    {-# OPTIONS -fno-warn-missing-signatures #-}

    -- | When there aren't enough registers to hold all the vregs we have to spill some of those
    --   vregs to slots on the stack. This module is used modify the code to use those slots.
    --
    module RegAlloc.Graph.Spill (
    	regSpill,
    	SpillStats(..),
    	accSpillSL
    )
    where
    import RegAlloc.Liveness
    import Instruction
    import Reg
    import Cmm	hiding (RegSet)
    import BlockId

    import State
    import Unique
    import UniqFM
    import UniqSet
    import UniqSupply
    import Outputable

    import Data.List
    import Data.Maybe
    import Data.Map			(Map)
    import Data.Set			(Set)
    import qualified Data.Map	as Map
    import qualified Data.Set	as Set

    -- | Spill all these virtual regs to stack slots.
    --
    --   TODO: See if we can split some of the live ranges instead of just globally
    --         spilling the virtual reg. This might make the spill cleaner's job easier.
    --
    --   TODO: On CISCy x86 and x86_64 we don't nessesarally have to add a mov instruction
    --         when making spills. If an instr is using a spilled virtual we may be able to
    --         address the spill slot directly.
    --
    regSpill
    	:: Instruction instr
    	=> [LiveCmmTop instr]		-- ^ the code
    	-> UniqSet Int			-- ^ available stack slots
    	-> UniqSet VirtualReg		-- ^ the regs to spill
    	-> UniqSM
    		([LiveCmmTop instr]	-- code with SPILL and RELOAD meta instructions added.
    		, UniqSet Int		-- left over slots
    		, SpillStats )		-- stats about what happened during spilling

    regSpill code slotsFree regs

    	-- not enough slots to spill these regs
    	| sizeUniqSet slotsFree < sizeUniqSet regs
    	= pprPanic "regSpill: out of spill slots!"
    		(  text "   regs to spill = " <> ppr (sizeUniqSet regs)
    		$$ text "   slots left    = " <> ppr (sizeUniqSet slotsFree))

    	| otherwise
    	= do
    		-- allocate a slot for each of the spilled regs
    		let slots	= take (sizeUniqSet regs) $ uniqSetToList slotsFree
    		let regSlotMap	= listToUFM
    				$ zip (uniqSetToList regs) slots

    		-- grab the unique supply from the monad
    		us	<- getUs

    		-- run the spiller on all the blocks
    		let (code', state')	=
    			runState (mapM (regSpill_top regSlotMap) code)
    				 (initSpillS us)

    		return	( code'
    			, minusUniqSet slotsFree (mkUniqSet slots)
    			, makeSpillStats state')

    -- | Spill some registers to stack slots in a top-level thing.
    regSpill_top
    	:: Instruction instr
    	=> RegMap Int 			-- ^ map of vregs to slots they're being spilled to.
    	-> LiveCmmTop instr		-- ^ the top level thing.
    	-> SpillM (LiveCmmTop instr)

    regSpill_top regSlotMap cmm
     = case cmm of
    	CmmData{}
    	 -> return cmm

    	CmmProc info label params sccs
    	 |  LiveInfo static firstId mLiveVRegsOnEntry liveSlotsOnEntry <- info
    	 -> do
    		-- We should only passed Cmms with the liveness maps filled in,  but we'll
    		-- create empty ones if they're not there just in case.
    		let liveVRegsOnEntry	= fromMaybe emptyBlockEnv mLiveVRegsOnEntry

    		-- The liveVRegsOnEntry contains the set of vregs that are live on entry to
    		-- each basic block. If we spill one of those vregs we remove it from that
    		-- set and add the corresponding slot number to the liveSlotsOnEntry set.
    		-- The spill cleaner needs this information to erase unneeded spill and
    		-- reload instructions after we've done a successful allocation.
    		let liveSlotsOnEntry' :: Map BlockId (Set Int)
    		    liveSlotsOnEntry'
    			= foldBlockEnv patchLiveSlot liveSlotsOnEntry liveVRegsOnEntry

    		let info'
    			= LiveInfo static firstId
    				(Just liveVRegsOnEntry)
    				liveSlotsOnEntry'

