[PATCH] D53524: [ThinLTO] Enable LTOUnit only when it is needed

[Teresa Johnson via Phabricator via cfe-commits]

tejohnson added a comment.

In https://reviews.llvm.org/D53524#1271357, @pcc wrote:

> The reason why LTO unit is always enabled is so that you can link translation units compiled with `-fsanitize=cfi` and/or `-fwhole-program-vtables` against translation units compiled without CFI/WPD. With this change we will see miscompiles in the translation units compiled with CFI/WPD if they use vtables in the translation units compiled without CFI/WPD. If we really need this option I think it should be an opt out.


Is there an important use case for support thing mixing and matching? The issue is that it comes at a cost to all ThinLTO compiles for codes with vtables by requiring them all to process IR during the thin link. Can we detect that TUs compiled with -flto-unit are being mixed with those not built without -flto-unit at the thin link time and issue an error?


Repository:
  rC Clang

https://reviews.llvm.org/D53524