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[clangd] Skip function bodies inside processed files while indexing

Description

[clangd] Skip function bodies inside processed files while indexing

Summary:
This significantly improves performance of background indexing.

We do not collect references and declarations inside the processed
files, so this does not affect the final indexing results.

The idea is borrowed from libclang, which has a similar optimization in
its indexing functionality.

Measurements show a nice decrease in indexing time, up to ~40% for
building the whole index. These are not proper benchmarks, so one should
not rely on these results too much.

  1. Rebuilding the whole index for LLVM:
    • Before. Total time: 14m58s. ./bin/clangd -pch-storage=memory < ./clangd.input 23917.67s user 515.86s system 2718% cpu 14:58.68 total
    • After. Total time: 8m41s. ./bin/clangd -pch-storage=memory < ./clangd.input 13627.29s user 288.10s system 2672% cpu 8:40.67 total
  1. Rebuilding index after removing shards matching '*clangd*' (case-insensitively):
    • Before. Total time: 30s. ./bin/clangd -pch-storage=memory < ./clangd.input 130.94s user 6.82s system 452% cpu 30.423 total
    • After. Total time: 26s. ./bin/clangd -pch-storage=memory < ./clangd.input 80.51s user 5.40s system 333% cpu 25.777 total

Reviewers: kadircet, sammccall

Reviewed By: kadircet

Subscribers: MaskRay, jkorous, arphaman, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D66226

Details

Event Timeline

I think we concluded we wanted to merge this into the release, which is apparently still possible. @hans

hans added a comment.Aug 26 2019, 12:55 AM

I think we concluded we wanted to merge this into the release, which is apparently still possible. @hans

Merged to release_90 in r369879.