https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98677
--- Comment #4 from Egor Suvorov <egor_suvorov at mail dot ru> --- Note that the issue requires both UBSanitizer and Valgrind enabled simultaneously. Running with just one of them does not result in an error. The versions are ones installed in Ubuntu 20.04.3 Focal Fossa (amd64) by running `sudo apt install clang-10 valgrind` (you can get VM image from https://www.osboxes.org/ubuntu-server/) https://launchpad.net/ubuntu/focal/amd64/clang-10/1:10.0.0-4ubuntu1 https://launchpad.net/ubuntu/focal/amd64/valgrind/1:3.15.0-1ubuntu9.1 Unfortunately, I was unable to get more verbose output from either clang or Valgrind. So it may be Ubuntu-specific issue. Actually, the problem is not reproducible with clang-12, so it may be already be fixed.
