[PATCH 02/13] OpenACC reference count overhaul

[Julian Brown <julian@codesourcery.com>]

This is a rebased version of the reference-count overhaul patch last
posted here:

  https://gcc.gnu.org/ml/gcc-patches/2019-11/msg02235.html

This version omits parts of the above patch already committed upstream and
merges some recent REFCOUNT_INFINITY changes. This patch causes the newish
PR92843 test to fail, though IMO that test relies on behaviour arising
from a rather nuanced reading of the spec. Hopefully we can resolve that
problem as a follow-up.

Tested alongside other patches in this series with offloading to
NVPTX. OK?

Julian

2019-11-22  Julian Brown  <julian@codesourcery.com>
            Thomas Schwinge  <thomas@codesourcery.com>

	libgomp/
	* libgomp.h (struct splay_tree_key_s): Substitute dynamic_refcount
	field for virtual_refcount.
	(enum gomp_map_vars_kind): Add GOMP_MAP_VARS_OPENACC_ENTER_DATA.
	(gomp_free_memmap): Remove prototype.
	* oacc-init.c (acc_shutdown_1): Iteratively call gomp_remove_var
	instead of calling gomp_free_memmap.
	* oacc-mem.c (acc_unmap_data): Open code instead of forcing
	target_mem_desc's to_free NULL then calling gomp_unmap_vars.  Handle
	REFCOUNT_INFINITY on target blocks.
	(present_create_copy): Use virtual_refcount instead of
	dynamic_refcount.  Re-do lookup for target pointer return value.
	(delete_copyout): Update for virtual_refcount semantics.
	(gomp_acc_insert_pointer, gomp_acc_remove_pointer, find_pointer):
	Remove functions.
	(find_group_last, goacc_enter_data_internal,
	goacc_exit_data_internal): New functions.
	(GOACC_enter_exit_data): Use goacc_enter_data_internal and
	goacc_exit_data_internal helper functions.
	* target.c (gomp_map_vars_internal): Handle
	GOMP_MAP_VARS_OPENACC_ENTER_DATA.  Update for virtual_refcount
	semantics.
	(gomp_unmap_vars_internal): Update for virtual_refcount semantics.
	(gomp_load_image_to_device, omp_target_associate_ptr): Zero-initialise
	virtual_refcount field instead of dynamic_refcount.
	(gomp_free_memmap): Remove function.
	* testsuite/libgomp.oacc-c-c++-common/unmap-infinity-1.c: New test.
	* testsuite/libgomp.c-c++-common/unmap-infinity-2.c: New test.
	* testsuite/libgomp.oacc-c-c++-common/subset-subarray-mappings-1-r-p.c:
	Remove PR92848 TODOs.
	* testsuite/libgomp.oacc-c-c++-common/pr92843-1.c: Add XFAIL.
---
 libgomp/libgomp.h                             |   9 +-
 libgomp/oacc-init.c                           |  10 +-
 libgomp/oacc-mem.c                            | 399 +++++++-----------
 libgomp/target.c                              |  53 +--
 .../libgomp.c-c++-common/unmap-infinity-2.c   |  19 +
 .../libgomp.oacc-c-c++-common/pr92843-1.c     |   1 +
 .../subset-subarray-mappings-1-r-p.c          |  16 -
 .../unmap-infinity-1.c                        |  17 +
 8 files changed, 228 insertions(+), 296 deletions(-)
 create mode 100644 libgomp/testsuite/libgomp.c-c++-common/unmap-infinity-2.c
 create mode 100644 libgomp/testsuite/libgomp.oacc-c-c++-common/unmap-infinity-1.c

diff --git a/libgomp/libgomp.h b/libgomp/libgomp.h
index 0f1f11284d5..865b9df2444 100644
--- a/libgomp/libgomp.h
+++ b/libgomp/libgomp.h
@@ -1007,8 +1007,11 @@ struct splay_tree_key_s {
   uintptr_t tgt_offset;
   /* Reference count.  */
   uintptr_t refcount;
-  /* Dynamic reference count.  */
-  uintptr_t dynamic_refcount;
+  /* Reference counts beyond those that represent genuine references in the
+     linked splay tree key/target memory structures, e.g. for multiple OpenACC
+     "present increment" operations (via "acc enter data") referring to the same
+     host-memory block.  */
+  uintptr_t virtual_refcount;
   struct splay_tree_aux *aux;
 };
 
