Internal change

PiperOrigin-RevId: 404920138

official/nlp/modeling/networks/funnel_transformer.py

@@ -14,6 +14,7 @@
 
 """Funnel Transformer network."""
 # pylint: disable=g-classes-have-attributes
+
 from typing import Union, Sequence
 from absl import logging
 import numpy as np
@@ -21,6 +22,10 @@ import tensorflow as tf
 
 from official.nlp.modeling import layers
 
+_MAX = 'max'
+_AVG = 'avg'
+_TRUNCATED_AVG = 'truncated_avg'
+
 
 def _pool_and_concat(mask, unpool_length: int, strides: Union[Sequence[int],
                                                               int],
@@ -63,6 +68,94 @@ def _pool_and_concat(mask, unpool_length: int, strides: Union[Sequence[int],
   return mask
 
 
+def _create_truncated_avg_transforms(seq_length: int,
+                                     pool_strides: Sequence[int]):
+  """Computes pooling transforms.
+
+  The pooling_transform is of shape [seq_length,
+  seq_length//pool_stride] and
+  pooling_transform[i,j] = 1.0/pool_stride if i//pool_stride == j
+                           0.0                otherwise.
+  It's in essense average pooling but truncate the final window if it
+  seq_length % pool_stride != 0.
+  For seq_length==6 and pool_stride==2, it is
+  [[ 0.5, 0.0, 0.0 ],
+   [ 0.5, 0.0, 0.0 ],
+   [ 0.0, 0.5, 0.0 ],
+   [ 0.0, 0.5, 0.0 ],
+   [ 0.0, 0.0, 0.5 ],
+   [ 0.0, 0.0, 0.5 ]]
+
+  Args:
+    seq_length: int, sequence length.
+    pool_strides: Sequence of pooling strides for each layer.
+
+  Returns:
+    pooling_transforms: Sequence of pooling transforms (Tensors) for each layer.
+  """
+
+  pooling_transforms = []
+  for pool_stride in pool_strides:
+    if pool_stride == 1:
+      pooling_transforms.append(None)
+    else:
+      pooled_seq_length = seq_length // pool_stride
+
+      pfac, sl, psl = pool_stride, seq_length, pooled_seq_length
+      transform = [[1.0 if (i // pfac) == j else 0.0
+                    for j in range(psl)]
+                   for i in range(sl)]
+      transform = tf.constant(
+          transform,
+          dtype=tf.keras.mixed_precision.global_policy().compute_dtype)
+
+      pooling_transforms.append(transform / pool_stride)
+      seq_length = pooled_seq_length
+
+  return pooling_transforms
+
+
+def _create_truncated_avg_masks(input_mask: tf.Tensor,
+                                pool_strides: Sequence[int],
+                                transforms: Sequence[tf.Tensor]):
+  """Computes attention masks.
+
+  For [1,1,1,0,0]
+
+  Args:
+    input_mask: Tensor of shape [batch_size, seq_length].
+    pool_strides: Sequence of pooling strides for each layer.
+    transforms: Sequnce of off-diagonal matrices filling with 0.0 and
+      1/pool_stride.
+
+  Returns:
+    attention_masks: Sequence of attention masks for each layer.
+  """
+
+  def create_2d_mask(from_length, mask):
+    return tf.einsum('F,BT->BFT', tf.ones([from_length], dtype=mask.dtype),
+                     mask)
+
+  attention_masks = []
+  seq_length = tf.shape(input_mask)[-1]
+  layer_mask = tf.cast(
+      input_mask, dtype=tf.keras.mixed_precision.global_policy().compute_dtype)
+  for pool_stride, transform in zip(pool_strides, transforms):
+    if pool_stride == 1:
+      attention_masks.append(create_2d_mask(seq_length, layer_mask))
+    else:
+      pooled_seq_length = seq_length // pool_stride
+      attention_masks.append(create_2d_mask(pooled_seq_length, layer_mask))
+
+      layer_mask = tf.cast(
+          tf.einsum('BF,FT->BT', layer_mask, transform) > 0.0,
+          dtype=layer_mask.dtype)
+      seq_length = pooled_seq_length
+  del seq_length
+
+  return attention_masks
+
+
 @tf.keras.utils.register_keras_serializable(package='Text')
 class FunnelTransformerEncoder(tf.keras.layers.Layer):
   """Funnel Transformer-based encoder network.
@@ -90,7 +183,7 @@ class FunnelTransformerEncoder(tf.keras.layers.Layer):
       dropout.
     attention_dropout: The dropout rate to use for the attention layers within
       the transformer layers.
-    pool_type: Pooling type. Choose from ['max', 'avg'].
+    pool_type: Pooling type. Choose from ['max', 'avg', 'truncated_avg'].
     pool_stride: An int or a list of ints. Pooling stride(s) to compress the
       sequence length. If set to int, each layer will have the same stride size.
       If set to list, the number of elements needs to match num_layers.
@@ -124,7 +217,7 @@ class FunnelTransformerEncoder(tf.keras.layers.Layer):
       inner_activation=lambda x: tf.keras.activations.gelu(x, approximate=True),
       output_dropout=0.1,
       attention_dropout=0.1,
-      pool_type='max',
+      pool_type=_MAX,
       pool_stride=2,
       unpool_length=0,
       initializer=tf.keras.initializers.TruncatedNormal(stddev=0.02),
@@ -207,12 +300,21 @@ class FunnelTransformerEncoder(tf.keras.layers.Layer):
         raise ValueError('Lengths of pool_stride and num_layers are not equal.')
       pool_strides = pool_stride
     # TODO(crickwu): explore tf.keras.layers.serialize method.
-    if pool_type == 'max':
+    if pool_type == _MAX:
       pool_cls = tf.keras.layers.MaxPooling1D
-    elif pool_type == 'avg':
+    elif pool_type == _AVG:
       pool_cls = tf.keras.layers.AveragePooling1D
+    elif pool_type == _TRUNCATED_AVG:
+      # TODO(b/203665205): unpool_length should be implemented.
+      if unpool_length != 0:
+        raise ValueError('unpool_length is not supported by truncated_avg now.')
+      # Compute the attention masks and pooling transforms.
+      self._pooling_transforms = _create_truncated_avg_transforms(
+          max_sequence_length, pool_strides)
     else:
       raise ValueError('pool_type not supported.')
+
+    if pool_type in (_MAX, _AVG):
       self._att_input_pool_layers = []
       for layer_pool_stride in pool_strides:
         att_input_pool_layer = pool_cls(
@@ -224,6 +326,7 @@ class FunnelTransformerEncoder(tf.keras.layers.Layer):
 
