[Git][ghc/ghc][wip/T18120] Fix specialisation for DFuns
Simon Peyton Jones
gitlab at gitlab.haskell.org
Fri May 1 14:20:15 UTC 2020
Simon Peyton Jones pushed to branch wip/T18120 at Glasgow Haskell Compiler / GHC
Commits:
a47b226c by Simon Peyton Jones at 2020-05-01T15:18:41+01:00
Fix specialisation for DFuns
When specialising a DFun we must take care to saturate the
unfolding. See Note [Specialising DFuns] in Specialise.
Fixes #18120
- - - - -
6 changed files:
- compiler/GHC/Core/Opt/Specialise.hs
- compiler/GHC/Core/Unfold.hs
- compiler/GHC/HsToCore/Binds.hs
- compiler/GHC/Tc/Gen/Sig.hs
- + testsuite/tests/simplCore/should_compile/T18120.hs
- testsuite/tests/simplCore/should_compile/all.T
Changes:
=====================================
compiler/GHC/Core/Opt/Specialise.hs
=====================================
@@ -1362,6 +1362,7 @@ specCalls mb_mod env existing_rules calls_for_me fn rhs
inl_prag = idInlinePragma fn
inl_act = inlinePragmaActivation inl_prag
is_local = isLocalId fn
+ is_dfun = isDFunId fn
-- Figure out whether the function has an INLINE pragma
-- See Note [Inline specialisations]
@@ -1384,22 +1385,34 @@ specCalls mb_mod env existing_rules calls_for_me fn rhs
spec_call :: SpecInfo -- Accumulating parameter
-> CallInfo -- Call instance
-> SpecM SpecInfo
- spec_call spec_acc@(rules_acc, pairs_acc, uds_acc) (CI { ci_key = call_args })
+ spec_call spec_acc@(rules_acc, pairs_acc, uds_acc) ci@(CI { ci_key = call_args })
= -- See Note [Specialising Calls]
- do { ( useful, rhs_env2, leftover_bndrs
+ do { let all_call_args | is_dfun = call_args ++ repeat UnspecArg
+ | otherwise = call_args
+ -- See Note [Specialising DFuns]
+ ; ( useful, rhs_env2, leftover_bndrs
, rule_bndrs, rule_lhs_args
- , spec_bndrs, dx_binds, spec_args) <- specHeader env rhs_bndrs call_args
+ , spec_bndrs1, dx_binds, spec_args) <- specHeader env rhs_bndrs all_call_args
+
+-- ; pprTrace "spec_call" (vcat [ text "call info: " <+> ppr ci
+-- , text "useful: " <+> ppr useful
+-- , text "rule_bndrs:" <+> ppr rule_bndrs
+-- , text "lhs_args: " <+> ppr rule_lhs_args
+-- , text "spec_bndrs:" <+> ppr spec_bndrs1
+-- , text "spec_args: " <+> ppr spec_args
+-- , text "dx_binds: " <+> ppr dx_binds
+-- , text "rhs_env2: " <+> ppr (se_subst rhs_env2)
+-- , ppr dx_binds ]) $
+-- return ()
; dflags <- getDynFlags
; if not useful -- No useful specialisation
|| already_covered dflags rules_acc rule_lhs_args
then return spec_acc
- else -- pprTrace "spec_call" (vcat [ ppr _call_info, ppr fn, ppr rhs_dict_ids
- -- , text "rhs_env2" <+> ppr (se_subst rhs_env2)
- -- , ppr dx_binds ]) $
+ else
do { -- Run the specialiser on the specialised RHS
-- The "1" suffix is before we maybe add the void arg
- ; (spec_rhs1, rhs_uds) <- specLam rhs_env2 (spec_bndrs ++ leftover_bndrs) rhs_body
+ ; (spec_rhs1, rhs_uds) <- specLam rhs_env2 (spec_bndrs1 ++ leftover_bndrs) rhs_body
