2 ( SlotEnv, liveSlotAnal, liveSlotTransfers, removeLiveSlotDefs
3 , layout, manifestSP, igraph, areaBuilder
4 , stubSlotsOnDeath ) -- to help crash early during debugging
8 import qualified Prelude as P
9 import Prelude hiding (zip, unzip, last)
19 import MkZipCfgCmm hiding (CmmBlock, CmmGraph)
23 import SMRep (ByteOff)
29 ------------------------------------------------------------------------
31 ------------------------------------------------------------------------
33 -- | Before we lay out the stack, we need to know something about the
34 -- liveness of the stack slots. In particular, to decide whether we can
35 -- reuse a stack location to hold multiple stack slots, we need to know
36 -- when each of the stack slots is used.
37 -- Although tempted to use something simpler, we really need a full interference
38 -- graph. Consider the following case:
40 -- 1 -> <spill x>; // y is dead out
41 -- 2 -> <spill y>; // x is dead out
42 -- 3 -> <spill x and y>
43 -- If we consider the arms in order and we use just the deadness information given by a
44 -- dataflow analysis, we might decide to allocate the stack slots for x and y
45 -- to the same stack location, which will lead to incorrect code in the third arm.
46 -- We won't make this mistake with an interference graph.
48 -- First, the liveness analysis.
49 -- We represent a slot with an area, an offset into the area, and a width.
50 -- Tracking the live slots is a bit tricky because there may be loads and stores
51 -- into only a part of a stack slot (e.g. loading the low word of a 2-word long),
52 -- e.g. Slot A 0 8 overlaps with Slot A 4 4.
54 -- The definition of a slot set is intended to reduce the number of overlap
55 -- checks we have to make. There's no reason to check for overlap between
56 -- slots in different areas, so we segregate the map by Area's.
57 -- We expect few slots in each Area, so we collect them in an unordered list.
58 -- To keep these lists short, any contiguous live slots are coalesced into
59 -- a single slot, on insertion.
61 slotLattice :: DataflowLattice SubAreaSet
62 slotLattice = DataflowLattice "live slots" emptyFM add False
63 where add new old = case foldFM addArea (False, old) new of
66 addArea a newSlots z = foldr (addSlot a) z newSlots
67 addSlot a slot (changed, map) =
68 let (c, live) = liveGen slot $ lookupWithDefaultFM map [] a
69 in (c || changed, addToFM map a live)
71 type SlotEnv = BlockEnv SubAreaSet
72 type SlotFix a = FuelMonad (BackwardFixedPoint Middle Last SubAreaSet a)
74 liveSlotAnal :: LGraph Middle Last -> FuelMonad SlotEnv
75 liveSlotAnal g = liftM zdfFpFacts (res :: SlotFix ())
76 where res = zdfSolveFromL emptyBlockEnv "live slot analysis" slotLattice
77 liveSlotTransfers (fact_bot slotLattice) g
79 -- Add the subarea s to the subareas in the list-set (possibly coalescing it with
80 -- adjacent subareas), and also return whether s was a new addition.
81 liveGen :: SubArea -> [SubArea] -> (Bool, [SubArea])
82 liveGen s set = liveGen' s set []
83 where liveGen' s [] z = (True, s : z)
84 liveGen' s@(a, hi, w) (s'@(a', hi', w') : rst) z =
85 if a /= a' || hi < lo' || lo > hi' then -- no overlap
86 liveGen' s rst (s' : z)
87 else if s' `contains` s then -- old contains new
89 else -- overlap: coalesce the slots
90 let new_hi = max hi hi'
92 in liveGen' (a, new_hi, new_hi - new_lo) rst z
93 where lo = hi - w -- remember: areas grow down
95 contains (a, hi, w) (a', hi', w') =
96 a == a' && hi >= hi' && hi - w <= hi' - w'
98 liveKill :: SubArea -> [SubArea] -> [SubArea]
99 liveKill (a, hi, w) set = -- pprTrace "killing slots in area" (ppr a) $
101 where liveKill' [] z = z
102 liveKill' (s'@(a', hi', w') : rst) z =
103 if a /= a' || hi < lo' || lo > hi' then -- no overlap
104 liveKill' rst (s' : z)
105 else -- overlap: split the old slot
106 let z' = if hi' > hi then (a, hi', hi' - hi) : z else z
107 z'' = if lo > lo' then (a, lo, lo - lo') : z' else z'
109 where lo = hi - w -- remember: areas grow down
112 -- Note: the stack slots that hold variables returned on the stack are not
113 -- considered live in to the block -- we treat the first node as a definition site.
