[PATCH] D155659: [WPD][LLD] Add option to validate RTTI is enabled on all native types and prevent devirtualization on types with native RTTI

[Di Mo via Phabricator via llvm-commits]

modimo added inline comments.


================
Comment at: llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp:2413
+  // case bail on the optimization.
+  if (ValidateAllVtablesHaveTypeInfos && !AllVtablesHaveTypeInfos)
+    return;
----------------
tejohnson wrote:
> modimo wrote:
> > tejohnson wrote:
> > > Rather than doing this down here in LTO/WPD could the linker simply unset the HasWholeProgramVisibility config flag? That would also allow WPD to proceed on types with hidden LTO visibility. This early return would prevent any and all WPD which seems overly conservative in the case of hidden LTO visibility classes. 
> > That makes sense although it does tie this flag's functionality to requiring `--lto-whole-program-visibility`. 
> > 
> > Doing that though means we can instead pass the blocklist to `updateVCallVisibilityInIndex`/`updateVCallVisibilityInModule` similarly to how D91583 does it for dynamically exported symbols which would be cleaner. Thoughts on that approach?
> > That makes sense although it does tie this flag's functionality to requiring --lto-whole-program-visibility.
> 
> What would be the use case of the proposed handling without --lto-whole-program-visibility? Are you saying that there are cases where the normal LTO visibility is incorrect?
> 
> > Doing that though means we can instead pass the blocklist to updateVCallVisibilityInIndex/updateVCallVisibilityInModule similarly to how D91583 does it for dynamically exported symbols which would be cleaner. Thoughts on that approach?
> 
> Yep I think that would be cleaner.
> What would be the use case of the proposed handling without --lto-whole-program-visibility? Are you saying that there are cases where the normal LTO visibility is incorrect?

I don't have a known case so this is more theoretical. Currently there's an assertion that it's on the user to make sure LTO visibility is correct but in this case and in D91583 we can catch violations and prevent them from causing problems. How much this should also apply to normal LTO visibility is a question but thinking more about it is orthogonal to this change.




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  https://reviews.llvm.org/D155659/new/

https://reviews.llvm.org/D155659