occurAnalysePgm, occurAnalyseExpr
) where
--- XXX This define is a bit of a hack, and should be done more nicely
-#define FAST_STRING_NOT_NEEDED 1
#include "HsVersions.h"
import CoreSyn
import CoreFVs
-import CoreUtils ( exprIsTrivial, isDefaultAlt )
+import CoreUtils ( exprIsTrivial, isDefaultAlt, isExpandableApp, mkCoerce )
import Id
-import IdInfo
+import NameEnv
+import NameSet
+import Name ( Name, localiseName )
import BasicTypes
+import Coercion
import VarSet
import VarEnv
+import Var
import Maybes ( orElse )
-import Digraph ( stronglyConnCompR, SCC(..) )
+import Digraph ( SCC(..), stronglyConnCompFromEdgedVerticesR )
import PrelNames ( buildIdKey, foldrIdKey, runSTRepIdKey, augmentIdKey )
-import Unique ( Unique )
-import UniqFM ( keysUFM, intersectUFM_C, foldUFM_Directly )
-import Util ( mapAndUnzip )
+import Unique
+import UniqFM
+import Util ( mapAndUnzip, filterOut )
+import Bag
import Outputable
-
+import FastString
import Data.List
\end{code}
Here's the externally-callable interface:
\begin{code}
-occurAnalysePgm :: [CoreBind] -> [CoreBind]
-occurAnalysePgm binds
- = snd (go initOccEnv binds)
+occurAnalysePgm :: Maybe (Activation -> Bool) -> [CoreRule]
+ -> [CoreBind] -> [CoreBind]
+occurAnalysePgm active_rule imp_rules binds
+ = snd (go (initOccEnv active_rule imp_rules) binds)
where
+ initial_uds = addIdOccs emptyDetails (rulesFreeVars imp_rules)
+ -- The RULES keep things alive!
+
go :: OccEnv -> [CoreBind] -> (UsageDetails, [CoreBind])
go _ []
- = (emptyDetails, [])
+ = (initial_uds, [])
go env (bind:binds)
= (final_usage, bind' ++ binds')
where
(bs_usage, binds') = go env binds
- (final_usage, bind') = occAnalBind env bind bs_usage
+ (final_usage, bind') = occAnalBind env env bind bs_usage
occurAnalyseExpr :: CoreExpr -> CoreExpr
-- Do occurrence analysis, and discard occurence info returned
-occurAnalyseExpr expr = snd (occAnal initOccEnv expr)
+occurAnalyseExpr expr
+ = snd (occAnal (initOccEnv all_active_rules []) expr)
+ where
+ -- To be conservative, we say that all inlines and rules are active
+ all_active_rules = Just (\_ -> True)
\end{code}
~~~~~~~~
\begin{code}
-occAnalBind :: OccEnv
+occAnalBind :: OccEnv -- The incoming OccEnv
+ -> OccEnv -- Same, but trimmed by (binderOf bind)
-> CoreBind
-> UsageDetails -- Usage details of scope
-> (UsageDetails, -- Of the whole let(rec)
[CoreBind])
-occAnalBind env (NonRec binder rhs) body_usage
- | not (binder `usedIn` body_usage) -- It's not mentioned
+occAnalBind env _ (NonRec binder rhs) body_usage
+ | isTyVar binder -- A type let; we don't gather usage info
+ = (body_usage, [NonRec binder rhs])
+
+ | not (binder `usedIn` body_usage) -- It's not mentioned
= (body_usage, [])
| otherwise -- It's mentioned in the body
- = (body_usage' +++ addRuleUsage rhs_usage binder, -- Note [Rules are extra RHSs]
- [NonRec tagged_binder rhs'])
+ = (body_usage' +++ rhs_usage3, [NonRec tagged_binder rhs'])
where
(body_usage', tagged_binder) = tagBinder body_usage binder
- (rhs_usage, rhs') = occAnalRhs env tagged_binder rhs
+ (rhs_usage1, rhs') = occAnalRhs env (Just tagged_binder) rhs
+ rhs_usage2 = addIdOccs rhs_usage1 (idUnfoldingVars binder)
+ rhs_usage3 = addIdOccs rhs_usage2 (idRuleVars binder)
+ -- See Note [Rules are extra RHSs] and Note [Rule dependency info]
\end{code}
Note [Dead code]
To that end, we build a Rec group for each cyclic strongly
connected component,
*treating f's rules as extra RHSs for 'f'*.
-
- When we make the Rec groups we include variables free in *either*
- LHS *or* RHS of the rule. The former might seems silly, but see
- Note [Rule dependency info].
-
- So in Example [eftInt], eftInt and eftIntFB will be put in the
- same Rec, even though their 'main' RHSs are both non-recursive.
+ More concretely, the SCC analysis runs on a graph with an edge
+ from f -> g iff g is mentioned in
+ (a) f's rhs
+ (b) f's RULES
+ These are rec_edges.
+
+ Under (b) we include variables free in *either* LHS *or* RHS of
+ the rule. The former might seems silly, but see Note [Rule
+ dependency info]. So in Example [eftInt], eftInt and eftIntFB
+ will be put in the same Rec, even though their 'main' RHSs are
+ both non-recursive.
* Note [Rules are visible in their own rec group]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We avoid infinite inlinings by choosing loop breakers, and
ensuring that a loop breaker cuts each loop. But what is a
- "loop"? In particular, a RULES is like an equation for 'f' that
- is *always* inlined if it are applicable. We do *not* disable
+ "loop"? In particular, a RULE is like an equation for 'f' that
+ is *always* inlined if it is applicable. We do *not* disable
rules for loop-breakers. It's up to whoever makes the rules to
- make sure that the rules themselves alwasys terminate. See Note
+ make sure that the rules themselves always terminate. See Note
[Rules for recursive functions] in Simplify.lhs
Hence, if
- f's RHS mentions g, and
+ f's RHS (or its INLINE template if it has one) mentions g, and
g has a RULE that mentions h, and
h has a RULE that mentions f
reachable by RULES from those starting points. That is the whole
reason for computing rule_fv_env in occAnalBind. (Of course we
only consider free vars that are also binders in this Rec group.)
+ See also Note [Finding rule RHS free vars]
Note that when we compute this rule_fv_env, we only consider variables
free in the *RHS* of the rule, in contrast to the way we build the
Rec group in the first place (Note [Rule dependency info])
+ Note that if 'g' has RHS that mentions 'w', we should add w to
+ g's loop-breaker edges. More concretely there is an edge from f -> g
+ iff
+ (a) g is mentioned in f's RHS
+ (b) h is mentioned in f's RHS, and
+ g appears in the RHS of a RULE of h
+ or a transitive sequence of rules starting with h
+
Note that in Example [eftInt], *neither* eftInt *nor* eftIntFB is
chosen as a loop breaker, because their RHSs don't mention each other.
And indeed both can be inlined safely.
rec_edges for the Rec block analysis
loop_breaker_edges for the loop breaker analysis
-
+ * Note [Finding rule RHS free vars]
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ Consider this real example from Data Parallel Haskell
+ tagZero :: Array Int -> Array Tag
+ {-# INLINE [1] tagZeroes #-}
+ tagZero xs = pmap (\x -> fromBool (x==0)) xs
+
+ {-# RULES "tagZero" [~1] forall xs n.
+ pmap fromBool <blah blah> = tagZero xs #-}
+ So tagZero's RHS mentions pmap, and pmap's RULE mentions tagZero.
+ However, tagZero can only be inlined in phase 1 and later, while
+ the RULE is only active *before* phase 1. So there's no problem.
+
+ To make this work, we look for the RHS free vars only for
+ *active* rules. That's the reason for the is_active argument
+ to idRhsRuleVars, and the occ_rule_act field of the OccEnv.
+
* Note [Weak loop breakers]
~~~~~~~~~~~~~~~~~~~~~~~~~
There is a last nasty wrinkle. Suppose we have
...more...
}
- Remmber that we simplify the RULES before any RHS (see Note
+ Remember that we simplify the RULES before any RHS (see Note
[Rules are visible in their own rec group] above).
So we must *not* postInlineUnconditionally 'g', even though
its RHS turns out to be trivial. (I'm assuming that 'g' is
- not choosen as a loop breaker.)
+ not choosen as a loop breaker.) Why not? Because then we
+ drop the binding for 'g', which leaves it out of scope in the
+ RULE!
We "solve" this by making g a "weak" or "rules-only" loop breaker,
with OccInfo = IAmLoopBreaker True. A normal "strong" loop breaker
has IAmLoopBreaker False. So
- Inline postInlineUnconditinoally
+ Inline postInlineUnconditionally
IAmLoopBreaker False no no
IAmLoopBreaker True yes no
other yes yes
* Note [Rule dependency info]
~~~~~~~~~~~~~~~~~~~~~~~~~~~
The VarSet in a SpecInfo is used for dependency analysis in the
- occurrence analyser. We must track free vars in *both* lhs and rhs. Why both?
- Consider
+ occurrence analyser. We must track free vars in *both* lhs and rhs.
+ Hence use of idRuleVars, rather than idRuleRhsVars in occAnalBind.
+ Why both? Consider
x = y
RULE f x = 4
Then if we substitute y for x, we'd better do so in the
rule's LHS too, so we'd better ensure the dependency is respected
+ * Note [Inline rules]
+ ~~~~~~~~~~~~~~~~~~~
+ None of the above stuff about RULES applies to Inline Rules,
+ stored in a CoreUnfolding. The unfolding, if any, is simplified
+ at the same time as the regular RHS of the function, so it should
+ be treated *exactly* like an extra RHS.
+
+ There is a danger that we'll be sub-optimal if we see this
+ f = ...f...
+ [INLINE f = ..no f...]
