module RegAlloc.Graph.SpillCost ( SpillCostRecord, plusSpillCostRecord, pprSpillCostRecord, SpillCostInfo, zeroSpillCostInfo, plusSpillCostInfo, slurpSpillCostInfo, chooseSpill, lifeMapFromSpillCostInfo ) where import RegAlloc.Liveness import Instruction import RegClass import Reg import GraphBase import BlockId import Cmm import UniqFM import UniqSet import Outputable import State import Data.List (nub, minimumBy) import Data.Maybe import Control.Monad type SpillCostRecord = ( VirtualReg -- register name , Int -- number of writes to this reg , Int -- number of reads from this reg , Int) -- number of instrs this reg was live on entry to type SpillCostInfo = UniqFM SpillCostRecord zeroSpillCostInfo :: SpillCostInfo zeroSpillCostInfo = emptyUFM -- | Add two spillCostInfos plusSpillCostInfo :: SpillCostInfo -> SpillCostInfo -> SpillCostInfo plusSpillCostInfo sc1 sc2 = plusUFM_C plusSpillCostRecord sc1 sc2 plusSpillCostRecord :: SpillCostRecord -> SpillCostRecord -> SpillCostRecord plusSpillCostRecord (r1, a1, b1, c1) (r2, a2, b2, c2) | r1 == r2 = (r1, a1 + a2, b1 + b2, c1 + c2) | otherwise = error "RegSpillCost.plusRegInt: regs don't match" -- | Slurp out information used for determining spill costs -- for each vreg, the number of times it was written to, read from, -- and the number of instructions it was live on entry to (lifetime) -- slurpSpillCostInfo :: (Outputable instr, Instruction instr) => LiveCmmTop instr -> SpillCostInfo slurpSpillCostInfo cmm = execState (countCmm cmm) zeroSpillCostInfo where countCmm CmmData{} = return () countCmm (CmmProc info _ _ (ListGraph blocks)) = mapM_ (countComp info) blocks countComp info (BasicBlock _ blocks) = mapM_ (countBlock info) blocks -- lookup the regs that are live on entry to this block in -- the info table from the CmmProc countBlock info (BasicBlock blockId instrs) | LiveInfo _ _ blockLive <- info , Just rsLiveEntry <- lookupBlockEnv blockLive blockId , rsLiveEntry_virt <- mapUniqSet (\(RegVirtual vr) -> vr) $ filterUniqSet isVirtualReg rsLiveEntry = countLIs rsLiveEntry_virt instrs | otherwise = error "RegAlloc.SpillCost.slurpSpillCostInfo: bad block" countLIs _ [] = return () -- skip over comment and delta pseudo instrs countLIs rsLive (SPILL{} : lis) = countLIs rsLive lis countLIs rsLive (RELOAD{} : lis) = countLIs rsLive lis countLIs rsLive (Instr instr Nothing : lis) | isMetaInstr instr = countLIs rsLive lis | otherwise = pprPanic "RegSpillCost.slurpSpillCostInfo" (text "no liveness information on instruction " <> ppr instr) countLIs rsLiveEntry (Instr instr (Just live) : lis) = do -- increment the lifetime counts for regs live on entry to this instr mapM_ incLifetime $ uniqSetToList rsLiveEntry -- increment counts for what regs were read/written from let (RU read written) = regUsageOfInstr instr mapM_ incUses $ catMaybes $ map takeVirtualReg $ nub read mapM_ incDefs $ catMaybes $ map takeVirtualReg $ nub written -- compute liveness for entry to next instruction. let takeVirtuals set = mapUniqSet (\(RegVirtual vr) -> vr) $ filterUniqSet isVirtualReg set let liveDieRead_virt = takeVirtuals (liveDieRead live) let liveDieWrite_virt = takeVirtuals (liveDieWrite live) let liveBorn_virt = takeVirtuals (liveBorn live) let rsLiveAcross = rsLiveEntry `minusUniqSet` liveDieRead_virt let rsLiveNext = (rsLiveAcross `unionUniqSets` liveBorn_virt) `minusUniqSet` liveDieWrite_virt countLIs rsLiveNext lis incDefs reg = modify $ \s -> addToUFM_C plusSpillCostRecord s reg (reg, 1, 0, 0) incUses reg = modify $ \s -> addToUFM_C plusSpillCostRecord s reg (reg, 0, 1, 0) incLifetime reg = modify $ \s -> addToUFM_C plusSpillCostRecord s reg (reg, 0, 0, 1) -- | Choose a node to spill from this graph chooseSpill :: SpillCostInfo -> Graph VirtualReg RegClass RealReg -> VirtualReg chooseSpill info graph = let cost = spillCost_length info graph node = minimumBy (\n1 n2 -> compare (cost $ nodeId n1) (cost $ nodeId n2)) $ eltsUFM $ graphMap graph in nodeId node -- | Chaitins spill cost function is: -- -- cost = sum loadCost * freq (u) + sum storeCost * freq (d) -- u <- uses (v) d <- defs (v) -- -- There are no loops in our code at the momemnt, so we can set the freq's to 1 -- We divide this by the degree if t -- -- -- If we don't have live range splitting then Chaitins function performs badly if we have -- lots of nested live ranges and very few registers. -- -- v1 v2 v3 -- def v1 . -- use v1 . -- def v2 . . -- def v3 . . . -- use v1 . . . -- use v3 . . . -- use v2 . . -- use v1 . -- -- -- defs uses degree cost -- v1: 1 3 3 1.5 -- v2: 1 2 3 1.0 -- v3: 1 1 3 0.666 -- -- v3 has the lowest cost, but if we only have 2 hardregs and we insert spill code for v3 -- then this isn't going to improve the colorability of the graph. -- -- When compiling SHA1, which as very long basic blocks and some vregs with very long live ranges -- the allocator seems to try and spill from the inside out and eventually run out of stack slots. -- -- Without live range splitting, its's better to spill from the outside in so set the cost of very -- long live ranges to zero -- {- spillCost_chaitin :: SpillCostInfo -> Graph Reg RegClass Reg -> Reg -> Float spillCost_chaitin info graph reg -- Spilling a live range that only lives for 1 instruction isn't going to help -- us at all - and we definately want to avoid trying to re-spill previously -- inserted spill code. | lifetime <= 1 = 1/0 -- It's unlikely that we'll find a reg for a live range this long -- better to spill it straight up and not risk trying to keep it around -- and have to go through the build/color cycle again. | lifetime > allocatableRegsInClass (regClass reg) * 10 = 0 -- otherwise revert to chaitin's regular cost function. | otherwise = fromIntegral (uses + defs) / fromIntegral (nodeDegree graph reg) where (_, defs, uses, lifetime) = fromMaybe (reg, 0, 0, 0) $ lookupUFM info reg -} -- Just spill the longest live range. spillCost_length :: SpillCostInfo -> Graph VirtualReg RegClass RealReg -> VirtualReg -> Float spillCost_length info _ reg | lifetime <= 1 = 1/0 | otherwise = 1 / fromIntegral lifetime where (_, _, _, lifetime) = fromMaybe (reg, 0, 0, 0) $ lookupUFM info reg lifeMapFromSpillCostInfo :: SpillCostInfo -> UniqFM (VirtualReg, Int) lifeMapFromSpillCostInfo info = listToUFM $ map (\(r, _, _, life) -> (r, (r, life))) $ eltsUFM info -- | Work out the degree (number of neighbors) of this node which have the same class. nodeDegree :: (VirtualReg -> RegClass) -> Graph VirtualReg RegClass RealReg -> VirtualReg -> Int nodeDegree classOfVirtualReg graph reg | Just node <- lookupUFM (graphMap graph) reg , virtConflicts <- length $ filter (\r -> classOfVirtualReg r == classOfVirtualReg reg) $ uniqSetToList $ nodeConflicts node = virtConflicts + sizeUniqSet (nodeExclusions node) | otherwise = 0 -- | Show a spill cost record, including the degree from the graph and final calulated spill cos pprSpillCostRecord :: (VirtualReg -> RegClass) -> (Reg -> SDoc) -> Graph VirtualReg RegClass RealReg -> SpillCostRecord -> SDoc pprSpillCostRecord regClass pprReg graph (reg, uses, defs, life) = hsep [ pprReg (RegVirtual reg) , ppr uses , ppr defs , ppr life , ppr $ nodeDegree regClass graph reg , text $ show $ (fromIntegral (uses + defs) / fromIntegral (nodeDegree regClass graph reg) :: Float) ]