[OG12,committed] libgomp: Fix USM bugs

diff --git a/libgomp/libgomp.h b/libgomp/libgomp.h
index e5345ebee53..7d55f3cf825 100644
--- a/libgomp/libgomp.h
+++ b/libgomp/libgomp.h
@@ -1196,6 +1196,7 @@  struct target_mem_desc;
 #define OFFSET_INLINED (~(uintptr_t) 0)
 #define OFFSET_POINTER (~(uintptr_t) 1)
 #define OFFSET_STRUCT (~(uintptr_t) 2)
+#define OFFSET_USM (~(uintptr_t) 3)
 
 /* Auxiliary structure for infrequently-used or API-specific data.  */
 
diff --git a/libgomp/target.c b/libgomp/target.c
index 50709f0677d..19db5a56f4a 100644
--- a/libgomp/target.c
+++ b/libgomp/target.c
@@ -692,6 +692,9 @@  gomp_map_pointer (struct target_mem_desc *tgt, struct goacc_asyncqueue *aq,
     {
       if (allow_zero_length_array_sections)
 	cur_node.tgt_offset = 0;
+      else if (devicep->is_usm_ptr_func
+	       && devicep->is_usm_ptr_func ((void*)cur_node.host_start))
+	cur_node.tgt_offset = cur_node.host_start;
       else
 	{
 	  gomp_mutex_unlock (&devicep->lock);
@@ -928,6 +931,7 @@  gomp_map_val (struct target_mem_desc *tgt, void **hostaddrs, size_t i)
   switch (tgt->list[i].offset)
     {
     case OFFSET_INLINED:
+    case OFFSET_USM:
       return (uintptr_t) hostaddrs[i];
 
     case OFFSET_POINTER:
@@ -1013,6 +1017,7 @@  gomp_map_vars_internal (struct gomp_device_descr *devicep,
     {
       int kind = get_kind (short_mapkind, kinds, i);
       bool implicit = get_implicit (short_mapkind, kinds, i);
+      tgt->list[i].offset = 0;
       if (hostaddrs[i] == NULL
 	  || (kind & typemask) == GOMP_MAP_FIRSTPRIVATE_INT)
 	{
@@ -1020,6 +1025,15 @@  gomp_map_vars_internal (struct gomp_device_descr *devicep,
 	  tgt->list[i].offset = OFFSET_INLINED;
 	  continue;
 	}
+      else if (devicep->is_usm_ptr_func
+	       && devicep->is_usm_ptr_func (hostaddrs[i]))
+	{
+	  /* The memory is visible from both host and target
+	     so nothing needs to be moved.  */
+	  tgt->list[i].key = NULL;
+	  tgt->list[i].offset = OFFSET_USM;
+	  continue;
+	}
       else if ((kind & typemask) == GOMP_MAP_USE_DEVICE_PTR
 	       || (kind & typemask) == GOMP_MAP_USE_DEVICE_PTR_IF_PRESENT)
 	{
@@ -1063,15 +1077,6 @@  gomp_map_vars_internal (struct gomp_device_descr *devicep,
 	    tgt->list[i].offset = 0;
 	  continue;
 	}
-      else if (devicep->is_usm_ptr_func
-	       && devicep->is_usm_ptr_func (hostaddrs[i]))
-	{
-	  /* The memory is visible from both host and target
-	     so nothing needs to be moved.  */
-	  tgt->list[i].key = NULL;
-	  tgt->list[i].offset = OFFSET_INLINED;
-	  continue;
-	}
       else if ((kind & typemask) == GOMP_MAP_STRUCT)
 	{
 	  size_t first = i + 1;
@@ -1441,6 +1446,8 @@  gomp_map_vars_internal (struct gomp_device_descr *devicep,
 	    bool implicit = get_implicit (short_mapkind, kinds, i);
 	    if (hostaddrs[i] == NULL)
 	      continue;
+	    if (tgt->list[i].offset == OFFSET_USM)
+	      continue;
 	    switch (kind & typemask)
 	      {
 		size_t align, len, first, last;
diff --git a/libgomp/testsuite/libgomp.fortran/usm-1.f90 b/libgomp/testsuite/libgomp.fortran/usm-1.f90
new file mode 100644
index 00000000000..7147e9925a2
--- /dev/null
+++ b/libgomp/testsuite/libgomp.fortran/usm-1.f90
@@ -0,0 +1,28 @@ 
+! { dg-do run }
+! { dg-require-effective-target omp_usm }
+
+! Ensure that USM works for implicit mappings.
+! This needs to cover both the initial mapping scan and the rescan that
+! happens when some of the mappings aren't no-ops (in this cases there are
+! some hidden pointers).
+
+program usm
+  use iso_fortran_env
+  use omp_lib
+  implicit none
+
+  !$omp requires unified_shared_memory
+
+  integer, parameter :: N = 1024
+  real(real64), allocatable :: x(:), y(:)
+  integer :: i
+
+  allocate(x(N), y(N))
+  !$omp target teams distribute parallel do simd
+  do i=1,N
+    y(i) = x(i)
+  enddo
+
+  deallocate(x,y)
+
+end program usm
diff --git a/libgomp/testsuite/libgomp.fortran/usm-2.f90 b/libgomp/testsuite/libgomp.fortran/usm-2.f90
new file mode 100644
index 00000000000..94e8284c475
--- /dev/null
+++ b/libgomp/testsuite/libgomp.fortran/usm-2.f90
@@ -0,0 +1,33 @@ 
+! { dg-do run }
+! { dg-require-effective-target omp_usm }
+
+! Ensure that USM doesn't break the use_device_ptr clause (host pointers and
+! target pointers being "unified").
+
+program usm
+  use iso_fortran_env
+  use omp_lib
+  implicit none
+
+  !$omp requires unified_shared_memory
+
+  integer, parameter :: N = 1024
+  real(real64), allocatable :: x(:), y(:)
+  integer :: i
+
+  allocate(x(N),y(N))
+
+  !$omp target data map(x)
+  ! The "i" variable is not explictly mapped yet, so ensures that both
+  ! mapping scan passes are tested.
+  !$omp target data map(i) use_device_ptr(x)
+  !$omp target teams distribute parallel do simd
+  do i=1,N
+    y(i) = x(i)
+  enddo
+  !$omp end target data 
+  !$omp end target data 
+
+  deallocate(x,y)
+
+end program usm