+ where f is recursive, but the INLINE is not. This can just about
+ happen with a sufficiently odd set of rules; eg
+
+ foo :: Int -> Int
+ {-# INLINE [1] foo #-}
+ foo x = x+1
+
+ bar :: Int -> Int
+ {-# INLINE [1] bar #-}
+ bar x = foo x + 1
+
+ {-# RULES "foo" [~1] forall x. foo x = bar x #-}
+
+ Here the RULE makes bar recursive; but it's INLINE pragma remains
+ non-recursive. It's tempting to then say that 'bar' should not be
+ a loop breaker, but an attempt to do so goes wrong in two ways:
+ a) We may get
+ $df = ...$cfoo...
+ $cfoo = ...$df....
+ [INLINE $cfoo = ...no-$df...]
+ But we want $cfoo to depend on $df explicitly so that we
+ put the bindings in the right order to inline $df in $cfoo
+ and perhaps break the loop altogether. (Maybe this
+ b)
+
+
+
Example [eftInt]
~~~~~~~~~~~~~~~
Example (from GHC.Enum):
\begin{code}
-occAnalBind env (Rec pairs) body_usage
- | not (any (`usedIn` body_usage) bndrs) -- NB: look at body_usage, not total_usage
- = (body_usage, []) -- Dead code
- | otherwise
- = (final_usage, map ({-# SCC "occAnalBind.dofinal" #-} do_final_bind) sccs)
+occAnalBind _ env (Rec pairs) body_usage
+ = foldr (occAnalRec env) (body_usage, []) sccs
+ -- For a recursive group, we
+ -- * occ-analyse all the RHSs
+ -- * compute strongly-connected components
+ -- * feed those components to occAnalRec
where
- bndrs = map fst pairs
- bndr_set = mkVarSet bndrs
-
- ---------------------------------------
- -- See Note [Loop breaking]
- ---------------------------------------
-
-------------Dependency analysis ------------------------------
- occ_anald :: [(Id, (UsageDetails, CoreExpr))]
- -- The UsageDetails here are strictly those arising from the RHS
- -- *not* from any rules in the Id
- occ_anald = [(bndr, occAnalRhs env bndr rhs) | (bndr,rhs) <- pairs]
-
- total_usage = foldl add_usage body_usage occ_anald
- add_usage body_usage (bndr, (rhs_usage, _))
- = body_usage +++ addRuleUsage rhs_usage bndr
-
- (final_usage, tagged_bndrs) = tagBinders total_usage bndrs
- final_bndrs | isEmptyVarSet all_rule_fvs = tagged_bndrs
- | otherwise = map tag_rule_var tagged_bndrs
-
- tag_rule_var bndr | bndr `elemVarSet` all_rule_fvs = makeLoopBreaker True bndr
- | otherwise = bndr
- all_rule_fvs = bndr_set `intersectVarSet` foldr (unionVarSet . idRuleVars) emptyVarSet bndrs
- -- Mark the binder with OccInfo saying "no preInlineUnconditionally" if
- -- it is used in any rule (lhs or rhs) of the recursive group
-
- ---- stuff for dependency analysis of binds -------------------------------
+ bndr_set = mkVarSet (map fst pairs)
+
sccs :: [SCC (Node Details)]
- sccs = {-# SCC "occAnalBind.scc" #-} stronglyConnCompR rec_edges
+ sccs = {-# SCC "occAnalBind.scc" #-} stronglyConnCompFromEdgedVerticesR rec_edges
- rec_edges :: [Node Details] -- The binders are tagged with correct occ-info
- rec_edges = {-# SCC "occAnalBind.assoc" #-} zipWith make_node final_bndrs occ_anald
- make_node tagged_bndr (_bndr, (rhs_usage, rhs))
- = ((tagged_bndr, rhs, rhs_fvs), idUnique tagged_bndr, out_edges)
+ rec_edges :: [Node Details]
+ rec_edges = {-# SCC "occAnalBind.assoc" #-} map make_node pairs
+
+ make_node (bndr, rhs)
+ = (details, varUnique bndr, keysUFM out_edges)
where
- rhs_fvs = intersectUFM_C (\b _ -> b) bndr_set rhs_usage
- out_edges = keysUFM (rhs_fvs `unionVarSet` idRuleVars tagged_bndr)
-
-
+ details = ND { nd_bndr = bndr, nd_rhs = rhs'
+ , nd_uds = rhs_usage3, nd_inl = inl_fvs}
+
+ (rhs_usage1, rhs') = occAnalRhs env Nothing rhs
+ rhs_usage2 = addIdOccs rhs_usage1 rule_fvs -- Note [Rules are extra RHSs]
+ rhs_usage3 = addIdOccs rhs_usage2 unf_fvs
+ unf = realIdUnfolding bndr -- Ignore any current loop-breaker flag
+ unf_fvs = stableUnfoldingVars unf
+ rule_fvs = idRuleVars bndr -- See Note [Rule dependency info]
+
+ inl_fvs = rhs_fvs `unionVarSet` unf_fvs
+ rhs_fvs = intersectUFM_C (\b _ -> b) bndr_set rhs_usage1
+ out_edges = intersectUFM_C (\b _ -> b) bndr_set rhs_usage3
-- (a -> b) means a mentions b
-- Given the usage details (a UFM that gives occ info for each free var of
-- the RHS) we can get the list of free vars -- or rather their Int keys --
-- which has n**2 cost, and this meant that edges_from alone
-- consumed 10% of total runtime!
- ---- Stuff to "re-constitute" bindings from dependency-analysis info ------
- do_final_bind (AcyclicSCC ((bndr, rhs, _), _, _)) = NonRec bndr rhs
- do_final_bind (CyclicSCC cycle)
- | no_rules = Rec (reOrderCycle cycle)
- | otherwise = Rec (concatMap reOrderRec (stronglyConnCompR loop_breaker_edges))
- where -- See Note [Choosing loop breakers] for looop_breker_edges
- loop_breaker_edges = map mk_node cycle
- mk_node (details@(_bndr, _rhs, rhs_fvs), k, _) = (details, k, new_ks)
- where
- new_ks = keysUFM (extendFvs rule_fv_env rhs_fvs rhs_fvs)
+-----------------------------
+occAnalRec :: OccEnv -> SCC (Node Details)
+ -> (UsageDetails, [CoreBind])
+ -> (UsageDetails, [CoreBind])
+
+ -- The NonRec case is just like a Let (NonRec ...) above
+occAnalRec _ (AcyclicSCC (ND { nd_bndr = bndr, nd_rhs = rhs, nd_uds = rhs_usage}, _, _))
+ (body_usage, binds)
+ | not (bndr `usedIn` body_usage)
+ = (body_usage, binds)
+
+ | otherwise -- It's mentioned in the body
+ = (body_usage' +++ rhs_usage,
+ NonRec tagged_bndr rhs : binds)
+ where
+ (body_usage', tagged_bndr) = tagBinder body_usage bndr
+
+
+ -- The Rec case is the interesting one
+ -- See Note [Loop breaking]
+occAnalRec env (CyclicSCC nodes) (body_usage, binds)
+ | not (any (`usedIn` body_usage) bndrs) -- NB: look at body_usage, not total_usage
+ = (body_usage, binds) -- Dead code
+
+ | otherwise -- At this point we always build a single Rec
+ = (final_usage, Rec pairs : binds)
+ where
+ bndrs = [b | (ND { nd_bndr = b }, _, _) <- nodes]
+ bndr_set = mkVarSet bndrs
+ non_boring bndr = isId bndr &&
+ (isStableUnfolding (realIdUnfolding bndr) || idHasRules bndr)
+
+ ----------------------------
+ -- Tag the binders with their occurrence info
+ total_usage = foldl add_usage body_usage nodes
+ add_usage usage_so_far (ND { nd_uds = rhs_usage }, _, _) = usage_so_far +++ rhs_usage
+ (final_usage, tagged_nodes) = mapAccumL tag_node total_usage nodes
+
+ tag_node :: UsageDetails -> Node Details -> (UsageDetails, Node Details)
+ -- (a) Tag the binders in the details with occ info
+ -- (b) Mark the binder with "weak loop-breaker" OccInfo
+ -- saying "no preInlineUnconditionally" if it is used
+ -- in any rule (lhs or rhs) of the recursive group
+ -- See Note [Weak loop breakers]
+ tag_node usage (details@ND { nd_bndr = bndr }, k, ks)
+ = (usage `delVarEnv` bndr, (details { nd_bndr = bndr2 }, k, ks))
+ where
+ bndr2 | bndr `elemVarSet` all_rule_fvs = makeLoopBreaker True bndr1
+ | otherwise = bndr1
+ bndr1 = setBinderOcc usage bndr
+ all_rule_fvs = bndr_set `intersectVarSet` foldr (unionVarSet . idRuleVars)
+ emptyVarSet bndrs
+
+ ----------------------------
+ -- Now reconstruct the cycle
+ pairs | any non_boring bndrs
+ = foldr (reOrderRec 0) [] $
+ stronglyConnCompFromEdgedVerticesR loop_breaker_edges
+ | otherwise
+ = reOrderCycle 0 tagged_nodes []
+
+ -- See Note [Choosing loop breakers] for loop_breaker_edges
+ loop_breaker_edges = map mk_node tagged_nodes
+ mk_node (details@(ND { nd_inl = inl_fvs }), k, _) = (details, k, new_ks)
+ where
+ new_ks = keysUFM (fst (extendFvs rule_fv_env inl_fvs))
------------------------------------
rule_fv_env :: IdEnv IdSet -- Variables from this group mentioned in RHS of rules
-- Domain is *subset* of bound vars (others have no rule fvs)
- rule_fv_env = rule_loop init_rule_fvs
-
- no_rules = null init_rule_fvs
- init_rule_fvs = [(b, rule_fvs)
- | b <- bndrs
- , let rule_fvs = idRuleRhsVars b `intersectVarSet` bndr_set
- , not (isEmptyVarSet rule_fvs)]
-
- rule_loop :: [(Id,IdSet)] -> IdEnv IdSet -- Finds fixpoint
- rule_loop fv_list
- | no_change = env
- | otherwise = rule_loop new_fv_list
- where
- env = mkVarEnv init_rule_fvs
- (no_change, new_fv_list) = mapAccumL bump True fv_list
- bump no_change (b,fvs)
- | new_fvs `subVarSet` fvs = (no_change, (b,fvs))
- | otherwise = (False, (b,new_fvs `unionVarSet` fvs))
- where
- new_fvs = extendFvs env emptyVarSet fvs
-
-idRuleRhsVars :: Id -> VarSet
--- Just the variables free on the *rhs* of a rule
--- See Note [Choosing loop breakers]
-idRuleRhsVars id = foldr (unionVarSet . ruleRhsFreeVars) emptyVarSet (idCoreRules id)
-
-extendFvs :: IdEnv IdSet -> IdSet -> IdSet -> IdSet
--- (extendFVs env fvs s) returns (fvs `union` env(s))
-extendFvs env fvs id_set
- = foldUFM_Directly add fvs id_set
- where
- add uniq _ fvs
- = case lookupVarEnv_Directly env uniq of
- Just fvs' -> fvs' `unionVarSet` fvs
- Nothing -> fvs
+ rule_fv_env = transClosureFV init_rule_fvs
+ init_rule_fvs
+ | Just is_active <- occ_rule_act env -- See Note [Finding rule RHS free vars]
+ = [ (b, rule_fvs)
+ | b <- bndrs
+ , isId b
+ , let rule_fvs = idRuleRhsVars is_active b
+ `intersectVarSet` bndr_set
+ , not (isEmptyVarSet rule_fvs)]
+ | otherwise
+ = []
\end{code}
@reOrderRec@ is applied to the list of (binder,rhs) pairs for a cyclic
\begin{code}
-type Node details = (details, Unique, [Unique]) -- The Ints are gotten from the Unique,
- -- which is gotten from the Id.
