--- /dev/null
+module CmmStackLayout
+ ( SlotEnv, liveSlotAnal, liveSlotTransfers, removeLiveSlotDefs
+ , layout, manifestSP, igraph, areaBuilder
+ , stubSlotsOnDeath ) -- to help crash early during debugging
+where
+
+import Constants
+import qualified Prelude as P
+import Prelude hiding (zip, unzip, last)
+
+import BlockId
+import CmmExpr
+import CmmProcPointZ
+import CmmTx
+import DFMonad
+import FiniteMap
+import Maybes
+import MkZipCfg
+import MkZipCfgCmm hiding (CmmBlock, CmmGraph)
+import Monad
+import Outputable
+import Panic
+import ZipCfg
+import ZipCfgCmmRep
+import ZipDataflow
+
+------------------------------------------------------------------------
+-- Stack Layout --
+------------------------------------------------------------------------
+
+-- | Before we lay out the stack, we need to know something about the
+-- liveness of the stack slots. In particular, to decide whether we can
+-- reuse a stack location to hold multiple stack slots, we need to know
+-- when each of the stack slots is used.
+-- Although tempted to use something simpler, we really need a full interference
+-- graph. Consider the following case:
+-- case <...> of
+-- 1 -> <spill x>; // y is dead out
+-- 2 -> <spill y>; // x is dead out
+-- 3 -> <spill x and y>
+-- If we consider the arms in order and we use just the deadness information given by a
+-- dataflow analysis, we might decide to allocate the stack slots for x and y
+-- to the same stack location, which will lead to incorrect code in the third arm.
+-- We won't make this mistake with an interference graph.
+
+-- First, the liveness analysis.
+-- We represent a slot with an area, an offset into the area, and a width.
+-- Tracking the live slots is a bit tricky because there may be loads and stores
+-- into only a part of a stack slot (e.g. loading the low word of a 2-word long),
+-- e.g. Slot A 0 8 overlaps with Slot A 4 4.
+--
+-- The definition of a slot set is intended to reduce the number of overlap
+-- checks we have to make. There's no reason to check for overlap between
+-- slots in different areas, so we segregate the map by Area's.
+-- We expect few slots in each Area, so we collect them in an unordered list.
+-- To keep these lists short, any contiguous live slots are coalesced into
+-- a single slot, on insertion.
+
+slotLattice :: DataflowLattice SubAreaSet
+slotLattice = DataflowLattice "live slots" emptyFM add True
+ where add new old = case foldFM addArea (False, old) new of
+ (True, x) -> aTx x
+ (False, x) -> noTx x
+ addArea a newSlots z = foldr (addSlot a) z newSlots
+ addSlot a slot (changed, map) =
+ let (c, live) = liveGen slot $ lookupWithDefaultFM map [] a
+ in (c || changed, addToFM map a live)
+
+type SlotEnv = BlockEnv SubAreaSet
+type SlotFix a = FuelMonad (BackwardFixedPoint Middle Last SubAreaSet a)
+
+liveSlotAnal :: LGraph Middle Last -> FuelMonad SlotEnv
+liveSlotAnal g = liftM zdfFpFacts (res :: SlotFix ())
+ where res = zdfSolveFromL emptyBlockEnv "live slot analysis" slotLattice
+ liveSlotTransfers (fact_bot slotLattice) g
+
+-- Add the subarea s to the subareas in the list-set (possibly coalescing it with
+-- adjacent subareas), and also return whether s was a new addition.
