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

where

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)
