5 , dualLiveLattice, dualLiveness
6 , insertSpillsAndReloads --- XXX todo check live-in at entry against formals
7 , dualLivenessWithInsertion
8 , spillAndReloadComments
13 , removeDeadAssignmentsAndReloads
29 import Outputable hiding (empty)
30 import qualified Outputable as PP
35 import Prelude hiding (zip)
37 -- The point of this module is to insert spills and reloads to
38 -- establish the invariant that at a call (or at any proc point with
39 -- an established protocol) all live variables not expected in
40 -- registers are sitting on the stack. We use a backward analysis to
41 -- insert spills and reloads. It should some day be followed by a
42 -- forward transformation to sink reloads as deeply as possible, so as
43 -- to reduce register pressure.
45 data ExtendWithSpills m
50 type M = ExtendWithSpills Middle
52 -- A variable can be expected to be live in a register, live on the
53 -- stack, or both. This analysis ensures that spills and reloads are
54 -- inserted as needed to make sure that every live variable needed
55 -- after a call is available on the stack. Spills are pushed back to
56 -- their reaching definitions, but reloads are dropped wherever needed
57 -- and will have to be sunk by a later forward transformation.
59 data DualLive = DualLive { on_stack :: RegSet, in_regs :: RegSet }
61 dualUnion :: DualLive -> DualLive -> DualLive
62 dualUnion (DualLive s r) (DualLive s' r') =
63 DualLive (s `unionUniqSets` s') (r `unionUniqSets` r')
65 dualUnionList :: [DualLive] -> DualLive
66 dualUnionList ls = DualLive ss rs
67 where ss = unionManyUniqSets $ map on_stack ls
68 rs = unionManyUniqSets $ map in_regs ls
70 _changeStack, changeRegs :: (RegSet -> RegSet) -> DualLive -> DualLive
71 _changeStack f live = live { on_stack = f (on_stack live) }
72 changeRegs f live = live { in_regs = f (in_regs live) }
75 dualLiveLattice :: DataflowLattice DualLive
77 DataflowLattice "variables live in registers and on stack" empty add False
78 where empty = DualLive emptyRegSet emptyRegSet
79 -- | compute in the Tx monad to track whether anything has changed
80 add new old = do stack <- add1 (on_stack new) (on_stack old)
81 regs <- add1 (in_regs new) (in_regs old)
82 return $ DualLive stack regs
83 add1 = fact_add_to liveLattice
85 dualLivenessWithInsertion :: BPass M Last DualLive
86 dualLivenessWithInsertion = a_ft_b_unlimited dualLiveness insertSpillsAndReloads
88 dualLiveness :: BAnalysis M Last DualLive
89 dualLiveness = BComp "dual liveness" exit last middle first
91 last = lastDualLiveness
92 middle = middleDualLiveness
94 empty = fact_bot dualLiveLattice
96 -- ^ could take a proc-point set and choose to spill here,
97 -- but it's probably better to run this pass, choose
98 -- proc-point protocols, insert more CopyIn nodes, and run
101 middleDualLiveness :: DualLive -> M -> DualLive
102 middleDualLiveness live (Spill regs) = live'
103 -- live-in on-stack requirements are satisfied;
104 -- live-out in-regs obligations are created
105 where live' = DualLive { on_stack = on_stack live `minusRegSet` regs
106 , in_regs = in_regs live `plusRegSet` regs }
108 middleDualLiveness live (Reload regs) = live'
109 -- live-in in-regs requirements are satisfied;
110 -- live-out on-stack obligations are created
111 where live' = DualLive { on_stack = on_stack live `plusRegSet` regs
112 , in_regs = in_regs live `minusRegSet` regs }
114 middleDualLiveness live (NotSpillOrReload m) = changeRegs (middleLiveness m) live