+liveGen :: SubArea -> [SubArea] -> (Bool, [SubArea])
+liveGen s set = liveGen' s set []
+ where liveGen' s [] z = (True, s : z)
+ liveGen' s@(a, hi, w) (s'@(a', hi', w') : rst) z =
+ if a /= a' || hi < lo' || lo > hi' then -- no overlap
+ liveGen' s rst (s' : z)
+ else if s' `contains` s then -- old contains new
+ (False, set)
+ else -- overlap: coalesce the slots
+ let new_hi = max hi hi'
+ new_lo = min lo lo'
+ in liveGen' (a, new_hi, new_hi - new_lo) rst z
+ where lo = hi - w -- remember: areas grow down
+ lo' = hi' - w'
+ contains (a, hi, w) (a', hi', w') =
+ a == a' && hi >= hi' && hi - w <= hi' - w'
+
+liveKill :: SubArea -> [SubArea] -> [SubArea]
+liveKill (a, hi, w) set = pprTrace "killing slots in area" (ppr a) $ liveKill' set []
+ where liveKill' [] z = z
+ liveKill' (s'@(a', hi', w') : rst) z =
+ if a /= a' || hi < lo' || lo > hi' then -- no overlap
+ liveKill' rst (s' : z)
+ else -- overlap: split the old slot
+ let z' = if hi' > hi then (a, hi', hi' - hi) : z else z
+ z'' = if lo > lo' then (a, lo, lo - lo') : z' else z'
+ in liveKill' rst z''
+ where lo = hi - w -- remember: areas grow down
+ lo' = hi' - w'
+
+-- Note: the stack slots that hold variables returned on the stack are not
+-- considered live in to the block -- we treat the first node as a definition site.
+-- BEWARE?: Am I being a little careless here in failing to check for the
+-- entry Id (which would use the CallArea Old).
+liveSlotTransfers :: BackwardTransfers Middle Last SubAreaSet
+liveSlotTransfers =
+ BackwardTransfers first liveInSlots liveLastIn
+ where first live id = delFromFM live (CallArea (Young id))
+
+-- Slot sets: adding slots, removing slots, and checking for membership.
+liftToArea :: Area -> ([SubArea] -> [SubArea]) -> SubAreaSet -> SubAreaSet
+addSlot, removeSlot :: SubAreaSet -> SubArea -> SubAreaSet
+elemSlot :: SubAreaSet -> SubArea -> Bool
+liftToArea a f map = addToFM map a $ f (lookupWithDefaultFM map [] a)
+addSlot live (a, i, w) = liftToArea a (snd . liveGen (a, i, w)) live
+removeSlot live (a, i, w) = liftToArea a (liveKill (a, i, w)) live
+elemSlot live (a, i, w) =
+ not $ fst $ liveGen (a, i, w) (lookupWithDefaultFM live [] a)
+
+removeLiveSlotDefs :: (DefinerOfSlots s, UserOfSlots s) => SubAreaSet -> s -> SubAreaSet
+removeLiveSlotDefs = foldSlotsDefd removeSlot
+
+liveInSlots :: (DefinerOfSlots s, UserOfSlots s) => SubAreaSet -> s -> SubAreaSet
+liveInSlots live x = foldSlotsUsed addSlot (removeLiveSlotDefs live x) x
+
+liveLastIn :: (BlockId -> SubAreaSet) -> Last -> SubAreaSet
+liveLastIn env l = liveInSlots (liveLastOut env l) l
+
+-- Don't forget to keep the outgoing parameters in the CallArea live,
+-- as well as the update frame.
+liveLastOut :: (BlockId -> SubAreaSet) -> Last -> SubAreaSet
+liveLastOut env l =
+ case l of
+ LastCall _ Nothing n _ ->
+ add_area (CallArea Old) n out -- add outgoing args (includes upd frame)
+ LastCall _ (Just k) n _ -> add_area (CallArea (Young k)) n out
+ _ -> out
+ where out = joinOuts slotLattice env l
+ add_area _ n live | n == 0 = live
+ add_area a n live =
+ addToFM live a $ snd $ liveGen (a, n, n) $ lookupWithDefaultFM live [] a
+
+-- The liveness analysis must be precise: otherwise, we won't know if a definition
+-- should really kill a live-out stack slot.
+-- But the interference graph does not have to be precise -- it might decide that
+-- any live areas interfere. To maintain both a precise analysis and an imprecise
+-- interference graph, we need to convert the live-out stack slots to graph nodes
+-- at each and every instruction; rather than reconstruct a new list of nodes
+-- every time, I provide a function to fold over the nodes, which should be a
+-- reasonably efficient approach for the implementations we envision.
+-- Of course, it will probably be much easier to program if we just return a list...
