module CmmSpillReload ( ExtendWithSpills(..) , DualLive(..) , dualLiveLattice, dualLiveTransfers, dualLiveness --, insertSpillsAndReloads --- XXX todo check live-in at entry against formals , dualLivenessWithInsertion , elimSpillAndReload , availRegsLattice , cmmAvailableReloads , insertLateReloads , insertLateReloads' , removeDeadAssignmentsAndReloads ) where import BlockId import CmmExpr import CmmTx import CmmLiveZ import DFMonad import MkZipCfg import OptimizationFuel import PprCmm() import ZipCfg import ZipCfgCmmRep import ZipDataflow import Maybes import Monad import Outputable hiding (empty) import qualified Outputable as PP import Panic import UniqSet import Maybe import Prelude hiding (zip) -- The point of this module is to insert spills and reloads to -- establish the invariant that at a call (or at any proc point with -- an established protocol) all live variables not expected in -- registers are sitting on the stack. We use a backward analysis to -- insert spills and reloads. It should some day be followed by a -- forward transformation to sink reloads as deeply as possible, so as -- to reduce register pressure. data ExtendWithSpills m = NotSpillOrReload m | Spill RegSet | Reload RegSet type M = ExtendWithSpills Middle -- A variable can be expected to be live in a register, live on the -- stack, or both. This analysis ensures that spills and reloads are -- inserted as needed to make sure that every live variable needed -- after a call is available on the stack. Spills are pushed back to -- their reaching definitions, but reloads are dropped wherever needed -- and will have to be sunk by a later forward transformation. data DualLive = DualLive { on_stack :: RegSet, in_regs :: RegSet } dualUnion :: DualLive -> DualLive -> DualLive dualUnion (DualLive s r) (DualLive s' r') = DualLive (s `unionUniqSets` s') (r `unionUniqSets` r') dualUnionList :: [DualLive] -> DualLive dualUnionList ls = DualLive ss rs where ss = unionManyUniqSets $ map on_stack ls rs = unionManyUniqSets $ map in_regs ls _changeStack, changeRegs :: (RegSet -> RegSet) -> DualLive -> DualLive _changeStack f live = live { on_stack = f (on_stack live) } changeRegs f live = live { in_regs = f (in_regs live) } dualLiveLattice :: DataflowLattice DualLive dualLiveLattice = DataflowLattice "variables live in registers and on stack" empty add True where empty = DualLive emptyRegSet emptyRegSet -- | compute in the Tx monad to track whether anything has changed add new old = do stack <- add1 (on_stack new) (on_stack old) regs <- add1 (in_regs new) (in_regs old) return $ DualLive stack regs add1 = fact_add_to liveLattice type LiveReloadFix a = FuelMonad (BackwardFixedPoint M Last DualLive a) dualLivenessWithInsertion :: BlockSet -> (Graph M Last) -> FuelMonad (Graph M Last) dualLivenessWithInsertion procPoints g = liftM zdfFpContents $ (res :: LiveReloadFix (Graph M Last)) where res = zdfRewriteFrom RewriteDeep emptyBlockEnv "dual liveness with insertion" dualLiveLattice (dualLiveTransfers procPoints) (insertSpillAndReloadRewrites procPoints) empty g empty = fact_bot dualLiveLattice -- = a_ft_b_unlimited dualLiveness insertSpillsAndReloads dualLiveness :: BlockSet -> Graph M Last -> FuelMonad (BlockEnv DualLive) dualLiveness procPoints g = liftM zdfFpFacts $ (res :: LiveReloadFix ()) where res = zdfSolveFrom emptyBlockEnv "dual liveness" dualLiveLattice (dualLiveTransfers procPoints) empty g empty = fact_bot dualLiveLattice dualLiveTransfers :: BlockSet -> BackwardTransfers M Last DualLive dualLiveTransfers procPoints = BackwardTransfers first middle last where last = lastDualLiveness middle = middleDualLiveness first live _id = if elemBlockSet _id procPoints then -- live at procPoint => spill DualLive { on_stack = on_stack live `plusRegSet` in_regs live , in_regs = emptyRegSet } else live middleDualLiveness :: DualLive -> M -> DualLive middleDualLiveness