cmm/CmmUtils.hs

    {-# LANGUAGE CPP, GADTs, RankNTypes #-}

    -----------------------------------------------------------------------------
    --
    -- Cmm utilities.
    --
    -- (c) The University of Glasgow 2004-2006
    --
    -----------------------------------------------------------------------------

    module CmmUtils(
            -- CmmType
            primRepCmmType, slotCmmType, slotForeignHint,
            typeCmmType, typeForeignHint, primRepForeignHint,

            -- CmmLit
            zeroCLit, mkIntCLit,
            mkWordCLit, packHalfWordsCLit,
            mkByteStringCLit,
            mkDataLits, mkRODataLits,
            mkStgWordCLit,

            -- CmmExpr
            mkIntExpr, zeroExpr,
            mkLblExpr,
            cmmRegOff,  cmmOffset,  cmmLabelOff,  cmmOffsetLit,  cmmOffsetExpr,
            cmmRegOffB, cmmOffsetB, cmmLabelOffB, cmmOffsetLitB, cmmOffsetExprB,
            cmmRegOffW, cmmOffsetW, cmmLabelOffW, cmmOffsetLitW, cmmOffsetExprW,
            cmmIndex, cmmIndexExpr, cmmLoadIndex, cmmLoadIndexW,
            cmmNegate,
            cmmULtWord, cmmUGeWord, cmmUGtWord, cmmUShrWord,
            cmmSLtWord,
            cmmNeWord, cmmEqWord,
            cmmOrWord, cmmAndWord,
            cmmSubWord, cmmAddWord, cmmMulWord, cmmQuotWord,
            cmmToWord,

            isTrivialCmmExpr, hasNoGlobalRegs,

            -- Statics
            blankWord,

            -- Tagging
            cmmTagMask, cmmPointerMask, cmmUntag, cmmIsTagged,
            cmmConstrTag1,

            -- Overlap and usage
            regsOverlap, regUsedIn,

            -- Liveness and bitmaps
            mkLiveness,

            -- * Operations that probably don't belong here
            modifyGraph,

            ofBlockMap, toBlockMap, insertBlock,
            ofBlockList, toBlockList, bodyToBlockList,
            toBlockListEntryFirst, toBlockListEntryFirstFalseFallthrough,
            foldGraphBlocks, mapGraphNodes, postorderDfs, mapGraphNodes1,

            -- * Ticks
            blockTicks
      ) where

    #include "HsVersions.h"

    import TyCon    ( PrimRep(..), PrimElemRep(..) )
    import RepType  ( UnaryType, SlotTy (..), typePrimRep1 )

    import SMRep
    import Cmm
    import BlockId
    import CLabel
    import Outputable
    import DynFlags
    import Util
    import CodeGen.Platform

    import Data.Word
    import Data.Maybe
    import Data.Bits
    import Hoopl

    ---------------------------------------------------
    --
    --      CmmTypes
    --
    ---------------------------------------------------

    primRepCmmType :: DynFlags -> PrimRep -> CmmType
    primRepCmmType _      VoidRep          = panic "primRepCmmType:VoidRep"
    primRepCmmType dflags LiftedRep        = gcWord dflags
    primRepCmmType dflags UnliftedRep      = gcWord dflags
    primRepCmmType dflags IntRep           = bWord dflags
    primRepCmmType dflags WordRep          = bWord dflags
    primRepCmmType _      Int64Rep         = b64
    primRepCmmType _      Word64Rep        = b64
    primRepCmmType dflags AddrRep          = bWord dflags
    primRepCmmType _      FloatRep         = f32
    primRepCmmType _      DoubleRep        = f64
    primRepCmmType _      (VecRep len rep) = vec len (primElemRepCmmType rep)

    slotCmmType :: DynFlags -> SlotTy -> CmmType
    slotCmmType dflags PtrSlot    = gcWord dflags
    slotCmmType dflags WordSlot   = bWord dflags
    slotCmmType _      Word64Slot = b64
    slotCmmType _      FloatSlot  = f32
    slotCmmType _      DoubleSlot = f64

