[PATCH] D19895: cmake: Introduce TEST_SUITE_C_FLAGS, TEST_SUITE_CXX_FLAGS, etc.

Tue May 3 19:14:23 PDT 2016

I tried setting CMAKE_C_FLAGS_RELEASE in the cache files and it fails: The problem I run into is that I have to pass an "-arch XXX" when compiling otherwise the you won't be able to link the executables with the libraries coming with the SDK for the cross compiler. The problem however is that various cmake tests use cmakes try_compile() which creates a mini CMakeLists.txt file and only passes along a select bunch of variables. It does not pass along CMAKE_C_FLAGS_RELEASE (or CMAKE_BUILD_TYPE).

So the only way I see this working is when the cache files set CMAKE_C_FLAGS which means extra flags by users have to come in different variables as proposed here.

- Matthias

Repository:
 rL LLVM

http://reviews.llvm.org/D19895 <http://reviews.llvm.org/D19895>

> On May 3, 2016, at 6:31 PM, Matthias Braun via llvm-commits <llvm-commits at lists.llvm.org> wrote:
> 
> Yeah CMAKE_C_FLAGS_RELEASE would work but feels like a hack as well... We would need to override the flags for DEBUG, RELEASE, MINSIZEREL and RELWITHDEBINFO to be on the safe side. And I kinda liked the fact that we currently can have 1 cache file specifying optimization flags like -flto, -fomit-frame-pointer etc. and combine that with another cache file that just sets stuff up for a different target. Admittedly there are ways to get this working...
> 
>> On May 3, 2016, at 6:24 PM, Justin Bogner via llvm-commits <llvm-commits at lists.llvm.org> wrote:
>> 
>> Matthias Braun via llvm-commits <llvm-commits at lists.llvm.org> writes:
>>> MatzeB created this revision.
>>> MatzeB added reviewers: cmatthews, kristof.beyls, jmolloy.
>>> MatzeB added a subscriber: llvm-commits.
>>> MatzeB set the repository for this revision to rL LLVM.
>>> Herald added a subscriber: mcrosier.
>>> 
>>> Intuitively one would use CMAKE_C_FLAGS, CMAKE_CXX_FLAGS and
>>> CMAKE_EXE_LINKER_FLAGS to inject custom flags into the build. However
>>> this clashes with the use of cmake cache files which want to add flags as well.
>>> A user specifying CMAKE_C_FLAGS would (accidentally) override the
>>> flags set by the cache files.
>> 
>> AFAIK The usual trick is to set CMAKE_C_FLAGS_RELEASE or
>> CMAKE_C_FLAGS_MINSIZEREL or whatever in the cache file, and leave the
>> CMAKE_C_FLAGS for the command line user to do what they want with.
>> 
>>> The solution here is to introduce a new set of flags called
>>> TEST_SUITE_C_FLAGS, TEST_SUITE_CXX_FLAGS and TEST_SUITE_EXE_LINKER_FLAGS
>>> as a means for users to specify additional flags. This way the flags
>>> will not override the settings from the cache file.
>>> 
>>> In order to educate users to use the new flags a warning message is
>>> displayed if CMAKE_C_FLAGS is set.
>>> 
>>> Repository:
>>> rL LLVM
>>> 
>>> http://reviews.llvm.org/D19895
>>> 
>>> Files:
>>> CMakeLists.txt
>>> cmake/caches/util/arch_flags.cmake
>>> 
>>> Index: cmake/caches/util/arch_flags.cmake
