-{-# OPTIONS -Wall -fno-warn-name-shadowing #-}
+
module CmmContFlowOpt
( runCmmOpts, cmmCfgOpts, cmmCfgOptsZ
- , branchChainElimZ, removeUnreachableBlocksZ
+ , branchChainElimZ, removeUnreachableBlocksZ, predMap
+ , replaceLabelsZ
)
where
+import BlockId
import Cmm
import CmmTx
import qualified ZipCfg as G
-import ZipCfgCmm
+import ZipCfgCmmRep
+
import Maybes
+import Monad
+import Panic
+import Prelude hiding (unzip, zip)
import Util
import UniqFM
cmmCfgOptsZ :: Tx CmmGraph
cmmCfgOpts = branchChainElim -- boring, but will get more exciting later
-cmmCfgOptsZ = branchChainElimZ `seqTx` removeUnreachableBlocksZ
+cmmCfgOptsZ =
+ branchChainElimZ `seqTx` blockConcatZ `seqTx` removeUnreachableBlocksZ
-- Here branchChainElim can ultimately be replaced
-- with a more exciting combination of optimisations
else
Nothing
in mapMaybe loop_to lone_branch_blocks
- lookup id = G.lookupBlockEnv env id `orElse` id
+ lookup id = lookupBlockEnv env id `orElse` id
-isLoneBranchZ :: CmmBlock -> Either (G.BlockId, G.BlockId) CmmBlock
-isLoneBranchZ (G.Block id (G.ZLast (G.LastOther (LastBranch target []))))
+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 G.BlockId -> CmmGraph -> CmmGraph
+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 args) = LastBranch (lookup id) args
- last (LastCondBranch e ti fi) = LastCondBranch e (lookup ti) (lookup fi)
- last (LastSwitch e tbl) = LastSwitch e (map (fmap lookup) tbl)
- last (LastCall tgt args (Just id)) = LastCall tgt args (Just $ lookup id)
- last exit_jump_return = exit_jump_return
- lookup id = G.lookupBlockEnv env id `orElse` id
+ 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