2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
7 module CgExpr ( cgExpr ) where
9 #include "HsVersions.h"
47 This module provides the support code for @StgToAbstractC@ to deal
48 with STG {\em expressions}. See also @CgClosure@, which deals
49 with closures, and @CgCon@, which deals with constructors.
52 cgExpr :: StgExpr -- input
56 %********************************************************
60 %********************************************************
62 ``Applications'' mean {\em tail calls}, a service provided by module
63 @CgTailCall@. This includes literals, which show up as
64 @(STGApp (StgLitArg 42) [])@.
67 cgExpr (StgApp fun args) = cgTailCall fun args
70 %********************************************************
72 %* STG ConApps (for inline versions) *
74 %********************************************************
77 cgExpr (StgConApp con args)
78 = do { amodes <- getArgAmodes args
79 ; cgReturnDataCon con amodes }
82 Literals are similar to constructors; they return by putting
83 themselves in an appropriate register and returning to the address on
88 = do { cmm_lit <- cgLit lit
89 ; performPrimReturn rep (CmmLit cmm_lit) }
91 rep = (typeCgRep) (literalType lit)
95 %********************************************************
97 %* PrimOps and foreign calls.
99 %********************************************************
101 NOTE about "safe" foreign calls: a safe foreign call is never compiled
102 inline in a case expression. When we see
104 case (ccall ...) of { ... }
106 We generate a proper return address for the alternatives and push the
107 stack frame before doing the call, so that in the event that the call
108 re-enters the RTS the stack is in a sane state.
111 cgExpr (StgOpApp (StgFCallOp fcall _) stg_args res_ty) = do
113 First, copy the args into temporaries. We're going to push
114 a return address right before doing the call, so the args
115 must be out of the way.
117 reps_n_amodes <- getArgAmodes stg_args
119 -- Get the *non-void* args, and jiggle them with shimForeignCall
120 arg_exprs = [ (shimForeignCallArg stg_arg expr, stg_arg)
121 | (stg_arg, (rep,expr)) <- stg_args `zip` reps_n_amodes,
124 arg_tmps <- sequence [ assignTemp arg
125 | (arg, _) <- arg_exprs]
126 let arg_hints = zipWith CmmHinted arg_tmps (map (typeForeignHint.stgArgType) stg_args)
128 Now, allocate some result regs.
130 (res_reps,res_regs,res_hints) <- newUnboxedTupleRegs res_ty
131 ccallReturnUnboxedTuple (zip res_reps (map (CmmReg . CmmLocal) res_regs)) $
132 emitForeignCall (zipWith CmmHinted res_regs res_hints) fcall
133 arg_hints emptyVarSet{-no live vars-}
135 -- tagToEnum# is special: we need to pull the constructor out of the table,
136 -- and perform an appropriate return.
138 cgExpr (StgOpApp (StgPrimOp TagToEnumOp) [arg] res_ty)
139 = ASSERT(isEnumerationTyCon tycon)
140 do { (_rep,amode) <- getArgAmode arg
141 ; amode' <- assignTemp amode -- We're going to use it twice,
142 -- so save in a temp if non-trivial
143 ; stmtC (CmmAssign nodeReg (tagToClosure tycon amode'))
144 ; performReturn emitReturnInstr }
146 -- If you're reading this code in the attempt to figure
147 -- out why the compiler panic'ed here, it is probably because
148 -- you used tagToEnum# in a non-monomorphic setting, e.g.,
149 -- intToTg :: Enum a => Int -> a ; intToTg (I# x#) = tagToEnum# x#
151 tycon = tyConAppTyCon res_ty
154 cgExpr (StgOpApp (StgPrimOp primop) args res_ty)
155 | primOpOutOfLine primop
156 = tailCallPrimOp primop args
158 | ReturnsPrim VoidRep <- result_info
159 = do cgPrimOp [] primop args emptyVarSet
160 performReturn emitReturnInstr
162 | ReturnsPrim rep <- result_info
163 = do res <- newTemp (typeCmmType res_ty)
164 cgPrimOp [res] primop args emptyVarSet
165 performPrimReturn (primRepToCgRep rep) (CmmReg (CmmLocal res))
167 | ReturnsAlg tycon <- result_info, isUnboxedTupleTyCon tycon
168 = do (reps, regs, _hints) <- newUnboxedTupleRegs res_ty
169 cgPrimOp regs primop args emptyVarSet{-no live vars-}
170 returnUnboxedTuple (zip reps (map (CmmReg . CmmLocal) regs))
172 | ReturnsAlg tycon <- result_info, isEnumerationTyCon tycon
173 -- c.f. cgExpr (...TagToEnumOp...)
174 = do tag_reg <- newTemp bWord -- The tag is a word
175 cgPrimOp [tag_reg] primop args emptyVarSet
176 stmtC (CmmAssign nodeReg
178 (CmmReg (CmmLocal tag_reg))))
179 performReturn emitReturnInstr
181 result_info = getPrimOpResultInfo primop
184 %********************************************************
186 %* Case expressions *
188 %********************************************************
189 Case-expression conversion is complicated enough to have its own
193 cgExpr (StgCase expr live_vars save_vars bndr srt alt_type alts)
194 = setSRT srt $ cgCase expr live_vars save_vars bndr alt_type alts
198 %********************************************************
202 %********************************************************
203 \subsection[let-and-letrec-codegen]{Converting @StgLet@ and @StgLetrec@}
206 cgExpr (StgLet (StgNonRec name rhs) expr)
207 = cgRhs name rhs `thenFC` \ (name, info) ->
208 addBindC name info `thenC`
211 cgExpr (StgLet (StgRec pairs) expr)
212 = fixC (\ new_bindings -> addBindsC new_bindings `thenC`
213 listFCs [ cgRhs b e | (b,e) <- pairs ]
214 ) `thenFC` \ new_bindings ->
216 addBindsC new_bindings `thenC`
221 cgExpr (StgLetNoEscape live_in_whole_let live_in_rhss bindings body)
222 = do { -- Figure out what volatile variables to save
223 ; nukeDeadBindings live_in_whole_let
224 ; (save_assts, rhs_eob_info, maybe_cc_slot)
225 <- saveVolatileVarsAndRegs live_in_rhss
227 -- Save those variables right now!
228 ; emitStmts save_assts
230 -- Produce code for the rhss
231 -- and add suitable bindings to the environment
232 ; cgLetNoEscapeBindings live_in_rhss rhs_eob_info
233 maybe_cc_slot bindings
236 ; setEndOfBlockInfo rhs_eob_info (cgExpr body) }
240 %********************************************************
244 %********************************************************
246 SCC expressions are treated specially. They set the current cost
250 cgExpr (StgSCC cc expr) = do emitSetCCC cc; cgExpr expr
253 %********************************************************
257 %********************************************************
260 cgExpr (StgTick m n expr) = do cgTickBox m n; cgExpr expr
263 %********************************************************
267 %********************************************************
270 cgExpr _ = panic "cgExpr"
273 %********************************************************
275 %* Non-top-level bindings *
277 %********************************************************
278 \subsection[non-top-level-bindings]{Converting non-top-level bindings}
280 We rely on the support code in @CgCon@ (to do constructors) and
281 in @CgClosure@ (to do closures).
284 cgRhs :: Id -> StgRhs -> FCode (Id, CgIdInfo)
285 -- the Id is passed along so a binding can be set up
287 cgRhs name (StgRhsCon maybe_cc con args)
288 = do { amodes <- getArgAmodes args
289 ; idinfo <- buildDynCon name maybe_cc con amodes
290 ; returnFC (name, idinfo) }
292 cgRhs name (StgRhsClosure cc bi fvs upd_flag srt args body)
293 = setSRT srt $ mkRhsClosure name cc bi fvs upd_flag args body
296 mkRhsClosure looks for two special forms of the right-hand side:
300 If neither happens, it just calls mkClosureLFInfo. You might think
301 that mkClosureLFInfo should do all this, but it seems wrong for the
302 latter to look at the structure of an expression
306 We look at the body of the closure to see if it's a selector---turgid,
307 but nothing deep. We are looking for a closure of {\em exactly} the
310 ... = [the_fv] \ u [] ->
312 con a_1 ... a_n -> a_i
316 mkRhsClosure :: Id -> CostCentreStack -> StgBinderInfo
317 -> [Id] -> UpdateFlag -> [Id] -> GenStgExpr Id Id
318 -> FCode (Id, CgIdInfo)
319 mkRhsClosure bndr cc bi
320 [the_fv] -- Just one free var
321 upd_flag -- Updatable thunk
323 body@(StgCase (StgApp scrutinee [{-no args-}])
324 _ _ _ srt -- ignore uniq, etc.