@@ -1139,6 +1142,7 @@ struct gomp_device_descr
 enum gomp_map_vars_kind
 {
   GOMP_MAP_VARS_OPENACC,
+  GOMP_MAP_VARS_OPENACC_ENTER_DATA,
   GOMP_MAP_VARS_TARGET,
   GOMP_MAP_VARS_DATA,
   GOMP_MAP_VARS_ENTER_DATA
@@ -1169,7 +1173,6 @@ extern void gomp_unmap_vars_async (struct target_mem_desc *, bool,
 				   struct goacc_asyncqueue *);
 extern void gomp_init_device (struct gomp_device_descr *);
 extern bool gomp_fini_device (struct gomp_device_descr *);
-extern void gomp_free_memmap (struct splay_tree_s *);
 extern void gomp_unload_device (struct gomp_device_descr *);
 extern bool gomp_remove_var (struct gomp_device_descr *, splay_tree_key);
 extern void gomp_remove_var_async (struct gomp_device_descr *, splay_tree_key,
diff --git a/libgomp/oacc-init.c b/libgomp/oacc-init.c
index a444c604d59..dd88b58a379 100644
--- a/libgomp/oacc-init.c
+++ b/libgomp/oacc-init.c
@@ -370,7 +370,15 @@ acc_shutdown_1 (acc_device_t d)
       if (walk->dev)
 	{
 	  gomp_mutex_lock (&walk->dev->lock);
-	  gomp_free_memmap (&walk->dev->mem_map);
+
+	  while (walk->dev->mem_map.root)
+	    {
+	      splay_tree_key k = &walk->dev->mem_map.root->key;
+	      if (k->aux)
+		k->aux->link_key = NULL;
+	      gomp_remove_var (walk->dev, k);
+	    }
+
 	  gomp_mutex_unlock (&walk->dev->lock);
 
 	  walk->dev = NULL;
diff --git a/libgomp/oacc-mem.c b/libgomp/oacc-mem.c
index 196b7e2a520..2a0e7236b92 100644
--- a/libgomp/oacc-mem.c
+++ b/libgomp/oacc-mem.c
@@ -406,7 +406,7 @@ acc_map_data (void *h, void *d, size_t s)
 			   &kinds, true, GOMP_MAP_VARS_OPENACC);
       splay_tree_key n = tgt->list[0].key;
       assert (n->refcount == 1);
-      assert (n->dynamic_refcount == 0);
+      assert (n->virtual_refcount == 0);
       /* Special reference counting behavior.  */
       n->refcount = REFCOUNT_INFINITY;
 
@@ -434,12 +434,9 @@ acc_unmap_data (void *h)
   acc_api_info api_info;
   bool profiling_p = GOACC_PROFILING_SETUP_P (thr, &prof_info, &api_info);
 
-  size_t host_size;
-
   gomp_mutex_lock (&acc_dev->lock);
 
   splay_tree_key n = lookup_host (acc_dev, h, 1);
-  struct target_mem_desc *t;
 
   if (!n)
     {
@@ -447,7 +444,7 @@ acc_unmap_data (void *h)
       gomp_fatal ("%p is not a mapped block", (void *)h);
     }
 
-  host_size = n->host_end - n->host_start;
+  size_t host_size = n->host_end - n->host_start;
 
   if (n->host_start != (uintptr_t) h)
     {
@@ -456,7 +453,7 @@ acc_unmap_data (void *h)
 		  (void *) n->host_start, (int) host_size, (void *) h);
     }
   /* TODO This currently doesn't catch 'REFCOUNT_INFINITY' usage different from
-     'acc_map_data'.  Maybe 'dynamic_refcount' can be used for disambiguating
+     'acc_map_data'.  Maybe 'virtual_refcount' can be used for disambiguating
      the different 'REFCOUNT_INFINITY' cases, or simply separate
      'REFCOUNT_INFINITY' values per different usage ('REFCOUNT_ACC_MAP_DATA'
      etc.)?  */
@@ -468,24 +465,25 @@ acc_unmap_data (void *h)
 		  (void *) h, (int) host_size);
     }
 
-  /* Mark for removal.  */
-  n->refcount = 1;
+  splay_tree_remove (&acc_dev->mem_map, n);
 
-  t = n->tgt;
+  struct target_mem_desc *tgt = n->tgt;
 
-  if (t->refcount == 2)
+  if (tgt->refcount == REFCOUNT_INFINITY)
     {
-      /* This is the last reference, so pull the descriptor off the
-         chain. This avoids gomp_unmap_vars via gomp_unmap_tgt from
-         freeing the device memory. */
-      t->tgt_end = 0;
-      t->to_free = 0;
+      gomp_mutex_unlock (&acc_dev->lock);
+      gomp_fatal ("cannot unmap target block");
+    }
+  else if (tgt->refcount > 1)
+    tgt->refcount--;
+  else
+    {
+      free (tgt->array);
+      free (tgt);
     }
 
   gomp_mutex_unlock (&acc_dev->lock);
 
