bug fix shard_index (#37042) (#37421)

Author: lilong12

paddle/fluid/operators/shard_index_op.cc

@@ -31,7 +31,7 @@ class ShardIndexOp : public framework::OperatorWithKernel {
                           "but the value given is %d.",
                           x_dims.size()));
     if (ctx->IsRuntime() || x_dims[x_dims.size() - 1] > 0) {
-      PADDLE_ENFORCE_GE(x_dims[x_dims.size() - 1], 1U,
+      PADDLE_ENFORCE_EQ(x_dims[x_dims.size() - 1], 1U,
                         platform::errors::InvalidArgument(
                             "The last dimension of Input(X) should be 1, "
                             "but the value given is %d.",

python/paddle/fluid/layers/nn.py

@@ -14914,28 +14914,37 @@ def deformable_roi_pooling(input,
 @deprecated(since="2.0.0", update_to="paddle.shard_index")
 def shard_index(input, index_num, nshards, shard_id, ignore_value=-1):
     """
-    Recompute the `input` indices according to the offset of the
-    shard. The length of the indices is evenly divided into N shards, and if
-    the `shard_id` matches the shard with the input index inside, the index is
-    recomputed on the basis of the shard offset, elsewise it is set to
-    `ignore_value`. The detail is as follows:
+    Reset the values of `input` according to the shard it beloning to.
+    Every value in `input` must be a non-negative integer, and
+    the parameter `index_num` represents the integer above the maximum
+    value of `input`. Thus, all values in `input` must be in the range
+    [0, index_num) and each value can be regarded as the offset to the beginning
+    of the range. The range is further split into multiple shards. Specifically,
+    we first compute the `shard_size` according to the following formula,
+    which represents the number of integers each shard can hold. So for the
+    i'th shard, it can hold values in the range [i*shard_size, (i+1)*shard_size).
     ::
 
         shard_size = (index_num + nshards - 1) // nshards
-        y = x % shard_size if x // shard_size == shard_id else ignore_value
 
-    NOTE: If the length of indices cannot be evely divided by the shard number,
-    the size of the last shard will be less than the calculated `shard_size`
+    For each value `v` in `input`, we reset it to a new value according to the
+    following formula:
+    ::
+   
+        v = v - shard_id * shard_size if shard_id * shard_size <= v < (shard_id+1) * shard_size else ignore_value
+
+    That is, the value `v` is set to the new offset within the range represented by the shard `shard_id`
+    if it in the range. Otherwise, we reset it to be `ignore_value`.
 
     Args:
-        input (Tensor): Input indices with data type int64 or int32. It's last dimension must be 1.
-        index_num (int): An integer defining the range of the index.
+        input (Tensor): Input tensor with data type int64 or int32. It's last dimension must be 1.
+        index_num (int): An integer represents the integer above the maximum value of `input`.
         nshards (int): The number of shards.
         shard_id (int): The index of the current shard.
         ignore_value (int): An integer value out of sharded index range.
 
     Returns:
-        Tensor: The sharded index of input.
+        Tensor.
 
     Examples:
         .. code-block:: python