[Git][ghc/ghc][wip/T22623] 2 commits: Fix shadowing lacuna in OccurAnal
Simon Peyton Jones (@simonpj)
gitlab at gitlab.haskell.org
Tue Dec 20 08:47:26 UTC 2022
Simon Peyton Jones pushed to branch wip/T22623 at Glasgow Haskell Compiler / GHC
Commits:
ba189bc7 by Simon Peyton Jones at 2022-12-20T08:47:17+00:00
Fix shadowing lacuna in OccurAnal
Issue #22623 demonstrated another lacuna in the implementation
of wrinkle (BS3) in Note [The binder-swap substitution] in
the occurrence analyser.
I was failing to add TyVar lambda binders using
addInScope/addOneInScope and that led to a totally bogus binder-swap
transformation.
Very easy to fix.
- - - - -
68144523 by Simon Peyton Jones at 2022-12-20T08:47:17+00:00
Fix an assertion check in addToEqualCtList
The old assertion saw that a constraint ct could rewrite itself
(of course it can) and complained (stupid).
Fixes #22645
- - - - -
9 changed files:
- compiler/GHC/Core/Opt/OccurAnal.hs
- compiler/GHC/Core/Opt/Simplify.hs
- compiler/GHC/Tc/Solver/Types.hs
- + testsuite/tests/simplCore/should_compile/T22623.hs
- + testsuite/tests/simplCore/should_compile/T22623a.hs
- testsuite/tests/simplCore/should_compile/all.T
- + testsuite/tests/typecheck/should_fail/T22645.hs
- + testsuite/tests/typecheck/should_fail/T22645.stderr
- testsuite/tests/typecheck/should_fail/all.T
Changes:
=====================================
compiler/GHC/Core/Opt/OccurAnal.hs
=====================================
@@ -1820,7 +1820,8 @@ occAnalLam :: OccEnv -> CoreExpr -> (WithUsageDetails CoreExpr)
occAnalLam env (Lam bndr expr)
| isTyVar bndr
- = let (WithUsageDetails usage expr') = occAnalLam env expr
+ = let env1 = addOneInScope env bndr
+ WithUsageDetails usage expr' = occAnalLam env1 expr
in WithUsageDetails usage (Lam bndr expr')
-- Important: Keep the 'env' unchanged so that with a RHS like
-- \(@ x) -> K @x (f @x)
@@ -2466,10 +2467,11 @@ data OccEnv
-- If x :-> (y, co) is in the env,
-- then please replace x by (y |> mco)
-- Invariant of course: idType x = exprType (y |> mco)
- , occ_bs_env :: !(VarEnv (OutId, MCoercion))
- , occ_bs_rng :: !VarSet -- Vars free in the range of occ_bs_env
+ , occ_bs_env :: !(IdEnv (OutId, MCoercion))
-- Domain is Global and Local Ids
-- Range is just Local Ids
+ , occ_bs_rng :: !VarSet
+ -- Vars (TyVars and Ids) free in the range of occ_bs_env
}
@@ -2546,14 +2548,15 @@ isRhsEnv (OccEnv { occ_encl = cxt }) = case cxt of
_ -> False
addOneInScope :: OccEnv -> CoreBndr -> OccEnv
+-- Needed for all Vars not just Ids
+-- See Note [The binder-swap substitution] (BS3)
addOneInScope env@(OccEnv { occ_bs_env = swap_env, occ_bs_rng = rng_vars }) bndr
| bndr `elemVarSet` rng_vars = env { occ_bs_env = emptyVarEnv, occ_bs_rng = emptyVarSet }
| otherwise = env { occ_bs_env = swap_env `delVarEnv` bndr }
addInScope :: OccEnv -> [Var] -> OccEnv
--- See Note [The binder-swap substitution]
--- It's only necessary to call this on in-scope Ids,
--- but harmless to include TyVars too
+-- Needed for all Vars not just Ids
+-- See Note [The binder-swap substitution] (BS3)
addInScope env@(OccEnv { occ_bs_env = swap_env, occ_bs_rng = rng_vars }) bndrs
| any (`elemVarSet` rng_vars) bndrs = env { occ_bs_env = emptyVarEnv, occ_bs_rng = emptyVarSet }
| otherwise = env { occ_bs_env = swap_env `delVarEnvList` bndrs }
@@ -2712,25 +2715,29 @@ Some tricky corners:
(BS3) We need care when shadowing. Suppose [x :-> b] is in occ_bs_env,
and we encounter:
- - \x. blah
- Here we want to delete the x-binding from occ_bs_env
-
- - \b. blah
- This is harder: we really want to delete all bindings that
- have 'b' free in the range. That is a bit tiresome to implement,
- so we compromise. We keep occ_bs_rng, which is the set of
- free vars of rng(occc_bs_env). If a binder shadows any of these
- variables, we discard all of occ_bs_env. Safe, if a bit
- brutal. NB, however: the simplifer de-shadows the code, so the
- next time around this won't happen.
