path: root/compiler/codeGen/StgCmmLayout.hs

-----------------------------------------------------------------------------
--
-- Building info tables.
--
-- (c) The University of Glasgow 2004-2006
--
-----------------------------------------------------------------------------

{-# OPTIONS -fno-warn-tabs #-}
-- The above warning supression flag is a temporary kludge.
-- While working on this module you are encouraged to remove it and
-- detab the module (please do the detabbing in a separate patch). See
--     http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#TabsvsSpaces
-- for details

module StgCmmLayout (
	mkArgDescr, 
        emitCall, emitReturn, adjustHpBackwards,

	emitClosureProcAndInfoTable,
	emitClosureAndInfoTable,

	slowCall, directCall, 

	mkVirtHeapOffsets, mkVirtConstrOffsets, getHpRelOffset, hpRel,

        ArgRep(..), toArgRep, argRepSizeW -- re-exported from StgCmmArgRep
  ) where


#include "HsVersions.h"

import StgCmmClosure
import StgCmmEnv
import StgCmmArgRep -- notably: ( slowCallPattern )
import StgCmmTicky
import StgCmmMonad
import StgCmmUtils
import StgCmmProf

import MkGraph
import SMRep
import Cmm
import CmmUtils
import CmmInfo
import CLabel
import StgSyn
import Id
import Name
import TyCon		( PrimRep(..) )
import BasicTypes	( RepArity )
import DynFlags
import Module

import Util
import Data.List
import Outputable
import FastString
import Control.Monad

------------------------------------------------------------------------
--		Call and return sequences
------------------------------------------------------------------------

-- | Return multiple values to the sequel
--
-- If the sequel is @Return@
--
-- >     return (x,y)
--
-- If the sequel is @AssignTo [p,q]@
--
-- >    p=x; q=y;
--
emitReturn :: [CmmExpr] -> FCode ReturnKind
emitReturn results
  = do { dflags    <- getDynFlags
       ; sequel    <- getSequel
       ; updfr_off <- getUpdFrameOff
       ; case sequel of
           Return _ ->
             do { adjustHpBackwards
                ; let e = CmmLoad (CmmStackSlot Old updfr_off) (gcWord dflags)
                ; emit (mkReturn dflags (entryCode dflags e) results updfr_off)
                }
           AssignTo regs adjust ->
             do { when adjust adjustHpBackwards
                ; emitMultiAssign  regs results }
       ; return AssignedDirectly
       }


-- | @emitCall conv fun args@ makes a call to the entry-code of @fun@,
-- using the call/return convention @conv@, passing @args@, and
-- returning the results to the current sequel.
--
emitCall :: (Convention, Convention) -> CmmExpr -> [CmmExpr] -> FCode ReturnKind
emitCall convs fun args
  = emitCallWithExtraStack convs fun args noExtraStack


-- | @emitCallWithExtraStack conv fun args stack@ makes a call to the
-- entry-code of @fun@, using the call/return convention @conv@,
-- passing @args@, pushing some extra stack frames described by
-- @stack@, and returning the results to the current sequel.
--
emitCallWithExtraStack
   :: (Convention, Convention) -> CmmExpr -> [CmmExpr]
   -> [CmmExpr] -> FCode ReturnKind
emitCallWithExtraStack (callConv, retConv) fun args extra_stack
  = do	{ dflags <- getDynFlags
        ; adjustHpBackwards
	; sequel <- getSequel
	; updfr_off <- getUpdFrameOff
        ; case sequel of
            Return _ -> do
              emit $ mkJumpExtra dflags callConv fun args updfr_off extra_stack
              return AssignedDirectly
            AssignTo res_regs _ -> do
              k <- newLabelC
              let area = Young k
                  (off, _, copyin) = copyInOflow dflags retConv area res_regs []
                  copyout = mkCallReturnsTo dflags fun callConv args k off updfr_off
                                   extra_stack
              emit (copyout <*> mkLabel k <*> copyin)
              return (ReturnedTo k off)
      }


adjustHpBackwards :: FCode ()
-- This function adjusts and heap pointers just before a tail call or
-- return.  At a call or return, the virtual heap pointer may be less 
-- than the real Hp, because the latter was advanced to deal with 
-- the worst-case branch of the code, and we may be in a better-case 
-- branch.  In that case, move the real Hp *back* and retract some 
-- ticky allocation count.
--
-- It *does not* deal with high-water-mark adjustment.
-- That's done by functions which allocate heap.
adjustHpBackwards
  = do	{ hp_usg <- getHpUsage
	; let rHp = realHp hp_usg
	      vHp = virtHp hp_usg
	      adjust_words = vHp -rHp
	; new_hp <- getHpRelOffset vHp

