nativeGen/PPC/CodeGen.hs

    {-# LANGUAGE CPP, GADTs #-}

    -----------------------------------------------------------------------------
    --
    -- Generating machine code (instruction selection)
    --
    -- (c) The University of Glasgow 1996-2004
    --
    -----------------------------------------------------------------------------

    -- This is a big module, but, if you pay attention to
    -- (a) the sectioning, and (b) the type signatures,
    -- the structure should not be too overwhelming.

    module PPC.CodeGen (
            cmmTopCodeGen,
            generateJumpTableForInstr,
            InstrBlock
    )

    where

    #include "HsVersions.h"
    #include "nativeGen/NCG.h"
    #include "../includes/MachDeps.h"

    -- NCG stuff:
    import CodeGen.Platform
    import PPC.Instr
    import PPC.Cond
    import PPC.Regs
    import CPrim
    import NCGMonad
    import Instruction
    import PIC
    import Format
    import RegClass
    import Reg
    import TargetReg
    import Platform

    -- Our intermediate code:
    import BlockId
    import PprCmm           ( pprExpr )
    import Cmm
    import CmmUtils
    import CmmSwitch
    import CLabel
    import Hoopl

    -- The rest:
    import OrdList
    import Outputable
    import Unique
    import DynFlags

    import Control.Monad    ( mapAndUnzipM, when )
    import Data.Bits
    import Data.Word

    import BasicTypes
    import FastString
    import Util

    -- -----------------------------------------------------------------------------
    -- Top-level of the instruction selector

    -- | 'InstrBlock's are the insn sequences generated by the insn selectors.
    -- They are really trees of insns to facilitate fast appending, where a
    -- left-to-right traversal (pre-order?) yields the insns in the correct
    -- order.

    cmmTopCodeGen
            :: RawCmmDecl
            -> NatM [NatCmmDecl CmmStatics Instr]

    cmmTopCodeGen (CmmProc info lab live graph) = do
      let blocks = toBlockListEntryFirst graph
      (nat_blocks,statics) <- mapAndUnzipM basicBlockCodeGen blocks
      dflags <- getDynFlags
      let proc = CmmProc info lab live (ListGraph $ concat nat_blocks)
          tops = proc : concat statics
          os   = platformOS $ targetPlatform dflags
          arch = platformArch $ targetPlatform dflags
      case arch of
        ArchPPC | os == OSAIX -> return tops
                | otherwise -> do
          picBaseMb <- getPicBaseMaybeNat
          case picBaseMb of
               Just picBase -> initializePicBase_ppc arch os picBase tops
               Nothing -> return tops
        ArchPPC_64 ELF_V1 -> return tops
                          -- generating function descriptor is handled in
                          -- pretty printer
        ArchPPC_64 ELF_V2 -> return tops
                          -- generating function prologue is handled in
                          -- pretty printer
        _          -> panic "PPC.cmmTopCodeGen: unknown arch"

    cmmTopCodeGen (CmmData sec dat) = do
      return [CmmData sec dat]  -- no translation, we just use CmmStatic

    basicBlockCodeGen
            :: Block CmmNode C C
            -> NatM ( [NatBasicBlock Instr]
                    , [NatCmmDecl CmmStatics Instr])

    basicBlockCodeGen block = do
      let (_, nodes, tail)  = blockSplit block
          id = entryLabel block
          stmts = blockToList nodes
      mid_instrs <- stmtsToInstrs stmts
      tail_instrs <- stmtToInstrs tail
      let instrs = mid_instrs `appOL` tail_instrs
      -- code generation may introduce new basic block boundaries, which
      -- are indicated by the NEWBLOCK instruction.  We must split up the
      -- instruction stream into basic blocks again.  Also, we extract
      -- LDATAs here too.
      let
            (top,other_blocks,statics) = foldrOL mkBlocks ([],[],[]) instrs

            mkBlocks (NEWBLOCK id) (instrs,blocks,statics)
              = ([], BasicBlock id instrs : blocks, statics)
            mkBlocks (LDATA sec dat) (instrs,blocks,statics)
              = (instrs, blocks, CmmData sec dat:statics)
            mkBlocks instr (instrs,blocks,statics)
              = (instr:instrs, blocks, statics)
      return (BasicBlock id top : other_blocks, statics)

    stmtsToInstrs :: [CmmNode e x] -> NatM InstrBlock
    stmtsToInstrs stmts
       = do instrss <- mapM stmtToInstrs stmts
            return (concatOL instrss)

    stmtToInstrs :: CmmNode e x -> NatM InstrBlock
    stmtToInstrs stmt = do
      dflags <- getDynFlags
      case stmt of
        CmmComment s   -> return (unitOL (COMMENT s))
        CmmTick {}     -> return nilOL
        CmmUnwind {}   -> return nilOL

        CmmAssign reg src
          | isFloatType ty -> assignReg_FltCode format reg src
          | target32Bit (targetPlatform dflags) &&
            isWord64 ty    -> assignReg_I64Code      reg src
          | otherwise        -> assignReg_IntCode format reg src
            where ty = cmmRegType dflags reg
                  format = cmmTypeFormat ty

        CmmStore addr src
          | isFloatType ty -> assignMem_FltCode format addr src
          | target32Bit (targetPlatform dflags) &&
            isWord64 ty      -> assignMem_I64Code      addr src
          | otherwise        -> assignMem_IntCode format addr src
            where ty = cmmExprType dflags src
                  format = cmmTypeFormat ty

        CmmUnsafeForeignCall target result_regs args
           -> genCCall target result_regs args

        CmmBranch id          -> genBranch id
        CmmCondBranch arg true false _ -> do
          b1 <- genCondJump true arg
          b2 <- genBranch false
          return (b1 `appOL` b2)
        CmmSwitch arg ids -> do dflags <- getDynFlags
                                genSwitch dflags arg ids
        CmmCall { cml_target = arg } -> genJump arg
        _ ->
          panic "stmtToInstrs: statement should have been cps'd away"

    --------------------------------------------------------------------------------
    -- | 'InstrBlock's are the insn sequences generated by the insn selectors.
    --      They are really trees of insns to facilitate fast appending, where a
    --      left-to-right traversal yields the insns in the correct order.
    --
    type InstrBlock
            = OrdList Instr

    -- | Register's passed up the tree.  If the stix code forces the register
    --      to live in a pre-decided machine register, it comes out as @Fixed@;
    --      otherwise, it comes out as @Any@, and the parent can decide which
    --      register to put it in.
    --
    data Register
            = Fixed Format Reg InstrBlock
            | Any   Format (Reg -> InstrBlock)

    swizzleRegisterRep :: Register -> Format -> Register
    swizzleRegisterRep (Fixed _ reg code) format = Fixed format reg code
    swizzleRegisterRep (Any _ codefn)     format = Any   format codefn

    -- | Grab the Reg for a CmmReg
    getRegisterReg :: Platform -> CmmReg -> Reg

    getRegisterReg _ (CmmLocal (LocalReg u pk))
      = RegVirtual $ mkVirtualReg u (cmmTypeFormat pk)

    getRegisterReg platform (CmmGlobal mid)
      = case globalRegMaybe platform mid of
            Just reg -> RegReal reg
            Nothing  -> pprPanic "getRegisterReg-memory" (ppr $ CmmGlobal mid)
            -- By this stage, the only MagicIds remaining should be the
            -- ones which map to a real machine register on this
            -- platform.  Hence ...

    -- | Convert a BlockId to some CmmStatic data
    jumpTableEntry :: DynFlags -> Maybe BlockId -> CmmStatic
    jumpTableEntry dflags Nothing = CmmStaticLit (CmmInt 0 (wordWidth dflags))
    jumpTableEntry _ (Just blockid) = CmmStaticLit (CmmLabel blockLabel)
        where blockLabel = mkAsmTempLabel (getUnique blockid)

    -- -----------------------------------------------------------------------------
    -- General things for putting together code sequences

    -- Expand CmmRegOff.  ToDo: should we do it this way around, or convert
    -- CmmExprs into CmmRegOff?
    mangleIndexTree :: DynFlags -> CmmExpr -> CmmExpr
    mangleIndexTree dflags (CmmRegOff reg off)
      = CmmMachOp (MO_Add width) [CmmReg reg, CmmLit (CmmInt (fromIntegral off) width)]
      where width = typeWidth (cmmRegType dflags reg)

    mangleIndexTree _ _
            = panic "PPC.CodeGen.mangleIndexTree: no match"

    -- -----------------------------------------------------------------------------
    --  Code gen for 64-bit arithmetic on 32-bit platforms

    {-
    Simple support for generating 64-bit code (ie, 64 bit values and 64
    bit assignments) on 32-bit platforms.  Unlike the main code generator
    we merely shoot for generating working code as simply as possible, and
    pay little attention to code quality.  Specifically, there is no
    attempt to deal cleverly with the fixed-vs-floating register
    distinction; all values are generated into (pairs of) floating
    registers, even if this would mean some redundant reg-reg moves as a
    result.  Only one of the VRegUniques is returned, since it will be
    of the VRegUniqueLo form, and the upper-half VReg can be determined
    by applying getHiVRegFromLo to it.
    -}

    data ChildCode64        -- a.k.a "Register64"
          = ChildCode64
               InstrBlock   -- code
               Reg          -- the lower 32-bit temporary which contains the
                            -- result; use getHiVRegFromLo to find the other
                            -- VRegUnique.  Rules of this simplified insn
                            -- selection game are therefore that the returned
                            -- Reg may be modified

    -- | Compute an expression into a register, but
    --      we don't mind which one it is.
    getSomeReg :: CmmExpr -> NatM (Reg, InstrBlock)
    getSomeReg expr = do
      r <- getRegister expr
      case r of
        Any rep code -> do
            tmp <- getNewRegNat rep
            return (tmp, code tmp)
        Fixed _ reg code ->
            return (reg, code)

    getI64Amodes :: CmmExpr -> NatM (AddrMode, AddrMode, InstrBlock)
    getI64Amodes addrTree = do
        Amode hi_addr addr_code <- getAmode D addrTree
        case addrOffset hi_addr 4 of
            Just lo_addr -> return (hi_addr, lo_addr, addr_code)
            Nothing      -> do (hi_ptr, code) <- getSomeReg addrTree
                               return (AddrRegImm hi_ptr (ImmInt 0),
                                       AddrRegImm hi_ptr (ImmInt 4),
                                       code)

    assignMem_I64Code :: CmmExpr -> CmmExpr -> NatM InstrBlock
    assignMem_I64Code addrTree valueTree = do
            (hi_addr, lo_addr, addr_code) <- getI64Amodes addrTree
            ChildCode64 vcode rlo <- iselExpr64 valueTree
            let
                    rhi = getHiVRegFromLo rlo

                    -- Big-endian store
                    mov_hi = ST II32 rhi hi_addr
                    mov_lo = ST II32 rlo lo_addr
            return (vcode `appOL` addr_code `snocOL` mov_lo `snocOL` mov_hi)

    assignReg_I64Code :: CmmReg  -> CmmExpr -> NatM InstrBlock
    assignReg_I64Code (CmmLocal (LocalReg u_dst _)) valueTree = do
       ChildCode64 vcode r_src_lo <- iselExpr64 valueTree
       let
             r_dst_lo = RegVirtual $ mkVirtualReg u_dst II32
             r_dst_hi = getHiVRegFromLo r_dst_lo
             r_src_hi = getHiVRegFromLo r_src_lo
             mov_lo = MR r_dst_lo r_src_lo
             mov_hi = MR r_dst_hi r_src_hi
       return (
            vcode `snocOL` mov_lo `snocOL` mov_hi
         )

    assignReg_I64Code _ _
       = panic "assignReg_I64Code(powerpc): invalid lvalue"

    iselExpr64        :: CmmExpr -> NatM ChildCode64
    iselExpr64 (CmmLoad addrTree ty) | isWord64 ty = do
        (hi_addr, lo_addr, addr_code) <- getI64Amodes addrTree
        (rlo, rhi) <- getNewRegPairNat II32
        let mov_hi = LD II32 rhi hi_addr
            mov_lo = LD II32 rlo lo_addr
        return $ ChildCode64 (addr_code `snocOL` mov_lo `snocOL` mov_hi)
                             rlo

    iselExpr64 (CmmReg (CmmLocal (LocalReg vu ty))) | isWord64 ty
       = return (ChildCode64 nilOL (RegVirtual $ mkVirtualReg vu II32))

