/compiler/cmm/CmmCommonBlockElim.hs
Haskell | 175 lines | 125 code | 24 blank | 26 comment | 22 complexity | 94c488dd60ef25f4cbf0b6096eaba769 MD5 | raw file
Possible License(s): BSD-3-Clause, BSD-2-Clause, LGPL-3.0
- {-# LANGUAGE GADTs #-}
- -- ToDo: remove -fno-warn-warnings-deprecations
- {-# OPTIONS_GHC -fno-warn-warnings-deprecations #-}
- -- ToDo: remove -fno-warn-incomplete-patterns
- {-# OPTIONS_GHC -fno-warn-incomplete-patterns #-}
- module CmmCommonBlockElim
- ( elimCommonBlocks
- )
- where
- import BlockId
- import Cmm
- import CmmUtils
- import Prelude hiding (iterate, succ, unzip, zip)
- import Compiler.Hoopl
- import Data.Bits
- import qualified Data.List as List
- import Data.Word
- import FastString
- import Control.Monad
- import Outputable
- import UniqFM
- import Unique
- my_trace :: String -> SDoc -> a -> a
- my_trace = if False then pprTrace else \_ _ a -> a
- -- Eliminate common blocks:
- -- If two blocks are identical except for the label on the first node,
- -- then we can eliminate one of the blocks. To ensure that the semantics
- -- of the program are preserved, we have to rewrite each predecessor of the
- -- eliminated block to proceed with the block we keep.
- -- The algorithm iterates over the blocks in the graph,
- -- checking whether it has seen another block that is equal modulo labels.
- -- If so, then it adds an entry in a map indicating that the new block
- -- is made redundant by the old block.
- -- Otherwise, it is added to the useful blocks.
- -- TODO: Use optimization fuel
- elimCommonBlocks :: CmmGraph -> CmmGraph
- elimCommonBlocks g =
- upd_graph g . snd $ iterate common_block reset hashed_blocks
- (emptyUFM, mapEmpty)
- where hashed_blocks = map (\b -> (hash_block b, b)) (reverse (postorderDfs g))
- reset (_, subst) = (emptyUFM, subst)
- -- Iterate over the blocks until convergence
- iterate :: (t -> a -> (Bool, t)) -> (t -> t) -> [a] -> t -> t
- iterate upd reset blocks state =
- case foldl upd' (False, state) blocks of
- (True, state') -> iterate upd reset blocks (reset state')
- (False, state') -> state'
- where upd' (b, s) a = let (b', s') = upd s a in (b || b', s') -- lift to track changes
- -- Try to find a block that is equal (or ``common'') to b.
- type BidMap = BlockEnv BlockId
- type State = (UniqFM [CmmBlock], BidMap)
- common_block :: (Outputable h, Uniquable h) => State -> (h, CmmBlock) -> (Bool, State)
- common_block (bmap, subst) (hash, b) =
- case lookupUFM bmap hash of
- Just bs -> case (List.find (eqBlockBodyWith (eqBid subst) b) bs,
- mapLookup bid subst) of
- (Just b', Nothing) -> addSubst b'
- (Just b', Just b'') | entryLabel b' /= b'' -> addSubst b'
- _ -> (False, (addToUFM bmap hash (b : bs), subst))
- Nothing -> (False, (addToUFM bmap hash [b], subst))
- where bid = entryLabel b
- addSubst b' = my_trace "found new common block" (ppr (entryLabel b')) $
- (True, (bmap, mapInsert bid (entryLabel b') subst))
- -- Given the map ``subst'' from BlockId -> BlockId, we rewrite the graph.
- upd_graph :: CmmGraph -> BidMap -> CmmGraph
- upd_graph g subst = mapGraphNodes (id, middle, last) g
- where middle = mapExpDeep exp
- last l = last' (mapExpDeep exp l)
- last' :: CmmNode O C -> CmmNode O C
- last' (CmmBranch bid) = CmmBranch $ sub bid
- last' (CmmCondBranch p t f) = cond p (sub t) (sub f)
- last' (CmmCall t (Just bid) a r o) = CmmCall t (Just $ sub bid) a r o
- last' l@(CmmCall _ Nothing _ _ _) = l
- last' (CmmForeignCall t r a bid u i) = CmmForeignCall t r a (sub bid) u i
- last' (CmmSwitch e bs) = CmmSwitch e $ map (liftM sub) bs
- cond p t f = if t == f then CmmBranch t else CmmCondBranch p t f
- exp (CmmStackSlot (CallArea (Young id)) off) =
- CmmStackSlot (CallArea (Young (sub id))) off
- exp (CmmLit (CmmBlock id)) = CmmLit (CmmBlock (sub id))
- exp e = e
- sub = lookupBid subst
- -- To speed up comparisons, we hash each basic block modulo labels.
- -- The hashing is a bit arbitrary (the numbers are completely arbitrary),
- -- but it should be fast and good enough.
