Simplify Jaxpr: remove the bound_subjaxpr field, all subjaxprs are in…

CHANGELOG.md

@@ -7,8 +7,10 @@ These are the release notes for JAX.
 ### Breaking changes
 
 * The minimum jaxlib version is now 0.1.38.
-* Simplified `Jaxpr` by removing the `Jaxpr.freevars` and changing the 
-  representation of `Jaxpr.bound_subjaxprs` to drop the environment values. 
+* Simplified `Jaxpr` by removing the `Jaxpr.freevars` and 
+  `Jaxpr.bound_subjaxprs`. The call primitives (`xla_call`, `xla_pmap`,
+   `sharded_call`, and `remat_call`) get a new parameter `call_jaxpr` with a
+   fully-closed (no `constvars`) JAXPR.  
 
 ### New features
 

jax/core.py

@@ -58,6 +58,19 @@ def __str__(self):
     return str(pp_jaxpr(self))
   __repr__ = __str__
 
+
+def subjaxprs(jaxpr):
+  """Generator for all subjaxprs found in the params of jaxpr.eqns.
+  Does not descend recursively into the found subjaxprs.
+  """
+  for eqn in jaxpr.eqns:
+    for param in eqn.params.values():
+      if type(param) is Jaxpr:
+        yield param
+      elif type(param) is TypedJaxpr:
+        yield param.jaxpr
+
+
 class TypedJaxpr(object):
   def __init__(self, jaxpr, literals, in_avals, out_avals):
     assert type(jaxpr) is Jaxpr
@@ -84,8 +97,8 @@ def jaxpr_as_fun(typed_jaxpr, *args):
   return eval_jaxpr(typed_jaxpr.jaxpr, typed_jaxpr.literals, *args)
 
 
-JaxprEqn = namedtuple('JaxprEqn', ['invars', 'outvars', 'primitive',
-                                   'bound_subjaxpr', 'params'])
+
+JaxprEqn = namedtuple('JaxprEqn', ['invars', 'outvars', 'primitive', 'params'])
 JaxprEqn.__repr__ = JaxprEqn.__str__ = lambda eqn: str(pp_eqn(eqn)).rstrip()
 new_jaxpr_eqn = JaxprEqn
 
@@ -149,6 +162,8 @@ def __repr__(self):
 
 class Primitive(object):
   multiple_results = False  # override for multi-output primitives
+  call_primitive = False  # override for higher-order primitives that are
+                          # processed in final style.
 
   def __init__(self, name):
     self.name = name
@@ -193,6 +208,24 @@ def abstract_eval(self, *args, **kwargs):
 
 # -------------------- lifting --------------------
 
+# TODO(necula): this belongs next to pe.new_eqn_recipe, but is needed in
+# core.py. Plan to move all these utilities to jaxpr.py.
+def extract_call_jaxpr(primitive, params):
+  """Extract the call primitive subjaxpr from the params.
+
+  Params:
+    params: a parameter dictionary for a primitive.
+  Returns: the subjaxpr and the params without the "jaxpr" value. If this is
+    not a call primitive then returns (None, params).
+  """
+  if not primitive.call_primitive:
+    return (None, params)
+  else:
+    assert "call_jaxpr" in params
+    new_params = dict(params)
+    del new_params["call_jaxpr"]
+    return (params["call_jaxpr"], new_params)
+
 
