[RFC] [OpenMP] Turn on -Wall compiler warnings by default

[Hahnfeld]

Summary

Instead, maintain a list of disabled options to still build libomp and
libomptarget without warnings. This includes -Wno-error and -Wno-pedantic
to silence warnings that LLVM enables when building in-tree.

I tested the following compilers:

• Clang 6.0, 7.0, 8.0
• GCC 4.8.5 (CentOS 7), GCC 6, 7, 8, 9
• Intel Compiler 16, 17, 18, 19

[JonChesterfield]

I like this a lot. Thanks

[jlpeyton]

Thanks for this cleanup! Just one comment.

openmp/cmake/config-ix.cmake

4–15

Should everything be check_cxx_compiler_flag()?

[Hahnfeld]

openmp/cmake/config-ix.cmake

4–15

This was also my first feeling, but my second thought was that we might have C files again in the future. For example, some very simple tools with OMPT might not need C++ and we'll want all warnings for them. However, that's a weak argument for now without a real use and I can change it to check_cxx_compiler_flag if you think that's more consistent.

[jlpeyton]

openmp/cmake/config-ix.cmake

4–15

After some thought, I think we should use check_cxx_compiler_flag() and here is my reasoning:
The trend with the openmp project has been turning C code/files/anything into C++, sometimes nominally, but C++ nonetheless. I think it is reasonable to assume language agnostic options (e.g., -Wall) are supported by both the C and corresponding C++ compiler. This assumption is seen in the append_if(HAVE_FLAG "-Wflag" C_FLAGS CXX_FLAGS) code in HandleOpenMPOptions.cmake. So any future C file should be able to use the flags without issue.

[Hahnfeld]

openmp/cmake/config-ix.cmake

4–15

Ok, so just to be sure: You propose to check with check_cxx_compiler_flag and still add the flag to CMAKE_C_FLAGS? I guess that sounds reasonable.

[jlpeyton]

openmp/cmake/config-ix.cmake

4–15

Yes.

[Hahnfeld]

Change check_c_compiler_flag() to check_cxx_compiler_flag().

[jlpeyton]

LGTM

openmp/cmake/HandleOpenMPOptions.cmake

-if (${OPENMP_STANDALONE_BUILD})
+if (OPENMP_STANDALONE_BUILD)
   # From HandleLLVMOptions.cmake
   function(append_if condition value)
     if (${condition})
       foreach(variable ${ARGN})
         set(${variable} "${${variable}} ${value}" PARENT_SCOPE)
       endforeach(variable)
     endif()
   endfunction()
 endif()
 
-if (${OPENMP_ENABLE_WERROR})
+# MSVC and clang-cl in compatibility mode map -Wall to -Weverything.
+# TODO: LLVM adds /W4 instead, check if that works for the OpenMP runtimes.
+if (NOT MSVC)
+  append_if(OPENMP_HAVE_WALL_FLAG "-Wall" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
+endif()
+if (OPENMP_ENABLE_WERROR)
   append_if(OPENMP_HAVE_WERROR_FLAG "-Werror" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
 endif()
 
+# Additional warnings that are not enabled by -Wall.
+append_if(OPENMP_HAVE_WCAST_QUAL_FLAG "-Wcast-qual" CMAKE_CXX_FLAGS)
+append_if(OPENMP_HAVE_WFORMAT_PEDANTIC_FLAG "-Wformat-pedantic" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
+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_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)
+
 append_if(OPENMP_HAVE_STD_GNUPP11_FLAG "-std=gnu++11" CMAKE_CXX_FLAGS)
 if (NOT OPENMP_HAVE_STD_GNUPP11_FLAG)
   append_if(OPENMP_HAVE_STD_CPP11_FLAG "-std=c++11" CMAKE_CXX_FLAGS)
 endif()

openmp/cmake/config-ix.cmake

 include(CheckCCompilerFlag)
 include(CheckCXXCompilerFlag)
 
+check_c_compiler_flag(-Wall OPENMP_HAVE_WALL_FLAG)
 check_c_compiler_flag(-Werror OPENMP_HAVE_WERROR_FLAG)
 