+ (i) \x. blah
+ Here we want to delete the x-binding from occ_bs_env
+
+ (ii) \b. blah
+ This is harder: we really want to delete all bindings that
+ have 'b' free in the range. That is a bit tiresome to implement,
+ so we compromise. We keep occ_bs_rng, which is the set of
+ free vars of rng(occc_bs_env). If a binder shadows any of these
+ variables, we discard all of occ_bs_env. Safe, if a bit
+ brutal. NB, however: the simplifer de-shadows the code, so the
+ next time around this won't happen.
These checks are implemented in addInScope.
-
- The occurrence analyser itself does /not/ do cloning. It could, in
- principle, but it'd make it a bit more complicated and there is no
- great benefit. The simplifer uses cloning to get a no-shadowing
- situation, the care-when-shadowing behaviour above isn't needed for
- long.
+ (i) is needed only for Ids, but (ii) is needed for tyvars too (#22623)
+ because if occ_bs_env has [x :-> ...a...] where `a` is a tyvar, we
+ must not replace `x` by `...a...` under /\a. ...x..., or similarly
+ under a case pattern match that binds `a`.
+
+ An alternative would be for the occurrence analyser to do cloning as
+ it goes. In principle it could do so, but it'd make it a bit more
+ complicated and there is no great benefit. The simplifer uses
+ cloning to get a no-shadowing situation, the care-when-shadowing
+ behaviour above isn't needed for long.
(BS4) The domain of occ_bs_env can include GlobaIds. Eg
case M.foo of b { alts }
=====================================
compiler/GHC/Core/Opt/Simplify.hs
=====================================
@@ -132,7 +132,11 @@ data SimplifyOpts = SimplifyOpts
{ so_dump_core_sizes :: !Bool
, so_iterations :: !Int
, so_mode :: !SimplMode
+
, so_pass_result_cfg :: !(Maybe LintPassResultConfig)
+ -- Nothing => Do not Lint
+ -- Just cfg => Lint like this
+
, so_hpt_rules :: !RuleBase
, so_top_env_cfg :: !TopEnvConfig
}
=====================================
compiler/GHC/Tc/Solver/Types.hs
=====================================
@@ -273,21 +273,29 @@ addToEqualCtList ct old_eqs
| debugIsOn
= case ct of
CEqCan { cc_lhs = TyVarLHS tv } ->
- let shares_lhs (CEqCan { cc_lhs = TyVarLHS old_tv }) = tv == old_tv
- shares_lhs _other = False
- in
- assert (all shares_lhs old_eqs) $
- assert (null ([ (ct1, ct2) | ct1 <- ct : old_eqs
- , ct2 <- ct : old_eqs
- , let { fr1 = ctFlavourRole ct1
- ; fr2 = ctFlavourRole ct2 }
- , fr1 `eqCanRewriteFR` fr2 ])) $
+ assert (all (shares_lhs tv) old_eqs) $
+ assertPpr (null bad_prs)
+ (vcat [ text "bad_prs" <+> ppr bad_prs
+ , text "ct:old_eqs" <+> ppr (ct : old_eqs) ]) $
(ct : old_eqs)
_ -> pprPanic "addToEqualCtList not CEqCan" (ppr ct)
| otherwise
= ct : old_eqs
+ where
+ shares_lhs tv (CEqCan { cc_lhs = TyVarLHS old_tv }) = tv == old_tv
+ shares_lhs _ _ = False
+ bad_prs = filter is_bad_pair (distinctPairs (ct : old_eqs))
+ is_bad_pair (ct1,ct2) = ctFlavourRole ct1 `eqCanRewriteFR` ctFlavourRole ct2
+
+distinctPairs :: [a] -> [(a,a)]
+-- distinctPairs [x1,...xn] is the list of all pairs [ ...(xi, xj)...]
