RetainerProfile.c 63.7 KB
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/* -----------------------------------------------------------------------------
 *
 * (c) The GHC Team, 2001
 * Author: Sungwoo Park
 *
 * Retainer profiling.
 *
 * ---------------------------------------------------------------------------*/

#ifdef PROFILING

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// Turn off inlining when debugging - it obfuscates things
#ifdef DEBUG
#define INLINE
#else
#define INLINE inline
#endif

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#include "PosixSource.h"
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#include "Rts.h"
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#include "RtsUtils.h"
#include "RetainerProfile.h"
#include "RetainerSet.h"
#include "Schedule.h"
#include "Printer.h"
#include "Weak.h"
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#include "sm/Sanity.h"
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#include "Profiling.h"
#include "Stats.h"
#include "ProfHeap.h"
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#include "Apply.h"
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#include "sm/Storage.h" // for END_OF_STATIC_LIST
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/*
  Note: what to change in order to plug-in a new retainer profiling scheme?
    (1) type retainer in ../includes/StgRetainerProf.h
    (2) retainer function R(), i.e., getRetainerFrom()
    (3) the two hashing functions, hashKeySingleton() and hashKeyAddElement(),
        in RetainerSet.h, if needed.
    (4) printRetainer() and printRetainerSetShort() in RetainerSet.c.
 */

/* -----------------------------------------------------------------------------
 * Declarations...
 * -------------------------------------------------------------------------- */

static nat retainerGeneration;	// generation

static nat numObjectVisited;	// total number of objects visited
static nat timesAnyObjectVisited; // number of times any objects are visited

/*
  The rs field in the profile header of any object points to its retainer
  set in an indirect way: if flip is 0, it points to the retainer set;
  if flip is 1, it points to the next byte after the retainer set (even
  for NULL pointers). Therefore, with flip 1, (rs ^ 1) is the actual
  pointer. See retainerSetOf().
 */

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StgWord flip = 0;     // flip bit
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                      // must be 0 if DEBUG_RETAINER is on (for static closures)

#define setRetainerSetToNull(c)   \
  (c)->header.prof.hp.rs = (RetainerSet *)((StgWord)NULL | flip)

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static void retainStack(StgClosure *, retainer, StgPtr, StgPtr);
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static void retainClosure(StgClosure *, StgClosure *, retainer);
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#ifdef DEBUG_RETAINER
static void belongToHeap(StgPtr p);
#endif

#ifdef DEBUG_RETAINER
/*
  cStackSize records how many times retainStack() has been invoked recursively,
  that is, the number of activation records for retainStack() on the C stack.
  maxCStackSize records its max value.
  Invariants:
    cStackSize <= maxCStackSize
 */
static nat cStackSize, maxCStackSize;

static nat sumOfNewCost;	// sum of the cost of each object, computed
				// when the object is first visited
static nat sumOfNewCostExtra;   // for those objects not visited during
                                // retainer profiling, e.g., MUT_VAR
static nat costArray[N_CLOSURE_TYPES];

nat sumOfCostLinear;		// sum of the costs of all object, computed
				// when linearly traversing the heap after
				// retainer profiling
nat costArrayLinear[N_CLOSURE_TYPES];
#endif

/* -----------------------------------------------------------------------------
 * Retainer stack - header
 *   Note:
 *     Although the retainer stack implementation could be separated *
 *     from the retainer profiling engine, there does not seem to be
 *     any advantage in doing that; retainer stack is an integral part
 *     of retainer profiling engine and cannot be use elsewhere at
 *     all.
 * -------------------------------------------------------------------------- */

typedef enum {
    posTypeStep,
    posTypePtrs,
    posTypeSRT,
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    posTypeLargeSRT,
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} nextPosType;

typedef union {
    // fixed layout or layout specified by a field in the closure
    StgWord step;

    // layout.payload
    struct {
    // See StgClosureInfo in InfoTables.h
#if SIZEOF_VOID_P == 8
	StgWord32 pos;
	StgWord32 ptrs;
#else
	StgWord16 pos;
	StgWord16 ptrs;
#endif
	StgPtr payload;
    } ptrs;

    // SRT
    struct {
	StgClosure **srt;
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	StgWord    srt_bitmap;
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    } srt;
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    // Large SRT
    struct {
	StgLargeSRT *srt;
	StgWord offset;
    } large_srt;
	
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} nextPos;

typedef struct {
    nextPosType type;
    nextPos next;
} stackPos;

typedef struct {
    StgClosure *c;
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    retainer c_child_r;
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    stackPos info;
} stackElement;

/*
  Invariants:
    firstStack points to the first block group.
    currentStack points to the block group currently being used.
    currentStack->free == stackLimit.
    stackTop points to the topmost byte in the stack of currentStack.
    Unless the whole stack is empty, stackTop must point to the topmost
    object (or byte) in the whole stack. Thus, it is only when the whole stack
    is empty that stackTop == stackLimit (not during the execution of push()
    and pop()).
    stackBottom == currentStack->start.
    stackLimit == currentStack->start + BLOCK_SIZE_W * currentStack->blocks.
  Note:
    When a current stack becomes empty, stackTop is set to point to
    the topmost element on the previous block group so as to satisfy
    the invariants described above.
 */
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static bdescr *firstStack = NULL;
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static bdescr *currentStack;
static stackElement *stackBottom, *stackTop, *stackLimit;

/*
  currentStackBoundary is used to mark the current stack chunk.
  If stackTop == currentStackBoundary, it means that the current stack chunk
  is empty. It is the responsibility of the user to keep currentStackBoundary
  valid all the time if it is to be employed.
 */
static stackElement *currentStackBoundary;

/*
  stackSize records the current size of the stack.
  maxStackSize records its high water mark.
  Invariants:
    stackSize <= maxStackSize
  Note:
    stackSize is just an estimate measure of the depth of the graph. The reason
    is that some heap objects have only a single child and may not result
    in a new element being pushed onto the stack. Therefore, at the end of
    retainer profiling, maxStackSize + maxCStackSize is some value no greater
    than the actual depth of the graph.
 */
#ifdef DEBUG_RETAINER
static int stackSize, maxStackSize;
#endif

// number of blocks allocated for one stack
#define BLOCKS_IN_STACK 1

/* -----------------------------------------------------------------------------
 * Add a new block group to the stack.
 * Invariants:
 *  currentStack->link == s.
 * -------------------------------------------------------------------------- */
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static INLINE void
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newStackBlock( bdescr *bd )
{
    currentStack = bd;
    stackTop     = (stackElement *)(bd->start + BLOCK_SIZE_W * bd->blocks);
    stackBottom  = (stackElement *)bd->start;
    stackLimit   = (stackElement *)stackTop;
    bd->free     = (StgPtr)stackLimit;
}

/* -----------------------------------------------------------------------------
 * Return to the previous block group.
 * Invariants:
 *   s->link == currentStack.
 * -------------------------------------------------------------------------- */
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static INLINE void
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returnToOldStack( bdescr *bd )
{
    currentStack = bd;
    stackTop = (stackElement *)bd->free;
    stackBottom = (stackElement *)bd->start;
    stackLimit = (stackElement *)(bd->start + BLOCK_SIZE_W * bd->blocks);
    bd->free = (StgPtr)stackLimit;
}

