llvmGen/LlvmCodeGen/Base.hs

    {-# LANGUAGE CPP #-}

    -- ----------------------------------------------------------------------------
    -- | Base LLVM Code Generation module
    --
    -- Contains functions useful through out the code generator.
    --

    module LlvmCodeGen.Base (

            LlvmCmmDecl, LlvmBasicBlock,
            LiveGlobalRegs,
            LlvmUnresData, LlvmData, UnresLabel, UnresStatic,

            LlvmVersion, supportedLlvmVersion, llvmVersionStr,

            LlvmM,
            runLlvm, liftStream, withClearVars, varLookup, varInsert,
            markStackReg, checkStackReg,
            funLookup, funInsert, getLlvmVer, getDynFlags, getDynFlag, getLlvmPlatform,
            dumpIfSetLlvm, renderLlvm, markUsedVar, getUsedVars,
            ghcInternalFunctions,

            getMetaUniqueId,
            setUniqMeta, getUniqMeta,

            cmmToLlvmType, widthToLlvmFloat, widthToLlvmInt, llvmFunTy,
            llvmFunSig, llvmFunArgs, llvmStdFunAttrs, llvmFunAlign, llvmInfAlign,
            llvmPtrBits, tysToParams, llvmFunSection,

            strCLabel_llvm, strDisplayName_llvm, strProcedureName_llvm,
            getGlobalPtr, generateExternDecls,

            aliasify,
        ) where

    #include "HsVersions.h"
    #include "ghcautoconf.h"

    import GhcPrelude

    import Llvm
    import LlvmCodeGen.Regs

    import CLabel
    import CodeGen.Platform ( activeStgRegs )
    import DynFlags
    import FastString
    import Cmm              hiding ( succ )
    import Outputable as Outp
    import Platform
    import UniqFM
    import Unique
    import BufWrite   ( BufHandle )
    import UniqSet
    import UniqSupply
    import ErrUtils
    import qualified Stream

    import Control.Monad (ap)

    -- ----------------------------------------------------------------------------
    -- * Some Data Types
    --

    type LlvmCmmDecl = GenCmmDecl [LlvmData] (Maybe CmmStatics) (ListGraph LlvmStatement)
    type LlvmBasicBlock = GenBasicBlock LlvmStatement

    -- | Global registers live on proc entry
    type LiveGlobalRegs = [GlobalReg]

    -- | Unresolved code.
    -- Of the form: (data label, data type, unresolved data)
    type LlvmUnresData = (CLabel, Section, LlvmType, [UnresStatic])

    -- | Top level LLVM Data (globals and type aliases)
    type LlvmData = ([LMGlobal], [LlvmType])

    -- | An unresolved Label.
    --
    -- Labels are unresolved when we haven't yet determined if they are defined in
    -- the module we are currently compiling, or an external one.
    type UnresLabel  = CmmLit
    type UnresStatic = Either UnresLabel LlvmStatic

    -- ----------------------------------------------------------------------------
    -- * Type translations
    --

    -- | Translate a basic CmmType to an LlvmType.
    cmmToLlvmType :: CmmType -> LlvmType
    cmmToLlvmType ty | isVecType ty   = LMVector (vecLength ty) (cmmToLlvmType (vecElemType ty))
                     | isFloatType ty = widthToLlvmFloat $ typeWidth ty
                     | otherwise      = widthToLlvmInt   $ typeWidth ty

    -- | Translate a Cmm Float Width to a LlvmType.
    widthToLlvmFloat :: Width -> LlvmType
    widthToLlvmFloat W32  = LMFloat
    widthToLlvmFloat W64  = LMDouble
    widthToLlvmFloat W80  = LMFloat80
    widthToLlvmFloat W128 = LMFloat128
    widthToLlvmFloat w    = panic $ "widthToLlvmFloat: Bad float size: " ++ show w

    -- | Translate a Cmm Bit Width to a LlvmType.
    widthToLlvmInt :: Width -> LlvmType
    widthToLlvmInt w = LMInt $ widthInBits w

    -- | GHC Call Convention for LLVM
    llvmGhcCC :: DynFlags -> LlvmCallConvention
    llvmGhcCC dflags
     | platformUnregisterised (targetPlatform dflags) = CC_Ccc
     | otherwise                                      = CC_Ghc

    -- | Llvm Function type for Cmm function
    llvmFunTy :: LiveGlobalRegs -> LlvmM LlvmType
    llvmFunTy live = return . LMFunction =<< llvmFunSig' live (fsLit "a") ExternallyVisible

    -- | Llvm Function signature
    llvmFunSig :: LiveGlobalRegs ->  CLabel -> LlvmLinkageType -> LlvmM LlvmFunctionDecl
    llvmFunSig live lbl link = do
      lbl' <- strCLabel_llvm lbl
      llvmFunSig' live lbl' link

    llvmFunSig' :: LiveGlobalRegs -> LMString -> LlvmLinkageType -> LlvmM LlvmFunctionDecl
    llvmFunSig' live lbl link
      = do let toParams x | isPointer x = (x, [NoAlias, NoCapture])
                          | otherwise   = (x, [])
           dflags <- getDynFlags
           return $ LlvmFunctionDecl lbl link (llvmGhcCC dflags) LMVoid FixedArgs
                                     (map (toParams . getVarType) (llvmFunArgs dflags live))
                                     (llvmFunAlign dflags)

    -- | Alignment to use for functions
    llvmFunAlign :: DynFlags -> LMAlign
    llvmFunAlign dflags = Just (wORD_SIZE dflags)

    -- | Alignment to use for into tables
    llvmInfAlign :: DynFlags -> LMAlign
    llvmInfAlign dflags = Just (wORD_SIZE dflags)

    -- | Section to use for a function
    llvmFunSection :: DynFlags -> LMString -> LMSection
    llvmFunSection dflags lbl
        | gopt Opt_SplitSections dflags = Just (concatFS [fsLit ".text.", lbl])
        | otherwise                     = Nothing

    -- | A Function's arguments
    llvmFunArgs :: DynFlags -> LiveGlobalRegs -> [LlvmVar]
    llvmFunArgs dflags live =
        map (lmGlobalRegArg dflags) (filter isPassed (activeStgRegs platform))
        where platform = targetPlatform dflags
              isLive r = not (isSSE r) || r `elem` alwaysLive || r `elem` live
              isPassed r = not (isSSE r) || isLive r
              isSSE (FloatReg _)  = True
              isSSE (DoubleReg _) = True
              isSSE (XmmReg _)    = True
              isSSE (YmmReg _)    = True
              isSSE (ZmmReg _)    = True
              isSSE _             = False

    -- | Llvm standard fun attributes
    llvmStdFunAttrs :: [LlvmFuncAttr]
    llvmStdFunAttrs = [NoUnwind]

    -- | Convert a list of types to a list of function parameters
    -- (each with no parameter attributes)
    tysToParams :: [LlvmType] -> [LlvmParameter]
    tysToParams = map (\ty -> (ty, []))

    -- | Pointer width
    llvmPtrBits :: DynFlags -> Int
    llvmPtrBits dflags = widthInBits $ typeWidth $ gcWord dflags

    -- ----------------------------------------------------------------------------
    -- * Llvm Version
    --

    -- | LLVM Version Number
    type LlvmVersion = (Int, Int)

    -- | The LLVM Version that is currently supported.
    supportedLlvmVersion :: LlvmVersion
    supportedLlvmVersion = sUPPORTED_LLVM_VERSION

    llvmVersionStr :: LlvmVersion -> String
    llvmVersionStr (major, minor) = show major ++ "." ++ show minor

    -- ----------------------------------------------------------------------------
    -- * Environment Handling
    --

    data LlvmEnv = LlvmEnv
      { envVersion :: LlvmVersion      -- ^ LLVM version
      , envDynFlags :: DynFlags        -- ^ Dynamic flags
      , envOutput :: BufHandle         -- ^ Output buffer
      , envUniq :: UniqSupply          -- ^ Supply of unique values
      , envFreshMeta :: MetaId         -- ^ Supply of fresh metadata IDs
      , envUniqMeta :: UniqFM MetaId   -- ^ Global metadata nodes
      , envFunMap :: LlvmEnvMap        -- ^ Global functions so far, with type
      , envAliases :: UniqSet LMString -- ^ Globals that we had to alias, see [Llvm Forward References]
      , envUsedVars :: [LlvmVar]       -- ^ Pointers to be added to llvm.used (see @cmmUsedLlvmGens@)

        -- the following get cleared for every function (see @withClearVars@)
      , envVarMap :: LlvmEnvMap        -- ^ Local variables so far, with type
      , envStackRegs :: [GlobalReg]    -- ^ Non-constant registers (alloca'd in the function prelude)
      }

    type LlvmEnvMap = UniqFM LlvmType

    -- | The Llvm monad. Wraps @LlvmEnv@ state as well as the @IO@ monad
    newtype LlvmM a = LlvmM { runLlvmM :: LlvmEnv -> IO (a, LlvmEnv) }

    instance Functor LlvmM where
        fmap f m = LlvmM $ \env -> do (x, env') <- runLlvmM m env
                                      return (f x, env')

    instance Applicative LlvmM where
        pure x = LlvmM $ \env -> return (x, env)
        (<*>) = ap

    instance Monad LlvmM where
        m >>= f  = LlvmM $ \env -> do (x, env') <- runLlvmM m env
                                      runLlvmM (f x) env'

    instance HasDynFlags LlvmM where
        getDynFlags = LlvmM $ \env -> return (envDynFlags env, env)

    instance MonadUnique LlvmM where
        getUniqueSupplyM = do
            us <- getEnv envUniq
            let (us1, us2) = splitUniqSupply us
            modifyEnv (\s -> s { envUniq = us2 })
            return us1

        getUniqueM = do
            us <- getEnv envUniq
            let (u,us') = takeUniqFromSupply us
            modifyEnv (\s -> s { envUniq = us' })
            return u

    -- | Lifting of IO actions. Not exported, as we want to encapsulate IO.
    liftIO :: IO a -> LlvmM a
    liftIO m = LlvmM $ \env -> do x <- m
                                  return (x, env)

    -- | Get initial Llvm environment.
    runLlvm :: DynFlags -> LlvmVersion -> BufHandle -> UniqSupply -> LlvmM () -> IO ()
    runLlvm dflags ver out us m = do
        _ <- runLlvmM m env
        return ()
      where env = LlvmEnv { envFunMap = emptyUFM
                          , envVarMap = emptyUFM
                          , envStackRegs = []
                          , envUsedVars = []
                          , envAliases = emptyUniqSet
                          , envVersion = ver
                          , envDynFlags = dflags
                          , envOutput = out
                          , envUniq = us
                          , envFreshMeta = MetaId 0
                          , envUniqMeta = emptyUFM
                          }

    -- | Get environment (internal)
    getEnv :: (LlvmEnv -> a) -> LlvmM a
    getEnv f = LlvmM (\env -> return (f env, env))

    -- | Modify environment (internal)
    modifyEnv :: (LlvmEnv -> LlvmEnv) -> LlvmM ()
    modifyEnv f = LlvmM (\env -> return ((), f env))

    -- | Lift a stream into the LlvmM monad
    liftStream :: Stream.Stream IO a x -> Stream.Stream LlvmM a x
    liftStream s = Stream.Stream $ do
      r <- liftIO $ Stream.runStream s
      case r of
        Left b        -> return (Left b)
        Right (a, r2) -> return (Right (a, liftStream r2))

    -- | Clear variables from the environment for a subcomputation
    withClearVars :: LlvmM a -> LlvmM a
    withClearVars m = LlvmM $ \env -> do
        (x, env') <- runLlvmM m env { envVarMap = emptyUFM, envStackRegs = [] }
        return (x, env' { envVarMap = emptyUFM, envStackRegs = [] })

    -- | Insert variables or functions into the environment.
    varInsert, funInsert :: Uniquable key => key -> LlvmType -> LlvmM ()
    varInsert s t = modifyEnv $ \env -> env { envVarMap = addToUFM (envVarMap env) s t }
    funInsert s t = modifyEnv $ \env -> env { envFunMap = addToUFM (envFunMap env) s t }

    -- | Lookup variables or functions in the environment.
    varLookup, funLookup :: Uniquable key => key -> LlvmM (Maybe LlvmType)
    varLookup s = getEnv (flip lookupUFM s . envVarMap)
    funLookup s = getEnv (flip lookupUFM s . envFunMap)

    -- | Set a register as allocated on the stack
    markStackReg :: GlobalReg -> LlvmM ()
    markStackReg r = modifyEnv $ \env -> env { envStackRegs = r : envStackRegs env }

    -- | Check whether a register is allocated on the stack
    checkStackReg :: GlobalReg -> LlvmM Bool
    checkStackReg r = getEnv ((elem r) . envStackRegs)

    -- | Allocate a new global unnamed metadata identifier
    getMetaUniqueId :: LlvmM MetaId
    getMetaUniqueId = LlvmM $ \env ->
        return (envFreshMeta env, env { envFreshMeta = succ $ envFreshMeta env })

    -- | Get the LLVM version we are generating code for
    getLlvmVer :: LlvmM LlvmVersion
    getLlvmVer = getEnv envVersion

    -- | Get the platform we are generating code for
    getDynFlag :: (DynFlags -> a) -> LlvmM a
    getDynFlag f = getEnv (f . envDynFlags)

    -- | Get the platform we are generating code for
    getLlvmPlatform :: LlvmM Platform
    getLlvmPlatform = getDynFlag targetPlatform

    -- | Dumps the document if the corresponding flag has been set by the user
    dumpIfSetLlvm :: DumpFlag -> String -> Outp.SDoc -> LlvmM ()
    dumpIfSetLlvm flag hdr doc = do
      dflags <- getDynFlags
      liftIO $ dumpIfSet_dyn dflags flag hdr doc

    -- | Prints the given contents to the output handle
    renderLlvm :: Outp.SDoc -> LlvmM ()
    renderLlvm sdoc = do

        -- Write to output
        dflags <- getDynFlags
        out <- getEnv envOutput
        liftIO $ Outp.bufLeftRenderSDoc dflags out
                   (Outp.mkCodeStyle Outp.CStyle) sdoc

        -- Dump, if requested
        dumpIfSetLlvm Opt_D_dump_llvm "LLVM Code" sdoc
        return ()

    -- | Marks a variable as "used"
    markUsedVar :: LlvmVar -> LlvmM ()
    markUsedVar v = modifyEnv $ \env -> env { envUsedVars = v : envUsedVars env }

    -- | Return all variables marked as "used" so far
    getUsedVars :: LlvmM [LlvmVar]
    getUsedVars = getEnv envUsedVars

    -- | Saves that at some point we didn't know the type of the label and
    -- generated a reference to a type variable instead
    saveAlias :: LMString -> LlvmM ()
    saveAlias lbl = modifyEnv $ \env -> env { envAliases = addOneToUniqSet (envAliases env) lbl }

    -- | Sets metadata node for a given unique
    setUniqMeta :: Unique -> MetaId -> LlvmM ()
    setUniqMeta f m = modifyEnv $ \env -> env { envUniqMeta = addToUFM (envUniqMeta env) f m }

    -- | Gets metadata node for given unique
    getUniqMeta :: Unique -> LlvmM (Maybe MetaId)
    getUniqMeta s = getEnv (flip lookupUFM s . envUniqMeta)

    -- ----------------------------------------------------------------------------
    -- * Internal functions
    --

    -- | Here we pre-initialise some functions that are used internally by GHC
    -- so as to make sure they have the most general type in the case that
    -- user code also uses these functions but with a different type than GHC
    -- internally. (Main offender is treating return type as 'void' instead of
    -- 'void *'). Fixes trac #5486.
    ghcInternalFunctions :: LlvmM ()
    ghcInternalFunctions = do
        dflags <- getDynFlags
        mk "memcpy" i8Ptr [i8Ptr, i8Ptr, llvmWord dflags]
        mk "memmove" i8Ptr [i8Ptr, i8Ptr, llvmWord dflags]
        mk "memset" i8Ptr [i8Ptr, llvmWord dflags, llvmWord dflags]
        mk "newSpark" (llvmWord dflags) [i8Ptr, i8Ptr]
      where
        mk n ret args = do
          let n' = fsLit n `appendFS` fsLit "$def"
              decl = LlvmFunctionDecl n' ExternallyVisible CC_Ccc ret
                                     FixedArgs (tysToParams args) Nothing
          renderLlvm $ ppLlvmFunctionDecl decl
          funInsert n' (LMFunction decl)

    -- ----------------------------------------------------------------------------
    -- * Label handling
    --

    -- | Pretty print a 'CLabel'.
    strCLabel_llvm :: CLabel -> LlvmM LMString
    strCLabel_llvm lbl = do
        platform <- getLlvmPlatform
        dflags <- getDynFlags
        let sdoc = pprCLabel platform lbl
            str = Outp.renderWithStyle dflags sdoc (Outp.mkCodeStyle Outp.CStyle)
        return (fsLit str)

    strDisplayName_llvm :: CLabel -> LlvmM LMString
    strDisplayName_llvm lbl = do
        platform <- getLlvmPlatform
        dflags <- getDynFlags
        let sdoc = pprCLabel platform lbl
            depth = Outp.PartWay 1
            style = Outp.mkUserStyle dflags Outp.reallyAlwaysQualify depth
            str = Outp.renderWithStyle dflags sdoc style
        return (fsLit (dropInfoSuffix str))

    dropInfoSuffix :: String -> String
    dropInfoSuffix = go
      where go "_info"        = []
            go "_static_info" = []
            go "_con_info"    = []
            go (x:xs)         = x:go xs
            go []             = []

    strProcedureName_llvm :: CLabel -> LlvmM LMString
    strProcedureName_llvm lbl = do
        platform <- getLlvmPlatform
        dflags <- getDynFlags
        let sdoc = pprCLabel platform lbl
            depth = Outp.PartWay 1
            style = Outp.mkUserStyle dflags Outp.neverQualify depth
            str = Outp.renderWithStyle dflags sdoc style
        return (fsLit str)

    -- ----------------------------------------------------------------------------
    -- * Global variables / forward references
    --

    -- | Create/get a pointer to a global value. Might return an alias if
    -- the value in question hasn't been defined yet. We especially make
    -- no guarantees on the type of the returned pointer.
    getGlobalPtr :: LMString -> LlvmM LlvmVar
    getGlobalPtr llvmLbl = do
      m_ty <- funLookup llvmLbl
      let mkGlbVar lbl ty = LMGlobalVar lbl (LMPointer ty) Private Nothing Nothing
      case m_ty of
        -- Directly reference if we have seen it already
        Just ty -> return $ mkGlbVar (llvmLbl `appendFS` fsLit "$def") ty Global
        -- Otherwise use a forward alias of it
        Nothing -> do
          saveAlias llvmLbl
          return $ mkGlbVar llvmLbl i8 Alias

    -- | Generate definitions for aliases forward-referenced by @getGlobalPtr@.
    --
    -- Must be called at a point where we are sure that no new global definitions
    -- will be generated anymore!
    generateExternDecls :: LlvmM ([LMGlobal], [LlvmType])
    generateExternDecls = do
      delayed <- fmap nonDetEltsUniqSet $ getEnv envAliases
      -- This is non-deterministic but we do not
      -- currently support deterministic code-generation.
      -- See Note [Unique Determinism and code generation]
      defss <- flip mapM delayed $ \lbl -> do
        m_ty <- funLookup lbl
        case m_ty of
          -- If we have a definition we've already emitted the proper aliases
          -- when the symbol itself was emitted by @aliasify@
          Just _ -> return []

          -- If we don't have a definition this is an external symbol and we
          -- need to emit a declaration
          Nothing ->
            let var = LMGlobalVar lbl i8Ptr External Nothing Nothing Global
            in return [LMGlobal var Nothing]

      -- Reset forward list
      modifyEnv $ \env -> env { envAliases = emptyUniqSet }
      return (concat defss, [])

    -- | Here we take a global variable definition, rename it with a
    -- @$def@ suffix, and generate the appropriate alias.
    aliasify :: LMGlobal -> LlvmM [LMGlobal]
    aliasify (LMGlobal var val) = do
        let LMGlobalVar lbl ty link sect align const = var

            defLbl = lbl `appendFS` fsLit "$def"
            defVar = LMGlobalVar defLbl ty Internal sect align const

            defPtrVar = LMGlobalVar defLbl (LMPointer ty) link Nothing Nothing const
            aliasVar = LMGlobalVar lbl i8Ptr link Nothing Nothing Alias
            aliasVal = LMBitc (LMStaticPointer defPtrVar) i8Ptr

        -- we need to mark the $def symbols as used so LLVM doesn't forget which
        -- section they need to go in. This will vanish once we switch away from
        -- mangling sections for TNTC.
        markUsedVar defVar

        return [ LMGlobal defVar val
               , LMGlobal aliasVar (Just aliasVal)
               ]

    -- Note [Llvm Forward References]
    --
    -- The issue here is that LLVM insists on being strongly typed at
    -- every corner, so the first time we mention something, we have to
    -- settle what type we assign to it. That makes things awkward, as Cmm
    -- will often reference things before their definition, and we have no
    -- idea what (LLVM) type it is going to be before that point.
    --
    -- Our work-around is to define "aliases" of a standard type (i8 *) in
    -- these kind of situations, which we later tell LLVM to be either
    -- references to their actual local definitions (involving a cast) or
    -- an external reference. This obviously only works for pointers.
    --
    -- In particular when we encounter a reference to a symbol in a chunk of
    -- C-- there are three possible scenarios,
    --
    --   1. We have already seen a definition for the referenced symbol. This
    --      means we already know its type.
    --
    --   2. We have not yet seen a definition but we will find one later in this
    --      compilation unit. Since we want to be a good consumer of the
    --      C-- streamed to us from upstream, we don't know the type of the
    --      symbol at the time when we must emit the reference.
    --
    --   3. We have not yet seen a definition nor will we find one in this
    --      compilation unit. In this case the reference refers to an
    --      external symbol for which we do not know the type.
    --
    -- Let's consider case (2) for a moment: say we see a reference to
    -- the symbol @fooBar@ for which we have not seen a definition. As we
    -- do not know the symbol's type, we assume it is of type @i8*@ and emit
    -- the appropriate casts in @getSymbolPtr@. Later on, when we
    -- encounter the definition of @fooBar@ we emit it but with a modified
    -- name, @fooBar$def@ (which we'll call the definition symbol), to
    -- since we have already had to assume that the symbol @fooBar@
    -- is of type @i8*@. We then emit @fooBar@ itself as an alias
    -- of @fooBar$def@ with appropriate casts. This all happens in
    -- @aliasify@.
    --
    -- Case (3) is quite similar to (2): References are emitted assuming
    -- the referenced symbol is of type @i8*@. When we arrive at the end of
    -- the compilation unit and realize that the symbol is external, we emit
    -- an LLVM @external global@ declaration for the symbol @fooBar@
    -- (handled in @generateExternDecls@). This takes advantage of the
    -- fact that the aliases produced by @aliasify@ for exported symbols
    -- have external linkage and can therefore be used as normal symbols.
    --
    -- Historical note: As of release 3.5 LLVM does not allow aliases to
    -- refer to declarations. This the reason why aliases are produced at the
    -- point of definition instead of the point of usage, as was previously
    -- done. See #9142 for details.
    --
    -- Finally, case (1) is trival. As we already have a definition for
    -- and therefore know the type of the referenced symbol, we can do
    -- away with casting the alias to the desired type in @getSymbolPtr@
    -- and instead just emit a reference to the definition symbol directly.
    -- This is the @Just@ case in @getSymbolPtr@.