Rewrite CorePrep and improve eta expansion

[ghc-hetmet.git] / compiler / coreSyn / CorePrep.lhs

diff --git a/compiler/coreSyn/CorePrep.lhs b/compiler/coreSyn/CorePrep.lhs
index db8bebc..b8dd80f 100644 (file)
--- a/compiler/coreSyn/CorePrep.lhs
+++ b/compiler/coreSyn/CorePrep.lhs
@@ -11,7 +11,8 @@ module CorePrep (
 
 #include "HsVersions.h"
 
 
 #include "HsVersions.h"
 

-import CoreUtils hiding (exprIsTrivial)
+import CoreUtils
+import CoreArity

 import CoreFVs
 import CoreLint
 import CoreSyn
 import CoreFVs
 import CoreLint
 import CoreSyn

@@ -36,6 +37,7 @@ import Util
 import Outputable
 import MonadUtils
 import FastString
 import Outputable
 import MonadUtils
 import FastString

+import Control.Monad

 \end{code}
 
 -- ---------------------------------------------------------------------------
 \end{code}
 
 -- ---------------------------------------------------------------------------

@@ -92,10 +94,41 @@ when type erasure is done for conversion to STG, we don't end up with
 any trivial or useless bindings.
 
   
 any trivial or useless bindings.
 
   

+Invariants
+~~~~~~~~~~
+Here is the syntax of the Core produced by CorePrep:

 
 

--- -----------------------------------------------------------------------------
--- Top level stuff
--- -----------------------------------------------------------------------------
+    Trivial expressions 
+       triv ::= lit |  var  | triv ty  |  /\a. triv  |  triv |> co
+
+    Applications
+       app ::= lit  |  var  |  app triv  |  app ty  |  app |> co
+
+    Expressions
+       body ::= app  
+              | let(rec) x = rhs in body     -- Boxed only
+              | case body of pat -> body
+             | /\a. body
+              | body |> co
+
+    Right hand sides (only place where lambdas can occur)
+       rhs ::= /\a.rhs  |  \x.rhs  |  body
+
+We define a synonym for each of these non-terminals.  Functions
+with the corresponding name produce a result in that syntax.
+
+\begin{code}
+type CpeTriv = CoreExpr           -- Non-terminal 'triv'
+type CpeApp  = CoreExpr           -- Non-terminal 'app'
+type CpeBody = CoreExpr           -- Non-terminal 'body'
+type CpeRhs  = CoreExpr           -- Non-terminal 'rhs'
+\end{code}
+
+%************************************************************************
+%*                                                                     *
+               Top level stuff
+%*                                                                     *
+%************************************************************************

 
 \begin{code}
 corePrepPgm :: DynFlags -> [CoreBind] -> [TyCon] -> IO [CoreBind]
 
 \begin{code}
 corePrepPgm :: DynFlags -> [CoreBind] -> [TyCon] -> IO [CoreBind]

@@ -119,15 +152,68 @@ corePrepExpr :: DynFlags -> CoreExpr -> IO CoreExpr
 corePrepExpr dflags expr = do
     showPass dflags "CorePrep"
     us <- mkSplitUniqSupply 's'
 corePrepExpr dflags expr = do
     showPass dflags "CorePrep"
     us <- mkSplitUniqSupply 's'

-    let new_expr = initUs_ us (corePrepAnExpr emptyCorePrepEnv expr)
+    let new_expr = initUs_ us (cpeBodyNF emptyCorePrepEnv expr)

     dumpIfSet_dyn dflags Opt_D_dump_prep "CorePrep" (ppr new_expr)
     return new_expr
     dumpIfSet_dyn dflags Opt_D_dump_prep "CorePrep" (ppr new_expr)
     return new_expr

-\end{code}

 
 

--- -----------------------------------------------------------------------------
--- Implicit bindings
--- -----------------------------------------------------------------------------
+corePrepTopBinds :: [CoreBind] -> UniqSM Floats
+-- Note [Floating out of top level bindings]
+corePrepTopBinds binds 
+  = go emptyCorePrepEnv binds
+  where
+    go _   []             = return emptyFloats
+    go env (bind : binds) = do (env', bind') <- cpeBind TopLevel env bind
+                               binds' <- go env' binds
+                               return (bind' `appendFloats` binds')

 
 

+mkDataConWorkers :: [TyCon] -> [CoreBind]
+-- See Note [Data constructor workers]
+mkDataConWorkers data_tycons
+  = [ NonRec id (Var id)       -- The ice is thin here, but it works
+    | tycon <- data_tycons,    -- CorePrep will eta-expand it
+      data_con <- tyConDataCons tycon,
+      let id = dataConWorkId data_con ]
+\end{code}
+
+Note [Floating out of top level bindings]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+NB: we do need to float out of top-level bindings
+Consider       x = length [True,False]
+We want to get
+               s1 = False : []
+               s2 = True  : s1
+               x  = length s2
+
+We return a *list* of bindings, because we may start with
+       x* = f (g y)
+where x is demanded, in which case we want to finish with
+       a = g y
+       x* = f a
+And then x will actually end up case-bound
+
+Note [CafInfo and floating]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+What happens to the CafInfo on the floated bindings?  By default, all
+the CafInfos will be set to MayHaveCafRefs, which is safe.
+
+This might be pessimistic, because the floated binding might not refer
+to any CAFs and the GC will end up doing more traversal than is
+necessary, but it's still better than not floating the bindings at
+all, because then the GC would have to traverse the structure in the
+heap instead.  Given this, we decided not to try to get the CafInfo on
+the floated bindings correct, because it looks difficult.
+
+But that means we can't float anything out of a NoCafRefs binding.
+Consider       f = g (h x)
+If f is NoCafRefs, we don't want to convert to
+              sat = h x
+               f = g sat
+where sat conservatively says HasCafRefs, because now f's info
+is wrong.  I don't think this is common, so we simply switch off
+floating in this case.
+
+Note [Data constructor workers]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 Create any necessary "implicit" bindings for data con workers.  We
 create the rather strange (non-recursive!) binding
 
 Create any necessary "implicit" bindings for data con workers.  We
 create the rather strange (non-recursive!) binding
 

@@ -143,235 +229,84 @@ Hmm.  Should we create bindings for dictionary constructors?  They are
 always fully applied, and the bindings are just there to support
 partial applications. But it's easier to let them through.
 
 always fully applied, and the bindings are just there to support
 partial applications. But it's easier to let them through.
 

-\begin{code}
-mkDataConWorkers :: [TyCon] -> [CoreBind]
-mkDataConWorkers data_tycons
-  = [ NonRec id (Var id)       -- The ice is thin here, but it works
-    | tycon <- data_tycons,    -- CorePrep will eta-expand it
-      data_con <- tyConDataCons tycon,
-      let id = dataConWorkId data_con ]
-\end{code}
-       
-
-\begin{code}
--- ---------------------------------------------------------------------------
--- Dealing with bindings
--- ---------------------------------------------------------------------------
-
-data FloatingBind = FloatLet CoreBind
-                 | FloatCase Id CoreExpr Bool
-                       -- Invariant: the expression is not a lambda
-                       -- The bool indicates "ok-for-speculation"
-
-data Floats = Floats OkToSpec (OrdList FloatingBind)
-
--- Can we float these binds out of the rhs of a let?  We cache this decision
--- to avoid having to recompute it in a non-linear way when there are
--- deeply nested lets.
-data OkToSpec
-   = NotOkToSpec       -- definitely not
-   | OkToSpec          -- yes
-   | IfUnboxedOk       -- only if floating an unboxed binding is ok
-
-emptyFloats :: Floats
-emptyFloats = Floats OkToSpec nilOL
-
-addFloat :: Floats -> FloatingBind -> Floats
-addFloat (Floats ok_to_spec floats) new_float
-  = Floats (combine ok_to_spec (check new_float)) (floats `snocOL` new_float)
-  where
-    check (FloatLet _) = OkToSpec
-    check (FloatCase _ _ ok_for_spec) 
-       | ok_for_spec  =  IfUnboxedOk
-       | otherwise    =  NotOkToSpec
-       -- The ok-for-speculation flag says that it's safe to
-       -- float this Case out of a let, and thereby do it more eagerly
-       -- We need the top-level flag because it's never ok to float
-       -- an unboxed binding to the top level
-
-unitFloat :: FloatingBind -> Floats
-unitFloat = addFloat emptyFloats
-
-appendFloats :: Floats -> Floats -> Floats
-appendFloats (Floats spec1 floats1) (Floats spec2 floats2)
-  = Floats (combine spec1 spec2) (floats1 `appOL` floats2)
-
-concatFloats :: [Floats] -> Floats
-concatFloats = foldr appendFloats emptyFloats
-
-combine :: OkToSpec -> OkToSpec -> OkToSpec
-combine NotOkToSpec _ = NotOkToSpec
-combine _ NotOkToSpec = NotOkToSpec
-combine IfUnboxedOk _ = IfUnboxedOk
-combine _ IfUnboxedOk = IfUnboxedOk
-combine _ _           = OkToSpec
-    
-instance Outputable FloatingBind where
-  ppr (FloatLet bind)        = text "FloatLet" <+> ppr bind
-  ppr (FloatCase b rhs spec) = text "FloatCase" <+> ppr b <+> ppr spec <+> equals <+> ppr rhs
-
-deFloatTop :: Floats -> [CoreBind]
--- For top level only; we don't expect any FloatCases
-deFloatTop (Floats _ floats)
-  = foldrOL get [] floats
-  where
-    get (FloatLet b) bs = b:bs
-    get b            _  = pprPanic "corePrepPgm" (ppr b)
-
-allLazy :: TopLevelFlag -> RecFlag -> Floats -> Bool
-allLazy top_lvl is_rec (Floats ok_to_spec _)
-  = case ok_to_spec of
-       OkToSpec    -> True
-       NotOkToSpec -> False
-       IfUnboxedOk -> isNotTopLevel top_lvl && isNonRec is_rec

 
 

--- ---------------------------------------------------------------------------
---                     Bindings
--- ---------------------------------------------------------------------------
+%************************************************************************
+%*                                                                     *
+               The main code
+%*                                                                     *
+%************************************************************************

 
 

-corePrepTopBinds :: [CoreBind] -> UniqSM Floats
-corePrepTopBinds binds 
-  = go emptyCorePrepEnv binds
-  where
-    go _   []             = return emptyFloats
-    go env (bind : binds) = do (env', bind') <- corePrepTopBind env bind
-                               binds' <- go env' binds
-                               return (bind' `appendFloats` binds')
+\begin{code}
+cpeBind :: TopLevelFlag
+       -> CorePrepEnv -> CoreBind
+       -> UniqSM (CorePrepEnv, Floats)
+cpeBind top_lvl env (NonRec bndr rhs)
+  = do { (_, bndr1) <- cloneBndr env bndr
+       ; let is_strict   = isStrictDmd (idNewDemandInfo bndr)
+             is_unlifted = isUnLiftedType (idType bndr)
+       ; (floats, bndr2, rhs2) <- cpePair top_lvl NonRecursive 
+                                                 (is_strict || is_unlifted) 
+                                         env bndr1 rhs
+       ; let new_float = mkFloat is_strict is_unlifted bndr2 rhs2

 
 

--- NB: we do need to float out of top-level bindings
--- Consider    x = length [True,False]
--- We want to get
---             s1 = False : []
---             s2 = True  : s1
---             x  = length s2
-
--- We return a *list* of bindings, because we may start with
---     x* = f (g y)
--- where x is demanded, in which case we want to finish with
---     a = g y
---     x* = f a
--- And then x will actually end up case-bound
---
--- What happens to the CafInfo on the floated bindings?  By
--- default, all the CafInfos will be set to MayHaveCafRefs,
--- which is safe.
---
--- This might be pessimistic, because eg. s1 & s2
--- might not refer to any CAFs and the GC will end up doing
--- more traversal than is necessary, but it's still better
--- than not floating the bindings at all, because then
--- the GC would have to traverse the structure in the heap
--- instead.  Given this, we decided not to try to get
--- the CafInfo on the floated bindings correct, because
--- it looks difficult.
-
---------------------------------
-corePrepTopBind :: CorePrepEnv -> CoreBind -> UniqSM (CorePrepEnv, Floats)
-corePrepTopBind env (NonRec bndr rhs) = do
-    (env', bndr') <- cloneBndr env bndr
-    (floats, rhs') <- corePrepRhs TopLevel NonRecursive env (bndr, rhs)
-    return (env', addFloat floats (FloatLet (NonRec bndr' rhs')))
-
-corePrepTopBind env (Rec pairs) = corePrepRecPairs TopLevel env pairs
-
---------------------------------
-corePrepBind ::  CorePrepEnv -> CoreBind -> UniqSM (CorePrepEnv, Floats)
-       -- This one is used for *local* bindings
-corePrepBind env (NonRec bndr rhs) = do
-    rhs1 <- etaExpandRhs bndr rhs
-    (floats, rhs2) <- corePrepExprFloat env rhs1
-    (_, bndr') <- cloneBndr env bndr
-    (floats', bndr'') <- mkLocalNonRec bndr' (bdrDem bndr) floats rhs2

         -- We want bndr'' in the envt, because it records
         -- the evaluated-ness of the binder
         -- We want bndr'' in the envt, because it records
         -- the evaluated-ness of the binder

-    return (extendCorePrepEnv env bndr bndr'', floats')
-
-corePrepBind env (Rec pairs) = corePrepRecPairs NotTopLevel env pairs
-
---------------------------------
-corePrepRecPairs :: TopLevelFlag -> CorePrepEnv
-                -> [(Id,CoreExpr)]     -- Recursive bindings
-                -> UniqSM (CorePrepEnv, Floats)
--- Used for all recursive bindings, top level and otherwise
-corePrepRecPairs lvl env pairs = do
-    (env', bndrs') <- cloneBndrs env (map fst pairs)
-    (floats_s, rhss') <- mapAndUnzipM (corePrepRhs lvl Recursive env') pairs
-    return (env', unitFloat (FloatLet (Rec (flatten (concatFloats floats_s) bndrs' rhss'))))
+       ; return (extendCorePrepEnv env bndr bndr2, 
+                        addFloat floats new_float) }
+
+cpeBind top_lvl env (Rec pairs)
+  = do { let (bndrs,rhss) = unzip pairs
+       ; (env', bndrs1) <- cloneBndrs env (map fst pairs)
+       ; stuff <- zipWithM (cpePair top_lvl Recursive False env') bndrs1 rhss
+
+       ; let (floats_s, bndrs2, rhss2) = unzip3 stuff
+             all_pairs = foldrOL add_float (bndrs1 `zip` rhss2)
+                                          (concatFloats floats_s)
+       ; return (extendCorePrepEnvList env (bndrs `zip` bndrs2),
+                        unitFloat (FloatLet (Rec all_pairs))) }

   where
        -- Flatten all the floats, and the currrent
        -- group into a single giant Rec
   where
        -- Flatten all the floats, and the currrent
        -- group into a single giant Rec

-    flatten (Floats _ floats) bndrs rhss = foldrOL get (bndrs `zip` rhss) floats
-
-    get (FloatLet (NonRec b r)) prs2 = (b,r) : prs2
-    get (FloatLet (Rec prs1))   prs2 = prs1 ++ prs2
-    get b                       _    = pprPanic "corePrepRecPairs" (ppr b)
-
---------------------------------
-corePrepRhs :: TopLevelFlag -> RecFlag
-           -> CorePrepEnv -> (Id, CoreExpr)
-           -> UniqSM (Floats, CoreExpr)
--- Used for top-level bindings, and local recursive bindings
-corePrepRhs top_lvl is_rec env (bndr, rhs) = do
-    rhs' <- etaExpandRhs bndr rhs
-    floats_w_rhs <- corePrepExprFloat env rhs'
-    floatRhs top_lvl is_rec bndr floats_w_rhs
-
-
--- ---------------------------------------------------------------------------
--- Making arguments atomic (function args & constructor args)
--- ---------------------------------------------------------------------------
-
--- This is where we arrange that a non-trivial argument is let-bound
-corePrepArg :: CorePrepEnv -> CoreArg -> RhsDemand
-          -> UniqSM (Floats, CoreArg)
-corePrepArg env arg dem = do
-    (floats, arg') <- corePrepExprFloat env arg
-    if exprIsTrivial arg' && allLazy NotTopLevel NonRecursive floats
-       -- Note [Floating unlifted arguments]
-     then return (floats, arg')
-     else do v <- newVar (exprType arg')
-             (floats', v') <- mkLocalNonRec v dem floats arg'
-             return (floats', Var v')
-
--- version that doesn't consider an scc annotation to be trivial.
-exprIsTrivial :: CoreExpr -> Bool
-exprIsTrivial (Var _)                  = True
-exprIsTrivial (Type _)                 = True
-exprIsTrivial (Lit _)                  = True
-exprIsTrivial (App e arg)              = isTypeArg arg && exprIsTrivial e
-exprIsTrivial (Note (SCC _) _)         = False
-exprIsTrivial (Note _ e)               = exprIsTrivial e
-exprIsTrivial (Cast e _)               = exprIsTrivial e
-exprIsTrivial (Lam b body) | isTyVar b = exprIsTrivial body
-exprIsTrivial _                        = False
-\end{code}
-
-Note [Floating unlifted arguments]
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-Consider    C (let v* = expensive in v)
-
-where the "*" indicates "will be demanded".  Usually v will have been
-inlined by now, but let's suppose it hasn't (see Trac #2756).  Then we
-do *not* want to get
-
-     let v* = expensive in C v
+    add_float (FloatLet (NonRec b r)) prs2 = (b,r) : prs2
+    add_float (FloatLet (Rec prs1))   prs2 = prs1 ++ prs2
+    add_float b                       _    = pprPanic "cpeBind" (ppr b)
+
+---------------
+cpePair :: TopLevelFlag -> RecFlag -> RhsDemand
+       -> CorePrepEnv -> Id -> CoreExpr
+       -> UniqSM (Floats, Id, CoreExpr)
+-- Used for all bindings
+cpePair top_lvl is_rec is_strict_or_unlifted env bndr rhs
+  = do { (floats, rhs') <- cpeRhs want_float (idArity bndr) env rhs
+
+               -- Record if the binder is evaluated
+       ; let bndr' | exprIsHNF rhs' = bndr `setIdUnfolding` evaldUnfolding
+                          | otherwise      = bndr
+
+       ; return (floats, bndr', rhs') }
+  where
+    want_float floats rhs 
+     | isTopLevel top_lvl = wantFloatTop bndr floats
+     | otherwise          = wantFloatNested is_rec is_strict_or_unlifted floats rhs

 
 

-because that has different strictness.  Hence the use of 'allLazy'.
-(NB: the let v* turns into a FloatCase, in mkLocalNonRec.)

 
 
 
 

-\begin{code}

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

--- Dealing with expressions
+--             CpeRhs: produces a result satisfying CpeRhs

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

-corePrepAnExpr :: CorePrepEnv -> CoreExpr -> UniqSM CoreExpr
-corePrepAnExpr env expr = do
-    (floats, expr) <- corePrepExprFloat env expr
-    mkBinds floats expr
-
-
-corePrepExprFloat :: CorePrepEnv -> CoreExpr -> UniqSM (Floats, CoreExpr)
+cpeRhs :: (Floats -> CpeRhs -> Bool)   -- Float the floats out
+       -> Arity                -- Guarantees an Rhs with this manifest arity
+       -> CorePrepEnv
+       -> CoreExpr     -- Expression and its type
+       -> UniqSM (Floats, CpeRhs)
+cpeRhs want_float arity env expr
+  = do { (floats, rhs) <- cpeRhsE env expr
+       ; if want_float floats rhs
+                then return (floats,      cpeEtaExpand arity rhs)
+                else return (emptyFloats, cpeEtaExpand arity (wrapBinds floats rhs)) }
+
+cpeRhsE :: CorePrepEnv -> CoreExpr -> UniqSM (Floats, CpeRhs)

 -- If
 --     e  ===>  (bs, e')
 -- then        
 -- If
 --     e  ===>  (bs, e')
 -- then        

@@ -380,76 +315,115 @@ corePrepExprFloat :: CorePrepEnv -> CoreExpr -> UniqSM (Floats, CoreExpr)
 -- For example
 --     f (g x)   ===>   ([v = g x], f v)
 
 -- For example
 --     f (g x)   ===>   ([v = g x], f v)
 

-corePrepExprFloat env (Var v) = do
-    v1 <- fiddleCCall v
-    let
-        v2 = lookupCorePrepEnv env v1
-    maybeSaturate v2 (Var v2) 0 emptyFloats (idType v2)
+cpeRhsE _env expr@(Type _) = return (emptyFloats, expr)
+cpeRhsE _env expr@(Lit _)  = return (emptyFloats, expr)
+cpeRhsE env expr@(App {})  = cpeApp env expr
+cpeRhsE env expr@(Var {})  = cpeApp env expr
+
+cpeRhsE env (Let bind expr)
+  = do { (env', new_binds) <- cpeBind NotTopLevel env bind
+       ; (floats, body) <- cpeRhsE env' expr
+       ; return (new_binds `appendFloats` floats, body) }
+
+cpeRhsE env (Note note expr)
+  | ignoreNote note
+  = cpeRhsE env expr
+  | otherwise        -- Just SCCs actually
+  = do { body <- cpeBodyNF env expr
+       ; return (emptyFloats, Note note body) }
+
+cpeRhsE env (Cast expr co)
+   = do { (floats, expr') <- cpeRhsE env expr
+        ; return (floats, Cast expr' co) }
+
+cpeRhsE env expr@(Lam {})
+   = do { let (bndrs,body) = collectBinders expr
+        ; (env', bndrs') <- cloneBndrs env bndrs
+       ; body' <- cpeBodyNF env' body
+       ; return (emptyFloats, mkLams bndrs' body') }
+
+cpeRhsE env (Case (Var id) bndr ty [(DEFAULT,[],expr)])
+  | Just (TickBox {}) <- isTickBoxOp_maybe id
+  = do { body <- cpeBodyNF env expr
+       ; return (emptyFloats, Case (Var id) bndr ty [(DEFAULT,[],body)]) }
+
+cpeRhsE env (Case scrut bndr ty alts)
+  = do { (floats, scrut') <- cpeBody env scrut
+       ; let bndr1 = bndr `setIdUnfolding` evaldUnfolding
+            -- Record that the case binder is evaluated in the alternatives
+       ; (env', bndr2) <- cloneBndr env bndr1
+       ; alts' <- mapM (sat_alt env') alts
+       ; return (floats, Case scrut' bndr2 ty alts') }
+  where
+    sat_alt env (con, bs, rhs)
+       = do { (env2, bs') <- cloneBndrs env bs
+            ; rhs' <- cpeBodyNF env2 rhs
+            ; return (con, bs', rhs') }