-type Details = (Id, -- Binder
- CoreExpr, -- RHS
- IdSet) -- RHS free vars (*not* include rules)
-
-reOrderRec :: SCC (Node Details)
- -> [(Id,CoreExpr)]
+type Node details = (details, Unique, [Unique]) -- The Ints are gotten from the Unique,
+ -- which is gotten from the Id.
+data Details
+ = ND { nd_bndr :: Id -- Binder
+ , nd_rhs :: CoreExpr -- RHS
+
+ , nd_uds :: UsageDetails -- Usage from RHS,
+ -- including RULES and InlineRule unfolding
+
+ , nd_inl :: IdSet -- Other binders *from this Rec group* mentioned in
+ } -- its InlineRule unfolding (if present)
+ -- AND the RHS
+ -- but *excluding* any RULES
+ -- This is the IdSet that may be used if the Id is inlined
+
+reOrderRec :: Int -> SCC (Node Details)
+ -> [(Id,CoreExpr)] -> [(Id,CoreExpr)]
-- Sorted into a plausible order. Enough of the Ids have
-- IAmALoopBreaker pragmas that there are no loops left.
-reOrderRec (AcyclicSCC ((bndr, rhs, _), _, _)) = [(bndr, rhs)]
-reOrderRec (CyclicSCC cycle) = reOrderCycle cycle
+reOrderRec _ (AcyclicSCC (ND { nd_bndr = bndr, nd_rhs = rhs }, _, _))
+ pairs = (bndr, rhs) : pairs
+reOrderRec depth (CyclicSCC cycle) pairs = reOrderCycle depth cycle pairs
-reOrderCycle :: [Node Details] -> [(Id,CoreExpr)]
-reOrderCycle []
+reOrderCycle :: Int -> [Node Details] -> [(Id,CoreExpr)] -> [(Id,CoreExpr)]
+reOrderCycle _ [] _
= panic "reOrderCycle"
-reOrderCycle [bind] -- Common case of simple self-recursion
- = [(makeLoopBreaker False bndr, rhs)]
- where
- ((bndr, rhs, _), _, _) = bind
+reOrderCycle _ [(ND { nd_bndr = bndr, nd_rhs = rhs }, _, _)] pairs
+ = -- Common case of simple self-recursion
+ (makeLoopBreaker False bndr, rhs) : pairs
-reOrderCycle (bind : binds)
+reOrderCycle depth (bind : binds) pairs
= -- Choose a loop breaker, mark it no-inline,
-- do SCC analysis on the rest, and recursively sort them out
- concatMap reOrderRec (stronglyConnCompR unchosen) ++
- [(makeLoopBreaker False bndr, rhs)]
-
+-- pprTrace "reOrderCycle" (ppr [b | (ND { nd_bndr = b }, _, _) <- bind:binds]) $
+ foldr (reOrderRec new_depth)
+ ([ (makeLoopBreaker False bndr, rhs)
+ | (ND { nd_bndr = bndr, nd_rhs = rhs }, _, _) <- chosen_binds] ++ pairs)
+ (stronglyConnCompFromEdgedVerticesR unchosen)
where
- (chosen_bind, unchosen) = choose_loop_breaker bind (score bind) [] binds
- (bndr, rhs, _) = chosen_bind
+ (chosen_binds, unchosen) = choose_loop_breaker [bind] (score bind) [] binds
+
+ approximate_loop_breaker = depth >= 2
+ new_depth | approximate_loop_breaker = 0
+ | otherwise = depth+1
+ -- After two iterations (d=0, d=1) give up
+ -- and approximate, returning to d=0
-- This loop looks for the bind with the lowest score
-- to pick as the loop breaker. The rest accumulate in
- choose_loop_breaker (details,_,_) _loop_sc acc []
- = (details, acc) -- Done
+ choose_loop_breaker loop_binds _loop_sc acc []
+ = (loop_binds, acc) -- Done
- choose_loop_breaker loop_bind loop_sc acc (bind : binds)
+ -- If approximate_loop_breaker is True, we pick *all*
+ -- nodes with lowest score, else just one
+ -- See Note [Complexity of loop breaking]
+ choose_loop_breaker loop_binds loop_sc acc (bind : binds)
| sc < loop_sc -- Lower score so pick this new one
- = choose_loop_breaker bind sc (loop_bind : acc) binds
+ = choose_loop_breaker [bind] sc (loop_binds ++ acc) binds
- | otherwise -- No lower so don't pick it
- = choose_loop_breaker loop_bind loop_sc (bind : acc) binds
+ | approximate_loop_breaker && sc == loop_sc
+ = choose_loop_breaker (bind : loop_binds) loop_sc acc binds
+
+ | otherwise -- Higher score so don't pick it
+ = choose_loop_breaker loop_binds loop_sc (bind : acc) binds
where
sc = score bind
score :: Node Details -> Int -- Higher score => less likely to be picked as loop breaker
- score ((bndr, rhs, _), _, _)
- | workerExists (idWorkerInfo bndr) = 10
- -- Note [Worker inline loop]
-
- | exprIsTrivial rhs = 4 -- Practically certain to be inlined
+ score (ND { nd_bndr = bndr, nd_rhs = rhs }, _, _)
+ | not (isId bndr) = 100 -- A type or cercion variable is never a loop breaker
+
+ | isDFunId bndr = 9 -- Never choose a DFun as a loop breaker
+ -- Note [DFuns should not be loop breakers]
+
+ | Just inl_source <- isStableCoreUnfolding_maybe (idUnfolding bndr)
+ = case inl_source of
+ InlineWrapper {} -> 10 -- Note [INLINE pragmas]
+ _other -> 3 -- Data structures are more important than this
+ -- so that dictionary/method recursion unravels
+ -- Note that this case hits all InlineRule things, so we
+ -- never look at 'rhs for InlineRule stuff. That's right, because
+ -- 'rhs' is irrelevant for inlining things with an InlineRule
+
+ | is_con_app rhs = 5 -- Data types help with cases: Note [Constructor applications]
+
+ | exprIsTrivial rhs = 10 -- Practically certain to be inlined
-- Used to have also: && not (isExportedId bndr)
-- But I found this sometimes cost an extra iteration when we have
-- rec { d = (a,b); a = ...df...; b = ...df...; df = d }
-- where df is the exported dictionary. Then df makes a really
-- bad choice for loop breaker
- | is_con_app rhs = 2 -- Data types help with cases
- -- Note [conapp]
+
+-- If an Id is marked "never inline" then it makes a great loop breaker
+-- The only reason for not checking that here is that it is rare
+-- and I've never seen a situation where it makes a difference,
+-- so it probably isn't worth the time to test on every binder
+-- | isNeverActive (idInlinePragma bndr) = -10
- | inlineCandidate bndr rhs = 1 -- Likely to be inlined
- -- Note [Inline candidates]
+ | isOneOcc (idOccInfo bndr) = 2 -- Likely to be inlined
- | otherwise = 0
-
- inlineCandidate :: Id -> CoreExpr -> Bool
- inlineCandidate _ (Note InlineMe _) = True
- inlineCandidate id _ = isOneOcc (idOccInfo id)
+ | canUnfold (realIdUnfolding bndr) = 1
+ -- The Id has some kind of unfolding
+ -- Ignore loop-breaker-ness here because that is what we are setting!
- -- Note [conapp]
- --
- -- It's really really important to inline dictionaries. Real
- -- example (the Enum Ordering instance from GHC.Base):
- --
- -- rec f = \ x -> case d of (p,q,r) -> p x
- -- g = \ x -> case d of (p,q,r) -> q x
- -- d = (v, f, g)
- --
- -- Here, f and g occur just once; but we can't inline them into d.
- -- On the other hand we *could* simplify those case expressions if
- -- we didn't stupidly choose d as the loop breaker.
- -- But we won't because constructor args are marked "Many".
- -- Inlining dictionaries is really essential to unravelling
- -- the loops in static numeric dictionaries, see GHC.Float.
