{-# LANGUAGE GADTs, BangPatterns, ScopedTypeVariables #-}
module CmmCommonBlockElim
( elimCommonBlocks
)
where
import GhcPrelude hiding (iterate, succ, unzip, zip)
import BlockId
import Cmm
import CmmUtils
import CmmSwitch (eqSwitchTargetWith)
import CmmContFlowOpt
-- import PprCmm ()
import Hoopl.Block
import Hoopl.Graph
import Hoopl.Label
import Hoopl.Collections
import Data.Bits
import Data.Maybe (mapMaybe)
import qualified Data.List as List
import Data.Word
import qualified Data.Map as M
import Outputable
import qualified TrieMap as TM
import UniqFM
import Unique
import Control.Arrow (first, second)
-- -----------------------------------------------------------------------------
-- 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.
-- To avoid comparing every block with every other block repeatedly, we group
-- them by
-- * a hash of the block, ignoring labels (explained below)
-- * the list of outgoing labels
-- The hash is invariant under relabeling, so we only ever compare within
-- the same group of blocks.
--
-- The list of outgoing labels is updated as we merge blocks (that is why they
-- are not included in the hash, which we want to calculate only once).
--
-- All in all, two blocks should never be compared if they have different
-- hashes, and at most once otherwise. Previously, we were slower, and people
-- rightfully complained: #10397
-- TODO: Use optimization fuel
elimCommonBlocks :: CmmGraph -> CmmGraph
elimCommonBlocks g = replaceLabels env $ copyTicks env g
where
env = iterate mapEmpty blocks_with_key
-- The order of blocks doesn't matter here. While we could use
-- revPostorder which drops unreachable blocks this is done in
-- ContFlowOpt already which runs before this pass. So we use
-- toBlockList since it is faster.
groups = groupByInt hash_block (toBlockList g) :: [[CmmBlock]]
blocks_with_key = [ [ (successors b, [b]) | b <- bs] | bs <- groups]
-- Invariant: The blocks in the list are pairwise distinct
-- (so avoid comparing them again)
type DistinctBlocks = [CmmBlock]
type Key = [Label]
type Subst = LabelMap BlockId
-- The outer list groups by hash. We retain this grouping throughout.
iterate :: Subst -> [[(Key, DistinctBlocks)]] -> Subst
iterate subst blocks
| mapNull new_substs = subst
| otherwise = iterate subst' updated_blocks
where
grouped_blocks :: [[(Key, [DistinctBlocks])]]
grouped_blocks = map groupByLabel blocks
merged_blocks :: [[(Key, DistinctBlocks)]]
(new_substs, merged_blocks) = List.mapAccumL (List.mapAccumL go) mapEmpty grouped_blocks
where
go !new_subst1 (k,dbs) = (new_subst1 `mapUnion` new_subst2, (k,db))
where
(new_subst2, db) = mergeBlockList subst dbs
subst' = subst `mapUnion` new_substs
updated_blocks = map (map (first (map (lookupBid subst')))) merged_blocks
-- Combine two lists of blocks.
-- While they are internally distinct they can still share common blocks.
mergeBlocks :: Subst -> DistinctBlocks -> DistinctBlocks -> (Subst, DistinctBlocks)
mergeBlocks subst existing new = go new
where
go [] = (mapEmpty, existing)
go (b:bs) = case List.find (eqBlockBodyWith (eqBid subst) b) existing of
-- This block is a duplicate. Drop it, and add it to the substitution
Just b' -> first (mapInsert (entryLabel b) (entryLabel b')) $ go bs
-- This block is not a duplicate, keep it.
