[all-commits] [llvm/llvm-project] 6f9646: [ELF] Parallelize --gc-sections mark phase (#189321)

[Fangrui Song via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 6f9646a598f25efa3c4db066d2d51fb248b13526
      https://github.com/llvm/llvm-project/commit/6f9646a598f25efa3c4db066d2d51fb248b13526
  Author: Fangrui Song <i at maskray.me>
  Date:   2026-04-02 (Thu, 02 Apr 2026)

  Changed paths:
    M lld/ELF/MarkLive.cpp

  Log Message:
  -----------
  [ELF] Parallelize --gc-sections mark phase (#189321)

Add `markParallel` using level-synchronized `parallelFor`. Each BFS
level is processed in parallel; newly discovered sections are collected
in per-thread queues and merged for the next level.

The parallel path is used when `!TrackWhyLive && partitions.size()==1`.
`parallelFor` naturally degrades to serial when `--threads=1`.

Uses depth-limited inline recursion (depth<3) and optimistic
load-then-exchange dedup for best performance.

Linking a Release+Asserts clang (--gc-sections, --time-trace) on an old
x86-64:

8 threads: markLive 315ms -> 82ms (-234ms). Total 1562ms -> 1350ms
(1.16x).
16 threads: markLive 199ms -> 50ms (-149ms). Total 1017ms -> 862ms
(1.18x).

and on Apple M4: markLive 61ms -> 13ms. Total 317.3ms -> 272.7ms
(1.16x).



To unsubscribe from these emails, change your notification settings at https://github.com/llvm/llvm-project/settings/notifications