2 {-# OPTIONS_GHC -fno-warn-warnings-deprecations -fno-warn-incomplete-patterns #-}
5 ( runCmmOpts, oldCmmCfgOpts, cmmCfgOpts
6 , branchChainElim, removeUnreachableBlocks, predMap
7 , replaceLabels, replaceBranches, runCmmContFlowOpts
15 import qualified OldCmm as Old
21 import Prelude hiding (succ, unzip, zip)
24 ------------------------------------
25 runCmmContFlowOpts :: Cmm -> Cmm
26 runCmmContFlowOpts prog = runCmmOpts cmmCfgOpts prog
28 oldCmmCfgOpts :: Old.ListGraph Old.CmmStmt -> Old.ListGraph Old.CmmStmt
29 cmmCfgOpts :: CmmGraph -> CmmGraph
31 oldCmmCfgOpts = oldBranchChainElim -- boring, but will get more exciting later
33 removeUnreachableBlocks . blockConcat . branchChainElim
34 -- Here branchChainElim can ultimately be replaced
35 -- with a more exciting combination of optimisations
37 runCmmOpts :: (g -> g) -> GenCmm d h g -> GenCmm d h g
38 -- Lifts a transformer on a single graph to one on the whole program
39 runCmmOpts opt = mapProcs (optProc opt)
41 optProc :: (g -> g) -> GenCmmTop d h g -> GenCmmTop d h g
42 optProc _ top@(CmmData {}) = top
43 optProc opt (CmmProc info lbl g) = CmmProc info lbl (opt g)
45 ------------------------------------
46 mapProcs :: (GenCmmTop d h s -> GenCmmTop d h s) -> GenCmm d h s -> GenCmm d h s
47 mapProcs f (Cmm tops) = Cmm (map f tops)
49 ----------------------------------------------------------------
50 oldBranchChainElim :: Old.ListGraph Old.CmmStmt -> Old.ListGraph Old.CmmStmt
51 -- If L is not captured in an instruction, we can remove any
52 -- basic block of the form L: goto L', and replace L with L' everywhere else.
53 -- How does L get captured? In a CallArea.
54 oldBranchChainElim (Old.ListGraph blocks)
55 | null lone_branch_blocks -- No blocks to remove
56 = Old.ListGraph blocks
58 = Old.ListGraph new_blocks
60 (lone_branch_blocks, others) = partitionWith isLoneBranch blocks
61 new_blocks = map (replaceLabels env) others
62 env = mkClosureBlockEnv lone_branch_blocks
64 isLoneBranch :: Old.CmmBasicBlock -> Either (BlockId, BlockId) Old.CmmBasicBlock
65 isLoneBranch (Old.BasicBlock id [Old.CmmBranch target]) | id /= target = Left (id, target)
66 isLoneBranch other_block = Right other_block
67 -- An infinite loop is not a link in a branch chain!
69 replaceLabels :: BlockEnv BlockId -> Old.CmmBasicBlock -> Old.CmmBasicBlock
70 replaceLabels env (Old.BasicBlock id stmts)
71 = Old.BasicBlock id (map replace stmts)
73 replace (Old.CmmBranch id) = Old.CmmBranch (lookup id)
74 replace (Old.CmmCondBranch e id) = Old.CmmCondBranch e (lookup id)
75 replace (Old.CmmSwitch e tbl) = Old.CmmSwitch e (map (fmap lookup) tbl)
76 replace other_stmt = other_stmt
78 lookup id = mapLookup id env `orElse` id
80 ----------------------------------------------------------------
81 branchChainElim :: CmmGraph -> CmmGraph
82 -- Remove any basic block of the form L: goto L',
83 -- and replace L with L' everywhere else,
84 -- unless L is the successor of a call instruction and L'
85 -- is the entry block. You don't want to set the successor
86 -- of a function call to the entry block because there is no good way
87 -- to store both the infotables for the call and from the callee,
88 -- while putting the stack pointer in a consistent place.
90 -- JD isn't quite sure when it's safe to share continuations for different
91 -- function calls -- have to think about where the SP will be,
92 -- so we'll table that problem for now by leaving all call successors alone.
94 | null lone_branch_blocks -- No blocks to remove
97 = replaceLabels env $ ofBlockList (g_entry g) (self_branches ++ others)
99 blocks = toBlockList g
100 (lone_branch_blocks, others) = partitionWith isLoneBranch blocks
101 env = mkClosureBlockEnv lone_branch_blocks
103 let loop_to (id, _) =
104 if lookup id == id then
105 Just $ blockOfNodeList (JustC (CmmEntry id), [], JustC (mkBranchNode id))
108 in mapMaybe loop_to lone_branch_blocks
109 lookup id = mapLookup id env `orElse` id
111 call_succs = foldl add emptyBlockSet blocks
112 where add :: BlockSet -> CmmBlock -> BlockSet
115 (CmmCall _ (Just k) _ _ _) -> setInsert k succs
116 (CmmForeignCall {succ=k}) -> setInsert k succs
118 isLoneBranch :: CmmBlock -> Either (BlockId, BlockId) CmmBlock
119 isLoneBranch block | (JustC (CmmEntry id), [], JustC (CmmBranch target)) <- blockToNodeList block,
120 id /= target && not (setMember id call_succs)
122 isLoneBranch other = Right other
123 -- An infinite loop is not a link in a branch chain!
