Fixes for PyTorch/XLA functionalization integration (#94537)

Fixes for PyTorch/XLA functionalization integration

---
Some notable changes include:
- More asserts in `FunctionalTensorWrapper`, so bugs show up more cleanly in cases where we e.g. forget to wrap an output
- Make the *_scatter ops `CompositeExplicitAutogradNonFunctional`, so we get a better error message and XLA doesn't accidentally try to us them
- Fix LTC/XLA codegen in core to handle multi-tensor out= ops with no returns
- Better erroring: Allow XLA to use the CPU fallback from core in a way so that it always errors on view ops, which XLA should no longer see.
- Update MetaConverter to exclude XLA tensors in raising NotImplemented…
- Add `_propagate_xla_data` op
- Add meta tensor support for some ops
Pull Request resolved: https://github.com/pytorch/pytorch/pull/94537
Approved by: https://github.com/bdhirsh

.github/ci_commit_pins/xla.txt

@@ -1 +1 @@
-503401a24e532a9019ef140199319221294045ee
+f9963f6c2d34b9662f93e5518adb15949be05f65

aten/src/ATen/FunctionalTensorWrapper.cpp

@@ -13,6 +13,7 @@
 #ifndef AT_PER_OPERATOR_HEADERS
 #include <ATen/Functions.h>
 #else
+#include <ATen/ops/_propagate_xla_data.h>
 #include <ATen/ops/_to_copy.h>
 #endif
 
@@ -51,6 +52,8 @@ FunctionalTensorWrapper::FunctionalTensorWrapper(const Tensor& value)
     ),
     value_(value)
 {
+  TORCH_INTERNAL_ASSERT(!at::functionalization::impl::isFunctionalTensor(value_));
+  TORCH_INTERNAL_ASSERT(!value_.key_set().has(c10::DispatchKey::Functionalize));
   set_constructor_metadata();
 }
 
@@ -130,6 +133,8 @@ FunctionalTensorWrapper::FunctionalTensorWrapper(const Tensor& view_value, const
     ),
     value_(view_value)
 {
+  TORCH_INTERNAL_ASSERT(!at::functionalization::impl::isFunctionalTensor(value_));
+  TORCH_INTERNAL_ASSERT(!value_.key_set().has(c10::DispatchKey::Functionalize));
   set_constructor_metadata();
   // Copy the original tensor's ViewMeta vector and push the current one.
   if (!base->view_metas_.empty()) {
@@ -168,7 +173,9 @@ void FunctionalTensorWrapper::mutate_view_meta(at::functionalization::ViewMeta m
   // So, these ops are special - they're mutation AND view ops. They get special codegen.
   // An example is transpose_, e.g. `a.transpose_()`
   // Calling transpose_() should ensure that a gets an alias, and append the new ViewMeta to a's current list of ViewMetas.
+  at::AutoDispatchSkipFunctionalize guard;
   value_ = meta.forward_fn(value_, meta.out_index);
+  TORCH_INTERNAL_ASSERT(!value_.key_set().has(c10::DispatchKey::Functionalize));
 }
 
 // Note [Functionalization: Mutation Removal]
@@ -200,15 +207,20 @@ void FunctionalTensorWrapper::replace_(const Tensor& other) {
   // TODO: going to need to change this if we want nested functionalize() transforms.
   TORCH_INTERNAL_ASSERT(!at::functionalization::impl::isFunctionalTensor(other));
   value_ = other;
+  TORCH_INTERNAL_ASSERT(!value_.key_set().has(c10::DispatchKey::Functionalize));
   // out= ops are allowed to resize the output tensors, mutating both the data and metadata of the tensor.
   // We need to propagate that metadata mutation to the wrapper (new size).
-  set_sizes_and_strides(value_.sym_sizes(), value_.sym_strides(), value_.sym_storage_offset());
+  auto sizes_ = value_.sym_sizes();
+  auto strides_ = value_.sym_strides();
+  auto storage_offset_ = value_.sym_storage_offset();
+  set_sizes_and_strides(sizes_, strides_, storage_offset_);
   if (dtype() != value_.unsafeGetTensorImpl()->dtype() || layout() != value_.unsafeGetTensorImpl()->layout()) {
     // .to() should not re-entrantly go through functionalization.
     at::AutoDispatchSkipFunctionalize guard;
     // and we want _to_copy() to show up in the graph, not the composite .to() operator
     // (this can happen if autograd has already run by the time we enter this code)
     value_ = at::_to_copy(value_, c10::TensorOptions().dtype(dtype()).layout(layout()));
+    TORCH_INTERNAL_ASSERT(!value_.key_set().has(c10::DispatchKey::Functionalize));
   }
 }
 