114 -- BEWARE?: Am I being a little careless here in failing to check for the
115 -- entry Id (which would use the CallArea Old).
116 liveSlotTransfers :: BackwardTransfers Middle Last SubAreaSet
118 BackwardTransfers first liveInSlots liveLastIn
119 where first id live = delFromFM live (CallArea (Young id))
121 -- Slot sets: adding slots, removing slots, and checking for membership.
122 liftToArea :: Area -> ([SubArea] -> [SubArea]) -> SubAreaSet -> SubAreaSet
123 addSlot, removeSlot :: SubAreaSet -> SubArea -> SubAreaSet
124 elemSlot :: SubAreaSet -> SubArea -> Bool
125 liftToArea a f map = addToFM map a $ f (lookupWithDefaultFM map [] a)
126 addSlot live (a, i, w) = liftToArea a (snd . liveGen (a, i, w)) live
127 removeSlot live (a, i, w) = liftToArea a (liveKill (a, i, w)) live
128 elemSlot live (a, i, w) =
129 not $ fst $ liveGen (a, i, w) (lookupWithDefaultFM live [] a)
131 removeLiveSlotDefs :: (DefinerOfSlots s, UserOfSlots s) => SubAreaSet -> s -> SubAreaSet
132 removeLiveSlotDefs = foldSlotsDefd removeSlot
134 liveInSlots :: (DefinerOfSlots s, UserOfSlots s) => s -> SubAreaSet -> SubAreaSet
135 liveInSlots x live = foldSlotsUsed addSlot (removeLiveSlotDefs live x) x
137 liveLastIn :: Last -> (BlockId -> SubAreaSet) -> SubAreaSet
138 liveLastIn l env = liveInSlots l (liveLastOut env l)
140 -- Don't forget to keep the outgoing parameters in the CallArea live,
141 -- as well as the update frame.
142 -- Note: We have to keep the update frame live at a call because of the
143 -- case where the function doesn't return -- in that case, there won't
144 -- be a return to keep the update frame live. We'd still better keep the
145 -- info pointer in the update frame live at any call site;
146 -- otherwise we could screw up the garbage collector.
147 liveLastOut :: (BlockId -> SubAreaSet) -> Last -> SubAreaSet
150 LastCall _ Nothing n _ _ ->
151 add_area (CallArea Old) n out -- add outgoing args (includes upd frame)
152 LastCall _ (Just k) n _ (Just _) ->
153 add_area (CallArea Old) n (add_area (CallArea (Young k)) n out)
154 LastCall _ (Just k) n _ Nothing ->
155 add_area (CallArea (Young k)) n out
157 where out = joinOuts slotLattice env l
158 add_area _ n live | n == 0 = live
160 addToFM live a $ snd $ liveGen (a, n, n) $ lookupWithDefaultFM live [] a
162 -- The liveness analysis must be precise: otherwise, we won't know if a definition
163 -- should really kill a live-out stack slot.
164 -- But the interference graph does not have to be precise -- it might decide that
165 -- any live areas interfere. To maintain both a precise analysis and an imprecise
166 -- interference graph, we need to convert the live-out stack slots to graph nodes
167 -- at each and every instruction; rather than reconstruct a new list of nodes
168 -- every time, I provide a function to fold over the nodes, which should be a
169 -- reasonably efficient approach for the implementations we envision.
170 -- Of course, it will probably be much easier to program if we just return a list...