    		-- Apply the spiller to all the basic blocks in the CmmProc.
    		sccs'		<- mapM (mapSCCM (regSpill_block regSlotMap)) sccs

    		return	$ CmmProc info' label params sccs'

     where	-- | Given a BlockId and the set of registers live in it,
    	--   if registers in this block are being spilled to stack slots,
    	--   then record the fact that these slots are now live in those blocks
    	--   in the given slotmap.
    	patchLiveSlot :: BlockId -> RegSet -> Map BlockId (Set Int) -> Map BlockId (Set Int)
    	patchLiveSlot blockId regsLive slotMap
    	 = let	curSlotsLive	= fromMaybe Set.empty
    				$ Map.lookup blockId slotMap

    		moreSlotsLive	= Set.fromList
    				$ catMaybes
    				$ map (lookupUFM regSlotMap)
    				$ uniqSetToList regsLive

    	  	slotMap'	= Map.insert blockId (Set.union curSlotsLive moreSlotsLive) slotMap

    	   in	slotMap'

    -- | Spill some registers to stack slots in a basic block.
    regSpill_block
    	:: Instruction instr
    	=> UniqFM Int		-- ^ map of vregs to slots they're being spilled to.
    	-> LiveBasicBlock instr
    	-> SpillM (LiveBasicBlock instr)

    regSpill_block regSlotMap (BasicBlock i instrs)
     = do	instrss'	<- mapM (regSpill_instr regSlotMap) instrs
     	return	$ BasicBlock i (concat instrss')

    -- | Spill some registers to stack slots in a single instruction.  If the instruction
    --   uses registers that need to be spilled, then it is prefixed (or postfixed) with
    --   the appropriate RELOAD or SPILL meta instructions.
    regSpill_instr
    	:: Instruction instr
    	=> UniqFM Int 		-- ^ map of vregs to slots they're being spilled to.
    	-> LiveInstr instr
    	-> SpillM [LiveInstr instr]

    regSpill_instr _ li@(LiveInstr _ Nothing)
     = do	return [li]

    regSpill_instr regSlotMap
    	(LiveInstr instr (Just _))
     = do
    	-- work out which regs are read and written in this instr
    	let RU rlRead rlWritten	= regUsageOfInstr instr

    	-- sometimes a register is listed as being read more than once,
    	--	nub this so we don't end up inserting two lots of spill code.
    	let rsRead_		= nub rlRead
    	let rsWritten_		= nub rlWritten

    	-- if a reg is modified, it appears in both lists, want to undo this..
    	let rsRead		= rsRead_    \\ rsWritten_
    	let rsWritten		= rsWritten_ \\ rsRead_
    	let rsModify		= intersect rsRead_ rsWritten_

    	-- work out if any of the regs being used are currently being spilled.
    	let rsSpillRead		= filter (\r -> elemUFM r regSlotMap) rsRead
    	let rsSpillWritten	= filter (\r -> elemUFM r regSlotMap) rsWritten
    	let rsSpillModify	= filter (\r -> elemUFM r regSlotMap) rsModify

    	-- rewrite the instr and work out spill code.
    	(instr1, prepost1)	<- mapAccumLM (spillRead   regSlotMap) instr  rsSpillRead
    	(instr2, prepost2)	<- mapAccumLM (spillWrite  regSlotMap) instr1 rsSpillWritten
    	(instr3, prepost3)	<- mapAccumLM (spillModify regSlotMap) instr2 rsSpillModify

    	let (mPrefixes, mPostfixes)	= unzip (prepost1 ++ prepost2 ++ prepost3)
    	let prefixes			= concat mPrefixes
    	let postfixes			= concat mPostfixes

