diff options
Diffstat (limited to 'compiler/simplCore/OccurAnal.hs')
| -rw-r--r-- | compiler/simplCore/OccurAnal.hs | 20 |
1 files changed, 18 insertions, 2 deletions
diff --git a/compiler/simplCore/OccurAnal.hs b/compiler/simplCore/OccurAnal.hs index b02ddc9540..52fa9d112c 100644 --- a/compiler/simplCore/OccurAnal.hs +++ b/compiler/simplCore/OccurAnal.hs @@ -56,10 +56,11 @@ Here's the externally-callable interface: -} occurAnalysePgm :: Module -- Used only in debug output + -> Bool -> (Activation -> Bool) -> [CoreRule] -> [CoreVect] -> VarSet -> CoreProgram -> CoreProgram -occurAnalysePgm this_mod active_rule imp_rules vects vectVars binds +occurAnalysePgm this_mod remove_dead active_rule imp_rules vects vectVars binds | isEmptyDetails final_usage = occ_anald_binds @@ -81,11 +82,16 @@ occurAnalysePgm this_mod active_rule imp_rules vects vectVars binds initial_uds = addManyOccsSet emptyDetails (rulesFreeVars imp_rules `unionVarSet` vectsFreeVars vects `unionVarSet` - vectVars) + vectVars `unionVarSet` + keepAliveVars) -- The RULES and VECTORISE declarations keep things alive! (For VECTORISE declarations, -- we only get them *until* the vectoriser runs. Afterwards, these dependencies are -- reflected in 'vectors' — see Note [Vectorisation declarations and occurrences].) + -- Note [Do not delete dead code in the desugarer] + keepAliveVars | remove_dead = emptyVarSet + | otherwise = mkVarSet $ concatMap bindersOf binds + -- Note [Preventing loops due to imported functions rules] imp_rule_edges = foldr (plusVarEnv_C unionVarSet) emptyVarEnv [ mapVarEnv (const maps_to) (exprFreeIds arg `delVarSetList` ru_bndrs imp_rule) @@ -2709,3 +2715,13 @@ andTailCallInfo :: TailCallInfo -> TailCallInfo -> TailCallInfo andTailCallInfo info@(AlwaysTailCalled arity1) (AlwaysTailCalled arity2) | arity1 == arity2 = info andTailCallInfo _ _ = NoTailCallInfo + +-- Note [Do not delete dead code in the desugarer] +-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +-- GHC plugins rightly want to access code that is maybe not exported and thus +-- “dead” from GHC's point of view. So we must not eliminate dead code before +-- the first time a user plugin had a chance to run. +-- +-- The desugarer runs the occurrence analyser; in that run we will add +-- all binders to the “body” of the module, thus preventing them from being +-- deleted or marked as dead. |