summaryrefslogtreecommitdiff
path: root/compiler/cmm/Hoopl/Graph.hs
blob: 0142f70c768e89d6f84c6b72924cd623155a866f (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
{-# LANGUAGE BangPatterns #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeFamilies #-}
module Hoopl.Graph
    ( Body
    , Graph
    , Graph'(..)
    , NonLocal(..)
    , addBlock
    , bodyList
    , emptyBody
    , labelsDefined
    , mapGraph
    , mapGraphBlocks
    , revPostorderFrom
    ) where


import GhcPrelude
import Util

import Hoopl.Label
import Hoopl.Block
import Hoopl.Collections

-- | A (possibly empty) collection of closed/closed blocks
type Body n = LabelMap (Block n C C)

-- | @Body@ abstracted over @block@
type Body' block (n :: * -> * -> *) = LabelMap (block n C C)

-------------------------------
-- | Gives access to the anchor points for
-- nonlocal edges as well as the edges themselves
class NonLocal thing where
  entryLabel :: thing C x -> Label   -- ^ The label of a first node or block
  successors :: thing e C -> [Label] -- ^ Gives control-flow successors

instance NonLocal n => NonLocal (Block n) where
  entryLabel (BlockCO f _)   = entryLabel f
  entryLabel (BlockCC f _ _) = entryLabel f

  successors (BlockOC   _ n) = successors n
  successors (BlockCC _ _ n) = successors n


emptyBody :: Body' block n
emptyBody = mapEmpty

bodyList :: Body' block n -> [(Label,block n C C)]
bodyList body = mapToList body

addBlock
    :: (NonLocal block, HasDebugCallStack)
    => block C C -> LabelMap (block C C) -> LabelMap (block C C)
addBlock block body = mapAlter add lbl body
  where
    lbl = entryLabel block
    add Nothing = Just block
    add _ = error $ "duplicate label " ++ show lbl ++ " in graph"


-- ---------------------------------------------------------------------------
-- Graph

-- | A control-flow graph, which may take any of four shapes (O/O,
-- O/C, C/O, C/C).  A graph open at the entry has a single,
-- distinguished, anonymous entry point; if a graph is closed at the
-- entry, its entry point(s) are supplied by a context.
type Graph = Graph' Block

-- | @Graph'@ is abstracted over the block type, so that we can build
-- graphs of annotated blocks for example (Compiler.Hoopl.Dataflow
-- needs this).
data Graph' block (n :: * -> * -> *) e x where
  GNil  :: Graph' block n O O
  GUnit :: block n O O -> Graph' block n O O
  GMany :: MaybeO e (block n O C)
        -> Body' block n
        -> MaybeO x (block n C O)
        -> Graph' block n e x


-- -----------------------------------------------------------------------------
-- Mapping over graphs

-- | Maps over all nodes in a graph.
mapGraph :: (forall e x. n e x -> n' e x) -> Graph n e x -> Graph n' e x
mapGraph f = mapGraphBlocks (mapBlock f)

-- | Function 'mapGraphBlocks' enables a change of representation of blocks,
-- nodes, or both.  It lifts a polymorphic block transform into a polymorphic
-- graph transform.  When the block representation stabilizes, a similar
-- function should be provided for blocks.
mapGraphBlocks :: forall block n block' n' e x .
                  (forall e x . block n e x -> block' n' e x)
               -> (Graph' block n e x -> Graph' block' n' e x)

mapGraphBlocks f = map
  where map :: Graph' block n e x -> Graph' block' n' e x
        map GNil = GNil
        map (GUnit b) = GUnit (f b)
        map (GMany e b x) = GMany (fmap f e) (mapMap f b) (fmap f x)

-- -----------------------------------------------------------------------------
-- Extracting Labels from graphs

labelsDefined :: forall block n e x . NonLocal (block n) => Graph' block n e x
              -> LabelSet
labelsDefined GNil      = setEmpty
labelsDefined (GUnit{}) = setEmpty
labelsDefined (GMany _ body x) = mapFoldlWithKey addEntry (exitLabel x) body
  where addEntry :: forall a. LabelSet -> ElemOf LabelSet -> a -> LabelSet
        addEntry labels label _ = setInsert label labels
        exitLabel :: MaybeO x (block n C O) -> LabelSet
        exitLabel NothingO  = setEmpty
        exitLabel (JustO b) = setSingleton (entryLabel b)


----------------------------------------------------------------

-- | Returns a list of blocks reachable from the provided Labels in the reverse
-- postorder.
--
-- This is the most important traversal over this data structure.  It drops
-- unreachable code and puts blocks in an order that is good for solving forward
-- dataflow problems quickly.  The reverse order is good for solving backward
-- dataflow problems quickly.  The forward order is also reasonably good for
-- emitting instructions, except that it will not usually exploit Forrest
-- Baskett's trick of eliminating the unconditional branch from a loop.  For
-- that you would need a more serious analysis, probably based on dominators, to
-- identify loop headers.
--
-- For forward analyses we want reverse postorder visitation, consider:
-- @
--      A -> [B,C]
--      B -> D
--      C -> D
-- @
-- Postorder: [D, C, B, A] (or [D, B, C, A])
-- Reverse postorder: [A, B, C, D] (or [A, C, B, D])
-- This matters for, e.g., forward analysis, because we want to analyze *both*
-- B and C before we analyze D.
revPostorderFrom
  :: forall block.  (NonLocal block)
  => LabelMap (block C C) -> Label -> [block C C]
revPostorderFrom graph start = go start_worklist setEmpty []
  where
    start_worklist = lookup_for_descend start Nil

    -- To compute the postorder we need to "visit" a block (mark as done)
    -- *after* visiting all its successors. So we need to know whether we
    -- already processed all successors of each block (and @NonLocal@ allows
    -- arbitrary many successors). So we use an explicit stack with an extra bit
    -- of information:
    -- * @ConsTodo@ means to explore the block if it wasn't visited before
    -- * @ConsMark@ means that all successors were already done and we can add
    --   the block to the result.
    --
    -- NOTE: We add blocks to the result list in postorder, but we *prepend*
    -- them (i.e., we use @(:)@), which means that the final list is in reverse
    -- postorder.
    go :: DfsStack (block C C) -> LabelSet -> [block C C] -> [block C C]
    go Nil                      !_           !result = result
    go (ConsMark block rest)    !wip_or_done !result =
        go rest wip_or_done (block : result)
    go (ConsTodo block rest)    !wip_or_done !result
        | entryLabel block `setMember` wip_or_done = go rest wip_or_done result
        | otherwise =
            let new_worklist =
                    foldr lookup_for_descend
                          (ConsMark block rest)
                          (successors block)
            in go new_worklist (setInsert (entryLabel block) wip_or_done) result

    lookup_for_descend :: Label -> DfsStack (block C C) -> DfsStack (block C C)
    lookup_for_descend label wl
      | Just b <- mapLookup label graph = ConsTodo b wl
      | otherwise =
           error $ "Label that doesn't have a block?! " ++ show label

data DfsStack a = ConsTodo a (DfsStack a) | ConsMark a (DfsStack a) | Nil