Use ODR for canonical types construction in LTO

[Richard Biener]

On June 20, 2019 4:06:58 PM GMT+02:00, Nathan Sidwell <nathan@acm.org> wrote:
>On 6/20/19 9:37 AM, Richard Biener wrote:
>
>> I've spent some thoughts on this and I wonder whether we can
>> re-implement classtype-as-base with fake inheritance (which would
>> also solve the TBAA alias set issue in a natural way).  That is,
>> we'd lay out structs as-base and make instances of it use a
>> 
>> class as-instance { as-base b; X pad1; Y pad2; };
>> 
>> with either explicit padding fields or with implicit ones
>> (I didn't check how we trick stor-layout to not pad the as-base
>> type to its natural alignment...).
>
>I think you might end up with unordered fields?  virtual empty bases 
>don't appear in the as-base variant, and I think they could appear in 
>the middle of the as-instance variant.  that might or might not be a 
>problem?

Certainly interesting, but if they are empty it might not be an issue if they are never referred to (address taken?) 

Richard. 

>nathan