[OpenMP] Replace libomp_check_linker_flag with llvm_check_compiler_linker_flag

[nikic]

Summary

Replace the custom libomp_check_linker_flag() implementation with llvm_check_compiler_linker_flag() from the common cmake utils. Due to the way the custom implementation is implemented (capturing output from an entire nested cmake invocation) it can easily end up incorrectly detection flags as unavailable, e.g. because error, unknown or similar occurs inside compiler flags, the directory name, etc.

Fixes https://github.com/llvm/llvm-project/issues/62240.

[tianshilei1992]

The openmp project may not be always built by LLVM, especially the host library libomp. Using llvm_check_compiler_linker_flag may cause CMake error if users don't use LLVM.

[nikic]

@tianshilei1992 This function is part of the common cmake utilities that openmp already requires, not the LLVM cmake utilities.

I did miss adding the necessary include though.

[tianshilei1992]

In D148798#4283471, @nikic wrote:

@tianshilei1992 This function is part of the common cmake utilities that openmp already requires, not the LLVM cmake utilities.

I did miss adding the necessary include though.

Hmm, okay. That is unexpected TBH because openmp is supposed to support to be built as a standalone project. For example, we do have a standalone release for OpenMP (https://github.com/llvm/llvm-project/releases/download/llvmorg-16.0.2/openmp-16.0.2.src.tar.xz). https://reviews.llvm.org/D130545 definitely broke it.

[jhuber6]

I'm not as familiar with libomp. Are we allowed to have explicit dependencies on LLVM? I know libomptarget requires LLVM, but I'm pretty sure libomp doesn't share the same rules. Worst case scenario we just copy the llvm_check_compiler_linker_flag.

[nikic]

In D148798#4283485, @tianshilei1992 wrote:

In D148798#4283471, @nikic wrote:

@tianshilei1992 This function is part of the common cmake utilities that openmp already requires, not the LLVM cmake utilities.

I did miss adding the necessary include though.

Hmm, okay. That is unexpected TBH because openmp is supposed to support to be built as a standalone project. For example, we do have a standalone release for OpenMP (https://github.com/llvm/llvm-project/releases/download/llvmorg-16.0.2/openmp-16.0.2.src.tar.xz). https://reviews.llvm.org/D130545 definitely broke it.

Nowadays all standalone builds (including the one for openmp) require at least the cmake tarball as well. This is the case for both projects like clang and runtimes like compiler-rt. I don't like this either, but it's the current situation...

I personally wouldn't mind just copying the relevant file into the openmp project, it just seems to go against the overall trend in the monorepo.

[tianshilei1992]

Okay, since it is already broken, it has nothing to do with this patch. We can revisit the cmake issue later.

openmp/runtime/cmake/LibompCheckLinkerFlag.cmake

-#
-#//===----------------------------------------------------------------------===//
-#//
-#// 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(GNUInstallDirs)
-
-# Checking a linker flag to build a shared library
-# There is no real trivial way to do this in CMake, so we implement it here
-# this will have ${boolean} = TRUE if the flag succeeds, otherwise FALSE.
-function(libomp_check_linker_flag flag boolean)
-  if(NOT DEFINED "${boolean}")
-  set(retval TRUE)
-  set(library_source
-    "int foo(int a) { return a*a; }")
-  set(cmake_source
-    "cmake_minimum_required(VERSION 3.13.4)
-     project(foo C)
-     set(CMAKE_SHARED_LINKER_FLAGS \"${flag}\")
-     add_library(foo SHARED src_to_link.c)")
-  # Compiling as a part of runtimes introduces ARCH-unknown-linux-gnu as a part
-  # of a working directory.  So adding a guard for unknown.
-  set(failed_regexes "[Ee]rror;[Uu]nknown[^-];[Ss]kipping;LINK : warning;Unsupported command line")
-  set(base_dir ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeTmp/link_flag_check_${boolean})
-  file(MAKE_DIRECTORY ${base_dir})
-  file(MAKE_DIRECTORY ${base_dir}/build)
-  file(WRITE ${base_dir}/src_to_link.c "${library_source}")
-  file(WRITE ${base_dir}/CMakeLists.txt "${cmake_source}")
-
-  message(STATUS "Performing Test ${boolean}")
-  try_compile(
-    try_compile_result
-    ${base_dir}/build
-    ${base_dir}
-    foo
-    OUTPUT_VARIABLE OUTPUT)
-
-  if(try_compile_result)
-    foreach(regex IN LISTS failed_regexes)
-      # Ignore the warning about the newer or unknown CUDA version.
-      if(("${OUTPUT}" MATCHES ${regex}) AND NOT ("${OUTPUT}" MATCHES "Unknown CUDA version"))
-        set(retval FALSE)
-      endif()
-    endforeach()
-  else()
-    set(retval FALSE)
-  endif()
-
-  if(${retval})
-    set(${boolean} 1 CACHE INTERNAL "Test ${boolean}")
-    message(STATUS "Performing Test ${boolean} - Success")
-    file(APPEND ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeOutput.log
-      "Performing C Linker Flag test ${boolean} succeeded with the following output:\n"
-      "${OUTPUT}\n"
-      "Source file was:\n${library_source}\n")
-  else()
-    set(${boolean} "" CACHE INTERNAL "Test ${boolean}")
-    message(STATUS "Performing Test ${boolean} - Failed")
-    file(APPEND ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeError.log
-      "Performing C Linker Flag test ${boolean} failed with the following output:\n"
-      "${OUTPUT}\n"
-      "Source file was:\n${library_source}\n")
-  endif()
-
-  set(${boolean} ${retval} PARENT_SCOPE)
-  endif()
-endfunction()

openmp/runtime/cmake/config-ix.cmake

 include(CheckCCompilerFlag)
 include(CheckCSourceCompiles)
 include(CheckCXXSourceCompiles)
 include(CheckCXXCompilerFlag)
 include(CheckIncludeFile)
 include(CheckLibraryExists)
 include(CheckIncludeFiles)
 include(CheckSymbolExists)
-include(LibompCheckLinkerFlag)
 include(LibompCheckFortranFlag)
 
