----------------------------------------------------------------------------- -- -- The register liveness determinator -- -- (c) The University of Glasgow 2004 -- ----------------------------------------------------------------------------- {-# OPTIONS -Wall -fno-warn-name-shadowing #-} module RegAlloc.Liveness ( RegSet, RegMap, emptyRegMap, BlockMap, emptyBlockMap, LiveCmmTop, LiveInstr (..), Liveness (..), LiveInfo (..), LiveBasicBlock, mapBlockTop, mapBlockTopM, mapGenBlockTop, mapGenBlockTopM, stripLive, stripLiveBlock, slurpConflicts, slurpReloadCoalesce, eraseDeltasLive, patchEraseLive, patchRegsLiveInstr, regLiveness ) where import Reg import Instruction import BlockId import Cmm hiding (RegSet) import PprCmm() import Digraph import Outputable import Unique import UniqSet import UniqFM import UniqSupply import Bag import State import FastString import Data.List import Data.Maybe ----------------------------------------------------------------------------- type RegSet = UniqSet Reg type RegMap a = UniqFM a emptyRegMap :: UniqFM a emptyRegMap = emptyUFM type BlockMap a = BlockEnv a emptyBlockMap :: BlockEnv a emptyBlockMap = emptyBlockEnv -- | A top level thing which carries liveness information. type LiveCmmTop instr = GenCmmTop CmmStatic LiveInfo (ListGraph (GenBasicBlock (LiveInstr instr))) -- the "instructions" here are actually more blocks, -- single blocks are acyclic -- multiple blocks are taken to be cyclic. -- | An instruction with liveness information. data LiveInstr instr = Instr instr (Maybe Liveness) -- | spill this reg to a stack slot | SPILL Reg Int -- | reload this reg from a stack slot | RELOAD Int Reg -- | Liveness information. -- The regs which die are ones which are no longer live in the *next* instruction -- in this sequence. -- (NB. if the instruction is a jump, these registers might still be live -- at the jump target(s) - you have to check the liveness at the destination -- block to find out). data Liveness = Liveness { liveBorn :: RegSet -- ^ registers born in this instruction (written to for first time). , liveDieRead :: RegSet -- ^ registers that died because they were read for the last time. , liveDieWrite :: RegSet } -- ^ registers that died because they were clobbered by something. -- | Stash regs live on entry to each basic block in the info part of the cmm code. data LiveInfo = LiveInfo [CmmStatic] -- cmm static stuff (Maybe BlockId) -- id of the first block (BlockMap RegSet) -- argument locals live on entry to this block -- | A basic block with liveness information. type LiveBasicBlock instr = GenBasicBlock (LiveInstr instr) instance Outputable instr => Outputable (LiveInstr instr) where ppr (SPILL reg slot) = hcat [ ptext (sLit "\tSPILL"), char ' ', ppr reg, comma, ptext (sLit "SLOT") <> parens (int slot)] ppr (RELOAD slot reg) = hcat [ ptext (sLit "\tRELOAD"), char ' ', ptext (sLit "SLOT") <> parens (int slot), comma, ppr reg] ppr (Instr instr Nothing) = ppr instr ppr (Instr instr (Just live)) = ppr instr $$ (nest 8 $ vcat [ pprRegs (ptext (sLit "# born: ")) (liveBorn live) , pprRegs (ptext (sLit "# r_dying: ")) (liveDieRead live) , pprRegs (ptext (sLit "# w_dying: ")) (liveDieWrite live) ] $+$ space) where pprRegs :: SDoc -> RegSet -> SDoc pprRegs name regs | isEmptyUniqSet regs = empty | otherwise = name <> (hcat $ punctuate space $ map ppr $ uniqSetToList regs) instance Outputable LiveInfo