@@ -243,6 +255,7 @@ void FunctionalTensorWrapper::maybe_replace_storage(const Tensor& other) {
   // Then it's safe to throw out the old storage and replace it with the new, larger one.
   storage_ = c10::Storage(c10::make_intrusive<functionalization::FunctionalStorageImpl>(other));
   value_ = other;
+  TORCH_INTERNAL_ASSERT(!value_.key_set().has(c10::DispatchKey::Functionalize));
   generation_ = 0;
   // And update the metadata on the wrapper to reflect the new sizes and strides
   set_sizes_and_strides(value_.sizes(), value_.strides());
@@ -484,6 +497,24 @@ void replace_(const ITensorListRef functional_tensor, ITensorListRef other) {
   }
 }
 
+void propagate_xla_data(const Tensor& functional_tensor, const Tensor& other) {
+  TORCH_INTERNAL_ASSERT_DEBUG_ONLY(isFunctionalTensor(functional_tensor));
+  if (functional_tensor.key_set().has(c10::DispatchKey::XLA)) {
+    at::_propagate_xla_data(at::functionalization::impl::unsafeGetFunctionalWrapper(functional_tensor)
+        ->value(), other);
+  }
+}
+
+void propagate_xla_data(const ITensorListRef functional_tensor, ITensorListRef other) {
+  TORCH_INTERNAL_ASSERT_DEBUG_ONLY(functional_tensor.size() == other.size());
+  auto functional_tensor_it = functional_tensor.begin();
+  auto other_it = other.begin();
+  for (const auto i : c10::irange(functional_tensor.size())) {
+    (void)i; // Suppress unused variable warning
+    propagate_xla_data(*functional_tensor_it++, *other_it++);
+  }
+}
+
 void commit_update(const Tensor& functional_tensor) {
   TORCH_INTERNAL_ASSERT_DEBUG_ONLY(isFunctionalTensor(functional_tensor));
   unsafeGetFunctionalWrapper(functional_tensor)->commit_update();

aten/src/ATen/FunctionalTensorWrapper.h

@@ -224,6 +224,15 @@ TORCH_API void replace_(
 TORCH_API void commit_update(const Tensor& functional_tensor);
 TORCH_API void commit_update(ITensorListRef functional_tensor);
 
+// These two methods are XLA-specific logic and are no-ops
+// for the normal functionalization flow.
+TORCH_API void propagate_xla_data(
+    const Tensor& functional_tensor,
+    const Tensor& other);
+TORCH_API void propagate_xla_data(
+    const ITensorListRef functional_tensor,
+    ITensorListRef other);
+
 Tensor create_functional_tensor_with_view_meta(
     const Tensor& view_to_wrap,
     const Tensor& base,

aten/src/ATen/native/CPUFallback.cpp

@@ -65,7 +65,7 @@ c10::optional<c10::Device> compute_target_device(std::vector<at::Tensor>& t_args
 }
 
 
-void cpu_fallback(const c10::OperatorHandle& op, torch::jit::Stack* stack) {
+void cpu_fallback(const c10::OperatorHandle& op, torch::jit::Stack* stack, bool error_on_views) {
   auto& schema_args = op.schema().arguments();
   const auto num_arguments = schema_args.size();
   auto arguments = torch::jit::last(stack, num_arguments);
@@ -176,9 +176,15 @@ void cpu_fallback(const c10::OperatorHandle& op, torch::jit::Stack* stack) {
             } else {
                 dev_str << "<none>";
             }
-            TORCH_WARN(false, "The operator ", op.schema().operator_name(), " appears to be a view operator, ",
-                        "but it has no implementation for the backend \"", dev_str.str(), "\". View operators don't support ",
-                        "falling back to run on the CPU, since the tensor's storage cannot be shared across devices.");
+            if (error_on_views) {
+                TORCH_CHECK(false, "The operator ", op.schema().operator_name(), " appears to be a view operator, ",
+                            "but it has no implementation for the backend \"", dev_str.str(), "\". View operators don't support ",
+                            "falling back to run on the CPU, since the tensor's storage cannot be shared across devices.");
+            } else {
+                TORCH_WARN(false, "The operator ", op.schema().operator_name(), " appears to be a view operator, ",
+                            "but it has no implementation for the backend \"", dev_str.str(), "\". View operators don't support ",
+                            "falling back to run on the CPU, since the tensor's storage cannot be shared across devices.");
+            }
           }
           // Case (2): copy case. Copy the cpu output tensor to the original device.
 