+# Additional warnings that are not enabled by -Wall.
+check_cxx_compiler_flag(-Wcast-qual OPENMP_HAVE_WCAST_QUAL_FLAG)
+check_c_compiler_flag(-Wformat-pedantic OPENMP_HAVE_WFORMAT_PEDANTIC_FLAG)
+check_c_compiler_flag(-Wsign-compare OPENMP_HAVE_WSIGN_COMPARE_FLAG)
+
+# Warnings that we want to disable because they are too verbose or fragile.
+check_c_compiler_flag(-Wno-extra OPENMP_HAVE_WNO_EXTRA_FLAG)
+check_c_compiler_flag(-Wno-pedantic OPENMP_HAVE_WNO_PEDANTIC_FLAG)
+check_c_compiler_flag(-Wno-maybe-uninitialized OPENMP_HAVE_WNO_MAYBE_UNINITIALIZED_FLAG)
+
 check_cxx_compiler_flag(-std=gnu++11 OPENMP_HAVE_STD_GNUPP11_FLAG)
 check_cxx_compiler_flag(-std=c++11 OPENMP_HAVE_STD_CPP11_FLAG)

openmp/runtime/cmake/LibompHandleFlags.cmake

if(NOT "${${flags}}" STREQUAL "") # if flags are empty, don't do anything
     list(REMOVE_DUPLICATES ${flags}) # remove duplicates
     list(REMOVE_ITEM ${flags} "") # remove empty items
     libomp_list_to_string("${${flags}}" flags_local)
     string(STRIP "${flags_local}" flags_local)
     set(${flags} "${flags_local}")
   endif()
 endmacro()
 
