----------------------------------------------------------------------------- -- -- Stg to C-- code generation: bindings -- -- (c) The University of Glasgow 2004-2006 -- ----------------------------------------------------------------------------- module StgCmmBind ( cgTopRhsClosure, cgBind, emitBlackHoleCode, pushUpdateFrame ) where #include "HsVersions.h" import StgCmmExpr import StgCmmMonad import StgCmmEnv import StgCmmCon import StgCmmHeap import StgCmmProf import StgCmmTicky import StgCmmGran import StgCmmLayout import StgCmmUtils import StgCmmClosure import MkZipCfgCmm import CoreSyn ( AltCon(..) ) import SMRep import Cmm import CmmUtils import CLabel import StgSyn import CostCentre import Id import Control.Monad import Name import Module import ListSetOps import Util import BasicTypes import Constants import Outputable import FastString import Maybes ------------------------------------------------------------------------ -- Top-level bindings ------------------------------------------------------------------------ -- For closures bound at top level, allocate in static space. -- They should have no free variables. cgTopRhsClosure :: Id -> CostCentreStack -- Optional cost centre annotation -> StgBinderInfo -> UpdateFlag -> SRT -> [Id] -- Args -> StgExpr -> FCode CgIdInfo cgTopRhsClosure id ccs _ upd_flag srt args body = do { -- LAY OUT THE OBJECT let name = idName id ; lf_info <- mkClosureLFInfo id TopLevel [] upd_flag args ; srt_info <- getSRTInfo srt ; mod_name <- getModuleName ; let descr = closureDescription mod_name name closure_info = mkClosureInfo True id lf_info 0 0 srt_info descr closure_label = mkLocalClosureLabel name (idCafInfo id) cg_id_info = litIdInfo id lf_info (CmmLabel closure_label) closure_rep = mkStaticClosureFields closure_info ccs True [] -- BUILD THE OBJECT, AND GENERATE INFO TABLE (IF NECESSARY) ; emitDataLits closure_label closure_rep ; let fv_details :: [(NonVoid Id, VirtualHpOffset)] (_, _, fv_details) = mkVirtHeapOffsets (isLFThunk lf_info) (addIdReps []) -- Don't drop the non-void args until the closure info has been made ; forkClosureBody (closureCodeBody True id closure_info ccs (nonVoidIds args) (length args) body fv_details) ; returnFC cg_id_info } ------------------------------------------------------------------------ -- Non-top-level bindings ------------------------------------------------------------------------ cgBind :: StgBinding -> FCode () cgBind (StgNonRec name rhs) = do { ((info, init), body) <- getCodeR $ cgRhs name rhs ; addBindC (cg_id info) info ; emit (init <*> body) } cgBind (StgRec pairs) = do { ((new_binds, inits), body) <- getCodeR $ fixC (\ new_binds_inits -> do { addBindsC $ fst new_binds_inits -- avoid premature deconstruction ; liftM unzip $ listFCs [ cgRhs b e | (b,e) <- pairs ] }) ; addBindsC new_binds ; emit (catAGraphs inits <*> body) } {- Recursive let-bindings are tricky. Consider the following pseudocode: let x = \_ -> ... y ... y = \_ -> ... z ... z = \_ -> ... x ... in ... For each binding, we need to allocate a closure, and each closure must capture the address of the other closures. We want to generate the following C-- code: // Initialization Code x = hp - 24; // heap address of x's closure y = hp - 40; // heap address of x's closure z = hp - 64; // heap address of x's closure // allocate and initialize x m[hp-8] = ... m[hp-16] = y // the closure for x captures y m[hp-24] = x_info; // allocate and initialize y m[hp-32] = z; // the closure for y captures z m[hp-40] = y_info; // allocate and initialize z ... For each closure, we must generate not only the code to allocate and initialize the closure itself, but also some Initialization Code that sets a variable holding the closure pointer. The complication here is that we don't