+ | otherwise = 0
+ -- Checking for a constructor application
-- Cheap and cheerful; the simplifer moves casts out of the way
-- The lambda case is important to spot x = /\a. C (f a)
-- which comes up when C is a dictionary constructor and
--
-- However we *also* treat (\x. C p q) as a con-app-like thing,
-- Note [Closure conversion]
- is_con_app (Var v) = isDataConWorkId v
+ is_con_app (Var v) = isConLikeId v
is_con_app (App f _) = is_con_app f
is_con_app (Lam _ e) = is_con_app e
is_con_app (Note _ e) = is_con_app e
is_con_app _ = False
makeLoopBreaker :: Bool -> Id -> Id
--- Set the loop-breaker flag
--- See Note [Weak loop breakers]
-makeLoopBreaker weak bndr = setIdOccInfo bndr (IAmALoopBreaker weak)
+-- Set the loop-breaker flag: see Note [Weak loop breakers]
+makeLoopBreaker weak bndr
+ = ASSERT2( isId bndr, ppr bndr ) setIdOccInfo bndr (IAmALoopBreaker weak)
\end{code}
-Note [Worker inline loop]
-~~~~~~~~~~~~~~~~~~~~~~~~
-Never choose a wrapper as the loop breaker! Because
-wrappers get auto-generated inlinings when importing, and
-that can lead to an infinite inlining loop. For example:
+Note [Complexity of loop breaking]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The loop-breaking algorithm knocks out one binder at a time, and
+performs a new SCC analysis on the remaining binders. That can
+behave very badly in tightly-coupled groups of bindings; in the
+worst case it can be (N**2)*log N, because it does a full SCC
+on N, then N-1, then N-2 and so on.
+
+To avoid this, we switch plans after 2 (or whatever) attempts:
+ Plan A: pick one binder with the lowest score, make it
+ a loop breaker, and try again
+ Plan B: pick *all* binders with the lowest score, make them
+ all loop breakers, and try again
+Since there are only a small finite number of scores, this will
+terminate in a constant number of iterations, rather than O(N)
+iterations.
+
+You might thing that it's very unlikely, but RULES make it much
+more likely. Here's a real example from Trac #1969:
+ Rec { $dm = \d.\x. op d
+ {-# RULES forall d. $dm Int d = $s$dm1
+ forall d. $dm Bool d = $s$dm2 #-}
+
+ dInt = MkD .... opInt ...
+ dInt = MkD .... opBool ...
+ opInt = $dm dInt
+ opBool = $dm dBool
+
+ $s$dm1 = \x. op dInt
+ $s$dm2 = \x. op dBool }
+The RULES stuff means that we can't choose $dm as a loop breaker
+(Note [Choosing loop breakers]), so we must choose at least (say)
+opInt *and* opBool, and so on. The number of loop breakders is
+linear in the number of instance declarations.
+
+Note [INLINE pragmas]
+~~~~~~~~~~~~~~~~~~~~~
+Avoid choosing a function with an INLINE pramga as the loop breaker!
+If such a function is mutually-recursive with a non-INLINE thing,
+then the latter should be the loop-breaker.
+
+Usually this is just a question of optimisation. But a particularly
+bad case is wrappers generated by the demand analyser: if you make
+then into a loop breaker you may get an infinite inlining loop. For
+example:
rec {
$wfoo x = ....foo x....
{-loop brk-} foo x = ...$wfoo x...
}
-
The interface file sees the unfolding for $wfoo, and sees that foo is
strict (and hence it gets an auto-generated wrapper). Result: an
infinite inlining in the importing scope. So be a bit careful if you
change this. A good example is Tree.repTree in
nofib/spectral/minimax. If the repTree wrapper is chosen as the loop
-breaker then compiling Game.hs goes into an infinite loop (this
-happened when we gave is_con_app a lower score than inline candidates).
+breaker then compiling Game.hs goes into an infinite loop. This
+happened when we gave is_con_app a lower score than inline candidates:
+
+ Tree.repTree
+ = __inline_me (/\a. \w w1 w2 ->
+ case Tree.$wrepTree @ a w w1 w2 of
+ { (# ww1, ww2 #) -> Branch @ a ww1 ww2 })
+ Tree.$wrepTree
+ = /\a w w1 w2 ->
+ (# w2_smP, map a (Tree a) (Tree.repTree a w1 w) (w w2) #)
+
+Here we do *not* want to choose 'repTree' as the loop breaker.
+
+Note [DFuns should not be loop breakers]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+It's particularly bad to make a DFun into a loop breaker. See
+Note [How instance declarations are translated] in TcInstDcls
+
+We give DFuns a higher score than ordinary CONLIKE things because
+if there's a choice we want the DFun to be the non-looop breker. Eg
+
+rec { sc = /\ a \$dC. $fBWrap (T a) ($fCT @ a $dC)
+
+ $fCT :: forall a_afE. (Roman.C a_afE) => Roman.C (Roman.T a_afE)
+ {-# DFUN #-}
+ $fCT = /\a \$dC. MkD (T a) ((sc @ a $dC) |> blah) ($ctoF @ a $dC)
+ }
+
+Here 'sc' (the superclass) looks CONLIKE, but we'll never get to it
+if we can't unravel the DFun first.
+
+Note [Constructor applications]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+It's really really important to inline dictionaries. Real
+example (the Enum Ordering instance from GHC.Base):
+
+ rec f = \ x -> case d of (p,q,r) -> p x
+ g = \ x -> case d of (p,q,r) -> q x
+ d = (v, f, g)
+
+Here, f and g occur just once; but we can't inline them into d.
+On the other hand we *could* simplify those case expressions if
+we didn't stupidly choose d as the loop breaker.
+But we won't because constructor args are marked "Many".
+Inlining dictionaries is really essential to unravelling
+the loops in static numeric dictionaries, see GHC.Float.
Note [Closure conversion]
~~~~~~~~~~~~~~~~~~~~~~~~~
\begin{code}
occAnalRhs :: OccEnv
- -> Id -> CoreExpr -- Binder and rhs
- -- For non-recs the binder is alrady tagged
- -- with occurrence info
+ -> Maybe Id -> CoreExpr -- Binder and rhs
+ -- Just b => non-rec, and alrady tagged with occurrence info
+ -- Nothing => Rec, no occ info
-> (UsageDetails, CoreExpr)
-
-occAnalRhs env id rhs
+ -- Returned usage details covers only the RHS,
+ -- and *not* the RULE or INLINE template for the Id
+occAnalRhs env mb_bndr rhs
= occAnal ctxt rhs
where
- ctxt | certainly_inline id = env
- | otherwise = rhsCtxt
- -- Note that we generally use an rhsCtxt. This tells the occ anal n
- -- that it's looking at an RHS, which has an effect in occAnalApp
- --
- -- But there's a problem. Consider
- -- x1 = a0 : []
- -- x2 = a1 : x1
- -- x3 = a2 : x2
- -- g = f x3
- -- First time round, it looks as if x1 and x2 occur as an arg of a
- -- let-bound constructor ==> give them a many-occurrence.
- -- But then x3 is inlined (unconditionally as it happens) and
- -- next time round, x2 will be, and the next time round x1 will be
- -- Result: multiple simplifier iterations. Sigh.
- -- Crude solution: use rhsCtxt for things that occur just once...
-
- certainly_inline id = case idOccInfo id of
- OneOcc in_lam one_br _ -> not in_lam && one_br
- _ -> False
-\end{code}
-
-
-
-\begin{code}
-addRuleUsage :: UsageDetails -> Id -> UsageDetails
--- Add the usage from RULES in Id to the usage
-addRuleUsage usage id
- = foldVarSet add usage (idRuleVars id)
+ -- See Note [Cascading inlines]
+ ctxt = case mb_bndr of
+ Just b | certainly_inline b -> env
+ _other -> rhsCtxt env
+
+ certainly_inline bndr -- See Note [Cascading inlines]
+ = case idOccInfo bndr of
+ OneOcc in_lam one_br _ -> not in_lam && one_br && active && not_stable
+ _ -> False
+ where
+ active = isAlwaysActive (idInlineActivation bndr)
+ not_stable = not (isStableUnfolding (idUnfolding bndr))
+
+addIdOccs :: UsageDetails -> VarSet -> UsageDetails
+addIdOccs usage id_set = foldVarSet add usage id_set
where
- add v u = addOneOcc u v NoOccInfo -- Give a non-committal binder info
- -- (i.e manyOcc) because many copies
- -- of the specialised thing can appear
+ add v u | isId v = addOneOcc u v NoOccInfo
+ | otherwise = u
+ -- Give a non-committal binder info (i.e NoOccInfo) because
+ -- a) Many copies of the specialised thing can appear
+ -- b) We don't want to substitute a BIG expression inside a RULE
+ -- even if that's the only occurrence of the thing
+ -- (Same goes for INLINE.)
\end{code}
+Note [Cascading inlines]
+~~~~~~~~~~~~~~~~~~~~~~~~
+By default we use an rhsCtxt for the RHS of a binding. This tells the
+occ anal n that it's looking at an RHS, which has an effect in
+occAnalApp. In particular, for constructor applications, it makes
+the arguments appear to have NoOccInfo, so that we don't inline into
+them. Thus x = f y
+ k = Just x
+we do not want to inline x.
+
+But there's a problem. Consider
+ x1 = a0 : []
+ x2 = a1 : x1
+ x3 = a2 : x2
+ g = f x3
+First time round, it looks as if x1 and x2 occur as an arg of a
+let-bound constructor ==> give them a many-occurrence.
+But then x3 is inlined (unconditionally as it happens) and
+next time round, x2 will be, and the next time round x1 will be
+Result: multiple simplifier iterations. Sigh.
+
+So, when analysing the RHS of x3 we notice that x3 will itself
+definitely inline the next time round, and so we analyse x3's rhs in
+an ordinary context, not rhsCtxt. Hence the "certainly_inline" stuff.
+
+Annoyingly, we have to approximiate SimplUtils.preInlineUnconditionally.
+If we say "yes" when preInlineUnconditionally says "no" the simplifier iterates
+indefinitely:
+ x = f y
+ k = Just x
+inline ==>
+ k = Just (f y)
+float ==>
+ x1 = f y
+ k = Just x1
+
+This is worse than the slow cascade, so we only want to say "certainly_inline"
+if it really is certain. Look at the note with preInlineUnconditionally
+for the various clauses.
