Reorganisation of the source tree

Most of the other users of the fptools build system have migrated to
Cabal, and with the move to darcs we can now flatten the source tree
without losing history, so here goes.

The main change is that the ghc/ subdir is gone, and most of what it
contained is now at the top level.  The build system now makes no
pretense at being multi-project, it is just the GHC build system.

No doubt this will break many things, and there will be a period of
instability while we fix the dependencies.  A straightforward build
should work, but I haven't yet fixed binary/source distributions.
Changes to the Building Guide will follow, too.

1 files changed, 2338 insertions, 0 deletions

diff --git a/rts/RetainerProfile.c b/rts/RetainerProfile.c
new file mode 100644
index 0000000000..c5c3de5314
--- /dev/null
+++ b/rts/RetainerProfile.c
@@ -0,0 +1,2338 @@
+/* -----------------------------------------------------------------------------
+ *
+ * (c) The GHC Team, 2001
+ * Author: Sungwoo Park
+ *
+ * Retainer profiling.
+ *
+ * ---------------------------------------------------------------------------*/
+
+#ifdef PROFILING
+
+// Turn off inlining when debugging - it obfuscates things
+#ifdef DEBUG
+#define INLINE
+#else
+#define INLINE inline
+#endif
+
+#include "Rts.h"
+#include "RtsUtils.h"
+#include "RetainerProfile.h"
+#include "RetainerSet.h"
+#include "Schedule.h"
+#include "Printer.h"
+#include "Storage.h"
+#include "RtsFlags.h"
+#include "Weak.h"
+#include "Sanity.h"
+#include "Profiling.h"
+#include "Stats.h"
+#include "BlockAlloc.h"
+#include "ProfHeap.h"
+#include "Apply.h"
+
+/*
+  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().
+ */
+
+StgWord flip = 0;     // flip bit
+                      // must be 0 if DEBUG_RETAINER is on (for static closures)
+
+#define setRetainerSetToNull(c)   \
+  (c)->header.prof.hp.rs = (RetainerSet *)((StgWord)NULL | flip)
+
+static void retainStack(StgClosure *, retainer, StgPtr, StgPtr);
+static void retainClosure(StgClosure *, StgClosure *, retainer);
+#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,
+    posTypeLargeSRT,
+} 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;
+	StgWord    srt_bitmap;
+    } srt;
+
+    // Large SRT
+    struct {
+	StgLargeSRT *srt;
+	StgWord offset;
+    } large_srt;
+	
+} nextPos;
+
+typedef struct {
+    nextPosType type;
+    nextPos next;
+} stackPos;
+
+typedef struct {
+    StgClosure *c;
+    retainer c_child_r;
+    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.
+ */
+static bdescr *firstStack = NULL;
+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.
+ * -------------------------------------------------------------------------- */
+static INLINE void
+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.
+ * -------------------------------------------------------------------------- */
+static INLINE void
+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.
+ * -------------------------------------------------------------------------- */
+static INLINE rtsBool
+isEmptyRetainerStack( void )
+{
+    return (firstStack == currentStack) && stackTop == stackLimit;
+}
+
+/* -----------------------------------------------------------------------------
+ * Returns size of stack
+ * -------------------------------------------------------------------------- */
+#ifdef DEBUG
+lnat
+retainerStackBlocks( void )
+{
+    bdescr* bd;
+    lnat res = 0;
+
+    for (bd = firstStack; bd != NULL; bd = bd->link) 
+      res += bd->blocks;
+
+    return res;
+}
+#endif
+
+/* -----------------------------------------------------------------------------
+ * Returns rtsTrue if stackTop is at the stack boundary of the current stack,
+ * i.e., if the current stack chunk is empty.
+ * -------------------------------------------------------------------------- */
+static INLINE rtsBool
+isOnBoundary( void )
+{
+    return stackTop == currentStackBoundary;
+}
+
+/* -----------------------------------------------------------------------------
+ * Initializes *info from ptrs and payload.
+ * Invariants:
+ *   payload[] begins with ptrs pointers followed by non-pointers.
+ * -------------------------------------------------------------------------- */
+static INLINE void
+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.
+ * -------------------------------------------------------------------------- */
+static INLINE StgClosure *
+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.
+ * -------------------------------------------------------------------------- */
+static INLINE void
+init_srt_fun( stackPos *info, StgFunInfoTable *infoTable )
+{
+    if (infoTable->i.srt_bitmap == (StgHalfWord)(-1)) {
+	info->type = posTypeLargeSRT;
+	info->next.large_srt.srt = (StgLargeSRT *)GET_FUN_SRT(infoTable);
+	info->next.large_srt.offset = 0;
+    } else {
+	info->type = posTypeSRT;
+	info->next.srt.srt = (StgClosure **)GET_FUN_SRT(infoTable);
+	info->next.srt.srt_bitmap = infoTable->i.srt_bitmap;
+    }
+}
+
+static INLINE void
+init_srt_thunk( stackPos *info, StgThunkInfoTable *infoTable )
+{
+    if (infoTable->i.srt_bitmap == (StgHalfWord)(-1)) {
+	info->type = posTypeLargeSRT;
+	info->next.large_srt.srt = (StgLargeSRT *)GET_SRT(infoTable);
+	info->next.large_srt.offset = 0;
+    } else {
+	info->type = posTypeSRT;
+	info->next.srt.srt = (StgClosure **)GET_SRT(infoTable);
+	info->next.srt.srt_bitmap = infoTable->i.srt_bitmap;
+    }
+}
+
+/* -----------------------------------------------------------------------------
+ * Find the next object from *info.
+ * -------------------------------------------------------------------------- */
+static INLINE StgClosure *
+find_srt( stackPos *info )
+{
+    StgClosure *c;
+    StgWord bitmap;
+
+    if (info->type == posTypeSRT) {
+	// Small SRT bitmap
+	bitmap = info->next.srt.srt_bitmap;
+	while (bitmap != 0) {
+	    if ((bitmap & 1) != 0) {
+#ifdef ENABLE_WIN32_DLL_SUPPORT
+		
+		if ((unsigned long)(*(info->next.srt.srt)) & 0x1)
+		    c = (* (StgClosure **)((unsigned long)*(info->next.srt.srt)) & ~0x1);
+		else
+		    c = *(info->next.srt.srt);
+#else
+		c = *(info->next.srt.srt);
+#endif
+		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;
+	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.
