If we already had a pointer-version, i.e.
struct __bounded_ptr {
int k;
[[gnu::counted_by(k) int *buf;
};
one could also rewrite the call to 'f1' to
int *p = f1 (3);
(struct __bound_ptr){ 3, f1(3) }.buf
and then the compound ref logic would do the right thing.
Martin
Am Mittwoch, dem 03.12.2025 um 07:43 +0100 schrieb Martin Uecker:
> Am Dienstag, dem 02.12.2025 um 21:21 +0000 schrieb Qing Zhao:
> >
> > > On Dec 2, 2025, at 15:56, Martin Uecker <[email protected]> wrote:
> > >
> > >
> > > Hi Qing,
> > >
> > > Am Dienstag, dem 02.12.2025 um 20:33 +0000 schrieb Qing Zhao:
> > > > Hi, Joseph and Martin:
> > > >
> > > > I am now working on PR96503 (attribute alloc_size effect lost after
> > > > inlining)
> > > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96503
> > > >
> > > > My first major questions are:
> > > >
> > > > for the simple case in the PR:
> > > >
> > > > __attribute__ ((alloc_size (1))) int* f1 (int n) { return f (n); }
> > > >
> > > > void h1 (void)
> > > > {
> > > > int *p = f1 (3);
> > > > __builtin_memset (p, 0, 3 * sizeof p); // missing warning
> > > > }
> > > >
> > > > 1. where in the IR we should insert the call to the internal function
> > > > .ACCESS_WITH_SIZE?
> > > >
> > > > My basic idea is: when the call to a routine marked with "alloc_size"
> > > > attribute, generate a call to .ACCESS_WITH_SIZE for its assigned
> > > > returned pointer.
> > > >
> > > > i.e, in the above example, when we see
> > > >
> > > > p = f1 (3)
> > > >
> > > > we will wrap the pointer "p" with .ACCESS_WITH_SIZE (p, 3, 0, 1), i.e,
> > > > .ACCESS_WITH_SIZE (p, 3, 0, 1) = f1 (3);
> > > >
> > > > is this reasonable?
> > >
> > > My guess would be that this should be
> > >
> > > p = .ACCESS_WITH_SIZE(f1(3), 3, 0, 1);
> >
> > Our current design of .ACCESS_WITH_SIZE is:
> >
> > ACCESS_WITH_SIZE (REF_TO_OBJ, REF_TO_SIZE,
> > TYPE_OF_SIZE + ACCESS_MODE, TYPE_SIZE_UNIT for element)
> > which returns the REF_TO_OBJ same as the 1st argument;
> >
> > Therefore, the first argument of the routine “.ACCESS_WITH_SIZE” is the
> > REF_TO_OBJ itself.
>
> How is the .ACCESS_WITH_SIZE discovered by BDOS
> when you do the following?
>
> .ACCESS_WITH_SIZE (p, 3, 0, 1) = f1 (3);
> use(p); // will BDOS find the information?
>
> It isn't clear to me how this would work.
>
> And isn't the object we are talking about the pointed-to array,
> so p would already be the ref itself.
>
> >
> > For the “alloc_size” attribute, we can consider it as an “counted_by”
> > attribute added
> > to the “returned pointer” of the function call.
>
> Now the counted_by is attached to the FAM and we pass a
> pointer to the FAM, so for me it seems we would need to pass
> the pointer to the object we want to bound.
>
> For size we can create a temporary object, or we need another
> version of .ACCESS_WITH_SIZE.
>
> Martin
>
>
> > So, adding the attribute to the pointer that is assigned by the returned
> > value of the
> > function is a reasonable approximation from my pointer of view.
> >
> > What do you think?
>
>
>
>
> >
> > >
> > > or am I missing something?
> > >
> > > >
> > > > 2. If the above idea is reasonable, where should I implement this in C
> > > > FE?
> > > >
> > > > What’s in my mind is: where a function returned value is assigned to a
> > > > pointer,
> > > > checking whether the function type has “alloc_size” attribute, if so,
> > > > wrapping
> > > > The pointer that the function assigned to to a call to
> > > > .ACCESS_WITH_SIZE.
> > > >
> > > > Which parts of the code, or which routines in C FE I should focus on?
> > >
> > > build_function_call_vec ?
> > Thanks, will take a look at it.
> >
> > Qing
> > >
> > > >
> > > > Let me know if you have any comments and suggestions.
> > >
> > >
> > > Martin
> > >
> > > >
> > > > Thanks a lot for your help.
> >