where ppr (LiveInfo static firstId liveOnEntry) = (vcat $ map ppr static) $$ text "# firstId = " <> ppr firstId $$ text "# liveOnEntry = " <> ppr liveOnEntry -- | map a function across all the basic blocks in this code -- mapBlockTop :: (LiveBasicBlock instr -> LiveBasicBlock instr) -> LiveCmmTop instr -> LiveCmmTop instr mapBlockTop f cmm = evalState (mapBlockTopM (\x -> return $ f x) cmm) () -- | map a function across all the basic blocks in this code (monadic version) -- mapBlockTopM :: Monad m => (LiveBasicBlock instr -> m (LiveBasicBlock instr)) -> LiveCmmTop instr -> m (LiveCmmTop instr) mapBlockTopM _ cmm@(CmmData{}) = return cmm mapBlockTopM f (CmmProc header label params (ListGraph comps)) = do comps' <- mapM (mapBlockCompM f) comps return $ CmmProc header label params (ListGraph comps') mapBlockCompM :: Monad m => (a -> m a') -> (GenBasicBlock a) -> m (GenBasicBlock a') mapBlockCompM f (BasicBlock i blocks) = do blocks' <- mapM f blocks return $ BasicBlock i blocks' -- map a function across all the basic blocks in this code mapGenBlockTop :: (GenBasicBlock i -> GenBasicBlock i) -> (GenCmmTop d h (ListGraph i) -> GenCmmTop d h (ListGraph i)) mapGenBlockTop f cmm = evalState (mapGenBlockTopM (\x -> return $ f x) cmm) () -- | map a function across all the basic blocks in this code (monadic version) mapGenBlockTopM :: Monad m => (GenBasicBlock i -> m (GenBasicBlock i)) -> (GenCmmTop d h (ListGraph i) -> m (GenCmmTop d h (ListGraph i))) mapGenBlockTopM _ cmm@(CmmData{}) = return cmm mapGenBlockTopM f (CmmProc header label params (ListGraph blocks)) = do blocks' <- mapM f blocks return $ CmmProc header label params (ListGraph blocks') -- | Slurp out the list of register conflicts and reg-reg moves from this top level thing. -- Slurping of conflicts and moves is wrapped up together so we don't have -- to make two passes over the same code when we want to build the graph. -- slurpConflicts :: Instruction instr => LiveCmmTop instr -> (Bag (UniqSet Reg), Bag (Reg, Reg)) slurpConflicts live = slurpCmm (emptyBag, emptyBag) live where slurpCmm rs CmmData{} = rs slurpCmm rs (CmmProc info _ _ (ListGraph blocks)) = foldl' (slurpComp info) rs blocks slurpComp info rs (BasicBlock _ blocks) = foldl' (slurpBlock info) rs blocks slurpBlock info rs (BasicBlock blockId instrs) | LiveInfo _ _ blockLive <- info , Just rsLiveEntry <- lookupBlockEnv blockLive blockId , (conflicts, moves) <- slurpLIs rsLiveEntry rs instrs = (consBag rsLiveEntry conflicts, moves) | otherwise = panic "Liveness.slurpConflicts: bad block" slurpLIs rsLive (conflicts, moves) [] = (consBag rsLive conflicts, moves) slurpLIs rsLive rs (Instr _ Nothing : lis) = slurpLIs rsLive rs lis -- we're not expecting to be slurping conflicts from spilled code slurpLIs _ _ (SPILL _ _ : _) = panic "Liveness.slurpConflicts: unexpected SPILL" slurpLIs _ _ (RELOAD _ _ : _) = panic "Liveness.slurpConflicts: unexpected RELOAD" slurpLIs rsLiveEntry (conflicts, moves) (Instr instr (Just live) : lis) = let -- regs that die because they are read for the last time at the start of an instruction -- are not live across it. rsLiveAcross = rsLiveEntry `minusUniqSet` (liveDieRead live) -- regs live on entry to the next instruction. -- be careful of orphans, make sure to delete dying regs _after_ unioning -- in the ones that are born here. rsLiveNext = (rsLiveAcross `unionUniqSets` (liveBorn