path: root/compiler/GHC/ByteCode/Asm.hs

{-# LANGUAGE CPP             #-}
{-# LANGUAGE DeriveFunctor   #-}
{-# LANGUAGE RecordWildCards #-}
{-# OPTIONS_GHC -optc-DNON_POSIX_SOURCE #-}
--
--  (c) The University of Glasgow 2002-2006
--

-- | Bytecode assembler and linker
module GHC.ByteCode.Asm (
        assembleBCOs, assembleOneBCO,
        bcoFreeNames,
        SizedSeq, sizeSS, ssElts,
        iNTERP_STACK_CHECK_THRESH,
        mkTupleInfoLit
  ) where

import GHC.Prelude

import GHC.ByteCode.Instr
import GHC.ByteCode.InfoTable
import GHC.ByteCode.Types
import GHCi.RemoteTypes
import GHC.Runtime.Interpreter
import GHC.Runtime.Heap.Layout hiding ( WordOff )

import GHC.Types.Name
import GHC.Types.Name.Set
import GHC.Types.Literal
import GHC.Types.Unique
import GHC.Types.Unique.DSet

import GHC.Utils.Outputable
import GHC.Utils.Panic
import GHC.Utils.Panic.Plain

import GHC.Core.TyCon
import GHC.Data.FastString
import GHC.Data.SizedSeq

import GHC.StgToCmm.Layout     ( ArgRep(..) )
import GHC.Platform
import GHC.Platform.Profile

import Control.Monad
import Control.Monad.ST ( runST )
import Control.Monad.Trans.Class
import Control.Monad.Trans.State.Strict

import Data.Array.MArray

import qualified Data.Array.Unboxed as Array
import Data.Array.Base  ( UArray(..) )

import Data.Array.Unsafe( castSTUArray )

import Foreign hiding (shiftL, shiftR)
import Data.Char        ( ord )
import Data.List        ( genericLength )
import Data.Map.Strict (Map)
import Data.Maybe (fromMaybe)
import qualified Data.Map.Strict as Map

-- -----------------------------------------------------------------------------
-- Unlinked BCOs

-- CompiledByteCode represents the result of byte-code
-- compiling a bunch of functions and data types

-- | Finds external references.  Remember to remove the names
-- defined by this group of BCOs themselves
bcoFreeNames :: UnlinkedBCO -> UniqDSet Name
bcoFreeNames bco
  = bco_refs bco `uniqDSetMinusUniqSet` mkNameSet [unlinkedBCOName bco]
  where
    bco_refs (UnlinkedBCO _ _ _ _ nonptrs ptrs)
        = unionManyUniqDSets (
             mkUniqDSet [ n | BCOPtrName n <- ssElts ptrs ] :
             mkUniqDSet [ n | BCONPtrItbl n <- ssElts nonptrs ] :
             map bco_refs [ bco | BCOPtrBCO bco <- ssElts ptrs ]
          )

-- -----------------------------------------------------------------------------
-- The bytecode assembler

-- The object format for bytecodes is: 16 bits for the opcode, and 16
-- for each field -- so the code can be considered a sequence of
-- 16-bit ints.  Each field denotes either a stack offset or number of
-- items on the stack (eg SLIDE), and index into the pointer table (eg
-- PUSH_G), an index into the literal table (eg PUSH_I/D/L), or a
-- bytecode address in this BCO.

