diff options
Diffstat (limited to 'compiler')
| -rw-r--r-- | compiler/GHC/Core/Opt/OccurAnal.hs | 34 |
1 files changed, 24 insertions, 10 deletions
diff --git a/compiler/GHC/Core/Opt/OccurAnal.hs b/compiler/GHC/Core/Opt/OccurAnal.hs index 901bc83077..5d31eb2cfd 100644 --- a/compiler/GHC/Core/Opt/OccurAnal.hs +++ b/compiler/GHC/Core/Opt/OccurAnal.hs @@ -869,14 +869,14 @@ occAnalRec env lvl (CyclicSCC details_s) (WithUsageDetails body_uds binds) (WithUsageDetails final_uds loop_breaker_nodes) = mkLoopBreakerNodes env lvl body_uds details_s ------------------------------ - active_rule_fvs :: VarSet - active_rule_fvs = mapUnionVarSet nd_active_rule_fvs details_s + weak_fvs :: VarSet + weak_fvs = mapUnionVarSet nd_weak_fvs details_s --------------------------- -- Now reconstruct the cycle pairs :: [(Id,CoreExpr)] - pairs | all_simple = reOrderNodes 0 active_rule_fvs loop_breaker_nodes [] - | otherwise = loopBreakNodes 0 active_rule_fvs loop_breaker_nodes [] + pairs | all_simple = reOrderNodes 0 weak_fvs loop_breaker_nodes [] + | otherwise = loopBreakNodes 0 weak_fvs loop_breaker_nodes [] -- In the common case when all are "simple" (no rules at all) -- the loop_breaker_nodes will include all the scope edges -- so a SCC computation would yield a single CyclicSCC result; @@ -966,8 +966,7 @@ There is a last nasty wrinkle. Suppose we have h = h_rhs g = h - ...more... - } + ...more... } Remember that we simplify the RULES before any RHS (see Note [Rules are visible in their own rec group] above). @@ -991,7 +990,11 @@ So q must remain in scope in the output program! We "solve" this by: Make q a "weak" loop breaker (OccInfo = IAmLoopBreaker True) - iff q is a mentioned in the RHS of an active RULE in the Rec group + iff q is a mentioned in the RHS of any RULE (active on not) + in the Rec group + +Note the "active or not" comment; even if a RULE is inactive, we +want its RHS free vars to stay alive (#20820)! A normal "strong" loop breaker has IAmLoopBreaker False. So: @@ -1007,8 +1010,8 @@ Annoyingly, since we simplify the rules *first* we'll never inline q into p's RULE. That trivial binding for q will hang around until we discard the rule. Yuk. But it's rare. - Note [Rules and loop breakers] -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Note [Rules and loop breakers] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ When we form the loop-breaker graph (Step 4 in Note [Recursive bindings: the grand plan]), we must be careful about RULEs. @@ -1028,7 +1031,7 @@ Hence, if h has a RULE that mentions f then we *must* choose f to be a loop breaker. Example: see Note -[Specialisation rules]. So out plan is this: +[Specialisation rules]. So our plan is this: Take the free variables of f's RHS, and augment it with all the variables reachable by a transitive sequence RULES from those @@ -1330,8 +1333,13 @@ data Details -- If all nodes are simple we don't need a loop-breaker -- dep-anal before reconstructing. + , nd_weak_fvs :: IdSet -- Variables bound in this Rec group that are free + -- in the RHS of any rule (active or not) for this bndr + -- See Note [Weak loop breakers] + , nd_active_rule_fvs :: IdSet -- Variables bound in this Rec group that are free -- in the RHS of an active rule for this bndr + -- See Note [Rules and loop breakers] , nd_score :: NodeScore } @@ -1375,6 +1383,7 @@ makeNode !env imp_rule_edges bndr_set (bndr, rhs) , nd_uds = scope_uds , nd_inl = inl_fvs , nd_simple = null rules_w_uds && null imp_rule_info + , nd_weak_fvs = weak_fvs , nd_active_rule_fvs = active_rule_fvs , nd_score = pprPanic "makeNodeDetails" (ppr bndr) } @@ -1431,6 +1440,7 @@ makeNode !env imp_rule_edges bndr_set (bndr, rhs) rule_uds = foldr add_rule_uds imp_rule_uds rules_w_uds add_rule_uds (_, l, r) uds = l `andUDs` r `andUDs` uds + -------- active_rule_fvs ------------ active_rule_fvs = foldr add_active_rule imp_rule_fvs rules_w_uds add_active_rule (rule, _, rhs_uds) fvs | is_active (ruleActivation rule) @@ -1438,6 +1448,10 @@ makeNode !env imp_rule_edges bndr_set (bndr, rhs) | otherwise = fvs + -------- weak_fvs ------------ + -- See Note [Weak loop breakers] + weak_fvs = foldr add_rule emptyVarSet rules_w_uds + add_rule (_, _, rhs_uds) fvs = udFreeVars bndr_set rhs_uds `unionVarSet` fvs mkLoopBreakerNodes :: OccEnv -> TopLevelFlag -> UsageDetails -- for BODY of let |