live)) `minusUniqSet` (liveDieWrite live) -- orphan vregs are the ones that die in the same instruction they are born in. -- these are likely to be results that are never used, but we still -- need to assign a hreg to them.. rsOrphans = intersectUniqSets (liveBorn live) (unionUniqSets (liveDieWrite live) (liveDieRead live)) -- rsConflicts = unionUniqSets rsLiveNext rsOrphans in case takeRegRegMoveInstr instr of Just rr -> slurpLIs rsLiveNext ( consBag rsConflicts conflicts , consBag rr moves) lis Nothing -> slurpLIs rsLiveNext ( consBag rsConflicts conflicts , moves) lis -- | For spill\/reloads -- -- SPILL v1, slot1 -- ... -- RELOAD slot1, v2 -- -- If we can arrange that v1 and v2 are allocated to the same hreg it's more likely -- the spill\/reload instrs can be cleaned and replaced by a nop reg-reg move. -- -- slurpReloadCoalesce :: Instruction instr => LiveCmmTop instr -> Bag (Reg, Reg) slurpReloadCoalesce live = slurpCmm emptyBag live where slurpCmm cs CmmData{} = cs slurpCmm cs (CmmProc _ _ _ (ListGraph blocks)) = foldl' slurpComp cs blocks slurpComp cs comp = let (moveBags, _) = runState (slurpCompM comp) emptyUFM in unionManyBags (cs : moveBags) slurpCompM (BasicBlock _ blocks) = do -- run the analysis once to record the mapping across jumps. mapM_ (slurpBlock False) blocks -- run it a second time while using the information from the last pass. -- We /could/ run this many more times to deal with graphical control -- flow and propagating info across multiple jumps, but it's probably -- not worth the trouble. mapM (slurpBlock True) blocks slurpBlock propagate (BasicBlock blockId instrs) = do -- grab the slot map for entry to this block slotMap <- if propagate then getSlotMap blockId else return emptyUFM (_, mMoves) <- mapAccumLM slurpLI slotMap instrs return $ listToBag $ catMaybes mMoves slurpLI :: Instruction instr => UniqFM Reg -- current slotMap -> LiveInstr instr -> State (UniqFM [UniqFM Reg]) -- blockId -> [slot -> reg] -- for tracking slotMaps across jumps ( UniqFM Reg -- new slotMap , Maybe (Reg, Reg)) -- maybe a new coalesce edge slurpLI slotMap li -- remember what reg was stored into the slot | SPILL reg slot <- li , slotMap' <- addToUFM slotMap slot reg = return (slotMap', Nothing) -- add an edge betwen the this reg and the last one stored into the slot | RELOAD slot reg <- li = case lookupUFM slotMap slot of Just reg2 | reg /= reg2 -> return (slotMap, Just (reg, reg2)) | otherwise -> return (slotMap, Nothing) Nothing -> return (slotMap, Nothing) -- if we hit a jump, remember the current slotMap | Instr instr _ <- li , targets <- jumpDestsOfInstr instr , not $ null targets = do mapM_ (accSlotMap slotMap) targets return (slotMap, Nothing) | otherwise = return (slotMap, Nothing) -- record a slotmap for an in edge to this block accSlotMap slotMap blockId = modify (\s -> addToUFM_C (++) s blockId [slotMap]) -- work out the slot map on entry to this block -- if we have slot maps for multiple in-edges then we need to merge them. getSlotMap blockId = do map <- get let slotMaps = fromMaybe [] (lookupUFM map blockId) return $ foldr mergeSlotMaps emptyUFM slotMaps mergeSlotMaps :: UniqFM Reg -> UniqFM Reg -> UniqFM Reg mergeSlotMaps map1 map2 = listToUFM $ [ (k, r1) | (k, r1) <- ufmToList map1 , case lookupUFM map2 k of Nothing -> False Just r2 -> r1 == r2 ] -- | Strip away liveness information, yielding NatCmmTop stripLive :: Instruction