2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 % $Id: CgExpr.lhs,v 1.47 2001/11/19 16:34:12 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, layOutDynConstr )
39 import CostCentre ( sccAbleCostCentre, isSccCountCostCentre )
40 import Id ( idPrimRep, idType, Id )
42 import PrimOp ( primOpOutOfLine, getPrimOpResultInfo, PrimOp(..), PrimOpResultInfo(..) )
43 import PrimRep ( PrimRep(..), isFollowableRep )
44 import TyCon ( isUnboxedTupleTyCon, isEnumerationTyCon )
45 import Type ( Type, typePrimRep, tyConAppArgs, tyConAppTyCon, repType )
46 import Maybes ( maybeToBool )
47 import ListSetOps ( assocMaybe )
48 import Unique ( mkBuiltinUnique )
49 import BasicTypes ( TopLevelFlag(..), RecFlag(..) )
50 import Util ( lengthIs )
54 This module provides the support code for @StgToAbstractC@ to deal
55 with STG {\em expressions}. See also @CgClosure@, which deals
56 with closures, and @CgCon@, which deals with constructors.
59 cgExpr :: StgExpr -- input
63 %********************************************************
67 %********************************************************
69 ``Applications'' mean {\em tail calls}, a service provided by module
70 @CgTailCall@. This includes literals, which show up as
71 @(STGApp (StgLitArg 42) [])@.
74 cgExpr (StgApp fun args) = cgTailCall fun args
77 %********************************************************
79 %* STG ConApps (for inline versions) *
81 %********************************************************
84 cgExpr (StgConApp con args)
85 = getArgAmodes args `thenFC` \ amodes ->
86 cgReturnDataCon con amodes
89 Literals are similar to constructors; they return by putting
90 themselves in an appropriate register and returning to the address on
95 = performPrimReturn (text "literal" <+> ppr lit) (CLit lit)
99 %********************************************************
101 %* STG PrimApps (unboxed primitive ops) *
103 %********************************************************
105 Here is where we insert real live machine instructions.
107 NOTE about _ccall_GC_:
109 A _ccall_GC_ is treated as an out-of-line primop (returns True
110 for primOpOutOfLine) so that when we see the call in case context
111 case (ccall ...) of { ... }
112 we get a proper stack frame on the stack when we perform it. When we
113 get in a tail-call position, however, we need to actually perform the
114 call, so we treat it as an inline primop.
117 cgExpr (StgOpApp op@(StgFCallOp _ _) args res_ty)
118 = primRetUnboxedTuple op args res_ty
120 -- tagToEnum# is special: we need to pull the constructor out of the table,
121 -- and perform an appropriate return.
123 cgExpr (StgOpApp (StgPrimOp TagToEnumOp) [arg] res_ty)
124 = ASSERT(isEnumerationTyCon tycon)
125 getArgAmode arg `thenFC` \amode ->
126 -- save the tag in a temporary in case amode overlaps
128 absC (CAssign dyn_tag amode) `thenC`
132 (CLbl (mkClosureTblLabel tycon) PtrRep)
133 dyn_tag PtrRep) PtrRep))
134 (\ sequel -> mkDynamicAlgReturnCode tycon dyn_tag sequel)
136 dyn_tag = CTemp (mkBuiltinUnique 0) IntRep
138 -- if you're reading this code in the attempt to figure
139 -- out why the compiler panic'ed here, it is probably because
140 -- you used tagToEnum# in a non-monomorphic setting, e.g.,
141 -- intToTg :: Enum a => Int -> a ; intToTg (I# x#) = tagToEnum# x#
145 tycon = tyConAppTyCon res_ty
148 cgExpr x@(StgOpApp op@(StgPrimOp primop) args res_ty)
149 | primOpOutOfLine primop
150 = tailCallPrimOp primop args
153 = ASSERT(primop /= SeqOp) -- can't handle SeqOp
155 getArgAmodes args `thenFC` \ arg_amodes ->
157 case (getPrimOpResultInfo primop) of
160 let result_amode = CReg (dataReturnConvPrim kind) in
162 (COpStmt [result_amode] op arg_amodes [{-no vol_regs-}])
163 (mkPrimReturnCode (text "primapp)" <+> ppr x))
165 -- otherwise, must be returning an enumerated type (eg. Bool).
166 -- we've only got the tag in R2, so we have to load the constructor
170 | isUnboxedTupleTyCon tycon -> primRetUnboxedTuple op args res_ty
172 | isEnumerationTyCon tycon ->
174 (COpStmt [dyn_tag] op arg_amodes [{-no vol_regs-}])
176 absC (CAssign (CReg node) closure_lbl) `thenC`
177 mkDynamicAlgReturnCode tycon dyn_tag sequel)
180 -- Pull a unique out of thin air to put the tag in.
181 -- It shouldn't matter if this overlaps with anything - we're
182 -- about to return anyway.
