[SYCL] Add libsycl, a SYCL RT library implementation project (#144372)

This patch introduces libsycl, a SYCL runtime library implementation, as
a top-level LLVM runtime project.
SYCL spec:
https://registry.khronos.org/SYCL/specs/sycl-2020/html/sycl-2020.html

Commit contains the basic folder layout and CMake infrastructure to
build a dummy SYCL library.

This is part of the SYCL support upstreaming effort. The relevant RFCs
can be found here:


https://discourse.llvm.org/t/rfc-add-full-support-for-the-sycl-programming-model/74080
https://discourse.llvm.org/t/rfc-sycl-runtime-upstreaming/74479

Upcoming PRs:
- UR offloading library fetch & build 
- partial implementation of sycl::platform: requires offloading layer,
requires classes for backend loading & enumeration.

---------

Signed-off-by: Tikhomirova, Kseniya <kseniya.tikhomirova@intel.com>
Co-authored-by: Alexey Bader <alexey.bader@intel.com>

14 files changed, 814 insertions, 0 deletions

diff --git a/libsycl/.clang-format b/libsycl/.clang-format
new file mode 100644
index 000000000000..24550f8b339e
--- /dev/null
+++ b/libsycl/.clang-format
@@ -0,0 +1,4 @@
+BasedOnStyle: LLVM
+
+# Preferred indentions of preprocessor statements.
+IndentPPDirectives: AfterHash
diff --git a/libsycl/.clang-tidy b/libsycl/.clang-tidy
new file mode 100644
index 000000000000..cdc7a2981a41
--- /dev/null
+++ b/libsycl/.clang-tidy
@@ -0,0 +1,17 @@
+Checks: >
+  -*,
+  clang-analyzer-*,
+  clang-diagnostic-*,
+  cppcoreguidelines-*,
+  -cppcoreguidelines-pro-bounds-array-to-pointer-decay,
+  -cppcoreguidelines-pro-bounds-constant-array-index,
+  -cppcoreguidelines-pro-bounds-pointer-arithmetic,
+  -cppcoreguidelines-pro-type-member-init,
+  -cppcoreguidelines-pro-type-union-access,
+  google-*,
+  -google-build-using-namespace,
+  -google-explicit-constructor,
+  -google-runtime-references,
+  misc-*,
+  -misc-macro-parentheses,
+  -misc-unused-parameters
diff --git a/libsycl/CMakeLists.txt b/libsycl/CMakeLists.txt
new file mode 100644
index 000000000000..fe08a4249bad
--- /dev/null
+++ b/libsycl/CMakeLists.txt
@@ -0,0 +1,126 @@
+#===============================================================================
+# Setup Project
+#===============================================================================
+cmake_minimum_required(VERSION 3.20.0)
+
+set(LLVM_SUBPROJECT_TITLE "libsycl")
+
+set(LIBSYCL_SOURCE_DIR  ${CMAKE_CURRENT_SOURCE_DIR})
+set(LIBSYCL_BINARY_DIR  ${CMAKE_CURRENT_BINARY_DIR})
+
+set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_CXX_STANDARD_REQUIRED YES)
+set(CMAKE_CXX_EXTENSIONS OFF)
+
+#===============================================================================
+# Limitations
+#===============================================================================
+
+if (CMAKE_SYSTEM_NAME STREQUAL Windows AND NOT MSVC)
+# Build with other compilers is not configured, not guaranteed and not tested.
+    message(FATAL_ERROR
+      "When compiling for Windows, libsycl requires a"
+      " version of Microsoft Visual C++ or another compiler"
+      " that uses the Visual C++ cl command-line syntax.")
+endif()
+
+#===============================================================================
+# Setup CMake Options
+#===============================================================================
+
+option(LIBSYCL_ENABLE_WERROR "Treat all warnings as errors in the libsycl project" OFF)
+option(LIBSYCL_ENABLE_PEDANTIC "Compile with pedantic enabled." OFF)
+
+#===============================================================================
+# Configure System
+#===============================================================================
+
+set_property(GLOBAL PROPERTY USE_FOLDERS ON)
+
+set(LIBSYCL_SHARED_OUTPUT_NAME "sycl" CACHE STRING "Output name for the shared libsycl runtime library.")
