Simplify calls to embedding_to_padding, we always end up converting t…

…he padding mask to a float tensor.

PiperOrigin-RevId: 164777753

tensor2tensor/layers/common_attention.py

@@ -166,17 +166,17 @@ def add_positional_embedding_nd(x, max_length, name):
 
 
 def embedding_to_padding(emb):
-  """Input embeddings -> is_padding.
+  """Calculates the padding mask based on which embeddings are all zero.
 
   We have hacked symbol_modality to return all-zero embeddings for padding.
 
   Args:
     emb: a Tensor with shape [..., depth].
   Returns:
-    a boolean Tensor with shape [...].
+    a float Tensor with shape [...].
   """
   emb_sum = tf.reduce_sum(tf.abs(emb), axis=-1)
-  return tf.equal(emb_sum, 0.0)
+  return tf.to_float(tf.equal(emb_sum, 0.0))
 
 
 def attention_bias_lower_triangle(length):
@@ -197,13 +197,13 @@ def attention_bias_ignore_padding(memory_padding):
   """Create an bias tensor to be added to attention logits.
 
   Args:
-    memory_padding: a boolean `Tensor` with shape [batch, memory_length].
+    memory_padding: a float `Tensor` with shape [batch, memory_length].
 
   Returns:
     a `Tensor` with shape [batch, 1, 1, memory_length].
   """
-  ret = tf.to_float(memory_padding) * -1e9
-  return tf.expand_dims(tf.expand_dims(ret, 1), 1)
+  ret = memory_padding * -1e9
+  return tf.expand_dims(tf.expand_dims(ret, axis=1), axis=1)
 
 
 def attention_bias_proximal(length):
@@ -523,8 +523,7 @@ def pad_l_and_r(x, pad_length):
     # [batch, heads, blocks, block_length, dim]
     k_new = tf.transpose(k_new, [2, 3, 0, 1, 4])
 
-    attention_bias = tf.expand_dims(
-        tf.to_float(embedding_to_padding(k_new)) * -1e9, axis=-2)
+    attention_bias = tf.expand_dims(embedding_to_padding(k_new) * -1e9, axis=-2)
 
     v_t = tf.transpose(v, [2, 0, 1, 3])
     v_new = tf.gather(v_t, gather_indices)