know the heap offsets a priori, which has two consequences: 1. we need a fixpoint 2. we can't trivially separate the Initialization Code from the code that compiles the right-hand-sides Note: We don't need this complication with let-no-escapes, because in that case, the names are bound to labels in the environment, and we don't need to emit any code to witness that binding. -} -------------------- cgRhs :: Id -> StgRhs -> FCode (CgIdInfo, CmmAGraph) -- The Id is passed along so a binding can be set up -- The returned values are the binding for the environment -- and the Initialization Code that witnesses the binding cgRhs name (StgRhsCon maybe_cc con args) = buildDynCon name maybe_cc con args cgRhs name (StgRhsClosure cc bi fvs upd_flag srt args body) = mkRhsClosure name cc bi (nonVoidIds fvs) upd_flag srt args body ------------------------------------------------------------------------ -- Non-constructor right hand sides ------------------------------------------------------------------------ mkRhsClosure :: Id -> CostCentreStack -> StgBinderInfo -> [NonVoid Id] -- Free vars -> UpdateFlag -> SRT -> [Id] -- Args -> StgExpr -> FCode (CgIdInfo, CmmAGraph) {- mkRhsClosure looks for two special forms of the right-hand side: a) selector thunks b) AP thunks If neither happens, it just calls mkClosureLFInfo. You might think that mkClosureLFInfo should do all this, but it seems wrong for the latter to look at the structure of an expression Note [Selectors] ~~~~~~~~~~~~~~~~ We look at the body of the closure to see if it's a selector---turgid, but nothing deep. We are looking for a closure of {\em exactly} the form: ... = [the_fv] \ u [] -> case the_fv of con a_1 ... a_n -> a_i Note [Ap thunks] ~~~~~~~~~~~~~~~~ A more generic AP thunk of the form x = [ x_1...x_n ] \.. [] -> x_1 ... x_n A set of these is compiled statically into the RTS, so we just use those. We could extend the idea to thunks where some of the x_i are global ids (and hence not free variables), but this would entail generating a larger thunk. It might be an option for non-optimising compilation, though. We only generate an Ap thunk if all the free variables are pointers, for semi-obvious reasons. -} ---------- Note [Selectors] ------------------ mkRhsClosure bndr cc bi [NonVoid the_fv] -- Just one free var upd_flag -- Updatable thunk _srt [] -- A thunk body@(StgCase (StgApp scrutinee [{-no args-}]) _ _ _ _ -- ignore uniq, etc. (AlgAlt _) [(DataAlt con, params, _use_mask, (StgApp selectee [{-no args-}]))]) | the_fv == scrutinee -- Scrutinee is the only free variable && maybeToBool maybe_offset -- Selectee is a component of the tuple && offset_into_int <= mAX_SPEC_SELECTEE_SIZE -- Offset is small enough = -- NOT TRUE: ASSERT(is_single_constructor) -- The simplifier may have statically determined that the single alternative -- is the only possible case and eliminated the others, even if there are -- other constructors in the datatype. It's still ok to make a selector -- thunk in this case, because we *know* which constructor the scrutinee -- will evaluate to. -- -- srt is discarded; it must be empty cgStdThunk bndr cc bi body lf_info [StgVarArg the_fv] where lf_info = mkSelectorLFInfo bndr offset_into_int (isUpdatable upd_flag) (_, params_w_offsets) = layOutDynConstr con (addIdReps params) -- Just want the layout maybe_offset = assocMaybe params_w_offsets (NonVoid selectee) Just the_offset = maybe_offset offset_into_int = the_offset - fixedHdrSize ---------- Note [Ap thunks] ------------------ mkRhsClosure bndr cc bi fvs upd_flag _srt [] -- No args; a thunk body@(StgApp fun_id args) | args `lengthIs` (arity-1) && all isFollowableArg (map (idCgRep . stripNV) fvs) && isUpdatable upd_flag && arity <= mAX_SPEC_AP_SIZE -- Ha! an Ap thunk = cgStdThunk bndr