    iselExpr64 (CmmLit (CmmInt i _)) = do
      (rlo,rhi) <- getNewRegPairNat II32
      let
            half0 = fromIntegral (fromIntegral i :: Word16)
            half1 = fromIntegral (fromIntegral (i `shiftR` 16) :: Word16)
            half2 = fromIntegral (fromIntegral (i `shiftR` 32) :: Word16)
            half3 = fromIntegral (fromIntegral (i `shiftR` 48) :: Word16)

            code = toOL [
                    LIS rlo (ImmInt half1),
                    OR rlo rlo (RIImm $ ImmInt half0),
                    LIS rhi (ImmInt half3),
                    OR rhi rhi (RIImm $ ImmInt half2)
                    ]
      return (ChildCode64 code rlo)

    iselExpr64 (CmmMachOp (MO_Add _) [e1,e2]) = do
       ChildCode64 code1 r1lo <- iselExpr64 e1
       ChildCode64 code2 r2lo <- iselExpr64 e2
       (rlo,rhi) <- getNewRegPairNat II32
       let
            r1hi = getHiVRegFromLo r1lo
            r2hi = getHiVRegFromLo r2lo
            code =  code1 `appOL`
                    code2 `appOL`
                    toOL [ ADDC rlo r1lo r2lo,
                           ADDE rhi r1hi r2hi ]
       return (ChildCode64 code rlo)

    iselExpr64 (CmmMachOp (MO_Sub _) [e1,e2]) = do
       ChildCode64 code1 r1lo <- iselExpr64 e1
       ChildCode64 code2 r2lo <- iselExpr64 e2
       (rlo,rhi) <- getNewRegPairNat II32
       let
            r1hi = getHiVRegFromLo r1lo
            r2hi = getHiVRegFromLo r2lo
            code =  code1 `appOL`
                    code2 `appOL`
                    toOL [ SUBFC rlo r2lo (RIReg r1lo),
                           SUBFE rhi r2hi r1hi ]
       return (ChildCode64 code rlo)

    iselExpr64 (CmmMachOp (MO_UU_Conv W32 W64) [expr]) = do
        (expr_reg,expr_code) <- getSomeReg expr
        (rlo, rhi) <- getNewRegPairNat II32
        let mov_hi = LI rhi (ImmInt 0)
            mov_lo = MR rlo expr_reg
        return $ ChildCode64 (expr_code `snocOL` mov_lo `snocOL` mov_hi)
                             rlo
    iselExpr64 expr
       = pprPanic "iselExpr64(powerpc)" (pprExpr expr)

    getRegister :: CmmExpr -> NatM Register
    getRegister e = do dflags <- getDynFlags
                       getRegister' dflags e

    getRegister' :: DynFlags -> CmmExpr -> NatM Register

    getRegister' dflags (CmmReg (CmmGlobal PicBaseReg))
      | OSAIX <- platformOS (targetPlatform dflags) = do
            let code dst = toOL [ LD II32 dst tocAddr ]
                tocAddr = AddrRegImm toc (ImmLit (text "ghc_toc_table[TC]"))
            return (Any II32 code)
      | target32Bit (targetPlatform dflags) = do
          reg <- getPicBaseNat $ archWordFormat (target32Bit (targetPlatform dflags))
          return (Fixed (archWordFormat (target32Bit (targetPlatform dflags)))
                        reg nilOL)
      | otherwise = return (Fixed II64 toc nilOL)

    getRegister' dflags (CmmReg reg)
      = return (Fixed (cmmTypeFormat (cmmRegType dflags reg))
                      (getRegisterReg (targetPlatform dflags) reg) nilOL)

    getRegister' dflags tree@(CmmRegOff _ _)
      = getRegister' dflags (mangleIndexTree dflags tree)

        -- for 32-bit architectuers, support some 64 -> 32 bit conversions:
        -- TO_W_(x), TO_W_(x >> 32)

    getRegister' dflags (CmmMachOp (MO_UU_Conv W64 W32)
                         [CmmMachOp (MO_U_Shr W64) [x,CmmLit (CmmInt 32 _)]])
     | target32Bit (targetPlatform dflags) = do
      ChildCode64 code rlo <- iselExpr64 x
      return $ Fixed II32 (getHiVRegFromLo rlo) code

    getRegister' dflags (CmmMachOp (MO_SS_Conv W64 W32)
                         [CmmMachOp (MO_U_Shr W64) [x,CmmLit (CmmInt 32 _)]])
     | target32Bit (targetPlatform dflags) = do
      ChildCode64 code rlo <- iselExpr64 x
      return $ Fixed II32 (getHiVRegFromLo rlo) code

    getRegister' dflags (CmmMachOp (MO_UU_Conv W64 W32) [x])
     | target32Bit (targetPlatform dflags) = do
      ChildCode64 code rlo <- iselExpr64 x
      return $ Fixed II32 rlo code

    getRegister' dflags (CmmMachOp (MO_SS_Conv W64 W32) [x])
     | target32Bit (targetPlatform dflags) = do
      ChildCode64 code rlo <- iselExpr64 x
      return $ Fixed II32 rlo code

    getRegister' dflags (CmmLoad mem pk)
     | not (isWord64 pk) = do
            let platform = targetPlatform dflags
            Amode addr addr_code <- getAmode D mem
            let code dst = ASSERT((targetClassOfReg platform dst == RcDouble) == isFloatType pk)
                           addr_code `snocOL` LD format dst addr
            return (Any format code)
     | not (target32Bit (targetPlatform dflags)) = do
            Amode addr addr_code <- getAmode DS mem
            let code dst = addr_code `snocOL` LD II64 dst addr
            return (Any II64 code)

              where format = cmmTypeFormat pk

    -- catch simple cases of zero- or sign-extended load
    getRegister' _ (CmmMachOp (MO_UU_Conv W8 W32) [CmmLoad mem _]) = do
        Amode addr addr_code <- getAmode D mem
        return (Any II32 (\dst -> addr_code `snocOL` LD II8 dst addr))

    getRegister' _ (CmmMachOp (MO_UU_Conv W8 W64) [CmmLoad mem _]) = do
        Amode addr addr_code <- getAmode D mem
        return (Any II64 (\dst -> addr_code `snocOL` LD II8 dst addr))

    -- Note: there is no Load Byte Arithmetic instruction, so no signed case here

    getRegister' _ (CmmMachOp (MO_UU_Conv W16 W32) [CmmLoad mem _]) = do
        Amode addr addr_code <- getAmode D mem
        return (Any II32 (\dst -> addr_code `snocOL` LD II16 dst addr))

    getRegister' _ (CmmMachOp (MO_SS_Conv W16 W32) [CmmLoad mem _]) = do
        Amode addr addr_code <- getAmode D mem
        return (Any II32 (\dst -> addr_code `snocOL` LA II16 dst addr))

    getRegister' _ (CmmMachOp (MO_UU_Conv W16 W64) [CmmLoad mem _]) = do
        Amode addr addr_code <- getAmode D mem
        return (Any II64 (\dst -> addr_code `snocOL` LD II16 dst addr))

    getRegister' _ (CmmMachOp (MO_SS_Conv W16 W64) [CmmLoad mem _]) = do
        Amode addr addr_code <- getAmode D mem
        return (Any II64 (\dst -> addr_code `snocOL` LA II16 dst addr))

    getRegister' _ (CmmMachOp (MO_UU_Conv W32 W64) [CmmLoad mem _]) = do
        Amode addr addr_code <- getAmode D mem
        return (Any II64 (\dst -> addr_code `snocOL` LD II32 dst addr))

    getRegister' _ (CmmMachOp (MO_SS_Conv W32 W64) [CmmLoad mem _]) = do
        -- lwa is DS-form. See Note [Power instruction format]
        Amode addr addr_code <- getAmode DS mem
        return (Any II64 (\dst -> addr_code `snocOL` LA II32 dst addr))

    getRegister' dflags (CmmMachOp mop [x]) -- unary MachOps
      = case mop of
          MO_Not rep   -> triv_ucode_int rep NOT

          MO_F_Neg w   -> triv_ucode_float w FNEG
          MO_S_Neg w   -> triv_ucode_int   w NEG

          MO_FF_Conv W64 W32 -> trivialUCode  FF32 FRSP x
          MO_FF_Conv W32 W64 -> conversionNop FF64 x

          MO_FS_Conv from to -> coerceFP2Int from to x
          MO_SF_Conv from to -> coerceInt2FP from to x

          MO_SS_Conv from to
            | from == to    -> conversionNop (intFormat to) x

            -- narrowing is a nop: we treat the high bits as undefined
          MO_SS_Conv W64 to
            | arch32    -> panic "PPC.CodeGen.getRegister no 64 bit int register"
            | otherwise -> conversionNop (intFormat to) x
          MO_SS_Conv W32 to
            | arch32    -> conversionNop (intFormat to) x
            | otherwise -> case to of
                W64 -> triv_ucode_int to (EXTS II32)
                W16 -> conversionNop II16 x
                W8  -> conversionNop II8 x
                _   -> panic "PPC.CodeGen.getRegister: no match"
          MO_SS_Conv W16 W8 -> conversionNop II8 x
          MO_SS_Conv W8  to -> triv_ucode_int to (EXTS II8)
          MO_SS_Conv W16 to -> triv_ucode_int to (EXTS II16)

          MO_UU_Conv from to
            | from == to -> conversionNop (intFormat to) x
            -- narrowing is a nop: we treat the high bits as undefined
          MO_UU_Conv W64 to
            | arch32    -> panic "PPC.CodeGen.getRegister no 64 bit target"
            | otherwise -> conversionNop (intFormat to) x
          MO_UU_Conv W32 to
            | arch32    -> conversionNop (intFormat to) x
            | otherwise ->
              case to of
               W64 -> trivialCode to False AND x (CmmLit (CmmInt 4294967295 W64))
               W16 -> conversionNop II16 x
               W8  -> conversionNop II8 x
               _   -> panic "PPC.CodeGen.getRegister: no match"
          MO_UU_Conv W16 W8 -> conversionNop II8 x
          MO_UU_Conv W8 to  -> trivialCode to False AND x (CmmLit (CmmInt 255 W32))
          MO_UU_Conv W16 to -> trivialCode to False AND x (CmmLit (CmmInt 65535 W32))
          _ -> panic "PPC.CodeGen.getRegister: no match"

        where
            triv_ucode_int   width instr = trivialUCode (intFormat    width) instr x
            triv_ucode_float width instr = trivialUCode (floatFormat  width) instr x

            conversionNop new_format expr
                = do e_code <- getRegister' dflags expr
                     return (swizzleRegisterRep e_code new_format)
            arch32 = target32Bit $ targetPlatform dflags

    getRegister' dflags (CmmMachOp mop [x, y]) -- dyadic PrimOps
      = case mop of
          MO_F_Eq _ -> condFltReg EQQ x y
          MO_F_Ne _ -> condFltReg NE  x y
          MO_F_Gt _ -> condFltReg GTT x y
          MO_F_Ge _ -> condFltReg GE  x y
          MO_F_Lt _ -> condFltReg LTT x y
          MO_F_Le _ -> condFltReg LE  x y

          MO_Eq rep -> condIntReg EQQ  (extendUExpr dflags rep x)
                                       (extendUExpr dflags rep y)
          MO_Ne rep -> condIntReg NE   (extendUExpr dflags rep x)
                                       (extendUExpr dflags rep y)

          MO_S_Gt rep -> condIntReg GTT  (extendSExpr dflags rep x)
                                         (extendSExpr dflags rep y)
          MO_S_Ge rep -> condIntReg GE   (extendSExpr dflags rep x)
                                         (extendSExpr dflags rep y)
          MO_S_Lt rep -> condIntReg LTT  (extendSExpr dflags rep x)
                                         (extendSExpr dflags rep y)
          MO_S_Le rep -> condIntReg LE   (extendSExpr dflags rep x)
                                         (extendSExpr dflags rep y)

          MO_U_Gt rep -> condIntReg GU   (extendUExpr dflags rep x)
                                         (extendUExpr dflags rep y)
          MO_U_Ge rep -> condIntReg GEU  (extendUExpr dflags rep x)
                                         (extendUExpr dflags rep y)
          MO_U_Lt rep -> condIntReg LU   (extendUExpr dflags rep x)
                                         (extendUExpr dflags rep y)
          MO_U_Le rep -> condIntReg LEU  (extendUExpr dflags rep x)
                                         (extendUExpr dflags rep y)

          MO_F_Add w  -> triv_float w FADD
          MO_F_Sub w  -> triv_float w FSUB
          MO_F_Mul w  -> triv_float w FMUL
          MO_F_Quot w -> triv_float w FDIV

