards ) where

#include "HsVersions.h"

import GhcPrelude

import CoreSyn
import MkCore hiding    ( wrapFloats )
import HscTypes         ( ModGuts(..) )
import CoreUtils
import CoreFVs
import CoreMonad        ( CoreM )
import Id               ( isOneShotBndr, idType, isJoinId, isJoinId_maybe )
import Var
import Type
import VarSet
import Util
import DynFlags
import Outputable
-- import Data.List        ( mapAccumL )
import BasicTypes       ( RecFlag(..), isRec )

{-
Top-level interface function, @floatInwards@.  Note that we do not
actually float any bindings downwards from the top-level.
-}

floatInwards :: ModGuts -> CoreM ModGuts
floatInwards :: ModGuts -> CoreM ModGuts
floatInwards pgm :: ModGuts
pgm@(ModGuts { mg_binds :: ModGuts -> CoreProgram
mg_binds = CoreProgram
binds })
  = do { DynFlags
dflags <- CoreM DynFlags
forall (m :: * -> *). HasDynFlags m => m DynFlags
getDynFlags
       ; ModGuts -> CoreM ModGuts
forall (m :: * -> *) a. Monad m => a -> m a
return (ModGuts
pgm { mg_binds :: CoreProgram
mg_binds = (Bind CoreBndr -> Bind CoreBndr) -> CoreProgram -> CoreProgram
forall a b. (a -> b) -> [a] -> [b]
map (DynFlags -> Bind CoreBndr -> Bind CoreBndr
fi_top_bind DynFlags
dflags) CoreProgram
binds }) }
  where
    fi_top_bind :: DynFlags -> Bind CoreBndr -> Bind CoreBndr
fi_top_bind DynFlags
dflags (NonRec CoreBndr
binder Expr CoreBndr
rhs)
      = CoreBndr -> Expr CoreBndr -> Bind CoreBndr
forall b. b -> Expr b -> Bind b
NonRec CoreBndr
binder (DynFlags -> FloatInBinds -> CoreExprWithFVs -> Expr CoreBndr
fiExpr DynFlags
dflags [] (Expr CoreBndr -> CoreExprWithFVs
freeVars Expr CoreBndr
rhs))
    fi_top_bind DynFlags
dflags (Rec [(CoreBndr, Expr CoreBndr)]
pairs)
      = [(CoreBndr, Expr CoreBndr)] -> Bind CoreBndr
forall b. [(b, Expr b)] -> Bind b
Rec [ (CoreBndr
b, DynFlags -> FloatInBinds -> CoreExprWithFVs -> Expr CoreBndr
fiExpr DynFlags
dflags [] (Expr CoreBndr -> CoreExprWithFVs
freeVars Expr CoreBndr
rhs)) | (CoreBndr
b, Expr CoreBndr
rhs) <- [(CoreBndr, Expr CoreBndr)]
pairs ]


{-
************************************************************************
*                                                                      *
\subsection{Mail from Andr\'e [edited]}
*                                                                      *
************************************************************************

{\em Will wrote: What??? I thought the idea was to float as far
inwards as possible, no matter what.  This is dropping all bindings
every time it sees a lambda of any kind.  Help! }

You are assuming we DO DO full laziness AFTER floating inwards!  We
have to [not float inside lambdas] if we don't.

If we indeed do full laziness after the floating inwards (we could
check the compilation flags for that) then I agree we could be more
aggressive and do float inwards past lambdas.

Actually we are not doing a proper full laziness (see below), which
was another reason for not floating inwards past a lambda.

This can easily be fixed.  The problem is that we float lets outwards,
but there are a few expressions which are not let bound, like case
scrutinees and case alternatives.  After floating inwards the
simplifier could decide to inline the let and the laziness would be
lost, e.g.

\begin{verbatim}
let a = expensive             ==> \b -> case expensive of ...
in \ b -> case a of ...
\end{verbatim}
The fix is
\begin{enumerate}
\item
to let bind the algebraic case scrutinees (done, I think) and
the case alternatives (except the ones with an
unboxed type)(not done, I think). This is best done in the
SetLevels.hs module, which tags things with their level numbers.
\item
do the full laziness pass (floating lets outwards).
\item
simplify. The simplifier inlines the (trivial) lets that were
 created but were not floated outwards.
\end{enumerate}

With the fix I think Will's suggestion that we can gain even more from
strictness by floating inwards past lambdas makes sense.

We still gain even without going past lambdas, as things may be
strict in the (new) context of a branch (where it was floated to) or
of a let rhs, e.g.
\begin{verbatim}
let a = something            case x of
in case x of                   alt1 -> case something of a -> a + a
     alt1 -> a + a      ==>    alt2 -> b
     alt2 -> b

let a = something           let b = case something of a -> a + a
in let b = a + a        ==> in (b,b)
in (b,b)
\end{verbatim}
Also, even if a is not found to be strict in the new context and is
still left as a let, if the branch is not taken (or b is not entered)
the closure for a is not built.

************************************************************************
*                                                                      *
\subsection{Main floating-inwards code}
*                                                                      *
************************************************************************
-}

type FreeVarSet  = DIdSet
type BoundVarSet = DIdSet

data FloatInBind = FB BoundVarSet FreeVarSet FloatBind
        -- The FreeVarSet is the free variables of the binding.  In the case
        -- of recursive bindings, the set doesn't include the bound
        -- variables.

type FloatInBinds = [FloatInBind]
        -- In reverse dependency order (innermost binder first)

fiExpr :: DynFlags
       -> FloatInBinds      -- Binds we're trying to drop
                            -- as far "inwards" as possible
       -> CoreExprWithFVs   -- Input expr
       -> CoreExpr          -- Result

fiExpr :: DynFlags -> FloatInBinds -> CoreExprWithFVs -> Expr CoreBndr
fiExpr DynFlags
_ FloatInBinds
to_drop (FVAnn
_, AnnLit Literal
lit)     = FloatInBinds -> Expr CoreBndr -> Expr CoreBndr
wrapFloats FloatInBinds
to_drop (Literal -> Expr CoreBndr
forall b. Literal -> Expr b
Lit Literal
lit)
                                       -- See Note [Dead bindings]
fiExpr DynFlags
_ FloatInBinds
to_drop (FVAnn
_, AnnType Type
ty)     = ASSERT( null to_drop ) Type ty
fiExpr DynFlags
_ FloatInBinds
to_drop (FVAnn
_, AnnVar CoreBndr
v)       = FloatInBinds -> Expr CoreBndr -> Expr CoreBndr
wrapFloats FloatInBinds
to_drop (CoreBndr -> Expr CoreBndr
forall b. CoreBndr -> Expr b
Var CoreBndr
v)
fiExpr DynFlags
_ FloatInBinds
to_drop (FVAnn
_, AnnCoercion Coercion
co) = FloatInBinds -> Expr CoreBndr -> Expr CoreBndr
wrapFloats FloatInBinds
to_drop (Coercion -> Expr CoreBndr
forall b. Coercion -> Expr b
Coercion Coercion
co)
fiExpr DynFlags
dflags FloatInBinds
to_drop (FVAnn
_, AnnCast CoreExprWithFVs
expr (FVAnn
co_ann, Coercion
co))
  = FloatInBinds -> Expr CoreBndr -> Expr CoreBndr
wrapFloats (FloatInBinds
drop_here FloatInBinds -> FloatInBinds -> FloatInBinds
forall a. [a] -> [a] -> [a]
++ FloatInBinds
co_drop) (Expr CoreBndr -> Expr CoreBndr) -> Expr CoreBndr -> Expr CoreBndr
forall a b. (a -> b) -> a -> b
$
    Expr CoreBndr -> Coercion -> Expr CoreBndr
forall b. Expr b -> Coercion -> Expr b
Cast (DynFlags -> FloatInBinds -> CoreExprWithFVs -> Expr CoreBndr
fiExpr DynFlags
dflags FloatInBinds
e_drop CoreExprWithFVs
expr) Coercion
co
  where
    [FloatInBinds
drop_here, FloatInBinds
e_drop, FloatInBinds
co_drop]
      = DynFlags -> Bool -> [FVAnn] -> FloatInBinds -> [FloatInBinds]
sepBindsByDropPoint DynFlags
dflags Bool
False
          [CoreExprWithFVs -> FVAnn
freeVarsOf CoreExprWithFVs
expr, FVAnn -> FVAnn
freeVarsOfAnn FVAnn
co_ann]
          FloatInBinds
to_drop

