[PATCH] D83652: Merge some of the PCH object support with modular codegen

Tue Jul 14 22:10:49 PDT 2020

llunak added a comment.

In D83652#2147539 <https://reviews.llvm.org/D83652#2147539>, @dblaikie wrote:

> Not quite - it's intended to implement the D48426 <https://reviews.llvm.org/D48426> functionality using an implementation strategy that is closer to modular code generation. Removing the need for the module flag, using the MODULAR_CODEGEN_DECLS list, etc. But only putting the dllexported entities in there (when using only building-pch-with-obj without -fmodules-codegen).

I see. I still suggest testing this on a real codebase for the reasons outlined above.

> Yep, that was essentially what I was wondering - since you were proposing a build mode/flags that would not be /Yc compatible, adding an explicit pch build and pch object build step - was wondering if the build system support for that was sufficiently available that it would be practical for users (like Chromium) to migrate to that kind of model and no longer need /Yc compatibility.

Not that I know for sure, but I personally doubt there's build system support for D83716 <https://reviews.llvm.org/D83716>. The only build system I've tried is LibreOffice's custom gbuild, where I've added the support for -fpch-codegen/debuginfo myself, and even there's I'm going to stick with -building-pch-with-obj, since it's simpler to compile yet another .cxx file with an extra flag rather than have a build step with .pch as yet another kind of input file. But /Yc is presumably supported by pretty much anything on Windows.

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