 def eval_jaxpr(jaxpr, consts, *args):
   def read(v):
@@ -210,11 +243,12 @@ def write(v, val):
   map(write, jaxpr.invars, args)
   for eqn in jaxpr.eqns:
     in_vals = map(read, eqn.invars)
-    if eqn.bound_subjaxpr:
-      subfuns = [lu.wrap_init(partial(eval_jaxpr, eqn.bound_subjaxpr, ()))]
+    call_jaxpr, params = extract_call_jaxpr(eqn.primitive, eqn.params)
+    if call_jaxpr:
+      subfuns = [lu.wrap_init(partial(eval_jaxpr, call_jaxpr, ()))]
     else:
       subfuns = []
-    ans = eqn.primitive.bind(*(subfuns + in_vals), **eqn.params)
+    ans = eqn.primitive.bind(*(subfuns + in_vals), **params)
     if eqn.primitive.multiple_results:
       map(write, eqn.outvars, ans)
     else:
@@ -626,6 +660,10 @@ def call_impl(f, *args, **params):
 # ------------------- Jaxpr printed representation -------------------
 
 def check_jaxpr(jaxpr):
+  """Checks well-formedness of a jaxpr.
+
+  Specifically it checks that all variabled used are previously defined.
+  """
   def context():
     return "\njaxpr:\n{}\n".format(jaxpr)
 
@@ -646,10 +684,16 @@ def write_env(env, v):
   map(write, jaxpr.constvars)
   map(write, jaxpr.invars)
   for eqn in jaxpr.eqns:
+    if eqn.primitive.call_primitive:
+      if "call_jaxpr" not in eqn.params:
+        raise Exception("Call primitive {} should have a 'call_jaxpr' parameter"
+                        .format(eqn.primitive))
     map(read, eqn.invars)
-    if eqn.bound_subjaxpr:
-      check_jaxpr(eqn.bound_subjaxpr)
     map(write, eqn.outvars)
+
+  for subjaxpr in subjaxprs(jaxpr):
+    check_jaxpr(subjaxpr)
+
   map(read, jaxpr.outvars)
 
 
@@ -664,10 +708,6 @@ def pp_eqn_compact(primitive_name, params):
 def pp_eqn(eqn):
   lhs = pp_vars(eqn.outvars)
   pp_subexpr = pp('')
-  if eqn.bound_subjaxpr:
-    pp_subexpr = pp_subexpr + (
-        pp_jaxpr(eqn.bound_subjaxpr).indent(2)
-        >> pp(' [ ]'))
   return (pp('{} = '.format(lhs)) >>
           pp(eqn.primitive.name) >> pp_kv_pairs(sorted(eqn.params.items()))
           >> pp(' ') >> pp(pp_vars(eqn.invars))) + pp_subexpr

jax/interpreters/ad.py

@@ -172,7 +172,7 @@ def is_linear(var):
 
   linear_eqns = []
   for eqn in jaxpr.eqns:
-    if not eqn.bound_subjaxpr:
+    if not eqn.primitive.call_primitive:
       if any(is_linear(v) for v in eqn.invars):
         linear_eqns.append(eqn)
       else:
@@ -183,20 +183,20 @@ def is_linear(var):
         else:
           write_primal(eqn.outvars[0], ans)
     else:
-      subjaxpr = eqn.bound_subjaxpr
+      call_jaxpr = eqn.params["call_jaxpr"]
       if any(is_linear(v) for v in eqn.invars):
         linear_eqns.append(eqn)
       elif eqn.primitive is not pe.remat_call_p:
         ans = _eval_subjaxpr_primals(
-            eqn.primitive, subjaxpr,
+            eqn.primitive, call_jaxpr,
             map(read_primal, eqn.invars), eqn.params)
         map(write_primal, eqn.outvars, ans)
 
       # we special-case remat_call here because it can be mixed linear /
       # nonlinear, so we always evaluate it even if it has a linear part
       if eqn.primitive is pe.remat_call_p:
         ans = _eval_subjaxpr_primals(
-            eqn.primitive, subjaxpr,
+            eqn.primitive, call_jaxpr,
             map(read_primal, eqn.invars), eqn.params)
         map(write_primal, eqn.outvars, ans)
 