             -- optimize addition with 32-bit immediate
             -- (needed for PIC)
          MO_Add W32 ->
            case y of
              CmmLit (CmmInt imm immrep) | Just _ <- makeImmediate W32 True imm
                -> trivialCode W32 True ADD x (CmmLit $ CmmInt imm immrep)
              CmmLit lit
                -> do
                    (src, srcCode) <- getSomeReg x
                    let imm = litToImm lit
                        code dst = srcCode `appOL` toOL [
                                        ADDIS dst src (HA imm),
                                        ADD dst dst (RIImm (LO imm))
                                    ]
                    return (Any II32 code)
              _ -> trivialCode W32 True ADD x y

          MO_Add rep -> trivialCode rep True ADD x y
          MO_Sub rep ->
            case y of
              CmmLit (CmmInt imm immrep) | Just _ <- makeImmediate rep True (-imm)
                -> trivialCode rep True ADD x (CmmLit $ CmmInt (-imm) immrep)
              _ -> case x of
                     CmmLit (CmmInt imm _)
                       | Just _ <- makeImmediate rep True imm
                       -- subfi ('substract from' with immediate) doesn't exist
                       -> trivialCode rep True SUBFC y x
                     _ -> trivialCodeNoImm' (intFormat rep) SUBF y x

          MO_Mul rep -> shiftMulCode rep True MULL x y
          MO_S_MulMayOflo rep -> do
            (src1, code1) <- getSomeReg x
            (src2, code2) <- getSomeReg y
            let
              format = intFormat rep
              code dst = code1 `appOL` code2
                           `appOL` toOL [ MULLO format dst src1 src2
                                        , MFOV  format dst
                                        ]
            return (Any format code)

          MO_S_Quot rep -> trivialCodeNoImmSign (intFormat rep) True DIV
                    (extendSExpr dflags rep x) (extendSExpr dflags rep y)
          MO_U_Quot rep -> trivialCodeNoImmSign (intFormat rep) False DIV
                    (extendUExpr dflags rep x) (extendUExpr dflags rep y)

          MO_S_Rem rep -> remainderCode rep True (extendSExpr dflags rep x)
                                                 (extendSExpr dflags rep y)
          MO_U_Rem rep -> remainderCode rep False (extendUExpr dflags rep x)
                                                  (extendUExpr dflags rep y)

          MO_And rep   -> case y of
            (CmmLit (CmmInt imm _)) | imm == -8 || imm == -4
                -> do
                    (src, srcCode) <- getSomeReg x
                    let clear_mask = if imm == -4 then 2 else 3
                        fmt = intFormat rep
                        code dst = srcCode
                                   `appOL` unitOL (CLRRI fmt dst src clear_mask)
                    return (Any fmt code)
            _ -> trivialCode rep False AND x y
          MO_Or rep    -> trivialCode rep False OR x y
          MO_Xor rep   -> trivialCode rep False XOR x y

          MO_Shl rep   -> shiftMulCode rep False SL x y
          MO_S_Shr rep -> shiftMulCode rep False SRA (extendSExpr dflags rep x) y
          MO_U_Shr rep -> shiftMulCode rep False SR (extendUExpr dflags rep x) y
          _         -> panic "PPC.CodeGen.getRegister: no match"

      where
        triv_float :: Width -> (Format -> Reg -> Reg -> Reg -> Instr) -> NatM Register
        triv_float width instr = trivialCodeNoImm (floatFormat width) instr x y

    getRegister' _ (CmmLit (CmmInt i rep))
      | Just imm <- makeImmediate rep True i
      = let
            code dst = unitOL (LI dst imm)
        in
            return (Any (intFormat rep) code)

    getRegister' _ (CmmLit (CmmFloat f frep)) = do
        lbl <- getNewLabelNat
        dflags <- getDynFlags
        dynRef <- cmmMakeDynamicReference dflags DataReference lbl
        Amode addr addr_code <- getAmode D dynRef
        let format = floatFormat frep
            code dst =
                LDATA (Section ReadOnlyData lbl)
                      (Statics lbl [CmmStaticLit (CmmFloat f frep)])
                `consOL` (addr_code `snocOL` LD format dst addr)
        return (Any format code)

    getRegister' dflags (CmmLit lit)
      | target32Bit (targetPlatform dflags)
      = let rep = cmmLitType dflags lit
            imm = litToImm lit
            code dst = toOL [
                  LIS dst (HA imm),
                  ADD dst dst (RIImm (LO imm))
              ]
        in return (Any (cmmTypeFormat rep) code)
      | otherwise
      = do lbl <- getNewLabelNat
           dflags <- getDynFlags
           dynRef <- cmmMakeDynamicReference dflags DataReference lbl
           Amode addr addr_code <- getAmode D dynRef
           let rep = cmmLitType dflags lit
               format = cmmTypeFormat rep
               code dst =
                LDATA (Section ReadOnlyData lbl) (Statics lbl [CmmStaticLit lit])
                `consOL` (addr_code `snocOL` LD format dst addr)
           return (Any format code)

    getRegister' _ other = pprPanic "getRegister(ppc)" (pprExpr other)

        -- extend?Rep: wrap integer expression of type rep
        -- in a conversion to II32 or II64 resp.
    extendSExpr :: DynFlags -> Width -> CmmExpr -> CmmExpr
    extendSExpr dflags W32 x
     | target32Bit (targetPlatform dflags) = x

    extendSExpr dflags W64 x
     | not (target32Bit (targetPlatform dflags)) = x

    extendSExpr dflags rep x =
        let size = if target32Bit $ targetPlatform dflags
                   then W32
                   else W64
        in CmmMachOp (MO_SS_Conv rep size) [x]

    extendUExpr :: DynFlags -> Width -> CmmExpr -> CmmExpr
    extendUExpr dflags W32 x
     | target32Bit (targetPlatform dflags) = x
    extendUExpr dflags W64 x
     | not (target32Bit (targetPlatform dflags)) = x
    extendUExpr dflags rep x =
        let size = if target32Bit $ targetPlatform dflags
                   then W32
                   else W64
        in CmmMachOp (MO_UU_Conv rep size) [x]

    -- -----------------------------------------------------------------------------
    --  The 'Amode' type: Memory addressing modes passed up the tree.

    data Amode
            = Amode AddrMode InstrBlock

    {-
    Now, given a tree (the argument to an CmmLoad) that references memory,
    produce a suitable addressing mode.

    A Rule of the Game (tm) for Amodes: use of the addr bit must
    immediately follow use of the code part, since the code part puts
    values in registers which the addr then refers to.  So you can't put
    anything in between, lest it overwrite some of those registers.  If
    you need to do some other computation between the code part and use of
    the addr bit, first store the effective address from the amode in a
    temporary, then do the other computation, and then use the temporary:

        code
        LEA amode, tmp
        ... other computation ...
        ... (tmp) ...
    -}

    {- Note [Power instruction format]
    In some instructions the 16 bit offset must be a multiple of 4, i.e.
    the two least significant bits must be zero. The "Power ISA" specification
    calls these instruction formats "DS-FORM" and the instructions with
    arbitrary 16 bit offsets are "D-FORM".

    The Power ISA specification document can be obtained from www.power.org.
    -}
    data InstrForm = D | DS

    getAmode :: InstrForm -> CmmExpr -> NatM Amode
    getAmode inf tree@(CmmRegOff _ _)
      = do dflags <- getDynFlags
           getAmode inf (mangleIndexTree dflags tree)

    getAmode _ (CmmMachOp (MO_Sub W32) [x, CmmLit (CmmInt i _)])
      | Just off <- makeImmediate W32 True (-i)
      = do
            (reg, code) <- getSomeReg x
            return (Amode (AddrRegImm reg off) code)

    getAmode _ (CmmMachOp (MO_Add W32) [x, CmmLit (CmmInt i _)])
      | Just off <- makeImmediate W32 True i
      = do
            (reg, code) <- getSomeReg x
            return (Amode (AddrRegImm reg off) code)

    getAmode D (CmmMachOp (MO_Sub W64) [x, CmmLit (CmmInt i _)])
      | Just off <- makeImmediate W64 True (-i)
      = do
            (reg, code) <- getSomeReg x
            return (Amode (AddrRegImm reg off) code)

    getAmode D (CmmMachOp (MO_Add W64) [x, CmmLit (CmmInt i _)])
      | Just off <- makeImmediate W64 True i
      = do
            (reg, code) <- getSomeReg x
            return (Amode (AddrRegImm reg off) code)

    getAmode DS (CmmMachOp (MO_Sub W64) [x, CmmLit (CmmInt i _)])
      | Just off <- makeImmediate W64 True (-i)
      = do
            (reg, code) <- getSomeReg x
            (reg', off', code')  <-
                         if i `mod` 4 == 0
                          then do return (reg, off, code)
                          else do
                               tmp <- getNewRegNat II64
                               return (tmp, ImmInt 0,
                                      code `snocOL` ADD tmp reg (RIImm off))
            return (Amode (AddrRegImm reg' off') code')

    getAmode DS (CmmMachOp (MO_Add W64) [x, CmmLit (CmmInt i _)])
      | Just off <- makeImmediate W64 True i
      = do
            (reg, code) <- getSomeReg x
            (reg', off', code')  <-
                         if i `mod` 4 == 0
                          then do return (reg, off, code)
                          else do
                               tmp <- getNewRegNat II64
                               return (tmp, ImmInt 0,
                                      code `snocOL` ADD tmp reg (RIImm off))
            return (Amode (AddrRegImm reg' off') code')

       -- optimize addition with 32-bit immediate
       -- (needed for PIC)
    getAmode _ (CmmMachOp (MO_Add W32) [x, CmmLit lit])
      = do
            dflags <- getDynFlags
            (src, srcCode) <- getSomeReg x
            let imm = litToImm lit
            case () of
                _ | OSAIX <- platformOS (targetPlatform dflags)
                  , isCmmLabelType lit ->
                        -- HA16/LO16 relocations on labels not supported on AIX
                        return (Amode (AddrRegImm src imm) srcCode)
                  | otherwise -> do
                        tmp <- getNewRegNat II32
                        let code = srcCode `snocOL` ADDIS tmp src (HA imm)
                        return (Amode (AddrRegImm tmp (LO imm)) code)
      where
          isCmmLabelType (CmmLabel {})        = True
          isCmmLabelType (CmmLabelOff {})     = True
          isCmmLabelType (CmmLabelDiffOff {}) = True
          isCmmLabelType _                    = False

    getAmode _ (CmmLit lit)
      = do
            dflags <- getDynFlags
            case platformArch $ targetPlatform dflags of
                 ArchPPC -> do
                     tmp <- getNewRegNat II32
                     let imm = litToImm lit
                         code = unitOL (LIS tmp (HA imm))
                     return (Amode (AddrRegImm tmp (LO imm)) code)
                 _        -> do -- TODO: Load from TOC,
                                -- see getRegister' _ (CmmLit lit)
                     tmp <- getNewRegNat II64
                     let imm = litToImm lit
                         code =  toOL [
                              LIS tmp (HIGHESTA imm),
                              OR tmp tmp (RIImm (HIGHERA imm)),
                              SL  II64 tmp tmp (RIImm (ImmInt 32)),
                              ORIS tmp tmp (HA imm)
                              ]
                     return (Amode (AddrRegImm tmp (LO imm)) code)

    getAmode _ (CmmMachOp (MO_Add W32) [x, y])
      = do
            (regX, codeX) <- getSomeReg x
            (regY, codeY) <- getSomeReg y
            return (Amode (AddrRegReg regX regY) (codeX `appOL` codeY))

    getAmode _ (CmmMachOp (MO_Add W64) [x, y])
      = do
            (regX, codeX) <- getSomeReg x
            (regY, codeY) <- getSomeReg y
            return (Amode (AddrRegReg regX regY) (codeX `appOL` codeY))

    getAmode _ other
      = do
            (reg, code) <- getSomeReg other
            let
                off  = ImmInt 0
            return (Amode (AddrRegImm reg off) code)

    --  The 'CondCode' type:  Condition codes passed up the tree.
    data CondCode
            = CondCode Bool Cond InstrBlock

    -- Set up a condition code for a conditional branch.

    getCondCode :: CmmExpr -> NatM CondCode

    -- almost the same as everywhere else - but we need to
    -- extend small integers to 32 bit or 64 bit first

    getCondCode (CmmMachOp mop [x, y])
      = do
        dflags <- getDynFlags
        case mop of
          MO_F_Eq W32 -> condFltCode EQQ x y
          MO_F_Ne W32 -> condFltCode NE  x y
          MO_F_Gt W32 -> condFltCode GTT x y
          MO_F_Ge W32 -> condFltCode GE  x y
          MO_F_Lt W32 -> condFltCode LTT x y
          MO_F_Le W32 -> condFltCode LE  x y

