x1 = [8,32,256,256]
x1 = x1.permute((0, 2, 3, 1)).flatten(1, 2)

x1.permute((0, 2, 3, 1))：[8,32,256,256]—>[8,256,256,32] 维度调转
flatten(1, 2)：[8,256,256,32] —>[8,65536,32] 2、3维度平摊为1维，由4维数据降为3维数据