PrimOps.cmm

/* -*- tab-width: 8 -*- */
/* -----------------------------------------------------------------------------
 *
 * (c) The GHC Team, 1998-2012
 *
 * Out-of-line primitive operations
 *
 * This file contains the implementations of all the primitive
 * operations ("primops") which are not expanded inline.  See
 * ghc/compiler/prelude/primops.txt.pp for a list of all the primops;
 * this file contains code for most of those with the attribute
 * out_of_line=True.
 *
 * Entry convention: the entry convention for a primop is the
 * NativeNodeCall convention, and the return convention is
 * NativeReturn.  (see compiler/cmm/CmmCallConv.hs)
 *
 * This file is written in a subset of C--, extended with various
 * features specific to GHC.  It is compiled by GHC directly.  For the
 * syntax of .cmm files, see the parser in ghc/compiler/cmm/CmmParse.y.
 *
 * ---------------------------------------------------------------------------*/

#include "Cmm.h"
#include "MachDeps.h"
#include "SMPClosureOps.h"

#ifdef __PIC__
import pthread_mutex_lock;
import pthread_mutex_unlock;
#endif
import CLOSURE base_ControlziExceptionziBase_nestedAtomically_closure;
import EnterCriticalSection;
import LeaveCriticalSection;
import CLOSURE ghczmprim_GHCziTypes_False_closure;
#if defined(USE_MINIINTERPRETER) || !defined(mingw32_HOST_OS)
import CLOSURE sm_mutex;
#endif
#ifdef PROFILING
import CLOSURE CCS_MAIN;
#endif

/*-----------------------------------------------------------------------------
  Array Primitives

  Basically just new*Array - the others are all inline macros.

  The slow entry point is for returning from a heap check, the saved
  size argument must be re-loaded from the stack.
  -------------------------------------------------------------------------- */

/* for objects that are *less* than the size of a word, make sure we
 * round up to the nearest word for the size of the array.
 */

stg_newByteArrayzh ( W_ n )
{
    W_ words, payload_words;
    gcptr p;

    MAYBE_GC_N(stg_newByteArrayzh, n);

    payload_words = ROUNDUP_BYTES_TO_WDS(n);
    words = BYTES_TO_WDS(SIZEOF_StgArrBytes) + payload_words;
    ("ptr" p) = ccall allocate(MyCapability() "ptr",words);
    TICK_ALLOC_PRIM(SIZEOF_StgArrBytes,WDS(payload_words),0);
    SET_HDR(p, stg_ARR_WORDS_info, CCCS);
    StgArrBytes_bytes(p) = n;
    return (p);
}

#define BA_ALIGN 16
#define BA_MASK  (BA_ALIGN-1)

stg_newPinnedByteArrayzh ( W_ n )
{
    W_ words, bytes, payload_words;
    gcptr p;

    MAYBE_GC_N(stg_newPinnedByteArrayzh, n);

    bytes = n;
    /* payload_words is what we will tell the profiler we had to allocate */
    payload_words = ROUNDUP_BYTES_TO_WDS(bytes);
    /* When we actually allocate memory, we need to allow space for the
       header: */
    bytes = bytes + SIZEOF_StgArrBytes;
    /* And we want to align to BA_ALIGN bytes, so we need to allow space
       to shift up to BA_ALIGN - 1 bytes: */
    bytes = bytes + BA_ALIGN - 1;
    /* Now we convert to a number of words: */
    words = ROUNDUP_BYTES_TO_WDS(bytes);

    ("ptr" p) = ccall allocatePinned(MyCapability() "ptr", words);
    TICK_ALLOC_PRIM(SIZEOF_StgArrBytes,WDS(payload_words),0);

    /* Now we need to move p forward so that the payload is aligned
       to BA_ALIGN bytes: */
    p = p + ((-p - SIZEOF_StgArrBytes) & BA_MASK);

    SET_HDR(p, stg_ARR_WORDS_info, CCCS);
    StgArrBytes_bytes(p) = n;
    return (p);
}

stg_newAlignedPinnedByteArrayzh ( W_ n, W_ alignment )
{
    W_ words, bytes, payload_words;
    gcptr p;

    again: MAYBE_GC(again);

    /* we always supply at least word-aligned memory, so there's no
       need to allow extra space for alignment if the requirement is less
       than a word.  This also prevents mischief with alignment == 0. */
    if (alignment <= SIZEOF_W) { alignment = 1; }

    bytes = n;

    /* payload_words is what we will tell the profiler we had to allocate */
    payload_words = ROUNDUP_BYTES_TO_WDS(bytes);

