[OpenMP] Fix detecting warning options for GCC

If testing for a warning option like -Wno-<foo> with GCC, GCC won't
print any diagnostic at all, leading to the options being accepted
incorrectly. However later, if compiling a file that actually prints
another warning, GCC will also print warnings about these -Wno-<foo>
options being unrecognized.

This avoids warning spam like this, for every OpenMP source file that
produces build warnings with GCC:

    cc1plus: warning: unrecognized command line option ‘-Wno-int-to-void-pointer-cast’
    cc1plus: warning: unrecognized command line option ‘-Wno-return-type-c-linkage’
    cc1plus: warning: unrecognized command line option ‘-Wno-covered-switch-default’
    cc1plus: warning: unrecognized command line option ‘-Wno-enum-constexpr-conversion’

This matches how such warning options are detected and added in
llvm/cmake/modules/HandleLLVMOptions.cmake, e.g. like this:

    check_cxx_compiler_flag("-Wclass-memaccess" CXX_SUPPORTS_CLASS_MEMACCESS_FLAG)
    append_if(CXX_SUPPORTS_CLASS_MEMACCESS_FLAG "-Wno-class-memaccess" CMAKE_CXX_FLAGS)

This also matches how LLDB warning options were restructured for
GCC compatibility in e546bbfda0ab91cf78c096d8c035851cc7c3b9f3.

Differential Revision: https://reviews.llvm.org/D139922

2 files changed, 20 insertions, 8 deletions

diff --git a/openmp/cmake/HandleOpenMPOptions.cmake b/openmp/cmake/HandleOpenMPOptions.cmake
index e0a9e0d023ab..53a2d053e424 100644
--- a/openmp/cmake/HandleOpenMPOptions.cmake
+++ b/openmp/cmake/HandleOpenMPOptions.cmake
@@ -25,9 +25,15 @@ append_if(OPENMP_HAVE_WIMPLICIT_FALLTHROUGH_FLAG "-Wimplicit-fallthrough" CMAKE_
 append_if(OPENMP_HAVE_WSIGN_COMPARE_FLAG "-Wsign-compare" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
 
 # Warnings that we want to disable because they are too verbose or fragile.
-append_if(OPENMP_HAVE_WNO_ENUM_CONSTEXPR_CONVERSION_FLAG "-Wno-enum-constexpr-conversion" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
-append_if(OPENMP_HAVE_WNO_EXTRA_FLAG "-Wno-extra" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
-append_if(OPENMP_HAVE_WNO_PEDANTIC_FLAG "-Wno-pedantic" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
-append_if(OPENMP_HAVE_WNO_MAYBE_UNINITIALIZED_FLAG "-Wno-maybe-uninitialized" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
+
+# GCC silently accepts any -Wno-<foo> option, but warns about those options
+# being unrecognized only if the compilation triggers other warnings to be
+# printed. Therefore, check for whether the compiler supports options in the
+# form -W<foo>, and if supported, add the corresponding -Wno-<foo> option.
+
+append_if(OPENMP_HAVE_WENUM_CONSTEXPR_CONVERSION_FLAG "-Wno-enum-constexpr-conversion" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
+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)
diff --git a/openmp/cmake/config-ix.cmake b/openmp/cmake/config-ix.cmake
index d88ea9f7e1ad..857cfe5da8d6 100644
--- a/openmp/cmake/config-ix.cmake
+++ b/openmp/cmake/config-ix.cmake
@@ -26,9 +26,15 @@ check_cxx_compiler_flag(-Wimplicit-fallthrough OPENMP_HAVE_WIMPLICIT_FALLTHROUGH
 check_cxx_compiler_flag(-Wsign-compare OPENMP_HAVE_WSIGN_COMPARE_FLAG)
 
 # Warnings that we want to disable because they are too verbose or fragile.
-check_cxx_compiler_flag(-Wno-enum-constexpr-conversion OPENMP_HAVE_WNO_ENUM_CONSTEXPR_CONVERSION_FLAG)
-check_cxx_compiler_flag(-Wno-extra OPENMP_HAVE_WNO_EXTRA_FLAG)
-check_cxx_compiler_flag(-Wno-pedantic OPENMP_HAVE_WNO_PEDANTIC_FLAG)
-check_cxx_compiler_flag(-Wno-maybe-uninitialized OPENMP_HAVE_WNO_MAYBE_UNINITIALIZED_FLAG)
+
+# GCC silently accepts any -Wno-<foo> option, but warns about those options
+# being unrecognized only if the compilation triggers other warnings to be
+# printed. Therefore, check for whether the compiler supports options in the
+# form -W<foo>, and if supported, add the corresponding -Wno-<foo> option.
+
+check_cxx_compiler_flag(-Wenum-constexpr-conversion OPENMP_HAVE_WENUM_CONSTEXPR_CONVERSION_FLAG)
+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)