          MO_F_Eq W64 -> condFltCode EQQ x y
          MO_F_Ne W64 -> condFltCode NE  x y
          MO_F_Gt W64 -> condFltCode GTT x y
          MO_F_Ge W64 -> condFltCode GE  x y
          MO_F_Lt W64 -> condFltCode LTT x y
          MO_F_Le W64 -> condFltCode LE  x y

          MO_Eq rep -> condIntCode EQQ  (extendUExpr dflags rep x)
                                        (extendUExpr dflags rep y)
          MO_Ne rep -> condIntCode NE   (extendUExpr dflags rep x)
                                        (extendUExpr dflags rep y)

          MO_S_Gt rep -> condIntCode GTT  (extendSExpr dflags rep x)
                                          (extendSExpr dflags rep y)
          MO_S_Ge rep -> condIntCode GE   (extendSExpr dflags rep x)
                                          (extendSExpr dflags rep y)
          MO_S_Lt rep -> condIntCode LTT  (extendSExpr dflags rep x)
                                          (extendSExpr dflags rep y)
          MO_S_Le rep -> condIntCode LE   (extendSExpr dflags rep x)
                                          (extendSExpr dflags rep y)

          MO_U_Gt rep -> condIntCode GU   (extendSExpr dflags rep x)
                                          (extendSExpr dflags rep y)
          MO_U_Ge rep -> condIntCode GEU  (extendSExpr dflags rep x)
                                          (extendSExpr dflags rep y)
          MO_U_Lt rep -> condIntCode LU   (extendSExpr dflags rep x)
                                          (extendSExpr dflags rep y)
          MO_U_Le rep -> condIntCode LEU  (extendSExpr dflags rep x)
                                          (extendSExpr dflags rep y)

          _ -> pprPanic "getCondCode(powerpc)" (pprMachOp mop)

    getCondCode _ = panic "getCondCode(2)(powerpc)"

    -- @cond(Int|Flt)Code@: Turn a boolean expression into a condition, to be
    -- passed back up the tree.

    condIntCode, condFltCode :: Cond -> CmmExpr -> CmmExpr -> NatM CondCode

    -- optimize pointer tag checks. Operation andi. sets condition register
    -- so cmpi ..., 0 is redundant.
    condIntCode cond (CmmMachOp (MO_And _) [x, CmmLit (CmmInt imm rep)])
                     (CmmLit (CmmInt 0 _))
      | not $ condUnsigned cond,
        Just src2 <- makeImmediate rep False imm
      = do
          (src1, code) <- getSomeReg x
          let code' = code `snocOL` AND r0 src1 (RIImm src2)
          return (CondCode False cond code')

    condIntCode cond x (CmmLit (CmmInt y rep))
      | Just src2 <- makeImmediate rep (not $ condUnsigned cond) y
      = do
            (src1, code) <- getSomeReg x
            dflags <- getDynFlags
            let format = archWordFormat $ target32Bit $ targetPlatform dflags
                code' = code `snocOL`
                  (if condUnsigned cond then CMPL else CMP) format src1 (RIImm src2)
            return (CondCode False cond code')

    condIntCode cond x y = do
        (src1, code1) <- getSomeReg x
        (src2, code2) <- getSomeReg y
        dflags <- getDynFlags
        let format = archWordFormat $ target32Bit $ targetPlatform dflags
            code' = code1 `appOL` code2 `snocOL`
              (if condUnsigned cond then CMPL else CMP) format src1 (RIReg src2)
        return (CondCode False cond code')

    condFltCode cond x y = do
        (src1, code1) <- getSomeReg x
        (src2, code2) <- getSomeReg y
        let
            code'  = code1 `appOL` code2 `snocOL` FCMP src1 src2
            code'' = case cond of -- twiddle CR to handle unordered case
                        GE -> code' `snocOL` CRNOR ltbit eqbit gtbit
                        LE -> code' `snocOL` CRNOR gtbit eqbit ltbit
                        _ -> code'
                     where
                        ltbit = 0 ; eqbit = 2 ; gtbit = 1
        return (CondCode True cond code'')

    -- -----------------------------------------------------------------------------
    -- Generating assignments

    -- Assignments are really at the heart of the whole code generation
    -- business.  Almost all top-level nodes of any real importance are
    -- assignments, which correspond to loads, stores, or register
    -- transfers.  If we're really lucky, some of the register transfers
    -- will go away, because we can use the destination register to
    -- complete the code generation for the right hand side.  This only
    -- fails when the right hand side is forced into a fixed register
    -- (e.g. the result of a call).

    assignMem_IntCode :: Format -> CmmExpr -> CmmExpr -> NatM InstrBlock
    assignReg_IntCode :: Format -> CmmReg  -> CmmExpr -> NatM InstrBlock

    assignMem_FltCode :: Format -> CmmExpr -> CmmExpr -> NatM InstrBlock
    assignReg_FltCode :: Format -> CmmReg  -> CmmExpr -> NatM InstrBlock

    assignMem_IntCode pk addr src = do
        (srcReg, code) <- getSomeReg src
        Amode dstAddr addr_code <- case pk of
                                    II64 -> getAmode DS addr
                                    _    -> getAmode D  addr
        return $ code `appOL` addr_code `snocOL` ST pk srcReg dstAddr

    -- dst is a reg, but src could be anything
    assignReg_IntCode _ reg src
        = do
            dflags <- getDynFlags
            let dst = getRegisterReg (targetPlatform dflags) reg
            r <- getRegister src
            return $ case r of
                Any _ code         -> code dst
                Fixed _ freg fcode -> fcode `snocOL` MR dst freg

    -- Easy, isn't it?
    assignMem_FltCode = assignMem_IntCode
    assignReg_FltCode = assignReg_IntCode

    genJump :: CmmExpr{-the branch target-} -> NatM InstrBlock

    genJump (CmmLit (CmmLabel lbl))
      = return (unitOL $ JMP lbl)

    genJump tree
      = do
            dflags <- getDynFlags
            genJump' tree (platformToGCP (targetPlatform dflags))

    genJump' :: CmmExpr -> GenCCallPlatform -> NatM InstrBlock

    genJump' tree (GCPLinux64ELF 1)
      = do
            (target,code) <- getSomeReg tree
            return (code
                   `snocOL` LD II64 r11 (AddrRegImm target (ImmInt 0))
                   `snocOL` LD II64 toc (AddrRegImm target (ImmInt 8))
                   `snocOL` MTCTR r11
                   `snocOL` LD II64 r11 (AddrRegImm target (ImmInt 16))
                   `snocOL` BCTR [] Nothing)

    genJump' tree (GCPLinux64ELF 2)
      = do
            (target,code) <- getSomeReg tree
            return (code
                   `snocOL` MR r12 target
                   `snocOL` MTCTR r12
                   `snocOL` BCTR [] Nothing)

    genJump' tree _
      = do
            (target,code) <- getSomeReg tree
            return (code `snocOL` MTCTR target `snocOL` BCTR [] Nothing)

    -- -----------------------------------------------------------------------------
    --  Unconditional branches
    genBranch :: BlockId -> NatM InstrBlock
    genBranch = return . toOL . mkJumpInstr

    -- -----------------------------------------------------------------------------
    --  Conditional jumps

    {-
    Conditional jumps are always to local labels, so we can use branch
    instructions.  We peek at the arguments to decide what kind of
    comparison to do.
    -}

    genCondJump
        :: BlockId      -- the branch target
        -> CmmExpr      -- the condition on which to branch
        -> NatM InstrBlock

    genCondJump id bool = do
      CondCode _ cond code <- getCondCode bool
      return (code `snocOL` BCC cond id)

    -- -----------------------------------------------------------------------------
    --  Generating C calls

    -- Now the biggest nightmare---calls.  Most of the nastiness is buried in
    -- @get_arg@, which moves the arguments to the correct registers/stack
    -- locations.  Apart from that, the code is easy.

    genCCall :: ForeignTarget      -- function to call
             -> [CmmFormal]        -- where to put the result
             -> [CmmActual]        -- arguments (of mixed type)
             -> NatM InstrBlock
    genCCall (PrimTarget MO_WriteBarrier) _ _
     = return $ unitOL LWSYNC

    genCCall (PrimTarget MO_Touch) _ _
     = return $ nilOL

    genCCall (PrimTarget (MO_Prefetch_Data _)) _ _
     = return $ nilOL

    genCCall (PrimTarget (MO_Clz width)) [dst] [src]
     = do dflags <- getDynFlags
          let platform = targetPlatform dflags
              reg_dst = getRegisterReg platform (CmmLocal dst)
          if target32Bit platform && width == W64
            then do
              ChildCode64 code vr_lo <- iselExpr64 src
              lbl1 <- getBlockIdNat
              lbl2 <- getBlockIdNat
              lbl3 <- getBlockIdNat
              let vr_hi = getHiVRegFromLo vr_lo
                  cntlz = toOL [ CMPL II32 vr_hi (RIImm (ImmInt 0))
                               , BCC NE lbl2
                               , BCC ALWAYS lbl1

                               , NEWBLOCK lbl1
                               , CNTLZ II32 reg_dst vr_lo
                               , ADD reg_dst reg_dst (RIImm (ImmInt 32))
                               , BCC ALWAYS lbl3

                               , NEWBLOCK lbl2
                               , CNTLZ II32 reg_dst vr_hi
                               , BCC ALWAYS lbl3

                               , NEWBLOCK lbl3
                               ]
              return $ code `appOL` cntlz
            else do
              let format = if width == W64 then II64 else II32
              (s_reg, s_code) <- getSomeReg src
              (pre, reg , post) <-
                case width of
                  W64 -> return (nilOL, s_reg, nilOL)
                  W32 -> return (nilOL, s_reg, nilOL)
                  W16 -> do
                    reg_tmp <- getNewRegNat format
                    return
                      ( unitOL $ AND reg_tmp s_reg (RIImm (ImmInt 65535))
                      , reg_tmp
                      , unitOL $ ADD reg_dst reg_dst (RIImm (ImmInt (-16)))
                      )
                  W8  -> do
                    reg_tmp <- getNewRegNat format
                    return
                      ( unitOL $ AND reg_tmp s_reg (RIImm (ImmInt 255))
                      , reg_tmp
                      , unitOL $ ADD reg_dst reg_dst (RIImm (ImmInt (-24)))
                      )
                  _   -> panic "genCall: Clz wrong format"
              let cntlz = unitOL (CNTLZ format reg_dst reg)
              return $ s_code `appOL` pre `appOL` cntlz `appOL` post

    genCCall (PrimTarget (MO_Ctz width)) [dst] [src]
     = do dflags <- getDynFlags
          let platform = targetPlatform dflags
              reg_dst = getRegisterReg platform (CmmLocal dst)
          if target32Bit platform && width == W64
            then do
              let format = II32
              ChildCode64 code vr_lo <- iselExpr64 src
              lbl1 <- getBlockIdNat
              lbl2 <- getBlockIdNat
              lbl3 <- getBlockIdNat
              x' <- getNewRegNat format
              x'' <- getNewRegNat format
              r' <- getNewRegNat format
              cnttzlo <- cnttz format reg_dst vr_lo
              let vr_hi = getHiVRegFromLo vr_lo
                  cnttz64 = toOL [ CMPL format vr_lo (RIImm (ImmInt 0))
                                 , BCC NE lbl2
                                 , BCC ALWAYS lbl1

                                 , NEWBLOCK lbl1
                                 , ADD x' vr_hi (RIImm (ImmInt (-1)))
                                 , ANDC x'' x' vr_hi
                                 , CNTLZ format r' x''
                                   -- 32 + (32 - clz(x''))
                                 , SUBFC reg_dst r' (RIImm (ImmInt 64))
                                 , BCC ALWAYS lbl3

                                 , NEWBLOCK lbl2
                                 ]
                            `appOL` cnttzlo `appOL`
                            toOL [ BCC ALWAYS lbl3