-- Top level assembler fn.
assembleBCOs
  :: Interp
  -> Profile
  -> [ProtoBCO Name]
  -> [TyCon]
  -> [RemotePtr ()]
  -> Maybe ModBreaks
  -> IO CompiledByteCode
assembleBCOs interp profile proto_bcos tycons top_strs modbreaks = do
  -- TODO: the profile should be bundled with the interpreter: the rts ways are
  -- fixed for an interpreter
  itblenv <- mkITbls interp profile tycons
  bcos    <- mapM (assembleBCO (profilePlatform profile)) proto_bcos
  (bcos',ptrs) <- mallocStrings interp bcos
  return CompiledByteCode
    { bc_bcos = bcos'
    , bc_itbls =  itblenv
    , bc_ffis = concatMap protoBCOFFIs proto_bcos
    , bc_strs = top_strs ++ ptrs
    , bc_breaks = modbreaks
    }

-- Find all the literal strings and malloc them together.  We want to
-- do this because:
--
--  a) It should be done when we compile the module, not each time we relink it
--  b) For -fexternal-interpreter It's more efficient to malloc the strings
--     as a single batch message, especially when compiling in parallel.
--
mallocStrings :: Interp -> [UnlinkedBCO] -> IO ([UnlinkedBCO], [RemotePtr ()])
mallocStrings interp ulbcos = do
  let bytestrings = reverse (execState (mapM_ collect ulbcos) [])
  ptrs <- interpCmd interp (MallocStrings bytestrings)
  return (evalState (mapM splice ulbcos) ptrs, ptrs)
 where
  splice bco@UnlinkedBCO{..} = do
    lits <- mapM spliceLit unlinkedBCOLits
    ptrs <- mapM splicePtr unlinkedBCOPtrs
    return bco { unlinkedBCOLits = lits, unlinkedBCOPtrs = ptrs }

  spliceLit (BCONPtrStr _) = do
    rptrs <- get
    case rptrs of
      (RemotePtr p : rest) -> do
        put rest
        return (BCONPtrWord (fromIntegral p))
      _ -> panic "mallocStrings:spliceLit"
  spliceLit other = return other

  splicePtr (BCOPtrBCO bco) = BCOPtrBCO <$> splice bco
  splicePtr other = return other

  collect UnlinkedBCO{..} = do
    mapM_ collectLit unlinkedBCOLits
    mapM_ collectPtr unlinkedBCOPtrs

  collectLit (BCONPtrStr bs) = do
    strs <- get
    put (bs:strs)
  collectLit _ = return ()

  collectPtr (BCOPtrBCO bco) = collect bco
  collectPtr _ = return ()


assembleOneBCO :: Interp -> Profile -> ProtoBCO Name -> IO UnlinkedBCO
assembleOneBCO interp profile pbco = do
  -- TODO: the profile should be bundled with the interpreter: the rts ways are
  -- fixed for an interpreter
  ubco <- assembleBCO (profilePlatform profile) pbco
  ([ubco'], _ptrs) <- mallocStrings interp [ubco]
  return ubco'

assembleBCO :: Platform -> ProtoBCO Name -> IO UnlinkedBCO
assembleBCO platform (ProtoBCO { protoBCOName       = nm
                             , protoBCOInstrs     = instrs
                             , protoBCOBitmap     = bitmap
                             , protoBCOBitmapSize = bsize
                             , protoBCOArity      = arity }) = do
  -- pass 1: collect up the offsets of the local labels.
  let asm = mapM_ (assembleI platform) instrs

      initial_offset = 0

      -- Jump instructions are variable-sized, there are long and short variants
      -- depending on the magnitude of the offset.  However, we can't tell what
      -- size instructions we will need until we have calculated the offsets of
      -- the labels, which depends on the size of the instructions...  So we
      -- first create the label environment assuming that all jumps are short,
      -- and if the final size is indeed small enough for short jumps, we are
      -- done.  Otherwise, we repeat the calculation, and we force all jumps in
      -- this BCO to be long.
      (n_insns0, lbl_map0) = inspectAsm platform False initial_offset asm
      ((n_insns, lbl_map), long_jumps)
        | isLarge (fromIntegral $ Map.size lbl_map0)
          || isLarge n_insns0
                    = (inspectAsm platform True initial_offset asm, True)
        | otherwise = ((n_insns0, lbl_map0), False)

      env :: LocalLabel -> Word
      env lbl = fromMaybe
        (pprPanic "assembleBCO.findLabel" (ppr lbl))
        (Map.lookup lbl lbl_map)