    /* When we actually allocate memory, we need to allow space for the
       header: */
    bytes = bytes + SIZEOF_StgArrBytes;
    /* And we want to align to <alignment> bytes, so we need to allow space
       to shift up to <alignment - 1> bytes: */
    bytes = bytes + alignment - 1;
    /* Now we convert to a number of words: */
    words = ROUNDUP_BYTES_TO_WDS(bytes);

    ("ptr" p) = ccall allocatePinned(MyCapability() "ptr", words);
    TICK_ALLOC_PRIM(SIZEOF_StgArrBytes,WDS(payload_words),0);

    /* Now we need to move p forward so that the payload is aligned
       to <alignment> bytes. Note that we are assuming that
       <alignment> is a power of 2, which is technically not guaranteed */
    p = p + ((-p - SIZEOF_StgArrBytes) & (alignment - 1));

    SET_HDR(p, stg_ARR_WORDS_info, CCCS);
    StgArrBytes_bytes(p) = n;
    return (p);
}

stg_isByteArrayPinnedzh ( gcptr ba )
// ByteArray# s -> Int#
{
    W_ bd, flags;
    bd = Bdescr(ba);
    // pinned byte arrays live in blocks with the BF_PINNED flag set.
    // See the comment in Storage.c:allocatePinned.
    flags = TO_W_(bdescr_flags(bd));
    return (flags & BF_PINNED != 0);
}

stg_isMutableByteArrayPinnedzh ( gcptr mba )
// MutableByteArray# s -> Int#
{
    jump stg_isByteArrayPinnedzh(mba);
}

// shrink size of MutableByteArray in-place
stg_shrinkMutableByteArrayzh ( gcptr mba, W_ new_size )
// MutableByteArray# s -> Int# -> State# s -> State# s
{
   ASSERT(new_size >= 0);
   ASSERT(new_size <= StgArrBytes_bytes(mba));

   OVERWRITING_CLOSURE_OFS(mba, (BYTES_TO_WDS(SIZEOF_StgArrBytes) +
                                 ROUNDUP_BYTES_TO_WDS(new_size)));
   StgArrBytes_bytes(mba) = new_size;
   LDV_RECORD_CREATE(mba);

   return ();
}

// resize MutableByteArray
//
// The returned MutableByteArray is either the original
// MutableByteArray resized in-place or, if not possible, a newly
// allocated (unpinned) MutableByteArray (with the original content
// copied over)
stg_resizzeMutableByteArrayzh ( gcptr mba, W_ new_size )
// MutableByteArray# s -> Int# -> State# s -> (# State# s,MutableByteArray# s #)
{
   W_ new_size_wds;

   ASSERT(new_size >= 0);

   new_size_wds = ROUNDUP_BYTES_TO_WDS(new_size);

   if (new_size_wds <= BYTE_ARR_WDS(mba)) {
      OVERWRITING_CLOSURE_OFS(mba, (BYTES_TO_WDS(SIZEOF_StgArrBytes) +
                                    new_size_wds));
      StgArrBytes_bytes(mba) = new_size;
      LDV_RECORD_CREATE(mba);

      return (mba);
   } else {
      (P_ new_mba) = call stg_newByteArrayzh(new_size);

      // maybe at some point in the future we may be able to grow the
      // MBA in-place w/o copying if we know the space after the
      // current MBA is still available, as often we want to grow the
      // MBA shortly after we allocated the original MBA. So maybe no
      // further allocations have occurred by then.

      // copy over old content
      prim %memcpy(BYTE_ARR_CTS(new_mba), BYTE_ARR_CTS(mba),
                   StgArrBytes_bytes(mba), SIZEOF_W);

      return (new_mba);
   }
}

// RRN: This one does not use the "ticketing" approach because it
// deals in unboxed scalars, not heap pointers.
stg_casIntArrayzh( gcptr arr, W_ ind, W_ old, W_ new )
/* MutableByteArray# s -> Int# -> Int# -> Int# -> State# s -> (# State# s, Int# #) */
{
    W_ p, h;

    p = arr + SIZEOF_StgArrBytes + WDS(ind);
    (h) = prim %cmpxchgW(p, old, new);

    return(h);
}


stg_newArrayzh ( W_ n /* words */, gcptr init )
{
    W_ words, size, p;
    gcptr arr;

    again: MAYBE_GC(again);