>>> ===================================================================
>>> --- cmake/caches/util/arch_flags.cmake
>>> +++ cmake/caches/util/arch_flags.cmake
>>> @@ -2,3 +2,5 @@
>>> set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${ARCH_FLAGS}" CACHE STRING "")
>>> set(CMAKE_MODULE_LINKER_FLAGS "${CMAKE_MODULE_LINKER_FLAGS} ${ARCH_FLAGS}" CACHE STRING "")
>>> set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} ${ARCH_FLAGS}" CACHE STRING "")
>>> +# Silence the warning in the toplevel CMakeLists.txt.
>>> +set(EXPECTED_CMAKE_C_FLAGS "${CMAKE_C_FLAGS}" CACHE STRING "")
>>> Index: CMakeLists.txt
>>> ===================================================================
>>> --- CMakeLists.txt
>>> +++ CMakeLists.txt
>>> @@ -12,13 +12,33 @@
>>> mark_as_advanced(CMAKE_INSTALL_PREFIX)
>>> # On the other hand we often want to switch compiler or cflags
>>> mark_as_advanced(CLEAR CMAKE_C_COMPILER CMAKE_CXX_COMPILER CMAKE_LINKER
>>> -  CMAKE_C_FLAGS CMAKE_C_FLAGS_DEBUG CMAKE_C_FLAGS_MINSIZEREL
>>> +  CMAKE_C_FLAGS_DEBUG CMAKE_C_FLAGS_MINSIZEREL
>>>  CMAKE_C_FLAGS_RELEASE CMAKE_C_FLAGS_RELWITHDEBINFO
>>> -  CMAKE_CXX_FLAGS CMAKE_CXX_FLAGS_DEBUG CMAKE_CXX_FLAGS_MINSIZEREL
>>> +  CMAKE_CXX_FLAGS_DEBUG CMAKE_CXX_FLAGS_MINSIZEREL
>>>  CMAKE_CXX_FLAGS_RELEASE CMAKE_CXX_FLAGS_RELWITHDEBINFO
>>> -  CMAKE_EXE_LINKER_FLAGS CMAKE_EXE_LINKER_FLAGS_DEBUG
>>> -  CMAKE_EXE_LINKER_FLAGS_MINSIZEREL CMAKE_EXE_LINKER_FLAGS_RELEASE
>>> -  CMAKE_EXE_LINKER_FLAGS_RELWITHDEBINFO)
>>> +  CMAKE_EXE_LINKER_FLAGS_DEBUG CMAKE_EXE_LINKER_FLAGS_MINSIZEREL
>>> +  CMAKE_EXE_LINKER_FLAGS_RELEASE CMAKE_EXE_LINKER_FLAGS_RELWITHDEBINFO)
>>> +
>>> +# Encourage people to use TEST_SUITE_C_FLAGS/TEST_SUITE_CXX_FLAGS so
>>> +# CMAKE_C_FLAGS can be used exclusively by -C cachefiles for specifying
>>> +# target flags without the user accidentally overriding them.
>>> +set(EXPECTED_CMAKE_C_FLAGS "" CACHE STRING
>>> +    "Allows cache files to disable the CMAKE_C_FLAGS warning message")
>>> +mark_as_advanced(EXPECTED_CMAKE_C_FLAGS)
>>> +if(NOT "${CMAKE_C_FLAGS}" STREQUAL "${EXPECTED_CMAKE_C_FLAGS}")
>>> +  message(WARNING "
>>> +Specifying CMAKE_C_FLAGS, CMAKE_CXX_FLAGS, \
>>> +CMAKE_EXE_LINKER_FLAGS is discouraged. Use TEST_SUITE_C_FLAGS, \
>>> +TEST_SUITE_CXX_FLAGS and TEST_SUITE_EXE_LINKER_FLAGS instead.\
>>> +")
>>> +endif()
>>> +mark_as_advanced(CMAKE_C_FLAGS CMAKE_CXX_FLAGS CMAKE_EXE_LINKER_FLAGS)
>>> +set(TEST_SUITE_C_FLAGS "" CACHE STRING "Flags used by the C compiler.")
>>> +set(TEST_SUITE_CXX_FLAGS "${TEST_SUITE_C_FLAGS}" CACHE STRING "Flags used by the C++ compiler.")
>>> +set(TEST_SUITE_EXE_LINKER_FLAGS "" CACHE STRING "Flags used by the linker.")
>>> +set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${TEST_SUITE_C_FLAGS}")
>>> +set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${TEST_SUITE_CXX_FLAGS}")
>>> +set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} ${TEST_SUITE_EXE_LINKER_FLAGS}")
>>> 
>>> project(test-suite C CXX)
>>> 
>>> 
>>> 
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