cc bi body lf_info payload where lf_info = mkApLFInfo bndr upd_flag arity -- the payload has to be in the correct order, hence we can't -- just use the fvs. payload = StgVarArg fun_id : args arity = length fvs ---------- Default case ------------------ mkRhsClosure bndr cc _ fvs upd_flag srt args body = do { -- LAY OUT THE OBJECT -- If the binder is itself a free variable, then don't store -- it in the closure. Instead, just bind it to Node on entry. -- NB we can be sure that Node will point to it, because we -- haven't told mkClosureLFInfo about this; so if the binder -- _was_ a free var of its RHS, mkClosureLFInfo thinks it *is* -- stored in the closure itself, so it will make sure that -- Node points to it... ; let is_elem = isIn "cgRhsClosure" bndr_is_a_fv = (NonVoid bndr) `is_elem` fvs reduced_fvs | bndr_is_a_fv = fvs `minusList` [NonVoid bndr] | otherwise = fvs -- MAKE CLOSURE INFO FOR THIS CLOSURE ; lf_info <- mkClosureLFInfo bndr NotTopLevel fvs upd_flag args ; mod_name <- getModuleName ; c_srt <- getSRTInfo srt ; let name = idName bndr descr = closureDescription mod_name name fv_details :: [(NonVoid Id, VirtualHpOffset)] (tot_wds, ptr_wds, fv_details) = mkVirtHeapOffsets (isLFThunk lf_info) (addIdReps (map stripNV reduced_fvs)) closure_info = mkClosureInfo False -- Not static bndr lf_info tot_wds ptr_wds c_srt descr -- BUILD ITS INFO TABLE AND CODE ; forkClosureBody $ -- forkClosureBody: (a) ensure that bindings in here are not seen elsewhere -- (b) ignore Sequel from context; use empty Sequel -- And compile the body closureCodeBody False bndr closure_info cc (nonVoidIds args) (length args) body fv_details -- BUILD THE OBJECT ; (use_cc, blame_cc) <- chooseDynCostCentres cc args body ; emit (mkComment $ mkFastString "calling allocDynClosure") ; let toVarArg (NonVoid a, off) = (NonVoid (StgVarArg a), off) ; (tmp, init) <- allocDynClosure closure_info use_cc blame_cc (map toVarArg fv_details) -- RETURN ; return $ (regIdInfo bndr lf_info tmp, init) } -- Use with care; if used inappropriately, it could break invariants. stripNV :: NonVoid a -> a stripNV (NonVoid a) = a ------------------------- cgStdThunk :: Id -> CostCentreStack -- Optional cost centre annotation -> StgBinderInfo -- XXX: not used?? -> StgExpr -> LambdaFormInfo -> [StgArg] -- payload -> FCode (CgIdInfo, CmmAGraph) cgStdThunk bndr cc _bndr_info body lf_info payload = do -- AHA! A STANDARD-FORM THUNK { -- LAY OUT THE OBJECT mod_name <- getModuleName ; let (tot_wds, ptr_wds, payload_w_offsets) = mkVirtHeapOffsets (isLFThunk lf_info) (addArgReps payload) descr = closureDescription mod_name (idName bndr) closure_info = mkClosureInfo False -- Not static bndr lf_info tot_wds ptr_wds NoC_SRT -- No SRT for a std-form closure descr ; (use_cc, blame_cc) <- chooseDynCostCentres cc [{- no args-}] body -- BUILD THE OBJECT ; (tmp, init) <- allocDynClosure closure_info use_cc blame_cc payload_w_offsets -- RETURN ; returnFC $ (regIdInfo bndr lf_info tmp, init) } mkClosureLFInfo :: Id -- The binder -> TopLevelFlag -- True of top level -> [NonVoid Id] -- Free vars -> UpdateFlag -- Update flag -> [Id] -- Args -> FCode LambdaFormInfo mkClosureLFInfo bndr top fvs upd_flag args | null args = return (mkLFThunk (idType bndr) top (map stripNV fvs) upd_flag) | otherwise = do { arg_descr <- mkArgDescr (idName bndr) args ; return (mkLFReEntrant top (map stripNV fvs) args arg_descr) } ------------------------------------------------------------------------ -- The code for closures} ------------------------------------------------------------------------ closureCodeBody :: Bool -- whether this is a top-level binding -> Id -- the closure's name -> ClosureInfo -- Lots of information about this closure -> CostCentreStack -- Optional cost centre attached to closure -> [NonVoid Id] -- incoming args to the closure -> Int -- arity, including void args -> StgExpr -> [(NonVoid Id, VirtualHpOffset)] -- the closure's free variables -> FCode () {- There are two main cases for the code for closures. * If there are *no arguments*, then the closure is a thunk, and not in normal form. So it should set up an update frame (if it is shared). NB: Thunks cannot have a primitive type! * If there is *at least one* argument, then this closure is in normal form, so there is no need to set up an update frame. The Macros for GrAnSim are produced at the beginning of the argSatisfactionCheck (by calling fetchAndReschedule). There info if Node points to closure is available. -- HWL -} closureCodeBody top_lvl bndr cl_info cc args arity body fv_details | length args == 0 -- No args i.e. thunk = emitClosureProcAndInfoTable top_lvl bndr cl_info [] $ (\ (node, _) -> thunkCode cl_info fv_details cc node arity body) closureCodeBody top_lvl bndr cl_info cc args arity body fv_details = ASSERT( length args > 0 ) do { -- Allocate the global ticky counter, -- and establish the ticky-counter -- label for this block let ticky_ctr_lbl = mkRednCountsLabel (closureName cl_info) $ clHasCafRefs cl_info ; emitTickyCounter cl_info (map stripNV args) ; setTickyCtrLabel ticky_ctr_lbl $ do -- Emit the main entry code ; emitClosureProcAndInfoTable top_lvl bndr cl_info args $ \(node, arg_regs) -> do -- Emit the slow-entry code (for entering a closure through a PAP) { mkSlowEntryCode cl_info arg_regs ; let lf_info = closureLFInfo cl_info node_points = nodeMustPointToIt lf_info ; tickyEnterFun cl_info ; whenC node_points (ldvEnterClosure cl_info) ; granYield arg_regs node_points -- Main payload ; entryHeapCheck (if node_points then Just node else Nothing) arity arg_regs $ do { enterCostCentre cl_info cc body ; fv_bindings <- mapM bind_fv fv_details -- Load free vars out of closure *after* ; if node_points then load_fvs node lf_info fv_bindings else return () ; cgExpr body }} -- heap check, to reduce live vars over check } -- A function closure pointer may be tagged, so we -- must take it into account when accessing the free variables. bind_fv :: (NonVoid Id, VirtualHpOffset) -> FCode (LocalReg, WordOff) bind_fv (id, off) = do { reg <- rebindToReg id; return (reg, off) } load_fvs :: LocalReg -> LambdaFormInfo -> [(LocalReg, WordOff)] -> FCode () load_fvs node lf_info = mapCs (\ (reg, off) -> emit $ mkTaggedObjectLoad reg node off tag) where tag = lfDynTag lf_info ----------------------------------------- -- The "slow entry" code for a function. This entry point takes its -- arguments on the stack. It loads the arguments into registers -- according to the calling convention, and jumps to the function's -- normal entry point. The function's closure is assumed to be in -- R1/node. -- -- The slow entry point is used for unknown calls: eg. stg_PAP_entry mkSlowEntryCode :: ClosureInfo -> [LocalReg] -> FCode () -- If this function doesn't have a specialised ArgDescr, we need -- to generate the function's arg bitmap and slow-entry code. -- Here, we emit the slow-entry code. mkSlowEntryCode cl_info (_ : arg_regs) -- first arg should already be in `Node' | Just (_, ArgGen _) <- closureFunInfo cl_info = emitProcWithConvention Slow (CmmInfo Nothing Nothing CmmNonInfoTable) slow_lbl arg_regs jump | otherwise = return () where caf_refs = clHasCafRefs cl_info name = closureName cl_info slow_lbl = mkSlowEntryLabel name caf_refs fast_lbl = enterLocalIdLabel name caf_refs jump = mkJump (mkLblExpr fast_lbl) (map (CmmReg . CmmLocal) arg_regs) initUpdFrameOff mkSlowEntryCode _ [] = panic "entering a closure with no arguments?" ----------------------------------------- thunkCode :: ClosureInfo -> [(NonVoid Id, VirtualHpOffset)] -> CostCentreStack -> LocalReg -> Int -> StgExpr -> FCode () thunkCode cl_info fv_details cc node arity body = do { let node_points = nodeMustPointToIt (closureLFInfo cl_info) ; tickyEnterThunk cl_info ; ldvEnterClosure cl_info -- NB: Node always points when profiling ; granThunk node_points -- Heap overflow check ; entryHeapCheck (if node_points then Just node else Nothing) arity [] $ do { -- Overwrite with black hole if necessary -- but *after* the heap-overflow check dflags <- getDynFlags ; whenC (blackHoleOnEntry dflags cl_info && node_points) (blackHoleIt cl_info) -- Push update frame ; setupUpdate cl_info node $ -- We only enter cc after setting up update so -- that cc of enclosing scope will be recorded -- in update frame CAF/DICT functions will be -- subsumed by this enclosing cc do { enterCostCentre cl_info cc body ; let lf_info = closureLFInfo cl_info ; fv_bindings <- mapM bind_fv fv_details ; load_fvs node lf_info fv_bindings ; cgExpr body }}} ------------------------------------------------------------------------ -- Update and black-hole wrappers ------------------------------------------------------------------------ blackHoleIt :: ClosureInfo -> FCode () -- Only called for closures with no args -- Node points to the closure blackHoleIt closure_info = emitBlackHoleCode (closureSingleEntry closure_info) emitBlackHoleCode :: Bool -> FCode () emitBlackHoleCode is_single_entry | eager_blackholing = do tickyBlackHole (not is_single_entry) emit (mkStore (CmmReg nodeReg) (CmmLit (CmmLabel bh_lbl))) | otherwise = nopC where bh_lbl | is_single_entry = mkCmmDataLabel rtsPackageId (fsLit "stg_SE_BLACKHOLE_info") | otherwise = mkCmmDataLabel rtsPackageId (fsLit "stg_BLACKHOLE_info") -- If we wanted to do eager blackholing with slop filling, -- we'd need to do it at the *end* of a basic block, otherwise -- we overwrite the free variables in the thunk that we still -- need. We have a patch for this from Andy Cheadle, but not -- incorporated yet. --SDM [6/2004] -- -- Profiling needs slop filling (to support LDV profiling), so -- currently eager blackholing doesn't work with profiling. -- -- Previously, eager blackholing was enabled when ticky-ticky -- was on. But it didn't work, and it wasn't strictly necessary -- to bring back minimal ticky-ticky, so now EAGER_BLACKHOLING -- is unconditionally disabled. -- krc 1/2007 eager_blackholing = False setupUpdate :: ClosureInfo -> LocalReg -> FCode () -> FCode () -- Nota Bene: this function does not change Node (even if it's a CAF), -- so that the cost centre in the original closure can still be -- extracted by a subsequent enterCostCentre setupUpdate closure_info node body | closureReEntrant closure_info = body | not (isStaticClosure closure_info) = if closureUpdReqd closure_info then do { tickyPushUpdateFrame; ; pushUpdateFrame [CmmReg (CmmLocal node), mkLblExpr mkUpdInfoLabel] body } else do { tickyUpdateFrameOmitted; body} | otherwise -- A static closure = do { tickyUpdateBhCaf closure_info ; if closureUpdReqd closure_info then do -- Blackhole the (updatable) CAF: { upd_closure <- link_caf closure_info True ; pushUpdateFrame [CmmReg (CmmLocal upd_closure), mkLblExpr mkUpdInfoLabel] body } else do {tickyUpdateFrameOmitted; body} } -- Push the update frame on the stack in the Entry area, -- leaving room for the return address that is already -- at the old end of the area. pushUpdateFrame :: [CmmExpr] -> FCode () -> FCode () pushUpdateFrame es body = do updfr <- getUpdFrameOff offset <- foldM push updfr es withUpdFrameOff offset body where push off e = do emit (mkStore (CmmStackSlot (CallArea Old) base) e) return base where base = off + widthInBytes (cmmExprWidth e) ----------------------------------------------------------------------------- -- Entering a CAF -- -- When a