#include "HsVersions.h"
+import PrelNames ( lazyIdKey, hasKey )
import CoreUtils
import CoreArity
import CoreFVs
-import CoreLint
+import CoreMonad ( endPass )
import CoreSyn
import Type
import Coercion
import TyCon
-import NewDemand
+import Demand
import Var
import VarSet
import VarEnv
8. Inject bindings for the "implicit" Ids:
* Constructor wrappers
* Constructor workers
- * Record selectors
We want curried definitions for all of these in case they
aren't inlined by some caller.
+9. Replace (lazy e) by e. See Note [lazyId magic] in MkId.lhs
+
This is all done modulo type applications and abstractions, so that
when type erasure is done for conversion to STG, we don't end up with
any trivial or useless bindings.
floats2 <- corePrepTopBinds implicit_binds
return (deFloatTop (floats1 `appendFloats` floats2))
- endPass dflags "CorePrep" Opt_D_dump_prep binds_out
+ endPass dflags "CorePrep" Opt_D_dump_prep binds_out []
return binds_out
corePrepExpr :: DynFlags -> CoreExpr -> IO CoreExpr
-> UniqSM (CorePrepEnv, Floats)
cpeBind top_lvl env (NonRec bndr rhs)
= do { (_, bndr1) <- cloneBndr env bndr
- ; let is_strict = isStrictDmd (idNewDemandInfo bndr)
+ ; let is_strict = isStrictDmd (idDemandInfo bndr)
is_unlifted = isUnLiftedType (idType bndr)
; (floats, bndr2, rhs2) <- cpePair top_lvl NonRecursive
(is_strict || is_unlifted)
-> 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
+ = do { (floats1, rhs1) <- cpeRhsE env rhs
+ ; let (rhs1_bndrs, _) = collectBinders rhs1
+ ; (floats2, rhs2)
+ <- if want_float floats1 rhs1
+ then return (floats1, rhs1)
+ else -- Non-empty floats will wrap rhs1
+ -- But: rhs1 might have lambdas, and we can't
+ -- put them inside a wrapBinds
+ if valBndrCount rhs1_bndrs <= arity
+ then -- Lambdas in rhs1 will be nuked by eta expansion
+ return (emptyFloats, wrapBinds floats1 rhs1)
+
+ else do { body1 <- rhsToBodyNF rhs1
+ ; return (emptyFloats, wrapBinds floats1 body1) }
+
+ ; (floats3, rhs') -- Note [Silly extra arguments]
+ <- if manifestArity rhs2 <= arity
+ then return (floats2, cpeEtaExpand arity rhs2)
+ else WARN(True, text "CorePrep: silly extra arguments:" <+> ppr bndr)
+ (do { v <- newVar (idType bndr)
+ ; let float = mkFloat False False v rhs2
+ ; return (addFloat floats2 float, cpeEtaExpand arity (Var v)) })
-- Record if the binder is evaluated
; let bndr' | exprIsHNF rhs' = bndr `setIdUnfolding` evaldUnfolding
| otherwise = bndr
- ; return (floats, bndr', rhs') }
+ ; return (floats3, bndr', rhs') }
where
+ arity = idArity bndr -- We must match this arity
want_float floats rhs
| isTopLevel top_lvl = wantFloatTop bndr floats
| otherwise = wantFloatNested is_rec is_strict_or_unlifted floats rhs
-
+{- Note [Silly extra arguments]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Suppose we had this
+ f{arity=1} = \x\y. e
+We *must* match the arity on the Id, so we have to generate
+ f' = \x\y. e
+ f = \x. f' x
+
+It's a bizarre case: why is the arity on the Id wrong? Reason
+(in the days of __inline_me__):
+ f{arity=0} = __inline_me__ (let v = expensive in \xy. e)
+When InlineMe notes go away this won't happen any more. But
+it seems good for CorePrep to be robust.
