path: root/ghc/compiler/codeGen/CgCon.lhs

%
% (c) The GRASP Project, Glasgow University, 1992-1998
%
\section[CgCon]{Code generation for constructors}

This module provides the support code for @StgToAbstractC@ to deal
with {\em constructors} on the RHSs of let(rec)s.  See also
@CgClosure@, which deals with closures.

\begin{code}
module CgCon (
	cgTopRhsCon, buildDynCon,
	bindConArgs, bindUnboxedTupleComponents,
	cgReturnDataCon
    ) where

#include "HsVersions.h"

import CgMonad
import AbsCSyn
import StgSyn

import AbsCUtils	( getAmodeRep )
import CgBindery	( getArgAmodes, bindNewToNode,
			  bindArgsToRegs, 
			  idInfoToAmode, stableAmodeIdInfo,
			  heapIdInfo, CgIdInfo, bindNewToStack
			)
import CgStackery	( mkTaggedVirtStkOffsets, freeStackSlots, 
			  updateFrameSize
			)
import CgUsages		( getRealSp, getVirtSp, setRealAndVirtualSp,
			  getSpRelOffset )
import CgRetConv	( assignRegs )
import Constants	( mAX_INTLIKE, mIN_INTLIKE, mAX_CHARLIKE, mIN_CHARLIKE,
			  mIN_UPD_SIZE )
import CgHeapery	( allocDynClosure, inPlaceAllocDynClosure )
import CgTailCall	( performReturn, mkStaticAlgReturnCode, doTailCall,
			  mkUnboxedTupleReturnCode )
import CLabel		( mkClosureLabel )
import ClosureInfo	( mkConLFInfo, mkLFArgument,
			  layOutDynCon, layOutDynClosure,
			  layOutStaticClosure, closureSize
			)
import CostCentre	( currentOrSubsumedCCS, dontCareCCS, CostCentreStack,
			  currentCCS )
import DataCon		( DataCon, dataConName, dataConTag, 
			  isUnboxedTupleCon, isNullaryDataCon, dataConId, 
			  dataConWrapId, dataConRepArity
			)
import Id		( Id, idName, idPrimRep )
import Literal		( Literal(..) )
import PrelInfo		( maybeCharLikeCon, maybeIntLikeCon )
import PrimRep		( PrimRep(..), isFollowableRep )
import Unique		( Uniquable(..) )
import Util
import Outputable
\end{code}

%************************************************************************
%*									*
\subsection[toplevel-constructors]{Top-level constructors}
%*									*
%************************************************************************

\begin{code}
cgTopRhsCon :: Id		-- Name of thing bound to this RHS
	    -> DataCon		-- Id
	    -> [StgArg]		-- Args
	    -> FCode (Id, CgIdInfo)
cgTopRhsCon id con args
  = ASSERT(not (isDllConApp con args))	-- checks for litlit args too
    ASSERT(length args == dataConRepArity con)
    let
	name          = idName id
    	closure_label = mkClosureLabel name
	lf_info       = mkConLFInfo con
    	cg_id_info    = stableAmodeIdInfo id (CLbl closure_label PtrRep) lf_info
    in

    (
	-- LAY IT OUT
    getArgAmodes args		`thenFC` \ amodes ->

    let
	(closure_info, amodes_w_offsets)
	  = layOutStaticClosure name getAmodeRep amodes lf_info
    in

	-- BUILD THE OBJECT
    absC (CStaticClosure
	    closure_label		-- Labelled with the name on lhs of defn
	    closure_info		-- Closure is static
	    (mkCCostCentreStack dontCareCCS) -- because it's static data
	    (map fst amodes_w_offsets)) -- Sorted into ptrs first, then nonptrs

    ) `thenC`

	-- RETURN
    returnFC (id, stableAmodeIdInfo id (CLbl closure_label PtrRep) lf_info)
\end{code}

%************************************************************************
%*									*
%* non-top-level constructors						*
%*									*
%************************************************************************
\subsection[code-for-constructors]{The code for constructors}

\begin{code}
buildDynCon :: Id		-- Name of the thing to which this constr will
				-- be bound
	    -> CostCentreStack	-- Where to grab cost centre from;
				-- current CCS if currentOrSubsumedCCS
	    -> DataCon		-- The data constructor
	    -> [CAddrMode]	-- Its args
	    -> FCode CgIdInfo	-- Return details about how to find it

-- We used to pass a boolean indicating whether all the
-- args were of size zero, so we could use a static
-- construtor; 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!
\end{code}

First we deal with the case of zero-arity constructors.  Now, 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.