-  gomp_unmap_vars (t, true);
-
   if (profiling_p)
     {
       thr->prof_info = NULL;
@@ -545,8 +543,10 @@ present_create_copy (unsigned f, void *h, size_t s, int async)
 
       assert (n->refcount != REFCOUNT_LINK);
       if (n->refcount != REFCOUNT_INFINITY)
-	n->refcount++;
-      n->dynamic_refcount++;
+	{
+	  n->refcount++;
+	  n->virtual_refcount++;
+	}
 
       gomp_mutex_unlock (&acc_dev->lock);
     }
@@ -557,7 +557,6 @@ present_create_copy (unsigned f, void *h, size_t s, int async)
     }
   else
     {
-      struct target_mem_desc *tgt;
       size_t mapnum = 1;
       unsigned short kinds;
       void *hostaddrs = h;
@@ -571,14 +570,16 @@ present_create_copy (unsigned f, void *h, size_t s, int async)
 
       goacc_aq aq = get_goacc_asyncqueue (async);
 
-      tgt = gomp_map_vars_async (acc_dev, aq, mapnum, &hostaddrs, NULL, &s,
-				 &kinds, true, GOMP_MAP_VARS_OPENACC);
-      n = tgt->list[0].key;
-      assert (n->refcount == 1);
-      assert (n->dynamic_refcount == 0);
-      n->dynamic_refcount++;
+      gomp_map_vars_async (acc_dev, aq, mapnum, &hostaddrs, NULL, &s, &kinds,
+			   true, GOMP_MAP_VARS_OPENACC_ENTER_DATA);
 
-      d = tgt->to_free;
+      gomp_mutex_lock (&acc_dev->lock);
+      n = lookup_host (acc_dev, h, s);
+      assert (n != NULL);
+      assert (n->tgt_offset == 0);
+      assert ((uintptr_t) h == n->host_start);
+      d = (void *) n->tgt->tgt_start;
+      gomp_mutex_unlock (&acc_dev->lock);
     }
 
   if (profiling_p)
@@ -696,26 +697,21 @@ delete_copyout (unsigned f, void *h, size_t s, int async, const char *libfnname)
 		  (void *) h, (int) s, (void *) n->host_start, (int) host_size);
     }
 
-  assert (n->refcount != REFCOUNT_LINK);
-  if (n->refcount != REFCOUNT_INFINITY
-      && n->refcount < n->dynamic_refcount)
-    {
-      gomp_mutex_unlock (&acc_dev->lock);
-      gomp_fatal ("Dynamic reference counting assert fail\n");
-    }
-
   if (f & FLAG_FINALIZE)
     {
       if (n->refcount != REFCOUNT_INFINITY)
-	n->refcount -= n->dynamic_refcount;
-      n->dynamic_refcount = 0;
+	n->refcount -= n->virtual_refcount;
+      n->virtual_refcount = 0;
     }
-  else if (n->dynamic_refcount)
+
+  if (n->virtual_refcount > 0)
     {
       if (n->refcount != REFCOUNT_INFINITY)
 	n->refcount--;
-      n->dynamic_refcount--;
+      n->virtual_refcount--;
     }
+  else if (n->refcount > 0 && n->refcount != REFCOUNT_INFINITY)
+    n->refcount--;
 
   if (n->refcount == 0)
     {
@@ -870,154 +866,138 @@ acc_update_self_async (void *h, size_t s, int async)
   update_dev_host (0, h, s, async);
 }
 
+/* Some types of (pointer) variables use several consecutive mappings, which
+   must be treated as a group for enter/exit data directives.  This function
+   returns the last mapping in such a group (inclusive), or POS for singleton
+   mappings.  */
 
-/* OpenACC 'enter data', 'exit data': 'GOACC_enter_exit_data' and its helper
-   functions.  */
-
-/* Special handling for 'GOMP_MAP_POINTER', 'GOMP_MAP_TO_PSET'.
-
-   Only the first mapping is considered in reference counting; the following
-   ones implicitly follow suit.  */
-
-static void
-goacc_insert_pointer (size_t mapnum, void **hostaddrs, size_t *sizes,
-		      void *kinds, int async)
+static int
+find_group_last (int pos, size_t mapnum, unsigned short *kinds)
 {
-  struct target_mem_desc *tgt;
-  struct goacc_thread *thr = goacc_thread ();
-  struct gomp_device_descr *acc_dev = thr->dev;
-
-  if (*hostaddrs == NULL)
-    return;
+  unsigned char kind0 = kinds[pos] & 0xff;
+  int first_pos = pos, last_pos = pos;
 