326 [(DataAlt con, params, _use_mask,
327 (StgApp selectee [{-no args-}]))])
328 | the_fv == scrutinee -- Scrutinee is the only free variable
329 && maybeToBool maybe_offset -- Selectee is a component of the tuple
330 && offset_into_int <= mAX_SPEC_SELECTEE_SIZE -- Offset is small enough
331 = -- NOT TRUE: ASSERT(is_single_constructor)
332 -- The simplifier may have statically determined that the single alternative
333 -- is the only possible case and eliminated the others, even if there are
334 -- other constructors in the datatype. It's still ok to make a selector
335 -- thunk in this case, because we *know* which constructor the scrutinee
337 setSRT srt $ cgStdRhsClosure bndr cc bi [the_fv] [] body lf_info [StgVarArg the_fv]
339 lf_info = mkSelectorLFInfo bndr offset_into_int
340 (isUpdatable upd_flag)
341 (_, params_w_offsets) = layOutDynConstr con (addIdReps params)
342 -- Just want the layout
343 maybe_offset = assocMaybe params_w_offsets selectee
344 Just the_offset = maybe_offset
345 offset_into_int = the_offset - fixedHdrSize
351 A more generic AP thunk of the form
353 x = [ x_1...x_n ] \.. [] -> x_1 ... x_n
355 A set of these is compiled statically into the RTS, so we just use
356 those. We could extend the idea to thunks where some of the x_i are
357 global ids (and hence not free variables), but this would entail
358 generating a larger thunk. It might be an option for non-optimising
361 We only generate an Ap thunk if all the free variables are pointers,
362 for semi-obvious reasons.
365 mkRhsClosure bndr cc bi
368 [] -- No args; a thunk
369 body@(StgApp fun_id args)
371 | args `lengthIs` (arity-1)
372 && all isFollowableArg (map idCgRep fvs)
373 && isUpdatable upd_flag
374 && arity <= mAX_SPEC_AP_SIZE
377 = cgStdRhsClosure bndr cc bi fvs [] body lf_info payload
380 lf_info = mkApLFInfo bndr upd_flag arity
381 -- the payload has to be in the correct order, hence we can't
383 payload = StgVarArg fun_id : args
390 mkRhsClosure bndr cc bi fvs upd_flag args body
391 = cgRhsClosure bndr cc bi fvs upd_flag args body
395 %********************************************************
397 %* Let-no-escape bindings
399 %********************************************************
401 cgLetNoEscapeBindings :: StgLiveVars -> EndOfBlockInfo
402 -> Maybe VirtualSpOffset -> GenStgBinding Id Id
404 cgLetNoEscapeBindings live_in_rhss rhs_eob_info maybe_cc_slot
405 (StgNonRec binder rhs)
406 = do { (binder,info) <- cgLetNoEscapeRhs live_in_rhss rhs_eob_info
408 NonRecursive binder rhs
409 ; addBindC binder info }
411 cgLetNoEscapeBindings live_in_rhss rhs_eob_info maybe_cc_slot (StgRec pairs)
412 = do { new_bindings <- fixC (\ new_bindings -> do
413 { addBindsC new_bindings
414 ; listFCs [ cgLetNoEscapeRhs full_live_in_rhss
415 rhs_eob_info maybe_cc_slot Recursive b e
416 | (b,e) <- pairs ] })
418 ; addBindsC new_bindings }
420 -- We add the binders to the live-in-rhss set so that we don't
421 -- delete the bindings for the binder from the environment!
422 full_live_in_rhss = live_in_rhss `unionVarSet` (mkVarSet [b | (b,_) <- pairs])
425 :: StgLiveVars -- Live in rhss
427 -> Maybe VirtualSpOffset
431 -> FCode (Id, CgIdInfo)
433 cgLetNoEscapeRhs full_live_in_rhss rhs_eob_info maybe_cc_slot rec binder
434 (StgRhsClosure cc bi _ _upd_flag srt args body)
435 = -- We could check the update flag, but currently we don't switch it off
436 -- for let-no-escaped things, so we omit the check too!
438 -- Updatable -> panic "cgLetNoEscapeRhs" -- Nothing to update!
439 -- other -> cgLetNoEscapeClosure binder cc bi live_in_whole_let live_in_rhss args body
440 setSRT srt $ cgLetNoEscapeClosure binder cc bi full_live_in_rhss rhs_eob_info
441 maybe_cc_slot rec args body
443 -- For a constructor RHS we want to generate a single chunk of code which
444 -- can be jumped to from many places, which will return the constructor.
445 -- It's easy; just behave as if it was an StgRhsClosure with a ConApp inside!
446 cgLetNoEscapeRhs full_live_in_rhss rhs_eob_info maybe_cc_slot rec binder
447 (StgRhsCon cc con args)
448 = setSRT NoSRT $ cgLetNoEscapeClosure binder cc noBinderInfo{-safe-}
449 full_live_in_rhss rhs_eob_info maybe_cc_slot rec
450 [] --No args; the binder is data structure, not a function
454 Little helper for primitives that return unboxed tuples.
457 newUnboxedTupleRegs :: Type -> FCode ([CgRep], [LocalReg], [ForeignHint])
458 newUnboxedTupleRegs res_ty =
460 ty_args = tyConAppArgs (repType res_ty)
461 (reps,hints) = unzip [ (rep, typeForeignHint ty) | ty <- ty_args,
462 let rep = typeCgRep ty,
464 make_new_temp rep = newTemp (argMachRep rep)
466 regs <- mapM make_new_temp reps
467 return (reps,regs,hints)