Currently the llint, and the baseline and DFG JITs use a separate call stack. That stack also grows up, opposite to the C call stack. To use LLVM, we need to migrate to use the C stack. Since we OSR exit across JIT's and llint, all execution engines need to use the common C stack.
This task is complete. The next step is to merge the code back to trunk: <rdar://problem/15904077>.