1 {-# OPTIONS_GHC -XNoMonoLocalBinds #-}
2 -- Norman likes local bindings
3 -- If this module lives on I'd like to get rid of this flag in due course
7 , dualLiveLattice, dualLiveTransfers, dualLiveness
8 --, insertSpillsAndReloads --- XXX todo check live-in at entry against formals
9 , dualLivenessWithInsertion
14 , removeDeadAssignmentsAndReloads
30 import Outputable hiding (empty)
31 import qualified Outputable as PP
35 import Prelude hiding (zip)
37 {- Note [Overview of spill/reload]
38 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
39 The point of this module is to insert spills and reloads to
40 establish the invariant that at a call (or at any proc point with
41 an established protocol) all live variables not expected in
42 registers are sitting on the stack. We use a backward analysis to
43 insert spills and reloads. It should be followed by a
44 forward transformation to sink reloads as deeply as possible, so as
45 to reduce register pressure.
47 A variable can be expected to be live in a register, live on the
48 stack, or both. This analysis ensures that spills and reloads are
49 inserted as needed to make sure that every live variable needed
50 after a call is available on the stack. Spills are pushed back to
51 their reaching definitions, but reloads are dropped wherever needed
52 and will have to be sunk by a later forward transformation.
55 data DualLive = DualLive { on_stack :: RegSet, in_regs :: RegSet }
57 dualUnion :: DualLive -> DualLive -> DualLive
58 dualUnion (DualLive s r) (DualLive s' r') =
59 DualLive (s `unionUniqSets` s') (r `unionUniqSets` r')
61 dualUnionList :: [DualLive] -> DualLive
62 dualUnionList ls = DualLive ss rs
63 where ss = unionManyUniqSets $ map on_stack ls
64 rs = unionManyUniqSets $ map in_regs ls
66 changeStack, changeRegs :: (RegSet -> RegSet) -> DualLive -> DualLive
67 changeStack f live = live { on_stack = f (on_stack live) }
68 changeRegs f live = live { in_regs = f (in_regs live) }
71 dualLiveLattice :: DataflowLattice DualLive
73 DataflowLattice "variables live in registers and on stack" empty add False
74 where empty = DualLive emptyRegSet emptyRegSet
75 -- | compute in the Tx monad to track whether anything has changed
76 add new old = do stack <- add1 (on_stack new) (on_stack old)
77 regs <- add1 (in_regs new) (in_regs old)
78 return $ DualLive stack regs
79 add1 = fact_add_to liveLattice
81 type LiveReloadFix a = FuelMonad (BackwardFixedPoint Middle Last DualLive a)
83 dualLivenessWithInsertion :: BlockSet -> (LGraph Middle Last) -> FuelMonad (LGraph Middle Last)
84 dualLivenessWithInsertion procPoints g@(LGraph entry _) =
85 liftM zdfFpContents $ (res :: LiveReloadFix (LGraph Middle Last))
86 where res = zdfBRewriteFromL RewriteDeep emptyBlockEnv "dual liveness with insertion"
87 dualLiveLattice (dualLiveTransfers entry procPoints)
88 (insertSpillAndReloadRewrites entry procPoints) empty g
89 empty = fact_bot dualLiveLattice
91 dualLiveness :: BlockSet -> LGraph Middle Last -> FuelMonad (BlockEnv DualLive)
92 dualLiveness procPoints g@(LGraph entry _) =
93 liftM zdfFpFacts $ (res :: LiveReloadFix ())
94 where res = zdfSolveFromL emptyBlockEnv "dual liveness" dualLiveLattice
95 (dualLiveTransfers entry procPoints) empty g
96 empty = fact_bot dualLiveLattice
98 dualLiveTransfers :: BlockId -> BlockSet -> BackwardTransfers Middle Last DualLive
99 dualLiveTransfers entry procPoints = BackwardTransfers first middle last
100 where last = lastDualLiveness
101 middle = middleDualLiveness
102 first id live = check live id $ -- live at procPoint => spill
103 if id /= entry && elemBlockSet id procPoints then
