/compiler/nativeGen/RegAlloc/Graph/Coalesce.hs
Haskell | 99 lines | 58 code | 21 blank | 20 comment | 1 complexity | edcd050e27bd85410cf7bdac452c5c8f MD5 | raw file
- -- | Register coalescing.
- module RegAlloc.Graph.Coalesce (
- regCoalesce,
- slurpJoinMovs
- ) where
- import RegAlloc.Liveness
- import Instruction
- import Reg
- import Cmm
- import Bag
- import Digraph
- import UniqFM
- import UniqSet
- import UniqSupply
- import Data.List
- -- | Do register coalescing on this top level thing
- --
- -- For Reg -> Reg moves, if the first reg dies at the same time the
- -- second reg is born then the mov only serves to join live ranges.
- -- The two regs can be renamed to be the same and the move instruction
- -- safely erased.
- regCoalesce
- :: Instruction instr
- => [LiveCmmDecl statics instr]
- -> UniqSM [LiveCmmDecl statics instr]
- regCoalesce code
- = do
- let joins = foldl' unionBags emptyBag
- $ map slurpJoinMovs code
- let alloc = foldl' buildAlloc emptyUFM
- $ bagToList joins
- let patched = map (patchEraseLive (sinkReg alloc)) code
-
- return patched
- -- | Add a v1 = v2 register renaming to the map.
- -- The register with the lowest lexical name is set as the
- -- canonical version.
- buildAlloc :: UniqFM Reg -> (Reg, Reg) -> UniqFM Reg
- buildAlloc fm (r1, r2)
- = let rmin = min r1 r2
- rmax = max r1 r2
- in addToUFM fm rmax rmin
- -- | Determine the canonical name for a register by following
- -- v1 = v2 renamings in this map.
- sinkReg :: UniqFM Reg -> Reg -> Reg
- sinkReg fm r
- = case lookupUFM fm r of
- Nothing -> r
- Just r' -> sinkReg fm r'
-
- -- | Slurp out mov instructions that only serve to join live ranges.
- --
- -- During a mov, if the source reg dies and the destiation reg is
- -- born then we can rename the two regs to the same thing and
- -- eliminate the move.
- slurpJoinMovs
- :: Instruction instr
- => LiveCmmDecl statics instr
- -> Bag (Reg, Reg)
- slurpJoinMovs live
- = slurpCmm emptyBag live
- where
- slurpCmm rs CmmData{}
- = rs
- slurpCmm rs (CmmProc _ _ _ sccs)
- = foldl' slurpBlock rs (flattenSCCs sccs)
- slurpBlock rs (BasicBlock _ instrs)
- = foldl' slurpLI rs instrs
-
- slurpLI rs (LiveInstr _ Nothing) = rs
- slurpLI rs (LiveInstr instr (Just live))
- | Just (r1, r2) <- takeRegRegMoveInstr instr
- , elementOfUniqSet r1 $ liveDieRead live
- , elementOfUniqSet r2 $ liveBorn live
- -- only coalesce movs between two virtuals for now,
- -- else we end up with allocatable regs in the live
- -- regs list..
- , isVirtualReg r1 && isVirtualReg r2
- = consBag (r1, r2) rs
-
- | otherwise
- = rs
-