I am working on making FileCheck stricter (in D54769 and D53710) so that it issues diagnostics when there's something wrong with tests.
This is a cleanup for dangling prefixes in the ARM codegen tests:
--check-prefixes=A,B
where A occurs in the check file, but B doesn't. This can be innocent if A does all the required checking, but can also be a bug in that test if it results in the test actually not checking anything if A only checks a common label. Test CodeGen/ARM/smml.ll is such an example