\begin{code}
buildDynCon binder cc con []
  = returnFC (stableAmodeIdInfo binder
				(CLbl (mkClosureLabel (idName (dataConWrapId con))) PtrRep)
    				(mkConLFInfo con))
\end{code}

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 asssign 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.

\begin{code}
buildDynCon binder cc con [arg_amode]
  | maybeIntLikeCon con && in_range_int_lit arg_amode
  = returnFC (stableAmodeIdInfo binder (CIntLike arg_amode) (mkConLFInfo con))
  where
    in_range_int_lit (CLit (MachInt val)) = val <= mAX_INTLIKE && val >= mIN_INTLIKE
    in_range_int_lit _other_amode	  = False

buildDynCon binder cc con [arg_amode]
  | maybeCharLikeCon con && in_range_char_lit arg_amode
  = returnFC (stableAmodeIdInfo binder (CCharLike arg_amode) (mkConLFInfo con))
  where
    in_range_char_lit (CLit (MachChar val)) = val <= mAX_CHARLIKE && val >= mIN_CHARLIKE
    in_range_char_lit _other_amode	    = False
\end{code}

Now the general case.

\begin{code}
buildDynCon binder ccs con args
  = allocDynClosure closure_info use_cc blame_cc amodes_w_offsets `thenFC` \ hp_off ->
    returnFC (heapIdInfo binder hp_off lf_info)
  where
    (closure_info, amodes_w_offsets)
      = layOutDynClosure (idName binder) getAmodeRep args lf_info
    lf_info = mkConLFInfo con

    use_cc	-- cost-centre to stick in the object
      = if currentOrSubsumedCCS ccs
	then CReg CurCostCentre
	else mkCCostCentreStack ccs

    blame_cc = use_cc -- cost-centre on which to blame the alloc (same)
\end{code}


%************************************************************************
%*									*
%* constructor-related utility function:				*
%*		bindConArgs is called from cgAlt of a case		*
%*									*
%************************************************************************
\subsection[constructor-utilities]{@bindConArgs@: constructor-related utility}

@bindConArgs@ $con args$ augments the environment with bindings for the
binders $args$, assuming that we have just returned from a @case@ which
found a $con$.

\begin{code}
bindConArgs 
	:: DataCon -> [Id]		-- Constructor and args
	-> Code

bindConArgs con args
  = ASSERT(not (isUnboxedTupleCon con))
    mapCs bind_arg args_w_offsets
   where
     bind_arg (arg, offset) = bindNewToNode arg offset mkLFArgument
     (_, args_w_offsets) = layOutDynCon con idPrimRep args
\end{code}

Unboxed tuples are handled slightly differently - the object is
returned in registers and on the stack instead of the heap.

\begin{code}
bindUnboxedTupleComponents
	:: [Id]					-- args
	-> FCode ([MagicId], 			-- regs assigned
		  [(VirtualSpOffset,Int)], 	-- tag slots
		  Bool)				-- any components on stack?

bindUnboxedTupleComponents args
 =  -- Assign as many components as possible to registers
    let (arg_regs, leftovers) = assignRegs [] (map idPrimRep args)
	(reg_args, stk_args) = splitAt (length arg_regs) args
    in

    -- Allocate the rest on the stack (ToDo: separate out pointers)
    getVirtSp `thenFC` \ vsp ->
    getRealSp `thenFC` \ rsp ->
    let (top_sp, stk_offsets, tags) = 
		mkTaggedVirtStkOffsets rsp idPrimRep stk_args
    in

    -- The stack pointer points to the last stack-allocated component
    setRealAndVirtualSp top_sp  		`thenC`

    -- need to explicitly free any empty slots we just jumped over
    (if vsp < rsp then freeStackSlots [vsp+1 .. rsp] else nopC) `thenC`

    bindArgsToRegs reg_args arg_regs 		`thenC`
    mapCs bindNewToStack stk_offsets 		`thenC`
    returnFC (arg_regs,tags, not (null stk_offsets))
\end{code}

%************************************************************************
%*									*
\subsubsection[CgRetConv-cgReturnDataCon]{Actually generate code for a constructor return}
%*									*
%************************************************************************