+ *     *c is not any of TSO, AP, PAP, AP_STACK, which means that
+ *        there cannot be any stack objects.
+ *  Note: SRTs are considered to  be children as well.
+ * -------------------------------------------------------------------------- */
+static INLINE void
+push( StgClosure *c, retainer c_child_r, StgClosure **first_child )
+{
+    stackElement se;
+    bdescr *nbd;      // Next Block Descriptor
+
+#ifdef DEBUG_RETAINER
+    // debugBelch("push(): stackTop = 0x%x, currentStackBoundary = 0x%x\n", stackTop, currentStackBoundary);
+#endif
+
+    ASSERT(get_itbl(c)->type != TSO);
+    ASSERT(get_itbl(c)->type != AP_STACK);
+
+    //
+    // 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 CAF_BLACKHOLE:
+    case BLACKHOLE:
+    case SE_BLACKHOLE:
+    case SE_CAF_BLACKHOLE:
+    case ARR_WORDS:
+	*first_child = NULL;
+	return;
+
+	// one child (fixed), no SRT
+    case MUT_VAR_CLEAN:
+    case MUT_VAR_DIRTY:
+	*first_child = ((StgMutVar *)c)->var;
+	return;
+    case THUNK_SELECTOR:
+	*first_child = ((StgSelector *)c)->selectee;
+	return;
+    case IND_PERM:
+    case IND_OLDGEN_PERM:
+    case IND_OLDGEN:
+	*first_child = ((StgInd *)c)->indirectee;
+	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
+    case MVAR:
+	// 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:
+    case STABLE_NAME:
+    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
+    case MUT_ARR_PTRS_CLEAN:
+    case MUT_ARR_PTRS_DIRTY:
+    case MUT_ARR_PTRS_FROZEN:
+    case MUT_ARR_PTRS_FROZEN0:
+	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:
+	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;
+
+    case THUNK:
+    case THUNK_2_0:
+	init_ptrs(&se.info, get_itbl(c)->layout.payload.ptrs, 
+		  (StgPtr)((StgThunk *)c)->payload);
+	*first_child = find_ptrs(&se.info);
+	if (*first_child == NULL)
+	    // no child from ptrs, so check SRT
+	    goto thunk_srt_only;
+	break;
+
+	// 1 fixed child, SRT
+    case FUN_1_0:
+    case FUN_1_1:
+	*first_child = c->payload[0];
+	ASSERT(*first_child != NULL);
+	init_srt_fun(&se.info, get_fun_itbl(c));
+	break;
+
+    case THUNK_1_0:
+    case THUNK_1_1:
+	*first_child = ((StgThunk *)c)->payload[0];
+	ASSERT(*first_child != NULL);
+	init_srt_thunk(&se.info, get_thunk_itbl(c));
+	break;
+
+    case FUN_STATIC:      // *c is a heap object.
+	ASSERT(get_itbl(c)->srt_bitmap != 0);
+    case FUN_0_1:
+    case FUN_0_2:
+    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:
+	ASSERT(get_itbl(c)->srt_bitmap != 0);
+    case THUNK_0_1:
+    case THUNK_0_2:
+    thunk_srt_only:
+        init_srt_thunk(&se.info, get_thunk_itbl(c));
+	*first_child = find_srt(&se.info);
+	if (*first_child == NULL)
+	    return;     // no child
+	break;
+	
+    case TVAR_WAIT_QUEUE:
+	*first_child = (StgClosure *)((StgTVarWaitQueue *)c)->waiting_tso;
+	se.info.next.step = 2;            // 2 = second
+	break;
+    case TVAR:
+	*first_child = (StgClosure *)((StgTVar *)c)->current_value;
+	break;
+    case TREC_HEADER:
+	*first_child = (StgClosure *)((StgTRecHeader *)c)->enclosing_trec;
+	break;
+    case TREC_CHUNK:
+	*first_child = (StgClosure *)((StgTRecChunk *)c)->prev_chunk;
+	se.info.next.step = 0;  // entry no.
+	break;
+
+	// cannot appear
+    case PAP:
+    case AP:
+    case AP_STACK:
+    case TSO:
+    case IND_STATIC:
+    case CONSTR_INTLIKE:
+    case CONSTR_CHARLIKE:
+    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_VEC_SMALL:
+    case RET_BIG:
+    case RET_VEC_BIG:
+	// invalid objects
+    case IND:
+    case BLOCKED_FETCH:
+    case FETCH_ME:
+    case FETCH_ME_BQ:
+    case RBH:
+    case REMOTE_REF:
+    case EVACUATED:
+    case INVALID_OBJECT:
+    default:
+	barf("Invalid object *c in push()");
+	return;
+    }
+
+    if (stackTop - 1 < stackBottom) {
+#ifdef DEBUG_RETAINER
+	// debugBelch("push() to the next stack.\n");
+#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.
+    *stackTop = se;
+
+#ifdef DEBUG_RETAINER
+    stackSize++;
+    if (stackSize > maxStackSize) maxStackSize = stackSize;
+    // ASSERT(stackSize >= 0);
+    // debugBelch("stackSize = %d\n", stackSize);
+#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
+ *    INLINE function (for the sake of execution speed).  popOffReal()
+ *    is called only within popOff() and nowhere else.
+ * -------------------------------------------------------------------------- */
+static void
+popOffReal(void)
+{
+    bdescr *pbd;    // Previous Block Descriptor
+
+#ifdef DEBUG_RETAINER
+    // debugBelch("pop() to the previous stack.\n");
+#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);
+	  debugBelch("stackSize = %d\n", stackSize);
+	*/
+#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);
+      debugBelch("stackSize = %d\n", stackSize);
+    */
+#endif
+}
+
+static INLINE void
+popOff(void) {
+#ifdef DEBUG_RETAINER
+    // debugBelch("\tpopOff(): stackTop = 0x%x, currentStackBoundary = 0x%x\n", stackTop, currentStackBoundary);
+#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);
+	  debugBelch("stackSize = %d\n", stackSize);
+	*/
+#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.