                                 , NEWBLOCK lbl3
                                 ]
              return $ code `appOL` cnttz64
            else do
              let format = if width == W64 then II64 else II32
              (s_reg, s_code) <- getSomeReg src
              (reg_ctz, pre_code) <-
                case width of
                  W64 -> return (s_reg, nilOL)
                  W32 -> return (s_reg, nilOL)
                  W16 -> do
                    reg_tmp <- getNewRegNat format
                    return (reg_tmp, unitOL $ ORIS reg_tmp s_reg (ImmInt 1))
                  W8  -> do
                    reg_tmp <- getNewRegNat format
                    return (reg_tmp, unitOL $ OR reg_tmp s_reg (RIImm (ImmInt 256)))
                  _   -> panic "genCall: Ctz wrong format"
              ctz_code <- cnttz format reg_dst reg_ctz
              return $ s_code `appOL` pre_code `appOL` ctz_code
            where
              -- cnttz(x) = sizeof(x) - cntlz(~x & (x - 1))
              -- see Henry S. Warren, Hacker's Delight, p 107
              cnttz format dst src = do
                let format_bits = 8 * formatInBytes format
                x' <- getNewRegNat format
                x'' <- getNewRegNat format
                r' <- getNewRegNat format
                return $ toOL [ ADD x' src (RIImm (ImmInt (-1)))
                              , ANDC x'' x' src
                              , CNTLZ format r' x''
                              , SUBFC dst r' (RIImm (ImmInt (format_bits)))
                              ]

    genCCall target dest_regs argsAndHints
     = do dflags <- getDynFlags
          let platform = targetPlatform dflags
          case target of
            PrimTarget (MO_S_QuotRem  width) -> divOp1 platform True  width
                                                       dest_regs argsAndHints
            PrimTarget (MO_U_QuotRem  width) -> divOp1 platform False width
                                                       dest_regs argsAndHints
            PrimTarget (MO_U_QuotRem2 width) -> divOp2 platform width dest_regs
                                                       argsAndHints
            PrimTarget (MO_U_Mul2 width) -> multOp2 platform width dest_regs
                                                    argsAndHints
            PrimTarget (MO_Add2 _) -> add2Op platform dest_regs argsAndHints
            PrimTarget (MO_SubWordC _) -> subcOp platform dest_regs argsAndHints
            PrimTarget (MO_AddIntC width) -> addSubCOp ADDO platform width
                                                       dest_regs argsAndHints
            PrimTarget (MO_SubIntC width) -> addSubCOp SUBFO platform width
                                                       dest_regs argsAndHints
            PrimTarget MO_F64_Fabs -> fabs platform dest_regs argsAndHints
            PrimTarget MO_F32_Fabs -> fabs platform dest_regs argsAndHints
            _ -> genCCall' dflags (platformToGCP platform)
                           target dest_regs argsAndHints
            where divOp1 platform signed width [res_q, res_r] [arg_x, arg_y]
                    = do let reg_q = getRegisterReg platform (CmmLocal res_q)
                             reg_r = getRegisterReg platform (CmmLocal res_r)
                             fmt   = intFormat width
                         (x_reg, x_code) <- getSomeReg arg_x
                         (y_reg, y_code) <- getSomeReg arg_y
                         return $       y_code `appOL` x_code
                                `appOL` toOL [ DIV fmt signed reg_q x_reg y_reg
                                             , MULL fmt reg_r reg_q (RIReg y_reg)
                                             , SUBF reg_r reg_r x_reg
                                             ]

                  divOp1 _ _ _ _ _
                    = panic "genCCall: Wrong number of arguments for divOp1"
                  divOp2 platform width [res_q, res_r]
                                        [arg_x_high, arg_x_low, arg_y]
                    = do let reg_q = getRegisterReg platform (CmmLocal res_q)
                             reg_r = getRegisterReg platform (CmmLocal res_r)
                             fmt   = intFormat width
                             half  = 4 * (formatInBytes fmt)
                         (xh_reg, xh_code) <- getSomeReg arg_x_high
                         (xl_reg, xl_code) <- getSomeReg arg_x_low
                         (y_reg, y_code) <- getSomeReg arg_y
                         s <- getNewRegNat fmt
                         b <- getNewRegNat fmt
                         v <- getNewRegNat fmt
                         vn1 <- getNewRegNat fmt
                         vn0 <- getNewRegNat fmt
                         un32 <- getNewRegNat fmt
                         tmp  <- getNewRegNat fmt
                         un10 <- getNewRegNat fmt
                         un1 <- getNewRegNat fmt
                         un0 <- getNewRegNat fmt
                         q1 <- getNewRegNat fmt
                         rhat <- getNewRegNat fmt
                         tmp1 <- getNewRegNat fmt
                         q0 <- getNewRegNat fmt
                         un21 <- getNewRegNat fmt
                         again1 <- getBlockIdNat
                         no1 <- getBlockIdNat
                         then1 <- getBlockIdNat
                         endif1 <- getBlockIdNat
                         again2 <- getBlockIdNat
                         no2 <- getBlockIdNat
                         then2 <- getBlockIdNat
                         endif2 <- getBlockIdNat
                         return $ y_code `appOL` xl_code `appOL` xh_code `appOL`
                                  -- see Hacker's Delight p 196 Figure 9-3
                                  toOL [ -- b = 2 ^ (bits_in_word / 2)
                                         LI b (ImmInt 1)
                                       , SL fmt b b (RIImm (ImmInt half))
                                         -- s = clz(y)
                                       , CNTLZ fmt s y_reg
                                         -- v = y << s
                                       , SL fmt v y_reg (RIReg s)
                                         -- vn1 = upper half of v
                                       , SR fmt vn1 v (RIImm (ImmInt half))
                                         -- vn0 = lower half of v
                                       , CLRLI fmt vn0 v half
                                         -- un32 = (u1 << s)
                                         --      | (u0 >> (bits_in_word - s))
                                       , SL fmt un32 xh_reg (RIReg s)
                                       , SUBFC tmp s
                                            (RIImm (ImmInt (8 * formatInBytes fmt)))
                                       , SR fmt tmp xl_reg (RIReg tmp)
                                       , OR un32 un32 (RIReg tmp)
                                         -- un10 = u0 << s
                                       , SL fmt un10 xl_reg (RIReg s)
                                         -- un1 = upper half of un10
                                       , SR fmt un1 un10 (RIImm (ImmInt half))
                                         -- un0 = lower half of un10
                                       , CLRLI fmt un0 un10 half
                                         -- q1 = un32/vn1
                                       , DIV fmt False q1 un32 vn1
                                         -- rhat = un32 - q1*vn1
                                       , MULL fmt tmp q1 (RIReg vn1)
                                       , SUBF rhat tmp un32
                                       , BCC ALWAYS again1

                                       , NEWBLOCK again1
                                         -- if (q1 >= b || q1*vn0 > b*rhat + un1)
                                       , CMPL fmt q1 (RIReg b)
                                       , BCC GEU then1
                                       , BCC ALWAYS no1

                                       , NEWBLOCK no1
                                       , MULL fmt tmp q1 (RIReg vn0)
                                       , SL fmt tmp1 rhat (RIImm (ImmInt half))
                                       , ADD tmp1 tmp1 (RIReg un1)
                                       , CMPL fmt tmp (RIReg tmp1)
                                       , BCC LEU endif1
                                       , BCC ALWAYS then1

                                       , NEWBLOCK then1
                                         -- q1 = q1 - 1
                                       , ADD q1 q1 (RIImm (ImmInt (-1)))
                                         -- rhat = rhat + vn1
                                       , ADD rhat rhat (RIReg vn1)
                                         -- if (rhat < b) goto again1
                                       , CMPL fmt rhat (RIReg b)
                                       , BCC LTT again1
                                       , BCC ALWAYS endif1

                                       , NEWBLOCK endif1
                                         -- un21 = un32*b + un1 - q1*v
                                       , SL fmt un21 un32 (RIImm (ImmInt half))
                                       , ADD un21 un21 (RIReg un1)
                                       , MULL fmt tmp q1 (RIReg v)
                                       , SUBF un21 tmp un21
                                         -- compute second quotient digit
                                         -- q0 = un21/vn1
                                       , DIV fmt False q0 un21 vn1
                                         -- rhat = un21- q0*vn1
                                       , MULL fmt tmp q0 (RIReg vn1)
                                       , SUBF rhat tmp un21
                                       , BCC ALWAYS again2

                                       , NEWBLOCK again2
                                         -- if (q0>b || q0*vn0 > b*rhat + un0)
                                       , CMPL fmt q0 (RIReg b)
                                       , BCC GEU then2
                                       , BCC ALWAYS no2

                                       , NEWBLOCK no2
                                       , MULL fmt tmp q0 (RIReg vn0)
                                       , SL fmt tmp1 rhat (RIImm (ImmInt half))
                                       , ADD tmp1 tmp1 (RIReg un0)
                                       , CMPL fmt tmp (RIReg tmp1)
                                       , BCC LEU endif2
                                       , BCC ALWAYS then2

                                       , NEWBLOCK then2
                                         -- q0 = q0 - 1
                                       , ADD q0 q0 (RIImm (ImmInt (-1)))
                                         -- rhat = rhat + vn1
                                       , ADD rhat rhat (RIReg vn1)
                                         -- if (rhat<b) goto again2
                                       , CMPL fmt rhat (RIReg b)
                                       , BCC LTT again2
                                       , BCC ALWAYS endif2

                                       , NEWBLOCK endif2
                                         -- compute remainder
                                         -- r = (un21*b + un0 - q0*v) >> s
                                       , SL fmt reg_r un21 (RIImm (ImmInt half))
                                       , ADD reg_r reg_r (RIReg un0)
                                       , MULL fmt tmp q0 (RIReg v)
                                       , SUBF reg_r tmp reg_r
                                       , SR fmt reg_r reg_r (RIReg s)
                                         -- compute quotient
                                         -- q = q1*b + q0
                                       , SL fmt reg_q q1 (RIImm (ImmInt half))
                                       , ADD reg_q reg_q (RIReg q0)
                                       ]
                  divOp2 _ _ _ _
                    = panic "genCCall: Wrong number of arguments for divOp2"
                  multOp2 platform width [res_h, res_l] [arg_x, arg_y]
                    = do let reg_h = getRegisterReg platform (CmmLocal res_h)
                             reg_l = getRegisterReg platform (CmmLocal res_l)
                             fmt = intFormat width
                         (x_reg, x_code) <- getSomeReg arg_x
                         (y_reg, y_code) <- getSomeReg arg_y
                         return $ y_code `appOL` x_code
                                `appOL` toOL [ MULL fmt reg_l x_reg (RIReg y_reg)
                                             , MULHU fmt reg_h x_reg y_reg
                                             ]
                  multOp2 _ _ _ _
                    = panic "genCall: Wrong number of arguments for multOp2"
                  add2Op platform [res_h, res_l] [arg_x, arg_y]
                    = do let reg_h = getRegisterReg platform (CmmLocal res_h)
                             reg_l = getRegisterReg platform (CmmLocal res_l)
                         (x_reg, x_code) <- getSomeReg arg_x
                         (y_reg, y_code) <- getSomeReg arg_y
                         return $ y_code `appOL` x_code
                                `appOL` toOL [ LI reg_h (ImmInt 0)
                                             , ADDC reg_l x_reg y_reg
                                             , ADDZE reg_h reg_h
                                             ]
                  add2Op _ _ _
                    = panic "genCCall: Wrong number of arguments/results for add2"

                  -- PowerPC subfc sets the carry for rT = ~(rA) + rB + 1,
                  -- which is 0 for borrow and 1 otherwise. We need 1 and 0
                  -- so xor with 1.
                  subcOp platform [res_r, res_c] [arg_x, arg_y]
                    = do let reg_r = getRegisterReg platform (CmmLocal res_r)
                             reg_c = getRegisterReg platform (CmmLocal res_c)
                         (x_reg, x_code) <- getSomeReg arg_x
                         (y_reg, y_code) <- getSomeReg arg_y
                         return $ y_code `appOL` x_code
                                `appOL` toOL [ LI reg_c (ImmInt 0)
                                             , SUBFC reg_r y_reg (RIReg x_reg)
                                             , ADDZE reg_c reg_c
                                             , XOR reg_c reg_c (RIImm (ImmInt 1))
                                             ]
                  subcOp _ _ _
                    = panic "genCCall: Wrong number of arguments/results for subc"
                  addSubCOp instr platform width [res_r, res_c] [arg_x, arg_y]
                    = do let reg_r = getRegisterReg platform (CmmLocal res_r)
                             reg_c = getRegisterReg platform (CmmLocal res_c)
                         (x_reg, x_code) <- getSomeReg arg_x
                         (y_reg, y_code) <- getSomeReg arg_y
                         return $ y_code `appOL` x_code
                                `appOL` toOL [ instr reg_r y_reg x_reg,
                                               -- SUBFO argument order reversed!
                                               MFOV (intFormat width) reg_c
                                             ]
                  addSubCOp _ _ _ _ _
                    = panic "genCall: Wrong number of arguments/results for addC"
                  fabs platform [res] [arg]
                    = do let res_r = getRegisterReg platform (CmmLocal res)
                         (arg_reg, arg_code) <- getSomeReg arg
                         return $ arg_code `snocOL` FABS res_r arg_reg
                  fabs _ _ _
                    = panic "genCall: Wrong number of arguments/results for fabs"

    -- TODO: replace 'Int' by an enum such as 'PPC_64ABI'
    data GenCCallPlatform = GCPLinux | GCPDarwin | GCPLinux64ELF !Int | GCPAIX

    platformToGCP :: Platform -> GenCCallPlatform
    platformToGCP platform = case platformOS platform of
        OSLinux  -> case platformArch platform of
            ArchPPC           -> GCPLinux
            ArchPPC_64 ELF_V1 -> GCPLinux64ELF 1
            ArchPPC_64 ELF_V2 -> GCPLinux64ELF 2
            _ -> panic "PPC.CodeGen.platformToGCP: Unknown Linux"
        OSAIX    -> GCPAIX
        OSDarwin -> GCPDarwin
        _ -> panic "PPC.CodeGen.platformToGCP: not defined for this OS"

    genCCall'
        :: DynFlags
        -> GenCCallPlatform
        -> ForeignTarget            -- function to call
        -> [CmmFormal]        -- where to put the result
        -> [CmmActual]        -- arguments (of mixed type)
        -> NatM InstrBlock

    {-
        The PowerPC calling convention for Darwin/Mac OS X
        is described in Apple's document
        "Inside Mac OS X - Mach-O Runtime Architecture".

