%
% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
\section[PrimOp]{Primitive operations (machine-level)}
\begin{code}
module PrimOp (
PrimOp(..), allThePrimOps,
primOpType, primOpSig,
primOpTag, maxPrimOpTag, primOpOcc,
tagToEnumKey,
primOpOutOfLine, primOpNeedsWrapper,
primOpOkForSpeculation, primOpIsCheap, primOpIsDupable,
getPrimOpResultInfo, PrimOpResultInfo(..),
PrimCall(..)
) where
#include "HsVersions.h"
import TysPrim
import TysWiredIn
import Demand
import Var ( TyVar )
import OccName ( OccName, pprOccName, mkVarOccFS )
import TyCon ( TyCon, isPrimTyCon, tyConPrimRep, PrimRep(..) )
import Type ( Type, mkForAllTys, mkFunTy, mkFunTys, tyConAppTyCon,
typePrimRep )
import BasicTypes ( Arity, Boxity(..) )
import ForeignCall ( CLabelString )
import Unique ( Unique, mkPrimOpIdUnique )
import Outputable
import FastTypes
import FastString
import Module ( PackageId )
\end{code}
%************************************************************************
%* *
\subsection[PrimOp-datatype]{Datatype for @PrimOp@ (an enumeration)}
%* *
%************************************************************************
These are in \tr{state-interface.verb} order.
\begin{code}
#include "primop-data-decl.hs-incl"
\end{code}
Used for the Ord instance
\begin{code}
primOpTag :: PrimOp -> Int
primOpTag op = iBox (tagOf_PrimOp op)
#include "primop-tag.hs-incl"
instance Eq PrimOp where
op1 == op2 = tagOf_PrimOp op1 ==# tagOf_PrimOp op2
instance Ord PrimOp where
op1 < op2 = tagOf_PrimOp op1 <# tagOf_PrimOp op2
op1 <= op2 = tagOf_PrimOp op1 <=# tagOf_PrimOp op2
op1 >= op2 = tagOf_PrimOp op1 >=# tagOf_PrimOp op2
op1 > op2 = tagOf_PrimOp op1 ># tagOf_PrimOp op2
op1 `compare` op2 | op1 < op2 = LT
| op1 == op2 = EQ
| otherwise = GT
instance Outputable PrimOp where
ppr op = pprPrimOp op
instance Show PrimOp where
showsPrec p op = showsPrecSDoc p (pprPrimOp op)
\end{code}
An @Enum@-derived list would be better; meanwhile... (ToDo)
\begin{code}
allThePrimOps :: [PrimOp]
allThePrimOps =
#include "primop-list.hs-incl"
\end{code}
\begin{code}
tagToEnumKey :: Unique
tagToEnumKey = mkPrimOpIdUnique (primOpTag TagToEnumOp)
\end{code}
%************************************************************************
%* *
\subsection[PrimOp-info]{The essential info about each @PrimOp@}
%* *
%************************************************************************
The @String@ in the @PrimOpInfos@ is the ``base name'' by which the user may
refer to the primitive operation. The conventional \tr{#}-for-
unboxed ops is added on later.
The reason for the funny characters in the names is so we do not
interfere with the programmer's Haskell name spaces.
We use @PrimKinds@ for the ``type'' information, because they're
(slightly) more convenient to use than @TyCons@.
\begin{code}
data PrimOpInfo
= Dyadic OccName
Type
| Monadic OccName
Type
| Compare OccName
Type
| GenPrimOp OccName
[TyVar]
[Type]
Type
mkDyadic, mkMonadic, mkCompare :: FastString -> Type -> PrimOpInfo
mkDyadic str ty = Dyadic (mkVarOccFS str) ty
mkMonadic str ty = Monadic (mkVarOccFS str) ty
mkCompare str ty = Compare (mkVarOccFS str) ty
mkGenPrimOp :: FastString -> [TyVar] -> [Type] -> Type -> PrimOpInfo
mkGenPrimOp str tvs tys ty = GenPrimOp (mkVarOccFS str) tvs tys ty
\end{code}
%************************************************************************
%* *
\subsubsection{Strictness}
%* *
%************************************************************************
Not all primops are strict!