Nothing -> second (b:) $ go bs
mergeBlockList :: Subst -> [DistinctBlocks] -> (Subst, DistinctBlocks)
mergeBlockList _ [] = pprPanic "mergeBlockList" empty
mergeBlockList subst (b:bs) = go mapEmpty b bs
where
go !new_subst1 b [] = (new_subst1, b)
go !new_subst1 b1 (b2:bs) = go new_subst b bs
where
(new_subst2, b) = mergeBlocks subst b1 b2
new_subst = new_subst1 `mapUnion` new_subst2
-- -----------------------------------------------------------------------------
-- Hashing and equality on blocks
-- Below here is mostly boilerplate: hashing blocks ignoring labels,
-- and comparing blocks modulo a label mapping.
-- To speed up comparisons, we hash each basic block modulo jump labels.
-- The hashing is a bit arbitrary (the numbers are completely arbitrary),
-- but it should be fast and good enough.
-- We want to get as many small buckets as possible, as comparing blocks is
-- expensive. So include as much as possible in the hash. Ideally everything
-- that is compared with (==) in eqBlockBodyWith.
type HashCode = Int
hash_block :: CmmBlock -> HashCode
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 n | dont_care n = 0 -- don't care
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 -- NB. ignore the label
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_node _ = error "hash_node: unknown Cmm node!"
hash_reg :: CmmReg -> Word32
hash_reg (CmmLocal localReg) = hash_unique localReg -- important for performance, see #10397
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 (CmmVec ls) = hash_list hash_lit ls
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
hash_unique :: Uniquable a => a -> Word32
hash_unique = cvt . getKey . getUnique
-- | Ignore these node types for equality
dont_care :: CmmNode O x -> Bool
dont_care CmmComment {} = True
dont_care CmmTick {} = True
dont_care CmmUnwind {} = True
dont_care _other = False
-- Utilities: equality and substitution on the graph.
-- Given a map ``subst'' from BlockID -> BlockID, we define equality.
eqBid :: LabelMap BlockId -> BlockId -> BlockId -> Bool
eqBid subst bid bid' = lookupBid subst bid == lookupBid subst bid'
lookupBid :: LabelMap BlockId -> BlockId -> BlockId
lookupBid subst bid = case mapLookup bid subst of
Just bid -> lookupBid subst bid
Nothing -> bid
-- Middle nodes and expressions can contain BlockIds, in particular in
-- CmmStackSlot and CmmBlock, so we have to use a special equality for
-- these.
--
eqMiddleWith :: (BlockId -> BlockId -> Bool)
-> CmmNode O O -> CmmNode O O -> Bool
eqMiddleWith eqBid (CmmAssign r1 e1) (CmmAssign r2 e2)
= r1 == r2 && eqExprWith eqBid e1 e2
eqMiddleWith eqBid (CmmStore l1 r1) (CmmStore l2 r2)
= eqExprWith eqBid l1 l2 && eqExprWith eqBid r1 r2
eqMiddleWith eqBid (CmmUnsafeForeignCall t1 r1 a1)
(CmmUnsafeForeignCall t2 r2 a2)
= t1 == t2 && r1 == r2 && eqListWith (eqExprWith eqBid) a1 a2
eqMiddleWith _ _ _ = False
eqExprWith :: (BlockId -> BlockId -> Bool)
-> CmmExpr -> CmmExpr -> Bool
eqExprWith eqBid = eq
where
CmmLit l1 `eq` CmmLit l2 = eqLit l1 l2
CmmLoad e1 _ `eq` CmmLoad e2 _ = e1 `eq` e2
CmmReg r1 `eq` CmmReg r2 = r1==r2
CmmRegOff r1 i1 `eq` CmmRegOff r2 i2 = r1==r2 && i1==i2