+ * -------------------------------------------------------------------------- */
+static INLINE void
+pop( StgClosure **c, StgClosure **cp, retainer *r )
+{
+    stackElement *se;
+
+#ifdef DEBUG_RETAINER
+    // debugBelch("pop(): stackTop = 0x%x, currentStackBoundary = 0x%x\n", stackTop, currentStackBoundary);
+#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
+	case MVAR:
+	    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;
+
+	case TVAR_WAIT_QUEUE:
+	    if (se->info.next.step == 2) {
+		*c = (StgClosure *)((StgTVarWaitQueue *)se->c)->next_queue_entry;
+		se->info.next.step++;             // move to the next step
+		// no popOff
+	    } else {
+		*c = (StgClosure *)((StgTVarWaitQueue *)se->c)->prev_queue_entry;
+		popOff();
+	    }
+	    *cp = se->c;
+	    *r = se->c_child_r;
+	    return;
+
+	case TVAR:
+	    *c = (StgClosure *)((StgTVar *)se->c)->first_wait_queue_entry;
+	    *cp = se->c;
+	    *r = se->c_child_r;
+	    popOff();
+	    return;
+
+	case TREC_HEADER:
+	    *c = (StgClosure *)((StgTRecHeader *)se->c)->current_chunk;
+	    *cp = se->c;
+	    *r = se->c_child_r;
+	    popOff();
+	    return;
+
+	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).
+	    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;
+	    }
+	    TRecEntry *entry = &((StgTRecChunk *)se->c)->entries[entry_no];
+	    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;
+	}
+
+	case CONSTR:
+	case STABLE_NAME:
+	case BCO:
+	case CONSTR_STATIC:
+	    // StgMutArrPtr.ptrs, no SRT
+	case MUT_ARR_PTRS_CLEAN:
+	case MUT_ARR_PTRS_DIRTY:
+	case MUT_ARR_PTRS_FROZEN:
+	case MUT_ARR_PTRS_FROZEN0:
+	    *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:
+	    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;
+
+	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;
+		}
+		init_srt_thunk(&se->info, get_thunk_itbl(se->c));
+	    }
+	    goto do_srt;
+
+	    // SRT
+	do_srt:
+	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 CAF_BLACKHOLE:
+	case BLACKHOLE:
+	case SE_BLACKHOLE:
+	case SE_CAF_BLACKHOLE:
+	case ARR_WORDS:
+	    // one child (fixed), no SRT
+	case MUT_VAR_CLEAN:
+	case MUT_VAR_DIRTY:
+	case THUNK_SELECTOR:
+	case IND_PERM:
+	case IND_OLDGEN_PERM:
+	case IND_OLDGEN:
+	case CONSTR_1_1:
+	    // cannot appear
+	case PAP:
+	case AP:
+	case AP_STACK:
+	case TSO:
+	case IND_STATIC:
+	case CONSTR_INTLIKE:
+	case CONSTR_CHARLIKE:
+	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_VEC_SMALL:
+	case RET_BIG:
+	case RET_VEC_BIG:
+	    // invalid objects
+	case IND:
+	case BLOCKED_FETCH:
+	case FETCH_ME:
+	case FETCH_ME_BQ:
+	case RBH:
+	case REMOTE_REF:
+	case EVACUATED:
+	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.
+ * -------------------------------------------------------------------------- */
+static INLINE void
+maybeInitRetainerSet( StgClosure *c )
+{
+    if (!isRetainerSetFieldValid(c)) {
+	setRetainerSetToNull(c);
+    }
+}
+
+/* -----------------------------------------------------------------------------
+ * Returns rtsTrue if *c is a retainer.
+ * -------------------------------------------------------------------------- */
+static INLINE rtsBool
+isRetainer( StgClosure *c )
+{
+    switch (get_itbl(c)->type) {
+	//
+	//  True case
+	//
+	// TSOs MUST be retainers: they constitute the set of roots.
+    case TSO:
+
+	// mutable objects
+    case MVAR:
+    case MUT_VAR_CLEAN:
+    case MUT_VAR_DIRTY:
+    case MUT_ARR_PTRS_CLEAN:
+    case MUT_ARR_PTRS_DIRTY:
+    case MUT_ARR_PTRS_FROZEN:
+    case MUT_ARR_PTRS_FROZEN0:
+
+	// 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:
+    case AP:
+    case AP_STACK:
+
+	// 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:
+
+	// Since the other mutvar-type things are retainers, seems
+	// like the right thing to do:
+    case TVAR:
+	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:
+	// blackholes
+    case CAF_BLACKHOLE:
+    case BLACKHOLE:
+    case SE_BLACKHOLE:
+    case SE_CAF_BLACKHOLE:
+	// indirection
+    case IND_PERM:
+    case IND_OLDGEN_PERM:
+    case IND_OLDGEN:
+	// static objects
+    case CONSTR_STATIC:
+    case FUN_STATIC:
+	// misc
+    case STABLE_NAME:
+    case BCO:
+    case ARR_WORDS:
+	// STM
+    case TVAR_WAIT_QUEUE:
+    case TREC_HEADER:
+    case TREC_CHUNK:
+	return rtsFalse;
+
+	//
+	// Error case
+	//
+	// IND_STATIC cannot be *c, *cp, *r in the retainer profiling loop.
+    case IND_STATIC:
+	// CONSTR_INTLIKE, CONSTR_CHARLIKE, and CONSTR_NOCAF_STATIC
+	// cannot be *c, *cp, *r in the retainer profiling loop.
+    case CONSTR_INTLIKE:
+    case CONSTR_CHARLIKE:
+    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_VEC_SMALL:
+    case RET_BIG:
+    case RET_VEC_BIG:
+	// other cases
+    case IND:
+    case BLOCKED_FETCH:
+    case FETCH_ME:
+    case FETCH_ME_BQ:
+    case RBH:
+    case REMOTE_REF:
+    case EVACUATED:
+    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
+ *    RetainerSet.c can simply do nothing.
+ *    If this is not the case, we can free all the retainer sets and
+ *    re-initialize the hash table.
+ *    See refreshAllRetainerSet() in RetainerSet.c.
+ * -------------------------------------------------------------------------- */
+static INLINE retainer
+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
+ * -------------------------------------------------------------------------- */
+static INLINE void
+associate( StgClosure *c, RetainerSet *s )
+{
+    // StgWord has the same size as pointers, so the following type
+    // casting is okay.