116 lastDualLiveness :: (BlockId -> DualLive) -> Last -> DualLive
117 lastDualLiveness env l = last l
118 where last (LastReturn) = empty
119 last (LastJump e) = changeRegs (gen e) empty
120 last (LastBranch id) = env id
121 last (LastCall tgt Nothing) = changeRegs (gen tgt) empty
122 last (LastCall tgt (Just k)) =
123 -- nothing can be live in registers at this point
125 if isEmptyUniqSet (in_regs live) then
126 DualLive (on_stack live) (gen tgt emptyRegSet)
128 panic "live values in registers at call continuation"
129 last (LastCondBranch e t f) = changeRegs (gen e) $ dualUnion (env t) (env f)
130 last (LastSwitch e tbl) = changeRegs (gen e) $ dualUnionList $
131 map env (catMaybes tbl)
132 empty = fact_bot dualLiveLattice
134 gen, kill :: UserOfLocalRegs a => a -> RegSet -> RegSet
135 gen a live = foldRegsUsed extendRegSet live a
136 kill a live = foldRegsUsed delOneFromUniqSet live a
138 insertSpillsAndReloads :: BFunctionalTransformation M Last DualLive
139 insertSpillsAndReloads = BComp "CPS spiller" exit last middle first
141 last = \_ _ -> Nothing
142 middle = middleInsertSpillsAndReloads
144 -- ^ could take a proc-point set and choose to spill here,
145 -- but it's probably better to run this pass, choose
146 -- proc-point protocols, insert more CopyIn nodes, and run
150 middleInsertSpillsAndReloads :: DualLive -> M -> Maybe (Graph M Last)
151 middleInsertSpillsAndReloads _ (Spill _) = Nothing
152 middleInsertSpillsAndReloads _ (Reload _) = Nothing
153 middleInsertSpillsAndReloads live (NotSpillOrReload m) = middle m
154 where middle (MidAssign (CmmLocal reg') _) =
155 if reg' `elemRegSet` on_stack live then -- must spill
156 my_trace "Spilling" (f4sep [text "spill" <+> ppr reg',
157 text "after", ppr m]) $
158 Just $ graphOfMiddles [NotSpillOrReload m, Spill $ mkRegSet [reg']]
161 middle (CopyIn _ formals _) =
162 -- only 'formals' can be in regs at this point
163 let regs' = kill formals (in_regs live) -- live in regs; must reload
164 is_stack_var r = elemRegSet r (on_stack live)
165 needs_spilling = -- a formal that is expected on the stack; must spill
166 foldRegsUsed (\rs r -> if is_stack_var r then extendRegSet rs r
167 else rs) emptyRegSet formals
168 in if isEmptyUniqSet regs' && isEmptyUniqSet needs_spilling then
171 let reload = if isEmptyUniqSet regs' then []
173 spill_reload = if isEmptyUniqSet needs_spilling then reload
174 else Spill needs_spilling : reload
175 middles = NotSpillOrReload m : spill_reload
177 my_trace "At CopyIn" (f4sep [text "Triggered by ", ppr live,
178 ppr (Reload regs' :: M),
179 ppr (Spill needs_spilling :: M),
180 text "after", ppr m]) $
181 Just $ graphOfMiddles middles
184 -- | For conversion back to vanilla C--
185 spillAndReloadComments :: M -> Middle
186 spillAndReloadComments (NotSpillOrReload m) = m
187 spillAndReloadComments (Spill regs) = show_regs "Spill" regs
188 spillAndReloadComments (Reload regs) = show_regs "Reload" regs
190 show_regs :: String -> RegSet -> Middle
191 show_regs s regs = MidComment $ mkFastString $ showSDoc $ ppr_regs s regs
194 ----------------------------------------------------------------
197 -- The idea is to compute at each point the set of registers such that
198 -- on every path to the point, the register is defined by a Reload
199 -- instruction. Then, if a use appears at such a point, we can safely
200 -- insert a Reload right before the use. Finally, we can eliminate
201 -- the early reloads along with other dead assignments.