    primElemRepCmmType :: PrimElemRep -> CmmType
    primElemRepCmmType Int8ElemRep   = b8
    primElemRepCmmType Int16ElemRep  = b16
    primElemRepCmmType Int32ElemRep  = b32
    primElemRepCmmType Int64ElemRep  = b64
    primElemRepCmmType Word8ElemRep  = b8
    primElemRepCmmType Word16ElemRep = b16
    primElemRepCmmType Word32ElemRep = b32
    primElemRepCmmType Word64ElemRep = b64
    primElemRepCmmType FloatElemRep  = f32
    primElemRepCmmType DoubleElemRep = f64

    typeCmmType :: DynFlags -> UnaryType -> CmmType
    typeCmmType dflags ty = primRepCmmType dflags (typePrimRep1 ty)

    primRepForeignHint :: PrimRep -> ForeignHint
    primRepForeignHint VoidRep      = panic "primRepForeignHint:VoidRep"
    primRepForeignHint LiftedRep    = AddrHint
    primRepForeignHint UnliftedRep  = AddrHint
    primRepForeignHint IntRep       = SignedHint
    primRepForeignHint WordRep      = NoHint
    primRepForeignHint Int64Rep     = SignedHint
    primRepForeignHint Word64Rep    = NoHint
    primRepForeignHint AddrRep      = AddrHint -- NB! AddrHint, but NonPtrArg
    primRepForeignHint FloatRep     = NoHint
    primRepForeignHint DoubleRep    = NoHint
    primRepForeignHint (VecRep {})  = NoHint

    slotForeignHint :: SlotTy -> ForeignHint
    slotForeignHint PtrSlot       = AddrHint
    slotForeignHint WordSlot      = NoHint
    slotForeignHint Word64Slot    = NoHint
    slotForeignHint FloatSlot     = NoHint
    slotForeignHint DoubleSlot    = NoHint

    typeForeignHint :: UnaryType -> ForeignHint
    typeForeignHint = primRepForeignHint . typePrimRep1

    ---------------------------------------------------
    --
    --      CmmLit
    --
    ---------------------------------------------------

    -- XXX: should really be Integer, since Int doesn't necessarily cover
    -- the full range of target Ints.
    mkIntCLit :: DynFlags -> Int -> CmmLit
    mkIntCLit dflags i = CmmInt (toInteger i) (wordWidth dflags)

    mkIntExpr :: DynFlags -> Int -> CmmExpr
    mkIntExpr dflags i = CmmLit $! mkIntCLit dflags i

    zeroCLit :: DynFlags -> CmmLit
    zeroCLit dflags = CmmInt 0 (wordWidth dflags)

    zeroExpr :: DynFlags -> CmmExpr
    zeroExpr dflags = CmmLit (zeroCLit dflags)

    mkWordCLit :: DynFlags -> Integer -> CmmLit
    mkWordCLit dflags wd = CmmInt wd (wordWidth dflags)

    mkByteStringCLit
      :: CLabel -> [Word8] -> (CmmLit, GenCmmDecl CmmStatics info stmt)
    -- We have to make a top-level decl for the string,
    -- and return a literal pointing to it
    mkByteStringCLit lbl bytes
      = (CmmLabel lbl, CmmData (Section sec lbl) $ Statics lbl [CmmString bytes])
      where
        -- This can not happen for String literals (as there \NUL is replaced by
        -- C0 80). However, it can happen with Addr# literals.
        sec = if 0 `elem` bytes then ReadOnlyData else CString

    mkDataLits :: Section -> CLabel -> [CmmLit] -> GenCmmDecl CmmStatics info stmt
    -- Build a data-segment data block
    mkDataLits section lbl lits
      = CmmData section (Statics lbl $ map CmmStaticLit lits)

    mkRODataLits :: CLabel -> [CmmLit] -> GenCmmDecl CmmStatics info stmt
    -- Build a read-only data block
    mkRODataLits lbl lits
      = mkDataLits section lbl lits
      where
        section | any needsRelocation lits = Section RelocatableReadOnlyData lbl
                | otherwise                = Section ReadOnlyData lbl
        needsRelocation (CmmLabel _)      = True
        needsRelocation (CmmLabelOff _ _) = True
        needsRelocation _                 = False

