In D41096#953086, @hfinkel wrote:

In D41096#953039, @craig.topper wrote:

Yes there are two variants of sklake-avx512, but there doesn't seem to be a good way of autodetecting this for march=native.

Your optimization manual suggests a relative timing test, so I'm guessing there's not (I wouldn't want to use that for -march=native because it wouldn't be deterministic). As a result, I think we'll just need to make a choice based on some combination of which is likely to be most common among our users and which is likely best on future hardware. Users will need to explicitly specify the architecture to get the other one.

It isn't enough:

/home/markus/llvm/compiler-rt/lib/esan/esan_sideline_linux.cpp: In static member function ‘static int __esan::SidelineThread::runSideline(void*)’:                                 
/home/markus/llvm/compiler-rt/lib/esan/esan_sideline_linux.cpp:73:22: error: aggregate ‘__esan::SidelineThread::runSideline(void*)::sigaltstack SigAltStack’ has incomplete type and cannot be defined
   struct sigaltstack SigAltStack;          
                      ^~~~~~~~~~~

The issue got fixed by r288486.

This breaks building with gcc: