使用不规则张量和 while 循环时，XLA 无法推导出跨步切片的编译时间常数输出形状

Question

是否可以使用以下最小示例experimental_compile=True？我已经看到这个论点有一些很大的加速，因此我很想弄清楚如何让它工作。谢谢！

import tensorflow as tf

print(tf.__version__)
# ===> 2.2.0-dev20200409

x = tf.reshape(tf.range(25, dtype=tf.float32), [5, 5])
row_lengths = tf.constant([2, 1, 2])
ragged_tensor = tf.RaggedTensor.from_row_lengths(x, row_lengths)

for i, tensor in enumerate(ragged_tensor):
    print(f"i: {i}\ntensor:\n{tensor}\n")
# ==>
# i: 0
# tensor:
# [[0. 1. 2. 3. 4.]
#  [5. 6. 7. 8. 9.]]

# i: 1
# tensor:
# [[10. 11. 12. 13. 14.]]

# i: 2
# tensor:
# [[15. 16. 17. 18. 19.]
#  [20. 21. 22. 23. 24.]]


@tf.function(autograph=False, experimental_compile=True)
def while_loop_fail():

    num_rows = ragged_tensor.nrows()

    def cond(i, _):
        return i < num_rows

    def body(i, running_total):
        return i + 1, running_total + tf.reduce_sum(ragged_tensor[i])

    _, total = tf.while_loop(cond, body, [0, 0.0])

    return total


while_loop_fail()
# ===>
# tensorflow.python.framework.errors_impl.InvalidArgumentError: XLA can't deduce compile time constant output shape for strided slice: [?,5], output shape must be a compile-time constant
#    [[{{node while/RaggedGetItem/strided_slice_4}}]]
#    [[while]]
#   This error might be occurring with the use of xla.compile. If it is not necessary that every Op be compiled with XLA, an alternative is to use auto_jit with OptimizerOptions.global_jit_level = ON_2 or the environment variable TF_XLA_FLAGS="tf_xla_auto_jit=2" which will attempt to use xla to compile as much of the graph as the compiler is able to. [Op:__inference_while_loop_fail_481]

Answer 1

对于遇到此类问题的任何人，我刚刚注意到在 TensorFlow 2.5 上这有效（替换为experimental_compile）jit_compile：

import tensorflow as tf

print(tf.__version__)
# 2.5.0

x = tf.reshape(tf.range(25, dtype=tf.float32), [5, 5])
row_lengths = tf.constant([2, 1, 2])
ragged_tensor = tf.RaggedTensor.from_row_lengths(x, row_lengths)

for i, tensor in enumerate(ragged_tensor):
    print(f"i: {i}\ntensor:\n{tensor}\n")
# ==>
# i: 0
# tensor:
# [[0. 1. 2. 3. 4.]
#  [5. 6. 7. 8. 9.]]

# i: 1
# tensor:
# [[10. 11. 12. 13. 14.]]

# i: 2
# tensor:
# [[15. 16. 17. 18. 19.]
#  [20. 21. 22. 23. 24.]]


@tf.function(autograph=False, jit_compile=True)
def while_loop_works():

    num_rows = ragged_tensor.nrows()

    def cond(i, _):
        return i < num_rows

    def body(i, running_total):
        return i + 1, running_total + tf.reduce_sum(ragged_tensor[i])

    _, total = tf.while_loop(cond, body, [0, 0.0])

    return total


while_loop_works()
# 2021-06-28 13:18:19.253261: I tensorflow/compiler/jit/xla_compilation_cache.cc:337] Compiled cluster using XLA!  This line is logged at most once for the lifetime of the process.
# <tf.Tensor: shape=(), dtype=float32, numpy=300.0>