[libcxx-commits] [libcxx] [libc++][test][msan] Fix bots after #67799 (PR #73152)

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huixie90 wrote:

So the problem is specifically to 

> Ubuntu with MSAN build on x86 with fp80 long double

The loop that it got stucks in is a CAS loop where there is an existing problem for fp80 where compare-exchange always return false because of the padding.  Inside the loop I have a workaround to copy the memory contents to “old” on a failing compare-exchange (and there is another exiting bug here that it does not seem to update the old for fp80) . Note normal assignment would not work because it does not assign the padding bits.  I suspect MSAN is intercepting my workaround here.  And yes we should really properly fix the issue rather than applying more and more workaround but we need the compiler side to help us. 

https://github.com/llvm/llvm-project/pull/73152