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authorLeif Metcalf <me@leif.nz>2021-01-20 15:33:47 +1300
committerLeif Metcalf <me@leif.nz>2021-01-25 00:55:12 -0500
commit53b8feaca2673cfae023c41745c137d897cd4ddc (patch)
treeaa90f3abc1f468e486b31467ce00f4b5a6351784
parentb18d9e97252c9dd12f08d3e6f56bfec6a6d2469a (diff)
downloadhaskell-53b8feaca2673cfae023c41745c137d897cd4ddc.tar.gz
StgLam is used exclusively in the work of CoreToStg, but there's nothing in the type of StgExpr that indicates this, so we're forced throughout the Stg.* codebase to handle cases like: case expr of ... StgLam lam -> panic "Unexpected StgLam" ... This patch removes the StgLam constructor from the base StgExpr so these cases no longer need to be handled. Instead, we use a new intermediate type in CoreToStg, PreStgRhs, to represent the RHS expression of a binding.
-rw-r--r--compiler/GHC/CoreToStg.hs61
-rw-r--r--compiler/GHC/Stg/CSE.hs4
-rw-r--r--compiler/GHC/Stg/DepAnal.hs2
-rw-r--r--compiler/GHC/Stg/FVs.hs3
-rw-r--r--compiler/GHC/Stg/Lift.hs1
-rw-r--r--compiler/GHC/Stg/Lift/Analysis.hs2
-rw-r--r--compiler/GHC/Stg/Lint.hs4
-rw-r--r--compiler/GHC/Stg/Stats.hs3
-rw-r--r--compiler/GHC/Stg/Syntax.hs47
-rw-r--r--compiler/GHC/Stg/Unarise.hs3
-rw-r--r--compiler/GHC/StgToCmm/Expr.hs2
11 files changed, 65 insertions, 67 deletions
diff --git a/compiler/GHC/CoreToStg.hs b/compiler/GHC/CoreToStg.hs
index bc890ea6cb..ee885eaacf 100644
--- a/compiler/GHC/CoreToStg.hs
+++ b/compiler/GHC/CoreToStg.hs
@@ -52,7 +52,6 @@ import GHC.Types.SrcLoc ( mkGeneralSrcSpan )
import GHC.Builtin.Names ( unsafeEqualityProofName )
import Control.Monad (ap)
-import Data.List.NonEmpty (nonEmpty, toList)
import Data.Maybe (fromMaybe)
import Data.Tuple (swap)
import qualified Data.Set as Set
@@ -326,7 +325,7 @@ coreToTopStgRhs
-> CtsM (StgRhs, CollectedCCs)
coreToTopStgRhs dflags ccs this_mod (bndr, rhs)
- = do { new_rhs <- coreToStgExpr rhs
+ = do { new_rhs <- coreToPreStgRhs rhs
; let (stg_rhs, ccs') =
mkTopStgRhs dflags this_mod ccs bndr new_rhs
@@ -359,6 +358,10 @@ coreToTopStgRhs dflags ccs this_mod (bndr, rhs)
-- Expressions
-- ---------------------------------------------------------------------------
+-- coreToStgExpr panics if the input expression is a value lambda. CorePrep
+-- ensures that value lambdas only exist as the RHS of bindings, which we
+-- handle with the function coreToPreStgRhs.
+
coreToStgExpr
:: CoreExpr
-> CtsM StgExpr
@@ -392,16 +395,13 @@ coreToStgExpr expr@(App _ _)
coreToStgExpr expr@(Lam _ _)
= let
(args, body) = myCollectBinders expr
- args' = filterStgBinders args
in
- extendVarEnvCts [ (a, LambdaBound) | a <- args' ] $ do
- body' <- coreToStgExpr body
- let
- result_expr = case nonEmpty args' of
- Nothing -> body'
- Just args'' -> StgLam args'' body'
+ case filterStgBinders args of
- return result_expr
+ [] -> coreToStgExpr body
+
+ _ -> pprPanic "coretoStgExpr" $
+ text "Unexpected value lambda:" $$ ppr expr
coreToStgExpr (Tick tick expr)
= do case tick of
@@ -674,23 +674,42 @@ coreToStgRhs :: (Id,CoreExpr)
-> CtsM StgRhs
coreToStgRhs (bndr, rhs) = do
- new_rhs <- coreToStgExpr rhs
+ new_rhs <- coreToPreStgRhs rhs
return (mkStgRhs bndr new_rhs)
+-- Represents the RHS of a binding for use with mk(Top)StgRhs.