-# Gets flags common to both the C and C++ compiler
-function(libomp_get_c_and_cxxflags_common flags)
+# C++ compiler flags
+function(libomp_get_cxxflags cxxflags)
   set(flags_local)
   libomp_append(flags_local -fno-exceptions LIBOMP_HAVE_FNO_EXCEPTIONS_FLAG)
   libomp_append(flags_local -fno-rtti LIBOMP_HAVE_FNO_RTTI_FLAG)
-  if(${OPENMP_STANDALONE_BUILD})
-    libomp_append(flags_local -Wsign-compare LIBOMP_HAVE_WNO_SIGN_COMPARE_FLAG)
-    libomp_append(flags_local -Wunused-function LIBOMP_HAVE_WNO_UNUSED_FUNCTION_FLAG)
-    libomp_append(flags_local -Wunused-local-typedef LIBOMP_HAVE_WNO_UNUSED_LOCAL_TYPEDEF_FLAG)
-    libomp_append(flags_local -Wunused-value LIBOMP_HAVE_WNO_UNUSED_VALUE_FLAG)
-    libomp_append(flags_local -Wunused-variable LIBOMP_HAVE_WNO_UNUSED_VARIABLE_FLAG)
-    libomp_append(flags_local -Wdeprecated-register LIBOMP_HAVE_WNO_DEPRECATED_REGISTER_FLAG)
-    libomp_append(flags_local -Wunknown-pragmas LIBOMP_HAVE_WNO_UNKNOWN_PRAGMAS_FLAG)
-    libomp_append(flags_local -Wcomment LIBOMP_HAVE_WNO_COMMENT_FLAG)
-    libomp_append(flags_local -Wself-assign LIBOMP_HAVE_WNO_SELF_ASSIGN_FLAG)
-    libomp_append(flags_local -Wformat-pedantic LIBOMP_HAVE_WNO_FORMAT_PEDANTIC_FLAG)
-  endif()
-  libomp_append(flags_local -Wno-switch LIBOMP_HAVE_WNO_SWITCH_FLAG)
+  libomp_append(flags_local -Wno-class-memaccess LIBOMP_HAVE_WNO_CLASS_MEMACCESS_FLAG)
   libomp_append(flags_local -Wno-covered-switch-default LIBOMP_HAVE_WNO_COVERED_SWITCH_DEFAULT_FLAG)
-  libomp_append(flags_local -Wno-gnu-anonymous-struct LIBOMP_HAVE_WNO_GNU_ANONYMOUS_STRUCT_FLAG)
-  libomp_append(flags_local -Wno-missing-field-initializers LIBOMP_HAVE_WNO_MISSING_FIELD_INITIALIZERS_FLAG)
+  libomp_append(flags_local -Wno-frame-address LIBOMP_HAVE_WNO_FRAME_ADDRESS_FLAG)
+  libomp_append(flags_local -Wno-implicit-fallthrough LIBOMP_HAVE_WNO_IMPLICIT_FALLTHROUGH_FLAG)
+  libomp_append(flags_local -Wno-int-in-bool-context LIBOMP_HAVE_WNO_INT_IN_BOOL_CONTEXT_FLAG)
   libomp_append(flags_local -Wno-missing-braces LIBOMP_HAVE_WNO_MISSING_BRACES_FLAG)
-  libomp_append(flags_local -Wno-vla-extension LIBOMP_HAVE_WNO_VLA_EXTENSION_FLAG)
+  libomp_append(flags_local -Wno-parentheses LIBOMP_HAVE_WNO_PARENTHESES_FLAG)
+  libomp_append(flags_local -Wno-strict-aliasing LIBOMP_HAVE_WNO_STRICT_ALIASING_FLAG)
   libomp_append(flags_local -Wstringop-overflow=0 LIBOMP_HAVE_WSTRINGOP_OVERFLOW_FLAG)
+  libomp_append(flags_local -Wno-stringop-truncation LIBOMP_HAVE_WNO_STRINGOP_TRUNCATION_FLAG)
+  libomp_append(flags_local -Wno-switch LIBOMP_HAVE_WNO_SWITCH_FLAG)
+  libomp_append(flags_local -Wno-uninitialized LIBOMP_HAVE_WNO_UNINITIALIZED_FLAG)
+  libomp_append(flags_local -Wno-unused-but-set-variable LIBOMP_HAVE_WNO_UNUSED_BUT_SET_VARIABLE_FLAG)
   libomp_append(flags_local /GS LIBOMP_HAVE_GS_FLAG)
   libomp_append(flags_local /EHsc LIBOMP_HAVE_EHSC_FLAG)
   libomp_append(flags_local /Oy- LIBOMP_HAVE_OY__FLAG)
   libomp_append(flags_local -mrtm LIBOMP_HAVE_MRTM_FLAG)
   # Intel(R) C Compiler flags
   libomp_append(flags_local /Qsafeseh LIBOMP_HAVE_QSAFESEH_FLAG)
   libomp_append(flags_local -Qoption,cpp,--extended_float_types LIBOMP_HAVE_EXTENDED_FLOAT_TYPES_FLAG)
   libomp_append(flags_local -Qlong_double LIBOMP_HAVE_LONG_DOUBLE_FLAG)
if(${IA32})
     libomp_append(flags_local /arch:SSE2 LIBOMP_HAVE_ARCH_SSE2_FLAG)
     libomp_append(flags_local -msse2 LIBOMP_HAVE_MSSE2_FLAG)
     libomp_append(flags_local -falign-stack=maintain-16-byte LIBOMP_HAVE_FALIGN_STACK_FLAG)
   elseif(${MIC})
     libomp_append(flags_local -mmic LIBOMP_HAVE_MMIC_FLAG)
     libomp_append(flags_local -ftls-model=initial-exec LIBOMP_HAVE_FTLS_MODEL_FLAG)
     libomp_append(flags_local "-opt-streaming-stores never" LIBOMP_HAVE_OPT_STREAMING_STORES_FLAG)
   endif()
-  set(${flags} ${flags_local} PARENT_SCOPE)
-endfunction()
-
-# C++ compiler flags
-function(libomp_get_cxxflags cxxflags)
-  set(cxxflags_local)
-  libomp_get_c_and_cxxflags_common(cxxflags_local)
-  if(${OPENMP_STANDALONE_BUILD})
-      libomp_append(cxxflags_local -Wcast-qual LIBOMP_HAVE_WCAST_QUAL_FLAG)
-  endif()
-  set(cxxflags_local ${cxxflags_local} ${LIBOMP_CXXFLAGS})
+  set(cxxflags_local ${flags_local} ${LIBOMP_CXXFLAGS})
   libomp_setup_flags(cxxflags_local)
   set(${cxxflags} ${cxxflags_local} PARENT_SCOPE)
 endfunction()
 
 # Assembler flags
 function(libomp_get_asmflags asmflags)
   set(asmflags_local)
   libomp_append(asmflags_local "-x assembler-with-cpp" LIBOMP_HAVE_X_ASSEMBLER_WITH_CPP_FLAG)

openmp/runtime/cmake/config-ix.cmake

 
 # Includes the architecture flag in both compile and link phase
 function(libomp_check_architecture_flag flag retval)
   set(CMAKE_REQUIRED_FLAGS "${flag}")
   check_c_compiler_flag("${flag}" ${retval})
   set(${retval} ${${retval}} PARENT_SCOPE)
 endfunction()
 
-# Checking C, CXX, Linker Flags
+# Checking CXX, Linker Flags
 check_cxx_compiler_flag(-fno-exceptions LIBOMP_HAVE_FNO_EXCEPTIONS_FLAG)
 check_cxx_compiler_flag(-fno-rtti LIBOMP_HAVE_FNO_RTTI_FLAG)
-check_cxx_compiler_flag(-Wcast-qual LIBOMP_HAVE_WCAST_QUAL_FLAG)
-check_c_compiler_flag(-Wunused-function LIBOMP_HAVE_WNO_UNUSED_FUNCTION_FLAG)
-check_c_compiler_flag(-Wunused-local-typedef LIBOMP_HAVE_WNO_UNUSED_LOCAL_TYPEDEF_FLAG)
-check_c_compiler_flag(-Wunused-value LIBOMP_HAVE_WNO_UNUSED_VALUE_FLAG)
-check_c_compiler_flag(-Wunused-variable LIBOMP_HAVE_WNO_UNUSED_VARIABLE_FLAG)
-check_c_compiler_flag(-Wswitch LIBOMP_HAVE_WNO_SWITCH_FLAG)
-check_c_compiler_flag(-Wcovered-switch-default LIBOMP_HAVE_WNO_COVERED_SWITCH_DEFAULT_FLAG)
-check_c_compiler_flag(-Wdeprecated-register LIBOMP_HAVE_WNO_DEPRECATED_REGISTER_FLAG)
-check_c_compiler_flag(-Wsign-compare LIBOMP_HAVE_WNO_SIGN_COMPARE_FLAG)
-check_c_compiler_flag(-Wgnu-anonymous-struct LIBOMP_HAVE_WNO_GNU_ANONYMOUS_STRUCT_FLAG)
-check_c_compiler_flag(-Wunknown-pragmas LIBOMP_HAVE_WNO_UNKNOWN_PRAGMAS_FLAG)
-check_c_compiler_flag(-Wmissing-field-initializers LIBOMP_HAVE_WNO_MISSING_FIELD_INITIALIZERS_FLAG)
-check_c_compiler_flag(-Wmissing-braces LIBOMP_HAVE_WNO_MISSING_BRACES_FLAG)
-check_c_compiler_flag(-Wcomment LIBOMP_HAVE_WNO_COMMENT_FLAG)
-check_c_compiler_flag(-Wself-assign LIBOMP_HAVE_WNO_SELF_ASSIGN_FLAG)
-check_c_compiler_flag(-Wvla-extension LIBOMP_HAVE_WNO_VLA_EXTENSION_FLAG)
-check_c_compiler_flag(-Wformat-pedantic LIBOMP_HAVE_WNO_FORMAT_PEDANTIC_FLAG)
-check_c_compiler_flag(-Wstringop-overflow=0 LIBOMP_HAVE_WSTRINGOP_OVERFLOW_FLAG)
-check_c_compiler_flag(-msse2 LIBOMP_HAVE_MSSE2_FLAG)
-check_c_compiler_flag(-ftls-model=initial-exec LIBOMP_HAVE_FTLS_MODEL_FLAG)
