[all-commits] [llvm/llvm-project] e5fbf8: [Coverage] Improve performance of propagating Coun...

[NAKAMURA Takumi via All-commits]

  Branch: refs/heads/users/chapuni/cov/expansion
  Home:   https://github.com/llvm/llvm-project
  Commit: e5fbf846113591b0abff151d91b01a5dd40abef1
      https://github.com/llvm/llvm-project/commit/e5fbf846113591b0abff151d91b01a5dd40abef1
  Author: NAKAMURA Takumi <geek4civic at gmail.com>
  Date:   2025-01-11 (Sat, 11 Jan 2025)

  Changed paths:
    M llvm/lib/ProfileData/Coverage/CoverageMappingReader.cpp

  Log Message:
  -----------
  [Coverage] Improve performance of propagating Counter of Expansions

This improves `-dump-coverage-mapping` (939,498 lines) for
`RISCVInstructionSelector.cpp` from 30m to 1m18s and also improves
`llvm-cov` for `check-llvm` from 33m to 24s.

The current implementation behaved O(N^2) order with hundreds
thousands of Expansions.

This assumes:
  - Records are partitioned by FileID.
    - ExpandedFileID doesn't point FileID==0, since it is the root.
  - The Count in Expansion is propagated from 1st Record in
    ExpandedFileID.

Therefore another fact below can be assumed.
  - Propagation chain consists of Expansions at each 1st Record.

This scans the Record at most a few times. O(N) is expected.

Fixes #113173



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