+    RSET(c) = (RetainerSet *)((StgWord)s | flip);
+}
+
+/* -----------------------------------------------------------------------------
+   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;
+	}
+    }
+}
+
+static INLINE StgPtr
+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;
+}
+
+/* -----------------------------------------------------------------------------
+ * 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) {
+#ifdef ENABLE_WIN32_DLL_SUPPORT
+	  if ( (unsigned long)(*srt) & 0x1 ) {
+	      retainClosure(*stgCast(StgClosure**,(stgCast(unsigned long, *srt) & ~0x1)), 
+			    c, c_child_r);
+	  } else {
+	      retainClosure(*srt,c,c_child_r);
+	  }
+#else
+	  retainClosure(*srt,c,c_child_r);
+#endif
+      }
+      p++;
+      bitmap = bitmap >> 1;
+  }
+}
+
+/* -----------------------------------------------------------------------------
+ *  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:
+ *    *c is one of the following: TSO, AP_STACK.
+ *    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
+retainStack( StgClosure *c, retainer c_child_r,
+	     StgPtr stackStart, StgPtr stackEnd )
+{
+    stackElement *oldStackBoundary;
+    StgPtr p;
+    StgRetInfoTable *info;
+    StgWord32 bitmap;
+    nat size;
+
+#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
+    // debugBelch("retainStack() called: oldStackBoundary = 0x%x, currentStackBoundary = 0x%x\n", oldStackBoundary, currentStackBoundary);
+#endif
+
+    ASSERT(get_itbl(c)->type != TSO || 
+	   (((StgTSO *)c)->what_next != ThreadRelocated &&
+	    ((StgTSO *)c)->what_next != ThreadComplete &&
+	    ((StgTSO *)c)->what_next != ThreadKilled));
+    
+    p = stackStart;
+    while (p < stackEnd) {
+	info = get_ret_itbl((StgClosure *)p);
+
+	switch(info->i.type) {
+
+	case UPDATE_FRAME:
+	    retainClosure(((StgUpdateFrame *)p)->updatee, c, c_child_r);
+	    p += sizeofW(StgUpdateFrame);
+	    continue;
+
+	case STOP_FRAME:
+	case CATCH_FRAME:
+	case CATCH_STM_FRAME:
+	case CATCH_RETRY_FRAME:
+	case ATOMICALLY_FRAME:
+	case RET_SMALL:
+	case RET_VEC_SMALL:
+	    bitmap = BITMAP_BITS(info->i.layout.bitmap);
+	    size   = BITMAP_SIZE(info->i.layout.bitmap);
+	    p++;
+	    p = retain_small_bitmap(p, size, bitmap, c, c_child_r);
+
+	follow_srt:
+	    retainSRT((StgClosure **)GET_SRT(info), info->i.srt_bitmap, c, c_child_r);
+	    continue;
+
+	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;
+	    continue;
+	}
+
+	    // large bitmap (> 32 entries, or > 64 on a 64-bit machine) 
+	case RET_BIG:
+	case RET_VEC_BIG:
+	    size = GET_LARGE_BITMAP(&info->i)->size;
+	    p++;
+	    retain_large_bitmap(p, GET_LARGE_BITMAP(&info->i),
+				size, c, c_child_r);
+	    p += size;
+	    // and don't forget to follow the SRT 
+	    goto follow_srt;
+
+	    // Dynamic bitmap: the mask is stored on the stack 
+	case RET_DYN: {
+	    StgWord dyn;
+	    dyn = ((StgRetDyn *)p)->liveness;
+
+	    // traverse the bitmap first
+	    bitmap = RET_DYN_LIVENESS(dyn);
+	    p      = (P_)&((StgRetDyn *)p)->payload[0];
+	    size   = RET_DYN_BITMAP_SIZE;
+	    p = retain_small_bitmap(p, size, bitmap, c, c_child_r);
+	    
+	    // skip over the non-ptr words
+	    p += RET_DYN_NONPTRS(dyn) + RET_DYN_NONPTR_REGS_SIZE;
+	    
+	    // follow the ptr words
+	    for (size = RET_DYN_PTRS(dyn); size > 0; size--) {
+		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);
+	    fun_info = get_fun_itbl(ret_fun->fun);
+	    
+	    p = (P_)&ret_fun->payload;
+	    switch (fun_info->f.fun_type) {
+	    case ARG_GEN:
+		bitmap = BITMAP_BITS(fun_info->f.b.bitmap);
+		size = BITMAP_SIZE(fun_info->f.b.bitmap);
+		p = retain_small_bitmap(p, size, bitmap, c, c_child_r);
+		break;
+	    case ARG_GEN_BIG:
+		size = GET_FUN_LARGE_BITMAP(fun_info)->size;
+		retain_large_bitmap(p, GET_FUN_LARGE_BITMAP(fun_info), 
+				    size, c, c_child_r);
+		p += size;
+		break;
+	    default:
+		bitmap = BITMAP_BITS(stg_arg_bitmaps[fun_info->f.fun_type]);
+		size = BITMAP_SIZE(stg_arg_bitmaps[fun_info->f.fun_type]);
+		p = retain_small_bitmap(p, size, bitmap, c, c_child_r);
+		break;
+	    }
+	    goto follow_srt;
+	}
+
+	default:
+	    barf("Invalid object found in retainStack(): %d",
+		 (int)(info->i.type));
+	}
+    }
+
+    // restore currentStackBoundary
+    currentStackBoundary = oldStackBoundary;
+#ifdef DEBUG_RETAINER
+    // debugBelch("retainStack() finished: currentStackBoundary = 0x%x\n", currentStackBoundary);
+#endif
+
+#ifdef DEBUG_RETAINER
+    cStackSize--;
+#endif
+}
+
+/* ----------------------------------------------------------------------------
+ * Call retainClosure for each of the children of a PAP/AP
+ * ------------------------------------------------------------------------- */
+
+static INLINE StgPtr
+retain_PAP_payload (StgClosure *pap,  retainer c_child_r, StgClosure *fun, 
+		    StgClosure** payload, StgWord n_args)
+{
+    StgPtr p;
+    StgWord bitmap;
+    StgFunInfoTable *fun_info;
+
+    retainClosure(fun, pap, c_child_r);
+    fun_info = get_fun_itbl(fun);
+    ASSERT(fun_info->i.type != PAP);
+
+    p = (StgPtr)payload;
+
+    switch (fun_info->f.fun_type) {
+    case ARG_GEN:
+	bitmap = BITMAP_BITS(fun_info->f.b.bitmap);
+	p = retain_small_bitmap(p, n_args, bitmap, 
+				pap, c_child_r);
+	break;
+    case ARG_GEN_BIG:
+	retain_large_bitmap(p, GET_FUN_LARGE_BITMAP(fun_info),
+			    n_args, pap, c_child_r);
+	p += n_args;
+	break;
+    case ARG_BCO:
+	retain_large_bitmap((StgPtr)payload, BCO_BITMAP(fun),
+			    n_args, pap, c_child_r);
+	p += n_args;
+	break;
+    default:
+	bitmap = BITMAP_BITS(stg_arg_bitmaps[fun_info->f.fun_type]);
+	p = retain_small_bitmap(p, n_args, bitmap, pap, c_child_r);
+	break;
+    }
+    return p;
+}
+
+/* -----------------------------------------------------------------------------
+ *  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.
