HEAD regression: Core Lint error/panic due to out-of-scope dictionary
(Originally discovered in a head.hackage CI job here.)
The futhark-0.24.2 Hackage library will emit a Core Lint error if you build it with GHC HEAD. Here is a minimized example:
{-# LANGUAGE Haskell2010 #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE UndecidableInstances #-}
{-# LANGUAGE NoMonoLocalBinds #-}
module Futhark.Optimise.Fusion.GraphRep (emptyGraph) where
import qualified Data.IntMap.Strict as IM
import qualified Data.Kind
import Data.Map.Strict (Map)
data NodeT = FreeNode VName
emptyGraph :: Stms SOACS -> [(Int, NodeT)]
emptyGraph stms = labelNodes inputnodes
where
labelNodes = zip [0 ..]
inputnodes = map FreeNode $ namesToList consumed
(_aliased, consumed) = analyseStms stms
data Aliases (rep :: Data.Kind.Type)
class RepTypes l where
type OpC l :: Data.Kind.Type -> Data.Kind.Type
instance RepTypes SOACS where
type OpC SOACS = SOAC
class Aliased rep where
instance AliasedOp (OpC rep (Aliases rep)) => Aliased (Aliases rep) where
class AliasedOp op where
instance Aliased rep => AliasedOp (SOAC rep) where
analyseStms ::
AliasedOp (OpC rep (Aliases rep)) =>
Stms rep ->
(Map VName Names, Names)
analyseStms = undefined
newtype Names = Names (IM.IntMap VName)
namesIntMap :: Names -> IM.IntMap VName
namesIntMap (Names m) = m
namesToList :: Names -> [VName]
namesToList = IM.elems . namesIntMap
data SOAC rep
data SOACS
data Stms rep
data VNameThis will pass -dcore-lint with GHC 9.6 and earlier, but fail with GHC HEAD:
$ ~/Software/ghc-9.7.20230620/bin/ghc Bug.hs -dcore-lint -dno-typeable-binds
[1 of 1] Compiling Futhark.Optimise.Fusion.GraphRep ( Bug.hs, Bug.o )
*** Core Lint errors : in result of Desugar (before optimization) ***
Bug.hs:17:12: warning:
Out of scope: $dAliased_a1oc :: Aliased (Aliases SOACS)
[LclId]
In the RHS of emptyGraph :: Stms SOACS -> [(Int, NodeT)]
In the body of lambda with binder stms_a10c :: Stms SOACS
In an occurrence of $dAliased_a1oc :: Aliased (Aliases SOACS)
Substitution: <InScope = {}
IdSubst = []
TvSubst = []
CvSubst = []>
*** Offending Program ***
Rec {
namesIntMap :: Names -> IntMap VName
[LclId]
namesIntMap
= \ (ds_d1xW :: Names) ->
let {
m_a12O :: IntMap VName
[LclId]
m_a12O = ds_d1xW `cast` (N:Names[0] :: Names ~R# IntMap VName) } in
m_a12O
namesToList :: Names -> [VName]
[LclId]
namesToList
= . @(IntMap VName) @[VName] @Names (elems @VName) namesIntMap
analyseStms
:: forall rep.
AliasedOp (OpC rep (Aliases rep)) =>
Stms rep -> (Map VName Names, Names)
[LclId]
analyseStms
= \ (@rep_a1cf)
($dAliasedOp_a1cg
:: AliasedOp (OpC rep_a1cf (Aliases rep_a1cf))) ->
let {
$dIP_a1xk :: HasCallStack
[LclId]
$dIP_a1xk
= emptyCallStack
`cast` (Sym (N:IP[0] <"callStack">_N <CallStack>_N)
:: CallStack ~R# (?callStack::CallStack)) } in
let {
$dIP_a1nY :: HasCallStack
[LclId]
$dIP_a1nY
= (pushCallStack
(unpackCString# "undefined"#,
SrcLoc
(unpackCString# "main"#)
(unpackCString# "Futhark.Optimise.Fusion.GraphRep"#)
(unpackCString# "Bug.hs"#)
(I# 40#)
(I# 15#)
(I# 40#)
(I# 24#))
($dIP_a1xk
`cast` (N:IP[0] <"callStack">_N <CallStack>_N
:: (?callStack::CallStack) ~R# CallStack)))
`cast` (Sym (N:IP[0] <"callStack">_N <CallStack>_N)
:: CallStack ~R# (?callStack::CallStack)) } in
undefined
@LiftedRep @(Stms rep_a1cf -> (Map VName Names, Names)) $dIP_a1nY
emptyGraph :: Stms SOACS -> [(Int, NodeT)]
[LclIdX]
emptyGraph
= \ (stms_a10c :: Stms SOACS) ->
let {
$dAliasedOp_a1ob :: AliasedOp (SOAC (Aliases SOACS))
[LclId]
$dAliasedOp_a1ob
= $fAliasedOpSOAC @(Aliases SOACS) $dAliased_a1oc } in
let {
$dAliased_a1oc :: Aliased (Aliases SOACS)
[LclId]
