2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 % $Id: CgExpr.lhs,v 1.37 2000/11/07 13:12:22 simonpj Exp $
6 %********************************************************
8 \section[CgExpr]{Converting @StgExpr@s}
10 %********************************************************
13 module CgExpr ( cgExpr ) where
15 #include "HsVersions.h"
17 import Constants ( mAX_SPEC_SELECTEE_SIZE, mAX_SPEC_AP_SIZE )
21 import AbsCUtils ( mkAbstractCs )
22 import CLabel ( mkClosureTblLabel )
24 import SMRep ( fixedHdrSize )
25 import CgBindery ( getArgAmodes, getArgAmode, CgIdInfo,
26 nukeDeadBindings, addBindC, addBindsC )
27 import CgCase ( cgCase, saveVolatileVarsAndRegs,
28 restoreCurrentCostCentre )
29 import CgClosure ( cgRhsClosure, cgStdRhsClosure )
30 import CgCon ( buildDynCon, cgReturnDataCon )
31 import CgLetNoEscape ( cgLetNoEscapeClosure )
32 import CgRetConv ( dataReturnConvPrim )
33 import CgTailCall ( cgTailCall, performReturn, performPrimReturn,
34 mkDynamicAlgReturnCode, mkPrimReturnCode,
35 tailCallPrimOp, returnUnboxedTuple
37 import ClosureInfo ( mkClosureLFInfo, mkSelectorLFInfo,
38 mkApLFInfo, layOutDynCon )
39 import CostCentre ( sccAbleCostCentre, isSccCountCostCentre )
40 import Id ( idPrimRep, idType, Id )
42 import DataCon ( dataConTyCon )
43 import PrimOp ( primOpOutOfLine, getPrimOpResultInfo, PrimOp(..), PrimOpResultInfo(..) )
44 import PrimRep ( PrimRep(..), isFollowableRep )
45 import TyCon ( maybeTyConSingleCon,
46 isUnboxedTupleTyCon, isEnumerationTyCon )
47 import Type ( Type, typePrimRep, splitTyConApp_maybe, repType )
48 import Maybes ( maybeToBool )
49 import ListSetOps ( assocMaybe )
50 import Unique ( mkBuiltinUnique )
51 import BasicTypes ( TopLevelFlag(..), RecFlag(..) )
55 This module provides the support code for @StgToAbstractC@ to deal
56 with STG {\em expressions}. See also @CgClosure@, which deals
57 with closures, and @CgCon@, which deals with constructors.
60 cgExpr :: StgExpr -- input
64 %********************************************************
68 %********************************************************
70 ``Applications'' mean {\em tail calls}, a service provided by module
71 @CgTailCall@. This includes literals, which show up as
72 @(STGApp (StgLitArg 42) [])@.
75 cgExpr (StgApp fun args) = cgTailCall fun args
78 %********************************************************
80 %* STG ConApps (for inline versions) *
82 %********************************************************
85 cgExpr (StgConApp con args)
86 = getArgAmodes args `thenFC` \ amodes ->
87 cgReturnDataCon con amodes
90 Literals are similar to constructors; they return by putting
91 themselves in an appropriate register and returning to the address on
96 = performPrimReturn (text "literal" <+> ppr lit) (CLit lit)
100 %********************************************************
102 %* STG PrimApps (unboxed primitive ops) *
104 %********************************************************
106 Here is where we insert real live machine instructions.
108 NOTE about _ccall_GC_:
110 A _ccall_GC_ is treated as an out-of-line primop (returns True
111 for primOpOutOfLine) so that when we see the call in case context
112 case (ccall ...) of { ... }
113 we get a proper stack frame on the stack when we perform it. When we
114 get in a tail-call position, however, we need to actually perform the
115 call, so we treat it as an inline primop.
118 cgExpr (StgPrimApp op@(CCallOp ccall) args res_ty)
119 = primRetUnboxedTuple op args res_ty
121 -- tagToEnum# is special: we need to pull the constructor out of the table,
122 -- and perform an appropriate return.