  -- pass 2: run assembler and generate instructions, literals and pointers
  let initial_state = (emptySS, emptySS, emptySS)
  (final_insns, final_lits, final_ptrs) <- flip execStateT initial_state $ runAsm platform long_jumps env asm

  -- precomputed size should be equal to final size
  massert (n_insns == sizeSS final_insns)

  let asm_insns = ssElts final_insns
      insns_arr = Array.listArray (0, fromIntegral n_insns - 1) asm_insns
      bitmap_arr = mkBitmapArray bsize bitmap
      ul_bco = UnlinkedBCO nm arity insns_arr bitmap_arr final_lits final_ptrs

  -- 8 Aug 01: Finalisers aren't safe when attached to non-primitive
  -- objects, since they might get run too early.  Disable this until
  -- we figure out what to do.
  -- when (notNull malloced) (addFinalizer ul_bco (mapM_ zonk malloced))

  return ul_bco

mkBitmapArray :: Word16 -> [StgWord] -> UArray Int Word64
-- Here the return type must be an array of Words, not StgWords,
-- because the underlying ByteArray# will end up as a component
-- of a BCO object.
mkBitmapArray bsize bitmap
  = Array.listArray (0, length bitmap) $
      fromIntegral bsize : map (fromInteger . fromStgWord) bitmap

-- instrs nonptrs ptrs
type AsmState = (SizedSeq Word16,
                 SizedSeq BCONPtr,
                 SizedSeq BCOPtr)

data Operand
  = Op Word
  | SmallOp Word16
  | LabelOp LocalLabel
-- (unused)  | LargeOp Word

data Assembler a
  = AllocPtr (IO BCOPtr) (Word -> Assembler a)
  | AllocLit [BCONPtr] (Word -> Assembler a)
  | AllocLabel LocalLabel (Assembler a)
  | Emit Word16 [Operand] (Assembler a)
  | NullAsm a
  deriving (Functor)

instance Applicative Assembler where
    pure = NullAsm
    (<*>) = ap

instance Monad Assembler where
  NullAsm x >>= f = f x
  AllocPtr p k >>= f = AllocPtr p (k >=> f)
  AllocLit l k >>= f = AllocLit l (k >=> f)
  AllocLabel lbl k >>= f = AllocLabel lbl (k >>= f)
  Emit w ops k >>= f = Emit w ops (k >>= f)

ioptr :: IO BCOPtr -> Assembler Word
ioptr p = AllocPtr p return

ptr :: BCOPtr -> Assembler Word
ptr = ioptr . return

lit :: [BCONPtr] -> Assembler Word
lit l = AllocLit l return

label :: LocalLabel -> Assembler ()
label w = AllocLabel w (return ())

emit :: Word16 -> [Operand] -> Assembler ()
emit w ops = Emit w ops (return ())

type LabelEnv = LocalLabel -> Word

largeOp :: Bool -> Operand -> Bool
largeOp long_jumps op = case op of
   SmallOp _ -> False
   Op w      -> isLarge w
   LabelOp _ -> long_jumps
-- LargeOp _ -> True

runAsm :: Platform -> Bool -> LabelEnv -> Assembler a -> StateT AsmState IO a
runAsm platform long_jumps e = go
  where
    go (NullAsm x) = return x
    go (AllocPtr p_io k) = do
      p <- lift p_io
      w <- state $ \(st_i0,st_l0,st_p0) ->
        let st_p1 = addToSS st_p0 p
        in (sizeSS st_p0, (st_i0,st_l0,st_p1))
      go $ k w
    go (AllocLit lits k) = do
      w <- state $ \(st_i0,st_l0,st_p0) ->
        let st_l1 = addListToSS st_l0 lits
        in (sizeSS st_l0, (st_i0,st_l1,st_p0))
      go $ k w
    go (AllocLabel _ k) = go k
    go (Emit w ops k) = do
      let largeOps = any (largeOp long_jumps) ops
          opcode
            | largeOps = largeArgInstr w
            | otherwise = w
          words = concatMap expand ops
          expand (SmallOp w) = [w]
          expand (LabelOp w) = expand (Op (e w))
          expand (Op w) = if largeOps then largeArg platform w else [fromIntegral w]
--        expand (LargeOp w) = largeArg platform w
      state $ \(st_i0,st_l0,st_p0) ->
        let st_i1 = addListToSS st_i0 (opcode : words)
        in ((), (st_i1,st_l0,st_p0))
      go k

