[libcxx-commits] [PATCH] D75955: [libcxx] Enable C++17 for the benchmarks

[Mark de Wever via Phabricator via libcxx-commits]

Mordante created this revision.
Mordante added a reviewer: ldionne.
Mordante added a project: libc++.
Herald added subscribers: dexonsmith, mgorny.
Herald added a reviewer: EricWF.
Herald added a reviewer: mclow.lists.

The benchmarks are intended to be build with C++17 but the CMAKE_CXX_STANDARD in the LLVM forces the build to use C++14 by default. This fixes the issue by setting the CXX_STANDARD property of the benchmark targets.

The CMake documentation is not clear whether this will use the C++1z fallback for older compilers. So this may break the benchmarks if somebody uses the benchmarks with pre C++17 compilers with the C++1z fallback.

This was discovered while investigating the build issue of D62778 <https://reviews.llvm.org/D62778>.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D75955

Files:
  libcxx/benchmarks/CMakeLists.txt


Index: libcxx/benchmarks/CMakeLists.txt
===================================================================
--- libcxx/benchmarks/CMakeLists.txt
+++ libcxx/benchmarks/CMakeLists.txt
@@ -72,16 +72,6 @@
 set(BENCHMARK_LIBCXX_INSTALL ${CMAKE_CURRENT_BINARY_DIR}/benchmark-libcxx)
 set(BENCHMARK_NATIVE_INSTALL ${CMAKE_CURRENT_BINARY_DIR}/benchmark-native)
 
-check_flag_supported("-std=c++17")
-mangle_name("LIBCXX_SUPPORTS_STD_EQ_c++17_FLAG" BENCHMARK_SUPPORTS_STD_CXX17_FLAG)
-if (${BENCHMARK_SUPPORTS_STD_CXX17_FLAG})
-  set(BENCHMARK_DIALECT_FLAG "-std=c++17")
-else()
-  # If the compiler doesn't support -std=c++17, attempt to fall back to -std=c++1z while still
-  # requiring C++17 language features.
-  set(BENCHMARK_DIALECT_FLAG "-std=c++1z")
-endif()
-
 set(BENCHMARK_TEST_COMPILE_FLAGS
     ${BENCHMARK_DIALECT_FLAG} -O2
     -fsized-deallocation
@@ -151,6 +141,7 @@
           OUTPUT_NAME "${name}.libcxx.out"
           RUNTIME_OUTPUT_DIRECTORY "${BENCHMARK_OUTPUT_DIR}"
           COMPILE_FLAGS "${BENCHMARK_TEST_LIBCXX_COMPILE_FLAGS}"
+          CXX_STANDARD 17
           LINK_FLAGS "${BENCHMARK_TEST_LIBCXX_LINK_FLAGS}")
   cxx_link_system_libraries(${libcxx_target})
   if (LIBCXX_BENCHMARK_NATIVE_STDLIB)


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