[SYCL][UR] Fix build with libc++ (#19521)

We previously added support for building `libsycl` individually with
`libc++`. At that time, `libsycl` didn't link against `libLLVM` so they
did not need to be using the same STL implementation.

Now, `libsycl` does link against `libLLVM`, one example
[here](https://github.com/intel/llvm/blob/sycl/sycl/source/CMakeLists.txt#L98).

Remove all the code that was to support `libsycl` in particular and just
make it work with the normal option LLVM uses, `LLVM_ENABLE_LIBCXX`.
Most of the code I added actually checks `LLVM_LIBCXX_USED`, because
LLVM checks at configure time if `libc++` actually works even when
passed `LLVM_ENABLE_LIBCXX`, and if it fails, it falls back to
`libstdc++`, and most of the time we actually want to know if we are
actually using `libc++`.

I added a CMake option `SYCL_LIBDEVICE_CXX_FLAGS` to set the flags for
libdevice because it will be required if someone doesn't use the LLVM
option and just does it through `CMAKE_CXX_FLAGS`, as those aren't used
for libdevice but it still uses the STL.

The two changes in
`unified-runtime/source/loader/layers/sanitizer/msan/msan_libdevice.hpp`
and `sycl/source/builtins/common_functions.cpp` fix compile errors with
`libc++`.

I also plan to add a job to the nightly to lock this down.

#19347

---------

Signed-off-by: Sarnie, Nick <[email protected]>

Author: sarnex

buildbot/configure.py

@@ -248,16 +248,9 @@ def do_configure(args, passthrough_args):
     cmake_cmd.append(llvm_dir)
 
     if args.use_libcxx:
-        if not (args.libcxx_include and args.libcxx_library):
-            sys.exit(
-                "Please specify include and library path of libc++ when building sycl "
-                "runtime with it"
-            )
         cmake_cmd.extend(
             [
-                "-DSYCL_USE_LIBCXX=ON",
-                "-DSYCL_LIBCXX_INCLUDE_PATH={}".format(args.libcxx_include),
-                "-DSYCL_LIBCXX_LIBRARY_PATH={}".format(args.libcxx_library),
+                "-DLLVM_ENABLE_LIBCXX=ON",
             ]
         )
 
@@ -380,15 +373,7 @@ def main():
         help="Additional CMake option not configured via script parameters",
     )
     parser.add_argument("--cmake-gen", default="Ninja", help="CMake generator")
-    parser.add_argument(
-        "--use-libcxx", action="store_true", help="build sycl runtime with libcxx"
-    )
-    parser.add_argument(
-        "--libcxx-include", metavar="LIBCXX_INCLUDE_PATH", help="libcxx include path"
-    )
-    parser.add_argument(
-        "--libcxx-library", metavar="LIBCXX_LIBRARY_PATH", help="libcxx library path"
-    )
+    parser.add_argument("--use-libcxx", action="store_true", help="build with libcxx")
     parser.add_argument(
         "--use-lld", action="store_true", help="Use LLD linker for build"
     )

libdevice/cmake/modules/SYCLLibdevice.cmake

@@ -55,9 +55,17 @@ set(compile_opts
 
 set(SYCL_LIBDEVICE_GCC_TOOLCHAIN "" CACHE PATH "Path to GCC installation")
 
+set(SYCL_LIBDEVICE_CXX_FLAGS "" CACHE STRING "C++ compiler flags for SYCL libdevice")
 if (NOT SYCL_LIBDEVICE_GCC_TOOLCHAIN STREQUAL "")
   list(APPEND compile_opts "--gcc-install-dir=${SYCL_LIBDEVICE_GCC_TOOLCHAIN}")
 endif()
+if(NOT SYCL_LIBDEVICE_CXX_FLAGS STREQUAL "")
+  separate_arguments(SYCL_LIBDEVICE_CXX_FLAGS NATIVE_COMMAND ${SYCL_LIBDEVICE_CXX_FLAGS})
+  list(APPEND compile_opts ${SYCL_LIBDEVICE_CXX_FLAGS})
+endif()
+if(LLVM_LIBCXX_USED)
+  list(APPEND compile_opts "-stdlib=libc++")
+endif()
 
 if (WIN32)
   list(APPEND compile_opts -D_ALLOW_RUNTIME_LIBRARY_MISMATCH)
@@ -644,6 +652,10 @@ if (NOT SYCL_LIBDEVICE_GCC_TOOLCHAIN STREQUAL "")
   list(APPEND imf_host_cxx_flags "--gcc-install-dir=${SYCL_LIBDEVICE_GCC_TOOLCHAIN}")
 endif()
 
+if(LLVM_LIBCXX_USED)
+  list(APPEND  imf_host_cxx_flags "-stdlib=libc++")
+endif()
+
 macro(mangle_name str output)
   string(STRIP "${str}" strippedStr)
   string(REGEX REPLACE "^/" "" strippedStr "${strippedStr}")

sycl/CMakeLists.txt

@@ -303,37 +303,18 @@ endif()
 
 # This function allows building multiple libraries with the same options.
 # Currently used by add_sycl_library and add_sycl_rt_library.
-# Currently handles linking with libcxx support and gcc workaround
+# Currently handles a gcc workaround
 function( add_common_options LIB_NAME)
-  if (SYCL_USE_LIBCXX)
-    if ((CMAKE_CXX_COMPILER_ID STREQUAL "GNU") OR
-      (CMAKE_CXX_COMPILER_ID STREQUAL "Clang"))
-      if ((NOT (DEFINED SYCL_LIBCXX_INCLUDE_PATH)) OR (NOT (DEFINED SYCL_LIBCXX_LIBRARY_PATH)))
-        message(FATAL_ERROR "When building with libc++ SYCL_LIBCXX_INCLUDE_PATHS and"
-                            "SYCL_LIBCXX_LIBRARY_PATH should be set")
-      endif()
-      target_link_libraries(${LIB_NAME} PRIVATE "-L${SYCL_LIBCXX_LIBRARY_PATH}" -Wl,-rpath,${SYCL_LIBCXX_LIBRARY_PATH} -nodefaultlibs -lc++ -lc++abi -lm -lc -lgcc_s -lgcc)
-      target_compile_options(${LIB_NAME} PRIVATE -nostdinc++)
-      target_include_directories(${LIB_NAME} PRIVATE "${SYCL_LIBCXX_INCLUDE_PATH}")
-      if (ARGC EQUAL 2)
-        target_compile_options(${ARGV1} PRIVATE -nostdinc++)
-        target_include_directories(${ARGV1} PRIVATE "${SYCL_LIBCXX_INCLUDE_PATH}")
-      endif()
-    else()
-      message(FATAL_ERROR "Build with libc++ is not yet supported for this compiler")
-    endif()
-  else()
     # Workaround for bug in GCC version 5 and higher.
     # More information https://bugs.launchpad.net/ubuntu/+source/gcc-5/+bug/1568899
     if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU" AND
         CMAKE_CXX_COMPILER_VERSION VERSION_GREATER 5.0)
       target_link_libraries(${ARGV0} PRIVATE gcc_s gcc)
     endif()
-  endif()
 endfunction(add_common_options)
 
 if (LLVM_ENABLE_ASSERTIONS AND NOT SYCL_DISABLE_STL_ASSERTIONS AND NOT WIN32)
-  if(SYCL_USE_LIBCXX)
+  if(LLVM_LIBCXX_USED)
     add_definitions(-D_LIBCPP_DEBUG=1)
     set(SYCL_CLANG_EXTRA_FLAGS "${SYCL_CLANG_EXTRA_FLAGS} -D_LIBCPP_DEBUG=1")
   else()

sycl/cmake/modules/AddSYCLExecutable.cmake

@@ -20,7 +20,7 @@ macro(add_sycl_executable ARG_TARGET_NAME)
   endforeach()
 
   if (LLVM_ENABLE_ASSERTIONS AND NOT SYCL_DISABLE_STL_ASSERTIONS)
-    if(SYCL_USE_LIBCXX)
+    if(LLVM_ENABLE_LIBCXX)
       set(_SYCL_EXTRA_FLAGS -D_LIBCPP_DEBUG=1)
     else()
       set(_SYCL_EXTRA_FLAGS -D_GLIBCXX_ASSERTIONS=1)

sycl/doc/GetStartedGuide.md

@@ -150,23 +150,19 @@ needed at the moment.
 ### Build DPC++ toolchain with libc++ library
 
 There is experimental support for building and linking DPC++ runtime with libc++
-library instead of libstdc++. To enable it the following CMake options should be
+library instead of libstdc++. To enable it the following CMake option should be
 used.
 
