[Custom operator] Fix custom operator backward=None bug

[jiahy0825]

PR types

Bug fixes

PR changes

OPs

Describe

Bug describes: when custom backward op outputs gradient with a discrete order, the output of some gradient=None.

For example: backward op's input = {a, b, c, d, e}, output = {a@GRAD, d@GRAD, e@GRAD}, the output of d@GRAD and e@GRAD will be None.

Reason: The order of RunCustomOpNode::operator(): line220 in custom_operator_node.cc is {a@GRAD, null, null, d@GRAD, e@GRAD}. However, the order of eager_api_run_custom_op: line560 in eager_functions.cc is {a@GRAD, d@GRAD, e@GRAD, null, null}.

Change: Change the order in RunCustomOpNode::operator() to {a@GRAD, d@GRAD, e@GRAD, null, null}

本 PR 修复了自定义算子反向 op 的输出值可能为 None 的 bug，当用户的输出梯度不是连续输出时（例如输出第0、3、4个前向输入的梯度时），第3、4个梯度会被置为 None，这是由于对反向 op 的输出梯度进行处理时，RunCustomOpNode::operator(): line220 和 eager_api_run_custom_op: line560的动作不一致。更改为按照RunCustomOpNode::operator()对齐，在反向 op 的输出梯度后面，填充不需要梯度的输出，修改后的返回值为 {第 0 个梯度，第 3 个梯度，第 4 个梯度，null, null}

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[JiabinYang]

LGTM