    // the mark area contains one byte for each 2^MUT_ARR_PTRS_CARD_BITS words
    // in the array, making sure we round up, and then rounding up to a whole
    // number of words.
    size = n + mutArrPtrsCardWords(n);
    words = BYTES_TO_WDS(SIZEOF_StgMutArrPtrs) + size;
    ("ptr" arr) = ccall allocate(MyCapability() "ptr",words);
    TICK_ALLOC_PRIM(SIZEOF_StgMutArrPtrs, WDS(size), 0);

    SET_HDR(arr, stg_MUT_ARR_PTRS_DIRTY_info, CCCS);
    StgMutArrPtrs_ptrs(arr) = n;
    StgMutArrPtrs_size(arr) = size;

    // Initialise all elements of the the array with the value in R2
    p = arr + SIZEOF_StgMutArrPtrs;
  for:
    if (p < arr + SIZEOF_StgMutArrPtrs + WDS(n)) {
        W_[p] = init;
        p = p + WDS(1);
        goto for;
    }

    return (arr);
}

stg_unsafeThawArrayzh ( gcptr arr )
{
    // SUBTLETY TO DO WITH THE OLD GEN MUTABLE LIST
    //
    // A MUT_ARR_PTRS lives on the mutable list, but a MUT_ARR_PTRS_FROZEN
    // normally doesn't.  However, when we freeze a MUT_ARR_PTRS, we leave
    // it on the mutable list for the GC to remove (removing something from
    // the mutable list is not easy).
    //
    // So that we can tell whether a MUT_ARR_PTRS_FROZEN is on the mutable list,
    // when we freeze it we set the info ptr to be MUT_ARR_PTRS_FROZEN0
    // to indicate that it is still on the mutable list.
    //
    // So, when we thaw a MUT_ARR_PTRS_FROZEN, we must cope with two cases:
    // either it is on a mut_list, or it isn't.  We adopt the convention that
    // the closure type is MUT_ARR_PTRS_FROZEN0 if it is on the mutable list,
    // and MUT_ARR_PTRS_FROZEN otherwise.  In fact it wouldn't matter if
    // we put it on the mutable list more than once, but it would get scavenged
    // multiple times during GC, which would be unnecessarily slow.
    //
    if (StgHeader_info(arr) != stg_MUT_ARR_PTRS_FROZEN0_info) {
        SET_INFO(arr,stg_MUT_ARR_PTRS_DIRTY_info);
        recordMutable(arr);
        // must be done after SET_INFO, because it ASSERTs closure_MUTABLE()
        return (arr);
    } else {
        SET_INFO(arr,stg_MUT_ARR_PTRS_DIRTY_info);
        return (arr);
    }
}

stg_copyArrayzh ( gcptr src, W_ src_off, gcptr dst, W_ dst_off, W_ n )
{
    copyArray(src, src_off, dst, dst_off, n)
}

stg_copyMutableArrayzh ( gcptr src, W_ src_off, gcptr dst, W_ dst_off, W_ n )
{
    copyMutableArray(src, src_off, dst, dst_off, n)
}

stg_copyArrayArrayzh ( gcptr src, W_ src_off, gcptr dst, W_ dst_off, W_ n )
{
    copyArray(src, src_off, dst, dst_off, n)
}

stg_copyMutableArrayArrayzh ( gcptr src, W_ src_off, gcptr dst, W_ dst_off, W_ n )
{
    copyMutableArray(src, src_off, dst, dst_off, n)
}

stg_cloneArrayzh ( gcptr src, W_ offset, W_ n )
{
    cloneArray(stg_MUT_ARR_PTRS_FROZEN_info, src, offset, n)
}

stg_cloneMutableArrayzh ( gcptr src, W_ offset, W_ n )
{
    cloneArray(stg_MUT_ARR_PTRS_DIRTY_info, src, offset, n)
}

// We have to escape the "z" in the name.
stg_freezzeArrayzh ( gcptr src, W_ offset, W_ n )
{
    cloneArray(stg_MUT_ARR_PTRS_FROZEN_info, src, offset, n)
}

stg_thawArrayzh ( gcptr src, W_ offset, W_ n )
{
    cloneArray(stg_MUT_ARR_PTRS_DIRTY_info, src, offset, n)
}

