cmm/CmmCallConv.hs

    module CmmCallConv (
      ParamLocation(..),
      assignArgumentsPos,
      assignStack,
      realArgRegsCover
    ) where

    #include "HsVersions.h"

    import CmmExpr
    import SMRep
    import Cmm (Convention(..))
    import PprCmm ()

    import DynFlags
    import Platform
    import Outputable

    -- Calculate the 'GlobalReg' or stack locations for function call
    -- parameters as used by the Cmm calling convention.

    data ParamLocation
      = RegisterParam GlobalReg
      | StackParam ByteOff

    instance Outputable ParamLocation where
      ppr (RegisterParam g) = ppr g
      ppr (StackParam p)    = ppr p

    -- |
    -- Given a list of arguments, and a function that tells their types,
    -- return a list showing where each argument is passed
    --
    assignArgumentsPos :: DynFlags
                       -> ByteOff           -- stack offset to start with
                       -> Convention
                       -> (a -> CmmType)    -- how to get a type from an arg
                       -> [a]               -- args
                       -> (
                            ByteOff              -- bytes of stack args
                          , [(a, ParamLocation)] -- args and locations
                          )

    assignArgumentsPos dflags off conv arg_ty reps = (stk_off, assignments)
        where
          regs = case (reps, conv) of
                   (_,   NativeNodeCall)   -> getRegsWithNode dflags
                   (_,   NativeDirectCall) -> getRegsWithoutNode dflags
                   ([_], NativeReturn)     -> allRegs dflags
                   (_,   NativeReturn)     -> getRegsWithNode dflags
                   -- GC calling convention *must* put values in registers
                   (_,   GC)               -> allRegs dflags
                   (_,   Slow)             -> nodeOnly
          -- The calling conventions first assign arguments to registers,
          -- then switch to the stack when we first run out of registers
          -- (even if there are still available registers for args of a
          -- different type).  When returning an unboxed tuple, we also
          -- separate the stack arguments by pointerhood.
          (reg_assts, stk_args)  = assign_regs [] reps regs
          (stk_off,   stk_assts) = assignStack dflags off arg_ty stk_args
          assignments = reg_assts ++ stk_assts

          assign_regs assts []     _    = (assts, [])
          assign_regs assts (r:rs) regs | isVecType ty   = vec
                                        | isFloatType ty = float
                                        | otherwise      = int
            where vec = case (w, regs) of
                          (W128, (vs, fs, ds, ls, s:ss))
                              | passVectorInReg W128 dflags -> k (RegisterParam (XmmReg s), (vs, fs, ds, ls, ss))
                          (W256, (vs, fs, ds, ls, s:ss))
                              | passVectorInReg W256 dflags -> k (RegisterParam (YmmReg s), (vs, fs, ds, ls, ss))
                          (W512, (vs, fs, ds, ls, s:ss))
                              | passVectorInReg W512 dflags -> k (RegisterParam (ZmmReg s), (vs, fs, ds, ls, ss))
                          _ -> (assts, (r:rs))
                  float = case (w, regs) of
                            (W32, (vs, fs, ds, ls, s:ss))
                                | passFloatInXmm          -> k (RegisterParam (FloatReg s), (vs, fs, ds, ls, ss))
                            (W32, (vs, f:fs, ds, ls, ss))
                                | not passFloatInXmm      -> k (RegisterParam f, (vs, fs, ds, ls, ss))
                            (W64, (vs, fs, ds, ls, s:ss))
                                | passFloatInXmm          -> k (RegisterParam (DoubleReg s), (vs, fs, ds, ls, ss))
                            (W64, (vs, fs, d:ds, ls, ss))
                                | not passFloatInXmm      -> k (RegisterParam d, (vs, fs, ds, ls, ss))
                            (W80, _) -> panic "F80 unsupported register type"
                            _ -> (assts, (r:rs))
                  int = case (w, regs) of
                          (W128, _) -> panic "W128 unsupported register type"
                          (_, (v:vs, fs, ds, ls, ss)) | widthInBits w <= widthInBits (wordWidth dflags)
                              -> k (RegisterParam (v gcp), (vs, fs, ds, ls, ss))
                          (_, (vs, fs, ds, l:ls, ss)) | widthInBits w > widthInBits (wordWidth dflags)
                              -> k (RegisterParam l, (vs, fs, ds, ls, ss))
                          _   -> (assts, (r:rs))
                  k (asst, regs') = assign_regs ((r, asst) : assts) rs regs'
                  ty = arg_ty r
                  w  = typeWidth ty
                  gcp | isGcPtrType ty = VGcPtr
                      | otherwise      = VNonGcPtr
                  passFloatInXmm = passFloatArgsInXmm dflags

    passFloatArgsInXmm :: DynFlags -> Bool
    passFloatArgsInXmm dflags = case platformArch (targetPlatform dflags) of
                                  ArchX86_64 -> True
                                  _          -> False