183 dyn_tag = CTemp (mkBuiltinUnique 0) IntRep
185 closure_lbl = CVal (CIndex
186 (CLbl (mkClosureTblLabel tycon) PtrRep)
187 dyn_tag PtrRep) PtrRep
191 %********************************************************
193 %* Case expressions *
195 %********************************************************
196 Case-expression conversion is complicated enough to have its own
200 cgExpr (StgCase expr live_vars save_vars bndr srt alts)
201 = cgCase expr live_vars save_vars bndr srt alts
205 %********************************************************
209 %********************************************************
210 \subsection[let-and-letrec-codegen]{Converting @StgLet@ and @StgLetrec@}
213 cgExpr (StgLet (StgNonRec srt name rhs) expr)
214 = cgRhs srt name rhs `thenFC` \ (name, info) ->
215 addBindC name info `thenC`
218 cgExpr (StgLet (StgRec srt pairs) expr)
219 = fixC (\ new_bindings -> addBindsC new_bindings `thenC`
220 listFCs [ cgRhs srt b e | (b,e) <- pairs ]
221 ) `thenFC` \ new_bindings ->
223 addBindsC new_bindings `thenC`
228 cgExpr (StgLetNoEscape live_in_whole_let live_in_rhss bindings body)
229 = -- Figure out what volatile variables to save
230 nukeDeadBindings live_in_whole_let `thenC`
231 saveVolatileVarsAndRegs live_in_rhss
232 `thenFC` \ (save_assts, rhs_eob_info, maybe_cc_slot) ->
233 -- ToDo: cost centre???
234 restoreCurrentCostCentre maybe_cc_slot `thenFC` \ restore_cc ->
236 -- Save those variables right now!
237 absC save_assts `thenC`
239 -- Produce code for the rhss
240 -- and add suitable bindings to the environment
241 cgLetNoEscapeBindings live_in_rhss rhs_eob_info maybe_cc_slot bindings `thenC`
244 setEndOfBlockInfo rhs_eob_info (cgExpr body)
248 %********************************************************
252 %********************************************************
254 SCC expressions are treated specially. They set the current cost
257 cgExpr (StgSCC cc expr)
258 = ASSERT(sccAbleCostCentre cc)
261 [mkCCostCentre cc, mkIntCLit (if isSccCountCostCentre cc then 1 else 0)]
266 ToDo: counting of dict sccs ...
268 %********************************************************
270 %* Non-top-level bindings *
272 %********************************************************
273 \subsection[non-top-level-bindings]{Converting non-top-level bindings}
275 We rely on the support code in @CgCon@ (to do constructors) and
276 in @CgClosure@ (to do closures).
279 cgRhs :: SRT -> Id -> StgRhs -> FCode (Id, CgIdInfo)
280 -- the Id is passed along so a binding can be set up
282 cgRhs srt name (StgRhsCon maybe_cc con args)
283 = getArgAmodes args `thenFC` \ amodes ->
284 buildDynCon name maybe_cc con amodes `thenFC` \ idinfo ->
285 returnFC (name, idinfo)
287 cgRhs srt name (StgRhsClosure cc bi fvs upd_flag args body)
288 = mkRhsClosure name cc bi srt fvs upd_flag args body
291 mkRhsClosure looks for two special forms of the right-hand side:
295 If neither happens, it just calls mkClosureLFInfo. You might think
296 that mkClosureLFInfo should do all this, but it seems wrong for the
297 latter to look at the structure of an expression
301 We look at the body of the closure to see if it's a selector---turgid,
302 but nothing deep. We are looking for a closure of {\em exactly} the
305 ... = [the_fv] \ u [] ->
307 con a_1 ... a_n -> a_i
311 mkRhsClosure bndr cc bi srt
312 [the_fv] -- Just one free var
313 upd_flag -- Updatable thunk
315 body@(StgCase (StgApp scrutinee [{-no args-}])
316 _ _ _ _ -- ignore uniq, etc.
317 (StgAlgAlts (Just tycon)
318 [(con, params, use_mask,
319 (StgApp selectee [{-no args-}]))]
321 | the_fv == scrutinee -- Scrutinee is the only free variable
322 && maybeToBool maybe_offset -- Selectee is a component of the tuple
323 && offset_into_int <= mAX_SPEC_SELECTEE_SIZE -- Offset is small enough
324 = -- NOT TRUE: ASSERT(is_single_constructor)
325 -- The simplifier may have statically determined that the single alternative
326 -- is the only possible case and eliminated the others, even if there are
327 -- other constructors in the datatype. It's still ok to make a selector
328 -- thunk in this case, because we *know* which constructor the scrutinee
330 cgStdRhsClosure bndr cc bi [the_fv] [] body lf_info [StgVarArg the_fv]
332 lf_info = mkSelectorLFInfo (idType bndr) offset_into_int
333 (isUpdatable upd_flag)
334 (_, params_w_offsets) = layOutDynConstr bogus_name con idPrimRep params
335 -- Just want the layout
336 maybe_offset = assocMaybe params_w_offsets selectee
337 Just the_offset = maybe_offset
338 offset_into_int = the_offset - fixedHdrSize
339 bogus_name = panic "mkRhsClosure"
345 A more generic AP thunk of the form
347 x = [ x_1...x_n ] \.. [] -> x_1 ... x_n
349 A set of these is compiled statically into the RTS, so we just use
350 those. We could extend the idea to thunks where some of the x_i are
351 global ids (and hence not free variables), but this would entail
352 generating a larger thunk. It might be an option for non-optimising
355 We only generate an Ap thunk if all the free variables are pointers,
356 for semi-obvious reasons.
359 mkRhsClosure bndr cc bi srt
362 [] -- No args; a thunk
363 body@(StgApp fun_id args)
365 | args `lengthIs` (arity-1)
366 && all isFollowableRep (map idPrimRep fvs)
367 && isUpdatable upd_flag
368 && arity <= mAX_SPEC_AP_SIZE
371 = cgStdRhsClosure bndr cc bi fvs [] body lf_info payload
374 lf_info = mkApLFInfo (idType bndr) upd_flag arity
375 -- the payload has to be in the correct order, hence we can't
377 payload = StgVarArg fun_id : args
384 mkRhsClosure bndr cc bi srt fvs upd_flag args body
385 = cgRhsClosure bndr cc bi srt fvs args body lf_info
387 lf_info = mkClosureLFInfo bndr NotTopLevel fvs upd_flag args
391 %********************************************************
393 %* Let-no-escape bindings
395 %********************************************************
397 cgLetNoEscapeBindings live_in_rhss rhs_eob_info maybe_cc_slot
398 (StgNonRec srt binder rhs)
399 = cgLetNoEscapeRhs live_in_rhss rhs_eob_info maybe_cc_slot
400 NonRecursive srt binder rhs
401 `thenFC` \ (binder, info) ->
404 cgLetNoEscapeBindings live_in_rhss rhs_eob_info maybe_cc_slot
406 = fixC (\ new_bindings ->
407 addBindsC new_bindings `thenC`
408 listFCs [ cgLetNoEscapeRhs full_live_in_rhss
409 rhs_eob_info maybe_cc_slot Recursive srt b e
411 ) `thenFC` \ new_bindings ->
413 addBindsC new_bindings
415 -- We add the binders to the live-in-rhss set so that we don't
416 -- delete the bindings for the binder from the environment!
417 full_live_in_rhss = live_in_rhss `unionVarSet` (mkVarSet [b | (b,r) <- pairs])
420 :: StgLiveVars -- Live in rhss
422 -> Maybe VirtualSpOffset
427 -> FCode (Id, CgIdInfo)
429 cgLetNoEscapeRhs full_live_in_rhss rhs_eob_info maybe_cc_slot rec srt binder
430 (StgRhsClosure cc bi _ upd_flag args body)
431 = -- We could check the update flag, but currently we don't switch it off
432 -- for let-no-escaped things, so we omit the check too!
434 -- Updatable -> panic "cgLetNoEscapeRhs" -- Nothing to update!
435 -- other -> cgLetNoEscapeClosure binder cc bi live_in_whole_let live_in_rhss args body
436 cgLetNoEscapeClosure binder cc bi srt full_live_in_rhss rhs_eob_info
437 maybe_cc_slot rec args body
439 -- For a constructor RHS we want to generate a single chunk of code which
440 -- can be jumped to from many places, which will return the constructor.
441 -- It's easy; just behave as if it was an StgRhsClosure with a ConApp inside!
442 cgLetNoEscapeRhs full_live_in_rhss rhs_eob_info maybe_cc_slot rec srt binder
443 (StgRhsCon cc con args)
444 = cgLetNoEscapeClosure binder cc noBinderInfo{-safe-} srt
445 full_live_in_rhss rhs_eob_info maybe_cc_slot rec
446 [] --No args; the binder is data structure, not a function
450 Little helper for primitives that return unboxed tuples.
454 primRetUnboxedTuple :: StgOp -> [StgArg] -> Type -> Code
455 primRetUnboxedTuple op args res_ty
456 = getArgAmodes args `thenFC` \ arg_amodes ->
458 put all the arguments in temporaries so they don't get stomped when
459 we push the return address.
463 arg_uniqs = map mkBuiltinUnique [0 .. n_args-1]
464 arg_reps = map getArgPrimRep args
465 arg_temps = zipWith CTemp arg_uniqs arg_reps
467 absC (mkAbstractCs (zipWith CAssign arg_temps arg_amodes)) `thenC`
469 allocate some temporaries for the return values.
472 ty_args = tyConAppArgs (repType res_ty)
473 prim_reps = map typePrimRep ty_args
474 temp_uniqs = map mkBuiltinUnique [ n_args .. n_args + length ty_args - 1]
475 temp_amodes = zipWith CTemp temp_uniqs prim_reps
477 returnUnboxedTuple temp_amodes (absC (COpStmt temp_amodes op arg_temps []))