[PATCH] D136624: [clang][modules] Account for non-affecting inputs in `ASTWriter`

[Jan Svoboda via Phabricator via cfe-commits]

jansvoboda11 added a comment.

In D136624#3880526 <https://reviews.llvm.org/D136624#3880526>, @Bigcheese wrote:

> This looks reasonable. Have you measured the performance impact of this change?

I have done comparison between this patch and https://github.com/apple/llvm-project/pull/5451 (that, instead of leaving non-affecting input files out, serializes one extra bit saying whether they are affecting or not). Both versions carried some additional patches that refine the computation of non-affecting module maps, that I plan to upstream shortly. I used Clang's `-ftime-trace` on a reasonably large project (1680 TUs, 638 implicitly-built modules). The results say that serialization got 7.09% slower, and deserialization 1.01% slower. The serialization slowdown I understand, but I expected deserialization to get faster, since we now have less of `SourceManager` to look through. Overall, PCM compilation got 4.35% slower.


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