Move UndefinedTensorImpl to c10 (meh) (#14817)

Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/14817

unfortunately, we still need this.

Reviewed By: ezyang

Differential Revision: D13348041

fbshipit-source-id: e8dcc89f5c71bd1ea2c9813990dac6e58e63b1fd

2 files changed, 74 insertions, 0 deletions

diff --git a/c10/core/UndefinedTensorImpl.cpp b/c10/core/UndefinedTensorImpl.cpp
new file mode 100644
index 0000000000..2e2265397e
--- /dev/null
+++ b/c10/core/UndefinedTensorImpl.cpp
@@ -0,0 +1,40 @@
+#include <c10/core/UndefinedTensorImpl.h>
+#include <c10/util/Exception.h>
+
+namespace c10 {
+
+// should this use the globalContext?  Can it get a context passed in somehow?
+UndefinedTensorImpl::UndefinedTensorImpl()
+: TensorImpl(UndefinedTensorId(), caffe2::TypeMeta(), nullptr, /* is variable */ false) {
+}
+
+IntList UndefinedTensorImpl::sizes() const {
+  AT_ERROR("sizes() called on undefined Tensor");
+}
+
+int64_t UndefinedTensorImpl::size(int64_t d) const {
+  AT_ERROR("size(dim) called on an undefined Tensor");
+}
+
+int64_t UndefinedTensorImpl::stride(int64_t d) const {
+  AT_ERROR("stride(dim) called on an undefined Tensor");
+}
+
+int64_t UndefinedTensorImpl::dim() const {
+  AT_ERROR("dim() called on undefined Tensor");
+}
+
+const Storage& UndefinedTensorImpl::storage() const {
+  AT_ERROR("storage() called on undefined Tensor");
+}
+
+int64_t UndefinedTensorImpl::storage_offset() const {
+  AT_ERROR("storage_offset() called on an undefined Tensor");
+}
+
+IntList UndefinedTensorImpl::strides() const {
+  AT_ERROR("strides() called on undefined Tensor");
+}
+UndefinedTensorImpl UndefinedTensorImpl::_singleton;
+
+}
diff --git a/c10/core/UndefinedTensorImpl.h b/c10/core/UndefinedTensorImpl.h
new file mode 100644
index 0000000000..5d268b7b82
--- /dev/null
+++ b/c10/core/UndefinedTensorImpl.h
@@ -0,0 +1,34 @@
+#pragma once
+
+#include <c10/core/TensorImpl.h>
+
+namespace c10 {
+
+struct C10_API UndefinedTensorImpl final : public TensorImpl {
+ public:
+  // Without this, we get:
+  //  error: identifier "at::UndefinedTensorImpl::_singleton" is undefined in device code
+  // (ostensibly because the constexpr tricks MSVC into trying to compile this
+  // function for device as well).
+#ifdef _WIN32
+  static inline TensorImpl * singleton() {
+#else
+  static constexpr inline TensorImpl * singleton() {
+#endif
+    return &_singleton;
+  }
+  IntList sizes() const override;
+  IntList strides() const override;
+  int64_t size(int64_t d) const override;
+  int64_t stride(int64_t d) const override;
+  int64_t dim() const override;
+  const Storage& storage() const override;
+  int64_t storage_offset() const override;
+private:
+  UndefinedTensorImpl();
+  static UndefinedTensorImpl _singleton;
+public:
+  friend struct UndefinedType;
+};
+
+} // namespace c10