Re: [PATCH 1/2] compiler.h: Introduce ptr_eq() to preserve address dependency

[Jonas Oberhauser <jonas.oberhauser@huaweicloud.com>]

Am 10/3/2024 um 3:23 PM schrieb Mathieu Desnoyers:
> What _does_ work however are the following two approaches:
> 
> 1) Perform the equality check on the original variables, creating
> new versions (with OPTIMIZER_HIDE_VAR) of both variables for the
> rest of their use, therefore making sure the pointer dereference
> are not derived from versions of the variables which were compared
> with another pointer. (as suggested by Boqun)

This should not be guaranteed to work, because right after the 
comparison the compiler can do b=a, then it doesn't matter how much you 
hide afterwards.

However it might work if you escape the addresses of a and b first, in 
which case the compiler will not do b=a anymore, but it might force the 
compiler to put a and b on the stack, which has some performance impact.

> 
> 2) Perform the equality check on the versions resulting of hiding
> both variables, making sure those versions of the variables are
> not dereferenced afterwards. (as suggested by Linus)
> 


jonas