CAF is first entered, it creates a black hole in the heap, -- and updates itself with an indirection to this new black hole. -- -- We update the CAF with an indirection to a newly-allocated black -- hole in the heap. We also set the blocking queue on the newly -- allocated black hole to be empty. -- -- Why do we make a black hole in the heap when we enter a CAF? -- -- - for a generational garbage collector, which needs a fast -- test for whether an updatee is in an old generation or not -- -- - for the parallel system, which can implement updates more -- easily if the updatee is always in the heap. (allegedly). -- -- When debugging, we maintain a separate CAF list so we can tell when -- a CAF has been garbage collected. -- newCAF must be called before the itbl ptr is overwritten, since -- newCAF records the old itbl ptr in order to do CAF reverting -- (which Hugs needs to do in order that combined mode works right.) -- -- ToDo [Feb 04] This entire link_caf nonsense could all be moved -- into the "newCAF" RTS procedure, which we call anyway, including -- the allocation of the black-hole indirection closure. -- That way, code size would fall, the CAF-handling code would -- be closer together, and the compiler wouldn't need to know -- about off_indirectee etc. link_caf :: ClosureInfo -> Bool -- True <=> updatable, False <=> single-entry -> FCode LocalReg -- Returns amode for closure to be updated -- To update a CAF we must allocate a black hole, link the CAF onto the -- CAF list, then update the CAF to point to the fresh black hole. -- This function returns the address of the black hole, so it can be -- updated with the new value when available. The reason for all of this -- is that we only want to update dynamic heap objects, not static ones, -- so that generational GC is easier. link_caf cl_info _is_upd = do { -- Alloc black hole specifying CC_HDR(Node) as the cost centre ; let use_cc = costCentreFrom (CmmReg nodeReg) blame_cc = use_cc ; (hp_rel, init) <- allocDynClosure bh_cl_info use_cc blame_cc [] ; emit init -- Call the RTS function newCAF to add the CAF to the CafList -- so that the garbage collector can find them -- This must be done *before* the info table pointer is overwritten, -- because the old info table ptr is needed for reversion ; emitRtsCallWithVols rtsPackageId (fsLit "newCAF") [ (CmmReg (CmmGlobal BaseReg), AddrHint), (CmmReg nodeReg, AddrHint) ] [node] False -- node is live, so save it. -- Overwrite the closure with a (static) indirection -- to the newly-allocated black hole ; emit (mkStore (cmmRegOffW nodeReg off_indirectee) (CmmReg (CmmLocal hp_rel)) <*> mkStore (CmmReg nodeReg) ind_static_info) ; return hp_rel } where bh_cl_info :: ClosureInfo bh_cl_info = cafBlackHoleClosureInfo cl_info ind_static_info :: CmmExpr ind_static_info = mkLblExpr mkIndStaticInfoLabel off_indirectee :: WordOff off_indirectee = fixedHdrSize + oFFSET_StgInd_indirectee*wORD_SIZE ------------------------------------------------------------------------ -- Profiling ------------------------------------------------------------------------ -- For "global" data constructors the description is simply occurrence -- name of the data constructor itself. Otherwise it is determined by -- @closureDescription@ from the let binding information. closureDescription :: Module -- Module -> Name -- Id of closure binding -> String -- Not called for StgRhsCon which have global info tables built in -- CgConTbls.lhs with a description generated from the data constructor closureDescription mod_name name = showSDocDump (char '<' <> (if isExternalName name then ppr name -- ppr will include the module name prefix else pprModule mod_name <> char '.' <> ppr name) <> char '>') -- showSDocDump, because we want to see the unique on the Name.