48d542d67c
When a block is unreachable, the `unreachable_code` pass will remove it, which is perfectly sensible. Jump tables factor into unreachability in an expected way: even if a block is listed in a jump table, the block might be unreachable if the jump table itself is unused (or used in an unreachable block). Unfortunately, the verifier still expects all block refs in all jump tables to be valid, even after DCE, which will not always be the case. This makes a simple change to the pass: after removing blocks, it scans jump tables. Any jump table that refers to an unreachable block must itself be unused, and so we just clear its entries. We do not bother removing it (and renumbering all later jumptables), and we do not bother computing full unused-ness of all jumptables, as that would be more expensive; it's sufficient to clear out the ones that refer to unreachable blocks, which are a subset of all unused jumptables. Fixes #2670.
This crate contains the core Cranelift code generator. It translates code from an intermediate representation into executable machine code.