Making batching rule for F.embedding DTensor-aware (#162117)

`vmap(F.embedding)(DTensor, DTensor)` was failing because F.embedding's
batching rule generates a new tensor via at::arange, at::arange
generates a regular tensor, and DTensor rightfully errors on mixed
DTensor-regular Tensor operations.

This PR fixes the problem by activating DTensor implicit replication on
just the at::arange and the subsequent add operation.

In order to accomplish this I move the DTensor implicit replication flag
to C++ (most batching rules are in C++).

Test Plan:
- new test

Pull Request resolved: https://github.com/pytorch/pytorch/pull/162117
Approved by: https://github.com/bdhirsh

aten/src/ATen/DTensorState.cpp

@@ -0,0 +1,17 @@
+#include <ATen/DTensorState.h>
+
+namespace at {
+
+namespace {
+thread_local bool kDTensorAllowImplicitReplication = false;
+}
+
+bool get_dtensor_allow_implicit_replication() {
+  return kDTensorAllowImplicitReplication;
+}
+
+void set_dtensor_allow_implicit_replication(bool enabled) {
+  kDTensorAllowImplicitReplication = enabled;
+}
+
+} // namespace at

aten/src/ATen/DTensorState.h

@@ -0,0 +1,34 @@
+#pragma once
+
+#include <c10/macros/Macros.h>
+
+namespace at {
+
+TORCH_API bool get_dtensor_allow_implicit_replication();
+TORCH_API void set_dtensor_allow_implicit_replication(bool enabled);
+
+struct DTensorAllowImplicitReplication {
+  DTensorAllowImplicitReplication()
+      : prev_dtensor_allow_implicit_replication_(
+            get_dtensor_allow_implicit_replication()) {
+    set_dtensor_allow_implicit_replication(true);
+  }
+
+  DTensorAllowImplicitReplication(const DTensorAllowImplicitReplication&) =
+      delete;
+  DTensorAllowImplicitReplication& operator=(
+      const DTensorAllowImplicitReplication&) = delete;
+  DTensorAllowImplicitReplication(DTensorAllowImplicitReplication&&) = delete;
+  DTensorAllowImplicitReplication& operator=(
+      DTensorAllowImplicitReplication&&) = delete;
+
+  ~DTensorAllowImplicitReplication() {
+    set_dtensor_allow_implicit_replication(
+        prev_dtensor_allow_implicit_replication_);
+  }
+
+ private:
+  bool prev_dtensor_allow_implicit_replication_;
+};
+
+} // namespace at

aten/src/ATen/ThreadLocalState.cpp

@@ -8,6 +8,7 @@
 #include <ATen/record_function.h>
 #include <ATen/SavedTensorHooks.h>
 #include <ATen/FunctionalTensorWrapper.h>
+#include <ATen/DTensorState.h>
 
 namespace at {
 
@@ -19,6 +20,7 @@ ThreadLocalState::ThreadLocalState()
       torch_dispatch_mode_state_(c10::impl::TorchDispatchModeTLS::get_state()), python_dispatcher_state_(c10::impl::PythonDispatcherTLS::get_state()),
       python_torch_function_state_(at::impl::PythonTorchFunctionTLS::get_state()),
       saved_tensors_default_hooks_state_(at::SavedTensorDefaultHooks::get_tls_state()), functionalization_reapply_views_state_(at::functionalization::impl::getFunctionalizationReapplyViewsTLS()),
+      dtensor_allow_implicit_replication_(at::get_dtensor_allow_implicit_replication()),
       saved_objects_(at::impl::ThreadLocalPythonObjects::get_state()) {
 #if !defined(CAFFE2_IS_XPLAT_BUILD) && !defined(C10_MOBILE) && !defined(BUILD_LITE_INTERPRETER)
   for(size_t i=0; i<autocast_dtypes_.size(); i++) {
@@ -52,6 +54,8 @@ void ThreadLocalState::setThreadLocalState(
 
   c10::impl::PythonDispatcherTLS::set_state(state.python_dispatcher_state_);
 
+  at::set_dtensor_allow_implicit_replication(state.dtensor_allow_implicit_replication_);
+
   c10::ThreadLocalDebugInfo::_forceCurrentDebugInfo(state.debug_info_);
 
   c10::impl::_force_tls_local_dispatch_key_set(state.dispatch_key_);

aten/src/ATen/ThreadLocalState.h

@@ -75,6 +75,8 @@ class TORCH_API ThreadLocalState {
 
   bool functionalization_reapply_views_state_;
 
+  bool dtensor_allow_implicit_replication_;
+
   // TLS for arbitrary python objects that is registered via hooks
   at::impl::ThreadLocalPythonObjects saved_objects_;
 

aten/src/ATen/functorch/BatchRulesModules.cpp

@@ -7,6 +7,7 @@
 #include <ATen/functorch/BatchRulesHelper.h>
 #include <ATen/functorch/PlumbingHelper.h>
 #include <ATen/core/dispatch/Dispatcher.h>
+#include <ATen/DTensorState.h>
 
