module CmmSpillReload ( DualLive(..) , dualLiveLattice, dualLiveTransfers, dualLiveness --, insertSpillsAndReloads --- XXX todo check live-in at entry against formals , dualLivenessWithInsertion , 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 be followed by a -- forward transformation to sink reloads as deeply as possible, so as -- to reduce register pressure. -- 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 Middle Last DualLive a) dualLivenessWithInsertion :: BlockSet -> (LGraph Middle Last) -> FuelMonad (LGraph Middle Last) dualLivenessWithInsertion procPoints g = liftM zdfFpContents $ (res :: LiveReloadFix (LGraph Middle Last)) where res = zdfBRewriteFromL RewriteDeep emptyBlockEnv "dual liveness with insertion" dualLiveLattice (dualLiveTransfers procPoints) (insertSpillAndReloadRewrites procPoints) empty g empty = fact_bot dualLiveLattice dualLiveness :: BlockSet -> LGraph Middle Last -> FuelMonad (BlockEnv DualLive) dualLiveness procPoints g = liftM zdfFpFacts $ (res :: LiveReloadFix ()) where res = zdfSolveFromL emptyBlockEnv "dual liveness" dualLiveLattice (dualLiveTransfers procPoints) empty g empty = fact_bot dualLiveLattice dualLiveTransfers :: BlockSet -> BackwardTransfers Middle 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 -> Middle -> DualLive middleDualLiveness live m = changeStack updSlots $ changeRegs (middleLiveness m) live where updSlots live = foldSlotsUsed reload (foldSlotsDefd spill live m) m spill live s@(RegSlot r, _, _) = check s $ deleteFromRegSet live r spill live _ = live reload live s@(RegSlot r, _, _) = check s $ extendRegSet live r reload live _ = live check (RegSlot (LocalReg _ ty), o, w) x | o == w && w == widthInBytes (typeWidth ty) = x check _ _ = panic "middleDualLiveness unsupported: slices" 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 :: UserOfLocalRegs a => a -> RegSet -> RegSet gen a live = foldRegsUsed extendRegSet live a insertSpillAndReloadRewrites :: BlockSet -> BackwardRewrites Middle 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 $ map reload $ uniqSetToList reloads else Nothing where reloads = in_regs live middleInsertSpillsAndReloads :: DualLive -> Middle -> Maybe (AGraph Middle Last) middleInsertSpillsAndReloads live m = middle m where middle (MidAssign (CmmLocal reg) (CmmLoad (CmmStackSlot (RegSlot reg') _) _)) | reg == reg' = Nothing 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 reg] else Nothing middle _ = Nothing -- Generating spill and reload code regSlot :: LocalReg -> CmmExpr regSlot r = CmmStackSlot (RegSlot r) (widthInBytes $ typeWidth $ localRegType r) spill, reload :: LocalReg -> Middle spill r = MidStore (regSlot r) (CmmReg $ CmmLocal r) reload r = MidAssign (CmmLocal r) (CmmLoad (regSlot r) $ localRegType r) spillHead :: ZHead Middle -> RegSet -> ZHead Middle reloadTail :: RegSet -> ZTail Middle Last -> ZTail Middle Last spillHead h regset = foldl spl h $ uniqSetToList regset where spl h r = ZHead h $ spill r reloadTail regset t = foldl rel t $ uniqSetToList regset where rel t r = ZTail (reload r) t ---------------------------------------------------------------- --- 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 Middle Last AvailRegs ()) cmmAvailableReloads :: LGraph Middle Last -> FuelMonad CmmAvail cmmAvailableReloads g = liftM zdfFpFacts $ (res :: AvailFix) where res = zdfSolveFromL emptyBlockEnv "available reloads" availRegsLattice avail_reloads_transfer empty g empty = (fact_bot availRegsLattice) avail_reloads_transfer :: ForwardTransfers Middle 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 :: Middle -> AvailRegs -> AvailRegs middleAvail 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 lastAvail :: AvailRegs -> Last -> LastOutFacts AvailRegs lastAvail _ (LastCall _ (Just k) _) = LastOutFacts [(k, AvailRegs emptyRegSet)] lastAvail avail l = LastOutFacts $ map (\id -> (id, avail)) $ succs l insertLateReloads :: LGraph Middle Last -> FuelMonad (LGraph Middle Last) insertLateReloads g = do env <- cmmAvailableReloads g 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 off tail) fuel = propagate (ZFirst id off) (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 (spillHead h used, oneLessFuel fuel) type LateReloadFix = FuelMonad (ForwardFixedPoint Middle Last AvailRegs (LGraph Middle Last)) insertLateReloads' :: (LGraph Middle Last) -> FuelMonad (LGraph Middle Last) insertLateReloads' g = liftM zdfFpContents $ (res :: LateReloadFix) where res = zdfFRewriteFromL 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 -> Middle -> Maybe (AGraph Middle Last) last :: AvailRegs -> Last -> Maybe (AGraph Middle 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 $ reloadTail used tail removeDeadAssignmentsAndReloads :: BlockSet -> (LGraph Middle Last) -> FuelMonad (LGraph Middle Last) removeDeadAssignmentsAndReloads procPoints g = liftM zdfFpContents $ (res :: LiveReloadFix (LGraph Middle Last)) where res = zdfBRewriteFromL 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 -> Middle -> Maybe (AGraph Middle Last) middleRemoveDeads live m = middle m where middle (MidAssign (CmmLocal reg') _) | not (reg' `elemRegSet` in_regs live) = Just emptyAGraph middle _ = Nothing --------------------- -- prettyprinting 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)