// RRN: Uses the ticketed approach; see casMutVar
stg_casArrayzh ( gcptr arr, W_ ind, gcptr old, gcptr new )
/* MutableArray# s a -> Int# -> a -> a -> State# s -> (# State# s, Int#, Any a #) */
{
    gcptr h;
    W_ p, len;

    p = arr + SIZEOF_StgMutArrPtrs + WDS(ind);
    (h) = prim %cmpxchgW(p, old, new);

    if (h != old) {
        // Failure, return what was there instead of 'old':
        return (1,h);
    } else {
        // Compare and Swap Succeeded:
        SET_HDR(arr, stg_MUT_ARR_PTRS_DIRTY_info, CCCS);
        len = StgMutArrPtrs_ptrs(arr);
        // The write barrier.  We must write a byte into the mark table:
        I8[arr + SIZEOF_StgMutArrPtrs + WDS(len) + (ind >> MUT_ARR_PTRS_CARD_BITS )] = 1;
        return (0,new);
    }
}

stg_newArrayArrayzh ( W_ n /* words */ )
{
    W_ words, size, p;
    gcptr arr;

    MAYBE_GC_N(stg_newArrayArrayzh, n);

    // the mark area contains one byte for each 2^MUT_ARR_PTRS_CARD_BITS words
    // in the array, making sure we round up, and then rounding up to a whole
    // number of words.
    size = n + mutArrPtrsCardWords(n);
    words = BYTES_TO_WDS(SIZEOF_StgMutArrPtrs) + size;
    ("ptr" arr) = ccall allocate(MyCapability() "ptr",words);
    TICK_ALLOC_PRIM(SIZEOF_StgMutArrPtrs, WDS(size), 0);

    SET_HDR(arr, stg_MUT_ARR_PTRS_DIRTY_info, W_[CCCS]);
    StgMutArrPtrs_ptrs(arr) = n;
    StgMutArrPtrs_size(arr) = size;

    // Initialise all elements of the array with a pointer to the new array
    p = arr + SIZEOF_StgMutArrPtrs;
  for:
    if (p < arr + SIZEOF_StgMutArrPtrs + WDS(n)) {
        W_[p] = arr;
        p = p + WDS(1);
        goto for;
    }

    return (arr);
}


/* -----------------------------------------------------------------------------
   SmallArray primitives
   -------------------------------------------------------------------------- */

stg_newSmallArrayzh ( W_ n /* words */, gcptr init )
{
    W_ words, size, p;
    gcptr arr;

    again: MAYBE_GC(again);

    words = BYTES_TO_WDS(SIZEOF_StgSmallMutArrPtrs) + n;
    ("ptr" arr) = ccall allocate(MyCapability() "ptr",words);
    TICK_ALLOC_PRIM(SIZEOF_StgSmallMutArrPtrs, WDS(n), 0);

    SET_HDR(arr, stg_SMALL_MUT_ARR_PTRS_DIRTY_info, CCCS);
    StgSmallMutArrPtrs_ptrs(arr) = n;

    // Initialise all elements of the the array with the value in R2
    p = arr + SIZEOF_StgSmallMutArrPtrs;
  for:
    if (p < arr + SIZEOF_StgSmallMutArrPtrs + WDS(n)) {
        W_[p] = init;
        p = p + WDS(1);
        goto for;
    }

    return (arr);
}

stg_unsafeThawSmallArrayzh ( gcptr arr )
{
    // See stg_unsafeThawArrayzh
    if (StgHeader_info(arr) != stg_SMALL_MUT_ARR_PTRS_FROZEN0_info) {
        SET_INFO(arr, stg_SMALL_MUT_ARR_PTRS_DIRTY_info);
        recordMutable(arr);
        // must be done after SET_INFO, because it ASSERTs closure_MUTABLE()
        return (arr);
    } else {
        SET_INFO(arr, stg_SMALL_MUT_ARR_PTRS_DIRTY_info);
        return (arr);
    }
}

stg_cloneSmallArrayzh ( gcptr src, W_ offset, W_ n )
{
    cloneSmallArray(stg_SMALL_MUT_ARR_PTRS_FROZEN_info, src, offset, n)
}

stg_cloneSmallMutableArrayzh ( gcptr src, W_ offset, W_ n )
{
    cloneSmallArray(stg_SMALL_MUT_ARR_PTRS_DIRTY_info, src, offset, n)
}

// We have to escape the "z" in the name.
stg_freezzeSmallArrayzh ( gcptr src, W_ offset, W_ n )
{
    cloneSmallArray(stg_SMALL_MUT_ARR_PTRS_FROZEN_info, src, offset, n)
}

stg_thawSmallArrayzh ( gcptr src, W_ offset, W_ n )
{
    cloneSmallArray(stg_SMALL_MUT_ARR_PTRS_DIRTY_info, src, offset, n)
}

stg_copySmallArrayzh ( gcptr src, W_ src_off, gcptr dst, W_ dst_off, W_ n)
{
    W_ dst_p, src_p, bytes;