+type Set x = FiniteMap x ()
+data IGraphBuilder n =
+ Builder { foldNodes :: forall z. SubArea -> (n -> z -> z) -> z -> z
+ , _wordsOccupied :: AreaMap -> AreaMap -> n -> [Int]
+ }
+
+areaBuilder :: IGraphBuilder Area
+areaBuilder = Builder fold words
+ where fold (a, _, _) f z = f a z
+ words areaSize areaMap a =
+ case lookupFM areaMap a of
+ Just addr -> [addr .. addr + (lookupFM areaSize a `orElse`
+ pprPanic "wordsOccupied: unknown area" (ppr a))]
+ Nothing -> []
+
+--slotBuilder :: IGraphBuilder (Area, Int)
+--slotBuilder = undefined
+
+-- Now, we can build the interference graph.
+-- The usual story: a definition interferes with all live outs and all other
+-- definitions.
+type IGraph x = FiniteMap x (Set x)
+type IGPair x = (IGraph x, IGraphBuilder x)
+igraph :: (Ord x) => IGraphBuilder x -> SlotEnv -> LGraph Middle Last -> IGraph x
+igraph builder env g = foldr interfere emptyFM (postorder_dfs g)
+ where foldN = foldNodes builder
+ interfere block igraph =
+ let (h, l) = goto_end (unzip block)
+ --heads :: ZHead Middle -> (IGraph x, SubAreaSet) -> IGraph x
+ heads (ZFirst _ _) (igraph, _) = igraph
+ heads (ZHead h m) (igraph, liveOut) =
+ heads h (addEdges igraph m liveOut, liveInSlots liveOut m)
+ -- add edges between a def and the other defs and liveouts
+ addEdges igraph i out = fst $ foldSlotsDefd addDef (igraph, out) i
+ addDef (igraph, out) def@(a, _, _) =
+ (foldN def (addDefN out) igraph,
+ addToFM out a (snd $ liveGen def (lookupWithDefaultFM out [] a)))
+ addDefN out n igraph =
+ let addEdgeNO o igraph = foldN o addEdgeNN igraph
+ addEdgeNN n' igraph = addEdgeNN' n n' $ addEdgeNN' n' n igraph
+ addEdgeNN' n n' igraph = addToFM igraph n (addToFM set n' ())
+ where set = lookupWithDefaultFM igraph emptyFM n
+ in foldFM (\ _ os igraph -> foldr addEdgeNO igraph os) igraph out
+ env' bid = lookupBlockEnv env bid `orElse` panic "unknown blockId in igraph"
+ in heads h $ case l of LastExit -> (igraph, emptyFM)
+ LastOther l -> (addEdges igraph l $ liveLastOut env' l,
+ liveLastIn env' l)
+
+-- Before allocating stack slots, we need to collect one more piece of information:
+-- what's the highest offset (in bytes) used in each Area?
+-- We'll need to allocate that much space for each Area.
+getAreaSize :: LGraph Middle Last -> AreaMap
+getAreaSize g@(LGraph _ off _) =
+ fold_blocks (fold_fwd_block first add_regslots last)
+ (unitFM (CallArea Old) off) g
+ where first id (StackInfo {argBytes = Just off}) z = add z (CallArea (Young id)) off
+ first _ _ z = z
+ add_regslots i z = foldSlotsUsed addSlot (foldSlotsDefd addSlot z i) i
+ last l@(LastOther (LastCall _ Nothing off _)) z =
+ add_regslots l (add z (CallArea Old) off)
+ last l@(LastOther (LastCall _ (Just k) off _)) z =
+ add_regslots l (add z (CallArea (Young k)) off)
+ last l z = add_regslots l z
+ addSlot z (a@(RegSlot _), off, _) = add z a off
+ addSlot z _ = z
+ add z a off = addToFM z a (max off (lookupWithDefaultFM z 0 a))
+
+
+-- Find the Stack slots occupied by the subarea's conflicts
+conflictSlots :: Ord x => IGPair x -> AreaMap -> AreaMap -> SubArea -> Set Int
+conflictSlots (ig, Builder foldNodes wordsOccupied) areaSize areaMap subarea =
+ foldNodes subarea foldNode emptyFM
+ where foldNode n set = foldFM conflict set $ lookupWithDefaultFM ig emptyFM n
+ conflict n' () set = liveInSlots areaMap n' set
+ -- Add stack slots occupied by igraph node n
+ liveInSlots areaMap n set = foldr setAdd set (wordsOccupied areaSize areaMap n)
+ setAdd w s = addToFM s w ()
+
+-- Find any open space on the stack, starting from the offset.