+
+if(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR AND NOT APPLE)
+  set(LIBSYCL_TARGET_SUBDIR ${LLVM_DEFAULT_TARGET_TRIPLE})
+  if(LIBSYCL_LIBDIR_SUBDIR)
+    string(APPEND LIBSYCL_TARGET_SUBDIR /${LIBSYCL_LIBDIR_SUBDIR})
+  endif()
+  cmake_path(NORMAL_PATH LIBSYCL_TARGET_SUBDIR)
+  set(LIBSYCL_LIBRARY_DIR ${LLVM_LIBRARY_OUTPUT_INTDIR}/${LIBSYCL_TARGET_SUBDIR})
+  set(LIBSYCL_INSTALL_LIBRARY_DIR lib${LLVM_LIBDIR_SUFFIX}/${LIBSYCL_TARGET_SUBDIR} CACHE STRING
+      "Path where built libsycl libraries should be installed.")
+  unset(LIBSYCL_TARGET_SUBDIR)
+else()
+  if(LLVM_LIBRARY_OUTPUT_INTDIR)
+    set(LIBSYCL_LIBRARY_DIR ${LLVM_LIBRARY_OUTPUT_INTDIR})
+  else()
+    set(LIBSYCL_LIBRARY_DIR ${CMAKE_BINARY_DIR}/lib${LIBSYCL_LIBDIR_SUFFIX})
+  endif()
+  set(LIBSYCL_INSTALL_LIBRARY_DIR lib${LIBSYCL_LIBDIR_SUFFIX} CACHE STRING
+      "Path where built libsycl libraries should be installed.")
+endif()
+
+set(LIBSYCL_INCLUDE_DIR include)
+set(LIBSYCL_BUILD_INCLUDE_DIR ${LLVM_BINARY_DIR}/${LIBSYCL_INCLUDE_DIR})
+set(LIBSYCL_SOURCE_INCLUDE_DIR ${CMAKE_CURRENT_SOURCE_DIR}/include)
+
+set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${LIBSYCL_LIBRARY_DIR})
+set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${LIBSYCL_LIBRARY_DIR})
+set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${LIBSYCL_LIBRARY_DIR})
+
+set(LIBSYCL_MAJOR_VERSION 0)
+set(LIBSYCL_MINOR_VERSION 1)
+set(LIBSYCL_PATCH_VERSION 0)
+set(LIBSYCL_VERSION_STRING "${LIBSYCL_MAJOR_VERSION}.${LIBSYCL_MINOR_VERSION}.${LIBSYCL_PATCH_VERSION}")
+set(LIBSYCL_ABI_NAMESPACE "__V${LIBSYCL_MAJOR_VERSION}" CACHE STRING
+    "The inline ABI namespace used by libsycl. It defaults to __Vn where `n` is the current ABI version.")
+if (NOT LIBSYCL_ABI_NAMESPACE MATCHES "__V.*")
+   message(FATAL_ERROR "LIBSYCL_ABI_NAMESPACE must be a reserved identifier, got '${LIBSYCL_ABI_NAMESPACE}'.")
+endif()
+
+#===============================================================================
+# Setup build & install rules
+#===============================================================================
+
+# Generate headers
+configure_file("${LIBSYCL_SOURCE_DIR}/src/version.hpp.in" "${LIBSYCL_BUILD_INCLUDE_DIR}/sycl/__impl/version.hpp")
+
+# Install generated headers.
+install(FILES
+  "${LIBSYCL_BUILD_INCLUDE_DIR}/sycl/__impl/version.hpp"
+  DESTINATION "${LIBSYCL_INCLUDE_DIR}/sycl/__impl"
+  COMPONENT sycl-headers)
+
+# This is a workaround to detect changes (add or modify) in subtree which
+# are not detected by copy_directory command.