    mkStgWordCLit :: DynFlags -> StgWord -> CmmLit
    mkStgWordCLit dflags wd = CmmInt (fromStgWord wd) (wordWidth dflags)

    packHalfWordsCLit :: DynFlags -> StgHalfWord -> StgHalfWord -> CmmLit
    -- Make a single word literal in which the lower_half_word is
    -- at the lower address, and the upper_half_word is at the
    -- higher address
    -- ToDo: consider using half-word lits instead
    --       but be careful: that's vulnerable when reversed
    packHalfWordsCLit dflags lower_half_word upper_half_word
       = if wORDS_BIGENDIAN dflags
         then mkWordCLit dflags ((l `shiftL` hALF_WORD_SIZE_IN_BITS dflags) .|. u)
         else mkWordCLit dflags (l .|. (u `shiftL` hALF_WORD_SIZE_IN_BITS dflags))
        where l = fromStgHalfWord lower_half_word
              u = fromStgHalfWord upper_half_word

    ---------------------------------------------------
    --
    --      CmmExpr
    --
    ---------------------------------------------------

    mkLblExpr :: CLabel -> CmmExpr
    mkLblExpr lbl = CmmLit (CmmLabel lbl)

    cmmOffsetExpr :: DynFlags -> CmmExpr -> CmmExpr -> CmmExpr
    -- assumes base and offset have the same CmmType
    cmmOffsetExpr dflags e (CmmLit (CmmInt n _)) = cmmOffset dflags e (fromInteger n)
    cmmOffsetExpr dflags e byte_off = CmmMachOp (MO_Add (cmmExprWidth dflags e)) [e, byte_off]

    cmmOffset :: DynFlags -> CmmExpr -> Int -> CmmExpr
    cmmOffset _ e                 0        = e
    cmmOffset _ (CmmReg reg)      byte_off = cmmRegOff reg byte_off
    cmmOffset _ (CmmRegOff reg m) byte_off = cmmRegOff reg (m+byte_off)
    cmmOffset _ (CmmLit lit)      byte_off = CmmLit (cmmOffsetLit lit byte_off)
    cmmOffset _ (CmmStackSlot area off) byte_off
      = CmmStackSlot area (off - byte_off)
      -- note stack area offsets increase towards lower addresses
    cmmOffset _ (CmmMachOp (MO_Add rep) [expr, CmmLit (CmmInt byte_off1 _rep)]) byte_off2
      = CmmMachOp (MO_Add rep)
                  [expr, CmmLit (CmmInt (byte_off1 + toInteger byte_off2) rep)]
    cmmOffset dflags expr byte_off
      = CmmMachOp (MO_Add width) [expr, CmmLit (CmmInt (toInteger byte_off) width)]
      where
        width = cmmExprWidth dflags expr

    -- Smart constructor for CmmRegOff.  Same caveats as cmmOffset above.
    cmmRegOff :: CmmReg -> Int -> CmmExpr
    cmmRegOff reg 0        = CmmReg reg
    cmmRegOff reg byte_off = CmmRegOff reg byte_off

    cmmOffsetLit :: CmmLit -> Int -> CmmLit
    cmmOffsetLit (CmmLabel l)      byte_off = cmmLabelOff l byte_off
    cmmOffsetLit (CmmLabelOff l m) byte_off = cmmLabelOff l (m+byte_off)
    cmmOffsetLit (CmmLabelDiffOff l1 l2 m) byte_off
                                            = CmmLabelDiffOff l1 l2 (m+byte_off)
    cmmOffsetLit (CmmInt m rep)    byte_off = CmmInt (m + fromIntegral byte_off) rep
    cmmOffsetLit _                 byte_off = pprPanic "cmmOffsetLit" (ppr byte_off)

    cmmLabelOff :: CLabel -> Int -> CmmLit
    -- Smart constructor for CmmLabelOff
    cmmLabelOff lbl 0        = CmmLabel lbl
    cmmLabelOff lbl byte_off = CmmLabelOff lbl byte_off