        PowerPC Linux uses the System V Release 4 Calling Convention
        for PowerPC. It is described in the
        "System V Application Binary Interface PowerPC Processor Supplement".

        Both conventions are similar:
        Parameters may be passed in general-purpose registers starting at r3, in
        floating point registers starting at f1, or on the stack.

        But there are substantial differences:
        * The number of registers used for parameter passing and the exact set of
          nonvolatile registers differs (see MachRegs.hs).
        * On Darwin, stack space is always reserved for parameters, even if they are
          passed in registers. The called routine may choose to save parameters from
          registers to the corresponding space on the stack.
        * On Darwin, a corresponding amount of GPRs is skipped when a floating point
          parameter is passed in an FPR.
        * SysV insists on either passing I64 arguments on the stack, or in two GPRs,
          starting with an odd-numbered GPR. It may skip a GPR to achieve this.
          Darwin just treats an I64 like two separate II32s (high word first).
        * I64 and FF64 arguments are 8-byte aligned on the stack for SysV, but only
          4-byte aligned like everything else on Darwin.
        * The SysV spec claims that FF32 is represented as FF64 on the stack. GCC on
          PowerPC Linux does not agree, so neither do we.

        PowerPC 64 Linux uses the System V Release 4 Calling Convention for
        64-bit PowerPC. It is specified in
        "64-bit PowerPC ELF Application Binary Interface Supplement 1.9"
        (PPC64 ELF v1.9).
        PowerPC 64 Linux in little endian mode uses the "Power Architecture 64-Bit
        ELF V2 ABI Specification -- OpenPOWER ABI for Linux Supplement"
        (PPC64 ELF v2).
        AIX follows the "PowerOpen ABI: Application Binary Interface Big-Endian
        32-Bit Hardware Implementation"

        According to all conventions, the parameter area should be part of the
        caller's stack frame, allocated in the caller's prologue code (large enough
        to hold the parameter lists for all called routines). The NCG already
        uses the stack for register spilling, leaving 64 bytes free at the top.
        If we need a larger parameter area than that, we just allocate a new stack
        frame just before ccalling.
    -}

    genCCall' dflags gcp target dest_regs args
      = ASSERT(not $ any (`elem` [II16]) $ map cmmTypeFormat argReps)
            -- we rely on argument promotion in the codeGen
        do
            (finalStack,passArgumentsCode,usedRegs) <- passArguments
                                                            (zip args argReps)
                                                            allArgRegs
                                                            (allFPArgRegs platform)
                                                            initialStackOffset
                                                            (toOL []) []

            (labelOrExpr, reduceToFF32) <- case target of
                ForeignTarget (CmmLit (CmmLabel lbl)) _ -> do
                    uses_pic_base_implicitly
                    return (Left lbl, False)
                ForeignTarget expr _ -> do
                    uses_pic_base_implicitly
                    return (Right expr, False)
                PrimTarget mop -> outOfLineMachOp mop

            let codeBefore = move_sp_down finalStack `appOL` passArgumentsCode
                codeAfter = move_sp_up finalStack `appOL` moveResult reduceToFF32

            case labelOrExpr of
                Left lbl -> do -- the linker does all the work for us
                    return (         codeBefore
                            `snocOL` BL lbl usedRegs
                            `appOL`  maybeNOP -- some ABI require a NOP after BL
                            `appOL`  codeAfter)
                Right dyn -> do -- implement call through function pointer
                    (dynReg, dynCode) <- getSomeReg dyn
                    case gcp of
                         GCPLinux64ELF 1 -> return ( dynCode
                           `appOL`  codeBefore
                           `snocOL` ST spFormat toc (AddrRegImm sp (ImmInt 40))
                           `snocOL` LD II64 r11 (AddrRegImm dynReg (ImmInt 0))
                           `snocOL` LD II64 toc (AddrRegImm dynReg (ImmInt 8))
                           `snocOL` MTCTR r11
                           `snocOL` LD II64 r11 (AddrRegImm dynReg (ImmInt 16))
                           `snocOL` BCTRL usedRegs
                           `snocOL` LD spFormat toc (AddrRegImm sp (ImmInt 40))
                           `appOL`  codeAfter)
                         GCPLinux64ELF 2 -> return ( dynCode
                           `appOL`  codeBefore
                           `snocOL` ST spFormat toc (AddrRegImm sp (ImmInt 24))
                           `snocOL` MR r12 dynReg
                           `snocOL` MTCTR r12
                           `snocOL` BCTRL usedRegs
                           `snocOL` LD spFormat toc (AddrRegImm sp (ImmInt 24))
                           `appOL`  codeAfter)
                         GCPAIX          -> return ( dynCode
                           -- AIX/XCOFF follows the PowerOPEN ABI
                           -- which is quite similiar to LinuxPPC64/ELFv1
                           `appOL`  codeBefore
                           `snocOL` ST spFormat toc (AddrRegImm sp (ImmInt 20))
                           `snocOL` LD II32 r11 (AddrRegImm dynReg (ImmInt 0))
                           `snocOL` LD II32 toc (AddrRegImm dynReg (ImmInt 4))
                           `snocOL` MTCTR r11
                           `snocOL` LD II32 r11 (AddrRegImm dynReg (ImmInt 8))
                           `snocOL` BCTRL usedRegs
                           `snocOL` LD spFormat toc (AddrRegImm sp (ImmInt 20))
                           `appOL`  codeAfter)
                         _              -> return ( dynCode
                           `snocOL` MTCTR dynReg
                           `appOL`  codeBefore
                           `snocOL` BCTRL usedRegs
                           `appOL`  codeAfter)
        where
            platform = targetPlatform dflags

            uses_pic_base_implicitly = do
                -- See Note [implicit register in PPC PIC code]
                -- on why we claim to use PIC register here
                when (positionIndependent dflags && target32Bit platform) $ do
                    _ <- getPicBaseNat $ archWordFormat True
                    return ()

            initialStackOffset = case gcp of
                                 GCPAIX          -> 24
                                 GCPDarwin       -> 24
                                 GCPLinux        -> 8
                                 GCPLinux64ELF 1 -> 48
                                 GCPLinux64ELF 2 -> 32
                                 _ -> panic "genCall': unknown calling convention"
                -- size of linkage area + size of arguments, in bytes
            stackDelta finalStack = case gcp of
                                    GCPAIX ->
                                        roundTo 16 $ (24 +) $ max 32 $ sum $
                                        map (widthInBytes . typeWidth) argReps
                                    GCPDarwin ->
                                        roundTo 16 $ (24 +) $ max 32 $ sum $
                                        map (widthInBytes . typeWidth) argReps
                                    GCPLinux -> roundTo 16 finalStack
                                    GCPLinux64ELF 1 ->
                                        roundTo 16 $ (48 +) $ max 64 $ sum $
                                        map (roundTo 8 . widthInBytes . typeWidth)
                                            argReps
                                    GCPLinux64ELF 2 ->
                                        roundTo 16 $ (32 +) $ max 64 $ sum $
                                        map (roundTo 8 . widthInBytes . typeWidth)
                                            argReps
                                    _ -> panic "genCall': unknown calling conv."

            argReps = map (cmmExprType dflags) args

            roundTo a x | x `mod` a == 0 = x
                        | otherwise = x + a - (x `mod` a)

            spFormat = if target32Bit platform then II32 else II64

            -- TODO: Do not create a new stack frame if delta is too large.
            move_sp_down finalStack
                   | delta > stackFrameHeaderSize dflags =
                            toOL [STU spFormat sp (AddrRegImm sp (ImmInt (-delta))),
                                  DELTA (-delta)]
                   | otherwise = nilOL
                   where delta = stackDelta finalStack
            move_sp_up finalStack
                   | delta > stackFrameHeaderSize dflags =
                            toOL [ADD sp sp (RIImm (ImmInt delta)),
                                  DELTA 0]
                   | otherwise = nilOL
                   where delta = stackDelta finalStack

            -- A NOP instruction is required after a call (bl instruction)
            -- on AIX and 64-Bit Linux.
            -- If the call is to a function with a different TOC (r2) the
            -- link editor replaces the NOP instruction with a load of the TOC
            -- from the stack to restore the TOC.
            maybeNOP = case gcp of
               -- See Section 3.9.4 of OpenPower ABI
               GCPAIX          -> unitOL NOP
               -- See Section 3.5.11 of PPC64 ELF v1.9
               GCPLinux64ELF 1 -> unitOL NOP
               -- See Section 2.3.6 of PPC64 ELF v2
               GCPLinux64ELF 2 -> unitOL NOP
               _               -> nilOL

            passArguments [] _ _ stackOffset accumCode accumUsed = return (stackOffset, accumCode, accumUsed)
            passArguments ((arg,arg_ty):args) gprs fprs stackOffset
                   accumCode accumUsed | isWord64 arg_ty
                                         && target32Bit (targetPlatform dflags) =
                do
                    ChildCode64 code vr_lo <- iselExpr64 arg
                    let vr_hi = getHiVRegFromLo vr_lo

                    case gcp of
                        GCPAIX -> -- same as for Darwin
                            do let storeWord vr (gpr:_) _ = MR gpr vr
                                   storeWord vr [] offset
                                       = ST II32 vr (AddrRegImm sp (ImmInt offset))
                               passArguments args
                                             (drop 2 gprs)
                                             fprs
                                             (stackOffset+8)
                                             (accumCode `appOL` code
                                                   `snocOL` storeWord vr_hi gprs stackOffset
                                                   `snocOL` storeWord vr_lo (drop 1 gprs) (stackOffset+4))
                                             ((take 2 gprs) ++ accumUsed)
                        GCPDarwin ->
                            do let storeWord vr (gpr:_) _ = MR gpr vr
                                   storeWord vr [] offset
                                       = ST II32 vr (AddrRegImm sp (ImmInt offset))
                               passArguments args
                                             (drop 2 gprs)
                                             fprs
                                             (stackOffset+8)
                                             (accumCode `appOL` code
                                                   `snocOL` storeWord vr_hi gprs stackOffset
                                                   `snocOL` storeWord vr_lo (drop 1 gprs) (stackOffset+4))
                                             ((take 2 gprs) ++ accumUsed)
                        GCPLinux ->
                            do let stackOffset' = roundTo 8 stackOffset
                                   stackCode = accumCode `appOL` code
                                       `snocOL` ST II32 vr_hi (AddrRegImm sp (ImmInt stackOffset'))
                                       `snocOL` ST II32 vr_lo (AddrRegImm sp (ImmInt (stackOffset'+4)))
                                   regCode hireg loreg =
                                       accumCode `appOL` code
                                           `snocOL` MR hireg vr_hi
                                           `snocOL` MR loreg vr_lo