{-
Applications: we do float inside applications, mainly because we
need to get at all the arguments.  The next simplifier run will
pull out any silly ones.
-}

fiExpr DynFlags
dflags FloatInBinds
to_drop ann_expr :: CoreExprWithFVs
ann_expr@(FVAnn
_,AnnApp {})
  = FloatInBinds -> Expr CoreBndr -> Expr CoreBndr
wrapFloats FloatInBinds
drop_here (Expr CoreBndr -> Expr CoreBndr) -> Expr CoreBndr -> Expr CoreBndr
forall a b. (a -> b) -> a -> b
$ FloatInBinds -> Expr CoreBndr -> Expr CoreBndr
wrapFloats FloatInBinds
extra_drop (Expr CoreBndr -> Expr CoreBndr) -> Expr CoreBndr -> Expr CoreBndr
forall a b. (a -> b) -> a -> b
$
    [Tickish CoreBndr] -> Expr CoreBndr -> Expr CoreBndr
mkTicks [Tickish CoreBndr]
ticks (Expr CoreBndr -> Expr CoreBndr) -> Expr CoreBndr -> Expr CoreBndr
forall a b. (a -> b) -> a -> b
$
    Expr CoreBndr -> [Expr CoreBndr] -> Expr CoreBndr
forall b. Expr b -> [Expr b] -> Expr b
mkApps (DynFlags -> FloatInBinds -> CoreExprWithFVs -> Expr CoreBndr
fiExpr DynFlags
dflags FloatInBinds
fun_drop CoreExprWithFVs
ann_fun)
           ((FloatInBinds -> CoreExprWithFVs -> Expr CoreBndr)
-> [FloatInBinds] -> [CoreExprWithFVs] -> [Expr CoreBndr]
forall a b c. (a -> b -> c) -> [a] -> [b] -> [c]
zipWith (DynFlags -> FloatInBinds -> CoreExprWithFVs -> Expr CoreBndr
fiExpr DynFlags
dflags) [FloatInBinds]
arg_drops [CoreExprWithFVs]
ann_args)
  where
    (CoreExprWithFVs
ann_fun, [CoreExprWithFVs]
ann_args, [Tickish CoreBndr]
ticks) = (Tickish CoreBndr -> Bool)
-> CoreExprWithFVs
-> (CoreExprWithFVs, [CoreExprWithFVs], [Tickish CoreBndr])
forall b a.
(Tickish CoreBndr -> Bool)
-> AnnExpr b a -> (AnnExpr b a, [AnnExpr b a], [Tickish CoreBndr])
collectAnnArgsTicks Tickish CoreBndr -> Bool
forall id. Tickish id -> Bool
tickishFloatable CoreExprWithFVs
ann_expr
    fun_ty :: Type
fun_ty  = Expr CoreBndr -> Type
exprType (CoreExprWithFVs -> Expr CoreBndr
forall bndr annot. AnnExpr bndr annot -> Expr bndr
deAnnotate CoreExprWithFVs
ann_fun)
    fun_fvs :: FVAnn
fun_fvs = CoreExprWithFVs -> FVAnn
freeVarsOf CoreExprWithFVs
ann_fun
    arg_fvs :: [FVAnn]
arg_fvs = (CoreExprWithFVs -> FVAnn) -> [CoreExprWithFVs] -> [FVAnn]
forall a b. (a -> b) -> [a] -> [b]
map CoreExprWithFVs -> FVAnn
freeVarsOf [CoreExprWithFVs]
ann_args

    (FloatInBinds
drop_here : FloatInBinds
extra_drop : FloatInBinds
fun_drop : [FloatInBinds]
arg_drops)
       = DynFlags -> Bool -> [FVAnn] -> FloatInBinds -> [FloatInBinds]
sepBindsByDropPoint DynFlags
dflags Bool
False
                             (FVAnn
extra_fvs FVAnn -> [FVAnn] -> [FVAnn]
forall a. a -> [a] -> [a]
: FVAnn
fun_fvs FVAnn -> [FVAnn] -> [FVAnn]
forall a. a -> [a] -> [a]
: [FVAnn]
arg_fvs)
                             FloatInBinds
to_drop
         -- Shortcut behaviour: if to_drop is empty,
         -- sepBindsByDropPoint returns a suitable bunch of empty
         -- lists without evaluating extra_fvs, and hence without
         -- peering into each argument

    (Type
_, FVAnn
extra_fvs) = ((Type, FVAnn) -> CoreExprWithFVs -> (Type, FVAnn))
-> (Type, FVAnn) -> [CoreExprWithFVs] -> (Type, FVAnn)
forall (t :: * -> *) b a.
Foldable t =>
(b -> a -> b) -> b -> t a -> b
foldl' (Type, FVAnn) -> CoreExprWithFVs -> (Type, FVAnn)
add_arg (Type
fun_ty, FVAnn
extra_fvs0) [CoreExprWithFVs]
ann_args
    extra_fvs0 :: FVAnn
extra_fvs0 = case CoreExprWithFVs
ann_fun of
                   (FVAnn
_, AnnVar CoreBndr
_) -> FVAnn
fun_fvs
                   CoreExprWithFVs
_             -> FVAnn
emptyDVarSet
          -- Don't float the binding for f into f x y z; see Note [Join points]
          -- for why we *can't* do it when f is a join point. (If f isn't a
          -- join point, floating it in isn't especially harmful but it's
          -- useless since the simplifier will immediately float it back out.)

    add_arg :: (Type,FreeVarSet) -> CoreExprWithFVs -> (Type,FreeVarSet)
    add_arg :: (Type, FVAnn) -> CoreExprWithFVs -> (Type, FVAnn)
add_arg (Type
fun_ty, FVAnn
extra_fvs) (FVAnn
_, AnnType Type
ty)
      = (HasDebugCallStack => Type -> Type -> Type
Type -> Type -> Type
piResultTy Type
fun_ty Type
ty, FVAnn
extra_fvs)

    add_arg (Type
fun_ty, FVAnn
extra_fvs) (FVAnn
arg_fvs, AnnExpr' CoreBndr FVAnn
arg)
      | AnnExpr' CoreBndr FVAnn -> Type -> Bool
noFloatIntoArg AnnExpr' CoreBndr FVAnn
arg Type
arg_ty
      = (Type
res_ty, FVAnn
extra_fvs FVAnn -> FVAnn -> FVAnn
`unionDVarSet` FVAnn
arg_fvs)
      | Bool
otherwise
      = (Type
res_ty, FVAnn
extra_fvs)
      where
       (Type
arg_ty, Type
res_ty) = Type -> (Type, Type)
splitFunTy Type
fun_ty

{- Note [Dead bindings]
~~~~~~~~~~~~~~~~~~~~~~~
At a literal we won't usually have any floated bindings; the
only way that can happen is if the binding wrapped the literal
/in the original input program/.  e.g.
   case x of { DEFAULT -> 1# }
But, while this may be unusual it is not actually wrong, and it did
once happen (#15696).

Note [Do not destroy the let/app invariant]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Watch out for
   f (x +# y)
We don't want to float bindings into here
   f (case ... of { x -> x +# y })
because that might destroy the let/app invariant, which requires
unlifted function arguments to be ok-for-speculation.

Note [Join points]
~~~~~~~~~~~~~~~~~~
Generally, we don't need to worry about join points - there are places we're
not allowed to float them, but since they can't have occurrences in those
places, we're not tempted.

