[PATCH] D69778: Make -fmodules-codegen and -fmodules-debuginfo work also with precompiled headers

Tue Mar 17 14:02:48 PDT 2020

dblaikie added a subscriber: rnk.
dblaikie added a comment.

In D69778#1779042 <https://reviews.llvm.org/D69778#1779042>, @llunak wrote:

> In D69778#1776472 <https://reviews.llvm.org/D69778#1776472>, @dblaikie wrote:
>
> > I guess one aspect is that -building-pch-with-obj seems like it duplicates the fmodules-codegen concept (both basically are a flag passed during pcm/pch build time that says "I promise to build an object file from this pcm/pch, so rely on that assumption when building other things that depend on the pcm/pch) - if I'd noticed the -building-pch-with-obj going in I would've made the point then.
>
>
> Is that described somewhere? There's no mention of modules codegen anywhere under clang/docs. I was under the impression that modules created the codegen part directly in the .pcm in ELF (or whatever) format.

Nah, not as yet - I think I provided some examples in this/other reviews you & I have been having, and in the clang tests. Ah, yeah, this one: https://reviews.llvm.org/D69779#1801771 (

>> But yeah, that's out of scope for this patch, but might be something that'd be good to look into to try to merge these features/codepaths more.
> 
> Note that AFAICT the -building-pch-with-obj flag is pretty much internal, used only by the MSVC-like PCH creation, so presumably this could be still unified more without any real harm. And I think I could do the work if it'd be agreed that this would be a good thing.

@rnk  - know anything about the history of -building-pch-with-obj and whether it could be replaced/merged with -fmodules-codegen? (-fmodules-codegen + -fmodules-debuginfo, perhaps?)

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