    SET_INFO(dst, stg_SMALL_MUT_ARR_PTRS_DIRTY_info);

    dst_p = dst + SIZEOF_StgSmallMutArrPtrs + WDS(dst_off);
    src_p = src + SIZEOF_StgSmallMutArrPtrs + WDS(src_off);
    bytes = WDS(n);
    prim %memcpy(dst_p, src_p, bytes, SIZEOF_W);

    return ();
}

stg_copySmallMutableArrayzh ( gcptr src, W_ src_off, gcptr dst, W_ dst_off, W_ n)
{
    W_ dst_p, src_p, bytes;

    SET_INFO(dst, stg_SMALL_MUT_ARR_PTRS_DIRTY_info);

    dst_p = dst + SIZEOF_StgSmallMutArrPtrs + WDS(dst_off);
    src_p = src + SIZEOF_StgSmallMutArrPtrs + WDS(src_off);
    bytes = WDS(n);
    if (src == dst) {
        prim %memmove(dst_p, src_p, bytes, SIZEOF_W);
    } else {
        prim %memcpy(dst_p, src_p, bytes, SIZEOF_W);
    }

    return ();
}

// RRN: Uses the ticketed approach; see casMutVar
stg_casSmallArrayzh ( gcptr arr, W_ ind, gcptr old, gcptr new )
/* SmallMutableArray# s a -> Int# -> a -> a -> State# s -> (# State# s, Int#, Any a #) */
{
    gcptr h;
    W_ p, len;

    p = arr + SIZEOF_StgSmallMutArrPtrs + WDS(ind);
    (h) = prim %cmpxchgW(p, old, new);

    if (h != old) {
        // Failure, return what was there instead of 'old':
        return (1,h);
    } else {
        // Compare and Swap Succeeded:
        SET_HDR(arr, stg_SMALL_MUT_ARR_PTRS_DIRTY_info, CCCS);
        return (0,new);
    }
}


/* -----------------------------------------------------------------------------
   MutVar primitives
   -------------------------------------------------------------------------- */

stg_newMutVarzh ( gcptr init )
{
    W_ mv;

    ALLOC_PRIM_P (SIZEOF_StgMutVar, stg_newMutVarzh, init);

    mv = Hp - SIZEOF_StgMutVar + WDS(1);
    SET_HDR(mv,stg_MUT_VAR_DIRTY_info,CCCS);
    StgMutVar_var(mv) = init;

    return (mv);
}

// RRN: To support the "ticketed" approach, we return the NEW rather
// than old value if the CAS is successful.  This is received in an
// opaque form in the Haskell code, preventing the compiler from
// changing its pointer identity.  The ticket can then be safely used
// in future CAS operations.
stg_casMutVarzh ( gcptr mv, gcptr old, gcptr new )
 /* MutVar# s a -> a -> a -> State# s -> (# State#, Int#, Any a #) */
{
    gcptr h;

    (h) = prim %cmpxchgW(mv + SIZEOF_StgHeader + OFFSET_StgMutVar_var, old, new);
    if (h != old) {
        return (1,h);
    } else {
        if (GET_INFO(mv) == stg_MUT_VAR_CLEAN_info) {
            ccall dirty_MUT_VAR(BaseReg "ptr", mv "ptr");
        }
        return (0,new);
    }
}

stg_atomicModifyMutVarzh ( gcptr mv, gcptr f )
{
    W_ z, x, y, r, h;

    /* If x is the current contents of the MutVar#, then
       We want to make the new contents point to

         (sel_0 (f x))

       and the return value is

         (sel_1 (f x))

        obviously we can share (f x).

         z = [stg_ap_2 f x]  (max (HS + 2) MIN_UPD_SIZE)
         y = [stg_sel_0 z]   (max (HS + 1) MIN_UPD_SIZE)
         r = [stg_sel_1 z]   (max (HS + 1) MIN_UPD_SIZE)
    */

#if MIN_UPD_SIZE > 1
#define THUNK_1_SIZE (SIZEOF_StgThunkHeader + WDS(MIN_UPD_SIZE))
#define TICK_ALLOC_THUNK_1() TICK_ALLOC_UP_THK(WDS(1),WDS(MIN_UPD_SIZE-1))
#else
#define THUNK_1_SIZE (SIZEOF_StgThunkHeader + WDS(1))
#define TICK_ALLOC_THUNK_1() TICK_ALLOC_UP_THK(WDS(1),0)
#endif