125 maybeReplaceLabels :: (CmmNode O C -> Bool) -> BlockEnv BlockId -> CmmGraph -> CmmGraph
126 maybeReplaceLabels lpred env =
127 replace_eid . mapGraphNodes (id, middle, last)
129 replace_eid g = g {g_entry = lookup (g_entry g)}
130 lookup id = fmap lookup (mapLookup id env) `orElse` id
132 middle = mapExpDeep exp
133 last l = if lpred l then mapExpDeep exp (last' l) else l
134 last' :: CmmNode O C -> CmmNode O C
135 last' (CmmBranch bid) = CmmBranch (lookup bid)
136 last' (CmmCondBranch p t f) = CmmCondBranch p (lookup t) (lookup f)
137 last' (CmmSwitch e arms) = CmmSwitch e (map (liftM lookup) arms)
138 last' (CmmCall t k a res r) = CmmCall t (liftM lookup k) a res r
139 last' (CmmForeignCall t r a bid u i) = CmmForeignCall t r a (lookup bid) u i
141 exp (CmmLit (CmmBlock bid)) = CmmLit (CmmBlock (lookup bid))
142 exp (CmmStackSlot (CallArea (Young id)) i) = CmmStackSlot (CallArea (Young (lookup id))) i
146 replaceLabels :: BlockEnv BlockId -> CmmGraph -> CmmGraph
147 replaceLabels = maybeReplaceLabels (const True)
149 replaceBranches :: BlockEnv BlockId -> CmmGraph -> CmmGraph
150 replaceBranches env g = mapGraphNodes (id, id, last) g
152 last :: CmmNode O C -> CmmNode O C
153 last (CmmBranch id) = CmmBranch (lookup id)
154 last (CmmCondBranch e ti fi) = CmmCondBranch e (lookup ti) (lookup fi)
155 last (CmmSwitch e tbl) = CmmSwitch e (map (fmap lookup) tbl)
156 last l@(CmmCall {}) = l
157 last l@(CmmForeignCall {}) = l
158 lookup id = fmap lookup (mapLookup id env) `orElse` id
160 ----------------------------------------------------------------
161 -- Build a map from a block to its set of predecessors. Very useful.
162 predMap :: [CmmBlock] -> BlockEnv BlockSet
163 predMap blocks = foldr add_preds mapEmpty blocks -- find the back edges
164 where add_preds block env = foldl (add (entryLabel block)) env (successors block)
166 mapInsert b' (setInsert bid (mapLookup b' env `orElse` setEmpty)) env
167 ----------------------------------------------------------------
168 -- If a block B branches to a label L, L is not the entry block,
169 -- and L has no other predecessors,
170 -- then we can splice the block starting with L onto the end of B.
171 -- Order matters, so we work bottom up (reverse postorder DFS).
172 -- This optimization can be inhibited by unreachable blocks, but
173 -- the reverse postorder DFS returns only reachable blocks.
175 -- To ensure correctness, we have to make sure that the BlockId of the block
176 -- we are about to eliminate is not named in another instruction.
178 -- Note: This optimization does _not_ subsume branch chain elimination.
179 blockConcat :: CmmGraph -> CmmGraph
180 blockConcat g@(CmmGraph {g_entry=eid}) =
181 replaceLabels concatMap $ ofBlockMap (g_entry g) blocks'
182 where blocks = postorderDfs g
183 (blocks', concatMap) =
184 foldr maybe_concat (toBlockMap g, mapEmpty) $ blocks
185 maybe_concat :: CmmBlock -> (LabelMap CmmBlock, LabelMap Label) -> (LabelMap CmmBlock, LabelMap Label)
186 maybe_concat b unchanged@(blocks', concatMap) =
187 let bid = entryLabel b
188 in case blockToNodeList b of
189 (JustC h, m, JustC (CmmBranch b')) ->
190 if canConcatWith b' then
191 (mapInsert bid (splice blocks' h m b') blocks',
192 mapInsert b' bid concatMap)
195 num_preds bid = liftM setSize (mapLookup bid backEdges) `orElse` 0
196 canConcatWith b' = b' /= eid && num_preds b' == 1
197 backEdges = predMap blocks
198 splice :: forall map n e x.
200 map (Block n e x) -> n C O -> [n O O] -> KeyOf map -> Block n C x
201 splice blocks' h m bid' =
202 case mapLookup bid' blocks' of
203 Nothing -> panic "unknown successor block"
204 Just block | (_, m', l') <- blockToNodeList block -> blockOfNodeList (JustC h, (m ++ m'), l')
205 ----------------------------------------------------------------
206 mkClosureBlockEnv :: [(BlockId, BlockId)] -> BlockEnv BlockId
207 mkClosureBlockEnv blocks = mapFromList $ map follow blocks
208 where singleEnv = mapFromList blocks :: BlockEnv BlockId
209 follow (id, next) = (id, endChain id next)
210 endChain orig id = case mapLookup id singleEnv of
211 Just id' | id /= orig -> endChain orig id'
213 ----------------------------------------------------------------
214 removeUnreachableBlocks :: CmmGraph -> CmmGraph
215 removeUnreachableBlocks g =
216 if length blocks < mapSize (toBlockMap g) then ofBlockList (g_entry g) blocks
218 where blocks = postorderDfs g