type LabelEnvMap = Map LocalLabel Word

data InspectState = InspectState
  { instrCount :: !Word
  , ptrCount :: !Word
  , litCount :: !Word
  , lblEnv :: LabelEnvMap
  }

inspectAsm :: Platform -> Bool -> Word -> Assembler a -> (Word, LabelEnvMap)
inspectAsm platform long_jumps initial_offset
  = go (InspectState initial_offset 0 0 Map.empty)
  where
    go s (NullAsm _) = (instrCount s, lblEnv s)
    go s (AllocPtr _ k) = go (s { ptrCount = n + 1 }) (k n)
      where n = ptrCount s
    go s (AllocLit ls k) = go (s { litCount = n + genericLength ls }) (k n)
      where n = litCount s
    go s (AllocLabel lbl k) = go s' k
      where s' = s { lblEnv = Map.insert lbl (instrCount s) (lblEnv s) }
    go s (Emit _ ops k) = go s' k
      where
        s' = s { instrCount = instrCount s + size }
        size = sum (map count ops) + 1
        largeOps = any (largeOp long_jumps) ops
        count (SmallOp _) = 1
        count (LabelOp _) = count (Op 0)
        count (Op _) = if largeOps then largeArg16s platform else 1
--      count (LargeOp _) = largeArg16s platform

-- Bring in all the bci_ bytecode constants.
#include "rts/Bytecodes.h"

largeArgInstr :: Word16 -> Word16
largeArgInstr bci = bci_FLAG_LARGE_ARGS .|. bci

largeArg :: Platform -> Word -> [Word16]
largeArg platform w = case platformWordSize platform of
   PW8 -> [fromIntegral (w `shiftR` 48),
           fromIntegral (w `shiftR` 32),
           fromIntegral (w `shiftR` 16),
           fromIntegral w]
   PW4 -> [fromIntegral (w `shiftR` 16),
           fromIntegral w]

largeArg16s :: Platform -> Word
largeArg16s platform = case platformWordSize platform of
   PW8 -> 4
   PW4 -> 2

assembleI :: Platform
          -> BCInstr
          -> Assembler ()
assembleI platform i = case i of
  STKCHECK n               -> emit bci_STKCHECK [Op n]
  PUSH_L o1                -> emit bci_PUSH_L [SmallOp o1]
  PUSH_LL o1 o2            -> emit bci_PUSH_LL [SmallOp o1, SmallOp o2]
  PUSH_LLL o1 o2 o3        -> emit bci_PUSH_LLL [SmallOp o1, SmallOp o2, SmallOp o3]
  PUSH8 o1                 -> emit bci_PUSH8 [SmallOp o1]
  PUSH16 o1                -> emit bci_PUSH16 [SmallOp o1]
  PUSH32 o1                -> emit bci_PUSH32 [SmallOp o1]
  PUSH8_W o1               -> emit bci_PUSH8_W [SmallOp o1]
  PUSH16_W o1              -> emit bci_PUSH16_W [SmallOp o1]
  PUSH32_W o1              -> emit bci_PUSH32_W [SmallOp o1]
  PUSH_G nm                -> do p <- ptr (BCOPtrName nm)
                                 emit bci_PUSH_G [Op p]
  PUSH_PRIMOP op           -> do p <- ptr (BCOPtrPrimOp op)
                                 emit bci_PUSH_G [Op p]
  PUSH_BCO proto           -> do let ul_bco = assembleBCO platform proto
                                 p <- ioptr (liftM BCOPtrBCO ul_bco)
                                 emit bci_PUSH_G [Op p]
  PUSH_ALTS proto          -> do let ul_bco = assembleBCO platform proto
                                 p <- ioptr (liftM BCOPtrBCO ul_bco)
                                 emit bci_PUSH_ALTS [Op p]
  PUSH_ALTS_UNLIFTED proto pk
                           -> do let ul_bco = assembleBCO platform proto
                                 p <- ioptr (liftM BCOPtrBCO ul_bco)
                                 emit (push_alts pk) [Op p]
  PUSH_ALTS_TUPLE proto tuple_info tuple_proto
                           -> do let ul_bco = assembleBCO platform proto
                                     ul_tuple_bco = assembleBCO platform
                                                                tuple_proto
                                 p <- ioptr (liftM BCOPtrBCO ul_bco)
                                 p_tup <- ioptr (liftM BCOPtrBCO ul_tuple_bco)
                                 info <- int (fromIntegral $
                                              mkTupleInfoSig tuple_info)
                                 emit bci_PUSH_ALTS_T
                                      [Op p, Op info, Op p_tup]
  PUSH_PAD8                -> emit bci_PUSH_PAD8 []
  PUSH_PAD16               -> emit bci_PUSH_PAD16 []
  PUSH_PAD32               -> emit bci_PUSH_PAD32 []
  PUSH_UBX8 lit            -> do np <- literal lit
                                 emit bci_PUSH_UBX8 [Op np]
  PUSH_UBX16 lit           -> do np <- literal lit
                                 emit bci_PUSH_UBX16 [Op np]
  PUSH_UBX32 lit           -> do np <- literal lit
                                 emit bci_PUSH_UBX32 [Op np]
  PUSH_UBX lit nws         -> do np <- literal lit
                                 emit bci_PUSH_UBX [Op np, SmallOp nws]

  PUSH_APPLY_N             -> emit bci_PUSH_APPLY_N []
  PUSH_APPLY_V             -> emit bci_PUSH_APPLY_V []
  PUSH_APPLY_F             -> emit bci_PUSH_APPLY_F []
  PUSH_APPLY_D             -> emit bci_PUSH_APPLY_D []
  PUSH_APPLY_L             -> emit bci_PUSH_APPLY_L []
  PUSH_APPLY_P             -> emit bci_PUSH_APPLY_P []
  PUSH_APPLY_PP            -> emit bci_PUSH_APPLY_PP []
  PUSH_APPLY_PPP           -> emit bci_PUSH_APPLY_PPP []
  PUSH_APPLY_PPPP          -> emit bci_PUSH_APPLY_PPPP []
  PUSH_APPLY_PPPPP         -> emit bci_PUSH_APPLY_PPPPP []
  PUSH_APPLY_PPPPPP        -> emit bci_PUSH_APPLY_PPPPPP []

  SLIDE     n by           -> emit bci_SLIDE [SmallOp n, SmallOp by]
  ALLOC_AP  n              -> emit bci_ALLOC_AP [SmallOp n]
  ALLOC_AP_NOUPD n         -> emit bci_ALLOC_AP_NOUPD [SmallOp n]
  ALLOC_PAP arity n        -> emit bci_ALLOC_PAP [SmallOp arity, SmallOp n]
  MKAP      off sz         -> emit bci_MKAP [SmallOp off, SmallOp sz]
  MKPAP     off sz         -> emit bci_MKPAP [SmallOp off, SmallOp sz]
  UNPACK    n              -> emit bci_UNPACK [SmallOp n]
  PACK      dcon sz        -> do itbl_no <- lit [BCONPtrItbl (getName dcon)]
                                 emit bci_PACK [Op itbl_no, SmallOp sz]
  LABEL     lbl            -> label lbl
  TESTLT_I  i l            -> do np <- int i
                                 emit bci_TESTLT_I [Op np, LabelOp l]
  TESTEQ_I  i l            -> do np <- int i
                                 emit bci_TESTEQ_I [Op np, LabelOp l]
  TESTLT_W  w l            -> do np <- word w
                                 emit bci_TESTLT_W [Op np, LabelOp l]
  TESTEQ_W  w l            -> do np <- word w
                                 emit bci_TESTEQ_W [Op np, LabelOp l]
  TESTLT_F  f l            -> do np <- float f
                                 emit bci_TESTLT_F [Op np, LabelOp l]
  TESTEQ_F  f l            -> do np <- float f
                                 emit bci_TESTEQ_F [Op np, LabelOp l]
  TESTLT_D  d l            -> do np <- double d
                                 emit bci_TESTLT_D [Op np, LabelOp l]
  TESTEQ_D  d l            -> do np <- double d
                                 emit bci_TESTEQ_D [Op np, LabelOp l]
  TESTLT_P  i l            -> emit bci_TESTLT_P [SmallOp i, LabelOp l]
  TESTEQ_P  i l            -> emit bci_TESTEQ_P [SmallOp i, LabelOp l]
  CASEFAIL                 -> emit bci_CASEFAIL []
  SWIZZLE   stkoff n       -> emit bci_SWIZZLE [SmallOp stkoff, SmallOp n]
  JMP       l              -> emit bci_JMP [LabelOp l]
  ENTER                    -> emit bci_ENTER []
  RETURN                   -> emit bci_RETURN []
  RETURN_UBX rep           -> emit (return_ubx rep) []
  RETURN_TUPLE             -> emit bci_RETURN_T []
  CCALL off m_addr i       -> do np <- addr m_addr
                                 emit bci_CCALL [SmallOp off, Op np, SmallOp i]
  BRK_FUN index uniq cc    -> do p1 <- ptr BCOPtrBreakArray
                                 q <- int (getKey uniq)
                                 np <- addr cc
                                 emit bci_BRK_FUN [Op p1, SmallOp index,
                                                   Op q, Op np]

  where
    literal (LitLabel fs (Just sz) _)
     | platformOS platform == OSMinGW32
         = litlabel (appendFS fs (mkFastString ('@':show sz)))
     -- On Windows, stdcall labels have a suffix indicating the no. of
     -- arg words, e.g. foo@8.  testcase: ffi012(ghci)
    literal (LitLabel fs _ _) = litlabel fs
    literal LitNullAddr       = int 0
    literal (LitFloat r)      = float (fromRational r)
    literal (LitDouble r)     = double (fromRational r)
    literal (LitChar c)       = int (ord c)
    literal (LitString bs)    = lit [BCONPtrStr bs]
       -- LitString requires a zero-terminator when emitted
    literal (LitNumber nt i) = case nt of
      LitNumInt     -> int (fromIntegral i)
      LitNumWord    -> int (fromIntegral i)
      LitNumInt8    -> int8 (fromIntegral i)
      LitNumWord8   -> int8 (fromIntegral i)
      LitNumInt16   -> int16 (fromIntegral i)
      LitNumWord16  -> int16 (fromIntegral i)
      LitNumInt32   -> int32 (fromIntegral i)
      LitNumWord32  -> int32 (fromIntegral i)
      LitNumInt64   -> int64 (fromIntegral i)
      LitNumWord64  -> int64 (fromIntegral i)
      LitNumInteger -> panic "GHC.ByteCode.Asm.literal: LitNumInteger"
      LitNumNatural -> panic "GHC.ByteCode.Asm.literal: LitNumNatural"

    -- We can lower 'LitRubbish' to an arbitrary constant, but @NULL@ is most
    -- likely to elicit a crash (rather than corrupt memory) in case absence
    -- analysis messed up.
    literal (LitRubbish {}) = int 0

    litlabel fs = lit [BCONPtrLbl fs]
    addr (RemotePtr a) = words [fromIntegral a]
    float = words . mkLitF
    double = words . mkLitD platform
    int = words . mkLitI
    int8 = words . mkLitI64 platform
    int16 = words . mkLitI64 platform
    int32 = words . mkLitI64 platform
    int64 = words . mkLitI64 platform
    words ws = lit (map BCONPtrWord ws)
    word w = words [w]

isLarge :: Word -> Bool
isLarge n = n > 65535

push_alts :: ArgRep -> Word16
push_alts V   = bci_PUSH_ALTS_V
push_alts P   = bci_PUSH_ALTS_P
push_alts N   = bci_PUSH_ALTS_N
push_alts L   = bci_PUSH_ALTS_L
push_alts F   = bci_PUSH_ALTS_F
push_alts D   = bci_PUSH_ALTS_D
push_alts V16 = error "push_alts: vector"
push_alts V32 = error "push_alts: vector"
push_alts V64 = error "push_alts: vector"

return_ubx :: ArgRep -> Word16
return_ubx V   = bci_RETURN_V
return_ubx P   = bci_RETURN_P
return_ubx N   = bci_RETURN_N
return_ubx L   = bci_RETURN_L
return_ubx F   = bci_RETURN_F
return_ubx D   = bci_RETURN_D
return_ubx V16 = error "return_ubx: vector"
return_ubx V32 = error "return_ubx: vector"
return_ubx V64 = error "return_ubx: vector"

{-
  we can only handle up to a fixed number of words on the stack,
  because we need a stg_ctoi_tN stack frame for each size N. See
  Note [unboxed tuple bytecodes and tuple_BCO].

  If needed, you can support larger tuples by adding more in
  StgMiscClosures.cmm, Interpreter.c and MiscClosures.h and
  raising this limit.

  Note that the limit is the number of words passed on the stack.
  If the calling convention passes part of the tuple in registers, the
  maximum number of tuple elements may be larger. Elements can also
  take multiple words on the stack (for example Double# on a 32 bit
  platform).

 -}
maxTupleNativeStackSize :: WordOff
maxTupleNativeStackSize = 62

{-
  Maximum number of supported registers for returning tuples.

  If GHC uses more more than these (because of a change in the calling
  convention or a new platform) mkTupleInfoSig will panic.

  You can raise the limits after modifying stg_ctoi_t and stg_ret_t
  (StgMiscClosures.cmm) to save and restore the additional registers.
 -}
maxTupleVanillaRegs, maxTupleFloatRegs, maxTupleDoubleRegs,
    maxTupleLongRegs :: Int
maxTupleVanillaRegs = 6
maxTupleFloatRegs = 6
maxTupleDoubleRegs = 6
maxTupleLongRegs = 1

{-
  Construct the tuple_info word that stg_ctoi_t and stg_ret_t use
  to convert a tuple between the native calling convention and the
  interpreter.

  See Note [GHCi tuple layout] for more information.
 -}
mkTupleInfoSig :: TupleInfo -> Word32
mkTupleInfoSig ti@TupleInfo{..}
  | tupleNativeStackSize > maxTupleNativeStackSize =
    pprPanic "mkTupleInfoSig: tuple too big for the bytecode compiler"
             (ppr tupleNativeStackSize <+> text "stack words." <+>
              text "Use -fobject-code to get around this limit"
             )
  | tupleVanillaRegs `shiftR` maxTupleVanillaRegs /= 0 =
    pprPanic "mkTupleInfoSig: too many vanilla registers" (ppr tupleVanillaRegs)
  | tupleLongRegs `shiftR` maxTupleLongRegs /= 0 =
    pprPanic "mkTupleInfoSig: too many long registers" (ppr tupleLongRegs)
  | tupleFloatRegs `shiftR` maxTupleFloatRegs /= 0 =
    pprPanic "mkTupleInfoSig: too many float registers" (ppr tupleFloatRegs)
  | tupleDoubleRegs `shiftR` maxTupleDoubleRegs /= 0 =
    pprPanic "mkTupleInfoSig: too many double registers" (ppr tupleDoubleRegs)
  {-
    Check that we can pack the register counts/bitmaps and stack size
    in the information word. In particular we check that each component
    fits in the bits we have reserved for it.

    This overlaps with some of the above checks. It's likely that if the
    number of registers changes, the number of bits will also need to be
    updated.
   -}
  | tupleNativeStackSize < 16384 && -- 14 bits stack usage
    tupleDoubleRegs < 64 && -- 6 bit bitmap (these can be shared with float)
    tupleFloatRegs < 64 && -- 6 bit bitmap (these can be shared with double)
    tupleLongRegs < 4 && -- 2 bit bitmap
    tupleVanillaRegs < 65536 && -- 4 bit count (tupleVanillaRegs is still a bitmap)
    -- check that there are no "holes", i.e. that R1..Rn are all in use
    tupleVanillaRegs .&. (tupleVanillaRegs + 1) == 0
    = fromIntegral tupleNativeStackSize .|.
      unRegBitmap (tupleLongRegs `shiftL` 14) .|.
      unRegBitmap (tupleDoubleRegs `shiftL` 16) .|.
      unRegBitmap (tupleFloatRegs `shiftL` 22) .|.
      fromIntegral (countTrailingZeros (1 + tupleVanillaRegs) `shiftL` 28)
  | otherwise = pprPanic "mkTupleInfoSig: unsupported tuple shape" (ppr ti)

mkTupleInfoLit :: Platform -> TupleInfo -> Literal
mkTupleInfoLit platform tuple_info =
  mkLitWord platform . fromIntegral $ mkTupleInfoSig tuple_info

-- Make lists of host-sized words for literals, so that when the
-- words are placed in memory at increasing addresses, the
-- bit pattern is correct for the host's word size and endianness.
mkLitI   ::             Int    -> [Word]
mkLitF   ::             Float  -> [Word]
mkLitD   :: Platform -> Double -> [Word]
mkLitI64 :: Platform -> Int64  -> [Word]

mkLitF f
   = runST (do
        arr <- newArray_ ((0::Int),0)
        writeArray arr 0 f
        f_arr <- castSTUArray arr
        w0 <- readArray f_arr 0
        return [w0 :: Word]
     )

mkLitD platform d = case platformWordSize platform of
   PW4 -> runST (do
        arr <- newArray_ ((0::Int),1)
        writeArray arr 0 d
        d_arr <- castSTUArray arr
        w0 <- readArray d_arr 0
        w1 <- readArray d_arr 1
        return [w0 :: Word, w1]
     )
   PW8 -> runST (do
        arr <- newArray_ ((0::Int),0)
        writeArray arr 0 d
        d_arr <- castSTUArray arr
        w0 <- readArray d_arr 0
        return [w0 :: Word]
     )

mkLitI64 platform ii = case platformWordSize platform of
   PW4 -> runST (do
        arr <- newArray_ ((0::Int),1)
        writeArray arr 0 ii
        d_arr <- castSTUArray arr
        w0 <- readArray d_arr 0
        w1 <- readArray d_arr 1
        return [w0 :: Word,w1]
     )
   PW8 -> runST (do
        arr <- newArray_ ((0::Int),0)
        writeArray arr 0 ii
        d_arr <- castSTUArray arr
        w0 <- readArray d_arr 0
        return [w0 :: Word]
     )

mkLitI i = [fromIntegral i :: Word]

iNTERP_STACK_CHECK_THRESH :: Int
iNTERP_STACK_CHECK_THRESH = INTERP_STACK_CHECK_THRESH