live (Spill regs) = live' -- live-in on-stack requirements are satisfied; -- live-out in-regs obligations are created where live' = DualLive { on_stack = on_stack live `minusRegSet` regs , in_regs = in_regs live `plusRegSet` regs } middleDualLiveness live (Reload regs) = live' -- live-in in-regs requirements are satisfied; -- live-out on-stack obligations are created where live' = DualLive { on_stack = on_stack live `plusRegSet` regs , in_regs = in_regs live `minusRegSet` regs } middleDualLiveness live (NotSpillOrReload m) = changeRegs (middleLiveness m) live lastDualLiveness :: (BlockId -> DualLive) -> Last -> DualLive lastDualLiveness env l = last l where last (LastReturn) = empty last (LastJump e) = changeRegs (gen e) empty last (LastBranch id) = env id last (LastCall tgt Nothing) = changeRegs (gen tgt) empty last (LastCall tgt (Just k)) = -- nothing can be live in registers at this point let live = env k in if isEmptyUniqSet (in_regs live) then DualLive (on_stack live) (gen tgt emptyRegSet) else pprTrace "Offending party:" (ppr k <+> ppr live) $ panic "live values in registers at call continuation" last (LastCondBranch e t f) = changeRegs (gen e) $ dualUnion (env t) (env f) last (LastSwitch e tbl) = changeRegs (gen e) $ dualUnionList $ map env (catMaybes tbl) empty = fact_bot dualLiveLattice gen, kill :: UserOfLocalRegs a => a -> RegSet -> RegSet gen a live = foldRegsUsed extendRegSet live a kill a live = foldRegsUsed delOneFromUniqSet live a insertSpillAndReloadRewrites :: BlockSet -> BackwardRewrites M Last DualLive insertSpillAndReloadRewrites procPoints = BackwardRewrites first middle last exit where middle = middleInsertSpillsAndReloads last = \_ _ -> Nothing exit = Nothing first live id = if elemBlockSet id procPoints && not (isEmptyUniqSet reloads) then Just $ mkMiddles $ [Reload reloads] else Nothing where reloads = in_regs live middleInsertSpillsAndReloads :: DualLive -> M -> Maybe (AGraph M Last) middleInsertSpillsAndReloads _ (Spill _) = Nothing middleInsertSpillsAndReloads _ (Reload _) = Nothing middleInsertSpillsAndReloads live m@(NotSpillOrReload nsr) = middle nsr where middle (MidAssign (CmmLocal reg) _) = if reg `elemRegSet` on_stack live then -- must spill my_trace "Spilling" (f4sep [text "spill" <+> ppr reg, text "after", ppr m]) $ Just $ mkMiddles [m, Spill $ mkRegSet [reg]] else Nothing middle (CopyIn _ formals _) = -- only 'formals' can be in regs at this point let regs' = kill formals (in_regs live) -- live in regs; must reload is_stack_var r = elemRegSet r (on_stack live) needs_spilling = filterRegsUsed is_stack_var formals -- a formal that is expected on the stack; must spill in if isEmptyUniqSet regs' && isEmptyUniqSet needs_spilling then Nothing else let code = if isEmptyUniqSet regs' then [] else Reload regs' : [] code' = if isEmptyUniqSet needs_spilling then code else Spill needs_spilling : code in my_trace "At CopyIn" (f4sep [text "Triggered by ", ppr live, ppr (Reload regs' :: M), ppr (Spill needs_spilling :: M), text "after", ppr m]) $ Just $ mkMiddles (m : code') middle _ = Nothing -- | For conversion back to vanilla C-- elimSpillAndReload :: StackSlotMap -> LGraph M l -> (StackSlotMap, LGraph Middle l) elimSpillAndReload slots g = toGraph $ fold_blocks block ((slots, [])) g where toGraph (slots, l) = (slots, of_block_list (lg_entry g) l) block (Block id t) (slots, blocks) = lift (\ t' -> Block id t' : blocks) $ tail t slots tail (ZLast l) slots = (slots, ZLast l) tail (ZTail m t) slots = middle m $ tail t slots middle (NotSpillOrReload m) (slots, t) = (slots, ZTail m t) middle (Spill regs) z = foldUniqSet spill z regs middle (Reload regs) z = foldUniqSet reload z regs move f r (slots, t) = lift (\ slot -> ZTail (f slot (CmmLocal r)) t) $ getSlot slots r spill = move (\ slot reg -> MidStore slot (CmmReg reg)) reload = move (\ slot reg -> MidAssign reg slot) lift f (slots, x) = (slots, f