3 ( runCmmOpts, cmmCfgOpts, cmmCfgOptsZ
4 , branchChainElimZ, removeUnreachableBlocksZ, predMap
5 , replaceLabelsZ, replaceBranches, runCmmContFlowOptsZs
12 import qualified ZipCfg as G
19 import Prelude hiding (unzip, zip)
22 ------------------------------------
23 runCmmContFlowOptsZs :: [CmmZ] -> [CmmZ]
24 runCmmContFlowOptsZs prog
25 = [ runTx (runCmmOpts cmmCfgOptsZ) cmm_top
28 cmmCfgOpts :: Tx (ListGraph CmmStmt)
29 cmmCfgOptsZ :: Tx (a, CmmGraph)
31 cmmCfgOpts = branchChainElim -- boring, but will get more exciting later
34 (branchChainElimZ `seqTx` blockConcatZ `seqTx` removeUnreachableBlocksZ) g
35 -- Here branchChainElim can ultimately be replaced
36 -- with a more exciting combination of optimisations
38 runCmmOpts :: Tx g -> Tx (GenCmm d h g)
39 -- Lifts a transformer on a single graph to one on the whole program
40 runCmmOpts opt = mapProcs (optProc opt)
42 optProc :: Tx g -> Tx (GenCmmTop d h g)
43 optProc _ top@(CmmData {}) = noTx top
44 optProc opt (CmmProc info lbl formals g) =
45 fmap (CmmProc info lbl formals) (opt g)
47 optGraph :: Tx g -> Tx (a, g)
48 optGraph opt (a, g) = fmap (\g' -> (a, g')) (opt g)
50 ------------------------------------
51 mapProcs :: Tx (GenCmmTop d h s) -> Tx (GenCmm d h s)
52 mapProcs f (Cmm tops) = fmap Cmm (mapTx f tops)
54 ----------------------------------------------------------------
55 branchChainElim :: Tx (ListGraph CmmStmt)
56 -- If L is not captured in an instruction, we can remove any
57 -- basic block of the form L: goto L', and replace L with L' everywhere else.
58 -- How does L get captured? In a CallArea.
59 branchChainElim (ListGraph blocks)
60 | null lone_branch_blocks -- No blocks to remove
61 = noTx (ListGraph blocks)
63 = aTx (ListGraph new_blocks)
65 (lone_branch_blocks, others) = partitionWith isLoneBranch blocks
66 new_blocks = map (replaceLabels env) others
67 env = mkClosureBlockEnv lone_branch_blocks
69 isLoneBranch :: CmmBasicBlock -> Either (BlockId, BlockId) CmmBasicBlock
70 isLoneBranch (BasicBlock id [CmmBranch target]) | id /= target = Left (id, target)
71 isLoneBranch other_block = Right other_block
72 -- An infinite loop is not a link in a branch chain!
74 replaceLabels :: BlockEnv BlockId -> CmmBasicBlock -> CmmBasicBlock
75 replaceLabels env (BasicBlock id stmts)
76 = BasicBlock id (map replace stmts)
78 replace (CmmBranch id) = CmmBranch (lookup id)
79 replace (CmmCondBranch e id) = CmmCondBranch e (lookup id)
80 replace (CmmSwitch e tbl) = CmmSwitch e (map (fmap lookup) tbl)
81 replace other_stmt = other_stmt
83 lookup id = lookupBlockEnv env id `orElse` id
84 ----------------------------------------------------------------
85 branchChainElimZ :: Tx CmmGraph
86 -- Remove any basic block of the form L: goto L',
87 -- and replace L with L' everywhere else,
88 -- unless L is the successor of a call instruction and L'
89 -- is the entry block. You don't want to set the successor
90 -- of a function call to the entry block because there is no good way
91 -- to store both the infotables for the call and from the callee,
92 -- while putting the stack pointer in a consistent place.
94 -- JD isn't quite sure when it's safe to share continuations for different
95 -- function calls -- have to think about where the SP will be,
96 -- so we'll table that problem for now by leaving all call successors alone.
97 branchChainElimZ g@(G.LGraph eid _)
98 | null lone_branch_blocks -- No blocks to remove
101 = aTx $ replaceLabelsZ env $ G.of_block_list eid (self_branches ++ others)
103 blocks = G.to_block_list g
104 (lone_branch_blocks, others) = partitionWith isLoneBranchZ blocks
105 env = mkClosureBlockEnvZ lone_branch_blocks
107 let loop_to (id, _) =
108 if lookup id == id then
109 Just (G.Block id (G.ZLast (G.mkBranchNode id)))
112 in mapMaybe loop_to lone_branch_blocks
113 lookup id = lookupBlockEnv env id `orElse` id
115 call_succs = foldl add emptyBlockSet blocks
117 case G.last (G.unzip b) of
118 LastOther (LastCall _ (Just k) _ _ _) -> extendBlockSet succs k
120 isLoneBranchZ :: CmmBlock -> Either (BlockId, BlockId) CmmBlock
121 isLoneBranchZ (G.Block id (G.ZLast (G.LastOther (LastBranch target))))
122 | id /= target && not (elemBlockSet id call_succs) = Left (id,target)
123 isLoneBranchZ other = Right other
124 -- An infinite loop is not a link in a branch chain!