-  if (acc_is_present (*hostaddrs, *sizes))
+  if (kind0 == GOMP_MAP_TO_PSET)
     {
-      splay_tree_key n;
-      gomp_mutex_lock (&acc_dev->lock);
-      n = lookup_host (acc_dev, *hostaddrs, *sizes);
-      assert (n->refcount != REFCOUNT_INFINITY
-	      && n->refcount != REFCOUNT_LINK);
-      gomp_mutex_unlock (&acc_dev->lock);
-
-      tgt = n->tgt;
-      for (size_t i = 0; i < tgt->list_count; i++)
-	if (tgt->list[i].key == n)
-	  {
-	    for (size_t j = 0; j < mapnum; j++)
-	      if (i + j < tgt->list_count && tgt->list[i + j].key)
-		{
-		  tgt->list[i + j].key->refcount++;
-		  tgt->list[i + j].key->dynamic_refcount++;
-		}
-	    return;
-	  }
-      /* Should not reach here.  */
-      gomp_fatal ("Dynamic refcount incrementing failed for pointer/pset");
+      while (pos + 1 < mapnum && (kinds[pos + 1] & 0xff) == GOMP_MAP_POINTER)
+	last_pos = ++pos;
+      /* We expect at least one GOMP_MAP_POINTER after a GOMP_MAP_TO_PSET.  */
+      assert (last_pos > first_pos);
+    }
+  else
+    {
+      /* GOMP_MAP_ALWAYS_POINTER can only appear directly after some other
+	 mapping.  */
+      if (pos + 1 < mapnum
+	  && (kinds[pos + 1] & 0xff) == GOMP_MAP_ALWAYS_POINTER)
+	return pos + 1;
+
+      /* We can have one or several GOMP_MAP_POINTER mappings after a to/from
+	 (etc.) mapping.  */
+      while (pos + 1 < mapnum && (kinds[pos + 1] & 0xff) == GOMP_MAP_POINTER)
+	last_pos = ++pos;
     }
 
-  gomp_debug (0, "  %s: prepare mappings\n", __FUNCTION__);
-  goacc_aq aq = get_goacc_asyncqueue (async);
-  tgt = gomp_map_vars_async (acc_dev, aq, mapnum, hostaddrs,
-			     NULL, sizes, kinds, true, GOMP_MAP_VARS_OPENACC);
-  splay_tree_key n = tgt->list[0].key;
-  assert (n->refcount == 1);
-  assert (n->dynamic_refcount == 0);
-  n->dynamic_refcount++;
-  gomp_debug (0, "  %s: mappings prepared\n", __FUNCTION__);
+  return last_pos;
 }
 
+/* Map variables for OpenACC "enter data".  We can't just call
+   gomp_map_vars_async once, because individual mapped variables might have
+   "exit data" called for them at different times.  */
+
 static void
-goacc_remove_pointer (void *h, size_t s, bool force_copyfrom, int async,
-		      int finalize, int mapnum)
+goacc_enter_data_internal (struct gomp_device_descr *acc_dev, size_t mapnum,
+			   void **hostaddrs, size_t *sizes,
+			   unsigned short *kinds, goacc_aq aq)
 {
-  struct goacc_thread *thr = goacc_thread ();
-  struct gomp_device_descr *acc_dev = thr->dev;
-  splay_tree_key n;
-  struct target_mem_desc *t;
-  int minrefs = (mapnum == 1) ? 2 : 3;
-
-  if (!acc_is_present (h, s))
-    return;
-
-  gomp_mutex_lock (&acc_dev->lock);
-
-  n = lookup_host (acc_dev, h, 1);
-
-  if (!n)
+  for (size_t i = 0; i < mapnum; i++)
     {
-      gomp_mutex_unlock (&acc_dev->lock);
-      gomp_fatal ("%p is not a mapped block", (void *)h);
-    }
-
-  gomp_debug (0, "  %s: restore mappings\n", __FUNCTION__);
+      int group_last = find_group_last (i, mapnum, kinds);
 
-  t = n->tgt;
+      gomp_map_vars_async (acc_dev, aq,
+			   (group_last - i) + 1,
+			   &hostaddrs[i], NULL,
+			   &sizes[i], &kinds[i], true,
+			   GOMP_MAP_VARS_OPENACC_ENTER_DATA);
 
-  assert (n->refcount != REFCOUNT_INFINITY
-	  && n->refcount != REFCOUNT_LINK);
-  if (n->refcount < n->dynamic_refcount)
-    {
-      gomp_mutex_unlock (&acc_dev->lock);
-      gomp_fatal ("Dynamic reference counting assert fail\n");
+      i = group_last;
     }
+}
 
-  if (finalize)
-    {
-      n->refcount -= n->dynamic_refcount;
-      n->dynamic_refcount = 0;
-    }
-  else if (n->dynamic_refcount)
-    {
-      n->refcount--;
-      n->dynamic_refcount--;
-    }
+/* Unmap variables for OpenACC "exit data", with optional finalization
+   (affecting all mappings in this operation).  */
 
-  gomp_mutex_unlock (&acc_dev->lock);
+static void
+goacc_exit_data_internal (struct gomp_device_descr *acc_dev, size_t mapnum,
+			  void **hostaddrs, size_t *sizes,
+			  unsigned short *kinds, bool finalize, goacc_aq aq)
+{
+  gomp_mutex_lock (&acc_dev->lock);
 