x) ---------------------------------------------------------------- --- sinking reloads -- The idea is to compute at each point the set of registers such that -- on every path to the point, the register is defined by a Reload -- instruction. Then, if a use appears at such a point, we can safely -- insert a Reload right before the use. Finally, we can eliminate -- the early reloads along with other dead assignments. data AvailRegs = UniverseMinus RegSet | AvailRegs RegSet availRegsLattice :: DataflowLattice AvailRegs availRegsLattice = DataflowLattice "register gotten from reloads" empty add False -- last True <==> debugging on where empty = UniverseMinus emptyRegSet -- | compute in the Tx monad to track whether anything has changed add new old = let join = interAvail new old in if join `smallerAvail` old then aTx join else noTx join interAvail :: AvailRegs -> AvailRegs -> AvailRegs interAvail (UniverseMinus s) (UniverseMinus s') = UniverseMinus (s `plusRegSet` s') interAvail (AvailRegs s) (AvailRegs s') = AvailRegs (s `timesRegSet` s') interAvail (AvailRegs s) (UniverseMinus s') = AvailRegs (s `minusRegSet` s') interAvail (UniverseMinus s) (AvailRegs s') = AvailRegs (s' `minusRegSet` s ) smallerAvail :: AvailRegs -> AvailRegs -> Bool smallerAvail (AvailRegs _) (UniverseMinus _) = True smallerAvail (UniverseMinus _) (AvailRegs _) = False smallerAvail (AvailRegs s) (AvailRegs s') = sizeUniqSet s < sizeUniqSet s' smallerAvail (UniverseMinus s) (UniverseMinus s') = sizeUniqSet s > sizeUniqSet s' extendAvail :: AvailRegs -> LocalReg -> AvailRegs extendAvail (UniverseMinus s) r = UniverseMinus (deleteFromRegSet s r) extendAvail (AvailRegs s) r = AvailRegs (extendRegSet s r) deleteFromAvail :: AvailRegs -> LocalReg -> AvailRegs deleteFromAvail (UniverseMinus s) r = UniverseMinus (extendRegSet s r) deleteFromAvail (AvailRegs s) r = AvailRegs (deleteFromRegSet s r) elemAvail :: AvailRegs -> LocalReg -> Bool elemAvail (UniverseMinus s) r = not $ elemRegSet r s elemAvail (AvailRegs s) r = elemRegSet r s type CmmAvail = BlockEnv AvailRegs type AvailFix = FuelMonad (ForwardFixedPoint M Last AvailRegs ()) cmmAvailableReloads :: Graph M Last -> FuelMonad CmmAvail cmmAvailableReloads g = liftM zdfFpFacts $ (res :: AvailFix) where res = zdfSolveFrom emptyBlockEnv "available reloads" availRegsLattice avail_reloads_transfer empty g empty = (fact_bot availRegsLattice) avail_reloads_transfer :: ForwardTransfers M Last AvailRegs avail_reloads_transfer = ForwardTransfers first middle last id where first avail _ = avail middle = flip middleAvail last = lastAvail -- | The transfer equations use the traditional 'gen' and 'kill' -- notations, which should be familiar from the dragon book. agen, akill :: UserOfLocalRegs a => a -> AvailRegs -> AvailRegs agen a live = foldRegsUsed extendAvail live a akill a live = foldRegsUsed deleteFromAvail live a -- Note: you can't sink the reload past a use. middleAvail :: M -> AvailRegs -> AvailRegs middleAvail (Spill _) = id middleAvail (Reload regs) = agen regs middleAvail (NotSpillOrReload m) = middle m where middle m live = middle' m $ foldRegsUsed deleteFromAvail live m middle' (MidComment {}) = id middle' (MidAssign lhs _expr) = akill lhs middle' (MidStore {}) = id middle' (MidUnsafeCall _tgt ress _args) = akill ress middle' (MidAddToContext {}) = id middle' (CopyIn _ formals _) = akill formals middle' (CopyOut {}) = id lastAvail :: AvailRegs -> Last -> LastOutFacts AvailRegs lastAvail _ (LastCall _ (Just k)) = LastOutFacts [(k, AvailRegs emptyRegSet)] lastAvail avail l = LastOutFacts $ map (\id -> (id, avail)) $ succs l insertLateReloads :: Graph M Last -> FuelMonad (Graph M Last) insertLateReloads g = do env <- cmmAvailableReloads g g <- lGraphOfGraph g liftM graphOfLGraph $ mapM_blocks (insertM env) g where insertM env b = fuelConsumingPass "late reloads" (insert b) where avail id = lookupBlockEnv