[OpenACC] Prototype OpenMP 5.1's omp_target_is_accessible

The OpenMP 5.1 `omp_target_is_accessible` function will be used in a
future patch to support OpenACC's `acc_is_present` function, which
currently uses Clacc's OpenMP extension `omp_target_range_is_present`
instead, but it's better to depend on standard OpenMP functions where
possible.

For now, all testing of `omp_target_is_accessible` will be via testing
for `acc_is_present`.  That is, `omp_target_is_accessible` is not well
tested outside of Clacc's OpenACC runtime, so it is not yet
recommended for general use in OpenMP code.

Author: jdenny-ornl

openmp/libomptarget/include/omptarget.h

@@ -141,7 +141,9 @@ int omp_get_num_devices(void);
 int omp_get_initial_device(void);
 void *omp_target_alloc(size_t size, int device_num);
 void omp_target_free(void *device_ptr, int device_num);
+// FIXME: OpenMP 5.0 and 5.1 say const void *ptr.
 int omp_target_is_present(void *ptr, int device_num);
+int omp_target_is_accessible(const void *ptr, size_t size, int device_num);
 typedef enum omp_present_t {
   omp_present_none = 0,
   omp_present_partial = 1,

openmp/libomptarget/src/api.cpp

@@ -216,6 +216,67 @@ EXTERN int omp_target_is_present(void *ptr, int device_num) {
   return rc;
 }
 
+EXTERN int omp_target_is_accessible(const void *ptr, size_t size,
+                                    int device_num) {
+  // OpenMP 5.1, sec. 3.8.4 "omp_target_is_accessible", p. 417, L21-22:
+  // "This routine returns true if the storage of size bytes starting at the
+  // address given by ptr is accessible from device device_num. Otherwise, it
+  // returns false."
+  //
+  // The meaning of "accessible" for unified shared memory is established in
+  // OpenMP 5.1, sec. 2.5.1 "requires directive".  More generally, the specified
+  // host memory is accessible if it can be accessed from the device either
+  // directly (because of unified shared memory or because device_num is the
+  // value returned by omp_get_initial_device()) or indirectly (because it's
+  // mapped to the device).
+  DP("Call to omp_target_is_accessible for device %d and address " DPxMOD "\n",
+     device_num, DPxPTR(ptr));
+
+  // FIXME: Is this right?
+  //
+  // Null pointer is permitted:
+  //
+  // OpenMP 5.1, sec. 3.8.4 "omp_target_is_accessible", p. 417, L15:
+  // "The value of ptr must be a valid host pointer or NULL (or C_NULL_PTR, for
+  // Fortran)."
+  //
+  // However, I found no specification of behavior in this case.
+  // omp_target_is_present has the same problem and is implemented the same way.
+  // Should size have any effect on the result when ptr is NULL?
+  if (!ptr) {
+    DP("Call to omp_target_is_accessible with NULL ptr, returning false\n");
+    return false;
+  }
+
+  if (device_num == omp_get_initial_device()) {
+    DP("Call to omp_target_is_accessible on host, returning true\n");
+    return true;
+  }
+
+  RTLsMtx->lock();
+  size_t Devices_size = Devices.size();
+  RTLsMtx->unlock();
+  if (Devices_size <= (size_t)device_num) {
+    DP("Call to omp_target_is_accessible with invalid device ID, returning "
+       "false\n");
+    return false;
+  }
+
+  DeviceTy &Device = Devices[device_num];
+  bool IsLast;    // not used
+  bool IsHostPtr; // not used
+  // TODO: How does the spec intend for the size=0 case to be handled?
+  // Currently, we return true if we would return true for size=1 (ptr is within
+  // a range that's accessible).  Does the spec clarify this somewhere?
+  void *TgtPtr = Device.getTgtPtrBegin(const_cast<void *>(ptr), size, IsLast,
+                                       /*UpdateRefCount=*/false,
+                                       /*UseHoldRefCount=*/false, IsHostPtr,
+                                       /*MustContain=*/true);
+  int rc = (TgtPtr != NULL);
+  DP("Call to omp_target_is_accessible returns %d\n", rc);
+  return rc;
+}
+
 EXTERN omp_present_t omp_target_range_is_present(void *ptr, size_t size,
                                                  int device_num) {
   DP("Call to omp_target_range_is_present for device %d and address " DPxMOD