 #include <utility>
 
@@ -44,8 +45,13 @@ static std::tuple<Tensor, std::optional<int64_t>> embedding_batch_rule(
   const auto weight_ = reshape_dim_into(*weight_bdim, 0, weight);
   auto indices_ = moveBatchDimToFront(indices, indices_bdim);
 
+  {
+    // getStepTensor returns a regular Tensor. If indices_ is a DTensor
+    // we want to allow this mixed DTensor-Tensor operation.
+    at::DTensorAllowImplicitReplication guard;
     const auto range = getStepTensor(indices, batch_size, num_embeddings);
     indices_ = indices_ + range;
+  }
   auto result = at::embedding_symint(weight_, indices_, std::move(padding_idx), scale_grad_by_freq, sparse);
   return std::make_tuple(std::move(result), 0);
 }

build_variables.bzl

@@ -1088,6 +1088,7 @@ aten_cpu_source_non_codegen_list = [
     "aten/src/ATen/DeviceAccelerator.cpp",
     "aten/src/ATen/Context.cpp",
     "aten/src/ATen/DLConvertor.cpp",
+    "aten/src/ATen/DTensorState.cpp",
     "aten/src/ATen/EmptyTensor.cpp",
     "aten/src/ATen/ExpandUtils.cpp",
     "aten/src/ATen/CachedTensorUtils.cpp",

test/distributed/tensor/test_dtensor.py

@@ -848,6 +848,30 @@ class DTensorMeshTest(DTensorTestBase):
             self.assertEqual(local_shard.shape, (4, 3))
             self.assertEqual(local_shard, torch.ones(4, 3) + torch.ones(3))
 
+    @with_comms
+    def test_vmap_embedding(self):
+        mesh = self.build_device_mesh()
+        batch_size, seq_len = 2, 6
+        output_dim = 32
+
+        indices = torch.zeros(*(batch_size, seq_len), dtype=torch.int64)
+        indices[0, 1] = 1
+        indices[1, 3] = 1
+        indices[1, 5] = 1
+        indices = DTensor.from_local(indices, mesh, [Shard(0)])
+
+        emb = torch.randn(
+            *(batch_size, 8, output_dim),
+            dtype=torch.float32,
+        )
+        emb = DTensor.from_local(emb, mesh, [Shard(0)])
+        result = torch.vmap(F.embedding)(indices, emb)
+        expected = [F.embedding(indices[i], emb[i]) for i in range(batch_size)]
+        expected = torch.stack(expected)
+        local_result = result.to_local()
+        local_expected = expected.to_local()
+        self.assertEqual(local_result, local_expected)
+
     @with_comms
     def test_auto_implicit_replication(self):
         mesh = self.build_device_mesh()

torch/_C/__init__.pyi.in

@@ -1852,6 +1852,9 @@ class _SetExcludeDispatchKeyGuard:
     def __enter__(self): ...
     def __exit__(self, *exc_info: object) -> None: ...
 
+def _get_dtensor_allow_implicit_replication() -> _bool: ...
+def _set_dtensor_allow_implicit_replication(value: _bool) -> None: ...
+
 # Defined in torch/csrc/utils/schema_info.h
 
 class _SchemaInfo:

torch/csrc/utils/python_dispatch.cpp

@@ -2,6 +2,7 @@
 #include <torch/csrc/utils/python_dispatch.h>
 
 #include <ATen/ATen.h>
+#include <ATen/DTensorState.h>
 #include <ATen/FuncTorchTLS.h>
 #include <ATen/FunctionalTensorWrapper.h>
 #include <ATen/TensorSubclassLikeUtils.h>
@@ -1045,6 +1046,13 @@ void initDispatchBindings(PyObject* module) {
   m.def("_only_lift_cpu_tensors", &torch::utils::only_lift_cpu_tensors);
   m.def("_set_only_lift_cpu_tensors", &torch::utils::set_only_lift_cpu_tensors);
 
+  m.def(
+      "_get_dtensor_allow_implicit_replication",
+      &at::get_dtensor_allow_implicit_replication);
+  m.def(
+      "_set_dtensor_allow_implicit_replication",
+      &at::set_dtensor_allow_implicit_replication);
+
   using c10::impl::TorchDispatchModeKey;
   py::enum_<TorchDispatchModeKey>(m, "_TorchDispatchModeKey")
       .value("FUNCTIONAL", TorchDispatchModeKey::FUNCTIONAL)

torch/distributed/tensor/_dispatch.py

@@ -125,7 +125,13 @@ class OpDispatcher:
     # as implicitly replicated or we throw error to user.
     # NOTE: It is EXTREMELY UNSAFE to turn this flag on by default so we intentionally leave
     # it as False by default.
-        self._allow_implicit_replication = False
+    @property
+    def _allow_implicit_replication(self) -> bool:
+        return torch._C._get_dtensor_allow_implicit_replication()
+
+    @_allow_implicit_replication.setter
+    def _allow_implicit_replication(self, value: bool) -> None:
+        return torch._C._set_dtensor_allow_implicit_replication(value)
 
     def dispatch(
         self,