/* -----------------------------------------------------------------------------
 *  Initializes the traverse stack.
 * -------------------------------------------------------------------------- */
static void
initializeTraverseStack( void )
{
    if (firstStack != NULL) {
	freeChain(firstStack);
    }

    firstStack = allocGroup(BLOCKS_IN_STACK);
    firstStack->link = NULL;
    firstStack->u.back = NULL;

    newStackBlock(firstStack);
}

/* -----------------------------------------------------------------------------
 * Frees all the block groups in the traverse stack.
 * Invariants:
 *   firstStack != NULL
 * -------------------------------------------------------------------------- */
static void
closeTraverseStack( void )
{
    freeChain(firstStack);
    firstStack = NULL;
}

/* -----------------------------------------------------------------------------
 * Returns rtsTrue if the whole stack is empty.
 * -------------------------------------------------------------------------- */
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static INLINE rtsBool
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isEmptyRetainerStack( void )
{
    return (firstStack == currentStack) && stackTop == stackLimit;
}

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/* -----------------------------------------------------------------------------
 * Returns size of stack
 * -------------------------------------------------------------------------- */
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#ifdef DEBUG
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lnat
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retainerStackBlocks( void )
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{
    bdescr* bd;
    lnat res = 0;

    for (bd = firstStack; bd != NULL; bd = bd->link) 
      res += bd->blocks;

    return res;
}
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#endif
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/* -----------------------------------------------------------------------------
 * Returns rtsTrue if stackTop is at the stack boundary of the current stack,
 * i.e., if the current stack chunk is empty.
 * -------------------------------------------------------------------------- */
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static INLINE rtsBool
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isOnBoundary( void )
{
    return stackTop == currentStackBoundary;
}

/* -----------------------------------------------------------------------------
 * Initializes *info from ptrs and payload.
 * Invariants:
 *   payload[] begins with ptrs pointers followed by non-pointers.
 * -------------------------------------------------------------------------- */
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static INLINE void
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init_ptrs( stackPos *info, nat ptrs, StgPtr payload )
{
    info->type              = posTypePtrs;
    info->next.ptrs.pos     = 0;
    info->next.ptrs.ptrs    = ptrs;
    info->next.ptrs.payload = payload;
}

/* -----------------------------------------------------------------------------
 * Find the next object from *info.
 * -------------------------------------------------------------------------- */
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static INLINE StgClosure *
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find_ptrs( stackPos *info )
{
    if (info->next.ptrs.pos < info->next.ptrs.ptrs) {
	return (StgClosure *)info->next.ptrs.payload[info->next.ptrs.pos++];
    } else {
	return NULL;
    }
}

/* -----------------------------------------------------------------------------
 *  Initializes *info from SRT information stored in *infoTable.
 * -------------------------------------------------------------------------- */
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static INLINE void
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init_srt_fun( stackPos *info, StgFunInfoTable *infoTable )
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{
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    if (infoTable->i.srt_bitmap == (StgHalfWord)(-1)) {
	info->type = posTypeLargeSRT;
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	info->next.large_srt.srt = (StgLargeSRT *)GET_FUN_SRT(infoTable);
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	info->next.large_srt.offset = 0;
    } else {
	info->type = posTypeSRT;
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	info->next.srt.srt = (StgClosure **)GET_FUN_SRT(infoTable);
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	info->next.srt.srt_bitmap = infoTable->i.srt_bitmap;
    }
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}

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static INLINE void
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init_srt_thunk( stackPos *info, StgThunkInfoTable *infoTable )
{
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    if (infoTable->i.srt_bitmap == (StgHalfWord)(-1)) {
	info->type = posTypeLargeSRT;
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	info->next.large_srt.srt = (StgLargeSRT *)GET_SRT(infoTable);
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	info->next.large_srt.offset = 0;
    } else {
	info->type = posTypeSRT;
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	info->next.srt.srt = (StgClosure **)GET_SRT(infoTable);
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	info->next.srt.srt_bitmap = infoTable->i.srt_bitmap;
    }
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}

/* -----------------------------------------------------------------------------
 * Find the next object from *info.
 * -------------------------------------------------------------------------- */
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static INLINE StgClosure *
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find_srt( stackPos *info )
{
    StgClosure *c;
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    StgWord bitmap;
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    if (info->type == posTypeSRT) {
	// Small SRT bitmap
	bitmap = info->next.srt.srt_bitmap;
	while (bitmap != 0) {
	    if ((bitmap & 1) != 0) {
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#if defined(__PIC__) && defined(mingw32_TARGET_OS)
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		if ((unsigned long)(*(info->next.srt.srt)) & 0x1)
		    c = (* (StgClosure **)((unsigned long)*(info->next.srt.srt)) & ~0x1);
		else
		    c = *(info->next.srt.srt);
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#else
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		c = *(info->next.srt.srt);
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#endif
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		bitmap = bitmap >> 1;
		info->next.srt.srt++;
		info->next.srt.srt_bitmap = bitmap;
		return c;
	    }
	    bitmap = bitmap >> 1;
	    info->next.srt.srt++;
	}
	// bitmap is now zero...
	return NULL;
    }
    else {
	// Large SRT bitmap
	nat i = info->next.large_srt.offset;
	StgWord bitmap;

	// Follow the pattern from GC.c:scavenge_large_srt_bitmap().
	bitmap = info->next.large_srt.srt->l.bitmap[i / BITS_IN(W_)];
	bitmap = bitmap >> (i % BITS_IN(StgWord));
	while (i < info->next.large_srt.srt->l.size) {
	    if ((bitmap & 1) != 0) {
		c = ((StgClosure **)info->next.large_srt.srt->srt)[i];
		i++;
		info->next.large_srt.offset = i;
		return c;
	    }
	    i++;
	    if (i % BITS_IN(W_) == 0) {
		bitmap = info->next.large_srt.srt->l.bitmap[i / BITS_IN(W_)];
	    } else {
		bitmap = bitmap >> 1;
	    }
	}
	// reached the end of this bitmap.
	info->next.large_srt.offset = i;
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	return NULL;
    }
}

/* -----------------------------------------------------------------------------
 *  push() pushes a stackElement representing the next child of *c
 *  onto the traverse stack. If *c has no child, *first_child is set
 *  to NULL and nothing is pushed onto the stack. If *c has only one
 *  child, *c_chlid is set to that child and nothing is pushed onto
 *  the stack.  If *c has more than two children, *first_child is set
 *  to the first child and a stackElement representing the second
 *  child is pushed onto the stack.