+file(GLOB_RECURSE HEADERS_IN_SYCL_DIR CONFIGURE_DEPENDS "${LIBSYCL_SOURCE_INCLUDE_DIR}/sycl/*")
+file(GLOB_RECURSE HEADERS_IN_CL_DIR CONFIGURE_DEPENDS "${LIBSYCL_SOURCE_INCLUDE_DIR}/CL/*")
+
+string(REPLACE "${LIBSYCL_SOURCE_INCLUDE_DIR}" "${LIBSYCL_BUILD_INCLUDE_DIR}"
+  OUT_HEADERS_IN_SYCL_DIR "${HEADERS_IN_SYCL_DIR}")
+string(REPLACE "${LIBSYCL_SOURCE_INCLUDE_DIR}/CL" "${LIBSYCL_BUILD_INCLUDE_DIR}/CL"
+  OUT_HEADERS_IN_CL_DIR "${HEADERS_IN_CL_DIR}")
+
+# Copy SYCL headers from sources to build directory
+add_custom_target(sycl-headers
+  DEPENDS ${OUT_HEADERS_IN_SYCL_DIR}
+          ${OUT_HEADERS_IN_CL_DIR})
+
+add_custom_command(
+  OUTPUT  ${OUT_HEADERS_IN_SYCL_DIR}
+          ${OUT_HEADERS_IN_CL_DIR}
+  DEPENDS ${HEADERS_IN_SYCL_DIR}
+          ${HEADERS_IN_CL_DIR}
+  COMMAND ${CMAKE_COMMAND} -E copy_directory ${LIBSYCL_SOURCE_INCLUDE_DIR}/sycl ${LIBSYCL_BUILD_INCLUDE_DIR}/sycl
+  COMMAND ${CMAKE_COMMAND} -E copy_directory ${LIBSYCL_SOURCE_INCLUDE_DIR}/CL ${LIBSYCL_BUILD_INCLUDE_DIR}/CL
+  COMMENT "Copying SYCL headers...")
+
+install(DIRECTORY "${LIBSYCL_SOURCE_INCLUDE_DIR}/sycl" DESTINATION ${LIBSYCL_INCLUDE_DIR} COMPONENT sycl-headers)
+install(DIRECTORY "${LIBSYCL_SOURCE_INCLUDE_DIR}/CL" DESTINATION ${LIBSYCL_INCLUDE_DIR} COMPONENT sycl-headers)
+
+set(LIBSYCL_RT_LIBS ${LIBSYCL_SHARED_OUTPUT_NAME})
+
+add_subdirectory(src)
+
+add_custom_target(libsycl-runtime-libraries
+  DEPENDS ${LIBSYCL_RT_LIBS}
+)
diff --git a/libsycl/LICENSE.txt b/libsycl/LICENSE.txt
new file mode 100644
index 000000000000..5715176572a4
--- /dev/null
+++ b/libsycl/LICENSE.txt
@@ -0,0 +1,278 @@
+==============================================================================
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diff --git a/libsycl/README.md b/libsycl/README.md
new file mode 100644
index 000000000000..9fed3fdc4efa
--- /dev/null
+++ b/libsycl/README.md
@@ -0,0 +1,20 @@
+## SYCL runtime library
+
+The libsycl subproject is an implementation of the SYCL runtime library as defined by the
+[SYCL 2020 specification](https://registry.khronos.org/SYCL/specs/sycl-2020/html/sycl-2020.html).
+
+Subproject documentation is available at: [SYCL RT documentation](./docs).
+
+libsycl runtime library and headers require C++17 support or higher.
+
+### How to use libsycl with Clang
+
+TODO
+
+#### How to build
+
+TODO
+
+# License
+
+See [LICENSE](./LICENSE.TXT) for details.
diff --git a/libsycl/docs/index.rst b/libsycl/docs/index.rst
new file mode 100644
index 000000000000..78e76e73284d
--- /dev/null
+++ b/libsycl/docs/index.rst
@@ -0,0 +1,79 @@
+=====================
+SYCL runtime implementation
+=====================
+
+.. contents::
+   :local:
+
+.. _index:
+
+Current Status
+========
+
+The implementation is in the very early stages of upstreaming. The first milestone is to get
+support for a simple SYCL application with device code using Unified Shared Memory:
+
+.. code-block:: c++
+
+   #include <sycl/sycl.hpp>
+   
+   class TestKernel;
+   
+   int main() {
+     sycl::queue q;
+   
+     const size_t dataSize = 32;
+     int *dataPtr = sycl::malloc_shared<int>(32, q);
+     for (int i = 0; i < dataSize; ++i)
+       dataPtr[i] = 0;
+   
+     q.submit([&](sycl::handler &cgh) {
+       cgh.parallel_for<TestKernel>(
+           sycl::range<1>(dataSize),
+           [=](sycl::id<1> idx) { dataPtr[idx] = idx[0]; });
+     });
+     q.wait();
+   
+     bool error = false;
+     for (int i = 0; i < dataSize; ++i)
+       if (dataPtr[i] != i) error = true;
+   
+     free(dataPtr, q);
+   
+     return error;
+   }
+
+This requires at least partial support of the following functionality on the libsycl side:
+  * ``sycl::platform`` class
+  * ``sycl::device`` class
+  * ``sycl::context`` class
+  * ``sycl::queue`` class
+  * ``sycl::handler`` class
+  * ``sycl::id`` and ``sycl::range`` classes
+  * Unified shared memory allocation/deallocation
+  * Program manager, an internal component for retrieving and using device images from the multi-architectural binaries
+
+Build steps
+========
+
+To build LLVM with libsycl runtime enabled the following script can be used.
+
+.. code-block:: console
+
+  #!/bin/sh
+
+  build_llvm=`pwd`/build-llvm
+  installprefix=`pwd`/install
+  llvm=`pwd`
+  mkdir -p $build_llvm
+  mkdir -p $installprefix
+
+  cmake -G Ninja -S $llvm/llvm -B $build_llvm \
+        -DLLVM_ENABLE_PROJECTS="clang;clang-tools-extra" \
+        -DLLVM_INSTALL_UTILS=ON \
+        -DCMAKE_INSTALL_PREFIX=$installprefix \
+        -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi;libsycl;libunwind" \
+        -DCMAKE_BUILD_TYPE=Release
+
+  ninja -C $build_llvm install
+  
\ No newline at end of file
diff --git a/libsycl/include/CL/sycl.hpp b/libsycl/include/CL/sycl.hpp
new file mode 100644
index 000000000000..7c5de5700c65
--- /dev/null
+++ b/libsycl/include/CL/sycl.hpp
@@ -0,0 +1,30 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 is a SYCL 1.2.1 standard header file. Deprecated.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBSYCL_CL_SYCL_HPP
+#define _LIBSYCL_CL_SYCL_HPP