	; emit (if adjust_words == 0
		then mkNop
		else mkAssign hpReg new_hp)	-- Generates nothing when vHp==rHp

	; tickyAllocHeap False adjust_words		-- ...ditto

	; setRealHp vHp
	}


-------------------------------------------------------------------------
--	Making calls: directCall and slowCall
-------------------------------------------------------------------------

-- General plan is:
--   - we'll make *one* fast call, either to the function itself
--     (directCall) or to stg_ap_<pat>_fast (slowCall)
--     Any left-over arguments will be pushed on the stack,
--
--     e.g. Sp[old+8]  = arg1
--          Sp[old+16] = arg2
--          Sp[old+32] = stg_ap_pp_info
--          R2 = arg3
--          R3 = arg4
--          call f() return to Nothing updfr_off: 32


directCall :: Convention -> CLabel -> RepArity -> [StgArg] -> FCode ReturnKind
-- (directCall f n args)
-- calls f(arg1, ..., argn), and applies the result to the remaining args
-- The function f has arity n, and there are guaranteed at least n args
-- Both arity and args include void args
directCall conv lbl arity stg_args
  = do  { argreps <- getArgRepsAmodes stg_args
        ; direct_call "directCall" conv lbl arity argreps }


slowCall :: CmmExpr -> [StgArg] -> FCode ReturnKind
-- (slowCall fun args) applies fun to args, returning the results to Sequel
slowCall fun stg_args 
  = do  { dflags <- getDynFlags
        ; argsreps <- getArgRepsAmodes stg_args
        ; let (rts_fun, arity) = slowCallPattern (map fst argsreps)
        ; r <- direct_call "slow_call" NativeNodeCall
                 (mkRtsApFastLabel rts_fun) arity ((P,Just fun):argsreps)
        ; emitComment $ mkFastString ("slow_call for " ++
                                      showSDoc dflags (ppr fun) ++
                                      " with pat " ++ unpackFS rts_fun)
        ; return r
        }


--------------
direct_call :: String
            -> Convention     -- e.g. NativeNodeCall or NativeDirectCall
            -> CLabel -> RepArity
            -> [(ArgRep,Maybe CmmExpr)] -> FCode ReturnKind
direct_call caller call_conv lbl arity args
  | debugIsOn && real_arity > length args  -- Too few args
  = do -- Caller should ensure that there enough args!
       pprPanic "direct_call" $
            text caller <+> ppr arity <+>
            ppr lbl <+> ppr (length args) <+>
            ppr (map snd args) <+> ppr (map fst args)

  | null rest_args  -- Precisely the right number of arguments
  = emitCall (call_conv, NativeReturn) target (nonVArgs args)

  | otherwise       -- Note [over-saturated calls]
  = do dflags <- getDynFlags
       emitCallWithExtraStack (call_conv, NativeReturn)
                              target
                              (nonVArgs fast_args)
                              (nonVArgs (stack_args dflags))
  where
    target = CmmLit (CmmLabel lbl)
    (fast_args, rest_args) = splitAt real_arity args
    stack_args dflags = slowArgs dflags rest_args
    real_arity = case call_conv of
                   NativeNodeCall -> arity+1
                   _              -> arity


-- When constructing calls, it is easier to keep the ArgReps and the
-- CmmExprs zipped together.  However, a void argument has no
-- representation, so we need to use Maybe CmmExpr (the alternative of
-- using zeroCLit or even undefined would work, but would be ugly).
--
getArgRepsAmodes :: [StgArg] -> FCode [(ArgRep, Maybe CmmExpr)]
getArgRepsAmodes = mapM getArgRepAmode
  where getArgRepAmode arg
           | V <- rep  = return (V, Nothing)
           | otherwise = do expr <- getArgAmode (NonVoid arg)
                            return (rep, Just expr)
           where rep = toArgRep (argPrimRep arg)

nonVArgs :: [(ArgRep, Maybe CmmExpr)] -> [CmmExpr]
nonVArgs [] = []
nonVArgs ((_,Nothing)  : args) = nonVArgs args
nonVArgs ((_,Just arg) : args) = arg : nonVArgs args

{-
Note [over-saturated calls]

The natural thing to do for an over-saturated call would be to call
the function with the correct number of arguments, and then apply the
remaining arguments to the value returned, e.g.

  f a b c d   (where f has arity 2)
  -->
  r = call f(a,b)
  call r(c,d)

but this entails
  - saving c and d on the stack
  - making a continuation info table
  - at the continuation, loading c and d off the stack into regs
  - finally, call r

Note that since there are a fixed number of different r's
(e.g.  stg_ap_pp_fast), we can also pre-compile continuations
that correspond to each of them, rather than generating a fresh
one for each over-saturated call.