    -- On X86_64, we always pass 128-bit-wide vectors in registers. On 32-bit X86
    -- and for all larger vector sizes on X86_64, LLVM's GHC calling convention
    -- doesn't currently passing vectors in registers. The patch to update the GHC
    -- calling convention to support passing SIMD vectors in registers is small and
    -- well-contained, so it may make it into LLVM 3.4. The hidden
    -- -fllvm-pass-vectors-in-regs flag will generate LLVM code that attempts to
    -- pass vectors in registers, but it must only be used with a version of LLVM
    -- that has an updated GHC calling convention.
    passVectorInReg :: Width -> DynFlags -> Bool
    passVectorInReg W128 dflags = case platformArch (targetPlatform dflags) of
                                    ArchX86_64 -> True
                                    _          -> gopt Opt_LlvmPassVectorsInRegisters dflags
    passVectorInReg _    dflags = gopt Opt_LlvmPassVectorsInRegisters dflags

    assignStack :: DynFlags -> ByteOff -> (a -> CmmType) -> [a]
                -> (
                     ByteOff              -- bytes of stack args
                   , [(a, ParamLocation)] -- args and locations
                   )
    assignStack dflags offset arg_ty args = assign_stk offset [] (reverse args)
     where
          assign_stk offset assts [] = (offset, assts)
          assign_stk offset assts (r:rs)
            = assign_stk off' ((r, StackParam off') : assts) rs
            where w    = typeWidth (arg_ty r)
                  size = (((widthInBytes w - 1) `div` word_size) + 1) * word_size
                  off' = offset + size
                  word_size = wORD_SIZE dflags

    -----------------------------------------------------------------------------
    -- Local information about the registers available

    type AvailRegs = ( [VGcPtr -> GlobalReg]   -- available vanilla regs.
                     , [GlobalReg]   -- floats
                     , [GlobalReg]   -- doubles
                     , [GlobalReg]   -- longs (int64 and word64)
                     , [Int]         -- XMM (floats and doubles)
                     )

    -- Vanilla registers can contain pointers, Ints, Chars.
    -- Floats and doubles have separate register supplies.
    --
    -- We take these register supplies from the *real* registers, i.e. those
    -- that are guaranteed to map to machine registers.

    getRegsWithoutNode, getRegsWithNode :: DynFlags -> AvailRegs
    getRegsWithoutNode dflags =
      ( filter (\r -> r VGcPtr /= node) (realVanillaRegs dflags)
      , realFloatRegs dflags
      , realDoubleRegs dflags
      , realLongRegs dflags
      , realXmmRegNos dflags)

    -- getRegsWithNode uses R1/node even if it isn't a register
    getRegsWithNode dflags =
      ( if null (realVanillaRegs dflags)
        then [VanillaReg 1]
        else realVanillaRegs dflags
      , realFloatRegs dflags
      , realDoubleRegs dflags
      , realLongRegs dflags
      , realXmmRegNos dflags)

    allFloatRegs, allDoubleRegs, allLongRegs :: DynFlags -> [GlobalReg]
    allVanillaRegs :: DynFlags -> [VGcPtr -> GlobalReg]
    allXmmRegs :: DynFlags -> [Int]

    allVanillaRegs dflags = map VanillaReg $ regList (mAX_Vanilla_REG dflags)
    allFloatRegs   dflags = map FloatReg   $ regList (mAX_Float_REG   dflags)
    allDoubleRegs  dflags = map DoubleReg  $ regList (mAX_Double_REG  dflags)
    allLongRegs    dflags = map LongReg    $ regList (mAX_Long_REG    dflags)
    allXmmRegs     dflags =                  regList (mAX_XMM_REG     dflags)

    realFloatRegs, realDoubleRegs, realLongRegs :: DynFlags -> [GlobalReg]
    realVanillaRegs :: DynFlags -> [VGcPtr -> GlobalReg]
    realXmmRegNos :: DynFlags -> [Int]

    realVanillaRegs dflags = map VanillaReg $ regList (mAX_Real_Vanilla_REG dflags)
    realFloatRegs   dflags = map FloatReg   $ regList (mAX_Real_Float_REG   dflags)
    realDoubleRegs  dflags = map DoubleReg  $ regList (mAX_Real_Double_REG  dflags)
    realLongRegs    dflags = map LongReg    $ regList (mAX_Real_Long_REG    dflags)

    realXmmRegNos dflags
        | isSse2Enabled dflags = regList (mAX_Real_XMM_REG     dflags)
        | otherwise            = []

    regList :: Int -> [Int]
    regList n = [1 .. n]

    allRegs :: DynFlags -> AvailRegs
    allRegs dflags = (allVanillaRegs dflags,
                      allFloatRegs dflags,
                      allDoubleRegs dflags,
                      allLongRegs dflags,
                      allXmmRegs dflags)

    nodeOnly :: AvailRegs
    nodeOnly = ([VanillaReg 1], [], [], [], [])

    -- This returns the set of global registers that *cover* the machine registers
    -- used for argument passing. On platforms where registers can overlap---right
    -- now just x86-64, where Float and Double registers overlap---passing this set
    -- of registers is guaranteed to preserve the contents of all live registers. We
    -- only use this functionality in hand-written C-- code in the RTS.
    realArgRegsCover :: DynFlags -> [GlobalReg]
    realArgRegsCover dflags
        | passFloatArgsInXmm dflags = map ($VGcPtr) (realVanillaRegs dflags) ++
                                      realLongRegs dflags ++
                                      map XmmReg (realXmmRegNos dflags)
        | otherwise                 = map ($VGcPtr) (realVanillaRegs dflags) ++
                                      realFloatRegs dflags ++
                                      realDoubleRegs dflags ++
                                      realLongRegs dflags ++
                                      map XmmReg (realXmmRegNos dflags)