diff options
Diffstat (limited to 'compiler/nativeGen/BlockLayout.hs')
| -rw-r--r-- | compiler/nativeGen/BlockLayout.hs | 635 |
1 files changed, 387 insertions, 248 deletions
diff --git a/compiler/nativeGen/BlockLayout.hs b/compiler/nativeGen/BlockLayout.hs index 7a39071541..56e3177dd8 100644 --- a/compiler/nativeGen/BlockLayout.hs +++ b/compiler/nativeGen/BlockLayout.hs @@ -6,6 +6,8 @@ {-# LANGUAGE DataKinds #-} {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE TypeFamilies #-} +{-# LANGUAGE GeneralizedNewtypeDeriving #-} +{-# LANGUAGE FlexibleContexts #-} module BlockLayout ( sequenceTop ) @@ -22,7 +24,6 @@ import BlockId import Cmm import Hoopl.Collections import Hoopl.Label -import Hoopl.Block import DynFlags (gopt, GeneralFlag(..), DynFlags, backendMaintainsCfg) import UniqFM @@ -41,11 +42,30 @@ import ListSetOps (removeDups) import OrdList import Data.List import Data.Foldable (toList) -import Hoopl.Graph import qualified Data.Set as Set +import Data.STRef +import Control.Monad.ST.Strict +import Control.Monad (foldM) {- + Note [CFG based code layout] + ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + + The major steps in placing blocks are as follow: + * Compute a CFG based on the Cmm AST, see getCfgProc. + This CFG will have edge weights representing a guess + on how important they are. + * After we convert Cmm to Asm we run `optimizeCFG` which + adds a few more "educated guesses" to the equation. + * Then we run loop analysis on the CFG (`loopInfo`) which tells us + about loop headers, loop nesting levels and the sort. + * Based on the CFG and loop information refine the edge weights + in the CFG and normalize them relative to the most often visited + node. (See `mkGlobalWeights`) + * Feed this CFG into the block layout code (`sequenceTop`) in this + module. Which will then produce a code layout based on the input weights. + ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~ Note [Chain based CFG serialization] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ @@ -60,8 +80,8 @@ import qualified Data.Set as Set but also how much a block would benefit from being placed sequentially after it's predecessor. For example blocks which are preceeded by an info table are more likely to end - up in a different cache line than their predecessor. So there is less benefit - in placing them sequentially. + up in a different cache line than their predecessor and we can't eliminate the jump + so there is less benefit to placing them sequentially. For example consider this example: @@ -81,56 +101,83 @@ import qualified Data.Set as Set Eg for our example we might end up with two chains like: [A->B->C->X],[D]. Blocks inside chains will always be placed sequentially. However there is no particular order in which chains are placed since - (hopefully) the blocks for which sequentially is important have already + (hopefully) the blocks for which sequentiality is important have already been placed in the same chain. ----------------------------------------------------------------------------- - First try to create a lists of good chains. + 1) First try to create a list of good chains. ----------------------------------------------------------------------------- - We do so by taking a block not yet placed in a chain and - looking at these cases: + Good chains are these which allow us to eliminate jump instructions. + Which further eliminate often executed jumps first. + + We do so by: + + *) Ignore edges which represent instructions which can not be replaced + by fall through control flow. Primarily calls and edges to blocks which + are prefixed by a info table we have to jump across. + + *) Then process remaining edges in order of frequency taken and: + + +) If source and target have not been placed build a new chain from them. + + +) If source and target have been placed, and are ends of differing chains + try to merge the two chains. - *) Check if the best predecessor of the block is at the end of a chain. - If so add the current block to the end of that chain. + +) If one side of the edge is a end/front of a chain, add the other block of + to edge to the same chain - Eg if we