Not only does this generate much less code, it is faster too.  We will
generate something like:

Sp[old+16] = c
Sp[old+24] = d
Sp[old+32] = stg_ap_pp_info
call f(a,b) -- usual calling convention

For the purposes of the CmmCall node, we count this extra stack as
just more arguments that we are passing on the stack (cml_args).
-}

-- | 'slowArgs' takes a list of function arguments and prepares them for
-- pushing on the stack for "extra" arguments to a function which requires
-- fewer arguments than we currently have.
slowArgs :: DynFlags -> [(ArgRep, Maybe CmmExpr)] -> [(ArgRep, Maybe CmmExpr)]
slowArgs _ [] = []
slowArgs dflags args -- careful: reps contains voids (V), but args does not
  | gopt Opt_SccProfilingOn dflags
              = save_cccs ++ this_pat ++ slowArgs dflags rest_args
  | otherwise =              this_pat ++ slowArgs dflags rest_args
  where
    (arg_pat, n)            = slowCallPattern (map fst args)
    (call_args, rest_args)  = splitAt n args

    stg_ap_pat = mkCmmRetInfoLabel rtsPackageId arg_pat
    this_pat   = (N, Just (mkLblExpr stg_ap_pat)) : call_args
    save_cccs  = [(N, Just (mkLblExpr save_cccs_lbl)), (N, Just curCCS)]
    save_cccs_lbl = mkCmmRetInfoLabel rtsPackageId (fsLit "stg_restore_cccs")

-------------------------------------------------------------------------
----	Laying out objects on the heap and stack
-------------------------------------------------------------------------

-- The heap always grows upwards, so hpRel is easy
hpRel :: VirtualHpOffset 	-- virtual offset of Hp
      -> VirtualHpOffset 	-- virtual offset of The Thing
      -> WordOff		-- integer word offset
hpRel hp off = off - hp

getHpRelOffset :: VirtualHpOffset -> FCode CmmExpr
getHpRelOffset virtual_offset
  = do dflags <- getDynFlags
       hp_usg <- getHpUsage
       return (cmmRegOffW dflags hpReg (hpRel (realHp hp_usg) virtual_offset))

mkVirtHeapOffsets
  :: DynFlags
  -> Bool		-- True <=> is a thunk
  -> [(PrimRep,a)]	-- Things to make offsets for
  -> (WordOff,		-- _Total_ number of words allocated
      WordOff,		-- Number of words allocated for *pointers*
      [(NonVoid a, VirtualHpOffset)])

-- Things with their offsets from start of object in order of
-- increasing offset; BUT THIS MAY BE DIFFERENT TO INPUT ORDER
-- First in list gets lowest offset, which is initial offset + 1.
--
-- Void arguments are removed, so output list may be shorter than
-- input list
--
-- mkVirtHeapOffsets always returns boxed things with smaller offsets
-- than the unboxed things

mkVirtHeapOffsets dflags is_thunk things
  = let non_void_things		      = filterOut (isVoidRep . fst)  things
	(ptrs, non_ptrs)    	      = partition (isGcPtrRep . fst) non_void_things
    	(wds_of_ptrs, ptrs_w_offsets) = mapAccumL computeOffset 0 ptrs
	(tot_wds, non_ptrs_w_offsets) = mapAccumL computeOffset wds_of_ptrs non_ptrs
    in
    (tot_wds, wds_of_ptrs, ptrs_w_offsets ++ non_ptrs_w_offsets)
  where
    hdr_size | is_thunk   = thunkHdrSize dflags
             | otherwise  = fixedHdrSize dflags

    computeOffset wds_so_far (rep, thing)
      = (wds_so_far + argRepSizeW dflags (toArgRep rep), 
	 (NonVoid thing, hdr_size + wds_so_far))

mkVirtConstrOffsets :: DynFlags -> [(PrimRep,a)] -> (WordOff, WordOff, [(NonVoid a, VirtualHpOffset)])
-- Just like mkVirtHeapOffsets, but for constructors
mkVirtConstrOffsets dflags = mkVirtHeapOffsets dflags False