We do need to be careful about jumps, however:

  joinrec j x y z = ... in
  jump j a b c

Previous versions often floated the definition of a recursive function into its
only non-recursive occurrence. But for a join point, this is a disaster:

  (joinrec j x y z = ... in
  jump j) a b c -- wrong!

Every jump must be exact, so the jump to j must have three arguments. Hence
we're careful not to float into the target of a jump (though we can float into
the arguments just fine).

Note [Floating in past a lambda group]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
* We must be careful about floating inside a value lambda.
  That risks losing laziness.
  The float-out pass might rescue us, but then again it might not.

* We must be careful about type lambdas too.  At one time we did, and
  there is no risk of duplicating work thereby, but we do need to be
  careful.  In particular, here is a bad case (it happened in the
  cichelli benchmark:
        let v = ...
        in let f = /\t -> \a -> ...
           ==>
        let f = /\t -> let v = ... in \a -> ...
  This is bad as now f is an updatable closure (update PAP)
  and has arity 0.

* Hack alert!  We only float in through one-shot lambdas,
  not (as you might guess) through lone big lambdas.
  Reason: we float *out* past big lambdas (see the test in the Lam
  case of FloatOut.floatExpr) and we don't want to float straight
  back in again.

  It *is* important to float into one-shot lambdas, however;
  see the remarks with noFloatIntoRhs.

So we treat lambda in groups, using the following rule:

 Float in if (a) there is at least one Id,
         and (b) there are no non-one-shot Ids

 Otherwise drop all the bindings outside the group.

This is what the 'go' function in the AnnLam case is doing.

(Join points are handled similarly: a join point is considered one-shot iff
it's non-recursive, so we float only into non-recursive join points.)

Urk! if all are tyvars, and we don't float in, we may miss an
      opportunity to float inside a nested case branch


Note [Floating coercions]
~~~~~~~~~~~~~~~~~~~~~~~~~
We could, in principle, have a coercion binding like
   case f x of co { DEFAULT -> e1 e2 }
It's not common to have a function that returns a coercion, but nothing
in Core prohibits it.  If so, 'co' might be mentioned in e1 or e2
/only in a type/.  E.g. suppose e1 was
  let (x :: Int |> co) = blah in blah2


But, with coercions appearing in types, there is a complication: we
might be floating in a "strict let" -- that is, a case. Case expressions
mention their return type. We absolutely can't float a coercion binding
inward to the point that the type of the expression it's about to wrap
mentions the coercion. So we include the union of the sets of free variables
of the types of all the drop points involved. If any of the floaters
bind a coercion variable mentioned in any of the types, that binder must
be dropped right away.

-}

fiExpr DynFlags
dflags FloatInBinds
to_drop lam :: CoreExprWithFVs
lam@(FVAnn
_, AnnLam CoreBndr
_ CoreExprWithFVs
_)
  | [CoreBndr] -> Bool
noFloatIntoLam [CoreBndr]
bndrs       -- Dump it all here
     -- NB: Must line up with noFloatIntoRhs (AnnLam...); see #7088
  = FloatInBinds -> Expr CoreBndr -> Expr CoreBndr
wrapFloats FloatInBinds
to_drop ([CoreBndr] -> Expr CoreBndr -> Expr CoreBndr
forall b. [b] -> Expr b -> Expr b
mkLams [CoreBndr]
bndrs (DynFlags -> FloatInBinds -> CoreExprWithFVs -> Expr CoreBndr
fiExpr DynFlags
dflags [] CoreExprWithFVs
body))

  | Bool
otherwise           -- Float inside
  = [CoreBndr] -> Expr CoreBndr -> Expr CoreBndr
forall b. [b] -> Expr b -> Expr b
mkLams [CoreBndr]
bndrs (DynFlags -> FloatInBinds -> CoreExprWithFVs -> Expr CoreBndr
fiExpr DynFlags
dflags FloatInBinds
to_drop CoreExprWithFVs
body)

  where
    ([CoreBndr]
bndrs, CoreExprWithFVs
body) = CoreExprWithFVs -> ([CoreBndr], CoreExprWithFVs)
forall bndr annot.
AnnExpr bndr annot -> ([bndr], AnnExpr bndr annot)
collectAnnBndrs CoreExprWithFVs
lam

{-
We don't float lets inwards past an SCC.
        ToDo: keep info on current cc, and when passing
        one, if it is not the same, annotate all lets in binds with current
        cc, change current cc to the new one and float binds into expr.
-}

fiExpr DynFlags
dflags FloatInBinds
to_drop (FVAnn
_, AnnTick Tickish CoreBndr
tickish CoreExprWithFVs
expr)
  | Tickish CoreBndr
tickish Tickish CoreBndr -> TickishScoping -> Bool
forall id. Tickish id -> TickishScoping -> Bool
`tickishScopesLike` TickishScoping
SoftScope
  = Tickish CoreBndr -> Expr CoreBndr -> Expr CoreBndr
forall b. Tickish CoreBndr -> Expr b -> Expr b
Tick Tickish CoreBndr
tickish (DynFlags -> FloatInBinds -> CoreExprWithFVs -> Expr CoreBndr
fiExpr DynFlags
dflags FloatInBinds
to_drop CoreExprWithFVs
expr)

  | Bool
otherwise -- Wimp out for now - we could push values in
  = FloatInBinds -> Expr CoreBndr -> Expr CoreBndr
wrapFloats FloatInBinds
to_drop (Tickish CoreBndr -> Expr CoreBndr -> Expr CoreBndr
forall b. Tickish CoreBndr -> Expr b -> Expr b
Tick Tickish CoreBndr
tickish (DynFlags -> FloatInBinds -> CoreExprWithFVs -> Expr CoreBndr
fiExpr DynFlags
dflags [] CoreExprWithFVs
expr))

{-
For @Lets@, the possible ``drop points'' for the \tr{to_drop}
bindings are: (a)~in the body, (b1)~in the RHS of a NonRec binding,
or~(b2), in each of the RHSs of the pairs of a @Rec@.

Note that we do {\em weird things} with this let's binding.  Consider:
\begin{verbatim}
let
    w = ...
in {
    let v = ... w ...
    in ... v .. w ...
}
\end{verbatim}
Look at the inner \tr{let}.  As \tr{w} is used in both the bind and
body of the inner let, we could panic and leave \tr{w}'s binding where
it is.  But \tr{v} is floatable further into the body of the inner let, and
{\em then} \tr{w} will also be only in the body of that inner let.

So: rather than drop \tr{w}'s binding here, we add it onto the list of
things to drop in the outer let's body, and let nature take its
course.

Note [extra_fvs (1): avoid floating into RHS]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider let x=\y....t... in body.  We do not necessarily want to float
a binding for t into the RHS, because it'll immediately be floated out
again.  (It won't go inside the lambda else we risk losing work.)
In letrec, we need to be more careful still. We don't want to transform
        let x# = y# +# 1#
        in
        letrec f = \z. ...x#...f...
        in ...
into
        letrec f = let x# = y# +# 1# in \z. ...x#...f... in ...
because now we can't float the let out again, because a letrec
can't have unboxed bindings.

So we make "extra_fvs" which is the rhs_fvs of such bindings, and
arrange to dump bindings that bind extra_fvs before the entire let.

Note [extra_fvs (2): free variables of rules]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider
  let x{rule mentioning y} = rhs in body
Here y is not free in rhs or body; but we still want to dump bindings
that bind y outside the let.  So we augment extra_fvs with the
idRuleAndUnfoldingVars of x.  No need for type variables, hence not using
idFreeVars.
-}

fiExpr DynFlags
dflags FloatInBinds
to_drop (FVAnn
_,AnnLet AnnBind CoreBndr FVAnn
bind CoreExprWithFVs
body)
  = DynFlags -> FloatInBinds -> CoreExprWithFVs -> Expr CoreBndr
fiExpr DynFlags
dflags (FloatInBinds
after FloatInBinds -> FloatInBinds -> FloatInBinds
forall a. [a] -> [a] -> [a]
++ FloatInBind
new_float FloatInBind -> FloatInBinds -> FloatInBinds
forall a. a -> [a] -> [a]
: FloatInBinds
before) CoreExprWithFVs
body
           -- to_drop is in reverse dependency order
  where
    (FloatInBinds
before, FloatInBind
new_float, FloatInBinds
after) = DynFlags
-> FloatInBinds
-> AnnBind CoreBndr FVAnn
-> FVAnn
-> (FloatInBinds, FloatInBind, FloatInBinds)
fiBind DynFlags
dflags FloatInBinds
to_drop AnnBind CoreBndr FVAnn
bind FVAnn
body_fvs
    body_fvs :: FVAnn
body_fvs    = CoreExprWithFVs -> FVAnn
freeVarsOf CoreExprWithFVs
body

{- Note [Floating primops]
~~~~~~~~~~~~~~~~~~~~~~~~~~
We try to float-in a case expression over an unlifted type.  The
motivating example was #5658: in particular, this change allows
array indexing operations, which have a single DEFAULT alternative
without any binders, to be floated inward.

