Re: HELP: Will the reordering happen? Re: [V3][PATCH 0/3] New attribute "counted_by" to annotate bounds for C99 FAM(PR108896)

[Qing Zhao <qing.zhao@oracle.com>]

> On Oct 24, 2023, at 7:56 PM, Siddhesh Poyarekar <siddhesh@gotplt.org> wrote:
> 
> On 2023-10-24 18:51, Qing Zhao wrote:
>> Thanks for the proposal!
>> So what you suggested is:
>> For every x.buf,  change it as a __builtin_with_size(x.buf, x.L) in the FE, then the call to the _bdos (x.buf, 1) will
>> Become:
>>    _bdos(__builtin_with_size(x.buf, x.L), 1)?
>> Then the implicit use of x.L in _bdos(x.buf.1) will become explicit?
> 
> Oops, I think Martin and I fell off-list in a subthread.  I clarified that my comment was that any such annotation at object reference is probably too late and hence not the right place for it; basically it has the same problems as the option A in your comment.  A better place to reinforce such a relationship would be the allocation+initialization site instead.

I think Martin’s proposal might work, it’s different than the option A:

A.  Add an additional argument, the size parameter,  to __bdos, 
     A.1, during FE;
     A.2, during gimplification phase;

Option A targets on the __bdos call, try to encode the implicit use to the call, this will not work when the real object has not been instantiation at the call site.

However, Martin’s proposal targets on the FMA array itself, it will enhance the FAM access naturally with the size information. And such FAM access with size info will propagated to the __bdos site later through inlining, etc. and then tree-object-size can use the size information at that point. At the same time, the implicit use of the size is recorded correctly. 

So, I think that this proposal is natural and reasonable.

Qing
> 
> Thanks,
> Sid