+
+#if defined(__clang__)
+#  pragma clang diagnostic push
+#  pragma clang diagnostic ignored "-Wpedantic"
+#  warning "CL/sycl.hpp is deprecated, use sycl/sycl.hpp"
+#  pragma clang diagnostic pop
+#endif
+
+#include <sycl/sycl.hpp>
+
+namespace cl {
+namespace sycl = ::sycl;
+}
+
+#endif // _LIBSYCL_CL_SYCL_HPP
diff --git a/libsycl/include/sycl/__impl/detail/config.hpp b/libsycl/include/sycl/__impl/detail/config.hpp
new file mode 100644
index 000000000000..cc9059762af1
--- /dev/null
+++ b/libsycl/include/sycl/__impl/detail/config.hpp
@@ -0,0 +1,59 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 macros defining attributes for
+/// exported methods and defining API namespaces.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBSYCL___IMPL_DETAIL_CONFIG_HPP
+#define _LIBSYCL___IMPL_DETAIL_CONFIG_HPP
+
+#include <sycl/__impl/version.hpp>
+
+#define _LIBSYCL_BEGIN_UNVERSIONED_NAMESPACE_SYCL namespace sycl {
+#define _LIBSYCL_END_UNVERSIONED_NAMESPACE_SYCL }
+
+#define _LIBSYCL_BEGIN_NAMESPACE_SYCL                                          \
+  _LIBSYCL_BEGIN_UNVERSIONED_NAMESPACE_SYCL inline namespace _LIBSYCL_ABI_NAMESPACE {
+#define _LIBSYCL_END_NAMESPACE_SYCL                                            \
+  }                                                                            \
+  _LIBSYCL_END_UNVERSIONED_NAMESPACE_SYCL
+
+#ifndef __SYCL_DEVICE_ONLY__
+
+#  ifndef _LIBSYCL_EXPORT
+#    ifdef _WIN32
+
+#      define _LIBSYCL_DLL_LOCAL
+
+#      ifdef _LIBSYCL_BUILDING_LIBRARY
+#        define _LIBSYCL_EXPORT __declspec(dllexport)
+#      else
+#        define _LIBSYCL_EXPORT __declspec(dllimport)
+#      endif //_LIBSYCL_BUILDING_LIBRARY
+
+#    else // _WIN32
+
+#      define _LIBSYCL_DLL_LOCAL [[__gnu__::__visibility__("hidden")]]
+#      define _LIBSYCL_EXPORT [[__gnu__::__visibility__("default")]]
+
+#    endif // _WIN32
+#  endif   // _LIBSYCL_EXPORT
+
+#else // __SYCL_DEVICE_ONLY__
+
+#  ifndef _LIBSYCL_EXPORT
+#    define _LIBSYCL_EXPORT
+#    define _LIBSYCL_DLL_LOCAL
+#  endif
+
+#endif // __SYCL_DEVICE_ONLY__
+
+#endif // _LIBSYCL___IMPL_DETAIL_CONFIG_HPP
diff --git a/libsycl/include/sycl/__impl/platform.hpp b/libsycl/include/sycl/__impl/platform.hpp
new file mode 100644
index 000000000000..bac59ac93d3d
--- /dev/null
+++ b/libsycl/include/sycl/__impl/platform.hpp
@@ -0,0 +1,31 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 platform class, which
+/// encapsulates a single platform on which kernel functions may be executed.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBSYCL___IMPL_PLATFORM_HPP
+#define _LIBSYCL___IMPL_PLATFORM_HPP
+
+#include <sycl/__impl/detail/config.hpp>
+
+_LIBSYCL_BEGIN_NAMESPACE_SYCL
+
+class _LIBSYCL_EXPORT platform {
+public:
+  /// Constructs a SYCL platform which contains the default device.
