Add host API for alltoallmem_on_stream collective operation (#333)

* Add host-side rocshmem_alltoallmem_on_stream function

Function signature:
  rocshmem_alltoallmem_on_stream(rocshmem_team_t team, void *dest,
                                 const void *source, size_t size,
                                 hipStream_t stream)

- The function launches rocshmem_alltoallmem_kernel which calls
device-side alltoall<char> workgroup collective through default context.
- Uses dynamic block size determination via occupancy API.
- Implemented for all backends.

* Fix incorrect sync buffer size allocation for alltoall in GDA and IPC backends

When allocating memory for alltoall_pSync_pool in setup_teams() and
teams_init() functions, the code incorrectly used ROCSHMEM_BCAST_SYNC_SIZE
instead of ROCSHMEM_ALLTOALL_SYNC_SIZE.

* Add functional test for team_alltoallmem_on_stream

This commit adds a new functional test to verify the correctness of
the host-side rocshmem_team_alltoallmem_on_stream API.

* Add documentation for rocshmem_alltoallmem_on_stream

This commit adds API documentation for the host-side
rocshmem_alltoallmem_on_stream function in the collective routines
section. The documentation includes:

include/rocshmem/rocshmem.hpp

@@ -349,6 +349,22 @@ __host__ void rocshmem_barrier_all();
  */
 __host__ void rocshmem_barrier_all_on_stream(hipStream_t stream);
 
+/**
+ * @brief enqueues an alltoall collective operation on given stream.
+ *
+ * @param[in] team    The team participating in the collective.
+ * @param[in] dest    Destination address. Must be an address on the symmetric
+ *                    heap.
+ * @param[in] source  Source address. Must be an address on the symmetric heap.
+ * @param[in] size    Number of bytes to transfer per pair of PEs.
+ * @param[in] stream  HIP stream on which to enqueue the operation.
+ *
+ * @return void
+ */
+__host__ void rocshmem_alltoallmem_on_stream(rocshmem_team_t team, void *dest,
+                                             const void *source, size_t size,
+                                             hipStream_t stream);
+
 /**
  * @brief registers the arrival of a PE at a barrier.
  * The caller is blocked until the synchronization is resolved.

include/rocshmem/rocshmem_COLL.hpp

@@ -607,6 +607,23 @@ __host__ int rocshmem_ctx_double_prod_reduce(
  */
 __global__ ATTR_NO_INLINE void rocshmem_barrier_all_kernel();
 
+/**
+ * @brief kernel for performing an alltoall collective operation.
+ * Caller enqueues the kernel on given stream
+ *
+ * @param[in] team    The team participating in the collective.
+ * @param[in] dest    Destination address. Must be an address on the symmetric
+ *                    heap.
+ * @param[in] source  Source address. Must be an address on the symmetric heap.
+ * @param[in] size    Number of bytes to transfer per pair of PEs.
+ *
+ * @return void
+ */
+__global__ ATTR_NO_INLINE void rocshmem_alltoallmem_kernel(rocshmem_team_t team,
+                                                           void *dest,
+                                                           const void *source,
+                                                           size_t size);
+
 /**
  * @brief perform a collective barrier between all PEs in the system.
  * The caller is blocked until the barrier is resolved.