llvmGen/LlvmCodeGen/CodeGen.hs

    {-# LANGUAGE CPP, GADTs #-}
    {-# OPTIONS_GHC -fno-warn-type-defaults #-}
    -- ----------------------------------------------------------------------------
    -- | Handle conversion of CmmProc to LLVM code.
    --
    module LlvmCodeGen.CodeGen ( genLlvmProc ) where

    #include "HsVersions.h"

    import GhcPrelude

    import Llvm
    import LlvmCodeGen.Base
    import LlvmCodeGen.Regs

    import BlockId
    import CodeGen.Platform ( activeStgRegs, callerSaves )
    import CLabel
    import Cmm
    import PprCmm
    import CmmUtils
    import CmmSwitch
    import Hoopl.Block
    import Hoopl.Graph
    import Hoopl.Collections

    import DynFlags
    import FastString
    import ForeignCall
    import Outputable hiding (panic, pprPanic)
    import qualified Outputable
    import Platform
    import OrdList
    import UniqSupply
    import Unique
    import Util

    import Control.Monad.Trans.Class
    import Control.Monad.Trans.Writer

    import Data.Semigroup   ( Semigroup )
    import qualified Data.Semigroup as Semigroup
    import Data.List ( nub )
    import Data.Maybe ( catMaybes )

    type Atomic = Bool
    type LlvmStatements = OrdList LlvmStatement

    data Signage = Signed | Unsigned deriving (Eq, Show)

    -- -----------------------------------------------------------------------------
    -- | Top-level of the LLVM proc Code generator
    --
    genLlvmProc :: RawCmmDecl -> LlvmM [LlvmCmmDecl]
    genLlvmProc (CmmProc infos lbl live graph) = do
        let blocks = toBlockListEntryFirstFalseFallthrough graph
        (lmblocks, lmdata) <- basicBlocksCodeGen live blocks
        let info = mapLookup (g_entry graph) infos
            proc = CmmProc info lbl live (ListGraph lmblocks)
        return (proc:lmdata)

    genLlvmProc _ = panic "genLlvmProc: case that shouldn't reach here!"

    -- -----------------------------------------------------------------------------
    -- * Block code generation
    --

    -- | Generate code for a list of blocks that make up a complete
    -- procedure. The first block in the list is expected to be the entry
    -- point and will get the prologue.
    basicBlocksCodeGen :: LiveGlobalRegs -> [CmmBlock]
                          -> LlvmM ([LlvmBasicBlock], [LlvmCmmDecl])
    basicBlocksCodeGen _    []                     = panic "no entry block!"
    basicBlocksCodeGen live (entryBlock:cmmBlocks)
      = do (prologue, prologueTops) <- funPrologue live (entryBlock:cmmBlocks)

           -- Generate code
           (BasicBlock bid entry, entryTops) <- basicBlockCodeGen entryBlock
           (blocks, topss) <- fmap unzip $ mapM basicBlockCodeGen cmmBlocks

           -- Compose
           let entryBlock = BasicBlock bid (fromOL prologue ++ entry)
           return (entryBlock : blocks, prologueTops ++ entryTops ++ concat topss)

    -- | Generate code for one block
    basicBlockCodeGen :: CmmBlock -> LlvmM ( LlvmBasicBlock, [LlvmCmmDecl] )
    basicBlockCodeGen block
      = do let (_, nodes, tail)  = blockSplit block
               id = entryLabel block
           (mid_instrs, top) <- stmtsToInstrs $ blockToList nodes
           (tail_instrs, top')  <- stmtToInstrs tail
           let instrs = fromOL (mid_instrs `appOL` tail_instrs)
           return (BasicBlock id instrs, top' ++ top)

    -- -----------------------------------------------------------------------------
    -- * CmmNode code generation
    --

    -- A statement conversion return data.
    --   * LlvmStatements: The compiled LLVM statements.
    --   * LlvmCmmDecl: Any global data needed.
    type StmtData = (LlvmStatements, [LlvmCmmDecl])

    -- | Convert a list of CmmNode's to LlvmStatement's
    stmtsToInstrs :: [CmmNode e x] -> LlvmM StmtData
    stmtsToInstrs stmts
       = do (instrss, topss) <- fmap unzip $ mapM stmtToInstrs stmts
            return (concatOL instrss, concat topss)

    -- | Convert a CmmStmt to a list of LlvmStatement's
    stmtToInstrs :: CmmNode e x -> LlvmM StmtData
    stmtToInstrs stmt = case stmt of

        CmmComment _         -> return (nilOL, []) -- nuke comments
        CmmTick    _         -> return (nilOL, [])
        CmmUnwind  {}        -> return (nilOL, [])

        CmmAssign reg src    -> genAssign reg src
        CmmStore addr src    -> genStore addr src

        CmmBranch id         -> genBranch id
        CmmCondBranch arg true false likely
                             -> genCondBranch arg true false likely
        CmmSwitch arg ids    -> genSwitch arg ids

        -- Foreign Call
        CmmUnsafeForeignCall target res args
            -> genCall target res args

        -- Tail call
        CmmCall { cml_target = arg,
                  cml_args_regs = live } -> genJump arg live

        _ -> panic "Llvm.CodeGen.stmtToInstrs"

    -- | Wrapper function to declare an instrinct function by function type
    getInstrinct2 :: LMString -> LlvmType -> LlvmM ExprData
    getInstrinct2 fname fty@(LMFunction funSig) = do

        let fv   = LMGlobalVar fname fty (funcLinkage funSig) Nothing Nothing Constant

        fn <- funLookup fname
        tops <- case fn of
          Just _  ->
            return []
          Nothing -> do
            funInsert fname fty
            un <- getUniqueM
            let lbl = mkAsmTempLabel un
            return [CmmData (Section Data lbl) [([],[fty])]]

        return (fv, nilOL, tops)

    getInstrinct2 _ _ = error "getInstrinct2: Non-function type!"

    -- | Declares an instrinct function by return and parameter types
    getInstrinct :: LMString -> LlvmType -> [LlvmType] -> LlvmM ExprData
    getInstrinct fname retTy parTys =
        let funSig = LlvmFunctionDecl fname ExternallyVisible CC_Ccc retTy
                        FixedArgs (tysToParams parTys) Nothing
            fty = LMFunction funSig
        in getInstrinct2 fname fty

    -- | Memory barrier instruction for LLVM >= 3.0
    barrier :: LlvmM StmtData
    barrier = do
        let s = Fence False SyncSeqCst
        return (unitOL s, [])

    -- | Foreign Calls
    genCall :: ForeignTarget -> [CmmFormal] -> [CmmActual]
                  -> LlvmM StmtData

    -- Write barrier needs to be handled specially as it is implemented as an LLVM
    -- intrinsic function.
    genCall (PrimTarget MO_WriteBarrier) _ _ = do
        platform <- getLlvmPlatform
        if platformArch platform `elem` [ArchX86, ArchX86_64, ArchSPARC]
           then return (nilOL, [])
           else barrier

    genCall (PrimTarget MO_Touch) _ _
     = return (nilOL, [])

    genCall (PrimTarget (MO_UF_Conv w)) [dst] [e] = runStmtsDecls $ do
        dstV <- getCmmRegW (CmmLocal dst)
        let ty = cmmToLlvmType $ localRegType dst
            width = widthToLlvmFloat w
        castV <- lift $ mkLocalVar ty
        ve <- exprToVarW e
        statement $ Assignment castV $ Cast LM_Uitofp ve width
        statement $ Store castV dstV

    genCall (PrimTarget (MO_UF_Conv _)) [_] args =
        panic $ "genCall: Too many arguments to MO_UF_Conv. " ++
        "Can only handle 1, given" ++ show (length args) ++ "."

    -- Handle prefetching data
    genCall t@(PrimTarget (MO_Prefetch_Data localityInt)) [] args
      | 0 <= localityInt && localityInt <= 3 = runStmtsDecls $ do
        let argTy = [i8Ptr, i32, i32, i32]
            funTy = \name -> LMFunction $ LlvmFunctionDecl name ExternallyVisible
                                 CC_Ccc LMVoid FixedArgs (tysToParams argTy) Nothing

        let (_, arg_hints) = foreignTargetHints t
        let args_hints' = zip args arg_hints
        argVars <- arg_varsW args_hints' ([], nilOL, [])
        fptr    <- liftExprData $ getFunPtr funTy t
        argVars' <- castVarsW Signed $ zip argVars argTy

        doTrashStmts
        let argSuffix = [mkIntLit i32 0, mkIntLit i32 localityInt, mkIntLit i32 1]
        statement $ Expr $ Call StdCall fptr (argVars' ++ argSuffix) []
      | otherwise = panic $ "prefetch locality level integer must be between 0 and 3, given: " ++ (show localityInt)

    -- Handle PopCnt, Clz, Ctz, and BSwap that need to only convert arg
    -- and return types
    genCall t@(PrimTarget (MO_PopCnt w)) dsts args =
        genCallSimpleCast w t dsts args

    genCall t@(PrimTarget (MO_Pdep w)) dsts args =
        genCallSimpleCast2 w t dsts args
    genCall t@(PrimTarget (MO_Pext w)) dsts args =
        genCallSimpleCast2 w t dsts args
    genCall t@(PrimTarget (MO_Clz w)) dsts args =
        genCallSimpleCast w t dsts args
    genCall t@(PrimTarget (MO_Ctz w)) dsts args =
        genCallSimpleCast w t dsts args
    genCall t@(PrimTarget (MO_BSwap w)) dsts args =
        genCallSimpleCast w t dsts args

    genCall (PrimTarget (MO_AtomicRMW width amop)) [dst] [addr, n] = runStmtsDecls $ do
        addrVar <- exprToVarW addr
        nVar <- exprToVarW n
        let targetTy = widthToLlvmInt width
            ptrExpr = Cast LM_Inttoptr addrVar (pLift targetTy)
        ptrVar <- doExprW (pLift targetTy) ptrExpr
        dstVar <- getCmmRegW (CmmLocal dst)
        let op = case amop of
                   AMO_Add  -> LAO_Add
                   AMO_Sub  -> LAO_Sub
                   AMO_And  -> LAO_And
                   AMO_Nand -> LAO_Nand
                   AMO_Or   -> LAO_Or
                   AMO_Xor  -> LAO_Xor
        retVar <- doExprW targetTy $ AtomicRMW op ptrVar nVar SyncSeqCst
        statement $ Store retVar dstVar

    genCall (PrimTarget (MO_AtomicRead _)) [dst] [addr] = runStmtsDecls $ do
        dstV <- getCmmRegW (CmmLocal dst)
        v1 <- genLoadW True addr (localRegType dst)
        statement $ Store v1 dstV

    genCall (PrimTarget (MO_Cmpxchg _width))
            [dst] [addr, old, new] = runStmtsDecls $ do
        addrVar <- exprToVarW addr
        oldVar <- exprToVarW old
        newVar <- exprToVarW new
        let targetTy = getVarType oldVar
            ptrExpr = Cast LM_Inttoptr addrVar (pLift targetTy)
        ptrVar <- doExprW (pLift targetTy) ptrExpr
        dstVar <- getCmmRegW (CmmLocal dst)
        retVar <- doExprW (LMStructU [targetTy,i1])
                  $ CmpXChg ptrVar oldVar newVar SyncSeqCst SyncSeqCst
        retVar' <- doExprW targetTy $ ExtractV retVar 0
        statement $ Store retVar' dstVar

    genCall (PrimTarget (MO_AtomicWrite _width)) [] [addr, val] = runStmtsDecls $ do
        addrVar <- exprToVarW addr
        valVar <- exprToVarW val
        let ptrTy = pLift $ getVarType valVar
            ptrExpr = Cast LM_Inttoptr addrVar ptrTy
        ptrVar <- doExprW ptrTy ptrExpr
        statement $ Expr $ AtomicRMW LAO_Xchg ptrVar valVar SyncSeqCst

    -- Handle memcpy function specifically since llvm's intrinsic version takes
    -- some extra parameters.
    genCall t@(PrimTarget op) [] args
     | Just align <- machOpMemcpyishAlign op = runStmtsDecls $ do
        dflags <- getDynFlags
        let isVolTy = [i1]
            isVolVal = [mkIntLit i1 0]
            argTy | MO_Memset _ <- op = [i8Ptr, i8,    llvmWord dflags, i32] ++ isVolTy
                  | otherwise         = [i8Ptr, i8Ptr, llvmWord dflags, i32] ++ isVolTy
            funTy = \name -> LMFunction $ LlvmFunctionDecl name ExternallyVisible
                                 CC_Ccc LMVoid FixedArgs (tysToParams argTy) Nothing

        let (_, arg_hints) = foreignTargetHints t
        let args_hints = zip args arg_hints
        argVars       <- arg_varsW args_hints ([], nilOL, [])
        fptr          <- getFunPtrW funTy t
        argVars' <- castVarsW Signed $ zip argVars argTy

        doTrashStmts
        let alignVal = mkIntLit i32 align
            arguments = argVars' ++ (alignVal:isVolVal)
        statement $ Expr $ Call StdCall fptr arguments []

    -- We handle MO_U_Mul2 by simply using a 'mul' instruction, but with operands
    -- twice the width (we first zero-extend them), e.g., on 64-bit arch we will
    -- generate 'mul' on 128-bit operands. Then we only need some plumbing to
    -- extract the two 64-bit values out of 128-bit result.
    genCall (PrimTarget (MO_U_Mul2 w)) [dstH, dstL] [lhs, rhs] = runStmtsDecls $ do
        let width = widthToLlvmInt w
            bitWidth = widthInBits w
            width2x = LMInt (bitWidth * 2)
        -- First zero-extend the operands ('mul' instruction requires the operands
        -- and the result to be of the same type). Note that we don't use 'castVars'
        -- because it tries to do LM_Sext.
        lhsVar <- exprToVarW lhs
        rhsVar <- exprToVarW rhs
        lhsExt <- doExprW width2x $ Cast LM_Zext lhsVar width2x
        rhsExt <- doExprW width2x $ Cast LM_Zext rhsVar width2x
        -- Do the actual multiplication (note that the result is also 2x width).
        retV <- doExprW width2x $ LlvmOp LM_MO_Mul lhsExt rhsExt
        -- Extract the lower bits of the result into retL.
        retL <- doExprW width $ Cast LM_Trunc retV width
        -- Now we right-shift the higher bits by width.
        let widthLlvmLit = LMLitVar $ LMIntLit (fromIntegral bitWidth) width
        retShifted <- doExprW width2x $ LlvmOp LM_MO_LShr retV widthLlvmLit
        -- And extract them into retH.
        retH <- doExprW width $ Cast LM_Trunc retShifted width
        dstRegL <- getCmmRegW (CmmLocal dstL)
        dstRegH <- getCmmRegW (CmmLocal dstH)
        statement $ Store retL dstRegL
        statement $ Store retH dstRegH

    -- MO_U_QuotRem2 is another case we handle by widening the registers to double
    -- the width and use normal LLVM instructions (similarly to the MO_U_Mul2). The
    -- main difference here is that we need to combine two words into one register
    -- and then use both 'udiv' and 'urem' instructions to compute the result.
    genCall (PrimTarget (MO_U_QuotRem2 w))
            [dstQ, dstR] [lhsH, lhsL, rhs] = runStmtsDecls $ do
        let width = widthToLlvmInt w
            bitWidth = widthInBits w
            width2x = LMInt (bitWidth * 2)
        -- First zero-extend all parameters to double width.
        let zeroExtend expr = do
                var <- exprToVarW expr
                doExprW width2x $ Cast LM_Zext var width2x
        lhsExtH <- zeroExtend lhsH
        lhsExtL <- zeroExtend lhsL
        rhsExt <- zeroExtend rhs
        -- Now we combine the first two parameters (that represent the high and low
        -- bits of the value). So first left-shift the high bits to their position
        -- and then bit-or them with the low bits.
        let widthLlvmLit = LMLitVar $ LMIntLit (fromIntegral bitWidth) width
        lhsExtHShifted <- doExprW width2x $ LlvmOp LM_MO_Shl lhsExtH widthLlvmLit
        lhsExt <- doExprW width2x $ LlvmOp LM_MO_Or lhsExtHShifted lhsExtL
        -- Finally, we can call 'udiv' and 'urem' to compute the results.
        retExtDiv <- doExprW width2x $ LlvmOp LM_MO_UDiv lhsExt rhsExt
        retExtRem <- doExprW width2x $ LlvmOp LM_MO_URem lhsExt rhsExt
        -- And since everything is in 2x width, we need to truncate the results and
        -- then return them.
        let narrow var = doExprW width $ Cast LM_Trunc var width
        retDiv <- narrow retExtDiv
        retRem <- narrow retExtRem
        dstRegQ <- lift $ getCmmReg (CmmLocal dstQ)
        dstRegR <- lift $ getCmmReg (CmmLocal dstR)
        statement $ Store retDiv dstRegQ
        statement $ Store retRem dstRegR

    -- Handle the MO_{Add,Sub}IntC separately. LLVM versions return a record from
    -- which we need to extract the actual values.
    genCall t@(PrimTarget (MO_AddIntC w)) [dstV, dstO] [lhs, rhs] =
        genCallWithOverflow t w [dstV, dstO] [lhs, rhs]
    genCall t@(PrimTarget (MO_SubIntC w)) [dstV, dstO] [lhs, rhs] =
        genCallWithOverflow t w [dstV, dstO] [lhs, rhs]

    -- Similar to MO_{Add,Sub}IntC, but MO_Add2 expects the first element of the
    -- return tuple to be the overflow bit and the second element to contain the
    -- actual result of the addition. So we still use genCallWithOverflow but swap
    -- the return registers.
    genCall t@(PrimTarget (MO_Add2 w)) [dstO, dstV] [lhs, rhs] =
        genCallWithOverflow t w [dstV, dstO] [lhs, rhs]

    genCall t@(PrimTarget (MO_SubWordC w)) [dstV, dstO] [lhs, rhs] =
        genCallWithOverflow t w [dstV, dstO] [lhs, rhs]

    -- Handle all other foreign calls and prim ops.
    genCall target res args = runStmtsDecls $ do
        dflags <- getDynFlags

        -- parameter types
        let arg_type (_, AddrHint) = i8Ptr
            -- cast pointers to i8*. Llvm equivalent of void*
            arg_type (expr, _) = cmmToLlvmType $ cmmExprType dflags expr

        -- ret type
        let ret_type [] = LMVoid
            ret_type [(_, AddrHint)] = i8Ptr
            ret_type [(reg, _)]      = cmmToLlvmType $ localRegType reg
            ret_type t = panic $ "genCall: Too many return values! Can only handle"
                            ++ " 0 or 1, given " ++ show (length t) ++ "."

        -- extract Cmm call convention, and translate to LLVM call convention
        platform <- lift $ getLlvmPlatform
        let lmconv = case target of
                ForeignTarget _ (ForeignConvention conv _ _ _) ->
                  case conv of
                     StdCallConv  -> case platformArch platform of
                                     ArchX86    -> CC_X86_Stdcc
                                     ArchX86_64 -> CC_X86_Stdcc
                                     _          -> CC_Ccc
                     CCallConv    -> CC_Ccc
                     CApiConv     -> CC_Ccc
                     PrimCallConv -> panic "LlvmCodeGen.CodeGen.genCall: PrimCallConv"
                     JavaScriptCallConv -> panic "LlvmCodeGen.CodeGen.genCall: JavaScriptCallConv"

                PrimTarget   _ -> CC_Ccc

        {-
            CC_Ccc of the possibilities here are a worry with the use of a custom
            calling convention for passing STG args. In practice the more
            dangerous combinations (e.g StdCall + llvmGhcCC) don't occur.

            The native code generator only handles StdCall and CCallConv.
        -}

        -- call attributes
        let fnAttrs | never_returns = NoReturn : llvmStdFunAttrs
                    | otherwise     = llvmStdFunAttrs

            never_returns = case target of
                 ForeignTarget _ (ForeignConvention _ _ _ CmmNeverReturns) -> True
                 _ -> False

        -- fun type
        let (res_hints, arg_hints) = foreignTargetHints target
        let args_hints = zip args arg_hints
        let ress_hints = zip res  res_hints
        let ccTy  = StdCall -- tail calls should be done through CmmJump
        let retTy = ret_type ress_hints
        let argTy = tysToParams $ map arg_type args_hints
        let funTy = \name -> LMFunction $ LlvmFunctionDecl name ExternallyVisible
                                 lmconv retTy FixedArgs argTy (llvmFunAlign dflags)

        argVars <- arg_varsW args_hints ([], nilOL, [])
        fptr    <- getFunPtrW funTy target

        let doReturn | ccTy == TailCall  = statement $ Return Nothing
                     | never_returns     = statement $ Unreachable
                     | otherwise         = return ()

        doTrashStmts

        -- make the actual call
        case retTy of
            LMVoid -> do
                statement $ Expr $ Call ccTy fptr argVars fnAttrs

            _ -> do
                v1 <- doExprW retTy $ Call ccTy fptr argVars fnAttrs
                -- get the return register
                let ret_reg [reg] = reg
                    ret_reg t = panic $ "genCall: Bad number of registers! Can only handle"
                                    ++ " 1, given " ++ show (length t) ++ "."
                let creg = ret_reg res
                vreg <- getCmmRegW (CmmLocal creg)
                if retTy == pLower (getVarType vreg)
                    then do
                        statement $ Store v1 vreg
                        doReturn
                    else do
                        let ty = pLower $ getVarType vreg
                        let op = case ty of
                                vt | isPointer vt -> LM_Bitcast
                                   | isInt     vt -> LM_Ptrtoint
                                   | otherwise    ->
                                       panic $ "genCall: CmmReg bad match for"
                                            ++ " returned type!"

                        v2 <- doExprW ty $ Cast op v1 ty
                        statement $ Store v2 vreg
                        doReturn

    -- | Generate a call to an LLVM intrinsic that performs arithmetic operation
    -- with overflow bit (i.e., returns a struct containing the actual result of the
    -- operation and an overflow bit). This function will also extract the overflow
    -- bit and zero-extend it (all the corresponding Cmm PrimOps represent the
    -- overflow "bit" as a usual Int# or Word#).
    genCallWithOverflow
      :: ForeignTarget -> Width -> [CmmFormal] -> [CmmActual] -> LlvmM StmtData
    genCallWithOverflow t@(PrimTarget op) w [dstV, dstO] [lhs, rhs] = do
        -- So far this was only tested for the following four CallishMachOps.
        let valid = op `elem`   [ MO_Add2 w
                                , MO_AddIntC w
                                , MO_SubIntC w
                                , MO_SubWordC w
                                ]
        MASSERT(valid)
        let width = widthToLlvmInt w
        -- This will do most of the work of generating the call to the intrinsic and
        -- extracting the values from the struct.
        (value, overflowBit, (stmts, top)) <-
          genCallExtract t w (lhs, rhs) (width, i1)
        -- value is i<width>, but overflowBit is i1, so we need to cast (Cmm expects
        -- both to be i<width>)
        (overflow, zext) <- doExpr width $ Cast LM_Zext overflowBit width
        dstRegV <- getCmmReg (CmmLocal dstV)
        dstRegO <- getCmmReg (CmmLocal dstO)
        let storeV = Store value dstRegV
            storeO = Store overflow dstRegO
        return (stmts `snocOL` zext `snocOL` storeV `snocOL` storeO, top)
    genCallWithOverflow _ _ _ _ =
        panic "genCallExtract: wrong ForeignTarget or number of arguments"

    -- | A helper function for genCallWithOverflow that handles generating the call
    -- to the LLVM intrinsic and extracting the result from the struct to LlvmVars.
    genCallExtract
        :: ForeignTarget           -- ^ PrimOp
        -> Width                   -- ^ Width of the operands.
        -> (CmmActual, CmmActual)  -- ^ Actual arguments.
        -> (LlvmType, LlvmType)    -- ^ LLVM types of the returned struct.
        -> LlvmM (LlvmVar, LlvmVar, StmtData)
    genCallExtract target@(PrimTarget op) w (argA, argB) (llvmTypeA, llvmTypeB) = do
        let width = widthToLlvmInt w
            argTy = [width, width]
            retTy = LMStructU [llvmTypeA, llvmTypeB]

        -- Process the arguments.
        let args_hints = zip [argA, argB] (snd $ foreignTargetHints target)
        (argsV1, args1, top1) <- arg_vars args_hints ([], nilOL, [])
        (argsV2, args2) <- castVars Signed $ zip argsV1 argTy

        -- Get the function and make the call.
        fname <- cmmPrimOpFunctions op
        (fptr, _, top2) <- getInstrinct fname retTy argTy
        -- We use StdCall for primops. See also the last case of genCall.
        (retV, call) <- doExpr retTy $ Call StdCall fptr argsV2 []

        -- This will result in a two element struct, we need to use "extractvalue"
        -- to get them out of it.
        (res1, ext1) <- doExpr llvmTypeA (ExtractV retV 0)
        (res2, ext2) <- doExpr llvmTypeB (ExtractV retV 1)

        let stmts = args1 `appOL` args2 `snocOL` call `snocOL` ext1 `snocOL` ext2
            tops = top1 ++ top2
        return (res1, res2, (stmts, tops))

    genCallExtract _ _ _ _ =
        panic "genCallExtract: unsupported ForeignTarget"

    -- Handle simple function call that only need simple type casting, of the form:
    --   truncate arg >>= \a -> call(a) >>= zext
    --
    -- since GHC only really has i32 and i64 types and things like Word8 are backed
    -- by an i32 and just present a logical i8 range. So we must handle conversions
    -- from i32 to i8 explicitly as LLVM is strict about types.
    genCallSimpleCast :: Width -> ForeignTarget -> [CmmFormal] -> [CmmActual]
                  -> LlvmM StmtData
    genCallSimpleCast w t@(PrimTarget op) [dst] args = do
        let width = widthToLlvmInt w
            dstTy = cmmToLlvmType $ localRegType dst

        fname                       <- cmmPrimOpFunctions op
        (fptr, _, top3)             <- getInstrinct fname width [width]

        dstV                        <- getCmmReg (CmmLocal dst)

        let (_, arg_hints) = foreignTargetHints t
        let args_hints = zip args arg_hints
        (argsV, stmts2, top2)       <- arg_vars args_hints ([], nilOL, [])
        (argsV', stmts4)            <- castVars Signed $ zip argsV [width]
        (retV, s1)                  <- doExpr width $ Call StdCall fptr argsV' []
        ([retV'], stmts5)           <- castVars (cmmPrimOpRetValSignage op) [(retV,dstTy)]
        let s2                       = Store retV' dstV

        let stmts = stmts2 `appOL` stmts4 `snocOL`
                    s1 `appOL` stmts5 `snocOL` s2
        return (stmts, top2 ++ top3)
    genCallSimpleCast _ _ dsts _ =
        panic ("genCallSimpleCast: " ++ show (length dsts) ++ " dsts")

    -- Handle simple function call that only need simple type casting, of the form:
    --   truncate arg >>= \a -> call(a) >>= zext
    --
    -- since GHC only really has i32 and i64 types and things like Word8 are backed
    -- by an i32 and just present a logical i8 range. So we must handle conversions
    -- from i32 to i8 explicitly as LLVM is strict about types.
    genCallSimpleCast2 :: Width -> ForeignTarget -> [CmmFormal] -> [CmmActual]
                  -> LlvmM StmtData
    genCallSimpleCast2 w t@(PrimTarget op) [dst] args = do
        let width = widthToLlvmInt w
            dstTy = cmmToLlvmType $ localRegType dst

        fname                       <- cmmPrimOpFunctions op
        (fptr, _, top3)             <- getInstrinct fname width (const width <$> args)

        dstV                        <- getCmmReg (CmmLocal dst)

        let (_, arg_hints) = foreignTargetHints t
        let args_hints = zip args arg_hints
        (argsV, stmts2, top2)       <- arg_vars args_hints ([], nilOL, [])
        (argsV', stmts4)            <- castVars Signed $ zip argsV (const width <$> argsV)
        (retV, s1)                  <- doExpr width $ Call StdCall fptr argsV' []
        ([retV'], stmts5)           <- castVars (cmmPrimOpRetValSignage op) [(retV,dstTy)]
        let s2                       = Store retV' dstV

        let stmts = stmts2 `appOL` stmts4 `snocOL`
                    s1 `appOL` stmts5 `snocOL` s2
        return (stmts, top2 ++ top3)
    genCallSimpleCast2 _ _ dsts _ =
        panic ("genCallSimpleCast2: " ++ show (length dsts) ++ " dsts")

    -- | Create a function pointer from a target.
    getFunPtrW :: (LMString -> LlvmType) -> ForeignTarget
               -> WriterT LlvmAccum LlvmM LlvmVar
    getFunPtrW funTy targ = liftExprData $ getFunPtr funTy targ

    -- | Create a function pointer from a target.
    getFunPtr :: (LMString -> LlvmType) -> ForeignTarget
              -> LlvmM ExprData
    getFunPtr funTy targ = case targ of
        ForeignTarget (CmmLit (CmmLabel lbl)) _ -> do
            name <- strCLabel_llvm lbl
            getHsFunc' name (funTy name)

        ForeignTarget expr _ -> do
            (v1, stmts, top) <- exprToVar expr
            dflags <- getDynFlags
            let fty = funTy $ fsLit "dynamic"
                cast = case getVarType v1 of
                    ty | isPointer ty -> LM_Bitcast
                    ty | isInt ty     -> LM_Inttoptr

                    ty -> panic $ "genCall: Expr is of bad type for function"
                                  ++ " call! (" ++ showSDoc dflags (ppr ty) ++ ")"

            (v2,s1) <- doExpr (pLift fty) $ Cast cast v1 (pLift fty)
            return (v2, stmts `snocOL` s1, top)

        PrimTarget mop -> do
            name <- cmmPrimOpFunctions mop
            let fty = funTy name
            getInstrinct2 name fty

    -- | Conversion of call arguments.
    arg_varsW :: [(CmmActual, ForeignHint)]
              -> ([LlvmVar], LlvmStatements, [LlvmCmmDecl])
              -> WriterT LlvmAccum LlvmM [LlvmVar]
    arg_varsW xs ys = do
        (vars, stmts, decls) <- lift $ arg_vars xs ys
        tell $ LlvmAccum stmts decls
        return vars

    -- | Conversion of call arguments.
    arg_vars :: [(CmmActual, ForeignHint)]
             -> ([LlvmVar], LlvmStatements, [LlvmCmmDecl])
             -> LlvmM ([LlvmVar], LlvmStatements, [LlvmCmmDecl])

    arg_vars [] (vars, stmts, tops)
      = return (vars, stmts, tops)

    arg_vars ((e, AddrHint):rest) (vars, stmts, tops)
      = do (v1, stmts', top') <- exprToVar e
           dflags <- getDynFlags
           let op = case getVarType v1 of
                   ty | isPointer ty -> LM_Bitcast
                   ty | isInt ty     -> LM_Inttoptr

                   a  -> panic $ "genCall: Can't cast llvmType to i8*! ("
                               ++ showSDoc dflags (ppr a) ++ ")"

           (v2, s1) <- doExpr i8Ptr $ Cast op v1 i8Ptr
           arg_vars rest (vars ++ [v2], stmts `appOL` stmts' `snocOL` s1,
                                   tops ++ top')

    arg_vars ((e, _):rest) (vars, stmts, tops)
      = do (v1, stmts', top') <- exprToVar e
           arg_vars rest (vars ++ [v1], stmts `appOL` stmts', tops ++ top')

    -- | Cast a collection of LLVM variables to specific types.
    castVarsW :: Signage
              -> [(LlvmVar, LlvmType)]
              -> WriterT LlvmAccum LlvmM [LlvmVar]
    castVarsW signage vars = do
        (vars, stmts) <- lift $ castVars signage vars
        tell $ LlvmAccum stmts mempty
        return vars

    -- | Cast a collection of LLVM variables to specific types.
    castVars :: Signage -> [(LlvmVar, LlvmType)]
             -> LlvmM ([LlvmVar], LlvmStatements)
    castVars signage vars = do
                    done <- mapM (uncurry (castVar signage)) vars
                    let (vars', stmts) = unzip done
                    return (vars', toOL stmts)

    -- | Cast an LLVM variable to a specific type, panicing if it can't be done.
    castVar :: Signage -> LlvmVar -> LlvmType -> LlvmM (LlvmVar, LlvmStatement)
    castVar signage v t | getVarType v == t
                = return (v, Nop)

                | otherwise
                = do dflags <- getDynFlags
                     let op = case (getVarType v, t) of
                          (LMInt n, LMInt m)
                              -> if n < m then extend else LM_Trunc
                          (vt, _) | isFloat vt && isFloat t
                              -> if llvmWidthInBits dflags vt < llvmWidthInBits dflags t
                                    then LM_Fpext else LM_Fptrunc
                          (vt, _) | isInt vt && isFloat t       -> LM_Sitofp
                          (vt, _) | isFloat vt && isInt t       -> LM_Fptosi
                          (vt, _) | isInt vt && isPointer t     -> LM_Inttoptr
                          (vt, _) | isPointer vt && isInt t     -> LM_Ptrtoint
                          (vt, _) | isPointer vt && isPointer t -> LM_Bitcast
                          (vt, _) | isVector vt && isVector t   -> LM_Bitcast

