[compiler-rt] r276256 - Attempt to fix clang-cmake-mips after r268977.

[Chris Bieneman via llvm-commits]

> On Jul 24, 2016, at 7:01 AM, Daniel Sanders <Daniel.Sanders at imgtec.com> wrote:
> 
>>>> What I think is happening is that the 'include(builtin-config-ix)' in lib/builtins/CMakeLists.txt includes the
>>>> 'set(TEST_COMPILE_ONLY On)' from cmake/builtin-config-ix.cmake which later causes
>>>> CAN_TARGET_mips64 to be set according to the compiler behaviour rather than the compiler+linker
>>>> behaviour. I can compile mips64 objects successfully on this machine but I can't link them.
>>> 
>>> This isn't what's happening but because 'set(TEST_COMPILE_ONLY On)' executes slightly after the CAN_TARGET_mips64 check.
>>> 
>>> It seems the truth of the matter is that r275780 on Monday fixed gcc builds by changing –mabi=n64 to –mabi=64. This didn't
>>> take effect until Wednesday because buildbot is configured to skip the cmake command if build.ninja exists. On Wednesday,
>>> we repaired the disk which eventually caused buildbot to wipe the build area and run the cmake command, introducing the
>>> failures. At this point, I couldn't find anything obvious in the blamelists for Wednesday so I looked into it and found the
>>> unconditional 'set(TEST_COMPILE_ONLY On)' which led me to r276256.
>>> 
>>> To summarize, I think the unconditional 'set(TEST_COMPILE_ONLY On)' is probably a bug that would have a similar effect to our buildbot failure but it wasn't the cause of it. Sorry for the noise.
>> 
>> This is actually intentional. It shouldn't impact the non-darwin build because the tests on the non-Apple branch are under if(COMPILER_RT_BUILTINS_STANDALONE_BUILD). In the Apple build, this
>> allows the builtins build to include architectures that aren't included in the sanitizer build.
>> 
>> -Chris
> 
> Ah ok. Do you expect to define CAN_TARGET_${arch} both before and after the 'set(TEST_COMPILE_ONLY On)' or just on one side of it? If the answer is both then I'll need to re-work this workaround since the checks after the 'set(TEST_COMPILE_ONLY On)' will currently re-use the cached CAN_TARGET_${arch} from before it and this won't account for the updated TEST_COMPILE_ONLY.

Actually, looking through this more closely (now that I’m not on vacation). On the Darwin side CAN_TARGET_${arch} isn’t used at all, we use CAN_TARGET_${os}_${arch} because the architecture alone isn’t enough. That said, we do still set the CAN_TARGET_${os}_${arch} values after TEST_COMPILE_ONLY is set.

It is expected that anything that passes the check before TEST_COMPILE_ONLY is set will also pass later, but there are cases where architectures will pass only after TEST_COMPILE_ONLY is On. In particular some of the embedded architectures are supported in the builtins build, but not the sanitizer builds.

-Chris