 *  Invariants:
 *     *c_child_r is the most recent retainer of *c's children.
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 *     *c is not any of TSO, AP, PAP, AP_STACK, which means that
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 *        there cannot be any stack objects.
 *  Note: SRTs are considered to  be children as well.
 * -------------------------------------------------------------------------- */
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static INLINE void
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push( StgClosure *c, retainer c_child_r, StgClosure **first_child )
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{
    stackElement se;
    bdescr *nbd;      // Next Block Descriptor

#ifdef DEBUG_RETAINER
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    // debugBelch("push(): stackTop = 0x%x, currentStackBoundary = 0x%x\n", stackTop, currentStackBoundary);
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#endif

    ASSERT(get_itbl(c)->type != TSO);
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    ASSERT(get_itbl(c)->type != AP_STACK);
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    //
    // fill in se
    //

    se.c = c;
    se.c_child_r = c_child_r;

    // fill in se.info
    switch (get_itbl(c)->type) {
	// no child, no SRT
    case CONSTR_0_1:
    case CONSTR_0_2:
    case ARR_WORDS:
	*first_child = NULL;
	return;

	// one child (fixed), no SRT
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    case MUT_VAR_CLEAN:
    case MUT_VAR_DIRTY:
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	*first_child = ((StgMutVar *)c)->var;
	return;
    case THUNK_SELECTOR:
	*first_child = ((StgSelector *)c)->selectee;
	return;
    case IND_PERM:
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    case BLACKHOLE:
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	*first_child = ((StgInd *)c)->indirectee;
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	return;
    case CONSTR_1_0:
    case CONSTR_1_1:
	*first_child = c->payload[0];
	return;

	// For CONSTR_2_0 and MVAR, we use se.info.step to record the position
	// of the next child. We do not write a separate initialization code.
	// Also we do not have to initialize info.type;

	// two children (fixed), no SRT
	// need to push a stackElement, but nothing to store in se.info
    case CONSTR_2_0:
	*first_child = c->payload[0];         // return the first pointer
	// se.info.type = posTypeStep;
	// se.info.next.step = 2;            // 2 = second
	break;

	// three children (fixed), no SRT
	// need to push a stackElement
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    case MVAR_CLEAN:
    case MVAR_DIRTY:
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	// head must be TSO and the head of a linked list of TSOs.
	// Shoule it be a child? Seems to be yes.
	*first_child = (StgClosure *)((StgMVar *)c)->head;
	// se.info.type = posTypeStep;
	se.info.next.step = 2;            // 2 = second
	break;

	// three children (fixed), no SRT
    case WEAK:
	*first_child = ((StgWeak *)c)->key;
	// se.info.type = posTypeStep;
	se.info.next.step = 2;
	break;

	// layout.payload.ptrs, no SRT
    case CONSTR:
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    case PRIM:
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    case MUT_PRIM:
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    case BCO:
    case CONSTR_STATIC:
	init_ptrs(&se.info, get_itbl(c)->layout.payload.ptrs,
		  (StgPtr)c->payload);
	*first_child = find_ptrs(&se.info);
	if (*first_child == NULL)
	    return;   // no child
	break;

	// StgMutArrPtr.ptrs, no SRT
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    case MUT_ARR_PTRS_CLEAN:
    case MUT_ARR_PTRS_DIRTY:
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    case MUT_ARR_PTRS_FROZEN:
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    case MUT_ARR_PTRS_FROZEN0:
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	init_ptrs(&se.info, ((StgMutArrPtrs *)c)->ptrs,
		  (StgPtr)(((StgMutArrPtrs *)c)->payload));
	*first_child = find_ptrs(&se.info);
	if (*first_child == NULL)
	    return;
	break;

    // layout.payload.ptrs, SRT
    case FUN:           // *c is a heap object.
    case FUN_2_0:
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	init_ptrs(&se.info, get_itbl(c)->layout.payload.ptrs, (StgPtr)c->payload);
	*first_child = find_ptrs(&se.info);
	if (*first_child == NULL)
	    // no child from ptrs, so check SRT
	    goto fun_srt_only;
	break;

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    case THUNK:
    case THUNK_2_0:
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	init_ptrs(&se.info, get_itbl(c)->layout.payload.ptrs, 
		  (StgPtr)((StgThunk *)c)->payload);
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	*first_child = find_ptrs(&se.info);
	if (*first_child == NULL)
	    // no child from ptrs, so check SRT
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	    goto thunk_srt_only;
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	break;

	// 1 fixed child, SRT
    case FUN_1_0:
    case FUN_1_1:
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	*first_child = c->payload[0];
	ASSERT(*first_child != NULL);
	init_srt_fun(&se.info, get_fun_itbl(c));
	break;

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    case THUNK_1_0:
    case THUNK_1_1:
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	*first_child = ((StgThunk *)c)->payload[0];
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	ASSERT(*first_child != NULL);
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	init_srt_thunk(&se.info, get_thunk_itbl(c));
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	break;

    case FUN_STATIC:      // *c is a heap object.
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	ASSERT(get_itbl(c)->srt_bitmap != 0);
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    case FUN_0_1:
    case FUN_0_2:
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    fun_srt_only:
        init_srt_fun(&se.info, get_fun_itbl(c));
	*first_child = find_srt(&se.info);
	if (*first_child == NULL)
	    return;     // no child
	break;

    // SRT only
    case THUNK_STATIC:
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	ASSERT(get_itbl(c)->srt_bitmap != 0);
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    case THUNK_0_1:
    case THUNK_0_2:
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    thunk_srt_only:
        init_srt_thunk(&se.info, get_thunk_itbl(c));
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	*first_child = find_srt(&se.info);
	if (*first_child == NULL)
	    return;     // no child
	break;
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    case TREC_CHUNK:
	*first_child = (StgClosure *)((StgTRecChunk *)c)->prev_chunk;
	se.info.next.step = 0;  // entry no.
	break;
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	// cannot appear
    case PAP:
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    case AP:
    case AP_STACK:
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    case TSO:
    case IND_STATIC:
    case CONSTR_NOCAF_STATIC:
	// stack objects
    case UPDATE_FRAME:
    case CATCH_FRAME:
    case STOP_FRAME:
    case RET_DYN:
    case RET_BCO:
    case RET_SMALL:
    case RET_BIG:
	// invalid objects
    case IND:
    case INVALID_OBJECT:
    default:
	barf("Invalid object *c in push()");
	return;
    }

    if (stackTop - 1 < stackBottom) {
#ifdef DEBUG_RETAINER
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	// debugBelch("push() to the next stack.\n");
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#endif
	// currentStack->free is updated when the active stack is switched
	// to the next stack.
	currentStack->free = (StgPtr)stackTop;

	if (currentStack->link == NULL) {
	    nbd = allocGroup(BLOCKS_IN_STACK);
	    nbd->link = NULL;
	    nbd->u.back = currentStack;
	    currentStack->link = nbd;
	} else
	    nbd = currentStack->link;

	newStackBlock(nbd);
    }

    // adjust stackTop (acutal push)
    stackTop--;
    // If the size of stackElement was huge, we would better replace the
    // following statement by either a memcpy() call or a switch statement
    // on the type of the element. Currently, the size of stackElement is
    // small enough (5 words) that this direct assignment seems to be enough.
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    // ToDo: The line below leads to the warning:
    //    warning: 'se.info.type' may be used uninitialized in this function
    // This is caused by the fact that there are execution paths through the
    // large switch statement above where some cases do not initialize this
    // field. Is this really harmless? Can we avoid the warning?
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    *stackTop = se;

#ifdef DEBUG_RETAINER
    stackSize++;
    if (stackSize > maxStackSize) maxStackSize = stackSize;
    // ASSERT(stackSize >= 0);
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    // debugBelch("stackSize = %d\n", stackSize);
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#endif
}

/* -----------------------------------------------------------------------------
 *  popOff() and popOffReal(): Pop a stackElement off the traverse stack.
 *  Invariants:
 *    stackTop cannot be equal to stackLimit unless the whole stack is
 *    empty, in which case popOff() is not allowed.
 *  Note:
 *    You can think of popOffReal() as a part of popOff() which is
 *    executed at the end of popOff() in necessary. Since popOff() is
 *    likely to be executed quite often while popOffReal() is not, we
 *    separate popOffReal() from popOff(), which is declared as an
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 *    INLINE function (for the sake of execution speed).  popOffReal()
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 *    is called only within popOff() and nowhere else.
 * -------------------------------------------------------------------------- */
static void
popOffReal(void)
{
    bdescr *pbd;    // Previous Block Descriptor

#ifdef DEBUG_RETAINER
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    // debugBelch("pop() to the previous stack.\n");
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#endif

    ASSERT(stackTop + 1 == stackLimit);
    ASSERT(stackBottom == (stackElement *)currentStack->start);

    if (firstStack == currentStack) {
	// The stack is completely empty.
	stackTop++;
	ASSERT(stackTop == stackLimit);
#ifdef DEBUG_RETAINER
	stackSize--;
	if (stackSize > maxStackSize) maxStackSize = stackSize;
	/*
	  ASSERT(stackSize >= 0);
693
	  debugBelch("stackSize = %d\n", stackSize);
694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713
	*/
#endif
	return;
    }

    // currentStack->free is updated when the active stack is switched back
    // to the previous stack.
    currentStack->free = (StgPtr)stackLimit;

    // find the previous block descriptor
    pbd = currentStack->u.back;
    ASSERT(pbd != NULL);

    returnToOldStack(pbd);

#ifdef DEBUG_RETAINER
    stackSize--;
    if (stackSize > maxStackSize) maxStackSize = stackSize;
    /*
      ASSERT(stackSize >= 0);
714
      debugBelch("stackSize = %d\n", stackSize);
715 716 717 718
    */
#endif
}

719
static INLINE void
720 721
popOff(void) {
#ifdef DEBUG_RETAINER
722
    // debugBelch("\tpopOff(): stackTop = 0x%x, currentStackBoundary = 0x%x\n", stackTop, currentStackBoundary);
723 724 725 726 727 728 729 730 731 732 733 734 735
#endif

    ASSERT(stackTop != stackLimit);
    ASSERT(!isEmptyRetainerStack());

    // <= (instead of <) is wrong!
    if (stackTop + 1 < stackLimit) {
	stackTop++;
#ifdef DEBUG_RETAINER
	stackSize--;
	if (stackSize > maxStackSize) maxStackSize = stackSize;
	/*
	  ASSERT(stackSize >= 0);
736
	  debugBelch("stackSize = %d\n", stackSize);
737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760
	*/
#endif
	return;
    }

    popOffReal();
}

/* -----------------------------------------------------------------------------
 *  Finds the next object to be considered for retainer profiling and store
 *  its pointer to *c.
 *  Test if the topmost stack element indicates that more objects are left,
 *  and if so, retrieve the first object and store its pointer to *c. Also,
 *  set *cp and *r appropriately, both of which are stored in the stack element.
 *  The topmost stack element then is overwritten so as for it to now denote
 *  the next object.
 *  If the topmost stack element indicates no more objects are left, pop
 *  off the stack element until either an object can be retrieved or
 *  the current stack chunk becomes empty, indicated by rtsTrue returned by
 *  isOnBoundary(), in which case *c is set to NULL.
 *  Note:
 *    It is okay to call this function even when the current stack chunk
 *    is empty.
 * -------------------------------------------------------------------------- */
761
static INLINE void
762
pop( StgClosure **c, StgClosure **cp, retainer *r )
763 764 765 766
{
    stackElement *se;

#ifdef DEBUG_RETAINER
767
    // debugBelch("pop(): stackTop = 0x%x, currentStackBoundary = 0x%x\n", stackTop, currentStackBoundary);
768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789
#endif

    do {
	if (isOnBoundary()) {     // if the current stack chunk is depleted
	    *c = NULL;
	    return;
	}

	se = stackTop;

	switch (get_itbl(se->c)->type) {
	    // two children (fixed), no SRT
	    // nothing in se.info
	case CONSTR_2_0:
	    *c = se->c->payload[1];
	    *cp = se->c;
	    *r = se->c_child_r;
	    popOff();
	    return;

	    // three children (fixed), no SRT
	    // need to push a stackElement
790 791
        case MVAR_CLEAN:
        case MVAR_DIRTY:
792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817
	    if (se->info.next.step == 2) {
		*c = (StgClosure *)((StgMVar *)se->c)->tail;
		se->info.next.step++;             // move to the next step
		// no popOff
	    } else {
		*c = ((StgMVar *)se->c)->value;
		popOff();
	    }
	    *cp = se->c;
	    *r = se->c_child_r;
	    return;

	    // three children (fixed), no SRT
	case WEAK:
	    if (se->info.next.step == 2) {
		*c = ((StgWeak *)se->c)->value;
		se->info.next.step++;
		// no popOff
	    } else {
		*c = ((StgWeak *)se->c)->finalizer;
		popOff();
	    }
	    *cp = se->c;
	    *r = se->c_child_r;
	    return;

818 819 820 821 822 823
	case TREC_CHUNK: {
	    // These are pretty complicated: we have N entries, each
	    // of which contains 3 fields that we want to follow.  So
	    // we divide the step counter: the 2 low bits indicate
	    // which field, and the rest of the bits indicate the
	    // entry number (starting from zero).
824
	    TRecEntry *entry;
825 826 827 828 829 830 831
	    nat entry_no = se->info.next.step >> 2;
	    nat field_no = se->info.next.step & 3;
	    if (entry_no == ((StgTRecChunk *)se->c)->next_entry_idx) {
		*c = NULL;
		popOff();
		return;
	    }
832
	    entry = &((StgTRecChunk *)se->c)->entries[entry_no];
833 834 835 836 837 838 839 840 841 842 843 844 845
	    if (field_no == 0) {
		*c = (StgClosure *)entry->tvar;
	    } else if (field_no == 1) {
		*c = entry->expected_value;
	    } else {
		*c = entry->new_value;
	    }
	    *cp = se->c;
	    *r = se->c_child_r;
	    se->info.next.step++;
	    return;
	}

846
	case CONSTR:
847
	case PRIM:
848
	case MUT_PRIM:
849 850 851
	case BCO:
	case CONSTR_STATIC:
	    // StgMutArrPtr.ptrs, no SRT
852 853
	case MUT_ARR_PTRS_CLEAN:
	case MUT_ARR_PTRS_DIRTY:
854
	case MUT_ARR_PTRS_FROZEN:
855
	case MUT_ARR_PTRS_FROZEN0:
856 857 858 859 860 861 862 863 864 865 866 867
	    *c = find_ptrs(&se->info);
	    if (*c == NULL) {
		popOff();
		break;
	    }
	    *cp = se->c;
	    *r = se->c_child_r;
	    return;

	    // layout.payload.ptrs, SRT
	case FUN:         // always a heap object
	case FUN_2_0:
868 869 870 871 872 873 874 875 876 877 878
	    if (se->info.type == posTypePtrs) {
		*c = find_ptrs(&se->info);
		if (*c != NULL) {
		    *cp = se->c;
		    *r = se->c_child_r;
		    return;
		}
		init_srt_fun(&se->info, get_fun_itbl(se->c));
	    }
	    goto do_srt;

