14 lifeMapFromSpillCostInfo
31 import Data.List (nub, minimumBy)
36 = ( Reg -- register name
37 , Int -- number of writes to this reg
38 , Int -- number of reads from this reg
39 , Int) -- number of instrs this reg was live on entry to
42 = UniqFM SpillCostRecord
45 zeroSpillCostInfo :: SpillCostInfo
46 zeroSpillCostInfo = emptyUFM
48 -- | Add two spillCostInfos
49 plusSpillCostInfo :: SpillCostInfo -> SpillCostInfo -> SpillCostInfo
50 plusSpillCostInfo sc1 sc2
51 = plusUFM_C plusSpillCostRecord sc1 sc2
53 plusSpillCostRecord :: SpillCostRecord -> SpillCostRecord -> SpillCostRecord
54 plusSpillCostRecord (r1, a1, b1, c1) (r2, a2, b2, c2)
55 | r1 == r2 = (r1, a1 + a2, b1 + b2, c1 + c2)
56 | otherwise = error "RegSpillCost.plusRegInt: regs don't match"
59 -- | Slurp out information used for determining spill costs
60 -- for each vreg, the number of times it was written to, read from,
61 -- and the number of instructions it was live on entry to (lifetime)
67 slurpSpillCostInfo cmm
68 = execState (countCmm cmm) zeroSpillCostInfo
70 countCmm CmmData{} = return ()
71 countCmm (CmmProc info _ _ (ListGraph blocks))
72 = mapM_ (countComp info) blocks
74 countComp info (BasicBlock _ blocks)
75 = mapM_ (countBlock info) blocks
77 -- lookup the regs that are live on entry to this block in
78 -- the info table from the CmmProc
79 countBlock info (BasicBlock blockId instrs)
80 | LiveInfo _ _ blockLive <- info
81 , Just rsLiveEntry <- lookupUFM blockLive blockId
82 = countLIs rsLiveEntry instrs
85 = error "RegLiveness.slurpSpillCostInfo: bad block"
90 -- skip over comment and delta pseudo instrs
91 countLIs rsLive (Instr instr Nothing : lis)
99 = pprPanic "RegSpillCost.slurpSpillCostInfo"
100 (text "no liveness information on instruction " <> ppr instr)
102 countLIs rsLiveEntry (Instr instr (Just live) : lis)
104 -- increment the lifetime counts for regs live on entry to this instr
105 mapM_ incLifetime $ uniqSetToList rsLiveEntry
107 -- increment counts for what regs were read/written from
108 let (RU read written) = regUsage instr
109 mapM_ incUses $ filter (not . isRealReg) $ nub read
110 mapM_ incDefs $ filter (not . isRealReg) $ nub written
112 -- compute liveness for entry to next instruction.
114 = rsLiveEntry `minusUniqSet` (liveDieRead live)
117 = (rsLiveAcross `unionUniqSets` (liveBorn live))
118 `minusUniqSet` (liveDieWrite live)
120 countLIs rsLiveNext lis
122 incDefs reg = modify $ \s -> addToUFM_C plusSpillCostRecord s reg (reg, 1, 0, 0)
123 incUses reg = modify $ \s -> addToUFM_C plusSpillCostRecord s reg (reg, 0, 1, 0)
124 incLifetime reg = modify $ \s -> addToUFM_C plusSpillCostRecord s reg (reg, 0, 0, 1)
127 -- | Choose a node to spill from this graph
131 -> Graph Reg RegClass Reg
134 chooseSpill info graph
135 = let cost = spillCost_length info graph
136 node = minimumBy (\n1 n2 -> compare (cost $ nodeId n1) (cost $ nodeId n2))
137 $ eltsUFM $ graphMap graph
143 -- | Chaitins spill cost function is:
145 -- cost = sum loadCost * freq (u) + sum storeCost * freq (d)
146 -- u <- uses (v) d <- defs (v)
148 -- There are no loops in our code at the momemnt, so we can set the freq's to 1
149 -- We divide this by the degree if t
152 -- If we don't have live range splitting then Chaitins function performs badly if we have
153 -- lots of nested live ranges and very few registers.
166 -- defs uses degree cost
171 -- v3 has the lowest cost, but if we only have 2 hardregs and we insert spill code for v3
172 -- then this isn't going to improve the colorability of the graph.
174 -- When compiling SHA1, which as very long basic blocks and some vregs with very long live ranges
175 -- the allocator seems to try and spill from the inside out and eventually run out of stack slots.
177 -- Without live range splitting, its's better to spill from the outside in so set the cost of very
178 -- long live ranges to zero
183 -> Graph Reg RegClass Reg
187 spillCost_chaitin info graph reg
188 -- Spilling a live range that only lives for 1 instruction isn't going to help
189 -- us at all - and we definately want to avoid trying to re-spill previously
190 -- inserted spill code.
191 | lifetime <= 1 = 1/0
193 -- It's unlikely that we'll find a reg for a live range this long
194 -- better to spill it straight up and not risk trying to keep it around
195 -- and have to go through the build/color cycle again.
196 | lifetime > allocatableRegsInClass (regClass reg) * 10
199 -- otherwise revert to chaitin's regular cost function.
200 | otherwise = fromIntegral (uses + defs) / fromIntegral (nodeDegree graph reg)
201 where (_, defs, uses, lifetime)
202 = fromMaybe (reg, 0, 0, 0) $ lookupUFM info reg
205 -- Just spill the longest live range.
208 -> Graph Reg RegClass Reg
212 spillCost_length info _ reg
213 | lifetime <= 1 = 1/0
214 | otherwise = 1 / fromIntegral lifetime
215 where (_, _, _, lifetime)
216 = fromMaybe (reg, 0, 0, 0) $ lookupUFM info reg
220 lifeMapFromSpillCostInfo :: SpillCostInfo -> UniqFM (Reg, Int)
221 lifeMapFromSpillCostInfo info
223 $ map (\(r, _, _, life) -> (r, (r, life)))
227 -- | Work out the degree (number of neighbors) of this node which have the same class.
228 nodeDegree :: Graph Reg RegClass Reg -> Reg -> Int
230 | Just node <- lookupUFM (graphMap graph) reg
231 , virtConflicts <- length $ filter (\r -> regClass r == regClass reg)
232 $ uniqSetToList $ nodeConflicts node
233 = virtConflicts + sizeUniqSet (nodeExclusions node)
239 -- | Show a spill cost record, including the degree from the graph and final calulated spill cos
240 pprSpillCostRecord :: Graph Reg RegClass Reg -> SpillCostRecord -> SDoc
241 pprSpillCostRecord graph (reg, uses, defs, life)
247 , ppr $ nodeDegree graph reg
248 , text $ show $ (fromIntegral (uses + defs) / fromIntegral (nodeDegree graph reg) :: Float) ]