+ *    *c0 can be TSO (as well as AP_STACK).
+ * -------------------------------------------------------------------------- */
+static void
+retainClosure( StgClosure *c0, StgClosure *cp0, retainer r0 )
+{
+    // c = Current closure
+    // cp = Current closure's Parent
+    // r = current closures' most recent Retainer
+    // c_child_r = current closure's children's most recent retainer
+    // first_child = first child of c
+    StgClosure *c, *cp, *first_child;
+    RetainerSet *s, *retainerSetOfc;
+    retainer r, c_child_r;
+    StgWord typeOfc;
+
+#ifdef DEBUG_RETAINER
+    // StgPtr oldStackTop;
+#endif
+
+#ifdef DEBUG_RETAINER
+    // oldStackTop = stackTop;
+    // debugBelch("retainClosure() called: c0 = 0x%x, cp0 = 0x%x, r0 = 0x%x\n", c0, cp0, r0);
+#endif
+
+    // (c, cp, r) = (c0, cp0, r0)
+    c = c0;
+    cp = cp0;
+    r = r0;
+    goto inner_loop;
+
+loop:
+    //debugBelch("loop");
+    // pop to (c, cp, r);
+    pop(&c, &cp, &r);
+
+    if (c == NULL) {
+#ifdef DEBUG_RETAINER
+	// debugBelch("retainClosure() ends: oldStackTop = 0x%x, stackTop = 0x%x\n", oldStackTop, stackTop);
+#endif
+	return;
+    }
+
+    //debugBelch("inner_loop");
+
+inner_loop:
+    // 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_INTLIKE:
+    case CONSTR_CHARLIKE:
+    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
+	    debugBelch("ThreadComplete or ThreadKilled encountered in retainClosure()\n");
+#endif
+	    goto loop;
+	}
+	if (((StgTSO *)c)->what_next == ThreadRelocated) {
+#ifdef DEBUG_RETAINER
+	    debugBelch("ThreadRelocated encountered in retainClosure()\n");
+#endif
+	    c = (StgClosure *)((StgTSO *)c)->link;
+	    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;
+    case CONSTR_INTLIKE:
+    case CONSTR_CHARLIKE:
+	// 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:
+	if (get_itbl(c)->srt_bitmap == 0) {
+	    // 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)
+	    associate(c, singleton(r));
+	else
+	    // s is actually the retainer set of *c!
+	    associate(c, s);
+
+	// compute c_child_r
+	c_child_r = isRetainer(c) ? getRetainerFrom(c) : r;
+    } else {
+	// This is not the first visit to *c.
+	if (isMember(r, retainerSetOfc))
+	    goto loop;          // no need to process child
+
+	if (s == NULL)
+	    associate(c, addElement(r, retainerSetOfc));
+	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) {
+		associate(c, s);
+	    }
+	    // Otherwise, just add R_r to the current retainer set of *c.
+	    else {
+		associate(c, addElement(r, retainerSetOfc));
+	    }
+	}
+
+	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
+
+    // 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:
+	retainStack(c, c_child_r,
+		    ((StgTSO *)c)->sp,
+		    ((StgTSO *)c)->stack + ((StgTSO *)c)->stack_size);
+	goto loop;
+
+    case PAP:
+    {
+	StgPAP *pap = (StgPAP *)c;
+	retain_PAP_payload(c, c_child_r, pap->fun, pap->payload, pap->n_args);
+	goto loop;
+    }
+
+    case AP:
+    {
+	StgAP *ap = (StgAP *)c;
+	retain_PAP_payload(c, c_child_r, ap->fun, ap->payload, ap->n_args);
+	goto loop;
+    }
+
+    case AP_STACK:
+	retainClosure(((StgAP_STACK *)c)->fun, c, c_child_r);
+	retainStack(c, c_child_r,
+		    (StgPtr)((StgAP_STACK *)c)->payload,
+		    (StgPtr)((StgAP_STACK *)c)->payload +
+		             ((StgAP_STACK *)c)->size);
+	goto loop;
+    }
+
+    push(c, c_child_r, &first_child);
+
+    // If first_child is null, c has no child.
+    // If first_child is not null, the top stack element points to the next
+    // object. push() may or may not push a stackElement on the stack.
+    if (first_child == NULL)
+	goto loop;
+
+    // (c, cp, r) = (first_child, c, c_child_r)
+    r = c_child_r;
+    cp = c;
+    c = first_child;
+    goto inner_loop;
+}
+
+/* -----------------------------------------------------------------------------
+ *  Compute the retainer set for every object reachable from *tl.
+ * -------------------------------------------------------------------------- */
+static void
+retainRoot( StgClosure **tl )
+{
+    // We no longer assume that only TSOs and WEAKs are roots; any closure can
+    // be a root.
+
+    ASSERT(isEmptyRetainerStack());
+    currentStackBoundary = stackTop;
+
+    if (*tl != &stg_END_TSO_QUEUE_closure && isRetainer(*tl)) {
+	retainClosure(*tl, *tl, getRetainerFrom(*tl));
+    } else {
+	retainClosure(*tl, *tl, CCS_SYSTEM);
+    }
+
+    // NOT TRUE: ASSERT(isMember(getRetainerFrom(*tl), retainerSetOf(*tl)));
+    // *tl might be a TSO which is ThreadComplete, in which
+    // case we ignore it for the purposes of retainer profiling.
+}
+
+/* -----------------------------------------------------------------------------
+ *  Compute the retainer set for each of the objects in the heap.
