1 -- | Graph coloring register allocator.
4 -- Live range splitting:
5 -- At the moment regs that are spilled are spilled for all time, even though
6 -- we might be able to allocate them a hardreg in different parts of the code.
8 -- As we're aggressively coalescing before register allocation proper we're not currently
9 -- using the coalescence information present in the graph.
11 -- The function that choosing the potential spills could be a bit cleverer.
13 -- Colors in graphviz graphs could be nicer.
16 module RegAllocColor (
23 import qualified GraphColor as Color
42 -- | The maximum number of build/spill cycles we'll allow.
43 -- We should only need 3 or 4 cycles tops.
44 -- If we run for any longer than this we're probably in an infinite loop,
45 -- It's probably better just to bail out and report a bug at this stage.
50 -- | The top level of the graph coloring register allocator.
53 :: UniqFM (UniqSet Reg) -- ^ the registers we can use for allocation
54 -> UniqSet Int -- ^ the set of available spill slots.
55 -> [LiveCmmTop] -- ^ code annotated with liveness information.
57 ( [NatCmmTop] -- ^ code with registers allocated.
58 , [RegAllocStats] ) -- ^ stats for each stage of allocation
60 regAlloc regsFree slotsFree code
62 (code_final, debug_codeGraphs, graph_final)
63 <- regAlloc_spin 0 trivColorable regsFree slotsFree [] code
68 regAlloc_spin (spinCount :: Int) triv regsFree slotsFree debug_codeGraphs code
70 -- check that we're not running off down the garden path.
71 when (spinCount > maxSpinCount)
72 $ pprPanic "regAlloc_spin: max build/spill cycle count exceeded."
73 ( text "It looks like the register allocator is stuck in an infinite loop."
74 $$ text "max cycles = " <> int maxSpinCount
75 $$ text "regsFree = " <> (hcat $ punctuate space $ map (docToSDoc . pprUserReg)
76 $ uniqSetToList $ unionManyUniqSets $ eltsUFM regsFree)
77 $$ text "slotsFree = " <> ppr (sizeUniqSet slotsFree))
79 -- build a conflict graph from the code.
80 graph <- buildGraph code
82 -- build a map of how many instructions each reg lives for
83 -- this lazy, it won't be computed unless we need to spill
84 let fmLife = plusUFMs_C (\(r1, l1) (r2, l2) -> (r1, l1 + l2))
85 $ map lifetimeCount code
87 -- the function to choose regs to leave uncolored
88 let spill = chooseSpill_maxLife fmLife
90 -- try and color the graph
91 let (graph_colored, rsSpill)
92 = Color.colorGraph regsFree triv spill graph
94 -- see if we've found a coloring
95 if isEmptyUniqSet rsSpill
97 -- patch the registers using the info in the graph
98 let code_patched = map (patchRegsFromGraph graph_colored) code
99 let code_nat = map stripLive code_patched
101 -- record what happened in this stage for debugging
105 , raGraph = graph_colored
106 , raPatchedCmm = code_patched }
109 , debug_codeGraphs ++ [stat]
113 -- spill the uncolored regs
114 (code_spilled, slotsFree', spillStats)
115 <- regSpill code slotsFree rsSpill
117 -- recalculate liveness
118 let code_nat = map stripLive code_spilled
119 code_relive <- mapM regLiveness code_nat
121 -- record what happened in this stage for debugging
124 { raLiveCmm = code_spilled
125 , raGraph = graph_colored
126 , raSpillStats = spillStats }
129 regAlloc_spin (spinCount + 1) triv regsFree slotsFree'
130 (debug_codeGraphs ++ [stat])
135 -- Simple maxconflicts isn't always good, because we
136 -- can naievely end up spilling vregs that only live for one or two instrs.
139 chooseSpill_maxConflicts
140 :: Color.Graph Reg RegClass Reg
143 chooseSpill_maxConflicts graph
144 = let node = maximumBy
146 (sizeUniqSet $ Color.nodeConflicts n1)
147 (sizeUniqSet $ Color.nodeConflicts n2))
148 $ eltsUFM $ Color.graphMap graph
156 -> Color.Graph Reg RegClass Reg
159 chooseSpill_maxLife life graph
160 = let node = maximumBy (\n1 n2 -> compare (getLife n1) (getLife n2))
161 $ eltsUFM $ Color.graphMap graph
163 -- Orphan vregs die in the same instruction they are born in.
164 -- They will be in the graph, but not in the liveness map.
165 -- Their liveness is 0.
167 = case lookupUFM life (Color.nodeId n) of
174 -- | Build a graph from the liveness and coalesce information in this code.
178 -> UniqSM (Color.Graph Reg RegClass Reg)
182 -- Add the reg-reg conflicts to the graph
183 let conflictSets = unionManyBags (map slurpConflicts code)
184 let graph_conflict = foldrBag graphAddConflictSet Color.initGraph conflictSets
187 -- Add the coalescences edges to the graph.
188 let coalesce = unionManyBags (map slurpJoinMovs code)
189 let graph_coalesce = foldrBag graphAddCoalesce graph_conflict coalesce
191 return $ graph_coalesce
194 -- | Add some conflict edges to the graph.
195 -- Conflicts between virtual and real regs are recorded as exlusions.
199 -> Color.Graph Reg RegClass Reg
200 -> Color.Graph Reg RegClass Reg
202 graphAddConflictSet set graph
203 = let reals = filterUFM isRealReg set
204 virtuals = filterUFM (not . isRealReg) set
206 graph1 = Color.addConflicts virtuals regClass graph
207 graph2 = foldr (\(r1, r2) -> Color.addExclusion r1 regClass r2)
210 | a <- uniqSetToList virtuals
211 , b <- uniqSetToList reals]
216 -- | Add some coalesences edges to the graph
217 -- Coalesences between virtual and real regs are recorded as preferences.
221 -> Color.Graph Reg RegClass Reg
222 -> Color.Graph Reg RegClass Reg
224 graphAddCoalesce (r1, r2) graph
225 | RealReg regno <- r1
226 = Color.addPreference (regWithClass r2) r1 graph
228 | RealReg regno <- r2
229 = Color.addPreference (regWithClass r1) r2 graph
232 = Color.addCoalesce (regWithClass r1) (regWithClass r2) graph
234 where regWithClass r = (r, regClass r)
237 -- | Patch registers in code using the reg -> reg mapping in this graph.
239 :: Color.Graph Reg RegClass Reg
240 -> LiveCmmTop -> LiveCmmTop
242 patchRegsFromGraph graph code
244 -- a function to lookup the hardreg for a virtual reg from the graph.
246 -- leave real regs alone.
250 -- this virtual has a regular node in the graph.
251 | Just node <- Color.lookupNode graph reg
252 = case Color.nodeColor node of
256 -- no node in the graph for this virtual, bad news.
258 = pprPanic "patchRegsFromGraph: register mapping failed."
259 ( text "There is no node in the graph for register " <> ppr reg
261 $$ Color.dotGraph (\x -> text "white") trivColorable graph)
263 in patchEraseLive patchF code
266 plusUFMs_C :: (elt -> elt -> elt) -> [UniqFM elt] -> UniqFM elt
268 = foldl (plusUFM_C f) emptyUFM maps