- hash_block :: CmmBlock -> Int
- hash_block block =
- fromIntegral (foldBlockNodesB3 (hash_fst, hash_mid, hash_lst) block (0 :: Word32) .&. (0x7fffffff :: Word32))
- -- UniqFM doesn't like negative Ints
- where hash_fst _ h = h
- hash_mid m h = hash_node m + h `shiftL` 1
- hash_lst m h = hash_node m + h `shiftL` 1
- hash_node :: CmmNode O x -> Word32
- hash_node (CmmComment (FastString u _ _ _ _)) = cvt u
- hash_node (CmmAssign r e) = hash_reg r + hash_e e
- hash_node (CmmStore e e') = hash_e e + hash_e e'
- hash_node (CmmUnsafeForeignCall t _ as) = hash_tgt t + hash_list hash_e as
- hash_node (CmmBranch _) = 23 -- would be great to hash these properly
- hash_node (CmmCondBranch p _ _) = hash_e p
- hash_node (CmmCall e _ _ _ _) = hash_e e
- hash_node (CmmForeignCall t _ _ _ _ _) = hash_tgt t
- hash_node (CmmSwitch e _) = hash_e e
- hash_reg :: CmmReg -> Word32
- hash_reg (CmmLocal _) = 117
- hash_reg (CmmGlobal _) = 19
- hash_e :: CmmExpr -> Word32
- hash_e (CmmLit l) = hash_lit l
- hash_e (CmmLoad e _) = 67 + hash_e e
- hash_e (CmmReg r) = hash_reg r
- hash_e (CmmMachOp _ es) = hash_list hash_e es -- pessimal - no operator check
- hash_e (CmmRegOff r i) = hash_reg r + cvt i
- hash_e (CmmStackSlot _ _) = 13
- hash_lit :: CmmLit -> Word32
- hash_lit (CmmInt i _) = fromInteger i
- hash_lit (CmmFloat r _) = truncate r
- hash_lit (CmmLabel _) = 119 -- ugh
- hash_lit (CmmLabelOff _ i) = cvt $ 199 + i
- hash_lit (CmmLabelDiffOff _ _ i) = cvt $ 299 + i
- hash_lit (CmmBlock _) = 191 -- ugh
- hash_lit (CmmHighStackMark) = cvt 313
- hash_tgt (ForeignTarget e _) = hash_e e
- hash_tgt (PrimTarget _) = 31 -- lots of these
- hash_list f = foldl (\z x -> f x + z) (0::Word32)
- cvt = fromInteger . toInteger
- -- Utilities: equality and substitution on the graph.
- -- Given a map ``subst'' from BlockID -> BlockID, we define equality.
- eqBid :: BidMap -> BlockId -> BlockId -> Bool
- eqBid subst bid bid' = lookupBid subst bid == lookupBid subst bid'
- lookupBid :: BidMap -> BlockId -> BlockId
- lookupBid subst bid = case mapLookup bid subst of
- Just bid -> lookupBid subst bid
- Nothing -> bid
- -- Equality on the body of a block, modulo a function mapping block IDs to block IDs.
- eqBlockBodyWith :: (BlockId -> BlockId -> Bool) -> CmmBlock -> CmmBlock -> Bool
- eqBlockBodyWith eqBid block block' = middles == middles' && eqLastWith eqBid last last'
- where (_, middles , JustC last :: MaybeC C (CmmNode O C)) = blockToNodeList block
- (_, middles', JustC last' :: MaybeC C (CmmNode O C)) = blockToNodeList block'
- eqLastWith :: (BlockId -> BlockId -> Bool) -> CmmNode O C -> CmmNode O C -> Bool
- eqLastWith eqBid (CmmBranch bid1) (CmmBranch bid2) = eqBid bid1 bid2
- eqLastWith eqBid (CmmCondBranch c1 t1 f1) (CmmCondBranch c2 t2 f2) =
- c1 == c2 && eqBid t1 t2 && eqBid f1 f2
- eqLastWith eqBid (CmmCall t1 c1 a1 r1 u1) (CmmCall t2 c2 a2 r2 u2) =
- t1 == t2 && eqMaybeWith eqBid c1 c2 && a1 == a2 && r1 == r2 && u1 == u2
- eqLastWith eqBid (CmmSwitch e1 bs1) (CmmSwitch e2 bs2) =
- e1 == e2 && eqListWith (eqMaybeWith eqBid) bs1 bs2
- eqLastWith _ _ _ = False
- eqListWith :: (a -> b -> Bool) -> [a] -> [b] -> Bool
- eqListWith eltEq es es' = all (uncurry eltEq) (List.zip es es')
- eqMaybeWith :: (a -> b -> Bool) -> Maybe a -> Maybe b -> Bool
- eqMaybeWith eltEq (Just e) (Just e') = eltEq e e'
- eqMaybeWith _ Nothing Nothing = True
- eqMaybeWith _ _ _ = False