Fix Haddock errors.
[ghc.git] / compiler / cmm / CmmContFlowOpt.hs
1
2 module CmmContFlowOpt
3 ( runCmmOpts, cmmCfgOpts, cmmCfgOptsZ
4 , branchChainElimZ, removeUnreachableBlocksZ, predMap
5 , replaceLabelsZ
6 )
7 where
8
9 import BlockId
10 import Cmm
11 import CmmTx
12 import qualified ZipCfg as G
13 import ZipCfgCmmRep
14
15 import Maybes
16 import Monad
17 import Panic
18 import Prelude hiding (unzip, zip)
19 import Util
20 import UniqFM
21
22 ------------------------------------
23 mapProcs :: Tx (GenCmmTop d h s) -> Tx (GenCmm d h s)
24 mapProcs f (Cmm tops) = fmap Cmm (mapTx f tops)
25
26
27 ------------------------------------
28 cmmCfgOpts :: Tx (ListGraph CmmStmt)
29 cmmCfgOptsZ :: Tx CmmGraph
30
31 cmmCfgOpts = branchChainElim -- boring, but will get more exciting later
32 cmmCfgOptsZ =
33 branchChainElimZ `seqTx` blockConcatZ `seqTx` removeUnreachableBlocksZ
34 -- Here branchChainElim can ultimately be replaced
35 -- with a more exciting combination of optimisations
36
37 runCmmOpts :: Tx g -> Tx (GenCmm d h g)
38 runCmmOpts opt = mapProcs (optGraph opt)
39
40 optGraph :: Tx g -> Tx (GenCmmTop d h g)
41 optGraph _ top@(CmmData {}) = noTx top
42 optGraph opt (CmmProc info lbl formals g) = fmap (CmmProc info lbl formals) (opt g)
43
44 ----------------------------------------------------------------
45 branchChainElim :: Tx (ListGraph CmmStmt)
46 -- Remove any basic block of the form L: goto L',
47 -- and replace L with L' everywhere else
48 branchChainElim (ListGraph blocks)
49 | null lone_branch_blocks -- No blocks to remove
50 = noTx (ListGraph blocks)
51 | otherwise
52 = aTx (ListGraph new_blocks)
53 where
54 (lone_branch_blocks, others) = partitionWith isLoneBranch blocks
55 new_blocks = map (replaceLabels env) others
56 env = mkClosureBlockEnv lone_branch_blocks
57
58 isLoneBranch :: CmmBasicBlock -> Either (BlockId, BlockId) CmmBasicBlock
59 isLoneBranch (BasicBlock id [CmmBranch target]) | id /= target = Left (id, target)
60 isLoneBranch other_block = Right other_block
61 -- An infinite loop is not a link in a branch chain!
62
63 replaceLabels :: BlockEnv BlockId -> CmmBasicBlock -> CmmBasicBlock
64 replaceLabels env (BasicBlock id stmts)
65 = BasicBlock id (map replace stmts)
66 where
67 replace (CmmBranch id) = CmmBranch (lookup id)
68 replace (CmmCondBranch e id) = CmmCondBranch e (lookup id)
69 replace (CmmSwitch e tbl) = CmmSwitch e (map (fmap lookup) tbl)
70 replace other_stmt = other_stmt
71
72 lookup id = lookupBlockEnv env id `orElse` id
73 ----------------------------------------------------------------
74 branchChainElimZ :: Tx CmmGraph
75 -- Remove any basic block of the form L: goto L',
76 -- and replace L with L' everywhere else
77 branchChainElimZ g@(G.LGraph eid _)
78 | null lone_branch_blocks -- No blocks to remove
79 = noTx g
80 | otherwise
81 = aTx $ replaceLabelsZ env $ G.of_block_list eid (self_branches ++ others)
82 where
83 (lone_branch_blocks, others) = partitionWith isLoneBranchZ (G.to_block_list g)
84 env = mkClosureBlockEnv lone_branch_blocks
85 self_branches =
86 let loop_to (id, _) =
87 if lookup id == id then
88 Just (G.Block id (G.ZLast (G.mkBranchNode id)))
89 else
90 Nothing
91 in mapMaybe loop_to lone_branch_blocks
92 lookup id = lookupBlockEnv env id `orElse` id
93
94 isLoneBranchZ :: CmmBlock -> Either (BlockId, BlockId) CmmBlock
95 isLoneBranchZ (G.Block id (G.ZLast (G.LastOther (LastBranch target))))
96 | id /= target = Left (id,target)
97 isLoneBranchZ other = Right other
98 -- An infinite loop is not a link in a branch chain!
