Use ODR for canonical types construction in LTO

[Nathan Sidwell]

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?

nathan

-- 
Nathan Sidwell