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%
% (c) The GRASP Project, Glasgow University, 1992-1996
%
\section[PrimRep]{Primitive machine-level kinds of things.}
At various places in the back end, we want to be to tag things with a
``primitive kind''---i.e., the machine-manipulable implementation
types.
\begin{code}
#include "HsVersions.h"
module PrimRep (
PrimRep(..),
separateByPtrFollowness, isFollowableRep, isFloatingRep,
getPrimRepSize, retPrimRepSize,
showPrimRep,
guessPrimRep
) where
IMP_Ubiq()
import Pretty -- pretty-printing code
import Util
#include "../../includes/GhcConstants.h"
\end{code}
%************************************************************************
%* *
\subsection[PrimRep-datatype]{The @PrimRep@ datatype}
%* *
%************************************************************************
\begin{code}
data PrimRep
= -- These pointer-kinds are all really the same, but we keep
-- them separate for documentation purposes.
PtrRep -- Pointer to a closure; a ``word''.
| CodePtrRep -- Pointer to code
| DataPtrRep -- Pointer to data
| RetRep -- Pointer to code or data (return vector or code pointer)
| CostCentreRep -- Pointer to a cost centre
| CharRep -- Machine characters
| IntRep -- integers (at least 32 bits)
| WordRep -- ditto (but *unsigned*)
| AddrRep -- addresses ("C pointers")
| FloatRep -- floats
| DoubleRep -- doubles
| ForeignObjRep -- This has to be a special kind because ccall
-- generates special code when passing/returning
-- one of these. [ADR]
| StablePtrRep -- We could replace this with IntRep but maybe
-- there's some documentation gain from having
-- it special? [ADR]
| ArrayRep -- Primitive array of Haskell pointers
| ByteArrayRep -- Primitive array of bytes (no Haskell pointers)
| VoidRep -- Occupies no space at all!
-- (Primitive states are mapped onto this)
deriving (Eq, Ord)
-- Kinds are used in PrimTyCons, which need both Eq and Ord
\end{code}
%************************************************************************
%* *
\subsection[PrimRep-predicates]{Follow-ness, sizes, and such---on @PrimitiveKinds@}
%* *
%************************************************************************
Whether or not the thing is a pointer that the garbage-collector
should follow.
Or, to put it another (less confusing) way, whether the object in
question is a heap object.
\begin{code}
isFollowableRep :: PrimRep -> Bool
isFollowableRep PtrRep = True
isFollowableRep ArrayRep = True
isFollowableRep ByteArrayRep = True
-- why is a MallocPtr followable? 4/96 SOF
-- isFollowableRep ForeignObjRep = True
isFollowableRep StablePtrRep = False
-- StablePtrs aren't followable because they are just indices into a
-- table for which explicit allocation/ deallocation is required.
isFollowableRep other = False
separateByPtrFollowness :: (a -> PrimRep) -> [a] -> ([a], [a])
separateByPtrFollowness kind_fun things
= sep_things kind_fun things [] []
-- accumulating params for follow-able and don't-follow things...
where
sep_things kfun [] bs us = (reverse bs, reverse us)
sep_things kfun (t:ts) bs us
= if (isFollowableRep . kfun) t then
sep_things kfun ts (t:bs) us
else
sep_things kfun ts bs (t:us)
\end{code}
@isFloatingRep@ is used to distinguish @Double@ and @Float@ which
cause inadvertent numeric conversions if you aren't jolly careful.
See codeGen/CgCon:cgTopRhsCon.
\begin{code}
isFloatingRep :: PrimRep -> Bool
isFloatingRep DoubleRep = True
isFloatingRep FloatRep = True
isFloatingRep other = False
\end{code}
\begin{code}
getPrimRepSize :: PrimRep -> Int
getPrimRepSize DoubleRep = DOUBLE_SIZE -- "words", of course
--getPrimRepSize FloatRep = 1
--getPrimRepSize CharRep = 1 -- ToDo: count in bytes?
--getPrimRepSize ArrayRep = 1 -- Listed specifically for *documentation*
--getPrimRepSize ByteArrayRep = 1
getPrimRepSize VoidRep = 0
getPrimRepSize other = 1
retPrimRepSize = getPrimRepSize RetRep
\end{code}
%************************************************************************
%* *
\subsection[PrimRep-instances]{Boring instance decls for @PrimRep@}
%* *
%************************************************************************
\begin{code}
instance Outputable PrimRep where
ppr sty kind = ppStr (showPrimRep kind)
showPrimRep :: PrimRep -> String
guessPrimRep :: String -> PrimRep -- a horrible "inverse" function
showPrimRep PtrRep = "P_" -- short for StgPtr
showPrimRep CodePtrRep = "P_" -- DEATH to StgFunPtr! (94/02/22 WDP)
-- but aren't code pointers and function pointers different sizes
-- on some machines (eg 80x86)? ADR
-- Are you trying to ruin my life, or what? (WDP)
showPrimRep DataPtrRep = "D_"
showPrimRep RetRep = "StgRetAddr"
showPrimRep CostCentreRep = "CostCentre"
showPrimRep CharRep = "StgChar"
showPrimRep IntRep = "I_" -- short for StgInt
showPrimRep WordRep = "W_" -- short for StgWord
showPrimRep AddrRep = "StgAddr"
showPrimRep FloatRep = "StgFloat"
showPrimRep DoubleRep = "StgDouble"
showPrimRep ArrayRep = "StgArray" -- see comment below
showPrimRep ByteArrayRep = "StgByteArray"
showPrimRep StablePtrRep = "StgStablePtr"
showPrimRep ForeignObjRep = "StgPtr" -- see comment below
showPrimRep VoidRep = "!!VOID_KIND!!"
guessPrimRep "D_" = DataPtrRep
guessPrimRep "StgRetAddr" = RetRep
guessPrimRep "StgChar" = CharRep
guessPrimRep "I_" = IntRep
guessPrimRep "W_" = WordRep
guessPrimRep "StgAddr" = AddrRep
guessPrimRep "StgFloat" = FloatRep
guessPrimRep "StgDouble" = DoubleRep
guessPrimRep "StgArray" = ArrayRep
guessPrimRep "StgByteArray" = ByteArrayRep
guessPrimRep "StgStablePtr" = StablePtrRep
\end{code}
All local C variables of @ArrayRep@ are declared in C as type
@StgArray@. The coercion to a more precise C type is done just before
indexing (by the relevant C primitive-op macro).
Nota Bene. There are three types associated with @ForeignObj@ (MallocPtr++):
\begin{itemize}
\item
@StgForeignObjClosure@ is the type of the thing the prim. op @mkForeignObj@ returns.
{- old comment for MallocPtr
(This typename is hardwired into @ppr_casm_results@ in
@PprAbsC.lhs@.)
-}
\item
@StgForeignObj@ is the type of the thing we give the C world.
\item
@StgPtr@ is the type of the (pointer to the) heap object which we
pass around inside the STG machine.
\end{itemize}
It is really easy to confuse the two. (I'm not sure this choice of
type names helps.) [ADR]
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