[PATCH] D144844: [C++20] [Modules] Offer -fno-import-inter-module-function-defs to avoid duplicated compilation in modules

Wed Mar 15 00:35:03 PDT 2023

iains added a comment.

In D144844#4195316 <https://reviews.llvm.org/D144844#4195316>, @ChuanqiXu wrote:

> Got your points. Let's postpone this one.
>
> But I want to emphasize that this patch (and the thin PCM) will decrease the performance. While LTO can save the regression, LTO is not widely used. (ThinLTO can only mitigate this.) I mean the default behavior shouldn't cause performance regression. We can offer a new alternative  for the users but we can't enable that by default simply now.

Agree that we (ideally, at least) should not decrease performance with a new feature.
However, "performance" also includes compilation speed in the 'no optimisation, debug' case - that is also considered very important.  So, perhaps, the short-term approach should be (as @dblaikie suggested) to include the bodies for `-O` >= 3?

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https://reviews.llvm.org/D144844