Commit be60e519 authored by simonpj@microsoft.com's avatar simonpj@microsoft.com
Browse files

Comments in Cmm

parent 95693ea9
......@@ -84,9 +84,13 @@ cpsTop hsc_env (CmmProc h l args (stackInfo@(entry_off, _), g)) =
dump Opt_D_dump_cmmz "Pre common block elimination" g
g <- return $ elimCommonBlocks g
dump Opt_D_dump_cmmz "Post common block elimination" g
----------- Proc points -------------------
procPoints <- run $ minimalProcPointSet callPPs g
g <- run $ addProcPointProtocols callPPs procPoints g
dump Opt_D_dump_cmmz "Post Proc Points Added" g
----------- Spills and reloads -------------------
g <-
-- pprTrace "pre Spills" (ppr g) $
dual_rewrite Opt_D_dump_cmmz "spills and reloads"
......@@ -101,10 +105,15 @@ cpsTop hsc_env (CmmProc h l args (stackInfo@(entry_off, _), g)) =
dual_rewrite Opt_D_dump_cmmz "Dead Assignment Elimination"
(removeDeadAssignmentsAndReloads procPoints) g
-- Remove redundant reloads (and any other redundant asst)
----------- Debug only: add code to put zero in dead stack slots----
-- Debugging: stubbing slots on death can cause crashes early
g <-
-- trace "post dead-assign elim" $
if opt_StubDeadValues then run $ stubSlotsOnDeath g else return g
--------------- Stack layout ----------------
slotEnv <- run $ liveSlotAnal g
mbpprTrace "live slot analysis results: " (ppr slotEnv) $ return ()
cafEnv <-
......@@ -116,15 +125,21 @@ cpsTop hsc_env (CmmProc h l args (stackInfo@(entry_off, _), g)) =
mbpprTrace "slotEnv extended for safe foreign calls: " (ppr slotEnv) $ return ()
let areaMap = layout procPoints slotEnv entry_off g
mbpprTrace "areaMap" (ppr areaMap) $ return ()
------------ Manifest the the stack pointer --------
g <- run $ manifestSP areaMap entry_off g
dump Opt_D_dump_cmmz "after manifestSP" g
-- UGH... manifestSP can require updates to the procPointMap.
-- We can probably do something quicker here for the update...
------------- Split into separate procedures ------------
procPointMap <- run $ procPointAnalysis procPoints g
dump Opt_D_dump_cmmz "procpoint map" procPointMap
gs <- run $ splitAtProcPoints l callPPs procPoints procPointMap
(CmmProc h l args (stackInfo, g))
mapM_ (dump Opt_D_dump_cmmz "after splitting") gs
------------- More CAFs and foreign calls ------------
let localCAFs = catMaybes $ map (localCAFInfo cafEnv) gs
mbpprTrace "localCAFs" (ppr localCAFs) $ return ()
gs <- liftM concat $ run $ foldM lowerSafeForeignCalls [] gs
......
......@@ -117,7 +117,10 @@ End of note -}
type SubArea = (Area, Int, Int) -- area, offset, width
type SubAreaSet = FiniteMap Area [SubArea]
type AreaMap = FiniteMap Area Int
-- Byte offset of the oldest byte of the Area,
-- relative to the oldest byte of the Old Area
data CmmLit
= CmmInt Integer Width
......
......@@ -127,18 +127,21 @@ forward = ForwardTransfers first middle last exit
-- those that are induced by calls in the original graph
-- and those that are introduced because they're reachable from multiple proc points.
callProcPoints :: CmmGraph -> ProcPointSet
minimalProcPointSet :: ProcPointSet -> CmmGraph -> FuelMonad ProcPointSet
callProcPoints g = fold_blocks add (unitBlockSet (lg_entry g)) g
where add b set = case last $ unzip b of
LastOther (LastCall _ (Just k) _ _ _) -> extendBlockSet set k
_ -> set
minimalProcPointSet :: ProcPointSet -> CmmGraph -> FuelMonad ProcPointSet
-- Given the set of successors of calls (which must be proc-points)
-- figure ou the minimal set of necessary proc-points
minimalProcPointSet callProcPoints g = extendPPSet g (postorder_dfs g) callProcPoints
type PPFix = FuelMonad (ForwardFixedPoint Middle Last Status ())
procPointAnalysis :: ProcPointSet -> CmmGraph -> FuelMonad (BlockEnv Status)
-- Once you know what the proc-points are, figure out
-- what proc-points each block is reachable from
procPointAnalysis procPoints g =
let addPP env id = extendBlockEnv env id ProcPoint
initProcPoints = foldl addPP emptyBlockEnv (blockSetToList procPoints)
......