+ * -------------------------------------------------------------------------- */
+static void
+computeRetainerSet( void )
+{
+    StgWeak *weak;
+    RetainerSet *rtl;
+    nat g;
+    StgPtr ml;
+    bdescr *bd;
+#ifdef DEBUG_RETAINER
+    RetainerSet tmpRetainerSet;
+#endif
+
+    GetRoots(retainRoot);	// for scheduler roots
+
+    // This function is called after a major GC, when key, value, and finalizer
+    // all are guaranteed to be valid, or reachable.
+    //
+    // The following code assumes that WEAK objects are considered to be roots
+    // for retainer profilng.
+    for (weak = weak_ptr_list; weak != NULL; weak = weak->link)
+	// retainRoot((StgClosure *)weak);
+	retainRoot((StgClosure **)&weak);
+
+    // Consider roots from the stable ptr table.
+    markStablePtrTable(retainRoot);
+
+    // The following code resets the rs field of each unvisited mutable
+    // object (computing sumOfNewCostExtra and updating costArray[] when
+    // debugging retainer profiler).
+    for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
+	// NOT TRUE: even G0 has a block on its mutable list
+        // ASSERT(g != 0 || (generations[g].mut_list == NULL));
+
+	// Traversing through mut_list is necessary
+	// because we can find MUT_VAR objects which have not been
+	// visited during retainer profiling.
+	for (bd = generations[g].mut_list; bd != NULL; bd = bd->link) {
+	    for (ml = bd->start; ml < bd->free; ml++) {
+
+		maybeInitRetainerSet((StgClosure *)*ml);
+		rtl = retainerSetOf((StgClosure *)*ml);
+
+#ifdef DEBUG_RETAINER
+		if (rtl == NULL) {
+		    // first visit to *ml
+		    // This is a violation of the interface rule!
+		    RSET(ml) = (RetainerSet *)((StgWord)(&tmpRetainerSet) | flip);
+		    
+		    switch (get_itbl((StgClosure *)ml)->type) {
+		    case IND_STATIC:
+			// no cost involved
+			break;
+		    case CONSTR_INTLIKE:
+		    case CONSTR_CHARLIKE:
+		    case CONSTR_NOCAF_STATIC:
+		    case CONSTR_STATIC:
+		    case THUNK_STATIC:
+		    case FUN_STATIC:
+			barf("Invalid object in computeRetainerSet(): %d", get_itbl((StgClosure*)ml)->type);
+			break;
+		    default:
+			// dynamic objects
+			costArray[get_itbl((StgClosure *)ml)->type] += cost((StgClosure *)ml);
+			sumOfNewCostExtra += cost((StgClosure *)ml);
+			break;
+		    }
+		}
+#endif
+	    }
+	}
+    }
+}
+
+/* -----------------------------------------------------------------------------
+ *  Traverse all static objects for which we compute retainer sets,
+ *  and reset their rs fields to NULL, which is accomplished by
+ *  invoking maybeInitRetainerSet(). This function must be called
+ *  before zeroing all objects reachable from scavenged_static_objects
+ *  in the case of major gabage collections. See GarbageCollect() in
+ *  GC.c.
+ *  Note:
+ *    The mut_once_list of the oldest generation must also be traversed?
+ *    Why? Because if the evacuation of an object pointed to by a static
+ *    indirection object fails, it is put back to the mut_once_list of
+ *    the oldest generation.
+ *    However, this is not necessary because any static indirection objects
+ *    are just traversed through to reach dynamic objects. In other words,
+ *    they are not taken into consideration in computing retainer sets.
+ * -------------------------------------------------------------------------- */
+void
+resetStaticObjectForRetainerProfiling( void )
+{
+#ifdef DEBUG_RETAINER
+    nat count;
+#endif
+    StgClosure *p;
+
+#ifdef DEBUG_RETAINER
+    count = 0;
+#endif
+    p = scavenged_static_objects;
+    while (p != END_OF_STATIC_LIST) {
+#ifdef DEBUG_RETAINER
+	count++;
+#endif
+	switch (get_itbl(p)->type) {
+	case IND_STATIC:
+	    // Since we do not compute the retainer set of any
+	    // IND_STATIC object, we don't have to reset its retainer
+	    // field.
+	    p = (StgClosure*)*IND_STATIC_LINK(p);
+	    break;
+	case THUNK_STATIC:
+	    maybeInitRetainerSet(p);
+	    p = (StgClosure*)*THUNK_STATIC_LINK(p);
+	    break;
+	case FUN_STATIC:
+	    maybeInitRetainerSet(p);
+	    p = (StgClosure*)*FUN_STATIC_LINK(p);
+	    break;
+	case CONSTR_STATIC:
+	    maybeInitRetainerSet(p);
+	    p = (StgClosure*)*STATIC_LINK(get_itbl(p), p);
+	    break;
+	default:
+	    barf("resetStaticObjectForRetainerProfiling: %p (%s)",
+		 p, get_itbl(p)->type);
+	    break;
+	}
+    }
+#ifdef DEBUG_RETAINER
+    // debugBelch("count in scavenged_static_objects = %d\n", count);
+#endif
+}
+
+/* -----------------------------------------------------------------------------
+ * Perform retainer profiling.
+ * N is the oldest generation being profilied, where the generations are
+ * numbered starting at 0.
+ * Invariants:
+ * Note:
+ *   This function should be called only immediately after major garbage
+ *   collection.
+ * ------------------------------------------------------------------------- */
+void
+retainerProfile(void)
+{
+#ifdef DEBUG_RETAINER
+  nat i;
+  nat totalHeapSize;        // total raw heap size (computed by linear scanning)
+#endif
+
+#ifdef DEBUG_RETAINER
+  debugBelch(" < retainerProfile() invoked : %d>\n", retainerGeneration);
+#endif
+
+  stat_startRP();
+
+  // We haven't flipped the bit yet.
+#ifdef DEBUG_RETAINER
+  debugBelch("Before traversing:\n");
+  sumOfCostLinear = 0;
+  for (i = 0;i < N_CLOSURE_TYPES; i++)
+    costArrayLinear[i] = 0;
+  totalHeapSize = checkHeapSanityForRetainerProfiling();
+
+  debugBelch("\tsumOfCostLinear = %d, totalHeapSize = %d\n", sumOfCostLinear, totalHeapSize);
+  /*
+  debugBelch("costArrayLinear[] = ");
+  for (i = 0;i < N_CLOSURE_TYPES; i++)
+    debugBelch("[%u:%u] ", i, costArrayLinear[i]);
+  debugBelch("\n");
+  */
+
+  ASSERT(sumOfCostLinear == totalHeapSize);
+
+/*
+#define pcostArrayLinear(index) \
+  if (costArrayLinear[index] > 0) \
+    debugBelch("costArrayLinear[" #index "] = %u\n", costArrayLinear[index])
+  pcostArrayLinear(THUNK_STATIC);
+  pcostArrayLinear(FUN_STATIC);
+  pcostArrayLinear(CONSTR_STATIC);
+  pcostArrayLinear(CONSTR_NOCAF_STATIC);
+  pcostArrayLinear(CONSTR_INTLIKE);
+  pcostArrayLinear(CONSTR_CHARLIKE);
+*/
+#endif
+
+  // Now we flips flip.