aten/src/ATen/native/CPUFallback.h

@@ -11,7 +11,7 @@ namespace at { namespace native {
 
 // This function implements a boxed fallback to CPU.
 // External backends can add their own custom logging on top if it to customize their own CPU fallbacks.
-TORCH_API void cpu_fallback(const c10::OperatorHandle& op, torch::jit::Stack* stack);
+TORCH_API void cpu_fallback(const c10::OperatorHandle& op, torch::jit::Stack* stack, bool error_on_views = false);
 
 // This is a helper function that backends can use to directly call their boxed CPU fallback
 // TODO: update and add a usage example after https://github.com/pytorch/pytorch/pull/58092 lands.

aten/src/ATen/native/Copy.cpp

@@ -320,6 +320,10 @@ void copy_ignoring_overlaps(const TensorBase &dst, const TensorBase &src) {
   copy_stub(iter.device_type(), iter, /*non_blocking=*/false);
 }
 
+void _propagate_xla_data(const Tensor& input, const Tensor& output) {
+  TORCH_INTERNAL_ASSERT(input.device().type() == kXLA, "This op should only be called by XLA")
+}
+
 DEFINE_DISPATCH(copy_stub);
 
 } // namespace native

aten/src/ATen/native/native_functions.yaml

@@ -5091,7 +5091,7 @@
   device_check: NoCheck
   device_guard: False
   dispatch:
-    CompositeExplicitAutograd: slice_scatter
+    CompositeExplicitAutogradNonFunctional: slice_scatter
   autogen: slice_scatter.out
   tags: core
 
@@ -5100,7 +5100,7 @@
   device_check: NoCheck
   device_guard: False
   dispatch:
-    CompositeExplicitAutograd: select_scatter_symint
+    CompositeExplicitAutogradNonFunctional: select_scatter_symint
   autogen: select_scatter.out
 
 - func: diagonal_scatter(Tensor self, Tensor src, int offset=0, int dim1=0, int dim2=1) -> Tensor
@@ -5108,7 +5108,7 @@
   device_check: NoCheck
   device_guard: False
   dispatch:
-    CompositeExplicitAutograd: diagonal_scatter
+    CompositeExplicitAutogradNonFunctional: diagonal_scatter
   autogen: diagonal_scatter.out
 
 - func: as_strided_scatter(Tensor self, Tensor src, SymInt[] size, SymInt[] stride, SymInt? storage_offset=None) -> Tensor
@@ -5116,7 +5116,7 @@
   device_check: NoCheck
   device_guard: False
   dispatch:
-    CompositeExplicitAutograd: as_strided_scatter_symint
+    CompositeExplicitAutogradNonFunctional: as_strided_scatter_symint
   autogen: as_strided_scatter.out
 
 - func: smm(Tensor self, Tensor mat2) -> Tensor
@@ -14724,4 +14724,7 @@
   python_module: nn
   dispatch:
     CompositeExplicitAutograd: wait_tensor
+
+# This op is ONLY used by pytorch/XLA in functionalization, and should never show up in vanilla eager mode or in any pytorch tracing contexts.
+- func: _propagate_xla_data(Tensor input, Tensor output) -> ()
   variants: function

test/test_meta.py

@@ -1221,6 +1221,11 @@ class TestMeta(TestCase):
         r = torch.empty(2 ** 52, device='meta', dtype=torch.qint8)
         self.assertEqual(r.device.type, 'meta')
 