104 DualLive { on_stack = on_stack live `plusRegSet` in_regs live
105 , in_regs = emptyRegSet }
107 check live id x = if id == entry then noLiveOnEntry id (in_regs live) x else x
109 middleDualLiveness :: Middle -> DualLive -> DualLive
110 middleDualLiveness m live =
111 changeStack updSlots $ changeRegs (middleLiveness m) (changeRegs regs_in live)
112 where regs_in live = case m of MidForeignCall {} -> emptyRegSet
114 updSlots live = foldSlotsUsed reload (foldSlotsDefd spill live m) m
115 spill live s@(RegSlot r, _, _) = check s $ deleteFromRegSet live r
117 reload live s@(RegSlot r, _, _) = check s $ extendRegSet live r
119 check (RegSlot (LocalReg _ ty), o, w) x
120 | o == w && w == widthInBytes (typeWidth ty) = x
121 check _ _ = panic "middleDualLiveness unsupported: slices"
123 lastDualLiveness :: Last -> (BlockId -> DualLive) -> DualLive
124 lastDualLiveness l env = last l
125 where last (LastBranch id) = env id
126 last l@(LastCall _ Nothing _ _ _) = changeRegs (gen l . kill l) empty
127 last l@(LastCall _ (Just k) _ _ _) =
128 -- nothing can be live in registers at this point, unless safe foreign call
130 live_in = DualLive (on_stack live) (gen l emptyRegSet)
131 in if isEmptyUniqSet (in_regs live) then live_in
132 else pprTrace "Offending party:" (ppr k <+> ppr live) $
133 panic "live values in registers at call continuation"
134 last l@(LastCondBranch _ t f) =
135 changeRegs (gen l . kill l) $ dualUnion (env t) (env f)
136 last l@(LastSwitch _ tbl) = changeRegs (gen l . kill l) $ dualUnionList $
137 map env (catMaybes tbl)
138 empty = fact_bot dualLiveLattice
140 gen :: UserOfLocalRegs a => a -> RegSet -> RegSet
141 gen a live = foldRegsUsed extendRegSet live a
142 kill :: DefinerOfLocalRegs a => a -> RegSet -> RegSet
143 kill a live = foldRegsDefd deleteFromRegSet live a
145 insertSpillAndReloadRewrites ::
146 BlockId -> BlockSet -> BackwardRewrites Middle Last DualLive
147 insertSpillAndReloadRewrites entry procPoints =
148 BackwardRewrites first middle last exit
149 where middle = middleInsertSpillsAndReloads
153 if id /= entry && elemBlockSet id procPoints then
154 case map reload (uniqSetToList (in_regs live)) of
156 is -> Just (mkMiddles is)
159 middleInsertSpillsAndReloads :: Middle -> DualLive -> Maybe (AGraph Middle Last)
160 middleInsertSpillsAndReloads m live = middle m
161 where middle (MidAssign (CmmLocal reg) (CmmLoad (CmmStackSlot (RegSlot reg') _) _))
162 | reg == reg' = Nothing
163 middle (MidAssign (CmmLocal reg) _) =
164 if reg `elemRegSet` on_stack live then -- must spill
165 my_trace "Spilling" (f4sep [text "spill" <+> ppr reg,
166 text "after", ppr m]) $
167 Just $ mkMiddles $ [m, spill reg]
169 middle (MidForeignCall _ _ fs _) =
170 case map spill (filter (flip elemRegSet (on_stack live)) fs) ++
171 map reload (uniqSetToList (kill fs (in_regs live))) of
173 reloads -> Just (mkMiddles (m : reloads))
176 -- Generating spill and reload code
177 regSlot :: LocalReg -> CmmExpr
178 regSlot r = CmmStackSlot (RegSlot r) (widthInBytes $ typeWidth $ localRegType r)
180 spill, reload :: LocalReg -> Middle
181 spill r = MidStore (regSlot r) (CmmReg $ CmmLocal r)
182 reload r = MidAssign (CmmLocal r) (CmmLoad (regSlot r) $ localRegType r)
184 ----------------------------------------------------------------
187 -- The idea is to compute at each point the set of registers such that
188 -- on every path to the point, the register is defined by a Reload
189 -- instruction. Then, if a use appears at such a point, we can safely
190 -- insert a Reload right before the use. Finally, we can eliminate
191 -- the early reloads along with other dead assignments.
