Create optimization _tf.py

optimization _tf.py

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+# Copyright 2019 The TensorFlow Authors, The Hugging Face Team. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# ==============================================================================
+"""Functions and classes related to optimization (weight updates)."""
+
+
+import re
+from typing import Callable, List, Optional, Union
+
+import tensorflow as tf
+
+
+try:
+    from tensorflow.keras.optimizers.legacy import Adam
+except ImportError:
+    from tensorflow.keras.optimizers import Adam
+
+
+class WarmUp(tf.keras.optimizers.schedules.LearningRateSchedule):
+    """
+    Applies a warmup schedule on a given learning rate decay schedule.
+
+    Args:
+        initial_learning_rate (`float`):
+            The initial learning rate for the schedule after the warmup (so this will be the learning rate at the end
+            of the warmup).
+        decay_schedule_fn (`Callable`):
+            The schedule function to apply after the warmup for the rest of training.
+        warmup_steps (`int`):
+            The number of steps for the warmup part of training.
+        power (`float`, *optional*, defaults to 1):
+            The power to use for the polynomial warmup (defaults is a linear warmup).
+        name (`str`, *optional*):
+            Optional name prefix for the returned tensors during the schedule.
+    """
+
+    def __init__(
+        self,
+        initial_learning_rate: float,
+        decay_schedule_fn: Callable,
+        warmup_steps: int,
+        power: float = 1.0,
+        name: str = None,
+    ):
+        super().__init__()
+        self.initial_learning_rate = initial_learning_rate
+        self.warmup_steps = warmup_steps
+        self.power = power
+        self.decay_schedule_fn = decay_schedule_fn
+        self.name = name
+
+    def __call__(self, step):
+        with tf.name_scope(self.name or "WarmUp") as name:
+            # Implements polynomial warmup. i.e., if global_step < warmup_steps, the
+            # learning rate will be `global_step/num_warmup_steps * init_lr`.
+            global_step_float = tf.cast(step, tf.float32)
+            warmup_steps_float = tf.cast(self.warmup_steps, tf.float32)
+            warmup_percent_done = global_step_float / warmup_steps_float
+            warmup_learning_rate = self.initial_learning_rate * tf.math.pow(warmup_percent_done, self.power)
+            return tf.cond(
+                global_step_float < warmup_steps_float,
+                lambda: warmup_learning_rate,
+                lambda: self.decay_schedule_fn(step - self.warmup_steps),
+                name=name,
+            )
+
+    def get_config(self):
+        return {
+            "initial_learning_rate": self.initial_learning_rate,
+            "decay_schedule_fn": self.decay_schedule_fn,
+            "warmup_steps": self.warmup_steps,
+            "power": self.power,
+            "name": self.name,
+        }
+
+
+def create_optimizer(
+    init_lr: float,
+    num_train_steps: int,
+    num_warmup_steps: int,
+    min_lr_ratio: float = 0.0,
+    adam_beta1: float = 0.9,
+    adam_beta2: float = 0.999,
+    adam_epsilon: float = 1e-8,
+    adam_clipnorm: Optional[float] = None,
+    adam_global_clipnorm: Optional[float] = None,
+    weight_decay_rate: float = 0.0,
+    power: float = 1.0,
+    include_in_weight_decay: Optional[List[str]] = None,
+):
+    """
+    Creates an optimizer with a learning rate schedule using a warmup phase followed by a linear decay.
+
+    Args:
+        init_lr (`float`):
+            The desired learning rate at the end of the warmup phase.
+        num_train_steps (`int`):
+            The total number of training steps.
+        num_warmup_steps (`int`):
+            The number of warmup steps.
+        min_lr_ratio (`float`, *optional*, defaults to 0):
+            The final learning rate at the end of the linear decay will be `init_lr * min_lr_ratio`.
+        adam_beta1 (`float`, *optional*, defaults to 0.9):
+            The beta1 to use in Adam.
+        adam_beta2 (`float`, *optional*, defaults to 0.999):
+            The beta2 to use in Adam.
+        adam_epsilon (`float`, *optional*, defaults to 1e-8):
+            The epsilon to use in Adam.
+        adam_clipnorm: (`float`, *optional*, defaults to `None`):
+            If not `None`, clip the gradient norm for each weight tensor to this value.
+        adam_global_clipnorm: (`float`, *optional*, defaults to `None`)
+            If not `None`, clip gradient norm to this value. When using this argument, the norm is computed over all
+            weight tensors, as if they were concatenated into a single vector.
+        weight_decay_rate (`float`, *optional*, defaults to 0):
+            The weight decay to use.
+        power (`float`, *optional*, defaults to 1.0):
+            The power to use for PolynomialDecay.
+        include_in_weight_decay (`List[str]`, *optional*):
+            List of the parameter names (or re patterns) to apply weight decay to. If none is passed, weight decay is
+            applied to all parameters except bias and layer norm parameters.
+    """
+    # Implements linear decay of the learning rate.
+    lr_schedule = tf.keras.optimizers.schedules.PolynomialDecay(
+        initial_learning_rate=init_lr,
+        decay_steps=num_train_steps - num_warmup_steps,
+        end_learning_rate=init_lr * min_lr_ratio,
+        power=power,
+    )
+    if num_warmup_steps:
+        lr_schedule = WarmUp(
+            initial_learning_rate=init_lr,
+            decay_schedule_fn=lr_schedule,
+            warmup_steps=num_warmup_steps,
+        )
+    if weight_decay_rate > 0.0:
+        optimizer = AdamWeightDecay(
+            learning_rate=lr_schedule,
+            weight_decay_rate=weight_decay_rate,
+            beta_1=adam_beta1,
+            beta_2=adam_beta2,
+            epsilon=adam_epsilon,
+            clipnorm=adam_clipnorm,
+            global_clipnorm=adam_global_clipnorm,
+            exclude_from_weight_decay=["LayerNorm", "layer_norm", "bias"],
+            include_in_weight_decay=include_in_weight_decay,
+        )
+    else:
+        optimizer = tf.keras.optimizers.Adam(
+            learning_rate=lr_schedule,
+            beta_1=adam_beta1,
+            beta_2=adam_beta2,
+            epsilon=adam_epsilon,
+            clipnorm=adam_clipnorm,
+            global_clipnorm=adam_global_clipnorm,
+        )
+    # We return the optimizer and the LR scheduler in order to better track the
+    # evolution of the LR independently of the optimizer.
+    return optimizer, lr_schedule
+
+
+class AdamWeightDecay(Adam):
+    """
+    Adam enables L2 weight decay and clip_by_global_norm on gradients. Just adding the square of the weights to the
+    loss function is *not* the correct way of using L2 regularization/weight decay with Adam, since that will interact
+    with the m and v parameters in strange ways as shown in [Decoupled Weight Decay
+    Regularization](https://arxiv.org/abs/1711.05101).
+
+    Instead we want to decay the weights in a manner that doesn't interact with the m/v parameters. This is equivalent
+    to adding the square of the weights to the loss with plain (non-momentum) SGD.
+
+    Args:
+        learning_rate (`Union[float, tf.keras.optimizers.schedules.LearningRateSchedule]`, *optional*, defaults to 1e-3):
+            The learning rate to use or a schedule.
+        beta_1 (`float`, *optional*, defaults to 0.9):
+            The beta1 parameter in Adam, which is the exponential decay rate for the 1st momentum estimates.
+        beta_2 (`float`, *optional*, defaults to 0.999):
+            The beta2 parameter in Adam, which is the exponential decay rate for the 2nd momentum estimates.
+        epsilon (`float`, *optional*, defaults to 1e-7):
+            The epsilon parameter in Adam, which is a small constant for numerical stability.
+        amsgrad (`bool`, *optional*, default to `False`):
+            Whether to apply AMSGrad variant of this algorithm or not, see [On the Convergence of Adam and
+            Beyond](https://arxiv.org/abs/1904.09237).
