path: root/compiler/main/StaticPtrTable.hs

-- | Code generation for the Static Pointer Table
--
-- (c) 2014 I/O Tweag
--
-- Each module that uses 'static' keyword declares an initialization function of
-- the form hs_spt_init_<module>() which is emitted into the _stub.c file and
-- annotated with __attribute__((constructor)) so that it gets executed at
-- startup time.
--
-- The function's purpose is to call hs_spt_insert to insert the static
-- pointers of this module in the hashtable of the RTS, and it looks something
-- like this:
--
-- > static void hs_hpc_init_Main(void) __attribute__((constructor));
-- > static void hs_hpc_init_Main(void) {
-- >
-- >   static StgWord64 k0[2] = {16252233372134256ULL,7370534374096082ULL};
-- >   extern StgPtr Main_r2wb_closure;
-- >   hs_spt_insert(k0, &Main_r2wb_closure);
-- >
-- >   static StgWord64 k1[2] = {12545634534567898ULL,5409674567544151ULL};
-- >   extern StgPtr Main_r2wc_closure;
-- >   hs_spt_insert(k1, &Main_r2wc_closure);
-- >
-- > }
--
-- where the constants are fingerprints produced from the static forms.
--
-- The linker must find the definitions matching the @extern StgPtr <name>@
-- declarations. For this to work, the identifiers of static pointers need to be
-- exported. This is done in SetLevels.newLvlVar.
--
-- There is also a finalization function for the time when the module is
-- unloaded.
--
-- > static void hs_hpc_fini_Main(void) __attribute__((destructor));
-- > static void hs_hpc_fini_Main(void) {
-- >
-- >   static StgWord64 k0[2] = {16252233372134256ULL,7370534374096082ULL};
-- >   hs_spt_remove(k0);
-- >
-- >   static StgWord64 k1[2] = {12545634534567898ULL,5409674567544151ULL};
-- >   hs_spt_remove(k1);
-- >
-- > }
--

{-# LANGUAGE ViewPatterns, TupleSections #-}
module StaticPtrTable
    ( sptCreateStaticBinds
    , sptModuleInitCode
    ) where

{- Note [Grand plan for static forms]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Static forms go through the compilation phases as follows.
Here is a running example:

   f x = let k = map toUpper
         in ...(static k)...

* The renamer looks for out-of-scope names in the body of the static
  form, as always If all names are in scope, the free variables of the
  body are stored in AST at the location of the static form.

* The typechecker verifies that all free variables occurring in the
  static form are floatable to top level (see Note [Meaning of
  IdBindingInfo] in TcRnTypes).  In our example, 'k' is floatable, even
  though it is bound in a nested let, we are fine.

* The desugarer replaces the static form with an application of the
  function 'makeStatic' (defined in module GHC.StaticPtr.Internal of
  base).  So we get

   f x = let k = map toUpper
         in ...fromStaticPtr (makeStatic location k)...

* The simplifier runs the FloatOut pass which moves the calls to 'makeStatic'
  to the top level. Thus the FloatOut pass is always executed, even when
  optimizations are disabled.  So we get

   k = map toUpper
   static_ptr = makeStatic location k
   f x = ...fromStaticPtr static_ptr...

  The FloatOut pass is careful to produce an /exported/ Id for a floated
  'makeStatic' call, so the binding is not removed or inlined by the
  simplifier.
  E.g. the code for `f` above might look like

    static_ptr = makeStatic location k
    f x = ...(case static_ptr of ...)...

  which might be simplified to

    f x = ...(case makeStatic location k of ...)...

  BUT the top-level binding for static_ptr must remain, so that it can be
  collected to populate the Static Pointer Table.

  Making the binding exported also has a necessary effect during the
  CoreTidy pass.

* The CoreTidy pass replaces all bindings of the form

  b = /\ ... -> makeStatic location value

  with

  b = /\ ... -> StaticPtr key (StaticPtrInfo "pkg key" "module" location) value

  where a distinct key is generated for each binding.

* If we are compiling to object code we insert a C stub (generated by
  sptModuleInitCode) into the final object which runs when the module is loaded,
  inserting the static forms defined by the module into the RTS's static pointer
  table.

* If we are compiling for the byte-code interpreter, we instead explicitly add
  the SPT entries (recorded in CgGuts' cg_spt_entries field) to the interpreter
  process' SPT table using the addSptEntry interpreter message. This happens
  in upsweep after we have compiled the module (see GhcMake.upsweep').
-}

import GhcPrelude

import CLabel
import CoreSyn
import CoreUtils (collectMakeStaticArgs)
import DataCon
import DynFlags
import HscTypes
import Id
import MkCore (mkStringExprFSWith)
import Module
import Name
import Outputable
import Platform
import PrelNames
import TcEnv (lookupGlobal)
import Type

import Control.Monad.Trans.Class (lift)
import Control.Monad.Trans.State
import Data.List
import Data.Maybe
import GHC.Fingerprint
import qualified GHC.LanguageExtensions as LangExt

-- | Replaces all bindings of the form
--
-- > b = /\ ... -> makeStatic location value
--
--  with
--
-- > b = /\ ... ->
-- >   StaticPtr key (StaticPtrInfo "pkg key" "module" location) value
--
--  where a distinct key is generated for each binding.
--
-- It also yields the C stub that inserts these bindings into the static
-- pointer table.
sptCreateStaticBinds :: HscEnv -> Module -> CoreProgram
                     -> IO ([SptEntry], CoreProgram)
sptCreateStaticBinds hsc_env this_mod binds
    | not (xopt LangExt.StaticPointers dflags) =
      return ([], binds)
    | otherwise = do
      -- Make sure the required interface files are loaded.
      _ <- lookupGlobal hsc_env unpackCStringName
      (fps, binds') <- evalStateT (go [] [] binds) 0
      return (fps, binds')
  where
    go fps bs xs = case xs of
      []        -> return (reverse fps, reverse bs)
      bnd : xs' -> do
        (fps', bnd') <- replaceStaticBind bnd
        go (reverse fps' ++ fps) (bnd' : bs) xs'

    dflags = hsc_dflags hsc_env

    -- Generates keys and replaces 'makeStatic' with 'StaticPtr'.
    --
    -- The 'Int' state is used to produce a different key for each binding.
    replaceStaticBind :: CoreBind
                      -> StateT Int IO ([SptEntry], CoreBind)
    replaceStaticBind (NonRec b e) = do (mfp, (b', e')) <- replaceStatic b e
                                        return (maybeToList mfp, NonRec b' e')
    replaceStaticBind (Rec rbs) = do
      (mfps, rbs') <- unzip <$> mapM (uncurry replaceStatic) rbs
      return (catMaybes mfps, Rec rbs')

    replaceStatic :: Id -> CoreExpr
                  -> StateT Int IO (Maybe SptEntry, (Id, CoreExpr))
    replaceStatic b e@(collectTyBinders -> (tvs, e0)) =
      case collectMakeStaticArgs e0 of
        Nothing      -> return (Nothing, (b, e))
        Just (_, t, info, arg) -> do
          (fp, e') <- mkStaticBind t info arg
          return (Just (SptEntry b fp), (b, foldr Lam e' tvs))

    mkStaticBind :: Type -> CoreExpr -> CoreExpr
                 -> StateT Int IO (Fingerprint, CoreExpr)
    mkStaticBind t srcLoc e = do
      i <- get
      put (i + 1)
      staticPtrInfoDataCon <-
        lift $ lookupDataConHscEnv staticPtrInfoDataConName
      let fp@(Fingerprint w0 w1) = mkStaticPtrFingerprint i
      info <- mkConApp staticPtrInfoDataCon <$>
            (++[srcLoc]) <$>
            mapM (mkStringExprFSWith (lift . lookupIdHscEnv))
                 [ unitIdFS $ moduleUnitId this_mod
                 , moduleNameFS $ moduleName this_mod
                 ]

      -- The module interface of GHC.StaticPtr should be loaded at least
      -- when looking up 'fromStatic' during type-checking.
      staticPtrDataCon <- lift $ lookupDataConHscEnv staticPtrDataConName
      return (fp, mkConApp staticPtrDataCon
                               [ Type t
                               , mkWord64LitWordRep dflags w0
                               , mkWord64LitWordRep dflags w1
                               , info
                               , e ])

    mkStaticPtrFingerprint :: Int -> Fingerprint
    mkStaticPtrFingerprint n = fingerprintString $ intercalate ":"
        [ unitIdString $ moduleUnitId this_mod
        , moduleNameString $ moduleName this_mod
        , show n
        ]

    -- Choose either 'Word64#' or 'Word#' to represent the arguments of the
    -- 'Fingerprint' data constructor.
    mkWord64LitWordRep dflags
      | platformWordSize (targetPlatform dflags) < 8 = mkWord64LitWord64
      | otherwise = mkWordLit dflags . toInteger

    lookupIdHscEnv :: Name -> IO Id
    lookupIdHscEnv n = lookupTypeHscEnv hsc_env n >>=
                         maybe (getError n) (return . tyThingId)

    lookupDataConHscEnv :: Name -> IO DataCon
    lookupDataConHscEnv n = lookupTypeHscEnv hsc_env n >>=
                              maybe (getError n) (return . tyThingDataCon)

    getError n = pprPanic "sptCreateStaticBinds.get: not found" $
      text "Couldn't find" <+> ppr n

-- | @sptModuleInitCode module fps@ is a C stub to insert the static entries
-- of @module@ into the static pointer table.
--
-- @fps@ is a list associating each binding corresponding to a static entry with
-- its fingerprint.
sptModuleInitCode :: Module -> [SptEntry] -> SDoc
sptModuleInitCode _ [] = Outputable.empty
sptModuleInitCode this_mod entries = vcat
    [ text "static void hs_spt_init_" <> ppr this_mod
           <> text "(void) __attribute__((constructor));"
    , text "static void hs_spt_init_" <> ppr this_mod <> text "(void)"
    , braces $ vcat $
        [  text "static StgWord64 k" <> int i <> text "[2] = "
           <> pprFingerprint fp <> semi
        $$ text "extern StgPtr "
           <> (ppr $ mkClosureLabel (idName n) (idCafInfo n)) <> semi
        $$ text "hs_spt_insert" <> parens
             (hcat $ punctuate comma
                [ char 'k' <> int i
                , char '&' <> ppr (mkClosureLabel (idName n) (idCafInfo n))
                ]
             )
        <> semi
        |  (i, SptEntry n fp) <- zip [0..] entries
        ]
    , text "static void hs_spt_fini_" <> ppr this_mod
           <> text "(void) __attribute__((destructor));"
    , text "static void hs_spt_fini_" <> ppr this_mod <> text "(void)"
    , braces $ vcat $
        [  text "StgWord64 k" <> int i <> text "[2] = "
           <> pprFingerprint fp <> semi
        $$ text "hs_spt_remove" <> parens (char 'k' <> int i) <> semi
        | (i, (SptEntry _ fp)) <- zip [0..] entries
        ]
    ]
  where
    pprFingerprint :: Fingerprint -> SDoc
    pprFingerprint (Fingerprint w1 w2) =
      braces $ hcat $ punctuate comma
                 [ integer (fromIntegral w1) <> text "ULL"
                 , integer (fromIntegral w2) <> text "ULL"
                 ]