[GCC 4.8] Initial check-in of GCC 4.8.0

Change-Id: I0719d8a6d0f69b367a6ab6f10eb75622dbf12771

1 files changed, 605 insertions, 0 deletions

diff --git a/gcc-4.8/libitm/method-ml.cc b/gcc-4.8/libitm/method-ml.cc
new file mode 100644
index 000000000..362a233ef
--- /dev/null
+++ b/gcc-4.8/libitm/method-ml.cc
@@ -0,0 +1,605 @@
+/* Copyright (C) 2012-2013 Free Software Foundation, Inc.
+   Contributed by Torvald Riegel <triegel@redhat.com>.
+
+   This file is part of the GNU Transactional Memory Library (libitm).
+
+   Libitm is free software; you can redistribute it and/or modify it
+   under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   Libitm is distributed in the hope that it will be useful, but WITHOUT ANY
+   WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+   FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+   more details.
+
+   Under Section 7 of GPL version 3, you are granted additional
+   permissions described in the GCC Runtime Library Exception, version
+   3.1, as published by the Free Software Foundation.
+
+   You should have received a copy of the GNU General Public License and
+   a copy of the GCC Runtime Library Exception along with this program;
+   see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include "libitm_i.h"
+
+using namespace GTM;
+
+namespace {
+
+// This group consists of all TM methods that synchronize via multiple locks
+// (or ownership records).
+struct ml_mg : public method_group
+{
+  static const gtm_word LOCK_BIT = (~(gtm_word)0 >> 1) + 1;
+  static const gtm_word INCARNATION_BITS = 3;
+  static const gtm_word INCARNATION_MASK = 7;
+  // Maximum time is all bits except the lock bit, the overflow reserve bit,
+  // and the incarnation bits).
+  static const gtm_word TIME_MAX = (~(gtm_word)0 >> (2 + INCARNATION_BITS));
+  // The overflow reserve bit is the MSB of the timestamp part of an orec,
+  // so we can have TIME_MAX+1 pending timestamp increases before we overflow.
+  static const gtm_word OVERFLOW_RESERVE = TIME_MAX + 1;
+
+  static bool is_locked(gtm_word o) { return o & LOCK_BIT; }
+  static gtm_word set_locked(gtm_thread *tx)
+  {
+    return ((uintptr_t)tx >> 1) | LOCK_BIT;
+  }
+  // Returns a time that includes the lock bit, which is required by both
+  // validate() and is_more_recent_or_locked().
+  static gtm_word get_time(gtm_word o) { return o >> INCARNATION_BITS; }
+  static gtm_word set_time(gtm_word time) { return time << INCARNATION_BITS; }
+  static bool is_more_recent_or_locked(gtm_word o, gtm_word than_time)
+  {
+    // LOCK_BIT is the MSB; thus, if O is locked, it is larger than TIME_MAX.
+    return get_time(o) > than_time;
+  }
+  static bool has_incarnation_left(gtm_word o)
+  {
+    return (o & INCARNATION_MASK) < INCARNATION_MASK;
+  }
+  static gtm_word inc_incarnation(gtm_word o) { return o + 1; }
+
+  // The shared time base.
+  atomic<gtm_word> time __attribute__((aligned(HW_CACHELINE_SIZE)));
+
+  // The array of ownership records.
+  atomic<gtm_word>* orecs __attribute__((aligned(HW_CACHELINE_SIZE)));
+  char tailpadding[HW_CACHELINE_SIZE - sizeof(atomic<gtm_word>*)];
+
+  // Location-to-orec mapping.  Stripes of 16B mapped to 2^19 orecs.
+  static const gtm_word L2O_ORECS = 1 << 19;
+  static const gtm_word L2O_SHIFT = 4;
+  static size_t get_orec(const void* addr)
+  {
+    return ((uintptr_t)addr >> L2O_SHIFT) & (L2O_ORECS - 1);
+  }
+  static size_t get_next_orec(size_t orec)
+  {
+    return (orec + 1) & (L2O_ORECS - 1);
+  }
+  // Returns the next orec after the region.
