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 [
125 if isFollowableArg (typeCgRep (stgArgType stg_arg))
126 then assignPtrTemp arg
127 else assignNonPtrTemp arg
128 | (arg, stg_arg) <- arg_exprs]
129 let arg_hints = zip arg_tmps (map (typeHint.stgArgType) stg_args)
131 Now, allocate some result regs.
133 (res_reps,res_regs,res_hints) <- newUnboxedTupleRegs res_ty
134 ccallReturnUnboxedTuple (zip res_reps (map (CmmReg . CmmLocal) res_regs)) $
135 emitForeignCall (zip res_regs res_hints) fcall
136 arg_hints emptyVarSet{-no live vars-}
138 -- tagToEnum# is special: we need to pull the constructor out of the table,
139 -- and perform an appropriate return.
141 cgExpr (StgOpApp (StgPrimOp TagToEnumOp) [arg] res_ty)
142 = ASSERT(isEnumerationTyCon tycon)
143 do { (rep,amode) <- getArgAmode arg
144 ; amode' <- if isFollowableArg rep
145 then assignPtrTemp amode
146 else assignNonPtrTemp amode
147 -- We're going to use it twice,
148 -- so save in a temp if non-trivial
149 ; stmtC (CmmAssign nodeReg (tagToClosure tycon amode'))
150 ; performReturn emitReturnInstr }
152 -- If you're reading this code in the attempt to figure
153 -- out why the compiler panic'ed here, it is probably because
154 -- you used tagToEnum# in a non-monomorphic setting, e.g.,
155 -- intToTg :: Enum a => Int -> a ; intToTg (I# x#) = tagToEnum# x#
157 tycon = tyConAppTyCon res_ty
160 cgExpr x@(StgOpApp op@(StgPrimOp primop) args res_ty)
161 | primOpOutOfLine primop
162 = tailCallPrimOp primop args
164 | ReturnsPrim VoidRep <- result_info
165 = do cgPrimOp [] primop args emptyVarSet
166 performReturn emitReturnInstr
168 | ReturnsPrim rep <- result_info
169 = do res <- if isFollowableArg (typeCgRep res_ty)
170 then newPtrTemp (argMachRep (typeCgRep res_ty))
171 else newNonPtrTemp (argMachRep (typeCgRep res_ty))
172 cgPrimOp [res] primop args emptyVarSet
173 performPrimReturn (primRepToCgRep rep) (CmmReg (CmmLocal res))
175 | ReturnsAlg tycon <- result_info, isUnboxedTupleTyCon tycon
176 = do (reps, regs, _hints) <- newUnboxedTupleRegs res_ty
177 cgPrimOp regs primop args emptyVarSet{-no live vars-}
178 returnUnboxedTuple (zip reps (map (CmmReg . CmmLocal) regs))
180 | ReturnsAlg tycon <- result_info, isEnumerationTyCon tycon
181 -- c.f. cgExpr (...TagToEnumOp...)
182 = do tag_reg <- if isFollowableArg (typeCgRep res_ty)
183 then newPtrTemp wordRep
184 else newNonPtrTemp wordRep
185 cgPrimOp [tag_reg] primop args emptyVarSet
186 stmtC (CmmAssign nodeReg
188 (CmmReg (CmmLocal tag_reg))))
189 performReturn emitReturnInstr
191 result_info = getPrimOpResultInfo primop
194 %********************************************************
196 %* Case expressions *
198 %********************************************************
199 Case-expression conversion is complicated enough to have its own
203 cgExpr (StgCase expr live_vars save_vars bndr srt alt_type alts)
204 = setSRT srt $ cgCase expr live_vars save_vars bndr alt_type alts
208 %********************************************************
212 %********************************************************
213 \subsection[let-and-letrec-codegen]{Converting @StgLet@ and @StgLetrec@}
216 cgExpr (StgLet (StgNonRec name rhs) expr)
217 = cgRhs name rhs `thenFC` \ (name, info) ->
218 addBindC name info `thenC`
221 cgExpr (StgLet (StgRec pairs) expr)
222 = fixC (\ new_bindings -> addBindsC new_bindings `thenC`
223 listFCs [ cgRhs b e | (b,e) <- pairs ]
224 ) `thenFC` \ new_bindings ->
226 addBindsC new_bindings `thenC`
231 cgExpr (StgLetNoEscape live_in_whole_let live_in_rhss bindings body)
232 = do { -- Figure out what volatile variables to save
233 ; nukeDeadBindings live_in_whole_let
234 ; (save_assts, rhs_eob_info, maybe_cc_slot)
235 <- saveVolatileVarsAndRegs live_in_rhss
237 -- Save those variables right now!
238 ; emitStmts save_assts
240 -- Produce code for the rhss
241 -- and add suitable bindings to the environment
242 ; cgLetNoEscapeBindings live_in_rhss rhs_eob_info
243 maybe_cc_slot bindings
246 ; setEndOfBlockInfo rhs_eob_info (cgExpr body) }
250 %********************************************************
254 %********************************************************
256 SCC expressions are treated specially. They set the current cost
260 cgExpr (StgSCC cc expr) = do emitSetCCC cc; cgExpr expr
263 %********************************************************
267 %********************************************************
270 cgExpr (StgTick m n expr) = do cgTickBox m n; cgExpr expr
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 bndr cc bi
317 [the_fv] -- Just one free var
318 upd_flag -- Updatable thunk
320 body@(StgCase (StgApp scrutinee [{-no args-}])
321 _ _ _ srt -- ignore uniq, etc.