look at block C and already have the chain (A -> B) - then we extend the chain to (A -> B -> C). + Eg if we look at edge (B -> C) and already have the chain (A -> B) + then we extend the chain to (A -> B -> C). - Combined with the fact that we process blocks in reverse post order - this means loop bodies and trivially sequential control flow already - ends up as a single chain. + +) If the edge was used to modify or build a new chain remove the edge from + our working list. - *) Otherwise we create a singleton chain from the block we are looking at. - Eg if we have from the example above already constructed (A->B) - and look at D we create the chain (D) resulting in the chains [A->B, D] + *) If there any blocks not being placed into a chain after these steps we place + them into a chain consisting of only this block. + + Ranking edges by their taken frequency, if + two edges compete for fall through on the same target block, the one taken + more often will automatically win out. Resulting in fewer instructions being + executed. + + Creating singleton chains is required for situations where we have code of the + form: + + A: goto B: + <infoTable> + B: goto C: + <infoTable> + C: ... + + As the code in block B is only connected to the rest of the program via edges + which will be ignored in this step we make sure that B still ends up in a chain + this way. ----------------------------------------------------------------------------- - We then try to fuse chains. + 2) We also try to fuse chains. ----------------------------------------------------------------------------- - There are edge cases which result in two chains being created which trivially - represent linear control flow. For example we might have the chains - [(A-B-C),(D-E)] with an cfg triangle: + As a result from the above step we still end up with multiple chains which + represent sequential control flow chunks. But they are not yet suitable for + code layout as we need to place *all* blocks into a single sequence. - A----->C->D->E - \->B-/ + In this step we combine chains result from the above step via these steps: - We also get three independent chains if two branches end with a jump - to a common successor. + *) Look at the ranked list of *all* edges, including calls/jumps across info tables + and the like. - We take care of these cases by fusing chains which are connected by an - edge. + *) Look at each edge and - We do so by looking at the list of edges sorted by weight. - Given the edge (C -> D) we try to find two chains such that: - * C is at the end of chain one. - * D is in front of chain two. - * If two such chains exist we fuse them. - We then remove the edge and repeat the process for the rest of the edges. + +) Given an edge (A -> B) try to find two chains for which + * Block A is at the end of one chain + * Block B is at the front of the other chain. + +) If we find such a chain we "fuse" them into a single chain, remove the + edge from working set and continue. + +) If we can't find such chains we skip the edge and continue. ----------------------------------------------------------------------------- - Place indirect successors (neighbours) after each other + 3) Place indirect successors (neighbours) after each other ----------------------------------------------------------------------------- We might have chains [A,B,C,X],[E] in a CFG of the sort: @@ -141,15 +188,11 @@ import qualified Data.Set as Set While E does not follow X it's still beneficial to place them near each other. This can be advantageous if eg C,X,E will end up in the same cache line. - TODO: If we remove edges as we use them (eg if we build up A->B remove A->B - from the list) we could save some more work in later phases. - - ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~ Note [Triangle Control Flow] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ - Checking if an argument is already evaluating leads to a somewhat + Checking if an argument is already evaluated leads to a somewhat special case which looks like this: A: @@ -204,11 +247,6 @@ import qualified Data.Set as Set neighbourOverlapp :: Int neighbourOverlapp = 2 --- | Only