879 880 881 882 883 884 885 886 887
	case THUNK:
	case THUNK_2_0:
	    if (se->info.type == posTypePtrs) {
		*c = find_ptrs(&se->info);
		if (*c != NULL) {
		    *cp = se->c;
		    *r = se->c_child_r;
		    return;
		}
888
		init_srt_thunk(&se->info, get_thunk_itbl(se->c));
889
	    }
890
	    goto do_srt;
891 892

	    // SRT
893
	do_srt:
894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917
	case THUNK_STATIC:
	case FUN_STATIC:
	case FUN_0_1:
	case FUN_0_2:
	case THUNK_0_1:
	case THUNK_0_2:
	case FUN_1_0:
	case FUN_1_1:
	case THUNK_1_0:
	case THUNK_1_1:
	    *c = find_srt(&se->info);
	    if (*c != NULL) {
		*cp = se->c;
		*r = se->c_child_r;
		return;
	    }
	    popOff();
	    break;

	    // no child (fixed), no SRT
	case CONSTR_0_1:
	case CONSTR_0_2:
	case ARR_WORDS:
	    // one child (fixed), no SRT
918 919
	case MUT_VAR_CLEAN:
	case MUT_VAR_DIRTY:
920 921 922 923 924
	case THUNK_SELECTOR:
	case IND_PERM:
	case CONSTR_1_1:
	    // cannot appear
	case PAP:
925 926
	case AP:
	case AP_STACK:
927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983
	case TSO:
	case IND_STATIC:
	case CONSTR_NOCAF_STATIC:
	    // stack objects
	case RET_DYN:
	case UPDATE_FRAME:
	case CATCH_FRAME:
	case STOP_FRAME:
	case RET_BCO:
	case RET_SMALL:
	case RET_BIG:
	    // invalid objects
	case IND:
	case INVALID_OBJECT:
	default:
	    barf("Invalid object *c in pop()");
	    return;
	}
    } while (rtsTrue);
}

/* -----------------------------------------------------------------------------
 * RETAINER PROFILING ENGINE
 * -------------------------------------------------------------------------- */

void
initRetainerProfiling( void )
{
    initializeAllRetainerSet();
    retainerGeneration = 0;
}

/* -----------------------------------------------------------------------------
 *  This function must be called before f-closing prof_file.
 * -------------------------------------------------------------------------- */
void
endRetainerProfiling( void )
{
#ifdef SECOND_APPROACH
    outputAllRetainerSet(prof_file);
#endif
}

/* -----------------------------------------------------------------------------
 *  Returns the actual pointer to the retainer set of the closure *c.
 *  It may adjust RSET(c) subject to flip.
 *  Side effects:
 *    RSET(c) is initialized to NULL if its current value does not
 *    conform to flip.
 *  Note:
 *    Even though this function has side effects, they CAN be ignored because
 *    subsequent calls to retainerSetOf() always result in the same return value
 *    and retainerSetOf() is the only way to retrieve retainerSet of a given
 *    closure.
 *    We have to perform an XOR (^) operation each time a closure is examined.
 *    The reason is that we do not know when a closure is visited last.
 * -------------------------------------------------------------------------- */
984
static INLINE void
985 986 987 988 989 990 991 992 993 994
maybeInitRetainerSet( StgClosure *c )
{
    if (!isRetainerSetFieldValid(c)) {
	setRetainerSetToNull(c);
    }
}

/* -----------------------------------------------------------------------------
 * Returns rtsTrue if *c is a retainer.
 * -------------------------------------------------------------------------- */
995
static INLINE rtsBool
996 997 998 999 1000 1001 1002 1003 1004 1005
isRetainer( StgClosure *c )
{
    switch (get_itbl(c)->type) {
	//
	//  True case
	//
	// TSOs MUST be retainers: they constitute the set of roots.
    case TSO:

	// mutable objects
1006
    case MUT_PRIM:
1007 1008
    case MVAR_CLEAN:
    case MVAR_DIRTY:
1009 1010
    case MUT_VAR_CLEAN:
    case MUT_VAR_DIRTY:
1011 1012
    case MUT_ARR_PTRS_CLEAN:
    case MUT_ARR_PTRS_DIRTY:
1013
    case MUT_ARR_PTRS_FROZEN:
1014
    case MUT_ARR_PTRS_FROZEN0:
1015 1016 1017 1018 1019 1020 1021 1022 1023

	// thunks are retainers.
    case THUNK:
    case THUNK_1_0:
    case THUNK_0_1:
    case THUNK_2_0:
    case THUNK_1_1:
    case THUNK_0_2:
    case THUNK_SELECTOR:
1024 1025
    case AP:
    case AP_STACK:
1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 1056

	// Static thunks, or CAFS, are obviously retainers.
    case THUNK_STATIC:

	// WEAK objects are roots; there is separate code in which traversing
	// begins from WEAK objects.
    case WEAK:
	return rtsTrue;

	//
	// False case
	//

	// constructors
    case CONSTR:
    case CONSTR_1_0:
    case CONSTR_0_1:
    case CONSTR_2_0:
    case CONSTR_1_1:
    case CONSTR_0_2:
	// functions
    case FUN:
    case FUN_1_0:
    case FUN_0_1:
    case FUN_2_0:
    case FUN_1_1:
    case FUN_0_2:
	// partial applications
    case PAP:
	// indirection
    case IND_PERM:
1057
    case BLACKHOLE:
1058 1059 1060 1061
	// static objects
    case CONSTR_STATIC:
    case FUN_STATIC:
	// misc
1062
    case PRIM:
1063 1064
    case BCO:
    case ARR_WORDS:
1065 1066
	// STM
    case TREC_CHUNK:
1067 1068 1069 1070 1071 1072 1073
	return rtsFalse;

	//
	// Error case
	//
	// IND_STATIC cannot be *c, *cp, *r in the retainer profiling loop.
    case IND_STATIC:
1074
	// CONSTR_NOCAF_STATIC
1075 1076 1077 1078 1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103
	// cannot be *c, *cp, *r in the retainer profiling loop.
    case CONSTR_NOCAF_STATIC:
	// Stack objects are invalid because they are never treated as
	// legal objects during retainer profiling.
    case UPDATE_FRAME:
    case CATCH_FRAME:
    case STOP_FRAME:
    case RET_DYN:
    case RET_BCO:
    case RET_SMALL:
    case RET_BIG:
	// other cases
    case IND:
    case INVALID_OBJECT:
    default:
	barf("Invalid object in isRetainer(): %d", get_itbl(c)->type);
	return rtsFalse;
    }
}

/* -----------------------------------------------------------------------------
 *  Returns the retainer function value for the closure *c, i.e., R(*c).
 *  This function does NOT return the retainer(s) of *c.
 *  Invariants:
 *    *c must be a retainer.
 *  Note:
 *    Depending on the definition of this function, the maintenance of retainer
 *    sets can be made easier. If most retainer sets are likely to be created
 *    again across garbage collections, refreshAllRetainerSet() in
1104
 *    RetainerSet.c can simply do nothing.
1105 1106 1107 1108
 *    If this is not the case, we can free all the retainer sets and
 *    re-initialize the hash table.
 *    See refreshAllRetainerSet() in RetainerSet.c.
 * -------------------------------------------------------------------------- */
1109
static INLINE retainer
1110 1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132
getRetainerFrom( StgClosure *c )
{
    ASSERT(isRetainer(c));