+check_cxx_compiler_flag(-Wno-class-memaccess LIBOMP_HAVE_WNO_CLASS_MEMACCESS_FLAG)
+check_cxx_compiler_flag(-Wno-covered-switch-default LIBOMP_HAVE_WNO_COVERED_SWITCH_DEFAULT_FLAG)
+check_cxx_compiler_flag(-Wno-frame-address LIBOMP_HAVE_WNO_FRAME_ADDRESS_FLAG)
+check_cxx_compiler_flag(-Wno-implicit-fallthrough LIBOMP_HAVE_WNO_IMPLICIT_FALLTHROUGH_FLAG)
+check_cxx_compiler_flag(-Wno-int-in-bool-context LIBOMP_HAVE_WNO_INT_IN_BOOL_CONTEXT_FLAG)
+check_cxx_compiler_flag(-Wno-missing-braces LIBOMP_HAVE_WNO_MISSING_BRACES_FLAG)
+check_cxx_compiler_flag(-Wno-parentheses LIBOMP_HAVE_WNO_PARENTHESES_FLAG)
+check_cxx_compiler_flag(-Wno-strict-aliasing LIBOMP_HAVE_WNO_STRICT_ALIASING_FLAG)
+check_cxx_compiler_flag(-Wstringop-overflow=0 LIBOMP_HAVE_WSTRINGOP_OVERFLOW_FLAG)
+check_cxx_compiler_flag(-Wno-stringop-truncation LIBOMP_HAVE_WNO_STRINGOP_TRUNCATION_FLAG)
+check_cxx_compiler_flag(-Wno-switch LIBOMP_HAVE_WNO_SWITCH_FLAG)
+check_cxx_compiler_flag(-Wno-uninitialized LIBOMP_HAVE_WNO_UNINITIALIZED_FLAG)
+check_cxx_compiler_flag(-Wno-unused-but-set-variable LIBOMP_HAVE_WNO_UNUSED_BUT_SET_VARIABLE_FLAG)
+check_cxx_compiler_flag(-msse2 LIBOMP_HAVE_MSSE2_FLAG)
+check_cxx_compiler_flag(-ftls-model=initial-exec LIBOMP_HAVE_FTLS_MODEL_FLAG)
 libomp_check_architecture_flag(-mmic LIBOMP_HAVE_MMIC_FLAG)
 libomp_check_architecture_flag(-m32 LIBOMP_HAVE_M32_FLAG)
 if(WIN32)
   if(MSVC)
     # Check Windows MSVC style flags.
     check_cxx_compiler_flag(/EHsc LIBOMP_HAVE_EHSC_FLAG)
     check_cxx_compiler_flag(/GS LIBOMP_HAVE_GS_FLAG)
     check_cxx_compiler_flag(/Oy- LIBOMP_HAVE_Oy__FLAG)
     check_cxx_compiler_flag(/arch:SSE2 LIBOMP_HAVE_ARCH_SSE2_FLAG)
     check_cxx_compiler_flag(/Qsafeseh LIBOMP_HAVE_QSAFESEH_FLAG)
   endif()
-  check_c_compiler_flag(-mrtm LIBOMP_HAVE_MRTM_FLAG)
+  check_cxx_compiler_flag(-mrtm LIBOMP_HAVE_MRTM_FLAG)
   # It is difficult to create a dummy masm assembly file
   # and then check the MASM assembler to see if these flags exist and work,
   # so we assume they do for Windows.
   set(LIBOMP_HAVE_SAFESEH_MASM_FLAG TRUE)
   set(LIBOMP_HAVE_COFF_MASM_FLAG TRUE)
   # Change Windows flags /MDx to /MTx
   foreach(libomp_lang IN ITEMS C CXX)
     foreach(libomp_btype IN ITEMS DEBUG RELWITHDEBINFO RELEASE MINSIZEREL)