There are a variety of reasons why we might want to use the native stack pointer register to track the STG stack: * Performance might be better for a variety of reasons: * we could possibly use `PUSH` instead of `MOV` on x86, which has a more succinct encoding * the LLVM backend would be able to make better assumptions about pointer aliasing(?) * microarchitecture implementations likely optimise for stack accesses * In conjunction with DWARF debug information we could more easily use `perf` and other performance measurement tools (e.g. #15929)