 
 

-corePrepExprFloat _env expr@(Type _)
-  = return (emptyFloats, expr)
+-- ---------------------------------------------------------------------------
+--             CpeBody: produces a result satisfying CpeBody
+-- ---------------------------------------------------------------------------

 
 

-corePrepExprFloat _env expr@(Lit _)
-  = return (emptyFloats, expr)
+cpeBodyNF :: CorePrepEnv -> CoreExpr -> UniqSM CpeBody
+cpeBodyNF env expr 
+  = do { (floats, body) <- cpeBody env expr
+       ; return (wrapBinds floats body) }

 
 

-corePrepExprFloat env (Let bind body) = do
-    (env', new_binds) <- corePrepBind env bind
-    (floats, new_body) <- corePrepExprFloat env' body
-    return (new_binds `appendFloats` floats, new_body)
+--------
+cpeBody :: CorePrepEnv -> CoreExpr -> UniqSM (Floats, CpeBody)
+cpeBody env expr
+  = do { (floats1, rhs) <- cpeRhsE env expr
+       ; (floats2, body) <- rhsToBody rhs
+       ; return (floats1 `appendFloats` floats2, body) }

 
 

-corePrepExprFloat env (Note n@(SCC _) expr) = do
-    expr1 <- corePrepAnExpr env expr
-    (floats, expr2) <- deLamFloat expr1
-    return (floats, Note n expr2)
+--------
+rhsToBody :: CpeRhs -> UniqSM (Floats, CpeBody)
+-- Remove top level lambdas by let-bindinig

 
 

-corePrepExprFloat env (Note other_note expr) = do
-    (floats, expr') <- corePrepExprFloat env expr
-    return (floats, Note other_note expr')
+rhsToBody (Note n expr)
+        -- You can get things like
+        --      case e of { p -> coerce t (\s -> ...) }
+  = do { (floats, expr') <- rhsToBody expr
+       ; return (floats, Note n expr') }

 
 

-corePrepExprFloat env (Cast expr co) = do
-    (floats, expr') <- corePrepExprFloat env expr
-    return (floats, Cast expr' co)
+rhsToBody (Cast e co)
+  = do { (floats, e') <- rhsToBody e
+       ; return (floats, Cast e' co) }

 
 

-corePrepExprFloat env expr@(Lam _ _) = do
-    (env', bndrs') <- cloneBndrs env bndrs
-    body' <- corePrepAnExpr env' body
-    return (emptyFloats, mkLams bndrs' body')
+rhsToBody expr@(Lam {})
+  | Just no_lam_result <- tryEtaReduce bndrs body
+  = return (emptyFloats, no_lam_result)
+  | all isTyVar bndrs          -- Type lambdas are ok
+  = return (emptyFloats, expr)
+  | otherwise                  -- Some value lambdas
+  = do { fn <- newVar (exprType expr)
+       ; let rhs   = cpeEtaExpand (exprArity expr) expr
+                    float = FloatLet (NonRec fn rhs)
+       ; return (unitFloat float, Var fn) }

   where
     (bndrs,body) = collectBinders expr
 
   where
     (bndrs,body) = collectBinders expr
 

-corePrepExprFloat env (Case (Var id) bndr ty [(DEFAULT,[],expr)])
-  | Just (TickBox {}) <- isTickBoxOp_maybe id = do
-    expr1 <- corePrepAnExpr env expr
-    (floats, expr2) <- deLamFloat expr1
-    return (floats, Case (Var id) bndr ty [(DEFAULT,[],expr2)])
-
-corePrepExprFloat env (Case scrut bndr ty alts) = do
-    (floats1, scrut1) <- corePrepExprFloat env scrut
-    (floats2, scrut2) <- deLamFloat scrut1
-    let
-        bndr1 = bndr `setIdUnfolding` evaldUnfolding
-        -- Record that the case binder is evaluated in the alternatives
-    (env', bndr2) <- cloneBndr env bndr1
-    alts' <- mapM (sat_alt env') alts
-    return (floats1 `appendFloats` floats2 , Case scrut2 bndr2 ty alts')
-  where
-    sat_alt env (con, bs, rhs) = do
-            (env2, bs') <- cloneBndrs env bs
-            rhs1 <- corePrepAnExpr env2 rhs
-            rhs2 <- deLam rhs1
-            return (con, bs', rhs2)
+rhsToBody expr = return (emptyFloats, expr)
+

 
 

-corePrepExprFloat env expr@(App _ _) = do
-    (app, (head,depth), ty, floats, ss) <- collect_args expr 0
-    MASSERT(null ss)   -- make sure we used all the strictness info
+
+-- ---------------------------------------------------------------------------
+--             CpeApp: produces a result satisfying CpeApp
+-- ---------------------------------------------------------------------------
+
+cpeApp :: CorePrepEnv -> CoreExpr -> UniqSM (Floats, CpeRhs)
+-- May return a CpeRhs because of saturating primops
+cpeApp env expr 
+  = do { (app, (head,depth), _, floats, ss) <- collect_args expr 0
+       ; MASSERT(null ss)      -- make sure we used all the strictness info

 
        -- Now deal with the function
 
        -- Now deal with the function

-    case head of
-      Var fn_id -> maybeSaturate fn_id app depth floats ty
-      _other    -> return (floats, app)
+       ; case head of
+           Var fn_id -> do { sat_app <- maybeSaturate fn_id app depth
+                          ; return (floats, sat_app) }
+           _other    -> return (floats, app) }

 
   where
 
   where

-

     -- Deconstruct and rebuild the application, floating any non-atomic
     -- arguments to the outside.  We collect the type of the expression,
     -- the head of the application, and the number of actual value arguments,
     -- Deconstruct and rebuild the application, floating any non-atomic
     -- arguments to the outside.  We collect the type of the expression,
     -- the head of the application, and the number of actual value arguments,

@@ -458,34 +432,34 @@ corePrepExprFloat env expr@(App _ _) = do
 
     collect_args
        :: CoreExpr
 
     collect_args
        :: CoreExpr

-       -> Int                            -- current app depth
-       -> UniqSM (CoreExpr,              -- the rebuilt expression
-                  (CoreExpr,Int),        -- the head of the application,
-                                         -- and no. of args it was applied to
-                  Type,                  -- type of the whole expr
-                  Floats,                -- any floats we pulled out
-                  [Demand])              -- remaining argument demands
-
-    collect_args (App fun arg@(Type arg_ty)) depth = do
-          (fun',hd,fun_ty,floats,ss) <- collect_args fun depth
-          return (App fun' arg, hd, applyTy fun_ty arg_ty, floats, ss)
-
-    collect_args (App fun arg) depth = do
-          (fun',hd,fun_ty,floats,ss) <- collect_args fun (depth+1)
-          let
+       -> Int                     -- Current app depth
+       -> UniqSM (CpeApp,         -- The rebuilt expression
+                  (CoreExpr,Int), -- The head of the application,
+                                  -- and no. of args it was applied to
+                  Type,           -- Type of the whole expr
+                  Floats,         -- Any floats we pulled out
+                  [Demand])       -- Remaining argument demands
+
+    collect_args (App fun arg@(Type arg_ty)) depth
+      = do { (fun',hd,fun_ty,floats,ss) <- collect_args fun depth
+           ; return (App fun' arg, hd, applyTy fun_ty arg_ty, floats, ss) }
+
+    collect_args (App fun arg) depth
+      = do { (fun',hd,fun_ty,floats,ss) <- collect_args fun (depth+1)
+           ; let