                          (vt, _) -> panic $ "castVars: Can't cast this type ("
                                      ++ showSDoc dflags (ppr vt) ++ ") to (" ++ showSDoc dflags (ppr t) ++ ")"
                     doExpr t $ Cast op v t
        where extend = case signage of
                Signed      -> LM_Sext
                Unsigned    -> LM_Zext

    cmmPrimOpRetValSignage :: CallishMachOp -> Signage
    cmmPrimOpRetValSignage mop = case mop of
        MO_Pdep _   -> Unsigned
        MO_Pext _   -> Unsigned
        _           -> Signed

    -- | Decide what C function to use to implement a CallishMachOp
    cmmPrimOpFunctions :: CallishMachOp -> LlvmM LMString
    cmmPrimOpFunctions mop = do

      dflags <- getDynFlags
      let intrinTy1 = "p0i8.p0i8." ++ showSDoc dflags (ppr $ llvmWord dflags)
          intrinTy2 = "p0i8." ++ showSDoc dflags (ppr $ llvmWord dflags)
          unsupported = panic ("cmmPrimOpFunctions: " ++ show mop
                            ++ " not supported here")

      return $ case mop of
        MO_F32_Exp    -> fsLit "expf"
        MO_F32_Log    -> fsLit "logf"
        MO_F32_Sqrt   -> fsLit "llvm.sqrt.f32"
        MO_F32_Fabs   -> fsLit "llvm.fabs.f32"
        MO_F32_Pwr    -> fsLit "llvm.pow.f32"

        MO_F32_Sin    -> fsLit "llvm.sin.f32"
        MO_F32_Cos    -> fsLit "llvm.cos.f32"
        MO_F32_Tan    -> fsLit "tanf"

        MO_F32_Asin   -> fsLit "asinf"
        MO_F32_Acos   -> fsLit "acosf"
        MO_F32_Atan   -> fsLit "atanf"

        MO_F32_Sinh   -> fsLit "sinhf"
        MO_F32_Cosh   -> fsLit "coshf"
        MO_F32_Tanh   -> fsLit "tanhf"

        MO_F64_Exp    -> fsLit "exp"
        MO_F64_Log    -> fsLit "log"
        MO_F64_Sqrt   -> fsLit "llvm.sqrt.f64"
        MO_F64_Fabs   -> fsLit "llvm.fabs.f64"
        MO_F64_Pwr    -> fsLit "llvm.pow.f64"

        MO_F64_Sin    -> fsLit "llvm.sin.f64"
        MO_F64_Cos    -> fsLit "llvm.cos.f64"
        MO_F64_Tan    -> fsLit "tan"

        MO_F64_Asin   -> fsLit "asin"
        MO_F64_Acos   -> fsLit "acos"
        MO_F64_Atan   -> fsLit "atan"

        MO_F64_Sinh   -> fsLit "sinh"
        MO_F64_Cosh   -> fsLit "cosh"
        MO_F64_Tanh   -> fsLit "tanh"

        MO_Memcpy _   -> fsLit $ "llvm.memcpy."  ++ intrinTy1
        MO_Memmove _  -> fsLit $ "llvm.memmove." ++ intrinTy1
        MO_Memset _   -> fsLit $ "llvm.memset."  ++ intrinTy2
        MO_Memcmp _   -> fsLit $ "memcmp"

        (MO_PopCnt w) -> fsLit $ "llvm.ctpop."  ++ showSDoc dflags (ppr $ widthToLlvmInt w)
        (MO_BSwap w)  -> fsLit $ "llvm.bswap."  ++ showSDoc dflags (ppr $ widthToLlvmInt w)
        (MO_Clz w)    -> fsLit $ "llvm.ctlz."   ++ showSDoc dflags (ppr $ widthToLlvmInt w)
        (MO_Ctz w)    -> fsLit $ "llvm.cttz."   ++ showSDoc dflags (ppr $ widthToLlvmInt w)

        (MO_Pdep w)   ->  let w' = showSDoc dflags (ppr $ widthInBits w)
                          in  if isBmi2Enabled dflags
                                then fsLit $ "llvm.x86.bmi.pdep."   ++ w'
                                else fsLit $ "hs_pdep"              ++ w'
        (MO_Pext w)   ->  let w' = showSDoc dflags (ppr $ widthInBits w)
                          in  if isBmi2Enabled dflags
                                then fsLit $ "llvm.x86.bmi.pext."   ++ w'
                                else fsLit $ "hs_pext"              ++ w'

        (MO_Prefetch_Data _ )-> fsLit "llvm.prefetch"

        MO_AddIntC w    -> fsLit $ "llvm.sadd.with.overflow."
                                 ++ showSDoc dflags (ppr $ widthToLlvmInt w)
        MO_SubIntC w    -> fsLit $ "llvm.ssub.with.overflow."
                                 ++ showSDoc dflags (ppr $ widthToLlvmInt w)
        MO_Add2 w       -> fsLit $ "llvm.uadd.with.overflow."
                                 ++ showSDoc dflags (ppr $ widthToLlvmInt w)
        MO_SubWordC w   -> fsLit $ "llvm.usub.with.overflow."
                                 ++ showSDoc dflags (ppr $ widthToLlvmInt w)

        MO_S_QuotRem {}  -> unsupported
        MO_U_QuotRem {}  -> unsupported
        MO_U_QuotRem2 {} -> unsupported
        -- We support MO_U_Mul2 through ordinary LLVM mul instruction, see the
        -- appropriate case of genCall.
        MO_U_Mul2 {}     -> unsupported
        MO_WriteBarrier  -> unsupported
        MO_Touch         -> unsupported
        MO_UF_Conv _     -> unsupported

        MO_AtomicRead _  -> unsupported
        MO_AtomicRMW _ _ -> unsupported
        MO_AtomicWrite _ -> unsupported
        MO_Cmpxchg _     -> unsupported

    -- | Tail function calls
    genJump :: CmmExpr -> [GlobalReg] -> LlvmM StmtData

    -- Call to known function
    genJump (CmmLit (CmmLabel lbl)) live = do
        (vf, stmts, top) <- getHsFunc live lbl
        (stgRegs, stgStmts) <- funEpilogue live
        let s1  = Expr $ Call TailCall vf stgRegs llvmStdFunAttrs
        let s2  = Return Nothing
        return (stmts `appOL` stgStmts `snocOL` s1 `snocOL` s2, top)

    -- Call to unknown function / address
    genJump expr live = do
        fty <- llvmFunTy live
        (vf, stmts, top) <- exprToVar expr
        dflags <- getDynFlags

        let cast = case getVarType vf of
             ty | isPointer ty -> LM_Bitcast
             ty | isInt ty     -> LM_Inttoptr

             ty -> panic $ "genJump: Expr is of bad type for function call! ("
                         ++ showSDoc dflags (ppr ty) ++ ")"

        (v1, s1) <- doExpr (pLift fty) $ Cast cast vf (pLift fty)
        (stgRegs, stgStmts) <- funEpilogue live
        let s2 = Expr $ Call TailCall v1 stgRegs llvmStdFunAttrs
        let s3 = Return Nothing
        return (stmts `snocOL` s1 `appOL` stgStmts `snocOL` s2 `snocOL` s3,
                top)

    -- | CmmAssign operation
    --
    -- We use stack allocated variables for CmmReg. The optimiser will replace
    -- these with registers when possible.
    genAssign :: CmmReg -> CmmExpr -> LlvmM StmtData
    genAssign reg val = do
        vreg <- getCmmReg reg
        (vval, stmts2, top2) <- exprToVar val
        let stmts = stmts2

        let ty = (pLower . getVarType) vreg
        dflags <- getDynFlags
        case ty of
          -- Some registers are pointer types, so need to cast value to pointer
          LMPointer _ | getVarType vval == llvmWord dflags -> do
              (v, s1) <- doExpr ty $ Cast LM_Inttoptr vval ty
              let s2 = Store v vreg
              return (stmts `snocOL` s1 `snocOL` s2, top2)

          LMVector _ _ -> do
              (v, s1) <- doExpr ty $ Cast LM_Bitcast vval ty
              let s2 = Store v vreg
              return (stmts `snocOL` s1 `snocOL` s2, top2)

          _ -> do
              let s1 = Store vval vreg
              return (stmts `snocOL` s1, top2)

    -- | CmmStore operation
    genStore :: CmmExpr -> CmmExpr -> LlvmM StmtData

    -- First we try to detect a few common cases and produce better code for
    -- these then the default case. We are mostly trying to detect Cmm code
    -- like I32[Sp + n] and use 'getelementptr' operations instead of the
    -- generic case that uses casts and pointer arithmetic
    genStore addr@(CmmReg (CmmGlobal r)) val
        = genStore_fast addr r 0 val

    genStore addr@(CmmRegOff (CmmGlobal r) n) val
        = genStore_fast addr r n val

    genStore addr@(CmmMachOp (MO_Add _) [
                                (CmmReg (CmmGlobal r)),
                                (CmmLit (CmmInt n _))])
                    val
        = genStore_fast addr r (fromInteger n) val

    genStore addr@(CmmMachOp (MO_Sub _) [
                                (CmmReg (CmmGlobal r)),
                                (CmmLit (CmmInt n _))])
                    val
        = genStore_fast addr r (negate $ fromInteger n) val

    -- generic case
    genStore addr val
        = getTBAAMeta topN >>= genStore_slow addr val

    -- | CmmStore operation
    -- This is a special case for storing to a global register pointer
    -- offset such as I32[Sp+8].
    genStore_fast :: CmmExpr -> GlobalReg -> Int -> CmmExpr
                  -> LlvmM StmtData
    genStore_fast addr r n val
      = do dflags <- getDynFlags
           (gv, grt, s1) <- getCmmRegVal (CmmGlobal r)
           meta          <- getTBAARegMeta r
           let (ix,rem) = n `divMod` ((llvmWidthInBits dflags . pLower) grt  `div` 8)
           case isPointer grt && rem == 0 of
                True -> do
                    (vval,  stmts, top) <- exprToVar val
                    (ptr, s2) <- doExpr grt $ GetElemPtr True gv [toI32 ix]
                    -- We might need a different pointer type, so check
                    case pLower grt == getVarType vval of
                         -- were fine
                         True  -> do
                             let s3 = MetaStmt meta $ Store vval ptr
                             return (stmts `appOL` s1 `snocOL` s2
                                     `snocOL` s3, top)

                         -- cast to pointer type needed
                         False -> do
                             let ty = (pLift . getVarType) vval
                             (ptr', s3) <- doExpr ty $ Cast LM_Bitcast ptr ty
                             let s4 = MetaStmt meta $ Store vval ptr'
                             return (stmts `appOL` s1 `snocOL` s2
                                     `snocOL` s3 `snocOL` s4, top)

                -- If its a bit type then we use the slow method since
                -- we can't avoid casting anyway.
                False -> genStore_slow addr val meta

    -- | CmmStore operation
    -- Generic case. Uses casts and pointer arithmetic if needed.
    genStore_slow :: CmmExpr -> CmmExpr -> [MetaAnnot] -> LlvmM StmtData
    genStore_slow addr val meta = do
        (vaddr, stmts1, top1) <- exprToVar addr
        (vval,  stmts2, top2) <- exprToVar val

        let stmts = stmts1 `appOL` stmts2
        dflags <- getDynFlags
        case getVarType vaddr of
            -- sometimes we need to cast an int to a pointer before storing
            LMPointer ty@(LMPointer _) | getVarType vval == llvmWord dflags -> do
                (v, s1) <- doExpr ty $ Cast LM_Inttoptr vval ty
                let s2 = MetaStmt meta $ Store v vaddr
                return (stmts `snocOL` s1 `snocOL` s2, top1 ++ top2)

            LMPointer _ -> do
                let s1 = MetaStmt meta $ Store vval vaddr
                return (stmts `snocOL` s1, top1 ++ top2)

            i@(LMInt _) | i == llvmWord dflags -> do
                let vty = pLift $ getVarType vval
                (vptr, s1) <- doExpr vty $ Cast LM_Inttoptr vaddr vty
                let s2 = MetaStmt meta $ Store vval vptr
                return (stmts `snocOL` s1 `snocOL` s2, top1 ++ top2)

            other ->
                pprPanic "genStore: ptr not right type!"
                        (PprCmm.pprExpr addr <+> text (
                            "Size of Ptr: " ++ show (llvmPtrBits dflags) ++
                            ", Size of var: " ++ show (llvmWidthInBits dflags other) ++
                            ", Var: " ++ showSDoc dflags (ppr vaddr)))

    -- | Unconditional branch
    genBranch :: BlockId -> LlvmM StmtData
    genBranch id =
        let label = blockIdToLlvm id
        in return (unitOL $ Branch label, [])

    -- | Conditional branch
    genCondBranch :: CmmExpr -> BlockId -> BlockId -> Maybe Bool -> LlvmM StmtData
    genCondBranch cond idT idF likely = do
        let labelT = blockIdToLlvm idT
        let labelF = blockIdToLlvm idF
        -- See Note [Literals and branch conditions].
        (vc, stmts1, top1) <- exprToVarOpt i1Option cond
        if getVarType vc == i1
            then do
                (vc', (stmts2, top2)) <- case likely of
                  Just b -> genExpectLit (if b then 1 else 0) i1  vc
                  _      -> pure (vc, (nilOL, []))
                let s1 = BranchIf vc' labelT labelF
                return (stmts1 `appOL` stmts2 `snocOL` s1, top1 ++ top2)
            else do
                dflags <- getDynFlags
                panic $ "genCondBranch: Cond expr not bool! (" ++ showSDoc dflags (ppr vc) ++ ")"

    -- | Generate call to llvm.expect.x intrinsic. Assigning result to a new var.
    genExpectLit :: Integer -> LlvmType -> LlvmVar -> LlvmM (LlvmVar, StmtData)
    genExpectLit expLit expTy var = do
      dflags <- getDynFlags

      let
        lit = LMLitVar $ LMIntLit expLit expTy

        llvmExpectName
          | isInt expTy = fsLit $ "llvm.expect." ++ showSDoc dflags (ppr expTy)
          | otherwise   = panic $ "genExpectedLit: Type not an int!"

      (llvmExpect, stmts, top) <-
        getInstrinct llvmExpectName expTy [expTy, expTy]
      (var', call) <- doExpr expTy $ Call StdCall llvmExpect [var, lit] []
      return (var', (stmts `snocOL` call, top))

    {- Note [Literals and branch conditions]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    It is important that whenever we generate branch conditions for
    literals like '1', they are properly narrowed to an LLVM expression of
    type 'i1' (for bools.) Otherwise, nobody is happy. So when we convert
    a CmmExpr to an LLVM expression for a branch conditional, exprToVarOpt
    must be certain to return a properly narrowed type. genLit is
    responsible for this, in the case of literal integers.

    Often, we won't see direct statements like:

        if(1) {
          ...
        } else {
          ...
        }

    at this point in the pipeline, because the Glorious Code Generator
    will do trivial branch elimination in the sinking pass (among others,)
    which will eliminate the expression entirely.

    However, it's certainly possible and reasonable for this to occur in
    hand-written C-- code. Consider something like:

        #if !defined(SOME_CONDITIONAL)
        #define CHECK_THING(x) 1
        #else
        #define CHECK_THING(x) some_operation((x))
        #endif

        f() {

          if (CHECK_THING(xyz)) {
            ...
          } else {
            ...
          }

        }

    In such an instance, CHECK_THING might result in an *expression* in
    one case, and a *literal* in the other, depending on what in
    particular was #define'd. So we must be sure to properly narrow the
    literal in this case to i1 as it won't be eliminated beforehand.

    For a real example of this, see ./rts/StgStdThunks.cmm

    -}

    -- | Switch branch
    genSwitch :: CmmExpr -> SwitchTargets -> LlvmM StmtData
    genSwitch cond ids = do
        (vc, stmts, top) <- exprToVar cond
        let ty = getVarType vc

        let labels = [ (mkIntLit ty ix, blockIdToLlvm b)
                     | (ix, b) <- switchTargetsCases ids ]
        -- out of range is undefined, so let's just branch to first label
        let defLbl | Just l <- switchTargetsDefault ids = blockIdToLlvm l
                   | otherwise                          = snd (head labels)

        let s1 = Switch vc defLbl labels
        return $ (stmts `snocOL` s1, top)

    -- -----------------------------------------------------------------------------
    -- * CmmExpr code generation
    --

    -- | An expression conversion return data:
    --   * LlvmVar: The var holding the result of the expression
    --   * LlvmStatements: Any statements needed to evaluate the expression
    --   * LlvmCmmDecl: Any global data needed for this expression
    type ExprData = (LlvmVar, LlvmStatements, [LlvmCmmDecl])

    -- | Values which can be passed to 'exprToVar' to configure its
    -- behaviour in certain circumstances.
    --
    -- Currently just used for determining if a comparison should return
    -- a boolean (i1) or a word. See Note [Literals and branch conditions].
    newtype EOption = EOption { i1Expected :: Bool }
    -- XXX: EOption is an ugly and inefficient solution to this problem.

    -- | i1 type expected (condition scrutinee).
    i1Option :: EOption
    i1Option = EOption True

    -- | Word type expected (usual).
    wordOption :: EOption
    wordOption = EOption False

    -- | Convert a CmmExpr to a list of LlvmStatements with the result of the
    -- expression being stored in the returned LlvmVar.
    exprToVar :: CmmExpr -> LlvmM ExprData
    exprToVar = exprToVarOpt wordOption

    exprToVarOpt :: EOption -> CmmExpr -> LlvmM ExprData
    exprToVarOpt opt e = case e of

        CmmLit lit
            -> genLit opt lit

        CmmLoad e' ty
            -> genLoad False e' ty

        -- Cmmreg in expression is the value, so must load. If you want actual
        -- reg pointer, call getCmmReg directly.
        CmmReg r -> do
            (v1, ty, s1) <- getCmmRegVal r
            case isPointer ty of
                 True  -> do
                     -- Cmm wants the value, so pointer types must be cast to ints
                     dflags <- getDynFlags
                     (v2, s2) <- doExpr (llvmWord dflags) $ Cast LM_Ptrtoint v1 (llvmWord dflags)
                     return (v2, s1 `snocOL` s2, [])

                 False -> return (v1, s1, [])

        CmmMachOp op exprs
            -> genMachOp opt op exprs

        CmmRegOff r i
            -> do dflags <- getDynFlags
                  exprToVar $ expandCmmReg dflags (r, i)

        CmmStackSlot _ _
            -> panic "exprToVar: CmmStackSlot not supported!"

    -- | Handle CmmMachOp expressions
    genMachOp :: EOption -> MachOp -> [CmmExpr] -> LlvmM ExprData

    -- Unary Machop
    genMachOp _ op [x] = case op of

        MO_Not w ->
            let all1 = mkIntLit (widthToLlvmInt w) (-1)
            in negate (widthToLlvmInt w) all1 LM_MO_Xor

        MO_S_Neg w ->
            let all0 = mkIntLit (widthToLlvmInt w) 0
            in negate (widthToLlvmInt w) all0 LM_MO_Sub

        MO_F_Neg w ->
            let all0 = LMLitVar $ LMFloatLit (-0) (widthToLlvmFloat w)
            in negate (widthToLlvmFloat w) all0 LM_MO_FSub

        MO_SF_Conv _ w -> fiConv (widthToLlvmFloat w) LM_Sitofp
        MO_FS_Conv _ w -> fiConv (widthToLlvmInt w) LM_Fptosi

        MO_SS_Conv from to
            -> sameConv from (widthToLlvmInt to) LM_Trunc LM_Sext

        MO_UU_Conv from to
            -> sameConv from (widthToLlvmInt to) LM_Trunc LM_Zext

        MO_FF_Conv from to
            -> sameConv from (widthToLlvmFloat to) LM_Fptrunc LM_Fpext

        MO_VS_Neg len w ->
            let ty    = widthToLlvmInt w
                vecty = LMVector len ty
                all0  = LMIntLit (-0) ty
                all0s = LMLitVar $ LMVectorLit (replicate len all0)
            in negateVec vecty all0s LM_MO_Sub

        MO_VF_Neg len w ->
            let ty    = widthToLlvmFloat w
                vecty = LMVector len ty
                all0  = LMFloatLit (-0) ty
                all0s = LMLitVar $ LMVectorLit (replicate len all0)
            in negateVec vecty all0s LM_MO_FSub

        MO_AlignmentCheck _ _ -> panic "-falignment-sanitisation is not supported by -fllvm"

        -- Handle unsupported cases explicitly so we get a warning
        -- of missing case when new MachOps added
        MO_Add _          -> panicOp
        MO_Mul _          -> panicOp
        MO_Sub _          -> panicOp
        MO_S_MulMayOflo _ -> panicOp
        MO_S_Quot _       -> panicOp
        MO_S_Rem _        -> panicOp
        MO_U_MulMayOflo _ -> panicOp
        MO_U_Quot _       -> panicOp
        MO_U_Rem _        -> panicOp

        MO_Eq  _          -> panicOp
        MO_Ne  _          -> panicOp
        MO_S_Ge _         -> panicOp
        MO_S_Gt _         -> panicOp
        MO_S_Le _         -> panicOp
        MO_S_Lt _         -> panicOp
        MO_U_Ge _         -> panicOp
        MO_U_Gt _         -> panicOp
        MO_U_Le _         -> panicOp
        MO_U_Lt _         -> panicOp

        MO_F_Add        _ -> panicOp
        MO_F_Sub        _ -> panicOp
        MO_F_Mul        _ -> panicOp
        MO_F_Quot       _ -> panicOp
        MO_F_Eq         _ -> panicOp
        MO_F_Ne         _ -> panicOp
        MO_F_Ge         _ -> panicOp
        MO_F_Gt         _ -> panicOp
        MO_F_Le         _ -> panicOp
        MO_F_Lt         _ -> panicOp

        MO_And          _ -> panicOp
        MO_Or           _ -> panicOp
        MO_Xor          _ -> panicOp
        MO_Shl          _ -> panicOp
        MO_U_Shr        _ -> panicOp
        MO_S_Shr        _ -> panicOp

        MO_V_Insert   _ _ -> panicOp
        MO_V_Extract  _ _ -> panicOp

        MO_V_Add      _ _ -> panicOp
        MO_V_Sub      _ _ -> panicOp
        MO_V_Mul      _ _ -> panicOp

        MO_VS_Quot    _ _ -> panicOp
        MO_VS_Rem     _ _ -> panicOp

        MO_VU_Quot    _ _ -> panicOp
        MO_VU_Rem     _ _ -> panicOp

        MO_VF_Insert  _ _ -> panicOp
        MO_VF_Extract _ _ -> panicOp

        MO_VF_Add     _ _ -> panicOp
        MO_VF_Sub     _ _ -> panicOp
        MO_VF_Mul     _ _ -> panicOp
        MO_VF_Quot    _ _ -> panicOp

        where
            negate ty v2 negOp = do
                (vx, stmts, top) <- exprToVar x
                (v1, s1) <- doExpr ty $ LlvmOp negOp v2 vx
                return (v1, stmts `snocOL` s1, top)

            negateVec ty v2 negOp = do
                (vx, stmts1, top) <- exprToVar x
                ([vx'], stmts2) <- castVars Signed [(vx, ty)]
                (v1, s1) <- doExpr ty $ LlvmOp negOp v2 vx'
                return (v1, stmts1 `appOL` stmts2 `snocOL` s1, top)

            fiConv ty convOp = do
                (vx, stmts, top) <- exprToVar x
                (v1, s1) <- doExpr ty $ Cast convOp vx ty
                return (v1, stmts `snocOL` s1, top)

            sameConv from ty reduce expand = do
                x'@(vx, stmts, top) <- exprToVar x
                let sameConv' op = do
                        (v1, s1) <- doExpr ty $ Cast op vx ty
                        return (v1, stmts `snocOL` s1, top)
                dflags <- getDynFlags
                let toWidth = llvmWidthInBits dflags ty
                -- LLVM doesn't like trying to convert to same width, so
                -- need to check for that as we do get Cmm code doing it.
                case widthInBits from  of
                     w | w < toWidth -> sameConv' expand
                     w | w > toWidth -> sameConv' reduce
                     _w              -> return x'

            panicOp = panic $ "LLVM.CodeGen.genMachOp: non unary op encountered"
                           ++ "with one argument! (" ++ show op ++ ")"

    -- Handle GlobalRegs pointers
    genMachOp opt o@(MO_Add _) e@[(CmmReg (CmmGlobal r)), (CmmLit (CmmInt n _))]
        = genMachOp_fast opt o r (fromInteger n) e

    genMachOp opt o@(MO_Sub _) e@[(CmmReg (CmmGlobal r)), (CmmLit (CmmInt n _))]
        = genMachOp_fast opt o r (negate . fromInteger $ n) e

    -- Generic case
    genMachOp opt op e = genMachOp_slow opt op e

    -- | Handle CmmMachOp expressions
    -- This is a specialised method that handles Global register manipulations like
    -- 'Sp - 16', using the getelementptr instruction.
    genMachOp_fast :: EOption -> MachOp -> GlobalReg -> Int -> [CmmExpr]
                   -> LlvmM ExprData
    genMachOp_fast opt op r n e
      = do (gv, grt, s1) <- getCmmRegVal (CmmGlobal r)
           dflags <- getDynFlags
           let (ix,rem) = n `divMod` ((llvmWidthInBits dflags . pLower) grt  `div` 8)
           case isPointer grt && rem == 0 of
                True -> do
                    (ptr, s2) <- doExpr grt $ GetElemPtr True gv [toI32 ix]
                    (var, s3) <- doExpr (llvmWord dflags) $ Cast LM_Ptrtoint ptr (llvmWord dflags)
                    return (var, s1 `snocOL` s2 `snocOL` s3, [])

                False -> genMachOp_slow opt op e

    -- | Handle CmmMachOp expressions
    -- This handles all the cases not handle by the specialised genMachOp_fast.
    genMachOp_slow :: EOption -> MachOp -> [CmmExpr] -> LlvmM ExprData

    -- Element extraction
    genMachOp_slow _ (MO_V_Extract l w) [val, idx] = runExprData $ do
        vval <- exprToVarW val
        vidx <- exprToVarW idx
        [vval'] <- castVarsW Signed [(vval, LMVector l ty)]
        doExprW ty $ Extract vval' vidx
      where
        ty = widthToLlvmInt w

    genMachOp_slow _ (MO_VF_Extract l w) [val, idx] = runExprData $ do
        vval <- exprToVarW val
        vidx <- exprToVarW idx
        [vval'] <- castVarsW Signed [(vval, LMVector l ty)]
        doExprW ty $ Extract vval' vidx
      where
        ty = widthToLlvmFloat w

    -- Element insertion
    genMachOp_slow _ (MO_V_Insert l w) [val, elt, idx] = runExprData $ do
        vval <- exprToVarW val
        velt <- exprToVarW elt
        vidx <- exprToVarW idx
        [vval'] <- castVarsW Signed [(vval, ty)]
        doExprW ty $ Insert vval' velt vidx
      where
        ty = LMVector l (widthToLlvmInt w)

    genMachOp_slow _ (MO_VF_Insert l w) [val, elt, idx] = runExprData $ do
        vval <- exprToVarW val
        velt <- exprToVarW elt
        vidx <- exprToVarW idx
        [vval'] <- castVarsW Signed [(vval, ty)]
        doExprW ty $ Insert vval' velt vidx
      where
        ty = LMVector l (widthToLlvmFloat w)

    -- Binary MachOp
    genMachOp_slow opt op [x, y] = case op of

        MO_Eq _   -> genBinComp opt LM_CMP_Eq
        MO_Ne _   -> genBinComp opt LM_CMP_Ne

        MO_S_Gt _ -> genBinComp opt LM_CMP_Sgt
        MO_S_Ge _ -> genBinComp opt LM_CMP_Sge
        MO_S_Lt _ -> genBinComp opt LM_CMP_Slt
        MO_S_Le _ -> genBinComp opt LM_CMP_Sle

        MO_U_Gt _ -> genBinComp opt LM_CMP_Ugt
        MO_U_Ge _ -> genBinComp opt LM_CMP_Uge
        MO_U_Lt _ -> genBinComp opt LM_CMP_Ult
        MO_U_Le _ -> genBinComp opt LM_CMP_Ule

        MO_Add _ -> genBinMach LM_MO_Add
        MO_Sub _ -> genBinMach LM_MO_Sub
        MO_Mul _ -> genBinMach LM_MO_Mul

        MO_U_MulMayOflo _ -> panic "genMachOp: MO_U_MulMayOflo unsupported!"

        MO_S_MulMayOflo w -> isSMulOK w x y

        MO_S_Quot _ -> genBinMach LM_MO_SDiv
        MO_S_Rem  _ -> genBinMach LM_MO_SRem

        MO_U_Quot _ -> genBinMach LM_MO_UDiv
        MO_U_Rem  _ -> genBinMach LM_MO_URem

        MO_F_Eq _ -> genBinComp opt LM_CMP_Feq
        MO_F_Ne _ -> genBinComp opt LM_CMP_Fne
        MO_F_Gt _ -> genBinComp opt LM_CMP_Fgt
        MO_F_Ge _ -> genBinComp opt LM_CMP_Fge
        MO_F_Lt _ -> genBinComp opt LM_CMP_Flt
        MO_F_Le _ -> genBinComp opt LM_CMP_Fle

        MO_F_Add  _ -> genBinMach LM_MO_FAdd
        MO_F_Sub  _ -> genBinMach LM_MO_FSub
        MO_F_Mul  _ -> genBinMach LM_MO_FMul
        MO_F_Quot _ -> genBinMach LM_MO_FDiv

        MO_And _   -> genBinMach LM_MO_And
        MO_Or  _   -> genBinMach LM_MO_Or
        MO_Xor _   -> genBinMach LM_MO_Xor
        MO_Shl _   -> genBinMach LM_MO_Shl
        MO_U_Shr _ -> genBinMach LM_MO_LShr
        MO_S_Shr _ -> genBinMach LM_MO_AShr

        MO_V_Add l w   -> genCastBinMach (LMVector l (widthToLlvmInt w)) LM_MO_Add
        MO_V_Sub l w   -> genCastBinMach (LMVector l (widthToLlvmInt w)) LM_MO_Sub
        MO_V_Mul l w   -> genCastBinMach (LMVector l (widthToLlvmInt w)) LM_MO_Mul

        MO_VS_Quot l w -> genCastBinMach (LMVector l (widthToLlvmInt w)) LM_MO_SDiv
        MO_VS_Rem  l w -> genCastBinMach (LMVector l (widthToLlvmInt w)) LM_MO_SRem

        MO_VU_Quot l w -> genCastBinMach (LMVector l (widthToLlvmInt w)) LM_MO_UDiv
        MO_VU_Rem  l w -> genCastBinMach (LMVector l (widthToLlvmInt w)) LM_MO_URem

        MO_VF_Add  l w -> genCastBinMach (LMVector l (widthToLlvmFloat w)) LM_MO_FAdd
        MO_VF_Sub  l w -> genCastBinMach (LMVector l (widthToLlvmFloat w)) LM_MO_FSub
        MO_VF_Mul  l w -> genCastBinMach (LMVector l (widthToLlvmFloat w)) LM_MO_FMul
        MO_VF_Quot l w -> genCastBinMach (LMVector l (widthToLlvmFloat w)) LM_MO_FDiv

        MO_Not _       -> panicOp
        MO_S_Neg _     -> panicOp
        MO_F_Neg _     -> panicOp

        MO_SF_Conv _ _ -> panicOp
        MO_FS_Conv _ _ -> panicOp
        MO_SS_Conv _ _ -> panicOp
        MO_UU_Conv _ _ -> panicOp
        MO_FF_Conv _ _ -> panicOp

        MO_V_Insert  {} -> panicOp
        MO_V_Extract {} -> panicOp

        MO_VS_Neg {} -> panicOp

        MO_VF_Insert  {} -> panicOp
        MO_VF_Extract {} -> panicOp

        MO_VF_Neg {} -> panicOp

        MO_AlignmentCheck {} -> panicOp

        where
            binLlvmOp ty binOp = runExprData $ do
                vx <- exprToVarW x
                vy <- exprToVarW y
                if getVarType vx == getVarType vy
                    then do
                        doExprW (ty vx) $ binOp vx vy

                    else do
                        -- Error. Continue anyway so we can debug the generated ll file.
                        dflags <- getDynFlags
                        let style = mkCodeStyle CStyle
                            toString doc = renderWithStyle dflags doc style
                            cmmToStr = (lines . toString . PprCmm.pprExpr)
                        statement $ Comment $ map fsLit $ cmmToStr x
                        statement $ Comment $ map fsLit $ cmmToStr y
                        doExprW (ty vx) $ binOp vx vy

            binCastLlvmOp ty binOp = runExprData $ do
                vx <- exprToVarW x
                vy <- exprToVarW y
                [vx', vy'] <- castVarsW Signed [(vx, ty), (vy, ty)]
                doExprW ty $ binOp vx' vy'

            -- | Need to use EOption here as Cmm expects word size results from
            -- comparisons while LLVM return i1. Need to extend to llvmWord type
            -- if expected. See Note [Literals and branch conditions].
            genBinComp opt cmp = do
                ed@(v1, stmts, top) <- binLlvmOp (\_ -> i1) (Compare cmp)
                dflags <- getDynFlags
                if getVarType v1 == i1
                    then case i1Expected opt of
                        True  -> return ed
                        False -> do
                            let w_ = llvmWord dflags
                            (v2, s1) <- doExpr w_ $ Cast LM_Zext v1 w_
                            return (v2, stmts `snocOL` s1, top)
                    else
                        panic $ "genBinComp: Compare returned type other then i1! "
                            ++ (showSDoc dflags $ ppr $ getVarType v1)

            genBinMach op = binLlvmOp getVarType (LlvmOp op)

            genCastBinMach ty op = binCastLlvmOp ty (LlvmOp op)

            -- | Detect if overflow will occur in signed multiply of the two
            -- CmmExpr's. This is the LLVM assembly equivalent of the NCG
            -- implementation. Its much longer due to type information/safety.
            -- This should actually compile to only about 3 asm instructions.
            isSMulOK :: Width -> CmmExpr -> CmmExpr -> LlvmM ExprData
            isSMulOK _ x y = runExprData $ do
                vx <- exprToVarW x
                vy <- exprToVarW y

                dflags <- getDynFlags
                let word  = getVarType vx
                let word2 = LMInt $ 2 * (llvmWidthInBits dflags $ getVarType vx)
                let shift = llvmWidthInBits dflags word
                let shift1 = toIWord dflags (shift - 1)
                let shift2 = toIWord dflags shift

                if isInt word
                    then do
                        x1     <- doExprW word2 $ Cast LM_Sext vx word2
                        y1     <- doExprW word2 $ Cast LM_Sext vy word2
                        r1     <- doExprW word2 $ LlvmOp LM_MO_Mul x1 y1
                        rlow1  <- doExprW word $ Cast LM_Trunc r1 word
                        rlow2  <- doExprW word $ LlvmOp LM_MO_AShr rlow1 shift1
                        rhigh1 <- doExprW word2 $ LlvmOp LM_MO_AShr r1 shift2
                        rhigh2 <- doExprW word $ Cast LM_Trunc rhigh1 word
                        doExprW word $ LlvmOp LM_MO_Sub rlow2 rhigh2

                    else
                        panic $ "isSMulOK: Not bit type! (" ++ showSDoc dflags (ppr word) ++ ")"

            panicOp = panic $ "LLVM.CodeGen.genMachOp_slow: unary op encountered"
                           ++ "with two arguments! (" ++ show op ++ ")"

    -- More then two expression, invalid!
    genMachOp_slow _ _ _ = panic "genMachOp: More then 2 expressions in MachOp!"

    -- | Handle CmmLoad expression.
    genLoad :: Atomic -> CmmExpr -> CmmType -> LlvmM ExprData

    -- First we try to detect a few common cases and produce better code for
    -- these then the default case. We are mostly trying to detect Cmm code
    -- like I32[Sp + n] and use 'getelementptr' operations instead of the
    -- generic case that uses casts and pointer arithmetic
    genLoad atomic e@(CmmReg (CmmGlobal r)) ty
        = genLoad_fast atomic e r 0 ty

    genLoad atomic e@(CmmRegOff (CmmGlobal r) n) ty
        = genLoad_fast atomic e r n ty

    genLoad atomic e@(CmmMachOp (MO_Add _) [
                                (CmmReg (CmmGlobal r)),
                                (CmmLit (CmmInt n _))])
                    ty
        = genLoad_fast atomic e r (fromInteger n) ty

    genLoad atomic e@(CmmMachOp (MO_Sub _) [
                                (CmmReg (CmmGlobal r)),
                                (CmmLit (CmmInt n _))])
                    ty
        = genLoad_fast atomic e r (negate $ fromInteger n) ty

    -- generic case
    genLoad atomic e ty
        = getTBAAMeta topN >>= genLoad_slow atomic e ty

    -- | Handle CmmLoad expression.
    -- This is a special case for loading from a global register pointer
    -- offset such as I32[Sp+8].
    genLoad_fast :: Atomic -> CmmExpr -> GlobalReg -> Int -> CmmType
                 -> LlvmM ExprData
    genLoad_fast atomic e r n ty = do
        dflags <- getDynFlags
        (gv, grt, s1) <- getCmmRegVal (CmmGlobal r)
        meta          <- getTBAARegMeta r
        let ty'      = cmmToLlvmType ty
            (ix,rem) = n `divMod` ((llvmWidthInBits dflags . pLower) grt  `div` 8)
        case isPointer grt && rem == 0 of
                True  -> do
                    (ptr, s2) <- doExpr grt $ GetElemPtr True gv [toI32 ix]
                    -- We might need a different pointer type, so check
                    case grt == ty' of
                         -- were fine
                         True -> do
                             (var, s3) <- doExpr ty' (MExpr meta $ loadInstr ptr)
                             return (var, s1 `snocOL` s2 `snocOL` s3,
                                         [])

                         -- cast to pointer type needed
                         False -> do
                             let pty = pLift ty'
                             (ptr', s3) <- doExpr pty $ Cast LM_Bitcast ptr pty
                             (var, s4) <- doExpr ty' (MExpr meta $ loadInstr ptr')
                             return (var, s1 `snocOL` s2 `snocOL` s3
                                        `snocOL` s4, [])

                -- If its a bit type then we use the slow method since
                -- we can't avoid casting anyway.
                False -> genLoad_slow atomic  e ty meta
      where
        loadInstr ptr | atomic    = ALoad SyncSeqCst False ptr
                      | otherwise = Load ptr

    -- | Handle Cmm load expression.
    -- Generic case. Uses casts and pointer arithmetic if needed.
    genLoad_slow :: Atomic -> CmmExpr -> CmmType -> [MetaAnnot] -> LlvmM ExprData
    genLoad_slow atomic e ty meta = runExprData $ do
        iptr <- exprToVarW e
        dflags <- getDynFlags
        case getVarType iptr of
             LMPointer _ -> do
                        doExprW (cmmToLlvmType ty) (MExpr meta $ loadInstr iptr)

             i@(LMInt _) | i == llvmWord dflags -> do
                        let pty = LMPointer $ cmmToLlvmType ty
                        ptr <- doExprW pty $ Cast LM_Inttoptr iptr pty
                        doExprW (cmmToLlvmType ty) (MExpr meta $ loadInstr ptr)

             other -> do pprPanic "exprToVar: CmmLoad expression is not right type!"
                            (PprCmm.pprExpr e <+> text (
                                "Size of Ptr: " ++ show (llvmPtrBits dflags) ++
                                ", Size of var: " ++ show (llvmWidthInBits dflags other) ++
                                ", Var: " ++ showSDoc dflags (ppr iptr)))
      where
        loadInstr ptr | atomic    = ALoad SyncSeqCst False ptr
                      | otherwise = Load ptr

    -- | Handle CmmReg expression. This will return a pointer to the stack
    -- location of the register. Throws an error if it isn't allocated on
    -- the stack.
    getCmmReg :: CmmReg -> LlvmM LlvmVar
    getCmmReg (CmmLocal (LocalReg un _))
      = do exists <- varLookup un
           dflags <- getDynFlags
           case exists of
             Just ety -> return (LMLocalVar un $ pLift ety)
             Nothing  -> fail $ "getCmmReg: Cmm register " ++ showSDoc dflags (ppr un) ++ " was not allocated!"
               -- This should never happen, as every local variable should
               -- have been assigned a value at some point, triggering
               -- "funPrologue" to allocate it on the stack.

    getCmmReg (CmmGlobal g)
      = do onStack <- checkStackReg g
           dflags <- getDynFlags
           if onStack
             then return (lmGlobalRegVar dflags g)
             else fail $ "getCmmReg: Cmm register " ++ showSDoc dflags (ppr g) ++ " not stack-allocated!"

    -- | Return the value of a given register, as well as its type. Might
    -- need to be load from stack.
    getCmmRegVal :: CmmReg -> LlvmM (LlvmVar, LlvmType, LlvmStatements)
    getCmmRegVal reg =
      case reg of
        CmmGlobal g -> do
          onStack <- checkStackReg g
          dflags <- getDynFlags
          if onStack then loadFromStack else do
            let r = lmGlobalRegArg dflags g
            return (r, getVarType r, nilOL)
        _ -> loadFromStack
     where loadFromStack = do
             ptr <- getCmmReg reg
             let ty = pLower $ getVarType ptr
             (v, s) <- doExpr ty (Load ptr)
             return (v, ty, unitOL s)

    -- | Allocate a local CmmReg on the stack
    allocReg :: CmmReg -> (LlvmVar, LlvmStatements)
    allocReg (CmmLocal (LocalReg un ty))
      = let ty' = cmmToLlvmType ty
            var = LMLocalVar un (LMPointer ty')
            alc = Alloca ty' 1
        in (var, unitOL $ Assignment var alc)

    allocReg _ = panic $ "allocReg: Global reg encountered! Global registers should"
                        ++ " have been handled elsewhere!"

    -- | Generate code for a literal
    genLit :: EOption -> CmmLit -> LlvmM ExprData
    genLit opt (CmmInt i w)
      -- See Note [Literals and branch conditions].
      = let width | i1Expected opt = i1
                  | otherwise      = LMInt (widthInBits w)
            -- comm  = Comment [ fsLit $ "EOption: " ++ show opt
            --                 , fsLit $ "Width  : " ++ show w
            --                 , fsLit $ "Width' : " ++ show (widthInBits w)
            --                 ]
        in return (mkIntLit width i, nilOL, [])

    genLit _ (CmmFloat r w)
      = return (LMLitVar $ LMFloatLit (fromRational r) (widthToLlvmFloat w),
                  nilOL, [])

    genLit opt (CmmVec ls)
      = do llvmLits <- mapM toLlvmLit ls
           return (LMLitVar $ LMVectorLit llvmLits, nilOL, [])
      where
        toLlvmLit :: CmmLit -> LlvmM LlvmLit
        toLlvmLit lit = do
            (llvmLitVar, _, _) <- genLit opt lit
            case llvmLitVar of
              LMLitVar llvmLit -> return llvmLit
              _ -> panic "genLit"

    genLit _ cmm@(CmmLabel l)
      = do var <- getGlobalPtr =<< strCLabel_llvm l
           dflags <- getDynFlags
           let lmty = cmmToLlvmType $ cmmLitType dflags cmm
           (v1, s1) <- doExpr lmty $ Cast LM_Ptrtoint var (llvmWord dflags)
           return (v1, unitOL s1, [])

    genLit opt (CmmLabelOff label off) = do
        dflags <- getDynFlags
        (vlbl, stmts, stat) <- genLit opt (CmmLabel label)
        let voff = toIWord dflags off
        (v1, s1) <- doExpr (getVarType vlbl) $ LlvmOp LM_MO_Add vlbl voff
        return (v1, stmts `snocOL` s1, stat)

    genLit opt (CmmLabelDiffOff l1 l2 off) = do
        dflags <- getDynFlags
        (vl1, stmts1, stat1) <- genLit opt (CmmLabel l1)
        (vl2, stmts2, stat2) <- genLit opt (CmmLabel l2)
        let voff = toIWord dflags off
        let ty1 = getVarType vl1
        let ty2 = getVarType vl2
        if (isInt ty1) && (isInt ty2)
           && (llvmWidthInBits dflags ty1 == llvmWidthInBits dflags ty2)

           then do
                (v1, s1) <- doExpr (getVarType vl1) $ LlvmOp LM_MO_Sub vl1 vl2
                (v2, s2) <- doExpr (getVarType v1 ) $ LlvmOp LM_MO_Add v1 voff
                return (v2, stmts1 `appOL` stmts2 `snocOL` s1 `snocOL` s2,
                            stat1 ++ stat2)

            else
                panic "genLit: CmmLabelDiffOff encountered with different label ty!"

    genLit opt (CmmBlock b)
      = genLit opt (CmmLabel $ infoTblLbl b)

    genLit _ CmmHighStackMark
      = panic "genStaticLit - CmmHighStackMark unsupported!"

    -- -----------------------------------------------------------------------------
    -- * Misc
    --

    -- | Find CmmRegs that get assigned and allocate them on the stack
    --
    -- Any register that gets written needs to be allcoated on the
    -- stack. This avoids having to map a CmmReg to an equivalent SSA form
    -- and avoids having to deal with Phi node insertion.  This is also
    -- the approach recommended by LLVM developers.
    --
    -- On the other hand, this is unnecessarily verbose if the register in
    -- question is never written. Therefore we skip it where we can to
    -- save a few lines in the output and hopefully speed compilation up a
    -- bit.
    funPrologue :: LiveGlobalRegs -> [CmmBlock] -> LlvmM StmtData
    funPrologue live cmmBlocks = do

      trash <- getTrashRegs
      let getAssignedRegs :: CmmNode O O -> [CmmReg]
          getAssignedRegs (CmmAssign reg _)  = [reg]
          -- Calls will trash all registers. Unfortunately, this needs them to
          -- be stack-allocated in the first place.
          getAssignedRegs (CmmUnsafeForeignCall _ rs _) = map CmmGlobal trash ++ map CmmLocal rs
          getAssignedRegs _                  = []
          getRegsBlock (_, body, _)          = concatMap getAssignedRegs $ blockToList body
          assignedRegs = nub $ concatMap (getRegsBlock . blockSplit) cmmBlocks
          isLive r     = r `elem` alwaysLive || r `elem` live

      dflags <- getDynFlags
      stmtss <- flip mapM assignedRegs $ \reg ->
        case reg of
          CmmLocal (LocalReg un _) -> do
            let (newv, stmts) = allocReg reg
            varInsert un (pLower $ getVarType newv)
            return stmts
          CmmGlobal r -> do
            let reg   = lmGlobalRegVar dflags r
                arg   = lmGlobalRegArg dflags r
                ty    = (pLower . getVarType) reg
                trash = LMLitVar $ LMUndefLit ty
                rval  = if isLive r then arg else trash
                alloc = Assignment reg $ Alloca (pLower $ getVarType reg) 1
            markStackReg r
            return $ toOL [alloc, Store rval reg]

      return (concatOL stmtss, [])

    -- | Function epilogue. Load STG variables to use as argument for call.
    -- STG Liveness optimisation done here.
    funEpilogue :: LiveGlobalRegs -> LlvmM ([LlvmVar], LlvmStatements)
    funEpilogue live = do

        -- Have information and liveness optimisation is enabled?
        let liveRegs = alwaysLive ++ live
            isSSE (FloatReg _)  = True
            isSSE (DoubleReg _) = True
            isSSE (XmmReg _)    = True
            isSSE (YmmReg _)    = True
            isSSE (ZmmReg _)    = True
            isSSE _             = False

        -- Set to value or "undef" depending on whether the register is
        -- actually live
        dflags <- getDynFlags
        let loadExpr r = do
              (v, _, s) <- getCmmRegVal (CmmGlobal r)
              return (Just $ v, s)
            loadUndef r = do
              let ty = (pLower . getVarType $ lmGlobalRegVar dflags r)
              return (Just $ LMLitVar $ LMUndefLit ty, nilOL)
        platform <- getDynFlag targetPlatform
        loads <- flip mapM (activeStgRegs platform) $ \r -> case () of
          _ | r `elem` liveRegs  -> loadExpr r
            | not (isSSE r)      -> loadUndef r
            | otherwise          -> return (Nothing, nilOL)

        let (vars, stmts) = unzip loads
        return (catMaybes vars, concatOL stmts)

    -- | A series of statements to trash all the STG registers.
    --
    -- In LLVM we pass the STG registers around everywhere in function calls.
    -- So this means LLVM considers them live across the entire function, when
    -- in reality they usually aren't. For Caller save registers across C calls
    -- the saving and restoring of them is done by the Cmm code generator,
    -- using Cmm local vars. So to stop LLVM saving them as well (and saving
    -- all of them since it thinks they're always live, we trash them just
    -- before the call by assigning the 'undef' value to them. The ones we
    -- need are restored from the Cmm local var and the ones we don't need
    -- are fine to be trashed.
    getTrashStmts :: LlvmM LlvmStatements
    getTrashStmts = do
      regs <- getTrashRegs
      stmts <- flip mapM regs $ \ r -> do
        reg <- getCmmReg (CmmGlobal r)
        let ty = (pLower . getVarType) reg
        return $ Store (LMLitVar $ LMUndefLit ty) reg
      return $ toOL stmts

    getTrashRegs :: LlvmM [GlobalReg]
    getTrashRegs = do plat <- getLlvmPlatform
                      return $ filter (callerSaves plat) (activeStgRegs plat)

    -- | Get a function pointer to the CLabel specified.
    --
    -- This is for Haskell functions, function type is assumed, so doesn't work
    -- with foreign functions.
    getHsFunc :: LiveGlobalRegs -> CLabel -> LlvmM ExprData
    getHsFunc live lbl
      = do fty <- llvmFunTy live
           name <- strCLabel_llvm lbl
           getHsFunc' name fty

    getHsFunc' :: LMString -> LlvmType -> LlvmM ExprData
    getHsFunc' name fty
      = do fun <- getGlobalPtr name
           if getVarType fun == fty
             then return (fun, nilOL, [])
             else do (v1, s1) <- doExpr (pLift fty)
                                   $ Cast LM_Bitcast fun (pLift fty)
                     return  (v1, unitOL s1, [])

    -- | Create a new local var
    mkLocalVar :: LlvmType -> LlvmM LlvmVar
    mkLocalVar ty = do
        un <- getUniqueM
        return $ LMLocalVar un ty

    -- | Execute an expression, assigning result to a var
    doExpr :: LlvmType -> LlvmExpression -> LlvmM (LlvmVar, LlvmStatement)
    doExpr ty expr = do
        v <- mkLocalVar ty
        return (v, Assignment v expr)

    -- | Expand CmmRegOff
    expandCmmReg :: DynFlags -> (CmmReg, Int) -> CmmExpr
    expandCmmReg dflags (reg, off)
      = let width = typeWidth (cmmRegType dflags reg)
            voff  = CmmLit $ CmmInt (fromIntegral off) width
        in CmmMachOp (MO_Add width) [CmmReg reg, voff]

    -- | Convert a block id into a appropriate Llvm label
    blockIdToLlvm :: BlockId -> LlvmVar
    blockIdToLlvm bid = LMLocalVar (getUnique bid) LMLabel

    -- | Create Llvm int Literal
    mkIntLit :: Integral a => LlvmType -> a -> LlvmVar
    mkIntLit ty i = LMLitVar $ LMIntLit (toInteger i) ty

    -- | Convert int type to a LLvmVar of word or i32 size
    toI32 :: Integral a => a -> LlvmVar
    toI32 = mkIntLit i32

    toIWord :: Integral a => DynFlags -> a -> LlvmVar
    toIWord dflags = mkIntLit (llvmWord dflags)

    -- | Error functions
    panic :: String -> a
    panic s = Outputable.panic $ "LlvmCodeGen.CodeGen." ++ s

    pprPanic :: String -> SDoc -> a
    pprPanic s d = Outputable.pprPanic ("LlvmCodeGen.CodeGen." ++ s) d

    -- | Returns TBAA meta data by unique
    getTBAAMeta :: Unique -> LlvmM [MetaAnnot]
    getTBAAMeta u = do
        mi <- getUniqMeta u
        return [MetaAnnot tbaa (MetaNode i) | let Just i = mi]

    -- | Returns TBAA meta data for given register
    getTBAARegMeta :: GlobalReg -> LlvmM [MetaAnnot]
    getTBAARegMeta = getTBAAMeta . getTBAA

    -- | A more convenient way of accumulating LLVM statements and declarations.
    data LlvmAccum = LlvmAccum LlvmStatements [LlvmCmmDecl]

    instance Semigroup LlvmAccum where
      LlvmAccum stmtsA declsA <> LlvmAccum stmtsB declsB =
            LlvmAccum (stmtsA Semigroup.<> stmtsB) (declsA Semigroup.<> declsB)

    instance Monoid LlvmAccum where
        mempty = LlvmAccum nilOL []
        mappend = (Semigroup.<>)

    liftExprData :: LlvmM ExprData -> WriterT LlvmAccum LlvmM LlvmVar
    liftExprData action = do
        (var, stmts, decls) <- lift action
        tell $ LlvmAccum stmts decls
        return var

    statement :: LlvmStatement -> WriterT LlvmAccum LlvmM ()
    statement stmt = tell $ LlvmAccum (unitOL stmt) []

    doExprW :: LlvmType -> LlvmExpression -> WriterT LlvmAccum LlvmM LlvmVar
    doExprW a b = do
        (var, stmt) <- lift $ doExpr a b
        statement stmt
        return var

    exprToVarW :: CmmExpr -> WriterT LlvmAccum LlvmM LlvmVar
    exprToVarW = liftExprData . exprToVar

    runExprData :: WriterT LlvmAccum LlvmM LlvmVar -> LlvmM ExprData
    runExprData action = do
        (var, LlvmAccum stmts decls) <- runWriterT action
        return (var, stmts, decls)

    runStmtsDecls :: WriterT LlvmAccum LlvmM () -> LlvmM (LlvmStatements, [LlvmCmmDecl])
    runStmtsDecls action = do
        LlvmAccum stmts decls <- execWriterT action
        return (stmts, decls)

    getCmmRegW :: CmmReg -> WriterT LlvmAccum LlvmM LlvmVar
    getCmmRegW = lift . getCmmReg

    genLoadW :: Atomic -> CmmExpr -> CmmType -> WriterT LlvmAccum LlvmM LlvmVar
    genLoadW atomic e ty = liftExprData $ genLoad atomic e ty

    doTrashStmts :: WriterT LlvmAccum LlvmM ()
    doTrashStmts = do
        stmts <- lift getTrashStmts
        tell $ LlvmAccum stmts mempty