; let spec_fn_ty1 = exprType spec_rhs1
-- Maybe add a void arg to the specialised function,
@@ -1407,14 +1420,13 @@ specCalls mb_mod env existing_rules calls_for_me fn rhs
-- See Note [Specialisations Must Be Lifted]
-- C.f. GHC.Core.Opt.WorkWrap.Utils.mkWorkerArgs
add_void_arg = isUnliftedType spec_fn_ty1 && not (isJoinId fn)
- (spec_rhs, spec_fn_ty, rule_rhs_args)
- | add_void_arg = ( Lam voidArgId spec_rhs1
- , mkVisFunTy voidPrimTy spec_fn_ty1
- , voidPrimId : spec_bndrs)
- | otherwise = (spec_rhs1, spec_fn_ty1, spec_bndrs)
-
- arity_decr = count isValArg rule_lhs_args - count isId rule_rhs_args
- join_arity_decr = length rule_lhs_args - length rule_rhs_args
+ (spec_bndrs, spec_rhs, spec_fn_ty)
+ | add_void_arg = ( voidPrimId : spec_bndrs1
+ , Lam voidArgId spec_rhs1
+ , mkVisFunTy voidPrimTy spec_fn_ty1)
+ | otherwise = (spec_bndrs1, spec_rhs1, spec_fn_ty1)
+
+ join_arity_decr = length rule_lhs_args - length spec_bndrs
spec_join_arity | Just orig_join_arity <- isJoinId_maybe fn
= Just (orig_join_arity - join_arity_decr)
| otherwise
@@ -1449,7 +1461,7 @@ specCalls mb_mod env existing_rules calls_for_me fn rhs
(idName fn)
rule_bndrs
rule_lhs_args
- (mkVarApps (Var spec_fn) rule_rhs_args)
+ (mkVarApps (Var spec_fn) spec_bndrs)
spec_rule
= case isJoinId_maybe fn of
@@ -1472,15 +1484,15 @@ specCalls mb_mod env existing_rules calls_for_me fn rhs
= (inl_prag { inl_inline = NoUserInline }, noUnfolding)
| otherwise
- = (inl_prag, specUnfolding dflags fn spec_bndrs spec_app arity_decr fn_unf)
-
- spec_app e = e `mkApps` spec_args
+ = (inl_prag, specUnfolding dflags spec_bndrs (`mkApps` spec_args)
+ rule_lhs_args fn_unf)
--------------------------------------
-- Adding arity information just propagates it a bit faster
-- See Note [Arity decrease] in GHC.Core.Opt.Simplify
-- Copy InlinePragma information from the parent Id.
-- So if f has INLINE[1] so does spec_fn
+ arity_decr = count isValArg rule_lhs_args - count isId spec_bndrs
spec_f_w_arity = spec_fn `setIdArity` max 0 (fn_arity - arity_decr)
`setInlinePragma` spec_inl_prag
`setIdUnfolding` spec_unf
@@ -1498,8 +1510,19 @@ specCalls mb_mod env existing_rules calls_for_me fn rhs
, spec_uds `plusUDs` uds_acc
) } }
-{- Note [Specialisation Must Preserve Sharing]
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+{- Note [Specialising DFuns]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+DFuns have a special sort of unfolding (DFunUnfolding), and these are
+hard to specialise a DFunUnfolding to give another DFunUnfolding
+unless the DFun is fully applied (#18120). So, in the case of DFunIds
+we simply extend the CallKey with trailing UnspecArgs, so we'll
+generate a rule that completely saturates the DFun.
+
+There is an ASSERT that checks this, in the DFunUnfolding case of
+GHC.Core.Unfold.specUnfolding.
