[PATCH] D22773: Modules: add command line option fmodules-disable-diagnostic-validation to disable validation of the diagnostic options when loading the module

[Manman Ren via cfe-commits]

manmanren added a comment.

In https://reviews.llvm.org/D22773#495524, @benlangmuir wrote:

> > the pcm could still be rewritten by a compilation that doesn't use a PCH, and then it would be out of date because of the timestamp instead of the diagnostic options
>
> > 
>
> > "a compilation that doesn't use a PCH", is that a different project? And we have two projects building in parallel? Just to make sure I understand.
>
>
> Two different projects (or targets, or whatever), but they don't even have to build at the same time.  They just have to share a cache. Suppose you have a project A with a PCH and -fmodules-disable-diagnostic-validation.  Suppose you have another project B that does not use this flag, and does not have a PCH.  With this patch, A and B can share a module cache.
>
> A builds a PCH that depends on some module X -- OK
>  B builds with -Werror.  Rebuilds X.pcm -- OK
>
> Now suppose we build A again because of some change:  it can't build because X.pcm changed, but we haven't rebuilt the PCH.


Got it, I will update the patch!

Manman


https://reviews.llvm.org/D22773