[Openmp-commits] [PATCH] D149726: [OpenMP] Use CMAKE_CXX_STANDARD for setting the C++ version

[Martin Storsjö via Phabricator via Openmp-commits]

mstorsjo updated this revision to Diff 519241.
mstorsjo added a comment.

Retain the C++17 checks for libomptarget, but done by checking `"cxx_std_17" IN_LIST CMAKE_CXX_COMPILE_FEATURES` instead of checking `OPENMP_HAVE_STD_CPP17_FLAG`.

Setting `CMAKE_CXX_EXTENSIONS` explicitly to `NO` too.

If the main `libomp` is supposed to be buildable with compilers that don't even support C++11, then it would probably be best in the long run to start setting `CMAKE_CXX_STANDARD` explicitly to the minimum level, so that all build configurations build in the same language mode - but I'd leave that up for others as a separate change.

Now this should be a no-op change for compiler that do use the `-std=c++17` syntax, while making things consistent with those others, for compilers with a different argument syntax.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D149726/new/

https://reviews.llvm.org/D149726

Files:
  openmp/CMakeLists.txt
  openmp/cmake/HandleOpenMPOptions.cmake
  openmp/cmake/config-ix.cmake


Index: openmp/cmake/config-ix.cmake
===================================================================
--- openmp/cmake/config-ix.cmake
+++ openmp/cmake/config-ix.cmake
@@ -36,5 +36,3 @@
 check_cxx_compiler_flag(-Wextra OPENMP_HAVE_WEXTRA_FLAG)
 check_cxx_compiler_flag(-Wpedantic OPENMP_HAVE_WPEDANTIC_FLAG)
 check_cxx_compiler_flag(-Wmaybe-uninitialized OPENMP_HAVE_WMAYBE_UNINITIALIZED_FLAG)
-
-check_cxx_compiler_flag(-std=c++17 OPENMP_HAVE_STD_CPP17_FLAG)
Index: openmp/cmake/HandleOpenMPOptions.cmake
===================================================================
--- openmp/cmake/HandleOpenMPOptions.cmake
+++ openmp/cmake/HandleOpenMPOptions.cmake
@@ -35,5 +35,3 @@
 append_if(OPENMP_HAVE_WEXTRA_FLAG "-Wno-extra" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
 append_if(OPENMP_HAVE_WPEDANTIC_FLAG "-Wno-pedantic" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
 append_if(OPENMP_HAVE_WMAYBE_UNINITIALIZED_FLAG "-Wno-maybe-uninitialized" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
-
-append_if(OPENMP_HAVE_STD_CPP17_FLAG "-std=c++17" CMAKE_CXX_FLAGS)
Index: openmp/CMakeLists.txt
===================================================================
--- openmp/CMakeLists.txt
+++ openmp/CMakeLists.txt
@@ -44,6 +44,10 @@
   set(OPENMP_TEST_CXX_COMPILER ${CMAKE_CXX_COMPILER} CACHE STRING
     "C++ compiler to use for testing OpenMP runtime libraries.")
   set(OPENMP_LLVM_TOOLS_DIR "" CACHE PATH "Path to LLVM tools for testing.")
+
+  set(CMAKE_CXX_STANDARD 17 CACHE STRING "C++ standard to conform to")
+  set(CMAKE_CXX_STANDARD_REQUIRED NO)
+  set(CMAKE_CXX_EXTENSIONS NO)
 else()
   set(OPENMP_ENABLE_WERROR ${LLVM_ENABLE_WERROR})
   # If building in tree, we honor the same install suffix LLVM uses.
@@ -56,6 +60,12 @@
     set(OPENMP_TEST_C_COMPILER ${LLVM_RUNTIME_OUTPUT_INTDIR}/clang.exe)
     set(OPENMP_TEST_CXX_COMPILER ${LLVM_RUNTIME_OUTPUT_INTDIR}/clang++.exe)
   endif()
+
+  # If not standalone, set CMAKE_CXX_STANDARD but don't set the global cache value,
+  # only set it locally for OpenMP.
+  set(CMAKE_CXX_STANDARD 17)
+  set(CMAKE_CXX_STANDARD_REQUIRED NO)
+  set(CMAKE_CXX_EXTENSIONS NO)
 endif()
 
 # Check and set up common compiler flags.
@@ -75,7 +85,7 @@
 # Since the device plugins are only supported on Linux anyway,
 # there is no point in trying to compile libomptarget on other OSes.
 # 32-bit systems are not supported either.
-if (APPLE OR WIN32 OR NOT OPENMP_HAVE_STD_CPP17_FLAG OR NOT CMAKE_SIZEOF_VOID_P EQUAL 8)
+if (APPLE OR WIN32 OR NOT "cxx_std_17" IN_LIST CMAKE_CXX_COMPILE_FEATURES OR NOT CMAKE_SIZEOF_VOID_P EQUAL 8)
   set(ENABLE_LIBOMPTARGET OFF)
 endif()
 
@@ -99,7 +109,7 @@
   # Check that the library can actually be built.
   if (APPLE OR WIN32)
     message(FATAL_ERROR "libomptarget cannot be built on Windows and MacOS X!")
-  elseif (NOT OPENMP_HAVE_STD_CPP17_FLAG)
+  elseif (NOT "cxx_std_17" IN_LIST CMAKE_CXX_COMPILE_FEATURES)
     message(FATAL_ERROR "Host compiler must support C++17 to build libomptarget!")
   elseif (NOT CMAKE_SIZEOF_VOID_P EQUAL 8)
     message(FATAL_ERROR "libomptarget on 32-bit systems are not supported!")


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