instr => LiveCmmTop instr -> NatCmmTop instr stripLive live = stripCmm live where stripCmm (CmmData sec ds) = CmmData sec ds stripCmm (CmmProc (LiveInfo info _ _) label params (ListGraph comps)) = CmmProc info label params (ListGraph $ concatMap stripComp comps) stripComp (BasicBlock _ blocks) = map stripLiveBlock blocks -- | Strip away liveness information from a basic block, -- and make real spill instructions out of SPILL, RELOAD pseudos along the way. stripLiveBlock :: Instruction instr => LiveBasicBlock instr -> NatBasicBlock instr stripLiveBlock (BasicBlock i lis) = BasicBlock i instrs' where (instrs', _) = runState (spillNat [] lis) 0 spillNat acc [] = return (reverse acc) spillNat acc (SPILL reg slot : instrs) = do delta <- get spillNat (mkSpillInstr reg delta slot : acc) instrs spillNat acc (RELOAD slot reg : instrs) = do delta <- get spillNat (mkLoadInstr reg delta slot : acc) instrs spillNat acc (Instr instr _ : instrs) | Just i <- takeDeltaInstr instr = do put i spillNat acc instrs spillNat acc (Instr instr _ : instrs) = spillNat (instr : acc) instrs -- | Erase Delta instructions. eraseDeltasLive :: Instruction instr => LiveCmmTop instr -> LiveCmmTop instr eraseDeltasLive cmm = mapBlockTop eraseBlock cmm where eraseBlock (BasicBlock id lis) = BasicBlock id $ filter (\(Instr i _) -> not $ isJust $ takeDeltaInstr i) $ lis -- | Patch the registers in this code according to this register mapping. -- also erase reg -> reg moves when the reg is the same. -- also erase reg -> reg moves when the destination dies in this instr. patchEraseLive :: Instruction instr => (Reg -> Reg) -> LiveCmmTop instr -> LiveCmmTop instr patchEraseLive patchF cmm = patchCmm cmm where patchCmm cmm@CmmData{} = cmm patchCmm (CmmProc info label params (ListGraph comps)) | LiveInfo static id blockMap <- info = let patchRegSet set = mkUniqSet $ map patchF $ uniqSetToList set blockMap' = mapBlockEnv patchRegSet blockMap info' = LiveInfo static id blockMap' in CmmProc info' label params $ ListGraph $ map patchComp comps patchComp (BasicBlock id blocks) = BasicBlock id $ map patchBlock blocks patchBlock (BasicBlock id lis) = BasicBlock id $ patchInstrs lis patchInstrs [] = [] patchInstrs (li : lis) | Instr i (Just live) <- li' , Just (r1, r2) <- takeRegRegMoveInstr i , eatMe r1 r2 live = patchInstrs lis | otherwise = li' : patchInstrs lis where li' = patchRegsLiveInstr patchF li eatMe r1 r2 live -- source and destination regs are the same | r1 == r2 = True -- desination reg is never used | elementOfUniqSet r2 (liveBorn live) , elementOfUniqSet r2 (liveDieRead live) || elementOfUniqSet r2 (liveDieWrite live) = True | otherwise = False -- | Patch registers in this LiveInstr, including the liveness information. -- patchRegsLiveInstr :: Instruction instr => (Reg -> Reg) -> LiveInstr instr -> LiveInstr instr patchRegsLiveInstr patchF li = case li of Instr instr Nothing -> Instr (patchRegsOfInstr instr patchF) Nothing Instr instr (Just live) -> Instr (patchRegsOfInstr instr patchF) (Just live { -- WARNING: have to go via lists here because patchF changes the uniq in the Reg liveBorn = mkUniqSet $ map patchF $ uniqSetToList $ liveBorn live , liveDieRead = mkUniqSet $ map patchF $ uniqSetToList $ liveDieRead live , liveDieWrite = mkUniqSet $ map patchF $ uniqSetToList $ liveDieWrite live }) SPILL reg slot -> SPILL (patchF reg) slot RELOAD slot reg -> RELOAD slot (patchF