+
Expressions
~~~~~~~~~~~
\begin{code}
-> (UsageDetails, -- Gives info only about the "interesting" Ids
CoreExpr)
-occAnal _ (Type t) = (emptyDetails, Type t)
-occAnal env (Var v) = (mkOneOcc env v False, Var v)
+occAnal _ expr@(Type _) = (emptyDetails, expr)
+occAnal _ expr@(Lit _) = (emptyDetails, expr)
+occAnal env expr@(Var v) = (mkOneOcc env v False, expr)
-- At one stage, I gathered the idRuleVars for v here too,
-- which in a way is the right thing to do.
-- But that went wrong right after specialisation, when
-- the *occurrences* of the overloaded function didn't have any
-- rules in them, so the *specialised* versions looked as if they
-- weren't used at all.
-\end{code}
-
-We regard variables that occur as constructor arguments as "dangerousToDup":
-\begin{verbatim}
-module A where
-f x = let y = expensive x in
- let z = (True,y) in
- (case z of {(p,q)->q}, case z of {(p,q)->q})
-\end{verbatim}
-
-We feel free to duplicate the WHNF (True,y), but that means
-that y may be duplicated thereby.
+occAnal _ (Coercion co)
+ = (addIdOccs emptyDetails (coVarsOfCo co), Coercion co)
+ -- See Note [Gather occurrences of coercion veriables]
+\end{code}
-If we aren't careful we duplicate the (expensive x) call!
-Constructors are rather like lambdas in this way.
+Note [Gather occurrences of coercion veriables]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+We need to gather info about what coercion variables appear, so that
+we can sort them into the right place when doing dependency analysis.
\begin{code}
-occAnal _ expr@(Lit _) = (emptyDetails, expr)
\end{code}
\begin{code}
-occAnal env (Note InlineMe body)
- = case occAnal env body of { (usage, body') ->
- (mapVarEnv markMany usage, Note InlineMe body')
- }
-
occAnal env (Note note@(SCC _) body)
= case occAnal env body of { (usage, body') ->
(mapVarEnv markInsideSCC usage, Note note body')
occAnal env (Cast expr co)
= case occAnal env expr of { (usage, expr') ->
- (markRhsUds env True usage, Cast expr' co)
+ let usage1 = markManyIf (isRhsEnv env) usage
+ usage2 = addIdOccs usage1 (coVarsOfCo co)
+ -- See Note [Gather occurrences of coercion veriables]
+ in (usage2, Cast expr' co)
-- If we see let x = y `cast` co
-- then mark y as 'Many' so that we don't
-- immediately inline y again.
occAnal env expr@(Lam _ _)
= case occAnal env_body body of { (body_usage, body') ->
let
- (final_usage, tagged_binders) = tagBinders body_usage binders
+ (final_usage, tagged_binders) = tagLamBinders body_usage binders'
+ -- Use binders' to put one-shot info on the lambdas
+
-- URGH! Sept 99: we don't seem to be able to use binders' here, because
-- we get linear-typed things in the resulting program that we can't handle yet.
-- (e.g. PrelShow) TODO
(really_final_usage,
mkLams tagged_binders body') }
where
- env_body = vanillaCtxt -- Body is (no longer) an RhsContext
+ env_body = vanillaCtxt (trimOccEnv env binders)
+ -- Body is (no longer) an RhsContext
(binders, body) = collectBinders expr
binders' = oneShotGroup env binders
linear = all is_one_shot binders'
is_one_shot b = isId b && isOneShotBndr b
occAnal env (Case scrut bndr ty alts)
- = case occ_anal_scrut scrut alts of { (scrut_usage, scrut') ->
- case mapAndUnzip (occAnalAlt alt_env bndr) alts of { (alts_usage_s, alts') ->
+ = case occ_anal_scrut scrut alts of { (scrut_usage, scrut') ->
+ case mapAndUnzip occ_anal_alt alts of { (alts_usage_s, alts') ->
let
alts_usage = foldr1 combineAltsUsageDetails alts_usage_s
- alts_usage' = addCaseBndrUsage alts_usage
- (alts_usage1, tagged_bndr) = tagBinder alts_usage' bndr
+ (alts_usage1, tagged_bndr) = tag_case_bndr alts_usage bndr
total_usage = scrut_usage +++ alts_usage1
in
total_usage `seq` (total_usage, Case scrut' tagged_bndr ty alts') }}
where
+ -- Note [Case binder usage]
+ -- ~~~~~~~~~~~~~~~~~~~~~~~~
-- The case binder gets a usage of either "many" or "dead", never "one".
-- Reason: we like to inline single occurrences, to eliminate a binding,
-- but inlining a case binder *doesn't* eliminate a binding.
-- case x of w { (p,q) -> f w }
-- into
-- case x of w { (p,q) -> f (p,q) }
- addCaseBndrUsage usage = case lookupVarEnv usage bndr of
- Nothing -> usage
- Just occ -> extendVarEnv usage bndr (markMany occ)
+ tag_case_bndr usage bndr
+ = case lookupVarEnv usage bndr of
+ Nothing -> (usage, setIdOccInfo bndr IAmDead)
+ Just _ -> (usage `delVarEnv` bndr, setIdOccInfo bndr NoOccInfo)
- alt_env = setVanillaCtxt env
- -- Consider x = case v of { True -> (p,q); ... }
- -- Then it's fine to inline p and q
+ alt_env = mkAltEnv env scrut bndr
+ occ_anal_alt = occAnalAlt alt_env bndr
occ_anal_scrut (Var v) (alt1 : other_alts)
- | not (null other_alts) || not (isDefaultAlt alt1)
- = (mkOneOcc env v True, Var v)
- occ_anal_scrut scrut _alts = occAnal vanillaCtxt scrut
- -- No need for rhsCtxt
+ | not (null other_alts) || not (isDefaultAlt alt1)
+ = (mkOneOcc env v True, Var v) -- The 'True' says that the variable occurs
+ -- in an interesting context; the case has
+ -- at least one non-default alternative
+ occ_anal_scrut scrut _alts
+ = occAnal (vanillaCtxt env) scrut -- No need for rhsCtxt
occAnal env (Let bind body)
- = case occAnal env body of { (body_usage, body') ->
- case occAnalBind env bind body_usage of { (final_usage, new_binds) ->
+ = case occAnal env_body body of { (body_usage, body') ->
+ case occAnalBind env env_body bind body_usage of { (final_usage, new_binds) ->
(final_usage, mkLets new_binds body') }}
+ where
+ env_body = trimOccEnv env (bindersOf bind)
occAnalArgs :: OccEnv -> [CoreExpr] -> (UsageDetails, [CoreExpr])
-occAnalArgs _env args
+occAnalArgs env args
= case mapAndUnzip (occAnal arg_env) args of { (arg_uds_s, args') ->
(foldr (+++) emptyDetails arg_uds_s, args')}
where
- arg_env = vanillaCtxt
+ arg_env = vanillaCtxt env
\end{code}
Applications are dealt with specially because we want
the "build hack" to work.
+Note [Arguments of let-bound constructors]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Consider
+ f x = let y = expensive x in
+ let z = (True,y) in
+ (case z of {(p,q)->q}, case z of {(p,q)->q})
+We feel free to duplicate the WHNF (True,y), but that means
+that y may be duplicated thereby.
+
+If we aren't careful we duplicate the (expensive x) call!
+Constructors are rather like lambdas in this way.
+
\begin{code}
occAnalApp :: OccEnv
-> (Expr CoreBndr, [Arg CoreBndr])
occAnalApp env (Var fun, args)
= case args_stuff of { (args_uds, args') ->
let
- final_args_uds = markRhsUds env is_pap args_uds
+ final_args_uds = markManyIf (isRhsEnv env && is_exp) args_uds
+ -- We mark the free vars of the argument of a constructor or PAP
+ -- as "many", if it is the RHS of a let(rec).
+ -- This means that nothing gets inlined into a constructor argument
+ -- position, which is what we want. Typically those constructor
+ -- arguments are just variables, or trivial expressions.
+ --
+ -- This is the *whole point* of the isRhsEnv predicate
+ -- See Note [Arguments of let-bound constructors]
in
(fun_uds +++ final_args_uds, mkApps (Var fun) args') }
where
fun_uniq = idUnique fun
fun_uds = mkOneOcc env fun (valArgCount args > 0)
- is_pap = isDataConWorkId fun || valArgCount args < idArity fun
+ is_exp = isExpandableApp fun (valArgCount args)
+ -- See Note [CONLIKE pragma] in BasicTypes
+ -- The definition of is_exp should match that in
+ -- Simplify.prepareRhs
-- Hack for build, fold, runST
args_stuff | fun_uniq == buildIdKey = appSpecial env 2 [True,True] args
(final_uds, mkApps fun' args') }}
-markRhsUds :: OccEnv -- Check if this is a RhsEnv
- -> Bool -- and this is true
- -> UsageDetails -- The do markMany on this
+markManyIf :: Bool -- If this is true
+ -> UsageDetails -- Then do markMany on this
-> UsageDetails
--- We mark the free vars of the argument of a constructor or PAP
--- as "many", if it is the RHS of a let(rec).
--- This means that nothing gets inlined into a constructor argument
--- position, which is what we want. Typically those constructor
--- arguments are just variables, or trivial expressions.
---
--- This is the *whole point* of the isRhsEnv predicate
-markRhsUds env is_pap arg_uds
- | isRhsEnv env && is_pap = mapVarEnv markMany arg_uds
- | otherwise = arg_uds
-
+markManyIf True uds = mapVarEnv markMany uds
+markManyIf False uds = uds
appSpecial :: OccEnv
-> Int -> CtxtTy -- Argument number, and context to use for it
appSpecial env n ctxt args
= go n args
where
- arg_env = vanillaCtxt
+ arg_env = vanillaCtxt env
go _ [] = (emptyDetails, []) -- Too few args
go 1 (arg:args) -- The magic arg
- = case occAnal (setCtxt arg_env ctxt) arg of { (arg_uds, arg') ->
+ = case occAnal (setCtxtTy arg_env ctxt) arg of { (arg_uds, arg') ->
case occAnalArgs env args of { (args_uds, args') ->
(arg_uds +++ args_uds, arg':args') }}
\end{code}
-Case alternatives
-~~~~~~~~~~~~~~~~~
-If the case binder occurs at all, the other binders effectively do too.
