Added check to partition kernel if size is smaller than items_per_blo…

…ck (#538) (#546)

Co-authored-by: Nick Breed <78807921+NB4444@users.noreply.github.com>
Co-authored-by: Nick Breed <nick@streamhpc.com>

rocprim/include/rocprim/device/detail/device_merge.hpp

@@ -1,4 +1,4 @@
-// Copyright (c) 2017-2022 Advanced Micro Devices, Inc. All rights reserved.
+// Copyright (c) 2017-2024 Advanced Micro Devices, Inc. All rights reserved.
 //
 // Permission is hereby granted, free of charge, to any person obtaining a copy
 // of this software and associated documentation files (the "Software"), to deal
@@ -68,24 +68,23 @@ void partition_kernel_impl(IndexIterator indices,
                            const unsigned int spacing,
                            BinaryFunction compare_function)
 {
-    const unsigned int flat_id = ::rocprim::detail::block_thread_id<0>();
-    const unsigned int flat_block_id = ::rocprim::detail::block_id<0>();
+    const unsigned int flat_id         = ::rocprim::detail::block_thread_id<0>();
+    const unsigned int flat_block_id   = ::rocprim::detail::block_id<0>();
     const unsigned int flat_block_size = ::rocprim::detail::block_size<0>();
+    const unsigned int input_size      = input1_size + input2_size;
+    const unsigned int id              = flat_block_id * flat_block_size + flat_id;
+    const unsigned int partition_id    = id * spacing;
+    const unsigned int partitions      = (input_size + spacing - 1) / spacing;
 
-    unsigned int id = flat_block_id * flat_block_size + flat_id;
+    if(id > partitions)
+    {
+        return;
+    }
 
-    unsigned int partition_id = id * spacing;
     size_t diag = min(static_cast<size_t>(partition_id), input1_size + input2_size);
 
-    unsigned int begin =
-        merge_path(
-            keys_input1,
-            keys_input2,
-            input1_size,
-            input2_size,
-            diag,
-            compare_function
-        );
+    unsigned int begin
+        = merge_path(keys_input1, keys_input2, input1_size, input2_size, diag, compare_function);
 
     indices[id] = begin;
 }
@@ -310,8 +309,10 @@ void merge_kernel_impl(IndexIterator indices,
     const unsigned int valid_in_last_block = count - block_offset;
     const bool         is_incomplete_block = valid_in_last_block < items_per_block;
 
-    const unsigned int p1 = indices[flat_block_id];
-    const unsigned int p2 = indices[flat_block_id + 1];
+    const unsigned int partitions = (count + items_per_block - 1) / items_per_block;
+
+    const unsigned int p1 = indices[rocprim::min(flat_block_id, partitions)];
+    const unsigned int p2 = indices[rocprim::min(flat_block_id + 1, partitions)];
 
     range_t range =
         compute_range(