124 cgExpr (StgPrimApp TagToEnumOp [arg] res_ty)
125 = ASSERT(isEnumerationTyCon tycon)
126 getArgAmode arg `thenFC` \amode ->
127 -- save the tag in a temporary in case amode overlaps
129 absC (CAssign dyn_tag amode) `thenC`
133 (CLbl (mkClosureTblLabel tycon) PtrRep)
134 dyn_tag PtrRep) PtrRep))
135 (\ sequel -> mkDynamicAlgReturnCode tycon dyn_tag sequel)
137 dyn_tag = CTemp (mkBuiltinUnique 0) IntRep
139 -- if you're reading this code in the attempt to figure
140 -- out why the compiler panic'ed here, it is probably because
141 -- you used tagToEnum# in a non-monomorphic setting, e.g.,
142 -- intToTg :: Enum a => Int -> a ; intToTg (I# x#) = tagToEnum# x#
146 (Just (tycon,_)) = splitTyConApp_maybe res_ty
149 cgExpr x@(StgPrimApp op args res_ty)
150 | primOpOutOfLine op = tailCallPrimOp op args
152 = ASSERT(op /= SeqOp) -- can't handle SeqOp
154 getArgAmodes args `thenFC` \ arg_amodes ->
156 case (getPrimOpResultInfo op) of
159 let result_amode = CReg (dataReturnConvPrim kind) in
161 (COpStmt [result_amode] op arg_amodes [{-no vol_regs-}])
162 (mkPrimReturnCode (text "primapp)" <+> ppr x))
164 -- otherwise, must be returning an enumerated type (eg. Bool).
165 -- we've only got the tag in R2, so we have to load the constructor
169 | isUnboxedTupleTyCon tycon -> primRetUnboxedTuple op args res_ty
171 | isEnumerationTyCon tycon ->
173 (COpStmt [dyn_tag] op arg_amodes [{-no vol_regs-}])
175 absC (CAssign (CReg node) closure_lbl) `thenC`
176 mkDynamicAlgReturnCode tycon dyn_tag sequel)
179 -- Pull a unique out of thin air to put the tag in.
180 -- It shouldn't matter if this overlaps with anything - we're
181 -- about to return anyway.
182 dyn_tag = CTemp (mkBuiltinUnique 0) IntRep
184 closure_lbl = CVal (CIndex
185 (CLbl (mkClosureTblLabel tycon) PtrRep)
186 dyn_tag PtrRep) PtrRep
190 %********************************************************
192 %* Case expressions *
194 %********************************************************
195 Case-expression conversion is complicated enough to have its own
199 cgExpr (StgCase expr live_vars save_vars bndr srt alts)
200 = cgCase expr live_vars save_vars bndr srt alts
204 %********************************************************
208 %********************************************************
209 \subsection[let-and-letrec-codegen]{Converting @StgLet@ and @StgLetrec@}
212 cgExpr (StgLet (StgNonRec name rhs) expr)
213 = cgRhs name rhs `thenFC` \ (name, info) ->
214 addBindC name info `thenC`
217 cgExpr (StgLet (StgRec pairs) expr)
218 = fixC (\ new_bindings -> addBindsC new_bindings `thenC`
219 listFCs [ cgRhs b e | (b,e) <- pairs ]
220 ) `thenFC` \ new_bindings ->
222 addBindsC new_bindings `thenC`
227 cgExpr (StgLetNoEscape live_in_whole_let live_in_rhss bindings body)
228 = -- Figure out what volatile variables to save
229 nukeDeadBindings live_in_whole_let `thenC`
230 saveVolatileVarsAndRegs live_in_rhss
231 `thenFC` \ (save_assts, rhs_eob_info, maybe_cc_slot) ->
232 -- ToDo: cost centre???
233 restoreCurrentCostCentre maybe_cc_slot `thenFC` \ restore_cc ->
235 -- Save those variables right now!