@@ -208,10 +208,10 @@ def is_linear(var):
       cts_in = map(read_cotangent, eqn.outvars)
     else:
       cts_in, = map(read_cotangent, eqn.outvars)
-    if eqn.bound_subjaxpr:
-      subjaxpr = eqn.bound_subjaxpr
+    if eqn.primitive.call_primitive:
+      call_jaxpr, params = core.extract_call_jaxpr(eqn.primitive, eqn.params)
       cts_out = get_primitive_transpose(eqn.primitive)(
-          eqn.params, subjaxpr, invals, cts_in)
+          params, call_jaxpr, invals, cts_in)
     else:
       cts_out = get_primitive_transpose(eqn.primitive)(cts_in, *invals, **eqn.params)
     cts_out = [zero] * len(eqn.invars) if cts_out is zero else cts_out
@@ -251,7 +251,7 @@ def is_linear(var):
   assert not jaxpr.constvars
   map(write_primal, jaxpr.invars, args)
   for eqn in jaxpr.eqns:
-    if not eqn.bound_subjaxpr:
+    if not eqn.primitive.call_primitive:
       if not any(is_linear(v) for v in eqn.invars):
         in_vals = map(read_primal, eqn.invars)
         ans = eqn.primitive.bind(*in_vals, **eqn.params)
@@ -260,11 +260,11 @@ def is_linear(var):
         else:
           write_primal(eqn.outvars[0], ans)
     else:
-      subjaxpr = eqn.bound_subjaxpr
+      call_jaxpr = eqn.params["call_jaxpr"]
       if (eqn.primitive is pe.remat_call_p or
           not any(is_linear(v) for v in eqn.invars)):
         ans = _eval_subjaxpr_primals(
-            eqn.primitive, subjaxpr,
+            eqn.primitive, call_jaxpr,
             map(read_primal, eqn.invars), eqn.params)
         map(write_primal, eqn.outvars, ans)
   return map(read_primal, jaxpr.outvars)
@@ -537,19 +537,19 @@ def traceable(num_primals, in_tree_def, *primals_and_tangents):
   yield out_flat, tree_def
 
 
-def call_transpose(primitive, params, jaxpr, args, ct):
+def call_transpose(primitive, params, call_jaxpr, args, ct):
   all_args, in_tree_def = tree_flatten(((), args, ct))  # empty consts
-  fun = lu.hashable_partial(lu.wrap_init(backward_pass), jaxpr)
+  fun = lu.hashable_partial(lu.wrap_init(backward_pass), call_jaxpr)
   fun, out_tree = flatten_fun_nokwargs(fun, in_tree_def)
   params = dict(params, name=wrap_name(params['name'], 'transpose'))
   out_flat = primitive.bind(fun, *all_args, **params)
   return tree_unflatten(out_tree(), out_flat)
 primitive_transposes[core.call_p] = partial(call_transpose, call_p)
 primitive_transposes[pe.remat_call_p] = partial(call_transpose, pe.remat_call_p)
 
-def map_transpose(primitive, params, jaxpr, args, ct):
+def map_transpose(primitive, params, call_jaxpr, args, ct):
   all_args, in_tree_def = tree_flatten(((), args, ct))  # empty consts
-  fun = lu.hashable_partial(lu.wrap_init(backward_pass), jaxpr)
+  fun = lu.hashable_partial(lu.wrap_init(backward_pass), call_jaxpr)
   fun, out_tree = flatten_fun_nokwargs(fun, in_tree_def)
   params = dict(params, name=wrap_name(params['name'], 'transpose'))
   out_flat = primitive.bind(fun, *all_args, **params)