171 type Set x = FiniteMap x ()
172 data IGraphBuilder n =
173 Builder { foldNodes :: forall z. SubArea -> (n -> z -> z) -> z -> z
174 , _wordsOccupied :: AreaMap -> AreaMap -> n -> [Int]
177 areaBuilder :: IGraphBuilder Area
178 areaBuilder = Builder fold words
179 where fold (a, _, _) f z = f a z
180 words areaSize areaMap a =
181 case lookupFM areaMap a of
182 Just addr -> [addr .. addr + (lookupFM areaSize a `orElse`
183 pprPanic "wordsOccupied: unknown area" (ppr a))]
186 --slotBuilder :: IGraphBuilder (Area, Int)
187 --slotBuilder = undefined
189 -- Now, we can build the interference graph.
190 -- The usual story: a definition interferes with all live outs and all other
192 type IGraph x = FiniteMap x (Set x)
193 type IGPair x = (IGraph x, IGraphBuilder x)
194 igraph :: (Ord x) => IGraphBuilder x -> SlotEnv -> LGraph Middle Last -> IGraph x
195 igraph builder env g = foldr interfere emptyFM (postorder_dfs g)
196 where foldN = foldNodes builder
197 interfere block igraph =
198 let (h, l) = goto_end (unzip block)
199 --heads :: ZHead Middle -> (IGraph x, SubAreaSet) -> IGraph x
200 heads (ZFirst _) (igraph, _) = igraph
201 heads (ZHead h m) (igraph, liveOut) =
202 heads h (addEdges igraph m liveOut, liveInSlots m liveOut)
203 -- add edges between a def and the other defs and liveouts
204 addEdges igraph i out = fst $ foldSlotsDefd addDef (igraph, out) i
205 addDef (igraph, out) def@(a, _, _) =
206 (foldN def (addDefN out) igraph,
207 addToFM out a (snd $ liveGen def (lookupWithDefaultFM out [] a)))
208 addDefN out n igraph =
209 let addEdgeNO o igraph = foldN o addEdgeNN igraph
210 addEdgeNN n' igraph = addEdgeNN' n n' $ addEdgeNN' n' n igraph
211 addEdgeNN' n n' igraph = addToFM igraph n (addToFM set n' ())
212 where set = lookupWithDefaultFM igraph emptyFM n
213 in foldFM (\ _ os igraph -> foldr addEdgeNO igraph os) igraph out
214 env' bid = lookupBlockEnv env bid `orElse` panic "unknown blockId in igraph"
215 in heads h $ case l of LastExit -> (igraph, emptyFM)
216 LastOther l -> (addEdges igraph l $ liveLastOut env' l,
219 -- Before allocating stack slots, we need to collect one more piece of information:
220 -- what's the highest offset (in bytes) used in each Area?
221 -- We'll need to allocate that much space for each Area.
222 getAreaSize :: ByteOff -> LGraph Middle Last -> AreaMap
223 getAreaSize entry_off g@(LGraph _ _) =
224 fold_blocks (fold_fwd_block first add_regslots last)
225 (unitFM (CallArea Old) entry_off) g
227 last l@(LastOther (LastCall _ Nothing args res _)) z =
228 add_regslots l (add (add z area args) area res)
229 where area = CallArea Old
230 last l@(LastOther (LastCall _ (Just k) args res _)) z =
231 add_regslots l (add (add z area args) area res)
232 where area = CallArea (Young k)
233 last l z = add_regslots l z
234 add_regslots i z = foldSlotsUsed addSlot (foldSlotsDefd addSlot z i) i
235 addSlot z (a@(RegSlot (LocalReg _ ty)), _, _) =
236 add z a $ widthInBytes $ typeWidth ty
238 add z a off = addToFM z a (max off (lookupWithDefaultFM z 0 a))
241 -- Find the Stack slots occupied by the subarea's conflicts
242 conflictSlots :: Ord x => IGPair x -> AreaMap -> AreaMap -> SubArea -> Set Int
243 conflictSlots (ig, Builder foldNodes wordsOccupied) areaSize areaMap subarea =
244 foldNodes subarea foldNode emptyFM
245 where foldNode n set = foldFM conflict set $ lookupWithDefaultFM ig emptyFM n
246 conflict n' () set = liveInSlots areaMap n' set
247 -- Add stack slots occupied by igraph node n
248 liveInSlots areaMap n set = foldr setAdd set (wordsOccupied areaSize areaMap n)
249 setAdd w s = addToFM s w ()
251 -- Find any open space on the stack, starting from the offset.
