[libc++] Require C++20 to build the benchmarks.

Some work-in-progress patches for the format header contain benchmarks.
The format header requires C++20 to build. This is a preparation to make
it easy to add these benchmarks.

Reviewed By: ldionne, #libc

Differential Revision: https://reviews.llvm.org/D96057

diff --git a/libcxx/benchmarks/CMakeLists.txt b/libcxx/benchmarks/CMakeLists.txt
index 0327f05..340de86 100644 (file)
--- a/libcxx/benchmarks/CMakeLists.txt
+++ b/libcxx/benchmarks/CMakeLists.txt
@@ -142,7 +142,7 @@ function(add_benchmark_test name source_file)
           RUNTIME_OUTPUT_DIRECTORY "${BENCHMARK_OUTPUT_DIR}"
           COMPILE_FLAGS "${BENCHMARK_TEST_LIBCXX_COMPILE_FLAGS}"
           LINK_FLAGS "${BENCHMARK_TEST_LIBCXX_LINK_FLAGS}"
-          CXX_STANDARD 17
+          CXX_STANDARD 20
           CXX_STANDARD_REQUIRED YES
           CXX_EXTENSIONS NO)
   cxx_link_system_libraries(${libcxx_target})
@@ -172,7 +172,7 @@ function(add_benchmark_test name source_file)
           INCLUDE_DIRECTORIES ""
           COMPILE_FLAGS "${BENCHMARK_TEST_NATIVE_COMPILE_FLAGS}"
           LINK_FLAGS "${BENCHMARK_TEST_NATIVE_LINK_FLAGS}"
-          CXX_STANDARD 17
+          CXX_STANDARD 20
           CXX_STANDARD_REQUIRED YES
           CXX_EXTENSIONS NO)
   endif()

diff --git a/libcxx/docs/ReleaseNotes.rst b/libcxx/docs/ReleaseNotes.rst
index 00ada48..d9302fe 100644 (file)
--- a/libcxx/docs/ReleaseNotes.rst
+++ b/libcxx/docs/ReleaseNotes.rst
@@ -43,4 +43,5 @@ New Features
 API Changes
 -----------
 
-- ...
+- Starting with libc++13 a C++20 capable compiler is required to build the
+  libc++ benchmarks.