    -- | Useful for creating an index into an array, with a statically known offset.
    -- The type is the element type; used for making the multiplier
    cmmIndex :: DynFlags
             -> Width       -- Width w
             -> CmmExpr     -- Address of vector of items of width w
             -> Int         -- Which element of the vector (0 based)
             -> CmmExpr     -- Address of i'th element
    cmmIndex dflags width base idx = cmmOffset dflags base (idx * widthInBytes width)

    -- | Useful for creating an index into an array, with an unknown offset.
    cmmIndexExpr :: DynFlags
                 -> Width           -- Width w
                 -> CmmExpr         -- Address of vector of items of width w
                 -> CmmExpr         -- Which element of the vector (0 based)
                 -> CmmExpr         -- Address of i'th element
    cmmIndexExpr dflags width base (CmmLit (CmmInt n _)) = cmmIndex dflags width base (fromInteger n)
    cmmIndexExpr dflags width base idx =
      cmmOffsetExpr dflags base byte_off
      where
        idx_w = cmmExprWidth dflags idx
        byte_off = CmmMachOp (MO_Shl idx_w) [idx, mkIntExpr dflags (widthInLog width)]

    cmmLoadIndex :: DynFlags -> CmmType -> CmmExpr -> Int -> CmmExpr
    cmmLoadIndex dflags ty expr ix = CmmLoad (cmmIndex dflags (typeWidth ty) expr ix) ty

    -- The "B" variants take byte offsets
    cmmRegOffB :: CmmReg -> ByteOff -> CmmExpr
    cmmRegOffB = cmmRegOff

    cmmOffsetB :: DynFlags -> CmmExpr -> ByteOff -> CmmExpr
    cmmOffsetB = cmmOffset

    cmmOffsetExprB :: DynFlags -> CmmExpr -> CmmExpr -> CmmExpr
    cmmOffsetExprB = cmmOffsetExpr

    cmmLabelOffB :: CLabel -> ByteOff -> CmmLit
    cmmLabelOffB = cmmLabelOff

    cmmOffsetLitB :: CmmLit -> ByteOff -> CmmLit
    cmmOffsetLitB = cmmOffsetLit

    -----------------------
    -- The "W" variants take word offsets

    cmmOffsetExprW :: DynFlags -> CmmExpr -> CmmExpr -> CmmExpr
    -- The second arg is a *word* offset; need to change it to bytes
    cmmOffsetExprW dflags  e (CmmLit (CmmInt n _)) = cmmOffsetW dflags e (fromInteger n)
    cmmOffsetExprW dflags e wd_off = cmmIndexExpr dflags (wordWidth dflags) e wd_off

    cmmOffsetW :: DynFlags -> CmmExpr -> WordOff -> CmmExpr
    cmmOffsetW dflags e n = cmmOffsetB dflags e (wordsToBytes dflags n)

    cmmRegOffW :: DynFlags -> CmmReg -> WordOff -> CmmExpr
    cmmRegOffW dflags reg wd_off = cmmRegOffB reg (wordsToBytes dflags wd_off)

    cmmOffsetLitW :: DynFlags -> CmmLit -> WordOff -> CmmLit
    cmmOffsetLitW dflags lit wd_off = cmmOffsetLitB lit (wordsToBytes dflags wd_off)

    cmmLabelOffW :: DynFlags -> CLabel -> WordOff -> CmmLit
    cmmLabelOffW dflags lbl wd_off = cmmLabelOffB lbl (wordsToBytes dflags wd_off)

    cmmLoadIndexW :: DynFlags -> CmmExpr -> Int -> CmmType -> CmmExpr
    cmmLoadIndexW dflags base off ty = CmmLoad (cmmOffsetW dflags base off) ty