+data PreStgRhs = PreStgRhs [Id] StgExpr -- The [Id] is empty for thunks
+
+-- Convert the RHS of a binding from Core to STG. This is a wrapper around
+-- coreToStgExpr that can handle value lambdas.
+coreToPreStgRhs :: CoreExpr -> CtsM PreStgRhs
+coreToPreStgRhs (Cast expr _) = coreToPreStgRhs expr
+coreToPreStgRhs expr@(Lam _ _) =
+ let
+ (args, body) = myCollectBinders expr
+ args' = filterStgBinders args
+ in
+ extendVarEnvCts [ (a, LambdaBound) | a <- args' ] $ do
+ body' <- coreToStgExpr body
+ return (PreStgRhs args' body')
+coreToPreStgRhs expr = PreStgRhs [] <$> coreToStgExpr expr
+
-- Generate a top-level RHS. Any new cost centres generated for CAFs will be
-- appended to `CollectedCCs` argument.
mkTopStgRhs :: DynFlags -> Module -> CollectedCCs
- -> Id -> StgExpr -> (StgRhs, CollectedCCs)
+ -> Id -> PreStgRhs -> (StgRhs, CollectedCCs)
-mkTopStgRhs dflags this_mod ccs bndr rhs
- | StgLam bndrs body <- rhs
- = -- StgLam can't have empty arguments, so not CAF
+mkTopStgRhs dflags this_mod ccs bndr (PreStgRhs bndrs rhs)
+ | not (null bndrs)
+ = -- The list of arguments is non-empty, so not CAF
( StgRhsClosure noExtFieldSilent
dontCareCCS
ReEntrant
- (toList bndrs) body
+ bndrs rhs
, ccs )
+ -- After this point we know that `bndrs` is empty,
+ -- so this is not a function binding
| StgConApp con args _ <- unticked_rhs
, -- Dynamic StgConApps are updatable
not (isDllConApp dflags this_mod con args)
@@ -732,14 +751,16 @@ mkTopStgRhs dflags this_mod ccs bndr rhs
-- Generate a non-top-level RHS. Cost-centre is always currentCCS,
-- see Note [Cost-centre initialization plan].
-mkStgRhs :: Id -> StgExpr -> StgRhs
-mkStgRhs bndr rhs
- | StgLam bndrs body <- rhs
+mkStgRhs :: Id -> PreStgRhs -> StgRhs
+mkStgRhs bndr (PreStgRhs bndrs rhs)
+ | not (null bndrs)
= StgRhsClosure noExtFieldSilent
currentCCS
ReEntrant
- (toList bndrs) body
+ bndrs rhs
+ -- After this point we know that `bndrs` is empty,
+ -- so this is not a function binding
| isJoinId bndr -- must be a nullary join point
= ASSERT(idJoinArity bndr == 0)
StgRhsClosure noExtFieldSilent
diff --git a/compiler/GHC/Stg/CSE.hs b/compiler/GHC/Stg/CSE.hs
index 61a7824188..b9e6782f77 100644
--- a/compiler/GHC/Stg/CSE.hs
+++ b/compiler/GHC/Stg/CSE.hs
@@ -95,8 +95,6 @@ import GHC.Prelude
import GHC.Core.DataCon
import GHC.Types.Id
import GHC.Stg.Syntax
-import GHC.Utils.Outputable
-import GHC.Utils.Panic
import GHC.Types.Basic (isWeakLoopBreaker)
import GHC.Types.Var.Env
import GHC.Core (AltCon(..))
