On 10/3/22 23:53, Jason Merrill wrote:
> On 9/30/22 18:50, Iain Sandoe wrote:
>> Hi Jason,
>>
>>> On 30 Sep 2022, at 23:06, Jason Merrill <jason@redhat.com> wrote:
>>>
>>> You can't use CONVERT_EXPR to convert between two class types, and it 
>>> was
>>> breaking copy elision.
>>>
>>> Unfortunately, this patch breaks symmetric-transfer-00-basic.C, where
>>> susp_type is Loopy<int>::handle_type.  How is this supposed to work?
>>
>> We are trying to save a type-erased handle (which the symmetric 
>> transfer makes
>> and indirect call through, nothing else).
> 
> The problem is you're treating one class directly as another class here, 
> without the indirection involved in usual type-erasure idioms.
> 
> It does seem that the gimplifier handles this fine, but it doesn't 
> correspond to anything in the language and much of the front end assumes 
> that CONVERT_EXPR is only used for scalars.  VIEW_CONVERT_EXPR would 
> better express that we're not doing anything to the value, just cheating 
> the type system.  That's still dodgy from a language perspective, but 
> probably safe enough in this case.

So I'm applying this: