codeGen/StgCmmCon.hs

    {-# LANGUAGE CPP #-}

    -----------------------------------------------------------------------------
    --
    -- Stg to C--: code generation for constructors
    --
    -- This module provides the support code for StgCmm to deal with with
    -- constructors on the RHSs of let(rec)s.
    --
    -- (c) The University of Glasgow 2004-2006
    --
    -----------------------------------------------------------------------------

    module StgCmmCon (
            cgTopRhsCon, buildDynCon, bindConArgs
        ) where

    #include "HsVersions.h"

    import StgSyn
    import CoreSyn  ( AltCon(..) )

    import StgCmmMonad
    import StgCmmEnv
    import StgCmmHeap
    import StgCmmLayout
    import StgCmmUtils
    import StgCmmClosure
    import StgCmmProf ( curCCS )

    import CmmExpr
    import CLabel
    import MkGraph
    import SMRep
    import CostCentre
    import Module
    import DataCon
    import DynFlags
    import FastString
    import Id
    import RepType (countConRepArgs)
    import Literal
    import PrelInfo
    import Outputable
    import Platform
    import Util
    import MonadUtils (mapMaybeM)

    import Control.Monad
    import Data.Char

    ---------------------------------------------------------------
    --      Top-level constructors
    ---------------------------------------------------------------

    cgTopRhsCon :: DynFlags
                -> Id               -- Name of thing bound to this RHS
                -> DataCon          -- Id
                -> [NonVoid StgArg] -- Args
                -> (CgIdInfo, FCode ())
    cgTopRhsCon dflags id con args =
        let id_info = litIdInfo dflags id (mkConLFInfo con) (CmmLabel closure_label)
        in (id_info, gen_code)
      where
       name          = idName id
       caffy         = idCafInfo id -- any stgArgHasCafRefs args
       closure_label = mkClosureLabel name caffy

       gen_code =
         do { this_mod <- getModuleName
            ; when (platformOS (targetPlatform dflags) == OSMinGW32) $
                  -- Windows DLLs have a problem with static cross-DLL refs.
                  MASSERT( not (isDllConApp dflags this_mod con (map fromNonVoid args)) )
            ; ASSERT( args `lengthIs` countConRepArgs con ) return ()

            -- LAY IT OUT
            ; let
                (tot_wds, --  #ptr_wds + #nonptr_wds
                 ptr_wds, --  #ptr_wds
                 nv_args_w_offsets) = mkVirtConstrOffsets dflags (addArgReps args)

                nonptr_wds = tot_wds - ptr_wds

                 -- we're not really going to emit an info table, so having
                 -- to make a CmmInfoTable is a bit overkill, but mkStaticClosureFields
                 -- needs to poke around inside it.
                info_tbl = mkDataConInfoTable dflags con True ptr_wds nonptr_wds

                get_lit (arg, _offset) = do { CmmLit lit <- getArgAmode arg
                                            ; return lit }

            ; payload <- mapM get_lit nv_args_w_offsets
                    -- NB1: nv_args_w_offsets is sorted into ptrs then non-ptrs
                    -- NB2: all the amodes should be Lits!
                    --      TODO (osa): Why?

            ; let closure_rep = mkStaticClosureFields
                                 dflags
                                 info_tbl
                                 dontCareCCS                -- Because it's static data
                                 caffy                      -- Has CAF refs
                                 payload

                    -- BUILD THE OBJECT
            ; emitDataLits closure_label closure_rep

            ; return () }

    ---------------------------------------------------------------
    --      Lay out and allocate non-top-level constructors
    ---------------------------------------------------------------

    buildDynCon :: Id                 -- Name of the thing to which this constr will
                                      -- be bound
                -> Bool               -- is it genuinely bound to that name, or just
                                      -- for profiling?
                -> CostCentreStack    -- Where to grab cost centre from;
                                      -- current CCS if currentOrSubsumedCCS
                -> DataCon            -- The data constructor
                -> [NonVoid StgArg]   -- Its args
                -> FCode (CgIdInfo, FCode CmmAGraph)
                   -- Return details about how to find it and initialization code
    buildDynCon binder actually_bound cc con args
        = do dflags <- getDynFlags
             buildDynCon' dflags (targetPlatform dflags) binder actually_bound cc con args

    buildDynCon' :: DynFlags
                 -> Platform
                 -> Id -> Bool
                 -> CostCentreStack
                 -> DataCon
                 -> [NonVoid StgArg]
                 -> FCode (CgIdInfo, FCode CmmAGraph)

    {- We used to pass a boolean indicating whether all the
    args were of size zero, so we could use a static
    constructor; but I concluded that it just isn't worth it.
    Now I/O uses unboxed tuples there just aren't any constructors
    with all size-zero args.

    The reason for having a separate argument, rather than looking at
    the addr modes of the args is that we may be in a "knot", and
    premature looking at the args will cause the compiler to black-hole!
    -}

    -------- buildDynCon': Nullary constructors --------------
    -- First we deal with the case of zero-arity constructors.  They
    -- will probably be unfolded, so we don't expect to see this case much,
    -- if at all, but it does no harm, and sets the scene for characters.
    --
    -- In the case of zero-arity constructors, or, more accurately, those
    -- which have exclusively size-zero (VoidRep) args, we generate no code
    -- at all.

    buildDynCon' dflags _ binder _ _cc con []
      | isNullaryRepDataCon con
      = return (litIdInfo dflags binder (mkConLFInfo con)
                    (CmmLabel (mkClosureLabel (dataConName con) (idCafInfo binder))),
                return mkNop)

    -------- buildDynCon': Charlike and Intlike constructors -----------
    {- The following three paragraphs about @Char@-like and @Int@-like
    closures are obsolete, but I don't understand the details well enough
    to properly word them, sorry. I've changed the treatment of @Char@s to
    be analogous to @Int@s: only a subset is preallocated, because @Char@
    has now 31 bits. Only literals are handled here. -- Qrczak

    Now for @Char@-like closures.  We generate an assignment of the
    address of the closure to a temporary.  It would be possible simply to
    generate no code, and record the addressing mode in the environment,
    but we'd have to be careful if the argument wasn't a constant --- so
    for simplicity we just always assign to a temporary.

    Last special case: @Int@-like closures.  We only special-case the
    situation in which the argument is a literal in the range
    @mIN_INTLIKE@..@mAX_INTLILKE@.  NB: for @Char@-like closures we can
    work with any old argument, but for @Int@-like ones the argument has
    to be a literal.  Reason: @Char@ like closures have an argument type
    which is guaranteed in range.

    Because of this, we use can safely return an addressing mode.

    We don't support this optimisation when compiling into Windows DLLs yet
    because they don't support cross package data references well.
    -}

    buildDynCon' dflags platform binder _ _cc con [arg]
      | maybeIntLikeCon con
      , platformOS platform /= OSMinGW32 || not (positionIndependent dflags)
      , NonVoid (StgLitArg (MachInt val)) <- arg
      , val <= fromIntegral (mAX_INTLIKE dflags) -- Comparisons at type Integer!
      , val >= fromIntegral (mIN_INTLIKE dflags) -- ...ditto...
      = do  { let intlike_lbl   = mkCmmClosureLabel rtsUnitId (fsLit "stg_INTLIKE")
                  val_int = fromIntegral val :: Int
                  offsetW = (val_int - mIN_INTLIKE dflags) * (fixedHdrSizeW dflags + 1)
                    -- INTLIKE closures consist of a header and one word payload
                  intlike_amode = cmmLabelOffW dflags intlike_lbl offsetW
            ; return ( litIdInfo dflags binder (mkConLFInfo con) intlike_amode
                     , return mkNop) }

    buildDynCon' dflags platform binder _ _cc con [arg]
      | maybeCharLikeCon con
      , platformOS platform /= OSMinGW32 || not (positionIndependent dflags)
      , NonVoid (StgLitArg (MachChar val)) <- arg
      , let val_int = ord val :: Int
      , val_int <= mAX_CHARLIKE dflags
      , val_int >= mIN_CHARLIKE dflags
      = do  { let charlike_lbl   = mkCmmClosureLabel rtsUnitId (fsLit "stg_CHARLIKE")
                  offsetW = (val_int - mIN_CHARLIKE dflags) * (fixedHdrSizeW dflags + 1)
                    -- CHARLIKE closures consist of a header and one word payload
                  charlike_amode = cmmLabelOffW dflags charlike_lbl offsetW
            ; return ( litIdInfo dflags binder (mkConLFInfo con) charlike_amode
                     , return mkNop) }

    -------- buildDynCon': the general case -----------
    buildDynCon' dflags _ binder actually_bound ccs con args
      = do  { (id_info, reg) <- rhsIdInfo binder lf_info
            ; return (id_info, gen_code reg)
            }
     where
      lf_info = mkConLFInfo con

      gen_code reg
        = do  { let (tot_wds, ptr_wds, args_w_offsets)
                      = mkVirtConstrOffsets dflags (addArgReps args)
                    nonptr_wds = tot_wds - ptr_wds
                    info_tbl = mkDataConInfoTable dflags con False
                                    ptr_wds nonptr_wds
              ; let ticky_name | actually_bound = Just binder
                               | otherwise = Nothing

              ; hp_plus_n <- allocDynClosure ticky_name info_tbl lf_info
                                              use_cc blame_cc args_w_offsets
              ; return (mkRhsInit dflags reg lf_info hp_plus_n) }
        where
          use_cc      -- cost-centre to stick in the object
            | isCurrentCCS ccs = curCCS
            | otherwise        = panic "buildDynCon: non-current CCS not implemented"

          blame_cc = use_cc -- cost-centre on which to blame the alloc (same)

    ---------------------------------------------------------------
    --      Binding constructor arguments
    ---------------------------------------------------------------

    bindConArgs :: AltCon -> LocalReg -> [NonVoid Id] -> FCode [LocalReg]
    -- bindConArgs is called from cgAlt of a case
    -- (bindConArgs con args) augments the environment with bindings for the
    -- binders args, assuming that we have just returned from a 'case' which
    -- found a con
    bindConArgs (DataAlt con) base args
      = ASSERT(not (isUnboxedTupleCon con))
        do dflags <- getDynFlags
           let (_, _, args_w_offsets) = mkVirtConstrOffsets dflags (addIdReps args)
               tag = tagForCon dflags con

               -- The binding below forces the masking out of the tag bits
               -- when accessing the constructor field.
               bind_arg :: (NonVoid Id, VirtualHpOffset) -> FCode (Maybe LocalReg)
               bind_arg (arg@(NonVoid b), offset)
                 | isDeadBinder b =
                     -- Do not load unused fields from objects to local variables.
                     -- (CmmSink can optimize this, but it's cheap and common enough
                     -- to handle here)
                     return Nothing
                 | otherwise      = do
                     emit $ mkTaggedObjectLoad dflags (idToReg dflags arg) base offset tag
                     Just <$> bindArgToReg arg

           mapMaybeM bind_arg args_w_offsets

    bindConArgs _other_con _base args
      = ASSERT( null args ) return []