......@@ -67,6 +67,8 @@ slotLattice = DataflowLattice "live slots" emptyFM add False
in (c || changed, addToFM map a live)
type SlotEnv = BlockEnv SubAreaSet
-- The sub-areas live on entry to the block
type SlotFix a = FuelMonad (BackwardFixedPoint Middle Last SubAreaSet a)
liveSlotAnal :: LGraph Middle Last -> FuelMonad SlotEnv
......@@ -218,6 +220,8 @@ igraph builder env g = foldr interfere emptyFM (postorder_dfs g)
-- what's the highest offset (in bytes) used in each Area?
-- We'll need to allocate that much space for each Area.
getAreaSize :: ByteOff -> LGraph Middle Last -> AreaMap
-- The domain of the returned mapping consists only of Areas
-- used for (a) variable spill slots, and (b) parameter passing ares for calls
getAreaSize entry_off g@(LGraph _ _) =
fold_blocks (fold_fwd_block first add_regslots last)
(unitFM (CallArea Old) entry_off) g
......@@ -234,6 +238,9 @@ getAreaSize entry_off g@(LGraph _ _) =
add z a $ widthInBytes $ typeWidth ty
addSlot z _ = z
add z a off = addToFM z a (max off (lookupWithDefaultFM z 0 a))
-- The 'max' is important. Two calls, to f and g, might share a common
-- continuation (and hence a common CallArea), but their number of overflow
-- parameters might differ.
-- Find the Stack slots occupied by the subarea's conflicts
......@@ -275,19 +282,30 @@ allocSlotFrom 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)
-- 1. Find the sub-areas S that conflict with r
-- 2. Find the stack slots used for S
-- 3. Choose a contiguous stack space s not in S (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.
-- Then, we allocate the Area subject to the following constraints:
-- a) It must be younger than all the sub-areas that are live on entry to the block
-- This constraint is only necessary for the successor of a call
-- b) It must not overlap with any already-allocated Area with which it conflicts
-- (ie at some point, not necessarily now, is live at the same time)
-- Part (b) is just the 1,2,3 part above
-- 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 -> ByteOff -> LGraph Middle Last -> AreaMap
-- The domain of the returned map includes an Area for EVERY block
-- including each block that is not the successor of a call (ie is not a proc-point)
-- That's how we return the info of what the SP should be at the entry of every block
layout procPoints env entry_off g =
let ig = (igraph areaBuilder env g, areaBuilder)
env' bid = lookupBlockEnv env bid `orElse` panic "unknown blockId in igraph"
......@@ -296,14 +314,21 @@ layout procPoints env entry_off g =
live_in (ZTail m l) = liveInSlots m (live_in l)
live_in (ZLast (LastOther l)) = liveLastIn l env'
live_in (ZLast LastExit) = emptyFM
-- Find the youngest live stack slot
-- Find the youngest live stack slot that has already been allocated
youngest_live :: AreaMap -- Already allocated
-> SubAreaSet -- Sub-areas live here
-> ByteOff -- Offset of the youngest byte of any
-- already-allocated, live sub-area
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 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
-- Update the successor's incoming SP.
setSuccSPs inSp bid areaMap =
case (lookupFM areaMap area, lookupBlockEnv (lg_blocks g) bid) of
......@@ -319,19 +344,23 @@ layout procPoints env entry_off g =
else addToFM areaMap area inSp
(_, Nothing) -> panic "Block not found in cfg"
where area = CallArea (Young bid)
allocLast (Block id _) areaMap l =
fold_succs (setSuccSPs inSp) l areaMap
where inSp = expectJust "sp in" $ lookupFM areaMap (CallArea (Young id))
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 l) = allocLast b areaMap l
......
......@@ -103,12 +103,15 @@ data Last
-- This is really needed at the *return* point rather than here
-- at the call, but in practice it's convenient to record it here.
cml_ret_off :: Maybe UpdFrameOffset
-- Stack offset for return (update frames);
-- The return offset should be Nothing only if we have to create
-- a new call, e.g. for a procpoint, in which case it's an invariant
-- that the call does not stand for a return or a tail call,
-- and the successor does not need an info table.
cml_ret_off :: Maybe ByteOff
-- For calls *only*, the byte offset of the base of the frame that
-- must be described by the info table for the return point.
-- The older words are an update frames, which have their own
-- info-table and layout information
-- From a liveness point of view, the stack words older than
-- cml_ret_off are treated as live, even if the sequel of
-- the call goes into a loop.
}
data MidCallTarget -- The target of a MidUnsafeCall
......
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