CmmMachOp op1 es1 `eq` CmmMachOp op2 es2 = op1==op2 && es1 `eqs` es2
CmmStackSlot a1 i1 `eq` CmmStackSlot a2 i2 = eqArea a1 a2 && i1==i2
_e1 `eq` _e2 = False
xs `eqs` ys = eqListWith eq xs ys
eqLit (CmmBlock id1) (CmmBlock id2) = eqBid id1 id2
eqLit l1 l2 = l1 == l2
eqArea Old Old = True
eqArea (Young id1) (Young id2) = eqBid id1 id2
eqArea _ _ = False
-- 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'
{-
| equal = pprTrace "equal" (vcat [ppr block, ppr block']) True
| otherwise = pprTrace "not equal" (vcat [ppr block, ppr block']) False
-}
= equal
where (_,m,l) = blockSplit block
nodes = filter (not . dont_care) (blockToList m)
(_,m',l') = blockSplit block'
nodes' = filter (not . dont_care) (blockToList m')
equal = eqListWith (eqMiddleWith eqBid) nodes nodes' &&
eqLastWith eqBid l l'
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 l1) (CmmCondBranch c2 t2 f2 l2) =
c1 == c2 && l1 == l2 && eqBid t1 t2 && eqBid f1 f2
eqLastWith eqBid (CmmCall t1 c1 g1 a1 r1 u1) (CmmCall t2 c2 g2 a2 r2 u2) =
t1 == t2 && eqMaybeWith eqBid c1 c2 && a1 == a2 && r1 == r2 && u1 == u2 && g1 == g2
eqLastWith eqBid (CmmSwitch e1 ids1) (CmmSwitch e2 ids2) =
e1 == e2 && eqSwitchTargetWith eqBid ids1 ids2
eqLastWith _ _ _ = False
eqMaybeWith :: (a -> b -> Bool) -> Maybe a -> Maybe b -> Bool
eqMaybeWith eltEq (Just e) (Just e') = eltEq e e'
eqMaybeWith _ Nothing Nothing = True
eqMaybeWith _ _ _ = False
eqListWith :: (a -> b -> Bool) -> [a] -> [b] -> Bool
eqListWith f (a : as) (b : bs) = f a b && eqListWith f as bs
eqListWith _ [] [] = True
eqListWith _ _ _ = False
-- | Given a block map, ensure that all "target" blocks are covered by
-- the same ticks as the respective "source" blocks. This not only
-- means copying ticks, but also adjusting tick scopes where
-- necessary.
copyTicks :: LabelMap BlockId -> CmmGraph -> CmmGraph
copyTicks env g
| mapNull env = g
| otherwise = ofBlockMap (g_entry g) $ mapMap copyTo blockMap
where -- Reverse block merge map
blockMap = toBlockMap g
revEnv = mapFoldlWithKey insertRev M.empty env
insertRev m k x = M.insertWith (const (k:)) x [k] m
-- Copy ticks and scopes into the given block
copyTo block = case M.lookup (entryLabel block) revEnv of
Nothing -> block
Just ls -> foldr copy block $ mapMaybe (flip mapLookup blockMap) ls
copy from to =
let ticks = blockTicks from
CmmEntry _ scp0 = firstNode from
(CmmEntry lbl scp1, code) = blockSplitHead to
in CmmEntry lbl (combineTickScopes scp0 scp1) `blockJoinHead`
foldr blockCons code (map CmmTick ticks)
-- Group by [Label]
-- See Note [Compressed TrieMap] in coreSyn/TrieMap about the usage of GenMap.
groupByLabel :: [(Key, DistinctBlocks)] -> [(Key, [DistinctBlocks])]
groupByLabel =
go (TM.emptyTM :: TM.ListMap (TM.GenMap LabelMap) (Key, [DistinctBlocks]))
where
go !m [] = TM.foldTM (:) m []
go !m ((k,v) : entries) = go (TM.alterTM k adjust m) entries
where --k' = map (getKey . getUnique) k
adjust Nothing = Just (k,[v])
adjust (Just (_,vs)) = Just (k,v:vs)
groupByInt :: (a -> Int) -> [a] -> [[a]]
groupByInt f xs = nonDetEltsUFM $ List.foldl' go emptyUFM xs
-- See Note [Unique Determinism and code generation]
where
go m x = alterUFM addEntry m (f x)
where
addEntry xs = Just $! maybe [x] (x:) xs