jax/interpreters/partial_eval.py

@@ -136,10 +136,10 @@ def process_call(self, call_primitive, f, tracers, params):
     lifted_jaxpr = convert_constvars_jaxpr(jaxpr)
     out_tracers = [JaxprTracer(self, PartialVal((out_pv, out_pv_const)), None)
                    for out_pv, out_pv_const in zip(out_pvs, out_pv_consts)]
+    new_params = dict(params, call_jaxpr=lifted_jaxpr)
     # The `jaxpr` already contains the env_vars at start of invars
     eqn = new_eqn_recipe(tuple(it.chain(const_tracers, env_tracers, tracers)),
-                         out_tracers, call_primitive, params,
-                         subjaxpr=lifted_jaxpr)
+                         out_tracers, call_primitive, new_params)
     for t in out_tracers:
       t.recipe = eqn
     return out_tracers
@@ -162,10 +162,10 @@ def process_map(self, map_primitive, f, tracers, params):
     new_params = dict(params,
                       mapped_invars=tuple([True] * len(const_tracers) +
                                           [False] * len(env_tracers) +
-                                          [True] * len(tracers)))
+                                          [True] * len(tracers)),
+                      call_jaxpr=lifted_jaxpr)
     eqn = new_eqn_recipe(tuple(it.chain(const_tracers, env_tracers, tracers)),
-                         out_tracers, map_primitive, new_params,
-                         subjaxpr=lifted_jaxpr)
+                         out_tracers, map_primitive, new_params)
     for t in out_tracers:
       t.recipe = eqn
     return out_tracers
@@ -187,10 +187,10 @@ def todo(x):
       lifted_jaxpr = convert_constvars_jaxpr(jaxpr)
       out_tracers = [JaxprTracer(trace, PartialVal((out_pv, out_pv_const)), None)
                      for out_pv, out_pv_const in zip(out_pvs, out_pv_consts)]
+      new_params = dict(params, call_jaxpr=lifted_jaxpr)
       # The `jaxpr` already contains the env_vars at start of invars
       eqn = new_eqn_recipe(tuple(it.chain(const_tracers, env_tracers)),
-                           out_tracers, call_primitive, params,
-                           subjaxpr=lifted_jaxpr)
+                           out_tracers, call_primitive, new_params)
       for t in out_tracers:
         t.recipe = eqn
       return out_tracers
@@ -215,11 +215,11 @@ def todo(x):
                      for out_pv, out_pv_const in zip(out_pvs, out_pv_consts)]
       new_params = dict(params,
                         mapped_invars=tuple([True] * len(const_tracers) +
-                                            [False] * len(env)))
+                                            [False] * len(env)),
+                        call_jaxpr=lifted_jaxpr)
       env_tracers = map(trace.full_raise, env)
       eqn = new_eqn_recipe(it.chain(const_tracers, env_tracers),
-                           out_tracers, map_primitive, new_params,
-                           subjaxpr=lifted_jaxpr)
+                           out_tracers, map_primitive, new_params)
       for t in out_tracers:
         t.recipe = eqn
       return out_tracers
@@ -383,38 +383,31 @@ def instantiate_const_at(trace, instantiate, tracer):
 ConstVar = namedtuple('ConstVar', ['val'])
 LambdaBinding = namedtuple('LambdaBinding', [])
 JaxprEqnRecipe = namedtuple('JaxprEqnRecipe',
-                            ['eqn_id', 'invars', 'outvars', 'primitive',
-                             'bound_subjaxpr', 'params'])
+                            ['eqn_id', 'invars', 'outvars', 'primitive', 'params'])
 
-
-def new_eqn_recipe(invars, outvars, primitive, params,
-                   subjaxpr=None):
+def new_eqn_recipe(invars, outvars, primitive, params):
   """Constructs a new JaxEqnRecipe.
 