193 data AvailRegs = UniverseMinus RegSet
197 availRegsLattice :: DataflowLattice AvailRegs
198 availRegsLattice = DataflowLattice "register gotten from reloads" empty add False
199 where empty = UniverseMinus emptyRegSet
200 -- | compute in the Tx monad to track whether anything has changed
202 let join = interAvail new old in
203 if join `smallerAvail` old then aTx join else noTx join
206 interAvail :: AvailRegs -> AvailRegs -> AvailRegs
207 interAvail (UniverseMinus s) (UniverseMinus s') = UniverseMinus (s `plusRegSet` s')
208 interAvail (AvailRegs s) (AvailRegs s') = AvailRegs (s `timesRegSet` s')
209 interAvail (AvailRegs s) (UniverseMinus s') = AvailRegs (s `minusRegSet` s')
210 interAvail (UniverseMinus s) (AvailRegs s') = AvailRegs (s' `minusRegSet` s )
212 smallerAvail :: AvailRegs -> AvailRegs -> Bool
213 smallerAvail (AvailRegs _) (UniverseMinus _) = True
214 smallerAvail (UniverseMinus _) (AvailRegs _) = False
215 smallerAvail (AvailRegs s) (AvailRegs s') = sizeUniqSet s < sizeUniqSet s'
216 smallerAvail (UniverseMinus s) (UniverseMinus s') = sizeUniqSet s > sizeUniqSet s'
218 extendAvail :: AvailRegs -> LocalReg -> AvailRegs
219 extendAvail (UniverseMinus s) r = UniverseMinus (deleteFromRegSet s r)
220 extendAvail (AvailRegs s) r = AvailRegs (extendRegSet s r)
222 delFromAvail :: AvailRegs -> LocalReg -> AvailRegs
223 delFromAvail (UniverseMinus s) r = UniverseMinus (extendRegSet s r)
224 delFromAvail (AvailRegs s) r = AvailRegs (deleteFromRegSet s r)
226 elemAvail :: AvailRegs -> LocalReg -> Bool
227 elemAvail (UniverseMinus s) r = not $ elemRegSet r s
228 elemAvail (AvailRegs s) r = elemRegSet r s
230 type AvailFix = FuelMonad (ForwardFixedPoint Middle Last AvailRegs ())
232 cmmAvailableReloads :: LGraph Middle Last -> FuelMonad (BlockEnv AvailRegs)
233 cmmAvailableReloads g = liftM zdfFpFacts $ (res :: AvailFix)
234 where res = zdfSolveFromL emptyBlockEnv "available reloads" availRegsLattice
235 avail_reloads_transfer empty g
236 empty = fact_bot availRegsLattice
238 avail_reloads_transfer :: ForwardTransfers Middle Last AvailRegs
239 avail_reloads_transfer = ForwardTransfers (flip const) middleAvail lastAvail id
241 middleAvail :: Middle -> AvailRegs -> AvailRegs
242 middleAvail (MidAssign (CmmLocal r) (CmmLoad l _)) avail
243 | l `isStackSlotOf` r = extendAvail avail r
244 middleAvail (MidAssign lhs _) avail = foldRegsDefd delFromAvail avail lhs
245 middleAvail (MidStore l (CmmReg (CmmLocal r))) avail
246 | l `isStackSlotOf` r = avail
247 middleAvail (MidStore (CmmStackSlot (RegSlot r) _) _) avail = delFromAvail avail r
248 middleAvail (MidStore {}) avail = avail
249 middleAvail (MidForeignCall {}) _ = AvailRegs emptyRegSet
250 middleAvail (MidComment {}) avail = avail
252 lastAvail :: Last -> AvailRegs -> LastOutFacts AvailRegs
253 lastAvail (LastCall _ (Just k) _ _ _) _ = LastOutFacts [(k, AvailRegs emptyRegSet)]