-For example
- case e of x { (a,b) -> rhs }
-is rather like
- let x = (a,b) in rhs
-If e turns out to be (e1,e2) we indeed get something like
- let a = e1; b = e2; x = (a,b) in rhs
+Note [Binders in case alternatives]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Consider
+ case x of y { (a,b) -> f y }
+We treat 'a', 'b' as dead, because they don't physically occur in the
+case alternative. (Indeed, a variable is dead iff it doesn't occur in
+its scope in the output of OccAnal.) It really helps to know when
+binders are unused. See esp the call to isDeadBinder in
+Simplify.mkDupableAlt
-Note [Aug 06]: I don't think this is necessary any more, and it helpe
- to know when binders are unused. See esp the call to
- isDeadBinder in Simplify.mkDupableAlt
+In this example, though, the Simplifier will bring 'a' and 'b' back to
+life, beause it binds 'y' to (a,b) (imagine got inlined and
+scrutinised y).
\begin{code}
occAnalAlt :: OccEnv
-> CoreBndr
-> CoreAlt
-> (UsageDetails, Alt IdWithOccInfo)
-occAnalAlt env _case_bndr (con, bndrs, rhs)
- = case occAnal env rhs of { (rhs_usage, rhs') ->
+occAnalAlt env case_bndr (con, bndrs, rhs)
+ = let
+ env' = trimOccEnv env bndrs
+ in
+ case occAnal env' rhs of { (rhs_usage1, rhs1) ->
let
- (final_usage, tagged_bndrs) = tagBinders rhs_usage bndrs
- final_bndrs = tagged_bndrs -- See Note [Aug06] above
-{-
- final_bndrs | case_bndr `elemVarEnv` final_usage = bndrs
- | otherwise = tagged_bndrs
- -- Leave the binders untagged if the case
- -- binder occurs at all; see note above
--}
+ proxies = getProxies env' case_bndr
+ (rhs_usage2, rhs2) = foldrBag wrapProxy (rhs_usage1, rhs1) proxies
+ (alt_usg, tagged_bndrs) = tagLamBinders rhs_usage2 bndrs
+ bndrs' = tagged_bndrs -- See Note [Binders in case alternatives]
in
- (final_usage, (con, final_bndrs, rhs')) }
+ (alt_usg, (con, bndrs', rhs2)) }
+
+wrapProxy :: ProxyBind -> (UsageDetails, CoreExpr) -> (UsageDetails, CoreExpr)
+wrapProxy (bndr, rhs_var, co) (body_usg, body)
+ | not (bndr `usedIn` body_usg)
+ = (body_usg, body)
+ | otherwise
+ = (body_usg' +++ rhs_usg, Let (NonRec tagged_bndr rhs) body)
+ where
+ (body_usg', tagged_bndr) = tagBinder body_usg bndr
+ rhs_usg = unitVarEnv rhs_var NoOccInfo -- We don't need exact info
+ rhs = mkCoerce co (Var (zapIdOccInfo rhs_var)) -- See Note [Zap case binders in proxy bindings]
\end{code}
%************************************************************************
%* *
-\subsection[OccurAnal-types]{OccEnv}
+ OccEnv
%* *
%************************************************************************
\begin{code}
data OccEnv
- = OccEnv OccEncl -- Enclosing context information
- CtxtTy -- Tells about linearity
+ = OccEnv { occ_encl :: !OccEncl -- Enclosing context information
+ , occ_ctxt :: !CtxtTy -- Tells about linearity
+ , occ_proxy :: ProxyEnv
+ , occ_rule_fvs :: ImpRuleUsage
+ , occ_rule_act :: Maybe (Activation -> Bool) -- Nothing => Rules are inactive
+ -- See Note [Finding rule RHS free vars]
+ }
+
+-----------------------------
-- OccEncl is used to control whether to inline into constructor arguments
-- For example:
-- x = (p,q) -- Don't inline p or q
| OccVanilla -- Argument of function, body of lambda, scruintee of case etc.
-- Do inline into constructor args here
+instance Outputable OccEncl where
+ ppr OccRhs = ptext (sLit "occRhs")
+ ppr OccVanilla = ptext (sLit "occVanilla")
+
type CtxtTy = [Bool]
-- [] No info
--
-- be applied many times; but when it is,
-- the CtxtTy inside applies
-initOccEnv :: OccEnv
-initOccEnv = OccEnv OccRhs []
+initOccEnv :: Maybe (Activation -> Bool) -> [CoreRule]
+ -> OccEnv
+initOccEnv active_rule imp_rules
+ = OccEnv { occ_encl = OccVanilla
+ , occ_ctxt = []
+ , occ_proxy = PE emptyVarEnv emptyVarSet
+ , occ_rule_fvs = findImpRuleUsage active_rule imp_rules
+ , occ_rule_act = active_rule }
-vanillaCtxt :: OccEnv
-vanillaCtxt = OccEnv OccVanilla []
+vanillaCtxt :: OccEnv -> OccEnv
+vanillaCtxt env = env { occ_encl = OccVanilla, occ_ctxt = [] }
-rhsCtxt :: OccEnv
-rhsCtxt = OccEnv OccRhs []
+rhsCtxt :: OccEnv -> OccEnv
+rhsCtxt env = env { occ_encl = OccRhs, occ_ctxt = [] }
-isRhsEnv :: OccEnv -> Bool
-isRhsEnv (OccEnv OccRhs _) = True
-isRhsEnv (OccEnv OccVanilla _) = False
-
-setVanillaCtxt :: OccEnv -> OccEnv
-setVanillaCtxt (OccEnv OccRhs ctxt_ty) = OccEnv OccVanilla ctxt_ty
-setVanillaCtxt other_env = other_env
+setCtxtTy :: OccEnv -> CtxtTy -> OccEnv
+setCtxtTy env ctxt = env { occ_ctxt = ctxt }
-setCtxt :: OccEnv -> CtxtTy -> OccEnv
-setCtxt (OccEnv encl _) ctxt = OccEnv encl ctxt
+isRhsEnv :: OccEnv -> Bool
+isRhsEnv (OccEnv { occ_encl = OccRhs }) = True
+isRhsEnv (OccEnv { occ_encl = OccVanilla }) = False
oneShotGroup :: OccEnv -> [CoreBndr] -> [CoreBndr]
-- The result binders have one-shot-ness set that they might not have had originally.
-- linearity context knows that c,n are one-shot, and it records that fact in
-- the binder. This is useful to guide subsequent float-in/float-out tranformations
-oneShotGroup (OccEnv _encl ctxt) bndrs
+oneShotGroup (OccEnv { occ_ctxt = ctxt }) bndrs
= go ctxt bndrs []
where
go _ [] rev_bndrs = reverse rev_bndrs
go ctxt (bndr:bndrs) rev_bndrs = go ctxt bndrs (bndr:rev_bndrs)
addAppCtxt :: OccEnv -> [Arg CoreBndr] -> OccEnv
-addAppCtxt (OccEnv encl ctxt) args
- = OccEnv encl (replicate (valArgCount args) True ++ ctxt)
+addAppCtxt env@(OccEnv { occ_ctxt = ctxt }) args
+ = env { occ_ctxt = replicate (valArgCount args) True ++ ctxt }
\end{code}
%************************************************************************
%* *
+ ImpRuleUsage
+%* *
+%************************************************************************
+
+\begin{code}
+type ImpRuleUsage = NameEnv UsageDetails
+ -- Maps an *imported* Id f to the UsageDetails for *local* Ids
+ -- used on the RHS for a *local* rule for f.
+\end{code}
+
+Note [ImpRuleUsage]
+~~~~~~~~~~~~~~~~
+Consider this, where A.g is an imported Id
+
+ f x = A.g x
+ {-# RULE "foo" forall x. A.g x = f x #-}
+
+Obviously there's a loop, but the danger is that the occurrence analyser
+will say that 'f' is not a loop breaker. Then the simplifier will
+optimise 'f' to
+ f x = f x
+and then gaily inline 'f'. Result infinite loop. More realistically,
+these kind of rules are generated when specialising imported INLINABLE Ids.
+
+Solution: treat an occurrence of A.g as an occurrence of all the local Ids
+that occur on the RULE's RHS. This mapping from imported Id to local Ids
+is held in occ_rule_fvs.
+
+\begin{code}
+findImpRuleUsage :: Maybe (Activation -> Bool) -> [CoreRule] -> ImpRuleUsage
+-- Find the *local* Ids that can be reached transitively,
+-- via local rules, from each *imported* Id.
