[Assess graduate-level ability to design and formally verify a compiler backend that preserves concurrency semantics on weak-memory architectures; test knowledge of weak-memory models (TSO/ARM/POWER), operational vs. axiomatic semantics, correct lowering of atomic primitives, fence insertion and placement, interactions with register allocation and instruction selection, construction of refinement/simulation proofs, mechanized proof techniques (Coq/Isabelle), litmus-test validation, proof decomposition strategies, and end-to-end verification workflows and toolchain integration.]