-- If we can arrange that v1 and v2 are allocated to the same hreg it's more likely
-- the spill/reload instrs can be cleaned and replaced by a nop reg-reg move.
--
--- TODO: This only works intra-block at the momement. It's be nice to join up the mappings
--- across blocks also.
--
slurpReloadCoalesce :: LiveCmmTop -> Bag (Reg, Reg)
slurpReloadCoalesce live
slurpCmm cs (CmmProc _ _ _ (ListGraph blocks))
= foldl' slurpComp cs blocks
- slurpComp cs (BasicBlock _ blocks)
- = foldl' slurpBlock cs blocks
+ slurpComp cs comp
+ = let (moveBags, _) = runState (slurpCompM comp) emptyUFM
+ in unionManyBags (cs : moveBags)
- slurpBlock cs (BasicBlock _ instrs)
- = let (_, mMoves) = mapAccumL slurpLI emptyUFM instrs
- in unionBags cs (listToBag $ catMaybes mMoves)
+ slurpCompM (BasicBlock _ blocks)
+ = do -- run the analysis once to record the mapping across jumps.
+ mapM_ (slurpBlock False) blocks
+
+ -- run it a second time while using the information from the last pass.
+ -- We /could/ run this many more times to deal with graphical control
+ -- flow and propagating info across multiple jumps, but it's probably
+ -- not worth the trouble.
+ mapM (slurpBlock True) blocks
+
+ slurpBlock propagate (BasicBlock blockId instrs)
+ = do -- grab the slot map for entry to this block
+ slotMap <- if propagate
+ then getSlotMap blockId
+ else return emptyUFM
+
+ (_, mMoves) <- mapAccumLM slurpLI slotMap instrs
+ return $ listToBag $ catMaybes mMoves
+
+ slurpLI :: UniqFM Reg -- current slotMap
+ -> LiveInstr
+ -> State (UniqFM [UniqFM Reg]) -- blockId -> [slot -> reg]
+ -- for tracking slotMaps across jumps
+
+ ( UniqFM Reg -- new slotMap
+ , Maybe (Reg, Reg)) -- maybe a new coalesce edge
- slurpLI :: UniqFM Reg -> LiveInstr -> (UniqFM Reg, Maybe (Reg, Reg))
slurpLI slotMap (Instr instr _)
-- remember what reg was stored into the slot
| SPILL reg slot <- instr
, slotMap' <- addToUFM slotMap slot reg
- = (slotMap', Nothing)
+ = return (slotMap', Nothing)
-- add an edge betwen the this reg and the last one stored into the slot
| RELOAD slot reg <- instr
= case lookupUFM slotMap slot of
Just reg2
- | reg /= reg2 -> (slotMap, Just (reg, reg2))
- | otherwise -> (slotMap, Nothing)
+ | reg /= reg2 -> return (slotMap, Just (reg, reg2))
+ | otherwise -> return (slotMap, Nothing)
+
+ Nothing -> return (slotMap, Nothing)
- Nothing -> (slotMap, Nothing)
+ -- if we hit a jump, remember the current slotMap
+ | targets <- jumpDests instr []
+ , not $ null targets
+ = do mapM_ (accSlotMap slotMap) targets
+ return (slotMap, Nothing)
| otherwise
- = (slotMap, Nothing)
+ = return (slotMap, Nothing)
+
+ -- record a slotmap for an in edge to this block
+ accSlotMap slotMap blockId
+ = modify (\s -> addToUFM_C (++) s blockId [slotMap])
+
+ -- work out the slot map on entry to this block
+ -- if we have slot maps for multiple in-edges then we need to merge them.
+ getSlotMap blockId
+ = do map <- get
+ let slotMaps = fromMaybe [] (lookupUFM map blockId)
+ return $ foldr mergeSlotMaps emptyUFM slotMaps
+
+ mergeSlotMaps :: UniqFM Reg -> UniqFM Reg -> UniqFM Reg
+ mergeSlotMaps map1 map2
+ = listToUFM
+ $ [ (k, r1) | (k, r1) <- ufmToList map1
+ , case lookupUFM map2 k of
+ Nothing -> False
+ Just r2 -> r1 == r2 ]
-- | Strip away liveness information, yielding NatCmmTop
Just assoc -> assoc
Nothing -> emptyAssoc
- instrs_reload <- cleanReload assoc [] instrs
+ instrs_reload <- cleanFwd assoc [] instrs
instrs_spill <- cleanSpill emptyUniqSet [] instrs_reload
return $ BasicBlock id instrs_spill
-- On a reload, if we know a reg already has the same value as a slot
-- then we don't need to do the reload.
