On Tue, Jan 13, 2015 at 11:24 AM, Reid Kleckner <[email protected]> wrote:
> On Tue, Jan 13, 2015 at 11:22 AM, Nico Weber <[email protected]> wrote: > >> On Tue, Jan 13, 2015 at 11:11 AM, Reid Kleckner <[email protected]> wrote: >> >>> I'm concerned that if you don't mark the vtable used enough, then >>> codegen will crash trying to emit a vtable for a class that it assumed >>> would be marked used because it's compiling a virtual call to a method of >>> such a class. However, it looks like Rafael completely nuked the >>> available_externally vtable emission optimization in r189852, which I >>> forgot about. The vtable code still has lots of rigging to allow >>> available_externally vtable emission, though. >>> >> >> At the moment, the only thing in coding adding to the DeferredVTables >> vector in codegen is getAddrOfVTable(), and that's only called for structor >> body emission (and apple kext vcalls). So I think this should be fine. >> > > Right, but we used to call it more, prior to PR13124 and r189852. I'm > reading that bug to see if it's something we want to add back. > I'm starting to think that even if we want to bring back the available_externally vtable optimization, it should only happen optimistically and should not rely on Sema to mark the vtable used. Looking at PR13124, though, that seems difficult... Anyway, I drop my objections. The available_externally vtable optimization doesn't exist and turns out to be very hard to implement in Clang today. =/
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