@@ -312,8 +310,6 @@ stgCseExpr _ (StgLit lit)
stgCseExpr env (StgOpApp op args tys)
= StgOpApp op args' tys
where args' = substArgs env args
-stgCseExpr _ (StgLam _ _)
- = pprPanic "stgCseExp" (text "StgLam")
stgCseExpr env (StgTick tick body)
= let body' = stgCseExpr env body
in StgTick tick body'
diff --git a/compiler/GHC/Stg/DepAnal.hs b/compiler/GHC/Stg/DepAnal.hs
index 223ab0c5bb..9bf4249f6f 100644
--- a/compiler/GHC/Stg/DepAnal.hs
+++ b/compiler/GHC/Stg/DepAnal.hs
@@ -91,8 +91,6 @@ annTopBindingsDeps this_mod bs = zip bs (map top_bind bs)
args bounds as
expr bounds (StgOpApp _ as _) =
args bounds as
- expr _ lam@StgLam{} =
- pprPanic "annTopBindingsDeps" (text "Found lambda:" $$ pprStgExpr panicStgPprOpts lam)
expr bounds (StgCase scrut scrut_bndr _ as) =
expr bounds scrut `unionVarSet`
alts (extendVarSet bounds scrut_bndr) as
diff --git a/compiler/GHC/Stg/FVs.hs b/compiler/GHC/Stg/FVs.hs
index 211a0cb315..bd699a1fe1 100644
--- a/compiler/GHC/Stg/FVs.hs
+++ b/compiler/GHC/Stg/FVs.hs
@@ -48,9 +48,7 @@ import GHC.Stg.Syntax
import GHC.Types.Id
import GHC.Types.Var.Set
import GHC.Core ( Tickish(Breakpoint) )
-import GHC.Utils.Outputable
import GHC.Utils.Misc
-import GHC.Utils.Panic
import Data.Maybe ( mapMaybe )
@@ -128,7 +126,6 @@ expr env = go
go (StgLit lit) = (StgLit lit, emptyDVarSet)
go (StgConApp dc as tys) = (StgConApp dc as tys, args env as)
go (StgOpApp op as ty) = (StgOpApp op as ty, args env as)
- go StgLam{} = pprPanic "StgFVs: StgLam" empty
go (StgCase scrut bndr ty alts) = (StgCase scrut' bndr ty alts', fvs)
where
(scrut', scrut_fvs) = go scrut
diff --git a/compiler/GHC/Stg/Lift.hs b/compiler/GHC/Stg/Lift.hs
index 27e63f9313..8f2337120e 100644
--- a/compiler/GHC/Stg/Lift.hs
+++ b/compiler/GHC/Stg/Lift.hs
@@ -229,7 +229,6 @@ liftExpr (StgApp f args) = do
pure (StgApp f' top_lvl_args)
liftExpr (StgConApp con args tys) = StgConApp con <$> traverse liftArgs args <*> pure tys
liftExpr (StgOpApp op args ty) = StgOpApp op <$> traverse liftArgs args <*> pure ty
-liftExpr (StgLam _ _) = pprPanic "stgLiftLams" (text "StgLam")
liftExpr (StgCase scrut info ty alts) = do
scrut' <- liftExpr scrut
withSubstBndr (binderInfoBndr info) $ \bndr' -> do
diff --git a/compiler/GHC/Stg/Lift/Analysis.hs b/compiler/GHC/Stg/Lift/Analysis.hs
index 5aef95c008..314e010ead 100644
--- a/compiler/GHC/Stg/Lift/Analysis.hs
+++ b/compiler/GHC/Stg/Lift/Analysis.hs
@@ -34,7 +34,6 @@ import qualified GHC.StgToCmm.ArgRep as StgToCmm.ArgRep
import qualified GHC.StgToCmm.Closure as StgToCmm.Closure
import qualified GHC.StgToCmm.Layout as StgToCmm.Layout
import GHC.Utils.Outputable
-import GHC.Utils.Panic
import GHC.Utils.Misc
import GHC.Types.Var.Set
@@ -223,7 +222,6 @@ tagSkeletonExpr (StgApp f args)
-- argument occurrences, see "GHC.Stg.Lift.Analysis#arg_occs".
| null args = unitVarSet f
| otherwise = mkArgOccs args
-tagSkeletonExpr (StgLam _ _) = pprPanic "stgLiftLams" (text "StgLam")
tagSkeletonExpr (StgCase scrut bndr ty alts)
= (skel, arg_occs, StgCase scrut' bndr' ty alts')
where
diff --git a/compiler/GHC/Stg/Lint.hs b/compiler/GHC/Stg/Lint.hs
index 1485a11458..742b29ee71 100644
--- a/compiler/GHC/Stg/Lint.hs
+++ b/compiler/GHC/Stg/Lint.hs
@@ -192,10 +192,6 @@ lintStgExpr app@(StgConApp con args _arg_tys) = do
lintStgExpr (StgOpApp _ args _) =
mapM_ lintStgArg args
-lintStgExpr lam@(StgLam _ _) = do
- opts <- getStgPprOpts
- addErrL (text "Unexpected StgLam" <+> pprStgExpr opts lam)
-
lintStgExpr (StgLet _ binds body) = do
binders <- lintStgBinds NotTopLevel binds
addLoc (BodyOfLetRec binders) $
diff --git a/compiler/GHC/Stg/Stats.hs b/compiler/GHC/Stg/Stats.hs
index 329f319a47..0f806a3175 100644
--- a/compiler/GHC/Stg/Stats.hs
+++ b/compiler/GHC/Stg/Stats.hs
@@ -32,7 +32,6 @@ import GHC.Prelude
import GHC.Stg.Syntax
import GHC.Types.Id (Id)
-import GHC.Utils.Panic
import Data.Map (Map)
import qualified Data.Map as Map
@@ -169,5 +168,3 @@ statExpr (StgCase expr _ _ alts)
where
stat_alts alts
= combineSEs (map statExpr [ e | (_,_,e) <- alts ])
-
-statExpr (StgLam {}) = panic "statExpr StgLam"
diff --git a/compiler/GHC/Stg/Syntax.hs b/compiler/GHC/Stg/Syntax.hs
index b38c2f1ab0..25d01079df 100644
--- a/compiler/GHC/Stg/Syntax.hs
+++ b/compiler/GHC/Stg/Syntax.hs
@@ -89,8 +89,6 @@ import GHC.Types.RepType ( typePrimRep1 )
import GHC.Utils.Misc
import GHC.Utils.Panic
-import Data.List.NonEmpty ( NonEmpty, toList )
-
{-
************************************************************************
* *
@@ -256,22 +254,6 @@ literals.