--
-cleanReload
+cleanFwd
:: Assoc Store -- ^ two store locations are associated if they have the same value
-> [LiveInstr] -- ^ acc
-> [LiveInstr] -- ^ instrs to clean (in backwards order)
-> CleanM [LiveInstr] -- ^ cleaned instrs (in forward order)
-cleanReload _ acc []
+cleanFwd _ acc []
= return acc
-- write out live range joins via spill slots to just a spill and a reg-reg move
-- hopefully the spill will be also be cleaned in the next pass
--
-cleanReload assoc acc (Instr i1 live1 : Instr i2 _ : instrs)
+cleanFwd assoc acc (Instr i1 live1 : Instr i2 _ : instrs)
| SPILL reg1 slot1 <- i1
, RELOAD slot2 reg2 <- i2
, slot1 == slot2
= do
modify $ \s -> s { sCleanedReloadsAcc = sCleanedReloadsAcc s + 1 }
- cleanReload assoc acc
+ cleanFwd assoc acc
(Instr i1 live1 : Instr (mkRegRegMoveInstr reg1 reg2) Nothing : instrs)
-cleanReload assoc acc (li@(Instr i1 _) : instrs)
+cleanFwd assoc acc (li@(Instr i1 _) : instrs)
| Just (r1, r2) <- isRegRegMove i1
= if r1 == r2
-- erase any left over nop reg reg moves while we're here
-- this will also catch any nop moves that the "write out live range joins" case above
-- happens to add
- then cleanReload assoc acc instrs
+ then cleanFwd assoc acc instrs
-- if r1 has the same value as some slots and we copy r1 to r2,
-- then r2 is now associated with those slots instead
$ delAssoc (SReg r2)
$ assoc
- cleanReload assoc' (li : acc) instrs
+ cleanFwd assoc' (li : acc) instrs
-cleanReload assoc acc (li@(Instr instr _) : instrs)
+cleanFwd assoc acc (li@(Instr instr _) : instrs)
| SPILL reg slot <- instr
= let assoc' = addAssoc (SReg reg) (SSlot slot) -- doing the spill makes reg and slot the same value
$ delAssoc (SSlot slot) -- slot value changes on spill
$ assoc
- in cleanReload assoc' (li : acc) instrs
+ in cleanFwd assoc' (li : acc) instrs
- | RELOAD slot reg <- instr
- = if elemAssoc (SSlot slot) (SReg reg) assoc
-
- -- if the reg and slot had the same value before reload
- -- then we don't need the reload.
- then do
- modify $ \s -> s { sCleanedReloadsAcc = sCleanedReloadsAcc s + 1 }
- cleanReload assoc acc instrs
-
- -- reg and slot had different values before reload
- else
- let assoc' = addAssoc (SReg reg) (SSlot slot) -- doing the reload makes reg and slot the same value
- $ delAssoc (SReg reg) -- reg value changes on reload
- $ assoc
- in cleanReload assoc' (li : acc) instrs
+ -- clean a reload instr
+ | RELOAD{} <- instr
+ = do (assoc', mli) <- cleanReload assoc li
+ case mli of
+ Nothing -> cleanFwd assoc' acc instrs
+ Just li' -> cleanFwd assoc' (li' : acc) instrs
-- remember the association over a jump
| targets <- jumpDests instr []
, not $ null targets
= do mapM_ (accJumpValid assoc) targets
- cleanReload assoc (li : acc) instrs
+ cleanFwd assoc (li : acc) instrs
-- writing to a reg changes its value.
| RU _ written <- regUsage instr
= let assoc' = foldr delAssoc assoc (map SReg $ nub written)
- in cleanReload assoc' (li : acc) instrs
+ in cleanFwd assoc' (li : acc) instrs
+
+
+-- | Try and rewrite a reload instruction to something more pleasing
+--
+cleanReload :: Assoc Store -> LiveInstr -> CleanM (Assoc Store, Maybe LiveInstr)
+cleanReload assoc li@(Instr (RELOAD slot reg) _)
+
+ -- if the reg we're reloading already has the same value as the slot
+ -- then we can erase the instruction outright
+ | elemAssoc (SSlot slot) (SReg reg) assoc
+ = do modify $ \s -> s { sCleanedReloadsAcc = sCleanedReloadsAcc s + 1 }
+ return (assoc, Nothing)
+
+ -- if we can find another reg with the same value as this slot then
+ -- do a move instead of a reload.
+ | Just reg2 <- findRegOfSlot assoc slot
+ = do modify $ \s -> s { sCleanedReloadsAcc = sCleanedReloadsAcc s + 1 }
+
+ let assoc' = addAssoc (SReg reg) (SReg reg2)
+ $ delAssoc (SReg reg)
+ $ assoc
+
+ return (assoc', Just $ Instr (mkRegRegMoveInstr reg2 reg) Nothing)
+
+ -- gotta keep this instr
+ -- update the association
+ | otherwise
+ = do let assoc' = addAssoc (SReg reg) (SSlot slot) -- doing the reload makes reg and slot the same value
+ $ delAssoc (SReg reg) -- reg value changes on reload
+ $ assoc
+
+ return (assoc', Just li)
+
+cleanReload _ _
+ = panic "RegSpillClean.cleanReload: unhandled instr"
-- | Clean out unneeded spill instructions.
intersects assocs = foldl1' intersectAssoc assocs
+-- | See if we have a reg with the same value as this slot in the association table.
+findRegOfSlot :: Assoc Store -> Int -> Maybe Reg
+findRegOfSlot assoc slot
+ | close <- closeAssoc (SSlot slot) assoc
+ , Just (SReg reg) <- find isStoreReg $ uniqSetToList close
+ = Just reg
+
+ | otherwise
+ = Nothing
+
---------------
type CleanM = State CleanS
= SSlot Int
| SReg Reg
+-- | Check if this is a reg store
+isStoreReg :: Store -> Bool
+isStoreReg ss
+ = case ss of
+ SSlot _ -> False
+ SReg _ -> True
+
-- spill cleaning is only done once all virtuals have been allocated to realRegs
--
instance Uniquable Store where
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