Because stacks aren’t unbounded. You grow and shrink them. Therefore, regardless of which direction it grows in, it also shrinks in the opposite direction with the same likelihood.
> fact that downward bump is just not what the HW expects you to do.
What fact is this? and what does it have to do with stack being bounded? (bounds of stack are unknown to most micro architectural state and only stored in OS structures).
HW prefetchers support access pattern in either direction, so do load/store instructions (stm(fd)/ldm(fd); ltp/stp;)
The fact that stacks are bounded means you both push and you pop. Just as frequently as a function calls another one resulting in memory ops moving to lower addresses, functions also return causing memory ops to move back to higher addresses. Pushes and pops are balanced. Why do we know they are balanced? Because the stack is bounded.
So - the direction of stack growth isn’t interesting to prefetching strategy.