+-- Sigh: this function seems more complicated than it is really worth
+findImpRuleUsage Nothing _ = emptyNameEnv
+findImpRuleUsage (Just is_active) rules
+ = mkNameEnv [ (f, mapUFM (\_ -> NoOccInfo) ls)
+ | f <- rule_names
+ , let ls = find_lcl_deps f
+ , not (isEmptyVarSet ls) ]
+ where
+ rule_names = map ru_fn rules
+ rule_name_set = mkNameSet rule_names
+
+ imp_deps :: NameEnv VarSet
+ -- (f,g) means imported Id 'g' appears in RHS of
+ -- rule for imported Id 'f', *or* does so transitively
+ imp_deps = foldr add_imp emptyNameEnv rules
+ add_imp rule acc
+ | is_active (ruleActivation rule)
+ = extendNameEnv_C unionVarSet acc (ru_fn rule)
+ (exprSomeFreeVars keep_imp (ru_rhs rule))
+ | otherwise = acc
+ keep_imp v = isId v && (idName v `elemNameSet` rule_name_set)
+ full_imp_deps = transClosureFV (ufmToList imp_deps)
+
+ lcl_deps :: NameEnv VarSet
+ -- (f, l) means localId 'l' appears immediately
+ -- in the RHS of a rule for imported Id 'f'
+ -- Remember, many rules might have the same ru_fn
+ -- so we do need to fold
+ lcl_deps = foldr add_lcl emptyNameEnv rules
+ add_lcl rule acc = extendNameEnv_C unionVarSet acc (ru_fn rule)
+ (exprFreeIds (ru_rhs rule))
+
+ find_lcl_deps :: Name -> VarSet
+ find_lcl_deps f
+ = foldVarSet (unionVarSet . lookup_lcl . idName) (lookup_lcl f)
+ (lookupNameEnv full_imp_deps f `orElse` emptyVarSet)
+ lookup_lcl :: Name -> VarSet
+ lookup_lcl g = lookupNameEnv lcl_deps g `orElse` emptyVarSet
+
+-------------
+transClosureFV :: Uniquable a => [(a, VarSet)] -> UniqFM VarSet
+-- If (f,g), (g,h) are in the input, then (f,h) is in the output
+transClosureFV fv_list
+ | no_change = env
+ | otherwise = transClosureFV new_fv_list
+ where
+ env = listToUFM fv_list
+ (no_change, new_fv_list) = mapAccumL bump True fv_list
+ bump no_change (b,fvs)
+ | no_change_here = (no_change, (b,fvs))
+ | otherwise = (False, (b,new_fvs))
+ where
+ (new_fvs, no_change_here) = extendFvs env fvs
+
+-------------
+extendFvs :: UniqFM VarSet -> VarSet -> (VarSet, Bool)
+-- (extendFVs env s) returns
+-- (s `union` env(s), env(s) `subset` s)
+extendFvs env s
+ = foldVarSet add (s, True) s
+ where
+ add v (vs, no_change_so_far)
+ = case lookupUFM env v of
+ Just fvs | not (fvs `subVarSet` s)
+ -> (vs `unionVarSet` fvs, False)
+ _ -> (vs, no_change_so_far)
+\end{code}
+
+
+%************************************************************************
+%* *
+ ProxyEnv
+%* *
+%************************************************************************
+
+\begin{code}
+data ProxyEnv -- See Note [ProxyEnv]
+ = PE (IdEnv -- Domain = scrutinee variables
+ (Id, -- The scrutinee variable again
+ [(Id,Coercion)])) -- The case binders that it maps to
+ VarSet -- Free variables of both range and domain
+\end{code}
+
+Note [ProxyEnv]
+~~~~~~~~~~~~~~~
+The ProxyEnv keeps track of the connection between case binders and
+scrutinee. Specifically, if
+ sc |-> (sc, [...(cb, co)...])
+is a binding in the ProxyEnv, then
+ cb = sc |> coi
+Typically we add such a binding when encountering the case expression
+ case (sc |> coi) of cb { ... }
+
+Things to note:
+ * The domain of the ProxyEnv is the variable (or casted variable)
+ scrutinees of enclosing cases. This is additionally used
+ to ensure we gather occurrence info even for GlobalId scrutinees;
+ see Note [Binder swap for GlobalId scrutinee]
+
+ * The ProxyEnv is just an optimisation; you can throw away any
+ element without losing correctness. And we do so when pushing
+ it inside a binding (see trimProxyEnv).
+
+ * One scrutinee might map to many case binders: Eg
+ case sc of cb1 { DEFAULT -> ....case sc of cb2 { ... } .. }
+
+INVARIANTS
+ * If sc1 |-> (sc2, [...(cb, co)...]), then sc1==sc2
+ It's a UniqFM and we sometimes need the domain Id
+
+ * Any particular case binder 'cb' occurs only once in entire range
+
+ * No loops
+
+The Main Reason for having a ProxyEnv is so that when we encounter
+ case e of cb { pi -> ri }
+we can find all the in-scope variables derivable from 'cb',
+and effectively add let-bindings for them (or at least for the
+ones *mentioned* in ri) thus:
+ case e of cb { pi -> let { x = ..cb..; y = ...cb.. }
+ in ri }
+In this way we'll replace occurrences of 'x', 'y' with 'cb',
+which implements the Binder-swap idea (see Note [Binder swap])
+
+The function getProxies finds these bindings; then we
+add just the necessary ones, using wrapProxy.
+
+Note [Binder swap]
+~~~~~~~~~~~~~~~~~~
+We do these two transformations right here:
+
+ (1) case x of b { pi -> ri }
+ ==>
+ case x of b { pi -> let x=b in ri }
+
+ (2) case (x |> co) of b { pi -> ri }
+ ==>
+ case (x |> co) of b { pi -> let x = b |> sym co in ri }
+
+ Why (2)? See Note [Case of cast]
+
+In both cases, in a particular alternative (pi -> ri), we only
+add the binding if
+ (a) x occurs free in (pi -> ri)
+ (ie it occurs in ri, but is not bound in pi)
+ (b) the pi does not bind b (or the free vars of co)
+We need (a) and (b) for the inserted binding to be correct.
+
+For the alternatives where we inject the binding, we can transfer
+all x's OccInfo to b. And that is the point.
+
+Notice that
+ * The deliberate shadowing of 'x'.
+ * That (a) rapidly becomes false, so no bindings are injected.
+
+The reason for doing these transformations here is because it allows
+us to adjust the OccInfo for 'x' and 'b' as we go.
+
+ * Suppose the only occurrences of 'x' are the scrutinee and in the
+ ri; then this transformation makes it occur just once, and hence
+ get inlined right away.
+
+ * If we do this in the Simplifier, we don't know whether 'x' is used
+ in ri, so we are forced to pessimistically zap b's OccInfo even
+ though it is typically dead (ie neither it nor x appear in the
+ ri). There's nothing actually wrong with zapping it, except that
+ it's kind of nice to know which variables are dead. My nose
+ tells me to keep this information as robustly as possible.
+
+The Maybe (Id,CoreExpr) passed to occAnalAlt is the extra let-binding
+{x=b}; it's Nothing if the binder-swap doesn't happen.
+
+There is a danger though. Consider
+ let v = x +# y
+ in case (f v) of w -> ...v...v...
+And suppose that (f v) expands to just v. Then we'd like to
+use 'w' instead of 'v' in the alternative. But it may be too
+late; we may have substituted the (cheap) x+#y for v in the
+same simplifier pass that reduced (f v) to v.
+
+I think this is just too bad. CSE will recover some of it.
+
+Note [Case of cast]
+~~~~~~~~~~~~~~~~~~~
+Consider case (x `cast` co) of b { I# ->
+ ... (case (x `cast` co) of {...}) ...
+We'd like to eliminate the inner case. That is the motivation for
+equation (2) in Note [Binder swap]. When we get to the inner case, we
+inline x, cancel the casts, and away we go.
+
+Note [Binder swap on GlobalId scrutinees]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+When the scrutinee is a GlobalId we must take care in two ways
+
+ i) In order to *know* whether 'x' occurs free in the RHS, we need its
+ occurrence info. BUT, we don't gather occurrence info for
+ GlobalIds. That's one use for the (small) occ_proxy env in OccEnv is
+ for: it says "gather occurrence info for these.
+
+ ii) We must call localiseId on 'x' first, in case it's a GlobalId, or
+ has an External Name. See, for example, SimplEnv Note [Global Ids in
+ the substitution].
+
+Note [getProxies is subtle]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The code for getProxies isn't all that obvious. Consider
+
+ case v |> cov of x { DEFAULT ->
+ case x |> cox1 of y { DEFAULT ->
+ case x |> cox2 of z { DEFAULT -> r
+
+These will give us a ProxyEnv looking like:
+ x |-> (x, [(y, cox1), (z, cox2)])
+ v |-> (v, [(x, cov)])
+
+From this we want to extract the bindings
+ x = z |> sym cox2
+ v = x |> sym cov
+ y = x |> cox1
+
+Notice that later bindings may mention earlier ones, and that
+we need to go "both ways".
+
+Note [Zap case binders in proxy bindings]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+From the original
+ case x of cb(dead) { p -> ...x... }
+we will get
+ case x of cb(live) { p -> let x = cb in ...x... }
+
+Core Lint never expects to find an *occurence* of an Id marked
+as Dead, so we must zap the OccInfo on cb before making the
+binding x = cb. See Trac #5028.
+
+Historical note [no-case-of-case]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+We *used* to suppress the binder-swap in case expressions when
+-fno-case-of-case is on. Old remarks:
+ "This happens in the first simplifier pass,
+ and enhances full laziness. Here's the bad case:
+ f = \ y -> ...(case x of I# v -> ...(case x of ...) ... )
+ If we eliminate the inner case, we trap it inside the I# v -> arm,
+ which might prevent some full laziness happening. I've seen this
+ in action in spectral/cichelli/Prog.hs:
+ [(m,n) | m <- [1..max], n <- [1..max]]
+ Hence the check for NoCaseOfCase."
+However, now the full-laziness pass itself reverses the binder-swap, so this
+check is no longer necessary.
+
+Historical note [Suppressing the case binder-swap]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+This old note describes a problem that is also fixed by doing the
+binder-swap in OccAnal:
+
+ There is another situation when it might make sense to suppress the
+ case-expression binde-swap. If we have
+
+ case x of w1 { DEFAULT -> case x of w2 { A -> e1; B -> e2 }
+ ...other cases .... }
+
+ We'll perform the binder-swap for the outer case, giving
+
+ case x of w1 { DEFAULT -> case w1 of w2 { A -> e1; B -> e2 }
+ ...other cases .... }
+
+ But there is no point in doing it for the inner case, because w1 can't
+ be inlined anyway. Furthermore, doing the case-swapping involves
+ zapping w2's occurrence info (see paragraphs that follow), and that
+ forces us to bind w2 when doing case merging. So we get
+
+ case x of w1 { A -> let w2 = w1 in e1
+ B -> let w2 = w1 in e2
+ ...other cases .... }
+
+ This is plain silly in the common case where w2 is dead.