 # Check for versioned symbols
 function(libomp_check_version_symbols retval)
   set(source_code
     "#include <stdio.h>
     void func1() { printf(\"Hello\"); }
     void func2() { printf(\"World\"); }

 check_cxx_source_compiles("${source_code}" LIBOMP_HAVE__MM_MALLOC)
 set(CMAKE_REQUIRED_FLAGS ${OLD_CMAKE_REQUIRED_FLAGS})
 check_symbol_exists(aligned_alloc "stdlib.h" LIBOMP_HAVE_ALIGNED_ALLOC)
 check_symbol_exists(posix_memalign "stdlib.h" LIBOMP_HAVE_POSIX_MEMALIGN)
 check_symbol_exists(_aligned_malloc "malloc.h" LIBOMP_HAVE__ALIGNED_MALLOC)
 
 # Check linker flags
 if(WIN32)
-  libomp_check_linker_flag(/SAFESEH LIBOMP_HAVE_SAFESEH_FLAG)
+  llvm_check_compiler_linker_flag(C /SAFESEH LIBOMP_HAVE_SAFESEH_FLAG)
 elseif(NOT APPLE)
-  libomp_check_linker_flag(-Wl,-x LIBOMP_HAVE_X_FLAG)
-  libomp_check_linker_flag(-Wl,--as-needed LIBOMP_HAVE_AS_NEEDED_FLAG)
-  libomp_check_linker_flag("-Wl,--version-script=${LIBOMP_SRC_DIR}/exports_test_so.txt" LIBOMP_HAVE_VERSION_SCRIPT_FLAG)
-  libomp_check_linker_flag(-static-libgcc LIBOMP_HAVE_STATIC_LIBGCC_FLAG)
-  libomp_check_linker_flag(-Wl,-z,noexecstack LIBOMP_HAVE_Z_NOEXECSTACK_FLAG)
+  llvm_check_compiler_linker_flag(C -Wl,-x LIBOMP_HAVE_X_FLAG)
+  llvm_check_compiler_linker_flag(C -Wl,--as-needed LIBOMP_HAVE_AS_NEEDED_FLAG)
+  llvm_check_compiler_linker_flag(C "-Wl,--version-script=${LIBOMP_SRC_DIR}/exports_test_so.txt" LIBOMP_HAVE_VERSION_SCRIPT_FLAG)
+  llvm_check_compiler_linker_flag(C -static-libgcc LIBOMP_HAVE_STATIC_LIBGCC_FLAG)
+  llvm_check_compiler_linker_flag(C -Wl,-z,noexecstack LIBOMP_HAVE_Z_NOEXECSTACK_FLAG)
 endif()
 
 # Check Intel(R) C Compiler specific flags
 if(CMAKE_C_COMPILER_ID STREQUAL "Intel" OR CMAKE_C_COMPILER_ID STREQUAL "IntelLLVM")
   check_cxx_compiler_flag(/Qlong_double LIBOMP_HAVE_LONG_DOUBLE_FLAG)
   check_cxx_compiler_flag(/Qdiag-disable:177 LIBOMP_HAVE_DIAG_DISABLE_177_FLAG)
   check_cxx_compiler_flag(/Qinline-min-size=1 LIBOMP_HAVE_INLINE_MIN_SIZE_FLAG)
   check_cxx_compiler_flag(-Qoption,cpp,--extended_float_types LIBOMP_HAVE_EXTENDED_FLOAT_TYPES_FLAG)
   check_cxx_compiler_flag(-falign-stack=maintain-16-byte LIBOMP_HAVE_FALIGN_STACK_FLAG)
   check_cxx_compiler_flag("-opt-streaming-stores never" LIBOMP_HAVE_OPT_STREAMING_STORES_FLAG)
-  libomp_check_linker_flag(-static-intel LIBOMP_HAVE_STATIC_INTEL_FLAG)
-  libomp_check_linker_flag(-no-intel-extensions LIBOMP_HAVE_NO_INTEL_EXTENSIONS_FLAG)
+  llvm_check_compiler_linker_flag(C -static-intel LIBOMP_HAVE_STATIC_INTEL_FLAG)
+  llvm_check_compiler_linker_flag(C -no-intel-extensions LIBOMP_HAVE_NO_INTEL_EXTENSIONS_FLAG)
   check_library_exists(irc_pic _intel_fast_memcpy "" LIBOMP_HAVE_IRC_PIC_LIBRARY)
 endif()
 
 # Checking Threading requirements
 find_package(Threads REQUIRED)
 if(WIN32)
   if(NOT CMAKE_USE_WIN32_THREADS_INIT)
     libomp_error_say("Need Win32 thread interface on Windows.")