-  if (n->refcount == 0)
+  for (size_t i = 0; i < mapnum; ++i)
     {
-      /* Set refcount to 1 to allow gomp_unmap_vars to unmap it.  */
-      n->refcount = 1;
-      t->refcount = minrefs;
-      for (size_t i = 0; i < t->list_count; i++)
-	if (t->list[i].key == n)
-	  {
-	    t->list[i].copy_from = force_copyfrom ? 1 : 0;
-	    break;
-	  }
+      unsigned char kind = kinds[i] & 0xff;
+      bool copyfrom = false;
 
-      /* If running synchronously, unmap immediately.  */
-      if (async < acc_async_noval)
-	gomp_unmap_vars (t, true);
-      else
+      switch (kind)
 	{
-	  goacc_aq aq = get_goacc_asyncqueue (async);
-	  gomp_unmap_vars_async (t, true, aq);
+	case GOMP_MAP_FROM:
+	case GOMP_MAP_FORCE_FROM:
+	case GOMP_MAP_ALWAYS_FROM:
+	  copyfrom = true;
+	  /* Fallthrough.  */
+
+	case GOMP_MAP_TO_PSET:
+	case GOMP_MAP_POINTER:
+	case GOMP_MAP_DELETE:
+	case GOMP_MAP_RELEASE:
+	  {
+	    struct splay_tree_key_s cur_node;
+	    cur_node.host_start = (uintptr_t) hostaddrs[i];
+	    cur_node.host_end = cur_node.host_start
+				+ (kind == GOMP_MAP_POINTER
+				   ? sizeof (void *) : sizes[i]);
+	    splay_tree_key n
+	      = splay_tree_lookup (&acc_dev->mem_map, &cur_node);
+
+	    if (n == NULL)
+	      continue;
+
+	    if (finalize)
+	      {
+		if (n->refcount != REFCOUNT_INFINITY)
+		  n->refcount -= n->virtual_refcount;
+		n->virtual_refcount = 0;
+	      }
+
+	    if (n->virtual_refcount > 0)
+	      {
+		if (n->refcount != REFCOUNT_INFINITY)
+		  n->refcount--;
+		n->virtual_refcount--;
+	      }
+	    else if (n->refcount > 0 && n->refcount != REFCOUNT_INFINITY)
+	      n->refcount--;
+
+	    if (copyfrom
+		&& (kind != GOMP_MAP_FROM || n->refcount == 0))
+	      gomp_copy_dev2host (acc_dev, aq, (void *) cur_node.host_start,
+				  (void *) (n->tgt->tgt_start + n->tgt_offset
+					    + cur_node.host_start
+					    - n->host_start),
+				  cur_node.host_end - cur_node.host_start);
+
+	    if (n->refcount == 0)
+	      gomp_remove_var_async (acc_dev, n, aq);
+	  }
+	  break;
+	default:
+	  gomp_fatal (">>>> goacc_exit_data_internal UNHANDLED kind 0x%.2x",
+			  kind);
 	}
     }
 
   gomp_mutex_unlock (&acc_dev->lock);
-
-  gomp_debug (0, "  %s: mappings restored\n", __FUNCTION__);
-}
-
-/* Return the number of mappings associated with 'GOMP_MAP_TO_PSET' or
-   'GOMP_MAP_POINTER'.  */
-
-static int
-find_pointer (int pos, size_t mapnum, unsigned short *kinds)
-{
-  if (pos + 1 >= mapnum)
-    return 0;
-
-  unsigned char kind = kinds[pos+1] & 0xff;
-
-  if (kind == GOMP_MAP_TO_PSET)
-    return 3;
-  else if (kind == GOMP_MAP_POINTER)
-    return 2;
-
-  return 0;
 }
 
 void
@@ -1147,98 +1127,13 @@ GOACC_enter_exit_data (int flags_m, size_t mapnum, void **hostaddrs,
       va_end (ap);
     }
 
-  /* In c, non-pointers and arrays are represented by a single data clause.
-     Dynamically allocated arrays and subarrays are represented by a data
-     clause followed by an internal GOMP_MAP_POINTER.
-
-     In fortran, scalars and not allocated arrays are represented by a
-     single data clause. Allocated arrays and subarrays have three mappings:
-     1) the original data clause, 2) a PSET 3) a pointer to the array data.
-  */
+  goacc_aq aq = get_goacc_asyncqueue (async);
 