\begin{code}
primOpStrictness :: PrimOp -> Arity -> StrictSig
#include "primop-strictness.hs-incl"
\end{code}
%************************************************************************
%* *
\subsubsection[PrimOp-comparison]{PrimOpInfo basic comparison ops}
%* *
%************************************************************************
@primOpInfo@ gives all essential information (from which everything
else, notably a type, can be constructed) for each @PrimOp@.
\begin{code}
primOpInfo :: PrimOp -> PrimOpInfo
#include "primop-primop-info.hs-incl"
\end{code}
Here are a load of comments from the old primOp info:
A @Word#@ is an unsigned @Int#@.
@decodeFloat#@ is given w/ Integer-stuff (it's similar).
@decodeDouble#@ is given w/ Integer-stuff (it's similar).
Decoding of floating-point numbers is sorta Integer-related. Encoding
is done with plain ccalls now (see PrelNumExtra.lhs).
A @Weak@ Pointer is created by the @mkWeak#@ primitive:
mkWeak# :: k -> v -> f -> State# RealWorld
-> (# State# RealWorld, Weak# v #)
In practice, you'll use the higher-level
data Weak v = Weak# v
mkWeak :: k -> v -> IO () -> IO (Weak v)
The following operation dereferences a weak pointer. The weak pointer
may have been finalized, so the operation returns a result code which
must be inspected before looking at the dereferenced value.
deRefWeak# :: Weak# v -> State# RealWorld ->
(# State# RealWorld, v, Int# #)
Only look at v if the Int# returned is /= 0 !!
The higher-level op is
deRefWeak :: Weak v -> IO (Maybe v)
Weak pointers can be finalized early by using the finalize# operation:
finalizeWeak# :: Weak# v -> State# RealWorld ->
(# State# RealWorld, Int#, IO () #)
The Int# returned is either
0 if the weak pointer has already been finalized, or it has no
finalizer (the third component is then invalid).
1 if the weak pointer is still alive, with the finalizer returned
as the third component.
A {\em stable name/pointer} is an index into a table of stable name
entries. Since the garbage collector is told about stable pointers,
it is safe to pass a stable pointer to external systems such as C
routines.
\begin{verbatim}
makeStablePtr# :: a -> State# RealWorld -> (# State# RealWorld, StablePtr# a #)
freeStablePtr :: StablePtr# a -> State# RealWorld -> State# RealWorld
deRefStablePtr# :: StablePtr# a -> State# RealWorld -> (# State# RealWorld, a #)
eqStablePtr# :: StablePtr# a -> StablePtr# a -> Int#
\end{verbatim}
It may seem a bit surprising that @makeStablePtr#@ is a @IO@
operation since it doesn't (directly) involve IO operations. The
reason is that if some optimisation pass decided to duplicate calls to
@makeStablePtr#@ and we only pass one of the stable pointers over, a
massive space leak can result. Putting it into the IO monad
prevents this. (Another reason for putting them in a monad is to
ensure correct sequencing wrt the side-effecting @freeStablePtr@
operation.)
An important property of stable pointers is that if you call
makeStablePtr# twice on the same object you get the same stable
pointer back.
Note that we can implement @freeStablePtr#@ using @_ccall_@ (and,
besides, it's not likely to be used from Haskell) so it's not a
primop.
Question: Why @RealWorld@ - won't any instance of @_ST@ do the job? [ADR]
Stable Names
~~~~~~~~~~~~
A stable name is like a stable pointer, but with three important differences:
(a) You can't deRef one to get back to the original object.
(b) You can convert one to an Int.
(c) You don't need to 'freeStableName'
The existence of a stable name doesn't guarantee to keep the object it
points to alive (unlike a stable pointer), hence (a).
Invariants:
(a) makeStableName always returns the same value for a given
object (same as stable pointers).
(b) if two stable names are equal, it implies that the objects
from which they were created were the same.
(c) stableNameToInt always returns the same Int for a given
stable name.
-- HWL: The first 4 Int# in all par... annotations denote:
-- name, granularity info, size of result, degree of parallelism
-- Same structure as _seq_ i.e. returns Int#
-- KSW: v, the second arg in parAt# and parAtForNow#, is used only to determine
-- `the processor containing the expression v'; it is not evaluated
These primops are pretty wierd.
dataToTag# :: a -> Int (arg must be an evaluated data type)
tagToEnum# :: Int -> a (result type must be an enumerated type)
The constraints aren't currently checked by the front end, but the
code generator will fall over if they aren't satisfied.
%************************************************************************
%* *
\subsubsection[PrimOp-ool]{Which PrimOps are out-of-line}
%* *
%************************************************************************
Some PrimOps need to be called out-of-line because they either need to
perform a heap check or they block.
\begin{code}
primOpOutOfLine :: PrimOp -> Bool
#include "primop-out-of-line.hs-incl"
\end{code}
primOpOkForSpeculation
~~~~~~~~~~~~~~~~~~~~~~
Sometimes we may choose to execute a PrimOp even though it isn't
certain that its result will be required; ie execute them
``speculatively''. The same thing as ``cheap eagerness.'' Usually
this is OK, because PrimOps are usually cheap, but it isn't OK for
(a)~expensive PrimOps and (b)~PrimOps which can fail.
PrimOps that have side effects also should not be executed speculatively.
Ok-for-speculation also means that it's ok *not* to execute the
primop. For example
case op a b of
r -> 3
Here the result is not used, so we can discard the primop. Anything
that has side effects mustn't be dicarded in this way, of course!
See also @primOpIsCheap@ (below).
\begin{code}
primOpOkForSpeculation :: PrimOp -> Bool
primOpOkForSpeculation op
= not (primOpHasSideEffects op || primOpOutOfLine op || primOpCanFail op)
\end{code}
primOpIsCheap
~~~~~~~~~~~~~
@primOpIsCheap@, as used in \tr{SimplUtils.lhs}. For now (HACK
WARNING), we just borrow some other predicates for a
what-should-be-good-enough test. "Cheap" means willing to call it more
than once, and/or push it inside a lambda. The latter could change the
behaviour of 'seq' for primops that can fail, so we don't treat them as cheap.
\begin{code}
primOpIsCheap :: PrimOp -> Bool
primOpIsCheap op = primOpOkForSpeculation op
\end{code}
primOpIsDupable
~~~~~~~~~~~~~~~
primOpIsDupable means that the use of the primop is small enough to
duplicate into different case branches. See CoreUtils.exprIsDupable.
\begin{code}
primOpIsDupable :: PrimOp -> Bool
primOpIsDupable op = not (primOpNeedsWrapper op)
\end{code}
\begin{code}
primOpCanFail :: PrimOp -> Bool
#include "primop-can-fail.hs-incl"
\end{code}
And some primops have side-effects and so, for example, must not be
duplicated.
This predicate means a little more than just "modifies the state of
the world". What it really means is "it cosumes the state on its
input". To see what this means, consider
let
t = case readMutVar# v s0 of (# s1, x #) -> (S# s1, x)
y = case t of (s,x) -> x
in
... y ... y ...
Now, this is part of an ST or IO thread, so we are guaranteed by
construction that the program uses the state in a single-threaded way.
Whenever the state resulting from the readMutVar# is demanded, the
readMutVar# will be performed, and it will be ordered correctly with
respect to other operations in the monad.
But there's another way this could go wrong: GHC can inline t into y,
and inline y. Then although the original readMutVar# will still be
correctly ordered with respect to the other operations, there will be
one or more extra readMutVar#s performed later, possibly out-of-order.