252 -- If the area is a CallArea or a spill slot for a pointer, then it must
254 freeSlotFrom :: Ord x => IGPair x -> AreaMap -> Int -> AreaMap -> Area -> Int
255 freeSlotFrom ig areaSize offset areaMap area =
256 let size = lookupFM areaSize area `orElse` 0
257 conflicts = conflictSlots ig areaSize areaMap (area, size, size)
258 -- CallAreas and Ptrs need to be word-aligned (round up!)
259 align = case area of CallArea _ -> align'
260 RegSlot r | isGcPtrType (localRegType r) -> align'
262 align' n = (n + (wORD_SIZE - 1)) `div` wORD_SIZE * wORD_SIZE
263 -- Find a space big enough to hold the area
264 findSpace curr 0 = curr
265 findSpace curr cnt = -- part of target slot, # of bytes left to check
266 if elemFM curr conflicts then
267 findSpace (align (curr + size)) size -- try the next (possibly) open space
268 else findSpace (curr - 1) (cnt - 1)
269 in findSpace (align (offset + size)) size
271 -- Find an open space on the stack, and assign it to the area.
272 allocSlotFrom :: Ord x => IGPair x -> AreaMap -> Int -> AreaMap -> Area -> AreaMap
273 allocSlotFrom ig areaSize from areaMap area =
274 if elemFM area areaMap then areaMap
275 else addToFM areaMap area $ freeSlotFrom ig areaSize from areaMap area
277 -- | Greedy stack layout.
278 -- Compute liveness, build the interference graph, and allocate slots for the areas.
279 -- We visit each basic block in a (generally) forward order.
280 -- At each instruction that names a register subarea r, we immediately allocate
281 -- any available slot on the stack by the following procedure:
282 -- 1. Find the nodes N' that conflict with r
283 -- 2. Find the stack slots used for N'
284 -- 3. Choose a contiguous stack space s not in N' (s must be large enough to hold r)
285 -- For a CallArea, we allocate the stack space only when we reach a function
286 -- call that returns to the CallArea's blockId.
287 -- We use a similar procedure, with one exception: the stack space
288 -- must be allocated below the youngest stack slot that is live out.
290 -- Note: The stack pointer only has to be younger than the youngest live stack slot
291 -- at proc points. Otherwise, the stack pointer can point anywhere.
292 layout :: ProcPointSet -> SlotEnv -> ByteOff -> LGraph Middle Last -> AreaMap
293 layout procPoints env entry_off g =
294 let ig = (igraph areaBuilder env g, areaBuilder)
295 env' bid = lookupBlockEnv env bid `orElse` panic "unknown blockId in igraph"
296 areaSize = getAreaSize entry_off g
297 -- Find the slots that are live-in to a block tail
298 live_in (ZTail m l) = liveInSlots m (live_in l)
299 live_in (ZLast (LastOther l)) = liveLastIn l env'
300 live_in (ZLast LastExit) = emptyFM
301 -- Find the youngest live stack slot
302 youngest_live areaMap live = fold_subareas young_slot live 0
303 where young_slot (a, o, _) z = case lookupFM areaMap a of
304 Just top -> max z $ top + o
306 fold_subareas f m z = foldFM (\_ s z -> foldr f z s) z m
307 -- Allocate space for spill slots and call areas
308 allocVarSlot = allocSlotFrom ig areaSize 0
309 -- Update the successor's incoming SP.
310 setSuccSPs inSp bid areaMap =
311 case (lookupFM areaMap area, lookupBlockEnv (lg_blocks g) bid) of
312 (Just _, _) -> areaMap -- succ already knows incoming SP
313 (Nothing, Just (Block _ _)) ->
314 if elemBlockSet bid procPoints then
315 let young = youngest_live areaMap $ env' bid
316 -- start = case returnOff stackInfo of Just b -> max b young
318 start = young -- maybe wrong, but I don't understand
319 -- why the preceding is necessary...