env id `orElse` AvailRegs emptyRegSet insert (Block id tail) fuel = propagate (ZFirst id) (avail id) tail fuel propagate h avail (ZTail m t) fuel = let (h', fuel') = maybe_add_reload h avail m fuel in propagate (ZHead h' m) (middleAvail m avail) t fuel' propagate h avail (ZLast l) fuel = let (h', fuel') = maybe_add_reload h avail l fuel in (zipht h' (ZLast l), fuel') maybe_add_reload h avail node fuel = let used = filterRegsUsed (elemAvail avail) node in if not (canRewriteWithFuel fuel) || isEmptyUniqSet used then (h,fuel) else (ZHead h (Reload used), oneLessFuel fuel) type LateReloadFix = FuelMonad (ForwardFixedPoint M Last AvailRegs (Graph M Last)) insertLateReloads' :: (Graph M Last) -> FuelMonad (Graph M Last) insertLateReloads' g = liftM zdfFpContents $ (res :: LateReloadFix) where res = zdfRewriteFrom RewriteShallow emptyBlockEnv "insert late reloads" availRegsLattice avail_reloads_transfer rewrites bot g bot = fact_bot availRegsLattice rewrites = ForwardRewrites first middle last exit first _ _ = Nothing middle :: AvailRegs -> M -> Maybe (AGraph M Last) last :: AvailRegs -> Last -> Maybe (AGraph M Last) middle avail m = maybe_reload_before avail m (ZTail m (ZLast LastExit)) last avail l = maybe_reload_before avail l (ZLast (LastOther l)) exit _ = Nothing maybe_reload_before avail node tail = let used = filterRegsUsed (elemAvail avail) node in if isEmptyUniqSet used then Nothing else Just $ mkZTail $ ZTail (Reload used) tail removeDeadAssignmentsAndReloads :: BlockSet -> (Graph M Last) -> FuelMonad (Graph M Last) removeDeadAssignmentsAndReloads procPoints g = liftM zdfFpContents $ (res :: LiveReloadFix (Graph M Last)) where res = zdfRewriteFrom RewriteDeep emptyBlockEnv "dead-assignment & -reload elim" dualLiveLattice (dualLiveTransfers procPoints) rewrites (fact_bot dualLiveLattice) g rewrites = BackwardRewrites first middle last exit exit = Nothing last = \_ _ -> Nothing middle = middleRemoveDeads first _ _ = Nothing middleRemoveDeads :: DualLive -> M -> Maybe (AGraph M Last) middleRemoveDeads _ (Spill _) = Nothing middleRemoveDeads live (Reload s) = if sizeUniqSet worth_reloading < sizeUniqSet s then Just $ if isEmptyUniqSet worth_reloading then emptyAGraph else mkMiddles [Reload worth_reloading] else Nothing where worth_reloading = intersectUniqSets s (in_regs live) middleRemoveDeads live (NotSpillOrReload m) = middle m where middle (MidAssign (CmmLocal reg') _) | not (reg' `elemRegSet` in_regs live) = Just emptyAGraph middle _ = Nothing --------------------- -- register usage instance UserOfLocalRegs m => UserOfLocalRegs (ExtendWithSpills m) where foldRegsUsed f z (Spill regs) = foldRegsUsed f z regs foldRegsUsed _f z (Reload _) = z foldRegsUsed f z (NotSpillOrReload m) = foldRegsUsed f z m --------------------- -- prettyprinting instance Outputable m => Outputable (ExtendWithSpills m) where ppr (Spill regs) = ppr_regs "Spill" regs ppr (Reload regs) = ppr_regs "Reload" regs ppr (NotSpillOrReload m) = ppr m instance Outputable m => DebugNodes (ExtendWithSpills m) Last ppr_regs :: String -> RegSet -> SDoc ppr_regs s regs = text s <+> commafy (map ppr $ uniqSetToList regs) where commafy xs = hsep $ punctuate comma xs instance Outputable DualLive where ppr (DualLive {in_regs = regs, on_stack = stack}) = if isEmptyUniqSet regs && isEmptyUniqSet stack then text "" else nest 2 $ fsep [if isEmptyUniqSet regs then PP.empty else (ppr_regs "live in regs =" regs), if isEmptyUniqSet stack then PP.empty else (ppr_regs "live on stack =" stack)] instance Outputable AvailRegs where ppr (UniverseMinus s) = if isEmptyUniqSet s then text "" else ppr_regs "available = all but" s ppr (AvailRegs s) = if isEmptyUniqSet s then text "" else ppr_regs "available = " s my_trace :: String -> SDoc -> a -> a my_trace = if False then pprTrace else \_ _ a -> a f4sep :: [SDoc] -> SDoc f4sep [] = fsep [] f4sep (d:ds) = fsep (d : map (nest 4) ds)