This issue replaces the SF bug tracker 1488798.
This problem is probably one of the most serious in the RVM currently. When loop unrolling is disabled and SSA enabled the created IR is corrupt. The error has in the past look like we were suffering from the "lost copy" problem, but implementing a naive solution to this didn't solve the problem. Their is sound logic behind the code so we need to identify a small test case where things are broken and then reason about what's wrong in leave SSA. This has been attempted once (with the code that removes an element from the live set) but the problem no longer appears to surface here.
Currently these optimizations are disabled but by RVM 3.0 they should be re-enable and this bug cured.
For a longer history of the bug see: