The textual IR is not backwards compatible, but the bitcode format has been best-effort auto-upgradeable for as long as I've been involved (2006). The policy is

The textual IR is not backwards compatible, but the bitcode format has been best-effort auto-upgradeable for as long as I've been involved (2006). The policy is documented here: https://llvm.org/docs/DeveloperPolicy.html#ir-backwards-compatibility https://llvm.org/docs/DeveloperPolicy.html#ir-backwards-comp...