+-- If the area is a CallArea or a spill slot for a pointer, then it must
+-- be word-aligned.
+freeSlotFrom :: Ord x => IGPair x -> AreaMap -> Int -> AreaMap -> Area -> Int
+freeSlotFrom ig areaSize offset areaMap area =
+ let size = lookupFM areaSize area `orElse` 0
+ conflicts = conflictSlots ig areaSize areaMap (area, size, size)
+ -- CallAreas and Ptrs need to be word-aligned (round up!)
+ align = case area of CallArea _ -> align'
+ RegSlot r | isGcPtrType (localRegType r) -> align'
+ RegSlot _ -> id
+ align' n = (n + (wORD_SIZE - 1)) `div` wORD_SIZE * wORD_SIZE
+ -- Find a space big enough to hold the area
+ findSpace curr 0 = curr
+ findSpace curr cnt = -- part of target slot, # of bytes left to check
+ if elemFM curr conflicts then
+ findSpace (align (curr + size)) size -- try the next (possibly) open space
+ else findSpace (curr - 1) (cnt - 1)
+ in findSpace (align (offset + size)) size
+
+-- Find an open space on the stack, and assign it to the area.
+allocSlotFrom :: Ord x => IGPair x -> AreaMap -> Int -> AreaMap -> Area -> AreaMap
+allocSlotFrom ig areaSize from areaMap area =
+ if elemFM area areaMap then areaMap
+ else addToFM areaMap area $ freeSlotFrom ig areaSize from areaMap area
+
+-- | Greedy stack layout.
+-- Compute liveness, build the interference graph, and allocate slots for the areas.
+-- We visit each basic block in a (generally) forward order.
+-- At each instruction that names a register subarea r, we immediately allocate
+-- any available slot on the stack by the following procedure:
+-- 1. Find the nodes N' that conflict with r
+-- 2. Find the stack slots used for N'
+-- 3. Choose a contiguous stack space s not in N' (s must be large enough to hold r)
+-- For a CallArea, we allocate the stack space only when we reach a function
+-- call that returns to the CallArea's blockId.
+-- We use a similar procedure, with one exception: the stack space
+-- must be allocated below the youngest stack slot that is live out.
+
+-- Note: The stack pointer only has to be younger than the youngest live stack slot
+-- at proc points. Otherwise, the stack pointer can point anywhere.
+layout :: ProcPointSet -> SlotEnv -> LGraph Middle Last -> AreaMap
+layout procPoints env g@(LGraph _ entrySp _) =
+ let builder = areaBuilder
+ ig = (igraph builder env g, builder)
+ env' bid = lookupBlockEnv env bid `orElse` panic "unknown blockId in igraph"
+ areaSize = getAreaSize g
+ -- Find the slots that are live-in to the block
+ live_in (ZTail m l) = liveInSlots (live_in l) m
+ live_in (ZLast (LastOther l)) = liveLastIn env' l
+ live_in (ZLast LastExit) = emptyFM
+ -- Find the youngest live stack slot
+ youngest_live areaMap live = fold_subareas young_slot live 0
+ where young_slot (a, o, _) z = case lookupFM areaMap a of
+ Just top -> max z $ top + o
+ Nothing -> z
+ fold_subareas :: (SubArea -> z -> z) -> SubAreaSet -> z -> z
+ fold_subareas f m z = foldFM (\_ s z -> foldr f z s) z m
+ -- Allocate space for spill slots and call areas
+ allocVarSlot = allocSlotFrom ig areaSize 0
+ allocCallSlot areaMap (Block id stackInfo t)
