[Git][ghc/ghc][wip/T22471] Be more careful when reporting unbound RULE binders
Simon Peyton Jones (@simonpj)
gitlab at gitlab.haskell.org
Thu Nov 17 23:01:54 UTC 2022
Simon Peyton Jones pushed to branch wip/T22471 at Glasgow Haskell Compiler / GHC
Commits:
14381901 by Simon Peyton Jones at 2022-11-17T23:01:30+00:00
Be more careful when reporting unbound RULE binders
See Note [Variables unbound on the LHS] in GHC.HsToCore.Binds.
Fixes #22471.
- - - - -
7 changed files:
- compiler/GHC/Core/FVs.hs
- compiler/GHC/Core/Subst.hs
- compiler/GHC/HsToCore.hs
- compiler/GHC/HsToCore/Binds.hs
- compiler/GHC/Tc/Gen/Rule.hs
- + testsuite/tests/simplCore/should_compile/T22471.hs
- testsuite/tests/simplCore/should_compile/all.T
Changes:
=====================================
compiler/GHC/Core/FVs.hs
=====================================
@@ -36,7 +36,7 @@ module GHC.Core.FVs (
ruleLhsFreeIds, ruleLhsFreeIdsList,
ruleRhsFreeVars, rulesRhsFreeIds,
- expr_fvs,
+ exprFVs,
-- * Orphan names
orphNamesOfType, orphNamesOfCo, orphNamesOfAxiom,
=====================================
compiler/GHC/Core/Subst.hs
=====================================
@@ -577,7 +577,7 @@ substDVarSet subst@(Subst _ _ tv_env cv_env) fvs
= tyCoFVsOfCo fv_co (const True) emptyVarSet $! acc
| otherwise
, let fv_expr = lookupIdSubst subst fv
- = expr_fvs fv_expr isLocalVar emptyVarSet $! acc
+ = exprFVs fv_expr (const True) emptyVarSet $! acc
------------------
substTickish :: Subst -> CoreTickish -> CoreTickish
=====================================
compiler/GHC/HsToCore.hs
=====================================
@@ -48,7 +48,7 @@ import GHC.Core.Type
import GHC.Core.TyCo.Compare( eqType )
import GHC.Core.TyCon ( tyConDataCons )
import GHC.Core
-import GHC.Core.FVs ( exprsSomeFreeVarsList )
+import GHC.Core.FVs ( exprsSomeFreeVarsList, exprFreeVars )
import GHC.Core.SimpleOpt ( simpleOptPgm, simpleOptExpr )
import GHC.Core.Utils
import GHC.Core.Unfold.Make
@@ -463,7 +463,7 @@ dsRule (L loc (HsRule { rd_name = name
-- Substitute the dict bindings eagerly,
-- and take the body apart into a (f args) form
; dflags <- getDynFlags
- ; case decomposeRuleLhs dflags bndrs'' lhs'' of {
+ ; case decomposeRuleLhs dflags bndrs'' lhs'' (exprFreeVars rhs'') of {
Left msg -> do { diagnosticDs msg; return Nothing } ;
Right (final_bndrs, fn_id, args) -> do
=====================================
compiler/GHC/HsToCore/Binds.hs
=====================================
@@ -708,7 +708,7 @@ dsSpec mb_poly_rhs (L loc (SpecPrag poly_id spec_co spec_inl))
-- , text "spec_co:" <+> ppr spec_co
-- , text "ds_rhs:" <+> ppr ds_lhs ]) $
dflags <- getDynFlags
- ; case decomposeRuleLhs dflags spec_bndrs ds_lhs of {
+ ; case decomposeRuleLhs dflags spec_bndrs ds_lhs (mkVarSet spec_bndrs) of {
Left msg -> do { diagnosticDs msg; return Nothing } ;
Right (rule_bndrs, _fn, rule_lhs_args) -> do
@@ -835,6 +835,7 @@ SPEC f :: ty [n] INLINE [k]
-}
decomposeRuleLhs :: DynFlags -> [Var] -> CoreExpr
+ -> VarSet -- Free vars of the RHS
-> Either DsMessage ([Var], Id, [CoreExpr])
-- (decomposeRuleLhs bndrs lhs) takes apart the LHS of a RULE,
-- The 'bndrs' are the quantified binders of the rules, but decomposeRuleLhs
@@ -842,47 +843,63 @@ decomposeRuleLhs :: DynFlags -> [Var] -> CoreExpr
--
-- Returns an error message if the LHS isn't of the expected shape
-- Note [Decomposing the left-hand side of a RULE]
-decomposeRuleLhs dflags orig_bndrs orig_lhs
- | not (null unbound) -- Check for things unbound on LHS
- -- See Note [Unused spec binders]
