5 ms·

And that ABI specific stack manipulation would be UB, so the optimizer can assume it doesn't happen. With no UB, that's not true.

• Dylan16807 3y ago
  You assume a langue without UB would allow stack manipulation. But then it would have to be defined. How would you possibly define it fully?
  • remexre 3y ago
    There's an area of memory into which variables with automatic storage duration are allocated at implementation-defined addrs, at any point exactly those variables have addresses.
    • Dylan16807 3y ago
      > at any point exactly those variables have addresses That doesn't sound like it lets me increment any stack address I want and store into the resulting pointer. And are return values still on the same stack? I probably should have said I meant the traditional kind of C stack.
      • remexre 3y ago
        > That doesn't sound like it lets me increment any stack address I want and store into the resulting pointer. Why not? > And are return values still on the same stack? Other implementation-defined things might have addresses too, those things just aren't variables. I think you might be able to still allow inlining without UB if you make it implementation-defined per call-site what other things might get addresses.
        • Dylan16807 3y ago
          > Why not? At this point the conversation has completely converged so I'm only going to reply over here: https://news.ycombinator.com/item?id=36169808 https://news.ycombinator.com/item?id=36169808