Re: [PATCH] Fix incorrect devirtualization (PR middle-end/48661)

[Jason Merrill <jason at redhat dot com>]

On 04/19/2011 12:07 AM, Jakub Jelinek wrote:
> On Mon, Apr 18, 2011 at 03:33:18PM -0700, Jason Merrill wrote:

> > Well, it means that we do dynamic adjustment at runtime.  If we're
> > able to do devirtualization, we should be able to figure out the
> > right offset as well, just not in 4.6.
>
> Sure, but how exactly?  If BV_VCALL_INDEX is non-NULL,
> I guess we need to find for the given binfo corresponding rtti_binfo
> that was (or would be if vtable isn't emitted in the current TU)
> used in build_rtti_vtbl_entries to compute the difference between
> BINFO_OFFSETs:

The vcall entries are added by add_vcall_offset; the rtti entry is just 
used for dynamic_cast<void*>.

> Or do you think it should just add to the delta the value read from the
> vcall_offset from the vtable?

That's what the thunk does; if devirtualization can look up the vcall 
offset in the vtable, then it should do that.

Jason