Note: it's the responsibility of the @cgReturnDataCon@ caller to be
sure the @amodes@ passed don't conflict with each other.
\begin{code}
cgReturnDataCon :: DataCon -> [CAddrMode] -> Code

cgReturnDataCon con amodes
  = ASSERT(length amodes == dataConRepArity con)
    getEndOfBlockInfo	`thenFC` \ (EndOfBlockInfo args_sp sequel) ->

    case sequel of

      CaseAlts _ (Just (alts, Just (maybe_deflt, (_,deflt_lbl))))
	| not (dataConTag con `is_elem` map fst alts)
	->
		-- Special case!  We're returning a constructor to the default case
		-- of an enclosing case.  For example:
		--
		--	case (case e of (a,b) -> C a b) of
		--	  D x -> ...
		--	  y   -> ...<returning here!>...
		--
		-- In this case,
		--	if the default is a non-bind-default (ie does not use y),
		--	then we should simply jump to the default join point;

		case maybe_deflt of
		    Nothing -> performReturn AbsCNop {- No reg assts -} jump_to_join_point
		    Just _  -> build_it_then jump_to_join_point
	where
	  is_elem = isIn "cgReturnDataCon"
	  jump_to_join_point sequel = absC (CJump (CLbl deflt_lbl CodePtrRep))
		-- Ignore the sequel: we've already looked at it above

	-- If the sequel is an update frame, we might be able to
	-- do update in place...
      UpdateCode
	|  not (isNullaryDataCon con)  -- no nullary constructors, please
	&& not (any isFollowableRep (map getAmodeRep amodes))
					-- no ptrs please (generational gc...)
	&& closureSize closure_info <= mIN_UPD_SIZE
					-- don't know the real size of the
					-- thunk, so assume mIN_UPD_SIZE

	-> 	-- get a new temporary and make it point to the updatee
	   let 
		uniq = getUnique con
	       	temp = CTemp uniq PtrRep 
	   in

	   profCtrC SLIT("TICK_UPD_CON_IN_PLACE") 
			[mkIntCLit (length amodes)] `thenC`

	   getSpRelOffset args_sp			`thenFC` \ sp_rel ->
	   absC (CAssign temp 
		    (CMacroExpr PtrRep UPD_FRAME_UPDATEE [CAddr sp_rel])) 
		`thenC`

	   	-- stomp all over it with the new constructor
	   inPlaceAllocDynClosure closure_info temp (CReg CurCostCentre) stuff 
		`thenC`

		-- don't forget to update Su from the update frame
	   absC (CMacroStmt UPDATE_SU_FROM_UPD_FRAME [CAddr sp_rel])  `thenC`

		-- set Node to point to the closure being returned
		-- (can't be done earlier: node might conflict with amodes)
	   absC (CAssign (CReg node) temp) `thenC`

	   	-- pop the update frame off the stack, and do the proper
	   	-- return.
	   let new_sp = args_sp - updateFrameSize in
	   setEndOfBlockInfo (EndOfBlockInfo new_sp (OnStack new_sp)) $
	   performReturn (AbsCNop) (mkStaticAlgReturnCode con)

	where (closure_info, stuff) 
		  = layOutDynClosure (dataConName con) 
			getAmodeRep amodes lf_info

	      lf_info = mkConLFInfo con

      other_sequel	-- The usual case

	  | isUnboxedTupleCon con ->
			-- Return unboxed tuple in registers
		  let (ret_regs, leftovers) = 
			 assignRegs [] (map getAmodeRep amodes)
		  in
		  profCtrC SLIT("TICK_RET_UNBOXED_TUP") 
				[mkIntCLit (length amodes)] `thenC`

		  doTailCall amodes ret_regs 
			mkUnboxedTupleReturnCode
			(length leftovers)  {- fast args arity -}
			AbsCNop {-no pending assigments-}
			Nothing {-not a let-no-escape-}
			False   {-node doesn't point-}
		
          | otherwise ->
		build_it_then (mkStaticAlgReturnCode con)

  where
    move_to_reg :: CAddrMode -> MagicId -> AbstractC
    move_to_reg src_amode dest_reg = CAssign (CReg dest_reg) src_amode

    build_it_then return =
		-- BUILD THE OBJECT IN THE HEAP
		-- The first "con" says that the name bound to this
		-- closure is "con", which is a bit of a fudge, but it only
		-- affects profiling

		-- This Id is also used to get a unique for a
		-- temporary variable, if the closure is a CHARLIKE.
		-- funnily enough, this makes the unique always come
		-- out as '54' :-)
	  buildDynCon (dataConId con) currentCCS con amodes	`thenFC` \ idinfo ->
	  idInfoToAmode PtrRep idinfo				`thenFC` \ amode ->


		-- RETURN
	  profCtrC SLIT("TICK_RET_NEW") [mkIntCLit (length amodes)] `thenC`
	  -- could use doTailCall here.
	  performReturn (move_to_reg amode node) return
\end{code}