On Thu, Jul 24, 2014 at 12:46 PM, Jan Hubicka <hubi...@ucw.cz> wrote: >> >> Aggregate copies and memcpy transferring the dynamic type for example. >> Being able to tbaa union accesses for another. And yes, placement new. > > I see that if we previously dropped all union accesses to 0, the current > scheme > is nice improvement. But it seem to me it may be in use only when one of > accesses is through union. > > How the memcpy case works? I always tought that memcpy does reads&writes in > set 0 > that makes it to introduce the necessary conflicts.
Yes, that's possible now (with MEM_REF), previously it was not and the memory model "fixed" it. > Similarly can't we make set 0 clobber of the memory retyped by placement new? We don't have a way to do that, but yes, we could. But as said, for PODs you don't even need placement new. You can just store with a new type. Richard. > If the clobber is hidden in external function call, we still have it as a side > effect of the call. It would have to survive all the way down to RTL... > > Honza