                               case gprs of
                                   hireg : loreg : regs | even (length gprs) ->
                                       passArguments args regs fprs stackOffset
                                                     (regCode hireg loreg) (hireg : loreg : accumUsed)
                                   _skipped : hireg : loreg : regs ->
                                       passArguments args regs fprs stackOffset
                                                     (regCode hireg loreg) (hireg : loreg : accumUsed)
                                   _ -> -- only one or no regs left
                                       passArguments args [] fprs (stackOffset'+8)
                                                     stackCode accumUsed
                        GCPLinux64ELF _ -> panic "passArguments: 32 bit code"

            passArguments ((arg,rep):args) gprs fprs stackOffset accumCode accumUsed
                | reg : _ <- regs = do
                    register <- getRegister arg
                    let code = case register of
                                Fixed _ freg fcode -> fcode `snocOL` MR reg freg
                                Any _ acode -> acode reg
                        stackOffsetRes = case gcp of
                                         -- The Darwin ABI requires that we reserve
                                         -- stack slots for register parameters
                                         GCPDarwin -> stackOffset + stackBytes
                                         -- ... so does the PowerOpen ABI.
                                         GCPAIX    -> stackOffset + stackBytes
                                         -- ... the SysV ABI 32-bit doesn't.
                                         GCPLinux -> stackOffset
                                         -- ... but SysV ABI 64-bit does.
                                         GCPLinux64ELF _ -> stackOffset + stackBytes
                    passArguments args
                                  (drop nGprs gprs)
                                  (drop nFprs fprs)
                                  stackOffsetRes
                                  (accumCode `appOL` code)
                                  (reg : accumUsed)
                | otherwise = do
                    (vr, code) <- getSomeReg arg
                    passArguments args
                                  (drop nGprs gprs)
                                  (drop nFprs fprs)
                                  (stackOffset' + stackBytes)
                                  (accumCode `appOL` code `snocOL` ST (cmmTypeFormat rep) vr stackSlot)
                                  accumUsed
                where
                    stackOffset' = case gcp of
                                   GCPDarwin ->
                                       -- stackOffset is at least 4-byte aligned
                                       -- The Darwin ABI is happy with that.
                                       stackOffset
                                   GCPAIX ->
                                       -- The 32bit PowerOPEN ABI is happy with
                                       -- 32bit-alignment as well...
                                       stackOffset
                                   GCPLinux
                                       -- ... the SysV ABI requires 8-byte
                                       -- alignment for doubles.
                                    | isFloatType rep && typeWidth rep == W64 ->
                                       roundTo 8 stackOffset
                                    | otherwise ->
                                       stackOffset
                                   GCPLinux64ELF _ ->
                                       -- Everything on the stack is mapped to
                                       -- 8-byte aligned doublewords
                                       stackOffset
                    stackOffset''
                         | isFloatType rep && typeWidth rep == W32 =
                             case gcp of
                             -- The ELF v1 ABI Section 3.2.3 requires:
                             -- "Single precision floating point values
                             -- are mapped to the second word in a single
                             -- doubleword"
                             GCPLinux64ELF 1 -> stackOffset' + 4
                             _               -> stackOffset'
                         | otherwise = stackOffset'

                    stackSlot = AddrRegImm sp (ImmInt stackOffset'')
                    (nGprs, nFprs, stackBytes, regs)
                        = case gcp of
                          GCPAIX ->
                              case cmmTypeFormat rep of
                              II8  -> (1, 0, 4, gprs)
                              II16 -> (1, 0, 4, gprs)
                              II32 -> (1, 0, 4, gprs)
                              -- The PowerOpen ABI requires that we skip a
                              -- corresponding number of GPRs when we use
                              -- the FPRs.
                              --
                              -- E.g. for a `double` two GPRs are skipped,
                              -- whereas for a `float` one GPR is skipped
                              -- when parameters are assigned to
                              -- registers.
                              --
                              -- The PowerOpen ABI specification can be found at
                              -- ftp://www.sourceware.org/pub/binutils/ppc-docs/ppc-poweropen/
                              FF32 -> (1, 1, 4, fprs)
                              FF64 -> (2, 1, 8, fprs)
                              II64 -> panic "genCCall' passArguments II64"
                              FF80 -> panic "genCCall' passArguments FF80"
                          GCPDarwin ->
                              case cmmTypeFormat rep of
                              II8  -> (1, 0, 4, gprs)
                              II16 -> (1, 0, 4, gprs)
                              II32 -> (1, 0, 4, gprs)
                              -- The Darwin ABI requires that we skip a
                              -- corresponding number of GPRs when we use
                              -- the FPRs.
                              FF32 -> (1, 1, 4, fprs)
                              FF64 -> (2, 1, 8, fprs)
                              II64 -> panic "genCCall' passArguments II64"
                              FF80 -> panic "genCCall' passArguments FF80"
                          GCPLinux ->
                              case cmmTypeFormat rep of
                              II8  -> (1, 0, 4, gprs)
                              II16 -> (1, 0, 4, gprs)
                              II32 -> (1, 0, 4, gprs)
                              -- ... the SysV ABI doesn't.
                              FF32 -> (0, 1, 4, fprs)
                              FF64 -> (0, 1, 8, fprs)
                              II64 -> panic "genCCall' passArguments II64"
                              FF80 -> panic "genCCall' passArguments FF80"
                          GCPLinux64ELF _ ->
                              case cmmTypeFormat rep of
                              II8  -> (1, 0, 8, gprs)
                              II16 -> (1, 0, 8, gprs)
                              II32 -> (1, 0, 8, gprs)
                              II64 -> (1, 0, 8, gprs)
                              -- The ELFv1 ABI requires that we skip a
                              -- corresponding number of GPRs when we use
                              -- the FPRs.
                              FF32 -> (1, 1, 8, fprs)
                              FF64 -> (1, 1, 8, fprs)
                              FF80 -> panic "genCCall' passArguments FF80"

            moveResult reduceToFF32 =
                case dest_regs of
                    [] -> nilOL
                    [dest]
                        | reduceToFF32 && isFloat32 rep   -> unitOL (FRSP r_dest f1)
                        | isFloat32 rep || isFloat64 rep -> unitOL (MR r_dest f1)
                        | isWord64 rep && target32Bit (targetPlatform dflags)
                           -> toOL [MR (getHiVRegFromLo r_dest) r3,
                                    MR r_dest r4]
                        | otherwise -> unitOL (MR r_dest r3)
                        where rep = cmmRegType dflags (CmmLocal dest)
                              r_dest = getRegisterReg platform (CmmLocal dest)
                    _ -> panic "genCCall' moveResult: Bad dest_regs"

            outOfLineMachOp mop =
                do
                    dflags <- getDynFlags
                    mopExpr <- cmmMakeDynamicReference dflags CallReference $
                                  mkForeignLabel functionName Nothing ForeignLabelInThisPackage IsFunction
                    let mopLabelOrExpr = case mopExpr of
                            CmmLit (CmmLabel lbl) -> Left lbl
                            _ -> Right mopExpr
                    return (mopLabelOrExpr, reduce)
                where
                    (functionName, reduce) = case mop of
                        MO_F32_Exp   -> (fsLit "exp", True)
                        MO_F32_Log   -> (fsLit "log", True)
                        MO_F32_Sqrt  -> (fsLit "sqrt", True)
                        MO_F32_Fabs  -> unsupported

                        MO_F32_Sin   -> (fsLit "sin", True)
                        MO_F32_Cos   -> (fsLit "cos", True)
                        MO_F32_Tan   -> (fsLit "tan", True)

                        MO_F32_Asin  -> (fsLit "asin", True)
                        MO_F32_Acos  -> (fsLit "acos", True)
                        MO_F32_Atan  -> (fsLit "atan", True)

                        MO_F32_Sinh  -> (fsLit "sinh", True)
                        MO_F32_Cosh  -> (fsLit "cosh", True)
                        MO_F32_Tanh  -> (fsLit "tanh", True)
                        MO_F32_Pwr   -> (fsLit "pow", True)

                        MO_F64_Exp   -> (fsLit "exp", False)
                        MO_F64_Log   -> (fsLit "log", False)
                        MO_F64_Sqrt  -> (fsLit "sqrt", False)
                        MO_F64_Fabs  -> unsupported

                        MO_F64_Sin   -> (fsLit "sin", False)
                        MO_F64_Cos   -> (fsLit "cos", False)
                        MO_F64_Tan   -> (fsLit "tan", False)

                        MO_F64_Asin  -> (fsLit "asin", False)
                        MO_F64_Acos  -> (fsLit "acos", False)
                        MO_F64_Atan  -> (fsLit "atan", False)

                        MO_F64_Sinh  -> (fsLit "sinh", False)
                        MO_F64_Cosh  -> (fsLit "cosh", False)
                        MO_F64_Tanh  -> (fsLit "tanh", False)
                        MO_F64_Pwr   -> (fsLit "pow", False)

                        MO_UF_Conv w -> (fsLit $ word2FloatLabel w, False)

                        MO_Memcpy _  -> (fsLit "memcpy", False)
                        MO_Memset _  -> (fsLit "memset", False)
                        MO_Memmove _ -> (fsLit "memmove", False)

                        MO_BSwap w   -> (fsLit $ bSwapLabel w, False)
                        MO_PopCnt w  -> (fsLit $ popCntLabel w, False)
                        MO_Clz w     -> (fsLit $ clzLabel w, False)
                        MO_Ctz w     -> (fsLit $ ctzLabel w, False)
                        MO_AtomicRMW w amop -> (fsLit $ atomicRMWLabel w amop, False)
                        MO_Cmpxchg w -> (fsLit $ cmpxchgLabel w, False)
                        MO_AtomicRead w  -> (fsLit $ atomicReadLabel w, False)
                        MO_AtomicWrite w -> (fsLit $ atomicWriteLabel w, False)

                        MO_S_QuotRem {}  -> unsupported
                        MO_U_QuotRem {}  -> unsupported
                        MO_U_QuotRem2 {} -> unsupported
                        MO_Add2 {}       -> unsupported
                        MO_SubWordC {}   -> unsupported
                        MO_AddIntC {}    -> unsupported
                        MO_SubIntC {}    -> unsupported
                        MO_U_Mul2 {}     -> unsupported
                        MO_WriteBarrier  -> unsupported
                        MO_Touch         -> unsupported
                        (MO_Prefetch_Data _ ) -> unsupported
                    unsupported = panic ("outOfLineCmmOp: " ++ show mop
                                      ++ " not supported")

    -- -----------------------------------------------------------------------------
    -- Generating a table-branch

    genSwitch :: DynFlags -> CmmExpr -> SwitchTargets -> NatM InstrBlock
    genSwitch dflags expr targets
      | OSAIX <- platformOS (targetPlatform dflags)
      = do
            (reg,e_code) <- getSomeReg (cmmOffset dflags expr offset)
            let fmt = archWordFormat $ target32Bit $ targetPlatform dflags
                sha = if target32Bit $ targetPlatform dflags then 2 else 3
            tmp <- getNewRegNat fmt
            lbl <- getNewLabelNat
            dynRef <- cmmMakeDynamicReference dflags DataReference lbl
            (tableReg,t_code) <- getSomeReg $ dynRef
            let code = e_code `appOL` t_code `appOL` toOL [
                                SL fmt tmp reg (RIImm (ImmInt sha)),
                                LD fmt tmp (AddrRegReg tableReg tmp),
                                MTCTR tmp,
                                BCTR ids (Just lbl)
                        ]
            return code

      | (positionIndependent dflags) || (not $ target32Bit $ targetPlatform dflags)
      = do
            (reg,e_code) <- getSomeReg (cmmOffset dflags expr offset)
            let fmt = archWordFormat $ target32Bit $ targetPlatform dflags
                sha = if target32Bit $ targetPlatform dflags then 2 else 3
            tmp <- getNewRegNat fmt
            lbl <- getNewLabelNat
            dynRef <- cmmMakeDynamicReference dflags DataReference lbl
            (tableReg,t_code) <- getSomeReg $ dynRef
            let code = e_code `appOL` t_code `appOL` toOL [
                                SL fmt tmp reg (RIImm (ImmInt sha)),
                                LD fmt tmp (AddrRegReg tableReg tmp),
                                ADD tmp tmp (RIReg tableReg),
                                MTCTR tmp,
                                BCTR ids (Just lbl)
                        ]
            return code
      | otherwise
      = do
            (reg,e_code) <- getSomeReg (cmmOffset dflags expr offset)
            let fmt = archWordFormat $ target32Bit $ targetPlatform dflags
                sha = if target32Bit $ targetPlatform dflags then 2 else 3
            tmp <- getNewRegNat fmt
            lbl <- getNewLabelNat
            let code = e_code `appOL` toOL [
                                SL fmt tmp reg (RIImm (ImmInt sha)),
                                ADDIS tmp tmp (HA (ImmCLbl lbl)),
                                LD fmt tmp (AddrRegImm tmp (LO (ImmCLbl lbl))),
                                MTCTR tmp,
                                BCTR ids (Just lbl)
                        ]
            return code
      where (offset, ids) = switchTargetsToTable targets

    generateJumpTableForInstr :: DynFlags -> Instr
                              -> Maybe (NatCmmDecl CmmStatics Instr)
    generateJumpTableForInstr dflags (BCTR ids (Just lbl)) =
        let jumpTable
                | (positionIndependent dflags)
                  || (not $ target32Bit $ targetPlatform dflags)
                = map jumpTableEntryRel ids
                | otherwise = map (jumpTableEntry dflags) ids
                    where jumpTableEntryRel Nothing
                            = CmmStaticLit (CmmInt 0 (wordWidth dflags))
                          jumpTableEntryRel (Just blockid)
                            = CmmStaticLit (CmmLabelDiffOff blockLabel lbl 0)
                                where blockLabel = mkAsmTempLabel (getUnique blockid)
        in Just (CmmData (Section ReadOnlyData lbl) (Statics lbl jumpTable))
    generateJumpTableForInstr _ _ = Nothing

