

-----------------------------------------------------------------------------
--
-- Stg to C-- code generation: the binding environment
--
-- (c) The University of Glasgow 2004-2006
--
-----------------------------------------------------------------------------
module GHC.StgToCmm.Env (
        CgIdInfo,

        litIdInfo, lneIdInfo, rhsIdInfo, mkRhsInit,
        idInfoToAmode,

        addBindC, addBindsC,

        bindArgsToRegs, bindToReg, rebindToReg,
        bindArgToReg, idToReg,
        getCgIdInfo, getCgInfo_maybe,
        maybeLetNoEscape,
        ) where

import GHC.Prelude

import GHC.Platform
import GHC.StgToCmm.Monad
import GHC.StgToCmm.Closure

import GHC.Cmm.CLabel

import GHC.Cmm.BlockId
import GHC.Cmm.Expr
import GHC.Cmm.Utils
import GHC.Types.Id
import GHC.Cmm.Graph
import GHC.Types.Name
import GHC.Core.Type
import GHC.Builtin.Types.Prim
import GHC.Types.Unique.FM
import GHC.Types.Var.Env

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

import GHC.Builtin.Names (getUnique)


-------------------------------------
--        Manipulating CgIdInfo
-------------------------------------

mkCgIdInfo :: Id -> LambdaFormInfo -> CmmExpr -> CgIdInfo
mkCgIdInfo id lf expr
  = CgIdInfo { cg_id = id, cg_lf = lf
             , cg_loc = CmmLoc expr }

litIdInfo :: Platform -> Id -> LambdaFormInfo -> CmmLit -> CgIdInfo
litIdInfo platform id lf lit
  = CgIdInfo { cg_id = id, cg_lf = lf
             , cg_loc = CmmLoc (addDynTag platform (CmmLit lit) tag) }
  where
    tag = lfDynTag platform lf

lneIdInfo :: Platform -> Id -> [NonVoid Id] -> CgIdInfo
lneIdInfo platform id regs
  = CgIdInfo { cg_id = id, cg_lf = lf
             , cg_loc = LneLoc blk_id (map (idToReg platform) regs) }
  where
    lf     = mkLFLetNoEscape
    blk_id = mkBlockId (idUnique id)


rhsIdInfo :: Id -> LambdaFormInfo -> FCode (CgIdInfo, LocalReg)
rhsIdInfo id lf_info
  = do platform <- getPlatform
       reg <- newTemp (gcWord platform)
       return (mkCgIdInfo id lf_info (CmmReg (CmmLocal reg)), reg)

mkRhsInit :: Platform -> LocalReg -> LambdaFormInfo -> CmmExpr -> CmmAGraph
mkRhsInit platform reg lf_info expr
  = mkAssign (CmmLocal reg) (addDynTag platform expr (lfDynTag platform lf_info))

-- | Returns a 'CmmExpr' for the *tagged* pointer
idInfoToAmode :: CgIdInfo -> CmmExpr
idInfoToAmode CgIdInfo { cg_loc = CmmLoc e } = e
idInfoToAmode cg_info
  = pprPanic "idInfoToAmode" (ppr (cg_id cg_info))        -- LneLoc

-- | A tag adds a byte offset to the pointer
addDynTag :: Platform -> CmmExpr -> DynTag -> CmmExpr
addDynTag = cmmOffsetB

maybeLetNoEscape :: CgIdInfo -> Maybe (BlockId, [LocalReg])
maybeLetNoEscape CgIdInfo { cg_loc = LneLoc blk_id args} = Just (blk_id, args)
maybeLetNoEscape _other                                      = Nothing



---------------------------------------------------------
--        The binding environment
--
-- There are three basic routines, for adding (addBindC),
-- modifying(modifyBindC) and looking up (getCgIdInfo) bindings.
---------------------------------------------------------

addBindC :: CgIdInfo -> FCode ()
addBindC stuff_to_bind = do
        binds <- getBinds
        setBinds $ extendVarEnv binds (cg_id stuff_to_bind) stuff_to_bind

addBindsC :: [CgIdInfo] -> FCode ()
addBindsC new_bindings = do
        binds <- getBinds
        let new_binds = foldl' (\ binds info -> extendVarEnv binds (cg_id info) info)
                               binds
                               new_bindings
        setBinds new_binds

-- Inside GHC the average module creates 385 external references
-- with noteable cgIdInfo (so not generated by mkLFArgument).
-- On average 200 of these are covered by True/False/[]
-- and nullary constructors make up ~80.
-- One would think it would be worthwhile to cache these.
-- Sadly it's not. See #16937

getCgIdInfo :: Id -> FCode CgIdInfo
getCgIdInfo id
  = do  { platform <- getPlatform
        ; local_binds <- getBinds -- Try local bindings first
        ; case lookupVarEnv local_binds id of {
            Just info -> -- pprTrace "getCgIdInfoLocal" (ppr id) $
              return info ;
            Nothing   -> do {

                -- Should be imported; make up a CgIdInfo for it
          let name = idName id
        ; if isExternalName name then
              let ext_lbl
                      | isBoxedType (idType id)
                      = mkClosureLabel name $ idCafInfo id
                      | isUnliftedType (idType id)
                          -- An unlifted external Id must refer to a top-level
                          -- string literal. See Note [Bytes label] in "GHC.Cmm.CLabel".
                      = assert (idType id `eqType` addrPrimTy) $
                        mkBytesLabel name
                      | otherwise
                      = pprPanic "GHC.StgToCmm.Env: label not found" (ppr id <+> dcolon <+> ppr (idType id))
              in return $
                  litIdInfo platform id (mkLFImported id) (CmmLabel ext_lbl)
          else
              cgLookupPanic id -- Bug, id is neither in local binds nor is external
        }}}

-- | Retrieve cg info for a name if it already exists.
getCgInfo_maybe :: Name -> FCode (Maybe CgIdInfo)
getCgInfo_maybe name
  = do  { local_binds <- getBinds -- Try local bindings first
        ; return $ lookupVarEnv_Directly local_binds (getUnique name) }

cgLookupPanic :: Id -> FCode a
cgLookupPanic id
  = do  local_binds <- getBinds
        pprPanic "GHC.StgToCmm.Env: variable not found"
                (vcat [ppr id,
                text "local binds for:",
                pprUFM local_binds $ \infos ->
                  vcat [ ppr (cg_id info) | info <- infos ]
              ])


------------------------------------------------------------------------
--        Interface functions for binding and re-binding names
------------------------------------------------------------------------

bindToReg :: NonVoid Id -> LambdaFormInfo -> FCode LocalReg
-- Bind an Id to a fresh LocalReg
bindToReg nvid@(NonVoid id) lf_info
  = do platform <- getPlatform
       let reg = idToReg platform nvid
       addBindC (mkCgIdInfo id lf_info (CmmReg (CmmLocal reg)))
       return reg

rebindToReg :: NonVoid Id -> FCode LocalReg
-- Like bindToReg, but the Id is already in scope, so
-- get its LF info from the envt
rebindToReg nvid@(NonVoid id)
  = do  { info <- getCgIdInfo id
        ; bindToReg nvid (cg_lf info) }

bindArgToReg :: NonVoid Id -> FCode LocalReg
bindArgToReg nvid@(NonVoid id) = bindToReg nvid (mkLFArgument id)

bindArgsToRegs :: [NonVoid Id] -> FCode [LocalReg]
bindArgsToRegs = mapM bindArgToReg

idToReg :: Platform -> NonVoid Id -> LocalReg
-- Make a register from an Id, typically a function argument,
-- free variable, or case binder
--
-- We re-use the Unique from the Id to make it easier to see what is going on
--
-- By now the Ids should be uniquely named; else one would worry
-- about accidental collision
idToReg platform (NonVoid id)
             = LocalReg (idUnique id)
                        (primRepCmmType platform (idPrimRep id))