reg) --------------------------------------------------------------------------------- -- Annotate code with register liveness information -- regLiveness :: Instruction instr => NatCmmTop instr -> UniqSM (LiveCmmTop instr) regLiveness (CmmData i d) = returnUs $ CmmData i d regLiveness (CmmProc info lbl params (ListGraph [])) = returnUs $ CmmProc (LiveInfo info Nothing emptyBlockEnv) lbl params (ListGraph []) regLiveness (CmmProc info lbl params (ListGraph blocks@(first : _))) = let first_id = blockId first sccs = sccBlocks blocks (ann_sccs, block_live) = computeLiveness sccs liveBlocks = map (\scc -> case scc of AcyclicSCC b@(BasicBlock l _) -> BasicBlock l [b] CyclicSCC bs@(BasicBlock l _ : _) -> BasicBlock l bs CyclicSCC [] -> panic "RegLiveness.regLiveness: no blocks in scc list") $ ann_sccs in returnUs $ CmmProc (LiveInfo info (Just first_id) block_live) lbl params (ListGraph liveBlocks) sccBlocks :: Instruction instr => [NatBasicBlock instr] -> [SCC (NatBasicBlock instr)] sccBlocks blocks = stronglyConnCompFromEdgedVertices graph where getOutEdges :: Instruction instr => [instr] -> [BlockId] getOutEdges instrs = concat $ map jumpDestsOfInstr instrs graph = [ (block, getUnique id, map getUnique (getOutEdges instrs)) | block@(BasicBlock id instrs) <- blocks ] -- ----------------------------------------------------------------------------- -- Computing liveness computeLiveness :: Instruction instr => [SCC (NatBasicBlock instr)] -> ([SCC (LiveBasicBlock instr)], -- instructions annotated with list of registers -- which are "dead after this instruction". BlockMap RegSet) -- blocks annontated with set of live registers -- on entry to the block. -- NOTE: on entry, the SCCs are in "reverse" order: later blocks may transfer -- control to earlier ones only. The SCCs returned are in the *opposite* -- order, which is exactly what we want for the next pass. computeLiveness sccs = livenessSCCs emptyBlockMap [] sccs livenessSCCs :: Instruction instr => BlockMap RegSet -> [SCC (LiveBasicBlock instr)] -- accum -> [SCC (NatBasicBlock instr)] -> ( [SCC (LiveBasicBlock instr)] , BlockMap RegSet) livenessSCCs blockmap done [] = (done, blockmap) livenessSCCs blockmap done (AcyclicSCC block : sccs) = let (blockmap', block') = livenessBlock blockmap block in livenessSCCs blockmap' (AcyclicSCC block' : done) sccs livenessSCCs blockmap done (CyclicSCC blocks : sccs) = livenessSCCs blockmap' (CyclicSCC blocks':done) sccs where (blockmap', blocks') = iterateUntilUnchanged linearLiveness equalBlockMaps blockmap blocks iterateUntilUnchanged :: (a -> b -> (a,c)) -> (a -> a -> Bool) -> a -> b -> (a,c) iterateUntilUnchanged f eq a b = head $ concatMap tail $ groupBy (\(a1, _) (a2, _) -> eq a1 a2) $ iterate (\(a, _) -> f a b) $ (a, panic "RegLiveness.livenessSCCs") linearLiveness :: Instruction instr => BlockMap RegSet -> [NatBasicBlock instr] -> (BlockMap RegSet, [LiveBasicBlock instr]) linearLiveness = mapAccumL livenessBlock -- probably the least efficient way to compare two -- BlockMaps for equality. equalBlockMaps a b = a' == b' where a' = map f $ blockEnvToList a b' = map f $ blockEnvToList b f (key,elt) = (key, uniqSetToList elt) -- | Annotate a basic block with register liveness information. -- livenessBlock :: Instruction instr => BlockMap RegSet -> NatBasicBlock instr -> (BlockMap RegSet, LiveBasicBlock instr) livenessBlock blockmap (BasicBlock