+-- where i /= j
+-- NB: does not return pairs (xi,xi), which would be stupid in the
+-- context of addToEqualCtList (#22645)
+distinctPairs [] = []
+distinctPairs (x:xs) = concatMap (\y -> [(x,y),(y,x)]) xs ++ distinctPairs xs
-- returns Nothing when the new list is empty, to keep the environments smaller
filterEqualCtList :: (Ct -> Bool) -> EqualCtList -> Maybe EqualCtList
=====================================
testsuite/tests/simplCore/should_compile/T22623.hs
=====================================
@@ -0,0 +1,34 @@
+{-# LANGUAGE GHC2021 #-}
+{-# LANGUAGE DataKinds #-}
+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE UndecidableInstances #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+
+module T22623 where
+
+import T22623a
+
+type BindNonEmptyList :: NonEmpty -> NonEmpty -> [Q]
+type family BindNonEmptyList (x :: NonEmpty) (y :: NonEmpty) :: [Q] where
+ BindNonEmptyList ('(:|) a as) c = Tail c ++ Foldr2 a c as
+
+sBindNonEmptyList ::
+ forall (t :: NonEmpty)
+ (c :: NonEmpty). SNonEmpty t -> SNonEmpty c -> SList (BindNonEmptyList t c :: [Q])
+sBindNonEmptyList
+ ((:%|) (sA :: SQ a) (sAs :: SList as)) (sC :: SNonEmpty c)
+ = let
+ sMyHead :: SNonEmpty c -> SQ (MyHead a c)
+ sMyHead ((:%|) x _) = x
+
+ sFoldr :: forall t. SList t -> SList (Foldr2 a c t)
+ sFoldr SNil = SNil
+ sFoldr (SCons _ sYs) = SCons (sMyHead sC) (sFoldr sYs)
+
+ sF :: Id (SLambda (ConstSym1 c))
+ sF = SLambda (const sC)
+
+ sBs :: SList (Tail c)
+ _ :%| sBs = applySing sF sA
+ in
+ sBs %++ sFoldr sAs
=====================================
testsuite/tests/simplCore/should_compile/T22623a.hs
=====================================
@@ -0,0 +1,60 @@
+{-# LANGUAGE GHC2021 #-}
+{-# LANGUAGE DataKinds #-}
+{-# LANGUAGE TypeFamilies #-}
+module T22623a where
+
+import Data.Kind
+
+type Id :: Type -> Type
+type family Id x
+type instance Id x = x
+
+data Q
+data SQ (x :: Q)
+
+data NonEmpty where
+ (:|) :: Q -> [Q] -> NonEmpty
+
+type Tail :: NonEmpty -> [Q]
+type family Tail y where
+ Tail ('(:|) _ y) = y
+type MyHead :: Q -> NonEmpty -> Q
+type family MyHead x y where
+ MyHead _ ('(:|) c _) = c
+
+type SList :: [Q] -> Type
+data SList z where
+ SNil :: SList '[]
+ SCons :: SQ x -> SList xs -> SList (x:xs)
+
+type SNonEmpty :: NonEmpty -> Type
+data SNonEmpty z where
+ (:%|) :: SQ x -> SList xs -> SNonEmpty (x :| xs)
+
+data TyFun
+type F = TyFun -> Type
+
+type Apply :: F -> Q -> NonEmpty
+type family Apply f x
+
+type ConstSym1 :: NonEmpty -> F
+data ConstSym1 (x :: NonEmpty) :: F
+type instance Apply (ConstSym1 x) _ = x
+
+type SLambda :: F -> Type
+newtype SLambda (f :: F) =
+ SLambda { applySing :: forall t. SQ t -> SNonEmpty (f `Apply` t) }
