Laurawly commented on a change in pull request #6839:
URL: https://github.com/apache/tvm/pull/6839#discussion_r537977579



##########
File path: python/tvm/topi/cuda/nms.py
##########
@@ -97,47 +97,44 @@ def get_valid_counts_ir(
     valid_count = ib.buffer_ptr(valid_count)
     out = ib.buffer_ptr(out)
     out_indices = ib.buffer_ptr(out_indices)
-    atomic_add_return = ib.allocate(
-        valid_count.dtype, (1,), name="atomic_add_return", scope="local"
-    )
-    one_count = tvm.tir.const(1, dtype=valid_count.dtype)
     one = tvm.tir.const(1, dtype=out.dtype)
-    score_threshold = tvm.ir.make_node("FloatImm", dtype="float32", 
value=score_threshold)
+    if isinstance(score_threshold, float):
+        score_threshold = tvm.ir.make_node("FloatImm", dtype="float32", 
value=score_threshold)
     id_index = tvm.ir.make_node("IntImm", dtype="int32", value=id_index)
     score_index = tvm.ir.make_node("IntImm", dtype="int32", value=score_index)
 
     max_threads = 
int(tvm.target.Target.current(allow_none=False).max_num_threads)
-    nthread_tx = max_threads
-    nthread_bx = batch_size * num_anchors // max_threads + 1
-    tx = te.thread_axis("threadIdx.x")
-    bx = te.thread_axis("blockIdx.x")
-    ib.scope_attr(tx, "thread_extent", nthread_tx)
-    ib.scope_attr(bx, "thread_extent", nthread_bx)
-    tid = bx * max_threads + tx
-    idxd = tvm.tir.indexdiv
-
-    # initialize valid_count
-    with ib.if_scope(tid < batch_size):
-        valid_count[tid] = 0
-    with ib.if_scope(tid < batch_size * num_anchors):
-        i = idxd(tid, num_anchors)
-        with ib.if_scope(
-            tvm.tir.all(
-                data[tid * elem_length + score_index] > score_threshold,
-                tvm.tir.any(id_index < 0, data[tid * elem_length + id_index] 
>= 0),
-            )
-        ):
-            atomic_add_return[0] = atomic_add(
-                tvm.tir.call_intrin("handle", "tir.address_of", 
valid_count[i]), one_count
-            )
-            with ib.for_range(0, elem_length) as k:
-                out[tid * elem_length + k] = data[tid * elem_length + k]
-                out_indices[tid + k] = tid + k
-        with ib.else_scope():
-            with ib.for_range(0, elem_length) as k:
-                out[tid * elem_length + k] = -one
-                out_indices[tid + k] = -one_count
-
+    with ib.new_scope():
+        nthread_tx = max_threads
+        nthread_bx = batch_size // max_threads + 1
+        tx = te.thread_axis("threadIdx.x")
+        bx = te.thread_axis("blockIdx.x")
+        ib.scope_attr(tx, "thread_extent", nthread_tx)
+        ib.scope_attr(bx, "thread_extent", nthread_bx)
+        tid = bx * max_threads + tx
+        with ib.if_scope(tid < batch_size):
+            valid_count[tid] = 0
+            i = tid
+            with ib.for_range(0, num_anchors) as j:
+                score = data[(i * num_anchors + j) * elem_length + score_index]
+                with ib.if_scope(
+                    tvm.tir.all(
+                        score > score_threshold,
+                        tvm.tir.any(
+                            id_index < 0, data[(i * num_anchors + j) * 
elem_length + id_index] >= 0
+                        ),
+                    )
+                ):
+                    with ib.for_range(0, elem_length) as k:
+                        out[(i * num_anchors + valid_count[i]) * elem_length + 
k] = data[
+                            (i * num_anchors + j) * elem_length + k
+                        ]
+                    out_indices[i * num_anchors + valid_count[i]] = j
+                    valid_count[i] += 1

Review comment:
       I see. So we lose parallelism in `num_anchors` (could be quite large) 
compared with the original implementation. Could you elaborate on why we are 
not getting correct output indices in current implementation?




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