- = Left (DsRuleBindersNotBound unbound orig_bndrs orig_lhs lhs2)
+decomposeRuleLhs dflags orig_bndrs orig_lhs rhs_fvs
| Var funId <- fun2
, Just con <- isDataConId_maybe funId
= Left (DsRuleIgnoredDueToConstructor con) -- See Note [No RULES on datacons]
- | Just (fn_id, args) <- decompose fun2 args2
- , let extra_bndrs = mk_extra_bndrs fn_id args
- = -- pprTrace "decomposeRuleLhs" (vcat [ text "orig_bndrs:" <+> ppr orig_bndrs
- -- , text "orig_lhs:" <+> ppr orig_lhs
- -- , text "lhs1:" <+> ppr lhs1
- -- , text "extra_bndrs:" <+> ppr extra_bndrs
- -- , text "fn_id:" <+> ppr fn_id
- -- , text "args:" <+> ppr args]) $
- Right (orig_bndrs ++ extra_bndrs, fn_id, args)
- | otherwise
+ | Nothing <- mb_lhs_app
= Left (DsRuleLhsTooComplicated orig_lhs lhs2)
+
+ | not (null unbound) -- Check for things unbound on LHS
+ -- See Note [Unused spec binders]
+ = -- pprTrace "decomposeRuleLhs 1" (vcat [ text "orig_bndrs:" <+> ppr orig_bndrs
+ -- , text "orig_lhs:" <+> ppr orig_lhs
+ -- , text "lhs_fvs:" <+> ppr lhs_fvs
+ -- , text "rhs_fvs:" <+> ppr rhs_fvs
+ -- , text "unbound:" <+> ppr unbound
+ -- ]) $
+ Left (DsRuleBindersNotBound unbound orig_bndrs orig_lhs lhs2)
+
+ | otherwise
+ = -- pprTrace "decomposeRuleLhs 2" (vcat [ text "orig_bndrs:" <+> ppr orig_bndrs
+ -- , text "orig_lhs:" <+> ppr orig_lhs
+ -- , text "lhs1:" <+> ppr lhs1
+ -- , text "extra_bndrs:" <+> ppr extra_bndrs
+ -- , text "fn_id:" <+> ppr fn_id
+ -- , text "args:" <+> ppr args
+ -- , text "args fvs:" <+> ppr (exprsFreeVarsList args)
+ -- ]) $
+ Right (trimmed_bndrs ++ extra_bndrs, fn_id, args)
+
where
- simpl_opts = initSimpleOpts dflags
+ simpl_opts = initSimpleOpts dflags
+ orig_bndr_set = mkVarSet orig_bndrs
+
lhs1 = drop_dicts orig_lhs
lhs2 = simpleOptExpr simpl_opts lhs1 -- See Note [Simplify rule LHS]
(fun2,args2) = collectArgs lhs2
- lhs_fvs = exprFreeVars lhs2
- unbound = filterOut (`elemVarSet` lhs_fvs) orig_bndrs
+ mb_lhs_app = decompose fun2 args2
+ Just (fn_id, args) = mb_lhs_app
- orig_bndr_set = mkVarSet orig_bndrs
+ -- See Note [Variables unbound on the LHS]
+ lhs_fvs = exprsFreeVars args
+ all_fvs = lhs_fvs `unionVarSet` rhs_fvs
+ trimmed_bndrs = filter (`elemVarSet` all_fvs) orig_bndrs
+ unbound = filterOut (`elemVarSet` lhs_fvs) trimmed_bndrs
+ -- Needed on RHS but not bound on LHS
-- Add extra tyvar binders: Note [Free tyvars on rule LHS]
-- and extra dict binders: Note [Free dictionaries on rule LHS]
- mk_extra_bndrs fn_id args
- = scopedSort unbound_tvs ++ unbound_dicts
+ extra_bndrs = scopedSort extra_tvs ++ extra_dicts
where
- unbound_tvs = [ v | v <- unbound_vars, isTyVar v ]
- unbound_dicts = [ mkLocalId (localiseName (idName d)) ManyTy (idType d)
- | d <- unbound_vars, isDictId d ]
- unbound_vars = [ v | v <- exprsFreeVarsList args
- , not (v `elemVarSet` orig_bndr_set)
- , not (v == fn_id) ]
+ extra_tvs = [ v | v <- extra_vars, isTyVar v ]
+ extra_dicts = [ mkLocalId (localiseName (idName d)) ManyTy (idType d)
+ | d <- extra_vars, isDictId d ]
+ extra_vars = [ v | v <- exprsFreeVarsList args
+ , not (v `elemVarSet` orig_bndr_set)
+ , not (v == fn_id) ]
-- fn_id: do not quantify over the function itself, which may
-- itself be a dictionary (in pathological cases, #10251)
@@ -926,6 +943,27 @@ decomposeRuleLhs dflags orig_bndrs orig_lhs
needed' = (needed `minusVarSet` rhs_fvs) `extendVarSet` d
{-
+Note [Variables unbound on the LHS]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+We obviously want to complain about
+ RULE forall x. f True = not x
+because the forall'd variable `x` is not bound on the LHS.