               (ss1, ss_rest)   = case ss of
                                    (ss1:ss_rest) -> (ss1,     ss_rest)
                                    []            -> (lazyDmd, [])
               (ss1, ss_rest)   = case ss of
                                    (ss1:ss_rest) -> (ss1,     ss_rest)
                                    []            -> (lazyDmd, [])

-              (arg_ty, res_ty) = expectJust "corePrepExprFloat:collect_args" $
+              (arg_ty, res_ty) = expectJust "cpeBody:collect_args" $

                                  splitFunTy_maybe fun_ty
 
                                  splitFunTy_maybe fun_ty
 

-          (fs, arg') <- corePrepArg env arg (mkDemTy ss1 arg_ty)
-          return (App fun' arg', hd, res_ty, fs `appendFloats` floats, ss_rest)
+           ; (fs, arg') <- cpeArg env (isStrictDmd ss1) arg arg_ty
+           ; return (App fun' arg', hd, res_ty, fs `appendFloats` floats, ss_rest) }

 
 

-    collect_args (Var v) depth = do
-          v1 <- fiddleCCall v
-          let v2 = lookupCorePrepEnv env v1
-          return (Var v2, (Var v2, depth), idType v2, emptyFloats, stricts)
+    collect_args (Var v) depth 
+      = do { v1 <- fiddleCCall v
+           ; let v2 = lookupCorePrepEnv env v1
+           ; return (Var v2, (Var v2, depth), idType v2, emptyFloats, stricts) }

        where
          stricts = case idNewStrictness v of
                        StrictSig (DmdType _ demands _)
        where
          stricts = case idNewStrictness v of
                        StrictSig (DmdType _ demands _)

@@ -498,254 +472,209 @@ corePrepExprFloat env expr@(App _ _) = do
                -- Here, we can't evaluate the arg strictly, because this 
                -- partial application might be seq'd
 
                -- Here, we can't evaluate the arg strictly, because this 
                -- partial application might be seq'd
 

-    collect_args (Cast fun co) depth = do
-          let (_ty1,ty2) = coercionKind co
-          (fun', hd, _, floats, ss) <- collect_args fun depth
-          return (Cast fun' co, hd, ty2, floats, ss)
+    collect_args (Cast fun co) depth
+      = do { let (_ty1,ty2) = coercionKind co
+           ; (fun', hd, _, floats, ss) <- collect_args fun depth
+           ; return (Cast fun' co, hd, ty2, floats, ss) }

           
     collect_args (Note note fun) depth
           
     collect_args (Note note fun) depth

-        | ignore_note note = do -- Drop these notes altogether
-                                -- They aren't used by the code generator
-          (fun', hd, fun_ty, floats, ss) <- collect_args fun depth
-         return (fun', hd, fun_ty, floats, ss)
+      | ignoreNote note         -- Drop these notes altogether
+      = collect_args fun depth  -- They aren't used by the code generator

 
        -- N-variable fun, better let-bind it
        -- ToDo: perhaps we can case-bind rather than let-bind this closure,
        -- since it is sure to be evaluated.
 
        -- N-variable fun, better let-bind it
        -- ToDo: perhaps we can case-bind rather than let-bind this closure,
        -- since it is sure to be evaluated.

-    collect_args fun depth = do
-          (fun_floats, fun') <- corePrepExprFloat env fun
-          fn_id <- newVar ty
-          (floats, fn_id') <- mkLocalNonRec fn_id onceDem fun_floats fun'
-          return (Var fn_id', (Var fn_id', depth), ty, floats, [])
+    collect_args fun depth
+      = do { (fun_floats, fun') <- cpeArg env True fun ty
+           ; return (fun', (fun', depth), ty, fun_floats, []) }

         where
          ty = exprType fun
 
         where
          ty = exprType fun
 

-    ignore_note        (CoreNote _) = True 
-    ignore_note        InlineMe     = True
-    ignore_note        _other       = False
-       -- We don't ignore SCCs, since they require some code generation
+-- ---------------------------------------------------------------------------
+--     CpeArg: produces a result satisfying CpeArg
+-- ---------------------------------------------------------------------------
+
+-- This is where we arrange that a non-trivial argument is let-bound
+cpeArg :: CorePrepEnv -> RhsDemand -> CoreArg -> Type
+       -> UniqSM (Floats, CpeTriv)
+cpeArg env is_strict arg arg_ty
+  | cpe_ExprIsTrivial arg      -- Do not eta expand etc a trivial argument
+  = cpeBody env arg    -- Must still do substitution though
+  | otherwise
+  = do { (floats, arg') <- cpeRhs want_float
+                                         (exprArity arg) env arg
+       ; v <- newVar arg_ty
+       ; let arg_float = mkFloat is_strict is_unlifted v arg'
+       ; return (addFloat floats arg_float, Var v) }
+  where
+    is_unlifted = isUnLiftedType arg_ty
+    want_float = wantFloatNested NonRecursive (is_strict || is_unlifted)
+\end{code}
+
+Note [Floating unlifted arguments]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Consider    C (let v* = expensive in v)
+
+where the "*" indicates "will be demanded".  Usually v will have been
+inlined by now, but let's suppose it hasn't (see Trac #2756).  Then we
+do *not* want to get
+
+     let v* = expensive in C v
+
+because that has different strictness.  Hence the use of 'allLazy'.
+(NB: the let v* turns into a FloatCase, in mkLocalNonRec.)
+

 
 ------------------------------------------------------------------------------
 -- Building the saturated syntax
 -- ---------------------------------------------------------------------------
 
 
 ------------------------------------------------------------------------------
 -- Building the saturated syntax
 -- ---------------------------------------------------------------------------
 

--- maybeSaturate deals with saturating primops and constructors
--- The type is the type of the entire application
-maybeSaturate :: Id -> CoreExpr -> Int -> Floats -> Type -> UniqSM (Floats, CoreExpr)
-maybeSaturate fn expr n_args floats ty
+maybeSaturate deals with saturating primops and constructors
+The type is the type of the entire application
+
+\begin{code}
+maybeSaturate :: Id -> CpeApp -> Int -> UniqSM CpeRhs
+maybeSaturate fn expr n_args

   | Just DataToTagOp <- isPrimOpId_maybe fn     -- DataToTag must have an evaluated arg
                                                 -- A gruesome special case
   | Just DataToTagOp <- isPrimOpId_maybe fn     -- DataToTag must have an evaluated arg
                                                 -- A gruesome special case

-  = do sat_expr <- saturate_it
+  = saturateDataToTag sat_expr

 
 

-        -- OK, now ensure that the arg is evaluated.
-        -- But (sigh) take into account the lambdas we've now introduced
-       let (eta_bndrs, eta_body) = collectBinders sat_expr
-       (eta_floats, eta_body') <- eval_data2tag_arg eta_body
-       if null eta_bndrs then
-           return (floats `appendFloats` eta_floats, eta_body')
-        else do
-           eta_body'' <- mkBinds eta_floats eta_body'
-           return (floats, mkLams eta_bndrs eta_body'')
-
-  | hasNoBinding fn = do sat_expr <- saturate_it
-                         return (floats, sat_expr)
-
-  | otherwise       = return (floats, expr)
+  | hasNoBinding fn       -- There's no binding
+  = return sat_expr

 
 

+  | otherwise 
+  = return expr

   where
     fn_arity    = idArity fn
     excess_arity = fn_arity - n_args
   where
     fn_arity    = idArity fn
     excess_arity = fn_arity - n_args

-
-    saturate_it :: UniqSM CoreExpr
-    saturate_it | excess_arity == 0 = return expr
-                | otherwise         = do us <- getUniquesM
-                                         return (etaExpand excess_arity us expr ty)
-
-       -- Ensure that the argument of DataToTagOp is evaluated
-    eval_data2tag_arg :: CoreExpr -> UniqSM (Floats, CoreExpr)
+    sat_expr     = cpeEtaExpand excess_arity expr
+
+-------------
+saturateDataToTag :: CpeApp -> UniqSM CpeApp
+-- Horrid: ensure that the arg of data2TagOp is evaluated
+--   (data2tag x) -->  (case x of y -> data2tag y)
+-- (yuk yuk) take into account the lambdas we've now introduced
+saturateDataToTag sat_expr
+  = do { let (eta_bndrs, eta_body) = collectBinders sat_expr
+       ; eta_body' <- eval_data2tag_arg eta_body
+       ; return (mkLams eta_bndrs eta_body') }
+  where
+    eval_data2tag_arg :: CpeApp -> UniqSM CpeBody

     eval_data2tag_arg app@(fun `App` arg)
         | exprIsHNF arg         -- Includes nullary constructors
     eval_data2tag_arg app@(fun `App` arg)
         | exprIsHNF arg         -- Includes nullary constructors

-        = return (emptyFloats, app)   -- The arg is evaluated
+        = return app           -- The arg is evaluated

         | otherwise                     -- Arg not evaluated, so evaluate it
         | otherwise                     -- Arg not evaluated, so evaluate it

-        = do arg_id <- newVar (exprType arg)
-             let
-                arg_id1 = setIdUnfolding arg_id evaldUnfolding
-             return (unitFloat (FloatCase arg_id1 arg False ),
-                     fun `App` Var arg_id1)
+        = do { arg_id <- newVar (exprType arg)
+             ; let arg_id1 = setIdUnfolding arg_id evaldUnfolding
+             ; return (Case arg arg_id1 (exprType app)
+                            [(DEFAULT, [], fun `App` Var arg_id1)]) }

 
     eval_data2tag_arg (Note note app)  -- Scc notes can appear
 
     eval_data2tag_arg (Note note app)  -- Scc notes can appear

-        = do (floats, app') <- eval_data2tag_arg app
-             return (floats, Note note app')
+        = do { app' <- eval_data2tag_arg app
+             ; return (Note note app') }

 
     eval_data2tag_arg other    -- Should not happen
        = pprPanic "eval_data2tag" (ppr other)
 
     eval_data2tag_arg other    -- Should not happen
        = pprPanic "eval_data2tag" (ppr other)

+\end{code}

 
 
 
 

--- ---------------------------------------------------------------------------
--- Precipitating the floating bindings
--- ---------------------------------------------------------------------------
-
-floatRhs :: TopLevelFlag -> RecFlag
-        -> Id
-        -> (Floats, CoreExpr)  -- Rhs: let binds in body
-        -> UniqSM (Floats,     -- Floats out of this bind
-                   CoreExpr)   -- Final Rhs
-
-floatRhs top_lvl is_rec _bndr (floats, rhs)
-  | isTopLevel top_lvl || exprIsHNF rhs,       -- Float to expose value or 
-    allLazy top_lvl is_rec floats              -- at top level
-  =    -- Why the test for allLazy? 
-       --      v = f (x `divInt#` y)
-       -- we don't want to float the case, even if f has arity 2,
-       -- because floating the case would make it evaluated too early
-    return (floats, rhs)
-    
-  | otherwise = do
-       -- Don't float; the RHS isn't a value
-    rhs' <- mkBinds floats rhs
-    return (emptyFloats, rhs')
-
--- mkLocalNonRec is used only for *nested*, *non-recursive* bindings
-mkLocalNonRec :: Id  -> RhsDemand      -- Lhs: id with demand
-             -> Floats -> CoreExpr     -- Rhs: let binds in body
-             -> UniqSM (Floats, Id)    -- The new Id may have an evaldUnfolding, 
-                                       -- to record that it's been evaluated
-
-mkLocalNonRec bndr dem floats rhs
-  | isUnLiftedType (idType bndr)
-       -- If this is an unlifted binding, we always make a case for it.
-  = ASSERT( not (isUnboxedTupleType (idType bndr)) )
-    let
-       float = FloatCase bndr rhs (exprOkForSpeculation rhs)
-    in
-    return (addFloat floats float, evald_bndr)
-
-  | isStrict dem 
-       -- It's a strict let so we definitely float all the bindings
-  = let                -- Don't make a case for a value binding,
-               -- even if it's strict.  Otherwise we get
-               --      case (\x -> e) of ...!
-       float | exprIsHNF rhs = FloatLet (NonRec bndr rhs)
-             | otherwise     = FloatCase bndr rhs (exprOkForSpeculation rhs)
-    in
-    return (addFloat floats float, evald_bndr)
-
-  | otherwise
-  = do (floats', rhs') <- floatRhs NotTopLevel NonRecursive bndr (floats, rhs)
-       return (addFloat floats' (FloatLet (NonRec bndr rhs')),
-               if exprIsHNF rhs' then evald_bndr else bndr)
-
-  where
-    evald_bndr = bndr `setIdUnfolding` evaldUnfolding
-       -- Record if the binder is evaluated
-
-
-mkBinds :: Floats -> CoreExpr -> UniqSM CoreExpr
--- Lambdas are not allowed as the body of a 'let'
-mkBinds (Floats _ binds) body 
-  | isNilOL binds = return body
-  | otherwise    = do { body' <- deLam body
-                       ; return (wrapBinds binds body') }
-
-wrapBinds :: OrdList FloatingBind -> CoreExpr -> CoreExpr
-wrapBinds binds body
-  = foldrOL mk_bind body binds
-  where
-    mk_bind (FloatCase bndr rhs _) body = Case rhs bndr (exprType body) [(DEFAULT, [], body)]
-    mk_bind (FloatLet bind)        body = Let bind body
-
----------------------
-etaExpandRhs :: CoreBndr -> CoreExpr -> UniqSM CoreExpr
-etaExpandRhs bndr rhs = do
-       -- Eta expand to match the arity claimed by the binder
-       -- Remember, CorePrep must not change arity
-       --
-       -- Eta expansion might not have happened already, 
-       -- because it is done by the simplifier only when 
-       -- there at least one lambda already.
-       -- 
-       -- NB1:we could refrain when the RHS is trivial (which can happen
-       --     for exported things).  This would reduce the amount of code
-       --     generated (a little) and make things a little words for
-       --     code compiled without -O.  The case in point is data constructor
-       --     wrappers.
-       --
-       -- NB2: we have to be careful that the result of etaExpand doesn't
-       --    invalidate any of the assumptions that CorePrep is attempting
-       --    to establish.  One possible cause is eta expanding inside of
-       --    an SCC note - we're now careful in etaExpand to make sure the
-       --    SCC is pushed inside any new lambdas that are generated.
-       --
-       -- NB3: It's important to do eta expansion, and *then* ANF-ising
-       --              f = /\a -> g (h 3)      -- h has arity 2
-       -- If we ANF first we get
-       --              f = /\a -> let s = h 3 in g s
-       -- and now eta expansion gives
-       --              f = /\a -> \ y -> (let s = h 3 in g s) y
-       -- which is horrible.
-       -- Eta expanding first gives
-       --              f = /\a -> \y -> let s = h 3 in g s y
-       --
-    us <- getUniquesM
-    let eta_rhs = etaExpand arity us rhs (idType bndr)
-
-    ASSERT2( manifestArity eta_rhs == arity, (ppr bndr <+> ppr arity <+> ppr (exprArity rhs)) 
-                                             $$ ppr rhs $$ ppr eta_rhs )
-       -- Assertion checks that eta expansion was successful
-      return eta_rhs
-  where
-       -- For a GlobalId, take the Arity from the Id.
-       -- It was set in CoreTidy and must not change
-       -- For all others, just expand at will
-    arity | isGlobalId bndr = idArity bndr
-         | otherwise       = exprArity rhs

 
 

--- ---------------------------------------------------------------------------
--- Eliminate Lam as a non-rhs (STG doesn't have such a thing)
--- We arrange that they only show up as the RHS of a let(rec)
--- ---------------------------------------------------------------------------

 
 

-deLam :: CoreExpr -> UniqSM CoreExpr
--- Takes an expression that may be a lambda, 
--- and returns one that definitely isn't:
---     (\x.e) ==>  let f = \x.e in f
-deLam expr = do
-    (Floats _ binds, expr) <- deLamFloat expr
-    return (wrapBinds binds expr)
+%************************************************************************
+%*                                                                     *
+               Simple CoreSyn operations
+%*                                                                     *
+%************************************************************************

 
 

+\begin{code}
+       -- We don't ignore SCCs, since they require some code generation
+ignoreNote :: Note -> Bool
+-- Tells which notes to drop altogether; they are ignored by code generation
+-- Do not ignore SCCs!
+-- It's important that we do drop InlineMe notes; for example
+--    unzip = __inline_me__ (/\ab. foldr (..) (..))
+-- Here unzip gets arity 1 so we'll eta-expand it. But we don't
+-- want to get this:
+--     unzip = /\ab \xs. (__inline_me__ ...) a b xs
+ignoreNote (CoreNote _) = True 
+ignoreNote InlineMe     = True
+ignoreNote _other       = False
+
+
+cpe_ExprIsTrivial :: CoreExpr -> Bool
+-- Version that doesn't consider an scc annotation to be trivial.
+cpe_ExprIsTrivial (Var _)                  = True
+cpe_ExprIsTrivial (Type _)                 = True
+cpe_ExprIsTrivial (Lit _)                  = True
+cpe_ExprIsTrivial (App e arg)              = isTypeArg arg && cpe_ExprIsTrivial e
+cpe_ExprIsTrivial (Note (SCC _) _)         = False
+cpe_ExprIsTrivial (Note _ e)               = cpe_ExprIsTrivial e
+cpe_ExprIsTrivial (Cast e _)               = cpe_ExprIsTrivial e
+cpe_ExprIsTrivial (Lam b body) | isTyVar b = cpe_ExprIsTrivial body
+cpe_ExprIsTrivial _                        = False
+\end{code}

 
 

-deLamFloat :: CoreExpr -> UniqSM (Floats, CoreExpr)
--- Remove top level lambdas by let-bindinig
+-- -----------------------------------------------------------------------------
+--     Eta reduction
+-- -----------------------------------------------------------------------------

 
 

-deLamFloat (Note n expr) = do
-        -- You can get things like
-        --      case e of { p -> coerce t (\s -> ...) }
-    (floats, expr') <- deLamFloat expr
-    return (floats, Note n expr')
+Note [Eta expansion]
+~~~~~~~~~~~~~~~~~~~~~
+Eta expand to match the arity claimed by the binder Remember,
+CorePrep must not change arity
+
+Eta expansion might not have happened already, because it is done by
+the simplifier only when there at least one lambda already.
+
+NB1:we could refrain when the RHS is trivial (which can happen
+    for exported things).  This would reduce the amount of code
+    generated (a little) and make things a little words for
+    code compiled without -O.  The case in point is data constructor
+    wrappers.
+
+NB2: we have to be careful that the result of etaExpand doesn't
+   invalidate any of the assumptions that CorePrep is attempting
+   to establish.  One possible cause is eta expanding inside of
+   an SCC note - we're now careful in etaExpand to make sure the
+   SCC is pushed inside any new lambdas that are generated.
+
+Note [Eta expansion and the CorePrep invariants]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+It turns out to be much much easier to do eta expansion
+*after* the main CorePrep stuff.  But that places constraints
+on the eta expander: given a CpeRhs, it must return a CpeRhs.
+
+For example here is what we do not want:
+               f = /\a -> g (h 3)      -- h has arity 2
+After ANFing we get
+               f = /\a -> let s = h 3 in g s
+and now we do NOT want eta expansion to give
+               f = /\a -> \ y -> (let s = h 3 in g s) y
+
+Instead CoreArity.etaExpand gives
+               f = /\a -> \y -> let s = h 3 in g s y

 
 

-deLamFloat (Cast e co) = do
-    (floats, e') <- deLamFloat e
-    return (floats, Cast e' co)
+\begin{code}
+cpeEtaExpand :: Arity -> CoreExpr -> CoreExpr
+cpeEtaExpand arity expr
+  | arity == 0 = expr
+  | otherwise  = etaExpand arity expr
+\end{code}

 
 

-deLamFloat expr 
-  | null bndrs = return (emptyFloats, expr)
-  | otherwise 
-  = case tryEta bndrs body of
-      Just no_lam_result -> return (emptyFloats, no_lam_result)
-      Nothing            -> do fn <- newVar (exprType expr)
-                               return (unitFloat (FloatLet (NonRec fn expr)), 
-                                         Var fn)
-  where
-    (bndrs,body) = collectBinders expr
+-- -----------------------------------------------------------------------------
+--     Eta reduction
+-- -----------------------------------------------------------------------------

 
 

--- Why try eta reduction?  Hasn't the simplifier already done eta?
--- But the simplifier only eta reduces if that leaves something
--- trivial (like f, or f Int).  But for deLam it would be enough to
--- get to a partial application:
---     \xs. map f xs ==> map f
+Why try eta reduction?  Hasn't the simplifier already done eta?
+But the simplifier only eta reduces if that leaves something
+trivial (like f, or f Int).  But for deLam it would be enough to
+get to a partial application:
+       case x of { p -> \xs. map f xs }
+    ==> case x of { p -> map f }

 
 

-tryEta :: [CoreBndr] -> CoreExpr -> Maybe CoreExpr
-tryEta bndrs expr@(App _ _)
+\begin{code}
+tryEtaReduce :: [CoreBndr] -> CoreExpr -> Maybe CoreExpr
+tryEtaReduce bndrs expr@(App _ _)

   | ok_to_eta_reduce f &&
     n_remaining >= 0 &&
     and (zipWith ok bndrs last_args) &&
   | ok_to_eta_reduce f &&
     n_remaining >= 0 &&
     and (zipWith ok bndrs last_args) &&

@@ -765,15 +694,15 @@ tryEta bndrs expr@(App _ _)
     ok_to_eta_reduce (Var f) = not (hasNoBinding f)
     ok_to_eta_reduce _       = False --safe. ToDo: generalise
 
     ok_to_eta_reduce (Var f) = not (hasNoBinding f)
     ok_to_eta_reduce _       = False --safe. ToDo: generalise
 

-tryEta bndrs (Let bind@(NonRec _ r) body)
+tryEtaReduce bndrs (Let bind@(NonRec _ r) body)

   | not (any (`elemVarSet` fvs) bndrs)
   | not (any (`elemVarSet` fvs) bndrs)

-  = case tryEta bndrs body of
+  = case tryEtaReduce bndrs body of

        Just e -> Just (Let bind e)
        Nothing -> Nothing
   where
     fvs = exprFreeVars r
 
        Just e -> Just (Let bind e)
        Nothing -> Nothing
   where
     fvs = exprFreeVars r
 

-tryEta _ _ = Nothing
+tryEtaReduce _ _ = Nothing

 \end{code}
 
 
 \end{code}
 
 

@@ -782,35 +711,121 @@ tryEta _ _ = Nothing
 -- -----------------------------------------------------------------------------
 
 \begin{code}
 -- -----------------------------------------------------------------------------
 
 \begin{code}

-data RhsDemand
-     = RhsDemand { isStrict  :: Bool,  -- True => used at least once
-                  _isOnceDem :: Bool   -- True => used at most once
-                 }
+type RhsDemand = Bool  -- True => used strictly; hence not top-level, non-recursive
+\end{code}

 
 

-mkDem :: Demand -> Bool -> RhsDemand
-mkDem strict once = RhsDemand (isStrictDmd strict) once
+%************************************************************************
+%*                                                                     *
+               Floats
+%*                                                                     *
+%************************************************************************

 
 

-mkDemTy :: Demand -> Type -> RhsDemand
-mkDemTy strict _ty = RhsDemand (isStrictDmd strict)
-                               False {- For now -}
+\begin{code}
+data FloatingBind 
+  = FloatLet CoreBind          -- Rhs of bindings are CpeRhss
+  | FloatCase Id CpeBody Bool   -- The bool indicates "ok-for-speculation"
+
+data Floats = Floats OkToSpec (OrdList FloatingBind)
+
+-- Can we float these binds out of the rhs of a let?  We cache this decision
+-- to avoid having to recompute it in a non-linear way when there are
+-- deeply nested lets.
+data OkToSpec
+   = NotOkToSpec       -- definitely not
+   | OkToSpec          -- yes
+   | IfUnboxedOk       -- only if floating an unboxed binding is ok

 
 

-bdrDem :: Id -> RhsDemand
-bdrDem id = mkDem (idNewDemandInfo id)
-                 False {- For now -}
+mkFloat :: Bool -> Bool -> Id -> CpeRhs -> FloatingBind
+mkFloat is_strict is_unlifted bndr rhs
+  | use_case  = FloatCase bndr rhs (exprOkForSpeculation rhs)
+  | otherwise = FloatLet (NonRec bndr rhs)
+  where
+    use_case = is_unlifted || is_strict && not (exprIsHNF rhs)
+               -- Don't make a case for a value binding,
+               -- even if it's strict.  Otherwise we get
+               --      case (\x -> e) of ...!
+             
+emptyFloats :: Floats
+emptyFloats = Floats OkToSpec nilOL

 
 

--- safeDem :: RhsDemand
--- safeDem = RhsDemand False False  -- always safe to use this
+wrapBinds :: Floats -> CoreExpr -> CoreExpr
+wrapBinds (Floats _ binds) body
+  = foldrOL mk_bind body binds
+  where
+    mk_bind (FloatCase bndr rhs _) body = Case rhs bndr (exprType body) [(DEFAULT, [], body)]
+    mk_bind (FloatLet bind)        body = Let bind body

 
 

-onceDem :: RhsDemand
-onceDem = RhsDemand False True   -- used at most once
-\end{code}
+addFloat :: Floats -> FloatingBind -> Floats
+addFloat (Floats ok_to_spec floats) new_float
+  = Floats (combine ok_to_spec (check new_float)) (floats `snocOL` new_float)
+  where
+    check (FloatLet _) = OkToSpec
+    check (FloatCase _ _ ok_for_spec) 
+       | ok_for_spec  =  IfUnboxedOk
+       | otherwise    =  NotOkToSpec
+       -- The ok-for-speculation flag says that it's safe to
+       -- float this Case out of a let, and thereby do it more eagerly
+       -- We need the top-level flag because it's never ok to float
+       -- an unboxed binding to the top level
+
+unitFloat :: FloatingBind -> Floats
+unitFloat = addFloat emptyFloats
+
+appendFloats :: Floats -> Floats -> Floats
+appendFloats (Floats spec1 floats1) (Floats spec2 floats2)
+  = Floats (combine spec1 spec2) (floats1 `appOL` floats2)
+
+concatFloats :: [Floats] -> OrdList FloatingBind
+concatFloats = foldr (\ (Floats _ bs1) bs2 -> appOL bs1 bs2) nilOL
+
+combine :: OkToSpec -> OkToSpec -> OkToSpec
+combine NotOkToSpec _ = NotOkToSpec
+combine _ NotOkToSpec = NotOkToSpec
+combine IfUnboxedOk _ = IfUnboxedOk
+combine _ IfUnboxedOk = IfUnboxedOk
+combine _ _           = OkToSpec
+    
+instance Outputable FloatingBind where
+  ppr (FloatLet bind)        = text "FloatLet" <+> ppr bind
+  ppr (FloatCase b rhs spec) = text "FloatCase" <+> ppr b <+> ppr spec <+> equals <+> ppr rhs

 
 

+deFloatTop :: Floats -> [CoreBind]
+-- For top level only; we don't expect any FloatCases
+deFloatTop (Floats _ floats)
+  = foldrOL get [] floats
+  where
+    get (FloatLet b) bs = b:bs
+    get b            _  = pprPanic "corePrepPgm" (ppr b)

 
 

+-------------------------------------------
+wantFloatTop :: Id -> Floats -> Bool
+       -- Note [CafInfo and floating]
+wantFloatTop bndr floats = mayHaveCafRefs (idCafInfo bndr)
+                          && allLazyTop floats
+
+wantFloatNested :: RecFlag -> Bool -> Floats -> CpeRhs -> Bool
+wantFloatNested is_rec strict_or_unlifted floats rhs
+  = strict_or_unlifted
+  || (allLazyNested is_rec floats && exprIsHNF rhs)
+       -- Why the test for allLazyNested? 
+       --      v = f (x `divInt#` y)
+       -- we don't want to float the case, even if f has arity 2,
+       -- because floating the case would make it evaluated too early
+
+allLazyTop :: Floats -> Bool
+allLazyTop (Floats OkToSpec _) = True
+allLazyTop _                  = False
+
+allLazyNested :: RecFlag -> Floats -> Bool
+allLazyNested _      (Floats OkToSpec    _) = True
+allLazyNested _      (Floats NotOkToSpec _) = False
+allLazyNested is_rec (Floats IfUnboxedOk _) = isNonRec is_rec
+\end{code}

 
 
 %************************************************************************
 %*                                                                     *
 
 
 %************************************************************************
 %*                                                                     *

-\subsection{Cloning}
+               Cloning

 %*                                                                     *
 %************************************************************************
 
 %*                                                                     *
 %************************************************************************
 

@@ -827,6 +842,9 @@ emptyCorePrepEnv = CPE emptyVarEnv
 extendCorePrepEnv :: CorePrepEnv -> Id -> Id -> CorePrepEnv
 extendCorePrepEnv (CPE env) id id' = CPE (extendVarEnv env id id')
 
 extendCorePrepEnv :: CorePrepEnv -> Id -> Id -> CorePrepEnv
 extendCorePrepEnv (CPE env) id id' = CPE (extendVarEnv env id id')
 

+extendCorePrepEnvList :: CorePrepEnv -> [(Id,Id)] -> CorePrepEnv
+extendCorePrepEnvList (CPE env) prs = CPE (extendVarEnvList env prs)
+

 lookupCorePrepEnv :: CorePrepEnv -> Id -> Id
 lookupCorePrepEnv (CPE env) id
   = case lookupVarEnv env id of
 lookupCorePrepEnv :: CorePrepEnv -> Id -> Id
 lookupCorePrepEnv (CPE env) id
   = case lookupVarEnv env id of