236 absC save_assts `thenC`
238 -- Produce code for the rhss
239 -- and add suitable bindings to the environment
240 cgLetNoEscapeBindings live_in_rhss rhs_eob_info maybe_cc_slot bindings `thenC`
243 setEndOfBlockInfo rhs_eob_info (cgExpr body)
247 %********************************************************
251 %********************************************************
253 SCC expressions are treated specially. They set the current cost
256 cgExpr (StgSCC cc expr)
257 = ASSERT(sccAbleCostCentre cc)
260 [mkCCostCentre cc, mkIntCLit (if isSccCountCostCentre cc then 1 else 0)]
265 ToDo: counting of dict sccs ...
267 %********************************************************
269 %* Non-top-level bindings *
271 %********************************************************
272 \subsection[non-top-level-bindings]{Converting non-top-level bindings}
274 We rely on the support code in @CgCon@ (to do constructors) and
275 in @CgClosure@ (to do closures).
278 cgRhs :: Id -> StgRhs -> FCode (Id, CgIdInfo)
279 -- the Id is passed along so a binding can be set up
281 cgRhs name (StgRhsCon maybe_cc con args)
282 = getArgAmodes args `thenFC` \ amodes ->
283 buildDynCon name maybe_cc con amodes `thenFC` \ idinfo ->
284 returnFC (name, idinfo)
286 cgRhs name (StgRhsClosure cc bi srt@(NoSRT) fvs upd_flag args body)
287 = mkRhsClosure name cc bi srt fvs upd_flag args body
288 cgRhs name (StgRhsClosure cc bi srt@(SRT _ _) fvs upd_flag args body)
289 = mkRhsClosure name cc bi srt fvs upd_flag args body
292 mkRhsClosure looks for two special forms of the right-hand side:
296 If neither happens, it just calls mkClosureLFInfo. You might think
297 that mkClosureLFInfo should do all this, but it seems wrong for the
298 latter to look at the structure of an expression
302 We look at the body of the closure to see if it's a selector---turgid,
303 but nothing deep. We are looking for a closure of {\em exactly} the
306 ... = [the_fv] \ u [] ->
308 con a_1 ... a_n -> a_i
312 mkRhsClosure bndr cc bi srt
313 [the_fv] -- Just one free var
314 upd_flag -- Updatable thunk
316 body@(StgCase (StgApp scrutinee [{-no args-}])
317 _ _ _ _ -- ignore uniq, etc.
319 [(con, params, use_mask,
320 (StgApp selectee [{-no args-}]))]
322 | the_fv == scrutinee -- Scrutinee is the only free variable
323 && maybeToBool maybe_offset -- Selectee is a component of the tuple
324 && offset_into_int <= mAX_SPEC_SELECTEE_SIZE -- Offset is small enough
325 = ASSERT(is_single_constructor)
326 cgStdRhsClosure bndr cc bi [the_fv] [] body lf_info [StgVarArg the_fv]
328 lf_info = mkSelectorLFInfo (idType bndr) offset_into_int
329 (isUpdatable upd_flag)
330 (_, params_w_offsets) = layOutDynCon con idPrimRep params
331 maybe_offset = assocMaybe params_w_offsets selectee
332 Just the_offset = maybe_offset
333 offset_into_int = the_offset - fixedHdrSize
334 is_single_constructor = maybeToBool (maybeTyConSingleCon tycon)
335 tycon = dataConTyCon con
342 A more generic AP thunk of the form
344 x = [ x_1...x_n ] \.. [] -> x_1 ... x_n
346 A set of these is compiled statically into the RTS, so we just use
347 those. We could extend the idea to thunks where some of the x_i are
348 global ids (and hence not free variables), but this would entail
349 generating a larger thunk. It might be an option for non-optimising
352 We only generate an Ap thunk if all the free variables are pointers,
353 for semi-obvious reasons.