+-}
-- ---------------------------------------------------------------------------
-- CpeRhs: produces a result satisfying CpeRhs
-- ---------------------------------------------------------------------------
-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')
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 (Var f `App` _ `App` arg)
+ | f `hasKey` lazyIdKey -- Replace (lazy a) by a
+ = cpeRhsE env arg -- See Note [lazyId magic] in MkId
+
+cpeRhsE env expr@(App {}) = cpeApp env expr
+
cpeRhsE env (Let bind expr)
= do { (env', new_binds) <- cpeBind NotTopLevel env bind
; (floats, body) <- cpeRhsE env' expr
; return (floats1 `appendFloats` floats2, body) }
--------
+rhsToBodyNF :: CpeRhs -> UniqSM CpeBody
+rhsToBodyNF rhs = do { (floats,body) <- rhsToBody rhs
+ ; return (wrapBinds floats body) }
+
+--------
rhsToBody :: CpeRhs -> UniqSM (Floats, CpeBody)
--- Remove top level lambdas by let-bindinig
+-- Remove top level lambdas by let-binding
rhsToBody (Note n expr)
-- You can get things like
collect_args (App fun arg) depth
= do { (fun',hd,fun_ty,floats,ss) <- collect_args fun (depth+1)
- ; let
+ ; let
(ss1, ss_rest) = case ss of
(ss1:ss_rest) -> (ss1, ss_rest)
[] -> (lazyDmd, [])
; let v2 = lookupCorePrepEnv env v1
; return (Var v2, (Var v2, depth), idType v2, emptyFloats, stricts) }
where
- stricts = case idNewStrictness v of
+ stricts = case idStrictness v of
StrictSig (DmdType _ demands _)
| listLengthCmp demands depth /= GT -> demands
-- length demands <= depth
= 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.
collect_args fun depth
= do { (fun_floats, fun') <- cpeArg env True fun ty
+ -- The True says that it's sure to be evaluated,
+ -- so we'll end up case-binding it
; return (fun', (fun', depth), ty, fun_floats, []) }
where
ty = exprType fun
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
+ | 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
+ = do { (floats1, arg1) <- cpeRhsE env arg -- arg1 can be a lambda
+ ; (floats2, arg2) <- if want_float floats1 arg1
+ then return (floats1, arg1)
+ else do { body1 <- rhsToBodyNF arg1
+ ; return (emptyFloats, wrapBinds floats1 body1) }
+ -- Else case: arg1 might have lambdas, and we can't
+ -- put them inside a wrapBinds
+
; v <- newVar arg_ty
- ; let arg_float = mkFloat is_strict is_unlifted v arg'
- ; return (addFloat floats arg_float, Var v) }
+ ; let arg3 = cpeEtaExpand (exprArity arg2) arg2
+ arg_float = mkFloat is_strict is_unlifted v arg3
+ ; return (addFloat floats2 arg_float, Var v) }
where
is_unlifted = isUnLiftedType arg_ty
want_float = wantFloatNested NonRecursive (is_strict || is_unlifted)
-- want to get this:
-- unzip = /\ab \xs. (__inline_me__ ...) a b xs
ignoreNote (CoreNote _) = True
-ignoreNote InlineMe = True
ignoreNote _other = False
emptyFloats :: Floats
emptyFloats = Floats OkToSpec nilOL
+isEmptyFloats :: Floats -> Bool
+isEmptyFloats (Floats _ bs) = isNilOL bs
+
wrapBinds :: Floats -> CoreExpr -> CoreExpr
wrapBinds (Floats _ binds) body
= foldrOL mk_bind body binds
-------------------------------------------
wantFloatTop :: Id -> Floats -> Bool
-- Note [CafInfo and floating]
-wantFloatTop bndr floats = mayHaveCafRefs (idCafInfo bndr)
- && allLazyTop floats
+wantFloatTop bndr floats = isEmptyFloats floats
+ || (mayHaveCafRefs (idCafInfo bndr)
+ && allLazyTop floats)
wantFloatNested :: RecFlag -> Bool -> Floats -> CpeRhs -> Bool
wantFloatNested is_rec strict_or_unlifted floats rhs
- = strict_or_unlifted
+ = isEmptyFloats floats
+ || strict_or_unlifted
|| (allLazyNested is_rec floats && exprIsHNF rhs)
-- Why the test for allLazyNested?
-- v = f (x `divInt#` y)
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