    	-- final code
    	let instrs'	=  prefixes
    			++ [LiveInstr instr3 Nothing]
    			++ postfixes

    	return
    {-		$ pprTrace "* regSpill_instr spill"
    			(  text "instr  = " <> ppr instr
    			$$ text "read   = " <> ppr rsSpillRead
    			$$ text "write  = " <> ppr rsSpillWritten
    			$$ text "mod    = " <> ppr rsSpillModify
    			$$ text "-- out"
    			$$ (vcat $ map ppr instrs')
    			$$ text " ")
    -}
    		$ instrs'

    spillRead regSlotMap instr reg
    	| Just slot	<- lookupUFM regSlotMap reg
    	= do 	(instr', nReg)	<- patchInstr reg instr

    		modify $ \s -> s
    			{ stateSpillSL 	= addToUFM_C accSpillSL (stateSpillSL s) reg (reg, 0, 1) }

    	 	return	( instr'
    			, ( [LiveInstr (RELOAD slot nReg) Nothing]
    			  , []) )

    	| otherwise	= panic "RegSpill.spillRead: no slot defined for spilled reg"

    spillWrite regSlotMap instr reg
    	| Just slot	<- lookupUFM regSlotMap reg
    	= do 	(instr', nReg)	<- patchInstr reg instr

    		modify $ \s -> s
    			{ stateSpillSL 	= addToUFM_C accSpillSL (stateSpillSL s) reg (reg, 1, 0) }

    	 	return	( instr'
    			, ( []
    			  , [LiveInstr (SPILL nReg slot) Nothing]))

    	| otherwise	= panic "RegSpill.spillWrite: no slot defined for spilled reg"

    spillModify regSlotMap instr reg
    	| Just slot	<- lookupUFM regSlotMap reg
    	= do	(instr', nReg)	<- patchInstr reg instr

    		modify $ \s -> s
    			{ stateSpillSL 	= addToUFM_C accSpillSL (stateSpillSL s) reg (reg, 1, 1) }

    		return	( instr'
    			, ( [LiveInstr (RELOAD slot nReg) Nothing]
    			  , [LiveInstr (SPILL nReg slot) Nothing]))

    	| otherwise	= panic "RegSpill.spillModify: no slot defined for spilled reg"

    -- | Rewrite uses of this virtual reg in an instr to use a different virtual reg
    patchInstr
    	:: Instruction instr
    	=> Reg -> instr -> SpillM (instr, Reg)

    patchInstr reg instr
     = do	nUnique		<- newUnique
     	let nReg	= case reg of
    				RegVirtual vr 	-> RegVirtual (renameVirtualReg nUnique vr)
    				RegReal{}	-> panic "RegAlloc.Graph.Spill.patchIntr: not patching real reg"
    	let instr'	= patchReg1 reg nReg instr
    	return		(instr', nReg)

    patchReg1
    	:: Instruction instr
    	=> Reg -> Reg -> instr -> instr

    patchReg1 old new instr
     = let	patchF r
    		| r == old	= new
    		| otherwise	= r
       in	patchRegsOfInstr instr patchF

    -- Spiller monad --------------------------------------------------------------
    data SpillS
    	= SpillS
    	{ -- | unique supply for generating fresh vregs.
    	  stateUS	:: UniqSupply

    	  -- | spilled vreg vs the number of times it was loaded, stored
    	, stateSpillSL	:: UniqFM (Reg, Int, Int) }

    initSpillS uniqueSupply
    	= SpillS
    	{ stateUS	= uniqueSupply
    	, stateSpillSL	= emptyUFM }

    type SpillM a	= State SpillS a

    newUnique :: SpillM Unique
    newUnique
     = do	us	<- gets stateUS
     	case splitUniqSupply us of
    	 (us1, us2)
    	  -> do let uniq = uniqFromSupply us1
    	  	modify $ \s -> s { stateUS = us2 }
    		return uniq

    accSpillSL (r1, s1, l1) (_, s2, l2)
    	= (r1, s1 + s2, l1 + l2)

    -- Spiller stats --------------------------------------------------------------
    data SpillStats
    	= SpillStats
    	{ spillStoreLoad	:: UniqFM (Reg, Int, Int) }

    makeSpillStats :: SpillS -> SpillStats
    makeSpillStats s
    	= SpillStats
    	{ spillStoreLoad	= stateSpillSL s }

    instance Outputable SpillStats where
     ppr stats
     	= (vcat $ map (\(r, s, l) -> ppr r <+> int s <+> int l)
    			$ eltsUFM (spillStoreLoad stats))