#if MIN_UPD_SIZE > 2
#define THUNK_2_SIZE (SIZEOF_StgThunkHeader + WDS(MIN_UPD_SIZE))
#define TICK_ALLOC_THUNK_2() TICK_ALLOC_UP_THK(WDS(2),WDS(MIN_UPD_SIZE-2))
#else
#define THUNK_2_SIZE (SIZEOF_StgThunkHeader + WDS(2))
#define TICK_ALLOC_THUNK_2() TICK_ALLOC_UP_THK(WDS(2),0)
#endif

#define SIZE (THUNK_2_SIZE + THUNK_1_SIZE + THUNK_1_SIZE)

    HP_CHK_GEN_TICKY(SIZE);

    TICK_ALLOC_THUNK_2();
    CCCS_ALLOC(THUNK_2_SIZE);
    z = Hp - THUNK_2_SIZE + WDS(1);
    SET_HDR(z, stg_ap_2_upd_info, CCCS);
    LDV_RECORD_CREATE(z);
    StgThunk_payload(z,0) = f;

    TICK_ALLOC_THUNK_1();
    CCCS_ALLOC(THUNK_1_SIZE);
    y = z - THUNK_1_SIZE;
    SET_HDR(y, stg_sel_0_upd_info, CCCS);
    LDV_RECORD_CREATE(y);
    StgThunk_payload(y,0) = z;

    TICK_ALLOC_THUNK_1();
    CCCS_ALLOC(THUNK_1_SIZE);
    r = y - THUNK_1_SIZE;
    SET_HDR(r, stg_sel_1_upd_info, CCCS);
    LDV_RECORD_CREATE(r);
    StgThunk_payload(r,0) = z;

  retry:
    x = StgMutVar_var(mv);
    StgThunk_payload(z,1) = x;
#ifdef THREADED_RTS
    (h) = prim %cmpxchgW(mv + SIZEOF_StgHeader + OFFSET_StgMutVar_var, x, y);
    if (h != x) { goto retry; }
#else
    StgMutVar_var(mv) = y;
#endif

    if (GET_INFO(mv) == stg_MUT_VAR_CLEAN_info) {
        ccall dirty_MUT_VAR(BaseReg "ptr", mv "ptr");
    }

    return (r);
}

/* -----------------------------------------------------------------------------
   Weak Pointer Primitives
   -------------------------------------------------------------------------- */

STRING(stg_weak_msg,"New weak pointer at %p\n")

stg_mkWeakzh ( gcptr key,
               gcptr value,
               gcptr finalizer /* or stg_NO_FINALIZER_closure */ )
{
    gcptr w;

    ALLOC_PRIM (SIZEOF_StgWeak)

    w = Hp - SIZEOF_StgWeak + WDS(1);
    SET_HDR(w, stg_WEAK_info, CCCS);

    StgWeak_key(w)         = key;
    StgWeak_value(w)       = value;
    StgWeak_finalizer(w)   = finalizer;
    StgWeak_cfinalizers(w) = stg_NO_FINALIZER_closure;

    StgWeak_link(w) = Capability_weak_ptr_list_hd(MyCapability());
    Capability_weak_ptr_list_hd(MyCapability()) = w;
    if (Capability_weak_ptr_list_tl(MyCapability()) == NULL) {
        Capability_weak_ptr_list_tl(MyCapability()) = w;
    }

    IF_DEBUG(weak, ccall debugBelch(stg_weak_msg,w));

    return (w);
}

stg_mkWeakNoFinalizzerzh ( gcptr key, gcptr value )
{
    jump stg_mkWeakzh (key, value, stg_NO_FINALIZER_closure);
}

STRING(stg_cfinalizer_msg,"Adding a finalizer to %p\n")

stg_addCFinalizzerToWeakzh ( W_ fptr,   // finalizer
                             W_ ptr,
                             W_ flag,   // has environment (0 or 1)
                             W_ eptr,
                             gcptr w )
{
    W_ c, info;

    ALLOC_PRIM (SIZEOF_StgCFinalizerList)

    c = Hp - SIZEOF_StgCFinalizerList + WDS(1);
    SET_HDR(c, stg_C_FINALIZER_LIST_info, CCCS);

    StgCFinalizerList_fptr(c) = fptr;
    StgCFinalizerList_ptr(c) = ptr;
    StgCFinalizerList_eptr(c) = eptr;
    StgCFinalizerList_flag(c) = flag;

    LOCK_CLOSURE(w, info);

    if (info == stg_DEAD_WEAK_info) {
        // Already dead.
        unlockClosure(w, info);
        return (0);
    }

    StgCFinalizerList_link(c) = StgWeak_cfinalizers(w);
    StgWeak_cfinalizers(w) = c;

    unlockClosure(w, info);

    recordMutable(w);