SIMD primops for unpacking SIMD vectors into an unboxed tuple of unboxed
scalars also need to be floated inward, but unpacks have a single non-DEFAULT
alternative that binds the elements of the tuple. We now therefore also support
floating in cases with a single alternative that may bind values.

But there are wrinkles

* Which unlifted cases do we float? See PrimOp.hs
  Note [PrimOp can_fail and has_side_effects] which explains:
   - We can float-in can_fail primops, but we can't float them out.
   - But we can float a has_side_effects primop, but NOT inside a lambda,
     so for now we don't float them at all.
  Hence exprOkForSideEffects

* Because we can float can-fail primops (array indexing, division) inwards
  but not outwards, we must be careful not to transform
     case a /# b of r -> f (F# r)
  ===>
    f (case a /# b of r -> F# r)
  because that creates a new thunk that wasn't there before.  And
  because it can't be floated out (can_fail), the thunk will stay
  there.  Disaster!  (This happened in nofib 'simple' and 'scs'.)

  Solution: only float cases into the branches of other cases, and
  not into the arguments of an application, or the RHS of a let. This
  is somewhat conservative, but it's simple.  And it still hits the
  cases like #5658.   This is implemented in sepBindsByJoinPoint;
  if is_case is False we dump all floating cases right here.

* #14511 is another example of why we want to restrict float-in
  of case-expressions.  Consider
     case indexArray# a n of (# r #) -> writeArray# ma i (f r)
  Now, floating that indexing operation into the (f r) thunk will
  not create any new thunks, but it will keep the array 'a' alive
  for much longer than the programmer expected.

  So again, not floating a case into a let or argument seems like
  the Right Thing

For @Case@, the possible drop points for the 'to_drop'
bindings are:
  (a) inside the scrutinee
  (b) inside one of the alternatives/default (default FVs always /first/!).

-}

fiExpr DynFlags
dflags FloatInBinds
to_drop (FVAnn
_, AnnCase CoreExprWithFVs
scrut CoreBndr
case_bndr Type
_ [(AltCon
con,[CoreBndr]
alt_bndrs,CoreExprWithFVs
rhs)])
  | HasDebugCallStack => Type -> Bool
Type -> Bool
isUnliftedType (CoreBndr -> Type
idType CoreBndr
case_bndr)
  , Expr CoreBndr -> Bool
exprOkForSideEffects (CoreExprWithFVs -> Expr CoreBndr
forall bndr annot. AnnExpr bndr annot -> Expr bndr
deAnnotate CoreExprWithFVs
scrut)
      -- See Note [Floating primops]
  = FloatInBinds -> Expr CoreBndr -> Expr CoreBndr
wrapFloats FloatInBinds
shared_binds (Expr CoreBndr -> Expr CoreBndr) -> Expr CoreBndr -> Expr CoreBndr
forall a b. (a -> b) -> a -> b
$
    DynFlags -> FloatInBinds -> CoreExprWithFVs -> Expr CoreBndr
fiExpr DynFlags
dflags (FloatInBind
case_float FloatInBind -> FloatInBinds -> FloatInBinds
forall a. a -> [a] -> [a]
: FloatInBinds
rhs_binds) CoreExprWithFVs
rhs
  where
    case_float :: FloatInBind
case_float = FVAnn -> FVAnn -> FloatBind -> FloatInBind
FB ([CoreBndr] -> FVAnn
mkDVarSet (CoreBndr
case_bndr CoreBndr -> [CoreBndr] -> [CoreBndr]
forall a. a -> [a] -> [a]
: [CoreBndr]
alt_bndrs)) FVAnn
scrut_fvs
                    (Expr CoreBndr -> CoreBndr -> AltCon -> [CoreBndr] -> FloatBind
FloatCase Expr CoreBndr
scrut' CoreBndr
case_bndr AltCon
con [CoreBndr]
alt_bndrs)
    scrut' :: Expr CoreBndr
scrut'     = DynFlags -> FloatInBinds -> CoreExprWithFVs -> Expr CoreBndr
fiExpr DynFlags
dflags FloatInBinds
scrut_binds CoreExprWithFVs
scrut
    rhs_fvs :: FVAnn
rhs_fvs    = CoreExprWithFVs -> FVAnn
freeVarsOf CoreExprWithFVs
rhs FVAnn -> [CoreBndr] -> FVAnn
`delDVarSetList` (CoreBndr
case_bndr CoreBndr -> [CoreBndr] -> [CoreBndr]
forall a. a -> [a] -> [a]
: [CoreBndr]
alt_bndrs)
    scrut_fvs :: FVAnn
scrut_fvs  = CoreExprWithFVs -> FVAnn
freeVarsOf CoreExprWithFVs
scrut

    [FloatInBinds
shared_binds, FloatInBinds
scrut_binds, FloatInBinds
rhs_binds]
       = DynFlags -> Bool -> [FVAnn] -> FloatInBinds -> [FloatInBinds]
sepBindsByDropPoint DynFlags
dflags Bool
False
           [FVAnn
scrut_fvs, FVAnn
rhs_fvs]
           FloatInBinds
to_drop

