[llvm] [SYCL] Add platform enumeration and info query using liboffload (PR #166927)

[Andrei Elovikov via llvm-commits]

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@@ -0,0 +1,70 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// This file contains the declaration of the SYCL enum class backend that is
+/// implementation-defined and is populated with a unique identifier for each
+/// SYCL backend that the SYCL implementation can support.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBSYCL___IMPL_BACKEND_HPP
+#define _LIBSYCL___IMPL_BACKEND_HPP
+
+#include <sycl/__impl/detail/config.hpp>
+
+#include <string_view>
+#include <type_traits>
+
+_LIBSYCL_BEGIN_NAMESPACE_SYCL
+
+// 4.1. Backends
+enum class backend : char {
+  opencl = 1,
+  level_zero = 2,
+  cuda = 3,
+  hip = 4,
+  all = 5,
+};
+
+namespace detail {
+template <typename T> struct is_backend_info_desc : std::false_type {};
+} // namespace detail
+
+// 4.5.1.1. Type traits backend_traits
+template <backend Backend> class backend_traits;
+
+template <backend Backend, typename SYCLObjectT>
+using backend_input_t =
+    typename backend_traits<Backend>::template input_type<SYCLObjectT>;
+template <backend Backend, typename SYCLObjectT>
+using backend_return_t =
+    typename backend_traits<Backend>::template return_type<SYCLObjectT>;
+
+namespace detail {
+inline std::string_view get_backend_name(const backend &Backend) {
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aelovikov-intel wrote:

I think we need to use something like `_LIBCPP_HIDE_FROM_ABI` here, if I understand the idea behind it correctly.

https://github.com/llvm/llvm-project/pull/166927