2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[PrimOp]{Primitive operations (machine-level)}
8 PrimOp(..), allThePrimOps,
9 primOpType, primOpSig, primOpUsg, primOpArity,
10 mkPrimOpIdName, primOpRdrName, primOpTag, primOpOcc,
14 primOpOutOfLine, primOpNeedsWrapper,
15 primOpOkForSpeculation, primOpIsCheap, primOpIsDupable,
18 getPrimOpResultInfo, PrimOpResultInfo(..)
21 #include "HsVersions.h"
23 import PrimRep -- most of it
27 import Demand ( wwLazy, wwPrim, wwStrict, StrictnessInfo(..) )
29 import Name ( Name, mkWiredInName )
30 import RdrName ( RdrName, mkRdrOrig )
31 import OccName ( OccName, pprOccName, mkVarOcc )
32 import TyCon ( TyCon )
33 import Type ( Type, mkForAllTys, mkFunTy, mkFunTys, typePrimRep,
34 splitFunTy_maybe, splitAlgTyConApp_maybe, splitTyConApp,
37 import Unique ( mkPrimOpIdUnique )
38 import BasicTypes ( Arity, Boxity(..) )
39 import PrelNames ( pREL_GHC, pREL_GHC_Name )
41 import Util ( zipWithEqual )
45 %************************************************************************
47 \subsection[PrimOp-datatype]{Datatype for @PrimOp@ (an enumeration)}
49 %************************************************************************
51 These are in \tr{state-interface.verb} order.
57 #include "primop-data-decl.hs-incl"
60 Used for the Ord instance
63 primOpTag :: PrimOp -> Int
64 primOpTag op = iBox (tagOf_PrimOp op)
67 -- tagOf_PrimOp :: PrimOp -> FastInt
68 #include "primop-tag.hs-incl"
69 tagOf_PrimOp op = pprPanic# "tagOf_PrimOp: pattern-match" (ppr op)
72 instance Eq PrimOp where
73 op1 == op2 = tagOf_PrimOp op1 ==# tagOf_PrimOp op2
75 instance Ord PrimOp where
76 op1 < op2 = tagOf_PrimOp op1 <# tagOf_PrimOp op2
77 op1 <= op2 = tagOf_PrimOp op1 <=# tagOf_PrimOp op2
78 op1 >= op2 = tagOf_PrimOp op1 >=# tagOf_PrimOp op2
79 op1 > op2 = tagOf_PrimOp op1 ># tagOf_PrimOp op2
80 op1 `compare` op2 | op1 < op2 = LT
84 instance Outputable PrimOp where
87 instance Show PrimOp where
88 showsPrec p op = showsPrecSDoc p (pprPrimOp op)
91 An @Enum@-derived list would be better; meanwhile... (ToDo)
93 allThePrimOps :: [PrimOp]
95 #include "primop-list.hs-incl"
98 %************************************************************************
100 \subsection[PrimOp-info]{The essential info about each @PrimOp@}
102 %************************************************************************
104 The @String@ in the @PrimOpInfos@ is the ``base name'' by which the user may
105 refer to the primitive operation. The conventional \tr{#}-for-
106 unboxed ops is added on later.
108 The reason for the funny characters in the names is so we do not
109 interfere with the programmer's Haskell name spaces.
111 We use @PrimKinds@ for the ``type'' information, because they're
112 (slightly) more convenient to use than @TyCons@.
115 = Dyadic OccName -- string :: T -> T -> T
117 | Monadic OccName -- string :: T -> T
119 | Compare OccName -- string :: T -> T -> Bool
122 | GenPrimOp OccName -- string :: \/a1..an . T1 -> .. -> Tk -> T
127 mkDyadic str ty = Dyadic (mkVarOcc str) ty
128 mkMonadic str ty = Monadic (mkVarOcc str) ty
129 mkCompare str ty = Compare (mkVarOcc str) ty
130 mkGenPrimOp str tvs tys ty = GenPrimOp (mkVarOcc str) tvs tys ty
133 %************************************************************************
135 \subsubsection{Strictness}
137 %************************************************************************
139 Not all primops are strict!
142 primOpStrictness :: PrimOp -> Arity -> StrictnessInfo
143 -- See Demand.StrictnessInfo for discussion of what the results
144 -- The arity should be the arity of the primop; that's why
145 -- this function isn't exported.
146 #include "primop-strictness.hs-incl"
149 %************************************************************************
151 \subsubsection[PrimOp-comparison]{PrimOpInfo basic comparison ops}
153 %************************************************************************
155 @primOpInfo@ gives all essential information (from which everything
156 else, notably a type, can be constructed) for each @PrimOp@.