fiExpr DynFlags
dflags FloatInBinds
to_drop (FVAnn
_, AnnCase CoreExprWithFVs
scrut CoreBndr
case_bndr Type
ty [AnnAlt CoreBndr FVAnn]
alts)
  = FloatInBinds -> Expr CoreBndr -> Expr CoreBndr
wrapFloats FloatInBinds
drop_here1 (Expr CoreBndr -> Expr CoreBndr) -> Expr CoreBndr -> Expr CoreBndr
forall a b. (a -> b) -> a -> b
$
    FloatInBinds -> Expr CoreBndr -> Expr CoreBndr
wrapFloats FloatInBinds
drop_here2 (Expr CoreBndr -> Expr CoreBndr) -> Expr CoreBndr -> Expr CoreBndr
forall a b. (a -> b) -> a -> b
$
    Expr CoreBndr
-> CoreBndr -> Type -> [Alt CoreBndr] -> Expr CoreBndr
forall b. Expr b -> b -> Type -> [Alt b] -> Expr b
Case (DynFlags -> FloatInBinds -> CoreExprWithFVs -> Expr CoreBndr
fiExpr DynFlags
dflags FloatInBinds
scrut_drops CoreExprWithFVs
scrut) CoreBndr
case_bndr Type
ty
         ((FloatInBinds -> AnnAlt CoreBndr FVAnn -> Alt CoreBndr)
-> [FloatInBinds] -> [AnnAlt CoreBndr FVAnn] -> [Alt CoreBndr]
forall a b c. (a -> b -> c) -> [a] -> [b] -> [c]
zipWith FloatInBinds -> AnnAlt CoreBndr FVAnn -> Alt CoreBndr
forall a b.
FloatInBinds -> (a, b, CoreExprWithFVs) -> (a, b, Expr CoreBndr)
fi_alt [FloatInBinds]
alts_drops_s [AnnAlt CoreBndr FVAnn]
alts)
  where
        -- Float into the scrut and alts-considered-together just like App
    [FloatInBinds
drop_here1, FloatInBinds
scrut_drops, FloatInBinds
alts_drops]
       = DynFlags -> Bool -> [FVAnn] -> FloatInBinds -> [FloatInBinds]
sepBindsByDropPoint DynFlags
dflags Bool
False
           [FVAnn
scrut_fvs, FVAnn
all_alts_fvs]
           FloatInBinds
to_drop

        -- Float into the alts with the is_case flag set
    (FloatInBinds
drop_here2 : [FloatInBinds]
alts_drops_s)
      | [ AnnAlt CoreBndr FVAnn
_ ] <- [AnnAlt CoreBndr FVAnn]
alts = [] FloatInBinds -> [FloatInBinds] -> [FloatInBinds]
forall a. a -> [a] -> [a]
: [FloatInBinds
alts_drops]
      | Bool
otherwise     = DynFlags -> Bool -> [FVAnn] -> FloatInBinds -> [FloatInBinds]
sepBindsByDropPoint DynFlags
dflags Bool
True [FVAnn]
alts_fvs FloatInBinds
alts_drops

    scrut_fvs :: FVAnn
scrut_fvs    = CoreExprWithFVs -> FVAnn
freeVarsOf CoreExprWithFVs
scrut
    alts_fvs :: [FVAnn]
alts_fvs     = (AnnAlt CoreBndr FVAnn -> FVAnn)
-> [AnnAlt CoreBndr FVAnn] -> [FVAnn]
forall a b. (a -> b) -> [a] -> [b]
map AnnAlt CoreBndr FVAnn -> FVAnn
forall a. (a, [CoreBndr], CoreExprWithFVs) -> FVAnn
alt_fvs [AnnAlt CoreBndr FVAnn]
alts
    all_alts_fvs :: FVAnn
all_alts_fvs = [FVAnn] -> FVAnn
unionDVarSets [FVAnn]
alts_fvs
    alt_fvs :: (a, [CoreBndr], CoreExprWithFVs) -> FVAnn
alt_fvs (a
_con, [CoreBndr]
args, CoreExprWithFVs
rhs)
      = (FVAnn -> CoreBndr -> FVAnn) -> FVAnn -> [CoreBndr] -> FVAnn
forall (t :: * -> *) b a.
Foldable t =>
(b -> a -> b) -> b -> t a -> b
foldl' FVAnn -> CoreBndr -> FVAnn
delDVarSet (CoreExprWithFVs -> FVAnn
freeVarsOf CoreExprWithFVs
rhs) (CoreBndr
case_bndrCoreBndr -> [CoreBndr] -> [CoreBndr]
forall a. a -> [a] -> [a]
:[CoreBndr]
args)
           -- Delete case_bndr and args from free vars of rhs
           -- to get free vars of alt

    fi_alt :: FloatInBinds -> (a, b, CoreExprWithFVs) -> (a, b, Expr CoreBndr)
fi_alt FloatInBinds
to_drop (a
con, b
args, CoreExprWithFVs
rhs) = (a
con, b
args, DynFlags -> FloatInBinds -> CoreExprWithFVs -> Expr CoreBndr
fiExpr DynFlags
dflags FloatInBinds
to_drop CoreExprWithFVs
rhs)

------------------
fiBind :: DynFlags
       -> FloatInBinds      -- Binds we're trying to drop
                            -- as far "inwards" as possible
       -> CoreBindWithFVs   -- Input binding
       -> DVarSet           -- Free in scope of binding
       -> ( FloatInBinds    -- Land these before
          , FloatInBind     -- The binding itself
          , FloatInBinds)   -- Land these after

fiBind :: DynFlags
-> FloatInBinds
-> AnnBind CoreBndr FVAnn
-> FVAnn
-> (FloatInBinds, FloatInBind, FloatInBinds)
fiBind DynFlags
dflags FloatInBinds
to_drop (AnnNonRec CoreBndr
id ann_rhs :: CoreExprWithFVs
ann_rhs@(FVAnn
rhs_fvs, AnnExpr' CoreBndr FVAnn
rhs)) FVAnn
body_fvs
  = ( FloatInBinds
extra_binds FloatInBinds -> FloatInBinds -> FloatInBinds
forall a. [a] -> [a] -> [a]
++ FloatInBinds
shared_binds          -- Land these before
                                           -- See Note [extra_fvs (1,2)]
    , FVAnn -> FVAnn -> FloatBind -> FloatInBind
FB (CoreBndr -> FVAnn
unitDVarSet CoreBndr
id) FVAnn
rhs_fvs'         -- The new binding itself
          (Bind CoreBndr -> FloatBind
FloatLet (CoreBndr -> Expr CoreBndr -> Bind CoreBndr
forall b. b -> Expr b -> Bind b
NonRec CoreBndr
id Expr CoreBndr
rhs'))
    , FloatInBinds
body_binds )                         -- Land these after

  where
    body_fvs2 :: FVAnn
body_fvs2 = FVAnn
body_fvs FVAnn -> CoreBndr -> FVAnn
`delDVarSet` CoreBndr
id

    rule_fvs :: FVAnn
rule_fvs = CoreBndr -> FVAnn
bndrRuleAndUnfoldingVarsDSet CoreBndr
id        -- See Note [extra_fvs (2): free variables of rules]
    extra_fvs :: FVAnn
extra_fvs | RecFlag -> CoreBndr -> AnnExpr' CoreBndr FVAnn -> Bool
noFloatIntoRhs RecFlag
NonRecursive CoreBndr
id AnnExpr' CoreBndr FVAnn
rhs
              = FVAnn
rule_fvs FVAnn -> FVAnn -> FVAnn
`unionDVarSet` FVAnn
rhs_fvs
              | Bool
otherwise
              = FVAnn
rule_fvs
        -- See Note [extra_fvs (1): avoid floating into RHS]
        -- No point in floating in only to float straight out again
        -- We *can't* float into ok-for-speculation unlifted RHSs
        -- But do float into join points

    [FloatInBinds
shared_binds, FloatInBinds
extra_binds, FloatInBinds
rhs_binds, FloatInBinds
body_binds]
        = DynFlags -> Bool -> [FVAnn] -> FloatInBinds -> [FloatInBinds]
sepBindsByDropPoint DynFlags
dflags Bool
False
            [FVAnn
extra_fvs, FVAnn
rhs_fvs, FVAnn
body_fvs2]
            FloatInBinds
to_drop

        -- Push rhs_binds into the right hand side of the binding
    rhs' :: Expr CoreBndr
rhs'     = DynFlags
-> FloatInBinds -> CoreBndr -> CoreExprWithFVs -> Expr CoreBndr
fiRhs DynFlags
dflags FloatInBinds
rhs_binds CoreBndr
id CoreExprWithFVs
ann_rhs
    rhs_fvs' :: FVAnn
rhs_fvs' = FVAnn
rhs_fvs FVAnn -> FVAnn -> FVAnn
`unionDVarSet` FloatInBinds -> FVAnn
floatedBindsFVs FloatInBinds
rhs_binds FVAnn -> FVAnn -> FVAnn
`unionDVarSet` FVAnn
rule_fvs
                        -- Don't forget the rule_fvs; the binding mentions them!