    -- -----------------------------------------------------------------------------
    -- 'condIntReg' and 'condFltReg': condition codes into registers

    -- Turn those condition codes into integers now (when they appear on
    -- the right hand side of an assignment).

    condIntReg, condFltReg :: Cond -> CmmExpr -> CmmExpr -> NatM Register

    condReg :: NatM CondCode -> NatM Register
    condReg getCond = do
        CondCode _ cond cond_code <- getCond
        dflags <- getDynFlags
        let
            code dst = cond_code
                `appOL` negate_code
                `appOL` toOL [
                    MFCR dst,
                    RLWINM dst dst (bit + 1) 31 31
                ]

            negate_code | do_negate = unitOL (CRNOR bit bit bit)
                        | otherwise = nilOL

            (bit, do_negate) = case cond of
                LTT -> (0, False)
                LE  -> (1, True)
                EQQ -> (2, False)
                GE  -> (0, True)
                GTT -> (1, False)

                NE  -> (2, True)

                LU  -> (0, False)
                LEU -> (1, True)
                GEU -> (0, True)
                GU  -> (1, False)
                _   -> panic "PPC.CodeGen.codeReg: no match"

            format = archWordFormat $ target32Bit $ targetPlatform dflags
        return (Any format code)

    condIntReg cond x y = condReg (condIntCode cond x y)
    condFltReg cond x y = condReg (condFltCode cond x y)

    -- -----------------------------------------------------------------------------
    -- 'trivial*Code': deal with trivial instructions

    -- Trivial (dyadic: 'trivialCode', floating-point: 'trivialFCode',
    -- unary: 'trivialUCode', unary fl-pt:'trivialUFCode') instructions.
    -- Only look for constants on the right hand side, because that's
    -- where the generic optimizer will have put them.

    -- Similarly, for unary instructions, we don't have to worry about
    -- matching an StInt as the argument, because genericOpt will already
    -- have handled the constant-folding.

    {-
    Wolfgang's PowerPC version of The Rules:

    A slightly modified version of The Rules to take advantage of the fact
    that PowerPC instructions work on all registers and don't implicitly
    clobber any fixed registers.

    * The only expression for which getRegister returns Fixed is (CmmReg reg).

    * If getRegister returns Any, then the code it generates may modify only:
            (a) fresh temporaries
            (b) the destination register
      It may *not* modify global registers, unless the global
      register happens to be the destination register.
      It may not clobber any other registers. In fact, only ccalls clobber any
      fixed registers.
      Also, it may not modify the counter register (used by genCCall).

      Corollary: If a getRegister for a subexpression returns Fixed, you need
      not move it to a fresh temporary before evaluating the next subexpression.
      The Fixed register won't be modified.
      Therefore, we don't need a counterpart for the x86's getStableReg on PPC.

    * SDM's First Rule is valid for PowerPC, too: subexpressions can depend on
      the value of the destination register.
    -}

    trivialCode
            :: Width
            -> Bool
            -> (Reg -> Reg -> RI -> Instr)
            -> CmmExpr
            -> CmmExpr
            -> NatM Register

    trivialCode rep signed instr x (CmmLit (CmmInt y _))
        | Just imm <- makeImmediate rep signed y
        = do
            (src1, code1) <- getSomeReg x
            let code dst = code1 `snocOL` instr dst src1 (RIImm imm)
            return (Any (intFormat rep) code)

    trivialCode rep _ instr x y = do
        (src1, code1) <- getSomeReg x
        (src2, code2) <- getSomeReg y
        let code dst = code1 `appOL` code2 `snocOL` instr dst src1 (RIReg src2)
        return (Any (intFormat rep) code)

    shiftMulCode
            :: Width
            -> Bool
            -> (Format-> Reg -> Reg -> RI -> Instr)
            -> CmmExpr
            -> CmmExpr
            -> NatM Register
    shiftMulCode width sign instr x (CmmLit (CmmInt y _))
        | Just imm <- makeImmediate width sign y
        = do
            (src1, code1) <- getSomeReg x
            let format = intFormat width
            let code dst = code1 `snocOL` instr format dst src1 (RIImm imm)
            return (Any format code)

    shiftMulCode width _ instr x y = do
        (src1, code1) <- getSomeReg x
        (src2, code2) <- getSomeReg y
        let format = intFormat width
        let code dst = code1 `appOL` code2 `snocOL` instr format dst src1 (RIReg src2)
        return (Any format code)

    trivialCodeNoImm' :: Format -> (Reg -> Reg -> Reg -> Instr)
                     -> CmmExpr -> CmmExpr -> NatM Register
    trivialCodeNoImm' format instr x y = do
        (src1, code1) <- getSomeReg x
        (src2, code2) <- getSomeReg y
        let code dst = code1 `appOL` code2 `snocOL` instr dst src1 src2
        return (Any format code)

    trivialCodeNoImm :: Format -> (Format -> Reg -> Reg -> Reg -> Instr)
                     -> CmmExpr -> CmmExpr -> NatM Register
    trivialCodeNoImm format instr x y = trivialCodeNoImm' format (instr format) x y

    trivialCodeNoImmSign :: Format -> Bool
                         -> (Format -> Bool -> Reg -> Reg -> Reg -> Instr)
                         -> CmmExpr -> CmmExpr -> NatM Register
    trivialCodeNoImmSign  format sgn instr x y
      = trivialCodeNoImm' format (instr format sgn) x y

    trivialUCode
            :: Format
            -> (Reg -> Reg -> Instr)
            -> CmmExpr
            -> NatM Register
    trivialUCode rep instr x = do
        (src, code) <- getSomeReg x
        let code' dst = code `snocOL` instr dst src
        return (Any rep code')

    -- There is no "remainder" instruction on the PPC, so we have to do
    -- it the hard way.
    -- The "sgn" parameter is the signedness for the division instruction

    remainderCode :: Width -> Bool -> CmmExpr -> CmmExpr -> NatM Register
    remainderCode rep sgn x y = do
        let fmt = intFormat rep
        (src1, code1) <- getSomeReg x
        (src2, code2) <- getSomeReg y
        let code dst = code1 `appOL` code2 `appOL` toOL [
                    DIV fmt sgn dst src1 src2,
                    MULL fmt dst dst (RIReg src2),
                    SUBF dst dst src1
                ]
        return (Any (intFormat rep) code)

    coerceInt2FP :: Width -> Width -> CmmExpr -> NatM Register
    coerceInt2FP fromRep toRep x = do
        dflags <- getDynFlags
        let arch =  platformArch $ targetPlatform dflags
        coerceInt2FP' arch fromRep toRep x

    coerceInt2FP' :: Arch -> Width -> Width -> CmmExpr -> NatM Register
    coerceInt2FP' ArchPPC fromRep toRep x = do
        (src, code) <- getSomeReg x
        lbl <- getNewLabelNat
        itmp <- getNewRegNat II32
        ftmp <- getNewRegNat FF64
        dflags <- getDynFlags
        dynRef <- cmmMakeDynamicReference dflags DataReference lbl
        Amode addr addr_code <- getAmode D dynRef
        let
            code' dst = code `appOL` maybe_exts `appOL` toOL [
                    LDATA (Section ReadOnlyData lbl) $ Statics lbl
                                     [CmmStaticLit (CmmInt 0x43300000 W32),
                                      CmmStaticLit (CmmInt 0x80000000 W32)],
                    XORIS itmp src (ImmInt 0x8000),
                    ST II32 itmp (spRel dflags 3),
                    LIS itmp (ImmInt 0x4330),
                    ST II32 itmp (spRel dflags 2),
                    LD FF64 ftmp (spRel dflags 2)
                ] `appOL` addr_code `appOL` toOL [
                    LD FF64 dst addr,
                    FSUB FF64 dst ftmp dst
                ] `appOL` maybe_frsp dst

            maybe_exts = case fromRep of
                            W8 ->  unitOL $ EXTS II8 src src
                            W16 -> unitOL $ EXTS II16 src src
                            W32 -> nilOL
                            _       -> panic "PPC.CodeGen.coerceInt2FP: no match"

            maybe_frsp dst
                    = case toRep of
                            W32 -> unitOL $ FRSP dst dst
                            W64 -> nilOL
                            _       -> panic "PPC.CodeGen.coerceInt2FP: no match"

        return (Any (floatFormat toRep) code')

    -- On an ELF v1 Linux we use the compiler doubleword in the stack frame
    -- this is the TOC pointer doubleword on ELF v2 Linux. The latter is only
    -- set right before a call and restored right after return from the call.
    -- So it is fine.
    coerceInt2FP' (ArchPPC_64 _) fromRep toRep x = do
        (src, code) <- getSomeReg x
        dflags <- getDynFlags
        let
            code' dst = code `appOL` maybe_exts `appOL` toOL [
                    ST II64 src (spRel dflags 3),
                    LD FF64 dst (spRel dflags 3),
                    FCFID dst dst
                ] `appOL` maybe_frsp dst

            maybe_exts = case fromRep of
                            W8 ->  unitOL $ EXTS II8 src src
                            W16 -> unitOL $ EXTS II16 src src
                            W32 -> unitOL $ EXTS II32 src src
                            W64 -> nilOL
                            _       -> panic "PPC.CodeGen.coerceInt2FP: no match"

            maybe_frsp dst
                    = case toRep of
                            W32 -> unitOL $ FRSP dst dst
                            W64 -> nilOL
                            _       -> panic "PPC.CodeGen.coerceInt2FP: no match"

        return (Any (floatFormat toRep) code')

    coerceInt2FP' _ _ _ _ = panic "PPC.CodeGen.coerceInt2FP: unknown arch"

    coerceFP2Int :: Width -> Width -> CmmExpr -> NatM Register
    coerceFP2Int fromRep toRep x = do
        dflags <- getDynFlags
        let arch =  platformArch $ targetPlatform dflags
        coerceFP2Int' arch fromRep toRep x

    coerceFP2Int' :: Arch -> Width -> Width -> CmmExpr -> NatM Register
    coerceFP2Int' ArchPPC _ toRep x = do
        dflags <- getDynFlags
        -- the reps don't really matter: F*->FF64 and II32->I* are no-ops
        (src, code) <- getSomeReg x
        tmp <- getNewRegNat FF64
        let
            code' dst = code `appOL` toOL [
                    -- convert to int in FP reg
                FCTIWZ tmp src,
                    -- store value (64bit) from FP to stack
                ST FF64 tmp (spRel dflags 2),
                    -- read low word of value (high word is undefined)
                LD II32 dst (spRel dflags 3)]
        return (Any (intFormat toRep) code')

    coerceFP2Int' (ArchPPC_64 _) _ toRep x = do
        dflags <- getDynFlags
        -- the reps don't really matter: F*->FF64 and II64->I* are no-ops
        (src, code) <- getSomeReg x
        tmp <- getNewRegNat FF64
        let
            code' dst = code `appOL` toOL [
                    -- convert to int in FP reg
                FCTIDZ tmp src,
                    -- store value (64bit) from FP to compiler word on stack
                ST FF64 tmp (spRel dflags 3),
                LD II64 dst (spRel dflags 3)]
        return (Any (intFormat toRep) code')

    coerceFP2Int' _ _ _ _ = panic "PPC.CodeGen.coerceFP2Int: unknown arch"

    -- Note [.LCTOC1 in PPC PIC code]
    -- The .LCTOC1 label is defined to point 32768 bytes into the GOT table
    -- to make the most of the PPC's 16-bit displacements.
    -- As 16-bit signed offset is used (usually via addi/lwz instructions)
    -- first element will have '-32768' offset against .LCTOC1.

    -- Note [implicit register in PPC PIC code]
    -- PPC generates calls by labels in assembly
    -- in form of:
    --     bl puts+32768@plt
    -- in this form it's not seen directly (by GHC NCG)
    -- that r30 (PicBaseReg) is used,
    -- but r30 is a required part of PLT code setup:
    --   puts+32768@plt:
    --       lwz     r11,-30484(r30) ; offset in .LCTOC1
    --       mtctr   r11
    --       bctr