+    def test_nan_to_num(self):
+        t = torch.tensor([float('nan'), float('inf'), -float('inf'), 3.14], device='meta')
+        r = t.nan_to_num()
+        self.assertEqual(r.device.type, 'meta')
+
     @onlyCPU
     def test_meta_autograd_no_error(self):
         lib = torch.library.Library("meta_test", "DEF")

torch/_meta_registrations.py

@@ -2676,6 +2676,27 @@ def meta_upsample_bilinear2d_aa(
     )
 
 
+# From aten/src/ATen/native/cuda/AmpKernels.cu
+@register_meta(aten._amp_foreach_non_finite_check_and_unscale_.default)
+def _amp_foreach_non_finite_check_and_unscale_(self, found_inf, inv_scale):
+    check(found_inf.numel() == 1, lambda: "found_inf must be a 1-element tensor.")
+    check(inv_scale.numel() == 1, lambda: "inv_scale must be a 1-element tensor.")
+    check(
+        found_inf.dtype.is_floating_point, lambda: "found_inf must be a float tensor."
+    )
+    check(
+        inv_scale.dtype.is_floating_point, lambda: "inv_scale must be a float tensor."
+    )
+
+
+# From aten/src/ATen/native/UnaryOps.cpp
+@register_meta([aten.nan_to_num.default, aten.nan_to_num.out])
+@out_wrapper()
+def nan_to_num(self, nan=None, posinf=None, neginf=None):
+    result_size = list(self.size())
+    return self.new_empty(result_size)
+
+
 # We must also trigger meta registrations from PrimTorch ref
 # decompositions
 import torch._refs

torch/_subclasses/meta_utils.py

@@ -463,7 +463,7 @@ class MetaConverter:
             or (ignore_subclass and isinstance(t, torch.Tensor))
             or isinstance(t, FakeTensor)
         ):
-            if any(
+            if t.device.type != "xla" and any(
                 [
                     t.is_sparse_csr,
                     t.layout in [torch.sparse_csc, torch.sparse_bsr, torch.sparse_bsc],

torch/csrc/lazy/core/shape_inference.cpp

@@ -51,6 +51,7 @@
 
 #include <ATen/AccumulateType.h>
 #include <ATen/CompositeExplicitAutogradFunctions.h>
+#include <ATen/CompositeExplicitAutogradNonFunctionalFunctions.h>
 #include <ATen/Dispatch.h>
 #include <ATen/ExpandUtils.h>
 #include <ATen/Functions.h>
@@ -1304,7 +1305,7 @@ std::vector<Shape> compute_shape_select_scatter(
       /*layout=*/c10::make_optional(src.layout()),
       /*device=*/c10::make_optional(c10::Device(c10::kMeta)),
       /*pin_memory=*/c10::nullopt);
-  auto out_meta = at::compositeexplicitautograd::select_scatter(
+  auto out_meta = at::compositeexplicitautogradnonfunctional::select_scatter(
       self_meta, src_meta, dim, index);
   return {Shape(out_meta.scalar_type(), out_meta.sizes().vec())};
 }
@@ -1329,7 +1330,7 @@ std::vector<Shape> compute_shape_diagonal_scatter(
       /*layout=*/c10::make_optional(src.layout()),
       /*device=*/c10::make_optional(c10::Device(c10::kMeta)),
       /*pin_memory=*/c10::nullopt);
-  auto out_meta = at::compositeexplicitautograd::diagonal_scatter(
+  auto out_meta = at::compositeexplicitautogradnonfunctional::diagonal_scatter(
       self_meta, src_meta, offset, dim1, dim2);
   return {Shape(out_meta.scalar_type(), out_meta.sizes().vec())};
 }
@@ -1355,8 +1356,9 @@ std::vector<Shape> compute_shape_slice_scatter_symint(
       /*layout=*/c10::make_optional(src.layout()),
       /*device=*/c10::make_optional(c10::Device(c10::kMeta)),
       /*pin_memory=*/c10::nullopt);
-  auto out_meta = at::compositeexplicitautograd::slice_scatter_symint(
-      self_meta, src_meta, dim, start, end, step);
+  auto out_meta =
+      at::compositeexplicitautogradnonfunctional::slice_scatter_symint(
+          self_meta, src_meta, dim, start, end, step);
   return {Shape(out_meta.scalar_type(), out_meta.sizes().vec())};
 }
 