 **Linux**:
 
 ```sh
--DSYCL_USE_LIBCXX=ON \
--DSYCL_LIBCXX_INCLUDE_PATH=<path to libc++ headers> \
--DSYCL_LIBCXX_LIBRARY_PATH=<path to libc++ and libc++abi libraries>
+-DLLVM_ENABLE_LIBCXX=ON
 ```
 
 You can also use configure script to enable:
 
 ```sh
-python %DPCPP_HOME%\llvm\buildbot\configure.py --use-libcxx \
---libcxx-include <path to libc++ headers> \
---libcxx-library <path to libc++ and libc++ abi libraries>
+python %DPCPP_HOME%\llvm\buildbot\configure.py --use-libcxx
 python %DPCPP_HOME%\llvm\buildbot\compile.py
 ```
 

sycl/source/builtins/common_functions.cpp

@@ -34,7 +34,7 @@ BUILTIN_COMMON(ONE_ARG, radians,
 
 BUILTIN_COMMON(ONE_ARG, sign, [](auto x) -> decltype(x) {
   using T = decltype(x);
-  if (std::isnan(x))
+  if (std::isnan(sycl::detail::cast_if_host_half(x)))
     return T(0.0);
   if (x > 0)
     return T(1.0);

sycl/test/lit.site.cfg.py.in

@@ -26,7 +26,7 @@ config.test_include_path = "@TEST_INCLUDE_PATH@"
 config.llvm_enable_projects = "@LLVM_ENABLE_PROJECTS@"
 
 config.sycl_threads_lib = '@SYCL_THREADS_LIB@'
-config.sycl_use_libcxx = '@SYCL_USE_LIBCXX@'
+config.sycl_use_libcxx = '@LLVM_LIBCXX_USEDX@'
 config.extra_environment = lit_config.params.get("extra_environment", "@LIT_EXTRA_ENVIRONMENT@")
 config.cuda = '@SYCL_BUILD_BACKEND_CUDA@'
 config.hip = '@SYCL_BUILD_BACKEND_HIP@'

unified-runtime/source/loader/CMakeLists.txt

@@ -211,21 +211,10 @@ if(UR_ENABLE_SANITIZER)
         # In in-tree build, if LLVM is built with libc++, we also need to build
         # symbolizer.cpp with libc++ abi and link libc++ in.
         if(NOT UR_STANDALONE_BUILD AND LLVM_LIBCXX_USED)
-            execute_process(
-                COMMAND ${CMAKE_CXX_COMPILER} --print-file-name=libc++.a
-                OUTPUT_VARIABLE LIBCXX_PATH
-                OUTPUT_STRIP_TRAILING_WHITESPACE)
-            execute_process(
-                COMMAND ${CMAKE_CXX_COMPILER} --print-file-name=libc++abi.a
-                OUTPUT_VARIABLE LIBCXX_ABI_PATH
-                OUTPUT_STRIP_TRAILING_WHITESPACE)
             set_property(SOURCE
                 ${symbolizer_sources}
                 APPEND_STRING PROPERTY COMPILE_FLAGS
                 " -stdlib=libc++ ")
-            if(NOT EXISTS ${LIBCXX_PATH} OR NOT EXISTS ${LIBCXX_ABI_PATH})
-                message(FATAL_ERROR "libc++ is required but can't find the libraries")
-            endif()
             # Link with gcc_s fisrt to avoid some symbols resolve to libc++/libc++abi/libunwind's one
             target_link_libraries(ur_loader PRIVATE gcc_s ${LIBCXX_PATH} ${LIBCXX_ABI_PATH})
         endif()

unified-runtime/source/loader/layers/sanitizer/msan/msan_libdevice.hpp

@@ -14,6 +14,7 @@
 #pragma once
 
 #include "sanitizer_common/sanitizer_libdevice.hpp"
+#include <cstddef>
 
 #if !defined(__SPIR__) && !defined(__SPIRV__)
 namespace ur_sanitizer_layer {

xpti/CMakeLists.txt

@@ -57,18 +57,6 @@ if (MSVC)
   set(CMAKE_CXX_FLAGS_DEBUG "")
 endif()
 
-if (SYCL_USE_LIBCXX)
-  if ((CMAKE_CXX_COMPILER_ID STREQUAL "GNU") OR
-    (CMAKE_CXX_COMPILER_ID STREQUAL "Clang"))
-    if ((NOT (DEFINED SYCL_LIBCXX_INCLUDE_PATH)) OR (NOT (DEFINED SYCL_LIBCXX_LIBRARY_PATH)))
-      message(FATAL_ERROR "When building with libc++ SYCL_LIBCXX_INCLUDE_PATHS and"
-                          "SYCL_LIBCXX_LIBRARY_PATH should be set")
-    endif()
-    set(CMAKE_CXX_FLAGS "-nostdinc++ -I ${SYCL_LIBCXX_INCLUDE_PATH} ${CMAKE_CXX_FLAGS}")
-  else()
-    message(FATAL_ERROR "Build with libc++ is not yet supported for this compiler")
-  endif()
-endif()
 set(CMAKE_BINARY_DIR ${CMAKE_SOURCE_DIR}/lib/${CMAKE_BUILD_TYPE})
 set(EXECUTABLE_OUTPUT_PATH ${CMAKE_BINARY_DIR})
 set(LIBRARY_OUTPUT_PATH ${CMAKE_BINARY_DIR})