323 [(DataAlt con, params, use_mask,
324 (StgApp selectee [{-no args-}]))])
325 | the_fv == scrutinee -- Scrutinee is the only free variable
326 && maybeToBool maybe_offset -- Selectee is a component of the tuple
327 && offset_into_int <= mAX_SPEC_SELECTEE_SIZE -- Offset is small enough
328 = -- NOT TRUE: ASSERT(is_single_constructor)
329 -- The simplifier may have statically determined that the single alternative
330 -- is the only possible case and eliminated the others, even if there are
331 -- other constructors in the datatype. It's still ok to make a selector
332 -- thunk in this case, because we *know* which constructor the scrutinee
334 setSRT srt $ cgStdRhsClosure bndr cc bi [the_fv] [] body lf_info [StgVarArg the_fv]
336 lf_info = mkSelectorLFInfo bndr offset_into_int
337 (isUpdatable upd_flag)
338 (_, params_w_offsets) = layOutDynConstr con (addIdReps params)
339 -- Just want the layout
340 maybe_offset = assocMaybe params_w_offsets selectee
341 Just the_offset = maybe_offset
342 offset_into_int = the_offset - fixedHdrSize
348 A more generic AP thunk of the form
350 x = [ x_1...x_n ] \.. [] -> x_1 ... x_n
352 A set of these is compiled statically into the RTS, so we just use
353 those. We could extend the idea to thunks where some of the x_i are
354 global ids (and hence not free variables), but this would entail
355 generating a larger thunk. It might be an option for non-optimising
358 We only generate an Ap thunk if all the free variables are pointers,
359 for semi-obvious reasons.
362 mkRhsClosure bndr cc bi
365 [] -- No args; a thunk
366 body@(StgApp fun_id args)
368 | args `lengthIs` (arity-1)
369 && all isFollowableArg (map idCgRep fvs)
370 && isUpdatable upd_flag
371 && arity <= mAX_SPEC_AP_SIZE
374 = cgStdRhsClosure bndr cc bi fvs [] body lf_info payload
377 lf_info = mkApLFInfo bndr upd_flag arity
378 -- the payload has to be in the correct order, hence we can't
380 payload = StgVarArg fun_id : args
387 mkRhsClosure bndr cc bi fvs upd_flag args body
388 = cgRhsClosure bndr cc bi fvs upd_flag args body
392 %********************************************************
394 %* Let-no-escape bindings
396 %********************************************************
398 cgLetNoEscapeBindings live_in_rhss rhs_eob_info maybe_cc_slot
399 (StgNonRec binder rhs)
400 = do { (binder,info) <- cgLetNoEscapeRhs live_in_rhss rhs_eob_info
402 NonRecursive binder rhs
403 ; addBindC binder info }
405 cgLetNoEscapeBindings live_in_rhss rhs_eob_info maybe_cc_slot (StgRec pairs)
406 = do { new_bindings <- fixC (\ new_bindings -> do
407 { addBindsC new_bindings
408 ; listFCs [ cgLetNoEscapeRhs full_live_in_rhss
409 rhs_eob_info maybe_cc_slot Recursive b e
410 | (b,e) <- pairs ] })
412 ; addBindsC new_bindings }
414 -- We add the binders to the live-in-rhss set so that we don't
415 -- delete the bindings for the binder from the environment!
416 full_live_in_rhss = live_in_rhss `unionVarSet` (mkVarSet [b | (b,r) <- pairs])
419 :: StgLiveVars -- Live in rhss
421 -> Maybe VirtualSpOffset
425 -> FCode (Id, CgIdInfo)
427 cgLetNoEscapeRhs full_live_in_rhss rhs_eob_info maybe_cc_slot rec binder
428 (StgRhsClosure cc bi _ upd_flag srt args body)
429 = -- We could check the update flag, but currently we don't switch it off
430 -- for let-no-escaped things, so we omit the check too!
432 -- Updatable -> panic "cgLetNoEscapeRhs" -- Nothing to update!
433 -- other -> cgLetNoEscapeClosure binder cc bi live_in_whole_let live_in_rhss args body
434 setSRT srt $ cgLetNoEscapeClosure binder cc bi full_live_in_rhss rhs_eob_info
435 maybe_cc_slot rec args body
437 -- For a constructor RHS we want to generate a single chunk of code which
438 -- can be jumped to from many places, which will return the constructor.
439 -- It's easy; just behave as if it was an StgRhsClosure with a ConApp inside!
440 cgLetNoEscapeRhs full_live_in_rhss rhs_eob_info maybe_cc_slot rec binder
441 (StgRhsCon cc con args)
442 = setSRT NoSRT $ cgLetNoEscapeClosure binder cc noBinderInfo{-safe-}
443 full_live_in_rhss rhs_eob_info maybe_cc_slot rec
444 [] --No args; the binder is data structure, not a function
448 Little helper for primitives that return unboxed tuples.
451 newUnboxedTupleRegs :: Type -> FCode ([CgRep], [LocalReg], [MachHint])
452 newUnboxedTupleRegs res_ty =
454 ty_args = tyConAppArgs (repType res_ty)
455 (reps,hints) = unzip [ (rep, typeHint ty) | ty <- ty_args,
456 let rep = typeCgRep ty,
458 make_new_temp rep = if isFollowableArg rep
459 then newPtrTemp (argMachRep rep)
460 else newNonPtrTemp (argMachRep rep)
462 regs <- mapM make_new_temp reps
463 return (reps,regs,hints)