{-
************************************************************************
* *
-StgLam
-* *
-************************************************************************
-
-StgLam is used *only* during CoreToStg's work. Before CoreToStg has finished it
-encodes (\x -> e) as (let f = \x -> e in f) TODO: Encode this via an extension
-to GenStgExpr à la TTG.
--}
-
- | StgLam
- (NonEmpty (BinderP pass))
- StgExpr -- Body of lambda
-
-{-
-************************************************************************
-* *
GenStgExpr: case-expressions
* *
************************************************************************
@@ -436,6 +418,30 @@ important):
-- are not allocated.
[StgArg] -- Args
+{-
+Note Stg Passes
+~~~~~~~~~~~~~~~
+Here is a short summary of the STG pipeline and where we use the different
+StgPass data type indexes:
+
+ 1. CoreToStg.Prep performs several transformations that prepare the desugared
+ and simplified core to be converted to STG. One of these transformations is
+ making it so that value lambdas only exist as the RHS of a binding.
+
+ 2. CoreToStg converts the prepared core to STG, specifically GenStg*
+ parameterised by 'Vanilla.
+
+ 3. Stg.Pipeline does a number of passes on the generated STG. One of these is
+ the lambda-lifting pass, which internally uses the 'LiftLams
+ parameterisation to store information for deciding whether or not to lift
+ each binding.
+
+ 4. Stg.FVs annotates closures with their free variables. To store these
+ annotations we use the 'CodeGen parameterisation.
+
+ 5. Stg.StgToCmm generates Cmm from the annotated STG.
+-}
+
-- | Used as a data type index for the stgSyn AST
data StgPass
= Vanilla
@@ -709,11 +715,6 @@ pprStgExpr opts e = case e of
StgApp func args -> hang (ppr func) 4 (interppSP args)
StgConApp con args _ -> hsep [ ppr con, brackets (interppSP args) ]
StgOpApp op args _ -> hsep [ pprStgOp op, brackets (interppSP args)]
- StgLam bndrs body -> let ppr_list = brackets . fsep . punctuate comma
- in sep [ char '\\' <+> ppr_list (map (pprBndr LambdaBind) (toList bndrs))
- <+> text "->"
- , pprStgExpr opts body
- ]
-- special case: let v = <very specific thing>
-- in
diff --git a/compiler/GHC/Stg/Unarise.hs b/compiler/GHC/Stg/Unarise.hs
index eb4c968f5b..40dff5f33b 100644
--- a/compiler/GHC/Stg/Unarise.hs
+++ b/compiler/GHC/Stg/Unarise.hs
@@ -336,9 +336,6 @@ unariseExpr rho (StgConApp dc args ty_args)
unariseExpr rho (StgOpApp op args ty)
= return (StgOpApp op (unariseFunArgs rho args) ty)
-unariseExpr _ e@StgLam{}
- = pprPanic "unariseExpr: found lambda" (pprStgExpr panicStgPprOpts e)
-
unariseExpr rho (StgCase scrut bndr alt_ty alts)
-- tuple/sum binders in the scrutinee can always be eliminated
| StgApp v [] <- scrut
diff --git a/compiler/GHC/StgToCmm/Expr.hs b/compiler/GHC/StgToCmm/Expr.hs
index 0048a4c9a2..7427547bf4 100644
--- a/compiler/GHC/StgToCmm/Expr.hs
+++ b/compiler/GHC/StgToCmm/Expr.hs
@@ -129,8 +129,6 @@ cgExpr (StgLetNoEscape _ binds expr) =
cgExpr (StgCase expr bndr alt_type alts) =
cgCase expr bndr alt_type alts
-cgExpr (StgLam {}) = panic "cgExpr: StgLam"
-
------------------------------------------------------------------------
-- Let no escape
------------------------------------------------------------------------