[libc++] Use CMake interface targets to setup benchmark flags

This is a re-application of da0592e4c8 which was reverted in
1454018dc1 because it was incompatible with older CMakes.
Instead, disable the benchmarks when CMake is too old to
support those idioms.

Differential Revision: https://reviews.llvm.org/D110285

libcxx/benchmarks/CMakeLists.txt

@@ -1,3 +1,8 @@
+if (CMAKE_VERSION VERSION_LESS 3.17)
+  message(WARNING "The libc++ benchmarks won't be available because the version of CMake is too old to support them.")
+  return()
+endif()
+
 include(ExternalProject)
 include(CheckCXXCompilerFlag)
 
@@ -75,56 +80,41 @@ set(BENCHMARK_OUTPUT_DIR ${CMAKE_CURRENT_BINARY_DIR})
 set(BENCHMARK_LIBCXX_INSTALL ${CMAKE_CURRENT_BINARY_DIR}/benchmark-libcxx)
 set(BENCHMARK_NATIVE_INSTALL ${CMAKE_CURRENT_BINARY_DIR}/benchmark-native)
 
+add_library(               cxx-benchmarks-flags INTERFACE)
+target_compile_features(   cxx-benchmarks-flags INTERFACE cxx_std_17)
+target_compile_options(    cxx-benchmarks-flags INTERFACE -O2 -fsized-deallocation)
+target_include_directories(cxx-benchmarks-flags INTERFACE "${BENCHMARK_LIBCXX_INSTALL}/include"
+                                                INTERFACE "${LIBCXX_SOURCE_DIR}/test/support")
 
-set(BENCHMARK_TEST_COMPILE_FLAGS
-    -O2
-    -fsized-deallocation
-    -I${BENCHMARK_LIBCXX_INSTALL}/include
-    -I${LIBCXX_SOURCE_DIR}/test/support
-)
-set(BENCHMARK_TEST_LIBCXX_COMPILE_FLAGS
-    ${BENCHMARK_TEST_COMPILE_FLAGS}
-    ${SANITIZER_FLAGS}
-    -Wno-user-defined-literals
-    -Wno-suggest-override
-)
-
-set(BENCHMARK_TEST_LIBCXX_LINK_FLAGS
-    -nodefaultlibs
-    -L${BENCHMARK_LIBCXX_INSTALL}/lib/
-    ${SANITIZER_FLAGS}
-)
-set(BENCHMARK_TEST_NATIVE_COMPILE_FLAGS
-  ${BENCHMARK_NATIVE_TARGET_FLAGS}
-  ${BENCHMARK_TEST_COMPILE_FLAGS}
-)
-set(BENCHMARK_TEST_NATIVE_LINK_FLAGS
-    ${BENCHMARK_NATIVE_TARGET_FLAGS}
-    -L${BENCHMARK_NATIVE_INSTALL}/lib
-)
-split_list(BENCHMARK_TEST_COMPILE_FLAGS)
-split_list(BENCHMARK_TEST_LIBCXX_COMPILE_FLAGS)
-split_list(BENCHMARK_TEST_LIBCXX_LINK_FLAGS)
-split_list(BENCHMARK_TEST_NATIVE_COMPILE_FLAGS)
-split_list(BENCHMARK_TEST_NATIVE_LINK_FLAGS)
-
+add_library(           cxx-benchmarks-flags-native INTERFACE)
+target_link_libraries( cxx-benchmarks-flags-native INTERFACE cxx-benchmarks-flags)
+target_compile_options(cxx-benchmarks-flags-native INTERFACE ${BENCHMARK_NATIVE_TARGET_FLAGS})
+target_link_options(   cxx-benchmarks-flags-native INTERFACE ${BENCHMARK_NATIVE_TARGET_FLAGS} "-L${BENCHMARK_NATIVE_INSTALL}/lib")
 if (LIBCXX_BENCHMARK_NATIVE_STDLIB STREQUAL "libstdc++")
   find_library(LIBSTDCXX_FILESYSTEM_TEST stdc++fs
         PATHS ${LIBCXX_BENCHMARK_NATIVE_GCC_TOOLCHAIN}
         PATH_SUFFIXES lib lib64
         DOC "The libstdc++ filesystem library used by the benchmarks"
     )
-    if (NOT "${LIBSTDCXX_FILESYSTEM_TEST}" STREQUAL "LIBSTDCXX_FILESYSTEM_TEST-NOTFOUND")
-      set(LIBSTDCXX_FILESYSTEM_LIB "stdc++fs")
-    endif()
+  if (LIBSTDCXX_FILESYSTEM_TEST)
+    target_link_libraries(cxx-benchmarks-flags-native INTERFACE -lstdc++fs)
+  endif()
+else()
+  target_link_libraries(cxx-benchmarks-flags-native INTERFACE -lc++fs -lc++experimental)
 endif()
 