edges heavier than this are considered --- for fusing two chains into a single chain. -fuseEdgeThreshold :: EdgeWeight -fuseEdgeThreshold = 0 - -- | Maps blocks near the end of a chain to it's chain AND -- the other blocks near the end. -- [A,B,C,D,E] Gives entries like (B -> ([A,B], [A,B,C,D,E])) @@ -224,40 +262,24 @@ type FrontierMap = LabelMap ([BlockId],BlockChain) newtype BlockChain = BlockChain { chainBlocks :: (OrdList BlockId) } -instance Eq (BlockChain) where - (BlockChain blks1) == (BlockChain blks2) - = fromOL blks1 == fromOL blks2 +-- All chains are constructed the same way so comparison +-- including structure is faster. +instance Eq BlockChain where + BlockChain b1 == BlockChain b2 = strictlyEqOL b1 b2 -- Useful for things like sets and debugging purposes, sorts by blocks -- in the chain. instance Ord (BlockChain) where (BlockChain lbls1) `compare` (BlockChain lbls2) - = (fromOL lbls1) `compare` (fromOL lbls2) + = ASSERT(toList lbls1 /= toList lbls2 || lbls1 `strictlyEqOL` lbls2) + strictlyOrdOL lbls1 lbls2 instance Outputable (BlockChain) where ppr (BlockChain blks) = parens (text "Chain:" <+> ppr (fromOL $ blks) ) -data WeightedEdge = WeightedEdge !BlockId !BlockId EdgeWeight deriving (Eq) - - --- | Non deterministic! (Uniques) Sorts edges by weight and nodes. -instance Ord WeightedEdge where - compare (WeightedEdge from1 to1 weight1) - (WeightedEdge from2 to2 weight2) - | weight1 < weight2 || weight1 == weight2 && from1 < from2 || - weight1 == weight2 && from1 == from2 && to1 < to2 - = LT - | from1 == from2 && to1 == to2 && weight1 == weight2 - = EQ - | otherwise - = GT - -instance Outputable WeightedEdge where - ppr (WeightedEdge from to info) = - ppr from <> text "->" <> ppr to <> brackets (ppr info) - -type WeightedEdgeList = [WeightedEdge] +chainFoldl :: (b -> BlockId -> b) -> b -> BlockChain -> b +chainFoldl f z (BlockChain blocks) = foldl' f z blocks noDups :: [BlockChain] -> Bool noDups chains = @@ -270,19 +292,21 @@ inFront :: BlockId -> BlockChain -> Bool inFront bid (BlockChain seq) = headOL seq == bid -chainMember :: BlockId -> BlockChain -> Bool -chainMember bid chain - = elem bid $ fromOL . chainBlocks $ chain --- = setMember bid . chainMembers $ chain - chainSingleton :: BlockId -> BlockChain chainSingleton lbl = BlockChain (unitOL lbl) +chainFromList :: [BlockId] -> BlockChain +chainFromList = BlockChain . toOL + chainSnoc :: BlockChain -> BlockId -> BlockChain chainSnoc (BlockChain blks) lbl = BlockChain (blks `snocOL` lbl) +chainCons :: BlockId -> BlockChain -> BlockChain +chainCons lbl (BlockChain blks) + = BlockChain (lbl `consOL` blks) + chainConcat :: BlockChain -> BlockChain -> BlockChain chainConcat (BlockChain blks1) (BlockChain blks2) = BlockChain (blks1 `appOL` blks2) @@ -311,52 +335,14 @@ takeL :: Int -> BlockChain -> [BlockId] takeL n (BlockChain blks) = take n . fromOL $ blks --- | For a given list of chains try to fuse chains with strong --- edges between them into a single chain. --- Returns the list of fused chains together with a set of --- used edges. The set of edges is indirectly encoded in the --- chains so doesn't need to be considered for later passes. -fuseChains :: WeightedEdgeList -> LabelMap BlockChain - -> (LabelMap BlockChain, Set.Set WeightedEdge) -fuseChains weights chains - = let fronts = mapFromList $ - map (\chain -> (headOL . chainBlocks $ chain,chain)) $ - mapElems chains :: LabelMap BlockChain - (chains', used, _) = applyEdges weights chains fronts Set.empty - in (chains', used) - where - applyEdges :: WeightedEdgeList -> LabelMap BlockChain - -> LabelMap BlockChain -> Set.Set WeightedEdge - -> (LabelMap BlockChain, Set.Set WeightedEdge, LabelMap BlockChain) - applyEdges [] chainsEnd chainsFront used - = (chainsEnd, used, chainsFront) - applyEdges (edge@(WeightedEdge from to w):edges) chainsEnd chainsFront used - --Since we order edges descending by weight we can stop here - | w <= fuseEdgeThreshold - = ( chainsEnd, used, chainsFront) - --Fuse the two chains - | Just c1 <- mapLookup from chainsEnd - , Just c2 <- mapLookup to chainsFront - , c1 /= c2 - = let newChain = chainConcat c1 c2 - front = headOL . chainBlocks $ newChain - end = lastOL . chainBlocks $ newChain - chainsFront' = mapInsert front newChain $ - mapDelete to chainsFront - chainsEnd' = mapInsert end newChain $ - mapDelete from chainsEnd - in applyEdges edges chainsEnd' chainsFront' - (Set.insert edge used) - | otherwise - --Check next edge - = applyEdges edges chainsEnd chainsFront used - +-- Note [Combining neighborhood chains] +-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -- See also Note [Chain based CFG serialization] -- We have the chains (A-B-C-D) and (E-F) and an Edge C->E. -- --- While placing the later after the former doesn't result in sequential --- control flow it is still be benefical since block C and E might end +-- While placing the latter after the former doesn't result in sequential +-- control flow it is still benefical. As block C and E might end -- up in the same cache line. -- -- So we place these chains next to each other even if we can't fuse them. @@ -365,7 +351,7 @@ fuseChains weights chains -- v -- - -> E -> F ... -- --- Simple heuristic to chose which chains we want to combine: +-- A simple heuristic to chose which chains we want to combine: -- * Process edges in descending priority. -- * Check if there is a edge near the end of one chain which goes -- to a block near the start of another edge. @@ -375,14 +361,22 @@ fuseChains weights chains -- us to find all edges between two chains, check the distance for all edges, -- rank them based on the distance and and only then we can select two chains -- to combine. Which would add a lot of complexity for little gain. +-- +-- So instead we just rank by the strength of the edge and use the first pair we +-- find. -- | For a given list of chains and edges try to combine chains with strong -- edges between them. -combineNeighbourhood :: WeightedEdgeList -> [BlockChain] - -> [BlockChain] +combineNeighbourhood :: [CfgEdge] -- ^ Edges to consider + -> [BlockChain] -- ^ Current chains of blocks + -> ([BlockChain], Set.Set (BlockId,BlockId)) + -- ^ Resulting list of block chains, and a set of edges which + -- were used to fuse chains and as such no longer need to be + -- considered. combineNeighbourhood edges chains = -- pprTraceIt "Neigbours" $ - applyEdges edges endFrontier startFrontier + -- pprTrace "combineNeighbours" (ppr edges) $ + applyEdges edges endFrontier startFrontier (Set.empty) where --Build maps from chain ends to chains endFrontier, startFrontier :: FrontierMap @@ -396,14 +390,14 @@ combineNeighbourhood edges chains let front = getFronts chain entry = (front,chain) in map (\x -> (x,entry)) front) chains - applyEdges :: WeightedEdgeList -> FrontierMap -> FrontierMap - -> [BlockChain] - applyEdges [] chainEnds _chainFronts = - ordNub $ map snd $ mapElems chainEnds - applyEdges ((WeightedEdge from to _w):edges) chainEnds chainFronts + applyEdges :: [CfgEdge] -> FrontierMap -> FrontierMap -> Set.Set (BlockId, BlockId) + -> ([BlockChain], Set.Set (BlockId,BlockId)) + applyEdges [] chainEnds _chainFronts combined = + (ordNub $ map snd $ mapElems chainEnds, combined) + applyEdges ((CfgEdge from to _w):edges) chainEnds chainFronts combined | Just (c1_e,c1) <- mapLookup from chainEnds , Just (c2_f,c2) <- mapLookup to chainFronts - , c1 /= c2 -- Avoid trying to concat a short chain with itself. + , c1 /= c2 -- Avoid trying to concat a chain with itself. = let newChain = chainConcat c1 c2 newChainFrontier = getFronts newChain newChainEnds = getEnds newChain @@ -437,165 +431,299 @@ combineNeighbourhood edges chains -- text "fronts" <+> ppr newFronts $$ -- text "ends" <+> ppr newEnds -- ) - applyEdges edges newEnds newFronts + applyEdges edges newEnds newFronts (Set.insert (from,to) combined) | otherwise - = --pprTrace "noNeigbours" (ppr ()) $ - applyEdges edges chainEnds chainFronts + = applyEdges edges chainEnds chainFronts combined where getFronts chain = takeL neighbourOverlapp chain getEnds chain = takeR neighbourOverlapp chain - - --- See [Chain based CFG serialization] -buildChains :: CFG -> [BlockId] - -> ( LabelMap BlockChain -- Resulting chains. +-- In the last stop we combine all chains into a single one. +-- Trying to place chains with