fiBind DynFlags
dflags FloatInBinds
to_drop (AnnRec [(CoreBndr, CoreExprWithFVs)]
bindings) FVAnn
body_fvs
  = ( FloatInBinds
extra_binds FloatInBinds -> FloatInBinds -> FloatInBinds
forall a. [a] -> [a] -> [a]
++ FloatInBinds
shared_binds
    , FVAnn -> FVAnn -> FloatBind -> FloatInBind
FB ([CoreBndr] -> FVAnn
mkDVarSet [CoreBndr]
ids) FVAnn
rhs_fvs'
         (Bind CoreBndr -> FloatBind
FloatLet ([(CoreBndr, Expr CoreBndr)] -> Bind CoreBndr
forall b. [(b, Expr b)] -> Bind b
Rec ([FloatInBinds]
-> [(CoreBndr, CoreExprWithFVs)] -> [(CoreBndr, Expr CoreBndr)]
fi_bind [FloatInBinds]
rhss_binds [(CoreBndr, CoreExprWithFVs)]
bindings)))
    , FloatInBinds
body_binds )
  where
    ([CoreBndr]
ids, [CoreExprWithFVs]
rhss) = [(CoreBndr, CoreExprWithFVs)] -> ([CoreBndr], [CoreExprWithFVs])
forall a b. [(a, b)] -> ([a], [b])
unzip [(CoreBndr, CoreExprWithFVs)]
bindings
    rhss_fvs :: [FVAnn]
rhss_fvs = (CoreExprWithFVs -> FVAnn) -> [CoreExprWithFVs] -> [FVAnn]
forall a b. (a -> b) -> [a] -> [b]
map CoreExprWithFVs -> FVAnn
freeVarsOf [CoreExprWithFVs]
rhss

        -- See Note [extra_fvs (1,2)]
    rule_fvs :: FVAnn
rule_fvs = (CoreBndr -> FVAnn) -> [CoreBndr] -> FVAnn
forall a. (a -> FVAnn) -> [a] -> FVAnn
mapUnionDVarSet CoreBndr -> FVAnn
bndrRuleAndUnfoldingVarsDSet [CoreBndr]
ids
    extra_fvs :: FVAnn
extra_fvs = FVAnn
rule_fvs FVAnn -> FVAnn -> FVAnn
`unionDVarSet`
                [FVAnn] -> FVAnn
unionDVarSets [ FVAnn
rhs_fvs | (CoreBndr
bndr, (FVAnn
rhs_fvs, AnnExpr' CoreBndr FVAnn
rhs)) <- [(CoreBndr, CoreExprWithFVs)]
bindings
                              , RecFlag -> CoreBndr -> AnnExpr' CoreBndr FVAnn -> Bool
noFloatIntoRhs RecFlag
Recursive CoreBndr
bndr AnnExpr' CoreBndr FVAnn
rhs ]

    (FloatInBinds
shared_binds:FloatInBinds
extra_binds:FloatInBinds
body_binds:[FloatInBinds]
rhss_binds)
        = DynFlags -> Bool -> [FVAnn] -> FloatInBinds -> [FloatInBinds]
sepBindsByDropPoint DynFlags
dflags Bool
False
            (FVAnn
extra_fvsFVAnn -> [FVAnn] -> [FVAnn]
forall a. a -> [a] -> [a]
:FVAnn
body_fvsFVAnn -> [FVAnn] -> [FVAnn]
forall a. a -> [a] -> [a]
:[FVAnn]
rhss_fvs)
            FloatInBinds
to_drop

    rhs_fvs' :: FVAnn
rhs_fvs' = [FVAnn] -> FVAnn
unionDVarSets [FVAnn]
rhss_fvs FVAnn -> FVAnn -> FVAnn
`unionDVarSet`
               [FVAnn] -> FVAnn
unionDVarSets ((FloatInBinds -> FVAnn) -> [FloatInBinds] -> [FVAnn]
forall a b. (a -> b) -> [a] -> [b]
map FloatInBinds -> FVAnn
floatedBindsFVs [FloatInBinds]
rhss_binds) FVAnn -> FVAnn -> FVAnn
`unionDVarSet`
               FVAnn
rule_fvs         -- Don't forget the rule variables!

    -- Push rhs_binds into the right hand side of the binding
    fi_bind :: [FloatInBinds]       -- one per "drop pt" conjured w/ fvs_of_rhss
            -> [(Id, CoreExprWithFVs)]
            -> [(Id, CoreExpr)]

    fi_bind :: [FloatInBinds]
-> [(CoreBndr, CoreExprWithFVs)] -> [(CoreBndr, Expr CoreBndr)]
fi_bind [FloatInBinds]
to_drops [(CoreBndr, CoreExprWithFVs)]
pairs
      = [ (CoreBndr
binder, DynFlags
-> FloatInBinds -> CoreBndr -> CoreExprWithFVs -> Expr CoreBndr
fiRhs DynFlags
dflags FloatInBinds
to_drop CoreBndr
binder CoreExprWithFVs
rhs)
        | ((CoreBndr
binder, CoreExprWithFVs
rhs), FloatInBinds
to_drop) <- String
-> [(CoreBndr, CoreExprWithFVs)]
-> [FloatInBinds]
-> [((CoreBndr, CoreExprWithFVs), FloatInBinds)]
forall a b. String -> [a] -> [b] -> [(a, b)]
zipEqual String
"fi_bind" [(CoreBndr, CoreExprWithFVs)]
pairs [FloatInBinds]
to_drops ]

------------------
fiRhs :: DynFlags -> FloatInBinds -> CoreBndr -> CoreExprWithFVs -> CoreExpr
fiRhs :: DynFlags
-> FloatInBinds -> CoreBndr -> CoreExprWithFVs -> Expr CoreBndr
fiRhs DynFlags
dflags FloatInBinds
to_drop CoreBndr
bndr CoreExprWithFVs
rhs
  | Just Int
join_arity <- CoreBndr -> Maybe Int
isJoinId_maybe CoreBndr
bndr
  , let ([CoreBndr]
bndrs, CoreExprWithFVs
body) = Int -> CoreExprWithFVs -> ([CoreBndr], CoreExprWithFVs)
forall bndr annot.
Int -> AnnExpr bndr annot -> ([bndr], AnnExpr bndr annot)
collectNAnnBndrs Int
join_arity CoreExprWithFVs
rhs
  = [CoreBndr] -> Expr CoreBndr -> Expr CoreBndr
forall b. [b] -> Expr b -> Expr b
mkLams [CoreBndr]
bndrs (DynFlags -> FloatInBinds -> CoreExprWithFVs -> Expr CoreBndr
fiExpr DynFlags
dflags FloatInBinds
to_drop CoreExprWithFVs
body)
  | Bool
otherwise
  = DynFlags -> FloatInBinds -> CoreExprWithFVs -> Expr CoreBndr
fiExpr DynFlags
dflags FloatInBinds
to_drop CoreExprWithFVs
rhs