+  static size_t get_orec_end(const void* addr, size_t len)
+  {
+    return (((uintptr_t)addr + len + (1 << L2O_SHIFT) - 1) >> L2O_SHIFT)
+        & (L2O_ORECS - 1);
+  }
+
+  virtual void init()
+  {
+    // We assume that an atomic<gtm_word> is backed by just a gtm_word, so
+    // starting with zeroed memory is fine.
+    orecs = (atomic<gtm_word>*) xcalloc(
+        sizeof(atomic<gtm_word>) * L2O_ORECS, true);
+    // This store is only executed while holding the serial lock, so relaxed
+    // memory order is sufficient here.
+    time.store(0, memory_order_relaxed);
+  }
+
+  virtual void fini()
+  {
+    free(orecs);
+  }
+
+  // We only re-initialize when our time base overflows.  Thus, only reset
+  // the time base and the orecs but do not re-allocate the orec array.
+  virtual void reinit()
+  {
+    // This store is only executed while holding the serial lock, so relaxed
+    // memory order is sufficient here.  Same holds for the memset.
+    time.store(0, memory_order_relaxed);
+    memset(orecs, 0, sizeof(atomic<gtm_word>) * L2O_ORECS);
+  }
+};
+
+static ml_mg o_ml_mg;
+
+
+// The multiple lock, write-through TM method.
+// Maps each memory location to one of the orecs in the orec array, and then
+// acquires the associated orec eagerly before writing through.
+// Writes require undo-logging because we are dealing with several locks/orecs
+// and need to resolve deadlocks if necessary by aborting one of the
+// transactions.
+// Reads do time-based validation with snapshot time extensions.  Incarnation
+// numbers are used to decrease contention on the time base (with those,
+// aborted transactions do not need to acquire a new version number for the
+// data that has been previously written in the transaction and needs to be
+// rolled back).
+// gtm_thread::shared_state is used to store a transaction's current
+// snapshot time (or commit time). The serial lock uses ~0 for inactive
+// transactions and 0 for active ones. Thus, we always have a meaningful
+// timestamp in shared_state that can be used to implement quiescence-based
+// privatization safety.
+class ml_wt_dispatch : public abi_dispatch
+{
+protected:
+  static void pre_write(gtm_thread *tx, const void *addr, size_t len)
+  {
+    gtm_word snapshot = tx->shared_state.load(memory_order_relaxed);
+    gtm_word locked_by_tx = ml_mg::set_locked(tx);
+
+    // Lock all orecs that cover the region.
+    size_t orec = ml_mg::get_orec(addr);
+    size_t orec_end = ml_mg::get_orec_end(addr, len);
+    do
+      {
+        // Load the orec.  Relaxed memory order is sufficient here because
+        // either we have acquired the orec or we will try to acquire it with
+        // a CAS with stronger memory order.
+        gtm_word o = o_ml_mg.orecs[orec].load(memory_order_relaxed);
+
+        // Check whether we have acquired the orec already.
+        if (likely (locked_by_tx != o))
+          {
+            // If not, acquire.  Make sure that our snapshot time is larger or
+            // equal than the orec's version to avoid masking invalidations of
+            // our snapshot with our own writes.
+            if (unlikely (ml_mg::is_locked(o)))
+              tx->restart(RESTART_LOCKED_WRITE);
+
+            if (unlikely (ml_mg::get_time(o) > snapshot))
+              {
+                // We only need to extend the snapshot if we have indeed read
+                // from this orec before.  Given that we are an update
+                // transaction, we will have to extend anyway during commit.
+                // ??? Scan the read log instead, aborting if we have read
+                // from data covered by this orec before?
+                snapshot = extend(tx);
+              }
+
+            // We need acquire memory order here to synchronize with other
+            // (ownership) releases of the orec.  We do not need acq_rel order
+            // because whenever another thread reads from this CAS'
+            // modification, then it will abort anyway and does not rely on
+            // any further happens-before relation to be established.
+            if (unlikely (!o_ml_mg.orecs[orec].compare_exchange_strong(
+                o, locked_by_tx, memory_order_acquire)))
+              tx->restart(RESTART_LOCKED_WRITE);
+
+            // We use an explicit fence here to avoid having to use release
+            // memory order for all subsequent data stores.  This fence will
+            // synchronize with loads of the data with acquire memory order.
+            // See post_load() for why this is necessary.
+            // Adding require memory order to the prior CAS is not sufficient,
+            // at least according to the Batty et al. formalization of the
+            // memory model.