   Params:
     invars: the tracers for the primitive inputs.
     outvars: the tracers for the primitive outputs.
     primitive: the primitive.
     params: the primitive params
-    subjaxpr: (optional) a sub-Jaxpr, used only for `xla_call` or `xla_pmap`.
-      If present, then `subjaxpr.invars` correspond to `invars.
   """
-  if subjaxpr is not None:
-    assert len(subjaxpr.constvars) == 0
-    assert len(subjaxpr.invars) == len(tuple(invars))
-    bound_subjaxpr = subjaxpr
-  else:
-    bound_subjaxpr = None
-
+  if primitive.call_primitive:
+    # TODO(necula): move these checks to core.check_jaxpr, and call it
+    # in more places.
+    assert "call_jaxpr" in params
   return JaxprEqnRecipe(object(), tuple(invars), map(ref, outvars), primitive,
-                        bound_subjaxpr, params)
+                        params)
+
 
 def recipe_to_eqn(unused_var, getvar, recipe):
-  _, in_tracers, out_tracer_refs, primitive, bound_subjaxpr, params = recipe
+  _, in_tracers, out_tracer_refs, primitive, params = recipe
   out_tracers = [t_ref() for t_ref in out_tracer_refs]
   invars  = [getvar(t) for t in in_tracers]
   outvars = [unused_var() if t is None else getvar(t) for t in out_tracers]
-  return new_jaxpr_eqn(invars, outvars, primitive, bound_subjaxpr, params)
+  return new_jaxpr_eqn(invars, outvars, primitive, params)
 
 def tracers_to_jaxpr(in_tracers, out_tracers):
   """Constructs Jaxpr given tracers for inputs and outputs.
@@ -520,6 +513,7 @@ def _split_aval(unknown, aval):
 
 
 remat_call_p = core.Primitive('remat_call')
+remat_call_p.call_primitive = True
 remat_call = partial(core.call_bind, remat_call_p)
 remat_call_p.def_custom_bind(remat_call)
 remat_call_p.def_impl(core.call_impl)
@@ -593,10 +587,9 @@ def _remat_partial_eval(trace, f, tracers, params):
   const_tracers = map(trace.new_instantiated_const, consts)
   lifted_jaxpr = convert_constvars_jaxpr(typed_jaxpr.jaxpr)
   out_tracers = [JaxprTracer(trace, out_pval, None) for out_pval in out_pvals]
+  new_params = dict(params, call_jaxpr=lifted_jaxpr)
   eqn = new_eqn_recipe(tuple(it.chain(const_tracers, instantiated_tracers)),
-                       out_tracers, remat_call_p,
-                       params,
-                       subjaxpr=lifted_jaxpr)
+                       out_tracers, remat_call_p, new_params)
   for t in out_tracers: t.recipe = eqn
   return out_tracers
 call_partial_eval_rules[remat_call_p] = _remat_partial_eval

jax/interpreters/pxla.py

@@ -640,14 +640,16 @@ def execute_replicated(compiled, backend, in_handler, out_handler, *args):
 
 
 xla_pmap_p = core.Primitive('xla_pmap')
+xla_pmap_p.call_primitive = True
 xla_pmap_p.multiple_results = True
 xla_pmap = partial(core.call_bind, xla_pmap_p)
 xla_pmap_p.def_custom_bind(xla_pmap)
 xla_pmap_p.def_impl(xla_pmap_impl)
 
-def _pmap_translation_rule(c, jaxpr, axis_env,
+def _pmap_translation_rule(c, axis_env,
                            in_nodes, name_stack, axis_name, axis_size,
-                           global_axis_size, devices, name, backend=None,
+                           global_axis_size, devices, name,
+                           call_jaxpr, backend=None,
                            mapped_invars=None):
   # We in-line here rather than generating a Call HLO as in the xla_call
   # translation rule just because the extra tuple stuff is a pain.
@@ -662,7 +664,7 @@ def _pmap_translation_rule(c, jaxpr, axis_env,
     for in_node, in_node_mapped in zip(in_nodes, mapped_invars))
 
   sharded_outs = xla.jaxpr_subcomp(
-      c, jaxpr, backend, new_env, (),
+      c, call_jaxpr, backend, new_env, (),
       extend_name_stack(name_stack, wrap_name(name, 'pmap')), *in_nodes_sharded)
   outs = [_xla_unshard(c, new_env, shard) for shard in sharded_outs]
   return c.Tuple(*outs)