strong edges next to each other. +mergeChains :: [CfgEdge] -> [BlockChain] + -> (BlockChain) +mergeChains edges chains + = -- pprTrace "combine" (ppr edges) $ + runST $ do + let addChain m0 chain = do + ref <- newSTRef chain + return $ chainFoldl (\m' b -> mapInsert b ref m') m0 chain + chainMap' <- foldM (\m0 c -> addChain m0 c) mapEmpty chains + merge edges chainMap' + where + -- We keep a map from ALL blocks to their respective chain (sigh) + -- This is required since when looking at an edge we need to find + -- the associated chains quickly. + -- We use a map of STRefs, maintaining a invariant of one STRef per chain. + -- When merging chains we can update the + -- STRef of one chain once (instead of writing to the map for each block). + -- We then overwrite the STRefs for the other chain so there is again only + -- a single STRef for the combined chain. + -- The difference in terms of allocations saved is ~0.2% with -O so actually + -- significant compared to using a regular map. + + merge :: forall s. [CfgEdge] -> LabelMap (STRef s BlockChain) -> ST s BlockChain + merge [] chains = do + chains' <- ordNub <$> (mapM readSTRef $ mapElems chains) :: ST s [BlockChain] + return $ foldl' chainConcat (head chains') (tail chains') + merge ((CfgEdge from to _):edges) chains + -- | pprTrace "merge" (ppr (from,to) <> ppr chains) False + -- = undefined + | cFrom == cTo + = merge edges chains + | otherwise + = do + chains' <- mergeComb cFrom cTo + merge edges chains' + where + mergeComb :: STRef s BlockChain -> STRef s BlockChain -> ST s (LabelMap (STRef s BlockChain)) + mergeComb refFrom refTo = do + cRight <- readSTRef refTo + chain <- pure chainConcat <*> readSTRef refFrom <*> pure cRight + writeSTRef refFrom chain + return $ chainFoldl (\m b -> mapInsert b refFrom m) chains cRight + + cFrom = expectJust "mergeChains:chainMap:from" $ mapLookup from chains + cTo = expectJust "mergeChains:chainMap:to" $ mapLookup to chains + + +-- See Note [Chain based CFG serialization] for the general idea. +-- This creates and fuses chains at the same time for performance reasons. + +-- Try to build chains from a list of edges. +-- Edges must be sorted **descending** by their priority. +-- Returns the constructed chains, along with all edges which +-- are irrelevant past this point, this information doesn't need +-- to be complete - it's only used to speed up the process. +-- An Edge is irrelevant if the ends are part of the same chain. +-- We say these edges are already linked +buildChains :: [CfgEdge] -> [BlockId] + -> ( LabelMap BlockChain -- Resulting chains, indexd by end if chain. , Set.Set (BlockId, BlockId)) --List of fused edges. -buildChains succWeights blocks - = let (_, fusedEdges, chains) = buildNext setEmpty mapEmpty blocks Set.empty - in (chains, fusedEdges) +buildChains edges blocks + = runST $ buildNext setEmpty mapEmpty mapEmpty edges Set.empty where - -- We keep a map from the last block in a chain to the chain itself. - -- This we we can easily check if an block should be appened to an + -- buildNext builds up chains from edges one at a time. + + -- We keep a map from the ends of chains to the chains. + -- This we we can easily check if an block should be appended to an -- existing chain! - buildNext :: LabelSet - -> LabelMap BlockChain -- Map from last element to chain. - -> [BlockId] -- Blocks to place - -> Set.Set (BlockId, BlockId) - -> ( [BlockChain] -- Placed Blocks - , Set.Set (BlockId, BlockId) --List of fused edges - , LabelMap BlockChain - ) - buildNext _placed chains [] linked = - ([], linked, chains) - buildNext placed chains (block:todo) linked - | setMember block placed - = buildNext placed chains todo linked + -- We store them using STRefs so we don't have to rebuild the spine of both + -- maps every time we update a chain. + buildNext :: forall s. LabelSet + -> LabelMap (STRef s BlockChain) -- Map from end of chain to chain. + -> LabelMap (STRef s BlockChain) -- Map from start of chain to chain. + -> [CfgEdge] -- Edges to check - ordered by decreasing weight + -> Set.Set (BlockId, BlockId) -- Used edges + -> ST s ( LabelMap BlockChain -- Chains by end + , Set.Set (BlockId, BlockId) --List of fused edges + ) + buildNext placed _chainStarts chainEnds [] linked = do + ends' <- sequence $ mapMap readSTRef chainEnds :: ST s (LabelMap BlockChain) + -- Any remaining blocks have to be made to singleton chains. + -- They might be combined with other chains later on outside this function. + let unplaced = filter (\x -> not (setMember x placed)) blocks + singletons = map (\x -> (x,chainSingleton x)) unplaced :: [(BlockId,BlockChain)] + return (foldl' (\m (k,v) -> mapInsert k v m) ends' singletons , linked) + buildNext placed chainStarts chainEnds (edge:todo) linked + | from == to + -- We skip self edges + = buildNext placed chainStarts chainEnds todo (Set.insert (from,to) linked) + | not (alreadyPlaced from) && + not (alreadyPlaced to) + = do + --pprTraceM "Edge-Chain:" (ppr edge) + chain' <- newSTRef $ chainFromList [from,to] + buildNext + (setInsert to (setInsert from placed)) + (mapInsert from chain' chainStarts) + (mapInsert to chain' chainEnds) + todo + (Set.insert (from,to) linked) + + | (alreadyPlaced from) && + (alreadyPlaced to) + , Just predChain <- mapLookup from chainEnds + , Just succChain <- mapLookup to chainStarts + , predChain /= succChain -- Otherwise we try to create a cycle. + = do + -- pprTraceM "Fusing edge" (ppr edge) + fuseChain predChain succChain + + | (alreadyPlaced from) && + (alreadyPlaced to) + = --pprTraceM "Skipping:" (ppr edge) >> + buildNext placed chainStarts chainEnds todo linked + | otherwise - = buildNext placed' chains' todo linked' + = do -- pprTraceM "Finding chain for:" (ppr edge $$ + -- text "placed" <+> ppr placed) + findChain where - placed' = (foldl' (flip setInsert) placed placedBlocks) - linked' = Set.union linked linkedEdges - (placedBlocks, chains', linkedEdges) = findChain block - - --Add the block to a existing or new chain - --Returns placed blocks, list of resulting chains - --and fused edges - findChain :: BlockId - -> ([BlockId],LabelMap BlockChain, Set.Set (BlockId, BlockId)) - findChain block - -- B) place block at end of existing chain if - -- there is no better block to append. - | (pred:_) <- preds - , alreadyPlaced pred - , Just predChain <- mapLookup pred chains - , (best:_) <- filter (not . alreadyPlaced) $ getSuccs pred - , best == lbl - = --pprTrace "B.2)" (ppr (pred,lbl)) $ - let newChain = chainSnoc predChain block - chainMap = mapInsert lbl newChain $ mapDelete pred chains - in ( [lbl] - , chainMap - , Set.singleton (pred,lbl) ) - + from = edgeFrom edge + to = edgeTo edge + alreadyPlaced blkId = (setMember blkId placed) + + -- Combine two chains into a single one. + fuseChain :: STRef s BlockChain -> STRef s BlockChain + -> ST s ( LabelMap BlockChain -- Chains by end + , Set.Set (BlockId, BlockId) --List of fused edges + ) + fuseChain fromRef toRef = do + fromChain <- readSTRef fromRef + toChain <- readSTRef toRef + let newChain = chainConcat fromChain toChain + ref <- newSTRef newChain + let start = head $ takeL 1 newChain + let end = head $ takeR 1 newChain + -- chains <- sequence $ mapMap readSTRef chainStarts + -- pprTraceM "pre-fuse chains:" $ ppr chains + buildNext + placed + (mapInsert start ref $ mapDelete to $ chainStarts) + (mapInsert end ref $ mapDelete from $ chainEnds) + todo + (Set.insert (from,to) linked) + + + --Add the block to a existing chain or creates a new chain + findChain :: ST s ( LabelMap BlockChain -- Chains by end + , Set.Set (BlockId, BlockId) --List of fused edges + ) + findChain + -- We can attach the block to the end of a chain + | alreadyPlaced from + , Just predChain <- mapLookup from chainEnds + = do + chain <- readSTRef predChain + let newChain = chainSnoc chain to + writeSTRef predChain newChain + let chainEnds' = mapInsert to predChain $ mapDelete from chainEnds + -- chains <- sequence $ mapMap readSTRef chainStarts + -- pprTraceM "from chains:" $ ppr chains + buildNext (setInsert to placed) chainStarts chainEnds' todo (Set.insert (from,to) linked) + -- We can attack it to the front of a chain + | alreadyPlaced to + , Just succChain <- mapLookup to chainStarts + = do + chain <- readSTRef succChain + let newChain = from `chainCons` chain + writeSTRef