$dAliased_a1oc = $fAliasedAliases @SOACS $dAliasedOp_a1od } in
let {
$dAliasedOp_a1od :: AliasedOp (OpC SOACS (Aliases SOACS))
[LclId]
$dAliasedOp_a1od
= $dAliasedOp_a1ob
`cast` (Sub (Sym (AliasedOp (D:R:OpCSOACS[0] <Aliases SOACS>_N))_N)
:: AliasedOp (SOAC (Aliases SOACS))
~R# AliasedOp (OpC SOACS (Aliases SOACS))) } in
let {
$dAliasedOp_a1o5 :: AliasedOp (OpC SOACS (Aliases SOACS))
[LclId]
$dAliasedOp_a1o5
= $dAliasedOp_a1ob
`cast` (Sub (Sym (AliasedOp (D:R:OpCSOACS[0] <Aliases SOACS>_N))_N)
:: AliasedOp (SOAC (Aliases SOACS))
~R# AliasedOp (OpC SOACS (Aliases SOACS))) } in
let {
ds_d1y2 :: (Map VName Names, Names)
[LclId]
ds_d1y2 = analyseStms @SOACS $dAliasedOp_a1o5 stms_a10c } in
let {
_aliased_a1o8 :: Map VName Names
[LclId]
_aliased_a1o8
= case ds_d1y2 of wild_00 { (_aliased_a1o8, consumed_a1o9) ->
_aliased_a1o8
} } in
let {
consumed_a1o9 :: Names
[LclId]
consumed_a1o9
= case ds_d1y2 of wild_00 { (_aliased_a1o8, consumed_a1o9) ->
consumed_a1o9
} } in
let {
_aliased_a10f :: Map VName Names
[LclId]
_aliased_a10f = _aliased_a1o8 } in
let {
consumed_a10g :: Names
[LclId]
consumed_a10g = consumed_a1o9 } in
let {
inputnodes_a10e :: [NodeT]
[LclId]
inputnodes_a10e
= letrec {
inputnodes_a1ov :: [NodeT]
[LclId]
inputnodes_a1ov
= $ @LiftedRep
@LiftedRep
@[VName]
@[NodeT]
(map @VName @NodeT (\ (ds_d1y1 :: VName) -> FreeNode ds_d1y1))
(namesToList consumed_a10g); } in
inputnodes_a1ov } in
let {
labelNodes_a10d :: forall {b}. [b] -> [(Int, b)]
[LclId]
labelNodes_a10d
= \ (@b_a1oC) ->
let {
$dEnum_a1wN :: Enum Int
[LclId]
$dEnum_a1wN = $fEnumInt } in
let {
$dNum_a1s2 :: Num Int
[LclId]
$dNum_a1s2 = $fNumInt } in
letrec {
labelNodes_a1wO :: [b_a1oC] -> [(Int, b_a1oC)]
[LclId]
labelNodes_a1wO
= zip @Int @b_a1oC (enumFrom @Int $dEnum_a1wN (I# 0#)); } in
labelNodes_a1wO } in
labelNodes_a10d @NodeT inputnodes_a10e
$fRepTypesSOACS [InlPrag=CONLIKE] :: RepTypes SOACS
[LclIdX[DFunId], Unf=DFun: \ -> C:RepTypes TYPE: SOACS]
$fRepTypesSOACS = C:RepTypes @SOACS
$fAliasedOpSOAC [InlPrag=CONLIKE]
:: forall rep. Aliased rep => AliasedOp (SOAC rep)
[LclIdX[DFunId],
Unf=DFun: \ (@rep_a109) (v_B1 :: Aliased rep_a109) ->
C:AliasedOp TYPE: SOAC rep_a109]
$fAliasedOpSOAC
= \ (@rep_a1xa) ($dAliased_a1xb :: Aliased rep_a1xa) ->
C:AliasedOp @(SOAC rep_a1xa)
$fAliasedAliases [InlPrag=CONLIKE]
:: forall rep.
AliasedOp (OpC rep (Aliases rep)) =>
Aliased (Aliases rep)
[LclIdX[DFunId],
Unf=DFun: \ (@rep_a10a)
(v_B1 :: AliasedOp (OpC rep_a10a (Aliases rep_a10a))) ->
C:Aliased TYPE: Aliases rep_a10a]
$fAliasedAliases
= \ (@rep_a1xf)
($dAliasedOp_a1xg
:: AliasedOp (OpC rep_a1xf (Aliases rep_a1xf))) ->
C:Aliased @(Aliases rep_a1xf)
end Rec }
*** End of Offense ***
<no location info>: error:
Compilation had errors
<no location info>: error: ExitFailure 1If you omit -dcore-lint, then GHC will panic:
$ ~/Software/ghc-9.7.20230620/bin/ghc Bug.hs
[1 of 1] Compiling Futhark.Optimise.Fusion.GraphRep ( Bug.hs, Bug.o )
<no location info>: error:
panic! (the 'impossible' happened)
GHC version 9.7.20230620:
lookupIdSubst
$dAliased_a1oc
InScope {stms_a10c b_a1oC analyseStms namesToList $fAliasedAliases
$fAliasedOpSOAC $fRepTypesSOACS}
Call stack:
CallStack (from HasCallStack):
callStackDoc, called at compiler/GHC/Utils/Panic.hs:191:37 in ghc-9.7-inplace:GHC.Utils.Panic
pprPanic, called at compiler/GHC/Core/Subst.hs:197:17 in ghc-9.7-inplace:GHC.Core.Subst
CallStack (from HasCallStack):
panic, called at compiler/GHC/Utils/Error.hs:503:29 in ghc-9.7-inplace:GHC.Utils.Error
Please report this as a GHC bug: https://www.haskell.org/ghc/reportabugI was able to trigger these bug using a GHC HEAD build at commit 1464a2a8.