+        weight_decay_rate (`float`, *optional*, defaults to 0):
+            The weight decay to apply.
+        include_in_weight_decay (`List[str]`, *optional*):
+            List of the parameter names (or re patterns) to apply weight decay to. If none is passed, weight decay is
+            applied to all parameters by default (unless they are in `exclude_from_weight_decay`).
+        exclude_from_weight_decay (`List[str]`, *optional*):
+            List of the parameter names (or re patterns) to exclude from applying weight decay to. If a
+            `include_in_weight_decay` is passed, the names in it will supersede this list.
+        name (`str`, *optional*, defaults to 'AdamWeightDecay'):
+            Optional name for the operations created when applying gradients.
+        kwargs:
+            Keyword arguments. Allowed to be {`clipnorm`, `clipvalue`, `lr`, `decay`}. `clipnorm` is clip gradients by
+            norm; `clipvalue` is clip gradients by value, `decay` is included for backward compatibility to allow time
+            inverse decay of learning rate. `lr` is included for backward compatibility, recommended to use
+            `learning_rate` instead.
+    """
+
+    def __init__(
+        self,
+        learning_rate: Union[float, tf.keras.optimizers.schedules.LearningRateSchedule] = 0.001,
+        beta_1: float = 0.9,
+        beta_2: float = 0.999,
+        epsilon: float = 1e-7,
+        amsgrad: bool = False,
+        weight_decay_rate: float = 0.0,
+        include_in_weight_decay: Optional[List[str]] = None,
+        exclude_from_weight_decay: Optional[List[str]] = None,
+        name: str = "AdamWeightDecay",
+        **kwargs,
+    ):
+        super().__init__(learning_rate, beta_1, beta_2, epsilon, amsgrad, name, **kwargs)
+        self.weight_decay_rate = weight_decay_rate
+        self._include_in_weight_decay = include_in_weight_decay
+        self._exclude_from_weight_decay = exclude_from_weight_decay
+
+    @classmethod
+    def from_config(cls, config):
+        """Creates an optimizer from its config with WarmUp custom object."""
+        custom_objects = {"WarmUp": WarmUp}
+        return super(AdamWeightDecay, cls).from_config(config, custom_objects=custom_objects)
+
+    def _prepare_local(self, var_device, var_dtype, apply_state):
+        super(AdamWeightDecay, self)._prepare_local(var_device, var_dtype, apply_state)
+        apply_state[(var_device, var_dtype)]["weight_decay_rate"] = tf.constant(
+            self.weight_decay_rate, name="adam_weight_decay_rate"
+        )
+
+    def _decay_weights_op(self, var, learning_rate, apply_state):
+        do_decay = self._do_use_weight_decay(var.name)
+        if do_decay:
+            return var.assign_sub(
+                learning_rate * var * apply_state[(var.device, var.dtype.base_dtype)]["weight_decay_rate"],
+                use_locking=self._use_locking,
+            )
+        return tf.no_op()
+
+    def apply_gradients(self, grads_and_vars, name=None, **kwargs):
+        grads, tvars = list(zip(*grads_and_vars))
+        return super(AdamWeightDecay, self).apply_gradients(zip(grads, tvars), name=name, **kwargs)
+
+    def _get_lr(self, var_device, var_dtype, apply_state):
+        """Retrieves the learning rate with the given state."""