356 mkRhsClosure bndr cc bi srt
359 [] -- No args; a thunk
360 body@(StgApp fun_id args)
362 | length args + 1 == arity
363 && all isFollowableRep (map idPrimRep fvs)
364 && isUpdatable upd_flag
365 && arity <= mAX_SPEC_AP_SIZE
368 = cgStdRhsClosure bndr cc bi fvs [] body lf_info payload
371 lf_info = mkApLFInfo (idType bndr) upd_flag arity
372 -- the payload has to be in the correct order, hence we can't
374 payload = StgVarArg fun_id : args
381 mkRhsClosure bndr cc bi srt fvs upd_flag args body
382 = getSRTLabel `thenFC` \ srt_label ->
384 mkClosureLFInfo bndr NotTopLevel fvs upd_flag args srt_label srt
386 cgRhsClosure bndr cc bi fvs args body lf_info
390 %********************************************************
392 %* Let-no-escape bindings
394 %********************************************************
396 cgLetNoEscapeBindings live_in_rhss rhs_eob_info maybe_cc_slot (StgNonRec binder rhs)
397 = cgLetNoEscapeRhs live_in_rhss rhs_eob_info maybe_cc_slot
398 NonRecursive binder rhs
399 `thenFC` \ (binder, info) ->
402 cgLetNoEscapeBindings live_in_rhss rhs_eob_info maybe_cc_slot (StgRec pairs)
403 = fixC (\ new_bindings ->
404 addBindsC new_bindings `thenC`
405 listFCs [ cgLetNoEscapeRhs full_live_in_rhss
406 rhs_eob_info maybe_cc_slot Recursive b e
408 ) `thenFC` \ new_bindings ->
410 addBindsC new_bindings
412 -- We add the binders to the live-in-rhss set so that we don't
413 -- delete the bindings for the binder from the environment!
414 full_live_in_rhss = live_in_rhss `unionVarSet` (mkVarSet [b | (b,r) <- pairs])
417 :: StgLiveVars -- Live in rhss
419 -> Maybe VirtualSpOffset
423 -> FCode (Id, CgIdInfo)
425 cgLetNoEscapeRhs full_live_in_rhss rhs_eob_info maybe_cc_slot rec binder
426 (StgRhsClosure cc bi srt _ upd_flag args body)
427 = -- We could check the update flag, but currently we don't switch it off
428 -- for let-no-escaped things, so we omit the check too!
430 -- Updatable -> panic "cgLetNoEscapeRhs" -- Nothing to update!
431 -- other -> cgLetNoEscapeClosure binder cc bi live_in_whole_let live_in_rhss args body
432 cgLetNoEscapeClosure binder cc bi srt full_live_in_rhss rhs_eob_info maybe_cc_slot rec args body
434 -- For a constructor RHS we want to generate a single chunk of code which
435 -- can be jumped to from many places, which will return the constructor.
436 -- It's easy; just behave as if it was an StgRhsClosure with a ConApp inside!
437 cgLetNoEscapeRhs full_live_in_rhss rhs_eob_info maybe_cc_slot rec binder
438 (StgRhsCon cc con args)
439 = cgLetNoEscapeClosure binder cc stgArgOcc{-safe-} NoSRT full_live_in_rhss rhs_eob_info maybe_cc_slot rec
440 [] --No args; the binder is data structure, not a function
444 Little helper for primitives that return unboxed tuples.
448 primRetUnboxedTuple :: PrimOp -> [StgArg] -> Type -> Code
449 primRetUnboxedTuple op args res_ty
450 = getArgAmodes args `thenFC` \ arg_amodes ->
452 put all the arguments in temporaries so they don't get stomped when
453 we push the return address.
457 arg_uniqs = map mkBuiltinUnique [0 .. n_args-1]
458 arg_reps = map getArgPrimRep args
459 arg_temps = zipWith CTemp arg_uniqs arg_reps
461 absC (mkAbstractCs (zipWith CAssign arg_temps arg_amodes)) `thenC`
463 allocate some temporaries for the return values.
466 (tc,ty_args) = case splitTyConApp_maybe (repType res_ty) of
467 Nothing -> pprPanic "primRetUnboxedTuple" (ppr res_ty)
469 prim_reps = map typePrimRep ty_args
470 temp_uniqs = map mkBuiltinUnique [ n_args .. n_args + length ty_args - 1]
471 temp_amodes = zipWith CTemp temp_uniqs prim_reps
473 returnUnboxedTuple temp_amodes (absC (COpStmt temp_amodes op arg_temps []))