    -- | Expand out synthetic instructions into single machine instrs.
    module SPARC.CodeGen.Expand (
            expandTop
    )

    where

    import GhcPrelude

    import SPARC.Instr
    import SPARC.Imm
    import SPARC.AddrMode
    import SPARC.Regs
    import SPARC.Ppr        ()
    import Instruction
    import Reg
    import Format
    import Cmm

    import Outputable
    import OrdList

    -- | Expand out synthetic instructions in this top level thing
    expandTop :: NatCmmDecl CmmStatics Instr -> NatCmmDecl CmmStatics Instr
    expandTop top@(CmmData{})
            = top

    expandTop (CmmProc info lbl live (ListGraph blocks))
            = CmmProc info lbl live (ListGraph $ map expandBlock blocks)

    -- | Expand out synthetic instructions in this block
    expandBlock :: NatBasicBlock Instr -> NatBasicBlock Instr

    expandBlock (BasicBlock label instrs)
     = let  instrs_ol       = expandBlockInstrs instrs
            instrs'         = fromOL instrs_ol
       in   BasicBlock label instrs'

    -- | Expand out some instructions
    expandBlockInstrs :: [Instr] -> OrdList Instr
    expandBlockInstrs []    = nilOL

    expandBlockInstrs (ii:is)
     = let  ii_doubleRegs   = remapRegPair ii
            is_misaligned   = expandMisalignedDoubles ii_doubleRegs

       in   is_misaligned `appOL` expandBlockInstrs is

    -- | In the SPARC instruction set the FP register pairs that are used
    --      to hold 64 bit floats are refered to by just the first reg
    --      of the pair. Remap our internal reg pairs to the appropriate reg.
    --
    --      For example:
    --          ldd [%l1], (%f0 | %f1)
    --
    --      gets mapped to
    --          ldd [$l1], %f0
    --
    remapRegPair :: Instr -> Instr
    remapRegPair instr
     = let  patchF reg
             = case reg of
                    RegReal (RealRegSingle _)
                            -> reg

                    RegReal (RealRegPair r1 r2)

                            -- sanity checking
                            | r1         >= 32
                            , r1         <= 63
                            , r1 `mod` 2 == 0
                            , r2         == r1 + 1
                            -> RegReal (RealRegSingle r1)

                            | otherwise
                            -> pprPanic "SPARC.CodeGen.Expand: not remapping dodgy looking reg pair " (ppr reg)

                    RegVirtual _
                            -> pprPanic "SPARC.CodeGen.Expand: not remapping virtual reg " (ppr reg)

       in   patchRegsOfInstr instr patchF

    -- Expand out 64 bit load/stores into individual instructions to handle
    --      possible double alignment problems.
    --
    --      TODO:   It'd be better to use a scratch reg instead of the add/sub thing.
    --              We might be able to do this faster if we use the UA2007 instr set
    --              instead of restricting ourselves to SPARC V9.
    --
    expandMisalignedDoubles :: Instr -> OrdList Instr
    expandMisalignedDoubles instr

            -- Translate to:
            --    add g1,g2,g1
            --    ld  [g1],%fn
            --    ld  [g1+4],%f(n+1)
            --    sub g1,g2,g1           -- to restore g1
            | LD FF64 (AddrRegReg r1 r2) fReg       <- instr
            =       toOL    [ ADD False False r1 (RIReg r2) r1
                            , LD  FF32  (AddrRegReg r1 g0)          fReg
                            , LD  FF32  (AddrRegImm r1 (ImmInt 4))  (fRegHi fReg)
                            , SUB False False r1 (RIReg r2) r1 ]

            -- Translate to
            --    ld  [addr],%fn
            --    ld  [addr+4],%f(n+1)
            | LD FF64 addr fReg                     <- instr
            = let   Just addr'      = addrOffset addr 4
              in    toOL    [ LD  FF32  addr        fReg
                            , LD  FF32  addr'       (fRegHi fReg) ]

            -- Translate to:
            --    add g1,g2,g1
            --    st  %fn,[g1]
            --    st  %f(n+1),[g1+4]
            --    sub g1,g2,g1           -- to restore g1
            | ST FF64 fReg (AddrRegReg r1 r2)       <- instr
            =       toOL    [ ADD False False r1 (RIReg r2) r1
                            , ST  FF32  fReg           (AddrRegReg r1 g0)
                            , ST  FF32  (fRegHi fReg)  (AddrRegImm r1 (ImmInt 4))
                            , SUB False False r1 (RIReg r2) r1 ]

            -- Translate to
            --    ld  [addr],%fn
            --    ld  [addr+4],%f(n+1)
            | ST FF64 fReg addr                     <- instr
            = let   Just addr'      = addrOffset addr 4
              in    toOL    [ ST  FF32  fReg           addr
                            , ST  FF32  (fRegHi fReg)  addr'         ]

            -- some other instr
            | otherwise
            = unitOL instr

    -- | The the high partner for this float reg.
    fRegHi :: Reg -> Reg
    fRegHi (RegReal (RealRegSingle r1))
            | r1            >= 32
            , r1            <= 63
            , r1 `mod` 2 == 0
            = (RegReal $ RealRegSingle (r1 + 1))

    -- Can't take high partner for non-low reg.
    fRegHi reg
            = pprPanic "SPARC.CodeGen.Expand: can't take fRegHi from " (ppr reg)