+
+type Foldr2 :: Q -> NonEmpty -> [Q] -> [Q]
+type family Foldr2 a c x where
+ Foldr2 _ _ '[] = '[]
+ Foldr2 a c (_:ys) = MyHead a c : Foldr2 a c ys
+
+type (++) :: [Q] -> [Q] -> [Q]
+type family (++) xs ys where
+ (++) '[] ys = ys
+ (++) ('(:) x xs) ys = '(:) x (xs ++ ys)
+
+(%++) :: forall (x :: [Q]) (y :: [Q]). SList x -> SList y -> SList (x ++ y)
+(%++) SNil sYs = sYs
+(%++) (SCons sX sXs) sYs = SCons sX (sXs %++ sYs)
=====================================
testsuite/tests/simplCore/should_compile/all.T
=====================================
@@ -458,3 +458,4 @@ test('T22494', [grep_errmsg(r'case') ], compile, ['-O -ddump-simpl -dsuppress-un
test('T22491', normal, compile, ['-O2'])
test('T21476', normal, compile, [''])
test('T22272', normal, multimod_compile, ['T22272', '-O -fexpose-all-unfoldings -fno-omit-interface-pragmas -fno-ignore-interface-pragmas'])
+test('T22623', normal, multimod_compile, ['T22623', '-O -v0'])
=====================================
testsuite/tests/typecheck/should_fail/T22645.hs
=====================================
@@ -0,0 +1,9 @@
+module T22645 where
+
+import Data.Coerce
+
+type T :: (* -> *) -> * -> *
+data T m a = MkT (m a)
+
+p :: Coercible a b => T Maybe a -> T Maybe b
+p = coerce
=====================================
testsuite/tests/typecheck/should_fail/T22645.stderr
=====================================
@@ -0,0 +1,15 @@
+
+T22645.hs:9:5: error: [GHC-25897]
+ • Couldn't match type ‘a’ with ‘b’ arising from a use of ‘coerce’
+ ‘a’ is a rigid type variable bound by
+ the type signature for:
+ p :: forall a b. Coercible a b => T Maybe a -> T Maybe b
+ at T22645.hs:8:1-44
+ ‘b’ is a rigid type variable bound by
+ the type signature for:
+ p :: forall a b. Coercible a b => T Maybe a -> T Maybe b
+ at T22645.hs:8:1-44
+ • In the expression: coerce
+ In an equation for ‘p’: p = coerce
+ • Relevant bindings include
+ p :: T Maybe a -> T Maybe b (bound at T22645.hs:9:1)
=====================================
testsuite/tests/typecheck/should_fail/all.T
=====================================
@@ -666,3 +666,4 @@ test('T21447', normal, compile_fail, [''])
test('T21530a', normal, compile_fail, [''])
test('T21530b', normal, compile_fail, [''])
test('T22570', normal, compile_fail, [''])
+test('T22645', normal, compile_fail, [''])
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/e3289d7e1e554b3c54dd605125b63930b606dd5a...68144523a0b5b7446808110abac4996b91ee2339
--
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/e3289d7e1e554b3c54dd605125b63930b606dd5a...68144523a0b5b7446808110abac4996b91ee2339
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