    -----------------------
    cmmULtWord, cmmUGeWord, cmmUGtWord, cmmUShrWord,
      cmmSLtWord,
      cmmNeWord, cmmEqWord,
      cmmOrWord, cmmAndWord,
      cmmSubWord, cmmAddWord, cmmMulWord, cmmQuotWord
      :: DynFlags -> CmmExpr -> CmmExpr -> CmmExpr
    cmmOrWord dflags  e1 e2 = CmmMachOp (mo_wordOr dflags)  [e1, e2]
    cmmAndWord dflags e1 e2 = CmmMachOp (mo_wordAnd dflags) [e1, e2]
    cmmNeWord dflags  e1 e2 = CmmMachOp (mo_wordNe dflags)  [e1, e2]
    cmmEqWord dflags  e1 e2 = CmmMachOp (mo_wordEq dflags)  [e1, e2]
    cmmULtWord dflags e1 e2 = CmmMachOp (mo_wordULt dflags) [e1, e2]
    cmmUGeWord dflags e1 e2 = CmmMachOp (mo_wordUGe dflags) [e1, e2]
    cmmUGtWord dflags e1 e2 = CmmMachOp (mo_wordUGt dflags) [e1, e2]
    --cmmShlWord dflags e1 e2 = CmmMachOp (mo_wordShl dflags) [e1, e2]
    cmmSLtWord dflags e1 e2 = CmmMachOp (mo_wordSLt dflags) [e1, e2]
    cmmUShrWord dflags e1 e2 = CmmMachOp (mo_wordUShr dflags) [e1, e2]
    cmmAddWord dflags e1 e2 = CmmMachOp (mo_wordAdd dflags) [e1, e2]
    cmmSubWord dflags e1 e2 = CmmMachOp (mo_wordSub dflags) [e1, e2]
    cmmMulWord dflags e1 e2 = CmmMachOp (mo_wordMul dflags) [e1, e2]
    cmmQuotWord dflags e1 e2 = CmmMachOp (mo_wordUQuot dflags) [e1, e2]

    cmmNegate :: DynFlags -> CmmExpr -> CmmExpr
    cmmNegate _      (CmmLit (CmmInt n rep)) = CmmLit (CmmInt (-n) rep)
    cmmNegate dflags e                       = CmmMachOp (MO_S_Neg (cmmExprWidth dflags e)) [e]

    blankWord :: DynFlags -> CmmStatic
    blankWord dflags = CmmUninitialised (wORD_SIZE dflags)

    cmmToWord :: DynFlags -> CmmExpr -> CmmExpr
    cmmToWord dflags e
      | w == word  = e
      | otherwise  = CmmMachOp (MO_UU_Conv w word) [e]
      where
        w = cmmExprWidth dflags e
        word = wordWidth dflags

    ---------------------------------------------------
    --
    --      CmmExpr predicates
    --
    ---------------------------------------------------

    isTrivialCmmExpr :: CmmExpr -> Bool
    isTrivialCmmExpr (CmmLoad _ _)      = False
    isTrivialCmmExpr (CmmMachOp _ _)    = False
    isTrivialCmmExpr (CmmLit _)         = True
    isTrivialCmmExpr (CmmReg _)         = True
    isTrivialCmmExpr (CmmRegOff _ _)    = True
    isTrivialCmmExpr (CmmStackSlot _ _) = panic "isTrivialCmmExpr CmmStackSlot"

    hasNoGlobalRegs :: CmmExpr -> Bool
    hasNoGlobalRegs (CmmLoad e _)              = hasNoGlobalRegs e
    hasNoGlobalRegs (CmmMachOp _ es)           = all hasNoGlobalRegs es
    hasNoGlobalRegs (CmmLit _)                 = True
    hasNoGlobalRegs (CmmReg (CmmLocal _))      = True
    hasNoGlobalRegs (CmmRegOff (CmmLocal _) _) = True
    hasNoGlobalRegs _ = False

    ---------------------------------------------------
    --
    --      Tagging
    --
    ---------------------------------------------------

    -- Tag bits mask
    --cmmTagBits = CmmLit (mkIntCLit tAG_BITS)
    cmmTagMask, cmmPointerMask :: DynFlags -> CmmExpr
    cmmTagMask dflags = mkIntExpr dflags (tAG_MASK dflags)
    cmmPointerMask dflags = mkIntExpr dflags (complement (tAG_MASK dflags))

