Correct way to express to the compiler "this does not get clobbered"?

[Andrea Corallo]

stefan@franke.ms writes:

> Am 4. Dezember 2020 00:00:28 MEZ schrieb Andrea Corallo via Gcc-help <gcc-help@gcc.gnu.org>:
>>David Brown <david.brown@hesbynett.no> writes:
>>
>>Hi David,
>>
>>> As "f()" runs, the value of "y->fun_ptr" changes with each step as
>>you
>>> get alternating "foo1", "foo2" outputs.  Thus it is clear (I hope)
>>that
>>> the compiler cannot assume that "y->fun_ptr" is not clobbered by the
>>> function call.
>>
>>Indeed that's clear.  The question is more if there's some way to
>>express
>>this to the compiler qualifying the variables in discussion without
>>changing the structure of the code.  This because as I wrote may be not
>>trivial to modify the code generator for optimal results.
>>
>>I understand this is probably not possible and there's no magic
>>attribute or qualifier to express this.
>>
>>Thanks
>>
>>  Andrea
>
> IMHO it's a bug that const members referenced by a const pointer are reloaded inside the loop.

I might open a bug but my understanding is that const is generally
not used for optimizations.  Am I wrong?

  Andrea