------------------
noFloatIntoLam :: [Var] -> Bool
noFloatIntoLam :: [CoreBndr] -> Bool
noFloatIntoLam [CoreBndr]
bndrs = (CoreBndr -> Bool) -> [CoreBndr] -> Bool
forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
any CoreBndr -> Bool
bad [CoreBndr]
bndrs
  where
    bad :: CoreBndr -> Bool
bad CoreBndr
b = CoreBndr -> Bool
isId CoreBndr
b Bool -> Bool -> Bool
&& Bool -> Bool
not (CoreBndr -> Bool
isOneShotBndr CoreBndr
b)
    -- Don't float inside a non-one-shot lambda

noFloatIntoRhs :: RecFlag -> Id -> CoreExprWithFVs' -> Bool
-- ^ True if it's a bad idea to float bindings into this RHS
noFloatIntoRhs :: RecFlag -> CoreBndr -> AnnExpr' CoreBndr FVAnn -> Bool
noFloatIntoRhs RecFlag
is_rec CoreBndr
bndr AnnExpr' CoreBndr FVAnn
rhs
  | CoreBndr -> Bool
isJoinId CoreBndr
bndr
  = RecFlag -> Bool
isRec RecFlag
is_rec -- Joins are one-shot iff non-recursive

  | Bool
otherwise
  = AnnExpr' CoreBndr FVAnn -> Type -> Bool
noFloatIntoArg AnnExpr' CoreBndr FVAnn
rhs (CoreBndr -> Type
idType CoreBndr
bndr)

noFloatIntoArg :: CoreExprWithFVs' -> Type -> Bool
noFloatIntoArg :: AnnExpr' CoreBndr FVAnn -> Type -> Bool
noFloatIntoArg AnnExpr' CoreBndr FVAnn
expr Type
expr_ty
  | HasDebugCallStack => Type -> Bool
Type -> Bool
isUnliftedType Type
expr_ty
  = Bool
True  -- See Note [Do not destroy the let/app invariant]

   | AnnLam CoreBndr
bndr CoreExprWithFVs
e <- AnnExpr' CoreBndr FVAnn
expr
   , ([CoreBndr]
bndrs, CoreExprWithFVs
_) <- CoreExprWithFVs -> ([CoreBndr], CoreExprWithFVs)
forall bndr annot.
AnnExpr bndr annot -> ([bndr], AnnExpr bndr annot)
collectAnnBndrs CoreExprWithFVs
e
   =  [CoreBndr] -> Bool
noFloatIntoLam (CoreBndr
bndrCoreBndr -> [CoreBndr] -> [CoreBndr]
forall a. a -> [a] -> [a]
:[CoreBndr]
bndrs)  -- Wrinkle 1 (a)
   Bool -> Bool -> Bool
|| (CoreBndr -> Bool) -> [CoreBndr] -> Bool
forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
all CoreBndr -> Bool
isTyVar (CoreBndr
bndrCoreBndr -> [CoreBndr] -> [CoreBndr]
forall a. a -> [a] -> [a]
:[CoreBndr]
bndrs)     -- Wrinkle 1 (b)
      -- See Note [noFloatInto considerations] wrinkle 2

  | Bool
otherwise  -- Note [noFloatInto considerations] wrinkle 2
  = Expr CoreBndr -> Bool
exprIsTrivial Expr CoreBndr
deann_expr Bool -> Bool -> Bool
|| Expr CoreBndr -> Bool
exprIsHNF Expr CoreBndr
deann_expr
  where
    deann_expr :: Expr CoreBndr
deann_expr = AnnExpr' CoreBndr FVAnn -> Expr CoreBndr
forall bndr annot. AnnExpr' bndr annot -> Expr bndr
deAnnotate' AnnExpr' CoreBndr FVAnn
expr

{- Note [noFloatInto considerations]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
When do we want to float bindings into
   - noFloatIntoRHs: the RHS of a let-binding
   - noFloatIntoArg: the argument of a function application

Definitely don't float in if it has unlifted type; that
would destroy the let/app invariant.

* Wrinkle 1: do not float in if
     (a) any non-one-shot value lambdas
  or (b) all type lambdas
  In both cases we'll float straight back out again
  NB: Must line up with fiExpr (AnnLam...); see #7088

  (a) is important: we /must/ float into a one-shot lambda group
  (which includes join points). This makes a big difference
  for things like
     f x# = let x = I# x#
            in let j = \() -> ...x...
               in if <condition> then normal-path else j ()
  If x is used only in the error case join point, j, we must float the
  boxing constructor into it, else we box it every time which is very
  bad news indeed.

* Wrinkle 2: for RHSs, do not float into a HNF; we'll just float right
  back out again... not tragic, but a waste of time.

  For function arguments we will still end up with this
  in-then-out stuff; consider
    letrec x = e in f x
  Here x is not a HNF, so we'll produce
    f (letrec x = e in x)
  which is OK... it's not that common, and we'll end up
  floating out again, in CorePrep if not earlier.
  Still, we use exprIsTrivial to catch this case (sigh)


************************************************************************
*                                                                      *
\subsection{@sepBindsByDropPoint@}
*                                                                      *
************************************************************************

This is the crucial function.  The idea is: We have a wad of bindings
that we'd like to distribute inside a collection of {\em drop points};
insides the alternatives of a \tr{case} would be one example of some
drop points; the RHS and body of a non-recursive \tr{let} binding
would be another (2-element) collection.

So: We're given a list of sets-of-free-variables, one per drop point,
and a list of floating-inwards bindings.  If a binding can go into
only one drop point (without suddenly making something out-of-scope),
in it goes.  If a binding is used inside {\em multiple} drop points,
then it has to go in a you-must-drop-it-above-all-these-drop-points
point.

We have to maintain the order on these drop-point-related lists.
-}

-- pprFIB :: FloatInBinds -> SDoc
-- pprFIB fibs = text "FIB:" <+> ppr [b | FB _ _ b <- fibs]

sepBindsByDropPoint
    :: DynFlags
    -> Bool                -- True <=> is case expression
    -> [FreeVarSet]        -- One set of FVs per drop point
                           -- Always at least two long!
    -> FloatInBinds        -- Candidate floaters
    -> [FloatInBinds]      -- FIRST one is bindings which must not be floated
                           -- inside any drop point; the rest correspond
                           -- one-to-one with the input list of FV sets

-- Every input floater is returned somewhere in the result;
-- none are dropped, not even ones which don't seem to be
-- free in *any* of the drop-point fvs.  Why?  Because, for example,
-- a binding (let x = E in B) might have a specialised version of
-- x (say x') stored inside x, but x' isn't free in E or B.

type DropBox = (FreeVarSet, FloatInBinds)

sepBindsByDropPoint :: DynFlags -> Bool -> [FVAnn] -> FloatInBinds -> [FloatInBinds]
sepBindsByDropPoint DynFlags
dflags Bool
is_case [FVAnn]
drop_pts FloatInBinds
floaters
  | FloatInBinds -> Bool
forall (t :: * -> *) a. Foldable t => t a -> Bool
null FloatInBinds
floaters  -- Shortcut common case
  = [] FloatInBinds -> [FloatInBinds] -> [FloatInBinds]
forall a. a -> [a] -> [a]
: [[] | FVAnn
_ <- [FVAnn]
drop_pts]

  | Bool
otherwise
  = ASSERT( drop_pts `lengthAtLeast` 2 )
    FloatInBinds -> [DropBox] -> [FloatInBinds]
go FloatInBinds
floaters ((FVAnn -> DropBox) -> [FVAnn] -> [DropBox]
forall a b. (a -> b) -> [a] -> [b]
map (\FVAnn
fvs -> (FVAnn
fvs, [])) (FVAnn
emptyDVarSet FVAnn -> [FVAnn] -> [FVAnn]
forall a. a -> [a] -> [a]
: [FVAnn]
drop_pts))
  where
    n_alts :: Int
n_alts = [FVAnn] -> Int
forall (t :: * -> *) a. Foldable t => t a -> Int
length [FVAnn]
drop_pts

    go :: FloatInBinds -> [DropBox] -> [FloatInBinds]
        -- The *first* one in the argument list is the drop_here set
        -- The FloatInBinds in the lists are in the reverse of
        -- the normal FloatInBinds order; that is, they are the right way round!

