X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2Fcmm%2FCmmSpillReload.hs;h=2dcfb027a39861679b9e5594872bf061bf29ac86;hp=5601350f74058778c960668fa5f100b9730eb15f;hb=2c8aabcad1d2f2c469cb8a10afa7b66beeaedd45;hpb=7ed4f0716220b03fe5e04100ddbbc9e37d5323fe diff --git a/compiler/cmm/CmmSpillReload.hs b/compiler/cmm/CmmSpillReload.hs index 5601350..2dcfb02 100644 --- a/compiler/cmm/CmmSpillReload.hs +++ b/compiler/cmm/CmmSpillReload.hs @@ -1,54 +1,60 @@ -{-# OPTIONS -Wall -fno-warn-name-shadowing #-} +{-# LANGUAGE GADTs, NoMonoLocalBinds, FlexibleContexts, ViewPatterns #-} +-- Norman likes local bindings +-- If this module lives on I'd like to get rid of this flag in due course + +{-# OPTIONS_GHC -fno-warn-warnings-deprecations #-} +{-# OPTIONS_GHC -fno-warn-incomplete-patterns #-} +#if __GLASGOW_HASKELL__ >= 701 +-- GHC 7.0.1 improved incomplete pattern warnings with GADTs +{-# OPTIONS_GHC -fwarn-incomplete-patterns #-} +#endif module CmmSpillReload - ( ExtendWithSpills(..) - , DualLive(..) - , dualLiveLattice, dualLiveness - , insertSpillsAndReloads --- XXX todo check live-in at entry against formals + ( DualLive(..) + , dualLiveLattice, dualLiveTransfers, dualLiveness + --, insertSpillsAndReloads --- XXX todo check live-in at entry against formals , dualLivenessWithInsertion - , spillAndReloadComments - , availRegsLattice - , cmmAvailableReloads + , rewriteAssignments + , removeDeadAssignmentsAndReloads ) where + +import BlockId +import Cmm import CmmExpr -import CmmTx -import CmmLiveZ -import DFMonad -import FastString -import Maybe -import MkZipCfg +import CmmLive +import OptimizationFuel +import StgCmmUtils + +import Control.Monad import Outputable hiding (empty) import qualified Outputable as PP -import Panic -import PprCmm() import UniqSet -import ZipCfg -import ZipCfgCmm -import ZipDataflow - --- 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. +import UniqFM +import Unique + +import Compiler.Hoopl hiding (Unique) +import Data.Maybe +import Prelude hiding (succ, zip) + +{- Note [Overview of spill/reload] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +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 } @@ -61,226 +67,596 @@ 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) } +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 False +dualLiveLattice = DataflowLattice "variables live in registers and on stack" empty add 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 - -dualLivenessWithInsertion :: BPass M Last DualLive -dualLivenessWithInsertion = a_ft_b_unlimited dualLiveness insertSpillsAndReloads - - -dualLiveness :: BAnalysis M Last DualLive -dualLiveness = BComp "dual liveness" exit last middle first - where exit = empty - last = lastDualLiveness - middle = middleDualLiveness - first live _id = live - empty = fact_bot dualLiveLattice - - -- ^ could take a proc-point set and choose to spill here, - -- but it's probably better to run this pass, choose - -- proc-point protocols, insert more CopyIn nodes, and run - -- this pass again - -middleDualLiveness :: DualLive -> M -> DualLive -middleDualLiveness live m@(Spill regs) = - -- live-in on-stack requirements are satisfied; - -- live-out in-regs obligations are created - my_trace "before" (f4sep [ppr m, text "liveness is", ppr live']) $ - live' - where live' = DualLive { on_stack = on_stack live `minusRegSet` regs - , in_regs = in_regs live `plusRegSet` regs } - -middleDualLiveness live m@(Reload regs) = - -- live-in in-regs requirements are satisfied; - -- live-out on-stack obligations are created - my_trace "before" (f4sep [ppr m, text "liveness is", ppr live']) $ - live' - 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 ress) = changeRegs (gen ress) empty - last (LastJump e args) = changeRegs (gen e . gen args) empty - last (LastBranch id args) = changeRegs (gen args) $ env id - last (LastCall tgt args Nothing) = changeRegs (gen tgt. gen args) empty - last (LastCall tgt args (Just k)) = - -- nothing can be live in registers at this point - -- only 'formals' can be in regs at this point - let live = env k in - if isEmptyUniqSet (in_regs live) then - DualLive (on_stack live) (gen tgt $ gen args emptyRegSet) - else - 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 - -insertSpillsAndReloads :: BFunctionalTransformation M Last DualLive -insertSpillsAndReloads = BComp "CPS spiller" exit last middle first - where exit = Nothing - last = \_ _ -> Nothing - middle = middleInsertSpillsAndReloads - first _ _ = Nothing - -- ^ could take a proc-point set and choose to spill here, - -- but it's probably better to run this pass, choose - -- proc-point protocols, insert more CopyIn nodes, and run - -- this pass again - - -middleInsertSpillsAndReloads :: DualLive -> M -> Maybe (Graph M Last) -middleInsertSpillsAndReloads _ (Spill _) = Nothing -middleInsertSpillsAndReloads _ (Reload _) = Nothing -middleInsertSpillsAndReloads live (NotSpillOrReload m) = middle m - 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 $ graphOfMiddles [NotSpillOrReload 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 = -- a formal that is expected on the stack; must spill - foldRegsUsed (\rs r -> if is_stack_var r then extendRegSet rs r - else rs) emptyRegSet formals - in if isEmptyUniqSet regs' && isEmptyUniqSet needs_spilling then - Nothing - else - let reload = if isEmptyUniqSet regs' then [] - else [Reload regs'] - spill_reload = if isEmptyUniqSet needs_spilling then reload - else Spill needs_spilling : reload - middles = NotSpillOrReload m : spill_reload - 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 $ graphOfMiddles middles - middle _ = Nothing - --- | For conversion back to vanilla C-- -spillAndReloadComments :: M -> Middle -spillAndReloadComments (NotSpillOrReload m) = m -spillAndReloadComments (Spill regs) = show_regs "Spill" regs -spillAndReloadComments (Reload regs) = show_regs "Reload" regs - -show_regs :: String -> RegSet -> Middle -show_regs s regs = MidComment $ mkFastString $ showSDoc $ ppr_regs s regs - + add _ (OldFact old) (NewFact new) = (changeIf $ change1 || change2, DualLive stack regs) + where (change1, stack) = add1 (on_stack old) (on_stack new) + (change2, regs) = add1 (in_regs old) (in_regs new) + add1 old new = if sizeUniqSet join > sizeUniqSet old then (True, join) else (False, old) + where join = unionUniqSets old new + +dualLivenessWithInsertion :: BlockSet -> CmmGraph -> FuelUniqSM CmmGraph +dualLivenessWithInsertion procPoints g = + liftM fst $ dataflowPassBwd g [] $ analRewBwd dualLiveLattice + (dualLiveTransfers (g_entry g) procPoints) + (insertSpillAndReloadRewrites g procPoints) + +dualLiveness :: BlockSet -> CmmGraph -> FuelUniqSM (BlockEnv DualLive) +dualLiveness procPoints g = + liftM snd $ dataflowPassBwd g [] $ analBwd dualLiveLattice $ dualLiveTransfers (g_entry g) procPoints + +dualLiveTransfers :: BlockId -> BlockSet -> (BwdTransfer CmmNode DualLive) +dualLiveTransfers entry procPoints = mkBTransfer3 first middle last + where first :: CmmNode C O -> DualLive -> DualLive + first (CmmEntry id) live = check live id $ -- live at procPoint => spill + if id /= entry && setMember id procPoints + then DualLive { on_stack = on_stack live `plusRegSet` in_regs live + , in_regs = emptyRegSet } + else live + where check live id x = if id == entry then noLiveOnEntry id (in_regs live) x else x + + middle :: CmmNode O O -> DualLive -> DualLive + middle m = changeStack updSlots + . changeRegs updRegs + where -- Reuse middle of liveness analysis from CmmLive + updRegs = case getBTransfer3 xferLive of (_, middle, _) -> middle m + + 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" + last :: CmmNode O C -> FactBase DualLive -> DualLive + last l fb = case l of + CmmBranch id -> lkp id + l@(CmmCall {cml_cont=Nothing}) -> changeRegs (gen l . kill l) empty + l@(CmmCall {cml_cont=Just k}) -> call l k + l@(CmmForeignCall {succ=k}) -> call l k + l@(CmmCondBranch _ t f) -> changeRegs (gen l . kill l) $ dualUnion (lkp t) (lkp f) + l@(CmmSwitch _ tbl) -> changeRegs (gen l . kill l) $ dualUnionList $ map lkp (catMaybes tbl) + where empty = fact_bot dualLiveLattice + lkp id = empty `fromMaybe` lookupFact id fb + call l k = DualLive (on_stack (lkp