   if (data_enter)
-    {
-      for (i = 0; i < mapnum; i++)
-	{
-	  unsigned char kind = kinds[i] & 0xff;
-
-	  /* Scan for pointers and PSETs.  */
-	  int pointer = find_pointer (i, mapnum, kinds);
-
-	  if (!pointer)
-	    {
-	      switch (kind)
-		{
-		case GOMP_MAP_ALLOC:
-		case GOMP_MAP_FORCE_ALLOC:
-		  acc_create_async (hostaddrs[i], sizes[i], async);
-		  break;
-		case GOMP_MAP_TO:
-		case GOMP_MAP_FORCE_TO:
-		  acc_copyin_async (hostaddrs[i], sizes[i], async);
-		  break;
-		default:
-		  gomp_fatal (">>>> GOACC_enter_exit_data UNHANDLED kind 0x%.2x",
-			      kind);
-		  break;
-		}
-	    }
-	  else
-	    {
-	      goacc_insert_pointer (pointer, &hostaddrs[i], &sizes[i], &kinds[i],
-				    async);
-	      /* Increment 'i' by two because OpenACC requires fortran
-		 arrays to be contiguous, so each PSET is associated with
-		 one of MAP_FORCE_ALLOC/MAP_FORCE_PRESET/MAP_FORCE_TO, and
-		 one MAP_POINTER.  */
-	      i += pointer - 1;
-	    }
-	}
-    }
+    goacc_enter_data_internal (acc_dev, mapnum, hostaddrs, sizes, kinds, aq);
   else
-    for (i = 0; i < mapnum; ++i)
-      {
-	unsigned char kind = kinds[i] & 0xff;
-
-	int pointer = find_pointer (i, mapnum, kinds);
-
-	if (!pointer)
-	  {
-	    switch (kind)
-	      {
-	      case GOMP_MAP_RELEASE:
-	      case GOMP_MAP_DELETE:
-		if (acc_is_present (hostaddrs[i], sizes[i]))
-		  {
-		    if (finalize)
-		      acc_delete_finalize_async (hostaddrs[i], sizes[i], async);
-		    else
-		      acc_delete_async (hostaddrs[i], sizes[i], async);
-		  }
-		break;
-	      case GOMP_MAP_FROM:
-	      case GOMP_MAP_FORCE_FROM:
-		if (finalize)
-		  acc_copyout_finalize_async (hostaddrs[i], sizes[i], async);
-		else
-		  acc_copyout_async (hostaddrs[i], sizes[i], async);
-		break;
-	      default:
-		gomp_fatal (">>>> GOACC_enter_exit_data UNHANDLED kind 0x%.2x",
-			    kind);
-		break;
-	      }
-	  }
-	else
-	  {
-	    bool copyfrom = (kind == GOMP_MAP_FORCE_FROM
-			     || kind == GOMP_MAP_FROM);
-	    goacc_remove_pointer (hostaddrs[i], sizes[i], copyfrom, async,
-				  finalize, pointer);
-	    /* See the above comment.  */
-	    i += pointer - 1;
-	  }
-      }
+    goacc_exit_data_internal (acc_dev, mapnum, hostaddrs, sizes, kinds,
+			      finalize, aq);
 
  out_prof:
   if (profiling_p)
diff --git a/libgomp/target.c b/libgomp/target.c
index 97c2b5c5e4d..23f9e1618ca 100644
--- a/libgomp/target.c
+++ b/libgomp/target.c
@@ -536,8 +536,10 @@ gomp_map_vars_internal (struct gomp_device_descr *devicep,
   struct target_mem_desc *tgt
     = gomp_malloc (sizeof (*tgt) + sizeof (tgt->list[0]) * mapnum);
   tgt->list_count = mapnum;
-  tgt->refcount = pragma_kind == GOMP_MAP_VARS_ENTER_DATA ? 0 : 1;
+  tgt->refcount = (pragma_kind == GOMP_MAP_VARS_ENTER_DATA
+		   || pragma_kind == GOMP_MAP_VARS_OPENACC_ENTER_DATA) ? 0 : 1;
   tgt->device_descr = devicep;
+  tgt->prev = NULL;
   struct gomp_coalesce_buf cbuf, *cbufp = NULL;
 
   if (mapnum == 0)
@@ -939,7 +941,7 @@ gomp_map_vars_internal (struct gomp_device_descr *devicep,
 		tgt->list[i].offset = 0;
 		tgt->list[i].length = k->host_end - k->host_start;
 		k->refcount = 1;
-		k->dynamic_refcount = 0;
+		k->virtual_refcount = 0;
 		tgt->refcount++;
 		array->left = NULL;
 		array->right = NULL;
@@ -1077,8 +1079,20 @@ gomp_map_vars_internal (struct gomp_device_descr *devicep,
   /* If the variable from "omp target enter data" map-list was already mapped,
      tgt is not needed.  Otherwise tgt will be freed by gomp_unmap_vars or
      gomp_exit_data.  */
-  if (pragma_kind == GOMP_MAP_VARS_ENTER_DATA && tgt->refcount == 0)
-    {
+  if ((pragma_kind == GOMP_MAP_VARS_ENTER_DATA
+       || pragma_kind == GOMP_MAP_VARS_OPENACC_ENTER_DATA)
+      && tgt->refcount == 0)
+    {
+      /* If we're about to discard a target_mem_desc with no "structural"
+	 references (tgt->refcount == 0), any splay keys linked in the tgt's
+	 list must have their virtual refcount incremented to represent that
+	 "lost" reference in order to implement the semantics of the OpenACC
+	 "present increment" operation properly.  */
+      if (pragma_kind == GOMP_MAP_VARS_OPENACC_ENTER_DATA)
+	for (i = 0; i < tgt->list_count; i++)
+	  if (tgt->list[i].key)
+	    tgt->list[i].key->virtual_refcount++;
+
       free (tgt);
       tgt = NULL;
     }
@@ -1216,7 +1230,14 @@ gomp_unmap_vars_internal (struct target_mem_desc *tgt, bool do_copyfrom,
 	continue;
 
       bool do_unmap = false;
-      if (k->refcount > 1 && k->refcount != REFCOUNT_INFINITY)
+      if (k->tgt == tgt
+	  && k->virtual_refcount > 0
+	  && k->refcount != REFCOUNT_INFINITY)
+	{
+	  k->virtual_refcount--;
+	  k->refcount--;
+	}
+      else if (k->refcount > 1 && k->refcount != REFCOUNT_INFINITY)
 	k->refcount--;
       else if (k->refcount == 1)
 	{
@@ -1373,7 +1394,7 @@ gomp_load_image_to_device (struct gomp_device_descr *devicep, unsigned version,
       k->tgt = tgt;
       k->tgt_offset = target_table[i].start;
       k->refcount = REFCOUNT_INFINITY;
-      k->dynamic_refcount = 0;
+      k->virtual_refcount = 0;
       k->aux = NULL;
       array->left = NULL;
       array->right = NULL;
@@ -1406,7 +1427,7 @@ gomp_load_image_to_device (struct gomp_device_descr *devicep, unsigned version,
       k->tgt = tgt;
       k->tgt_offset = target_var->start;
       k->refcount = target_size & link_bit ? REFCOUNT_LINK : REFCOUNT_INFINITY;
-      k->dynamic_refcount = 0;
+      k->virtual_refcount = 0;
       k->aux = NULL;
       array->left = NULL;
       array->right = NULL;
@@ -1641,22 +1662,6 @@ gomp_unload_device (struct gomp_device_descr *devicep)
     }
 }
 
-/* Free address mapping tables.  MM must be locked on entry, and remains locked
-   on return.  */
-
-attribute_hidden void
-gomp_free_memmap (struct splay_tree_s *mem_map)
-{
-  while (mem_map->root)
-    {
-      struct target_mem_desc *tgt = mem_map->root->key.tgt;
-
-      splay_tree_remove (mem_map, &mem_map->root->key);
-      free (tgt->array);
-      free (tgt);
-    }
-}
-
 /* Host fallback for GOMP_target{,_ext} routines.  */
 
 static void
@@ -2668,7 +2673,7 @@ omp_target_associate_ptr (const void *host_ptr, const void *device_ptr,
       k->tgt = tgt;
       k->tgt_offset = (uintptr_t) device_ptr + device_offset;
       k->refcount = REFCOUNT_INFINITY;
-      k->dynamic_refcount = 0;
+      k->virtual_refcount = 0;
       k->aux = NULL;
       array->left = NULL;
       array->right = NULL;
diff --git a/libgomp/testsuite/libgomp.c-c++-common/unmap-infinity-2.c b/libgomp/testsuite/libgomp.c-c++-common/unmap-infinity-2.c
new file mode 100644
index 00000000000..3931c5aba25
--- /dev/null
+++ b/libgomp/testsuite/libgomp.c-c++-common/unmap-infinity-2.c
@@ -0,0 +1,19 @@
+int foo[16];
+#pragma omp declare target (foo)
+
+__attribute__((used)) void bar (void)
+{
+  #pragma omp target parallel for
+  for (int i = 0; i < 16; i++)
+    foo[i] = i;
+}
+
+int
+main (int argc, char *argv[])
+{
+  int *foo_copy = foo;
+  /* Try to trigger the unmapping of a REFCOUNT_INFINITY target block.  This
+     does nothing at the time of writing.  */
+  #pragma omp target exit data map(delete: foo_copy[0:16])
+  return 0;
+}
diff --git a/libgomp/testsuite/libgomp.oacc-c-c++-common/pr92843-1.c b/libgomp/testsuite/libgomp.oacc-c-c++-common/pr92843-1.c
index db5b35b08d9..f16c46a37bf 100644
--- a/libgomp/testsuite/libgomp.oacc-c-c++-common/pr92843-1.c
+++ b/libgomp/testsuite/libgomp.oacc-c-c++-common/pr92843-1.c
@@ -1,6 +1,7 @@
 /* Verify that 'acc_copyout' etc. is a no-op if there's still a structured
    reference count.  */
 
+/* { dg-xfail-run-if "TODO PR92843" { *-*-* } } */
 /* { dg-skip-if "" { *-*-* } { "*" } { "-DACC_MEM_SHARED=0" } } */
 