openmp/libomptarget/src/exports

@@ -30,6 +30,7 @@ VERS1.0 {
     omp_target_alloc;
     omp_target_free;
     omp_target_is_present;
+    omp_target_is_accessible;
     omp_target_range_is_present;
     omp_target_memcpy;
     omp_target_memcpy_rect;

openmp/runtime/src/include/omp.h.var

@@ -142,6 +142,7 @@
     extern void* __KAI_KMPC_CONVENTION  omp_target_alloc(size_t, int);
     extern void  __KAI_KMPC_CONVENTION  omp_target_free(void *, int);
     extern int   __KAI_KMPC_CONVENTION  omp_target_is_present(void *, int);
+    extern int   __KAI_KMPC_CONVENTION  omp_target_is_accessible(const void *, size_t, int);
     extern int   __KAI_KMPC_CONVENTION  omp_target_memcpy(void *, void *, size_t, size_t, size_t, int, int);
     extern int   __KAI_KMPC_CONVENTION  omp_target_memcpy_rect(void *, void *, size_t, int, const size_t *,
                                             const size_t *, const size_t *, const size_t *, const size_t *, int, int);

openmp/runtime/src/kmp_ftn_entry.h

@@ -986,6 +986,11 @@ void FTN_STDCALL FTN_TARGET_FREE(void *device_ptr, int device_num) {}
 
 int FTN_STDCALL FTN_TARGET_IS_PRESENT(void *ptr, int device_num) { return 0; }
 
+int FTN_STDCALL FTN_TARGET_IS_ACCESSIBLE(const void *ptr, size_t size,
+                                         int device_num) {
+  return 0;
+}
+
 typedef enum omp_present_t {
   omp_present_none = 0,
   omp_present_partial = 1,

openmp/runtime/src/kmp_ftn_os.h

@@ -114,6 +114,7 @@
 #define FTN_TARGET_ALLOC omp_target_alloc
 #define FTN_TARGET_FREE omp_target_free
 #define FTN_TARGET_IS_PRESENT omp_target_is_present
+#define FTN_TARGET_IS_ACCESSIBLE omp_target_is_accessible
 #define FTN_TARGET_RANGE_IS_PRESENT omp_target_range__is_present
 #define FTN_TARGET_MEMCPY omp_target_memcpy
 #define FTN_TARGET_MEMCPY_RECT omp_target_memcpy_rect
@@ -238,6 +239,7 @@
 #define FTN_TARGET_ALLOC omp_target_alloc_
 #define FTN_TARGET_FREE omp_target_free_
 #define FTN_TARGET_IS_PRESENT omp_target_is_present_
+#define FTN_TARGET_IS_ACCESSIBLE omp_target_is_accessible_
 #define FTN_TARGET_RANGE_IS_PRESENT omp_target_range_is_present_
 #define FTN_TARGET_MEMCPY omp_target_memcpy_
 #define FTN_TARGET_MEMCPY_RECT omp_target_memcpy_rect_
@@ -364,6 +366,7 @@
 #define FTN_TARGET_ALLOC OMP_TARGET_ALLOC
 #define FTN_TARGET_FREE OMP_TARGET_FREE
 #define FTN_TARGET_IS_PRESENT OMP_TARGET_IS_PRESENT
+#define FTN_TARGET_IS_ACCESSIBLE OMP_TARGET_IS_ACCESSIBLE
 #define FTN_TARGET_RANGE_IS_PRESENT OMP_TARGET_RANGE_IS_PRESENT
 #define FTN_TARGET_MEMCPY OMP_TARGET_MEMCPY
 #define FTN_TARGET_MEMCPY_RECT OMP_TARGET_MEMCPY_RECT
@@ -488,6 +491,7 @@
 #define FTN_TARGET_ALLOC OMP_TARGET_ALLOC_
 #define FTN_TARGET_FREE OMP_TARGET_FREE_
 #define FTN_TARGET_IS_PRESENT OMP_TARGET_IS_PRESENT_
+#define FTN_TARGET_IS_ACCESSIBLE OMP_TARGET_IS_ACCESSIBLE
 #define FTN_TARGET_RANGE_IS_PRESENT OMP_TARGET_RANGE_IS_PRESENT_
 #define FTN_TARGET_MEMCPY OMP_TARGET_MEMCPY_
 #define FTN_TARGET_MEMCPY_RECT OMP_TARGET_MEMCPY_RECT_