----------------------------------------------------------------------------- -- -- The register liveness determinator -- -- (c) The University of Glasgow 2004 -- ----------------------------------------------------------------------------- {-# OPTIONS -w #-} -- The above warning supression flag is a temporary kludge. -- While working on this module you are encouraged to remove it and fix -- any warnings in the module. See -- http://hackage.haskell.org/trac/ghc/wiki/CodingStyle#Warnings -- for details module RegLiveness ( RegSet, RegMap, emptyRegMap, BlockMap, emptyBlockMap, LiveCmmTop, LiveInstr (..), Liveness (..), LiveInfo (..), LiveBasicBlock, mapBlockTop, mapBlockTopM, mapGenBlockTop, mapGenBlockTopM, stripLive, spillNatBlock, slurpConflicts, lifetimeCount, eraseDeltasLive, patchEraseLive, patchRegsLiveInstr, regLiveness ) where #include "HsVersions.h" import MachRegs import MachInstrs import PprMach import RegAllocInfo import Cmm import Digraph import Outputable import Unique import UniqSet import UniqFM import UniqSupply import Bag import State import Data.List import Data.Maybe ----------------------------------------------------------------------------- type RegSet = UniqSet Reg type RegMap a = UniqFM a emptyRegMap = emptyUFM type BlockMap a = UniqFM a emptyBlockMap = emptyUFM -- | A top level thing which carries liveness information. type LiveCmmTop = GenCmmTop CmmStatic LiveInfo (GenBasicBlock LiveInstr) -- 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 (Maybe Liveness) -- | 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 = GenBasicBlock LiveInstr instance Outputable LiveInstr where ppr (Instr instr Nothing) = ppr instr ppr (Instr instr (Just live)) = ppr instr $$ (nest 8 $ vcat [ pprRegs (ptext SLIT("# born: ")) (liveBorn live) , pprRegs (ptext SLIT("# r_dying: ")) (liveDieRead live) , pprRegs (ptext SLIT("# w_dying: ")) (liveDieWrite live) ] $+$ space) where pprRegs :: SDoc -> RegSet -> SDoc pprRegs name regs | isEmptyUniqSet regs = empty | otherwise = name <> (hcat $ punctuate space $ map (docToSDoc . pprUserReg) $ uniqSetToList regs) instance Outputable LiveInfo where ppr (LiveInfo static firstId liveOnEntry) = (vcat $ map ppr static) $$ text "# firstId = " <> ppr firstId $$ text "# liveOnEntry = " <> ppr liveOnEntry -- | map a function across all the basic blocks in this code -- mapBlockTop :: (LiveBasicBlock -> LiveBasicBlock) -> LiveCmmTop -> LiveCmmTop 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 -> m LiveBasicBlock) -> LiveCmmTop -> m LiveCmmTop mapBlockTopM f cmm@(CmmData{}) = return cmm mapBlockTopM f (CmmProc header label params comps) = do comps' <- mapM (mapBlockCompM f) comps return $ CmmProc header label params comps' 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 i -> GenCmmTop d h 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 i -> m (GenCmmTop d h i)) mapGenBlockTopM f cmm@(CmmData{}) = return cmm mapGenBlockTopM f (CmmProc header label params blocks) = do blocks' <- mapM f blocks return $ CmmProc header label params 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 :: LiveCmmTop -> (Bag (UniqSet Reg), Bag (Reg, Reg)) slurpConflicts live = slurpCmm (emptyBag, emptyBag) live where slurpCmm rs CmmData{} = rs slurpCmm rs (CmmProc info _ _ blocks) = foldl' (slurpComp info) rs blocks slurpComp info rs (BasicBlock i blocks) = foldl' (slurpBlock info) rs blocks slurpBlock info rs (BasicBlock blockId instrs) | LiveInfo _ _ blockLive <- info , Just rsLiveEntry <- lookupUFM blockLive blockId , (conflicts, moves) <- slurpLIs rsLiveEntry rs instrs = (consBag rsLiveEntry conflicts, moves) | otherwise = error "RegLiveness.slurpBlock: bad block" slurpLIs rsLive (conflicts, moves) [] = (consBag rsLive conflicts, moves) slurpLIs rsLive rs (Instr _ Nothing : lis) = slurpLIs rsLive rs lis slurpLIs rsLiveEntry (conflicts, moves) (li@(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 isRegRegMove instr of Just rr -> slurpLIs rsLiveNext ( consBag rsConflicts conflicts , consBag rr moves) lis Nothing -> slurpLIs rsLiveNext ( consBag rsConflicts conflicts , moves) lis -- | Strip away liveness information, yielding NatCmmTop stripLive :: LiveCmmTop -> NatCmmTop stripLive live = stripCmm live where stripCmm (CmmData sec ds) = CmmData sec ds stripCmm (CmmProc (LiveInfo info _ _) label params comps) = CmmProc info label params (concatMap stripComp comps) stripComp (BasicBlock i blocks) = map stripBlock blocks stripBlock (BasicBlock i instrs) = BasicBlock i (map stripLI instrs) stripLI (Instr instr _) = instr -- | Make real spill instructions out of SPILL, RELOAD pseudos spillNatBlock :: NatBasicBlock -> NatBasicBlock spillNatBlock (BasicBlock i is) = BasicBlock i instrs' where (instrs', _) = runState (spillNat [] is) 0 spillNat acc [] = return (reverse acc) spillNat acc (instr@(DELTA i) : instrs) = do put i spillNat acc instrs 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 : instrs) = spillNat (instr : acc) instrs -- | Slurp out a map of how many times each register was live upon entry to an instruction. lifetimeCount :: LiveCmmTop -> UniqFM (Reg, Int) -- ^ reg -> (reg, count) lifetimeCount cmm = countCmm emptyUFM cmm where countCmm fm CmmData{} = fm countCmm fm (CmmProc info _ _ blocks) = foldl' (countComp info) fm blocks countComp info fm (BasicBlock i blocks) = foldl' (countBlock info) fm blocks countBlock info fm (BasicBlock blockId instrs) | LiveInfo _ _ blockLive <- info , Just rsLiveEntry <- lookupUFM blockLive blockId = countLIs rsLiveEntry fm instrs | otherwise = error "RegLiveness.countBlock: bad block" countLIs rsLive fm [] = fm countLIs rsLive fm (Instr _ Nothing : lis) = countLIs rsLive fm lis countLIs rsLiveEntry fm (Instr _ (Just live) : lis) = let rsLiveAcross = rsLiveEntry `minusUniqSet` (liveDieRead live) rsLiveNext = (rsLiveAcross `unionUniqSets` (liveBorn live)) `minusUniqSet` (liveDieWrite live) add r fm = addToUFM_C (\(r1, l1) (_, l2) -> (r1, l1 + l2)) fm r (r, 1) fm' = foldUniqSet add fm rsLiveEntry in countLIs rsLiveNext fm' lis -- | Erase Delta instructions. eraseDeltasLive :: LiveCmmTop -> LiveCmmTop eraseDeltasLive cmm = mapBlockTop eraseBlock cmm where isDelta (DELTA _) = True isDelta _ = False eraseBlock (BasicBlock id lis) = BasicBlock id $ filter (\(Instr i _) -> not $ isDelta 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 :: (Reg -> Reg) -> LiveCmmTop -> LiveCmmTop patchEraseLive patchF cmm = patchCmm cmm where patchCmm cmm@CmmData{} = cmm patchCmm cmm@(CmmProc info label params comps) | LiveInfo static id blockMap <- info = let patchRegSet set = mkUniqSet $ map patchF $ uniqSetToList set blockMap' = mapUFM patchRegSet blockMap info' = LiveInfo static id blockMap' in CmmProc info' label params $ 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) <- isRegRegMove 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 :: (Reg -> Reg) -> LiveInstr -> LiveInstr patchRegsLiveInstr patchF li = case li of Instr instr Nothing -> Instr (patchRegs instr patchF) Nothing Instr instr (Just live) -> Instr (patchRegs 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 }) --------------------------------------------------------------------------------- -- Annotate code with register liveness information -- regLiveness :: NatCmmTop -> UniqSM LiveCmmTop regLiveness cmm@(CmmData sec d) = returnUs $ CmmData sec d regLiveness cmm@(CmmProc info lbl params []) = returnUs $ CmmProc (LiveInfo info Nothing emptyUFM) lbl params [] regLiveness cmm@(CmmProc info lbl params blocks@(first:rest)) = 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 liveBlocks sccBlocks :: [NatBasicBlock] -> [SCC NatBasicBlock] sccBlocks blocks = stronglyConnComp graph where getOutEdges :: [Instr] -> [BlockId] getOutEdges instrs = foldl' (\a x -> jumpDests x a) [] instrs graph = [ (block, getUnique id, map getUnique (getOutEdges instrs)) | block@(BasicBlock id instrs) <- blocks ] -- ----------------------------------------------------------------------------- -- Computing liveness computeLiveness :: [SCC NatBasicBlock] -> ([SCC LiveBasicBlock], -- 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 :: BlockMap RegSet -> [SCC LiveBasicBlock] -- accum -> [SCC NatBasicBlock] -> ([SCC LiveBasicBlock], 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, error "RegisterAlloc.livenessSCCs") linearLiveness :: BlockMap RegSet -> [NatBasicBlock] -> (BlockMap RegSet, [LiveBasicBlock]) linearLiveness = mapAccumL livenessBlock -- probably the least efficient way to compare two -- BlockMaps for equality. equalBlockMaps a b = a' == b' where a' = map f $ ufmToList a b' = map f $ ufmToList b f (key,elt) = (key, uniqSetToList elt) -- | Annotate a basic block with register liveness information. -- livenessBlock :: BlockMap RegSet -> NatBasicBlock -> (BlockMap RegSet, LiveBasicBlock) livenessBlock blockmap block@(BasicBlock block_id instrs) = let (regsLiveOnEntry, instrs1) = livenessBack emptyUniqSet blockmap [] (reverse instrs) blockmap' = addToUFM 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 :: RegSet -- regs live on this instr -> [LiveInstr] -> [LiveInstr] livenessForward rsLiveEntry [] = [] livenessForward rsLiveEntry (li@(Instr instr mLive) : lis) | Nothing <- mLive = li : livenessForward rsLiveEntry lis | Just live <- mLive , RU read written <- regUsage 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 -- | Calculate liveness going backwards, -- filling in when regs die, and what regs are live across each instruction livenessBack :: RegSet -- regs live on this instr -> BlockMap RegSet -- regs live on entry to other BBs -> [LiveInstr] -- instructions (accum) -> [Instr] -- instructions -> (RegSet, [LiveInstr]) livenessBack liveregs blockmap 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 liveregs blockmap (instr@COMMENT{}) = (liveregs, Instr instr Nothing) liveness1 liveregs blockmap (instr@DELTA{}) = (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 = regUsage 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 = jumpDests instr [] -- where we go from here not_a_branch = null targets targetLiveRegs target = case lookupUFM blockmap target of Just ra -> ra Nothing -> emptyBlockMap 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)