DWARF does contain turing-complete VM for doing unwinding, so theoretically it should already be possible to make a compiler that gives precise debug info every

DWARF does contain turing-complete VM for doing unwinding, so theoretically it should already be possible to make a compiler that gives precise debug info everywhere, no new protocol necessary. But completely-reversible-anywhere optimizations are rather limiting, disallowing a bunch of things; including, but not limited to, dead code elimination (more generally, forgetting some fraction of state from somewhere), identical code merging, and instruction reordering (esp. vectorization, which essentially reorders across multiple loop iterations), severely limiting what your optimizer can even do.