k)) (gen l emptyRegSet) + +gen :: UserOfLocalRegs a => a -> RegSet -> RegSet +gen a live = foldRegsUsed extendRegSet live a +kill :: DefinerOfLocalRegs a => a -> RegSet -> RegSet +kill a live = foldRegsDefd deleteFromRegSet live a + +insertSpillAndReloadRewrites :: CmmGraph -> BlockSet -> CmmBwdRewrite DualLive +insertSpillAndReloadRewrites graph procPoints = deepBwdRw3 first middle nothing + -- Beware: deepBwdRw with one polymorphic function seems more reasonable here, + -- but GHC miscompiles it, see bug #4044. + where first :: CmmNode C O -> Fact O DualLive -> CmmReplGraph C O + first e@(CmmEntry id) live = return $ + if id /= (g_entry graph) && setMember id procPoints then + case map reload (uniqSetToList spill_regs) of + [] -> Nothing + is -> Just $ mkFirst e <*> mkMiddles is + else Nothing + where + -- If we are splitting procedures, we need the LastForeignCall + -- to spill its results to the stack because they will only + -- be used by a separate procedure (so they can't stay in LocalRegs). + splitting = True + spill_regs = if splitting then in_regs live + else in_regs live `minusRegSet` defs + defs = case mapLookup id firstDefs of + Just defs -> defs + Nothing -> emptyRegSet + -- A LastForeignCall may contain some definitions, which take place + -- on return from the function call. Therefore, we build a map (firstDefs) + -- from BlockId to the set of variables defined on return to the BlockId. + firstDefs = mapFold addLive emptyBlockMap (toBlockMap graph) + addLive :: CmmBlock -> BlockEnv RegSet -> BlockEnv RegSet + addLive b env = case lastNode b of + CmmForeignCall {succ=k, res=defs} -> add k (mkRegSet defs) env + _ -> env + add bid defs env = mapInsert bid defs'' env + where defs'' = case mapLookup bid env of + Just defs' -> timesRegSet defs defs' + Nothing -> defs + + middle :: CmmNode O O -> Fact O DualLive -> CmmReplGraph O O + middle (CmmAssign (CmmLocal reg) (CmmLoad (CmmStackSlot (RegSlot reg') _) _)) _ | reg == reg' = return Nothing + middle m@(CmmAssign (CmmLocal reg) _) live = return $ + 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 _ _ = return Nothing + + nothing _ _ = return Nothing + +regSlot :: LocalReg -> CmmExpr +regSlot r = CmmStackSlot (RegSlot r) (widthInBytes $ typeWidth $ localRegType r) + +spill, reload :: LocalReg -> CmmNode O O +spill r = CmmStore (regSlot r) (CmmReg $ CmmLocal r) +reload r = CmmAssign (CmmLocal r) (CmmLoad (regSlot r) $ localRegType r) + +removeDeadAssignmentsAndReloads :: BlockSet -> CmmGraph -> FuelUniqSM CmmGraph +removeDeadAssignmentsAndReloads procPoints g = + liftM fst $ dataflowPassBwd g [] $ analRewBwd dualLiveLattice + (dualLiveTransfers (g_entry g) procPoints) + rewrites + where rewrites = deepBwdRw3 nothing middle nothing + -- Beware: deepBwdRw with one polymorphic function seems more reasonable here, + -- but GHC panics while compiling, see bug #4045. + middle :: CmmNode O O -> Fact O DualLive -> CmmReplGraph O O + middle (CmmAssign (CmmLocal reg') _) live | not (reg' `elemRegSet` in_regs live) = return $ Just emptyGraph + -- XXX maybe this should be somewhere else... + middle (CmmAssign lhs (CmmReg rhs)) _ | lhs == rhs = return $ Just emptyGraph + middle (CmmStore lhs (CmmLoad rhs _)) _ | lhs == rhs = return $ Just emptyGraph + middle _ _ = return Nothing + + nothing _ _ = return Nothing ---------------------------------------------------------------- ---- 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 True - 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) - -cmmAvailableReloads :: LGraph M Last -> BlockEnv AvailRegs -cmmAvailableReloads g = env - where env = runDFA availRegsLattice $ - do run_f_anal transfer (fact_bot availRegsLattice) g - allFacts - transfer :: FAnalysis M Last AvailRegs - transfer = FComp "available-reloads analysis" first middle last exit - exit _ = LastOutFacts [] - 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 - -middleAvail :: M -> AvailRegs -> AvailRegs -middleAvail (Spill _) = id -middleAvail (Reload regs) = agen regs -middleAvail (NotSpillOrReload m) = middle m - where middle (MidNop) = id - middle (MidComment {}) = id - middle (MidAssign lhs _expr) = akill lhs - middle (MidStore {}) = id - middle (MidUnsafeCall _tgt ress _args) = akill ress - middle (CopyIn _ formals _) = akill formals - middle (CopyOut {}) = id - -lastAvail :: AvailRegs -> Last -> LastOutFacts AvailRegs -lastAvail avail l = LastOutFacts $ map (\id -> (id, avail)) $ succs l +--- Usage information + +-- We decorate all register assignments with usage information, +-- that is, the maximum number of times the register is referenced +-- while it is live along all outgoing control paths. There are a few +-- subtleties here: +-- +-- - If a register goes dead, and then becomes live again, the usages +-- of the disjoint live range don't count towards the original range. +-- +-- a = 1; // used once +-- b = a; +-- a = 2; // used once +-- c = a; +-- +-- - A register may be used multiple times, but these all reside in +-- different control paths, such that any given execution only uses +-- it once. In that case, the usage count may still be 1. +-- +-- a = 1; // used once +-- if (b) { +-- c = a + 3; +-- } else { +-- c = a + 1; +-- } +-- +-- This policy corresponds to an inlining strategy that does not +-- duplicate computation but may increase binary size. +-- +-- - If we naively implement a usage count, we have a counting to +-- infinity problem across joins. Furthermore, knowing that +-- something is used 2 or more times in one runtime execution isn't +-- particularly useful for optimizations (inlining may be beneficial, +-- but there's no way of knowing that without register pressure +-- information.) +-- +-- while (...) { +-- // first iteration, b used once +-- // second iteration, b used twice +-- // third iteration ... +-- a = b; +-- } +-- // b used zero times +-- +-- There is an orthogonal question, which is that for every runtime +-- execution, the register may be used only once, but if we inline it +-- in every conditional path, the binary size might increase a lot. +-- But tracking this information would be tricky, because it violates +-- the finite lattice restriction Hoopl requires for termination; +-- we'd thus need to supply an alternate proof, which is probably +-- something we should defer until we actually have an optimization +-- that would take advantage of this. (This might also interact +-- strangely with liveness information.) +-- +-- a = ...; +-- // a is used one time, but in X different paths +-- case (b) of +-- 1 -> ... a ... +-- 2 -> ... a ... +-- 3 -> ... a ... +-- ... +-- +-- This analysis is very similar to liveness analysis; we just keep a +-- little extra info. (Maybe we should move it to CmmLive, and subsume +-- the old liveness analysis.) + +data RegUsage = SingleUse | ManyUse + deriving (Ord, Eq, Show) +-- Absence in map = ZeroUse + +{- +-- minBound is bottom, maxBound is top, least-upper-bound is max +-- ToDo: Put this in Hoopl. Note that this isn't as useful as I +-- originally hoped, because you usually want to leave out the bottom +-- element when you have things like this put in maps. Maybe f is +-- useful on its own as a combining function. +boundedOrdLattice :: (Bounded a, Ord a) => String -> DataflowLattice a +boundedOrdLattice n = DataflowLattice n minBound f + where f _ (OldFact x) (NewFact y) + | x >= y = (NoChange, x) + | otherwise = (SomeChange, y) +-} + +-- Custom node type we'll rewrite to. CmmAssign nodes to local +-- registers are replaced with AssignLocal nodes. +data WithRegUsage n e x where + Plain :: n e x -> WithRegUsage n e x + AssignLocal :: LocalReg -> CmmExpr -> RegUsage -> WithRegUsage n O O + +instance UserOfLocalRegs (n e x) => UserOfLocalRegs (WithRegUsage n e x) where + foldRegsUsed f z (Plain n) = foldRegsUsed f z n + foldRegsUsed f z (AssignLocal _ e _) = foldRegsUsed f z e + +instance DefinerOfLocalRegs (n e x) => DefinerOfLocalRegs (WithRegUsage n e x) where + foldRegsDefd f z (Plain n) = foldRegsDefd f z n + foldRegsDefd f z (AssignLocal r _ _) = foldRegsDefd f z r + +instance NonLocal n => NonLocal (WithRegUsage n) where + entryLabel (Plain n) = entryLabel n + successors (Plain n) = successors