159 primOpInfo :: PrimOp -> PrimOpInfo
160 #include "primop-primop-info.hs-incl"
163 Here are a load of comments from the old primOp info:
165 A @Word#@ is an unsigned @Int#@.
167 @decodeFloat#@ is given w/ Integer-stuff (it's similar).
169 @decodeDouble#@ is given w/ Integer-stuff (it's similar).
171 Decoding of floating-point numbers is sorta Integer-related. Encoding
172 is done with plain ccalls now (see PrelNumExtra.lhs).
174 A @Weak@ Pointer is created by the @mkWeak#@ primitive:
176 mkWeak# :: k -> v -> f -> State# RealWorld
177 -> (# State# RealWorld, Weak# v #)
179 In practice, you'll use the higher-level
181 data Weak v = Weak# v
182 mkWeak :: k -> v -> IO () -> IO (Weak v)
184 The following operation dereferences a weak pointer. The weak pointer
185 may have been finalized, so the operation returns a result code which
186 must be inspected before looking at the dereferenced value.
188 deRefWeak# :: Weak# v -> State# RealWorld ->
189 (# State# RealWorld, v, Int# #)
191 Only look at v if the Int# returned is /= 0 !!
193 The higher-level op is
195 deRefWeak :: Weak v -> IO (Maybe v)
197 Weak pointers can be finalized early by using the finalize# operation:
199 finalizeWeak# :: Weak# v -> State# RealWorld ->
200 (# State# RealWorld, Int#, IO () #)
202 The Int# returned is either
204 0 if the weak pointer has already been finalized, or it has no
205 finalizer (the third component is then invalid).
207 1 if the weak pointer is still alive, with the finalizer returned
208 as the third component.
210 A {\em stable name/pointer} is an index into a table of stable name
211 entries. Since the garbage collector is told about stable pointers,
212 it is safe to pass a stable pointer to external systems such as C
216 makeStablePtr# :: a -> State# RealWorld -> (# State# RealWorld, StablePtr# a #)
217 freeStablePtr :: StablePtr# a -> State# RealWorld -> State# RealWorld
218 deRefStablePtr# :: StablePtr# a -> State# RealWorld -> (# State# RealWorld, a #)
219 eqStablePtr# :: StablePtr# a -> StablePtr# a -> Int#
222 It may seem a bit surprising that @makeStablePtr#@ is a @IO@
223 operation since it doesn't (directly) involve IO operations. The
224 reason is that if some optimisation pass decided to duplicate calls to
225 @makeStablePtr#@ and we only pass one of the stable pointers over, a
226 massive space leak can result. Putting it into the IO monad
227 prevents this. (Another reason for putting them in a monad is to
228 ensure correct sequencing wrt the side-effecting @freeStablePtr@
231 An important property of stable pointers is that if you call
232 makeStablePtr# twice on the same object you get the same stable
235 Note that we can implement @freeStablePtr#@ using @_ccall_@ (and,
236 besides, it's not likely to be used from Haskell) so it's not a
239 Question: Why @RealWorld@ - won't any instance of @_ST@ do the job? [ADR]
244 A stable name is like a stable pointer, but with three important differences:
246 (a) You can't deRef one to get back to the original object.
247 (b) You can convert one to an Int.
248 (c) You don't need to 'freeStableName'
250 The existence of a stable name doesn't guarantee to keep the object it
251 points to alive (unlike a stable pointer), hence (a).
255 (a) makeStableName always returns the same value for a given
256 object (same as stable pointers).
258 (b) if two stable names are equal, it implies that the objects
259 from which they were created were the same.
261 (c) stableNameToInt always returns the same Int for a given
265 [Alastair Reid is to blame for this!]
267 These days, (Glasgow) Haskell seems to have a bit of everything from
268 other languages: strict operations, mutable variables, sequencing,
269 pointers, etc. About the only thing left is LISP's ability to test
270 for pointer equality. So, let's add it in!
273 reallyUnsafePtrEquality :: a -> a -> Int#
276 which tests any two closures (of the same type) to see if they're the
277 same. (Returns $0$ for @False@, $\neq 0$ for @True@ - to avoid
278 difficulties of trying to box up the result.)
280 NB This is {\em really unsafe\/} because even something as trivial as
281 a garbage collection might change the answer by removing indirections.
