Invariant: all paths through a function should leave each variable with 0 net refs. (This includes paths out via exceptions.)
## Refcounting in the rewriter, baseline jit, and llvm jit
## Debugging
A use-after-free will typically show up as a segfault (where the accessed memory location is something like 0xdbdbdbdb), or as an "Object has negative ref count" error message. In both cases, I find it best to do `watch -l op->ob_refcnt`. I find it helpful to open up a text file and write down what each of the ref operations means, and then figure out which ones were extra or which ones were missing.
If you get extra refs at the end, try to bisect down the program until you find the point that the ref was leaked. Unfortunately there is not a good way to enumerate all live objects to figure out what they are.
If the program ends with a message such as "10 refs remaining!", try to bisect down the program until you find the point that the ref was leaked. Unfortunately there is not a good way to enumerate all live objects to figure out what they are.
## Refcounting in the rewriter, baseline jit, and llvm jit
If the assertion `assert(var->reftype != RefType::UNKNOWN)` fails in Rewriter::commitReturning(), this means that someone forgot to call `setType` on a refcounted RewriterVar. Unfortunately, we don't have any tracking of where RewriterVars get created, so we will use GDB to help us.
