"fix error"

paddle/operators/mul_op.cc

@@ -68,8 +68,8 @@ class MulOpGrad : public framework::OperatorWithKernel {
                             "Input(Out@GRAD) should not be null");
     auto *x_grad = ctx.Output<Tensor>(framework::GradVarName("X"));
     auto *y_grad = ctx.Output<Tensor>(framework::GradVarName("Y"));
-    auto dim0 = ctx.Input<Tensor>(framework::GradVarName("X"))->dims();
-    auto dim1 = ctx.Input<Tensor>(framework::GradVarName("Y"))->dims();
+    auto dim0 = ctx.Output<Tensor>(framework::GradVarName("X"))->dims();
+    auto dim1 = ctx.Output<Tensor>(framework::GradVarName("Y"))->dims();
     auto out_dims = ctx.Input<Tensor>(framework::GradVarName("Out"))->dims();
     PADDLE_ENFORCE(dim0[0] * dim1[0] == out_dims[0],
                    "Out@GRAD[0] must equal to X[0] * Y[0]");