 #include <assert.h>
diff --git a/libgomp/testsuite/libgomp.oacc-c-c++-common/subset-subarray-mappings-1-r-p.c b/libgomp/testsuite/libgomp.oacc-c-c++-common/subset-subarray-mappings-1-r-p.c
index 9b5d83c66dd..907b8587773 100644
--- a/libgomp/testsuite/libgomp.oacc-c-c++-common/subset-subarray-mappings-1-r-p.c
+++ b/libgomp/testsuite/libgomp.oacc-c-c++-common/subset-subarray-mappings-1-r-p.c
@@ -156,20 +156,16 @@ f1 (void)
 
       assert (acc_is_present (&myblock[i], SUBSET));
       assert (acc_is_present (myblock, SIZE));
-#if 0 //TODO PR92848
       if (last)
 	cb_ev_free_expected = true;
-#endif
 #if OPENACC_RUNTIME
       acc_delete (&myblock[i], SUBSET);
 #else
 # pragma acc exit data delete (myblock[i:SUBSET])
 #endif
-#if 0 //TODO PR92848
       assert (!cb_ev_free_expected);
       if (last)
 	assert (cb_ev_free_device_ptr == cb_ev_alloc_device_ptr);
-#endif
       assert (acc_is_present (&myblock[i], SUBSET) != last);
       assert (acc_is_present (myblock, SIZE) != last);
     }
@@ -331,9 +327,7 @@ f3 ()
   assert (acc_is_present (h, SIZE));
   assert (acc_is_present (&h[2], SIZE - 2));
 
-#if 0 //TODO PR92848
   cb_ev_free_expected = true;
-#endif
 #if OPENACC_RUNTIME
   acc_delete (h, SIZE);
 #else
@@ -343,10 +337,8 @@ f3 ()
 #  pragma acc exit data delete (h)
 # endif
 #endif
-#if 0 //TODO PR92848
   assert (!cb_ev_free_expected);
   assert (cb_ev_free_device_ptr == cb_ev_alloc_device_ptr);
-#endif
 
   assert (!acc_is_present (h, SIZE));
   assert (!acc_is_present (&h[2], SIZE - 2));
@@ -401,19 +393,15 @@ f_lib_22 (void)
   memset (h, c1, SIZE);
   /* Now 'copyout' not the whole but only a "subset" subarray, missing one
      SUBSET at the beginning, and half a SUBSET at the end...  */
-#if 0 //TODO PR92848
   cb_ev_free_expected = true;
-#endif
 #if OPENACC_RUNTIME
   acc_copyout (h + SUBSET, SIZE - SUBSET - SUBSET / 2);
 #else
 # pragma acc exit data copyout (h[SUBSET:SIZE - SUBSET - SUBSET / 2])
 #endif
-#if 0 //TODO PR92848
   /* ..., yet, expect the device memory object to be 'free'd...  */
   assert (!cb_ev_free_expected);
   assert (cb_ev_free_device_ptr == cb_ev_alloc_device_ptr);
-#endif
   /* ..., and the mapping to be removed...  */
   assert (!acc_is_present (h, SIZE));
   assert (!acc_is_present (&h[SUBSET], SIZE - SUBSET - SUBSET / 2));
@@ -474,19 +462,15 @@ f_lib_30 (void)
   assert (aligned_address (cb_ev_alloc_device_ptr) == d);
 
   /* We 'delete' not the whole but only a "subset" subarray...  */
-#if 0 //TODO PR92848
   cb_ev_free_expected = true;
-#endif
 #if OPENACC_RUNTIME
   acc_delete (h, SIZE - SUBSET);
 #else
 # pragma acc exit data delete (h[0:SIZE - SUBSET])
 #endif
-#if 0 //TODO PR92848
   /* ..., yet, expect the device memory object to be 'free'd...  */
   assert (!cb_ev_free_expected);
   assert (cb_ev_free_device_ptr == cb_ev_alloc_device_ptr);
-#endif
   /* ..., and the mapping to be removed.  */
   assert (!acc_is_present (h, SIZE));
   assert (!acc_is_present (h, SIZE - SUBSET));
diff --git a/libgomp/testsuite/libgomp.oacc-c-c++-common/unmap-infinity-1.c b/libgomp/testsuite/libgomp.oacc-c-c++-common/unmap-infinity-1.c
new file mode 100644
index 00000000000..872f0c1de5c
--- /dev/null
+++ b/libgomp/testsuite/libgomp.oacc-c-c++-common/unmap-infinity-1.c
@@ -0,0 +1,17 @@
+/* { dg-skip-if "" { *-*-* } { "*" } { "-DACC_MEM_SHARED=0" } } */
+
+#include <openacc.h>
+
+int foo[16];
+#pragma acc declare device_resident(foo)
+
+int
+main (int argc, char *argv[])
+{
+  acc_init (acc_device_default);
+  acc_unmap_data ((void *) foo);
+/* { dg-output "libgomp: cannot unmap target block" } */
+  return 0;
+}
+
+/* { dg-shouldfail "" } */
-- 
2.23.0