#if defined(RETAINER_SCHEME_INFO)
    // Retainer scheme 1: retainer = info table
    return get_itbl(c);
#elif defined(RETAINER_SCHEME_CCS)
    // Retainer scheme 2: retainer = cost centre stack
    return c->header.prof.ccs;
#elif defined(RETAINER_SCHEME_CC)
    // Retainer scheme 3: retainer = cost centre
    return c->header.prof.ccs->cc;
#endif
}

/* -----------------------------------------------------------------------------
 *  Associates the retainer set *s with the closure *c, that is, *s becomes
 *  the retainer set of *c.
 *  Invariants:
 *    c != NULL
 *    s != NULL
 * -------------------------------------------------------------------------- */
1133
static INLINE void
1134
associate( StgClosure *c, RetainerSet *s )
1135 1136 1137 1138 1139 1140
{
    // StgWord has the same size as pointers, so the following type
    // casting is okay.
    RSET(c) = (RetainerSet *)((StgWord)s | flip);
}

1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168
/* -----------------------------------------------------------------------------
   Call retainClosure for each of the closures covered by a large bitmap.
   -------------------------------------------------------------------------- */

static void
retain_large_bitmap (StgPtr p, StgLargeBitmap *large_bitmap, nat size,
		     StgClosure *c, retainer c_child_r)
{
    nat i, b;
    StgWord bitmap;
    
    b = 0;
    bitmap = large_bitmap->bitmap[b];
    for (i = 0; i < size; ) {
	if ((bitmap & 1) == 0) {
	    retainClosure((StgClosure *)*p, c, c_child_r);
	}
	i++;
	p++;
	if (i % BITS_IN(W_) == 0) {
	    b++;
	    bitmap = large_bitmap->bitmap[b];
	} else {
	    bitmap = bitmap >> 1;
	}
    }
}

1169
static INLINE StgPtr
1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183
retain_small_bitmap (StgPtr p, nat size, StgWord bitmap,
		     StgClosure *c, retainer c_child_r)
{
    while (size > 0) {
	if ((bitmap & 1) == 0) {
	    retainClosure((StgClosure *)*p, c, c_child_r);
	}
	p++;
	bitmap = bitmap >> 1;
	size--;
    }
    return p;
}

1184 1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217 1218 1219 1220 1221 1222 1223 1224 1225 1226 1227 1228 1229
/* -----------------------------------------------------------------------------
 * Call retainClosure for each of the closures in an SRT.
 * ------------------------------------------------------------------------- */

static void
retain_large_srt_bitmap (StgLargeSRT *srt, StgClosure *c, retainer c_child_r)
{
    nat i, b, size;
    StgWord bitmap;
    StgClosure **p;
    
    b = 0;
    p = (StgClosure **)srt->srt;
    size   = srt->l.size;
    bitmap = srt->l.bitmap[b];
    for (i = 0; i < size; ) {
	if ((bitmap & 1) != 0) {
	    retainClosure((StgClosure *)*p, c, c_child_r);
	}
	i++;
	p++;
	if (i % BITS_IN(W_) == 0) {
	    b++;
	    bitmap = srt->l.bitmap[b];
	} else {
	    bitmap = bitmap >> 1;
	}
    }
}

static INLINE void
retainSRT (StgClosure **srt, nat srt_bitmap, StgClosure *c, retainer c_child_r)
{
  nat bitmap;
  StgClosure **p;

  bitmap = srt_bitmap;
  p = srt;

  if (bitmap == (StgHalfWord)(-1)) {  
      retain_large_srt_bitmap( (StgLargeSRT *)srt, c, c_child_r );
      return;
  }

  while (bitmap != 0) {
      if ((bitmap & 1) != 0) {
1230
#if defined(__PIC__) && defined(mingw32_TARGET_OS)
1231
	  if ( (unsigned long)(*srt) & 0x1 ) {
1232
	      retainClosure(* (StgClosure**) ((unsigned long) (*srt) & ~0x1), 
1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 1245
			    c, c_child_r);
	  } else {
	      retainClosure(*srt,c,c_child_r);
	  }
#else
	  retainClosure(*srt,c,c_child_r);
#endif
      }
      p++;
      bitmap = bitmap >> 1;
  }
}

1246 1247 1248 1249 1250 1251
/* -----------------------------------------------------------------------------
 *  Process all the objects in the stack chunk from stackStart to stackEnd
 *  with *c and *c_child_r being their parent and their most recent retainer,
 *  respectively. Treat stackOptionalFun as another child of *c if it is
 *  not NULL.
 *  Invariants:
1252
 *    *c is one of the following: TSO, AP_STACK.
1253 1254 1255 1256 1257 1258 1259 1260 1261 1262 1263 1264
 *    If *c is TSO, c == c_child_r.
 *    stackStart < stackEnd.
 *    RSET(c) and RSET(c_child_r) are valid, i.e., their
 *    interpretation conforms to the current value of flip (even when they
 *    are interpreted to be NULL).
 *    If *c is TSO, its state is not any of ThreadRelocated, ThreadComplete,
 *    or ThreadKilled, which means that its stack is ready to process.
 *  Note:
 *    This code was almost plagiarzied from GC.c! For each pointer,
 *    retainClosure() is invoked instead of evacuate().
 * -------------------------------------------------------------------------- */
static void
1265
retainStack( StgClosure *c, retainer c_child_r,
1266
	     StgPtr stackStart, StgPtr stackEnd )
1267 1268
{
    stackElement *oldStackBoundary;
1269 1270
    StgPtr p;
    StgRetInfoTable *info;
1271
    StgWord32 bitmap;
1272
    nat size;
1273 1274 1275 1276 1277 1278 1279 1280 1281 1282 1283 1284 1285 1286 1287 1288

#ifdef DEBUG_RETAINER
    cStackSize++;
    if (cStackSize > maxCStackSize) maxCStackSize = cStackSize;
#endif

    /*
      Each invocation of retainStack() creates a new virtual
      stack. Since all such stacks share a single common stack, we
      record the current currentStackBoundary, which will be restored
      at the exit.
    */
    oldStackBoundary = currentStackBoundary;
    currentStackBoundary = stackTop;

#ifdef DEBUG_RETAINER
1289
    // debugBelch("retainStack() called: oldStackBoundary = 0x%x, currentStackBoundary = 0x%x\n", oldStackBoundary, currentStackBoundary);
1290 1291
#endif

1292 1293 1294 1295 1296
    ASSERT(get_itbl(c)->type != TSO || 
	   (((StgTSO *)c)->what_next != ThreadRelocated &&
	    ((StgTSO *)c)->what_next != ThreadComplete &&
	    ((StgTSO *)c)->what_next != ThreadKilled));
    
1297 1298
    p = stackStart;
    while (p < stackEnd) {
1299
	info = get_ret_itbl((StgClosure *)p);
1300

1301
	switch(info->i.type) {
1302 1303 1304 1305 1306 1307 1308 1309

	case UPDATE_FRAME:
	    retainClosure(((StgUpdateFrame *)p)->updatee, c, c_child_r);
	    p += sizeofW(StgUpdateFrame);
	    continue;

	case STOP_FRAME:
	case CATCH_FRAME:
1310 1311 1312
	case CATCH_STM_FRAME:
	case CATCH_RETRY_FRAME:
	case ATOMICALLY_FRAME:
1313
	case RET_SMALL:
1314 1315
	    bitmap = BITMAP_BITS(info->i.layout.bitmap);
	    size   = BITMAP_SIZE(info->i.layout.bitmap);
1316
	    p++;
1317 1318
	    p = retain_small_bitmap(p, size, bitmap, c, c_child_r);