254 lastAvail l avail = LastOutFacts $ map (\id -> (id, avail)) $ succs l
256 type LateReloadFix = FuelMonad (ForwardFixedPoint Middle Last AvailRegs CmmGraph)
258 availRewrites :: ForwardRewrites Middle Last AvailRegs
259 availRewrites = ForwardRewrites first middle last exit
260 where first _ _ = Nothing
261 middle m avail = maybe_reload_before avail m (mkMiddle m)
262 last l avail = maybe_reload_before avail l (mkLast l)
264 maybe_reload_before avail node tail =
265 let used = filterRegsUsed (elemAvail avail) node
266 in if isEmptyUniqSet used then Nothing
267 else Just $ reloadTail used tail
268 reloadTail regset t = foldl rel t $ uniqSetToList regset
269 where rel t r = mkMiddle (reload r) <*> t
272 insertLateReloads :: (LGraph Middle Last) -> FuelMonad (LGraph Middle Last)
273 insertLateReloads g = liftM zdfFpContents $ (res :: LateReloadFix)
274 where res = zdfFRewriteFromL RewriteShallow emptyBlockEnv "insert late reloads"
275 availRegsLattice avail_reloads_transfer availRewrites bot g
276 bot = fact_bot availRegsLattice
278 removeDeadAssignmentsAndReloads :: BlockSet -> (LGraph Middle Last) -> FuelMonad (LGraph Middle Last)
279 removeDeadAssignmentsAndReloads procPoints g@(LGraph entry _) =
280 liftM zdfFpContents $ (res :: LiveReloadFix (LGraph Middle Last))
281 where res = zdfBRewriteFromL RewriteDeep emptyBlockEnv "dead-assignment & -reload elim"
282 dualLiveLattice (dualLiveTransfers entry procPoints)
283 rewrites (fact_bot dualLiveLattice) g
284 rewrites = BackwardRewrites nothing middleRemoveDeads nothing Nothing
285 nothing _ _ = Nothing
287 middleRemoveDeads :: Middle -> DualLive -> Maybe (AGraph Middle Last)
288 middleRemoveDeads (MidAssign (CmmLocal reg') _) live
289 | not (reg' `elemRegSet` in_regs live) = Just emptyAGraph
290 middleRemoveDeads _ _ = Nothing
294 ---------------------
297 ppr_regs :: String -> RegSet -> SDoc
298 ppr_regs s regs = text s <+> commafy (map ppr $ uniqSetToList regs)
299 where commafy xs = hsep $ punctuate comma xs
301 instance Outputable DualLive where
302 ppr (DualLive {in_regs = regs, on_stack = stack}) =
303 if isEmptyUniqSet regs && isEmptyUniqSet stack then
304 text "<nothing-live>"
306 nest 2 $ fsep [if isEmptyUniqSet regs then PP.empty
307 else (ppr_regs "live in regs =" regs),
308 if isEmptyUniqSet stack then PP.empty
309 else (ppr_regs "live on stack =" stack)]
311 instance Outputable AvailRegs where
312 ppr (UniverseMinus s) = if isEmptyUniqSet s then text "<everything available>"
313 else ppr_regs "available = all but" s
314 ppr (AvailRegs s) = if isEmptyUniqSet s then text "<nothing available>"
315 else ppr_regs "available = " s
317 my_trace :: String -> SDoc -> a -> a
318 my_trace = if False then pprTrace else \_ _ a -> a
320 f4sep :: [SDoc] -> SDoc
322 f4sep (d:ds) = fsep (d : map (nest 4) ds)