126 maybeReplaceLabels :: (Last -> Bool) -> BlockEnv BlockId -> CmmGraph -> CmmGraph
127 maybeReplaceLabels lpred env =
128 replace_eid . G.map_nodes id middle last
130 replace_eid (G.LGraph eid blocks) = G.LGraph (lookup eid) blocks
131 middle = mapExpDeepMiddle exp
132 last l = if lpred l then mapExpDeepLast exp (last' l) else l
133 last' (LastBranch bid) = LastBranch (lookup bid)
134 last' (LastCondBranch p t f) = LastCondBranch p (lookup t) (lookup f)
135 last' (LastSwitch e arms) = LastSwitch e (map (liftM lookup) arms)
136 last' (LastCall t k a res r) = LastCall t (liftM lookup k) a res r
137 exp (CmmLit (CmmBlock bid)) = CmmLit (CmmBlock (lookup bid))
138 exp (CmmStackSlot (CallArea (Young id)) i) =
139 CmmStackSlot (CallArea (Young (lookup id))) i
141 lookup id = fmap lookup (lookupBlockEnv env id) `orElse` id
143 replaceLabelsZ :: BlockEnv BlockId -> CmmGraph -> CmmGraph
144 replaceLabelsZ = maybeReplaceLabels (const True)
146 -- replaceBranchLabels :: BlockEnv BlockId -> CmmGraph -> CmmGraph
147 -- replaceBranchLabels env g@(LGraph _ _) = maybeReplaceLabels lpred env g
148 -- where lpred (LastBranch _) = True
151 replaceBranches :: BlockEnv BlockId -> CmmGraph -> CmmGraph
152 replaceBranches env g = map_nodes id id last g
154 last (LastBranch id) = LastBranch (lookup id)
155 last (LastCondBranch e ti fi) = LastCondBranch e (lookup ti) (lookup fi)
156 last (LastSwitch e tbl) = LastSwitch e (map (fmap lookup) tbl)
157 last l@(LastCall {}) = l
158 lookup id = fmap lookup (lookupBlockEnv env id) `orElse` id
160 ----------------------------------------------------------------
161 -- Build a map from a block to its set of predecessors. Very useful.
162 predMap :: G.LastNode l => G.LGraph m l -> BlockEnv BlockSet
163 predMap g = G.fold_blocks add_preds emptyBlockEnv g -- find the back edges
164 where add_preds b env = foldl (add b) env (G.succs b)
165 add (G.Block bid _) env b' =
166 extendBlockEnv env b' $
167 extendBlockSet (lookupBlockEnv env b' `orElse` emptyBlockSet) bid
168 ----------------------------------------------------------------
169 -- If a block B branches to a label L, L is not the entry block,
170 -- and L has no other predecessors,
171 -- then we can splice the block starting with L onto the end of B.
172 -- Because this optimization can be inhibited by unreachable blocks,
173 -- we first take a pass to drops unreachable blocks.
174 -- Order matters, so we work bottom up (reverse postorder DFS).
176 -- To ensure correctness, we have to make sure that the BlockId of the block
177 -- we are about to eliminate is not named in another instruction.
179 -- Note: This optimization does _not_ subsume branch chain elimination.
180 blockConcatZ :: Tx CmmGraph
181 blockConcatZ = removeUnreachableBlocksZ `seqTx` blockConcatZ'
182 blockConcatZ' :: Tx CmmGraph
183 blockConcatZ' g@(G.LGraph eid blocks) =
184 tx $ replaceLabelsZ concatMap $ G.LGraph eid blocks'
185 where (changed, blocks', concatMap) =
186 foldr maybe_concat (False, blocks, emptyBlockEnv) $ G.postorder_dfs g
187 maybe_concat b@(G.Block bid _) (changed, blocks', concatMap) =
188 let unchanged = (changed, extendBlockEnv blocks' bid b, concatMap)
189 in case G.goto_end $ G.unzip b of
190 (h, G.LastOther (LastBranch b')) ->
191 if canConcatWith b' then
192 (True, extendBlockEnv blocks' bid $ splice blocks' h b',
193 extendBlockEnv concatMap b' bid)
196 num_preds bid = liftM sizeBlockSet (lookupBlockEnv backEdges bid) `orElse` 0
197 canConcatWith b' = b' /= eid && num_preds b' == 1
198 backEdges = predMap g
199 splice blocks' h bid' =
200 case lookupBlockEnv blocks' bid' of
201 Just (G.Block _ t) -> G.zip $ G.ZBlock h t
202 Nothing -> panic "unknown successor block"
203 tx = if changed then aTx else noTx
204 ----------------------------------------------------------------
205 mkClosureBlockEnv :: [(BlockId, BlockId)] -> BlockEnv BlockId
206 mkClosureBlockEnv blocks = mkBlockEnv $ map follow blocks
207 where singleEnv = mkBlockEnv blocks
208 follow (id, next) = (id, endChain id next)
209 endChain orig id = case lookupBlockEnv singleEnv id of
210 Just id' | id /= orig -> endChain orig id'
212 mkClosureBlockEnvZ :: [(BlockId, BlockId)] -> BlockEnv BlockId
213 mkClosureBlockEnvZ blocks = mkBlockEnv $ map follow blocks
214 where singleEnv = mkBlockEnv blocks
215 follow (id, next) = (id, endChain id next)
216 endChain orig id = case lookupBlockEnv singleEnv id of
217 Just id' | id /= orig -> endChain orig id'
219 ----------------------------------------------------------------
220 removeUnreachableBlocksZ :: Tx CmmGraph
221 removeUnreachableBlocksZ g@(G.LGraph id blocks) =
222 if length blocks' < sizeBEnv blocks then aTx $ G.of_block_list id blocks'
224 where blocks' = G.postorder_dfs g