{-# LANGUAGE GADTs #-}
module GHC.Cmm.ContFlowOpt
    ( cmmCfgOpts
    , cmmCfgOptsProc
    , removeUnreachableBlocksProc
    , replaceLabels
    )
where

import GHC.Prelude hiding (succ, unzip, zip)

import GHC.Cmm.Dataflow.Block hiding (blockConcat)
import GHC.Cmm.Dataflow.Graph
import GHC.Cmm.Dataflow.Label
import GHC.Cmm.BlockId
import GHC.Cmm
import GHC.Cmm.Utils
import GHC.Cmm.Switch (mapSwitchTargets, switchTargetsToList)
import GHC.Data.Maybe
import GHC.Platform
import GHC.Utils.Misc
import GHC.Utils.Outputable
import GHC.Utils.Panic

import Control.Monad


-- Note [What is shortcutting]
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~
-- Consider this Cmm code:
--
-- L1: ...
--     goto L2;
-- L2: goto L3;
-- L3: ...
--
-- Here L2 is an empty block and contains only an unconditional branch
-- to L3. In this situation any block that jumps to L2 can jump
-- directly to L3:
--
-- L1: ...
--     goto L3;
-- L2: goto L3;
-- L3: ...
--
-- In this situation we say that we shortcut L2 to L3. One of
-- consequences of shortcutting is that some blocks of code may become
-- unreachable (in the example above this is true for L2).


-- Note [Control-flow optimisations]
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-- This optimisation does three things:
--
--   - If a block finishes in an unconditional branch to another block
--     and that is the only jump to that block we concatenate the
--     destination block at the end of the current one.
--
--   - If a block finishes in a call whose continuation block is a
--     goto, then we can shortcut the destination, making the
--     continuation block the destination of the goto - but see Note
--     [Shortcut call returns].
--
--   - For any block that is not a call we try to shortcut the
--     destination(s). Additionally, if a block ends with a
--     conditional branch we try to invert the condition.
--
-- Blocks are processed using postorder DFS traversal. A side effect
-- of determining traversal order with a graph search is elimination
-- of any blocks that are unreachable.
--
-- Transformations are improved by working from the end of the graph
-- towards the beginning, because we may be able to perform many
-- shortcuts in one go.


-- Note [Shortcut call returns]
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-- We are going to maintain the "current" graph (LabelMap CmmBlock) as
-- we go, and also a mapping from BlockId to BlockId, representing
-- continuation labels that we have renamed.  This latter mapping is
-- important because we might shortcut a CmmCall continuation.  For
-- example:
--
--    Sp[0] = L
--    call g returns to L
--    L: goto M
--    M: ...
--
-- So when we shortcut the L block, we need to replace not only
-- the continuation of the call, but also references to L in the
-- code (e.g. the assignment Sp[0] = L):
--
--    Sp[0] = M
--    call g returns to M
--    M: ...
--
-- So we keep track of which labels we have renamed and apply the mapping
-- at the end with replaceLabels.


-- Note [Shortcut call returns and proc-points]
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-- Consider this code that you might get from a recursive
-- let-no-escape:
--
--       goto L1
--      L1:
--       if (Hp > HpLim) then L2 else L3
--      L2:
--       call stg_gc_noregs returns to L4
--      L4:
--       goto L1
--      L3:
--       ...
--       goto L1
--
-- Then the control-flow optimiser shortcuts L4.  But that turns L1
-- into the call-return proc point, and every iteration of the loop
-- has to shuffle variables to and from the stack.  So we must *not*
-- shortcut L4.
--
-- Moreover not shortcutting call returns is probably fine.  If L4 can
-- concat with its branch target then it will still do so.  And we
-- save some compile time because we don't have to traverse all the
-- code in replaceLabels.
--
-- However, we probably do want to do this if we are splitting proc
-- points, because L1 will be a proc-point anyway, so merging it with
-- L4 reduces the number of proc points.  Unfortunately recursive
-- let-no-escapes won't generate very good code with proc-point
-- splitting on - we should probably compile them to explicitly use
-- the native calling convention instead.

cmmCfgOpts :: Bool -> CmmGraph -> CmmGraph
cmmCfgOpts :: Bool
-> GenGenCmmGraph LabelMap CmmNode
-> GenGenCmmGraph LabelMap CmmNode
cmmCfgOpts Bool
split GenGenCmmGraph LabelMap CmmNode
g = (GenGenCmmGraph LabelMap CmmNode, LabelMap Label)
-> GenGenCmmGraph LabelMap CmmNode
forall a b. (a, b) -> a
fst (Bool
-> GenGenCmmGraph LabelMap CmmNode
-> (GenGenCmmGraph LabelMap CmmNode, LabelMap Label)
blockConcat Bool
split GenGenCmmGraph LabelMap CmmNode
g)

cmmCfgOptsProc :: Bool -> CmmDecl -> CmmDecl
cmmCfgOptsProc :: Bool -> CmmDecl -> CmmDecl
cmmCfgOptsProc Bool
split (CmmProc GenCmmTopInfo LabelMap
info CLabel
lbl [GlobalRegUse]
live GenGenCmmGraph LabelMap CmmNode
g) = GenCmmTopInfo LabelMap
-> CLabel
-> [GlobalRegUse]
-> GenGenCmmGraph LabelMap CmmNode
-> CmmDecl
forall d h g.
h -> CLabel -> [GlobalRegUse] -> g -> GenCmmDecl d h g
CmmProc GenCmmTopInfo LabelMap
info' CLabel
lbl [GlobalRegUse]
live GenGenCmmGraph LabelMap CmmNode
g'
    where (GenGenCmmGraph LabelMap CmmNode
g', LabelMap Label
env) = Bool
-> GenGenCmmGraph LabelMap CmmNode
-> (GenGenCmmGraph LabelMap CmmNode, LabelMap Label)
blockConcat Bool
split GenGenCmmGraph LabelMap CmmNode
g
          info' :: GenCmmTopInfo LabelMap
info' = GenCmmTopInfo LabelMap
info{ info_tbls = new_info_tbls }
          new_info_tbls :: LabelMap CmmInfoTable
new_info_tbls = [(Label, CmmInfoTable)] -> LabelMap CmmInfoTable
forall v. [(Label, v)] -> LabelMap v
mapFromList (((Label, CmmInfoTable) -> (Label, CmmInfoTable))
-> [(Label, CmmInfoTable)] -> [(Label, CmmInfoTable)]
forall a b. (a -> b) -> [a] -> [b]
map (Label, CmmInfoTable) -> (Label, CmmInfoTable)
upd_info (LabelMap CmmInfoTable -> [(Label, CmmInfoTable)]
forall b. LabelMap b -> [(Label, b)]
mapToList (GenCmmTopInfo LabelMap -> LabelMap CmmInfoTable
forall (f :: * -> *). GenCmmTopInfo f -> f CmmInfoTable
info_tbls GenCmmTopInfo LabelMap
info)))

          -- If we changed any labels, then we have to update the info tables
          -- too, except for the top-level info table because that might be
          -- referred to by other procs.
          upd_info :: (Label, CmmInfoTable) -> (Label, CmmInfoTable)
upd_info (Label
k,CmmInfoTable
info)
             | Just Label
k' <- Label -> LabelMap Label -> Maybe Label
forall a. Label -> LabelMap a -> Maybe a
mapLookup Label
k LabelMap Label
env
             = (Label
k', if Label
k' Label -> Label -> Bool
forall a. Eq a => a -> a -> Bool
== GenGenCmmGraph LabelMap CmmNode -> Label
forall (s :: * -> *) (n :: Extensibility -> Extensibility -> *).
GenGenCmmGraph s n -> Label
g_entry GenGenCmmGraph LabelMap CmmNode
g'
                       then CmmInfoTable
info
                       else CmmInfoTable
info{ cit_lbl = infoTblLbl k' })
             | Bool
otherwise
             = (Label
k,CmmInfoTable
info)
cmmCfgOptsProc Bool
_ CmmDecl
top = CmmDecl
top


blockConcat :: Bool -> CmmGraph -> (CmmGraph, LabelMap BlockId)
blockConcat :: Bool
-> GenGenCmmGraph LabelMap CmmNode
-> (GenGenCmmGraph LabelMap CmmNode, LabelMap Label)
blockConcat Bool
splitting_procs g :: GenGenCmmGraph LabelMap CmmNode
g@CmmGraph { g_entry :: forall (s :: * -> *) (n :: Extensibility -> Extensibility -> *).
GenGenCmmGraph s n -> Label
g_entry = Label
entry_id }
  = (LabelMap Label
-> GenGenCmmGraph LabelMap CmmNode
-> GenGenCmmGraph LabelMap CmmNode
replaceLabels LabelMap Label
shortcut_map (GenGenCmmGraph LabelMap CmmNode
 -> GenGenCmmGraph LabelMap CmmNode)
-> GenGenCmmGraph LabelMap CmmNode
-> GenGenCmmGraph LabelMap CmmNode
forall a b. (a -> b) -> a -> b
$ Label -> LabelMap CmmBlock -> GenGenCmmGraph LabelMap CmmNode
ofBlockMap Label
new_entry LabelMap CmmBlock
new_blocks, LabelMap Label
shortcut_map')
  where
     -- We might be able to shortcut the entry BlockId itself.
     -- Remember to update the shortcut_map, since we also have to
     -- update the info_tbls mapping now.
     (Label
new_entry, LabelMap Label
shortcut_map')
       | Just CmmBlock
entry_blk <- Label -> LabelMap CmmBlock -> Maybe CmmBlock
forall a. Label -> LabelMap a -> Maybe a
mapLookup Label
entry_id LabelMap CmmBlock
new_blocks
       , Just Label
dest      <- CmmBlock -> Maybe Label
canShortcut CmmBlock
entry_blk
       = (Label
dest, Label -> Label -> LabelMap Label -> LabelMap Label
forall v. Label -> v -> LabelMap v -> LabelMap v
mapInsert Label
entry_id Label
dest LabelMap Label
shortcut_map)
       | Bool
otherwise
       = (Label
entry_id, LabelMap Label
shortcut_map)

     -- blocks are sorted in reverse postorder, but we want to go from the exit
     -- towards beginning, so we use foldr below.
     blocks :: [CmmBlock]
blocks = GenGenCmmGraph LabelMap CmmNode -> [CmmBlock]
revPostorder GenGenCmmGraph LabelMap CmmNode
g
     blockmap :: LabelMap CmmBlock
blockmap = (LabelMap CmmBlock -> CmmBlock -> LabelMap CmmBlock)
-> LabelMap CmmBlock -> [CmmBlock] -> LabelMap CmmBlock
forall b a. (b -> a -> b) -> b -> [a] -> b
forall (t :: * -> *) b a.
Foldable t =>
(b -> a -> b) -> b -> t a -> b
foldl' ((CmmBlock -> LabelMap CmmBlock -> LabelMap CmmBlock)
-> LabelMap CmmBlock -> CmmBlock -> LabelMap CmmBlock
forall a b c. (a -> b -> c) -> b -> a -> c
flip CmmBlock -> LabelMap CmmBlock -> LabelMap CmmBlock
forall (block :: Extensibility -> Extensibility -> *).
(NonLocal block, HasDebugCallStack) =>
block 'Closed 'Closed
-> LabelMap (block 'Closed 'Closed)
-> LabelMap (block 'Closed 'Closed)
addBlock) LabelMap CmmBlock
forall (block :: (Extensibility -> Extensibility -> *)
                 -> Extensibility -> Extensibility -> *)
       (n :: Extensibility -> Extensibility -> *).
Body' LabelMap block n
emptyBody [CmmBlock]
blocks

     -- Accumulator contains three components:
     --  * map of blocks in a graph
     --  * map of shortcut labels. See Note [Shortcut call returns]
     --  * map containing number of predecessors for each block. We discard
     --    it after we process all blocks.
     (LabelMap CmmBlock
new_blocks, LabelMap Label
shortcut_map, LabelMap Int
_) =
           (CmmBlock
 -> (LabelMap CmmBlock, LabelMap Label, LabelMap Int)
 -> (LabelMap CmmBlock, LabelMap Label, LabelMap Int))
-> (LabelMap CmmBlock, LabelMap Label, LabelMap Int)
-> [CmmBlock]
-> (LabelMap CmmBlock, LabelMap Label, LabelMap Int)
forall a b. (a -> b -> b) -> b -> [a] -> b
forall (t :: * -> *) a b.
Foldable t =>
(a -> b -> b) -> b -> t a -> b
foldr CmmBlock
-> (LabelMap CmmBlock, LabelMap Label, LabelMap Int)
-> (LabelMap CmmBlock, LabelMap Label, LabelMap Int)
maybe_concat (LabelMap CmmBlock
blockmap, LabelMap Label
forall v. LabelMap v
mapEmpty, LabelMap Int
initialBackEdges) [CmmBlock]
blocks

     -- Map of predecessors for initial graph. We increase number of
     -- predecessors for entry block by one to denote that it is
     -- target of a jump, even if no block in the current graph jumps
     -- to it.
     initialBackEdges :: LabelMap Int
initialBackEdges = Label -> LabelMap Int -> LabelMap Int
incPreds Label
entry_id ([CmmBlock] -> LabelMap Int
predMap [CmmBlock]
blocks)

     maybe_concat :: CmmBlock
                  -> (LabelMap CmmBlock, LabelMap BlockId, LabelMap Int)
                  -> (LabelMap CmmBlock, LabelMap BlockId, LabelMap Int)
     maybe_concat :: CmmBlock
-> (LabelMap CmmBlock, LabelMap Label, LabelMap Int)
-> (LabelMap CmmBlock, LabelMap Label, LabelMap Int)
maybe_concat CmmBlock
block (!LabelMap CmmBlock
blocks, !LabelMap Label
shortcut_map, !LabelMap Int
backEdges)
        -- If:
        --   (1) current block ends with unconditional branch to b' and
        --   (2) it has exactly one predecessor (namely, current block)
        --
        -- Then:
        --   (1) append b' block at the end of current block
        --   (2) remove b' from the map of blocks
        --   (3) remove information about b' from predecessors map
        --
        -- Since we know that the block has only one predecessor we call
        -- mapDelete directly instead of calling decPreds.
        --
        -- Note that we always maintain an up-to-date list of predecessors, so
        -- we can ignore the contents of shortcut_map
        | CmmBranch Label
b' <- CmmNode 'Open 'Closed
last
        , Label -> Bool
hasOnePredecessor Label
b'
        , Just CmmBlock
blk' <- Label -> LabelMap CmmBlock -> Maybe CmmBlock
forall a. Label -> LabelMap a -> Maybe a
mapLookup Label
b' LabelMap CmmBlock
blocks
        = let bid' :: Label
bid' = CmmBlock -> Label
forall (x :: Extensibility). Block CmmNode 'Closed x -> Label
forall (thing :: Extensibility -> Extensibility -> *)
       (x :: Extensibility).
NonLocal thing =>
thing 'Closed x -> Label
entryLabel CmmBlock
blk'
          in ( Label -> LabelMap CmmBlock -> LabelMap CmmBlock
forall v. Label -> LabelMap v -> LabelMap v
mapDelete Label
bid' (LabelMap CmmBlock -> LabelMap CmmBlock)
-> LabelMap CmmBlock -> LabelMap CmmBlock
forall a b. (a -> b) -> a -> b
$ Label -> CmmBlock -> LabelMap CmmBlock -> LabelMap CmmBlock
forall v. Label -> v -> LabelMap v -> LabelMap v
mapInsert Label
bid (Block CmmNode 'Closed 'Open -> CmmBlock -> CmmBlock
splice Block CmmNode 'Closed 'Open
head CmmBlock
blk') LabelMap CmmBlock
blocks
             , LabelMap Label
shortcut_map
             , Label -> LabelMap Int -> LabelMap Int
forall v. Label -> LabelMap v -> LabelMap v
mapDelete Label
b' LabelMap Int
backEdges )

        -- If:
        --   (1) we are splitting proc points (see Note
        --       [Shortcut call returns and proc-points]) and
        --   (2) current block is a CmmCall or CmmForeignCall with
        --       continuation b' and
        --   (3) we can shortcut that continuation to dest
        -- Then:
        --   (1) we change continuation to point to b'
        --   (2) create mapping from b' to dest
        --   (3) increase number of predecessors of dest by 1
        --   (4) decrease number of predecessors of b' by 1
        --
        -- Later we will use replaceLabels to substitute all occurrences of b'
        -- with dest.
        | Bool
splitting_procs
        , Just Label
b'   <- CmmNode 'Open 'Closed -> Maybe Label
callContinuation_maybe CmmNode 'Open 'Closed
last
        , Just CmmBlock
blk' <- Label -> LabelMap CmmBlock -> Maybe CmmBlock
forall a. Label -> LabelMap a -> Maybe a
mapLookup Label
b' LabelMap CmmBlock
blocks
        , Just Label
dest <- CmmBlock -> Maybe Label
canShortcut CmmBlock
blk'
        = ( Label -> CmmBlock -> LabelMap CmmBlock -> LabelMap CmmBlock
forall v. Label -> v -> LabelMap v -> LabelMap v
mapInsert Label
bid (Block CmmNode 'Closed 'Open -> CmmNode 'Open 'Closed -> CmmBlock
forall (n :: Extensibility -> Extensibility -> *)
       (e :: Extensibility).
Block n e 'Open -> n 'Open 'Closed -> Block n e 'Closed
blockJoinTail Block CmmNode 'Closed 'Open
head (Label -> CmmNode 'Open 'Closed
update_cont Label
dest)) LabelMap CmmBlock
blocks
          , Label -> Label -> LabelMap Label -> LabelMap Label
forall v. Label -> v -> LabelMap v -> LabelMap v
mapInsert Label
b' Label
dest LabelMap Label
shortcut_map
          , Label -> LabelMap Int -> LabelMap Int
decPreds Label
b' (LabelMap Int -> LabelMap Int) -> LabelMap Int -> LabelMap Int
forall a b. (a -> b) -> a -> b
$ Label -> LabelMap Int -> LabelMap Int
incPreds Label
dest LabelMap Int
backEdges )

        -- If:
        --   (1) a block does not end with a call
        -- Then:
        --   (1) if it ends with a conditional attempt to invert the
        --       conditional
        --   (2) attempt to shortcut all destination blocks
        --   (3) if new successors of a block are different from the old ones
        --       update the of predecessors accordingly
        --
        -- A special case of this is a situation when a block ends with an
        -- unconditional jump to a block that can be shortcut.
        | Maybe Label
Nothing <- CmmNode 'Open 'Closed -> Maybe Label
callContinuation_maybe CmmNode 'Open 'Closed
last
        = let oldSuccs :: [Label]
oldSuccs = CmmNode 'Open 'Closed -> [Label]
forall (e :: Extensibility). CmmNode e 'Closed -> [Label]
forall (thing :: Extensibility -> Extensibility -> *)
       (e :: Extensibility).
NonLocal thing =>
thing e 'Closed -> [Label]
successors CmmNode 'Open 'Closed
last
              newSuccs :: [Label]
newSuccs = CmmNode 'Open 'Closed -> [Label]
forall (e :: Extensibility). CmmNode e 'Closed -> [Label]
forall (thing :: Extensibility -> Extensibility -> *)
       (e :: Extensibility).
NonLocal thing =>
thing e 'Closed -> [Label]
successors CmmNode 'Open 'Closed
rewrite_last
          in ( Label -> CmmBlock -> LabelMap CmmBlock -> LabelMap CmmBlock
forall v. Label -> v -> LabelMap v -> LabelMap v
mapInsert Label
bid (Block CmmNode 'Closed 'Open -> CmmNode 'Open 'Closed -> CmmBlock
forall (n :: Extensibility -> Extensibility -> *)
       (e :: Extensibility).
Block n e 'Open -> n 'Open 'Closed -> Block n e 'Closed
blockJoinTail Block CmmNode 'Closed 'Open
head CmmNode 'Open 'Closed
rewrite_last) LabelMap CmmBlock
blocks
             , LabelMap Label
shortcut_map
             , if [Label]
oldSuccs [Label] -> [Label] -> Bool
forall a. Eq a => a -> a -> Bool
== [Label]
newSuccs
               then LabelMap Int
backEdges
               else (Label -> LabelMap Int -> LabelMap Int)
-> LabelMap Int -> [Label] -> LabelMap Int
forall a b. (a -> b -> b) -> b -> [a] -> b
forall (t :: * -> *) a b.
Foldable t =>
(a -> b -> b) -> b -> t a -> b
foldr Label -> LabelMap Int -> LabelMap Int
incPreds ((Label -> LabelMap Int -> LabelMap Int)
-> LabelMap Int -> [Label] -> LabelMap Int
forall a b. (a -> b -> b) -> b -> [a] -> b
forall (t :: * -> *) a b.
Foldable t =>
(a -> b -> b) -> b -> t a -> b
foldr Label -> LabelMap Int -> LabelMap Int
decPreds LabelMap Int
backEdges [Label]
oldSuccs) [Label]
newSuccs )

        -- Otherwise don't do anything
        | Bool
otherwise
        = ( LabelMap CmmBlock
blocks, LabelMap Label
shortcut_map, LabelMap Int
backEdges )
        where
          (Block CmmNode 'Closed 'Open
head, CmmNode 'Open 'Closed
last) = CmmBlock -> (Block CmmNode 'Closed 'Open, CmmNode 'Open 'Closed)
forall (n :: Extensibility -> Extensibility -> *)
       (e :: Extensibility).
Block n e 'Closed -> (Block n e 'Open, n 'Open 'Closed)
blockSplitTail CmmBlock
block
          bid :: Label
bid = CmmBlock -> Label
forall (x :: Extensibility). Block CmmNode 'Closed x -> Label
forall (thing :: Extensibility -> Extensibility -> *)
       (x :: Extensibility).
NonLocal thing =>
thing 'Closed x -> Label
entryLabel CmmBlock
block

          -- Changes continuation of a call to a specified label
          update_cont :: Label -> CmmNode 'Open 'Closed
update_cont Label
dest =
              case CmmNode 'Open 'Closed
last of
                CmmCall{}        -> CmmNode 'Open 'Closed
last { cml_cont = Just dest }
                CmmForeignCall{} -> CmmNode 'Open 'Closed
last { succ = dest }
                CmmNode 'Open 'Closed
_                -> String -> CmmNode 'Open 'Closed
forall a. HasCallStack => String -> a
panic String
"Can't shortcut continuation."