+add_library(           cxx-benchmarks-flags-libcxx INTERFACE)
+target_link_libraries( cxx-benchmarks-flags-libcxx INTERFACE cxx-benchmarks-flags)
+target_compile_options(cxx-benchmarks-flags-libcxx INTERFACE ${SANITIZER_FLAGS} -Wno-user-defined-literals -Wno-suggest-override)
+target_link_options(   cxx-benchmarks-flags-libcxx INTERFACE -nodefaultlibs "-L${BENCHMARK_LIBCXX_INSTALL}/lib" ${SANITIZER_FLAGS})
+
 set(libcxx_benchmark_targets)
 
 function(add_benchmark_test name source_file)
   set(libcxx_target ${name}_libcxx)
   list(APPEND libcxx_benchmark_targets ${libcxx_target})
   add_executable(${libcxx_target} EXCLUDE_FROM_ALL ${source_file})
+  target_link_libraries(${libcxx_target} PRIVATE cxx-benchmarks-flags-libcxx)
   add_dependencies(${libcxx_target} cxx google-benchmark-libcxx)
   add_dependencies(cxx-benchmarks ${libcxx_target})
   if (LIBCXX_ENABLE_SHARED)
@@ -143,27 +133,15 @@ function(add_benchmark_test name source_file)
     PROPERTIES
           OUTPUT_NAME "${name}.libcxx.out"
           RUNTIME_OUTPUT_DIRECTORY "${BENCHMARK_OUTPUT_DIR}"
-          COMPILE_FLAGS "${BENCHMARK_TEST_LIBCXX_COMPILE_FLAGS}"
-          LINK_FLAGS "${BENCHMARK_TEST_LIBCXX_LINK_FLAGS}"
-          CXX_STANDARD 17
-          CXX_STANDARD_REQUIRED YES
           CXX_EXTENSIONS NO)
   cxx_link_system_libraries(${libcxx_target})
   if (LIBCXX_BENCHMARK_NATIVE_STDLIB)
-    if (LIBCXX_BENCHMARK_NATIVE_STDLIB STREQUAL "libstdc++" AND NOT DEFINED LIBSTDCXX_FILESYSTEM_LIB
-        AND "${name}" STREQUAL "filesystem")
-      return()
-    endif()
     set(native_target ${name}_native)
     add_executable(${native_target} EXCLUDE_FROM_ALL ${source_file})
+    target_link_libraries(${native_target} PRIVATE cxx-benchmarks-flags-native)
     add_dependencies(${native_target} google-benchmark-native
                                       google-benchmark-libcxx)
     target_link_libraries(${native_target} PRIVATE -lbenchmark)
-    if (LIBCXX_BENCHMARK_NATIVE_STDLIB STREQUAL "libstdc++")
-      target_link_libraries(${native_target} PRIVATE ${LIBSTDCXX_FILESYSTEM_LIB})
-    elseif (LIBCXX_BENCHMARK_NATIVE_STDLIB STREQUAL "libc++")
-      target_link_libraries(${native_target} PRIVATE -lc++fs -lc++experimental)
-    endif()
     if (LIBCXX_HAS_PTHREAD_LIB)
       target_link_libraries(${native_target} PRIVATE -pthread)
     endif()
@@ -172,11 +150,6 @@ function(add_benchmark_test name source_file)
       PROPERTIES
           OUTPUT_NAME "${name}.native.out"
           RUNTIME_OUTPUT_DIRECTORY "${BENCHMARK_OUTPUT_DIR}"
-          INCLUDE_DIRECTORIES ""
-          COMPILE_FLAGS "${BENCHMARK_TEST_NATIVE_COMPILE_FLAGS}"
-          LINK_FLAGS "${BENCHMARK_TEST_NATIVE_LINK_FLAGS}"
-          CXX_STANDARD 17
-          CXX_STANDARD_REQUIRED YES
           CXX_EXTENSIONS NO)
   endif()
 endfunction()