+  flip = flip ^ 1;
+
+#ifdef DEBUG_RETAINER
+  stackSize = 0;
+  maxStackSize = 0;
+  cStackSize = 0;
+  maxCStackSize = 0;
+#endif
+  numObjectVisited = 0;
+  timesAnyObjectVisited = 0;
+
+#ifdef DEBUG_RETAINER
+  debugBelch("During traversing:\n");
+  sumOfNewCost = 0;
+  sumOfNewCostExtra = 0;
+  for (i = 0;i < N_CLOSURE_TYPES; i++)
+    costArray[i] = 0;
+#endif
+
+  /*
+    We initialize the traverse stack each time the retainer profiling is
+    performed (because the traverse stack size varies on each retainer profiling
+    and this operation is not costly anyhow). However, we just refresh the
+    retainer sets.
+   */
+  initializeTraverseStack();
+#ifdef DEBUG_RETAINER
+  initializeAllRetainerSet();
+#else
+  refreshAllRetainerSet();
+#endif
+  computeRetainerSet();
+
+#ifdef DEBUG_RETAINER
+  debugBelch("After traversing:\n");
+  sumOfCostLinear = 0;
+  for (i = 0;i < N_CLOSURE_TYPES; i++)
+    costArrayLinear[i] = 0;
+  totalHeapSize = checkHeapSanityForRetainerProfiling();
+
+  debugBelch("\tsumOfCostLinear = %d, totalHeapSize = %d\n", sumOfCostLinear, totalHeapSize);
+  ASSERT(sumOfCostLinear == totalHeapSize);
+
+  // now, compare the two results
+  /*
+    Note:
+      costArray[] must be exactly the same as costArrayLinear[].
+      Known exceptions:
+        1) Dead weak pointers, whose type is CONSTR. These objects are not
+           reachable from any roots.
+  */
+  debugBelch("Comparison:\n");
+  debugBelch("\tcostArrayLinear[] (must be empty) = ");
+  for (i = 0;i < N_CLOSURE_TYPES; i++)
+    if (costArray[i] != costArrayLinear[i])
+      // nothing should be printed except MUT_VAR after major GCs
+      debugBelch("[%u:%u] ", i, costArrayLinear[i]);
+  debugBelch("\n");
+
+  debugBelch("\tsumOfNewCost = %u\n", sumOfNewCost);
+  debugBelch("\tsumOfNewCostExtra = %u\n", sumOfNewCostExtra);
+  debugBelch("\tcostArray[] (must be empty) = ");
+  for (i = 0;i < N_CLOSURE_TYPES; i++)
+    if (costArray[i] != costArrayLinear[i])
+      // nothing should be printed except MUT_VAR after major GCs
+      debugBelch("[%u:%u] ", i, costArray[i]);
+  debugBelch("\n");
+
+  // only for major garbage collection
+  ASSERT(sumOfNewCost + sumOfNewCostExtra == sumOfCostLinear);
+#endif
+
+  // post-processing
+  closeTraverseStack();
+#ifdef DEBUG_RETAINER
+  closeAllRetainerSet();
+#else
+  // Note that there is no post-processing for the retainer sets.
+#endif
+  retainerGeneration++;
+
+  stat_endRP(
+    retainerGeneration - 1,   // retainerGeneration has just been incremented!
+#ifdef DEBUG_RETAINER
+    maxCStackSize, maxStackSize,
+#endif
+    (double)timesAnyObjectVisited / numObjectVisited);
+}
+
+/* -----------------------------------------------------------------------------
+ * DEBUGGING CODE
+ * -------------------------------------------------------------------------- */
+
+#ifdef DEBUG_RETAINER
+
+#define LOOKS_LIKE_PTR(r) ((LOOKS_LIKE_STATIC_CLOSURE(r) || \
+        ((HEAP_ALLOCED(r) && ((Bdescr((P_)r)->flags & BF_FREE) == 0)))) && \
+        ((StgWord)(*(StgPtr)r)!=0xaaaaaaaa))
+
+static nat
+sanityCheckHeapClosure( StgClosure *c )
+{
+    StgInfoTable *info;
+
+    ASSERT(LOOKS_LIKE_GHC_INFO(c->header.info));
+    ASSERT(!closure_STATIC(c));
+    ASSERT(LOOKS_LIKE_PTR(c));
+
+    if ((((StgWord)RSET(c) & 1) ^ flip) != 0) {
+	if (get_itbl(c)->type == CONSTR &&
+	    !strcmp(get_itbl(c)->prof.closure_type, "DEAD_WEAK") &&
+	    !strcmp(get_itbl(c)->prof.closure_desc, "DEAD_WEAK")) {
+	    debugBelch("\tUnvisited dead weak pointer object found: c = %p\n", c);
+	    costArray[get_itbl(c)->type] += cost(c);
+	    sumOfNewCost += cost(c);
+	} else
+	    debugBelch(
+		    "Unvisited object: flip = %d, c = %p(%d, %s, %s), rs = %p\n",
+		    flip, c, get_itbl(c)->type,
+		    get_itbl(c)->prof.closure_type, get_itbl(c)->prof.closure_desc,
+		    RSET(c));
+    } else {
+	// debugBelch("sanityCheckHeapClosure) S: flip = %d, c = %p(%d), rs = %p\n", flip, c, get_itbl(c)->type, RSET(c));
+    }
+
+    return closure_sizeW(c);
+}
+
+static nat
+heapCheck( bdescr *bd )
+{
+    StgPtr p;
+    static nat costSum, size;
+
+    costSum = 0;
+    while (bd != NULL) {
+	p = bd->start;
+	while (p < bd->free) {
+	    size = sanityCheckHeapClosure((StgClosure *)p);
+	    sumOfCostLinear += size;
+	    costArrayLinear[get_itbl((StgClosure *)p)->type] += size;
+	    p += size;
+	    // no need for slop check; I think slops are not used currently.
