This bug is super elusive. I can't repro. It's strange since FinalObjectUse is only used for Identity's that ToThis's are replaced with.
This bug really represents some weirdness, where even though we didn't see a FinalObjectUse at the point where we decide to start the FTL phases, we end up introducing a FinalObjectUse later. That shouldn't happen.
But, we won't ever see this bug again after https://bugs.webkit.org/show_bug.cgi?id=124092. So, I'm marking it as a dupe.
*** This bug has been marked as a duplicate of bug 124092 ***