99
100 replaceLabelsZ :: BlockEnv BlockId -> CmmGraph -> CmmGraph
101 replaceLabelsZ env = replace_eid . G.map_nodes id id last
102 where
103 replace_eid (G.LGraph eid blocks) = G.LGraph (lookup eid) blocks
104 last (LastBranch id) = LastBranch (lookup id)
105 last (LastCondBranch e ti fi) = LastCondBranch e (lookup ti) (lookup fi)
106 last (LastSwitch e tbl) = LastSwitch e (map (fmap lookup) tbl)
107 last (LastCall tgt (Just id)) = LastCall tgt (Just $ lookup id)
108 last exit_jump_return = exit_jump_return
109 lookup id = lookupBlockEnv env id `orElse` id
110
111 ----------------------------------------------------------------
112 -- Build a map from a block to its set of predecessors. Very useful.
113 predMap :: G.LastNode l => G.LGraph m l -> BlockEnv BlockSet
114 predMap g = G.fold_blocks add_preds emptyBlockEnv g -- find the back edges
115 where add_preds b env = foldl (add b) env (G.succs b)
116 add (G.Block bid _) env b' =
117 extendBlockEnv env b' $
118 extendBlockSet (lookupBlockEnv env b' `orElse` emptyBlockSet) bid
119 ----------------------------------------------------------------
120 blockConcatZ :: Tx CmmGraph
121 -- If a block B branches to a label L, and L has no other predecessors,
122 -- then we can splice the block starting with L onto the end of B.
123 -- Because this optmization can be inhibited by unreachable blocks,
124 -- we bundle it with a pass that drops unreachable blocks.
125 -- Order matters, so we work bottom up (reverse postorder DFS).
126 -- Note: This optimization does _not_ subsume branch chain elimination.
127 blockConcatZ = removeUnreachableBlocksZ `seqTx` blockConcatZ'
128 blockConcatZ' :: Tx CmmGraph
129 blockConcatZ' g@(G.LGraph eid blocks) = tx $ G.LGraph eid blocks'
130 where (changed, blocks') = foldr maybe_concat (False, blocks) $ G.postorder_dfs g
131 maybe_concat b@(G.Block bid _) (changed, blocks') =
132 let unchanged = (changed, extendBlockEnv blocks' bid b)
133 in case G.goto_end $ G.unzip b of
134 (h, G.LastOther (LastBranch b')) ->
135 if num_preds b' == 1 then
136 (True, extendBlockEnv blocks' bid $ splice blocks' h b')
137 else unchanged
138 _ -> unchanged
139 num_preds bid = liftM sizeBlockSet (lookupBlockEnv backEdges bid) `orElse` 0
140 backEdges = predMap g
141 splice blocks' h bid' =
142 case lookupBlockEnv blocks' bid' of
143 Just (G.Block _ t) -> G.zip $ G.ZBlock h t
144 Nothing -> panic "unknown successor block"
145 tx = if changed then aTx else noTx
146 ----------------------------------------------------------------
147 mkClosureBlockEnv :: [(BlockId, BlockId)] -> BlockEnv BlockId
148 mkClosureBlockEnv blocks = mkBlockEnv $ map follow blocks
149 where singleEnv = mkBlockEnv blocks
150 follow (id, next) = (id, endChain id next)
151 endChain orig id = case lookupBlockEnv singleEnv id of
152 Just id' | id /= orig -> endChain orig id'
153 _ -> id
154 ----------------------------------------------------------------
155 removeUnreachableBlocksZ :: Tx CmmGraph
156 removeUnreachableBlocksZ g@(G.LGraph id blocks) =
157 if length blocks' < sizeUFM blocks then aTx $ G.of_block_list id blocks'
158 else noTx g
159 where blocks' = G.postorder_dfs g