+ | elemBlockSet id procPoints =
+ let young = youngest_live areaMap $ live_in t
+ start = case returnOff stackInfo of Just b -> max b young
+ Nothing -> young
+ z = allocSlotFrom ig areaSize start areaMap (CallArea (Young id))
+ in pprTrace "allocCallSlot for" (ppr id <+> ppr young <+> ppr (live_in t) <+> ppr z) z
+ allocCallSlot areaMap _ = areaMap
+ -- mid foreign calls need to have info tables placed on the stack
+ allocMidCall m@(MidForeignCall (Safe bid _) _ _ _) t areaMap =
+ let young = youngest_live areaMap $ removeLiveSlotDefs (live_in t) m
+ area = CallArea (Young bid)
+ areaSize' = addToFM areaSize area (widthInBytes (typeWidth gcWord))
+ in allocSlotFrom ig areaSize' young areaMap area
+ allocMidCall _ _ areaMap = areaMap
+ alloc m t areaMap =
+ foldSlotsDefd alloc' (foldSlotsUsed alloc' (allocMidCall m t areaMap) m) m
+ where alloc' areaMap (a@(RegSlot _), _, _) = allocVarSlot areaMap a
+ alloc' areaMap _ = areaMap
+ layoutAreas areaMap b@(Block _ _ t) = layout areaMap t
+ where layout areaMap (ZTail m t) = layout (alloc m t areaMap) t
+ layout areaMap (ZLast _) = allocCallSlot areaMap b
+ areaMap = foldl layoutAreas (addToFM emptyFM (CallArea Old) 0) (postorder_dfs g)
+ in pprTrace "ProcPoints" (ppr procPoints) $
+ pprTrace "Area SizeMap" (ppr areaSize) $
+ pprTrace "Entry SP" (ppr entrySp) $
+ pprTrace "Area Map" (ppr areaMap) $ areaMap
+
+-- After determining the stack layout, we can:
+-- 1. Replace references to stack Areas with addresses relative to the stack
+-- pointer.
+-- 2. Insert adjustments to the stack pointer to ensure that it is at a
+-- conventional location at each proc point.
+-- Because we don't take interrupts on the execution stack, we only need the
+-- stack pointer to be younger than the live values on the stack at proc points.
+-- 3. Compute the maximum stack offset used in the procedure and replace
+-- the stack high-water mark with that offset.
+manifestSP :: ProcPointSet -> BlockEnv Status -> AreaMap ->
+ LGraph Middle Last -> FuelMonad (LGraph Middle Last)
+manifestSP procPoints procMap areaMap g@(LGraph entry args blocks) =
+ liftM (LGraph entry args) blocks'
+ where blocks' = foldl replB (return emptyBlockEnv) (postorder_dfs g)
+ slot a = pprTrace "slot" (ppr a) $
+ lookupFM areaMap a `orElse` panic "unallocated Area"
+ slot' (Just id) = slot $ CallArea (Young id)
+ slot' Nothing = slot $ CallArea Old
+ sp_high = maxSlot slot g
+ proc_entry_sp = slot (CallArea Old) + args
+ sp_on_entry id | id == entry = proc_entry_sp
+ sp_on_entry id =
+ case lookupBlockEnv blocks id of
+ Just (Block _ (StackInfo {argBytes = Just o}) _) -> slot' (Just id) + o
+ _ ->
+ case expectJust "sp_on_entry" (lookupBlockEnv procMap id) of
+ ReachedBy pp ->
+ case blockSetToList pp of
+ [id] -> sp_on_entry id
+ _ -> panic "block not reached by one proc point"
+ ProcPoint -> pprPanic "procpoint doesn't take any arguments?"
+ (ppr id <+> ppr g <+> ppr procPoints <+> ppr procMap)
+
+ -- On entry to procpoints, the stack pointer is conventional;
+ -- otherwise, we check the SP set by predecessors.