     self._pool_strides = pool_strides  # This is a list here.
     self._unpool_length = unpool_length
+    self._pool_type = pool_type
 
     self._config = {
         'vocab_size': vocab_size,
@@ -280,11 +383,13 @@ class FunnelTransformerEncoder(tf.keras.layers.Layer):
     encoder_outputs = []
     x = embeddings
     # TODO(b/195972228): attention_mask can be co-generated with pooling.
+    if self._pool_type in (_MAX, _AVG):
       attention_mask = _pool_and_concat(
           attention_mask,
           unpool_length=self._unpool_length,
           strides=self._pool_strides[0],
           axes=[1])
+
       for i, layer in enumerate(self._transformer_layers):
         # Bypass no pooling cases.
         if self._pool_strides[i] == 1:
@@ -307,12 +412,36 @@ class FunnelTransformerEncoder(tf.keras.layers.Layer):
               strides=[self._pool_strides[i + 1], self._pool_strides[i]],
               axes=[1, 2])
         encoder_outputs.append(x)
+    elif self._pool_type == _TRUNCATED_AVG:
+      attention_masks = _create_truncated_avg_masks(mask, self._pool_strides,
+                                                    self._pooling_transforms)
+      for i, layer in enumerate(self._transformer_layers):
+        attention_mask = attention_masks[i]
+        # Bypass no pooling cases.
+        if self._pool_strides[i] == 1:
+          x = layer([x, x, attention_mask])
+        else:
+          pooled_inputs = tf.einsum(
+              'BFD,FT->BTD',
+              tf.cast(x[:, self._unpool_length:, :],
+                      tf.keras.mixed_precision.global_policy().compute_dtype
+                     ),  # extra casting for faster mixed computation.
+              self._pooling_transforms[i])
+          query_inputs = tf.concat(
+              values=(tf.cast(
+                  x[:, :self._unpool_length, :],
+                  dtype=pooled_inputs.dtype), pooled_inputs),
+              axis=1)
+          x = layer([query_inputs, x, attention_mask])
+        encoder_outputs.append(x)
 
     last_encoder_output = encoder_outputs[-1]
     first_token_tensor = last_encoder_output[:, 0, :]
     pooled_output = self._pooler_layer(first_token_tensor)
 
     return dict(
+        word_embeddings=word_embeddings,
+        embedding_output=embeddings,
         sequence_output=encoder_outputs[-1],
         pooled_output=pooled_output,
         encoder_outputs=encoder_outputs)

official/nlp/modeling/networks/funnel_transformer_test.py

@@ -38,6 +38,8 @@ class FunnelTransformerEncoderTest(parameterized.TestCase, tf.test.TestCase):
     tf.keras.mixed_precision.set_global_policy("float32")
 
   @parameterized.named_parameters(
+      ("mix_truncated_avg", "mixed_float16", tf.float16, "truncated_avg"),
+      ("float32_truncated_avg", "float32", tf.float32, "truncated_avg"),
       ("mix_max", "mixed_float16", tf.float16, "max"),
       ("float32_max", "float32", tf.float32, "max"),
       ("mix_avg", "mixed_float16", tf.float16, "avg"),
@@ -57,6 +59,7 @@ class FunnelTransformerEncoderTest(parameterized.TestCase, tf.test.TestCase):
         num_layers=num_layers,
         pool_stride=pool_stride,
         pool_type=pool_type,
+        max_sequence_length=sequence_length,
         unpool_length=0)
     # Create the inputs (note that the first dimension is implicit).
     word_ids = tf.keras.Input(shape=(sequence_length,), dtype=tf.int32)
@@ -71,8 +74,14 @@ class FunnelTransformerEncoderTest(parameterized.TestCase, tf.test.TestCase):
     self.assertIsInstance(test_network.pooler_layer, tf.keras.layers.Dense)
 
     # Stride=2 compresses sequence length to half the size at each layer.
-    # This configuration gives each layer of seq length: 21->11->6->3.
+    # For pool_type = max or avg,
+    # this configuration gives each layer of seq length: 21->11->6->3.
+    # For pool_type = truncated_avg,
+    # seq length: 21->10->5->2.
+    if pool_type in ["max", "avg"]:
       expected_data_shape = [None, 3, hidden_size]
+    else:
+      expected_data_shape = [None, 2, hidden_size]
     expected_pooled_shape = [None, hidden_size]
 
     self.assertAllEqual(expected_data_shape, data.shape.as_list())