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/* -----------------------------------------------------------------------------
*
* (c) The GHC Team, 1998-2004
*
* Code to perform updates.
*
* This file is written in a subset of C--, extended with various
* features specific to GHC. It is compiled by GHC directly. For the
* syntax of .cmm files, see the parser in ghc/compiler/GHC/Cmm/Parser.y.
*
* ---------------------------------------------------------------------------*/
#include "Cmm.h"
#include "rts/prof/LDV.h"
#include "Updates.h"
#if !defined(UnregisterisedCompiler)
import CLOSURE UPD_CON_IN_NEW_ctr;
import CLOSURE UPD_OLD_IND_ctr;
import CLOSURE UPD_NEW_IND_ctr;
import CLOSURE stg_BLACKHOLE_info;
#endif
/*
* The update code is PERFORMANCE CRITICAL, if you make any changes
* here make sure you eyeball the assembly and check that the fast
* path (update in generation 0) is optimal.
*
* The return(ret) bit is passed down and pinned on the end of each
* branch (there end up being two major branches in the code), since
* we don't mind duplicating this jump.
*/
INFO_TABLE_RET ( stg_upd_frame, UPDATE_FRAME,
UPDATE_FRAME_FIELDS(W_,P_,info_ptr,_ccs,_unused,updatee) )
return (P_ ret) /* the closure being returned */
{
ASSERT(HpAlloc == 0); // Note [HpAlloc]
/* ToDo: it might be a PAP, so we should check... */
TICK_UPD_CON_IN_NEW(sizeW_fromITBL(%GET_STD_INFO(updatee)));
updateWithIndirection(updatee, ret, return (ret));
}
/*
* An update frame where the updatee has been replaced by a BLACKHOLE
* closure by threadPaused. We may have threads to wake up, and we
* also have to check whether the blackhole has been updated by
* another thread in the meantime.
*/
INFO_TABLE_RET ( stg_marked_upd_frame, UPDATE_FRAME,
UPDATE_FRAME_FIELDS(W_,P_,info_ptr,_ccs,_unused,updatee) )
return (P_ ret) /* the closure being returned */
{
W_ v;
ASSERT(HpAlloc == 0); // Note [HpAlloc]
// we know the closure is a BLACKHOLE
v = StgInd_indirectee(updatee);
if (GETTAG(v) != 0) (likely: False) {
// updated by someone else: discard our value and use the
// other one to increase sharing, but check the blocking
// queues to see if any threads were waiting on this BLACKHOLE.
ccall checkBlockingQueues(MyCapability() "ptr", CurrentTSO "ptr");
return (v);
}
// common case: it is still our BLACKHOLE
if (v == CurrentTSO) (likely: True) {
updateWithIndirection(updatee, ret, return (ret));
}
// The other cases are all handled by the generic code
ccall updateThunk (MyCapability() "ptr", CurrentTSO "ptr",
updatee "ptr", ret "ptr");
return (ret);
}
/*
* Special update frame code for CAFs and eager-blackholed thunks: it
* knows how to update blackholes, but is distinct from
* stg_marked_upd_frame so that lazy blackholing won't treat it as the
* high watermark.
*/
INFO_TABLE_RET ( stg_bh_upd_frame, UPDATE_FRAME,
UPDATE_FRAME_FIELDS(W_,P_,info_ptr,ccs,_unused,updatee) )
return (P_ ret) /* the closure being returned */
{
// This all compiles away to a single jump instruction (sigh)
jump RET_LBL(stg_marked_upd_frame)
( UPDATE_FRAME_FIELDS(,,info_ptr,ccs,_unused,updatee) )
(ret);
}
/* Note [HpAlloc]
* ~~~~~~~~~~~~~~
* HpAlloc is required to be zero unless we just bumped Hp and failed
* the heap check: see HeapStackCheck.cmm. Failures that result from
* HpAlloc being non-zero are very hard to track down, because they
* manifest as spurious heap corruption that happens only with +RTS
* -N2 or greater (because then we have a lot more
* interruptCapability() calls happening). Hence, we assert
* HpAlloc==0 as often as possible, and in the update code is a good
* place to do that.
*/
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