bwendling wrote:
> > ```c
> > struct x {
> > int a;
> > char foo[2][40];
> > int b;
> > int c;
> > };
> >
> > size_t f(struct x *p, int idx) {
> > return __builtin_dynamic_object_size(&p->foo[idx], 1);
> > }
> > ```
>
> If I'm following correctly, the return here is 0, 40, or 80, depending on the
> value of idx? That's not a constant, but the computation is entirely
> syntactic; it doesn't matter what "p" actually points to. So clang can lower
> the builtin itself. Currently it doesn't, I think, because all the relevant
> code is in ExprConstant, but the code could be adapted.
Right. That's what I want to add to the front-end.
> The problem, really, is that we can't easily extend that approach to stuff
> like the following:
>
> ```c
> size_t f(struct x *p, int idx) {
> char *c = &p->foo[idx];
> return __builtin_dynamic_object_size(c, 1);
> }
> ```
Yup! I've been forbidden from doing this in the back-end, so I have to jump
through hoops now and do partial solutions and hope that it works for most
people and that when we get it wrong it doesn't hurt security (spoilers: it
will).
https://github.com/llvm/llvm-project/pull/78526
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