+
+Note [Specialisation Must Preserve Sharing]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider a function:
f :: forall a. Eq a => a -> blah
@@ -2089,7 +2112,7 @@ isSpecDict _ = False
-- -- Specialised function helpers
-- , [c, i, x]
-- , [dShow1 = $dfShow dShowT2]
--- , [T1, T2, dEqT1, dShow1]
+-- , [T1, T2, c, i, dEqT1, dShow1]
-- )
specHeader
:: SpecEnv
@@ -2106,12 +2129,13 @@ specHeader
-- RULE helpers
, [OutBndr] -- Binders for the RULE
- , [CoreArg] -- Args for the LHS of the rule
+ , [OutExpr] -- Args for the LHS of the rule
-- Specialised function helpers
, [OutBndr] -- Binders for $sf
, [DictBind] -- Auxiliary dictionary bindings
, [OutExpr] -- Specialised arguments for unfolding
+ -- Same length as "args for LHS of rule"
)
-- We want to specialise on type 'T1', and so we must construct a substitution
=====================================
compiler/GHC/Core/Unfold.hs
=====================================
@@ -173,47 +173,47 @@ mkInlinableUnfolding dflags expr
where
expr' = simpleOptExpr dflags expr
-specUnfolding :: DynFlags -> Id -> [Var] -> (CoreExpr -> CoreExpr) -> Arity
+specUnfolding :: DynFlags
+ -> [Var] -> (CoreExpr -> CoreExpr)
+ -> [CoreArg] -- LHS arguments in the RULE
-> Unfolding -> Unfolding
-- See Note [Specialising unfoldings]
--- specUnfolding spec_bndrs spec_app arity_decrease unf
--- = \spec_bndrs. spec_app( unf )
+-- specUnfolding spec_bndrs spec_args unf
+-- = \spec_bndrs. unf spec_args
--
-specUnfolding dflags fn spec_bndrs spec_app arity_decrease
+specUnfolding dflags spec_bndrs spec_app rule_lhs_args
df@(DFunUnfolding { df_bndrs = old_bndrs, df_con = con, df_args = args })
- = ASSERT2( arity_decrease == count isId old_bndrs - count isId spec_bndrs
- , ppr df $$ ppr spec_bndrs $$ ppr (spec_app (Var fn)) $$ ppr arity_decrease )
+ = ASSERT2( rule_lhs_args `equalLength` old_bndrs
+ , ppr df $$ ppr rule_lhs_args )
+ -- For this ASSERT see Note [DFunUnfoldings] in GHC.Core.Opt.Specialise
mkDFunUnfolding spec_bndrs con (map spec_arg args)
- -- There is a hard-to-check assumption here that the spec_app has
- -- enough applications to exactly saturate the old_bndrs
-- For DFunUnfoldings we transform
- -- \old_bndrs. MkD <op1> ... <opn>
+ -- \obs. MkD <op1> ... <opn>
-- to
- -- \new_bndrs. MkD (spec_app(\old_bndrs. <op1>)) ... ditto <opn>
- -- The ASSERT checks the value part of that
+ -- \sbs. MkD ((\obs. <op1>) spec_args) ... ditto <opn>
where
- spec_arg arg = simpleOptExpr dflags (spec_app (mkLams old_bndrs arg))
+ spec_arg arg = simpleOptExpr dflags $
+ spec_app (mkLams old_bndrs arg)
-- The beta-redexes created by spec_app will be
-- simplified away by simplOptExpr
-specUnfolding dflags _ spec_bndrs spec_app arity_decrease
+specUnfolding dflags spec_bndrs spec_app rule_lhs_args
(CoreUnfolding { uf_src = src, uf_tmpl = tmpl
, uf_is_top = top_lvl
, uf_guidance = old_guidance })
| isStableSource src -- See Note [Specialising unfoldings]
- , UnfWhen { ug_arity = old_arity
- , ug_unsat_ok = unsat_ok
- , ug_boring_ok = boring_ok } <- old_guidance
- = let guidance = UnfWhen { ug_arity = old_arity - arity_decrease
- , ug_unsat_ok = unsat_ok
- , ug_boring_ok = boring_ok }
- new_tmpl = simpleOptExpr dflags (mkLams spec_bndrs (spec_app tmpl))
- -- The beta-redexes created by spec_app will be
- -- simplified away by simplOptExpr
+ , UnfWhen { ug_arity = old_arity } <- old_guidance
+ = mkCoreUnfolding src top_lvl new_tmpl
+ (old_guidance { ug_arity = old_arity - arity_decrease })
+ where
+ new_tmpl = simpleOptExpr dflags $
+ mkLams spec_bndrs $
+ spec_app tmpl -- The beta-redexes created by spec_app
+ -- will besimplified away by simplOptExpr
+ arity_decrease = count isValArg rule_lhs_args - count isId spec_bndrs
- in mkCoreUnfolding src top_lvl new_tmpl guidance
-specUnfolding _ _ _ _ _ _ = noUnfolding
+specUnfolding _ _ _ _ _ = noUnfolding
{- Note [Specialising unfoldings]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
=====================================
compiler/GHC/HsToCore/Binds.hs
=====================================
@@ -694,20 +694,19 @@ dsSpec mb_poly_rhs (L loc (SpecPrag poly_id spec_co spec_inl))
dflags <- getDynFlags
; case decomposeRuleLhs dflags spec_bndrs ds_lhs of {
Left msg -> do { warnDs NoReason msg; return Nothing } ;
- Right (rule_bndrs, _fn, args) -> do
+ Right (rule_bndrs, _fn, rule_lhs_args) -> do
{ this_mod <- getModule
; let fn_unf = realIdUnfolding poly_id
- spec_unf = specUnfolding dflags poly_id spec_bndrs core_app arity_decrease fn_unf
+ spec_unf = specUnfolding dflags spec_bndrs core_app rule_lhs_args fn_unf
spec_id = mkLocalId spec_name spec_ty
`setInlinePragma` inl_prag
`setIdUnfolding` spec_unf
- arity_decrease = count isValArg args - count isId spec_bndrs
; rule <- dsMkUserRule this_mod is_local_id
(mkFastString ("SPEC " ++ showPpr dflags poly_name))
rule_act poly_name
- rule_bndrs args
+ rule_bndrs rule_lhs_args
(mkVarApps (Var spec_id) spec_bndrs)
; let spec_rhs = mkLams spec_bndrs (core_app poly_rhs)
=====================================
compiler/GHC/Tc/Gen/Sig.hs
=====================================
@@ -634,7 +634,6 @@ to connect the two, something like
This wrapper is put in the TcSpecPrag, in the ABExport record of
the AbsBinds.
-
f :: (Eq a, Ix b) => a -> b -> Bool
{-# SPECIALISE f :: (Ix p, Ix q) => Int -> (p,q) -> Bool #-}
f = <poly_rhs>
@@ -662,8 +661,6 @@ Note that
* The RHS of f_spec, <poly_rhs> has a *copy* of 'binds', so that it
can fully specialise it.
-
-
From the TcSpecPrag, in GHC.HsToCore.Binds we generate a binding for f_spec and a RULE:
f_spec :: Int -> b -> Int
@@ -702,14 +699,14 @@ Some wrinkles
So we simply do this:
- Generate a constraint to check that the specialised type (after
- skolemiseation) is equal to the instantiated function type.
+ skolemisation) is equal to the instantiated function type.
- But *discard* the evidence (coercion) for that constraint,
so that we ultimately generate the simpler code
f_spec :: Int -> F Int
f_spec = <f rhs> Int dNumInt
RULE: forall d. f Int d = f_spec
- You can see this discarding happening in
+ You can see this discarding happening in tcSpecPrag
3. Note that the HsWrapper can transform *any* function with the right
type prefix
=====================================
testsuite/tests/simplCore/should_compile/T18120.hs
=====================================
@@ -0,0 +1,34 @@
+{-# LANGUAGE ConstraintKinds #-}
+{-# LANGUAGE DataKinds #-}
+{-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE PolyKinds #-}
+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE TypeOperators #-}
+{-# LANGUAGE UndecidableInstances #-}
+{-# LANGUAGE UndecidableSuperClasses #-}
+module Bug where
+
+import Data.Kind
+
+type family
+ AllF (c :: k -> Constraint) (xs :: [k]) :: Constraint where
+ AllF _c '[] = ()
+ AllF c (x ': xs) = (c x, All c xs)
+
+class (AllF c xs, SListI xs) => All (c :: k -> Constraint) (xs :: [k]) where
+instance All c '[] where
+instance (c x, All c xs) => All c (x ': xs) where
+
+class Top x
+instance Top x
+
+type SListI = All Top
+
+class All SListI (Code a) => Generic (a :: Type) where
+ type Code a :: [[Type]]
+
+data T = MkT Int
+instance Generic T where
+ type Code T = '[ '[Int] ]
=====================================
testsuite/tests/simplCore/should_compile/all.T
=====================================
@@ -318,3 +318,4 @@ test('T17966',
test('T17810', normal, multimod_compile, ['T17810', '-fspecialise-aggressively -dcore-lint -O -v0'])
test('T18013', normal, multimod_compile, ['T18013', '-v0 -O'])
test('T18098', normal, compile, ['-dcore-lint -O2'])
+test('T18120', normal, compile, ['-dcore-lint -O'])
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/a47b226c654d0125596f5f0c90b4958128aa558c
--
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/a47b226c654d0125596f5f0c90b4958128aa558c
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