320 in allocSlotFrom ig areaSize start areaMap area
321 else addToFM areaMap area inSp
322 (_, Nothing) -> panic "Block not found in cfg"
323 where area = CallArea (Young bid)
324 allocLast (Block id _) areaMap l =
325 fold_succs (setSuccSPs inSp) l areaMap
326 where inSp = expectJust "sp in" $ lookupFM areaMap (CallArea (Young id))
327 allocMidCall m@(MidForeignCall (Safe bid _) _ _ _) t areaMap =
328 let young = youngest_live areaMap $ removeLiveSlotDefs (live_in t) m
329 area = CallArea (Young bid)
330 areaSize' = addToFM areaSize area (widthInBytes (typeWidth gcWord))
331 in allocSlotFrom ig areaSize' young areaMap area
332 allocMidCall _ _ areaMap = areaMap
334 foldSlotsDefd alloc' (foldSlotsUsed alloc' (allocMidCall m t areaMap) m) m
335 where alloc' areaMap (a@(RegSlot _), _, _) = allocVarSlot areaMap a
336 alloc' areaMap _ = areaMap
337 layoutAreas areaMap b@(Block _ t) = layout areaMap t
338 where layout areaMap (ZTail m t) = layout (alloc m t areaMap) t
339 layout areaMap (ZLast l) = allocLast b areaMap l
340 initMap = addToFM (addToFM emptyFM (CallArea Old) 0)
341 (CallArea (Young (lg_entry g))) 0
342 areaMap = foldl layoutAreas initMap (postorder_dfs g)
343 in -- pprTrace "ProcPoints" (ppr procPoints) $
344 -- pprTrace "Area SizeMap" (ppr areaSize) $
345 -- pprTrace "Entry SP" (ppr entrySp) $
346 -- pprTrace "Area Map" (ppr areaMap) $
349 -- After determining the stack layout, we can:
350 -- 1. Replace references to stack Areas with addresses relative to the stack
352 -- 2. Insert adjustments to the stack pointer to ensure that it is at a
353 -- conventional location at each proc point.
354 -- Because we don't take interrupts on the execution stack, we only need the
355 -- stack pointer to be younger than the live values on the stack at proc points.
356 -- 3. Compute the maximum stack offset used in the procedure and replace
357 -- the stack high-water mark with that offset.
358 manifestSP :: AreaMap -> ByteOff -> LGraph Middle Last -> FuelMonad (LGraph Middle Last)
359 manifestSP areaMap entry_off g@(LGraph entry _blocks) =
360 liftM (LGraph entry) $ foldl replB (return emptyBlockEnv) (postorder_dfs g)
361 where slot a = -- pprTrace "slot" (ppr a) $
362 lookupFM areaMap a `orElse` panic "unallocated Area"
363 slot' (Just id) = slot $ CallArea (Young id)
364 slot' Nothing = slot $ CallArea Old
365 sp_high = maxSlot slot g
366 proc_entry_sp = slot (CallArea Old) + entry_off
369 case Z.last (unzip b) of
370 LastOther (LastCall {cml_cont = Just succ, cml_ret_args = off}) ->
371 extendBlockEnv env succ off
373 spEntryMap = fold_blocks add_sp_off (mkBlockEnv [(entry, entry_off)]) g
374 spOffset id = lookupBlockEnv spEntryMap id `orElse` 0
376 sp_on_entry id | id == entry = proc_entry_sp
377 sp_on_entry id = slot' (Just id) + spOffset id
379 -- On entry to procpoints, the stack pointer is conventional;
380 -- otherwise, we check the SP set by predecessors.