    -- Used to untag a possibly tagged pointer
    -- A static label need not be untagged
    cmmUntag :: DynFlags -> CmmExpr -> CmmExpr
    cmmUntag _ e@(CmmLit (CmmLabel _)) = e
    -- Default case
    cmmUntag dflags e = cmmAndWord dflags e (cmmPointerMask dflags)

    -- Test if a closure pointer is untagged
    cmmIsTagged :: DynFlags -> CmmExpr -> CmmExpr
    cmmIsTagged dflags e = cmmNeWord dflags (cmmAndWord dflags e (cmmTagMask dflags)) (zeroExpr dflags)

    cmmConstrTag1 :: DynFlags -> CmmExpr -> CmmExpr
    -- Get constructor tag, but one based.
    cmmConstrTag1 dflags e = cmmAndWord dflags e (cmmTagMask dflags)

    -----------------------------------------------------------------------------
    -- Overlap and usage

    -- | Returns True if the two STG registers overlap on the specified
    -- platform, in the sense that writing to one will clobber the
    -- other. This includes the case that the two registers are the same
    -- STG register. See Note [Overlapping global registers] for details.
    regsOverlap :: DynFlags -> CmmReg -> CmmReg -> Bool
    regsOverlap dflags (CmmGlobal g) (CmmGlobal g')
      | Just real  <- globalRegMaybe (targetPlatform dflags) g,
        Just real' <- globalRegMaybe (targetPlatform dflags) g',
        real == real'
        = True
    regsOverlap _ reg reg' = reg == reg'

    -- | Returns True if the STG register is used by the expression, in
    -- the sense that a store to the register might affect the value of
    -- the expression.
    --
    -- We must check for overlapping registers and not just equal
    -- registers here, otherwise CmmSink may incorrectly reorder
    -- assignments that conflict due to overlap. See Trac #10521 and Note
    -- [Overlapping global registers].
    regUsedIn :: DynFlags -> CmmReg -> CmmExpr -> Bool
    regUsedIn dflags = regUsedIn_ where
      _   `regUsedIn_` CmmLit _         = False
      reg `regUsedIn_` CmmLoad e  _     = reg `regUsedIn_` e
      reg `regUsedIn_` CmmReg reg'      = regsOverlap dflags reg reg'
      reg `regUsedIn_` CmmRegOff reg' _ = regsOverlap dflags reg reg'
      reg `regUsedIn_` CmmMachOp _ es   = any (reg `regUsedIn_`) es
      _   `regUsedIn_` CmmStackSlot _ _ = False

    --------------------------------------------
    --
    --        mkLiveness
    --
    ---------------------------------------------

    mkLiveness :: DynFlags -> [Maybe LocalReg] -> Liveness
    mkLiveness _      [] = []
    mkLiveness dflags (reg:regs)
      = take sizeW bits ++ mkLiveness dflags regs
      where
        sizeW = case reg of
                  Nothing -> 1
                  Just r -> (widthInBytes (typeWidth (localRegType r)) + wORD_SIZE dflags - 1)
                            `quot` wORD_SIZE dflags
                            -- number of words, rounded up
        bits = repeat $ is_non_ptr reg -- True <=> Non Ptr

        is_non_ptr Nothing    = True
        is_non_ptr (Just reg) = not $ isGcPtrType (localRegType reg)

    -- ============================================== -
    -- ============================================== -
    -- ============================================== -

    ---------------------------------------------------
    --
    --      Manipulating CmmGraphs
    --
    ---------------------------------------------------

    modifyGraph :: (Graph n C C -> Graph n' C C) -> GenCmmGraph n -> GenCmmGraph n'
    modifyGraph f g = CmmGraph {g_entry=g_entry g, g_graph=f (g_graph g)}

    toBlockMap :: CmmGraph -> LabelMap CmmBlock
    toBlockMap (CmmGraph {g_graph=GMany NothingO body NothingO}) = body

    ofBlockMap :: BlockId -> LabelMap CmmBlock -> CmmGraph
    ofBlockMap entry bodyMap = CmmGraph {g_entry=entry, g_graph=GMany NothingO bodyMap NothingO}

    insertBlock :: CmmBlock -> LabelMap CmmBlock -> LabelMap CmmBlock
    insertBlock block map =
      ASSERT(isNothing $ mapLookup id map)
      mapInsert id block map
      where id = entryLabel block

    toBlockList :: CmmGraph -> [CmmBlock]
    toBlockList g = mapElems $ toBlockMap g

