+ add new old =
+ let join = interAvail new old in
+ if join `smallerAvail` old then aTx join else noTx join
+
+
+interAvail :: AvailRegs -> AvailRegs -> AvailRegs
+interAvail (UniverseMinus s) (UniverseMinus s') = UniverseMinus (s `plusRegSet` s')
+interAvail (AvailRegs s) (AvailRegs s') = AvailRegs (s `timesRegSet` s')
+interAvail (AvailRegs s) (UniverseMinus s') = AvailRegs (s `minusRegSet` s')
+interAvail (UniverseMinus s) (AvailRegs s') = AvailRegs (s' `minusRegSet` s )
+
+smallerAvail :: AvailRegs -> AvailRegs -> Bool
+smallerAvail (AvailRegs _) (UniverseMinus _) = True
+smallerAvail (UniverseMinus _) (AvailRegs _) = False
+smallerAvail (AvailRegs s) (AvailRegs s') = sizeUniqSet s < sizeUniqSet s'
+smallerAvail (UniverseMinus s) (UniverseMinus s') = sizeUniqSet s > sizeUniqSet s'
+
+extendAvail :: AvailRegs -> LocalReg -> AvailRegs
+extendAvail (UniverseMinus s) r = UniverseMinus (deleteFromRegSet s r)
+extendAvail (AvailRegs s) r = AvailRegs (extendRegSet s r)
+
+deleteFromAvail :: AvailRegs -> LocalReg -> AvailRegs
+deleteFromAvail (UniverseMinus s) r = UniverseMinus (extendRegSet s r)
+deleteFromAvail (AvailRegs s) r = AvailRegs (deleteFromRegSet s r)
+
+cmmAvailableReloads :: LGraph M Last -> BlockEnv AvailRegs
+cmmAvailableReloads g = env
+ where env = runDFA availRegsLattice $
+ do run_f_anal transfer (fact_bot availRegsLattice) g
+ allFacts
+ transfer :: FAnalysis M Last AvailRegs
+ transfer = FComp "available-reloads analysis" first middle last exit
+ exit _ = LastOutFacts []
+ first avail _ = avail
+ middle = flip middleAvail
+ last = lastAvail
+
+
+-- | The transfer equations use the traditional 'gen' and 'kill'
+-- notations, which should be familiar from the dragon book.
+agen, akill :: UserOfLocalRegs a => a -> AvailRegs -> AvailRegs
+agen a live = foldRegsUsed extendAvail live a
+akill a live = foldRegsUsed deleteFromAvail live a
+
+middleAvail :: M -> AvailRegs -> AvailRegs
+middleAvail (Spill _) = id
+middleAvail (Reload regs) = agen regs
+middleAvail (NotSpillOrReload m) = middle m
+ where middle (MidNop) = id
+ middle (MidComment {}) = id
+ middle (MidAssign lhs _expr) = akill lhs
+ middle (MidStore {}) = id
+ middle (MidUnsafeCall _tgt ress _args) = akill ress
+ middle (CopyIn _ formals _) = akill formals
+ middle (CopyOut {}) = id
+
+lastAvail :: AvailRegs -> Last -> LastOutFacts AvailRegs
+lastAvail avail l = LastOutFacts $ map (\id -> (id, avail)) $ succs l