make XLA work on more models

tensorpack/tfutils/summary.py

@@ -222,19 +222,26 @@ def add_moving_summary(*args, **kwargs):
     # allow ctx to be none
     if ctx is not None and not ctx.is_main_training_tower:
         return []
+
+    graph = tf.get_default_graph()
+    try:
+        control_flow_ctx = graph._get_control_flow_context()
+        # XLA does not support summaries anyway
+        # However, this function will generate unnecessary dependency edges,
+        # which makes the tower function harder to compile under XLA, so we skip it
+        if control_flow_ctx is not None and control_flow_ctx.IsXLAContext():
+            return
+    except Exception:
+        pass
+
     if tf.get_variable_scope().reuse is True:
         logger.warn("add_moving_summary() called under reuse=True scope, ignored.")
         return []
 
-    if len(args) == 1 and isinstance(args[0], (list, tuple)):
-        logger.warn("add_moving_summary() takes positional args instead of an iterable of tensors!")
-        args = args[0]
-
     for x in args:
         assert isinstance(x, (tf.Tensor, tf.Variable)), x
         assert x.get_shape().ndims == 0, \
             "add_moving_summary() only accepts scalar tensor! Got one with {}".format(x.get_shape())
-    # TODO variable not saved under distributed
 
     ema_ops = []
     for c in args:
@@ -245,7 +252,8 @@ def add_moving_summary(*args, **kwargs):
             # assign_moving_average creates variables with op names, therefore clear ns first.
             with _enter_vs_reuse_ns('EMA') as vs:
                 ema_var = tf.get_variable(name, shape=c.shape, dtype=c.dtype,
-                                          initializer=tf.constant_initializer(), trainable=False)
+                                          initializer=tf.constant_initializer(),
+                                          trainable=False)
                 ns = vs.original_name_scope
             with tf.name_scope(ns):     # reuse VS&NS so that EMA_1 won't appear
                 ema_op = moving_averages.assign_moving_average(

tensorpack/train/tower.py

@@ -177,7 +177,16 @@ class SingleCostTrainer(TowerTrainer):
     """See `tf.gradients`. """
 
     XLA_COMPILE = False
-    """ Use :func:`xla.compile` to compile the tower function. """
+    """ Use :func:`xla.compile` to compile the tower function.
+    Note that XLA has very strong requirements on the tower function, e.g.:
+
+    1. limited op support
+    2. inferrable shape
+    3. no summary support
+
+    and many tower functions cannot be compiled by XLA.
+    Don't use it if you don't understand it.
+    """
 
     @call_only_once
     def setup_graph(self, inputs_desc, input, get_cost_fn, get_opt_fn):
@@ -230,9 +239,13 @@ class SingleCostTrainer(TowerTrainer):
 
         def get_grad_fn():
             ctx = get_current_tower_context()
-            cost = get_cost_fn(*input.get_input_tensors())
+            inputs = input.get_input_tensors()
+
+            def compute_grad_from_inputs(*inputs):
+                cost = get_cost_fn(*inputs)
                 assert isinstance(cost, tf.Tensor), cost
                 assert cost.shape.ndims == 0, "Cost must be a scalar, but found {}!".format(cost)
+
                 if not ctx.is_training:
                     return None     # this is the tower function, could be called for inference
 
@@ -250,25 +263,22 @@ class SingleCostTrainer(TowerTrainer):
                 return grads
 
             if not self.XLA_COMPILE:
-            return get_grad_fn
+                return compute_grad_from_inputs(*inputs)
             else:
                 from tensorflow.contrib.compiler import xla
 
-            def xla_get_grad_fn():
                 def xla_func():
-                    grads = get_grad_fn()
+                    grads = compute_grad_from_inputs(*inputs)
                     # unpack, because the return value
                     # of xla function cannot have nested structure
                     grads = [x[0] for x in grads]
                     return grads
 
                 grads_no_vars = xla.compile(xla_func)
-                # repack again
-                ctx = get_current_tower_context()
                 if ctx.has_own_variables:
                     varlist = ctx.get_collection_in_tower(tf.GraphKeys.TRAINABLE_VARIABLES)
                 else:
                     varlist = tf.trainable_variables()
                 return list(zip(grads_no_vars, varlist))
 
-            return xla_get_grad_fn
+        return get_grad_fn