-------------------------------------------------------------------------
--
--	Making argument descriptors
--
--  An argument descriptor describes the layout of args on the stack,
--  both for 	* GC (stack-layout) purposes, and 
--		* saving/restoring registers when a heap-check fails
--
-- Void arguments aren't important, therefore (contrast constructSlowCall)
--
-------------------------------------------------------------------------

-- bring in ARG_P, ARG_N, etc.
#include "../includes/rts/storage/FunTypes.h"

mkArgDescr :: Name -> [Id] -> FCode ArgDescr
mkArgDescr _nm args
  = do dflags <- getDynFlags
       let arg_bits = argBits dflags arg_reps
           arg_reps = filter isNonV (map idArgRep args)
           -- Getting rid of voids eases matching of standard patterns
       case stdPattern arg_reps of
           Just spec_id -> return (ArgSpec spec_id)
           Nothing      -> return (ArgGen arg_bits)

argBits :: DynFlags -> [ArgRep] -> [Bool]	-- True for non-ptr, False for ptr
argBits _      []           = []
argBits dflags (P   : args) = False : argBits dflags args
argBits dflags (arg : args) = take (argRepSizeW dflags arg) (repeat True)
                    ++ argBits dflags args

----------------------
stdPattern :: [ArgRep] -> Maybe Int
stdPattern reps
  = case reps of
	[]    -> Just ARG_NONE	-- just void args, probably
	[N]   -> Just ARG_N
	[P]   -> Just ARG_P
	[F]   -> Just ARG_F
	[D]   -> Just ARG_D
	[L]   -> Just ARG_L
	[V16] -> Just ARG_V16

	[N,N] -> Just ARG_NN
	[N,P] -> Just ARG_NP
	[P,N] -> Just ARG_PN
	[P,P] -> Just ARG_PP

	[N,N,N] -> Just ARG_NNN
	[N,N,P] -> Just ARG_NNP
	[N,P,N] -> Just ARG_NPN
	[N,P,P] -> Just ARG_NPP
	[P,N,N] -> Just ARG_PNN
	[P,N,P] -> Just ARG_PNP
	[P,P,N] -> Just ARG_PPN
	[P,P,P] -> Just ARG_PPP

	[P,P,P,P]     -> Just ARG_PPPP
	[P,P,P,P,P]   -> Just ARG_PPPPP
	[P,P,P,P,P,P] -> Just ARG_PPPPPP
	
	_ -> Nothing

-------------------------------------------------------------------------
--
--	Generating the info table and code for a closure
--
-------------------------------------------------------------------------

-- Here we make an info table of type 'CmmInfo'.  The concrete
-- representation as a list of 'CmmAddr' is handled later
-- in the pipeline by 'cmmToRawCmm'.
-- When loading the free variables, a function closure pointer may be tagged,
-- so we must take it into account.

emitClosureProcAndInfoTable :: Bool                    -- top-level? 
                            -> Id                      -- name of the closure
                            -> LambdaFormInfo
                            -> CmmInfoTable
                            -> [NonVoid Id]            -- incoming arguments
                            -> ((Int, LocalReg, [LocalReg]) -> FCode ()) -- function body
                            -> FCode ()
emitClosureProcAndInfoTable top_lvl bndr lf_info info_tbl args body
 = do   { dflags <- getDynFlags
        -- Bind the binder itself, but only if it's not a top-level
        -- binding. We need non-top let-bindings to refer to the
        -- top-level binding, which this binding would incorrectly shadow.
        ; node <- if top_lvl then return $ idToReg dflags (NonVoid bndr)
                  else bindToReg (NonVoid bndr) lf_info
        ; let node_points = nodeMustPointToIt dflags lf_info
        ; arg_regs <- bindArgsToRegs args
        ; let args' = if node_points then (node : arg_regs) else arg_regs
              conv  = if nodeMustPointToIt dflags lf_info then NativeNodeCall
                                                          else NativeDirectCall
              (offset, _, _) = mkCallEntry dflags conv args' []
        ; emitClosureAndInfoTable info_tbl conv args' $ body (offset, node, arg_regs)
        }

-- Data constructors need closures, but not with all the argument handling
-- needed for functions. The shared part goes here.
emitClosureAndInfoTable ::
  CmmInfoTable -> Convention -> [LocalReg] -> FCode () -> FCode ()
emitClosureAndInfoTable info_tbl conv args body
  = do { blks <- getCode body
       ; let entry_lbl = toEntryLbl (cit_lbl info_tbl)
       ; emitProcWithConvention conv (Just info_tbl) entry_lbl args blks
       }