    IF_DEBUG(weak, ccall debugBelch(stg_cfinalizer_msg,w));

    return (1);
}

stg_finalizzeWeakzh ( gcptr w )
{
    gcptr f, list;
    W_ info;

    LOCK_CLOSURE(w, info);

    // already dead?
    if (info == stg_DEAD_WEAK_info) {
        unlockClosure(w, info);
        return (0,stg_NO_FINALIZER_closure);
    }

    f    = StgWeak_finalizer(w);
    list = StgWeak_cfinalizers(w);

    // kill it
#ifdef PROFILING
    // @LDV profiling
    // A weak pointer is inherently used, so we do not need to call
    // LDV_recordDead_FILL_SLOP_DYNAMIC():
    //    LDV_recordDead_FILL_SLOP_DYNAMIC((StgClosure *)w);
    // or, LDV_recordDead():
    //    LDV_recordDead((StgClosure *)w, sizeofW(StgWeak) - sizeofW(StgProfHeader));
    // Furthermore, when PROFILING is turned on, dead weak pointers are exactly as
    // large as weak pointers, so there is no need to fill the slop, either.
    // See stg_DEAD_WEAK_info in StgMiscClosures.hc.
#endif

    //
    // Todo: maybe use SET_HDR() and remove LDV_recordCreate()?
    //
    unlockClosure(w, stg_DEAD_WEAK_info);

    LDV_RECORD_CREATE(w);

    if (list != stg_NO_FINALIZER_closure) {
      ccall runCFinalizers(list);
    }

    /* return the finalizer */
    if (f == stg_NO_FINALIZER_closure) {
        return (0,stg_NO_FINALIZER_closure);
    } else {
        return (1,f);
    }
}

stg_deRefWeakzh ( gcptr w )
{
    W_ code, info;
    gcptr val;

    info = GET_INFO(w);

    if (info == stg_WHITEHOLE_info) {
        // w is locked by another thread. Now it's not immediately clear if w is
        // alive or not. We use lockClosure to wait for the info pointer to become
        // something other than stg_WHITEHOLE_info.

        LOCK_CLOSURE(w, info);
        unlockClosure(w, info);
    }

    if (info == stg_WEAK_info) {
        code = 1;
        val = StgWeak_value(w);
    } else {
        code = 0;
        val = w;
    }
    return (code,val);
}

/* -----------------------------------------------------------------------------
   Floating point operations.
   -------------------------------------------------------------------------- */

stg_decodeFloatzuIntzh ( F_ arg )
{
    W_ p;
    W_ tmp, mp_tmp1, mp_tmp_w, r1, r2;

    STK_CHK_GEN_N (WDS(2));

    reserve 2 = tmp {

        mp_tmp1  = tmp + WDS(1);
        mp_tmp_w = tmp;

        /* Perform the operation */
        ccall __decodeFloat_Int(mp_tmp1 "ptr", mp_tmp_w "ptr", arg);

        r1 = W_[mp_tmp1];
        r2 = W_[mp_tmp_w];
    }

    /* returns: (Int# (mantissa), Int# (exponent)) */
    return (r1, r2);
}

stg_decodeDoublezu2Intzh ( D_ arg )
{
    W_ p, tmp;
    W_ mp_tmp1, mp_tmp2, mp_result1, mp_result2;
    W_ r1, r2, r3, r4;

    STK_CHK_GEN_N (WDS(4));

    reserve 4 = tmp {

        mp_tmp1    = tmp + WDS(3);
        mp_tmp2    = tmp + WDS(2);
        mp_result1 = tmp + WDS(1);
        mp_result2 = tmp;

        /* Perform the operation */
        ccall __decodeDouble_2Int(mp_tmp1 "ptr", mp_tmp2 "ptr",
                                  mp_result1 "ptr", mp_result2 "ptr",
                                  arg);

        r1 = W_[mp_tmp1];
        r2 = W_[mp_tmp2];
        r3 = W_[mp_result1];
        r4 = W_[mp_result2];
    }

    /* returns:
       (Int# (mant sign), Word# (mant high), Word# (mant low), Int# (expn)) */
    return (r1, r2, r3, r4);
}

/* Double# -> (# Int64#, Int# #) */
stg_decodeDoublezuInt64zh ( D_ arg )
{
    CInt exp;
    I64  mant;
    W_   mant_ptr;

