!2268 add bprop for ScatterMax

Merge pull request !2268 from yanzhenxiang2020/open_ScatterMax_bprop

mindspore/ops/_grad/grad_array_ops.py

@@ -496,6 +496,17 @@ def get_bprop_tensor_scatter_update(self):
     return bprop
 
 
+@bprop_getters.register(P.ScatterMax)
+def get_bprop_scatter_max(self):
+    """Generate bprop for ScatterMax"""
+    gather = P.GatherV2()
+
+    def bprop(x, indices, update, out, dout):
+        return dout, zeros_like(indices), gather(dout, indices, 0)
+
+    return bprop
+
+
 @bprop_getters.register(P.Argmax)
 def get_bprop_argmax(self):
     """Generate bprop for Argmax"""