+            atomic_thread_fence(memory_order_release);
+
+            // We log the previous value here to be able to use incarnation
+            // numbers when we have to roll back.
+            // ??? Reserve capacity early to avoid capacity checks here?
+            gtm_rwlog_entry *e = tx->writelog.push();
+            e->orec = o_ml_mg.orecs + orec;
+            e->value = o;
+          }
+        orec = o_ml_mg.get_next_orec(orec);
+      }
+    while (orec != orec_end);
+
+    // Do undo logging.  We do not know which region prior writes logged
+    // (even if orecs have been acquired), so just log everything.
+    tx->undolog.log(addr, len);
+  }
+
+  static void pre_write(const void *addr, size_t len)
+  {
+    gtm_thread *tx = gtm_thr();
+    pre_write(tx, addr, len);
+  }
+
+  // Returns true iff all the orecs in our read log still have the same time
+  // or have been locked by the transaction itself.
+  static bool validate(gtm_thread *tx)
+  {
+    gtm_word locked_by_tx = ml_mg::set_locked(tx);
+    // ??? This might get called from pre_load() via extend().  In that case,
+    // we don't really need to check the new entries that pre_load() is
+    // adding.  Stop earlier?
+    for (gtm_rwlog_entry *i = tx->readlog.begin(), *ie = tx->readlog.end();
+        i != ie; i++)
+      {
+	// Relaxed memory order is sufficient here because we do not need to
+	// establish any new synchronizes-with relationships.  We only need
+	// to read a value that is as least as current as enforced by the
+	// callers: extend() loads global time with acquire, and trycommit()
+	// increments global time with acquire.  Therefore, we will see the
+	// most recent orec updates before the global time that we load.
+        gtm_word o = i->orec->load(memory_order_relaxed);
+        // We compare only the time stamp and the lock bit here.  We know that
+        // we have read only committed data before, so we can ignore
+        // intermediate yet rolled-back updates presented by the incarnation
+        // number bits.
+        if (ml_mg::get_time(o) != ml_mg::get_time(i->value)
+            && o != locked_by_tx)
+          return false;
+      }
+    return true;
+  }
+
+  // Tries to extend the snapshot to a more recent time.  Returns the new
+  // snapshot time and updates TX->SHARED_STATE.  If the snapshot cannot be
+  // extended to the current global time, TX is restarted.
+  static gtm_word extend(gtm_thread *tx)
+  {
+    // We read global time here, even if this isn't strictly necessary
+    // because we could just return the maximum of the timestamps that
+    // validate sees.  However, the potential cache miss on global time is
+    // probably a reasonable price to pay for avoiding unnecessary extensions
+    // in the future.
+    // We need acquire memory oder because we have to synchronize with the
+    // increment of global time by update transactions, whose lock
+    // acquisitions we have to observe (also see trycommit()).
+    gtm_word snapshot = o_ml_mg.time.load(memory_order_acquire);
+    if (!validate(tx))
+      tx->restart(RESTART_VALIDATE_READ);
+
+    // Update our public snapshot time.  Probably useful to decrease waiting
+    // due to quiescence-based privatization safety.
+    // Use release memory order to establish synchronizes-with with the
+    // privatizers; prior data loads should happen before the privatizers
+    // potentially modify anything.
+    tx->shared_state.store(snapshot, memory_order_release);
+    return snapshot;
+  }
+
+  // First pass over orecs.  Load and check all orecs that cover the region.
+  // Write to read log, extend snapshot time if necessary.
+  static gtm_rwlog_entry* pre_load(gtm_thread *tx, const void* addr,
+      size_t len)
+  {
+    // Don't obtain an iterator yet because the log might get resized.
+    size_t log_start = tx->readlog.size();
+    gtm_word snapshot = tx->shared_state.load(memory_order_relaxed);
+    gtm_word locked_by_tx = ml_mg::set_locked(tx);
+
+    size_t orec = ml_mg::get_orec(addr);
+    size_t orec_end = ml_mg::get_orec_end(addr, len);
+    do
+      {
+        // We need acquire memory order here so that this load will
+        // synchronize with the store that releases the orec in trycommit().
+        // In turn, this makes sure that subsequent data loads will read from
+        // a visible sequence of side effects that starts with the most recent
+        // store to the data right before the release of the orec.
+        gtm_word o = o_ml_mg.orecs[orec].load(memory_order_acquire);
+
+        if (likely (!ml_mg::is_more_recent_or_locked(o, snapshot)))
+          {
+            success:
+            gtm_rwlog_entry *e = tx->readlog.push();
+            e->orec = o_ml_mg.orecs + orec;
+            e->value = o;
+          }
+        else if (!ml_mg::is_locked(o))
+          {
+            // We cannot read this part of the region because it has been
+            // updated more recently than our snapshot time.  If we can extend
+            // our snapshot, then we can read.
+            snapshot = extend(tx);
+            goto success;
+          }
+        else
+          {
+            // If the orec is locked by us, just skip it because we can just
+            // read from it.  Otherwise, restart the transaction.
+            if (o != locked_by_tx)
+              tx->restart(RESTART_LOCKED_READ);
+          }
+        orec = o_ml_mg.get_next_orec(orec);
+      }
+    while (orec != orec_end);
+    return &tx->readlog[log_start];
+  }
+
+  // Second pass over orecs, verifying that the we had a consistent read.
+  // Restart the transaction if any of the orecs is locked by another
+  // transaction.
+  static void post_load(gtm_thread *tx, gtm_rwlog_entry* log)
+  {
+    for (gtm_rwlog_entry *end = tx->readlog.end(); log != end; log++)
+      {
+        // Check that the snapshot is consistent.  We expect the previous data
+        // load to have acquire memory order, or be atomic and followed by an
+        // acquire fence.
+        // As a result, the data load will synchronize with the release fence
+        // issued by the transactions whose data updates the data load has read
+        // from.  This forces the orec load to read from a visible sequence of
+        // side effects that starts with the other updating transaction's
+        // store that acquired the orec and set it to locked.
+        // We therefore either read a value with the locked bit set (and
+        // restart) or read an orec value that was written after the data had
+        // been written.  Either will allow us to detect inconsistent reads
+        // because it will have a higher/different value.
+	// Also note that differently to validate(), we compare the raw value
+	// of the orec here, including incarnation numbers.  We must prevent
+	// returning uncommitted data from loads (whereas when validating, we
+	// already performed a consistent load).
+        gtm_word o = log->orec->load(memory_order_relaxed);
+        if (log->value != o)
+          tx->restart(RESTART_VALIDATE_READ);
+      }
+  }
+
+  template <typename V> static V load(const V* addr, ls_modifier mod)
+  {
+    // Read-for-write should be unlikely, but we need to handle it or will
+    // break later WaW optimizations.
+    if (unlikely(mod == RfW))
+      {
+	pre_write(addr, sizeof(V));
+	return *addr;
+      }
+    if (unlikely(mod == RaW))
+      return *addr;
+    // ??? Optimize for RaR?
+
+    gtm_thread *tx = gtm_thr();
+    gtm_rwlog_entry* log = pre_load(tx, addr, sizeof(V));
+
+    // Load the data.
+    // This needs to have acquire memory order (see post_load()).
+    // Alternatively, we can put an acquire fence after the data load but this
+    // is probably less efficient.
+    // FIXME We would need an atomic load with acquire memory order here but
+    // we can't just forge an atomic load for nonatomic data because this
+    // might not work on all implementations of atomics.  However, we need
+    // the acquire memory order and we can only establish this if we link
+    // it to the matching release using a reads-from relation between atomic
+    // loads.  Also, the compiler is allowed to optimize nonatomic accesses
+    // differently than atomic accesses (e.g., if the load would be moved to
+    // after the fence, we potentially don't synchronize properly anymore).
+    // Instead of the following, just use an ordinary load followed by an
+    // acquire fence, and hope that this is good enough for now:
+    // V v = atomic_load_explicit((atomic<V>*)addr, memory_order_acquire);
+    V v = *addr;
+    atomic_thread_fence(memory_order_acquire);
+
+    // ??? Retry the whole load if it wasn't consistent?
+    post_load(tx, log);
+
+    return v;
+  }
+
+  template <typename V> static void store(V* addr, const V value,
+      ls_modifier mod)
+  {
+    if (likely(mod != WaW))
+      pre_write(addr, sizeof(V));
+    // FIXME We would need an atomic store here but we can't just forge an
+    // atomic load for nonatomic data because this might not work on all
+    // implementations of atomics.  However, we need this store to link the
+    // release fence in pre_write() to the acquire operation in load, which
+    // is only guaranteed if we have a reads-from relation between atomic
+    // accesses.  Also, the compiler is allowed to optimize nonatomic accesses
+    // differently than atomic accesses (e.g., if the store would be moved
+    // to before the release fence in pre_write(), things could go wrong).
+    // atomic_store_explicit((atomic<V>*)addr, value, memory_order_relaxed);
+    *addr = value;
+  }
+
+public:
+  static void memtransfer_static(void *dst, const void* src, size_t size,
+      bool may_overlap, ls_modifier dst_mod, ls_modifier src_mod)
+  {
+    gtm_rwlog_entry* log = 0;
+    gtm_thread *tx = 0;
+
+    if (src_mod == RfW)
+      {
+        tx = gtm_thr();
+        pre_write(tx, src, size);
+      }
+    else if (src_mod != RaW && src_mod != NONTXNAL)
+      {
+        tx = gtm_thr();
+        log = pre_load(tx, src, size);
+      }
+    // ??? Optimize for RaR?
+
+    if (dst_mod != NONTXNAL && dst_mod != WaW)
+      {
+        if (src_mod != RfW && (src_mod == RaW || src_mod == NONTXNAL))
+          tx = gtm_thr();
+        pre_write(tx, dst, size);
+      }
+
+    // FIXME We should use atomics here (see store()).  Let's just hope that
+    // memcpy/memmove are good enough.
+    if (!may_overlap)
+      ::memcpy(dst, src, size);
+    else
+      ::memmove(dst, src, size);
+
+    // ??? Retry the whole memtransfer if it wasn't consistent?
+    if (src_mod != RfW && src_mod != RaW && src_mod != NONTXNAL)
+      {
+	// See load() for why we need the acquire fence here.
+	atomic_thread_fence(memory_order_acquire);
+	post_load(tx, log);
+      }
+  }
+
+  static void memset_static(void *dst, int c, size_t size, ls_modifier mod)
+  {
+    if (mod != WaW)
+      pre_write(dst, size);
+    // FIXME We should use atomics here (see store()).  Let's just hope that
+    // memset is good enough.
+    ::memset(dst, c, size);
+  }
+
+  virtual gtm_restart_reason begin_or_restart()
+  {
+    // We don't need to do anything for nested transactions.
+    gtm_thread *tx = gtm_thr();
+    if (tx->parent_txns.size() > 0)
+      return NO_RESTART;
+
+    // Read the current time, which becomes our snapshot time.
+    // Use acquire memory oder so that we see the lock acquisitions by update
+    // transcations that incremented the global time (see trycommit()).
+    gtm_word snapshot = o_ml_mg.time.load(memory_order_acquire);
+    // Re-initialize method group on time overflow.
+    if (snapshot >= o_ml_mg.TIME_MAX)
+      return RESTART_INIT_METHOD_GROUP;
+
+    // We don't need to enforce any ordering for the following store. There
+    // are no earlier data loads in this transaction, so the store cannot
+    // become visible before those (which could lead to the violation of
+    // privatization safety). The store can become visible after later loads
+    // but this does not matter because the previous value will have been
+    // smaller or equal (the serial lock will set shared_state to zero when
+    // marking the transaction as active, and restarts enforce immediate
+    // visibility of a smaller or equal value with a barrier (see
+    // rollback()).
+    tx->shared_state.store(snapshot, memory_order_relaxed);
+    return NO_RESTART;
+  }
+
+  virtual bool trycommit(gtm_word& priv_time)
+  {
+    gtm_thread* tx = gtm_thr();
+
+    // If we haven't updated anything, we can commit.
+    if (!tx->writelog.size())
+      {
+        tx->readlog.clear();
+        return true;
+      }
+
+    // Get a commit time.
+    // Overflow of o_ml_mg.time is prevented in begin_or_restart().
+    // We need acq_rel here because (1) the acquire part is required for our
+    // own subsequent call to validate(), and the release part is necessary to
+    // make other threads' validate() work as explained there and in extend().
