[Torch] chunk and unsafe chunk (apache#8718)

* alternative chunk op was implemented in pytorch frontend. aten::unsafe_chunk was added to op map in pytorch frontend

* chunk was replaced by new one in pytorch frontend. it is faster in 2.5 times

Co-authored-by: Valery Chernov <[email protected]>

python/tvm/relay/frontend/pytorch.py

@@ -1594,28 +1594,11 @@ def chunk(self, inputs, input_types):
         else:
             unif_size = int(dim / num_chunks)
 
-        chunks = []
-        for i in range(0, dim, unif_size):
-            begin = [0] * len(shape)
-            end = shape[:]
-            begin[axis] = i
-            end[axis] = i + unif_size
-            stride = [1] * len(shape)
+        indeces = []
+        for i in range(unif_size, dim, unif_size):
+            indeces.append(i)
 
-            chunk_out = _op.transform.strided_slice(data, begin=begin, end=end, strides=stride)
-            chunks.append(chunk_out)
-
-        if dim % num_chunks:
-            begin = [0] * len(shape)
-            end = shape[:]
-            begin[axis] = unif_size * (num_chunks - 1)
-            end[axis] = dim
-            stride = [1] * len(shape)
-
-            chunk_out = _op.transform.strided_slice(data, begin=begin, end=end, strides=stride)
-            chunks.append(chunk_out)
-
-        return chunks
+        return _op.split(data, indeces, axis)
 
     def matmul(self, inputs, input_types):
 
@@ -2681,6 +2664,7 @@ def create_convert_map(self):
             "aten::alpha_dropout": self.dropout,
             "aten::mean": self.mean,
             "aten::chunk": self.chunk,
+            "aten::unsafe_chunk": self.chunk,
             "aten::matmul": self.matmul,
             "aten::bmm": self.matmul,
             "aten::expand": self.expand,