+
+It can be a bit delicate when dictionaries are involved.
+Consider #22471
+ {-# RULES "foo" forall (f :: forall a. [a] -> Int).
+ foo (\xs. 1 + f xs) = 2 + foo f #-}
+
+We get two dicts on the LHS, one from `1` and one from `+`.
+For reasons described in Note [The SimplifyRule Plan] in
+GHC.Tc.Gen.Rule, we quantify separately over those dictionaries:
+ forall f (d1::Num Int) (d2 :: Num Int).
+ foo (\xs. (+) d1 (fromInteger d2 1) xs) = ...
+
+Now the desugarer shortcircuits (fromInteger d2 1) to (I# 1); so d2 is
+not mentioned at all (on LHS or RHS)! We don't want to complain about
+and unbound d2. Hence the trimmed_bndrs.
+
Note [Decomposing the left-hand side of a RULE]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
There are several things going on here.
@@ -956,6 +994,9 @@ Moreover, we have to do something rather similar for dictionaries;
see Note [Free dictionaries on rule LHS]. So that's why we look for
type variables free on the LHS, and quantify over them.
+This relies on there not being any in-scope tyvars, which is true for
+user-defined RULEs, which are always top-level.
+
Note [Free dictionaries on rule LHS]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
When the LHS of a specialisation rule, (/\as\ds. f es) has a free dict,
=====================================
compiler/GHC/Tc/Gen/Rule.hs
=====================================
@@ -167,7 +167,8 @@ tcRule (HsRule { rd_ext = ext
, text "rule_ty:" <+> ppr rule_ty
, text "ty_bndrs:" <+> ppr ty_bndrs
, text "qtkvs ++ tpl_ids:" <+> ppr (qtkvs ++ tpl_ids)
- , vcat [ ppr id <+> dcolon <+> ppr (idType id) | id <- tpl_ids ]
+ , text "tpl_id info:" <+>
+ vcat [ ppr id <+> dcolon <+> ppr (idType id) | id <- tpl_ids ]
])
-- SimplfyRule Plan, step 5
=====================================
testsuite/tests/simplCore/should_compile/T22471.hs
=====================================
@@ -0,0 +1,13 @@
+{-# OPTIONS_GHC -Wno-inline-rule-shadowing #-}
+-- Otherwise we get stuff about (+) may inline, which is
+-- true enough, but not the point of this test
+
+module T22471 where
+
+foo :: (forall a. [a] -> Int) -> Int
+foo len = len [1,2,3] + len "abc"
+
+{-# RULES "foo" forall (f :: forall a. [a] -> Int).
+ foo (\xs -> 1 + f xs) = 2 + foo f #-}
+
+
=====================================
testsuite/tests/simplCore/should_compile/all.T
=====================================
@@ -437,6 +437,7 @@ test('T22097', [grep_errmsg(r'case.*wgoEven') ], multimod_compile, ['T22097', '-
test('T13873', [ grep_errmsg(r'SPEC') ], compile, ['-O -ddump-rules'])
test('T22357', normal, compile, ['-O'])
+test('T22471', normal, compile, ['-O'])
test('T22347', normal, compile, ['-O -fno-full-laziness'])
test('T22347a', normal, compile, ['-O2 -fno-full-laziness'])
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/143819010b69f00ac562a20543f6d0e96256c6cf
--
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/143819010b69f00ac562a20543f6d0e96256c6cf
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