+  platform();
+
+}; // class platform
+
+_LIBSYCL_END_NAMESPACE_SYCL
+
+#endif // _LIBSYCL___IMPL_PLATFORM_HPP
diff --git a/libsycl/include/sycl/sycl.hpp b/libsycl/include/sycl/sycl.hpp
new file mode 100644
index 000000000000..76399eba758d
--- /dev/null
+++ b/libsycl/include/sycl/sycl.hpp
@@ -0,0 +1,19 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 is a SYCL 2020 standard header file.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBSYCL_SYCL_HPP
+#define _LIBSYCL_SYCL_HPP
+
+#include <sycl/__impl/platform.hpp>
+
+#endif // _LIBSYCL_SYCL_HPP
diff --git a/libsycl/src/CMakeLists.txt b/libsycl/src/CMakeLists.txt
new file mode 100644
index 000000000000..206b85681cb8
--- /dev/null
+++ b/libsycl/src/CMakeLists.txt
@@ -0,0 +1,98 @@
+list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/../../runtimes/cmake/Modules")
+include(WarningFlags)
+
+function(add_sycl_rt_library LIB_TARGET_NAME LIB_OBJ_NAME LIB_OUTPUT_NAME)
+  if (NOT LLVM_ENABLE_PIC)
+    message( FATAL_ERROR "Position-Independent Code generation is required for libsycl shared library" )
+  endif()
+
+  cmake_parse_arguments(ARG "" "" "COMPILE_OPTIONS;SOURCES" ${ARGN})
+
+  add_library(${LIB_OBJ_NAME} OBJECT ${ARG_SOURCES})
+
+  # Common compilation step setup
+  target_compile_definitions(${LIB_OBJ_NAME} PRIVATE
+              $<$<STREQUAL:${CMAKE_SYSTEM_NAME},Windows>:_LIBSYCL_BUILDING_LIBRARY>)
+  cxx_add_warning_flags(${LIB_OBJ_NAME} ${LIBSYCL_ENABLE_WERROR} ${LIBSYCL_ENABLE_PEDANTIC})
+
+  target_include_directories(
+    ${LIB_OBJ_NAME}
+    PRIVATE
+      ${CMAKE_CURRENT_SOURCE_DIR}
+      ${LIBSYCL_BUILD_INCLUDE_DIR}
+  )
+
+  add_library(${LIB_TARGET_NAME} SHARED
+              $<TARGET_OBJECTS:${LIB_OBJ_NAME}>)
+
+  add_dependencies(${LIB_OBJ_NAME}
+    sycl-headers
+  )
+
+  set_target_properties(${LIB_TARGET_NAME} PROPERTIES LINKER_LANGUAGE CXX)
+
+  if (CMAKE_SYSTEM_NAME STREQUAL Windows)
+    # Install stripped PDB
+    set(PDB_FILENAME "${LIB_TARGET_NAME}$<$<CONFIG:Debug>:d>")
+    check_linker_flag(CXX "LINKER:/PDBSTRIPPED:${PDB_FILENAME}.stripped.pdb"
+                          LINKER_SUPPORTS_PDBSTRIPPED)
+    if(LINKER_SUPPORTS_PDBSTRIPPED)
+      target_link_options(${LIB_TARGET_NAME}
+                          PRIVATE "LINKER:/PDBSTRIPPED:${PDB_FILENAME}.stripped.pdb")
+      install(FILES "${CMAKE_CURRENT_BINARY_DIR}/${PDB_FILENAME}.stripped.pdb"
+              DESTINATION ${CMAKE_INSTALL_PREFIX}/bin
+              RENAME "${PDB_FILENAME}.pdb"
+              COMPONENT ${LIB_TARGET_NAME}
+              OPTIONAL)
+    endif()
+
+    target_compile_options(${LIB_OBJ_NAME} PUBLIC /EHsc)
+  else()
+    target_compile_options(${LIB_OBJ_NAME} PUBLIC
+                           -fvisibility=hidden -fvisibility-inlines-hidden)
+
+    if (UNIX AND NOT APPLE)
+      set(linker_script "${CMAKE_CURRENT_SOURCE_DIR}/ld-version-script.txt")
+      target_link_libraries(
+          ${LIB_TARGET_NAME} PRIVATE "-Wl,--version-script=${linker_script}")
+      set_target_properties(${LIB_TARGET_NAME} PROPERTIES LINK_DEPENDS ${linker_script})
+    endif()
+  endif()
+
+  find_package(Threads REQUIRED)
+
+  target_link_libraries(${LIB_TARGET_NAME}
+    PRIVATE
+      ${CMAKE_DL_LIBS}
+      ${CMAKE_THREAD_LIBS_INIT}
+  )
+
+  set_target_properties(${LIB_TARGET_NAME} PROPERTIES
+                        VERSION ${LIBSYCL_VERSION_STRING}
+                        SOVERSION ${LIBSYCL_VERSION_STRING})
+  set_target_properties(${LIB_TARGET_NAME} PROPERTIES OUTPUT_NAME ${LIB_OUTPUT_NAME})
+endfunction(add_sycl_rt_library)
+
+set(LIBSYCL_SOURCES
+    "platform.cpp"
+)
+
+set(LIB_NAME "sycl")
+set(LIB_OUTPUT_NAME "${LIB_NAME}")
+if (CMAKE_SYSTEM_NAME STREQUAL Windows)
+  if (CMAKE_MSVC_RUNTIME_LIBRARY AND (NOT CMAKE_MSVC_RUNTIME_LIBRARY MATCHES "DLL$"))
+      message(FATAL_ERROR "libsycl requires a DLL version of the MSVC CRT.")
+  endif()
+  if ((NOT CMAKE_MSVC_RUNTIME_LIBRARY AND uppercase_CMAKE_BUILD_TYPE STREQUAL "DEBUG")
+      OR (CMAKE_MSVC_RUNTIME_LIBRARY STREQUAL "MultiThreadedDebugDLL"))
+    set(LIB_OUTPUT_NAME "${LIB_OUTPUT_NAME}d")
+  endif()
+endif()
+
+add_sycl_rt_library(${LIB_NAME} sycl_object ${LIB_OUTPUT_NAME}
+                    SOURCES ${LIBSYCL_SOURCES})
+
+install(TARGETS ${LIBSYCL_RT_LIBS}
+  ARCHIVE DESTINATION "lib${LLVM_LIBDIR_SUFFIX}" COMPONENT libsycl
+  LIBRARY DESTINATION "lib${LLVM_LIBDIR_SUFFIX}" COMPONENT libsycl
+  RUNTIME DESTINATION "bin" COMPONENT libsycl)
diff --git a/libsycl/src/ld-version-script.txt b/libsycl/src/ld-version-script.txt
new file mode 100644
index 000000000000..a347d202a367
--- /dev/null
+++ b/libsycl/src/ld-version-script.txt
@@ -0,0 +1,20 @@
+{
+  /* Symbols to be exported are selected based on mangled names rather than   */
+  /* the demangled names provided by the `extern "C++"` matcher because it is */
+  /* easy to express "export everything defined in the sycl namespace" using  */
+  /* the former. Matching demangled names is more complicated in the presence */
+  /* of examples like:                                                        */
+  /*   "vtable for sycl::foo"                  (should be exported)           */
+  /*   "vtable for std::__internal<sycl::foo>" (should not be exported)       */
+
+  global:
+    /* Export everything from sycl namespace */
+    _ZNK4sycl*;  /* function */
+    _ZN4sycl*;   /* function */
+    _ZTIN4sycl*; /* typeinfo */
+    _ZTSN4sycl*; /* typeinfo name */
+    _ZTVN4sycl*; /* vtable */
+
+  local:
+    *;
+};
diff --git a/libsycl/src/platform.cpp b/libsycl/src/platform.cpp
new file mode 100644
index 000000000000..b5d6517ee212
--- /dev/null
+++ b/libsycl/src/platform.cpp
@@ -0,0 +1,17 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include <sycl/__impl/platform.hpp>
+
+#include <stdexcept>
+
+_LIBSYCL_BEGIN_NAMESPACE_SYCL
+
+platform::platform() { throw std::runtime_error("Unimplemented"); }
+
+_LIBSYCL_END_NAMESPACE_SYCL
diff --git a/libsycl/src/version.hpp.in b/libsycl/src/version.hpp.in
new file mode 100644
index 000000000000..a7215761e9d4
--- /dev/null
+++ b/libsycl/src/version.hpp.in
@@ -0,0 +1,16 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 SYCL RT version macro.
+///
+//===----------------------------------------------------------------------===//
+#define _LIBSYCL_MAJOR_VERSION ${LIBSYCL_MAJOR_VERSION}
+#define _LIBSYCL_MINOR_VERSION ${LIBSYCL_MINOR_VERSION}
+#define _LIBSYCL_PATCH_VERSION ${LIBSYCL_PATCH_VERSION}
+#define _LIBSYCL_ABI_NAMESPACE ${LIBSYCL_ABI_NAMESPACE}