    go :: FloatInBinds -> [DropBox] -> [FloatInBinds]
go [] [DropBox]
drop_boxes = (DropBox -> FloatInBinds) -> [DropBox] -> [FloatInBinds]
forall a b. (a -> b) -> [a] -> [b]
map (FloatInBinds -> FloatInBinds
forall a. [a] -> [a]
reverse (FloatInBinds -> FloatInBinds)
-> (DropBox -> FloatInBinds) -> DropBox -> FloatInBinds
forall b c a. (b -> c) -> (a -> b) -> a -> c
. DropBox -> FloatInBinds
forall a b. (a, b) -> b
snd) [DropBox]
drop_boxes

    go (bind_w_fvs :: FloatInBind
bind_w_fvs@(FB FVAnn
bndrs FVAnn
bind_fvs FloatBind
bind) : FloatInBinds
binds) drop_boxes :: [DropBox]
drop_boxes@(DropBox
here_box : [DropBox]
fork_boxes)
        = FloatInBinds -> [DropBox] -> [FloatInBinds]
go FloatInBinds
binds [DropBox]
new_boxes
        where
          -- "here" means the group of bindings dropped at the top of the fork

          (Bool
used_here : [Bool]
used_in_flags) = [ FVAnn
fvs FVAnn -> FVAnn -> Bool
`intersectsDVarSet` FVAnn
bndrs
                                        | (FVAnn
fvs, FloatInBinds
_) <- [DropBox]
drop_boxes]

          drop_here :: Bool
drop_here = Bool
used_here Bool -> Bool -> Bool
|| Bool
cant_push

          n_used_alts :: Int
n_used_alts = (Bool -> Bool) -> [Bool] -> Int
forall a. (a -> Bool) -> [a] -> Int
count Bool -> Bool
forall a. a -> a
id [Bool]
used_in_flags -- returns number of Trues in list.

          cant_push :: Bool
cant_push
            | Bool
is_case   = Int
n_used_alts Int -> Int -> Bool
forall a. Eq a => a -> a -> Bool
== Int
n_alts   -- Used in all, don't push
                                                  -- Remember n_alts > 1
                          Bool -> Bool -> Bool
|| (Int
n_used_alts Int -> Int -> Bool
forall a. Ord a => a -> a -> Bool
> Int
1 Bool -> Bool -> Bool
&& Bool -> Bool
not (DynFlags -> FloatBind -> Bool
floatIsDupable DynFlags
dflags FloatBind
bind))
                             -- floatIsDupable: see Note [Duplicating floats]

            | Bool
otherwise = FloatBind -> Bool
floatIsCase FloatBind
bind Bool -> Bool -> Bool
|| Int
n_used_alts Int -> Int -> Bool
forall a. Ord a => a -> a -> Bool
> Int
1
                             -- floatIsCase: see Note [Floating primops]

          new_boxes :: [DropBox]
new_boxes | Bool
drop_here = (DropBox -> DropBox
insert DropBox
here_box DropBox -> [DropBox] -> [DropBox]
forall a. a -> [a] -> [a]
: [DropBox]
fork_boxes)
                    | Bool
otherwise = (DropBox
here_box DropBox -> [DropBox] -> [DropBox]
forall a. a -> [a] -> [a]
: [DropBox]
new_fork_boxes)

          new_fork_boxes :: [DropBox]
new_fork_boxes = String
-> (DropBox -> Bool -> DropBox) -> [DropBox] -> [Bool] -> [DropBox]
forall a b c. String -> (a -> b -> c) -> [a] -> [b] -> [c]
zipWithEqual String
"FloatIn.sepBinds" DropBox -> Bool -> DropBox
insert_maybe
                                        [DropBox]
fork_boxes [Bool]
used_in_flags

          insert :: DropBox -> DropBox
          insert :: DropBox -> DropBox
insert (FVAnn
fvs,FloatInBinds
drops) = (FVAnn
fvs FVAnn -> FVAnn -> FVAnn
`unionDVarSet` FVAnn
bind_fvs, FloatInBind
bind_w_fvsFloatInBind -> FloatInBinds -> FloatInBinds
forall a. a -> [a] -> [a]
:FloatInBinds
drops)

          insert_maybe :: DropBox -> Bool -> DropBox
insert_maybe DropBox
box Bool
True  = DropBox -> DropBox
insert DropBox
box
          insert_maybe DropBox
box Bool
False = DropBox
box

    go FloatInBinds
_ [DropBox]
_ = String -> [FloatInBinds]
forall a. String -> a
panic String
"sepBindsByDropPoint/go"


{- Note [Duplicating floats]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

For case expressions we duplicate the binding if it is reasonably
small, and if it is not used in all the RHSs This is good for
situations like
     let x = I# y in
     case e of
       C -> error x
       D -> error x
       E -> ...not mentioning x...

If the thing is used in all RHSs there is nothing gained,
so we don't duplicate then.
-}

floatedBindsFVs :: FloatInBinds -> FreeVarSet
floatedBindsFVs :: FloatInBinds -> FVAnn
floatedBindsFVs FloatInBinds
binds = (FloatInBind -> FVAnn) -> FloatInBinds -> FVAnn
forall a. (a -> FVAnn) -> [a] -> FVAnn
mapUnionDVarSet FloatInBind -> FVAnn
fbFVs FloatInBinds
binds

fbFVs :: FloatInBind -> DVarSet
fbFVs :: FloatInBind -> FVAnn
fbFVs (FB FVAnn
_ FVAnn
fvs FloatBind
_) = FVAnn
fvs

wrapFloats :: FloatInBinds -> CoreExpr -> CoreExpr
-- Remember FloatInBinds is in *reverse* dependency order
wrapFloats :: FloatInBinds -> Expr CoreBndr -> Expr CoreBndr
wrapFloats []               Expr CoreBndr
e = Expr CoreBndr
e
wrapFloats (FB FVAnn
_ FVAnn
_ FloatBind
fl : FloatInBinds
bs) Expr CoreBndr
e = FloatInBinds -> Expr CoreBndr -> Expr CoreBndr
wrapFloats FloatInBinds
bs (FloatBind -> Expr CoreBndr -> Expr CoreBndr
wrapFloat FloatBind
fl Expr CoreBndr
e)

floatIsDupable :: DynFlags -> FloatBind -> Bool
floatIsDupable :: DynFlags -> FloatBind -> Bool
floatIsDupable DynFlags
dflags (FloatCase Expr CoreBndr
scrut CoreBndr
_ AltCon
_ [CoreBndr]
_) = DynFlags -> Expr CoreBndr -> Bool
exprIsDupable DynFlags
dflags Expr CoreBndr
scrut
floatIsDupable DynFlags
dflags (FloatLet (Rec [(CoreBndr, Expr CoreBndr)]
prs))    = ((CoreBndr, Expr CoreBndr) -> Bool)
-> [(CoreBndr, Expr CoreBndr)] -> Bool
forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
all (DynFlags -> Expr CoreBndr -> Bool
exprIsDupable DynFlags
dflags (Expr CoreBndr -> Bool)
-> ((CoreBndr, Expr CoreBndr) -> Expr CoreBndr)
-> (CoreBndr, Expr CoreBndr)
-> Bool
forall b c a. (b -> c) -> (a -> b) -> a -> c
. (CoreBndr, Expr CoreBndr) -> Expr CoreBndr
forall a b. (a, b) -> b
snd) [(CoreBndr, Expr CoreBndr)]
prs
floatIsDupable DynFlags
dflags (FloatLet (NonRec CoreBndr
_ Expr CoreBndr
r)) = DynFlags -> Expr CoreBndr -> Bool
exprIsDupable DynFlags
dflags Expr CoreBndr
r

floatIsCase :: FloatBind -> Bool
floatIsCase :: FloatBind -> Bool
floatIsCase (FloatCase {}) = Bool
True
floatIsCase (FloatLet {})  = Bool
False