+	}
+	ASSERT(p == bd->free);
+	costSum += bd->free - bd->start;
+	bd = bd->link;
+    }
+
+    return costSum;
+}
+
+static nat
+smallObjectPoolCheck(void)
+{
+    bdescr *bd;
+    StgPtr p;
+    static nat costSum, size;
+
+    bd = small_alloc_list;
+    costSum = 0;
+
+    // first block
+    if (bd == NULL)
+	return costSum;
+
+    p = bd->start;
+    while (p < alloc_Hp) {
+	size = sanityCheckHeapClosure((StgClosure *)p);
+	sumOfCostLinear += size;
+	costArrayLinear[get_itbl((StgClosure *)p)->type] += size;
+	p += size;
+    }
+    ASSERT(p == alloc_Hp);
+    costSum += alloc_Hp - bd->start;
+
+    bd = bd->link;
+    while (bd != NULL) {
+	p = bd->start;
+	while (p < bd->free) {
+	    size = sanityCheckHeapClosure((StgClosure *)p);
+	    sumOfCostLinear += size;
+	    costArrayLinear[get_itbl((StgClosure *)p)->type] += size;
+	    p += size;
+	}
+	ASSERT(p == bd->free);
+	costSum += bd->free - bd->start;
+	bd = bd->link;
+    }
+
+    return costSum;
+}
+
+static nat
+chainCheck(bdescr *bd)
+{
+    nat costSum, size;
+
+    costSum = 0;
+    while (bd != NULL) {
+	// bd->free - bd->start is not an accurate measurement of the
+	// object size.  Actually it is always zero, so we compute its
+	// size explicitly.
+	size = sanityCheckHeapClosure((StgClosure *)bd->start);
+	sumOfCostLinear += size;
+	costArrayLinear[get_itbl((StgClosure *)bd->start)->type] += size;
+	costSum += size;
+	bd = bd->link;
+    }
+
+    return costSum;
+}
+
+static nat
+checkHeapSanityForRetainerProfiling( void )
+{
+    nat costSum, g, s;
+
+    costSum = 0;
+    debugBelch("START: sumOfCostLinear = %d, costSum = %d\n", sumOfCostLinear, costSum);
+    if (RtsFlags.GcFlags.generations == 1) {
+	costSum += heapCheck(g0s0->to_blocks);
+	debugBelch("heapCheck: sumOfCostLinear = %d, costSum = %d\n", sumOfCostLinear, costSum);
+	costSum += chainCheck(g0s0->large_objects);
+	debugBelch("chainCheck: sumOfCostLinear = %d, costSum = %d\n", sumOfCostLinear, costSum);
+    } else {
+	for (g = 0; g < RtsFlags.GcFlags.generations; g++)
+	for (s = 0; s < generations[g].n_steps; s++) {
+	    /*
+	      After all live objects have been scavenged, the garbage
+	      collector may create some objects in
+	      scheduleFinalizers(). These objects are created throught
+	      allocate(), so the small object pool or the large object
+	      pool of the g0s0 may not be empty.
+	    */
+	    if (g == 0 && s == 0) {
+		costSum += smallObjectPoolCheck();
+		debugBelch("smallObjectPoolCheck(): sumOfCostLinear = %d, costSum = %d\n", sumOfCostLinear, costSum);
+		costSum += chainCheck(generations[g].steps[s].large_objects);
+		debugBelch("chainCheck(): sumOfCostLinear = %d, costSum = %d\n", sumOfCostLinear, costSum);
+	    } else {
+		costSum += heapCheck(generations[g].steps[s].blocks);
+		debugBelch("heapCheck(): sumOfCostLinear = %d, costSum = %d\n", sumOfCostLinear, costSum);
+		costSum += chainCheck(generations[g].steps[s].large_objects);
+		debugBelch("chainCheck(): sumOfCostLinear = %d, costSum = %d\n", sumOfCostLinear, costSum);
+	    }
+	}
+    }
+
+    return costSum;
+}
+
+void
+findPointer(StgPtr p)
+{
+    StgPtr q, r, e;
+    bdescr *bd;
+    nat g, s;
+
+    for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
+	for (s = 0; s < generations[g].n_steps; s++) {
+	    // if (g == 0 && s == 0) continue;
+	    bd = generations[g].steps[s].blocks;
+	    for (; bd; bd = bd->link) {
+		for (q = bd->start; q < bd->free; q++) {
+		    if (*q == (StgWord)p) {
+			r = q;
+			while (!LOOKS_LIKE_GHC_INFO(*r)) r--;
+			debugBelch("Found in gen[%d], step[%d]: q = %p, r = %p\n", g, s, q, r);
+			// return;
+		    }
+		}
+	    }
+	    bd = generations[g].steps[s].large_objects;
+	    for (; bd; bd = bd->link) {
+		e = bd->start + cost((StgClosure *)bd->start);
+		for (q = bd->start; q < e; q++) {
+		    if (*q == (StgWord)p) {
+			r = q;
+			while (*r == 0 || !LOOKS_LIKE_GHC_INFO(*r)) r--;
+			debugBelch("Found in gen[%d], large_objects: %p\n", g, r);
+			// return;
+		    }
+		}
+	    }
+	}
+    }
+}
+
+static void
+belongToHeap(StgPtr p)
+{
+    bdescr *bd;
+    nat g, s;
+
+    for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
+	for (s = 0; s < generations[g].n_steps; s++) {
+	    // if (g == 0 && s == 0) continue;
+	    bd = generations[g].steps[s].blocks;
+	    for (; bd; bd = bd->link) {
+		if (bd->start <= p && p < bd->free) {
+		    debugBelch("Belongs to gen[%d], step[%d]", g, s);
+		    return;
+		}
+	    }
+	    bd = generations[g].steps[s].large_objects;
+	    for (; bd; bd = bd->link) {
+		if (bd->start <= p && p < bd->start + getHeapClosureSize((StgClosure *)bd->start)) {
+		    debugBelch("Found in gen[%d], large_objects: %p\n", g, bd->start);
+		    return;
+		}
+	    }
+	}
+    }
+}
+#endif /* DEBUG_RETAINER */
+
+#endif /* PROFILING */