+
+ Even so, I can't see a good way to implement this idea. I tried
+ not doing the binder-swap if the scrutinee was already evaluated
+ but that failed big-time:
+
+ data T = MkT !Int
+
+ case v of w { MkT x ->
+ case x of x1 { I# y1 ->
+ case x of x2 { I# y2 -> ...
+
+ Notice that because MkT is strict, x is marked "evaluated". But to
+ eliminate the last case, we must either make sure that x (as well as
+ x1) has unfolding MkT y1. THe straightforward thing to do is to do
+ the binder-swap. So this whole note is a no-op.
+
+It's fixed by doing the binder-swap in OccAnal because we can do the
+binder-swap unconditionally and still get occurrence analysis
+information right.
+
+\begin{code}
+extendProxyEnv :: ProxyEnv -> Id -> Coercion -> Id -> ProxyEnv
+-- (extendPE x co y) typically arises from
+-- case (x |> co) of y { ... }
+-- It extends the proxy env with the binding
+-- y = x |> co
+extendProxyEnv pe scrut co case_bndr
+ | scrut == case_bndr = PE env1 fvs1 -- If case_bndr shadows scrut,
+ | otherwise = PE env2 fvs2 -- don't extend
+ where
+ PE env1 fvs1 = trimProxyEnv pe [case_bndr]
+ env2 = extendVarEnv_Acc add single env1 scrut1 (case_bndr,co)
+ single cb_co = (scrut1, [cb_co])
+ add cb_co (x, cb_cos) = (x, cb_co:cb_cos)
+ fvs2 = fvs1 `unionVarSet` tyCoVarsOfCo co
+ `extendVarSet` case_bndr
+ `extendVarSet` scrut1
+
+ scrut1 = mkLocalId (localiseName (idName scrut)) (idType scrut)
+ -- Localise the scrut_var before shadowing it; we're making a
+ -- new binding for it, and it might have an External Name, or
+ -- even be a GlobalId; Note [Binder swap on GlobalId scrutinees]
+ -- Also we don't want any INLINE or NOINLINE pragmas!
+
+-----------
+type ProxyBind = (Id, Id, Coercion)
+ -- (scrut variable, case-binder variable, coercion)
+
+getProxies :: OccEnv -> Id -> Bag ProxyBind
+-- Return a bunch of bindings [...(xi,ei)...]
+-- such that let { ...; xi=ei; ... } binds the xi using y alone
+-- See Note [getProxies is subtle]
+getProxies (OccEnv { occ_proxy = PE pe _ }) case_bndr
+ = -- pprTrace "wrapProxies" (ppr case_bndr) $
+ go_fwd case_bndr
+ where
+ fwd_pe :: IdEnv (Id, Coercion)
+ fwd_pe = foldVarEnv add1 emptyVarEnv pe
+ where
+ add1 (x,ycos) env = foldr (add2 x) env ycos
+ add2 x (y,co) env = extendVarEnv env y (x,co)
+
+ go_fwd :: Id -> Bag ProxyBind
+ -- Return bindings derivable from case_bndr
+ go_fwd case_bndr = -- pprTrace "go_fwd" (vcat [ppr case_bndr, text "fwd_pe =" <+> ppr fwd_pe,
+ -- text "pe =" <+> ppr pe]) $
+ go_fwd' case_bndr
+
+ go_fwd' case_bndr
+ | Just (scrut, co) <- lookupVarEnv fwd_pe case_bndr
+ = unitBag (scrut, case_bndr, mkSymCo co)
+ `unionBags` go_fwd scrut
+ `unionBags` go_bwd scrut [pr | pr@(cb,_) <- lookup_bwd scrut
+ , cb /= case_bndr]
+ | otherwise
+ = emptyBag
+
+ lookup_bwd :: Id -> [(Id, Coercion)]
+ -- Return case_bndrs that are connected to scrut
+ lookup_bwd scrut = case lookupVarEnv pe scrut of
+ Nothing -> []
+ Just (_, cb_cos) -> cb_cos
+
+ go_bwd :: Id -> [(Id, Coercion)] -> Bag ProxyBind
+ go_bwd scrut cb_cos = foldr (unionBags . go_bwd1 scrut) emptyBag cb_cos
+
+ go_bwd1 :: Id -> (Id, Coercion) -> Bag ProxyBind
+ go_bwd1 scrut (case_bndr, co)
+ = -- pprTrace "go_bwd1" (ppr case_bndr) $
+ unitBag (case_bndr, scrut, co)
+ `unionBags` go_bwd case_bndr (lookup_bwd case_bndr)
+
+-----------
+mkAltEnv :: OccEnv -> CoreExpr -> Id -> OccEnv
+-- Does two things: a) makes the occ_ctxt = OccVanilla
+-- b) extends the ProxyEnv if possible
+mkAltEnv env scrut cb
+ = env { occ_encl = OccVanilla, occ_proxy = pe' }
+ where
+ pe = occ_proxy env
+ pe' = case scrut of
+ Var v -> extendProxyEnv pe v (mkReflCo (idType v)) cb
+ Cast (Var v) co -> extendProxyEnv pe v co cb
+ _other -> trimProxyEnv pe [cb]
+
+-----------
+trimOccEnv :: OccEnv -> [CoreBndr] -> OccEnv
+trimOccEnv env bndrs = env { occ_proxy = trimProxyEnv (occ_proxy env) bndrs }
+
+-----------
+trimProxyEnv :: ProxyEnv -> [CoreBndr] -> ProxyEnv
+-- We are about to push this ProxyEnv inside a binding for 'bndrs'
+-- So dump any ProxyEnv bindings which mention any of the bndrs
+trimProxyEnv (PE pe fvs) bndrs
+ | not (bndr_set `intersectsVarSet` fvs)
+ = PE pe fvs
+ | otherwise
+ = PE pe' (fvs `minusVarSet` bndr_set)
+ where
+ pe' = mapVarEnv trim pe
+ bndr_set = mkVarSet bndrs
+ trim (scrut, cb_cos) | scrut `elemVarSet` bndr_set = (scrut, [])
+ | otherwise = (scrut, filterOut discard cb_cos)
+ discard (cb,co) = bndr_set `intersectsVarSet`
+ extendVarSet (tyCoVarsOfCo co) cb
+\end{code}
+
+
+%************************************************************************
+%* *
\subsection[OccurAnal-types]{OccEnv}
%* *
%************************************************************************
\begin{code}
type UsageDetails = IdEnv OccInfo -- A finite map from ids to their usage
+ -- INVARIANT: never IAmDead
+ -- (Deadness is signalled by not being in the map at all)
(+++), combineAltsUsageDetails
:: UsageDetails -> UsageDetails -> UsageDetails
emptyDetails = (emptyVarEnv :: UsageDetails)
usedIn :: Id -> UsageDetails -> Bool
-v `usedIn` details = isExportedId v || v `elemVarEnv` details
+v `usedIn` details = isExportedId v || v `elemVarEnv` details
type IdWithOccInfo = Id
-tagBinders :: UsageDetails -- Of scope
- -> [Id] -- Binders
- -> (UsageDetails, -- Details with binders removed
- [IdWithOccInfo]) -- Tagged binders
-
-tagBinders usage binders
- = let
- usage' = usage `delVarEnvList` binders
- uss = map (setBinderOcc usage) binders
- in
- usage' `seq` (usage', uss)
+tagLamBinders :: UsageDetails -- Of scope
+ -> [Id] -- Binders
+ -> (UsageDetails, -- Details with binders removed
+ [IdWithOccInfo]) -- Tagged binders
+-- Used for lambda and case binders
+-- It copes with the fact that lambda bindings can have InlineRule
+-- unfoldings, used for join points
+tagLamBinders usage binders = usage' `seq` (usage', bndrs')
+ where
+ (usage', bndrs') = mapAccumR tag_lam usage binders
+ tag_lam usage bndr = (usage2, setBinderOcc usage bndr)
+ where
+ usage1 = usage `delVarEnv` bndr
+ usage2 | isId bndr = addIdOccs usage1 (idUnfoldingVars bndr)
+ | otherwise = usage1
tagBinder :: UsageDetails -- Of scope
-> Id -- Binders
\begin{code}
mkOneOcc :: OccEnv -> Id -> InterestingCxt -> UsageDetails
-mkOneOcc _env id int_cxt
+mkOneOcc env id int_cxt
| isLocalId id = unitVarEnv id (OneOcc False True int_cxt)
- | otherwise = emptyDetails
+ | PE env _ <- occ_proxy env
+ , id `elemVarEnv` env = unitVarEnv id NoOccInfo
+ | Just uds <- lookupNameEnv (occ_rule_fvs env) (idName id)
+ = uds
+ | otherwise = emptyDetails
markMany, markInsideLam, markInsideSCC :: OccInfo -> OccInfo
-markMany IAmDead = IAmDead
-markMany _ = NoOccInfo
+markMany _ = NoOccInfo
markInsideSCC occ = markMany occ
addOccInfo, orOccInfo :: OccInfo -> OccInfo -> OccInfo
-addOccInfo IAmDead info2 = info2
-addOccInfo info1 IAmDead = info1
-addOccInfo _ _ = NoOccInfo
+addOccInfo a1 a2 = ASSERT( not (isDeadOcc a1 || isDeadOcc a2) )
+ NoOccInfo -- Both branches are at least One
+ -- (Argument is never IAmDead)
-- (orOccInfo orig new) is used
-- when combining occurrence info from branches of a case
-orOccInfo IAmDead info2 = info2
-orOccInfo info1 IAmDead = info1
orOccInfo (OneOcc in_lam1 _ int_cxt1)
(OneOcc in_lam2 _ int_cxt2)
= OneOcc (in_lam1 || in_lam2)
False -- False, because it occurs in both branches
(int_cxt1 && int_cxt2)
-orOccInfo _ _ = NoOccInfo
+orOccInfo a1 a2 = ASSERT( not (isDeadOcc a1 || isDeadOcc a2) )
+ NoOccInfo
\end{code}
projects / ghc-hetmet.git / blobdiff