On Tue, 29 Sept 2026 at 08:04, Mathieu Desnoyers
<[email protected]> wrote:
>
> I agree that doing it in asm would generate better code. Also, I've
> been told that clang now preserves the address dependency in this
> scenario, so perhaps we'd want to use preprocessor conditionals to
> select how to implement ptr_eq based on:
>
> - architecture (allowing asm implementation overrides),
> - compiler (e.g. if compiler is clang >= version X, just do a plain
> comparison). Likewise for gcc if it ever decides to fix this
> behavior.
>
> I think this "hide var" hack is a fallback which can be used as a
> starting point, and then we can specialize based on architecture and
> compiler.
>
> Or do you prefer this in a different order ?
Oh, if there's some sane way to tell that the compiler already honors
address dependencies, then that should be done first and the whole
thing should just become a simple
(a) == (b)
for that situation - allowing the compiler then the freedom to do
whatever (which can involve not using a register at all, but a compare
to memory, or whatever - the compiler might have reasons to avoid the
'cmp' and use another sequence entirely)
Then a "if we have an architecture fallback".
And then that OPTIMIZER_HIDE_VAR() thing as a last fallback.
Linus