    -- | like 'toBlockList', but the entry block always comes first
    toBlockListEntryFirst :: CmmGraph -> [CmmBlock]
    toBlockListEntryFirst g
      | mapNull m  = []
      | otherwise  = entry_block : others
      where
        m = toBlockMap g
        entry_id = g_entry g
        Just entry_block = mapLookup entry_id m
        others = filter ((/= entry_id) . entryLabel) (mapElems m)

    -- | Like 'toBlockListEntryFirst', but we strive to ensure that we order blocks
    -- so that the false case of a conditional jumps to the next block in the output
    -- list of blocks. This matches the way OldCmm blocks were output since in
    -- OldCmm the false case was a fallthrough, whereas in Cmm conditional branches
    -- have both true and false successors. Block ordering can make a big difference
    -- in performance in the LLVM backend. Note that we rely crucially on the order
    -- of successors returned for CmmCondBranch by the NonLocal instance for CmmNode
    -- defind in cmm/CmmNode.hs. -GBM
    toBlockListEntryFirstFalseFallthrough :: CmmGraph -> [CmmBlock]
    toBlockListEntryFirstFalseFallthrough g
      | mapNull m  = []
      | otherwise  = dfs setEmpty [entry_block]
      where
        m = toBlockMap g
        entry_id = g_entry g
        Just entry_block = mapLookup entry_id m

        dfs :: LabelSet -> [CmmBlock] -> [CmmBlock]
        dfs _ [] = []
        dfs visited (block:bs)
          | id `setMember` visited = dfs visited bs
          | otherwise              = block : dfs (setInsert id visited) bs'
          where id = entryLabel block
                bs' = foldr add_id bs (successors block)
                add_id id bs = case mapLookup id m of
                                  Just b  -> b : bs
                                  Nothing -> bs

    ofBlockList :: BlockId -> [CmmBlock] -> CmmGraph
    ofBlockList entry blocks = CmmGraph { g_entry = entry
                                        , g_graph = GMany NothingO body NothingO }
      where body = foldr addBlock emptyBody blocks

    bodyToBlockList :: Body CmmNode -> [CmmBlock]
    bodyToBlockList body = mapElems body

    mapGraphNodes :: ( CmmNode C O -> CmmNode C O
                     , CmmNode O O -> CmmNode O O
                     , CmmNode O C -> CmmNode O C)
                  -> CmmGraph -> CmmGraph
    mapGraphNodes funs@(mf,_,_) g =
      ofBlockMap (entryLabel $ mf $ CmmEntry (g_entry g) GlobalScope) $
      mapMap (mapBlock3' funs) $ toBlockMap g

    mapGraphNodes1 :: (forall e x. CmmNode e x -> CmmNode e x) -> CmmGraph -> CmmGraph
    mapGraphNodes1 f = modifyGraph (mapGraph f)

    foldGraphBlocks :: (CmmBlock -> a -> a) -> a -> CmmGraph -> a
    foldGraphBlocks k z g = mapFold k z $ toBlockMap g

    postorderDfs :: CmmGraph -> [CmmBlock]
    postorderDfs g = {-# SCC "postorderDfs" #-} postorder_dfs_from (toBlockMap g) (g_entry g)

    -------------------------------------------------
    -- Tick utilities

    -- | Extract all tick annotations from the given block
    blockTicks :: Block CmmNode C C -> [CmmTickish]
    blockTicks b = reverse $ foldBlockNodesF goStmt b []
      where goStmt :: CmmNode e x -> [CmmTickish] -> [CmmTickish]
            goStmt  (CmmTick t) ts = t:ts
            goStmt  _other      ts = ts