203 data AvailRegs = UniverseMinus RegSet
207 availRegsLattice :: DataflowLattice AvailRegs
208 availRegsLattice = DataflowLattice "register gotten from reloads" empty add True
209 where empty = UniverseMinus emptyRegSet
210 -- | compute in the Tx monad to track whether anything has changed
212 let join = interAvail new old in
213 if join `smallerAvail` old then aTx join else noTx join
216 interAvail :: AvailRegs -> AvailRegs -> AvailRegs
217 interAvail (UniverseMinus s) (UniverseMinus s') = UniverseMinus (s `plusRegSet` s')
218 interAvail (AvailRegs s) (AvailRegs s') = AvailRegs (s `timesRegSet` s')
219 interAvail (AvailRegs s) (UniverseMinus s') = AvailRegs (s `minusRegSet` s')
220 interAvail (UniverseMinus s) (AvailRegs s') = AvailRegs (s' `minusRegSet` s )
222 smallerAvail :: AvailRegs -> AvailRegs -> Bool
223 smallerAvail (AvailRegs _) (UniverseMinus _) = True
224 smallerAvail (UniverseMinus _) (AvailRegs _) = False
225 smallerAvail (AvailRegs s) (AvailRegs s') = sizeUniqSet s < sizeUniqSet s'
226 smallerAvail (UniverseMinus s) (UniverseMinus s') = sizeUniqSet s > sizeUniqSet s'
228 extendAvail :: AvailRegs -> LocalReg -> AvailRegs
229 extendAvail (UniverseMinus s) r = UniverseMinus (deleteFromRegSet s r)
230 extendAvail (AvailRegs s) r = AvailRegs (extendRegSet s r)
232 deleteFromAvail :: AvailRegs -> LocalReg -> AvailRegs
233 deleteFromAvail (UniverseMinus s) r = UniverseMinus (extendRegSet s r)
234 deleteFromAvail (AvailRegs s) r = AvailRegs (deleteFromRegSet s r)
236 elemAvail :: AvailRegs -> LocalReg -> Bool
237 elemAvail (UniverseMinus s) r = not $ elemRegSet r s
238 elemAvail (AvailRegs s) r = elemRegSet r s
240 cmmAvailableReloads :: LGraph M Last -> BlockEnv AvailRegs
241 cmmAvailableReloads g = env
242 where env = runDFA availRegsLattice $
243 do run_f_anal transfer (fact_bot availRegsLattice) g
245 transfer :: FAnalysis M Last AvailRegs
246 transfer = FComp "available-reloads analysis" first middle last exit
247 exit _ = LastOutFacts []
248 first avail _ = avail
249 middle = flip middleAvail
253 -- | The transfer equations use the traditional 'gen' and 'kill'
254 -- notations, which should be familiar from the dragon book.
255 agen, akill :: UserOfLocalRegs a => a -> AvailRegs -> AvailRegs
256 agen a live = foldRegsUsed extendAvail live a
257 akill a live = foldRegsUsed deleteFromAvail live a
259 middleAvail :: M -> AvailRegs -> AvailRegs
260 middleAvail (Spill _) = id
261 middleAvail (Reload regs) = agen regs
262 middleAvail (NotSpillOrReload m) = middle m
263 where middle (MidComment {}) = id
264 middle (MidAssign lhs _expr) = akill lhs
265 middle (MidStore {}) = id
266 middle (MidUnsafeCall _tgt ress _args) = akill ress
267 middle (CopyIn _ formals _) = akill formals
268 middle (CopyOut {}) = id
270 lastAvail :: AvailRegs -> Last -> LastOutFacts AvailRegs
271 lastAvail _ (LastCall _ (Just k)) = LastOutFacts [(k, AvailRegs emptyRegSet)]
272 lastAvail avail l = LastOutFacts $ map (\id -> (id, avail)) $ succs l
274 insertLateReloads :: LGraph M Last -> DFTx (LGraph M Last)
275 insertLateReloads g = mapM_blocks insertM g