          -- Attempts to shortcut successors of last node
          shortcut_last :: CmmNode 'Open 'Closed
shortcut_last = (Label -> Label) -> CmmNode 'Open 'Closed -> CmmNode 'Open 'Closed
mapSuccessors Label -> Label
shortcut CmmNode 'Open 'Closed
last
            where
              shortcut :: Label -> Label
shortcut Label
l =
                 case Label -> LabelMap CmmBlock -> Maybe CmmBlock
forall a. Label -> LabelMap a -> Maybe a
mapLookup Label
l LabelMap CmmBlock
blocks of
                   Just CmmBlock
b | Just Label
dest <- CmmBlock -> Maybe Label
canShortcut CmmBlock
b -> Label
dest
                   Maybe CmmBlock
_otherwise -> Label
l

          rewrite_last :: CmmNode 'Open 'Closed
rewrite_last
            -- Sometimes we can get rid of the conditional completely.
            | CmmCondBranch CmmExpr
_cond Label
t Label
f Maybe Bool
_l <- CmmNode 'Open 'Closed
shortcut_last
            , Label
t Label -> Label -> Bool
forall a. Eq a => a -> a -> Bool
== Label
f
            = Label -> CmmNode 'Open 'Closed
CmmBranch Label
t

            -- See Note [Invert Cmm conditionals]
            | CmmCondBranch CmmExpr
cond Label
t Label
f Maybe Bool
l <- CmmNode 'Open 'Closed
shortcut_last
            , Label -> Bool
hasOnePredecessor Label
t -- inverting will make t a fallthrough
            , Maybe Bool -> Bool
likelyTrue Maybe Bool
l Bool -> Bool -> Bool
|| (Label -> Int
numPreds Label
f Int -> Int -> Bool
forall a. Ord a => a -> a -> Bool
> Int
1)
            , Just CmmExpr
cond' <- CmmExpr -> Maybe CmmExpr
maybeInvertCmmExpr CmmExpr
cond
            = CmmExpr -> Label -> Label -> Maybe Bool -> CmmNode 'Open 'Closed
CmmCondBranch CmmExpr
cond' Label
f Label
t (Maybe Bool -> Maybe Bool
invertLikeliness Maybe Bool
l)

            -- If all jump destinations of a switch go to the
            -- same target eliminate the switch.
            | CmmSwitch CmmExpr
_expr SwitchTargets
targets <- CmmNode 'Open 'Closed
shortcut_last
            , (Label
t:[Label]
ts) <- SwitchTargets -> [Label]
switchTargetsToList SwitchTargets
targets
            , (Label -> Bool) -> [Label] -> Bool
forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
all (Label -> Label -> Bool
forall a. Eq a => a -> a -> Bool
== Label
t) [Label]
ts
            = Label -> CmmNode 'Open 'Closed
CmmBranch Label
t

            | Bool
otherwise
            = CmmNode 'Open 'Closed
shortcut_last

          likelyTrue :: Maybe Bool -> Bool
likelyTrue (Just Bool
True)   = Bool
True
          likelyTrue Maybe Bool
_             = Bool
False

          invertLikeliness :: Maybe Bool -> Maybe Bool
          invertLikeliness :: Maybe Bool -> Maybe Bool
invertLikeliness         = (Bool -> Bool) -> Maybe Bool -> Maybe Bool
forall a b. (a -> b) -> Maybe a -> Maybe b
forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
fmap Bool -> Bool
not

          -- Number of predecessors for a block
          numPreds :: Label -> Int
numPreds Label
bid = Label -> LabelMap Int -> Maybe Int
forall a. Label -> LabelMap a -> Maybe a
mapLookup Label
bid LabelMap Int
backEdges Maybe Int -> Int -> Int
forall a. Maybe a -> a -> a
`orElse` Int
0

          hasOnePredecessor :: Label -> Bool
hasOnePredecessor Label
b = Label -> Int
numPreds Label
b Int -> Int -> Bool
forall a. Eq a => a -> a -> Bool
== Int
1

{-
  Note [Invert Cmm conditionals]
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  The native code generator always produces jumps to the true branch.
  Falling through to the false branch is however faster. So we try to
  arrange for that to happen.
  This means we invert the condition if:
  * The likely path will become a fallthrough.
  * We can't guarantee a fallthrough for the false branch but for the
    true branch.

  In some cases it's faster to avoid inverting when the false branch is likely.
  However determining when that is the case is neither easy nor cheap so for
  now we always invert as this produces smaller binaries and code that is
  equally fast on average. (On an i7-6700K)

  TODO:
  There is also the edge case when both branches have multiple predecessors.
  In this case we could assume that we will end up with a jump for BOTH
  branches. In this case it might be best to put the likely path in the true
  branch especially if there are large numbers of predecessors as this saves
  us the jump that's not taken. However I haven't tested this and as of early
  2018 we almost never generate cmm where this would apply.
-}

-- Functions for incrementing and decrementing number of predecessors. If
-- decrementing would set the predecessor count to 0, we remove entry from the
-- map.
-- Invariant: if a block has no predecessors it should be dropped from the
-- graph because it is unreachable. maybe_concat is constructed to maintain
-- that invariant, but calling replaceLabels may introduce unreachable blocks.
-- We rely on subsequent passes in the Cmm pipeline to remove unreachable
-- blocks.
incPreds, decPreds :: BlockId -> LabelMap Int -> LabelMap Int
incPreds :: Label -> LabelMap Int -> LabelMap Int
incPreds Label
bid LabelMap Int
edges = (Int -> Int -> Int) -> Label -> Int -> LabelMap Int -> LabelMap Int
forall v. (v -> v -> v) -> Label -> v -> LabelMap v -> LabelMap v
mapInsertWith Int -> Int -> Int
forall a. Num a => a -> a -> a
(+) Label
bid Int
1 LabelMap Int
edges
decPreds :: Label -> LabelMap Int -> LabelMap Int
decPreds Label
bid LabelMap Int
edges = case Label -> LabelMap Int -> Maybe Int
forall a. Label -> LabelMap a -> Maybe a
mapLookup Label
bid LabelMap Int
edges of
                       Just Int
preds | Int
preds Int -> Int -> Bool
forall a. Ord a => a -> a -> Bool
> Int
1 -> Label -> Int -> LabelMap Int -> LabelMap Int
forall v. Label -> v -> LabelMap v -> LabelMap v
mapInsert Label
bid (Int
preds Int -> Int -> Int
forall a. Num a => a -> a -> a
- Int
1) LabelMap Int
edges
                       Just Int
_                 -> Label -> LabelMap Int -> LabelMap Int
forall v. Label -> LabelMap v -> LabelMap v
mapDelete Label
bid LabelMap Int
edges
                       Maybe Int
_                      -> LabelMap Int
edges


-- Checks if a block consists only of "goto dest". If it does than we return
-- "Just dest" label. See Note [What is shortcutting]
canShortcut :: CmmBlock -> Maybe BlockId
canShortcut :: CmmBlock -> Maybe Label
canShortcut CmmBlock
block
    | (CmmNode 'Closed 'Open
_, Block CmmNode 'Open 'Open
middle, CmmBranch Label
dest) <- CmmBlock
-> (CmmNode 'Closed 'Open, Block CmmNode 'Open 'Open,
    CmmNode 'Open 'Closed)
forall (n :: Extensibility -> Extensibility -> *).
Block n 'Closed 'Closed
-> (n 'Closed 'Open, Block n 'Open 'Open, n 'Open 'Closed)
blockSplit CmmBlock
block
    , (CmmNode 'Open 'Open -> Bool) -> [CmmNode 'Open 'Open] -> Bool
forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
all CmmNode 'Open 'Open -> Bool
forall {e :: Extensibility} {x :: Extensibility}.
CmmNode e x -> Bool
dont_care ([CmmNode 'Open 'Open] -> Bool) -> [CmmNode 'Open 'Open] -> Bool
forall a b. (a -> b) -> a -> b
$ Block CmmNode 'Open 'Open -> [CmmNode 'Open 'Open]
forall (n :: Extensibility -> Extensibility -> *).
Block n 'Open 'Open -> [n 'Open 'Open]
blockToList Block CmmNode 'Open 'Open
middle
    = Label -> Maybe Label
forall a. a -> Maybe a
Just Label
dest
    | Bool
otherwise
    = Maybe Label
forall a. Maybe a
Nothing
    where dont_care :: CmmNode e x -> Bool
dont_care CmmComment{} = Bool
True
          dont_care CmmTick{}    = Bool
True
          dont_care CmmNode e x
_other       = Bool
False

-- Concatenates two blocks. First one is assumed to be open on exit, the second
-- is assumed to be closed on entry (i.e. it has a label attached to it, which
-- the splice function removes by calling snd on result of blockSplitHead).
splice :: Block CmmNode C O -> CmmBlock -> CmmBlock
splice :: Block CmmNode 'Closed 'Open -> CmmBlock -> CmmBlock
splice Block CmmNode 'Closed 'Open
head CmmBlock
rest = CmmNode 'Closed 'Open
entry CmmNode 'Closed 'Open
-> Block CmmNode 'Open 'Open -> Block CmmNode 'Closed 'Open
forall (n :: Extensibility -> Extensibility -> *)
       (x :: Extensibility).
n 'Closed 'Open -> Block n 'Open x -> Block n 'Closed x
`blockJoinHead` Block CmmNode 'Open 'Open
code0 Block CmmNode 'Closed 'Open
-> Block CmmNode 'Open 'Closed -> CmmBlock
forall (n :: Extensibility -> Extensibility -> *)
       (e :: Extensibility) (x :: Extensibility).
Block n e 'Open -> Block n 'Open x -> Block n e x
`blockAppend` Block CmmNode 'Open 'Closed
code1
  where (CmmEntry Label
lbl CmmTickScope
sc0, Block CmmNode 'Open 'Open
code0) = Block CmmNode 'Closed 'Open
-> (CmmNode 'Closed 'Open, Block CmmNode 'Open 'Open)
forall (n :: Extensibility -> Extensibility -> *)
       (x :: Extensibility).
Block n 'Closed x -> (n 'Closed 'Open, Block n 'Open x)
blockSplitHead Block CmmNode 'Closed 'Open
head
        (CmmEntry Label
_   CmmTickScope
sc1, Block CmmNode 'Open 'Closed
code1) = CmmBlock -> (CmmNode 'Closed 'Open, Block CmmNode 'Open 'Closed)
forall (n :: Extensibility -> Extensibility -> *)
       (x :: Extensibility).
Block n 'Closed x -> (n 'Closed 'Open, Block n 'Open x)
blockSplitHead CmmBlock
rest
        entry :: CmmNode 'Closed 'Open
entry = Label -> CmmTickScope -> CmmNode 'Closed 'Open
CmmEntry Label
lbl (CmmTickScope -> CmmTickScope -> CmmTickScope
combineTickScopes CmmTickScope
sc0 CmmTickScope
sc1)

-- If node is a call with continuation call return Just label of that
-- continuation. Otherwise return Nothing.
callContinuation_maybe :: CmmNode O C -> Maybe BlockId
callContinuation_maybe :: CmmNode 'Open 'Closed -> Maybe Label
callContinuation_maybe (CmmCall { cml_cont :: CmmNode 'Open 'Closed -> Maybe Label
cml_cont = Just Label
b }) = Label -> Maybe Label
forall a. a -> Maybe a
Just Label
b
callContinuation_maybe (CmmForeignCall { succ :: CmmNode 'Open 'Closed -> Label
succ = Label
b })   = Label -> Maybe Label
forall a. a -> Maybe a
Just Label
b
callContinuation_maybe CmmNode 'Open 'Closed
_ = Maybe Label
forall a. Maybe a
Nothing


-- Map over the CmmGraph, replacing each label with its mapping in the
-- supplied LabelMap.
replaceLabels :: LabelMap BlockId -> CmmGraph -> CmmGraph
replaceLabels :: LabelMap Label
-> GenGenCmmGraph LabelMap CmmNode
-> GenGenCmmGraph LabelMap CmmNode
replaceLabels LabelMap Label
env GenGenCmmGraph LabelMap CmmNode
g
  | LabelMap Label -> Bool
forall a. LabelMap a -> Bool
mapNull LabelMap Label
env = GenGenCmmGraph LabelMap CmmNode
g
  | Bool
otherwise   = GenGenCmmGraph LabelMap CmmNode -> GenGenCmmGraph LabelMap CmmNode
replace_eid (GenGenCmmGraph LabelMap CmmNode
 -> GenGenCmmGraph LabelMap CmmNode)
-> GenGenCmmGraph LabelMap CmmNode
-> GenGenCmmGraph LabelMap CmmNode
forall a b. (a -> b) -> a -> b
$ (forall (e :: Extensibility) (x :: Extensibility).
 CmmNode e x -> CmmNode e x)
-> GenGenCmmGraph LabelMap CmmNode
-> GenGenCmmGraph LabelMap CmmNode
mapGraphNodes1 CmmNode e x -> CmmNode e x
forall (e :: Extensibility) (x :: Extensibility).
CmmNode e x -> CmmNode e x
txnode GenGenCmmGraph LabelMap CmmNode
g
   where
     replace_eid :: GenGenCmmGraph LabelMap CmmNode -> GenGenCmmGraph LabelMap CmmNode
replace_eid GenGenCmmGraph LabelMap CmmNode
g = GenGenCmmGraph LabelMap CmmNode
g {g_entry = lookup (g_entry g)}
     lookup :: Label -> Label
lookup Label
id = Label -> LabelMap Label -> Maybe Label
forall a. Label -> LabelMap a -> Maybe a
mapLookup Label
id LabelMap Label
env Maybe Label -> Label -> Label
forall a. Maybe a -> a -> a
`orElse` Label
id

     txnode :: CmmNode e x -> CmmNode e x
     txnode :: forall (e :: Extensibility) (x :: Extensibility).
CmmNode e x -> CmmNode e x
txnode (CmmBranch Label
bid) = Label -> CmmNode 'Open 'Closed
CmmBranch (Label -> Label
lookup Label
bid)
     txnode (CmmCondBranch CmmExpr
p Label
t Label
f Maybe Bool
l) =
       CmmExpr -> Label -> Label -> Maybe Bool -> CmmNode 'Open 'Closed
mkCmmCondBranch (CmmExpr -> CmmExpr
exp CmmExpr
p) (Label -> Label
lookup Label
t) (Label -> Label
lookup Label
f) Maybe Bool
l
     txnode (CmmSwitch CmmExpr
e SwitchTargets
ids) =
       CmmExpr -> SwitchTargets -> CmmNode 'Open 'Closed
CmmSwitch (CmmExpr -> CmmExpr
exp CmmExpr
e) ((Label -> Label) -> SwitchTargets -> SwitchTargets
mapSwitchTargets Label -> Label
lookup SwitchTargets
ids)
     txnode (CmmCall CmmExpr
t Maybe Label
k [GlobalRegUse]
rg Int
a Int
res Int
r) =
       CmmExpr
-> Maybe Label
-> [GlobalRegUse]
-> Int
-> Int
-> Int
-> CmmNode 'Open 'Closed
CmmCall (CmmExpr -> CmmExpr
exp CmmExpr
t) ((Label -> Label) -> Maybe Label -> Maybe Label
forall (m :: * -> *) a1 r. Monad m => (a1 -> r) -> m a1 -> m r
liftM Label -> Label
lookup Maybe Label
k) [GlobalRegUse]
rg Int
a Int
res Int
r
     txnode fc :: CmmNode e x
fc@CmmForeignCall{} =
       CmmNode e x
fc{ args = map exp (args fc), succ = lookup (succ fc) }
     txnode CmmNode e x
other = (CmmExpr -> CmmExpr) -> CmmNode e x -> CmmNode e x
forall (e :: Extensibility) (x :: Extensibility).
(CmmExpr -> CmmExpr) -> CmmNode e x -> CmmNode e x
mapExpDeep CmmExpr -> CmmExpr
exp CmmNode e x
other

     exp :: CmmExpr -> CmmExpr
     exp :: CmmExpr -> CmmExpr
exp (CmmLit (CmmBlock Label
bid))                = CmmLit -> CmmExpr
CmmLit (Label -> CmmLit
CmmBlock (Label -> Label
lookup Label
bid))
     exp (CmmStackSlot (Young Label
id) Int
i) = Area -> Int -> CmmExpr
CmmStackSlot (Label -> Area
Young (Label -> Label
lookup Label
id)) Int
i
     exp CmmExpr
e                                      = CmmExpr
e

mkCmmCondBranch :: CmmExpr -> Label -> Label -> Maybe Bool -> CmmNode O C
mkCmmCondBranch :: CmmExpr -> Label -> Label -> Maybe Bool -> CmmNode 'Open 'Closed
mkCmmCondBranch CmmExpr
p Label
t Label
f Maybe Bool
l =
  if Label
t Label -> Label -> Bool
forall a. Eq a => a -> a -> Bool
== Label
f then Label -> CmmNode 'Open 'Closed
CmmBranch Label
t else CmmExpr -> Label -> Label -> Maybe Bool -> CmmNode 'Open 'Closed
CmmCondBranch CmmExpr
p Label
t Label
f Maybe Bool
l

-- Build a map from a block to its set of predecessors.
predMap :: [CmmBlock] -> LabelMap Int
predMap :: [CmmBlock] -> LabelMap Int
predMap [CmmBlock]
blocks = (CmmBlock -> LabelMap Int -> LabelMap Int)
-> LabelMap Int -> [CmmBlock] -> LabelMap Int
forall a b. (a -> b -> b) -> b -> [a] -> b
forall (t :: * -> *) a b.
Foldable t =>
(a -> b -> b) -> b -> t a -> b
foldr CmmBlock -> LabelMap Int -> LabelMap Int
forall {v} {thing :: Extensibility -> Extensibility -> *}
       {e :: Extensibility}.
(Num v, NonLocal thing) =>
thing e 'Closed -> LabelMap v -> LabelMap v
add_preds LabelMap Int
forall v. LabelMap v
mapEmpty [CmmBlock]
blocks
  where
    add_preds :: thing e 'Closed -> LabelMap v -> LabelMap v
add_preds thing e 'Closed
block LabelMap v
env = (Label -> LabelMap v -> LabelMap v)
-> LabelMap v -> [Label] -> LabelMap v
forall a b. (a -> b -> b) -> b -> [a] -> b
forall (t :: * -> *) a b.
Foldable t =>
(a -> b -> b) -> b -> t a -> b
foldr Label -> LabelMap v -> LabelMap v
forall {v}. Num v => Label -> LabelMap v -> LabelMap v
add LabelMap v
env (thing e 'Closed -> [Label]
forall (e :: Extensibility). thing e 'Closed -> [Label]
forall (thing :: Extensibility -> Extensibility -> *)
       (e :: Extensibility).
NonLocal thing =>
thing e 'Closed -> [Label]
successors thing e 'Closed
block)
      where add :: Label -> LabelMap v -> LabelMap v
add Label
lbl LabelMap v
env = (v -> v -> v) -> Label -> v -> LabelMap v -> LabelMap v
forall v. (v -> v -> v) -> Label -> v -> LabelMap v -> LabelMap v
mapInsertWith v -> v -> v
forall a. Num a => a -> a -> a
(+) Label
lbl v
1 LabelMap v
env

-- Remove unreachable blocks from procs
removeUnreachableBlocksProc :: Platform -> CmmDecl -> CmmDecl
removeUnreachableBlocksProc :: Platform -> CmmDecl -> CmmDecl
removeUnreachableBlocksProc Platform
_ proc :: CmmDecl
proc@(CmmProc GenCmmTopInfo LabelMap
info CLabel
lbl [GlobalRegUse]
live GenGenCmmGraph LabelMap CmmNode
g)
   | [CmmBlock]
used_blocks [CmmBlock] -> Int -> Bool
forall a. [a] -> Int -> Bool
`lengthLessThan` LabelMap CmmBlock -> Int
forall a. LabelMap a -> Int
mapSize (GenGenCmmGraph LabelMap CmmNode -> LabelMap CmmBlock
toBlockMap GenGenCmmGraph LabelMap CmmNode
g)
   = GenCmmTopInfo LabelMap
-> CLabel
-> [GlobalRegUse]
-> GenGenCmmGraph LabelMap CmmNode
-> CmmDecl
forall d h g.
h -> CLabel -> [GlobalRegUse] -> g -> GenCmmDecl d h g
CmmProc GenCmmTopInfo LabelMap
info' CLabel
lbl [GlobalRegUse]
live GenGenCmmGraph LabelMap CmmNode
g'
   | Bool
otherwise
   = CmmDecl
proc
   where
     g' :: GenGenCmmGraph LabelMap CmmNode
g'    = Label -> [CmmBlock] -> GenGenCmmGraph LabelMap CmmNode
ofBlockList (GenGenCmmGraph LabelMap CmmNode -> Label
forall (s :: * -> *) (n :: Extensibility -> Extensibility -> *).
GenGenCmmGraph s n -> Label
g_entry GenGenCmmGraph LabelMap CmmNode
g) [CmmBlock]
used_blocks
     info' :: GenCmmTopInfo LabelMap
info' = GenCmmTopInfo LabelMap
info { info_tbls = keep_used (info_tbls info) }
             -- Remove any info_tbls for unreachable

     keep_used :: LabelMap CmmInfoTable -> LabelMap CmmInfoTable
     keep_used :: LabelMap CmmInfoTable -> LabelMap CmmInfoTable
keep_used LabelMap CmmInfoTable
bs = (LabelMap CmmInfoTable
 -> Label -> CmmInfoTable -> LabelMap CmmInfoTable)
-> LabelMap CmmInfoTable
-> LabelMap CmmInfoTable
-> LabelMap CmmInfoTable
forall t b. (t -> Label -> b -> t) -> t -> LabelMap b -> t
mapFoldlWithKey LabelMap CmmInfoTable
-> Label -> CmmInfoTable -> LabelMap CmmInfoTable
keep LabelMap CmmInfoTable
forall v. LabelMap v
mapEmpty LabelMap CmmInfoTable
bs

     keep :: LabelMap CmmInfoTable -> Label -> CmmInfoTable -> LabelMap CmmInfoTable
     keep :: LabelMap CmmInfoTable
-> Label -> CmmInfoTable -> LabelMap CmmInfoTable
keep LabelMap CmmInfoTable
env Label
l CmmInfoTable
i | Label
l Label -> LabelSet -> Bool
`setMember` LabelSet
used_lbls = Label
-> CmmInfoTable -> LabelMap CmmInfoTable -> LabelMap CmmInfoTable
forall v. Label -> v -> LabelMap v -> LabelMap v
mapInsert Label
l CmmInfoTable
i LabelMap CmmInfoTable
env
                  | Bool
otherwise               = LabelMap CmmInfoTable
env

     used_blocks :: [CmmBlock]
     used_blocks :: [CmmBlock]
used_blocks = GenGenCmmGraph LabelMap CmmNode -> [CmmBlock]
revPostorder GenGenCmmGraph LabelMap CmmNode
g

     used_lbls :: LabelSet
     used_lbls :: LabelSet
used_lbls = [Label] -> LabelSet
setFromList ([Label] -> LabelSet) -> [Label] -> LabelSet
forall a b. (a -> b) -> a -> b
$ (CmmBlock -> Label) -> [CmmBlock] -> [Label]
forall a b. (a -> b) -> [a] -> [b]
map CmmBlock -> Label
forall (x :: Extensibility). Block CmmNode 'Closed x -> Label
forall (thing :: Extensibility -> Extensibility -> *)
       (x :: Extensibility).
NonLocal thing =>
thing 'Closed x -> Label
entryLabel [CmmBlock]
used_blocks
removeUnreachableBlocksProc Platform
platform data' :: CmmDecl
data'@(CmmData Section
_ GenCmmStatics 'False
_) =
    String -> SDoc -> CmmDecl
forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"removeUnreachableBlocksProc: passed data declaration instead of procedure" (Platform -> CmmDecl -> SDoc
forall env a. OutputableP env a => env -> a -> SDoc
pdoc Platform
platform CmmDecl
data')