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module CmmContFlowOpt
( runCmmOpts, cmmCfgOpts, cmmCfgOptsZ
, branchChainElimZ, removeUnreachableBlocksZ, predMap
, replaceLabelsZ
)
where
import BlockId
import Cmm
import CmmTx
import qualified ZipCfg as G
import ZipCfgCmmRep
import Maybes
import Monad
import Panic
import Prelude hiding (unzip, zip)
import Util
import UniqFM
------------------------------------
mapProcs :: Tx (GenCmmTop d h s) -> Tx (GenCmm d h s)
mapProcs f (Cmm tops) = fmap Cmm (mapTx f tops)
------------------------------------
cmmCfgOpts :: Tx (ListGraph CmmStmt)
cmmCfgOptsZ :: Tx CmmGraph
cmmCfgOpts = branchChainElim -- boring, but will get more exciting later
cmmCfgOptsZ =
branchChainElimZ `seqTx` blockConcatZ `seqTx` removeUnreachableBlocksZ
-- Here branchChainElim can ultimately be replaced
-- with a more exciting combination of optimisations
runCmmOpts :: Tx g -> Tx (GenCmm d h g)
runCmmOpts opt = mapProcs (optGraph opt)
optGraph :: Tx g -> Tx (GenCmmTop d h g)
optGraph _ top@(CmmData {}) = noTx top
optGraph opt (CmmProc info lbl formals g) = fmap (CmmProc info lbl formals) (opt g)
----------------------------------------------------------------
branchChainElim :: Tx (ListGraph CmmStmt)
-- Remove any basic block of the form L: goto L',
-- and replace L with L' everywhere else
branchChainElim (ListGraph blocks)
| null lone_branch_blocks -- No blocks to remove
= noTx (ListGraph blocks)
| otherwise
= aTx (ListGraph new_blocks)
where
(lone_branch_blocks, others) = partitionWith isLoneBranch blocks
new_blocks = map (replaceLabels env) others
env = mkClosureBlockEnv lone_branch_blocks
isLoneBranch :: CmmBasicBlock -> Either (BlockId, BlockId) CmmBasicBlock
isLoneBranch (BasicBlock id [CmmBranch target]) | id /= target = Left (id, target)
isLoneBranch other_block = Right other_block
-- An infinite loop is not a link in a branch chain!
replaceLabels :: BlockEnv BlockId -> CmmBasicBlock -> CmmBasicBlock
replaceLabels env (BasicBlock id stmts)
= BasicBlock id (map replace stmts)
where
replace (CmmBranch id) = CmmBranch (lookup id)
replace (CmmCondBranch e id) = CmmCondBranch e (lookup id)
replace (CmmSwitch e tbl) = CmmSwitch e (map (fmap lookup) tbl)
replace other_stmt = other_stmt
lookup id = lookupBlockEnv env id `orElse` id
----------------------------------------------------------------
branchChainElimZ :: Tx CmmGraph
-- Remove any basic block of the form L: goto L',
-- and replace L with L' everywhere else
branchChainElimZ g@(G.LGraph eid _)
| null lone_branch_blocks -- No blocks to remove
= noTx g
| otherwise
= aTx $ replaceLabelsZ env $ G.of_block_list eid (self_branches ++ others)
where
(lone_branch_blocks, others) = partitionWith isLoneBranchZ (G.to_block_list g)
env = mkClosureBlockEnv lone_branch_blocks
self_branches =
let loop_to (id, _) =
if lookup id == id then
Just (G.Block id (G.ZLast (G.mkBranchNode id)))
else
Nothing
in mapMaybe loop_to lone_branch_blocks
lookup id = lookupBlockEnv env id `orElse` id
isLoneBranchZ :: CmmBlock -> Either (BlockId, BlockId) CmmBlock
isLoneBranchZ (G.Block id (G.ZLast (G.LastOther (LastBranch target))))
| id /= target = Left (id,target)
isLoneBranchZ other = Right other
-- An infinite loop is not a link in a branch chain!
replaceLabelsZ :: BlockEnv BlockId -> CmmGraph -> CmmGraph
replaceLabelsZ env = replace_eid . G.map_nodes id id last
where
replace_eid (G.LGraph eid blocks) = G.LGraph (lookup eid) blocks
last (LastBranch id) = LastBranch (lookup id)
last (LastCondBranch e ti fi) = LastCondBranch e (lookup ti) (lookup fi)
last (LastSwitch e tbl) = LastSwitch e (map (fmap lookup) tbl)
last (LastCall tgt (Just id)) = LastCall tgt (Just $ lookup id)
last exit_jump_return = exit_jump_return
lookup id = lookupBlockEnv env id `orElse` id
----------------------------------------------------------------
-- Build a map from a block to its set of predecessors. Very useful.
predMap :: G.LastNode l => G.LGraph m l -> BlockEnv BlockSet
predMap g = G.fold_blocks add_preds emptyBlockEnv g -- find the back edges
where add_preds b env = foldl (add b) env (G.succs b)
add (G.Block bid _) env b' =
extendBlockEnv env b' $
extendBlockSet (lookupBlockEnv env b' `orElse` emptyBlockSet) bid
----------------------------------------------------------------
blockConcatZ :: Tx CmmGraph
-- If a block B branches to a label L, and L has no other predecessors,
-- then we can splice the block starting with L onto the end of B.
-- Because this optmization can be inhibited by unreachable blocks,
-- we bundle it with a pass that drops unreachable blocks.
-- Order matters, so we work bottom up (reverse postorder DFS).
-- Note: This optimization does _not_ subsume branch chain elimination.
blockConcatZ = removeUnreachableBlocksZ `seqTx` blockConcatZ'
blockConcatZ' :: Tx CmmGraph
blockConcatZ' g@(G.LGraph eid blocks) = tx $ G.LGraph eid blocks'
where (changed, blocks') = foldr maybe_concat (False, blocks) $ G.postorder_dfs g
maybe_concat b@(G.Block bid _) (changed, blocks') =
let unchanged = (changed, extendBlockEnv blocks' bid b)
in case G.goto_end $ G.unzip b of
(h, G.LastOther (LastBranch b')) ->
if num_preds b' == 1 then
(True, extendBlockEnv blocks' bid $ splice blocks' h b')
else unchanged
_ -> unchanged
num_preds bid = liftM sizeBlockSet (lookupBlockEnv backEdges bid) `orElse` 0
backEdges = predMap g
splice blocks' h bid' =
case lookupBlockEnv blocks' bid' of
Just (G.Block _ t) -> G.zip $ G.ZBlock h t
Nothing -> panic "unknown successor block"
tx = if changed then aTx else noTx
----------------------------------------------------------------
mkClosureBlockEnv :: [(BlockId, BlockId)] -> BlockEnv BlockId
mkClosureBlockEnv blocks = mkBlockEnv $ map follow blocks
where singleEnv = mkBlockEnv blocks
follow (id, next) = (id, endChain id next)
endChain orig id = case lookupBlockEnv singleEnv id of
Just id' | id /= orig -> endChain orig id'
_ -> id
----------------------------------------------------------------
removeUnreachableBlocksZ :: Tx CmmGraph
removeUnreachableBlocksZ g@(G.LGraph id blocks) =
if length blocks' < sizeUFM blocks then aTx $ G.of_block_list id blocks'
else noTx g
where blocks' = G.postorder_dfs g
|