succChain newChain + let chainStarts' = mapInsert from succChain $ mapDelete to chainStarts + -- chains <- sequence $ mapMap readSTRef chainStarts' + -- pprTraceM "to chains:" $ ppr chains + buildNext (setInsert from placed) chainStarts' chainEnds todo (Set.insert (from,to) linked) + -- The placed end of the edge is part of a chain already and not an end. | otherwise - = --pprTrace "single" (ppr lbl) - ( [lbl] - , mapInsert lbl (chainSingleton lbl) chains - , Set.empty) + = do + let block = if alreadyPlaced to then from else to + --pprTraceM "Singleton" $ ppr block + let newChain = chainSingleton block + ref <- newSTRef newChain + buildNext (setInsert block placed) (mapInsert block ref chainStarts) + (mapInsert block ref chainEnds) todo (linked) where alreadyPlaced blkId = (setMember blkId placed) - lbl = block - getSuccs = map fst . getSuccEdgesSorted succWeights - preds = map fst $ getSuccEdgesSorted predWeights lbl - --For efficiency we also create the map to look up predecessors here - predWeights = reverseEdges succWeights - - --- We make the CFG a Hoopl Graph, so we can reuse revPostOrder. -newtype BlockNode (e :: Extensibility) (x :: Extensibility) = BN (BlockId,[BlockId]) -instance NonLocal (BlockNode) where - entryLabel (BN (lbl,_)) = lbl - successors (BN (_,succs)) = succs - -fromNode :: BlockNode C C -> BlockId -fromNode (BN x) = fst x - -sequenceChain :: forall a i. (Instruction i, Outputable i) => LabelMap a -> CFG - -> [GenBasicBlock i] -> [GenBasicBlock i] +-- | Place basic blocks based on the given CFG. +-- See Note [Chain based CFG serialization] +sequenceChain :: forall a i. (Instruction i, Outputable i) + => LabelMap a -- ^ Keys indicate an info table on the block. + -> CFG -- ^ Control flow graph and some meta data. + -> [GenBasicBlock i] -- ^ List of basic blocks to be placed. + -> [GenBasicBlock i] -- ^ Blocks placed in sequence. sequenceChain _info _weights [] = [] sequenceChain _info _weights [x] = [x] sequenceChain info weights' blocks@((BasicBlock entry _):_) = - --Optimization, delete edges of weight <= 0. - --This significantly improves performance whenever - --we iterate over all edges, which is a few times! let weights :: CFG - weights - = filterEdges (\_f _t edgeInfo -> edgeWeight edgeInfo > 0) weights' + weights = --pprTrace "cfg'" (pprEdgeWeights cfg') + cfg' + where + (_, globalEdgeWeights) = {-# SCC mkGlobalWeights #-} mkGlobalWeights entry weights' + cfg' = {-# SCC rewriteEdges #-} + mapFoldlWithKey + (\cfg from m -> + mapFoldlWithKey + (\cfg to w -> setEdgeWeight cfg (EdgeWeight w) from to ) + cfg m ) + weights' + globalEdgeWeights + + directEdges :: [CfgEdge] + directEdges = sortBy (flip compare) $ catMaybes . map relevantWeight $ (infoEdgeList weights) + where + relevantWeight :: CfgEdge -> Maybe CfgEdge + relevantWeight edge@(CfgEdge from to edgeInfo) + | (EdgeInfo CmmSource { trans_cmmNode = CmmCall {} } _) <- edgeInfo + -- Ignore edges across calls + = Nothing + | mapMember to info + , w <- edgeWeight edgeInfo + -- The payoff is small if we jump over an info table + = Just (CfgEdge from to edgeInfo { edgeWeight = w/8 }) + | otherwise + = Just edge + blockMap :: LabelMap (GenBasicBlock i) blockMap = foldl' (\m blk@(BasicBlock lbl _ins) -> mapInsert lbl blk m) mapEmpty blocks - toNode :: BlockId -> BlockNode C C - toNode bid = - -- sorted such that heavier successors come first. - BN (bid,map fst . getSuccEdgesSorted weights' $ bid) - - orderedBlocks :: [BlockId] - orderedBlocks - = map fromNode $ - revPostorderFrom (fmap (toNode . blockId) blockMap) entry - (builtChains, builtEdges) = {-# SCC "buildChains" #-} --pprTraceIt "generatedChains" $ - --pprTrace "orderedBlocks" (ppr orderedBlocks) $ - buildChains weights orderedBlocks + --pprTrace "blocks" (ppr (mapKeys blockMap)) $ + buildChains directEdges (mapKeys blockMap) - rankedEdges :: WeightedEdgeList - -- Sort edges descending, remove fused eges + rankedEdges :: [CfgEdge] + -- Sort descending by weight, remove fused edges rankedEdges = - map (\(from, to, weight) -> WeightedEdge from to weight) . - filter (\(from, to, _) - -> not (Set.member (from,to) builtEdges)) . - sortWith (\(_,_,w) -> - w) $ weightedEdgeList weights + filter (\edge -> not (Set.member (edgeFrom edge,edgeTo edge) builtEdges)) $ + directEdges - (fusedChains, fusedEdges) + (neighbourChains, combined) = ASSERT(noDups $ mapElems builtChains) - {-# SCC "fuseChains" #-} - --(pprTrace "RankedEdges" $ ppr rankedEdges) $ - --pprTraceIt "FusedChains" $ - fuseChains rankedEdges builtChains - - rankedEdges' = - filter (\edge -> not $ Set.member edge fusedEdges) $ rankedEdges - - neighbourChains - = ASSERT(noDups $ mapElems fusedChains) {-# SCC "groupNeighbourChains" #-} - --pprTraceIt "ResultChains" $ - combineNeighbourhood rankedEdges' (mapElems fusedChains) + -- pprTraceIt "NeighbourChains" $ + combineNeighbourhood rankedEdges (mapElems builtChains) + + + allEdges :: [CfgEdge] + allEdges = {-# SCC allEdges #-} + sortOn (relevantWeight) $ filter (not . deadEdge) $ (infoEdgeList weights) + where + deadEdge :: CfgEdge -> Bool + deadEdge (CfgEdge from to _) = let e = (from,to) in Set.member e combined || Set.member e builtEdges + relevantWeight :: CfgEdge -> EdgeWeight + relevantWeight (CfgEdge _ _ edgeInfo) + | EdgeInfo (CmmSource { trans_cmmNode = CmmCall {}}) _ <- edgeInfo + -- Penalize edges across calls + = weight/(64.0) + | otherwise + = weight + where + -- negate to sort descending + weight = negate (edgeWeight edgeInfo) + + masterChain = + {-# SCC "mergeChains" #-} + -- pprTraceIt "MergedChains" $ + mergeChains allEdges neighbourChains --Make sure the first block stays first - ([entryChain],chains') - = ASSERT(noDups $ neighbourChains) - partition (chainMember entry) neighbourChains - (entryChain':entryRest) - | inFront entry entryChain = [entryChain] - | (rest,entry) <- breakChainAt entry entryChain + prepedChains + | inFront entry masterChain + = [masterChain] + | (rest,entry) <- breakChainAt entry masterChain = [entry,rest] | otherwise = pprPanic "Entry point eliminated" $ - ppr ([entryChain],chains') + ppr masterChain - prepedChains - = entryChain':(entryRest++chains') :: [BlockChain] blockList - -- = (concatMap chainToBlocks prepedChains) - = (concatMap fromOL $ map chainBlocks prepedChains) + = ASSERT(noDups [masterChain]) + (concatMap fromOL $ map chainBlocks prepedChains) --chainPlaced = setFromList $ map blockId blockList :: LabelSet chainPlaced = setFromList $ blockList :: LabelSet @@ -605,14 +733,22 @@ sequenceChain info weights' blocks@((BasicBlock entry _):_) = in filter (\block -> not (isPlaced block)) blocks placedBlocks = + -- We want debug builds to catch this as it's a good indicator for + -- issues with CFG invariants. But we don't want to blow up production + -- builds if something slips through. + ASSERT(null unplaced) --pprTraceIt "placedBlocks" $ - blockList ++ unplaced + -- ++ [] is stil kinda expensive + if null unplaced then blockList else blockList ++ unplaced getBlock bid = expectJust "Block placment" $ mapLookup bid blockMap in --Assert we placed all blocks given as input ASSERT(all (\bid -> mapMember bid blockMap) placedBlocks) dropJumps info $ map getBlock placedBlocks +{-# SCC dropJumps #-} +-- | Remove redundant jumps between blocks when we can rely on +-- fall through. dropJumps :: forall a i. Instruction i => LabelMap a -> [GenBasicBlock i] -> [GenBasicBlock i] dropJumps _ [] = [] @@ -641,7 +777,8 @@ sequenceTop => DynFlags -- Determine which layout algo to use -> NcgImpl statics instr jumpDest -> Maybe CFG -- ^ CFG if we have one. - -> NatCmmDecl statics instr -> NatCmmDecl statics instr + -> NatCmmDecl statics instr -- ^ Function to serialize + -> NatCmmDecl statics instr sequenceTop _ _ _ top@(CmmData _ _) = top sequenceTop dflags ncgImpl edgeWeights @@ -650,11 +787,13 @@ sequenceTop dflags ncgImpl edgeWeights --Use chain based algorithm , Just cfg <- edgeWeights = CmmProc info lbl live ( ListGraph $ ncgMakeFarBranches ncgImpl info $ + {-# SCC layoutBlocks #-} sequenceChain info cfg blocks ) | otherwise --Use old algorithm = let cfg = if dontUseCfg then Nothing else edgeWeights in CmmProc info lbl live ( ListGraph $ ncgMakeFarBranches ncgImpl info $ + {-# SCC layoutBlocks #-} sequenceBlocks cfg info blocks) where dontUseCfg = gopt Opt_WeightlessBlocklayout dflags || |