+ replB :: FuelMonad (BlockEnv CmmBlock) -> CmmBlock -> FuelMonad (BlockEnv CmmBlock)
+ replB blocks (Block id o t) =
+ do bs <- replTail (Block id o) spIn t
+ pprTrace "spIn" (ppr id <+> ppr spIn)$
+ liftM (flip (foldr insertBlock) bs) blocks
+ where spIn = sp_on_entry id
+ replTail :: (ZTail Middle Last -> CmmBlock) -> Int -> (ZTail Middle Last) ->
+ FuelMonad ([CmmBlock])
+ replTail h spOff (ZTail m@(MidForeignCall (Safe bid _) _ _ _) t) =
+ replTail (\t' -> h (setSp spOff spOff' (ZTail (middle spOff m) t'))) spOff' t
+ where spOff' = slot' (Just bid) + widthInBytes (typeWidth gcWord)
+ replTail h spOff (ZTail m t) = replTail (h . ZTail (middle spOff m)) spOff t
+ replTail h spOff (ZLast (LastOther l)) = fixSp h spOff l
+ replTail h _ l@(ZLast LastExit) = return [h l]
+ middle spOff m = mapExpDeepMiddle (replSlot spOff) m
+ last spOff l = mapExpDeepLast (replSlot spOff) l
+ replSlot spOff (CmmStackSlot a i) = CmmRegOff (CmmGlobal Sp) (spOff - (slot a + i))
+ replSlot spOff (CmmLit CmmHighStackMark) = -- replacing the high water mark
+ CmmLit (CmmInt (toInteger (max 0 (sp_high - proc_entry_sp))) (typeWidth bWord))
+ replSlot _ e = e
+ -- The block must establish the SP expected at each successsor.
+ fixSp :: (ZTail Middle Last -> CmmBlock) -> Int -> Last -> FuelMonad ([CmmBlock])
+ fixSp h spOff l@(LastCall _ k n _) = updSp h spOff (slot' k + n) l
+ fixSp h spOff l@(LastBranch k) =
+ let succSp = sp_on_entry k in
+ if succSp /= spOff then
+ pprTrace "updSp" (ppr k <> ppr spOff <> ppr (sp_on_entry k)) $
+ updSp h spOff succSp l
+ else return $ [h (ZLast (LastOther (last spOff l)))]
+ fixSp h spOff l = liftM (uncurry (:)) $ fold_succs succ l $ return (b, [])
+ where b = h (ZLast (LastOther (last spOff l)))
+ succ succId z =
+ let succSp = sp_on_entry succId in
+ if succSp /= spOff then
+ do (b, bs) <- z
+ (b', bs') <- insertBetween b [setSpMid spOff succSp] succId
+ return (b', bs ++ bs')
+ else z
+ updSp h old new l = return [h $ setSp old new $ ZLast $ LastOther (last new l)]
+ setSpMid sp sp' = MidAssign (CmmGlobal Sp) e
+ where e = CmmMachOp (MO_Add wordWidth) [CmmReg (CmmGlobal Sp), off]
+ off = CmmLit $ CmmInt (toInteger $ sp - sp') wordWidth
+ setSp sp sp' t = if sp == sp' then t else ZTail (setSpMid sp sp') t
+
+
+-- To compute the stack high-water mark, we fold over the graph and
+-- compute the highest slot offset.
+maxSlot :: (Area -> Int) -> CmmGraph -> Int
+maxSlot slotOff g = fold_blocks (fold_fwd_block (\ _ _ x -> x) highSlot highSlot) 0 g
+ where highSlot i z = foldSlotsUsed add (foldSlotsDefd add z i) i
+ add z (a, i, w) = max z (slotOff a + i)
+
+-----------------------------------------------------------------------------
+-- | Sanity check: stub pointers immediately after they die
+-----------------------------------------------------------------------------
+-- This will miss stack slots that are last used in a Last node,
+-- but it should do pretty well...
+
+type StubPtrFix = FuelMonad (BackwardFixedPoint Middle Last SubAreaSet CmmGraph)
+
+stubSlotsOnDeath :: (LGraph Middle Last) -> FuelMonad (LGraph Middle Last)
+stubSlotsOnDeath g = liftM zdfFpContents $ (res :: StubPtrFix)
+ where res = zdfBRewriteFromL RewriteShallow emptyBlockEnv "stub ptrs" slotLattice
+ liveSlotTransfers rewrites (fact_bot slotLattice) g
+ rewrites = BackwardRewrites first middle last Nothing
+ first _ _ = Nothing
+ last _ _ = Nothing
+ middle liveSlots m = foldSlotsUsed (stub liveSlots m) Nothing m
+ stub liveSlots m rst subarea@(a, off, w) =
+ if elemSlot liveSlots subarea then rst
+ else let store = mkStore (CmmStackSlot a off)
+ (stackStubExpr (widthFromBytes w))
+ in case rst of Nothing -> Just (mkMiddle m <*> store)
+ Just g -> Just (g <*> store)
projects / ghc-hetmet.git / blobdiff