+    gtm_word ct = o_ml_mg.time.fetch_add(1, memory_order_acq_rel) + 1;
+
+    // Extend our snapshot time to at least our commit time.
+    // Note that we do not need to validate if our snapshot time is right
+    // before the commit time because we are never sharing the same commit
+    // time with other transactions.
+    // No need to reset shared_state, which will be modified by the serial
+    // lock right after our commit anyway.
+    gtm_word snapshot = tx->shared_state.load(memory_order_relaxed);
+    if (snapshot < ct - 1 && !validate(tx))
+      return false;
+
+    // Release orecs.
+    // See pre_load() / post_load() for why we need release memory order.
+    // ??? Can we use a release fence and relaxed stores?
+    gtm_word v = ml_mg::set_time(ct);
+    for (gtm_rwlog_entry *i = tx->writelog.begin(), *ie = tx->writelog.end();
+        i != ie; i++)
+      i->orec->store(v, memory_order_release);
+
+    // We're done, clear the logs.
+    tx->writelog.clear();
+    tx->readlog.clear();
+
+    // Need to ensure privatization safety. Every other transaction must
+    // have a snapshot time that is at least as high as our commit time
+    // (i.e., our commit must be visible to them).
+    priv_time = ct;
+    return true;
+  }
+
+  virtual void rollback(gtm_transaction_cp *cp)
+  {
+    // We don't do anything for rollbacks of nested transactions.
+    // ??? We could release locks here if we snapshot writelog size.  readlog
+    // is similar.  This is just a performance optimization though.  Nested
+    // aborts should be rather infrequent, so the additional save/restore
+    // overhead for the checkpoints could be higher.
+    if (cp != 0)
+      return;
+
+    gtm_thread *tx = gtm_thr();
+    gtm_word overflow_value = 0;
+
+    // Release orecs.
+    for (gtm_rwlog_entry *i = tx->writelog.begin(), *ie = tx->writelog.end();
+        i != ie; i++)
+      {
+        // If possible, just increase the incarnation number.
+        // See pre_load() / post_load() for why we need release memory order.
+	// ??? Can we use a release fence and relaxed stores?  (Same below.)
+        if (ml_mg::has_incarnation_left(i->value))
+          i->orec->store(ml_mg::inc_incarnation(i->value),
+              memory_order_release);
+        else
+          {
+            // We have an incarnation overflow.  Acquire a new timestamp, and
+            // use it from now on as value for each orec whose incarnation
+            // number cannot be increased.
+            // Overflow of o_ml_mg.time is prevented in begin_or_restart().
+            // See pre_load() / post_load() for why we need release memory
+            // order.
+            if (!overflow_value)
+              // Release memory order is sufficient but required here.
+              // In contrast to the increment in trycommit(), we need release
+              // for the same reason but do not need the acquire because we
+              // do not validate subsequently.
+              overflow_value = ml_mg::set_time(
+                  o_ml_mg.time.fetch_add(1, memory_order_release) + 1);
+            i->orec->store(overflow_value, memory_order_release);
+          }
+      }
+
+    // We need this release fence to ensure that privatizers see the
+    // rolled-back original state (not any uncommitted values) when they read
+    // the new snapshot time that we write in begin_or_restart().
+    atomic_thread_fence(memory_order_release);
+
+    // We're done, clear the logs.
+    tx->writelog.clear();
+    tx->readlog.clear();
+  }
+
+  virtual bool supports(unsigned number_of_threads)
+  {
+    // Each txn can commit and fail and rollback once before checking for
+    // overflow, so this bounds the number of threads that we can support.
+    // In practice, this won't be a problem but we check it anyway so that
+    // we never break in the occasional weird situation.
+    return (number_of_threads * 2 <= ml_mg::OVERFLOW_RESERVE);
+  }
+
+  CREATE_DISPATCH_METHODS(virtual, )
+  CREATE_DISPATCH_METHODS_MEM()
+
+  ml_wt_dispatch() : abi_dispatch(false, true, false, false, 0, &o_ml_mg)
+  { }
+};
+
+} // anon namespace
+
+static const ml_wt_dispatch o_ml_wt_dispatch;
+
+abi_dispatch *
+GTM::dispatch_ml_wt ()
+{
+  return const_cast<ml_wt_dispatch *>(&o_ml_wt_dispatch);
+}