block_id instrs) = let (regsLiveOnEntry, instrs1) = livenessBack emptyUniqSet blockmap [] (reverse instrs) blockmap' = extendBlockEnv blockmap block_id regsLiveOnEntry instrs2 = livenessForward regsLiveOnEntry instrs1 output = BasicBlock block_id instrs2 in ( blockmap', output) -- | Calculate liveness going forwards, -- filling in when regs are born livenessForward :: Instruction instr => RegSet -- regs live on this instr -> [LiveInstr instr] -> [LiveInstr instr] livenessForward _ [] = [] livenessForward rsLiveEntry (li@(Instr instr mLive) : lis) | Nothing <- mLive = li : livenessForward rsLiveEntry lis | Just live <- mLive , RU _ written <- regUsageOfInstr instr = let -- Regs that are written to but weren't live on entry to this instruction -- are recorded as being born here. rsBorn = mkUniqSet $ filter (\r -> not $ elementOfUniqSet r rsLiveEntry) written rsLiveNext = (rsLiveEntry `unionUniqSets` rsBorn) `minusUniqSet` (liveDieRead live) `minusUniqSet` (liveDieWrite live) in Instr instr (Just live { liveBorn = rsBorn }) : livenessForward rsLiveNext lis livenessForward _ _ = panic "RegLiveness.livenessForward: no match" -- | Calculate liveness going backwards, -- filling in when regs die, and what regs are live across each instruction livenessBack :: Instruction instr => RegSet -- regs live on this instr -> BlockMap RegSet -- regs live on entry to other BBs -> [LiveInstr instr] -- instructions (accum) -> [instr] -- instructions -> (RegSet, [LiveInstr instr]) livenessBack liveregs _ done [] = (liveregs, done) livenessBack liveregs blockmap acc (instr : instrs) = let (liveregs', instr') = liveness1 liveregs blockmap instr in livenessBack liveregs' blockmap (instr' : acc) instrs -- don't bother tagging comments or deltas with liveness liveness1 :: Instruction instr => RegSet -> BlockMap RegSet -> instr -> (RegSet, LiveInstr instr) liveness1 liveregs _ instr | isMetaInstr instr = (liveregs, Instr instr Nothing) liveness1 liveregs blockmap instr | not_a_branch = (liveregs1, Instr instr (Just $ Liveness { liveBorn = emptyUniqSet , liveDieRead = mkUniqSet r_dying , liveDieWrite = mkUniqSet w_dying })) | otherwise = (liveregs_br, Instr instr (Just $ Liveness { liveBorn = emptyUniqSet , liveDieRead = mkUniqSet r_dying_br , liveDieWrite = mkUniqSet w_dying })) where RU read written = regUsageOfInstr instr -- registers that were written here are dead going backwards. -- registers that were read here are live going backwards. liveregs1 = (liveregs `delListFromUniqSet` written) `addListToUniqSet` read -- registers that are not live beyond this point, are recorded -- as dying here. r_dying = [ reg | reg <- read, reg `notElem` written, not (elementOfUniqSet reg liveregs) ] w_dying = [ reg | reg <- written, not (elementOfUniqSet reg liveregs) ] -- union in the live regs from all the jump destinations of this -- instruction. targets = jumpDestsOfInstr instr -- where we go from here not_a_branch = null targets targetLiveRegs target = case lookupBlockEnv blockmap target of Just ra -> ra Nothing -> emptyRegMap live_from_branch = unionManyUniqSets (map targetLiveRegs targets) liveregs_br = liveregs1 `unionUniqSets` live_from_branch -- registers that are live only in the branch targets should -- be listed as dying here. live_branch_only = live_from_branch `minusUniqSet` liveregs r_dying_br = uniqSetToList (mkUniqSet r_dying `unionUniqSets` live_branch_only)