282 Still, no-one's forcing you to use it. If you're worried about little
283 things like loss of referential transparency, you might like to wrap
284 it all up in a monad-like thing as John O'Donnell and John Hughes did
285 for non-determinism (1989 (Fraserburgh) Glasgow FP Workshop
288 I'm thinking of using it to speed up a critical equality test in some
289 graphics stuff in a context where the possibility of saying that
290 denotationally equal things aren't isn't a problem (as long as it
291 doesn't happen too often.) ADR
293 To Will: Jim said this was already in, but I can't see it so I'm
294 adding it. Up to you whether you add it. (Note that this could have
295 been readily implemented using a @veryDangerousCCall@ before they were
299 -- HWL: The first 4 Int# in all par... annotations denote:
300 -- name, granularity info, size of result, degree of parallelism
301 -- Same structure as _seq_ i.e. returns Int#
302 -- KSW: v, the second arg in parAt# and parAtForNow#, is used only to determine
303 -- `the processor containing the expression v'; it is not evaluated
305 These primops are pretty wierd.
307 dataToTag# :: a -> Int (arg must be an evaluated data type)
308 tagToEnum# :: Int -> a (result type must be an enumerated type)
310 The constraints aren't currently checked by the front end, but the
311 code generator will fall over if they aren't satisfied.
315 primOpInfo op = pprPanic "primOpInfo:" (ppr op)
319 %************************************************************************
321 \subsubsection[PrimOp-ool]{Which PrimOps are out-of-line}
323 %************************************************************************
325 Some PrimOps need to be called out-of-line because they either need to
326 perform a heap check or they block.
329 #include "primop-out-of-line.hs-incl"
333 primOpOkForSpeculation
334 ~~~~~~~~~~~~~~~~~~~~~~
335 Sometimes we may choose to execute a PrimOp even though it isn't
336 certain that its result will be required; ie execute them
337 ``speculatively''. The same thing as ``cheap eagerness.'' Usually
338 this is OK, because PrimOps are usually cheap, but it isn't OK for
339 (a)~expensive PrimOps and (b)~PrimOps which can fail.
341 PrimOps that have side effects also should not be executed speculatively.
343 Ok-for-speculation also means that it's ok *not* to execute the
347 Here the result is not used, so we can discard the primop. Anything
348 that has side effects mustn't be dicarded in this way, of course!
350 See also @primOpIsCheap@ (below).
354 primOpOkForSpeculation :: PrimOp -> Bool
355 -- See comments with CoreUtils.exprOkForSpeculation
356 primOpOkForSpeculation op
357 = not (primOpHasSideEffects op || primOpOutOfLine op || primOpCanFail op)
363 @primOpIsCheap@, as used in \tr{SimplUtils.lhs}. For now (HACK
364 WARNING), we just borrow some other predicates for a
365 what-should-be-good-enough test. "Cheap" means willing to call it more
366 than once. Evaluation order is unaffected.
369 primOpIsCheap :: PrimOp -> Bool
370 primOpIsCheap op = False
371 -- March 2001: be less eager to inline PrimOps
372 -- Was: not (primOpHasSideEffects op || primOpOutOfLine op)
377 primOpIsDupable means that the use of the primop is small enough to
378 duplicate into different case branches. See CoreUtils.exprIsDupable.
381 primOpIsDupable :: PrimOp -> Bool
382 -- See comments with CoreUtils.exprIsDupable
383 -- We say it's dupable it isn't implemented by a C call with a wrapper
384 primOpIsDupable op = not (primOpNeedsWrapper op)
389 primOpCanFail :: PrimOp -> Bool
390 #include "primop-can-fail.hs-incl"
393 And some primops have side-effects and so, for example, must not be
397 primOpHasSideEffects :: PrimOp -> Bool
398 #include "primop-has-side-effects.hs-incl"
401 Inline primitive operations that perform calls need wrappers to save
402 any live variables that are stored in caller-saves registers.
405 primOpNeedsWrapper :: PrimOp -> Bool
406 #include "primop-needs-wrapper.hs-incl"
410 primOpArity :: PrimOp -> Arity
412 = case (primOpInfo op) of
416 GenPrimOp occ tyvars arg_tys res_ty -> length arg_tys
418 primOpType :: PrimOp -> Type -- you may want to use primOpSig instead
420 = case (primOpInfo op) of
421 Dyadic occ ty -> dyadic_fun_ty ty
422 Monadic occ ty -> monadic_fun_ty ty
423 Compare occ ty -> compare_fun_ty ty
425 GenPrimOp occ tyvars arg_tys res_ty ->
426 mkForAllTys tyvars (mkFunTys arg_tys res_ty)
428 mkPrimOpIdName :: PrimOp -> Name
429 -- Make the name for the PrimOp's Id
430 -- We have to pass in the Id itself because it's a WiredInId
431 -- and hence recursive
433 = mkWiredInName pREL_GHC (primOpOcc op) (mkPrimOpIdUnique (primOpTag op))
435 primOpRdrName :: PrimOp -> RdrName
436 primOpRdrName op = mkRdrOrig pREL_GHC_Name (primOpOcc op)
438 primOpOcc :: PrimOp -> OccName
439 primOpOcc op = case (primOpInfo op) of
443 GenPrimOp occ _ _ _ -> occ
445 -- primOpSig is like primOpType but gives the result split apart:
446 -- (type variables, argument types, result type)
447 -- It also gives arity, strictness info
449 primOpSig :: PrimOp -> ([TyVar], [Type], Type, Arity, StrictnessInfo)
451 = (tyvars, arg_tys, res_ty, arity, primOpStrictness op arity)
453 arity = length arg_tys
454 (tyvars, arg_tys, res_ty)
455 = case (primOpInfo op) of
456 Monadic occ ty -> ([], [ty], ty )
457 Dyadic occ ty -> ([], [ty,ty], ty )
458 Compare occ ty -> ([], [ty,ty], boolTy)
459 GenPrimOp occ tyvars arg_tys res_ty
460 -> (tyvars, arg_tys, res_ty)
462 -- primOpUsg is like primOpSig but the types it yields are the
463 -- appropriate sigma (i.e., usage-annotated) types,
464 -- as required by the UsageSP inference.
466 primOpUsg :: PrimOp -> ([TyVar],[Type],Type)
467 #include "primop-usage.hs-incl"
469 -- Things with no Haskell pointers inside: in actuality, usages are
470 -- irrelevant here (hence it doesn't matter that some of these
471 -- apparently permit duplication; since such arguments are never
472 -- ENTERed anyway, the usage annotation they get is entirely irrelevant
473 -- except insofar as it propagates to infect other values that *are*
477 -- Helper bits & pieces for usage info.
479 mkZ = mkUTy usOnce -- pointed argument used zero
480 mkO = mkUTy usOnce -- pointed argument used once
481 mkM = mkUTy usMany -- pointed argument used multiply
482 mkP = mkUTy usOnce -- unpointed argument
483 mkR = mkUTy usMany -- unpointed result
486 = case primOpSig op of
487 (tyvars, arg_tys, res_ty, _, _)
488 -> (tyvars, map mkP arg_tys, mkR res_ty)
491 = case primOpSig op of
492 (tyvars, arg_tys, res_ty, _, _)
493 -> (tyvars, zipWithEqual "primOpUsg" ($) fs arg_tys, g res_ty)
496 = case splitFunTy_maybe ty of
497 Just (a,b) -> mkFunTy (f a) (g b)
498 Nothing -> pprPanic "primOpUsg:inFun" (ppr op <+> ppr ty)
501 = case splitTyConApp ty of
502 (tc,tys) -> ASSERT( tc == tupleTyCon Unboxed (length fs) )
503 mkTupleTy Unboxed (length fs) (zipWithEqual "primOpUsg" ($) fs tys)
507 data PrimOpResultInfo
508 = ReturnsPrim PrimRep
511 -- Some PrimOps need not return a manifest primitive or algebraic value
512 -- (i.e. they might return a polymorphic value). These PrimOps *must*
513 -- be out of line, or the code generator won't work.
515 getPrimOpResultInfo :: PrimOp -> PrimOpResultInfo
516 getPrimOpResultInfo op
517 = case (primOpInfo op) of
518 Dyadic _ ty -> ReturnsPrim (typePrimRep ty)
519 Monadic _ ty -> ReturnsPrim (typePrimRep ty)
520 Compare _ ty -> ReturnsAlg boolTyCon
521 GenPrimOp _ _ _ ty ->
522 let rep = typePrimRep ty in
524 PtrRep -> case splitAlgTyConApp_maybe ty of
525 Nothing -> pprPanic "getPrimOpResultInfo"
527 Just (tc,_,_) -> ReturnsAlg tc
528 other -> ReturnsPrim other
531 The commutable ops are those for which we will try to move constants
532 to the right hand side for strength reduction.
535 commutableOp :: PrimOp -> Bool
536 #include "primop-commutable.hs-incl"
541 dyadic_fun_ty ty = mkFunTys [ty, ty] ty
542 monadic_fun_ty ty = mkFunTy ty ty
543 compare_fun_ty ty = mkFunTys [ty, ty] boolTy
548 pprPrimOp :: PrimOp -> SDoc
550 = getPprStyle $ \ sty ->
551 if ifaceStyle sty then -- For interfaces Print it qualified with PrelGHC.
552 ptext SLIT("PrelGHC.") <> pprOccName occ
556 occ = primOpOcc other_op