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%
% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
\section[CgUpdate]{Manipulating update frames}
\begin{code}
module CgUpdate ( pushUpdateFrame, reserveSeqFrame, pushSeqFrame ) where
#include "HsVersions.h"
import CgMonad
import AbsCSyn
import CgStackery ( allocStackTop, updateFrameSize, seqFrameSize )
import CgUsages ( getVirtSp, getSpRelOffset )
import Panic ( assertPanic )
\end{code}
%********************************************************
%* *
%* Setting up update frames *
%* *
%********************************************************
\subsection[setting-update-frames]{Setting up update frames}
@pushUpdateFrame@ $updatee$ pushes a general update frame which
points to $updatee$ as the thing to be updated. It is only used
when a thunk has just been entered, so the (real) stack pointers
are guaranteed to be nicely aligned with the top of stack.
@pushUpdateFrame@ adjusts the virtual and tail stack pointers
to reflect the frame pushed.
\begin{code}
pushUpdateFrame :: CAddrMode -> Code -> Code
pushUpdateFrame updatee code
=
#ifdef DEBUG
getEndOfBlockInfo `thenFC` \ eob_info ->
ASSERT(case eob_info of { EndOfBlockInfo _ (OnStack _) -> True;
_ -> False})
#endif
allocStackTop updateFrameSize `thenFC` \ _ ->
getVirtSp `thenFC` \ vsp ->
setEndOfBlockInfo (EndOfBlockInfo vsp UpdateCode) (
-- Emit the push macro
absC (CMacroStmt PUSH_UPD_FRAME [
updatee,
int_CLit0 -- we just entered a closure, so must be zero
])
`thenC` code
)
int_CLit0 = mkIntCLit 0 -- out here to avoid pushUpdateFrame CAF (sigh)
\end{code}
We push a SEQ frame just before evaluating the scrutinee of a case, if
the scrutinee has a polymorphic or function type. The SEQ frame acts
as a barrier in case the scrutinee evaluates to a partial application.
reserveSeqFrame takes the EndOfBlockInfo for the case expression and
updates the sequel to a SeqFrame, reserving room for the frame at
args_sp. When the scrutinee comes around to pushing a return address,
it will also push the SEQ frame, using pushSeqFrame.
\begin{code}
reserveSeqFrame :: EndOfBlockInfo -> EndOfBlockInfo
reserveSeqFrame (EndOfBlockInfo args_sp (CaseAlts amode stuff))
= EndOfBlockInfo (args_sp + seqFrameSize) (SeqFrame amode stuff)
pushSeqFrame :: VirtualSpOffset -> FCode VirtualSpOffset
pushSeqFrame args_sp
= getSpRelOffset args_sp `thenFC` \ sp_rel ->
absC (CMacroStmt PUSH_SEQ_FRAME [CAddr sp_rel]) `thenC`
returnFC (args_sp - seqFrameSize)
\end{code}
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