On Thu, 24 Mar 2005 11:29:09 -0800, Mark Mitchell <[EMAIL PROTECTED]> wrote:
> 19317 C++ problems with temporary return values > > This patch breaks Qt builds. One of my patches is implicated, but I > believe that the consensus is that this is an NRV bug. Jason made > several attempts at fixing this. Does anyone know what the current > status is? Basically, the problem is that the return slot optimization in expand_call is incompatible with the NRVO; if the callee shares the return slot with a variable, the caller can't share it with an object which escapes. expand_call has no way of checking whether "target" escapes, so I think we probably just need to disable the optimization there. I was trying to implement the optimization at the tree level by making the return slot argument explicit in the GIMPLE form, with CALL_EXPR_HAS_RETURN_SLOT. This caused problems with some code that didn't know to check that flag...which led me to think that if it requires a lot of special handling, perhaps the flag is the wrong way to make the return slot explicit. But I don't have a better idea atm. Jason
