[PATCH] D47108: [CodeGenCXX] Add -fforce-emit-vtables

[Piotr Padlewski via Phabricator via cfe-commits]

Prazek added a comment.

In https://reviews.llvm.org/D47108#1109014, @rjmccall wrote:

> I thought we already had places in Sema that marked inline virtual methods as used, instantiated templates, etc. for devirtualization purposes when optimization was enabled.  Did we rip that out?


I only recall the emitting available_externally vtables opportunistically, that is emitting it only if all the inline virtual functions are present (and they are not hidden).
(https://reviews.llvm.org/D33437)

> The problem we've had over and over with devirtualization is that we have to emit a perfect v-table because LLVM lacks a lot of the key vocabulary for talking about incomplete information.  For example, if something weird happens and we don't have a definition for an inline virtual method, ideally we'd just say "well, you can't devirtualize this slot", then try to fix that as incremental progress; but instead we have to get everything just right or else disable the whole optimization.  Note that vague-linkage v-tables mean that we'd also need to be able to say things like "there is an object with a definition that looks like this, but its symbol is not available and you can't emit it yourself".

That is correcty, my intention was that this flag would cause all inline virtual functions to be emitted. Can you give a hint how to achieve this in the sane way?


Repository:
  rL LLVM

https://reviews.llvm.org/D47108