381 replB :: FuelMonad (BlockEnv CmmBlock) -> CmmBlock -> FuelMonad (BlockEnv CmmBlock)
382 replB blocks (Block id t) =
383 do bs <- replTail (Block id) spIn t
384 -- pprTrace "spIn" (ppr id <+> ppr spIn) $ do
385 liftM (flip (foldr insertBlock) bs) blocks
386 where spIn = sp_on_entry id
387 replTail :: (ZTail Middle Last -> CmmBlock) -> Int -> (ZTail Middle Last) ->
388 FuelMonad ([CmmBlock])
389 replTail h spOff (ZTail m@(MidForeignCall (Safe bid _) _ _ _) t) =
390 replTail (\t' -> h (setSp spOff spOff' (ZTail (middle spOff m) t'))) spOff' t
391 where spOff' = slot' (Just bid) + widthInBytes (typeWidth gcWord)
392 replTail h spOff (ZTail m t) = replTail (h . ZTail (middle spOff m)) spOff t
393 replTail h spOff (ZLast (LastOther l)) = fixSp h spOff l
394 replTail h _ l@(ZLast LastExit) = return [h l]
395 middle spOff m = mapExpDeepMiddle (replSlot spOff) m
396 last spOff l = mapExpDeepLast (replSlot spOff) l
397 replSlot spOff (CmmStackSlot a i) = CmmRegOff (CmmGlobal Sp) (spOff - (slot a + i))
398 replSlot _ (CmmLit CmmHighStackMark) = -- replacing the high water mark
399 CmmLit (CmmInt (toInteger (max 0 (sp_high - proc_entry_sp))) (typeWidth bWord))
401 -- The block must establish the SP expected at each successsor.
402 fixSp :: (ZTail Middle Last -> CmmBlock) -> Int -> Last -> FuelMonad ([CmmBlock])
403 fixSp h spOff l@(LastCall _ k n _ _) = updSp h spOff (slot' k + n) l
404 fixSp h spOff l@(LastBranch k) =
405 let succSp = sp_on_entry k in
406 if succSp /= spOff then
407 -- pprTrace "updSp" (ppr k <> ppr spOff <> ppr (sp_on_entry k)) $
408 updSp h spOff succSp l
409 else return $ [h (ZLast (LastOther (last spOff l)))]
410 fixSp h spOff l = liftM (uncurry (:)) $ fold_succs succ l $ return (b, [])
411 where b = h (ZLast (LastOther (last spOff l)))
413 let succSp = sp_on_entry succId in
414 if succSp /= spOff then
416 (b', bs') <- insertBetween b [setSpMid spOff succSp] succId
417 return (b', bs ++ bs')
419 updSp h old new l = return [h $ setSp old new $ ZLast $ LastOther (last new l)]
420 setSpMid sp sp' = MidAssign (CmmGlobal Sp) e
421 where e = CmmMachOp (MO_Add wordWidth) [CmmReg (CmmGlobal Sp), off]
422 off = CmmLit $ CmmInt (toInteger $ sp - sp') wordWidth
423 setSp sp sp' t = if sp == sp' then t else ZTail (setSpMid sp sp') t
426 -- To compute the stack high-water mark, we fold over the graph and
427 -- compute the highest slot offset.
428 maxSlot :: (Area -> Int) -> CmmGraph -> Int
429 maxSlot slotOff g = fold_blocks (fold_fwd_block (\ _ x -> x) highSlot highSlot) 0 g
430 where highSlot i z = foldSlotsUsed add (foldSlotsDefd add z i) i
431 add z (a, i, _) = max z (slotOff a + i)
433 -----------------------------------------------------------------------------
434 -- | Sanity check: stub pointers immediately after they die
435 -----------------------------------------------------------------------------
436 -- This will miss stack slots that are last used in a Last node,
437 -- but it should do pretty well...
439 type StubPtrFix = FuelMonad (BackwardFixedPoint Middle Last SubAreaSet CmmGraph)
441 stubSlotsOnDeath :: (LGraph Middle Last) -> FuelMonad (LGraph Middle Last)
442 stubSlotsOnDeath g = liftM zdfFpContents $ (res :: StubPtrFix)
443 where res = zdfBRewriteFromL RewriteShallow emptyBlockEnv "stub ptrs" slotLattice
444 liveSlotTransfers rewrites (fact_bot slotLattice) g
445 rewrites = BackwardRewrites first middle last Nothing
448 middle m liveSlots = foldSlotsUsed (stub liveSlots m) Nothing m
449 stub liveSlots m rst subarea@(a, off, w) =
450 if elemSlot liveSlots subarea then rst
451 else let store = mkStore (CmmStackSlot a off)
452 (stackStubExpr (widthFromBytes w))
453 in case rst of Nothing -> Just (mkMiddle m <*> store)
454 Just g -> Just (g <*> store)