276 where env = cmmAvailableReloads g
277 avail id = lookupBlockEnv env id `orElse` AvailRegs emptyRegSet
278 insertM b = functionalDFTx "late reloads" (insert b)
279 insert (Block id tail) fuel = propagate (ZFirst id) (avail id) tail fuel
280 propagate h avail (ZTail m t) fuel =
281 let (h', fuel') = maybe_add_reload h avail m fuel in
282 propagate (ZHead h' m) (middleAvail m avail) t fuel'
283 propagate h avail (ZLast l) fuel =
284 let (h', fuel') = maybe_add_reload h avail l fuel in
285 (zipht h' (ZLast l), fuel')
286 maybe_add_reload h avail node fuel =
287 let used = foldRegsUsed
288 (\u r -> if elemAvail avail r then extendRegSet u r else u)
290 in if fuel == 0 || isEmptyUniqSet used then (h, fuel)
291 else (ZHead h (Reload used), fuel-1)
294 removeDeadAssignmentsAndReloads :: BPass M Last DualLive
295 removeDeadAssignmentsAndReloads = a_ft_b dualLiveness remove_deads
296 where remove_deads = BComp "dead-assignment & -reload elim" exit last middle first
298 last = \_ _ -> Nothing
299 middle = middleRemoveDeads
302 middleRemoveDeads :: DualLive -> M -> Maybe (Graph M Last)
303 middleRemoveDeads _ (Spill _) = Nothing
304 middleRemoveDeads live (Reload s) =
305 if sizeUniqSet worth_reloading < sizeUniqSet s then
306 Just $ if isEmptyUniqSet worth_reloading then emptyGraph
307 else graphOfMiddles [Reload worth_reloading]
310 where worth_reloading = intersectUniqSets s (in_regs live)
311 middleRemoveDeads live (NotSpillOrReload m) = middle m
312 where middle (MidAssign (CmmLocal reg') _)
313 | not (reg' `elemRegSet` in_regs live) = Just emptyGraph
318 ---------------------
321 instance UserOfLocalRegs m => UserOfLocalRegs (ExtendWithSpills m) where
322 foldRegsUsed f z (Spill regs) = foldRegsUsed f z regs
323 foldRegsUsed _f z (Reload _) = z
324 foldRegsUsed f z (NotSpillOrReload m) = foldRegsUsed f z m
326 ---------------------
329 instance Outputable m => Outputable (ExtendWithSpills m) where
330 ppr (Spill regs) = ppr_regs "Spill" regs
331 ppr (Reload regs) = ppr_regs "Reload" regs
332 ppr (NotSpillOrReload m) = ppr m
334 instance Outputable (LGraph M Last) where
337 instance DebugNodes M Last
339 ppr_regs :: String -> RegSet -> SDoc
340 ppr_regs s regs = text s <+> commafy (map ppr $ uniqSetToList regs)
341 where commafy xs = hsep $ punctuate comma xs
343 instance Outputable DualLive where
344 ppr (DualLive {in_regs = regs, on_stack = stack}) =
345 if isEmptyUniqSet regs && isEmptyUniqSet stack then
346 text "<nothing-live>"
348 nest 2 $ fsep [if isEmptyUniqSet regs then PP.empty
349 else (ppr_regs "live in regs =" regs),
350 if isEmptyUniqSet stack then PP.empty
351 else (ppr_regs "live on stack =" stack)]
353 instance Outputable AvailRegs where
354 ppr (UniverseMinus s) = if isEmptyUniqSet s then text "<everything available>"
355 else ppr_regs "available = all but" s
356 ppr (AvailRegs s) = if isEmptyUniqSet s then text "<nothing available>"
357 else ppr_regs "available = " s
359 my_trace :: String -> SDoc -> a -> a
360 my_trace = if False then pprTrace else \_ _ a -> a
362 f4sep :: [SDoc] -> SDoc
364 f4sep (d:ds) = fsep (d : map (nest 4) ds)