Control: forwarded -1 https://bugs.llvm.org/show_bug.cgi?id=30587 (They actually found it independently, but it's clearly the same bug.)
They don't have a fix for this one; they do have fixes for https://bugs.llvm.org/show_bug.cgi?id=31571 / https://bugs.llvm.org/show_bug.cgi?id=28127 (similar problems in LLVM's own tools), but it's not yet clear whether these can help us.