1319
	follow_srt:
1320
	    retainSRT((StgClosure **)GET_SRT(info), info->i.srt_bitmap, c, c_child_r);
1321
	    continue;
1322

1323 1324 1325 1326 1327 1328 1329 1330 1331 1332
	case RET_BCO: {
	    StgBCO *bco;
	    
	    p++;
	    retainClosure((StgClosure *)*p, c, c_child_r);
	    bco = (StgBCO *)*p;
	    p++;
	    size = BCO_BITMAP_SIZE(bco);
	    retain_large_bitmap(p, BCO_BITMAP(bco), size, c, c_child_r);
	    p += size;
1333
	    continue;
1334
	}
1335

1336
	    // large bitmap (> 32 entries, or > 64 on a 64-bit machine) 
1337
	case RET_BIG:
1338
	    size = GET_LARGE_BITMAP(&info->i)->size;
1339
	    p++;
1340
	    retain_large_bitmap(p, GET_LARGE_BITMAP(&info->i),
1341 1342 1343 1344
				size, c, c_child_r);
	    p += size;
	    // and don't forget to follow the SRT 
	    goto follow_srt;
1345

1346 1347 1348 1349 1350 1351
	    // Dynamic bitmap: the mask is stored on the stack 
	case RET_DYN: {
	    StgWord dyn;
	    dyn = ((StgRetDyn *)p)->liveness;

	    // traverse the bitmap first
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	    bitmap = RET_DYN_LIVENESS(dyn);
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	    p      = (P_)&((StgRetDyn *)p)->payload[0];
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	    size   = RET_DYN_BITMAP_SIZE;
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	    p = retain_small_bitmap(p, size, bitmap, c, c_child_r);
	    
	    // skip over the non-ptr words
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	    p += RET_DYN_NONPTRS(dyn) + RET_DYN_NONPTR_REGS_SIZE;
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	    // follow the ptr words
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	    for (size = RET_DYN_PTRS(dyn); size > 0; size--) {
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		retainClosure((StgClosure *)*p, c, c_child_r);
		p++;
	    }
	    continue;
	}

	case RET_FUN: {
	    StgRetFun *ret_fun = (StgRetFun *)p;
	    StgFunInfoTable *fun_info;
	    
	    retainClosure(ret_fun->fun, c, c_child_r);
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	    fun_info = get_fun_itbl(UNTAG_CLOSURE(ret_fun->fun));
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	    p = (P_)&ret_fun->payload;
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	    switch (fun_info->f.fun_type) {
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	    case ARG_GEN:
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		bitmap = BITMAP_BITS(fun_info->f.b.bitmap);
		size = BITMAP_SIZE(fun_info->f.b.bitmap);
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		p = retain_small_bitmap(p, size, bitmap, c, c_child_r);
		break;
	    case ARG_GEN_BIG:
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		size = GET_FUN_LARGE_BITMAP(fun_info)->size;
		retain_large_bitmap(p, GET_FUN_LARGE_BITMAP(fun_info), 
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				    size, c, c_child_r);
		p += size;
		break;
	    default:
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		bitmap = BITMAP_BITS(stg_arg_bitmaps[fun_info->f.fun_type]);
		size = BITMAP_SIZE(stg_arg_bitmaps[fun_info->f.fun_type]);
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		p = retain_small_bitmap(p, size, bitmap, c, c_child_r);
		break;
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	    }
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	    goto follow_srt;
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	}
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	default:
	    barf("Invalid object found in retainStack(): %d",
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		 (int)(info->i.type));
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	}
    }

    // restore currentStackBoundary
    currentStackBoundary = oldStackBoundary;
#ifdef DEBUG_RETAINER
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    // debugBelch("retainStack() finished: currentStackBoundary = 0x%x\n", currentStackBoundary);
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#endif

#ifdef DEBUG_RETAINER
    cStackSize--;
#endif
}

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/* ----------------------------------------------------------------------------
 * Call retainClosure for each of the children of a PAP/AP
 * ------------------------------------------------------------------------- */

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static INLINE StgPtr
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retain_PAP_payload (StgClosure *pap,    /* NOT tagged */
                    retainer c_child_r, /* NOT tagged */ 
                    StgClosure *fun,    /* tagged */
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		    StgClosure** payload, StgWord n_args)
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{
    StgPtr p;
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    StgWord bitmap;
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    StgFunInfoTable *fun_info;

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    retainClosure(fun, pap, c_child_r);
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    fun = UNTAG_CLOSURE(fun);
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    fun_info = get_fun_itbl(fun);
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    ASSERT(fun_info->i.type != PAP);

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    p = (StgPtr)payload;
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    switch (fun_info->f.fun_type) {
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    case ARG_GEN:
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	bitmap = BITMAP_BITS(fun_info->f.b.bitmap);
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	p = retain_small_bitmap(p, n_args, bitmap, 
				pap, c_child_r);
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	break;
    case ARG_GEN_BIG:
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	retain_large_bitmap(p, GET_FUN_LARGE_BITMAP(fun_info),
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			    n_args, pap, c_child_r);
	p += n_args;
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	break;
    case ARG_BCO:
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	retain_large_bitmap((StgPtr)payload, BCO_BITMAP(fun),
			    n_args, pap, c_child_r);
	p += n_args;
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	break;
    default:
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	bitmap = BITMAP_BITS(stg_arg_bitmaps[fun_info->f.fun_type]);
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	p = retain_small_bitmap(p, n_args, bitmap, pap, c_child_r);
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	break;
    }
    return p;
}

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/* -----------------------------------------------------------------------------
 *  Compute the retainer set of *c0 and all its desecents by traversing.
 *  *cp0 is the parent of *c0, and *r0 is the most recent retainer of *c0.
 *  Invariants:
 *    c0 = cp0 = r0 holds only for root objects.
 *    RSET(cp0) and RSET(r0) are valid, i.e., their
 *    interpretation conforms to the current value of flip (even when they
 *    are interpreted to be NULL).
 *    However, RSET(c0) may be corrupt, i.e., it may not conform to
 *    the current value of flip. If it does not, during the execution
 *    of this function, RSET(c0) must be initialized as well as all
 *    its descendants.
 *  Note:
 *    stackTop must be the same at the beginning and the exit of this function.
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 *    *c0 can be TSO (as well as AP_STACK).
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 * -------------------------------------------------------------------------- */
static void
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retainClosure( StgClosure *c0, StgClosure *cp0, retainer r0 )
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{
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    // c = Current closure                          (possibly tagged)
    // cp = Current closure's Parent                (NOT tagged)
    // r = current closures' most recent Retainer   (NOT tagged)
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    // c_child_r = current closure's children's most recent retainer
    // first_child = first child of c
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    StgClosure *c, *cp, *first_child;
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    RetainerSet *s, *retainerSetOfc;
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    retainer r, c_child_r;
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    StgWord typeOfc;

#ifdef DEBUG_RETAINER
    // StgPtr oldStackTop;
#endif

#ifdef DEBUG_RETAINER
    // oldStackTop = stackTop;
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    // debugBelch("retainClosure() called: c0 = 0x%x, cp0 = 0x%x, r0 = 0x%x\n", c0, cp0, r0);
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#endif

    // (c, cp, r) = (c0, cp0, r0)
    c = c0;
    cp = cp0;
    r = r0;
    goto inner_loop;

loop:
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    //debugBelch("loop");
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    // pop to (c, cp, r);
    pop(&c, &cp, &r);

    if (c == NULL) {
#ifdef DEBUG_RETAINER
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	// debugBelch("retainClosure() ends: oldStackTop = 0x%x, stackTop = 0x%x\n", oldStackTop, stackTop);
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#endif
	return;
    }

1515
    //debugBelch("inner_loop");
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inner_loop:
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    c = UNTAG_CLOSURE(c);

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    // c  = current closure under consideration,
    // cp = current closure's parent,
    // r  = current closure's most recent retainer
    //
    // Loop invariants (on the meaning of c, cp, r, and their retainer sets):
    //   RSET(cp) and RSET(r) are valid.
    //   RSET(c) is valid only if c has been visited before.
    //
    // Loop invariants (on the relation between c, cp, and r)
    //   if cp is not a retainer, r belongs to RSET(cp).
    //   if cp is a retainer, r == cp.

    typeOfc = get_itbl(c)->type;

#ifdef DEBUG_RETAINER
    switch (typeOfc) {
    case IND_STATIC:
    case CONSTR_NOCAF_STATIC:
    case CONSTR_STATIC:
    case THUNK_STATIC:
    case FUN_STATIC:
	break;
    default:
	if (retainerSetOf(c) == NULL) {   // first visit?
	    costArray[typeOfc] += cost(c);
	    sumOfNewCost += cost(c);
	}
	break;
    }
#endif

    // special cases
    switch (typeOfc) {
    case TSO:
	if (((StgTSO *)c)->what_next == ThreadComplete ||
	    ((StgTSO *)c)->what_next == ThreadKilled) {
#ifdef DEBUG_RETAINER
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	    debugBelch("ThreadComplete or ThreadKilled encountered in retainClosure()\n");
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#endif
	    goto loop;
	}
	if (((StgTSO *)c)->what_next == ThreadRelocated) {
#ifdef DEBUG_RETAINER
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	    debugBelch("ThreadRelocated encountered in retainClosure()\n");
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#endif
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	    c = (StgClosure *)((StgTSO *)c)->_link;
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	    goto inner_loop;
	}
	break;

    case IND_STATIC:
	// We just skip IND_STATIC, so its retainer set is never computed.
	c = ((StgIndStatic *)c)->indirectee;
	goto inner_loop;
	// static objects with no pointers out, so goto loop.
    case CONSTR_NOCAF_STATIC:
	// It is not just enough not to compute the retainer set for *c; it is
	// mandatory because CONSTR_NOCAF_STATIC are not reachable from
	// scavenged_static_objects, the list from which is assumed to traverse
	// all static objects after major garbage collections.
	goto loop;
    case THUNK_STATIC:
    case FUN_STATIC:
1583
	if (get_itbl(c)->srt_bitmap == 0) {
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	    // No need to compute the retainer set; no dynamic objects
	    // are reachable from *c.
	    //
	    // Static objects: if we traverse all the live closures,
	    // including static closures, during each heap census then
	    // we will observe that some static closures appear and
	    // disappear.  eg. a closure may contain a pointer to a
	    // static function 'f' which is not otherwise reachable
	    // (it doesn't indirectly point to any CAFs, so it doesn't
	    // appear in any SRTs), so we would find 'f' during
	    // traversal.  However on the next sweep there may be no
	    // closures pointing to 'f'.
	    //
	    // We must therefore ignore static closures whose SRT is
	    // empty, because these are exactly the closures that may
	    // "appear".  A closure with a non-empty SRT, and which is
	    // still required, will always be reachable.
	    //
	    // But what about CONSTR_STATIC?  Surely these may be able
	    // to appear, and they don't have SRTs, so we can't
	    // check.  So for now, we're calling
	    // resetStaticObjectForRetainerProfiling() from the
	    // garbage collector to reset the retainer sets in all the
	    // reachable static objects.
	    goto loop;
	}
    default:
	break;
    }

    // The above objects are ignored in computing the average number of times
    // an object is visited.
    timesAnyObjectVisited++;

    // If this is the first visit to c, initialize its retainer set.
    maybeInitRetainerSet(c);
    retainerSetOfc = retainerSetOf(c);

    // Now compute s:
    //    isRetainer(cp) == rtsTrue => s == NULL
    //    isRetainer(cp) == rtsFalse => s == cp.retainer
    if (isRetainer(cp))
	s = NULL;
    else
	s = retainerSetOf(cp);

    // (c, cp, r, s) is available.

    // (c, cp, r, s, R_r) is available, so compute the retainer set for *c.
    if (retainerSetOfc == NULL) {
	// This is the first visit to *c.
	numObjectVisited++;

	if (s == NULL)
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	    associate(c, singleton(r));
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	else
	    // s is actually the retainer set of *c!
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	    associate(c, s);
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	// compute c_child_r
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	c_child_r = isRetainer(c) ? getRetainerFrom(c) : r;
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    } else {
	// This is not the first visit to *c.
1647
	if (isMember(r, retainerSetOfc))
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	    goto loop;          // no need to process child

	if (s == NULL)
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	    associate(c, addElement(r, retainerSetOfc));
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	else {
	    // s is not NULL and cp is not a retainer. This means that
	    // each time *cp is visited, so is *c. Thus, if s has
	    // exactly one more element in its retainer set than c, s
	    // is also the new retainer set for *c.
	    if (s->num == retainerSetOfc->num + 1) {
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		associate(c, s);
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	    }
	    // Otherwise, just add R_r to the current retainer set of *c.
	    else {
1662
		associate(c, addElement(r, retainerSetOfc));
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	    }
	}

	if (isRetainer(c))
	    goto loop;          // no need to process child

	// compute c_child_r
	c_child_r = r;
    }

    // now, RSET() of all of *c, *cp, and *r is valid.
    // (c, c_child_r) are available.

    // process child

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    // Special case closures: we process these all in one go rather
    // than attempting to save the current position, because doing so
    // would be hard.
    switch (typeOfc) {
    case TSO:
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	retainStack(c, c_child_r,
		    ((StgTSO *)c)->sp,
		    ((StgTSO *)c)->stack + ((StgTSO *)c)->stack_size);
	goto loop;
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    case PAP:
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    {
	StgPAP *pap = (StgPAP *)c;
	retain_PAP_payload(c, c_child_r, pap->fun, pap->payload, pap->n_args);
	goto loop;
    }

1695
    case AP:
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    {
	StgAP *ap = (StgAP *)c;
	retain_PAP_payload(c, c_child_r, ap->fun, ap->payload, ap->n_args);
1699
	goto loop;
1700
    }
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    case AP_STACK:
	retainClosure(((StgAP_STACK *)c)->fun, c, c_child_r);
1704
	retainStack(c, c_child_r,
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		    (StgPtr)((StgAP_STACK *)c)->payload,
		    (StgPtr)((StgAP_STACK *)c)->payload +
		             ((StgAP_STACK *)c)->size);
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	goto loop;
    }

    push(c, c_child_r, &first_child);

    // If first_child is null,