+        if apply_state is None:
+            return self._decayed_lr_t[var_dtype], {}
+
+        apply_state = apply_state or {}
+        coefficients = apply_state.get((var_device, var_dtype))
+        if coefficients is None:
+            coefficients = self._fallback_apply_state(var_device, var_dtype)
+            apply_state[(var_device, var_dtype)] = coefficients
+
+        return coefficients["lr_t"], {"apply_state": apply_state}
+
+    def _resource_apply_dense(self, grad, var, apply_state=None):
+        lr_t, kwargs = self._get_lr(var.device, var.dtype.base_dtype, apply_state)
+        decay = self._decay_weights_op(var, lr_t, apply_state)
+        with tf.control_dependencies([decay]):
+            return super(AdamWeightDecay, self)._resource_apply_dense(grad, var, **kwargs)
+
+    def _resource_apply_sparse(self, grad, var, indices, apply_state=None):
+        lr_t, kwargs = self._get_lr(var.device, var.dtype.base_dtype, apply_state)
+        decay = self._decay_weights_op(var, lr_t, apply_state)
+        with tf.control_dependencies([decay]):
+            return super(AdamWeightDecay, self)._resource_apply_sparse(grad, var, indices, **kwargs)
+
+    def get_config(self):
+        config = super().get_config()
+        config.update({"weight_decay_rate": self.weight_decay_rate})
+        return config
+
+    def _do_use_weight_decay(self, param_name):
+        """Whether to use L2 weight decay for `param_name`."""
+        if self.weight_decay_rate == 0:
+            return False
+
+        if self._include_in_weight_decay:
+            for r in self._include_in_weight_decay:
+                if re.search(r, param_name) is not None:
+                    return True
+
+        if self._exclude_from_weight_decay:
+            for r in self._exclude_from_weight_decay:
+                if re.search(r, param_name) is not None:
+                    return False
+        return True
+
+
+# Extracted from https://github.com/OpenNMT/OpenNMT-tf/blob/master/opennmt/optimizers/utils.py
+class GradientAccumulator(object):
+    """
+    Gradient accumulation utility. When used with a distribution strategy, the accumulator should be called in a
+    replica context. Gradients will be accumulated locally on each replica and without synchronization. Users should
+    then call `.gradients`, scale the gradients if required, and pass the result to `apply_gradients`.
+    """
+
+    # We use the ON_READ synchronization policy so that no synchronization is
+    # performed on assignment. To get the value, we call .value() which returns the
+    # value on the current replica without synchronization.
+
+    def __init__(self):
+        """Initializes the accumulator."""
+        self._gradients = []
+        self._accum_steps = None
+
+    @property
+    def step(self):
+        """Number of accumulated steps."""
+        if self._accum_steps is None:
+            self._accum_steps = tf.Variable(
+                tf.constant(0, dtype=tf.int64),
+                trainable=False,
+                synchronization=tf.VariableSynchronization.ON_READ,
+                aggregation=tf.VariableAggregation.ONLY_FIRST_REPLICA,
+            )
+
+        return self._accum_steps.value()
+
+    @property
+    def gradients(self):
+        """The accumulated gradients on the current replica."""
+        if not self._gradients:
+            raise ValueError("The accumulator should be called first to initialize the gradients")
+        return [gradient.value() if gradient is not None else gradient for gradient in self._gradients]
+
+    def __call__(self, gradients):
+        """Accumulates `gradients` on the current replica."""
+        if not self._gradients:
+            _ = self.step  # Create the step variable.
+            self._gradients.extend(
+                [
+                    tf.Variable(
+                        tf.zeros_like(gradient),
+                        trainable=False,
+                        synchronization=tf.VariableSynchronization.ON_READ,
+                        aggregation=tf.VariableAggregation.ONLY_FIRST_REPLICA,
+                    )
+                    if gradient is not None
+                    else gradient
+                    for gradient in gradients
+                ]
+            )
+        if len(gradients) != len(self._gradients):
+            raise ValueError(f"Expected {len(self._gradients)} gradients, but got {len(gradients)}")
+
+        for accum_gradient, gradient in zip(self._gradients, gradients):
+            if accum_gradient is not None and gradient is not None:
+                accum_gradient.assign_add(gradient)
+
+        self._accum_steps.assign_add(1)
+
+    def reset(self):
+        """Resets the accumulated gradients on the current replica."""
+        if not self._gradients:
+            return
+        self._accum_steps.assign(0)
+        for gradient in self._gradients:
+            if gradient is not None:
+                gradient.assign(tf.zeros_like(gradient))