n + +liftRegUsage :: Graph n e x -> Graph (WithRegUsage n) e x +liftRegUsage = mapGraph Plain + +eraseRegUsage :: Graph (WithRegUsage CmmNode) e x -> Graph CmmNode e x +eraseRegUsage = mapGraph f + where f :: WithRegUsage CmmNode e x -> CmmNode e x + f (AssignLocal l e _) = CmmAssign (CmmLocal l) e + f (Plain n) = n + +type UsageMap = UniqFM RegUsage + +usageLattice :: DataflowLattice UsageMap +usageLattice = DataflowLattice "usage counts for registers" emptyUFM (joinUFM f) + where f _ (OldFact x) (NewFact y) + | x >= y = (NoChange, x) + | otherwise = (SomeChange, y) + +-- We reuse the names 'gen' and 'kill', although we're doing something +-- slightly different from the Dragon Book +usageTransfer :: BwdTransfer (WithRegUsage CmmNode) UsageMap +usageTransfer = mkBTransfer3 first middle last + where first _ f = f + middle :: WithRegUsage CmmNode O O -> UsageMap -> UsageMap + middle n f = gen_kill n f + last :: WithRegUsage CmmNode O C -> FactBase UsageMap -> UsageMap + -- Checking for CmmCall/CmmForeignCall is unnecessary, because + -- spills/reloads have already occurred by the time we do this + -- analysis. + -- XXX Deprecated warning is puzzling: what label are we + -- supposed to use? + -- ToDo: With a bit more cleverness here, we can avoid + -- disappointment and heartbreak associated with the inability + -- to inline into CmmCall and CmmForeignCall by + -- over-estimating the usage to be ManyUse. + last n f = gen_kill n (joinOutFacts usageLattice n f) + gen_kill a = gen a . kill a + gen a f = foldRegsUsed increaseUsage f a + kill a f = foldRegsDefd delFromUFM f a + increaseUsage f r = addToUFM_C combine f r SingleUse + where combine _ _ = ManyUse + +usageRewrite :: BwdRewrite FuelUniqSM (WithRegUsage CmmNode) UsageMap +usageRewrite = mkBRewrite3 first middle last + where first _ _ = return Nothing + middle :: Monad m => WithRegUsage CmmNode O O -> UsageMap -> m (Maybe (Graph (WithRegUsage CmmNode) O O)) + middle (Plain (CmmAssign (CmmLocal l) e)) f + = return . Just + $ case lookupUFM f l of + Nothing -> emptyGraph + Just usage -> mkMiddle (AssignLocal l e usage) + middle _ _ = return Nothing + last _ _ = return Nothing + +type CmmGraphWithRegUsage = GenCmmGraph (WithRegUsage CmmNode) +annotateUsage :: CmmGraph -> FuelUniqSM (CmmGraphWithRegUsage) +annotateUsage vanilla_g = + let g = modifyGraph liftRegUsage vanilla_g + in liftM fst $ dataflowPassBwd g [(g_entry g, fact_bot usageLattice)] $ + analRewBwd usageLattice usageTransfer usageRewrite +---------------------------------------------------------------- +--- Assignment tracking + +-- The idea is to maintain a map of local registers do expressions, +-- such that the value of that register is the same as the value of that +-- expression at any given time. We can then do several things, +-- as described by Assignment. + +-- Assignment describes the various optimizations that are valid +-- at a given point in the program. +data Assignment = +-- This assignment can always be inlined. It is cheap or single-use. + AlwaysInline CmmExpr +-- This assignment should be sunk down to its first use. (This will +-- increase code size if the register is used in multiple control flow +-- paths, but won't increase execution time, and the reduction of +-- register pressure is worth it.) + | AlwaysSink CmmExpr +-- We cannot safely optimize occurrences of this local register. (This +-- corresponds to top in the lattice structure.) + | NeverOptimize + +-- Extract the expression that is being assigned to +xassign :: Assignment -> Maybe CmmExpr +xassign (AlwaysInline e) = Just e +xassign (AlwaysSink e) = Just e +xassign NeverOptimize = Nothing + +-- Extracts the expression, but only if they're the same constructor +xassign2 :: (Assignment, Assignment) -> Maybe (CmmExpr, CmmExpr) +xassign2 (AlwaysInline e, AlwaysInline e') = Just (e, e') +xassign2 (AlwaysSink e, AlwaysSink e') = Just (e, e') +xassign2 _ = Nothing + +-- Note: We'd like to make decisions about "not optimizing" as soon as +-- possible, because this will make running the transfer function more +-- efficient. +type AssignmentMap = UniqFM Assignment + +assignmentLattice :: DataflowLattice AssignmentMap +assignmentLattice = DataflowLattice "assignments for registers" emptyUFM (joinUFM add) + where add _ (OldFact old) (NewFact new) + = case (old, new) of + (NeverOptimize, _) -> (NoChange, NeverOptimize) + (_, NeverOptimize) -> (SomeChange, NeverOptimize) + (xassign2 -> Just (e, e')) + | e == e' -> (NoChange, old) + | otherwise -> (SomeChange, NeverOptimize) + _ -> (SomeChange, NeverOptimize) + +-- Deletes sinks from assignment map, because /this/ is the place +-- where it will be sunk to. +deleteSinks :: UserOfLocalRegs n => n -> AssignmentMap -> AssignmentMap +deleteSinks n m = foldRegsUsed (adjustUFM f) m n + where f (AlwaysSink _) = NeverOptimize + f old = old + +-- Invalidates any expressions that use a register. +invalidateUsersOf :: CmmReg -> AssignmentMap -> AssignmentMap +-- foldUFM_Directly :: (Unique -> elt -> a -> a) -> a -> UniqFM elt -> a +invalidateUsersOf reg m = foldUFM_Directly f m m -- [foldUFM performance] + where f u (xassign -> Just e) m | reg `regUsedIn` e = addToUFM_Directly m u NeverOptimize + f _ _ m = m +{- This requires the entire spine of the map to be continually rebuilt, + - which causes crazy memory usage! +invalidateUsersOf reg = mapUFM (invalidateUsers' reg) + where invalidateUsers' reg (xassign -> Just e) | reg `regUsedIn` e = NeverOptimize + invalidateUsers' _ old = old +-} + +-- Note [foldUFM performance] +-- These calls to fold UFM no longer leak memory, but they do cause +-- pretty killer amounts of allocation. So they'll be something to +-- optimize; we need an algorithmic change to prevent us from having to +-- traverse the /entire/ map continually. + +middleAssignment :: WithRegUsage CmmNode O O -> AssignmentMap -> AssignmentMap + +-- Algorithm for annotated assignments: +-- 1. Delete any sinking assignments that were used by this instruction +-- 2. Add the assignment to our list of valid local assignments with +-- the correct optimization policy. +-- 3. Look for all assignments that reference that register and +-- invalidate them. +middleAssignment n@(AssignLocal r e usage) assign + = invalidateUsersOf (CmmLocal r) . add . deleteSinks n $ assign + where add m = addToUFM m r + $ case usage of + SingleUse -> AlwaysInline e + ManyUse -> decide e + decide CmmLit{} = AlwaysInline e + decide CmmReg{} = AlwaysInline e + decide CmmLoad{} = AlwaysSink e + decide CmmStackSlot{} = AlwaysSink e + decide CmmMachOp{} = AlwaysSink e + -- We'll always inline simple operations on the global + -- registers, to reduce register pressure: Sp - 4 or Hp - 8 + -- EZY: Justify this optimization more carefully. + decide CmmRegOff{} = AlwaysInline e + +-- Algorithm for unannotated assignments of global registers: +-- 1. Delete any sinking assignments that were used by this instruction +-- 2. Look for all assignments that reference this register and +-- invalidate them. +middleAssignment (Plain n@(CmmAssign reg@(CmmGlobal _) _)) assign + = invalidateUsersOf reg . deleteSinks n $ assign + +-- Algorithm for unannotated assignments of *local* registers: do +-- nothing (it's a reload, so no state should have changed) +middleAssignment (Plain (CmmAssign (CmmLocal _) _)) assign = assign + +-- Algorithm for stores: +-- 1. Delete any sinking assignments that were used by this instruction +-- 2. Look for all assignments that load from memory locations that +-- were clobbered by this store and invalidate them. +middleAssignment (Plain n@(CmmStore lhs rhs)) assign + = let m = deleteSinks n assign + in foldUFM_Directly f m m -- [foldUFM performance] + where f u (xassign -> Just x) m | (lhs, rhs) `clobbers` (u, x) = addToUFM_Directly m u NeverOptimize + f _ _ m = m +{- Also leaky + = mapUFM_Directly p . deleteSinks n $ assign + -- ToDo: There's a missed opportunity here: even if a memory + -- access we're attempting to sink gets clobbered at some + -- location, it's still /better/ to sink it to right before the + -- point where it gets clobbered. How might we do this? + -- Unfortunately, it's too late to change the assignment... + where p r (xassign -> Just x) | (lhs, rhs) `clobbers` (r, x) = NeverOptimize + p _ old = old +-} + +-- Assumption: Unsafe foreign calls don't clobber memory +-- Since foreign calls clobber caller saved registers, we need +-- invalidate any assignments that reference those global registers. +-- This is kind of expensive. (One way to optimize this might be to +-- store extra information about expressions that allow this and other +-- checks to be done cheaply.) +middleAssignment (Plain n@(CmmUnsafeForeignCall{})) assign + = deleteCallerSaves (foldRegsDefd (\m r -> addToUFM m r NeverOptimize) (deleteSinks n assign) n) + where deleteCallerSaves m = foldUFM_Directly f m m + f u (xassign -> Just x) m | wrapRecExpf g x False = addToUFM_Directly m u NeverOptimize + f _ _ m = m + g (CmmReg (CmmGlobal r)) _ | callerSaves r = True + g (CmmRegOff (CmmGlobal r) _) _ | callerSaves r = True + g _ b = b + +middleAssignment (Plain (CmmComment {})) assign + = assign + +-- Assumptions: +-- * Writes using Hp do not overlap with any other memory locations +-- (An important invariant being relied on here is that we only ever +-- use Hp to allocate values on the heap, which appears to be the +-- case given hpReg usage, and that our heap writing code doesn't +-- do anything stupid like overlapping writes.) +-- * Stack slots do not overlap with any other memory locations +-- * Stack slots for different areas do not overlap +-- * Stack slots within the same area and different offsets may +-- overlap; we need to do a size check (see 'overlaps'). +-- * Register slots only overlap with themselves. (But this shouldn't +-- happen in practice, because we'll fail to inline a reload across +-- the next spill.) +-- * Non stack-slot stores always conflict with each other. (This is +-- not always the case; we could probably do something special for Hp) +clobbers :: (CmmExpr, CmmExpr) -- (lhs, rhs) of clobbering CmmStore + -> (Unique, CmmExpr) -- (register, expression) that may be clobbered + -> Bool +clobbers (CmmRegOff (CmmGlobal Hp) _, _) (_, _) = False +clobbers (CmmReg (CmmGlobal Hp), _) (_, _) = False +-- ToDo: Also catch MachOp case +clobbers (ss@CmmStackSlot{}, CmmReg (CmmLocal r)) (u, CmmLoad (ss'@CmmStackSlot{}) _) + | getUnique r == u, ss == ss' = False -- No-op on the stack slot (XXX: Do we need this special case?) +clobbers (CmmStackSlot (CallArea a) o, rhs) (_, expr) = f expr + where f (CmmLoad (CmmStackSlot (CallArea a') o') t) + = (a, o, widthInBytes (cmmExprWidth rhs)) `overlaps` (a', o', widthInBytes (typeWidth t)) + f (CmmLoad e _) = containsStackSlot e + f (CmmMachOp _ es) = or (map f es) + f _ = False + -- Maybe there's an invariant broken if this actually ever + -- returns True + containsStackSlot (CmmLoad{}) = True -- load of a load, all bets off + containsStackSlot (CmmMachOp _ es) = or (map containsStackSlot es) + containsStackSlot (CmmStackSlot{}) = True + containsStackSlot _ = False +clobbers (CmmStackSlot (RegSlot l) _, _) (_, expr) = f expr + where f (CmmLoad (CmmStackSlot (RegSlot l') _) _) = l == l' + f _ = False +clobbers _ (_, e) = f e + where f (CmmLoad (CmmStackSlot _ _) _) = False + f (CmmLoad{}) = True -- conservative + f (CmmMachOp _ es) = or (map f es) + f _ = False + +-- Check for memory overlapping. +-- Diagram: +-- 4 8 12 +-- s -w- o +-- [ I32 ] +-- [ F64 ] +-- s' -w'- o' +type CallSubArea = (AreaId, Int, Int) -- area, offset, width +overlaps :: CallSubArea -> CallSubArea -> Bool +overlaps (a, _, _) (a', _, _) | a /= a' = False +overlaps (_, o, w) (_, o', w') = + let s = o - w + s' = o' - w' + in (s' < o) && (s < o) -- Not LTE, because [ I32 ][ I32 ] is OK + +lastAssignment :: WithRegUsage CmmNode O C -> AssignmentMap -> [(Label, AssignmentMap)] +-- Variables are dead across calls, so invalidating all mappings is justified +lastAssignment (Plain (CmmCall _ (Just k) _ _ _)) assign = [(k, mapUFM (const NeverOptimize) assign)] +lastAssignment (Plain (CmmForeignCall {succ=k})) assign = [(k, mapUFM (const NeverOptimize) assign)] +lastAssignment l assign = map (\id -> (id, deleteSinks l assign)) $ successors l + +assignmentTransfer :: FwdTransfer (WithRegUsage CmmNode) AssignmentMap +assignmentTransfer = mkFTransfer3 (flip const) middleAssignment ((mkFactBase assignmentLattice .) . lastAssignment) + +assignmentRewrite :: FwdRewrite FuelUniqSM (WithRegUsage CmmNode) AssignmentMap +assignmentRewrite = mkFRewrite3 first middle last + where + first _ _ = return Nothing + middle :: WithRegUsage CmmNode O O -> AssignmentMap -> GenCmmReplGraph (WithRegUsage CmmNode) O O + middle (Plain m) assign = return $ rewrite assign (precompute assign m) mkMiddle m + middle (AssignLocal l e u) assign = return $ rewriteLocal assign (precompute assign (CmmAssign (CmmLocal l) e)) mkMiddle l e u + last (Plain l) assign = return $ rewrite assign (precompute assign l) mkLast l + -- Tuple is (inline?, reloads) + precompute assign n = foldRegsUsed f (False, []) n -- duplicates are harmless + where f (i, l) r = case lookupUFM assign r of + Just (AlwaysSink e) -> (i, (Plain (CmmAssign (CmmLocal r) e)):l) + Just (AlwaysInline _) -> (True, l) + Just NeverOptimize -> (i, l) + -- This case can show up when we have + -- limited optimization fuel. + Nothing -> (i, l) + rewrite _ (False, []) _ _ = Nothing + -- Note [CmmCall Inline Hack] + -- Conservative hack: don't do any inlining on what will + -- be translated into an OldCmm CmmCalls, since the code + -- produced here tends to be unproblematic and I need to write + -- lint passes to ensure that we don't put anything in the + -- arguments that could be construed as a global register by + -- some later translation pass. (For example, slots will turn + -- into dereferences of Sp). See [Register parameter passing]. + -- ToDo: Fix this up to only bug out if all inlines were for + -- CmmExprs with global registers (we can't use the + -- straightforward mapExpDeep call, in this case.) ToDo: We miss + -- an opportunity here, where all possible inlinings should + -- instead be sunk. + rewrite _ (True, []) _ n | not (inlinable n) = Nothing -- see [CmmCall Inline Hack] + rewrite assign (i, xs) mk n = Just $ mkMiddles xs <*> mk (Plain (inline i assign n)) + + rewriteLocal _ (False, []) _ _ _ _ = Nothing + rewriteLocal assign (i, xs) mk l e u = Just $ mkMiddles xs <*> mk n' + where n' = AssignLocal l e' u + e' = if i then wrapRecExp (inlineExp assign) e else e + -- inlinable check omitted, since we can always inline into + -- assignments. + + inline :: Bool -> AssignmentMap -> CmmNode e x -> CmmNode e x + inline False _ n = n + inline True _ n | not (inlinable n) = n -- see [CmmCall Inline Hack] + inline True assign n = mapExpDeep (inlineExp assign) n + + inlineExp assign old@(CmmReg (CmmLocal r)) + = case lookupUFM assign r of + Just (AlwaysInline x) -> x + _ -> old + inlineExp assign old@(CmmRegOff (CmmLocal r) i) + = case lookupUFM assign r of + Just (AlwaysInline x) -> + case x of + (CmmRegOff r' i') -> CmmRegOff r' (i + i') + _ -> CmmMachOp (MO_Add rep) [x, CmmLit (CmmInt (fromIntegral i) rep)] + where rep = typeWidth (localRegType r) + _ -> old + inlineExp _ old = old + + inlinable :: CmmNode e x -> Bool + inlinable (CmmCall{}) = False + inlinable (CmmForeignCall{}) = False + inlinable (CmmUnsafeForeignCall{}) = False + inlinable _ = True + +rewriteAssignments :: CmmGraph -> FuelUniqSM CmmGraph +rewriteAssignments g = do + g' <- annotateUsage g + g'' <- liftM fst $ dataflowPassFwd g' [(g_entry g, fact_bot assignmentLattice)] $ + analRewFwd assignmentLattice assignmentTransfer assignmentRewrite + return (modifyGraph eraseRegUsage g'') --------------------- -- 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 (LGraph M Last) where - ppr = pprLgraph - -instance DebugNodes 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 @@ -295,9 +671,7 @@ instance Outputable DualLive where if isEmptyUniqSet stack then PP.empty else (ppr_regs "live on stack =" stack)] -instance Outputable AvailRegs where - ppr (UniverseMinus s) = ppr_regs "available = all but" s - ppr (AvailRegs s) = ppr_regs "available = " s +-- ToDo: Outputable instance for UsageMap and AssignmentMap my_trace :: String -> SDoc -> a -> a my_trace = if False then pprTrace else \_ _ a -> a