Sure, I just think my (not that well thought-out, but still) suggestion mitigates bugs in existing source code with fresh compiler support better than this thin

Sure, I just think my (not that well thought-out, but still) suggestion mitigates bugs in existing source code with fresh compiler support better than this thing does. A compiler/runtime using new instructions to make instruction addresses hard to clobber could instead use instructions keeping on-stack array sizes in the array pointer and maintaining it through pointer arithmetic. A compiler/runtime know when an array size is too large to fit into 23 bits, certainly on-stack arrays are never that big so your sister comment's problem about "4G" is not that big of a problem, just don't do this with large arrays. It'd require somewhat more ISA & compiler changes but it'd solve more problems that just the one problem they solve, and I think the security of this would be easier to demonstrate, too.