This really happened; see #3207.
The property we need to capture about readMutVar# is that it consumes
the State# value on its input. We must retain the linearity of the
State#.
Our fix for this is to declare any primop that must be used linearly
as having side-effects. When primOpHasSideEffects is True,
primOpOkForSpeculation will be False, and hence primOpIsCheap will
also be False, and applications of the primop will never be
duplicated.
\begin{code}
primOpHasSideEffects :: PrimOp -> Bool
#include "primop-has-side-effects.hs-incl"
\end{code}
Inline primitive operations that perform calls need wrappers to save
any live variables that are stored in caller-saves registers.
\begin{code}
primOpNeedsWrapper :: PrimOp -> Bool
#include "primop-needs-wrapper.hs-incl"
\end{code}
\begin{code}
primOpType :: PrimOp -> Type
primOpType op
= case primOpInfo op of
Dyadic _occ ty -> dyadic_fun_ty ty
Monadic _occ ty -> monadic_fun_ty ty
Compare _occ ty -> compare_fun_ty ty
GenPrimOp _occ tyvars arg_tys res_ty ->
mkForAllTys tyvars (mkFunTys arg_tys res_ty)
primOpOcc :: PrimOp -> OccName
primOpOcc op = case primOpInfo op of
Dyadic occ _ -> occ
Monadic occ _ -> occ
Compare occ _ -> occ
GenPrimOp occ _ _ _ -> occ
primOpSig :: PrimOp -> ([TyVar], [Type], Type, Arity, StrictSig)
primOpSig op
= (tyvars, arg_tys, res_ty, arity, primOpStrictness op arity)
where
arity = length arg_tys
(tyvars, arg_tys, res_ty)
= case (primOpInfo op) of
Monadic _occ ty -> ([], [ty], ty )
Dyadic _occ ty -> ([], [ty,ty], ty )
Compare _occ ty -> ([], [ty,ty], boolTy)
GenPrimOp _occ tyvars arg_tys res_ty -> (tyvars, arg_tys, res_ty)
\end{code}
\begin{code}
data PrimOpResultInfo
= ReturnsPrim PrimRep
| ReturnsAlg TyCon
getPrimOpResultInfo :: PrimOp -> PrimOpResultInfo
getPrimOpResultInfo op
= case (primOpInfo op) of
Dyadic _ ty -> ReturnsPrim (typePrimRep ty)
Monadic _ ty -> ReturnsPrim (typePrimRep ty)
Compare _ _ -> ReturnsAlg boolTyCon
GenPrimOp _ _ _ ty | isPrimTyCon tc -> ReturnsPrim (tyConPrimRep tc)
| otherwise -> ReturnsAlg tc
where
tc = tyConAppTyCon ty
\end{code}
The commutable ops are those for which we will try to move constants
to the right hand side for strength reduction.
\begin{code}
commutableOp :: PrimOp -> Bool
#include "primop-commutable.hs-incl"
\end{code}
Utils:
\begin{code}
dyadic_fun_ty, monadic_fun_ty, compare_fun_ty :: Type -> Type
dyadic_fun_ty ty = mkFunTys [ty, ty] ty
monadic_fun_ty ty = mkFunTy ty ty
compare_fun_ty ty = mkFunTys [ty, ty] boolTy
\end{code}
Output stuff:
\begin{code}
pprPrimOp :: PrimOp -> SDoc
pprPrimOp other_op = pprOccName (primOpOcc other_op)
\end{code}
%************************************************************************
%* *
\subsubsection[PrimCall]{User-imported primitive calls}
%* *
%************************************************************************
\begin{code}
data PrimCall = PrimCall CLabelString PackageId
instance Outputable PrimCall where
ppr (PrimCall lbl pkgId)
= text "__primcall" <+> ppr pkgId <+> ppr lbl
\end{code}