@@ -1380,8 +1382,9 @@ std::vector<Shape> compute_shape_as_strided_scatter_symint(
       /*layout=*/c10::make_optional(src.layout()),
       /*device=*/c10::make_optional(c10::Device(c10::kMeta)),
       /*pin_memory=*/c10::nullopt);
-  auto out_meta = at::compositeexplicitautograd::as_strided_scatter_symint(
-      self_meta, src_meta, size, stride, storage_offset);
+  auto out_meta =
+      at::compositeexplicitautogradnonfunctional::as_strided_scatter_symint(
+          self_meta, src_meta, size, stride, storage_offset);
   return {Shape(out_meta.scalar_type(), out_meta.sizes().vec())};
 }
 

torch/csrc/utils/tensor_new.cpp

@@ -432,6 +432,7 @@ Tensor internal_new_from_data(
   // to dispatch to it.
   // TODO: arguably it should have an autograd implementation that noops
   at::AutoDispatchBelowADInplaceOrView guard;
+
   return at::lift_fresh(tensor);
 }
 

torchgen/dest/register_dispatch_key.py

@@ -323,10 +323,21 @@ class RegisterDispatchKey:
                 for i, ret_name in enumerate(return_names)
             )
             returns = f'{sig.returns_type().cpp_type()}({", ".join(return_names)})'
-        else:
+        elif len(return_names) == 1:
             ret_name = return_names[0]
             updates = f"{copy_op}({func_res}, {ret_name});"
             returns = ret_name
+        else:
+            assert len(f.func.arguments.out) == 1
+            returns = ""
+            out_arg = f.func.arguments.out[0]
+            if out_arg.type.is_list_like():
+                updates = f"""\
+    for (int64_t i = 0; i < {func_res}.size(); ++i) {{
+        {copy_op}({func_res}[i], {out_arg.name}[i]);
+    }}"""
+            else:
+                updates = f"{copy_op}({func_res}, {out_arg.name});"
 
         functional_sig = self.wrapper_kernel_sig(g.functional)
         wrapper_name = sig.name()

torchgen/gen_functionalization_type.py

@@ -499,6 +499,7 @@ def wrap_propagate_mutations_and_return(
     ):
         updates.append(
             f"""\
+  at::functionalization::impl::propagate_xla_data({outer_arg}, {inner_ret});
   at::functionalization::impl::replace_({outer_arg}, {inner_ret});
   at::functionalization::impl::commit_update({outer_arg});
   at::functionalization::impl::sync({outer_arg});"""
@@ -541,6 +542,11 @@ def emit_inplace_functionalization_body(
         for a in f.func.arguments.flat_all
         if a.type.is_tensor_like() and a.annotation is None
     ]
+    non_mutated_tensor_names = [
+        a.name
+        for a in f.func.arguments.flat_all
+        if a.type == BaseType(BaseTy.Tensor) and a.annotation is None
+    ]
     # all mutable inputs must be functional tensors in order to participate in functionalization
     check_all_mutated_args_are_functional = " && ".join(
         ["true"]
@@ -556,6 +562,14 @@ def emit_inplace_functionalization_body(
             for a in non_mutated_names
         ]
     )
+
+    check_any_non_mutated_tensors_are_xla = " || ".join(
+        ["false"]
+        + [
+            f"{a}.device().type() == c10::DeviceType::XLA"
+            for a in non_mutated_tensor_names
+        ]
+    )
     # These are used in the cases where we don't functionalize and redispatch to the inplace op
     # case 1: we hit an inplace op that doesn't have an out-of-place equivalent
     # case 2: we hit an inplace ops but our inputs are not functional tensors (in which case our kernel just no-ops)
@@ -619,7 +633,9 @@ def emit_inplace_functionalization_body(
       }}
       {unwrap_tensor_args_str}
       if (!({check_all_mutated_args_are_functional})) {{
-        if (({check_any_non_mutated_args_are_functional})) {{
+        // We want to disable this check if there are any XLA tensors.
+        // cpu_tensor.copy_(xla_tensor) is valid code.
+        if (!({check_any_non_mutated_tensors_are_xla}) && ({check_any_non_mutated_args_are_functional})) {{
          // case 1: trying to mutate a non functional tensor with a functional tensor is an error
          TORCH_INTERNAL_ASSERT(false,
            "mutating a non-functional tensor with a functional tensor is not allowed.",