    STK_CHK_GEN_N (SIZEOF_INT64);
    reserve BYTES_TO_WDS(SIZEOF_INT64) = mant_ptr {
        (exp) = ccall __decodeDouble_Int64(mant_ptr "ptr", arg);
        mant = I64[mant_ptr];
    }

    return (mant, TO_W_(exp));
}

/* -----------------------------------------------------------------------------
 * Concurrency primitives
 * -------------------------------------------------------------------------- */

stg_forkzh ( gcptr closure )
{
    MAYBE_GC_P(stg_forkzh, closure);

    gcptr threadid;

    ("ptr" threadid) = ccall createIOThread( MyCapability() "ptr",
                                  RtsFlags_GcFlags_initialStkSize(RtsFlags),
                                  closure "ptr");

    /* start blocked if the current thread is blocked */
    StgTSO_flags(threadid) = %lobits16(
        TO_W_(StgTSO_flags(threadid)) |
        TO_W_(StgTSO_flags(CurrentTSO)) & (TSO_BLOCKEX | TSO_INTERRUPTIBLE));

    ccall scheduleThread(MyCapability() "ptr", threadid "ptr");

    // context switch soon, but not immediately: we don't want every
    // forkIO to force a context-switch.
    Capability_context_switch(MyCapability()) = 1 :: CInt;

    return (threadid);
}

stg_forkOnzh ( W_ cpu, gcptr closure )
{
again: MAYBE_GC(again);

    gcptr threadid;

    ("ptr" threadid) = ccall createIOThread(
        MyCapability() "ptr",
        RtsFlags_GcFlags_initialStkSize(RtsFlags),
        closure "ptr");

    /* start blocked if the current thread is blocked */
    StgTSO_flags(threadid) = %lobits16(
        TO_W_(StgTSO_flags(threadid)) |
        TO_W_(StgTSO_flags(CurrentTSO)) & (TSO_BLOCKEX | TSO_INTERRUPTIBLE));

    ccall scheduleThreadOn(MyCapability() "ptr", cpu, threadid "ptr");

    // context switch soon, but not immediately: we don't want every
    // forkIO to force a context-switch.
    Capability_context_switch(MyCapability()) = 1 :: CInt;

    return (threadid);
}

stg_yieldzh ()
{
    // when we yield to the scheduler, we have to tell it to put the
    // current thread to the back of the queue by setting the
    // context_switch flag.  If we don't do this, it will run the same
    // thread again.
    Capability_context_switch(MyCapability()) = 1 :: CInt;
    jump stg_yield_noregs();
}

stg_myThreadIdzh ()
{
    return (CurrentTSO);
}

stg_labelThreadzh ( gcptr threadid, W_ addr )
{
#if defined(DEBUG) || defined(TRACING) || defined(DTRACE)
    ccall labelThread(MyCapability() "ptr", threadid "ptr", addr "ptr");
#endif
    return ();
}

stg_isCurrentThreadBoundzh (/* no args */)
{
    W_ r;
    (r) = ccall isThreadBound(CurrentTSO);
    return (r);
}

stg_threadStatuszh ( gcptr tso )
{
    W_ why_blocked;
    W_ what_next;
    W_ ret, cap, locked;

    what_next   = TO_W_(StgTSO_what_next(tso));
    why_blocked = TO_W_(StgTSO_why_blocked(tso));
    // Note: these two reads are not atomic, so they might end up
    // being inconsistent.  It doesn't matter, since we
    // only return one or the other.  If we wanted to return the
    // contents of block_info too, then we'd have to do some synchronisation.

    if (what_next == ThreadComplete) {
        ret = 16;  // NB. magic, matches up with GHC.Conc.threadStatus
    } else {
        if (what_next == ThreadKilled) {
            ret = 17;
        } else {
            ret = why_blocked;
        }
    }

    cap = TO_W_(Capability_no(StgTSO_cap(tso)));

    if ((TO_W_(StgTSO_flags(tso)) & TSO_LOCKED) != 0) {
        locked = 1;
    } else {
        locked = 0;
    }

    return (ret,cap,locked);
}

/* -----------------------------------------------------------------------------
 * TVar primitives
 * -------------------------------------------------------------------------- */

// Catch retry frame -----------------------------------------------------------

#define CATCH_RETRY_FRAME_FIELDS(w_,p_,info_ptr,        \
                                 p1, p2,                \
                                 running_alt_code,      \
                                 first_code,            \
                                 alt_code)              \
  w_ info_ptr,                                          \
  PROF_HDR_FIELDS(w_,p1,p2)                             \
  w_ running_alt_code,                                  \
  p_ first_code,                                        \
  p_ alt_code


INFO_TABLE_RET(stg_catch_retry_frame, CATCH_RETRY_FRAME,