diff options
Diffstat (limited to 'compiler/GHC/Core/Subst.hs')
| -rw-r--r-- | compiler/GHC/Core/Subst.hs | 40 |
1 files changed, 32 insertions, 8 deletions
diff --git a/compiler/GHC/Core/Subst.hs b/compiler/GHC/Core/Subst.hs index 36f3bad0d4..be05e1c44c 100644 --- a/compiler/GHC/Core/Subst.hs +++ b/compiler/GHC/Core/Subst.hs @@ -14,7 +14,7 @@ module GHC.Core.Subst ( TvSubstEnv, IdSubstEnv, InScopeSet, -- ** Substituting into expressions and related types - deShadowBinds, substSpec, substRulesForImportedIds, + deShadowBinds, substRuleInfo, substRulesForImportedIds, substTy, substCo, substExpr, substExprSC, substBind, substBindSC, substUnfolding, substUnfoldingSC, lookupIdSubst, lookupTCvSubst, substIdType, substIdOcc, @@ -622,7 +622,7 @@ substIdType subst@(Subst _ _ tv_env cv_env) id substIdInfo :: Subst -> Id -> IdInfo -> Maybe IdInfo substIdInfo subst new_id info | nothing_to_do = Nothing - | otherwise = Just (info `setRuleInfo` substSpec subst new_id old_rules + | otherwise = Just (info `setRuleInfo` substRuleInfo subst new_id old_rules `setUnfoldingInfo` substUnfolding subst old_unf) where old_rules = ruleInfo info @@ -668,14 +668,13 @@ substIdOcc subst v = case lookupIdSubst subst v of other -> pprPanic "substIdOcc" (vcat [ppr v <+> ppr other, ppr subst]) ------------------ --- | Substitutes for the 'Id's within the 'WorkerInfo' given the new function 'Id' -substSpec :: Subst -> Id -> RuleInfo -> RuleInfo -substSpec subst new_id (RuleInfo rules rhs_fvs) - = seqRuleInfo new_spec `seq` new_spec +-- | Substitutes for the 'Id's within the 'RuleInfo' given the new function 'Id' +substRuleInfo :: Subst -> Id -> RuleInfo -> RuleInfo +substRuleInfo subst new_id (RuleInfo rules rhs_fvs) + = RuleInfo (map (substRule subst subst_ru_fn) rules) + (substDVarSet subst rhs_fvs) where subst_ru_fn = const (idName new_id) - new_spec = RuleInfo (map (substRule subst subst_ru_fn) rules) - (substDVarSet subst rhs_fvs) ------------------ substRulesForImportedIds :: Subst -> [CoreRule] -> [CoreRule] @@ -738,6 +737,31 @@ looked at the idInfo for 'f'; result <<loop>>. In any case we don't need to optimise the RHS of rules, or unfoldings, because the simplifier will do that. +Another place this went wrong was in `substRuleInfo`, which would immediately force +the lazy call to substExpr, which led to an infinite loop (as reported by #20112). + +This time the call stack looked something like: + +* `substRecBndrs` +* `substIdBndr` +* `substIdInfo` +* `substRuleInfo` +* `substRule` +* `substExpr` +* `mkTick` +* `isSaturatedConApp` +* Look at `IdInfo` for thing we are currently substituting because the rule is attached to `transpose` and mentions it in the `RHS` of the rule. + +and the rule was + +{-# RULES +"transpose/overlays1" forall xs. transpose (overlays1 xs) = overlays1 (fmap transpose xs) +#-} + +This rule was attached to `transpose`, but also mentions itself in the RHS so we have +to be careful to not force the `IdInfo` for transpose when dealing with the RHS of the rule. + + Note [substTickish] ~~~~~~~~~~~~~~~~~~~~~~ |